In the house there is a main Mikrotik router and few (Ubiquiti) wireless access points. In one room there is "Mikrotik Chateau 12" router set-up as a wireless access point.
I added SIM card to that "Chateau" router and now I want to make it highly available wireless access point that turns into a router if main router or main router's internet goes down. This means setting up firewall rules, dhcp server, setting up NAT. The reason why I am not setting up NAT and firewall rules right away (so it would be very straightforward) is because I would like to keep UPNP functionality of main router accessible to the computers, so online games can make use of upnp.
What are my options? Or script is the only way to go? Someone point me to the right direction.