[c-nsp] Maximum spannig tree instances

[Clinton Work]

You need to enable MAC reduction (extended vlan range) if you want to 
support all 4096 STP instances on a 6500.  I have personally seen over 
3000+ STP instances running using PVST+ with MAC reduction enabled.  MAC 
reduction will steal bits from the bridge priority in order create 4096 
unique bridge IDs.  The CPU load with PVST+ compared with MST is  vary 
dramatic.  As long as you stay away from the older 10/100 Ethernet cards 
PVST/ RPVST should scale fairly well.  I have seen PVST+ start to fail 
when you reach 75,000 virtual ports and MST can easily handle over 
100,000 virtual ports.

Clinton. 

A.L.M.Buxey at lboro.ac.uk wrote:
> regarding maximum STP instances... I believe theres a platform limit
> of 1024 because of the MAC to VLAN bridge mapping on the platform -
> but, from the values above, you can see that virtual ports would
> hit you quite quickly without appropriate control of the VLANs
>
> alan
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Clinton Work
Airdrie, AB