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VLAN Trunking 4

November 24th, 2018 in SWITCH 300-115 Go to comments

Question 1

Question 2

Question 3

Question 4

Explanation

If an access port receives a packet with an 802.1Q tag in the header other than the access VLAN value, that port drops the packet without learning its MAC source address.

Reference: https://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus5000/sw/layer2/b_Cisco_Nexus_5000_Series_NX-OS_/Cisco_Nexus_5000_Series_NX-OS__chapter6.html

In fact this question is unclear because if an access port receives an 802.1Q tagged frame with its VLAN value, the access port will accept it (answer D)

Question 5

Question 6

Explanation

802.1Q frames are distinguished from ordinary Ethernet frames by the insertion of a 4-byte VLAN tag into the Ethernet header. The DATA field may vary from 46 to 1500 bytes. Therefore the minimum Ethernet frame size is 68 bytes (6bytes + 6bytes + 4 bytes + 2 bytes + 46 bytes of DATA + 4 bytes) while the maximum size is 1522 bytes.

802.1q_header.png

Comments
  1. ugurdy
    February 3rd, 2019

    Q1 is not correct. There is only one vlan.dat file on the switch and voice vlan in it. And also “B” could be correct, but it is not a MUST.

    B and D should be the correct answers.

  2. Q3
    February 14th, 2019

    only one answer is correct and that is A

  3. Network+
    February 20th, 2019

    Q3: A question about a configuration with a dot1q enabled trunk port. (Choose two)

    A. Supports VLANs 1-4096
    B. Does not support tagging native VLAN
    C. Dot1q supports tagging 1000 VLANs including the native VLAN
    D. ?
    E. ?

    Correct answers: A & B according to Cisco documents:

    802.1Q is the IEEE standard for tagging frames on a trunk and supports up to 4096 VLANs. In 802.1Q, the trunking device inserts a 4-byte tag into the original frame and recomputes the frame check sequence (FCS) before the device sends the frame over the trunk link. At the receiving end, the tag is removed and the frame is forwarded to the assigned VLAN. 802.1Q does not tag frames on the native VLAN.

    https://www.cisco.com/c/en/us/support/docs/lan-switching/8021q/17056-741-4.html

  4. Stormcontrol
    March 5th, 2019

    @ Network+,
    FYI

    The command below enables you tag the native vlan traffic

    (config)#vlan dot1q tag native

    https://www.cisco.com/c/m/en_us/techdoc/dc/reference/cli/nxos/commands/l2/vlan-dot1q-tag-native.html

  5. Q3 – dot1q
    May 27th, 2019

    Don’t forget that A is slightly wrong. Extended vlans only go up to 4094, but I imagine that the real question would note that (or be tricky about it. Beware of Cisco)

  6. Q5 – Must be true trunking
    May 27th, 2019

    Answer A: While it is best practice for the Native Vlans to match, it is not a requirement and trunking would still work. You would just get syslog messages saying that there is a mismatched native vlan. Anything allowed on the trunk that isn’t the native vlan would work fine.

    From the official cert guide, Chapter 4 VLANs and Trunks – “You can bring up a trunk with different VLANs on each end; however, both switches will log error messages about the mismatch, and the potential exists that the traffic will not pass correctly between THE TWO NATIVE VLANs”

    That last sentence is the only left-field chance I could see them arguing about how it is a requirement, because if the potential for the native vlan to fail is there, then MAYBE one could say that to formulate a proper trunk, matching the native vlans is a requirement.

  7. Henry
    June 13th, 2019

    What commands can be used to verify the trunking configuration of a router performing inter-VLAN routing? (Choose two.)
    A. router# show trunk
    B. router# show vlans
    C. router# show vtp status
    D. router# show ip interface brief
    E. router# show ip route

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