MST and PVST+ Interoperability

(Rene Molenaar) #1

This topic is to discuss the following lesson:

(stefano n) #2

PVST+ calculates an instance for each spanning-tree instance.

PVST+ calculate a stp instance for each vlan ? RIGHT?

(Lazaros Agapides) #3

Hello Stefano.

PVST+ as its name suggests creates an spanning tree instance for EACH VLAN. MST on the other hand can have many VLANs participate in a single spanning tree instance thus reducing the number of spanning tree instances and thus consuming fewer system resources (CPU, Memory etc).

I hope this has been helpful!

Laz

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(Ehsan V) #4

So is this the same methodology between between connecting switches that do say RSTP and PVRST? Say I want to connect a non-Cisco switch to a Cisco model. Would the same lessons detailed here be valid when connecting a single-instance RSTP switch to a Cisco switch that does PVRST and has one instance per VLAN?

(Lazaros Agapides) #5

Hello Ehsan

Essentially, PVRST uses multiple instances of IEEE 802.1w. Most non-cisco devices that support RSTP will support one instance of PVRST. In most cases, because PVRST is backward compatible with RSTP, the PVRST implementation will revert to RSTP. So you are essentially correct in your descsription.

I hope this has been helpful!

Laz

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(Ehsan V) #6

Thank you very much Lazaros!

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