Content

| 7.6 |  | Network Design Issues for Voice |
| 7.6.8 |  | Voice VLAN configuration |

The voice VLAN is disabled and the CoS value is not trusted by default on Catalyst IOS switches such as the 2950 and 3550.

Before enabling the voice VLAN QoS should be enabled 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 interface configuration command.

> Switch(config)#mls qos
> Switch(config-if)#mls qos trust

The syntax to configure the voice VLAN is:

> Switch(config-if)#switchport voice vlan {vlan-id | dot1p | none | untagged}

To instruct the Cisco IP phone to forward all voice traffic through a specified VLAN use the following command:

> Switch(config-if)#switchport voice vlan vlan-id

By default, the Cisco IP phone forwards the voice traffic with an 802.1Q priority of 5. Valid VLAN IDs are from 1 to 4094.

A alternative to specifying a particular voice VLAN on the switch is to instruct the switch port to use 802.1P priority tagging for voice traffic and to use the default native VLAN (VLAN 0) to carry all traffic. By default, if enabled the Cisco IP phone forwards the voice traffic with an 802.1P priority of 5.

> Switch(config-if)#switchport voice vlan dot1p

To display the voice VLAN for an interface, use the show interfaces interface-id switchport privileged EXEC command.

> Switch#show interfaces interface-id switchport

Use the no form of this command to return to the default setting.

> no switchport voice vlan