Open Shortest Path First (OSPF) is an open-standard Link State routing protocol. Link State routing protocols advertise the state of their links. When a Link State router begins operating on a network link, information associated with that logical network is added to its local Link State Database (LSDB). The local router then sends Hello messages on its operational links to determine whether other Link State routers are operating on the interfaces as well. OSPF runs directly over Internet Protocol using IP protocol number 89.