dnsop W. Kumari
Internet-Draft Google
Intended status: Informational A. Sullivan
Expires: April 2, 2016 Dyn
September 30, 2015
The ALT Special Use Top Level Domain
draft-ietf-dnsop-alt-tld-03
Abstract
This document reserves a string (ALT) to be used as a TLD label in
non-DNS contexts or for names that have no meaning in a global
context. It also provides advice and guidance to developers
developing alternate namespaces.
[ Ed note: This document lives in GitHub at:
https://github.com/wkumari/draft-wkumari-dnsop-alt-tld . Issues and
pull requests happily accepted. ]
Status of This Memo
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This Internet-Draft will expire on April 2, 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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publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements notation . . . . . . . . . . . . . . . . . . 2
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2
2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. The ALT namespace . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Choice of the ALT Name . . . . . . . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
4.1. Domain Name Reservation Considerations . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
7. Normative References . . . . . . . . . . . . . . . . . . . . 8
Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
Many protocols and systems need to name entities. Names that look
like DNS names (a series of labels separated with dots) have become
common, even in systems that are not part of the global DNS
administered by IANA.
This document provides a solution that may be more appropriate than
[RFC6761] in many cases.
This document reserves the label "ALT" (short for "Alternate") as a
Special Use Domain ([RFC6761]). This label is intended to be used as
the final label to signify that the name is not rooted in the DNS,
and that normal registration and lookup rules do not apply.
1.1. Requirements notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
1.2. Terminology
This document assumes familiarity with DNS terms and concepts.
Please see [RFC1034] for background and concepts, and
[I-D.ietf-dnsop-dns-terminology] for terminology.
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o DNS name: Domain names that are intended to be used with DNS
resolution, either in the global DNS or in some other context
o DNS context: The namespace anchored at the globally-unique DNS
root. This is the namespace or context that "normal" DNS uses.
o non-DNS context: Any other (alternate) namespace.
o pseudo-TLD: A label that appears in a fully-qualified domain name
in the position of a TLD, but which is not registered in the
global DNS.
o TLD: The last visible label in either a fully-qualified domain
name or a name that is qualified relative to the root. See the
discussion in Section 2.
2. Background
The DNS data model is based on a tree structure, and has a single
root. Conventionally, a name immediately beneath the root is called
a "Top Level Domain" or "TLD". TLDs usually delegate portions of
their namespace to others, who may then delegate further. The
hierarchical, distributed and caching nature of the DNS has made it
the primary resolution system on the Internet.
Domain names are terminated by a zero-length label, so the root label
is normally invisible. Truly fully-qualified names indicate the root
label explicitly, thus: "an.example.tld.". Most of the time, names
are written implicitly relative to the root, thus: "an.example.tld".
In both of these cases, the TLD is the last label that is visible in
presentation format -- in this example, the string "tld". (This
little bit of pedantry is here because, in different contexts, people
can use the term "fully-qualified domain name" to refer to either of
these uses.) It is worth noting that the root label is present in
the on-wire format of fully-qualified domain names, even if not
displayed in the presentation form.
The success of the DNS makes it a natural starting point for systems
that need to name entities in a non-DNS context, or that have no
unique meaning in a global context. These name resolutions,
therefore, occur in a namespace distinct from the DNS.
In many cases, these systems build a DNS-style tree parallel to, but
separate from, the global DNS. They often use a pseudo-TLD to cause
resolution in the alternate namespace, using browser plugins, shims
in the name resolution process, or simply applications that perform
special handling of this particular alternate namespace.
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In many cases, the creators of these alternate namespaces have chosen
a convenient or descriptive string and started using it. These new
strings are "alternate" strings and are not registered anywhere or
part of the DNS. However they appear to users and to some
applications to be TLDs. Issues may arise if they are looked up in
the DNS. These include:
o User confusion: If someone emails a link of the form
foo.bar.pseudo-TLD to someone who does not have the necessary
software to resolve names in the pseudo-TLD namespace, the name
will not resolve and the user may become confused.
o Excess traffic hitting the DNS root: Lookups leak out of the
pseudo-TLD namespace and end up hitting the DNS root nameservers.
o Collisions: If the pseudo-TLD is eventually delegated from the
root zone, the lookup behavior will change in a non-deterministic
fashion.
o Lack of success for the user's original goal.
An alternate name resolution system might be specifically designed to
provide confidentiality of the looked up name, and to provide a
distributed and censorship-resistant namespace. This goal would
necessarily be defeated if the queries leak into the DNS, because the
attempt to look up the name would be visible at least to the
operators of root name servers and to any entity viewing the DNS
lookups going to the root nameservers.
3. The ALT namespace
In order to avoid the above issues, we reserve the ALT label. Unless
the name desired is globally unique, has meaning on the global
context and is delegated in the DNS, it should be considered an
alternate namespace, and follow the ALT label scheme outlined below.
The ALT label MAY be used in any domain name as a pseudo-TLD to
signify that this is an alternate (non-DNS) namespace.
Alternate namespaces should differentiate themselves from other
alternate namespaces by choosing a name and using it in the label
position just before the pseudo-TLD (ALT). For example, a group
wishing to create a namespace for Friends Of Olaf might choose the
string "foo" and use any set of labels under foo.alt.
As they are in an alternate namespace, they have no significance in
the regular DNS context and so should not be looked up in the DNS
context. Some of these requests will inevitably leak into the DNS
context (for example, because clicks on a link in a browser that does
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not have a extension installed that implements the alternate
namespace resolution), and so the ALT TLD has been added to the
"Locally Served DNS Zones" ( [RFC6303]) registry to limit how far
these flow.
Groups wishing to create new alternate namespaces SHOULD create their
alternate namespace under a label that names their namespace, and
under the ALT label. They SHOULD choose a label that they expect to
be unique and, ideally, descriptive. There is no IANA controlled
registry for names under the ALT TLD - it is an unmanaged namespace,
and developers are responsible for dealing with any collisions that
may occur under .alt. Informal lists of namespaces under .alt may
appear to assist the developer community.
[Editor note (to be removed before publication): There was
significant discussion on an IANA registry for the ALT namespace -
please consult the lists for full thread, but the consensus seems to
be that it would be better for the IETF / IANA to not administer a
registry for this. It is expected one or more unofficial lists will
be created where people can list the strings that they are using. ]
Currently deployed projects and protocols that are using pseudo-TLDs
may decide to move under the ALT TLD, but this is not a requirement.
Rather, the ALT TLD is being reserved so that current and future
projects of a similar nature have a designated place to create
alternate resolution namespaces that will not conflict with the
regular DNS context.
3.1. Choice of the ALT Name
A number of names other than "ALT" were considered and discarded. In
order for this technique to be effective the names need to continue
to follow both the DNS format and conventions (a prime consideration
for alternate name formats is that they can be entered in places that
normally take DNS context names); this rules out using suffixes that
do not follow the usual letter, digit, and hyphen label convention.
Another proposal was that the ALT TLD instead be a reservation under
.arpa. This was considered, but rejected for several reasons,
including:
1. We wished this to make it clear that this is not in the DNS
context, and .arpa clearly is.
2. The use of the string .alt is intended to evoke the alt.*
hierarchy in Usenet.
3. We wanted the string to be short and easily used.
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4. A name underneath .arpa would consume at least five additional
octets of the total 255 octets available in domain names, which
could put pressure on applications that need long machine-
generated names.
5. We are suggesting that the string "ALT" get special treatment in
resolvers, and shim software. We are concerned that using
subdomains of an existing TLD (like .arpa) might end up with bad
implementations misconfiguring / overriding the TLD itself and
breaking .arpa.
There is a concern that if there were placed under .arpa,
inexperienced nameserver operators may inadvertently cover .arpa. A
more significant concern is that the scope of the issue if the query
does leak, and the fact that this would then make the root of the
alternate naming namespace a third level domain, and not a second
one. A project may be willing to have a name of the form
example.alt, but example.alt.arpa may be not look as good.
4. IANA Considerations
The IANA is requested to add the ALT string to the "Special-Use
Domain Name" registry ([RFC6761], and reference this document. In
addition, the "Locally Served DNS Zones" ([RFC6303]) registry should
be updated to reference this document.
4.1. Domain Name Reservation Considerations
This section is to satisfy the requirement in Section 5 of RFC6761.
The domain "alt.", and any names falling within ".alt.", are special
in the following ways:
1. Human users are expected to know that strings that end in .alt
behave differently to normal DNS names. Users are expected to
have applications running on their machines that intercept
strings of the form <namespace>.alt and perform special handing
of them. If the user tries to resolve a name of the form
<namespace>.alt without the <namespace> plugin installed, the
request will leak into the DNS, and receive a negative response.
2. Writers of application software that implement a non-DNS
namespace are expected to intercept names of the form
<namespace>.alt and perform application specific handing with
them. Other applications are not intended to perform any special
handing.
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3. In general, writers of name resolution APIs and libraries do not
need to perform special handing of these names. If developers of
other namespaces implement their namespace through a "shim" or
library, they will need to intercept and perform their own
handling.
4. Caching DNS servers SHOULD recognize these names as special and
SHOULD NOT, by default, attempt to look up NS records for them,
or otherwise query authoritative DNS servers in an attempt to
resolve these names. Instead, caching DNS servers SHOULD
generate immediate negative responses for all such queries.
5. Authoritative DNS servers SHOULD recognize these names as special
and SHOULD, by default, generate immediate negative responses for
all such queries, unless explicitly configured by the
administrator to give positive answers for private-address
reverse-mapping names.
6. DNS server operators SHOULD be aware that queries for names
ending in .alt are not DNS names, and were leaked into the DNS
context (for example, by a missing browser plugin). This
information may be useful for support or debugging purposes.
7. DNS Registries/Registrars MUST NOT grant requests to register
"alt" names in the normal way to any person or entity. These
"alt" names are defined by protocol specification to be
nonexistent, and they fall outside the set of names available for
allocation by registries/registrars.
5. Security Considerations
One of the motivations for the creation of the alt pseudo-TLD is that
unmanaged labels in the managed root name space are subject to
unexpected takeover if the manager of the root name space decides to
delegate the unmanaged label.
The unmanaged and "registration not required" nature of labels
beneath .alt provides the opportunity for an attacker to re-use the
chosen label and thereby possibly compromise applications dependent
on the special host name.
6. Acknowledgements
We would also like to thank Joe Abley, Mark Andrews, Marc Blanchet,
John Bond, Stephane Bortzmeyer, David Cake, David Conrad, Patrik
Faltstrom, Olafur Gudmundsson, Paul Hoffman, Joel Jaeggli, Ted Lemon,
Edward Lewis, George Michaelson, Ed Pascoe, Arturo Servin, and Paul
Vixie for feedback.
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7. Normative References
[I-D.ietf-dnsop-dns-terminology]
Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", draft-ietf-dnsop-dns-terminology-05 (work in
progress), September 2015.
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<http://www.rfc-editor.org/info/rfc1034>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC6303] Andrews, M., "Locally Served DNS Zones", BCP 163, RFC
6303, DOI 10.17487/RFC6303, July 2011,
<http://www.rfc-editor.org/info/rfc6303>.
[RFC6761] Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
RFC 6761, DOI 10.17487/RFC6761, February 2013,
<http://www.rfc-editor.org/info/rfc6761>.
Appendix A. Changes / Author Notes.
[RFC Editor: Please remove this section before publication ]
From -02 to -03:
o Incorporate suggestions from Stephane and Paul Hoffman.
From -01 to -02:
o Merged a bunch of changes from Paul Hoffman. Thanks for sending a
git pull.
From -00 to 01:
o Removed the "delegated to new style AS112 servers" text -this was
legacy from the omnicient AS112 days. (Joe Abley)
o Removed the "Advice to implemntors" section. This used to
recommend that people used a subdomain of a domain in the DNS. It
was pointed out that this breaks things badly if the domain
expires.
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o Added text about why we don't want to adminster a registry for
ALT.
From Individual-06 to DNSOP-00
o Nothing changed, simply renamed draft-wkumari-dnsop-alt-tld to
draft-ietf-dnsop-alt-tld
From -05 to -06
o Incorporated comments from a number of people, including a number
of suggestion heard at the IETF meeting in Dallas, and the DNSOP
Interim meeting in May, 2015.
o Removed the "Let's have an (optional) IANA registry for people to
(opportinistically) register their string, if they want that
option" stuff. It was, um, optional....
From -04 to -05
o Went through and made sure that I'd captured the feedback
received.
o Comments from Ed Lewis.
o Filled in the "Domain Name Reservation Considerations" section of
RFC6761.
o Removed examples from .Onion.
From -03 to -04
o Incorporated some comments from Paul Hoffman
From -02 to -03
o After discussions with chairs, made this much more generic (not
purely non-DNS), and some cleanup.
From -01 to -02
o Removed some fluffy wording, tightened up the language some.
From -00 to -01.
o Fixed the abstract.
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o Recommended that folk root their non-DNS namespace under a DNS
namespace that they control (Joe Abley)
Authors' Addresses
Warren Kumari
Google
1600 Amphitheatre Parkway
Mountain View, CA 94043
US
Email: warren@kumari.net
Andrew Sullivan
Dyn
150 Dow Street
Manchester, NH 03101
US
Email: asullivan@dyn.com
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