MST and PVST interoperability

[iores]

Hi,

Does MST and PVST domain need to have same vlans configured in order for interoperability to work?

E.g. if vlans 10 and 20 are configured in MST domain, do they need to be configured in PVST domain, as well?

[M02@rt37 · Accepted solution]

Hello @iores

It is not required that both mst and pvst+ domains have the exact same vlan configured; however, every vlan that exist on the PVST side must be mapped to an MST instance on the MST side. If a vlan is present on the PVST+ switch but is not mapped to any instance in the MST configuration, the MST switch will drop the PVST+ BPDUs for that vlan, potentially causing SPT inconsistencies or loops. Therefore, while the MST domain can have additional vlan not present in the PVST+ domain, it must account for all PVST+ vlanS in its instance-to-VLAN mapping to ensure stable interroperability.

[paul driver]

Hello

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@iores wrote:
E.g. if vlans 10 and 20 are configured in MST domain, do they need to be configured in PVST domain, as well?

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Only if those vlans are to be extended between the two stp domains
MST is per instance so as/when you initially create the MST domain all vlans by default will be mapped to mst 0 unless you decide to associate certain vlans to a different or an additional MST instance.

Note:- regards PVST simulation.

• if the MST domain is to become the CIST root then instance 0+ priority's needs to be of a preferred value (lower) than all vlans of the PVST+ domain
• if the PVST+ domain is to become the CIST root then its all vlans stp priority needs to be of a preferred (lower) over the MST domains instance 0+ , Additionally PVST+ vlan 1 needs to be of a less preferred value (higher) than all other PVST+ vlans