/ˌoʊ ˌɛs ˌpiː ˈɛf/
noun — "the protocol that maps the fastest paths across a network."
OSPF (Open Shortest Path First) is a link-state routing protocol used in Internet Protocol (IP) networks to determine optimal routing paths. Unlike distance-vector protocols, OSPF maintains a complete topology of the network by exchanging link-state advertisements (LSAs) between routers. This allows each router to independently compute the shortest path to every destination using Dijkstra’s algorithm, enabling fast convergence and efficient routing in large, complex networks.
Technically, OSPF operates within a hierarchical structure, dividing networks into areas to reduce routing overhead and improve scalability. It supports IPv4 and IPv6 addressing, authentication for secure routing, and features such as route summarization, load balancing, and route redistribution with other protocols. Routers running OSPF elect a designated router (DR) and backup DR for each broadcast network segment to streamline LSA flooding and reduce redundant updates.
Key characteristics of OSPF include:
- Link-state routing: each router knows the full network topology for precise path calculation.
- Fast convergence: rapidly adapts to network changes and failures.
- Hierarchical design: uses areas and backbone (Area 0) to scale efficiently.
- Authentication: ensures only trusted routers exchange routing information.
- Support for multiple networks: compatible with IPv4 and IPv6.
In practical workflows, network engineers deploy OSPF in enterprise and service provider networks to maintain reliable routing. When a link fails, OSPF quickly propagates updated LSAs so all routers recompute shortest paths, minimizing downtime. It is often used alongside other protocols like BGP (BGP) for inter-domain routing, while internal areas optimize resource usage and simplify management.
Conceptually, OSPF is like a constantly updated GPS for routers: each router knows the layout of the network and recalculates the fastest route whenever a road (link) changes.
Intuition anchor: OSPF ensures data takes the shortest, most efficient path across a network, adapting instantly to changes in topology.