LSDB (Link State Database)

What is LSDB?

LSDB is the database used in the OSPF (Open Shortest Path First) consist of the structure of the area. It is built with the information of LSA (Link State Advertisements). Each OSPF area has a specific LSDB (Link State Database). In other words, OSPF routers has a different LSDB for each area. And all the routers in the same area have identical LSDBs.

LSDB (Link State Database) is built with LSAs. In other words, Link State Advertisement is the collection of LSAs in an OSPF network. These LSAs includes the relationship of the OSPF nodes and according to this information Link State Database is built.

OSPF uses Dijkstra SFP (Shortest Path First) algorithm. Routers performs separate SFP (Shortest Path First) Algorithm for each area and LSDB (Link State Database).  With these calculations, the best path towards any destination is determined.

There are different router roles in OSPF network. One of them is OSPF Area Border Router (ABR). ABRs has different interfaces in different OSPF areas. So, in an ABR, there are one more LSDBs. In other words, for each area, one LSDB is created in the ABR. The other OSPF routers which belong to only one area, has only one Link State Database.

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What is LSA?

We have answered what is LSDB question. Now, it is time to explain what is LSA? LSA is the abbreviation of Link State Advertisement. They are the small amounts information about OSPF network. They include relationship of the OSPF neighbors and according to these information, LSDB (Link State Database) is built.

There are different OSPF LSA Types used in OSPF network. Five of them are common OSPF LSA types. Beside these common LSA types, there are also different LSA types used in OSPF network. We have discussed these different LSA types with the other details of Link State Advertisement in another lesson.

Below, you can find the five common LSA types and the other ones:

• Type 1 (Router LSA)
• Type 2 (Network LSA)
• Type 3 (ABR Summary LSA)
• Type 4 (ASBR Summary LSA)
• Type 5 (ASBR Externel LSA)
• Type 6 (Group Summary)
• Type 7 (NSSA External LSA)
• Type 8 (External Attributes LSA)
• Type 9, 10, 11 (Opaque LSAs)

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Summary

We have learned basically what is LSDB and what is LSA. LSAs are the information message about the network. LSDB (Link State Database) is the database build with LSAs for each area.

There are different routers in an OSPF network. One of them is Area Border Router (ABR). And ABRs has one LSDB for each area. And other routers which are in only one area, has one LSDB.

Lastly, there are various LSA types and we use them to build Link State Databases in OSPF network. Five of these LSA types are common and the other ones are also used for various pusposes in the OSPF network.

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