Absolute OpenBSD, 2nd Edition

Packet Filtering with Lists and Macros

PF includes many ways to have one rule reference several similar items, or symbolically represent something with a variable. The basic ways are lists and macros.

Using Lists

A list is a way to represent several similar items in one rule. You might want to use a list if, for example, you want a particular group of TCP ports open on a certain group of hosts, and your rule entries would be repetitions of one rule with minor changes. Opening ports 80 and 443 to one host requires two rules: one for each port. If you have 30 web servers, you would need 60 rules. This is a pain to maintain and error-prone, but lists let you express these common elements more easily.

A list is represented in curly braces within ...