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Difficulty: MediumOSPFv2 Neighbor Adjacencies and Router ID

Two Cisco routers, R10 and R20, are connected over an Ethernet segment and configured for OSPFv2 routing. Which two configuration parameters must match identically on the interconnecting interfaces of both routers for an OSPFv2 neighbor adjacency to form successfully? (Select two.)

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

Answer

The OSPF Area ID and the Hello and Dead timer intervals must match identically on both connected interfaces.
To form an OSPFv2 neighbor adjacency, connected interfaces must reside in the same OSPF Area ID and have identical Hello and Dead timer settings. If either parameter differs, the routers fail to proceed past the INIT state.

Step-by-Step Solution

1
Analyze OSPFv2 Hello packet contents required for adjacency validation
Identified fields that must match in Hello packets: Area ID, Subnet Mask, Hello/Dead timers, Authentication, and Stub area flags.
OSPF routers exchange Hello packets to negotiate neighbor relationships and verify matching network parameters.
2
Evaluate the requirement for Area ID and Timers
Area ID and Hello/Dead timer values are required to match across adjacent interfaces.
A mismatch in Area ID or Hello/Dead timers causes routers to ignore Hello packets or drop neighbor relationships.
3
Evaluate Router ID and Process ID requirements
Router IDs must be unique across routers, and Process IDs are locally significant.
Process ID is only used locally by Cisco IOS to identify the OSPF process instance, while Router ID identifies the node uniquely within the OSPF autonomous system.

Key Concept

OSPFv2 Mandatory Neighbor Adjacency Parameters
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Topics

OSPFv2 Neighbor Adjacencies and Router ID

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