OSPF (Open Shortest Path First) is an open-standard link state protocol. It's the most widely deployed interior gateway protocol.
OSPF characteristics:
- Uses cost based on bandwidth
- Supports VLSM and CIDR
- Administrative distance:
- Fast convergence (seconds, not minutes)
- Hierarchical design with areas
OSPF routers build a complete topology map and run Dijkstra's algorithm to calculate shortest paths. Because all routers have the same view, routing loops are impossible during normal operation.