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Customer Review

2,725 of 2,795 people found the following review helpful
4.0 out of 5 stars Does the job well/tip for Comcast users, September 29, 2011
Verified Purchase(What's this?)
This review is from: ARRIS SURFboard SB6121 DOCSIS 3.0 Cable Modem (Black,Retail Packaging) (Personal Computers)
Out of nowhere, I was having excruciatingly slow internet speed on Comcast. The Comcast tech advised that my Motorola SB 4100 was at the "end of life" and that I should upgrade. Skeptical, I purchased this modem which is a DOCSIS 3.0 (and backwards compatible) modem. It worked. I went from a 2mbps download speed to over 17mbps. What a difference. There was one installation glitch that you need to be aware of. When you hook up the modem (connect the coax cable, connect the ethernet cable, and plug it in, that's it), and then try to get online, it will direct you to a Comcast self-activation screen (no other site is available). After entering my account number and phone number and hitting the "next" button, I got a blank screen, and nothing happens. So I called Comcast and they said that usually happens if you are doing an upgrade; it mostly works only for a new service connection. However, it is a simple matter to give the tech your MAC address and the serial number. After about 5 minutes, while he stayed on the line, it came alive, no problem. BUT, here's the thing: the serial number they need is the CUSTOMER serial number. This is only found on the bottom of the Motorola box the modem came in. This is different from the "S/N" serial number that is on the label that is on the instruction sheet and on the bottom of the modem itself. The customer S/N has letters in it; the regular S/N has only numbers in it and is too long. My first Comcast tech didn't know that and it took a day to sort it out. Other than that, it works well with my iMac and Apple Airport Extreme Base wireless router. Enjoy
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Tracked by 14 customers

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Showing 1-10 of 91 posts in this discussion
Initial post: Dec 21, 2011 11:45:21 AM PST
r2s says:
Comcast needs the Mac address of the modem to set it up not the serial number

Posted on Dec 22, 2011 11:26:27 AM PST
Thank you for mentioning that! I tried registering mine and hadn't the faintest clue what it meant when the service rep for Teksavvy here in Canada asked me for the "customer serial number"! I guess I have to take a look at the actual box now. :D

Posted on Dec 23, 2011 1:55:19 PM PST
Burnzie743 says:
What internet plan do you have with Comcast? I have the cheapest one, with speeds no more than 15mbps down, and have heard that I wouldn't even notice a difference anyway if I upgraded (I currently have a Linksys CM100).
Thanks ahead of time.

Posted on Jan 4, 2012 2:42:53 PM PST
I just had the same problem with Comcast re: S/N. They kept telling me the s/n on the install sheet that came with the modem was too long. It took my Internet search and finding this review to figure out they needed the customer s/n which is only printed on the cardboard box the modem came packaged in. Gigantic waste of an hour. Wish I read this review first.

Posted on Jan 4, 2012 3:58:04 PM PST
Sahi says:
I had similar problem with the Customer Serial Number mentioned here and was about to cancel my internet order and then I did this search to find here on Amazon this post. Thank you to all for sharing the info.Motorola SB6121 SURFboard DOCSIS 3.0 Cable Modem

Posted on Jan 4, 2012 8:04:40 PM PST
Comcast never asked me for the serial number- just the MAC address. Works great!

Posted on Jan 6, 2012 9:35:34 AM PST
doctor don says:
Would you get a blank screen if you tried to access the setup before you connected the new modem?

And to r2s: Where are you that you don't need to provide Comcast with the customer serial number?

Posted on Feb 4, 2012 8:04:29 PM PST
Ray M. says:
Comcast tech couldn't set up my internet because he used the S/N. Left me no choice but to rent their cable modem. After I read your review, I called Comcast myself and gave them the customer S/N. Now the SB6121 works fine. I can return their modem and save $7 a month.
Thank you so much for posting the review. It is so silly for Motorola to use two S/N number to confuse the customer.

Posted on Feb 8, 2012 9:32:48 AM PST
I ran into a similar issue where I hit the self activation page after plugging in the new modem. I was able to reach step 2 of 3 but it hung and didn't finish the registration after finding the modem and pulling the serial number from it. The page said it would need 10 mins and took 20 to finally fail.

I ran the activation one more time and it took maybe 2 mins and then it worked perfect. I almost had to call a human.

In reply to an earlier post on Feb 8, 2012 8:32:10 PM PST
doctor don says:
ernest -

Did you turn off TV and computer (and unplug the modem) before connecting the Motorola SB6121?
And then did you turn on your computer after making the connections that had been to your previous modem?
And then did you have to navigate to the self activation page or did it come up on your computer automatically?
Did you use the Customer S/N from the start?
Was it necessary to provide the MAC ID number?
Was access to cable TV interrupted while the SB6121 was being difficult, or was it only internet access that was slow to be recognized?

Before I proceed with the above, I'd like to make sure it will be as painless as possible.
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