Refer to the exhibit. Company XYZ has 150 branch locations across the U.S. Each branch is connected to two aggregation routers, one router in each data center. The network is configured with multiple

When branch locations redistribute external routes, those routes generate Type 5 LSAs that flood throughout the entire OSPF domain and trigger SPF recalculation on every router. Declaring the branch areas as NSSAs causes external routes to be carried as Type 7 LSAs, which are scoped to the local area; the ABR aggregation routers then selectively convert only summarized Type 7 entries into Type 5 LSAs for the backbone, dramatically reducing LSA flooding domain-wide while still allowing the ABRs to advertise optimal inter-area paths to the data centers.

Distribute lists filter prefixes from being installed in routing tables or redistributed, but they do not reduce the number of LSAs generated or flooded, so SPF recomputation frequency across the domain is unchanged.

OSPF summarization on ABRs reduces the count of Type 3 inter-area LSAs sent into other areas but does not address Type 5 external LSA flooding or the SPF load caused by changes inside the branch areas themselves.

A totally stubby area blocks all Type 3, 4, and 5 LSAs and injects only a default route, which prevents the routers from learning specific paths to each data center and directly violates the optimal-path requirement.