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VTP Lab 2

March 9th, 2017 in Lab Sim, LabSim Go to comments

Question

Answer and Explanation

1) “CORE should be the root bridge for VLAN 20; however, DSW1 is currently the root bridge for VLAN 20” -> We need to make CORE switch the root bridge for VLAN 20.

By using the “show spanning-tree” command as shown above, we learned that DSW1 is the root bridge for VLAN 20 (notice the line “This bridge is the root”).

DSW1>enable
DSW1#show spanning-tree

VTP_Lab2_show_spanning-tree

To determine the root bridge, switches send and compare their priorities and MAC addresses with each other. The switch with the lowest priority value will have highest priority and become the root bridge. Therefore, we can deduce that the priority of DSW1 switch is lower than the priority of the CORE switch so it becomes the root bridge. To make the CORE the root bridge we need to increase the DSW1’s priority value, the best value should be 61440 because it is the biggest value allowed to assign and it will surely greater than of CORE switch. (You can use another value but make sure it is greater than the CORE priority value by checking if the CORE becomes the root bridge or not; and that value must be in increments of 4096).

(Notice that the terms bridge and switch are used interchangeably when discussing STP)

DSW1#configure terminal
DSW1(config)#spanning-tree vlan 20 priority 61440

2) “Traffic for VLAN 30 should be forwarding over the gig 1/0/6 trunk port between DSW1 and DSW2. However VLAN 30 is currently using gig 1/0/5”

DSW1 is the root bridge for VLAN 30 (you can re-check with the show spanning-tree command as above), so all the ports are in forwarding state for VLAN 30. But the question said that VLAN 30 is currently using Gig1/0/5 so we can guess that port Gig1/0/6 on DSW2 is in blocking state (for VLAN 30 only), therefore all traffic for VLAN 30 will go through port Gig1/0/5.

VTP_Lab2_VLAN30_Blocking

The root bridge for VLAN 30, DSW1, originates the Bridge Protocol Data Units (BPDUs) and switch DSW2 receives these BPDUS on both Gig1/0/5 and Gig1/0/6 ports. It compares the two BPDUs received, both have the same bridge-id so it checks the port cost, which depends on the bandwidth of the link. In this case both have the same bandwidth so it continues to check the sender’s port id (includes port priority and the port number of the sending interface). The lower port-id value will be preferred so the interface which received this port-id will be the root and the other interface (higher port-id value) will be blocked.

In this case port Gig1/0/6 of DSW2 received a Priority Number of 128.6 (means that port priority is 128 and port number is 6) and it is greater than the value received on port Gig1/0/5 (with a Priority Number of 128.5) so port Gig1/0/6 will be blocked. You can check again with the “show spanning-tree” command. Below is the output (notice this command is issued on DSW1 – this is the value DSW2 received and used to compare).

VTP_Lab2_show_spanning-tree_VLAN30

Therefore, all we need to do is to change the priority of port Gig1/0/6 to a lower value so the neighboring port will be in forwarding state. Notice that we only need to change this value for VLAN 30, not for all VLANs.

DSW1(config)#interface g1/0/6
DSW1(config-if)#spanning-tree vlan 30 port-priority 64
DSW1(config-if)#exit

3) “Traffic for VLAN 40 should be forwarding over the gig 1/0/5 trunk port between DSW1 and DSW2. However VLAN 40 is currently using gig 1/0/6”

Next we need to make sure traffic for VLAN 40 should be forwarding over Gig1/0/5 ports. It is a similar job, right? But wait, we are not allowed to make any configurations on DSW2, how can we change its port-priority for VLAN 40? There is another solution for this…

Besides port-priority parameter, there is another value we can change: the Cost value (or Root Path Cost). Although it depends on the bandwidth of the link but a network administrator can change the cost of a spanning tree, if necessary, by altering the configuration parameter in such a way as to affect the choice of the root of the spanning tree.

Notice that the Root Path Cost is the cost calculated by adding the cost in the received hello to the cost of the interface the hello BPDU was received. Therefore if you change the cost on an interface of DSW1 then only DSW1 will learn the change.

By default, the cost of a 100Mbps link is 19 but we can change this value to make sure that VLAN 40 will use interface Gig1/0/5.

DSW1(config)#interface g1/0/5
DSW1(config-if)#spanning-tree vlan 40 cost 1

DSW1(config-if)#end

You should re-check to see if everything was configured correctly:

DSW1#show spanning-tree

Save the configuration:

DSW1#copy running-config startup-config

(Notice: Many reports said the copy running-config startup-config didn’t work but they still got the full mark)

Remember these facts about Spanning-tree:

Path Selection:

1) Prefer the neighbor advertising the lowest root ID
2) Prefer the neighbor advertising the lowest cost to root
3) Prefer the neighbor with the lowest bridge ID
4) Prefer the lowest sender port ID

Spanning-tree cost:

spanningtree_cost

Other good resource for reference:

http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a00800ae96a.shtml

 

Other lab-sims in this site:

LACP with STP Sim
MLS and EIGRP Sim
VTP Lab
Spanning Tree Lab Sim
AAAdot1x Lab Sim

 

Comments
Comment pages
1 2 48
  1. ZWS
    May 7th, 2015

    Just passed my exam, thank to Certprepare

  2. vtp
    May 18th, 2015

    What has this got to do with VTP?

    Surely it a STP LAB !!

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    May 20th, 2015

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  4. Arbaz khan
    May 28th, 2015

    Dear Friends Please tell me that these Labs surely will come in exam 300-115???

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    June 15th, 2015

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  6. RD
    June 16th, 2015

    Does any one know if the test will allow you to use the ? for help

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    June 29th, 2015

    Hey can any1 tell me where too download this sim, kinda having one of those days

  8. sh steve
    July 21st, 2015

    I fail to see what this lab has to do with VTP?

  9. shabrangh
    July 31st, 2015

    there is no question????????
    just answer???
    where is question source?

  10. Aliz
    August 18th, 2015

    Is the question still in 300-115? Thank you!

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  12. Anonymous
    August 24th, 2015

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  13. HeLP………
    September 26th, 2015

    ………………….

    HI ALL

    Instead of changing cost for VLAN 40 wouldnt it be valid also if we make DSW1 as root for VLAN 40 by lowering the priority then DSW2 and by default it will start forwarding through gi 1/0/5????????
    ???????????????????

  14. Help
    October 16th, 2015

    do we have to use NO SHUT DOWN command here ??

  15. study for Switch
    October 21st, 2015

    Has anyone got this lab. I just finsihed going through jvd dump but did not find it in there. Please confirm.

  16. Fathy
    October 26th, 2015

    Where is the VTP ??? This is STP completely !!

  17. p4
    November 9th, 2015

    can we try DSW1(config)#spanning-tree vlan 20 root secondary?

    can above statement alone make dsw1 secondary or it would only work for a matching vlan 20 root primary on CORE switch?

    just curious

  18. Fepac
    November 11th, 2015

    Guys,

    Is the question still in 300-115 exam?

    I think that this question is not a 300-115 question

    Tks!

  19. Slave
    December 4th, 2015

    Sir’s

    May I ask for your help on this? Cost not working on Packet tracer. Any suggestion what to do with this? Thanks

    DSW1(config)#int g0/1
    DSW1(config-if)#spanning-tree vlan 40 cost 1
    ^
    % Invalid input detected at ‘^’ marker.

    DSW1(config-if)#

  20. CCNPtaker
    December 13th, 2015

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    I’ve simulated this using real switches and i have no problem at all.
    i spend only $250 on 3 switches.
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  21. CCNPtaker @p4
    December 13th, 2015

    in real world, that command will work, but in exam, it might work or not. better yet, stick to the certprepare answer

  22. Anonymous
    January 3rd, 2016

    hi can some one tell me 164 q dumps till valid because same are showing on actual test com and updated on 24 nov 2015

  23. niko
    January 6th, 2016

    hi !

    i don’t see the questions, just the explanation…..

    can anyone help me

  24. jkw
    January 7th, 2016

    sign up for $9 a month as a member and you will get access to the questions and test engine to practice MCQ and lab

  25. passed
    January 12th, 2016

    Passed yesterday. There are some new questions. Sorry I cant remember. But most questions came from Cisco.ActualTests.300-115.v2016-01-06.by.Waelaabed.178q.vce in http://www.examcollection.com/300-115.html

  26. k
    January 13th, 2016

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  27. mostafa
    January 19th, 2016

    Hi,
    Cost command not supported on Packet tracer. However, it works on GNS3.

  28. needmoreqs
    January 24th, 2016

    is this still part of the exam?

  29. Anonymous
    February 26th, 2016

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  30. Aymen
    March 21st, 2016

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    April 12th, 2016

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  32. netrider
    April 25th, 2016

    Traffic for VLAN 40 should be forwarding over the gig 1/0/5 trunk port between DSW1 and DSW2. However VLAN 40 is currently using gig 1/0/6.

    Why not use:

    DSW1(config)# int gi1/0/5
    DSW1(config-if)#spanning-tree vlan 40 port-priority 64

    instead of DSW1(config-if)#spanning-tree vlan 40 cost 1

  33. Al
    April 29th, 2016

    Is this still part of the exam ?

  34. Rabbitbaby
    May 2nd, 2016

    DSW2 is the root for VLAN 40. None of its ports are blocked since they are all designated ports (decided by lowest bridge ID in this case). If you change the port priority on either port of DSW1 connected to DSW2 then those values are sent in the BPDU toward DSW2. They are not used by DSW1 to make any spanning-tree decisions. When DSW2 receives the lower port ID made up of the lower port number, it does nothing with it because there is no tie to break on DSW2. It won the root election for VLAN 40 so doesn’t need local port cost (zero for the root on both ports) and doesn’t need the DSW1 BPDU values for port cost or port number. However, changing port cost on DSW1 causes DSW1 to add that new cost to the path cost received in from DSW2 to reach the root (which happens to be DSW2). DSW1 receives a BPDU from DSW2 on both ports. The path cost that the root sent in the BPDU is 0 since DSW2 is the root for VLAN 40. DSW1 adds your new lower cost to the path cost of 0 on port g1/0/5 and gets a root path cost of 1. It adds whatever the DSW1 local port cost is to the path cost of g1/0/6 (look on DSW1 with “show spanning-tree VLAN 40”) and gets a higher root path cost. The lower root path cost is through g1/0/5 so spanning-tree blocks g1/0/6 and forwards for g1/0/5 for VLAN 40. Remember that setting port cost on a switch port is used by the local switch where you set it as BPDUs come inbound to calculate root path cost. In contrast, setting port priority causes spanning-tree to send that value in BPDUs to the remote switch, where only the remote switch may use it as a tie breaker. The local switch does not use its own port cost as a tie breaker.

  35. Rabbitbaby
    May 2nd, 2016

    above should read “…and doesn’t need the BPDU values for port priority or port number.) and the last line should read “The local switch does not use its own PORT PRIORITY as a tie breaker.” – wish I could edit my comment above.

  36. Rabbitbaby
    May 2nd, 2016

    Making dsw1 the root violates the diagram showing how the network is supposed to work. You have to solve within the confines of the requirements.

  37. Rabbitbaby
    May 2nd, 2016

    LOTS OF CORRECTIONS: DSW2 is the root for VLAN 40. None of its ports are blocked since they are all designated ports (decided by lowest bridge ID in this case). If you change the port priority on either port of DSW1 connected to DSW2 then those values are sent in the BPDU toward DSW2. They are not used by DSW1 to make any spanning-tree decisions. When DSW2 receives the lower port ID, which includes the lower port priority you configured on DSW1, it does nothing with it because there is no tie to break on DSW2. It won the root election for VLAN 40 so doesn’t need its own local port cost (zero for the root on both ports) and doesn’t need to use the DSW1 BPDU values for port priority or port number to break any ties. However, changing port cost on DSW1 causes DSW1 to add that new cost to the path cost received in from DSW2 to reach the root (which happens to be DSW2). DSW1 receives a BPDU from DSW2 on both ports. The path cost to the root that the root sent in the BPDU is 0 since DSW2 is the root for VLAN 40. DSW1 adds your new lower locally configured port cost to the root path cost of 0 taken from the BPDU received on port g1/0/5 and gets a root path cost of 1. It adds whatever the DSW1 local port cost is to the root path cost of g1/0/6 (look on DSW1 with “show spanning-tree VLAN 40”) and gets a higher root path cost than 1. The lower root path cost is through g1/0/5 so spanning-tree blocks g1/0/6 and forwards for g1/0/5 for VLAN 40. Remember that port cost on a switch port is used by the local switch and is added to path cost in BPDUs that come inbound to calculate root path cost. In contrast, setting port priority causes spanning-tree to send that value in BPDUs to a remote switch, where only the remote switch may use it as a tie breaker. The local switch does not use its own port priority as a tie breaker.

  38. ditorsa
    May 30th, 2016

    Has someone taken the exam recently with this LAB included ?

  39. dayo
    June 2nd, 2016

    has someone taken the exam recently with this lab included

  40. Nav
    June 3rd, 2016

    Passed (3-June-2016). 201q (300-115) is still valid dumps

  41. Anonymous
    June 3rd, 2016

    Please give me 201

  42. Zay Yar
    June 3rd, 2016

    please give me (300-115)201q

  43. Anonymous
    June 5th, 2016

    is VTP Lab 2 include in Exma??

  44. Anonymous
    June 5th, 2016

    I will attend next week . But is VTP Lab 2 in exam???

  45. Bond
    June 5th, 2016

    I will attend next week . But is VTP Lab 2 in exam???Please suggest

  46. Walt
    June 15th, 2016

    can some one share 201.Q dump please ?

  47. Paypal
    July 1st, 2016

    Nav,
    Please send me the dump to jsmausadd at gmail. Thanks

  48. Paypal
    July 1st, 2016

    Nav,
    Correction: Please send me the dump to jsmausad at gmail. Thanks

  49. Pra
    July 13th, 2016

    Any one send me the latest dump to my mail id : {email not allowed}

  50. Jia
    July 20th, 2016

    this question is not in the latest dumps,

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