Changing Spanning Tree Priority ramifications

[RonaldNutter]

I am getting ready to make changes to our spanning-tree configuration in the data center.  In familiarizing myself with the network I noticed that our core switch (6509) wasnt the spanning-tree root for the datacenter. 

When I enter the spanning-tree priority command on the central 6509, will it be a hitless change (i.e. will there be any disruption to the network) ?  All switches are connected to the core/central 6509 by a direct connection. 

I know that when I change from pvst to rapid-pvst that the network will bounce because of the change in configurations to all of the switches.

Ron

[Jon Marshall]

Ron

If you change the STP root then all switches will need to reconverge on the new root bridge. It may be that uplinks that are currently forwarding need to be blocked and vice-versa. This will be done on a per vlan basis but assuming you want to do this for all vlans then it will affect all traffic.

You should do this out of hours in a small outage window.

Jon

[Giuseppe Larosa]

Hello Ron,

the change of root bridge is not hitless because all switches have to agree on the new root, so I would suggest to perfom it in a maintenance window

Hope to help

Giuseppe

[Ven Taylor]

Changing your root bridge is going to cause all of your switches to recalculate their root port, designated port, blocked ports, etc.  Spanning-tree will have to re-converge.  If you're doing this without RPVST, you're definitely going to notice it.

Each device will have to run through the blocking/listening/learning/forwarding process again.  This process takes about 20 seconds.

Ven