Internet Engineering Task Force                                T. Narten
Internet-Draft                                                J. Johnson
Intended status: Standards Track                                     IBM
Expires: January 9, 2011                                    July 8, 2010

   Definition of the UUID-based DHCPv6 Unique Identifier (DUID-UUID)


   This document defines a new DHCPv6 Unique Identifier (DUID) type,
   called DUID-UUID.  DUID-UUIDs are derived from the already
   standardized UUID format.  DUID-UUID makes it possible for devices to
   use UUIDs to identify themselves to DHC servers and vice versa.
   UUIDs are globally unique and readily available on many systems,
   making them convenient identifiers to leverage within DHCP.

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   This Internet-Draft will expire on January 9, 2011.

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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  DUID-UUID Format  . . . . . . . . . . . . . . . . . . . . . . . 4
   3.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 5
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   6.  Normative References  . . . . . . . . . . . . . . . . . . . . . 5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 6

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1.  Introduction

   In DHCPv6, clients identify themselves to servers via DHCP Unique
   Identifiers (DUIDs) [RFC3315].  DUIDs are identifiers that DHCP
   servers treat as opaque objects with no internal structure.  DUIDs
   are intended to be globally unique, with no two devices using the
   same DUID.  Three DUIDs types have been defined so far:

   DUID-LLT -  the Link-Layer address of one of the device's network
           interfaces, concatenated with a timestamp

   DUID-EN -  an Enterprise Number plus additional information specific
           to the enterprise

   DUID-LL -  the Link-Layer address of one of the device's network

   The intention of DUIDs is that they remain constant over time, so
   that they can be used as permanent identifiers for a device.  In the
   case of DUID-LLTs, they are intended to be generated once, and then
   stored in stable storage and reused from that point forward.

   In DHCPv4, all clients identify themselves to servers via the MAC
   address of the interface on which the DHCP packet is sent.  The MAC
   address identifier generally remains constant across machine
   restarts, installation of new operating system releases, changes in
   hardware configuration such as addition or removal of storage
   devices, etc.  While the MAC address will change if the network
   interface is replaced, this is a relatively uncommon event.

   In contrast, the DUID-LLT and DUID-LL identifiers that a given device
   may use are less likely to remain constant on some types of devices
   and deployments.  Specifically, when a machine goes through a multi-
   step boot process, it may first load a simple boot loader, followed
   by a one or more secondary loaders before the eventual actual target
   system is loaded.  In IPv4, all steps of a multi-step boot processes
   that invoke DHCP are guaranteed to use the same MAC identifier during
   each stage.  In contrast, with DHCPv6, it is more difficult to ensure
   or arrange that each boot stage uses the same identifier.  First,
   there are multiple DUID types, and different systems might choose to
   use different formats.  Second, even if the different stages used
   DUID-LL or DUID-LLT, on devices with multiple interfaces, there is no
   way to guarantee that the same interface (and hence DUID) will be
   selected.  Finally, in the case of DUID-LLT, even if the same
   interface were chosen, there is no guarantee that each stage would
   use the same timestamp value.  While a DUID-EN could be defined and
   used, such usage would be proprietary by definition.

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   This document defines a new DUID type, based on the Universally
   Unique IDentifier (UUID) [RFC4122].  UUIDs are already use in
   practice and serve as an existing identifier that could be leveraged
   by DHCP.  For example, x86 based systems ship with an embedded UUID
   in firmware that could be accessed for this purpose.

   Although many UUIDs are in use today, not all UUIDs meet the
   requirements of the DHCP protocol (see Section 9 of [RFC3315]).  DHCP
   UUIDs should be persistant across system restarts, across system
   reconfiguration events, system software and operating system upgrades
   or reinstallation, and be easily available to any part of the boot
   process that requires access to the DHCP UUID.  For example, UUIDs
   used in Microsoft's Component Object Module (COM), and for labeling
   partitions in filesystems, are likely not appropriate as they may not
   be accessible to firmware boot loaders, and can change over time.

   Implementations of this specification must use a DUID that is
   persistent across system restart and reconfiguration events, and that
   is available to all DHCP protocol agents that may need to identify
   themselves.  For instance, a DUID that is part of the system
   firmware, or managed by the system firmware, would satisfy this

   It should be noted that use of a DUID-UUID will not by itself solve
   all the problems motivating this document.  Given the availablility
   of a suitable DUID-UUID, implementations will still need to take
   steps to ensure that all boot stages use the same DUID-UUID as
   appropriate.  Given that DHCP has already defined multiple DUID
   types, the question of which of several DUIDs to select from already
   exists and is not a new problem.

2.  DUID-UUID Format

   The DUID-UUID is carried within Client Identifier or Server
   Identifier options.  It has the following format:

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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |          DUID-Type (TBD)      |    UUID (128 bits)            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
   |                                                               |
   |                                                               |
   |                                -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                |

                            DUID-UUID format. .

                                 Figure 1

   DUID-Type -  TBD (16 bits)

   UUID -  An RFC4122 UUID (128 bits)

3.  Acknowledgements

   This document was inspired by a discussion on the DHC mailing list in
   November, 2009 on the topic of netboot for IPv6.  Specifically, some
   scenarios were described where it was difficult to do something in
   DHCPv6 that had worked well in DHCPv4.

4.  IANA Considerations

   IANA has assigned the value TBD for use by DHCPv6 DUID-UUID type
   described in this document.

5.  Security Considerations

   This document does not create any new security considerations.

6.  Normative References

   [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
              and M. Carney, "Dynamic Host Configuration Protocol for
              IPv6 (DHCPv6)", RFC 3315, July 2003.

   [RFC4122]  Leach, P., Mealling, M., and R. Salz, "A Universally
              Unique IDentifier (UUID) URN Namespace", RFC 4122,
              July 2005.

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Authors' Addresses

   Thomas Narten


   Jarrod B. Johnson


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