Changing one switch from PVST to MST

[Psmurali89]

Hi All

There are 4 switches in the DC, 3 switches are configured as MST and by mistake one switch is PVST. This is causing an issue now so am looking to change that one PVST switch to MST. 

All switches are L2, the PVST switch has got only 10 L2 vlans in trunk port that connects to ISP and two uplink port to MST switch. I understand when i change from PVST to MST, it will cause approx. 30 sec downtime in that switch. But will it affect other MST switches as well? 

[marce1000]

 - FYI : https://www.cisco.com/c/en/us/support/docs/switches/catalyst-6500-series-switches/72844-MST.html , which includes https://www.cisco.com/c/en/us/support/docs/switches/catalyst-6500-series-switches/72844-MST.html#mst1 , things may also depend on what the issue is that you mention but don't describe in detail.

 M.

[Psmurali89]

Hi, 

Thank you, Am receiving PVST simulation failure in MST switch and the port is being blocked in MST switch. So which is why am looking to change the PVST switch to MST. 

There is no distribution or core layer as such. Its a simple L2 switches connected in chain. 

Below is the MST config in 3 switches: 

spanning-tree mode mst
spanning-tree extend system-id
spanning-tree mst configuration
name xxx
revision 1
instance 1 vlan 1-4094

Below is PVST config in one switch: 

spanning-tree mode pvst
spanning-tree extend system-id

Am looking to change PVST switch to MST (using same MST config as above). I understand this will cause downtime in that particular switch. But just want to clarify if this will affect other 3 MST switch - in other ways - will it cause downtime in other 3 MST switches? 

[marce1000]

                           >...will it cause downtime in other 3 MST switches? 

  - I would presume not , if the changed one is not intended to become the root of the spanning tree (for the vlans)

 M.

[MHM Cisco World]

check the link below it will give you some help to solve issue. 
https://garzum.net/pvst-and-mst-incompatibility/