OSPF LSA Types ( Link State Advertisement ) Explained

ospf lsa types

In this article we will examine OSPF LSA types and i think it will help for the people who prepare for CCNP routing exam. Because in the CCNP routing exam you may often face the questions about this topic.OSPF LSAs ( Link State Advertisement ) create the Link State Database of the router and they are exchanged between routers running OSPF.

ospf lsa types

LSA TYPE 1: Type 1 LSA is known as Router LSA. Each router creates this LSA according to their link states which may be stub, transit or point-to point. Type-1 LSA summarizes the active interfaces of the router. And may be you can face “what is LSA ID of a router” question too. The answer is easy : Router’s “Router-ID” is the LSA ID of the router too.

LSA TYPE 2: Type 2 LSA is known as Network LSA which is generated by Designated Router. Type 2 LSAs summarize routers on the segment it is adjacent to. Type 2 LSAs don’t pass over the Area Border Routers , they just stay in the area that belong to like LSA Type 1.

LSA TYPE 3: Type 3 LSA is the Summary LSA which is created by Area Border Routers (ABR ) and contains information about inter area routes.

LSA TYPE 4: Type 4 LSA is the Summary LSA which is created by Area Border Routers (ABR ) and transported to other areas to create shortest path three of an Autonomous System Boundary Router ( ASBR )

LSA TYPE 5:  Type 5 LSA is External LSA which is generated by Autonomous System Boundary Router ( ASBR ).  This LSA contains external route information which is redistributed in OSPF domain. Type 5 LSAs aren’t allowed in stub areas.

LSA TYPE 7: Type 7 LSA is NSSA ( Not So Stubby Area ) External LSA which is generated by Autonomous System Boundary Router ( ASBR ) . Type 5 LSAs aren’t allowed in stub areas but Type 7 LSAs are allowed that’s why Type-7 is used for some situations.
OSPF LSA types are examined in this article. We are going to look how we configure these LSA types with an example on another lesson.

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