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Difficulty: MediumRapid PVST+ Spanning Tree Protocol Operations and Roles

A non-root switch running Rapid PVST+ receives BPDUs on multiple interfaces with identical path costs to the Root Bridge. Place the tie-breaker criteria in the correct sequential order (from first evaluated to last evaluated) that the switch uses to select its Root Port.

  1. 1Lowest cumulative root path cost
  2. 2Lowest sender Bridge ID (BID)
  3. 3Lowest sender port priority
  4. 4Lowest sender port number

Answer

The correct order of evaluation for selecting a Root Port in Rapid PVST+ is: 1) Lowest cumulative root path cost, 2) Lowest sender Bridge ID (BID), 3) Lowest sender port priority, and 4) Lowest sender port number.
When a non-root switch running Rapid PVST+ must select a Root Port from multiple candidate interfaces, it follows a strict four-step tie-breaker sequence: first, it checks for the lowest cumulative root path cost; second, the lowest sender Bridge ID (BID); third, the lowest sender port priority; and fourth, the lowest sender port number (interface ID).

Step-by-Step Solution

1
Evaluate Root Path Cost
The switch identifies paths with the lowest total cost to reach the Root Bridge.
STP primary objective is forwarding traffic over the shortest cost path.
2
Evaluate Sender Bridge ID
If path costs are equal across multiple candidate ports, compare neighboring switches' BIDs.
Breaks ties when multiple neighboring switches offer equal-cost paths.
3
Evaluate Sender Port Priority
If connected to the same neighbor over multiple links, compare the neighbor's port priority values.
Differentiates multiple links arriving from a single neighboring switch.
4
Evaluate Sender Port Number
If sender port priority values are identical (default 128), select the port connected to the lower sender port number.
Provides a definitive final tie-breaker for parallel connections.

Key Concept

Rapid PVST+ Root Port Selection Tie-Breaker Sequence
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Topics

Rapid PVST+ Spanning Tree Protocol Operations and Roles

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