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Zorluk: KolayOSPFv2 Neighbor Adjacencies and Router ID

A network administrator is configuring OSPFv2 between two routers on a point-to-point link. After configuring the router interfaces, the administrator notices that the routers fail to establish an OSPF neighbor relationship. Troubleshooting reveals that the two connecting interfaces were assigned different OSPF Area IDs. What is the outcome of this configuration mismatch?

  1. The routers drop the incoming Hello packets and fail to form any neighbor relationship.Cevap
  2. B
    The routers progress to the 2-WAY state but cannot elect a Designated Router (DR).
  3. C
    The routers form a neighbor adjacency, but routes from the mismatched area are filtered out.
  4. D
    The routers become stuck in the EXSTART state during database exchange.

Cevap

The routers drop the incoming Hello packets and fail to form any neighbor relationship.
For two routers to establish an OSPFv2 neighbor adjacency, several parameters in their Hello packets must match exactly, including the Area ID, Hello/Dead timers, Subnet Mask (on broadcast networks), Authentication, and Stub area flag. If the Area ID does not match, the router discards the received Hello packet immediately, preventing any neighbor state transition.

Adım Adım Çözüm

1
Identify the mandatory parameters that must match in OSPFv2 Hello packets.
OSPF Hello packets contain field parameters including Area ID, Hello and Dead intervals, Subnet Mask, Authentication key, and Stub area flag.
OSPFv2 strictly validates these fields upon receipt of a Hello packet from a potential neighbor.
2
Evaluate the effect of an Area ID mismatch.
When a router receives a Hello packet containing an Area ID that does not match the receiving interface's configured Area ID, the router discards the packet.
Receiving interfaces must belong to the exact same logical area to exchange topology information.
3
Determine the resulting neighbor state.
Because Hello packets are dropped, neither router sees itself listed in the neighbor's Hello packet, preventing any neighbor state progression.
Without valid Hello processing, the neighbor relationship remains down.

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OSPFv2 Neighbor Adjacency Mandatory Matching Parameters
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OSPFv2 Neighbor Adjacencies and Router ID

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