200-301 Question 346
Single answerAn engineer is configuring OSPF on a router and notices that the Router ID is not explicitly set. The router has the following IP addresses configured on its interfaces:
- Loopback0: 192.168.1.1/24
- GigabitEthernet0/0: 10.1.1.1/24
- GigabitEthernet0/1: 172.16.1.1/24 Which IP address will the router use as the OSPF Router ID?
- A
192.168.1.1
- B
10.1.1.1
- C
172.16.1.1
- D
The Router ID will not be set until manually configured
Show answer and explanation
Correct answer: A
Explanation
When determining the OSPF Router ID, the router first checks for a manually configured Router ID. If none is configured, it selects the highest IP address on any loopback interface. If no loopback interfaces are configured, it selects the highest IP address on any active physical interface. In this scenario, 192.168.1.1 is the highest IP address on a loopback interface, so it is chosen as the Router ID.
- A. Correct.
Correct. If the Router ID is not manually configured, OSPF selects the highest IP address on a loopback interface. In this case, 192.168.1.1 is the highest IP on a loopback interface.
- B. Incorrect.
Incorrect. While 10.1.1.1 is an IP address on a physical interface, OSPF prioritizes loopback interface addresses over physical interface addresses when selecting the Router ID.
- C. Incorrect.
Incorrect. 172.16.1.1 is an IP address on a physical interface, but OSPF prefers loopback interface addresses over physical interfaces when choosing the Router ID.
- D. Incorrect.
Incorrect. The Router ID will be automatically derived if not manually configured, as long as there are valid IP addresses on the router's interfaces.