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475 Views 10 Replies Latest reply: Feb 29, 2012 6:58 AM by arteq RSS

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STP port states

Feb 29, 2012 4:06 AM

Keith 166 posts since
Jan 5, 2011

Hi,

 

I am confused with the STP port states, how long a port will transistion from Block to Forwarding, from the Cisco LAN Switching it describes a port will wait for 15 sec before going into listening state and wait another 15 sec in the learning state so that a total 0f of 30 sec.

 

Then it go on to say that the forward delay controls both states of only 15 secs

 

 

Cisco LAN Switching (CCIE Professional Development)

 

  • arteq 1,733 posts since
    Sep 11, 2011
    Currently Being Moderated
    2. Feb 29, 2012 4:47 AM (in response to Keith)
    Re: STP port states

    consider that with plain old stp it may take anywhere from 30-50 seconds to fully transition from blocking to forwarding...  15 and 15 comprise the listening and learning to forwarding transition, which can take the whole of 30 seconds... think of basic stp as a simple yardstick measure; there are a variety of methods to reduce convergence...

  • cadetalain 2,642 posts since
    Sep 18, 2008
    Currently Being Moderated
    4. Feb 29, 2012 5:00 AM (in response to Keith)
    Re: STP port states

    Hi,

     

    15s + 15 s = 30 s

  • Aninda 302 posts since
    Jun 19, 2010
    Currently Being Moderated
    6. Feb 29, 2012 5:15 AM (in response to Keith)
    Re: STP port states

    Not sure what the book is trying to imply, but the listening and learning states are 15 seconds EACH. So thats 30 seconds in total just like everyone has been saying so far.

  • cadetalain 2,642 posts since
    Sep 18, 2008
    Currently Being Moderated
    7. Feb 29, 2012 5:17 AM (in response to Keith)
    Re: STP port states

    Hi,

    fwd delay is 15s and you must wait 2 X fwd delay so it makes 30 s

  • arteq 1,733 posts since
    Sep 11, 2011
    Currently Being Moderated
    8. Feb 29, 2012 5:25 AM (in response to Keith)
    Re: STP port states

    i've done this with my lab, you can actually see the transition from lis to lrn on the switch using sh spann... while each transition state may not take all of 15 seconds each, it is a good barometer...  remember that nothing is written in stone, and actual results may very depending on equipment...  30 to 50 total is the conventional wisdom with 15s each ascribed to lis and lrn states... not sure how much clearer this can be...

  • arteq 1,733 posts since
    Sep 11, 2011
    Currently Being Moderated
    10. Feb 29, 2012 6:58 AM (in response to Keith)
    Re: STP port states

    wow...

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