Introduction to FreeS/WAN

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Web links

The Linux FreeS/WAN Project

The main project web site is

Links to other project-related sites are provided in our introduction section.

Add-ons and patches for FreeS/WAN

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.

  • There are a number of "features" of IPsec which we do not implement because they reduce security. See this discussion. We do not recommend using patches that implement these. One example is aggressive mode.
  • We do not recommend adding "features" of any sort unless they are clearly necessary, or at least have clear benefits. For example, FreeS/WAN would not become more secure if it offerred a choice of 14 ciphers. If even one was flawed, it would certainly become less secure for anyone using that cipher. Even with 14 wonderful ciphers, it would be harder to maintain and administer, hence more vulnerable to various human errors.

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.

Current patches

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.

Older patches

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.

VPN masquerade patches

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.

Distributions including FreeS/WAN

The introductory section of our document set lists several Linux distributions which include FreeS/WAN.

Things FreeS/WAN uses or could use

  • /dev/random support page, discussion of and code for the Linux random number driver. Out-of-date when we last checked (January 2000), but still useful.
  • other programs related to random numbers:
  • a Linux L2TP Daemon which might be useful for communicating with Windows 2000 which builds L2TP tunnels over its IPsec connections
  • to use opportunistic encryption, you need a recent version of BIND. You can get one from the Internet Software Consortium who maintain BIND.

Other approaches to VPNs for Linux

  • other Linux IPsec implementations
  • ENskip, a free implementation of Sun's SKIP protocol
  • vpnd, a non-IPsec VPN daemon for Linux which creates tunnels using Blowfish encryption
  • Zebedee, a simple GPLd tunnel-building program with Linux and Win32 versions. The name is from Zlib compression, Blowfish encryption and Diffie-Hellman key exchange.
  • There are at least two PPTP implementations for Linux
  • CIPE (crypto IP encapsulation) project, using their own lightweight protocol to encrypt between routers
  • tinc, a VPN Daemon

There is a list of Linux VPN software in the Linux Security Knowledge Base.

The IPsec Protocols

General IPsec or VPN information

IPsec overview documents or slide sets

IPsec information in languages other than English

RFCs and other reference documents

Analysis and critiques of IPsec protocols

  • Counterpane's evaluation of the protocols
  • Simpson's IKE Considered Dangerous paper. Note that this is a link to an archive of our mailing list. There are several replies in addition to the paper itself.
  • Fate Labs Virual Private Problems: the Broken Dream
  • Catherine Meadows' paper Analysis of the Internet Key Exchange Protocol Using the NRL Protocol Analyzer, in PDF or Postscript.
  • Perlman and Kaufmnan
  • Bellovin's papers page including his:
    • Security Problems in the TCP/IP Protocol Suite (1989)
    • Problem Areas for the IP Security Protocols (1996)
    • Probable Plaintext Cryptanalysis of the IP Security Protocols (1997)
  • An errata list for the IPsec RFCs.

Background information on IP

  • An IP tutorial that seems to be written mainly for Netware or Microsoft LAN admins entering a new world
  • IANA, Internet Assigned Numbers Authority
  • CIDR, Classless Inter-Domain Routing
  • Also see our bibliography

IPsec Implementations

Linux products

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

  • Redcreek provide an open source Linux driver for their PCI hardware VPN card. This card has a 100 Mbit Ethernet port, an Intel 960 CPU plus more specialised crypto chips, and claimed encryption performance of 45 Mbit/sec. The PC sees it as an Ethernet board.
  • Paktronix offer a Linux-based VPN with hardware encryption
  • Watchguard use Linux in their Firebox product.
  • Entrust offer a developers' toolkit for using their PKI for IPsec authentication
  • According to a report on our mailing list, Axent have a Linux version of their product.

IPsec in router products

All the major router vendors support IPsec, at least in some models.

  • Cisco IPsec information
  • Ascend, now part of Lucent, have some IPsec-based products
  • Bay Networks, now part of Nortel, use IPsec in their Contivity switch product line
  • 3Com have a number of VPN products, some using IPsec

IPsec in firewall products

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.

Operating systems with IPsec support

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:

  • Microsoft have put IPsec in their Windows 2000 and XP products
  • IBM announce a release of OS390 with IPsec support via a crypto co-processor
  • Sun include IPsec in Solaris 8
  • Hewlett Packard offer IPsec for their Unix machines
  • Certicom have IPsec available for the Palm.
  • There were reports before the release that Apple's Mac OS X would have IPsec support built in, but it did not seem to be there when we last checked. If you find, it please let us know via the mailing list.

IPsec on network cards

Network cards with built-in IPsec acceleration are available from at least Intel, 3Com and Redcreek.

Open source IPsec implementations

Other Linux IPsec implementations

We like to think of FreeS/WAN as the Linux IPsec implementation, but it is not the only one. Others we know of are:

  • pipsecd, a lightweight implementation of IPsec for Linux. Does not require kernel recompilation.
  • Petr Novak's ipnsec, based on the OpenBSD IPsec code and using Photuris for key management
  • A now defunct project at U of Arizona (export controlled)
  • NIST Cerebus (export controlled)

IPsec for BSD Unix

  • KAME, several large Japanese companies co-operating on IPv6 and IPsec
  • US Naval Research Lab implementation of IPv6 and of IPsec for IPv4 (export controlled)
  • OpenBSD includes IPsec as a standard part of the distribution
  • IPsec for FreeBSD
  • a FAQ on NetBSD's IPsec implementation

IPsec for other systems


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.

Interoperability results

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:

  • interop results from a bakeoff in Atlanta, September 1999.
  • a French company, HSC's, interoperability test data covers FreeS/WAN, Open BSD, KAME, Linux pipsecd, Checkpoint, Red Creek Ravlin, and Cisco IOS
  • ICSA offer certification programs for various security-related products. See their list of certified IPsec products. Linux FreeS/WAN is not currently on that list, but several products with which we interoperate are.
  • VPNC have a page on why they are not yet doing interoperability testing and a page on the spec conformance testing that they are doing
  • a review comparing a dozen commercial IPsec implemetations. Unfortunately, the reviewers did not look at Open Source implementations such as FreeS/WAN or OpenBSD.
  • results from interoperability tests at a conference. FreeS/WAN was not tested there.
  • test results from the IPSEC 2000 conference

Interoperability test sites

Linux links

Basic and tutorial Linux information

General Linux sites


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.

Advanced routing

The Linux IP stack has some new features in 2.4 kernels. Some HowTos have been written:

Security for Linux

See also the LDP material above.

Linux firewalls

Our FreeS/WAN and firewalls document includes links to several sets of scripts known to work with FreeS/WAN.

Other information sources:

Miscellaneous Linux information

Crypto and security links

Crypto and security resources

The standard link collections

Two enormous collections of links, each the standard reference in its area:

Gene Spafford's COAST hotlist
Computer and network security.
Peter Gutmann's Encryption and Security-related Resources

Frequently Asked Question (FAQ) documents


See also the interesting papers section below.

Crypto and security standards

Crypto quotes

There are several collections of cryptographic quotes on the net:

Cryptography law and policy

Surveys of crypto law

Organisations opposing crypto restrictions

Other information on crypto policy

  • RFC 1984, the IAB and IESG Statement on Cryptographic Technology and the Internet.
  • John Young's collection of documents of interest to the cryptography, open government and privacy movements, organized chronologically
  • AT&T researcher Matt Blaze's Encryption, Privacy and Security Resource Page
  • A good overview of the issues from Australia.

See also our documentation section on the history and politics of cryptography.

Cryptography technical information

Collections of crypto links

Lists of online cryptography papers

Particularly interesting papers

These papers emphasize important issues around the use of cryptography, and the design and management of secure systems.

Computer and network security

Security links

Firewall links

VPN links

Security tools

Links to home pages

David Wagner at Berkeley provides a set of links to home pages of cryptographers, cypherpunks and computer security people.

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