Concept Guide

priority priority Enter keyword priority then a value in increments of 16 as the priority. The range is
from 0 to 240. The default is 128.
rootguard Enter the keyword rootguard to enable root guard on an RSTP port or port-channel
interface.
Defaults Not congured.
Command Modes INTERFACE
Supported Modes Full–Switch
Command History
Version Description
9.9(0.0) Introduced on the FN IOM.
8.3.16.1 Introduced on the MXL 10/40GbE Switch IO Module.
Usage Information
The BPDU guard option prevents the port from participating in an active STP topology in case a BPDU appears
on a port unintentionally, or is miscongured, or is subject to a DOS attack. This option places the port into an Error
Disable state if a BPDU appears and a message is logged so that the administrator can take corrective action.
NOTE: A port congured as an edge port, on an RSTP switch, immediately transitions to the Forwarding
state. Only congure ports connected to end-hosts as edge ports. Consider an edge port similar to a
port with a spanning-tree portfast enabled.
If you do not enable shutdown-on-violation, BPDUs are still sent to the RPM CPU.
You cannot enable STP root guard and loop guard 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 displays: % Error:
RootGuard is configured. Cannot configure LoopGuard
.
Enabling Portfast BPDU guard and loop guard at the same time on a port results 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.
Example
Dell(conf)#interface gigabitethernet 4/0
Dell(conf-if-gi-4/0)#spanning-tree rstp edge-port
Dell(conf-if-gi-4/0)#show config
!
interface GigabitEthernet 4/0
no ip address
switchport
spanning-tree rstp edge-port
no shutdown
Dell#
Rapid Spanning Tree Protocol (RSTP) 1139