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Hi (: I have tried to detect ports used for UDP and TCP. I send a UDP message and check port used in NAT and then send messages back to that port. I also send a UDP message from another listener, detect the port used in NAT, close that listener and then host a network on the same port hoping the NAT will also use that port when communicating. But it seems like it either gets another port or only the UDP part was opened on that port. I would very much like to get the possibility to detect the port used for a regular network message.

I think the main problem is that I can't send out on a socket or a regular network message before the port used in NAT is detected. Both require a connection first, which can't be established before I send something out on a socket or a network message to get the NAT to open the TCP part also. If I connect from the device I want the get through the NAT as a client, I connect to the receiving device's chosen port, I can't specify which port I want to use for the sending device, only which port to connect to. To sum up, if I bind the interface/port used for opening and detecting a port with UDP to a TCP connection, this connection can't be connected to before it has sent data out, which is impossible because it requires a connection in the first place that can't be established because no data has been sent out thus the TCP part of the port is not yet opened.

A regular Catch-22 situation