LSA types summary

Let me summarize the LSA types for you:

• Type 1 – Router LSA: The Router LSA is generated by each router for each area it is located. In the link-state ID you will find the originating router’s ID.
• Type 2 – Network LSA: Network LSAs are generated by the DR. The link-state ID will be the router ID of the DR.
• Type 3 – Summary LSA: The summary LSA is created by the ABR and flooded into other areas.
• Type 4 – Summary ASBR LSA: Other routers need to know where to find the ASBR. This is why the ABR will generate a summary ASBR LSA which will include the router ID of the ASBR in the link-state ID field.
• Type 5 – External LSA: also known as autonomous system external LSA: The external LSAs are generated by the ASBR.
• Type 6 – Multicast LSA: Not supported and not used.
• Type 7 – External LSA: also known as not-so-stubby-area (NSSA) LSA: As you can see area 1 is a NSSA (not-so-stubby-area) which doesn’t allow external LSAs (type 5). To overcome this issue we are generating type 7 LSAs instead.

OSPF LSA

LSA in OSPF

The link-state advertisement (LSA) is a basic communication means of the OSPF routingprotocol for the Internet Protocol (IP). It communicates the router's local routingtopology to all other local routers in the same OSPF area.

RE: OSPF LSA Types

• 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 6: Multicast OSPF LSA.
• LSA Type 7: Not-so-stubby area LSA.
• LSA Type 8: External attribute LSA for BGP.

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