Cisco Catalyst 2960 Series, Configuration Manual

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Trunk ports can carry any number of voice VLANs, similar to regular VLANs. The
configuration of voice VLANs is not supported on trunk ports. Note
• Before you enable voice VLAN, we recommend 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. If you use the auto-QoS feature, these settings are
automatically configured.
• You must enable CDP on the switch port connected to the Cisco IP Phone to send the configuration to
the phone. (CDP is globally enabled by default on all switch interfaces.)
Restrictions for Voice VLANs
You cannot configure static secure MAC addresses in the voice VLAN.
Information About Voice VLAN
Voice VLANs
The voice VLAN feature enables access ports to carry IP voice traffic from an IP phone. When the switch is
connected to a Cisco 7960 IP Phone, the phone sends voice traffic with Layer 3 IP precedence and Layer 2
class of service (CoS) values, which are both set to 5 by default. Because the sound quality of an IP phone
call can deteriorate if the data is unevenly sent, the switch supports quality of service (QoS) based on IEEE
802.1p CoS. QoS uses classification and scheduling to send network traffic from the switch in a predictable
manner.
The Cisco 7960 IP Phone is a configurable device, and you can configure it to forward traffic with an IEEE
802.1p priority. You can configure the switch to trust or override the traffic priority assigned by a Cisco
IP Phone.
Cisco IP Phone Voice Traffic
You can configure an access port with an attached Cisco IP Phone to use one VLAN for voice traffic and
another VLAN for data traffic from a device attached to the phone. You can configure access ports on the
switch to send Cisco Discovery Protocol (CDP) packets that instruct an attached phone to send voice traffic
to the switch in any of these ways:
• In the voice VLAN tagged with a Layer 2 CoS priority value
• In the access VLAN tagged with a Layer 2 CoS priority value
• In the access VLAN, untagged (no Layer 2 CoS priority value)
Consolidated Platform Configuration Guide, Cisco IOS Release 15.2(4)E (Catalyst 2960-X Switches)
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Restrictions for Voice VLANs