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Difficulty: EasySTP Port States and PortFast Benefits

A network administrator enables Cisco PortFast on a switch port connected directly to an end-user workstation. Which operational benefit does PortFast provide in this scenario?

  1. The port immediately transitions from blocking to the forwarding state, bypassing listening and learning states to prevent DHCP timeouts.Answer
  2. B
    The port suppresses the transmission and reception of all Bridge Protocol Data Units (BPDUs) across switch-to-switch trunk links.
  3. C
    The port automatically calculates and adjusts the switch bridge priority by increments of 4096 to ensure it becomes the root port.
  4. D
    The port converts the access connection into an 802.1Q trunk port to safely interconnect neighboring distribution switches without delay.

Answer

The port immediately transitions from blocking to the forwarding state, bypassing listening and learning states to prevent DHCP timeouts.
Enabling PortFast on an access port connected to an end-user device allows the port to immediately transition from blocking to forwarding. By skipping the standard listening and learning states (which take 30 seconds combined), host devices receive network access right away, preventing issue scenarios like DHCP address acquisition timing out during bootup.

Step-by-Step Solution

1
Identify the standard 802.1D Spanning Tree Protocol (STP) transition sequence.
Standard STP transitions ports through Blocking → Listening (15s) → Learning (15s) → Forwarding.
This total 30-second delay prevents temporary Layer 2 loops during topology convergence.
2
Evaluate the effect of PortFast on an access interface.
PortFast allows an edge interface connected to a host (like a workstation) to immediately enter the Forwarding state upon link activation.
End-user hosts cannot create Layer 2 switching loops, so waiting through listening and learning states is unnecessary and often causes client protocol timeouts (e.g., DHCP).

Key Concept

STP PortFast operational behavior on edge ports
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Topics

STP Port States and PortFast Benefits

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