Spanning-Tree Guard - Cisco ME 3400 Command Reference Manual

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.
Syntax Description loop
none
root
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 Release
12.2(25)EX
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.
Cisco ME 3400 Ethernet Access Switch Command Reference
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spanning-tree guard {loop | none | root}
no spanning-tree guard
Enable loop guard.
Disable root guard or loop guard.
Enable root guard.
Modification
This command was introduced.
Chapter 2 Cisco ME 3400 Ethernet Access Switch Cisco IOS Commands
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