Which protocol determines routing paths by computing shortest-path trees and exchanging link-state information?

• A. BGP
• B. OSPF
• C. RIP
• D. EIGRP

Answer: (B)

Determining routing paths by computing a shortest-path tree from a complete view of the network is the hallmark of a link-state routing approach. In a link-state protocol, every router disseminates its local link information to all other routers in the same area, building a common, up-to-date map of the network—the link-state database. Each router then runs a shortest-path algorithm (Dijkstra’s SPF) on that map to derive the best path to every destination, based on a cost metric such as link speed. This yields fast convergence and scalable hierarchical design when the network is divided into areas.

OSPF embodies this approach: it floods link-state advertisements to construct the topology database, and every router uses the SPF algorithm to compute the shortest-path tree to all destinations. This combination of a complete topology view and SPF-based routing is what keeps OSPF efficient and scalable in large networks.

In contrast, BGP operates as a path-vector protocol driven by policies and AS-path attributes rather than a shared topology and SPF; it doesn’t build a network-wide shortest-path tree. RIP uses a distance-vector method, exchanging hop counts and relying on Bellman-Ford, which doesn’t construct a full SPF-based map. EIGRP is a hybrid protocol that uses its own distance-vector-like updates and the DUAL algorithm, not a full link-state SPF computation with a flooded topology database.