Phones drop if CDP is disabled

Unanswered Question
Oct 12th, 2009
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Hi Guys,

Just a quick one, any reason why a phone would go from a registered state to stuck on configuring IP when CDP is turned off on the switch. If CDP is turned back on they come back and are fine.

I thought CDP was only needed for the boot process ?

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gogasca Mon, 10/12/2009 - 12:13
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CDP is needed for Voice VLAN, if IP Phone may not be able to communicate properly to CUCM if no VVLAN.

Take a look at this:


Any reason to disable CDP in the switch?

sebastiandm Mon, 10/12/2009 - 14:04
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I already have seperate voice and data vlans and the phones are registered, however if i disable cdp the phones immediately into configuring IP.

My understanding is that the phones only require cdp to obtain the vvlan, ip address, sub mask, DG, dhcp and tftp server information. Once it has this info and is registered it should not lose it if CDP is turned off.

I can understand if the phones were reset after cdp was turned off but this is not the case.

Thanks in advance.


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