Please follow the above link and you will find a book that explains the three reasons why a STP switch will issue a TCN:
â¢ A port moves from a forwarding state to a blocking state on the same switch (it probably lost the designated port or the root port)
â¢ A non-root switch receives an update notification on a port from a downstream neighboring switch.
â¢ A switch is forwarding traffic to a segment and another port moves into a forwarding state
How can you explain the third condition? What exactly does this mean?