OSPF LSA Types

Type 4

-A type 4 summary LSA is generated by an ABR only when an ASBR exists within an area. A type 4 LSA identifies the ASBR and provides a route to it.

Type 1

-AKA router link entries. -All routers advertise their directly connected OSPF-enabled links in a type 1 LSA and forward their network information to OSPF neighbors. The LSA contains a list of the directly connected interfaces, link types, and link states. -Type 1 LSAs are flooded only within the area in which they originated. -The type 1 LSA link ID is identified by the router ID of the originating router.

Type 2

-Only exists for multiaccess and non-broadcast multiaccess (NBMA) networks where there is a DR elected and at least two routers on the multiaccess segment. -The purpose of a type 2 LSA is to give other routers information about multiaccess networks within the same area. -Are also referred to as network link entries.

Type 5

-Type 5 external LSAs describe routes to networks outside the OSPF autonomous system. Type 5 LSAs are originated by the ASBR and are flooded to the entire autonomous system.

Type 3

-Used by ABRs to advertise networks from other areas. -ABRs collect type 1 LSAs in the LSDB. After an OSPF area has converged, the ABR creates a type 3 LSA for each of its learned OSPF networks. Therefore, an ABR with many OSPF routes must create type 3 LSAs for each network.