MSTP configuration help

[bobbydazzler]

Hello,

I have a question regarding MSTP implementation. We are in the migration process to replace a standalone 6509 by two Nexus 9K switches.
We used to have MSTP running between the 6509 (root) site A and the nexus SFP site B. All others switches are in pvst. We have dedicated fibers connecting the switches with different vlan for each client. I was using MSTP in order to do that, but there might be a better solution ?

Attached is the layer 2 topology of the current situation, partly migrated some fibers to the Nexus and mstp in a messy state. I would like to migrate the final fibers of client C (in green) to the top Nexus and switch on the link between the 6509 and the Nexus (link in blue).

Could I configure MSTP only between the Nexus SFP of site A/B ? And keep the 6509 in pvst ? Which one of the Nexus should be root ?

Looking forward to any advice.

[MHM Cisco World]

why you dont need to  run MST in c6K ?

run multi STP modes , hmm it not optimal 
MHM

[bobbydazzler]

Should I run mstp on all the switches?

[MHM Cisco World]

1- run MST in all SW that what I suggest 
2- if you want to run PVST + MST then see below how we can config SW that run PVST to simulate MST 

https://www.cisco.com/c/en/us/support/docs/lan-switching/multiple-instance-stp-mistp-8021s/116464-configure-pvst-00.html

MHM

[MHM Cisco World]

Did you read the link ?
there are two cases be careful the priority not always higher and it not for all VLAN 
please be careful and read the link I share more than one time, if you have Q please ask before run any command 

PVST Simulation

With such a topology (a mixture of MST and non-MST regions), the root bridge of CIST is in one of two places:

• Within a MST region
• Within a non-MST region.

PVST simulation runs seamlessly with two critical rules:

• If the root bridge for CIST is within a non-MST region, the spanning-tree priority of VLANs 2 and above within that domain must be better (lesser) than that of VLAN 1.
  
  
• If the root bridge for CIST is within a MST region, VLANs 2 and above defined in the non-MST domains must have their spanning-tree priorities worse (greater) than that of the CIST root.

[paul driver]

Hello @MHM Cisco World 
PVST+ simulation is something you do need to be aware of however it will NOT negate having mst/pvst+ stp domain, they will indeed work together you just need to be aware of the "gotchas" doing so.

[MHM Cisco World]

friend please check Link I share, I know what I talking about mix PVST+MST can lead to pvst_inc and BLK port.
MHM

""Often, MST regions are connected to other domains - Per VLAN Spanning Tree Plus (PVST+) or rapid-PVST+ regions. These switches that run PVST+ (or rapid) cannot process MST-type Bridge Protocol Data Units (BPDUs). For this reason, there must be a backward-compatibility mechanism that runs so that these two domains can interact with each other seamlessly. This is what PVST simulation addresses and achieves.

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.""

[paul driver]

Hello

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@MHM Cisco World wrote:

friend please check Link I share, I know what I talking about mix PVST+MST can lead to pvst_inc and BLK port.

---

PVST+ simulation isnt something you enable, its something you need to be aware of and negate from happening when you have to connect pvst+ stp domains to mst stp domains 

Which means you CAN connect these two stp domains together

[MHM Cisco World]

Which means you CAN connect these two stp domains together <<- did I mention different in my previous comment ?
I mention he must be careful never mention he can not mix 
and again I suggest use same STP mode if he can

MHM

[bobbydazzler]

Thank you for taking the time to help out.
The issue running MST in all SW is that the RJ45 Nk9 in site A have loads of VLANs that are not needed on other sites.
If I run MST + PVST, how would you configure MST ? MST on Nk9 SFP on site A and B and all other switches on PVST ?

Regards

[MHM Cisco World]

the MST is config with two  instance only no need more 
each instance contain half of VLAN available in SW even VLAN not use new but can use in feature.
MST dont send like PVST using VLAN tag so it dont matter if the VLAN is use in one SW and dont use in other SW 
anyway to help you I run lab and show you case
using MST 
using mix MST + PVST

MHM

[paul driver]

Hello
If you want to run mst & pvst domains then have the Nk9 in site B to be the root for the whole STP estate, just make sure on the PVST+ switches  the stp priority's for all vlans are higher(less preferred) then the MST domain.

[bobbydazzler]

Thank you for taking the time to help out on my case.
Should I configure the Nk9 Site B and Site A on MST ? and the others swtiches can stay in pvst ?
The problem running mst on all the swiches is that few vlans are used between sites but each site has quite a lot of VLANs, especially the Nk9 on site A and B.

[Georg Pauwen]

Hello,

I have not followed the entire thread, but I am just thinking why not simply use MST on all switches, and then manually prune the Vlans you don't need ?

[paul driver]

Hello

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@Georg Pauwen wrote:
why not simply use MST on all switches, and then manually prune the Vlans you don't need ?

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MST is per instance not per vlan as such vlans, you should not be pruning any vlans off any trunks