Which OSPF area type explicitly allows Type-7 LSAs to summarize external routes and does not carry Type-5 LSAs?

Which OSPF area type explicitly allows Type-7 LSAs to summarize external routes and does not carry Type-5 LSAs?

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

Answer: (C)

Not-So-Stubby Areas (NSSA) are designed to carry external routes in a controlled way inside the area. Inside an NSSA, external routes are advertised as Type-7 LSAs, which allows external networks to be imported without flooding the entire domain with Type-5 LSAs. Importantly, the NSSA itself does not carry Type-5 LSAs; those external routes are kept as Type-7 within the area. When the routes must reach the rest of the OSPF domain, the NSSA’s ABR converts the Type-7 LSAs into Type-5 LSAs for distribution to non-NSSA areas. This combination—Type-7 LSAs for external routes inside the area, with no internal Type-5 LSAs—fits the described behavior. Other area types either do not support Type-7 LSAs in the area or rely on Type-5 LSAs inside the area, so NSSA is the correct fit.

Not-So-Stubby Areas (NSSA) are designed to carry external routes in a controlled way inside the area. Inside an NSSA, external routes are advertised as Type-7 LSAs, which allows external networks to be imported without flooding the entire domain with Type-5 LSAs. Importantly, the NSSA itself does not carry Type-5 LSAs; those external routes are kept as Type-7 within the area. When the routes must reach the rest of the OSPF domain, the NSSA’s ABR converts the Type-7 LSAs into Type-5 LSAs for distribution to non-NSSA areas. This combination—Type-7 LSAs for external routes inside the area, with no internal Type-5 LSAs—fits the described behavior. Other area types either do not support Type-7 LSAs in the area or rely on Type-5 LSAs inside the area, so NSSA is the correct fit.