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Difficulty: EasySTP Port States and PortFast Benefits

An edge switch port connected directly to an end-host is configured with Cisco STP PortFast. Which operational benefit does PortFast provide when this link transitions to an up state?

  1. The interface immediately transitions to the forwarding state by bypassing the listening and learning states.Answer
  2. B
    The interface automatically filters all incoming BPDU frames to block rogue switches from participating in root bridge elections.
  3. C
    The interface lowers its local bridge priority value by increments of 4096 to ensure designated port election success.
  4. D
    The interface completely disables Spanning Tree Protocol operations across the entire VLAN to improve packet throughput.

Answer

The interface immediately transitions to the forwarding state by bypassing the listening and learning states.
Enabling PortFast on a Cisco switch access port connected to an end device allows the port to bypass the 802.1D listening and learning states, transitioning immediately to the forwarding state to eliminate initialization delays.

Step-by-Step Solution

1
Analyze standard 802.1D STP port state transitions.
Standard ports move from Blocking to Listening (15s) to Learning (15s) before reaching Forwarding (30 seconds total delay).
This delay prevents temporary Layer 2 loops while topology information propagates.
2
Determine the impact of enabling PortFast on an access interface connected to an end-host.
The interface skips the Listening and Learning states and enters the Forwarding state immediately upon link-up.
End-user hosts do not form loops, so bypassing convergence timers prevents network timeouts for protocols like DHCP.

Key Concept

STP PortFast operational mechanism and convergence benefit
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Topics

STP Port States and PortFast Benefits

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