Open Source IP Testing Tool?

winter@ES asks: "I'm looking for some "IP impairment" software for Linux. What I'd like is the ability to write some scripts that filtered/routed all traffic flowing through a box, with rules like 'For all traffic going to IP x.x.x.x, delay all frames by 400 miliseconds; reorder every 5th frame, and drop every 3rd frame.' There are remarkably few hardware/software solutions out there that I've been able to find to do this kind of thing, and the solutions that do exist are mostly targeted at backbone ATM-based networks. Anyone know of a nice open source tool for simulating poor network conditions?"