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

Rules and Keywords
IPFilter Keywords
Chapter 226
IPFilter Keywords
IPFilter rules are built using keywords and parameters that combine to
filter packets coming in and out of a system. The following sections
describe the keywords that form the basic building blocks of IPFilter
rules. These sections include the purpose of the keywords and examples
of how to use them in rules.
NOTE For more information about IPFilter rule syntax, see the ipf (5) manpage.
pass and block: Controlling IP Traffic
The first keyword in any IPFilter rule is usually either pass or block. To
allow packets into the IPFilter system, use pass. For example, to allow
all incoming packets, use:
pass in all
To deny all incoming packets, use:
block in all
in and out: Bidirectional Filtering
You can explicitly pass and block both inbound and outbound traffic.
Inbound traffic is all traffic that enters the firewall on any interface.
Outbound traffic is all traffic that leaves on any interface, whether
locally generated or passing through. Packets coming in are not only
filtered as they enter the firewall, they are also filtered as they exit.
To block all incoming packets, use the following rule:
block in all
To pass all outgoing packets, use the following rule:
pass out all
You can use in and out with all other keywords. IPFilter filtering
techniques are applicable to both inbound and outbound traffic.