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I upgraded my Xfinity plan from 50 Mbps to 300Mbps after purchasing an SB8200 modem.

When the modem is connected directly to my computer, I get 300Mbps.
When the modem is connected to my router I get the speed of my old Xfinity plan: 50Mbps.
I am using two CAT5e cables, each of which, when connected directly from modem to computer get 300 Mbps. 
I did a hardware reset of my router with no change.
My router: TP-link AC2300 

Any ideas what might be going on?

 

SB8200 is compatible with your current speed plan and could please tell us to which ethernet port on the modem your router is connected? To isolate the issue.

Router Internet port to Modem port #1

Two new data points:

  1. I was using two CAT5e cables. I replaced them with two CAT6 cables with no change - still getting 50ish Mbps.
  1. My phone is getting 250ish Mbps via WiFi through this router.

I figured out what was happening and seemly solved the problem.

Killer Intelligence Center was causing the problem even though I had disabled it (Task Manager | Startup apps) long ago, and it wasn't running. Or at least there was no indication at all that it was running.

In Killer Intelligence Center settings, the manual bandwidth setting (under Auto Bandwidth) was set to 60Mbps. Auto Bandwidth was ON. I had to turn off Auto Bandwidth to change the manual setting.

I set the manual bandwidth setting to 300 and it solved the problem.

When I set it back to 60Mbps, I get a speed of about 54Mbps, seemingly under any circumstance:

  • Killer Intelligence Center disabled or enabled in startup.
  • Killer Intelligence Center running or not running.
  • "Auto Bandwidth" setting on or off.

I believe this would have to be called a bug in Killer Intelligence Center.

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