124Configuring a voice VLANConfiguration prerequisitesBefore you configure a voice VLAN, complete the following tasks:• Create a VLAN• Configure QoS priority settings for voice VLAN traffic on an interface before enabling voice VLANon the interface.If the configuration order is reversed, your priority configuration will fail. For more information, see"Configuring QoS priority settings for voice traffic on an interface."• Configure the voice VLAN assignment mode.For more information, see "Configuring a port to operate in automatic voice VLAN assignment mode"and "Configuring a port to operate in manual voice VLAN assignment mode."NOTE:• A port can belong to only one voice VLAN at a time.• Voice VLAN cannot be enabled on a port with Link Aggregation Control Protocol (LACP) enabled.Configuring QoS priority settings for voice traffic on aninterfaceIn voice VLAN applications, you can improve the quality of voice traffic by configuring the appropriateQoS priority settings, including the Class of Service (CoS) and Differentiated Services Code Point (DSCP)values, for voice traffic. Voice traffic carries its own QoS priority settings. You can configure the deviceeither to modify or not to modify the QoS priority settings carried by incoming voice traffic.Follow these steps to configure QoS priority settings for voice traffic:To do... Use the command... RemarksEnter system view system-view —Enter Layer 2 Ethernet interfaceviewinterface interface-typeinterface-number —Configure the interface to trust theQoS priority settings in incomingvoice traffic, but not to modify theCoS and DSCP values marked forincoming traffic of the voice VLANvoice vlan qos trustRequiredUse either commandBy default, an interface modifies theCoS value and the DSCP valuemarked for voice VLAN traffic into 6and 46 respectively.The voice vlan qos command and thevoice vlan qos trust command canoverwrite each other, whichever isconfigured last.Configure the interface to modifythe CoS and DSCP values markedfor incoming traffic of the voiceVLAN into specified valuesvoice vlan qos cos-valuedscp-value
