MST settings for Catalyst 9K core with Nexus 9K top-of-rack

[TStawney]

We are trying to simplify our STP configuration in preparation for the introduction of Meraki switches to our environment. We currently have a Catalyst 9K core with Nexus 9K switches at top of rack and Catalyst 2960's at the access layer. We would like to create a single MST region containing all VLANs, but know we need to exclude the reserved VLANs from the Nexus switches. What is the simplest way of accomplishing this? Do we create a separate region that has the excluded VLANs?

[Reza Sharifi]

I would just create one MST region and add all the VLANs to it. No need to worry about the reserved VLANs because they can not be mapped to any instance as they are reserved for internal use. See line3 in the guidelines and limitation section of this document. 

https://www.cisco.com/c/en/us/td/docs/switches/datacenter/sw/5_x/nx-os/layer2/configuration/guide/Cisco_Nexus_7000_Series_NX-OS_Layer_2_Switching_Configuration_Guide_Release_5-x_chapter8.html#con_1705861

HTH

[TStawney]

But those VLANs can be mapped on the Catalyst switches, which would lead to an inconsistent configuration, right? The region configuration needs to be identical across all switches, Catalyst & Nexus, correct?

[Reza Sharifi]

On the Catalyst, I would not map them to any instance. Just map the VLANs you are going to use and leave the private vlan as they are.

HTH 

[TStawney]

I'm not sure what you mean by that. The Catalyst puts VLANs 1-4094 in instance 0 by default. The only way I've found to remove a VLAN is by assigning it to another instance.

[TStawney]

Sorry, I was confusing regions and instances in my original post. 

I just noticed that the reserved VLANs are included in instance 0 on the Nexus switches. Do we need to move all the non-reserved VLANs into a separate instance, or can we just leave everything in the default instance 0?

Default config:

Name      []

Revision  0     Instances configured 1

Instance  Vlans mapped

--------  ---------------------------------------------------------------------

0         1-4094

or

Config to separate reserved VLANs:

Name      []

Revision  0     Instances configured 2

Instance  Vlans mapped

--------  ---------------------------------------------------------------------

0         3968-4094

1         1-3967

[Reza Sharifi]

I would move all the non-reseved VLANs to a different instance and live the reserved once in 0.

HTH