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Zorluk: ZorOSPFv2 Network Types and DR/BDR Selection

An engineer inspects the operational status of an active OSPFv2 broadcast network using the following Cisco IOS CLI output from router HQ-R1:

text
HQ-R1# show ip ospf interface GigabitEthernet0/0
GigabitEthernet0/0 is up, line protocol is up
Internet Address 10.10.10.1/24, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type BROADCAST, Cost: 1
Transmit Delay is 1 sec, State DR, Priority 1
Designated Router (ID) 1.1.1.1, Interface address 10.10.10.1
Backup Designated router (ID) 2.2.2.2, Interface address 10.10.2.2
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:03
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 2.2.2.2 (Backup Designated Router)

A third router, HQ-R3 (Router ID 3.3.3.3), is subsequently connected to the same Ethernet switch segment with its OSPF interface priority configured as 255. If all existing routers remain powered on with active OSPF processes, which statement correctly describes the OSPF role assignment for HQ-R3 once neighbor adjacencies settle?

  1. HQ-R3 operates as a DROTHER because active DR and BDR roles in OSPFv2 are non-preemptive.Cevap
  2. B
    HQ-R3 immediately preempts HQ-R1 as the Designated Router because its priority of 255 exceeds HQ-R1's priority of 1.
  3. C
    HQ-R3 replaces HQ-R2 as the Backup Designated Router while HQ-R1 remains the Designated Router.
  4. D
    HQ-R3 is automatically reassigned an interface priority of 0 by IOS to prevent preemption, preventing it from forming adjacencies.

Cevap

HQ-R3 becomes a DROTHER because OSPFv2 DR and BDR elections are non-preemptive once operational roles are established on a multiaccess network segment.
In OSPFv2 broadcast multiaccess networks, DR and BDR elections are non-preemptive. Once a DR and BDR are elected and active, adding a new router with a higher interface priority (such as 255) will not trigger a role change. The new router assumes the DROTHER role until the DR or BDR router fails, disconnects, or has its OSPF process reset.

Adım Adım Çözüm

1
Analyze the existing OSPFv2 segment state from the CLI output.
HQ-R1 (1.1.1.1) is actively serving as the Designated Router (DR) and HQ-R2 (2.2.2.2) is serving as the Backup Designated Router (BDR).
The election process has already taken place and active DR/BDR roles are currently filled.
2
Evaluate the impact of introducing HQ-R3 with interface priority 255 onto the broadcast network.
HQ-R3 establishes adjacency but does not trigger a re-election for DR or BDR.
OSPFv2 DR/BDR elections are strictly non-preemptive. A newly attached router will not displace an active DR or BDR regardless of priority or Router ID.
3
Determine the final OSPF state of HQ-R3.
HQ-R3 transitions to the DROTHER state on the multiaccess link.
Because both DR and BDR roles are already filled, HQ-R3 functions as a 2-WAY / FULL neighbor (DROTHER) with non-DR/BDR routers.

Anahtar Kavram

OSPFv2 Non-Preemptive DR/BDR Election Rule
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Konular

OSPFv2 Network Types and DR/BDR Selection

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