BackboneFast & STP failures ...

[steven.cascio]

I am currently looking at a net that is experiencing loops due to STP failures. In looking at the core/dist configs (65xx’s) Backbonefast is set but at the access layer (2950’s) Backbonefast is not set. All recommendations I have seen is that Backbonefast should be set on *ALL* switches … but I have not seen any risks for not following this recommendation. What is the risk of the config as I have described (in terms of uncontrolled loops) … is it worth investigating this as a contributing problem?

Thanks,

Steve

[ssoberlik]

Steve,

If a new switch is introduced into a shared-medium topology, BackboneFast is not activated. The new switch begins sending inferior BPDUs that say it is the root switch. However, the other switches ignore these inferior BPDUs and the new switch learns that Switch B is the designated bridge to Switch A, the root switch. For more information, try this URL:

Understanding How BackboneFast Works

http://www.cisco.com/en/US/products/hw/switches/ps679/products_configuration_guide_chapter09186a008007f75f.html#xtocid14769