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Difficulty: EasySTP Port States and PortFast Benefits

A switch port running standard IEEE 802.1D Spanning Tree Protocol (STP) detects an active connection to an end device. Arrange the STP port states in the correct sequential order from initial physical link detection to fully active data frame forwarding.

  1. 1Blocking State
  2. 2Listening State
  3. 3Learning State
  4. 4Forwarding State

Answer

The correct sequential progression of 802.1D STP port states is: Blocking State, Listening State, Learning State, and Forwarding State.
Under standard IEEE 802.1D, a newly connected port progresses through four distinct states to ensure network loops do not form: Blocking (drops data, listens for BPDUs), Listening (discards data, sends/receives BPDUs, no MAC learning), Learning (discards data, learns MAC addresses), and finally Forwarding (forwards data frames normally).

Step-by-Step Solution

1
Identify the initial state upon link up.
The port starts in the Blocking state to avoid creating temporary switching loops while BPDU information is evaluated.
802.1D requires all non-designated/non-root ports or newly activated ports to block user traffic initially.
2
Determine the transition following BPDU analysis.
The port transitions to the Listening state for the duration of the Forward Delay timer (15 seconds).
During Listening, the port sends and receives BPDUs to elect root bridges and assign port roles without forwarding traffic or learning MAC addresses.
3
Determine the step after topology role determination.
The port enters the Learning state for a second Forward Delay timer interval (15 seconds).
Learning allows the switch to build its MAC address table from source MACs in incoming frames to minimize flooding when forwarding begins.
4
Identify the final operational state.
The port reaches the Forwarding state.
Once the learning phase expires without topology conflicts, the interface fully forwards user data frames and processes BPDUs.

Key Concept

802.1D Spanning Tree Protocol Port State Transitions
Estimated Time:45s
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Topics

STP Port States and PortFast Benefits

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