HP-UX IPFilter A.03.05.13 Administrator's Guide: HP-UX 11i v3

HP-UX IPFilter Configuration Examples
firewall
Appendix A 167
firewall
#Configuring IP Filter for firewall usage.
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Step 1 - Block out "bad" IP packets.
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Run the perl script "mkfilters". This will generate a list of
blocking rules which:
a) blocks all packets which might belong to an IP Spoofing
attack;
b) blocks all packets with IP options;
c) blocks all packets which have a length which is too short
for any legal packet;
Step 2 - Convert Network Security Policy to filter rules.
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Draw up a list of which services you want to allow users to use
on the Internet (e.g. WWW, ftp, etc). Draw up a separate list
for what you want each host that is part of your firewall to be
allowed to do, including communication with internal hosts.
Step 3 - Create TCP "keep state" rules.
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For each service that uses TCP, create a rule as follows:
pass in on <int-a> proto tcp from <int-net> to any port
<ext-service> flags S/SA keep state
where
* "int-a" is the internal interface of the firewall. That is,
it is the closest to your internal network in terms of network
hops.
* "int-net" is the internal network IP# subnet address range.
This might be something like 10.1.0.0/16, or 128.33.1.0/24
* "ext-service" is the service to which you wish to connect or
if it doesn’t have a proper name, a number can be used. The
translation of "ext-service" as a name to a number is
controlled with the /etc/services file.