Question: I have the following problem. My client program monitor for availability of server in the local network (using Bonjour, but it does not rally mater). As soon as a server is "noticed" by the client application, the client tries to create a socket: `Socket(serverIP,serverPort);`.

At some point the client can loose the server (Bonjour says that server is not visible in the network anymore). So, the client decide to `close` the socket, because it is not valid anymore.

At some moment the server appears again. So, the client tries to create a new socket associated with this server. But! The server can refuse to create this socket since it (server) has already a socket associated with the client IP and client port. It happens because the socket was closed by the client, not by the server. Can it happen? And if it is the case, how this problem can be solved?

Well, I understand that it is unlikely that the client will try to connect to the server from the same port (client port), since client selects its ports randomly. But it still can happen (just by chance). Right?

Answer: 
Yes, close the socket, as soon as you detect a failure.

The socket will be "stuck" in "close\_wait" if not closed properly.
Even if the socket is closed, it's state will be in time\_wait for a short period. 

However, if You design the application to use a different local port for each new connection, there is no need to wait for the old socket to be closed. 

(As you are then creating a completly different socket, since a socket is identified by the remote-ip, remote port, local ip and local port.)
If you close server socket only in case of blocking socket then client socket will be closed but not vice versa.

otherwise it would be better socket in both end. Because socket is a heavy weigt for you system. It will use a local port and a remote port of your system forever.

Thanks
Sunil Kumar Sahoo