Modem be not plug and play . spend about 45 minute on the phone with Comcast to get modem working . have to supply the serial number and MAC ID number . however , when I get it work , my speed go from 13mb download with the my old Motorola Surfboard to 33mb download with the 6120 . similarly , upload go from 1.3 mb to 6mb . Works great once it be configure with you isp .