Configuring Filters 10-1
Chapter 10Configuring Filters
This chapterprovides information about configuring and using filters for your Model RP114Web
Safe Router.
Filtersare used to block certain packets, reduce traffic, and prevent securitybreaches. The router
uses packetfilters to determine whether to allow or deny passage of each data packet, based on
informationfound in the packet. A filter is defined by rules declaring what information is to be
checked andwhat action is to be taken (forward or discard) when a match is found. Twotypes of
packet filtersare supported by the router: IP protocol filters and generic or“device” filters. An IP
protocolfilter screens the packet based on IP address and port information contained in the packet.
A genericfilter looks for a specified pattern of bits at a specified location in the packet.
In the configuration of IP filters, it is necessary to specify ports and protocols by their assigned
numbersinstead of names. A comprehensive list of protocol and port numbers for common IP
trafficcan be found in IETF RFC1700, “Assigned Numbers.” Many common port numbers are
also listedon any Windows PC in a file called \windows\services.
TheModel RP114 router allow you to customize filter sets according to your needs.The following
sectionsdescribe how to configure the filter sets for your router.

Router Filter Structure

Youcan configure up to 12 filter sets, each with up to six rules. For IP packets, these rules involve
comparingthe protocol type of a data packet (for example, TCP, UDP), sourceor destination
address,or port number. Also, a generic filter may bedefined to merely test for a byte or pattern of
bytes in a particular location in the packet. W hen a rule is met (or not met), a user-specified ac tion
is taken. This action may be to forward the packet, drop the packet , or got o the next rule.