Cisco 3020 - Cisco Catalyst Blade Switch Specifications download pdf (Page 473)

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Cisco Catalyst Blade Switch for HP Command Reference

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Chapter 2 Cisco Catalyst Blade Switch 3020 for HP Cisco IOS Commands

spanning-tree guard

Use the spanning-tree guard interface configuration command to enable root guard or loop guard on

all the VLANs associated with the selected interface. 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 You can enable root guard or loop guard when the switch is operating in the per-VLAN spanning-tree

plus (PVST+), 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 interface. If this interface is in the root-inconsistent (blocked)

state, it automatically transitions to the listening state.

Do not enable root guard on interfaces that will be used by the UplinkFast feature. With UplinkFast, the

backup interfaces (in the blocked state) replace the root port in the case of a failure. However, if root

guard is also enabled, all the backup interfaces used by the UplinkFast feature are placed in the

root-inconsistent state (blocked) and prevented from reaching the forwarding state. The UplinkFast

feature is not available when the switch is operating in the rapid-PVST+ or MST mode.

Loop guard is most effective when it is configured on the entire switched network. When the switch is

operating in PVST+ or rapid-PVST+ mode, loop guard prevents alternate and root ports from becoming

designated ports, and spanning tree does not send bridge protocol data units (BPDUs) on root or alternate

loop Enable loop guard.

none Disable root guard or loop guard.

root Enable root guard.

Release Modification

12.2(25)SEF This command was introduced.

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