OSPF is a dynamic link-state routing protocol that uses a link-state database (LSDB) to build and calculate the shortest path to all known destinations. It is through the use of Dijkstra’s SPF algorithm that the information contained within the LSDB is calculated into routes.
The shortest path algorithm by itself is quite complicated, and its inner workings were covered in depth in Chapter 3, “OSPF Communication.” It is important to have a good understanding of Dijkstra’s SPF algorithm to achieve the maximum benefit of this chapter. The following is a high-level, simplified way of looking at the various steps used by the algorithm. The full SPF recalculation is as follows:
Upon initialization or due to a change in routing ...