Communication between two computers without opening ports, using a third computer to set up the connection

Question

Let\'s say I have a server, and two clients connected to it. (via TCP, but it doesn\'t matter)

My goal is to allow a direct connection between those two clients. This is

Answer 1

Punching TCP holes in NAT is sometimes/often possible (it depends of the NAT behavior). This is not a simple subject to learn, but read the corresponding chapter about NAT traversal from Practical JXTA II (available online on Scribd) to understand the nature of the issues to solve.

Then, read this. It comes from the guy who wrote that: http://nutss.gforge.cis.cornell.edu/stunt.php (one of the links in your question).

I am not a C/C++ specialist, but the issues to solve are not language specific. As long as you have access to TCP from your code base, that's enough. Keep in mind that implementing UDP traversal is easier than TCP.

Hope these tips help.

P.S.: I am not aware of a C/C++ implementation of the solution. The code mentioned in Cornell's link is NOT operational as confirmed by the author. I tried to resuscitate it myself, but he let me know it was completely tweaked for research purposes and far from production ready.