Command Reference Guide

Spanning Tree Protocol (STP) | 1429
Command
History
Usage
Information
If you enable portfast bpduguard on an interface and the interface receives a BPDU, the
software disables the interface and sends a message stating that fact. The port is in
ERR_DISABLE mode, yet appears in the
show interface commands as enabled. If
shutdown-on-violation is not enabled, BPDUs will still be sent to the RPM CPU.
STP loop guard and root guard are supported on a port or port-channel enabled in any
Spanning Tree mode: Spanning Tree Protocol (STP), Rapid Spanning Tree Protocol (RSTP),
Multiple Spanning Tree Protocol (MSTP), and Per-VLAN Spanning Tree Plus (PVST+).
Root guard is supported on any STP-enabled port or port-channel except when used as a
stacking port. When enabled on a port, root guard applies to all VLANs configured on the
port.
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.
Do not enable Portfast BPDU guard and loop guard at the same time on a port. Enabling both
features may result 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.
To display the type of STP guard (Portfast BPDU, root, or loop guard) enabled on a port,
enter the show spanning-tree 0 command.
Version 8.3.10.1 Introduced the loopguard and rootguard options on the S4810.
Version 8.4.2.1 Introduced the loopguard and rootguard options on the E-Series TeraScale,
C-Series, and S-Series.
Version 8.3.7.0 Introduced on S4810
Version 8.2.1.0 Introduced shutdown-on-violation option.
Version 7.7.1.0 Introduced on S-Series.
Version 7.5.1.0 Introduced on C-Series.
Version 6.2.1.1 Introduced.