CDP neighbor question

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Oct 31st, 2007
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I have a question in regards to CDP that i'm not 100% certain about.

When you type in the 'show cdp neighbors' command. Does it show the directly connected neighbors to that router? Does it include switches also if they are directly connected. I am presuming that hosts are not detected as they are not cisco devices and it is uncommon to connect pc's to routers via ethernet.


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Kevin Dorrell Wed, 10/31/2007 - 20:37
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Yes, it shows all the directly connected Cisco devices, including switches. The feature works on both switches and routers.

Note that CDP has to be enabled at both ends of a link for anything to be detected; you cannot get it to work in one direction only.

Kevin Dorrell


paul.matthews Thu, 11/01/2007 - 01:56
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Kevin is right - I'll also add that even Cisco phones show up in CDP!

That can be awkward of one has a large switch in an IPT environment as CDP shows several hundred devices. What I do on a switch occupied by phones is

sh cdp nei | exc SEP

to filter out entries that are phones.

Some of the more "recent" additions to the Cisco portfolio do not necessarily fully support CDP - like the CSS - it will send but not listen for example.

CDP travels one cisco hop. normally you see one device per interfave at the most. If you see several devices on one interface, you almost certainly have a non-cisco switch or a hub as your immediate next hop.


bpdons123 Thu, 11/01/2007 - 02:18
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Thank you very much for your feedback. Much appreciated


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