Properties of an Ideal Naming Service
draft-trammell-inip-pins-04

Versions: 00 01 02 03 04                                                
Network Working Group                                        B. Trammell
Internet-Draft                                                ETH Zurich
Intended status: Informational                        September 20, 2017
Expires: March 24, 2018


                 Properties of an Ideal Naming Service
                      draft-trammell-inip-pins-04

Abstract

   This document specifies a set of necessary functions and desirable
   properties of an ideal system for resolving names to addresses and
   associated information for establishing communication associations in
   the Internet.  For each property, it briefly explains the rationale
   behind it, and how the property is or could be met with the present
   Domain Name System.  It is intended to start a discussion within the
   IAB's Names and Identifiers program about gaps between the present
   reality of DNS and the naming service the Internet needs by returning
   to first principles.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on March 24, 2018.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect



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   to this document.  Code Components extracted from this document must
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Query Interface . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Name to Address . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Address to Name . . . . . . . . . . . . . . . . . . . . .   4
     3.3.  Name to Name  . . . . . . . . . . . . . . . . . . . . . .   4
     3.4.  Name to Auxiliary Information . . . . . . . . . . . . . .   5
     3.5.  Name/Address to Auxiliary Information . . . . . . . . . .   5
   4.  Authority Interface . . . . . . . . . . . . . . . . . . . . .   5
   5.  Properties  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  Semantics . . . . . . . . . . . . . . . . . . . . . . . .   5
       5.1.1.  Meaningfulness  . . . . . . . . . . . . . . . . . . .   5
       5.1.2.  Distinguishability  . . . . . . . . . . . . . . . . .   6
       5.1.3.  Minimal Structure . . . . . . . . . . . . . . . . . .   6
     5.2.  Authority . . . . . . . . . . . . . . . . . . . . . . . .   6
       5.2.1.  Federation of Authority . . . . . . . . . . . . . . .   6
       5.2.2.  Uniqueness of Authority . . . . . . . . . . . . . . .   6
       5.2.3.  Transparency of Authority . . . . . . . . . . . . . .   7
       5.2.4.  Revocability of Authority . . . . . . . . . . . . . .   7
       5.2.5.  Consensus on Root of Authority  . . . . . . . . . . .   7
     5.3.  Authenticity  . . . . . . . . . . . . . . . . . . . . . .   7
       5.3.1.  Authenticity of Delegation  . . . . . . . . . . . . .   7
       5.3.2.  Authenticity of Response  . . . . . . . . . . . . . .   8
       5.3.3.  Authenticity of Negative Response . . . . . . . . . .   8
     5.4.  Consistency . . . . . . . . . . . . . . . . . . . . . . .   8
       5.4.1.  Dynamic Consistency . . . . . . . . . . . . . . . . .   8
       5.4.2.  Explicit Inconsistency  . . . . . . . . . . . . . . .   8
       5.4.3.  Global Invariance . . . . . . . . . . . . . . . . . .   9
     5.5.  Performance Properties  . . . . . . . . . . . . . . . . .   9
       5.5.1.  Availability  . . . . . . . . . . . . . . . . . . . .   9
       5.5.2.  Lookup Latency  . . . . . . . . . . . . . . . . . . .  10
       5.5.3.  Bandwidth Efficiency  . . . . . . . . . . . . . . . .  10
       5.5.4.  Query Linkability . . . . . . . . . . . . . . . . . .  10
       5.5.5.  Explicit Tradeoff . . . . . . . . . . . . . . . . . .  10
     5.6.  Trust in Infrastructure . . . . . . . . . . . . . . . . .  11
   6.  Observations  . . . . . . . . . . . . . . . . . . . . . . . .  11
     6.1.  Delegation and redirection are separate operations  . . .  11
     6.2.  Queries and assertion contexts are presently implicit . .  11
     6.3.  Unicode alone may not be sufficient for distinguishable
           names . . . . . . . . . . . . . . . . . . . . . . . . . .  12
     6.4.  Implicit inconsistency makes global invariance



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           challenging to verify . . . . . . . . . . . . . . . . . .  12
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  13
   10. Informative References  . . . . . . . . . . . . . . . . . . .  13
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   The Internet's Domain Name System (DNS) [RFC1035] is an excellent
   illustration of the advantages of the decentralized architecture that
   have made the Internet able to scale to its present size.  However,
   the choices made in the evolution of the DNS since its initial design
   are only one path through the design space of Internet-scale naming
   services.  Many other naming services have been proposed, though none
   has been remotely as successful for general- purpose use in the
   Internet.

   This document returns to first principles, to determine the
   dimensions of the design space of desirable properties of an
   Internet-scale naming service.  It is a work in progress, intended to
   start a discussion within the IAB's Names and Identifiers program
   about gaps between the present reality of DNS and the naming service
   the Internet needs.

   Section 3 and Section 4 define the set of operations a naming service
   should provide for queriers and authorities, Section 5 defines a set
   of desirable properties of the provision of this service, and
   Section 6 examines implications of these properties.

2.  Terminology

   The following capitalized terms are defined and used in this
   document:

   o  Subject: A name, address, or name-address pair about which the
      naming service can answer queries

   o  Association: A mapping between a Subject and information about
      that Subject

   o  Authority: An entity that has the right to determine which
      Associations exist within its namespace

   o  Delegation: An Association that indicates that an Authority has
      given the right to make assertions about the Associations within
      the part of a namespace identified by a Subject to a subordinate
      Authority.



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3.  Query Interface

   At its core, a naming service must provide a few basic functions for
   queriers, associating a Subject of a query with information about
   that subject.  The information available from a naming service is
   that which is necessary for a querier to establish a connection with
   some other entity in the Internet, given a name identifying it.

3.1.  Name to Address

   Given a Subject name, the naming service returns a set of addresses
   associated with that name, if such an association exists, where the
   association is determined by the authority for that name.  Names may
   be associated with addresses in one or more address families (e.g.
   IP version 4, IP version 6).  A querier may specify which address
   families it is interested in receiving addresses for, and the naming
   system treats all address families equally.

   This mapping is implemented in the DNS protocol via the A and AAAA
   RRTYPES.

3.2.  Address to Name

   Given an Subject address, the naming service returns a set of names
   associated with that address, if such an association exists, where
   the association is determined by the authority for that address.

   This mapping is implemented in the DNS protocol via the PTR RRTYPE.
   IPv4 mappings exist within the in-addr.arpa. zone, and IPv6 mappings
   in the ip6.arpa. zone.  This mechanism has the disadvantage that
   delegations in IPv4 only happen on octet (8-bit) boundaries, and in
   IPv6 only happen on hex digit (4-bit) boundaries, which make
   delegations on other prefixes operationally difficult.

3.3.  Name to Name

   Given a Subject name, the naming service returns a set of object
   names associated with that name, if such an association exists, where
   the association is determined by the authority for the subject name.

   This mapping is implemented in the DNS protocol via the CNAME RRTYPE.
   CNAME does not allow the association of multiple object names with a
   single subject, and CNAME may not combine with other RRTYPEs (e.g.
   NS, MX) arbitrarily.







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3.4.  Name to Auxiliary Information

   Given a Subject name, the naming service returns other auxiliary
   information associated with that name that is useful for establishing
   communication over the Internet with the entities associated with
   that name.

   Most of the other RRTYPES in the DNS protocol implement these sort of
   mappings.

3.5.  Name/Address to Auxiliary Information

   As a name might be associated with more than one address, auxiliary
   information as above may be associated with a name/address pair, as
   opposed to just with a name.

   This mapping is not presently supported by the DNS protocol.

4.  Authority Interface

   The query interface is not the only interface to the naming service:
   the interface a naming service presents to an Authority allows
   updates to the set of Associations and Delegations in that
   Authority's namespace.  Updates consist of additions of, changes to,
   and deletions of Associations and Delegations.  In the present DNS,
   this interface consists of the publication of a new zone file with an
   incremented version number, but other authority interfaces are
   possible.

5.  Properties

   The following properties are desirable in a naming service providing
   the functions in Section 3 and Section 4.

5.1.  Semantics

   Since the point of a naming service is to replace network-layer
   identifiers with more useful identifiers for humans (whether end
   users, software developers, or network administrators), the Subject
   names the naming service can provide must meet two semantic criteria:

5.1.1.  Meaningfulness

   A naming service must provide the ability to name objects that its
   human users find more meaningful than the objects themselves.






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5.1.2.  Distinguishability

   A naming service must make it possible to guarantee that two
   different names are easily distinguishable from each other by its
   human users.

5.1.3.  Minimal Structure

   A naming service should impose as little structure on the names it
   supports as practical in order to be universally applicable.  Naming
   services that impose a given organizational structure on the names
   expressible using the service will not translate well to societies
   where that organizational structure is not prevalent.

5.2.  Authority

   Every Association among names, addresses, and auxiliary data is
   subject to some Authority: an entity which has the right to determine
   which Associations and Subjects exist in its namespace.  The
   following are properties of Authorities in our ideal naming service:

5.2.1.  Federation of Authority

   An Authority can delegate some part of its namespace to some other
   subordinate Authority.  This property allows the naming service to
   scale to the size of the Internet, and leads to a tree-structured
   namespace, where each Delegation is itself identified with a Subject
   at a given level in the namespace.

   In the DNS protocol, this federation of authority is implemented
   through delegation using the NS RRTYPE, redirecting queries to
   subordinate authorities recursively to the final authority.  When
   DNSSEC is used, the DS RRTYPE is used to verify this delegation.

5.2.2.  Uniqueness of Authority

   For a given Subject, there is a single Authority that has the right
   to determine the Associations and/or Delegations for that subject.
   The unitary authority for the root of the namespace tree may be
   special, though; see Section 5.2.5.

   In the DNS protocol as deployed, unitary authority is approximated by
   the entity identified by the SOA RRTYPE.  The existence of
   registrars, which use the Extensible Provisioning Protocol (EPP)
   [RFC5730] to modify entries in the zones under the authority of a
   top-level domain registry, complicates this somewhat.





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5.2.3.  Transparency of Authority

   A querier can determine the identity of the Authority for a given
   Association.  An Authority cannot delegate its rights or
   responsibilities with respect to a subject without that Delegation
   being exposed to the querier.

   In DNS, the authoritative name server(s) to which a query is
   delegated via the NS RRTYPE are known.  However, we note that in the
   case of authorities which delegate the ability to write to the zone
   to other entities (i.e., the registry-registrar relationship), the
   current DNS provides no facility for a querier to understand on whose
   behalf an authoritative assertion is being made; this information is
   instead available via WHOIS.  To our knowledge, no present DNS name
   servers use WHOIS information retrieved out of band to make policy
   decisions.

5.2.4.  Revocability of Authority

   An ideal naming service allows the revocation and replacement of an
   authority at any level in the namespace, and supports the revocation
   and replacement of authorities with minimal operational disruption.

   The current DNS allows the replacement of any level of delegation
   except the root through changes to the appropriate NS and DS records.
   Authority revocation in this case is as consistent as any other
   change to the DNS.

5.2.5.  Consensus on Root of Authority

   Authority at the top level of the namespace tree is delegated
   according to a process such that there is universal agreement
   throughout the Internet as to the subordinates of those Delegations.

5.3.  Authenticity

   A querier must be able to verify that the answers that it gets from
   the naming service are authentic.

5.3.1.  Authenticity of Delegation

   Given a Delegation from a superordinate to a subordinate Authority, a
   querier can verify that the superordinate Authority authorized the
   Delegation.

   Authenticity of delegation in DNS is provided by DNSSEC [RFC4033].





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5.3.2.  Authenticity of Response

   The authenticity of every answer is verifiable by the querier.  The
   querier can confirm that the Association returned in the answer is
   correct according to the Authority for the Subject of the query.

   Authenticity of response in DNS is provided by DNSSEC.

5.3.3.  Authenticity of Negative Response

   Some queries will yield no answer, because no such Association
   exists.  In this case, the querier can confirm that the Authority for
   the Subject of the query asserts this lack of Association.

   Authenticity of negative response in DNS is provided by DNSSEC.

5.4.  Consistency

   Consistency in a naming service is important.  The naming service
   should provide the most globally consistent view possible of the set
   of associations that exist at a given point in time, within the
   limits of latency and bandwidth tradeoffs.

5.4.1.  Dynamic Consistency

   When an Authority makes changes to an Association, every query for a
   given Subject returns either the new valid result or a previously
   valid result, with known and/or predictable bounds on "how
   previously".  Given that additions of, changes to, and deletions of
   associations may have different operational causes, different bounds
   may apply to different operations.

   The time-to-live (TTL) on a resource record in DNS provides a
   mechanism for expiring old resource records.  We note that this
   mechanism makes additions to the system propagate faster than changes
   and deletions, which may not be a desirable property.  However, as no
   context information is explicitly available in DNS, the DNS cannot be
   said to be dynamically consistent, as different implicitly
   inconsistent views of an association may be persistent.

5.4.2.  Explicit Inconsistency

   Some techniques require giving different answers to different
   queries, even in the absence of changes: the stable state of the
   namespace is not globally consistent.  This inconsistency should be
   explicit: a querier can know that an answer might be dependent on its
   identity, network location, or other factors.




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   One example of such desirable inconsistency is the common practice of
   "split horizon" DNS, where an organization makes internal names
   available on its own network, but only the names of externally-
   visible subjects available to the Internet at large.

   Another is the common practice of DNS-based content distribution, in
   which an authoritative name server gives different answers for the
   same query depending on the network location from which the query was
   received, or depending on the subnet in which the end client
   originating a query is located (via the EDNS Client Subnet extension
   {RFC7871}}).  Such inconsistency based on client identity or network
   address may increase query linkability (see Section 5.5.4).

   These forms of inconsistency are implicit, not explicit, in the
   current DNS.  We note that while DNS can be deployed to allow
   essentially unlimited kinds of inconsistency in its responses, there
   is no protocol support for a query to express the kind of consistency
   it desires, or for a response to explicitly note that it is
   inconsistent.  [RFC7871] does allow a querier to note that it would
   specifically like the view of the state of the namespace offered to a
   certain part of the network, and as such can be seen as inchoate
   support for this property.

5.4.3.  Global Invariance

   An Association which is not intended to be explicitly inconsistent by
   the Authority issuing it must return the same result for every Query
   for it, regardless of the identity or location of the querier.

   This property is not provided by DNS, as it depends on the robust
   support on the Explicit Inconsistency property above.  Examples of
   global invariance failures include geofencing and DNS-based
   censorship ordered by a local jurisdiction.

5.5.  Performance Properties

   A naming service must provide appropriate performance guarantees to
   its clients.  As these properties deal with the operational
   parameters of the naming service, interesting tradeoffs are available
   among them, both at design time as well as at run time (on which see
   Section 5.5.5).

5.5.1.  Availability

   The naming service as a whole is resilient to failures of individual
   nodes providing the naming service, as well as to failures of links
   among them.  Intentional prevention of successful, authenticated
   query by an adversary should be as hard as practical.



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   The DNS protocol was designed to be highly available through the use
   of secondary nameservers.  Operational practices (e.g. anycast
   deployment) also increase the availability of DNS as currently
   deployed.

5.5.2.  Lookup Latency

   The time for the entire process of looking up a name and other
   necessary associated data from the point of view of the querier,
   amortized over all queries for all connections, should not
   significantly impact connection setup or resumption latency.

5.5.3.  Bandwidth Efficiency

   The bandwidth cost for looking up a name and other associated data
   necessary for establishing communication with a given Subject, from
   the point of view of the querier, amortized over all queries for all
   connections, should not significantly impact total bandwidth demand
   for an application.

5.5.4.  Query Linkability

   It should be costly for an adversary to monitor the infrastructure in
   order to link specific queries to specific queriers.

   DNS over TLS [RFC7858] and DNS over DTLS [RFC8094] provide this
   property between a querier and a recursive resolver; mixing by the
   recursive helps with mitigating upstream linkability.

5.5.5.  Explicit Tradeoff

   A querier should be able to indicate the desire for a benefit with
   respect to one performance property by accepting a tradeoff in
   another, including:

   o  Reduced latency for reduced dynamic consistency

   o  Increased dynamic consistency for increased latency

   o  Reduced request linkability for increased latency and/or reduced
      dynamic consistency

   o  Reduced aggregate bandwidth use for increased latency and/or
      reduced dynamic consistency

   There is no support for explicit tradeoffs in performance properties
   available to clients in the present DNS.




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5.6.  Trust in Infrastructure

   A querier should not need to trust any entity other than the
   authority as to the correctness of association information provided
   by the naming service.  Specifically, the querier should not need to
   trust any intermediary of infrastructure between itself and the
   authority, other than that under its own control.

   DNS provides this property with DNSSEC.  However, the lack of
   mandatory DNSSEC, and the lack of a viable transition strategy to
   mandatory DNSSEC, means that trust in infrastructure will remain
   necessary for DNS even with large scale DNSSEC deployment.

6.  Observations

   On a cursory examination, many of the properties of our ideal name
   service can be met, or could be met, by the present DNS protocol or
   extensions thereto.  We note that there are further possibilities for
   the future evolution of naming services meeting these properties.
   This section contains random observations that might inform future
   work.

6.1.  Delegation and redirection are separate operations

   Any system which can provide the authenticity properties in
   Section 5.3 is freed from one of the design characteristics of the
   present domain name system: the requirement to bind a zone of
   authority to a specific set of authoritative servers.  Since the
   authenticity of delegation must be a protected by a chain of
   signatures back to the root of authority, the location within the
   infrastructure where an authoritative mapping "lives" is no longer
   bound to a specific name server.  While the present design of DNS
   does have its own scalability advantages, this implication allows a
   much larger design space to be explored for future name service work,
   as a Delegation need not always be implemented via redirection to
   another name server.

6.2.  Queries and assertion contexts are presently implicit

   Much of the difficulty with explicit inconsistency (Section 5.4.2)
   derives from the fact that assertions and queries about subjects
   exist within a context: .local names on the local network (whether
   link or site local), split-DNS names within the context of the
   "inside" side of the recursive resolver, DNS geographic load
   balancing within the geographic context of the client.  Because DNS
   provides no protocol-level support for expressing these contexts,
   they remain implicit.




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   We note that protocol-level support for this context explicit could
   point toward solutions for a variety of problems in currently
   deployed naming services, from generalized solutions with privacy/
   efficiency tradeoffs ({RFC7871}} aside), to explicit redirection to
   alternate naming resolution for "special" names [RFC6761].

6.3.  Unicode alone may not be sufficient for distinguishable names

   Allowing names to be encoded in Unicode goes a long way toward
   meeting the meaningfulness property (see Section 5.1.1) for the
   majority of speakers of human languages.  However, as noted by the
   Internet Architecture Board (see [IAB-UNICODE7]) and discussed at the
   Locale-free Unicode Identifiers (LUCID) BoF at IETF 92 in Dallas in
   March 2015 (see [LUCID]), it is not in the general case sufficient
   for distinguishability (see Section 5.1.2).  An ideal naming service
   may therefore have to supplement Unicode by providing runtime support
   for disambiguation of queries and assertions where the results may be
   indistinguishable.

6.4.  Implicit inconsistency makes global invariance challenging to
      verify

   DNS does not provide a generalized form of explicit inconsistency, so
   efforts to verify global invariance, or rather, to discover
   Associations for which global invariance does not hold, are
   necessarily effort-intensive and dynamic.  For example, the Open
   Observatory of Network Interference performs DNS consistency checking
   from multiple volunteer vantage points for a set of targeted (i.e.,
   likely to be globally variant) domain names; see
   https://ooni.torproject.org/nettest/dns-consistency/

7.  IANA Considerations

   This document has no actions for IANA.

8.  Security Considerations

   Protocols implementing name resolution systems that meet these ideal
   properties will have to consider tradeoffs, especially with respect
   to privacy (Section 5.5.4) versus performance, as in Section 5.5.5.
   Many properties are security and privacy relevant.  All the
   properties in Section 5.3 must hold for a client to be able to trust
   that assertions about a name are as intended by the authority for
   that name.  Section 5.1.2 specifies a property which, when it does
   not hold, may be exploitable for phishing attacks, and Section 5.2.3
   specifies a property which may ease operational defense against
   malware abuse of the naming system.




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9.  Acknowledgments

   This document is, in part, an output of design work on naming
   services at the Network Security Group at ETH Zurich.  Thanks to the
   group, including Daniele Asoni, Steve Matsumoto, and Stephen Shirley,
   for discussions leading to this document.  Thanks as well to Ted
   Hardie, Wendy Selzter, Andrew Sullivan, and Suzanne Woolf for input
   and feedback.

10.  Informative References

   [I-D.ietf-dprive-dns-over-tls]
              Zi, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
              and P. Hoffman, "Specification for DNS over TLS", draft-
              ietf-dprive-dns-over-tls-09 (work in progress), March
              2016.

   [I-D.ietf-dprive-dnsodtls]
              Reddy, T., Wing, D., and P. Patil, "Specification for DNS
              over Datagram Transport Layer Security (DTLS)", draft-
              ietf-dprive-dnsodtls-15 (work in progress), December 2016.

   [IAB-UNICODE7]
              IAB, ., "IAB Statement on Identifiers and Unicode 7.0.0",
              n.d., <https://www.iab.org/documents/
              correspondence-reports-documents/2015-2/
              iab-statement-on-identifiers-and-unicode-7-0-0/>.

   [LUCID]    Freytag, A. and A. Sullivan, "LUCID problem (slides, IETF
              92 LUCID BoF)", n.d.,
              <https://www.ietf.org/proceedings/92/slides/
              slides-92-lucid-0.pdf>.

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

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements",
              RFC 4033, DOI 10.17487/RFC4033, March 2005,
              <https://www.rfc-editor.org/info/rfc4033>.

   [RFC5730]  Hollenbeck, S., "Extensible Provisioning Protocol (EPP)",
              STD 69, RFC 5730, DOI 10.17487/RFC5730, August 2009,
              <https://www.rfc-editor.org/info/rfc5730>.






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Internet-Draft                    PINS                    September 2017


   [RFC6761]  Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
              RFC 6761, DOI 10.17487/RFC6761, February 2013,
              <https://www.rfc-editor.org/info/rfc6761>.

   [RFC7858]  Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
              and P. Hoffman, "Specification for DNS over Transport
              Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
              2016, <https://www.rfc-editor.org/info/rfc7858>.

   [RFC7871]  Contavalli, C., van der Gaast, W., Lawrence, D., and W.
              Kumari, "Client Subnet in DNS Queries", RFC 7871,
              DOI 10.17487/RFC7871, May 2016,
              <https://www.rfc-editor.org/info/rfc7871>.

   [RFC8094]  Reddy, T., Wing, D., and P. Patil, "DNS over Datagram
              Transport Layer Security (DTLS)", RFC 8094,
              DOI 10.17487/RFC8094, February 2017,
              <https://www.rfc-editor.org/info/rfc8094>.

Author's Address

   Brian Trammell
   ETH Zurich
   Universitaetstrasse 6
   Zurich  8092
   Switzerland

   Email: ietf@trammell.ch























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