DNS Queries over CoAP (DoC)
draft-lenders-dns-over-coap-02
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
|
|
|---|---|---|---|
| Authors | Martine Sophie Lenders , Christian Amsüss , Cenk Gündoğan , Thomas C. Schmidt , Matthias Wählisch | ||
| Last updated | 2021-10-25 | ||
| Replaces | draft-lenders-dns-over-coaps | ||
| Replaced by | draft-ietf-core-dns-over-coap | ||
| RFC stream | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-lenders-dns-over-coap-02
CoRE M.S. Lenders
Internet-Draft FU Berlin
Intended status: Standards Track C. Amsüss
Expires: 28 April 2022
C. Gündoğan
T.C. Schmidt
HAW Hamburg
M. Wählisch
FU Berlin
25 October 2021
DNS Queries over CoAP (DoC)
draft-lenders-dns-over-coap-02
Abstract
This document defines a protocol for sending DNS messages over the
Constrained Application Protocol (CoAP). These CoAP messages are
protected by DTLS-Secured CoAP (CoAPS) or Object Security for
Constrained RESTful Environments (OSCORE) to provide encrypted DNS
message exchange for constrained devices in the Internet of Things
(IoT).
Discussion Venues
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on TODO
Source for this draft and an issue tracker can be found at
https://github.com/anr-bmbf-pivot/draft-dns-over-coap.
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 https://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."
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This Internet-Draft will expire on 28 April 2022.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
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provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Selection of a DoC Server . . . . . . . . . . . . . . . . . . 4
3.1. URI Alternatives . . . . . . . . . . . . . . . . . . . . 4
4. Basic Message Exchange . . . . . . . . . . . . . . . . . . . 4
4.1. The "application/dns-message" Content-Format . . . . . . 4
4.2. DNS Queries in CoAP Requests . . . . . . . . . . . . . . 5
4.2.1. Request Format . . . . . . . . . . . . . . . . . . . 5
4.2.2. Support of CoAP Caching . . . . . . . . . . . . . . . 5
4.2.3. Examples . . . . . . . . . . . . . . . . . . . . . . 5
4.3. DNS Responses in CoAP Responses . . . . . . . . . . . . . 6
4.3.1. Response Codes and Handling DNS and CoAP errors . . . 6
4.3.2. Support of CoAP Caching . . . . . . . . . . . . . . . 6
4.3.3. Examples . . . . . . . . . . . . . . . . . . . . . . 7
5. CoAP/CoRE Integration . . . . . . . . . . . . . . . . . . . . 7
5.1. Proxies and caching . . . . . . . . . . . . . . . . . . . 7
5.2. OBSERVE (modifications)? . . . . . . . . . . . . . . . . 8
5.3. OSCORE . . . . . . . . . . . . . . . . . . . . . . . . . 8
6. URI configuration . . . . . . . . . . . . . . . . . . . . . . 9
7. Considerations for Unencrypted Use . . . . . . . . . . . . . 9
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
10.1. Normative References . . . . . . . . . . . . . . . . . . 10
10.2. Informative References . . . . . . . . . . . . . . . . . 10
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 12
A.1. Since draft-lenders-dns-over-coap-01 . . . . . . . . . . 12
A.2. Since draft-lenders-dns-over-coap-00 . . . . . . . . . . 12
A.3. Since draft-lenders-dns-over-coaps-00 . . . . . . . . . . 12
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 13
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
This document defines DNS over CoAP (DoC), a protocol to send DNS
[RFC1035] queries and get DNS responses over the Constrained
Application Protocol (CoAP) [RFC7252]. Each DNS query-response pair
is mapped into a CoAP message exchange. Each CoAP message is secured
by DTLS [RFC6347] or Object Security for Constrained RESTful
Environments (OSCORE) [RFC8613] to ensure message integrity and
confidentiality.
The application use case of DoC is inspired by DNS over HTTPS
[RFC8484] (DoH). DoC, however, aims for the deployment in the
constrained Internet of Things (IoT), which usually conflicts with
the requirements introduced by HTTPS.
To prevent TCP and HTTPS resource requirements, constrained IoT
devices could use DNS over DTLS [RFC8094]. In contrast to DNS over
DTLS, DoC utilizes CoAP features to mitigate drawbacks of datagram-
based communication. These features include: block-wise transfer,
which solves the Path MTU problem of DNS over DTLS (see [RFC8094],
section 5); CoAP proxies, which provide an additional level of
caching; re-use of data structures for application traffic and DNS
information, which saves memory on constrained devices.
To prevent resource requirements of DTLS or TLS on top of UDP (e.g.,
introduced by DNS over QUIC [I-D.ietf-dprive-dnsoquic]), DoC allows
for lightweight end-to-end payload encryption based on OSCORE.
- FETCH coaps://[2001:db8::1]/
/
/
CoAP request
+--------+ [DNS query] +--------+ DNS query +--------+
| DoC |---------------->| DoC |...............>| DNS |
| Client |<----------------| Server |<...............| Server |
+--------+ CoAP response +--------+ DNS response +--------+
[DNS response]
Figure 1: Basic DoC architecture
The most important components of DoC can be seen in Figure 1: A DoC
client tries to resolve DNS information by sending DNS queries
carried within CoAP requests to a DoC server. That DoC server may or
may not resolve that DNS information itself by using other DNS
transports with an upstream DNS server. The DoC server then replies
to the DNS queries with DNS responses carried within CoAP responses.
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TBD: additional feature sets of CoAP/CoRE
* resource directory for DoC service discovery,
* ...
2. Terminology
A server that provides the service specified in this document is
called a "DoC server" to differentiate it from a classic "DNS
server". Correspondingly, a client using this protocol to retrieve
the DNS information is called a "DoC client".
The term "constrained nodes" is used as defined in [RFC7228].
The terms "CoAP payload" and "CoAP body" are used as defined in
[RFC7959].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Selection of a DoC Server
TBD:
* URI or should we rather go straight to CRI?
* Support for more than one URI by DoC server.
* DoC server identity, key exchange, ...
3.1. URI Alternatives
TBD:
* CRI [I-D.ietf-core-href] or CoRAL [I-D.ietf-core-coral]
4. Basic Message Exchange
4.1. The "application/dns-message" Content-Format
This document defines the Internet media type "application/dns-
message" for the CoAP Content-Format. This media type is defined as
in [RFC8484] Section 6, i.e., a single DNS message encoded in the DNS
on-the-wire format [RFC1035].
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4.2. DNS Queries in CoAP Requests
A DoC client encodes a single DNS query in one or more CoAP request
messages the CoAP FETCH [RFC8132] method. Requests SHOULD include an
Accept option to indicate the type of content that can be parsed in
the response.
To enable reliable message exchange, the CoAP request SHOULD be
carried in a Confirmable (CON) message.
4.2.1. Request Format
When sending a CoAP request, a DoC client MUST include the DNS query
in the body (i.e. the payload, or the concatenated payloads) of the
CoAP request. As specified in [RFC8132] Section 2.3.1, the type of
content of the body MUST be indicated using the Content-Format
option. This document specifies the usage of Content-Format
"application/dns-message" (details see Section 4.1).
If block-wise transfer [RFC7959] is supported by the client, more
than one CoAP request message MAY be used. If more than one CoAP
request message is used to encode the DNS query, it must be chained
together using the Block1 option in those CoAP requests.
The FETCH request is sent to the URI specified in Section 3.
A DoC server MUST be able to parse requests of Content-Format
"application/dns-message".
4.2.2. Support of CoAP Caching
The DoC client SHOULD set the ID field of the DNS header always to 0
to enable a CoAP cache (e.g., a CoAP proxy en-route) to respond to
the same DNS queries with a cache entry. This ensures that the CoAP
Cache-Key (see [RFC8132] Section 2) does not change when multiple DNS
queries for the same DNS data, carried in CoAP requests, are issued.
4.2.3. Examples
The following example illustrates the usage of a CoAP message to
resolve "example.org. IN AAAA" based on the URI
"coaps://[2001:db8::1]/". The CoAP body is encoded in "application/
dns-message" Content Format.
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FETCH coaps://[2001:db8::1]/
Content-Format: application/dns-message
Accept: application/dns-message
Payload: 00 00 01 20 00 02 00 00 00 00 00 00 07 65 78 61 [binary]
6d 70 6c 65 03 6f 72 67 00 00 1c 00 01 c0 0c 00 [binary]
01 00 01 [binary]
4.3. DNS Responses in CoAP Responses
Each DNS query-response pair is mapped to a CoAP REST request-
response operation, which may consist of several CoAP request-
response pairs if block-wise transfer is involved. DNS responses are
provided in the body (i.e. the payload, or the concatenated payloads)
of the CoAP response. A DoC server MUST indicate the type of content
of the body using the Content-Format option, and MUST be able to
produce responses in the "application/dns-message" Content-Format
(details see Section 4.1) when requested. A DoC client MUST
understand responses in "application/dns-message" format when it does
not send an Accept option.
If supported, a DoC server MAY transfer the DNS response in more than
one CoAP responses using the Block2 option [RFC7959].
4.3.1. Response Codes and Handling DNS and CoAP errors
A DNS response indicates either success or failure in the Response
code of the DNS header (see [RFC1035] Section 4.1.1). It is
RECOMMENDED that CoAP responses that carry any valid DNS response use
a "2.05 Content" response code.
CoAP responses use non-successful response codes MUST NOT contain any
payload and may only be used on errors in the CoAP layer or when a
request does not fulfill the requirements of the DoC protocol.
Communication errors with a DNS server (e.g., timeouts) SHOULD be
indicated by including a SERVFAIL DNS response in a successful CoAP
response.
A DoC client might try to repeat a non-successful exchange unless
otherwise prohibited. The DoC client might also decide to repeat a
non-successful exchange with a different URI, for instance, when the
response indicates an unsupported Content-Format.
4.3.2. Support of CoAP Caching
It is RECOMMENDED to set the Max-Age option of a response to the
minimum TTL in the Answer section of a DNS response. This prevents
expired records unintentionally being served from a CoAP cache.
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It is RECOMMENDED that DoC servers set an ETag option on large
responses (TBD: more concrete guidance) that have a short Max-Age
relative to the expected clients' caching time. Thus, clients that
need to revalidate a response can do so using the established ETag
mechanism. With responses large enough to be fragmented, it's best
practice for servers to set an ETag anyway. As specified in
[RFC7252] and [RFC8132], if the response associated with the ETag is
still valid, the response uses the "2.03 Valid" code and consequently
carries no payload.
4.3.3. Examples
The following examples illustrate the replies to the query
"example.org. IN AAAA record", recursion turned on. Successful
responses carry one answer record including address
2001:db8:1::1:2:3:4 and TTL 58719.
A successful response:
2.05 Content
Content-Format: application/dns-message
Max-Age: 58719
Payload: 00 00 81 a0 00 01 00 01 00 00 00 00 07 65 78 61 [binary]
6d 70 6c 65 03 6f 72 67 00 00 1c 00 01 c0 0c 00 [binary]
1c 00 01 00 01 37 49 00 10 20 01 0d b8 00 01 00 [binary]
00 00 01 00 02 00 03 00 04 [binary]
When a DNS error (SERVFAIL in this case) is noted in the DNS
response, the CoAP response still indicates success:
2.05 Content
Content-Format: application/dns-message
Payload: 00 00 81 a2 00 01 00 00 00 00 00 00 07 65 78 61 [binary]
6d 70 6c 65 03 6f 72 67 00 00 1c 00 01 [binary]
When an error occurs on the CoAP layer, the DoC server SHOULD respond
with an appropriate CoAP error, for instance "4.15 Unsupported
Content-Format" if the Content-Format option in the request was not
set to "application/dns-message" and the Content-Format is not
otherwise supported by the server.
5. CoAP/CoRE Integration
5.1. Proxies and caching
TBD:
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* TTL vs. Max-Age (https://github.com/anr-bmbf-pivot/draft-dns-over-
coap/issues/5)
* Responses that are not globally valid
* General CoAP proxy problem, but what to do when DoC server is a
DNS proxy, response came not yet in but retransmission by DoC
client was received (see Figure 2)
- send empty ACK (maybe move to best practices appendix
(https://github.com/anr-bmbf-pivot/draft-dns-over-coap/
issues/6#issuecomment-895880206))
DoC client DoC proxy DNS server
| CoAP req [rt 1] | |
|------------------>| DNS query [rt 1] |
| |------------------->|
| CoAP req [rt 2] | |
|------------------>| DNS resp |
| CoAP resp |<-------------------|
|<------------------| |
| | |
Figure 2: CoAP retransmission (rt) is received before DNS
query could have been fulfilled.
5.2. OBSERVE (modifications)?
* TBD
* DoH has considerations on Server Push to deliver additional,
potentially outstanding requests + response to the DoC client for
caching
* OBSERVE does not include the request it would have been generated
from ==> cannot be cached without corresponding request having
been send over the wire.
* If use case exists: extend OBSERVE with option that contains
"promised" request (see [RFC7540], section 8.2)?
* Other caveat: clients can't cache, only proxys so value needs to
be evaluated
* Potential use case: [RFC8490] Section 4.1.2
5.3. OSCORE
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* TBD
* With OSCORE DTLS might not be required
6. URI configuration
* TBD
* Maybe out-of-scope?
* DHCP and RA options to deliver? [I-D.peterson-doh-dhcp]
* CoRE-RD [I-D.ietf-core-resource-directory] (...; can not express
URI templates)
* When no actual templating is involved: regular resource discovery
("rt=core.dns"?) through .well-known/core
7. Considerations for Unencrypted Use
* TBD
* DTLS-transport should be used
* Non-DTLS can have benefits: Blockwise-transfer for IEEE 802.15.4,
additional layer of caching, ...
8. Security Considerations
TODO Security
9. IANA Considerations
IANA is requested to assign CoAP Content-Format ID for the DNS
message media type in the "CoAP Content-Formats" sub-registry, within
the "CoRE Parameters" registry [RFC7252], corresponding the
"application/dns-message" media type from the "Media Types" registry:
Media-Type: application/dns-message
Encoding: -
Id: TBD
Reference: [TBD-this-spec]
10. References
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10.1. Normative References
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/rfc/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/rfc/rfc2119>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/rfc/rfc6347>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/rfc/rfc7252>.
[RFC7959] Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in
the Constrained Application Protocol (CoAP)", RFC 7959,
DOI 10.17487/RFC7959, August 2016,
<https://www.rfc-editor.org/rfc/rfc7959>.
[RFC8132] van der Stok, P., Bormann, C., and A. Sehgal, "PATCH and
FETCH Methods for the Constrained Application Protocol
(CoAP)", RFC 8132, DOI 10.17487/RFC8132, April 2017,
<https://www.rfc-editor.org/rfc/rfc8132>.
[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/rfc/rfc8174>.
[RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
"Object Security for Constrained RESTful Environments
(OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019,
<https://www.rfc-editor.org/rfc/rfc8613>.
10.2. Informative References
[I-D.ietf-core-coral]
Amsüss, C. and T. Fossati, "The Constrained RESTful
Application Language (CoRAL)", Work in Progress, Internet-
Draft, draft-ietf-core-coral-04, 25 October 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-core-
coral-04>.
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[I-D.ietf-core-href]
Bormann, C. and H. Birkholz, "Constrained Resource
Identifiers", Work in Progress, Internet-Draft, draft-
ietf-core-href-06, 25 July 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-core-
href-06>.
[I-D.ietf-core-resource-directory]
Amsüss, C., Shelby, Z., Koster, M., Bormann, C., and P. V.
D. Stok, "CoRE Resource Directory", Work in Progress,
Internet-Draft, draft-ietf-core-resource-directory-28, 7
March 2021, <https://datatracker.ietf.org/doc/html/draft-
ietf-core-resource-directory-28>.
[I-D.ietf-dprive-dnsoquic]
Huitema, C., Dickinson, S., and A. Mankin, "DNS over
Dedicated QUIC Connections", Work in Progress, Internet-
Draft, draft-ietf-dprive-dnsoquic-06, 20 October 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-dprive-
dnsoquic-06>.
[I-D.peterson-doh-dhcp]
Peterson, T., "DNS over HTTP resolver announcement Using
DHCP or Router Advertisements", Work in Progress,
Internet-Draft, draft-peterson-doh-dhcp-01, 21 October
2019, <https://datatracker.ietf.org/doc/html/draft-
peterson-doh-dhcp-01>.
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014,
<https://www.rfc-editor.org/rfc/rfc7228>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<https://www.rfc-editor.org/rfc/rfc7540>.
[RFC8094] Reddy, T., Wing, D., and P. Patil, "DNS over Datagram
Transport Layer Security (DTLS)", RFC 8094,
DOI 10.17487/RFC8094, February 2017,
<https://www.rfc-editor.org/rfc/rfc8094>.
[RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS
(DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
<https://www.rfc-editor.org/rfc/rfc8484>.
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[RFC8490] Bellis, R., Cheshire, S., Dickinson, J., Dickinson, S.,
Lemon, T., and T. Pusateri, "DNS Stateful Operations",
RFC 8490, DOI 10.17487/RFC8490, March 2019,
<https://www.rfc-editor.org/rfc/rfc8490>.
Appendix A. Change Log
TBD:
* Request text duplication (https://github.com/anr-bmbf-pivot/draft-
dns-over-coap/issues/4)
A.1. Since draft-lenders-dns-over-coap-01
(https://datatracker.ietf.org/doc/html/draft-lenders-dns-over-
coap-01)
* Remove GET and POST methods
* Add note on ETag and response codes
* Provide requirement conflict for DNS over QUIC
* Clarify Content-Format / Accept handling
A.2. Since draft-lenders-dns-over-coap-00
(https://datatracker.ietf.org/doc/html/draft-lenders-dns-over-
coap-00)
* Soften Content-Format requirements in Section 4.2.1 and
Section 4.3
* Clarify "CoAP payload"/"CoAP body" terminology
* Fix nits and typos
A.3. Since draft-lenders-dns-over-coaps-00
(https://datatracker.ietf.org/doc/html/draft-lenders-dns-over-
coaps-00)
* Clarification in abstract that both DTLS and OSCORE can be used as
secure transport
* Restructuring of Section 4:
- Add dedicated Section 4.1 on Content-Format
- Add overview table about usable and required features for
request method types to Section 4.2
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- Add dedicated Section 4.2.2 and Section 4.3.2 on caching
requirements for CoAP requests and responses
* Fix nits and typos
Acknowledgments
TODO acknowledge.
Authors' Addresses
Martine Sophie Lenders
Freie Universität Berlin
Email: m.lenders@fu-berlin.de
Christian Amsüss
Email: christian@amsuess.com
Cenk Gündoğan
HAW Hamburg
Email: cenk.guendogan@haw-hamburg.de
Thomas C. Schmidt
HAW Hamburg
Email: t.schmidt@haw-hamburg.de
Matthias Wählisch
Freie Universität Berlin
Email: m.waehlisch@fu-berlin.de
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