How OSPF LSAs Decide Every Route

In OSPF, LSAs (Link State Advertisements) are the important building blocks of the routing database. They describe the network topology and are used to calculate the best path between the OSPF speaking routers.

OSPF defines 11 LSA types, and most enterprise deployments frequently encounter Types 1–7.

OSPF LSA/PacketRoute.com

1. 1. Router LSA
2. 2. Network LSA
3. 3. Summary LSA
4. 4. ASBR Summary LSA
5. 5. External LSA
6. 6. Multicast LSA
7. 7. NSSA External LSA
8. 8. External Attributes LSA
9. 9. Type-9, 10 and 11 Opaque LSA

LSA Route Mapping

Now that we’ve covered all LSA types, the next step is to understand how these LSAs translate into actual routes in the routing table — because that’s what ultimately impacts traffic flow.

Route TypeLSA TypeO (Intra-area)Type 1, 2O IA (Inter-area)Type 3, 4O E1/E2 (External)Type 5O N1/N2 (NSSA)Type 7

Understanding OSPF LSA types is essential for troubleshooting route propagation, multi-area behavior, and redistribution scenarios. By knowing which routers generate which LSAs — and where they are flooded — engineers can quickly identify routing anomalies and design scalable OSPF domains.