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rfc:rfc6355

Internet Engineering Task Force (IETF) T. Narten Request for Comments: 6355 J. Johnson Category: Standards Track IBM ISSN: 2070-1721 August 2011

 Definition 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 in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://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 to BCP 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 2011

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
 2.  Background  . . . . . . . . . . . . . . . . . . . . . . . . . . 2
 3.  UUID Considerations . . . . . . . . . . . . . . . . . . . . . . 3
 4.  DUID-UUID Format  . . . . . . . . . . . . . . . . . . . . . . . 4
 5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 4
 6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
 7.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
 8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
   8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 5
   8.2.  Informative Reference . . . . . . . . . . . . . . . . . . . 5

1. 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
             interfaces

Narten & 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 (see Section 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 2011

6. 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. References

8.1. 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.com

Narten & Johnson Standards Track [Page 5]

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