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.
Read our troubleshooting document.
Use the users mailing list for problem reports, rather than mailing developers directly.
Try irc.freenode.net#freeswan.
Premium support is also available.
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 offering 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.
In general, we welcome contributions from the community. Various contributed patches, either to fix bugs or to add features, have been incorporated into our distribution. Other patches, not yet included in the distribution, are listed in our web links section.
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.
There are:
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: Even a limited machine can be useful
A mid-range PC (say 800 MHz with good network cards) can do a lot of IPsec
There are limits
See our FreeSWAN 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 FreeSWAN 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, openswan 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 Openswan 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 Openswan.
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.
(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:
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 Openswan). 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 mailing 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:
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
| openswan -> 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 openswan 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 openswan. (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 openswan 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 openswan 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: leftsubnet=a.b.c.0/25 head office network rightsubnet=a.b.c.129/32 extruded to a road warrior. Note that this is not in a.b.c.0/25 a.b.c.0/24 whole network, including both the above
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
either RSA authentication standard in the FreeS/WAN distribution or X.509 certificates requires Openswan or a patch?.
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 FreeSWAN 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:
ipsec0).
See ipsec.conf? 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 FreeSWAN 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 L2TP? 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:
ping from x.y.z.2 to a.b.c.2 or vice versa
Succeeds if tunnel is working. This is the only valid test of the tunnel.
ping from gate2 to a.b.c.2 or vice versa
Does not use tunnel. gate2 is not on protected subnet.
ping from gate1 to x.y.z.2 or vice versa
Does not use tunnel. gate1 is not on protected subnet.
ping from gate1 to gate2 or vice versa
Does not use tunnel. Neither gate is on a protected subnet.
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? use numeric IP addresses rather than names which will require a DNS lookup.
Names that do not require a lookup are fine. For example:
rightid=@lancelot.example.org
leftid=@camelot.example.org
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 openswan. 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:
address
address
name
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)?:
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?.
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 openswan 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.
As another user pointed out, keeping the connect
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@openswan.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 ... headers are added to create an outer packet >around it... > >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?.
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?.
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 our 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/local/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 openswan-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 > openswan-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 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:
uname -a
ls
/ls /boot
/ but lilo wants it in /boot, then you should uncomment the INSTALL_PATH=/boot line in the kernel Makefile.
more /etc/lilo.conf
lilo has correct information
lilo
/etc/lilo.conf has been transferred to the boot sector
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 openswan 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:
<