DNS Privacy Considerations
RFC 7626

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Internet Engineering Task Force (IETF)                     S. Bortzmeyer
Request for Comments: 7626                                         AFNIC
Category: Informational                                      August 2015
ISSN: 2070-1721

                       DNS Privacy Considerations

Abstract

   This document describes the privacy issues associated with the use of
   the DNS by Internet users.  It is intended to be an analysis of the
   present situation and does not prescribe solutions.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7626.

Copyright Notice

   Copyright (c) 2015 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
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   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.

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RFC 7626                       DNS Privacy                   August 2015

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Risks . . . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  The Alleged Public Nature of DNS Data . . . . . . . . . .   4
     2.2.  Data in the DNS Request . . . . . . . . . . . . . . . . .   5
     2.3.  Cache Snooping  . . . . . . . . . . . . . . . . . . . . .   6
     2.4.  On the Wire . . . . . . . . . . . . . . . . . . . . . . .   7
     2.5.  In the Servers  . . . . . . . . . . . . . . . . . . . . .   8
       2.5.1.  In the Recursive Resolvers  . . . . . . . . . . . . .   8
       2.5.2.  In the Authoritative Name Servers . . . . . . . . . .   9
       2.5.3.  Rogue Servers . . . . . . . . . . . . . . . . . . . .  10
     2.6.  Re-identification and Other Inferences  . . . . . . . . .  11
     2.7.  More Information  . . . . . . . . . . . . . . . . . . . .  11
   3.  Actual "Attacks"  . . . . . . . . . . . . . . . . . . . . . .  11
   4.  Legalities  . . . . . . . . . . . . . . . . . . . . . . . . .  12
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  13
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  17
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  17

1.  Introduction

   This document is an analysis of the DNS privacy issues, in the spirit
   of Section 8 of [RFC6973].

   The Domain Name System is specified in [RFC1034], [RFC1035], and many
   later RFCs, which have never been consolidated.  It is one of the
   most important infrastructure components of the Internet and often
   ignored or misunderstood by Internet users (and even by many
   professionals).  Almost every activity on the Internet starts with a
   DNS query (and often several).  Its use has many privacy implications
   and this is an attempt at a comprehensive and accurate list.

   Let us begin with a simplified reminder of how the DNS works.  (See
   also [DNS-TERMS].)  A client, the stub resolver, issues a DNS query
   to a server, called the recursive resolver (also called caching
   resolver or full resolver or recursive name server).  Let's use the
   query "What are the AAAA records for www.example.com?" as an example.
   AAAA is the QTYPE (Query Type), and www.example.com is the QNAME
   (Query Name).  (The description that follows assumes a cold cache,
   for instance, because the server just started.)  The recursive
   resolver will first query the root name servers.  In most cases, the
   root name servers will send a referral.  In this example, the
   referral will be to the .com name servers.  The resolver repeats the
   query to one of the .com name servers.  The .com name servers, in

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