PVST+

PVST+ Overview

Per-VLAN spanning tree protocol plus (PVST+) is a Cisco proprietary protocol that expands on the Spanning Tree Protocol (STP) by allowing a separate spanning tree for each VLAN. Cisco first developed this protocol as PVST, which worked with the Cisco ISL trunking protocol, and then later developed PVST+ which utilizes the 802.1Q trunking protocol.

{loadposition adposition5}By creating a separate spanning tree for each VLAN, data traffic from the different VLANs can take different paths across the network, as opposed to all switched traffic taking the same path. This can effectively create a load balancing situation and improve network efficiency.

By default the Cisco switches in Packet Tracer appear to be using PVST+ as the default implementation of spanning tre protocol.

IOS CLI Commands

Activate the PVST protocol:
switch(config)#spanning-tree mode pvst

Rig the root bridge election and force the switch to be the root bridge or backup root bridge by manually setting the bridge priority number to a number lower than default number of 32768.
switch(config)#spanning-tree vlan <num> priority <num>

Rig the root bridge election and force the switch to be the root bridge or backup root bridge by automatically using the root primary or root secondary designation. This command simply changes the bridge priority number to predefined numbers lower than the default
switch(config)#spanning-tree vlan <num> root primary
switch(config)#spanning-tree vlan <num> root secondary

Video Tutorials

In part 1, I configure switches to utilize PVST+ features within a multi VLAN network

If you want to follow along with the tutorial, download the PT starter file here: PVST-begin.zip

In part 2, I finish PVST+ configurations including Portfast and BPDUguard on the switch access ports

In part 3, I test the PVST+ network implementation by running ICMP Ping tests and show commands

Author: Dan

Dan teaches computer networking and security classes at Central Oregon Community College.

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