Network Working Group P. Hoffman
Internet-Draft ICANN
Intended status: Standards Track P. McManus
Expires: December 8, 2017 Mozilla
June 06, 2017
DNS Queries over HTTPS
draft-hoffman-dns-over-https-01
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
https:// URIs.
[ This paragraph is to be removed when this document is published as
an RFC ] Comments on this draft can be sent to the DNS over HTTP
mailing list at https://www.ietf.org/mailman/listinfo/dnsoverhttp .
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 8, 2017.
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Protocol Requirements . . . . . . . . . . . . . . . . . . . . 4
4.1. Non-requirements . . . . . . . . . . . . . . . . . . . . 4
5. The HTTP Request . . . . . . . . . . . . . . . . . . . . . . 4
5.1. DNS Wire Format . . . . . . . . . . . . . . . . . . . . . 5
5.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . 6
6. The HTTP Response . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 7
7. HTTP Integration . . . . . . . . . . . . . . . . . . . . . . 7
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8.1. Registration of Well-Known URI . . . . . . . . . . . . . 8
8.2. Registration of application/dns-udpwireformat Media Type 8
9. Security Considerations . . . . . . . . . . . . . . . . . . . 10
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
11.1. Normative References . . . . . . . . . . . . . . . . . . 10
11.2. Informative References . . . . . . . . . . . . . . . . . 11
Appendix A. Previous Work on DNS over HTTP or in Other Formats . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
The Internet does not always provide end to end reachability for
native DNS. On-path network devices may spoof DNS responses, block
DNS requests, or just redirect DNS queries to different DNS servers
that give less-than-honest answers.
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
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proposals have made it beyond early discussion, partially due to
disagreement about what the appropriate formatting should be and
partially because they did not follow HTTP best practices.
This document defines a specific protocol for sending DNS [RFC1035]
queries and getting DNS responses over modern versions of HTTP
[RFC7540] using https:// (and therefore TLS [RFC5246] security for
integrity and confidentiality).
The described approach is more than a tunnel over HTTP. It
establishes default media formatting types for requests and responses
but uses normal HTTP content negotiation mechanisms for selecting
alternatives that endpoints may prefer in anticipation of serving new
use cases. In addition to this media type negotiation, it aligns
itself with HTTP features such as caching, proxying, and compression.
The integration with HTTP provides a transport suitable for both
traditional DNS clients and native web applications seeking access to
the DNS.
2. Terminology
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
protocol). Similarly, a client that supports this protocol is called
a "DNS API client".
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in BCP 14, RFC 2119
[RFC2119].
3. Use Cases
There are two primary use cases for this protocol.
The primary one is to prevent on-path network devices from
interfering with native DNS operations. This interference includes,
but is not limited to, spoofing DNS responses, blocking DNS requests,
and tracking. HTTP authentication and proxy friendliness are
expected to make this protocol function in some environments where
DNS directly on TLS ([RFC7858]) would not.
A secondary use case is web applications that want to access DNS
information. Standardizing an HTTPS mechanism allows this to be done
in a way consistent with the cross-origin resource sharing [CORS]
security model of the web and also integrate the caching mechanisms
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of DNS with those of HTTP. These applications may be interested in
using a different media type than traditional clients.
[ 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
The protocol described here bases its design on the following
protocol requirements:
o The protocol must use normal HTTP semantics.
o The queries and responses must be able to be flexible enough to
express every normal DNS query.
o The protocol must allow implementations to use HTTP's content
negotiation mechanism.
o The protocol must ensure interoperable media formats through a
mandatory to implement format wherein a query must be able to
contain one or more EDNS extensions, including those not yet
defined.
o The protocol must use a secure transport that meets the
requirements for modern https://.
4.1. Non-requirements
o Supporting network-specific DNS64 [RFC6147]
o Supporting other network-specific inferences from plaintext DNS
queries
o Supporting insecure HTTP
o Supporting legacy HTTP versions
5. The HTTP Request
The URI scheme MUST be https.
The path SHOULD be "/.well-known/dns-query" but a different path can
be used if the DNS API Client has prior knowledge about a DNS API
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service on a different path at the origin being used. (See Section 8
for the registration of this in the well-known URI registry.) Using
the well-known path allows automated discovery of a DNS API Service,
and also helps contextualize DNS Query requests pushed over an active
HTTP/2 connection.
A DNS API Client encodes the 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
body of the HTTP request and the Content-Type request header
indicates the media type of the message. POST-ed requests are
smaller than their GET equivalents.
When using the GET method, the URI path MUST contain a query
parameter of the form content-type=TTT and another of the form
body=BBBB, where "TTT" is the media type of the format used for the
body parameter, and "BBB" is the content of the body encoded with
base64url [RFC4648]. Using the GET method is friendlier to many HTTP
cache implementations.
The DNS API Client SHOULD include an HTTP "Accept:" request header to
say what type of content can be understood in response. The client
MUST be prepared to process "application/dns-udpwireformat"
{{dnswire} responses but MAY process any other type it receives.
In order to maximize cache friendliness, DNS API clients using media
formats that include DNS ID, such as application/dns-udpwireformat,
should use a DNS ID of 0 in every DNS request. HTTP semantics
correlate the request and response, thus eliminating the need for the
ID in a media type such as application/dns-udpwireformat.
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.
5.1. DNS Wire Format
The media type is "application/dns-udpwireformat". The body is the
DNS on-the-wire format is defined in [