Cisco Catalyst 2960 Series, Configuration Manual

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◦ They both use IEEE 802.1p or untagged frames.
◦ The Cisco IP Phone uses IEEE 802.1p frames, and the device uses untagged frames.
◦ The Cisco IP Phone uses untagged frames, and the device uses IEEE 802.1p frames.
◦ The Cisco IP Phone uses IEEE 802.1Q frames, and the voice VLAN is the same as the access
VLAN.
• The Cisco IP Phone and a device attached to the phone cannot communicate if they are in the same
VLAN and subnet but use different frame types because traffic in the same subnet is not routed (routing
would eliminate the frame type difference).
• Voice VLAN ports can also be these port types:
◦ Dynamic access port.
◦ IEEE 802.1x authenticated port.
If you enable IEEE 802.1x on an access port on which a voice VLAN is configured and
to which a Cisco IP Phone is connected, the phone loses connectivity to the switch for
up to 30 seconds. Note
◦ Protected port.
◦ A source or destination port for a SPAN or RSPAN session.
◦ Secure port.
When you enable port security on an interface that is also configured with a voice VLAN,
you must set the maximum allowed secure addresses on the port to two plus the maximum
number of secure addresses allowed on the access VLAN. When the port is connected
to a Cisco IP Phone, the phone requires up to two MAC addresses. The phone address
is learned on the voice VLAN and might also be learned on the access VLAN. Connecting
a PC to the phone requires additional MAC addresses.
Note
Default Voice VLAN Configuration
The voice VLAN feature is disabled by default.
When the voice VLAN feature is enabled, all untagged traffic is sent according to the default CoS priority of
the port.
The CoS value is not trusted for IEEE 802.1p or IEEE 802.1Q tagged traffic.
Consolidated Platform Configuration Guide, Cisco IOS Release 15.2(4)E (Catalyst 2960-X Switches)
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Information About Voice VLAN