UDP hole punching host-specific failure

Question

I wrote a program that sets-up peer-to-peer links. The programm, which can be found at http://basyl.co.uk/code/punch/doc/files/Readme-txt.html, is in two parts: a server that r

Answer 1

So in summary, the client doesn't work on a particular host when the server is on the same host. Any suggestions for reasons for this behaviour

Could it be that the server sees clientA as being on 127.0.0.1 (or maybe a non-routable LAN address?) and not its public IP-address?

If clientB tries to contact clientA using the wrong address, it's obvious why the UDP-datagram doesn't get to the intended recipient.

or for ways I could investigate this further?

Some output from tcpdump from both the server (AKA clientA) and clientB would help a lot. You might want to use -i any and maybe -s 0.