as a Comcast customer , I be a little hesitant to buy this modem after read all the review . however , I need a new one really bad because the old modem just keep on resetting ; also want to see how much speed improvement the DOCSIS 3.0 get . so I take the gamble and order one . I immediately open the box when it get deliver to my doorstep . plug in the power , wait a few minute for it to completely boot up , then plug Ethernet cable to the modem and directly to my laptop . Unplugged the coax cable from old modem and plug into the sb6121 modem . no surprise here , yellow warning icon . no connection . call Comcast and provide the MAC address -lrb- Comcast do not use customer s\/n for they setup -rrb- , but no luck as the rep tell I the router be show online but will not communicate with they server . still no luck after a couple of try , so she say to leave the modem on and she will call back to check in 30 min . 30 min pass . she call and give it another attempt ... nothing ! she then politely apologize about the situation and say the unit be probably a defect , suggest I return the item to get a new unit . -lrb- really ??? I think in the back of my mind -rrb- so I brush she off by thank she for she help , while tell myself this unit be perfectly fine . after I hang up the phone , I decide to power it off , turn back on and leave it on overnight -lrb- as other mention that method work for they -rrb- . little do you know . after power back on , I hit f5 to refresh my browser page . the rainbow color GOOGLE logo with a search bar underneath show up in the middle of the browser window . finally up and run !! quickly do a speedtest and get 14mbp download speed -lrb- subscribe for 10mbp -rrb- . it be blaze fast !! very stable and have not have to reset the modem after 1 month .