There's also no reason to spoof the MAC addresses of real subscribers.<p>If your modem's external MAC isn't in Comcast's (global!) subscriber table, they give your modem a "walledgarden" default configuration file that causes it to reset frequently, and a poisoned DHCP DNS that directs all queries to their "Subscribe Now!" webserver.<p>Some of the European ISPs have countermeasures that rotate the names of the configs frequently, but Comcast doesn't do that -- if you've modified your modem, all you have to do is have your modem ask for a different config file (the names of which it will sniff from your neighbors), and set a different DNS server on the modem's immediate clients.