STP instances limitation on 2950

Unanswered Question
Sep 4th, 2008

I do have a 2950 switch that has 64 STP instance limitation. Can this switch model support more than 64 STP instances? Thank you

I have this problem too.
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Overall Rating: 4.5 (2 ratings)
francisco_1 Thu, 09/04/2008 - 07:28

It depends on your software version you are using but normally on the 2950 low-end switch supports the per-VLAN spanning tree (PVST) with a maximum of 64 spanning-tree instances. The remaining VLANs operate with STP disabled.

If you go a model up say the 2960 In PVST+ or rapid-PVST+ mode, the switch supports up to 128 spanning-tree instances.

In MSTP mode, the switch supports up to 65 MST instances.

pmpesha Thu, 09/04/2008 - 08:13

Thanks for the input. I am on Version 12.1(22)EA11. Is there a recommended version for the 2950, that will support more that 64 STP instances? Thanks.

francisco_1 Thu, 09/04/2008 - 08:21


from 12.1(22)EA11 and later the supported Spanning-Tree Instances are the same as above.


Pls kindly rate.

pmpesha Thu, 09/04/2008 - 08:26


Thanks, If Iam uderstanding you correctly, to get a support for more instances, I do have to upgrade my switch to 2960, or a 3560, 3750.


francisco_1 Thu, 09/04/2008 - 08:32

On 3750, In PVST+ or rapid-PVST+ mode, the switch stack supports up to 128 spanning-tree instances.

On 3550, The switch supports the per-VLAN spanning tree (PVST) and a maximum of 128 spanning-tree instances

So yes if you move to a higer model from the 2950 you get more instances.

May i ask why you need more instances?

pmpesha Thu, 09/04/2008 - 08:50

We have about 4 2950 swiches that are dedicated for icu monitoring. They have two vlans. Every time a change is made to our STP root, their systems get disconnected. The disconnected behavior started after the layer 2 hardenning changes. Things like guard root on the core and guard loop on the access switchs, etc. After discovering the issue, we removed the hardenning on these four switches, and the down stream ports on the core, specifically for these switches. The problem went away, until we created a new vlan which triggered the STP updates, the STP instance are at the muximum on these switches, then we started having disconnection!

francisco_1 Thu, 09/04/2008 - 09:02


Create a new discussion for your STP issues so we can help you properly.

Can you pls rate this discussion.


glen.grant Thu, 09/04/2008 - 13:07

Can you explain why you need even 64 instances on a 2950 ? If you are hooked to a server with more than 64 all that needs to be done is to "manually" prune (remove) off all vlans on the connecting links that are not needed on that 2950.

"switchport trunk allowed vlan XX" .


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