Impact on layer 2 network and Switches - Running more than 1100 VLAN with PVST+

[zahid.kalwar]

What will be the impact on the network and switches if we create let say 1100 to 1400 VLANs with PVST+ on Cisco Cat Switches - i.e CPU will be high, not supported or any other STP related issues. What is the best practice.

Thanks,

ZK

[Francesco Molino]

Hi

Pvst will run 1 stp instance per vlan and more instance you use more cpu you consume.
Platforms have a limited number of stp which can be checked out on the documentation guide. For example 9500 can have 128 stp instances max.

In these circumstances, I will prefer mstp where you'll run 1 instance for a group of vlans.

[zahid.kalwar]

Thanks Francesco.

Could you please send few links so that I can read about more cpu consumption for each instance and limit of instance for few switch platforms.

Thanks.

[lucasfreitas83]

Hello Zahid,

I think not to exist a document that describe CPU consumption and that each model supports.

To verify models supports, verify in the datasheet.

The Cisco troubleshoot documents, mentioned.

A Layer 2 spanning-tree instance runs for every VLAN configured on a Layer 2 switch by the per-VLAN spanning-tree (PVST) feature. The CPU time utilized by spanning tree varies depending upon the number of spanning-tree instances and the number of active interfaces. The more instances and the more active interfaces, the greater the CPU utilization.

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3750/software/troubleshooting/cpu_util.html#38092

Please rate and mark posts accordingly if you have found any of the information provided useful.
It will hopefully assist others with similar issues in the future.

Best regards,
Lucas Freitas

[Francesco Molino]

There are no such documentation. You can get these infos from troubleshooting guide.