What does the term “link state” refer to in routing protocols like OSPF?

The term “link state” in routing protocols like OSPF (Open Shortest Path First) refers to the sharing of link information by routers. In link-state protocols, each router maintains a complete map of the network topology by exchanging information about the state of its links (connections) with other routers. This information includes details about the router's interfaces, the status of those interfaces (up or down), and metrics like link cost. By sharing this information, OSPF routers can independently compute the best path to each destination using algorithms like Dijkstra's algorithm, ensuring efficient and accurate routing within the network.

In contrast, the other options do not accurately capture the concept of "link state" as it relates to OSPF. For instance, the speed of the network connections pertains to bandwidth but does not encapsulate the essence of link-state information sharing. Similarly, the physical state of the network cables is irrelevant to the logical routing decisions made by OSPF, and securing links between routers does not define the operational characteristics of link state protocols. Understanding this distinction is key to grasping how OSPF operates and how it differs from distance-vector routing protocols, which do not rely on a complete network topology view.