Which OSPF area type is designed to retain external routes within the area using Type-7 LSAs, while not carrying external Type-5 LSAs into the area?

Which OSPF area type is designed to retain external routes within the area using Type-7 LSAs, while not carrying external Type-5 LSAs into the area?

• A. Totally Stubby Area
• B. Stub area
• C. NSSA
• D. Normal area

Answer: (C)

Not-So-Stubby Area is designed to keep external routes contained within the area while still allowing redistribution. Inside an NSSA, external routes are learned and represented as Type-7 LSAs, so those routes stay inside the NSSA and aren’t flooded into the rest of the OSPF domain as Type-5 LSAs. When traffic leaves the NSSA toward the backbone or other areas, the ABR translates those Type-7 LSAs into Type-5 LSAs, allowing the routes to be advertised outside the NSSA if needed. This behavior—representing external routes with Type-7 LSAs and not carrying Type-5 LSAs into the area—fits NSSA precisely, unlike stub or totally stubby areas, which suppress or alter external LSAs differently, or a normal area where Type-5 LSAs flow freely.

Not-So-Stubby Area is designed to keep external routes contained within the area while still allowing redistribution. Inside an NSSA, external routes are learned and represented as Type-7 LSAs, so those routes stay inside the NSSA and aren’t flooded into the rest of the OSPF domain as Type-5 LSAs. When traffic leaves the NSSA toward the backbone or other areas, the ABR translates those Type-7 LSAs into Type-5 LSAs, allowing the routes to be advertised outside the NSSA if needed. This behavior—representing external routes with Type-7 LSAs and not carrying Type-5 LSAs into the area—fits NSSA precisely, unlike stub or totally stubby areas, which suppress or alter external LSAs differently, or a normal area where Type-5 LSAs flow freely.