LAN Switching Configuration Guide, Cisco IOS XE Release 3S
Configuring Routing Between VLANs with IEEE 802.1Q Encapsulation
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Contents

Configuring Routing Between VLANs with IEEE 802.1Q Encapsulation

This chapter describes the required and optional tasks for configuring routing between VLANs with IEEE 802.1Q encapsulation.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest feature information and caveats, see 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 document.

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

Restrictions for Configuring Routing Between VLANs with IEEE 802.1Q Encapsulation

Shared port adapters (SPAs) on Cisco ASR 1000 Series Aggregation Services Router have a limit of 8,000 TCAM entries, which limits the number of VLANs you can create on a single SPA.

Information About Configuring Routing Between VLANs with IEEE 802.1Q Encapsulation

Configuring Routing Between VLANs with IEEE 802.1Q Encapsulation

The IEEE 802.1Q protocol is used to interconnect multiple switches and routers, and for defining VLAN topologies. The IEEE 802.1Q standard is extremely restrictive to untagged frames. The standard provides only a per-port VLANs solution for untagged frames. For example, assigning untagged frames to VLANs takes into consideration only the port from which they have been received. Each port has a parameter called a permanent virtual identification (Native VLAN) that specifies the VLAN assigned to receive untagged frames.

The main characteristics of IEEE 802.1Q are as follows:

  • Assigns frames to VLANs by filtering.
  • The standard assumes the presence of a single spanning tree and of an explicit tagging scheme with one-level tagging.

How to Configure Routing Between VLANs with IEEE 802.1Q Encapsulation

Configuring IP Routing over IEEE 802.1Q

IP routing over IEEE 802.1Q extends IP routing capabilities to include support for routing IP frame types in VLAN configurations using the IEEE 802.1Q encapsulation.

To route IP over IEEE 802.1Q between VLANs, you need to customize the subinterface to create the environment in which it will be used. Perform the tasks described in the following sections in the order in which they appear:

Enabling IP Routing

IP routing is automatically enabled in the Cisco IOS XE software for routers. To reenable IP routing if it has been disabled, perform the following steps.

Once you have IP routing enabled on the router, you can customize the characteristics to suit your environment. If necessary, refer to the IP configuration chapters in the Cisco IOS XE IP Routing Protocols Configuration Guide , Release 2, for guidelines on configuring IP.

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    ip routing

    4.    end


DETAILED STEPS
     Command or ActionPurpose
    Step 1 enable


    Example:
    Router> enable
     

    Enables privileged EXEC mode.

    • Enter your password if prompted.
     
    Step 2 configure terminal


    Example:
    Router# configure terminal
     

    Enters global configuration mode.

     
    Step 3 ip routing


    Example:
    Router(config)# ip routing
     

    Enables IP routing on the router.

     
    Step 4 end


    Example:
    Router(config)# exit
     

    Exits privileged EXEC mode.

     

    Defining the VLAN Encapsulation Format

    To define the encapsulation format as IEEE 802.1Q, perform the following steps.

    SUMMARY STEPS

      1.    enable

      2.    configure terminal

      3.    interface gigabitethernet card / spaslot / port . subinterface-number

      4.    encapsulation dot1q vlanid

      5.    end


    DETAILED STEPS
       Command or ActionPurpose
      Step 1 enable


      Example:
      Router> enable
       

      Enables privileged EXEC mode.

      • Enter your password if prompted.
       
      Step 2 configure terminal


      Example:
      Router# configure terminal
       

      Enters global configuration mode.

       
      Step 3 interface gigabitethernet card / spaslot / port . subinterface-number


      Example:
      Router(config)# interface gigabitethernet 0/0/0.101
       

      Specifies the subinterface on which IEEE 802.1Q will be used, and enters interface configuration mode.

       
      Step 4 encapsulation dot1q vlanid


      Example:
      Router(config-subif)# encapsulation dot1q 101
       

      Defines the encapsulation format as IEEE 802.1Q (dot1q), and specifies the VLAN identifier

       
      Step 5 end


      Example:
      Router(config-subif)# end
       

      Exits subinterface configuration mode.

       

      Assigning an IP Address to Network Interface

      An interface can have one primary IP address. To assign a primary IP address and a network mask to a network interface, perform the following steps.

      SUMMARY STEPS

        1.    enable

        2.    configure terminal

        3.    interface gigabitethernet card / spaslot / port . subinterface-number

        4.    ip address ip-address mask

        5.    end


      DETAILED STEPS
         Command or ActionPurpose
        Step 1 enable


        Example:
        Router> enable
         

        Enables privileged EXEC mode.

        • Enter your password if prompted.
         
        Step 2 configure terminal


        Example:
        Router# configure terminal
         

        Enters global configuration mode.

         
        Step 3 interface gigabitethernet card / spaslot / port . subinterface-number


        Example:
        Router(config)# interface gigabitethernet 0/0/0.101
         

        Specifies the subinterface on which IEEE 802.1Q will be used, and enters interface configuration mode.

         
        Step 4 ip address ip-address mask


        Example:
        Router(config-subif)# ip address 10.0.0.0 255.0.0.0
         

        Sets a primary IP address for an interface.

        • Enter the primary IP address for an interface.
        Note   

        A mask identifies the bits that denote the network number in an IP address. When you use the mask to subnet a network, the mask is then referred to as a subnet mask.

         
        Step 5 end


        Example:
        Router(config-subif)# end
         

        Exits subinterface configuration mode.

         

        Monitoring and Maintaining VLAN Subinterfaces

        To indicate whether a VLAN is a native VLAN, perform the following steps.

        SUMMARY STEPS

          1.    enable

          2.    show vlans

          3.    end


        DETAILED STEPS
           Command or ActionPurpose
          Step 1 enable


          Example:
          Router> enable
           

          Enables privileged EXEC mode.

          • Enter your password if prompted.
           
          Step 2 show vlans


          Example:
          Router# show vlans
           

          Displays VLAN information.

           
          Step 3 end


          Example:
          Router# end
           

          Exits privileged EXEC mode.

           

          Configuration Examples for Configuring Routing Between VLANs with IEEE 802.1Q Encapsulation

          Configuring IP Routing over IEEE 802.1Q Example

          This configuration example shows IP being routed on VLAN 101:

          !
ip routing
!
interface gigabitethernet 4/1/1.101
  encapsulation dot1q 101
  ip addr 10.0.0.0 255.0.0.0
!

          Additional References

          Related Documents

          Related Topic

          Document Title

          IP LAN switching commands: complete command syntax, command mode, defaults, usage guidelines, and examples

          Cisco IOS LAN Switching Services Command Reference

          Standards

          Standard

          Title

          No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.

          --

          MIBs

          MIB

          MIBs Link

          No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature.

          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

          RFCs

          RFC

          Title

          No new or modified RFCs are supported by this feature, and support for existing standards has not been modified by this feature.

          --

          Technical Assistance

          Description

          Link

          The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies.

          To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds.

          Access to most tools on the Cisco Support website requires a Cisco.com user ID and password.

          http:/​/​www.cisco.com/​cisco/​web/​support/​index.html

          Feature Information for Configuring Routing Between VLANs with IEEE 802.1Q Encapsulation

          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 www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

          Table 1 Feature Information for Configuring Routing Between VLANs with IEEE 802.1Q Encapsulation

          Feature Name

          Releases

          Feature Information

          Configuring Routing Between VLANs with IEEE 802.1Q Encapsulation

          Cisco IOS XE Release 2.1

          This feature was introduced on the Cisco ASR 1000 Series Aggregation Services Routers.