I just ran into the same thing today.

I have a Red Hat Linux box that suddenly stopped being able to get proper DHCP responses. So I unplugged it, and plugged in my wireless router instead. Same problem. Tried a different wireless router. Same problem.

So I call Comcast tech support, and just to humor them, I did all the stupid unplug/reboot stuff that I knew wasn't going to work. Same problem. Tried plugging my Mac laptop to the cable modem. Same problem.

OK, so I plug in and have them set up an older cable modem I have lying around. Linux box and wireless routers don't work, but my Mac laptop gets a web page that prompts me to install their software.

Against my better judgment, I install the software. Now my Mac laptop works, but only when it's directly plugged into the modem. But the Linux box, and the two wireless routers still can't get a proper DHCP response. So my laptop now only works if it's tethered to the cable modem. Not much of a laptop now, is it?

So I complain to them, and they suggest I get one of their new cable modems models (that I have to rent.)

Did that. Same thing--Mac laptop works, nothing else does.

I hope you're right in that the "blocking" of these MAC addresses is only temporary somehow. I'll try it connecting them again tomorrow and see what happens.

RE: Comcast's DHCP is STILL broken