Motorola SB-6120 Cable Modem

For the past several years I have been utilizing Cox Communications High-Speed Internet meaning that I am using a cable modem to access the Internet from home. At the time we moved into our home the phone company was not yet offering DSL in adequate speeds due to the length our house was from the trunk it would be a long time before DSL would be an option.

Since we have Cox Communications engineers living in our neighborhood the lines running to the junction box were very clean and the speed was very good. The problem with cable modem service has always been that the more people that use the service in an area the slower it got. In our case, I have not noticed a significant slow down as new users have come on.

For several years I have been using a Motorola SB-5101 Cable Modem. This Surfboard modem has been a workhorse and has run steadily without much more than an occasional reboot usually after a power outage or service disruption.

Motorola_SB6120Recently we received notification that Cox Communications is beginning to offer a new ultra high-speed package capable of up to 28Mbps downloads with 2.5Mbps upload speed. Given the amount of data I transfer between client and server during my development cycles, I am always looking for an upgrade in service.

The new internet service came with one caveat. It requires a DOCSIS 3.0 compliant modem. Unfortunately for me the SB-5101 is DOCSIS 2.0 meaning it will not work with the faster connection. So while the Motorola SP-5101 is still working fine I needed to replace it with a faster modem.

After some research I concluded that the Motorola SB-6120 would comply with the minimum requirements by Cox Communications. At the time the SB-6120 was in relatively short supply requiring me to order it and wait and wait.

I received notification that the modem had shipped about the same time as our local electronics vendor received their shipment meaning that I had to wait for shipping time. The last four days have been murder as I waited for the new modem to arrive.

The package arrived today and I eagerly opened the box and unpacked the modem. It has an industrial look to it with mesh sides which should help with air flow and heat dispensation. Cable modems don’t usually run hot but considering I live in Arizona everything runs hot regardless of what heat the electronics generate.

There really isn’t a lot to this modem. On the back are three ports. The top port is an RJ-45 Ethernet port for connecting to my Apple AirPort Express. The center port is a cable connector for attaching an RJ-6 or RJ-59 coax cable. The bottom port is the power port for plugging the cable modem into the wall.

The front of the cable modem is likewise fairly simple with five status lights. The top light for power, the second for data received followed by send data. The bottom two lights are an online indicator and a link light.

After unplugging the old SB-5101 I removed the unit and replaced it with the SB-6120. After connecting the power cable, coax cable, and Ethernet cable the modem was powered up. After self-diagnostics it appeared to be working correctly.

I think called Cox Communications and sat on the phone for what seemed like an eternity. I was finally connected to a technician who activated the new modem and deactivated the old modem in their system. Soon the receive and send lights began blinking and I was up and running.

I completed the order for upgraded service and it should be active shortly. I’ll soon be cruising the “information superhighway” with a brand new V-8 blazing past the other packets as I travel around the Internet.


  1. Rod vanAusdall says:

    I have the 6120 surfboard and I stress at the outset there is nothing wrong with it – it works flawlessly.

    I use this modem on two computers- one computer (XP OS) the modem is fine and shows a RED LIGHT at the “LINK” label on the modem when operating.

    The other computer VISTA OS (which I am trouble shooting – a problem not connected with the surfboard 6120) when hooked to the 6120 modem (very slow connection speed – no fault of the modem) shows a BLUE LIGHT at the “LINK” when connected, and operating on the internet.

    If you know why the difference in the color of this light I will appreciate knowing.

    I again stress there is no flaw in the modem but perhaps knowledge of the light colors will help in my troubleshooting the faulty computer.


    • Jeff Summers says:

      Hi Ron,

      According to the users guide for the Motorola 6120 SurfBoard, a blue light on the Link means that a device is connected using High-Speed Gigabit Ethernet (1000Base-T) while an amber light means the device is connected at Ethernet (10Base-T) or Fast Ethernet (100Base-T). It sounds as though your Vista machine may be miscalculating the line speed compared to your XP machine.

  2. mari says:

    I just bought the motorola 6120 surfboard and I have noticed that all the lights stay solid but the last one blinks all the time. It keeps blinking while using the internet or not. Why is that?

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