CCNA -Open Shortest Path First (OSPF) routing protocol and its characteristics

Explain the Open Shortest Path First (OSPF) routing protocol and its characteristics.

OSPF (Open Shortest Path First) is a link-state routing protocol that is widely used in large enterprise networks. Here are its characteristics:

  • Link-State Protocol: OSPF is a link-state routing protocol, which means that routers in an OSPF network maintain a database of the network topology. Each router floods information about its directly connected links to all other routers in the network.
  • Areas: OSPF networks are organized into areas to improve scalability. OSPF routers within the same area have detailed knowledge of the area’s topology, while routers between areas only have summarized information about the topology of other areas.
  • Cost: OSPF uses cost as its metric, which is based on the bandwidth of the link. The cost of a link is calculated using the formula cost = reference bandwidth / interface bandwidth. The reference bandwidth by default is 100 Mbps.
  • Hierarchical Design: OSPF networks are designed hierarchically, with backbone areas (Area 0) at the top level and other areas connected to the backbone. This hierarchical design improves network scalability and reduces the routing overhead.
  • Fast Convergence: OSPF has fast convergence times compared to distance-vector routing protocols like RIP. This is because OSPF routers only need to update their routing tables when there is a change in the network topology, rather than waiting for periodic updates.
  • Authentication: OSPF supports authentication to secure routing updates exchanged between OSPF routers.
  • Types of OSPF Routers: OSPF routers can be categorized into several types, including internal routers, area border routers (ABRs), and autonomous system boundary routers (ASBRs).


Router(config)# router ospf 1
Router(config-router)# network area 0


In this example, OSPF is enabled on the router with process ID 1, and the network is advertised into OSPF with area 0.

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