Soru

Zorluk: OrtaOSPFv2 Network Types and DR/BDR Selection

Four OSPFv2 routers are connected to a shared multi-access Ethernet segment. Place the steps of the OSPF Designated Router (DR) election logic in the correct order of evaluation, from the initial eligibility filter to the final operational behavior.

  1. 1Exclude any interface configured with an OSPF priority of 0 from candidate eligibility.
  2. 2Select the router candidate with the highest OSPF interface priority value.
  3. 3Break priority ties by selecting the candidate router with the numerically highest OSPF Router ID.
  4. 4Enforce non-preemption by maintaining the active DR role even if a router with a higher priority boots later.

Cevap

The correct operational sequence is: Exclude routers with an OSPF priority of 0, select the candidate with the highest interface priority, break ties using the highest OSPF Router ID, and finally enforce non-preemption so an established DR remains active.
On multi-access broadcast networks, OSPF DR/BDR election begins by filtering out any router configured with priority 0. For remaining eligible routers, the router with the highest OSPF interface priority is preferred. If priorities are equal, the router with the highest Router ID breaks the tie. Once a DR is elected, the process is non-preemptive, meaning new routers joining the segment will not replace an active DR even if they have superior metrics.

Adım Adım Çözüm

1
Filter out non-candidate routers.
Routers with `ip ospf priority 0` are excluded from election participation.
Setting priority to 0 explicitly forces a router to remain a DROTHER.
2
Evaluate interface priority values.
The candidate with the highest interface priority (range 1-255) is designated as winner.
Interface priority is the primary metric in OSPF DR/BDR elections.
3
Evaluate Router IDs if priorities match.
The router with the highest Router ID is selected.
Router ID acts as the definitive tie-breaker when OSPF priorities are tied.
4
Apply non-preemptive election rules.
The elected DR retains its role until the process or link resets.
OSPF prevents network instability and adjacencies reset by disallowing preemption.

Anahtar Kavram

OSPFv2 DR/BDR Election Logic and Precedence Rules
Bu soruyu puanla