OSPF LSA Types

 1 - Router LSA

 2 - Network LSA

 3 - Network summary LSA

 4 - ASBR Summary LSA

 5 - AS External LSA

 6 - Group Membership LSA

 7 - NSSA External LSA


1 - Router LSA

                Router link advertisements are passed within an area by all OSPF routers and describe the router links to the network. These are only flooded within a particular area.

2 - Network LSA
                Network links advertisements are flooded within an area by the DR and describes a multi-access network i.e. the routers attached to particular networks.

3 - Network summary LSA
                Network Summary link advertisements are passed between areas by ABRs and describes networks within and area.

4 - ASBR Summary LSA
                ASBR summary link advertisements are passed between areas and describe the path to the AS BOUNDARY router(ASBR). These do not get flooded into totally stubby areas.

5 - AS External LSA
                AS externel link advertisements are passed between and flooded into areas by ASBRs and describe extenal destinations outside the autonomous system. the areas that do not receive these are stub, Tottally stubby and Not so stubby areas. There are two types of external link advertisements, Type 1 and Type 2. Type 1 packets add the external cost to the internal cost of each link passed. This is useful when there are multiple ASBRs advertising the same route into an area as you can decide a preferred route. Type 2 packets only have and external cost assigned so is fine for a single ASBR advertising and external route.

6 - Group Membership LSA
               Multicast OSPF routers flood this Group Membership link entry.

7 - NSSA External LSA

               NSSA AS external routes flooded by the ASBR. The ABR converts these into Type 5 LSAs before flooding them into a backbone. The diffence between Type 7 and Type 5 LSAs is that Type %s are flooded into multiple areas whereas Type 7s are only flooded into NSSAs.