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Forum Replies

  1. let me clarify this, correct me if im wrong. this is what i understand on this lesson

    • Link between Sw A and Sw B is down. so Switch B will not receive any BPDU's from root bridge, claiming he's the root bridge.
    • since the link between A and B is down, Switch B's BPDU will send through Switch C.
    • Now switch C receives this BPDU and identifies it as inferior BPDU.
    • Since it receives an inferior BPDU, Switch C will send a Root Link Query on its Root Port to check if the root bridge is still available (this is the purpose of RLQ? to check if root bridge is availa
    ... Continue reading in our forum

  2. Hi John,

    All steps that you described are correct, that’s how it works.

    SwitchB doesn’t have a link to the root bridge so it claims to be the new root bridge. SwitchC which is still connected to the root doesn’t agree so it drops the inferior BPDU from SwitchB.

    We want to get rid of the max age timer, that’s 20 seconds so instead we let SwitchC do a quick “check” to see if the root bridge is still reachable by sending a RLQ. When it receives a RLQ reply, it knows the root is still there and it can age out the interface immediately.

    In case you don’t get a RLQ r

    ... Continue reading in our forum

  3. Mohammad,
    Switch C receives an inferior BPDU (meaning a worse BPDU) on Fa0/16. This worse BPDU was created by Switch B because after Switch B’s link to Switch A went down, Switch B now believes it is the Root Bridge. Since it is the job of the Root Bridge to create BPDUs, Switch B is doing what it thinks is the proper activity. However, Switch C knows that Switch B is mistaken. It knows this because Switch C is still able to receive superior BPDUs (meaning better) from the true Root Bridge, Switch A.

    Bridge ID is determined by a combination of Priority and

    ... Continue reading in our forum

  4. Hi Samer,

    It’s best to use PVRST. Uplink fast and backbone fast are two enhancements for “classic” spanning-tree. Rapid spanning tree has similar mechanisms so you don’t need to configure this anymore.


  5. SW1 receives a new packet called a (RLQ) Root Link Query from SW3. As soon as SW3 receives an inferior BPDU it will send a root link query on its root port and non-designated ports to check if the root bridge is still available.

    Is this true? It will send an RLQ on non-designated ports?

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