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STP & VTP Questions

March 16th, 2020 Go to comments

Note: If you are not sure about STP or VTP, please read our Spanning Tree Protocol STP Tutorial and VLAN Trunking Protocol VTP Tutorial.

Question 1

Question 2

Explanation

The purpose of Port Fast is to minimize the time interfaces must wait for spanning-tree to converge, it is effective only when used on interfaces connected to end stations.

Reference: https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3560/software/release/12-2_55_se/configuration/guide/3560_scg/swstpopt.html

Question 3

Explanation

Enabling the PortFast feature causes a switch or a trunk port to enter the STP forwarding-state immediately or upon a linkup event, thus bypassing the listening and learning states.

Note: To enable portfast on a trunk port you need the trunk keyword “spanning-tree portfast trunk

Question 4

Explanation

The VTP mode of SW2 is transparent so it only forwards the VTP updates it receives to its trunk links without processing them.

Comments (7) Comments
  1. DR D
    May 11th, 2020

    I am pretty sure the answer to #2 is B. I have conferred with a few experts and another study guide. You show C here and on the section quizzes.

  2. DR D
    May 11th, 2020

    or maybe not…I am finding information online that also gives the answer you all have. Apparently there is some debate.

  3. DR D
    May 11th, 2020

    I got some explanation on this from an expert. I was told that the “spanning-tree portfast” command does put the port into a an automatic forwarding state BUT it has nothing to do with reloading the switch. Thus, the best answer provided is B (but none of them are really good). Please share if you all have more information.

  4. shiraz
    May 23rd, 2020

    I also think the correct answer to #2 is B @9Tut

  5. Anwar
    May 24th, 2020

    #2 Seems like Answer is C. It immediately puts the port into the forwarding state when the switch is reloaded

    Understanding Port Fast
    Port Fast immediately brings an interface configured as an access or trunk port to the forwarding state from a blocking state, bypassing the listening and learning states. You can use Port Fast on interfaces connected to a single workstation or server, as shown in Figure 18-1, to allow those devices to immediately connect to the network, rather than waiting for the spanning tree to converge.
    Ref:
    https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3560/software/release/12-2_55_se/configuration/guide/3560_scg/swstpopt.html

  6. Youpi Alex
    August 27th, 2020

    Regarding #2, B is the correct answer.

    When you enable PortFast on a switch or trunk port, the port is immediately transitioned to the spanning tree forwarding state. So C is not correct, because you don’t need to reload the switch to Apply it. Imagine that on production environment, it’s impossible.

    Spanning-tree porfast minimizes STP convergence time, because it doesn’t need to recalculate TCN for portfast edge ports.

  7. 9tut
    August 27th, 2020

    @Youpi Alex: Thanks for your information, we updated Q.2.

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