spanning-tree backbonefast + rapid-pvst+ on CatOS

Unanswered Question
Mar 9th, 2010

Dear all,

I have a question about my 6500 CatOS, so those both 6500 Catos are used to connect all my Servers to them, those two 6500 they have redundant Link to our two core switch with layer 2 and 3 switches.

My question is we have backbonefast enabled on both those 6500 Switches running CatOS, so Cisco advise that we have to disable backbonefast before migrating to RPVST, what is the impact to disable this feature on my switches running currently PVST+?

Thanks for your answer and suggestions.

I have this problem too.
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KARUPPUCHAMY MA... Tue, 03/09/2010 - 02:26


Spanning Tree UplinkFast and BackboneFast features are PVST+ features. These are disabled when you enable rapid-PVST+ because those features are built within rapid-PVST+. Therefore, during the migration you can remove those commands. The configuration of the features such as PortFast, BPDUguard, BPDUfilter, root guard, and loopguard are applicable in rapid-PVST+ mode also. The usage of these features are the same as in PVST+       mode. If you have already enabled these features in the PVST+ mode, the       features remain active after the migration to rapid-PVST+ mode.

If you want to migrate your network into RSTP,Better first migrate all the access layer switch to RSTP.then move to server farm switches .Finally make changes of backbone devices.

During the migration process, you can run the LAN in mixed mode, such as       a few switches in PVST+ and a few switches in rapid-PVST+ mode. In mixed mode,       you do not receive the complete advantages of rapid-PVST+. The overall       convergence time is the same as the convergence time of PVST+ mode. In order to       take full advantage of rapid-PVST+, all the switches in the spanning tree       topology must run the rapid-PVST+.



belal.sadozai Tue, 03/09/2010 - 02:44

Hello Karuppu,

Thanks for your quick answer, you pasted this response from the link below:) I have already read it...

But Cisco advise that we have to disable backbonefast before migratin:

  1. Access2 migration:
    1. Access2> (enable) set spantree backbonefast disable
    Backbonefast disabled for all VLANs. Access2> (enable) set spantree mode rapid-pvst+ PVST+ database cleaned up. Spantree mode set to RAPID-PVST+. Access2> (enable) clear spantree uplinkfast This command will cause all portcosts, portvlancosts, and the bridge priority on all vlans to be set to default. Do you want to continue (y/n) [n]? y VLANs 1-4094 bridge priority set to 32768. The port cost of all bridge ports set to default value. The portvlancost of all bridge ports set to default value. uplinkfast all-protocols field set to off. uplinkfast disabled for bridge.
    is there an impact to remove backbonefast like removing uplinkfast from the CatOS?
  • Thanks

    KARUPPUCHAMY MA... Tue, 03/09/2010 - 02:50


    At that time of migration you can remove, there will be no impact.Because all these futures are enabled by default in RSTP.

    But before that if you removed the future, then there will be small impact in STP convergence.Nothing big deal.

    Because i was in one project that the same thing we had a migration from PVST to RSTP then, VTP client server mode to trasparent mode.

    Our Backbone switches are Cat6500 with catos, we have migrated from access layer switches to RSTP first then we moved towards backbone switch on weekly basis.we didnt find any issues on the above,



    belal.sadozai Tue, 03/09/2010 - 05:01

    Yes here the message you got if you dont disable backbonefast

    before migration:

    CatOS does not allow you to change the mode to rapid-PVST if the BackboneFast feature is enabled. You have to disable BackboneFast before the migration. UplinkFast acts as same as it behaves in IOS.

    Access2> (enable) set spantree mode rapid-pvst+
    Cannot change the spantree mode to RAPID-PVST+ when backbonefast is enabled.

    So I must disable it before go to RPVST, and how about IOS? do you know the impact? to disable it because our backbone is two cat6500 IOS, the two other cat6500 CatOS are only used to connect Servers.



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