Chapter 2 Advanced Routing for FortiOS 5.0 : Open Shortest Path First (OSPF) : OSPF Background and concepts : Background
  
Background
OSPF version 2 was defined in 1998 in RFC 2328. OSPF was designed to support classless IP addressing, and variable subnet masks. This was a shortcoming of the earlier RIP protocols.
Updates to OSPF version 2 are included in OSPF version 3 defined in 2008 in RFC 5340. OSPF3 includes support for IPv6 addressing where previously OSPF2 only supports IPv4 addressing.
The main benefit of OSPF is that it detects link failures in the network quickly and within seconds has converged network traffic successfully without any networking loops. Also OSPF has many features to control which routes are propagated and which are not, maintaining smaller routing tables. OSPF can also provide better load-balancing on external links than other interior routing protocols.