I seem to be having the same problem as a few others on here. I recently purchased my own modem/router (2 in 1) setup, and have had nothing but problems. The model is the Arris SB6700-AC. I found out that during provisioning the incorrect MAC address was in fact entered. After the correction was made, I thought there would be no problems. However, it seems as though I have access to IPv6 but not IPv4. I’ve talked to Comcast several times and they let me know it’s my router’s problem and I spoke with Arrris and they let me know that it’s an issue on Comcast’s end. I know there’s a way to fix this.