C6220 configuration with Xfinity 400Mb

[mjd50]

C6220 v1.2.11

I recently upgraded my Xfinity service to 400Mb but can never see a speed test over 250. My network interface is configured for 1000Mb, i have CAT6 cable. Is there anything on the modem/router that needs to be changed? 

[FURRYe38]

Please post a copy and paste of the modems connection status page.
Have the ISP check the signal and line quality UP to the modem. Be sure the ISP provisions the modem correctly.
Be sure there are no coax cable line splitters in the between the modem and ISP service box. 
Be sure your using good quality RG6 coax cable up to the modem. 
Be sure to power OFF the modem for 1 minute them back ON.
https://community.netgear.com/t5/Cable-Modems-Routers/General-info-and-Troubleshooting-for-Cable-Mod...

[plemans]

You won't see >250mbps out of the C6220. its an 8x4 modem and its not even approved up to those speeds with xfinity. I'm actually impressed you're getting that much out of it. 

If you're wanting to hit the 400mbps speeds you're paying for, you'd need to upgrade the modem. I'd recommend upgrading to one that supports docsis 3.1 as we're seeing more ISP's require docsis 3.1 for lower speed tiers.