Configuring A Filter Rule - ZyXEL Communications Prestige 128 Plus User Manual

Prestige 128+ ISDN Router

11.3 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.
11.3.1 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.
Filter Configuration 11-7