For the networking wizards: I have a setup with a cable connection and a RUT240 as backup. Failover provided by TP-Link ER605, that switches from cable modem to RUT in case of cable disconnect. Setup works like a charm.
Where my networking understanding fails is when I want to use the RUT240 as a wifi access point as well (it's located outside, all other APs are located inside behind the ER605). It works as long as it uses the 4G connection, but I want to route the clients connected to the RUT via the ER605, so that they use the cable connection when available, and only 4G when necessary. See below a simplified overview of the network.
Question: is this possible, and if so, how i should configure the RUT Lan interface?