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Prestige 128IMH ISDN Modem/ Router/Hub
Filter Configuration 10-7
10.3 Configuring a Filter Rule
To configure a filter rule, enter its number in Menu 21.1 - Filter Rules Summary and press Enter
to open Menu 21.1.1 for the rule.
There are three types of filter rules: TCP/IP, IPX and Generic. Depending on the type of rule, the
parameters below the type will be different. Use the space bar to select the type of rule that you
wish to create in the Filter Type field and press Enter to open the respective menu.
The network layer (TCP/IP and IPX) filters are collectively called protocol filters. When
NAT/SUA (Network Address Translation/Single User Account) is enabled, the inside IP address
and port number are replaced on a connection-by-connection basis, which makes it impossible to
know the exact address and port on the wire. Therefore, the Prestige applies the protocol filters to
the “native” IP address and port number before NAT/SUA for outgoing packets and after
NAT/SUA for incoming packets. On the other hand, the generic, or device, filters are applied to
the raw packets that appear on the wire.
To speed up filtering, all rules in a filter set must be of the same class, i.e., protocol filters or
generic filters. The class of a filter set is determined by the first rule that you create. When
applying the filter sets to a port, separate menu fields are provided for protocol and device filter
sets. If you include a protocol filter set in a device filters field or vice versa, the Prestige will
warn you and will not allow you to save.
10.3.1 TCP/IP Filter Rule
This section shows you how to configure a TCP/IP filter rule. TCP/IP rules allow you to base the
rule on the fields in the IP and the upper layer protocol, e.g., UDP and TCP, headers.
To configure a TCP/IP rules, select TCP/IP Filter Rule from the Filter Type field and press Enter
to open Menu 21.1.1 - TCP/IP Filter Rule, as shown below.