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Catalyst 6500 Series Switch Command Reference—Release 8.4
OL-6244-01
Chapter 2 Catalyst 6500 Series Switch and ROM Monitor Commands
set spantree guard
set spantree guard
To enable or disable the spanning tree root guard or loop guard feature on a per-port basis, use the set
spantree guard command.
set spantree guard {none | root | loop} mod/port
Syntax Description
Defaults The default is root guard and loop guard are disabled.
Command Types Switch command.
Command Modes Privileged.
Usage Guidelines If you enable loop guard on a channel and the first link becomes unidirectional, loop guard will block
the entire channel until the affected port is removed from the channel.
You can use the root guard feature to prevent switches from becoming the root switch. The root guard
feature forces a port to become a designated port so that no switch on the other end of the link can
become a root switch.
When you enable root guard, it is automatically applied to all of the active instances or VLANs to which
that port belongs. When you disable root guard, it is disabled for the specified ports. If a port goes into
the root-inconsistent state, it automatically goes into the listening state. Disabling loop guard moves all
loop-inconsistent ports to the listening state.
When using the loop guard feature, follow these guidelines:
• Use care when enabling loop guard. Loop guard is useful only in those topologies where there are
blocked ports. Topologies where there are no blocked ports are loop free by definition and do not
need this feature to be enabled.
• Enable loop guard only on root and alternate root ports.
• Use loop guard mainly on access switches.
• You cannot enable loop guard on PortFast-enabled or dynamic VLAN ports.
• You cannot enable PortFast on loop guard-enabled ports.
• You cannot enable loop guard if root guard is enabled.
none Disables the spanning tree guard feature.
root Enables the root guard feature.
loop Enables the loop guard feature.
mod/port Number of the module and ports on the module.