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RSTP confusion

Hi everyone.

I have some questions about RSTP. Cisco says that UplinkFast and BAckboneFast are natively included into RSTP thus ARE NOT SUPPORTED IN IT. But what a hell does this mean? What will RSTP switch do if it lose root port??? Recalculate STP with proposal-agreement sync? Or will launch something similar to UplinkFast? It is a little bit confusing. Please help, because I dont get it.

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Cisco Employee

RSTP confusion

Hello Volodymyr,

Yes, you are correct. RSTP internally contains mechanisms that make up the core of UplinkFast and BackboneFast extensions. It may not do things in exactly the same way but it achieves the same goals.

You are also correct in stating that with RSTP, it is pointless to turn on the UplinkFast and BackboneFast. In fact, you can't even do that: if you have RSTP activated then the commands spanning-tree uplinkfast and spanning-tree backbonefast may be present in the configuration but will be ignored and will have no effect.

Best regards,

Peter

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New Member

RSTP confusion

Hi,

If RSTP running switch loses its root port , spanning tree will converge . There won't be any recalculation.

RSTP has backbonefast and uplinkfast inbuilt in it. As compared to STP, RSTP doesnt have listening state so it will directly transition from blocking to learning . Hence speeding up the convergence by 20 seconds

HTH,

Sukanya

PS: Please rate helpful posts...

Cisco Employee

RSTP confusion

Hi Volodymyr,

The Cisco UplinkFast and BackboneFast are optimizations to the basic STP algorithm. When RSTP was developed and standardized, the main algorithms on which UplinkFast and BackboneFast were based were adapted and incorporated into RSTP design. In other words, RSTP natively contains algorithms that were inspired and partially retaken from UplinkFast and BackboneFast extensions and that provide the same function as Uplink/BackboneFast without actually needing to activate them explicitly.

So with RSTP, you have UplinkFast-alike and BackboneFast-alike functionality immediately as soon as you activate RSTP, and it makes no sense to activate these mechanisms explicitly. These commands would have no effect on RSTP operation, anyway.

Does this make it more clear? Please welcome to ask further!

Best regards,

Peter

RSTP confusion

Yeap))) I have read Cisco materials more carefully. The answer is out there. There is no Uplink and Backbone FAst features in RSTP, but there are a little bit similar features. So as I can conclude Uplink and Backbone features are included in Rapid-PVST but it is pointless to turn them on since RSTP algorithm is naturally better by its calculation. Right?

Cisco Employee

RSTP confusion

Hello Volodymyr,

Yes, you are correct. RSTP internally contains mechanisms that make up the core of UplinkFast and BackboneFast extensions. It may not do things in exactly the same way but it achieves the same goals.

You are also correct in stating that with RSTP, it is pointless to turn on the UplinkFast and BackboneFast. In fact, you can't even do that: if you have RSTP activated then the commands spanning-tree uplinkfast and spanning-tree backbonefast may be present in the configuration but will be ignored and will have no effect.

Best regards,

Peter

RSTP confusion

Thanks)))

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