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Difficulty: MediumRapid PVST+ Spanning Tree Protocol Operations and Roles

A Cisco switch running Rapid PVST+ receives BPDUs across multiple candidate paths leading toward the Root Bridge. Place the tie-breaking criteria evaluated by the switch to elect its Root Port in the correct sequential order from first (1st) to last (4th).

  1. 1Select the path with the lowest cumulative Root Path Cost to the Root Bridge.
  2. 2Select the path via the neighbor with the lowest sender Bridge ID (BID).
  3. 3Select the path with the lowest sender Port ID (Port Priority plus Port Number).
  4. 4Select the interface with the lowest local (receiver) Port ID (Port Priority plus Port Number).

Answer

The correct sequence for Rapid PVST+ Root Port election is: 1) Lowest cumulative Root Path Cost, 2) Lowest sender Bridge ID, 3) Lowest sender Port ID, and 4) Lowest local (receiver) Port ID.
Rapid PVST+ follows a strict four-step decision tree to select a single Root Port on a non-root switch: 1) Lowest cumulative Root Path Cost, 2) Lowest sender Bridge ID (BID), 3) Lowest sender Port ID, and 4) Lowest local (receiver) Port ID.

Step-by-Step Solution

1
Evaluate incoming BPDU path cost values
Identify the link offering the lowest cumulative Root Path Cost to the Root Bridge
Rapid PVST+ prioritizes overall network topology bandwidth and cost over local port attributes.
2
Evaluate upstream switch Bridge IDs if path costs are equal
Select the neighbor switch that has the lowest BID value (Priority + System ID Extension + MAC Address)
When path costs match, preference is given to paths traversing higher-priority upstream bridges.
3
Evaluate sender Port IDs if BIDs are equal
Select the interface connected to the upstream neighbor port with the lowest Port ID
Multiple parallel links to the same upstream neighbor share identical Root Path Costs and sender BIDs.
4
Evaluate local receiver Port IDs if sender Port IDs are identical
Select the local receiving interface with the lowest Port ID
Serves as the final deterministic tie-breaker when connecting through an unmanaged hub or shared medium.

Key Concept

Rapid PVST+ Root Port Selection Tie-Breaker Order
Estimated Time:1m 15s
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Topics

Rapid PVST+ Spanning Tree Protocol Operations and Roles

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