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Forum Replies

  1. Hi Rene

    It is a great lesson to understand the Topology change on the STP. I have a question which is related to the switches which receives only BPDU with TCN flag set from the Root bridge

    Assume that Switch network has few more switches and TCN notification generated by switch ( switch A on the diagram) has not been pass through on these switches . I need to know what would be the mac address aging time for the other switches which receives BPDU’s with TCN flag set. My understanding is if a switch in the switch network received the TCN from the Root bridge t

    ... Continue reading in our forum

  2. Hello Rene,

    I am getting confused with this concepts in STP, The more i read the more i am getting confused
    Please help me upnderstand this concepts, I 've wriiten my understanding and questions.

    In a Steady state Network assuming the packet between computer A and Computer B takes (Switch B --> Switch A --> Switch C --> Switch D)

    **Question related to interface states and convergence time**

    Switch C (Root Bridge) generates configuration BPDU’s and sends it to Switch A and Switch D and in turn they relay it to switch B
    When we have an indirect link failure (shut

    ... Continue reading in our forum

  3. Hi Rene,

    What are the scenarios when the TCN bit is set or a TCN BPDU is sent by a switch? Is it only when a port goes down or comes back up in a switch or even when a root bridge gets updated in a switch?

  4. EDIT: Having looked into this further, I don’t think the process as described in the article is actually correct… if the root port on SW1 goes down, rather than sending a TCN, it will start sending inferior BPDUs to SW2. That’s according to this: https://learningnetwork.cisco.com/thread/63525

    In the scenario given, it says that SW2 receives the TCN from SW1 and then immediately makes Fa0/19 the new root port.

    A topology change doesn’t necessarily mean that the root port needs to change, so how does it know to immediately change the root port? My suspicion is th

    ... Continue reading in our forum

  5. Thanks for the reply Laz.

    According to this article, switches in a spanning tree topology send TCNs out of their root port. In the scenario, SW1’s port fa0/14 is not a root port therefore it shouldn’t send a TCN out of that port.

    Or is it the case that if a switch detects that it’s root port has gone down, it sends a TCN out of designated ports instead?

    These are the tiny little details that make STP operation very hard to master :slight_smile:

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