Home > CDP & LLDP Questions 4

CDP & LLDP Questions 4

November 25th, 2018 in SWITCH 300-115 Go to comments

Question 1

Explanation

VLAN 1 is always used for CDP, VTP, PAgP traffic (except DTP uses native VLAN) even if VLAN 1 is not the native VLAN. If VLAN 1 is not the native VLAN then CDP, VTP, PAgP traffic will be tagged on the trunk.

Question 2

Question 3


Explanation

The command “no lldp transmit” disallows sending LLDP packets on the interface.

Reference: https://www.cisco.com/c/en/us/td/docs/wireless/access_point/atnms-ap-82/configuration/guide/cg-82-book/cg-chap-LLDP.pdf

Note: The “lldp receive” command enables the reception of LLDP packets on an interface.

Reference: https://www.cisco.com/c/en/us/td/docs/switches/datacenter/sw/5_x/nx-os/system_management/configuration/guide/sm_nx_os_cg/sm_lldp.html

Question 4

Question 5

Question 6

Explanation

The command “lldp timer rate” is used to set the sending frequency of LLDP updates in seconds. The range is 5 to 65534 seconds; the default is 30 seconds.

Reference: https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst2960/software/release/12-2_58_se/configuration/guide/2960scg/swlldp.pdf

Question 7

Explanation

LLDP and CDP can run simultaneously. LDDP uses multicast address 01-80-C2-00-00-0E and the default time between protocol frames is 30 seconds

Question 8

Question 9

Comments
  1. Armin
    February 5th, 2019

    Hi All,

    Q2
    I think B. LLDP frame has its own CRC also True.
    https://www.cisco.com/c/en/us/td/docs/routers/ncs4000/software/configure/guide/configurationguide/configurationguide_chapter_0111011.pdf (page 2)

    LLDP Frame Format
    LLDP frames use the IEEE 802.3 format, which consists of the following fields:
    • Destination address (6 bytes)—Uses a multicast address of 01-80-C2-00-00-0E.
    • Source address (6 bytes)—MAC address of the sending device or port.
    • LLDP Ethertype (2 bytes)—Uses 88-CC.
    • LLDP PDU (1500 bytes)—LLDP payload consisting of TLVs.
    • FCS (4 bytes)—Cyclic Redundancy Check (CRC) for error checking.

  2. Shab
    February 7th, 2019

    Question 8
    Which two statements about frame LLDP is true?
    A. Frame has destination multicast address
    B. LLDP data unit has sequence of Type-length-Value (TLVs)
    C. Frame has CRC

    based on : https://learningnetwork.cisco.com/docs/DOC-26851 I think A,B,C there of them are Correct?

  3. sfot
    February 27th, 2019

    Q4
    not sure
    CDP can be disabled on interface only with “no cdp enable”

    can you confirm ?

  4. Q4
    March 7th, 2019

    @sfot main point is that CDP can be disable globally too….not ONLY per interface. Per interface is “no cdp enable”, globally is “no cdp run”

  5. Scylla
    March 23rd, 2019

    As per my understanding there is only one answer for Qestion 4. that is answer D “send periodic multicast”. But answer A “disabled when native VLAN mismatched” is incorrect.
    Please response if you have different view about this.

  6. Anonymous
    April 22nd, 2019

    Q4

    A question about which is true about CDP? (Choose two)

    A. disabled when native VLAN mismatched
    B. can be disable on interface only
    C. send periodic broadcast
    D. send periodic multicast

    I think the answer is B&D. I do not think that cisco implies with the word “only” that it is possible to do that only on interface and not in the global configiration. I think the meaning is that it is possible to do per interface… you can disable it “only” on one/two interfaces if you want.

    Reference:
    “When CDP is enabled globally using the cdp run command, it is enabled by default on all supported interfaces (except for Frame Relay multipoint subinterfaces) to send and receive CDP information. You can disable CDP on an interface that supports CDP with the no cdp enable command.”

    https://www.cisco.com/c/en/us/support/docs/network-management/discovery-protocol-cdp/43485-cdponios43485.html#topicenab

  7. kilu
    May 4th, 2019

    Hello!

    Q8.
    A is correct no doubt.

    But C is correct as well, look at Armin post.

    Not sure about B tho?

  8. Henry
    May 25th, 2019

    Q4 : B and D

    “can be disable on interface only”
    = can be disabled per interface
    = can be disabled on a specific interface.

  9. This_Guy
    June 24th, 2019

    Q4
    I think Scylla is right about Q4. CDP is not disabled by a native vlan mismatch, it can help discover vlan mismatches to fix for trunks to form. Answer should be B and D. (Choose Two)

  10. Anonymous
    September 4th, 2019

    Q4
    I think Q4 is correct. CDP can be disabled globally so not B.
    B. can be disable on interface only

  11. Dmytro
    September 6th, 2019

    Hello all!
    About Q2 and Q8, I think than answers with TLV and multicast are right, but not about variant with CRC. You can read more about it:
    https://en.wikipedia.org/wiki/Link_Layer_Discovery_Protocol
    You can see, that LLDP use FSC but not CRC.

  12. Efiko
    September 20th, 2019

    I agree with Dmytro… I’m sure you meant to say FCS, not FSC.

    I suspect Cisco was trying to test understanding here.

    The last field of the LLDP frame is FCS (Frame Check Sequence). Its content is the numeric result of the CRC’s mathematical computation of the content of the frame. It is added to the frame at source. The destination node carries out the same CRC mathematical computation and compares the result obtained to the FCS of the received frame and frame will be seen to have arrived in tact if both are the same.

    So CRC (Cyclic Redundancy Check) is simply an algorithm used for the above described mathematical computation.

    So LLDP Frame has FCS, not CRC. That leaves A and B as the correct answers.

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