IPtables (known as Netfilter) was written by Paul Russell and the other
members of the Netfiler Project
Team. It was meant as a replacement for IPChains that was implemented
in the 2.2.x series kernels. It offers true 1:1 NAT capabilities, Packet
filtering and connection tracking.
One major upshot of this is that due to the implementation of connection
tracking you can allow incoming connections by whether or not they relate to
an established connection. There is still some need for helper modules for
some connection types. (FTP and IRC at the moment)
