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The following are the prerequisites for voice VLANs:
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. |
The following are the restrictions for voice VLANs:
Information About Voice VLAN
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.
This network configuration is one way to connect a Cisco 7960 IP Phone.
The Cisco IP Phone contains an integrated three-port 10/100 switch. The ports provide dedicated connections to these devices:
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:
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). |
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:
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. |
Note |
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. |
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
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).
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:
Command or Action | Purpose | |||
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Step 1 |
configure terminal Example: Switch# configure terminal |
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Step 2 |
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 3 |
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:
|
||
Step 4 |
end Example: Switch(config-if)# end |
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Step 5 |
show interfaces
interface-id
switchport Example: Switch# show interfaces gigabitethernet1/0/1 switchport |
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Step 6 |
copy running-config startup-config Example: Switch# copy running-config startup-config |
To display voice VLAN configuration for an interface, use the show interfaces interface-id switchport privileged EXEC command.
Configuration Examples for Voice VLANs
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.
This example shows how to enable switch port voice detect on a Cisco IP Phone:
Switch# configure terminal Enter configuration commands, one per line. End with CNTL/Z. Switch(config)# interface gigabitethernet 1/0/1 Switch(config-if)# switchport voice? detect detection enhancement keyword vlan VLAN for voice traffic Switch(config-if)# switchport voice detect? cisco-phone Cisco IP Phone Switch(config-if)# switchport voice detect cisco-phone? full-duplex Cisco IP Phone Switch(config-if)# switchport voice detect cisco-phone full-duplex full-duplex full duplex keyword Switch(config-if)# end
This example shows how to disable switchport voice detect on a Cisco IP Phone:
Switch# configure terminal Enter configuration commands, one per line. End with CNTL/Z. Switch(config)# interface gigabitethernet 1/0/1 Switch(config-if)# no switchport voice detect cisco-phone Switch(config-if)# no switchport voice detect cisco-phone full-duplex
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
After configuring voice VLANs, you can configure the following:
Related Topic | Document Title |
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For complete syntax and usage information for the commands used in this chapter. |
Standard/RFC | Title |
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MIB | MIBs Link |
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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: |
Description | Link |
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Release | Modification |
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Cisco IOS 15.0(2)EX1 |
This feature was introduced. |