OSPF Router and LSA Types

This will be another bullet point style post, as I have not fully delved into these LSA types with labs yet. One thing I have noticed, “show ip ospf database” will not give you the LSA type or number just in one of the columns of the output, they will need to be known by the headers in the column (I believe, need to verify). I will need to update this once my understanding of the LSA types develops, but I’ll put some initial information on both OSPF router acronyms and LSA information as I have it (some CCNA refresher material):

  • Area 0 is the Backbone area, any OSPF router with an interface in Area 0 is a Backbone router (Including ABR’s and Internal routers)
  • ABR = Area Boarder Router, has at least one interface in Area 0, and another interface in a non-Backbone area
  • Internal Router = All interfaces in a single Area
  • ASBR = Autonomous System (Boundary / Boarder) Router, an OSPF router that is injecting routes into OSPF via Route Redistribution
  • LSA Type 1 = Generated by every OSPF router for every Area that router has an OSPF link in, literally floods the link state of all its links to one Area (Area 0?)
  • LSA Type 2 = Only sent by DR’s, will show in the ospf database as the DR’s RID as the Advertising Rtr
  • LSA’s 1 and 2 are confined to a single Area (another plus for multi-area OSPF)
  • LSA Type 3 = Summary Network Link States, summarize inter-Area routes from one Area to another, generated by ABRs, not flooded into Total Stub Areas
  • LSA Type 4 = Describes path to ASBR, generated by ABRs, not flooded into Total Stub Areas
  • LSA Type 5 = Describes links external to the OSPF domain, this link describes networks injected via Route Redistribution, generated only by ASBRs, not flooded into Stub and Total Stub Areas
  • LSA Type 6 = Specialty LSA only generated by routers using Multicast extensions to OSPF (MOSPF)
  • LSA Type 7 = Only generated by ASBRs and sent into NSSAs (Not So Stubby Area), once the are sent in they do not come back out, unless the router in the NSSA convert them into Type 5 LSA’s and send them back out of their NSSA

Summary of what LSAs OSPF Router types send:

  • LSA Type 1 = Sent by all router
  • LSA Type 2 = Sent by DRs only
  • LSA Type 3, 4 = Sent by ABRs only
  • LSA Type 5, 7 = Sent by ASBRs only
  • LSA Type 6 = Reserved for MOSPF


Will try to clean this up as I move on with my studies, but will definitely be moving forward into OSPF Stub areas and hope these LSA types are expanded upon there.

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