Multiple roots in MST

[anshul_srivastava]

Hi All,

I am running 3 MST instances running on (including MST0) wherein i have defined SW1 as root for the MST0 & 1 while SW2 root for MST2. Both switches are interconnected. These switches also connect to the access switches. The issue is all switches (including SW1, SW2 and access switches) in the network are acting as spanning-tree root except for the MST0. MST0 is showing the right configured root.

According to my understanding the spanning tree should have one declared root. Need your help in correcting my understanding. Note the network is running fine.

BR..

[Reza Sharifi]

Hi,

Have you changed the priority on each switch?

spanning-tree mst 1 priority 8192

spanning-tree mst 2 priority 8192

HTH

[anshul_srivastava]

Hi Reza,

I have changed the priorities on the switches. What i found is that the switches are seeing the other switch in different MST region and the ports towards the confiugred root are in master forward state.

BR

[Ryan Newell]

Hello,

Your instance mappings must match. Instance one on switch two has VLAN 899. Switch one has VLAN 889.

Regards,

Ryan

[anshul_srivastava]

Yes that i figured out but even after the changes it is not working.

BR

[Ryan Newell]

Hello,

Could you please repost your configuration?

Ryan

[anwaryp]

I think the previous rapid-pvst is conflicting with mst.

Try to remove rapid-pvst configuration and then activate mst

no spanning-tree mode mst

no spanning-tree mode rapid-pvst.

[anwaryp]

Also, remove rpvst root priority command if exist in running configuration