Motorola SB6121 SURFboard DOCSIS® 3.0 Cable Modem

January 30, 2012

Motorola SB6121 front viewIf you’re a current or future customer of Comcast’s Internet broad band service and are interested in purchasing your own Cable modem, you can view the list of their compatible modems at their DOCSIS® Device Compatibility and Capability website page. This page provides a list of all Comcast’s currently approved cable modems and EMTA devices.

The website gives you the ability to select devices based on your Speed Tier. It also has an option you can check to show “Show only the latest models (DOCSIS® 3.0 and above) “. If you’re a broadband performance person, once you enable these filtering options the list of devices will be reduced to the best of the best. Once of these will be the Motorola SURFboard SB6121 DOCSIS® 3.0 Cable Modem.

This cable modem builds upon the success of Motorola’s popular SB6120 cable modem. It harnesses the power of DOCSIS® 3.0 technology to bond up to four downstream channels and four upstream channels–providing you advanced multimedia services with data rates of more than 100 Mbps in each direction.

Built For The Future

As part of Motorola’s DOCSIS® 3.0 Ultra-Broadband family of cable modem products, the SB6121 includes an enhanced tuner that supports up to a 1 GHz downstream input, which allows cable operators to increase the frequency spectrum for deployment of new high-value services–such as bandwidth on-demand, commercial services, interactive gaming, and IPTV. The SB6121 features a 10/100/1000Base-T Ethernet (RJ-45) port, as well as intuitive, easy-to-read front-panel operational status LEDs.

The modem device also supports both IPv4 and IPv6 expanded network addressing capabilities.

Built Rock Solid

The SB6121 is the only Motorola cable modem which meets all three stars of Comcast’s certification criteria. This is the highest and most thorough level of testing available.

Features (From Motorola’s SB6121 Website Page)

Easy to Set Up and Use

Motorola SB6121 back view

  • Plug and play installation
  • Front panel LEDs indicate status and simplify troubleshooting
  • Multi-language user guides
  • Supports standard internet software
  • User-friendly online diagnostics


  • Stylish and space-saving enclosure
  • Offers innovative, high-bandwidth data and multimedia services to customers
  • Backward-compatible to DOCSIS®/EuroDOCSIS® 1.x and 2.0
  • Earth-friendly

Advanced Services Ready

  • DOCSIS® 3.0-certified (EuroDOCSIS 3.0-based)
  • Channel bonding of up to 4 downstream and 4 upstream channels
  • 1 GHz capable tuners
  • Supports IPv4 and IPv6 to expand network addressing capabilities

Versatile and Convenient

  • Compatible with Windows, Macintosh, and UNIX computers
  • GigE (RJ-45) data port enable flexible, high-speed connectivity with Auto Negotiate and Auto MDIX

Reliable and Secure

  • Enhanced security: supports Advanced Encryption Services (AES) traffic encryption
  • Remotely configurable and monitorable using SNMP and TFTP

What’s in the Box

  • Motorola SURFboard SB6121, Ethernet cable, installation sheet

System Requirements

The SB6121 is compatible with the following operating systems:

  • Windows 7
  • Windows Vista, Service Pack 1 or later
  • Windows XP, Service Pack 2 or later
  • Mac 10.4 or later (Ethernet connection only)
  • UNIX (Ethernet connection only)
  • Linux (Ethernet connection only)

There are a lot of positive reviews of this cable modem on Amazon’s website. Overall, if you are a Comcast customer it appears from the reviews that the modem works very well with their cable broadband service. Other providers may have compatibility issues however, so make sure to check if this Motorola SB6121 cable modem is compatible with their service offerings.

Where can you buy the Motorola SB6121 SURFboard modem?

I would recommend that you buy the Motorola SB6121 SURFboard DOCSIS 3.0 Cable Modem at Their prices are usually very competitive and they often provide free super-saver shipping. Another great resource at Amazon is that there are usually a lot of real customer reviews to help you make you buying decision.

Kim Scott - July 6, 2012

When you install this modem, if you’re replacing a Comcast rental, ensure you have the MAC (CMAC or HFC MAC) address handy, and call Comcast first & tell them you want to provision a new modem. After several hours of trying to use their webpage that comes up, I had to call. [Also, ensure you have the correct MAC address; for example, a “D” can look like a zero (“0”) w/those tiny letters ;-)] FYI, the modem seems to be working great for me, even with my Ooma telo box to provide VOIP [If you’re using Comcast VOIP/phone or will be, this modem won’t work I think; you need a telephony modem]

    Craig - July 6, 2012

    You are correct, this will not work if you’re using Comcast VOIP/phone also.

McAllen Homes for Sale - March 8, 2012

Nice post! Keep up the good work!

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