[vpn-help] NAT Traversal - Using same outbound port as inbound port

Ben Ellis ben at collstream.co.uk
Thu Mar 18 11:20:48 CDT 2010

            Myself and a colleague are behind a Draytek 2800 Vigor and
are both running 64-bit windows (7 and Vista).


            We are connecting to a Cisco PIX using the latest Shrewsoft
client (2.1.6).


            When we connect individually we have no problem, but if we
both try to connect simultaneously (using different VPN Group Ids) one
of us gets disconnected.


            However, everyone else using the Cisco client on 32-bit
windows doesn't have a problem.


            I noticed in the NAT Sessions that the shrewsoft software is
attempting Nat-Traversal on OUTBOUND port 4500, whereas the Cisco client
connects on a random outbound port. I suspect what is happening is when
both clients try to connect using Nat-T with the same outbound port, the
Draytek is dropping the NAT-Session for the first client in favour of
the second for outbound traffic on 4500.


            Can I configure Shrewsoft VPN Client to use a different
local endpoint port, while still connecting to the 4500 port on the
destination endpoint?


            Thanks & Regards,



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