This section gives an overview of:
This section is intended to cover only the essentials, things you should know before trying to use FreeS/WAN.
For more detailed background information, see the history and politics and IPsec protocols sections.
FreeS/WAN is a Linux implementation of the IPsec (IP security) protocols. IPsec provides encryption and authentication services at the IP (Internet Protocol) level of the network protocol stack.
Working at this level, IPsec can protect any traffic carried over IP, unlike other encryption which generally protects only a particular higher-level protocol -- PGP for mail, SSH for remote login, SSL for web work, and so on. This approach has both considerable advantages and some limitations. For discussion, see our IPsec section
IPsec can be used on any machine which does IP networking. Dedicated IPsec gateway machines can be installed wherever required to protect traffic. IPsec can also run on routers, on firewall machines, on various application servers, and on end-user desktop or laptop machines.
Three protocols are used
Our implementation has three main parts:
IPsec is optional for the current (version 4) Internet Protocol. FreeS/WAN adds IPsec to the Linux IPv4 network stack. Implementations of IP version 6 are required to include IPsec. Work toward integrating FreeS/WAN into the Linux IPv6 stack has started.
For more information on IPsec, see our IPsec protocols section, our collection of IPsec links or the RFCs which are the official definitions of these protocols.
IPsec is designed to let different implementations work together. We provide:
The VPN Consortium fosters cooperation among implementers and interoperability among implementations. Their web site has much more information.
IPsec has a number of security advantages. Here are some independently written articles which discuss these:
SANS institute papers. See the
section on Encryption &VPNs.
Cisco's white papers on "Networking Solutions".
Advantages of ISCS (Linux Integrated Secure Communications System;
includes FreeS/WAN and other software).
Because IPsec operates at the network layer, it is remarkably flexible and can be used to secure nearly any type of Internet traffic. Two applications, however, are extremely widespread:
There is enough opportunity in these applications that vendors are flocking to them. IPsec is being built into routers, into firewall products, and into major operating systems, primarily to support these applications. See our list of implementations for details.
We support both of those applications, and various less common IPsec applications as well, but we also add one of our own:
This is an extension we are adding to the protocols. FreeS/WAN is the first prototype implementation, though we hope other IPsec implementations will adopt the technique once we demonstrate it. See project goals below for why we think this is important.
A somewhat more detailed description of each of these applications is below. Our quickstart section will show you how to build each of them.
A VPN, or Virtual Private N etwork lets two networks communicate securely when the only connection between them is over a third network which they do not trust.
The method is to put a security gateway machine between each of the communicating networks and the untrusted network. The gateway machines encrypt packets entering the untrusted net and decrypt packets leaving it, creating a secure tunnel through it.
If the cryptography is strong, the implementation is careful, and the administration of the gateways is competent, then one can reasonably trust the security of the tunnel. The two networks then behave like a single large private network, some of whose links are encrypted tunnels through untrusted nets.
Actual VPNs are often more complex. One organisation may have fifty branch offices, plus some suppliers and clients, with whom it needs to communicate securely. Another might have 5,000 stores, or 50,000 point-of-sale devices. The untrusted network need not be the Internet. All the same issues arise on a corporate or institutional network whenever two departments want to communicate privately with each other.
Administratively, the nice thing about many VPN setups is that large parts of them are static. You know the IP addresses of most of the machines involved. More important, you know they will not change on you. This simplifies some of the admin work. For cases where the addresses do change, see the next section.
The prototypical "Road Warrior" is a traveller connecting to home base from a laptop machine. Administratively, most of the same problems arise for a telecommuter connecting from home to the office, especially if the telecommuter does not have a static IP address.
For purposes of this document:
These require somewhat different setup than VPN gateways with static addresses and with client systems behind them, but are basically not problematic.
There are some difficulties which appear for some road warrior connections:
In most situations, however, FreeS/WAN supports road warrior connections just fine.
One of the reasons we are working on FreeS/WAN is that it gives us the opportunity to add what we call opportuntistic encryption. This means that any two FreeS/WAN gateways will be able to encrypt their traffic, even if the two gateway administrators have had no prior contact and neither system has any preset information about the other.
Both systems pick up the authentication information they need from the DNS (domain name service), the service they already use to look up IP addresses. Of course the administrators must put that information in the DNS, and must set up their gateways with opportunistic encryption enabled. Once that is done, everything is automatic. The gateways look for opportunities to encrypt, and encrypt whatever they can. Whether they also accept unencrypted communication is a policy decision the administrator can make.
This technique can give two large payoffs:
Opportunistic encryption is not (yet?) a standard part of the IPsec protocols, but an extension we are proposing and demonstrating. For details of our design, see links below.
Only one current product we know of implements a form of opportunistic encryption. Secure sendmail will automatically encrypt server-to-server mail transfers whenever possible.
A complication, which applies to any type of connection -- VPN, Road Warrior or opportunistic -- is that a secure connection cannot be created magically. There must be some mechanism which enables the gateways to reliably identify each other. Without this, they cannot sensibly trust each other and cannot create a genuinely secure link.
Any link they do create without some form of authentication will be vulnerable to a man-in-the-middle attack. If Alice and Bob are the people creating the connection, a villian who can re-route or intercept the packets can pose as Alice while talking to Bob and pose as Bob while talking to Alice. Alice and Bob then both talk to the man in the middle, thinking they are talking to each other, and the villain gets everything sent on the bogus "secure" connection.
There are two ways to build links securely, both of which exclude the man-in-the middle:
Automatic keying is much more secure, since if an enemy gets one key only messages between the previous re-keying and the next are exposed. It is therefore the usual mode of operation for most IPsec deployment, and the mode we use in our setup examples. FreeS/WAN does support manual keying for special circumstanes. See this section.
For automatic keying, the two systems must authenticate each other during the negotiations. There is a choice of methods for this:
Public key techniques are much preferable, for reasons discussed later, and will be used in all our setup examples. FreeS/WAN does also support auto-keying with shared secret authentication. See this section.
For complete information on the project, see our web site, freeswan.org.
In summary, we are implementing the IPsec protocols for Linux and extending them to do opportunistic encryption.
Our overall goal in FreeS/WAN is to make the Internet more secure and more private.
Our IPsec implementation supports VPNs and Road Warriors of course. Those are important applications. Many users will want FreeS/WAN to build corporate VPNs or to provide secure remote access.
However, our goals in building it go beyond that. We are trying to help build security into the fabric of the Internet so that anyone who choses to communicate securely can do so, as easily as they can do anything else on the net.
More detailed objectives are:
If we can get opportunistic encryption implemented and widely deployed, then it becomes impossible for even huge well-funded agencies to monitor the net.
See also our section on history and politics of cryptography, which includes our project leader's rationale for starting the project.
Two of the team are from the US and can therefore contribute no code:
The rest of the team are Canadians, working in Canada. ( Why Canada?)
The project is funded by civil libertarians who consider our goals worthwhile. Most of the team are paid for this work.
People outside this core team have made substantial contributions. See
Additional contributions are welcome. See the FAQ for details.
Unfortunately the export laws of some countries restrict the distribution of strong cryptography. FreeS/WAN is therefore not in the standard Linux kernel and not in all CD or web distributions.
FreeS/WAN is, however, quite widely used. Products we know of that use it are listed below. We would appreciate hearing, via the mailing lists, of any we don't know of.
FreeS/WAN is included in various general-purpose Linux distributions, mostly from countries (shown in brackets) with more sensible laws:
For distributions which do not include FreeS/WAN and are not Redhat (which we develop and test on), there is additional information in our compatibility section.
The server edition of Corel Linux (Canada) also had FreeS/WAN, but Corel have dropped that product line.
FreeS/WAN is also included in several distributions aimed at the market for turnkey business servers:
Several distributions intended for firewall and router applications include FreeS/WAN:
There are also several sets of scripts available for managing a firewall which is also acting as a FreeS/WAN IPsec gateway. See this list.
Several vendors use FreeS/WAN as the IPsec component of a turnkey firewall or VPN product.
Software-only products:
Products that include the hardware:
Rebel.com, makers of the Netwinder Linux machines (ARM or Crusoe based), had a product that used FreeS/WAN. The company is in receivership so the future of the Netwinder is at best unclear. PKIX patches for FreeS/WAN developed at Rebel are listed in our web links document.
FreeS/WAN documentation up to version 1.5 was available only in HTML. Now we ship two formats:
and provide a Makefile to generate other formats if required:
The Makefile assumes the htmldoc tool is available. You can download it from Easy Software.
All formats should be available at the following websites:
The distribution tarball has only the two HTML formats.
Note: If you need the latest doc version, for example to see if anyone has managed to set up interoperation between FreeS/WAN and whatever, then you should download the current snapshot. What is on the web is documentation as of the last release. Snapshots have all changes I've checked in to date.
As with most things on any Unix-like system, most parts of Linux FreeS/WAN are documented in online manual pages. We provide a list of FreeS/WAN man pages, with links to HTML versions of them.
The man pages describing configuration files are:
Man pages for common commands include:
You can read these either in HTML using the links above or with the man(1) command.
In the event of disagreement between this HTML documentation and the man pages, the man pages are more likely correct since they are written by the implementers. Please report any such inconsistency on the mailing list.
Text files in the main distribution directory are README, INSTALL, CREDITS, CHANGES, BUGS and COPYING.
The Libdes encryption library we use has its own documentation. You can find it in the library directory..
Throughout this documentation, I write as if the reader had at least a general familiarity with Linux, with Internet Protocol networking, and with the basic ideas of system and network security. Of course that will certainly not be true for all readers, and quite likely not even for a majority.
However, I must limit amount of detail on these topics in the main text. For one thing, I don't understand all the details of those topics myself. Even if I did, trying to explain everything here would produce extremely long and almost completely unreadable documentation.
If one or more of those areas is unknown territory for you, there are plenty of other resources you could look at:
Also, I do make an effort to provide some background material in these documents. All the basic ideas behind IPsec and FreeS/WAN are explained here. Explanations that do not fit in the main text, or that not everyone will need, are often in the glossary , which is the largest single file in this document set. There is also a background file containing various explanations too long to fit in glossary definitions. All files are heavily sprinkled with links to each other and to the glossary. If some passage makes no sense to you, try the links.
For other reference material, see the bibliography and our collection of web links.
Of course, no doubt I get this (and other things) wrong sometimes. Feedback via the mailing lists is welcome.
Until quite recently, there was only one FreeS/WAN mailing list, and archives of it were:
The two archives use completely different search engines. You might want to try both.More recently we have expanded to five lists, each with its own archive.
More information on mailing lists.
Various user-written HowTo documents are available. The ones covering FreeS/WAN-to-FreeS/WAN connections are:
User-wriiten HowTo material may be especially helpful if you need to interoperate with another IPsec implementation. We have neither the equipment nor the manpower to test such configurations. Users seem to be doing an admirable job of filling the gaps.
Check what version of FreeS/WAN user-written documents cover. The software is under active development and the current version may be significantly different from what an older document describes.
Two design documents show team thinking on new developments:
Both documents are works in progress and are frequently revised. For the latest version, see the design mailing list. Comments should go to that list.
There is now an Internet Draft on Opportunistic Encryption by Michael Richardson, Hugh Redelmeier and Henry Spencer. This is a first step toward getting the protocol standardised so there can be multiple implementations of it. Discussion of it takes place on the IETF IPsec Working Group mailing list.
A number of papers giving further background on FreeS/WAN, or exploring its future or its applications, are also available:
Several of these provoked interesting discussions on the mailing lists, worth searching for in the archives.
There are also several papers in languages other than English, see our web links.
All code and documentation written for this project is distributed under either the GNU General Public License (GPL) or the GNU Library General Public License. For details see the COPYING file in the distribution.
Not all code in the distribution is ours, however. See the CREDITS file for details. In particular, note that the Libdes library and the version of MD5 that we use each have their own license.
FreeS/WAN is available from a number of sites.
Our primary site, is at xs4all (Thanks, folks!) in Holland:
There are also mirror sites all over the world:
Thanks to those folks as well.
There is also an archive of Linux crypto software called "munitions", with its own mirrors in a number of countries. It includes FreeS/WAN, though not always the latest version. Some of its sites are:
Any of those will have a list of other "munitions" mirrors. There is also a CD available.
For more detailed background information, see:
To begin working with FreeS/WAN, go to our quickstart guide.
Out of the box, FreeS/WAN 2.x will attempt to encrypt all your IP traffic. It will try to establish IPsec connections for:
FreeS/WAN 2.x uses hidden, automatically enabled ipsec.conf connections to do this.
This behaviour is part of our campaign to get Opportunistic Encryption (OE) widespread in the Linux world, so that any two Linux boxes can encrypt to one another without prearrangement. There's one catch, however: you must set up a few DNS records to distribute RSA public keys and (if applicable) IPsec gateway information.
If you start FreeS/WAN before you have set up these DNS records, your connectivity will be slow, and messages relating to the built in connections will clutter your logs. If you are unable to set up DNS for OE, you will wish to disable the hidden connections.
As of FreeS/WAN 2.01, Opportunistic Encryption (OE) uses DNS TXT resource records (RRs) only (rather than TXT with KEY). This change causes a "flag day". Users of FreeS/WAN 2.00 (or earlier) OE who are upgrading may need to post additional resource records.
If you are running initiate-only OE, you must put up a TXT record in any forward domain as per our quickstart instructions. This replaces your old forward KEY.
If you are running full OE, you require no updates. You already have the needed TXT record in the reverse domain. However, to facilitate future features, you may also wish to publish that TXT record in a forward domain as instructed here.
If you are running OE on a gateway (and encrypting on behalf of subnetted boxes) you require no updates. You already have the required TXT record in your gateway's reverse map, and the TXT records for any subnetted boxes require no updating. However, to facilitate future features, you may wish to publish your gateway's TXT record in a forward domain as shown here.
During the transition, you may wish to leave any old KEY records up for some time. They will provide limited backward compatibility.
We want to make it easy for you to declare security policy as it applies to IPsec connections.
Policy Groups make it simple to say:
FreeS/WAN then implements these policies, creating OE connections if and when needed. You can use Policy Groups along with connections you explicitly define in ipsec.conf.
For more information, see our Policy Group HOWTO.
Free/SWAN 2.x ships with the automatically enabled, hidden connection packetdefault. This configures a FreeS/WAN box as an OE gateway for any hosts located behind it. As mentioned above, you must configure some DNS records for OE to work.
As the name implies, this connection functions as a default. If you have more specific connections, such as policy groups which configure your FreeS/WAN box as an OE gateway for a local subnet, these will apply before packetdefault. You can view packetdefault 's specifics in man ipsec.conf .
FreeS/WAN often doesn't work with reverse path filtering. At start time, FreeS/WAN now turns rp_filter off, and logs a warning.
FreeS/WAN does not turn it back on again. You can do this yourself with a command like:
echo 1 > /proc/sys/net/ipv4/conf/eth0/rp_filter
For eth0, substitute the interface which FreeS/WAN was affecting.
The FreeS/WAN team promised config-file compatibility throughout the 1.x series. That means a 1.5 config file can be directly imported into a fresh 1.99 install with no problems.
With FreeS/WAN 2.x, we've given ourselves permission to make the config file easier to use. The cost: some FreeS/WAN 1.x configurations will not work properly. Many of the new features are, however, backward compatible.
... so long as you paste this line, with no preceding whitespace, at the top of your config file:
version 2
If the new defaults bite you, use this ipsec.conf fragment to simulate the old default values.
We've obsoleted various directives which almost no one was using:
dump
plutobackgroundload
no_eroute_pass
lifetime
rekeystart
rekeytries
For most of these, there is some other way to elicit the desired behaviour. See this post.
We've made some settings, which almost everyone was using, defaults. For example:
interfaces=%defaultroute
plutoload=%search
plutostart=%search
uniqueids=yes
We've also changed some default values to help with OE and Policy Groups:
authby=rsasig ## not secret!!!
leftrsasigkey=%dnsondemand ## looks up missing keys in DNS when needed.
rightrsasigkey=%dnsondemand
Of course, you can still override any defaults by explictly declaring something else in your connection.
A post with a list of many ipsec.conf changes.
Current ipsec.conf manual.
Note: When upgrading from 1-series to 2-series RPMs, rpm -U will not work.
You must instead erase the 1.x RPMs, then install the 2.x set:
rpm -e freeswan
rpm -e freeswan-module
On erasing, your old ipsec.conf should be moved to ipsec.conf.rpmsave. Keep this. You will probably want to copy your existing connections to the end of your new 2.x file.
Install the RPMs suitable for your kernel version, such as:
rpm -ivh freeswan-module-2.03_2.4.20_20.9-0.i386.rpm
rpm -ivh freeswan-userland-2.03_2.4.20_20.9-0.i386.rpm
Or, to splice the files:
cat /etc/ipsec.conf /etc/ipsec.conf.rpmsave > /etc/ipsec.conf.tmp
mv /etc/ipsec.conf.tmp /etc/ipsec.conf
Then, remove the redundant conn %default and config setup sections. Unless you have done any special configuring here, you'll likely want to remove the 1.x versions. Remove conn OEself, if present.
This page will get you started using Linux FreeS/WAN with opportunistic encryption (OE). OE enables you to set up IPsec tunnels without co-ordinating with another site administrator, and without hand configuring each tunnel. If enough sites support OE, a "FAX effect" occurs, and many of us can communicate without eavesdroppers.
As of FreeS/WAN 2.01, OE uses DNS TXT resource records (RRs) only (rather than TXT with KEY). This change causes a "flag day". Users of FreeS/WAN 2.00 (or earlier) OE who are upgrading may require additional resource records, as detailed in our upgrading document. OE setup instructions here are for 2.02 or later.
To set up opportunistic encryption, you will need:
Note: Currently, only Linux FreeS/WAN supports opportunistic encryption.
Our instructions are for a recent Red Hat with a 2.4-series stock or Red Hat updated kernel. For other ways to install, see our install document.
If we have prebuilt RPMs for your Red Hat system, this command will get them:
ncftpget ftp://ftp.xs4all.nl/pub/crypto/freeswan/binaries/RedHat-RPMs/`uname -r | tr -d 'a-wy-z'`/\*
If that fails, you will need to try another install method. Our kernel modules will only work on the Red Hat kernel they were built for, since they are very sensitive to small changes in the kernel.
If it succeeds, you will have userland tools, a kernel module, and an RPM signing key:
freeswan-module-2.03_2.4.20_20.9-0.i386.rpm
freeswan-userland-2.03_2.4.20_20.9-0.i386.rpm
freeswan-rpmsign.asc
If you're running RedHat 8.x or later, import the RPM signing key into the RPM database:
rpm --import freeswan-rpmsign.asc
For RedHat 7.x systems, you'll need to add it to your PGP keyring:
pgp -ka freeswan-rpmsign.asc
Check the digital signatures on both RPMs using:
rpm --checksig freeswan*.rpm
You should see that these signatures are good:
freeswan-module-2.03_2.4.20_20.9-0.i386.rpm: pgp md5 OK
freeswan-userland-2.03_2.4.20_20.9-0.i386.rpm: pgp md5 OK
Become root:
su
Install your RPMs with:
rpm -ivh freeswan*.rpm
If you're upgrading from FreeS/WAN 1.x RPMs, and have problems with that command, see this note.
Then, start FreeS/WAN:
service ipsec start
To check that you have a successful install, run:
ipsec verify
You should see as part of the verify output:
Checking your system to see if IPsec got installed and started correctly
Version check and ipsec on-path [OK]
Checking for KLIPS support in kernel [OK]
Checking for RSA private key (/etc/ipsec.secrets) [OK]
Checking that pluto is running [OK]
...
If any of these first four checks fails, see our troubleshooting guide.
Determine the best form of opportunism your system can support.
When you set up initiate-only Opportunistic Encryption (iOE):
You cannot network a group of initiator-only machines if none of these is capable of responding to OE. If one is capable of responding, you may be able to create a hub topology using routing.
Find a DNS forward domain (e.g. example.com) where you can publish your key. You'll need access to the DNS zone files for that domain. This is common for a domain you own. Some free DNS providers, such as this one, also provide this service.
Dynamic IP users take note: the domain where you place your key need not be associated with the IP address for your system, or even with your system's usual hostname.
Choose a name within that domain which you will use to identify your machine. It's convenient if this can be the same as your hostname:
[root@xy root]# hostname --fqdn
xy.example.com
This name in FQDN (fully-qualified domain name) format will be your ID, for DNS key lookup and IPsec negotiation.
Generate a forward TXT record containing your system's public key with a command like:
ipsec showhostkey --txt @xy.example.com
using your chosen ID in place of xy.example.com. This command takes the contents of /etc/ipsec.secrets and reformats it into something usable by ISC's BIND. The result should look like this (with the key data trimmed down for clarity):
; RSA 2192 bits xy.example.com Thu Jan 2 12:41:44 2003
IN TXT "X-IPsec-Server(10)=@xy.example.com"
"AQOF8tZ2... ...+buFuFn/"
Insert the record into DNS, or have a system adminstrator do it for you. It may take up to 48 hours for the record to propagate, but it's usually much quicker.
Check your DNS work
ipsec verify --host xy.example.com
As part of the verify output, you ought to see something like:
...
Looking for TXT in forward map: xy.example.com [OK]
...
For this type of opportunism, only the forward test is relevant; you can ignore the tests designed to find reverse records.
If your ID is the same as your hostname, you're ready to go. FreeS/WAN will use its built-in connections to create your iOE functionality.
If you have chosen a different ID, you must tell FreeS/WAN about it via ipsec.conf:
config setup
myid=@myname.freedns.example.com
and restart FreeS/WAN:
service ipsec restart
The new ID will be applied to the built-in connections.
Note: you can create more complex iOE configurations as explained in our policy groups document, or disable OE using these instructions.
That's it! Test your connections.
Full opportunism allows you to initiate and receive opportunistic connections on your machine.
To set up full opportunism, first set up a forward TXT record as for initiator-only OE , using an ID (for example, your hostname) that resolves to your IP. Do not configure /etc/ipsec.conf, but continue with the instructions for full opportunism, below.
Note that this forward record is not currently necessary for full OE, but will facilitate future features.
You must be able to publish your DNS RR directly in the reverse domain. FreeS/WAN will not follow a PTR which appears in the reverse, since a second lookup at connection start time is too costly.
This record serves to publicize your FreeS/WAN public key. In addition, it lets others know that this machine can receive opportunistic connections, and asserts that the machine is authorized to encrypt on its own behalf.
Use the command:
ipsec showhostkey --txt 192.0.2.11
where you replace 192.0.2.11 with your public IP.
The record (with key shortened) looks like:
; RSA 2048 bits xy.example.com Sat Apr 15 13:53:22 2000
IN TXT "X-IPsec-Server(10)=192.0.2.11" " AQOF8tZ2...+buFuFn/"
Send these records to your ISP, to be published in your IP's reverse map. It may take up to 48 hours for these to propagate, but usually takes much less time.
Check your DNS work with
ipsec verify --host xy.example.com
As part of the verify output, you ought to see something like:
...
Looking for TXT in reverse map: 11.2.0.192.in-addr.arpa [OK]
...
which indicates that you've passed the reverse-map test.
FreeS/WAN 2.x ships with full OE enabled, so you don't need to configure anything. To enable OE out of the box, FreeS/WAN 2.x uses the policy group private-or-clear, which creates IPsec connections if possible (using OE if needed), and allows traffic in the clear otherwise. You can create more complex OE configurations as described in our policy groups document, or disable OE using these instructions .
If you've previously configured for initiator-only opportunism, remove myid= from config setup, so that peer FreeS/WANs will look up your key by IP. Restart FreeS/WAN so that your change will take effect, with
service ipsec restart
If you are running a default install of RedHat 8.x, take note: you will need to alter your iptables rule setup to allow IPSec traffic through your firewall. See our firewall document for sample iptables rules.
That's it. Now, test your connection.
Instructions are in the next section.
Be sure IPsec is running. You can see whether it is with:
ipsec setup status
If need be, you can restart it with:
service ipsec restart
Load a FreeS/WAN test website from the host on which you're running FreeS/WAN. Note: the feds may be watching these sites. Type one of:
links oetest.freeswan.org
links oetest.freeswan.nl
A positive result looks like this:
You seem to be connecting from: 192.0.2.11 which DNS says is:
gateway.example.com
_________________________________________________________________
Status E-route
OE enabled 16 192.139.46.73/32 -> 192.0.2.11/32 =>
tun0x2097@192.0.2.11
OE enabled 176 192.139.46.77/32 -> 192.0.2.11/32 =>
tun0x208a@192.0.2.11
If you see this, congratulations! Your OE host or gateway will now encrypt its own traffic whenever it can. For more OE tests, please see our testing document. If you have difficulty, see our OE troubleshooting tips.
Please see our policy groups document for more ways to set up Opportunistic Encryption.
You may also wish to make some pre-configured connections.
See the OE troubleshooting hints in our troubleshooting guide.
Please see this list of known issues with Opportunistic Encryption.
Policy Groups are an elegant general mechanism to configure FreeS/WAN. They are useful for many FreeS/WAN users.
In previous FreeS/WAN versions, you needed to configure each IPsec connection explicitly, on both local and remote hosts. This could become complex.
By contrast, Policy Groups allow you to set local IPsec policy for lists of remote hosts and networks, simply by listing the hosts and networks which you wish to have special treatment in one of several Policy Group files. FreeS/WAN then internally creates the connections needed to implement each policy.
In the next section we describe our five Base Policy Groups, which you can use to configure IPsec in many useful ways. Later, we will show you how to create an IPsec VPN using one line of configuration for each remote host or network.
FreeS/WAN offers these Base Policy Groups:
Notes:
The Base Policy Groups which build IPsec connections rely on Opportunistic Encryption. To use the following examples, you must first become OE-capable, as described in our quickstart guide.
Simply place CIDR blocks (names, IPs or IP ranges) in /etc/ipsec.d/policies/[groupname], and reread the policy group files.
For example, the private-or-clear policy tells FreeS/WAN to prefer encrypted communication to the listed CIDR blocks. Failing that, it allows talk in the clear.
To make this your default policy, place fullnet in the private-or-clear policy group file:
[root@xy root]# cat /etc/ipsec.d/policies/private-or-clear
# This file defines the set of CIDRs (network/mask-length) to which
# communication should be private, if possible, but in the clear otherwise.
....
0.0.0.0/0
and reload your policies with
ipsec auto --rereadgroups
Use this test to verify opportunistic connections.
Defining IPsec security policy with Base Policy Groups is like creating a shopping list: just put CIDR blocks in the appropriate group files. For example:
[root@xy root]# cd /etc/ipsec.d/policies
[root@xy policies]# cat private
192.0.2.96/27 # The finance department
192.0.2.192/29 # HR
192.0.2.12 # HR gateway
irc.private.example.com # Private IRC server
[root@xy policies]# cat private-or-clear
0.0.0.0/0 # My default policy: try to encrypt.
[root@xy policies]# cat clear
192.0.2.18/32 # My POP3 server
192.0.2.19/32 # My Web proxy
[root@xy policies]# cat block
spamsource.example.com
To make these settings take effect, type:
ipsec auto --rereadgroups
Notes:
You can create an IPsec VPN between several hosts, with only one line of configuration per host, using the private policy group.
First, use our quickstart guide to set up each participating host with a FreeS/WAN install and OE.
In one host's /etc/ipsec.d/policies/private, list the peers to which you wish to protect traffic. For example:
[root@xy root]# cd /etc/ipsec.d/policies
[root@xy policies]# cat private
192.0.2.9 # several hosts at example.com
192.0.2.11
192.0.2.12
irc.private.example.com
Copy the private file to each host. Remove the local host, and add the initial host.
scp2 /etc/ipsec.d/policies/private root@192.0.2.12:/etc/ipsec.d/policies/private
On each host, reread the policy groups with
ipsec auto --rereadgroups
That's it! You're configured.
Test by pinging between two hosts. After a second or two, traffic should flow, and
ipsec eroute
should yield something like
192.0.2.11/32 -> 192.0.2.8/32 => tun0x149f@192.0.2.8
where your host IPs are substituted for 192.0.2.11 and 192.0.2.8.
If traffic does not flow, there may be an error in your OE setup. Revisit our quickstart guide.
Our next two examples show you how to add subnets to this IPsec VPN.
To protect traffic to a subnet behind your FreeS/WAN gateway, you'll need additional DNS records, and new policy groups. To set up the DNS, see our quickstart guide. To create five new policy groups for your subnet, copy these connections to /etc/ipsec.conf. Substitute your subnet's IPs for 192.0.2.128/29.
conn private-net
also=private # inherits settings (eg. auto=start) from built in conn
leftsubnet=192.0.2.128/29 # your subnet's IPs here
conn private-or-clear-net
also=private-or-clear
leftsubnet=192.0.2.128/29
conn clear-or-private-net
also=clear-or-private
leftsubnet=192.0.2.128/29
conn clear-net
also=clear
leftsubnet=192.0.2.128/29
conn block-net
also=block
leftsubnet=192.0.2.128/29
Copy the gateway's files to serve as the initial policy group files for the new groups:
cp -p /etc/ipsec.d/policies/private /etc/ipsec.d/policies/private-net
cp -p /etc/ipsec.d/policies/private-or-clear /etc/ipsec.d/policies/private-or-clear-net
cp -p /etc/ipsec.d/policies/clear-or-private /etc/ipsec.d/policies/clear-or-private-net
cp -p /etc/ipsec.d/policies/clear /etc/ipsec.d/policies/clear-net
cp -p /etc/ipsec.d/policies/block /etc/ipsec.d/policies/block
Tip: Since a missing policy group file is equivalent to a file with no entries, you need only create files for the connections you'll use.
To test one of your new groups, place the fullnet 0.0.0.0/0 in private-or-clear-net. Perform the subnet test in our quickstart guide. You should see a connection, and
ipsec eroute
should include an entry which mentions the subnet node's IP and the OE test site IP, like this:
192.0.2.131/32 -> 192.139.46.77/32 => tun0x149f@192.0.2.11
Suppose you wish to secure traffic to a subnet 192.0.2.192/29 behind a FreeS/WAN box 192.0.2.12.
First, add DNS entries to configure 192.0.2.12 as an opportunistic gateway for that subnet. Instructions are in our quickstart guide. Next, create a private-net group on 192.0.2.12 as described in Example 4.
On each other host, add the subnet 192.0.2.192/29 to private , yielding for example
[root@xy root]# cd /etc/ipsec.d/policies
[root@xy policies]# cat private
192.0.2.9 # several hosts at example.com
192.0.2.11
192.0.2.12 # HR department gateway
192.0.2.192/29 # HR subnet
irc.private.example.com
and reread policy groups with
ipsec auto --rereadgroups
That's all the configuration you need.
Test your VPN by pinging from a machine on 192.0.2.192/29 to any other host:
[root@192.0.2.194]# ping 192.0.2.11
After a second or two, traffic should flow, and
ipsec eroute
should yield something like
192.0.2.11/32 -> 192.0.2.194/32 => tun0x149f@192.0.2.12
Key:
| 1. | 192.0.2.11/32 | Local start point of the protected traffic. |
| 2. | 192.0.2.194/32 | Remote end point of the protected traffic. |
| 3. | 192.0.2.12 | Remote FreeS/WAN node (gateway or host). May be the same as (2). |
| 4. | [not shown] | Local FreeS/WAN node (gateway or host), where you've produced the output. May be the same as (1). |
For additional assurance, you can verify with a packet sniffer that the traffic is being encrypted.
Note
Our Base Policy Groups are created using hidden connections. These are spelled out in man ipsec.conf and defined in /usr/lib/ipsec/_confread.
A policy group is built using a special connection description in ipsec.conf, which:
To create a new group:
To disable OE (eg. policy groups and packetdefault), cut and paste the following lines to /etc/ipsec.conf:
conn block
auto=ignore
conn private
auto=ignore
conn private-or-clear
auto=ignore
conn clear-or-private
auto=ignore
conn clear
auto=ignore
conn packetdefault
auto=ignore
Restart FreeS/WAN so that the changes take effect:
ipsec setup restart
This is a collection of questions and answers, mostly taken from the FreeS/WAN mailing list. See the project web site for more information. All the FreeS/WAN documentation is online there.
Contributions to the FAQ are welcome. Please send them to the project mailing list.
FreeS/WAN is a Linux implementation of the IPsec protocols, providing security services at the IP (Internet Protocol) level of the network.
For more detail, see our introduction document or the FreeS/WAN project web site.
To start setting it up, go to our quickstart guide.
Our web links document has information on IPsec for other systems.
It may guide you to a solution. If not, see its problem reporting section.
Basically, what it says is give us the output from ipsec barf from both gateways. Without full information, we cannot diagnose a problem. However, ipsec barf produces a lot of output. If at all possible, please make barfs accessible via the web or FTP rather than sending enormous mail messages.
FreeS/WAN developers, volunteers and users can often be found there. Be patient and be prepared to provide lots of information to support your question.
If your question was really interesting, and you found an answer, please share that with the class by posting to the users mailing list. That way others with the same problem can find your answer in the archives.
See the next several questions.
There are a number of Linux distributions or firewall products which include FreeS/WAN. See this list. Using one of these, chosen to match your requirements and budget, may save you considerable time and effort.
If you don't know your requirements, start by reading Schneier's Secrets and Lies. That gives the best overview of security issues I have seen. Then consider hiring a consultant (see next question) to help define your requirements.
If you want the help of a contractor, or to hire staff with FreeS/WAN expertise, you could:
For companies offerring support, see the next question.
Many of the distributions or firewall products which include FreeS/WAN (see this list) come with commercial support or have it available as an option.
Various companies specialize in commercial support of open source software. Our project leader was a founder of the first such company, Cygnus Support. It has since been bought by Redhat. Another such firm is Linuxcare.
The current release is the highest-numbered tarball on our distribution site. Almost always, any of the mirrors will have the same file, though perhaps not for a day or so after a release.
Unfortunately, the web site is not always updated as quickly as it should be.
We try to do a release approximately every six to eight weeks.
If pre-release tests fail and the fix appears complex, or more generally if the code does not appear stable when a release is scheduled, we will just skip that release.
For serious bugs, we may bring out an extra bug-fix release. These get numbers in the normal release series. For example, there was a bug found in FreeS/WAN 1.6, so we did another release less than two weeks later. The bug-fix release was called 1.7.
Any problems we are aware of at the time of a release are documented in the BUGS file for that release. You should also look at the CHANGES file.
Bugs discovered after a release are discussed on the mailing lists. The easiest way to check for any problems in the current code would be to peruse the List In Brief.
You are free to modify FreeS/WAN in any way. See the discussion of licensing in our introduction document.
Before investing much energy in any such project, we suggest that you
This may prevent duplicated effort, or lead to interesting collaborations.
Users have also contributed heavily to documentation, both by creating their own HowTos and by posting things on the mailing lists which I have quoted in these HTML docs.
There are, however, some caveats.
FreeS/WAN is being implemented in Canada, by Canadians, largely to ensure that is it is entirely free of export restrictions. See this discussion. We cannot accept code contributions from US residents or citizens, not even one-line bugs fixes. The reasons for this were recently discussed extensively on the mailing list, in a thread starting here.
Not all contributions are of interest to us. The project has a set of fairly ambitious and quite specific goals, described in our introduction. Contributions that lead toward these goals are likely to be welcomed enthusiastically. Other contributions may be seen as lower priority, or even as a distraction.
Discussion of possible contributions takes place on the design mailing list.
The only formal design documents are a few papers in the last category above. All the other categories, however, have things to say about design as well.
The IPsec protocols are designed to support interoperation. In theory, any two IPsec implementations should be able to talk to each other. In practice, it is considerably more complex. We have a whole interoperation document devoted to this problem.
An important part of that document is links to the many user-written HowTos on interoperation between FreeS/WAN and various other implementations. Often the users know more than the developers about these issues (and almost always more than me :-), so these documents may be your best resource.
Linux FreeS/WAN can interoperate with many IPsec implementations, including earlier versions of Linux FreeS/WAN itself.
In a few cases, there are some complications. See our interoperation document for details.
There is no hard limit, but see below.
There is no hard limit, but see next question.
A quick summary:
Beyond about 50 tunnels it needs careful management.
See our FreeS/WAN performance document for details.
We build and test on Redhat distributions, but FreeS/WAN runs just fine on several other distributions, sometimes with minor fiddles to adapt to the local environment. Details are in our compatibility document. Also, some distributions or products come with FreeS/WAN included.
FreeS/WAN is intended to run on all CPUs Linux supports . We know of it being used in production on x86, ARM, Alpha and MIPS. It has also had successful tests on PPC and SPARC, though we don't know of actual use there. Details are in our compatibility document.
FreeS/WAN is designed to work on any SMP architecture Linux supports, and has been tested successfully on at least dual processor Intel architecture machines. Details are in our compatibility document.
It might, but we strongly recommend using a recent 2.2 or 2.4 series kernel. Sometimes the newer versions include security fixes which can be quite important on a gateway.
Also, we use recent kernels for development and testing, so those are better tested and, if you do encounter a problem, more easily supported. If something breaks applying recent FreeS/WAN patches to an older kernel, then "update your kernel" is almost certain to be the first thing we suggest. It may be the only suggestion we have.
The precise kernel versions supported by a particular FreeS/WAN release are given in the README file of that release.
See the following question for more on kernels.
Sometimes yes, but quite often, no.
Kernel versions supported are given in the README file of each FreeS/WAN release. Typically, they are whatever production kernels were current at the time of our release (or shortly before; we might release for kernel n just as Linus releases n+1 ). Often FreeS/WAN will work on slightly later kernels as well, but of course this cannot be guaranteed.
For example, FreeS/WAN 1.91 was released for kernels 2.2.19 or 2.4.5, the current kernels at the time. It also worked on 2.4.6, 2.4.7 and 2.4.8, but 2.4.9 had changes that caused compilation errors if it was patched with FreeS/WAN 1.91.
When such changes appear, we put a fix in the FreeS/WAN snapshots, and distribute it with our next release. However, this is not a high priority for us, and it may take anything from a few days to several weeks for such a problem to find its way to the top of our kernel programmer's To-Do list. In the meanwhile, you have two choices:
We don't even try to keep up with kernel changes outside the main 2.2 and 2.4 branches, such as the 2.4.x-ac patched versions from Alan Cox or the 2.5 series of development kernels. We'd rather work on developing the FreeS/WAN code than on chasing these moving targets. We are, however, happy to get patches for problems discovered there.
See also the Choosing a kernel section of our installation document.
IPsec is designed to work over any network that IP works over, and FreeS/WAN is intended to work over any network interface hardware that Linux supports.
If you have working IP on some unusual interface -- perhaps Arcnet, Token Ring, ATM or Gigabit Ethernet -- then IPsec should "just work".
That said, practice is sometimes less tractable than theory. Our testing is done almost entirely on:
If you have some other interface, especially an uncommon one, it is entirely possible you will get bitten either by a FreeS/WAN bug which our testing did not turn up, or by a bug in the driver that shows up only with our loads.
If IP works on your interface and FreeS/WAN doesn't, seek help on the mailing lists.
Another FAQ section describes MTU problems . These are a possibility for some interfaces.
Yes, FreeSwan works fine, though some network drivers have problems with jumbo sized ethernet frames. If you used interfaces=%defaultroute you do not need to change anything, but if you specified an interface (eg eth0) then remember you must change that to reflect the VLAN interface (eg eth0.2 for VLAN ID 2).
The "eepro100" module is known to be broken, use the e100 driver for those cards instead (included in 2.4 as 'alternative driver' for the Intel EtherExpressPro/100.
You do not need to change any MTU setting (those are workarounds that are only needed for buggy drivers)
This FAQ contributed by Paul Wouters.
For a discussion of which parts of the IPsec specifications FreeS/WAN does and does not implement, see our compatibility document.
For information on some often-requested features, see below.
Absolutely. See this FreeS/WAN-FreeS/WAN configuration example. If only one site is using FreeS/WAN, there may be a relevant HOWTO on our interop page.
Yes. We call the remote users "Road Warriors". Check out our FreeS/WAN-FreeS/WAN Road Warrior Configuration Example.
If your Road Warrior is a Windows or Mac PC, you may need to install an IPsec implementation on that machine. Our interop page lists many available brands, and features links to several HOWTOs.
Yes, but there are severe restrictions, so we strongly recommend using RSA keys for authentication instead.
See this FAQ question.
Yes, it is a common practice to use IPsec over wireless networks because their built-in encryption, WEP, is insecure.
There is some discussion in our advanced configuration document. See also the WaveSEC site.
Vanilla FreeS/WAN does not support X.509, but Andreas Steffen and others have provided a popular, well-supported X.509 patch.
Linux FreeS/WAN features Opportunistic Encryption, an alternative Public Key Infrastructure based on Secure DNS.
Andreas Steffen's X.509 patch (v. 1.42+) supports Smart Cards. The patch does not ship with vanilla FreeS/WAN, but will be incorporated into Super FreeS/WAN 2.01+. The patch implements the PCKS#15 Cryptographic Token Information Format Standard, using the OpenSC smartcard library functions.
Older news:
A user-supported patch to FreeS/WAN 1.3, for smart card style authentication, is available on Bastiaan's site. It supports skeyid and ibutton. This patch is not part of Super FreeS/WAN.
For a while progress on this front was impeded by a lack of standard. The IETF working group has now nearly completed its recommended solution to the problem; meanwhile several vendors have implemented various things.
Of course, there are various ways to avoid any requirement for user authentication in IPsec. Consider the situation where road warriors build IPsec tunnels to your office net and you are considering requiring user authentication during tunnel negotiation. Alternatives include:
If either of those is trustworthy, it is not clear that you need user authentication in IPsec.
Vanilla FreeS/WAN does not, but thanks to Mathieu Lafon and Arkoon Network Security, there's a patch to support this.
The NAT traversal patch has some issues with PSKs, so you may wish to authenticate with RSA keys, or X.509 (requires a patch which is also included in Super FreeS/WAN). Doing the latter also has advantages when dealing with large numbers of clients who may be behind NAT; instead of having to make an individual Roadwarrior connection for each virtual IP, you can use the "rightsubnetwithin" parameter to specify a range. See these rightsubnetwithin instructions.
Some IPsec implementations allow you to make the source address on packets sent by a Road Warrior machine be something other than the address of its interface to the Internet. This is sometimes described as assigning a virtual identity to that machine.
FreeS/WAN does not directly support this, but it can be done. See this FAQ question.
No, single DES is not used either at the IKE level for negotiating connections or at the IPsec level for actually building them.
Single DES is insecure. As we see it, it is more important to deliver real security than to comply with a standard which has been subverted into allowing use of inadequate methods. See this discussion.
If you want to interoperate with an IPsec implementation which offers only DES, see our interoperation document.
AES is a new US government block cipher standard to replace the obsolete DES.
At time of writing (March 2002), the FreeS/WAN distribution does not yet support AES but user-written patches are available to add it. Our kernel programmer is working on integrating those patches into the distribution, and there is active discussion of this on the design mailimg list.
Currently triple DES is the only cipher supported. AES will almost certainly be added (see previous question), and it is likely that in the process we will also add the other two AES finalists with open licensing, Twofish and Serpent.
We are extremely reluctant to add other ciphers. This would make both use and maintenance of FreeS/WAN more complex without providing any clear benefit. Complexity is emphatically not desirable in a security product.
Various users have written patches to add other ciphers. We provide links to these.
Yes, you can, so long as you pay attention to the selection rule, which can be summarized "the most specific connection wins". We describe the rule in our policy groups document, and provide a more technical explanation in man ipsec.conf.
A good guideline: If you have a regular connection defined in ipsec.conf, ensure that a subset of that connection is not listed in a less restrictive policy group. Otherwise, FreeS/WAN will use the subset, with its more specific source/destination pair.
Here's an example. Suppose you are the system administrator at 192.0.2.2. You have this connection in ipsec.conf: ipsec.conf :
conn net-to-net
left=192.0.2.2 # you are here
right=192.0.2.8
rightsubnet=192.0.2.96/27
....
If you then place a host or net within rightsubnet, (let's say 192.0.2.98) in private-or-clear, you may find that 192.0.2.2 at times communicates in the clear with 192.0.2.98. That's consistent with the rule, but may be contrary to your expectations.
On the other hand, it's safe to put a larger subnet in a less restrictive policy group file. If private-or-clear contains 192.0.2.0/24, then the more specific net-to-net connection is used for any communication to 192.0.2.96/27. The more general policy applies only to communication with hosts or subnets in 192.0.2.0/24 without a more specific policy or connection.
Yes. Use these instructions.
Yes, you can do this. Here are the details, in a mailing list message from Pluto programmer Hugh Redelmeier:
| How can I reload config's without restarting all of pluto and klips? I am using
| FreeSWAN -> PGPNet in a medium sized production environment, and would like to be
| able to add new connections ( i am using include config/* ) without dropping current
| SA's.
|
| Can this be done?
|
| If not, are there plans to add this kind of feature?
ipsec auto --add whatever
This will look in the usual place (/etc/ipsec.conf) for a conn named
whatever and add it.
If you added new secrets, you need to do
ipsec auto --rereadsecrets
before Pluto needs to know those secrets.
| I have looked (perhaps not thoroughly enough tho) to see how to do this:
There may be more bits to look for, depending on what you are trying
to do.
Another useful command here is ipsec auto --replace <conn_name> which re-reads data for a named connection.
Yes. This is done all the time. See the discussion in our setup document. The only restriction is that the subnets on the two ends must not overlap. See the next question.
Here is a mailing list message on the topic. The user incorrectly thinks you need a 2.4 kernel for this -- actually various people have been doing it on 2.0 and 2.2 for quite some time -- but he has it right for 2.4.
Subject: Double NAT and freeswan working :)
Date: Sun, 11 Mar 2001
From: Paul Wouters <paul@xtdnet.nl>
Just to share my pleasure, and make an entry for people who are searching
the net on how to do this. Here's the very simple solution to have a double
NAT'ed network working with freeswan. (Not sure if this is old news, but I'm
not on the list (too much spam) and I didn't read this in any HOWTO/FAQ/doc
on the freeswan site yet (Sandy, put it in! :)
10.0.0.0/24 --- 10.0.0.1 a.b.c.d ---- a.b.c.e {internet} ----+
|
10.0.1.0/24 --- 10.0.1.1 f.g.h.i ---- f.g.h.j {internet} ----+
the goal is to have the first network do a VPN to the second one, yet also
have NAT in place for connections not destinated for the other side of the
NAT. Here the two Linux security gateways have one real IP number (cable
modem, dialup, whatever.
The problem with NAT is you don't want packets from 10.*.*.* to 10.*.*.*
to be NAT'ed. While with Linux 2.2, you can't, with Linux 2.4 you can.
(This has been tested and works for 2.4.2 with Freeswan snapshot2001mar8b)
relevant parts of /etc/ipsec.conf:
left=f.g.h.i
leftsubnet=10.0.1.0/24
leftnexthop=f.g.h.j
leftfirewall=yes
leftid=@firewall.netone.nl
leftrsasigkey=0x0........
right=a.b.c.d
rightsubnet=10.0.0.0/24
rightnexthop=a.b.c.e
rightfirewall=yes
rightid=@firewall.nettwo.nl
rightrsasigkey=0x0......
# To authorize this connection, but not actually start it, at startup,
# uncomment this.
auto=add
and now the real trick. Setup the NAT correctly on both sites:
iptables -t nat -F
iptables -t nat -A POSTROUTING -o eth0 -d \! 10.0.0.0/8 -j MASQUERADE
This tells the NAT code to only do NAT for packets with destination other then
10.* networks. note the backslash to mask the exclamation mark to protect it
against the shell.
Happy painting :)
Paul
No. The notion that IP addresses are unique is one of the fundamental principles of the IP protocol. Messing with it is exceedingly perilous.
Fairly often a situation comes up where a company has several branches, all using the same non-routable addresses, perhaps 192.168.0.0/24. This works fine as long as those nets are kept distinct. The IP masquerading on their firewalls ensures that packets reaching the Internet carry the firewall address, not the private address.
This can break down when IPsec enters the picture. FreeS/WAN builds a tunnel that pokes through both masquerades and delivers packets from leftsubnet to rightsubnet and vice versa. For this to work, the two subnets must be distinct.
There are several solutions to this problem.
Usually, you re-number the subnets. Perhaps the Vancouver office becomes 192.168.101.0/24, Calgary 192.168.102.0/24 and so on. FreeS/WAN can happily handle this. With, for example leftsubnet=192.168.101.0/24 and rightsubnet=192.168.102.0/24 in a connection description, any machine in Calgary can talk to any machine in Vancouver. If you want to be more restrictive and use something like leftsubnet=192.168.101.128/25 and rightsubnet=192.168.102.240/28 so only certain machines on each end have access to the tunnel, that's fine too.
You could also split the subnet into smaller ones, for example using 192.168.1.0/25 in Vancouver and rightsubnet=192.168.0.128/25 in Calgary.
Alternately, you can just give up routing directly to machines on the subnets. Omit the leftsubnet and rightsubnet parameters from your connection descriptions. Your IPsec tunnels will then run between the public interfaces of the two firewalls. Packets will be masqueraded both before they are put into tunnels and after they emerge. Your Vancouver client machines will see only one Calgary machine, the firewall.
Often it would be convenient to be able to give a Road Warrior an IP address which appears to be on the local network. Some IPsec implementations have support for this, sometimes calling the feature "virtual identity".
Currently (Sept 2002) FreeS/WAN does not support this, and we have no definite plans to add it. The difficulty is that is not yet a standard mechanism for it. There is an Internet Draft for a method of doing it using DHCP which looks promising. FreeS/WAN may support that in a future release.
In the meanwhile, you can do it yourself using the Linux iproute2(8) facilities. Details are in this paper.
Another method has also been discussed on the mailing list.:
For example, you might have:
You then set up routing so that the office machines use the IPsec gateway as their route to a.b.c.128/25. The leftsubnet parameter tells the road warriors to use tunnels to reach a.b.c.0/25, so you should have two-way communication. Depending or your network and applications, there may be some additional work to do on DNS or Windows configuration
Yes. This is easily done, using
In either case, each Road Warrior must have a different key or certificate.
It is also possible using pre-shared key authentication, though we don't recommend this; see the next question for details.
If you expect to have more than a few dozen Road Warriors connecting simultaneously, you may need a fairly powerful gateway machine. See our document on FreeS/WAN performance.
Yes, but avoid it if possible.
You can have multiple Road Warriors using shared secret authentication only if they all use the same secret. You must also set:
uniqueids=no
in the connection definition.
Why it's less secure:
This is a designed-in limitation of the IKE key negotiation protocol, not a problem with our implementation.
We very strongly recommend that you avoid using shared secret authentication for multiple Road Warriors. Use RSA authentication instead.
The longer story: When using shared secrets, the protocol requires that the responding gateway be able to determine which secret to use at a time when all it knows about the initiator is an IP address. This works fine if you know the initiator's address in advance and can use it to look up the appropiriate secret. However, it fails for Road Warriors since the gateway cannot know their IP addresses in advance.
With RSA signatures (or certificates) the protocol is slightly different. The initiator provides an identifier early in the exchange and the responder can use that identifier to look up the correct key or certificate. See above.
From project technical lead Henry Spencer:
> Do QoS add to FreeS/WAN? > For example integrating DiffServ and FreeS/WAN? With a current version of FreeS/WAN, you will have to add hidetos=no to the config-setup section of your configuration file. By default, the TOS field of tunnel packets is zeroed; with hidetos=no, it is copied from the packet inside. (This is a modest security hole, which is why it is no longer the default.) DiffServ does not interact well with tunneling in general. Ways of improving this are being studied.
Copying the TOS (type of service) information from the encapsulated packet to the outer header reveals the TOS information to an eavesdropper. This does not tell him much, but it might be of use in traffic analysis. Since we do not have to give it to him, our default is not to.
Even with the TOS hidden, you can still:
See ipsec.conf(5) for more on the hidetos= parameter.
There is no general mechanism to do this is in the IPsec protocols.
From time to time, there is discussion on the IETF Working Group mailing list of adding a "keep-alive" mechanism (which some say should be called "make-dead"), but it is a fairly complex problem and no consensus has been reached on whether or how it should be done.
The protocol does have optional delete-SA messages which one side can send when it closes a connection in hopes this will cause the other side to do the same. FreeS/WAN does not currently support these. In any case, they would not solve the problem since:
However, connections do have limited lifetimes and you can control how many attempts your gateway makes to rekey before giving up. For example, you can set:
conn default
keyingtries=3
keylife=30m
With these settings old connections will be cleaned up. Within 30 minutes of the other end dying, rekeying will be attempted. If it succeeds, the new connection replaces the old one. If it fails, no new connection is created. Either way, the old connection is taken down when its lifetime expires.
Here is a mailing list message on the topic from FreeS/WAN tech support person Claudia Schmeing:
You ask how to determine whether a tunnel is redundant:
> Can anybody explain the best way to determine this. Esp when a RW has
> disconnected? I thought 'ipsec auto --status' might be one way.
If a tunnel goes down from one end, Linux FreeS/WAN on the
other end has no way of knowing this until it attempts to rekey.
Once it tries to rekey and fails, it will 'know' that the tunnel is
down.
Because it doesn't have a way of knowing the state until this point,
it will also not be able to tell you the state via ipsec auto --status.
> However, comparing output from a working tunnel with that of one that
> was closed
> did not show clearly show tunnel status.
If your tunnel is down but not 'unrouted' (see man ipsec_auto), you
should not be able to ping the opposite side of the tunnel. You can
use this as an indicator of tunnel status.
On a related note, you may be interested to know that as of 1.7,
redundant tunnels caused by RW disconnections are likely to be
less of a pain. From doc/CHANGES:
There is a new configuration parameter, uniqueids, to control a new Pluto
option: when a new connection is negotiated with the same ID as an old
one, the old one is deleted immediately. This should help eliminate
dangling Road Warrior connections when the same Road Warrior reconnects.
It thus requires that IDs not be shared by hosts (a previously legal but
probably useless capability). NOTE WELL: the sample ipsec.conf now has
uniqueids=yes in its config-setup section.
Cheers,
Claudia
This is possible, but not easy. FreeS/WAN technical lead Henry Spencer wrote:
> 5. If the ISDN link goes down in between and is reestablished, the SAs > are still up but the eroute are deleted and the IPsec interface shows > garbage (with ifconfig) > 6. Only restarting IPsec will bring the VPN back online. This one is awkward to solve. If the real interface that the IPsec interface is mounted on goes down, it takes most of the IPsec machinery down with it, and a restart is the only good way to recover. The only really clean fix, right now, is to split the machines in two: 1. A minimal machine serves as the network router, and only it is aware that the link goes up and down. 2. The IPsec is done on a separate gateway machine, which thinks it has a permanent network connection, via the router. This is clumsy but it does work. Trying to do both functions within a single machine is tricky. There is a software package (diald) which will give the illusion of a permanent connection for demand-dialed modem connections; I don't know whether it's usable for ISDN, or whether it can be made to cooperate properly with FreeS/WAN. Doing a restart each time the interface comes up *does* work, although it is a bit painful. I did that with PPP when I was running on a modem link; it wasn't hard to arrange the PPP scripts to bring IPsec up and down at the right times. (I'd meant to investigate diald but never found time.) In principle you don't need to do a complete restart on reconnect, but you do have to rebuild some things, and we have no nice clean way of doing only the necessary parts.
In the same thread, one user commented:
Subject: Re: linux-ipsec: IPsec and Dial Up Connections Date: Wed, 22 Nov 2000 From: Andy Bradford <andyb@calderasystems.com> On Wed, 22 Nov 2000 19:47:11 +0100, Philip Reetz wrote: > Are there any ideas what might be the cause of the problem and any way > to work around it. > Any help is highly appreciated. On my laptop, when using ppp there is a ip-up script in /etc/ppp that will be executed each time that the ppp interface is brought up. Likewise there is an ip-down script that is called when it is taken down. You might consider custimzing those to stop and start FreeS/WAN with each connection. I believe that ISDN uses the same files, though I could be wrong---there should be something similar though.
Yes. Normally this is not necessary, but it is useful in a few special cases. For example, if you must route non-IP packets such as IPX, you will need to use a tunneling protocol that can route these packets. IPsec can be layered around it for extra security. Another example: you can provide failover protection for high availability (HA) environments by combining IPsec with other tools. Ken Bantoft describes one such setup in Using FreeS/WAN with Linux-HA, GRE, OSPF and BGP for enterprise grade VPN solutions.
GRE over IPsec is covered as part of that document. Here are links to other GRE resources. Jacco de Leuw has created this page on L2TP over IPsec with instructions for FreeS/WAN and several other brands of IPsec software.
Please let us know of other useful links via the mailing lists.
Your local PC needs to know how to translate NetBIOS names to IP addresses. It may do this either via a local LMHOSTS file, or using a local or remote WINS server. The WINS server is preferable since it provides a centralized source of the information to the entire network. To use a WINS server over the VPN (or any IP-based network), you must enable "NetBIOS over TCP".
Samba can emulate a WINS server on Linux.
See also several discussions in our September 2002 Users archives
FreeS/WAN is a fairly complex product. (Neither the networks it runs on nor the protocols it uses are simple, so it could hardly be otherwise.) It therefore sometimes exhibits behaviour which can be somewhat confusing, or has problems which are not easy to diagnose. This section tries to explain those problems.
Setup and configuration of FreeS/WAN are covered in other documentation sections:
However, we also list some of the commonest problems here.
This question is dealt with in the advanced configuration section under the heading multiple tunnels.
The standard subnet-to-subnet tunnel protects traffic only between the subnets. To test it, you must use pings that go from one subnet to the other.
For example, suppose you have:
subnet a.b.c.0/24
|
eth1 = a.b.c.1
gate1
eth0 = 192.0.2.8
|
~ internet ~
|
eth0 = 192.0.2.11
gate2
eth1 = x.y.z.1
|
subnet x.y.z.0/24
and the connection description:
conn abc-xyz
left=192.0.2.8
leftsubnet=a.b.c.0/24
right=192.0.2.11
rightsubnet=x.y.z.0/24
You can test this connection description only by sending a ping that will actually go through the tunnel. Assuming you have machines at addresses a.b.c.2 and x.y.z.2, pings you might consider trying are:
Only the first of these is a useful test of this tunnel. The others do not use the tunnel. Depending on other details of your setup and routing, they:
In some cases, you may be able to get around this. For the example network above, you could use:
ping -I a.b.c.1 x.y.z.1
Both the adresses given are within protected subnets, so this should go through the tunnel.
If required, you can build additional tunnels so that all the machines involved can talk to all the others. See multiple tunnels in the advanced configuration document for details.
Users fairly often report various problems involving long delays, sometimes on tunnel setup and sometimes on operations done through the tunnel, occasionally on simple things like ping or more often on more complex operations like doing NFS or Samba through the tunnel.
Almost always, these turn out to involve failure of a DNS lookup. The timeouts waiting for DNS are typically set long so that you won't time out when a query involves multiple lookups or long paths. Genuine failures therefore produce long delays before they are detected.
A mailing list message from project technical lead Henry Spencer:
> ... when i run /etc/rc.d/init.d/ipsec start, i get: > ipsec_setup: Starting FreeS/WAN IPsec 1.5... > and it just sits there, doesn't give back my bash prompt. Almost certainly, the problem is that you're using DNS names in your ipsec.conf, but DNS lookups are not working for some reason. You will get your prompt back... eventually. But the DNS timeouts are long. Doing something about this is on our list, but it is not easy.
In the meanwhile, we recommend that connection descriptions in ipsec.conf(5) use numeric IP addresses rather than names which will require a DNS lookup.
Names that do not require a lookup are fine. For example:
These are fine. The @ sign prevents any DNS lookup. However, do not attempt to give the gateway address as left=camelot.example.org . That requires a lookup.
A post from one user after solving a problem with long delays:
Subject: Final Answer to Delay!!! Date: Mon, 19 Feb 2001 From: "Felippe Solutions" <felippe@solutionstecnologia.com.br> Sorry people, but seems like the Delay problem had nothing to do with freeswan. The problem was DNS as some people sad from the beginning, but not the way they thought it was happening. Samba, ssh, telnet and other apps try to reverse lookup addresses when you use IP numbers (Stupid that ahh). I could ping very fast because I always ping with "-n" option, but I don't know the option on the other apps to stop reverse addressing so I don't use it.
This post is fairly typical. These problems are often tricky and frustrating to diagnose, and most turn out to be DNS-related.
One suggestion for diagnosis: test with both names and addresses if possible. For example, try all of:
If these behave differently, the problem must be DNS-related since the three commands do exactly the same thing except for DNS lookups.
IPsec connections are designed to carry only packets travelling between pre-defined connection endpoints. As project technical lead Henry Spencer put it:
IPsec tunnels are not just virtual wires; they are virtual wires with built-in access controls. Negotiation of an IPsec tunnel includes negotiation of access rights for it, which don't include packets to/from other IP addresses. (The protocols themselves are quite inflexible about this, so there are limits to what we can do about it.)
For fairly obvious security reasons, and to comply with the IPsec RFCs, KLIPS drops any packets it receives that are not allowed on the tunnels currently defined. So if you send it packets with route(8), and suitable tunnels are not defined, the packets vanish. Whether this is reported in the logs depends on the setting of klipsdebug in your ipsec.conf(5) file.
To rescue vanishing packets, you must ensure that suitable tunnels for them exist, by editing the connection descriptions in ipsec.conf(5). For example, supposing you have a simple setup:
leftsubnet -- leftgateway === internet === roadwarrior
If you want to give the roadwarrior access to some resource that is located behind the left gateway but is not in the currently defined left subnet, then the usual procedure is to define an additional tunnel for those packets by creating a new connection description.
In some cases, it may be easier to alter an existing connection description, enlarging the definition of leftsubnet. For example, instead of two connection descriptions with 192.168.8.0/24 and 192.168.9.0/24 as their leftsubnet parameters, you can use a single description with 192.168.8.0/23.
If you have multiple endpoints on each side, you need to ensure that there is a route for each pair of endpoints. See this example.
This is a special case of the vanishing packet problem described in the previous question. Whenever KLIPS sees packets for which it does not have a tunnel, it drops them.
When a tunnel goes away, either because negotiations with the other gateway failed or because you gave an ipsec auto --down command, the route to its other end is left pointing into KLIPS, and KLIPS will drop packets it has no tunnel for.
This is a documented design decision, not a bug. FreeS/WAN must not automatically adjust things to send packets via another route. The other route might be insecure.
Of course, re-routing may be necessary in many cases. In those cases, you have to do it manually or via scripts. We provide the ipsec auto --unroute command for these cases.
From ipsec_auto(8):
Normally, pluto establishes a route to the destination specified for a connection as part of the --up operation. However, the route and only the route can be established with the --route operation. Until and unless an actual connection is established, this discards any packets sent there, which may be preferable to having them sent elsewhere based on a more general route (e.g., a default route).
Normally, pluto's route to a destination remains in place when a --down operation is used to take the connection down (or if connection setup, or later automatic rekeying, fails). This permits establishing a new connection (perhaps using a different specification; the route is altered as necessary) without having a ``window'' in which packets might go elsewhere based on a more general route. Such a route can be removed using the --unroute operation (and is implicitly removed by --delete).
See also this mailing list message.
If firewalls filter out:
then IPsec cannot work. The first thing to check if packets seem to be vanishing is the firewall rules on the two gateway machines and any other machines along the path that you have access to.
For details, see our document on firewalls .
Some advice from technical lead Henry Spencer on diagnosing such problems:
> > Packets vanishing between the hardware interface and the ipsecN interface > > is usually the result of firewalls not being configured to let them in... > > Thanks for the suggestion. If only it were that simple! My ipchains startup > script does take care of that, but just in case I manually inserted rules > accepting everything from london on dublin. No difference. The other thing to check is whether the "RX packets dropped" count on the ipsecN interface (run "ifconfig ipsecN", for N=1 or whatever, to see the counts) is rising. If so, then there's some sort of configuration mismatch between the two ends, and IPsec itself is rejecting them. If none of the ipsecN counts is rising, then the packets are never reaching the IPsec machinery, and the problem is almost certainly in firewalls etc.
Networks being what they are, IPsec connections can be broken for any number of reasons, ranging from hardware failures to various software problems such as the path MTU problems discussed elsewhere in the FAQ. Fortunately, various diagnostic tools exist that help you sort out many of the possible problems.
There is one situation, however, where FreeS/WAN (using default settings) may destroy a connection for no readily apparent reason. This occurs when things are misconfigured so that two tunnels from the same gateway expect the same subnet on the far end.
In this situation, the first tunnel comes up fine and works until the second is established. At that point, because of the way we track connections internally, the first tunnel ceases to exist as far as this gateway is concerned. Of course the far end does not know that, and a storm of error messages appears on both systems as it tries to use the tunnel.
If the far end gives up, goes back to square one and negotiates a new tunnel, then that wipes out the second tunnel and ...
The solution is simple. Do not build multiple conn descriptions with the same remote subnet.
This is actually intended to be a feature, rather than a bug. Consider the situation where a single remote system goes down, then comes back up and reconnects to the gateway. It is useful to have the gateway tear down the old tunnel and recover resources when the reconnection is made. It recognises that situation by checking the remote subnet for each tunnel it builds and discarding duplicates. This works fine as long as you don't configure multiple tunnels with the same remote subnet.
If this behaviour is inconvenient for you, you can disable it by setting uniqueids=no in ipsec.conf(5).
When an underlying connection (eg. ppp) goes down, FreeS/WAN will not recover properly without a little help. Here are the symptoms that FreeS/WAN user Michael Carmody noticed:
> After about 24 hours the freeswan connection takes over the default route. > > i.e instead of deafult gateway pointing to the router via eth0, it becomes a > pointer to the router via ipsec0. > All internet access is then lost as all replies (and not just the link I > wanted) are routed out ipsec0 and the router doesn't respond to the ipsec > traffic.
If you're using a FreeS/WAN 2.x/KLIPS system, simply re-attach the IPsec virtual interface with ipsec tnconfig command such as:
ipsec tnconfig --attach --virtual ipsec0 --physical ppp0
In your command, name the physical and virtual interfaces as they appear paired on your system during regular uptime. For a system with several physical/virtual interface pairs on flaky links, you'll need more than one such command. If you're using FreeS/WAN 1.x, you must restart FreeS/WAN, which is more time consuming.
Here is a script which can help to automate the process of FreeS/WAN restart at need. It could easily be adapted to use tnconfig instead.
Attempting to look at IPsec packets by running monitoring tools on the IPsec gateway machine can produce silly results. That machine is mangling the packets for IPsec, and possibly for firewall or NAT purposes as well. If the internals of the machine's IP stack are not what the monitoring tool expects, then the tool can misinterpret them and produce nonsense output.
See our testing document for more detail.
As far as traceroute can see, the two gateways are one hop apart; the data packet goes directly from one to the other through the tunnel. Of course the outer packets that implement the tunnel pass through whatever lies between the gateways, but those packets are built and dismantled by the gateways. Traceroute does not see them and cannot report anything about their path.
Here is a mailing list message with more detail.
Date: Mon, 14 May 2001 To: linux-ipsec@freeswan.org From: "John S. Denker" <jsd@research.att.com< Subject: Re: traceroute: one virtual hop At 02:20 PM 5/14/01 -0400, Claudia Schmeing wrote: > >> > A bonus question: traceroute in subnet to subnet enviroment looks like: >> > >> > traceroute to andris.dmz (172.20.24.10), 30 hops max, 38 byte packets >> > 1 drama (172.20.1.1) 0.716 ms 0.942 ms 0.434 ms >> > 2 * * * >> > 3 andris.dmz (172.20.24.10) 73.576 ms 78.858 ms 79.434 ms >> > >> > Why aren't there the other hosts which take part in the delivery during > * * * ? > >If there is an ipsec tunnel between GateA and Gate B, this tunnel forms a >'virtual wire'. When it is tunneled, the original packet becomes an inner >packet, and new ESP and/or AH headers are added to create an outer packet >around it. You can see an example of how this is done for AH at >doc/ipsec.html#AH . For ESP it is similar. > >Think about the packet's path from the inner packet's perspective. >It leaves the subnet, goes into the tunnel, and re-emerges in the second >subnet. This perspective is also the only one available to the >'traceroute' command when the IPSec tunnel is up. Claudia got this exactly right. Let me just expand on a couple of points: *) GateB is exactly one (virtual) hop away from GateA. This is how it would be if there were a physically private wire from A to B. The virtually private connection should work the same, and it does. *) While the information is in transit from GateA to GateB, the hop count of the outer header (the "envelope") is being decremented. The hop count of the inner header (the "contents" of the envelope) is not decremented and should not be decremented. The hop count of the outer header is not derived from and should not be derived from the hop count of the inner header. Indeed, even if the packets did time out in transit along the tunnel, there would be no way for traceroute to find out what happened. Just as information cannot leak _out_ of the tunnel to the outside, information cannot leak _into_ the tunnel from outside, and this includes ICMP messages from routers along the path. There are some cases where one might wish for information about what is happening at the IP layer (below the tunnel layer) -- but the protocol makes no provision for this. This raises all sorts of conceptual issues. AFAIK nobody has ever cared enough to really figure out what _should_ happen, let alone implement it and standardize it. *) I consider the "* * *" to be a slight bug. One might wish for it to be replaced by "GateB GateB GateB". It has to do with treating host-to-subnet traffic different from subnet-to-subnet traffic (and other gory details). I fervently hope KLIPS2 will make this problem go away. *) If you want to ask questions about the link from GateA to GateB at the IP level (below the tunnel level), you have to ssh to GateA and launch a traceroute from there.
It is often useful in debugging to test things one at a time:
FreeS/WAN releases are tested for all of these, so you can be reasonably certain they can do them all. Of course, that does not mean they will on the first try, especially if you have some unusual configuration.
The rest of this section gives information on diagnosing the problem when each of the above steps fails.
Suspect one of:
This is a fairly common problem when attempting to configure multiple manually keyed connections from a single gateway.
Each connection must be identified by a unique SPI value. For automatic connections, these values are assigned automatically. For manual connections, you must set them with spi= statements in ipsec.conf(5).
Each manual connection must have a unique SPI value in the range 0x100 to 0x999. Two or more with the same value will fail. For details, see our doc section Using manual keying in production and the man page ipsec.conf(5).
The most common reason for this behaviour is a firewall dropping the UDP port 500 packets used in key negotiation.
Other possibilities:
One common configuration error is forgetting that you need auto=add to load the connection description on the receiving end so it recognises the connection when the other end asks for it.
Some possibile problems are discussed in out interoperation document.
When we first added compression, we saw some problems:
We have not seen either problem in some time (at least six months as I write in March 2002), but if you have some unusual configuration then you may see them.
If tests with ping(1) and a small packet size succeed, but tests or transfers with larger packet sizes fail, suspect problems with packet fragmentation and perhaps path MTU discovery.
Our troubleshooting document covers these problems. Information on the underlying mechanism is in our background document.
This is described under I cannot ping... above.
Pluto needs the GMP (GNU
Multi-Precision) library for the large integer calculations it uses in public key cryptography. This error message indicates a failure to find the library. You must install it before Pluto will compile.
The GMP library is included in most Linux distributions. Typically, there are two RPMs, libgmp and libgmp-devel, You need to install both, either from your distribution CDs or from your vendor's web site.
On Debian, a mailing list message reports that the command to give is apt-get install gmp2.
For more information and the latest version, see the GMP home page.
We have had several reports of this message appearing, all on SPARC Linux. Here is a mailing message on a solution:
> ipsec_sha1.c: In function `SHA1Transform': > ipsec_sha1.c:95: virtual memory exhausted I'm seeing exactly the same problem on an Ultra with 256MB ram and 500 MB swap. Except I am compiling version 1.5 and its Red Hat 6.2. I can get around this by using -O instead of -O2 for the optimization level. So it is probably a bug in the optimizer on the sparc complier. I'll try and chase this down on the sparc lists.
Here is a discussion of this error from FreeS/WAN "listress" (mailing list tech support person) Claudia Schmeing. The "FAQ on the network unreachable error" which she refers to is the next question below.
> I reached the point where the two boxes (both on dial-up connections, but > treated as static IPs by getting the IP and editing ipsec.conf after the > connection is established) to the point where they exchange some info, but I > get an error like "route-client command exited with status 7 \n internal > error". > Where can I find a description of this error? In general, if the FAQ doesn't cover it, you can search the mailing list archives - I like to use http://www.sandelman.ottawa.on.ca/linux-ipsec/ but you can see doc/mail.html for different archive formats. Your error comes from the _updown script, which performs some routing and firewall functions to help Linux FreeS/WAN. More info is available at doc/firewall.html and man ipsec.conf. Its routing is integral to the health of Linux FreeS/WAN; it also provides facility to insert custom firewall rules to be executed when you create or destroy a connection. Yours is, of course, a routing error. You can be fairly sure the routing machinery is saying "network is unreachable". There's a FAQ on the "network is unreachable" error, but more information is available now; read on. If your _updown script is recent (for example if it shipped with Linux FreeS/WAN 1.91), you will see another debugging line in your logs that looks something like this: > output: /usr/lib/ipsec/_updown: `route add -net 128.174.253.83 > netmask 255.255.255.255 dev ipsec0 gw 66.92.93.161' failed This is, of course, the system route command that exited with status 7, (ie. failed). Man route for details. Seeing the command typed out yields more information. If your _updown script is older, you may wish to update it to show the command explicitly. Three parameters fed to the route command: net, netmask and gw [gateway] are derived from things you've put in ipsec.conf. Net and netmask are derived from the peer's IP and mask. In more detail: You may see a routing error when routing to a client (ie. subnet), or to a host (IPSec gateway or freestanding host; a box that does IPSec for itself). In _updown, the "route-client" section is responsible to set up the route for IPSec'd (usually, read 'tunneled') packets headed to a peer subnet. Similarly, route-host routes IPSec'd packets to a peer host or IPSec gateway. When routing to a 'client', net and netmask are ipsec.conf's left- or rightsubnet (whichever is not local). Similarly, when routing to a 'host' the net is left or right. Host netmask is always /32, indicating a single machine. Gw is nexthop's value. Again, the value in question is left- or rightnexthop, whichever is local. Where left/right or left-/rightnexthop has the special value %defaultroute (described in man ipsec.conf), gw will automagically get the value of the next hop on the default route. Q: "What's a nexthop and why do I need one?" A: 'nexthop' is a routing kluge; its value is the next hop away from the machine that's doing IPSec, and toward your IPSec peer. You need it to get the processed packets out of the local system and onto the wire. While we often route other packets through the machine that's now doing IPSec, and are done with it, this does not suffice here. After packets are processed with IPSec, this machine needs to know where they go next. Of course using the 'IPSec gateway' as their routing gateway would cause an infinite loop! [To visualize this, see the packet flow diagram at doc/firewall.html.] To avoid this, we route packets through the next hop down their projected path. Now that you know the background, consider: 1. Did you test routing between the gateways in the absence of Linux FreeS/WAN, as recommended? You need to ensure the two machines that will be running Linux FreeS/WAN can route to one another before trying to make a secure connection. 2. Is there anything obviously wrong with the sense of your route command? Normally, this problem is caused by an incorrect local nexthop parameter. Check out the use of %defaultroute, described in man ipsec.conf. This is a simple way to set nexthop for most people. To figure nexthop out by hand, traceroute in-the-clear to your IPSec peer. Nexthop is the traceroute's first hop after your IPSec gateway.
This message is not from FreeS/WAN, but from the Linux IP stack itself. That stack is seeing packets it has no route for, either because your routing was broken before FreeS/WAN started or because FreeS/WAN's changes broke it.
Here is a message from Claudia suggesting ways to diagnose and fix such problems:
You write, > I have correctly installed freeswan-1.8 on RH7.0 kernel 2.2.17, but when > I setup a VPN connection with the other machine(RH5.2 Kernel 2.0.36 > freeswan-1.0, it works well.) it told me that > "SIOCADDRT:Network is unreachable"! But the network connection is no > problem. Often this error is the result of a misconfiguration. Be sure that you can route successfully in the absence of Linux FreeS/WAN. (You say this is no problem, so proceed to the next step.) Use a custom copy of the default updownscript. Do not change the route commands, but add a diagnostic message revealing the exact text of the route command. Is there a problem with the sense of the route command that you can see? If so, then re-examine those ipsec.conf settings that are being sent to the route command. You may wish to use the ipsec auto --route and --unroute commands to troubleshoot the problem. See man ipsec_auto for details.
Since the above message was written, we have modified the updown script to provide a better diagnostic for this problem. Check /var/log/messages.
See also the FAQ question route-client (or host) exited with status 7.
These messages indicate an installation failure. The kernel you are running does not contain the KLIPS (kernel IPsec) code.
Note that the "modprobe: Can't locate module ipsec" message appears even if you are not using modules. If there is no KLIPS in your kernel, FreeS/WAN tries to load it as a module. If that fails, you get this message.
Commands you can quickly try are:
If those don't find the problem, you have to go back and check through the install procedure to see what was missed.
Here is one of Claudia's messages on the topic:
> I tried to install freeswan 1.8 on my mandrake 7.2 test box. ... > It does show version and some output for whack. Yes, because the Pluto (daemon) part of ipsec is installed correctly, but as we see below the kernel portion is not. > However, I get the following from /var/log/messages: > > Mar 11 22:11:55 pavillion ipsec_setup: Starting FreeS/WAN IPsec 1.8... > Mar 11 22:12:02 pavillion ipsec_setup: modprobe: Can't locate module ipsec > Mar 11 22:12:02 pavillion ipsec_setup: Fatal error, kernel appears to lack > KLIPS. This is your problem. You have not successfully installed a kernel with IPSec machinery in it. Did you build Linux FreeS/WAN as a module? If so, you need to ensure that your new module has been installed in the directory where your kernel loader normally finds your modules. If not, you need to ensure that the new IPSec-enabled kernel is being loaded correctly. See also doc/install.html, and INSTALL in the distro.
Quoting Henry:
Note that by default, FreeS/WAN is now set up to
(a) authenticate with RSA keys, and
(b) fetch the public key of the far end from DNS.
Explicit attention to ipsec.conf will be needed if you want
to do something different.
and Claudia, responding to the same user:
You write, > My current setup in ipsec.conf is leftrsasigkey=%dns I have > commented this and authby=rsasig out. I am able to get ipsec running, > but what I find is that the documentation only specifies for %dns are > there any other values that can be placed in this variable other than > %dns and the key? I am also assuming that this is where I would place > my public key for the left and right side as well is this correct? Valid values for authby= are rsasig and secret, which entail authentication by RSA signature or by shared secret, respectively. Because you have commented authby=rsasig out, you are using the default value of authby=secret. When using RSA signatures, there are two ways to get the public key for the IPSec peer: either copy it directly into *rsasigkey= in ipsec.conf, or fetch it from dns. The magic value %dns for *rsasigkey parameters says to try to fetch the peer's key from dns. For any parameters, you may find their significance and special values in man ipsec.conf. If you are setting up keys or secrets, be sure also to reference man ipsec.secrets.
This is a fatal error. FreeS/WAN cannot cope with two or more interfaces using the same IP address. You must re-configure to avoid this.
A mailing list message on the topic from Pluto developer Hugh Redelmeier:
| I'm trying to get freeswan working between two machine where one has a ppp | interface. | I've already suceeded with two machines with ethernet ports but the ppp | interface is causing me problems. | basically when I run ipsec start i get | ipsec_setup: Starting FreeS/WAN IPsec 1.7... | ipsec_setup: 003 IP interfaces ppp1 and ppp0 share address 192.168.0.10! | ipsec_setup: 003 IP interfaces ppp1 and ppp2 share address 192.168.0.10! | ipsec_setup: 003 IP interfaces ppp0 and ppp2 share address 192.168.0.10! | ipsec_setup: 003 no public interfaces found | | followed by lots of cannot work out interface for connection messages | | now I can specify the interface in ipsec.conf to be ppp0 , but this does | not affect the above behaviour. A quick look in server.c indicates that the | interfaces value is not used but some sort of raw detect happens. | | I guess I could prevent the formation of the extra ppp interfaces or | allocate them different ip but I'd rather not. if at all possible. Any | suggestions please. Pluto won't touch an interface that shares an IP address with another. This will eventually change, but it probably won't happen soon. For now, you will have to give the ppp1 and ppp2 different addresses.
A mailing list message form technical lead Henry Spencer:
> When FreeS/WAN IPsec 1.7 is starting on my 2.0.38 Linux kernel the following > error message is generated: > ipsec_setup: Cannot adjust kernel flags, no /proc/sys/net/ipsec directory! > What is supposed to create this directory and how can I fix this problem? I think that directory is a 2.2ism, although I'm not certain (I don't have a 2.0.xx system handy any more for testing). Without it, some of the ipsec.conf config-setup flags won't work, but otherwise things should function.
You also need to enable the /proc filesystem in your kernel configuration for these operations to work.
Pluto messages often indicate where Pluto is in the IKE protocols. The letters indicate Main mode or Q uick mode and Initiator or Responder. The numerals are message sequence numbers. For more detail, see our IPsec section.
From Pluto programmer Hugh Redelmeier:
| Jan 17 16:21:10 remus Pluto[13631]: "jumble" #1: responding to Main Mode from Road Warrior 130.205.82.46 | Jan 17 16:21:11 remus Pluto[13631]: "jumble" #1: no suitable connection for peer @banshee.wittsend.com | | The connection "jumble" has nothing to do with the incoming | connection requests, which were meant for the connection "banshee". You are right. The message tells you which Connection Pluto is currently using, which need not be the right one. It need not be the right one now for the negotiation to eventually succeed! This is described in ipsec_pluto(8) in the section "Road Warrior Support". There are two times when Pluto will consider switching Connections for a state object. Both are in response to receiving ID payloads (one in Phase 1 / Main Mode and one in Phase 2 / Quick Mode). The second is not unique to Road Warriors. In fact, neither is the first any more (two connections for the same pair of hosts could differ in Phase 1 ID payload; probably nobody else has tried this).
Older versions of FreeS/WAN used this message. The same error now gives the "we have no ipsecN ..." error described just below.
Your tunnel has no IP address which matches the IP address of any of the available IPsec interfaces. Either you've misconfigured the connection, or you need to define an appropriate IPsec interface connection. interfaces=%defaultroute works in many cases.
A longer story: Pluto needs to know whether it is running on the machine which the connection description calls left or on right. It figures that out by:
Normally a match is found. Then Pluto knows where it is and can set up other things (for example, if it is left) using parameters such as leftsubnet and leftnexthop, and sending its outgoing packets to right.
If no match is found, it emits the above error message.
This error message occurs when a remote system attempts to negotiate a connection and Pluto does not have a connection description that matches what the remote system has requested. The most common cause is a configuration error on one end or the other.
Parameters involved in this match are left, right , leftsubnet and rightsubnet.
The match must be exact. For example, if your left subnet is a.b.c.0/24 then neither a single machine in that net nor a smaller subnet such as a.b.c.64/26 will be considered a match.
The message can also occur when an appropriate description exists but Pluto has not loaded it. Use an auto=add statement in the connection description, or an ipsec auto --add <conn_name> command, to correct this.
An explanation from the Pluto developer:
| Jul 12 15:00:22 sohar58 Pluto[574]: "corp_road" #2: cannot respond to IPsec
| SA request because no connection is known for
| 216.112.83.112/32===216.112.83.112...216.67.25.118
This is the first message from the Pluto log showing a problem. It
means that PGPnet is trying to negotiate a set of SAs with this
topology:
216.112.83.112/32===216.112.83.112...216.67.25.118
^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^ ^^^^^^^^^^^^^
client on our side our host PGPnet host, no client
None of the conns you showed look like this.
Use
ipsec auto --status
to see a snapshot of what connections are in pluto, what
negotiations are going on, and what SAs are established.
The leftsubnet= (client) in your conn is 216.112.83.64/26. It must
exactly match what pluto is looking for, and it does not.
This is similar to the no connection known error, but occurs at a different point in Pluto processing.
Here is one of Claudia's messages explaining the problem:
You write, > What could be the reason of the following error? > "no suitable connection for peer '@xforce'" When a connection is initiated by the peer, Pluto must choose which entry in the conf file best matches the incoming connection. A preliminary choice is made on the basis of source and destination IPs, since that information is available at that time. A payload containing an ID arrives later in the negotiation. Based on this id and the *id= parameters, Pluto refines its conn selection. ... The message "no suitable connection" indicates that in this refining step, Pluto does not find a connection that matches that ID. Please see "Selecting a connection when responding" in man ipsec_pluto for more details.
See also Connection names in Pluto error messages.
Here is one of Claudia's messages discussing this problem:
You write,
> May 22 10:46:31 debian Pluto[25834]: packet from x.y.z.p:10014:
> initial Main Mode message from x.y.z.p:10014
but no connection has been authorized
This error occurs early in the connection negotiation process,
at the first step of IKE negotiation (Main Mode), which is itself the
first of two negotiation phases involved in creating an IPSec connection.
Here, Linux FreeS/WAN receives a packet from a potential peer, which
requests that they begin discussing a connection.
The "no connection has been authorized" means that there is no connection
description in Linux FreeS/WAN's internal database that can be used to
link your ipsec interface with that peer.
"But of course I configured that connection!"
It may be that the appropriate connection description exists in ipsec.conf
but has not been added to the database with ipsec auto --add myconn or the
auto=add method. Or, the connection description may be misconfigured.
The only parameters that are relevant in this decision are left= and right= .
Local and remote ports are also taken into account -- we see that the port
is printed in the message above -- but there is no way to control these
in ipsec.conf.
Failure at "no connection has been authorized" is similar to the
"no connection is known for..." error in the FAQ, and the "no suitable
connection" error described in the snapshot's FAQ. In all three cases,
Linux FreeS/WAN is trying to match parameters received in the
negotiation with the connection description in the local config file.
As it receives more information, its matches take more parameters into
account, and become more precise: first the pair of potential peers,
then the peer IDs, then the endpoints (including any subnets).
The "no suitable connection for peer *" occurs toward the end of IKE
(Main Mode) negotiation, when the IDs are matched.
"no connection is known for a/b===c...d" is seen at the beginning of IPSec
(Quick Mode, phase 2) negotiation, when the connections are matched using
left, right, and any information about the subnets.
This message occurs when the other system attempts to negotiate a connection using single DES, which we do not support because it is insecure.
Our interoperation document has suggestions for how to deal with systems that attempt to use single DES.
This message means that the other gateway has made a proposal for connection parameters, but nothing they proposed is acceptable to Pluto. Possible causes include:
A more detailed explanation, from Pluto programmer Hugh Redelmeier:
Background:
When one IKE system (for example, Pluto) is negotiating with another
to create an SA, the Initiator proposes a bunch of choices and the
Responder replies with one that it has selected.
The structure of the choices is fairly complicated. An SA payload
contains a list of lists of "Proposals". The outer list is a set of
choices: the selection must be from one element of this list.
Each of these elements is a list of Proposals. A selection must be
made from each of the elements of the inner list. In other words,
*all* of them apply (that is how, for example, both AH and ESP can
apply at once).
Within each of these Proposals is a list of Transforms. For each
Proposal selected, one Transform must be selected (in other words,
each Proposal provides a choice of Transforms).
Each Transform is made up of a list of Attributes describing, well,
attributes. Such as lifetime of the SA. Such as algorithm to be
used. All the Attributes apply to a Transform.
You will have noticed a pattern here: layers alternate between being
disjunctions ("or") and conjunctions ("and").
For Phase 1 / Main Mode (negotiating an ISAKMP SA), this structure is
cut back. There must be exactly one Proposal. So this degenerates to
a list of Transforms, one of which must be chosen.
In your case, no proposal was considered acceptable to Pluto (the
Responder). So negotiation ceased. Pluto logs the reason it rejects
each Transform. So look back in the log to see what is going wrong.
On Fri, 29 Jun 2001, Rodrigo Gruppelli wrote: > ...Well, it seem that there's > another problem with it. When I try to generate a pair of RSA keys, > rsasigkey cores dump... *That* is a neon sign flashing "GMP LIBRARY IS BROKEN". Rsasigkey calls GMP a lot, and our own library a little bit, and that's very nearly all it does. Barring bugs in its code or our library -- which have happened, but not very often -- a problem in rsasigkey is a problem in GMP.
See the next question for how to deal with GMP errors.
Pluto has died. Signal 4 is SIGILL, illegal instruction.
The most likely cause is that your GMP (GNU multi-precision) library is compiled for a different processor than what you are running on. Pluto uses that library for its public key calculations.
Try getting the GMP sources and recompile for your processor type. Most Linux distributions will include this source, or you can download it from the GMP home page.
From John Denker, on the mailing list:
1) The log message some IKE message we sent has been rejected with ECONNREFUSED (kernel supplied no details) is much more suitable than the previous version. Thanks. 2) Minor suggestion for further improvement: it might be worth mentioning that the command tcpdump -i eth1 icmp[0] != 8 and icmp[0] != 0 is useful for tracking down the details in question. We shouldn't expect all IPsec users to figure that out on their own. The log message might even provide a hint as to where to look in the docs.
Reply From Pluto developer Hugh Redelmeier
Good idea. I've added a bit pluto(8)'s BUGS section along these lines. I didn't have the heart to lengthen this message.
This message means KLIPS has received a packet for which no IPsec tunnel has been defined.
Here is a more detailed duscussion from the team's tech support person Claudia Schmeing, responding to a query on the mailing list:
> Why ipsec reports no eroute! ???? IP Masq... is disabled. In general, more information is required so that people on the list may give you informed input. See doc/prob.report.
The document she refers to has since been replaced by a section of the troubleshooting document.
However, I can make some general comments on this type of error. This error usually looks something like this (clipped from an archived message): > ttl:64 proto:1 chk:45459 saddr:192.168.1.2 daddr:192.168.100.1 > ... klips_debug:ipsec_findroute: 192.168.1.2->192.168.100.1 > ... klips_debug:rj_match: * See if we match exactly as a host destination > ... klips_debug:rj_match: ** try to match a leaf, t=0xc1a260b0 > ... klips_debug:rj_match: *** start searching up the tree, t=0xc1a260b0 > ... klips_debug:rj_match: **** t=0xc1a260c8 > ... klips_debug:rj_match: **** t=0xc1fe5960 > ... klips_debug:rj_match: ***** not found. > ... klips_debug:ipsec_tunnel_start_xmit: Original head/tailroom: 2, 28 > ... klips_debug:ipsec_tunnel_start_xmit: no eroute!: ts=47.3030, dropping. What does this mean? - -------------------- "eroute" stands for "extended route", and is a special type of route internal to Linux FreeS/WAN. For more information about this type of route, see the section of man ipsec_auto on ipsec auto --route. "no eroute!" here means, roughly, that Linux FreeS/WAN cannot find an appropriate tunnel that should have delivered this packet. Linux FreeS/WAN therefore drops the packet, with the message "no eroute! ... dropping", on the assumption that this packet is not a legitimate transmission through a properly constructed tunnel. How does this situation come about? - ----------------------------------- Linux FreeS/WAN has a number of connection descriptions defined in ipsec.conf. These must be successfully brought "up" to form actual tunnels. (see doc/setup.html's step 15, man ipsec.conf and man ipsec_auto for details). Such connections are often specific to the endpoints' IPs. However, in some cases they may be more general, for example in the case of Road Warriors where left or right is the special value %any. When Linux FreeS/WAN receives a packet, it verifies that the packet has come through a legitimate channel, by checking that there is an appropriate tunnel through which this packet might legitimately have arrived. This is the process we see above. First, it checks for an eroute that exactly matches the packet. In the example above, we see it checking for a route that begins at 192.168.1.2 and ends at 192.168.100.1. This search favours the most specific match that would apply to the route between these IPs. So, if there is a connection description exactly matching these IPs, the search will end there. If not, the code will search for a more general description matching the IPs. If there is no match, either specific or general, the packet will be dropped, as we see, above. Unless you are working with Road Warriors, only the first, specific part of the matching process is likely to be relevant to you. "But I defined the tunnel, and it came up, why do I have this error?" - --------------------------------------------------------------------- One of the most common causes of this error is failure to specify enough connection descriptions to cover all needed tunnels between any two gateways and their respective subnets. As you have noticed, troubleshooting this error may be complicated by the use of IP Masq. However, this error is not limited to cases where IP Masq is used. See doc/configuration.html#multitunnel for a detailed example of the solution to this type of problem.
The documentation section she refers to is now here.
This error message occurs when two manual connections are set up with the same SPI value.
See the FAQ for One manual connection works, but second one fails.
This message is harmless. The IKE protocol provides for a number of optional messages types:
An implementation is never required to send these, but they are allowed to. The receiver is not required to do anything with them. FreeS/WAN ignores them, but notifies you via the logs.
For the "ignoring delete SA Payload" message, see also our discussion of cleaning up dead tunnels.
This message can appear when you've upgraded an X.509-enabled Linux FreeS/WAN with a vanilla Linux FreeS/WAN. To use your X.509 configs you will need to overwrite the new install with Super FreeS/WAN, or add the X.509 patch by hand.
As a matter of policy, some of our mailing lists need to be open to non-subscribers. Project management feel strongly that maintaining this openness is more important than blocking spam.
This has been discussed several times at some length on the list. See the list archives. Bringing the topic up again is unlikely to be useful. Please don't. Or at the very least, please don't without reading the archives and being certain that whatever you are about to suggest has not yet been discussed.
Project technical lead Henry Spencer summarised one discussion:
For the third and last time: this list *will* *not* do address-based filtering. This is a policy decision, not an implementation problem. The decision is final, and is not open to discussion. This needs to be communicated better to people, and steps are being taken to do that.
Adding this FAQ section is one of the steps he refers to.
You have various options other than just putting up with the spam, filtering it yourself, or unsubscribing:
A number of tools are available to filter mail.
If you use your ISP's mail server rather than running your own, consider suggesting to the ISP that they tag suspected spam as this ISP does. They could just refuse mail from dubious sources, but that is tricky and runs some risk of losing valuable mail or senselessly annoying senders and their admins. However, they can safely tag and deliver dubious mail. The tags can greatly assist your filtering.
For information on tracking down spammers, see these HowTos, or the Sputum site. Sputum have a Linux anti-spam screensaver available for download.
Here is a more detailed message from Henry:
On Mon, 15 Jan 2001, Jay Vaughan wrote:
> I know I'm flogging a dead horse here, but I'm curious as to the reasons for
> an aversion for a subscriber-only mailing list?
Once again: for legal reasons, it is important that discussions of these
things be held in a public place -- the list -- and we do not want to
force people to subscribe to the list just to ask one question, because
that may be more than merely inconvenient for them. There are also real
difficulties with people who are temporarily forced to use alternate
addresses; that is precisely the time when they may be most in need of
help, yet a subscribers-only policy shuts them out.
These issues do not apply to most mailing lists, but for a list that is
(necessarily) the primary user support route for a crypto package, they
are very important. This is *not* an ordinary mailing list; it has to
function under awkward constraints that make various simplistic solutions
inapplicable or undesirable.
> We're *ALL* sick of hearing about list management problems, not just you
> old-timers, so why don't you DO SOMETHING EFFECTIVE ABOUT IT...
Because it's a lot harder than it looks, and many existing "solutions"
have problems when examined closely.
> A suggestion for you, based on 10 years of experience with management of my
> own mailing lists would be to use mailman, which includes pretty much every
> feature under the sun that you guys need and want, plus some. The URL for
> mailman...
I assure you, we're aware of mailman. Along with a whole bunch of others,
including some you almost certainly have never heard of (I hadn't!).
> As for the argument that the list shouldn't be configured to enforce
> subscription - I contend that it *SHOULD* AT LEAST require manual address
> verification in order for posts to be redirected.
You do realize, I hope, that interposing such a manual step might cause
your government to decide that this is not truly a public forum, and thus
you could go to jail if you don't get approval from them before mailing to
it? If you think this sounds irrational, your government is noted for
making irrational decisions in this area; we can't assume that they will
suddenly start being sensible. See above about awkward constraints. You
may be willing to take the risk, but we can't, in good conscience, insist
that all users with problems do so.
Henry Spencer
henry@spsystems.net
and a message on the topic from project leader John Gilmore:
Subject: Re: The linux-ipsec list's topic
Date: Sat, 30 Dec 2000
From: John Gilmore <gnu@toad.com>
I'll post this single message, once only, in this discussion, and then
not burden the list with any further off-topic messages. I encourage
everyone on the list to restrain themself from posting ANY off-topic
messages to the linux-ipsec list.
The topic of the linux-ipsec mailing list is the FreeS/WAN software.
I frequently see "discussions about spam on a list" overwhelm the
volume of "actual spam" on a list. BOTH kinds of messages are
off-topic messages. Twenty anti-spam messages take just as long to
detect and discard as twenty spam messages.
The Linux-ipsec list encourages on-topic messages from people who have
not joined the list itself. We will not censor messages to the list
based on where they originate, or what return address they contain.
In other words, non-subscribers ARE allowed to post, and this will not
change. My own valid contributions have been rejected out-of-hand by
too many other mailing lists for me to want to impose that censorship
on anybody else's contributions. And every day I see the damage that
anti-spam zeal is causing in many other ways; that zeal is far more
damaging to the culture of the Internet than the nuisance of spam.
In general, it is the responsibility of recipients to filter,
prioritize, or otherwise manage the handling of email that comes to
them. It is not the responsibility of the rest of the Internet
community to refrain from sending messages to recipients that they
might not want to see. If your software infrastructure for managing
your incoming email is insufficient, then improve it. If you think
the signal-to-noise ratio on linux-ipsec is too poor, then please
unsubscribe. But don't further increase the noise by posting to the
linux-ipsec list about those topics.
John Gilmore
founder & sponsor, FreeS/WAN project
The various components of Linux FreeS/WAN are of course documented in standard Unix manual pages, accessible via the man(1) command.
Links here take you to an HTML version of the man pages.
These files are also discussed in the configuration section.
Many users will never give most of the FreeS/WAN commands directly. Configure the files listed above correctly and everything should be automatic.
The exceptions are commands for mainpulating the RSA keys used in Pluto authentication:
Note that:
The following commands are fairly likely to be used, if only for testing and status checks:
The lower-level utilities listed below are normally invoked via scripts listed above, but they can also be used directly when required.
FreeS/WAN, or other IPsec implementations, frequently run on gateway machines, the same machines running firewall or packet filtering code. This document discusses the relation between the two.
The firewall code in 2.4 and later kernels is called Netfilter. The user-space utility to manage a firewall is iptables(8). See the netfilter/iptables web site for details.
The basic constraint is that an IPsec gateway must have packet filters that allow IPsec packets, at least when talking to other IPsec gateways:
Your gateway and the other IPsec gateways it communicates with must be able to exchange these packets for IPsec to work. Firewall rules must allow UDP 500 and at least one of AH or ESP on the interface that communicates with the other gateway.
For nearly all FreeS/WAN applications, you must allow UDP port 500 and the ESP protocol.
There are two ways to set this up:
Both methods are described in more detail below.
It is possible to set up both firewalling and IPsec with appropriate scripts at boot and then not use leftupdown= and rightupdown=, or use them only for simple up and down operations.
Basically, the technique is
Since Pluto authenticates its partners during the negotiation, and KLIPS drops packets for which no tunnel has been negotiated, this may be all you need.
In simple cases, you need only a few rules, as in this example:
# allow IPsec # # IKE negotiations iptables -I INPUT -p udp --sport 500 --dport 500 -j ACCEPT iptables -I OUTPUT -p udp --sport 500 --dport 500 -j ACCEPT # ESP encryption and authentication iptables -I INPUT -p 50 -j ACCEPT iptables -I OUTPUT -p 50 -j ACCEPT
This should be all you need to allow IPsec through lokkit, which ships with Red Hat 9, on its medium security setting. Once you've tweaked to your satisfaction, save your active rule set with:
service iptables save
However, while it is certainly possible to create an elaborate set of rules yourself (please let us know via the mailing list if you do), it may be both easier and more secure to use a set which has already been published and tested.
The published rule sets we know of are described in the next section.
It is therefore reasonably straightforward to filter these packets in whatever way suits your situation.
In some cases rules that work fine before you add IPsec may require modification to work with IPsec.
This is especially likely for rules that deal with interfaces on the Internet side of your system. IPsec adds a new interface; often the rules must change to take account of that.
For example, consider the rules given in this section of the Netfilter documentation:
Most people just have a single PPP connection to the Internet, and don't
want anyone coming back into their network, or the firewall:
## Insert connection-tracking modules (not needed if built into kernel).
# insmod ip_conntrack
# insmod ip_conntrack_ftp
## Create chain which blocks new connections, except if coming from inside.
# iptables -N block
# iptables -A block -m state --state ESTABLISHED,RELATED -j ACCEPT
# iptables -A block -m state --state NEW -i ! ppp0 -j ACCEPT
# iptables -A block -j DROP
## Jump to that chain from INPUT and FORWARD chains.
# iptables -A INPUT -j block
# iptables -A FORWARD -j block
On an IPsec gateway, those rules may need to be modified. The above allows new connections from anywhere except ppp0. That means new connections from ipsec0 are allowed.
Do you want to allow anyone who can establish an IPsec connection to your gateway to initiate TCP connections to any service on your network? Almost certainly not if you are using opportunistic encryption. Quite possibly not even if you have only explicitly configured connections.
To disallow incoming connections from ipsec0, change the middle section above to:
## Create chain which blocks new connections, except if coming from inside.
# iptables -N block
# iptables -A block -m state --state ESTABLISHED,RELATED -j ACCEPT
# iptables -A block -m state --state NEW -i ppp+ -j DROP
# iptables -A block -m state --state NEW -i ipsec+ -j DROP
# iptables -A block -m state --state NEW -i -j ACCEPT
# iptables -A block -j DROP
The original rules accepted NEW connections from anywhere except ppp0. This version drops NEW connections from any PPP interface (ppp+) and from any ipsec interface (ipsec+), then accepts the survivors.
Of course, these are only examples. You will need to adapt them to your own situation.
Several sets of firewall rules that work with FreeS/WAN are available.
One user, Rob Hutton, posted his boot time scripts to the mailing list, and we included them in previous versions of this documentation. They are still available from our web site. However, they were for an earlier FreeS/WAN version so we no longer recommend them. Also, they had some bugs. See this message.
Those scripts were based on David Ranch's scripts for his "Trinity OS" for setting up a secure Linux. Check his home page for the latest version and for information on his book on securing Linux. If you are going to base your firewalling on Ranch's scripts, we recommend using his latest version, and sending him any IPsec modifications you make for incorporation into later versions.
We have had several mailing lists reports of good results using FreeS/WAN with Seawall (the Seattle Firewall). See that project's home page on Sourceforge.
Another set of firewall scripts with IPsec support are the RCF or rc.firewall scripts. See their home page.
Asgard's Realm has set of firewall scripts with FreeS/WAN support, for 2.4 kernels and iptables.
One user gave considerable detail on his scripts, including supporting IPX through the tunnel. His message was too long to conveniently be quoted here, so I've put it in a separate file.
The ipsec.conf(5) configuration file has three pairs of parameters used to specify an interface between FreeS/WAN and firewalling code.
Note that using these is not required if you have a static firewall setup. In that case, you just set your firewall up at boot time (in a way that permits the IPsec connections you want) and do not change it thereafter. Omit all the FreeS/WAN firewall parameters and FreeS/WAN will not attempt to adjust firewall rules at all. See above for some information on appropriate scripts.
However, if you want your firewall rules to change when IPsec connections change, then you need to use these parameters.
One pair of parmeters are set in the config setup section of the ipsec.conf(5) file and affect all connections:
They can also be used in other ways. For example, you might have prepluto add a module to your kernel for the secure network interface or make a dialup connection, and then have postpluto remove the module or take the connection down.
The other parameters are set in connection descriptions. They can be set in individual connection descriptions, and could even call different scripts for each connection for maximum flexibility. In most applications, however, it makes sense to use only one script and to call it from conn %default section so that it applies to all connections.
You can:
Note that only one of these should be used. You cannot sensibly use both. Since our default script is obsolete (designed for firewalls using ipfwadm(8) on 2.0 kernels), most users who need this service will need to write a custom script.
We supply a default script named _updown.
Set these to yes and Pluto will call our default script _updown with appropriate arguments whenever it:
The supplied default _updown script is appropriate for simple cases using the ipfwadm(8) firewalling package.
You can also write your own script and have Pluto call it. Just put the script's name in one of these ipsec.conf(5) lines:
Your script should take the same arguments and use the same environment variables as _updown. See the "updown command" section of the ipsec_pluto(8) man page for details.
Note that you should not modify our _updown script in place . If you did that, then upgraded FreeS/WAN, the upgrade would install a new default script, overwriting your changes.
Our _updown is for firewalls using ipfwadm(8), the firewall code for the 2.0 series of Linux kernels. If you are using the more recent packages ipchains(8) (for 2.2 kernels) or iptables(8) (2.4 kernels), then you must do one of:
You can write a script to do whatever you need with firewalling. Specify its name in a [left|right]updown= parameter in ipsec.conf(5) and Pluto will automatically call it for you.
The arguments Pluto passes such a script are the same ones it passes to our default _updown script, so the best way to build yours is to copy ours and modify the copy.
Note, however, that you should not modify our _updown script in place. If you did that, then upgraded FreeS/WAN, the upgrade would install a new default script, overwriting your changes.
Network Address Translation, also known as IP masquerading, is a method of allocating IP addresses dynamically, typically in circumstances where the total number of machines which need to access the Internet exceeds the supply of IP addresses.
Any attempt to perform NAT operations on IPsec packets between the IPsec gateways creates a basic conflict:
For AH, which authenticates parts of the packet header including source and destination IP addresses, this is fatal. If NAT changes those fields, AH authentication fails.
For IKE and ESP it is not necessarily fatal, but is certainly an unwelcome complication.
This problem can be avoided by having the masquerading take place on or behind the IPsec gateway.
This can be done physically with two machines, one physically behind the other. A picture, using SG to indicate IPsec S ecurity Gateways, is:
clients --- NAT ----- SG ---------- SG
two machines
In this configuration, the actual client addresses need not be given in the leftsubnet= parameter of the FreeS/WAN connection description. The security gateway just delivers packets to the NAT box; it needs only that machine's address. What that machine does with them does not affect FreeS/WAN.
A more common setup has one machine performing both functions:
clients ----- NAT/SG ---------------SG
one machine
Here you have a choice of techniques depending on whether you want to make your client subnet visible to clients on the other end:
In this case, no masquerading is done. Packets to or from the client subnet are encrypted or decrypted without any change to their client subnet addresses, although of course the encapsulating packets use gateway addresses in their headers. Clients behind the right security gateway see a route via that gateway to the left subnet.
We recommend not trying to build IPsec connections which pass through a NAT machine. This setup poses problems:
clients --- SG --- NAT ---------- SG
If you must try it, some references are:
Other documents which may be relevant include:
Of course simply allowing UDP 500 and ESP packets is not the whole story. Various other issues arise in making IPsec and packet filters co-exist and even co-operate. Some of them are summarised below.
Basic IPsec packet filtering rules deal only with packets addressed to or sent from your IPsec gateway.
It is a separate policy decision whether to permit such packets to pass through the gateway so that client machines can build end-to-end IPsec tunnels of their own. This may not be practical if you are using NAT (IP masquerade) on your gateway, and may conflict with some corporate security policies.
Where possible, allowing this is almost certainly a good idea. Using IPsec on an end-to-end basis is more secure than gateway-to-gateway.
Doing it is quite simple. You just need firewall rules that allow UDP port 500 and protocols 50 and 51 to pass through your gateway. If you wish, you can of course restrict this to certain hosts.
One application of this is for the telecommuter who might have:
Sunset==========West------------------East ================= firewall --- the Internet
home network untrusted net corporate network
The subnet on the right is 0.0.0.0/0, the whole Internet. The West gateway is set up so that it allows only IPsec packets to East in or out.
This configuration is used in AT&T Research's network. For details, see the papers links in our introduction.
Another application would be to set up firewall rules so that an internal machine, such as an employees-only web server, could not talk to the outside world except via specific IPsec tunnels.
It is possible to use firewall rules to restrict UDP 500, ESP and AH packets so that these packets are accepted only from known gateways. This is not strictly necessary since FreeS/WAN will discard packets from unknown gateways. You might, however, want to do it for any of a number of reasons. For example:
It is not possible to use only static firewall rules for this filtering if you do not know the other gateways' IP addresses in advance, for example if you have "road warriors" who may connect from a different address each time or if want to do opportunistic encryption to arbitrary gateways. In these cases, you can accept UDP 500 IKE packets from anywhere, then use the updown script feature of pluto(8) to dynamically adjust firewalling for each negotiated tunnel.
Firewall packet filtering does not much reduce the risk of a denial of service attack on FreeS/WAN. The firewall can drop packets from unknown gateways, but KLIPS does that quite efficiently anyway, so you gain little. The firewall cannot drop otherwise legitmate packets that fail KLIPS authentication, so it cannot protect against an attack designed to exhaust resources by making FreeS/WAN perform many expensive authentication operations.
In summary, firewall filtering of IPsec packets from unknown gateways is possible but not strictly necessary.
When the IPsec gateway is also acting as your firewall, other packet filtering rules will be in play. In general, those are outside the scope of this document. See our Linux firewall links for information. There are a few types of packet, however, which can affect the operation of FreeS/WAN or of diagnostic tools commonly used with it. These are discussed below.
ICMP is the Internet Control Message Protocol. It is used for messages between IP implementations themselves, whereas IP used is used between the clients of those implementations. ICMP is, unsurprisingly, used for control messages. For example, it is used to notify a sender that a desination is not reachable, or to tell a router to reroute certain packets elsewhere.
ICMP handling is tricky for firewalls.
ICMP does not use ports. Messages are distinguished by a "message type" field and, for some types, by an additional "code" field. The definitive list of types and codes is on the IANA site.
One expert uses this definition for ICMP message types to be dropped at the firewall.
# ICMP types which lack socially redeeming value. # 5 Redirect # 9 Router Advertisement # 10 Router Selection # 15 Information Request # 16 Information Reply # 17 Address Mask Request # 18 Address Mask Reply badicmp='5 9 10 15 16 17 18'
A more conservative approach would be to make a list of allowed types and drop everything else.
Whichever way you do it, your ICMP filtering rules on a FreeS/WAN gateway should allow at least the following ICMP packet types:
It is fairly common for firewalls to drop ICMP echo packets addressed to machines behind the firewall. If that is your policy, please create an exception for such packets arriving via an IPsec tunnel, at least during intial testing of those tunnels.
The traceroute(1) utility uses UDP port numbers from 33434 to approximately 33633. Generally, these should be allowed through for troubleshooting.
Some firewalls drop these packets to prevent outsiders exploring the protected network with traceroute(1). If that is your policy, consider creating an exception for such packets arriving via an IPsec tunnel, at least during intial testing of those tunnels.
Windows 2000 does, and products designed for compatibility with it may, build L2TP tunnels over IPsec connections.
For this to work, you must allow UDP protocol 1701 packets coming out of your tunnels to continue to their destination. You can, and probably should, block such packets to or from your external interfaces, but allow them from ipsec0.
See also our Windows 2000 interoperation discussion.
IPsec uses three main types of packet:
All of those packets should have appropriate IPsec gateway addresses in both the to and from IP header fields. Firewall rules can check this if you wish, though it is not strictly necessary. This is discussed in more detail later.
IPsec processing of incoming packets authenticates them then removes the ESP or AH header and decrypts if necessary. Successful processing exposes an inner packet which is then delivered back to the firewall machinery, marked as having arrived on an ipsec[0-3] interface. Firewall rules can use that interface label to distinguish these packets from unencrypted packets which are labelled with the physical interface they arrived on (or perhaps with a non-IPsec virtual interface such as ppp0).
One of our users sent a mailing list message with a diagram of the packet flow.
Some protocols, such as TCP and UDP, have the notion of ports. Others protocols, including ESP and AH, do not. Quite a few IPsec newcomers have become confused on this point. There are no ports in the ESP or AH protocols, and no ports used for them. For these protocols, the idea of ports is completely irrelevant.
The protocol numbers for ESP or AH are used in the 'next header' field of the IP header. On most non-IPsec packets, that field would have one of:
Each header in the sequence tells what the next header will be. IPsec adds headers for ESP or AH near the beginning of the sequence. The original headers are kept and the 'next header' fields adjusted so that all headers can be correctly interpreted.
For example, using [ ] to indicate data protected by ESP and unintelligible to an eavesdropper between the gateways:
Part of the ESP header itself is encrypted, which is why the [ indicating protected data appears in the middle of some lines above. The next header field of the ESP header is protected. This makes traffic analysis more difficult. The next header field would tell an eavesdropper whether your packet was UDP to the gateway, TCP to the gateway, or encapsulated IP. It is better not to give this information away. A clever attacker may deduce some of it from the pattern of packet sizes and timings, but we need not make it easy.
IPsec allows various combinations of these to match local policies, including combinations that use both AH and ESP headers or that nest multiple copies of these headers.
For example, suppose my employer has an IPsec VPN running between two offices so all packets travelling between the gateways for those offices are encrypted. If gateway policies allow it (The admins could block UDP 500 and protocols 50 and 51 to disallow it), I can build an IPsec tunnel from my desktop to a machine in some remote office. Those packets will have one ESP header throughout their life, for my end-to-end tunnel. For part of the route, however, they will also have another ESP layer for the corporate VPN's encapsulation. The whole header scheme for a packet on the Internet might be:
The first ESP (outermost) header is for the corporate VPN. The inner ESP header is for the secure machine-to-machine link.
Here are some mailing list comments from pluto(8) developer Hugh Redelmeier on an earlier draft of this document:
There are many important things left out
- firewalling is important but must reflect (implement) policy. Since
policy isn't the same for all our customers, and we're not experts,
we should concentrate on FW and MASQ interactions with FreeS/WAN.
- we need a diagram to show packet flow WITHIN ONE MACHINE, assuming
IKE, IPsec, FW, and MASQ are all done on that machine. The flow is
obvious if the components are run on different machines (trace the
cables).
IKE input:
+ packet appears on public IF, as UDP port 500
+ input firewalling rules are applied (may discard)
+ Pluto sees the packet.
IKE output:
+ Pluto generates the packet & writes to public IF, UDP port 500
+ output firewalling rules are applied (may discard)
+ packet sent out public IF
IPsec input, with encapsulated packet, outer destination of this host:
+ packet appears on public IF, protocol 50 or 51. If this
packet is the result of decapsulation, it will appear
instead on the paired ipsec IF.
+ input firewalling rules are applied (but packet is opaque)
+ KLIPS decapsulates it, writes result to paired ipsec IF
+ input firewalling rules are applied to resulting packet
as input on ipsec IF
+ if the destination of the packet is this machine, the
packet is passed on to the appropriate protocol handler.
If the original packet was encapsulated more than once
and the new outer destination is this machine, that
handler will be KLIPS.
+ otherwise:
* routing is done for the resulting packet. This may well
direct it into KLIPS for encoding or encrypting. What
happens then is described elsewhere.
* forwarding firewalling rules are applied
* output firewalling rules are applied
* the packet is sent where routing specified
IPsec input, with encapsulated packet, outer destination of another host:
+ packet appears on some IF, protocol 50 or 51
+ input firewalling rules are applied (but packet is opaque)
+ routing selects where to send the packet
+ forwarding firewalling rules are applied (but packet is opaque)
+ packet forwarded, still encapsulated
IPsec output, from this host or from a client:
+ if from a client, input firewalling rules are applied as the
packet arrives on the private IF
+ routing directs the packet to an ipsec IF (this is how the
system decides KLIPS processing is required)
+ if from a client, forwarding firewalling rules are applied
+ KLIPS eroute mechanism matches the source and destination
to registered eroutes, yielding a SPI group. This dictates
processing, and where the resulting packet is to be sent
(the destinations SG and the nexthop).
+ output firewalling is not applied to the resulting
encapsulated packet
- Until quite recently, KLIPS would double encapsulate packets that
didn't strictly need to be. Firewalling should be prepared for
those packets showing up as ESP and AH protocol input packets on
an ipsec IF.
- MASQ processing seems to be done as if it were part of the
forwarding firewall processing (this should be verified).
- If a firewall is being used, it is likely the case that it needs to
be adjusted whenever IPsec SAs are added or removed. Pluto invokes
a script to do this (and to adjust routing) at suitable times. The
default script is only suitable for ipfwadm-managed firewalls. Under
LINUX 2.2.x kernels, ipchains can be managed by ipfwadm (emulation),
but ipchains more powerful if manipulated using the ipchains command.
In this case, a custom updown script must be used.
We think that the flexibility of ipchains precludes us supplying an
updown script that would be widely appropriate.
This document covers several general places where you might have a problem:
This document also contains notes which expand on points made in these sections, and tips for problem reporting. If the other end of your connection is not FreeS/WAN, you'll also want to read our interoperation document.
With the RPM method:
freeswan-userland-2.03_2.4.20_20.9-0.i386.rpm
freeswan-module-2.03_2.4.20_20.9-0.i386.rpm
When installing from source, you may find these problems:
ipsec verify checks a number of FreeS/WAN essentials. Here are some hints on what do to when your system doesn't check out:
| Problem | Status | Action |
| ipsec not on-path |
Add /usr/sbin to your PATH. | |
| Missing KLIPS support | critical | See this FAQ. |
| No RSA private key |
Follow these instructions to create an RSA key pair for your host. RSA keys are:
| |
| pluto not running | critical |
service ipsec start |
| No port 500 hole | critical | Open port 500 for IKE negotiation. |
| Port 500 check N/A | Check that port 500 is open for IKE negotiation. | |
| Failed DNS checks | Opportunistic encryption requires information from DNS. To set this up, see our instructions. | |
| No public IP address | Check that the interface which you want to protect with IPSec is up and running. |
OE should work with no local configuration, if you have posted DNS TXT records according to the instructions in our quickstart guide. If you encounter trouble, try these hints. We welcome additional hints via the users' mailing list.
| Symptom | Problem | Action |
You're running FreeS/WAN 2.01 (or later), and initiating a
connection to FreeS/WAN 2.00 (or earlier). In your logs, you see a
message like:
no RSA public key known for '192.0.2.13'; DNS search for KEY failed (no KEY record for 13.2.0.192.in-addr.arpa.)The older FreeS/WAN logs no error. | A protocol level incompatibility between 2.01 (or later) and 2.00 (or earlier) causes this error. It occurs when a FreeS/WAN 2.01 (or later) box for which no KEY record is posted attempts to initiate an OE connection to older FreeS/WAN versions (2.00 and earlier). Note that older versions can initiate to newer versions without this error. | If you control the peer host, upgrade its FreeS/WAN to 2.01 (or later), and post new style TXT records for it. If not, but if you know its sysadmin, perhaps a quick note is in order. If neither option is possible, you can ease the transition by posting an old style KEY record (created with a command like "ipsec showhostkey --key") to the reverse map for the FreeS/WAN 2.01 (or later) box. |
| OE host is very slow to contact other hosts. | Slow DNS service while running OE. | It's a good idea to run a caching DNS
server on your OE host, as outlined in
this mailing list message. If your DNS servers are elsewhere, put
their IPs in the clear policy group, and re-read groups with
ipsec auto --rereadgroups |
Can't Opportunistically initiate for 192.0.2.2 to 192.0.2.3: no TXT record for 13.2.0.192.in-addr.arpa. | Peer is not set up for OE. |
None. Plenty of hosts on the Internet do not run OE. If, however, you have set OE up on that peer, this may indicate that you need to wait up to 48 hours for its DNS records to propagate. |
ipsec verify does not find DNS records:
...
Looking for TXT in forward map:
xy.example.com...[FAILED]
Looking for TXT in reverse map...[FAILED]
...
You also experience authentication failure:
Possible authentication failure: no acceptable response to our first encrypted message | DNS records are not posted or have not propagated. | Did you post the DNS records necessary for OE? If not, do so using the instructions in our quickstart guide. If so, wait up to 48 hours for the DNS records to propagate. |
| ipsec verify does not find DNS records, and you experience authentication failure. | For iOE, your ID does not match location of forward DNS record. | In config setup , change myid= to match the forward DNS where you posted the record. Restart FreeS/WAN. For reference, see our iOE instructions. |
| ipsec verify finds DNS records, yet there is still authentication failure. ( ? ) | DNS records are malformed. | Re-create the records and send new copies to your DNS administrator. |
| ipsec verify finds DNS records, yet there is still authentication failure. ( ? ) | DNS records show different keys for a gateway vs. its subnet hosts. | All TXT records for boxes protected by an OE gateway must contain the gateway's public key. Re-create and re-post any incorrect records using these instructions. |
| OE gateway loses connectivity to its subnet. The gateway's routing table shows routes to the subnet through IPsec interfaces. | The subnet is part of the private or block policy group on the gateway. | Remove the subnet from the group, and
reread groups with
ipsec auto --rereadgroups |
| OE does not work to hosts on the local LAN. | This is a known issue. | See this list of known issues with OE. |
FreeS/WAN does not seem to be executing your default policy. In
your logs, you see a message like:
/etc/ipsec.d/policies/iprivate-or-clear" line 14: subnet "0.0.0.0/0", source 192.0.2.13/32, already "private-or-clear" | Fullnet in a policy group file defines your default policy. Fullnet should normally be present in only one policy group file. The fine print: you can have two default policies defined so long as they protect different local endpoints (e.g. the FreeS/WAN gateway and a subnet). | Find all policies which
contain fullnet with:
grep -F 0.0.0.0/0 /etc/ipsec.d/policies/*then remove the unwanted occurrence(s). |
When you fail to bring up a tunnel, you'll need to find out:
before you can diagnose your problem .
You can see connection states (STATE_MAIN_I1 and so on) when you bring up a connection on the command line. If you have missed this, or brought up your connection automatically, use:
ipsec auto --status
The most relevant state is the last one reached.
Negotiations should proceed though various states, in the processes of:
These are done and a connection is established when you see messages like:
000 #21: "myconn" STATE_MAIN_I4 (ISAKMP SA established)...
000 #2: "myconn" STATE_QUICK_I2 (sent QI2, IPsec SA established)...
Look for the key phrases are "ISAKMP SA established" and "IPSec SA established", with the relevant connection name. Often, this happens at STATE_MAIN_I4 and STATE_QUICK_I2, respectively.
ipsec auto --status will tell you what states have been achieved, rather than the current state. Since determining the current state is rather more difficult to do, current state information is not available from Linux FreeS/WAN. If you are actively bringing a connection up, the status report's last states for that connection likely reflect its current state. Beware, though, of the case where a connection was correctly brought up but is now downed: Linux FreeS/WAN will not notice this until it attempts to rekey. Meanwhile, the last known state indicates that the connection has been established.
If your connection is stuck at STATE_MAIN_I1, skip straight to here.
Solving most errors will require you to find verbose error text, either on the command line or in the logs.
Note that you can get more detail from ipsec auto using the --verbose flag:
ipsec auto --verbose --up west-east
More complete information can be gleaned from the log files.
The amount of description you'll get here depends on ipsec.conf debug settings, klipsdebug= and plutodebug=. When troubleshooting, set at least one of these to all, and when done, reset it to none so your logs don't fill up. Note that you must have enabled the klipsdebug compile-time option for the klipsdebug configuration switch to work.
For negotiation problems plutodebug is most relevant. klipsdebug applies mainly to attempts to use an already-established connection. See also this description of the division of duties within Linux FreeS/WAN.
After raising your debug levels, restart Linux FreeS/WAN to ensure that ipsec.conf is reread, then recreate the error to generate verbose logs.
ipsec barf (8) collects a bunch of useful debugging information, including these logs Use the command
ipsec barf > barf.west
to generate one.
Search out the failure point in your logs. Are there a handful of lines which succinctly describe how things are going wrong or contrary to your expectation? Sometimes the failure point is not immediately obvious: Linux FreeS/WAN's errors are usually not marked "Error". Have a look in the FAQ for what some common failures look like.
Tip: problems snowball. Focus your efforts on the first problem, which is likely to be the cause of later errors.
Also find error text on the peer IPSec box. This gives you two perspectives on the same failure.
At times you will require information which only one side has. The peer can merely indicate the presence of an error, and its approximate point in the negotiations. If one side keeps retrying, it may be because there is a show stopper on the other side. Have a look at the other side and figure out what it doesn't like.
If the other end is not Linux FreeS/WAN, the principle is the same: replicate the error with its most verbose logging on, and capture the output to a file.
This error commonly happens because IKE (port 500) packets, needed to negotiate an IPSec connection, cannot travel freely between your IPSec gateways. See our firewall document for details.
Other errors require a bit more digging. Use the following resources:
If you have failed to solve your problem with the help of these resources, send a detailed problem report to the users list, following these guidelines.
Test your connection by sending packets through it. The simplest way to do this is with ping, but the ping needs to test the correct tunnel. See this example scenario if you don't understand this.
If your ping returns, test any other connections you've brought u all check out, great. You may wish to test with large packets for MTU problems.
If your ping fails to return, generate an ipsec barf debugging report on each IPSec gateway. On a non-Linux FreeS/WAN implementation, gather equivalent information. Use this, and the tips in the next sections, to troubleshoot. Are you sure that both endpoints are capable of hearing and responding to ping?
IPSec may be dropping your ping packets since they do not belong in the tunnels you have constructed:
In either case, you will often see a message like:
klipsdebug... no eroute
which we discuss in this FAQ.
Note:
If you've confirmed your configuration assumptions, the problem is almost certainly with routing or firewalling. Isolate the problem using interface statistics, firewall statistics, or a packet sniffer.
Interface reports and firewall statistics can help you track down lost packets at a glance. Check any firewall statistics you may be keeping on your IPSec gateways, for dropped packets.
Tip: You can take a snapshot of the packets processed by your firewall with:
iptables -L -n -v
You can get creative with "diff" to find out what happens to a particular packet during transmission.
Both cat /proc/net/dev and ifconfig display interface statistics, and both are included in ipsec barf. Use either to check if any interface has dropped packets. If you find that one has, test whether this is related to your ping. While you ping continuously, print that interface's statistics several times. Does its drop count increase in proportion to the ping? If so, check why the packets are dropped there.
To do this, look at the firewall rules that apply to that interface. If the interface is an IPSec interface, more information may be available in the log. Grep for the word "drop" in a log which was created with klipsdebug=all as the error happened.
See also this discussion on interpreting ifconfig statistics.
If you have checked configuration assumptions, routing, and firewall rules, and your interface statistics yield no clue, it remains for you to investigate the mystery of the lost packet by the most thorough method: with a packet sniffer (providing, of course, that this is legal where you are working).
In order to detect packets on the ipsec virtual interfaces, you will need an up-to-date sniffer (tcpdump, ethereal, ksnuffle) on your IPSec gateway machines. You may also find it useful to sniff the ping endpoints.
Ping, and examine each interface along the projected path, checking for your ping's arrival. If it doesn't get to the the next stop, you have narrowed down where to look for it. In this way, you can isolate a problem area, and narrow your troubleshooting focus.
Within a machine running Linux FreeS/WAN, this packet flow diagram will help you anticipate a packet's path.
Note that:
Once you isolate where the packet is lost, take a closer look at firewall rules, routing and configuration assumptions as they affect that specific area. If the packet is lost on an IPSec gateway, comb through klipsdebug output for anomalies.
If the packet goes through both gateways successfully and reaches the ping target, but does not return, suspect routing. Check that the ping target routes packets back to the IPSec gateway.
Here, too, log information can be useful. Start with the guidelines above.
For connection use problems, set klipsdebug=all. Note that you must have enabled the klipsdebug compile-time option to do this. Restart Linux FreeS/WAN so that it rereads ipsec.conf, then recreate the error condition. When searching through klipsdebug data, look especially for the keywords "drop" (as in dropped packets) and "error".
Often the problem with connection use is not software error, but rather that the software is behaving contrary to expectation.
To interpret the Linux FreeS/WAN log text you've found, use the same resources as indicated for troubleshooting connection negotiation: the FAQ , our background document, and the list archives. Looking in the KLIPS code is only for the very brave.
If you are still stuck, send a detailed problem report to the users' list.
If each of your connections passed the ping test, you may wish to test by pinging with large packets (2000 bytes or larger). If it does not return, suspect MTU issues, and see this discussion.
In most users' view, a simple ping test, and perhaps a large-packet ping test suffice to indicate a working IPSec connection.
Some people might like to do additional stress tests prior to production use. They may be interested in this testing protocol we use at interoperation conferences, aka "bakeoffs". We also have a testing directory that ships with the release.
Ask for troubleshooting help on the users' mailing list, users@lists.freeswan.org. While sometimes an initial query with a quick description of your intent and error will twig someone's memory of a similar problem, it's often necessary to send a second mail with a complete problem report.
When reporting problems to the mailing list(s), please include:
Here are some good general guidelines on bug reporting: How To Ask Questions The Smart Way and How to Report Bugs Effectively.
To report a problem, send mail about it to the users' list. If you are certain that you have found a bug, report it to the bugs list. If you encounter a problem while doing your own coding on the Linux FreeS/WAN codebase and think it is of interest to the design team, notify the design list. When in doubt, default to the users' list. More information about the mailing lists is found here.
For a number of reasons -- including export-control regulations affecting almost any private discussion of encryption software -- we prefer that problem reports and discussions go to the lists, not directly to the team. Beware that the list goes worldwide; US citizens, read this important information about your export laws. If you're using this software, you really should be on the lists. To get onto them, visit lists.freeswan.org.
If you do send private mail to our coders or want a private reply from them, please make sure that the return address on your mail (From or Reply-To header) is a valid one. They have more important things to do than to unravel addresses that have been mangled in an attempt to confuse spammers.
The following sections supplement the Guide: information available on your system; testing between security gateways; ifconfig reports for KLIPS debugging; using GDB on Pluto.
Linux FreeS/WAN logs to:
Check both places to get full information. If you find nothing, check your syslogd.conf(5) to see where your /etc/syslog.conf or equivalent is directing authpriv messages.
Other man pages are on this list and in
Sometimes you need to test a subnet-subnet tunnel. This is a tunnel between two security gateways, which protects traffic on behalf of the subnets behind these gateways. On this network:
Sunset==========West------------------East=========Sunrise
IPSec gateway IPSec gateway
local net untrusted net local net
you might name this tunnel sunset-sunrise. You can test this tunnel by having a machine behind one gateway ping a machine behind the other gateway, but this is not always convenient or even possible.
Simply pinging one gateway from the other is not useful. Such a ping does not normally go through the tunnel. The tunnel handles traffic between the two protected subnets, not between the gateways . Depending on the routing in place, a ping might
Neither event tells you anything about the tunnel. You can explicitly create an eroute to force such packets through the tunnel, or you can create additional tunnels as described in our configuration document, but those may be unnecessary complications in your situation.
The trick is to explicitly test between both gateways' private-side IP addresses. Since the private-side interfaces are on the protected subnets, the resulting packets do go via the tunnel. Use either ping -I or traceroute -i, both of which allow you to specify a source interface. (Note: unsupported on older Linuxes). The same principles apply for a road warrior (or other) case where only one end of your tunnel is a subnet.
When diagnosing problems using ifconfig statistics, you may wonder what type of activity increments a particular counter for an ipsecN device. Here's an index, posted by KLIPS developer Richard Guy Briggs:
Here is a catalogue of the types of errors that can occur for which
statistics are kept when transmitting and receiving packets via klips.
I notice that they are not necessarily logged in the right counter.
. . .
Sources of ifconfig statistics for ipsec devices
rx-errors:
- packet handed to ipsec_rcv that is not an ipsec packet.
- ipsec packet with payload length not modulo 4.
- ipsec packet with bad authenticator length.
- incoming packet with no SA.
- replayed packet.
- incoming authentication failed.
- got esp packet with length not modulo 8.
tx_dropped:
- cannot process ip_options.
- packet ttl expired.
- packet with no eroute.
- eroute with no SA.
- cannot allocate sk_buff.
- cannot allocate kernel memory.
- sk_buff internal error.
The standard counters are:
struct enet_statistics
{
int rx_packets; /* total packets received */
int tx_packets; /* total packets transmitted */
int rx_errors; /* bad packets received */
int tx_errors; /* packet transmit problems */
int rx_dropped; /* no space in linux buffers */
int tx_dropped; /* no space available in linux */
int multicast; /* multicast packets received */
int collisions;
/* detailed rx_errors: */
int rx_length_errors;
int rx_over_errors; /* receiver ring buff overflow */
int rx_crc_errors; /* recved pkt with crc error */
int rx_frame_errors; /* recv'd frame alignment error */
int rx_fifo_errors; /* recv'r fifo overrun */
int rx_missed_errors; /* receiver missed packet */
/* detailed tx_errors */
int tx_aborted_errors;
int tx_carrier_errors;
int tx_fifo_errors;
int tx_heartbeat_errors;
int tx_window_errors;
};
of which I think only the first 6 are useful.
You may need to use the GNU debugger, gdb(1), on Pluto. This should be necessary only in unusual cases, for example if you encounter a problem which the Pluto developer cannot readily reproduce or if you are modifying Pluto.
Here are the Pluto developer's suggestions for doing this:
Can you get a core dump and use gdb to find out what Pluto was doing
when it died?
To get a core dump, you will have to set dumpdir to point to a
suitable directory (see ipsec.conf(5)).
To get gdb to tell you interesting stuff:
$ script
$ cd dump-directory-you-chose
$ gdb /usr/lib/ipsec/pluto core
(gdb) where
(gdb) quit
$ exit
The resulting output will have been captured by the script command in
a file called "typescript". Send it to the list.
Do not delete the core file. I may need to ask you to print out some
more relevant stuff.
Note that the dumpdir parameter takes effect only when the IPsec subsystem is restarted -- reboot or ipsec setup restart.
Much of this document is quoted directly from the Linux FreeS/WAN mailing list. Thanks very much to the community of testers, patchers and commenters there, especially the ones quoted below but also various contributors we haven't quoted.
In general, do not expect Linux FreeS/WAN to do everything yet. This is a work-in-progress and some parts of the IPsec specification are not yet implemented.
Things we do, as of version 1.96:
In negotiating a keying connection (ISAKMP SA, Phase 1) we propose both groups when we are the initiator, and accept either when a peer proposes them. Once the keying connection is made, we propose only the alternative agreed there for data connections (IPsec SA's, Phase 2) negotiated over that keying connection.
In negotiations, we propose both of these and accept either.
All combinations of implemented transforms are supported. Note that some form of packet-level authentication is required whenever encryption is used. Without it, the encryption will not be secure.
Things we deliberately omit which are required in the RFCs are:
Since these are the only encryption algorithms and DH group the RFCs require, it is possible in theory to have a standards-conforming implementation which will not interpoperate with FreeS/WAN. Such an implementation would be inherently insecure, so we do not consider this a problem.
Anyway, most implementations sensibly include more secure options as well, so dropping null encryption, single DES and Group 1 does not greatly hinder interoperation in practice.
We also do not implement some optional features allowed by the RFCs:
In theory, this should cause no interoperation problems since all implementations are required to support the more secure main mode, whether or not they also allow aggressive mode.
In practice, it does sometimes produce problems with implementations such as Windows 2000 where aggressive mode is the default. Typically, these are easily solved with a configuration change that overrides that default.
Things we don't yet do, as of version 1.96:
Currently Triple DES is the only encryption method Pluto will negotiate.
No additional encryption transforms are implemented, though the RFCs allow them and some other IPsec implementations support various of them. We are not eager to add more. See this FAQ question.
AES, the successor to the DES standard, is an excellent candidate for inclusion in FreeS/WAN, see links to user patches.
No optional additional authentication transforms are currently implemented. Likely SHA-256, SHA-384 and SHA-512 will be added when AES is.
To fully comply with the RFCs, it is not enough just to accept only packets which survive any firewall rules in place to limit what IPsec packets get in, and then pass KLIPS authentication. That is what FreeS/WAN currently does.
We should also apply additional tests, for example ensuring that all packets emerging from a particular tunnel have source and destination addresses that fall within the subnets defined for that tunnel, and that packets with those addresses that did not emerge from the appropriate tunnel are disallowed.
This will be done as part of a KLIPS rewrite. See these links and the design mailing list for discussion.
We use PF-key Version Two for communication between the KLIPS kernel code and the Pluto Daemon. PF-Key v2 is defined by RFC 2367.
The "PF" stands for Protocol Family. PF-Inet defines a kernel/userspace interface for the TCP/IP Internet protocols (TCP/IP), and other members of the PF series handle Netware, Appletalk, etc. PF-Key is just a PF for key-related matters.
PF-Key came out of Berkeley Unix work and is used in the various BSD IPsec implementations, and in Solaris. This means there is some hope of porting our Pluto(8) to one of the BSD distributions, or of running their photurisd(8) on Linux if you prefer Photuris key management over IKE.
It is, however, more complex than that. The PK-Key RFC deliberately deals only with keying, not policy management. The three PF-Key implementations we have looked at -- ours, OpenBSD and KAME -- all have extensions to deal with security policy, and the extensions are different. There have been discussions aimed at sorting out the differences, perhaps for a version three PF-Key spec. All players are in favour of this, but everyone involved is busy and it is not clear whether or when these discussions might bear fruit.
We develop and test on Redhat Linux using the most recent kernel in the 2.2 and 2.4 series. In general, we recommend you use the latest kernel in one of those series. Complications and caveats are discussed below.
Consider upgrading to the 2.2 kernel series. If you want to stay with the 2.0 series, then we strongly recommend 2.0.39. Some useful security patches were added in 2.0.38.
Various versions of the code have run at various times on most 2.0.xx kernels, but the current version is only lightly tested on 2.0.39, and not at all on older kernels.
Some of our patches for older kernels are shipped in 2.0.37 and later, so they are no longer provided in FreeS/WAN. This means recent versions of FreeS/WAN will probably not compile on anything earlier than 2.0.37.
In general, we suggest the latest 2.2 kernel or 2.4 for production use.
Of course no release can be guaranteed to run on kernels more recent than it is, so quite often there will be no stable FreeS/WAN for the absolute latest kernel. See the FAQ for discussion.
We develop and test on Redhat 6.1 for 2.2 kernels, and on Redhat 7.1 or 7.2 for 2.4, so minor changes may be required for other distributions.
There are some problems with FreeS/WAN on Redhat 7.0. They are soluble, but we recommend you upgrade to a later Redhat instead..
Redhat 7 ships with two compilers.
Kernel Makefiles have gcc as a default, and must be adjusted to use kgcc before a kernel will compile on 7.0. This mailing list message gives details:
Subject: Re: AW: Installing IPsec on Redhat 7.0 Date: Thu, 1 Feb 2001 14:32:52 -0200 (BRST) From: Mads Rasmussen <mads@cit.com.br> > From www.redhat.com/support/docs/gotchas/7.0/gotchas-7-6.html#ss6.1 cd to /usr/src/linux and open the Makefile in your favorite editor. You will need to look for a line similar to this: CC = $(CROSS_COMPILE)gcc -D__KERNEL__ -I$(HPATH) This line specifies which C compiler to use to build the kernel. It should be changed to: CC = $(CROSS_COMPILE)kgcc -D__KERNEL__ -I$(HPATH) for Red Hat Linux 7. The kgcc compiler is egcs 2.91.66. From here you can proceed with the typical compiling steps.
Check the mailing list archive for more recent news.
SuSE 6.3 and later versions, at least in Europe, ship with FreeS/WAN included.
FreeS/WAN packages distributed for SuSE 7.0-7.2 were somehow miscompiled. You can find fixed packages on Kurt Garloff's page.
Here are some notes for an earlier SuSE version.
Date: Mon, 30 Nov 1998
From: Peter Onion <ponion@srd.bt.co.uk>
... I got Saturdays snapshot working between my two SUSE5.3 machines at home.
The mods to the install process are quite simple. From memory and looking at
the files on the SUSE53 machine here at work....
And extra link in each of the /etc/init.d/rc?.d directories called K35ipsec
which SUSE use to shut a service down.
A few mods in /etc/init.d/ipsec to cope with the different places that SUSE
put config info, and remove the inculsion of /etc/rc.d/init.d/functions and .
/etc/sysconfig/network as they don't exists and 1st one isn't needed anyway.
insert ". /etc/rc.config" to pick up the SUSE config info and use
if test -n "$NETCONFIG" -a "$NETCONFIG" != "YAST_ASK" ; then
to replace
[ ${NETWORKING} = "no" ] && exit 0
Create /etc/sysconfig as SUSE doesn't have one.
I think that was all (but I prob forgot something)....
You may also need to fiddle initialisation scripts to ensure that /var/run/pluto.pid is removed when rebooting. If this file is present, Pluto does not come up correctly.
Subject: Re: linux-IPsec: Slackware distribution Date: Thu, 15 Apr 1999 12:07:01 -0700 From: Evan Brewer <dmessiah@silcon.com> > Very shortly, I will be needing to install IPsec on at least gateways that > are running Slackware. . . . The only trick to getting it up is that on the slackware dist there is no init.d directory in /etc/rc.d .. so create one. Then, what I do is take the IPsec startup script which normally gets put into the init.d directory, and put it in /etc/rc.d and name ir rc.ipsec .. then I symlink it to the file in init.d. The only file in the dist you need to really edit is the utils/Makefile, setup4: Everything else should be just fine.
A year or so later:
Subject: Re: HTML Docs- Need some cleanup? Date: Mon, 8 Jan 2001 From: Jody McIntyre <jodym@oeone.com> I have successfully installed FreeS/WAN on several Slackware 7.1 machines. FreeS/WAN installed its rc.ipsec file in /etc/rc.d. I had to manually call this script from rc.inet2. This seems to be an easier method than Evan Brewer's.
A recent (Nov 2001) mailing list points to a web page on setting up several types of tunnel, including IPsec, on Debian.
Some older information:
Subject: FreeS/WAN 1.0 on Debian 2.1
Date: Tue, 20 Apr 1999
From: Tim Miller <cerebus+counterpane@haybaler.sackheads.org>
Compiled and installed without error on a Debian 2.1 system
with kernel-source-2.0.36 after pointing RCDIR in utils/Makefile to
/etc/init.d.
/var/lock/subsys/ doesn't exist on Debian boxen, needs to be
created; not a fatal error.
Finally, IPsec scripts appear to be dependant on GNU awk
(gawk); the default Debian awk (mawk-1.3.3-2) had fatal difficulties.
With gawk installed and /etc/alternatives/awk linked to /usr/bin/gawk
operation appears flawless.
The scripts in question have been modified since this was posted. Awk versions should no longer be a problem.
Subject: Re: HTML Docs- Need some cleanup? Date: Mon, 08 Jan 2001 From: Andy Bradford <andyb@calderasystems.com> On Sun, 07 Jan 2001 22:59:05 EST, Sandy Harris wrote: > Intel Linux distributions other than Redhat 5.x and 6.x > Redhat 7.0 > SuSE Linux > SuSE Linux 5.3 > Slackware > Debian Can you please include Caldera in this list? I have tested it since FreeS/Wan 1.1 and it works great with our systems---provided one follows the FreeS/Wan documentation. :-) Thank you, Andy
FreeS/WAN has been run sucessfully on a number of different CPU architectures. If you have tried it on one not listed here, please post to the mailing list.
Subject: linux-ipsec: Netwinder diffs Date: Wed, 06 Jan 1999 From: rhatfield@plaintree.com I had a mistake in my IPsec-auto, so I got things working this morning. Following are the diffs for my changes. Probably not the best and cleanest way of doing it, but it works. . . .
These diffs are in the 0.92 and later distributions, so these should work out-of-the-box on Netwinder.
Subject: Compiling FreeS/WAN 1.1 on YellowDog Linux (PPC) Date: 11 Dec 1999 From: Darron Froese <darron@fudgehead.com> I'm summarizing here for the record - because it's taken me many hours to do this (multiple times) and because I want to see IPsec on more linuxes than just x86. Also, I can't remember if I actually did summarize it before... ;-) I'm working too many late hours. That said - here goes. 1. Get your linux kernel and unpack into /usr/src/linux/ - I used 2.2.13. <http://www.kernel.org/pub/linux/kernel/v2.2/linux-2.2.13.tar.bz2> 2. Get FreeS/WAN and unpack into /usr/src/freeswan-1.1 <ftp://ftp.xs4all.nl/pub/crypto/freeswan/freeswan-1.1.tar.gz> 3. Get the gmp src rpm from here: <ftp://ftp.yellowdoglinux.com//pub/yellowdog/champion-1.1/SRPMS/SRPMS/gmp-2.0.2-9a.src.rpm> 4. Su to root and do this: rpm --rebuild gmp-2.0.2-9a.src.rpm You will see a lot of text fly by and when you start to see the rpm recompiling like this: Executing: %build + umask 022 + cd /usr/src/redhat/BUILD + cd gmp-2.0.2 + libtoolize --copy --force Remember to add `AM_PROG_LIBTOOL' to `configure.in'. You should add the contents of `/usr/share/aclocal/libtool.m4' to `aclocal.m4'. + CFLAGS=-O2 -fsigned-char + ./configure --prefix=/usr Hit Control-C to stop the rebuild. NOTE: We're doing this because for some reason the gmp source provided with FreeS/WAN 1.1 won't build properly on ydl. cd /usr/src/redhat/BUILD/ cp -ar gmp-2.0.2 /usr/src/freeswan-1.1/ cd /usr/src/freeswan-1.1/ rm -rf gmp mv gmp-2.0.2 gmp 5. Open the freeswan Makefile and change the line that says: KERNEL=$(b)zimage (or something like that) to KERNEL=vmlinux 6. cd ../linux/ 7. make menuconfig Select an option or two and then exit - saving your changes. 8. cd ../freeswan-1.1/ ; make menugo That will start the whole process going - once that's finished compiling, you have to install your new kernel and reboot. That should build FreeS/WAN on ydl (I tried it on 1.1).And a later message on the same topic:
Subject: Re: FreeS/WAN, PGPnet and E-mail Date: Sat, 22 Jan 2000 From: Darron Froese <darron@fudgehead.com> on 1/22/00 6:47 PM, Philip Trauring at philip@trauring.com wrote: > I have a PowerMac G3 ... The PowerMac G3 can run YDL 1.1 just fine. It should also be able to run FreeS/WAN 1.2patch1 with a couple minor modifications: 1. In the Makefile it specifies a bzimage for the kernel compile - you have to change that to vmlinux for the PPC. 2. The gmp source that comes with FreeS/WAN (for whatever reason) fails to compile. I have gotten around this by getting the gmp src rpm from here: ftp://ftp.yellowdoglinux.com//pub/yellowdog/champion-1.1/SRPMS/SRPMS/gmp-2.0.2-9a.src.rpm If you rip the source out of there - and place it where the gmp source resides it will compile just fine.
FreeS/WAN no longer includes GMP source.
One user reports success on the Mach-based micro kernel Linux.
Subject: Smiles on sparc and ppc Date: Fri, 10 Mar 2000 From: Jake Hill <jah@alien.bt.co.uk> You may or may not be interested to know that I have successfully built FreeS/WAN on a number of non intel alpha architectures; namely on ppc and sparc and also on osfmach3/ppc (MkLinux). I can report that it just works, mostly, with few changes.
Subject: IT WORKS (again) between intel & alpha :-))))) Date: Fri, 29 Jan 1999 From: Peter Onion <ponion@srd.bt.co.uk> Well I'm happy to report that I've got an IPsec connection between by intel & alpha machines again :-)) If you look back on this list to 7th of December I wrote... -On 07-Dec-98 Peter Onion wrote: -> -> I've about had enuf of wandering around inside the kernel trying to find out -> just what is corrupting outgoing packets... - -Its 7:30 in the evening ..... - -I FIXED IT :-)))))))))))))))))))))))))))))))) - -It was my own fault :-(((((((((((((((((( - -If you ask me very nicly I'll tell you where I was a little too over keen to -change unsigned long int __u32 :-) OPSE ... - -So tomorrow it will full steam ahead to produce a set of diffs/patches against -0.91 - -Peter Onion.
In general (there have been some glitches), FreeS/WAN has been running on Alphas since then.
Several users have reported success with FreeS/WAN on SPARC Linux. Here is one mailing list message:
Subject: Smiles on sparc and ppc Date: Fri, 10 Mar 2000 From: Jake Hill <jah@alien.bt.co.uk> You may or may not be interested to know that I have successfully built FreeS/WAN on a number of non intel alpha architectures; namely on ppc and sparc and also on osfmach3/ppc (MkLinux). I can report that it just works, mostly, with few changes. I have a question, before I make up some patches. I need to hack gmp/mpn/powerpc32/*.s to build them. Is this ok? The changes are trivial, but could I also use a different version of gmp? Is it vanilla here? I guess my only real headache is from ipchains, which appears to stop running when IPsec has been started for a while. This is with 2.2.14 on sparc.
This message, from a different mailing list, may be relevant for anyone working with FreeS/WAN on Suns:
Subject: UltraSPARC DES assembler
Date: Thu, 13 Apr 2000
From: svolaf@inet.uni2.dk (Svend Olaf Mikkelsen)
To: coderpunks@toad.com
An UltraSPARC assembler version of the LibDES/SSLeay/OpenSSL des_enc.c
file is available at http://inet.uni2.dk/~svolaf/des.htm.
This brings DES on UltraSPARC from slower than Pentium at the same
clock speed to significantly faster.
We know FreeS/WAN runs on at least some MIPS processors because Lasat manufacture an IPsec box based on an embedded MIPS running Linux with FreeS/WAN. We have no details.
The Merilus Firecard, a Linux firewall on a PCI card, is based on a Crusoe processor and supports FreeS/WAN.
Subject: Re: Crypto hardware support Date: Mon, 03 Jul 2000 From: Dan DeVault <devault@tampabay.rr.com> .... I have been running uClinux with FreeS/WAN 1.4 on a system built by Moreton Bay ( http://www.moretonbay.com ) and it was using a Coldfire processor and was able to do the Triple DES encryption at just about 1 mbit / sec rate....... they put a Hi/Fn 7901 hardware encryption chip on their board and now their system does over 25 mbit of 3DES encryption........ pretty significant increase if you ask me.
FreeS/WAN is designed to work on SMP (symmetric multi-processing) Linux machines and is regularly tested on dual processor x86 machines.
We do not know of any testing on multi-processor machines with other CPU architectures or with more than two CPUs. Anyone who does test this, please report results to the mailing list .
The current design does not make particularly efficient use of multiprocessor machines; some of the kernel work is single-threaded.
Supporting hardware cryptography accelerators has not been a high priority for the development team because it raises a number of fairly complex issues:
That said, we have a report of FreeS/WAN working with one crypto accelerator and some work is going on to modify KLIPS to create a clean generic interface to such products. See this web page for some of the design discussion.
More recently, a patch to support some hardware accelerators has been posted:
Subject: [Design] [PATCH] H/W acceleration patch Date: Tue, 18 Sep 2001 From: "Martin Gadbois" <martin.gadbois@colubris.com> Finally!! Here's a web site with H/W acceleration patch for FreeS/WAN 1.91, including S/W and Hifn 7901 crypto support. http://sources.colubris.com/ Martin Gadbois
Hardware accelerators could take performance well beyond what FreeS/WAN can do in software (discussed here ). Here is some discussion off the IETF IPsec list, October 2001:
... Currently shipping chips deliver, 600 mbps throughput on a single stream of 3DES IPsec traffic. There are also chips that use multiple cores to do 2.4 gbps. We (Cavium) and others have announced even faster chips. ... Mid 2002 versions will handle at line rate (OC48 and OC192) IPsec and SSL/TLS traffic not only 3DES CBC but also AES and arc4.
The patches to date support chips that have been in production for some time, not the state-of-the-art latest-and-greatest devices described in that post. However, they may still outperform software and they almost certainly reduce CPU overhead.
The Internet currently runs on version four of the IP protocols. IPv4 is what is in the standard Linux IP stack, and what FreeS/WAN was built for. In IPv4, IPsec is an optional feature.
The next version of the IP protocol suite is version six, usually abbreviated either as "IPv6" or as "IPng" for "IP: the next generation". For IPv6, IPsec is a required feature. Any machine doing IPv6 is required to support IPsec, much as any machine doing (any version of) IP is required to support ICMP.
There is a Linux implementation of IPv6 in Linux kernels 2.2 and above. For details, see the FAQ. It does not yet support IPsec. The USAGI project are also working on IPv6 for Linux.
FreeS/WAN was originally built for the current standard, IPv4, but we are interested in seeing it work with IPv6. Some progress has been made, and a patched version with IPv6 support is available. For more recent information, check the mailing list.
IPv6 has been specified by an IETF working group. The group's page lists over 30 RFCs to date, and many Internet Drafts as well. The overview is RFC 2460. Major features include:
A number of projects are working on IPv6 implementation. A prominent Open Source effort is KAME, a collaboration among several large Japanese companies to implement IPv6 for Berkeley Unix. Other major players are also working on IPv6. For example, see pages at:
The 6bone (IPv6 backbone) testbed network has been up for some time. There is an active IPv6 user group.
One of the design goals for IPv6 was that it must be possible to convert from v4 to v6 via a gradual transition process. Imagine the mess if there were a "flag day" after which the entire Internet used v6, and all software designed for v4 stopped working. Almost every computer on the planet would need major software changes! There would be huge costs to replace older equipment. Implementers would be worked to death before "the day", systems administrators and technical support would be completely swamped after it. The bugs in every implementation would all bite simultaneously. Large chunks of the net would almost certainly be down for substantial time periods. ...
Fortunately, the design avoids any "flag day". It is therefore a little tricky to tell how quickly IPv6 will take over. The transition has certainly begun. For examples, see announcements from NTT and Nokia. However, it is not yet clear how quickly the process will gain momentum, or when it will be completed. Likely large parts of the Internet will remain with IPv4 for years to come.
The FreeS/WAN project needs you! We rely on the user community to keep up to date. Mail users@lists.freeswan.org with your interop success stories.
Please note: Most of our interop examples feature Linux FreeS/WAN 1.x config files. You can convert them to 2.x files fairly easily with the patch in our Upgrading Guide.
| FreeS/WAN VPN | Road Warrior | OE | |||||
| PSK | RSA Secret | X.509
(requires patch) |
NAT-Traversal
(requires patch) |
Manual
Keying | |||
| More Compatible | |||||||
| FreeS/WAN | Yes | Yes | Yes | Yes | Yes | Yes | Yes |
| isakmpd (OpenBSD) | Yes | Yes | Yes | No | |||
| Kame (FreeBSD,
NetBSD, MacOSX) aka racoon | Yes | Yes | Yes | Yes | No | ||
| McAfee VPN
was PGPNet | Yes | Yes | Yes | Yes | No | ||
| Microsoft
Windows 2000/XP | Yes | Yes | Yes | No | |||
| SSH Sentinel | Yes | Yes | Maybe | Yes | No | ||
| Safenet SoftPK
/SoftRemote | Yes | Yes | Yes | No | |||
| Other | |||||||
| 6Wind | Yes | No | |||||
| Alcatel Timestep | Yes | No | |||||
| Apple Macintosh
System 10+ | Maybe | Yes | Maybe | Maybe | No | ||
| AshleyLaurent
VPCom | Yes | No | |||||
| Borderware | Yes | No | No | ||||
| Check Point FW-1/VPN-1 | Yes | Yes | Yes | No | |||
| Cisco with 3DES | Yes | Maybe | Maybe | No | |||
| Equinux VPN Tracker
(for Mac OS X) | Yes | Yes | Yes | Maybe | No | ||
| F-Secure | Yes | Maybe | Yes | Yes | No | ||
| Gauntlet GVPN | Yes | Yes | No | ||||
| IBM AIX | Yes | Maybe | No | ||||
| IBM AS/400 | Yes | No | |||||
| Intel Shiva
LANRover/Net Structure | Yes | No | |||||
| LanCom (formerly ELSA) | Yes | No | |||||
| Linksys | Maybe | No | Yes | No | |||
| Lucent | Partial | No | |||||
| Netasq | Yes | No | |||||
| netcelo | Yes | No | |||||
| Netgear fvs318 | Yes | No | |||||
| Netscreen 100
or 5xp | Yes | Maybe | No | ||||
| Nortel Contivity | Partial | Yes | Maybe | No | |||
| RadGuard | Yes | No | |||||
| Raptor | Yes | Yes | No | ||||
| Redcreek Ravlin | Yes/Partial | No | |||||
| SonicWall | Yes | Maybe | No | No | |||
| Sun Solaris | Yes | Yes | Yes | No | |||
| Symantec | Yes | No | |||||
| Watchguard
Firebox | Yes | Yes | No | ||||
| Xedia Access Point
/QVPN | Yes | No | |||||
| Zyxel Zywall
/Prestige | Yes | No | |||||
| PSK | RSA Secret | X.509
(requires patch) |
NAT-Traversal
(requires patch) |
Manual
Keying | |||
| FreeS/WAN VPN | Road Warrior | OE | |||||
| Yes | People report that this works for them. |
| [Blank] | We don't know. |
| No | We have reason to believe it was, at some point, not possible to get this to work. |
| Partial | Partial success. For example, a connection can be created from one end only. |
| Yes/Partial | Mixed reports. |
| Maybe | We think the answer is "yes", but need confirmation. |
Vanilla FreeS/WAN implements these parts of the IPSec specifications. You can add more with Super FreeS/WAN, but what we offer may be enough for many users.
We offer a set of proposals which is not user-adjustable, but covers all combinations that we can offer. FreeS/WAN always proposes triple DES encryption and Perfect Forward Secrecy (PFS). In addition, we propose Diffie Hellman groups 5 and 2 (in that order), and MD5 and SHA-1 hashes. We accept the same proposals, in the same order of preference.
Other interop notes:
See our documentation at freeswan.org and the Super FreeS/WAN docs at freeswan.ca. Some user-written HOWTOs for FreeS/WAN-FreeS/WAN connections are listed in our Introduction.
See also:
OpenBSD FAQ: Using
IPsec
Hans-Joerg Hoexer's interop Linux-OpenBSD (PSK)
Skyper's configuration
(PSK)
French page with configs (X.509)
Kame homepage, with FAQ
NetBSD's IPSec FAQ
Ghislaine's post explaining some interop peculiarities
Itojun's Kame-FreeS/WAN interop tips (PSK)
Ghislaine
Labouret's French page with links to matching FreeS/WAN and Kame
configs (RSA)
Markus
Wernig's HOWTO (X.509, BSD gateway)
Frodo's Kame-FreeS/WAN interop (X.509)
Kame as a WAVEsec
client.
Tim Carr's
Windows Interop Guide (X.509)
Hans-Joerg Hoexer's Guide for Linux-PGPNet (PSK)
Kai Martius' instructions using RSA Key-Extractor Tool (RSA)
Christian
Zeng's page (RSA) based on Kai's work. English or German.
Oscar Delgado's PDF (X.509, no configs)
Ryan's HOWTO
for FreeS/WAN-PGPNet (X.509). Through a Linksys Router with IPsec
Passthru enabled.
Jean-Francois
Nadeau's Practical Configuration (Road Warrior with PSK)
Wouter
Prins' HOWTO (Road Warrior with X.509)
Rekeying problem with FreeS/WAN and older PGPNets
DHCP over IPSEC HOWTO for FreeS/WAN (requires X.509 and dhcprelay patches)
Tim Carr's
Windows Interop Guide (X.509)
James
Carter's instructions (X.509, NAT-T)
Jean-Francois
Nadeau's Net-net Configuration (PSK)
Telenor's
Node-node Config (Transport-mode PSK)
Marcus Mueller's HOWTO using his
VPN config tool (X.509). Tool also works with PSK.
Nate Carlson's HOWTO using same tool (Road Warrior with X.509).
Unusually, FreeS/WAN is the Road Warrior here.
Oscar Delgado's PDF (X.509, no configs)
Tim Scannell's Windows XP Additional Checklist (X.509)
Microsoft's page on Win2k TCP/IP security features
Microsoft's Win2k IPsec debugging tips
MS VPN may fall back to 1DES
SSH's
Sentinel-FreeSWAN interop PDF (X.509)
Nadeem Hassan's SUSE-to-Sentinel article (Road warrior with X.509)
O-Zone's Italian HOWTO (Road Warrior, X.509, DHCP)
Whit Blauvelt's SoftRemote tips
Tim Wilson's tips (X.509)
Workaround for a "gotcha"
Jean-Francois
Nadeau's Practical Configuration (Road Warrior with PSK)
Terradon Communications' PDF (Road Warrior with PSK)
Seaan.net's PDF (Road Warrior to Subnet, with PSK)
Red Baron Consulting's PDF (Road Warrior with X.509)
French page with configs (X.509)
Alain Sabban's settings (PSK or PSK road warrior; through static NAT)
Derick Cassidy's configs (PSK)
David Kerry's Timestep settings (PSK)
Kevin Gerbracht's ipsec.conf (X.509)
James Carter's instructions (X.509, NAT-T)
Successful interop report, no details
Philip Reetz' configs (PSK)
Borderware server does not support FreeS/WAN road warriors
Older Borderware may not support Diffie Hellman groups 2, 5
AERAsec's Firewall-1 NG site (PSK, X.509, Road Warrior with X.509,
other algorithms)
AERAsec's detailed Check Point-FreeS/WAN support matrix
Checkpoint.com PDF: Linux as a VPN Client to FW-1 (PSK)
PhoneBoy's Check Point FAQ (on
Check Point only, not FreeS/WAN)
Chris Harwell's tips &FreeS/WAN configs (PSK)
Daniel Tombeil's configs (PSK)
SANS
Institute HOWTO (PSK). Detailed, with extensive references.
Short HOWTO
(PSK)
French page with configs for Cisco IOS, PIX and VPN 3000 (X.509)
Dave McFerren's sample configs (PSK)
Wolfgang Tremmel's sample configs (PSK road warrior)
Old doc from Pete Davis, with William Watson's updated Tips (PSK)
Some PIX specific information:
Waikato Linux
Users' Group HOWTO. Nice detail (PSK)
John Leach's configs (PSK)
Greg
Robinson's settings (PSK)
Scott's ipsec.conf for PIX (PSK, FreeS/WAN side only)
Rick Trimble's PIX and FreeS/WAN settings (PSK)
Cisco VPN support
page
Cisco IPsec information page
Equinux provides this excellent interop PDF (PSK, RSA, X.509).
pingworks.de's
"Connecting F-Secure's VPN+ to Linux FreeS/WAN" (PSK road warrior)
Same thing
as PDF
Success report, no detail (PSK)
Success report, no detail (Manual)
Richard Reiner's ipsec.conf (PSK)
Might work without that pesky firewall... (PSK)
In late July, 2003 Alexandar Antik reported success interoperating
with Gauntlet 6.0 for Solaris (X.509). Unfortunately the message is not
properly archived at this time.
IBM's "Built-In Network Security with AIX" (PSK, X.509)
IBM's tip: importing Linux FreeS/WAN settings into AIX's ikedb
(PSK)
Richard Welty's tips and tricks
Snowcrash's configs
(PSK)
Old configs from an
interop (PSK)
The day Shiva tickled a Pluto bug (PSK)
Follow up: success!
Jakob Curdes successfully created a PSK connection with the LanCom 1612 in August 2003.
Ken Bantoft's
instructions (Road Warrior with PSK)
Nate Carlson's caveats
Sample HOWTO
through a Linksys Router
Nadeem Hasan's configs
Brock Nanson's tips
Partial success report; see also the next message in thread
French page with configs (X.509)
French page with configs (X.509)
Errol Neal's settings (PSK)
Corey Rogers' configs (PSK, no PFS)
Jordan Share's configs (PSK, 2 subnets, through static NAT)
Set src proxy_id to your protected subnet/mask
French page with ipsec.conf, Netscreen screen shots (X.509, may need to
revert to PSK...)
A report of a company using Netscreen with FreeS/WAN on a large scale (FreeS/WAN road warriors?)
JJ Streicher-Bremer's mini HOWTO for old &new software. (PSK with two
subnets)
French page with configs (X.509). This succeeds using the above
X.509 tip.
Marko Hausalo's configs (PSK). Note: These do create a connection,
as you can see by "IPsec SA established".
Claudia Schmeing's comments
Peter Mazinger's settings (PSK)
Peter Gerland's configs (PSK)
Charles Griebel's configs (PSK).
Lumir Srch's tips (PSK)
John Hardy's configs (Manual)
Older Raptors want 3DES keys in 3 parts (Manual).
Different keys for each direction? (Manual)
Paul Wouters'
config (PSK)
Dilan Arumainathan's configuration (PSK)
Dariush's setup...
only opens one way (PSK)
Andreas Steffen's tips (X.509)
Reports of some successful interops from a fellow @sun.com. See
also
these follow up posts.
Aleks Shenkman's configs (Manual in transport mode)
Andreas Steffen's configs for Symantec 200R (PSK)
WatchGuard's HOWTO (PSK)
Ronald C. Riviera's Settings (PSK)
Walter Wickersham's Notes (PSK)
Max Enders' Configs (Manual)
Old known issue with auto keying
Tips on key generation and format (Manual)
Hybrid IPsec/L2TP connection settings (X.509)
Xedia's LAN-LAN links don't use multiple tunnels
That explanation, continued
Zyxel's Zywall to FreeS/WAN instructions (PSK)
Zyxel's Prestige to FreeS/WAN instructions (PSK). Note: not all
Prestige versions include VPN software.
Fabrice
Cahen's HOWTO (PSK)
In normal operation, the main concern is the overhead for encryption, decryption and authentication of the actual IPsec (ESP and/or AH) data packets. Tunnel setup and rekeying occur so much less frequently than packet processing that, in general, their overheads are not worth worrying about.
At startup, however, tunnel setup overheads may be significant. If you reboot a gateway and it needs to establish many tunnels, expect some delay. This and other issues for large gateways are discussed below.
The University of Wales at Aberystwyth has done quite detailed speed tests and put their results on the web.
Davide Cerri's thesis (in Italian) includes performance results for FreeS/WAN and for TLS. He posted an English summary on the mailing list.
Steve Bellovin used one of AT&T Research's FreeS/WAN gateways as his data source for an analysis of the cache sizes required for key swapping in IPsec. Available as text or PDF slides for a talk on the topic.
See also the NAI work mentioned in the next section.
We can come up with a formula that roughly relates CPU speed to the rate of IPsec processing possible. It is far from exact, but should be usable as a first approximation.
An analysis of authentication overheads for high-speed networks, including some tests using FreeS/WAN, is on the NAI Labs site. In particular, see figure 3 in this PDF document. Their estimates of overheads, measured in Pentium II cycles per byte processed are:
| IPsec | authentication | encryption | cycles/byte | |
|---|---|---|---|---|
| Linux IP stack alone | no | no | no | 5 |
| IPsec without crypto | yes | no | no | 11 |
| IPsec, authentication only | yes | SHA-1 | no | 24 |
| IPsec with encryption | yes | yes | yes | not tested |
Overheads for IPsec with encryption were not tested in the NAI work, but Antoon Bosselaers' web page gives cost for his optimised Triple DES implementation as 928 Pentium cycles per block, or 116 per byte. Adding that to the 24 above, we get 140 cycles per byte for IPsec with encryption.
At 140 cycles per byte, a 140 MHz machine can handle a megabyte -- 8 megabits -- per second. Speeds for other machines will be proportional to this. To saturate a link with capacity C megabits per second, you need a machine running at C * 140/8 = C * 17.5 MHz.
However, that estimate is not precise. It ignores the differences between:
and does not account for some overheads you will almost certainly have:
so we suggest using C * 25 to get an estimate with a bit of a built-in safety factor.
This covers only IP and IPsec processing. If you have other loads on your gateway -- for example if it is also working as a firewall -- then you will need to add your own safety factor atop that.
This estimate matches empirical data reasonably well. For example, Metheringham's tests, described below, show a 733 topping out between 32 and 36 Mbit/second, pushing data as fast as it can down a 100 Mbit link. Our formula suggests you need at least an 800 to handle a fully loaded 32 Mbit link. The two results are consistent.
Some examples using this estimation method:
| Interface | Machine speed in MHz | |||
|---|---|---|---|---|
| Type | Mbit per
second | Estimate
Mbit*25 | Minimum IPSEC gateway | Minimum with other
load
(e.g. firewall) |
| DSL | 1 | 25 MHz | whatever you have | 133, or better if you have it |
| cable modem | 3 | 75 MHz | ||
| any link, light load | 5 | 125 MHz | 133 | 200+, almost any surplus machine |
| Ethernet | 10 | 250 MHz | surplus 266 or 300 | 500+ |
| fast link, moderate load | 20 | 500 MHz | 500 | 800+, any current off-the-shelf PC |
| T3 or E3 | 45 | 1125 MHz | 1200 | 1500+ |
| fast Ethernet | 100 | 2500 MHz | // not feasible with 3DES in software on current machines // | |
| OC3 | 155 | 3875 MHz | ||
Such an estimate is far from exact, but should be usable as minimum requirement for planning. The key observations are:
AES is a new US government block cipher standard, designed to replace the obsolete DES. If FreeS/WAN using 3DES is not fast enough for your application, the AES patch may help.
To date (March 2002) we have had only one mailing list report of measurements with the patch applied. It indicates that, at least for the tested load on that user's network, AES roughly doubles IPsec throughput. If further testing confirms this, it may prove possible to saturate an OC3 link in software on a high-end box.
Also, some work is being done toward support of hardware IPsec acceleration which might extend the range of requirements FreeS/WAN could meet.
CPU speed may be the main issue for IPsec performance, but of course it isn't the only one.
You need good ethernet cards or other network interface hardware to get the best performance. See this ethernet information page and this Linux network driver page.
The current FreeS/WAN kernel code is largely single-threaded. It is SMP safe, and will run just fine on a multiprocessor machine ( discussion), but the load within the kernel is not shared effectively. This means that, for example to saturate a T3 -- which needs about a 1200 MHz machine -- you cannot expect something like a dual 800 to do the job.
On the other hand, SMP machines do tend to share loads well so -- provided one CPU is fast enough for the IPsec work -- a multiprocessor machine may be ideal for a gateway with a mixed load.
FreeS/WAN allows a single gateway machine to build tunnels to many others. There may, however, be some problems for large numbers as indicated in this message from the mailing list:
Subject: Re: Maximum number of ipsec tunnels? Date: Tue, 18 Apr 2000 From: "John S. Denker" <jsd@research.att.com> Christopher Ferris wrote: >> What are the maximum number ipsec tunnels FreeS/WAN can handle?? Henry Spencer wrote: >There is no particular limit. Some of the setup procedures currently >scale poorly to large numbers of connections, but there are (clumsy) >workarounds for that now, and proper fixes are coming. 1) "Large" numbers means anything over 50 or so. I routinely run boxes with about 200 tunnels. Once you get more than 50 or so, you need to worry about several scalability issues: a) You need to put a "-" sign in syslogd.conf, and rotate the logs daily not weekly. b) Processor load per tunnel is small unless the tunnel is not up, in which case a new half-key gets generated every 90 seconds, which can add up if you've got a lot of down tunnels. c) There's other bits of lore you need when running a large number of tunnels. For instance, systematically keeping the .conf file free of conflicts requires tools that aren't shipped with the standard freeswan package. d) The pluto startup behavior is quadratic. With 200 tunnels, this eats up several minutes at every restart. I'm told fixes are coming soon. 2) Other than item (1b), the CPU load depends mainly on the size of the pipe attached, not on the number of tunnels.
It is worth noting that item (1b) applies only to repeated attempts to re-key a data connection (IPsec SA, Phase 2) over an established keying connection (ISAKMP SA, Phase 1). There are two ways to reduce this overhead using settings in ipsec.conf(5):
The overheads for establishing keying connections (ISAKMP SAs, Phase 1) are lower because for these Pluto does not perform expensive operations before receiving a reply from the peer.
A gateway that does a lot of rekeying -- many tunnels and/or low settings for tunnel lifetimes -- will also need a lot of random numbers from the random(4) driver.
Even a 486 can handle a T1 line, according to this mailing list message:
Subject: Re: linux-ipsec: IPSec Masquerade Date: Fri, 15 Jan 1999 11:13:22 -0500 From: Michael Richardson . . . A 486/66 has been clocked by Phil Karn to do 10Mb/s encryption.. that uses all the CPU, so half that to get some CPU, and you have 5Mb/s. 1/3 that for 3DES and you get 1.6Mb/s....
and a piece of mail from project technical lead Henry Spencer:
Oh yes, and a new timing point for Sandy's docs... A P60 -- yes, a 60MHz Pentium, talk about antiques -- running a host-to-host tunnel to another machine shows an FTP throughput (that is, end-to-end results with a real protocol) of slightly over 5Mbit/s either way. (The other machine is much faster, the network is 100Mbps, and the ether cards are good ones... so the P60 is pretty definitely the bottleneck.)
From the above, and from general user experience as reported on the list, it seems clear that a cheap surplus machine -- a reasonable 486, a minimal Pentium box, a Sparc 5, ... -- can easily handle a home office or a small company connection using any of:
If available, we suggest using a Pentium 133 or better. This should ensure that, even under maximum load, IPsec will use less than half the CPU cycles. You then have enough left for other things you may want on your gateway -- firewalling, web caching, DNS and such.
Here is some additional data from the mailing list.
Subject: FreeSWAN (specically KLIPS) performance measurements
Date: Thu, 01 Feb 2001
From: Nigel Metheringham <Nigel.Metheringham@intechnology.co.uk>
I've spent a happy morning attempting performance tests against KLIPS
(this is due to me not being able to work out the CPU usage of KLIPS so
resorting to the crude measurements of maximum throughput to give a
baseline to work out loading of a box).
Measurements were done using a set of 4 boxes arranged in a line, each
connected to the next by 100Mbit duplex ethernet. The inner 2 had an
ipsec tunnel between them (shared secret, but I was doing measurements
when the tunnel was up and running - keying should not be an issue
here). The outer pair of boxes were traffic generators or traffic sink.
The crypt boxes are Compaq DL380s - Uniprocessor PIII/733 with 256K
cache. They have 128M main memory. Nothing significant was running on
the boxes other than freeswan. The kernel was a 2.2.19pre7 patched
with freeswan and ext3.
Without an ipsec tunnel in the chain (ie the 2 inner boxes just being
100BaseT routers), throughput (measured with ttcp) was between 10644
and 11320 KB/sec
With an ipsec tunnel in place, throughput was between 3268 and 3402
KB/sec
These measurements are for data pushed across a TCP link, so the
traffic on the wire between the 2 ipsec boxes would have been higher
than this....
vmstat (run during some other tests, so not affecting those figures) on
the encrypting box shows approx 50% system & 50% idle CPU - which I
don't believe at all. Interactive feel of the box was significantly
sluggish.
I also tried running the kernel profiler (see man readprofile) during
test runs.
A box doing primarily decrypt work showed basically nothing happening -
I assume interrupts were off.
A box doing encrypt work showed the following:-
Ticks Function Load
~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~
956 total 0.0010
532 des_encrypt2 0.1330
110 MD5Transform 0.0443
97 kmalloc 0.1880
39 des_encrypt3 0.1336
23 speedo_interrupt 0.0298
14 skb_copy_expand 0.0250
13 ipsec_tunnel_start_xmit 0.0009
13 Decode 0.1625
11 handle_IRQ_event 0.1019
11 .des_ncbc_encrypt_end 0.0229
10 speedo_start_xmit 0.0188
9 satoa 0.0225
8 kfree 0.0118
8 ip_fragment 0.0121
7 ultoa 0.0365
5 speedo_rx 0.0071
5 .des_encrypt2_end 5.0000
4 _stext 0.0140
4 ip_fw_check 0.0035
2 rj_match 0.0034
2 ipfw_output_check 0.0200
2 inet_addr_type 0.0156
2 eth_copy_and_sum 0.0139
2 dev_get 0.0294
2 addrtoa 0.0143
1 speedo_tx_buffer_gc 0.0024
1 speedo_refill_rx_buf 0.0022
1 restore_all 0.0667
1 number 0.0020
1 net_bh 0.0021
1 neigh_connected_output 0.0076
1 MD5Final 0.0083
1 kmem_cache_free 0.0016
1 kmem_cache_alloc 0.0022
1 __kfree_skb 0.0060
1 ipsec_rcv 0.0001
1 ip_rcv 0.0014
1 ip_options_fragment 0.0071
1 ip_local_deliver 0.0023
1 ipfw_forward_check 0.0139
1 ip_forward 0.0011
1 eth_header 0.0040
1 .des_encrypt3_end 0.0833
1 des_decrypt3 0.0034
1 csum_partial_copy_generic 0.0045
1 call_out_firewall 0.0125
Hope this data is helpful to someone... however the lack of visibility
into the decrypt side makes things less clear
Another user reported some results for connections with and without IP compression:
Subject: [Users] Speed with compression
Date: Fri, 29 Jun 2001
From: John McMonagle <johnm@advocap.org>
Did a couple tests with compression using the new 1.91 freeswan.
Running between 2 sites with cable modems. Both using approximately
130 mhz pentium.
Transferred files with ncftp.
Compressed file was a 6mb compressed installation file.
Non compressed was 18mb /var/lib/rpm/packages.rpm
Compressed vpn regular vpn
Compress file 42.59 kBs 42.08 kBs
regular file 110.84 kBs 41.66 kBs
Load was about 0 either way.
Ping times were very similar a bit above 9 ms.
Compression looks attractive to me.
Later in the same thread, project technical lead Henry Spencer added:
> is there a reason not to switch compression on? I have large gateway boxes > connecting 3 connections, one of them with a measly DS1 link... Run some timing tests with and without, with data and loads representative of what you expect in production. That's the definitive way to decide. If compression is a net loss, then obviously, leave it turned off. If it doesn't make much difference, leave it off for simplicity and hence robustness. If there's a substantial gain, by all means turn it on. If both ends support compression and can successfully negotiate a compressed connection (trivially true if both are FreeS/WAN 1.91), then the crucial question is CPU cycles. Compression has some overhead, so one question is whether *your* data compresses well enough to save you more CPU cycles (by reducing the volume of data going through CPU-intensive encryption/decryption) than it costs you. Last time I ran such tests on data that was reasonably compressible but not deliberately contrived to be so, this generally was not true -- compression cost extra CPU cycles -- so compression was worthwhile only if the link, not the CPU, was the bottleneck. However, that was before the slow-compression bug was fixed. I haven't had a chance to re-run those tests yet, but it sounds like I'd probably see a different result.The bug he refers to was a problem with the compression libraries that had us using C code, rather than assembler, for compression. It was fixed before 1.91.
If you want to measure the loads FreeS/WAN puts on a system, note that tools such as top or measurements such as load average are more-or-less useless for this. They are not designed to measure something that does most of its work inside the kernel.
Here is a message from FreeS/WAN kernel programmer Richard Guy Briggs on this:
> I have a batch of boxes doing Freeswan stuff. > I want to measure the CPU loading of the Freeswan tunnels, but am > having trouble seeing how I get some figures out... > > - Keying etc is in userspace so will show up on the per-process > and load average etc (ie pluto's load) Correct. > - KLIPS is in the kernel space, and does not show up in load average > I think also that the KLIPS per-packet processing stuff is running > as part of an interrupt handler so it does not show up in the > /proc/stat system_cpu or even idle_cpu figures It is not running in interrupt handler. It is in the bottom half. This is somewhere between user context (careful, this is not userspace!) and hardware interrupt context. > Is this correct, and is there any means of instrumenting how much the > cpu is being loaded - I don't like the idea of a system running out of > steam whilst still showing 100% idle CPU :-) vmstat seems to do a fairly good job, but use a running tally to get a good idea. A one-off call to vmstat gives different numbers than a running stat. To do this, put an interval on your vmstat command line.and another suggestion from the same thread:
Subject: Re: Measuring the CPU usage of Freeswan Date: Mon, 29 Jan 2001 From: Patrick Michael Kane <modus@pr.es.to> The only truly accurate way to accurately track FreeSWAN CPU usage is to use a CPU soaker. You run it on an unloaded system as a benchmark, then start up FreeSWAN and take the difference to determine how much FreeSWAN is eating. I believe someone has done this in the past, so you may find something in the FreeSWAN archives. If not, someone recently posted a URL to a CPU soaker benchmark tool on linux-kernel.
Not all types of testing are described here. Other parts of the documentation describe some tests:
The test setups and procedures described here can also be used in other testing, but this document focuses on testing the IPsec functionality of FreeS/WAN.
This section teaches you how to test your opportunistically encrypted (OE) connections. To set up OE, please see the easy instructions in our quickstart guide.
This test is for basic OE functionality. For additional tests, keep reading.
Be sure IPsec is running. You can see whether it is with:
ipsec setup status
If need be, you can restart it with:
service ipsec restart
Load a FreeS/WAN test website from the host on which you're running FreeS/WAN. Note: the feds may be watching these sites. Type one of:
links oetest.freeswan.org
links oetest.freeswan.nl
A positive result looks like this:
You seem to be connecting from: 192.0.2.11 which DNS says is:
gateway.example.com
_________________________________________________________________
Status E-route
OE enabled 16 192.139.46.73/32 -> 192.0.2.11/32 =>
tun0x2097@192.0.2.11
OE enabled 176 192.139.46.77/32 -> 192.0.2.11/32 =>
tun0x208a@192.0.2.11
If you see this, congratulations! Your OE box will now encrypt its own traffic whenever it can. If you have difficulty, see our OE troubleshooting tips.
If you've set up FreeS/WAN to protect a subnet behind your gateway, you'll need to run another simple test, which can be done from a machine running any OS. That's right, your Windows box can be protected by opportunistic encryption without any FreeS/WAN install or configuration on that box. From each protected subnet node , load the FreeS/WAN website with:
links oetest.freeswan.org
links oetest.freeswan.nl
A positive result looks like this:
You seem to be connecting from: 192.0.2.98 which DNS says is:
box98.example.com
_________________________________________________________________
Status E-route
OE enabled 16 192.139.46.73/32 -> 192.0.2.98/32 =>
tun0x134ed@192.0.2.11
OE enabled 176 192.139.46.77/32 -> 192.0.2.11/32 =>
tun0x134d2@192.0.2.11
If you see this, congratulations! Your OE gateway will now encrypt traffic for this subnet node whenever it can. If you have difficulty, see our OE troubleshooting tips.
When testing OE, you will often find it useful to execute this command on the FreeS/WAN host:
ipsec eroute
If you have established a connection (either for or for a subnet node) you will see a result like:
192.0.2.11/32 -> 192.139.46.73/32 => tun0x149f@192.139.46.38
Key:
| 1. | 192.0.2.11/32 | Local start point of the protected traffic. |
| 2. | 192.0.2.194/32 | Remote end point of the protected traffic. |
| 3. | 192.0.48.38 | Remote FreeS/WAN node (gateway or host). May be the same as (2). |
| 4. | [not shown] | Local FreeS/WAN node (gateway or host), where you've produced the output. May be the same as (1). |
For extra assurance, you may wish to use a packet sniffer such as tcpdump to verify that packets are being encrypted. You should see output that indicates ESP encrypted data, for example:
02:17:47.353750 PPPoE [ses 0x1e12] IP 154: xy.example.com > oetest.freeswan.org: ESP(spi=0x87150d16,seq=0x55)
User Mode Linux allows you to run Linux as a user process on another Linux machine.
As of 1.92, the distribution has a new directory named testing. It contains a collection of test scripts and sample configurations. Using these, you can bring up several copies of Linux in user mode and have them build tunnels to each other. This lets you do some testing of a FreeS/WAN configuration on a single machine.
You need a moderately well-endowed machine for this to work well. Each UML wants about 16 megs of memory by default, which is plenty for FreeS/WAN usage. Typical regression testing only occasionally uses as many as 4 UMLs. If one is doing nothing else with the machine (in particular, not running X on it), then 128 megs and a 500MHz CPU are fine.
Documentation on these scripts is here. There is also documentation on automated testing here.A common test setup is to put a machine with dual Ethernet cards in between two gateways under test. You need at least five machines; two gateways, two clients and a testing machine in the middle.
The central machine both routes packets and provides a place to run diagnostic software for checking IPsec packets. See next section for discussion of using tcpdump(8) for this.
This makes things more complicated than if you just connected the two gateway machines directly to each other, but it also makes your test setup much more like the environment you actually use IPsec in. Those environments nearly always involve routing, and quite a few apparent IPsec failures turn out to be problems with routing or with firewalls dropping packets. This approach lets you deal with those problems on your test setup.
What you end up with looks like:
subnet a.b.c.0/24
|
eth1 = a.b.c.1
gate1
eth0 = 192.168.p.1
|
|
eth0 = 192.168.p.2
route/monitor box
eth1 = 192.168.q.2
|
|
eth0 = 192.168.q.1
gate2
eth1 = x.y.z.1
|
subnet x.y.z.0/24
Where p and q are any convenient values that do not interfere with other routes you may have. The ipsec.conf(5) file then has, among other things:
conn abc-xyz
left=192.168.p.1
leftnexthop=192.168.p.2
right=192.168.q.1
rightnexthop=192.168.q.2
Once that works, you can remove the "route/monitor box", and connect the two gateways to the Internet. The only parameters in ipsec.conf(5) that need to change are the four shown above. You replace them with values appropriate for your Internet connection, and change the eth0 IP addresses and the default routes on both gateways.
Note that nothing on either subnet needs to change. This lets you test most of your IPsec setup before connecting to the insecure Internet.
A number of tools are available for looking at packets. We will discuss using tcpdump(8), a common Linux tool included in most distributions. Alternatives offerring more-or-less the same functionality include:
See also this index of packet sniffers.
tcpdump(8) may misbehave if run on the gateways themselves. It is designed to look into a normal IP stack and may become confused if you ask it to display data from a stack which has IPsec in play.
At one point, the problem was quite severe. Recent versions of tcpdump, however, understand IPsec well enough to be usable on a gateway. You can get the latest version from tcpdump.org.
Even with a recent tcpdump, some care is required. Here is part of a post from Henry on the topic:
> a) data from sunset to sunrise or the other way is not being > encrypted (I am using tcpdump (ver. 3.4) -x/ping -p to check > packages) What *interface* is tcpdump being applied to? Use the -i option to control this. It matters! If tcpdump is looking at the ipsecN interfaces, e.g. ipsec0, then it is seeing the packets before they are encrypted or after they are decrypted, so of course they don't look encrypted. You want to have tcpdump looking at the actual hardware interfaces, e.g. eth0. Actually, the only way to be *sure* what you are sending on the wire is to have a separate machine eavesdropping on the traffic. Nothing you can do on the machines actually running IPsec is 100% guaranteed reliable in this area (although tcpdump is a lot better now than it used to be).
The most certain way to examine IPsec packets is to look at them on the wire. For security, you need to be certain, so we recommend doing that. To do so, you need a separate sniffer machine located between the two gateways. This machine can be routing IPsec packets, but it must not be an IPsec gateway. Network configuration for such testing is discussed above.
Here's another mailing list message with advice on using tcpdump(8):
Subject: RE: [Users] Encrypted??? Date: Thu, 29 Nov 2001 From: "Joe Patterson" <jpatterson@asgardgroup.com> tcpdump -nl -i $EXT-IF proto 50 -nl tells it not to buffer output or resolve names (if you don't do that it may confuse you by not outputing anything for a while), -i $EXT-IF (replace with your external interface) tells it what interface to listen on, and proto 50 is ESP. Use "proto 51" if for some odd reason you're using AH, and "udp port 500" if you want to see the isakmp key exchange/tunnel setup packets. You can also run `tcpdump -nl -i ipsec0` to see what traffic is on that virtual interface. Anything you see there *should* be either encrypted or dropped (unless you've turned on some strange options in your ipsec.conf file) Another very handy thing is ethereal (http://www.ethereal.com/) which runs on just about anything, has a nice gui interface (or a nice text-based interface), and does a great job of protocol breakdown. For ESP and AH it'll basically just tell you that there's a packet of that protocol, and what the spi is, but for isakmp it'll actually show you a lot of the tunnel setup information (until it gets to the point in the protocol where isakmp is encrypted....)
The question of how to verify that messages are actually encrypted has been extensively discussed on the mailing list. See this thread.
If you just want to verify that packets are encrypted, look at them with a packet sniffer (see previous section ) located between the gateways. The packets should, except for some of the header information, be utterly unintelligible. The output of good encryption looks exactly like random noise.
A packet sniffer can only tell you that the data you looked at was encrypted. If you have stronger requirements -- for example if your security policy requires verification that plaintext is not leaked during startup or under various anomolous conditions -- then you will need to devise much more thorough tests. If you do that, please post any results or methodological details which your security policy allows you to make public.
You can put recognizable data into ping packets with something like:
ping -p feedfacedeadbeef 11.0.1.1
"feedfacedeadbeef" is a legal hexadecimal pattern that is easy to pick out of hex dumps.
For other protocols, you may need to check if you have encrypted data or ASCII text. Encrypted data has approximately equal frequencies for all 256 possible characters. ASCII text has most characters in the printable range 0x20-0x7f, a few control characters less than 0x20, and none at all in the range 0x80-0xff. 0x20, space, is a good character to look for. In normal English text space occurs about once in seven characters, versus about once in 256 for random or encrypted data.
One thing to watch for: the output of good compression, like that of good encryption, looks just like random noise. You cannot tell just by looking at a data stream whether it has been compressed, encrypted, or both. You need a little care not to mistake compressed data for encrypted data in your testing.
Note also that weak encryption also produces random-looking output. You cannot tell whether the encryption is strong by looking at the output. To be sure of that, you would need to have both the algorithms and the implementation examined by experts.
For IPsec, you can get partial assurance from interoperability tests. See our interop document. When twenty products all claim to implement 3DES, and they all talk to each other, you can be fairly sure they have it right. Of course, you might wonder whether all the implementers are consipring to trick you or, more plausibly, whether some implementations might have "back doors" so they can get also it wrong when required.. If you're seriously worried about things like that, you need to get the code you use audited (good luck if it is not Open Source), or perhaps to talk to a psychiatrist about treatments for paranoia.
Additional information on testing can be found in these mailing list messages:
This section lists many of the options available when configuring a Linux kernel, and explains how they should be set on a FreeS/WAN IPsec gateway.
Note that in many cases you do not need to mess with these.
You may have a Linux distribution which comes with FreeS/WAN installed (see this list). In that case, you need not do a FreeS/WAN installation or a kernel configuration. Of course, you might still want to configure and rebuild your kernel to improve performance or security. This can be done with standard tools described in the Kernel HowTo.
If you need to install FreeS/WAN, then you do need to configure a kernel. However, you may choose to do that using the simplest procedure:
This document is for those who choose to configure their FreeS/WAN kernel themselves.
Help text for most kernel options is included with the kernel files, and is accessible from within the configuration utilities. We assume you will refer to that, and to the Kernel HowTo, as necessary. This document covers only the FreeS/WAN-specific aspects of the problem.
To avoid duplication, this document section does not cover settings for the additional IPsec-related kernel options which become available after you have patched your kernel with FreeS/WAN patches. There is help text for those available from within the configuration utility.
We assume a common configuration in which the FreeS/WAN IPsec gateway is also doing ipchains(8) firewalling for a local network, and possibly masquerading as well.
Some suggestions below are labelled as appropriate for "a true paranoid". By this we mean they may cause inconvenience and it is not entirely clear they are necessary, but they appear to be the safest choice. Not using them might entail some risk. Of course one suggested mantra for security administrators is: "I know I'm paranoid. I wonder if I'm paranoid enough."
Six labels are used to indicate how options should be set. We mark the labels with [square brackets]. For two of these labels, you have no choice:
those must be set correctly or FreeS/WAN will not work
FreeS/WAN should work with any settings of the others, though of course not all combinations have been tested. We do label these in various ways, but these labels are only suggestions.
Of course complexity is an enemy in any effort to build secure systems. For maximum security, any feature that can reasonably be turned off should be. "If in doubt, leave it out."
Indentation is based on the nesting shown by 'make menuconfig' with a 2.2.16 kernel for the i386 architecture.
For most FreeS/WAN work, no is the preferred setting. Using new or untested components is too risky for a security gateway.
However, for some hardware (such as the author's network cards) the only drivers available are marked new/experimental. In such cases, you must enable this option or your cards will not appear under "network device support". A true paranoid would leave this option off and replace the cards.
With modules disabled, an attacker cannot install a bogus module. The only way he can achieve the same effects is to install a new kernel and reboot. This is considerably more likely to be noticed.
Many FreeS/WAN gateways run with modules enabled. This simplifies some administrative tasks and some ipchains features are available only as modules. Once an enemy has root on your machine your security is nil, so arguably defenses which come into play only in that situation are pointless.
echo 1 > /proc/sys/net/ipv4/ipforwardturns IP forwarding on.
Disabling this option breaks many firewall scripts. A true paranoid would disable it anyway since it might conceivably be of use to an attacker.
Even if the IPsec gateway is not your primary firewall, we suggest setting this so that you can protect the gateway with at least basic local packet filters.
It should be possible to use IPv4 FreeS/WAN on a machine which also does IPv6. This combination is not yet well tested. We would be quite interested in hearing results from anyone expermenting with it, via the mailing list.
We do not recommend using IPv6 on production FreeS/WAN gateways until more testing has been done.
We do not recommend this. Keep the software on your gateway as simple as possible. If you need a Linux-based Appletalk or IPX server, use a separate machine.
The development team test almost entirely on 10 or 100 megabit Ethernet and modems. In principle, any device that can do IP should be just fine for IPsec, but in the real world any device that has not been well-tested is somewhat risky. By all means try it, but don't bet your project on it until you have solid test results.
If you disabled experimental drivers in the Code maturity section above, then those drivers will not be shown here. Check that option before going off to hunt for missing drivers.
If you want Linux to automatically find more than one ethernet interface at boot time, you need to:
append="ether=0,0,eth0 ether=0,0,eth1"to your /etc/lilo.conf file. In some cases you may need to specify parameters such as IRQ or base address. The example uses "0,0" for these, which tells the system to search. If the search does not succeed on your hardware, then you should retry with explicit parameters. See the lilo.conf(5) man page for details.
If you are comfortable with C source code, it is likely a good idea to go in and adjust the #define lines in /usr/src/linux/drivers/char/random.c to ensure that all sources of randomness are enabled. Relying solely on keyboard and mouse randomness is dubious procedure for a gateway machine. You could also increase the randomness pool size from the default 512 bytes (128 32-bit words).
This document describes various options for FreeS/WAN configuration which are less used or more complex (often both) than the standard cases described in our config and quickstart documents.
Nearly all of the overhead in IPsec processing is in the encryption and authentication of packets. Our performance document discusses these overheads.
Beside those overheads, the cost of managing additional tunnels is trivial. Whether your gateway supports one tunnel or ten just does not matter. A hundred might be a problem; there is a section on this in the performance document.
So, in nearly all cases, if using multiple tunnels gives you a reasonable way to describe what you need to do, you should describe it that way in your configuration files.
For example, one user recently asked on a mailing list about this network configuration:
netA---gwA---gwB---netB
|----netC
netA and B are secured netC not.
netA and gwA can not access netC
The user had constructed only one tunnel, netA to netB, and wanted to know how to use ip-route to get netC packets into it. This is entirely unnecessary. One of the replies was:
The simplest way and indeed the right way to
solve this problem is to set up two connections:
leftsubnet=NetA
left=gwA
right=gwB
rightsubnet=NetB
and
leftsubnet=NetA
left=gwA
right=gwB
rightsubnet=NetC
This would still be correct even if we added nets D, E, F, ... to the above diagram and needed twenty tunnels.
Of course another possibility would be to just use one tunnel, with a subnet mask that includes both netB and netC (or B, C, D, ...). See next section.
In general, you can construct as many tunnels as you need. Networks like netC in this example that do not connect directly to the gateway are fine, as long as the gateway can route to them.
The number of tunnels can become an issue if it reaches 50 or so. This is discussed in the performance document. Look there for information on supporting hundreds of Road Warriors from one gateway.
If you find yourself with too many tunnels for some reason like having eight subnets at one location and nine at another so you end up with 9*8=72 tunnels, read the next section here.
The subnets used in leftsubnet and rightsubnet can be of any size that fits your needs, and they need not correspond to physical networks.
You adjust the size by changing the subnet mask , the number after the slash in the subnet description. For example
As an example of using these in connection descriptions, suppose your company's head office has four physical networks using the address ranges:
You can use exactly those subnets in your connection descriptions, or use larger subnets to grant broad access if required:
or use smaller subnets to restrict access:
To be exact, 192.68.103.64/28 means all addresses whose top 28 bits match 192.168.103.64. There are 16 of these because there are 16 possibilities for the remainingg 4 bits. Their addresses are 192.168.103.64 to 192.168.103.79.
Each connection description can use a different subnet if required.
It is possible to use all the examples above on the same FreeS/WAN gateway, each in a different connection description, perhaps for different classes of user or for different remote offices.
It is also possible to have multiple tunnels using different leftsubnet descriptions with the same right. For example, when the marketing manager is on the road he or she might have access to:
This takes three tunnels, but tunnels are cheap. If the laptop is set up to build all three tunnels automatically, then he or she can access all these machines concurrently, perhaps from different windows.
Here is the usual network picture for a site-to-site VPN::
Sunset==========West------------------East=========Sunrise
local net untrusted net local net
and for the Road Warrior::
telecommuter's PC or
traveller's laptop
Sunset==========West------------------East
corporate LAN untrusted net
Other configurations are also possible.
A telecommuter might have:
Sunset==========West------------------East ================= firewall --- the Internet
home network untrusted net corporate network
This can be described as a special case of the general subnet-to-subnet connection. The subnet on the right is 0.0.0.0/0, the whole Internet.
West (the home gateway) can have its firewall rules set up so that only IPsec packets to East are allowed out. It will then behave as if its only connection to the world was a wire to East.
When machines on the home network need to reach the Internet, they do so via the tunnel, East and the corporate firewall. From the viewpoint of the Internet (perhaps of some EvilDoer trying to break in!), those home office machines are behind the firewall and protected by it.
Another possible configuration comes up when you do not trust the local network, either because you have very high security standards or because your are using easily-intercepted wireless signals.
Some wireless networks have built-in encryption called WEP, but its security is dubious. It is a fairly common practice to use IPsec instead.
In this case, part of your network may look like this:
West-----------------------------East == the rest of your network
workstation untrusted wireless net
Of course, there would likely be several wireless workstations, each with its own IPsec tunnel to the East gateway.
The connection descriptions look much like Road Warrior descriptions:
The rightsubnet= parameter might be set in any of several ways:
Of course you can mix and match these as required. For example, a university might allow faculty full Internet access while letting student laptops connect only to a group of lab machines.
One choice you need to make before configuring additional connections is what type or types of connections you will use. There are several options, and you can use more than one concurrently.
IPsec allows two types of connections, with manual or automatic keying. FreeS/WAN starts them with commands such as:
ipsec manual --up name
ipsec auto --up name
The difference is in how they are keyed.
A third method, using RSA keys embedded in X.509 certtificates, is provided by user patches.
Manually keyed connections provide weaker security than automatically keyed connections. An opponent who reads ipsec.secrets(5) gets your encryption key and can read all data encrypted by it. If he or she has an archive of old messages, all of them back to your last key change are also readable.
With automatically-(re)-keyed connections, an opponent who reads ipsec.secrets(5) gets the key used to authenticate your system in IKE -- the shared secret or your private key, depending what authentication mechanism is in use. However, he or she does not automatically gain access to any encryption keys or any data.
An attacker who has your authentication key can mount a man-in-the-middle attack and, if that succeeds, he or she will get encryption keys and data. This is a serious danger, but it is better than having the attacker read everyting as soon as he or she breaks into ipsec.secrets(5).. Moreover, the keys change often so an opponent who gets one key does not get a large amount of data. To read all your data, he or she would have to do a man-in-the-middle attack at every key change.
We discuss using manual keying in production below, but this is not recommended except in special circumstances, such as needing to communicate with some implementation that offers no auto-keyed mode compatible with FreeS/WAN.
Manual keying may also be useful for testing. There is some discussion of this in our FAQ.
The IKE protocol which Pluto uses to negotiate connections between gateways must use some form of authentication of peers. A gateway must know who it is talking to before it can create a secure connection. We support two basic methods for this authentication:
There are, howver, several variations on the RSA theme, using different methods of managing the RSA keys:
Public keys in ipsec.conf(5 ) give a reasonably straightforward method of specifying keys for explicitly configured connections.
Putting public keys in DNS allows us to support opportunistic encryption. Any two FreeS/WAN gateways can provide secure communication, without either of them having any preset information about the other.
X.509 certificates may be required to interface to various PKIs.
Authentication with a public key method such as RSA has some important advantages over using shared secrets.
If the branch offices need to talk to each other, this becomes problematic. You need another 20*19/2 = 190 secrets for branch-to-branch communication, each known to exactly two branches. Now all the branch admins have the headache of handling 20 keys, each shared with exactly one other branch or with head office.
For larger numbers of branches, the number of connections and secrets increases quadratically and managing them becomes a nightmare. A 1000-gateway fully connected network needs 499,500 secrets, each known to exactly two players. There are ways to reduce this problem, for example by introducing a central key server, but these involve additional communication overheads, more administrative work, and new threats that must be carefully guarded against.
As network size increaes, the number of public keys used increases linearly with the number of nodes. This still requires careful administration in large applications, but is nothing like the disaster of a quadratic increase. On a 1000-gateway network, you have 1000 private keys, each of which must be kept secure on one machine, and 1000 public keys which must be distributed. This is not a trivial problem, but it is manageable.
There is also a disadvantage:
This is partly counterbalanced by the fact that the key is never transmitted and remains under your control at all times. It is likely necessary, however, to take account of this in setting security policy. For example, you should change gateway keys when an administrator leaves the company, and should change them periodically in any case.
Overall, public key methods are more secure, more easily managed and more flexible. We recommend that they be used for all connections, unless there is a compelling reason to do otherwise.
Generally, public key methods are preferred for reasons given above, but shared secrets can be used with no loss of security, just more work and perhaps more need to take precautions.
What I call "shared secrets" are sometimes also called "pre-shared keys". They are used only for for authentication, never for encryption. Calling them "pre-shared keys" has confused some users into thinking they were encryption keys, so I prefer to avoid the term..
If you are interoperating with another IPsec implementation, you may find its documentation calling them "passphrases".
If shared secrets are to be used to authenticate communication for the Diffie-Hellman key exchange in the IKE protocol, then those secrets must be stored in /etc/ipsec.secrets. For details, see the ipsec.secrets(5) man page.
A few considerations are vital:
Each line has the IP addresses of the two gateways plus the secret. It should look something like this:
10.0.0.1 11.0.0.1 : PSK "jxTR1lnmSjuj33n4W51uW3kTR55luUmSmnlRUuWnkjRj3UuTV4T3USSu23Uk55nWu5TkTUnjT"
PSK indicates the use of a pre-s hared key. The quotes and the whitespace shown are required.
You can use any character string as your secret. For security, it should be both long and extremely hard to guess. We provide a utility to generate such strings, ipsec_ranbits(8).
You want the same secret on the two gateways used, so you create a line with that secret and the two gateway IP addresses. The installation process supplies an example secret, useful only for testing. You must change it for production use.
You must deliver this file, or the relevant part of it, to the other gateway machine by some secure means. Don't just FTP or mail the file! It is vital that the secrets in it remain secret. An attacker who knew those could easily have all the data on your "secure" connection.
This file must be owned by root and should have permissions rw-------.
You can use a shared secret to support a single road warrior connecting to your gateway, and this is a reasonable thing to do in some circumstances. Public key methods have advantages, discussed above, but they are not critical in this case.
To do this, the line in ipsec.secrets(5) is something like:
10.0.0.1 0.0.0.0 : PSK "jxTR1lnmSjuj33n4W51uW3kTR55luUmSmnlRUuWnkjRj3UuTV4T3USSu23Uk55nWu5TkTUnjT"where the 0.0.0.0 means that any IP address is acceptable.
For more than one road warrior, shared secrets are not recommended. If shared secrets are used, then when the responder needs to look up the secret, all it knows about the sender is an IP address. This is fine if the sender is at a fixed IP address specified in the config file. It is also fine if only one road warrior uses the wildcard 0.0.0.0 address. However, if you have more than one road warrior using shared secret authentication, then they must all use that wildcard and therefore all road warriors using PSK autentication must use the same secret. Obviously, this is insecure.
For multiple road warriors, use public key authentication. Each roadwarrior can then have its own identity (our leftid= or rightid= parameters), its own public/private key pair, and its own secure connection.
Generally, automatic keying is preferred over manual keying for production use because it is both easier to manage and more secure. Automatic keying frees the admin from much of the burden of managing keys securely, and can provide perfect forward secrecy. This is discussed in more detail above.
However, it is possible to use manual keying in production if that is what you want to do. This might be necessary, for example, in order to interoperate with some device that either does not provide automatic keying or provides it in some version we cannot talk to.
Note that with manual keying all security rests with the keys . If an adversary acquires your keys, you've had it. He or she can read everything ever sent with those keys, including old messages he or she may have archived.
You need to be really paranoid about keys if you're going to rely on manual keying for anything important.
Linux FreeS/WAN provides some facilities to help with this. In particular, it is good policy to keep keys in separate files so you can edit configuration information in /etc/ipsec.conf without exposing keys to "shoulder surfers" or network snoops. We support this with the also= and include syntax in ipsec.conf(5).
See the last example in our examples file. In the /etc/ipsec.conf conn samplesep section, it has the line:
also=samplesep-keys
which tells the "ipsec manual" script to insert the configuration description labelled "samplesep-keys" if it can find it. The /etc/ipsec.conf file must also have a line such as:
include ipsec.*.conf
which tells it to read other files. One of those other files then might contain the additional data:
conn samplesep-keys spi=0x200 esp=3des-md5-96 espenckey=0x01234567_89abcdef_02468ace_13579bdf_12345678_9abcdef0 espauthkey=0x12345678_9abcdef0_2468ace0_13579bdf
The first line matches the label in the "also=" line, so the indented lines are inserted. The net effect is exactly as if the inserted lines had occurred in the original file in place of the "also=" line.
Variables set here are:
Note that the example keys we supply are intended only for testing. For real use, you should go to automatic keying. If that is not possible, create your own keys for manual mode and keep them secret
Of course, any files containing keys must have 600 permissions and be owned by root.
If you connect in this way to multiple sites, we recommend that you keep keys for each site in a separate file and adopt some naming convention that lets you pick them all up with a single "include" line. This minimizes the risk of losing several keys to one error or attack and of accidentally giving another site admin keys which he or she has no business knowing.
Also note that if you have multiple manually keyed connections on a single machine, then the spi parameter must be different for each one. Any 3-digit hex number is OK, provided they are different for each connection. We reserve the range 0x100 to 0xfff for manual connections. Pluto assigns SPIs from 0x1000 up for automatically keyed connections.
If ipsec.conf(5) contains keys for manual mode connections, then it too must have permissions rw-------. We recommend instead that, if you must manual keying in production, you keep the keys in separate files.
Note also that ipsec.conf is installed with permissions rw-r--r--. If you plan to use manually keyed connections for anything more than initial testing, you must:
We recommend the latter method for all but the simplest configurations.
You can create new random keys with the ranbits(8) utility. For example, the commands:
umask 177
ipsec ranbits 192 > temp
ipsec ranbits 128 >> temp
create keys in the sizes needed for our default algorithms:
If you want to use SHA instead of MD5, that requires a 160-bit key
Note that any temporary files used must be kept secure since they contain keys. That is the reason for the umask command above. The temporary file should be deleted as soon as you are done with it. You may also want to change the umask back to its default value after you are finished working on keys.
The ranbits utility may pause for a few seconds if not enough entropy is available immediately. See ipsec_ranbits(8) and random(4) for details. You may wish to provide some activity to feed entropy into the system. For example, you might move the mouse around, type random characters, or do du /usr > /dev/null in the background.
You can tell the system to set up connections automatically at boot time by putting suitable stuff in /etc/ipsec.conf on both systems. The relevant section of the file is labelled by a line reading config setup.
Details can be found in the ipsec.conf(5) man page. We also provide a file of example configurations.
The most likely options are something like:
Note that for PPP, you give the ppp[0-9] device name here, not the underlying device such as modem (or eth1 if you are using PPPoE).
Note that Pluto does not currently pay attention to this variable. The variable controls setup messages only.
"yes" is strongly recommended for production use so that the keying daemon (Pluto) will automatically re-key the connections regularly. The ipsec-auto parameters ikelifetime, ipseclifetime and reykeywindow give you control over frequency of rekeying.
If plutoload is "%search", Pluto will load any connections whose description includes "auto=add" or "auto=start".
If plutostart is "%search", Pluto will start any connections whose description includes "auto=start".
Note that, for a connection intended to be permanent, both gateways should be set try to start the tunnel. This allows quick recovery if either gateway is rebooted or has its IPsec restarted. If only one gateway is set to start the tunnel and the other gateway restarts, the tunnel may not be rebuilt.
The example assumes you are at the Reno office and will use IPsec to Vancouver, New York City and Amsterdam.
Consider a pair of subnets, each with a security gateway, connected via the Internet:
192.168.100.0/24 left subnet
|
192.168.100.1
North Gateway
101.101.101.101 left
|
101.101.101.1 left next hop
[Internet]
202.202.202.1 right next hop
|
202.202.202.202 right
South gateway
192.168.200.1
|
192.168.200.0/24 right subnet
A tunnel specification such as:
conn northnet-southnet
left=101.101.101.101
leftnexthop=101.101.101.1
leftsubnet=192.168.100.0/24
leftfirewall=yes
right=202.202.202.202
rightnexthop=202.202.202.1
rightsubnet=192.168.200.0/24
rightfirewall=yes
will allow machines on the two subnets to talk to each other. You might
test this by pinging from polarbear (192.168.100.7) to penguin
(192.168.200.5).
However, this does not cover other traffic you might want to secure. To handle all the possibilities, you might also want these connection descriptions:
conn northgate-southnet
left=101.101.101.101
leftnexthop=101.101.101.1
right=202.202.202.202
rightnexthop=202.202.202.1
rightsubnet=192.168.200.0/24
rightfirewall=yes
conn northnet-southgate
left=101.101.101.101
leftnexthop=101.101.101.1
leftsubnet=192.168.100.0/24
leftfirewall=yes
right=202.202.202.202
rightnexthop=202.202.202.1
Without these, neither gateway can do IPsec to the remote subnet. There is no IPsec tunnel or eroute set up for the traffic.
In our example, with the non-routable 192.168.* addresses used, packets would simply be discarded. In a different configuration, with routable addresses for the remote subnet, they would be sent unencrypted since there would be no IPsec eroute and there would be a normal IP route.
You might also want:
conn northgate-southgate
left=101.101.101.101
leftnexthop=101.101.101.1
right=202.202.202.202
rightnexthop=202.202.202.1
This is required if you want the two gateways to speak IPsec to each other.
This requires a lot of duplication of details. Judicious use of also= and include can reduce this problem.
Note that, while FreeS/WAN supports all four tunnel types, not all implementations do. In particular, some versions of Windows 2000 and the freely downloadable version of PGP provide only "client" functionality. You cannot use them as gateways with a subnet behind them. To get that functionality, you must upgrade to Windows 2000 server or the commercially available PGP products.
Subject: Re: linux-ipsec: IPSec packets not entering tunnel? Date: Mon, 20 Nov 2000 From: Justin Guyett <jfg@sonicity.com> On Mon, 20 Nov 2000, Claudia Schmeing wrote: > Right Left > "home" "office" > 10.92.10.0/24 ---- 24.93.85.110 ========= 216.175.164.91 ---- 10.91.10.24/24 > > I've created all four tunnels, and can ping to test each of them, > *except* homegate-officenet. I keep wondering why people create all four tunnels. Why not route traffic generated from home to 10.91.10.24/24 out ipsec0 with iproute2? And 99% of the time you don't need to access "office" directly, which means you can eliminate all but the subnet<->subnet connection.and FreeS/WAN technical lead Henry Spencer's comment:
> I keep wondering why people create all four tunnels. Why not route > traffic generated from home to 10.91.10.24/24 out ipsec0 with iproute2? This is feasible, given some iproute2 attention to source addresses, but it isn't something we've documented yet... (partly because we're still making some attempt to support 2.0.xx kernels, which can't do this, but mostly because we haven't caught up with it yet). > And 99% of the time you don't need to access "office" directly, which > means you can eliminate all but the subnet<->subnet connection. Correct in principle, but people will keep trying to ping to or from the gateways during testing, and sometimes they want to run services on the gateway machines too.
Full opportunism allows you to initiate and receive opportunistic connections on your machine. The remaining instructions in this section assume you have first set up full opportunism on your gateway using these instructions. Both sets of instructions require mailing DNS records to your ISP. Collect DNS records for both the gateway (above) and the subnet nodes (below) before contacting your ISP.
You need these so that your Opportunistic peers can:
On the gateway, generate a TXT record with:
ipsec showhostkey --txt 192.0.2.11
Use your gateway address in place of 192.0.2.11.
You should see (keys are trimmed for clarity throughout our example):
; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000
IN TXT "X-IPsec-Server(10)=192.0.2.11" " AQOF8tZ2...+buFuFn/"
This MUST BE the same key as in your gateway's TXT record, or nothing will work.
In a text file, make one copy of this TXT record for each subnet node:
; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000
IN TXT "X-IPsec-Server(10)=192.0.2.11" " AQOF8tZ2...+buFuFn/"
; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000
IN TXT "X-IPsec-Server(10)=192.0.2.11" " AQOF8tZ2...+buFuFn/"
; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000
IN TXT "X-IPsec-Server(10)=192.0.2.11" " AQOF8tZ2...+buFuFn/"
Above each entry, insert a line like this:
98.2.0.192.in-addr.arpa. IN PTR arthur.example.com.
It must include:
The result will be a file of TXT records, like this:
98.2.0.192.in-addr.arpa. IN PTR arthur.example.com.
; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000
IN TXT "X-IPsec-Server(10)=192.0.2.11" " AQOF8tZ2...+buFuFn/"
99.2.0.192.in-addr.arpa. IN PTR ford.example.com.
; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000
IN TXT "X-IPsec-Server(10)=192.0.2.11" " AQOF8tZ2...+buFuFn/"
100.2.0.192.in-addr.arpa. IN PTR trillian.example.com.
; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000
IN TXT "X-IPsec-Server(10)=192.0.2.11" " AQOF8tZ2...+buFuFn/"
Ask your ISP to publish all the reverse DNS records you have collected. There may be a delay of up to 48 hours as the records propagate.
Check a couple of records with commands like this one:
ipsec verify --host ford.example.com
ipsec verify --host trillian.example.com
The verify command checks for TXT records for both the subnet host and its gateway. You should see output like:
...
Looking for TXT in reverse map: 99.2.0.192.in-addr.arpa [OK]
...
Looking for TXT in reverse map: 11.2.0.192.in-addr.arpa [OK]
...
Looking for TXT in reverse map: 100.2.0.192.in-addr.arpa [OK]
...
Looking for TXT in reverse map: 11.2.0.192.in-addr.arpa [OK]
...
FreeS/WAN 2.x ships with a built-in, automatically enabled OE connection conn packetdefault which applies OE, if possible, to all outbound traffic routed through the FreeS/WAN box. The ipsec.conf(5) manual describes this connection in detail. While the effect is much the same as private-or-clear, the implementation is different: notably, it does not use policy groups.
You can create more complex OE configurations for traffic forwarded through a FreeS/WAN box, as explained in our policy groups document, or disable OE using these instructions.
What we call extruded subnets are a special case of VPNs.
If your buddy has some unused IP addresses, in his subnet far off at the other side of the Internet, he can loan them to you... provided that the connection between you and him is fast enough to carry all the traffic between your machines and the rest of the Internet. In effect, he "extrudes" a part of his address space over the network to you, with your Internet traffic appearing to originate from behind his Internet gateway.
As far as the Internet is concerned, your new extruded net is behind your buddy's gateway. You route all your packets for the Internet at large out his gateway, and receive return packets the same way. You route your local packets locally.
Suppose your friend has a.b.c.0/24 and wants to give you a.b.c.240/28. The initial situation is:
subnet gateway Internet a.b.c.0/24 a.b.c.1 p.q.r.swhere anything from the Internet destined for any machine in a.b.c.0/24 is routed via p.q.r.s and that gateway knows what to do from there.
Of course it is quite normal for various smaller subnets to exist behind your friend's gateway. For example, your friend's company might have a.b.c.16/28=development, a.b.c.32/28=marketing and so on. The Internet neither knows not cares about this; it just delivers packets to the p.q.r.s and lets the gateway do whatever needs to be done from there.
What we want to do is take a subnet, perhaps a.b.c.240/28, out of your friend's physical location while still having your friend's gateway route to it. As far as the Internet is concerned, you remain behind that gateway.
subnet gateway Internet your gate extruded
a.b.c.0/24 a.b.c.1 p.q.r.s d.e.f.g a.b.c.240/28
========== tunnel ==========
The extruded addresses have to be a complete subnet.
In our example, the friend's security gateway is also his Internet gateway, but this is not necessary. As long as all traffic from the Internet to his addresses passes through the Internet gate, the security gate could be a machine behind that. The IG would need to route all traffic for the extruded subnet to the SG, and the SG could handle the rest.
First, configure your subnet using the extruded addresses. Your security gateway's interface to your subnet needs to have an extruded address (possibly using a Linux virtual interface , if it also has to have a different address). Your gateway needs to have a route to the extruded subnet, pointing to that interface. The other machines at your site need to have addresses in that subnet, and default routes pointing to your gateway.
If any of your friend's machines need to talk to the extruded subnet, they need to have a route for the extruded subnet, pointing at his gateway.
Then set up an IPsec subnet-to-subnet tunnel between your gateway and his, with your subnet specified as the extruded subnet, and his subnet specified as "0.0.0.0/0".
The tunnel description should be:
conn extruded
left=p.q.r.s
leftsubnet=0.0.0.0/0
right=d.e.f.g
rightsubnet=a.b.c.0/28
If either side was doing firewalling for the extruded subnet before the IPsec connection is set up, you'll need to poke holes in your firewall to allow packets through.
And it all just works. Your SG routes traffic for 0.0.0.0/0 -- that is, the whole Internet -- through the tunnel to his SG, which then sends it onward as if it came from his subnet. When traffic for the extruded subnet arrives at his SG, it gets sent through the tunnel to your SG, which passes it to the right machine.
Remember that when ipsec_manual or ipsec_auto takes a connection down, it does not undo the route it made for that connection. This lets you take a connection down and bring up a new one, or a modified version of the old one, without having to rebuild the route it uses and without any risk of packets which should use IPsec accidentally going out in the clear. Because the route always points into KLIPS, the packets will always go there. Because KLIPS temporarily has no idea what to do with them (no eroute for them), they will be discarded.
If you do want to take the route down, this is what the "unroute" operation in manual and auto is for. Just do an unroute after doing the down.
Note that the route for a connection may have replaced an existing non-IPsec route. Nothing in Linux FreeS/WAN will put that pre-IPsec route back. If you need it back, you have to create it with the route command.
Please note that Super FreeS/WAN now features DHCP-over-IPsec, which is an alternate procedure for Virtual IP address assignment.
Here is a mailing list message about another way to configure for road warrior support:
Subject: Re: linux-ipsec: understanding the vpn
Date: Thu, 28 Oct 1999 10:43:22 -0400
From: Irving Reid <irving@nevex.com>
> local-------linux------internet------mobile
> LAN box user
> ...
> now when the mobile user connects to the linux box
> it is given a virtual IP address, i have configured it to
> be in the 10.x.x.x range. mobile user and linux box
> have a tunnel between them with these IP addresses.
> Uptil this all is fine.
If it is possible to configure your mobile client software *not* to
use a virtual IP address, that will make your life easier. It is easier
to configure FreeS/WAN to use the actual address the mobile user gets
from its ISP.
Unfortunately, some Windows clients don't let you choose.
> what i would like to know is that how does the mobile
> user communicate with other computers on the local
> LAN , of course with the vpn ?
> what IP address should the local LAN
> computers have ? I guess their default gateway
> should be the linux box ? and does the linux box need
> to be a 2 NIC card box or one is fine.
As someone else stated, yes, the Linux box would usually be the default
IP gateway for the local lan.
However...
If you mobile user has software that *must* use a virtual IP address,
the whole picture changes. Nobody has put much effort into getting
FreeS/WAN to play well in this environment, but here's a sketch of one
approach:
Local Lan 1.0.0.0/24
|
+- Linux FreeS/WAN 1.0.0.2
|
| 1.0.0.1
Router
| 2.0.0.1
|
Internet
|
| 3.0.0.1
Mobile User
Virtual Address: 1.0.0.3
Note that the Local Lan network (1.0.0.x) can be registered, routable
addresses.
Now, the Mobile User sets up an IPSec security association with the
Linux box (1.0.0.2); it should ESP encapsulate all traffic to the
network 1.0.0.x **EXCEPT** UDP port 500. 500/udp is required for the key
negotiation, which needs to work outside of the IPSec tunnel.
On the Linux side, there's a bunch of stuff you need to do by hand (for
now). FreeS/WAN should correctly handle setting up the IPSec SA and
routes, but I haven't tested it so this may not work...
The FreeS/WAN conn should look like:
conn mobile
right=1.0.0.2
rightsubnet=1.0.0.0/24
rightnexthop=1.0.0.1
left=0.0.0.0 # The infamous "road warrior"
leftsubnet=1.0.0.3/32
Note that the left subnet contains *only* the remote host's virtual
address.
Hopefully the routing table on the FreeS/WAN box ends up looking like
this:
% netstat -rn
Kernel IP routing table
Destination Gateway Genmask Flags MSS Window irtt Iface
1.0.0.0 0.0.0.0 255.255.255.0 U 1500 0 0 eth0
127.0.0.0 0.0.0.0 255.0.0.0 U 3584 0 0 lo
0.0.0.0 1.0.0.1 0.0.0.0 UG 1500 0 0 eth0
1.0.0.3 1.0.0.1 255.255.255.255 UG 1433 0 0 ipsec0
So, if anybody sends a packet for 1.0.0.3 to the Linux box, it should
get bundled up and sent through the tunnel. To get the packets for
1.0.0.3 to the Linux box in the first place, you need to use "proxy
ARP".
How this works is: when a host or router on the local Ethernet segment
wants to send a packet to 1.0.0.3, it sends out an Ethernet level
broadcast "ARP request". If 1.0.0.3 was on the local LAN, it would
reply, saying "send IP packets for 1.0.0.3 to my Ethernet address".
Instead, you need to set up the Linux box so that _it_ answers ARP
requests for 1.0.0.3, even though that isn't its IP address. That
convinces everyone else on the lan to send 1.0.0.3 packets to the Linux
box, where the usual FreeS/WAN processing and routing take over.
% arp -i eth0 -s 1.0.0.3 -D eth0 pub
This says, if you see an ARP request on interface eth0 asking for
1.0.0.3, respond with the Ethernet address of interface eth0.
Now, as I said at the very beginning, if it is *at all* possible to
configure your client *not* to use the virtual IP address, you can avoid
this whole mess.
Sometimes you have to cope with a situation where the network interface(s) aren't all there at boot. The common example is notebooks with PCMCIA.
The key issue here is that the config setup section of the /etc/ipsec.conf configuration file lists the connection between ipsecN and hardware interfaces, in the interfaces= variable. At any time when ipsec setup start or ipsec setup restart is run this variable must correspond to the current real situation. More precisely, it must not mention any hardware interfaces which don't currently exist. The difficulty is that an ipsec setup start command is normally run at boot time so interfaces that are not up then are mis-handled.
Normally, an ipsec setup start is run at boot time. However, if the hardware situation at boot time is uncertain, one of two things must be done.
chkconfig --level 2345 ipsec offThat's for modern Red Hats or other Linuxes with chkconfig. Systems which lack this will require fiddling with symlinks in /etc/rc.d/rc?.d or the equivalent.
interfaces=in the configuration file. KLIPS and Pluto will be started, but won't do anything.
When the hardware *is* in place, IPsec has to be made aware of it. Someday there may be a nice way to do this.
Right now, the way to do it is to fix the /etc/ipsec.conf file appropriately, so interfaces reflects the new situation, and then restart the IPsec subsystem. This does break any existing IPsec connections.
If IPsec wasn't brought up at boot time, do
ipsec setup startwhile if it was, do
ipsec setup restartwhich won't be as quick.
If some of the hardware is to be taken out, before doing that, amend the configuration file so interfaces no longer includes it, and do
ipsec setup restart
Again, this breaks any existing connections.
Sometimes you might want to create a tunnel without encryption. Often this is a bad idea, even if you have some data which need not be private. See this discussion.
The IPsec protocols provide two ways to do build such tunnels:
There are several ways to handle this.
Note that if Alice and Bob want end-to-end security, they must build a tunnel end-to-end between their machines or use some other end-to-end tool such as PGP or SSL that suits their data. The only question is whether the admins build some special unencrypted tunnel for those already-encrypted packets.
This document will teach you how to install Linux FreeS/WAN. If your distribution comes with Linux FreeS/WAN, we offer tips to get you started.
To install FreeS/WAN you must:
There are three basic ways to get FreeS/WAN onto your system:
FreeS/WAN comes with these distributions.
If you're running one of these, include FreeS/WAN in the choices you make during installation, or add it later using the distribution's tools.
Your distribution may have integrated extra features, such as Andreas Steffen's X.509 patch, into FreeS/WAN. It may also use custom startup script locations or directory names.
If your FreeS/WAN came with your distribution, you may wish to generate a fresh RSA key pair. FreeS/WAN will use these keys for authentication.
To do this, become root, and type:
ipsec newhostkey --output /etc/ipsec.secrets --hostname xy.example.com
chmod 600 /etc/ipsec.secrets
where you replace xy.example.com with your machine's fully-qualified domain name. Generate some randomness, for example by wiggling your mouse, to speed the process.
The resulting ipsec.secrets looks like:
: RSA {
# RSA 2192 bits xy.example.com Sun Jun 8 13:42:19 2003
# for signatures only, UNSAFE FOR ENCRYPTION
#pubkey=0sAQOFppfeE3cC7wqJi...
Modulus: 0x85a697de137702ef0...
# everything after this point is secret
PrivateExponent: 0x16466ea5033e807...
Prime1: 0xdfb5003c8947b7cc88759065...
Prime2: 0x98f199b9149fde11ec956c814...
Exponent1: 0x9523557db0da7a885af90aee...
Exponent2: 0x65f6667b63153eb69db8f300dbb...
Coefficient: 0x90ad00415d3ca17bebff123413fc518...
}
# do not change the indenting of that "}"
In the actual file, the strings are much longer.
You can now start FreeS/WAN and test whether it's been successfully installed..
These instructions are for a recent Red Hat with a stock Red Hat kernel. We know that Mandrake and SUSE also produce FreeS/WAN RPMs. If you're running either, install using your distribution's tools.
Decide which functionality you need:
For 2.6 kernels, get the latest FreeS/WAN userland RPM, for example:
freeswan-userland-2.03.9-0.i386.rpm
Note: FreeS/WAN's support for 2.6 kernel IPsec is preliminary. Please see 2.6.known-issues, and the latest mailing list reports.
Change to your new FreeS/WAN directory, and make and install the
For 2.4 kernels, get both kernel and userland RPMs. Check your kernel version with
uname -r
Get a kernel module which matches that version. For example:
freeswan-module-2.03_2.4.20_20.9-0.i386.rpm
Note: These modules will only work on the Red Hat kernel they were built for, since they are very sensitive to small changes in the kernel.
Get FreeS/WAN utilities to match. For example:
freeswan-userland-2.03_2.4.20_20.9-0.i386.rpm
While you're at our ftp site, grab the RPM signing key
freeswan-rpmsign.asc
If you're running RedHat 8.x or later, import this key into the RPM database:
rpm --import freeswan-rpmsign.asc
For RedHat 7.x systems, you'll need to add it to your PGP keyring:
pgp -ka freeswan-rpmsign.asc
Check the digital signatures on both RPMs using:
rpm --checksig freeswan*.rpm
You should see that these signatures are good:
freeswan-module-2.03_2.4.20_20.9-0.i386.rpm: pgp md5 OK
freeswan-userland-2.03_2.4.20_20.9-0.i386.rpm: pgp md5 OK
Become root:
su
For a first time install, use:
rpm -ivh freeswan*.rpm
To upgrade existing RPMs (and keep all .conf files in place), use:
rpm -Uvh freeswan*.rpm
If you're upgrading from FreeS/WAN 1.x to 2.x RPMs, and encounter problems, see this note.
Now, start FreeS/WAN and test your install.
Your choices are:
Download the source tarball you've chosen, along with any patches.
While you're at our ftp site, get our source signing key
freeswan-sigkey.asc
Add it to your PGP keyring:
pgp -ka freeswan-sigkey.asc
Check the signature using:
pgp freeswan-2.03.tar.gz.sig freeswan-2.03.tar.gz
You should see something like:
Good signature from user "Linux FreeS/WAN Software Team (build@freeswan.org)".
Signature made 2002/06/26 21:04 GMT using 2047-bit key, key ID 46EAFCE1
As root, unpack your FreeS/WAN source into /usr/src.
su
mv freeswan-2.03.tar.gz /usr/src
cd /usr/src
tar -xzf freeswan-2.03.tar.gz
Now's the time to add any patches. The contributor may have special instructions, or you may simply use the patch command.
Choose one of the methods below.
Note: FreeS/WAN's support for 2.6 kernel IPsec is preliminary. Please see 2.6.known-issues, and the latest mailing list reports.
Change to your new FreeS/WAN directory, and make and install the FreeS/WAN userland tools.
cd /usr/src/freeswan-2.03
make programs
make install
Now, start FreeS/WAN and test your install.
To make a modular version of KLIPS, along with other FreeS/WAN programs you'll need, use the command sequence below. This will change to your new FreeS/WAN directory, make the FreeS/WAN module (and other stuff), and install it all.
cd /usr/src/freeswan-2.03
make oldmod
make minstall
Start FreeS/WAN and test your install.
To link KLIPS statically into your kernel (using your old kernel settings), and install other FreeS/WAN components, do:
cd /usr/src/freeswan-2.03
make oldmod
make minstall
Reboot your system and test your install.
For other ways to compile KLIPS, see our Makefile.
Bring FreeS/WAN up with:
service ipsec start
This is not necessary if you've rebooted.
To check that you have a successful install, run:
ipsec verify
You should see at least:
Checking your system to see if IPsec got installed and started correctly
Version check and ipsec on-path [OK]
Checking for KLIPS support in kernel [OK]
Checking for RSA private key (/etc/ipsec.secrets) [OK]
Checking that pluto is running [OK]
If any of these first four checks fails, see our troubleshooting guide.
There are at least a couple of things on your system that might interfere with FreeS/WAN, and now's a good time to check these:
You'll need to configure FreeS/WAN for your local site. Have a look at our opportunism quickstart guide to see if that easy method is right for your needs. Or, see how to configure a network-to-network or Road Warrior style VPN.
This page will teach you how to configure a simple network-to-network link or a Road Warrior connection between two Linux FreeS/WAN boxes.
See also these related documents:
The network-to-network setup allows you to connect two office networks into one Virtual Private Network, while the Road Warrior connection secures a laptop's telecommute to work. Our examples also show the basic procedure on the Linux FreeS/WAN side where another IPsec peer is in play.
Shortcut to net-to-net.
Shortcut to Road Warrior.
To configure the network-to-network connection you must have:
For the Road Warrior you need:
If both IPs are dynamic, your situation is a bit trickier. Your best bet is a variation on the Road Warrior, as described in this mailing list message.
For each gateway, compile the following information:
On your local Linux FreeS/WAN gateway, print your IPsec public key:
ipsec showhostkey --left
The output should look like this (with the key shortened for easy reading):
# RSA 2048 bits xy.example.com Fri Apr 26 15:01:41 2002
leftrsasigkey=0sAQOnwiBPt...
Don't have a key? Use ipsec newhostkey to create one.
Get a console on the remote side:
ssh2 ab.example.com
In that window, type:
ipsec showhostkey --right
You'll see something like:
# RSA 2192 bits ab.example.com Thu May 16 15:26:20 2002
rightrsasigkey=0sAQOqH55O...
Back on the local gate, copy our template to /etc/ipsec.conf . (on Mandrake, /etc/freeswan/ipsec.conf). Substitute the information you've gathered for our example data.
conn net-to-net
left=192.0.2.2 # Local vitals
leftsubnet=192.0.2.128/29 #
leftid=@xy.example.com #
leftrsasigkey=0s1LgR7/oUM... #
leftnexthop=%defaultroute # correct in many situations
right=192.0.2.9 # Remote vitals
rightsubnet=10.0.0.0/24 #
rightid=@ab.example.com #
rightrsasigkey=0sAQOqH55O... #
rightnexthop=%defaultroute # correct in many situations
auto=add # authorizes but doesn't start this
# connection at startup
"Left" and "right" should represent the machines that have FreeS/WAN installed on them, and "leftsubnet" and "rightsubnet" machines that are being protected. /32 is assumed for left/right and left/rightsubnet parameters.
Copy conn net-to-net to the remote-side /etc/ipsec.conf. If you've made no other modifications to either ipsec.conf, simply:
scp2 ipsec.conf root@ab.example.com:/etc/ipsec.conf
Locally, type:
ipsec auto --up net-to-net
You should see:
104 "net-net" #223: STATE_MAIN_I1: initiate
106 "net-net" #223: STATE_MAIN_I2: sent MI2, expecting MR2
108 "net-net" #223: STATE_MAIN_I3: sent MI3, expecting MR3
004 "net-net" #223: STATE_MAIN_I4: ISAKMP SA established
112 "net-net" #224: STATE_QUICK_I1: initiate
004 "net-net" #224: STATE_QUICK_I2: sent QI2, IPsec SA established
The important thing is IPsec SA established. If you're unsuccessful, see our troubleshooting tips.
If you are using IP masquerade or Network Address Translation (NAT) on either gateway, you must now exempt the packets you wish to tunnel from this treatment. For example, if you have a rule like:
iptables -t nat -A POSTROUTING -o eth0 -s 10.0.0.0/24 -j MASQUERADE
change it to something like:
iptables -t nat -A POSTROUTING -o eth0 -s 10.0.0.0/24 -d \! 192.0.2.128/29 -j MASQUERADE
This may be necessary on both gateways.
Sit at one of your local subnet nodes (not the gateway), and ping a subnet node on the other (again, not the gateway).
ping fileserver.toledo.example.com
While still pinging, go to the local gateway and snoop your outgoing interface, for example:
tcpdump -i ppp0
You want to see ESP (Encapsulating Security Payload) packets moving back and forth between the two gateways at the same frequency as your pings:
19:16:32.046220 192.0.2.2 > 192.0.2.9: ESP(spi=0x3be6c4dc,seq=0x3)
19:16:32.085630 192.0.2.9 > 192.0.2.2: ESP(spi=0x5fdd1cf8,seq=0x6)
If you see this, congratulations are in order! You have a tunnel which will protect any IP data from one subnet to the other, as it passes between the two gates. If not, go and troubleshoot.
Note: your new tunnel protects only net-net traffic, not gateway-gateway, or gateway-subnet. If you need this (for example, if machines on one net need to securely contact a fileserver on the IPsec gateway), you'll need to create extra connections .
Now that your connection works, name it something sensible, like:
conn winstonnet-toledonet
To have the tunnel come up on-boot, replace
auto=add
with:
auto=start
Copy these changes to the other side, for example:
scp2 ipsec.conf root@ab.example.com:/etc/ipsec.conf
Enjoy!
You'll need to know:
On your laptop, print your IPsec public key:
ipsec showhostkey --left
The output should look like this (with the key shortened for easy reading):
# RSA 2192 bits road.example.com Sun Jun 9 02:45:02 2002
leftrsasigkey=0sAQPIPN9uI...
Don't have a key? See these instructions.
Get a console on the gateway:
ssh2 xy.example.com
View the gateway's public key with:
ipsec showhostkey --right
This will yield something like
# RSA 2048 bits xy.example.com Fri Apr 26 15:01:41 2002
rightrsasigkey=0sAQOnwiBPt...
On your laptop, copy this template to /etc/ipsec.conf. (on Mandrake, /etc/freeswan/ipsec.conf). Substitute the information you've gathered for our example data.
conn road
left=%defaultroute # Picks up our dynamic IP
leftnexthop=%defaultroute #
leftid=@road.example.com # Local information
leftrsasigkey=0sAQPIPN9uI... #
right=192.0.2.10 # Remote information
rightsubnet=10.0.0.0/24 #
rightid=@xy.example.com #
rightrsasigkey=0sAQOnwiBPt... #
auto=add # authorizes but doesn't start this
# connection at startup
The template for the gateway is different. Notice how it reverses left and right, in keeping with our convention that Left is Local, Right Remote. Be sure to switch your rsasigkeys in keeping with this.
ssh2 xy.example.com
vi /etc/ipsec.conf
and add:
conn road
left=192.0.2.2 # Gateway's information
leftid=@xy.example.com #
leftsubnet=192.0.2.128/29 #
leftrsasigkey=0sAQOnwiBPt... #
rightnexthop=%defaultroute # correct in many situations
right=%any # Wildcard: we don't know the laptop's IP
rightid=@road.example.com #
rightrsasigkey=0sAQPIPN9uI... #
auto=add # authorizes but doesn't start this
# connection at startup
You must start the connection from the Road Warrior side. On your laptop, type:
ipsec auto --start net-to-net
You should see:
104 "net-net" #223: STATE_MAIN_I1: initiate 106 "road" #301: STATE_MAIN_I2: sent MI2, expecting MR2 108 "road" #301: STATE_MAIN_I3: sent MI3, expecting MR3 004 "road" #301: STATE_MAIN_I4: ISAKMP SA established 112 "road" #302: STATE_QUICK_I1: initiate 004 "road" #302: STATE_QUICK_I2: sent QI2, IPsec SA established
Look for IPsec SA established. If you're unsuccessful, see our troubleshooting tips.
If you are using IP masquerade or Network Address Translation (NAT) on either gateway, you must now exempt the packets you wish to tunnel from this treatment. For example, if you have a rule like:
iptables -t nat -A POSTROUTING -o eth0 -s 10.0.0.0/24 -j MASQUERADE
change it to something like:
iptables -t nat -A POSTROUTING -o eth0 -s 10.0.0.0/24 -d \! 192.0.2.128/29 -j MASQUERADE
From your laptop, ping a subnet node behind the remote gateway. Do not choose the gateway itself for this test.
ping ns.winston.example.com
Snoop the packets exiting the laptop, with a command like:
tcpdump -i wlan0
You have success if you see (Encapsulating Security Payload) packets travelling in both directions:
19:16:32.046220 192.0.2.2 > 192.0.2.9: ESP(spi=0x3be6c4dc,seq=0x3)
19:16:32.085630 192.0.2.9 > 192.0.2.2: ESP(spi=0x5fdd1cf8,seq=0x6)
If you do, great! Traffic between your Road Warrior and the net behind your gateway is protected. If not, see our troubleshooting hints.
Your new tunnel protects only traffic addressed to the net, not to the IPsec gateway itself. If you need the latter, you'll want to make an extra tunnel..
On both ends, name your connection wisely, like:
conn mike-to-office
On the laptop only, replace
auto=add
with:
auto=start
so that you'll be connected on-boot.
Happy telecommuting!
If you're using RSA keys, as we did in this example, you can add as many Road Warriors as you like. The left/rightid parameter lets Linux FreeS/WAN distinguish between multiple Road Warrior peers, each with its own public key.
The situation is different for shared secrets (PSK). During a PSK negotiation, ID information is not available at the time Pluto is trying to determine which secret to use, so, effectively, you can only define one Roadwarrior connection. All your PSK road warriors must therefore share one secret.
Using the principles illustrated here, you can try variations such as:
Or, look at some of our more complex configuration examples..
This section discusses a number of issues which have three things in common:
Grouping them here lets us provide the explanations some users will need without unduly complicating the main text.
The explanations here are intended to be adequate for FreeS/WAN purposes (please comment to the users mailing list if you don't find them so), but they are not trying to be complete or definitive. If you need more information, see the references provided in each section.
Opportunistic encryption requires that the gateway systems be able to fetch public keys, and other IPsec-related information, from each other's DNS (Domain Name Service) records.
DNS is a distributed database that maps names to IP addresses and vice versa.
Much good reference material is available for DNS, including:
We give only a brief overview here, intended to help you use DNS for FreeS/WAN purposes.
Although the implementation is distributed, it is often useful to speak of DNS as if it were just two enormous tables:
Both maps can optionally contain additional data. For opportunistic encryption, we insert the data need for IPsec authentication.
A system named gateway.example.com with IP address 10.20.30.40 should have at least two DNS records, one in each map:
For both maps there is a hierarchy of DNS servers and a system of delegating authority so that, for example:
DNS zones are the units of delegation. There is a hierarchy of zones.
Returning to the example records:
gateway.example.com. IN A 10.20.30.40
40.30.20.10.in-addr.arpa. IN PTR gateway.example.com.
some syntactic details are:
The capitalised strings after IN indicate the type of record. Possible types include:
To set up for opportunistic encryption, you add some TXT records to your DNS data. Details are in our quickstart document.
DNS information is extensively cached. With no caching, a lookup by your system of "www.freeswan.org" might involve:
However, this can be a bit inefficient. For example, if you are in the Phillipines, the closest a root server is in Japan. That might send you to a .org server in the US, and then to freeswan.org in Holland. If everyone did all those lookups every time they clicked on a web link, the net would grind to a halt.
Nameservers therefore cache information they look up. When you click on another link at www.freeswan.org, your local nameserver has the IP address for that server in its cache, and no further lookups are required.
Intermediate results are also cached. If you next go to lists.freeswan.org, your nameserver can just ask the freeswan.org nameserver for that address; it does not need to query the root or .org nameservers because it has a cached address for the freeswan.org zone server.
Of course, like any cacheing mechanism, this can create problems of consistency. What if the administrator for freeswan.org changes the IP address, or the authentication key, for www.freeswan.org? If you use old information from the cache, you may get it wrong. On the other hand, you cannot afford to look up fresh information every time. Nor can you expect the freeswan.org server to notify you; that isn't in the protocols.
The solution that is in the protocols is fairly simple. Cacheable records are marked with Time To Live (TTL) information. When the time expires, the caching server discards the record. The next time someone asks for it, the server fetches a fresh copy. Of course, a server may also discard records before their TTL expires if it is running out of cache space.
This implies that there will be some delay before the new version of a changed record propagates around the net. Until the TTLs on all copies of the old record expire, some users will see it because that is what is in their cache. Other users may see the new record immediately because they don't have an old one cached.
It seems, from mailing list reports, to be moderately common for problems to crop up in which small packets pass through the IPsec tunnels just fine but larger packets fail.
These problems are caused by various devices along the way mis-handling either packet fragments or path MTU discovery.
IPsec makes packets larger by adding an ESP or AH header. This can tickle assorted bugs in fragment handling in routers and firewalls, or in path MTU discovery mechanisms, and cause a variety of symptoms which are both annoying and, often, quite hard to diagnose.
An explanation from project technical lead Henry Spencer:
The problem is IP fragmentation; more precisely, the problem is that the second, third, etc. fragments of an IP packet are often difficult for filtering mechanisms to classify. Routers cannot rely on reassembling the packet, or remembering what was in earlier fragments, because the fragments may be out of order or may even follow different routes. So any general, worst-case filtering decision pretty much has to be made on each fragment independently. (If the router knows that it is the only route to the destination, so all fragments *must* pass through it, reassembly would be possible... but most routers don't want to bother with the complications of that.) All fragments carry roughly the original IP header, but any higher-level header is (for IP purposes) just the first part of the packet data... so only the first fragment carries that. So, for example, on examining the second fragment of a TCP packet, you could tell that it's TCP, but not what port number it is destined for -- that information is in the TCP header, which appears in the first fragment only. The result of this classification difficulty is that stupid routers and over-paranoid firewalls may just throw fragments away. To get through them, you must reduce your MTU enough that fragmentation will not occur. (In some cases, they might be willing to attempt reassembly, but have very limited resources to devote to it, meaning that packets must be small and fragments few in number, leading to the same conclusion: smaller MTU.)
In addition to the problem Henry describes, you may also have trouble with path MTU discovery.
By default, FreeS/WAN uses a large MTU for the ipsec device. This avoids some problems, but may complicate others. Here's an explanation from Claudia:
Here are a couple of pieces of background information. Apologies if you
have seen these already. An excerpt from one of my old posts:
An MTU of 16260 on ipsec0 is usual. The IPSec device defaults to this
high MTU so that it does not fragment incoming packets before encryption
and encapsulation. If after IPSec processing packets are larger than 1500,
[ie. the mtu of eth0] then eth0 will fragment them.
Adding IPSec headers adds a certain number of bytes to each packet.
The MTU of the IPSec interface refers to the maximum size of the packet
before the IPSec headers are added. In some cases, people find it helpful
to set ipsec0's MTU to 1500-(IPSec header size), which IIRC is about 1430.
That way, the resulting encapsulated packets don't exceed 1500. On most
networks, packets less than 1500 will not need to be fragmented.
and... (from Henry Spencer)
The way it *ought* to work is that the MTU advertised by the ipsecN
interface should be that of the underlying hardware interface, less a
pinch for the extra headers needed.
Unfortunately, in certain situations this breaks many applications.
There is a widespread implicit assumption that the smallest MTUs are
at the ends of paths, not in the middle, and another that MTUs are
never less than 1500. A lot of code is unprepared to handle paths
where there is an "interior minimum" in the MTU, especially when it's
less than 1500. So we advertise a big MTU and just let the resulting
big packets fragment.
This usually works, but we do get bitten in cases where some intermediate
point can't handle all that fragmentation. We can't win on this one.
The MTU can be changed with an overridemtu= statement in the config setup section of ipsec.conf.5.
For a discussion of MTU issues and some possible solutions using Linux advanced routing facilities, see the Linux 2.4 Advanced Routing HOWTO. For a discussion of MTU and NAT (Network Address Translation), see James Carter's MTU notes.
Network Address T ranslation is a service provided by some gateway machines. Calling it NAPT (adding the word Port) would be more precise, but we will follow the widespread usage.
A gateway doing NAT rewrites the headers of packets it is forwarding, changing one or more of:
On Linux 2.4, NAT services are provided by the netfilter(8) firewall code. There are several Netfilter HowTos including one on NAT.
For older versions of Linux, this was referred to as "IP masquerade" and different tools were used. See this resource page.
Putting an IPsec gateway behind a NAT gateway is not recommended. See our firewalls document.
The most common application of NAT uses private non-routable addresses.
Often a home or small office network will have:
Of course this poses a problem since several machines cannot use one address. The best solution might be to obtain more addresses, but often this is impractical or uneconomical.
A common solution is to have:
The client machines are set up with reserved non-routable IP addresses defined in RFC 1918. The masquerading gateway, the machine with the actual link to the Internet, rewrites packet headers so that all packets going onto the Internet appear to come from one IP address, that of its Internet interface. It then gets all the replies, does some table lookups and more header rewriting, and delivers the replies to the appropriate client machines.
As far as anyone else on the Internet is concerned, the systems behind the gateway are completely hidden. Only one machine with one IP address is visible.
For IPsec on such a gateway, you can entirely ignore the NAT in:
Those can be set up exactly as they would be if your gateway had no other systems behind it.
You do, however, have to take account of the NAT in firewall rules which affect packet forwarding.
NAT to routable addresses is also possible, but is less common and may make for rather tricky routing problems. We will not discuss it here. See the Netfilter HowTos.
So far it has only one entry.
From: Poltorak Serguei <poltorak@dataforce.net>
Subject: [Users] Using FreeS/WAN
Date: Tue, 16 Oct 2001
Hello.
I'm using FreeS/WAN IPsec for half a year. I learned a lot of things about
it and I think it would be interesting for someone to see the result of my
experiments and usage of FreeS/WAN. If you find a mistake in this
file, please e-mail me. And excuse me for my english... I'm learning.. :)
I'll talk about vary simple configuration:
addresses prefix = 192.168
lan1 sgw1 .0.0/24 (Internet) sgw2 lan2
.1.0/24---[ .1.1 ; .0.1 ]===================[ .0.10 ; . 2.10 ]---.2.0/24
We need to let lan1 see lan2 across Internet like it is behind sgw1. The
same for lan2. And we need to do IPX bridge for Novel Clients and NDS
synchronization.
my config:
------------------- ipsec.conf -------------------
conn lan1-lan2
type=tunnel
compress=yes
#-------------------
left=192.168.0.1
leftsubnet=192.168.1.0/24
#-------------------
right=192.168.0.10
rightsubnet=192.168.2.0/24
#-------------------
auth=esp
authby=secret
--------------- end of ipsec.conf ----------------
ping .2.x from .1.y (y != 1)
It works?? Fine. Let's continue...
Why y != 1 ?? Because kernel of sgw1 have 2 IP addresses and it will choose
the first IP (which is used to go to Internet) .0.1 and the packet won't go
through IPsec tunnel :( But if do ping on .1.1 kernel will respond from
that address (.1.1) and the packet will be tunneled. The same problem occurred then
.2.x sends a packet to .1.2 which is down at the moment. What happens? .1.1
sends ARP requesting .1.2... after 3 tries it send to .2.x an destunreach,
but from his "natural" IP or .0.1 . So the error message won't be delivered!
It's a big problem...
Resolution... One can manipulate with ipsec0 or ipsec0:0 to solve the
problem (if ipsec0 has .1.1 kernel will send packets correctly), but there
are powerful and elegant iproute2 :) We simply need to change source address
of packet that goes to other secure lan. This is done with
ip route replace 192.168.2.0/24 via 192.168.0.10 dev ipsec0 src 192.168.1.1
Cool!! Now it works!!
The second step. We want install firewall on sgw1 and sgw2. Encryption of
traffic without security isn't a good idea. I don't use {left|right}firewall,
because I'm running firewall from init scripts.
We want IPsec data between lan1-lan2, some ICMP errors (destination
unreachable, TTL exceeded, parameter problem and source quench), replying on
pings from both lans and Internet, ipxtunnel data for IPX and of course SSH
between sgw1 and sgw2 and from/to one specified host.
I'm using ipchains. With iptables there are some changes.
---------------- rc.firewall ---------------------
#!/bin/sh
#
# Firewall for IPsec lan1-lan2
#
IPC=/sbin/ipchains
ANY=0.0.0.0/0
# left
SGW1_EXT=192.168.0.1
SGW1_INT=192.168.1.1
LAN1=192.168.1.0/24
# right
SGW2_EXT=192.168.0.10
SGW2_INT=192.168.2.10
LAN2=192.168.2.0/24
# SSH from and to this host
SSH_PEER_HOST=_SOME_HOST_
# this is for left. exchange these values for right.
MY_EXT=$SGW1_EXT
MY_INT=$SGW1_INT
PEER_EXT=$SGW2_EXT
PEER_INT=$SGW2_INT
INT_IF=eth1
EXT_IF=eth0
IPSEC_IF=ipsec0
MY_LAN=$LAN1
PEER_LAN=$LAN2
$IPC -F
$IPC -P input DENY
$IPC -P forward DENY
$IPC -P output DENY
# Loopback traffic
$IPC -A input -i lo -j ACCEPT
$IPC -A output -i lo -j ACCEPT
# for IPsec SGW1-SGW2
## IKE
$IPC -A input -p udp -s $PEER_EXT 500 -d $MY_EXT 500 -i $EXT_IF -j ACCEPT
$IPC -A output -p udp -s $MY_EXT 500 -d $PEER_EXT 500 -i $EXT_IF -j ACCEPT
## ESP
$IPC -A input -p 50 -s $PEER_EXT -d $MY_EXT -i $EXT_IF -j ACCEPT
### we don't need this line ### $IPC -A output -p 50 -s $MY_EXT -d $PEER_EXT -i $EXT_IF -j ACCEPT
## forward LAN1-LAN2
$IPC -A forward -s $MY_LAN -d $PEER_LAN -i $IPSEC_IF -j ACCEPT
$IPC -A forward -s $PEER_LAN -d $MY_LAN -i $INT_IF -j ACCEPT
$IPC -A output -s $PEER_LAN -d $MY_LAN -i $INT_IF -j ACCEPT
$IPC -A input -s $PEER_LAN -d $MY_LAN -i $IPSEC_IF -j ACCEPT
$IPC -A input -s $MY_LAN -d $PEER_LAN -i $INT_IF -j ACCEPT
$IPC -A output -s $MY_LAN -d $PEER_LAN -i $IPSEC_IF -j ACCEPT
# ICMP
#
## Dest unreachable
### from/to Internet
$IPC -A input -p icmp --icmp-type destination-unreachable -s $ANY -d $MY_EXT -i $EXT_IF -j ACCEPT
$IPC -A output -p icmp --icmp-type destination-unreachable -s $MY_EXT -d $ANY -i $EXT_IF -j ACCEPT
### from/to Lan
$IPC -A input -p icmp --icmp-type destination-unreachable -s $ANY -d $MY_INT -i $INT_IF -j ACCEPT
$IPC -A output -p icmp --icmp-type destination-unreachable -s $MY_INT -d $ANY -i $INT_IF -j ACCEPT
### from/to Peer Lan
$IPC -A input -p icmp --icmp-type destination-unreachable -s $ANY -d $MY_INT -i $IPSEC_IF -j ACCEPT
$IPC -A output -p icmp --icmp-type destination-unreachable -s $MY_INT -d $ANY -i $IPSEC_IF -j ACCEPT
#
## Source quench
### from/to Internet
$IPC -A input -p icmp --icmp-type source-quench -s $ANY -d $MY_EXT -i $EXT_IF -j ACCEPT
$IPC -A output -p icmp --icmp-type source-quench -s $MY_EXT -d $ANY -i $EXT_IF -j ACCEPT
### from/to Lan
$IPC -A input -p icmp --icmp-type source-quench -s $ANY -d $MY_INT -i $INT_IF -j ACCEPT
$IPC -A output -p icmp --icmp-type source-quench -s $MY_INT -d $ANY -i $INT_IF -j ACCEPT
### from/to Peer Lan
$IPC -A input -p icmp --icmp-type source-quench -s $ANY -d $MY_INT -i $IPSEC_IF -j ACCEPT
$IPC -A output -p icmp --icmp-type source-quench -s $MY_INT -d $ANY -i $IPSEC_IF -j ACCEPT
#
## Parameter problem
### from/to Internet
$IPC -A input -p icmp --icmp-type parameter-problem -s $ANY -d $MY_EXT -i $EXT_IF -j ACCEPT
$IPC -A output -p icmp --icmp-type parameter-problem -s $MY_EXT -d $ANY -i $EXT_IF -j ACCEPT
### from/to Lan
$IPC -A input -p icmp --icmp-type parameter-problem -s $ANY -d $MY_INT -i $INT_IF -j ACCEPT
$IPC -A output -p icmp --icmp-type parameter-problem -s $MY_INT -d $ANY -i $INT_IF -j ACCEPT
### from/to Peer Lan
$IPC -A input -p icmp --icmp-type parameter-problem -s $ANY -d $MY_INT -i $IPSEC_IF -j ACCEPT
$IPC -A output -p icmp --icmp-type parameter-problem -s $MY_INT -d $ANY -i $IPSEC_IF -j ACCEPT
#
## Time To Live exceeded
### from/to Internet
$IPC -A input -p icmp --icmp-type time-exceeded -s $ANY -d $MY_EXT -i $EXT_IF -j ACCEPT
$IPC -A output -p icmp --icmp-type time-exceeded -s $MY_EXT -d $ANY -i $EXT_IF -j ACCEPT
### to Lan
$IPC -A input -p icmp --icmp-type time-exceeded -s $ANY -d $MY_INT -i $INT_IF -j ACCEPT
$IPC -A output -p icmp --icmp-type time-exceeded -s $MY_INT -d $ANY -i $INT_IF -j ACCEPT
### to Peer Lan
$IPC -A input -p icmp --icmp-type time-exceeded -s $ANY -d $MY_INT -i $IPSEC_IF -j ACCEPT
$IPC -A output -p icmp --icmp-type time-exceeded -s $MY_INT -d $ANY -i $IPSEC_IF -j ACCEPT
# ICMP PINGs
## from Internet
$IPC -A input -p icmp -s $ANY -d $MY_EXT --icmp-type echo-request -i $EXT_IF -j ACCEPT
$IPC -A output -p icmp -s $MY_EXT -d $ANY --icmp-type echo-reply -i $EXT_IF -j ACCEPT
## from LAN
$IPC -A input -p icmp -s $ANY -d $MY_INT --icmp-type echo-request -i $INT_IF -j ACCEPT
$IPC -A output -p icmp -s $MY_INT -d $ANY --icmp-type echo-reply -i $INT_IF -j ACCEPT
## from Peer LAN
$IPC -A input -p icmp -s $ANY -d $MY_INT --icmp-type echo-request -i $IPSEC_IF -j ACCEPT
$IPC -A output -p icmp -s $MY_INT -d $ANY --icmp-type echo-reply -i $IPSEC_IF -j ACCEPT
# SSH
## from SSH_PEER_HOST
$IPC -A input -p tcp -s $SSH_PEER_HOST -d $MY_EXT 22 -i $EXT_IF -j ACCEPT
$IPC -A output -p tcp \! -y -s $MY_EXT 22 -d $SSH_PEER_HOST -i $EXT_IF -j ACCEPT
## to SSH_PEER_HOST
$IPC -A input -p tcp \! -y -s $SSH_PEER_HOST 22 -d $MY_EXT -i $EXT_IF -j ACCEPT
$IPC -A output -p tcp -s $MY_EXT -d $SSH_PEER_HOST 22 -i $EXT_IF -j ACCEPT
## from PEER
$IPC -A input -p tcp -s $PEER_EXT -d $MY_EXT 22 -i $EXT_IF -j ACCEPT
$IPC -A output -p tcp \! -y -s $MY_EXT 22 -d $PEER_EXT -i $EXT_IF -j ACCEPT
## to PEER
$IPC -A input -p tcp \! -y -s $PEER_EXT 22 -d $MY_EXT -i $EXT_IF -j ACCEPT
$IPC -A output -p tcp -s $MY_EXT -d $PEER_EXT 22 -i $EXT_IF -j ACCEPT
# ipxtunnel
$IPC -A input -p udp -s $PEER_INT 2005 -d $MY_INT 2005 -i $IPSEC_IF -j ACCEPT
$IPC -A output -p udp -s $MY_INT 2005 -d $PEER_INT 2005 -i $IPSEC_IF -j ACCEPT
---------------- end of rc.firewall ----------------------
To understand this we need to look on this scheme:
++-----------------------<----------------------------+
|| ipsec0 |
\/ |
eth0 +--------+ /---------/ yes /---------/ yes +-----------------------+
------>| INPUT |-->/ ?local? /----->/ ?IPsec? /----->| decrypt &decapsulate |
eth1 +--------+ /---------/ /---------/ +-----------------------+
|| no || no
\/ \/
+----------+ +---------+ +-------+
| routing | | local | | local |
| decision | | deliver | | send |
+----------+ +---------+ +-------+
|| ||
\/ \/
+---------+ +----------+
| forward | | routing |
+---------+ | decision |
|| +----------+
|| ||
++----------------<-----------------++
||
\/
+--------+ eth0
| OUTPUT | eth1
+--------+ ipsec0
||
\/
/---------/ yes +-----------------------+
/ ?IPsec? /----->| encrypt &encapsulate |
/---------/ +-----------------------+
|| no ||
|| ||
|| \/ eth0, eth1
++-----------------------++-------------->
This explain how a packet traverse TCP/IP stack in IPsec capable kernel.
FIX ME, please, if there are any errors
Test the new firewall now.
Now about IPX. I tried 3 programs for tunneling IPX: tipxd, SIB and ipxtunnel
tipxd didn't send packets.. :(
SIB and ipxtunnel worked fine :)
With ipxtunnel there was a little problem. In sources there are an error.
--------------------- in main.c ------------------------
< bytes += p.len;
---
> bytes += len;
--------------------------------------------------------
After this FIX everything goes right...
------------------- /etc/ipxtunnel.conf ----------------
port 2005
remote 192.168.101.97 2005
interface eth1
--------------- end of /etc/ipxtunnel.conf -------------
I use IPX tunnel between .1.1 and .2.10 so we don't need to encrypt nor
authenticate encapsulated IPX packets, it is done with IPsec.
If you don't wont to use iproute2 to change source IP you need to use SIB
(it is able to bind local address) or establish tunnel between .0.1 and
.0.10 (external IPs, you need to do encryption in the program, but it isn't
strong).
For now I'm using ipxtunnel.
I think that's all for the moment. If there are any error, please e-mail me:
poltorak@df.ru . It would be cool if someone puts the scheme of TCP/IP in
kernel and firewall example on FreeS/WAN's manual pages.
PoltoS
"make check" is a target in the top level makefile. It takes care of running a number of unit and system tests to confirm that FreeSWAN has been compiled correctly, and that no new bugs have been introduced.
As FreeSWAN contains both kernel and userspace components, doing testing of FreeSWAN requires that the kernel be simulated. This is typically difficult to do as a kernel requires that it be run on bare hardware. A technology has emerged that makes this simpler. This is User Mode Linux.
User-Mode Linux is a way to build a Linux kernel such that it can run as a process under another Linux (or in the future other) kernel. Presently, this can only be done for 2.4 guest kernels. The host kernel can be 2.2 or 2.4.
"make check" expects to be able to build User-Mode Linux kernels with FreeSWAN included. To do this it needs to have some files downloaded and extracted prior to running "make check". This is described in the UML testing document.
After having run the example in the UML testing document and successfully brought up the four machine combination, you are ready to use "make check"
"make check" works by walking the FreeSWAN source tree invoking the
"check" target at each node. At present there are tests defined only
for the klips directory. These tests will use the UML
infrastructure to test out pieces of the klips code.
The results of the tests can be recorded. If the environment
variable $REGRESSRESULTS is non-null, then the results of
each test will be recorded. This can be used as part of a nightly
regression testing system, see Nightly testing
for more details.
"make check" otherwise prints a minimal amount of output for each test, and indicates pass/fail status of each test as they are run. Failed tests do not cause failure of the target in the form of exit codes.
Each test consists of a set of directories under testing/
. There are directories for klips, pluto,
packaging and libraries. Each directory has a list
of tests to run is stored in a file called TESTLIST in
that directory. e.g. testing/klips/TESTLIST.
This isn't actually a shell script. It just looks like one. Some tools other than /bin/sh process it. Lines that start with # are comments.
# test-kind directory-containing-test expectation [PR#]
The first word provides the test type, detailed below.
The second word is the name of the test to run. This the directory in which the test case is to be found..
The third word may be one of:
The fourth word may be a number, which is a PR# if the test is failing.
Each test directory has a file in it called testparams.sh
. This file sets a number of environment variables to define the
parameters of the test.
klips/test/fixups) to apply
to sanitize the console output of the machine under test. These are
typically perl, awk or sed scripts that remove things in the kernel
output that change each time the test is run and/or compiled.a file of commands that is fed into the virtual machine's console in single user mode prior to starting the tests. This file will usually set up any eroute's and SADB entries that are required for the test.
Lines beginning with # are skipped. Blank lines are skipped.
Otherwise, a shell prompted is waited for each time (consisting of
\n#) and then the command is sent. Note that the prompt is waited
for before the command and not after, so completion of the last command
in the script is not required. This is often used to invoke a program
to monitor the system, e.g. ipsec pf_key.
a file of commands that is fed into the virtual machine's console in single user mode, before the packets are sent. On single machine tests, this script doesn't provide any more power than INIT_SCRIPT, but is implemented for consistency's sake.
a file of commands that is fed into the virtual machine's console in single user mode after the final packet is sent. Similar to INIT_SCRIPT, above. If not specified, then the single command "halt" is sent. If specified, then the script should end with a halt command to nicely shutdown the UML.
uml_netjig will be printed to stderr during the test. In
addition, the jig will be invoked with --debug, which causes it to log
its process ID, and wait 60 seconds before continuing. This can be used
if you are trying to debug the uml_netjig program itself. The klipstest function starts a program (
testing/utils/uml_netjig/uml_netjig) to setup a bunch of I/O
sockets (that simulate network interfaces). It then exports the
references to these sockets to the environment and invokes (using
system()) a given script. It waits for the script to finish.
The script invoked (testing/utils/host-test.tcl) is a
TCL expect script that arranges
to start the UML and configure it appropriately for the test. The
configuration is done with the script given above for INIT_SCRIPT
. The TCL script then forks, leaves the UML in the background and exits.
uml_netjig continues. It then starts listening to the simulated network
answering ARPs and inserting packets as appropriate.
The klipstest function invokes uml_netjig with
arguments to capture output from network interface(s) and insert
packets as appropriate:
uml_netjig. The klipstest function then uses
tcpdump on the file to produce text output, which is compared to the
file given.uml_netjig. It should contain
"--exitonempty" of uml_netjig should exit when all of the input (
PUBINPUT,PRIVINPUT) packets have been injected.uml_netjig. It should contain "--arpreply"
if uml_netjig should reply to ARP requests. One will
typically set this to avoid having to fudge the ARP cache manually. The basic concept of the mkinsttest test type is that
it performs a "make install" to a temporary $DESTDIR. The resulting
tree can then be examined to determine if it was done properly. The
files can be uninstalled to determine if the file list was correct, or
the contents of files can be examined more precisely.
find $ROOT ( -type f -or -type -l ) will be
done to get a list of a real files and symlinks. The resulting file
will be compared to the file listed by this option.reffile samplefileone record per line. A diff between the provided reference file, and the sample file (located in the temporary installation root) will be done for each record.
The rpm_build_install_test type is to verify that the
proper packing list is produced by "make rpm", and that the mechanisms
for building the kernel modules produce consistent results.
The libtest test is for testing library routines. The library file
is expected to provided an #ifdef by the name of
library
. The libtest type invokes the C compiler to compile this
file, links it against libfreeswan.a (to resolve any other
dependancies) and runs the test with the -r argument to
invoke a regression test.
The library test case is expected to do a self-test, exiting with status code 0 if everything is okay, and with non-zero otherwise. A core dump (exit code greater than 128) is noted specifically.
Unlike other tests, there are no subdirectories required, or other parameters to set.
The umlplutotest function starts a pair of user mode line processes. This is a 2-host version of umlXhost. The "EAST" and "WEST" slots are defined.
The umlXtest function starts an arbitrary number of user mode line processes.
The script invoked (testing/utils/Xhost-test.tcl) is a
TCL expect script that arranges
to start each UML and configure it appropriately for the test. It then
starts listening (using uml_netjig) to the simulated network answering
ARPs and inserting packets as appropriate.
umlXtest has a series of slots, each of which should be filled by a host. The list of slots is controlled by the variable, XHOST_LIST. This variable should be set to a space seperated list of slots. The former umlplutotest is now implemented as a variation of the umlXhost test, with XHOST_LIST="EAST WEST".
For each host slot that is defined, a series of variables should be filled in, defining what configuration scripts to use for that host.
The following are used to control the console input and output to the system. Where the string ${host} is present, the host slot should be filled in. I.e. for the two host system with XHOST_LIST="EAST WEST", then the variables: EAST_INIT_SCRIPT and WEST_INIT_SCRIPT will exist.
a file of commands that is fed into the virtual machine's console in single user mode prior to starting the tests. This file will usually set up any eroute's and SADB entries that are required for the test. Similar to INIT_SCRIPT, above.
a file of commands that is fed into the virtual machine's console in single user mode, before the packets are sent. This set of commands is run after all of the virtual machines are initialized. I.e. after EAST_INIT_SCRIPT AND WEST_INIT_SCRIPT. This script can therefore do things that require that all machines are properly configured.
a file of commands that is fed into the virtual machine's console in single user mode, after the packets are sent. This set of commands is run before any of the virtual machines have been shut down. (I.e. before EAST_FINAL_SCRIPT AND WEST_FINAL_SCRIPT.) This script can therefore catch post-activity status reports.
a file of commands that is fed into the virtual machine's console in single user mode after the final packet is sent. Similar to INIT_SCRIPT, above. If not specified, then the single command "halt" is sent. Note that when this script is run, the other virtual machines may already have been killed. If specified, then the script should end with a halt command to nicely shutdown the UML.
Some additional flags apply to all hosts:
klips/test/fixups) to apply
to sanitize the console output of the machine under test. These are
typically perl, awk or sed scripts that remove things in the kernel
output that change each time the test is run and/or compiled.In addition to input to the console, the networks may have input fed to them:
There are two additional environment variables that may be set on the command line:
The kernel_patch_test function takes some kernel source, copies it with lndir, and then applies the patch as produced by "make kernelpatch".
The following are used to control the input and output to the system:
The module_compile test attempts to build the KLIPS module against a given set of kernel source. This is also done by the RPM tests, but in a very specific manner.
There are two variations of this test - one where the kernel either doesn't need to be configured, or is already done, and tests were there is a local configuration file.
Where the kernel doesn't need to be configured, the kernel source that is found is simply used. It may be a RedHat-style kernel, where one can cause it to configure itself via rhconfig.h-style definitions. Or, it may just be a kernel tree that has been configured.
If the variable KERNEL_CONFIG_FILE is set, then a new directory is created for the kernel source. It is populated with lndir(1). The referenced file is then copied in as .config, and "make oldconfig" is used to configure the kernel. This resulting kernel is then used as the reference source.
In all cases, the kernel source is found the same was for the kernelpatch test, i.e. via KERNEL_VERSION/KERNEL_NAME and KERNEL_${KERNEL_NAME}${KERNEL_VERSION}_SRC.
Once there is kernel source, the module is compiled using the top-level "make module" target.
The test is considered successful if an executable is found in OUTPUT/module/ipsec.o at the end of the test.
User mode linux is a way to compile a linux kernel such that it can run as a process in another linux system (potentially as a *BSD or Windows process later). See http://user-mode-linux.sourceforge.net/
UML is a good platform for testing and experimenting with FreeS/WAN. It allows several network nodes to be simulated on a single machine. Creating, configuring, installing, monitoring, and controling these nodes is generally easier and easier to script with UML than real hardware.
You'll need about 500Mb of disk space for a full sunrise-east-west-sunset setup. You can possibly get this down by 130Mb if you remove the sunrise/sunset kernel build. If you just want to run, then you can even remove the east/west kernel build.
Nothing need be done as super user. In a couple of steps, we note where super user is required to install commands in system-wide directories, but ~/bin could be used instead. UML seems to use a system-wide /tmp/uml directory so different users may interfere with one another. Later UMLs use ~/.uml instead, so multiple users running UML tests should not be a problem, but note that a single user running the UML tests will only be able run one set. Further, UMLs sometimes get stuck and hang around. These "zombies" (most will actually be in the "T" state in the process table) will interfere with subsequent tests.
As of 2003/3/1, the Light-Weight Resolver is used by pluto. This requires that BIND9 be running. It also requires that BIND9 development libraries be present in the build environment. The DNSSEC code is only truly functional in BIND9 snapshots. The library code could be 9.2.2, we believe. We are using BIND9 20021115 snapshot code from ftp://ftp.isc.org/isc/bind9/snapshots.
FreeS/WAN may well require a newer BIND than is on your system. Many distributions have moved to BIND9.2.2 recently due to a security advisory. BIND is five components.
The only piece that we need for *building* is #4. That's the only part that has to be on the build host. What is the difference between resolver and util libs? If you want to edit testing/baseconfigs/all/etc/bind, you'll need a snapshot version. The resolver library contains the resolver. FreeS/WAN has its own copy of that in lib/liblwres.
cd /c2/kernel
tar xzvf ../download/pub/linux/kernel/v2.4/linux-2.4.19.tar.gz
mkdir -p /c2/user-mode-linux/basic-root
cd /c2/user-mode-linux/basic-root
tar xzvf ../download/umlfreeroot-15.1.tar.gz
mkdir -p /c2/freeswan/sandbox
cd /c2/freeswan/sandbox
tar xzvf ../download/snapshot.tar.gz
./configure
make
./configure
make
# Need to be superuser to install in system directories.
# Installing in ~/bin would be an alternative.
su -c "make install"
cd tools
make all
# Need to be superuser to install in system directories.
# Installing in ~/bin would be an alternative.
su -c "make install BIN_DIR=/usr/bin"
cd /c2/freeswan/sandbox/freeswan-1.97/testing/utils cp
umlsetup-sample.sh ../../umlsetup.sh cd $TESTINGROOT/utils
sh make-uml.sh
It will grind for awhile. If there are errors it will bail. If so, run
it under "script" and send the output to bugs@lists.freeswan.org. for i in sunrise sunset east west
do
xterm -name $i -title $i -e $POOLSPACE/$i/start.sh & done
With User-Mode-Linux, you can debug the kernel using GDB. See http://user-mode-linux.sourceforge.net/debugging.html.
Typically, one will want to address a test case for a failing situation. Running GDB from Emacs, or from other front ends is possible. First start GDB.
Tell it to open the UMLPOOL/swan/linux program.
Note the PID of GDB:
marajade-[projects/freeswan/mgmt/planning] mcr 1029 %ps ax | grep gdb 1659 pts/9 SN 0:00 /usr/bin/gdb -fullname -cd /mara4/freeswan/kernpatch/UMLPOOL/swan/ linux
Set the following in the environment:
UML_east_OPT="debug gdb-pid=1659"
Then start the user-mode-linux in the test scheme you wish:
marajade-[kernpatch/testing/klips/east-icmp-02] mcr 1220 %../../utils/runme.shThe user-mode-linux will stop on boot, giving you a chance to attach to the process:
(gdb) file linux Reading symbols from linux...done. (gdb) attach 1 Attaching to program: /mara4/freeswan/kernpatch/UMLPOOL/swan/linux, process 1 0xa0118bc1 in kill () at hostfs_kern.c:770
At this point, break points should be created as appropriate.
If you are running a standard test, after all the packets are sent, the UML will be shutdown. This can cause problems, because the UML may get terminated while you are debugging.
The environment variable NETJIGWAITUSER can be set to
"waituser". If so, then the testing system will prompt before exiting
the test.
The environment variable UML_GETTY if set, will cause
each UML to spawn a getty on /dev/tty1, and will wait for it to exit
before continuing.
uml_netjig can be compiled with a built-in tcpdump. This uses
not-yet-released code from
www.tcpdump.org. Please see the instructions in
testing/utils/uml_netjig/Makefile.
Cryptography has a long and interesting history, and has been the subject of considerable political controversy.
The classic book on the history of cryptography is David Kahn's The Codebreakers. It traces codes and codebreaking from ancient Egypt to the 20th century.
Diffie and Landau Privacy on the Line: The Politics of Wiretapping and Encryption covers the history from the First World War to the 1990s, with an emphasis on the US.
During the Second World War, the British "Ultra" project achieved one of the greatest intelligence triumphs in the history of warfare, breaking many Axis codes. One major target was the Enigma cipher machine, a German device whose users were convinced it was unbreakable. The American "Magic" project had some similar triumphs against Japanese codes.
There are many books on this period. See our bibliography for several. Two I particularly like are:
Bletchley Park, where much of the Ultra work was done, now has a museum and a web site.
The Ultra work introduced three major innovations.
So by the end of the war, Allied code-breakers were expert at large-scale mechanised code-breaking. The payoffs were enormous.
The wartime innovations were enthusiastically adopted by post-war and Cold War signals intelligence agencies. Presumably many nations now have some agency capable of sophisticated attacks on communications security, and quite a few engage in such activity on a large scale.
America's NSA, for example, is said to be both the world's largest employer of mathematicians and the world's largest purchaser of computer equipment. Such claims may be somewhat exaggerated, but beyond doubt the NSA -- and similar agencies in other countries -- have some excellent mathematicians, lots of powerful computers, sophisticated software, and the organisation and funding to apply them on a large scale. Details of the NSA budget are secret, but there are some published estimates.
Changes in the world's communications systems since WW II have provided these agencies with new targets. Cracking the codes used on an enemy's military or diplomatic communications has been common practice for centuries. Extensive use of radio in war made large-scale attacks such as Ultra possible. Modern communications make it possible to go far beyond that. Consider listening in on cell phones, or intercepting electronic mail, or tapping into the huge volumes of data on new media such as fiber optics or satellite links. None of these targets existed in 1950. All of them can be attacked today, and almost certainly are being attacked.
The Ultra story was not made public until the 1970s. Much of the recent history of codes and code-breaking has not been made public, and some of it may never be. Two important books are:
Note that these books cover only part of what is actually going on, and then only the activities of nations open and democratic enough that (some of) what they are doing can be discovered. A full picture, including:
might be really frightening.
Until quite recently, cryptography was primarily a concern of governments, especially of the military, of spies, and of diplomats. Much of it was extremely secret.
In recent years, that has changed a great deal. With computers and networking becoming ubiquitous, cryptography is now important to almost everyone. Among the developments since the 1970s:
This has led to a complex ongoing battle between various mainly government groups wanting to control the spread of crypto and various others, notably the computer industry and the cypherpunk crypto advocates, wanting to encourage widespread use.
Steven Levy has written a fine history of much of this, called Crypto: How the Code rebels Beat the Government -- Saving Privacy in the Digital Age.
The FreeS/WAN project is to a large extent an outgrowth of cypherpunk ideas. Our reasons for doing the project can be seen in these quotes from the Cypherpunk Manifesto:
Privacy is necessary for an open society in the electronic age. ...We cannot expect governments, corporations, or other large, faceless organizations to grant us privacy out of their beneficence. It is to their advantage to speak of us, and we should expect that they will speak. ...
We must defend our own privacy if we expect to have any. ...
Cypherpunks write code. We know that someone has to write software to defend privacy, and since we can't get privacy unless we all do, we're going to write it. We publish our code so that our fellow Cypherpunks may practice and play with it. Our code is free for all to use, worldwide. We don't much care if you don't approve of the software we write. We know that software can't be destroyed and that a widely dispersed system can't be shut down.
Cypherpunks deplore regulations on cryptography, for encryption is fundamentally a private act. ...
For privacy to be widespread it must be part of a social contract. People must come and together deploy these systems for the common good. ...
To quote project leader John Gilmore:
We are literally in a race between our ability to build and deploy technology, and their ability to build and deploy laws and treaties. Neither side is likely to back down or wise up until it has definitively lost the race.
If FreeS/WAN reaches its goal of making opportunistic encryption widespread so that secure communication can become the default for a large part of the net, we will have struck a major blow.
The political problem is that nearly all governments want to monitor their enemies' communications, and some want to monitor their citizens. They may be very interested in protecting some of their own communications, and often some types of business communication, but not in having everyone able to communicate securely. They therefore attempt to restrict availability of strong cryptography as much as possible.
Things various governments have tried or are trying include:
The government believes not only the governments associated with Echelon are able to intercept communication systems, but that it is an activity of the investigative authorities and intelligence services of many countries with governments of different political signature.Even if they have nothing on the scale of Echelon, most intelligence agencies and police forces certainly have some interception capability.
Of course governments are by no means the only threat to privacy and security on the net. Other threats include:
One study enumerates threats and possible responses for small and medium businesses. VPNs are a key part of the suggested strategy.
We consider privacy a human right. See the UN's Universal Declaration of Human Rights, article twelve:
No one shall be subjected to arbitrary interference with his privacy, family, home or correspondence, nor to attacks upon his honor and reputation. Everyone has the right to the protection of the law against such interference or attacks.
Our objective is to help make privacy possible on the Internet using cryptography strong enough not even those well-funded government agencies are likely to break it. If we can do that, the chances of anyone else breaking it are negliible.
Many groups are working in different ways to defend privacy on the net and elsewhere. Please consider contributing to one or more of these groups:
For more on these issues see:
There are several collections of crypto quotes on the net.
See also the bibliography and our list of web references on cryptography law and policy.
The remainder of this section includes two pieces of writing by our project leader
and discussions of:
and a section on press coverage of FreeS/WAN.
FreeS/WAN project founder John Gilmore wrote a web page about why we are doing this. The version below is slightly edited, to fit this format and to update some links. For a version without these edits, see his home page.
My project for 1996 was to secure 5% of the Internet traffic against passive wiretapping. It didn't happen in 1996, so I'm still working on it in 1997, 1998, and 1999! If we get 5% in 1999 or 2000, we can secure 20% the next year, against both active and passive attacks; and 80% the following year. Soon the whole Internet will be private and secure. The project is called S/WAN or S/Wan or Swan for Secure Wide Area Network; since it's free software, we call it FreeSwan to distinguish it from various commercial implementations. RSA came up with the term "S/WAN". Our main web site is at http://www.freeswan.org/. Want to help?
The idea is to deploy PC-based boxes that will sit between your local area network and the Internet (near your firewall or router) which opportunistically encrypt your Internet packets. Whenever you talk to a machine (like a Web site) that doesn't support encryption, your traffic goes out "in the clear" as usual. Whenever you connect to a machine that does support this kind of encryption, this box automatically encrypts all your packets, and decrypts the ones that come in. In effect, each packet gets put into an "envelope" on one side of the net, and removed from the envelope when it reaches its destination. This works for all kinds of Internet traffic, including Web access, Telnet, FTP, email, IRC, Usenet, etc.
The encryption boxes are standard PC's that use freely available Linux software that you can download over the Internet or install from a cheap CDROM.
This wasn't just my idea; lots of people have been working on it for years. The encryption protocols for these boxes are called IPSEC (IP Security). They have been developed by the IP Security Working Group of the Internet Engineering Task Force, and will be a standard part of the next major version of the Internet protocols ( IPv6). For today's (IP version 4) Internet, they are an option.
The Internet Architecture Board and Internet Engineering Steering Group have taken a strong stand that the Internet should use powerful encryption to provide security and privacy. I think these protocols are the best chance to do that, because they can be deployed very easily, without changing your hardware or software or retraining your users. They offer the best security we know how to build, using the Triple-DES, RSA, and Diffie-Hellman algorithms.
This "opportunistic encryption box" offers the "fax effect". As each person installs one for their own use, it becomes more valuable for their neighbors to install one too, because there's one more person to use it with. The software automatically notices each newly installed box, and doesn't require a network administrator to reconfigure it. Instead of "virtual private networks" we have a "REAL private network"; we add privacy to the real network instead of layering a manually-maintained virtual network on top of an insecure Internet.
The US government would like to control the deployment of IP Security with its crypto export laws. This isn't a problem for my effort, because the cryptographic work is happening outside the United States. A foreign philanthropist, and others, have donated the resources required to add these protocols to the Linux operating system. Linux is a complete, freely available operating system for IBM PC's and several kinds of workstation, which is compatible with Unix. It was written by Linus Torvalds, and is still maintained by a talented team of expert programmers working all over the world and coordinating over the Internet. Linux is distributed under the GNU Public License, which gives everyone the right to copy it, improve it, give it to their friends, sell it commercially, or do just about anything else with it, without paying anyone for the privilege.
Organizations that want to secure their network will be able to put two Ethernet cards into an IBM PC, install Linux on it from a $30 CDROM or by downloading it over the net, and plug it in between their Ethernet and their Internet link or firewall. That's all they'll have to do to encrypt their Internet traffic everywhere outside their own local area network.
Travelers will be able to run Linux on their laptops, to secure their connection back to their home network (and to everywhere else that they connect to, such as customer sites). Anyone who runs Linux on a standalone PC will also be able to secure their network connections, without changing their application software or how they operate their computer from day to day.
There will also be numerous commercially available firewalls that use this technology. RSA Data Security is coordinating the S/Wan (Secure Wide Area Network) project among more than a dozen vendors who use these protocols. There's a compatability chart that shows which vendors have tested their boxes against which other vendors to guarantee interoperatility.
Eventually it will also move into the operating systems and networking protocol stacks of major vendors. This will probably take longer, because those vendors will have to figure out what they want to do about the export controls.
My initial goal of securing 5% of the net by Christmas '96 was not met. It was an ambitious goal, and inspired me and others to work hard, but was ultimately too ambitious. The protocols were in an early stage of development, and needed a lot more protocol design before they could be implemented. As of April 1999, we have released version 1.0 of the software ( freeswan-1.0.tar.gz), which is suitable for setting up Virtual Private Networks using shared secrets for authentication. It does not yet do opportunistic encryption, or use DNSSEC for authentication; those features are coming in a future release.
The first prototype implementation of Domain Name System Security was funded by DARPA as part of their Information Survivability program. Trusted Information Systems wrote a modified version of BIND, the widely-used Berkeley implementation of the Domain Name System.
TIS, ISC, and I merged the prototype into the standard version of BIND. The first production version that supports KEY and SIG records is bind-4.9.5. This or any later version of BIND will do for publishing keys. It is available from the Internet Software Consortium. This version of BIND is not export-controlled since it does not contain any cryptography. Later releases starting with BIND 8.2 include cryptography for authenticating DNS records, which is also exportable. Better documentation is needed.
Because I can. I have made enough money from several successful startup companies, that for a while I don't have to work to support myself. I spend my energies and money creating the kind of world that I'd like to live in and that I'd like my (future) kids to live in. Keeping and improving on the civil rights we have in the United States, as we move more of our lives into cyberspace, is a particular goal of mine.
Would you like to help? I can use people who are willing to write documentation, install early releases for testing, write cryptographic code outside the United States, sell pre-packaged software or systems including this technology, and teach classes for network administrators who want to install this technology. To offer to help, send me email at gnu@toad.com. Tell me what country you live in and what your citizenship is (it matters due to the export control laws; personally I don't care). Include a copy of your resume and the URL of your home page. Describe what you'd like to do for the project, and what you're uniquely qualified for. Mention what other volunteer projects you've been involved in (and how they worked out). Helping out will require that you be able to commit to doing particular things, meet your commitments, and be responsive by email. Volunteer projects just don't work without those things.
From a message project leader John Gilmore posted to the mailing list:
John Denker wrote: > Indeed there are several ways in which the documentation overstates the > scope of what this project does -- starting with the name > FreeS/WAN. There's a big difference between having an encrypted IP tunnel > versus having a Secure Wide-Area Network. This software does a fine job of > the former, which is necessary but not sufficient for the latter. The goal of the project is to make it very hard to tap your wide area communications. The current system provides very good protection against passive attacks (wiretapping and those big antenna farms). Active attacks, which involve the intruder sending packets to your system (like packets that break into sendmail and give them a root shell :-) are much harder to guard against. Active attacks that involve sending people (breaking into your house and replacing parts of your computer with ones that transmit what you're doing) are also much harder to guard against. Though we are putting effort into protecting against active attacks, it's a much bigger job than merely providing strong encryption. It involves general computer security, and general physical security, which are two very expensive problems for even a site to solve, let alone to build into a whole society. The societal benefit of building an infrastructure that protects well against passive attacks is that it makes it much harder to do undetected bulk monitoring of the population. It's a defense against police-states, not against policemen. Policemen can put in the effort required to actively attack sites that they have strong suspicions about. But police states won't be able to build systems that automatically monitor everyone's communications. Either they will be able to monitor only a small subset of the populace (by targeting those who screwed up their passive security), or their monitoring activities will be detectable by those monitored (active attacks leave packet traces or footprints), which can then be addressed through the press and through political means if they become too widespread. FreeS/WAN does not protect very well against traffic analysis, which is a kind of widespread police-state style monitoring that still reveals significant information (who's talking to who) without revealing the contents of what was said. Defenses against traffic analysis are an open research problem. Zero Knowledge Systems is actively deploying a system designed to thwart it, designed by Ian Goldberg. The jury is out on whether it actually works; a lot more experience with it will be needed.
Notes on things mentioned in that message:
Various groups, especially governments and especially the US government, have a long history of advocating various forms of bogus security.
We regard bogus security as extremely dangerous. If users are deceived into relying on bogus security, then they may be exposed to large risks. They would be better off having no security and knowing it. At least then they would be careful about what they said.
Avoiding bogus security is a key design criterion for everything we do in FreeS/WAN. The most conspicuous example is our refusal to support single DES. Other IPsec "features" which we do not implement are discussed in our compatibility document.
Various governments have made persistent attempts to encourage or mandate "escrowed encrytion", also called "key recovery", or GAK for "government access to keys". The idea is that cryptographic keys be held by some third party and turned over to law enforcement or security agencies under some conditions.
Mary had a little key - she kept it in escrow, and every thing that Mary said, the feds were sure to know.
A crypto quotes page attributes this to Sam Simpson.
There is an excellent paper available on Risks of Escrowed Encryption, from a group of cryptographic luminaries which included our project leader.
Like any unnecessary complication, GAK tends to weaken security of any design it infects. For example:
FreeS/WAN does not support escrowed encryption, and never will.
Various governments, and some vendors, have also made persistent attempts to convince people that:
This is utter nonsense.
Weak systems touted include:
The notion that choice of ciphers or keysize should be determined by a trade-off between security requirements and overheads is pure bafflegab.
For example, suppose public key operations use use 1% of the time in a hybrid system and you triple the cost of public key operations. The cost of symmetric cipher operations is unchanged at 99% of the original total cost, so the overall effect is a jump from 99 + 1 = 100 to 99 + 3 = 102, a 2% rise in system cost.
In short, there has never been any technical reason to use inadequate ciphers. The only reason there has ever been for anyone to use such ciphers is that government agencies want weak ciphers used so that they can crack them. The alleged savings are simply propaganda.
Mary had a little key (It's all she could export), and all the email that she sent was opened at the Fort.
A crypto quotes page attributes this to Ron Rivest. NSA headquarters is at Fort Meade, Maryland.
Our policy in FreeS/WAN is to use only cryptographic components with adequate keylength and no known weaknesses.
Detailed discussion of which IPsec features we implement or omit is in out compatibility document.
These decisions imply that we cannot fully conform to the IPsec RFCs, since those have DES as the only required cipher and Group 1 as the only required DH group. (In our view, the standards were subverted into offerring bogus security.) Fortunately, we can still interoperate with most other IPsec implementations since nearly all implementers provide at least 3DES and Group 2 as well.
We hope that eventually the RFCs will catch up with our (and others') current practice and reject dubious components. Some of our team and a number of others are working on this in IETF working groups.
Of course, making systems secure does involve costs, and trade-offs can be made between cost and security. However, the real trade-offs have nothing to do with using weaker ciphers.
There can be substantial hardware and software costs. There are often substantial training costs, both to train administrators and to increase user awareness of security issues and procedures. There are almost always substantial staff or contracting costs.
Security takes staff time for planning, implementation, testing and auditing. Some of the issues are subtle; you need good (hence often expensive) people for this. You also need people to monitor your systems and respond to problems. The best safe ever built is insecure if an attacker can work on it for days without anyone noticing. Any computer is insecure if the administrator is "too busy" to check the logs.
Moreover, someone in your organisation (or on contract to it) needs to spend considerable time keeping up with new developments. EvilDoers will know about new attacks shortly after they are found. You need to know about them before your systems are attacked. If your vendor provides a patch, you need to apply it. If the vendor does nothing, you need to complain or start looking for another vendor.
For a fairly awful example, see this report. In that case over a million credit card numbers were taken from e-commerce sites, using security flaws in Windows NT servers. Microsoft had long since released patches for most or all of the flaws, but the site administrators had not applied them.
At an absolute minimum, you must do something about such issues before an exploitation tool is posted to the net for downloading by dozens of "script kiddies". Such a tool might appear at any time from the announcement of the security hole to several months later. Once it appears, anyone with a browser and an attitude can break any system whose administrators have done nothing about the flaw.
Compared to those costs, cipher overheads are an insignificant factor in the cost of security.
The only thing using a weak cipher can do for you is to cause all your other investment to be wasted.
Many nations restrict the export of cryptography and some restrict its use by their citizens or others within their borders.
US laws, as currently interpreted by the US government, forbid export of most cryptographic software from the US in machine-readable form without government permission. In general, the restrictions apply even if the software is widely-disseminated or public-domain and even if it came from outside the US originally. Cryptography is legally a munition and export is tightly controlled under the EAR Export Administration Regulations.
If you are a US citizen, your brain is considered US territory no matter where it is physically located at the moment. The US believes that its laws apply to its citizens everywhere, not just within the US. Providing technical assistance or advice to foreign "munitions" projects is illegal. The US government has very little sense of humor about this issue and does not consider good intentions to be sufficient excuse. Beware.
The official website for these regulations is run by the Commerce Department's Bureau of Export Administration (BXA).
The Bernstein case challenges the export restrictions on Constitutional grounds. Code is speech so restrictions on export of code violate the First Amendment's free speech provisions. This argument has succeeded in two levels of court so far. It is quite likely to go on to the Supreme Court.
The regulations were changed substantially in January 2000, apparently as a government attempt to get off the hook in the Bernstein case. It is now legal to export public domain source code for encryption, provided you notify the BXA.
There are, however, still restrictions in force. Moreover, the regulations can still be changed again whenever the government chooses to do so. Short of a Supreme Court ruling (in the Berstein case or another) that overturns the regulations completely, the problem of export regulation is not likely to go away in the forseeable future.
The FreeS/WAN project cannot accept software contributions, not even small bug fixes, from US citizens or residents. We want it to be absolutely clear that our distribution is not subject to US export law. Any contribution from an American might open that question to a debate we'd prefer to avoid. It might also put the contributor at serious legal risk.
Of course Americans can still make valuable contributions (many already have) by reporting bugs, or otherwise contributing to discussions, on the project mailing list. Since the list is public, this is clearly constitutionally protected free speech.
Note, however, that the export laws restrict Americans from providing technical assistance to foreign "munitions" projects. The government might claim that private discussions or correspondence with FreeS/WAN developers were covered by this. It is not clear what the courts would do with such a claim, so we strongly encourage Americans to use the list rather than risk the complications.
Some quotes from prominent cryptography experts:
The real aim of current policy is to ensure the continued effectiveness of US information warfare assets against individuals, businesses and governments in Europe and elsewhere.
Ross Anderson, Cambridge University
If the government were honest about its motives, then the debate about crypto export policy would have ended years ago.
Bruce Schneier, Counterpane Systems
The NSA regularly lies to people who ask it for advice on export control. They have no reason not to; accomplishing their goal by any legal means is fine by them. Lying by government employees is legal.
John Gilmore.
The Internet Architecture Board (IAB) and the Internet Engineering Steering Group (IESG) made a strong statement in favour of worldwide access to strong cryptography. Essentially the same statement is in the appropriately numbered RFC 1984. Two critical paragraphs are:
... various governments have actual or proposed policies on access to cryptographic technology ...(a) ... export controls ...
(b) ... short cryptographic keys ...
(c) ... keys should be in the hands of the government or ...
(d) prohibit the use of cryptology ...We believe that such policies are against the interests of consumers and the business community, are largely irrelevant to issues of military security, and provide only a marginal or illusory benefit to law enforcement agencies, ...
The IAB and IESG would like to encourage policies that allow ready access to uniform strong cryptographic technology for all Internet users in all countries.
Our goal in the FreeS/WAN project is to build just such "strong cryptographic technology" and to distribute it "for all Internet users in all countries".
More recently, the same two bodies (IESG and IAB) have issued RFC 2804 on why the IETF should not build wiretapping capabilities into protocols for the convenience of security or law enforcement agenicies. The abstract from that document is:
The Internet Engineering Task Force (IETF) has been asked to take a position on the inclusion into IETF standards-track documents of functionality designed to facilitate wiretapping.A quote from the debate leading up to that RFC:This memo explains what the IETF thinks the question means, why its answer is "no", and what that answer means.
We should not be building surveillance technology into standards. Law enforcement was not supposed to be easy. Where it is easy, it's called a police state.
Jeff Schiller of MIT, in a discussion of FBI demands for wiretap capability on the net, as quoted by Wired.
The Raven mailing list was set up for this IETF discussion.
Our goal is to go beyond that RFC and prevent Internet wiretapping entirely.
Restrictions on the export of cryptography are not just US policy, though some consider the US at least partly to blame for the policies of other nations in this area.
A number of countries:
Argentina, Australia, Austria, Belgium, Bulgaria, Canada, Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Japan, Luxembourg, Netherlands, New Zealand, Norway, Poland, Portugal, Republic of Korea, Romania, Russian Federation, Slovak Republic, Spain, Sweden, Switzerland, Turkey, Ukraine, United Kingdom and United States
have signed the Wassenaar Arrangement which restricts export of munitions and other tools of war. Cryptographic sofware is covered there.
Wassenaar details are available from the Wassenaar Secretariat, and elsewhere in a more readable HTML version.
For a critique see the GILC site:
The Global Internet Liberty Campaign (GILC) has begun a campaign calling for the removal of cryptography controls from the Wassenaar Arrangement.The aim of the Wassenaar Arrangement is to prevent the build up of military capabilities that threaten regional and international security and stability . . .
There is no sound basis within the Wassenaar Arrangement for the continuation of any export controls on cryptographic products.
We agree entirely.
An interesting analysis of Wassenaar can be found on the cyber-rights.org site.
We believe our software is entirely exempt from these controls since the Wassenaar General Software Note says:
The Lists do not control "software" which is either:
- Generally available to the public by . . . retail . . . or
- "In the public domain".
There is a note restricting some of this, but it is a sub-heading under point 1, so it appears not to apply to public domain software.
Their glossary defines "In the public domain" as:
. . . "technology" or "software" which has been made available without restrictions upon its further dissemination.N.B. Copyright restrictions do not remove "technology" or "software" from being "in the public domain".
We therefore believe that software freely distributed under the GNU Public License, such as Linux FreeS/WAN, is exempt from Wassenaar restrictions.
Most of the development work is being done in Canada. Our understanding is that the Canadian government accepts this interpretation.
Recent copies of the freely modifiable and distributable source code exist in many countries. Citizens all over the world participate in its use and evolution, and guard its ongoing distribution. Even if Canadian policy were to change, the software would continue to evolve in countries which do not restrict exports, and would continue to be imported from there into unfree countries. "The Net culture treats censorship as damage, and routes around it."
You can help. If you don't know of a Linux FreeS/WAN archive in your own country, please download it now to your personal machine, and consider making it publicly accessible if that doesn't violate your own laws. If you have the resources, consider going one step further and setting up a mirror site for the whole munitions Linux crypto software archive.
If you make Linux CD-ROMs, please consider including this code, in a way that violates no laws (in a free country, or in a domestic-only CD product).
Please send a note about any new archive mirror sites or CD distributions to linux-ipsec@clinet.fi so we can update the documentation.
Lists of current mirror sites and of distributions which include FreeS/WAN are in our introduction section.
DES, the Data Encryption S tandard, can no longer be considered secure. While no major flaws in its innards are known, it is fundamentally inadequate because its 56-bit key is too short. It is vulnerable to brute-force search of the whole key space, either by large collections of general-purpose machines or even more quickly by specialized hardware. Of course this also applies to any other cipher with only a 56-bit key. The only reason anyone could have for using a 56 or 64-bit key is to comply with various export laws intended to ensure the use of breakable ciphers.
Non-government cryptologists have been saying DES's 56-bit key was too short for some time -- some of them were saying it in the 70's when DES became a standard -- but the US government has consistently ridiculed such suggestions.
A group of well-known cryptographers looked at key lengths in a 1996 paper. They suggested a minimum of 75 bits to consider an existing cipher secure and a minimum of 90 bits for new ciphers. More recent papers, covering both symmetric and public key systems are at cryptosavvy.com and rsa.com. For all algorithms, the minimum keylengths recommended in such papers are significantly longer than the maximums allowed by various export laws.
In a 1998 ruling, a German court described DES as "out-of-date and not safe enough" and held a bank liable for using it.
The question of DES security has now been settled once and for all. In early 1998, the Electronic Frontier Foundation built a DES-cracking machine. It can find a DES key in an average of a few days' search. The details of all this, including complete code listings and complete plans for the machine, have been published in Cracking DES, by the Electronic Frontier Foundation.
That machine cost just over $200,000 to design and build. "Moore's Law" is that machines get faster (or cheaper, for the same speed) by roughly a factor of two every 18 months. At that rate, their $200,000 in 1998 becomes $50,000 in 2001.
However, Moore's Law is not exact and the $50,000 estimate does not allow for the fact that a copy based on the published EFF design would cost far less than the original. We cannot say exactly what such a cracker would cost today, but it would likely be somewhere between $10,000 and $100,000.
A large corporation could build one of these out of petty cash. The cost is low enough for a senior manager to hide it in a departmental budget and avoid having to announce or justify the project. Any government agency, from a major municipal police force up, could afford one. Or any other group with a respectable budget -- criminal organisations, political groups, labour unions, religious groups, ... Or any millionaire with an obsession or a grudge, or just strange taste in toys.
One might wonder if a private security or detective agency would have one for rent. They wouldn't need many clients to pay off that investment.
As for the security and intelligence agencies of various nations, they may have had DES crackers for years, and theirs may be much faster. It is difficult to make most computer applications work well on parallel machines, or to design specialised hardware to accelerate them. Cipher-cracking is one of the very few exceptions. It is entirely straightforward to speed up cracking by just adding hardware. Within very broad limits, you can make it as fast as you like if you have the budget. The EFF's $200,000 machine breaks DES in a few days. An aviation website gives the cost of a B1 bomber as $200,000,000. Spending that much, an intelligence agency could break DES in an average time of six and a half minutes.
That estimate assumes they use the EFF's 1998 technology and just spend more money. They may have an attack that is superior to brute force, they quite likely have better chip technology (Moore's law, a bigger budget, and whatever secret advances they may have made) and of course they may have spent the price of an aircraft carrier, not just one aircraft.
In short, we have no idea how quickly these organisations can break DES. Unless they're spectacularly incompetent or horribly underfunded, they can certainly break it, but we cannot guess how quickly. Pick any time unit between days and milliseconds; none is entirely unbelievable. More to the point, none of them is of any comfort if you don't want such organisations reading your communications.
Note that this may be a concern even if nothing you do is a threat to anyone's national security. An intelligence agency might well consider it to be in their national interest for certain companies to do well. If you're competing against such companies in a world market and that agency can read your secrets, you have a serious problem.
One might wonder about technology the former Soviet Union and its allies developed for cracking DES during the Cold War. They must have tried; the cipher was an American standard and widely used. Certainly those countries have some fine mathematicians, and those agencies had budget. How well did they succeed? Is their technology now for sale or rent?
Before the definitive EFF effort, DES had been cracked several times by people using many machines. See this press release for example.
A major corporation, university, or government department could break DES by using spare cycles on their existing collection of computers, by dedicating a group of otherwise surplus machines to the problem, or by combining the two approaches. It might take them weeks or months, rather than the days required for the EFF machine, but they could do it.
What about someone working alone, without the resources of a large organisation? For them, cracking DES will not be easy, but it may be possible. A few thousand dollars buys a lot of surplus workstations. A pile of such machines will certainly heat your garage nicely and might break DES in a few months or years. Or enroll at a university and use their machines. Or use an employer's machines. Or crack security somewhere and steal the resources to crack a DES key. Or write a virus that steals small amounts of resources on many machines. Or . . .
None of these approaches are easy or break DES really quickly, but an attacker only needs to find one that is feasible and breaks DES quickly enough to be dangerous. How much would you care to bet that this will be impossible if the attacker is clever and determined? How valuable is your data? Are you authorised to risk it on a dubious bet?
In short, it is now absolutely clear that DES is not secure against
That is why Linux FreeS/WAN disables all transforms which use plain DES for encryption.
DES is in the source code, because we need DES to implement our default encryption transform, Triple DES. We urge you not to use single DES. We do not provide any easy way to enable it in FreeS/WAN, and our policy is to provide no assistance to anyone wanting to do so.
The same is true, in spades, of ciphers -- DES or others -- crippled by 40-bit keys, as many ciphers were required to be until recently under various export laws. A brute force search of such a cipher's keyspace is 216 times faster than a similar search against DES. The EFF's machine can do a brute-force search of a 40-bit key space in seconds. One contest to crack a 40-bit cipher was won by a student using a few hundred idle machines at his university. It took only three and half hours.
We do not, and will not, implement any 40-bit cipher.
Triple DES, usually abbreviated 3DES, applies DES three times, with three different keys. DES seems to be basically an excellent cipher design; it has withstood several decades of intensive analysis without any disastrous flaws being found. It's only major flaw is that the small keyspace allows brute force attacks to succeeed. Triple DES enlarges the key space to 168 bits, making brute-force search a ridiculous impossibility.
3DES is currently the only block cipher implemented in FreeS/WAN. 3DES is, unfortunately, about 1/3 the speed of DES, but modern CPUs still do it at quite respectable speeds. Some speed measurements for our code are available.
The AES project has chosen a replacement for DES, a new standard cipher for use in non-classified US government work and in regulated industries such as banking. This cipher will almost certainly become widely used for many applications, including IPsec.
The winner, announced in October 2000 after several years of analysis and discussion, was the Rijndael cipher from two Belgian designers.
It is almost certain that FreeS/WAN will add AES support. AES patches are already available.
Strong Internet Privacy Software Free for Linux Users Worldwide Toronto, ON, April 14, 1999 - The Linux FreeS/WAN project today released free software to protect the privacy of Internet communications using strong encryption codes. FreeS/WAN automatically encrypts data as it crosses the Internet, to prevent unauthorized people from receiving or modifying it. One ordinary PC per site runs this free software under Linux to become a secure gateway in a Virtual Private Network, without having to modify users' operating systems or application software. The project built and released the software outside the United States, avoiding US government regulations which prohibit good privacy protection. FreeS/WAN version 1.0 is available immediately for downloading at http://www.xs4all.nl/~freeswan/. "Today's FreeS/WAN release allows network administrators to build excellent secure gateways out of old PCs at no cost, or using a cheap new PC," said John Gilmore, the entrepreneur who instigated the project in 1996. "They can build operational experience with strong network encryption and protect their users' most important communications worldwide." "The software was written outside the United States, and we do not accept contributions from US citizens or residents, so that it can be freely published for use in every country," said Henry Spencer, who built the release in Toronto, Canada. "Similar products based in the US require hard-to-get government export licenses before they can be provided to non-US users, and can never be simply published on a Web site. Our product is freely available worldwide for immediate downloading, at no cost." FreeS/WAN provides privacy against both quiet eavesdropping (such as "packet sniffing") and active attempts to compromise communications (such as impersonating participating computers). Secure "tunnels" carry information safely across the Internet between locations such as a company's main office, distant sales offices, and roaming laptops. This protects the privacy and integrity of all information sent among those locations, including sensitive intra-company email, financial transactions such as mergers and acquisitions, business negotiations, personal medical records, privileged correspondence with lawyers, and information about crimes or civil rights violations. The software will be particularly useful to frequent wiretapping targets such as private companies competing with government-owned companies, civil rights groups and lawyers, opposition political parties, and dissidents. FreeS/WAN provides privacy for Internet packets using the proposed standard Internet Protocol Security (IPSEC) protocols. FreeS/WAN negotiates strong keys using Diffie-Hellman key agreement with 1024-bit keys, and encrypts each packet with 168-bit Triple-DES (3DES). A modern $500 PC can set up a tunnel in less than a second, and can encrypt 6 megabits of packets per second, easily handling the whole available bandwidth at the vast majority of Internet sites. In preliminary testing, FreeS/WAN interoperated with 3DES IPSEC products from OpenBSD, PGP, SSH, Cisco, Raptor, and Xedia. Since FreeS/WAN is distributed as source code, its innards are open to review by outside experts and sophisticated users, reducing the chance of undetected bugs or hidden security compromises. The software has been in development for several years. It has been funded by several philanthropists interested in increased privacy on the Internet, including John Gilmore, co-founder of the Electronic Frontier Foundation, a leading online civil rights group. Press contacts: Hugh Daniel, +1 408 353 8124, hugh@toad.com Henry Spencer, +1 416 690 6561, henry@spsystems.net * FreeS/WAN derives its name from S/WAN, which is a trademark of RSA Data Security, Inc; used by permission.
This section provides information on the IPsec protocols which FreeS/WAN implements. For more detail, see the RFCs .
The basic idea of IPsec is to provide security functions, authentication and encryption, at the IP (Internet Protocol) level. This requires a higher-level protocol (IKE) to set things up for the IP-level services (ESP and AH).
Three protocols are used in an IPsec implementation:
The term "IPsec" (also written as IPSEC) is slightly ambiguous. In some contexts, it includes all three of the above but in other contexts it refers only to AH and ESP.
There is more detail below, but a quick summary of how the whole thing works is:
Both phases of IKE are repeated periodically to automate re-keying.
Authentication and encryption functions for network data can, of course, be provided at other levels. Many security protocols work at levels above IP.
and so on. Other techniques work at levels below IP. For example, data on a communications circuit or an entire network can be encrypted by specialised hardware. This is common practice in high-security applications.
There are, however, advantages to doing it at the IP level instead of, or as well as, at other levels.
IPsec is the most general way to provide these services for the Internet.
IPsec, however, can protect any protocol running above IP and any medium which IP runs over. More to the point, it can protect a mixture of application protocols running over a complex combination of media. This is the normal situation for Internet communication; IPsec is the only general solution.
IPsec can also provide some security services "in the background", with no visible impact on users. To use PGP encryption and signatures on mail, for example, the user must at least:
These systems can be designed so that the burden on users is not onerous, but any system will place some requirements on users. No such system can hope to be secure if users are sloppy about meeting those requirements. The author has seen username and password stuck on terminals with post-it notes in an allegedly secure environment, for example.
IPsec is designed to secure IP links between machines. It does that well, but it is important to remember that there are many things it does not do. Some of the important limitations are:
Of course, there is another side to this. IPsec can be a powerful tool for improving system and network security. For example, requiring packet authentication makes various spoofing attacks harder and IPsec tunnels can be extremely useful for secure remote administration of various things.
For example, if you need mail encrypted from the sender's desktop to the recipient's desktop and decryptable only by the recipient, use PGP or another such system. IPsec can encrypt any or all of the links involved -- between the two mail servers, or between either server and its clients. It could even be used to secure a direct IP link from the sender's desktop machine to the recipient's, cutting out any sort of network snoop. What it cannot ensure is end-to-end user-to-user security. If only IPsec is used to secure mail, then anyone with appropriate privileges on any machine where that mail is stored (at either end or on any store-and-forward servers in the path) can read it.
In another common setup, IPsec encrypts packets at a security gateway machine as they leave the sender's site and decrypts them on arrival at the gateway to the recipient's site. This does provide a useful security service -- only encrypted data is passed over the Internet -- but it does not even come close to providing an end-to-end service. In particular, anyone with appropriate privileges on either site's LAN can intercept the message in unencrypted form.
Note, however, that IPsec authentication of the underlying communication can make various attacks on higher-level protocols more difficult. In particular, authentication prevents man-in-the-middle attacks.
IPsec shifts the ground for DoS attacks; the attacks possible against systems using IPsec are different than those that might be used against other systems. It does not, however, eliminate the possibility of such attacks.
IPsec is not designed to defend against this. Partial defenses are certainly possible, and some are described below, but it is not clear that any complete defense can be provided.
While IPsec does not provide all functions of a mail encryption package, it can encrypt your mail. In particular, it can ensure that all mail passing between a pair or a group of sites is encrypted. An attacker looking only at external traffic, without access to anything on or behind the IPsec gateway, cannot read your mail. He or she is stymied by IPsec just as he or she would be by PGP.
The advantage is that IPsec can provide the same protection for anything transmitted over IP. In a corporate network example, PGP lets the branch offices exchange secure mail with head office. SSL and SSH allow them to securely view web pages, connect as terminals to machines, and so on. IPsec can support all those applications, plus database queries, file sharing (NFS or Windows), other protocols encapsulated in IP (Netware, Appletalk, ...), phone-over-IP, video-over-IP, ... anything-over-IP. The only limitation is that IP Multicast is not yet supported, though there are Internet Draft documents for that.
IPsec creates secure tunnels through untrusted networks . Sites connected by these tunnels form VPNs, Virtual Private Networks.
IPsec gateways can be installed wherever they are required.
Which of these, or of the many other possible variants, to use is up to you. IPsec provides mechanisms; you provide the policy .
No end user action is required for IPsec security to be used; they don't even have to know about it. The site administrators, of course, do have to know about it and to put some effort into making it work. Poor administration can compromise IPsec as badly as the post-it notes mentioned above. It seems reasonable, though, for organisations to hope their system administrators are generally both more security-conscious than end users and more able to follow computer security procedures. If not, at least there are fewer of them to educate or replace.
IPsec can be, and often should be, used with along with security protocols at other levels. If two sites communicate with each other via the Internet, then IPsec is the obvious way to protect that communication. If two others have a direct link between them, either link encryption or IPsec would make sense. Choose one or use both. Whatever you use at and below the IP level, use other things as required above that level. Whatever you use above the IP level, consider what can be done with IPsec to make attacks on the higher levels harder. For example, man-in-the-middle attacks on various protocols become difficult if authentication at packet level is in use on the potential victims' communication channel.
Where appropriate, IPsec can provide authentication without encryption. One might do this, for example:
Authentication has lower overheads than encryption.
The protocols provide four ways to build such connections, using either an AH-only connection or ESP using null encryption, and in either manually or automatically keyed mode. FreeS/WAN supports only one of these, manually keyed AH-only connections, and we do not recommend using that. Our reasons are discussed under Resisting traffic analysis a few sections further along.
Originally, the IPsec encryption protocol ESP didn't do integrity checking. It only did encryption. Steve Bellovin found many ways to attack ESP used without authentication. See his paper Problem areas for the IP Security Protocols. To make a secure connection, you had to add an AH Authentication Header as well as ESP. Rather than incur the overhead of several layers (and rather than provide an ESP layer that didn't actually protect the traffic), the IPsec working group built integrity and replay checking directly into ESP.
Today, typical usage is one of:
Other variants are allowed by the standard, but not much used:
Some of these variants cannot be used with FreeS/WAN because we do not support ESP-null and do not support automatic keying of AH-only connections.
There are fairly frequent suggestions that AH be dropped entirely from the IPsec specifications since ESP and null encryption can handle that situation. It is not clear whether this will occur. My guess is that it is unlikely.
The above describes combinations possible on a single IPsec connection. In a complex network you may have several layers of IPsec in play, with any of the above combinations at each layer.
For example, a connection from a desktop machine to a database server might require AH authentication. Working with other host, network and database security measures, AH might be just the thing for access control. You might decide not to use ESP encryption on such packets, since it uses resources and might complicate network debugging. Within the site where the server is, then, only AH would be used on those packets.
Users at another office, however, might have their whole connection (AH headers and all) passing over an IPsec tunnel connecting their office to the one with the database server. Such a tunnel should use ESP encryption and authentication. You need authentication in this layer because without authentication the encryption is vulnerable and the gateway cannot verify the AH authentication. The AH is between client and database server; the gateways aren't party to it.
In this situation, some packets would get multiple layers of IPsec applied to them, AH on an end-to-end client-to-server basis and ESP from one office's security gateway to the other.
Traffic analysis is the attempt to derive useful intelligence from encrypted traffic without breaking the encryption.
Is your CEO exchanging email with a venture capital firm? With bankruptcy trustees? With an executive recruiting agency? With the holder of some important patents? If an eavesdropper learns about any of those, then he has interesting intelligence on your company, whether or not he can read the messages themselves.
Even just knowing that there is network traffic between two sites may tell an analyst something useful, especially when combined with whatever other information he or she may have. For example, if you know Company A is having cashflow problems and Company B is looking for aquisitions, then knowing that packets are passing between the two is interesting. It is more interesting if you can tell it is email, and perhaps yet more if you know the sender and recipient.
Except in the simplest cases, traffic analysis is hard to do well. It requires both considerable resources and considerable analytic skill. However, intelligence agencies of various nations have been doing it for centuries and many of them are likely quite good at it by now. Various commercial organisations, especially those working on "targeted marketing" may also be quite good at analysing certain types of traffic.
In general, defending against traffic analysis is also difficult. Inventing a really good defense could get you a PhD and some interesting job offers.
IPsec is not designed to stop traffic analysis and we know of no plausible method of extending it to do so. That said, there are ways to make traffic analysis harder. This section describes them.
One might choose to use encryption even where it appears unnecessary in order to make analysis more difficult. Consider two offices which pass a small volume of business data between them using IPsec and also transfer large volumes of Usenet news. At first glance, it would seem silly to encrypt the newsfeed, except possibly for any newsgroups that are internal to the company. Why encrypt data that is all publicly available from many sites?
However, if we encrypt a lot of news and send it down the same connection as our business data, we make traffic analysis much harder. A snoop cannot now make inferences based on patterns in the volume, direction, sizes, sender, destination, or timing of our business messages. Those messages are hidden in a mass of news messages encapsulated in the same way.
If we're going to do this we need to ensure that keys change often enough to remain secure even with high volumes and with the adversary able to get plaintext of much of the data. We also need to look at other attacks this might open up. For example, can the adversary use a chosen plaintext attack, deliberately posting news articles which, when we receive and encrypt them, will help break our encryption? Or can he block our business data transmission by flooding us with silly news articles? Or ...
Also, note that this does not provide complete protection against traffic analysis. A clever adversary might still deduce useful intelligence from statistical analysis (perhaps comparing the input newsfeed to encrypted output, or comparing the streams we send to different branch offices), or by looking for small packets which might indicate establishment of TCP connections, or ...
As a general rule, though, to improve resistance to traffic analysis, you should encrypt as much traffic as possible, not just as much as seems necessary.
This also applies to using multiple layers of encryption. If you have an IPsec tunnel between two branch offices, it might appear silly to send PGP-encrypted email through that tunnel. However, if you suspect someone is snooping your traffic, then it does make sense:
Similar arguments apply for SSL-encrypted web traffic or SSH-encrypted remote login sessions, even for end-to-end IPsec tunnels between systems in the two offices.
It may also help to use fewer tunnels. For example, if all you actually need encrypted is connections between:
You might build one tunnel per mail server and one per remote database user, restricting traffic to those applications. This gives the traffic analyst some information, however. He or she can distinguish the tunnels by looking at information in the ESP header and, given that distinction and the patterns of tunnel usage, might be able to figure out something useful. Perhaps not, but why take the risk?
We suggest instead that you build one tunnel per branch office, encrypting everything passing from head office to branches. This has a number of advantages:
Of course you might also want to add additional tunnels. For example, if some of the database data is confidential and should not be exposed even within the company, then you need protection from the user's desktop to the database server. We suggest you do that in whatever way seems appropriate -- IPsec, SSH or SSL might fit -- but, whatever you choose, pass it between locations via a gateway-to-gateway IPsec tunnel to provide some resistance to traffic analysis.
IPsec combines a number of cryptographic techniques, all of them well-known and well-analyzed. The overall design approach was conservative; no new or poorly-understood components were included.
This section gives a brief overview of each technique. It is intended only as an introduction. There is more information, and links to related topics, in our glossary. See also our bibliography and cryptography web links.
The encryption in the ESP encapsulation protocol is done with a block cipher .
We do not implement single DES. It is insecure. Our default, and currently only, block cipher is triple DES.
The Rijndael block cipher has won the AES competition to choose a relacement for DES. It will almost certainly be added to FreeS/WAN and to other IPsec implementations. Patches are already available.
IPsec packet authentication is done with the HMAC construct. This is not just a hash of the packet data, but a more complex operation which uses both a hashing algorithm and a key. It therefore does more than a simple hash would. A simple hash would only tell you that the packet data was not changed in transit, or that whoever changed it also regenerated the hash. An HMAC also tells you that the sender knew the HMAC key.
For IPsec HMAC, the output of the hash algorithm is truncated to 96 bits. This saves some space in the packets. More important, it prevents an attacker from seeing all the hash output bits and perhaps creating some sort of attack based on that knowledge.
The IPsec RFCs require two hash algorithms -- MD5 and SHA-1 -- both of which FreeS/WAN implements.
Various other algorithms -- such as RIPEMD and Tiger -- are listed in the RFCs as optional. None of these are in the FreeS/WAN distribution, or are likely to be added, although user patches exist for several of them.
Additional hash algorithms -- SHA-256, SHA-384 and SHA-512 -- may be required to give hash strength matching the strength of AES. These are likely to be added to FreeS/WAN along with AES.
The Diffie-Hellman key agreement protocol allows two parties (A and B or Alice and Bob) to agree on a key in such a way that an eavesdropper who intercepts the entire conversation cannot learn the key.
The protocol is based on the discrete logarithm problem and is therefore thought to be secure. Mathematicians have been working on that problem for years and seem no closer to a solution, though there is no proof that an efficient solution is impossible.
The RSA algorithm (named for its inventors -- Rivest, Shamir and Adleman) is a very widely used public key cryptographic technique. It is used in IPsec as one method of authenticating gateways for Diffie-Hellman key negotiation.
There are three protocols used in an IPsec implementation:
The term "IPsec" is slightly ambiguous. In some contexts, it includes all three of the above but in other contexts it refers only to AH and ESP.
The IKE protocol sets up IPsec (ESP or AH) connections after negotiating appropriate parameters (algorithms to be used, keys, connection lifetimes) for them. This is done by exchanging packets on UDP port 500 between the two gateways.
IKE (RFC 2409) was the outcome of a long, complex process in which quite a number of protocols were proposed and debated. Oversimplifying mildly, IKE combines:
For all the details, you would need to read the four RFCs just mentioned (over 200 pages) and a number of others. We give a summary below, but it is far from complete.
IKE negotiations have two phases.
Both of these phases use the UDP protocol and port 500 for their negotiations.
After both IKE phases are complete, you have IPsec SAs to carry your encrypted data. These use the ESP or AH protocols. These protocols do not have ports. Ports apply only to UDP or TCP.
The IKE protocol is designed to be extremely flexible. Among the things that can be negotiated (separately for each SA) are:
The protocol also allows implementations to add their own encryption algorithms, authentication algorithms or Diffie-Hellman groups. We do not support any such extensions, but there are some patches that do.
There are a number of complications:
These complications can of course lead to problems, particularly when two different implementations attempt to interoperate. For example, we have seen problems such as:
Despite this, we do interoperate successfully with many implementations, including both Windows 2000 and PGPnet. Details are in our interoperability document.
Each phase (see previous section)of IKE involves a series of messages. In Pluto error messages, these are abbreviated using:
For example, the six messages of a main mode negotiation, in sequence, are labelled:
MI1 ---------->
<---------- MR1
MI2 ---------->
<---------- MR2
MI3 ---------->
<---------- MR3
Here is our Pluto developer explaining some of this on the mailing list:
When one IKE system (for example, Pluto) is negotiating with another
to create an SA, the Initiator proposes a bunch of choices and the
Responder replies with one that it has selected.
The structure of the choices is fairly complicated. An SA payload
contains a list of lists of "Proposals". The outer list is a set of
choices: the selection must be from one element of this list.
Each of these elements is a list of Proposals. A selection must be
made from each of the elements of the inner list. In other words,
*all* of them apply (that is how, for example, both AH and ESP can
apply at once).
Within each of these Proposals is a list of Transforms. For each
Proposal selected, one Transform must be selected (in other words,
each Proposal provides a choice of Transforms).
Each Transform is made up of a list of Attributes describing, well,
attributes. Such as lifetime of the SA. Such as algorithm to be
used. All the Attributes apply to a Transform.
You will have noticed a pattern here: layers alternate between being
disjunctions ("or") and conjunctions ("and").
For Phase 1 / Main Mode (negotiating an ISAKMP SA), this structure is
cut back. There must be exactly one Proposal. So this degenerates to
a list of Transforms, one of which must be chosen.
IPsec offers two services, authentication and encryption. These can be used separately but are often used together.
There is a separate authentication operation at the IKE level, in which each gateway authenticates the other. This can be done in a variety of ways.
In IPsec this is done using a block cipher (normally Triple DES for Linux). In the most used setup, keys are automatically negotiated, and periodically re-negotiated, using the IKE (Internet Key Exchange) protocol. In Linux FreeS/WAN this is handled by the Pluto Daemon.
The IPsec protocol offering encryption is ESP, Encapsulated Security Payload. It can also include a packet authentication service.
Note that encryption should always be used with some packet authentication service. Unauthenticated encryption is vulnerable to man-in-the-middle attacks. Also note that encryption does not prevent traffic analysis.
Packet authentication can be provided separately from encryption by adding an authentication header (AH) after the IP header but before the other headers on the packet. This is the subject of this section. Details are in RFC 2402.
Each of the several headers on a packet header contains a "next protocol" field telling the system what header to look for next. IP headers generally have either TCP or UDP in this field. When IPsec authentication is used, the packet IP header has AH in this field, saying that an Authentication Header comes next. The AH header then has the next header type -- usually TCP, UDP or encapsulated IP.
IPsec packet authentication can be added in transport mode, as a modification of standard IP transport. This is shown in this diagram from the RFC:
BEFORE APPLYING AH
----------------------------
IPv4 |orig IP hdr | | |
|(any options)| TCP | Data |
----------------------------
AFTER APPLYING AH
---------------------------------
IPv4 |orig IP hdr | | | |
|(any options)| AH | TCP | Data |
---------------------------------
||
except for mutable fields
Athentication can also be used in tunnel mode, encapsulating the underlying IP packet beneath AH and an additional IP header.
||
IPv4 | new IP hdr* | | orig IP hdr* | | |
|(any options)| AH | (any options) |TCP | Data |
------------------------------------------------
||
| in the new IP hdr |
This would normally be used in a gateway-to-gateway tunnel. The receiving gateway then strips the outer IP header and the AH header and forwards the inner IP packet.
The mutable fields referred to are things like the time-to-live field in the IP header. These cannot be included in authentication calculations because they change as the packet travels.
The actual authentication data in the header is typically 96 bits and depends both on a secret shared between sender and receiver and on every byte of the data being authenticated. The technique used is HMAC, defined in RFC 2104.
The algorithms involved are the MD5 Message Digest Algorithm or SHA, the Secure Hash Algorithm. For details on their use in this application, see RFCs 2403 and 2404 respectively.
For descriptions of the algorithms themselves, see RFC 1321 for MD5 and FIPS (Federal Information Processing Standard) number 186 from NIST, the US National Institute of Standards and Technology for SHA. Applied Cryptography covers both in some detail, MD5 starting on page 436 and SHA on 442.
These algorithms are intended to make it nearly impossible for anyone to alter the authenticated data in transit. The sender calculates a digest or hash value from that data and includes the result in the authentication header. The recipient does the same calculation and compares results. For unchanged data, the results will be identical. The hash algorithms are designed to make it extremely difficult to change the data in any way and still get the correct hash.
Since the shared secret key is also used in both calculations, an interceptor cannot simply alter the authenticated data and change the hash value to match. Without the key, he or she (or even the dreaded They) cannot produce a usable hash.
The authentication header includes a sequence number field which the sender is required to increment for each packet. The receiver can ignore it or use it to check that packets are indeed arriving in the expected sequence.
This provides partial protection against replay attacks in which an attacker resends intercepted packets in an effort to confuse or subvert the receiver. Complete protection is not possible since it is necessary to handle legitmate packets which are lost, duplicated, or delivered out of order, but use of sequence numbers makes the attack much more difficult.
The RFCs require that sequence numbers never cycle, that a new key always be negotiated before the sequence number reaches 2^32-1. This protects both against replays attacks using packets from a previous cyclce and against birthday attacks on the the packet authentication algorithm.
In Linux FreeS/WAN, the sequence number is ignored for manually keyed connections and checked for automatically keyed ones. In manual mode, there is no way to negotiate a new key, or to recover from a sequence number problem, so we don't use sequence numbers.
The ESP protocol is defined in RFC 2406. It provides one or both of encryption and packet authentication. It may be used with or without AH packet authentication.
Note that some form of packet authentication should always be used whenever data is encrypted. Without authentication, the encryption is vulnerable to active attacks which may allow an enemy to break the encryption. ESP should always either include its own authentication or be used with AH authentication.
The RFCs require support for only two mandatory encryption algorithms -- DES, and null encryption -- and for two authentication methods -- keyed MD5 and keyed SHA. Implementers may choose to support additional algorithms in either category.
The authentication algorithms are the same ones used in the IPsec authentication header.
We do not implement single DES since DES is insecure. Instead we provide triple DES or 3DES . This is currently the only encryption algorithm supported.
We do not implement null encryption since it is obviously insecure.
IPsec can connect in two modes. Transport mode is a host-to-host connection involving only two machines. In tunnel mode, the IPsec machines act as gateways and trafiic for any number of client machines may be carried.
Security gateways are required to support tunnel mode connections. In this mode the gateways provide tunnels for use by client machines behind the gateways. The client machines need not do any IPsec processing; all they have to do is route things to gateways.
Host machines (as opposed to security gateways) with IPsec implementations must also support transport mode. In this mode, the host does its own IPsec processing and routes some packets via IPsec.
KLIPS is KerneL IP SEC Support, the modifications necessary to support IPsec within the Linux kernel. KILPS does all the actual IPsec packet-handling, including
KLIPS also checks all non-IPsec packets to ensure they are not bypassing IPsec security policies.
Pluto(8) is a daemon which implements the IKE protocol. It
Pluto is controlled mainly by the ipsec.conf(5) configuration file.
The ipsec(8) command is a front end shellscript that allows control over IPsec activity.
The configuration file for Linux FreeS/WAN is
/etc/ipsec.conf
For details see the ipsec.conf(5) manual page .
There are several ways IPsec can manage keys. Not all are implemented in Linux FreeS/WAN.
IPsec allows keys to be manually set. In Linux FreeS/WAN, such keys are stored with the connection definitions in /etc/ipsec.conf.
Manual keying is useful for debugging since it allows you to test the KLIPS kernel IPsec code without the Pluto daemon doing key negotiation.
In general, however, automatic keying is preferred because it is more secure.
In automatic keying, the Pluto daemon negotiates keys using the IKE Internet Key Exchange protocol. Connections are automatically re-keyed periodically.
This is considerably more secure than manual keying. In either case an attacker who acquires a key can read every message encrypted with that key, but automatic keys can be changed every few hours or even every few minutes without breaking the connection or requiring intervention by the system administrators. Manual keys can only be changed manually; you need to shut down the connection and have the two admins make changes. Moreover, they have to communicate the new keys securely, perhaps with PGP or SSH . This may be possible in some cases, but as a general solution it is expensive, bothersome and unreliable. Far better to let Pluto handle these chores; no doubt the administrators have enough to do.
Also, automatic keying is inherently more secure against an attacker who manages to subvert your gateway system. If manual keying is in use and an adversary acquires root privilege on your gateway, he reads your keys from /etc/ipsec.conf and then reads all messages encrypted with those keys.
If automatic keying is used, an adversary with the same privileges can read /etc/ipsec.secrets, but this does not contain any keys, only the secrets used to authenticate key exchanges. Having an adversary able to authenticate your key exchanges need not worry you overmuch. Just having the secrets does not give him any keys. You are still secure against passive attacks. This property of automatic keying is called perfect forward secrecy, abbreviated PFS.
Unfortunately, having the secrets does allow an active attack, specifically a man-in-the-middle attack. Losing these secrets to an attacker may not be quite as disastrous as losing the actual keys, but it is still a serious security breach. These secrets should be guarded as carefully as keys.
It would be possible to exchange keys without authenticating the players. This would support opportunistic encryption -- allowing any two systems to encrypt their communications without requiring a shared PKI or a previously negotiated secret -- and would be secure against passive attacks. It would, however, be highly vulnerable to active man-in-the-middle attacks. RFC 2408 therefore specifies that all ISAKMP key management interactions must be authenticated.
There is room for debate here. Should we provide immediate security against passive attacks and encourage widespread use of encryption, at the expense of risking the more difficult active attacks? Or should we wait until we can implement a solution that can both be widespread and offer security against active attacks?
So far, we have chosen the second course, complying with the RFCs and waiting for secure DNS (see below) so that we can do opportunistic encryption right.
The IPsec RFCs allow key exchange based on authentication services provided by Secure DNS. Once Secure DNS service becomes widely available, we expect to make this the primary key management method for Linux FreeS/WAN. It is the best way we know of to support opportunistic encryption, allowing two systems without a common PKI or previous negotiation to secure their communication.
We currently have code to acquire RSA keys from DNS but do not yet have code to validate Secure DNS signatures.
The IPsec RFCs allow key exchange based on authentication services provided by a PKI or Public Key Infrastructure. With many vendors selling such products and many large organisations building these infrastructures, this will clearly be an important application of IPsec and one Linux FreeS/WAN will eventually support.
On the other hand, this is not as high a priority for Linux FreeS/WAN as solutions based on secure DNS. We do not expect any PKI to become as universal as DNS.
Some patches to handle authentication with X.509 certificates, which most PKIs use, are available.
Photuris is another key management protocol, an alternative to IKE and ISAKMP, described in RFCs 2522 and 2523 which are labelled "experimental". Adding Photuris support to Linux FreeS/WAN might be a good project for a volunteer. The likely starting point would be the OpenBSD photurisd code.
SKIP is yet another key management protocol, developed by Sun. At one point it was fairly widely used, but it now seems moribund, displaced by IKE. Sun now (as of Solaris 8.0) ship an IPsec implementation using IKE. We have no plans to implement SKIP. If a user were to implement it, we would almost certainly not want to add the code to our distribution.
The Linux FreeS/WAN project has several email lists for user support, bug reports and software development discussions.
We had a single list on clinet.fi for several years (Thanks, folks!), then one list on freeswan.org, but now we've split into several lists:
To subscribe to any of these, you can:
Archives of these lists are available via the web interface.
For most questions, please check the FAQ first, and if that does not have an answer, ask on the users list. "My configuration doesn't work." does not belong on the bugs list, and "Can FreeS/WAN do such-and-such" or "How do I configure it to..." do not belong in design discussions.
Cross-posting the same message to two or more of these lists is discouraged. Quite a few people read more than one list and getting multiple copies is annoying.
US citizens or residents are asked not to post code to the lists, not even one-line bug fixes. The project cannot accept code which might entangle it in US export restrictions .
Non-subscribers can post to some of these lists. This is necessary; someone working on a gateway install who encounters a problem may not have access to a subscribed account.
Some spam turns up on these lists from time to time. For discussion of why we do not attempt to filter it, see the FAQ. Please do not clutter the lists with complaints about this.
Searchable archives of the old single list have existed for some time. At time of writing, it is not yet clear how they will change for the new multi-list structure.
Note that these use different search engines. Try both.
Archives of the new lists are available via the web interface.
PAML is the standard reference for Publicly Accessible Mailing Lists. When we last checked, it had over 7500 lists on an amazing variety of topics. It also has FAQ information and a search engine.
There is an index of Linux mailing lists available.
A list of computer security mailing lists, with descriptions.
Most links in this section point to subscription addresses for the various lists. Send the one-line message "subscribe list_name " to subscribe to any of them.
Our introduction document gives a list of products that include FreeS/WAN. If you have, or are considering, one of those, check the supplier's web site for information on mailing lists for their users.
Each of the scure distribution projects also has its own web site and mailing list. Some of the sites are:
Each IETF working group has an associated mailing list where much of the work takes place.
The main project web site is www.freeswan.org.
Links to other project-related sites are provided in our introduction section.
Some user-contributed patches have been integrated into the FreeS/WAN distribution. For a variety of reasons, those listed below have not.
Note that not all patches are a good idea.
This is not to say that patches are necessarily bad, only that using them requires some deliberation. For example, there might be perfectly good reasons to add a specific cipher in your application: perhaps GOST to comply with government standards in Eastern Europe, or AES for performance benefits.
Patches believed current::
There is also one add-on that takes the form of a modified FreeS/WAN distribution, rather than just patches to the standard distribution:
Before using any of the above,, check the mailing lists for news of newer versions and to see whether they have been incorporated into more recent versions of FreeS/WAN.
These patches are for older versions of FreeS/WAN and will likely not work with the current version. Older versions of FreeS/WAN may be available on some of the distribution sites, but we recommend using the current release.
Finally, there are some patches to other code that may be useful with FreeS/WAN:
Note that this is not required if the same machine does IPsec and masquerading, only if you want a to locate your IPsec gateway on a masqueraded network. See our firewalls document for discussion of why this is problematic.
At last report, this patch could not co-exist with FreeS/WAN on the same machine.
The introductory section of our document set lists several Linux distributions which include FreeS/WAN.
There is a list of Linux VPN software in the Linux Security Knowledge Base.
Vendors using FreeS/WAN in turnkey firewall or VPN products are listed in our introduction.
Other vendors have Linux IPsec products which, as far as we know, do not use FreeS/WAN
All the major router vendors support IPsec, at least in some models.
Many firewall vendors offer IPsec, either as a standard part of their product, or an optional extra. A few we know about are:
Vendors using FreeS/WAN in turnkey firewall products are listed in our introduction.
All the major open source operating systems support IPsec. See below for details on BSD-derived Unix variants.
Among commercial OS vendors, IPsec players include:
Network cards with built-in IPsec acceleration are available from at least Intel, 3Com and Redcreek.
We like to think of FreeS/WAN as the Linux IPsec implementation, but it is not the only one. Others we know of are:
The IPsec protocols are designed so that different implementations should be able to work together. As they say "the devil is in the details". IPsec has a lot of details, but considerable success has been achieved.
Linux FreeS/WAN has been tested for interoperability with many other IPsec implementations. Results to date are in our interoperability section.
Various other sites have information on interoperability between various IPsec implementations:
Nearly any Linux documentation you are likely to want can be found at the Linux Documentation Project or LDP.
You may not need to go to the LDP to get this material. Most Linux distributions include the HowTos on their CDs and several include the Guides as well. Also, most of the Guides and some collections of HowTos are available in book form from various publishers.
Much of the LDP material is also available in languages other than English. See this LDP page.
The Linux IP stack has some new features in 2.4 kernels. Some HowTos have been written:
See also the LDP material above.
Our FreeS/WAN and firewalls document includes links to several sets of scripts known to work with FreeS/WAN.
Other information sources:
Two enormous collections of links, each the standard reference in its area:
See also the interesting papers section below.
There are several collections of cryptographic quotes on the net:
See also our documentation section on the history and politics of cryptography.
These papers emphasize important issues around the use of cryptography, and the design and management of secure systems.
Note: A fairly nasty bug exists in all commercial PGP versions from 5.5 through 6.5.3. If you have one of those, upgrade now.
David Wagner at Berkeley provides a set of links to home pages of cryptographers, cypherpunks and computer security people.
Entries are in alphabetical order. Some entries are only one line or one paragraph long. Others run to several paragraphs. I have tried to put the essential information in the first paragraph so you can skip the other paragraphs if that seems appropriate.
Other glossaries which overlap this one include:
Several Internet glossaries are available as RFCs:
More general glossary or dictionary information:
There are many more mirrors of this dictionary.
There are also many mirrors of this. See the home page for a list.
IPsec always does 3DES with three different keys, as required by RFC 2451. For an explanation of the two-key variant, see two key triple DES. Both use an EDE encrypt-decrypt-encrpyt sequence of operations.
Double DES is ineffective. Using two 56-bit keys, one might expect an attacker to have to do 2112 work to break it. In fact, only 257 work is required with a meet-in-the-middle attack, though a large amount of memory is also required. Triple DES is vulnerable to a similar attack, but that just reduces the work factor from the 2168 one might expect to 2 112. That provides adequate protection against brute force attacks, and no better attack is known.
3DES can be somewhat slow compared to other ciphers. It requires three DES encryptions per block. DES was designed for hardware implementation and includes some operations which are difficult in software. However, the speed we get is quite acceptable for many uses. See our performance document for details.
Fifteen proposals meeting NIST's basic criteria were submitted in 1998 and subjected to intense discussion and analysis, "round one" evaluation. In August 1999, NIST narrowed the field to five "round two" candidates:
Three of the five finalists -- Rijndael, Serpent and Twofish -- have completely open licenses.
In October 2000, NIST announced the winner -- Rijndael.
For more information, see:
AES will be added to a future release of Linux FreeS/WAN. Likely we will add all three of the finalists with good licenses. User-written AES patches are already available.
Adding AES may also require adding stronger hashes, SHA-256, SHA-384 and SHA-512.
Bruce Schneier extends these with many others such as Eve the Eavesdropper and Victor the Verifier. His extensions seem to be in the process of becoming standard as well. See page 23 of Applied Cryptography
Alice and Bob have an amusing biography on the web.
Outside IPsec, passwords are perhaps the most common authentication mechanism. Their function is essentially to authenticate the person's identity to the system. Passwords are generally only as secure as the network they travel over. If you send a cleartext password over a tapped phone line or over a network with a packet sniffer on it, the security provided by that password becomes zero. Sending an encrypted password is no better; the attacker merely records it and reuses it at his convenience. This is called a replay attack.
A common solution to this problem is a challenge-response system. This defeats simple eavesdropping and replay attacks. Of course an attacker might still try to break the cryptographic algorithm used, or the random number generator.
IPsec uses the Diffie-Hellman key exchange protocol to create keys. An authentication mechansim is required for this. FreeS/WAN normally uses RSA for this. Other methods supported are discussed in our advanced configuration document.
Having an attacker break the authentication is emphatically not a good idea. An attacker that breaks authentication, and manages to subvert some other network entities (DNS, routers or gateways), can use a man-in-the middle attack to break the security of your IPsec connections.
However, having an attacker break the authentication in automatic keying is not quite as bad as losing the key in manual keying.
That said, the secrets used for authentication, stored in ipsec.secrets(5), should still be protected as tightly as cryptographic keys.
For more detail, see our document on FreeS/WAN performance.
Resisting such attacks is part of the motivation for:
The second person has 1 chance in 365 (ignoring leap years) of matching the first. If they don't match, the third person's chances of matching one of them are 2/365. The 4th, 3/365, and so on. The total of these chances grows more quickly than one might guess.
DES is among the the best known and widely used block ciphers, but is now obsolete. Its 56-bit key size makes it highly insecure today. Triple DES is the default block cipher for Linux FreeS/WAN.
The current generation of block ciphers -- such as Blowfish, CAST-128 and IDEA -- all use 64-bit blocks and 128-bit keys. The next generation, AES, uses 128-bit blocks and supports key sizes up to 256 bits.
The Block Cipher Lounge web site has more information.
This is not required by the IPsec RFCs and not currently used in Linux FreeS/WAN.
Longer keys protect against brute force attacks. Each extra bit in the key doubles the number of possible keys and therefore doubles the work a brute force attack must do. A large enough key defeats any brute force attack.
For example, the EFF's DES Cracker searches a 56-bit key space in an average of a few days. Let us assume an attacker that can find a 64-bit key (256 times harder) by brute force search in a second (a few hundred thousand times faster). For a 96-bit key, that attacker needs 232 seconds, about 135 years. Against a 128-bit key, he needs 232 times that, over 500,000,000,000 years. Your data is then obviously secure against brute force attacks. Even if our estimate of the attacker's speed is off by a factor of a million, it still takes him over 500,000 years to crack a message.
This is why
Cautions:
Inadequate keylength always indicates a weak cipher but it
is important to note that adequate keylength does not necessarily
indicate a strong cipher. There are many attacks other than brute
force, and adequate keylength only guarantees resistance to
brute force. Any cipher, whatever its key size, will be weak if design
or implementation flaws allow other attacks.
Also, once you have adequate keylength (somewhere around 90 or 100 bits), adding more key bits make no practical difference , even against brute force. Consider our 128-bit example above that takes 500,000,000,000 years to break by brute force. We really don't care how many zeroes there are on the end of that, as long as the number remains ridiculously large. That is, we don't care exactly how large the key is as long as it is large enough.
There may be reasons of convenience in the design of the cipher to support larger keys. For example Blowfish allows up to 448 bits and RC4 up to 2048, but beyond 100-odd bits it makes no difference to practical security.
See Web of Trust for an alternate model.
This is not required by the IPsec RFCs and not currently used in Linux FreeS/WAN.
An initialisation vector (IV) must be provided. It is XORed into the first block before encryption. The IV need not be secret but should be different for each message and unpredictable.
FreeS/WAN policy group files accept CIDR blocks of the format address/[mask], where address may take the form name.domain.tld. An absent mask is assumed to be /32.
This is more secure than passwords against two simple attacks:
A challenge-response system never sends a password, either cleartext or encrypted. An attacker cannot record the response to one challenge and use it as a response to a later challenge. The random number is different each time.
Of course an attacker might still try to break the cryptographic algorithm used, or the random number generator.
Four standard modes were defined for DES in FIPS 81. They can actually be applied with any block cipher.
| ECB | Electronic CodeBook | encrypt each block independently | |
| CBC | Cipher Block Chaining
| XOR previous block ciphertext into new block plaintext before encrypting new block | |
| CFB | Cipher FeedBack | ||
| OFB | Output FeedBack |
IPsec uses CBC mode since this is only marginally slower than ECB and is more secure. In ECB mode the same plaintext always encrypts to the same ciphertext, unless the key is changed. In CBC mode, this does not occur.
Various other modes are also possible, but none of them are used in IPsec.
We generally use the term in the first sense. Vendors of Windows IPsec solutions often use it in the second. See this discussion.
Web references include this US government site and this global home page.
For current information, see their web site.
If the attacker puts bogus source information in the first packet, such that the second is never delivered, the responder may wait a long time for the third to come back. If responder has already allocated memory for the connection data structures, and if many of these bogus packets arrive, the responder may run out of memory.
The two example attacks discussed were both quite effective when first discovered, capable of crashing or disabling many operating systems. They were also well-publicised, and today far fewer systems are vulnerable to them.
DES is seriously insecure against current attacks.
Linux FreeS/WAN does not include DES, even though the RFCs specify it. We strongly recommend that single DES not be used.
This is not required by the IPsec RFCs and not currently used in Linux FreeS/WAN. DESX would be the easiest additional transform to add; there would be very little code to write. It would be much faster than 3DES and almost certainly more secure than DES. However, since it is not in the RFCs other IPsec implementations cannot be expected to have it.
The protocol is secure against all passive attacks , but it is not at all resistant to active man-in-the-middle attacks. If a third party can impersonate Bob to Alice and vice versa, then no useful secret can be created. Authentication of the participants is a prerequisite for safe Diffie-Hellman key exchange. IPsec can use any of several authentication mechanisims. Those supported by FreeS/WAN are discussed in our configuration section.
The Diffie-Hellman key exchange is based on the discrete logarithm problem and is secure unless someone finds an efficient solution to that problem.
Given a prime p and generator g (explained under discrete log below), Alice:
Meanwhile Bob:
Now Alice and Bob can both calculate the shared secret s = g^(ab). Alice knows a and B, so she calculates s = B^a. Bob knows A and b so he calculates s = A^b.
An eavesdropper will know p and g since these are made public, and can intercept A and B but, short of solving the discrete log problem, these do not let him or her discover the secret s.
Receiver:
If the public-key system is secure and the verification succeeds, then the receiver knows
Such an encrypted message digest can be treated as a signature since it cannot be created without both the document and the private key which only the sender should possess. The legal issues are complex, but several countries are moving in the direction of legal recognition for digital signatures.
The discrete log problem is the basis of several cryptographic systems, including the Diffie-Hellman key exchange used in the IKE protocol. The useful property is that exponentiation is relatively easy but the inverse operation, finding the logarithm, is hard. The cryptosystems are designed so that the user does only easy operations (exponentiation in the field) but an attacker must solve the hard problem (discrete log) to crack the system.
There are several variants of the problem for different types of field. The IKE/Oakley key determination protocol uses two variants, either over a field modulo a prime or over a field defined by an elliptic curve. We give an example modulo a prime below. For the elliptic curve version, consult an advanced text such as Handbook of Applied Cryptography.
Given a prime p, a generator g for the field modulo that prime, and a number x in the field, the problem is to find y such that g^y = x.
For example, let p = 13. The field is then the integers from 0 to 12. Any integer equals one of these modulo 13. That is, the remainder when any integer is divided by 13 must be one of these.
2 is a generator for this field. That is, the powers of two modulo 13 run through all the non-zero numbers in the field. Modulo 13 we have:
y x
2^0 == 1
2^1 == 2
2^2 == 4
2^3 == 8
2^4 == 3 that is, the remainder from 16/13 is 3
2^5 == 6 the remainder from 32/13 is 6
2^6 == 12 and so on
2^7 == 11
2^8 == 9
2^9 == 5
2^10 == 10
2^11 == 7
2^12 == 1
Exponentiation in such a field is not difficult. Given, say,
The discrete log problem is the reverse. In our example, given
Note, however, that no-one has proven such methods do not exist. If a solution to either variant were found, the security of any crypto system using that variant would be destroyed. This is one reason IKE supports two variants. If one is broken, we can switch to the other.
The sequence is:
For the two-key version, key1=key3.
The "advantage" of this EDE order of operations is that it makes it simple to interoperate with older devices offering only single DES. Set key1=key2=key3 and you have the worst of both worlds, the overhead of triple DES with the "security" of single DES. Since both the security of single DES and the overheads of triple DES are seriously inferior to many other ciphers, this is a spectacularly dubious "advantage".
Major variants include symmetric encryption in which sender and receiver use the same secret key and public key methods in which the sender uses one of a matched pair of keys and the receiver uses the other. Many current systems, including IPsec, are hybrids combining the two techniques.
For example, the Internet may route all traffic for a particular company to that firm's corporate gateway. It then becomes the company's problem to get packets to various machines on their subnets in various departments. They may decide to treat a branch office like a subnet, giving it IP addresses "on" their corporate net. This becomes an extruded subnet.
Packets bound for it are delivered to the corporate gateway, since as far as the outside world is concerned, that subnet is part of the corporate network. However, instead of going onto the corporate LAN (as they would for, say, the accounting department) they are then encapsulated and sent back onto the Internet for delivery to the branch office.
For information on doing this with Linux FreeS/WAN, look in our advanced configuration section.
"Free software" is a matter of liberty, not price. To understand the concept, you should think of "free speech", not "free beer.""Free software" refers to the users' freedom to run, copy, distribute, study, change and improve the software.
See also GNU, GNU General Public License, and the FSF site.
The exact techniques used in IPsec are defined in RFC 2104. They are referred to as HMAC-MD5-96 and HMAC-SHA-96 because they output only 96 bits of the hash. This makes some attacks on the hash functions harder.
IDEA is not required by the IPsec RFCs and not currently used in Linux FreeS/WAN.
IDEA is patented and, with strictly limited exceptions for personal use, using it requires a license from Ascom.
See this web site for more details, and our compatibility document for information on FreeS/WAN and the Linux implementation of IPv6.
This is the standard Linux FreeS/WAN is implementing. For more details, see our IPsec Overview. For the standards, see RFCs listed in our RFCs document.
Configuring for initiate-only opportunistic encryption is described in our quickstart document.
In the Linux release numbering system, an even second digit as in 2. 2.x indicates a stable or production kernel while an odd number as in 2.3.x indicates an experimental or development kernel. Most users should run a recent kernel version from the production series. The development kernels are primarily for people doing kernel development. Others should consider using development kernels only if they have an urgent need for some feature not yet available in production kernels.
Today Linux is a complete Unix replacement available for several CPU architectures -- Intel, DEC/Compaq Alpha, Power PC, both 32-bit SPARC and the 64-bit UltraSPARC, SrongARM, . . . -- with support for multiple CPUs on some architectures.
Linux FreeS/WAN is intended to run on all CPUs supported by Linux and is known to work on several. See our compatibility section for a list.
See our IPsec section for more detail. For the code see our primary site or one of the mirror sites on this list.
This allows multiple security projects to take different approaches to security enhancement without tying the kernel down to one particular approach. As I understand the history, several projects were pressing Linus to incorporate their changes, the various sets of changes were incompatible, and his answer was more-or-less "a plague on all your houses; I'll give you an interface, but I won't incorporate anything".
It seems to be working. There is a fairly active LSM mailing list, and several projects are already using the interface.
For example, if Alice and Bob are negotiating a key via the Diffie-Hellman key agreement, and are not using authentication to be certain they are talking to each other, then an attacker able to insert himself in the communication path can deceive both players.
Call the attacker Mallory. For Bob, he pretends to be Alice. For Alice, he pretends to be Bob. Two keys are then negotiated, Alice-to-Mallory and Bob-to-Mallory. Alice and Bob each think the key they have is Alice-to-Bob.
A message from Alice to Bob then goes to Mallory who decrypts it, reads it and/or saves a copy, re-encrypts using the Bob-to-Mallory key and sends it along to Bob. Bob decrypts successfully and sends a reply which Mallory decrypts, reads, re-encrypts and forwards to Alice.
To make this attack effective, Mallory must
If he manages it, however, it is devastating. He not only gets to read all the messages; he can alter messages, inject his own, forge anything he likes, . . . In fact, he controls the communication completely.
For example, a document labelled "secret, zebra" might be readable only by someone with secret clearance working on Project Zebra. Ideally, the system will prevent any transfer outside those boundaries. For example, even if you can read it, you should not be able to e-mail it (unless the recipient is appropriately cleared) or print it (unless certain printers are authorised for that classification).
Mandatory access control is a required feature for some levels of Rainbow Book or Common Criteria classification, but has not been widely used outside the military and government. There is a good discussion of the issues in Anderson's Security Engineering.
The Security Enhanced Linux project is adding mandatory access control to Linux.
MD5 is one of two message digest algorithms available in IPsec. The other is SHA. SHA produces a longer hash and is therefore more resistant to birthday attacks, but this is not a concern for IPsec. The HMAC method used in IPsec is secure even if the underlying hash is not particularly strong against this attack.
Hans Dobbertin found a weakness in MD5, and people often ask whether this means MD5 is unsafe for IPsec. It doesn't. The IPsec RFCs discuss Dobbertin's attack and conclude that it does not affect MD5 as used for HMAC in IPsec.
Double DES encryption and decryption can be written:
C = E(k2,E(k1,P))
P = D(k1,D(k2,C))
Where C is ciphertext, P is plaintext, E is encryption, D is decryption, k1 is one key, and k2 is the other key. If we know a P, C pair, we can try and find the keys with a brute force attack, trying all possible k1, k2 pairs. Since each key is 56 bits, there are 2 112 such pairs and this attack is painfully inefficient.
The meet-in-the middle attack re-writes the equations to calculate a middle value M:
M = E(k1,P)
M = D(k2,C)
Now we can try some large number of D(k2,C) decryptions with various values of k2 and store the results in a table. Then start doing E(k1,P) encryptions, checking each result to see if it is in the table.
With enough table space, this breaks double DES with
The memory requirements for such attacks can be prohibitive, but there is a whole body of research literature on methods of reducing them.
IP packets, which can be up to 64K bytes each, must be packaged into lower-level packets of the appropriate size for the underlying network(s) and re-assembled on the other end. When a packet must pass over multiple networks, each with its own MTU, and many of the MTUs are unknown to the sender, this becomes a fairly complex problem. See path MTU discovery for details.
Often the MTU is a few hundred bytes on serial links and 1500 on Ethernet. There are, however, serial link protocols which use a larger MTU to avoid fragmentation at the ethernet/serial boundary, and newer (especially gigabit) Ethernet networks sometimes support much larger packets because these are more efficient in some applications.
Almost invariably, the phrase "non-routable address" means one of the addresses reserved by RFC 1918 for private networks:
These addresses are commonly used on private networks, e.g. behind a Linux machines doing IP masquerade. Machines within the private network can address each other with these addresses. All packets going outside that network, however, have these addresses replaced before they reach the Internet.
If any packets using these addresses do leak out, they do not go far. Most routers automatically discard all such packets.
Various other addresses -- the 127.0.0.0/8 block reserved for local use, 0.0.0.0, various broadcast and network addresses -- cannot be routed over the Internet, but are not normally included in the meaning when the phrase "non-routable address" is used.
Some history of NSA documents were declassified in response to a FOIA (Freedom of Information Act) request.
Linux FreeS/WAN currently supports the three groups based on finite fields modulo a prime (Groups 1, 2 and 5) and does not support the elliptic curve groups (3 and 4). For a description of the difference of the types, see discrete logarithms.
Given those three conditions, it can easily be proved that the cipher is perfectly secure, in the sense that an attacker with intercepted message in hand has no better chance of guessing the message than an attacker who has not intercepted the message and only knows the message length. No such proof exists for any other cipher.
There are, however, several problems with this "perfect" cipher.
First, it is wildly impractical for most applications. Key management is at best difficult, often completely impossible.
Second, it is extremely fragile. Small changes which violate the conditions listed above do not just weaken the cipher liitle. Quite often they destroy its security completely.
Marketing claims about the "unbreakable" security of various products which somewhat resemble one-time pads are common. Such claims are one of the surest signs of cryptographic snake oil; most systems marketed with such claims are worthless.
Finally, even if the system is implemented and used correctly, it is highly vulnerable to a substitution attack. If an attacker knows some plaintext and has an intercepted message, he can discover the pad.
In general then, despite its theoretical perfection, the one-time-pad has very limited practical application.
See also the one time pad FAQ.
Setting up for opportunistic encryption is described in our quickstart document.
Configuring passive OE is described in our policy groups document.
Configuring passive OE is described in our policy groups document.
This is done as follows:
Since this requires co-operation of many systems, and since the next packet may travel a different path, this is one of the trickier areas of IP programming. Bugs that have shown up over the years have included:
Since IPsec adds a header, it increases packet size and may require fragmentation even where incoming and outgoing MTU are equal.
then the system has PFS. The attacker needs the short-term keys in order to read the trafiic and merely having the long-term key does not allow him to infer those. Of course, it may allow him to conduct another attack (such as man-in-the-middle) which gives him some short-term keys, but he does not automatically get them just by acquiring the long-term key.
See also Phil Karn's definition.
The 2.xx versions of PGP used the RSA public key algorithm and used IDEA as the symmetric cipher. These versions are described in RFC 1991 and in Garfinkel's book. Since version 5, the products from PGP Inc. have used Diffie-Hellman public key methods and CAST-128 symmetric encryption. These can verify signatures from the 2.xx versions, but cannot exchange encryted messages with them.
An IETF working group has issued RFC 2440 for an "Open PGP" standard, similar to the 5.x versions. PGP Inc. staff were among the authors. A free Gnu Privacy Guard based on that standard is now available.
For more information on PGP, including how to obtain it, see our cryptography links.
Versions 6.5 and later of the PGP product include PGPnet, an IPsec client for Macintosh or for Windows 95/98/NT. See our interoperation document.
There are several PKI products on the market. Typically they use a hierarchy of Certification Authorities (CAs). Often they use LDAP access to X.509 directories to implement this.
See Web of Trust for a different sort of infrastructure.
This is required, for example, when users of a corporate PKI need to communicate with people at client, supplier or government organisations, any of which may have a different PKI in place. I should be able to talk to you securely whenever:
At time of writing (March 1999), this is not yet widely implemented but is under quite active development by several groups.
One half of each pair, called the public key, is made public. The other half, called the private key, is kept secret. Messages can then be sent by anyone who knows the public key to the holder of the private key. Encrypt with the public key and you know that only someone with the matching private key can decrypt.
Public key techniques can be used to create digital signatures and to deal with key management issues, perhaps the hardest part of effective deployment of symmetric ciphers. The resulting hybrid cryptosystems use public key methods to manage keys for symmetric ciphers.
Many organisations are currently creating PKIs, public key infrastructures to make these benefits widely available.
See this reference page.
The Rainbow books are now mainly obsolete, replaced by the international Common Criteria standards.
See RFC 1750 for the theory.
See the manual pages for ipsec_ranbits(8) and ipsec_prng(3) for more on FreeS/WAN's use of randomness. Both depend on the random(4) device driver..
A couple of years ago, there was extensive mailing list discussion (archived here )of Linux /dev/random and FreeS/WAN. Since then, the design of the random(4) driver has changed considerably. Linux 2.4 kernels have the new driver..
Our list of IPsec and other security-related RFCs is here, along with information on methods of obtaining them.
There are also several classes of non-routable IP addresses.
RSA can be used to provide either encryption or digital signatures. In IPsec, it is used only for signatures. These provide gateway-to-gateway authentication for IKE negotiations.
For a full explanation of the algorithm, consult one of the standard references such as Applied Cryptography. A simple explanation is:
The great 17th century French mathematician Fermat proved that,
for any prime p and number x, 0 <= x < p:
x^p == x modulo p
x^(p-1) == 1 modulo p, non-zero x
From this it follows that if we have a pair of primes p, q and two numbers e, d such that:
ed == 1 modulo lcm( p-1, q-1)
where lcm() is least common multiple, then
x^ed == x modulo pq
So we construct such as set of numbers p, q, e, d and publish the product N=pq and e as the public key. Using c for ciphertext and i for the input plaintext, encryption is then:
c = i^e modulo N
An attacker cannot deduce i from the cyphertext c, short of either factoring N or solving the discrete logarithm problem for this field. If p, q are large primes (hundreds or thousands of bits) no efficient solution to either problem is known.
The receiver, knowing the private key (N and d), can readily recover the plaintext p since:
c^d == (i^e)^d modulo N
== i^ed modulo N
== i modulo N
This gives an effective public key technique, with only a couple of problems. It uses a good deal of computer time, since calculations with large integers are not cheap, and there is no proof it is necessarily secure since no-one has proven either factoring or discrete log cannot be done efficiently. Quite a few good mathematicians have tried both problems, and no-one has announced success, but there is no proof they are insoluble.
An SA is defined by three things -- the destination, the protocol ( AH orESP) and the SPI, security parameters index. It is used as an index to look up other things such as session keys and intialisation vectors.
For more detail, see our section on IPsec and/or RFC 2401.
According to their web pages, this work will include extending mandatory access controls to IPsec tunnels.
Recent versions of SE Linux code use the Linux Security Module interface.
IPsec can use this plus Diffie-Hellman key exchange to bootstrap itself. This allows opportunistic encryption. Any pair of machines which can authenticate each other via DNS can communicate securely, without either a pre-existing shared secret or a shared PKI.
For automatic keying mode, the IPsec RFCs require that the sender generate sequence numbers for each packet, but leave it optional whether the receiver does anything with them.
SHA is one of two message digest algorithms available in IPsec. The other is MD5. Some people do not trust SHA because it was developed by the NSA. There is, as far as we know, no cryptographic evidence that SHA is untrustworthy, but this does not prevent that view from being strongly held.
The NSA made one small change after the release of the original SHA. They did not give reasons. Iit may be a defense against some attack they found and do not wish to disclose. Technically the modified algorithm should be called SHA-1, but since it has replaced the original algorithm in nearly all applications, it is generally just referred to as SHA..
For more detail, see our IPsec section and/or RFC 2401.
For more information on SSH, including how to obtain it, see our cryptography links.
IPsec does not use stream ciphers. Their main application is link-level encryption, for example of voice, video or data streams on a wire or a radio signal.
The '24' is shorthand for a mask with the top 24 bits one and the rest zero. This is exactly the same as 255.255.255.0 which has three all-ones bytes and one all-zeros byte.
These indicate that, for this range of addresses, the top 24 bits are to be treated as naming a network (often referred to as "the 101.101.101.0/24 subnet") while most combinations of the low 8 bits can be used to designate machines on that network. Two addresses are reserved; 101.101.101.0 refers to the subnet rather than a specific machine while 101.101.101.255 is a broadcast address. 1 to 254 are available for machines.
It is common to find subnets arranged in a hierarchy. For example, a large company might have a /16 subnet and allocate /24 subnets within that to departments. An ISP might have a large subnet and allocate /26 subnets (64 addresses, 62 usable) to business customers and /29 subnets (8 addresses, 6 usable) to residential clients.
Symmetric cryptography contrasts with public key or asymmetric systems where the two players use different keys.
The great difficulty in symmetric cryptography is, of course, key management. Sender and receiver must have identical keys and those keys must be kept secret from everyone else. Not too much of a problem if only two people are involved and they can conveniently meet privately or employ a trusted courier. Quite a problem, though, in other circumstances.
It gets much worse if there are many people. An application might be written to use only one key for communication among 100 people, for example, but there would be serious problems. Do you actually trust all of them that much? Do they trust each other that much? Should they? What is at risk if that key is compromised? How are you going to distribute that key to everyone without risking its secrecy? What do you do when one of them leaves the company? Will you even know?
On the other hand, if you need unique keys for every possible connection between a group of 100, then each user must have 99 keys. You need either 99*100/2 = 4950 secure key exchanges between users or a central authority that securely distributes 100 key packets, each with a different set of 99 keys.
Either of these is possible, though tricky, for 100 users. Either becomes an administrative nightmare for larger numbers. Moreover, keys must be changed regularly, so the problem of key distribution comes up again and again. If you use the same key for many messages then an attacker has more text to work with in an attempt to crack that key. Moreover, one successful crack will give him or her the text of all those messages.
In short, the hardest part of conventional cryptography is key management. Today the standard solution is to build a hybrid system using public key techniques to manage keys.
In an industrial espionage situation, one might deduce something interesting just by knowing that company A and company B were talking, especially if one were able to tell which departments were involved, or if one already knew that A was looking for acquisitions and B was seeking funds for expansion.
In general, traffic analysis by itself is not very useful. However, in the context of a larger intelligence effort where quite a bit is already known, it can be very useful. When you are solving a complex puzzle, every little bit helps.
IPsec itself does not defend against traffic analysis, but carefully thought out systems using IPsec can provide at least partial protection. In particular, one might want to encrypt more traffic than was strictly necessary, route things in odd ways, or even encrypt dummy packets, to confuse the analyst. We discuss this here.
3DES with three keys has 3*56 = 168 bits of key but has only 112-bit strength against a meet-in-the-middle attack, so it is possible that the two key version is just as strong. Last I looked, this was an open question in the research literature.
RFC 2451 defines triple DES for IPsec as the three-key variant. The two-key variant should not be used and is not implemented directly in Linux FreeS/WAN. It cannot be used in automatically keyed mode without major fiddles in the source code. For manually keyed connections, you could make Linux FreeS/WAN talk to a two-key implementation by setting two keys the same in /etc/ipsec.conf.
IPsec is not the only technique available for building VPNs, but it is the only method defined by RFCs and supported by many vendors. VPNs are by no means the only thing you can do with IPsec, but they may be the most important application for many users.
See Global Trust Register for an interesting addition to the web of trust.
Critics refer to WEP as "Wiretap Equivalent Privacy", and consider it a horribly flawed design based on bogus "requirements". You do not control radio waves as you might control your wires, so the metaphor in the rationale is utterly inapplicable. A security policy that chooses not to invest resources in protecting against certain attacks which can only be conducted by people physically plugged into your LAN may or may not be reasonable. The same policy is completely unreasonable when someone can "plug in" from a laptop half a block away..
There has been considerable analysis indicating that WEP is seriously flawed. A FAQ on attacks against WEP is available. Part of it reads:
... attacks are practical to mount using only inexpensive off-the-shelf equipment. We recommend that anyone using an 802.11 wireless network not rely on WEP for security, and employ other security measures to protect their wireless network. Note that our attacks apply to both 40-bit and the so-called 128-bit versions of WEP equally well.
WEP appears to be yet another instance of governments, and unfortunately some vendors and standards bodies, deliberately promoting hopelessly flawed "security" products, apparently mainly for the benefit of eavesdropping agencies. See this discussion .
Use of X.509 services, via the LDAP protocol, for certification of keys is allowed but not required by the IPsec RFCs. It is not yet implemented in Linux FreeS/WAN.
For extensive bibliographic links, see the Collection of Computer Science Bibliographies
See our web links for material available online.
An overview, mainly concentrating on policy and strategic issues rather than the technical details. Both authors work for PKI vendor Entrust.
The standard reference on the Domain Name Service and Berkeley Internet Name Daemon.
Easily the best book for the security professional I have seen. Highly recommended. See the book web page.
This is quite readable, but Schneier's Secrets and Lies might be an easier introduction.
The sequel.
This book has a short section on FreeS/WAN and includes Caldera Linux on CD.
A fine book on firewalls in particular and security in general from two of AT&T's system adminstrators.
Bellovin has also done a number of papers on IPsec and co-authored a paper on a large FreeS/WAN application.
If you need to deal with the details of the network protocols, read either this series or the Stevens and Wright series before you start reading the RFCs.
To conclusively demonstrate that DES is inadequate for continued use, the EFF built a machine for just over $200,000 that breaks DES encryption in under five days on average, under nine in the worst case.
The book provides details of their design and, perhaps even more important, discusses why they felt the project was necessary. Recommended for anyone interested in any of the three topics mentioned in the subtitle.
See also the EFF page on this project and our discussion of DES insecurity.
SATAN is a Security Administrator's Tool for Analysing Networks. This book is a tutorial in its use.
A thoughtful and rather scary book.
An excellent introduction and user manual for the PGP email-encryption package. PGP is a good package with a complex and poorly-designed user interface. This book or one like it is a must for anyone who has to use it at length.
The book covers using PGP in Unix, PC and Macintosh environments, plus considerable background material on both the technical and political issues around cryptography.
The book is now seriously out of date. It does not cover recent developments such as commercial versions since PGP 5, the Open PGP standard or GNU PG..
A standard reference.
Spafford's web page has an excellent collection of crypto and security links.
A history of codes and code-breaking from ancient Egypt to the 20th century. Well-written and exhaustively researched. Highly recommended, even though it does not have much on computer cryptography.
Now becoming somewhat dated in places, but still a good introductory book and general reference.
This has had a number of favorable reviews, including this one on Slashdot. The book has a web site.
Highly recommended. A fine history of recent (about 1970-2000) developments in the field, and the related political controversies. FreeS/WAN project founder and leader John Gilmore appears several times.
The book does not cover IPsec or FreeS/WAN, but this project is very much another battle in the same war. See our discussion of the politics.
From their web page:
This book is a register of the fingerprints of the world's most important public keys; it implements a top-level certification authority (CA) using paper and ink rather than in an electronic system.
An excellent reference. Read Schneier before tackling this.
Probably the funniest technical book ever written, this is a vicious but well-reasoned attack on the OSI "seven layer model" and all that went with it. Several chapters of it are also available as RFCs 871 to 875.
The best general treatment of computer-mediated communication we have seen. It naturally has much to say about the Internet, but also covers UUCP, Fidonet and so on.
SANS is a respected organisation, this guide is part of a well-known series, and Ranch has previously written the useful Trinity OS guide to securing Linux, so my guess would be this is a pretty good book. I haven't read it yet, so I'm not certain. It can be ordered online from SANS.
Note (Mar 1, 2002): a new edition with different editors in the works. Expect it this year.
A standard reference on computer cryptography. For more recent essays, see the author's company's web site.
An interesting discussion of security and privacy issues, written with more of an "executive overview" approach rather than a narrow focus on the technical issues. Highly recommended.
This is worth reading even if you already understand security issues, or think you do. To go deeper, follow it with Anderson's Security Engineering.
This is the only O'Reilly book, out of a dozen I own, that I'm disappointed with. It deals mainly with building VPNs with various proprietary tools -- PPTP, SSH, Cisco PIX, ... -- and touches only lightly on IPsec-based approaches.
That said, it appears to deal competently with what it does cover and it has readable explanations of many basic VPN and security concepts. It may be exactly what some readers require, even if I find the emphasis unfortunate.
Available online from Security Portal. It has fairly extensive coverage of IPsec.
See the book's home page
A novel in which cryptography and the net figure prominently. Highly recommended: I liked it enough I immediately went out and bought all the author's other books.
There is also a paperback edition. Sequels are expected.
If you need to deal with the details of the network protocols, read either this series or the Comer series before you start reading the RFCs.
A good book, with detailed coverage of ipchains(8) firewalls and of many related issues.
The Linux FreeS/WAN distribution is available from our primary distribution site and various mirror sites. To give people more control over their downloads, the RFCs that define IP security are bundled separately in the file RFCs.tar.gz.
The file you are reading is included in the main distribution and is available on the web site. It describes the RFCs included in the RFCs.tar.gz bundle and gives some pointers to other ways to get them.
RFCs are downloadble at many places around the net such as:
browsable in HTML form at others such as:
and some of them are available in translation:
There is also a published Big Book of IPSEC RFCs.
Internet Drafts, working documents which sometimes evolve into RFCs, are also available.
Note: some of these may be obsolete, replaced by later drafts or by RFCs.
Some things used by IPsec, such as DES and SHA, are defined by US government standards called FIPS. The issuing organisation, NIST, have a FIPS home page.
All filenames are of the form rfc*.txt, with the * replaced with the RFC number.
RFC# Title
2401 Security Architecture for the Internet Protocol 2411 IP Security Document Roadmap
2402 IP Authentication Header 2406 IP Encapsulating Security Payload (ESP)
2367 PF_KEY Key Management API, Version 2 2407 The Internet IP Security Domain of Interpretation for ISAKMP 2408 Internet Security Association and Key Management Protocol (ISAKMP) 2409 The Internet Key Exchange (IKE) 2412 The OAKLEY Key Determination Protocol 2528 Internet X.509 Public Key Infrastructure
2085 HMAC-MD5 IP Authentication with Replay Prevention 2104 HMAC: Keyed-Hashing for Message Authentication 2202 Test Cases for HMAC-MD5 and HMAC-SHA-1 2207 RSVP Extensions for IPSEC Data Flows 2403 The Use of HMAC-MD5-96 within ESP and AH 2404 The Use of HMAC-SHA-1-96 within ESP and AH 2405 The ESP DES-CBC Cipher Algorithm With Explicit IV 2410 The NULL Encryption Algorithm and Its Use With IPsec 2451 The ESP CBC-Mode Cipher Algorithms 2521 ICMP Security Failures Messages
1321 The MD5 Message-Digest Algorithm 1828 IP Authentication using Keyed MD5 1829 The ESP DES-CBC Transform 1851 The ESP Triple DES Transform 1852 IP Authentication using Keyed SHA
2137 Secure Domain Name System Dynamic Update 2230 Key Exchange Delegation Record for the DNS 2535 Domain Name System Security Extensions 2536 DSA KEYs and SIGs in the Domain Name System (DNS) 2537 RSA/MD5 KEYs and SIGs in the Domain Name System (DNS) 2538 Storing Certificates in the Domain Name System (DNS) 2539 Storage of Diffie-Hellman Keys in the Domain Name System (DNS)
2521 ICMP Security Failures Messages 2522 Photuris: Session-Key Management Protocol 2523 Photuris: Extended Schemes and Attributes
1750 Randomness Recommendations for Security 1918 Address Allocation for Private Internets 1984 IAB and IESG Statement on Cryptographic Technology and the Internet 2144 The CAST-128 Encryption Algorithm
This file is a guide to the locations of files within the FreeS/WAN distribution. Everything described here should be on your system once you download, gunzip, and untar the distribution.
This distribution contains two major subsystems
plus assorted odds and ends.
The top directory has essential information in text files:
The doc directory contains the bulk of the documentation, most of it in HTML format. See the index file for details.
KLIPS is KerneL IP Security. It lives in the klips directory, of course.
The "make insert" step of installation installs the patches and makes a symbolic link from the kernel tree to klips/net/ipsec. The odd name of klips/net/ipsec is dictated by some annoying limitations of the scripts which build the Linux kernel. The symbolic-link business is a bit messy, but all the alternatives are worse.
These are all normally invoked by ipsec(8) with commands such as
ipsec tncfg argumentsThere are section 8 man pages for all of these; the names have "ipsec_" as a prefix, so your man command should be something like:
man 8 ipsec_tncfg
Pluto is our key management and negotiation daemon. It lives in the pluto directory, along with its low-level user utility, whack.
There are no subdirectories. Documentation is a man page, pluto.8. This covers whack as well.
The utils directory contains a growing collection of higher-level user utilities, the commands that administer and control the software. Most of the things that you will actually have to run yourself are in there.
ipsec(8) is normally the only program installed in a standard directory, /usr/sbin. It is used to invoke the others, both those listed below and the ones in klips/utils mentioned above.
There are .8 manual pages for these. look is covered in barf.8. The man pages have an "ipsec_" prefix so your man command should be something like:
man 8 ipsec_auto
Examples are in various files with names utils/*.eg
The lib directory is the FreeS/WAN library, also steadily growing,
used by both user-level and kernel code.
It includes section 3 man pages for
the library routines.
Note that this library has its own license, different from the GPL used for other code in FreeS/WAN.
The library includes its own documentation.
Older versions (up to 1.7) of FreeS/WAN included a copy of this library in the FreeS/WAN distribution.
Since 1.8, we have begun to rely on the system copy of GMP.
User mode linux is a way to compile a linux kernel such that it can run as a process in another linux system (potentially as a *BSD or Windows process later). See http://user-mode-linux.sourceforge.net/
UML is a good platform for testing and experimenting with FreeS/WAN. It allows several network nodes to be simulated on a single machine. Creating, configuring, installing, monitoring, and controling these nodes is generally easier and easier to script with UML than real hardware.
You'll need about 500Mb of disk space for a full sunrise-east-west-sunset setup. You can possibly get this down by 130Mb if you remove the sunrise/sunset kernel build. If you just want to run, then you can even remove the east/west kernel build.
Nothing need be done as super user. In a couple of steps, we note where super user is required to install commands in system-wide directories, but ~/bin could be used instead. UML seems to use a system-wide /tmp/uml directory so different users may interfere with one another. Later UMLs use ~/.uml instead, so multiple users running UML tests should not be a problem, but note that a single user running the UML tests will only be able run one set. Further, UMLs sometimes get stuck and hang around. These "zombies" (most will actually be in the "T" state in the process table) will interfere with subsequent tests.
As of 2003/3/1, the Light-Weight Resolver is used by pluto. This requires that BIND9 be running. It also requires that BIND9 development libraries be present in the build environment. The DNSSEC code is only truly functional in BIND9 snapshots. The library code could be 9.2.2, we believe. We are using BIND9 20021115 snapshot code from ftp://ftp.isc.org/isc/bind9/snapshots.
FreeS/WAN may well require a newer BIND than is on your system. Many distributions have moved to BIND9.2.2 recently due to a security advisory. BIND is five components.
The only piece that we need for *building* is #4. That's the only part that has to be on the build host. What is the difference between resolver and util libs? If you want to edit testing/baseconfigs/all/etc/bind, you'll need a snapshot version. The resolver library contains the resolver. FreeS/WAN has its own copy of that in lib/liblwres.
cd /c2/kernel
tar xzvf ../download/pub/linux/kernel/v2.4/linux-2.4.19.tar.gz
mkdir -p /c2/user-mode-linux/basic-root
cd /c2/user-mode-linux/basic-root
tar xzvf ../download/umlfreeroot-15.1.tar.gz
mkdir -p /c2/freeswan/sandbox
cd /c2/freeswan/sandbox
tar xzvf ../download/snapshot.tar.gz
./configure
make
./configure
make
# Need to be superuser to install in system directories.
# Installing in ~/bin would be an alternative.
su -c "make install"
cd tools
make all
# Need to be superuser to install in system directories.
# Installing in ~/bin would be an alternative.
su -c "make install BIN_DIR=/usr/bin"
cd /c2/freeswan/sandbox/freeswan-1.97/testing/utils cp
umlsetup-sample.sh ../../umlsetup.sh cd $TESTINGROOT/utils
sh make-uml.sh
It will grind for awhile. If there are errors it will bail. If so, run
it under "script" and send the output to bugs@lists.freeswan.org. for i in sunrise sunset east west
do
xterm -name $i -title $i -e $POOLSPACE/$i/start.sh & done
With User-Mode-Linux, you can debug the kernel using GDB. See http://user-mode-linux.sourceforge.net/debugging.html.
Typically, one will want to address a test case for a failing situation. Running GDB from Emacs, or from other front ends is possible. First start GDB.
Tell it to open the UMLPOOL/swan/linux program.
Note the PID of GDB:
marajade-[projects/freeswan/mgmt/planning] mcr 1029 %ps ax | grep gdb 1659 pts/9 SN 0:00 /usr/bin/gdb -fullname -cd /mara4/freeswan/kernpatch/UMLPOOL/swan/ linux
Set the following in the environment:
UML_east_OPT="debug gdb-pid=1659"
Then start the user-mode-linux in the test scheme you wish:
marajade-[kernpatch/testing/klips/east-icmp-02] mcr 1220 %../../utils/runme.shThe user-mode-linux will stop on boot, giving you a chance to attach to the process:
(gdb) file linux Reading symbols from linux...done. (gdb) attach 1 Attaching to program: /mara4/freeswan/kernpatch/UMLPOOL/swan/linux, process 1 0xa0118bc1 in kill () at hostfs_kern.c:770
At this point, break points should be created as appropriate.
If you are running a standard test, after all the packets are sent, the UML will be shutdown. This can cause problems, because the UML may get terminated while you are debugging.
The environment variable NETJIGWAITUSER can be set to
"waituser". If so, then the testing system will prompt before exiting
the test.
The environment variable UML_GETTY if set, will cause
each UML to spawn a getty on /dev/tty1, and will wait for it to exit
before continuing.
uml_netjig can be compiled with a built-in tcpdump. This uses
not-yet-released code from
www.tcpdump.org. Please see the instructions in
testing/utils/uml_netjig/Makefile.
"make check" is a target in the top level makefile. It takes care of running a number of unit and system tests to confirm that FreeSWAN has been compiled correctly, and that no new bugs have been introduced.
As FreeSWAN contains both kernel and userspace components, doing testing of FreeSWAN requires that the kernel be simulated. This is typically difficult to do as a kernel requires that it be run on bare hardware. A technology has emerged that makes this simpler. This is User Mode Linux.
User-Mode Linux is a way to build a Linux kernel such that it can run as a process under another Linux (or in the future other) kernel. Presently, this can only be done for 2.4 guest kernels. The host kernel can be 2.2 or 2.4.
"make check" expects to be able to build User-Mode Linux kernels with FreeSWAN included. To do this it needs to have some files downloaded and extracted prior to running "make check". This is described in the UML testing document.
After having run the example in the UML testing document and successfully brought up the four machine combination, you are ready to use "make check"
"make check" works by walking the FreeSWAN source tree invoking the
"check" target at each node. At present there are tests defined only
for the klips directory. These tests will use the UML
infrastructure to test out pieces of the klips code.
The results of the tests can be recorded. If the environment
variable $REGRESSRESULTS is non-null, then the results of
each test will be recorded. This can be used as part of a nightly
regression testing system, see Nightly testing
for more details.
"make check" otherwise prints a minimal amount of output for each test, and indicates pass/fail status of each test as they are run. Failed tests do not cause failure of the target in the form of exit codes.
Each test consists of a set of directories under testing/
. There are directories for klips, pluto,
packaging and libraries. Each directory has a list
of tests to run is stored in a file called TESTLIST in
that directory. e.g. testing/klips/TESTLIST.
This isn't actually a shell script. It just looks like one. Some tools other than /bin/sh process it. Lines that start with # are comments.
# test-kind directory-containing-test expectation [PR#]
The first word provides the test type, detailed below.
The second word is the name of the test to run. This the directory in which the test case is to be found..
The third word may be one of:
The fourth word may be a number, which is a PR# if the test is failing.
Each test directory has a file in it called testparams.sh
. This file sets a number of environment variables to define the
parameters of the test.
klips/test/fixups) to apply
to sanitize the console output of the machine under test. These are
typically perl, awk or sed scripts that remove things in the kernel
output that change each time the test is run and/or compiled.a file of commands that is fed into the virtual machine's console in single user mode prior to starting the tests. This file will usually set up any eroute's and SADB entries that are required for the test.
Lines beginning with # are skipped. Blank lines are skipped.
Otherwise, a shell prompted is waited for each time (consisting of
\n#) and then the command is sent. Note that the prompt is waited
for before the command and not after, so completion of the last command
in the script is not required. This is often used to invoke a program
to monitor the system, e.g. ipsec pf_key.
a file of commands that is fed into the virtual machine's console in single user mode, before the packets are sent. On single machine tests, this script doesn't provide any more power than INIT_SCRIPT, but is implemented for consistency's sake.
a file of commands that is fed into the virtual machine's console in single user mode after the final packet is sent. Similar to INIT_SCRIPT, above. If not specified, then the single command "halt" is sent. If specified, then the script should end with a halt command to nicely shutdown the UML.
uml_netjig will be printed to stderr during the test. In
addition, the jig will be invoked with --debug, which causes it to log
its process ID, and wait 60 seconds before continuing. This can be used
if you are trying to debug the uml_netjig program itself. The klipstest function starts a program (
testing/utils/uml_netjig/uml_netjig) to setup a bunch of I/O
sockets (that simulate network interfaces). It then exports the
references to these sockets to the environment and invokes (using
system()) a given script. It waits for the script to finish.
The script invoked (testing/utils/host-test.tcl) is a
TCL expect script that arranges
to start the UML and configure it appropriately for the test. The
configuration is done with the script given above for INIT_SCRIPT
. The TCL script then forks, leaves the UML in the background and exits.
uml_netjig continues. It then starts listening to the simulated network
answering ARPs and inserting packets as appropriate.
The klipstest function invokes uml_netjig with
arguments to capture output from network interface(s) and insert
packets as appropriate:
uml_netjig. The klipstest function then uses
tcpdump on the file to produce text output, which is compared to the
file given.uml_netjig. It should contain
"--exitonempty" of uml_netjig should exit when all of the input (
PUBINPUT,PRIVINPUT) packets have been injected.uml_netjig. It should contain "--arpreply"
if uml_netjig should reply to ARP requests. One will
typically set this to avoid having to fudge the ARP cache manually. The basic concept of the mkinsttest test type is that
it performs a "make install" to a temporary $DESTDIR. The resulting
tree can then be examined to determine if it was done properly. The
files can be uninstalled to determine if the file list was correct, or
the contents of files can be examined more precisely.
find $ROOT ( -type f -or -type -l ) will be
done to get a list of a real files and symlinks. The resulting file
will be compared to the file listed by this option.reffile samplefileone record per line. A diff between the provided reference file, and the sample file (located in the temporary installation root) will be done for each record.
The rpm_build_install_test type is to verify that the
proper packing list is produced by "make rpm", and that the mechanisms
for building the kernel modules produce consistent results.
The libtest test is for testing library routines. The library file
is expected to provided an #ifdef by the name of
library
. The libtest type invokes the C compiler to compile this
file, links it against libfreeswan.a (to resolve any other
dependancies) and runs the test with the -r argument to
invoke a regression test.
The library test case is expected to do a self-test, exiting with status code 0 if everything is okay, and with non-zero otherwise. A core dump (exit code greater than 128) is noted specifically.
Unlike other tests, there are no subdirectories required, or other parameters to set.
The umlplutotest function starts a pair of user mode line processes. This is a 2-host version of umlXhost. The "EAST" and "WEST" slots are defined.
The umlXtest function starts an arbitrary number of user mode line processes.
The script invoked (testing/utils/Xhost-test.tcl) is a
TCL expect script that arranges
to start each UML and configure it appropriately for the test. It then
starts listening (using uml_netjig) to the simulated network answering
ARPs and inserting packets as appropriate.
umlXtest has a series of slots, each of which should be filled by a host. The list of slots is controlled by the variable, XHOST_LIST. This variable should be set to a space seperated list of slots. The former umlplutotest is now implemented as a variation of the umlXhost test, with XHOST_LIST="EAST WEST".
For each host slot that is defined, a series of variables should be filled in, defining what configuration scripts to use for that host.
The following are used to control the console input and output to the system. Where the string ${host} is present, the host slot should be filled in. I.e. for the two host system with XHOST_LIST="EAST WEST", then the variables: EAST_INIT_SCRIPT and WEST_INIT_SCRIPT will exist.
a file of commands that is fed into the virtual machine's console in single user mode prior to starting the tests. This file will usually set up any eroute's and SADB entries that are required for the test. Similar to INIT_SCRIPT, above.
a file of commands that is fed into the virtual machine's console in single user mode, before the packets are sent. This set of commands is run after all of the virtual machines are initialized. I.e. after EAST_INIT_SCRIPT AND WEST_INIT_SCRIPT. This script can therefore do things that require that all machines are properly configured.
a file of commands that is fed into the virtual machine's console in single user mode, after the packets are sent. This set of commands is run before any of the virtual machines have been shut down. (I.e. before EAST_FINAL_SCRIPT AND WEST_FINAL_SCRIPT.) This script can therefore catch post-activity status reports.
a file of commands that is fed into the virtual machine's console in single user mode after the final packet is sent. Similar to INIT_SCRIPT, above. If not specified, then the single command "halt" is sent. Note that when this script is run, the other virtual machines may already have been killed. If specified, then the script should end with a halt command to nicely shutdown the UML.
Some additional flags apply to all hosts:
klips/test/fixups) to apply
to sanitize the console output of the machine under test. These are
typically perl, awk or sed scripts that remove things in the kernel
output that change each time the test is run and/or compiled.In addition to input to the console, the networks may have input fed to them:
There are two additional environment variables that may be set on the command line:
The kernel_patch_test function takes some kernel source, copies it with lndir, and then applies the patch as produced by "make kernelpatch".
The following are used to control the input and output to the system:
The module_compile test attempts to build the KLIPS module against a given set of kernel source. This is also done by the RPM tests, but in a very specific manner.
There are two variations of this test - one where the kernel either doesn't need to be configured, or is already done, and tests were there is a local configuration file.
Where the kernel doesn't need to be configured, the kernel source that is found is simply used. It may be a RedHat-style kernel, where one can cause it to configure itself via rhconfig.h-style definitions. Or, it may just be a kernel tree that has been configured.
If the variable KERNEL_CONFIG_FILE is set, then a new directory is created for the kernel source. It is populated with lndir(1). The referenced file is then copied in as .config, and "make oldconfig" is used to configure the kernel. This resulting kernel is then used as the reference source.
In all cases, the kernel source is found the same was for the kernelpatch test, i.e. via KERNEL_VERSION/KERNEL_NAME and KERNEL_${KERNEL_NAME}${KERNEL_VERSION}_SRC.
Once there is kernel source, the module is compiled using the top-level "make module" target.
The test is considered successful if an executable is found in OUTPUT/module/ipsec.o at the end of the test.
The nightly regression testing system consists of several shell scripts and some perl scripts. The goal is to check out a fresh tree, run "make check" on it, record the results and summarize the results to the team and to the web site.
Output can be found on adams , although the tests are actually run on another project machine.
The best way to do nightly testing is to setup a new account. We call the account "build" - you could call it something else, but there may still be some references to ~build in the scripts.
As few files as possible need to be extracted from the source tree - files are run from the source tree whenever possible. However, there are some bootstrap and configuration files that are necessary.
There are 7 files in testing/utils that are involved:
For more info on KERNPOOL, UMLPATCH, BASICROOT and SHAREDIR, see User-Mode-Linux testing guide.