STP Field Notes

April 13, 2026

Configuration, verification, and operational behavior of Spanning Tree

bash

conf t
spanning-tree mode mst
spanning-tree mst configuration
name CCNPv8
revision 2
instance 1 vlan 2,3
instance 2 vlan 3,4
!show pending
exit
end

Spanning Tree Protocol (STP) Configuration Cheatsheet

1. Verify STP Configuration

Show STP Information

bash

show spanning-tree

Show STP Status for a Specific VLAN

bash

show spanning-tree vlan [vlan-id]

Show STP Details on Interfaces

bash

show spanning-tree interface [interface-id]

2. Configure STP Modes

Enable STP (Default for most Cisco switches)

bash

no spanning-tree vlan [vlan-id]

Enable PVST+ (Default on Cisco Switches)

bash

spanning-tree mode pvst

Enable Rapid PVST+

bash

spanning-tree mode rapid-pvst

Enable MST

bash

spanning-tree mode mst

3. Adjust STP Parameters

Set Bridge Priority

bash

spanning-tree vlan [vlan-id] priority [value]

Default Range: 0-61440, increments of 4096
Default Value: 32768

Set Bridge Cost

bash

spanning-tree cost [value]

Default Values: Varies by interface speed (e.g., 100 Mbps = 19)

Set Hello Time

bash

spanning-tree hello-time [seconds]

Default Value: 2 seconds

Set Forward Delay

bash

spanning-tree forward-delay [seconds]

Default Value: 15 seconds

Set Max Age

bash

spanning-tree max-age [seconds]

Default Value: 20 seconds

Set Root Bridge Priority

bash

spanning-tree vlan [vlan-id] root primary

Or use root secondary for a secondary root bridge

Configure Portfast

bash

spanning-tree portfast

Use spanning-tree portfast trunk for trunk ports

Configure BPDU Guard

bash

spanning-tree bpduguard enable

Configure BPDU Filter

bash

spanning-tree bpdufilter enable

Configure Edge Port (PortFast)

bash

spanning-tree portfast edge

4. MST Configuration

Define MST Instances

bash

spanning-tree mst configuration
instance [instance-id] vlan [vlan-id]
name [name]
revision [number]

Map VLANs to MST Instances

bash

instance [instance-id] vlan [vlan-list]

Verify MST Configuration

bash

show spanning-tree mst configuration

Examples

Configure PVST+ and Set Bridge Priority

bash

Switch# configure terminal
Switch(config)# spanning-tree mode pvst
Switch(config)# spanning-tree vlan 1 priority 4096

Configure PortFast on an Interface

bash

Switch# configure terminal
Switch(config)# interface GigabitEthernet0/1
Switch(config-if)# spanning-tree portfast

Configure MST Instances

bash

Switch# configure terminal
Switch(config)# spanning-tree mst configuration
Switch(config-mst)# instance 1 vlan 10,20
Switch(config-mst)# instance 2 vlan 30
Switch(config-mst)# name MST-PROTOCOL
Switch(config-mst)# revision 1

Set Root Bridge Priority

bash

Switch# configure terminal
Switch(config)# spanning-tree vlan 1 root primary

Key Concepts

Root Bridge: The central switch with the lowest Bridge ID.
Port Cost: Determines the best path to the root bridge; lower costs are preferred.
BPDU (Bridge Protocol Data Unit): Messages exchanged between switches to maintain STP.
PortFast: Allows ports to transition to the forwarding state immediately, used for end-user devices.
BPDU Guard: Prevents unauthorized devices from affecting the STP topology.
MSTP: Supports multiple spanning trees, allowing different STP instances per VLAN.