Hello, i have 2 deco m4 and 2 w2400. first two of them I have installed as wireless, then I want to add 2400 as a third device, where I want to add in this room there is a good signal also a good wireless signal from my deco wifi network, but I want to add a third via Ethernet backhaul.

How do I know if the third device is connected via Ethernet cable or via wireless? how? How can I be sure that I add a third device via cable? i connected the cable from the main deco to the third device.