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Zorluk: OrtaOSPFv2 Neighbor Adjacencies and Router ID

An administrator inspects the OSPFv2 interface settings on router HQ-R1 and observes a Hello interval of 10 seconds and a Dead interval of 40 seconds on interface GigabitEthernet0/1 (10.0.12.1/24, Area 0). On the directly connected router BR-R1 interface GigabitEthernet0/1 (10.0.12.2/24), OSPFv2 is configured in Area 0 with a Hello interval of 15 seconds and a Dead interval of 60 seconds. What is the outcome of the OSPFv2 neighbor relationship between HQ-R1 and BR-R1?

  1. The routers fail to establish a neighbor relationship, and neither router accepts the other as a valid neighbor.Cevap
  2. B
    The routers progress to the EXSTART state but remain stuck because timer parameters cannot be negotiated.
  3. C
    The routers reach the 2-WAY state and elect a Designated Router, but cannot exchange Database Descriptor packets.
  4. D
    The routers successfully form a FULL adjacency, but routes learned with non-default timers receive an infinite metric.

Cevap

The routers fail to establish a neighbor relationship because OSPF Hello and Dead timer intervals must match on directly connected interfaces.
For two routers to form an OSPFv2 neighbor adjacency, several parameters in their Hello packets must match: Area ID, Subnet Mask, Hello Interval, Dead Interval, Stub Area Flag, and Authentication. Because HQ-R1 has a Hello/Dead timer configuration of 10s/40s while BR-R1 has 15s/60s, the Hello packets received by each router fail validation and are discarded, preventing any neighbor relationship from forming.

Adım Adım Çözüm

1
Analyze OSPF Hello packet parameter requirements for neighbor adjacency.
Identified that Hello interval, Dead interval, Area ID, Subnet Mask, and Authentication parameters must match in Hello packets.
OSPF routers drop incoming Hello packets if any mandatory Hello packet fields do not match the local configuration.
2
Compare the configured OSPF timer values between HQ-R1 and BR-R1.
HQ-R1 uses Hello/Dead of 10s/40s while BR-R1 uses Hello/Dead of 15s/60s.
The mismatched Hello (10s vs 15s) and Dead (40s vs 60s) intervals prevent packet validation.
3
Determine the resulting OSPF neighbor state.
No neighbor state is formed.
Because Hello packets are dropped upon receipt, neither router moves past the Down state for this peer.

Anahtar Kavram

OSPFv2 Mandatory Neighbor Adjacency Parameters
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Konular

OSPFv2 Neighbor Adjacencies and Router ID

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