[c-nsp] Maximum spannig tree instances

[Clinton Work]

The short answer is that the 6500 platform spanning-tree scalability is 
limited by virtual ports and the complexity of your spanning-tree 
topology.  If you only have a couple of trunks carrying all 4096 VLANs 
then you'll be fine.  If you have a lot FastE ports trunking hundreds of 
VLANs then you will quickly run into the virtual port limits. 

The 12.2SXF release notes indicate the virtual port limits which can be 
checked against the "show vlan virtual-port" command output.  The 
documentation isn't clear, but the 6500 spanning-tree limits are based 
upon virtual ports rather than logical ports (ex CatOS, 4500, ..).  If 
you check that 12.2SXI release notes you'll see that Cisco included 
enhancements that increase the virtual port scalability numbers.   Note, 
RST is listed as RPVST+ in the table. 

http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SXF/native/release/notes/OL_4164.html#wp26366

Shine Joseph wrote:
> Hi,
>
> I searched in the archives if I could find the answer to my this query. =
> The result was negative.
>
> How many spanning-tree instances are possible in Rapid PVST+ and MST =
> modes in Cisco 6500 series switches with Sup720?
>
> The only documentation that I could see which says about total number of =
> virtual ports per line card and total active logical ports. There is no =
> reference to  number of instances.
>
> The following netpro link mentions about 4096 instances, but this point =
> is not validated.
> http://forums.cisco.com/eforum/servlet/NetProf?page=3Dnetprof&forum=3DNet=
> work%20Infrastructure&topic=3DLAN%2C%20Switching%20and%20Routing&topicID=3D=
> .ee71a04&CommCmd=3DMB%3Fcmd%3Dpass_through%26location%3Doutline%40%5E1%40=
> %40.2cc1484e/2#selected_message
>
> Any links or pointers would be much appreciated.
>
> Thanks in advance,
> Shine
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-- 
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Clinton Work
Airdrie, AB