Using the RESTRICTLOWPORTS parameter to control access to unreserved ports below port 1024

When the RESTRICTLOWPORTS parameter is specified on the UDPCONFIG or TCPCONFIG profile statements, an application cannot obtain a port in the range 1 - 1023 that has not been reserved by a PORT or PORTRANGE statement, unless the application is APF-authorized or has OMVS superuser [UID(0)] authority. z/OS® Communications Server client applications that need to bind to a low port are provided as APF-authorized.

Tip: When you configure the RESTRICTLOWPORTS parameter on the TCPCONFIG or UDPCONFIG profile statements, PORT UNRSV statements for the corresponding protocol control access only to unreserved ports above port 1023.
Parent topic: Controlling access to unreserved ports