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DNS Queries over HTTPS

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This is an older version of an Internet-Draft that was ultimately published as RFC 8484.
Authors Paul E. Hoffman , Patrick McManus
Last updated 2017-10-28
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Network Working Group                                         P. Hoffman
Internet-Draft                                                     ICANN
Intended status: Standards Track                              P. McManus
Expires: April 21, 2018                                          Mozilla
                                                        October 18, 2017

                         DNS Queries over HTTPS


   DNS queries sometimes experience problems with end to end
   connectivity at times and places where HTTPS flows freely.

   HTTPS provides the most practical mechanism for reliable end to end
   communication.  Its use of TLS provides integrity and confidentiality
   guarantees and its use of HTTP allows it to interoperate with
   proxies, firewalls, and authentication systems where required for

   This document describes how to run DNS service over HTTP using
   https:// URIs.

   [[ There is a repository for this draft at ]].

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 21, 2018.

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Copyright Notice

   Copyright (c) 2017 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
   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Protocol Requirements . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Non-requirements  . . . . . . . . . . . . . . . . . . . .   4
   5.  The HTTP Request  . . . . . . . . . . . . . . . . . . . . . .   4
     5.1.  DNS Wire Format . . . . . . . . . . . . . . . . . . . . .   5
     5.2.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .   6
   6.  The HTTP Response . . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  Example . . . . . . . . . . . . . . . . . . . . . . . . .   7
   7.  HTTP Integration  . . . . . . . . . . . . . . . . . . . . . .   7
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
     8.1.  Registration of Well-Known URI  . . . . . . . . . . . . .   8
     8.2.  Registration of application/dns-udpwireformat Media Type    8
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  10
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  10
     11.2.  Informative References . . . . . . . . . . . . . . . . .  11
   Appendix A.  Previous Work on DNS over HTTP or in Other Formats .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   The Internet does not always provide end to end reachability for
   native DNS.  On-path network devices may spoof DNS responses, block
   DNS requests, or just redirect DNS queries to different DNS servers
   that give less-than-honest answers.

   Over time, there have been many proposals for using HTTP and HTTPS as
   a substrate for DNS queries and responses.  To date, none of those

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   proposals have made it beyond early discussion, partially due to
   disagreement about what the appropriate formatting should be and
   partially because they did not follow HTTP best practices.

   This document defines a specific protocol for sending DNS [RFC1035]
   queries and getting DNS responses over modern versions of HTTP
   [RFC7540] using https:// (and therefore TLS [RFC5246] security for
   integrity and confidentiality).

   The described approach is more than a tunnel over HTTP.  It
   establishes default media formatting types for requests and responses
   but uses normal HTTP content negotiation mechanisms for selecting
   alternatives that endpoints may prefer in anticipation of serving new
   use cases.  In addition to this media type negotiation, it aligns
   itself with HTTP features such as caching, proxying, and compression.

   The integration with HTTP provides a transport suitable for both
   traditional DNS clients and native web applications seeking access to
   the DNS.

2.  Terminology

   A server that supports this protocol is called a "DNS API server" to
   differentiate it from a "DNS server" (one that uses the regular DNS
   protocol).  Similarly, a client that supports this protocol is called
   a "DNS API client".

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   and "OPTIONAL" are to be interpreted as described in BCP 14, RFC 2119

3.  Use Cases

   There are two primary use cases for this protocol.

   The primary one is to prevent on-path network devices from
   interfering with native DNS operations.  This interference includes,
   but is not limited to, spoofing DNS responses, blocking DNS requests,
   and tracking.  HTTP authentication and proxy friendliness are
   expected to make this protocol function in some environments where
   DNS directly on TLS ([RFC7858]) would not.

   A secondary use case is web applications that want to access DNS
   information.  Standardizing an HTTPS mechanism allows this to be done
   in a way consistent with the cross-origin resource sharing [CORS]
   security model of the web and also integrate the caching mechanisms

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   of DNS with those of HTTP.  These applications may be interested in
   using a different media type than traditional clients.

   [ This paragraph is to be removed when this document is published as
   an RFC ] Note that these use cases are different than those in a
   similar protocol described at [I-D.ietf-dnsop-dns-wireformat-http].
   The use case for that protocol is proxying DNS queries over HTTP
   instead of over DNS itself.  The use cases in this document all
   involve query origination instead of proxying.

4.  Protocol Requirements

   The protocol described here bases its design on the following
   protocol requirements:

   o  The protocol must use normal HTTP semantics.

   o  The queries and responses must be able to be flexible enough to
      express every normal DNS query.

   o  The protocol must allow implementations to use HTTP's content
      negotiation mechanism.

   o  The protocol must ensure interoperable media formats through a
      mandatory to implement format wherein a query must be able to
      contain one or more EDNS extensions, including those not yet

   o  The protocol must use a secure transport that meets the
      requirements for modern https://.

4.1.  Non-requirements

   o  Supporting network-specific DNS64 [RFC6147]

   o  Supporting other network-specific inferences from plaintext DNS

   o  Supporting insecure HTTP

   o  Supporting legacy HTTP versions

5.  The HTTP Request

   The URI scheme MUST be https.

   The path SHOULD be "/.well-known/dns-query" but a different path can
   be used if the DNS API Client has prior knowledge about a DNS API

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   service on a different path at the origin being used.  (See Section 8
   for the registration of this in the well-known URI registry.)  Using
   the well-known path allows automated discovery of a DNS API Service,
   and also helps contextualize DNS Query requests pushed over an active
   HTTP/2 connection.

   A DNS API Client encodes the DNS query into the HTTP request using
   either the HTTP GET or POST methods.

   When using the POST method, the DNS query is included as the message
   body of the HTTP request and the Content-Type request header
   indicates the media type of the message.  POST-ed requests are
   smaller than their GET equivalents.

   When using the GET method, the URI path MUST contain a query
   parameter of the form content-type=TTT and another of the form
   body=BBBB, where "TTT" is the media type of the format used for the
   body parameter, and "BBB" is the content of the body encoded with
   base64url [RFC4648].  Using the GET method is friendlier to many HTTP
   cache implementations.

   The DNS API Client SHOULD include an HTTP "Accept:" request header to
   say what type of content can be understood in response.  The client
   MUST be prepared to process "application/dns-udpwireformat"
   {{dnswire} responses but MAY process any other type it receives.

   In order to maximize cache friendliness, DNS API clients using media
   formats that include DNS ID, such as application/dns-udpwireformat,
   should use a DNS ID of 0 in every DNS request.  HTTP semantics
   correlate the request and response, thus eliminating the need for the
   ID in a media type such as application/dns-udpwireformat.

   DNS API clients can use HTTP/2 padding and compression in the same
   way that other HTTP/2 clients use (or don't use) them.

5.1.  DNS Wire Format

   The media type is "application/dns-udpwireformat".  The body is the
   DNS on-the-wire format is defined in [RFC1035].  The body MUST be
   encoded with base64url [RFC4648].  Padding characters for base64url
   MUST NOT be included.

   DNS API clients using the DNS wire format MAY have one or more
   EDNS(0) extensions [RFC6891] in the request.

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5.2.  Examples

   For example, assume a DNS API server is following this specification
   on origin and the well-known path.
   The DNS API client chooses to send its requests in appliation/dns-
   udpwirefomat but indicates it can parse replies in that format or as
   a JSON-based content type.

   The examples uses HTTP/2 formatting from [RFC7540].

   A query for the IN A records for "" with recursion
   turned on using the GET method and a wireformat request would be:

   :method = GET
   :scheme = https
   :authority =
   :path = /.well-known/dns-query?  (no CR)
           content-type=application/dns-udpwireformat&  (no CR)
   accept = application/dns-udpwireformat, application/simpledns+json

   The same DNS query, using the POST method would be:

   :method = POST
   :scheme = https
   :authority =
   :path = /.well-known/dns-query
   accept = application/dns-udpwireformat, application/simpledns+json
   content-type = application/dns-udpwireformat
   content-length = 33

   <33 bytes represented by the following hex encoding>
   abcd 0100 0001 0000 0000 0000 0377 7777
   0765 7861 6d70 6c65 0363 6f6d 0000 0100

6.  The HTTP Response

   Different response media types will provide more or less information
   from a DNS response.  For example, one response type might include
   the information from the DNS header bytes while another might omit
   it.  The amount and type of information that a media type gives is
   solely up to the format, and not defined in this protocol.

   At the time this is published, the response types are works in
   progress.  The only known response type is "application/dns-
   udpwireformat", but it is likely that at least one JSON-based
   response format will be defined in the future.

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   The DNS response for "application/dns-udpwireformat" in Section 5.1
   MAY have one or more EDNS(0) extensions, depending on the extension
   definition of the extensions given in the DNS request.

   Native HTTP methods are used to correlate requests and responses.
   Responses may be returned in a different temporal order than requests
   were made using the protocols native multi-streaming functionality.

   In the HTTP responses, the HTTP cache headers SHOULD be set to expire
   at the same time as the shortest DNS TTL in the response.  Because
   DNS provides only caching but not revalidation semantics, DNS over
   HTTP responses should not carry revalidation response headers (such
   as Last-Modified: or Etag:) or return 304 responses.

   A DNS API Server MUST be able to process application/dns-
   udpwireformat request messages.

   A DNS API Server SHOULD respond with HTTP status code 415 upon
   receiving a media type it is unable to process.

   This document does not change the definition of any HTTP response
   codes or otherwise proscribe their use.

6.1.  Example

   This is an example response for a query for the IN A records for
   "" with recursion turned on.  The response bears one
   record with an address of and a TTL of 128 seconds.

   :status = 200
   content-type = application/dns-udpwireformat
   content-length = 64
   cache-control = max-age=128

   <64 bytes represented by the following hex encoding>
   abcd 8180 0001 0001 0000 0000 0377 7777
   0765 7861 6d70 6c65 0363 6f6d 0000 0100

   0103 7777 7707 6578 616d 706c 6503 636f
   6d00 0001 0001 0000 0080 0004 5db8 d822

7.  HTTP Integration

   In order to satisfy the security requirements of DNS over HTTPS, this
   protocol MUST use HTTP/2 [RFC7540] or its successors.  HTTP/2
   enforces a modern TLS profile necessary for achieving the security
   requirements of this protocol.

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   This protocol MUST be used with https scheme URI [RFC7230].

   The messages in classic UDP based DNS [RFC1035] are inherently
   unordered and have low overhead.  A competitive HTTP transport needs
   to support reordering, priority, parallelism, and header compression.
   For this additional reason, this protocol MUST use HTTP/2 [RFC7540]
   or its successors.

8.  IANA Considerations

8.1.  Registration of Well-Known URI

   This specification registers a Well-Known URI [RFC5785]:

   o  URI Suffix: dns-query

   o  Change Controller: IETF

   o  Specification Document(s): [this specification]

8.2.  Registration of application/dns-udpwireformat Media Type

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   Subject: Registration of MIME media type

   MIME media type name: application

   MIME subtype name: dns-udpwireformat

   Required parameters: n/a

   Optional parameters: n/a

   Encoding considerations: This is a binary format. The contents are a
   DNS message as defined in RFC 1035. The format used here is for DNS
   over UDP, which is the format defined in the diagrams in RFC 1035.

   Security considerations:  The security considerations for carrying
   this data are the same for carrying DNS without encryption.

   Interoperability considerations:  None.

   Published specification:  This document.

   Applications that use this media type:
     Systems that want to exchange full DNS messages.

   Additional information:

   Magic number(s):  n/a

   File extension(s):  n/a

   Macintosh file type code(s):  n/a

   Person & email address to contact for further information:
      Paul Hoffman,

   Intended usage:  COMMON

   Restrictions on usage:  n/a

   Author:  Paul Hoffman,

   Change controller:  IESG

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9.  Security Considerations

   Running DNS over https:// relies on the security of the underlying
   HTTP connection.  By requiring at least [RFC7540] levels of support
   for TLS this protocol expects to use current best practices for
   secure transport.

   Session level encryption has well known weaknesses with respect to
   traffic analysis which might be particularly acute when dealing with
   DNS queries.  Sections 10.6 (Compression) and 10.7 (Padding) of
   [RFC7540] provide some further advice on mitigations within an HTTP/2

   A server that is acting both as a normal web server and a DNS API
   server is in a position to choose which DNS names it forces a client
   to resolve (through its web service) and also be the one to answer
   those queries (through its DNS API service).  An untrusted DNS API
   server can thus easily cause damage by poisoning a client's cache
   with names that the DNS API server chooses to poison.  A client MUST
   NOT trust a DNS API server simply because it was discovered, or
   because the client was told to trust the DNS API server by an
   untrusted party.  Instead, a client MUST only trust DNS API server
   that is configured as trustworthy.

10.  Acknowledgments

   Joe Hildebrand contributed lots of material for a different iteration
   of this document.  Helpful early comments were given by Ben Schwartz
   and Mark Nottingham.

11.  References

11.1.  Normative References

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
              November 1987, <>.

   [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-

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,

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   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008, <https://www.rfc-

   [RFC5785]  Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
              Uniform Resource Identifiers (URIs)", RFC 5785,
              DOI 10.17487/RFC5785, April 2010, <https://www.rfc-

   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing",
              RFC 7230, DOI 10.17487/RFC7230, June 2014,

   [RFC7540]  Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
              Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
              DOI 10.17487/RFC7540, May 2015, <https://www.rfc-

   [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, <>.

11.2.  Informative References

   [CORS]     W3C, "Cross-Origin Resource Sharing", 2014,

              Song, L., Vixie, P., Kerr, S., and R. Wan, "DNS wire-
              format over HTTP", draft-ietf-dnsop-dns-wireformat-http-01
              (work in progress), March 2017.

   [RFC6147]  Bagnulo, M., Sullivan, A., Matthews, P., and I. van
              Beijnum, "DNS64: DNS Extensions for Network Address
              Translation from IPv6 Clients to IPv4 Servers", RFC 6147,
              DOI 10.17487/RFC6147, April 2011, <https://www.rfc-

   [RFC6891]  Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
              for DNS (EDNS(0))", STD 75, RFC 6891,
              DOI 10.17487/RFC6891, April 2013, <https://www.rfc-

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Appendix A.  Previous Work on DNS over HTTP or in Other Formats

   The following is an incomplete list of earlier work that related to
   DNS over HTTP/1 or representing DNS data in other formats.

   The list includes links to the site (because these
   documents are all expired) and web sites of software.






Authors' Addresses

   Paul Hoffman


   Patrick McManus


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