User's Manual

Reference Manual for the Model FWAG114 Cable/DSL Wireless ProSafe Firewall
Firewall Protection and Content Filtering 4-11
Services
Services are functions performed by server computers at the request of client computers. For
example, Web servers serve web pages, time servers serve time and date information, and game
hosts serve data about other players’ moves. When a computer on the Internet sends a request for
service to a server computer, the requested service is identified by a service or port number. This
number appears as the destination port number in the transmitted IP packets. For example, a packet
that is sent with destination port number 80 is an HTTP (Web server) request.
The service numbers for many common protocols are defined by the Internet Engineering Task
Force (IETF) and published in RFC1700, “Assigned Numbers.” Service numbers for other
applications are typically chosen from the range 1024 to 65535 by the authors of the application.
Although the FWAG114 already holds a list of many service port numbers, you are not limited to
these choices. Use the Services menu to add additional services and applications to the list for use
in defining firewall rules. The Services menu shows a list of services that you have defined, as
shown in
Figure 4-7:
Figure 4-7: Services menu