In other routers (Cisco, UBNT EdgeOS), this would be achieved using “default-information originate”.
I have 2 Bal 30 LTE’s, which are Hub and Slave of a PepVPN configured with ‘disaster recovery’. They each share an area with the border-router of the ‘main office’ (which is a UBNT EdgeMax). In my simple scenario, I want the office-border-router to rely on OSPF LSA’s to choose the best route to the internet (the Hub Bal30 with DSL … unless DSL is down again … in which case the Bal30 with Cellular is the way to go).
This 'poor man’s high availability" is good enough for us, but it’s only going to work if the Bal 30 will advertise itself as having 0.0.0.0/0, and I can’t see how to achieve that.