Home > VTP Lab 2

VTP Lab 2

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


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#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.


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).


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

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


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:


Other good resource for reference:



Other lab-sims in this site:

LACP with STP Sim
Spanning Tree Lab Sim
AAAdot1x Lab Sim


Comment pages
1 4 5 6 48
  1. FailKaki
    March 27th, 2019

    Dump is valid……but fail :(, Need to more focus on L2 Technology & Infrastructure Security
    HSRP Router Type
    VTP v3

  2. SAP HANA Dumps
    April 3rd, 2019

    Nice Post! I appreciate to you for this post. Really you are the best.

  3. SAP HANA Dumps
    April 3rd, 2019

    Good! You are the best one.

  4. Exam Certifications
    April 3rd, 2019
  5. Rose
    April 12th, 2019

    Dumps are valid. Thanks certprepare. Labs- VTPV3,HSRP,AAAdot1x(don’t use named Acl)…..new updated questions from premium membership, 5to6 Drag and drops. few new questions…Passed with 8xx. Thanks cert!

  6. My CCNA expiration is near
    April 24th, 2019

    Badly need the latest dumps for CCNP switch. Please! :(

  7. carlosg56
    May 7th, 2019

    This lab is not from VTP, it’s from STP

  8. Rose
    May 16th, 2019

    anyone needs Iphelper dump can email me: ballking242(at)gmail(dot)com

  9. lislabo
    June 8th, 2019

    `Hi, can you kindly share CCNP SWITCH 300-115 (UPDATE) dump premium file to (( lislaboo@gmail . com ))
    I have exams next week
    Thank You.

  10. lislabo
    June 12th, 2019

    @Rose: thank you for valid dump. I passed SWITCH.
    Thanks again! You are the best!

  11. Rose
    June 12th, 2019


  12. Anonymous
    June 18th, 2019

    Rose can you please share you ccnp switching dump to me at

    itmann (at)outlook(DOT)com

  13. RB1000
    July 31st, 2019

    I passed the exam today, the score is 900, I have the right dump, my email mkm963 at outlook. com

  14. RB1000 is FAKE
    August 1st, 2019

    RB1000 with mkm963 at outlook. com IS FAKE!!

  15. Rose
    August 1st, 2019

    @Anonymous: contact me: ballking242 @ gmail . com

  16. sk
    August 6th, 2019

    hi all how good are these sims an question for the 300-115?

  17. mujib
    August 8th, 2019

    Hi Rose, I saw that you are helping others to pass the ccnp switch. So please send me latest Dump
    if possible to me on my email syedmr4 at yahoo.co.uk

  18. Scofield
    August 20th, 2019


    I see that you are the shinning star Congratulations with your ccnp switch, kindly mail me the valid dumps if you stil have will appreciate your help you can mail me on mikescofield791 at gmail.com


  19. Dmytro
    September 7th, 2019

    Why this lab named VTP Lab 2?
    I see only STP configuration…

  20. Anonymous
    November 20th, 2019

    For Q2.

    Even if I changed the port-priority of gig 1/0/6 (Gi0/2) to a lower value than gig 1/0/5 (Gi0/1),
    gig 1/0/6 (Gi0/2) is not transitioning to forwarding state…Im using packet tracer and GNS3…
    how about in the exam?, if this happens, could I change the port cost instead?…

  21. OldSoldier
    December 6th, 2019

    Please help with recent 300-115 SWITCH DUMPS

    paitu2003 at gmail

    is my mail


  22. JG
    January 4th, 2020

    @ Rose With regards to the VTPv3 sim did you use certprep answers ? there seem to be confusion about it

    Thanks…anyone have an idea can share as well

    January 19th, 2020

    Has anyone seen the AAA Sim on the test???

Comment pages
1 4 5 6 48
  1. No trackbacks yet.