CDP

Typically the Network Infrastructure of an Enterprises will have many devices connected like mesh. For instance let us imagine a switch in Block 1 connected with another switch in Block 2 connected with many trunk links. In this case it is very difficult to find which cable connected to which port number. As a solution for this…

CDP (Cisco Discovery Protocol) is a proprietary protocol designed by Cisco System for Cisco devices. CDP helps administrators in collecting information about cisco devices. In this article we will explain CDP protocol in details.

CDP is a data link layer protocol. It is enabled by default on latest model of Cisco Switches and Routers. Those device can send and receive CDP messages dynamically.

CDP messages are generated as layer 2 multicast frames. It uses SNAP ( Subnetwork Access Protocol) frame type. The media types which can support SNAP, they are Ethernet, Token Ring, fiber distributed data interface (FDDI), Asynchronous Transfer Mode (ATM), Point-to-Point Protocol (PPP), High- Level Data Link Control (HDLC), and Frame Relay.

CDP Information

CDP messages contain useful information about cisco device as following:-

  • IOS version number
  • Hardware platform
  • Hardware capabilities
  • Layer 3 address
  • Interface that generate CDP message
  • Port ID
  • Number of seconds for CDP advertisement
  • Device type
  • Host name of Neighoring device

CDP messages are generated in every 60 seconds. Hold down time for missing neighbor is 180 seconds. Since CDP is a layer two protocol, CDP messages are not routed across the device

some relevant commands for CDP

Switch# show cdp neighbor

Router# show cdp interface

Router# show cdp neighbors details

Router# show cdp entry *

Router # show cdp entry router

Router # show cdp counters

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