UDP Hole Punching Java Example

Question

I want to do UDP Hole Punching with two clients with the help of a server with a static IP. The server waits for the two clients on port 7070 and 7071. After that it sends t

Answer 1

UDP hole punching can't be achieved with all types of NAT. There is no universal or reliable way defined for all types of NAT. It is even very difficult for symmetric NAT.

Depending on the NAT behaviour, the port mapping could be different for different devices sending the UDP packets. Like, If A sends a UDP packet to B, it may get some port like 50000. But if A sends a UDP packet to C, then it may get a different mapping like 50002. So, in your case sending a packet to server may give a client some port but sending a packet to other client may give some other port.

You shall read more about NAT behaviour here:

http://tools.ietf.org/html/rfc4787

https://tools.ietf.org/html/rfc5128

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