•Inuntrusted mode, alltraffic in IEEE 802.1Q or IEEE 802.1p frames received through the access port
onthe Cisco IP Phone receive a configured Layer 2 CoS value. The default Layer 2 CoS value is 0.
Untrustedmode is the default.
Untaggedtraffic from the device attached to the Cisco IP Phone passes through the phone unchanged,
regardlessof the trust state of the access port on the phone.
Note
Related Topics
Configuringthe Priority of IncomingData Frames, on page 155
Example:Configuring a Port Connected to an IPPhone Notto ChangeFrame Priority, on page 158
Voice VLAN Configuration Guidelines
•Becausea Cisco 7960 IP Phone also supports a connection to a PC or other device, a port connecting
theswitch to a Cisco IP Phone can carry mixed traffic. You can configure a port to decide how the Cisco
IPPhone carriesvoice traffic and data traffic.
•Thevoice VLAN should be present and active on the switch for the IP phone to correctly communicate
onthe voice VLAN. Use the show vlan privileged EXEC command to see if the VLAN is present (listed
inthe display). If the VLAN isnot listed,create the voice VLAN.
•ThePower overEthernet (PoE)switches are capableof automaticallyproviding power toCisco
pre-standardand IEEE 802.3af-compliant powered devices if they are not being powered by an AC
powersource.
•Beforeyou enable voice VLAN, we recommend that you enable QoS on the switch by entering the mls
qosglobal configuration command and configure the port trust state to trust by entering the mls qos
trustcos interface configuration command. Ifyou usethe auto-QoSfeature, these settingsare
automaticallyconfigured.
•Youmust enable CDP on the switch port connected to the Cisco IP Phone to send the configuration to
thephone. (CDP is globally enabled by default on all switch interfaces.).
•ThePort Fast feature is automatically enabled when voice VLAN is configured. When you disable voice
VLAN,the Port Fast feature is not automatically disabled.
•Ifthe Cisco IP Phoneand adevice attached to the phone are in the same VLAN, they must be in the
sameIP subnet. Theseconditions indicate that they are in the same VLAN:
◦Theyboth useIEEE 802.1p or untagged frames.
◦TheCisco IP Phone uses IEEE 802.1p frames, and the device uses untagged frames.
◦TheCisco IP Phone uses untagged frames, and the device uses IEEE 802.1p frames.
◦TheCisco IP Phone uses IEEE 802.1Q frames,and the voice VLAN is the same as the access
VLAN.
•TheCisco IP Phone and adevice attached to the phone cannot communicate if they are in the same
VLANand subnet but use different frame types because traffic in the same subnet is not routed (routing
wouldeliminate the frame type difference).
Catalyst 2960-XR Switch VLAN Configuration Guide, Cisco IOS Release 15.0(2)EX1
152 OL-29440-01
Configuring Voice VLANs
Voice VLAN Configuration Guidelines