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Network Working Group                                         P. Hoffman
Internet-Draft                                                     ICANN
Intended status: Standards Track                          April 10, 2017
Expires: October 12, 2017


               Running DNS in Existing HTTP/2 Connections
                 draft-hoffman-dns-in-existing-http2-00

Abstract

   Intermediaries such as governments and ISPs spoof DNS responses, and
   block DNS requests to particular recursive resolvers, for a variety
   of reasons.  They spoof by capturing traffic on port 53, or by
   redirecting port 853 traffic in the hopes that the client is using
   opportunistic encryption.  They block if they know the address of a
   resolver that they don't like, such as public resolvers that give
   honest answers.

   This document describes how to run DNS service over existing HTTP/2
   connections over TLS, such as those being used for HTTP for basic web
   service.  This design prevents intermediaries from spoofing DNS
   responses, and makes it impossible for intermediaries to block the
   use of those recursive resolvers without blocking the desired HTTP
   connections.  It also prevents intermediaries or passive observers
   from seeing the DNS traffic.  This design is meant for communication
   between a DNS stub resolver and a DNS recursive resolver.

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 http://datatracker.ietf.org/drafts/current/.

   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 October 12, 2017.







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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
   (http://trustee.ietf.org/license-info) 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.  DNS in Existing HTTP/2 over TLS Connections . . . . . . . . .   3
     2.1.  HTTP/2 DNS Frame Definition . . . . . . . . . . . . . . .   3
     2.2.  Service Discovery . . . . . . . . . . . . . . . . . . . .   4
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     5.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   HTTP/2 [RFC7540] over TLS is now used widely by many web sites.
   Large web sites who care about good DNS resolution service (that is,
   DNS resolution that is not subject to getting wrong answers from
   intermediaries) might want to offer DNS resolution on the same
   servers as those running HTTP/2 over TLS.  Running DNS over existing
   HTTP/2 over TLS connection prevents intermediaries from spoofing DNS
   responses, and makes it impossible for intermediaries to block the
   use of those recursive resolvers without blocking the desired HTTP
   connections.

   This document covers only the use case of getting DNS service once a
   HTTP/2 over TLS connection is already set up.  That means that the
   user already has some DNS service before getting to the DNS resolver
   that is running in the existing HTTP/2 connection.  That original DNS
   service might be standard DNS running on port 53 ([RFC1035]), or DNS-
   in-TLS running on port 853 ([RFC7858]), or even DNS in its own HTTP/2
   over TLS connection that could be defined in the future.  Regardless,
   this document is describing a second DNS service for the user, one



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   that was bootstrapped by running DNS in a way that might have been
   spoofed by an intermediary.

   A beneficial effect of using DNS over existing HTTP/2 over TLS
   connections after using DNS over port 53 is that the DNS messages are
   then encrypted.

   A parallel document, [draft-hoffman-dns-in-existing-quic], covers
   approximately the same use cases as this one, but describes how to
   carry DNS in QUIC streams.

2.  DNS in Existing HTTP/2 over TLS Connections

   **** This section, which is the meat of the protocol, is completely
   tentative.  People might have strong opinions on how to best run DNS
   over HTTP/2.  The choice of using a new frame is an early guess for a
   protocol that meets the desing objectives given above; the HTTPBIS WG
   might have (much) better alternatives.  For example, reserved streams
   might be a better idea than a new type of frame.  ****

   This document defines a new type of HTTP/2 frame, "DNS".

   DNS in HTTP/2 is run as a stream of DNS frames.  The DNS stub
   resolver opens an HTTP/2 stream if it is not already open.  The stub
   resolver then sends DNS wire-format requests ([RFC1035]), and the
   recursive resolver sends wire-format requests in the same stream.
   The wire format used is that for DNS over UDP (not with the extra
   two-octet header defined in [RFC1035] for TCP).  Either side can
   close the HTTP/2 stream for DNS whenever they wish.

2.1.  HTTP/2 DNS Frame Definition

   DNS frames (type=0xTBD) convey variable-length sequences of octets
   associated with a DNS message.  One or more DNS frames are used, for
   instance, to carry a DNS request or response payload.

   DNS frames MAY also contain padding.  Padding can be added to DNS
   frames to obscure the size of messages.  Padding is a security
   feature; see Section 4.

   The format of the DNS frame is:










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   +---------------+
   |Pad Length? (8)|
   +---------------+-----------------------------------------------+
   |                         DNS message (*)                     ...
   +---------------------------------------------------------------+
   |                           Padding (*)                       ...
   +---------------------------------------------------------------+

                        Figure 1: DNS frame format

   The DNS frame contains the following fields:

   Pad Length:  An 8-bit field containing the length of the frame
      padding in units of octets.  This field is conditional (as
      signified by a "?" in the diagram) and is only present if the
      PADDED flag is set for the frame.

   DNS message:  The wire-format of the message.  The wire format used
      is that for DNS over UDP (not with the extra two-octet header
      defined in [RFC1035] for TCP).

   Padding:  Padding octets that contain no application semantic value.
      This is handled identically to padding in the DATA frame in
      [RFC7540].

   The DNS frame uses the END_STREAM and PADDED frame flags, identically
   to the DATA frame in [RFC7540].

   DNS frames MUST be associated with a stream.  If a DNS frame is
   received whose stream identifier field is 0x0, the recipient MUST
   respond with a connection error of type PROTOCOL_ERROR.

   DNS frames are subject to flow control identical to the DATA frame in
   [RFC7540].

2.2.  Service Discovery

   The DNS stub resolver discovers whether the HTTP/2 server with the
   exisiting connection supports DNS resolution by attempting to open a
   DNS stream in the HTTP/2 connection.  Because opening a HTTP/2 stream
   requires sending protocol data, the stub resolver needs to pick a DNS
   request to use as a probe for DNS resolution service.  The stub
   resolver might send a request for data it actually wants, or it could
   send a request that it does not care about, such as the A record for
   example.com.






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3.  IANA Considerations

   This section will eventually have a request to assign a new value,
   TBD, to the "HTTP/2 Frame Type" registry.

4.  Security Considerations

   Running DNS over existing HTTP/2 over TLS connections relies on the
   security of the TLS connections themselves.

   A beneficial effect of using DNS over existing HTTP/2 over TLS
   connections after using DNS over port 53 is that the DNS messages are
   then encrypted.

   *** Copy some text about the uses (and abuses) of padding from
   Section 10.7 of RFC 7540 here. ***

5.  References

5.1.  Normative References

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
              November 1987, <http://www.rfc-editor.org/info/rfc1035>.

   [RFC7540]  Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
              Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
              DOI 10.17487/RFC7540, May 2015,
              <http://www.rfc-editor.org/info/rfc7540>.

   [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, <http://www.rfc-editor.org/info/rfc7858>.

5.2.  Informative References

   [draft-hoffman-dns-in-existing-quic]
              Hoffman, P., "Running DNS in Existing QUIC Connections",
              2017, <https://tools.ietf.org/id/draft-hoffman-dns-in-
              existing-quic>.

Author's Address

   Paul Hoffman
   ICANN

   Email: paul.hoffman@icann.org



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