Cisco Discovery Protocol(CDP) and Link Layer Dicovery Protocol(LLDP) in Data Link

The Cisco Discovery Protocol is a proprietary protocol of the Cisco System. Cisco discovery protocol is a datalink layer of layer 2 discovery protocol. It provides access to media and physical addressing

The main focus is to share directly connected equipment information such as IP address and operating system version to neighbors. The On-demand Routing propagates the IP prefix through the CDP protocol. It determines the data transmission format and control of network access.

Link Layer Discovery Protocol is a standard protocol whereas Cisco Discovery Protocol is owned by Cisco System. The CDP supports the IEEE 8021ab version of LLDP.


Data Link Layer

In OSI architectural network model, the Data link layer is Layer 2 which shares and discovers connected neighboring devices. The Cisco Discovery Protocol and Link Layer Discovery Protocol are used to manage the network. Also helps monitor, and detect intruders and any failure in a network topology for improving performance and troubleshooting.

Cisco Discovery Protocol

The Cisco Discovery Protocol discovers and shares the local or remote Cisco devices with all neighboring attached devices. It gathers information on all connected devices for network administrators to troubleshoot and manage the network. It is a tool for network discovery as it discovers neighbor devices across LAN and WAN.

The protocol is owned and developed by Cisco System and is a layer 2 discovery protocol.

The CDP share information such as IP Address, and operating system version and connects other Cisco Devices. The On-demand Routing propagates the IP prefix through the CDP protocol so that dynamic routing protocol had not to be used. CDP stores the received information in a tabular form and can be viewed by command from a neighbor device.

The message transmission is using multicast frames, not by higher layer protocol to multicast destination addresses. The CDP can discover changes in the network, can prompt messages informing the threat or intrusion, and warn the user. A Custom CDP packet is sent by monitoring the CDP monitor for detecting spoofing attacks. CDP is prone to cyber-attacks and a common type of attack is the Denial of service by the cybercriminal.

The Cisco Discovery Protocol only works with Cisco devices. The Cisco discovery protocol transfers messages in a subnetwork access protocol whose interface is header compatible.

The Cisco Discovery Protocol works in

  • ATM

  • Ethernet

  • Frame relay

  • Token ring

  • Point-to-point protocol

The CDP message information transmitted consists of −

  • IP Address of Cisco device

  • IOS Software

  • Device name

  • Capabilities of hardware

  • Information of interface

Cisco Discovery Protocol Advantages

  • CDP detects and locates the device in the network layer protocol and real-time transport protocol. CDP tells the device configuration.

  • Detects the switch/router which is configured wrong by detecting its IP address of it.

  • Troubleshoot the devices for detecting issues in the network by using CDP as a diagnostic tool.

  • TLV field can be used for troubleshooting.

Link layer Discovery Protocol

Link Layer Discovery Protocol is the standard version of the protocol that discovers and gathers information on noncisco devices and Cisco devices which advertise to neighboring connected devices and help detect the threats in the network. LLDP uses Ethernet Frames and is based on IEEE 802.1AB.

The Link Layer Discovery Protocol can be used in multi-vendor devices. The LLDP functionality is the same as CDP but works not only on Cisco devices but other vendor devices. The CDP and LLDP are to supply network information between directly connected network devices or entities. LLDP uses TLV which is a set of attributes containing type, length, and value description to discover the interlinked devices. LLDP-using devices send and receive information using TLV in directly connected neighbors. This information can be accessed by simple network management protocol. Such information consists of link aggregation, IP address, Virtual LAN, MDI power, MAC address, Port name, system name, or capabilities of neighboring devices.

LLDP can be used for power over Ethernet, Data center bridging, or Virtual LAN by enhancing with the Media Endpoint Discovery(MED) which accomplishes the requirements.

Link Layer Discovery Potocol Advantages

  • The LLDP works in noncisco devices

  • It is an alternative to CDP and an open standard protocol

  • Extension using Media Endpoint Discovery(MED)

The disadvantage of Link Layer Discovery protocol

  • VMWare switches work in CDP for the discovery of neighbor devices.

  • It is costly to implement.


The data link layer discovers, gathers and shares information about interlinked devices in the network with neighboring devices. This information can be used for monitoring, analyzing, troubleshooting, recording, and detecting intrusion and failure in the network. CDP and LLDP both are in Layer 2 which is a discovery protocol and to manage the network both CDP and LLDP work similarly with slight differences.

Updated on: 14-Apr-2023


Kickstart Your Career

Get certified by completing the course

Get Started