Monday, December 15, 2008



Points to remeber :

When the voice VLAN feature is enabled, all untagged traffic is sent according to the default CoS priority of the port.

The CoS value is not trusted for IEEE 802.1p or IEEE 802.1Q tagged traffic.

Voice VLAN configuration is only supported on switch access ports; voice VLAN configuration is not supported on trunk ports.You can configure a voice VLAN only on Layer 2 ports.

The voice VLAN should be present and active on the switch for the IP phone to correctly communicate on the voice VLAN.

Do not configure voice VLAN on private VLAN ports.

Before you enable voice VLAN, it is recommended that you enable QoS on the switch by entering the mls qos global configuration command and configure the port trust state to trust by entering the mls qos trust cos interface configuration command.

You cannot configure static secure MAC addresses in the voice VLAN.

The Port Fast feature is automatically enabled when voice VLAN is configured. When you disable voice VLAN, the Port Fast feature is not automatically disabled.

Configuration Example :

This example shows how to configure a port connected to a Cisco IP Phone to use the CoS value to classify incoming traffic, to use IEEE 802.1p priority tagging for voice traffic, and to use the default native VLAN (VLAN 0) to carry all traffic:

Switch# configure terminal
Switch(config)# mls qos
Switch(config)# interface gigabitethernet0/5
Switch(config-if)# mls qos trust cos
Switch(config-if)# switchport voice vlan dot1p
Switch(config-if)# end

This example shows how to configure a port connected to a Cisco IP Phone to not change the priority of frames received from the PC or the attached device:

Switch# configure terminal
Switch(config)# interface gigabitethernet0/7
Switch(config-if)# switchport priority extend trust
Switch(config-if)# end


Switch# show interfaces interface-id switchport

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