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.