draft-ietf-doh-dns-over-https-03.txt   draft-ietf-doh-dns-over-https-04.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: August 6, 2018 Mozilla Expires: September 22, 2018 Mozilla
February 02, 2018 March 21, 2018
DNS Queries over HTTPS DNS Queries over HTTPS
draft-ietf-doh-dns-over-https-03 draft-ietf-doh-dns-over-https-04
Abstract Abstract
DNS queries sometimes experience problems with end to end
connectivity at times and places where HTTPS flows freely.
HTTPS provides the most practical mechanism for reliable end to end
communication. Its use of TLS provides integrity and confidentiality
guarantees and its use of HTTP allows it to interoperate with
proxies, firewalls, and authentication systems where required for
transit.
This document describes how to run DNS service over HTTP using This document describes how to run DNS service over HTTP using
https:// URIs. https:// URIs.
[[ There is a repository for this draft at https://github.com/dohwg/ [[ There is a repository for this draft at https://github.com/dohwg/
draft-ietf-doh-dns-over-https [1] ]]. draft-ietf-doh-dns-over-https [1] ]].
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
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
skipping to change at page 1, line 44 skipping to change at page 1, line 35
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 August 6, 2018. This Internet-Draft will expire on September 22, 2018.
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.
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 Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
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. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Protocol Requirements . . . . . . . . . . . . . . . . . . . . 3
4. Protocol Requirements . . . . . . . . . . . . . . . . . . . . 4 3.1. Non-requirements . . . . . . . . . . . . . . . . . . . . 4
4.1. Non-requirements . . . . . . . . . . . . . . . . . . . . 5 4. The HTTP Request . . . . . . . . . . . . . . . . . . . . . . 4
5. The HTTP Request . . . . . . . . . . . . . . . . . . . . . . 5 4.1. DNS Wire Format . . . . . . . . . . . . . . . . . . . . . 5
5.1. DNS Wire Format . . . . . . . . . . . . . . . . . . . . . 6 4.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . 5
5.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . 6 5. The HTTP Response . . . . . . . . . . . . . . . . . . . . . . 7
6. The HTTP Response . . . . . . . . . . . . . . . . . . . . . . 7 5.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 8 6. HTTP Integration . . . . . . . . . . . . . . . . . . . . . . 8
7. HTTP Integration . . . . . . . . . . . . . . . . . . . . . . 9 6.1. Cache Interaction . . . . . . . . . . . . . . . . . . . . 8
7.1. Cache Interaction . . . . . . . . . . . . . . . . . . . . 9 6.2. HTTP/2 . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.2. HTTP/2 . . . . . . . . . . . . . . . . . . . . . . . . . 10 6.3. Server Push . . . . . . . . . . . . . . . . . . . . . . . 10
7.3. Server Push . . . . . . . . . . . . . . . . . . . . . . . 10 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 7.1. Registration of application/dns-udpwireformat Media Type 10
8.1. Registration of application/dns-udpwireformat Media Type 10 8. Security Considerations . . . . . . . . . . . . . . . . . . . 12
9. Security Considerations . . . . . . . . . . . . . . . . . . . 12 9. Operational Considerations . . . . . . . . . . . . . . . . . 13
10. Operational Considerations . . . . . . . . . . . . . . . . . 13 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 11.1. Normative References . . . . . . . . . . . . . . . . . . 14
12.1. Normative References . . . . . . . . . . . . . . . . . . 13 11.2. Informative References . . . . . . . . . . . . . . . . . 15
12.2. Informative References . . . . . . . . . . . . . . . . . 15 11.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 16
12.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Appendix A. Previous Work on DNS over HTTP or in Other Formats . 16
Appendix A. Previous Work on DNS over HTTP or in Other Formats . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction 1. Introduction
The Internet does not always provide end to end reachability for The Internet does not always provide end to end reachability for
native DNS. On-path network devices may spoof DNS responses, block native DNS. On-path network devices may spoof DNS responses, block
DNS requests, or just redirect DNS queries to different DNS servers DNS requests, or just redirect DNS queries to different DNS servers
that give less-than-honest answers. that give less-than-honest answers. These are also sometimes
delivered with poor performance or reduced feature sets.
Over time, there have been many proposals for using HTTP and HTTPS as Over time, there have been many proposals for using HTTP and HTTPS as
a substrate for DNS queries and responses. To date, none of those a substrate for DNS queries and responses. To date, none of those
proposals have made it beyond early discussion, partially due to proposals have made it beyond early discussion, partially due to
disagreement about what the appropriate formatting should be and disagreement about what the appropriate formatting should be and
partially because they did not follow HTTP best practices. partially because they did not follow HTTP best practices.
This document defines a specific protocol for sending DNS [RFC1035] This document defines a specific protocol for sending DNS [RFC1035]
queries and getting DNS responses over HTTP [RFC7540] using https:// queries and getting DNS responses over HTTP [RFC7540] using https://
(and therefore TLS [RFC5246] security for integrity and (and therefore TLS [RFC5246] security for integrity and
confidentiality). Each DNS query-response pair is mapped into a HTTP confidentiality). Each DNS query-response pair is mapped into a HTTP
request-response pair. request-response pair.
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, proxying, and compression. itself with HTTP features such as caching, redirection, proxying,
authentication, and compression.
The integration with HTTP provides a transport suitable for both The integration with HTTP provides a transport suitable for both
traditional DNS clients and native web applications seeking access to traditional DNS clients and native web applications seeking access to
the DNS. the DNS.
Two primary uses cases were considered during this protocol's
development. They included preventing on-path devices from
interfering with DNS operations and allowing web applications to
access DNS information via existing browser APIs in a safe way
consistent with Cross Origin Resource Sharing (CORS) [CORS]. There
are certainly other uses for this work.
2. Terminology 2. Terminology
A server that supports this protocol is called a "DNS API server" to A server that supports this protocol is called a "DNS API server" to
differentiate it from a "DNS server" (one that uses the regular DNS differentiate it from a "DNS server" (one that uses the regular DNS
protocol). Similarly, a client that supports this protocol is called protocol). Similarly, a client that supports this protocol is called
a "DNS API client". a "DNS API client".
In this document, the key words "MUST", "MUST NOT", "REQUIRED", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
and "OPTIONAL" are to be interpreted as described in BCP 14, RFC 2119 "OPTIONAL" in this document are to be interpreted as described in BCP
[RFC2119]. 14, RFC8174 [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Use Cases
There are two initial use cases for this protocol.
The primary use case is to prevent on-path network devices from
interfering with DNS operations. This interference includes, but is
not limited to, spoofing DNS responses, blocking DNS requests, and
tracking.
In this use, clients - whether operating systems or individual
applications - will be explicitly configured to use a DOH server as a
recursive resolver by its user (or administrator). They might use
the DOH server for all queries, or only for a subset of them. The
specific configuration mechanism is out of scope for this document.
A secondary use case is allowing web applications to access DNS
information, by using existing APIs in browsers to access it over
HTTP in a safe way consistent with Cross Origin Resource Sharing
(CORS) [CORS].
This is technically already possible (since the server controls both
the HTTP resources it exposes and the use of browser APIs by its
content), but standardization might make this easier to accomplish.
Note that in this second use, the browser does not consult the DOH
server or use its responses for any DNS lookups outside the scope of
the application using them; i.e., there is (currently) no API that
allows a Web site to poison DNS for others.
[[ This paragraph is to be removed when this document is published as
an RFC ]] Note that these use cases are different than those in a
similar protocol described at [I-D.ietf-dnsop-dns-wireformat-http].
The use case for that protocol is proxying DNS queries over HTTP
instead of over DNS itself. The use cases in this document all
involve query origination instead of proxying.
4. Protocol Requirements 3. Protocol Requirements
The protocol described here bases its design on the following The protocol described here bases its design on the following
protocol requirements: protocol requirements:
o The protocol must use normal HTTP semantics. o The protocol must use normal HTTP semantics.
o The queries and responses must be able to be flexible enough to o The queries and responses must be able to be flexible enough to
express every normal DNS query. express every normal DNS query.
o The protocol must allow implementations to use HTTP's content o The protocol must allow implementations to use HTTP's content
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o The protocol must ensure interoperable media formats through a o The protocol must ensure interoperable media formats through a
mandatory to implement format wherein a query must be able to mandatory to implement format wherein a query must be able to
contain future modifications to the DNS protocol including the contain future modifications to the DNS protocol including the
inclusion of one or more EDNS extensions (including those not yet inclusion of one or more EDNS extensions (including those not yet
defined). defined).
o The protocol must use a secure transport that meets the o The protocol must use a secure transport that meets the
requirements for HTTPS. requirements for HTTPS.
4.1. Non-requirements 3.1. Non-requirements
o Supporting network-specific DNS64 [RFC6147] o Supporting network-specific DNS64 [RFC6147]
o Supporting other network-specific inferences from plaintext DNS o Supporting other network-specific inferences from plaintext DNS
queries queries
o Supporting insecure HTTP o Supporting insecure HTTP
o Supporting legacy HTTP versions o Supporting legacy HTTP versions
5. The HTTP Request 4. The HTTP Request
To make a DNS API query a DNS API client encodes a single DNS query To make a DNS API query a DNS API client encodes a single DNS query
into an HTTP request using either the HTTP GET or POST method and the into an HTTP request using either the HTTP GET or POST method and the
other requirements of this section. The DNS API server defines the other requirements of this section. The DNS API server defines the
URI used by the request. Configuration and discovery of the URI is URI used by the request. Configuration and discovery of the URI is
done out of band from this protocol. done out of band from this protocol.
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 body of the HTTP request and the Content-Type request header
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. smaller than their GET equivalents.
When using the GET method the URI path MUST contain a query parameter When using the GET method the URI path MUST contain a query parameter
with the name of "ct" and a value indicating the media-format used name-value pair [QUERYPARAMETER] with the name of "ct" and a value
for the dns parameter. The value may either be an explicit media indicating the media-format used for the dns parameter. The value
type (e.g. ct=application/dns-udpwireformat&dns=...) or it may be may either be an explicit media type (e.g. ct=application/dns-
empty. An empty value indicates the default application/dns- udpwireformat&dns=...) or it may be empty. An empty value indicates
udpwireformat type (e.g. ct&dns=...). the default application/dns-udpwireformat type (e.g. ct&dns=...).
When using the GET method the URI path MUST contain a query parameter When using the GET method the URI path MUST contain a query parameter
with the name of "dns". The value of the parameter is the content of with the name of "dns". The value of the parameter is the content of
the request potentially encoded with base64url [RFC4648]. the request potentially encoded with base64url [RFC4648].
Specifications that define media types for use with DOH, such as DNS Specifications that define media types for use with DOH, such as DNS
Wire Format Section 5.1 of this document, MUST indicate if the body Wire Format Section 4.1 of this document, MUST indicate if the dns
parameter uses base64url encoding. parameter uses base64url encoding.
Using the GET method is friendlier to many HTTP cache Using the GET method is friendlier to many HTTP cache
implementations. implementations.
The DNS API Client SHOULD include an HTTP "Accept:" request header to The DNS API client SHOULD include an HTTP "Accept:" request header to
say what type of content can be understood in response. The client say what type of content can be understood in response. The client
MUST be prepared to process "application/dns-udpwireformat" MUST be prepared to process "application/dns-udpwireformat"
Section 5.1 responses but MAY process any other type it receives. Section 4.1 responses but MAY process any other type it receives.
In order to maximize cache friendliness, DNS API clients using media In order to maximize cache friendliness, DNS API clients using media
formats that include DNS ID, such as application/dns-udpwireformat, formats that include DNS ID, such as application/dns-udpwireformat,
SHOULD use a DNS ID of 0 in every DNS request. HTTP correlates SHOULD use a DNS ID of 0 in every DNS request. HTTP correlates
request and response, thus eliminating the need for the ID in a media request and response, thus eliminating the need for the ID in a media
type such as application/dns-udpwireformat and the use of a varying type such as application/dns-udpwireformat and the use of a varying
DNS ID can cause semantically equivalent DNS queries to be cached DNS ID can cause semantically equivalent DNS queries to be cached
separately. separately.
DNS API clients can use HTTP/2 padding and compression in the same DNS API clients can use HTTP/2 padding and compression in the same
way that other HTTP/2 clients use (or don't use) them. way that other HTTP/2 clients use (or don't use) them.
5.1. DNS Wire Format 4.1. DNS Wire Format
The media type is "application/dns-udpwireformat". The data payload is the DNS on-the-wire format defined in [RFC1035].
The format is for DNS over UDP. (Note that this is different than
the wire format used in [RFC7858].
The body is the DNS on-the-wire format defined in [RFC1035]. When using the GET method, the data payload MUST be encoded with
base64url [RFC4648] and then placed as a name value pair in the query
portion of the URI with name "dns". Padding characters for base64url
MUST NOT be included.
When using the GET method, the body MUST be encoded with base64url When using the POST method, the data payload MUST NOT be encoded and
[RFC4648] and then placed as a name value pair in the query portion is used directly as the HTTP message body.
of the URI with name "dns". Padding characters for base64url MUST
NOT be included.
When using the POST method, the body MUST NOT be encoded. DNS API clients using the DNS wire format MAY have one or more EDNS
extensions [RFC6891] in the request.
DNS API clients using the DNS wire format MAY have one or more The media type is "application/dns-udpwireformat".
EDNS(0) extensions [RFC6891] in the request.
5.2. Examples 4.2. Examples
These examples use HTTP/2 style formatting from [RFC7540]. These examples use HTTP/2 style formatting from [RFC7540].
These examples use a DNS API service located at These examples use a DNS API service located at
https://dnsserver.example.net/dns-query to resolve the IN A records. https://dnsserver.example.net/dns-query to resolve the IN A records.
The requests are represented as application/dns-udpwirefomat typed The requests are represented as application/dns-udpwirefomat typed
bodies, but the client indicates it can parse responses in either bodies.
that format or as a hypothetical JSON-based content type. The
application/simpledns+json type used by this example is currently
fictitious.
The first example request uses GET to request www.example.com The first example request uses GET to request www.example.com
:method = GET :method = GET
:scheme = https :scheme = https
:authority = dnsserver.example.net :authority = dnsserver.example.net
:path = /dns-query?ct& (no space or CR) :path = /dns-query?ct& (no space or CR)
dns=AAABAAABAAAAAAAAA3d3dwdleGFtcGxlA2NvbQAAAQAB dns=AAABAAABAAAAAAAAA3d3dwdleGFtcGxlA2NvbQAAAQAB
accept = application/dns-udpwireformat, application/simpledns+json accept = application/dns-udpwireformat
The same DNS query for www.example.com, using the POST method would The same DNS query for www.example.com, using the POST method would
be: be:
:method = POST :method = POST
:scheme = https :scheme = https
:authority = dnsserver.example.net :authority = dnsserver.example.net
:path = /dns-query :path = /dns-query
accept = application/dns-udpwireformat, application/simpledns+json accept = application/dns-udpwireformat
content-type = application/dns-udpwireformat content-type = application/dns-udpwireformat
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
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
skipping to change at page 7, line 41 skipping to change at page 6, line 51
61 6e 64 61 72 64 2d 62 61 73 65 36 34 07 65 78 61 6e 64 61 72 64 2d 62 61 73 65 36 34 07 65 78
61 6d 70 6c 65 03 63 6f 6d 00 00 01 00 01 61 6d 70 6c 65 03 63 6f 6d 00 00 01 00 01
:method = GET :method = GET
:scheme = https :scheme = https
:authority = dnsserver.example.net :authority = dnsserver.example.net
:path = /dns-query?ct& (no space or CR) :path = /dns-query?ct& (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-udpwireformat, application/simpledns+json accept = application/dns-udpwireformat
6. The HTTP Response 5. The HTTP Response
An HTTP response with a 2xx status code ([RFC7231] Section 6.3)
indicates a valid DNS response to the query made in the HTTP request.
A valid DNS response includes both success and failure responses.
For example, a DNS failure response such as SERVFAIL or NXDOMAIN will
be the message in a successful 2xx HTTP response even though there
was a failure at the DNS layer. Responses with non-successful HTTP
status codes do not contain DNS answers to the question in the
corresponding request. Some of these non-successful HTTP responses
(e.g. redirects or authentication failures) could allow clients to
make new requests to satisfy the original question.
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
the information from the DNS header bytes while another might omit the information from the DNS header bytes while another might omit
it. The amount and type of information that a media type gives is it. The amount and type of information that a media type gives is
solely up to the format, and not defined in this protocol. solely up to the format, and not defined in this protocol.
At the time this is published, the response types are works in At the time this is published, the response types are works in
progress. The only response type defined in this document is progress. The only response type defined in this document is
"application/dns-udpwireformat", but it is possible that at least one "application/dns-udpwireformat", but it is possible that other
JSON-based response format will be defined in the future. response formats will be defined in the future.
The DNS response for "application/dns-udpwireformat" in Section 5.1 The DNS response for "application/dns-udpwireformat" in Section 4.1
MAY have one or more EDNS(0) extensions, depending on the extension MAY have one or more EDNS extensions, depending on the extension
definition of the extensions given in the DNS request. definition of the extensions given in the DNS request.
Each DNS request-response pair is matched to one HTTP request- Each DNS request-response pair is matched to one HTTP request-
response pair. The responses may be processed and transported in any response pair. The responses may be processed and transported in any
order using HTTP's multi-streaming functionality ([RFC7540] order using HTTP's multi-streaming functionality ([RFC7540]
Section 5}). Section 5}).
The Answer section of a DNS response contains one or more RRsets. The Answer section of a DNS response can contain zero or more RRsets.
(RRsets are defined in [RFC7719].) According to [RFC2181], each (RRsets are defined in [RFC7719].) According to [RFC2181], each
resource record in an RRset is supposed to have the Time To Live resource record in an RRset has Time To Live (TTL) freshness
(TTL) freshness information. Different RRsets in the Answer section information. Different RRsets in the Answer section can have
can have different TTLs, though it is only possible for the HTTP different TTLs, although it is only possible for the HTTP response to
response to have a single freshness lifetime. The HTTP response have a single freshness lifetime. The HTTP response freshness
freshness lifetime ([RFC7234] Section 4.2) should be coordinated with lifetime ([RFC7234] Section 4.2) should be coordinated with the RRset
the Resource Record bearing the smallest TTL in the Answer section of with the smallest TTL in the Answer section of the response.
the response. Specifically, the HTTP freshness lifetime SHOULD be Specifically, the HTTP freshness lifetime SHOULD be set to expire at
set to expire at the same time any of the DNS Records reach a 0 TTL. the same time any of the DNS resource records in the Answer section
The response freshness lifetime MUST NOT be greater than that reach a 0 TTL. The response freshness lifetime MUST NOT be greater
indicated by the DNS Record with the smallest TTL in the response. than that indicated by the DNS resoruce record with the smallest TTL
in the response.
A DNS API Client that receives a response without an explicit 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
freshness lifetime MUST NOT be greater than the MINIMUM field from
that SOA record. Otherwise, the HTTP response MUST set a freshness
lifetime ([RFC7234] Section 4.2) of 0 by using a mechanism such as
"Cache-Control: no-cache" ([RFC7234] Section 5.2.1.4).
A DNS API client that receives a response without an explicit
freshness lifetime MUST NOT assign that response a heuristic freshness lifetime MUST NOT assign that response a heuristic
freshness ([RFC7234] Section 4.2.2.) greater than that indicated by freshness ([RFC7234] Section 4.2.2.) greater than that indicated by
the DNS Record with the smallest TTL in the response. the DNS Record with the smallest TTL in the response.
A DNS API Server MUST be able to process application/dns- A DNS API server MUST be able to process application/dns-
udpwireformat request messages. udpwireformat request messages.
A DNS API Server SHOULD respond with HTTP status code 415 A DNS API server SHOULD respond with HTTP status code 415
(Unsupported Media Type) upon receiving a media type it is unable to (Unsupported Media Type) upon receiving a media type it is unable to
process. process.
This document does not change the definition of any HTTP response This document does not change the definition of any HTTP response
codes or otherwise proscribe their use. codes or otherwise proscribe their use.
6.1. Example 5.1. Example
This is an example response for a query for the IN A records for This is an example response for a query for the IN A records for
"www.example.com" with recursion turned on. The response bears one "www.example.com" with recursion turned on. The response bears one
record with an address of 192.0.2.1 and a TTL of 128 seconds. record with an address of 192.0.2.1 and a TTL of 128 seconds.
:status = 200 :status = 200
content-type = application/dns-udpwireformat content-type = application/dns-udpwireformat
content-length = 64 content-length = 64
cache-control = max-age=128 cache-control = max-age=128
<64 bytes represented by the following hex encoding> <64 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 01 00 07 65 78 61 6d 70 6c 65 03 63 6f 6d 00 00 01 00
01 03 77 77 77 07 65 78 61 6d 70 6c 65 03 63 6f 01 03 77 77 77 07 65 78 61 6d 70 6c 65 03 63 6f
6d 00 00 01 00 01 00 00 00 80 00 04 C0 00 02 01 6d 00 00 01 00 01 00 00 00 80 00 04 C0 00 02 01
7. HTTP Integration 6. HTTP Integration
This protocol MUST be used with the https scheme URI [RFC7230]. This protocol MUST be used with the https scheme URI [RFC7230].
7.1. Cache Interaction 6.1. Cache Interaction
A DOH API Client may utilize a hierarchy of caches that include both A DOH API client may utilize a hierarchy of caches that include both
HTTP and DNS specific caches. HTTP cache entries may be bypassed HTTP and DNS specific caches. HTTP cache entries may be bypassed
with HTTP mechanisms such as the Cache-Control no-cache directive with HTTP mechanisms such as the "Cache-Control no-cache" directive;
however DNS caches do not have a similar mechanism. however DNS caches do not have a similar mechanism.
A DOH response that was previously stored in an HTTP cache will A DOH response that was previously stored in an HTTP cache will
contain the [RFC7234] Age response header indicating the elapsed time contain the [RFC7234] Age response header indicating the elapsed time
between when the entry was placed in the HTTP cache and the current between when the entry was placed in the HTTP cache and the current
DOH response. DNS API clients should subtract this time from the DNS DOH response. DNS API clients should subtract this time from the DNS
TTL if they are re-sharing the information in a non HTTP context TTL if they are re-sharing the information in a non HTTP context
(e.g. their own DNS cache) to determine the remaining time to live of (e.g. their own DNS cache) to determine the remaining time to live of
the DNS record. the DNS record.
skipping to change at page 10, line 13 skipping to change at page 9, line 41
extenuating circumstances defined in [RFC5861]. extenuating circumstances defined in [RFC5861].
All HTTP servers, including DNS API servers, need to consider cache All HTTP servers, including DNS API servers, need to consider cache
interaction when they generate responses that are not globally valid. interaction when they generate responses that are not globally valid.
For instance, if a DNS API server customized a response based on the For instance, if a DNS API server customized a response based on the
client's identity then it would not want to globally allow reuse of client's identity then it would not want to globally allow reuse of
that response. This could be accomplished through a variety of HTTP that response. This could be accomplished through a variety of HTTP
techniques such as a Cache-Control max-age of 0, or perhaps by the techniques such as a Cache-Control max-age of 0, or perhaps by the
Vary response header. Vary response header.
7.2. HTTP/2 6.2. HTTP/2
The minimum version of HTTP used by DOH SHOULD be HTTP/2 [RFC7540]. The minimum version of HTTP used by DOH SHOULD be HTTP/2 [RFC7540].
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 for many uses cases. poor performance for many uses cases.
7.3. Server Push 6.3. 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 is a trusted service for the DOH establish that the HTTP request URI is a trusted service for the DOH
query. For HTTP requests initiated by the DNS API client this trust query. For HTTP requests initiated by the DNS API client this trust
is implicit in the selection of URI. For HTTP server push ([RFC7540] is implicit in the selection of URI. For HTTP server push ([RFC7540]
Section 8.2) extra care must be taken to ensure that the pushed URI Section 8.2) 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 is one that the client would have directed the same query to if the
client had initiated the request. This specification does not extend client had initiated the request. This specification does not extend
DNS resolution privileges to URIs that are not recognized by the DNS resolution privileges to URIs that are not recognized by the
client as trusted DNS API servers. client as trusted DNS API servers.
8. IANA Considerations 7. IANA Considerations
8.1. Registration of application/dns-udpwireformat Media Type 7.1. Registration of application/dns-udpwireformat 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-udpwireformat application/dns-udpwireformat
MIME media type name: application MIME media type name: application
MIME subtype name: dns-udpwireformat MIME subtype name: dns-udpwireformat
Required parameters: n/a Required parameters: n/a
skipping to change at page 12, 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. Security Considerations 8. 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. Implementations utilizing HTTP/2 benefit from the TLS transport. This mitigates classic amplication attacks for UDP-based
profile defined in [RFC7540] Section 9.2. DNS. Implementations utilizing HTTP/2 benefit from the TLS 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. Sections 10.6 (Compression) and 10.7 (Padding) of DNS queries. HTTP/2 provides further advice about the use of
[RFC7540] provide some further advice on mitigations within an HTTP/2 compression (Section 10.6 of [RFC7540]) and padding (Section 10.7 of
context. [RFC7540]).
The HTTPS connection provides transport security for the interaction The HTTPS connection provides transport security for the interaction
between the DNS API server and client, but does not inherently ensure between the DNS API server and client, but does not inherently ensure
the authenticity of DNS data. A DNS API client may also perform full the authenticity of DNS data. A DNS API client may also perform full
DNSSEC validation of answers received from a DNS API server or it may DNSSEC validation of answers received from a DNS API server or it may
choose to trust answers from a particular DNS API server, much as a choose to trust answers from a particular DNS API server, much as a
DNS client might choose to trust answers from its recursive DNS DNS client might choose to trust answers from its recursive DNS
resolver. resolver. This capability might be affected by the response media
type.
[[ From the WG charter:
The working group will analyze the security and privacy issues that
could arise from accessing DNS over HTTPS. In particular, the
working group will consider the interaction of DNS and HTTP caching.
]] Section 6.1 describes the interaction of this protocol with HTTP
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
the security implications of HTTP caching for other protocols that
use HTTP.
A server that is acting both as a normal web server and a DNS API A server that is acting both as a normal web server and a DNS API
server is in a position to choose which DNS names it forces a client server is in a position to choose which DNS names it forces a client
to resolve (through its web service) and also be the one to answer to resolve (through its web service) and also be the one to answer
those queries (through its DNS API service). An untrusted DNS API those queries (through its DNS API service). An untrusted DNS API
server can thus easily cause damage by poisoning a client's cache server can thus easily cause damage by poisoning a client's cache
with names that the DNS API server chooses to poison. A client MUST with names that the DNS API server chooses to poison. A client MUST
NOT trust a DNS API server simply because it was discovered, or NOT trust a DNS API server simply because it was discovered, or
because the client was told to trust the DNS API server by an because the client was told to trust the DNS API server by an
untrusted party. Instead, a client MUST only trust DNS API server untrusted party. Instead, a client MUST only trust DNS API server
that is configured as trustworthy. that is configured as trustworthy.
[[ From the WG charter: A client can use DNS over HTTPS as one of multiple mechanisms to
obtain DNS data. If a client of this protocol encounters an HTTP
The working group may define mechanisms for discovery of DOH servers error after sending a DNS query, and then falls back to a different
similar to existing mechanisms for discovering other DNS servers if DNS retrieval mechanism, doing so can weaken the privacy expected by
the chairs determine that there is both sufficient interest and the user of the client.
working group consensus.
]]
10. Operational Considerations 9. 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 which is queried can influence the end result. Therefore a server which 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. queries. For example, in the case of DNS64 [RFC6147], the choice
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 DNS API Client and the DNS API party communication between the DNS API client and the DNS API
Server. Filtering or inspection systems that rely on unsecured server. Filtering or inspection systems that rely on unsecured
transport of DNS will not function in a DNS over HTTPS environment. transport of DNS will not function in a DNS over HTTPS environment.
Many HTTPS implementations perform real time third party checks of Many HTTPS implementations perform real time third party checks of
the revocation status of the certificates being used by TLS. If this the revocation status of the certificates being used by TLS. If this
check is done as part of the DNS API server connection procedure and check is done as part of the DNS API server connection procedure and
the check itself requires DNS resolution to connect to the third the check itself requires DNS resolution to connect to the third
party a deadlock can occur. The use of an OCSP [RFC6960] server is party a deadlock can occur. The use of an OCSP [RFC6960] server is
one example of how this can happen. DNS API servers SHOULD utilize one example of how this can happen. DNS API servers SHOULD utilize
OCSP Stapling [RFC6961] to provide the client with certificate OCSP Stapling [RFC6961] to provide the client with certificate
revocation information that does not require contacting a third revocation information that does not require contacting a third
party. party.
A DNS API client may face a similar bootstrapping problem when the A DNS API client may face a similar bootstrapping problem when the
HTTP request needs to resolve the hostname portion of the DNS URI. HTTP request needs to resolve the hostname portion of the DNS URI.
Just as the address of a traditional DNS nameserver cannot be Just as the address of a traditional DNS nameserver cannot be
originally determined from that same server, a DOH client cannot use originally determined from that same server, a DOH client cannot use
its DOH server to initially resolve the server's host name into an its DOH server to initially resolve the server's host name into an
address. Alternative strategies a client might employ include making address. Alternative strategies a client might employ include making
the initial resolution part of the configuration, IP based URIs and the 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
still authenticating the resulting connection via HTTPS. still authenticating the resulting connection via HTTPS.
11. Acknowledgments HTTP [RFC7230] is a stateless application level protocol and
therefore DOH implementations do not provide stateful ordering
guarantees between different requests. DOH cannot be used as a
transport for other protocols that require strict ordering.
10. Acknowledgments
Joe Hildebrand contributed lots of material for a different iteration Joe Hildebrand contributed lots of material for a different iteration
of this document. Helpful early comments were given by Ben Schwartz of this document. Helpful early comments were given by Ben Schwartz
and Mark Nottingham. and Mark Nottingham.
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
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[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 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, (TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008, DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>. <https://www.rfc-editor.org/info/rfc5246>.
[RFC6960] Santesson, S., Myers, M., Ankney, R., Malpani, A., [RFC6960] Santesson, S., Myers, M., Ankney, R., Malpani, A.,
skipping to change at page 14, line 35 skipping to change at page 14, line 38
[RFC6961] Pettersen, Y., "The Transport Layer Security (TLS) [RFC6961] Pettersen, Y., "The Transport Layer Security (TLS)
Multiple Certificate Status Request Extension", RFC 6961, Multiple Certificate Status Request Extension", RFC 6961,
DOI 10.17487/RFC6961, June 2013, DOI 10.17487/RFC6961, June 2013,
<https://www.rfc-editor.org/info/rfc6961>. <https://www.rfc-editor.org/info/rfc6961>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing", Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014, RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>. <https://www.rfc-editor.org/info/rfc7230>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014,
<https://www.rfc-editor.org/info/rfc7231>.
[RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, [RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching", Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
RFC 7234, DOI 10.17487/RFC7234, June 2014, RFC 7234, DOI 10.17487/RFC7234, June 2014,
<https://www.rfc-editor.org/info/rfc7234>. <https://www.rfc-editor.org/info/rfc7234>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext [RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540, Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015, DOI 10.17487/RFC7540, May 2015,
<https://www.rfc-editor.org/info/rfc7540>. <https://www.rfc-editor.org/info/rfc7540>.
[RFC7541] Peon, R. and H. Ruellan, "HPACK: Header Compression for [RFC7541] Peon, R. and H. Ruellan, "HPACK: Header Compression for
HTTP/2", RFC 7541, DOI 10.17487/RFC7541, May 2015, HTTP/2", RFC 7541, DOI 10.17487/RFC7541, May 2015,
<https://www.rfc-editor.org/info/rfc7541>. <https://www.rfc-editor.org/info/rfc7541>.
12.2. Informative References [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
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-dnsop-dns-wireformat-http] [QUERYPARAMETER]
Song, L., Vixie, P., Kerr, S., and R. Wan, "DNS wire- "application/x-www-form-urlencoded Parsing", n.d.,
format over HTTP", draft-ietf-dnsop-dns-wireformat-http-01 <https://url.spec.whatwg.org/#application/
(work in progress), March 2017. x-www-form-urlencoded>.
[RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS
Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997, Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997,
<https://www.rfc-editor.org/info/rfc2181>. <https://www.rfc-editor.org/info/rfc2181>.
[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>.
[RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van [RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van
skipping to change at page 15, line 43 skipping to change at page 16, line 5
[RFC6950] Peterson, J., Kolkman, O., Tschofenig, H., and B. Aboba, [RFC6950] Peterson, J., Kolkman, O., Tschofenig, H., and B. Aboba,
"Architectural Considerations on Application Features in "Architectural Considerations on Application Features in
the DNS", RFC 6950, DOI 10.17487/RFC6950, October 2013, the DNS", RFC 6950, DOI 10.17487/RFC6950, October 2013,
<https://www.rfc-editor.org/info/rfc6950>. <https://www.rfc-editor.org/info/rfc6950>.
[RFC7719] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS [RFC7719] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", RFC 7719, DOI 10.17487/RFC7719, December Terminology", RFC 7719, DOI 10.17487/RFC7719, December
2015, <https://www.rfc-editor.org/info/rfc7719>. 2015, <https://www.rfc-editor.org/info/rfc7719>.
12.3. URIs [RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over Transport
Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2016, <https://www.rfc-editor.org/info/rfc7858>.
11.3. URIs
[1] https://github.com/dohwg/draft-ietf-doh-dns-over-https [1] https://github.com/dohwg/draft-ietf-doh-dns-over-https
Appendix A. Previous Work on DNS over HTTP or in Other Formats Appendix A. 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.
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