Users Guide

Version Description
7.4.1.0 Added the optional Bridge Port Data Unit (BPDU) guard.
6.2.1.1 Introduced.
Usage Information
The BPDU guard option prevents the port from participating in an active STP topology in case a BPDU appears on
a port unintentionally, or is miscongured, or is subject to a DOS attack. This option places the port into the Error
Disable state if a BPDU appears, and a message is logged so that the administrator can take corrective action.
NOTE: A port congured as an edge port, on a PVST switch, immediately transitions to the forwarding
state. Only ports connected to end-hosts should be congured as an edge port. Consider an edge port
similar to a port with a spanning-tree portfast enabled.
If you do not enable shutdown-on-violation, BPDUs are still sent to the route process module (RPM) CPU.
You cannot enable root guard and loop guard at the same time on a port. For example, if you congure
loop guard on a port on which root guard is already congured, the following error message is displayed: %
Error: RootGuard is configured. Cannot configure LoopGuard.
When used in a PVST+ network, loop guard is performed per-port or per-port channel at a VLAN level. If no
BPDUs are received on a VLAN interface, the port or port-channel transitions to a Loop-Inconsistent (blocking)
state only for this VLAN.
Enabling Portfast BPDU guard and loop guard at the same time on a port results in a port that remains in a
Blocking state and prevents trac from owing through it. For example, when Portfast BPDU guard and loop
guard are both congured:
• If a BPDU is received from a remote device, BPDU guard places the port in an Err-Disabled Blocking state and
no trac is forwarded on the port.
• If no BPDU is received from a remote device, loop guard places the port in a Loop-Inconsistent Blocking state
and no trac is forwarded on the port.
Example
Dell(conf-if-te-1/1/1/1)# spanning-tree pvst vlan 3 cost 1800
Dell(conf-if-te-1/1/1/1)# end
Dell(conf-if-te-1/1/1/1)# show config
!
interface TenGigabitEthernet 1/1/1/1
no ip address
switchport
spanning-tree pvst vlan 3 cost 18000
no shutdown
Dell(conf-if-te-1/1/1/1)# end
Dell#
Related Commands
• show spanning-tree pvst — views the PVST+ conguration.
Per-VLAN Spanning Tree Plus (PVST+) 1207