Cdp

KEY POINT

CDP is a Cisco-proprietary protocol that operates between Cisco devices at the data link layer. CDP information is sent only between directly connected Cisco devices; a Cisco device never forwards a CDP frame.

CDP enables systems that support different network layer protocols to communicate and enables other Cisco devices on the network to be discovered. CDP provides a summary of directly connected switches, routers, and other Cisco devices.

CDP is a media- and protocol-independent protocol that is enabled by default on each supported interface of Cisco devices (such as routers, access servers, and switches). The physical media must support Subnetwork Access Protocol encapsulation. Figure 3-34 illustrates the relationship between CDP and other protocols.

Figure 3-34 CDP Runs at the Data Link Layer and Enables the Discovery of Directly Connected Cisco Devices

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Upper-Layer Addresses

TCP/IP

Novell IPX AppleTalk

Others

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Cisco Proprietary Data-Link Protocol

CDP discovers and shows information about directly connected Cisco devices

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Media Supporting SNAP

Relay ATM

Others

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