Independent Submission                                          E. Lewis
Internet-Draft                                                     ICANN
Expires: March 16, 2017                         Date: September 16, 2016
Intended Status: unknown

                               Domain Names


This document researches the origin of the term Domain Name in the
Request for Comments document series, documenting that the term did
not originate in the documents defining the Domain Name System.  The
document describes how the term came to be used, how the DNS followed,
and surveys the diverse ways Domain Names have been interpreted within
various protocols over time.  The purpose of this is to give a solid
foundation for work on Domain Names across all protocols making use of
Domain Names.

Status of This Memo

This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.

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time.  It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."

This Internet-Draft will expire on March 16, 2017.

Copyright Notice

Copyright (c) 2016 IETF Trust and the persons identified as the
document authors.  All rights reserved.

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Provisions Relating to IETF Documents
( in effect on the date of
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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 . . . . . . . . . . . . . . . . . . . . . . . . .  1
2. Emergence of Domain Names  . . . . . . . . . . . . . . . . . .  1
3. Dialects, so to speak, of Domain Names . . . . . . . . . . . .  1
4. Interoperability Considerations  . . . . . . . . . . . . . . .  1
5. Defintion(s) of Domain Names . . . . . . . . . . . . . . . . .  1
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  1
7. IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  1
8. Security Considerations  . . . . . . . . . . . . . . . . . . .  1
9. References . . . . . . . . . . . . . . . . . . . . . . . . . .  1
10. Author's Address  . . . . . . . . . . . . . . . . . . . . . .  1


The closest mailing list to this topic is  Or maybe  Private comments may also be directed at the editor.

This section (and sub-sections) **probably** should be removed
prior to publication.

Note on changes from earlier edition:

Minor edits plus the re-introduction of definition(s) of Domain Names.
The re-introduction of the definitions comes from discussions held
at IETF 96, if just to put the words back in a document.  Whether
the scope of this document is to include them in a final version is
not clear.

1. Introduction

What is the motivation behind the document and what is the anticipated

1.1 Motivation for this Document

Why bother to define Domain Names now, three decades after the
earliest mentions in RFC documents?  There are many examples of
names as identifiers in existence, a lot of running code.  There is
a large industry built on management of names as well, a lot of
financial investment made.  Would not a definition appearing now be
merely an academic exercise or worse, a disruption to what seems to
be a reliable system?

A desire to examine this topic is a reaction to the discussion
related to the Special Use Domain Name Registry as described in
"Special Use Domain Names" [RFC 6761] and the process of adding
"ONION" to that registry, as described in "The '.onion' Special-Use
Domain Name" [RFC 7686].  Concerns raised on a mailing list used to
discuss the latter RFC included specific criterial to declare a name
as special as well as the conflict with other processes, such as the
process launched from "Memorandum of Understanding Concerning the
Technical Work of the Internet Assigned Numbers Authority" [RFC 2860],
for registering a name in the DNS.

During reviews of this document, documented studies of other
difficulties have surfaced.  "IAB Thoughts on Encodings for
Internationalized Domain Names" [RFC 6055] documents issues related to
converting human-readable forms of Domain Names in forms useful to
automated applications when there is no clear architecture or precise
definition of how to handle Domain Names. "Issues in Identifier
Comparison for Security Purposes" [RFC 6943] documents issues related
to the same conversion as related to evaluating security policies.  The
presence of these studies suggest a need to examine the architecture
of naming and identifiers.

The beneficiaries of such work include both the developers of software
that makes use of names and identifiers.  A single piece of code could
be used in different naming environments if the code can determine how
to process a name.  With code reusable across different environments,
another benefit are innovators exploring new means of identifying

1.2 Goal

The work ahead has the ingredients of a "clarification" - a loose
or poorly worded initial definition, multiple diverse valid
interpretations in use, and a need to converge on a more precise
definition which may cause some issues with backwards compatibility.
This document sets out to establish that a clarification is warranted.

1.3 Background

Two or three decades into the history of Domain Names, a popular
notion has taken hold that Domains Names were defined and specified
in the definition of the Domain Name System (DNS).  There are two
documents that form the basic definition of the DNS, "Domain names -
concepts and facilities" and "Domain names - implementation and
specification" referred to as RFC 1034 and RFC 1035, respectively.
(Note that there is another pair of Request for Comments documents
with the same titles that precede RFC 1034 and RFC 1035, those were
declared obsolete in favor of the newer documents.) Together RFC 1034
and RFC 1035 form STD 13, a full standard cataloged by the RFC Editor.
The definitions of DNS domain names within RFC 1034 and RFC 1035 have
become the apparently-authoritative source for discussions on what is
a Domain Name.

Throughout this document the term "Domain Names" is capitalized to
emphasize the concept of the names and DNS is used to describe the
protocol and algorithms described in STD 13, including any applicable
updates, related standards track documents and experimental track

The term domain is a generic term.  And there are many naming
systems in existence.  The use of the term Domain Names in this
document refers to the roughly-defined set of protocols and their
applications' use of a naming structure that is prevalent amongst
many protocols defined in IETF RFC documents.

The truth is, STD 13 does not define Domain Names, the documents define
only how Domain Names are used and processed in the DNS.  However the
way in which the RFC documents read seem to lend to the confusion.

RFC 1034, section 2 begins with this text:

"This RFC introduces domain style names, their use for Internet mail
and host address support, and the protocols and servers used to
implement domain name facilities."

Which seems to indicate that RFC 1034 is the origin of Domain Names.
Immediately following is section 2.1, entitled "The history of domain
names" which includes the following text.

"The result was several ideas about name spaces and their management
[IEN-116, RFC-799, RFC-819, RFC-830].  The proposals varied, but a
common thread was the idea of a hierarchical name space, with the
hierarchy roughly corresponding to organizational structure, and names
using "."  as the character to mark the boundary between hierarchy
levels.  A design using a distributed database and generalized
resources was described in [RFC-882, RFC-883].  Based on experience
with several implementations, the system evolved into the scheme
described in this memo."

The DNS as it is known today did not invent Domain Names (work on the
Simple Mail Transfer Protocol did) and, for what it's worth, wasn't
the first attempt at an Internet naming system (described in RFC 819
"The Domain Naming Convention for Internet User Applications").

One important phrase to keep in mind is:

"To simplify implementations,"

which appears in both RFC 1034 and RFC 1035 as well as their
predecessors RFC 882 and RFC 883.  This gives credence to the notion
that Domain Names exist beyond the DNS.

2. Emergence of Domain Names

Domain Names emerged from the need to build a hierarchy around the
growing number of identified hosts exchanging email.  RFC 788, "SIMPLE
MAIL TRANSFER PROTOCOL", explains, in its section 3.7:

"At some not too distant future time it might be necessary to
expand the mailbox format to include a region or name domain
identifier.  There is quite a bit of discussion on this at
present, and is likely that SMTP will be revised in the future to
take into account naming domains."

Knowing the origins of a concept helps setting the correct boundaries
for discussion.  The past isn't meant to restrict the future but
meant to help provide a context, include forgotten ideas, and help
identify rational for scope creep.

RFC 799 "Internet Name Domains" has (arguably) the first formation of
what is a Domain Name:

"In its most general form, a standard internet mailbox name has
the syntax

                  <user>.<host>@<domain> ,

where <user> is the name of a user known at the host <host> in the
name domain <domain>."

Prior to this, domain referred to principally an administrative
domain, such as the initial organizations involved in networks at the

RFC 801 "NCP/TCP TRANSITION PLAN" contains this, indicating the
passage from the host tables:

"It might be advantageous to do away with the host name table and
use a Name Server instead, or to keep a relatively small table as
a cache of recently used host names."

RFC 805 "Computer Mail Meeting Notes" contains this:

"The conclusion in this area was that the current "user@host" mailbox
identifier should be extended to 'user@host.domain' where 'domain'
could be a hierarchy of domains."

RFC 819 "The Domain Naming Convention for Internet User Applications"
contains this:

"A decision has recently been reached to
replace the simple name field, "<host>", by a composite name field,
'<domain>' "

A domain name began to take on its current form:

"Internet Convention:  Fred@F.ISI.ARPA"

In addition, "simple name" is defined as what we now call a label, and
a "complete (fully qualified) name" is defined as "concatenation of
the simple names of the domain structure tree nodes starting with its
own name and ending with the top level node name".  Noticeably
absent is a terminating dot or any mention or representation of a

RFC 819 defines ARPA as a top-level name (as opposed to top-level
domain name).  This is an early mention of the role of top-level

This walk through history relies solely on the record left behind
inside RFCs.  The precise chain of events is likely slightly
different and nuanced.  The point of the exercise is to show that
Domain Names are a concept the emerged over time, spawned the DNS
with its domain names, a definition of host names derived from the
host tables, and was heavily influenced by SMTP as the driving
application.  The definition of the FTP protocol, originally defined
in RFC 959 "FILE TRANSFER PROTOCOL", never mentions hosts, domains or
host names.  But no formal definition of Domain Names has been
written and recorded.

3. Dialects, so to speak, of Domain Names

Subtypes of Domain Names have come to be defined for different
protocols, evolving and sometimes building on previous definitions.

3.1 Domain Names as Restricted for DNS

The DNS protocol place size restrictions on Domain Names and defines
rules for matching domain names, treating sets of Domain Names as
equivalent to each other.  (This matching refers to treating upper
case and lower case ASCII letters as equivalent.)  The DNS defines
the format used to transmit the names across the network as well as
rules for displaying them inside text zone files.  The DNS creates
the notion that names are assigned by an authority per zone.

Placing size restrictions on Domain Names is significant in reducing
the overall population of names that can be represented in the DNS.
The matching rules have the effect of creating (to use a term from
graph theory) cliques, distorting the tree-nature of the Domain Name
graph.  A clique is a completely connected sub-graph implying cyclic
paths, a tree is a graph that is acyclic.  In sum, the treatment of
ASCII (and only ASCII) cases as equivalent is a distortion of the
Domain Name hierarchy.

DNS defines two formats for domain names.  One is the "on-the-wire"
format used inside messages, a flags-and-length octet followed by
some count of octets for each label with the final length of 0
representing the root.  The other is a version that can be rendered
in printable ASCII characters, complete with a means to represent
other characters via an escape sequence.  This does not alter the
Domain Name concept but has implications when it comes to
interoperating with other protocol definitions of their domain name

DNS assumes that there is, in concept, a central authority creating
names within the DNS management structure (called a zone).  Although
the DNS does not define how a central authority is implemented nor
how it coins names, the names have to come from a single point to
appear in a zone.  There are other means for claiming names, an
example will be mentioned later.

DNS domain names could appear to be the same as address literals, such
as "" or "0:0:0:0:0:FFFF::".  Such DNS domain
names are not used for two reasons.  Applications expecting a
Domain Name (as a comment line parameter as an example) would
opt to treat the string as an address literal and would therefore
not look for the string in the DNS domain name space.  The management
model of the DNS would prefer to aggregate (as in routing) addresses
belonging together in the same zone, resulting in labels appearing in
reverse order.  E.g., the network address would be
represented by a DNS domain name as ""
as described in RFC 1035.  For IPv6, the convention used is documented
in "DNS Extensions to Support IP Version 6" [RFC 3596], section 2.5.

See also "Issues in Identifier Comparison for Security Purposes" [RFC
6943] section 3.1, "Host Names", in particular section 3.1.1 and 3.1.2
on address literals, and section 4.1, "Conflation."

DNS domain names have become the dominant definition of domain names
due to the success (scale) of the DNS on the public Internet.  Many
protocols interact with the DNS but instead of supporting the
complete definition of DNS domain names, the protocols rely on a
subset more commonly called host names.

3.2 Host Names

Work on the definition of a host name began well before the issuance
of the STD 13 documents defining DNS.  The rules for the Preferred
Syntax in RFC 1034 conform to the host name rules outlined in RFC
952.  The host name definition was presented again in RFC 1123
"Requirements for Internet Hosts -- Application and Support" (which
is part of STD 3).  In section 2.1 of RFC 1123, one (of two mentions)
definition of host name is presented, noting that the definition is a
relaxation of what is in RFC 952.

Host names are subsets of DNS domain names in the sense that the
character set is limited.  In particular, only "let" (i.e.,
presumably letters a-z), "digits" and "hyphen" can be used, with
hyphen only internal to a label.  (This description is meant to be
illustrative, not normative.  See the grammar presented on page 5 of
RFC 952 for specifics.) RFC 1945 "Hypertext Transfer Protocol --
HTTP/1.0", Section 3.2.2 "http URL" specifically references section
2.1 of RFC 1123.  The reference is explicit.

"Simple Mail Transfer Protocol" [RFC 5321] refers to RFC 1035 for a
definition of domain names but includes text close to what is in the
previous paragraph, noting that domain names as used in SMTP refer to
both hosts and to other entities.  RFC 5321 updates RFC 1123, but
does not cite the latter for a definition of host names.  RFC 5321
additionally requires brackets to surround address literals,
referring to the use case as an "alternative to a domain name."

See also "IAB Thoughts on Encodings for Internationalized Domain Names"
[RFC 6055], particularly section 3 entitled "Use of Non-ASCII in DNS"
for more thoughts on host names.

3.3 URI Authority and Domain Names

In "Uniform Resource Identifier (URI): Generic Syntax" [RFC 3986], also
known as STD 66, mentions in its section 3.2.2 (page 20) that the host
subcomponent of the URI Authority (section 3.2) "should conform to the
DNS syntax".  This comes after discussion that the host subcomponent
is not strongly tied to the DNS, i.e., names can be managed via a
concept other than the DNS.  There's no discussion on the rationale
but this enables the reuse of code parsing and marshalling the host
subcomponent between different Domain Name environments.

This reinforces the notion that there's a need to understand how Domain
Names interoperate amongst protocols and applications. And reinforces
the need to derive or make explicit a way for client software to know
how to resolve a name, that is, convert a name into a network address.

3.4 Internet Protocol Address Literals

The above definition includes address literals such as for
IPv4 and even IPv6 literals such as ::ffff:  Yes, these
qualify as Domain Names.  In some protocols, these domain names are
specified as being preceded by a "#" (find this and cite) or encased
in square brackets "[" and "]" (SMTP mentioned already).  In the DNS,
as previously described in section 3.1, they are represented
according to appropriate conventions.

3.5 Internationalized Domain Names in Applications

The original uses of Domain Names (such as DNS domain names
and host names) assumed the ASCII character set.  Specifically,
making the labels case insensitive prohibited a straightforward use
of any method of representation of non-ASCII characters.

"Internationalized Domain Names for Applications (IDNA): Definitions
and Document Framework" [RFC 5890], with associated other documents,
defines IDNA2008 as a convention for handling non-ASCII characters in
DNS domain names.  In figure 1 of that document, the sets of legal DNS
domain name formats are defined.  Noted in the footnotes of the
figure, applications unaware of IDNA2008 cannot distinguish the subsets
defined by the document meaning this definition is not an alteration
of Domain Names, but, like host names, yet another subset of DNS
domain names.

3.6 Restricted for DNS Registration

"Suggested Practices for Registration of Internationalized Domain Names
(IDN)" [RFC 4290] presents reasons why registration of DNS domain
names is restricted, in the context of IDN.  (That RFC refers to an
older form than IDNA2008, but the concepts still apply.)  This is yet
another convention related to DNS domain names, excluding names that
would lead to undesirable outcomes.

3.7 Tor Network Names

The Tor network is an activity organized by the Tor Project, Inc.,
described on its main web page
"".  One component of the
network are Domain Names ending in ".onion".  (There are other
suffixes in use, but it isn't very clear how they are used, defined
or whether they are active.)

The way in which Domain Names are used in Tor is described in two web
documents "Tor Rendezvous Specification" [RENDEV] and "Special
Hostnames in Tor" [OHOST] available from the project's website.

Syntactically, a Tor domain name fits within the DNS domain name
definition but the manner of assignment is different in a manner
incompatible with the DNS.  (Not better or worse, still significantly
different.)  Tor domain names are derived from cryptographic keys and
organized by distributed hash tables, instead of assigned by a central
authority per zone.

3.8 X.509

"Internet X.509 Public Key Infrastructure Certificate and Certificate
Revocation List (CRL) Profile" [RFC 5280], section "Subject
Alternative Name" a dNSName is defined to be a host name, with the
further restriction that the name " " cannot be used.  (The sublte
irony is that a name consisting of just a blank would hardly qualify
as a Domain Name.)

3.9 Multicast DNS

Multicast DNS uses a name space ending with ".local." as described in
"Multicast DNS" [RFC 6762].  The rules for Multicast DNS domain names
differ from DNS domain names.  Multicast DNS domain names are encoded
as Net-Unicode as defined in RFC5198 " Unicode Format for Network
Interchange" with the DNS domain name tradition of case folding the
ASCII letters when matching names.  Appendix F of RFC 6762 gives an
explanation of why the punycode algorithm is not used.

3.10 /etc/hosts

The precursor to DNS, host tables, still exists in remnants in many
operating systems.  There are library functions, used by applications
to resolve DNS domain names, that can return names of arbitrary
length (meaning, for example longer than what DNS domain names are
defined to be).

RFC 3493, "Basic Socket Interface Extensions for IPv6", addresses
this in Section 6, further documentation can be found as part of
The Open Group Base Specifications Issue 7 [IEEE1003.1] and Microsoft
Winsock Functions [WINSOCK].

3.11 Other Protocols

This section is used to list (some) other protocols that use Domain
Names but in general do not impose any other restrictions that what
has been mentioned above.

SSH, documented in "The Secure Shell (SSH) Protocol Architecture"
[RFC 4251] uses host names, using the name when storing public keys
of hosts.  SSH clients, not necessarily the protocol, illustrate how
applications juggle the different forms of Domain Names.  SSH can be
invoked to open a secure shell with a host via its DNS domain
name/host name or it can be used to open a secure shell with a host
via its Multicast DNS domain name. Or, many others, including name of a
purely local, per-user scope.  (Note that SSH does not distinguish
between DNS names and Multicast DNS domain names in the protocol
definition, the difference is handled in resolution libraries belonging
to the computing platform.)

FTP, defined in "FILE TRANSFER PROTOCOL (FTP)" [RFC 959], is silent on
domain names but client implementations of the protocol behave as SSH
clients, being un aware the differences between definitions of Domain

DHCP, defined in "Dynamic Host Configuration Protocol" [RFC 2131],
includes domain names in its Domain Search Option [RFC 3397 "Dynamic
Host Configuration Protocol (DHCP) Domain Search Option"].  The
encoding of Domain Names used is the on-the-wire format of the DNS,
using DNS-defined message compression.  DHCP handles Domain Names in
other options such as in RFC 4702 defined "The DHCP Client FQDN
Option", in the same format.  The significance of this is that most
other protocols represent DNS domain names or host names in a human
readable form, DHCP is using the machine-friendly format.

3.12 Other others

If there is a use of Domain Names not listed here it is merely an
omission.  The goal in this document is to provide a survey that
is sufficient to avoid hand-waving arguments, recognizing the
diminishing return in trying to build a complete roster of uses
of Domain Names.  If there are omissions that ought to be included,
please send references for the use case to the author (while this is
an Internet Draft, that is).

4. Interoperability Considerations

Any single protocol is able to define a format for a conceptual Domain
Name.  Examples given above show that many protocols have done so.
From the examples it is clear that the way in which protocols have
interpreted Domain Names has varied, leading to, at least, user
interfaces having to have built-in intelligence when handling names
and, at worst, a growing confusion over how the Domain Name space is
to be managed.

When protocols having different formats and rules for Domain Names
interact, software implementing the protocols translate one protocol's
domain name format to another's format.  Even when the translation is
straightforward, software often fails to handle error conditions well.
(Is there a citation for that?)

Often times the clash of definitions impacts the design of a new
protocol and/or an extension of a protocol.  For example, adding
non-ASCII domain names has to be done with backwards compatibility
with an installed base of ASCII-assuming code.  This clash can
inhibit new uses of Domain Names.

Search lists are a Domain Name mechanism studied in "SSAC Advisory
on DNS 'Search List' Processing" [SAC 064].   One of the particular
use cases related to this topic is the issuance of search lists via
DHCP and then used by any user-client protocol implementation.  This
emphasizes an interoperability consideration for how Domain Names
are treated in different protocols, not just among implementations of
one protocol.

The definition of a Fully Qualified Domain Name has two forms.  The
discussion over FQDN involved human-readable names.  The principle
question is whether to require the terminating dot or to assume it
when the end of an input string is hit.  Some protocol clients will
silently add a dot when a user types in a name to a command line,
others will do so if there is a dot inside the name.  [No reference]
But some definitions, such as the one in the previously referenced
SSAC advisory, require the terminating dot to be included before a name
is considered to be fully qualified.

The Special Use Domain Names registry lists Domain Names that are to
be treated in a manner inconsistent with the DNS normal processing
rules.  This registry contains Domain Names regardless of whether the
name is a DNS domain name and regardless whether the name is a
top-level (domain) name [RFC 819] or is positioned elsewhere in the
tree structure.

These are reasons this document is needed.  The reason for the
confusion over what's a legal domain name stems from
application-defined restrictions.  For example, using a one-label
domain name ("dotless") for sending email is not a problem with the
DNS nor the name in concept, but is a problem for mail implementations
that expect more than one label.  (One-label names may be assumed to
be in ARPA host table format.)  The "IAB Statement: Dotless Domains
Considered Harmful" [IAB Stmt] elaborates.

5. Defintion(s) of Domain Names

Looking through the early documents, and using the experience of the
past decades, this new definition of Domain Names is stated:

A Domain Name is a sequence of labels concatenated by a designated
separating character.  The Domain Name Space is organized in a strict
hierarchical manner with a recognized root Domain Name.  The
organization follows the rules of tree structure as defined by the
field of graph theory in mathematics [Diestel].

Each label represents a node in a conceptual tree.  The sequence of
labels is concatenated from the deepest node in the tree up to the
root node.  "Fully qualified" refers to a sequence that ends with the
root node.

When considering a fully qualifed name, the first label of the name
is the name of the deepest node in the tree, the last label is the
name of the node is the root.  The top-level label, top-level name,
or top-level domain is the label just before the root (or last)
label.  ("First" and "last" regardless of whether the name appears
in a left-to-right script or a right-to-left script.)

Excluded from the definition is the appearance or representation of
the labels, the designated separator character's representation, the
ordering of the sequence in appearance, such as left-to-right or
right-to-left, nor the written script nor encoding.  The definition
is purely conceptual.

In RFC 819 "Simple Mail Transfer Protocol", the designated separating
character is the dot ('.') as represented in the ASCII [RFC 20]
[ANSIX34] character set.  This is the earliest application definition
of how it represents Domain Names.

5.1 Definition from Lyman Chapin

Included here is an emailed definition from Lyman Chapin, appearing
in the archives of  The definition is in-line
with the previous one offered except that it refers to a finite name
space due to length restrictions.

"In graph-theoretic terms, the domain name space constitutes a
labelled directed rooted tree in which the syntax of the label
associated with each vertex other than the unlabelled root is
defined by RFCs 1035, 1123, and 2181. The term 'nth level domain
name label' refers to a member of the set of all vertices for which
the path to the root contains n edges. For n=1 the term most often
used is 'top level domain name label' or simply 'top level domain'
(TLD). A fully qualified domain name is a sequence of labels that
represents a path from the root to a leaf vertex of the domain name
space. The shorter term 'domain name' is not formally defined; in
common usage it may be the shorthand equivalent of 'fully qualified
domain name' (FQDN) or refer to any non-empty subset of the sequence
of labels formally identified by a fully qualified domain name.

"In this formulation, the term 'domain name space' refers to the
complete graph consisting of all possible vertices and edges - not
just those with which a specific meaning has been associated (what
we might call 'allocated' labels). It is a finite graph because the
length of the longest possible FQDN is finite. At any point in time,
there is another labelled directed rooted tree - a sub-graph of the
domain name space - containing only vertices that represent
allocated labels."

5.2 "Inverted"

Others have described or defined Domain Names in books.  In "DNS and
BIND" [DNSBIND], a definition is published which includes the term
"inverted" when describing the name space, referring to botanical
trees as having roots beneath the trunk of a tree and the mathematical
tree with the root depicted at the top.  For the full text of that
definition, consult the reference.

5.3 Limitation

There are many ways to build a name space, Domain Names are just one
example.  Domain Names are intended to build a name space that can
scale tremendously as opposed to a name space for closed cluster of
involved objects.  Domain Names are used across many protocols
defined inside and outside the IETF and have been defined to
interoperate across implementations and protocols.  This does not
make Domain Names an official or required standard despite the name
space's widespread use.

5.4 Is This a Domain Name?

In the vein of questions like "but is it art?" as to whether an
object is art worthy of display in a museum, one can question
whether any string with a dot in it is a Domain Name.  For example,
is this multi-sentence paragraph a Domain Name?  It has
characters and dots in it.

The important question is not whether a string is an example of a
Domain Name based on its appearence.  The use of a string is what
makes it a Domain Name.  A path name of a file with an extension
looks like a Domain Name with the extension separated by a dot, if one
allows the directory seperating character (a '/' perhaps) as a legal
member of a label.  Within an OS, this is a file/path name.  In a
protocol it might be used as if it were a domain name.

6. Acknowledgements

The definition of domain names was lifted from an email from Lyman
Chapin.  The URL for that message is (combine the two lines):

Comments from Andrew Sullivan, Paul Hoffman, George Michaelson,
Kevin Darcy, Joe Abley, Jim Reid, Tony Finch, Robert Edmonds,
hellekin, Stephane Bortzmeyer, Ray Bellis, Bob Harold, Alec Muffett,
Stuart Cheshire, Dave Thaler, Niall O'Reilly and a growing list of
others I am losing track of.  Not to imply endorsement.

7. IANA Considerations


8. Security Considerations

Nothing direct.  This document proposes a definition of the term
"Domain Name" and surveys how it has been variously applied.  In
some sense, loosely defined terms give rise to security hazards.
Beyond that, there is no impact of "security."

9. References

Many references are in-line throughout the text with titles to ease
comprehension of the prose.  All documents cited are listed here.
Whether there is a normative/informative split will depend what, if
any, track this document is processed.  For now, consider this a
reading list on the topic.

ANSIX34    American National Standards Institute (formerly United
           States of America Standards Institute), "USA Code for
           Information Interchange", ANSI X3.4-1968, 1968

DNSBIND    Cricket Liu, Paul Albitz, DNS and BIND (5th Edition),
           O'Reilly Media, Inc., 2006

RFC 20     Cerf, V., "ASCII format for network interchange", STD 80,
           RFC 20, DOI 10.17487/RFC0020, October 1969,

RFC 788    Postel, J., "Simple Mail Transfer Protocol", RFC 788, DOI
           10.17487/RFC0788, November 1981,

RFC 799    Mills, D., "Internet name domains", RFC 799, DOI
           10.17487/RFC0799, September 1981,

RFC 801    Postel, J., "NCP/TCP transition plan", RFC 801, DOI
           10.17487/RFC0801, November 1981,

RFC 805    Postel, J., "Computer mail meeting notes", RFC 805, DOI
           10.17487/RFC0805, February 1982,

RFC 819    Postel, J., "Computer mail meeting notes", RFC 805, DOI
           10.17487/RFC0805, February 1982,

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

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

RFC 952    Mockapetris, P., "Domain names: Implementation
           specification", RFC 883, DOI 10.17487/RFC0883, November
           1983, <>.

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

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

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

RFC 1123   Braden, R., Ed., "Requirements for Internet Hosts -
           Application and Support", STD 3, RFC 1123, DOI
           10.17487/RFC1123, October 1989,

RFC 1945   Berners-Lee, T., Fielding, R., and H. Frystyk, "Hypertext
           Transfer Protocol -- HTTP/1.0", RFC 1945, DOI
           10.17487/RFC1945, May 1996,

RFC 2131   Droms, R., "Dynamic Host Configuration Protocol", RFC 2131,
           DOI 10.17487/RFC2131, March 1997,

RFC 2860   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, <>.

RFC 3397   Aboba, B. and S. Cheshire, "Dynamic Host Configuration
           Protocol (DHCP) Domain Search Option", RFC 3397,
           DOI 10.17487/RFC3397, November 2002,

RFC 3492   Costello, A., "Punycode: A Bootstring encoding of Unicode
           for Internationalized Domain Names in Applications (IDNA)",
           RFC 3492, DOI 10.17487/RFC3492, March 2003,

RFC 3493   Gilligan, R., Thomson, S., Bound, J., McCann, J., and W.
           Stevens, "Basic Socket Interface Extensions for IPv6",
           RFC 3493, DOI 10.17487/RFC3493, February 2003,

RFC 3596   Thomson, S., Huitema, C., Ksinant, V., and M. Souissi,
           "DNS Extensions to Support IP Version 6", RFC 3596,
           DOI 10.17487/RFC3596, October 2003,

RFC 3986   Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
           Resource Identifier (URI): Generic Syntax", STD 66, RFC
           3986, DOI 10.17487/RFC3986, January 2005,

RFC 4251   Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
           Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251,
           January 2006, <>.

RFC 4290   Klensin, J., "Suggested Practices for Registration of
           Internationalized Domain Names (IDN)", RFC 4290, DOI
           10.17487/RFC4290, December 2005,

RFC 4702   Stapp, M., Volz, B., and Y. Rekhter, "The Dynamic Host
           Configuration Protocol (DHCP) Client Fully Qualified Domain
           Name (FQDN) Option", RFC 4702, DOI 10.17487/RFC4702,
           October 2006, <>.

RFC 5198   Klensin, J. and M. Padlipsky, "Unicode Format for Network
           Interchange", RFC 5198, DOI 10.17487/RFC5198, March 2008,

RFC 5280   Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
           Housley, R., and W. Polk, "Internet X.509 Public Key
           Infrastructure Certificate and Certificate Revocation
           List (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280,
           May 2008, <>.

RFC 5321   Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, DOI
           10.17487/RFC5321, October 2008,

RFC 5890   Klensin, J., "Internationalized Domain Names for
           Applications (IDNA): Definitions and Document Framework",
           RFC 5890, DOI 10.17487/RFC5890, August 2010,

RFC 6055   Thaler, D., Klensin, J., and S. Cheshire, "IAB Thoughts
           on Encodings for Internationalized Domain Names", RFC 6055,
           DOI 10.17487/RFC6055, February 2011,

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

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

RFC 6943   Thaler, D., Ed., "Issues in Identifier Comparison for
           Security Purposes", RFC 6943, DOI 10.17487/RFC6943,
           May 2013, <>.

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

Diestel    Diestel, R., "Graph Theory", Springer-Verlag, Heidelberg
           Graduate Texts in Mathematics, Volume 173 ISBN
           978-3-642-14278-9, July 2010 (2005, 2000, 1997),

SAC064     ICANN Security and Stability Committee, "SSAC Advisory on
           Search List Processing", SAC064, February 2014,

RENDEV     Anonymous, "Tor Rendezvous Specification", Undated,

OHOST      Nick Mathewson, "Special Hostnames in Tor", Undated,

IABStmt    IAB, 2013, <

IEEE1003   The Open Group Base Specifications Issue 7, IEEE Std
           1003.1, 2013 Edition, Copyright 2001-2013 The IEEE
           and The Open Group,

WINSOCK    URL only, <

10. Author's Address

   Edward Lewis
   801 17th Street NW
   Suite 401
   Washington DC, 20006 US

Lewis                  Expires January 1, 2016                [Page  1]