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Difficulty: MediumOSPFv2 Neighbor Adjacencies and Router ID

A network engineer is configuring OSPFv2 between two Cisco routers connected over an Ethernet link. Which TWO parameters must match between the routers for an OSPFv2 neighbor adjacency to form successfully? (Select TWO.)

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

Answer

The OSPF Area ID and the Hello and Dead timer intervals must match between the connecting router interfaces.
For two OSPFv2 routers to establish an adjacency, several key Hello packet parameters must match identically: the Area ID, Hello and Dead timers, IP subnet mask, and authentication credentials. If the Area ID or timer values differ, the routers will remain unable to form a neighbor relationship.

Step-by-Step Solution

1
Analyze OSPF Hello packet requirements for neighbor discovery
Identify parameters that are checked in received Hello packets before forming an adjacency.
OSPF routers inspect specific fields in incoming Hello packets to ensure network compatibility.
2
Evaluate mandatory matching parameters
Area ID, Hello/Dead timers, Subnet Mask, and Authentication parameters must match across the link.
Mismatches in Area ID or timers cause the routers to ignore or drop Hello packets from each other.
3
Evaluate non-matching or unique parameters
OSPF Process ID is local to the device and does not need to match. OSPF Router ID must be unique across routers.
Process ID is only used internally by IOS to distinguish OSPF instances, and duplicate Router IDs cause routing instability.

Key Concept

OSPFv2 Neighbor Adjacency Requirements
Estimated Time:1m 0s
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Topics

OSPFv2 Neighbor Adjacencies and Router ID

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