In OSPF, what is the effect of SPF calculation within an area?

• A. It floods LSAs to all routers in the area.
• B. It assigns static routes to all destinations.
• C. It discovers new neighbor adjacencies only during stable operation.
• D. It computes the shortest path tree to destinations based on the area’s topology using Dijkstra.

Answer: (D)

OSPF computes a separate shortest-path tree for each area by running the SPF algorithm on that area's link-state database. Using Dijkstra’s algorithm, it weighs each link by its cost and builds the least-cost paths from the router to every destination reachable within that area. The result is the best next-hop for reaching each destination, which OSPF then installs into the routing table. Flooding of LSAs is how routers learn the area topology, but SPF is the calculation step that turns that topology into actual routes. SPF is not about static routes, and neighbor adjacencies are discovered by Hello messages and LSDB exchanges, not by the SPF process. SPF runs whenever the area topology changes, not only during stable operation.