David’s Cisco Networking Blog

Feb 13 2009   10:55PM GMT

What is CDP and how can it help you?



Posted by: David Davis
Tags:
CDP
Cisco
cisco discovery protocol
ios
troubleshooting

he Cisco Discovery Protocol (CDP) is a proprietary layer 2 management protocol for networks. CDP provides network device inventory, connectivity information, and IP next hop info. It works on LANs and WANs. CDP also works no matter the layer 3 network in use. This, no matter if you are running TCP/IP, Decnet, or Novell IPX- CDP will still function and provide the same info. CDP is excellent for troubleshooting.

I have used CDP to find out what the IP address is of a misconfigured router or switch on the other side of a WAN link. CDP can be enabled/disabled at the interfae level or globally on the whole router/switch.

Here are 6 CDP commands you should know:

  1. cdp run and cdp no run – to enable and disable CDP globally
  2. cdp enable and no cdp enable – to enable and disable cdp per interface
  3. show cdp neighbors – to view see what routers and switches are connected to you on the LAN or WAN.
  4. show cdp interfaces – to see which of your interfaces are participating in the CDP exchange
  5. show cdp entry – to look at a particular switch or router that is a neighbor
  6. show traffic - to see statistics about how many CDP packets have been exchanged

Also, you can also set cdp timers and clear cdp statistics.

For more information on CDP see the Cisco IOS Configuration Fundamentals Configuration Guide, Configuring Cisco Discovery Protocol (CDP) section.

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