I've had this modem for about a month now. It works flawlessly. In fact it increased my speed from roughly 20mb/s to 40mb/s over cox. Its a nice compact unit, and has a couple keyholes for wall/shelf mounting. Motorola SURFboard® SB6121 DOCSIS 3.0 Cable Modem
I simply replaced my RR modem with this one and powered it up. The speeds were crippled and when I tried to bring up a web page, I was presented with a message "Your MAC address is unknown, please call TWC/RoadRunner and give the Agent the new MAC address". I called the number given and after 10 minutes got ahold of a technician who took the new MAC address and assigned it to my account. Within a few moments the modem disconnected. I unplugged it and plugged it back in, and when it came up, I was at full speed again. My d/l speed went from 8MB to 11MB and my ping dropped from 39ms to 21 ms.
Motorola SURFboard® SB6121 DOCSIS 3.0 Cable Modem eXtreme Broadband Cable Modem I bought this cable modem figuring it would be my last modem for a while and that it would pay out versus renting from ComCast. At the time I bought it, it WAS on Comcast's list of approved modems. Bad decision. For whatever reason, the modem just plain didn't work properly, never achieving anything close to the 60/10 service I was paying for with Comcast. After numerous phone sessions and three on-site tech visits, one very smart and methodical tech finally figured out the modem was defective, and replaced it with Comcast's own. I'm blazing away now at 62/12, and happy as a clam. My advice: don't buy your own modem (especially this one), just cough up the monthly rental fee and let your cable provider provide the modem that they KNOW works with their system. In my case, it was not even close to being worth all the grief I went through simply to save the few bucks I might have saved! One last note: the Comcast tech that finally figured out the problem said that one of the reasons he suspected that the Motorola was the problem was that the scuttlebutt among Comcast techs is that a LOT of these modems are defective and are basically pieces of junk!
IT GETS WORSE: I called Motorola's tech support to arrange a refund, and talked with a very arrogant tech, then his very arrogant supervisor. Bottom line.... you ain't gonna get a refund from Motorola if it doesn't work. Here's their "warranty:"
"Because it is impossible for Motorola to know the purposes for which you acquired this Product or the uses to which you will put this Product, you assume full responsibility for the selection of the Product [even though it's on Comcast's approved modem list], and for its installation and use. While every reasonable effort has been made to insure that you will receive a Product that you can use and enjoy, Motorola does not warrant that the functions of the Product will meet your requirements or that the operation of the Product will be uninterrupted or error-free. MOTOROLA IS NOT RESPONSIBLE FOR PROBLEMS OR DAMAGE CAUSED BY THE INTERACTION OF THE PRODUCT WITH ANY OTHER SOFTWARE OF HARDWARE, ALL WARRANTIES ARE VOID IF THE PRODUCT IS OPENED, ALTERED, AND/OR DAMAGED. THESE ARE YOUR SOLE AND EXCLUSIVE REMEDIES for any and all claims that you may have arising out of or in connection with this Product, whether made or suffered by your or another person and whether baswed in contract or tort."
I am sure the Motorola SURFboard® SB6121 DOCSIS 3.0 Cable Modem is a very capable modem considering it is a Motorola product; however, I had to put 2 stars to get peoples attention. The Motorola SURFboard® SB6121 DOCSIS 3.0 Cable Modem is not yet on COMCAST's list of supported modems. I thought that waiting 4 months since the release of this product would give COMCAST time to obtain the software required to add the SB6121 to their network. Well, I was wrong. It is a shame to give this product 2 stars when I never even got the chance run it through its paces. I would rather give COMCAST 2 stars for being lazy. The COMCAST tech that came to setup my modem said that the COMCAST system identified my modem; however, that was about it. He connected a different modem to show me that modems on the list will work. He said that he has a Motorola SB6120 SURFboard DOCSIS 3.0 eXtreme Broadband Cable Modem at home and that it works just fine. So unfortunately, I have to return the SB6121 and I ordered the SB6120. I am not slamming Amazon or this product. I just wanted to make COMCAST customers or future COMCAST customers aware that the SB6121 will not work on the COMCAST network YET.
I has having good success with a 3-year old Motorola Surfboard modem, but had been reading that newer modems = faster speeds without having to upgrade service. I checked with Cox Communications to see if the SB6121 was compatible with their service and they said it was so I ordered it.
Plugged it in and called them with the MAC & Serial numbers - was up and running in 6 minutes, including 3 minutes of hold time and a minute to restart my router and computer.
Ran a speed test through speedtest.net prior to switching modems. Old modem had PING of 27ms, 23.77Mbps download, 2.62Mbps upload.
New modem test 10 minutes later: PING 18mx, 41.19Mbps download, 4.33Mbps upload.
Not bad for a $100 investment and no additional charges from Cox.
Highly recommended if your provider is setup to operate with this modem. - Surfboard - Comcast - Sb6120 - Docsis 3'
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