Stp vs Pvst+

Unanswered Question
Jun 17th, 2009

On cisco switches pvst+ is by default running.Means as soon as you create any vlan single spanning tree instance starts running fot tht particular vlan.

But if i disable pvst+........then switch runs a Common spanning tree instance for all vlans?

what is the difference between pvst and pvst+?

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Overall Rating: 3 (1 ratings)
Giuseppe Larosa Wed, 06/17/2009 - 00:58

Hello Alexandr,

PVST was a previous version of PVST+ that had problems in dealing with 802.1Q trunks.

PVST+ is supported since catos 4.x

In modern IOS switches the following STP modes are available:


Rapid PVST


the last two uses instances that are rapid as per 802.1W standard.

Rapid PVST is simply using a rapid STP instance for each Vlan.

MST 802.1s uses instances for sets of vlans achieving greater scalability at a price of increased management activity.


actually a prestandard MSTP version exist on some IOS versions/platforms.

the global command is

spanning-tree mode xx

You cannot revert to simple CST 802.1D on cisco switches.

But you can have fall back on a per port basis.

Hope to help


liuguiqing Wed, 06/17/2009 - 21:49

PVST was a previous version of PVST+ that had problems in dealing with 802.1Q trunks.

Do you know what problems ?

I have got in trouble with stp ,

but i can't sure it's cause by pvst or not .

Giuseppe Larosa Wed, 06/17/2009 - 23:21

Hello Liuquiqinq,

PVST+ has a mechanism that allows to support 802.1Q trunks: it uses a proprietary format for STP BPDU that is not processed by 802.1D standard switches and allows them to reach another cisco switch.

for more details

The older PVST was able to work well only on ISL trunk links.

It is unlike you are using the older PVST because PVST+ is supported since catos 4.x however some problems can happen in a multivendor environment.

Hope to help



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