Cisco CCNA Spanning Tree Protocol (STP) 4

Question 1

What does the STP BPDU Guard feature do when it detects a BPDU on a PortFast-enabled port?

Accepted Answer

It immediately puts the port into err-disabled state

Answer

BPDU Guard places the port in err-disabled state when a BPDU is received, protecting the network from unauthorized switches.

Question 2

In a network running PVST+, how many STP instances are maintained?

Accepted Answer

One per VLAN

Answer

PVST+ (Per-VLAN Spanning Tree Plus) maintains a separate STP instance for each VLAN, allowing different root bridges per VLAN.

Question 3

Which STP enhancement prevents a port from becoming a designated port if it stops receiving BPDUs, protecting against unidirectional link failures?

Accepted Answer

Loop Guard

Answer

Loop Guard places a port in a loop-inconsistent blocking state if BPDUs stop arriving, preventing it from incorrectly transitioning to Forwarding.

Question 4

A switch administrator wants to ensure a specific switch always becomes the root bridge for VLAN 1. Which command achieves this?

Accepted Answer

spanning-tree vlan 1 root primary

Answer

The 'spanning-tree vlan 1 root primary' command sets the bridge priority to ensure this switch wins the root bridge election.

Question 5

What is the maximum number of hops allowed in an MST (Multiple Spanning Tree) region before a BPDU is discarded?

Accepted Answer

20

Answer

MST uses a max hops field (default 20) instead of the traditional max age timer to limit BPDU propagation within a region.

Cisco CCNA Practice Test