OSPF LSA types - explanation and differences

Latest reply: Sep 5, 2018 13:53:23 1122 1 2 1

This post highlights the OSPF LSA types - explanation and differences. Please have a look below for details.

LSA Types explanation


Each router in an AS generates one or more types of LSAs, depending on the router's type. Multiple LSAs form an LSDB. OSPF encapsulates routing information into LSAs for transmission. Commonly used LSAs include:

  • LSA Type 1: Router LSA;

  • LSA Type 2: Network LSA;

  • LSA Type 3: Summary LSA;

  • LSA Type 4: Summary ASBR LSA;

  • LSA Type 5: Autonomous system external LSA;

  • LSA Type 7: Not-so-stubby area LSA.

Router-LSA (Type 1)

A router-LSA describes the link status and cost of a router. Router-LSAs are generated by a router and advertised within the area to which the router belongs.



Network-LSA (Type 2)

A network-LSA describes the link status of all routers on the local network segment. Network-LSAs are generated by a DR on a broadcast or non-broadcast multiple access (NBMA) network and advertised within the area to which the DR belongs.


Network-Summary-LSA (Type 3)

A network-summary-LSA is advertised by an ABR and it describes routes on a network segment in an area. The routes are advertised to other areas.



ASBR-Summary-LSA (Type 4)

An ASBR-summary-LSA describes routes to the ASBR in an area. The routes are advertised to all areas except the area to which the ASBR belongs. It is also generated by an ABR.



AS-External-LSA (Type 5)

An AS-external-LSA describes AS external routes. AS-external-LSAs are generated by an ASBR. Among the five types of LSAs, only AS-external-LSAs can be advertised to all areas except stub areas and not-so-stubby areas (NSSAs).



NSSA-LSA (Type 7)

An NSSA-LSA describes AS external routes. It is originated by an ASBR and only flooded in NSSAs (Not So Stubby Areas).






If you are going to present your HCNP  certification, you might want to study and dominate this. The LSA types is one the most recurrent subject in the HCNP test.  

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Created Sep 5, 2018 13:53:23 Helpful(0) Helpful(0)

Thanks for the clarify these points and the advice to keep improving on our knowledge for HCNP Test.
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