Like another recent reviewer, this Docsis 3.0 cable modem may not work with Comcast, even though SB6120 is listed as one of the "approved cable modem 3.0" on Comcast's website. Google "sb6120 comcast problem" and you'll find more details.
The comcast technican/installer was at my house and spent 45 minutes trying to make it work. The SB6120 seemed to be having problem syncing with the server and kept getting reset continuously. The technician was on the phone with the support team, and at the end he said it was defective. He put in a comcast supplied 2.0 RCA modem and it worked. Amazon shipped me a different replacement SB6120 4 days later, and the replacement showed the exact same symtom and would continously reset and wouldn't sync. The comcast phone support agent told me they are able to see the device but somehow it still didn't work properly... We swapped the comcast RCA modem in and it worked right away again.
Bottom line is that there appears to be some compatibility issues with Comcast & SB6120, at least for some. I tried two different ones and they both had the same issues. Again, google "sb6120 comcast problem", do your research and make the decision yourself. Unless the batch of SB6120 from amazon is defective, there probably are some firmware or compatbility issues for some of the modems, even though Comcast lists SB6120 as an approved modem...maybe just hit or miss.
Having tried two of these, I am giving up and am now paying more to get a zoom 5341 3.0 modem instead. Good luck and thanks for reading. Hope this helps.
Update: ZOOM 5341 has been running strong after 6 months of use. I have not had a single issue with it and it has been very stable and very speedy(upload/download).
Update(2/28/2012): A few people hinted or complained about my review. They basically said "SB6120 works for them so there must not be any compatibility issue with Comcast". Oh please, I already clearly stated that you "MAY" have incompatibility with Comcast, at least for SOME of the people. As of Feb 2012, there are ~= 1000 five star review on this, and ~= 110 one star review! This clearly indicates ~= 10% of the people are having serious problem with SB6120. At least a significant number of those 1 star review are related to Comcast compatibility issue. I still stand by my review: you mileage may vary with this on Comcast. Good luck everybody!
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