PVST to MST

[Psmurali89]

Hi All,

I got 3 existing stack switches in MST with the below config. 

!

spanning-tree mode mst

spanning-tree extend system-id

!

spanning-tree mst configuration

name xxxx

revision 1

instance 1 vlan 1-4094

!

spanning-tree mst 0-1 priority 8192

!

We connected another standalone switch to stack1 and by mistake we configured as PVST. All switches are L2 only. I want to change this one switch from PVST to MST using the same config above. Will this have impact on all other 3 stack switches? I will be making this change in maintenance window anyway. 

[Psmurali89]

Hi Paul, 

Thank you very much detailed explanation and it is very helpful. 

Just to confirm, if I change DC2 from PVST to MST using the same priority of 8192 as DC1, the DC1 should still be the root for vlan810 (I have only 2 VLAN's between DC1 & DC2 and they both are in same state), which means

DC2 Twe1/0/10 will be Root, 

          Gi1/0/3 will be FWD 

DC1 Twe2/0/22 will be Desg  

         po6 will be root 

So this change will not cause any major issue (am planning to do it out of hours just in case)? 

[paul driver · Accepted solution]

Hello

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@Psmurali89 wrote:

Hi Paul, 

Thank you very much detailed explanation and it is very helpful. 

Just to confirm, if I change DC2 from PVST to MST using the same priority of 8192 as DC1, the DC1 should still be the root for vlan810

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FYI DC1 is NOT the root for vlan 810, its whatever is attached to DC1 PO6 that is.

DC2 root port is via Twe1/0/10 interface  to wards  DC1
DC1 root port is via PO6 interface towards "another switch"

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@Psmurali89 wrote:

So this change will not cause any major issue (am planning to do it out of hours just in case)? 

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I don't have a full topology of your network, but based on the output you have provided, then no it should not cause an issue, however I would "Strongly suggest to perform this under a change window"

[Psmurali89]

Hi Paul

Thank you very much.