12\/14\/2011 just receive the Motorola SB6121 SURFboard DOCSIS 3.0 Cable Modem today . follow the self-install instruction include with the modem , use Comcast internet , and a Medialink Wireless N router , and be up and run in 20 minute . note ; also use a Windows OS laptop for the setup , with internet Explorer . here 's how my setup go . disconnect you old modem . connect the sb6121 modem to you internet coaxle cable . now connect the ethernet cable to both the sb6121 modem and you computer . power up the sb6121 modem and wait for all light to stop flash -lrb- must have solid light -rrb- , then power up you computer . now , open internet Explorer browser and wait for the Xfinity screen to automatically show up on you internet Explorer 's screen . enter you Comcast account number and the phone number associate with you Comcast account on the screen , where ask , and press next . the sb6121 modem will then be automatically identify and recognize . Press next to accept the Motorola sb6121 cable modem , then wait a few minute for the next screen to show up while the information be be process , then press finish . 3 screen total . disconnect the ethernet cable from you computer and connect it to you router . now , power both the sb6121 and you router off and wait 10 seconds . now , power the sb6121 modem on and wait for all the light to show themselves . now , power on you router . you should be able to go online wirelessly . literally that simple . the Comcast Xfinity self-install screen do not ask I for a MAC address or a serial number . total time - about 20 minute to remove the old modem and install the sb6121 . best part , no have to call tech support and no frustration ! I be quite surprised at how easy the sb6121 be to install , as it seem like I be one of those guy who take 2-3 hour to hook anything up . seem like there be always that one thing I do not know , or think , about , and I be usually on the phone with tech support for a while have a lackluster time . I replace a old Comcast RCA modem which I have no problem with , but be tire of rent from Comcast at $ 84 per year . the sb6121 will pay for itself in a year 's time , be a 3 docsis modem versus 2 on my old modem , and work well thus far .