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STP Questions

August 4th, 2011 in ICND2 Go to comments

Here you will find answers to STP Questions

If you are not sure about STP, please read my Spanning Tree Protocol tutorial first.

Question 1

STP_root_bridge_selection.jpg

Which switch will be chosen as root bridge and why?

A. Sw-B, because it has the highest MAC address
B. Sw-A, because it has the lowest MAC address
C. Sw-C, because it has the lowest priority
D. Sw-D, because it has the highest priority

Answer: C

Explanation

The bridge with the lowest bridge ID will become the root bridge. The bridge ID = Priority + MAC so the lowest priority will be chosen first. If all switches’ priorities all equal then their MAC will be compared (the lowest is the best).

Question 2

STP_blocking_port.jpg

Spanning Tree Protocol has created a loop-free logical topology in the network that is pictured. How many ports have been placed in the blocking mode?

A. two
B. none
C. three
D. one
E. four


Answer: A

Explanation

The best way to solve this question is to suppose that one of these switches is the root switch (bridge). For example, if we choose S2 the root bridge and all of its ports will be in forwarding state (so that they are not blocked).

Also suppose that S1 has higher priority than S3 -> the port on S3 connected to S1 will be blocked.

STP_blocking_port_root_port.jpg

The most difficult problem is that how can we know which port on S4 will be in blocking state. Well, it depends on the Sending Port ID on S4 (Port ID = port priority + port index). If using default values, the default port priority’s value is the same, so S4 will compare port index values, which are unique to each port on the switch. One more time, we suppose S4 connects to S1 via Fa0/1 and S4 connects to S3 via Fa0/2. Because Fa0/2 is inferior to Fa0/1, S4 will select the port connected with Fa0/1 as its root port and block the other port.

STP_blocking_port_block_port.jpg

Question 3

STP_blocking_port.jpg

What is the way that Spanning Tree Protocol prevents switching loops based on the exhibit provided?

A. STP shuts down S3 to eliminate the switching loops.
B. STP identifies cables that must be disconnected to eliminate the redundant paths.
C. STP load balances traffic evenly across the redundant links.
D. STP places ports into the blocking state to disable the redundant paths.
E. STP allows the switches to communicate with a router that makes the traffic forwarding decisions.


Answer: D

Question 4

The following network was designed to provide reliability through redundancy.

STP_loop_free.jpg

Both of the IDF switches, S3 and S4, are in connection with both of the MDF switches, S1 and S2. A loop-free switching environment is nedded, which configuration scenario will achieve this?

A. Spanning Tree Protocol should be running on all switches.
B. Spanning Tree Protocol should be running only on the root bridge.
C. Spanning Tree Protocol is not needed in this network.
D. Spanning Tree Protocol should be running on only the MDF switches S1 and S2.


Answer: A

Question 5

Which two values are used by Spanning Tree Protocol to elect a root bridge? (Choose two)

A. Amount of RAM
B. Bridge priority
C. IOS version
D. IP address
E. MAC address
F. Speed of the links


Answer: B E

Question 6

Which two of these statements regarding RSTP are correct? (Choose two)

A. RSTP cannot operate with PVST+.
B. RSTP defines new port roles.
C. RSTP defines no new port states.
D. RSTP is a proprietary implementation of IEEE 802.1 D STP.
E. RSTP is compatible with the original IEEE 802.1 D STP.


Answer: B E

Question 7

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

Comments (84) Comments
  1. NiggaPlz
    June 9th, 2011

    “Also suppose that S1 has higher priority than S3 -> the port on S3 connected to S1 will be blocked.”

    So on switches that connect multiple segments, the switch with the +higher+ priority wins?

  2. xallax
    June 9th, 2011

    i thought it was LOWER priority wins…
    http://www.ccnacertificationguide.com/Root_Bridge_Election.php

  3. Anonymous
    June 20th, 2011

    If the cost is the same on a given segment, the port with the lowest bid becomes the designated port. The other port on this segment will be put into the blocking state.

  4. Anonymous
    July 16th, 2011

    Question 7 is C not A lowest MAC wins

  5. Anonymous
    July 16th, 2011

    Yes I am an idiot… I see the “8” now.

  6. 508122
    July 20th, 2011

    That is correct, the answer to Question 7 is A because it has the lower priority (32768) – Please read about the election process again.

  7. Anonymous
    July 28th, 2011

    I think on question 2 you got it backwards, If the switch has a lower priority, then its ports will be in fowarding / root port mode and the inferior higher priority switch will be in blocking mode???

  8. jimdozer999
    August 3rd, 2011

    The reason the lower Priority and MAC ID’s win the root election, is to help retain compatibility with older equipment. Older Switches may not support features of newer switches; therefore, some aspects like RSTP on newer switches would disable the network on the older LAN. You would however, lose the ability of RSTP on the newer switches.

  9. twigonometry
    August 13th, 2011

    I would have thought answer D to question 4 is just as valid as answer A. See: http://www.cisco.com/en/US/tech/tk389/tk689/technologies_tech_note09186a0080890613.shtml

    “Note: Switches that do not run STP still forward the bridge protocol data units (BPDUs) that they receive. In this way, the other switches on the VLAN that have a running STP instance can break loops. Therefore, STP must run on enough switches in order to break all the loops in the network. For example, at least one switch on each loop in the VLAN must run STP. You do not need to run STP on all switches in the VLAN. However, if you run STP only on a minimal set of switches, a change to the network can introduce a loop into the network and can result in a broadcast storm.”

    If we run STP on just two switches that would be enough to put one port into blocking mode thus breaking the loop??

  10. PhxAZ
    August 15th, 2011

    anyone have any dumps on the fram-relay sim where you map layer to ip address
    and also ask about what password you use to access dubi router
    four part sim question?

  11. Anonymous
    August 26th, 2011

    Lost of guys are confused the blocking state of a switch

  12. Grrr
    September 8th, 2011
  13. Descender421
    September 19th, 2011

    On question 2 under the second answer diagram, the Switch 4, Fa0/1 isn’t a root port, is it? Shouldn’t it be a designated port? Or am I wrong.

  14. Descender421
    September 19th, 2011

    Disregard previous.

  15. Bruno
    September 25th, 2011

    Q1 question: How come that we have “Priority 1” and “65535” in the exhibit in question??
    Those values are NOT vlaid values for spanning-tree priority?? The correct values starts from 0 and steps in increments of 4096?? so did I miss anything ?

  16. mmallery@embarqmail.com
    November 13th, 2011

    Can you send me the latest updates, Thank you

  17. Raynm3n
    December 11th, 2011

    @Bruno

    Hi! yes – you are missing the Extended System ID, and CISCO per-VLAN STP approach.
    As every switch has its VLAN 1 in place this will make its priority 0 + 1 = 1.
    In case of 65535 the Extended is disabled making possible to span for the entire pool of 0 – 65535. Some switches wont allow the Extended SysID to be disabled but I think on catalyst 6500 for example, putting a priority on 65535 will make that switch not to be candidate for ROOT Bridge ever.

    Regards

  18. vin
    December 16th, 2011

    Q6 shouldn’t “A” be correct too? RSTP should only be able to support PVRST and MIST right?

  19. Anonymous
    December 16th, 2011

    @vin

    According to Wendell Odem-ICND2, P.88, it says PVST+ does not support RSTP. But a quick google search says they can work together. Is Wendell wrong on this, anyone know?

  20. BARRY
    December 20th, 2011

    @Anonymous,
    I started hating Wendell Odom when I read the first few chapters of his ICND1/2 books… he is impossible to understand. Read the Todd Lemle book Edition 6th

  21. anyone
    December 25th, 2011

    @Anonymous

    yep, try to read for Todd Lammle or Richard Deal.

  22. baby_boy
    January 15th, 2012

    is this updated?

  23. CiscoGuy
    January 27th, 2012

    2 questions can be found in the TestKing software for 640-816.

  24. WKC
    January 28th, 2012

    Passed ICND2 today with 944!! I didn’t have any of these questions on my exam

  25. alin
    February 1st, 2012

    could you tell me how many questions are from P4S with 204 questions?

  26. Rick
    February 8th, 2012

    @Barry
    I find the opposite – I prefer Odams books to Lammles. Quite easy to understand.

  27. WTF
    March 1st, 2012

    I had question 6 today. Passed

  28. Lazanya
    March 19th, 2012

    Wendell Odom is the best, very easy to understand and straight forward. his book helped me pass ICND1 and will going for ICND2 next two weeks. I have Todd’s books but never liked them.

  29. ccnawhoopwhoop
    March 27th, 2012

    Hi Guys,
    I just passed with 888 – probably could’ve/should’ve been higher. I worked off a brain dump from the leading exam prep guys (I think we all know who I’m referring to!!) but only dipped into this site from time to time.
    My recommendation is to know the braindumps inside out but also to know this site inside out(especially the q.s that people say they encountered in the exam). 3 questions that weren’t on the braindump, but were on the exam are to be found on this site – thank god I’d encountered them before because they were Sims and they were quite difficult!!
    Also, Cisoc/vue are changing the order of the multiple choice answers – this could cause issues if some one has learned them by order (but who in their right mind would do that!!!!) Just beware of this!!!
    Thanks for all the help guys, this is a brilliant resource!!

  30. Kratos
    March 27th, 2012

    ccnawhoopwhoop

    Hi there could u plz tell us what kind of labs u got ?

  31. Syed Mehmood Ali
    March 31st, 2012

    I have passes the exam with 944 marks none of them questions came into my exam.

  32. Syed Mehmood Ali
    March 31st, 2012

    I have got vtp sim and frame-relay sim which is located in 9tut.com under hotspot section but with different names and DLCI numbers

  33. NerroAzurro
    March 31st, 2012

    Question 6 was on my exam.

  34. Anonymous
    April 3rd, 2012

    To – ccnawhoopwhoop

    could please provide me with the braindump link… im doing my exam at the end of April

    ultracoel@yahoo.com

    Thanks, its much appreciated!

  35. chas
    April 12th, 2012

    None of these were on the exam today. Passed with 944.

  36. WSL
    April 22nd, 2012

    Passed ICND2 today with 986/1000 🙂

    Q6 was there 🙂

  37. webgirl
    May 2nd, 2012

    q.7 – answer C. 9tut, please consider

  38. 9tut
    May 3rd, 2012

    @webgirl: Q7 the answer is A because A has lowest bridge priority (32768) and lowest MAC.

  39. ST
    May 22nd, 2012

    Q6 Came out

  40. mikemonk
    June 14th, 2012

    Had Q6 today! Also had Q1, but in a different format.

  41. hopeful
    June 28th, 2012

    taking mine in 2 weeks,, good study questions, but remember to read and understand the concept

  42. Byron S.
    July 5th, 2012

    Question 1, I thought priorities needed to be in increments of 4096? Wouldn’t that make switches B, C, & D, invalid?

  43. Dragon_Puncher
    July 18th, 2012

    @All who say the answer to Q7 should be other than A:

    First criteria for root bridge selection is priority. IF priority is tie, THEN MAC address!! In this case, priority tie is between answers A and B. Since A has lower MAC address, A wins election. Answer is A.

  44. Alboma
    July 29th, 2012

    Hmmm, when you are explaining Q2, shouldn’t S1 has lower priority to S3, then S3 port to S1 is in blocking state?

  45. Anonymous
    August 18th, 2012

    Passed ICND2 888/1000. Q1 was on the exam plus they asked to identify which switches and their ports were in root, designated, and blocking port modes.

  46. jainal
    August 28th, 2012

    please explain me question no7

  47. Brandon
    September 1st, 2012

    Passed ICND2 today, 930!!! Saw question 6.

  48. MAZIN
    September 9th, 2012

    Passed ICND2 Exam

    Q1 with extra questions

  49. ppp
    September 10th, 2012

    Passed Icnd2 today. Q7 of http://www.9tut.com/ccna-stp-questions and Q13 of http://www.9tut.com/ccna-stp-questions-2 were on the exam.

  50. AliChowdhury
    September 15th, 2012

    Hi guys, I am going to perform my ICND2 test soon. Someone plz help me with some latest question papers………

  51. Tedy_bear
    September 15th, 2012

    @9tut Please check the Diagram and Explanation for typo mistake [ lower than higher ]
    New Updated Questions 10 – Q1 / STP Questions – Q2
    ——————————————————————–
    1. S2 – Root Bridge – all ports designated – forwarding state
    2. S1 – Non Root Bridge – is the winner in that LAN segment suppose that S1 has lower Bridge ID
    S1 – Port is the winner in that segment – S1 has lower priority than S3 -> the port on S3 connected to S1 will be blocked.

    1. Elects one root bridge – The root bridge is the bridge with the lowest bridge ID. = [ lower priority or lower MAC Address ]
    2. Select one root port per nonroot bridge – Root port is the port that is closest to the root bridge.
    Every non-root bridge must have a root port. All root ports are placed in forwarding state.
    3. Select one designated port on each network LAN segment to forward traffic ==> Lower Bridge ID / Lower Cost
    1. A lower Root Bridge ID
    2. A lower path cost to the Root
    3. A lower Sending Bridge ID
    4. A lower Sending Port ID
    Other switch ports on the segment typically become nondesignated ports and are blocked

  52. zeromahesh
    September 27th, 2012

    I think question 2 explanations are having some problem. Please consider..
    1.In explanation one it says lower priority side will be blocked.. I think it’s wrong..
    2.In explanation two it says lower port id will be blocked (this can be used when two ports are connected to same switch) rather than considering upper switch priority.. I think it’s also wrong..
    Please help.. If I’m wrong.. just tell me..

  53. Black
    October 8th, 2012

    Just pass ICND 1 today with a score 899 .Thanks 9tut and CBT Nuggets!!!!!!

  54. gsb
    October 24th, 2012

    Passed icnd1 812, 9tut helped in a huge way, watch the english vs american grammer!! in the CLI.

  55. creativeme
    October 25th, 2012

    @ zero mahesh- even i have the same doubt,.

    in the question 2, the answer(explanation) given seems confusing.

    I think that if S1 has higher priority than S3 ->then shouldnt the port on S1 connected to S3 be blocked.

    instead of what is given as

    ” S1 has higher priority than S3 -> the port on S3 connected to S1 will be blocked”

    Thanks

  56. creativeme
    October 25th, 2012

    @ 9tut, your comments on the comment post by twignometry made on aug 13th 2011 on this page, will be very helpful, as i also have the same doubt. Thanks

  57. creativeme
    October 25th, 2012

    also in question 1, switch c has a priority ” 1 ” but in stp – we have to give the priority in multiples of “4096” ranging from 1 to 65535. how can we assign prio to be 1??

    “Raynm3n” in the comment section has explained the reason stating to be “Extended System ID, and CISCO per-VLAN STP approach”.But when i googled it, i could not find any good explanation. Can anyone pls explain abt this ? Thanks.

  58. Rakesh K Verma
    November 19th, 2012

    Thank you 9tut ,admin i secured 937 in ICND1.Thanks a lot…..

  59. stan
    January 19th, 2013

    Thanks to God Almighty and to you 9tut, i took both my ICND 1&2 and passed with a score of 912/1000 and 888/1000 respectively, i can’t exactly remember the No. of questions that came in the exam from your site because they were too many, i just felt as if i was revising, thanks alot.

  60. Q
    February 15th, 2013

    Questions were great but i think they were a little to easy! Im a ccent here.

  61. Q
    February 15th, 2013

    Looking for stuff that makes me angry that i dont know it lol i passed icnd 1 feb 1 age 21

  62. n2forlife
    February 27th, 2013

    Taking the INCD2 on March 4th…
    Thanks for all the great input and this informative site… this site is well worth my donation.
    If anyone has the latest/newest dumps please email them to me @ ( unvmm@yahoo.com).
    Thanks in advance!

  63. hennels
    March 4th, 2013

    n2forlife – How did you exam go?

  64. Anonymous
    March 4th, 2013

    3/4 – passed. no questions on exam from this page

  65. Eirik
    April 9th, 2013

    please send icnd2 dumps to eirikashe@yahoo

  66. name here
    April 12th, 2013

    Had questions 1 and 6 today. Passed with an 888.

  67. Nick
    April 15th, 2013

    Question 6 was on today’s exam. April 15.

  68. Anonymous
    April 23rd, 2013

    q 1 and 6 was on my test today 930/1000

  69. Anonymous
    May 22nd, 2013

    i passed today question 5 and 6 where there

  70. It’sme
    June 8th, 2013

    Took the test yesterday. Got 804, needed 825. Question number six was on the exam

  71. S
    June 20th, 2013

    Had none of these questions yesterday.

  72. Rusty
    July 17th, 2013

    Passed ICND2 Yesterday! I am so Ecstatic!!! Thanks 9tut, this along with studying vigorously hard helped with passing the exam.. A lot of questions are still valid from the site

  73. Pratap
    August 1st, 2013

    I have confusion about below question

    Question 6

    Which two of these statements regarding RSTP are correct? (Choose two)

    A. RSTP cannot operate with PVST+.
    B. RSTP defines new port roles.
    C. RSTP defines no new port states.
    D. RSTP is a proprietary implementation of IEEE 802.1 D STP.
    E. RSTP is compatible with the original IEEE 802.1 D STP.

    Answer: B E

  74. Fabricio Garibay
    August 6th, 2013

    @Pratap

    Question 6

    A. Wrong
    B. Right new port roles
    -Discarding
    -Learning
    -Forwarding
    C. Wrong
    D. wrong
    E. RSTP is compatible with old STP

  75. Thyreme
    August 12th, 2013

    @Fabricio
    Nice explanation

  76. KetaSchoolBoy
    August 14th, 2013

    Had 5 and 6 on exam this weekend..

  77. BINARYlad
    August 24th, 2013

    Please send me all the answers because I don’t actually want to learn anything….I want to walk into a job and mess up the network as all i know is which radio button to click. I AM A ROBOT. TIME TO REBOOT. I WANT TO CHEAT MYSELF TO THE JOB CENTRE.

  78. Ginah
    September 12th, 2013

    Guyz help with tips im taking icnd 2mrw

  79. Fel
    September 16th, 2013

    None of these were on the exam today. Passed with 916.

  80. TrickedbyCisco
    September 19th, 2013

    Fail. Took the supposed ICND2 640-816 today and there was nothing like the material contained on this site. No VTP, No VLSM, No Drags and Drop (except 1, had Split Horizon), no ACL or NAT. It was all about SNMP and Netflow. 2 Different SIMS OSPF and EIGRP (not on this site or dump) A lot IPV6. I nailed ICND1 exam but this wasnt the test I prepared for. Please reply.

  81. TrickedbyCisco
    September 19th, 2013

    Sorry, I lie to mess with everyone.

  82. TrickedbyCisco
    September 20th, 2013

    No. For some reason overlapped and I got 200-100. Didnt know 200-100 was there already and Fail. 640-816 next Monday.

  83. ompster
    September 28th, 2013

    these are some great questions. inline with the heavymod dumps and does anyone else hate that the lower priority wins the election in STP but in OSPF its the highest that wins… just sayin

  84. chandra_rc16@yahoo.com
    October 7th, 2013

    Question 2:
    —————-
    Also suppose that S1 has higher priority than S3 -> the port on S3 connected to S1 will be blocked.
    —————-
    Here S1 should have lower priority than S3 —> then only the port on s3 connected to s1 will be blocked.

    Regards,
    Chandu