Users Guide

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 congured on the port.
STP root guard and loop guard cannot be enabled at the same time on a port. For example, if you congure loop
guard on a port on which root guard is already congured, 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 trac from owing through it. For example, when Portfast
BPDU guard and loop guard are both congured:
• If a BPDU is received from a remote device, BPDU guard places the port in an Err-Disabled Blocking state and
no trac 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 trac 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.
Spanning Tree Protocol (STP) 1485