Cisco IE 4000, Software Configuration Manual

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Configuring Voice VLAN
Information About Configuring Voice VLAN
Figure 35 Cisco 7960 IP Phone Connected to a Switch
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)
Note: In all configurations, the voice traffic carries a Layer 3 IP precedence value (the default is 5 for voice traffic and 3
for voice control 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).
Cisco IP Phone Data Traffic
The switch can also process tagged data traffic (traffic in IEEE 802.1Q or IEEE 802.1p frame types) from the device
attached to the access port on the Cisco IP phone (see
Figure 35 on page 310 ). You can configure Layer 2 access ports
on the switch to send CDP packets that instruct the attached phone to configure the phone access port in one of these
modes:

In trusted mode, all traffic received through the access port on the Cisco IP phone passes through the phone
unchanged.

In untrusted mode, all traffic in IEEE 802.1Q or IEEE 802.1p frames received through the access port on the Cisco IP
phone receive a configured Layer 2 CoS value. The default Layer 2 CoS value is 0. Untrusted mode is the default.
Note: Untagged traffic from the device attached to the Cisco IP phone passes through the phone unchanged, regardless
of the trust state of the access port on the phone.
3-port
switch
P1 P3
P2
Access
port
Cisco IP Phone 7960
PC
101351
Phone
ASIC