Nov 04

CDP, Important Commands, and it Use


CDP stands for Cisco discovery protocol, this is essential for increasing the network efficiency, especially when the network changes dynamically. It’s a network discovery tool for assisting network administrator to identify neighbouring cisco devices. This is enabled on Cisco devices not limited to switches and routers and runs on all LAN and WAN that supports subnetwork access protocol. CDP packet communication are every 60 seconds on each device and the amount of information that it collects depends on device and version of operating system. It can include messages with parameters such as hardware, hostname, duplex setting, IP addresses, active interfaces of CDP devices.

For CDP to run on any device, the only requirement is that the interface should support Subnetwork Access Protocol(SNAP).

Benefits on usage of CDP on networks

  • Allows the use of various network layer protocols and with the real-time transport protocol, it helps to discover any devices on network and figures out on how it is configured.
  • It enables to discover the IP address of a misconfigured router or switch on other side of a WAN link
  • Helps in troubleshooting Type-Length-Value fields

Important commands and its usage

For the usage of CDP, below are important commands that to be noted

  • show cdp
  • show cdp neighbor
  • show cdp neighbor detail
  • show cdp interface

show cdp – This command will show CDP packets that are sent for every 60 seconds and hold time of the packets.

show cdp neighbor – This command will output details of connected neighbors. The output will result in below parameters

  • DeviceID – It is the name of the device.
  • Local interface – It is the interface of the local device.
  • Hold Time – It will provide information on lifetime of the entry to be stored in table
  • Capability – Example output values for this parameter are R: Router, S: Switch
  • Platform – It will provide information on the platform of the neighbor device to which switch is connected.
  • Port ID – It’s the neighbor port id connected to the switch

show cdp neighbor detail – It gives details on each neighbor that are on network with the parameters – DeviceID, Entry addresses, Platform, Interface, Hold time, Version, advertisement, Duplex.

show cdp interface – It will output the interfaces on which the CDP is enabled and gives status on protocol whether it’s up or down. And it also provides details on time interval in which packets sent on network and hold time of the packets on network.

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