Software Configuration Guide, Cisco IOS Release 15.2(2)E (Catalyst 2960, 2960-S, 2960-SF and 2960-Plus Switches)
Configuring Voice VLANs
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Configuring Voice VLANs

Configuring Voice VLANs

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table at the end of this module.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to http:/​/​www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

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.
  • 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.

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).


Related References

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.


Related References

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.
  • 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.).
  • 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:
    • Dynamic access port.
    • IEEE 802.1x authenticated port.

      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.


    • Protected port.
    • A source or destination port for a SPAN or RSPAN session.
    • Secure port.

      Note


      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.


How to Configure Voice VLAN

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.

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 STEPS

    1.    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 ActionPurpose
    Step 1 enable


    Example:
    Switch> enable
    
    
     

    Enables privileged EXEC mode. Enter your password if prompted.

     

    Step 2configure terminal


    Example:
    
    Switch# configure terminal
    
    
     

    Enters the global configuration mode.

     
    Step 3interface interface-id


    Example:
    
    Switch(config)# interface gigabitethernet1/0/1
    
    
     

    Specifies the interface connected to the phone, and enters interface configuration mode.

     
    Step 4mls 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 5switchport 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 6end


    Example:
    Switch(config-if)# end
    
    
     

    Returns to privileged EXEC mode.

     
    Step 7Use 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 8copy 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 STEPS

      1.    configure terminal

      2.    interface interface-id

      3.    switchport priority extend {cos value | trust}

      4.    end

      5.    show interfaces interface-id switchport

      6.    copy running-config startup-config


    DETAILED STEPS
       Command or ActionPurpose
      Step 1configure terminal


      Example:
      
      Switch# configure terminal
      
      
       

      Enters the global configuration mode.

       
      Step 2interface interface-id


      Example:
      
      Switch(config)# interface gigabitethernet1/0/1
      
      
       

      Specifies the interface connected to the Cisco IP Phone, and enters interface configuration mode.

       
      Step 3switchport 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 4end


      Example:
      
      Switch(config-if)# end
      
      
       

      Returns to privileged EXEC mode.

       
      Step 5show interfaces interface-id switchport


      Example:
      
      Switch# show interfaces gigabitethernet1/0/1 switchport
      
      
       

      Verifies your entries.

       
      Step 6copy running-config startup-config


      Example:
      
      Switch# copy running-config startup-config
      
      
       

      (Optional) Saves your entries in the configuration file.

       
      Related Concepts
      Related References

      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 Trunking
      • VTP