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Difficulty: MediumSTP Port States and PortFast Benefits

An administrator enables Cisco STP PortFast on edge access ports connected to end-user workstations. Which two operational benefits or behaviors result from enabling PortFast on these interfaces? (Select two.)

  1. The interface transitions immediately to the Forwarding state upon linkup, bypassing the 802.1D Listening and Learning states.Answer
  2. Link state changes on the interface do not trigger Spanning Tree Protocol Topology Change Notifications (TCNs).Answer
  3. C
    The interface completely ceases sending and receiving Spanning Tree BPDU frames across the link.
  4. D
    The switch dynamically recalculates the STP root bridge priority value using 4096 increments whenever an edge port connects.

Answer

Enabling PortFast on edge access ports allows the interface to bypass the Listening and Learning states to reach Forwarding immediately, and prevents link state changes on that port from triggering Topology Change Notifications (TCNs).
Enabling PortFast on an edge access port allows it to immediately enter the Forwarding state upon link activation without waiting through the Listening and Learning states. Additionally, link status transitions on PortFast ports do not generate Topology Change Notifications (TCNs), keeping MAC address tables stable across the switched network.

Step-by-Step Solution

1
Analyze standard 802.1D convergence states.
Standard STP ports spend 15 seconds in Listening and 15 seconds in Learning before Forwarding, totaling a 30-second delay.
PortFast bypasses Listening and Learning for edge devices so DHCP and other initial network communications do not time out.
2
Analyze topology change notification impact.
Edge port state changes do not indicate a core topology failure.
Suppressing TCNs on PortFast ports stops switches across the LAN from reducing MAC table aging timers unnecessarily.

Key Concept

STP PortFast operational mechanics and TCN suppression
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Topics

STP Port States and PortFast Benefits

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