Cisco Discovery Protocol (CDP) is a Cisco proprietary protocol which is used to collect information about neighboring routers and switches. It operates at Layer2 (data link layer) and comes in two versions CDPv1 (initial release) available since IOS version 10.3 and CDPv2 available from IOS Version 12.0(3)T. CDP is very useful when you need to gather information about the network topology like IP addresses, device capabilities, platform and also offers a quick way for troubleshooting and documenting the network. CDP is enabled by default on all available interfaces. CDP traffic between devices is not encrypted so this can be a real security issue. As best practice is recommended that CDP should be disabled mainly on devices that connects to external networks.