Open Shortest Path First (OSPF) Type 4 link-state advertisements (LSAs) are also called autonomous system boundary router (ASBR) summary LSAs. ASBR summary LSAs are used to advertise the location of an ASBR so that routers can determine the best next-hop path. Type 4 LSAs are generated by area border routers (ABRs) and are flooded throughout an area except into stub areas.

Type 1 LSAs, which are also called router LSAs, contain router ID and interface IP address information for a single router. Router LSAs, which are generated by all OSPF routers, are not propagated outside the area? they are flooded only within the local area.

Type 2 LSAs, which are also called network LSAs, contain subnet and neighbor router information. Network LSAs, which are generated by designated routers (DRs), are not propagated outside the area in which they originate? they are flooded only within the local area.

Type 3 LSAs, which are also called network summary LSAs, contain subnet information for an entire area. Network summary LSAs, which are generated by ABRs, are advertised between areas throughout an autonomous system (AS) except into totally stubby areas.

Type 5 LSAs, which are also called AS-external LSAs, contain subnet information for an external AS. AS-external LSAs, which are generated by ASBRs, are advertised throughout an AS except into stub areas, totally stubby areas, and not-so-stubby areas (NSSAs).