Internet Engineering Task Force                                  L. Song
Internet-Draft                                Beijing Internet Institute
Intended status: Experimental                                   P. Vixie
Expires: March 19, 2017                                             TISF
                                                                 S. Kerr
                                                                  R. Wan
                                              Beijing Internet Institute
                                                      September 15, 2016

                       DNS wire-format over HTTP


   This memo introduces a way to tunnel DNS data over HTTP.  This may be
   useful in any situation where DNS is not working properly, such as
   when there is middlebox misbehavior.

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
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   This Internet-Draft will expire on March 19, 2017.

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   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   ( in effect on the date of
   publication of this document.  Please review these documents
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Methodology and Configuration . . . . . . . . . . . . . . . .   3
   3.  DNS-over-HTTP Message Format  . . . . . . . . . . . . . . . .   4
     3.1.  Request Method  . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Response Status Code  . . . . . . . . . . . . . . . . . .   5
     3.3.  Header Fields . . . . . . . . . . . . . . . . . . . . . .   6
     3.4.  Message Body  . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   5.  IANA considerations . . . . . . . . . . . . . . . . . . . . .   7
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   8
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   RFC 1035 [RFC1035] specifies the wire format for DNS messages.  It
   also specifies DNS transport on UDP and TCP on port 53, which is
   still used today.  However, there are other ways to access DNS
   database, for example in a different data format or via alternative
   DNS transport.  These approaches are summarized in [draft-shane-

   One of alternative way of using DNS described in that document is to
   transport DNS binary data inside HTTP, with the goal of improving DNS
   service availability.  The DNS traffic is simply sent as web traffic
   using port 80/443 over HTTP.  It can bypass badly behaving middle
   boxes like firewalls, proxies or traffic shaping devices on path
   which might interfere with normal DNS traffic [RFC5625] [DOTSE]

   This approach has the advantage that HTTP usually makes it through
   even the worst coffee shop or hotel room firewalls, as Internet users
   expect web browsing to always work.  It also benefits from HTTP's
   support for persistent TCP connections (see section 6.3 in
   [RFC7230]).  Note that 5966bis [I-D.ietf-dnsop-5966bis] specifies the
   persistent feature for DNS on TCP port 53, but current DNS software
   does not generally support this mode of operation.  Finally, HTTPS
   provides data integrity and privacy.

   One alternative idea is to simply use a VPN, rather than a custom
   protocol for this purpose.  While this is possible, the DNS over HTTP
   wire format protocol presented here works on an actual HTTP server,
   so it can be hosted on a machine that also serves web pages.  This

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   means that DNS over HTTP is slightly more "stealthy" than a VPN, in
   that it can be indistinguishable from normal web traffic.

   Unlike a REST DNS API using JSON [I-D.bortzmeyer-dns-json] or XML
   [I-D.mohan-dns-query-xml] encoding for DNS data, in this approach
   wire-format data is wrapped with a HTTP header and transmitted on
   port 80 or 443.  The protocol is intended to serve as a sort of DNS
   VPN, and does not introduce another format of DNS data.  It is also
   possible as a new DNS APIs for advanced usage in application
   development.  For example, web developers can create arbitrary HTTP/
   HTTPS queries and get DNS responses in their JavaScript apps.

   This memo aims to describe how the DNS binary over HTTP concept
   works.  Hopefully implementations by different developers following
   this memo can speak with each other.

   This mechanism is designed for client stub resolver to recursive
   server.  DNS zone transfer, DNS updates, and anything other than
   simple DNS queries are out-of-scope for this document.

2.  Methodology and Configuration

   As mentioned in introduction, the basic methodology is wrapping the
   DNS wire-format data into an HTTP header and transmitting on port 80
   or 443.  However, there are two different scenarios for

   Scenario 1:

   The DNS server implementation handles DNS queries and responses via
   both UDP and TCP on port 53, and HTTP on port 80 or 443.  It works as

   1.  The client creates a DNS query message.

   2.  The client encapsulates the DNS message in a HTTP message body
       and assigns parameters with the HTTP header.

   3.  The client connects to the server and issues an HTTP POST request
       method.  This may re-use an existing HTTP connection.

   4.  The server decapsulates the HTTP packet to get the DNS query, and
       resolves the DNS query.

   5.  The server encapsulates the DNS response in HTTP and sends it
       back via the HTTP session.

   Scenario 2:

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   In this scenario there is a DNS-HTTP proxy sitting between stub-
   resolver and the recursive server.  The stub uses a client proxy and
   the recursive server uses a server proxy.  This works like a DNS VPN
   and transmits wire-format DNS messages over HTTP between the proxy
   client and a server, as follows:

   1.  The stub-resolver sends a DNS query (over UDP or TCP) to the
       proxy client.

   2.  The proxy client encapsulates the DNS message in an HTTP message
       body and assigns parameters with the HTTP header.

   3.  The proxy client connects to the proxy server and issues an HTTP
       POST request method.  This may re-use an existing HTTP

   4.  The proxy server decapsulates the HTTP packet to get the DNS
       query, and sends it to a real DNS server over UDP/TCP.

   5.  The proxy server encapsulates the DNS response in HTTP and sends
       it back via the HTTP session.

   6.  The proxy client decapsulates the DNS message from the HTTP
       response and sends it back to the stub-resolver via previous DNS
       session (either UDP or TCP).

   It is possible that these scenarios are mixed.  The server may speak
   DNS over HTTP directly and the client use a proxy, or the other way

   Note that the proxy client can be implemented listening to a loop-
   back address in the same host with stub-resolver.  The proxy server
   can be implemented as a caching server as well.  It is also possible
   to use the proxy server as a regular web server at the same time that
   is acting as a proxy server.

3.  DNS-over-HTTP Message Format

   DNS over HTTP is not tied to a specific version of HTTP, and should
   work with HTTP 1.1 [RFC7230] and HTTP/2 [RFC7540].  This section
   describes the details of the DNS over HTTP message format.

3.1.  Request Method

   A DNS message is sent over HTTP from the client to the server via a
   properly-formed HTTP request.  This is a POST method request [section
   4.3.3 in RFC 7231 [RFC7231]].  If a GET method request is sent to the

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   server, it optionally returns a human-readable page showing
   information targeted at users.

   Note that choosing POST (and not GET) as the request method for DNS
   wire-format over HTTP is mainly based on two reasons.  One is that
   the protocol is designed using HTTP as a tunnel-like technology
   carrying data from one side to another, not a web service with
   RESTful framework.  Another is that from the view of implementation
   some servers or middleboxes may ignore an undefined entity-body if
   using GET; and HTTP libraries have varying support for using GET with
   a payload.

   The target URI is provided explicitly by the services provider.
   Derived from the target URI, the request-target in request-line
   identifies the target resource upon which to apply the request.  To
   avoid URI conflicts and enhance interoperability, DNS wire-format
   over HTTP uses a well-known URI.  As defined in RFC 5785 [RFC5785],
   it begins with the characters "/.well-known/" and the name "dns-
   wireformat".  So the request-target for DNS wire-format over HTTP
   SHOULD be '/.well-known/dns-wireformat'.

   A DNS transaction over HTTP has no specific requirements for the
   transport protocol; developers can use any version of HTTP to
   accomplish the transaction.  But developers should be aware that HTTP
   1.1 [RFC7230] and HTTP/2 [RFC7540] do have differences in performance
   regarding multiplexing.  HTTP/2 is fully multiplexed, instead of
   ordered and blocking.  Because there is a general desire to achieve
   similar performance with DNS over UDP, the modern HTTP/2 is preferred
   for DNS over HTTP implementation.  Note that there should be no
   problem for advanced HTTP protocol in the future deployed for DNS
   over HTTP.

3.2.  Response Status Code

   The status code [Section 6 of [RFC7231]], only reflects the status of
   the HTTP connection.  If the request has succeeded, the status code
   is 200 (OK).

   If the request fails, the proxy server will supply an appropriate
   error code, typically 4xx (client error) if the client has provided a
   query that the server cannot understand for some reasons, or 5xx
   (server error) if some server-side problem prevented a query from

   To be clear, a failure on the DNS side should result in a status code
   of 200 (OK) as long as the HTTP request is valid and can be answered.
   The DNS error will be returned via the encapsulated DNS message.

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3.3.  Header Fields

   By definition header fields are key:value pairs that can be used to
   communicate data about the message, its payload, the target resource,
   or the connection (for example control data).

   The Content-Type: header field should be set to "application/dns-

   We add one a new header field:

   Proxy-DNS-Transport: xyz

   Where xyz is either UDP or TCP, which is the client's indication of
   how it received the underlying DNS query, and which the server will
   use when sending the query to the far-end DNS server.  This means if
   a stub DNS client asks for TCP, then that's what the far-end DNS
   server will see, and likewise for UDP.

   Exposing the transport protocol of the query allows the HTTP server
   proxy to send DNS queries to the recursive resolver that look like
   those that the DNS client is sending to the client proxy.  If the
   stub resolver sent a UDP packet, then this allows the recursive
   resolver to implement the logic of truncating the packet properly,
   instead of requiring that the HTTP client proxy somehow manage that

   For a stub resolver that connects directly via HTTP to the HTTP
   server proxy then this flag should be set to TCP, as the entire
   response can always be delivered so truncation is never required.

   The client MUST include this option.  If it is missing then it is an
   error and the server should respond with HTTP code 400 (bad request).

3.4.  Message Body

   As mentioned, the message body is DNS wire-format data.  It is worth
   mentioning that DNS messages sent over TCP connections is prefixed
   with a two-byte length field which gives the message length [section
   4.2.2 in RFC 1035 [RFC1035]], excluding the two-byte length field.
   This length field allows the low-level processing to assemble a
   complete message before beginning to parse it.  In the context of
   HTTP, there is content-length header field [section 3.3.2 in
   [RFC7230]]in which the field-value is the same with two bytes length
   field in DNS over TCP.

   Since this two-byte length field is redundant, when the client proxy
   receives a DNS message over TCP, it MUST NOT include the length field

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   in the message sent to the server.  The length in the content-length
   header is only the size of the DNS message itself, and MUST NOT
   include this two-byte length header.

4.  Security Considerations

   This protocol does not introduce any new security considerations
   since it is built on the DNS and HTTP protocols.

   Since this protocol transmits DNS messages, all of the security
   concerns that stub resolvers and recursive resolvers have with DNS
   messages apply.  However, since HTTP uses TCP as the underlying
   protocol, DNS reflection or amplification attacks are not possible.

   Since HTTP is used, all of the security concerns of HTTP are also

   Servers and clients SHOULD use TLS for communication.  It provides
   privacy and integrity for HTTP sessions.  If TLS is used, then all of
   the security concerns of TLS are also present.

   As specified in RFC 5246 [RFC5246], both the HTTP server and client
   can be authenticated or not authenticated.  Clients SHOULD
   authenticate the certificate of the HTTP server they connect to.  The
   DNS service providers can decide whether to authenticate the client
   side based on their own requirement for security and privacy.  For
   example, clients of an open resolver do not require authentication.

   Note that the ability to perform DNS queries in this way may allow
   users to bypass local DNS policy.  This is problematic in any
   environment where administrators need to enforce specific DNS
   behavior, such as an enterprise environment.  The protocol outlined
   here does not introduce any new capabilities in this area, but by
   creating a more standardized way of doing this it may cause
   operational problems for enterprise administrators.

5.  IANA considerations

   Registration for a new Media Type: dns-wireformat

   Registration for a new HTTP header field: Proxy-DNS-Transport

   Registration for a new Well-Known URI: "dns-wireformat"

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6.  Acknowledgments

   Thanks to Bob Harold, Paul Hoffman, and Julian Reschke for review.

7.  References

   [DOTSE]    and , "DNSSEC Tests of Consumer Broadband Routers",
              February 2008,

              Bortzmeyer, S., "JSON format to represent DNS data",
              draft-bortzmeyer-dns-json-01 (work in progress), February

              Dickinson, J., Dickinson, S., Bellis, R., Mankin, A., and
              D. Wessels, "DNS Transport over TCP - Implementation
              Requirements", draft-ietf-dnsop-5966bis-04 (work in
              progress), November 2015.

              Parthasarathy, M. and P. Vixie, "Representing DNS messages
              using XML", draft-mohan-dns-query-xml-00 (work in
              progress), September 2011.

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

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

   [RFC5625]  Bellis, R., "DNS Proxy Implementation Guidelines",
              BCP 152, RFC 5625, DOI 10.17487/RFC5625, August 2009,

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

   [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,

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   [RFC7231]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
              DOI 10.17487/RFC7231, 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,

   [SAC035]   ICANN Security and Stability Advisory Committee, "DNSSEC
              Impact on Broadband Routers and Firewalls", 2008.

Authors' Addresses

   Linjian Song
   Beijing Internet Institute
   2508 Room, 25th Floor, Tower A, Time Fortune
   Beijing  100028
   P. R. China


   Paul Vixie
   11400 La Honda Road
   Woodside, California  94062


   Shane Kerr
   Beijing Internet Institute
   2/F, Building 5, No.58 Jinghai Road, BDA
   Beijing  100176


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   Runxia Wan
   Beijing Internet Institute
   2508 Room, 25th Floor, Tower A, Time Fortune
   Beijing  100028
   P. R. China


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