spanning tree

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Feb 7th, 2008
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can anyone tell me if PVST is the same as multiple spanning tree groups? I have seen on nortel switches that when you create vlans, they all exist in 1 STG, why is this? and if I was to create a spanning tree group per vlan, would that be called multiple spanning tree groups ?

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shrikar.dange Thu, 02/07/2008 - 02:50
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Pvst is not a MST.Pvst is cisco propreitery protocol.Pvst means having a separate spanning tree instance per vlan.While in MST you can map number of vlans to different instances.


If you have 10 vlans then in PVST mode you have 10 STP instances running for each VLAN.While in MST you can map vlans to instances according to your can have 2 instaces of STP with 5 vlans mapped to each instance.

Nortel supports only single instance of STP commonly known as CST (so do many other vendors in the market).

If you want to create a STP instance per vlan then it would be called PVST (default on catalyst switches) and it is a cisco propritery can not be used on other vendor switches.

In MST mode you can map vlans to different STP instances to load balance and as per your topology.



shri :)


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