Spanning-Tree Extend System-Id - Cisco Catalyst 3750-X Command Reference Manual

Cisco ios release 15.2(1)e and later

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Chapter 2 Catalyst 3750-X and 3560-X Switch Cisco IOS Commands

spanning-tree extend system-id

Use the spanning-tree extend system-id global configuration command on the switch stack or on a

standalone switch to enable the extended system ID feature.

Though visible in the command-line help strings, the no version of this command is not supported. You

cannot disable the extended system ID feature.

Syntax Description

This command has no arguments or keywords.

The extended system ID is enabled.

Command Modes

Global configuration

Command History

Usage Guidelines

The switch supports the IEEE 802.1t spanning-tree extensions. Some of the bits previously used for the

switch priority are now used for the extended system ID (VLAN identifier for the per-VLAN

spanning-tree plus [PVST+] and rapid PVST+ or as an instance identifier for the multiple spanning tree

The spanning tree uses the extended system ID, the switch priority, and the allocated spanning-tree MAC

address to make the bridge ID unique for each VLAN or multiple spanning-tree instance. Because the

switch stack appears as a single switch to the rest of the network, all switches in the stack use the same

bridge ID for a given spanning tree. If the stack master fails, the stack members recalculate their bridge

IDs of all running spanning trees based on the new MAC address of the stack master.

Support for the extended system ID affects how you manually configure the root switch, the secondary

root switch, and the switch priority of a VLAN. For more information, see the

If your network consists of switches that do not support the extended system ID and switches that do

support it, it is unlikely that the switch with the extended system ID support will become the root switch.

The extended system ID increases the switch priority value every time the VLAN number is greater than

the priority of the connected switches.

spanning-tree extend system-id

Modification

This command was introduced.

"spanning-tree vlan"

Catalyst 3750-X and 3560-X Switch Command Reference

spanning-tree extend system-id

"spanning-tree mst root"

Catalyst 3560-x