Examkin

Question

Difficulty: MediumRapid PVST+ Spanning Tree Protocol Operations and Roles

A network engineer is auditing an enterprise switch network operating with Rapid PVST+. Which two statements correctly describe the port roles and operational mechanisms of Rapid PVST+? (Select two.)

  1. An Alternate port serves as a backup path toward the Root Bridge and can immediately transition to the Root Port role if the active Root Port fails.Answer
  2. A Backup port provides redundant connectivity to a shared segment where another port on the same local switch is functioning as the Designated port.Answer
  3. C
    Bridge priorities for a VLAN can be set in custom increments of 1024 because of the 12-bit System ID Extension field.
  4. D
    Enabling PortFast on switch-to-switch trunk links is required to allow Rapid PVST+ proposal-agreement handshakes to bypass traditional STP timers.

Answer

The correct statements are that an Alternate port serves as a backup path toward the Root Bridge and can transition immediately upon root port failure, and that a Backup port provides redundant connectivity to a shared segment where another port on the same switch is the Designated port.
Rapid PVST+ defines explicit port roles to achieve rapid convergence. An Alternate port provides a backup path to the root bridge and takes over immediately if the root port fails. A Backup port provides a redundant link to a shared collision domain where another interface on the same switch is already the designated port.

Step-by-Step Solution

1
Evaluate the definition and convergence behavior of Rapid PVST+ Alternate ports.
Alternate ports receive BPDUs from other switches and act as backup root paths, transitioning immediately to root ports without forwarding delays during failures.
Rapid PVST+ optimizes convergence by allowing pre-calculated alternate paths to become root ports instantaneously.
2
Evaluate the definition and function of Rapid PVST+ Backup ports.
Backup ports receive BPDUs from another interface on the exact same switch on a shared medium where the local switch is designated.
This redundant port role specifically addresses self-loop scenarios on shared collision domains.
3
Verify bridge priority calculation rules for Rapid PVST+.
Configurable base priorities must be multiples of 4096 due to the 4-bit priority portion of the extended bridge ID.
Increments of 1024 are invalid and will be rejected by Cisco IOS CLI.
4
Analyze PortFast placement guidelines and Rapid PVST+ handshake mechanics.
Proposal-agreement handshakes function on point-to-point links automatically; PortFast is restricted to edge ports.
Misconfiguring PortFast on trunks bypasses standard loop protection mechanisms.

Key Concept

Rapid PVST+ Port Roles and Operational Characteristics
Rate this question

Topics

Rapid PVST+ Spanning Tree Protocol Operations and Roles

More questions from this topic