Examkin

Question

Difficulty: MediumSTP Port States and PortFast Benefits

A network administrator configures Cisco STP PortFast globally on an enterprise access switch. Which two operational benefits or characteristics occur when PortFast is active on an access port connected to a host workstation? (Select two.)

  1. The port immediately transitions from the Blocking state to the Forwarding state, skipping the Listening and Learning states.Answer
  2. The switch prevents the generation of Topology Change Notifications (TCNs) when the interface changes link state.Answer
  3. C
    The interface completely disables sending and receiving BPDUs, allowing it to safely connect to other switches without forming loops.
  4. D
    PortFast automatically modifies the switch priority by an increment of 4096 to ensure the host port becomes the Root Port.

Answer

The correct benefits are that the interface transitions immediately to the Forwarding state (bypassing Listening and Learning states) and that the switch avoids sending Topology Change Notifications (TCNs) when the port status changes.
PortFast is intended for edge ports connected to single end-hosts (such as PCs or printers). It provides two core benefits: immediate transition to the Forwarding state (bypassing the 30-second total Listening and Learning delay) and preventing linkup/linkdown events on host ports from generating Topology Change Notifications (TCNs) that force CAM table aging across the network.

Step-by-Step Solution

1
Analyze standard 802.1D STP convergence timers on edge ports.
Standard STP ports undergo Listening (15 seconds) and Learning (15 seconds) states before reaching Forwarding (total 30 seconds delay), which can cause DHCP client timeouts on host devices.
Identify the primary operational problem PortFast is designed to solve.
2
Evaluate the direct state transition change caused by PortFast.
PortFast allows edge ports to transition immediately from Blocking to Forwarding, bypassing the 30-second convergence delay.
Confirm the first correct operational trait of PortFast.
3
Evaluate the network-wide impact of edge port state changes.
PortFast suppresses TCN generation on edge link flaps, protecting the switch fabric from unnecessary MAC table age-out events.
Confirm the second correct operational benefit of PortFast.

Key Concept

Cisco STP PortFast Operational Behavior and TCN Suppression
Estimated Time:1m 15s
Rate this question

Topics

STP Port States and PortFast Benefits

More questions from this topic