draft-ietf-doh-dns-over-https-02.txt   draft-ietf-doh-dns-over-https-03.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: June 1, 2018 Mozilla Expires: August 6, 2018 Mozilla
November 28, 2017 February 02, 2018
DNS Queries over HTTPS DNS Queries over HTTPS
draft-ietf-doh-dns-over-https-02 draft-ietf-doh-dns-over-https-03
Abstract Abstract
DNS queries sometimes experience problems with end to end DNS queries sometimes experience problems with end to end
connectivity at times and places where HTTPS flows freely. connectivity at times and places where HTTPS flows freely.
HTTPS provides the most practical mechanism for reliable end to end HTTPS provides the most practical mechanism for reliable end to end
communication. Its use of TLS provides integrity and confidentiality communication. Its use of TLS provides integrity and confidentiality
guarantees and its use of HTTP allows it to interoperate with guarantees and its use of HTTP allows it to interoperate with
proxies, firewalls, and authentication systems where required for proxies, firewalls, and authentication systems where required for
transit. 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 ]]. 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 http://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 June 1, 2018. This Internet-Draft will expire on August 6, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Protocol Requirements . . . . . . . . . . . . . . . . . . . . 4 4. Protocol Requirements . . . . . . . . . . . . . . . . . . . . 4
4.1. Non-requirements . . . . . . . . . . . . . . . . . . . . 5 4.1. Non-requirements . . . . . . . . . . . . . . . . . . . . 5
5. The HTTP Request . . . . . . . . . . . . . . . . . . . . . . 5 5. The HTTP Request . . . . . . . . . . . . . . . . . . . . . . 5
5.1. DNS Wire Format . . . . . . . . . . . . . . . . . . . . . 6 5.1. DNS Wire Format . . . . . . . . . . . . . . . . . . . . . 6
5.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . 6 5.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . 6
6. The HTTP Response . . . . . . . . . . . . . . . . . . . . . . 7 6. The HTTP Response . . . . . . . . . . . . . . . . . . . . . . 7
6.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 8 6.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 8
7. HTTP Integration . . . . . . . . . . . . . . . . . . . . . . 8 7. HTTP Integration . . . . . . . . . . . . . . . . . . . . . . 9
7.1. HTTP/2 . . . . . . . . . . . . . . . . . . . . . . . . . 9 7.1. Cache Interaction . . . . . . . . . . . . . . . . . . . . 9
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 7.2. HTTP/2 . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1. Registration of Well-Known URI . . . . . . . . . . . . . 9 7.3. Server Push . . . . . . . . . . . . . . . . . . . . . . . 10
8.2. Registration of application/dns-udpwireformat Media Type 9 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
9. Security Considerations . . . . . . . . . . . . . . . . . . . 11 8.1. Registration of application/dns-udpwireformat Media Type 10
10. Operational Considerations . . . . . . . . . . . . . . . . . 12 9. Security Considerations . . . . . . . . . . . . . . . . . . . 12
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12 10. Operational Considerations . . . . . . . . . . . . . . . . . 13
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
12.1. Normative References . . . . . . . . . . . . . . . . . . 12 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
12.2. Informative References . . . . . . . . . . . . . . . . . 13 12.1. Normative References . . . . . . . . . . . . . . . . . . 13
Appendix A. Previous Work on DNS over HTTP or in Other Formats . 14 12.2. Informative References . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15 12.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Appendix A. Previous Work on DNS over HTTP or in Other Formats . 15
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.
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
skipping to change at page 4, line 14 skipping to change at page 4, line 18
the DOH server for all queries, or only for a subset of them. The the DOH server for all queries, or only for a subset of them. The
specific configuration mechanism is out of scope for this document. specific configuration mechanism is out of scope for this document.
A secondary use case is allowing web applications to access DNS A secondary use case is allowing web applications to access DNS
information, by using existing APIs in browsers to access it over information, by using existing APIs in browsers to access it over
HTTP in a safe way consistent with Cross Origin Resource Sharing HTTP in a safe way consistent with Cross Origin Resource Sharing
(CORS) [CORS]. (CORS) [CORS].
This is technically already possible (since the server controls both This is technically already possible (since the server controls both
the HTTP resources it exposes and the use of browser APIs by its the HTTP resources it exposes and the use of browser APIs by its
content), but standardisation might make this easier to accomplish. content), but standardization might make this easier to accomplish.
Note that in this second use, the browser does not consult the DOH 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 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 the application using them; i.e., there is (currently) no API that
allows a Web site to poison DNS for others. allows a Web site to poison DNS for others.
[[ This paragraph is to be removed when this document is published as [[ 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 an RFC ]] Note that these use cases are different than those in a
similar protocol described at [I-D.ietf-dnsop-dns-wireformat-http]. similar protocol described at [I-D.ietf-dnsop-dns-wireformat-http].
The use case for that protocol is proxying DNS queries over HTTP The use case for that protocol is proxying DNS queries over HTTP
skipping to change at page 4, line 43 skipping to change at page 4, line 47
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
negotiation mechanism. negotiation mechanism.
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 one or more EDNS extensions, including those not yet contain future modifications to the DNS protocol including the
defined. inclusion of one or more EDNS extensions (including those not yet
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 modern HTTPS. requirements for HTTPS.
4.1. Non-requirements 4.1. 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 5. The HTTP Request
To make a DNS API query, a DNS API client sends an HTTP request to To make a DNS API query a DNS API client encodes a single DNS query
the URI of the DNS API. 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
The URI scheme MUST be https. URI used by the request. Configuration and discovery of the URI is
done out of band from this protocol.
A client can be configured with a DNS API URI, or it can discover the
URI. This document defines a well-known URI path of "/.well-known/
dns-query" so that a discovery process that produces a domain name or
domain name and port can be used to construct the DNS API URI. (See
Section 8 for the registration of this in the well-known URI
registry.) DNS API servers SHOULD use this well-known path to help
contextualize DNS Query requests that use server push [RFC7540].
A DNS API Client encodes a single DNS query into the HTTP request
using either the HTTP GET or POST 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.
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 for with the name of "ct" and a value indicating the media-format used
the body parameter. The value may either be an explicit media type for the dns parameter. The value may either be an explicit media
(e.g. ct=application/dns-udpwireformat&body=...) or it may be empty. type (e.g. ct=application/dns-udpwireformat&dns=...) or it may be
An empty value indicates the default application/dns-udpwireformat empty. An empty value indicates the default application/dns-
type (e.g. ct&body=...). 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 body. 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 encoded with base64url [RFC4648]. Using the GET method the request potentially encoded with base64url [RFC4648].
is friendlier to many HTTP cache implementations. 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
parameter uses base64url encoding.
Using the GET method is friendlier to many HTTP cache
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 5.1 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 5.1. DNS Wire Format
The media type is "application/dns-udpwireformat". The body is the The media type is "application/dns-udpwireformat".
DNS on-the-wire format is defined in [RFC1035].
The body is the DNS on-the-wire format defined in [RFC1035].
When using the GET method, the body MUST be encoded with base64url When using the GET method, the body MUST be encoded with base64url
[RFC4648]. Padding characters for base64url MUST NOT be included. [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 POST method, the body is not encoded. When using the POST method, the body MUST NOT be encoded.
DNS API clients using the DNS wire format MAY have one or more DNS API clients using the DNS wire format MAY have one or more
EDNS(0) extensions [RFC6891] in the request. EDNS(0) extensions [RFC6891] in the request.
5.2. Examples 5.2. Examples
These examples use HTTP/2 style formatting from [RFC7540]. These examples use HTTP/2 style formatting from [RFC7540].
For this example assume a DNS API server is following this These examples use a DNS API service located at
specification on origin https://dnsserver.example.net/ and the well- https://dnsserver.example.net/dns-query to resolve the IN A records.
known path. The DNS API client chooses to send its requests in
application/dns-udpwirefomat but indicates it can parse replies in The requests are represented as application/dns-udpwirefomat typed
bodies, but the client indicates it can parse responses in either
that format or as a hypothetical JSON-based content type. The that format or as a hypothetical JSON-based content type. The
application/simpledns+json type used by this example is currently application/simpledns+json type used by this example is currently
fictitious. fictitious.
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 = /.well-known/dns-query?ct& (no CR) :path = /dns-query?ct& (no space or CR)
body=q80BAAABAAAAAAAAA3d3dwdleGFtcGxlA2NvbQAAAQAB dns=AAABAAABAAAAAAAAA3d3dwdleGFtcGxlA2NvbQAAAQAB
accept = application/dns-udpwireformat, application/simpledns+json accept = application/dns-udpwireformat, application/simpledns+json
The same DNS query for www.example.com, using the POST method would
The same DNS query, using the POST method would be: be:
:method = POST :method = POST
:scheme = https :scheme = https
:authority = dnsserver.example.net :authority = dnsserver.example.net
:path = /.well-known/dns-query :path = /dns-query
accept = application/dns-udpwireformat, application/simpledns+json accept = application/dns-udpwireformat, application/simpledns+json
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>
abcd 0100 0001 0000 0000 0000 0377 7777 00 00 01 00 00 01 00 00 00 00 00 00 03 77 77 77
0765 7861 6d70 6c65 0363 6f6d 0000 0100 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-
distinct-from-standard-base64.example.com is shown as an example to
emphasize that the encoding alphabet of base64url is different than
regular base64 and that padding is omitted.
The DNS query is 94 bytes represented by the following hex encoding
00 00 01 00 00 01 00 00 00 00 00 00 01 61 3e 36
32 63 68 61 72 61 63 74 65 72 6c 61 62 65 6c 2d
6d 61 6b 65 73 2d 62 61 73 65 36 34 75 72 6c 2d
64 69 73 74 69 6e 63 74 2d 66 72 6f 6d 2d 73 74
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
:method = GET
:scheme = https
:authority = dnsserver.example.net
:path = /dns-query?ct& (no space or CR)
dns=AAABAAABAAAAAAAAAWE-NjJjaGFyYWN0ZXJsYWJl (no space or CR)
bC1tYWtlcy1iYXNlNjR1cmwtZGlzdGluY3QtZnJvbS1z (no space or CR)
dGFuZGFyZC1iYXNlNjQHZXhhbXBsZQNjb20AAAEAAQ
accept = application/dns-udpwireformat, application/simpledns+json
6. The HTTP Response 6. The HTTP Response
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 known response type is "application/dns- progress. The only response type defined in this document is
udpwireformat", but it is possible that at least one JSON-based "application/dns-udpwireformat", but it is possible that at least one
response format will be defined in the future. JSON-based response format 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 5.1
MAY have one or more EDNS(0) extensions, depending on the extension MAY have one or more EDNS(0) extensions, depending on the extension
definition of the extensions given in the DNS request. definition of the extensions given in the DNS request.
Native HTTP methods are used to correlate requests and responses. Each DNS request-response pair is matched to one HTTP request-
Responses may be returned in a different temporal order than requests response pair. The responses may be processed and transported in any
were made using the protocols native multi-streaming functionality. order using HTTP's multi-streaming functionality ([RFC7540]
Section 5}).
The Answer section of a DNS response contains one or more RRsets. The Answer section of a DNS response contains one 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 is supposed to have the Time To Live
(TTL) freshness information. Different RRsets in the Answer section (TTL) freshness information. Different RRsets in the Answer section
can have different TTLs, though it is only possible for the HTTP can have different TTLs, though it is only possible for the HTTP
response to have a single freshness lifetime. The HTTP response response to have a single freshness lifetime. The HTTP response
freshness lifetime ([RFC7234] Section 4.2) should be coordinated with freshness lifetime ([RFC7234] Section 4.2) should be coordinated with
the Resource Record bearing the smallest TTL in the Answer section of the Resource Record bearing the smallest TTL in the Answer section of
the response. The HTTP freshness lifetime SHOULD be set to expire at the response. Specifically, the HTTP freshness lifetime SHOULD be
the same time any of the DNS Records reach a 0 TTL. The response set to expire at the same time any of the DNS Records reach a 0 TTL.
freshness lifetime MUST NOT be greater than that indicated by the DNS The response freshness lifetime MUST NOT be greater than that
Record with the smallest TTL in the response. indicated by the DNS Record with the smallest TTL in the response.
A DNS API Client that receives a response without an explicit 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 upon A DNS API Server SHOULD respond with HTTP status code 415
receiving a media type it is unable to process. (Unsupported Media Type) upon receiving a media type it is unable to
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.
HTTP revalidation of cached DNS information may be of limited value
as revalidation provides only a bandwidth benefit and DNS
transactions are normally latency bound instead. Furthermore, the
HTTP response headers that enable revalidation (such as "Last-
Modified" and "Etag") are often fairly large when compared to the
overall DNS response size, and have a variable nature that creates
constant pressure on the HTTP/2 compression dictionary [RFC7541].
Other types of DNS data, such as zone transfers, may be larger and
benefit more from revalidation. DNS API servers may wish to consider
whether providing these optional response headers is worthwhile.
6.1. Example 6.1. 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 93.184.216.34 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>
abcd 8180 0001 0001 0000 0000 0377 7777 00 00 81 80 00 01 00 01 00 00 00 00 03 77 77 77
0765 7861 6d70 6c65 0363 6f6d 0000 0100 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
0103 7777 7707 6578 616d 706c 6503 636f 6d 00 00 01 00 01 00 00 00 80 00 04 C0 00 02 01
6d00 0001 0001 0000 0080 0004 5db8 d822
7. HTTP Integration 7. HTTP Integration
This protocol MUST be used with https scheme URI [RFC7230]. This protocol MUST be used with the https scheme URI [RFC7230].
7.1. HTTP/2 7.1. Cache Interaction
A DOH API Client may utilize a hierarchy of caches that include both
HTTP and DNS specific caches. HTTP cache entries may be bypassed
with HTTP mechanisms such as the Cache-Control no-cache directive
however DNS caches do not have a similar mechanism.
A DOH response that was previously stored in an HTTP cache will
contain the [RFC7234] Age response header indicating the elapsed time
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
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
the DNS record.
HTTP revalidation (e.g. via If-None-Match request headers) of cached
DNS information may be of limited value to DOH as revalidation
provides only a bandwidth benefit and DNS transactions are normally
latency bound. Furthermore, the HTTP response headers that enable
revalidation (such as "Last-Modified" and "Etag") are often fairly
large when compared to the overall DNS response size, and have a
variable nature that creates constant pressure on the HTTP/2
compression dictionary [RFC7541]. Other types of DNS data, such as
zone transfers, may be larger and benefit more from revalidation.
DNS API servers may wish to consider whether providing these
validation enabling response headers is worthwhile.
The stale-while-revalidate and stale-if-error cache control
directives may be well suited to a DOH implementation when allowed by
server policy. Those mechanisms allow a client, at the server's
discretion, to reuse a cache entry that is no longer fresh under some
extenuating circumstances defined in [RFC5861].
All HTTP servers, including DNS API servers, need to consider cache
interaction when they generate responses that are not globally valid.
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
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
Vary response header.
7.2. 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 acheive 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 would 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.
8. IANA Considerations 7.3. Server Push
8.1. Registration of Well-Known URI
This specification registers a Well-Known URI [RFC5785]:
o URI Suffix: dns-query
o Change Controller: IETF Before using DOH response data for DNS resolution, the client MUST
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
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
is one that the client would have directed the same query to if the
client had initiated the request. This specification does not extend
DNS resolution privileges to URIs that are not recognized by the
client as trusted DNS API servers.
o Specification Document(s): [this specification] 8. IANA Considerations
8.2. Registration of application/dns-udpwireformat Media Type 8.1. 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 11, line 22 skipping to change at page 12, line 22
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. Sections 10.6 (Compression) and 10.7 (Padding) of
[RFC7540] provide some further advice on mitigations within an HTTP/2 [RFC7540] provide some further advice on mitigations within an HTTP/2
context. context.
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 recurvise DNS DNS client might choose to trust answers from its recursive DNS
resolver. resolver.
[[ From the WG charter: [[ From the WG charter:
The working group will analyze the security and privacy issues that The working group will analyze the security and privacy issues that
could arise from accessing DNS over HTTPS. In particular, the could arise from accessing DNS over HTTPS. In particular, the
working group will consider the interaction of DNS and HTTP caching. working group will consider the interaction of DNS and HTTP caching.
]] ]]
skipping to change at page 12, line 29 skipping to change at page 13, line 29
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
HTTP request needs to resolve the hostname portion of the DNS URI.
Just as the address of a traditional DNS nameserver cannot be
originally determined from that same server, a DOH client cannot use
its DOH server to initially resolve the server's host name into an
address. Alternative strategies a client might employ include making
the initial resolution part of the configuration, IP based URIs and
corresponding IP based certificates for HTTPS, or resolving the DNS
API Server's hostname via traditional DNS or another DOH server while
still authenticating the resulting connection via HTTPS.
11. Acknowledgments 11. 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 12. References
12.1. Normative References 12.1. Normative References
[RFC1035] Mockapetris, P., "Domain names - implementation and [RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>. November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, <https://www.rfc- DOI 10.17487/RFC2119, March 1997,
editor.org/info/rfc2119>. <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, <https://www.rfc- DOI 10.17487/RFC5246, August 2008,
editor.org/info/rfc5246>. <https://www.rfc-editor.org/info/rfc5246>.
[RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
Uniform Resource Identifiers (URIs)", RFC 5785,
DOI 10.17487/RFC5785, April 2010, <https://www.rfc-
editor.org/info/rfc5785>.
[RFC6960] Santesson, S., Myers, M., Ankney, R., Malpani, A., [RFC6960] Santesson, S., Myers, M., Ankney, R., Malpani, A.,
Galperin, S., and C. Adams, "X.509 Internet Public Key Galperin, S., and C. Adams, "X.509 Internet Public Key
Infrastructure Online Certificate Status Protocol - OCSP", Infrastructure Online Certificate Status Protocol - OCSP",
RFC 6960, DOI 10.17487/RFC6960, June 2013, RFC 6960, DOI 10.17487/RFC6960, June 2013,
<https://www.rfc-editor.org/info/rfc6960>. <https://www.rfc-editor.org/info/rfc6960>.
[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, <https://www.rfc- DOI 10.17487/RFC6961, June 2013,
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>.
[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, <https://www.rfc- DOI 10.17487/RFC7540, May 2015,
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 12.2. 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] [I-D.ietf-dnsop-dns-wireformat-http]
Song, L., Vixie, P., Kerr, S., and R. Wan, "DNS wire- Song, L., Vixie, P., Kerr, S., and R. Wan, "DNS wire-
format over HTTP", draft-ietf-dnsop-dns-wireformat-http-01 format over HTTP", draft-ietf-dnsop-dns-wireformat-http-01
(work in progress), March 2017. (work in progress), March 2017.
[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
Content", RFC 5861, DOI 10.17487/RFC5861, May 2010,
<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
Beijnum, "DNS64: DNS Extensions for Network Address Beijnum, "DNS64: DNS Extensions for Network Address
Translation from IPv6 Clients to IPv4 Servers", RFC 6147, Translation from IPv6 Clients to IPv4 Servers", RFC 6147,
DOI 10.17487/RFC6147, April 2011, <https://www.rfc- DOI 10.17487/RFC6147, April 2011,
editor.org/info/rfc6147>. <https://www.rfc-editor.org/info/rfc6147>.
[RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms [RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
for DNS (EDNS(0))", STD 75, RFC 6891, for DNS (EDNS(0))", STD 75, RFC 6891,
DOI 10.17487/RFC6891, April 2013, <https://www.rfc- DOI 10.17487/RFC6891, April 2013,
editor.org/info/rfc6891>. <https://www.rfc-editor.org/info/rfc6891>.
[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
[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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