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.
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 setup section will show you how to build each of them.
A VPN, or Virtual Private Network 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:
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.
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.
People outside this core team have made substantial contributions. See
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.
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.
Software-only products:
Some caution is required on this. The RPMs are specific to a Linux distribution and an attempt to use them on another distribution is likely to cause problems.
RPMs for FreeS/WAN 1.91 and Red Hat 7.1 are available for download from Steamballoon. Check there for later versions.
As of version 1.93, the FreeS/WAN distribution incorporates some of the Steamballoon work, providing a facility for building your own RPMs. Details are in our installation document.
FreeS/WAN documentation up to version 1.5 was available only in HTML. Now we ship two formats:
The Makefile assumes the htmldoc tool is available. You can
download it from Easy Software. You
may need to get source code and change some of the limits in
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.
Text files in the main distribution directory are README, INSTALL, CREDITS, CHANGES, BUGS and COPYING.
FreeS/WAN commands and library routines are documented in standard Unix manual pages, accessible via the man(1) command. We also provide them in HTML, accessible from this index. In the event of disagreement between this HowTo 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.
The gmp (GNU multi-precision arithmetic) and Libdes (encryption) libraries which we use each have their own documentation. You can find it in those library directories.
However, I must limit amount of detail on these topics in the main text. If I tried to explain everything here, the result would be completely unreadable.
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. 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.
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 current team thinking on new developments:
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.
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.
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:
More complex requirements are covered elsewhere:
However, please read this quick start section first , before tackling the others.
There are two easy ways to install FreeS/WAN:
If you are using one of them, just include FreeS/WAN in the choices you make during installation, or add it to your configuration later using the distribution's tools.
Sources for RPM packages of FreeS/WAN are:
Note that:
You need to download at least two RPMs:
Once you have them, install the RPMs with rpm -i commands. You will need to be root to install the kernel.
If your distribution does not include FreeS/WAN and no RPMs are available, see our installation from source document.
That's it. FreeS/WAN is installed.
RSA is a public key cryptographic technique. Keys are created as matched pairs. Each pair includes:
For FreeS/WAN, both keys for your system are in the ipsec.secrets(5) file. Maintaining security of this file is essential since it holds your private key.
To generate your key pair, give these commands as root:
ipsec newhostkey > /etc/ipsec.secrets
chmod 600 /etc/ipsec.secrets
Key generation may take some time, even on a fast system. Also, it
needs a lot of random numbers so you may need to
switch consoles and do something like typing a lot of text or running
The RSA keys we generate are suitable only for authentication, not for encryption. IPsec uses them only for authentication. See our IPsec section for details.
Opportunistic encryption makes setup and adminstration of IPsec simple.
For opportunistic encryption, you do not need to communicate with the administrator of a site before establishing secure communications to that site. In particular, you do not have to send them your keys or collect and authenticate theirs. All you have to do is set up your end correctly and from there on, everything is automatic.
In this section, we treat the simplest case:
There are two steps:
Once this is done, your system will automatically encrypt whenever it can.
# general IPsec setup
config setup
# Use the default interface
interfaces=%defaultroute
# Use auto= parameters in conn descriptions to control startup actions.
plutoload=%search
plutostart=%search
# defaults for subsequent connection descriptions
conn %default
# How to authenticate gateways
authby=rsasig
# Try to start all connections by default
auto=start
# description for opportunistic connections
conn us-to-anyone
also=our_stuff # our system details, stored below
left=%opportunistic # anyone we can authenticate via DNS
rekey=no # let unused connections die
# description of our system
# included in other connection descriptions via also= lines
# must come after the lines that use it
conn our_stuff
# all connections should use our default route
# also controls the source address on IPsec packets
right=%defaultroute
# our identity for IPsec negotiations
# must match what is in DNS and ipsec.secrets(5)
rightid=xy.example.com
The last line above is the only one that you need to edit for your system. All the rest is identical for any standalone machine doing opportunistic encryption.
There is no need to provide any keys in this file. Your private key is in ipsec.secrets(5) and, for opportunistic encryption, the public keys for remote gateways are all looked up in DNS.
What follows here is a simple technique suitable for systems which always initiate any opportunistic encryption they are involved in. If you need to let others inititiate -- for example, if you run services on your machine and want remote clients to be able to acess them securely -- then you need the more complex techniques described in the gateways section.
For example, a reverse lookup on the IP address for a home gateway might give 123.adsl.kalamazoo.example.net, and a forward lookup for example.dyndns.org might point to that gateway. You could use either of these names as your ID for IPsec purposes, if the admins at either example.net or dyndns.org co-operate.
If not, you can use any domain whose DNS adminstrator is willing to help out. You do not need an A record (address record, associating your chosen name with an address) in that domain, only a KEY record.
You can generate a DNS KEY record containing your system's public key with the command:
ipsec showhostkey
The result should look like this (with the key data trimmed down for
clarity):
; RSA 2048 bits xy.example.com Sat Apr 15 13:53:22 2000 xy.example.com. IN KEY 0x4200 4 1 AQOF8tZ2...+buFuFn/
The name here is taken from ipsec.secrets(5). If it is not what you want, edit that file to correct it, then run ipsec showhostkey again.
The name must also match what you used for rightid= in ipsec.conf(5).
Give this record to the DNS administrator, for insertion into the zone file of the domain.
There are two steps in the setup. Setting up your ipsec.conf(5) for this is quite simple. Setting up the DNS entries to support it is a bit more complex.
You need only make a few additions to in the ipsec.conf(5) file to expand from a standalone system (which protects only its own traffic) to a gateway (which protects traffic for other systems):
A few other things in ipsec.conf(5) will be changed as well in our example:
With those changes, the ipsec.conf(5) file is:
# general IPsec setup
config setup
# Use the default interface
interfaces=%defaultroute
# Use auto= parameters in conn descriptions to control startup actions.
plutoload=%search
plutostart=%search
# defaults for subsequent connection descriptions
conn %default
# How to authenticate gateways
authby=rsasig
# Default is to load all connection descriptions
# but not try to start the connection
# Some conns may over-ride this with auto=start
auto=add
# opportunistic connections to our gateway
conn us-to-anyone
also=gate_stuff # our system details, stored below
right=%opportunistic # anyone we can authenticate via DNS
rekey=no # let unused connections die
# opportunistic connections for client systems
# our gateway will build opportunistic tunnels on behalf of any
# machine in the specified subnet
conn subnet-to-anyone
also=gate_stuff # our system details, stored below
also=public_subnet # subnet description, below
right=%opportunistic # anyone we can authenticate via DNS
rekey=no # let unused connections die
# description of our gateway system
# included in other connection descriptions via also= lines
# must come after the lines that use it
conn gate_stuff
# all connections should use our default route
# also controls the source address on IPsec packets
left=%defaultroute
# our identity for IPsec negotiations
# must match what is in DNS and ipsec.secrets(5)
leftid=gateway.example.com
# description of the subnet this gateway encrypts for
# numbers used here are arbitrary, just for example
conn public_subnet
leftsubnet=1.2.3.0/24
# opportunistic connections for additional systems
conn second-to-anyone
also=gate_stuff # our system details, stored below
also=second_subnet # subnet description, below
right=%opportunistic # anyone we can authenticate via DNS
rekey=no # let unused connections die
# description of a second subnet this gateway encrypts for
# numbers used here are arbitrary, just for example
conn second_subnet
leftsubnet=4.5.6.0/24
There is one small thing to be careful of here. An also= line must appear in the file before the conn it references, so the first section above must appear before conn gate_stuff.
The subnets used in these descriptions need not correspond to physical subnets. This is discussed in more detail in our advanced configuration document.
DNS setup for an opportunistic gateway involves several types of record:
; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000 gateway.example.com. IN KEY 0x4200 4 1 AQOF8tZ2...+buFuFn/This can be generated with ipsec showhostkey.
The record you need looks like this:
; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000 4.3.2.1.in-addr.arpa. IN KEY 0x4200 4 1 AQOF8tZ2...+buFuFn/
Generate a record with
As always, IP addresses in the reverse map are written backwards. In the above example, the gateway IP address is 1.2.3.4.
; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000 IN TXT "X-IPsec-Server(10)=1.2.3.4 AQOF8tZ2...+buFuFn/"This record must be generated on the gateway so it can get the key from ipsec.secrets(5). The command is:
ipsec showhostkey --txt 1.2.3.4
You must supply the gateway IP address on the command line.
One of these records is required in the reverse map for each system using this gateway for opportunistic IPsec.
A common requirement is for pre-configured connections between a specfic network and some set of remote machines. For example, an office network will often need to provide remote access services for:
We refer to the remote machines as "Road Warriors". For purposes of IPsec, anyone with a dynamic IP address is a road warrior.
Of course, if both the warrior and the gateway at the office are set up for opportunistic encryption, then you may not need the pre-configured connection. Here we assume that you do need it. For example:
This section has three sub-sections:
On either end, the opportunistic setup is unaffected by this. You leave it in place so both systems can continue to do opportunistic encryption with everyone but each other.
To set up an explicitly configured connection, you need some information about the system on the other end.
The gateway adminstrator needs to know some things about each Road Warrior:
To get this information, in a format suitable for insertion directly into the gateway's ipsec.conf(5) file, issue this command on the Warrior machine:
ipsec showhostkey --rightThe output should look like this (with the key shortened for easy reading):
rightid=xy.example.com rightrsasigkey=
The Road Warrior needs to know:
This information should be provided in a convenient format, ready for insertion in the Warrior's ipsec.conf(5) file. For example:
left=1.2.3.4 leftsubnet=5.6.7.0/24 leftid=gateway.example.com leftrsasigkey=
The gateway administrator typically needs to generate this only once. The same file can be given to all Warriors.
Of course it is also possible to provide different versions (in particular, access to differnet subnets) to different groups of Warriors. See our advanced configuration document.
To set up a Road Warrior machine, we start from the opportunistic client setup shown above. We need not change anything there, only add a connection description for the pre-configured tunnel.
# pre-configured link to office network
conn us-to-office
also=our_stuff # our system details, stored below
#
# information obtained from office system admin
# goes to the right of the = signs in these lines
# values shown here are just for example
#
left=1.2.3.4 # gateway IP address
leftsubnet=5.6.7.0/24 # the office network
leftid=gateway.example.com
# real keys are much longer than shown here
leftrsasigkey=
Everything else remains as it was when we had only opportunistic connections.
We could easily add more connections as required, perhaps one each for his office, her office, the kid's school, ... The file would grow longer, but nothing already in the file would need to change.
If your gateway uses NAT to allow machines to access the Internet without having their own routable IP addresses, then from the point of view of anyone else on the Internet:
Firewall rules do need to be a little more complex to support the NAT. See the firewall section below for details.
For a more detailed discussion of NAT, see our background section.
Adding road warrior support so people can connect remotely to your office network is straightforward.
We start from the opportunistic gateway setup shown above.
Instead, we suggest you give each warrior its own file, choosing some directory and naming convention that suits your system and style.
For this example, we use the directory /etc/ipsec.road and use filenames based on IPsec ID, so the Warrior using ID xy.example.com gets a file named xy.conf.
Using such files, you need add only one line to ipsec.conf(5). With our naming convention, the line is:
include /etc/ipsec.road/*.conf
FreeS/WAN will then read all those files and behave as if they were part of the ipsec.conf(5) file.
This needs to come before the conn gate_stuff section, so that the Warriors' connection descriptions can use also=gate_stuff. A convenient place for the line is right after the conn %default section.
Each of the Road Warrior files then contains a connection description for that Warrior. For example:
# connection description for Road Warrior "xy" conn gate-xy # use the gateway description in ipsec.conf(5) also=gate_stuff # allow connection attempt from any address # attempt fails if caller cannot authenticate right=%any # authentication information rightid=xy.example.com rightrsasigkey=
With this technique, it becomes fairly simple to administer a gateway that supports many Road Warriors. For example:
To add a new user, simply add a suitable file.
To disable an account -- for example if a key is compromised -- first remove the file, then take any existing connection down with:
ipsec auto --down connectionand delete it from Pluto's internal database with:
ipsec auto --delete connection
If you have many users, it would be worthwhile to write scripts to automate such tasks.
Of course, if both offices are set up for opportunistic encryption and the security policies in place allow you to use that, explicitly configured tunnels become unnecessary. However, this will not always be the case.
Of course, a network-to-network tunnel requires its own connection description, so you have to add that. There are two ways to do this.
# sample tunnel
# The network here looks like:
# leftsubnet====left----leftnexthop......rightnexthop----right====rightsubnet
# If left and right are on the same Ethernet, omit leftnexthop and rightnexthop.
conn sample
# left security gateway (public-network address)
left=10.0.0.1
# next hop to reach right
leftnexthop=10.44.55.66
# subnet behind left (omit if there is no subnet)
leftsubnet=172.16.0.0/24
# right s.g., subnet behind it, and next hop to reach left
right=10.12.12.1
rightnexthop=10.88.77.66
rightsubnet=192.168.0.0/24
auto=start
Due to an unfortunate interaction between FreeS/WAN and the kernel
routing code, you must specify leftnexthop (the router which
left sends packets to in order to get them delivered to right) and
rightnexthop (vice versa).
The *nexthop parameters will be eliminated in a future release, but perhaps not soon. We know they should go, but getting them out is not a simple problem. For now, live with them.
This description can be generated on either machine and simply inserted in the ipsec.conf(5) file on the other. No change is required or desired.
When using left=%defaultroute, you do not need to specify leftnexthop. left does not need to know rightnexthop either, so on left the connection description can be:
conn sample
# left security gateway (public-network address)
left=%defaultroute
# subnet behind left (omit if there is no subnet)
leftsubnet=172.16.0.0/24
# right s.g., subnet behind it
right=10.12.12.1
rightsubnet=192.168.0.0/24
auto=start
On right it is:
conn sample
# left security gateway (public-network address)
left=10.0.0.1
# subnet behind left (omit if there is no subnet)
leftsubnet=172.16.0.0/24
# right s.g., subnet behind it
right=%defaultroute
rightsubnet=192.168.0.0/24
auto=start
This section describes simple firewall setups, suitable for getting a FreeS/WAN machine running. A separate FreeS/WAN and firewalls document provides more detail.
The first step is to allow IPsec packets (IKE on UDP port 500 plus ESP, protocol 50) in and out of your gateway. A script to set up iptables(8) rules for this is:
# edit this line to match the interface you use as default route # ppp0 is correct for many modem, DSL or cable connections # but perhaps not for you world=ppp0 # # allow IPsec # # IKE negotiations iptables -A INPUT -p udp -i $world --sport 500 --dport 500 -j ACCEPT iptables -A OUTPUT -p udp -o $world --sport 500 --dport 500 -j ACCEPT # ESP encrypton and authentication iptables -A INPUT -p 50 -i $world -j ACCEPT iptables -A OUTPUT -p 50 -o $world -j ACCEPT
Optionally, you could restrict this, allowing these packets only to and from a list of known gateways.
A second firewalling step -- access controls built into the IPsec protocols -- is automatically applied:
Optionally, you can add a third step using whatever additional firewall rules are required for your situation. These rules can recognise packets emerging from IPsec. They are marked as arriving on an interface such as ipsec0, rather than eth0, ppp0 or whatever. For example, in an iptables(8) rule set, you would use:
However, on a gateway there are additional things to do:
You need additional rules to handle these things. For example, adding some rules to the set shown above we get:
# edit this line to match the interface you use as default route # ppp0 is correct for many modem, DSL or cable connections # but perhaps not for you world=ppp0 # # edit these lines to describe your internal subnet and interface localnet=42.42.42.0/24 internal=eth1 # # allow IPsec # # IKE negotiations iptables -A INPUT -p udp -i $world --sport 500 --dport 500 -j ACCEPT iptables -A OUTPUT -p udp -o $world --sport 500 --dport 500 -j ACCEPT # ESP encrypton and authentication iptables -A INPUT -p 50 -i $world -j ACCEPT iptables -A OUTPUT -p 50 -o $world -j ACCEPT # # packet forwarding for an IPsec gateway # # handle packets emerging from IPsec # ipsec+ means any of ipsec0, ipsec1, ... iptables -A FORWARD -d $localnet -i ipsec+ -j ACCEPT # simple rule for outbound packets # let local net send anything # IPsec will encrypt some of it iptables -A FORWARD -s $localnet -i $internal -j ACCEPT
On a production gateway, you would no doubt need tighter rules than the above. For details, see:
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.
For more detail, see our introduction document or the FreeS/WAN project web site.
Basically, what it says is give us the output from
Use the mailing list for problem reports, rather than mailing developers directly. This gives you access to more expertise, including users who may have encountered and solved the same problems. In particular, for problems involving interoperation with another IPsec implementation, the users often know more than the developers.
Using the list may also be important in relation to various cryptography export laws. A US citizen who provides technical assistance to foreign cryptographic work might be charged under the arms export regulations. Such a charge would be easier to defend if the discussion took place on a public mailing list than if it were done in private mail.
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.
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.
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.
See our FreeS/WAN performance document for more detail.
In practice, it is considerably more complex. We have a whole interop document devoted to it.
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.
FreeS/WAN is intended to run on all CPUs Linux supports . As of June 2000, 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 has been tested on multiprocessor Intel Linux and worked there. Note, however, that we do not test this often and have never tested on multiprocessor machines of other architectures.
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:
See also the Choosing a kernel section of our installation document.
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 IP works on your interface and FreeS/WAN doesn't, seek help on the mailing lists.
For information on some often-requested features, see below.
This application is discussed in our introduction and an example given in our FreeS/WAN configuration document.
This application is discussed in our introduction and an example given in our FreeS/WAN configuration document.
Road warriors using Windows or Macintosh may need an IPsec client program for their machines.
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 configuration document.
On the other hand, it is a priority for some users and user-contributed patches to add X.509 certificate support to FreeS/WAN have been available for some time. From mailing list reports, they seem to be quite widely used and to work well.
See the patches section of our web references document for details.
In the absence of a standard, user authentication has not been a priority for the FreeS/WAN team, and is unlikely to become one. This would be a good project for a volunteer, perhaps a staff member or contractor at some company that needs the feature. Certainly our team would co-operate with such an effort; we just don't have time to do it.
The patches section of our web links document has links to some user work on this.
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:
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.
| 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
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
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.