As you know, public IP addresses are controlled by world-wide registrars, and are unique globally. Port numbers are not so controlled, but over the decades certain ports have become standard for certain services. The port numbers are unique only within a computer system. Port numbers are 16-bit unsigned numbers. The port numbers are divided into three ranges: the Well Known Ports (0..1023) - "The Well Known Ports are assigned by the IANA and on most systems can only be used by system (or root) processes or by programs executed by privileged users." , the Registered Ports (1024..49151), and the Dynamic and/or Private Ports (49152..65535).

Ports are used in the TCP [RFC793] to name the ends of logical connections which carry long term conversations. For the purpose of providing services to unknown callers, a service contact port is defined. This list specifies the port used by the server process as its contact port. The contact port is sometimes called the "well-known port".

To the extent possible, these same port assignments are used with the UDP [RFC768].

Updated On: 12.07.04