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Zorluk: OrtaOSPFv2 Neighbor Adjacencies and Router ID

A Cisco router is running OSPFv2 with an active Loopback 0 interface (10.10.10.1/32) and a GigabitEthernet0/0 interface (192.168.1.1/24). No explicit router ID command was configured under the OSPF process, so OSPF selected 10.10.10.1 as the Router ID when the process initialized. A network engineer subsequently configures a new Loopback 1 interface with IP address 172.16.100.1/32 and brings it into an operational up/up state. Which statement accurately describes the status of the OSPF Router ID immediately after Loopback 1 is brought up?

  1. The OSPF Router ID remains 10.10.10.1 until the OSPF process is restarted or the router is reloaded.Cevap
  2. B
    The OSPF Router ID automatically changes to 172.16.100.1 because Loopback 1 has a higher IP address than Loopback 0.
  3. C
    The OSPF Router ID automatically changes to 192.168.1.1 because active physical interfaces take precedence whenever interface changes occur.
  4. D
    The OSPF process shuts down automatically because changing interface parameters while OSPF is active invalidates existing adjacencies.

Cevap

The OSPF Router ID remains 10.10.10.1 until the OSPF process is restarted or the router is reloaded.
OSPF Router ID selection is non-preemptive. Once the OSPF routing process selects a Router ID at startup (10.10.10.1 from the active Loopback 0), it retains that Router ID even if another interface with a higher IP address (such as Loopback 1 at 172.16.100.1) is subsequently configured and brought up. The new Router ID will only take effect if the OSPF process is manually reset (using 'clear ip ospf process') or if the router is rebooted.

Adım Adım Çözüm

1
Determine initial OSPF Router ID election outcome.
OSPF selected 10.10.10.1 because Loopback 0 was the highest IP active loopback interface when the OSPF process initialized.
OSPF follows election precedence: manual 'router-id' command > highest IP among active loopbacks > highest IP among active physical interfaces.
2
Analyze OSPF Router ID election behavior upon configuration changes.
The OSPF process maintains its currently active Router ID and does not preempt it when a new interface with a higher IP address is brought up.
Router ID stability prevents unnecessary SPF recalculations and neighbor adjacency resets. A process restart (e.g., using 'clear ip ospf process') is required to force re-election.

Anahtar Kavram

OSPFv2 Router ID Non-Preemptive Election Logic
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Konular

OSPFv2 Neighbor Adjacencies and Router ID

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