A Linux kernel packet control tool, iptables along with netfilters and the NAT subsystem form the framework of the Linux 2.4 x and Linux 2.6 x systems. Targeted towards system administrators, iptables is a user space program run from the command prompt and is used to configure the Linux 2.4.x and Linux 2.6.x packet filtering ruleset that uses IPV4 and IPV6 protocols for data transmission. Each rule in an iptables consists of a number of classifiers called iptables matches and one action that is connected with the classifiers called the iptables target.

Version 1.4.3.2 provides a few enhancements over the previous releases, the main improvement being in the field of bug fixtures. The package also includes ip6tables which is used for configuration of IPv6 packet filter. The entire framework supports numerous functions like packet filtering, network address translation, NA[P]T (including port address) and packet mangling. Since the Network Address Translation (NAT) subsystem also forms a part of this framework, iptables can be applied to NAT as well.

For proper operation, iptables require a kernel that features the iptables packet filter. This is included in the kernel versions 2.4.x and 2.6.x.

Some of the features of iptables include:

. Provision for adding/removing/or modifying the rules in the packet filters set.
. Listing all the contents of the packet filter ruleset.
. Listing and zeroing in on per rule counters of the packet filter ruleset.
. Provision for the support of all kinds of network addresses and port translation features.
. Provision for stateless packet filtering facilities for IPV4 and IPV6 as well as stateful packet filtering for IPV4.
. Use of multiple layers of APIs for third party extensions along with the support for a large number of plug ins and modules kept in a container called patch – o- matic repository.