Is 600 Mbps possible with a DOCSIS 3.0 Modem?

That modem should get to 600 Mbps no problem.

Are you running the speedtest with a Cat5e or better Ethernet cable directly connected from your PC to the modem?

Cat 6 through Netgear R6400 router to PC.

Try a test wired direct to the modem from the computer. As darkangelic suggests. (Don't forget to powercycle the modem when changing the device directly connected to it).

It's certainly approved for the speed on mydeviceinfo.

https://mydeviceinfo.xfinity.com/

(and what EG said).

What do you get directly connected to the CM600 ? What do you get for the upload speed ?

I'll try that later today.

Upload seems ok being a consistent 23.8

Direct Modem to PC, 6 tests using speedtest.net on Brave browser:

(533, 614, 615, 517, 539, 509) Ave: 555 Mbps

Thru Router (the normal set up) same test:

(413, 412, 404, 412, 401, 416) Ave: 410 Mbps

Upload was 24 Mbps on all tests.

So, I guess I need to investigate my router to see if there are some settings to change. I would think the wired connection would be a true pass thru? 

Something else to note, I did the same tests on Chrome browser and the results were an average 50 Mbps slower than on the Brave browser, interesting.

If there are any QOS settings enabled in the router, try disabling them.

The other thing is with Extreme Pro 600, you should be aiming to get around 700/720 with overprovision.

Speedtests, browsers, apps, equipment used ect; results can vary.

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@jda54669 wrote:

Direct Modem to PC, 6 tests using speedtest.net on Brave browser:

(533, 614, 615, 517, 539, 509) Ave: 555 Mbps

 

Thru Router (the normal set up) same test:

(413, 412, 404, 412, 401, 416) Ave: 410 Mbps

 

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Seems like your modem is OK. Try using the free the Ookla Speedtest App for Windows or MacOS. 

Thanks for that tip, I didn't know Ookla had a windows app. So using that method and going thru my router I got an average of 432 Mbps Down and 29 Mbps Up. A little better with the download and upload.

I haven't had time yet to get into the router settings so I need to try that. I'm going to keep at it to see how close I can get to the 600 Mbps. 

I checked the router, QoS was not enabled for upload or download. Any other suggestions?

Had the same problem with 600mbps account.

solution is udating the browsers, chrome, explorer, and firefox all have throttling issues, several NEWER browsers will allow for fast 600 plus access.

try opera or swift or brave.