TCP/IP Guide

OSPF Route Determination Using SPF Trees

The key data structure maintained by each router in an OSPF AS is the LSDB, which contains a representation of the topology of either the entire AS (in the basic topology) or a single area (in the hierarchical topology). As you have seen, each router in the AS or area has the same LSDB, so it represents a neutral view of the connections between routers and networks.

The SPF Tree

Each router needs to participate in keeping the LSDB up-to-date, but it also has its own concerns. It needs to be able to determine what routes it should use for datagrams it receives from its connected networks—this is, after all, the entire point of a routing protocol. To find the best route, it must determine the shortest path ...