Is OSPF a distance vector or link-state routing protocol?

OSPF, or Open Shortest Path First, is classified as a link-state routing protocol. This classification is based on the way OSPF routers share information about the state of their links rather than just distance metrics.

In a link-state protocol like OSPF, each router maintains a complete map of the network topology. This is achieved by routers sending Link State Advertisements (LSAs) to all other routers within the same area. These LSAs contain information about the router's neighbors and the state of the connections to those neighbors. From this information, each router builds a database of the entire network's topology. By using Dijkstra's algorithm, OSPF calculates the shortest path to each destination based on the collected link-state information.

The ability to see the entire topology allows OSPF to swiftly adapt to changes in the network, such as link failures or topology changes, making it more efficient in larger networks. This characteristic differentiates OSPF significantly from distance vector protocols, which only share information about their immediate neighbors and calculate the best paths based on distance metrics, often leading to slower convergence and the potential for routing loops.