Uniform Resource Names for Device Identifiers
RFC 9039

Document Type RFC - Proposed Standard (June 2021; No errata)
Authors Jari Arkko  , Cullen Jennings  , Zach Shelby 
Last updated 2021-06-30
Replaces draft-arkko-core-dev-urn
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Internet Engineering Task Force (IETF)                          J. Arkko
Request for Comments: 9039                                      Ericsson
Category: Standards Track                                    C. Jennings
ISSN: 2070-1721                                                    Cisco
                                                               Z. Shelby
                                                            Edge Impulse
                                                               June 2021

             Uniform Resource Names for Device Identifiers

Abstract

   This document describes a new Uniform Resource Name (URN) namespace
   for hardware device identifiers.  A general representation of device
   identity can be useful in many applications, such as in sensor data
   streams and storage or in equipment inventories.  A URN-based
   representation can be passed along in applications that need the
   information.

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 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9039.

Copyright Notice

   Copyright (c) 2021 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
   (https://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.

Table of Contents

   1.  Introduction
   2.  Requirements Language
   3.  DEV URN Definition
     3.1.  Purpose
     3.2.  Syntax
       3.2.1.  Character Case and URN-Equivalence
     3.3.  Assignment
     3.4.  Security and Privacy
     3.5.  Interoperability
     3.6.  Resolution
     3.7.  Documentation
     3.8.  Additional Information
     3.9.  Revision Information
   4.  DEV URN Subtypes
     4.1.  MAC Addresses
     4.2.  1-Wire Device Identifiers
     4.3.  Organization-Defined Identifiers
     4.4.  Organization Serial Numbers
     4.5.  Organization Product and Serial Numbers
     4.6.  Future Subtypes
   5.  Examples
   6.  Security Considerations
     6.1.  Privacy
     6.2.  Validity
   7.  IANA Considerations
   8.  References
     8.1.  Normative References
     8.2.  Informative References
   Acknowledgments
   Authors' Addresses

1.  Introduction

   This document describes a new Uniform Resource Name (URN) [RFC8141]
   namespace for hardware device identifiers.  A general representation
   of device identity can be useful in many applications, such as in
   sensor data streams and storage or in equipment inventories [RFC7252]
   [RFC8428] [CoRE-RD].

   A URN-based representation can be passed along in applications that
   need the information.  It fits particularly well for protocols
   mechanisms that are designed to carry URNs [RFC7230] [RFC7540]
   [RFC3261] [RFC7252].  Finally, URNs can also be easily carried and
   stored in formats such as XML [W3C.REC-xml-19980210], JSON [RFC8259],
   or SenML [RFC8428].  Using URNs in these formats is often preferable
   as they are universally recognized and self-describing and therefore
   avoid the need to agree to interpret an octet string as a specific
   form of a Media Access Control (MAC) address, for instance.  Passing
   URNs may consume additional bytes compared to, for instance, passing
   4-byte binary IPv4 addresses, but the former offers some flexibility
   in return.

   This document defines identifier URN types for situations where no
   such convenient type already exists.  For instance, [RFC6920] defines
   cryptographic identifiers, [RFC7254] defines International Mobile
   station Equipment Identity (IMEI) identifiers for use with 3GPP
   cellular systems, and [RFC8464] defines Mobile Equipment Identity
   (MEID) identifiers for use with 3GPP2 cellular systems.  Those URN
   types should be employed when such identifiers are transported; this
   document does not redefine these identifiers in any way.

   Universally Unique Identifier (UUID) URNs [RFC4122] are another
   alternative way to represent device identifiers and already support
   MAC addresses as one type of identifier.  However, UUIDs can be
   inconvenient in environments where it is important that the
   identifiers be as simple as possible and where additional
   requirements on stable storage, real-time clocks, and identifier
   length can be prohibitive.  Often, UUID-based identifiers are
   preferred for general purpose uses instead of the MAC-based device
   URNs defined in this document.  The device URNs are recommended for
   constrained environments.

   Future device identifier types can extend the device URN type defined
   in this document (see Section 7), or they can define their own URNs.

   Note that long-term stable unique identifiers are problematic for
   privacy reasons and should be used with care as described in
   [RFC7721].

   The rest of this document is organized as follows.  Section 3 defines
   the "DEV" URN type, and Section 4 defines subtypes for IEEE MAC-48,
   EUI-48 and EUI-64 addresses, and 1-Wire device identifiers.
   Section 5 gives examples.  Section 6 discusses the security and
   privacy considerations of the new URN type.  Finally, Section 7
   specifies the IANA registration for the new URN type and sets
   requirements for subtype allocations within this type.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  DEV URN Definition

   Namespace Identifier:  "dev"

   Version:  1

   Date:  2020-06-24

   Registrant:  IETF and the CORE Working Group.  Should the working
      group cease to exist, discussion should be directed to the
      Applications and Real-Time Area or general IETF discussion forums,
      or the IESG.

3.1.  Purpose

   The DEV URNs identify devices with device-specific identifiers such
   as network card hardware addresses.  DEV URNs are scoped to be
   globally applicable (see [RFC8141], Section 6.4.1) and, in general,
   enable systems to use these identifiers from multiple sources in an
   interoperable manner.  Note that in some deployments, ensuring
   uniqueness requires care if manual or local assignment mechanisms are
   used, as discussed in Section 3.3.

   Some typical DEV URN applications include equipment inventories and
   smart object systems.

   DEV URNs can be used in various ways in applications, software
   systems, and network components, in tasks ranging from discovery (for
   instance, when discovering 1-Wire network devices or detecting MAC-
   addressable devices on a LAN) to intrusion detection systems and
   simple catalogues of system information.

   While it is possible to implement resolution systems for specific
   applications or network locations, DEV URNs are typically not used in
   a way that requires resolution beyond direct observation of the
   relevant identifier fields in local link communication.  However, it
   is often useful to be able to pass device identifier information in
   generic URN fields in databases or protocol fields, which makes the
   use of URNs for this purpose convenient.

   The DEV URN namespace complements existing namespaces such as those
   involving IMEI or UUID identifiers.  DEV URNs are expected to be a
   part of the IETF-provided basic URN types, covering identifiers that
   have previously not been possible to use in URNs.

3.2.  Syntax

   The identifier is expressed in ASCII characters and has a
   hierarchical structure as follows:

   devurn = "urn:dev:" body componentpart
   body = macbody / owbody / orgbody / osbody / opsbody / otherbody
   macbody = %s"mac:" hexstring
   owbody = %s"ow:" hexstring
   orgbody = %s"org:" posnumber "-" identifier *( ":" identifier )
   osbody = %s"os:" posnumber "-" serial *( ":" identifier )
   opsbody = %s"ops:" posnumber "-" product "-" serial
             *( ":" identifier )
   otherbody = subtype ":" identifier *( ":" identifier )
   subtype = LALPHA *(DIGIT / LALPHA)
   identifier = 1*devunreserved
   identifiernodash = 1*devunreservednodash
   product = identifiernodash
   serial = identifier
   componentpart = *( "_" identifier )
   devunreservednodash = ALPHA / DIGIT / "."
   devunreserved = devunreservednodash / "-"
   hexstring = 1*(hexdigit hexdigit)
   hexdigit = DIGIT / "a" / "b" / "c" / "d" / "e" / "f"
   posnumber = NZDIGIT *DIGIT
   ALPHA =  %x41-5A / %x61-7A
   LALPHA =  %x41-5A
   NZDIGIT = %x31-39
   DIGIT =  %x30-39

   The above syntax is represented in Augmented Backus-Naur Form (ABNF)
   as defined in [RFC5234] and [RFC7405].  The syntax also copies the
   DIGIT and ALPHA rules originally defined in [RFC5234], exactly as
   defined there.

   The device identifier namespace includes five subtypes (see
   Section 4), and more may be defined in the future as specified in
   Section 7.

   The optional underscore-separated components at the end of the DEV
   URN depict individual aspects of a device.  The specific strings and
   their semantics are up to the designers of the device but could be
   used to refer to specific interfaces or functions within the device.

   With the exception of the MAC address and 1-Wire DEV URNs, each DEV
   URN may also contain optional colon-separated identifiers.  These are
   provided for extensibility.

   There are no special character encoding rules or considerations for
   conforming with the URN syntax beyond those applicable for URNs in
   general [RFC8141] or the context where these URNs are carried (e.g.,
   inside JSON [RFC8259] or SenML [RFC8428]).  Due to the SenML rules in
   [RFC8428], Section 4.5.1, it is not desirable to use percent-encoding
   in DEV URNs, and the subtypes defined in this specification do not
   really benefit from percent-encoding.  However, this specification
   does not deviate from the general syntax of URNs or their processing
   and normalization rules as specified in [RFC3986] and [RFC8141].

   DEV URNs do not use r-, q-, or f-components as defined in [RFC8141].

   Specific subtypes of DEV URNs may be validated through mechanisms
   discussed in Section 4.

   The string representation of the device identifier URN is fully
   compatible with the URN syntax.

3.2.1.  Character Case and URN-Equivalence

   The DEV URN syntax allows both uppercase and lowercase characters.
   The URN-equivalence of the DEV URNs is defined per [RFC8141],
   Section 3.1, i.e., two URNs are URN-equivalent if their assigned-name
   portions are octet-by-octet equal after applying case normalization
   to the URI scheme ("urn") and namespace identifier ("dev").  The rest
   of the DEV URN is compared in a case-sensitive manner.  It should be
   noted that URN-equivalence matching merely quickly shows that two
   URNs are definitely the same for the purposes of caching and other
   similar uses.  Two DEV URNs may still refer to the same entity and
   may not be found to be URN-equivalent according to the [RFC8141]
   definition.  For instance, in ABNF, strings are case insensitive (see
   [RFC5234], Section 2.3), and a MAC address could be represented
   either with uppercase or lowercase hexadecimal digits.

   Character case is not otherwise significant for the DEV URN subtypes
   defined in this document.  However, future subtypes might include
   identifiers that use encodings such as base64, which encodes strings
   in a larger variety of characters and might even encode binary data.

   To facilitate equivalence checks, it is RECOMMENDED that
   implementations always use lowercase letters where they have a choice
   in case, unless there is a reason otherwise.  (Such a reason might
   be, for instance, the use of a subtype that requires the use of both
   uppercase and lowercase letters.)

3.3.  Assignment

   The process for identifier assignment is dependent on the used
   subtype and is documented in the specific subsection under Section 4.

   Device identifiers are generally expected to identify a unique
   device, barring the accidental issue of multiple devices with the
   same identifiers.  In many cases, device identifiers can also be
   changed by users or are sometimes assigned in an algorithmic or local
   fashion.  Any potential conflicts arising from such assignments are
   not something that the DEV URNs as such manage; they simply are there
   to refer to a particular identifier.  And, of course, a single device
   may (and often does) have multiple identifiers, e.g., identifiers
   associated with different link technologies it supports.

   The DEV URN type SHOULD only be used for hardware-based identifiers
   that are expected to be persistent (with some limits, as discussed
   above).

3.4.  Security and Privacy

   As discussed in Section 6, care must be taken in the use of device-
   identifier-based identifiers due to their nature as long-term
   identifiers that are not normally changeable.  Leakage of these
   identifiers outside systems where their use is justified should be
   controlled.

3.5.  Interoperability

   There are no specific interoperability concerns.

3.6.  Resolution

   The device identifiers are not expected to be globally resolvable.
   No identifier resolution system is expected.  Systems may perform
   local matching of identifiers to previously seen identifiers or
   configured information, however.

3.7.  Documentation

   See RFC 9039.

3.8.  Additional Information

   See Section 1 for a discussion of related namespaces.

3.9.  Revision Information

   This is the first version of this registration.

4.  DEV URN Subtypes

4.1.  MAC Addresses

   DEV URNs of the "mac" subtype are based on the EUI-64 identifier
   [IEEE.EUI64] derived from a device with a built-in 64-bit EUI-64.
   The EUI-64 is formed from 24 or 36 bits of organization identifier
   followed by 40 or 28 bits of device-specific extension identifier
   assigned by that organization.

   In the DEV URN "mac" subtype, the hexstring is simply the full EUI-64
   identifier represented as a hexadecimal string.  It is always exactly
   16 characters long.

   MAC-48 and EUI-48 identifiers are also supported by the same DEV URN
   subtype.  To convert a MAC-48 address to an EUI-64 identifier, the
   Organizationally Unique Identifier (OUI) of the MAC-48 address (the
   first three octets) becomes the organization identifier of the EUI-64
   (the first three octets).  The fourth and fifth octets of the EUI are
   set to the fixed value 0xffff (hexadecimal).  The last three octets
   of the MAC-48 address become the last three octets of the EUI-64.
   The same process is used to convert an EUI-48 identifier, but the
   fixed value 0xfffe is used instead.

   Identifier assignment for all of these identifiers rests within the
   IEEE Registration Authority.

   Note that where randomized MAC addresses are used, the resulting DEV
   URNs cannot be expected to have uniqueness, as discussed in
   Section 3.3.

4.2.  1-Wire Device Identifiers

   The 1-Wire system is a device communications bus system designed by
   Dallas Semiconductor Corporation. (1-Wire is a registered trademark.)
   1-Wire devices are identified by a 64-bit identifier that consists of
   an 8-bit family code, a 48-bit identifier unique within a family, and
   an 8-bit Cyclic Redundancy Check (CRC) code [OW].

   In DEV URNs with the "ow" subtype, the hexstring is a representation
   of the full 64-bit identifier as a hexadecimal string.  It is always
   exactly 16 characters long.  Note that the last two characters
   represent the 8-bit CRC code.  Implementations MAY check the validity
   of this code.

   Family code and identifier assignment for all 1-Wire devices rests
   with the manufacturers.

4.3.  Organization-Defined Identifiers

   Device identifiers that have only a meaning within an organization
   can also be used to represent vendor-specific or experimental
   identifiers or identifiers designed for use within the context of an
   organization.

   Organizations are identified by their Private Enterprise Number (PEN)
   [RFC2578].  These numbers can be obtained from IANA.  Current PEN
   assignments can be viewed at <https://www.iana.org/assignments/
   enterprise-numbers/>, and new assignments are requested at
   <https://pen.iana.org/pen/PenApplication.page>.

   Note that when included in an "org" DEV URN, the number cannot be
   zero or have leading zeroes, as the ABNF requires the number to start
   with a non-zero digit.

4.4.  Organization Serial Numbers

   The "os" subtype specifies an organization and serial number.
   Organizations are identified by their PEN.  As with the organization-
   defined identifiers (Section 4.3), PEN number assignments are
   maintained by IANA, and assignments for new organizations can be made
   easily.

      |  Historical note: The "os" subtype was originally defined in the
      |  Open Mobile Alliance "Lightweight Machine to Machine" standard
      |  [LwM2M] but has been incorporated here to collect all syntaxes
      |  associated with DEV URNs in one place.  At the same time, the
      |  syntax of this subtype was changed to avoid the possibility of
      |  characters that are not allowed in the SenML Name field (see
      |  [RFC8428], Section 4.5.1).

   Organization serial number DEV URNs consist of the PEN number and the
   serial number.  As with other DEV URNs, for carrying additional
   information and extensibility, optional colon-separated identifiers
   and underscore-separated components may also be included.  The serial
   numbers themselves are defined by the organization, and this
   specification does not specify how they are allocated.

   Organizations are also encouraged to select serial number formats
   that avoid the possibility of ambiguity in the form of leading zeroes
   or otherwise.

4.5.  Organization Product and Serial Numbers

   The DEV URN "ops" subtype was originally defined in the LwM2M
   standard but has been incorporated here to collect all syntaxes
   associated with DEV URNs in one place.  The "ops" subtype specifies
   an organization, product class, and a serial number.  Organizations
   are identified by their PEN.  Again, as with the organization-defined
   identifiers (Section 4.3), PEN number assignments are maintained by
   IANA.

      |  Historical note: As with the "os" subtype, the "ops" subtype
      |  was originally defined in the Open Mobile Alliance "Lightweight
      |  Machine to Machine" standard [LwM2M].

   Organization product and serial number DEV URNs consist of the PEN
   number, product class, and the serial number.  As with other DEV
   URNs, for carrying additional information and extensibility, optional
   colon-separated identifiers and underscore-separated components may
   also be included.  Both the product class and serial numbers
   themselves are defined by the organization, and this specification
   does not specify how they are allocated.

   Organizations are also encouraged to select product and serial number
   formats that avoid possibility for ambiguity.

4.6.  Future Subtypes

   Additional subtypes may be defined in future specifications.  See
   Section 7.

   The DEV URN "example" subtype is reserved for use in examples.  It
   has no specific requirements beyond those expressed by the ABNF in
   Section 3.2.

5.  Examples

   The following provides some examples of DEV URNs:

   +=========================================+=========================+
   | URN                                     | Description             |
   +=========================================+=========================+
   | urn:dev:mac:0024beffff804ff1            | The MAC-48 address of   |
   |                                         | 0024be804ff1,           |
   |                                         | converted to EUI-64     |
   |                                         | format                  |
   +-----------------------------------------+-------------------------+
   | urn:dev:mac:0024befffe804ff1            | The EUI-48 address of   |
   |                                         | 0024be804ff1,           |
   |                                         | converted to EUI-64     |
   |                                         | format                  |
   +-----------------------------------------+-------------------------+
   | urn:dev:mac:acde48234567019f            | The EUI-64 address of   |
   |                                         | acde48234567019f        |
   +-----------------------------------------+-------------------------+
   | urn:dev:ow:10e2073a01080063             | A 1-Wire temperature    |
   |                                         | sensor                  |
   +-----------------------------------------+-------------------------+
   | urn:dev:ow:264437f5000000ed_humidity    | The humidity part of    |
   |                                         | a multi-sensor device   |
   +-----------------------------------------+-------------------------+
   | urn:dev:ow:264437f5000000ed_temperature | The temperature part    |
   |                                         | of a multi-sensor       |
   |                                         | device                  |
   +-----------------------------------------+-------------------------+
   | urn:dev:org:32473-foo                   | An organization-        |
   |                                         | specific URN in the     |
   |                                         | example organization    |
   |                                         | 32473 in [RFC5612]      |
   +-----------------------------------------+-------------------------+
   | urn:dev:os:32473-123456                 | Device 123456 in the    |
   |                                         | example organization    |
   |                                         | in [RFC5612]            |
   +-----------------------------------------+-------------------------+
   | urn:dev:os:32473-12-34-56               | A serial number with    |
   |                                         | dashes in it            |
   +-----------------------------------------+-------------------------+
   | urn:dev:ops:32473-Refrigerator-5002     | Refrigerator serial     |
   |                                         | number 5002 in the      |
   |                                         | example organization    |
   |                                         | in [RFC5612]            |
   +-----------------------------------------+-------------------------+
   | urn:dev:example:new-1-2-3_comp          | An example of           |
   |                                         | something that is not   |
   |                                         | defined today, and is   |
   |                                         | not one of the mac,     |
   |                                         | ow, os, or ops          |
   |                                         | subtypes                |
   +-----------------------------------------+-------------------------+

                                  Table 1

   The DEV URNs themselves can then appear in various contexts.  A
   simple example of this is the use of DEV URNs in SenML data.  This
   example from [RFC8428] shows a measurement from a 1-Wire temperature
   gauge encoded in the JSON syntax:

      [
        {"n":"urn:dev:ow:10e2073a01080063","u":"Cel","v":23.1}
      ]

6.  Security Considerations

   On most devices, the user can display device identifiers.  Depending
   on circumstances, device identifiers may or may not be modified or
   tampered with by the user.  An implementation of the DEV URN MUST
   preserve such limitations and behaviors associated with the device
   identifiers.  In particular, a device identifier that is intended to
   be immutable should not become mutable as a part of implementing the
   DEV URN type.  More generally, nothing in this document should be
   construed to override what the relevant device specifications have
   already said about the identifiers.

6.1.  Privacy

   Other devices in the same network may or may not be able to identify
   the device.  For instance, on an Ethernet network, the MAC address of
   a device is visible to all other devices.

   DEV URNs often represent long-term stable unique identifiers for
   devices.  Such identifiers may have privacy and security implications
   because they may enable correlating information about a specific
   device over a long period of time, location tracking, and device-
   specific vulnerability exploitation [RFC7721].  Also, in some
   systems, there is no easy way to change the identifier.  Therefore,
   these identifiers need to be used with care, and special care should
   be taken to avoid leaking identifiers outside of the system that is
   intended to use them.

6.2.  Validity

   Information about identifiers may have significant effects in some
   applications.  For instance, in many sensor systems, the identifier
   information is used for deciding how to use the data carried in a
   measurement report.  In some other systems, identifiers may be used
   in policy decisions.

   It is important that systems be designed to take into account the
   possibility of devices reporting incorrect identifiers (either
   accidentally or maliciously) and the manipulation of identifiers in
   communications by illegitimate entities.  Integrity protection of
   communications or data objects, the use of trusted devices, and
   various management practices can help address these issues.

   Similar to the advice in [RFC4122], Section 6: Do not assume that DEV
   URNs are hard to guess.

7.  IANA Considerations

   Per this document, IANA has registered a new URN namespace for "dev",
   as described in Section 3.

   IANA has created a "DEV URN Subtypes" registry under "Device
   Identification".  The initial values in this registry are as follows:

      +=========+===========================+=======================+
      | Subtype | Description               | Reference             |
      +=========+===========================+=======================+
      | mac     | MAC Addresses             | RFC 9039, Section 4.1 |
      +---------+---------------------------+-----------------------+
      | ow      | 1-Wire Device Identifiers | RFC 9039, Section 4.2 |
      +---------+---------------------------+-----------------------+
      | org     | Organization-Defined      | RFC 9039, Section 4.3 |
      |         | Identifiers               |                       |
      +---------+---------------------------+-----------------------+
      | os      | Organization Serial       | RFC 9039, Section 4.4 |
      |         | Numbers                   |                       |
      +---------+---------------------------+-----------------------+
      | ops     | Organization Product and  | RFC 9039, Section 4.5 |
      |         | Serial Numbers            |                       |
      +---------+---------------------------+-----------------------+
      | example | Reserved for examples     | RFC 9039, Section 4.6 |
      +---------+---------------------------+-----------------------+

                                  Table 2

   Additional subtypes for DEV URNs can be defined through Specification
   Required or IESG Approval [RFC8126].  These allocations are
   appropriate when there is a new namespace of some type of device
   identifier that is defined in a stable fashion and has a publicly
   available specification.

   Note that the organization (Section 4.3) device identifiers can also
   be used in some cases, at least as a temporary measure.  It is
   preferable, however, that long-term usage of a broadly employed
   device identifier be registered with IETF rather than used through
   the organization device identifier type.

8.  References

8.1.  Normative References

   [IEEE.EUI64]
              IEEE, "Guidelines for Use of Extended Unique Identifier
              (EUI), Organizationally Unique Identifier (OUI), and
              Company ID (CID)", August 2017,
              <https://standards.ieee.org/content/dam/ieee-
              standards/standards/web/documents/tutorials/eui.pdf>.

   [OW]       Maxim, "Guide to 1-Wire Communication", June 2008,
              <https://www.maximintegrated.com/en/design/technical-
              documents/tutorials/1/1796.html>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC2578]  McCloghrie, K., Ed., Perkins, D., Ed., and J.
              Schoenwaelder, Ed., "Structure of Management Information
              Version 2 (SMIv2)", STD 58, RFC 2578,
              DOI 10.17487/RFC2578, April 1999,
              <https://www.rfc-editor.org/info/rfc2578>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <https://www.rfc-editor.org/info/rfc3986>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/info/rfc5234>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC8141]  Saint-Andre, P. and J. Klensin, "Uniform Resource Names
              (URNs)", RFC 8141, DOI 10.17487/RFC8141, April 2017,
              <https://www.rfc-editor.org/info/rfc8141>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

8.2.  Informative References

   [CoRE-RD]  Amsüss, C., Ed., Shelby, Z., Koster, M., Bormann, C., and
              P. van der Stok, "CoRE Resource Directory", Work in
              Progress, Internet-Draft, draft-ietf-core-resource-
              directory-28, 7 March 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-core-
              resource-directory-28>.

   [LwM2M]    Alliance, O. M., "OMA Lightweight Machine to Machine
              Requirements", OMA Standard Candidate Version 1.2, January
              2019, <https://www.openmobilealliance.org/release/
              LightweightM2M/V1_2-20190124-C/OMA-RD-LightweightM2M-
              V1_2-20190124-C.pdf>.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              DOI 10.17487/RFC3261, June 2002,
              <https://www.rfc-editor.org/info/rfc3261>.

   [RFC4122]  Leach, P., Mealling, M., and R. Salz, "A Universally
              Unique IDentifier (UUID) URN Namespace", RFC 4122,
              DOI 10.17487/RFC4122, July 2005,
              <https://www.rfc-editor.org/info/rfc4122>.

   [RFC5612]  Eronen, P. and D. Harrington, "Enterprise Number for
              Documentation Use", RFC 5612, DOI 10.17487/RFC5612, August
              2009, <https://www.rfc-editor.org/info/rfc5612>.

   [RFC6920]  Farrell, S., Kutscher, D., Dannewitz, C., Ohlman, B.,
              Keranen, A., and P. Hallam-Baker, "Naming Things with
              Hashes", RFC 6920, DOI 10.17487/RFC6920, April 2013,
              <https://www.rfc-editor.org/info/rfc6920>.

   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing",
              RFC 7230, DOI 10.17487/RFC7230, June 2014,
              <https://www.rfc-editor.org/info/rfc7230>.

   [RFC7252]  Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
              Application Protocol (CoAP)", RFC 7252,
              DOI 10.17487/RFC7252, June 2014,
              <https://www.rfc-editor.org/info/rfc7252>.

   [RFC7254]  Montemurro, M., Ed., Allen, A., McDonald, D., and P.
              Gosden, "A Uniform Resource Name Namespace for the Global
              System for Mobile Communications Association (GSMA) and
              the International Mobile station Equipment Identity
              (IMEI)", RFC 7254, DOI 10.17487/RFC7254, May 2014,
              <https://www.rfc-editor.org/info/rfc7254>.

   [RFC7405]  Kyzivat, P., "Case-Sensitive String Support in ABNF",
              RFC 7405, DOI 10.17487/RFC7405, December 2014,
              <https://www.rfc-editor.org/info/rfc7405>.

   [RFC7540]  Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
              Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
              DOI 10.17487/RFC7540, May 2015,
              <https://www.rfc-editor.org/info/rfc7540>.

   [RFC7721]  Cooper, A., Gont, F., and D. Thaler, "Security and Privacy
              Considerations for IPv6 Address Generation Mechanisms",
              RFC 7721, DOI 10.17487/RFC7721, March 2016,
              <https://www.rfc-editor.org/info/rfc7721>.

   [RFC8259]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,
              <https://www.rfc-editor.org/info/rfc8259>.

   [RFC8428]  Jennings, C., Shelby, Z., Arkko, J., Keranen, A., and C.
              Bormann, "Sensor Measurement Lists (SenML)", RFC 8428,
              DOI 10.17487/RFC8428, August 2018,
              <https://www.rfc-editor.org/info/rfc8428>.

   [RFC8464]  Atarius, R., "A URN Namespace for Device Identity and
              Mobile Equipment Identity (MEID)", RFC 8464,
              DOI 10.17487/RFC8464, September 2018,
              <https://www.rfc-editor.org/info/rfc8464>.

   [W3C.REC-xml-19980210]
              Sperberg-McQueen, C., Bray, T., and J. Paoli, "Extensible
              Markup Language (XML) 1.0", W3C Recommendation, February
              1998, <http://www.w3.org/TR/1998/REC-xml-19980210>.

Acknowledgments

   The authors would like to thank Ari Keränen, Stephen Farrell,
   Christer Holmberg, Peter Saint-Andre, Wouter Cloetens, Jaime Jimenez,
   Joseph Knapp, Padmakumar Subramani, Mert Ocak, Hannes Tschofenig, Jim
   Schaad, Thomas Fossati, Carsten Bormann, Marco Tiloca, Barry Leiba,
   Amanda Baber, Juha Hakala, Dale Worley, Warren Kumari, Benjamin
   Kaduk, Brian Weis, John Klensin, Dave Thaler, Russ Housley, Dan
   Romascanu, Éric Vyncke, Roman Danyliw, and Ahmad Muhanna for their
   feedback and interesting discussions in this problem space.  We would
   also like to note prior documents that focused on specific device
   identifiers, such as [RFC7254] and [RFC8464].

Authors' Addresses

   Jari Arkko
   Ericsson
   FI-02420 Jorvas
   Finland

   Email: jari.arkko@piuha.net

   Cullen Jennings
   Cisco
   170 West Tasman Drive
   San Jose, CA 95134
   United States of America

   Phone: +1 408 421-9990
   Email: fluffy@iii.ca

   Zach Shelby
   Edge Impulse
   3031 Tisch Way
   San Jose, CA 95128
   United States of America

   Email: zach@edgeimpulse.com