Home > CDP & LLDP Questions

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 (0) Comments
  1. No comments yet.
Add a Comment