link state algorithm (LSA)

In the link-state algorithm( LSA), a dynamic routing, the calculation of the routing table is based on a complete topology base: The LSA database contains information about distances to other routers as well as additional information about the hierarchical structure in which routers are connected to each other.

The link-state algorithm typically distinguishes between area routers( hierarchy level 1) and backbone routers(hierarchy level 2), so there are at least two hierarchy levels. In the case of table changes, only the changes are passed on to the neighbors within their own hierarchy level, not to all systems. Various metrics are possible for calculation, not only the number of hops between two end systems.

The link-state algorithm, which is also used in Shortest Path First( SPF), is less prone to produce cycles on topology changesand converges faster, i.e., finds the constant optimal route faster after changes in network operation. It also generates less overhead: Routers do not send their complete table, but only the information about which direct active neighbors they have. From this distributed database, each router calculates the new routes for itself. Within the TCP/ IP protocols, the SPF variant Open Shortest Path First ( OSPF) has established itself as an alternative to the Routing Information Protocol( RIP).