was this a double NAT issue with Chromecast I am having the same issue with my SONOS and ATT MCell Trying to figure out how to get DECO in Router mode and not lose my SONOS and MCell which won't work...

I ran into this myself Make sure you have it set up to go Bell Router - out to Deco and then wire from Deco to switch and then everything and all the decos coming off the switch you can't have...