LSA (Link State Advertisement) Types Explanation

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3.  LSA TYPE 1: (Router link entry)
• Type 1 LSA is known as Router LSA. Each router creates this
LSA according to their link states which may be stub, transit or
point-to point. Type-1 LSA summarizes the active interfaces of
the router. And may be you can face "what is LSA ID of a
router" question too. The answer is easy : Router's "Router-ID"
is the LSA ID of the router too.
• Its Identify by the letter O in the routing table
• LSA type 1 is flooded within any area & its generated by all
routers

4.  LSA TYPE 2: ( Network link entry)
• Type 2 LSA is known as Network LSA which is generated by
Designated Router. Type 2 LSAs summarize routers on the
segment it is adjacent to. Type 2 LSAs don't pass over the
Area Border Routers , they just stay in the area that belong
• its generated by DR/BDR in multi access networks
• Describes the the set of routers attaché to that multi access
network
• Number type 2 LSA display in point to point network to like
LSA Type 1.

5.  LSA TYPE 3: (summery link Entry)
• Type 3 LSA is the Summary LSA which is created by Area
Border Routers (ABR ) and contains information about inter
area routes.
• Describes the networks in given area to the back bone area
and vice versa
• Flooded through out the back bone area or from back bone
area to other areas
• Identify by the letter IA in the routing table.

6.  LSA TYPE 4: (Summary Network Link Entry)
• Type 4 LSA is the Summary LSA which is created by Area
Border Routers (ABR) and transported to other areas to
create shortest path three of an Autonomous System
Boundary Router (ASBR)
• LSA type 4 is not seen in the routing table, LSA type 4 is only
seen in the Link State Database
• Generated by the ASBR.
• In a multi area it will be given to the ABR of the same area,
and the ABR will flood the LSAs to the other areas.
• When LSA type 4s are flooded, LSA type 5s are seen as well.

7.  LSA TYPE 5: (Autonomous System External Link Entry)
• Type 5 LSA is External LSA which is generated
by Autonomous System Boundary Router (ASBR). This LSA
contains external route information which is redistributed in
OSPF domain. Type 5 LSAs aren't allowed in stub areas.
• Identified but the letter E1 or E2 in the routing table.
• Generated by the ASBR
• Flooded throughout an OSPF autonomous system except
STUB, Totally STUB and NSSA areas.
• When LSA type 5s are flooded, LSA type 4s are seen as well.

8.  LSA TYPE 6: This is not support by Cisco
 LSA TYPE 7: (Not so Stubby Autonomous System
External Link Entry)
• Type 7 LSA is NSSA (Not So Stubby Area) External LSA
which is generated by Autonomous System Boundary Router
(ASBR) . Type 5 LSAs aren't allowed in stub areas but Type 7
LSAs are allowed that's why Type-7 is used for some
situations.
• Generated by the ASBR in a NSSA
• Identified by the letter N1 or N2 in the routing table of the
routers in that particular NSSA.
• These LSAs are then translated to LSA type 5 and flooded
into the Backbone area.