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Getting started with OSPF: LSA types

Hey all, I am back. Now that we know so much about OSPF areas and specific area routers, let us find out the types of LSA packets originated by these routers.

Here the types of LSA flowing within OSPF network.

  1. Router LSA: These are the Type 1 LSAs. Each router in an area originates a router-LSA. These are flooded in a single area only, as shown below.


Router-LSA (Type 1)

2. Network LSA: These are originated by the network’s Designated Router(DR). These describe all routers attached to the network, including the DR itself. These are flooded within the area only. You can see that in the following image.


Network LSA (Type 2)

3. Summary LSAs (Area Summary): Summary-LSAs are the Type 3 and 4 LSAs. These LSAs are originated by area border routers(ABRs). These describe inter-area networks. Type 3 LSA, describe the areas directly connected to the ABR, as shown below.


Summary LSA (Type 3)

4. Summary LSA (ASBR summary): Type-4 LSAs describe information about ASBR. All the ABRs carry forward this information as type 4 LSAs within areas.


Summary LSA (Type 4)

5. External LSA: These are the Type 5 LSAs. These LSAs are originated by  AS boundary routers(ASBRs) and describe networks external to the AS. As you can see in the following network image, external network information is forwarded by ASBR into AS. ABRs just forward these LSAs as type 5 into areas.


External LSA (Type 5)

So, different types of areas, routers and now LSAs. Well that is why, it is the most popular routing protocol. I hope that now you have a clear view about OSPF.

Happy networking with OSPF..!!! 🙂

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