Re: MSTP backward compatibility ?

Hello,

The spanning-tree root for all Vlans has to be in MSTP, for that to work.

I recommend you to read these excellent blog posts who clearly explain what
is happening there.

http://blog.ine.com/2008/07/27/mstp-tutorial-part-i-inside-a-region/
http://blog.ine.com/2008/09/24/mstp-tutorial-part-ii-outside-a-region/

Regards,
Rares

On Tue, Mar 1, 2011 at 10:33 PM, Jacek <q.192.168.1.0_at_gmail.com> wrote:

> I have a question regarding MSTP backward compatibility with PVST.
> According
> to Cisco documentation "MSTP maintain backward compatibility with equipment
> that is based on PVST+"
>
> I am testing this in the lab and and it does not work. In the topology
> below
> I have MSTP and PVST switches connected. I tried several combination of stp
> priority on different switches and it looks like MST and PVST switches will
> not exchange stp priority at all.
>
> Here is the scenario:
>
> SW1=======SW2 ---> MSTP
> || \\ // ||
> || \\// ||
> || //\\ ||
> || // \\ ||
> SW3=======SW4 ---> PVST
>
> For example, if I configure SW4 to be root bridge for vlan 10 I will end up
> with two switches claiming to be root for vlan 10: SW1 and sw4 will claim
> to
> be root.
>
> It looks to me that MST and PVST switches do not exchange stp priority, any
> ideas about "backward compatibility" ?
>
> BTW, I tested a mix of RSTP and PVST+ in the similar topology and it worked
> OK.
>
>
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Received on Tue Mar 01 2011 - 22:45:11 ART