OSPF – LSA Types

 

  • LSA 1 (Router LSA)

Generated by all routers in an area to describe their directly attached links (Intra-area routes). These do not leave the area.

  • LSA 2 (Network LSA)

Generated by the DR of a broadcast or Nonbroadcast segment to describe the neighbors connected to the segment. These do not leave the area.

  • LSA 3 (Summary LSA)

Generated by the ABR to describe a route to neighbors outside the area. (Inter-area routes)

  • LSA 4 (Summary LSA)

Generated by the ABR to describe a route to an ASBR to neighbors outside the area.

  • LSA 5 (External LSA)

Generated by ASBR to describe routes redistributed into the area. These routes appear as E1 or E2 in the routing table. E2 (default) uses a static cost throughout the OSPF domain as it only takes the cost into account that is reported at redistribution. E1 uses a cumulative cost of the cost reported into the OSPF domain at redistribution plus the local cost to the ASBR.

  • LSA 6 (Multicast LSA)

Not supported on Cisco routers.

  • LSA 7 (NSSA External LSA)

Generated by an ASBR inside a NSSA to describe routes redistributed into the NSSA. LSA 7 is translated into LSA 5 as it leaves the NSSA. These routes appear as N1 or N2 in the ip routing table inside the NSSA. Much like LSA 5, N2 is a static cost while N1 is a cumulative cost that includes the cost upto the ASBR.

A good (and free) document for OSPF is the Cisco┬┤s OSPF Design Guide, which can be found at:

http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094e9e.shtml

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