I buy this modem after extensive research and the great product review . it be a `` 3 star '' rate approved modem for comcast\/xfinity . the self setup be dead simple - connect the cable input to the modem , power up and let it sync with the signal . then I directly connect the modem to my laptop and `` fire up '' the browser which take I to the activation page for Comcast . inpute the information request -lrb- account no. , mac id , phone number -rrb- and activate the modem . in less than 30 minute I be online with blaze speed . I than connect my router to the modem and the network be up and run . I be amaze and really pleased with myself , Comcast and Motorola . the modem perform great for a few hour , than the problem start . I lose connection and signal sync . ok - decide to do a hard restart : I disconnect the modem , disconnect the power and the cable . do a hard restart , reconnect the cable and ethernet and be back online - for about one hour . I lose connection again . call Comcast - good tech support who check thing at he end and instruct I to do another hard restart . I be back online for the rest of the evening . however , when I get up in the morning I be again offline . at that point I check the Comcast Broadband forum for some answer . this be a known issue with many user of the sb6121 and be trace to the quality of the signal from the isp . if the signal be less than ideal -lrb- snr , Power Level -rrb- any noise will kick you offline and the modem will not self recover . you will have to do a hard restart each time to get back online . when online , you 'll get great internet speed . but you 'll suffer from frequent disconnect and the need to reboot the modem . aside from the inconvenience , the need for frequent hard reboot can not be good for the durability of the modem . so unless you have good signal quality from the isp I would recommend you buy another modem . in my case -lrb- after research the user Forum -rrb- , I switch to a zoom 5341j . so far after 2 day - no problem . by the way , after look at the certification rating on the Xfinity\/Comcast Approved Modems list more closely , I learn the `` star '' be not a measure of quality or performance of the modem . the star be a measure of the level of test the modem have go through during certification . each star be another level of testing . in summary - the Motorola sb6121 be a good modem but maybe too sensitive the signal quality for some user .