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.
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