From bridge mode to router mode on failover

Hi,

i have following situation and need help to setup following failover situation:

We have a normal IT network with 3rd party modem/router/switches in a building and a critical part of the infrastucture is behind a Teltonika router which has also UPS backup. On a power failure or when there is no WAN connection we need operate the critical infrastucture in a stand-alone mode. This means we have two modes:

  1. In normal operation we would use the Teltonika in bridge mode.
  2. Failover would use cellular, but it automatically we would need to enable router mode to handle all the direct connected devices.

Can anyone please help how to solve this. Thanks a lot.