Network Working Group T. Hardie
Internet-Draft January 28, 2016
Intended status: Informational
Expires: July 31, 2016
Considerations for establishing resolution contexts for Internet Names
draft-hardie-resolution-contexts-01
Abstract
This document examines the question of how to signal the appropriate
resolution context for Internet names. It starts from the premise
that the Domain Name System is by far the most common resolution
context but that it is not the only extant or potential resolution
context for Internet names.
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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. It seems likely that this is
because of a wish to use protocols defined for DNS names as if they
were defined for their non-DNS Internet names. The .onion example
was driven at least in part, in other words, because its users wanted
https://identifier.onion/ to work as a signal that the resource was a
web site, even if dereferencing the authority section did not use the
DNS. 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 key practical question that follows from the existence of
alternative resolution contexts for a globally shared naming context
is how you can determine what resolution context is associated with a
particular Internet name. In particular, it is important to
determine whether it is part of the Domain name set of Internet
names. The de facto signal in use now is the top-most label of the
Internet name. If that label 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
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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). 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.
3. Available Alternatives
There are many potential ways to signal that an Internet name is not
within the DNS context, but a only subset of those ways allow for
those names to be used in protocol contexts which currently expect
DNS-based names. A non-exhaustive list is set out below. It is
important to recognize that any Internet name designed to be used in
such a context must accept limitations to achieve it. Some of those
limitations are syntactic, but the most important is that it must be
a unique name within a directed graph within the overall Internet
namespace.
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,
the deployment of loopback root zones [RFC7706] will reduce the
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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. Scope considerations
While this problem clearly has a potentially serious impact on both
the scope of the relevant namespaces and on the code complexity
required to deal with them, it is important to note that there are
many Internet scale namespaces which do not present this problem. An
illustrative example may be taken from the instant messaging systems
like WhatsApp. As a mobile application, it confirms identity using
E.164 numbers (by sending an SMS to the submitted number) and
represents other users using the strings present in each phone's
contact list, so it does not need to maintain a globally unique
presentation form for its users. While it may use the DNS for
resolution of its servers, it clearly could avoid that indirection by
distributing resolution hints pointing to anycast servers, much as
the DNS root does. Within an app context, in other words, namespaces
completely independent of each other and the DNS can reach Internet
scale. These may, like Twitter handles, overlap the Internet
namespace when used from browser contexts. @ExampleName may be clear
within a Twitter app context,but ExampleName@twitter.com is commonly
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used outside it. Some context marker is required to avoid ambiguity
and the potential for fishing, as ExampleName may be one individual
in the twitter context and a different one in Facebook's, but that
context marker need not be the DNS.
5. 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.
6. 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
to stand up services which would mimic those present elsewhere,
allowing the attacker to subvert the connection, steal credentials,
7. IANA Considerations
This document currently has no actions for IANA.
8. 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.
9. Informative References
[TOR] The Tor Project, "Tor", 2013,
.
[RFC0819] Su, Z. and J. Postel, "The Domain Naming Convention for
Internet User Applications", RFC 819,
DOI 10.17487/RFC0819, August 1982,
.
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[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, .
[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,
.
[RFC5891] Klensin, J., "Internationalized Domain Names in
Applications (IDNA): Protocol", RFC 5891,
DOI 10.17487/RFC5891, August 2010,
.
[RFC6761] Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
RFC 6761, DOI 10.17487/RFC6761, February 2013,
.
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
DOI 10.17487/RFC6762, February 2013,
.
[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,
.
[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,
.
[RFC7686] Appelbaum, J. and A. Muffett, "The ".onion" Special-Use
Domain Name", RFC 7686, DOI 10.17487/RFC7686, October
2015, .
[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.
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Author's Address
Ted Hardie
Email: ted.ietf@gmail.com
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