ADD WG                                                          T. Reddy
Internet-Draft                                                    Akamai
Intended status: Standards Track                            M. Boucadair
Expires: 15 October 2022                                          Orange
                                                           13 April 2022


                        DNS Resolver Information
                    draft-reddy-add-resolver-info-05

Abstract

   This document specifies a method for DNS resolvers to publish
   information about themselves.  Clients can use the resolver
   information to identify the capabilities of DNS resolvers.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on 15 October 2022.

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   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   provided without warranty as described in the Revised BSD License.





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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 . . . . . . . . . . . . . . . . . . . . . . .   6
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   Historically, DNS stub resolvers communicated with recursive
   resolvers without needing to know anything about the features
   supported by these recursive resolvers.  As more and more recursive
   resolvers expose different features that may impact the delivered DNS
   service, means to help stub resolvers to identify the capabilities of
   the resolver are valuable.  Typically, stub resolvers can discover
   and authenticate encrypted DNS servers provided by a local network,
   for example, using the techniques specified in [I-D.ietf-add-dnr] and
   [I-D.ietf-add-ddr].  However, these stub resolvers need a means to
   retrieve information from the discovered recursive resolvers about
   their capabilities.

   This document fills that void by specifying a method for stub
   resolvers to retrieve such information.  To that aim, 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.

   Retrieved information can be used to feed the server selection
   procedure.

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.




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   This document makes use of the terms defined in [RFC8499].

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

3.  Retrieving Resolver Information

   A stub resolver that wants to retrieve the resolver information may
   use the RRtype "RESINFO" defined in this document (see Section 7.1).

   The content of the RDATA in a response to RRtype query is 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 retrieve the resolver information using the RESINFO RRtype
   and QNAME of the designated resolver.

4.  Format of the Resolver Information

   The resolver information is returned as a JSON object.  Precisely,
   the JSON object MUST use the I-JSON message format [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 JSON object returned by a DNS query may contain any name/value
   pairs.  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).  These names MUST be 63
   characters or shorter.

   All names in the returned object MUST either be defined in the IANA
   registry Section 7.2 or begin with the substring "temp-" for names
   defined for local use only.

5.  Resolver Information

   The resolver information includes the following attributes:

   qnameminimization:  If the DNS server supports QNAME minimisation



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      [RFC7816] to improve DNS privacy, the parameter value is set to
      true.  This is a mandatory attribute.

   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.

   resinfourl:  An 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) for
      troubleshooting purpose.  The server MUST support the content-type
      'text/html'.  The DNS client MUST reject the URL if the scheme is
      not "https".  The client MUST validate that both the encrypted DNS
      server and the resolver information server are owned and managed
      by the same entity by establishing a TLS connection to the domain
      name in the URL and checking if the subjectAltName entry in the
      server certificate includes the name of the encrypted DNS server.
      If this match fails, the client MUST ignore the resolver
      information.  As such, the URL should be treated only as
      diagnostic information for IT staff.  This is a mandatory
      attribute.

   New attributes can be defined as per the procedure defined in
   Section 7.2.

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

   Figure 1 shows an example of resolver information.

   {
     "qnameminimization": true,
     "extendeddnserror": [
       15,
       16,
       17
     ],
     "resinfourl": "https://resolver.example.com/guide",
   }

                Figure 1: An Example of Resolver Information








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6.  Security Considerations

   Unless a DNS request to retrieve the resolver information is
   encrypted (e.g., 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 or retrieved before the
   encrypted connection is established to the DNS server by using local
   DNSSEC validation.

7.  IANA Considerations

      Note to the RFC Editor: Please update [RFCXXXX] with the RFC
      number to be assigned to this document.

7.1.  RESINFO RRtype

   This document requests IANA to register a new value from the
   "Resource Record (RR) TYPEs" subregistry of the "Domain Name System
   (DNS) Parameters" registry available at [RRTYPE]:

   Type: RESINFO
   Value: TBD
   Meaning: Resolver Information as an I-JSON
   Reference: [RFCXXXX]

7.2.  DNS Resolver Information Registration

   This document requests IANA to create a new registry entitled "DNS
   Resolver Information".  This registry contains definitions of the
   names that can be used to provide the resolver information.

   The registration procedure is Specification Required (Section 4.6 of
   [RFC8126]).

   The structure of the registry is as follows:

   Name:  The name to be used in the JSON object.  The name MUST conform
      to the definition of "string" in I-JSON message format.  The IANA
      registry MUST NOT register names that begin with "temp-", so these
      names can be used freely by any implementer.

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

   Description:  Provides a description of the attribute

   Specification:  The reference specification for the registered
      element.



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   The initial content of this registry is provided in Table 1.

    +===================+=========+===================+===============+
    | Name              | Value   | Specification     | Specification |
    |                   | Type    |                   |               |
    +===================+=========+===================+===============+
    | qnameminimization | boolean | Indicates whether | [RFCXXXX]     |
    |                   |         | qnameminimization |               |
    |                   |         | is enabled or not |               |
    +-------------------+---------+-------------------+---------------+
    | extendeddnserror  | number  | Lists the set of  | [RFCXXXX]     |
    |                   |         | extended DNS      |               |
    |                   |         | errors            |               |
    +-------------------+---------+-------------------+---------------+
    | resinfourl        | string  | Provides an       | [RFCXXXX]     |
    |                   |         | unstructured      |               |
    |                   |         | resolver          |               |
    |                   |         | information that  |               |
    |                   |         | is used for       |               |
    |                   |         | troubleshooting   |               |
    +-------------------+---------+-------------------+---------------+

                     Table 1: Initial RESINFO Registry


8.  Acknowledgments

   This specification leverages the work that has been documented in
   [I-D.pp-add-resinfo].

   Thanks to Tommy Jensen, Vittorio Bertola, Vinny Parla, Chris Box, Ben
   Schwartz, Tony Finch, Daniel Kahn Gillmor, Eric Rescorla and Shashank
   Jain for the discussion and comments.

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>.

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

   [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>.

   [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>.

   [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>.

9.2.  Informative References

   [I-D.ietf-add-ddr]
              Pauly, T., Kinnear, E., Wood, C. A., McManus, P., and T.
              Jensen, "Discovery of Designated Resolvers", Work in
              Progress, Internet-Draft, draft-ietf-add-ddr-06, 4 April
              2022, <https://www.ietf.org/archive/id/draft-ietf-add-ddr-
              06.txt>.

   [I-D.ietf-add-dnr]
              Boucadair, M., Reddy, T., Wing, D., Cook, N., and T.
              Jensen, "DHCP and Router Advertisement Options for the
              Discovery of Network-designated Resolvers (DNR)", Work in
              Progress, Internet-Draft, draft-ietf-add-dnr-06, 22 March
              2022, <https://www.ietf.org/archive/id/draft-ietf-add-dnr-
              06.txt>.

   [I-D.pp-add-resinfo]
              Sood, P. and P. Hoffman, "DNS Resolver Information Self-
              publication", Work in Progress, Internet-Draft, draft-pp-
              add-resinfo-02, 30 June 2020,
              <https://www.ietf.org/archive/id/draft-pp-add-resinfo-
              02.txt>.






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   [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>.

   [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>.

   [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>.

   [RRTYPE]   IANA, "Resource Record (RR) TYPEs",
              <http://www.iana.org/assignments/dns-parameters/dns-
              parameters.xhtml#dns-parameters-4>.

Authors' Addresses

   Tirumaleswar Reddy
   Akamai
   Embassy Golf Link Business Park
   Bangalore 560071
   Karnataka
   India
   Email: kondtir@gmail.com


   Mohamed Boucadair
   Orange
   35000 Rennes
   France
   Email: mohamed.boucadair@orange.com













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