[Openswan Users] NAT-T

Oliver Tomkins oliver.tomkins at alliedvehicles.co.uk
Fri Mar 24 14:52:19 CET 2006

As ever thanks very much for your help.

I added

nat_traversal=yes, virtual_private line, rightsubnet=vhost:%no,%priv to 
the ipsec.conf and opened port 4500 on the firewall.

The client machine appears to connect fine - the client can browse the 
network etc,

However when I'm packet sniffing on the firewall I only see UDP traffic 
rather the ESP traffic that I normally see with our non-nat clients?

Am I missing something obvious here?



Paul Wouters wrote:
> On Thu, 23 Mar 2006, Oliver Tomkins wrote:
>> 1) We're using the 2.6.15-1.1833_FC4 kernel.  Am I correct in thinking that
>> the NAT-T patch is already applied to this kernel?
> No. If you use NETKEY, then you do not need the NAT-T patch, as NETKEY has its
> own nat-t capabilties build in. If you use KLIPS, you need the NAT-T patch.
> KLIPS does not come with FC kernels.
>> 2) As NAT-T is enabled globally in the ipsec.conf am I correct in thinking
>> this will not have an effect on the clients connecting from non NAT sources.
> It depends on your configuration. If you use nat_traversal=yes, the proper
> virtual_private line, and use: rightsubnet=vhost:%no,%priv then it should
> not influence you non-natted connections.
>> 3) All our existing non NAT clients connect with type=transport which has
>> security implications with NAT-T. Is this only for the clients connecting from
>> behind a NAT router?
> You will have major problems if you need to support l2tp/transport mode connections
> from behind NAT. Particularly, users with the same NAT'ed IP address behind
> different NAT routers, and having multiple roadwarriors behind the same NAT
> router. We are working on fixing these issues, but we are still looking for
> resources to help us complete this project. This is not supported in openswan-2.4.x
> Paul

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