Routing algorithms: distance vector and link state

In 1956 Edsger Dijkstra, a young programmer at the Mathematical Centre in Amsterdam, needed a demonstration for the new ARMAC computer that people without a mathematics background could follow. He chose a question anyone understands: what is the shortest route between two Dutch cities?

He worked out the method sitting on a café terrace with his fiancée, Ria, and later called it a twenty-minute invention. It appeared in 1959 as a three-page note. Today the same algorithm runs inside every OSPF and IS-IS router, recomputing routes each time the topology changes.