Port numbers are used on various socket calls. They are also included in both the header of a TCP segment and a UDP datagram. You can assign port numbers to your own server applications by adding entries to the z/OS® UNIX file or to the data set.
The following example reflects a situation where more than one application needs to listen on the same port, and the application or applications bind to INADDR_ANY.
PORT
512 TCP RXSERVE ; Remote Execution Server (default)
512 TCP OMVS BIND 9.67.113.2 ; orexecd Remote Execution Server (MVS97USS)
514 TCP RXSERVE ; Remote Shell Server (default)
514 TCP OMVS BIND 9.67.113.2 ; orshd Remote Shell Server (MVS97USS)
Result: Clients who use MVS97 for remote execution get RXSERVE, and clients who use MVS97USS get OMVS orshd.