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Difficulty: EasyOSPFv2 Neighbor Adjacencies and Router ID

An administrator configures OSPFv2 on a Cisco router with an active Loopback0 interface assigned IP address 10.254.1.1/32 and an active GigabitEthernet0/0 interface assigned IP address 172.20.10.1/24. Within OSPF router configuration mode, the administrator executes the command `router-id 1.1.1.1`. What IP address will the router process select as its OSPF Router ID upon initialization?

Answer: 1.1.1.1

Answer

1.1.1.1
The explicit `router-id` command takes highest priority in OSPFv2 Router ID selection. Therefore, 1.1.1.1 is selected as the Router ID.

Step-by-Step Solution

1
Evaluate the OSPF Router ID election priority rules.
The selection order is: 1) Manually configured `router-id` command, 2) Highest IPv4 address on active loopback interfaces, 3) Highest IPv4 address on active physical interfaces.
An explicit manual configuration takes top priority and overrides dynamic interface election logic.
2
Apply the parameters given in the scenario to determine the winning Router ID.
Because `router-id 1.1.1.1` is explicitly configured under the OSPF process, the router selects 1.1.1.1 regardless of Loopback0 (10.254.1.1) or GigabitEthernet0/0 (172.20.10.1).
Interface IP addresses are only evaluated when an explicit `router-id` command is absent.

Key Concept

OSPFv2 Router ID Selection Precedence
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Topics

OSPFv2 Neighbor Adjacencies and Router ID

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