Question

Now I want to use a serversocket to listen port x, in the same time I want to use the port x to establish a socket to other serversocket, that means there is a serversocket and a socket will use one same port, is that possible?
I know for socket, it is four tuple, one port can have multiple socket, but for a socket and serversocket?
thank you for your attention!

Answer 1

It’s hard to understand your question because it’s not clear when you say “port” whether you mean source port or destination port.

If your question is, “Can I accept inbound connections on port X and also make outbound connections to port X?” The answer is yes. (You can bind to and connect to the same port.)

If your question is, “Can I listen on port X and also make outbound connections from port X?” The answer is no — unless you use two different local IP addresses. For TCP on a single IP address, you can only bind to the port once. If you bind to listen, from then on, the port is reserved for the incoming connections you will accept — you cannot bind to it again to make outgoing connections from it.