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Difficulty: MediumSpanning Tree Protocol Operations

A network administrator is evaluating the converged state of an enterprise network running standard IEEE 802.1D Spanning Tree Protocol (STP) across multiple interconnected switches. Which of the following statements correctly describe port roles and operational behavior in a fully converged 802.1D STP topology? (Select TWO.)

  1. Every non-root switch elects exactly one Root Port, which is the local port providing the lowest cumulative path cost to the Root Bridge.Answer
  2. B
    During root bridge election, switches select the device with the highest numerical Bridge Priority value as the Root Bridge.
  3. Each active network segment selects one Designated Port, which forwards traffic downstream away from the Root Bridge.Answer
  4. D
    Trunk links with native VLAN mismatches bypass standard STP timer states to immediately isolate broadcast loops.
  5. E
    If two switches share the default Bridge Priority value, the switch with the higher MAC address wins the Root Bridge election.

Answer

The correct statements are that every non-root switch elects exactly one Root Port offering the lowest cumulative path cost to the Root Bridge, and that each active network segment selects one Designated Port to forward traffic downstream.
In standard 802.1D STP, every non-root switch must select exactly one Root Port based on the lowest cumulative root path cost. Additionally, every active network segment between switches must select one Designated Port to handle forwarding for that segment without creating loops.

Step-by-Step Solution

1
Analyze Root Port selection criteria in standard STP.
Confirm that each non-root switch designates exactly one interface facing the Root Bridge with the minimum cumulative path cost as its Root Port.
Root Ports establish the single active path from non-root switches back to the Root Bridge.
2
Analyze Designated Port selection across network segments.
Confirm that each network segment (link) has exactly one Designated Port placed in the Forwarding state.
Designated Ports handle frame transmission away from the Root Bridge onto individual LAN segments.
3
Evaluate root bridge election tiebreaker and priority logic to rule out incorrect options.
STP always prefers lower numerical values for both Bridge Priority and MAC address.
Higher numerical priority values or MAC addresses lose the Root Bridge election.

Key Concept

Spanning Tree Protocol Port Roles and Election Logic
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Topics

Spanning Tree Protocol Operations

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