Configuring Voice VLAN

Before enabling a voice VLAN, CISCO recommand that QoS is enabled (by entering the mls qos command) and the port trust state is set on the interface(by entering the mls qos trust cos command).


You can configure a port to carry voice traffic in one of 2 ways:

•Configure the port to carry Voice Traffic in IEEE 802.1Q Frames
or
•Configure the port to carry Voice Traffic in IEEE 802.1p Priority-Tagged Frames

DOT1Q
To configure a port to carry voice traffic in IEEE 802.1Q frames for a specific VLAN.

mls qos
Interface Fa0/X
mls qos trust cos
switchport access vlan X
switchport voice vlan Y (Tells the phone to use a dot1q header for VLAN Y)

n.b. The voice VLAN should be present and active on the switch when using its own vlan.

DOT1P
To configure a port to instruct the IP phone to carry traffic through the native data vlan.

mls qos
interface Fa0/X
mls qos trust cos
switchport access vlan X
switchport voice vlan dot1p (Tells the phone to use native data vlan)

By default voice traffic is sent with a cos value of 5 and data traffic with a cos value of 0.

Use the following commands to instruct the phone to change the cos value of data packets.

mls qos trust device cisco-phone
switchport priority extended cos 1 (Tells phone to set data traffic with cos 1)