OSPF LSA Types Explained
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This document discusses the different LSA (Link State Advertisement) types in OSPF (Open Shortest Path First) networking. It explains that LSA types 1 and 2 are intra-area and do not leave the area, while type 3 are inter-area and describe routes outside the area. LSA types 5 and 7 describe redistributed routes from other protocols into an OSPF area, with type 5 generated by ASBR (Autonomous System Boundary Router) and type 7 by ASBR within a NSSA (Not-So-Stubby Area).
OSPF LSA Types Explained
- 1. LSA Types Explained Complete Understanding of LSA Types Is The Cornerstone To Understanding OSPF Areas and OSPF Area Behaviors Complete Understanding of OSPF Area Behaviors Is The Cornerstone of Good OSPF Network Design and Traffic Flow
- 2. OSPF LSA Types Explained
- 3. LSA Type 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.
- 4. LSA Type 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.
- 5. LSA Type 3 (Summary LSA) Generated by the ABR to describe a route to neighbors outside the area. (Inter-area routes)
- 6. LSA Type 4 (Summary LSA) Generated by the ABR to describe a route to an ASBR to neighbors outside the area.
- 7. LSA Type 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.
- 8. LSA Type 6 (Multicast LSA) Not supported on Cisco routers
- 9. LSA Type 7 (NSSA 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 up to the ASBR.