SecurityFocus.com has the article. "Over the past several years, the use of Linux as a firewall platform has grown significantly. Linux firewalling code has come a long way since the
time ipfwadm was introduced in kernel 1.2. Recent changes in linux firewalling code include netfilter architecture (controlled from the command
line by iptables utility), which was introduced in stable kernel 2.4. The newest version 2.4 of Linux kernel (first released in January 2001) presents
many new security enhancements such as: enhanced capabilities, better support for encryption (for VPN and encrypted file systems) and
netfilter architecture, which is a re-implementation of Linux's firewalling code and which remains fully backward-compatible due to the use of
ipchains and ipfwadm loadable kernel modules."
April 23, 2001