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CCNA – STP

May 5th, 2015 Go to comments

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

Question 1

Explanation

First by comparing their MAC addresses we learn that switch B will be root bridge as it has lowest MAC. Therefore all of its ports are designated ports -> C & D are correct.

On the link between switch A & switch C there must have one designated port and one non-designated (blocked) port. We can figure out which port is designated port by comparing their MAC address again. A has lower MAC so Fa0/1 of switch A will be designated port while Fa0/1 of switch C will be blocked -> B is correct.

Question 2

Explanation

The path cost to the root bridge is the most important value to determine which port will become the root port on each non-root switch. In particular, the port with lowest cost to the root bridge will become root port (on non-root switch).

Question 3

Explanation

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 4

Question 5

Explanation

If we connect two switches via 2 or more links and do not enable STP on these switches then a loop (which creates multiple copies of the same unicast frame) will occur. It is an example of an improperly implemented redundant topology.

Question 6

Explanation

Answer A is not correct because Host A & B can access the server in VLAN 9 via Switch1 -> Switch2 -> Switch3 path.

Answer B is not correct because VLAN3 can communicate with other VLANs via port Fa0/7 on Switch1

Answer C is not correct because Host B can transfer files to VLAN 9 via Switch1 -> Switch2 -> Switch3 path. All the links on this path are FastEthernet so we cannot it would be significantly slower.

Answer D is the best choice as Fa0/9 on Switch1 may be the main path to reach VLAN 9 and it is in forwarding state. If the cable connected to Fa0/9 is disconnected, STP needs less than a minute to re-converge (moving from blocking -> listening -> learning -> forwarding state). Then the network function would resume and Host B will access VLAN 9 via Switch1 -> Switch2 -> Switch3 path.

Question 7

Explanation

PVST+ is based on IEEE802.1D Spanning Tree Protocol (STP). But PVST+ has only 3 port states (discarding, learning and forwarding) while STP has 5 port states (blocking, listening, learning, forwarding and disabled). So discarding is a new port state in PVST+.

Question 8

Question 9

Explanation

Spanning Tree Protocol convergence (Layer 2 convergence) happens when bridges and switches have transitioned to either the forwarding or blocking state. When layer 2 is converged, root bridge is elected and all port roles (Root, Designated and Non-Designated) in all switches are selected.

Question 10

Comments (50) Comments
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  1. goodlucktoall
    September 27th, 2013

    Question 1 was in today’s exam. Thanks 9tut.

  2. sahar
    September 28th, 2013

    thanks 9tut for update questions :D

  3. Anonymous
    September 28th, 2013

    Pls update question 6 picture

  4. Adeel
    September 29th, 2013

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  5. GDR!
    September 29th, 2013

    Question 6 image is broken…

  6. NDANE
    October 1st, 2013

    There is nothing to border about New ccna what about CCNP has any thing change in CCNP

  7. NDANE
    October 1st, 2013

    The CCNP is dived into how many branch thank in advance

  8. yogesh jadhav
    October 7th, 2013

    anybody explain me question no .10.answer

  9. p@ko
    October 8th, 2013

    Hey yogesh

    Try to relate the question 10 with the question 1 and you´ll see that is very similar!!

  10. Anonymous
    October 8th, 2013

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  11. Bufu
    October 22nd, 2013

    Hey Yogesh, sorry for late reply about your question, actually when show writte command sh spanning-tree int or sh spanning-tree int fa0/1 or whatever interface connected to the switch, this will display path cost, designated port and non designated port, so for the switch to be root brigde it must has all states designated, one it has blocked state is not a root brigde anymore, reason can be due to it’s max path cost than any other in the topology

  12. yogesh jadhav
    October 22nd, 2013

    thanx friend

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    October 24th, 2013

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  14. Yogi
    October 27th, 2013

    if i study questions from 9tut and dumps is that enough to pass

  15. biacosta
    November 28th, 2013

    Just took it yesterday, I PASSED with a 920, thanks to 9tut…woooohhhooooo!!!!

  16. Newbie
    December 4th, 2013

    Can someone explain Q6 answer? Seems A is also true? TIA “)

  17. papashango
    December 4th, 2013

    Hi Newbie, for normal operations Switch1,2 and 3 will converge and one port will be in blocking state(STP) if we assume that the primary root for B to communicate with sever is thorugh switch1 port fa0/9 then fa0/7 will be the redundant route to the server. when fa0/9 goes down STP will go through listening, learning to forwarding state. this make D the correct answer for Q6

  18. Shawn
    December 9th, 2013

    I have a Questions on “Q3”.
    I think “D” is also “Right”
    Am I wrong?

    Does anybody know why “D” is wrong?

  19. Syrinx
    December 19th, 2013

    Shawn, it is because D uses the term “layer 3”, but switching is layer 2.

  20. sam
    December 27th, 2013

    can any one explain the question 8?

  21. Abdullah
    January 17th, 2014

    Hi, can anyone ps email me info on how to get the latest VCE 3.4.2 crack version or the version that can open recent dumps.
    My email address is: mehdi01912330796@gmail.com
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  22. mary
    January 29th, 2014

    Q 6 icant understand …..thx u

  23. shota
    February 9th, 2014

    in first questions, one of the answer is mistake.. lower mac has switch C.. because cafe and face, ther is face higher.. there will be correct answers ACD

  24. where?
    February 10th, 2014

    srsly now what r u talking about, the correct answer is there get your information straight.

  25. Anonymous
    February 27th, 2014

    Hi everyone is any explanation about Q6 ? i am really confused about it .

  26. Daya
    March 6th, 2014

    Answer for Q6.
    When a port is disconnected from the switch, new Election process will be taken off. the election process will take few minutes. at that time the network will be slow. Once the election is over, the network will start function normally..
    So answer is
    D. For less than a minute, Host B would not be able to access the server in VLAN9. Then normal network function would resume.

  27. yo
    March 9th, 2014

    please let us know if you recently passed CCNA and what is the name of dump u used

    Thanks.

  28. Al7
    March 12th, 2014

    I cleared 200-120

    Question 5 in today’s exam

    Almost all questions from 9tut

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  29. yo
    March 12th, 2014

    What dump did you study?

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  30. Veronica
    April 2nd, 2014

    please can somebody explain mi question 1,3, and 10?? rest are ok but this 3 questions im lost. Thank you!

  31. N/A
    April 7th, 2014

    Q1.
    Switch B is the Rood Bridge since all switches have a default priority and it has the lowest MAC Address. The Root Bridge will always have all its ports in a “Designated” status.

    Both Siwtch A and C will have interface Fa0/0 as “Root” since they connect to the Root Bridge (Switch B).

    Last, we need to select which Fa0/1 out of switch A and C will be in a designated status. Since the MAC address of Switch 1 is lower the it becomes “Designated”.

    Q3. With PVST you can configure the Root Bridge to be on different switches for each VLAN if you anted to.

    Q10. Since we see that VLAN2 is a in BLK status we can assume that there is another interface that connects to the root bridge, and the way that STP elects which port to be in a forwarding status is with the lowest path cost. That is why we can choose C, because this interface has a higher path cost then another interface that connects tot he Root Bridge.

  32. Eliakim
    April 22nd, 2014

    I feel ready for the theory, can someone please tell me a site where i can find some laboratories to make practice..?

  33. imp
    May 4th, 2014

    in q 10 the ans must be A “A. This switch has more than one interface connected to the root network segment in VLAN 2.” then only an int could be im ALTN BLK (option C)

  34. Anup
    May 15th, 2014

    @imp: For the question no.10 “C” is the right answer coz ….. The port will be blocked only when it has highest cost to reach the root bridge hence we conclude answer is C.

  35. Confused !
    July 8th, 2014

    Q3,5,6,7 were in the today exam

  36. Strange
    July 16th, 2014

    Question 7 was in the exam recently

  37. ibrahim youssouf
    July 29th, 2014

    bonjour.
    j’aimerai composer cisco .juste je pose la question est ce que ce possible de compose en français .

  38. chinmay sharma
    August 7th, 2014

    I could not understand Q10 and the answer.Somebody pls explain me that question and its answer

  39. John
    August 7th, 2014

    Question 10 is a bit tricky.

    Note that only two VLANs are in Root FWD mode. This indicates that there are one of three things going on:

    1. Two Root switches – one for each VLAN (In this case one for 1+3, and one for 2).
    2. Root cost was modified on the -current- switch using: (configure-if)# spanning-tree vlan 2 cost (on a different IF also connected to the root switch)
    3. Port priority was modified on the -root- switch: (configure-if)# spanning-tree vlan 2 port-priority (on a different IF connecting to this switch)

    Option 2 and 3 can use a topology of two switches with redundant connections to one another.
    For option 1 it has to be atleast three switches (fully meshed).
    All three options point to answer C because all point to difference in cost (apart from option 3 since priority isn’t even a possible answer).

    As for answer A. I’m not 100% sure what they mean by “segment”. I’m thinking two switches with one extra link between them.

    This would, with default configurations, put ALL VLANs in the same STP state on each interface. For it to result in discontigous STP states between VLANs, there has to be modifications to the cost or priority – which leads to answer C anyway.

    It’s all about the way STP chooses path: 1. Root cost – 2. BID – 3. Interface priority (low) – 4. Interface number (low)

    Hope this helps.

  40. Sandy6933
    August 9th, 2014

    Thanks for the awesome explanation!

    Keep writing :)

  41. Des†rosiers
    August 9th, 2014

    Passed Marks: 975, 99.8% from 9tut no need to exert effort for latest dumps. Labs EIGRP, ACL Sim 1 & 2, practice all modifications coz it was given on random. 9tut is enough to pass the exam. GoodLuck. .

  42. candea
    August 12th, 2014

    Destrosiers: what do u mean by modification in labs ? thanks.

  43. Anonymous
    August 26th, 2014

    check the labs given here and you will know

  44. JoseLuis
    September 4th, 2014

    Hello

    I have a doubt with the Questioon 8.

    I think it can not be possible to be right, because, despite the SW-C has the lower priotity, the IOS can’t let you type vlan priorities without an increment of 4096, we can not put priority 1, the IOS wont allow it!

    must be a mistake

  45. JasonR
    September 6th, 2014

    @JoseLuis,

    I believe you are correct? 0 not 1, or any increment of 4096. That would mean the priority of SWB and D are also incorrect, as 32769 and 65536 are not /4096.

    This Cisco document seems to suggest 0 can be set but not random #’s- http://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/10588-74.html

    Anyone else more knowledgeable weigh in on this?

  46. JasonR
    September 6th, 2014

    Think I figured it out. PVST BIDs include the extended System ID (VID). So manually entered BID of 0 in a PVST environment with VLAN 1 would make BID 1, and 32769, etc.

  47. Rani
    September 6th, 2014

    Q5 in 5th Sep 2014 exam

  48. Dilan
    September 10th, 2014

    Question number 1 ,,,,MAC address of switch A & switch C ,, why Switch A F0/1 be the designated port it has higher MAC address than Switch C ?

  49. Guillermos
    September 10th, 2014

    The election for the root port is the Lowest MAC Dilan.

  50. HB
    September 16th, 2014

    Passed today with 958

    Q10 was on test

    thanx 9tut

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