Ideal MSTP configuration for interoperating with Meraki switches?

[nnraymond]

I'm trying to resolve an STP problem which has taken our whole network down the last two days, and I want to make sure I have the ideal MSTP configuration on our Catalyst 6509 for interoperating with all our switches, especially Meraki but also some legacy HP.

Initially I had this configuration on our core switch when I transitioned it from PVST to MSTP:

spanning-tree mode mst
spanning-tree extend system-id
spanning-tree mst 0-1 priority 8192
spanning-tree vlan 1-4094 priority 8192

We're a school district, and I set this up during the summer when very few staff were in the buildings. Reading up on  MSTP there were suggestions about creating regions and instances, so I added this:

spanning-tree mst configuration
name region1
instance 1 vlan 3-4, 6-8, 12-16, 100, 110, 120, 200, 300, 999-1000

I didn't see effects, positive or negative, to adding this. Are they necessary or helpful in any way, or should I just remove the region and instance to the core switch?

For further mitigation today I added "spanning-tree guard root" to all ports on the Catalyst 6509 and added this to the config:

spanning-tree portfast edge bpduguard default  

I'm hoping this will help prevent spanning tree from going totally haywire again. Today and yesterday at around 10am STP topology changes became so rapid on the network that most of the switches only saw themselves as root and the Meraki switches got in such a state that they needed a full reboot even with almost everything unplugged from them so they could even respond normally to pings on their admin interfaces. On advice of Meraki support I administratively disabled the redundant switch trunk links at multiple sites with the idea being it would simplify the tree (which is 6 switch layers deep) and hopefully keep convergence time under control going forward. We'll LAG/bond those links in the future, and we're also planning to move some of the layer 3 switch routing to inside buildings and change their uplinks from trunks to access to further simplify the spanning tree topology.

[Philip D'Ath]

I've used mst using the single root instance without issue.

I've also found the MS 14.x firmware train to be much better with spanning tree.

[paul driver]

Hello
When you have a mixture of MST and on MST stp domains you need to be aware of PVST simluation, which if isnt adhere to can cause you stp issues on your network.

Please review the attached PDF:

[nnraymond]

I have changed all of our Cisco switches to MST, none of them are running PVST at this point. The Meraki and HP switches are running RSTP. Does that document still apply? It says: "This simulation must be run only on boundary ports − these are ports that are directly connected to the PVST+ domain switches. The receipt of a Shared Spanning Tree Protocol (SSTP) BPDU on the port of a switch that runs MST causes the PVST simulation mechanism to trigger."

[Philip D'Ath]

MST and the "standard" implementation of RSTP (which Meraki uses) interoperate nicely.

[Giuseppe Larosa]

Hello @nnraymond ,

as noted by @Philip D'Ath      RSTP  ( single instance )  can interwork with MST using only the MST 0 instance and having all VLANs associated to it ( the root instance )

The PVST emulation applies to scenarios where you have an MST region that interacts with a PVST or Rapid PVST set of switches on one or more boundary links.

Having you migrated all your switches to MST all you need is to emulate RSTP with MST as explained above.

Hope to help

Giuseppe

[paul driver]

Hello

if you have mst throughout you stp estate then no the pvst simulation wouldn’t  be applicable However as mst runs on a per instance stp and not per vlan you should not be doing any manually pruning of your vlans.