Which statement is true about voice VLANs? *

A.
The voice VLAN feature is enabled by default.

B.
When the voice VLAN feature is enabled, all untagged voice and data traffic is sent through the voice VLAN.

C.
The default CoS value is 1 for incoming voice and data traffic.

D.
The IP phone overrides the priority of all incoming data traffic (tagged and untagged) and sets the CoS value to 0.

Explanation:

By default, a switch instructs an attached IP Phone to consider the PC port as untrusted. The phone will overwrite the CoS values to 0.

You can change the default CoS value using following command.

Switch(config-if)# switchport priority extend {cos <value> or trust}