I be rent the Motorola Surfboard 5120 -lrb- sb5120 -rrb- from Comcast for $ 5\/month . this seem reasonable to I up until I find this modem for $ 30 include shipping . I will make my money back on the purchase in 6 month . excellent deal ! as other have mention all you have to do be call Comcast to activate this modem by give they the MAC address . it be both on the box , and on the unit itself . this process take I a grand total of about 15 minute once I open the box . this modem have plenty of speed out of the box . in response to other 's get up to 30 mb\/s , this be not go to be a cap on the modem 's ability . this instead be a cap limit by you service provider . this be a DOCSIS 2.0 Modem , which mean it can handle up to 42.88 mb\/s raw throughput -lrb- include overhead -rrb- or more simply 38 mb\/s -lrb- usable datum -rrb- . for I , I pay for 12 mb\/s on Comcast , and have see this modem get upward of 14 mb\/s , although this say nothing as to what the modem itself can handle . it be just Comcast not limit I strictly enough to what I have pay for .