Which of the following descriptions of the NSSA area is wrong?

Question

Options

• AThe ABR in the NSSA area will convert Type 7 LSA into Type 5 LSA, and inject the LSA into the backbone area, thereby flooding the entire OSPF domain
• BThe NSSA area can import external routes without learning external routes from other areas of the OSPF network
• CType 5 LSA can be directly flooded into other areas by the ABR in the NSSA area to the NSSA area
• DThe ABR in the NSSA will automatically inject a default route into the area, which is described in type 7 LSA

• A
  3% (1)
• B
  3% (1)
• C
  82% (28)
• D
  12% (4)

Explanation

Option C is wrong because Type 5 LSAs are explicitly blocked from entering NSSA areas - that is the defining characteristic of an NSSA. External routes originating inside an NSSA are described using Type 7 LSAs, which stay within the NSSA; it is the ABR that translates them into Type 5 LSAs when redistributing outward to the backbone and other areas, not the other way around.

Options A, B, and D are all accurate descriptions of NSSA behavior. A correctly describes the Type 7-to-Type 5 conversion performed by the ABR at the area boundary. B correctly states that NSSA allows local external route import while still blocking incoming Type 5 LSAs from the rest of the OSPF domain. D correctly states that the NSSA ABR automatically generates a Type 7 default route into the area so internal routers have a path to reach external destinations.

Memory tip: Think of the NSSA boundary as a one-way valve for external routes. Type 7 LSAs flow outward from the NSSA and are converted to Type 5 at the ABR; Type 5 LSAs never flow inward into the NSSA. Any answer suggesting Type 5 enters the NSSA is wrong.

No community discussion yet for this question.