OSPF LSA
Link-State Advertisement — the building blocks OSPF routers exchange to describe the network's topology. Each router advertises its links and states as LSAs; together they build a shared map that each router runs Dijkstra on to find shortest paths.
Common types: Type 1 (Router LSA) — a router's own links within an area; Type 2 (Network LSA) — describes a multiaccess network, generated by the DR; Type 3 (Summary LSA) — routes between areas, generated by the ABR; Type 5 (External LSA) — routes redistributed into OSPF from other protocols, generated by the ASBR. LSAs are flooded within their area and age out (refreshed every 30 minutes). All routers in an area get the same set → an identical topology database → the same path calculation. Understanding the LSA types is the key to troubleshooting and designing OSPF. Related to OSPF area and route redistribution.