What is Cisco Discovery Protocol (CDP)

The Cisco Discovery Protocol (CDP) is a Cisco proprietary Layer 2 (Data Link Layer) network protocol developed by Cisco to share information about other directly connected Cisco devices, such as the operating system version and IP address.

Cisco Discovery Protocol (CDP) messages received from a neighbor Cisco device are not forwarded to any other devices by default. This means that Cisco Discovery Protocol (CDP) is passed only to directly connected Cisco devices. Each Cisco device (which supports Cisco Discovery Protocol (CDP)) stores the messages received from neighbor devices in a table that can be viewed using the show cdp neighbors command.

Cisco devices send Cisco Discovery Protocol (CDP) messages to the multicast destination address 01:00:0C:CC:CC:CC. CDP messages are sent every 60 seconds on interfaces that support Subnetwork Access Protocol (SNAP) headers. The support for Subnetwork Access Protocol (SNAP) is not available with every data link layer media type. The media types which are supported for Cisco Discovery Protocol (CDP) are Ethernet, Token Ring, FDDI, PPP, HDLC, ATM, and Frame Relay.

Cisco Discovery Protocol (CDP) message contain information about

• IOS software version

• Name of the device (configured with hostname command)

• Hardware capabilities (routing/switching)

• Hardware platform

• The IP addresses of the device

• The interface which generated the Cisco Discovery Protocol (CDP)  message