单项选择题 Routers A and B are connected with a point-to-point OC-3 interface. Each routers OC-3 interface is configured for both Level 1 and Level 2. The routers are configured in different areas. How many IS-IS adjacencies exist between the two routers?（）

多项选择题 What are two attributes of the Extended IS-Reachability TLV 22?（）

多项选择题 In JUNOS software, which three routing protocols can be used to route IPv6?（）