KB.15.15

Configuring MSTP on the switch automatically configures the IST instance and places

all statically and dynamically configured VLANs on the switch into the IST instance.

This command creates a new MST instance (MSTI) and moves the VLANs specified

from the IST to the MSTI.

You must map at least one VLAN to an MSTI when you create it. You cannot map

a VLAN ID to more than one instance. You can create up to 16 MSTIs in a region.

The no form of the command removes one or more VLANs from the specified MSTI.

If no VLANs are specified, the no form of the command deletes the specified MSTI.

When removing a VLAN from an MSTI, the VLAN returns to the IST instance, where

it remains or is re-assigned to another MSTI configured in the region.

NOTE: The valid VLAN IDs to map to a specified MSTI are from 1 to 4094. The

VLAN ID-to-MSTI mapping does not require a VLAN to be already configured on

the switch. The MSTP VLAN enhancement allows preconfiguring MSTP topologies

before the VLAN IDs associated with each instance exist on a switch.

When using preconfigured VLAN ID-to-MSTI topologies, ensure that MSTP switches

remain in the same region by mapping all VLAN IDs used in the region to the same

MSTIs on each regional switch.

Each MST instance supports a different set of VLANs. A VLAN that is mapped to

an MST instance cannot be a member of another MST instance.

The MSTP VLAN configuration enhancement allows you to ensure that the same

VLAN ID-to-MSTI assignments exist on each MSTP switch in a region. Before a static

VLAN is configured or a dynamic VLAN is learned on the switch, use the

spanning-tree instance vlan command to map VLANs to each MST instance

in the region. Later, when the VLAN is created, the switch automatically assigns it

to the MST instance to which you had previously mapped it.

Configuring MSTP instances with the VLAN range option (Example)

Using the spanning-tree instance command with the VLAN range option configures the

entire range of VLANs, even if the range includes VLANs that are not currently present on the

switch.

96 Multiple instance spanning tree operation