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Zorluk: OrtaOSPFv2 Neighbor Adjacencies and Router ID

Router R1 and Router R2 are directly connected via their GigabitEthernet0/0 interfaces. An administrator configures OSPFv2 on both interfaces in Area 0. On R1, GigabitEthernet0/0 uses default OSPF timers (Hello 10 seconds, Dead 40 seconds). On R2, the Hello timer is manually set to 15 seconds and the Dead timer to 60 seconds. What will be the outcome of this OSPFv2 configuration between R1 and R2?

  1. The routers will fail to establish an OSPF neighbor relationship because Hello and Dead timers must match exactly.Cevap
  2. B
    The routers will form an adjacency and reach the FULL state, but routing updates will fail to synchronize.
  3. C
    The routers will dynamically negotiate timers during the EXSTART state and become stuck in EXSTART.
  4. D
    The routers will achieve a 2-WAY neighbor state but will fail to elect a Designated Router (DR).

Cevap

The routers will fail to establish an OSPF neighbor relationship because Hello and Dead timers must match exactly.
For two OSPFv2 routers to form a neighbor relationship, key parameters in their Hello packets must match exactly. These include Area ID, Subnet Mask, Hello Interval, Dead Interval, Authentication settings, and Option flags. Because R1 has timers set to 10s/40s and R2 has timers set to 15s/60s, neither router will process the other's Hello packets as valid, preventing any neighbor relationship from forming.

Adım Adım Çözüm

1
Identify the OSPF Hello packet parameters required for neighbor discovery.
Mandatory matching fields include Area ID, Subnet Mask, Hello/Dead intervals, Authentication, and Stub flag.
When a router receives an OSPF Hello packet, it compares these fields against its local interface parameters.
2
Compare the configured timer values on R1 and R2.
R1 uses Hello 10s / Dead 40s, while R2 uses Hello 15s / Dead 60s.
Because the values do not match, both routers silently drop the incoming Hello packets from each other.
3
Determine the final neighbor state.
No neighbor relationship is established.
Without matching parameters in Hello packets, routers cannot progress to the INIT or 2-WAY neighbor state.

Anahtar Kavram

OSPFv2 Mandatory Hello Packet Matching Parameters
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Konular

OSPFv2 Neighbor Adjacencies and Router ID

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