dnsop                                                          W. Kumari
Internet-Draft                                                    Google
Intended status: Informational                               A. Sullivan
Expires: October 18, 2014                                            Dyn
                                                          April 16, 2014

                  The ALT Special Use Top Level Domain


   This document reserves a string (ALT) to be used as a TLD label in
   non-DNS contexts.  It also provides advice / 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
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   This Internet-Draft will expire on October 18, 2014.

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   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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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  . . . . . . . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Appendix A.  Changes / Author Notes.  . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   Many protocols and systems need to name entities.  The DNS "standard"
   of a series of labels separated with dots has become common, even in
   systems that are not actually part of the DNS.

   This document reserves the string "ALT" (short for Alternate) as a
   Special Use Domain ([RFC6761]) that should be used in the right-most
   label position to signify that this 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 administered by ICANN.  This is the
      namespace / context that "normal" DNS uses.

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

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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

   The success of the DNS makes it a natural starting point for systems
   that need to name entities in a non-DNS context.  These name
   resolutions occur in a namespace distinct from the DNS.  A number of
   good examples of these sorts of systems are documented in Special-Use
   Domain Names of Peer-to-Peer Systems

   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 this 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 / descriptive string and started using this.
   These new strings are "alternate" strings, and not actually
   registered anywhere or part of the DNS.  However they appear to be
   TLDs, as they are the in the right-most position of a name.  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, they may become

   o  Excess traffic hitting the DNS root.  Lookups may 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.

   One of the primary design goals of a number of these alternate name
   resolution systems it to provide confidentiality of the names being

   A significant number of these alternate name resolution systems are
   specifically designed to provide confidentiality of the looked up

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   name, and provide a distributed and censorship resistant namespace.
   For example, the Tor project use of .onion is intended to provide a
   confidential and alternate name resolution process.  This goal may be
   defeated if the queries leak into the DNS, for example if a Tor user
   shares a link with a friend who doesn't have the Tor browser

3.  The ALT namespace

   In order to avoid the above issues we reserve the .ALT label.  This
   label should be used as a pseudo-TLD (in the right most (TLD)
   position of a name) to signify that this is an alternate (non-DNS)

   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.  For example, a group wishing
   create a namespace for Friends Of Olaf they may 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
   rules to deal with these.

   1.  Stub resolvers MAY elect not to send queries to any upstream
       resolver for names in the ALT TLD.

   2.  Iterative resolvers SHOULD follow the advice in [RFC6303],
       Section 3.

   3.  The root zone nameservers should either return NXDOMAIN
       responses, or the ALT TLD should be delegated to "new style"
       AS112 nameservers.

   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.  As there is no registry for 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 not expected to move
   under the ALT TLD (but may do so if they wish; this is a common
   resource).  Rather, the ALT TLD is being reserved so that future
   projects of a similar nature have a designated place to create

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   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 followed the DNS format (a prime consideration for alternate name
   formats be that they can be entered in places that normally take DNS
   context names), this rules out using suffixes that are not themselves
   DNS labels.  Another proposal was that the ALT TLD instead be a
   reservation under .arpa.  This was considered, but rejected because
   of we are suggesting that this be served as an [RFC6303] and that
   recursive operators configure themselves to serve empty authoritative
   zones for the reserved labeled.  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 example.alt.arpa may be not look
   as good [TODO: Better wording here.  Don't want to say "vanity" ! ]

4.  Advice to developers

   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
   tor.example.com it could "root" their namespace under
   onion.tor.example.com.  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
   "onion.example.com" 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 dissident.onion.example.com (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 example.com name servers and then the

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   onion.example.com nameservers.  This means that the fact that a user
   is resolving disident.onion.example.com would be visible to a large
   number of people.  Furthermore, the onion.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 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.

   [ Ed: There are two options here.  Option 1: We could ask the IANA to
   run a "First Come First Served" registry for labels under the ALT
   TLD.  By registry I mean a "standard" IANA registry, not a registry
   in the DNS sense of the word (IANA would publish on a webpage "Foo |
   fred@example.com | Used for the foo project").  Option 2: This is a
   fully uncoordinated space (in the same way that people have been
   picking pseudo-TLDs up till now) -- pick something that, as far as
   you know others are not using... There are pros and cons to both -- I
   don't want to overload the IANA, have people stage a land-grab for
   names, or give the impression that this is a "real" TLD.  Thoughts?
   Currently we say there is no registry (Section 3), but that can be

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 registry-free 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 (and any other
   poor sod who gets sucked into this) in advance.

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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

              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 -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

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   Warren Kumari
   1600 Amphitheatre Parkway
   Mountain View, CA  94043

   Email: warren@kumari.net

   Andrew Sullivan
   150 Dow Street
   Manchester, NH  03101

   Email: asullivan@dyn.com

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