@sntehran 

Thanks for reaching out. I understand that you are using your Deco Mesh system with an Xfinity modem/router, and when you set the Xfinity device to bridge mode, your Deco router's light turns red and loses Internet connectivity. When you disable bridge mode, the Deco works again.

Here's some important information to help clarify and troubleshoot your setup:

Deco Mesh systems (such as Deco BE11000) do not have built-in modem functionality. They require an active Internet connection from a modem or ONT (Optical Network Terminal). The Deco connects to your modem/router via Ethernet and acts as your main router or access point.

Key points for your setup:
1) If your Xfinity device is a modem/router combo, putting it into bridge mode disables its router functions and turns it into a pure modem. The Deco should then be able to obtain the Internet connection directly from the modem. If the Deco's light turns red in bridge mode, it means it is not receiving an Internet signal.
2) Make sure the Ethernet cable from the Xfinity modem is connected to the WAN/LAN port on the main Deco unit.
3) After enabling bridge mode on the Xfinity device, power cycle both the modem and the Deco. Sometimes, the modem needs to be restarted to properly assign an IP address to the Deco.
4) If you have multiple Ethernet ports on the Xfinity modem, only one may be active for Internet after bridge mode is enabled. Try connecting the Deco to the first Ethernet port (usually labeled as 'LAN 1' or similar).
5) If the Deco still does not work in bridge mode, try connecting a computer directly to the modem's Ethernet port to check if you can access the Internet. If not, contact Xfinity to confirm that bridge mode is set up correctly and that the modem is providing an Internet signal.

Additional Notes:
• The Deco Mesh system cannot function as a modem. It requires an external modem or ONT to access the Internet.
• If you use the Deco with an existing router (not in bridge mode), you can connect the Deco to a LAN port of the router. In this case, the Deco will work as a router or access point, but you may have double NAT (which can affect certain applications).
• For more details on using Deco with an existing router, please refer to: https://www.tp-link.com/support/faq/3665/

If you continue to experience issues, please provide more details about your Xfinity device model and how you are connecting the Deco. We're here to help!