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| 3.8 |  | RSTP and MST Configuration |
| 3.8.3 |  | Enabling RSTP and MSTP |

For two or more switches to be in the same MST region, they must have the same VLAN-to-instance mapping, the same configuration revision number, and the same name.

A region can have one member or multiple members with the same MST configuration. Each member must be capable of processing RSTP BPDUs. There is no limit to the number of MST regions in a network, but each region can support up to 16 spanning tree instances. A VLAN can be assigned to only one spanning tree instance at a time.

Beginning in privileged EXEC mode, follow the steps outlined in Figure to specify the MST region configuration and enable MSTP.

To return to the default MST region configuration, use the no spanning-tree mst configuration global configuration command. To return to the default VLAN-to-instance map, use the no instance instance-id [vlan vlan-range] MST configuration command. To return to the default name, use the no name MST configuration command. To return to the default revision number, use the no revision MST configuration command.

To re-enable PVST, use the no spanning-tree mode or the spanning-tree mode pvst global configuration command.

The example in Figure shows how to enter MST configuration mode, map VLANs 10 to 20 to MST instance 1, name the region region1, set the configuration revision to 1, display the pending configuration, apply the changes, and return to global configuration mode. MST information is not propagated in VTP updates, so this configuration must be done on all of the appropriate switches.