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Versions: 00 01

Network Working Group                                        T. Peterson
Internet-Draft                                             July 22, 2019
Intended status: Standards Track
Expires: January 23, 2020


  DNS over Transport Layer Security announcements using DHCP or Router
                             Advertisements
                       draft-peterson-dot-dhcp-01

Abstract

   This specification describes a DHCP option and Router Advertisement
   (RA) extension to inform clients of the presence of DNS resolvers
   with Transport Layer Security (TLS).

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
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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 23, 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
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.




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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   2
   3.  The DNS over TLS Option . . . . . . . . . . . . . . . . . . .   2
     3.1.  IPv4 DHCP Option  . . . . . . . . . . . . . . . . . . . .   3
     3.2.  IPv6 DHCP Option  . . . . . . . . . . . . . . . . . . . .   3
     3.3.  The DoT IPv6 RA Option  . . . . . . . . . . . . . . . . .   3
     3.4.  Trust Anchoring . . . . . . . . . . . . . . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   DHCPv4 [RFC2131], DHCPv6 [RFC3646], and IPv6 Router Announcements
   [RFC8106] all provide means to inform clients of available resolvers
   using the incumbent DNS protocol for querying, however there is no
   means of specifying alternate protocols to perform DNS queries.

2.  Conventions and Definitions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   "DoT", "Do53" and other related abbreviations follow the definitions
   as defined in [I-D.draft-hoffman-dns-terminology-ter-01].

3.  The DNS over TLS Option

   The DoT DHCP/RA option informs the client that a DoT service is
   available for use for answering DNS queries using the same IP
   address(es) returned in Do53 DNS Server DHCP/RA options.  Thus
   networks which announce DoT services MUST announce DNS resolver
   availability via their respective options, and provide a TLS
   certificate on the DoT service which passes verification ([RFC6125])
   against the DNS Host Name provided in the DoT DHCP/RA option.

   The maximum length of the DNS Host Name that can be carried in IPv4
   DHCP is 255 bytes, so DNS Host Names longer than 255 bytes SHOULD NOT
   be used in IPv6 DHCP or IPv6 RA.



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3.1.  IPv4 DHCP Option

   The format of the IPv4 DoT DHCP option is shown below.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Code     |      Len      |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
   |                                                               |
   |                          DNS Host Name                        |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Code:  The DoT DHCPv4 option (one octet)

   Len:  Length of the DNS Host Name

   DNS Host Name:  The DNS Host Name

3.2.  IPv6 DHCP Option

   The format of the IPv6 Captive-Portal DHCP option is shown below.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          option-code          |           option-len          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                           DNS Host Name                       |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   option-code:  TODO (two octets)

   option-len:  Length of the DNS Host Name, in octects

   DNS Servers:  The DNS Host Name

3.3.  The DoT IPv6 RA Option

   The format of the DoT Router Advertisement option is shown below.








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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Type     |      Len      |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
   |                                                               |
   |                          DNS Host Name                        |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:  TODO (one octet)

   Len:  The length of the DNS Host Name, in octets

   DNS Server:  The DNS Host Name

3.4.  Trust Anchoring

   TODO: Put in considerations for using DANE and/or existing
   certificate authorities for trust anchoring.

4.  Security Considerations

   An attacker with the ability to inject DHCP messages could include
   this option and present a malicious resolver.

   TODO: Further risk and threat assessments.

5.  IANA Considerations

   TODO: This section must be updated after assignments have been
   issued.

   This document requires the assignment of an option code assigned
   under the "BOOTP Vendor Extensions and DHCP Options"
   [bootp-registry], in addition to an option code assigned under the
   "Option Codes" registry under DHCPv6 parameters [dhcpv6-registry].

   Also, an assignment for an IPv6 RA Option Type from the "IPv6
   Neighbor Discovery Option Formats" registry under ICMPv6 paramters
   [icmpv6-registry].

6.  References








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6.1.  Normative References

   [I-D.draft-hoffman-dns-terminology-ter-01]
              Hoffman, P., "Terminology for DNS Transports and
              Location", draft-hoffman-dns-terminology-ter-01 (work in
              progress), April 2019.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC2132]  Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
              Extensions", RFC 2132, DOI 10.17487/RFC2132, March 1997,
              <https://www.rfc-editor.org/info/rfc2132>.

   [RFC3646]  Droms, R., Ed., "DNS Configuration options for Dynamic
              Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3646,
              DOI 10.17487/RFC3646, December 2003,
              <https://www.rfc-editor.org/info/rfc3646>.

   [RFC6125]  Saint-Andre, P. and J. Hodges, "Representation and
              Verification of Domain-Based Application Service Identity
              within Internet Public Key Infrastructure Using X.509
              (PKIX) Certificates in the Context of Transport Layer
              Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
              2011, <https://www.rfc-editor.org/info/rfc6125>.

   [RFC8106]  Jeong, J., Park, S., Beloeil, L., and S. Madanapalli,
              "IPv6 Router Advertisement Options for DNS Configuration",
              RFC 8106, DOI 10.17487/RFC8106, March 2017,
              <https://www.rfc-editor.org/info/rfc8106>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

6.2.  Informative References

   [bootp-registry]
              "Dynamic Host Configuration Protocol (DHCP) and Bootstrap
              Protocol (BOOTP) Parameters", n.d.,
              <http://www.iana.org/assignments/bootp-dhcp-parameters>.

   [dhcpv6-registry]
              "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
              n.d., <http://www.iana.org/assignments/dhcpv6-parameters>.




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   [icmpv6-registry]
              "Internet Control Message Protocol version 6 (ICMPv6)
              Parameters", n.d.,
              <http://www.iana.org/assignments/icmpv6-parameters>.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, DOI 10.17487/RFC2131, March 1997,
              <https://www.rfc-editor.org/info/rfc2131>.

Acknowledgments

   The author would like to acknowledge the extensive feedback from
   Martin Thomson.

Author's Address

   Thomas Peterson

   Email: nosretep.samoht@gmail.com
































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