HOW PVST WORKS (Per-VLAN Spanning Tree Explained Simply) CCNA Switching #networking #ccna

HOW PVST WORKS (Per-VLAN Spanning Tree Explained Simply) CCNA Switching

PVST stands for Per-VLAN Spanning Tree. It is a Cisco-proprietary Spanning Tree Protocol implementation that runs a separate Spanning Tree instance for each VLAN on a switch.

In practical terms, PVST allows different VLANs to have different Layer-2 topologies and different root switches, giving more flexibility and better load-balancing than traditional STP.

What PVST Does

On a switch from Cisco:

Each VLAN runs its own STP process

Each VLAN can elect a different root bridge

Ports can be:

Forwarding for one VLAN

Blocking for another VLAN

This means traffic from different VLANs can take different physical paths through the network.

Why PVST Is Useful

Traditional STP (IEEE 802.1D):

One STP instance for the entire switch

One root bridge for all VLANs

PVST:

One STP instance per VLAN

Multiple root bridges possible

Benefits:

Better utilization of redundant links

Per-VLAN traffic engineering

Improved resilience and control

Simple Example

Imagine two distribution switches:

Switch A is root for VLAN 10

Switch B is root for VLAN 20

Traffic pattern:

VLAN 10 prefers paths toward Switch A

VLAN 20 prefers paths toward Switch B

Both uplinks are actively used instead of one sitting idle.

PVST Variants You’ll Encounter
Name Description
PVST Original Cisco per-VLAN STP (based on 802.1D)
PVST+ Enhanced version that interoperates with standard 802.1D
Rapid PVST+ Per-VLAN version of Rapid Spanning Tree (802.1w)
Key Characteristics

Uses 802.1Q VLAN tagging

Sends STP BPDUs per VLAN

Cisco-specific (not standard across all vendors)

Quick Configuration Example
Switch(config)# spanning-tree mode pvst
or (more common today):

Switch(config)# spanning-tree mode rapid-pvst

Short Summary

PVST = One Spanning Tree per VLAN.
It allows independent topology control and load-balancing for each VLAN on Cisco switches.
If you want clean explanations with visuals and real-world logic, this video is for you!

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