A router interface with OSPF will then advertise its link cost to neighboring routers through multicast, known as the hello procedure. Unless the administrator has made a configuration, the link cost of a path connected to a router is determined by the bit rate (1 Gbit/s, 10 Gbit/s, etc.) of the interface. The state of a given route in the network is the cost, and OSPF algorithm allows every router to calculate the cost of the routes to any given reachable destination. Īs a link-state routing protocol, OSPF maintains link-state databases, which are really network topology maps, on every router on which it is implemented. OSPF was quickly adopted because it became known for reliably calculating routes through large and complex local area networks. Therefore, OSPF undertakes route cost calculation on the basis of link-cost parameters, which can be weighted by the administrator. OSPF was developed so that the shortest path through a network was calculated based on the cost of the route, taking into account bandwidth, delay and load. Demand grew for a dynamic routing protocol that could calculate the fastest route to a destination. But RIP did not adapt its routing according to changing network conditions, such as data-transfer rate. RIP successfully implemented dynamic routing, where routing tables change if the network topology changes. The first routing protocol that was widely implemented, the Routing Information Protocol (RIP), calculated the shortest route based on hops, that is the number of routers that an IP packet had to traverse to reach the destination host. Routing protocols like OSPF calculate the shortest route to a destination through the network based on an algorithm. The development work for OSPF prior to its codification as open standard was undertaken largely by the Digital Equipment Corporation, which developed its own proprietary DECnet protocols. OSPF was first standardized in 1989 as RFC 1131, which is now known as OSPF version 1. As a link-state routing protocol it was based on the link-state algorithm developed for the ARPANET in 1980 and the IS-IS routing protocol. It implements Dijkstra's algorithm, also known as the shortest path first (SPF) algorithm. OSPF was designed as an interior gateway protocol (IGP), for use in an autonomous system such as a local area network (LAN). IS-IS, another LSR-based protocol, is more common in large service provider networks. OSPF is a widely used IGP in large enterprise networks. OSPF supports the Classless Inter-Domain Routing (CIDR) addressing model. The updates for IPv6 are specified as OSPF Version 3 in RFC 5340 (2008). It is defined as OSPF Version 2 in RFC 2328 (1998) for IPv4. It uses a link state routing (LSR) algorithm and falls into the group of interior gateway protocols (IGPs), operating within a single autonomous system (AS). Open Shortest Path First ( OSPF) is a routing protocol for Internet Protocol (IP) networks.