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Difficulty: MediumSTP Port States and PortFast Benefits

An enterprise network administrator is resolving network initialization delays for workstations connected to access ports on a Cisco Catalyst switch. The administrator decides to configure Cisco PortFast on these access interfaces. How does enabling PortFast alter the IEEE 802.1D Spanning Tree Protocol (STP) port state transition behavior upon link up?

  1. The interface bypasses the Listening and Learning states, transitioning immediately into the Forwarding state.Answer
  2. B
    The interface disables Spanning Tree Protocol operation completely so it can be safely used on switch-to-switch trunk connections without forming loops.
  3. C
    The interface automatically increases its bridge priority by a system extension value of 4096 to prevent loop formation.
  4. D
    The interface forces connected host devices to match the 802.1Q native VLAN configuration before frame processing begins.

Answer

Enabling PortFast on an access interface causes it to bypass the standard 802.1D Listening and Learning states, transitioning immediately into the Forwarding state upon link activation.
Enabling PortFast on a Cisco switch access port allows the interface connected to an end device to bypass the 802.1D Listening (15s) and Learning (15s) states, transitioning immediately to the Forwarding state upon link activation. This eliminates initialization delays that cause host DHCP request timeouts.

Step-by-Step Solution

1
Analyze standard IEEE 802.1D Spanning Tree Protocol port convergence timers.
Standard 802.1D requires an access port to spend 15 seconds in the Listening state and 15 seconds in the Learning state (totaling 30 seconds) before reaching Forwarding.
These delays prevent transient bridging loops while the switch learns MAC addresses and listens for BPDUs.
2
Determine the impact of Cisco PortFast when configured on edge access ports connected to single end-user hosts.
The port skips Listening and Learning, moving directly to Forwarding upon link up.
Since end-user workstations do not initiate bridging loops, skipping intermediate timers prevents DHCP timeouts and initialization delays.

Key Concept

STP Port States and PortFast Benefits
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Topics

STP Port States and PortFast Benefits

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