Signaling That an Authoritative DNS server offers DoT
draft-levine-dprive-signal-01

• Status
• IESG evaluation record
• IESG writeups
• Email expansions
• History

• Versions
• 00
• 01
• 02

Network Working Group                                          J. Levine
Internet-Draft                                      Taughannock Networks
Intended status: Informational                          November 4, 2019
Expires: May 7, 2020

         Signaling That an Authoritative DNS server offers DoT
                     draft-levine-dprive-signal-01

Abstract

   DNS resolvers that wish to use DNS over TLS to authoritative servers
   (ADoT) need some way to tell whether server offers DoT.  This
   document describes some ways that a server might signal that it uses
   DoT.

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 https://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 May 7, 2020.

Copyright Notice

   Copyright (c) 2019 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
   (https://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.

Levine                     Expires May 7, 2020                  [Page 1]
Internet-Draft               ADoT signalling               November 2019

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  General observations  . . . . . . . . . . . . . . . . . . . .   2
   3.  Signaling methods . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  EDNS0 option  . . . . . . . . . . . . . . . . . . . . . .   3
     3.2.  DNSKEY flags  . . . . . . . . . . . . . . . . . . . . . .   3
     3.3.  Other DNS records . . . . . . . . . . . . . . . . . . . .   3
     3.4.  SRV records . . . . . . . . . . . . . . . . . . . . . . .   3
     3.5.  DANE TLSA . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.6.  Special server names  . . . . . . . . . . . . . . . . . .   4
   4.  References - Normative  . . . . . . . . . . . . . . . . . . .   4
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   The Domain Name System[RFC1034] [RFC1035] uses a directed presumably
   acyclic graph of servers to provide authoritative answers to queries.
   The link from one server to the next is provided by an NS record in
   the zone on the upper server that points to the lower server.  For
   zones signed with DNSSEC, the upper server zone contains DS records
   that contain hashes of signing keys in DNSKEY records in the zone on
   the lower server.

2.  General observations

   Depending on your threat model it may be a problem if an intermediate
   party can intercept the signal and force a DoT client to use
   unencrypted DNS.

   The probe query would generally use query minimization to limit
   leakage of the requested name.  Even so, if a server handles many
   zones, this leaks the name of the zone being probed.

   Some zones have servers run by multiple operators.  (The DNS root is
   a well known example.)  It is possible that some of the servers will
   offer ADoT and some will not.  Some of the schemes below handle per-
   server signals, some don't.

   In several of the following schemes, the client probes the server to
   see whether it offers ADoT.  In those cases, the client presumably
   remembers what servers it's probed so there's only one probe per
   server.

Levine                     Expires May 7, 2020                  [Page 2]
Internet-Draft               ADoT signalling               November 2019

3.  Signaling methods

   This is a working list of possible signaling methods.  Just because
   they're in the list doesn't mean that anyone thinks they're a good
   idea.

3.1.  EDNS0 option

   We define a new EDNS0 option edns-adot.  The client sends an edns-
   adot option in its request, and the server responds with a value of 0
   or 1 to say whether it supports ADoT.  The option could be served by
   the upper level server along with the NS records, which avoids the
   extra probe, or by the lower level server.

   This is easy to implement, but since the OPT isn't signed, it's