MSTP Root Bridge Selection

[fgasimzade]

Hello Everyone,

We have an mstp configured across our switches for a really long time. All works as expected, however, I can not understand, why the below command is used on some switches, including our Root

spanning-tree vlan 1-1000 priority 20480

As far as I understand, this command must be only configured on the root bridge to lower its priority value. But in our case, as I said before, it is also configured on some non-root bridges and when I issue sh spanning-tree bridge priority on those switches I get the default value of 32768. I was expecting to see 20480 though. 

Can you please clarify this issue for me

Thank you

[Reza Sharifi]

Hi,

Usually, the default priority is 32768 but if you have configured the switch with 20480, that is what you should see in the output.

Can you post the output of  "sh spanning-tree bridge priority" for one of the vlans? Also, what type of switch is that?

HTH

[Peter Paluch · Accepted solution]

Hello,

If you run MSTP, the "spanning-tree vlan" commands are ignored. With MST, the bridge priorities are configured with "spanning-tree mst <instance> priority <priority>" instead.

I suspect that the "spanning-tree vlan" commands on your MST-enabled switches are some leftovers from the pre-MST times, or perhaps someone applied them in the past in the hopes the would have an effect, but with MST enabled, they are ignored.

Please feel welcome to ask further!

Best regards,
Peter

[MHM Cisco World]

I agree with @Peter Paluch
I think in past some one apply this command.
but can we see show spanning tree summary