This was a first provisioning of my SBG7880-AC modem/wifi combo unit with Xfinity in Seattle.
After resolving several issues requiring 4 visits from Comcast support (bad fiber bundle in apartment building), I finally got internet. However, I was only able to browse google, apple, youtube, facebook, and wikipedia. Possibly others, but not most, including microsoft and amazon. Others have found the same issue, often with the same modem, but it is not a problem with the modem and there is no need to return it (despite what comcast support tells you).
In my case, the wrong MAC address was entered during provisioning. On seeing others resolve their issues by private messaging ComcastJohnN, I messaged him on a Saturnday night and he responded, found, and fixed the issue within 10 minutes (I do not suggest everyone abuse John's Saturday nights, but it is testimony to his dedication and customer service). In his words:
This usually happens when the wrong MAC is used in the provisioning process. It has to be the CMAC (also called CM MAC, HFC MAC or Cable MAC.) If one of the other MAC addresses on the modem is used, or if it's just not entered correctly, it will break DHCP and your router won't get a valid IPv4 address and you'll only be able to reach IPv6 sites.
It may be that it happens more with this modem because the modem lists two MAC addresses, a "WAN MAC" and an "HFC MAC". Provisioning services just ask for the MAC address and its not clear which one, and they often don't know either. So they enter the first one, which is wrong. If you buy this modem and have it provisioned, make sure they use the second "HFC MAC" address. Even when they correct it, which they can do over the phone, as of Dec 2017 you need someone like ComcastJohnN to fix the error in the backend server--Comcast support do not have access to this and do not know how to do this.
Thanks again John, and I hope Comcast can come up with a way for Support to be able to fix this themselves and give you your Saturnday nights back!
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