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OSPF Areas & LSA Types: Scaling Link-State Routing

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OSPF areas: why a flat network doesn't scale

In a single-area OSPF domain, every router floods its Link State Advertisements (LSAs) to every other router. Each router runs Dijkstra's SPF algorithm over the full topology. With 500 routers, every topology change re-triggers SPF on all 500 — O(n²) flooding and O(n log n) SPF for each.

Areas solve this: subdivide the network into smaller zones. LSA flooding is contained within each area. SPF runs per-area, not domain-wide. Area 0 (the backbone) provides the transit path between areas.

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