shortest path first (Internetworking) (SPF)

Shortest Path First(SPF) is a routing algorithm in the context of loop suppression. Each router builds its own topology using the spanning tree method, in which the spanning tree forms the root and the shortest distances to each reachable destination.

This method is called Shortest Path First (SPF) because the shortest path in each case is taken as the route. If there are alternative routes with the same distance, the load is distributed equally. Of course, the calculated tree topology is different for each router. For different metrics such as delay, number of hops, or reliability, a router constructs different trees. The metric is aligned according to the specified type in the service field( ToS) of the IP header. Since this data field is three bits long, it can take eight different values (D, T, and R bits can be combined); consequently, a maximum of eight metrics are possible.

The SPF algorithm is implemented in Open Shortest Path First( OSPF).