A network engineer inspects a Cisco router named Branch-R1 that was recently configured for OSPFv2 routing. The interface configuration and operational states on Branch-R1 are as follows:
- Loopback 0: 192.168.50.1/32 (Status: Administratively Down)
- Loopback 1: 10.10.10.1/32 (Status: Up/Up)
- GigabitEthernet 0/0: 172.16.200.1/24 (Status: Up/Up)
- GigabitEthernet 0/1: 10.200.1.1/30 (Status: Up/Up)
No manual OSPF router ID has been configured under the `router ospf 1` process. Which IP address will OSPFv2 select as the Router ID for Branch-R1 upon initialization?
- 10.10.10.1Answer
- B192.168.50.1
- C172.16.200.1
- D10.200.1.1
Answer
10.10.10.1 is selected as the OSPF Router ID because it is the highest IP address among active operational loopback interfaces.
OSPF Router ID election follows a strict hierarchy: 1) Manually configured router ID (`router-id` command), 2) Highest IPv4 address on an active (Up/Up) loopback interface, 3) Highest IPv4 address on an active (Up/Up) non-loopback/physical interface. Because Loopback 0 is administratively down, Loopback 1 (10.10.10.1) is the only active loopback interface and is selected.
Step-by-Step Solution
Key Concept
OSPFv2 Router ID Selection Hierarchy