06-17-2009 12:42 AM - edited 03-06-2019 06:18 AM
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+?
06-17-2009 12:58 AM
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:
PVST+
Rapid PVST
MST
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.
note:
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
Giuseppe
06-17-2009 09:49 PM
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 .
06-17-2009 11:21 PM
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
http://www.cisco.com/en/US/products/hw/switches/ps700/products_white_paper09186a00801b49a4.shtml
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
Giuseppe
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