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, enable QoS on the
switch by entering the trust device cisco-phone 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.
By default, the voice VLAN
feature is disabled. When the 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 802.1Q or for IEEE 802.1p tagged traffic.
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:
How to Configure Voice VLAN
Configuring Cisco IP Phone Voice Traffic
(CLI)
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).
Procedure | Command or Action | Purpose |
---|
Step 1 | configure
terminal
Example:
Device# configure terminal
|
Enters the global
configuration mode.
|
Step 2 | interface
interface-id
Example:
Device(config)# interface gigabitethernet1/0/1
|
Specifies the
interface connected to the phone, and enters interface configuration mode.
|
Step 3 | trust device cisco-phone
Example:
Device(config-if)# trust device cisco-phone
|
Configures the
interface to trust incoming traffic packets for the Cisco IP phone.
|
Step 4 | switchport voice vlan
{vlan-id |
dot1p |
none |
untagged}
Example:
Device(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 5 | end
Example:
Device(config-if)# end
|
Returns to
privileged EXEC mode.
|
Step 6 | Use one of the
following:
- show interfaces
interface-id
switchport
- show running-config
interface
interface-id
Example:
Device# show interfaces gigabitethernet1/0/1 switchport
or
Device# show running-config interface gigabitethernet1/0/1
|
Verifies your
voice VLAN entries or your QoS and voice VLAN entries.
|
Step 7 | copy
running-config startup-config
Example:
Device# copy running-config startup-config
|
(Optional) Saves
your entries in the configuration file.
|
Configuring the Priority of Incoming Data Frames
(CLI)
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:
Procedure | Command or Action | Purpose |
---|
Step 1 |
enable
Example:
Device> enable
|
Enables privileged EXEC mode.
|
Step 2 | configure
terminal
Example:
Device# configure terminal
|
Enters the global
configuration mode.
|
Step 3 | interface
interface-id
Example:
Device(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:
Device(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:
Device(config-if)# end
|
Returns to
privileged EXEC mode.
|
Step 6 | show
interfaces
interface-id
switchport
Example:
Device# show interfaces gigabitethernet1/0/1 switchport
|
Verifies your
entries.
|
Step 7 | copy
running-config startup-config
Example:
Device# 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.
Where to Go Next
After configuring voice VLANs, you can configure the following:
VLANs
-
VLAN groups
VLAN Trunking
VTP
Private VLANs
Additional
References
Related
Documents
Related
Topic
|
Document
Title
|
For
complete syntax and usage information for the commands used in this chapter.
|
VLAN Command Reference
(Catalyst 3850 Switches)
Layer 2/3 Command Reference
(Catalyst 3850 Switches)
Command Reference (Catalyst 9500 Series Switches)
Command Reference (Catalyst 9300 Series Switches)
|
Standards and
RFCs
Standard/RFC
|
Title
|
RFC
1573
|
Evolution
of the Interfaces Group of MIB-II
|
RFC 1757
|
Remote
Network Monitoring Management
|
RFC 2021
|
SNMPv2
Management Information Base for the Transmission Control Protocol using SMIv2
|
MIBs
MIB
|
MIBs
Link
|
All the 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
|
Technical
Assistance
Description
|
Link
|
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Support website provides extensive online resources, including documentation
and tools for troubleshooting and resolving technical issues with Cisco
products and technologies.
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Feeds.
Access to
most tools on the Cisco Support website requires a Cisco.com user ID and
password.
|
http://www.cisco.com/support
|
Feature History and Information for Voice VLAN
Release
|
Modification
|
Cisco IOS XE 3.2SE
|
This feature was introduced.
|