使用0作为端口时的C＃，Socket.Bind

Question

In MSDN, there is a sentence,

"If you do not care which local port is used, you can create an IPEndPoint using 0 for the port number. In this case, the service provider will assign an available port number between 1024 and 5000"

My confusion is: When the Client want to connect to server,

Does the client still need to know which port the server is listening?

Or the Client just connect to the 0 port.

Thanks.

Answer 1

The client still needs to know which port the server was actually bound to, and connect to that.

An example of this in action is in the FTP protocol. Normally when using active mode, the server uses one (known) port for commands, and binds an extra dynamic port for data transfer. When a data transfer starts, the server sends the actual port in a message to the client over the command channel , and the client then connects to the (psudo-random) data port it just got informed about to get the actual file data.

Answer 2

when you connect to server ,you must know ip+port decide your application to link which process on the remoting server.

socket connect like that

your :IP server:Ip < =============================================================> your : port server:port

so in client. you do not care which local port. when you connect to the server ,server had know the port .