Command Line Reference Guide

1354 | Spanning Tree Protocol (STP)
www.dell.com | support.dell.com
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. When you configure loop
guard on a port, an existing root guard configuration is disabled. When you configure root guard on a
port, an existing loop guard configuration is disabled.
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.