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Broadview Heights, OH

[OH] Slow internet access: Router? Modem?

Strange issues here with Cox Cable internet speeds and the connection between my Netgear WNDR4500 router and Motorola SB6120 modem.

The past week my internet speed slowed to a crawl. Videos played only a few frames before pausing; other downloads took minutes rather than seconds. Running the tests on Speedtest dot Net showed download speeds under 1M (!) with faster uploads in the 8M range.

Several resets/reboots and my WNDR4500 started linking with my SB6120 modem at 100M (yellow LED) vs 1G (blue LED). Download speeds jumped dramatically to the 25M range! Slower connection between the router and modem yielded faster internet speed.

Is there a conflict somewhere that limits the router-modem link to 100M? The router and PC still link at Gigabit speeds. And the slower router-modem link has produced startlingly better internet connect speeds.

Anyone got any clues? I'm leaving it all alone for now as my internal LAN still works at 1G and internet downloads are good again.

-- Chuck


Wichita, KS
If directly to the cable modem really works well, then it is your router issues that slows things down after receives the data from the cable modem.


Broadview Heights, OH
The slow internet speeds show up when the modem is connecting to either the router OR the PC at a 1G connection rate. Blue Link LED on the Motorola 6120.

On a good day this can be in the 5M-8M range but as low as 0.5M!. 100M connection out of the modem, which only seems to activate accidentally, has speeds in the 25M range.

I'm thinking this is some sort of bottleneck or negotiation issue in the modem caused by communicating at the Gigabyte speed. Wish I knew someone with this modem.

The modem is several months old. The router is a week old but I recall sporadic speed loss with the previous Netgear WNDR3700.

-- Chuck

Irish Shark
Play Like A Champion Today
Las Vegas, NV
reply to santose
In doing some research on the MODEM and router, I found this.

"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 [...]. "

»Motorola sb6120 issues. Read here

There are more: Google
Motorola SB6120 Cox issues
"You can observe a lot by watching". Yogi Berra

Chesapeake, VA
reply to santose
I don't think any firmware issues apply here but I'm curious about the 100BaseT vs 1Gbps link negotiation between the modem and the router. This could indication a physical/data link layer connectivity issue between the two. If you connect a PC with a Gigabit interface does the link light on the modem turn blue and stay that way?


Phoenix, AZ
reply to Irish Shark
latest version for the 6120 should be


Broadview Heights, OH
Firmware Name: SB612X-

On a Cat 5 cable the modem and router negotiate and connect at 1G speeds. But I get this (or slower) connection.

With a Cat 7 cable the modem and router negotiate and connect at 100M speeds. And I got this connection seconds ago:

Note the upload speeds are essentially the same.

Not sure what chokes the connection. Modem? Router?

-- Chuck