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P100IH ISDN Router
Filter Configuration 9-7
Abbreviation Description
SP Source Port number
DA Destination Address
DP Destination Port number
z
If the filter type is GEN (generic), the following abbreviations listed in the following table will be
used.
Table 9-3 Abbreviations Used If Filter Type Is GEN
Abbreviation Description
Off Offset
Len Length
Refer to the next section for information on configuring the filter rules.
9.3 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 two types of filter rules:
TCP/IP
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.
9.3.1 Filter Types and NAT
The network layer filters are collectively called protocol filters. When NAT (Network Address Translation)
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 for outgoing packets and after NAT
for incoming packets. On the other hand, the generic, or device, filters are applied to the raw packets that
appear on the wire. They are applied at the point when the Prestige is receiving and sending the packets; i.e.
the interface. The interface can be an Ethernet port or any other hardware port. The following diagram
illustrates this.