Cisco Discovery Protocol

Definition of Cisco Discovery Protocol

Cisco Discovery Protocol (CDP) is a proprietary network protocol developed by Cisco Systems, used for discovering and sharing information about neighboring devices on the same network. It operates at the data link layer (Layer 2) of the OSI model, allowing network devices to obtain information such as IP addresses, device types, and device capabilities. CDP assists in simplifying network infrastructure management and troubleshooting by facilitating communication between Cisco devices.


The phonetics of the keyword “Cisco Discovery Protocol” are:SIS-koh / Dih-SKUH-vuh-ree / PROH-tuh-kawl

Key Takeaways

  1. Cisco Discovery Protocol (CDP) is a proprietary Layer 2 protocol that enables network devices to discover, identify, and share information about themselves with other adjacent devices on the same network.
  2. CDP is supported on almost all Cisco routers, switches, and IP phones, allowing users to gather information such as hardware platform, software version, IP addresses, and neighboring devices, helping with network troubleshooting and diagnostics.
  3. While CDP can be useful, it may present security risks if unwanted users access sensitive data. Therefore, it’s essential to disable CDP on interfaces when not required or to use a management VLAN for network security.

Importance of Cisco Discovery Protocol

Cisco Discovery Protocol (CDP) is an essential layer 2 network protocol in the field of networking technology, specifically designed for Cisco devices.

Its importance lies in its capability to facilitate the discovery, identification, and sharing of crucial information about neighboring devices such as IP addresses, device type, platform, and capabilities.

This functionality enables network administrators to efficiently manage and troubleshoot their network infrastructure by providing an accurate representation of the topology and interconnections, helping in understanding the network’s layout and finding misconfigurations.

As a proprietary protocol, CDP also highlights Cisco’s commitment to delivering sophisticated tools for maintaining and enhancing network performance, security, and reliability.


Cisco Discovery Protocol (CDP) is a proprietary Layer 2 network protocol developed by Cisco Systems, designed to facilitate the process of network discovery and management by enabling network administrators to gather essential information about directly connected devices. The primary purpose of CDP is to simplify the network troubleshooting and documentation process by automatically discovering and delivering information about neighboring equipment such as device identifiers, IP addresses, platform details, and even capabilities.

This valuable data helps in mapping out the network topology and speeds up tasks like addressing network configuration issues and determining optimal paths for critical traffic. CDP operates on Cisco routers, switches, and IP phones, as well as on other networking devices manufactured by organizations that support this protocol.

It functions independently of network layer protocols, by periodically sending update messages known as advertisements, to multicast addresses. These messages have information about the device and its directly connected neighbors.

By exchanging and storing this information, CDP builds a comprehensive and real-time view of network connections and device functions which becomes a crucial asset when diagnosing connectivity issues or planning network expansions. To maintain accurate knowledge of the network, CDP dynamically updates the information if any changes are detected, allowing network administrators to focus on higher-level tasks while staying informed about essential network components.

Examples of Cisco Discovery Protocol

Cisco Discovery Protocol (CDP) is a proprietary layer 2 protocol used by Cisco devices to discover and share information about each other. Here are three real-world examples of using CDP in various networking scenarios:

Network Mapping and Troubleshooting: In a large network with a mix of Cisco switches, routers, access points, and IP phones, network administrators can use CDP to map out the network topology and quickly identify the types of devices present, their IP addresses, and their physical connections. By issuing CDP commands such as “show cdp neighbors” or “show cdp entry”, network administrators can gather valuable information about connected devices, helping them in troubleshooting connectivity issues or identifying devices that may need updates or reconfiguration.

Voice over IP (VoIP) Network Implementation: When deploying VoIP networks using Cisco IP phones and switches, CDP can be used to simplify the configuration process and ensure proper functionality. When a Cisco IP phone is connected to a Cisco switch, it uses CDP to automatically discover the Voice VLAN configured on the switch and join it without needing manual intervention. This streamlines the deployment process and helps ensure proper separation between voice and data traffic, enhancing call quality and security.

Dynamic Power Allocation with Power over Ethernet (PoE) devices: In a network with PoE devices such as IP cameras and wireless access points, Cisco switches can use CDP to dynamically allocate power to devices based on their requirements. CDP shares information about the power needs of connected devices, allowing the switch to manage its PoE budgets effectively and allocate power as needed. This helps in optimizing energy consumption and preventing power overloading on the switch.

Cisco Discovery Protocol FAQ

What is the Cisco Discovery Protocol (CDP)?

The Cisco Discovery Protocol (CDP) is a proprietary Layer 2 network protocol developed by Cisco Systems. It is used to discover information about neighboring Cisco devices, such as their IP addresses, device types, and the interfaces they use to connect to each other.

Which devices support CDP?

CDP is supported by a wide range of Cisco devices, including routers, switches, and IP phones. Additionally, some non-Cisco devices that run third-party software, such as servers running the CDP agent, can also support CDP.

How does CDP work?

CDP operates over Ethernet, Fast Ethernet, and other data link layer protocols. Devices with CDP enabled periodically send out CDP messages that contain information about themselves. Neighboring devices with CDP enabled receive these messages and update their CDP tables accordingly.

What information is shared using CDP?

CDP messages contain various types of information about the devices, such as device identifiers, IP addresses, device capabilities, and the interfaces they use to connect to each other. This information can be useful for network administrators to discover and troubleshoot connectivity issues in their networks.

How can you view the information gathered by CDP?

On a Cisco device with CDP enabled, you can use the “show cdp neighbors” command to view information about neighboring devices. You can also use other CDP-related commands, such as “show cdp traffic” and “show cdp entry”, to gather more detailed information about the devices and their communication with each other.

Can CDP be disabled?

Yes, CDP can be disabled on a per-interface or per-device basis. To disable CDP on an interface, use the “no cdp enable” command in interface configuration mode. To disable CDP globally on a device, use the “no cdp run” command in global configuration mode.

Related Technology Terms

  • Layer 2 Communication Protocol
  • Network Devices Discovery
  • qed

  • CDP Messages
  • Neighbor Information
  • Topology Mapping

Sources for More Information


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