Independent Submission E. Lewis
Expires: January 1, 2017 Date: July 1, 2016
Intended Status: unknown
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
Status of This Memo
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Table of Contents
0. NOTE TO RFC EDITOR AND REVIEWERS
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 1
2. Emergence of Domain Names . . . . . . . . . . . . . . . . . . 1
3. Dialects, so to speak, of Domain Names . . . . . . . . . . . . 1
4. Interoperability Considerations . . . . . . . . . . . . . . . 1
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 1
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 1
7. Security Considerations . . . . . . . . . . . . . . . . . . . 1
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 1
9. Author's Address . . . . . . . . . . . . . . . . . . . . . . . 1
0. NOTE TO RFC EDITOR AND REVIEWERS
The closest mailing list to this topic is email@example.com. Or maybe
firstname.lastname@example.org. 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:
The document's scope has been reduced, at least for now. The document
sticks to history and current observations without proposing a
definition nor an architecture. There's too many degrees of freedom
in the definition/architecture space at the moment to make a useful
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
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.
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
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 'email@example.com' where 'domain'
could be a hierarchy of domains."
RFC 819 "The Domain Naming Convention for Internet User Applications"
"A decision has recently been reached to
replace the simple name field, "<host>", by a composite name field,
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 "192.0.2.1" or "0:0:0:0:0:FFFF::192.0.2.1". 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 192.0.2.1 would be
represented by a DNS domain name as "188.8.131.52.in-addr.arpa."
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 192.0.2.1 for
IPv4 and even IPv6 literals such as ::ffff:192.0.2.1. 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
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
"https://www.torproject.org/index.html.en". 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.
"Internet X.509 Public Key Infrastructure Certificate and Certificate
Revocation List (CRL) Profile" [RFC 5280], section 184.108.40.206 "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.
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. (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
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
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.
The definition of domain names was lifted from an email from Lyman
Chapin. The URL for that message is (combine the two lines):
The definition has since been removed from this draft.
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 and a growing list of others I am losing
track of. Not to imply endorsement.
6. IANA Considerations
7. 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."
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
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
RFC 952 Mockapetris, P., "Domain names: Implementation
specification", RFC 883, DOI 10.17487/RFC0883, November
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, <http://www.rfc-editor.org/info/rfc1035>.
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, <http://www.rfc-editor.org/info/rfc2860>.
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, <http://www.rfc-editor.org/info/rfc4251>.
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, <http://www.rfc-editor.org/info/rfc4702>.
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, <http://www.rfc-editor.org/info/rfc5280>.
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, <http://www.rfc-editor.org/info/rfc6943>.
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, <https://www.iab.org/documents/
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, <https://msdn.microsoft.com/en-us/library/
9. Author's Address
801 17th Street NW
Washington DC, 20006 US
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