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Catalyst 2960 Switch SoftwareConfiguration Guide
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Chapter14 Configuring Voice VLAN
Understanding Voice VLAN
Figure14-1 Cisco7960 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 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).
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 Figure14- 1). You can configure
Layer 2 access 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:
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 IEEE 802.1Q or IEEE 802.1p f rames 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.
Note Untagged traffic from the device attached to the Cisco IP Phone passes through the IP Phone unchanged,
regardless of the trust state of the access port on the IP Phone.
3-port
switch
P1 P3
P2
Access
port
Cisco IP Phone 7960
PC
101351
Phone
ASIC