PRE-STD BPDU's

Answered Question
Oct 13th, 2006
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Hi all


when a switch interface receoved a PRE-STD BPDU is create an error message and teh receiving interface has to be configured to only accept PRE-STD bpdus.


I am running MST/RSTP between my switches.


However, this is happening to me even if the sending switch is actually a new 3750 and running an IOS that I know uses IEEE MST format.


Why woudl a new switch with new IOS send PRE-STD bpdud?


TIA


Sam

Correct Answer by Francois Tallet about 10 years 10 months ago

Hi Sam,

Well, nothing much more that what I mentioned previously. A standard switch only sends pre-standard bpdus on an interface:

-if it has received a pre-standard bpdu on the interface

-or if it is explicitly configured to send pre-standard bpdu on this interface.

If you see another behavior, it's a bug!

Regards,

Francois

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Francois Tallet Fri, 10/13/2006 - 17:52
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Hi Sam,

If a standard switch receives a pre-standard bpdu, it automatically start sending pre-standard bpdus itself. Of course, the other possibility would be that your standard switch is configured on the interface to send pre-standard bpdus.

Regards,

Francois

PS: initially, we wanted to always auto-detect pre-standard switches. But in some cases, the auto-detection fails. That's why we had to add the interface command.

cisco_lad2004 Fri, 10/13/2006 - 22:50
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Hi Francois


yes I agree, what I do not understand is why this new switch is doing it. it is a 3750 with new IOS. I am using a similar switch and IOS in my metro ring and it is acting fine. The receiving switch (which was already configured) was also sending and receving STD BPDU before the insertion of the new 3750 in the ring. The configuration of the swiches is consistent. so I dont understand why pre-STD BPDU are sent or received at all.


does this happen when an old switch model is used, older IOS and as u mentionned specifically configured interface ? what triggers PRE-STD BPDU's.


TIA


Sam

Correct Answer
Francois Tallet Mon, 10/16/2006 - 08:51
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Hi Sam,

Well, nothing much more that what I mentioned previously. A standard switch only sends pre-standard bpdus on an interface:

-if it has received a pre-standard bpdu on the interface

-or if it is explicitly configured to send pre-standard bpdu on this interface.

If you see another behavior, it's a bug!

Regards,

Francois

cisco_lad2004 Tue, 10/17/2006 - 06:15
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Hi Francois


Then it is a bug :-)

I am using same switch type and IOS and al is fine. teh latter switch was the last introduction.


Once again many thanks


Sam



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