Platform limit of 64 STP instances exceeded

MurielleBRAZIER · ‎02-27-2012

Hi

We are using C2950G-48-EI (12.1(22)EA12) switchs on our lan.

We have created a lot of vlans (more than 64) and set up the spanning-tree for each one.

On the switches a syslog message "Platform limit of 64 STP instances exceeded" is displayed.

I understand that exceeding this limit should cause performance issues. How can I :

Increase this limit ?

known the limit implemented (in order to anticipate problems by futur ?)

Thanks for your help...

Murielle

Jon Marshall · ‎02-27-2012

Murielle

You can't increase it as it is a hardware limitation not software. Couple of options -

1) do you need all vlans on all switches. If not then limit the vlans on each switch by using the "switchport trunk allowed vlans ..." on the trunk links. If the vlan is not allowed on the trunk link then STP is not run across the link and to the switch

2) look at MSTP where you can group vlans into STP instances which means you can run a lot less STP instances. See the config guide for details -

http://www.cisco.com/en/US/docs/switches/lan/catalyst2950/software/release/12.1_22_ea11x/configuration/guide/swmstp.html

Jon

Peter Paluch · ‎02-27-2012

Jon,

It is so good seeing and reading your responses once again!

Best regards,

Peter

milan.kulik · ‎02-28-2012

Hi Murielle,

just to add to Jon's reply:

I remember I met the same problem several years ago and the IOS behaviour was really strange:

When 65 VLANs were created, it just stopped an STP instance running in one of the VLANs.

But not in that VLAN which was created as the last one! Just in one random VLAN :-((

So this limit was not just a performance issue, it could create L2 loops in the LAN easily.

Hopefully Cisco guys fixed that behaviour a little in the meantime, but still I'm afraid it's quite dangerous.

BR,

Milan