Contents

IPv6 Generic Prefix

The IPv6 generic prefix feature simplifies network renumbering and allows for automated prefix definition. An IPv6 generic (or general) prefix (for example, /48) holds a short prefix, based on which a number of longer, more-specific prefixes (for example, /64) can be defined. When the general prefix is changed, all of the more-specific prefixes based on it will change, too.

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

Information About IPv6 Generic Prefix

IPv6 General Prefixes

The upper 64 bits of an IPv6 address are composed from a global routing prefix plus a subnet ID, as defined in RFC 3513. A general prefix (for example, /48) holds a short prefix, based on which a number of longer, more-specific prefixes (for example, /64) can be defined. When the general prefix is changed, all of the more-specific prefixes based on it will change, too. This function greatly simplifies network renumbering and allows for automated prefix definition.

For example, a general prefix might be 48 bits long (“/48”) and the more specific prefixes generated from it might be 64 bits long (“/64”). In the following example, the leftmost 48 bits of all the specific prefixes will be the same, and they are the same as the general prefix itself. The next 16 bits are all different. 

 General prefix: 2001:DB8:2222::/48
Specific prefix: 2001:DB8:2222:0000::/64
Specific prefix: 2001:DB8:2222:0001::/64
Specific prefix: 2001:DB8:2222:4321::/64
Specific prefix: 2001:DB8:2222:7744::/64

General prefixes can be defined in several ways:

  • Manually
  • Based on a 6to4 interface
  • Dynamically, from a prefix received by a Dynamic Host Configuration Protocol (DHCP) for IPv6 prefix delegation client

More specific prefixes, based on a general prefix, can be used when configuring IPv6 on an interface.

How to Configure IPv6 Generic Prefix

Defining a General Prefix Manually

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    ipv6 general-prefix prefix-name {ipv6-prefix/prefix-length | 6to4 interface-type interface-number}


DETAILED STEPS
     Command or ActionPurpose
    Step 1 enable


    Example:
    Device> enable
     

    Enables privileged EXEC mode.

    • Enter your password if prompted.
     
    Step 2 configure terminal


    Example:
    Device# configure terminal
     

    Enters global configuration mode.

     
    Step 3 ipv6 general-prefix prefix-name {ipv6-prefix/prefix-length | 6to4 interface-type interface-number}


    Example:
    Device(config)# ipv6 general-prefix my-prefix 2001:DB8:2222::/48
     

    Defines a general prefix for an IPv6 address.

     

    Defining a General Prefix Based on a 6to4 Interface

    SUMMARY STEPS

      1.    enable

      2.    configure terminal

      3.    ipv6 general-prefix prefix-name {ipv6-prefix / prefix-length | 6to4 interface-type interface-number


    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 ipv6 general-prefix prefix-name {ipv6-prefix / prefix-length | 6to4 interface-type interface-number


      Example:
      Router(config)# ipv6 general-prefix my-prefix 6to4 gigabitethernet 0/0/0
       

      Defines a general prefix for an IPv6 address.

      When defining a general prefix based on a 6to4 interface, specify the 6to4 keyword and the interface-type interface-numberarguments.

      When defining a general prefix based on an interface used for 6to4 tunneling, the general prefix will be of the form 2001:a.b.c.d::/48, where "a.b.c.d" is the IPv4 address of the interface referenced.

       

      Using a General Prefix in IPv6

      SUMMARY STEPS

        1.    enable

        2.    configure terminal

        3.    interface type number

        4.    ipv6 address {ipv6-address / prefix-length | prefix-name sub-bits/prefix-length


      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 type number


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

        Specifies an interface type and number, and places the router in interface configuration mode.

         
        Step 4 ipv6 address {ipv6-address / prefix-length | prefix-name sub-bits/prefix-length


        Example:
        Router(config-if) ipv6 address my-prefix 2001:DB8:0:7272::/64
         

        Configures an IPv6 prefix name for an IPv6 address and enables IPv6 processing on the interface.

         

        Additional References

        Related Documents

        Related Topic

        Document Title

        IPv6 addressing and connectivity

        IPv6 Configuration Guide

        Cisco IOS commands

        Cisco IOS Master Commands List, All Releases

        IPv6 commands

        Cisco IOS IPv6 Command Reference

        Cisco IOS IPv6 features

        Cisco IOS IPv6 Feature Mapping

        Standards and RFCs

        Standard/RFC

        Title

        RFCs for IPv6

        IPv6 RFCs

        MIBs

        MIB

        MIBs Link

        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

        Technical Assistance

        Description

        Link

        The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

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

        Feature Information for IPv6 Generic Prefix

        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

        Feature Name

        Releases

        Feature Information

        IPv6 Generic Prefix

        12.3(4)T

        The upper 64 bits of an IPv6 address are composed from a global routing prefix plus a subnet ID. A general prefix (for example, /48) holds a short prefix, based on which a number of longer, more-specific, prefixes (for example, /64) can be defined.

        The following commands were introduced or modified: ipv6 address, ipv6 general-prefix.

        IPv6 Generic Prefix

        IPv6 Generic Prefix

        The IPv6 generic prefix feature simplifies network renumbering and allows for automated prefix definition. An IPv6 generic (or general) prefix (for example, /48) holds a short prefix, based on which a number of longer, more-specific prefixes (for example, /64) can be defined. When the general prefix is changed, all of the more-specific prefixes based on it will change, too.

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

        Information About IPv6 Generic Prefix

        IPv6 General Prefixes

        The upper 64 bits of an IPv6 address are composed from a global routing prefix plus a subnet ID, as defined in RFC 3513. A general prefix (for example, /48) holds a short prefix, based on which a number of longer, more-specific prefixes (for example, /64) can be defined. When the general prefix is changed, all of the more-specific prefixes based on it will change, too. This function greatly simplifies network renumbering and allows for automated prefix definition.

        For example, a general prefix might be 48 bits long (“/48”) and the more specific prefixes generated from it might be 64 bits long (“/64”). In the following example, the leftmost 48 bits of all the specific prefixes will be the same, and they are the same as the general prefix itself. The next 16 bits are all different. 

         General prefix: 2001:DB8:2222::/48
Specific prefix: 2001:DB8:2222:0000::/64
Specific prefix: 2001:DB8:2222:0001::/64
Specific prefix: 2001:DB8:2222:4321::/64
Specific prefix: 2001:DB8:2222:7744::/64

        General prefixes can be defined in several ways:

        • Manually
        • Based on a 6to4 interface
        • Dynamically, from a prefix received by a Dynamic Host Configuration Protocol (DHCP) for IPv6 prefix delegation client

        More specific prefixes, based on a general prefix, can be used when configuring IPv6 on an interface.

        How to Configure IPv6 Generic Prefix

        Defining a General Prefix Manually

        SUMMARY STEPS

          1.    enable

          2.    configure terminal

          3.    ipv6 general-prefix prefix-name {ipv6-prefix/prefix-length | 6to4 interface-type interface-number}


        DETAILED STEPS
           Command or ActionPurpose
          Step 1 enable


          Example:
          Device> enable
           

          Enables privileged EXEC mode.

          • Enter your password if prompted.
           
          Step 2 configure terminal


          Example:
          Device# configure terminal
           

          Enters global configuration mode.

           
          Step 3 ipv6 general-prefix prefix-name {ipv6-prefix/prefix-length | 6to4 interface-type interface-number}


          Example:
          Device(config)# ipv6 general-prefix my-prefix 2001:DB8:2222::/48
           

          Defines a general prefix for an IPv6 address.

           

          Defining a General Prefix Based on a 6to4 Interface

          SUMMARY STEPS

            1.    enable

            2.    configure terminal

            3.    ipv6 general-prefix prefix-name {ipv6-prefix / prefix-length | 6to4 interface-type interface-number


          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 ipv6 general-prefix prefix-name {ipv6-prefix / prefix-length | 6to4 interface-type interface-number


            Example:
            Router(config)# ipv6 general-prefix my-prefix 6to4 gigabitethernet 0/0/0
             

            Defines a general prefix for an IPv6 address.

            When defining a general prefix based on a 6to4 interface, specify the 6to4 keyword and the interface-type interface-numberarguments.

            When defining a general prefix based on an interface used for 6to4 tunneling, the general prefix will be of the form 2001:a.b.c.d::/48, where "a.b.c.d" is the IPv4 address of the interface referenced.

             

            Using a General Prefix in IPv6

            SUMMARY STEPS

              1.    enable

              2.    configure terminal

              3.    interface type number

              4.    ipv6 address {ipv6-address / prefix-length | prefix-name sub-bits/prefix-length


            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 type number


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

              Specifies an interface type and number, and places the router in interface configuration mode.

               
              Step 4 ipv6 address {ipv6-address / prefix-length | prefix-name sub-bits/prefix-length


              Example:
              Router(config-if) ipv6 address my-prefix 2001:DB8:0:7272::/64
               

              Configures an IPv6 prefix name for an IPv6 address and enables IPv6 processing on the interface.

               

              Additional References

              Related Documents

              Related Topic

              Document Title

              IPv6 addressing and connectivity

              IPv6 Configuration Guide

              Cisco IOS commands

              Cisco IOS Master Commands List, All Releases

              IPv6 commands

              Cisco IOS IPv6 Command Reference

              Cisco IOS IPv6 features

              Cisco IOS IPv6 Feature Mapping

              Standards and RFCs

              Standard/RFC

              Title

              RFCs for IPv6

              IPv6 RFCs

              MIBs

              MIB

              MIBs Link

              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

              Technical Assistance

              Description

              Link

              The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

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

              Feature Information for IPv6 Generic Prefix

              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

              Feature Name

              Releases

              Feature Information

              IPv6 Generic Prefix

              12.3(4)T

              The upper 64 bits of an IPv6 address are composed from a global routing prefix plus a subnet ID. A general prefix (for example, /48) holds a short prefix, based on which a number of longer, more-specific, prefixes (for example, /64) can be defined.

              The following commands were introduced or modified: ipv6 address, ipv6 general-prefix.