Dell Networking N4000 Series Configuration Manual page 754

Figure 22-20. MSTP Configuration Example
To make multiple switches be part of the same MSTP region, make sure the
STP operational mode for all switches is MSTP . Also, make sure the MST
region name and revision level are the same for all switches in the region.
To configure the switches:
1 Create VLAN 10 (Switch A and Switch B) and VLAN 20 (all switches).
NOTE:
this VLAN must be created to allow the formation of MST regions made up of
all bridges that exchange the same MST Configuration Identifier. It is only
within these MST Regions that multiple instances can exist.
console#configure
console(config)#vlan 10,20
console(config-vlan10,20)#exit
console(config-vlan)#exit
2 Set the STP operational mode to MSTP.
console(config)#spanning-tree mode mst
3 Create MST instance 10 and associate it to VLAN 10.
console(config)#spanning-tree mst configuration
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Configuring the Spanning Tree Protocol
Even Switch B does not have any ports that are members of VLAN 10,