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Question

Difficulty: MediumRapid PVST+ Spanning Tree Protocol Operations and Roles

A switch running Rapid PVST+ receives BPDUs across multiple active interfaces and must determine which port will assume the Root Port role for a specific VLAN. Place the decision criteria evaluated by the switch in the correct sequential order, starting from the first criterion evaluated to the last.

  1. 1Lowest cumulative Root Path Cost to the Root Bridge
  2. 2Lowest upstream neighbor Bridge ID (Sender BID)
  3. 3Lowest upstream neighbor Port ID (Sender Port ID)
  4. 4Lowest local Port ID on the receiving switch

Answer

The correct sequence for selecting a Rapid PVST+ Root Port is: 1. Lowest cumulative Root Path Cost to the Root Bridge, 2. Lowest upstream neighbor Bridge ID (Sender BID), 3. Lowest upstream neighbor Port ID (Sender Port ID), 4. Lowest local Port ID on the receiving switch.
When selecting a Root Port, a Rapid PVST+ non-root switch evaluates received BPDU criteria in a strict hierarchical order: cumulative Root Path Cost first, followed by sender Bridge ID, sender Port ID, and finally local Port ID.

Step-by-Step Solution

1
Evaluate path efficiency
Identify the interface with the lowest cumulative cost to reach the Root Bridge.
STP prioritizes path efficiency before comparing device or port identifiers.
2
Evaluate upstream device identity
If path costs are equal, compare the Bridge IDs of the neighboring switches sending the BPDUs.
Connecting to a neighbor with a lower Bridge ID takes precedence when costs match.
3
Evaluate upstream port identity
If connected via multiple links to the same upstream switch, compare the Port IDs (port priority + port number) transmitted by the neighbor.
The upstream switch's lower sending port ID breaks ties for parallel links to the same neighbor.
4
Evaluate local port identity
If all received BPDU fields are identical, compare the local receiving switch's Port IDs.
The local switch uses its own lowest port ID as the final deterministic tie-breaker.

Key Concept

Rapid PVST+ Root Port Selection Algorithm
Estimated Time:1m 30s
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Topics

Rapid PVST+ Spanning Tree Protocol Operations and Roles

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