1-5
Catalyst 3750-X and 3560-X Switch Software Configuration Guide
OL-25303-03
Chapter 1 Configuring Voice VLAN
Configuring Voice VLAN
Configuring Cisco IP Phone Voice Traffic
You can configure a port connected to the Cisco IP Phone to send CDP packets to the phone to configure
the way in which the phone sends voice traffic. The phone can carry voice traffic in IEEE 802.1Q frames
for a specified voice VLAN with a Layer 2 CoS value. It can use IEEE 802.1p priority tagging to give
voice traffic a higher priority and forward all voice traffic through the native (access) VLAN. The Cisco
IP Phone can also send untagged voice traffic or use its own configuration to send voice traffic in the
access VLAN. In all configurations, the voice traffic carries a Layer 3 IP precedence value (the default
is 5).
Beginning in privileged EXEC mode, follow these steps to configure voice traffic on a port:
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
interface interface-id Specify the interface connected to the phone, and enter interface
configuration mode.
Step 3
mls qos trust cos Configure the interface to classify incoming traffic packets by using the
packet CoS value. For untagged packets, the port default CoS value is used.
Note Before configuring the port trust state, you must first globally enable
QoS by using the mls qos global configuration command.
Step 4
switchport voice {detect
cisco-phone [full-duplex] | vlan
{vlan-id | dot1p | none | untagged}}
Configure how the Cisco IP Phone carries voice traffic:
• detect—Configure the interface to detect and recognize a Cisco IP
phone.
• cisco-phone—When you initially implement the switchport voice detect
command, this is the only allowed option. The default is no switchport
voice detect cisco-phone [full-duplex].
• full-duplex—(Optional) Configure the switch to only accept a
full-duplex Cisco IP phone.
Note Before configuring the switch port to detect and recognize a Cisco IP
phone, confirm that the phone is powered by PoE. The configuration
fails when power is provided by an AC source.
• vlan-id—Configure the phone to forward all voice traffic through the
specified VLAN. By default, the Cisco IP Phone forwards the voice
traffic with an IEEE 802.1Q priority of 5. Valid VLAN IDs are 1 to
4094.
• dot1p—Configure the switch to accept voice and data IEEE 802.1p
priority frames tagged with VLAN ID 0 (the native VLAN). By default,
the switch drops all voice and data traffic tagged with VLAN 0. If
configured for 802.1p the Cisco IP Phone forwards the traffic with an
IEEE 802.1p priority of 5.
• none—Allow the phone to use its own configuration to send untagged
voice traffic.
• untagged—Configure the phone to send untagged voice traffic.
Step 5
end Return to privileged EXEC mode.
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