My outbound Internet connection stopped working again this morning, and (like the last couple times) evidence pointed towards my router, not the modem or anything provided by Comcast.
(As I said last time, I’m convinced there were originally multiple problems leading to confusion and increasing troubleshooting difficulty, but it appears I owe Comcast at least a partial apology.)
The good news is there’s a software fix, which can be invoked remotely (unfortunately not from outside the house since outbound connectivity is down, but it does mean I don’t have to walk over to the equipment closet to power cycle modems or routers): “mii-tool -r -R eth1” made everything happy again.
The router in question is a Netgear WNDR3700 running OpenWrt 10.03 “backfire”. I wonder whether this happens to others and whether it’s a hardware or software bug. I’m hoping a newer version of OpenWrt might fix it (but since release candidates of 10.03.1 have been appearing for 15 months now, I’m giving up hope for a new official release; newer version probably just means trunk); alternately, it won’t be too hard to whip up a monitoring script that tries to ping the modem and does the mii-tool reset whenever it doesn’t see a response.