What is CDP (Cisco Discovery Protocol) and use of CDP (Cisco Discovery Protocol)?

Cisco Discovery Protocol (CDP) is data link layer protocol that allows you to find information about the connections between devices. Cisco Discovery Protocol (CDP) is a nifty tool from Cisco that gives you a boost if your network is primarily made of Cisco devices because Cisco devices use this communication protocol to identify other Cisco devices. Most Cisco Enterprise devices support CDP.

CDP essentially allows you to identify Cisco devices on your network and see how they are connected.

CDP (Cisco Discovery Protocol) is a Cisco proprietary protocol that runs between direct connected network entities (routers, switches, remote access devices, IP telephones etc.). The purpose of the protocol is to supply a network entity with information about its direct connected neighbors

The Cisco Discovery Protocol (CDP) is a proprietary Data Link Layerprotocol developed by Cisco Systems. It is used to share information about other directly connected Cisco equipment, such as the operating system version and IP address.

CDP is primarily used to obtain protocol addresses of neighboring devices and discover the platform of those devices. CDP can also be used to display information about the interfaces your router uses. CDP is media- and protocol-independent, and runs on all Cisco-manufactured equipment including routers, bridges, access servers, and switches.

The Cisco Discovery Protocol (CDP) is a proprietary Data Link Layer protocol developed by Cisco Systems. It is used to share information about other directly connected Cisco equipment, such as the operating system version and IP address. CDP can also be used for On-Demand Routing, which is a method of including routing information in CDP announcements so that dynamic routing protocols do not need to be used in simple networks.

CDP ( Cisco Discovery Protocol) is a proprietary protocol designed by Cisco System for Cisco devices. CDP helps administrators in collecting information about cisco devices. In this article I will explain CDP protocol in details.

CDP is a data link layer protocol. It is available in IOS from version 10.3. Routers and catalyst switches support CDP. CDP is enabled by default on all supporting devices. Supporting device can receive and send CDP messages. CDP messages are not forwarded. It means you can get CDP information only about the directly connected devices.

CDP messages are generated as layer two frames and distributed as multicasts. CDP uses SNAP ( Subnetwork Access Protocol) frame type. SNAP is not supported by all media types. Media types supported by SNAP are Ethernet, Token Ring, fiber distributed data interface (FDDI), Asynchronous Transfer Mode (ATM), Point-to-Point Protocol (PPP), High- Level Data Link Control (HDLC), and Frame Relay. With SNAP, CDP is also limited with these media types only.

CDP Information

CDP messages contain useful information about cisco device including following:-

• IOS version number
• Hardware platform
• Hardware capabilities
• Layer 3 address (IP address) of device
• Interface that generate CDP message
• Port ID
• Number of seconds for CDP advertisement is valid
• Device type
• Name of device configured with hostname

CDP messages are generated in every 60 seconds. Hold down time for missing neighbor is 180 seconds. Since CDP is a layer two protocol, CDP messages are not routed across the device.

CDP Examples:

For this example you could use any Cisco network simulator software. I personally choose packet tracer for this article. Create a topology as showing in following image, or download this pre-created topology and load in packet tracer.

Cisco proprietary protocol that run on cisco devices for neighbour discovery..