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Friday, July 15, 2016

OSPF LSA Types

OSPF uses a LSDB (link state database) and fills this with LSAs (link state advertisement).


Here Some details about all SLA types:-


  • LSA Type 1 (Router LSA)

Router Link State Advertisements Type 1 are generated by every router for each link that belongs to an area. They are flooded only inside of area to which they belong. Link ID of this LSA is the Router ID of the router that generated it.


  • LSA Type 2 (Network LSA)

Generated by Designated Router (DR) for multiaccess networks and describe the routers that are connected to that segment. They are sent inside the area to which the network segment belong.


  • LSA Type 3 (Summary LSA)

Type 3 LSAs are generated by Area Border Routers (ABRs). In type 3 LSAs are advertised networks from an area to the rest of the areas in AS. Advertised networks in Type 4 LSA can be summarized or not. The link-state id used by this LSA is the network number advertised.


  • LSA Type 4 (ASBR Summary LSA)

Generated by ABRs, this type of LSA contain routes to ASBRs. Link id used is router ID of the ASBR described. Are not flooded in stub areas.

  • LSA Type 5 (External LSA)

Autonomous system external LSAs are generated by ASBRs and contain routes to networks that are external to current AS. Link-state ID is network number advertised in LSA. Type 5 LSAs are not flooded inside any stub areas.


  • LSA Type 6 (Multicast LSA)

This type of LSA is used for multicast applications. Not supported on Cisco.


  • LSA Type 7 (NSSA External LSA)

Type 7 LSA allow injection of external routes through Not-so-Stubby-Areas (NSSA). Generally external routes are advertised by type 5 LSA but they are not allowed inside any stub area.
 Type 7 LSA is generated by NSSA ASBR and is translated into type 5 LSA as it leaves the area by NSSA ABR, which is then propagated throughout the network as type 5 LSA.

  • LSA Type 8 (External LSA for BGP)

Used to work with BGP.


  • LSA Type 9,10,11 (Opaque LSAs)