I be use the sb6121 cable modem with Comcast cable . setup be fast and easy . plug in the box in place of the old one , and call Comcast . the service representative know what he be do . it take about 20 min from when I call to everything work properly -lrb- include hold time -rrb- . Make sure to have the MAC address handy when you call . for this packaging , the MAC be on the sticker on the bottom of the unit , as well as inside the cardboard packaging on the sticker on a paper strip . the indicator on the box be great . the receive and transmit indicator be bright blue if it detect a docsis 3.0 connection , green if it detect a docsis 2.0 connection . these receive , transmit , and online indicator be steady if connect properly . very easy to know the status at a glance from across the room . a note : on initial powerup -lrb- before call Comcast -rrb- , the receive \/ transmit light settle on green , and that have I wonder what be go on . it turn out that Comcast have to get the correct profile download on the box , and the right configuration setup at they end before the indicator be meaningful .