Contents Previous Next

# FreeS/WAN FAQ

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.

## Questions

- What is FreeS/WAN?
- How do I report a problem or seek help?
- Generic questions

- This is too complicated. Isn't there an easier way?
- Can I get commercial support for this product?
- Can I modify FreeS/WAN to ...?
- Can I contribute to the project?
- Is there detailed design documentation?
- Can FreeS/WAN talk to ...?
- Can different FreeS/WAN versions talk to each other?
- Does FreeS/WAN run on my version of Linux?
- Does FreeS/WAN run on the latest kernel version?
- Is a ... fast enough to handle FreeS/WAN with ... connections?

- Compilation problems

- gmp.h: No such file or directory
- ... virtual memory exhausted

- Life's little mysteries

- I cannot ping ....
- It takes forever to ...
- I send packets to the tunnel with route(8) but they vanish
- When a tunnel goes down, packets vanish
- The firewall ate my packets!
- Dropped connections
- TCPdump on the gateway shows strange things
- Traceroute does not show anything between the gateways

- Testing in stages

- Manually keyed connections don't work
- One manual connection works, but second one fails
- Manual connections work, but automatic keying doesn't
- IPSEC works, but connections using compression fail
- Small packets work, but large transfers fail
- Subnet-to-subnet works, but tests from the gateways don't

- Interpreting error messages

- SIOCADDRT:Network is unreachable
- ipsec_setup: Fatal error, kernel appears to lack KLIPS
- ipsec_setup: ... failure to fetch key for ... from DNS
- ipsec_setup: ... interfaces ... and ... share address ...
- ipsec_setup: Cannot adjust kernel flags
- Connection names in Pluto error messages
- Pluto: ... can't orient connection
- Pluto: ... no connection is known
- Pluto: ... no suitable connection ...
- Pluto: ... no connection has been authorized
- Pluto: ... OAKLEY_DES_CBC is not supported.
- Pluto: ... no acceptable transform
- ECONNREFUSED error message
- klips_debug: ... no eroute!
- ... trouble writing to /dev/ipsec ... SA already in use
- ... ignoring ... payload

- Can I ...

- Can I reload connection info without restarting?
- Can I use several masqueraded subnets?
- Can I use subnets masqueraded to the same addresses?
- Can I assign a road warrior an address on my net?
- Can I use Quality of Service routing with FreeS/WAN?
- Can I recognise dead tunnels and shut them down?
- Can I build IPSEC tunnels over a demand-dialed link?
- Can I build GRE tunnels over IPSEC?
- Does FreeS/WAN support X.509 or other PKI certificates?
- Does FreeS/WAN support Radius or other user authentication?
- Does FreeS/WAN support single DES encryption?

- Why don't you restrict the mailing lists to reduce spam?

## What is FreeS/WAN?

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.

## How do I report a problem or seek help?

See our problem reporting document. Basically, what it says is give us the output from ipsec barf from both gateways. Without full information, we cannot diagnose a problem. However, ipsec barf produces a lot of output. If at all possible, please make barfs accessible via the web or FTP rather than sending enormous mail messages.

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.

## Generic questions

### This is too complicated. Isn't there an easier way?

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.)

If you want the help of a contractor, or to hire staff with FreeS/WAN expertise, you could:

- check availability in your area through your local Linux User Group (LUG Index)
- try asking on our mailing list

For companies offerring support, see the next question.

### Can I get commercial support for this product?

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.

### Can I modify FreeS/WAN to ...?

You are free to modify FreeS/WAN in any way. See the discussion of licensing in our introduction document.

### Can I contribute to the project?

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.

### Is there detailed design documentation?

There are:

- RFCs specifying the protocols we implement
- man pages for our utilities, library functions and file formats
- comments in the source code
- HTML documentation written primarily for users
- archived discussions from the mailing lists
- other papers mentioned in our introduction

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.

### Can FreeS/WAN talk to ...?

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 interop document devoted to it.

### Can different FreeS/WAN versions talk to each other?

Linux FreeS/WAN can interoperate with many IPSEC implementations, including earlier versions of Linux FreeS/WAN itself.

In general, new versions will use existing configuration files, at least until the next major version number change. For example, 1.8 can use files created for 1.7, 1.6, even back to 1.0, but not from 0.92. This behaviour will continue until we release 2.0.

As of 1.8, however, conf file checking has become stricter, so that an error that may have slipped past the checks in an earlier version may be caught in a later one. From 1.8's doc/CHANGES:

          The internal configuration-file reader is progressively getting
          fussier about what it will accept, which may cause problems for
          illegal ipsec.conf files whose sins previously passed unnoticed.
          IN PARTICULAR, the "auto" parameter's values are now checked for
          legality everywhere.

### Does FreeS/WAN run on my version of Linux?

We build and test on Redhat distributions, but FreeS/WAN runs just fine on several other distributions, sometimes with minor fiddles to adapt to the local environment. Details are in our compatibility document. Also, some distributions or products come with FreeS/WAN included.

FreeS/WAN is intended to run on all CPUs Linux supports . 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.

### Does FreeS/WAN run on the latest kernel version?

Sometimes yes, but quite often, no.

Released versions of FreeS/WAN run on 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). For example, FreeS/WAN 1.91 runs on kernel 2.2.19 or 2.4.5. Often they will run on slightly earlier or later kernels as well, but we test on the current production kernels, so those are strongly recommended.

The kernel is under active development and it is not uncommon for changes to appear that cause problems for FreeS/WAN. For example, 2.4.6 or 2.4.7 may have changes that break FreeS/WAN 1.91. Or not; you can't tell in advance. 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:

- either stick with a slightly older kernel, even if it is not the latest and greatest. This is recommended for production systems; new versions may have new bugs.
- or fix the problem yourself and send us a patch, via the Users mailing list.

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 (when they appear) 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.

### Is a ... fast enough to handle FreeS/WAN with ... connections?

Certainly FreeS/WAN can run happily on limited machines. Very roughly:

- a 486 machines can handle a T1, ADSL or cable link (but the machine may be breathing hard)
- a current (mid-2001) technology PC can easily handle at least a 10 Mbit/second link

Beyond that, the picture is not clear. Much depends on details of your network, your traffic, and other loads on both machine and net.

See our FreeS/WAN performance document and our discussion of many tunnels for one gateway for more detail.

## Compilation problems

### gmp.h: No such file or directory

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.

### ... virtual memory exhausted

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.

## Life's little mysteries

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:

- Installation
- Configuration
- Troubleshooting

However, we also list some of the commonest problems here.

### I cannot ping ....

This question is dealt with in the 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 = 1.2.3.4
                 |

           ~ internet ~

                 |
          eth0 = 4.3.2.1
             gate2
          eth1 = x.y.z.1
                  |
           subnet x.y.z.0/24

and the connection description:

    conn abc-xyz
         left=1.2.3.4
         leftsubnet=a.b.c.0/24
         right=4.3.2.1
         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:

- either fail, telling you nothing about the tunnel
- or succeed, telling you nothing about the tunnel since these packets use some other route

If required, you can of course build additional tunnels so that all the machines involved can talk to all the others. See multiple tunnels in the configuration document for details.

### It takes forever to ...

Users fairly often report various problems involving long delays, sometimes on tunnel setup and sometimes on operations done through the tunnel, occasionally on simple things like ping or more often on more complex operations like doing NFS or Samba through the tunnel.

Almost always, these turn out to involve failure of a DNS lookup. The timeouts waiting for DNS are typically set long so that you won't time out when a query involves multiple lookups or long paths. Genuine failures therefore produce long delays before they are detected.

A mailing list message from project technical lead Henry Spencer:

    > ... when i run /etc/rc.d/init.d/ipsec start, i get:
    > ipsec_setup: Starting FreeS/WAN IPSEC 1.5...
    > and it just sits there, doesn't give back my bash prompt.

    Almost certainly, the problem is that you're using DNS names in your
    ipsec.conf, but DNS lookups are not working for some reason.  You will
    get your prompt back... eventually.  But the DNS timeouts are long.
    Doing something about this is on our list, but it is not easy.

In the meanwhile, we recommend that connection descriptions in ipsec.conf(5) use numeric IP addresses rather than names which will require a DNS lookup.

Names that do not require a lookup are fine. For example:

- a road warrior might use the identity rightid=@lancelot.example.org
- the gateway might use 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
    freeswan.

    The problem was DNS as some people sad from the beginning, but not the way
    they thought it was happening. Samba, ssh, telnet and other apps try to
    reverse lookup addresses when you use IP numbers (Stupid that ahh).

    I could ping very fast because I always ping with "-n" option, but I don't
    know the option on the other apps to stop reverse addressing so I don't use
    it.

This post is fairly typical. These problems are often tricky and frustrating to diagnose, and most turn out to be DNS-related.

One suggestion for diagnosis: test with both names and addresses if possible. For example, try all of:

- ping address
- ping -n address
- ping name

If these behave differently, the problem must be DNS-related since the three commands do exactly the same thing except for DNS lookups.

### I send packets to the tunnel with route(8) but they vanish

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 our configuration document for an example.

### When a tunnel goes down, packets vanish

This is a special case of the vanishing packet problem described in the previous question. Whenever KLIPS sees packets for which it does not have a tunnel, it drops them.

When a tunnel goes away, either because negotiations with the other gateway failed or because you gave an ipsec auto --down command, the route to its other end is left pointing into KLIPS, and KLIPS will drop packets it has no tunnel for.

This is a documented design decision, not a bug. FreeS/WAN must not automatically adjust things to send packets via another route. The other route might be insecure.

Of course, re-routing may be necessary in many cases. In those cases, you have to do it manually or via scripts. We provide the ipsec auto --unroute command for these cases.

From ipsec_auto(8):

> Normally, pluto establishes a route to the destination specified for a connection as part of the --up operation. However, the route and only the route can be established with the --route operation. Until and unless an actual connection is established, this discards any packets sent there, which may be preferable to having them sent elsewhere based on a more general route (e.g., a default route).

> Normally, pluto's route to a destination remains in place when a --down operation is used to take the connection down (or if connection setup, or later automatic rekeying, fails). This permits establishing a new connection (perhaps using a different specification; the route is altered as necessary) without having a ``window'' in which packets might go elsewhere based on a more general route. Such a route can be removed using the --unroute operation (and is implicitly removed by --delete).

See also this mailing list message.

### The firewall ate my packets!

If firewalls filter out:

- either the UDP port 500 packets used in IKE negotiations
- or the ESP and AH (protocols 50 and 51) packets used to implement the IPSEC tunnel

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 .

### Dropped connections

Networks being what they are, IPSEC connections can be broken for any number of reasons, ranging from hardware failures to various software problems such as the path MTU problems discussed elsewhere in the FAQ. Fortunately, various diagnostic tools exist that help you sort out many of the possible problems.

There is one situation, however, where FreeS/WAN (using default settings) may destroy a connection for no readily apparent reason. This occurs when things are misconfigured so that two tunnels from the same gateway expect the same subnet on the far end.

In this situation, the first tunnel comes up fine and works until the second is established. At that point, because of the way we track connections internally, the first tunnel ceases to exist as far as this gateway is concerned. Of course the far end does not know that, and a storm of error messages appears on both systems as it tries to use the tunnel.

If the far end gives up, goes back to square one and negotiates a new tunnel, then that wipes out the second tunnel and ...

The solution is simple. Do not build multiple conn descriptions with the same remote subnet.

This is actually intended to be a feature, rather than a bug. Consider the situation where a single remote system goes down, then comes back up and reconnects to the gateway. It is useful to have the gateway tear down the old tunnel and recover resources when the reconnection is made. It recognises that situation by checking the remote subnet for each tunnel it builds and discarding duplicates. This works fine as long as you don't configure multiple tunnels with the same remote subnet.

If this behaviour is inconvenient for you, you can disable it by setting uniqueids=no in ipsec.conf(5).

### TCPdump on the gateway shows strange things

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.

At one point, this problem was quite severe. On more recent systems, the problem has been solved. The version of tcpdump shipped with Redhat 6.2, for example, understands IPSEC well enough to be usable on a gateway. If in doubt about your version of tcpdump, you can get the latest version from tcpdump.org.

Even if you have a version of tcpdump that works on gateways however, the most certain way to examine IPSEC packets is to look at them on the wire. For security, you need to be certain, so we recommend doing that. To do so, you need a separate sniffer machine located between the two gateways. This machine can be routing IPSEC packets, but it must not be an IPSEC gateway.

A common test setup is to put a machine with dual Ethernet cards in between two gateways under test. The central machine both routes packets and provides a place to safely run tcpdump or other sniffing tools. What you end up with looks like:

#### Testing network

          subnet a.b.c.0/24
                 |
          eth1 = a.b.c.1
             gate1
          eth0 = 192.168.p.1
                 |
                 |
          eth0 = 192.168.p.2
             route/monitor box
          eth1 = 192.168.q.2
                 |
                 |
          eth0 = 192.168.q.1
             gate2
          eth1 = x.y.z.1
                  |
           subnet x.y.z.0/24

With p and q any convenient values that do not interfere with other routes you may have. The ipsec.conf(5) file then has, among other things:

    conn abc=xyz
          left=192.168.p.1
          leftnexthop=192.168.p.2
          right=192.168.q.1
          rightnexthop=192.168.q.2

Once that works, you can remove the "route/monitor box", and connect the two gateways to the Internet. The only parameters in ipsec.conf(5) that need to change are the four shown above. You replace them with values appropriate for your Internet connection, and change the eth0 IP addresses and the default routes on both gateways.

Note that nothing on either subnet needs to change. This lets you test most of your IPSEC setup before connecting to the insecure Internet.

### Traceroute does not show anything between the gateways

As far as traceroute can see, the two gateways are one hop apart; the data packet goes directly from one to the other through the tunnel. Of course the outer packets that implement the tunnel pass through whatever lies between the gateways, but those packets are built and dismantled by the gateways. Traceroute does not see them and cannot report anything about their path.

Here is a mailing list message with more detail.

    Date: Mon, 14 May 2001
    To: linux-ipsec@freeswan.org
    From: "John S. Denker" <jsd@research.att.com<
    Subject: Re: traceroute: one virtual hop

    At 02:20 PM 5/14/01 -0400, Claudia Schmeing wrote:
    >
    >> > A bonus question: traceroute in subnet to subnet enviroment looks like:
    >> >
    >> > traceroute to andris.dmz (172.20.24.10), 30 hops max, 38 byte packets
    >> > 1  drama (172.20.1.1)  0.716 ms  0.942 ms  0.434 ms
    >> > 2  * * *
    >> > 3  andris.dmz (172.20.24.10)  73.576 ms  78.858 ms  79.434 ms
    >> >
    >> > Why aren't there the other hosts which take part in the delivery during
    >    * * * ?
    >
    >If there is an ipsec tunnel between GateA and Gate B, this tunnel forms a
    >'virtual wire'.  When it is tunneled, the original packet becomes an inner
    >packet, and new ESP and/or AH headers are added to create an outer packet
    >around it. You can see an example of how this is done for AH at
    >doc/ipsec.html#AH . For ESP it is similar.
    >
    >Think about the packet's path from the inner packet's perspective.
    >It leaves the subnet, goes into the tunnel, and re-emerges in the second
    >subnet. This perspective is also the only one available to the
    >'traceroute' command when the IPSec tunnel is up.

    Claudia got this exactly right.  Let me just expand on a couple of points:

    *) GateB is exactly one (virtual) hop away from GateA.  This is how it
    would be if there were a physically private wire from A to B.  The
    virtually private connection should work the same, and it does.

    *) While the information is in transit from GateA to GateB, the hop count
    of the outer header (the "envelope") is being decremented.  The hop count
    of the inner header (the "contents" of the envelope) is not decremented and
    should not be decremented.  The hop count of the outer header is not
    derived from and should not be derived from the hop count of the inner header.

    Indeed, even if the packets did time out in transit along the tunnel, there
    would be no way for traceroute to find out what happened.  Just as
    information cannot leak _out_ of the tunnel to the outside, information
    cannot leak _into_ the tunnel from outside, and this includes ICMP messages
    from routers along the path.

    There are some cases where one might wish for information about what is
    happening at the IP layer (below the tunnel layer) -- but the protocol
    makes no provision for this.  This raises all sorts of conceptual issues.
    AFAIK nobody has ever cared enough to really figure out what _should_
    happen, let alone implement it and standardize it.

    *) I consider the "* * *" to be a slight bug.  One might wish for it to be
    replaced by "GateB GateB GateB".  It has to do with treating host-to-subnet
    traffic different from subnet-to-subnet traffic (and other gory details).
    I fervently hope KLIPS2 will make this problem go away.

    *) If you want to ask questions about the link from GateA to GateB at the
    IP level (below the tunnel level), you have to ssh to GateA and launch a
    traceroute from there.

## Testing in stages

It is often useful in debugging to test things one at a time:

- disable IPSEC entirely, e.g. by turning it off with chkconfig(8), and make sure routing works
- Once that works, try a manually keyed connection. This does not require key negotiation between Pluto and the key daemon on the other end.
- Once that works, try automatically keyed connections
- Once IPSEC works, add packet compression
- Once everything seems to work, try stress tests with large transfers, many connections, frequent re-keying, ...

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.

### Manually keyed connections don't work

Suspect one of:

- mis-configuration of IPSEC system in the /etc/ipsec.conf file
  e.g. incorrect interface or next hop information
- mis-configuration of manual connection in the /etc/ipsec.conf file
- routing problems causing IPSEC packets to be lost
- bugs in KLIPS
- mismatch between the transforms we support and those another IPSEC implementation offers.

### One manual connection works, but second one fails

This is fairly common problem when attempting to configure multiple manually keyed connections from a single gateway.

Each connection must be identified by a unique SPI value. For automatic connections, these values are assigned automatically. For manual connections, you must set them with spi= statements in ipsec.conf(5).

Each manual connection must have a unique SPI value in the range 0x100 to 0x999. Two or more with the same value will fail. For details, see our HTML doc section Using manual keying in production and the man page ipsec.conf(5).

### Manual connections work, but automatic keying doesn't

The most common reason for this behaviour is a firewall dropping the UDP port 500 packets used in key negotiation.

Other possibilities:

- mis-configuration of auto connection in the /etc/ipsec.conf file.

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.

- error in shared secret in /etc/ipsec.secrets
- one gateway lacks a route to the other so Pluto's UDP packets are lost
- bugs in Pluto
- incompatibilities between Pluto's IKE implementation and the IKE at the other end of the tunnel.

Some possibile problems are discussed in out interoperation document.

### IPSEC works, but connections using compression fail

Suspect one of:

- (especially if small packets are OK, but large ones fail) compatibility issues with other implementations. We follow the RFCs and omit some extra material that many compression libraries add by default. Others may have the extras left in.
- bugs in the FreeS/WAN IPComp code, which is new for 1.6 and not yet heavily tested

### Small packets work, but large transfers fail

If tests with ping(1) and a small packet size succeed, but tests or transfers with larger packet sizes fail, suspect problems with path MTU discovery.

IPSEC makes packets larger by adding an ESP or AH header. This can tickle assorted bugs in path MTU discovery mechanisms and cause a variety of annoying symptoms. Here is one example of a discussion of this problem off the mailing list:

    Date: Mon, 3 Apr 2000
    From: "Michael H. Warfield" <mhw@wittsend.com>

    Paul Koning wrote:

    >  Chris>  It appears that the Osicom router discards IP
    >  Chris> fragments...

    > Amazing.  A device that discards fragments isn't a router, it's at
    > best a boat anchor.

            It may not be exactly what it appears.  I ran into a similar problem
    with an ISDN link a while ago giving similar symptoms.  Turned out that
    the device was negotiating an MTU that it really couldn't handle and the
    device in front of it (a Linux box with always defragment enabled) was
    defragmenting the huge IPSec datagrams and then refragmenting them into
    hunks that the ISDN PPP thought it could handle but couldn't.  Problem was
    solved by manually capping the MTU on the ISDN link to a smaller value.

            I gave the FreeSwan guys a hard time until tracking it down since
    FreeSwan was the only thing that appeared to be able to tickle the bug.
    Nothing else seemed to be broken.  What it really was that MTU discovery
    was avoiding the problem on normal links and it was only the IPSEC tunnels
    that were creating huge datagrams that went through the defragment/refragment
    process.

            Point here is that it "appeared" as though the ISDN link was
    failing to handle fragments when it was really a configuration error and
    a software bug resulting in a bad MTU that was really the culprit.  So
    it may not be that the router is not handling fragments.  It may be that
    it's missconfigured or has some other bug that only FreeSwan is tripping
    over.

### Subnet-to-subnet works, but tests from the gateways don't

This is described under I cannot ping... above.

## Interpreting error messages

### SIOCADDRT:Network is unreachable

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 FreeS/WAN "listress" (mailing list tech support person) Claudia Schmeing suggesting ways to diagnose and fix such problems:

    You write,
    > I have correctly installed freeswan-1.8 on RH7.0 kernel 2.2.17, but when
    > I setup a VPN connection with the other machine(RH5.2 Kernel 2.0.36
    > freeswan-1.0, it works well.) it told me that
    > "SIOCADDRT:Network is unreachable"!  But the network connection is no
    > problem.

    Often this error is the result of a misconfiguration.

    Be sure that you can route successfully in the absence of Linux
    FreeS/WAN. (You say this is no problem, so proceed to the next step.)

    Use a custom copy of the default updownscript. Do not change the route
    commands, but add a diagnostic message revealing the exact text of the
    route command. Is there a problem with the sense of the route command
    that you can see? If so, then re-examine those ipsec.conf settings
    that are being sent to the route command.

    You may wish to use the ipsec auto --route and --unroute commands to
    troubleshoot the problem. See man ipsec_auto for details.

Since the above message was written, we have modified the updown script to provide a better diagnostic for this problem. Check /var/log/messages.

### ipsec_setup: Fatal error, kernel appears to lack KLIPS

This message indicates an installation failure. The kernel you are running does not contain the KLIPS (kernel IPSEC) code.

Commands you can quickly try are:

uname -a
  to get details, including compilation date and time, of the currently running kernel
ls /
ls /boot
  to ensure a new kernel is where it should be. If kernel compilation puts it in / but lilo wants it in /boot , then you should uncomment the INSTALL_PATH=/boot line in the kernel Makefile.
more /etc/lilo.conf
  to see that lilo has correct information
lilo
  to ensure that information in /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 freeswan 1.8 on my mandrake 7.2 test box. ...

    > It does show version and some output for whack.

    Yes, because the Pluto (daemon) part of ipsec is installed correctly, but
    as we see below the kernel portion is not.

    > However, I get the following from /var/log/messages:
    >
    > Mar 11 22:11:55 pavillion ipsec_setup: Starting FreeS/WAN IPSEC 1.8...
    > Mar 11 22:12:02 pavillion ipsec_setup: modprobe: Can't locate module ipsec
    > Mar 11 22:12:02 pavillion ipsec_setup: Fatal error, kernel appears to lack
    > KLIPS.

    This is your problem. You have not successfully installed a kernel with
    IPSec machinery in it.

    Did you build Linux FreeS/WAN as a module? If so, you need to ensure that
    your new module has been installed in the directory where your kernel
    loader normally finds your modules. If not, you need to ensure
    that the new IPSec-enabled kernel is being loaded correctly.

    See also doc/install.html, and INSTALL in the distro.

### ipsec_setup: ... failure to fetch key for ... from DNS

Quoting Henry:

    Note that by default, FreeS/WAN is now set up to
         (a) authenticate with RSA keys, and
         (b) fetch the public key of the far end from DNS.
    Explicit attention to  ipsec.conf will be needed if you want
    to do something different.

and Claudia, responding to the same user:

    You write,

    >       My current setup in ipsec.conf is leftrsasigkey=%dns I have
    > commented this and authby=rsasig out. I am able to get ipsec running,
    > but what I find is that the documentation only specifies for %dns are
    > there any other values that can be placed in this variable other than
    > %dns and the key? I am also assuming that this is where I would place
    > my public key for the left and right side as well is this correct?

    Valid values for authby= are rsasig and secret, which entail authentication
    by RSA signature or by shared secret, respectively. Because you have
    commented authby=rsasig out, you are using the default value of authby=secret.

    When using RSA signatures, there are two ways to get the public key for the
    IPSec peer: either copy it directly into *rsasigkey= in ipsec.conf, or
    fetch it from dns. The magic value %dns for *rsasigkey parameters says to
    try to fetch the peer's key from dns.

    For any parameters, you may find their significance and special values in
    man ipsec.conf. If you are setting up keys or secrets, be sure also to
    reference man ipsec.secrets.

### ipsec_setup: ... interfaces ... and ... share address ...

This is a fatal error. FreeS/WAN cannot cope with two or more interfaces using the same IP address. You must re-configure to avoid this.

A mailing list message on the topic from Pluto developer Hugh Redelmeier:

    | I'm trying to get freeswan working between two machine where one has a ppp
    | interface.
    | I've already suceeded with  two machines with ethernet ports but  the ppp
    | interface is causing me problems.
    |  basically when I run ipsec start  i get
    | ipsec_setup: Starting FreeS/WAN IPSEC 1.7...
    | ipsec_setup: 003 IP interfaces ppp1 and ppp0 share address 192.168.0.10!
    | ipsec_setup: 003 IP interfaces ppp1 and ppp2 share address 192.168.0.10!
    | ipsec_setup: 003 IP interfaces ppp0 and ppp2 share address 192.168.0.10!
    | ipsec_setup: 003 no public interfaces found
    |
    | followed by lots of cannot work out interface for connection messages
    |
    | now I can specify the interface in ipsec.conf to be ppp0 , but this does
    | not affect the above behaviour. A quick look in server.c indicates that the
    | interfaces value  is not used but some sort of raw detect happens.
    |
    | I guess I could prevent the formation of the extra ppp interfaces or
    | allocate them different ip but I'd  rather not. if at all possible. Any
    | suggestions please.

    Pluto won't touch an interface that shares an IP address with another.
    This will eventually change, but it probably won't happen soon.

    For now, you will have to give the ppp1 and ppp2 different addresses.

### ipsec_setup: Cannot adjust kernel flags

A mailing list message form technical lead Henry Spencer:

    > When FreeS/WAN IPSEC 1.7 is starting on my 2.0.38 Linux kernel the following
    > error message is generated:
    > ipsec_setup: Cannot adjust kernel flags, no /proc/sys/net/ipsec directory!
    > What is supposed to create this directory and how can I fix this problem?

    I think that directory is a 2.2ism, although I'm not certain (I don't have
    a 2.0.xx system handy any more for testing).  Without it, some of the
    ipsec.conf config-setup flags won't work, but otherwise things should
    function.

You also need to enable the /proc filesystem in your kernel configuration for these operations to work.

### Connection names in Pluto error messages

From Pluto programmer Hugh Redelmeier:

    | Jan 17 16:21:10 remus Pluto[13631]: "jumble" #1: responding to Main Mode from Road Warrior 130.205.82.46
    | Jan 17 16:21:11 remus Pluto[13631]: "jumble" #1: no suitable connection for peer @banshee.wittsend.com
    |
    |     The connection "jumble" has nothing to do with the incoming
    | connection requests, which were meant for the connection "banshee".

    You are right.  The message tells you which Connection Pluto is
    currently using, which need not be the right one.  It need not be the
    right one now for the negotiation to eventually succeed!  This is
    described in ipsec_pluto(8) in the section "Road Warrior Support".

    There are two times when Pluto will consider switching Connections for
    a state object.  Both are in response to receiving ID payloads (one in
    Phase 1 / Main Mode and one in Phase 2 / Quick Mode).  The second is
    not unique to Road Warriors.  In fact, neither is the first any more
    (two connections for the same pair of hosts could differ in Phase 1 ID
    payload; probably nobody else has tried this).

### Pluto: ... can't orient connection

Each Pluto needs to know whether it is running on the machine which the connection description calls left or on right . It figures that out by:

- looking at the interfaces given in interfaces= lines in the config setup section
- discovering the IP addresses for those interfaces
- searching for a match between those addresses and the ones given in left= or right= lines.

Normally a match is found. Then Pluto knows where it is and can set up other things (for example, if it is left) using parameters such as leftsubnet and leftnexthop, and sending its outgoing packets to right.

If no match is found, it emits the above error message.

### Pluto: ... no connection is known

This error message occurs when a remote system attempts to negotiate a connection and Pluto does not have a connection description that matches what the remote system has requested. The most common cause is a configuration error on one end or the other.

Parameters involved in this match are left, right , leftsubnet and rightsubnet.

The match must be exact. For example, if your left subnet is a.b.c.0/24 then neither a single machine in that net nor a smaller subnet such as a.b.c.64/26 will be considered a match.

The message can also occur when an appropriate description exists but Pluto has not loaded it. Use an auto=add statement in the connection description, or an ipsec auto --add <conn_name> command, to correct this.

An explanation from the Pluto developer:

    | Jul 12 15:00:22 sohar58 Pluto[574]: "corp_road" #2: cannot respond to IPsec
    | SA request because no connection is known for
    | 216.112.83.112/32===216.112.83.112...216.67.25.118

    This is the first message from the Pluto log showing a problem.  It
    means that PGPnet is trying to negotiate a set of SAs with this
    topology:

    216.112.83.112/32===216.112.83.112...216.67.25.118
    ^^^^^^^^^^^^^^^^^   ^^^^^^^^^^^^^^   ^^^^^^^^^^^^^
    client on our side  our host         PGPnet host, no client

    None of the conns you showed look like this.

    Use
            ipsec auto --status
    to see a snapshot of what connections are in pluto, what
    negotiations are going on, and what SAs are established.

    The leftsubnet= (client) in your conn is 216.112.83.64/26.  It must
    exactly match what pluto is looking for, and it does not.

### Pluto: ... no suitable connection ...

This is similar to the no connection known error, but occurs at a different point in Pluto processing.

Here is one of Claudia's messages explaining the problem:

    You write,

    > What could be the reason of the following error?
    > "no suitable connection for peer '@xforce'"

    When a connection is initiated by the peer, Pluto must choose which entry in
    the conf file best matches the incoming connection. A preliminary choice is
    made on the basis of source and destination IPs, since that information is
    available at that time.

    A payload containing an ID arrives later in the negotiation. Based on this
    id and the *id= parameters, Pluto refines its conn selection. ...

    The message "no suitable connection" indicates that in this refining step,
    Pluto does not find a connection that matches that ID.

    Please see "Selecting a connection when responding" in man ipsec_pluto for
    more details.

See also Connection names in Pluto error messages.

### Pluto: ... no connection has been authorized

Here is one of Claudia's messages discussing this problem:

    You write,

    >  May 22 10:46:31 debian Pluto[25834]: packet from x.y.z.p:10014:
    >  initial Main Mode message from x.y.z.p:10014
                                but no connection has been authorized

    This error occurs early in the connection negotiation process,
    at the first step of IKE negotiation (Main Mode), which is itself the
    first of two negotiation phases involved in creating an IPSec connection.

    Here, Linux FreeS/WAN receives a packet from a potential peer, which
    requests that they begin discussing a connection.

    The "no connection has been authorized" means that there is no connection
    description in Linux FreeS/WAN's internal database that can be used to
    link your ipsec interface with that peer.

    "But of course I configured that connection!"

    It may be that the appropriate connection description exists in ipsec.conf
    but has not been added to the database with ipsec auto --add myconn or the
    auto=add method. Or, the connection description may be misconfigured.

    The only parameters that are relevant in this decision are left= and right= .
    Local and remote ports are also taken into account -- we see that the port
    is printed in the message above -- but there is no way to control these
    in ipsec.conf.

    Failure at "no connection has been authorized" is similar to the
    "no connection is known for..." error in the FAQ, and the "no suitable
    connection" error described in the snapshot's FAQ. In all three cases,
    Linux FreeS/WAN is trying to match parameters received in the
    negotiation with the connection description in the local config file.

    As it receives more information, its matches take more parameters into
    account, and become more precise:  first the pair of potential peers,
    then the peer IDs, then the endpoints (including any subnets).

    The "no suitable connection for peer *" occurs toward the end of IKE
    (Main Mode) negotiation, when the IDs are matched.

    "no connection is known for a/b===c...d" is seen at the beginning of IPSec
    (Quick Mode, phase 2) negotiation, when the connections are matched using
    left, right, and any information about the subnets.

### Pluto: ... OAKLEY_DES_CBC is not supported.

This message occurs when the other system attempts to negotiate a connection using single DES, which we do not support because it is insecure.

Our interoperation document has suggestions for how to deal with systems that attempt to use single DES.

### Pluto: ... no acceptable transform

This message means that the other gateway has made a proposal for connection parameters, but nothing they proposed is acceptable to Pluto. Possible causes include:

- misconfiguration on either end
- policy incompatibilities, for example we require encrypted connections but they are trying to create one with just authentication
- interoperation problems, for example they offer only single DES and FreeS/WAN does not support that. (see below for DES problems)

A more detailed explanation, from Pluto programmer Hugh Redelmeier:

    Background:

    When one IKE system (for example, Pluto) is negotiating with another
    to create an SA, the Initiator proposes a bunch of choices and the
    Responder replies with one that it has selected.

    The structure of the choices is fairly complicated.  An SA payload
    contains a list of lists of "Proposals".  The outer list is a set of
    choices: the selection must be from one element of this list.

    Each of these elements is a list of Proposals.  A selection must be
    made from each of the elements of the inner list.  In other words,
    *all* of them apply (that is how, for example, both AH and ESP can
    apply at once).

    Within each of these Proposals is a list of Transforms.  For each
    Proposal selected, one Transform must be selected (in other words,
    each Proposal provides a choice of Transforms).

    Each Transform is made up of a list of Attributes describing, well,
    attributes.  Such as lifetime of the SA.  Such as algorithm to be
    used.  All the Attributes apply to a Transform.

    You will have noticed a pattern here: layers alternate between being
    disjunctions ("or") and conjunctions ("and").

    For Phase 1 / Main Mode (negotiating an ISAKMP SA), this structure is
    cut back.  There must be exactly one Proposal.  So this degenerates to
    a list of Transforms, one of which must be chosen.

    In your case, no proposal was considered acceptable to Pluto (the
    Responder).  So negotiation ceased.  Pluto logs the reason it rejects
    each Transform.  So look back in the log to see what is going wrong.

### ECONNREFUSED error message

From John Denker, on the mailing list:

    1)  The log message
      some IKE message we sent has been rejected with
      ECONNREFUSED (kernel supplied no details)
    is much more suitable than the previous version.  Thanks.

    2) Minor suggestion for further improvement: it might be worth mentioning
    that the command
      tcpdump -i eth1 icmp[0] != 8 and icmp[0] != 0
    is useful for tracking down the details in question.  We shouldn't expect
    all IPsec users to figure that out on their own.  The log message might
    even provide a hint as to where to look in the docs.

Reply From Pluto developer Hugh Redelmeier

    Good idea.

    I've added a bit pluto(8)'s BUGS section along these lines.
    I didn't have the heart to lengthen this message.

- klips_debug: ... no eroute! This message means KLIPS has received a packet for which no IPSEC tunnel has been defined.

Here is a more detailed duscussion from the team's tech support person Claudia Schmeing, responding to a query on the mailing list:

    > Why ipsec reports no eroute! ???? IP Masq... is disabled.
    In general, more information is required so that people on the list may
    give you informed input. See doc/prob.report.

    However, I can make some general comments on this type of error.

    This error usually looks something like this (clipped from an archived
    message):

    > ttl:64 proto:1 chk:45459 saddr:192.168.1.2 daddr:192.168.100.1
    > ... klips_debug:ipsec_findroute: 192.168.1.2->192.168.100.1
    > ... klips_debug:rj_match: * See if we match exactly as a host destination
    > ... klips_debug:rj_match: ** try to match a leaf, t=0xc1a260b0
    > ... klips_debug:rj_match: *** start searching up the tree, t=0xc1a260b0
    > ... klips_debug:rj_match: **** t=0xc1a260c8
    > ... klips_debug:rj_match: **** t=0xc1fe5960
    > ... klips_debug:rj_match: ***** not found.
    > ... klips_debug:ipsec_tunnel_start_xmit: Original head/tailroom: 2, 28
    > ... klips_debug:ipsec_tunnel_start_xmit: no eroute!: ts=47.3030, dropping.

    What does this mean?
    - --------------------

    "eroute" stands for "extended route", and is a special type of route
    internal to Linux FreeS/WAN. For more information about this type of route,
    see the section of man ipsec_auto on ipsec auto --route.

    "no eroute!" here means, roughly, that Linux FreeS/WAN cannot find an
    appropriate tunnel that should have delivered this packet. Linux
    FreeS/WAN therefore drops the packet, with the message "no eroute! ...
    dropping", on the assumption that this packet is not a legitimate
    transmission through a properly constructed tunnel.

    How does this situation come about?
    - -----------------------------------

    Linux FreeS/WAN has a number of connection descriptions defined in
    ipsec.conf. These must be successfully brought "up" to form actual tunnels.
    (see doc/setup.html's step 15, man ipsec.conf and man ipsec_auto
    for details).

    Such connections are often specific to the endpoints' IPs. However, in
    some cases they may be more general, for example in the case of
    Road Warriors where left or right is the special value %any.

    When Linux FreeS/WAN receives a packet, it verifies that the packet has
    come through a legitimate channel, by checking that there is an
    appropriate tunnel through which this packet might legitimately have
    arrived. This is the process we see above.

    First, it checks for an eroute that exactly matches the packet. In the
    example above, we see it checking for a route that begins at 192.168.1.2
    and ends at 192.168.100.1. This search favours the most specific match that
    would apply to the route between these IPs. So, if there is a connection
    description exactly matching these IPs, the search will end there. If not,
    the code will search for a more general description matching the IPs.
    If there is no match, either specific or general, the packet will be
    dropped, as we see, above.

    Unless you are working with Road Warriors, only the first, specific part
    of the matching process is likely to be relevant to you.

    "But I defined the tunnel, and it came up, why do I have this error?"
    - ---------------------------------------------------------------------

    One of the most common causes of this error is failure to specify enough
    connection descriptions to cover all needed tunnels between any two
    gateways and their respective subnets. As you have noticed, troubleshooting
    this error may be complicated by the use of IP Masq. However, this error is
    not limited to cases where IP Masq is used.

    See doc/configuration.html#multitunnel for a detailed example of the
    solution to this type of problem.

### ... trouble writing to /dev/ipsec ... SA already in use

From the mailing list:

    > When I activate one manual tunnels it works, but when I try to activate
    > another tunnel, it gives an error message...
    > tunnel_2: Had trouble writing to /dev/ipsec SA:tun0x200@202.103.5.63 --
    > SA already in use.  Delete old one first.

    Please read the Using manual keying in production discussion in
    config.html, specifically the part about needing a different spi
    (or spibase) setting for each connection.

This problem is also discussed in this FAQ under the heading One manual connection works, but second one fails.

### ... ignoring ... payload

This message is harmless. The IKE protocol provides for a number of optional messages types:

- delete SA
- initial contact
- vendor ID
- ...

An implementation is never required to send these, but they are allowed to. The receiver is not required to do anything with them. FreeS/WAN ignores them, but notifies you via the logs.

For the "ignoring delete SA Payload" message, see also the discussion below of cleaning up dead tunnels.

## Can I ...

### Can I reload connection info without restarting?

Yes, you can do this. Here are the details, in a mailing list message from Pluto programmer Hugh Redelmeier:

    | How can I reload config's without restarting all of pluto and klips?  I am using
    | FreeSWAN -> PGPNet in a medium sized production environment, and would like to be
    | able to add new connections ( i am using include config/* ) without dropping current
    | SA's.
    |
    | Can this be done?
    |
    | If not, are there plans to add this kind of feature?

            ipsec auto --add whatever
    This will look in the usual place (/etc/ipsec.conf) for a conn named
    whatever and add it.

    If you added new secrets, you need to do
            ipsec auto --rereadsecrets
    before Pluto needs to know those secrets.

    | I have looked (perhaps not thoroughly enough tho) to see how to do this:

    There may be more bits to look for, depending on what you are trying
    to do.

Another useful command here is ipsec auto --replace <conn_name> which re-reads data for a named connection.

### Can I use several masqueraded subnets?

Yes. This is done all the time. See the discussion in our setup document. The only restriction is that the subnets on the two ends must not overlap. See the next question.

Here is a mailing list message on the topic. The user incorrectly thinks you need a 2.4 kernel for this -- actually various people have been doing it on 2.0 and 2.2 for quite some time -- but he has it right for 2.4.

    Subject: Double NAT and freeswan working :)
       Date: Sun, 11 Mar 2001
       From: Paul Wouters <paul@xtdnet.nl>

    Just to share my pleasure, and make an entry for people who are searching
    the net on how to do this. Here's the very simple solution to have a double
    NAT'ed network working with freeswan. (Not sure if this is old news, but I'm
    not on the list (too much spam) and I didn't read this in any HOWTO/FAQ/doc
    on the freeswan site yet (Sandy, put it in! :)

    10.0.0.0/24 --- 10.0.0.1 a.b.c.d  ---- a.b.c.e {internet} ----+
                                                                  |
    10.0.1.0/24 --- 10.0.1.1 f.g.h.i  ---- f.g.h.j {internet} ----+

    the goal is to have the first network do a VPN to the second one, yet also
    have NAT in place for connections not destinated for the other side of the
    NAT. Here the two Linux security gateways have one real IP number (cable
    modem, dialup, whatever.

    The problem with NAT is you don't want packets from 10.*.*.* to 10.*.*.*
    to be NAT'ed. While with Linux 2.2, you can't, with Linux 2.4 you can.

    (This has been tested and works for 2.4.2 with Freeswan snapshot2001mar8b)

    relevant parts of /etc/ipsec.conf:

            left=f.g.h.i
            leftsubnet=10.0.1.0/24
            leftnexthop=f.g.h.j
            leftfirewall=yes
            leftid=@firewall.netone.nl
            leftrsasigkey=0x0........
            right=a.b.c.d
            rightsubnet=10.0.0.0/24
            rightnexthop=a.b.c.e
            rightfirewall=yes
            rightid=@firewall.nettwo.nl
            rightrsasigkey=0x0......
            # To authorize this connection, but not actually start it, at startup,
            # uncomment this.
            auto=add

    and now the real trick. Setup the NAT correctly on both sites:

    iptables -t nat -F
    iptables -t nat -A POSTROUTING -o eth0 -d \! 10.0.0.0/8 -j MASQUERADE

    This tells the NAT code to only do NAT for packets with destination other then
    10.* networks. note the backslash to mask the exclamation mark to protect it
    against the shell.

    Happy painting :)

    Paul

### Can I use subnets masqueraded to the same addresses?

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.

### Can I assign a road warrior an address on my net?

Yes, but it is tricky. This has been discussed on the mailing list. The discussion was not entirely clear to me, so I cannot yet document the procedures. At this point, all I know is:

- You can use a variant of the extruded subnet procedure.
- You have to avoid having the road warrior's assigned address within the range you actually use at home base. See previous question.
- On the other hand, you want the roadwarrior's address to be within the range that seems to be on your network.

For example, you might have:

leftsubnet=a.b.c.0/25
  head office network
rightsubnet=a.b.c.240/32
  extruded to a road warrior
a.b.c.0/24
  whole network, including both the above

### Can I use Quality of Service routing with FreeS/WAN?

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 information from the encapsulated packet to the outer header reveals the TOS information to an eavesdropper. It is not clear whether or how an attacker could use this information, but since we do not have to give it to him, our default is not to.

See ipsec.conf(5) for more on the hidetos= parameter.

### Can I recognise dead tunnels and shut them down?

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:

- a gateway that crashes or hangs would not send the messages
- the sender is not required to send them
- they are not authenticated, so any receiver that trusts them leaves itself open to a denial of service attack
- the receiver is not required to do anything about them
- the receiver cannot acknowledge them; the protocol provides no mechanism for that
- since they are not acknowledged, the sender cannot rely on them

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

### Can I build IPSEC tunnels over a demand-dialed link?

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.

### Can I build GRE tunnels over IPSEC?

This is possible in theory, but we are short on practical details. If you do this, please let us know via the mailing lists.

Theere is a list message with links to relevant resources.

### Does FreeS/WAN support X.509 or other PKI certificates?

FreeS/WAN, as distributed, does not currently support use of X.509 or other PKI certificates for authentication of gateways. We are concentrating on moving toward authentication via Secure DNS and opportunistic encryption; X.509 support is not (or at least not yet) on the priority list.

On the other hand, it is a priority for some users and user-contributed patches are available to add X.509 certificate support to FreeS/WAN now. See the patches section of our web references document for details.

### Does FreeS/WAN support Radius or other user authentication?

Not yet. So far, there is no standard way to authenticate users for IPSEC, though there is a very active IETF working group looking at the problem, and several vendors have implemented various things already.

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.

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 you can trust the road warrior machines, then set them up so that only authorised users can create tunnels. If your road warriors use laptops, consider the possibility of theft.
- If the tunnel only provides access to particular servers and you can trust those servers, then set the servers up to require user authentication.

If either of those is trustworthy, it is not clear that you need user authentication in IPSEC.

### Does FreeS/WAN support single DES encryption?

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.

## Why don't you restrict the mailing lists to reduce spam?

As a matter of policy, some of our mailing lists need to be open to non-subscribers. Project management feel strongly that maintaining this openness is more important than blocking spam.

- Users should be able to get help or report bugs without subscribing.
- Even a user who is subscribed may not have access to his or her subscribed account when he or she needs help, miles from home base in the middle of setting up a client's gateway.
- There is arguably a legal requirement for this policy. A US resident or citizen could be charged under munitions export laws for providing technical assistance to a foreign cryptographic project. Such a charge would be more easily defended if the discussion takes place in public, on an open list.

This has been discussed several times at some length on the list. See the list archives. Bringing the topic up again is unlikely to be useful. Please don't. Or at the very least, please don't without reading the archives and being certain that whatever you are about to suggest has not yet been discussed.

Project technical lead Henry Spencer summarised one discussion:

> For the third and last time: this list *will* *not* do address-based filtering. This is a policy decision, not an implementation problem. The decision is final, and is not open to discussion. This needs to be communicated better to people, and steps are being taken to do that.

Adding this FAQ section is one of the steps he refers to.

You have various options other than just putting up with the spam, filtering it yourself, or unsubscribing:

- subscribe only to one or both of our lists with restricted posting rules:
  - briefs , weekly list summaries
  - announce , project-related announcements
- read the other lists via the archives

A number of tools are available to filter mail.

- Many mail readers include some filtering capability.
- Many Linux distributions include procmail(8) for server-side filtering.
- The Spam Bouncer is a set of procmail(8) filters designed to combat spam.
- Roaring Penguin have a MIME defanger that removes potentially dangerous attachments.

If you use your ISP's mail server rather than running your own, consider suggesting to the ISP that they tag suspected spam as this ISP does. They could just refuse mail from dubious sources, but that is tricky and runs some risk of losing valuable mail or senselessly annoying senders and their admins. However, they can safely tag and deliver dubious mail. The tags can greatly assist your filtering.

For information on tracking down spammers, see these HowTos, or the Sputum site. Sputum have a Linux anti-spam screensaver available for download.

Here is a more detailed message from Henry:

    On Mon, 15 Jan 2001, Jay Vaughan wrote:
    > I know I'm flogging a dead horse here, but I'm curious as to the reasons for
    > an aversion for a subscriber-only mailing list?

    Once again:  for legal reasons, it is important that discussions of these
    things be held in a public place -- the list -- and we do not want to
    force people to subscribe to the list just to ask one question, because
    that may be more than merely inconvenient for them.  There are also real
    difficulties with people who are temporarily forced to use alternate
    addresses; that is precisely the time when they may be most in need of
    help, yet a subscribers-only policy shuts them out.

    These issues do not apply to most mailing lists, but for a list that is
    (necessarily) the primary user support route for a crypto package, they
    are very important.  This is *not* an ordinary mailing list; it has to
    function under awkward constraints that make various simplistic solutions
    inapplicable or undesirable.

    > We're *ALL* sick of hearing about list management problems, not just you
    > old-timers, so why don't you DO SOMETHING EFFECTIVE ABOUT IT...

    Because it's a lot harder than it looks, and many existing "solutions"
    have problems when examined closely.

    > A suggestion for you, based on 10 years of experience with management of my
    > own mailing lists would be to use mailman, which includes pretty much every
    > feature under the sun that you guys need and want, plus some.  The URL for
    > mailman...

    I assure you, we're aware of mailman.  Along with a whole bunch of others,
    including some you almost certainly have never heard of (I hadn't!).

    > As for the argument that the list shouldn't be configured to enforce
    > subscription - I contend that it *SHOULD* AT LEAST require manual address
    > verification in order for posts to be redirected.

    You do realize, I hope, that interposing such a manual step might cause
    your government to decide that this is not truly a public forum, and thus
    you could go to jail if you don't get approval from them before mailing to
    it?  If you think this sounds irrational, your government is noted for
    making irrational decisions in this area; we can't assume that they will
    suddenly start being sensible.  See above about awkward constraints.  You
    may be willing to take the risk, but we can't, in good conscience, insist
    that all users with problems do so.

                                                              Henry Spencer
                                                           henry@spsystems.net

and a message on the topic from project leader John Gilmore:

    Subject: Re: The linux-ipsec list's topic
       Date: Sat, 30 Dec 2000
       From: John Gilmore <gnu@toad.com>

    I'll post this single message, once only, in this discussion, and then
    not burden the list with any further off-topic messages.  I encourage
    everyone on the list to restrain themself from posting ANY off-topic
    messages to the linux-ipsec list.

    The topic of the linux-ipsec mailing list is the FreeS/WAN software.

    I frequently see "discussions about spam on a list" overwhelm the
    volume of "actual spam" on a list. BOTH kinds of messages are
    off-topic messages.  Twenty anti-spam messages take just as long to
    detect and discard as twenty spam messages.

    The Linux-ipsec list encourages on-topic messages from people who have
    not joined the list itself.  We will not censor messages to the list
    based on where they originate, or what return address they contain.
    In other words, non-subscribers ARE allowed to post, and this will not
    change.  My own valid contributions have been rejected out-of-hand by
    too many other mailing lists for me to want to impose that censorship
    on anybody else's contributions.  And every day I see the damage that
    anti-spam zeal is causing in many other ways; that zeal is far more
    damaging to the culture of the Internet than the nuisance of spam.

    In general, it is the responsibility of recipients to filter,
    prioritize, or otherwise manage the handling of email that comes to
    them.  It is not the responsibility of the rest of the Internet
    community to refrain from sending messages to recipients that they
    might not want to see.  If your software infrastructure for managing
    your incoming email is insufficient, then improve it.  If you think
    the signal-to-noise ratio on linux-ipsec is too poor, then please
    unsubscribe.  But don't further increase the noise by posting to the
    linux-ipsec list about those topics.

            John Gilmore
            founder sponsor, FreeS/WAN project

Contents Previous Next