Книга: Iptables Tutorial 1.2.2
The first section you should note within the example rc.firewall.txt is the configuration section. This should always be changed since it contains the information that is vital to your actual configuration. For example, your IP address will always change, hence it is available here. The $INET_IP should always be a fully valid IP address, if you got one (if not, then you should probably look closer at the rc.DHCP.firewall.txt, however, read on since this script will introduce a lot of interesting stuff anyways). Also, the $INET_IFACE variable should point to the actual device used for your Internet connection. This could be eth0, eth1, ppp0, tr0, etc just to name a few possible device names.
This script does not contain any special configuration options for DHCP or PPPoE, hence these sections are empty. The same goes for all sections that are empty, they are, however, left there so you can spot the differences between the scripts in a more efficient way. If you need these parts, then you could always create a mix of the different scripts, or (brace yourself) create your own from scratch.
The Local Area Network section contains most of the configuration options for your LAN, which are necessary. For example, you need to specify the IP address of the physical interface connected to the LAN as well as the IP range which the LAN uses and the interface that the box is connected to the LAN through.
Also, as you may see there is a Localhost configuration section. We do provide it, however you will with 99% certainty not change any of the values within this section since you will almost always use the 127.0.0.1 IP address and the interface will almost certainly be named lo. Also, just below the Localhost configuration, you will find a brief section that pertains to the iptables. Mainly, this section only consists of the $IPTABLES variable, which will point the script to the exact location of the iptables application. This may vary a bit, and the default location when compiling the iptables package by hand is /usr/local/sbin/iptables. However, many distributions put the actual application in another location such as /usr/sbin/iptables and so on.