Internet Engineering Task Force (IETF) T. Narten

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.

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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

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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,

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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.

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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: [email protected]

Jarrod B. Johnson
IBM

EMail: [email protected]

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