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?（）

What are the three OSPF authentication methods supported on the ERX Edge Router?（）