Network Working Group                                           T. Lemon
Internet-Draft                                             Nominum, Inc.
Intended status: Informational                                  R. Droms
Expires: December 8, 29, 2017
                                                               W. Kumari
                                                           June 6, 27, 2017

               Special-Use Domain Names Problem Statement


   The Special-Use Domain Names IANA registry policy defined in RFC 6761
   has been shown through experience to present unanticipated
   challenges.  This memo presents a list, intended to be comprehensive,
   of the problems that have been identified.  In addition it reviews
   the history of Domain Names and summarizes current IETF publications
   and some publications from other organizations relating to Special-
   Use Domain Names.

Status of This Memo

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   This Internet-Draft will expire on December 8, 29, 2017.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3   4
   3.  Problems associated with Special-Use Domain Names . . . . . .   4
   4.  Existing Practice Regarding Special-Use Domain Names  . . . .   9
     4.1.  Primary Special-Use Domain Name Documents . . . . . . . .   9  10
       4.1.1.  IAB Technical Comment on the Unique DNS Root  . . . .  10
       4.1.2.  Special-Use Domain Names  . . . . . . . . . . . . . .  11
       4.1.3.  MoU Concerning the Technical Work of the IANA . . . .  13
       4.1.4.  Liaison Statement on Technical Use of Domain
               Names . . . . . . . . . . . . . . . . . . . . . . . .  14
     4.2.  Secondary documents relating to the Special-Use
           Domain Name question  . . . . . . . . . . . . . . . . . .  14
       4.2.1.  Multicast DNS . . . . . . . . . . . . . . . . . . . .  14
       4.2.2.  The .onion Special-Use Top-Level Domain Name  . . . .  15
       4.2.3.  Locally Served DNS Zones  . . . . . . . . . . . . . .  15
       4.2.4.  Name Collision in the DNS . . . . . . . . . . . . . .  15  16
       4.2.5.  SSAC Advisory on the Stability of the Domain
               Namespace . . . . . . . . . . . . . . . . . . . . . .  16
       4.2.6.  Discovery of the IPv6 Prefix Used for IPv6 Address
               Synthesis . . . . . . . . . . . . . . . . . . . . . .  16
       4.2.7.  Additional Reserved Top Level Domains . . . . . . . .  16  17
   5.  History . . . . . . . . . . . . . . . . . . . . . . . . . . .  17
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  18
   7.  IANA considerations . . . . . . . . . . . . . . . . . . . . .  18  19
   8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  18  19
   9.  RFC Editor Considerations . . . . . . . . . . . . . . . . . .  19
   10. Informative References  . . . . . . . . . . . . . . . . . . .  19
   Appendix A.  Change Log.  . . . . . . . . . . . . . . . . . . . .  22  23
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  27  28

1.  Introduction

   One of the key services required to use the Internet is name
   resolution.  Name resolution is the process of translating a symbolic
   name into some object or set of objects to which the name refers,
   most typically one or more IP addresses.  These names are often
   referred to as Domain Names.  When reading this document, care must
   be taken to not assume that the term Domain Name implies the use of
   the Domain Name System [RFC1034] for resolving these names.  An
   excellent presentation on this topic can be found in Domain Names

   Special-Use Domain Names [RFC6761] created an IANA registry for
   Special-Use Domain Names [SDO-IANA-SUDR], defined policies for adding
   to the registry, and made some suggestions about how those policies
   might be implemented.  Since the publication of RFC 6761, the IETF
   has been asked to designate several new Special-Use Domain Names in
   this registry.  During the evaluation process for these Special-Use
   Domain Names, the IETF encountered several different sorts of issues.
   Because of this, the IETF has decided to investigate the problem and
   decide if and how the RFC 6761 process can be improved, or whether it
   should be deprecated.  The IETF DSNOP working group charter was
   extended to include conducting a review of the process for adding
   names to the registry that is defined in RFC 6761.  This document is
   a product of that review.

   Based on current ICANN and IETF practice, including RFC 6761, there
   are several different types of names in the root of the Domain

   o  Reserved by the IETF for technical purposes

   o  Assigned by ICANN to the public DNS root; some names reserved by
      the IETF for technical purposes may appear in the Global DNS root
      for reasons pertaining to the operation of the DNS

   o  ICANN Reserved Names; names that may not be applied for as TLDs
      (see [SDO-ICANN-DAG], Section, Reserved Names,
      Section, Treatment of Country or Territory Names, et

   o  Used by other organizations without following established

   o  Names that are unused and are available for assignment to one of
      the previous categories

   This document presents a list, believed to be complete, of the
   problems associated with the assignment of Special-Use Domain Names.
   In support of its analysis of the particular set of issues described
   here, the document also includes descriptions of existing practice as
   it relates to the use of domain names, a brief history of domain
   names, and some observations by various IETF participants who have
   experience with various aspects of the current situation.

2.  Terminology

   This document uses the terminology from RFC 7719 [RFC7719].  Other
   terms used in this document are defined here:

   Domain Name  This document uses the term "Domain Name" as defined in
      section 2 of RFC 7719 [RFC7719].

   Domain Namespace  The set of all possible Domain Names.

   Special-Use Domain Name  A Domain Name listed in the Special-Use
      Domain Names registry [SDO-IANA-SUDR].

   For the sake of brevity this document uses some abbreviations, which
   are expanded here:

   IANA  Internet Assigned Numbers Authority

   ICANN  Internet Corporation for Assigned Names and Numbers

   TLD  Top-Level Domain, as defined in section 2 of RFC 7719 [RFC7719]

   gTLD  Generic Top-Level Domain (see section 2 of RFC 2352 [RFC2352])

3.  Problems associated with Special-Use Domain Names

   This section presents a list of problems that have been identified
   with respect to the assignment of Special-Use Domain Names.
   Solutions to these problems, including their costs or tradeoffs, are
   out of scope for this document.  They will be covered in a separate
   document.  New problems that might be created in the process of
   solving problems described in this document are also out of scope:
   these problems are expected to be addressed in the process of
   evaluating potential solutions.

   Special-Use Domain Names exist to solve a variety of problems.  This
   document has two goals: enumerate all of the problems that have been
   identified to which Special-Use Domain Names are a solution and
   enumerate all of the problems that have been raised in the process of
   trying to use RFC 6761 as it was intended.  As some of those problems
   may fall into both categories, this document makes no attempt to
   categorize the problems.

   There is a broad diversity of opinion about this set of problems.
   Not every participant agrees that each of the problems enumerated in
   this document is actually a problem.  This document takes no position
   on the relative validity of the various problems that have been
   enumerated, nor on the organization responsible for addressing each
   individual problem, if it is to be addressed.  The sole purposes of
   the document are to enumerate those problems, provide the reader with
   context for thinking about them and provide a context for future
   discussion of solutions, regardless of whether such solutions may be
   work for IETF, ICANN, IANA or some other group.

   This is the list of problems:

   o  No formal coordination process exists between  Although the IETF and ICANN
      as they follow their respective name assignment processes have a liaison relationship through
      which special-use allocations can be discussed, there exists no
      formal process for coordinating these allocations (see
      Section 4.1.3).  The lack of coordination complicates the
      management of the root of the Domain Namespace and could lead to
      conflicts in name assignments [SDO-ICANN-SAC090].

   o  There is no explicit scoping as to what can constitute a
      "technical use" [RFC2860] and what cannot, and there is also no
      consensus within the IETF as to what this term means.

   o  Not all developers of protocols on the internet agree that
      authority over the entire Domain Namespace should reside solely
      with the IETF and ICANN.

   o  Although IETF and ICANN nominally have authority over this
      namespace, neither organization can enforce that authority over
      any third party who wants to just start using a subset of the
      namespace.  Such parties may observe that the IETF has never
      asserted control or authority over what protocols are "allowed" on
      the internet, and that the principle of "permissionless
      innovation" suggests there should be a way for people to include
      new uses of domain names in new protocols and applications.

   o  Organizations do in fact sometimes use subsets of the Domain
      Namespace without following established processes.  Reasons a
      third party might do this include:

      *  Unaware that a process exists for assigning such names

      *  Intended use is covered by gTLD process [SDO-ICANN-DAG], but no
         gTLD process is ongoing

      *  Intended use is covered by gTLD process, but the third party
         doesn't want to pay a fee

      *  Intended use is covered by some IETF process, but the third
         party doesn't want to follow the process

      *  Intended use is covered by ICANN or IETF process, but third
         party expects that the outcome will be refusal or non-action

      *  Unaware that a name intended to be used only locally may
         nevertheless leak

      *  Unaware that a name used locally with informal allocation may
         subsequently be allocated formally, creating operational

   o  There is demand for more than one name resolution protocol for
      Domain Names.  Domain Names contain no metadata to indicate which
      protocol to use to resolve them.  Domain name resolution APIs do
      not provide a way to specify which protocol to use.

   o  When a Special-Use Domain Name is added to the Special-Use Domain
      Names registry, not all software that processes such names will
      understand the special use of that name.  In many cases, name
      resolution software will use the Domain Name System for resolution
      of names not known to have a special use.  Consequently, any such
      use will result in queries for Special-Use Domain Names being sent
      to Domain Name System authoritative servers.  These queries may
      constitute an operational problem for operators of root zone
      authoritative name servers.  These queries may also inadvertently
      reveal private information through the contents of the query,
      which is a privacy consideration.

   o  The RFC 6761 process is sufficiently uncertain that some protocol
      developers have assumed they could not get a name assigned; the
      process of assigning the first new name ('.local') using the RFC
      6761 process took more than ten years from beginning to end:
      longer by a factor of ten than any other part of the protocol
      development process (largely because this ten years included time
      to develop the process as well as use it).  Other uses of the
      process have proceeded more smoothly, but there is a reasonably
      justified perception that using this process is likely to be slow
      and difficult, with an uncertain outcome.

   o  There is strong resistance within the IETF to assigning Domain
      Names to resolution systems outside of the DNS, for a variety of

      *  Requires a mechanism for identifying which of a set of
         resolution processes is required in order to resolve a
         particular name.

      *  Assertion of authority: there is a sense that the Domain
         Namespace is "owned" by the IETF or by ICANN, and so, if a name
         is claimed outside of that process, the person or entity that
         claimed that name should suffer some consequence that would,
         presumably, deter future circumvention of the official process.

      *  More than one name resolution protocol is bad, in the sense
         that a single protocol is less complicated to implement and

      *  The semantics of alternative resolution protocols may differ
         from the DNS protocol; DNS has the concept of RRtypes; other
         protocols may not support RRtypes, or may support some entirely
         different data structuring mechanism.

      *  If there is an IETF process through which a TLD can be assigned
         at zero cost other than time, this process will be used as an
         alternative to the more costly process of getting the name
         registered through ICANN.

      *  A name might be assigned for a particular purpose when a more
         general use of the name would be more beneficial.

      *  If the IETF assigns a name that some third party or parties
         believes belongs to them in some way, the IETF could become
         embroiled in an expensive dispute with those parties.

   o  If there were no process for assigning names for technical use
      through the IETF, there is a concern that protocols that require
      such names would not be able to get them.

   o  In some cases where the IETF has made assignments through the RFC
      6761 process, technical mistakes have been made due to
      misunderstandings as to the actual process that RFC 6761 specifies
      (e.g., treating the list of suggested considerations for assigning
      a name as a set of requirements all of which must be met).  In
      other cases, the IETF has made de facto assignments of Special-Use
      Domain Names without following the RFC 6761 process.

   o  There are several Domain Name TLDs that are in use without due
      process for a variety of purposes.  The status of these names need
      to be clarified and recorded to avoid future disputes about their
      use [SDO-ICANN-COLL].

   o  In principle, the RFC 6761 process could be used to document the
      existence of Domain Names that are not safe to assign, and provide
      information on how those names are used in practice.  However,
      attempts to use RFC 6761 to accomplish this documentation have not
      been successful (for example, see "Additional Reserved Top Level
      Domains [I-D.chapin-additional-reserved-tlds] and Section 4.2.7).

      One side effect of the lack of documentation is that any
      mitigation effect on the root name servers or on privacy
      considerations has been missed.

   o  A Domain Name can be identified as either a DNS name by placing it
      in the DNS zone(s) or as a Special-Use Domain Name by adding it to
      the IANA registry.  Some names are in both places; for example,
      some locally served zone names are in DNS zones and documented in
      the Special-Use Domain Names registry.  At present, the only way a
      Domain Name can be added to the Special-Use Domain Name registry
      is for the IETF to take responsibility for the name and designate
      it for "technical use".  There are other potential uses for Domain
      Names that should be recorded in the registry, but for which the
      IETF should not take responsibility.

   o  The IETF may in some cases see the need to document that a name is
      in use without claiming that the use of the name is the IETF's use
      of the name.  No mechanism exists in the current registry to mark
      names in this way.

   o  There is no formal process during any of the review stages for a
      document in which a check is made to ensure that the document does
      not unintentionally violate IETF process for adding special-use
      domain names to the registry, as was the case, for example, in RFC
      7788 [RFC7788].

   o  Use of the registry is inconsistent -- some Special-Use Domain
      Name RFCs specify specifically add registry entries, some don't; some
      delegation, how and whether special-use name delegations should be
      done, some don't.

   o  There exists no safe, non-process-violating mechanism for ad-hoc
      assignment of Special-Use Domain Names.

   o  It is generally assumed that protocols that need a Special-Use
      Domain Name need a mnemonic, single-label, human-readable Special-
      Use Domain Name, for use in user interfaces such as command lines
      or URL entry fields.  While this assumption is correct in some
      cases, it is likely not correct in all cases; for example, in
      applications where the DNS name is never visible to a user.

   o  RFC 6761 uses the term "Domain Name" to describe the thing for
      which special uses are registered.  This creates a great deal of
      confusion because some readers take "Domain Name" to imply the use
      of the DNS protocol.

   o  The use of DNSSEC with Special-Use Domain Names is an open issue.
      There is no consensus or guidance about how to use DNSSEC with
      various classes of Special-Use Domain Names.  Considerations in
      the use of DNSSEC with Special-Use Domain Names include:

      *  What class of Special-Use Domain Name is under consideration:
         non-DNS, locally served zone, other?

      *  Does the Special-Use Domain Name require a delegation in the
         root zone; if so, should that delegation be signed or not?  If
         there is no delegation, then this will be treated by validating
         resolvers as a secure denial of existence for that zone.  This
         would not be appropriate for a name being resolved using the
         DNS protocol.

      *  A process would be required through which the IETF can cause a
         delegation in the root zone to be instantiated.

      *  What are the recommended practices for using DNS with the
         specific Special-Use Domain Name?

   The problems we have stated here represent the current understanding
   of the authors of the document as to the complete set of problems
   that have been identified during discussion by the working group on
   this topic.  The remainder of this document provides additional
   context that will be needed for reasoning about these problems.

4.  Existing Practice Regarding Special-Use Domain Names

   There are three primary (see Section 4.1) and numerous secondary
   (Section 4.2) documents to consider when thinking about the Special-
   Use Domain Names process.

   How names are resolved is ambiguous, in the sense that some names are
   Special-Use Domain names that require special handling, and some
   names can be resolved using the DNS protocol with no special

   The assignment of Internet Names is not under the sole control of any
   one organization.  IETF has authority in some cases, but only with
   respect to "technical uses."  ICANN at present is the designated
   administrator of the root zone, but generally not of zones other than
   the root zone.  Neither of these authorities can in any practical
   sense exclude the practice of ad-hoc use of names.  Unauthorized use
   of domain names can be accomplished by any entity that has control
   over one or more name servers or resolvers, in the context of any
   hosts and services that that entity operates.  It can also be
   accomplished by authors of software who decide that a Special-Use
   Domain Name is the right way to indicate the use of an alternate
   resolution mechanism.

4.1.  Primary Special-Use Domain Name Documents

   The primary documents are considered primary because they directly
   address the IETF's past thoughts on this topic in a general way, and
   also because they describe what the IETF does in practice.  Only one
   of these documents is an IETF consensus document.

4.1.1.  IAB Technical Comment on the Unique DNS Root

   This document [RFC2826] is not an IETF consensus document, and
   appears to have been written to address a different problem than the
   Special-Use Domain Name problem.  However, it speaks directly to
   several of the key issues that must be considered, and, coming as it
   does from the IAB, it is rightly treated as having significant
   authority despite not being an IETF consensus document.

   This document should be considered required reading for IETF
   participants who wish to express an informed opinion on the topic of
   Special-Use Domain Names.  The main points that appear relevant to
   the Special-Use Domain Names problem are:

   o  The Internet requires a globally unique namespace: a namespace in
      which any given name refers to the same information (has the same
      meaning) no matter who requests that information and no matter
      from which specific name server they request it.

   o  Private networks may operate private namespaces, with names that
      have meanings only locally (within the private network) but still
      require that names in the public namespace be globally unique.

   o  The Domain Name System [RFC1035] is not the only protocol that may
      be used for resolving domain names.

   o  Users cannot be assumed to know how to distinguish between
      symbolic references that have local meaning and references that
      have global meaning.  Users may therefore share references that
      incorporate Domain Names with no global meaning (for example, a
      URL of 'http://mysite.example.corp', where 'example.corp' is a
      domain used privately and informally as described in

   o  Such references might refer to the object the user intends to
      share within that user's context, but either refer to some other
      object any recipient's context, or might not refer to any object
      at all in a recipient's context.  The effect of this reference
      escaping the context in which it is valid is that the user's
      intended communication will not be able to be understood by the
      recipients of the communication.

   o  This same problem can also occur when a single user copies a name
      from one context in which it has one meaning, into a different
      context in which it has a different meaning -- for example copying
      a '.onion' Domain Name out of a Tor Browser [TOR], where it has
      meaning, and pasting this name into an ssh client that doesn't
      support connecting over the Tor network.

   We can summarize the advice in this document as follows:

   o  Domain Names with unambiguous global meaning are preferable to
      Domain Names with local meaning which will be ambiguous.
      Nevertheless both globally-meaningful and locally-special names
      are in use and must be supported.

   o  At the time of the writing of this document the IAB was of the
      opinion that there might well be more than one name resolution
      protocol used to resolve Domain Names.

4.1.2.  Special-Use Domain Names

   The second important document is "Special-Use Domain Names"
   [RFC6761].  RFC 6761 represents the current IETF consensus on
   designating and recording Special-Use Domain Names.  The IETF has
   experienced problems with the designation process described in RFC
   6761; these concerns motivate this document.  Familiarity with RFC
   6761 is a prerequisite for having an informed opinion on the topic of
   Special-Use Domain Names.

   RFC 6761 defines two aspects of Special-Use Domain Names: designating
   a Domain Name to have a special purpose and registering that special
   use in the Special-Use Domain Names registry.  The designation
   process is defined in a single sentence (RFC 6761, section 4):

      If it is determined that special handling of a name is required in
      order to implement some desired new functionality, then an IETF
      "Standards Action" or "IESG Approval" specification [RFC5226] MUST
      be published describing the new functionality.

   This sentence requires that any designation of a Special-Use Domain
   Name is subject to the same open review and consensus process as used
   to produce and publish all other IETF specifications.

   The registration process is a purely mechanical process, in which the
   existence of the newly designated Special-Use Domain Name is
   recorded, with a pointer to a section in the relevant specification
   document that defines the ways in which special handling is to be
   applied to the name.

   RFC 6761 provided the process whereby Multicast DNS [RFC6762]
   designated ".local" as a Special-Use Domain Name and included it in
   the Special-Use Domain Names registry.  It itself also enumerated a
   set of names that had been previously used or defined to have special
   uses prior to the publication of RFC 6761.  Since there had been no
   registry for these names prior to the publication of RFC 6761, the
   documents defining these names could not have added them to the

   There are at least several important points to think of with respect
   to the RFC 6761:

   o  A Special-Use Domain Name may be a name that should be resolved
      using the DNS protocol with no special handling.  An example of
      this is 'IN-ADDR.ARPA.' (which is an example of a Special-Use
      Domain Name that is not a TLD).

   o  A Special-Use Domain Name may be a name that is resolved using the
      DNS protocol, requires no special handling in the stub resolver,
      but requires special handling in the recursive resolver.  An
      example of this would be ""

   o  A Special-Use Domain Name may be a name that requires special
      handling in the stub resolver.  An example would be a Special-Use
      Top-Level Domain Name like '.local' which acts as a signal to
      indicate that the local stub resolver should use a non-DNS
      protocol for name resolution.

   o  The current IETF consensus (from a process perspective, not
      necessarily from the perspective of what would be consensus if the
      IETF were to attempt to produce a new consensus document) is that
      all of these purposes for Special-Use Domain Names are valid.

   The term "stub resolver" in this case does not mean "DNS protocol
   stub resolver."  The stub resolver is the entity within a particular
   software stack that takes a question about a Domain Name and answers
   it.  One way a stub resolver can answer such a question is using the
   DNS protocol, but it is in the stub resolver, as we are using the
   term here, that the decision as to whether to use a protocol, and if
   so which protocol, or whether to use a local database of some sort,
   is made.

   RFC 6761 does not limit Special-Use Domain Names to TLDs.  However,
   at present, all Special-Use Domain Names registered in the IANA
   Special-Use Domain Names registry [SDO-IANA-SUDR] are either intended
   to be resolved using the DNS protocol, or are TLDs, or both.  That
   is, at present there exist no Special-Use Domain Names which require
   special handling by stub resolvers and which are not at the top level
   of the naming hierarchy.

   One point to take from this is that there is already a requirement in
   RFC 6762 that when a stub resolvers encounter resolver encounters the special label,
   '.LOCAL' at the top level of a domain name, they it can only use the mDNS
   protocol be used for resolving to resolve that Domain Name.

4.1.3.  MoU Concerning the Technical Work of the IANA

   There exists a Memorandum of Understanding [RFC2860] between the IETF
   and ICANN (Internet Corporation for Assigned Names and Numbers) which
   discusses how names and numbers will be managed through the IANA
   (Internet Assigned Numbers Authority).  This document is important to
   the discussion of Special-Use Domain Names because, while it
   delegates authority for managing the Domain Name System Namespace
   generally to ICANN, it reserves to the IETF the authority that RFC
   6761 formalizes:

      Note that (a) assignments of Domain Names for technical uses (such
      as Domain Names for inverse DNS lookup), (b) assignments of
      specialised address blocks (such as multicast or anycast blocks),
      and (c) experimental assignments are not considered to be policy
      issues, and shall remain subject to the provisions of this
      Section 4.

   The above text is an addendum to the following:

      Two particular assigned spaces present policy issues in addition
      to the technical considerations specified by the IETF: the
      assignment of Domain Names, and the assignment of IP address
      blocks.  These policy issues are outside the scope of this MOU.

   In general, then, the assignment of names in the DNS root zone, and
   the management of the DNS namespace, is a function that is performed
   by ICANN.  However, the MoU specifically exempts domain names
   assigned for technical use, and uses the example of domains used for
   inverse DNS lookup.  Both 'IN-ADDR.ARPA' and 'IP6.ARPA' are in the
   Special-Use Domain Names registry.

   Implicit in the MoU is the fact that the IETF and ICANN retain,
   between them, sole authority for assigning any names from the Domain
   Namespace.  Both the IETF and ICANN have internal processes for
   making such assignments.

   The point here is not to say what the implications of this statement
   in the MoU are, but rather to call the reader's attention to the
   existence of this statement.

4.1.4.  Liaison Statement on Technical Use of Domain Names

   As a result of processing requests to add names to the Special-Use
   Domain Name registry, as documented in
   [I-D.chapin-additional-reserved-tlds] and
   [I-D.grothoff-iesg-special-use-p2p-names], a review was chartered of
   the process defined in RFC 6761 for adding names to the registry (as
   explained earlier).  The Liaison Statement [SDO-IAB-ICANN-LS]
   notified ICANN of the review, affirmed that the discussion would be
   "open and transparent to participation by interested parties" and
   explicitly invited members of the ICANN community to participate.

4.2.  Secondary documents relating to the Special-Use Domain Name

   In addition to these documents, there are several others with which
   participants in this discussion should be familiar.

4.2.1.  Multicast DNS

   Multicast DNS [RFC6762] defines the Multicast DNS protocol, which
   uses the '.LOCAL' Special-Use Top-Level Domain Name.  Section 3
   describes the semantics of "multicast DNS names."  It is of
   considerable historical importance to note that the -00 version of
   this document, an individual submission, was published in July of
   2001.  This version contains substantially the same text in section
   3, and was discussed in the DNSEXT working group at IETF 51 in August
   of 2001[IETF-PRO-51].  The first version of this document designated
   '.LOCAL.ARPA' as the Special-Use Domain Name.  This idea was strongly
   opposed by DNSEXT working group participants, and as a result the
   author eventually switched to using '.LOCAL'.

   The history of RFC 6762 is documented in substantial detail in
   Appendix H of RFC 6762; some notable milestones include the initial
   proposal to replace Appletalk's NBP in July 1997, the chartering of
   the Zeroconf working group in September 1999, assignment of a
   multicast address for link-local name discovery in April of 2000.  A
   companion requirements document, eventually published as [RFC6760]
   was first published in September of 2001.

   The point of mentioning these dates is so that discussions involving
   the time when the '.LOCAL' domain was first deployed, and the context
   in which it was deployed, may be properly informed.

4.2.2.  The .onion Special-Use Top-Level Domain Name

   The .onion Special-Use Top-Level Domain Name [RFC7686] is important
   because it is the most recent IETF action on the topic of Special-Use
   Domain Names; although it does not set new policy, the mere fact of
   its publication is worth thinking about.

   Two important points to consider about this document are that:

   o  The IETF gained consensus to publish it

   o  The  Devising a resolution to the situation was somewhat forced, both constrained by at least
      two factors.  First, there was no process for allocating special-
      use domain names at the fact time that the .onion project started using
      the name, and since at the time the scope of its
      unilateral use by The Tor Project without following of the RFC 6761
      process, and because name was
      expected to be very constrained, the developers chose to allocate
      it unilaterally rather than asking the IETF or some other SDO to
      create a deadline new process.

      Second, for some time, the CA/Browser Forum [SDO-CABF] had been set by
      issuing certificates for what they referred to as "internal
      names."  Internal names are names allocated unilaterally for use
      in site-specific contexts.  Issuing certificates for such names
      came to be considered problematic, since no formal process for
      testing the CA/Browser validity of such names existed.  Consequently, CA/
      Browser Forum [SDO-CABF-INT] after which all .onion PKI decided to phase out the use of such names in
      certificates would
      expire [SDO-CABF-INT], and set a deadline after which no new certificates
      certs for such names would be issued, unless issued [SDO-CABF-DEADLINE].  Because
      the .onion name had been allocated unilaterally, it was affected
      by this policy.

      The IETF's designation of .onion as a Special-Use Top-Level Domain
      Name were was needed to be recognized by facilitate the
      IETF. development of a certificate
      issuance process specific to .onion domain names

4.2.3.  Locally Served DNS Zones

   Locally Served DNS Zones [RFC6303] describes a particular use case
   for zones that exist by definition, and that are resolved using the
   DNS protocol, but that cannot have a global meaning, because the host
   IP addresses they reference are not unique.  This applies to a
   variety of addresses, including Private IPv4 addresses [RFC1918],
   Unique Local IPv6 Unicast Addresses [RFC4193] (in which this practice
   was first described) and IANA-Reserved IPv4 Prefix for Shared Address
   Space [RFC6598].

   This use case is distinct from the use-case for Special-Use Domain
   Names like '.local' and '.onion' in that the names are resolved using
   the DNS protocol (but do require extensions or exceptions to the
   usual DNS resolution to enforce resolution in a local context rather
   than the global DNS context).  But it shares the problem that such
   names cannot be assumed either to be unique or to be functional in
   all contexts for all Internet-connected hosts.

4.2.4.  Name Collision in the DNS

   Name Collision in the DNS [SDO-ICANN-COLL] is a study commissioned by
   ICANN that attempts to characterize the potential risk to the
   Internet of adding global DNS delegations for names that were not
   previously delegated in the DNS, not reserved under any RFC, but also
   known to be (.home) or surmised to be (.corp) in significant use for
   Special-Use-type reasons (local scope DNS, or other resolution
   protocols altogether).

4.2.5.  SSAC Advisory on the Stability of the Domain Namespace

   ICANN SSAC ([SDO-ICANN-SSAC]) Advisory on the Stability of the Domain
   Namespace [SDO-ICANN-SAC090] reports on some issues surrounding the
   conflicting uses, interested parties and processes related to the
   Domain Namespace.  The document recommends the development of
   collaborative processes among the various interested parties to
   coordinate their activities related to the Domain Namespace.

4.2.6.  Discovery of the IPv6 Prefix Used for IPv6 Address Synthesis

   Discovery of the IPv6 Prefix Used for IPv6 Address Synthesis
   [RFC7050] is an example of a document that successfully used the RFC
   6761 process to designate '' as a Special-Use Domain
   Name; in this case the process worked smoothly and without

   Unfortunately, while the IETF process worked smoothly, in the sense
   that there was little controversy or delay in approving the new use,
   it did not work correctly: the name "" was never added
   to the Special-Use Domain Names registry.  This appears to have
   happened because the document did not explicitly request the addition
   of an entry for "" in the SUDN registry.  This is an
   illustration of one of the problems that we have with the 6761
   process: it is apparently fairly easy to miss the step of adding the
   name to the registry.

4.2.7.  Additional Reserved Top Level Domains

   Additional Reserved Top Level Domains
   [I-D.chapin-additional-reserved-tlds] is an example of a document
   that attempted to reserve several TLDs identified by ICANN as
   particularly at risk for collision as Special-Use Domain Names with
   no documented use.  This attempt failed.

   Although this document failed to gain consensus to publish, the need
   it was intended to fill still exists.  Unfortunately, although a fair
   amount is known about the use of these names, no RFC documents how
   they are used, and why it would be a problem to delegate them.
   Additionally, to the extent that the uses being made of these names
   are valid, no document exists indicating when it might make sense to
   use them, and when it would not make sense to use them.

   RFC 7788 [RFC7788] defines the Domain Name TLD ".home" for use as the
   default name for name resolution relative to a home network context.
   Although, as defined in RFC 7788, ".home" is a Special-Use Domain
   Name, RFC 7788 did not follow the process specified in RFC 6761: it
   did not request that ".home" be added to the IANA Special-Use Domain
   Name registry.  This was recognized as a mistake, and resulted in the
   publication of an errata, [ERRATA-4677].  Additionally, ".home" is an
   example of an attempt to reuse a Domain Name that has already been
   put into use for other purposes without following established
   processes[SDO-ICANN-COLL], which further complicates the situation.
   At the time this document was written, the IETF was developing a
   solution to this problem.

5.  History

   Newcomers to the problem of resolving Domain Names may be under the
   mistaken impression that the DNS sprang, as in the Greek legend of
   Athena, directly from Paul Mockapetris' forehead.  This is not the
   case.  At the time of the writing of the IAB technical document,
   memories would have been fresh of the evolutionary process that led
   to the DNS' dominance as a protocol for Domain Name resolution.

   In fact, in the early days of the Internet, hostnames were resolved
   using a text file, HOSTS.TXT, which was maintained by a central
   authority, the Network Information Center, and distributed to all
   hosts on the Internet using the File Transfer Protocol (FTP)
   [RFC0959].  The inefficiency of this process is cited as a reason for
   the development of the DNS [RFC0882] [RFC0883] in 1983.

   However, the transition from HOSTS.TXT to the DNS was not smooth.
   For example, Sun Microsystems's Network Information System
   [CORP-SUN-NIS], at the time known as Yellow Pages, was an active
   competitor to the DNS, although it failed to provide a complete
   solution to the global naming problem.

   Another example was NetBIOS Name Service, also known as WINS
   [RFC1002].  This protocol was used mostly by Microsoft Windows
   machines, but also by open source BSD and Linux operating systems to
   do name resolution using Microsoft's own name resolution protocol.

   Most modern operating systems can still use the '/etc/hosts' file for
   name resolution.  Many still have a name service switch that can be
   configured on the host to resolve some domains using NIS or WINS.
   Most have the capability to resolve names using mDNS by recognizing
   the special meaning of the '.local' Special-Use Top Level Domain

   The Sun Microsystems model of having private domains within a
   corporate site, while supporting the global Domain Name system for
   off-site, persisted even after the NIS protocol fell into disuse.
   Microsoft used to recommend that site administrators use a "private"
   TLD for internal use, and this practice was very much a part of the
   zeitgeist at the time (see section 5.1 of [SDO-ICANN-COLL] and
   Appendix G of [RFC6762]).  This attitude is at the root of the
   widespread practice of simply picking an unused TLD and using it for
   experimental purposes, which persists even at the time of writing of
   this memo.

   This history is being presented because discussions about Special-Use
   Domain Names in the IETF often come down to the question of why users
   of new name resolution protocols choose to use Domain Names, rather
   than using some other naming concept that doesn't overlap with the
   namespace that, in modern times is, by default, resolved using the

   The answer is that as a consequence of this long history of resolving
   Domain Names using a wide variety of name resolution systems, Domain
   Names are required in a large variety of contexts in user interfaces
   and applications programming interfaces.  Any name that appears in
   such a context is a Domain Name.  So developers of new name
   resolution systems that must work in existing contexts actually have
   no choice: they must use a Special-Use Domain Name to segregate a
   portion of the namespace for use with their system.

6.  Security Considerations

   This document mentions various security and privacy considerations in
   the text.  However, this document creates no new security or privacy

7.  IANA considerations

   This document has no actions for IANA.

8.  Contributors

   This document came about as a result of conversations that occurred
   in the conference hotel lobby, the weekend before IETF 95, when the
   original author, Ted Lemon, was trying to come up with a better
   problem statement.  Stuart Cheshire, Mark Andrews, David Conrad, Paul
   Ebersman and Aaron Falk all made helpful and insightful observations
   or patiently answered questions.  This should not be taken as an
   indication that any of these folks actually agree with what the
   document says, but their generosity with time and thought are
   appreciated in any case.

   Ralph started out as an innocent bystander, but discussion with him
   was the key motivating factor in the writing of this document, and he
   agreed to co-author it without too much arm-twisting.  Warren spent a
   lot of time working with us on this document after it was first
   published, and joined as an author in order to make sure that the
   work got finished; without him the -01 and -02 versions might not
   have happened.

   This document also owes a great deal to Ed Lewis' excellent work on
   what a "Domain Name" is [I-D.lewis-domain-names].

9.  Informative References

   [RFC0882]  Mockapetris, P., "Domain names:  RFC Editor Considerations

   The authors were unable to find dates for references
   [SDO-CABF-DEADLINE] and [SDO-CABF].  Please fix up those references
   as appropriate (and remove this section before publication).

10.  Informative References

              Sun Microsystems, "Large System and Network
              Administration", March 1990.

              Internet Architecture Board, "Errata ID: 4677 (RFC7788)",
              April 2016, <>.

              Chapin, L. and M. McFadden, "Additional Reserved Top Level
              Domains", draft-chapin-additional-reserved-tlds-02 (work
              in progress), March 2015.

              Grothoff, C., Wachs, M., hellekin, h., Appelbaum, J., and
              L. Ryge, "Special-Use Domain Names of Peer-to-Peer
              Systems", draft-grothoff-iesg-special-use-p2p-names-04
              (work in progress), January 2015.

              Lewis, E., "Domain Names, A Case for Clarifying", draft-
              lewis-domain-names-07 (work in progress), June 2017.

              Internet Engineering Task Force, "Proceedings of the 51st
              IETF", August 2001,

   [RFC0882]  Mockapetris, P., "Domain names: Concepts and facilities",
              RFC 882, DOI 10.17487/RFC0882, November 1983,

   [RFC0883]  Mockapetris, P., "Domain names: Implementation
              specification", RFC 883, DOI 10.17487/RFC0883, November
              1983, <>.

   [RFC0959]  Postel, J. and J. Reynolds, "File Transfer Protocol",
              STD 9, RFC 959, DOI 10.17487/RFC0959, October 1985,

   [RFC1002]  NetBIOS Working Group in the Defense Advanced Research
              Projects Agency, Internet Activities Board, and End-to-End
              Services Task Force, "Protocol standard for a NetBIOS
              service on a TCP/UDP transport: Detailed specifications",
              STD 19, RFC 1002, DOI 10.17487/RFC1002, March 1987,

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
              November 1987, <>.

   [RFC1918]  Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,
              and E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996,

   [RFC2352]  Vaughan, O., "A Convention For Using Legal Names as Domain
              Names", RFC 2352, DOI 10.17487/RFC2352, May 1998,

   [RFC2826]  Internet Architecture Board, "IAB Technical Comment on the
              Unique DNS Root", RFC 2826, DOI 10.17487/RFC2826, May
              2000, <>.

   [RFC2860]  Carpenter, B., Baker, F., and M. Roberts, "Memorandum of
              Understanding Concerning the Technical Work of the
              Internet Assigned Numbers Authority", RFC 2860,
              DOI 10.17487/RFC2860, June 2000,

   [RFC4193]  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
              Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,

   [RFC6303]  Andrews, M., "Locally Served DNS Zones", BCP 163,
              RFC 6303, DOI 10.17487/RFC6303, July 2011,

   [RFC6598]  Weil, J., Kuarsingh, V., Donley, C., Liljenstolpe, C., and
              M. Azinger, "IANA-Reserved IPv4 Prefix for Shared Address
              Space", BCP 153, RFC 6598, DOI 10.17487/RFC6598, April
              2012, <>.

   [RFC6760]  Cheshire, S. and M. Krochmal, "Requirements for a Protocol
              to Replace the AppleTalk Name Binding Protocol (NBP)",
              RFC 6760, DOI 10.17487/RFC6760, February 2013,

   [RFC6761]  Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
              RFC 6761, DOI 10.17487/RFC6761, February 2013,

   [RFC6762]  Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
              DOI 10.17487/RFC6762, February 2013,

   [RFC7050]  Savolainen, T., Korhonen, J., and D. Wing, "Discovery of
              the IPv6 Prefix Used for IPv6 Address Synthesis",
              RFC 7050, DOI 10.17487/RFC7050, November 2013,

   [RFC7686]  Appelbaum, J. and A. Muffett, "The ".onion" Special-Use
              Domain Name", RFC 7686, DOI 10.17487/RFC7686, October
              2015, <>.

   [RFC7719]  Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
              Terminology", RFC 7719, DOI 10.17487/RFC7719, December
              2015, <>.

   [RFC7788]  Stenberg, M., Barth, S., and P. Pfister, "Home Networking
              Control Protocol", RFC 7788, DOI 10.17487/RFC7788, April
              2016, <>.

              Chapin, L. and M. McFadden, "Additional Reserved Top Level
              Domains", draft-chapin-additional-reserved-tlds-02 (work
              in progress), March 2015.

              Grothoff, C., Wachs, M., hellekin, h., Appelbaum, J., and
              L. Ryge, "Special-Use Domain Names of Peer-to-Peer
              Systems", draft-grothoff-iesg-special-use-p2p-names-04
              (work in progress), January 2015.

              Lewis, E., "Domain Names, A Case

              CA/Browser Forum, "CA/Browser Forum", ??? ????,

              CA/Browser Forum, "Ballot 144 - Validation Rules for Clarifying", draft-
              lewis-domain-names-07 (work in progress), June 2017.
              .onion Names", February 2015,

              CA/Browser Forum, "SSL Certificates for Internal Server
              Names", ??? ????, <

              CA/Browser Forum, "Guidance on the Deprecation of Internal
              Server Names and Reserved IP Addresses", June 2012,

              Internet Architecture Board, "Liaison Statement from the
              IAB to the ICANN Board on Technical Use of Domain Names",
              September 2015, <

              Internet Assigned Numbers Authority, "Special-Use Domain
              Names registry", October 2015,

              Interisle Consulting Group, LLC, "Name Collisions in the
              DNS", August 2013,

              Internet Assigned Numbers Authority, "Special-Use Domain
              Names registry", October 2015,

              ICANN Security and Stability Advisory Committee, "SSAC
              Advisory on the Stability of the Domain Namespace",
              December 2016,

              ICANN Security and Stability Advisory Committee, "SSAC
              Advisory on the Stability of the Domain Namespace",
              December 2016, <>.

              Internet Assigned Numbers Authority, "Special-Use Domain
              Names registry", October 2015,

              Internet Assigned Numbers Authority, "Special-Use Domain
              Names registry", October 2015,

              Internet Architecture Board, "Liaison Statement from the
              IAB to the ICANN Board on Technical Use of Domain Names",
              September 2015, <

              Internet Architecture Board, "Errata ID: 4677 (RFC7788)",
              April 2016, <>.

              Sun Microsystems, "Large System and Network
              Administration", March 1990.

              Internet Engineering Task Force, "Proceedings of the 51st
              IETF", August 2001,

   [TOR]      The Tor Project, "Tor", 2017,

Appendix A.  Change Log.

   -03 to -04:

   o  Issue #72: Corrected original text to reflect that RFC 7050
      neglected to request an SUDN registry entry for "",
      but any inference about the cause for the oversight would be

   o  Issue #69: Edited Joel's suggested text.

   o  Issue #67: Minor change to Joel's suggested text.

   o  Issue #66: Edited second text update suggested by Joel and
      reverted third change back to the original text.

   o  Issue #64: Minor changes to text suggested by Joel.

   o  Issue #61: Minor edit based on authors' consensus in response to
      Joel's comment.

   o  Addressed Joel / Benoit's AD comments.  See GH issues

   -02 to -03 (in Github):

      Passes idnits except for errors resulting from a reference to an
      RFC 2119 keyword and a citation of RFC 5226 with no matching
      reference in quoted text at line 493.

      Issue #60: Add new section "6.  Summary" -- Petr Spacek

      Issue #57: Document needs an "Security Considerations" section

      Numerous editorial changes for consistency; e.g. use "Special-Use
      Domain Names" throughout.

      Issue #58: Document needs an "IANA Considerations" section

      Issue #39: Overlapping bullets in Section 3, with proposed
      restructuring -- Russ Housley

      Issue #55: Editorial improvement to Section 3 (4) -- John

      Issue #34: Separate two problems in paragraph that begins "No
      mechanism exists for adding a name to the registry...." (2 issues)
      -- Suzanne Woolf

      Issue #52: Editorial improvement to Section 3 (1) -- John

      Issue #51: Clarification in Introduction -- John Dickinson

      Issue #49: Should cite
      -- George Michaelson

      Issue #50: IETF precedence in Special-Use names registry -- Ted

      Issue #48: 4.1.2 cites sub-domains of .ARPA arguing for special
      use TLD -- George Michaelson
      Issue #47: 4.3 should be made more prominent -- George Michaelson

      Issue #43: Spell out SUDN and SUTLDN rather than use acronyms --
      Russ Housley

      Issue #41: Reword bullet in Section 3 regarding Domain Name TLDs
      that have been commandeered, as reported in SDO-ICANN-COLL -- Russ

      Issue #40: Note that time to publish spec for .local included
      inventing SUDN registry -- Russ Housley

      Issue #37: Title should be "Special-Use Domain Names Problem
      Statement" -- Russ Housley

      Issue #36: Expand on desire for Special-Use names to be human-
      readable -- Suzanne Woolf

      Issue #35: Clarify "No process exists [...]" to include both IETF
      process and other process -- Suzanne Woolf

      Issue #31: Add justification for concern about IETF's ability to
      assign names for technical use -- Suzanne Woolf

      Issue #12: Add DNSSEC to text -- John Levine

      Issue #6: Without a process, we just have chaos -- Stuart Cheshire

      Issue #32: Have assignments through RFC 6761 really had "technical
      mistakes"? -- Suzanne Wolff

      Issue #29: Add a reason to bypass external process: expectation
      for use of new name to be restricted to local scope -- Suzanne
      Issue #27: Is "technical use" really ambiguous; too inclusive for
      some people and too limited for others -- Suzanne Wolff

      Issue #24: Replacement for "commandeer" (2 issues)-- Suzanne Wolff

      Issue #22: Clarify importance of the "root of the Domain
      Namespace" -- Suzanne Wolff

      Issue #21: Section 3 - clarify paragraphs 2 and 3 -- Suzanne Wolff

      Issue #20: Section 3: Clarify sentences beginning "Solutions to
      these problems..." -- Suzanne Wolff

      Issue #19: Define "default" or "assumed" use of domain names to be
      within DNS -- Suzanne Wolff

      Issue #18: Cite definition of RFC 7719 and domain names draft in
      definition of "domain name" -- Suzanne Wolff

      Issue #45: Correct usages of Tor Browser and Tor -- Russ Housley

      Issue #46: Reformat citation of RFC 2860 -- Russ Housley

      Issue #44: Clean up reference to SDO-ICANN-DAG in first bullet in
      section 3 -- Russ Housley (

      Issue #42: Add reference to SDO-ICANN-SAC090 in section 4.2.5 --
      Russ Housley (

      Issue #30: Leaked queries aren't an operational problem in
      practice -- Suzanne Wolf (

      Address some of the simpler issues, including:

      Issue #13: Spelling of Tor -- Jeremy Rand
      Issue #14: Change SDO to "organizations" -- Suzanne Woolf

      Issue #16: Match number of "policies" and "that policy" -- Suzanne

      Issue #17: Clarify sentence beginning with "In support of the
      particular set of problems described here...." -- Suzanne.

      Issue #23: Match number of "names" and "a TLD" -- Suzanne.

   -01 to -02:

      Language cleanup from Ted.

   -00 to -01:

      Improved the terminology.

      Included reference to SAC090.

      Added ICANN Reserved Names (e.g .icann, .iesg, .arin) to types of

      Improved background.

      Noted that semantics may differ between resolution contexts.

      Pointer to .home / .corp / .mail, other "toxic" names

      Readability fixes.

   -04 to ietf-00

      Document adopted by WG.

      Significant changes from CfA integrated, please refer to diff.

   -03 to -04:

   o  Replaced 'Internet Names' with 'Domain Names' - suggestion by John

   -02 to -03:

   o  Readability fixes, small grammar updates.

   -01 to -02:

   o  Cleaned up the abstract.

   o  Fixed the case of Internet

   o  Reference to Ed Lewis' "Domain Names"

   o  Fleshed out the problems, primarily the coordination, collisions

   -00 to -01:

   o  Large refactoring, basically a rewrite.  Incorporated comments,
      removed a bunch of unneeded text, etc.

Authors' Addresses

   Ted Lemon
   Nominum, Inc.
   800 Bridge Parkway
   Redwood City, California  94065
   United States of America

   Phone: +1 650 381 6000

   Ralph Droms


   Warren Kumari
   1600 Amphitheatre Parkway
   Mountain View, CA  94043