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Considerations for establishing resolution contexts for Internet Names
draft-hardie-resolution-contexts-00

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Author Ted Hardie
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draft-hardie-resolution-contexts-00
Network Working Group                                          T. Hardie
Internet-Draft                                         December 03, 2015
Intended status: Informational
Expires: June 5, 2016

 Considerations for establishing resolution contexts for Internet Names
                  draft-hardie-resolution-contexts-00

Abstract

   The effort to register .onion [RFC7686] in the IANA special names
   registry[RFC6761] has given rise to considerable discussion of how
   the namespace associated with the DNS relates to other namespaces
   used on the Internet.  A brief history of this has been set out in
   [I-D.lewis-domain-names].  This document focuses on the question of
   how to signal resolution context within a unified namespace that
   contains both DNS and non-DNS names.

Status of This Memo

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   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on June 5, 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
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   include Simplified BSD License text as described in Section 4.e of

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

1.  Introduction

   The history in [I-D.lewis-domain-names] and the usage in [RFC3986]
   both suggest that names registered in the domain name system are part
   of a larger set of Internet names.  If we model the system of
   Internet names as a set of directed graphs in an absolute naming
   context, following RFC 819 [RFC0819], an Internet name is not
   necessarily a name in the domain name system, but is simply a unique
   name associated with that particular directed graph.  The resolution
   of the name, in other words, is independent from it being an
   "Internet name".  The DNS is a common, but not the only, resolution
   context for Internet names.

2.  Resolution Contexts

   The Domain Name System [RFC1034][RFC1035] provides the most common
   resolution system for Internet names by many orders of magnitude.  It
   has not, however, met all resolution requirements.  Multicast DNS
   [RFC6762] uses an alternative resolution service, as does TOR [TOR].
   Tor's .onion names, in particular, appear to be effectively Internet
   names within a globally shared naming context; they simply happen to
   use an alternative resolution method.

   The key practical question that follows from the existence of
   alternative resolution contexts is how you can determine whether or
   not a particular Internet name is part of the Domain name set of
   Internet names, or part of a different set.  The de facto signal we
   are using now is the top-most label of the Internet name.  If it is
   within the known set of DNS top-most labels, we have a definite yes.
   If it is within an established set of non-DNS top-most labels, we
   have a definite no.

   There are at least two unfortunate sets of potentially conflicting
   cases, where people are using labels with the intent to use this
   signal but have not risen to the level of "established no".  In the
   first case, their usage may be mistaken for non-fully qualified names
   within the domain name system, resulting in the construction of a new
   Internet name where one was not intended (e.g. www.sld.allium
   becoming www.sld.allium.corp.example.com, rather than .allium being
   used as signal that this Internet name is not within the set of
   domain names).  The second case, which may overlap, is one in which
   the growth of the set of names in domain name system causes overlap
   (a new gTLD like .allium being assigned would conflict with the
   attempted use of .allium as a resolution context signal).

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   The risks of the two conflicting cases are pretty obvious, but
   despite that the use of a pseudo-TLD signal seems desirable to many
   setting up alternative resolution contexts.  It seems likely that
   this is because the services within the alternative resolution
   contexts wish to use protocols defined for DNS names as if they were
   defined for their Internet names.  The .onion example was driven, in
   other words, at least in part because its users wanted
   https://identifier.onion/ to work.  In order to share the HTTPS URI
   context, they needed to minimize the changes to the form of the URI.
   That meant using https:// with a resolution trigger, rather than
   changing the URI (tor-https://, for example).

   The implication for the universe of architecturally appropriate
   responses is that any means for signalling that a name is not within
   the DNS context but is still meant to be an Internet name must
   continue to allow those Internet names to be used in common protocol
   contexts.  It also means that any Internet name must expect
   restrictions to achieve that (viz. it must be a unique name within a
   directed graph within the overall Internet name namespace).

3.  Available Alternatives

   Given that restriction, the universe of possible resolution context
   signals seems to be limited.  One option is using a designated sub-
   tree of the Internet namespace for non-DNS resolutions, with labels
   within the tree indicating which resolution context is meant.
   [I-D.ietf-dnsop-alt-tld] describes one specific approach to this
   option.  While the use of this sub-tree may be esthetically less
   pleasing than a pseudo-TLD, it avoids the ambiguities which may arise
   during the development of alternative resolution context.

   A second alternative is to fix either the set of top-level domains or
   the number of resolution contexts, so that ambiguity cannot occur.
   While a fixed set of top-level domains might have seemed practical
   when the number of TLDs was limited to country codes and a strictly
   limited set of generic top-level domains, this has ceased to be a
   practical alternative.  Similarly, the creation of alternative
   resolution contexts cannot be effectively stifled, even were this
   desirable; those interested can implement and deploy them without
   registration of any kind.  That these may not interoperate or
   conflict with other deployments is, of course, a risk.

   A third alternative within the DNS context is to continue the current
   registration of pseudo-TLDs and accept the consequences of ambiguity.
   This will mean that conflicts between resolution context pseudo-TLDs
   and potential future TLDs must be managed and that the operational
   impact must be addressed.  A focus on deployment of mitigation
   strategies may reduce the operational consequences.  As an example,

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   the deployment of loopback root zones [RFC7706] will reduce the
   impact of queries for pseudo-TLDs leaking to the root DNS name
   servers.  Similarly, policies for names registered as pseudo-TLDs may
   also limit potential conflict.

   An alternative to signals within the DNS is making alternative
   signals easier.  URI registrations have gotten significantly
   easier[RFC7595] over time, but it might be possible to lower the bar
   further by creating a convention for using alternative resolution
   contexts.

   As an example, we could set aside a string delimiter for this purpose
   as we set aside xn- to single out the ACE encoding for
   Internationalized Domain Names [RFC5891].  That string delimiter
   could then be used to construct faceted URI schemes, one aspect of
   which contained the usual protocol indicator and the other the
   resolution context.  The ABNF for scheme is:

   scheme = ALPHA *( ALPHA / DIGIT / "+" / "-" / "." )

   Setting aside a string delimiter such as +.+ would allow something
   like https://identifier.onion/ to become https+._tor//identifier/.
   This would require updates to URI parsing libraries that intended to
   handle alternative resolution contexts, but the use of a common
   delimiter would lower the amount of code needed both to identify the
   core protocol and the alternative resolution contexts.  It might
   remain esthetically less pleasing, however, and it would prevent the
   use of IDNA-permitted characters as resolution context identifiers,
   something which the DNS-based solutions do allow.

4.  Conclusions

   There are clearly trade-offs among the available alternatives, as
   each has its own drawbacks as an indicator of resolution context.
   Given, however, that the existence of multiple signals could generate
   even further interoperability issues and operational concerns, the
   creation of multiple signals is undesirable.  Any system which allows
   Internet names from alternate resolution contexts to be used in
   common protocol systems can likely be made to work, provided its
   drawbacks are accounted for and mitigated appropriately.

5.  Security Considerations

   This document describes a number of potential method for establishing
   a resolution context for an Internet name.  Should the resolution
   context to be used with a name not be sufficiently clear, it may be
   possible to provide alternative information in a different context.
   That alternative information could provide an avenue for an attacker

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   to stand up services which would mimic those present elsewhere,
   allowing the attacker to subvert the connection, steal credentials,

6.  IANA Considerations

   This document currently has no actions for IANA.

7.  Acknowledgements

   Thanks to Ed Lewis, Suzanne Wolff, and Andrew Sullivan for
   conversations leading up to this document; all errors of fact and
   judgement are, however, the author's.

8.  Informative References

   [TOR]      The Tor Project, "Tor", 2013,
              <https://www.torproject.org/>.

   [RFC0819]  Su, Z. and J. Postel, "The Domain Naming Convention for
              Internet User Applications", RFC 819,
              DOI 10.17487/RFC0819, August 1982,
              <http://www.rfc-editor.org/info/rfc819>.

   [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>.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
              November 1987, <http://www.rfc-editor.org/info/rfc1035>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <http://www.rfc-editor.org/info/rfc3986>.

   [RFC5891]  Klensin, J., "Internationalized Domain Names in
              Applications (IDNA): Protocol", RFC 5891,
              DOI 10.17487/RFC5891, August 2010,
              <http://www.rfc-editor.org/info/rfc5891>.

   [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>.

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

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   [RFC7706]  Kumari, W. and P. Hoffman, "Decreasing Access Time to Root
              Servers by Running One on Loopback", RFC 7706,
              DOI 10.17487/RFC7706, November 2015,
              <http://www.rfc-editor.org/info/rfc7706>.

   [RFC7595]  Thaler, D., Ed., Hansen, T., and T. Hardie, "Guidelines
              and Registration Procedures for URI Schemes", BCP 35,
              RFC 7595, DOI 10.17487/RFC7595, June 2015,
              <http://www.rfc-editor.org/info/rfc7595>.

   [RFC7686]  Appelbaum, J. and A. Muffett, "The ".onion" Special-Use
              Domain Name", RFC 7686, DOI 10.17487/RFC7686, October
              2015, <http://www.rfc-editor.org/info/rfc7686>.

   [I-D.ietf-dnsop-alt-tld]
              Kumari, W. and A. Sullivan, "The ALT Special Use Top Level
              Domain", draft-ietf-dnsop-alt-tld-03 (work in progress),
              September 2015.

   [I-D.lewis-domain-names]
              Lewis, E., "Domain Names", draft-lewis-domain-names-01
              (work in progress), September 2015.

Author's Address

   Ted Hardie

   Email: ted.ietf@gmail.com

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