Short version: Does Comcast block Mac Addresses? Long version: Yesterday, I thought my Comcast High Speed Internet connection went down. I thought at first it was Comcast having issues, but I first tried to rule out a problem on my end. I connected the cable modem directly to my computer (normally, the modem goes straight to a Linksys router), but still no connection. After calling tech support, as a last resort, she suggested I try plugging the modem in directly to another computer. I did, and much to my surprise it worked. She said most likely my router and/or first computer's NIC was bad. It wasn't very plausible to me, but I had no other explanation. I even switched back to the router, just to tell myself that it wasn't Comcast that was glitching and was just all of the sudden working, but I still could not get an internet connection. Several minutes later, I had a sudden realization. There was something that my router and my NIC had in common. I had the router spoof that NIC's Mac Address. So when I switched the router's spoofing to the second computer's MAC addy, voila, everything was working again. So again, the only possible explanation I have is that Comcast blocked the original MAC address I was using. So my question is, have Comcast been known to do that, and if so, why?