The portfast feature is a Cisco proprietary change in the STP implementation. Note that STP is still running on ports with portfast. The switch never generates a TCN when a port configured for portfast is going up or down. Tracking the Source of a TCN In itself, a topology change is not a bad thing, but as a good network administrator, it is better to know where they are coming from in order to be sure they are not related to a real problem. Identifying the bridge that issued the topology change is not an easy task, though not technically very complex.
Most bridges only count the number of TCNs they have issued or received.
Starting from the root, it is then possible to go downstream to the initiator bridge. See information on the show spantree statistics command for more information. Conclusion Remember that a TCN does not start a STP recalculation. The number or the rate of topology changes is not an issue in itself. The problem is to know what the topology change means.