FVS338 ProSafe VPN Firewall 50 Re ference Manual
4-18 Firewall Protection and Content Filtering
v1.0, March 2008
Outbound Rules Example – Blocking Instant Messenger
Outbound rules let you prevent users from using applications such as AOL Instant Messenger,
Real Audio or other non-essential sites.
If you want to block AOL Instant Messenger usage by employees during working hours, you can
create an outbound rule to block that application from any internal IP address to any external
address according to the schedule that you have created in the Schedule menu. You can also have
the firewall log any attempt to use Instant Messenger during that blocked period.
.
Adding Customized Services
Services are functions performed by server computers at the request of clie nt computers. You can
configure up to 125 custom services.
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 man y common protocols are defined by the Internet Engineering Task
Force (IETF) and published in RFC1 700, “Assigned Internet Protocol Numbers.” Service numbers
for other applications are typically chosen from the range 1024 to 65535 by the authors of the
application.
Figure 4-12