STP Basics and Concepts 4

Question 1

Which STP enhancement runs a separate spanning tree instance per VLAN on Cisco switches?

Accepted Answer

PVST+

Answer

Per-VLAN Spanning Tree Plus (PVST+) runs an independent STP instance for each VLAN, allowing load balancing across redundant links.

Question 2

In STP, what does the 'port ID' consist of?

Accepted Answer

Port priority and port number

Answer

The port ID is an 8-bit priority (default 128) combined with the port number, used as a final tiebreaker in root port selection.

Question 3

What is the STP behavior when two switches are connected by two parallel links and one switch is non-root?

Accepted Answer

One port becomes root port; the other is blocked

Answer

STP blocks one of the redundant ports on the non-root switch to eliminate the loop, keeping only the lowest-cost path active.

Question 4

Which STP timer defines how frequently the root bridge sends BPDUs?

Accepted Answer

Hello time

Answer

The hello time (default 2 seconds) controls the interval at which the root bridge generates and sends configuration BPDUs.

Question 5

What is the effect of configuring PortFast on a switch port?

Accepted Answer

The port skips Listening and Learning and goes directly to Forwarding

Answer

PortFast bypasses the 30-second STP convergence delay by moving end-device ports directly to the Forwarding state.

(STP) Spanning Tree Protocol Practice Test