Dell EMC SmartFabric OS10 User Guide Release 10.5.0

MSTP determines the root bridge according to the lowest bridge ID. To increase the likelihood of a bridge to be selected as a root bridge, assign a lower bridge priority numerical value to that bridge.

You can set the priority value to 0 to force a switch to become the root switch. Value 0 is the highest priority.

• Assign a bridge priority number to a specific instance in CONFIGURATION mode, from 0 to 61440 in increments of 4096, default 32768.

  spanning-tree mst instance-number priority priority

Assign root bridge priority

OS10(config)# spanning-tree mst 0 priority 32768

OS10# show spanning-tree active
Spanning tree enabled protocol msti with force-version mst
MSTI 0 VLANs mapped 1,31-4093
Executing IEEE compatible Spanning Tree Protocol
Root ID    Priority 32768, Address 3417.4455.667f
Root Bridge hello time 2, max age 20, forward delay 15, max hops 20
Bridge ID    Priority 32768, Address 90b1.1cf4.a523
Configured hello time 2, max age 20, forward delay 15, max hops 20
CIST regional root ID Priority 32768, Address 90b1.1cf4.a523
CIST external path cost 500
Interface                                           Designated
Name           PortID   Prio  Cost  Sts  Cost Bridge ID     PortID
---------------------------------------------------------------------------
ethernet1/1/5  128.276  128   500   FWD  0    32768   3417.4455.667f  128.146
ethernet1/1/6  128.280  128   500   BLK  0    32768   3417.4455.667f  128.150
Interface
Name           Role PortID   Prio Cost Sts  Cost Link-type Edge
--------------------------------------------------------------
ethernet1/1/5  Root 128.276  128  500  FWD  0    AUTO      No
ethernet1/1/6  Altr 128.280  128  500  BLK  0    AUTO      No