Examkin

Question

Difficulty: MediumSTP Port States and PortFast Benefits

An administrator connects a switch access port to a user workstation without enabling Cisco PortFast. Place the standard IEEE 802.1D Spanning Tree Protocol (STP) port states in the chronological sequence that the interface transitions through from initial physical link up to active user data forwarding.

  1. 1Blocking state: The port discards user frame traffic and learns no MAC addresses, but receives BPDUs to monitor for bridge loops.
  2. 2Listening state: The port discards user frame traffic and does not learn MAC addresses, but actively transmits and receives BPDUs to determine active topology roles.
  3. 3Learning state: The port continues to discard user data frames, but begins inspecting ingress frames to populate the switch MAC address table.
  4. 4Forwarding state: The port actively transmits and receives user data frames, updates MAC address tables, and processes BPDUs.

Answer

The correct chronological sequence of IEEE 802.1D STP port state transitions is: Blocking state, Listening state, Learning state, and Forwarding state.
In classic IEEE 802.1D Spanning Tree Protocol (STP), an edge port not configured with PortFast undergoes a strict 30-second convergence timer sequence: Blocking (initial loop prevention) -> Listening (15s, BPDU exchange and role selection) -> Learning (15s, MAC table population without data forwarding) -> Forwarding (active data packet processing).

Step-by-Step Solution

1
Identify initial link state
Port enters Blocking state
Standard 802.1D STP defaults unconfigured edge ports to Blocking to safely prevent loops during initial topology evaluation.
2
Transition to neighbor discovery and role determination
Port enters Listening state for 15 seconds (Forward Delay)
BPDUs are transmitted and processed to elect root bridges and designate root/designated port roles.
3
Prepare Layer 2 forwarding tables
Port enters Learning state for 15 seconds (Forward Delay)
MAC addresses are learned from incoming frames to populate the CAM table, mitigating flooding when forwarding begins.
4
Complete convergence to operational status
Port enters Forwarding state
With topology determined and MAC table initialized, user frames are actively forwarded.

Key Concept

IEEE 802.1D STP Port State Transitions
Estimated Time:1m 15s
Rate this question

Topics

STP Port States and PortFast Benefits

More questions from this topic