Application Layer Packet Shaping on Linux
sommere writes "We have added application layer (layer-7) filtering to Linux. That means that you can set up your linux-router/linux-switch to prioritize mail over the web over kazaa or gnutella regardless of what port each program is using. Colleges have been paying thousands of dollars for packet shapers to prioritize their networks, now you can do it for free. Get your kernel patch at l7-filter.sourceforge.net."
For those not ready to upgrade to Linux 2.5, and for those on other platforms, there is Trickle, a userland traffic shaper for Linux, *BSD and Solaris. It works on a per-process basis (or on groups of processes to limit aggregate traffic consumption), does not require root-level access nor kernel patches, and is, of course, open source.
If you put your ISP on a commodity linux box and expect five 9's you need to back off the medication.
While not five 9's, I do run an ISP off of commodity Linux boxes and achieve three 9's (8.77 hours out of the year downtime) -- we're a commercial ISP and frankly, if that's not good enough for you, go buy someone else's service. I can't get three 9's downtime out of my upstream ISP if you count the scheduled downtime (which my three 9's figure does count).