Administrator Guide

Version 8.2.1.0 Introduced the hardware shutdown-on-violation option.
Version 7.6.1.0 Introduced on the S-Series.
Version 7.5.1.0 Introduced on the C-Series.
Version 7.4.1.0 Added the optional Bridge Port Data Unit (BPDU) guard.
Version 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 misconfigured, 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 configured as an edge port, on a PVST switch, immediately
transitions to the forwarding state. Only ports connected to end-hosts should
be configured 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 configure loop guard on a port on which root guard is already
configured, 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 traffic from flowing through it.
For example, when Portfast BPDU guard and loop guard are both configured:
• If a BPDU is received from a remote device, BPDU guard places the port in an
Err-Disabled Blocking state and no traffic 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 traffic is forwarded on the port.
Example
Dell(conf-if-gi-1/1)#spanning-tree pvst vlan 3 cost 18000
Dell(conf-if-gi-1/1)#end
Dell(conf-if-gi-1/1)#show config
!
interface GigabitEthernet 1/1
no ip address
switchport
spanning-tree pvst vlan 3 cost 18000
no shutdown
Dell(conf-if-gi-1/1)#end
Dell#
1216
Per-VLAN Spanning Tree Plus (PVST+)