My husband was setting up an experiment to test his fixes on Apache Traffic Server (ATS). He had set up his iptables, his routing tables, and processes, but still the packets were not going past ATS.
I managed to save the day by spending 5 minutes staring at his rules and channeling all those hours of staring fruitlessly at similar rules setting up my own torrent proxy experiments. The word "rp_filter" popped out of my mouth. And for once, that was it! Sometimes the seemingly useless and arcane is just what is needed.