Linksys makes a line of cheap, ubiquitous router/firewall boxes well-suited for use on a home DSL connection and popular among Linux hackers. This HOWTO gives hints and tips for managing Linksys routers from a Linux system.
The specific recipes described here are derived from long experience with a BEFSR41, the 4-port router/firewall box. I have also configured a BEFW11S4v2, the 4-port router with 80211b wireless, and it behaves so similarly to the BEFSR41 that I suspect they're using the firmware images mostly generated from common source code — in fact, it wouldn't surprise me if it were the same firmware, doing port tests to figure out what pieces of the user interface it should enable. The firmware and web interfaces on all these blue boxes are very similar, and most of the advice should generalize.
You can also view the latest version of this HOWTO on the World Wide Web via the URL http://www.tldp.org/HOWTO/Linksys-Blue-Box-HOWTO.html.
Copyright (c) 2003, Eric S. Raymond.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is located at www.gnu.org/copyleft/fdl.html.
Feel free to mail any questions or comments about this HOWTO to Eric S. Raymond, <esr@snark.thyrsus.com>. But please don't ask me to troubleshoot your general networking problems; if you do, I'll just ignore you.