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CDP & LLDP Questions

November 22nd, 2018 Go to comments
CDP Quick Summary:

Cisco Discovery Protocol (CDP) is a Layer 2 protocol that runs on Cisco devices and enables networking applications to learn about directly connected devices nearby. The information contained in Cisco Discovery Protocol advertisements varies based on the type of device and the installed version of the operating system. Some of the information that Cisco Discovery Protocol can learn includes:
+ Cisco IOS version running on Cisco devices
+ Hardware platform of devices
+ IP addresses of interfaces on devices
+ Locally connected devices advertising Cisco Discovery Protocol
+ Interfaces active on Cisco devices, including encapsulation type
+ Hostname
+ Duplex setting
+ VLAN Trunking Protocol (VTP) domain
+ Native VLAN

Reference: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/cdp/configuration/15-mt/cdp-15-mt-book/nm-cdp-discover.html

Question 1


CDP is enabled by default on all Cisco routers. If it is turned off by any reason, we can turn it on again with the following command on global configuration mode:

Router(config)#cdp run

Note: CDP can be turned on or turned off on each interface. For example to turn off CDP on an interface we use this command:

Router(config-if)#no cdp enable

Question 2


Link Layer Discovery Protocol (LLDP) is a industry standard protocol that allows devices to advertise, and discover connected devices, and there capabilities (same as CDP of Cisco). To enable it on Cisco devices, we have to use this command under global configuration mode:

Sw(config)# lldp run

Question 3


The Cisco Discovery Protocol (CDP) is a proprietary Data Link Layer protocol (Layer 2 protocol) developed by Cisco. It is used to share information about other directly connected Cisco equipment, such as the operating system version and IP address. The most popular command with CDP is “show cdp neighbors” to discover who is the neighbors.


There are 3 columns we should pay more attention to:

+ Local Interface (Local Intrfce): the interfaces on the device you are using “show cdp neighbors” command. In this case it is the interface of HOME router
+ Platform: the platform of neighbor device

+ Port ID: the neighbor device’s port or interface on which the CDP packets are multicast

Question 4


Only the “show cdp neighbor detail” gives us information about the IP address of the connected device. Below is an example of this command.


Question 5

Question 6

Question 7

Question 8

Question 9


Type Length Values (TLVs) are blocks of information embedded in CDP advertisements which gives details like IP address, device-id, platform…

Question 10


LLDP for Media Endpoint Devices (LLDP-MED) is an extension to LLDP that operates between endpoint devices such as IP phones and network devices such as switches. It specifically provides support for voice over IP (VoIP) applications.

Reference: https://www.cisco.com/c/en/us/td/docs/switches/blades/3030/software/release/12-2_37_se/configuration_/guide/swlldp.html

Note: There is no LLDP-VOIP extension

Question 11

Which two TLVs does LLDP support? (Choose two)

A. system description
B. port duplex
C. management address
D. native VLAN
E. spanning tree


Answer: A C


The switch supports these basic management TLVs. These are mandatory LLDP TLVs.
+ Port description
+ System name
+ System description
+ System capabilities
+ Management address

Question 12

Comments (12) Comments
  1. hah
    February 8th, 2017

    where is the question for this?

  2. Anonymous
    February 23rd, 2017

    where is the question .. i just find the answer !!!!!!!!!!

  3. Mr. Ro
    February 23rd, 2017

    Try to check the follow link:
    There, You’ll find the question.

  4. Neil
    February 27th, 2017

    CDP runs on?

    a) Native VLAN)
    b) VLAN 1?

  5. Anonymous
    March 28th, 2017

    hey people we must go through the questions first before you start reading answers its inconveniencing for some to be asking for questions kind regards Cyber Pandor

  6. ss
    March 29th, 2017


  7. Delta.Rar
    April 28th, 2017

    It is more profitable to get more understanding on each tutorial of the Cisco course and in that way it gets easy to relate questions and answers with much more feel to it; yet again it makes you not to be left behind.

  8. rajput……..
    May 14th, 2017

    cdp runs on ?

  9. @neil
    July 8th, 2017

    All CDP packets include a VLAN ID. If you configure CDP on a Layer 2 access port, the CDP packets sent from that access port include the access port VLAN ID. If you configure CDP on a Layer 2 trunk port, the CDP packets sent from that trunk port include the lowest configured VLAN ID allowed on that trunk port. The trunk port can receive CDP packets that include any VLAN ID in the allowed VLAN list for that trunk port.


  10. NotAexpert
    June 29th, 2018

    Which statement about LLDP is true?
    A. It is a Cisco proprietary protocol.
    B. It is configured in global configuration mode.
    C. The LLDP update frequency is a fixed value.
    D. It runs over the transport layer.

    B is true, but also C, because

    lldp timer seconds

    switch(config)# lldp timer 50
    (Optional) Specifies the transmission frequency of LLDP updates in seconds.
    The range is 5 to 254 seconds; the default is 30 seconds.

  11. NotAexpert
    June 29th, 2018

    I am sorry, of course the value is variable.

  12. zamil
    November 2nd, 2018

    Q 7

    LLDP supports a set of attributes that it uses to discover neighbor devices. These attributes contain type, length, and value descriptions and are referred to as TLVs. LLDP supported devices can use TLVs to receive and send information to their neighbors. This protocol can advertise details such as configuration information, device capabilities, and device identity.
    The switch supports these basic management TLVs. These are mandatory LLDP TLVs.
    + Port description TLV
    + System name TLV
    + System description TLV
    + System capabilities TLV
    + Management address TLV
    These organizationally specific LLDP TLVs are also advertised to support LLDP-MED.
    + Port VLAN ID TLV ((IEEE 802.1 organizationally specific TLVs)
    + MAC/PHY configuration/status TLV(IEEE 802.3 organizationally specific TLVs)

    -> No VTP information is supported in LLDP.

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