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The ALT Special Use Top Level Domain

The information below is for an old version of the document.
Document Type This is an older version of an Internet-Draft whose latest revision is Replaced
Authors Warren "Ace" Kumari , Andrew Sullivan
Last updated 2015-01-02
Replaced by draft-ietf-dnsop-alt-tld
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dnsop                                                          W. Kumari
Internet-Draft                                                    Google
Intended status: Informational                               A. Sullivan
Expires: July 6, 2015                                                Dyn
                                                         January 2, 2015

                  The ALT Special Use Top Level Domain


   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.

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
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   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 July 6, 2015.

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
   ( in effect on the date of
   publication of this document.  Please review these documents
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   described in the Simplified BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements notation . . . . . . . . . . . . . . . . . .   2
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  The ALT namespace . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Advice to developers  . . . . . . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Appendix A.  Changes / Author Notes.  . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

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 which should be used in most cases
   instead of [RFC6761].  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",
   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.

   o  DNS context: The namespace anchored at the globally-unique DNS
      root.  This is the namespace / context that "normal" DNS uses.

   o  non-DNS context: Any other / alternate namespace.

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   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 is a tree, and so 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

   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, to save
   typing, 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.)

   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 can
   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,
   shims in the name resolution process, or simply applications that
   only use this alternate namespace.

   In many cases the creators of these alternate namespaces have simply
   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
      .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.

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   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.  It is
   RECOMMENDED that users register their usage of this string with the
   IANA in Registry TBD, but users are not required to do so.  This is
   intended to help prevent collisions, but uniqueness is NOT

   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
   rules to deal with these.  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.

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   These rules are intended to limit how far unintentional / non-global
   queries flow.

   Groups wishing to create 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 / descriptive.  They SHOULD consult the TBD registry to
   see if anyone has published that they are already using this string,
   and if so, would be wise to choose an alternative string or risk the
   possibility of collisions with some other application.  As there is
   no requirement to register the use of a label in the ALT namespace,
   uniqueness is not guaranteed.

   Currently deployed projects and protocols that are using pseudo-TLDs
   (for example, the ".onion" pseudo-TLD (and other labels in
   [I-D.grothoff-iesg-special-use-p2p-names]) are encouraged but not
   required to move under the ALT TLD.  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.

   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.

   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.

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   There is a concern that if there were placed under .arpa, less
   experienced 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 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/collisions.  In
   the rare instance in which it is NOT desirable to have the name in
   the DNS, the .ALT namespace may be used.

   An option would be for name resolution systems that operate outside
   to DNS to "root" themselves under a DNS name that the project or
   organization controls.  So, for example if the Tor project controls it could "root" their namespace under  The concept of "rooting" a non-DNS context in
   a DNS context requires some explanation.  This document tries to
   mitigate collisions in the DNS context.  This means that if a name
   from the alternate naming system gets resolved in the DNS, it should
   not conflict or cause unexpected behavior.  By "rooting a non-DNS
   context namespace in the DNS context, under a name controlled by the
   project" we mean that the rightmost set of labels should, if resolved
   in the DNS context be in a domain controlled by the developers /
   project.  This means that, in the above example the software
   implementing the alternate namespace (browser plugins, custom stub
   resolvers, etc) would then match on names that end in the string
   "" and provide the alternate name resolution
   (instead of matching on the strings ending in ".onion".)

   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 a query for one of these names (for
   example (this is not a real .onion
   address)) 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 name servers and then the nameservers.  This means that the fact that a user
   is resolving would be visible to a large
   number of people.  Furthermore, the nameservers
   become a good oracle to determine what names exist, and who is trying
   to reach them.

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   For projects that are very latency sensitive, or which desire to
   provide confidentiality we recommend rooting 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.

   The IANA is requested to create and administer a new, first come,
   first served registry named "ALT pseudo-TLD labels".

   The fields in the registry should be:

   Label: An ASCII string containing a maximum of 63 characters, using
   only letters (a-z), digits (0-9), and hyphen (-).

   Description: A short, textual description explaining what the label
   is used for.

   Reference: A link to a stable reference, such as an RFC, or contact
   information for a person responsible for the reservation.

   [ Ed: This section needs much cleanup - looking for something similar
   family-numbers.xhtml (with people for things that don't have RFC
   references) ]

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 ot thank Paul Hoffman for feedback.

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8.  References

8.1.  Normative References

              Grothoff, C., Wachs, M., hellekin, h., and J. Appelbaum,
              "Special-Use Domain Names of Peer-to-Peer Systems", draft-
              grothoff-iesg-special-use-p2p-names-02 (work in progress),
              March 2014.

   [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

              Abley, J., Dickson, B., Kumari, W., and G. Michaelson,
              "AS112 Redirection using DNAME", draft-ietf-dnsop-
              as112-dname-06 (work in progress), November 2014.

              Manderson, T., Vegoda, L., and S. Kent, "RPKI Objects
              issued by IANA", draft-ietf-sidr-iana-objects-03 (work in
              progress), May 2011.

Appendix A.  Changes / Author Notes.

   [RFC Editor: Please remove this section before publication ]

   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

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   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)

Authors' Addresses

   Warren Kumari
   1600 Amphitheatre Parkway
   Mountain View, CA  94043


   Andrew Sullivan
   150 Dow Street
   Manchester, NH  03101


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