14-7
Software Configuration Guide—Release 12.2(25)SG
OL-7659-03
Chapter14 Configuring STP Features
Overview of BPDU Guard
Overview of BPDU Guard
Spanning Tree BPDU guard shuts down PortFast-configured interfaces that receive BPDUs, rather than
putting them into the spanning tree blocking state. In a valid configuration, PortFast-configured
interfaces do not receive BPDUs. Reception of a BPDU by a PortFast-configured interface signals an
invalid configuration, such as connection of an unauthorized device. BPDU guard provides a secure
response to invalid configurations, because the administrator must manually put the interface back in
service.
Note When the BPDU guard feature is enabled, spanning tree applies the BPDU guard feature to all
PortFast-configured interfaces.
Enabling BPDU Guard
To enable BPDU guard to shut down PortFast-configured interfaces that receive BPDUs, perform this
task:
This example shows how to enable BPDU guard:
Switch(config)# spanning-tree portfast bpduguard
Switch(config)# end
Switch#
This example shows how to verify the BPDU configuration:
Switch# show spanning-tree summary totals
Root bridge for: none.
PortFast BPDU Guard is enabled
Etherchannel misconfiguration guard is enabled
UplinkFast is disabled
BackboneFast is disabled
Default pathcost method used is short
Name Blocking Listening Learning Forwarding STP Active
-------------------- -------- --------- -------- ---------- ----------
34 VLANs 0 0 0 36 36
Switch#
Command Purpose
Step1 Switch(config)# [no] spanning-tree portfast
bpduguard
Enables BPDU guard on all the switch’s
PortFast-configured interfaces.
You can use the no keyword to disable BPDU guard.
Step2 Switch(config)# end Exits configuration mode.
Step3 Switch# show spanning-tree summary totals Verifies the BPDU configuration.