ZyXEL Communications ZYWALL10 - Manual (Page 101)

ZyWALL 10 Internet Security Gateway
7-2 Filters
7.1.1 The Filter Structure of the ZyWALL
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 telnetting. 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 7-10 for the
logic flow when executing an IP filter.