An Open Shortest Path First (OSPF) router will use the Dijkstra algorithm to determine the best route for packets. The OSPF routing process determines the best route for packets by analyzing its link state database and building a shortest path first (SPF) tree. The SPF tree is a simplified view of the entire network topology and contains the shortest route to any destination on the network. Although every router in an area has the same link state database, each router can calculate its own SPF tree to determine the best route to any location on the network. The SPF tree is typically recalculated only if a router receives a link state packet that indicates a change on the network. Because link state updates are only transmitted within an area, OSPF routers in other areas do not recalculate their SPF trees
when a change occurs in an area to which they are not connected.

An OSPF router will not use the Bellman-Ford algorithm to determine the best route for packets. The Bellman-Ford algorithm is used by distance vector routing protocols, such as Routing Information Protocol (RIP), to determine the best routes to locations on the network.

An OSPF router will not use the path-vector algorithm to determine the best route for packets. The path-vector algorithm, which is used by Border Gateway Protocol (BGP) to determine the best routes to locations on the network, is based on the Bellman-Ford algorithm.

An OSPF router will not use the Diffusing Update Algorithm (DUAL) to determine the best route for packets. The DUAL algorithm is a hybrid of distance-vector routing protocols and is used by Enhanced Interior Gateway Routing Protocol (EIGRP) to determine the best routes to locations on the network.

An OSPF router will not use the Diffie-Hellman algorithm to determine the best route for packets. The Diffie-Hellman algorithm is not used by dynamic routing processes. The Diffie-Hellman algorithm is commonly used by IP Security (IPSec) to generate shared keying material and to securely transfer the information necessary to establish a security association (SA) with an IPSec peer.