Cisco Certified Network Associate (CCNA) Practice Exam

What is NOT a requirement for OSPF routers to become neighbors?

1. Subnet

2. Unique Router IDs

3. IPv4 Addressing

4. Correct authentication

The correct answer is: IPv4 Addressing

For OSPF (Open Shortest Path First) routers to establish neighbor relationships, certain conditions must be met. These conditions ensure that routers can communicate and exchange routing information effectively. The requirement pertaining to IPv4 addressing is not necessary for routers to become neighbors in an OSPF network. While OSPF typically operates over IPv4, OSPF can also be implemented over IPv6, termed OSPFv3. Therefore, the basic requirement for neighbor formation does not hinge solely on the presence of IPv4 addresses. Routers can still form OSPF neighbor adjacencies through other addressing schemes as long as they follow the necessary configurations in OSPF. On the other hand, having matching subnets between routers (to enable communication at layer 2), unique router IDs (to identify each router in the network uniquely), and correct authentication (if configured to ensure secure communication) are critical for establishing OSPF neighbor relationships. These aspects ensure that OSPF can properly gauge other routers within the network and form adjacencies, which are essential for the OSPF protocol to function correctly.