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Difficulty: EasyOSPFv2 Neighbor Adjacencies and Router ID

When establishing an OSPFv2 neighbor relationship between two Cisco routers on a broadcast multiaccess network, which parameter in the Hello packet must match on both routers?

  1. OSPF Area IDAnswer
  2. B
    OSPF Process ID
  3. C
    OSPF Router ID
  4. D
    OSPF Interface Priority

Answer

OSPF Area ID
For two routers to form an OSPFv2 neighbor adjacency, several parameters in the Hello packet must match exactly, including the OSPF Area ID, Hello/Dead timers, IP subnet mask, authentication details, and stub area flag. If the Area ID differs, the routers discard the Hello packets and fail to form an adjacency.

Step-by-Step Solution

1
Identify mandatory parameters exchanged in OSPF Hello packets that must match for neighbor formation.
Hello packet fields that must match include Area ID, Subnet Mask, Hello and Dead intervals, Authentication parameters, and Stub area flag.
OSPF requires routers to reside in the same area to exchange Link State Advertisements (LSAs) for that area.
2
Evaluate non-matching or locally significant parameters.
Process ID is locally significant, Router IDs must be unique, and Router Priority determines DR/BDR election roles.
These parameters do not need to match across neighbors for the adjacency to form.

Key Concept

OSPFv2 Hello Packet Parameter Requirements for Adjacency
Estimated Time:45s
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Topics

OSPFv2 Neighbor Adjacencies and Router ID

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