@Panyk_Attak 

If you want to make a single mesh with your two Decos in router mode, I believe one Deco must be connected between the xfinity box and the switch.

See this : https://www.tp-link.com/us/support/faq/1794/

Why do you want to configure the Xfi in bridge mode?

  @yves_b 

At the moment just using the Xfinity gateway does ok wifi on the 2nd floor. Previously I had been using a 2-piece Deco mesh system in our old house on a modem we owned. I am trying to increase the wifi on the peripherals of the house footage for better Ring camera performance and also smart TV, and general wifi useage on the upper floor. I thought that the Deco systems did not do repeater mode, so I assumed that the bridge was necessary to disable the wifi from the Xfi and use the Deco units to push wifi. I tried it last night two ways;

1) I had one unit plugged into a cat6 connection on the 1st floor and tried to setup the wifi network from there, but the unit went red at the final stage

2) I then plugged one of the Deco units directly into the Xfi in the basement and again it went red at the last stage of wifi setup

I think I had initial issues setting up my old network, but cannot remember how I got around it in the smaller house.

Perhaps I need to reset the Xfi modem as well during the initial setup process? I was hoping I could use the cat6 wiring as a means of extending the wifi a little bit to carry to the 2nd floor. Was a rollercoaster of emotions as the little blue light went from 'Final setup stages' to a solid red light mocking me.

  @Panyk_Attak 

When plugging the main Deco directly into the Xfi, did you select the "AP" mode of the Deco?  If not, I suggest trying that.

  @Panyk_Attak I could be wrong but imo, when you Xfi in bridge mode means it disables its routing & Wifi broadcast features. Therefore, if you connect a switch directly after Xfi now, nobody is gonna handle IP addresses or do routing. Even if you ISP does that for you, and ISP gives the switch those info, the switch (if not a layer 3 switch) which mostly works in Layer 2 OSI model, means it will not care about IP addresses, it only do switching in local subnet using MAC addresses.

In your case, you can try to see if you can disable Wifi broadcasting feature only on Xfi (keep routing feature on), then connect that to a switch > connect other Deco units in AP mode, cause you already have Xfi do routing already. See if that works, otherwise just keeps Xfi in normal mode, then connect to the switch, then running Deco in AP as usual. If you worry about Xfi wifi signal vs the Deco wifi signal, check if you can reduce transmit rate on Xfi. Good luck!