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Zorluk: ZorOSPFv2 Neighbor Adjacencies and Router ID

A network administrator initializes OSPFv2 on a Cisco router named R1. The router has the following interface states and IP addresses configured prior to starting the OSPF process:

- Interface GigabitEthernet0/0: IP address 172.16.10.1/24 (Up/Up)
- Interface GigabitEthernet0/1: IP address 192.168.1.254/24 (Up/Up)
- Interface Loopback0: IP address 10.1.1.1/32 (Up/Up)
- Interface Loopback1: IP address 10.2.2.1/32 (Administratively Down)

The administrator enables OSPF process 1 without explicitly setting a router ID. After OSPF initializes, the administrator enters `router-id 1.1.1.1` under the `router ospf 1` process configuration prompt and changes Loopback1 to the Up/Up state. No further commands are entered.

Which two statements correctly describe the resulting OSPF Router ID behavior on router R1? (Select two.)

  1. The active OSPF Router ID remains 10.1.1.1 until the OSPF process is reset or restarted.Cevap
  2. Executing the clear ip ospf process command is required to apply 1.1.1.1 as the active OSPF Router ID.Cevap
  3. C
    The active OSPF Router ID automatically updates to 1.1.1.1 as soon as the router-id command is entered.
  4. D
    The active OSPF Router ID dynamically changes to 10.2.2.1 when Loopback1 transitions to the Up/Up state.

Cevap

The active OSPF Router ID remains 10.1.1.1 until the process is reset, and executing the clear ip ospf process command is required to apply 1.1.1.1 as the active OSPF Router ID.
When OSPF process 1 initializes without an explicit router-id configured, it evaluates active interfaces. Loopback1 is administratively down, so Loopback0 (10.1.1.1) is chosen as the active OSPF Router ID. OSPF Router ID election is non-preemptive, meaning subsequent configuration changes—such as configuring a manual router-id or enabling a higher IP loopback interface—will not change the active Router ID immediately. The statement indicating that the active Router ID remains 10.1.1.1 until reset and the statement indicating that executing 'clear ip ospf process' is required to activate 1.1.1.1 are both correct.

Adım Adım Çözüm

1
Determine initial Router ID election upon starting OSPF process 1.
Loopback0 (10.1.1.1/32) is selected because it is the highest IP among active (up/up) loopback interfaces. Loopback1 is administratively down and ignored.
OSPF Router ID tie-breaker order is: 1) Manual router-id command, 2) Highest IP among active loopbacks, 3) Highest IP among active physical interfaces.
2
Analyze the impact of issuing 'router-id 1.1.1.1' on a running OSPF process.
The command is saved to running-config, but the active Router ID remains 10.1.1.1.
OSPF Router ID selection in Cisco IOS is non-preemptive. Changes do not take effect dynamically while the process is actively running.
3
Analyze the impact of bringing Loopback1 (10.2.2.1) to Up/Up state.
The active Router ID is unaffected.
Interface state changes after initialization do not preempt an established active OSPF Router ID.
4
Identify the required action to activate the new router-id command.
Executing 'clear ip ospf process' in EXEC mode resets the OSPF process and applies 1.1.1.1.
Clearing the OSPF process forces re-evaluation, allowing the manually configured router-id command (highest priority) to take effect.

Anahtar Kavram

OSPFv2 Router ID Selection Precedence and Non-Preemptive Behavior
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OSPFv2 Neighbor Adjacencies and Router ID

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