Source Port Number

The source port number in an IP packet is by convention a number greater than 1,024.

This number is assigned on an as needed basis by Internet applications. It is normally the next available number above 1,024 at the time of the connection request.

This number is not in any way affiliated with a particular Internet application. All Internet applications have access to the same pool of source port numbers.

Because of its lack of affiliation with any Internet application and because of its random assignment, a source port number by itself is not useful to firewalls. It becomes useful only in conjunction with other pieces of addressing information.