Reference Guide

Command History
Version 8.3.11.1 Introduced on the Z9000.
Version 8.4.2.1 Added support for the optional guard keyword on the C-Series, S-
Series, and E-Series TeraScale.
Version 8.3.7.0 Introduced on the S4810.
Version 8.2.1.0 Introduced the hardware shutdown-on-violation options.
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 on the E-Series.
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 an 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 an RSTP switch, immediately transitions to
the Forwarding state. You should only configure ports connected to end-hosts as edge
ports. 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 RPM CPU.
You cannot enable STP 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 displays: % Error: RootGuard is configured. Cannot
configure LoopGuard.
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
FTOS(conf)#interface gigabitethernet 4/0
FTOS(conf-if-gi-4/0)#spanning-tree rstp edge-port
FTOS(conf-if-gi-4/0)#show config
!
interface GigabitEthernet 4/0
no ip address
switchport
spanning-tree rstp edge-port
no shutdown
FTOS#
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