Internet DRAFT - draft-wkumari-dnsop-alt-tld
draft-wkumari-dnsop-alt-tld
dnsop W. Kumari
Internet-Draft Google
Intended status: Informational A. Sullivan
Expires: November 19, 2015 Dyn
May 18, 2015
The ALT Special Use Top Level Domain
draft-wkumari-dnsop-alt-tld-06
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 accpeted. ]
Status of This Memo
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This Internet-Draft will expire on November 19, 2015.
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Copyright (c) 2015 IETF Trust and the persons identified as the
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to this document. Code Components extracted from this document must
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements notation . . . . . . . . . . . . . . . . . . 2
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. The ALT namespace . . . . . . . . . . . . . . . . . . . . . . 4
4. Advice to developers . . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5.1. Domain Name Reservation Considerations . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . 8
Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 9
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.
This document provides a solution that may be more appropriate than
[RFC6761] in many cases. RFC6761 specifies Special Use TLDs which
should only be used in exceptional circumstances.
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 (apart from the zero-length terminating 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].
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1.2. Terminology
This document assumes familiarity with DNS terms and concepts.
Please see [RFC1034] for background and concepts.
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 the
global DNS administered by IANA. They often use a pseudo-TLD to
cause resolution in the alternate namespace, using browser plugins,
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shims in the name resolution process, or simply applications that
perform special handling of this alternate namespace.
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 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 behavior may be non-deterministic.
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.
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. Unfortunately simply saying that "something should not
happen" doesn't actually stop it from happening, so we need some
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rules to guide implementors and operators. The ALT TLD is delegated
to "new style" AS112 servers, and so recursive and stub resolvers
will get NXDOMAIN for all queries.
1. Iterative resolvers SHOULD follow the advice in [RFC6303],
Section 3.
2. The ALT TLD is delegated to "new style" AS112 nameservers
([I-D.ietf-dnsop-as112-dname] ), which will return NXDOMAIN for
all queries.
These rules are intended to limit how far unintentional queries (i.e.
those not intended for the global DNS) 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.
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 future projects of a
similar nature have a designated place to create alternate resolution
namespaces that will not conflict with the regular DNS context.
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.
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.
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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. Advice to developers
Often, a subdomain of an existing, owned domain may suffice. When
that is so, using a subdomain in the DNS is always preferable, and
safest in terms of not risking misuse, duplications, or collisions.
In the rare instance in which it is not desirable to have the name in
the DNS, the .ALT namespace may be used.
In a number of cases the purpose of the alternate name resolution
system is to provide confidentiality. For these systems the above
advice is problematic. If the query for one of these names (for
example harry.foo.example.com were to leak into the DNS, the query
would hit the recursive resolver, and (assuming empty caches) would
then hit the root, the .com name servers, the example.com name
servers and then the foo.example.com nameservers. This means that
the fact that a user is resolving harry.foo.example.com would be
visible to a large number of people. Furthermore, the
harry.foo.example.com nameservers become a good oracle to determine
what names exist, and who is trying to reach them.
For projects that are very latency sensitive, or that desire to
provide confidentiality, we recommend anchoring the alternate
namespace under the .ALT TLD.
5. 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.
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5.1. 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 stings
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.
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 debuggung 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
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nonexistent, and they fall outside the set of names available for
allocation by registries/registrars.
6. 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.
7. Acknowledgements
The authors understand that there is much politics surrounding the
delegation of a new TLD and thank the ICANN liaison in advance.
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.
8. References
8.1. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6303] Andrews, M., "Locally Served DNS Zones", BCP 163, RFC
6303, July 2011.
[RFC6761] Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
RFC 6761, February 2013.
8.2. Informative References
[I-D.ietf-dnsop-as112-dname]
Abley, J., Dickson, B., Kumari, W., and G. Michaelson,
"AS112 Redirection using DNAME", draft-ietf-dnsop-
as112-dname-06 (work in progress), November 2014.
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Appendix A. Changes / Author Notes.
[RFC Editor: Please remove this section before publication ]
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.
o Recommended that folk root their non-DNS namespace under a DNS
namespace that they control (Joe Abley)
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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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