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Understanding Voice VLAN
Figure 16-1 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 Cisco IP Phone to
send voice traffic to the switch in any of these ways:
•
•
•
In all configurations, the voice traffic carries a Layer 3 IP precedence value (the default is 5 for voice
Note
traffic and 3 for voice control traffic).
Cisco IP Phone Data Traffic
The switch can also process tagged data traffic (traffic in 802.1Q or 802.1p frame types) from the device
attached to the access port on the Cisco IP Phone (see
ports on the switch to send CDP packets that instruct the attached Cisco IP Phone to configure the IP
phone access port in one of these modes:
•
•
Untagged traffic from the device attached to the Cisco IP Phone passes through the IP phone unchanged,
Note
regardless of the trust state of the access port on the IP phone.
Catalyst 3750 Switch Software Configuration Guide
16-2
Cisco IP Phone 7960
Phone
ASIC
P1
3-port
switch
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)
In trusted mode, all traffic received through the access port on the Cisco IP Phone passes through
the IP phone unchanged.
In untrusted mode, all traffic in 802.1Q or 802.1p frames received through the access port on the IP
phone receive a configured Layer 2 CoS value. The default Layer 2 CoS value is 0. Untrusted mode
is the default.
P2
PC
P3
Access
port
Figure
Chapter 16
Configuring Voice VLAN
16-1). You can configure Layer 2 access
78-16180-02
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