Defining the Spanning Tree Protocol – STP
Example: determining the active topology

Here is a scenario with switches running STP and exchanging information as shown above. From this information, exchange will yield the following final results:

  • The election of a root bridge as a Layer 2 topology point of reference
  • The determination of the best lowest cost path to the root bridge
  • The election of a designated switch and corresponding designated port for every switched segment
  • The removal of loops in the switched network by transitioning redundant switch ports to a disabled port role
  • Determination of the "active topology" for each instance or VLAN running STP

The active topology is the final set of communication paths that are created by switch ports forwarding frames. Once the active topology has been established, using Topology Change Notifications, the switched network must reconfigure the activity topology if a link failure occurs.