@gliebisch If you're about to connect your main router and the AP with an ethernet cable you should use Access Point mode for the AP. If you want a different SSIDs for the 2.4 GHz and 5 GHz wireless...

@grovefire If your inquiry is whether BE550 supports AP mode then yes - it supports two working modes: 1.Wireless Router Mode 2.Access Point Mode - details.

@rpg255 A way to mitigate this would be to use a UPS device to protect at least your modem.

@i_r_dippy When I'm using TP-Link routers and Internet connection is not available, I still can access my local network if that's your inquiry.

@Razorek Use this guide for building an etehrnet backhaul between those two. According to this thread both your router should support Easymesh ethernet backhaul. If you still can get ethernet...

@rborgia Check this thread.