In many networks, the optimal STP topology is determined as part of the network design and then implemented through manipulation of STP priority and cost values. Situations may occur where STP was not considered in the network design and implementation, or where it was considered or implemented before the network underwent significant growth and change. In such situations, it is important to know how to analyze the actual STP topology in the operational network.
A big part of troubleshooting consists of comparing the actual state of the network against the expected state of the network and spotting the differences to gather clues about the troubleshooting problem. A network professional should be able to examine the switches and determine the actual topology, and be able to understand what the underling spanning tree topology should be.