Cisco Certified Network Associate (CCNA) Practice Exam

What is required for two OSPF v3 routers to successfully form a neighborship?

1. Router IDs must be unique

2. Both interfaces must be in passive mode

3. Authentication is optional

4. Hello and Dead timers can differ

The correct answer is: Router IDs must be unique

For two OSPFv3 routers to successfully establish a neighborship, it is essential that their Router IDs are unique. The Router ID is a 32-bit value that uniquely identifies a router within an OSPF network. When OSPFv3 routers attempt to form adjacencies, they exchange Hello packets, which contain their Router IDs. If two routers share the same Router ID, they will not be able to establish a neighborship because the OSPF protocol requires each router's identifier to be unique in the broadcast domain. In contrast, while it is true that authentication can enhance security in OSPFv3, it is optional and not a fundamental requirement for neighborship formation. Similarly, both routers can have differing Hello and Dead timers; although this may affect the time it takes for adjacencies to stabilize, it does not prevent the formation of a neighborship. Lastly, putting interfaces in passive mode would prevent OSPF packets from being sent or received, making it impossible to establish the required OSPF adjacency. Therefore, the uniqueness of Router IDs is a critical aspect of forming successful OSPFv3 neighborships.