Which protocol is a link-state routing protocol?

• A. RIPv2
• B. OSPF
• C. BGP
• D. EIGRP

Answer: (B)

The main idea being tested is how routing protocols learn and represent network topology. A link-state routing protocol works by each router building a complete map of the network and using that map to compute the best paths.

OSPF is a textbook example of this approach. Routers generate and flood link-state advertisements that describe the state and cost of their links, so every router learns the entire network topology. With this full view, each router runs Dijkstra’s shortest-path first algorithm to build a shortest-path tree and determine the best next hop for every destination. This leads to fast convergence and accurate routing decisions.

Other protocols use different mechanisms. A distance-vector protocol, like RIP v2, shares routing information with immediate neighbors and relies on hop counts to determine routes, which can be slower to converge and more prone to certain routing anomalies. Path-vector protocols, such as BGP, exchange path attributes between autonomous systems and are oriented toward inter-domain routing rather than maintaining a complete intra-domain topology. EIGRP is a hybrid that incorporates distance-vector features with some topology awareness but is not strictly a pure link-state protocol.