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Item#: N82E16825122015

MOTOROLA SB6121 SURFboard Cable Modem Up To 172 Mbps Down and 131 Mbps Up RJ-45, Gigabit Ethernet DOCSIS 3.0, 2.0 and 1.1, Euro-DOCSIS 3.0

  • Gigabit Ethernet connectivity
  • DOCSIS 3.0-certified (EuroDOCSIS 3.0-based)
  • Channel bonding of up to 4 downstream and 4 upstream channels
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SB6121 SURFboard Cable Modem RJ-45

Building upon the success of the SB6120, Motorola's SURFboard SB6121 delivers your complete personal media experience, at lightning-fast broadband speed. 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 100Mbps in each direction. That makes gaming, shopping, downloading, working, high-quality voice and video conferencing, and peer-to-peer networking applications far more efficient than ever before.



SB6121 Easy to Set Up and Use
  • 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

Advanced Services Ready
  • DOCSIS 3.0-certified (EuroDOCSIS 3.0-based)
  • Channel bonding of up to four downstream and four upstream channels
  • 1GHz capable tuners
  • Supports IPv4 and IPv6 to expand network addressing capabilities
Versatile and Convenient
  • Compatible with Windows, Macintosh, and UNIX computers.
  • Gigabit Ethernet (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

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

What Is DOCSIS 3.0?

With the DOCSIS 3.0 specification, cable Internet providers can take advantage of the extra capacity provided by channel-bonding technology in order to offer ultra-fast broadband services. Channel bonding allows parallel data pipes to act as a single broadband conduit. With each channel capable of providing around 40Mbps of data, the Motorola SURFboard SB6121's four downstream channels can provide a theoretical maximum of 160Mbps of throughput.

Currently, cable providers max out at around 50Mbps of downstream data throughput, but DOCSIS 3.0 will enable cable Internet providers to continue to improve the speed of their networks.

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)

What's in the Box

Motorola SURFboard SB6121, Ethernet cable, Installation sheet


Learn more about the Motorola SB6121




Cable Modem
1 x RJ-45, Gigabit Ethernet
Cable Interface
75ohm F-connector
DOCSIS 3.0, 2.0 and 1.1, Euro-DOCSIS 3.0
Max Transmission Rate
Up To 172 Mbps Down and 131 Mbps Up


Data Protocol: TCP/IP

Power: 9W (nominal)

Input Power: 105 to 125 VAC, 60 Hz

-Modulation: 64 or 256 QAM

-Capture Bandwidth: 100 MHz (edge to edge)

-Maximum Theoretical Data Rate:
DOCSIS: 171.537 Mbps (4 channels) / 42.884 (single channel)@ 256 QAM at 5.36 Msym/s
EuroDOCSIS: 222.464 Mbps (4 channels) / 55.616 (single channel)@ 256 QAM at 6.952 Msym/s.

DOCSIS: = 24 MHz
EuroDOCSIS: = 32 MHz.

-Symbol Rate:
DOCSIS: 64 QAM 5.057 Msym/s; 256 QAM 5.361 Msym/s

EuroDOCSIS: 64 QAM 6.952 Msym/s; 256 QAM 6.952 Msym/s.

-Operating Level Range: –15 to 15 dBmV

-Security: DOCSIS 3.0 Security (BPI+, EAE, SSD)

-Network Management: SNMP v2 & v3

-Provisioning Supports: IP addressing using IPv4 and/or IPv6 (dual stack).

-Modulation: QPSK and 8, 16, 32, 64, 128 QAM

-Maximum Channel Rate
DOCSIS 131.072 Mbps (4 channels) / 32.768 Mbps (single channel): @ 128 QAM at 6.4 MHz
EuroDOCSIS 131.072 Mbps (4 channels) / 32.768 Mbps (single channel): @ 128 QAM at 6.4 MHz.

-Channel Width 200 kHz, 400 kHz, 800 kHz, 1.6 MHz, 3.2 MHz, 6.4 MHz

-Symbol Rates: 160, 320, 640, 1280, 2560, 5120 ksym/s

-Frequency Range: DOCSIS 5-42 MHz (edge to edge), EuroDOCSIS and optional DOCSIS 5 to 65 MHz (edge to edge)

Compatibility PC: 90496, Pentium, or later; Windows Vista, 2000, XP or 7 or Linux with Ethernet connection (older versions of Windows, although not specifically supported, will work with this cable modem).
Macintosh: Power PC or later; OS 9 or higher, Ethernet connection.
UNIX: Ethernet connection.
Home Networking: Ethernet router or wireless access point.


Package Contents
Ethernet Cable
Power Supply
Software License & Regulatory Card
Product Guide (Install Sheet)

Manufacturer Warranty

1 Year Limited Warranty
1 Year Limited Warranty

Quick Info


  • Limited Warranty period (parts): 1 year
  • Limited Warranty period (labor): 1 year

Customer Reviews of the Motorola SB6121

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  • Larry M.
  • 10/20/2014 7:54:26 AM
  • Tech Level: Somewhat High
  • Ownership: more than 1 year
  • Verified Owner

5 out of 5 eggsStop paying rental fees

Pros: Works great with Comcast. Pays for itself within a year.

Cons: none yet.

Did you find this review helpful? Yes No

  • Steven C.
  • 10/14/2014 6:21:05 AM
  • Tech Level: Somewhat High
  • Ownership: more than 1 year
  • Verified Owner

5 out of 5 eggsFlawless

Pros: Works perfect. No problems - highly recommended.

Cons: None.

Other Thoughts: If you like the reliability of your refrigerator, you'll like this product.

Did you find this review helpful? Yes No

  • Christopher C.
  • 10/8/2014 10:30:47 AM
  • Tech Level: Somewhat High
  • Ownership: 1 week to 1 month
  • Verified Owner

5 out of 5 eggsSuper speeds

Pros: Surprisingly small size
Simple to connect
Just works out of the box, no setup required

Cons: None

Other Thoughts: This modem gives me more flexibility and a faster wired connection speed than the Comcast wireless access point they provided me. The difference in Wi-fi is like night and day, but then again I have a decent w-ifi router attached to this modem. Comcast didn't even put up a fight when I activated this and returned the rental device, even congratulated me on buying my own equipment. Curious :-/

Did you find this review helpful? Yes No

  • Matthew S.
  • 10/4/2014 9:24:30 AM
  • Tech Level: High
  • Ownership: 1 day to 1 week

5 out of 5 eggsDoes what it says on the label

Pros: Easy setup
No need to call Xfinity/Comcast to activate
Works with my internet tier (50mbps)

Cons: Plastic film on the front is near impossible to completely remove. Box was not sealed shut.

Other Thoughts: I got this to replace the substandard Arris/Technicolor residential gateways Comcast provides with a rental fee.
I had problems with their devices, so I purchased this and a Netgear R7000 router. Speeds upstairs went from 10 to 50Mbps and range has improved.

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  • John J.
  • 9/30/2014 5:28:49 PM
  • Tech Level: Somewhat High
  • Ownership: 1 month to 1 year
  • Verified Owner

4 out of 5 eggsWorks Great

Pros: Simple to setup

Cons: None really.

Other Thoughts: Once Comcast came out and actually, physically hooked up my cable internet, the thing worked great!

Did you find this review helpful? Yes No

  • Daniel B.
  • 9/28/2014 11:49:25 AM
  • Tech Level: High
  • Ownership: more than 1 year
  • Verified Owner

5 out of 5 eggsNice steady cable modem

Pros: Nice cable modem that works with Comcast's High Speed Internet. Has performed great in the year and a half that I own it. Fast video streaming to my 5 family PCs. Never failed in all this time of daily use.

Cons: Came in one color option, BLACK, which cannot be hidden in my white room, with white computers, cables, walls, etc... Wish it came in white color back when I bought it. Motorola is such a big company they should always offer a choice of white or black color. NO WIFI feature (when I bought it more than a year ago). if you need WiFi, buy their other model that has that feature.

Other Thoughts: Great product , has worked for me everyday in the past year and a half.

0 out of 1 people found this review helpful. Did you? Yes No

  • Chris F.
  • 9/27/2014 3:01:03 PM
  • Tech Level: Somewhat High
  • Ownership: 1 month to 1 year
  • Verified Owner

4 out of 5 eggsStable, fast, annoyingly bright.

Pros: Supported by almost every cable company that doesn't make you buy a modem from them. DOCSIS 3.0, high efficiency switching power supply. Very well ventilated.

Cons: External power adapter makes device lightweight and tipsy compared to Arris-brand modems (also more expensive to replace if the cord gets damaged). Unnecessary night light (see other).

Other Thoughts: I hate how bright this thing is. I owned a Motorola SB5120 for eight years before this, and the lights only showed on the front panel, so I had a piece of electrical tape that ran down the front (with a foldover tab at the top so I could peel it back easy to check them if needed). The 6121 has a crystal clear front panel that allows the (now much brighter) LEDs to shine out the front AND deflect out the edges of the panel. So I now have to put tape over the left and right edges as well as down the front. But that still doesn't solve it. Unlike on earlier designs where the LEDs were isolated from the rest of the unit, these easy shine back into the modem as well, and since the modem has a perforated "grater-style" panels for it's housing, this means I get light out the back and up the walls, too. I'll have to move it to a enclosed area I guess since I can't just cover all the vent holes.

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  • James H.
  • 9/27/2014 10:21:27 AM
  • Tech Level: Average
  • Ownership: 1 day to 1 week
  • Verified Owner

1 out of 5 eggsHow do you backdate the software?

Pros: Prompt shipment.

Cons: Doesn't connect with TWC Akron OH. I ordered a Mot SB6121 for myself, installed it on TWC in Columbus OH last month and all is going fine. So I ordered one for my sister in Akron OH. After a day on-line with their service techs, she had to have a tech visit her home. They said "the old software on the Mot worked fine but the latest version no longer works with TWC in the Akron area". How do you backdate the software in a Mot SB6121?

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  • Anonymous
  • 9/25/2014 9:37:43 PM
  • Tech Level: Average
  • Ownership: 1 day to 1 week

5 out of 5 eggsTwc campatible

Pros: great connects to twc servers

Cons: can not handle multiple connections properly

0 out of 1 people found this review helpful. Did you? Yes No

  • JUDY L.
  • 9/25/2014 1:45:53 PM
  • Tech Level: High
  • Ownership: 1 month to 1 year
  • Verified Owner

4 out of 5 eggsWorks for me

Pros: Works well and I am Happy with this Modem.
It does not get hot...warm. But not hot.

Cons: *I Can NOT change the Default Address. =Very disappointing.

*I can only access the modem by connecting CAT5 directly.

*The modem's Options are non existent but the page gives you a lot of information.

*The logs show a lot of Failed Updates from my ISP. But that could be many factors and not the modem's fault. If it needs it then revert back to defaults threw the Modems Gateway Page.

Other Thoughts: The Default address is:

The settings are set by your/my ISP. Which I consider a con also but it fluctuates. And the reason I gave it 4/5. But it deserves a good ratting. Don't let my "4 Eggs" deter you. The SB6121 is a Solid Buy :)

Another Note: SB6141 isn't a better choice. This one (SB6121) is the one I would pick for an Internet Service Provider.

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Item#: N82E16825122015
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