Which type of OSPF area restricts external routes from other areas but allows external routes to be flooded by ASBRs within its own area?

A.
not-so-stubby area

B.
backbone area

C.
stub area with no-summaries configured

D.
stub area

Explanation:
* Configure a not-so-stubby area (NSSA). An NSSA allows external routes to be flooded within the area. These routes are then leaked into other areas.
* You cannot configure an area as being both a stub area and an NSSA.
* The remaining statements are explained separately.

The NSSA Option for OSPF areas is defined in RFC 1587. The NSSA option partially undoes a portion of what the stub area is designed to do. The OSPF stub area eliminates the propagation of external routes in an area by creating a default route that is propagated into the NSSA by the ABR. The NSSA standard creates a new type of LSA, the type 7 (NSSA External) LSA, and floods that through the NSSA. ABRs for the NSSA translate type 7 LSAs and propagate them to the backbone area and other type-5-LSA capable areas as type 5 (external) LSAs. ASBRs in the NSSA are not actually advertised into the backbone area as type 4 (ASBR summary) LSAs.