How to verify the Secondary Root?

As you know  we can configure the designated switch as the "Primary root role" or the "Secondary root role" using the following commands:

spanning-tree vlan 10 root primay
spanning-tree vlan 20 root secondary
  

Although these commands are just "macros" that we cannot see them in the running configuration, it is still easy to verify the "Primary root role" is correctly configured: We just use "show spanning-tree" command to check the designated switch is really the current "Root Bridge".

The interesting question is how can we quickly verify the "Secondary root role" is correctly configured, instead of checking all the switches' Bridge ID to make sure the designated switch is really the "Secondary root"?

I think the following method is a good one to try out.

1. Have the "Primary root" resign itself, so the real "Secondary" can be promoted to Root
2. Use "show spanning-tree" command again now to see the new Root bridge is really the designated switch.

Warning: such operation would cause short network outage while the "Secondary root" is being promoted.

The key here is how to make "Primary" resign itself. We can just turn off its spanning tree function on the designated Primary root by this command:

no spanning-tree vlan 20

Of course, to restore the change, we just re-enable the spanning tree function of the designate Primary root switch by this command:

spanning-tree vlan 20