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Trunking Questions

November 18th, 2018 Go to comments

Question 1


Below is an example of the output of this command. Interface Ethernet1/0 is operating in trunking mode.


Question 2


The “show interfaces trunk” command and “show interfaces switchport” command can be used to verify the status of an interface (trunking or not). The outputs of these commands are shown below (port Ethernet 1/0 has been configured as trunk):



The “show ip interface brief” command only gives us information about the IP address, the status (up/down) of an interface:


The “show interfaces vlan” command only gives us information about that VLAN, not about which ports are the trunk links:


Question 3


The “Operational Mode” is “static access” so this port is currently in access mode.

Question 4


IEEE 802.1Q is the networking standard that supports Virtual LANs (VLANs) on an Ethernet network. It is a protocol that allows VLANs to communicate with one another using a router. 802.1Q trunks support tagged and untagged frames.

If a switch receives untagged frames on a trunk port, it believes that frame is a part of the native VLAN. Also, frames from a native VLAN are not tagged when exiting the switch via a trunk port.

The 802.1q frame format is same as 802.3. The only change is the addition of 4 bytes fields. That additional header includes a field with which to identify the VLAN number. Because inserting this header changes the frame, 802.1Q encapsulation forces a recalculation of the original FCS field in the Ethernet trailer.

Note: Frame Check Sequence (FCS) is a four-octet field used to verify that the frame was received without loss or error. FCS is based on the contents of the entire frame.

Question 5


In switches that support both InterSwitch Link (ISL) and 802.1Q trunking encapsulations, we need to specify an trunking protocol so we must use the command “switchport trunk encapsulation dot1q” command first to set the trunk mode to 802.1Q. Then we configure trunking interface with the “switchport mode trunk” command. Then we explicitly allow vlan 20 with the command “switchport trunk allowed vlan 20” command. By default all VLANs are allowed to pass but after entering this command, only VLAN 20 is allowed.

Question 6


Maybe this question wanted to ask “if the other end is configured with trunk/access/desirable mode” then which mode is compatible so that the link can work. In that case both “dynamic auto” and “dynamic desirable” mode are correct. The difference between these two modes is “dynamic auto” is passively waiting for the other end to request to form a trunk while “dynamic desirable” will actively attempt to negotiate to convert the link into a trunk.

Question 7


The picture below shows the fields in IEEE 802.1Q frame.


The SA field is the source address field. The field should be set to the MAC address of the switch port that transmits the frame. It is a 48-bit value (6 bytes). The receiving device may ignore the SA field of the frame.

In fact there is another correct answer for this question: DA (Destination Address) which also consists of 6 bytes. Maybe there is a mistake or typo in this question.

Question 8


Control traffic like CDP, DTP, PAgP, and VTP uses VLAN 1 to operate, even if you change the native VLAN.

Question 9


Although some books and websites said DTP is disabled if the switch port is configured as trunk or access mode (via the command “switchport mode trunk” or “switchport mode access”) but in fact DTP is still running in these modes. Please read at http://packetlife.net/blog/2008/sep/30/disabling-dynamic-trunking-protocol-dtp/. The only way to disable DTP on a switch port is to use the “switchport nonegotiate” command. But notice this command can only be used after configuring that switch port in “trunk” or “access” mode.

Therefore this is a question with no correct answer but if we have to choose an answer, we will choose answer A. At least it is correct in theory.

Question 10


The Dynamic Trunking Protocol (DTP) is a proprietary networking protocol developed by Cisco Systems for the purpose of negotiating trunking on a link between two VLAN-aware switches, and for negotiating the type of trunking encapsulation to be used. It is a Layer 2 protocol and it is enabled by default on Cisco switches (so the interfaces of your switches will be in “dynamic auto” or “dynamic desirable” mode). If you want to turn it off, use the “switchport nonegotiate” under interface mode.


Comments (17) Comments
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  1. ccna
    July 23rd, 2018

    please correct q 9
    ansswer is D

  2. Hisham
    July 29th, 2018

    Question 9: How can you disable DTP on a switch port?
    A. Configure the switch port as a trunk.
    B. Add an interface on the switch to a channel group.
    C. Change the operational mode to static access.
    D. Change the administrative mode to access.

    The answer should be (D)

    This question probably wants you to know the difference between administrative and operational modes:

    The configuration we put in place represents the “administrative mode”.
    The state the port ends up in is “operational mode”

    So if we set a port to dynamic, and it ends up as an access port, due to NOT negotiating a trunk, it would end up as:

    Administrative Mode: dynamic auto
    Operational Mode: static access

    Source: https://learningnetwork.cisco.com/thread/29256

  3. NAN
    August 9th, 2018

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

  4. NAN
    August 9th, 2018

    http: // t.cn /RDf8DJW

  5. Anonymous
    August 9th, 2018

    why the questions are not showing ?

  6. jay
    September 6th, 2018

    guys how can i see the questions first ??????

  7. Anonymous
    September 29th, 2018

    How can you disable DTP on a switch port?
    A. Configure the switch port as a trunk.
    B. Add an interface on the switch to a channel group.
    C. Change the operational mode to static access.
    D. Change the administrative mode to access.

    The answer Should be D

  8. Q8
    October 16th, 2018

    Answer A is correct.

    All management traffic is sent on VLAN 1, even if VLAN 1 is pruned.
    But DTP & STP frames are transmited over the native VLAN unless using PVST+.


  9. Plypots
    December 19th, 2018

    Question 6.
    Which mode is compatible with Trunk, Access, and desirable ports?
    A. Trunk Ports
    B. Access Ports
    C. Dynamic Auto
    D. Dynamic Desirable

    NONE! There is NO compatible mode for a Trunk port, Access Port AND Desirable Port.
    Because Access is included in the group, nothing will work.

    These kinds of question are infuriating! Due to the confusing nature, these kinds of questions make people taking the test second guess themselves.

  10. Hakan
    March 28th, 2019

    Q8 answer should be A, DTP uses native VLAN not VLAN 1.

  11. bill
    April 30th, 2019

    had exam. question came up:

    if both end of trunk ports are set as Dynamic Auto, what will happen?

    – trunks will fail to initiate
    – trunks will form immediately
    -become access port

    i chose trunks will fail to initiate. but i think real answer is they become access port. any ideas?

  12. anonymous
    July 14th, 2019

    @bill, I think your answer is right. trunk will fail to initiate

  13. Anonymous
    September 22nd, 2019

    May someone check the Q8, seems to me both A and D are correct, which one is the better choice?

  14. Anonymous
    October 17th, 2019

    Broadcasring refers to transmitting a packet that will be recceived by every device on the network. which of the following determines how often a broadcast can occur?
    a. IP address
    b. Domain
    c. The applications running on the internetwork
    d. The traffic

  15. Anonymous
    October 17th, 2019

    In homes and small businesses, we typically use flat networks. What feature distinguishes switched networks from flat networks?

  16. Anonymous
    October 17th, 2019

    In homes and small businesses, we typically use flat networks. What feature distinguishes switched networks from flat networks?
    a. Switches increase the workload on individual computer
    b. Switches increase network performance
    c. If a host sends out broadcast them all ports on switches forward it
    d. Switched network has big issues of security

  17. Gayathri
    January 10th, 2020

    Question 7 doesn’t both DA/SA are 6 bytes field?

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