arno-iptables-firewall is a front-end for iptables. Its configuration script
will set up a secure and restrictive firewall by just asking a few questions.
This includes configuring internal networks for Internet access via NAT and
potential network services like http or ssh. Moreover, it provides advanced
additional features that can be enabled in the well documented configuration
file.

NOTE - The setup script will *not* run automatically after your package was
installed. In order to run the script you have to issue the following command:

# arno-iptables-firewall-configure

To enable the startup of the firewall at boot-time you need to create a symlink
as follows (in order to disable it, either remove the symlink or "chmod -x" the
startup script):

# ln -sv /etc/rc.d/rc.arno-iptables-firewall /etc/rc.d/rc.firewall
# chmod +x /etc/rc.d/rc.arno-iptables-firewall

You can also start the firewall manually with one of the following commands:

# /etc/rc.d/rc.arno-iptables-firewall start

# arno-iptables-firewall start

IMPORTANT - A few security notes from the upstream author:

1) If possible make sure that the firewall is started before the (ADSL) Internet
connection is enabled. For a ppp-interface that doesn't exist yet you can use
the wildcard device called "ppp+" (but you can only use ppp+ if there aren't any
other ppp interfaces).

2) Don't change any (security) settings ('EXPERT SETTINGS') if you don't really
understand what they mean. Changing them anyway could have a big impact on the
security of your machine.

3) A lot of people complain that their server stopped working after installing
the firewall. This is the *correct* behaviour for a firewall: blocking *all*
incoming traffic by default. Configure your OPEN_TCP (e.g.) accordingly.