Internet Engineering Task Force (IETF) T. Lemon
Request for Comments: 8244 Nominum, Inc.
Category: Informational R. Droms
ISSN: 2070-1721
W. Kumari
Google
October 2017
Special-Use Domain Names Problem Statement
Abstract
The policy defined in RFC 6761 for IANA registrations in the
"Special-Use Domain Names" registry has been shown, through
experience, to present challenges that were not anticipated when RFC
6761 was written. This memo presents a list, intended to be
comprehensive, of the problems that have since 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.
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.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
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). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see 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/rfc8244.
Lemon, et al. Informational [Page 1]RFC 8244 Special-Use Domain Names Problem October 2017
Copyright Notice
Copyright (c) 2017 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
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Problems Associated with Special-Use Domain Names . . . . . . 4
4. Existing Practice regarding Special-Use Domain Names . . . . 10
4.1. Primary Special-Use Domain Name Documents . . . . . . . . 10
4.1.1. IAB Technical Comment on the Unique DNS Root . . . . 10
4.1.2. Special-Use Domain Names . . . . . . . . . . . . . . 12
4.1.3. MoU Concerning the Technical Work of IANA . . . . . . 13
4.1.4. Liaison Statement on Technical Use of Domain Names . 14
4.1.5. IAB Statement on the Registration of Special Use
Names in the ARPA Domain . . . . . . . . . . . . . . 15
4.2. Secondary Documents Relating to the Special-Use Domain
Name Question . . . . . . . . . . . . . . . . . . . . . . 15
4.2.1. Multicast DNS . . . . . . . . . . . . . . . . . . . . 15
4.2.2. The '.onion' Special-Use Top-Level Domain Name . . . 16
4.2.3. Locally Served DNS Zones . . . . . . . . . . . . . . 16
4.2.4. Name Collision in the DNS . . . . . . . . . . . . . . 17
4.2.5. SSAC Advisory on the Stability of the Domain
Namespace . . . . . . . . . . . . . . . . . . . . . . 17
4.2.6. Discovery of the IPv6 Prefix Used for IPv6 Address
Synthesis . . . . . . . . . . . . . . . . . . . . . . 17
4.2.7. Additional Reserved Top-Level Domains . . . . . . . . 18
5. History . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
6. Security Considerations . . . . . . . . . . . . . . . . . . . 20
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
8. Informative References . . . . . . . . . . . . . . . . . . . 20
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25
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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 not to 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
[DOMAIN-NAMES].
"Special-Use Domain Names" [RFC6761] created the "Special-Use Domain
Names" IANA registry [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 process defined in RFC 6761 can be improved, or
whether it should be deprecated. The IETF DNSOP 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
Namespace:
o Names reserved by the IETF for technical purposes
o Names 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 "Reserved Names" and "Treatment of Country or Territory
Names" (Sections 2.2.1.2.1 and 2.2.1.4.1, respectively) of
[SDO-ICANN-DAG]).
o Names used by other organizations without following established
processes
o Names that are unused and are available for assignment to one of
the previous categories
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This document presents a list, derived from a variety of sources,
including discussion in the IETF DNSOP Working Group, of the problems
associated with the assignment of Special-Use Domain Names. The list
is intended to be an unfiltered compilation of issues. 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 trade-offs, are
out of scope for this document and 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.
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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. This document only
enumerates the problems, provides the reader with context for
thinking about them, and provides a context for future discussion of
solutions, regardless of whether such solutions may work for IETF,
ICANN, IANA, or some other group.
The list of problems is not presented in order of importance; numbers
are assigned so that each problem can easily be referenced by number,
not to indicate priority. The list of problems is as follows:
1. Although the IETF and ICANN 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].
2. There is no explicit scoping as to what can constitute a
"technical use" [RFC2860] and what cannot; there is also no
consensus within the IETF as to what this term means.
3. Not all developers of protocols on the Internet agree that
authority over the entire Domain Namespace should reside solely
with the IETF and ICANN.
4. Although the 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.
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5. Organizations do in fact sometimes use subsets of the Domain
Namespace without following established processes. Reasons a
third party might do this include:
1. Lack of knowledge that a process exists for assigning such
names.
2. Intended use is covered by the gTLD process [SDO-ICANN-DAG],
but no gTLD process is ongoing.
3. Intended use is covered by the gTLD process, but the third
party doesn't want to pay a fee.
4. Intended use is covered by some IETF process, but the third
party doesn't want to follow the process.
5. Intended use is covered by an ICANN or IETF process, but the
third party expects that the outcome will be refusal or non-
action.
6. Lack of knowledge that a name intended to be used only
locally may nevertheless leak.
7. Lack of knowledge that a name used locally with informal
allocation may subsequently be allocated formally, creating
operational problems.
6. 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.
7. 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.
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8. Some protocol developers have assumed that they could not
succeed in getting a name assigned through the IETF using the
process defined in RFC 6761. This is because when the IETF has
attempted to follow the process defined in RFC 6761, it has been
slow and uncertain. For example, the process of assigning the
first new name ('.local') using the process defined in RFC 6761
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.
9. There is strong resistance within the IETF to assigning domain
names to resolution systems outside of the DNS, for a variety of
reasons:
1. It requires a mechanism for identifying which set of
resolution processes is required in order to resolve a
particular name.
2. Assertion of authority: there is a sense that the Domain
Namespace is "owned" by the IETF or by ICANN, so, if a name
is claimed without following their processes, the person or
entity that claimed that name should suffer some consequence
that would, presumably, deter future circumvention of the
official processes.
3. More than one name resolution protocol is bad, in the sense
that a single protocol is less complicated to implement and
deploy.
4. The semantics of alternative resolution protocols may differ
from the DNS protocol; DNS has the concept of RRtypes,
whereas other protocols may not support RRtypes or may
support some entirely different data structuring mechanism.
5. 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.
6. A name might be assigned for a particular purpose when a
more general use of the name would be more beneficial.
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7. If the IETF assigns a name that some third party or parties
believe belongs to them in some way, the IETF could become
embroiled in an expensive dispute with those parties.
10. 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.
11. In some cases where the IETF has made assignments through the
process defined in RFC 6761, 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 process in RFC
6761 (see [RFC7050] and [RFC7788]).
12. There are several Top-Level Domain Names 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].
13. In principle, the process defined in RFC 6761 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" [RESERVED-TLDS] and
Section 4.2.7 of this document). 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.
14. A domain name can be identified as either a DNS name by placing
it in the DNS zone(s) or 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.
15. In some cases, the IETF may see the need to document that a name
is in use without claiming that the use of the name is the
IETF's particular use of the name. No mechanism exists in the
current registry to mark names in this way.
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16. During any of the review stages of a document, there is no
formal process in which a check is made to ensure that the
document does not unintentionally violate the IETF process for
adding Special-Use Domain Names to the registry, as was the
case, for example, in RFC 7788 [RFC7788].
17. Use of the registry is inconsistent -- some Special-Use Domain
Name RFCs specifically add registry entries, some don't; some
specify how and whether special-use name delegations should be
done, some don't.
18. There exists no safe, non-process-violating mechanism for ad hoc
assignment of Special-Use Domain Names.
19. 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 domain name is never
visible to a user.
20. 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.
21. 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:
1. What class of Special-Use Domain Name is under
consideration: non-DNS, locally served zone, or other?
2. 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.
3. A process would be required through which the IETF can cause
a delegation in the root zone to be instantiated.
4. What are the recommended practices for using DNS with the
specific Special-Use Domain Name?
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The above list represents the current understanding of the authors 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 related to 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 handling.
The assignment of Internet Names is not under the sole control of any
one organization. The IETF has authority in some cases, but only
with respect to "technical uses". At present, ICANN 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 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.
4.1.1. IAB Technical Comment on the Unique DNS Root
[RFC2826] is not an IETF consensus document, and it 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:
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RFC 8244 Special-Use Domain Names Problem October 2017
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 they
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. Therefore, users may 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
[SDO-ICANN-COLL]).
o While such a reference in the user's context refers to the object
the user wishes to share, when the reference is used in a
different context, it could refer either to some different object
in the recipient's context or to no object at all. 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.
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 that 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.
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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 provides the process whereby "Multicast DNS" [RFC6762]
designated '.local' as a Special-Use Domain Name and included it in
the "Special-Use Domain Names" registry. RFC 6761 also enumerates a
set of names that were previously used or defined to have special
uses prior to its publication. 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 registry.
Several important points to think about with respect to RFC 6761 are:
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).
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o A Special-Use Domain Name may be a name that is resolved using the
DNS protocol and that requires no special handling in the stub
resolver but that requires special handling in the recursive
resolver. An example of this would be '10.in-addr.arpa.'.
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.
In this case, the term "stub resolver" 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; however, 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 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 "Special-
Use Domain Names" registry [SDO-IANA-SUDR] either are intended to be
resolved using the DNS protocol, are TLDs, or are both. That is, at
present there exist no Special-Use Domain Names that 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 resolver encounters the special label,
'local' as the rightmost label of a domain name, it can only use the
Multicast DNS (mDNS) protocol to resolve that domain name.
4.1.3. MoU Concerning the Technical Work of IANA
There exists a Memorandum of Understanding (MoU) [RFC2860] between
the IETF and ICANN that discusses how names and numbers will be
managed through IANA. This document is important to the discussion
of Special-Use Domain Names because, while it delegates authority for
managing the DNS Namespace generally to ICANN, it reserves to the
IETF the authority that is then formalized in RFC 6761. RFC 2860
specifically states:
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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.
The assignment of names in the DNS root zone, and the management of
the Domain Namespace, is by default 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
When the IETF received processing requests to add names to the
"Special-Use Domain Names" registry, as documented in [RESERVED-TLDS]
and [P2P-DOMAIN-NAMES], the IETF chartered a review of the process
defined in RFC 6761 for adding names to the registry (as explained
earlier). The IETF sent a liaison statement [SDO-IAB-ICANN-LS] to
ICANN to notify them of the review, affirm that the discussion would
be "open and transparent to participation by interested parties", and
explicitly invite members of the ICANN community to participate.
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4.1.5. IAB Statement on the Registration of Special Use Names in the
ARPA Domain
As part of the process of resolving the controversy mentioned in
Section 4.2.7, the IAB issued a statement saying, in part:
There is currently no process defined with ICANN for special use
names to be delegated in the root zone; it has seemed likely to take
significant effort to create one. The IAB has noted that .arpa can
be used "for technical infrastructure established by IETF standards"
[SDO-IAB-SUDN-REG].
Given the lack of an established process with ICANN, IETF documents
cannot reserve names in the root of the DNS namespace if those names
are to be delegated (that is, used by the DNS protocol). It would be
possible to work with ICANN to develop a process for such
delegations, but the success of that joint work, and the amount of
time it would take, would still be uncertain.
4.2. Secondary Documents Relating to the Special-Use Domain Name
Question
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
the document that eventually became RFC 6762, an individual
submission, was published in July of 2001. The version posted at
that time contains substantially the same text in Section 3 as RFC
6762 did when published and was discussed in the DNSEXT Working Group
at IETF 51 in August of 2001 [IETF-PRO-51]. The July 2001 draft
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 Name Binding Protocol (NBP) in July
1997, the chartering of the Zeroconf Working Group in September 1999,
and the 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.
Lemon, et al. Informational [Page 15]RFC 8244 Special-Use Domain Names Problem October 2017
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 a 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 Devising a resolution to the situation was constrained by at least
two factors. First, there was no process for allocating Special-
Use Domain Names at the time that the '.onion' project started
using the name; at the time, and since the scope of use of the
name was expected to be very constrained, the developers chose to
allocate it unilaterally rather than asking the IETF or some other
Standards Development Organization (SDO) to create a new process.
Second, for some time, the CA/Browser Forum [SDO-CABF] had been
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 validity of such names existed. Consequently, the CA/
Browser Forum decided to phase out the use of such names in
certificates [SDO-CABF-INT] and set a deadline after which no new
certificates for such names would be issued [SDO-CABF-DEADLINE].
Because the '.onion' domain was allocated unilaterally, this would
mean that certificates for subdomains of '.onion' could no longer
be issued.
The IETF's designation of '.onion' as a Special-Use Top-Level
Domain Name was needed to facilitate the development of a
certificate issuance process specific to '.onion' domain names
[SDO-CABF-BALLOT144].
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],
Lemon, et al. Informational [Page 16]RFC 8244 Special-Use Domain Names Problem October 2017
"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 they do require extensions or exceptions to the
usual DNS resolution to enforce resolution in a local context rather
than the global DNS context). It shares the problem that such names
can be assumed neither to be unique across all contexts nor
functional for all Internet-connected hosts.
4.2.4. Name Collision in the DNS
"Name Collision in the DNS" [SDO-ICANN-COLL] is a study that was
commissioned by ICANN in an attempt to characterize the potential
risk to the Internet of adding global DNS delegations for names that
were not previously delegated in the DNS and were not reserved under
any RFC, but were also known to be (in the case of '.home') or
surmised to be (in the case of '.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
The ICANN Security and Stability Advisory Committee (SSAC)
[SDO-ICANN-SSAC] specification "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 specification 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
process in RFC 6761 to designate '.ipv4only.arpa' as a Special-Use
Domain Name; in this case, the process worked smoothly and without
controversy.
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 'ipv4only.arpa' 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 'ipv4only.arpa' in the "Special-Use Domain Names"
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RFC 8244 Special-Use Domain Names Problem October 2017
registry. This is an illustration of one of the problems that we
have with the process in RFC 6761: 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" [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 the aforementioned document failed to gain consensus to be
published, the need it was intended to fill still exists.
Unfortunately, although a fair amount is known about the use of these
names, no RFC exists that describes 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 Top-Level Domain Name '.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 "Special-Use
Domain Names" registry. This was recognized as a mistake and
resulted in the posting of an errata report [Err4677]. 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 RFC 8244 was written, the IETF was developing
a solution to this problem.
5. History
A newcomer to the problem of resolving domain names may be under the
impression that the DNS sprang fully formed directly from Paul
Mockapetris' head (as was the birth of Athena in Greek Mythology).
This is not the case. At the time the IAB technical document was
written [RFC2826], memories would have been fresh of the evolutionary
process that led to 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)
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RFC 8244 Special-Use Domain Names Problem October 2017
[RFC959]. The inefficiency of this process is cited as a reason for
the development of the DNS [RFC882] [RFC883] in 1983.
However, the transition from HOSTS.TXT to the DNS was not smooth.
For example, Sun Microsystems' Network Information System (NIS)
[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 the 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
Name.
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 apparently 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
DNS.
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.
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RFC 8244 Special-Use Domain Names Problem October 2017
6. Security Considerations
This document mentions various security and privacy considerations in
the text. However, this document creates no new security or privacy
concerns.
7. IANA Considerations
This document does not require any IANA actions.
8. Informative References
[CORP-SUN-NIS]
Wikipedia, "Network Information Service", August 2017,
<https://en.wikipedia.org/wiki/
Network_Information_Service>.
[DOMAIN-NAMES]
Lewis, E., "Domain Names, A Case for Clarifying", Work in
Progress, draft-lewis-domain-names-09, August 2017.
[Err4677] RFC Errata, "Erratum ID 4677", RFC 7788,
<https://www.rfc-editor.org/errata/eid4677>.
[IETF-PRO-51]
IETF, "Proceedings of the 51st IETF Meeting", August 2001,
<http://www.ietf.org/proceedings/51/51-45.htm#TopOfPage>.
[P2P-DOMAIN-NAMES]
Grothoff, C., Wachs, M., Wolf, H., Ed., Appelbaum, J., and
L. Ryge, "Special-Use Domain Names of Peer-to-Peer
Systems", Work in Progress, draft-grothoff-iesg-special-
use-p2p-names-04, January 2015.
[PROBLEM-SPECIAL-NAMES]
Huston, G., Koch, P., Durand, A., and W. Kumari, "Problem
Statement for the Reservation of Special-Use Domain Names
using RFC6761", Work in Progress, draft-adpkja-dnsop-
special-names-problem-06, September 2016.
[RESERVED-TLDS]
Chapin, L. and M. McFadden, "Additional Reserved Top Level
Domains", Work in Progress, draft-chapin-additional-
reserved-tlds-02, March 2015.
Lemon, et al. Informational [Page 20]RFC 8244 Special-Use Domain Names Problem October 2017
[RFC882] Mockapetris, P., "Domain names: Concepts and facilities",
RFC 882, DOI 10.17487/RFC0882, November 1983,
<https://www.rfc-editor.org/info/rfc882>.
[RFC883] Mockapetris, P., "Domain names: Implementation
specification", RFC 883, DOI 10.17487/RFC0883, November
1983, <https://www.rfc-editor.org/info/rfc883>.
[RFC959] Postel, J. and J. Reynolds, "File Transfer Protocol",
STD 9, RFC 959, DOI 10.17487/RFC0959, October 1985,
<https://www.rfc-editor.org/info/rfc959>.
[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,
<https://www.rfc-editor.org/info/rfc1002>.
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/info/rfc1034>.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[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,
<https://www.rfc-editor.org/info/rfc1918>.
[RFC2352] Vaughan, O., "A Convention For Using Legal Names as Domain
Names", RFC 2352, DOI 10.17487/RFC2352, May 1998,
<https://www.rfc-editor.org/info/rfc2352>.
[RFC2826] Internet Architecture Board, "IAB Technical Comment on the
Unique DNS Root", RFC 2826, DOI 10.17487/RFC2826, May
2000, <https://www.rfc-editor.org/info/rfc2826>.
[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,
<https://www.rfc-editor.org/info/rfc2860>.
Lemon, et al. Informational [Page 21]RFC 8244 Special-Use Domain Names Problem October 2017
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,
<https://www.rfc-editor.org/info/rfc4193>.
[RFC6303] Andrews, M., "Locally Served DNS Zones", BCP 163,
RFC 6303, DOI 10.17487/RFC6303, July 2011,
<https://www.rfc-editor.org/info/rfc6303>.
[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, <https://www.rfc-editor.org/info/rfc6598>.
[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,
<https://www.rfc-editor.org/info/rfc6760>.
[RFC6761] Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
RFC 6761, DOI 10.17487/RFC6761, February 2013,
<https://www.rfc-editor.org/info/rfc6761>.
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
DOI 10.17487/RFC6762, February 2013,
<https://www.rfc-editor.org/info/rfc6762>.
[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,
<https://www.rfc-editor.org/info/rfc7050>.
[RFC7686] Appelbaum, J. and A. Muffett, "The ".onion" Special-Use
Domain Name", RFC 7686, DOI 10.17487/RFC7686, October
2015, <https://www.rfc-editor.org/info/rfc7686>.
[RFC7719] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", RFC 7719, DOI 10.17487/RFC7719, December
2015, <https://www.rfc-editor.org/info/rfc7719>.
[RFC7788] Stenberg, M., Barth, S., and P. Pfister, "Home Networking
Control Protocol", RFC 7788, DOI 10.17487/RFC7788, April
2016, <https://www.rfc-editor.org/info/rfc7788>.
[SDO-CABF] CA/Browser Forum, "CA/Browser Forum Home Page",
<https://cabforum.org>.
Lemon, et al. Informational [Page 22]RFC 8244 Special-Use Domain Names Problem October 2017
[SDO-CABF-BALLOT144]
CA/Browser Forum, "Ballot 144 - Validation Rules for
.onion Names", February 2015, <https://cabforum.org/2015/
02/18/ballot-144-validation-rules-dot-onion-names>.
[SDO-CABF-DEADLINE]
CA/Browser Forum, "SSL Certificates for Internal Server
Names", January 2013,
<https://www.digicert.com/internal-names.htm>.
[SDO-CABF-INT]
CA/Browser Forum, "Guidance on the Deprecation of Internal
Server Names and Reserved IP Addresses", June 2012,
<https://cabforum.org/internal-names/>.
[SDO-IAB-ICANN-LS]
IETF, "Liaison Statement from the IAB to the ICANN Board
on Technical Use of Domain Names", September 2014,
<https://datatracker.ietf.org/liaison/1351>.
[SDO-IAB-SUDN-REG]
IAB, "Internet Architecture Board statement on the
registration of special use names in the ARPA domain",
March 2017, <https://www.iab.org/documents/
correspondence-reports-documents/2017-2/iab-statement-on-
the-registration-of-special-use-names-in-the-arpa-
domain/>.
[SDO-IANA-SUDR]
IANA, "Special-Use Domain Names", <http://www.iana.org/
assignments/special-use-domain-names>.
[SDO-ICANN-COLL]
Interisle Consulting Group, LLC, "Name Collision in the
DNS", Version 1.5, August 2013, <https://www.icann.org/
en/system/files/files/name-collision-02aug13-en.pdf>.
[SDO-ICANN-DAG]
ICANN, "gTLD Applicant Guidebook", Version 2012-06-04,
June 2012, <https://newgtlds.icann.org/en/applicants/agb/
guidebook-full-04jun12-en.pdf>.
[SDO-ICANN-SAC090]
ICANN Security and Stability Advisory Committee, "SSAC
Advisory on the Stability of the Domain Namespace",
ICANN SAC090, December 2016, <https://www.icann.org/en/
system/files/files/sac-090-en.pdf>.
Lemon, et al. Informational [Page 23]RFC 8244 Special-Use Domain Names Problem October 2017
[SDO-ICANN-SSAC]
ICANN, "Security and Stability Advisory Committee (SSAC)",
December 2016, <https://www.icann.org/groups/ssac>.
[TOR] Tor, "Tor - Anonymity Online",
<https://www.torproject.org>.
Contributors
Mark Andrews, Stuart Cheshire, David Conrad, Paul Ebersman, Aaron
Falk, and Suzanne Woolf 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.
Stephane Bortzmeyer, John Dickinson, Bob Harold, Paul Hoffman, Russ
Housley, Joel Jaeggli, Andrew McConachie, George Michaelson, Petr
Spacek, and others provided significant review and/or useful
comments.
This document also owes a great deal to Ed Lewis' excellent work on
what a "domain name" is [DOMAIN-NAMES].
We would also like to acknowledge the authors of
[PROBLEM-SPECIAL-NAMES], including Alain Durand, Geoff Huston, Peter
Koch, and Joe Abley, for their efforts to frame the issues and engage
the working group, as well as their contributions to the list of
issues from their document [PROBLEM-SPECIAL-NAMES].
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Authors' Addresses
Ted Lemon
Nominum, Inc.
800 Bridge Parkway
Redwood City, CA 94065
United States of America
Phone: +1 650 381 6000
Email: ted.lemon@nominum.com
Ralph Droms
Email: rdroms.ietf@gmail.com
Warren Kumari
Google
1600 Amphitheatre Parkway
Mountain View, CA 94043
United States of America
Email: warren@kumari.net
Lemon, et al. Informational [Page 25]
