Reference Guide
Rapid Spanning Tree Protocol (RSTP) | 1315
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 mis-configured, 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.
If
shutdown-on-violation is not enabled, BPDUs will still be sent to the RPM CPU.
STP root guard and loop guard cannot be enabled 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.
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#
tc-flush-standard
c e s
Enable the MAC address flushing upon receiving every topology change notification.
Version 7.6.1.0 Support added for S-Series
Version 7.5.1.0 Support added for C-Series
Version 7.4.1.0 Added the optional Bridge Port Data Unit (BPDU) guard.
Version 6.2.1.1 Introduced for E-Series
Note: A port configured as an edge port, on an RSTP switch, will immediately
transition to the forwarding state. Only ports connected to end-hosts should be
configured as edge ports. Consider an edge port similar to a port with a
spanning-tree portfast enabled.