### Module introduction

This module allows you to configure the IPtables firewall features found in the 2.4 series of Linux kernels. Unlike some other firewall configuration programs, instead of creating a shell script that sets up the firewall, it reads and edits a save file in the format read and written by `iptables-restore` and `iptables-save` respectively.

If you already have a firewall on your system that has been setup manually or from a script file, the module will offer to convert it to an IPtables save file for you, and create a script to be run at boot time to activate the rules in the file. However, if you do this then you should no longer edit your firewall rules script and should disable it from running at boot time as well.

### IPtables overview

Every network packet that comes into, goes out from or is forwarded by your system is checked against one or more chains to determine what will happen to it. Each chain contains zero or more rules, each of which has a condition (to determine which packets it matches) and an action (to control what happens to those matching packets). Each chain also has a default action that controls what happens to packets that do not match any rule.

Each chain is part of a table, of which there are currently three :

- Packet filtering (`filter`)
  The chains in this table can be used to control data coming into your system from other hosts on the network, data sent out from your system by users and processes, and data forwarded by your system if it is acting as a router.

- Network address translation (`nat`)
  This table can be used for setting up NAT or masquerading, which is useful if you want to give an entire network of machines access to the internet through only one real IP address.

- Packet alteration (`mangle`)
  This chain is for modifying packets forwarded by or sent out from your system.

In addition to the standard chains that are part of each table, you can also create your own chains that can be run by rules in the build-in chains. This can be useful for grouping and sharing rules that might be used in multiple places.

### The main page

The main page of this module lists all the chains and rules from one of the available tables, selected from the list in the top-left. Below is a section for each chain in the current table, with all rules in each chain listed and their conditions described to the best of the module's ability. For each chain, you can change the default action using the drop-down list if the chain is one of the build-in ones for the table, or delete it with the Delete chain button if it is user-defined.

You can click on any rule in a chain to edit it, click on the arrows on the right of each row to move it up or down, or click on the Add rule button to add a new one. Adding or editing a rule will take you to a page on which you can select the action for each rule, and the conditions for which the action is executed.

At the bottom of the page is a button for making the current firewall configuration active, by loading it into the kernel with the `iptables-restore` command. Below it is a button for doing the reverse - taking the configuration that is currently in the kernel and making it available for editing. Finally, if your distribution supports it, there is a button to change whether the firewall is activated at boot time or not.