A network administrator initializes OSPFv2 process 1 on a Cisco router named Branch-GW. The router does not have an explicit `router-id` command configured under `router ospf 1`. The operational status and IPv4 addresses of the router interfaces are listed below:
- Loopback1: 10.10.10.10/32 (Up / Up)
- Loopback2: 10.200.1.1/32 (Up / Up)
- Loopback3: 172.16.50.1/32 (Up / Up)
- GigabitEthernet0/0: 192.168.100.1/24 (Up / Up)
- GigabitEthernet0/1: 192.168.200.1/24 (Up / Up)
What IPv4 address will OSPFv2 elect as the router ID for Branch-GW?
Answer: 172.16.50.1
Answer
172.16.50.1
OSPFv2 elects the router ID using a strict three-tier precedence hierarchy: 1) Manually configured `router-id` command, 2) Highest IPv4 address among active (Up/Up) loopback interfaces, 3) Highest IPv4 address among active physical interfaces. Because no manual router ID is specified, OSPF evaluates the active loopback interfaces. Among Loopback1 (10.10.10.10), Loopback2 (10.200.1.1), and Loopback3 (172.16.50.1), Loopback3 has the highest IPv4 address (172.16.50.1). Active loopbacks take precedence over physical interfaces, so the higher physical interface addresses (192.168.100.1 and 192.168.200.1) are ignored.
Step-by-Step Solution
Key Concept
OSPFv2 Router ID Election Priority Logic
Estimated Time:1m 0s