As systems administrators, its often funny how new and interesting information ends up in our hands. Sometimes, its through an intentional course of study; other times, it seems to arrive by accident. Thats exactly how the concept of using a halted Linux computer as a firewall occurred to me. I was at work, perusing an internal corporate mailing list and saw a message about something that was once present in Linux. The message referred to a method for shutting down a Linux box while ipchains is still running, and having the box continue to perform firewall tasks.