Two ISP routers and an OpenWrt device for redundancy?

[Umpfda]

I can use two routers in my home.

Router A is from my ISP. I can deactivate the DHCP server on it and the gateway ip address is configured to 192.168.0.1.
Router B is behind an ethernet port in my flat. It's provided by my property management. I have no access to it, a DHCP server is running on it. It's gateway address is configured to 192.168.0.254. Currently an openwrt device configured as dump ap is directly connected to it.

Is it possible to install a redundancy setup here? Normally i want to route everything over router A, but if this fails i want to switch to router B.

My idea was to let the openwrt device function as the DHCP server in the network. On router A i can deactivate the DHCP server. DHCP requests should never reach router B, as the only connection to it is going over the openwrt device. Perhaps i have to setup a firewall rule to it, but that part seems to be solvable to me.

But i have problems with the second part. Detecting that router A fails and then switch all devices in the network to router B. Is there a way to do this? Is this even the correct way to do this?

[eduperez]

The "mwan3" package does exactly that.

[randyrodriguez]

I followed this tutorial setting up multiwan on openwrt. https://youtu.be/vHWYH_5ooEY

[Umpfda]

Thank you guys, that's exactly what i was searching for. Multiwan, sometimes you just need to know the correct term to search for.

I've read through the user guide of mwan3 and watched the video.

I think i have only one last question before i will try to setup my openwrt device. I understand that i have to setup a vlan on the ports connected to the routers. But in router A there is also an ethernet switch. Is it possible to still use that ethernet switch?

[Umpfda]

I think i misunderstood something. I will just try it.

[ulmwind]

It is better not to use it. You should connect both routers to OpenWRT router, so it will have two wan interfaces.