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Latest post 04-20-2017 6:16 PM by Martinl. 4 replies.
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  • 04-12-2017 4:26 AM

    spanning tree question




    i don`t understand this point into red square , please anyone explain this point to me



    i draw this picture and i need help to understand this point into red square into the book

    how we choose rp and dp into this diagram?

    why we make access ports into sw-3 and sw-4 as dp ? why sw-3 and sw-4 send out bpdu from these ports to end hosts?

    • Post Points: 35
  • 04-20-2017 3:18 AM In reply to

    Re: spanning tree question

    please anyone have any reply?

    • Post Points: 20
  • 04-20-2017 3:59 AM In reply to

    Re: spanning tree question


    please anyone have any reply?


    when your switch connects two ports to an hub, since the hub represents a unic collision domain, the two ports tie for DP election even though the switch gives to each port a separate collision domain. So they can't be both DP at same time.

    At that point normal STP election occurs and port-priority with lowest value is evaluated first to be elected as designated port. If priority is equal then lowest port number becomes designated port.

    • Post Points: 5
  • 04-20-2017 5:09 AM In reply to

    • peety
    • Top 25 Contributor
    • Joined on 02-23-2011
    • Redmond, WA, USA
    • Elite
    • Points 19,825

    Re: spanning tree question

    Why wouldn't access ports on sw3 and sw4 become dp? They face away from the root, so by default they'll want to become dp. For the same reason, they have to send BPDU unless you've enabled bpdufilter: access ports can always form a loop depending on what they're wired to.

    CCIE R&S #34583

    Now based in Redmond, WA

    • Post Points: 5
  • 04-20-2017 6:16 PM In reply to

    Re: spanning tree question


    • Post Points: 5
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