Is Multiple-Spanning-Tree the right solution for us?

[Bastian-Uz]

Hello Community,

in the near future we will facing the problem that we run out of spanning-tree instances by using rapid-pvst.
Not on all switches, but on the access-layer equipment. Here we can use only max 128 instances.

Reducing/pruning the VLANs on the access-layer is not possible, because we have firewalls and customers connected and we need the VLANs. Pruning is not enough… if we prune all VLANs that not been needed on the access-layer, we just delay the problem for a few months.

As an alternative to rapid-pvst, we have considered to migrate to mstp.

I've been studying some documents, I've also set up a lab (as good as possible), but i keep running always into problems.

I have attached a picture with examples, how our customers are connected.
This picture includes 3 common scenarios:
Customer-A has also MSTP running, other region and on Arube Switches. He has 4 Uplinks, all Access-Ports in two different VLANs (works well with rpvst on our site).
If I understand that right, this scenario will no longer work because his boundary-ports blocking all ports except for the one pointing to root.
In my Labs I run always in this problem and I can’t find a solution.
I tried to deal with cost and priority’s but if I understand that right, boundary-communication run’s always cst (no m-records, … so only one port will be in forwarding-state). Is that right?

Next question: will I run with rapid-pvst customers in the same problem?
If I understand that right, when we are the root, our boundary-ports are all on forwarding-state, so I think that the rapid-pvst will block all ports they will causing loops? Right!?

Extra Information: In some cases, customers can have his own equipment with no possibility for us to manage them. We only give them the Internet-Uplinks (Access or trunked Ports. Somtimes single, sometimes redundant in one or more vlans)

Thanks and best regards,

Bastian

[balaji.bandi]

There is good explantion how this can be used in large evniroment. but your requirement only mentioned diagram - you can use what suites for you.

but I would suggest having control on the trunk to allow only respected VLAN to allow rather all VLAN  to control the SPT to minimize the convergency.

https://community.cisco.com/t5/switching/migrating-from-rapid-pvst-to-mst/td-p/1792071

https://etherealmind.com/blessay-should-i-use-pvst-or-mstp-and-why/

[Bastian-Uz]

Hello Balaji,

thank you for your answer. I know this posts... but i was in hope to find a solution that allows "vlan load-sharing" between different regions.
We have some customers  with multiple uplinks in differen vlans, so with a single forwarding stp-instance we run into problems.

Today i found this post.
https://nwktimes.blogspot.com/2019/02/consideration-when-connection-mstp.html

...after reading this it was clearly for me that mstp-to-different-mstp supports only cst (thats not good in our situaltion and we have the need to research for an solution)

...good news are that mst-to-rpvst will work in our cases. We are the root, all out ports are forwarding and rpvst is blocking the needed ports.

Thank you very much and nice evening...

BR, Bastian

[balaji.bandi · Accepted solution]

Nice and Glad, you found the way move forward.