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VLAN Trunking 2

September 16th, 2017 in SWITCH 300-115 Go to comments

Question 1

Explanation

The 802.1q frame format is same as 802.3. The only change is the addition of 4 bytes (32 bits) 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.

Question 2

Question 3

Question 4

Question 5

Question 6

Question 7

Question 8

Question 9

Explanation

The “switchport mode trunk” is the most important command to identify if a port is configured in access or trunk mode. In this case because of the “switchport mode trunk” command, the “switchport access vlan 700” does not have any effect.

There is no “switchport trunk native vlan …” command so it is using the default native VLAN, which is 1.

Comments
  1. mikeSWE
    July 19th, 2017

    @certprepare URGENT exam in 2 days!!!

    I have dumps that have different answers on q5 (AC) q11 (D) and q12 (DF)

    Those are the correct answers in my dump brand new dump btw.

    Can someone please confirm if the answer here on these questions are the correct answers?

  2. BoZZ
    August 13th, 2017

    Question 6 – answer should be A and C. Trunks never add or remove tags. Access and voice vlan config does.

    Question 11 – answer B is correct, “tag native” causes all vlans to get tagged, even from native vlan which is not tagged by default.
    https:// supportforums.cisco.com /discussion/11823136/native-vlan-tagging

    Question 12 – C and D are correct.
    “the main enhancement introduced by MST is that several VLANs can be mapped to a single spanning tree instance.”
    https:// http://www.cisco.com /c/en/us/support/docs/lan-switching/spanning-tree-protocol/24248-147.html#mst_region

  3. BoZZ
    August 14th, 2017

    Question 13 – Answer is C. “show interface trunk” shows trunk ports after the trunk is established (not when port is made a trunk port), which is possible when other side is also configured correctly.

  4. Peter Pan
    August 20th, 2017

    Q5. Which 2 are the correct answers ?

    All 3 seem correct.

  5. Anonymous
    September 9th, 2017

    Would love some updates on this page for the previous users questions.

  6. f
    October 2nd, 2017

    whats is the difrent between q4 and q8 ?

    • remove VLAN 100 from the allowed VLAN lis:
    o switchport trunk allowed vlan remove vlan 100
    o switchport trunk allowed vlan 1-80,99,101-250

    • two commands are used to remove VLAN 55 from the trunk port:
    o switchport trunk allowed vlan remove 55
    o switchport trunk allowed vlan except 55

    can some one explain please ?

  7. Anonymous
    October 12th, 2017

    Here is the complete command with options.

    Switch(config-if)# switchport trunk allowed vlan { vlan-list | all |
    { add | except | remove } vlan-list }

    You can tailor the list of allowed VLANs on the trunk by using the switchport trunk
    allowed vlan command with one of the following:
    ■ vlan-list: An explicit list of VLAN numbers, separated by commas or dashes.

    ■ all: All active VLANs (1 to 4094) will be allowed.

    ■ add vlan-list : A list of VLAN numbers will be added to the already configured list;
    this is a shortcut to keep from typing a long list of numbers.

    ■ except vlan-list : All VLANs (1 to 4094) will be allowed, except for the VLAN numbers
    listed; this is a shortcut to keep from typing a long list of numbers.

    ■ remove vlan-list : A list of VLAN numbers will be removed from the already configured
    list; this is a shortcut to keep from typing a long list of numbers.

  8. Anonymous
    October 12th, 2017

    c3550#configure terminal
    Enter configuration commands, one per line. End with CNTL/Z.
    c3550(config)#int fa0/2
    c3550(config-if)#switchport trunk encapsulation dot1q
    c3550(config-if)#switchport mode trunk
    c3550(config-if)#switchport trunk allowed vlan remove 5-10,12
    c3550(config-if)#switchport trunk allowed vlan add 7
    c3550(config-if)#end
    c3550#show interfaces fastEthernet 0/2 trunk

    Port Mode Encapsulation Status Native vlan
    Fa0/2 on 802.1q trunking 1

    Port Vlans allowed on trunk
    Fa0/2 1-4,7,11,13-4094

    Port Vlans allowed and active in management domain
    Fa0/2 1

    Port Vlans in spanning tree forwarding state and not pruned
    Fa0/2 1
    c3550#

  9. superB
    October 19th, 2017

    Q4 – some corrections here with words, I hope it helps. Also Q8 below.
    (@certprepare and @f)

    This is correct sintax for “allowed vlan” – after remove, except or add come numbers only.
    Switch(config-if)#switchport trunk allowed vlan ?
    WORD VLAN IDs of the allowed VLANs when this port is in trunking mode
    add add VLANs to the current list
    all all VLANs
    except all VLANs except the following
    none no VLANs
    remove remove VLANs from the current list
    !
    Switch(config-if)#switchport trunk allowed vlan remove ?
    VLAN ID of a allowed VLAN when this port is in trunking mode
    Switch(config-if)#switchport trunk allowed vlan except ?
    VLAN ID of a allowed VLAN when this port is in trunking mode
    Switch(config-if)#switchport trunk allowed vlan add ?
    VLAN ID of a allowed VLAN when this port is in trunking mode
    !
    !

    Second “vlan” word in each command line is WRONG.
    A. switchport trunk allowed vlan remove vlan 100
    B. switchport trunk allowed vlan 1-80,99,101-250
    C. switchport trunk allowed vlan except vlan 100

    Therefore both A. and C. options are WRONG.
    B. option is CORRECT

    For option A. to be correct, it should be:
    A. switchport trunk allowed vlan remove 100

    For option C. to be correct, it should be:
    C. switchport trunk allowed vlan except 100

    ========================

    Q8 has correct answers and commands:
    B. switchport trunk allowed vlan remove 55
    C. switchport trunk allowed vlan except 55

    ========================

    Pay attention when taking the exam!

  10. superB
    October 19th, 2017

    Switch(config-if)#switchport trunk allowed vlan remove ?
    VLAN ID of a allowed VLAN when this port is in trunking mode
    Switch(config-if)#switchport trunk allowed vlan except ?
    VLAN ID of a allowed VLAN when this port is in trunking mode
    Switch(config-if)#switchport trunk allowed vlan add ?
    VLAN ID of a allowed VLAN when this port is in trunking mode
    !

  11. superB
    October 19th, 2017

    Hmm, when I summit, it removes “greater than” and “less than” signs. Let me try again.

    Switch(config-if)#switchport trunk allowed vlan remove ?
    1-1005 VLAN ID of a allowed VLAN when this port is in trunking mode
    Switch(config-if)#switchport trunk allowed vlan except ?
    1-1005 VLAN ID of a allowed VLAN when this port is in trunking mode
    Switch(config-if)#switchport trunk allowed vlan add ?
    1-1005 VLAN ID of a allowed VLAN when this port is in trunking mode
    !

  12. stovepipe
    November 12th, 2017

    Q4. EXHIBIT – switchport trunk allowed vlan 1,80,99-250
    Which two commands will remove VLAN 100 from the allowed VLAN list? (Choose two)

    A. switchport trunk allowed vlan remove vlan 100
    B. switchport trunk allowed vlan 1-80,99,101-250
    C. switchport trunk allowed vlan except vlan 100

    If B is one of the correct answers, should there be a comma (,) between the 1 and 80 as it is listed in the question?

  13. Mike
    November 13th, 2017
  14. Anonymous
    January 16th, 2018

    Q6. I think that correct answer is B

    TPID
    The QinQ frame contains the modified tag protocol identifier (TPID) value of VLAN Tags. By default, the VLAN tag uses the TPID field to identify the protocol type of the tag. The value of this field, as defined in IEEE 802.1Q, is 0x8100.

    The device determines whether a received frame carries a service provider VLAN tag or a customer VLAN tag by checking the corresponding TPID value. After receiving a frame, the device compares the compares the configured TPID value with the value of the TPID field in the frame. If the two match, the frame carries the corresponding VLAN tag. For example, if a frame carries VLAN tags with the TPID values of 0x9100 and 0x8100, respectively, while the configured TPID value of the service provider VLAN tag is 0x9100 and that of the VLAN tag for a customer network is 0x8200, the device considers that the frame carries only the service provider VLAN tag but not the customer VLAN tag.

    In addition, the systems of different vendors might set the TPID of the outer VLAN tag of QinQ frames to different values. For compatibility with these systems, you can modify the TPID value so that the QinQ frames, when sent to the public network, carry the TPID value identical to the value of a particular vendor to allow interoperability with the devices of that vendor. The TPID in an Ethernet frame has the same position with the protocol type field in a frame without a VLAN tag. In order to avoid problems in packet forwarding and handling in the network, you cannot set the TPID value to any of the values in this table:

  15. abcd
    January 28th, 2018

    Q4. only B is correct, A & C are wrong. the syntax of the commands are wrong. the correct syntax is:
    C3560(config-if)#switchport trunk allowed vlan remove 100
    C3560(config-if)#switchport trunk allowed vlan except 100

  16. abcd
    January 28th, 2018

    Q5, answer A is wrong, incorrect syntax.

    C1941(config)#int g0/0.116
    C1941(config-subif)#
    C1941(config-subif)#encapsulation dot1Q
    % Incomplete command.

    C1941(config-subif)#

    must specify the vlan number after the dot1Q keyword.

    note: the auxiliary voice vlan is tagged.

  17. 1WAY
    February 10th, 2018

    Anonymous is correct, and Q6 needs a Cisco citation or at the least a clear explanation. From what I can see Cisco doesn’t conform strictly to the 802.1ad (Q-in-Q) standard and uses 0x8100 for both inner and outer tags. If that’s the case why ask a question in a Cisco exam that where they don’t conform to that standard.

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