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Types of link-state advertisements (LSAs) used in Open Shortest Path First (OSPF)

Routing and switching expert Sudhanshu Gupta explains the different types of link-state advertisements (LSAs) that would be used for Open Shortest Path First (OSPF), in this expert answer.

What are the different types of link-state advertisements (LSAs) that will be used in Open Shortest Path First (OSPF)?

The following are the types of LSAs you would usually find in an OSPF network:

LSA types found in OSPF networks

Type # Name Description
Type 1 router LSA A router sends this to describe neighbors and its own interfaces.
Type 2 network LSA For broadcast networks only; this LSA is flooded by the DR and lists OSPF-speaking routers on the network.
Type 3 network summary LSA Sent by an ASBR to advertise networks reachable through it. A stub area router will also use this for the default route.
Type 4 ASBR-summary LSA Sent by ASBR, but only internally. This describes to the others how to get to the ASBR itself, and uses only internal metrics.
Type 5 AS-external LSA Used to describe external routes to internal areas. Can be used to advertise "this is the way to the Internet" (or some subset of).
Type 6 Group summary Used in multicast (MOSPF). Ignore this.
Type 7 NSSA area import.  
Type 8 External Attributes LSA This is very rarely deployed and is used when BGP information is carried across OSPF AS.
Type 9, 10, 11 All are Opaque LSAs. They are designated for future specifically for application specific purposes.
This was first published in May 2008

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