[Openswan Users] Setting the IKE UDP port

Marcus Better marcus+keyword+openswan.0a8cde at dactylis.com
Fri Jul 9 13:00:17 CEST 2004

Hi all,

I have a problem with a NAT router which requires me to change the IKE UDP
port from the default (500). I accomplished this on the initiating end for
the source port by putting plutoopts="--ikeport 5000" in ipsec.conf.  How
can I also set the destination port for this particular connection to
something different from the default?

The reason for this is as follows: I am behind a NAT router that I do not
control, and that has decided I am not allowed to have anything to do with
port 500. Even if I use a different source port, but the destination port
is 500, the router will translate the source port also to 500. I verified
this using tcpdump on the receiving end of the connection. As a result,
the return traffic is sent to the router's port 500 and apparently blocked

So if I can also set a different destination port, the router should pass 
the traffic, and I should be able to use NAT-T to continue.


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