I want to connect to computers, each one of them behind a NAT router. I read that STUN only works with one computer behind a NAT router. Is that true? If so, how can I solve that double-NAT problem?
Thanks, Thomas
TURN is a set of extensions to STUN that help to solve the double-NAT problem. You still need a server in the cloud, and the clients need to register. Source for some free servers is available.
From the TURN internet draft:
As described in [RFC5128] and [RFC4787], hole punching techniques
will fail if both hosts are behind NATs that are not well-behaved. For example, if both hosts are behind NATs that have a mapping behavior of "address dependent mapping" or "address and port dependent mapping", then hole punching techniques generally fail.
If you dó not have a central server, you May consider using upnp if available to create a hole in the router. Azureus/vuze does this.
来源：https://stackoverflow.com/questions/2116403/nat-traversal-with-java