Modem work great with Comcast . I upgrade from a fail sb5100 . connection be very stable with 25 mbp download\/4mbps upload speed . it be very easy to setup without a call to Comcast . it take about 10 minute to complete the configuration of the new modem . here be what I do : 1 -rrb- power down computer , modem and router , if you use one . 2 -rrb- disconnect cable that go to old modem . 3 -rrb- connect internet cable to new modem . 4 -rrb- connect a ethernet cable from modem to computer . there be one supply with modem . 5 -rrb- power on new modem and wait for all four light to stop flash , this might take a while . 6 -rrb- Start computer and open up you internet browser . the browser will go to the xfinity configuration page automatically . 7 -rrb- if you be already a xfinity customer hit the blue login link . if you be a new customer fill in you account number and phone number . 8 -rrb- follow the online instruction to complete the new modem activation . 9 -rrb- once you establish a internet connection you be do . if you be use a wireless router continue with this : 1 -rrb- power off the computer and modem . 2 -rrb- disconnect ethernet cable from modem to computer . 3 -rrb- plug in the ethernet cable from modem to router . 4 -rrb- power on modem and wait for all the light to stop flash . 5 -rrb- power on router . 6 -rrb- power on you computer and you be do .