OSPF
Open Shortest Path First — a link-state interior gateway protocol that computes shortest paths by cost.
OSPF (Open Shortest Path First) is a link-state interior gateway protocol. Each router floods link-state advertisements through an autonomous system, then runs Dijkstra’s Shortest Path First algorithm on the topology database to compute loop-free routes. Because every router holds an identical map, OSPF reconverges much faster than distance-vector protocols like RIP, which rely on hop count and periodic updates. For the exam, OSPF’s metric is cost (derived from bandwidth), not hop count. Both OSPF and EIGRP are classless IGPs, but EIGRP is Cisco-proprietary, while OSPF is an open standard — RFC 2328 for OSPFv2, RFC 5340 for OSPFv3 (IPv6).
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