Compatible Systems 5.4 - Manual (Page 219)

Chapter 13 - AppleTalk Filtering 213
all packets. For NBP request and reply packets the NBPName, NBPType and
NBPZone rules are also used. All other rules are ignored.
Get Zone List
The get-zone-list interpreter allows the filtering of outgoing get-zone-list
replies on an interface. These replies contain the zone list displayed by the
Chooser on a Macintosh when it is opened. Thus, the get-zone-list interpreter
allows control of the zones that are seen on a Macintosh behind a device. The
only rules used in this interpreter are the network, net-range and zone rules.
All other rules are ignored.
Routing Filters (RTMP)
The RTMP interpreter allows network numbers in input and output Apple-
Talk RTMP routing packets to be filtered on an interface. The only rules used
in this interpreter are the network and net-range rules. All other rules are
ignored.
Basic AppleTalk Filter Rules and Syntax
At a minimum, every non-comment line in a filter set must include an action.
However, an action alone will not create a useful filter rule (except for setting
a default rule as noted above).
Every line in a packet filter set must begin with the actions permit, or deny,
or the comment indicator #.
• Lines which begin with permit specify that a packet meeting the condi-
tions should be passed by the filter.
• Lines which begin with deny specify that a packet meeting the condi-
tions should be dropped by the filter.
• Lines which begin with # specify that the text on the line is a comment
and should be ignored.
AppleTalk Filter Options
The basic action specified in the rule will almost always be accompanied with
an option. AppleTalk filter options use some or all of a set of operators to
determine whether the filter rule matches the information being examined or
not. These operators are discussed below:
• eq, ==, or = These are allowable ways of writing an “equality” operator
which will match if the value in the packet/information is equal to the
value specified in the option expression.
• lt or < These are allowable ways of writing a “less than” operator which
will match the packet/information if its value is less than the value spec-
ified in the option expression.