HP-UX IPFilter Version A.03.05.14 Administrator's Guide

Firewall Building Concepts
Creating a Complete Filter by Interface
Chapter 476
Creating a Complete Filter by Interface
When you create a ruleset, you should set up rules for all directions and
all interfaces. The default state of IPFilter is to pass packets both in and
out. Instead of relying on the IPFilter default behavior, make every
ruleset as specific as possible, interface by interface, until all possibilities
are explicitly covered.
For example, if you have an IPFilter system with a lan1 interface, and a
lan0 interface, configure the following rules:
pass out quick on lan1
pass in quick on lan1
block out quick on lan0 from any to 192.168.0.0/16
block out quick on lan0 from any to 172.16.0.0/12
block out quick on lan0 from any to 10.0.0.0/8
pass out quick on lan0 from 20.20.20.0/24 to any
block out quick on lan0 from any to any
block in quick on lan0 from 192.168.0.0/16 to any
block in quick on lan0 from 172.16.0.0/12 to any
block in quick on lan0 from 10.0.0.0/8 to any
block in quick on lan0 from 127.0.0.0/8 to any
block in log quick on lan0 from 20.20.20.0/24 to any
pass in all
In this example, no restrictions are on traffic in and out on lan1. Traffic
has significant restrictions both in and out of lan0.
NOTE When setting up your ruleset, be sure that you add rules for all
appropriate directions and interfaces.