5ghz & 2.4ghz XB7T Gateway

If this is with a Comcast rented gateway device, this used to be the way. Many have posted here recently that it can no longer be done.. YMMV....

https://www.xfinity.com/support/articles/change-wifi-mode-admin-tool-xfinity-xfi 

Could you please send our team a direct message with your full name and full address? Our team can most definitely take a further look at this issue. To send a "Peer to peer" ("Private") message:
Click "Sign In" if necessary
• Click the "Peer to peer chat" icon
• Click the "New message" (pencil and paper) icon
• Type "Xfinity Support" in the "To:" line and select "Xfinity Support" from the drop-down list which appears. The "Xfinity Support" graphic replaces the "To:" line
• Type your message in the text area near the bottom of the window
• Press Enter to send it

@user_bef1bb  Does it still work ? 

@XfinityXavier @user_bef1bb 

Please circle back here and post any possible solutions for the issue here in the open forums so that all readers here may benefit from the exchange / info. This is in keeping with the spirit for which these public help forums were originally intended. Thank you.

It can still be done. Xfinity defaults to their mixed mode or whatever its called where both the 2.4GHz and 5GHz band is "managed" by the router. The problem I had is my phone would connect at 5GHz while simpler devices like smart lightbulbs, cameras, and my smart bathroom scale at 2.4GHz because that was all they are capable of which left my apps to connect to these things disconnected despite being on the same SSID. So yeah.... you can but its less easy.

You need to start with your gateway. I'm thinking as we're both Xfinity it will work the same. If so, open a browser to 10.0.0.1 and login as admin. I did and can check my setup out:

So the problem is their no longer seems to be any way to configure the setup via a web browser. They push you to their Xfinity app...

I'll be back in a sec to add to this from my phone then...

Alright so that's the screens to go through to get to the settings. The first mobile screenshot is the one you need to drill into to split your wireless bands. Obviously ignore the not recommended if you know what you're doing. Getting there is each successive screen I drill down. Even after you get it setup you can see at that last screenie I uploaded-- the first you encounter with the Xfinity app, they STILL constantly offer to "simplify" my network which as I noted why I did this, then their simplification would break my network devices again.