Which of the description of Router ID in OSPF, which of the following is incorrect?

Question

Options

• AIf the router-id command is not configured and the Loopback interface address is not configured, select the largest one from the IP addresses of its physical interfaces as the Router ID.
• BIf the router-id command is not manually configured and a loopback interface address is configured, select the largest loopback interface address as the Router ID.
• CAfter the Router ID is changed, the Router ID of each protocol will change, no additional operations are required.
• DIf the Router ID is manually configured using the router-id command, OSPF will use this Router ID first.

• A
  11% (4)
• B
  3% (1)
• C
  83% (30)
• D
  3% (1)

Explanation

Option C is incorrect because changing the Router ID in OSPF does not take effect automatically - it requires an additional operation, specifically resetting the OSPF process (e.g., reset ospf process on Huawei or clear ip ospf process on Cisco), or rebooting the router. Without this reset, the old Router ID remains active and the change is not applied.

Options A and B are both accurate descriptions of OSPF's Router ID selection hierarchy: when no manual router-id is set, OSPF first prefers the highest loopback interface IP (B), and only falls back to the highest physical interface IP if no loopback exists (A). Option D is also correct - a manually configured router-id always takes top priority over both loopback and physical interface addresses.

Memory tip: Think of OSPF's Router ID as a "birth certificate" - once assigned, it won't change mid-session on its own. You have to explicitly restart the process to issue a new one. This also helps you remember the selection priority: Manual > Loopback > Physical, highest address wins at each tier.

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