Configuring MST instance parameters

When you enable MSTP on the switch, a spanning tree instance is enabled automatically. The switch supports up to 16 configurable MST instances for each VLAN group that you want to operate as an active topology within the region to which the switch belongs. When creating an instance, you must include a minimum of one VID. You can add more VIDs later if desired.


spanning-tree instance 1..16 vlan vid [vid..vid]
no spanning-tree instance 1..16 vlan vid [vid..vid]

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 you specify 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 you remove a VLAN from an MSTI, the VLAN returns to the IST instance, where it can remain or be re-assigned to another MSTI configured in the region.


Starting in software release 13.x.x, you can enter the spanning-tree instance vlan command before a static or dynamic VLAN is configured on the switch to preconfigure VLAN ID-to-MSTI mappings. No error message is displayed. Later, each newly configured VLAN that has already been associated with an MSTI is automatically assigned to the MSTI.

This new default behavior differs from automatically including configured (static and dynamic) VLANs in the IST instance and requiring the manual assigning of individual static VLANs to an MSTI.


The valid VLAN IDs that you can 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 you to preconfigure MSTP topologies before the VLAN IDs associated with each instance exist on a switch.

When using preconfigured VLAN ID-to-MSTI topologies, be sure 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.

When upgrading switch software to release 13.x.x and later, the existing MSTP topology configuration is automatically saved. All existing VLAN ID-to-MSTI assignments are maintained on a switch for uninterrupted MSTP network operation.