Is it possible to send an IpEndPoint over the network to another computer in order to send a response to the first (UDP) from another computer?

Question

UDP

IpEndPoint contains ip and port, this works well for white addresses, will this scheme work for gray IPs? Server with white IP, client with gray one.

Answer 1

If you send information containing a white IP from the server to the client, everything should be fine.
If you send information containing a gray IP from the client to the server, then the network device that performs NAT on the client's network (changing gray addresses to white ones) must understand the transfer protocol, replace gray addresses and ports with white ones inside your packet and open the corresponding ports additional temporary NAT tunnels. This technology is called "ip inspect". If your protocol is proprietary, then it is unlikely that network equipment will be able to decode it in order to modify the IP and port transmitted inside it.