Took Comcast about 2 hour to install , over the phone , late August 17 , 2012 . laptop gigabit controller would not properly recognize modem and would run only at 10 mb instead of 1000 . use a Dell XPS l511z to connect to modem . when I hook the laptop up before call Comcast the LAN would run at 1000 mb . Comcast could not get the lan to run over 10 , so they suggest try another computer . use a older xp m140 laptop purchase 6 year ago but run Windows 7 and it work at its network card 's max rate , 100 mb . restart modem and then hook it to Netgear router -lrb- 100 mb WAN input -rrb- and it seem to work fine with wire lan run at 100 mb , but the internet do go out unexpectedly once but start right up when I reset the router , but not the modem . the modem show it be get a internet connection , but the router show no internet connection . have Comcast blast -lrb- advertise here in dc metro area at 50 down\/10 up -rrb- . Got letter from Comcast recommend upgrade to 3.0 modem and this modem get they 3 star test and be recommend . previous modem Motorola SB5101 work fine and be 5 year old , but its download max be about 38 and sometimes just over 40 , but speed vary a lot and it be never consistent . upload be usually less than 4 . with sb6121 , speed be consistently 52 download and 10 upload . wifus download be about half the wire rate when the laptop be close to router , use Netgear usb 72 mb wireless . wifus upload be 10 . it seem to be work well .