draft-ietf-doh-dns-over-https-05.txt   draft-ietf-doh-dns-over-https-06.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: October 4, 2018 Mozilla Expires: October 11, 2018 Mozilla
April 02, 2018 April 09, 2018
DNS Queries over HTTPS DNS Queries over HTTPS
draft-ietf-doh-dns-over-https-05 draft-ietf-doh-dns-over-https-06
Abstract Abstract
This document describes how to run DNS service over HTTP using This document describes how to run DNS service over HTTP (DOH) using
https:// URIs. https:// URIs.
[[ There is a repository for this draft at https://github.com/dohwg/
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.
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 October 4, 2018. This Internet-Draft will expire on October 11, 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
skipping to change at page 2, line 13 skipping to change at page 2, line 11
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. Protocol Requirements . . . . . . . . . . . . . . . . . . . . 3 3. Protocol Requirements . . . . . . . . . . . . . . . . . . . . 3
3.1. Non-requirements . . . . . . . . . . . . . . . . . . . . 4 3.1. Non-requirements . . . . . . . . . . . . . . . . . . . . 4
4. The HTTP Request . . . . . . . . . . . . . . . . . . . . . . 4 4. The HTTP Exchange . . . . . . . . . . . . . . . . . . . . . . 4
4.1. DNS Wire Format . . . . . . . . . . . . . . . . . . . . . 5 4.1. The HTTP Request . . . . . . . . . . . . . . . . . . . . 4
4.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . 5 4.1.1. HTTP Request Examples . . . . . . . . . . . . . . . . 5
5. The HTTP Response . . . . . . . . . . . . . . . . . . . . . . 6 4.2. The HTTP Response . . . . . . . . . . . . . . . . . . . . 6
5.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.2.1. HTTP Response Example . . . . . . . . . . . . . . . . 7
6. HTTP Integration . . . . . . . . . . . . . . . . . . . . . . 8 5. HTTP Integration . . . . . . . . . . . . . . . . . . . . . . 7
6.1. Cache Interaction . . . . . . . . . . . . . . . . . . . . 8 5.1. Cache Interaction . . . . . . . . . . . . . . . . . . . . 7
6.2. HTTP/2 . . . . . . . . . . . . . . . . . . . . . . . . . 9 5.2. HTTP/2 . . . . . . . . . . . . . . . . . . . . . . . . . 9
6.3. Server Push . . . . . . . . . . . . . . . . . . . . . . . 9 5.3. Server Push . . . . . . . . . . . . . . . . . . . . . . . 9
6.4. Content Negotiation . . . . . . . . . . . . . . . . . . . 10 5.4. Content Negotiation . . . . . . . . . . . . . . . . . . . 9
6. DNS Wire Format . . . . . . . . . . . . . . . . . . . . . . . 9
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
7.1. Registration of application/dns-udpwireformat Media Type 10 7.1. Registration of message/dns Media Type . . . . . . . . . 10
8. Security Considerations . . . . . . . . . . . . . . . . . . . 12 8. Security Considerations . . . . . . . . . . . . . . . . . . . 12
9. Operational Considerations . . . . . . . . . . . . . . . . . 13 9. Operational Considerations . . . . . . . . . . . . . . . . . 13
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
11.1. Normative References . . . . . . . . . . . . . . . . . . 14 11.1. Normative References . . . . . . . . . . . . . . . . . . 14
11.2. Informative References . . . . . . . . . . . . . . . . . 15 11.2. Informative References . . . . . . . . . . . . . . . . . 15
11.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 16
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 . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction 1. Introduction
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. 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
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Two primary uses cases were considered during this protocol's Two primary uses cases were considered during this protocol's
development. They included preventing on-path devices from development. They included preventing on-path devices from
interfering with DNS operations and allowing web applications to interfering with DNS operations and allowing web applications to
access DNS information via existing browser APIs in a safe way access DNS information via existing browser APIs in a safe way
consistent with Cross Origin Resource Sharing (CORS) [CORS]. There consistent with Cross Origin Resource Sharing (CORS) [CORS]. There
are certainly other uses for this work. 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 on one or more URIs is called a
differentiate it from a "DNS server" (one that uses the regular DNS "DNS API server" to differentiate it from a "DNS server" (one that
protocol). Similarly, a client that supports this protocol is called uses the regular DNS protocol). Similarly, a client that supports
a "DNS API client". this protocol is called a "DNS API 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, RFC8174 [RFC8174] when, and only when, they appear in all 14, RFC8174 [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
3. 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
skipping to change at page 4, line 14 skipping to change at page 4, line 14
3.1. 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
4. The HTTP Request 4. The HTTP Exchange
4.1. The HTTP Request
A DNS API client encodes a single DNS query into an HTTP request A DNS API client encodes a single DNS query into an HTTP request
using either the HTTP GET or POST method and the other requirements using either the HTTP GET or POST method and the other requirements
of this section. The DNS API server defines the URI used by the of this section. The DNS API server defines the URI used by the
request through the use of a URI Template [RFC6570]. Configuration request through the use of a URI Template [RFC6570]. Configuration
and discovery of the URI Template is done out of band from this and discovery of the URI Template is done out of band from this
protocol. protocol.
The URI template defined in this document is processed without any The URI Template defined in this document is processed without any
variables for requests using POST, and with the single variable "dns" variables when the HTTP method is POST. When the HTTP method is GET
for requests using GET. The value of the dns parameter is the the single variable "dns" is defined as the content of the DNS
content of the request (as described in Section 4.1), encoded with request (as described in Section 6), encoded with base64url
base64url [RFC4648]. [RFC4648].
Future specifications for new media types MUST define the variables Future specifications for new media types MUST define the variables
used for URI Template processing with this protocol. used for URI Template processing with this protocol.
DNS API servers MUST implement both the POST and GET methods. DNS API 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 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.
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
indicate what type of content can be understood in response. indicate what type of content can be understood in response.
Irrespective of the value of the Accept request header, the client Irrespective of the value of the Accept request header, the client
MUST be prepared to process "application/dns-udpwireformat" MUST be prepared to process "message/dns" (as described in Section 6)
Section 4.1 responses but MAY also process any other type it responses but MAY also process any other type it receives.
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 message/dns, SHOULD use a DNS ID
SHOULD use a DNS ID of 0 in every DNS request. HTTP correlates of 0 in every DNS request. HTTP correlates the request and response,
request and response, thus eliminating the need for the ID in a media thus eliminating the need for the ID in a media type such as message/
type such as application/dns-udpwireformat and the use of a varying dns. The use of a varying DNS ID can cause semantically equivalent
DNS ID can cause semantically equivalent DNS queries to be cached 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.
4.1. DNS Wire Format 4.1.1. HTTP Request Examples
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]. Also note that while [RFC1035] says
"Messages carried by UDP are restricted to 512 bytes", that was later
updated by [RFC6891], and this protocol allows DNS on-the-wire format
payloads of any size.
When using the GET method, the data payload MUST be encoded with
base64url [RFC4648] and then provided as a variable named "dns" to
the URI Template expansion. Padding characters for base64url MUST
NOT be included.
When using the POST method, the data payload MUST NOT be encoded and
is used directly as the HTTP message body.
DNS API clients using the DNS wire format MAY have one or more EDNS
options [RFC6891] in the request.
The media type is "application/dns-udpwireformat".
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 with a URI Template of These examples use a DNS API 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-udpwirefomat typed The requests are represented as message/dns typed bodies.
bodies.
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?dns=AAABAAABAAAAAAAAA3d3dwdleGFtcGxlA2NvbQAAAQAB :path = /dns-query?dns=AAABAAABAAAAAAAAA3d3dwdleGFtcGxlA2NvbQAAAQAB
accept = application/dns-udpwireformat accept = message/dns
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 accept = message/dns
content-type = application/dns-udpwireformat content-type = message/dns
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
emphasize that the encoding alphabet of base64url is different than emphasize that the encoding alphabet of base64url is different than
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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? (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-udpwireformat accept = message/dns
5. The HTTP Response 4.2. The HTTP Response
An HTTP response with a 2xx status code ([RFC7231] Section 6.3) 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. indicates a valid DNS response to the query made in the HTTP request.
A valid DNS response includes both success and failure responses. A valid DNS response includes both success and failure responses.
For example, a DNS failure response such as SERVFAIL or NXDOMAIN will For example, a DNS failure response such as SERVFAIL or NXDOMAIN will
be the message in a successful 2xx HTTP response even though there be the message in a successful 2xx HTTP response even though there
was a failure at the DNS layer. Responses with non-successful HTTP was a failure at the DNS layer. Responses with non-successful HTTP
status codes do not contain DNS answers to the question in the status codes do not contain DNS answers to the question in the
corresponding request. Some of these non-successful HTTP responses corresponding request. Some of these non-successful HTTP responses
(e.g., redirects or authentication failures) could allow clients to (e.g., redirects or authentication failures) could allow clients to
make new requests to satisfy the original question. 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 other "message/dns", but it is possible that other response formats will be
response formats will be defined in the future. defined in the future.
The DNS response for "application/dns-udpwireformat" in Section 4.1
MAY have one or more EDNS options, depending on the extension
definition of the extensions given in the DNS request.
Each DNS request-response pair is matched to one HTTP request-
response pair. The responses may be processed and transported in any
order using HTTP's multi-streaming functionality ([RFC7540]
Section 5}).
The Answer section of a DNS response can contain zero or more RRsets. The DNS response for "message/dns" in Section 6 MAY have one or more
(RRsets are defined in [RFC7719].) According to [RFC2181], each EDNS options, depending on the extension definition of the extensions
resource record in an RRset has Time To Live (TTL) freshness given in the DNS request.
information. Different RRsets in the Answer section can have
different TTLs, although it is only possible for the HTTP response to
have a single freshness lifetime. The HTTP response freshness
lifetime ([RFC7234] Section 4.2) should be coordinated with the RRset
with the smallest TTL in the Answer section of the response.
Specifically, the HTTP freshness lifetime SHOULD be set to expire at
the same time any of the DNS resource records in the Answer section
reach a 0 TTL. The response freshness lifetime MUST NOT be greater
than that indicated by the DNS resoruce record with the smallest TTL
in the response.
If the DNS response has no records in the Answer section, and the DNS Each DNS request-response pair is matched to one HTTP exchange. The
response has an SOA record in the Authority section, the response responses may be processed and transported in any order using HTTP's
freshness lifetime MUST NOT be greater than the MINIMUM field from multi-streaming functionality ([RFC7540] Section 5).
that SOA record. (See [RFC2308].) 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 Section 5.1 discusses the relationship between DNS and HTTP response
freshness lifetime MUST NOT assign that response a heuristic caching.
freshness ([RFC7234] Section 4.2.2.) greater than that indicated by
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 message/dns request
udpwireformat request messages. 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 4.2.1. HTTP Response Example
codes or otherwise proscribe their use.
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 = message/dns
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
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].
6.1. Cache Interaction 5.1. Cache Interaction
A DNS API client may utilize a hierarchy of caches that include both A DNS 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.
The Answer section of a DNS response can contain zero or more RRsets.
(RRsets are defined in [RFC7719].) According to [RFC2181], each
resource record in an RRset has Time To Live (TTL) freshness
information. Different RRsets in the Answer section can have
different TTLs, although it is only possible for the HTTP response to
have a single freshness lifetime. The HTTP response freshness
lifetime ([RFC7234] Section 4.2) should be coordinated with the RRset
with the smallest TTL in the Answer section of the response.
Specifically, the HTTP freshness lifetime SHOULD be set to expire at
the same time any of the DNS resource records in the Answer section
reach a 0 TTL. The response freshness lifetime MUST NOT be greater
than that indicated by the DNS resoruce record with the smallest TTL
in the response.
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. (See [RFC2308].) 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 ([RFC7234] Section 4.2.2.) greater than that indicated by
the DNS Record with the smallest TTL in the response.
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 (e.g., their own DNS cache) to determine the remaining time to live
of the DNS record. of the DNS record.
HTTP revalidation (e.g., via If-None-Match request headers) of cached HTTP revalidation (e.g., via If-None-Match request headers) of cached
DNS information may be of limited value to DOH as revalidation DNS information may be of limited value to DOH as revalidation
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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.
6.2. HTTP/2 5.2. 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.
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 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.
6.4. Content Negotiation 5.4. Content Negotiation
In order to maximize interoperability, DNS API clients and DNS API In order to maximize interoperability, DNS API clients and DNS API
servers MUST support the "application/dns-udpwireformat" media type. servers MUST support the "message/dns" media type. Other media types
Other media types MAY be used as defined by HTTP Content Negotiation MAY be used as defined by HTTP Content Negotiation ([RFC7231]
([RFC7231] Section 3.4). Section 3.4).
6. DNS Wire Format
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]. Also note that while [RFC1035] says
"Messages carried by UDP are restricted to 512 bytes", that was later
updated by [RFC6891], and this protocol allows DNS on-the-wire format
payloads of any size.
When using the GET method, the data payload MUST be encoded with
base64url [RFC4648] and then provided as a variable named "dns" to
the URI Template expansion. Padding characters for base64url MUST
NOT be included.
When using the POST method, the data payload MUST NOT be encoded and
is used directly as the HTTP message body.
DNS API clients using the DNS wire format MAY have one or more EDNS
options [RFC6891] in the request.
The media type is "message/dns".
7. IANA Considerations 7. IANA Considerations
7.1. Registration of application/dns-udpwireformat Media Type 7.1. Registration of message/dns 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 message/dns
MIME media type name: application MIME media type name: message
MIME subtype name: dns-udpwireformat MIME subtype name: dns
Required parameters: n/a Required parameters: n/a
Optional parameters: original_transport Optional parameters: n/a
The "original_transport" parameter has two defined values,
"udp" and "tcp". This parameter is only expected to be used by
servers.
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: The security considerations for carrying
this data are the same for carrying DNS without encryption. this data are the same for carrying DNS without encryption.
Interoperability considerations: None. Interoperability considerations: None.
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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. This capability might be affected by the response media resolver. This capability might be affected by the response media
type. 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.
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
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transport for other protocols that require strict ordering. transport for other protocols that require strict ordering.
If a DNS API server responds to a DNS API client with a DNS message If a DNS API server responds to a DNS API client with a DNS message
that has the TC (truncation) bit set in the header, that indicates that has the TC (truncation) bit set in the header, that indicates
that the DNS API server was not able to retrieve a full answer for that the DNS API server was not able to retrieve a full answer for
the query and is providing the best answer it could get. This the query and is providing the best answer it could get. This
protocol does not require that a DNS API server that cannot get an protocol does not require that a DNS API server that cannot get an
untruncated answer send back such an answer; it can instead send back untruncated answer send back such an answer; it can instead send back
an HTTP error to indicate that it cannot give a useful answer. an HTTP error to indicate that it cannot give a useful answer.
This protocol does not define any use for the "original_transport"
optional parameter of the application/dns-udpwireformat media type.
10. Acknowledgments 10. Acknowledgments
This work required a high level of cooperation between experts in This work required a high level of cooperation between experts in
different technologies. Thank you Ray Bellis, Stephane Bortzmeyer, different technologies. Thank you Ray Bellis, Stephane Bortzmeyer,
Manu Bretelle, Tony Finch, Daniel Kahn Gilmor, Olafur Guomundsson, Manu Bretelle, Tony Finch, Daniel Kahn Gilmor, Olafur Guomundsson,
Wes Hardaker, Rory Hewitt, Joe Hildebrand, David Lawrence, Eliot Wes Hardaker, Rory Hewitt, Joe Hildebrand, David Lawrence, Eliot
Lear, John Mattson, Alex Mayrhofer, Mark Nottingham, Jim Reid, Adam Lear, John Mattson, Alex Mayrhofer, Mark Nottingham, Jim Reid, Adam
Roach, Ben Schwartz, Davey Song, Daniel Stenberg, Andrew Sullivan, Roach, Ben Schwartz, Davey Song, Daniel Stenberg, Andrew Sullivan,
Martin Thomson, and Sam Weiler. Martin Thomson, and Sam Weiler.
skipping to change at page 16, line 41 skipping to change at page 16, line 36
[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>.
[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>.
11.3. URIs
[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.
o https://tools.ietf.org/html/draft-mohan-dns-query-xml o https://tools.ietf.org/html/draft-mohan-dns-query-xml
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