Network Working Group T. Peterson Internet-Draft April 27, 2019 Intended status: Standards Track Expires: October 29, 2019 DNS over Transport Layer Security announcements using DHCP or Router Advertisements draft-peterson-dot-dhcp-00 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 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 October 29, 2019. 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. Peterson Expires October 29, 2019 [Page 1] Internet-Draft DoT using DHCP or Router Advertisements April 2019 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Conventions and Definitions . . . . . . . . . . . . . . . . . 2 3. The DNS over TLS Option . . . . . . . . . . . . . . . . . . . 2 3.1. IPv4 DHCP Option . . . . . . . . . . . . . . . . . . . . 2 3.2. IPv6 DHCP Option . . . . . . . . . . . . . . . . . . . . 3 3.3. The DoT IPv6 RA Option . . . . . . . . . . . . . . . . . 3 4. Security Considerations . . . . . . . . . . . . . . . . . . . 4 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 4 6.1. Normative References . . . . . . . . . . . . . . . . . . 4 6.2. Informative References . . . . . . . . . . . . . . . . . 4 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 5 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5 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. 3. The DNS over TLS Option 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 Servers | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Code: The DoT DHCPv4 option (one octet) Peterson Expires October 29, 2019 [Page 2] Internet-Draft DoT using DHCP or Router Advertisements April 2019 Length: Length of the DNS Servers list in octects DNS Servers: One or more IPv4 addresses of DNS servers 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 Servers | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ option-code: TODO (two octets) option-len: Length of the list of DNS servers in octects, which MUST be a multiple of 16 DNS Servers: IPv6 addresses of DNS servers 3.3. The DoT IPv6 RA Option The format of the DoT Router Advertisement 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Len | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | DNS Servers | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: TODO (one octet) Length: 8-bit unsigned integer representing the entire length of all fields, in units of 8 bytes. The minimum value is 3 if one DNS server is contained in the option. Every additional DNS server increases the length by 2. This field is used by the receiver to determine the number of DNS server addresses in the option. Peterson Expires October 29, 2019 [Page 3] Internet-Draft DoT using DHCP or Router Advertisements April 2019 DNS Servers: One or more IPv6 addresses of DNS servers. The number of addresses is determined by the Length field. That is, the number of addresses is equal to (Length - 1) / 2. 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 6.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . 6.2. Informative References [bootp-registry] "Dynamic Host Configuration Protocol (DHCP) and Bootstrap Protocol (BOOTP) Parameters", n.d., . [dhcpv6-registry] "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", n.d., . Peterson Expires October 29, 2019 [Page 4] Internet-Draft DoT using DHCP or Router Advertisements April 2019 [icmpv6-registry] "Internet Control Message Protocol version 6 (ICMPv6) Parameters", n.d., . [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, DOI 10.17487/RFC2131, March 1997, . [RFC3646] Droms, R., Ed., "DNS Configuration options for Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3646, DOI 10.17487/RFC3646, December 2003, . [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, . Acknowledgments TODO Author's Address Thomas Peterson Email: nosretep.samoht@gmail.com Peterson Expires October 29, 2019 [Page 5]