Understanding Multiple Spanning Tree Protocol (MSTP)

Multiple Spanning Tree Protocol as defined in IEEE802.1s or IEEE802.1Q-2005 provides the ability to manage multiple VLANs from a single Multiple Spanning Tree (MST) instance. MST allows the formation of MST regions that can run multiple MST instances (MSTIs). Multiple regions and other STP bridges are interconnected using one single common spanning tree (CST).

MSTP regions are be defined to be a collection of switches that must have the same VLANs on all of the switches. Each MST region must a root bridge. The root bridge may not reside outside of the region. MST for a single region is supported. This enables multiple MST instances within a single region.

The following commands support the configuration of MST instances on a local switch:


CLI (network-admin@Leaf1) > mst-config-create

instance-id id

Specify the ID as a number between 0 and 63 for MST configuration.

vlans vlan-list

Specify the list of VLANs associated with the MST configuration 

bridge-priority bridge-priority-number

Specify the bridge priority number for MST. 


Additional commands for MST include the following:

  • mst-config-delete
  • mst-config-modify
  • mst-config-show

To configure MST, use the following commands:

CLI (network-admin@Leaf1) > mst-config-create instance-id 1-63 vlans vlan-list bridge-priority 4096

The bridge priority is a value from 0 to 65536, with a default value of 0. The value increments by 4096 each time.

For example, the values can be 0, 4096, 8192, up to 65536.