Port numbers are assigned in various ways, based on three ranges:
User Ports (1024-49151)
Dynamic and/or Private Ports (49152-65535);
The difference uses of these ranges is described in [RFC6335]. System Ports are assigned by IETF process for standards-track protocols, as per [RFC6335]. User Ports are assigned by IANA using the “IETF Review” process, the “IESG Approval” process, or the “Expert Review” process, as per [RFC6335]. Dynamic Ports are not assigned.
The registration procedures for service names and port numbers are described in [RFC6335].