Cisco 300 Series Cli Manual page 1109

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Voice VLAN Commands
The port is added to the voice VLAN if a packet with a source MAC address OUI
address (defined by voice vlan oui-table) is trapped on the port. Note: The packet
VLAN ID does not have to be the voice VLAN, it can be any VLAN.
The port joins the voice VLAN as a tagged port.
If the time since the last MAC address with a source MAC address OUI address
was received on the interface exceeds the timeout limit (configured by voice vlan
aging-timeout), the interface is removed from the voice VLAN.
Example
The following example enables OUI voice VLAN configuration on
2.
gi1
switchxxxxxx(config)# interface gi12
switchxxxxxx(config-if)# voice vlan enable
1109 OL-32830-01 Command Line Interface Reference Guide