OSPF LSA Types
LSAs are building block of OSPF, OSPF use the LSA (link state advertisement) for building the topology table and database. There are total 11 types of LSA but famous types are as follow.
1. LSA Type-1| Router LSA from one network
2. LSA Type-2| Network LSA from more network (DR Generated)
3. LSA Type-3| Summary LSA (ABR summary Route)
4. LSA Type-4| Summary LSA (just IP address of ASBR)
5. LSA Type-5| External LSA (ASBR summary Route)
6. LSA type-6 (not supported by Cisco)
7. LSA type-7
LSA Type-1| Router LSA
LSA type 1 defining router properties like RID and all interface IP addresses on that router that are in same area. Each router creates its own Type 1 LSA to represent itself for each area to which it connects.
LSA Type-2| Network LSA
LSA type 2 are also known as network LSA and it is advertises for all the router connect in same Ethernet segment or switch. Type 2 LSA is created by the DR on the network, and represents the subnet and the router interfaces connected to that network.
LSA Type-3| Summary LSA
LSA type-3 is summary LSA and contains all the summary routes for an area. It is created by ABRs to represent subnets listed in one area’s type 1 and 2 LSAs when being advertised into another area. Type-3 LSAs are always created whether you are summarizing or not.
LSA Type-4| Summary LSA
LSA type-4 is also summary LSA and it is location of ASBR or you can say IP address of ASBR. The reason of creating type-4 LSA is that in OSPF process whenever some internal ASB want to advertise routes to ASBR, use the LSA-4 or IP address of ASBR.
LSA Type-5| External LSA
LSA type-5 is generated by ASBR for injecting the external routes to backbone area. ASBR send the LSA type-5 to backbone router which contain the external routes updates e.g. RIP, EIGRP updates.
Type-6 LSAs are not supported by Cisco IOS.
A not-so-stubby area (NSSA) is a type of stub area that can import autonomous system external routes and send them to other areas. Since Type 5 LSAs are not allowed in NSSA areas, so the ASBR in NSSA generates a type 7 LSA instead, this type-7 LSA passes to backbone area and then converted back to types-5 LSA.
Not supported by Cisco routers.
LSA Type-9 | LSA Type-10 | LSA Type-11
These LSA are for future use, recently type-10 LSA is using in MPLS.