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

Given your conceptual outline, I think there is an issue at point 4. Although A punches a hole through its own NAT, when B attempts to reach this hole it is unaware of the port on A's NAT (or more correctly/commonly - NAPT) and hence A's NAT drops the packet when B attempts to communicate.