There are eleven types of OSPF LSAs:
Type 1 = Router LSA: This is generated by every OSPF-enabled router on every interface that participates in OSPF. Advertises all routers in the area.
- show ip ospf database = “Router Link States”
- Link-state ID = RID of the originating router
Type 2 = Network LSA: This is flooded by the DR in multi-access networks to notify routers of who the responsible designated router is for that segment.
- show ip ospf database = “Net Link States”
- Appears as “O” in the routing table
- Link-state ID = IP Address of the DR interface for that multi-access segment
Type 3 = Summary LSA: This is generated by an ABR to advertise routes from one area to another (eg., LSA to Area 0 signifying Area 1 routes and vice versa). Summarization is not on by default.
- show ip ospf database = “Summary Net Link States”
- Appears as “O IA” in the routing table
- Link-state ID = Destination network ID
Type 4 = ASBR Summary LSA: This is generated by an ABR to notify routers of the presence of an ASBR in a particular area (eg., if there is an ASBR attached to Area 1, the ABR between Area 1 and Area 0 would forward a Type 4 LSA to Area 0 announcing the presence of an ASBR in Area 1 etc.)
- show ip ospf database = “Summary ASB Link States”
- Does not appear in the routing table
- Link-state ID = RID of the ASBR in another area
Type 5 = Autonomous System LSA: This is generated by an ASBR, one for each route that is redistributed into OSPF. Flooded everywhere, except for special areas.
- show ip ospf database = “Type-5 AS External Link States”
- Appears as “O E2” in the routing table
- Link-state ID = External network ID that has been redistributed
(Types 6 – 11 = Other types, depending on the network environment)
- Type 6 = For multicast OSPF applications
- Type 7 = Used in NSSA for external routes
- Type 8/9 = Used in OSPFv3 for link-local and intra-area prefixes
- Type 10/11 = Opaque (generic) LSAs for future extension
Stuck-in-Active: Journal of an IT-Network Administrator 