AlanStudio Linux Tutorial

Whatt Is iptables?


Originally, the most popular firewall/NAT package running on Linux was ipchains, 
but it had a number of shortcomings. To rectify this, the Netfilter organization 
decided to create a new product called iptables, giving it such improvements as:


    * Better integration with the Linux kernel with the capability of loading 
      iptables-specific kernel modules designed for improved speed and reliability.

    * Stateful packet inspection. This means that the firewall keeps track of each 
      connection passing through it and in certain cases will view the contents of 
      data flows in an attempt to anticipate the next action of certain protocols.
      This is an important feature in the support of active FTP and DNS, as well
      as many other network services.

    * Filtering packets based on a MAC address and the values of the flags in the
      TCP header. This is helpful in preventing attacks using malformed packets and
      in restricting access from locally attached servers to other networks in spite 
      of their IP addresses.

    * System logging that provides the option of adjusting the level of detail of 
      the reporting.

    * Better network address translation.

    * Support for transparent integration with such Web proxy programs as Squid.

    * A rate limiting feature that helps iptables block some types of denial of service
      (DoS) attacks. 


Considered a faster and more secure alternative to ipchains, iptables has become the
default firewall package installed under RedHat and Fedora Linux.
reference link: http://www.linuxhomenetworking.com/wiki/index.php/