OSPF LSA Types for ASBR in Connected Area

C

In Open Shortest Path First (OSPF) routing protocol, the Autonomous System Boundary Router (ASBR) is a router that connects one OSPF area to another and redistributes routes between them. OSPF uses different Link State Advertisement (LSA) types to share information about network topology among routers.

When an ASBR is connected to an area that is different from the area where the ABR resides, OSPF sends an LSA to describe the ASBR to the other areas. The type of LSA sent in this case is determined by the type of area the ASBR is connected to.

Option A: Type 7 LSAs are used in Not-So-Stubby-Area (NSSA) and describe external routes that are injected into the area by the ASBR.

Option B: Type 5 LSAs are used in standard areas to describe external routes that are injected into the OSPF domain by the ASBR.

Option C: Type 4 LSAs are used by the ABR to describe a summary of routes to an ASBR that is located in another area. This LSA type is used in OSPF multi-area networks to provide a route to the ASBR in another area.

Option D: Type 3 LSAs are used by the ABR to describe inter-area routes between different areas. These LSAs are used to propagate information about prefixes from one area to another.

Therefore, the correct answer is Option B: Type 5. When an ASBR is connected to a standard OSPF area, the ABR sends a Type 5 LSA to describe the external routes that the ASBR is injecting into the OSPF domain.