OSPF protocol was developed due to a need in the internet community to introduce a high functionality non-proprietary Internal Gateway Protocol (IGP) for the TCP/IP protocol family. The discussion of the creation of a common interoperable IGP for the Internet started in 1988 and did not get formalized until 1991. At that time the OSPF Working Group requested that OSPF be considered for advancement to Draft Internet Standard.
The OSPF protocol is based on link-state technology, which is a departure from the Bellman-Ford vector based algorithms used in traditional Internet routing protocols such as RIP. OSPF has introduced new concepts such as authentication of routing updates, Variable Length Subnet Masks (VLSM), route summarization, and so forth.
The OSPF protocol consists of three subprotocols:
1. Hello
2. Exchange
3. Flooding
Hello is used to check that links are operational and to select what is called a designated router. Hello packets are sent at regular intervals that are customized by the network administrator on each OSPF router. The Exchange protocol is used during startup of a router where it receives a copy of the network database from a neighboring router. The Flooding protocol is used to propagate link state changes through the network.