As a link-state protocol, OSPF operates differently from distance vector routing protocols. Link-state routers identify neighboring routers and then communicate with the identified neighbors. OSPF has its own terminology. The new terms are shown in Figure .

Information is gathered from OSPF neighbors about the status, or links, of each OSPF router. This information is flooded to all its neighbors. Flooding is a process that sends information out all ports, with the exception of the port on which the information was received. An OSPF router advertises its own link states and passes on received link states.

The routers process the information about link-states and build a link-state database. Every router in the OSPF area will have the same link-state database. Every router has the same information about the state of the links and the neighbors of every other router.

Then each router runs the SPF algorithm on its own copy of the database. This calculation determines the best route to a destination. The SPF algorithm adds up the cost, which is a value that is usually based on bandwidth. The lowest cost path is added to the routing table, which is also known as the forwarding database.

OSPF routers record information about their neighbors in the adjacency database.

To reduce the number of exchanges of routing information among several neighbors on the same network, OSPF routers elect a Designated Router (DR) and a Backup Designated Router (BDR) that serve as focal points for routing information exchange.

Interactive Media Activity Crossword Puzzle: OSPF Terminology When the student has completed this activity, the student will understand the different OSPF terminology.

   

Web Links Open Shortest Path First (OSPF) http://www.cisco.com/univercd/cc/ td/doc/cisintwk/ito_doc/ospf.htm