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MSTP Nonsense

With MSTP, if I remove a vlan from a trunk port, that switch will send a TCN BPDU per that, out to all neighbors and all switches in that same instance will Max Age their CAM tables for all vlans in that instance right?

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Cisco Employee

MSTP Nonsense

Hi,

With MSTP, if I remove a vlan from a trunk port, that switch will send a  TCN BPDU per that, out to all neighbors and all switches in that same  instance will Max Age their CAM tables for all vlans in that instance  right?

No, I do not believe that is the case. MSTP reacts to topological changes in instances only. Adding or removing a VLAN from the list of allowed VLANs on a trunk is not a topological change, as the parameters on which the instance spanning tree is built do not change.

That being said, manipulating with individual VLANs on trunks if MSTP is in use is calling for trouble - you may end up with a partitioned VLAN. If allowing or disallowing VLANs on trunks, these manipulations should be done always for the entire set of VLANs that is mapped onto a single MST instance.

Please feel welcome to ask further.

Best regards,

Peter

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