Spanning Tree Protocol: Topology Events

Spanning Tree Protocol is a constantly running protocol that never goes into an IDLE state when a loop free network has been negotiated with the other switches on the LAN.  Each time it receives a Hello BPDU it’s re-evaluating the superior BPDU each time, so STP can react appropriately at any time of a network failure.

STP Topology Events include:

  • a TCN BPDU (Topology Change Notification) is received by a Designated Port of a switch
  • A port moves from forwarding state and the switch has at lease one Designated Port
  • A port moves from the Learning or Forwarding states to Blocking
  • A switch becomes the Root Switch

Upon detection of a topology event, each switch begins forwarding their originating BPDUs with the updated contents so a new root path is determined.



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