[c-nsp] Maximum spannig tree instances

[David Hughes]

On 14/07/2009, at 11:26 PM, Jon Lewis wrote:

>>
>
> But isn't that the whole point of MST?  Most of what I've read about  
> it talks about doing setups where you only have 2 or 3 instances,  
> with all your vlans in the 2nd and or 3rd instance.

Yup.  In a DC / Hosting environment it's a must.  Particularly if you  
have large VMWare type clusters where there can be 100's of unique  
vlans that need to be presented to all cluster nodes.  Can't do that  
with any form of Per Vlan STP on top-of-rack or blade-chassis  
switches.  In a classic "dual attached L2 access layer" there are only  
2 possible paths so 2 MST instances does the job.  Having more STP  
instances than paths to the root bridge adds no value at all.


David
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