What Is OSPF?

Date First Published: 3rd June 2022

Topic: Computer Networking

Subtopic: Internet Protocols

Article Type: Computer Terms & Definitions

Difficulty Level: 10/10

Learn more about what OSPF is in this article.

Short for Open Shortest Path First, OSPF is a routing protocol used to determine the shortest and most efficient path from one router to another in a LAN. The OSPF algorithm will compare the available options and calculate the most efficient way data can be transmitted as long as the network is IP-based.

This protocol has replaced the older routing protocol, RIP (Routing Information Protocol). Using OSPF, a router that detects a change in the routing table or in the network will multicast that information to all other OSPF hosts in the network in order for them to have the same routing table information.

Note:

OSPF is different from RIP, since it sends only the part of the routing table that has changed and only when a change has occurred. RIP requires routers to send routing table information every 30 seconds.

Versions

OSPFv1 does not exist. No one ever remembers it and it has never been supported. Instead, the first version of OSPF was defined in RFC 1131 in 1989. It was OSPFv2. 

OSPFv3 is the enhanced version of OSPF that supports IPv6. It was defined in RFC 2328 in 1998. Even though the addresses have expanded to 128 bits in IPv6, area and router identifications are still 32-bit numbers. It uses a multicast range of FF02::5 for OSPF routes and FF02::6 when sending updates and acknowledgements. Another new feature of OSPFv3 is the capability to assign the router ID, area ID, and link-state ID with a 32-bit value without IP addresses, enabling OSPFV3 to be routable over almost any network layer protocol.

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