if all OSPF routers on a broadcast network have the same OSPF priority, which parameter is used to determine the new BDR at the time of a DR failure?（）

Given the set of routers, each with an interface on the same multi-access network:

Which router can never be a designated router on that multi-access network?（）

You are running OSPF between two ERX Edge Routers across an OC-12c link with HDLC encapsulation.
How many designated routers are present for this link?（）

What is the default authentication method on an OSPF interface?（）