Administrator Guide

Version Description
8.3.10.1 Introduced the loopguard and rootguard options on the S4810.
8.4.2.1 Introduced the loopguard and rootguard options on the E-Series, C-Series, and S-
Series.
8.3.7.0 Introduced on the S4810.
8.2.1.0 Introduced the shutdown-on-violation option.
7.7.1.0 Introduced on the S-Series.
7.5.1.0 Introduced on the C-Series.
6.2.1.1 Introduced on the E-Series.
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 you do not enable shutdown-on-violation, BPDUs are still 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.
1586
Spanning Tree Protocol (STP)