200-301 Question 348
Single answerA network administrator is configuring OSPF on a router. The router has multiple interfaces with the following IP addresses and priorities:
- Loopback0: 192.168.1.1/32 (no priority assigned)
- Ethernet0: 10.0.0.1/24 (OSPF priority 100)
- Ethernet1: 172.16.0.1/16 (OSPF priority 50)
The administrator does not manually assign a router ID. What will the OSPF router ID be after the OSPF process starts?
- A
192.168.1.1
- B
10.0.0.1
- C
172.16.0.1
- D
The router ID cannot be determined without manual configuration
Show answer and explanation
Correct answer: A
Explanation
OSPF selects the router ID based on the following order of preference: 1) Manually configured router ID, 2) The highest IP address of an active loopback interface, 3) The highest IP address of any active interface. Since there is no manual configuration in this scenario, OSPF selects the highest IP address of the active loopback interface, which is 192.168.1.1.
- A. Correct.
Correct. When a router ID is not manually configured, OSPF will select the highest IP address of any active loopback interface. In this case, the Loopback0 interface has the highest IP address, 192.168.1.1.
- B. Incorrect.
Incorrect. Ethernet0 has a higher OSPF priority, but OSPF uses the highest IP address of a loopback interface first, not the priority.
- C. Incorrect.
Incorrect. Ethernet1 has a lower priority and is not a loopback interface, so it will not be selected.
- D. Incorrect.
Incorrect. OSPF can determine the router ID automatically if there are active interfaces.