NAT traversal with Java

Question

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

Answer 1

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.

Answer 2

UDP hole punching and TCP hole punching

Answer 3

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.