OSPF stands for Open Shortest Path First, as the name indicates its a link state protocol. In link-state protocols, the link part of the protocol is the interface on the router, while the state is how it relates to its neighbors, which would include its address and network information. Before you get started, check out this short list of terms used in this section:

  • Link State Advertisement (LSA): A simple update on a router’s link status, so one will be sent when a link is connected, disconnected, or otherwise changed

  • Topological database: A table in the router’s memory that contains link information about all known routers (see Chapter 6 of this minibook)

  • SPF algorithm: A mathematical calculation that uses the Dijkstra algorithm (named after a Dutch mathematician) to determine the shortest path to destinations and that has been heavily applied to computer networks

  • SPF tree: A listing all of the routes to any destination with an order of preference

Each router that has been configured for an OSPF area sends out a Link State Advertisement (LSA) at regular intervals. All of this link-state information is stored in a topological database, after which an SPF algorithm is applied to the data in the database.



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