Configuring Voice VLANs
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Prerequisites for Voice VLANs
The following are the prerequisites for voice VLANs:
Voice VLAN configuration is only supported on switch access ports; voice VLAN configuration is not supported on trunk ports.
 Note |
Trunk ports can carry any number of voice VLANs, similar to regular VLANs. The configuration of voice VLANs is not supported on trunk ports.
|
Before you enable voice VLAN, we recommend that you enable QoS on the switch by entering the mls qos global configuration command and configure the port trust state to trust by entering the mls qos trust cos interface configuration command. If you use the auto-QoS feature, these settings are automatically configured.
You must enable CDP on the switch port connected to the Cisco IP Phone to send the configuration to the phone. (CDP is globally enabled by default on all switch interfaces.)
Restrictions for
Voice VLANs
You cannot configure
static secure MAC addresses in the voice VLAN.
Information About Voice VLAN
Voice VLANs
The voice VLAN feature enables access ports to carry IP
voice traffic from an IP phone. When the
switch is connected to a Cisco 7960 IP Phone,
the phone sends voice traffic with Layer 3 IP precedence and Layer 2 class of
service (CoS) values, which are both set to 5 by default. Because the sound
quality of an IP phone call can deteriorate if the data is unevenly sent, the
switch supports quality of service (QoS)
based on IEEE 802.1p CoS. QoS uses classification and scheduling to send
network traffic from the
switch in a predictable manner.
The Cisco 7960 IP Phone is a
configurable device, and you can configure it to forward traffic with an IEEE
802.1p priority. You can configure the
switch to trust or override the traffic
priority assigned by a Cisco IP Phone.
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 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. You can configure Layer 2 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:
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.
 Note |
Untagged traffic from the device attached to the Cisco IP Phone passes through the phone unchanged, regardless of the trust state of the access port on the phone.
|
Voice VLAN Configuration Guidelines
-
Because
a Cisco 7960 IP Phone also supports a connection to a PC or other device, a
port connecting the
switch to a Cisco IP Phone can carry mixed
traffic. You can configure a port to decide how the Cisco IP Phone carries
voice traffic and data traffic.
-
The voice VLAN should be
present and active on the
switch for the IP phone to correctly
communicate on the voice VLAN. Use the
show vlan privileged EXEC command to see if the
VLAN is present (listed in the display). If the VLAN is not listed, create the
voice VLAN.
-
The Power over Ethernet (PoE)
switches are capable of automatically providing
power to Cisco pre-standard and IEEE 802.3af-compliant powered devices if they
are not being powered by an AC power source.
-
The Port Fast feature is
automatically enabled when voice VLAN is configured. When you disable voice
VLAN, the Port Fast feature is not automatically disabled.
-
If the Cisco IP Phone and a
device attached to the phone are in the same VLAN, they must be in the same IP
subnet. These conditions indicate that they are in the same VLAN:
-
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:
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.
How to Configure Voice VLAN
Configuring Cisco IP
Phone Voice Traffic
You can configure a
port connected to the Cisco IP Phone to send CDP packets to the phone to
configure the way in which the phone sends voice traffic. The phone can carry
voice traffic in IEEE 802.1Q frames for a specified voice VLAN with a Layer 2
CoS value. It can use IEEE 802.1p priority tagging to give voice traffic a
higher priority and forward all voice traffic through the native (access) VLAN.
The Cisco IP Phone can also send untagged voice traffic or use its own
configuration to send voice traffic in the access VLAN. In all configurations,
the voice traffic carries a Layer 3 IP precedence value (the default is 5).
SUMMARY STEPS1.
enable
2.
configure
terminal
3.
interface
interface-id
4.
mls qos trust
cos
5.
switchport voice
{vlan{vlan-id |
dot1p |
none |
untagged}}
6.
end
7.
Use one of the
following:
- show interfaces
interface-id
switchport
- show running-config
interface
interface-id
8.
copy
running-config startup-config
DETAILED STEPS | Command or Action | Purpose |
---|
Step 1 |
enable
Example:
Switch> enable
|
Enables
privileged EXEC mode. Enter your password if prompted.
|
Step 2 | configure
terminal
Example:
Switch# configure terminal
|
Enters the global
configuration mode.
|
Step 3 | interface
interface-id
Example:
Switch(config)# interface gigabitethernet1/0/1
|
Specifies the
interface connected to the phone, and enters interface configuration mode.
|
Step 4 | mls qos trust
cos
Example:
Switch(config-if)# mls qos trust cos
|
Configures the
interface to classify incoming traffic packets by using the packet CoS value.
For untagged packets, the port default CoS value is used.
Note
|
Before configuring
the port trust state, you must first globally enable QoS by using the
mls qos global configuration command.
|
|
Step 5 | switchport voice
{vlan{vlan-id |
dot1p |
none |
untagged}}
Example:
Switch(config-if)# switchport voice vlan dot1p
|
Configures the
voice VLAN.
-
vlan-id—Configures the phone to forward all voice
traffic through the specified VLAN. By default, the Cisco IP Phone forwards the
voice traffic with an IEEE 802.1Q priority of 5. Valid VLAN IDs are 1 to 4094.
-
dot1p—Configures the
switch to accept voice and data IEEE 802.1p
priority frames tagged with VLAN ID 0 (the native VLAN). By default, the
switch drops all voice and data traffic
tagged with VLAN 0. If configured for 802.1p the Cisco IP Phone forwards the
traffic with an IEEE 802.1p priority of 5.
-
none—Allows the phone to use its own configuration
to send untagged voice traffic.
-
untagged—Configures the phone to send untagged
voice traffic.
|
Step 6 | end
Example:
Switch(config-if)# end
|
Returns to
privileged EXEC mode.
|
Step 7 | Use one of the
following:
- show interfaces
interface-id
switchport
- show running-config
interface
interface-id
Example:
Switch# show interfaces gigabitethernet1/0/1 switchport
or
Switch# show running-config interface gigabitethernet1/0/1
|
Verifies your
voice VLAN entries or your QoS and voice VLAN entries.
|
Step 8 | copy
running-config startup-config
Example:
Switch# copy running-config startup-config
|
(Optional) Saves
your entries in the configuration file.
|
Configuring the Priority of Incoming Data Frames
You
can connect a PC or other data device to a Cisco IP Phone port. To process
tagged data traffic (in IEEE 802.1Q or IEEE 802.1p frames), you can configure
the
switch to send CDP packets to instruct the
phone how to send data packets from the device attached to the access port on
the Cisco IP Phone. The PC can generate packets with an assigned CoS value. You
can configure the phone to not change (trust) or to override (not trust) the
priority of frames arriving on the phone port from connected devices.
Follow these steps to set the
priority of data traffic received from the non-voice port on the Cisco IP
Phone:
SUMMARY STEPS1.
enable
2.
configure
terminal
3.
interface
interface-id
4.
switchport priority
extend {cos
value |
trust}
5.
end
6.
show
interfaces
interface-id
switchport
7.
copy
running-config startup-config
DETAILED STEPS | Command or Action | Purpose |
---|
Step 1 |
enable
Example:
Switch> enable
|
Enables
privileged EXEC mode. Enter your password if prompted.
|
Step 2 | configure
terminal
Example:
Switch# configure terminal
|
Enters the global
configuration mode.
|
Step 3 | interface
interface-id
Example:
Switch(config)# interface gigabitethernet1/0/1
|
Specifies the
interface connected to the Cisco IP Phone, and enters interface configuration
mode.
|
Step 4 | switchport priority
extend {cos
value |
trust}
Example:
Switch(config-if)# switchport priority extend trust
|
Sets the priority
of data traffic received from the Cisco IP Phone access port:
-
cos
value—Configures the phone to override the
priority received from the PC or the attached device with the specified CoS
value. The value is a number from 0 to 7, with 7 as the highest priority. The
default priority is
cos 0.
-
trust—Configures the phone access port to trust
the priority received from the PC or the attached device.
|
Step 5 | end
Example:
Switch(config-if)# end
|
Returns to
privileged EXEC mode.
|
Step 6 | show
interfaces
interface-id
switchport
Example:
Switch# show interfaces gigabitethernet1/0/1 switchport
|
Verifies your
entries.
|
Step 7 | copy
running-config startup-config
Example:
Switch# copy running-config startup-config
|
(Optional) Saves
your entries in the configuration file.
|
Monitoring Voice VLAN
To display voice VLAN configuration for an interface, use the show interfaces interface-id switchport privileged EXEC command.
Configuration Examples
Example: Configuring Cisco IP Phone Voice Traffic
This example shows how to configure a port connected to a Cisco IP Phone to use the CoS value to classify incoming traffic and to accept voice and data priority traffic tagged with VLAN ID 0:
Switch# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Switch(config)# interface gigabitethernet1/0/1
Switch(config-if)# mls qos trust cos
Switch(config-if)# switchport voice vlan dot1p
Switch(config-if)# end
To return the port to its default setting, use the no switchport voice vlan interface configuration command.
Example: Configuring the Priority of Incoming Data Frames
This example shows how to configure a port connected to a Cisco IP Phone to not change the priority of frames received from the PC or the attached device:
Switch# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Switch(config)# interface gigabitethernet1/0/1
Switch(config-if)# switchport priority extend trust
Switch(config-if)# end
To return the port to its default setting, use the no switchport priority extend interface configuration command.
Where to Go Next
After configuring voice VLANs, you can configure the following:
Additional References
Related Documents
Related Topic |
Document Title |
For complete syntax and usage information for the commands used in this chapter.
|
Catalyst 2960-X Switch VLAN Management Command Reference
|
MIBs
MIB |
MIBs Link |
All supported MIBs for this release.
|
To locate and download MIBs for selected platforms, Cisco IOS
releases, and feature sets, use Cisco MIB Locator found at the
following URL:
http://www.cisco.com/go/mibs
|
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Feature History and Information for Voice VLAN
Release |
Modification |
Cisco IOS 15.0(2)EX
|
This feature was introduced.
|