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New Member

A voice vlan port must be a trunk?

Hi all,

I had saw some discuss in other forum said that a voice vlan port in 3550 must be a trunk port, and the data traffic vlan should be the native vlan of the trunk. But some body that the port need not be a trunk. Also the doc of 3550 does not say that the port must be a trunk. And I tried to use command "switchport mode access" "switchport access vlan x" "switchport voice vlan y" in a same port and there is no error. but at that time when I try to use command "show vlan" to verify the config, the display just showed that the port is in vlan x. Is there any body knows the answer? And can I use "switchport mode access" in a voice vlan port? Thank You!

Best Regards

Teru Lei

New Member

Re: A voice vlan port must be a trunk?


You will need to trunk the port (802.1Q) into the IP Phone if you are connecting a PC to the back of the Phone and therefore wish to put the voice and data on seperate VLAN's. This way when the phone boots up CDP (through the use of voice vlan or auxiliary vlan) can advise it which VLAN it belongs to etc. I mentioned 802.1Q this is so you can set the COS field for your QOS value at layer 2.

Check out the following document which explains it nicely:

Hope that helps


New Member

Re: A voice vlan port must be a trunk?


the problem is that in link you give, there is no indication about the trunk so ,

it is on by default?

The other problem is that on the same link there is no indication about what to do when you have a pc behind the phone. the only reference is on the QOS design guide for AVVID and on this doc there is a strange indication:

voice vlan for phone

ACCESS vlan fo rPC behind phone!!!

Any comment on it? And the native vlan of the trunk???

Thanks for any suggestion,


Cisco Employee

Re: A voice vlan port must be a trunk?

since IOS 12.1(9)EA1 there is a new approach to connecting Cisco IP phones implemented in Catalyst2950/3550 switches. This is closely resembling the Auxiliary VLAN on CatOS switches, it's called Voice Vlan and it does not require the port to be trunking.

However, if you wish to configure the port to be a trunk like in a 3500XL switch, you should be able to do that as well.


interface FastEthernet0/23

switchport trunk encapsulation dot1q

switchport trunk native vlan 128 <<<

switchport mode trunk

switchport voice vlan 210 <<<

spanning-tree portfast