< draft-ietf-add-ddr-01.txt		draft-ietf-add-ddr-02.txt >
	ADD T. Pauly		ADD T. Pauly
	Internet-Draft E. Kinnear		Internet-Draft E. Kinnear
	Intended status: Standards Track Apple Inc.		Intended status: Standards Track Apple Inc.
	Expires: 16 December 2021 C.A. Wood		Expires: 9 January 2022 C.A. Wood
	Cloudflare		Cloudflare
	P. McManus		P. McManus
	Fastly		Fastly
	T. Jensen		T. Jensen
	Microsoft		Microsoft
	14 June 2021		8 July 2021
	Discovery of Designated Resolvers		Discovery of Designated Resolvers
	draft-ietf-add-ddr-01		draft-ietf-add-ddr-02
	Abstract		Abstract
	This document defines Discovery of Designated Resolvers (DDR), a		This document defines Discovery of Designated Resolvers (DDR), a
	mechanism for DNS clients to use DNS records to discover a resolver's		mechanism for DNS clients to use DNS records to discover a resolver's
	encrypted DNS configuration. This mechanism can be used to move from		encrypted DNS configuration. This mechanism can be used to move from
	unencrypted DNS to encrypted DNS when only the IP address of an		unencrypted DNS to encrypted DNS when only the IP address of a
	encrypted resolver is known. It can also be used to discover support		resolver is known. It can also be used to discover support for
	for encrypted DNS protocols when the name of an encrypted resolver is		encrypted DNS protocols when the name of an encrypted resolver is
	known. This mechanism is designed to be limited to cases where		known. This mechanism is designed to be limited to cases where
	unencrypted resolvers and their designated resolvers are operated by		unencrypted resolvers and their designated resolvers are operated by
	the same entity or cooperating entities.		the same entity or cooperating entities.
	Discussion Venues		Discussion Venues
	This note is to be removed before publishing as an RFC.		This note is to be removed before publishing as an RFC.
	Discussion of this document takes place on the Adaptive DNS Discovery		Discussion of this document takes place on the Adaptive DNS Discovery
	Working Group mailing list (add@ietf.org), which is archived at		Working Group mailing list (add@ietf.org), which is archived at
	skipping to change at page 2, line 10 ¶		skipping to change at page 2, line 10 ¶
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at https://datatracker.ietf.org/drafts/current/.		Drafts is at https://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on 16 December 2021.		This Internet-Draft will expire on 9 January 2022.
	Copyright Notice		Copyright Notice
	Copyright (c) 2021 IETF Trust and the persons identified as the		Copyright (c) 2021 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents (https://trustee.ietf.org/		Provisions Relating to IETF Documents (https://trustee.ietf.org/
	license-info) in effect on the date of publication of this document.		license-info) in effect on the date of publication of this document.
	Please review these documents carefully, as they describe your rights		Please review these documents carefully, as they describe your rights
	skipping to change at page 2, line 33 ¶		skipping to change at page 2, line 33 ¶
	as described in Section 4.e of the Trust Legal Provisions and are		as described in Section 4.e of the Trust Legal Provisions and are
	provided without warranty as described in the Simplified BSD License.		provided without warranty as described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
	1.1. Specification of Requirements . . . . . . . . . . . . . . 3		1.1. Specification of Requirements . . . . . . . . . . . . . . 3
	2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3		2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
	3. DNS Service Binding Records . . . . . . . . . . . . . . . . . 4		3. DNS Service Binding Records . . . . . . . . . . . . . . . . . 4
	4. Discovery Using Resolver IP Addresses . . . . . . . . . . . . 5		4. Discovery Using Resolver IP Addresses . . . . . . . . . . . . 5
	4.1. Authenticated Discovery . . . . . . . . . . . . . . . . . 5		4.1. Authenticated Discovery . . . . . . . . . . . . . . . . . 6
	4.2. Opportunistic Discovery . . . . . . . . . . . . . . . . . 6		4.2. Opportunistic Discovery . . . . . . . . . . . . . . . . . 6
	5. Discovery Using Resolver Names . . . . . . . . . . . . . . . 6		5. Discovery Using Resolver Names . . . . . . . . . . . . . . . 7
	6. Deployment Considerations . . . . . . . . . . . . . . . . . . 7		6. Deployment Considerations . . . . . . . . . . . . . . . . . . 7
	6.1. Caching Forwarders . . . . . . . . . . . . . . . . . . . 7		6.1. Caching Forwarders . . . . . . . . . . . . . . . . . . . 8
	6.2. Certificate Management . . . . . . . . . . . . . . . . . 8		6.2. Certificate Management . . . . . . . . . . . . . . . . . 8
	7. Security Considerations . . . . . . . . . . . . . . . . . . . 8		7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
	8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8		8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
	8.1. Special Use Domain Name "resolver.arpa" . . . . . . . . . 8		8.1. Special Use Domain Name "resolver.arpa" . . . . . . . . . 9
	9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9		9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
	9.1. Normative References . . . . . . . . . . . . . . . . . . 9		9.1. Normative References . . . . . . . . . . . . . . . . . . 9
	9.2. Informative References . . . . . . . . . . . . . . . . . 9		9.2. Informative References . . . . . . . . . . . . . . . . . 10
	Appendix A. Rationale for using SVCB records . . . . . . . . . . 10		Appendix A. Rationale for using SVCB records . . . . . . . . . . 11
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
	1. Introduction		1. Introduction
	When DNS clients wish to use encrypted DNS protocols such as DNS-		When DNS clients wish to use encrypted DNS protocols such as DNS-
	over-TLS (DoT) [RFC7858] or DNS-over-HTTPS (DoH) [RFC8484], they		over-TLS (DoT) [RFC7858] or DNS-over-HTTPS (DoH) [RFC8484], they
	require additional information beyond the IP address of the DNS		require additional information beyond the IP address of the DNS
	server, such as the resolver's hostname, non-standard ports, or URL		server, such as the resolver's hostname, non-standard ports, or URL
	paths. However, common configuration mechanisms only provide the		paths. However, common configuration mechanisms only provide the
	resolver's IP address during configuration. Such mechanisms include		resolver's IP address during configuration. Such mechanisms include
	network provisioning protocols like DHCP [RFC2132] and IPv6 Router		network provisioning protocols like DHCP [RFC2132] and IPv6 Router
	Advertisement (RA) options [RFC8106], as well as manual		Advertisement (RA) options [RFC8106], as well as manual
	configuration.		configuration.
	This document defines two mechanisms for clients to discover		This document defines two mechanisms for clients to discover
	designated resolvers using DNS server Service Binding (SVCB,		designated resolvers using DNS server Service Binding (SVCB,
	[I-D.ietf-dnsop-svcb-https]) records:		[I-D.ietf-dnsop-svcb-https]) records:
	1. When only an IP address of an Unencrypted Resolver is known, the		1. When only an IP address of an Unencrypted Resolver is known, the
	client queries a special use domain name to discover DNS SVCB		client queries a special use domain name to discover DNS SVCB
	records associated with the Unencrypted Resolver (Section 4).		records associated with one or more Encrypted Resolvers the
			Unencrypted Resolver has designated for use when support for DNS
			encryption is requested (Section 4).
	2. When the hostname of an encrypted DNS server is known, the client		2. When the hostname of an Encrypted Resolver is known, the client
	requests details by sending a query for a DNS SVCB record. This		requests details by sending a query for a DNS SVCB record. This
	can be used to discover alternate encrypted DNS protocols		can be used to discover alternate encrypted DNS protocols
	supported by a known server, or to provide details if a resolver		supported by a known server, or to provide details if a resolver
	name is provisioned by a network (Section 5).		name is provisioned by a network (Section 5).
	Both of these approaches allow clients to confirm that a discovered		Both of these approaches allow clients to confirm that a discovered
	Encrypted Resolver is designated by the originally provisioned		Encrypted Resolver is designated by the originally provisioned
	resolver. "Designated" in this context means that the resolvers are		resolver. "Designated" in this context means that the resolvers are
	operated by the same entity or cooperating entities; for example, the		operated by the same entity or cooperating entities; for example, the
	resolvers are accessible on the same IP address, or there is a		resolvers are accessible on the same IP address, or there is a
	skipping to change at page 4, line 27 ¶		skipping to change at page 4, line 28 ¶
	DNS resolvers can advertise one or more Designated Resolvers that may		DNS resolvers can advertise one or more Designated Resolvers that may
	offer support over encrypted channels and are controlled by the same		offer support over encrypted channels and are controlled by the same
	entity.		entity.
	When a client discovers Designated Resolvers, it learns information		When a client discovers Designated Resolvers, it learns information
	such as the supported protocols, ports, and server name to use in		such as the supported protocols, ports, and server name to use in
	certificate validation. This information is provided in Service		certificate validation. This information is provided in Service
	Binding (SVCB) records for DNS Servers, defined by		Binding (SVCB) records for DNS Servers, defined by
	[I-D.schwartz-svcb-dns].		[I-D.schwartz-svcb-dns].
	The following is an example of an SVCB record describing a DoH		The following is an example of an SVCB record describing a DoH server
	server:		discovered by querying for "_dns.example.net":
	_dns.example.net 7200 IN SVCB 1 . (		_dns.example.net 7200 IN SVCB 1 . (
	alpn=h2 dohpath=/dns-query{?dns} )		alpn=h2 dohpath=/dns-query{?dns} )
	The following is an example of an SVCB record describing a DoT		The following is an example of an SVCB record describing a DoT server
	server:		discovered by querying for "_dns.example.net":
	_dns.example.net 7200 IN SVCB 1 dot.example.net (		_dns.example.net 7200 IN SVCB 1 dot.example.net (
	alpn=dot port=8530 )		alpn=dot port=8530 )
	If multiple Designated Resolvers are available, using one or more		If multiple Designated Resolvers are available, using one or more
	encrypted DNS protocols, the resolver deployment can indicate a		encrypted DNS protocols, the resolver deployment can indicate a
	preference using the priority fields in each SVCB record		preference using the priority fields in each SVCB record
	[I-D.ietf-dnsop-svcb-https].		[I-D.ietf-dnsop-svcb-https].
			To avoid name lookup deadlock, Designated Resolvers SHOULD follow the
			guidance in Section 10 of [RFC8484] regarding the avoidance of DNS-
			based references that block the completion of the TLS handshake.
	This document focuses on discovering DoH and DoT Designated		This document focuses on discovering DoH and DoT Designated
	Resolvers. Other protocols can also use the format defined by		Resolvers. Other protocols can also use the format defined by
	[I-D.schwartz-svcb-dns]. However, if any protocol does not involve		[I-D.schwartz-svcb-dns]. However, if any protocol does not involve
	some form of certificate validation, new validation mechanisms will		some form of certificate validation, new validation mechanisms will
	need to be defined to support validating designation as defined in		need to be defined to support validating designation as defined in
	Section 4.1.		Section 4.1.
	4. Discovery Using Resolver IP Addresses		4. Discovery Using Resolver IP Addresses
	When a DNS client is configured with an Unencrypted Resolver IP		When a DNS client is configured with an Unencrypted Resolver IP
	address, it SHOULD query the resolver for SVCB records for		address, it SHOULD query the resolver for SVCB records for
	"dns://resolver.arpa" before making other queries. Specifically, the		"dns://resolver.arpa" before making other queries. Specifically, the
	client issues a query for "_dns.resolver.arpa" with the SVCB resource		client issues a query for "_dns.resolver.arpa" with the SVCB resource
	record type (64) [I-D.ietf-dnsop-svcb-https].		record type (64) [I-D.ietf-dnsop-svcb-https].
			Because this query is for an SUDN, which no entity can claim
			ownership over, the SVCB response MUST NOT use the "." value for the
			SvcDomainName. Instead, the domain name used for DoT or used to
			construct the DoH template MUST be provided.
			The following is an example of an SVCB record describing a DoH server
			discovered by querying for "_dns.resolver.arpa":
			_dns.resolver.arpa 7200 IN SVCB 1 doh.example.net (
			alpn=h2 dohpath=/dns-query{?dns} )
			The following is an example of an SVCB record describing a DoT server
			discovered by querying for "_dns.resolver.arpa":
			_dns.resolver.arpa 7200 IN SVCB 1 dot.example.net (
			alpn=dot port=8530 )
	If the recursive resolver that receives this query has one or more		If the recursive resolver that receives this query has one or more
	Designated Resolvers, it will return the corresponding SVCB records.		Designated Resolvers, it will return the corresponding SVCB records.
	When responding to these special queries for "dns://resolver.arpa",		When responding to these special queries for "dns://resolver.arpa",
	the recursive resolver SHOULD include the A and AAAA records for the		the recursive resolver SHOULD include the A and AAAA records for the
	name of the Designated Resolver in the Additional Answers section.		name of the Designated Resolver in the Additional Answers section.
	This will allow the DNS client to make queries over an encrypted		This will allow the DNS client to make queries over an encrypted
	connection without waiting to resolve the Encrypted Resolver name per		connection without waiting to resolve the Encrypted Resolver name per
	[I-D.ietf-dnsop-svcb-https]. If no A/AAAA records or SVCB IP address		[I-D.ietf-dnsop-svcb-https]. If no A/AAAA records or SVCB IP address
	hints are included, clients will be forced to delay use of the		hints are included, clients will be forced to delay use of the
	Encrypted Resolver until an additional DNS lookup for the A and AAAA		Encrypted Resolver until an additional DNS lookup for the A and AAAA
	skipping to change at page 9, line 20 ¶		skipping to change at page 9, line 36 ¶
	the rationale behind "ipv4only.arpa" in [RFC8880].		the rationale behind "ipv4only.arpa" in [RFC8880].
	9. References		9. References
	9.1. Normative References		9.1. Normative References
	[I-D.ietf-dnsop-svcb-https]		[I-D.ietf-dnsop-svcb-https]
	Schwartz, B., Bishop, M., and E. Nygren, "Service binding		Schwartz, B., Bishop, M., and E. Nygren, "Service binding
	and parameter specification via the DNS (DNS SVCB and		and parameter specification via the DNS (DNS SVCB and
	HTTPS RRs)", Work in Progress, Internet-Draft, draft-ietf-		HTTPS RRs)", Work in Progress, Internet-Draft, draft-ietf-
	dnsop-svcb-https-05, 21 April 2021,		dnsop-svcb-https-06, 16 June 2021,
	<https://www.ietf.org/archive/id/draft-ietf-dnsop-svcb-		<https://www.ietf.org/archive/id/draft-ietf-dnsop-svcb-
	https-05.txt>.		https-06.txt>.
	[I-D.ietf-tls-esni]		[I-D.ietf-tls-esni]
	Rescorla, E., Oku, K., Sullivan, N., and C. A. Wood, "TLS		Rescorla, E., Oku, K., Sullivan, N., and C. A. Wood, "TLS
	Encrypted Client Hello", Work in Progress, Internet-Draft,		Encrypted Client Hello", Work in Progress, Internet-Draft,
	draft-ietf-tls-esni-10, 8 March 2021,		draft-ietf-tls-esni-12, 7 July 2021,
	<https://www.ietf.org/archive/id/draft-ietf-tls-esni-		<https://www.ietf.org/archive/id/draft-ietf-tls-esni-
	10.txt>.		12.txt>.
	[I-D.schwartz-svcb-dns]		[I-D.schwartz-svcb-dns]
	Schwartz, B., "Service Binding Mapping for DNS Servers",		Schwartz, B., "Service Binding Mapping for DNS Servers",
	Work in Progress, Internet-Draft, draft-schwartz-svcb-dns-		Work in Progress, Internet-Draft, draft-schwartz-svcb-dns-
	03, 19 April 2021, <https://www.ietf.org/archive/id/draft-		03, 19 April 2021, <https://www.ietf.org/archive/id/draft-
	schwartz-svcb-dns-03.txt>.		schwartz-svcb-dns-03.txt>.
	[RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.		[RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.
	J., and E. Lear, "Address Allocation for Private		J., and E. Lear, "Address Allocation for Private
	Internets", BCP 5, RFC 1918, DOI 10.17487/RFC1918,		Internets", BCP 5, RFC 1918, DOI 10.17487/RFC1918,
End of changes. 20 change blocks.
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