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Here's what I'm trying to do: I'm trying to get the information on which switch/port that a jack wired to. On that jack, there is a Cisco IP phone (7942), and a computer plugged into its data port.

When I look at the CDP packets from the computer attached to it, I get the phone's CDP information (i.e. it sees the phone as a switch).

Is there a way to CDP packets, or the information on the switch behind the phone?

  • Show CDP neighbors from the switch and find the phone that you have identified? Otherwise you might be able to turn on LLDP on the switch and see that through the phone, but that's not a 100% answer. – cpt_fink Apr 14 '15 at 4:14
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While you could just bypass the phone and plug the computer directly into the wall jack and look at the CDP packets, the simplest solution is to run 'terminal monitor' on the switch and then unplug and plug the phone back into the wall socket. You'll see which interface goes up/down.

I've done this dozens of times when troubleshooting legacy networks with dubious documentation.

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