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OSPF – Open Shortest Path First

Vangie Beal
Last Updated May 24, 2021 7:51 am

Short for Open Shortest Path First, an interior gateway routing protocol developed for IP networks based on the shortest path first or link-state algorithm.

Routers use link-state algorithms to send routing information to all nodes in an internetwork by calculating the shortest path to each node based on a topography of the Internet constructed by each node. Each router sends that portion of the routing table (keeps track of routes to particular network destinations) that describes the state of its own links, and it also sends the complete routing structure (topography).

The advantage of shortest path first algorithms is that they results in smaller more frequent updates everywhere. They converge quickly, thus preventing such problems as routing loops and Count-to-Infinity (when routers continuously increment the hop count to a particular network). This makes for a stable network.

The disadvantage of shortest path first algorithms is that they require a lot of CPU power and memory. In the end, the advantages out weigh the disadvantages.

OSPF Version 2 is defined in RFC1583. It is rapidly replacing RIP on the Internet.