draft-ietf-doh-dns-over-https-13.txt   draft-ietf-doh-dns-over-https-14.txt 
Network Working Group P. Hoffman Network Working Group P. Hoffman
Internet-Draft ICANN Internet-Draft ICANN
Intended status: Standards Track P. McManus Intended status: Standards Track P. McManus
Expires: February 9, 2019 Mozilla Expires: February 17, 2019 Mozilla
August 08, 2018 August 16, 2018
DNS Queries over HTTPS (DoH) DNS Queries over HTTPS (DoH)
draft-ietf-doh-dns-over-https-13 draft-ietf-doh-dns-over-https-14
Abstract Abstract
This document defines a protocol for sending DNS queries and getting This document defines a protocol for sending DNS queries and getting
DNS responses over HTTPS. Each DNS query-response pair is mapped DNS responses over HTTPS. Each DNS query-response pair is mapped
into an HTTP exchange. into an HTTP exchange.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
skipping to change at page 1, line 33 skipping to change at page 1, line 33
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 February 9, 2019. This Internet-Draft will expire on February 17, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Protocol Requirements . . . . . . . . . . . . . . . . . . . . 3 3. Selection of DoH Server . . . . . . . . . . . . . . . . . . . 3
3.1. Non-requirements . . . . . . . . . . . . . . . . . . . . 4 4. The HTTP Exchange . . . . . . . . . . . . . . . . . . . . . . 4
4. Selection of DoH Server . . . . . . . . . . . . . . . . . . . 4 4.1. The HTTP Request . . . . . . . . . . . . . . . . . . . . 4
5. The HTTP Exchange . . . . . . . . . . . . . . . . . . . . . . 4 4.1.1. HTTP Request Examples . . . . . . . . . . . . . . . . 5
5.1. The HTTP Request . . . . . . . . . . . . . . . . . . . . 4 4.2. The HTTP Response . . . . . . . . . . . . . . . . . . . . 6
5.1.1. HTTP Request Examples . . . . . . . . . . . . . . . . 5 4.2.1. Handling DNS and HTTP Errors . . . . . . . . . . . . 6
5.2. The HTTP Response . . . . . . . . . . . . . . . . . . . . 7 4.2.2. HTTP Response Example . . . . . . . . . . . . . . . . 7
5.2.1. Handling DNS and HTTP Errors . . . . . . . . . . . . 7 5. HTTP Integration . . . . . . . . . . . . . . . . . . . . . . 7
5.2.2. HTTP Response Example . . . . . . . . . . . . . . . . 7 5.1. Cache Interaction . . . . . . . . . . . . . . . . . . . . 7
6. HTTP Integration . . . . . . . . . . . . . . . . . . . . . . 8 5.2. HTTP/2 . . . . . . . . . . . . . . . . . . . . . . . . . 9
6.1. Cache Interaction . . . . . . . . . . . . . . . . . . . . 8 5.3. Server Push . . . . . . . . . . . . . . . . . . . . . . . 9
6.2. HTTP/2 . . . . . . . . . . . . . . . . . . . . . . . . . 10 5.4. Content Negotiation . . . . . . . . . . . . . . . . . . . 10
6.3. Server Push . . . . . . . . . . . . . . . . . . . . . . . 10 6. Definition of the application/dns-message media type . . . . 10
6.4. Content Negotiation . . . . . . . . . . . . . . . . . . . 10 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
7. Definition of the application/dns-message media type . . . . 10 7.1. Registration of application/dns-message Media Type . . . 10
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 12
8.1. Registration of application/dns-message Media Type . . . 11 8.1. On The Wire . . . . . . . . . . . . . . . . . . . . . . . 12
9. Privacy Considerations . . . . . . . . . . . . . . . . . . . 13 8.2. In The Server . . . . . . . . . . . . . . . . . . . . . . 12
9.1. On The Wire . . . . . . . . . . . . . . . . . . . . . . . 13 9. Security Considerations . . . . . . . . . . . . . . . . . . . 14
9.2. In The Server . . . . . . . . . . . . . . . . . . . . . . 13 10. Operational Considerations . . . . . . . . . . . . . . . . . 14
10. Security Considerations . . . . . . . . . . . . . . . . . . . 15 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
11. Operational Considerations . . . . . . . . . . . . . . . . . 15 11.1. Normative References . . . . . . . . . . . . . . . . . . 16
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 11.2. Informative References . . . . . . . . . . . . . . . . . 17
12.1. Normative References . . . . . . . . . . . . . . . . . . 17 Appendix A. Protocol Development . . . . . . . . . . . . . . . . 19
12.2. Informative References . . . . . . . . . . . . . . . . . 18 Appendix B. Previous Work on DNS over HTTP or in Other Formats . 19
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 20 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 20
Previous Work on DNS over HTTP or in Other Formats . . . . . . . 20 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction 1. Introduction
This document defines a specific protocol for sending DNS [RFC1035] This document defines a specific protocol, DNS over HTTPS (DoH), for
queries and getting DNS responses over HTTP [RFC7540] using https sending DNS [RFC1035] queries and getting DNS responses over HTTP
URIs (and therefore TLS [RFC5246] security for integrity and [RFC7540] using https [RFC2818] URIs (and therefore TLS [RFC8446]
confidentiality). Each DNS query-response pair is mapped into an security for integrity and confidentiality). Each DNS query-response
HTTP exchange. pair is mapped into an HTTP exchange.
The described approach is more than a tunnel over HTTP. It The described approach is more than a tunnel over HTTP. It
establishes default media formatting types for requests and responses establishes default media formatting types for requests and responses
but uses normal HTTP content negotiation mechanisms for selecting but uses normal HTTP content negotiation mechanisms for selecting
alternatives that endpoints may prefer in anticipation of serving new alternatives that endpoints may prefer in anticipation of serving new
use cases. In addition to this media type negotiation, it aligns use cases. In addition to this media type negotiation, it aligns
itself with HTTP features such as caching, redirection, proxying, itself with HTTP features such as caching, redirection, proxying,
authentication, and compression. authentication, and compression.
The integration with HTTP provides a transport suitable for both The integration with HTTP provides a transport suitable for both
existing DNS clients and native web applications seeking access to existing DNS clients and native web applications seeking access to
the DNS. the DNS.
Two primary uses cases were considered during this protocol's Two primary use cases were considered during this protocol's
development. They included preventing on-path devices from development. They were preventing on-path devices from interfering
interfering with DNS operations and allowing web applications to with DNS operations and allowing web applications to access DNS
access DNS information via existing browser APIs in a safe way information via existing browser APIs in a safe way consistent with
consistent with Cross Origin Resource Sharing (CORS) [CORS]. No Cross Origin Resource Sharing (CORS) [CORS]. No special effort has
special effort has been taken to enable or prevent application to been taken to enable or prevent application to other use cases. This
other use cases. This document focuses on communication between DNS document focuses on communication between DNS clients (such as
clients (such as operating system stub resolvers) and recursive operating system stub resolvers) and recursive resolvers.
resolvers.
2. Terminology 2. Terminology
A server that supports this protocol is called a "DoH server" to A server that supports this protocol is called a "DoH server" to
differentiate it from a "DNS server" (one that only provides DNS differentiate it from a "DNS server" (one that only provides DNS
service over one or more of the other transport protocols service over one or more of the other transport protocols
standardized for DNS). Similarly, a client that supports this standardized for DNS). Similarly, a client that supports this
protocol is called a "DoH client". protocol is called a "DoH client".
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
3. Protocol Requirements 3. Selection of DoH Server
[[ RFC Editor: Please remove this entire section before publication.
]]
The protocol described here bases its design on the following
protocol requirements:
o The protocol must use normal HTTP semantics.
o The queries and responses must be able to be flexible enough to
express every DNS query that would normally be sent in DNS over
UDP (including queries and responses that use DNS extensions, but
not those that require multiple responses).
o The protocol must permit the addition of new formats for DNS
queries and responses.
o The protocol must ensure interoperability by specifying a single
format for requests and responses that is mandatory to implement.
That format must be able to support future modifications to the
DNS protocol including the inclusion of one or more EDNS options
(including those not yet defined).
o The protocol must use a secure transport that meets the
requirements for HTTPS.
3.1. Non-requirements
o Supporting network-specific DNS64 [RFC6147]
o Supporting other network-specific inferences from plaintext DNS
queries
o Supporting insecure HTTP
4. Selection of DoH Server
Configuration, discovery, and updating of the URI Template [RFC6570] The DoH client is configured with a URI Template [RFC6570] which
(see Section 5.1) is done out of band from this protocol. Note that describes how to construct the URL to use for resolution.
configuration might be manual (such as a user typing URI Templates in Configuration, discovery, and updating of the URI Template is done
a user interface for "options") or automatic (such as URI Templates out of band from this protocol. Note that configuration might be
being supplied in responses from DHCP or similar protocols). DoH manual (such as a user typing URI Templates in a user interface for
Servers MAY support more than one URI Template. This allows the "options") or automatic (such as URI Templates being supplied in
different endpoints to have different properties such as different responses from DHCP or similar protocols). DoH Servers MAY support
authentication requirements or service level guarantees. more than one URI Template. This allows the different endpoints to
have different properties such as different authentication
requirements or service level guarantees.
A DoH client uses configuration to select the URI, and thus the DoH A DoH client uses configuration to select the URI, and thus the DoH
server, that is to be used for resolution. [RFC2818] defines how server, that is to be used for resolution. [RFC2818] defines how
HTTPS verifies the DoH server's identity. HTTPS verifies the DoH server's identity.
A DoH client MUST NOT use a different URI simply because it was A DoH client MUST NOT use a different URI simply because it was
discovered outside of the client's configuration, or because a server discovered outside of the client's configuration (such as through
offers an unsolicited response that appears to be a valid answer to a HTTP/2 push), or because a server offers an unsolicited response that
DNS query. This specification does not extend DNS resolution appears to be a valid answer to a DNS query. This specification does
privileges to URIs that are not recognized by the DoH client as not extend DNS resolution privileges to URIs that are not recognized
configured URIs. Such scenarios may create additional operational, by the DoH client as configured URIs. Such scenarios may create
tracking, and security hazards that require limitations for safe additional operational, tracking, and security hazards that require
usage. A future specification may support this use case. limitations for safe usage. A future specification may support this
use case.
5. The HTTP Exchange 4. The HTTP Exchange
5.1. The HTTP Request 4.1. The HTTP Request
A DoH client encodes a single DNS query into an HTTP request using A DoH client encodes a single DNS query into an HTTP request using
either the HTTP GET or POST method and the other requirements of this either the HTTP GET or POST method and the other requirements of this
section. The DoH server defines the URI used by the request through section. The DoH server defines the URI used by the request through
the use of a URI Template. the use of a URI Template.
The URI Template defined in this document is processed without any The URI Template defined in this document is processed without any
variables when the HTTP method is POST. When the HTTP method is GET variables when the HTTP method is POST. When the HTTP method is GET
the single variable "dns" is defined as the content of the DNS the single variable "dns" is defined as the content of the DNS
request (as described in Section 7), encoded with base64url request (as described in Section 6), encoded with base64url
[RFC4648]. [RFC4648].
Future specifications for new media types MUST define the variables Future specifications for new media types for DoH MUST define the
used for URI Template processing with this protocol. variables used for URI Template processing with this protocol.
DoH servers MUST implement both the POST and GET methods. DoH servers MUST implement both the POST and GET methods.
When using the POST method the DNS query is included as the message When using the POST method the DNS query is included as the message
body of the HTTP request and the Content-Type request header field body of the HTTP request and the Content-Type request header field
indicates the media type of the message. POST-ed requests are indicates the media type of the message. POST-ed requests are
smaller than their GET equivalents. generally smaller than their GET equivalents.
Using the GET method is friendlier to many HTTP cache Using the GET method is friendlier to many HTTP cache
implementations. implementations.
The DoH client SHOULD include an HTTP "Accept" request header field The DoH client SHOULD include an HTTP "Accept" request header field
to indicate what type of content can be understood in response. to indicate what type of content can be understood in response.
Irrespective of the value of the Accept request header field, the Irrespective of the value of the Accept request header field, the
client MUST be prepared to process "application/dns-message" (as client MUST be prepared to process "application/dns-message" (as
described in Section 7) responses but MAY also process any other type described in Section 6) responses but MAY also process other DNS-
it receives. related media types it receives.
In order to maximize cache friendliness, DoH clients using media In order to maximize HTTP cache friendliness, DoH clients using media
formats that include DNS ID, such as application/dns-message, SHOULD formats that include the ID field from the DNS message header, such
use a DNS ID of 0 in every DNS request. HTTP correlates the request as application/dns-message, SHOULD use a DNS ID of 0 in every DNS
and response, thus eliminating the need for the ID in a media type request. HTTP correlates the request and response, thus eliminating
such as application/dns-message. The use of a varying DNS ID can the need for the ID in a media type such as application/dns-message.
cause semantically equivalent DNS queries to be cached separately. The use of a varying DNS ID can cause semantically equivalent DNS
queries to be cached separately.
DoH clients can use HTTP/2 padding and compression in the same way DoH clients can use HTTP/2 padding and compression [RFC7540] in the
that other HTTP/2 clients use (or don't use) them. same way that other HTTP/2 clients use (or don't use) them.
5.1.1. HTTP Request Examples 4.1.1. HTTP Request Examples
These examples use HTTP/2 style formatting from [RFC7540]. These examples use HTTP/2 style formatting from [RFC7540].
These examples use a DoH service with a URI Template of These examples use a DoH service with a URI Template of
"https://dnsserver.example.net/dns-query{?dns}" to resolve IN A "https://dnsserver.example.net/dns-query{?dns}" to resolve IN A
records. records.
The requests are represented as application/dns-message typed bodies. The requests are represented as application/dns-message typed bodies.
The first example request uses GET to request www.example.com The first example request uses GET to request www.example.com
skipping to change at page 6, line 26 skipping to change at page 5, line 42
:path = /dns-query :path = /dns-query
accept = application/dns-message accept = application/dns-message
content-type = application/dns-message content-type = application/dns-message
content-length = 33 content-length = 33
<33 bytes represented by the following hex encoding> <33 bytes represented by the following hex encoding>
00 00 01 00 00 01 00 00 00 00 00 00 03 77 77 77 00 00 01 00 00 01 00 00 00 00 00 00 03 77 77 77
07 65 78 61 6d 70 6c 65 03 63 6f 6d 00 00 01 00 07 65 78 61 6d 70 6c 65 03 63 6f 6d 00 00 01 00
01 01
In this example, the 33 bytes are the DNS message in DNS wire format. In this example, the 33 bytes are the DNS message in DNS wire format
[RFC1035] starting with the DNS header.
Finally, a GET based query for a.62characterlabel-makes-base64url- Finally, a GET based query for a.62characterlabel-makes-base64url-
distinct-from-standard-base64.example.com is shown as an example to distinct-from-standard-base64.example.com is shown as an example to
emphasize that the encoding alphabet of base64url is different than emphasize that the encoding alphabet of base64url is different than
regular base64 and that padding is omitted. regular base64 and that padding is omitted.
The DNS query, expressed in DNS wire format, is 94 bytes represented The DNS query, expressed in DNS wire format, is 94 bytes represented
by the following: by the following:
00 00 01 00 00 01 00 00 00 00 00 00 01 61 3e 36 00 00 01 00 00 01 00 00 00 00 00 00 01 61 3e 36
skipping to change at page 7, line 5 skipping to change at page 6, line 21
:method = GET :method = GET
:scheme = https :scheme = https
:authority = dnsserver.example.net :authority = dnsserver.example.net
:path = /dns-query? (no space or CR) :path = /dns-query? (no space or CR)
dns=AAABAAABAAAAAAAAAWE-NjJjaGFyYWN0ZXJsYWJl (no space or CR) dns=AAABAAABAAAAAAAAAWE-NjJjaGFyYWN0ZXJsYWJl (no space or CR)
bC1tYWtlcy1iYXNlNjR1cmwtZGlzdGluY3QtZnJvbS1z (no space or CR) bC1tYWtlcy1iYXNlNjR1cmwtZGlzdGluY3QtZnJvbS1z (no space or CR)
dGFuZGFyZC1iYXNlNjQHZXhhbXBsZQNjb20AAAEAAQ dGFuZGFyZC1iYXNlNjQHZXhhbXBsZQNjb20AAAEAAQ
accept = application/dns-message accept = application/dns-message
5.2. The HTTP Response 4.2. The HTTP Response
The only response type defined in this document is "application/dns- The only response type defined in this document is "application/dns-
message", but it is possible that other response formats will be message", but it is possible that other response formats will be
defined in the future. A DoH server MUST be able to process defined in the future. A DoH server MUST be able to process
application/dns-message request messages. application/dns-message request messages.
Different response media types will provide more or less information Different response media types will provide more or less information
from a DNS response. For example, one response type might include from a DNS response. For example, one response type might include
information from the DNS header bytes while another might omit it. information from the DNS header bytes while another might omit it.
The amount and type of information that a media type gives is solely The amount and type of information that a media type gives is solely
up to the format, and not defined in this protocol. up to the format, and not defined in this protocol.
Each DNS request-response pair is matched to one HTTP exchange. The Each DNS request-response pair is mapped to one HTTP exchange. The
responses may be processed and transported in any order using HTTP's responses may be processed and transported in any order using HTTP's
multi-streaming functionality ([RFC7540] Section 5). multi-streaming functionality ([RFC7540] Section 5).
Section 6.1 discusses the relationship between DNS and HTTP response Section 5.1 discusses the relationship between DNS and HTTP response
caching. caching.
5.2.1. Handling DNS and HTTP Errors 4.2.1. Handling DNS and HTTP Errors
DNS response codes indicate either success or failure for the DNS DNS response codes indicate either success or failure for the DNS
query. A successful HTTP response with a 2xx status code ([RFC7231] query. A successful HTTP response with a 2xx status code ([RFC7231]
Section 6.3) can be used for any valid DNS response, regardless of Section 6.3) is used for any valid DNS response, regardless of the
the DNS response code. For example, a successful 2xx HTTP status DNS response code. For example, a successful 2xx HTTP status code is
code is used even with a DNS message whose DNS response code used even with a DNS message whose DNS response code indicates
indicates failure, such as SERVFAIL or NXDOMAIN. failure, such as SERVFAIL or NXDOMAIN.
HTTP responses with non-successful HTTP status codes do not contain HTTP responses with non-successful HTTP status codes do not contain
replies to the original DNS question in the HTTP request. DoH replies to the original DNS question in the HTTP request. DoH
clients need to use the same semantic processing of non-successful clients need to use the same semantic processing of non-successful
HTTP status codes as other HTTP clients. This might mean that the HTTP status codes as other HTTP clients. This might mean that the
DoH client retries the query with the same DoH server, such as DoH client retries the query with the same DoH server, such as if
authorization failures (HTTP status code 401 [RFC7235] Section 3.1). there are authorization failures (HTTP status code 401 [RFC7235]
It could also mean that the DoH client retries with a different DoH Section 3.1). It could also mean that the DoH client retries with a
server, such as for unsupported media types (HTTP status code 415, different DoH server, such as for unsupported media types (HTTP
[RFC7231] Section 6.5.13), or where the server cannot generate a status code 415, [RFC7231] Section 6.5.13), or where the server
representation suitable for the client (HTTP status code 406, cannot generate a representation suitable for the client (HTTP status
[RFC7231] Section 6.5.6), and so on. code 406, [RFC7231] Section 6.5.6), and so on.
5.2.2. HTTP Response Example 4.2.2. HTTP Response Example
This is an example response for a query for the IN AAAA records for This is an example response for a query for the IN AAAA records for
"www.example.com" with recursion turned on. The response bears one "www.example.com" with recursion turned on. The response bears one
answer record with an address of 2001:db8:abcd:12:1:2:3:4 and a TTL answer record with an address of 2001:db8:abcd:12:1:2:3:4 and a TTL
of 3709 seconds. of 3709 seconds.
:status = 200 :status = 200
content-type = application/dns-message content-type = application/dns-message
content-length = 61 content-length = 61
cache-control = max-age=3709 cache-control = max-age=3709
<61 bytes represented by the following hex encoding> <61 bytes represented by the following hex encoding>
00 00 81 80 00 01 00 01 00 00 00 00 03 77 77 77 00 00 81 80 00 01 00 01 00 00 00 00 03 77 77 77
07 65 78 61 6d 70 6c 65 03 63 6f 6d 00 00 1c 00 07 65 78 61 6d 70 6c 65 03 63 6f 6d 00 00 1c 00
01 c0 0c 00 1c 00 01 00 00 0e 7d 00 10 20 01 0d 01 c0 0c 00 1c 00 01 00 00 0e 7d 00 10 20 01 0d
b8 ab cd 00 12 00 01 00 02 00 03 00 04 b8 ab cd 00 12 00 01 00 02 00 03 00 04
6. HTTP Integration 5. HTTP Integration
This protocol MUST be used with the https scheme URI [RFC7230]. This protocol MUST be used with the https scheme URI [RFC7230].
Section 9 and Section 10 discuss additional considerations for the Section 8 and Section 9 discuss additional considerations for the
integration with HTTP. integration with HTTP.
6.1. Cache Interaction 5.1. Cache Interaction
A DoH exchange can pass through a hierarchy of caches that include A DoH exchange can pass through a hierarchy of caches that include
both HTTP- and DNS-specific caches. These caches may exist between both HTTP- and DNS-specific caches. These caches may exist between
the DoH server and client, or on the DoH client itself. HTTP caches the DoH server and client, or on the DoH client itself. HTTP caches
are by design generic; that is, they do not understand this protocol. are by design generic; that is, they do not understand this protocol.
Even if a DoH client has modified its cache implementation to be Even if a DoH client has modified its cache implementation to be
aware of DoH semantics, it does not follow that all upstream caches aware of DoH semantics, it does not follow that all upstream caches
(for example, inline proxies, server-side gateways and Content (for example, inline proxies, server-side gateways and Content
Delivery Networks) will be. Delivery Networks) will be.
As a result, DoH servers need to carefully consider the HTTP caching As a result, DoH servers need to carefully consider the HTTP caching
metadata they send in response to GET requests (POST requests are not metadata they send in response to GET requests (responses to POST
cacheable unless specific response header fields are sent; this is requests are not cacheable unless specific response header fields are
not widely implemented, and not advised for DoH). sent; this is not widely implemented, and not advised for DoH).
In particular, DoH servers SHOULD assign an explicit freshness In particular, DoH servers SHOULD assign an explicit HTTP freshness
lifetime ([RFC7234] Section 4.2) so that the DoH client is more lifetime ([RFC7234] Section 4.2) so that the DoH client is more
likely to use fresh DNS data. This requirement is due to HTTP caches likely to use fresh DNS data. This requirement is due to HTTP caches
being able to assign their own heuristic freshness (such as that being able to assign their own heuristic freshness (such as that
described in [RFC7234] Section 4.2.2), which would take control of described in [RFC7234] Section 4.2.2), which would take control of
the cache contents out of the hands of the DoH server. the cache contents out of the hands of the DoH server.
The assigned freshness lifetime of a DoH HTTP response MUST be less The assigned freshness lifetime of a DoH HTTP response MUST be less
than or equal to the smallest TTL in the Answer section of the DNS than or equal to the smallest TTL in the Answer section of the DNS
response. A freshness lifetime equal to the smallest TTL in the response. A freshness lifetime equal to the smallest TTL in the
Answer section is RECOMMENDED. For example, if a HTTP response Answer section is RECOMMENDED. For example, if a HTTP response
carries three RRsets with TTLs of 30, 600, and 300, the HTTP carries three RRsets with TTLs of 30, 600, and 300, the HTTP
freshness lifetime should be 30 seconds (which could be specified as freshness lifetime should be 30 seconds (which could be specified as
"Cache-Control: max-age=30"). This requirement helps assure that "Cache-Control: max-age=30"). This requirement helps prevent exipred
none of the RRsets contained in a DNS response are served stale from RRsets in messages in an HTTP cache from unintentionally being
an HTTP cache. served.
If the DNS response has no records in the Answer section, and the DNS If the DNS response has no records in the Answer section, and the DNS
response has an SOA record in the Authority section, the response response has an SOA record in the Authority section, the response
freshness lifetime MUST NOT be greater than the MINIMUM field from freshness lifetime MUST NOT be greater than the MINIMUM field from
that SOA record (see [RFC2308]). that SOA record (see [RFC2308]).
The stale-while-revalidate and stale-if-error Cache-Control The stale-while-revalidate and stale-if-error Cache-Control
directives ([RFC5861]) could be well-suited to a DoH implementation directives ([RFC5861]) could be well-suited to a DoH implementation
when allowed by server policy. Those mechanisms allow a client, at when allowed by server policy. Those mechanisms allow a client, at
the server's discretion, to reuse a cache entry that is no longer the server's discretion, to reuse an HTTP cache entry that is no
fresh. In such a case, the client reuses all of a cached entry, or longer fresh. In such a case, the client reuses all of a cached
none of it. entry, or none of it.
DoH servers also need to consider caching when generating responses DoH servers also need to consider HTTP caching when generating
that are not globally valid. For instance, if a DoH server responses that are not globally valid. For instance, if a DoH server
customizes a response based on the client's identity, it would not customizes a response based on the client's identity, it would not
want to allow global reuse of that response. This could be want to allow global reuse of that response. This could be
accomplished through a variety of HTTP techniques such as a Cache- accomplished through a variety of HTTP techniques such as a Cache-
Control max-age of 0, or by using the Vary response header field Control max-age of 0, or by using the Vary response header field
([RFC7231] Section 7.1.4) to establish a secondary cache key ([RFC7231] Section 7.1.4) to establish a secondary cache key
([RFC7234] Section 4.1). ([RFC7234] Section 4.1).
DoH clients MUST account for the Age response header field's value DoH clients MUST account for the Age response header field's value
([RFC7234]) when calculating the DNS TTL of a response. For example, ([RFC7234]) when calculating the DNS TTL of a response. For example,
if an RRset is received with a DNS TTL of 600, but the Age header if an RRset is received with a DNS TTL of 600, but the Age header
field indicates that the response has been cached for 250 seconds, field indicates that the response has been cached for 250 seconds,
the remaining lifetime of the RRset is 350 seconds. This requirement the remaining lifetime of the RRset is 350 seconds. This requirement
applies to both DoH client HTTP caches and DoH client DNS caches. applies to both DoH client HTTP caches and DoH client DNS caches.
DoH clients can request an uncached copy of a response by using the DoH clients can request an uncached copy of a HTTP response by using
"no-cache" request cache control directive ([RFC7234], the "no-cache" request cache control directive ([RFC7234],
Section 5.2.1.4) and similar controls. Note that some caches might Section 5.2.1.4) and similar controls. Note that some caches might
not honor these directives, either due to configuration or not honor these directives, either due to configuration or
interaction with traditional DNS caches that do not have such a interaction with traditional DNS caches that do not have such a
mechanism. mechanism.
HTTP conditional requests ([RFC7232]) may be of limited value to DoH, HTTP conditional requests ([RFC7232]) may be of limited value to DoH,
as revalidation provides only a bandwidth benefit and DNS as revalidation provides only a bandwidth benefit and DNS
transactions are normally latency bound. Furthermore, the HTTP transactions are normally latency bound. Furthermore, the HTTP
response header fields that enable revalidation (such as "Last- response header fields that enable revalidation (such as "Last-
Modified" and "Etag") are often fairly large when compared to the Modified" and "Etag") are often fairly large when compared to the
overall DNS response size, and have a variable nature that creates overall DNS response size, and have a variable nature that creates
constant pressure on the HTTP/2 compression dictionary [RFC7541]. constant pressure on the HTTP/2 compression dictionary [RFC7541].
Other types of DNS data, such as zone transfers, may be larger and Other types of DNS data, such as zone transfers, may be larger and
benefit more from revalidation. benefit more from revalidation.
6.2. HTTP/2 5.2. HTTP/2
HTTP/2 [RFC7540] is the minimum RECOMMENDED version of HTTP for use HTTP/2 [RFC7540] is the minimum RECOMMENDED version of HTTP for use
with DoH. with DoH.
The messages in classic UDP-based DNS [RFC1035] are inherently The messages in classic UDP-based DNS [RFC1035] are inherently
unordered and have low overhead. A competitive HTTP transport needs unordered and have low overhead. A competitive HTTP transport needs
to support reordering, parallelism, priority, and header compression to support reordering, parallelism, priority, and header compression
to achieve similar performance. Those features were introduced to to achieve similar performance. Those features were introduced to
HTTP in HTTP/2 [RFC7540]. Earlier versions of HTTP are capable of HTTP in HTTP/2 [RFC7540]. Earlier versions of HTTP are capable of
conveying the semantic requirements of DoH but may result in very conveying the semantic requirements of DoH but may result in very
poor performance. poor performance.
6.3. Server Push 5.3. Server Push
Before using DoH response data for DNS resolution, the client MUST Before using DoH response data for DNS resolution, the client MUST
establish that the HTTP request URI can be used for the DoH query. establish that the HTTP request URI can be used for the DoH query.
For HTTP requests initiated by the DoH client, this is implicit in For HTTP requests initiated by the DoH client, this is implicit in
the selection of URI. For HTTP server push ([RFC7540] Section 8.2) the selection of URI. For HTTP server push ([RFC7540] Section 8.2)
extra care must be taken to ensure that the pushed URI is one that extra care must be taken to ensure that the pushed URI is one that
the client would have directed the same query to if the client had the client would have directed the same query to if the client had
initiated the request. initiated the request (in addition to the other security checks
normally needed for server push).
6.4. Content Negotiation 5.4. Content Negotiation
In order to maximize interoperability, DoH clients and DoH servers In order to maximize interoperability, DoH clients and DoH servers
MUST support the "application/dns-message" media type. Other media MUST support the "application/dns-message" media type. Other media
types MAY be used as defined by HTTP Content Negotiation ([RFC7231] types MAY be used as defined by HTTP Content Negotiation ([RFC7231]
Section 3.4). Those media types MUST be flexible enough to express Section 3.4). Those media types MUST be flexible enough to express
every DNS query that would normally be sent in DNS over UDP every DNS query that would normally be sent in DNS over UDP
(including queries and responses that use DNS extensions, but not (including queries and responses that use DNS extensions, but not
those that require multiple responses). those that require multiple responses).
7. Definition of the application/dns-message media type 6. Definition of the application/dns-message media type
The data payload for the application/dns-message media type is a The data payload for the application/dns-message media type is a
single message of the DNS on-the-wire format defined in Section 4.2.1 single message of the DNS on-the-wire format defined in Section 4.2.1
of [RFC1035], which in turn refers to the full wire format defined in of [RFC1035], which in turn refers to the full wire format defined in
Section 4.1 of that RFC. Section 4.1 of that RFC.
Although [RFC1035] says "Messages carried by UDP are restricted to Although [RFC1035] says "Messages carried by UDP are restricted to
512 bytes", that was later updated by [RFC6891]. This media type 512 bytes", that was later updated by [RFC6891]. This media type
restricts the maximum size of the DNS message to 65535 bytes. restricts the maximum size of the DNS message to 65535 bytes.
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ignore the value given for the EDNS UDP payload size in DNS requests. ignore the value given for the EDNS UDP payload size in DNS requests.
When using the GET method, the data payload for this media type MUST When using the GET method, the data payload for this media type MUST
be encoded with base64url [RFC4648] and then provided as a variable be encoded with base64url [RFC4648] and then provided as a variable
named "dns" to the URI Template expansion. Padding characters for named "dns" to the URI Template expansion. Padding characters for
base64url MUST NOT be included. base64url MUST NOT be included.
When using the POST method, the data payload for this media type MUST When using the POST method, the data payload for this media type MUST
NOT be encoded and is used directly as the HTTP message body. NOT be encoded and is used directly as the HTTP message body.
8. IANA Considerations 7. IANA Considerations
8.1. Registration of application/dns-message Media Type 7.1. Registration of application/dns-message Media Type
To: ietf-types@iana.org To: ietf-types@iana.org
Subject: Registration of MIME media type Subject: Registration of MIME media type
application/dns-message application/dns-message
MIME media type name: application MIME media type name: application
MIME subtype name: dns-message MIME subtype name: dns-message
Required parameters: n/a Required parameters: n/a
Optional parameters: n/a Optional parameters: n/a
Encoding considerations: This is a binary format. The contents are a Encoding considerations: This is a binary format. The contents are a
DNS message as defined in RFC 1035. The format used here is for DNS DNS message as defined in RFC 1035. The format used here is for DNS
over UDP, which is the format defined in the diagrams in RFC 1035. over UDP, which is the format defined in the diagrams in RFC 1035.
Security considerations: The security considerations for carrying Security considerations: See [this document].
this data are the same for carrying DNS without encryption. The content is a DNS message, and thus not executable code.
Interoperability considerations: None. Interoperability considerations: None.
Published specification: This document. Published specification: This document.
Applications that use this media type: Applications that use this media type:
Systems that want to exchange full DNS messages. Systems that want to exchange full DNS messages.
Additional information: Additional information:
skipping to change at page 13, line 5 skipping to change at page 12, line 5
Paul Hoffman, paul.hoffman@icann.org Paul Hoffman, paul.hoffman@icann.org
Intended usage: COMMON Intended usage: COMMON
Restrictions on usage: n/a Restrictions on usage: n/a
Author: Paul Hoffman, paul.hoffman@icann.org Author: Paul Hoffman, paul.hoffman@icann.org
Change controller: IESG Change controller: IESG
9. Privacy Considerations 8. Privacy Considerations
[RFC7626] discusses DNS privacy considerations in both "On the wire" [RFC7626] discusses DNS privacy considerations in both "On the wire"
(Section 2.4), and "In the server" (Section 2.5) contexts. This is (Section 2.4), and "In the server" (Section 2.5) contexts. This is
also a useful framing for DoH's privacy considerations. also a useful framing for DoH's privacy considerations.
9.1. On The Wire 8.1. On The Wire
DoH encrypts DNS traffic and requires authentication of the server. DoH encrypts DNS traffic and requires authentication of the server.
This mitigates both passive surveillance [RFC7258] and active attacks This mitigates both passive surveillance [RFC7258] and active attacks
that attempt to divert DNS traffic to rogue servers ([RFC7626] that attempt to divert DNS traffic to rogue servers ([RFC7626]
Section 2.5.1). DNS over TLS [RFC7858] provides similar protections, Section 2.5.1). DNS over TLS [RFC7858] provides similar protections,
while direct UDP and TCP based transports are vulnerable to this while direct UDP and TCP based transports are vulnerable to this
class of attack. class of attack. An experimental effort to offer guidance on
choosing the padding length can be found in
[I-D.ietf-dprive-padding-policy].
Additionally, the use of the HTTPS default port 443 and the ability Additionally, the use of the HTTPS default port 443 and the ability
to mix DoH traffic with other HTTPS traffic on the same connection to mix DoH traffic with other HTTPS traffic on the same connection
can deter unprivileged on-path devices from interfering with DNS can deter unprivileged on-path devices from interfering with DNS
operations and make DNS traffic analysis more difficult. operations and make DNS traffic analysis more difficult.
9.2. In The Server 8.2. In The Server
The DNS wire format [RFC1035] contains no client identifiers; The DNS wire format [RFC1035] contains no client identifiers;
however, various transports of DNS queries and responses do provide however, various transports of DNS queries and responses do provide
data that can be used to correlate requests. HTTPS presents new data that can be used to correlate requests. HTTPS presents new
considerations for correlation, such as explicit HTTP cookies and considerations for correlation, such as explicit HTTP cookies and
implicit fingerprinting of the unique set and ordering of HTTP implicit fingerprinting of the unique set and ordering of HTTP
request header fields. request header fields.
A DoH implementation is built on IP, TCP, TLS, and HTTP. Each layer A DoH implementation is built on IP, TCP, TLS, and HTTP. Each layer
contains one or more common features that can be used to correlate contains one or more common features that can be used to correlate
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At the IP level, the client address provides obvious correlation At the IP level, the client address provides obvious correlation
information. This can be mitigated by use of a NAT, proxy, VPN, or information. This can be mitigated by use of a NAT, proxy, VPN, or
simple address rotation over time. It may be aggravated by use of a simple address rotation over time. It may be aggravated by use of a
DNS server that can correlate real-time addressing information with DNS server that can correlate real-time addressing information with
other personal identifiers, such as when a DNS server and DHCP server other personal identifiers, such as when a DNS server and DHCP server
are operated by the same entity. are operated by the same entity.
DNS implementations that use one TCP connection for multiple DNS DNS implementations that use one TCP connection for multiple DNS
requests directly group those requests. Long-lived connections have requests directly group those requests. Long-lived connections have
better performance behaviors than short-lived connections, but group better performance behaviors than short-lived connections, but group
more requests. TCP-based solutions may also seek performance through more requests which can expose more information to correlation and
consolidation. TCP-based solutions may also seek performance through
the use of TCP Fast Open [RFC7413]. The cookies used in TCP Fast the use of TCP Fast Open [RFC7413]. The cookies used in TCP Fast
Open allow servers to correlate TCP sessions. Open allow servers to correlate TCP sessions.
TLS-based implementations often achieve better handshake performance TLS-based implementations often achieve better handshake performance
through the use of some form of session resumption mechanism such as through the use of some form of session resumption mechanism such as
session tickets [RFC5077]. Session resumption creates trivial [RFC8446] Section 2.2. Session resumption creates trivial mechanisms
mechanisms for a server to correlate TLS connections together. for a server to correlate TLS connections together.
HTTP's feature set can also be used for identification and tracking HTTP's feature set can also be used for identification and tracking
in a number of different ways. For example, authentication request in a number of different ways. For example, authentication request
header fields explicitly identify profiles in use, and HTTP Cookies header fields explicitly identify profiles in use, and HTTP Cookies
are designed as an explicit state-tracking mechanism between the are designed as an explicit state-tracking mechanism between the
client and serving site and often are used as an authentication client and serving site and often are used as an authentication
mechanism. mechanism.
Additionally, the User-Agent and Accept-Language request header Additionally, the User-Agent and Accept-Language request header
fields often convey specific information about the client version or fields often convey specific information about the client version or
skipping to change at page 15, line 5 skipping to change at page 14, line 5
context, when deciding whether or not to enable them. context, when deciding whether or not to enable them.
Implementations are advised to expose the minimal set of data needed Implementations are advised to expose the minimal set of data needed
to achieve the desired feature set. to achieve the desired feature set.
Determining whether or not a DoH implementation requires HTTP cookie Determining whether or not a DoH implementation requires HTTP cookie
[RFC6265] support is particularly important because HTTP cookies are [RFC6265] support is particularly important because HTTP cookies are
the primary state tracking mechanism in HTTP. HTTP Cookies SHOULD the primary state tracking mechanism in HTTP. HTTP Cookies SHOULD
NOT be accepted by DOH clients unless they are explicitly required by NOT be accepted by DOH clients unless they are explicitly required by
a use case. a use case.
10. Security Considerations 9. Security Considerations
Running DNS over HTTPS relies on the security of the underlying HTTP Running DNS over HTTPS relies on the security of the underlying HTTP
transport. This mitigates classic amplification attacks for UDP- transport. This mitigates classic amplification attacks for UDP-
based DNS. Implementations utilizing HTTP/2 benefit from the TLS based DNS. Implementations utilizing HTTP/2 benefit from the TLS
profile defined in [RFC7540] Section 9.2. profile defined in [RFC7540] Section 9.2.
Session-level encryption has well-known weaknesses with respect to Session-level encryption has well-known weaknesses with respect to
traffic analysis which might be particularly acute when dealing with traffic analysis which might be particularly acute when dealing with
DNS queries. HTTP/2 provides further advice about the use of DNS queries. HTTP/2 provides further advice about the use of
compression ([RFC7540] Section 10.6) and padding ([RFC7540] compression ([RFC7540] Section 10.6) and padding ([RFC7540]
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The HTTPS connection provides transport security for the interaction The HTTPS connection provides transport security for the interaction
between the DoH server and client, but does not provide the response between the DoH server and client, but does not provide the response
integrity of DNS data provided by DNSSEC. DNSSEC and DoH are integrity of DNS data provided by DNSSEC. DNSSEC and DoH are
independent and fully compatible protocols, each solving different independent and fully compatible protocols, each solving different
problems. The use of one does not diminish the need nor the problems. The use of one does not diminish the need nor the
usefulness of the other. It is the choice of a client to either usefulness of the other. It is the choice of a client to either
perform full DNSSEC validation of answers or to trust the DoH server perform full DNSSEC validation of answers or to trust the DoH server
to do DNSSEC validation and inspect the AD (Authentic Data) bit in to do DNSSEC validation and inspect the AD (Authentic Data) bit in
the returned message to determine whether an answer was authentic or the returned message to determine whether an answer was authentic or
not. As noted in Section 5.2, different response media types will not. As noted in Section 4.2, different response media types will
provide more or less information from a DNS response so this choice provide more or less information from a DNS response so this choice
may be affected by the response media type. may be affected by the response media type.
Section 6.1 describes the interaction of this protocol with HTTP Section 5.1 describes the interaction of this protocol with HTTP
caching. An adversary that can control the cache used by the client caching. An adversary that can control the cache used by the client
can affect that client's view of the DNS. This is no different than can affect that client's view of the DNS. This is no different than
the security implications of HTTP caching for other protocols that the security implications of HTTP caching for other protocols that
use HTTP. use HTTP.
In the absence of DNSSEC information, a DoH server can give a client In the absence of DNSSEC information, a DoH server can give a client
invalid data in response to a DNS query. Section 4 disallows the use invalid data in response to a DNS query. Section 3 disallows the use
of DoH DNS responses that do not originate from configured servers. of DoH DNS responses that do not originate from configured servers.
This prohibition does not guarantee protection against invalid data, This prohibition does not guarantee protection against invalid data,
but it does reduce the risk. but it does reduce the risk.
11. Operational Considerations 10. Operational Considerations
Local policy considerations and similar factors mean different DNS Local policy considerations and similar factors mean different DNS
servers may provide different results to the same query, for instance servers may provide different results to the same query, for instance
in split DNS configurations [RFC6950]. It logically follows that the in split DNS configurations [RFC6950]. It logically follows that the
server that is queried can influence the end result. Therefore a server that is queried can influence the end result. Therefore a
client's choice of DNS server may affect the responses it gets to its client's choice of DNS server may affect the responses it gets to its
queries. For example, in the case of DNS64 [RFC6147], the choice queries. For example, in the case of DNS64 [RFC6147], the choice
could affect whether IPv6/IPv4 translation will work at all. could affect whether IPv6/IPv4 translation will work at all.
The HTTPS channel used by this specification establishes secure two- The HTTPS channel used by this specification establishes secure two-
party communication between the DoH client and the DoH server. party communication between the DoH client and the DoH server.
Filtering or inspection systems that rely on unsecured transport of Filtering or inspection systems that rely on unsecured transport of
DNS will not function in a DNS over HTTPS environment. DNS will not function in a DNS over HTTPS environment due to the
confidentiality and integrity protection provided by TLS.
Some HTTPS client implementations perform real time third-party Some HTTPS client implementations perform real time third-party
checks of the revocation status of the certificates being used by checks of the revocation status of the certificates being used by
TLS. If this check is done as part of the DoH server connection TLS. If this check is done as part of the DoH server connection
procedure and the check itself requires DNS resolution to connect to procedure and the check itself requires DNS resolution to connect to
the third party a deadlock can occur. The use of OCSP [RFC6960] the third party a deadlock can occur. The use of OCSP [RFC6960]
servers or AIA for CRL fetching ([RFC5280] Section 4.2.2.1) are servers or AIA for CRL fetching ([RFC5280] Section 4.2.2.1) are
examples of how this deadlock can happen. To mitigate the examples of how this deadlock can happen. To mitigate the
possibility of deadlock, DoH servers SHOULD NOT rely on DNS-based possibility of deadlock, the authentication given DoH servers SHOULD
references to external resources in the TLS handshake. For OCSP, the NOT rely on DNS-based references to external resources in the TLS
server can bundle the certificate status as part of the handshake handshake. For OCSP, the server can bundle the certificate status as
using a mechanism appropriate to the version of TLS, such as using part of the handshake using a mechanism appropriate to the version of
[RFC6066] Section 8 for TLS version 1.2. AIA deadlocks can be TLS, such as using [RFC8446] Section 4.4.2.1 for TLS version 1.3.
avoided by providing intermediate certificates that might otherwise AIA deadlocks can be avoided by providing intermediate certificates
be obtained through additional requests. Note that these deadlocks that might otherwise be obtained through additional requests. Note
also need to be considered for server that a DoH server might that these deadlocks also need to be considered for servers that a
redirect to. DoH server might redirect to.
A DoH client may face a similar bootstrapping problem when the HTTP A DoH client may face a similar bootstrapping problem when the HTTP
request needs to resolve the hostname portion of the DNS URI. Just request needs to resolve the hostname portion of the DNS URI. Just
as the address of a traditional DNS nameserver cannot be originally as the address of a traditional DNS nameserver cannot be originally
determined from that same server, a DoH client cannot use its DoH determined from that same server, a DoH client cannot use its DoH
server to initially resolve the server's host name into an address. server to initially resolve the server's host name into an address.
Alternative strategies a client might employ include making the Alternative strategies a client might employ include making the
initial resolution part of the configuration, IP-based URIs and initial resolution part of the configuration, IP-based URIs and
corresponding IP-based certificates for HTTPS, or resolving the DNS corresponding IP-based certificates for HTTPS, or resolving the DNS
API server's hostname via traditional DNS or another DoH server while API server's hostname via traditional DNS or another DoH server while
skipping to change at page 17, line 11 skipping to change at page 16, line 11
was not able to retrieve a full answer for the query but is providing was not able to retrieve a full answer for the query but is providing
the best answer it could get. A DoH server can reply to queries with the best answer it could get. A DoH server can reply to queries with
an HTTP error for queries that it cannot fulfill. In this same an HTTP error for queries that it cannot fulfill. In this same
example, a DoH server could use an HTTP error instead of a non-error example, a DoH server could use an HTTP error instead of a non-error
response that has the TC bit set. response that has the TC bit set.
Many extensions to DNS, using [RFC6891], have been defined over the Many extensions to DNS, using [RFC6891], have been defined over the
years. Extensions that are specific to the choice of transport, such years. Extensions that are specific to the choice of transport, such
as [RFC7828], are not applicable to DoH. as [RFC7828], are not applicable to DoH.
12. References 11. References
12.1. Normative References 11.1. Normative References
[RFC1035] Mockapetris, P., "Domain names - implementation and [RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>. November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS [RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS
NCACHE)", RFC 2308, DOI 10.17487/RFC2308, March 1998, NCACHE)", RFC 2308, DOI 10.17487/RFC2308, March 1998,
<https://www.rfc-editor.org/info/rfc2308>. <https://www.rfc-editor.org/info/rfc2308>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006, Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/info/rfc4648>. <https://www.rfc-editor.org/info/rfc4648>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>.
[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265, [RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
DOI 10.17487/RFC6265, April 2011, DOI 10.17487/RFC6265, April 2011,
<https://www.rfc-editor.org/info/rfc6265>. <https://www.rfc-editor.org/info/rfc6265>.
[RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M., [RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
and D. Orchard, "URI Template", RFC 6570, and D. Orchard, "URI Template", RFC 6570,
DOI 10.17487/RFC6570, March 2012, DOI 10.17487/RFC6570, March 2012,
<https://www.rfc-editor.org/info/rfc6570>. <https://www.rfc-editor.org/info/rfc6570>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
skipping to change at page 18, line 42 skipping to change at page 17, line 37
<https://www.rfc-editor.org/info/rfc7541>. <https://www.rfc-editor.org/info/rfc7541>.
[RFC7626] Bortzmeyer, S., "DNS Privacy Considerations", RFC 7626, [RFC7626] Bortzmeyer, S., "DNS Privacy Considerations", RFC 7626,
DOI 10.17487/RFC7626, August 2015, DOI 10.17487/RFC7626, August 2015,
<https://www.rfc-editor.org/info/rfc7626>. <https://www.rfc-editor.org/info/rfc7626>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
12.2. Informative References [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
11.2. Informative References
[CORS] "Cross-Origin Resource Sharing", n.d., [CORS] "Cross-Origin Resource Sharing", n.d.,
<https://fetch.spec.whatwg.org/#http-cors-protocol>. <https://fetch.spec.whatwg.org/#http-cors-protocol>.
[I-D.ietf-dprive-padding-policy] [I-D.ietf-dprive-padding-policy]
Mayrhofer, A., "Padding Policy for EDNS(0)", draft-ietf- Mayrhofer, A., "Padding Policy for EDNS(0)", draft-ietf-
dprive-padding-policy-06 (work in progress), July 2018. dprive-padding-policy-06 (work in progress), July 2018.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818,
DOI 10.17487/RFC2818, May 2000, DOI 10.17487/RFC2818, May 2000,
<https://www.rfc-editor.org/info/rfc2818>. <https://www.rfc-editor.org/info/rfc2818>.
[RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,
"Transport Layer Security (TLS) Session Resumption without
Server-Side State", RFC 5077, DOI 10.17487/RFC5077,
January 2008, <https://www.rfc-editor.org/info/rfc5077>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>. <https://www.rfc-editor.org/info/rfc5280>.
[RFC5861] Nottingham, M., "HTTP Cache-Control Extensions for Stale [RFC5861] Nottingham, M., "HTTP Cache-Control Extensions for Stale
Content", RFC 5861, DOI 10.17487/RFC5861, May 2010, Content", RFC 5861, DOI 10.17487/RFC5861, May 2010,
<https://www.rfc-editor.org/info/rfc5861>. <https://www.rfc-editor.org/info/rfc5861>.
[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)
Extensions: Extension Definitions", RFC 6066,
DOI 10.17487/RFC6066, January 2011,
<https://www.rfc-editor.org/info/rfc6066>.
[RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van [RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van
Beijnum, "DNS64: DNS Extensions for Network Address Beijnum, "DNS64: DNS Extensions for Network Address
Translation from IPv6 Clients to IPv4 Servers", RFC 6147, Translation from IPv6 Clients to IPv4 Servers", RFC 6147,
DOI 10.17487/RFC6147, April 2011, DOI 10.17487/RFC6147, April 2011,
<https://www.rfc-editor.org/info/rfc6147>. <https://www.rfc-editor.org/info/rfc6147>.
[RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms [RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
for DNS (EDNS(0))", STD 75, RFC 6891, for DNS (EDNS(0))", STD 75, RFC 6891,
DOI 10.17487/RFC6891, April 2013, DOI 10.17487/RFC6891, April 2013,
<https://www.rfc-editor.org/info/rfc6891>. <https://www.rfc-editor.org/info/rfc6891>.
skipping to change at page 20, line 27 skipping to change at page 19, line 10
[RFC7830] Mayrhofer, A., "The EDNS(0) Padding Option", RFC 7830, [RFC7830] Mayrhofer, A., "The EDNS(0) Padding Option", RFC 7830,
DOI 10.17487/RFC7830, May 2016, DOI 10.17487/RFC7830, May 2016,
<https://www.rfc-editor.org/info/rfc7830>. <https://www.rfc-editor.org/info/rfc7830>.
[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., [RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over Transport and P. Hoffman, "Specification for DNS over Transport
Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2016, <https://www.rfc-editor.org/info/rfc7858>. 2016, <https://www.rfc-editor.org/info/rfc7858>.
Acknowledgments Appendix A. Protocol Development
This work required a high level of cooperation between experts in This appendix describes the requirements used to design DoH. These
different technologies. Thank you Ray Bellis, Stephane Bortzmeyer, requirements are listed here to help readers understand the current
Manu Bretelle, Sara Dickinson, Massimiliano Fantuzzi, Tony Finch, protocol, not to limit how the protocol might be developed in the
Daniel Kahn Gilmor, Olafur Gudmundsson, Wes Hardaker, Rory Hewitt, future. This appendix is non-normative.
Joe Hildebrand, David Lawrence, Eliot Lear, John Mattsson, Alex
Mayrhofer, Mark Nottingham, Jim Reid, Adam Roach, Ben Schwartz, Davey
Song, Daniel Stenberg, Andrew Sullivan, Martin Thomson, and Sam
Weiler.
Previous Work on DNS over HTTP or in Other Formats The protocol described in this document based its design on the
following protocol requirements:
o The protocol must use normal HTTP semantics.
o The queries and responses must be able to be flexible enough to
express every DNS query that would normally be sent in DNS over
UDP (including queries and responses that use DNS extensions, but
not those that require multiple responses).
o The protocol must permit the addition of new formats for DNS
queries and responses.
o The protocol must ensure interoperability by specifying a single
format for requests and responses that is mandatory to implement.
That format must be able to support future modifications to the
DNS protocol including the inclusion of one or more EDNS options
(including those not yet defined).
o The protocol must use a secure transport that meets the
requirements for HTTPS.
The following were considered non-requirements:
o Supporting network-specific DNS64 [RFC6147]
o Supporting other network-specific inferences from plaintext DNS
queries
o Supporting insecure HTTP
Appendix B. Previous Work on DNS over HTTP or in Other Formats
The following is an incomplete list of earlier work that related to The following is an incomplete list of earlier work that related to
DNS over HTTP/1 or representing DNS data in other formats. DNS over HTTP/1 or representing DNS data in other formats.
The list includes links to the tools.ietf.org site (because these The list includes links to the tools.ietf.org site (because these
documents are all expired) and web sites of software. documents are all expired) and web sites of software.
o https://tools.ietf.org/html/draft-mohan-dns-query-xml o https://tools.ietf.org/html/draft-mohan-dns-query-xml
o https://tools.ietf.org/html/draft-daley-dnsxml o https://tools.ietf.org/html/draft-daley-dnsxml
skipping to change at page 21, line 4 skipping to change at page 20, line 15
The list includes links to the tools.ietf.org site (because these The list includes links to the tools.ietf.org site (because these
documents are all expired) and web sites of software. documents are all expired) and web sites of software.
o https://tools.ietf.org/html/draft-mohan-dns-query-xml o https://tools.ietf.org/html/draft-mohan-dns-query-xml
o https://tools.ietf.org/html/draft-daley-dnsxml o https://tools.ietf.org/html/draft-daley-dnsxml
o https://tools.ietf.org/html/draft-dulaunoy-dnsop-passive-dns-cof o https://tools.ietf.org/html/draft-dulaunoy-dnsop-passive-dns-cof
o https://tools.ietf.org/html/draft-bortzmeyer-dns-json o https://tools.ietf.org/html/draft-bortzmeyer-dns-json
o https://www.nlnetlabs.nl/projects/dnssec-trigger/ o https://www.nlnetlabs.nl/projects/dnssec-trigger/
Acknowledgments
This work required a high level of cooperation between experts in
different technologies. Thank you Ray Bellis, Stephane Bortzmeyer,
Manu Bretelle, Sara Dickinson, Massimiliano Fantuzzi, Tony Finch,
Daniel Kahn Gilmor, Olafur Gudmundsson, Wes Hardaker, Rory Hewitt,
Joe Hildebrand, David Lawrence, Eliot Lear, John Mattsson, Alex
Mayrhofer, Mark Nottingham, Jim Reid, Adam Roach, Ben Schwartz, Davey
Song, Daniel Stenberg, Andrew Sullivan, Martin Thomson, and Sam
Weiler.
Authors' Addresses Authors' Addresses
Paul Hoffman Paul Hoffman
ICANN ICANN
Email: paul.hoffman@icann.org Email: paul.hoffman@icann.org
Patrick McManus Patrick McManus
Mozilla Mozilla
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