STP election...when does it end?

Discussion in 'Cisco' started by ciscopimpenator@gmail.com, Apr 13, 2007.

  1. Guest

    I'm reading a book that talks about STP.

    They give a diagram of 3 switches that are competing for root bridge
    status. My question is when does the election end exactly? The
    book talks about the process of exchanging BPDU's with each switch
    advertising themselves as root bridge. Then after they realize their
    buddy next to them has a better a bridge ID they advertise him as the
    root bridge.

    So now we have all three switches realizing one of them is root
    bridge. When does the election end exactly? After they receive 5
    consecutive BPDU's stating that SW1(switch 1) is root bridge? Are
    their timers? It never mentions exactly how it ends. It just says
    SW1 wins!!! How did they decide SW1 wins?
    , Apr 13, 2007
    #1
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  2. Guest

    I kept reading and found the answer. The ports are in a listening
    state by a default time of 15 seconds. For this amount of time they
    listen for BPDU's and forward them. Is this correct? By the time
    they transition to learning they should know who the root bridge is.
    , Apr 13, 2007
    #2
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  3. saintjmf Guest

    On Apr 12, 11:39 pm, ""
    <> wrote:
    > I kept reading and found the answer. The ports are in a listening
    > state by a default time of 15 seconds. For this amount of time they
    > listen for BPDU's and forward them. Is this correct? By the time
    > they transition to learning they should know who the root bridge is.


    Yes that is correct.
    Listening and learning I believe.

    There is also some setting cant remember right now but it can be set
    to adjust this by putting in the possible switch traversals into the
    equation.
    saintjmf, Apr 13, 2007
    #3
  4. David Rosa Guest

    On Apr 13, 3:58 am, ""
    <> wrote:
    > I'm reading a book that talks about STP.
    >
    > They give a diagram of 3 switches that are competing for root bridge
    > status. My question is when does the election end exactly? The
    > book talks about the process of exchanging BPDU's with each switch
    > advertising themselves as root bridge. Then after they realize their
    > buddy next to them has a better a bridge ID they advertise him as the
    > root bridge.
    >
    > So now we have all three switches realizing one of them is root
    > bridge. When does the election end exactly? After they receive 5
    > consecutive BPDU's stating that SW1(switch 1) is root bridge? Are
    > their timers? It never mentions exactly how it ends. It just says
    > SW1 wins!!! How did they decide SW1 wins?


    When a switch learn a BPDU with a root bridge and a priority more low
    that it stop sending BPDU's and only look new BPDU's.
    David Rosa, Apr 15, 2007
    #4
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