ZyXEL Communications Internet Security Gateway ZyWALL 2 Series - Manual (Page 438)

ZyWALL 2 Series User’s Guide
30-2 Filter Configuration
Figure 30-1 Outgoing Packet Filtering Process
For incoming packets, your ZyWALL applies data filters only. Packets are processed depending upon
whether a match is found. The following sections describe how to configure filter sets.
30.1.1
Filter Structure
A filter set consists of one or more filter rules. Usually, you would group related rules, e.g., all the rules for
NetBIOS, into a single set and give it a descriptive name. The ZyWALL allows you to configure up to twelve
filter sets with six rules in each set, for a total of 72 filter rules in the system. You cannot mix device filter
rules and protocol filter rules within the same set. You can apply up to four filter sets to a particular port to
block multiple types of packets. With each filter set having up to six rules, you can have a maximum of 24
rules active for a single port.
Sets of factory default filter rules have been configured in menu 21 to prevent NetBIOS traffic from
triggering calls and to prevent incoming telnet sessions. A summary of their filter rules is shown in the
figures that follow.
The following figure illustrates the logic flow when executing a filter rule. See also Figure 30-6 for the logic
flow when executing an IP filter.
Data
Outgoing
Packet
Drop
packet
Built-in
default
Call Filters
User-defined
Call Filters
(if applicable)
Initiate call
if line not up
Active Data
Send packet
and reset
Idle Timer
Or Or
Drop packet
if line not up Drop packet
if line not up
Send packet
but do not reset
Idle Timer
Send packet
but do not reset
Idle Timer
Match Match Match
No
match
No
match
No
match
Call Filtering