Cisco Discovery Protocol (CDP) is a proprietary tool that enables access to protocol and address information on directly connected devices. CDP runs over the data link layer, allowing devices running different network layer protocols to learn about each other. CDP summary information includes device identifiers, address lists, port identifiers, and platform.
Figure 12-1. CDP
CDP runs over all LANs, Frame Relay, ATM, and other WANs employing Subnetwork Access Protocol (SNAP) encapsulation. CDP starts by default on bootup and sends updates every 60 seconds.