Backup channel via 3g modem?

Question

Mikrotik

Hello everyone,
There is RB951Ui-2HPnD, the first ethernet looks at the provider, the rest with wlan in the bridge, RB912UAG-5HPnD is connected to the fifth port, which is configured in the bridge, in which the only ethernet and wlan. There is a Sierra Wireless MC8781 3g board that can be installed in the RB912UAG-5HPnD access point.
Question: can I make it so that switching to 3g happens automatically when the main channel drops, and if so, how to implement it?

Answer 1

Wow, something beautiful doesn’t immediately come to mind, but I think you can do this:
1. Set up a map and connection from 3g to 912
2. On 912 we have a separate interface, when traffic is directed to which there will be Internet.
3. Made additional local addresses between the two devices (for a cleaner and more transparent operation of the main NAT on 951)
4. Made no 951 second routing rule for the network 0.0.0.0/0 where the gateway will be the additional local address 912
. \ enable routing rules.

Answer 2

Everything is clear except for
3. Made additional local addresses between the two devices (for a cleaner and more transparent operation of the main NAT on 951)
The addresses that are used for administration will not work? And if you make additional addresses, on which interfaces should you hang them?
5. Made the switch by disabling \ enabling routing rules.
Here, too, it is not entirely clear, can you be more detailed?
Thanks