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Adding VLAN to existing MSTP configuration


Adding VLAN to existing MSTP configuration

I understand how to create an initial MSTP spanning tree configuration but I can't seem to find information on the proper way to add vlans to an existing spanning tree configuration.

Do I just re-execute the command "spanning-tree instance n vlan n n n n" specify the existing vlans and just add the new vlans to it?

Thanks in advance.

Jeff Carrell
Honored Contributor

Re: Adding VLAN to existing MSTP configuration

yes, and remember to do so on EVERY switch in the same MSTP region...

and while doing this, the MSTP configs of those switches in the same MSTP regions will be in different MSTP regions until they all are the same again - hence you will see some spanning tree convergence occurring on the switches (until all are the same MSTP configs)...

Mohammed Faiz
Honored Contributor

Re: Adding VLAN to existing MSTP configuration

Yes, as Jeff says your MSTP domain won't re-converge until your VLAN to MSTI mappings match on each switch again.
I had to do this recently and the best way that I found to do it was to add the VLAN to every switch and tag it on the relevant ports. As we don't have any production VLANs in the IST this part doesn't involve any downtime.
Then you can run the "spanning-tree instance n vlan x" command on each switch in turn starting at the bottom of the tree and working back to the root (just be careful of where in the tree the machine you're runnning the commands from is).
As long as you can run the commands on each switch quite quickly (you may want to try PCM for this) the disruption to the network should be less than a few seconds.
Esteemed Contributor

Re: Adding VLAN to existing MSTP configuration

Hi David,

best practice regarding MST configuration: Create instances with some more VLANs you have in use. This will avoid touching the MST config when you will add a VLAN. In other words: It is not mandatory that a VLAN ID in the MST configuration has to exist on the switch. You just can define some "spare" VLANs for future use.


Ingentive Networks GmbH