The Cisco Discovery Protocol, formerly known as Cisco CDP, is a Layer-2 protocol used to obtain, learn and share information and data about other Cisco equipment directly connected nearby. The information includes hardware platforms, IP addresses and operating systems (OSes).
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The Cisco Discovery Protocol, which runs on Cisco devices, is used to help network-layer protocols learn about each other and determine how the connected devices are configured. The Cisco Discovery Protocol runs on all Cisco equipment, including routers and switches. It is enabled by default and can send and receive messages about the state of other devices.
The information of each message varies, depending on the device and version of the operating system. Besides hardware platform and IP addresses, the messages can contain info regarding hostname, duplex settings and the interfaces active on Cisco devices. The Cisco Discovery Protocol stores the information it receives in a table, which is refreshed every time a message is received.
When it comes to VMware, the Cisco Discovery Protocol allows ESXi administrators to determine which Cisco port is connected to a certain vSwitch. When the protocol is connected to a vSwitch, administrators can view properties of the Cisco switch such as software version and device ID. Cisco Discovery Protocol Version 2 passes native VLAN information between Cisco switches, which was something Version 1 did not do. If there is a native VLAN mismatch, an error messages will appear on the console.
According to Cisco, the only prerequisite for the Cisco Discovery Protocol is that interface must support Subnetwork Access Protocol headers.