STUN is a protocol that allows routers to find out about themselves by talking to a STUN server.
There’s an open-source STUN client at http://sourceforge.net/projects/stun/.
~/sw/stund$ ./client stun.xten.com STUN client version 0.96 Primary: Indepndent Mapping, Port Dependent Filter, preserves ports, no hairpin Return value is 0x000017
Hmmm. No hairpin – that’s good I guess… 🙂