Cisco Certified Network Associate (CCNA) Practice Exam

In the context of OSPF v.3, what does the 'router-id' command specify?

1. Router's IP address

2. OSPF process ID

3. Unique router identifier

4. Network type

The correct answer is: Unique router identifier

The 'router-id' command in the context of OSPF version 3 specifies the unique router identifier. This identifier is a 32-bit value that is essential for OSPF to function correctly. Each OSPF router must have a unique router ID within the OSPF domain to prevent routing loops and ensure accurate routing decisions. The OSPF process uses this identifier to maintain routes and facilitate neighbor relationships. In OSPF, the router ID is typically set manually using the 'router-id' command, or it can be automatically assigned based on the highest IP address of the active interfaces on the router or the highest loopback interface address if available. Having a unique router ID is critical for effective OSPF operation, especially in larger networks where multiple routers might interact. Understanding the unique role of the router ID helps clarify the functioning of OSPF and is fundamental for configuring and troubleshooting OSPF in networking environments.