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?（）

单项选择题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?（）

A.0
B.1
C.2
D.3

单项选择题What is the default authentication method on an OSPF interface?（）

A.A
B.B
C.C
D.D

多项选择题What are the three OSPF authentication methods supported on the ERX Edge Router?（）

A.A
B.B
C.C
D.D
E.E

单项选择题Where is OSPF authentication configured on the ERX Edge Router?（）

A.A
B.B
C.C
D.D

单项选择题During OSPF adjacency formation, in which state is a router in when an OSPF hello packet has been sent but bi-directional communication has not been achieved?（）

A.A
B.B
C.C
D.D