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Independent Submission                                        E. Lewis
Internet-Draft                                                   ICANN
Expires: March 19, 2016                       Date: September 19, 2015
Intended Status: unknown

                            Domain Names
                    draft-lewis-domain-names-00.txt

Abstract

This document states a definition of Domain Name beyond the use of
the term within the Domain Name System.  The document includes a
survey of 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.

Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF).  Note that other groups may also distribute
working documents as Internet-Drafts.  The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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 19, 2016.

Copyright Notice

Copyright (c) 2015 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

0.  NOTE TO RFC EDITOR AND REVIEWERS  . . . . . . . . . . . . . .   1
1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   1
2.  Reaching a definition of a Domain Name  . . . . . . . . . . .   1
3.  Subtypes of Domain Names  . . . . . . . . . . . . . . . . . .   1
4.  Interoperability Considerations   . . . . . . . . . . . . . .   1
5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   1
6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   1
7.  Security Considerations . . . . . . . . . . . . . . . . . . .   1
8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   1
9.  Authors' Addresses  . . . . . . . . . . . . . . . . . . . . .   1

0.  NOTE TO RFC EDITOR AND REVIEWERS

A suitable venue for discussion of this document is the dnsop working
group.  Private comments may also be directed at the editor.

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

1. Introduction

Two or three decades into the history of Domain Names, a popular
notion has taken hold that Domains Names were defined and specified
STD 13, the definition of the Domain Name System (DNS).  The
definitions within RFC 1034 and RFC 1035 have become the
apparently-authoritative source for discussions on what is a Domain
Name.

The truth is, RFC 1034 and RFC 1035 do not define Domain Names, those
documents define only how Domain Names are used and processed in the
DNS.  But the way in which those RFCs are written seem to lend to the
confusion.

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
documents.

1.1 Deconstructing RFC 1034's Introduction

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.

1.2 Purpose of the Document

This document has a goal of establishing a definition of Domain Names
for the purpose of continuing efforts to innovate in naming systems.
The path by which this document aims to meet the goal is to describe
in more detail the original definition of Domain Names (which never
seems to have been documented in an RFC) and then to illustrate how
Domain Names have been interpreted in the DNS, SMTP, X.509 Certificate
(PKIX), URNs and other environments.

1.3 Why Write This Now?

RFC 6761 defines "Special Use Domain Names" which has engendered much
confusion of the role of Domain Names with respect to the DNS,
particularly Top-Level Domains, which have come to have special
meanings.

2. Reaching a definition of a Domain Name

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."

2.1 Historical Perspective

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
time.

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
root.

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
names.

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.

2.2 Newly Stated Definition of "Domain Name"

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.

What is excluded in this definition is the appearance or
representation of the labels, the designated separator character's
representation, the ordering of the sequence, such as left-to-right
or right-to-left, nor the written script nor encoding. This
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.

2.3 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.

3. Subtypes 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
use.

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.

A DNS domain name "192.0.2.1." can be configured and used in the
protocol.  The usefulness of this is limited by the concerns
described later on in Interoperability Considerations.  An outcome of
that the convention of representing the Domain Name "192.0.2.1." as
"1.2.0.192.in-addr.arpa."

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.

RFC 5321 " Simple Mail Transfer Protocol" 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."

3.3 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).

3.4 Internationalized Domain Names in Applications

The original definitions 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.

RFC 5890 "Internationalized Domain Names for Applications (IDNA):
Definitions and Document Framework", 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 sub
sets 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.

3.5 Restricted for DNS Registration

RFC 4290 "Suggested Practices for Registration of Internationalized
Domain Names (IDN)" 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.

3.6 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.

According to an email message, ".onion" names may (in the future)
exceed the length limits of a label imposed on DNS domain names,
reaching 64, 80, or more bytes. [DNSOP1]

3.7 X.509

In RFC 5280 "Internet X.509 Public Key Infrastructure Certificate and
Certificate Revocation List (CRL) Profile", section 4.2.1.6 "Subject
Alternative Name" a dNSName is defined to be a host name, with the
further restriction that the name " " cannot be used.

3.8 Multicast DNS

Multicast DNS uses a name space ending with ".local." as described in
RFC 6762, "Multicast DNS".  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.

3.9 Other Protocols

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

SSH [RFC 4251 "The Secure Shell (SSH) Protocol Architecture"] 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.

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

DHCP [RFC 2131 "Dynamic Host Configuration Protocol"] includes domain
names in it's 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.

4. Interoperability Considerations

Any single protocol is able to define a format for a conceptual Domain
Name.  Examples given above show that many protocol 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 SAC064 "SSAC
Advisory on DNS 'Search List' Processing".   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.  Many protocol clients will
silently add a dot when a user types in a name to a command line.  But
some definitions, such as the one in SAC064 require the terminating
dot to be included before a name is considered to be fully qualified.

The Special Use Domain Names registry defined in RFC 6761 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.)

4.1(*) Use of Top-Level Domains as Protocol Identifiers

(Would like to have "dns" and "dns<digit>" added to the Special Use
Domain Names registry.  As well as the digits [address literals].)

(*) - I am not sure this belongs in this document.  The idea is what
one can select a name space by the top-level domain (label).  I
believe this would be scope creep for this document.  Leaving it
here for consideration.

5. Acknowledgements

Input received from Andrew Sullivan and Paul Hoffman.  Not to imply
endorsements of the text.

6. IANA Considerations

None.

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."

8. 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

RFC 20     Cerf, V., "ASCII format for network interchange", STD 80,
           RFC 20, DOI 10.17487/RFC0020, October 1969,
           <http://www.rfc-editor.org/info/rfc20>.

RFC 788    Postel, J., "Simple Mail Transfer Protocol", RFC 788, DOI
           10.17487/RFC0788, November 1981,
           <http://www.rfc-editor.org/info/rfc788>.

RFC 799    Mills, D., "Internet name domains", RFC 799, DOI
           10.17487/RFC0799, September 1981,
           <http://www.rfc-editor.org/info/rfc799>.

RFC 801    Postel, J., "NCP/TCP transition plan", RFC 801, DOI
           10.17487/RFC0801, November 1981,
           <http://www.rfc-editor.org/info/rfc801>.

RFC 805    Postel, J., "Computer mail meeting notes", RFC 805, DOI
           10.17487/RFC0805, February 1982,
           <http://www.rfc-editor.org/info/rfc805>.

RFC 819    Postel, J., "Computer mail meeting notes", RFC 805, DOI
           10.17487/RFC0805, February 1982,
           <http://www.rfc-editor.org/info/rfc805>.

RFC 882    Mockapetris, P., "Domain names: Concepts and facilities",
           RFC 882, DOI 10.17487/RFC0882, November 1983,
           <http://www.rfc-editor.org/info/rfc882>.

RFC 883    Mockapetris, P., "Domain names: Implementation
           specification", RFC 883, DOI 10.17487/RFC0883, November
           1983, <http://www.rfc-editor.org/info/rfc883>.

RFC 952    Mockapetris, P., "Domain names: Implementation
           specification", RFC 883, DOI 10.17487/RFC0883, November
           1983, <http://www.rfc-editor.org/info/rfc883>.

RFC 959    Postel, J. and J. Reynolds, "File Transfer Protocol", STD
           9, RFC 959, DOI 10.17487/RFC0959, October 1985,
           <http://www.rfc-editor.org/info/rfc959>.

RFC 1034   Mockapetris, P., "Domain names - concepts and facilities",
           STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
           <http://www.rfc-editor.org/info/rfc1034>.

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,
           <http://www.rfc-editor.org/info/rfc1123>.

RFC 1945   Berners-Lee, T., Fielding, R., and H. Frystyk, "Hypertext
           Transfer Protocol -- HTTP/1.0", RFC 1945, DOI
           10.17487/RFC1945, May 1996,
           <http://www.rfc-editor.org/info/rfc1945>.

RFC 2131   Droms, R., "Dynamic Host Configuration Protocol", RFC 2131,
           DOI 10.17487/RFC2131, March 1997,
           <http://www.rfc-editor.org/info/rfc2131>.

RFC 3397   Aboba, B. and S. Cheshire, "Dynamic Host Configuration
           Protocol (DHCP) Domain Search Option", RFC 3397,
           DOI 10.17487/RFC3397, November 2002,
           <http://www.rfc-editor.org/info/rfc3397>.

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,
           <http://www.rfc-editor.org/info/rfc3492>.

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,
           <http://www.rfc-editor.org/info/rfc4290>.

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,
           <http://www.rfc-editor.org/info/rfc5198>.

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,
           <http://www.rfc-editor.org/info/rfc5321>.

RFC 5890   Klensin, J., "Internationalized Domain Names for
           Applications (IDNA): Definitions and Document Framework",
           RFC 5890, DOI 10.17487/RFC5890, August 2010,
           <http://www.rfc-editor.org/info/rfc5890>.

RFC 6761   Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
           RFC 6761, DOI 10.17487/RFC6761, February 2013,
           <http://www.rfc-editor.org/info/rfc6761>.

RFC 6762   Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
           DOI 10.17487/RFC6762, February 2013,
           <http://www.rfc-editor.org/info/rfc6762>.

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),
           <http://diestel-graph-theory.com>

SAC064     ICANN Security and Stability Committee, "SSAC Advisory on
           Search List Processing", SAC064, February 2014,
           <https://www.icann.org/en/system/files/files/sac-064-en.pdf>

RENDEV     Anonymous, "Tor Rendezvous Specification", Undated,
           <https://gitweb.torproject.org/torspec.git/tree/
           rend-spec.txt>

OHOST      Nick Mathewson, "Special Hostnames in Tor", Undated,
           <https://gitweb.torproject.org/torspec.git/tree/
           address-spec.txt>

DNSOP1     Alex Muffett, "Re: [DNSOP] Last Call:
           <draft-ietf-dnsop-onion-tld-00.txt> (The .onion Special-Use
           Domain Name) to Proposed Standard", DNSOP@IETF.ORG archived
           message, August 2015,
           <https://www.ietf.org/mail-archive/web/dnsop/current/
           sg15231.html>

9. Author's Address

   Edward Lewis
   ICANN
   801 17th Street NW
   Suite 401
   Washington DC, 20006 US
   edward.lewis@icann.org

Lewis                  Expires March 19, 2016                [Page  1]


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