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Understanding Voice VLAN
Figure 15-1
Figure 15-1
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 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 IEEE 802.1Q or IEEE 802.1p frame types) from
the device attached to the access port on the Cisco IP Phone (see
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:
•
•
Catalyst 2928 Switch Software Configuration Guide
15-2
shows one way to connect a Cisco 7960 IP Phone.
Cisco 7960 IP Phone Connected to a Switch
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 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.
P2
PC
P3
Access
port
Chapter 15
Configuring Voice VLAN
Figure
15-1). You can configure Layer 2
OL-23389-01
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Troubleshooting
