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Zorluk: OrtaOSPFv2 Network Types and DR/BDR Selection

A network administrator configures four routers (R1, R2, R3, and R4) on a single multiaccess Ethernet segment running OSPFv2. The OSPF interface parameters are configured as follows:

- R1: OSPF Priority = 100, Router ID = 1.1.1.1
- R2: OSPF Priority = 0, Router ID = 4.4.4.4
- R3: OSPF Priority = 100, Router ID = 3.3.3.3
- R4: OSPF Priority = 50, Router ID = 2.2.2.2

All four routers boot simultaneously and form neighbor relationships. Which role will router R2 assume on this network segment?

  1. DROTHER, because an interface priority of 0 explicitly excludes the router from becoming a DR or BDR.Cevap
  2. B
    DR (Designated Router), because its Router ID of 4.4.4.4 is the highest among all connected routers.
  3. C
    BDR (Backup Designated Router), because its high Router ID places it second after priority evaluation.
  4. D
    DR (Designated Router), because priority 0 causes immediate preemption of the existing DR.

Cevap

Router R2 will assume the role of DROTHER because an interface priority of 0 prevents it from participating in the DR/BDR election.
On an OSPF broadcast network, routers elect a DR and BDR based on the highest interface priority. If there is a tie in priority, the highest Router ID breaks the tie. However, any interface configured with an OSPF priority of 0 is strictly excluded from participating in the election and will immediately assume the role of DROTHER, regardless of how high its Router ID is.

Adım Adım Çözüm

1
Evaluate the OSPF interface priority settings for all routers on the broadcast network segment.
R1 has priority 100, R3 has priority 100, R4 has priority 50, and R2 has priority 0.
OSPF DR/BDR elections first compare interface priority values (range 0 to 255, default 1).
2
Identify the impact of an interface priority setting of 0.
Router R2 with priority 0 is disqualified from DR and BDR election.
An OSPF interface priority of 0 explicitly instructs the OSPF process that the router must never become a DR or BDR.
3
Determine the elected roles for all participating routers.
R3 becomes DR (priority 100, highest Router ID 3.3.3.3 among eligible routers), R1 becomes BDR (priority 100, Router ID 1.1.1.1), and R2 becomes DROTHER.
Only routers with a priority greater than 0 participate in DR/BDR selection.

Anahtar Kavram

OSPFv2 DR/BDR Election Exclusion via Priority 0
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Konular

OSPFv2 Network Types and DR/BDR Selection

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