Customer Reviews: Motorola SB6120 SURFboard DOCSIS 3.0 eXtreme Broadband Cable Modem
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VINE VOICEon October 24, 2009
I was renting a modem from Comcast for $4 per month which really was horrible. The modem would crash, reboot, not work, etc... I spoke to some Comcast tech's on Twitter and they recommended I go and buy this modem since it was not yet being distributed by them in my area. Voila, off to Amazon I went.

I purchased the modem, it arrived the next day. I turned everything off....router, computer, etc. The setup was as follows:

A. Plug cable into new modem.
B. Plug ethernet cable from modem to your computer (first time only).
C. Power up modem.
D. Power up computer.
E. For Comcast - Web page comes up that allows you to change your modem.
F. Enter some your account number, etc.
G. DONE....shutdown modem, and plug ethernet cable to Router.
H. Enjoy DOCSIS 3.0

I have had this thing for a few weeks now and it works perfectly well on a daily basis. We are actually getting what we pay for...which was not the case with the old junk that comcast provided. We are getting about 60mbps down and 12mbps up...on a good day.

Motorola has an excellent modem again..
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on September 30, 2009
As I understand it, this is a great modem to use if you have a very expensive, extremely high speed internet package. The reason for this is that it has bonded channels technology that enables you to get more bandwidth (at high speeds) than the Motorola Surfboard 5120 or 5101. So if you have the top of the line internet package, and a very fast computer, and if the cable internet in your area supports DOCSIS 3.0, this thing could work screaming fast for you.

I do not have screaming fast internet, although my computer is pretty bleeding fast. I can't afford that kind of cost for a monthly subscription, because it is a constant and forever drain of a lot of money, and I don't earn that much money where I can do that.

I am located in the Phoenix, Arizona area, and have the $40/month Preferred internet package. My downstream bandwidth varies a lot by the time of day, it ranges between 13Mbps all the way up to about 23Mbps when almost everyone else is in bed sleeping.

My upstream bandwidth is capped real low, as with most consumer internet packages, so it hardly varies at all. It's almost always the same, at about 1Mbps.

If you want an accurate test of your internet bandwidth, do not use the main bandwidth testing sites. Their tests are way too short in duration and give you an extremely exaggerated notion of your top speeds. Go to testmy dot net and use the largest size tests they will allow you to.

Before purchasing this modem from an unnamed extremely large local retailer, I had read lots and lots of reviews saying that this modem dramatically improved the speed of relatively slow connections. I tested my bandwidth both before and after very thoroughly, both upstream and down. In the before part of my tests, I was using a Motorola Surfboard 5120. I saw absolutely no significant difference in either my upstream or downstream speeds after switching in the newer model. The reason this happened is because the 6120 is designed with the bonded channel DOCSIS 3.0 technology that provides you with more bandwidth *in very high speed applications only*.

So, if you have a bleeding fast internet connection, and your internet service provider supports DOCSIS 3.0 in your area, then you could see quite a large improvement in your bandwidth from this modem, according to everything I have read and heard. However, if like me, you cannot afford that speed of connection, you would be much better off saving your money and either keeping your Motorola Surboard 5120 or 5101, or getting one of those instead, since they are less expensive.
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on January 22, 2011
As a Comcast Customer, I'm sure I wasn't the only person annoyed by the modem rental increase at the beginning of the year (2011). I never really thought about it before, but I was paying more per year to rent an old DOCSIS 2.0 modem Comcast gave me (which had likely been in countless homes before my own) than I'd spend one time to purchase my own. So, I decided to ditch the rental and own.

At first, I thought I'd just buy what I already had: a Motorola SURFboard SB5120 DOCSIS 2.0. So glad I didn't! Instead I shelled out a bit more money and picked up the Motorola SB6120 SURFboard DOCSIS 3.0.

I read the reviews on Amazon prior to purchase, but was skeptical about the claims of increased speed with this modem. It didn't make sense to me, as I'm paying for an internet package with certain limitations on download/upload speed. It only seemed logical that better technology wouldn't be able to surpass limitations the package I pay for has in place. But in the end, what drove me to choose the SB6120 over the SB5120 was the idea of future-proofing; if I'm paying for it, I might as well get the better option.

Once I had the SB6120 running as my own modem, however, I was pleasantly surprised. My Comcast Internet package deal, which has not changed throughout my recent modem replacement, is as follows: Performance 12 Mbps download/2 Mbps upload with powerboost. Also, my area supports DOCSIS 3.0, so my package, utilizing a DOCSIS 3.0 modem, would automatically increase to 15/3 with powerboost. I took some speed tests ( before and after the new modem, and here's what I got on average:

SB5120 DOCSIS 2.0 Modem:
12 Mbps/2 Mbps

SB6120 DOCSIS 3.0 Modem:
20 Mbps/3 Mbps

Now, is this definitive proof that the SB6120 performs miracles with your internet speed? To many, I'm sure it's debatable. I've read a lot online about how people similar to me (similar internet packages) are getting increased speeds with a DOCSIS 3.0 modem, but there's always someone who quickly dismisses such claims as lies (they typically site powerboost as the cause for such "speed increases").

For me, I don't know. All I can say is that, with my set-up (note: I'm a gamer and run a PS3), I now have a faster internet connection with my new DOCSIS 3.0 modem, which mean the games I play online are blazing fast. Perhaps the old 2.0 was junk, perhaps something else, but the one thing I know for certain is that all I did was update my modem. I'm very satisfied with this purchase.

EDIT: As of 01/22/11, there have been no issues with modem. Have not had to powercycle or reset modem for any reason. Setting up with Comcast was a bit of a pain--was transferred to the wrong department twice, and the directions I received from the technician I spoke with were unclear, but since successfully completing set-up of modem, have had no issues whatsoever.

EDIT: As of 01/31/11: Modem went offline for at least 11 hours after 5 days of uninterrupted connection (occurred on 01/26). Location: Colorado. Recently read 2 other reviews by Comcast customers using this modem in Colorado, and they are not happy. Other than being offline on the 26th for several hours, no other issues to date. Previous modem would also go offline for hours on occasion, so I believe it has to be my connection. Still happy with the equipment. It can work in Colorado.

EDIT: As of 03/12/11: This will be my last update unless the modem malfunctions. Since January 26, 2011, no issues whatsoever to report. I have read that modem may have issues being plugged into a powerstip, and that instead modem should be plugged directly into wall outlet. Modem was actually plugged into wall outlet on the 26th when only issue occurred; since then, have had unit plugged into powerstrip, and again, no issues.

Lastly, read that increase in speed may be due to internet provider's lax perameter's with service during update to DOCSIS 3.0. Apparently, once conversion is complete and Comcast has a better handle on things, download/upload speeds should be more strictly enforced, thus: you get what you pay for and even this unit won't work miracles with speed increases. We'll see.

Note: This modem was selling for $75 new on Amazon back in January. Sorry to see that they've jacked the price up so high, but glad I bought mine when I did.
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on January 11, 2011
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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on May 22, 2010
Updated 07/26/11:
If you are a Cox customer, at this time I would recommend you purchase the Cisco DPC3010(8x4 channel) directly from Cox. If you are a Cox Digital Phone customer also, You can lease for FREE the Cisco DPQ3212(8x4 channel)eMTA modem which handles both your phone and internet in one device. The Motorola modems are fine but are only 4x4 channel and have a low tolerance for excess noise on the return path. and do not play nice with some Cox equipment. But most customers do not have problems with the Motorola.

Depending upon price, I think at this point I would wait a few weeks or months and purchase the Moto SB6121
The Moto SB6121 is the new version of the SB6120, actually it is Hardware Version 5, and ships with FW Version
Motorola SURFboard® SB6121 DOCSIS 3.0 Cable Modem
As of March 30th 2011, The newer SB6121 is not yet Approved by Cox, yet one reviewer has posted success at provisioning.

Update May 28, 2011: Cox AZ pushed FW SB612X- to the SB6120.

Update March 2011: Newer SB6120 modems are shipping with Firmware, this Firmware may cause problems with provisioning on some Cox systems. If you experience a problem ask to have the firmware downgraded to or just leave the modem connected overnight to see if Cox auto-updates the Firmware, before calling in to provision. Also FW 1.0.3.x will not Channel Bond a very small number of Cox nodes. In this case you will need FW or
Cox should be releasing a new Firmware Version in the near future.

CAUTION: If you have Cox HSI, before you provision your new SB6120 modem, connect it to your computer and check the firmware version. Once connected to your computer open a browser and type, to access the diagnostic pages. If it is, call Cox prior to provisioning, to downgrade your modem's firmware. Cox has stated at DSLR Forums that FW does "Brick" modems [...].

You can login to DSLR Forums » US Cable Support » Cox HSI to have Cox Authorized Techs change your modem Firmware.

Much faster than an SB5120, about 5-10Mbps faster DLs (when bonding 4 DL channels), without upgrading your HSI Tier. So if you are in an upgraded DOCSIS 3 area or want to be ready and future proofed get this modem.

My Modem shipped with Firmware version SB6120-, which is the fastest I have seen w/ Cox. If your modem should ship with Firmware SB6120- and you are with Cox HSI and having DL speed issues, ask to have it moved back to However, Cox will not move you back to if your modem gets moved to They will however move you back to Cox is no longer auto updating FW to

Firmware SB6120- did indeed have a speed issue w/ Cox and cut download speeds in half, (especially over longer distances) [...].
Firmware Version, was not compatible w/ Cox and they never released this FW version. As it reportedly bricked some modems in testing.

I had my modem moved back to FW version SB6120-, and that solved the DL speed issues. But FW versions and, have disappearing log entry issues and possible random rebooting issues. Although I have not experienced any random rebooting. Motorola really needs to work on a fast and stable Firmware update that is compatible with Cox.

Update August 07, 2010: I am still on firmware version SB6120-, and DOCSIS 3 issues have seemed to diminish for me in the Phoenix market. Cox does have a newer firmware version, I have not tried it and it is not widely distributed, but users on seem to be happy with

Here is a list of Current Firmware Options for the SB6120 that Cox is using or has tested, firmwares are known to behave differently on specific vendor's CMTS, (A cable modem termination system or CMTS is a piece of equipment typically located in a cable company's headend or hubsite, and used to provide high speed data services). All Moto SB6120 firmwares so far do seem to have issues, It is best to ask for help from a cable tech for your provider if they participate at DSLR Forums, and find out which firmware works best for your area. or call your provider and ask. You can check your firmware in the diagnostic menu @ - Fast, but has rebooting, syncing issues - Fast, but has rebooting, syncing issues, Retail Moto Release (Cox doesn't have this FW to reflash if you change) - More stable, but slow to very slow speed issues, - More stable, but slow to very slow speed issues, » Google SB6120 Speed Concerns - Known to Brick Modems, Cox is not using - As of 09/01/10 This is the current Cox firmware for this modem, There are issues on certain vendor's CMTS, recent rebooting and time-outs have been reported. - New Cox Firmware update pushed to AZ on 05/28/11.
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on May 21, 2009
just made a quick call to comcast to give them the modem's MAC address and now my internet is blazing. I'm on the comcast 22Mb download tier but speed test is showing an average of 35Mb down / 6Mb up. really fast.
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on June 9, 2015
again, since june 2015 , this modem is no longer compatible with comcast. It WILL work if you are using it right now, but if you move, new customer, or want to reconnect with comcast, they WILL NOT take this. just a head up to all the folks that going for comcast.

5 starts for this beast modem!
review image
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on June 10, 2009
I had the older SB5120 and lately I have had to restart the router about 2 times a weeks when I was using massive bandwidth.

The new modem works great with my Comcast service here in Olympia, WA. Took 5 min on the phone for the Comcast Tech to authenticate the new router.
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on May 8, 2010
Motorola on May 6th, 2010, sent out a firmware push that bricked thousands of these modems on Charter, Comcast, Roadrunner, Time Warner, and Cox.

I am now forced to lease a modem from Charter again, as my 6120 is now only good for a paperweight. Of course I cannot return to Amazon because its past the 90 days on electronics, and Motorola told me this morning they will not RMA it because the software on their end works, and they approved of the software push.

Sounds like this modem is no longer going to be supported with any of these cable companies, and we are all SOL on the units we have right now.

Thanks for nothing Motorola.
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on June 28, 2009
Comcast installer hooked up the cable and installed the modem I purchased from Amazon. The modem had to be registered in their systems, but the whole process only took him about 20 minutes. When I hooked up my wireless router, it took a couple of reboots of the SB6120 for the modem to register the router and to open up for internet traffic. The modem itself is quite fast and I get the full 16MB per second that I pay for. Construction is solid and it is thus far a high quality device.
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