voice vlan

Unanswered Question
Feb 13th, 2007

i hav a 3550 switch and ip phones connected on it.Pcs are connected frm the ip phone .i hav two vlans one for voice and one for data.My question is

is it needed to configure the ports as trunk ports.In some cisco docs its saying that it should be a trunk port.

if so why?

If anybody can give better explanation plz.

Thanks in advance

I have this problem too.
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royalblues Tue, 02/13/2007 - 04:39


If it is a Cisco switch you do not need a trunk configuration.

When you enable voice vlan, a special-case 802.1Q trunk automatically is enabled through a CDP information exchange between the switch and the IP Phone. The trunk contains only two VLANs a voice VLAN (tagged VVID) and the data VLAN. The switch port's access VLAN is used as the data VLAN that carries packets to and from a PC that is connected to the phone's PC port.

If an IP Phone is removed and a PC is connected to the same switch port, the PC still will be capable of operating because the data VLAN still will appear as the access VLANeven though the special trunk no longer is enabled.

The trunk configuration is required though if a Avaya IP phone is conencted to the Cisco switch.

HTH, rate if it does


csco11063007 Tue, 02/13/2007 - 09:51

so if it is a cisco switch no need of configuring trunk?

or if it is a cisco switch and avaya ip phone then only the trunk is needed

which one is correct? u said both....

mchandak Tue, 02/13/2007 - 09:57

On the 3550 if u have a cisco phone and a PC, u dont need to configure the port as trunk. U can leave the port as access port.

royalblues Tue, 02/13/2007 - 22:56

You are correct.

If it is a cisco switch and a cisco IP phone, no need to configure trunks.

If it is a cisco switch connected to an avaya IP phone, you need to configure the interface as trunk

Hope this is clear


Please rate all posts

csco11063007 Wed, 02/14/2007 - 05:56


I hope ur answer is ok.But cisco is again confusing me.Plz check this attached doc frm cisco(page no.9)

I want know whether multiple vlan information pass on a access port or not?



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