VLAN 0 Priority Tagging Support

The VLAN 0 Priority Tagging Support feature enables 802.1Q Ethernet frames to be transmitted with the VLAN ID tag set to zero. These frames are called priority tagged frames. Setting the VLAN ID tag to zero allows the VLAN ID tag to be ignored and the Ethernet frame to be processed according to the priority configured in the 802.1P bits of the 802.1Q Ethernet frame header.

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Restrictions for VLAN 0 Priority Tagging Support

  • QinQ is not supported with this feature.

Information About VLAN 0 Priority Tagging Support

802.1Q Tagging

The 802.1Q standard defines a system of VLAN tagging for Ethernet frames and also contains a provision for a quality of service (QoS) prioritization scheme known as 802.1P, which indicates the priority level of the frame. The 802.1Q standard adds this information to the Ethernet header, as shown in the figure below. The priority level values range from zero (best effort) to seven (highest). These values can be used to prioritize different classes of traffic such as voice and video. The VLAN ID tag specifies the VLAN to which the frame belongs. The priority bits define the priority with which the frames are processed.

Figure 1. 802.1Q Ethernet Frame

Native VLANs

When a particular VLAN ID is assigned as a native VLAN, frames that are sent from that native VLAN subinterface are not tagged. Similarly, any untagged frames received on that subinterface are associated with the native VLAN. A native VLAN sends only untagged frames, but can receive both tagged and untagged frames.

VLAN 0 Priority Tagging Overview

The VLAN 0 Priority Tagging feature is installed on the customer premises equipment (CPE). In the illustration below, the 802.1Q frames are sent in the upstream direction from the CPE to the internet service provider (ISP). The frames are transmitted with the 802.1Q VLAN tag set to zero and the 802.1P priority bits configured as per the priority with which the frames are to be processed. When these frames are received at the ISP end, the header is stripped off and the frame is processed as per the configuration of the 802.1P priority bits. If the VLAN ID has a nonzero value, the header is retained and the frame is transmitted to the specified VLAN subinterface. High priority frames are sent ahead of low priority frames, and this prioritization is weighted, that is, low priority traffic is not completely suppressed even if high priority traffic exceeds the line rate.

Figure 2. VLAN 0 Priority Tagging

The VLAN 0 Priority Tagging Support feature also allows VLAN 0 to be set as a native VLAN using the encapsulation priority-tagged native command. Setting the VLAN 0 subinterface as a native VLAN allows this subinterface to receive both tagged and untagged frames but transmit only untagged frames. The encapsulation priority-tagged native tx-tagged command configures the native VLAN with VLAN 0 to receive both tagged and untagged frames but to transmit only tagged frames.

How to Configure VLAN 0 Priority Tagging Support

Configuring VLAN 0 Priority Tagging

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    interface type number

    4.    encapsulation priority-tagged

    5.    end


DETAILED STEPS
     Command or ActionPurpose
    Step 1 enable


    Example:
    Device> enable
     
    Enters privileged EXEC mode.

    • Enter your password if prompted.

     
    Step 2configure terminal


    Example:
    Device# configure terminal
     

    Enters global configuration mode.

     
    Step 3interface type number


    Example:
    Device(config)# interface Ethernet 0/0.1
     

    Configures an interface and enters subinterface configuration mode.

     
    Step 4encapsulation priority-tagged


    Example:
    Device(config-subif)# encapsulation priority-tagged
     

    Sets the VLAN ID tag of the subinterface to zero.

     
    Step 5end


    Example:
    Device(config-subif)# end
     

    Exits subinterface configuration mode and returns to privileged EXEC mode.

     

    Configuring a VLAN 0 Subinterface as a Native VLAN

    SUMMARY STEPS

      1.    enable

      2.    configure terminal

      3.    interface type number

      4.    encapsulation priority-tagged

      5.    encapsulation priority-tagged native

      6.    end


    DETAILED STEPS
       Command or ActionPurpose
      Step 1 enable


      Example:
       Device> enable
       
      Enables privileged EXEC mode.

      • Enter your password if prompted.

       
      Step 2configure terminal


      Example:
      Device# configure terminal
       

      Enters global configuration mode.

       
      Step 3interface type number


      Example:
      Device(config)# interface Ethernet 0/0.1
       

      Configures an interface and enters subinterface configuration mode.

       
      Step 4encapsulation priority-tagged


      Example:
      Device(config-subif)# encapsulation priority-tagged
       

      Sets the VLAN ID tag of the subinterface to zero.

       
      Step 5encapsulation priority-tagged native


      Example:
      Device(config-subif)# encapsulation priority-tagged native
       

      Configures the priority-tagged subinterface as a native VLAN.

       
      Step 6end


      Example:
      Device(config-subif)# end
       

      Exits subinterface configuration mode and returns to privileged EXEC mode.

       

      Configuring Native VLAN to Transmit Tagged Frames

      SUMMARY STEPS

        1.    enable

        2.    configure terminal

        3.    interface type number

        4.    encapsulation priority-tagged

        5.    encapsulation priority-tagged native

        6.    encapsulation priority-tagged native tx-tagged

        7.    end


      DETAILED STEPS
         Command or ActionPurpose
        Step 1 enable


        Example:
        Device> enable
         
        Enters privileged EXEC mode.

        • Enter your password if prompted.

         
        Step 2configure terminal


        Example:
        Device# configure terminal
         

        Enters global configuration mode.

         
        Step 3interface type number


        Example:
        Device(config)# interface Ethernet 0/0.1
         

        Configures an interface and enters subinterface configuration mode.

         
        Step 4encapsulation priority-tagged


        Example:
        Device(config-subif)# encapsulation priority-tagged
         

        Sets the VLAN ID tag of the subinterface to zero.

         
        Step 5encapsulation priority-tagged native


        Example:
        Device(config-subif)# encapsulation priority-tagged native
         

        Configures the priority tagged subinterface as a native VLAN.

         
        Step 6encapsulation priority-tagged native tx-tagged


        Example:
        Device(config-subif)# encapsulation priority-tagged native tx-tagged
         

        Configures the priority tagged native VLAN interface to transmit tagged frames.

         
        Step 7end


        Example:
        Device(config-subif)# end
         

        Exits subinterface configuration mode and returns to privileged EXEC mode.

         

        Configuration Examples for VLAN 0 Priority Tagging Support

        Example: Configuring a Priority Tagged Native VLAN Interface to Transmit Tagged Frames

        Device> enable
Device# configure terminal
Device(config)# interface Ethernet 0/0.1
Device(config-subif)# encapsulation priority tagged
Device(config-subif)# encapsulation priority-tagged native 
Device(config-subif)# encapsulation priority-tagged native tx-tagged
Device(config-subif)# end

        Additional References

        Related Documents

        Related Topic

        Document Title

        Cisco IOS commands

        Cisco IOS Master Commands List, All Releases

        ATM commands

        Cisco IOS Asynchronous Transfer Mode Command Reference

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        Feature Information for VLAN 0 Priority Tagging Support

        The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

        Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to . An account on Cisco.com is not required.
        Table 1 Feature Information for VLAN 0 Priority Tagging Support

        Feature Name

        Releases

        Feature Information

        VLAN 0 Priority Tagging Support

        15.2(3)T

        The VLAN 0 Priority Tagging Support feature enables 802.1Q Ethernet frames to be transmitted with the VLAN ID tag set to zero.

        The following command was introduced or modifief: encapsulation priority-tagged.