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2339 Views 0 Replies Latest reply: Nov 30, 2011 2:49 AM by Stephen RSS

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STP inferior BPDU on a blocked port

Nov 30, 2011 2:49 AM

Stephen 527 posts since
Apr 22, 2011

Hi Guys,

 

I can't get my head around this comment regarding inferior BPDU's:

 

" If the inferior BPDU arrives on a blocked port, the root port and other blocked ports on the switch become alternate paths to the root bridge." 

 

Why does the root port suddenly become an alternate port on the switch that received the inferior BPDU?  The BPDU is inferior, indicating that an indirect link failure has occurred.  So in this scenario, the blocked port would just ignore the inferior BPDU until the max age time, and then send out a superior BPDU so that the port can transition from listening ---> forwarding.  However , what is the reason the root port gets set as an alternate port?  You're just basically killing your working switch.

 

 

Regards,

 

Stephen

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