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Difficulty: MediumOSPFv2 Neighbor Adjacencies and Router ID

Two Cisco routers are connected via a point-to-point Ethernet link and are configured to form an OSPFv2 neighbor relationship. Which two parameters transmitted within the OSPF Hello packet must match between both routers for an OSPFv2 neighbor adjacency to be successfully established? (Choose two.)

  1. Area IDAnswer
  2. Hello and Dead timer intervalsAnswer
  3. C
    OSPF Process ID
  4. D
    OSPF Router ID

Answer

The correct parameters that must match in the OSPF Hello packet are the Area ID and the Hello and Dead timer intervals.
To form an OSPFv2 neighbor relationship, neighboring routers must share identical parameters in their Hello packets. Specifically, the Area ID and the configured Hello and Dead timer intervals must match. If either setting differs, the routers will refuse to transition past the INIT neighbor state.

Step-by-Step Solution

1
Analyze OSPF Hello packet contents required for neighbor formation.
Identify parameters exchange requirements during the Init and 2-Way neighbor state transitions.
OSPF routers inspect Hello packets received on an interface to verify compatible parameters.
2
Evaluate required matching parameters versus local settings.
Confirm that Area ID, Subnet Mask (on multiaccess links), Hello/Dead timers, Authentication, and Stub flags must match.
If any mandatory parameter mismatches, the Hello packet is discarded or the neighbor remains in the INIT state.
3
Evaluate non-matching parameters.
Determine that Process ID is local only, and Router ID must be unique rather than identical.
Process ID identifies local IOS memory processes, while duplicate Router IDs cause database conflict.

Key Concept

OSPFv2 Neighbor Adjacency Requirements
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Topics

OSPFv2 Neighbor Adjacencies and Router ID

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