I be sure the Motorola surfboard  sb6121 DOCSIS 3.0 Cable Modem be a very capable modem consider it be a Motorola product ; however , I have to put 2 star to get people attention . the Motorola surfboard  sb6121 DOCSIS 3.0 Cable Modem be not yet on COMCAST 's list of support modem . I think that wait 4 month since the release of this product would give COMCAST time to obtain the software require to add the sb6121 to they network . well , I be wrong . it be a shame to give this product 2 star when I never even get the chance run it through its pace . I would rather give COMCAST 2 star for be lazy . the COMCAST tech that come to setup my modem say that the COMCAST system identify my modem ; however , that be about it . he connect a different modem to show I that modem on the list will work . he say that he have a  Motorola SB6120 SURFboard DOCSIS 3.0 eXtreme Broadband Cable Modem  so unfortunately , I have to return the sb6121 and I order the sb6120 . I be not slam Amazon or this product . I just want to make COMCAST customer or future COMCAST customer aware that the sb6121 will not work on the COMCAST network YET .