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New Member

can MST interoperate with PVRST?


We have a small network running MST. Planning to migrate it to PVRST for easier configuraiton.

Plan to change it on the core first. It means the core switcheswill run PVRST for a few weeks before the edges are mgirated from MST to PVRST.

Any problem with this setup?

Any comment is greatly appreciated.

Cisco Employee

Re: can MST interoperate with PVRST?

It can. Follow the recommendations in the following page

Re: can MST interoperate with PVRST?

There are some few constraints introduced by the interaction MST/PVST. It is generally simpler and more efficient to have an MST core with PVST access switches connected to it. I would thus rather recommend you start migrating to Rapid-PVST from the edge.

That's just a recommendation either way should work.

In any case, the CIST in the MST region must:

-have better information than any other vlan instance in the PVST region


-worse information than any other vlan instance in the PVST region

I think there is a quick explanation about that in the document that Prashanth referred to.

If the root for the PVST vlans are in the MST region, you can keep vlan load balancing and fast switchover between uplinks in case of failure.



New Member

Re: can MST interoperate with PVRST?

Thanks for the feedback.

I tot the docu was for PVST and MST only. So it works on MST and PVRST?

Will read it more carefully.

The network currently only have one MST instance (dont know configured by whom...), so I think it should be safe if even if we migrate it from the core switches.


Re: can MST interoperate with PVRST?

Yes, interaction between MST and Rapid-PVST is supported.

Note that when MST talk to Rapid-PVST, there is no proposal agreement mechanism between them. The reason is that MST only runs a single instance while RPVST runs several instances. MST cannot generate a specific agreement on a per-vlan basis. Actually, it could because of a recent change in RSTP/MST, but it is not implemented (probably not worth it). To sum this up, MST will interoperate with Rapid-PVST, but at the same speed as it would with plain PVST.



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