STP Configuration Examples

Here are practical configuration examples for enabling and configuring Spanning Tree Protocol on Cisco switches:

Basic STP Configuration

# Enter global configuration mode
Switch> enable
Switch# configure terminal

# Enable Spanning Tree (enabled by default on Cisco)
Switch(config)# spanning-tree mode pvst
# Options: pvst (Per-VLAN STP), rapid-pvst, mst

# Set bridge priority to influence root bridge election
# Lower priority = more likely to become root (default: 32768)
Switch(config)# spanning-tree vlan 1 priority 4096
# Priority must be in increments of 4096 (0-61440)

# Or use shortcut to make this switch root
Switch(config)# spanning-tree vlan 1 root primary

# Configure port cost (influences path selection)
Switch(config)# interface gigabitEthernet 0/1
Switch(config-if)# spanning-tree cost 4
Switch(config-if)# exit

# Configure port priority (lower = preferred)
Switch(config)# interface gigabitEthernet 0/2
Switch(config-if)# spanning-tree port-priority 64
Switch(config-if)# exit

Rapid STP (RSTP) Configuration

# Enable Rapid Per-VLAN Spanning Tree
Switch(config)# spanning-tree mode rapid-pvst

# Configure PortFast for access ports (skips listening/learning)
Switch(config)# interface fastEthernet 0/5
Switch(config-if)# spanning-tree portfast
Switch(config-if)# exit

# Enable BPDU Guard (shuts port if BPDU received)
Switch(config)# interface fastEthernet 0/5
Switch(config-if)# spanning-tree bpduguard enable
Switch(config-if)# exit

Verification Commands

# View spanning tree status
Switch# show spanning-tree

# View STP for specific VLAN
Switch# show spanning-tree vlan 1

# View brief summary
Switch# show spanning-tree summary

# View root bridge information
Switch# show spanning-tree root

# View interface STP details
Switch# show spanning-tree interface gigabitEthernet 0/1

# View STP topology changes
Switch# show spanning-tree detail

Sample Output

Switch# show spanning-tree vlan 1

VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    4097
             Address     0019.e86a.6f80
             This bridge is the root
             
  Bridge ID  Priority    4097
             Address     0019.e86a.6f80
             
Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- ----
Gi0/1            Desg FWD 4         128.1    P2p
Gi0/2            Desg FWD 4         128.2    P2p

Key Status Codes:

• FWD = Forwarding
• BLK = Blocking
• LRN = Learning
• LIS = Listening

These configurations ensure your network has loop prevention while maintaining redundancy!