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Date:      Mon, 10 Aug 2009 21:31:15 +0100
From:      Jonathan Belson <jon@witchspace.com>
To:        freebsd-questions@freebsd.org
Subject:   ipfw, NAT and CISCO IPSec VPNs
Message-ID:  <4A808393.80501@witchspace.com>

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Hiya

I've got a pretty standard network which uses a FreeBSD server to perform NAT 
between my internal IPs (192.168.0.x) and the outside world.  Everything is 
working tickety-boo, but I'm trying to tweak my firewall rules (ipfw, based on 
the 'SsIiMmPpLlEe' firewall template in rc.firewall) to allow a CISCO 
IPSec-based VPN client on a local machine to connect to a remote server (tunnel).

tcpdump shows that the client attempts to send packets to the remote VPN server 
on port 500 (isakmp) as you'd expect, but it's not getting any packets back and 
so the connection fails.

The following suggests that you can solve the problem by not changing the source 
port of the NATed packets, but gives a sample using pf:

http://lists.freebsd.org/pipermail/freebsd-net/2005-October/008749.html

Other posts I've read say you can simply forward packets from the remote VPN 
server to the machine running the VPN client, but (needless to say) I haven't 
been able to get this to work:

http://groups.google.com/group/comp.unix.bsd/browse_thread/thread/85d775a73e352aa5/f62e6b0d67b2d576

Any suggestions from people who have done similar before?

Cheers,

--Jon



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