vlans on ip phone 7912G

Unanswered Question
Jul 23rd, 2009


I have received several CISCO IP PHONE 7912G. I saw it is possible to connect a PC to de telephone because it integrates a switch with 802.1Q.

I configured the ports on a switch in mode trunk with 802.1Q encapsulation with two vlans. The phones will be connected to this switch.

But how do I configure the telephone?

How will he know that one VLAN is for the telephone and the other for the PC?

is it possible to acces the telephone switch?


I have this problem too.
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Adrian Saavedra Thu, 07/23/2009 - 08:43


Phone will learn Voice Vlan by means of CDP (Cisco Discovery Protocol).

If your switch doesn't run/support discovery protocol, you'll need to specify the Administrative Vlan from Setting->Network Configuration from the IP Phone.

Hope it helps.


- Adrián.

languedoc Thu, 07/23/2009 - 13:52

Thanks for your answer.

Administrative vlan is the default vlan used to manage a switch, why should I configure it on the telephone?.

The concept are not clear to me.

In my switch i have the administrative vlan 1 and also 2 other vlans

vlan 10 for telephones

vlan 30 for the local network

So in my case should configure the vlan 30 as administrative vlan on my telephone is that rigth? who receives the administrative vlan, the telephone or the pc connted to it?

How can I do it with CDP?


Adrian Saavedra Thu, 07/23/2009 - 13:57


On IP Phone Menu, the "Administrative Vlan" should be set to your Voice Vlan, that is 10.

CDP is enabled by default in the switchports, if not you can enable with cdp enable.


- Adrián.

languedoc Sun, 07/26/2009 - 23:10

Hi .

I did the following configuration:

interface FastEthernet0/23

switchport trunk encapsulation dot1q

switchport trunk native vlan 20

switchport trunk allowed vlan 1,20,10,1002-1005

switchport mode trunk

switchport voice vlan 10

cdp enable


when I check network parameters on the telephone it tells me:

Operational vlan "vlan 10"

Administrative vlan "empty"

wath did I do wrong?



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