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200-101 · Question #213
200-101 Question #213: Real Exam Question with Answer & Explanation
The correct answer is D: 2.2.2.2. OSPF Router ID selection follows the priority: manual configuration first, then highest loopback IP, then highest active physical interface IP. With no manual ID set, the highest loopback address is chosen.
Question
Refer to the exhibit. If the router Cisco returns the given output and has not had its router ID set manually, what value will OSPF use as its router ID?
Options
- A192.168.1.1
- B172.16.1.1
- C1.1.1.1
- D2.2.2.2
Explanation
OSPF Router ID selection follows the priority: manual configuration first, then highest loopback IP, then highest active physical interface IP. With no manual ID set, the highest loopback address is chosen.
Common mistakes.
- A. 192.168.1.1 is likely a physical interface address; physical interface IPs are only considered for Router ID selection when no loopback interfaces exist, and even then only the highest is chosen.
- B. 172.16.1.1 is a lower IP address than 2.2.2.2; OSPF selects the highest available loopback IP, not a lower one.
- C. 1.1.1.1 is numerically lower than 2.2.2.2; since OSPF picks the highest loopback IP and 2.2.2.2 is higher, 1.1.1.1 would not be selected.
Concept tested. OSPF Router ID automatic selection from loopback interfaces
Reference. https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/7039-1.html
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