MSTP interaction with RSTP

Unanswered Question

Hi All,

Bit of a strange question, regarding MSTP on a 6500 running 12.2(33)SXH

I have picked up a difference in the docs between the config guide for this version and the previous version.

The previous version has a chapter on pre-standard MSTP and says trunks need to have all vlans allowed on them.

The current version does not say that, but our TAC engineer says it should.

We are connecting to another vendor running pure RSTP, the docs say this should just work and it uses the CIST to do the work.

We have all vlans configured to MST instance 1.

On the other side, we only have a few vlans existing (this is an edge switch)

When we removed a vlan from the allowed vlan list on the switchport, we had major problems.

Has anybody got any experience of MSTP/RSTP interaction?

Seen anything like this?


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Francois Tallet Thu, 12/13/2007 - 12:26
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Hi Ian,

The recommendation regarding the native vlan might be important for some platforms (there was a thread about that just few days ago). On the 6500, it should not be necessary.

Keeping all the vlans allowed on the trunk (and avoiding instance 0, that what I see you are doing) are just suggestions for engineers who are so used to PVST+ that they could be surprised by MST behavior. Considering that you are planning to use a single instance, all this is not applicable to your case anyway. I would just use MST with absolutely no configuration (i.e. I would not even map all the vlans to instance 1), and everything should be fine with your third party bridge running a "real" (non-PVST) RSTP.




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