UDP Holepunching behind NAT

Question

I am trying to implement a simple sketch of UDP-Holepunching in Java to test it\'s concept and use it in my C/C++ application later on.

Concept:

As from Wikip

Answer 1

Your code seems to be correct. I tested your code and it works fine. The concept is also correct. But please check whether both the clients you run are within same NAT device or different NAT devices. If your are running both the clients under same NAT device then it may not work because not all NAT devices support hair pinning i.e, both clients send packets to NAT's external IP which needs to be passed to itself. For more information refer this link: http://tools.ietf.org/html/rfc4787#section-6