Reference Guide

1474 | Spanning Tree Protocol (STP)
www.dell.com | support.dell.com
Command Modes
INTERFACE
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 8.3.19.0 Introduced on S4820T
Version 8.3.19.1 Introduced the loopguard and rootguard options on the S4820T.
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.