Which routing protocol uses a link-state algorithm to determine shortest paths in large networks?

Which routing protocol uses a link-state algorithm to determine shortest paths in large networks?

• A. RIP
• B. BGP
• C. ISIS
• D. OSPF

Answer: (D)

The main idea is how a link-state routing protocol determines the best paths. In a link-state approach, every router learns the state of its own links and floods that information to all other routers, building a complete map of the network called the Link-State Database. With this full topology, each router runs a shortest-path algorithm (that’s Dijkstra’s algorithm) to calculate the best route to every destination. Because each router has the same global view, the routes are normally optimal and the network can scale well, especially when designers divide it into areas to contain changes and reduce complexity. OSPF is the classic example of this approach. It floods link-state advertisements to construct a consistent network map, uses a cost metric (often based on link bandwidth) for the calculations, and uses areas to manage large topologies. This combination—flooding of topology information, local SPF computation, and hierarchical design—makes OSPF well-suited for large networks. RIP uses a distance-vector method with hop-count as its metric, which tends to converge slowly and doesn’t scale well. BGP operates as a path-vector protocol for interdomain routing with policy-based decisions, not shortest-path calculations via SPF. ISIS is another link-state protocol, but in many courses OSPF is the primary example taught for determining shortest paths in large networks.

The main idea is how a link-state routing protocol determines the best paths. In a link-state approach, every router learns the state of its own links and floods that information to all other routers, building a complete map of the network called the Link-State Database. With this full topology, each router runs a shortest-path algorithm (that’s Dijkstra’s algorithm) to calculate the best route to every destination. Because each router has the same global view, the routes are normally optimal and the network can scale well, especially when designers divide it into areas to contain changes and reduce complexity.

OSPF is the classic example of this approach. It floods link-state advertisements to construct a consistent network map, uses a cost metric (often based on link bandwidth) for the calculations, and uses areas to manage large topologies. This combination—flooding of topology information, local SPF computation, and hierarchical design—makes OSPF well-suited for large networks.

RIP uses a distance-vector method with hop-count as its metric, which tends to converge slowly and doesn’t scale well. BGP operates as a path-vector protocol for interdomain routing with policy-based decisions, not shortest-path calculations via SPF. ISIS is another link-state protocol, but in many courses OSPF is the primary example taught for determining shortest paths in large networks.