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on July 11, 2010
Firstly, the channel bonding is definitely noticeable. I went from a model-year 2000 Motorola SB4200 to this modem. Using a bandwidth tester, my downstream automatically went from 12mbps to 20mbps, sustained! What was more impressive though, was the upstream bandwidth--jumped from 1.4 mbps to 4-5! I don't believe Comcast has my area serviced with DOCSIS 3.0 just yet, but I know it's coming soon.

As far as setup goes, this is what I did:

1) Connect your cable modem to everything, and plug in the ethernet to your computer directly. Try to avoid sending your coax cable through any splitters. My house has the coax coming in from a pole so I can visually ensure this.

2) Plug it in, and wait for all the LEDs to light up. On a PC, type in CMD in the run command box, and type in ipconfig. On a mac, simply check the network pane in the system preferences.

3)You should see your external IP address. If you see anything like 192.168.XXX.X, wait a little longer and try again. It look about 6 minutes for my modem to assign my computer the external IP.

4)If steps 1-3 have worked successfully, then all is well because you are physically connected and working! All that's left is the MAC-address registration. If you open a web browser, an activation page should load. You'll have the option of activating as a customer or a technician. I chose technician because the customer activation had me downloading some sort of clunky software.

5)Now make sure you enter your account information correctly. Go through the steps. At some point, the page will perform a diagnostic test. If you're a geek like me, you can check some of the values like the SNR, TX, RX levels against this guide [...]

6)If you decide to connect your modem to a router (which I'd guess most people would do), make sure you reboot your modem after you reconnect your ethernet cable into your router's WAN port.

At any time, you can access the router diagnostic page by typing in It's quite handy.

Hope this helps!
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on May 10, 2010
We were experiencing random and frequent disconnects from our Charter 10MBPs cable line using hardware they provided. They came out a few times to check the line but couldn't find any issues. At that time, we were renting an older Motorola Surfboard (DOCSIS 2.0) cable modem and they swapped it out for a comparable Ambit model to see if that would fix the issue. At first, things seemed fine, but the modem starting rebooting itself and the problem came back. We finally found out there was a good amount of noise coming in on Charter's line and they couldn't do much to fix it.

It was very stressful having an unstable connection and also paying to rent a piece of hardware that wouldn't deal with a problem on their end. Knowing we will stick with some sort of cable provider in the future, whoever the ISP is (currently and unfortunately, Charter is the only option here), we decided to try out the Motorola SB6120 SURFboard DOCSIS 3.0 eXtreme Broadband Cable Modem because of its high ratings and knowing we'd have something compatible in the future with the DOCSIS 3.0.

We've had the modem hooked up for over a month now and haven't experienced one disconnect. Our upload and download speed have almost doubled and the device doesn't even get the slightest hot (the other modems we've had got a little hot before our disconnect problem). Not only did this modem fix our problem, but we don't have to pay Charter for their modified and problematic hardware anymore. This pays for itself within a year.

The installation was very easy. I had to reboot our Linksys Wireless N gigabit router a few times for the light on the SB6120 to turn blue (if it's amber, it means it doesn't have an outgoing gigabit connection). After it propagated with Charter's servers, it's just been sitting there and doing it's job in the best way possible.

I highly recommend this router, especially if you are tired of low grade hardware that the ISPs rent to you. If you are playing games, streaming HD media, or just surfing and want something reliable, then definitely try this modem out.
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on October 9, 2009
2009 Dec. 8: The speeds have increased, not decrease in the past few months. I still receive a low of 20 Mb/sec and as high as 25 Mb/sec. I have never had to reboot the box. This is as low maintenance as I have ever had from a DSL box or my prior Motorola cable box. Friends who have purchased this have seen the same improvements in their home systems. They are also Comcast, but in Chicago. My family in Chicago also liked the no fuss setup using the Apple Airport Extreme for their all PC network and thrilled to extend their system with an Apple Airport Express on their long house.

2009 Oct. 9: I have had a great experience the first week of use with the new SB6120 modem.

The good: 20Mb/sec download and 10Mb/sec upload when it originally was 4.5 down and 1.4 up with a SB5100. This is a must buy for the bandwidth increase. Once correctly setting up the Airport Extreme, it is a joy.

The bad: I tried to substitute the SB6120 directly into my home system. But I realized that there were some problems with how the group of products were not working together well. My stumbling block started with a call to Motorola which gave advice in which they said that the SB6120 was not powerful enough to front end to a router. What? Anyway, after I correctly setup the system the next day; it worked beautifully.

Here is one setup for the Apple AirPort Extreme Base Station (Simultaneous Dual-Band) (MC340LL/A) that allowed my system to be up and running in only 20 minutes, including the call to Comcast service to activate the SB6120: The Airport Extreme setup I used is...

1) Choose the configuration for the incoming data with the DHCP option.
2) Then share a single public IP address on the router, with the DHCP and NAT.
3) And the important part of the procedure: When switching between connecting a computer to your SB6120 and connecting your AirPort Extreme, be sure that you cycle power on the SB6120 so that it can reassociate with the change in unit. Why? Comcast will usually have you test out your connection of a new modem directly to a computer. Cycling the power on the SB6120 allows for hooking everything back up to the Airport Extreme, without the new modem not communicating to the router correctly.

Thanks to William Boyd Jr. for the correct information.
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on December 9, 2014
Works great, better than paying a monthly fee to rent from the cable company. It's paid for itself already. Do the math and then buy it, save some money. Really are you going to go without broadband internet any time soon? Doubtful so go ahead and tell your cable company to keep their rental. Just remember to at least use a good power strip with surge protection or a battery backup.
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on December 26, 2012
This was right on top of the bestseller list when I bought it, even though there was a newer model available. And I don't regret making this call. Very smartly made. Has perforations all around so it never gets too hot. I've never had to even look at it once I configured it. Sleek and light. Superb product. Highly recommended.
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on December 13, 2015
I am relieved that I made a good investment. My cable provider was charging me $$ every bill cycle. This has been no issue product. Recently my cable provider upgraded my internet speed and this modem is capable of handling that as well, though it is few years old.
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on November 28, 2011
Since my old Motorola Surfboard cable modem had worked flawlessly for about 7 years, I decided to again go with Motorola when my cable company said I needed to upgrade to a DOCSIS 3.0 modem. I ordered the Motorola SB6120 Surfboard DOCSIS 3.0 eXtreme Broadband Cable Modem from Amazon. The first Modem I received was DOA with no lights displayed when it was plugged in and was consequently returned. The second Modem received worked when it was plugged in, but wouldn't download any faster than 1.44 Mbps. Cable company tested the line and everything was well within their operating parameters. The second SB6120 was returned for a refund. Even though the modems didn't work, the communications and the return processes were effortless and I remain a satisfied Amazon customer.
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on March 24, 2015
Good enough for TWC extreme in DFW. 30mbps down and 5.5 up. The phone call to TWC to ask for promotional rate, and the return of the rental modem decreased my internet cost by $25 per month plus tax. That's a fast payback. I bought this instead of the SB6140 since it gets the job done at half the price and nothing lasts forever.
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on February 4, 2015
This modem has only one Ethernet LAN port and does not serve DHCP. This may be a limitation, depending on your needs. I have a firwall with DHCP server and a 10 port Ethernet switch. I am using a wireless access point that is capable of providing DHCP addressing as well. So this modem meets my needs. It is very fast, as described. Comcast has warned me that if I provided my own modem, they were no responsible if I did not get full bandwidth. I receive 70 Mbps downloads very consistently. I pay for 70 Mbps from Comcast and this modem delivers. I recommend this modem with the caveats described.
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on October 2, 2011
Advertised as new but the item I receievd was not in its original box and packed as if it were a refurbished unit.
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