UDP - client behind NAT, server behind NAT question

Hello group,

I'm trying to set up a UDP link between a mobile client on a GPRS
network, and a base server, both behind NAT.

Currently I'm getting the client-> server leg OK, and I'm replying to
the translated address on the client's network, but I've just realised
that I need to deal with the source of the server's reply.

So if the server is listening on, say 85.1.1.66 : 7000 , it's no good
me replying from an internal private address, as this will get NATted
as the packets leave the server system.

I have to make sure my return message originates with 85.1.1.66 : 7000
don't I? Currently port 7000 is being forwarded to my private address
inside the server's firewall. Maybe I just need to send my reply on
port 7000. Does that work in the reverse direction (can't try it til
Monday)?

Sorry if this is a horribly newbie question, but I'm an applications
programmer whose been chucked off the UDP cliff :-)

If this is not the likely problem, could someone just suggest how
addresses etc affect the passed messages in the client NAT / NAT server
scenario.

cheers, Jim
Received on Mon May 1 00:52:49 2006