Basically, it seems that reference implies Comcast, even though they might not even know it themselves, is requiring *two* MAC addresses for authentication:
- The MAC address of the docsis3 Costco cable modem, and,
- Some other MAC address (which seems to be the router, by default).
Had I known that when we set it up, I would have made the router DE:AD:BE:EF:CA:FE, which at least I can remember.
There was one disturbing sentence in your reference:
"some ISPs have started to recognize the MAC addresses of popular routers and disconnect service if a router is detected."
A router is a requirement, not an option; so if they are doing that, they stink as ISPs.