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38 Switching Configuration
• When a dot1p priority is associated with the Voice VLAN port instead of a VLAN ID, then the priority
information is passed onto the VOIP phone using the LLDP-MED mechanism. By this method, the
voice data coming from the VOIP phone is tagged with VLAN 0 and with the exchanged priority; thus
regular data arriving on the switch is given the default priority of the port (default 0), and the voice
traffic is received with a higher priority.
You can configure the switch to override the data traffic CoS. This feature can override the 802.1 priority of
the data traffic packets arriving at the port enabled for Voice VLAN. Therefore, any rogue client that is also
connected to the Voice VLAN port does not deteriorate the voice traffic.
Interaction with LLDP-MED
The interactions with LLDP-MED are important for Voice VLAN:
• LLDP-MED notifies the Voice VLAN component of the presence and absence of a VoIP phone on the
network.
• The Voice VLAN component interacts with LLDP-MED for applying VLAN ID, priority and tag
information to the VoIP phone traffic.
For release 2.0 and earlier, the Voice VLAN feature can only be used by IP phones that support LLDP-MED,
e.g. 4610SW Avaya phones.
Example#1: Configuring Voice VLAN
The commands in this example create a VLAN for voice traffic with a VLAN ID of 25. Then, Voice VLAN is
administratively enabled on the switch. Finally, port 1/g12 is set to an 802.1Q VLAN and then enabled for
Voice VLAN traffic.
console#configure
console(config)#vlan database
console(config-vlan)#vlan 25
console(config-vlan)#exit
console(config)#voice vlan
console(config)#interface ethernet 1/g12
console(config-if-1/g12)#switchport mode general
console(config-if-1/g12)#voice vlan 25
console(config-if-1/g12)#exit
console(config)#exit
console#show voice vlan interface 1/g12
Interface...................................... 1/g12
Voice VLAN Interface Mode...................... Enabled
Voice VLAN ID.................................. 25
Voice VLAN COS Override........................ False
Voice VLAN Port Status......................... Disabled
Voice VLAN Authentication...................... Enabled