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Difficulty: EasySTP Port States and PortFast Benefits

A network administrator is configuring edge ports on a Cisco Catalyst switch connected to user workstations. Which two statements describe the operational benefits and behaviors when Cisco PortFast is enabled on an access interface? (Select TWO.)

  1. The interface bypasses the Listening and Learning STP states, transitioning directly to Forwarding upon link connection.Answer
  2. Link state changes on the PortFast-enabled port do not cause the switch to generate Topology Change Notifications (TCNs).Answer
  3. C
    PortFast should be enabled on switch-to-switch trunk links to eliminate convergence delays between infrastructure switches.
  4. D
    PortFast automatically reduces the switch's system priority in increments of 4096 to optimize STP root bridge selection.

Answer

The correct benefits are that the interface bypasses the Listening and Learning STP states to transition directly to Forwarding, and link state changes on the port do not cause the switch to generate Topology Change Notifications (TCNs).
PortFast provides two primary operational advantages on end-user access ports: first, it bypasses the Listening (15s) and Learning (15s) states to move immediately into Forwarding state when a link comes online. Second, it suppresses Topology Change Notification (TCN) messages when the port changes status, preventing unnecessary MAC table aging throughout the campus network.

Step-by-Step Solution

1
Identify the main objective of configuring Cisco PortFast on switch ports.
PortFast is intended strictly for access ports connected to end-user devices such as PCs, printers, or IP phones.
End-user devices do not run Spanning Tree Protocol or form Layer 2 redundant loops under normal topology conditions.
2
Analyze state transition behavior for PortFast-enabled ports.
Upon link activation, the port skips the 15-second Listening and 15-second Learning timer delays and immediately enters Forwarding.
Eliminating this 30-second delay ensures client hosts do not experience address assignment timeouts during initial network startup.
3
Evaluate the impact of PortFast on STP topology updates across the network.
Port transitions on PortFast interfaces are prevented from triggering Topology Change Notifications (TCNs) sent toward the Root Bridge.
Suppressing TCNs avoids unnecessary flushing of MAC address tables across the entire switching domain when host ports connect or disconnect.

Key Concept

STP PortFast Benefits and Operational Trait
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Topics

STP Port States and PortFast Benefits

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