200-301 Question 347
Single answerA network engineer is configuring OSPF on a router and notices that no Router ID has been explicitly assigned. The router has the following interfaces configured: Loopback0 (192.168.1.1/32), Loopback1 (10.1.1.1/32), and a physical interface GigabitEthernet0/0 (172.16.1.1/24). What Router ID will OSPF select by default?
- A
192.168.1.1
- B
10.1.1.1
- C
172.16.1.1
- D
The OSPF process will fail to start without a manually configured Router ID
Show answer and explanation
Correct answer: A
Explanation
When OSPF determines the Router ID, it prioritizes loopback interfaces over physical interfaces. If multiple loopback interfaces exist, the highest IP address among them is chosen. In this scenario, Loopback0 (192.168.1.1) has the highest IP address, so it is selected as the Router ID.
- A. Correct.
Correct. OSPF selects the highest IP address of any configured loopback interface as the Router ID if no Router ID is manually configured.
- B. Incorrect.
Incorrect. While Loopback1 has a valid IP address, it is not the highest IP among the loopback interfaces. The highest loopback address is 192.168.1.1.
- C. Incorrect.
Incorrect. OSPF only considers physical interface IPs if there are no loopback interfaces configured. Since there are loopback interfaces in this scenario, physical interfaces are not considered.
- D. Incorrect.
Incorrect. OSPF does not require a manually configured Router ID to start. It will automatically select a Router ID based on the highest IP address of loopback interfaces or, if none exist, the highest IP of physical interfaces.