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Internet Engineering Task Force (IETF)                         T. NartenRequest for Comments: 6355                                    J. JohnsonCategory: Standards Track                                            IBMISSN: 2070-1721                                              August 2011Definition of the UUID-Based DHCPv6 Unique Identifier (DUID-UUID)Abstract   This document defines a new DHCPv6 Unique Identifier (DUID) type   called DUID-UUID.  DUID-UUIDs are derived from the already-   standardized Universally Unique IDentifier (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.Status of This Memo   This is an Internet Standards Track document.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   Internet Standards is available inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6355.Copyright Notice   Copyright (c) 2011 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Narten & Johnson             Standards Track                    [Page 1]

RFC 6355                        DUID-UUID                    August 2011Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .22.  Background  . . . . . . . . . . . . . . . . . . . . . . . . . .23.  UUID Considerations . . . . . . . . . . . . . . . . . . . . . .34.  DUID-UUID Format  . . . . . . . . . . . . . . . . . . . . . . .45.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . .46.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . .57.  Security Considerations . . . . . . . . . . . . . . . . . . . .58.  References  . . . . . . . . . . . . . . . . . . . . . . . . . .58.1.  Normative References  . . . . . . . . . . . . . . . . . . .58.2.  Informative Reference . . . . . . . . . . . . . . . . . . .51.  Introduction   DHCP Unique Identifiers (DUIDs) are used in DHCPv6 to identify   clients and servers.  This document defines a new DHCP Unique   Identifier (DUID) type that embeds a Universally Unique IDentifier   (UUID) [RFC4122].  UUIDs are already in widespread use and serve as   an existing identifier that could be leveraged by DHCPv6.  For   example, x86-based systems ship with an embedded UUID in firmware   that is readily available to the software running on the device.   Although DUIDs are new to DHCPv6, identifying clients in DHCP via a   UUID is not.  DHCPv4 [RFC2132] defines a Client Machine Identifier   Option (option 97) that embeds a UUID (aka a Globally Unique   Identifier (GUID)) [RFC4578].  This document extends that capability   to DHCPv6.   Terminology specific to IPv6 and DHCPv6 is used as defined in the   "Terminology" sections of [RFC3315].2.  Background   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 previously:   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               interfacesNarten & Johnson             Standards Track                    [Page 2]

RFC 6355                        DUID-UUID                    August 2011   DUIDs are intended to 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, stored in stable   storage, and reused from that point forward.   One issue that has arisen concerns devices that employ multi-step   network boot loading.  An initial step (typically run out of   firmware) loads a small image that, in turn, loads a second image and   so forth until the actual target system is loaded.  Each step in the   booting process may invoke DHCP.  In some operational environments,   it is important that each step in the sequence use the same DUID, so   that the server knows it is getting requests from the same device and   can return the proper configuration information (including the   pointer to the correct image to load).   Unfortunately, none of the previously defined DUIDs are ideal for   multi-step network booting.  The DUID-LLT and DUID-LL identifiers   that a given device may use are not guaranteed to remain constant   across each booting step.  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 is   chosen, it can be difficult to ensure that each stage uses the same   timestamp value.  While a DUID-EN could be defined and used, such   usage is proprietary by definition.   This document defines a new DUID type, based on the Universally   Unique IDentifier (UUID) [RFC4122].  UUIDs are already used in   practice and serve as an existing identifier that could be leveraged   by DHCP.  In some environments, a UUID-based DUID is preferable to   the other existing DUID types.   It should be noted that use of a DUID-UUID will not, by itself, solve   all the network boot problems described in this document.  Given the   availability 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 defining a new DUID type does not, by itself, help.  It   is believed, however, that network boot services can be configured to   use a DUID-UUID and that other software can do so as well.  Ensuring   this happens in general is beyond the scope of this document.3.  UUID Considerations   Although many UUIDs are in use today, not all UUIDs meet DHCP's   requirements (seeSection 9 of [RFC3315]).  DHCP UUIDs should be   persistent across system restarts, system reconfiguration events,Narten & Johnson             Standards Track                    [Page 3]

RFC 6355                        DUID-UUID                    August 2011   system software and operating system upgrades or reinstallation as   well as 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 using DUID-UUID must select a   UUID 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 UUID that is part of   the system firmware, or managed by the system firmware, satisfies   this requirement.4.  DUID-UUID Format   The DUID-UUID is carried within Client Identifier or Server   Identifier options.  It has the following format:    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 (4)        |    UUID (128 bits)            |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |   |                                                               |   |                                                               |   |                                -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                                |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-                        Figure 1: DUID-UUID Format   DUID-Type -  DUID-UUID (4) - (16 bits)   UUID -  An [RFC4122] UUID (128 bits)5.  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.   We would like to thank the following individuals in particular for   their specific comments and suggestions on this document: Thomas   Huth, Andre Kostur, Stephen Jacob, Suresh Krishnan, Ted Lemon, Bernie   Volz, and Vincent Zimmer.Narten & Johnson             Standards Track                    [Page 4]

RFC 6355                        DUID-UUID                    August 20116.  IANA Considerations   IANA has assigned the value 4 for use by the DHCPv6 DUID-UUID type.7.  Security Considerations   DHCP traffic between a client and server is sent in the clear.  An   eavesdropper residing on the path between the client and server could   see DHCP traffic and obtain the UUID for a particular machine.  This   may raise some privacy issues but is not a new issue brought on by   the use of the DUID type defined in this document.8.  References8.1.  Normative References   [RFC2132]  Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor              Extensions",RFC 2132, March 1997.   [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 2005.8.2.  Informative Reference   [RFC4578]  Johnston, M. and S. Venaas, "Dynamic Host Configuration              Protocol (DHCP) Options for the Intel Preboot eXecution              Environment (PXE)",RFC 4578, November 2006.Authors' Addresses   Thomas Narten   IBM   EMail: narten@us.ibm.com   Jarrod B. Johnson   IBM   EMail: jarrod.b.johnson@gmail.comNarten & Johnson             Standards Track                    [Page 5]