cisco 9500-40x - Max number of STP instances only 128

[carl_townshend]

Hi All

We cam across an issue on our 9500-40X switch, we had loads of errors saying max number of stp instances reached or something similar, this was at 128 only.

However when I run the command, show sdm prefer, it shows the below and tells me it should be 1024

Why is this not the case?

128 instances seems low to me

This is the Distribution template.
Number of VLANs: 4094
Unicast MAC addresses: 65536
Overflow Unicast MAC addresses: 1024
L2 Multicast entries: 16384
Overflow L2 Multicast entries: 1024
L3 Multicast entries: 16384
Overflow L3 Multicast entries: 1024
Directly connected routes: 49152
Indirect routes: 65536
STP Instances: 1024

[Reza Sharifi]

Carl,

128 instances is a lot if instance. You can have one or 2 instances and put 500 or a 1000 VLANs per instance. You don't need to put each vlan in a different instance. 

HTH

[carl_townshend]

Yes I am aware of that using MST instances, however my 12 year old Cat 6509 has way more instances that that so why a new switch has less I do not know, also the SDM template says more, so it does not add up

[Reza Sharifi]

6500 is different as the limitation is based on chassis and/or the line cards. 

Here is a document showing the limitation per platform. Note that this document is a  bit old.

As for the 9500 128 vs 1024, it would make sense for it to be at 1024 since 9500 is considerd a core switch but not sure why you get the 128 limitation error. It could also be a bug in the IOS version.

https://blog.habets.se/2009/06/Spanning-tree-limits.html

HTH