The bind() call binds a unique local port to an existing socket. Note that, on successful completion of a socket() call, the new socket descriptor does not have an associated port.

The bind() call can specify the required port or let the system choose. A listener application should always bind to the same well-known port, so that clients can know which port to use.

Even if an application specifies a value of 0 for the IP address on the bind(), the system administrator can override that value by specifying the BIND parameter on the PORT reservation statement in the TCP/IP profile. This has an effect similar to the application specifying an explicit IP address on the bind() function. For more information, see z/OS Communications Server: IP Configuration Reference.