Link State Database

Upon initialization, each router transmits a link state advertisement (LSA) on each of its interfaces. LSAs are collected by each router and entered into the LSDB of each router. After all LSAs are received, the router uses the link state database (LSDB) to calculate the best routes for use in the IP routing table. OSPF uses flooding to distribute LSAs between routers. Any change in routing information is sent to all of the routers in the network. All routers within an area have the exact same LSDB.

The following table describes LSA type numbers.

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LSA Type Numbers

Type Number Description
1 Router LSA
2 Network LSA
3 Summary LSA
4 AS summary LSA
5 AS external LSA
7 NSSA external LSA
9 Link local—Opaque
10 Area scoping—Opaque
11 AS scoping—Opaque