CDP stands for Cisco Discovery Protocol is a proprietary data link layer. It is developed by Cisco Systems. As we know every device has a protocol address, and it is possible to identify these addresses by CDP. It also provides information about the interfaces used by the router. It works on all equipment manufactured by Cisco. With CDP, you can discover ports, IP addresses and capabilities of other devices. By default, the Cisco Discovery Protocol (CDP) messages are not forwarded to any other devices if the messages are received from a neighbour Cisco device. IOS provides CDP from the version of 10.3.CDP is enabled by default on all supporting devices. It is easy for the administrator to collect all the information about local devices.

CDP helps the administrator to verify the network diagrams and also possible to correct inconsistencies if any identified. All the information stored in CDP changes according to the device type and version of OS running on it.

CDP serve only on Cisco devices. Information that is passed by the CDP is called announcements.

These announcements are:

  • Hostname
  • Originating information port identifier
  • Native virtual local area network (VLAN)
  • Device type
  • Device model
  • Duplex settings

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Following are the Cisco Discovery Protocol IOS Commands:

  • Show CDP
  • Show CDP neighbour
  • Show CDP neighbour detail
  • Show CDP interface
  1. show CDP:  using this command we can access information about CDP

                    Syntax: show CDP

                    This command has no arguments

  1. Show CDP neighbours: using this command we get information about the neighbour devices. Normally this command provides information like device name, a local interface, hold time, capability, platform, port id.

          Syntax: show CDP neighbours [type number] [detail]

Device ID: device name

Local interface: interface located on a local device

Hold time: how much time the entry needs to keep in table

Capability: It determines the capability of the directly connected device.

                    S indicates that the directly connected device is a switch

                    R indicates a router

Platform: It is the platform to which switch is connected

Port ID: port id of the neighbour device which is connected to the switch


           3) Show CDP neighbour details: provides all the information about neighbour Devices.

          4) Show CDP interface: It shows the CDP enabled interfaces

                                    Syntax: show CDP interface [type number]

CDP table holds all the information and this table get refreshed every time it receives an announcement. After receiving the announcement the Hold time is reinitialized. Hold time decides how long an entry exists in the table. If there is no announcement is generated within 180 seconds, the entry is removed automatically from the table.

Download Important Cisco Discovery Protocol(CDP) IOS Models in pdf – Click here