I have a similar issue with thread (http://forums.xfinity.com/t5/Your-Home-Network/No-IPv4-only-IPv6-Arris-SBG7580/m-p/3098198). I can access some web sites (xfinity, google, facebook, microsoft, etc.) but cannot access many other web sites (e.g., amazon, ebay, craigslist, etc.).
I have Arris SBG7580AC cable modem gateway(router).
Could you(ComcastJohnN) please fix the issue for me?
I gave the right HFC MAC address and confirmed it with technicians. Even tier 2 technician cannot fix it (no clue) and said that he would escalate it. Hope somebody fix it soon.
I can help. Please send me a private message by clicking on my name, "ComcastChe" then click private message me. In the body of this message please verify your first and last name, and the account number or phone number associated with your services.