after read a ton of feedback and talk to Comcast about DOCSIS 3.0 cable modem that they support , I decide to order the Motorola sb6121 . the next decision be to save a few $ $ by order the brown box\/environmentally safe packaging . do not care if it come in a plain box , just as long as its a brand-new unit . the item arrive via USPS -lrb- super slow and forget about they ability to track package -rrb- after the seller promptly ship the product . after receive the item , I immediately -lrb- and excitedly -rrb- install it and then , nothing ... I call Comcast and have a technician on the phone while we try to figure out why the unit be unable to receive the cable signal . after 15-20 frustrating minute of plug and unplug , the technician inform I that the cable modem be DOA and suggest that I send it back . I have to re-install the old 2.0 cable modem that still work , albeit on a much slower speed . one thing about the experience be the return policy of Amazon be amazing . I be a huge fan and I be a bigger fan now after this experience . great job Amazon . just sad that I do not get a work unit for whatever reason . the 3 star be for the promptness of the seller in ship the item and Amazon 's return policy .