we subscribe to Comcast high speed internet service and have enjoy it far more than we battle with Verizon . we have a Motorola modem before and it work great for a couple of year - until Friday , June 15th , we could not get a connection for any longer than 30-45 seconds before the modem would restart itself over and over and over . the service rep at Comcast infer that we must have a bad modem so we buy a brand new Motorola Surfboard 6121 and we have the same problem ! we bring out the Comcast technician who test the line and assure we that the line be good but the modem be not work right . so I get a second new Surfboard 6121 modem and that do not work either !! we daughter , who also have Comcast , tell we that they have a Arris 7640 modem and so we order that . the Arris modem come and presto , it work . I always think that Motorola be a excellent modem but , for some reason , they be not compatible with Comcast in Massachusetts . good luck - I know how frustrate it be .