Hands-On Lab: Assigning Spanning Tree Priority to Multiple VLANs Simultaneously

Lab Objective

Configure a single switch as the root bridge for a range of VLANs using one command that applies to all of them simultaneously, rather than issuing a separate priority command for each individual VLAN, and verify the priority applied correctly to every VLAN in the range.

Lab Purpose

Cisco's default Spanning Tree implementation, PVST+, runs a completely separate Spanning Tree instance for every VLAN, each with its own independent root bridge election. On a switch supporting dozens of VLANs, configuring priority one VLAN at a time is tedious — the VLAN range syntax solves this directly.

Lab Topology

Switch1 (intended root for VLANs 10-50)

VLANs 10, 20, 30, 40, and 50 already exist
on the switch and are carried on its trunk links

Task 1: Verify Current Priority Across the VLAN Range

Check the current default priority for VLANs 10, 20, 30, 40, and 50 individually.

Task 2: Configure Priority for All Five VLANs in One Command

Using a single command with a VLAN range, set the priority for VLANs 10 through 50 to 4096.

Task 3: Verify the Priority Applied to Every VLAN in the Range

Check each VLAN individually and confirm all five now show the new priority.

Task 4: Confirm Root Bridge Status Per VLAN

Confirm the switch is recognized as root for each of the five VLANs independently.

Solution and Verification

Switch1# show spanning-tree vlan 10 | include Priority
Bridge ID  Priority    32768

Switch1# show spanning-tree vlan 50 | include Priority
Bridge ID  Priority    32768
-- Every VLAN currently sits at the default,
-- and would each need its own individual
-- command without using a range

Switch1(config)# spanning-tree vlan 10,20,30,40,50 priority 4096

-- A hyphenated range also works identically:
-- spanning-tree vlan 10-50 priority 4096
-- (matches only VLANs that actually exist
--  within that numeric range)

Switch1# show spanning-tree vlan 10 | include Priority
Bridge ID  Priority    4096

Switch1# show spanning-tree vlan 20 | include Priority
Bridge ID  Priority    4096

Switch1# show spanning-tree vlan 50 | include Priority
Bridge ID  Priority    4096
-- All five VLANs updated from a single command

Switch1# show spanning-tree vlan 30 | include Root
Root ID    Priority    4096
           This bridge is the root

Switch1# show spanning-tree vlan 40 | include Root
Root ID    Priority    4096
           This bridge is the root
-- Confirmed root for each VLAN independently,
-- since PVST+ maintains a completely separate
-- election and topology per VLAN

Key Takeaway

Because PVST+ runs an entirely independent Spanning Tree instance per VLAN, changing priority for one VLAN never affects any other — the VLAN range syntax is purely a configuration-time convenience for applying the identical change across many instances at once, not a sign that those VLANs somehow share a single underlying tree.