OSPF Neighbor / Adjacency

OSPF neighbors form adjacencies to exchange routing information (LSAs).

Updated: 2026-03-05

Definition

OSPF routers discover neighbors using Hello packets and form adjacencies when parameters match.

Once adjacent, they exchange LSAs to build a shared topology database.

Key points

Hello/dead timers must match
Network type and area must match
Authentication mismatch breaks adjacency

Common mistakes

Timer mismatch causing stuck neighbors.
Area mismatch or wrong network type configuration.

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