[c-nsp] Spanning Tree Instances

[Bill Foster]

It looks to be a limitation of the platform.  Taken from the release 
notes for 12.2(55)SE for Catalyst 3750X switch:

The switch supports 128 spanning-tree instances. If a switch has more 
active VLANs than supported spanning-tree instances, spanning tree can 
be enabled on 128 VLANs and is disabled on the remaining VLANs. If you 
have already used all available spanning-tree instances on a switch, 
adding another VLAN anywhere in the VTP domain creates a VLAN on that 
switch that is not running spanning-tree. If you have the default 
allowed list on the trunk ports of that switch (which is to allow all 
VLANs), the new VLAN is carried on all trunk ports. Depending on the 
topology of the network, this could create a loop in the new VLAN that 
would not be broken, particularly if there are several adjacent switches 
that all have run out of spanning-tree instances. You can prevent this 
possibility by setting allowed lists on the trunk ports of switches that 
have used up their allocation of spanning-tree instances.

And I know the "feature" exists on the classic 10/100 Catalyst 3750s as 
I have seen it happen on them as well.

Bill Foster
Network Support Specialist
UW-Madison

On 5/1/13 7:49 AM, cisco-nsp-request at puck.nether.net wrote:
> Send cisco-nsp mailing list submissions to
> 	cisco-nsp at puck.nether.net
>
> To subscribe or unsubscribe via the World Wide Web, visit
> 	https://puck.nether.net/mailman/listinfo/cisco-nsp
> or, via email, send a message with subject or body 'help' to
> 	cisco-nsp-request at puck.nether.net
>
> You can reach the person managing the list at
> 	cisco-nsp-owner at puck.nether.net
>
> When replying, please edit your Subject line so it is more specific
> than "Re: Contents of cisco-nsp digest..."
>
>
> Today's Topics:
>
>     1. Spanning Tree Instances (Leigh Harrison)
>     2. Ang:  ME3600X Output Drops (Gustav.Ulander at steria.se)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Fri, 23 Mar 2012 12:48:06 +0000
> From: "Leigh Harrison" <lharrison at convergencegroup.co.uk>
> To: <cisco-nsp at puck.nether.net>
> Cc: Clive Webster <cwebster at convergencegroup.co.uk>
> Subject: [c-nsp] Spanning Tree Instances
> Message-ID:
> 	<BE13605B4C12654284C937196842A00020254F at condc02.ConvergenceGroup.local>
> 	
> Content-Type: text/plain; charset="us-ascii"
>
> Hello all,
>
> We have run into an issue on a 3750 switch where it has run out of spanning tree instances.
>
> Is this a limitation of PVST or is it a limitation of the switch?  I can't seem to find good clarity anywhere.  I have some 6509's and nexus 7k's and I'm wondering if they're going to suffer from the same fate...
>
> Leigh
>
>
> Leigh Harrison, CCIE#15331
>
> Head of Design & Infrastructure
>
> ----------------------------------------------------------------------------------------------
> Telephone:                                0121 711 5527
> Mobile:                                      07872 811 889
> Facsimile:                                  0845 270 2710
> Tech Support:                            0845 270 2989
> E-Mail:                                      lharrison at convergencegroup.co.uk<mailto:lharrison at convergencegroup.co.uk>
> Group Website:                          www.convergencegroup.co.uk<http://www.convergencegroup.co.uk/>
> Media & Broadcast Website:        www.media-net.co<http://www.media-net.co/>
> Bullet Internet Website:              www.bulletinternet.co.uk<http://www.bulletinternet.co.uk/>
> ----------------------------------------------------------------------------------------------
>
>