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Cisco discovery protocol cdp how cdp work example and guide

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Cisco Discovery Protocol CDP


Cisco Discovery Protocol (CDP) is a proprietary protocol designed by Cisco to help administrators collect information about both locally attached and remote devices. By using CDP, you can gather hardware and protocol information about neighbor devices, which is useful info for troubleshooting the network.
CDP messages are generated every 60 seconds as multicast messages on each of its active interfaces.
The information shared in a CDP packet about a Cisco device includes the following:
  • Name of the device configured with the hostname command
  • IOS software version
  • Hardware capabilities, such as routing, switching, and/or bridging
  • Hardware platform, such as 2600, 2950, or 1900
  • The layer-3 address(es) of the device
  • The interface the CDP update was generated on
CDP allows devices to share basic configuration information without even configuring any protocol specific information and is enabled by default on all interfaces.
CDP is a Datalink Protocol occurring at Layer 2 of the OSI model.
CDP is not routable and can only go over to directly connected devices.
CDP is enabled, by default, on all Cisco devices. CDP updates are generated as multicasts every 60 seconds with a hold-down period of 180 seconds for a missing neighbor. The no cdp run command globally disables CDP, while the no cdp enable command disables CDP on an interface. Use show cdp neighbors to list out your directly connected Cisco neighboring devices. Adding the detail parameter will display the layer-3 addressing configured on the neighbor.

How could CDP help you?

Manoj has just been hired as a senior network consultant at a large bank in Lucknow, Uttar Pradesh. He is expected to be able to take care of any problem that comes up. No problem at all here—he only has to worry about people possibly not getting the right money transaction if the network goes down. Manoj starts his job happily.
Soon, of course, the network has some problems. He asks one of the junior administrators for a network map so he can troubleshoot the network. This person tells him that the old senior administrator (who just got fired) had them with him and now no one can find them. Cashiers are calling every couple of minutes because they can’t get the necessary information they need to take care of their customers. What should he do?
CDP to the rescue! Thank God this bank has all Cisco routers and switches and that CDP is enabled by default on all Cisco devices. Also, luckily, the dissatisfied administrator who just got fired didn't turn off CDP on any devices before he left. All Manoj has to do now is to use the show cdp neighbor detail command to find all the information he needs about each device to help draw out the bank network .

Cisco Discovery Protocols Configuration commands

Router#show cdp Displays global CDP information (such as timers)
Router#show cdp neighbors Displays information about neighbors
Router#show cdp neighbors detail Displays more detail about the neighbor device
Router#show cdp entry word Displays information about the device named word
Router#show cdp entry * Displays information about all devices
Router#show cdp interface Displays information about interfaces that have CDP running
Router#show cdp interface x Displays information about specific interface x running CDP
Router#show cdp traffic Displays traffic information—packets in/out/version
Router(config)#cdp holdtime x Changes the length of time to keep CDP packets
Router(config)#cdp timer x Changes how often CDP updates are sent
Router(config)#cdp run Enables CDP globally (on by default)
Router(config)#no cdp run Turns off CDP globally
Router(config-if)#cdp enable Enables CDP on a specific interface
Router(config-if)#cdp enable Enables CDP on a specific interface
Router(config-if)#no cdp enable Turns off CDP on a specific interface
Router#clear cdp counters Resets traffic counters to 0
Router#clear cdp table Deletes the CDP table
Router#debug cdp adjacency Monitors CDP neighbor information
Router#debug cdp events Monitors all CDP events
Router#debug cdp ip Monitors CDP events specifically for IP
Router#debug cdp packets Monitors CDP packet-related information

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