单项选择题 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?（）

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