How does OSPF determine the best path in a network with multiple routes?

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How does OSPF determine the best path in a network with multiple routes?

Asked on Dec 01, 2025

Answer

OSPF (Open Shortest Path First) determines the best path by using the Dijkstra algorithm to calculate the shortest path tree based on link-state information. It assigns a cost to each route, which is typically based on bandwidth, and selects the path with the lowest cumulative cost.

Example Concept: OSPF uses a metric called "cost" to evaluate the best path to each destination. The cost is inversely proportional to the bandwidth of the link, meaning higher bandwidth links have lower costs. OSPF routers exchange link-state advertisements (LSAs) to build a complete topology of the network, and then apply the Dijkstra algorithm to determine the shortest path tree. The path with the lowest total cost from source to destination is selected as the best route.

Additional Comment:

OSPF supports equal-cost multi-path (ECMP) routing, allowing traffic to be distributed across multiple best paths of equal cost.
OSPF areas help reduce routing overhead by segmenting large networks into smaller, manageable sections.
OSPF's hierarchical design improves scalability and reduces the frequency of routing updates.
Link-state updates ensure that all routers have a consistent view of the network topology.

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