MST Spanning Tree question

[kirk.brookover]

I need to add some new VLAN's to our core 6509's.  The last time I did this I believe the addition of the (vlan xxx) caused spanning tree to reconverge across all MST instances. Our Spanning Tree configuration is below.  Is that the correct behaviour of spanning tree when adding a new vlan?  or should only instance 0 reconverge as that is where the new VLAN would initially be put in.  Please let me know if more information/clarification is needed.

spanning-tree mode mst
spanning-tree loopguard default
spanning-tree portfast default
spanning-tree portfast bpduguard default
no spanning-tree optimize bpdu transmission
!
spanning-tree mst configuration
name core
revision 10
instance 1 vlan 21, 50, 60, 100, 172, 200, 202, 206, 208, 245, 247, 251
instance 1 vlan 254
instance 2 vlan 22, 55, 65, 101, 197, 201, 205, 207, 209, 244, 246, 250
instance 2 vlan 252
instance 3 vlan 239-240, 700
instance 4 vlan 95, 400, 850
instance 5 vlan 96, 851
instance 6 vlan 198-199, 219, 800-825
instance 7 vlan 500, 510-516, 520, 547-548
instance 8 vlan 701-704
!

[burleyman · Accepted solution]

With MST any incremental change will cause the complete MST database to be reinitialized. So you should do this during a maintenance window. One of the draw backs of MST.

Mike

[kirk.brookover]

Thank you, in that case is there a best way to add multiple VLAN's to minimize the outage?  Script the changes and hopefully they all go in 1 convergence?

[burleyman]

Here is a good doc on understanding MST. Also I think if you add them all in at the same time it will just converge once.

Mike