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Versions: (draft-song-dns-wireformat-http) 00 01 02 03

Internet Engineering Task Force                                  L. Song
Internet-Draft                                Beijing Internet Institute
Intended status: Experimental                                   P. Vixie
Expires: January 3, 2019                                            TISF
                                                                 S. Kerr
                                                            July 2, 2018

                  An Proxy Use Case of DNS over HTTPS


   This memo introduces a DNS proxy use case to tunnel DNS query and
   response using DNS over HTTPs (DOH) protocol, a newly proposed DNS
   transport.  The proxy use case is useful as a incremental adoption
   tool when DOH is not widely available in old-transport client and

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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   Internet-Drafts are draft documents valid for a maximum of six months
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   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 January 3, 2019.

Copyright Notice

   Copyright (c) 2018 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
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   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of

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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.  Use case description  . . . . . . . . . . . . . . . . . . . .   3
   3.  Original transport indicator in DOH proxy . . . . . . . . . .   4
   4.  Implementation considerations . . . . . . . . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   6.  IANA considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

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.  To enhance the availability of honest DNS, a new
   DNS transport: DNS over HTTPs (DOH) [I-D.ietf-doh-dns-over-https] is
   proposed which transport DNS over HTTPs , in a way to cure DNS's
   long-time suffering from on-path attack by spoofing and blocking.

   This memo introduces a DNS proxy use case to leverage the DOH
   protocol as a substrate to tunnel DNS data over HTTPs which is called
   DOH proxy in the rest of the document.  It is useful especially when
   most DNS stub-resolvers and far-end servers are not aware the new DOH
   protocol, but a public or private proxy using DOH can be deployed and
   offer DOH capacity to users to bypass the networks where DNS is not
   working properly.

   Just as a normal DNS proxy described in [RFC5625], DOH proxy works as
   a simple DNS forwarder keeping the transparency principle, so any
   "hop-by-hop" mechanisms or newly introduced protocol extensions
   operate as if the proxy were not there.

   In order to keep the transparency of DOH proxy, a new variable
   "proto" in URI Template is defined for DOH proxy use case.  It allows
   the proxy server use the same transport protocol (UDP or TCP) to
   forward DNS query to far-end server just as the stub-client does
   without DOH proxy.

   May REMOVE BEFORE PUBLICATION: Comparing using a general VPN, the DOH
   proxy can work on an actual HTTP server, so it can be hosted on a
   machine that also serves web pages.  This means that DNS over HTTP is
   slightly more "stealthy" than a VPN, in that it can be
   indistinguishable from normal web traffic.

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2.  Use case description

   The typical scenario is that a DOH proxy sitting between stub-
   resolver and the recursive server.  The stub-resolver is configured
   sending DNS query to a DOH proxy and expects reply from the same DOH
   proxy . Just as a normal DNS proxy described in [RFC5625], DOH proxy
   works as a simple DNS forwarder keeping the transparency principle.
   The only difference is DOH proxy consist two part, a proxy client as
   a initiator of DOH tunnel and a proxy server as a terminator.  The
   proxy client speaks DOH with proxy server carrying the same DNS query
   received from stub-resolver.The proxy server will forward the exact
   DNS query received from stub-resolver to the configued recursive

   To keep the transparency principle of DOH proxy, any "hop-by-hop"
   mechanisms or newly introduced protocol extensions operate as if the
   DOH proxy were not there.  Different from the native DOH protocol, in
   DOH proxy use case, there should be a indication introduced for proxy
   client to tell the proxy server original transport (UDP or TCP) the
   stub-resolver uses to send DNS query to proxy client.

   For example if the proxy client receives the query via UDP, then it
   will notify the proxy server with a "proto=udp" indicator which is
   defined in Section 3.  If proxy client receives the query via TCP,
   then it will carry a "proto=tcp" indicator with the same DNS query
   without the two-byte length field defined in DNS over TCP [section
   4.2.2 in [RFC1035]].

   Besides the original transport indicator, as specified in DOH
   document, the proxy server MUST be able to process both "application/
   dns-message"request messages and forward the query to a configured
   recursive server using the same transport between sub-resolver and
   proxy client.  The response will be delivered back to sub-resolver
   accordingly.  In DOH proxy use case, each DNS query-response pair is
   mapped into a DOH query-response pair.  And the transport for DNS
   query and response MUST be the same.

   It is possible that a proxy client as a module can be deployed in the
   same host with the sub-client listening to a loop-back address.  A
   proxy server can be implemented that way to host a recursive DNS
   process as well.  The can be combined to form four deployment
   scenarios of DOH proxy use case.

   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.

   Note that the proxy client will face the same bootstrapping problem
   described in DOH when the HTTPs request needs to resolve the name of

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   server and send the request to on IP address.  The strategy is either
   use the IP directly or use another resolver (like the normal DHCP-
   supplied resolver) to lookup the IP of the server.

3.  Original transport indicator in DOH proxy

   In DOH document[I-D.ietf-doh-dns-over-https], the HTTP request uses a
   URI defined by the DOH server through the use of a URI Template in
   which no variables is defined.  In this document, a new variable
   "proto" is defined as the indicator of original transport.  For
   example, The URI "https://example.com/proxy_dns?proto=tcp" will cause
   the server to make a request using TCP.  And the URL
   "https://example.com/proxy_dns?proto=udp" will cause the server to
   make a request using UDP.

4.  Implementation considerations

   The DOH proxy may return TC bit to the sub-resolver which will cause
   TCP fallback starting from the sub-resolver.  An alternative advised
   is that the proxy has to have sufficient smarts to recognize the
   returned TC bit and re-issue the request over TCP to the back-end DNS

   Another implementation is suggested that DOH proxy server has a pool
   of TCP connections from the proxy to the back-end DNS server(s), over
   which incoming requests can be multiplexed.

5.  Security Considerations

   The DOH proxy use case does not introduce new protocol and any new
   security considerations since it is built on the DNS over HTTPS
   protocols.  All security considerations and recommendations apply in
   DOH proxy use case.

   Since DOH proxy is a also a special DNS proxy, the security
   recommendations of DNS proxy RFC 5625 [RFC5625] also apply in DOH
   proxy use case.

   Note that the ability to perform DNS queries in this way may allow
   users to bypass local DNS policy.  This may be 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.

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6.  IANA considerations

   No IANA considerations for DOH proxy

7.  Acknowledgments

   Thanks to Bob Harold, Paul Hoffman, Julian Reschke, Martin Thomson,
   Tony Finch ,Ray Bellis and Erik Kline for their review and comments.

8.  References

              Hoffman, P. and P. McManus, "DNS Queries over HTTPS
              (DoH)", draft-ietf-doh-dns-over-https-12 (work in
              progress), June 2018.

   [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>.

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

Authors' Addresses

   Linjian Song
   Beijing Internet Institute
   2nd Floor, Building 5, No.58 Jing Hai Wu Lu, BDA
   Beijing  100176
   P. R. China

   Email: songlinjian@gmail.com
   URI:   http://www.biigroup.com/

   Paul Vixie
   11400 La Honda Road
   Woodside, California  94062

   Email: vixie@tisf.net
   URI:   http://www.redbarn.org/

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   Shane Kerr
   Antoon Coolenlaan 41
   Uithoorn  1422 GN

   Email: shane@time-travellers.org

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