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I recently switched from Comcast to Cox and my working modem is now no longer working with Cox, I can access to IPv6 websites but no IPv4 websites. I had this issue with Comcast when I bought the Arris SB7580 modem but they were able fix the problem. I need help from Cox technical folks because the tech guy on the phone were not able to fix the issue.
How did they fix it with Comcast? Also, how long has the modem been online with Cox now? It might require a automatic firmware update which happens in 48-72hrs.
Also, how are you using the modem(gateway)? Do you have it bridged to use your own router or is it your main router?