Watchguard Firebox X15 User Manual page 21

Ports
Some protocols, such as HTTP, have ports with assigned numbers.
For example, most computers transmit e-mail on port 25 because
the SMTP protocol is assigned to port 25. Other programs are
assigned port numbers dynamically for each connection. The IANA
(Internet Assigned Numbers Authority) keeps a list of well known
ports. You can see this list at www.iana.org/assignments/port-num-
bers.
Most services are given a port number in the range from 0 to 1024,
but possible port numbers range from 0 to 65535.
User Guide 7