I buy this modem to stop pay a rental fee to Comcast . it be a compatible modem with they system and have be provide I with the same level of service\/speed as the rental do . one strange thing : apparently if you give Comcast the serial number , it automatically create the MAC address . in my case , it be create the wrong MAC address . if you be on the phone with Comcast and connectivity be a issue , ask they to read the number back to you and check they against what be on the modem . I unfortunately have to have a tech come to my home but check and see if this be you problem before they send someone out .