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STP Questions 2

November 17th, 2018 Go to comments

Note: If you are not sure about Spanning Tree Protocol, please read our Spanning Tree Protocol STP Tutorial.

Question 1


When you enable PortFast on the switch, spanning tree places ports in the forwarding state immediately, instead of going through the listening, learning, and forwarding states.

Question 2

Question 3


Root port is the port on non-root bridge which is closest to the root bridge (in term of cost). Therefore when a port receives the best BPDU on a non-root bridge it will become the root port.

Question 4


We can configure the port priority to change the preferred forwarding interface as we wish. For example we can change the port priority of an interface for VLAN 20 to 64 as follows:

Switch(config-if)#spanning-tree vlan 20 port-priority 64

Question 5


Per VLAN Spanning Tree (PVST) maintains a spanning tree instance for each VLAN configured in the network. It means a switch can be the root bridge of a VLAN while another switch can be the root bridge of other VLANs in a common topology. For example, Switch 1 can be the root bridge for Voice data while Switch 2 can be the root bridge for Video data. If designed correctly, it can optimize the network traffic.

Question 6

Question 7

Question 8


PortFast BPDU guard prevents loops by moving a nontrunking port into an errdisable state when a BPDU is received on that port.

In a valid configuration, PortFast-configured interfaces do not receive BPDUs (because PortFast should only be configured on interfaces which are connected to hosts). If a PortFast-configured interface receives a BPDU, an invalid configuration exists. BPDU guard provides a secure response to invalid configurations because the administrator must manually put the interface back in service.

Reference: http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst4000/8-2glx/configuration/guide/stp_enha.html

Question 9

Question 10


First, the question asks what switch services the printers, so it can be Switch 3 or Switch 4 which is connected directly to the Printers.

Next, by comparing the MAC address of Switch 3 and Switch 4 we found that the MAC of Switch 3 is smaller. Therefore the interface connected to the Printers of Switch 3 will become designated interface and the interface of Switch 4 will be blocked. The picture below shows the roles of all ports:


DP: Designated Port
RP: Root Port
BP: Blocked Port

(Please notice that Switch 1 will become the root bridge because of its lowest priority, not Switch 3)


Comments (23) Comments
  1. Joel
    June 13th, 2017

    Found this VCE with the CCNA questions, can anyone confirm if this are valid https://drive.google.com/open?id=0B5mAFqgydmCza1ViTmFlNkQwYzg

  2. Lanny
    June 19th, 2017

    Thanks for sharing Joel, the dumps are valid.

  3. Anonymous
    June 24th, 2017

    Cannot open, please help

  4. Anonymous
    July 6th, 2017

    Or to be rude but q3 is bit confusing with the question be asked

  5. Anonymous
    July 6th, 2017


  6. Mike
    July 27th, 2017

    Question 9
    Ans: 802.1Q and STP

  7. Anonymous
    August 6th, 2017

    @Mike, 802.1D is the IEEE MAC Bridges standard which includes Bridging, Spanning Tree and others. IEEE 802.1Q is the networking standard that supports virtual LANs (VLANs) on an Ethernet network.

  8. Anonymous
    September 2nd, 2017

    Why does question 14 and 15 have different answers but asking for the same thing

  9. Anonymous
    September 4th, 2017

    Regarding Q14, I believe the correct answer is B, according to the official documentation from Cisco:

  10. 9tut
    September 4th, 2017

    @Anonymous: Yes, answer B is the correct answer. It is very difficult to understand when it stands alone. Thanks for your contribution!

  11. anon
    September 9th, 2017

    I question the explanation and answer on 14.

    Just because you lower the priority does not mean the election process halts right then. the process has to find which one has the lowest priority first. Once that is confirmed then it would stop.

    So I think A is a valid answer.

  12. johnyb
    November 9th, 2017

    Which statement about spanning-tree root-bridge election is true?
    A. It is always performed automatically
    B. Each VLAN must have its own root bridge
    C. Each VLAN must use the same root bridge
    D. Each root bridge must reside on the same root switch

    What is the correct answer in this question??A or C??

  13. Dave
    November 11th, 2017

    @johnyb the correct answer is B

  14. DELES
    February 12th, 2018

    @Johnb > It is A, as more than one VLAN can have the same root bridge

  15. NAN
    August 9th, 2018

    Share a useful link, the content inside is true and effective.

  16. NAN
    August 9th, 2018

    htt p:/ /t.cn/ RDf8DJW

  17. Johnny fdz
    January 5th, 2019

    i don’t know what is asking!

  18. Colin
    February 4th, 2019

    Which switch would STP choose to become the root bridge in the selection process?
    A. 32768: 11-22-33-44-55-66
    B. 32768: 22-33-44-55-66-77
    C. 32769: 11-22-33-44-55-65
    D. 32769: 22-33-44-55-66-78

    Answer: A

    Should the answer not be ‘C’ as it has a higher priority??

  19. colin
    February 4th, 2019

    Ignore that…lower priority!! **face palm!!**

  20. Ken Chanpitou
    April 2nd, 2019

    I need a recommend from whom who has an experience with ccna exam how can i find a dump for read a question? anyone can assist about this? many thanks.

  21. Anonymous
    June 1st, 2019

    @Ken Chanpito type mediafire in search here in the site and you will find it.

  22. jh
    November 6th, 2019

    why are there references in the comments to q14 & q15 when i only see up to q10 ?

  23. spantella
    February 14th, 2020

    Question 2
    Which switch would STP choose to become the root bridge in the selection process?
    A. 32768: 11-22-33-44-55-66
    B. 32768: 22-33-44-55-66-77
    C. 32769: 11-22-33-44-55-65
    D. 32769: 22-33-44-55-66-78

    Answer: A ..?

    Should the answer not be ā€˜Cā€™ as it has a LOWEST priority?? 65 is Lower than 66…

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