Cisco Discovery Protocol(CDP)

Network discovery with CDP:
Cisco Discovery Protocol (CDP) is a powerful network monitoring and troubleshooting tool. CDP is an information-gathering tool used by network administrators to get information about directly connected Cisco devices. CDP is a proprietary tool that enables you to access a summary of protocol and address information about Cisco devices that are directly connected. By default, each Cisco device sends periodic messages, which are known as CDP advertisements, to directly connected Cisco devices. These advertisements contain information such as the types of devices that are connected, the router interfaces they are connected to, the interfaces used to make the connections, and the model numbers of the devices.

Most network devices, by definition, do not work in isolation. A Cisco device frequently has other Cisco devices as neighbors on the network. Information gathered from other devices can assist you in making network design decisions, troubleshooting, and making changes to equipment. CDP can be used as a network discovery tool, helping you to build a logical topology of a network when such documentation is missing or lacking in detail.
CDP Operation:
CDP runs at the Data Link layer connecting the physical media to the upper-layer protocols (ULPs). Because CDP operates at the Data Link layer, two or more Cisco network devices, such as routers that support different Network layer protocols (for example, IP and Novell IPX), can learn about each other.

When a Cisco device boots up, CDP starts up by default. CDP automatically discovers neighboring Cisco devices running CDP, regardless of which protocol or suites are running. CDP exchanges hardware and software device information with its directly connected CDP neighbors.
CDP provides the following information about each CDP neighbor device:

Device identifiers - For example, the configured host name of a switch
Address list - Up to one Network layer address for each protocol supported
Port identifier - The name of the local and remote port-in the form of an ASCII character string such as ethernet0
Capabilities list - For example, whether this device is a router or a switch
Platform - The hardware platform of the device; for example, a Cisco 7200 series router


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