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Question number: 348

» Basic CS » Networks

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Describe in Detail

What is OSPF?


OSPF autonomous system

OSPF Autonomous System

OSPF autonomous system

  • Stands for Open Shortest Path First.

  • A routing protocol for internet protocol.

  • Used a link state routing algorithm and falls into the group of interior gateway protocols, operating within a single autonomous system.

  • Outing protocol has largely replaced the older Routing Information Protocol in corporate networks.

  • Link-state routing protocol means that the routers exchange topology information with their nearest neighbour.

  • Calculates end-to-end paths through the autonomous system using a variant of the Dijkstra algorithm.

Working of OSPF:

  • OSPF network works based on area and autonomy.

  • OSPF network divided into groups called areas- OSPF is based on functional areas like a building or the floor of a building.

  • Autonomous systems (AS) are collections of areas- for example, every router in an organization cab probably be part of a single AS. These regions are automatically configured and routed by the router.


  • A link state routing protocol like OSPF provides complete knowledge of topology allowing routers to calculate routes satisfying particular criteria- shortest distance, least cost, least time, best QoS etc.

  • For traffic engineering purpose, route can be constrained to meet particular quality of service.


  • Link state routing protocol does not scale well with more routers in the routing domain.

  • Number of routers increases the size and frequency of the topology updates, and time taken to calculate routes.