STP port timers???

Unanswered Question
Sep 23rd, 2008
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Hi all,


I'm currently preparing for the CCIE R&S exam and recently ran into a WORKBOOK PREPARATION question on STP timers for which I believe the provided answer is incorrect. I have not had any feedback to my questions, so I was hoping anyone here might feel inclined to assist in clearing this up?!


The question is to have switchports take 40 seconds to forward traffic after initialization in a standard 802.1D enviroment.


The workbook solution is to configure ForwardDelay as 10secs. The logic behind this is that in regular 802.1D without Portfast configured, a port will need 2xForwardDelay (Listening+Learning) + 20seconds Blocking State, before Forwarding. The solution goes further to suggest that there is an implicit 20second Blocking state that cannot be changed.


I have been researching and testing this but cannot confirm this stated solution whatsoever. My own solution would be a ForwardDelay of 20seconds, since all ports move straight into Listening state after initialization. There may be an initial Blocking state, but no Debug output I have seen to date supports this. I have seen some Cisco Documentation that states that all ports start out in Blocking State, but again, I have not been able to see this in action.


I realize that within 802.1D there is the MaxAge timer which may cause a currently Blocking port to remain Blocking before flushing BPDU information and transitioning into Listening and Learning to Forwarding, but this does not apply to initializing interfaces.


Any comments, pointers or even better, hard proof would be very much appreciated!!!!


Thanks,

Reinier


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