MST Priority 0 and Root commands

[prashanma]

Hi Team,

I have question for team. Do we need to use both following command in MSTP primary use, or can we use one of them ?

spanning tree mst 0 priority 0
spanning tree mst o root

[luis_cordova]

Hi @prashanma 

spanning tree mst 0 root <primary/secondary>

This command indicates that this switch will have the lowest priority(primary), so it will be chosen as rootbridge

https://www.cisco.com/c/m/en_us/techdoc/dc/reference/cli/n5k/commands/spanning-tree-mst-root.html

spanning tree mst 0 priority <number>
This command indicates that this switch will have the priority you indicate. The priority must be with intervals of 4096.

https://www.cisco.com/c/m/en_us/techdoc/dc/reference/cli/n5k/commands/spanning-tree-mst-priority.html

In summary, the first command dynamically assigns priority and the second command does it manually.

Regards

[prashanma]

So we can use either both commands or "priority command" for make a switch as root

[kapslock]

Yes you can use both commands to change a switchs priority.

With "spanning-tree mst 0 priority 0" - you set the priority of instance 0 to the lowest possible priority of 0, manually.

With "spanning tree mst 0 root" - the switch, by it self, looks at the current roots priority and decrements that value by 4096 and inhert that lower value it self and claims root.

[Deepak Kumar]

Hi,

Both commands having a little different behavior as:

spanning tree mst 0 priority 0: With this command will set Priority 0 to the MST region 0 means it will become root permanently.

spanning tree mst o root: This command will check priority and change self priority lower than others and become root. but a letter on, If you added a new switch with lower priority compare to current root bridge ID  then the newly added switch will become root bridge and this command will not take any action on this event.