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Cisco ME 3400 Ethernet Access Switch Command Reference
OL-9640-10
Chapter 2 Cisco ME 3400 Ethernet Access Switch Cisco IOS Commands
spanning-tree guard
spanning-tree guard
Use the spanning-tree guard interface configuration command on a network node interface (NNI) or
enhanced network interface (ENI) with STP enabled to enable root guard or loop guard on all the VLANs
associated with the selected NNI. Root guard restricts which interface is allowed to be the spanning-tree
root port or the path-to-the root for the switch. Loop guard prevents alternate or root ports from
becoming designated ports when a failure creates a unidirectional link. Use the no form of this command
to return to the default setting.
spanning-tree guard {loop | none | root}
no spanning-tree guard
Syntax Description
Defaults Root guard is disabled.
Loop guard is configured according to the spanning-tree loopguard default global configuration
command (globally disabled).
Command Modes Interface configuration
Command History
Usage Guidelines Spanning Tree Protocol (STP) is not supported on user network interfaces (UNIs). You can configure
spanning-tree guard only on NNIs or on enhanced network interfaces ENIs on which STP has been
enabled. To set a port as an NNI or ENI, enter the port-type {nni | eni} interface configuration
command. To enable STP on an ENI, enter the spanning-tree interface configuration command.
You can enable root guard or loop guard when the switch is operating in the per-VLAN spanning-tree
plus (PVST+), the rapid-PVST+, or the multiple spanning-tree (MST) mode.
When root guard is enabled, if spanning-tree calculations cause an interface to be selected as the root
port, the interface transitions to the root-inconsistent (blocked) state to prevent the customer’s switch
from becoming the root switch or being in the path to the root. The root port provides the best path from
the switch to the root switch.
When the no spanning-tree guard or the no spanning-tree guard none command is entered, root guard
is disabled for all VLANs on the selected NNI. If this interface is in the root-inconsistent (blocked) state,
it automatically transitions to the listening state.
loop Enable loop guard.
none Disable root guard or loop guard.
root Enable root guard.
Release Modification
12.2(25)EX This command was introduced.
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