I have a network with the following structure. The server in PC2 is simple socket server TCP in 8080 port. I need to access to PC2 from other external network by socket client. This socket client knows the public IP (85.xxx.xxx.x), the private IP (192.168.0.21) and the port. How I can access PC2 without port forwarding on the router? If possible, I would like to have a reference in any programming language of this case.