Voice Vlans

Voice Vlans

Why do we have them?

We use them to Separate Voice traffic from the data traffic. When you can add QOS and monitor the Traffic separately. Its signaled to the IP PHONE from CDP. There are a few options to get the VLAN's going


Combined Voice and Data Vlan. We do this with Soft phones. The Switch port is set to Access Mode and the Data and Voice share that Vlan

Separate Voice and Data Vlans

2 Vlans on 1 switch port. Data frames are left untagged, The voice frames are Tagged. This allows us to identify which packets are which is will need QOS and so on.

Trunks with Voice Vlan.

Set the port as a trunk instead of a access port. Data will go as the Native Vlan and the Voice will go as the Voice Vlan. We still get QOS features with the separate Vlans.


With IP precedence and COS(layer 2 QOS) set, by default this is 5, but it55 can be changed and will be changed as we move forward into setting up VLAN.


The IP phone itself is a swich and on the Switch Port we can setup the Voice and Data Vlan on how to tag traffic.

The IP phone can

Tag voice VLAN TRAFFIC with Layer 2(COS)
Untaged with no COS


With the Data we can send it through the IP phone trusted where its not checked. Untrusted where we tag it with COS of our choice.


Config examples

Single Vlan

interface FastEthernet0/1/0
Switchport mode access
switchport access vlan 101
switchport voice vlan dot1p
spanning-tree portfast


Multi Vlan
Switchport mode access
switchport access vlan 101
switchport voice vlan 100
spanning-tree portfast


Remember to have your voice vlans in lower vlan numbers if possible so spanning tree can re converge.