Prerequisites for Voice VLANs
The following are the prerequisites for voice VLANs:
Voice VLAN configuration is only supported on device access ports; voice VLAN configuration is not supported on trunk ports.
Trunk ports can carry any number of voice VLANs, similar to regular VLANs. The configuration of voice VLANs is not supported on trunk ports.
Before you enable voice VLAN, enable QoS on the device by entering the trust device cisco-phone interface configuration command. If you use the auto QoS feature, these settings are automatically configured.
You must enable CDP on the device port connected to the Cisco IP Phone to send the configuration to the phone. (CDP is globally enabled by default on all device interfaces.)