PVST Interopability

Unanswered Question
Sep 16th, 2009
User Badges:

I am running Cisco switches running PVST with a switch that does not do PVST. When STP is turned on on all switches, the non Cisco switch is essentially transparent to the Cisco switches as far as STP is concerned (the per VLAN BPDUs are simply forwarded by the swtich). The only VLAN instance they interoperate on is VLAN1, which is not useful.


Is there any way to essentially turn off Per VLAN STP behavior on a Cisco switch? What is common solution to interoperate a Cisco switch with one that does not understand per VLAN STP?

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 3 (1 ratings)
Loading.
Peter Paluch Wed, 09/16/2009 - 10:34
User Badges:
  • Cisco Employee,

Hello,


There is no way to turn of the per-VLAN operation of any STP protocol on Cisco Catalyst switches. There are only PVST, Rapid-PVST and MST variants available.


You are completely correct that if you have a switch that does not understand PVST or Rapid-PVST then it simply tunnels the PVST BPDUs and processes only the normal STP or Rapid-STP BPDUs that are derived from the VLAN 1.


The question, however, should not be how to turn off the per-VLAN operation of STP protocols on Cisco switch, but rather, how to turn on this functionality on your non-Cisco switch. I wonder what is the design of your non-Cisco switch if it supports multiple VLANs, yet does not support the per-VLAN STP operation. That does not make much sense, frankly.


As for the open and standards-based version of STP for multiple VLANs, it is the MSTP. Does your non-Cisco switch support the MSTP?


If your switch supports VLANs but does not support MSTP or some other VLAN-aware STP then its usability in redundant topologies with multiple VLANs is strongly limited if not impossible. But if it does not support multiple VLANs that it should not be connected to your Cisco switch by a trunk but only by an access port that runs only the STP instance for the access VLAN on that port that should be understandable to the non-Cisco switch.


Best regards,

Peter


Giuseppe Larosa Wed, 09/16/2009 - 12:35
User Badges:
  • Super Silver, 17500 points or more
  • Hall of Fame,

    Founding Member

Hello,

as Peter suggests check if the product (non cisco switch) supports 802.1s MST standard.


However, moving to MST takes some work and planning.


if the switch is confined at the access layer you may consider to go on with this setup.


To be noted that there are also switches that support only one instance of rapid STP described in 802.1W.


Hope to help

Giuseppe


iyde Mon, 09/21/2009 - 22:47
User Badges:
  • Silver, 250 points or more

Hi.


I had a situation where I needed Cisco switches to cooperate with non-Cisco switches and run 802.1s. The way to make that work was actually to configure the Cisco switch for MST but put all VLAN in instance 0 (in practice not doing any VLAN-to-instance assignment).

Maybe it could be of help to you because it is for sure not a good thing to disable Spanning Tree.

HTH

Actions

This Discussion