Modem, router or Comcast?


Thread Starter
Active SatelliteGuys Member
Feb 11, 2013
I'm trying to figure out if my internet speed problems are with my equipment or with the Comcast line. I only have internet with Comcast (no cable). My equipment is a Motorola SB6121 Surfboard cable modem and Netgear N600 router, both were bought at the same time about 43 months ago.

Almost every day or every other day my internet speed is very slow, about 4-5 Mbps (should be 20 - 25 Mbps) that I have to reboot my cable modem and router, then the computer. Usually after I do this the speed is back where it's supposed to be. I'm just trying to determine which part is making my download speed so slow on a regular basis.

Thanks in advance for the help,


A mighty and noble race originating on Altair IV.
Pub Member / Supporter
Jan 4, 2007
Fairfax, VA
I've had this issue (rarely) on Cox, and each time it has been their problem and not mine. But to help diagnose, if I were you, I'd buy another router (since many are so cheap) and see if that fixes the problem. Do you own the Motorola as well?

Perhaps Comcast (who presumably provisioned that modem) can log into it and see what the error counters indicate. I have never interacted with Comcast so I have no idea how good their technical support might be. Cox's is pretty good, but I'm paying for a SOHO account with Cox Business, so I may be getting better service because of that.

. Raine

SatelliteGuys Pro
Pub Member / Supporter
Aug 6, 2013
North America, CT.
If you're using DHCP, try putting both the modem and router into the same subnet, if they aren't already. As in if say the modem's IP is something like and the router's is like, change the router to, or a IP within the same subnet that the modem is in. You'll have to reboot computers, games, etc, whatever that's connected to your LAN and on, after you do this.

I don't know what subnets or IP's your router and modem have, just used the ones above as examples, but you should be able to look up the default IP's online with no trouble, if you left the router and modem as default and don't know them.


SatelliteGuys Pro
Dec 5, 2014
Are you wired, wireless or both?

Have you tried bypassing the router?

First thing I would do is connect the modem directly to your PC. If you have no speed issues then it’s the router, if you continue to have speed issues then is the modem, or a Comcast problem.

If it’s a router problem, next thing I would do is check your routers firmware. If you don’t have the latest firmware, I would download it and then do a factory reset and start from scratch. I’d also replace all Ethernet cables involved if so inclined.

Do you experience slowdowns during peak times? Are you in a populated area? While DOCSIS 3 has alleviated many of the ‘cable slows down during peak times’ cries, that modem only bonds 4 channels, which is great if your area only has four channel bonding. I’m not an expert when it comes to Comcast, but they are pretty aggressive with upgrades, your area should have 8 or maybe even 16 bonded channels.

And I would never in a million years get a combo modem/wireless gateway. Separate components is the only way to go. Easier to swap devices in and out, more customizable, more tweaking to increase performance. I’m even done with wireless routers. Wired router with a dedicated WAP is the only way I roll these days.

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