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Wednesday, October 27, 2010


Up to 11 LSA types are present but these are the 6 most common:

LSA Type 1 - Router (or Router Link state)

Each router create and flood LSA type 1 for himself. In these LSA's the router describe his directly connected interfaces,

the neighbor routers on each link, in each area. The LSA itself identified by a Link Stated ID (LSID) which is the Router ID (RID).

LSA Type 2 - Network (or Net Link state)

One per network, Advertised by the DR and represent his interfaces in this subnet.

LSA Type 3 - Summary (or Summary Net state)

Created by an ABR to represent LSA's type 1 and 2 when being advertised from one area into another. Define the links and the cost but no topology data.

Take note that ABR's never pass LSA type 1 and 2 from one area to another.

LSA Type 4 - ASBR Summary

Like type 3 LSA except it advertise a host route used to reach an ASBR

LSA Type 5 - AS External

Created by an ASBR for external routes injected into OSPF

LSA Type 7 - NSSA External

Created by an ASBR inside an NSSA area, instead of type 5 LSAs.


So in order to summarize this:

Type 1 and 2 are intra-area LSA's, type 3 is Inter-area and cross different areas, Type 4 pointing a route to an ASBR, type 5 describe external routes were type 7 do the same but in special area called NSSA.

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