UDP hole punch possible?

Question

I'm trying to see if UDP hole punching is possible behind a certain NAT, but I've found that when the computer behind the NAT sends out UDP packets to two different IPs to the same port while being bound to the same port, the NAT assignes two different external port numbers. So behind this particular NAT, I believe UDP hole punching is impossible, is this correct?

Thanks

Answer 1

Not necessarily. The router might be willing to respond to IGD.

Answer 2

it's mean your NaT Symetric, And if your NaT is Symetric it's given different External ports for each connection.And it's not possible to connect Hole punching from two way but it's still possible to connect p2p. But only possible if agent side using conic Nat. Search for that.

But if two locations using Symetric NaT there is no way to connect p2p connection with Udp Hole Punching.

1. a:Symetric => b:symetric ---- not possible
2. a:Conic => b:Conic ------------ possible easily
3. a:Symetric => b:Coinc --------- possible / only one way handshake 4: a:Conic => b:symetric --------- not possible / but possible to connect one way handshake

But You can still use port prediction methods. it's mean you must guess wich port can be use in connection and try to connect it ( Tcp Hole Punch )

For Conic NaT can See About UDP Hole Punching Please Check Sample in https://github.com/turapulku/NaT-Traversal-UDP-Hole-punch.git

That's still developing but for now it's i hope it's helpful

Answer 3

You can use this web site to confirm the behavior of this particular NAT.

http://nattest.net.in.tum.de/test.php

It will check your NAT type and test if UDP/TCP hole punching is possible.

But since you already knew the port assignment is random, the UDP hole punching is not possible. Using UPnP to is another way, but does not work behind nested NATs.