DNS Resolver Information
draft-reddy-add-resolver-info-00

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Document Type Active Internet-Draft (individual)
Authors Tirumaleswar Reddy.K  , Mohamed Boucadair 
Last updated 2021-03-29
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ADD WG                                                          T. Reddy
Internet-Draft                                                    McAfee
Intended status: Standards Track                            M. Boucadair
Expires: September 29, 2021                                       Orange
                                                          March 28, 2021

                        DNS Resolver Information
                    draft-reddy-add-resolver-info-00

Abstract

   This document describes methods for DNS resolvers to publish
   information about themselves.  Applications and operating systems can
   use the resolver information to identify the capabilities of the
   resolver.

Status of This Memo

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   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 September 29, 2021.

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   Copyright (c) 2021 IETF Trust and the persons identified as the
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Retrieving Resolver Information . . . . . . . . . . . . . . .   3
   4.  Format of the Resolver Information  . . . . . . . . . . . . .   3
   5.  Resolver Information  . . . . . . . . . . . . . . . . . . . .   3
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
     7.1.  RESINFO RRtype  . . . . . . . . . . . . . . . . . . . . .   5
     7.2.  DNS Resolver Information Registration . . . . . . . . . .   5
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   Historically, DNS stub resolvers typically communicated with the
   recursive resolvers without needing to know anything about the
   features of the recursive resolvers.  More recently, recursive
   resolvers have different features that may help the stub resolvers
   identify the capabilities of the resolver.  Thus stub resolvers can
   discover and authenticate encrypted DNS servers provided by a local
   network, for example using the techniques proposed in [I-D.ietf-add-
   dnr] and [I-D.ietf-add-ddr].  Thus stub resolvers need a way to get
   information from the discovered recursive resolvers about its
   capabilities.

   This document specifies a method for stub resolvers to ask recursive
   resolvers for such information.  In short, a new RRtype is defined
   for stub resolvers to query the recursive resolvers.  The information
   that a resolver might want to give is defined in Section 5.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119][RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   This document makes use of the terms defined in [RFC8499] and
   [I-D.ietf-dnsop-terminology-ter].

   'Encrypted DNS' refers to a DNS protocol that provides an encrypted
   channel between a DNS client and server (e.g., DoT, DoH, or DoQ).

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3.  Retrieving Resolver Information

   A stub resolver that wants to get information about a resolver can
   use the RRtype "RESINFO" defined in this document, and the IANA
   assignment is given in Section 7.1.  The contents of the RDATA in the
   response to this query are defined in Section 5.  If the resolver
   understands the RESINFO RRtype, the RRset in the Answer section MUST
   have exactly one record.

   The client can retrieve the resolver information using the RESINFO
   RRtype and QNAME of the domain name that is used to authenticate the
   DNS server (referred to as ADN in [I-D.ietf-add-dnr]).  If the
   special use domain name "resolver.arpa" defined in [I-D.ietf-add-ddr]
   is used to discover the Encrypted DNS server, the client can first
   retrieve a CNAME that aliases `_dns.resolver.arpa` to
   `_dns.$HOSTNAME` and then retrieve the resolver information using the
   RESINFO RRtype and QNAME of the `$HOSTNAME`.

4.  Format of the Resolver Information

   The resolver information is returned as a JSON object.  The JSON
   object MUST use the I-JSON message format defined in [RFC7493].  Note
   that [RFC7493] was based on [RFC7159], but [RFC7159] was replaced by
   [RFC8259].  Requiring the use of I-JSON instead of more general JSON
   format greatly increases the likelihood of interoperability.

   The names in this object are defined in an IANA registry.  The JSON
   object returned by a DNS query MAY contain any name/value pairs.  All
   names in the returned object MUST either be defined in the IANA
   registry or, if for local use only, begin with the substring "temp-".

   The IANA registry Section 7.2 will never register names that begin
   with "temp-".  All names MUST consist only of lower-case ASCII
   characters, digits, and hyphens (that is, Unicode characters U+0061
   through 007A, U+0030 through U+0039, and U+002D), and MUST be 63
   characters or shorter.  The IANA registry will not register names
   that begin with "temp-", so these names can be used freely by any
   implementer.  Note that the message returned by the resolver MUST be
   in I-JSON format.  I-JSON requires that the message MUST be encoded
   in UTF8.

5.  Resolver Information

   The resolver information includes the following attributes:

   qnameminimization:  If the DNS server supports QNAME minimisation
      [RFC7816] to improve DNS privacy, the parameter value is set to
      true.  This is a mandatory attribute.

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   extendeddnserror:  If the DNS server supports extended DNS error
      (EDE) [RFC8914] to return additional information about the cause
      of DNS errors, the parameter lists the possible extended DNS error
      codes that can be returned by the DNS server.  This is an optional
      attribute.

      *  Note that the extended error code "Blocked" defined in
         Section 4.16 of [RFC8914] identifies access to domains is
         blocked due to an policy by the operator of the DNS server,
         extended error code "Censored" defined in Section 4.17 of
         [RFC8914] identifies access to domains is blocked based on a
         requirement from an external entity and the extended error code
         "Filtered" defined in Section 4.18 of [RFC8914] identifies
         access to domains is blocked based on the request from the
         client to blacklist domains.

   clientauth:  If the DNS server requires client authentication, the
      parameter value is set to true.  For example, when not on the
      enterprise network (e.g., at home or coffee shop) yet needing to
      access the enterprise Encrypted DNS server, roaming users can use
      client authentication to access the Enterprise provided Encrypted
      DNS server.  This is an optional attribute.

   resinfourl:  A URL that points to the generic unstructured resolver
      information (e.g., DoH APIs supported, possible HTTP status codes
      returned by the DoH server, how to report a problem, etc.) for
      troubleshooting purpose.  This is an optional attribute.

   identityurl:  A URL that points to a human-friendly description of
      the resolver identity to display to the end-user.

   Figure 1 shows an example of resolver information.

   {

    "qnameminimization":true,
    "extendeddnserror": [15, 16, 17],
    "clientauth": false,
    "resinfourl": "https://resolver.example.com/guide",
    "identityurl": "https://resolver.example.com/user-friendly-name"
   }

               Figure 1: An Example of Resolver Information

   As specified in [RFC7493], the I-JSON object is encoded as UTF8.
   [RFC7493] explicitly allows the returned objects to be in any order.

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6.  Security Considerations

   Unless a DNS request to retrieve the resolver information is sent
   over DNS-over-TLS (DoT) [RFC7858] or DNS-over- HTTPS (DoH) [RFC8484],
   the response is susceptible to forgery.  The DNS resolver information
   can be retrieved after the encrypted connection is established to the
   DNS server.  If the client wishes to retrieve the resolver
   information before the encryption connection is established to the
   DNS resolver, the client MUST use local DNSSEC validation.

7.  IANA Considerations

7.1.  RESINFO RRtype

   This document defines a new DNS RR type, RESINFO, whose value TBD
   will be allocated by IANA from the "Resource Record (RR) TYPEs" sub-
   registry of the "Domain Name System (DNS) Parameters" registry:

   Type: RESINFO
   Value: TBD
   Meaning: Resolver Information as an I-JSON

7.2.  DNS Resolver Information Registration

   IANA will create a new registry titled "DNS Resolver Information"
   that will contain definitions of the names that can be used to
   provide the resolver information.  The registration procedure is by
   Specification Required, as defined in [RFC8126].  The registry has
   the following fields for each element:

Name: The name to be used in the JSON object. This name MUST NOT
begin with "temp-". This name MUST conform to the definition
of "string" in I-JSON message format.

Value type: The type of data to be used in the JSON object.

Specification: The name of the specification for the registered element.

   IANA will add the names "resinfourl", "identityurl",
   "extendeddnserror" and "qnameminimization" to the DNS Resolver
   Information registry.

8.  Acknowledgments

   This specification leverages the work that has been done in
   [I-D.pp-add-resinfo].  Thanks to Tommy Jensen, Vittorio Bertola,
   Vinny Parla, Chris Box, Ben Schwartz and Shashank Jain for the
   discussion and comments.

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9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC7493]  Bray, T., Ed., "The I-JSON Message Format", RFC 7493,
              DOI 10.17487/RFC7493, March 2015,
              <https://www.rfc-editor.org/info/rfc7493>.

   [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>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8484]  Hoffman, P. and P. McManus, "DNS Queries over HTTPS
              (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
              <https://www.rfc-editor.org/info/rfc8484>.

   [RFC8499]  Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
              Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
              January 2019, <https://www.rfc-editor.org/info/rfc8499>.

9.2.  Informative References

   [I-D.ietf-dnsop-terminology-ter]
              Hoffman, P., "Terminology for DNS Transports and
              Location", draft-ietf-dnsop-terminology-ter-02 (work in
              progress), August 2020.

   [I-D.pp-add-resinfo]
              Sood, P. and P. Hoffman, "DNS Resolver Information Self-
              publication", draft-pp-add-resinfo-02 (work in progress),
              June 2020.

   [RFC7159]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
              2014, <https://www.rfc-editor.org/info/rfc7159>.

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   [RFC7816]  Bortzmeyer, S., "DNS Query Name Minimisation to Improve
              Privacy", RFC 7816, DOI 10.17487/RFC7816, March 2016,
              <https://www.rfc-editor.org/info/rfc7816>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC8259]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,
              <https://www.rfc-editor.org/info/rfc8259>.

   [RFC8310]  Dickinson, S., Gillmor, D., and T. Reddy, "Usage Profiles
              for DNS over TLS and DNS over DTLS", RFC 8310,
              DOI 10.17487/RFC8310, March 2018,
              <https://www.rfc-editor.org/info/rfc8310>.

   [RFC8914]  Kumari, W., Hunt, E., Arends, R., Hardaker, W., and D.
              Lawrence, "Extended DNS Errors", RFC 8914,
              DOI 10.17487/RFC8914, October 2020,
              <https://www.rfc-editor.org/info/rfc8914>.

Authors' Addresses

   Tirumaleswar Reddy
   McAfee, Inc.
   Embassy Golf Link Business Park
   Bangalore, Karnataka  560071
   India

   Email: kondtir@gmail.com

   Mohamed Boucadair
   Orange
   Rennes  35000
   France

   Email: mohamed.boucadair@orange.com

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