I buy this here on amazon about 5 week ago . we have decide to use Comcast for ` Internet only ' and take the Arris cable modem back to the Comcast support center . that be say , the physical hook up of the Motorola sb6121 be very easy . Comcast technical support be just , I guess , not use to self installer here . I be on the phone 3 night in a row with Comcast technical support to get to the internal Comcast network , where I could get the Comcast url for activation of the modem . the thing be , by this point , I have give my new indian friend the MAC address of my new modem several different time . aw well , at least we be make progress . come home from work on a Friday evening , after spend the previous 3 evening talk to Comcast support , I get to the same activation url at Comcast and decide to give it a rest . after all , I have my new discounted premium DirectTV package to relax with . cut to the chase , by the next Monday -lrb- 6 day after I start my change over to self installation -rrb- I be able to get to the internet ok . I find that I have to release and renew the dhcp address that Comcast have give I and the new dn be quite different from the one I have previously with the Arris modem . anyway , since dn be clear up and I suspect be add to Comcast 's proxy to the outside world , I have have 100 % up time on the Comcast network .