ZyXEL Communications ZYWALL10 User Manual

ZyWALL 10 Internet Security Gateway

Filters

7-15

After you’ve created the filter set, you must apply it.
Step 1. 

Enter 11 from the main menu to go to menu 11.

Go to the Edit Filter Sets field, press the [SPACE BAR] to select Yes and press [ENTER].

This brings you to menu 11.5. Apply a filter set (our example filter set 3) as shown in Figure
7-17.

Press [ENTER] to confirm after you enter the set numbers and to leave menu 11.5.

There are two classes of filter rules, Generic Filter (Device) rules and Protocol Filter (TCP/IP) rules.
Generic Filter rules act on the raw data from/to LAN and WAN. Protocol Filter rules act on the IP packets.
Generic and TCP/IP filter rules are discussed in more detail in the next section. 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
ZyWALL 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

Menu 21.1.3 - Filter Rules Summary

 # A Type                       Filter Rules                              M m n
 - - ---- --------------------------------------------------------------- - - -
 1 Y IP   Pr=6, SA=0.0.0.0, DA=0.0.0.0, DP=23                             N D F
 2 N
 3 N
 4 N
 5 N
 6 N

                 Enter Filter Rule Number (1-6) to Configure: 1

This shows you that you have
configured and activated (A =
Y) a TCP/IP filter rule (Type =
IP, Pr = 6) for destination
telnet ports (DP = 23).

M = N means an action can be taken
immediately. The action is to drop the
packet (m = D) if the action is matched and
to forward the packet immediately (n = F) if
the action is not matched no matter whether
there are more rules to be checked (there
aren’t in this example).