When a link fails, the routers at its two ends describe the network afresh and flood the news to everyone in the area; every router then reruns SPF on the new database. The demo cuts the R1B–R1D link in area 1 of the network from the earlier demos, while a host on R1A's LAN sends a steady stream of packets to ABR-1B, …

Inside an area every router holds the whole map, but no router LSA ever leaves its area. Routes between areas are carried by the ABRs as summary LSAs: a prefix and a cost, with nothing of the links behind them. This demo follows one such route from area 2 to area 1 across the network from the Hello , Database Exchange …

Every router in an OSPF area holds the same database, and runs Shortest Path First (SPF) on it to find the cheapest path to everywhere in the area. This demo takes area 1 of the network from the Hello and Database Exchange demos, strips it down to a graph, and runs Dijkstra's algorithm on it one decision at a time. …

Two OSPF neighbors that have agreed to become adjacent still hold different link-state databases. The database exchange makes them identical: each describes what it holds, asks for what it lacks, and receives it. This demo runs that exchange on the same network as the Hello protocol demo , one adjacency at a time. Open …

The Hello protocol is how OSPF routers find each other, agree that they can talk, and elect a Designated Router on a shared segment. This demo runs it on a fixed network of eleven routers; there is nothing to configure, only a scenario to watch. Open full screen ↗ recommended: the drawing is large Next: OSPF Database …