Counting to Infinity: Shortest Paths, Protocols and Timetables

Deep End Era. Engineering with Sankalp · Oct 28, 2026 · 52m

A brother runs a national internet backbone; his sister builds a city's transit trip planner. Both say their routing problem is harder, and both are solving the same mathematics. Part eight of The Deep End's algorithms series works through Dijkstra's algorithm by ear, shows why it breaks with negative weights and how Bellman–Ford fixes that, and follows both algorithms into the internet's two rival routing designs, including the day in 1980 when one faulty router took down the entire ARPANET and the routers that count slowly to infinity. Then we turn to timetables, where the fastest…