rfc9953.original.md   rfc9953.md 
--- ---
v: 3 title: "DNS over the Constrained Application Protocol (DoC)"
title: "DNS over CoAP (DoC)"
abbrev: DoC abbrev: DoC
docname: draft-ietf-core-dns-over-coap-20 docname: draft-ietf-core-dns-over-coap-20
number: 9953
ipr: trust200902
lang: en
consensus: true
obsoletes:
updates:
pi: [toc, symrefs, sortrefs]
category: std category: std
submissiontype: IETF submissiontype: IETF
v: 3
v3xml2rfc: date: 2026-03
silence: area: WIT
- Found SVG with width or height specified
area: Applications
workgroup: CoRE workgroup: CoRE
keyword: keyword:
- Internet-Draft
- CoRE - CoRE
- CoAP - CoAP
- DNS - DNS
venue:
group: CoRE
type: Working Group
mail: core@ietf.org
arch: "https://mailarchive.ietf.org/arch/browse/core/"
github: "core-wg/draft-dns-over-coap"
latest: "https://core-wg.github.io/draft-dns-over-coap/draft-ietf-core-dns-over-c
oap.html"
author: author:
- name: Martine Sophie Lenders - name: Martine Sophie Lenders
org: TUD Dresden University of Technology org: TUD Dresden University of Technology
abbrev: TU Dresden abbrev: TU Dresden
street: Helmholtzstr. 10 street: Helmholtzstr. 10
city: Dresden city: Dresden
code: D-01069 code: D-01069
country: Germany country: Germany
email: martine.lenders@tu-dresden.de email: martine.lenders@tu-dresden.de
skipping to change at line 83 skipping to change at line 78
RFC8484: doh RFC8484: doh
RFC8613: oscore RFC8613: oscore
RFC8765: dns-push RFC8765: dns-push
RFC8768: coap-hop-limit RFC8768: coap-hop-limit
RFC8949: cbor RFC8949: cbor
RFC9147: dtls13 RFC9147: dtls13
RFC9460: svcb RFC9460: svcb
RFC9461: svcb-dns RFC9461: svcb-dns
RFC9462: ddr RFC9462: ddr
RFC9463: dnr RFC9463: dnr
I-D.ietf-core-coap-dtls-alpn: coap-dtls-alpn PRE-RFC9952:
title: >
The Application-Layer Protocol Negotiation (ALPN) ID Specification for the Cons
trained Application Protocol (CoAP) over DTLS
target: https://www.rfc-editor.org/info/rfc9952
seriesinfo:
RFC: PRE-9952
DOI: 10.17487/PRE-RFC9952
date: March 2026
author:
-
ins: M. S. Lenders
surname: Lenders
fullname: Martine Sophie Lenders
-
ins: C. Amsüss
surname: Amsüss
fullname: Christian Amsüss
-
ins: T. C. Schmidt
surname: Schmidt
fullname: Thomas C. Schmidt
-
ins: M. Wählisch
surname: Wählisch
fullname: Matthias Wählisch
informative: informative:
BCP219: dns-terminology BCP219: dns-terminology
BCP237: dnssec BCP237: dnssec
RFC3833: dns-threats RFC3833: dns-threats
RFC6690: core-link-format RFC6690: core-link-format
RFC7228: constr-nodes RFC7228: constr-nodes
RFC7858: dot RFC7858: dot
RFC8094: dodtls RFC8094: dodtls
RFC9076: dns-privacy RFC9076: dns-privacy
RFC9176: core-rd RFC9176: core-rd
RFC9250: doq RFC9250: doq
RFC9528: edhoc RFC9528: edhoc
I-D.ietf-core-href: cri I-D.ietf-core-href:
I-D.ietf-core-transport-indication: transport-indication display: CRI
I-D.ietf-iotops-7228bis: constr-nodes-bis I-D.ietf-core-transport-indication:
I-D.amsuess-core-cachable-oscore: cachable-oscore display: TRANSPORT-IND
DoC-paper: DOI.10.1145/3609423 I-D.ietf-iotops-7228bis:
I-D.ietf-core-corr-clar: core-corrclar display: RFC7228bis
I-D.amsuess-core-cachable-oscore:
display: CACHABLE-OSCORE
DoC-paper:
seriesinfo:
DOI: 10.1145/3609423
title: 'Securing Name Resolution in the IoT: DNS over CoAP'
author:
- name: Martine S. Lenders
ins: M. Lenders
org: TU Dresden, Germany
- name: Christian Amsüss
ins: C. Amsüss
org: Unaffiliated, Vienna, Austria
- name: Cenk Gündogan
ins: C. Gündogan
org: Huawei Technologies, Munich, Germany
- name: Marcin Nawrocki
ins: M. Nawrocki
org: TU Dresden, Germany
- name: Thomas C. Schmidt
ins: T. Schmidt
org: HAW Hamburg, Hamburg, Germany
- name: Matthias Wählisch
ins: M. Wählisch
org: TU Dresden & Barkhausen Institut, Dresden, Germany
date: '2023-09-28'
refcontent: Proceedings of the ACM on Networking, vol. 1, no. CoNEXT2, pp. 1-25
I-D.ietf-core-corr-clar:
display: CoAP-CORR-CLAR
REST: REST:
target: https://www.ics.uci.edu/~fielding/pubs/dissertation/fielding_dissertation .pdf target: https://www.ics.uci.edu/~fielding/pubs/dissertation/fielding_dissertation .pdf
title: Architectural Styles and the Design of Network-based Software Architecture s title: Architectural Styles and the Design of Network-based Software Architecture s
author: author:
ins: R. Fielding ins: R. Fielding
name: Roy Thomas Fielding name: Roy Thomas Fielding
org: University of California, Irvine org: University of California, Irvine
date: 2000 date: 2000
seriesinfo: refcontent:
"Ph.D.": "Dissertation, University of California, Irvine" "Ph.D. Dissertation, University of California, Irvine"
format: format:
HTML: https://ics.uci.edu/~fielding/pubs/dissertation/top.htm HTML: https://ics.uci.edu/~fielding/pubs/dissertation/top.htm
PDF: https://www.ics.uci.edu/~fielding/pubs/dissertation/fielding_dissertation. pdf PDF: https://www.ics.uci.edu/~fielding/pubs/dissertation/fielding_dissertation. pdf
--- abstract --- abstract
<!--[rfced] FYI: We updated [I-D.ietf-core-coap-dtls-alpn] to [PRE-RFC9952]
for now. We will make the final updates in RFCXML (i.e., remove "PRE-").
-->
<!--[rfced] Please note that the title of the document has been
updated as follows. The abbreviation has been expanded per Section 3.6
of RFC 7322 ("RFC Style Guide"). We also added "the". Please review.
Original:
DNS over CoAP (DoC)
Current:
DNS over the Constrained Application Protocol (DoC)
-->
<!--[rfced] May we remove "(CoAPS)" in the Abstract as this
term/abbreviation is not used elsewhere in the document? Please
review.
Original:
These CoAP messages can be protected by (D)TLS-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).
Perhaps:
These CoAP messages can be protected by (D)TLS-Secured CoAP or
Object Security for Constrained RESTful Environments (OSCORE) to
provide encrypted DNS message exchange for constrained devices in
the Internet of Things (IoT).
-->
This document defines a protocol for exchanging DNS queries (OPCODE 0) over the This document defines a protocol for exchanging DNS queries (OPCODE 0) over the
Constrained Application Protocol (CoAP). These CoAP messages can be protected Constrained Application Protocol (CoAP). These CoAP messages can be protected
by (D)TLS-Secured CoAP (CoAPS) or Object Security for Constrained RESTful by (D)TLS-Secured CoAP (CoAPS) or Object Security for Constrained RESTful
Environments (OSCORE) to provide encrypted DNS message exchange for Environments (OSCORE) to provide encrypted DNS message exchange for
constrained devices in the Internet of Things (IoT). constrained devices in the Internet of Things (IoT).
--- middle --- middle
Introduction Introduction
============ ============
This document defines DNS over CoAP (DoC), a protocol to send DNS This document defines DNS over CoAP (DoC), a protocol to send DNS
{{-dns}} queries and get DNS responses over the Constrained Application {{-dns}} queries and get DNS responses over the Constrained Application
Protocol (CoAP) {{-coap}} using OPCODE 0 (Query). Each DNS query-response pair is map ped into a Protocol (CoAP) {{-coap}} using OPCODE 0 (Query). Each DNS query-response pair is map ped into a
CoAP message exchange. Each CoAP message can be secured by DTLS 1.2 or newer {{-dtls1 2}} {{-dtls13}} CoAP message exchange. Each CoAP message can be secured by DTLS 1.2 or newer {{-dtls1 2}} {{-dtls13}}
as well as Object Security for Constrained RESTful Environments (OSCORE) {{-oscore}} as well as Object Security for Constrained RESTful Environments (OSCORE) {{-oscore}}
but also TLS 1.3 or newer {{-coap-tcp}} {{?RFC8446}} and TLS 1.3 or newer {{-coap-tcp}} {{?RFC8446}}
to ensure message integrity and confidentiality. to ensure message integrity and confidentiality.
The application use case of DoC is inspired by DNS over HTTPS {{-doh}} The application use case of DoC is inspired by DNS over HTTPS (DoH) {{-doh}}.
(DoH). DoC, however, aims for deployment in the constrained Internet of However, DoC aims for deployment in the constrained Internet of
Things (IoT), which usually conflicts with the requirements introduced by Things (IoT), which usually conflicts with the requirements introduced by
HTTPS. HTTPS.
Constrained IoT devices may be restricted in memory, power consumption, Constrained IoT devices may be restricted in memory, power consumption,
link-layer frame sizes, throughput, and latency. They may link-layer frame sizes, throughput, and latency. They may
only have a handful kilobytes of both RAM and ROM. They may sleep for long only have a handful kilobytes of both RAM and ROM. They may sleep for long
durations of time, after which they need to refresh the named resources they durations of time, after which they need to refresh the named resources they
know about. Name resolution in such scenarios must take into account link know about. Name resolution in such scenarios must take into account link-layer
layer frame sizes of only a few hundred bytes, bit rates in the magnitude frame sizes of only a few hundred bytes, bit rates in the magnitude
of kilobits per second, and latencies of several seconds {{-constr-nodes}} {{-constr- of kilobits per second, and latencies of several seconds {{-constr-nodes}} {{I-D.ietf
nodes-bis}} [^remove-constr-nodes]. -iotops-7228bis}}.
[^remove-constr-nodes]: RFC Ed.: Please remove the {{-constr-nodes}} reference and re <!--[rfced] FYI: draft-ietf-iotops-7228bis has not been published yet
place it with {{-constr-nodes-bis}} throughout the document in case {{-constr-nodes-b (currently, its IESG state is "I-D Exists"). Thus, we have left
is}} becomes an RFC before publication. references to RFC 7228 and draft-ietf-iotops-7228bis as is.
Author note:
Please remove the {{-constr-nodes}} reference and replace
it with {{I-D.ietf-iotops-7228bis}} throughout the document in case
{{I-D.ietf-iotops-7228bis}} becomes an RFC before publication.
-->
In order not to be burdened by the resource requirements of TCP and HTTPS, constraine d IoT devices could use DNS over DTLS {{-dodtls}}. In order not to be burdened by the resource requirements of TCP and HTTPS, constraine d IoT devices could use DNS over DTLS {{-dodtls}}.
In contrast to DNS over DTLS, DoC In contrast to DNS over DTLS, DoC
can take advantage of CoAP features to mitigate drawbacks of datagram-based can take advantage of CoAP features to mitigate drawbacks of datagram-based
communication. These features include: block-wise transfer {{-coap-blockwise}}, which communication. These features include (1) block-wise transfer {{-coap-blockwise}}, wh
solves ich solves
the Path MTU problem of DNS over DTLS (see {{-dodtls, Section 5}}); CoAP the Path MTU problem of DNS over DTLS (see {{-dodtls, Section 5}}), (2) CoAP
proxies, which provide an additional level of caching; re-use of data proxies, which provide an additional level of caching, and (3) reuse of data
structures for application traffic and DNS information, which saves memory structures for application traffic and DNS information, which saves memory
on constrained devices. on constrained devices.
To avoid the resource requirements of DTLS or TLS on top of UDP (e.g., introduced by DNS over DTLS {{-dodtls}} or DNS over QUIC {{-doq}}), DoC allows for lightweight mess age protection based on OSCORE. To avoid the resource requirements of DTLS or TLS on top of UDP (e.g., introduced by DNS over DTLS {{-dodtls}} or DNS over QUIC {{-doq}}), DoC allows for lightweight mess age protection based on OSCORE.
~~~ aasvg ~~~ aasvg
. FETCH coaps://[2001:db8::1]/ . FETCH coaps://[2001:db8::1]/
/ /
/ /
CoAP request CoAP request
+------+ [DNS query] +------+------+ DNS query .---------------. +------+ [DNS query] +------+------+ DNS query .---------------.
| DoC |---------------->| DoC | DNS |--- --- --- --->| DNS | | DoC |---------------->| DoC | DNS |--- --- --- --->| DNS |
|Client|<----------------|Server|Client|<--- --- --- ---| Infrastructure | |Client|<----------------|Server|Client|<--- --- --- ---| Infrastructure |
+------+ CoAP response +------+------+ DNS response '---------------' +------+ CoAP response +------+------+ DNS response '---------------'
[DNS response] [DNS response]
\ / \ / \ / \ /
'------DNS over CoAP------' '----DNS over UDP/HTTPS/QUIC/...----' '------DNS over CoAP------' '----DNS over UDP/HTTPS/QUIC/...----'
~~~ ~~~
{: #fig-overview-arch title="Basic DoC architecture"} {: #fig-overview-arch title="Basic DoC Architecture"}
<!--[rfced] FYI - We updated "authoritive name server" to "authoritative name
server" to match other usage in this document and in other RFCs.
Original:
That DoC server can be the authoritive name server for the queried
record or a DNS client (i.e., a stub or recursive resolver) that
resolves DNS information by using other DNS transports such as DNS
over UDP [STD13], DNS over HTTPS [RFC8484], or DNS over QUIC
[RFC9250] when communicating with the upstream DNS infrastructure.
Updated:
That DoC server can be the authoritative name server for the queried
record or a DNS client (i.e., a stub or recursive resolver) that
resolves DNS information by using other DNS transports such as DNS
over UDP [STD13], DNS over HTTPS [RFC8484], or DNS over QUIC
[RFC9250] when communicating with the upstream DNS infrastructure.
-->
The most important components of DoC can be seen in {{fig-overview-arch}}: a DoC The most important components of DoC can be seen in {{fig-overview-arch}}: a DoC
client tries to resolve DNS information by sending DNS queries carried within client tries to resolve DNS information by sending DNS queries carried within
CoAP requests to a DoC server. CoAP requests to a DoC server.
That DoC server can be the authoritive name server for the queried record or a DNS cl ient (i.e., a stub or recursive resolver) that resolves DNS information by using othe r DNS transports such That DoC server can be the authoritative name server for the queried record or a DNS client (i.e., a stub or recursive resolver) that resolves DNS information by using ot her DNS transports such
as DNS over UDP {{-dns}}, DNS over HTTPS {{-doh}}, or DNS over QUIC {{-doq}} when com municating with the upstream as DNS over UDP {{-dns}}, DNS over HTTPS {{-doh}}, or DNS over QUIC {{-doq}} when com municating with the upstream
DNS infrastructure. DNS infrastructure.
Using that information, the DoC server then replies to the queries of the DoC client with DNS Using that information, the DoC server then replies to the queries of the DoC client with DNS
responses carried within CoAP responses. responses carried within CoAP responses.
A DoC server MAY also serve as DNSSEC validator to provide DNSSEC validation to the m ore A DoC server MAY also serve as a DNSSEC validator to provide DNSSEC validation to the more
constrained DoC clients. constrained DoC clients.
Note that this specification is distinct from DoH, since the CoAP-specific FETCH meth Note that this specification is distinct from DoH because the CoAP-specific FETCH met
od {{-coap-fetch}} is used. hod {{-coap-fetch}} is used.
This has the benefit of having the DNS query in the body as when using the POST metho A benefit of using this method is having the DNS query in the body such as when using
d, but still with the same caching advantages of responses to requests that use the G the POST method, but with the same caching advantages of responses to requests that
ET method. use the GET method.
Having the DNS query in the body means that we do not need extra base64 encoding, whi Having the DNS query in the body means that there is no need for extra base64 encodin
ch would increase g, which would increase
code complexity and message sizes. code complexity and message sizes.
Also, this allows for the block-wise transfer of queries {{-coap-blockwise}}. Also, this allows for the block-wise transfer of queries {{-coap-blockwise}}.
Terminology and Conventions Terminology and Conventions
=========================== ===========================
{::boilerplate bcp14-tagged} {::boilerplate bcp14-tagged}
A server that provides the service specified in this document is called a "DoC A server that provides the service specified in this document is called a "DoC
server" to differentiate it from a classic "DNS server". server" to differentiate it from a classic "DNS server".
A DoC server acts either as a DNS stub resolver or a DNS recursive resolver {{-dns-te rminology}}. A DoC server acts as either a DNS stub resolver or a DNS recursive resolver {{-dns-te rminology}}.
As such, the DoC server communicates with an "upstream DNS infrastructure" or a singl e "upstream DNS server". As such, the DoC server communicates with an "upstream DNS infrastructure" or a singl e "upstream DNS server".
A "DoC resource" is a CoAP resource {{-coap}} at the DoC server that DoC clients can target to send a DNS query in a CoAP request. A "DoC resource" is a CoAP resource {{-coap}} at the DoC server that DoC clients can target in order to send a DNS query in a CoAP request.
A client using the service specified in this document to retrieve the A client using the service specified in this document to retrieve
DNS information is called a "DoC client". the DNS information is called a "DoC client".
The term "constrained nodes" is used as defined in {{-constr-nodes}}. The term "constrained nodes" is used as defined in {{-constr-nodes}}.
{{-core-link-format}} describes that "Constrained RESTful Environments (CoRE)" realiz e the Representational State Transfer (REST) architecture {{REST}} in a suitable form for such constrained nodes. {{-core-link-format}} describes that Constrained RESTful Environments (CoRE) realize the Representational State Transfer (REST) architecture {{REST}} in a suitable form f or such constrained nodes.
A DoC server can provide Observe capabilities as defined in {{-coap-observe, Section 1.2}}. A DoC server can provide Observe capabilities as defined in {{-coap-observe, Section 1.2}}.
As part of that, it administers a "list of observers". As part of that, it administers a "list of observers". DoC clients using these capabi
DoC clients using these capabilities are "observers" as defined in {{-coap-observe, S lities are "observers" as defined in {{-coap-observe, Section 1.2}}.
ection 1.2}} in that case. A "notification" is a CoAP response message with an Observe option; see {{-coap-obser
A "notification" is a CoAP response message with an Observe option, see {{-coap-obser ve, Section 4.2}}.
ve, Section 4.2}}.
The terms "payload" and "body" are used as defined in {{-coap-blockwise, Section 2}}. The terms "payload" and "body" are used as defined in {{-coap-blockwise, Section 2}}.
Note that, when block-wise transfer is not used, the terms "payload" and "body" are t o be understood as equal. Note that, when block-wise transfer is not used, the terms "payload" and "body" are t o be understood as equal.
For better readability, in the examples in this document the binary payload and resou In the examples in this document, the binary payload and resource records are shown i
rce records are shown in a hexadecimal representation as well as a human-readable for n a hexadecimal representation as well as a human-readable format for better readabil
mat. ity. However, in the actual message sent and received, they are encoded in the binary
In the actual message sent and received, however, they are encoded in the binary mess message format defined in {{-dns}}.
age format defined in {{-dns}}.
Selection of a DoC Server {#sec:doc-server-selection} Selection of a DoC Server {#sec:doc-server-selection}
========================= =========================
While there is no path specified for the DoC resource, it is RECOMMENDED to use the r oot path "/" While there is no path specified for the DoC resource, it is RECOMMENDED to use the r oot path "/"
to keep the CoAP requests small. to keep the CoAP requests small.
The DoC client needs to know the DoC server and the DoC resource at the DoC server. The DoC client needs to know the DoC server and the DoC resource at the DoC server.
Possible options to assure this could be manual configuration of a Uniform Resource I Possible options to assure this could be (1) manual configuration of a Uniform Resour
dentifier (URI) {{-uri}} or Constrained Resource Identifier (CRI) {{-cri}}, ce Identifier (URI) {{-uri}} or Constrained Resource Identifier (CRI) {{I-D.ietf-core
or automatic configuration, e.g., using a CoRE resource directory -href}}
or (2) automatic configuration, e.g., using a CoRE resource directory
{{-core-rd}}, DHCP or Router Advertisement options {{-dnr}}, or discovery of designat ed resolvers {{-core-rd}}, DHCP or Router Advertisement options {{-dnr}}, or discovery of designat ed resolvers
{{-ddr}}. {{-ddr}}.
Automatic configuration MUST only be done from a trusted source. Automatic configuration MUST only be done from a trusted source.
## Discovery by Resource Type ## Discovery by Resource Type
For discovery of the DoC resource through a link mechanism that allows describing a r esource type For discovery of the DoC resource through a link mechanism that allows describing a r esource type
(e.g., the Resource Type attribute in {{-core-link-format}}), this document introduce s the resource type "core.dns". (e.g., the Resource Type attribute in {{-core-link-format}}), this document introduce s the resource type "core.dns".
It can be used to identify a generic DNS resolver that is available to the client. It can be used to identify a generic DNS resolver that is available to the client.
## Discovery using SVCB Resource Records or DNR ## Discovery Using SVCB Resource Records or DNR
A DoC server can also be discovered using Service Binding (SVCB) Resource Records (RR A DoC server can also be discovered using Service Binding (SVCB) Resource Records (RR
) {{-svcb}} {{-svcb-dns}} resolved via another DNS service (e.g., provided by an unen s) {{-svcb}} {{-svcb-dns}} resolved via another DNS service (e.g., provided by an une
crypted local resolver) or Discovery of Network-designated Resolvers (DNR) ncrypted local resolver) or Discovery of Network-designated Resolvers (DNR)
Service Parameters {{-dnr}} via DHCP or Router Advertisements. Service Parameters {{-dnr}} via DHCP or Router Advertisements.
{{-coap-tcp}} defines the Application-Layer Protocol Negotiation (ALPN) ID for CoAP o {{-coap-tcp}} defines the Application-Layer Protocol Negotiation (ALPN) ID for CoAP o
ver TLS servers and {{-coap-dtls-alpn}} defines the ALPN ID for CoAP over DTLS server ver TLS servers and {{PRE-RFC9952}} defines the ALPN ID for CoAP over DTLS servers.
s. DoC servers that use only OSCORE {{-oscore}} and Ephemeral Diffie-Hellman Over COSE (
DoC servers that use only OSCORE {{-oscore}} and Ephemeral Diffie-Hellman Over COSE ( EDHOC) {{-edhoc}} (COSE stands for "Concise Binary Object Notation (CBOR) Object Sign
EDHOC) {{-edhoc}} (with COSE abbreviating "Concise Binary Object Notation (CBOR) Obje ing and Encryption" {{?RFC9052}}) to support security cannot be discovered using thes
ct Signing and Encryption" {{?RFC9052}}) to support security cannot be discovered usi e SVCB RR or DNR mechanisms.
ng these SVCB RR or DNR mechanisms. Specifying an alternate discovery mechanism is out of the scope of this document.
Specifying an alternate discovery mechanism is out of scope of this document.
This document is not an SVCB mapping document for the CoAP schemes This document is not an SVCB mapping document for the CoAP schemes
as defined in {{Section 2.4.3 of -svcb}}. as defined in {{Section 2.4.3 of -svcb}}.
A full SVCB mapping is specified in {{-transport-indication}}. A full SVCB mapping is specified in {{I-D.ietf-core-transport-indication}}.
It generalizes mechanisms for all CoAP services. It generalizes mechanisms for all CoAP services.
This document introduces only the discovery of DoC services. This document introduces only the discovery of DoC services.
This document specifies "docpath" as This document specifies "docpath" as
a single-valued SvcParamKey that is mandatory for DoC SVCB records. a single-valued Service Parameter Key (SvcParamKey) that is mandatory for DoC SVCB re cords.
If the "docpath" SvcParamKey is absent, the service should not be considered a valid DoC service. If the "docpath" SvcParamKey is absent, the service should not be considered a valid DoC service.
The docpath is devided up into segments of the absolute path to the DoC resource (doc path-segment), The docpath is divided up into segments of the absolute path to the DoC resource (doc path-segment),
each a sequence of 1-255 octets. each a sequence of 1-255 octets.
In ABNF {{-abnf}}: In ABNF {{-abnf}}:
~~~ ~~~ abnf
docpath-segment = 1*255OCTET docpath-segment = 1*255OCTET
~~~ ~~~
Note that this restricts the length of each docpath-segment to at most 255 octets. Note that this restricts the length of each docpath-segment to at most 255 octets.
Paths with longer segments cannot be advertised with the "docpath" SvcParam and are t hus NOT Paths with longer segments cannot be advertised with the "docpath" SvcParam and are t hus NOT
RECOMMENDED for the path to the DoC resource. RECOMMENDED for the path to the DoC resource.
The presentation format value of "docpath" SHALL be a comma-separated list ({{Appendi x A.1 of -svcb}}) The presentation format value of "docpath" SHALL be a comma-separated list ({{Appendi x A.1 of -svcb}})
of 0 or more docpath-segments. of 0 or more docpath-segments.
The root path "/" is represented by 0 docpath-segments, i.e., an empty list. The root path "/" is represented by 0 docpath-segments, i.e., an empty list.
The same considerations for the "," and "\" characters in docpath-segments for zone-f The same considerations apply for the "," and "\" characters in docpath-segments for
ile zone-file
implementations as for the alpn-ids in an "alpn" SvcParam apply ({{Section 7.1.1 of - implementations and the alpn-ids in an "alpn" SvcParam ({{Section 7.1.1 of -svcb}}).
svcb}}).
The wire-format value for "docpath" consists of 0 or more sequences of octets prefixe d by their The wire-format value for "docpath" consists of 0 or more sequences of octets prefixe d by their
respective length as a single octet. respective length as a single octet.
We call this single octet the length octet. We call this single octet the length octet.
The length octet and the corresponding sequence form a length-value pair. The length octet and the corresponding sequence form a length-value pair.
These length-value pairs are concatenated to form the SvcParamValue. These length-value pairs are concatenated to form the SvcParamValue.
These pairs MUST exactly fill the SvcParamValue; otherwise, the SvcParamValue is malf ormed. These pairs MUST exactly fill the SvcParamValue; otherwise, the SvcParamValue is malf ormed.
Each such length-value pair represents one segment of the absolute path to the DoC re source. Each such length-value pair represents one segment of the absolute path to the DoC re source.
The root path "/" is represented by 0 length-value pairs, i.e., SvcParamValue length 0. The root path "/" is represented by 0 length-value pairs, i.e., SvcParamValue length 0.
Note that this format uses the same encoding as the "alpn" SvcParam and can reuse the <!-- [rfced] Please clarify "is of length 0 and 24 octets" in this sentence.
Original:
As long as each docpath-
segment is of length 0 and 24 octets, it is easily transferred into
the path representation in CRIs [I-D.ietf-core-href] by masking each
length octet with the CBOR text string major type 3 (0x60 as an
octet, see [RFC8949]).
Perhaps:
As long as each docpath-
segment has a length between 0 and 24 octets, it is easily transferred into
the path representation in CRIs [CRI] by masking each length octet
with the CBOR text string major type 3 (0x60 as an octet; see
[RFC8949]).
-->
<!--[rfced] We are having trouble parsing this sentence. Please let us
know if it can be revised as shown below for clarity.
Original:
Likewise, it can be transferred into a URI path-abempty form by
replacing each length octet with the "/" character None of the
abovementioned prevent longer docpath-segments than the considered,
they just make the translation harder, as they require to make space
for the longer delimiters, in turn requiring to move octets.
Perhaps:
Likewise, it can be transferred into a URI path-abempty form by
replacing each length octet with the "/" character. None of the
abovementioned prevent longer docpath-segments than the considered
ones; they just make the translation harder as space is required
for the longer delimiters, which in turn require octets to be
moved.
-->
<!-- [rfced] May we update "going through" to "with" here to improve clarity?
Original:
The construction algorithm for DoC
requests is as follows, going through the provided records in order
of their priority.
Perhaps:
The construction algorithm for DoC
requests is as follows, with the provided records in order
of their priority.
-->
Note that this format uses the same encoding as the "alpn" SvcParam, and it can reuse
the
decoders and encoders for that SvcParam with the adaption that a length of zero is al lowed. decoders and encoders for that SvcParam with the adaption that a length of zero is al lowed.
As long as each docpath-segment is of length 0 and 24 octets, it is easily transferre d into the path As long as each docpath-segment is of length 0 and 24 octets, it is easily transferre d into the path
representation in CRIs {{-cri}} by masking each length octet with the CBOR text strin representation in CRIs {{I-D.ietf-core-href}} by masking each length octet with the C
g major type 3 BOR text string major type 3
(`0x60` as an octet, see {{-cbor}}). (`0x60` as an octet; see {{-cbor}}).
Furthermore, it is easily transferable into a sequence of CoAP Uri-Path options by Furthermore, it is easily transferable into a sequence of CoAP Uri-Path options by
mapping each length octet into the Option Delta and Option Length of the correspondin g CoAP Uri-Path mapping each length octet into the Option Delta and Option Length of the correspondin g CoAP Uri-Path
option, provided the docpath-segments are all of a length between 0 and 12 octets (se e {{-coap, option, provided the docpath-segments are all of a length between 0 and 12 octets (se e {{-coap,
Section 3.1}}). Section 3.1}}). Likewise, it can be transferred into a URI path-abempty form by repla
Likewise, it can be transferred into a URI path-abempty form by replacing each length cing each length octet with the "/" character
octet with the "/" character
None of the abovementioned prevent longer docpath-segments than the considered, they just make the None of the abovementioned prevent longer docpath-segments than the considered, they just make the
translation harder, as they require to make space for the longer delimiters, in turn requiring to move octets. translation harder, as they require to make space for the longer delimiters, in turn requiring to move octets.
To use the service binding from an SVCB RR or DNR Encrypted DNS option, the DoC clien t MUST send a DoC request constructed from the SvcParams including "docpath". To use the service binding from an SVCB RR or DNR Encrypted DNS option, the DoC clien t MUST send a DoC request constructed from the SvcParams including "docpath".
The construction algorithm for DoC requests is as follows, going through the provided records in order of their priority. The construction algorithm for DoC requests is as follows, going through the provided records in order of their priority.
For the purposes of this algorithm, the DoC client is assumed to be SVCB-optional (se e {{Section 3 of -svcb}}). For the purposes of this algorithm, the DoC client is assumed to be SVCB-optional (se e {{Section 3 of -svcb}}).
<!-- [rfced] How may we update the third item in the series for parallel
structure? Would either removing "from" or adding "information" be correct?
Original:
This may include (1) A
or AAAA RRs associated with the target name and delivered with the
SVCB RR (see [RFC9462]), (2) "ipv4hint" or "ipv6hint" SvcParams
from the SVCB RR (see [RFC9461]), or (3) from IPv4 or IPv6
addresses provided if DNR [RFC9463] is used.
Perhaps A (cut "from"):
This may include (1) A
or AAAA RRs associated with the target name and delivered with the
SVCB RR (see [RFC9462]), (2) "ipv4hint" or "ipv6hint" SvcParams
from the SVCB RR (see [RFC9461]), or (3) IPv4 or IPv6
addresses provided if DNR [RFC9463] is used.
or
Perhaps B (add "information"):
This may include (1) A
or AAAA RRs associated with the target name and delivered with the
SVCB RR (see [RFC9462]), (2) "ipv4hint" or "ipv6hint" SvcParams
from the SVCB RR (see [RFC9461]), or (3) information from IPv4 or IPv6
addresses provided if DNR [RFC9463] is used.
-->
- If the "alpn" SvcParam value for the service is "coap", a CoAP request for CoAP ove r TLS MUST be constructed {{-coap-tcp}}. - If the "alpn" SvcParam value for the service is "coap", a CoAP request for CoAP ove r TLS MUST be constructed {{-coap-tcp}}.
If it is "co", a CoAP request for CoAP over DTLS MUST be constructed {{-coap-dtls-a lpn}}. If it is "co", a CoAP request for CoAP over DTLS MUST be constructed {{PRE-RFC9952} }.
Any other SvcParamKeys specifying a transport are out of the scope of this document . Any other SvcParamKeys specifying a transport are out of the scope of this document .
- The destination address for the request SHOULD be taken from additional information about the target. - The destination address for the request SHOULD be taken from additional information about the target.
This may include (1) A or AAAA RRs associated with the target name and delivered wi th the SVCB RR (see {{-ddr}}), (2) "ipv4hint" or "ipv6hint" SvcParams from the SVCB R R (see {{-svcb-dns}}), or (3) from IPv4 or IPv6 addresses provided if DNR {{-dnr}} is used. This may include (1) A or AAAA RRs associated with the target name and delivered wi th the SVCB RR (see {{-ddr}}), (2) "ipv4hint" or "ipv6hint" SvcParams from the SVCB R R (see {{-svcb-dns}}), or (3) from IPv4 or IPv6 addresses provided if DNR {{-dnr}} is used.
As a fallback, an address MAY be queried for the target name of the SVCB record fro m another DNS service. As a fallback, an address MAY be queried for the target name of the SVCB record fro m another DNS service.
- The destination port for the request MUST be taken from the "port" SvcParam value, if present. - The destination port for the request MUST be taken from the "port" SvcParam value, if present.
Otherwise, take the default port of the CoAP transport, e.g., with regards to this specification TCP port 5684 for "coap" or UDP port 5684 for "co". Otherwise, take the default port of the CoAP transport, e.g., with regards to this specification, the default is TCP port 5684 for "coap" or UDP port 5684 for "co".
This document introduces no limitations on the ports that can be used. This document introduces no limitations on the ports that can be used.
If a malicious SVCB record allows its originator to influence message payloads, {{S ection 12 of -svcb}} recommends placing such restrictions in the SVCB mapping documen t. If a malicious SVCB record allows its originator to influence message payloads, {{S ection 12 of -svcb}} recommends placing such restrictions in the SVCB mapping documen t.
The records used in this document only infuence the Uri-Path option. The records used in this document only influence the Uri-Path option.
That option is only sent in the plaintext of an encrytped (D)TLS channel, That option is only sent in the plaintext of an encrypted (D)TLS channel
and thus does not warrant any limitations. and thus does not warrant any limitations.
- The request URI's hostname component MUST be the Authentication Domain Name (ADN) w hen obtained through DNR - The request URI's hostname component MUST be the Authentication Domain Name (ADN) w hen obtained through DNR
and MUST be the target name of the SVCB record when obtained through a `_dns` query and MUST be the target name of the SVCB record when obtained through a `_dns` query
(if AliasMode is used, to the target name of the AliasMode record). (if AliasMode is used to the target name of the AliasMode record).
This can be achieved efficiently by setting that name in TLS Server Name Indication This can be achieved efficiently by setting that name in TLS Server Name Indication
(SNI) {{?RFC8446}}, (SNI) {{?RFC8446}}
or by setting the Uri-Host option on each request. or by setting the Uri-Host option on each request.
- For each element in the CBOR sequence of the "docpath" SvcParam value, a Uri-Path o ption MUST be added to the request. - For each element in the CBOR sequence of the "docpath" SvcParam value, a Uri-Path o ption MUST be added to the request.
- If the request constructed this way receives a response, the same SVCB record MUST be used for construction of future DoC queries. - If the request constructed this way receives a response, the same SVCB record MUST be used for construction of future DoC queries.
If not, or if the endpoint becomes unreachable, the algorithm repeats with the SVCB RR or DNR Encrypted DNS option with the next highest Service Priority as a fallback (see {{Sections 2.4.1 and 3 of -svcb}}). If not, or if the endpoint becomes unreachable, the algorithm repeats with the SVCB RR or DNR Encrypted DNS option with the next highest Service Priority as a fallback (see {{Sections 2.4.1 and 3 of -svcb}}).
A more generalized construction algorithm for any CoAP request can be found in {{-tra nsport-indication}}. A more generalized construction algorithm for any CoAP request can be found in {{I-D. ietf-core-transport-indication}}.
### Examples ### Examples
[^replace-hex] <!--[rfced] Per the following note, we have replaced "ff 0a" with "00 0a" in
the examples in Section 3.2.1 (per IANA's assignment of "10" for
"docpath"). Please confirm that this is correct and let us know if any further
updates are needed.
[^replace-hex]: RFC Ed.: Since the number for "docpath" was not assigned at the time Author note:
of writing, we Since the number for "docpath" was not assigned at the time of
used the hex `ff 0a` (in decimal 65290; from the private use range of SvcParamKey writing, we used the hex `ff 0a` (in decimal 65290; from the
s) throughout private use range of SvcParamKeys) throughout this section. Before
this section. Before publication, please replace `ff 0a` with the hexadecimal rep publication, please replace `ff 0a` with the hexadecimal
resentation of representation of the final value assigned by IANA in this
the final value assigned by IANA in this section. Please remove this paragraph af section. Please remove this paragraph after that.
ter that. -->
A typical SVCB resource record response for a DoC server at the root path "/" of the server looks A typical SVCB resource record response for a DoC server at the root path "/" of the server looks
like the following (the "docpath" SvcParam is the last 4 bytes `ff 0a 00 00` in the b inary): like the following (the "docpath" SvcParam is the last 4 bytes `00 0a 00 00` in the b inary):
Resource record (binary): ~~~
04 5f 64 6e 73 07 65 78 61 6d 70 6c 65 03 6f 72 Resource record (binary):
67 00 00 40 00 01 00 00 06 28 00 1e 00 01 03 64 04 5f 64 6e 73 07 65 78 61 6d 70 6c 65 03 6f 72
6e 73 07 65 78 61 6d 70 6c 65 03 6f 72 67 00 00 67 00 00 40 00 01 00 00 06 28 00 1e 00 01 03 64
01 00 03 02 63 6f ff 0a 00 00 6e 73 07 65 78 61 6d 70 6c 65 03 6f 72 67 00 00
01 00 03 02 63 6f 00 0a 00 00
Resource record (human-readable): Resource record (human-readable):
_dns.example.org. 1576 IN SVCB 1 dns.example.org ( _dns.example.org. 1576 IN SVCB 1 dns.example.org (
alpn=co docpath ) alpn=co docpath )
~~~
{: gi="sourcecode"}
The root path is RECOMMENDED but not required. Here are two examples where the "docpa th" represents The root path is RECOMMENDED but not required. Here are two examples where the "docpa th" represents
paths of varying depth. First, "/dns" is provided in the following example paths of varying depth. First, "/dns" is provided in the following example
(the last 8 bytes `ff 0a 00 04 03 64 6e 73`): (the last 8 bytes `00 0a 00 04 03 64 6e 73`):
Resource record (binary): ~~~
04 5f 64 6e 73 07 65 78 61 6d 70 6c 65 03 6f 72 Resource record (binary):
67 00 00 40 00 01 00 00 00 55 00 22 00 01 03 64 04 5f 64 6e 73 07 65 78 61 6d 70 6c 65 03 6f 72
6e 73 07 65 78 61 6d 70 6c 65 03 6f 72 67 00 00 67 00 00 40 00 01 00 00 00 55 00 22 00 01 03 64
01 00 03 02 63 6f ff 0a 00 04 03 64 6e 73 6e 73 07 65 78 61 6d 70 6c 65 03 6f 72 67 00 00
01 00 03 02 63 6f 00 0a 00 04 03 64 6e 73
Resource record (human-readable): Resource record (human-readable):
_dns.example.org. 85 IN SVCB 1 dns.example.org ( _dns.example.org. 85 IN SVCB 1 dns.example.org (
alpn=co docpath=dns ) alpn=co docpath=dns )
~~~
{: gi="sourcecode"}
Second, an examples for the path "/n/s" (the last 8 bytes `ff 0a 00 04 01 6e 01 73`): Second, see an example for the path "/n/s" (the last 8 bytes `00 0a 00 04 01 6e 01 73 `):
Resource record (binary): ~~~
04 5f 64 6e 73 07 65 78 61 6d 70 6c 65 03 6f 72 Resource record (binary):
67 00 00 40 00 01 00 00 06 6b 00 22 00 01 03 64 04 5f 64 6e 73 07 65 78 61 6d 70 6c 65 03 6f 72
6e 73 07 65 78 61 6d 70 6c 65 03 6f 72 67 00 00 67 00 00 40 00 01 00 00 06 6b 00 22 00 01 03 64
01 00 03 02 63 6f ff 0a 00 04 01 6e 01 73 6e 73 07 65 78 61 6d 70 6c 65 03 6f 72 67 00 00
01 00 03 02 63 6f 00 0a 00 04 01 6e 01 73
Resource record (human-readable): Resource record (human-readable):
_dns.example.org. 643 IN SVCB 1 dns.example.org ( _dns.example.org. 643 IN SVCB 1 dns.example.org (
alpn=co docpath=n,s ) alpn=co docpath=n,s )
~~~
{: gi="sourcecode"}
If the server also provides DNS over HTTPS, "dohpath" and "docpath" MAY co-exist: If the server also provides DNS over HTTPS, "dohpath" and "docpath" MAY coexist:
Resource record (binary): ~~~
04 5f 64 6e 73 07 65 78 61 6d 70 6c 65 03 6f 72 Resource record (binary):
67 00 00 40 00 01 00 00 01 ad 00 2b 00 01 03 64 04 5f 64 6e 73 07 65 78 61 6d 70 6c 65 03 6f 72
6e 73 07 65 78 61 6d 70 6c 65 03 6f 72 67 00 00 67 00 00 40 00 01 00 00 01 ad 00 2b 00 01 03 64
01 00 06 02 68 33 02 63 6f 00 07 00 07 2f 7b 3f 6e 73 07 65 78 61 6d 70 6c 65 03 6f 72 67 00 00
64 6e 73 7d ff 0a 00 00 01 00 06 02 68 33 02 63 6f 00 07 00 07 2f 7b 3f
64 6e 73 7d 00 0a 00 00
Resource record (human-readable): Resource record (human-readable):
_dns.example.org. 429 IN SVCB 1 dns.example.org ( _dns.example.org. 429 IN SVCB 1 dns.example.org (
alpn=h3,co dohpath=/{?dns} docpath ) alpn=h3,co dohpath=/{?dns} docpath )
~~~
{: gi="sourcecode"}
Basic Message Exchange Basic Message Exchange
====================== ======================
The "application/dns-message" Content-Format {#sec:content-format} The "application/dns-message" Content-Format {#sec:content-format}
-------------------------------------------- --------------------------------------------
This document defines a CoAP Content-Format identifier for the Internet This document defines a CoAP Content-Format ID for the Internet
media type "application/dns-message" to be the mnemonic 553 — based on the port assig media type "application/dns-message" to be the mnemonic 553, based on the port assign
nment of DNS. ment of DNS.
This media type is defined as in {{Section 6 of -doh}}, i.e., a single DNS message en coded in the DNS on-the-wire format {{-dns}}. This media type is defined as in {{Section 6 of -doh}}, i.e., a single DNS message en coded in the DNS on-the-wire format {{-dns}}.
Both DoC client and DoC server MUST be able to parse contents in the "application/dns -message" Content-Format. Both DoC client and DoC server MUST be able to parse contents in the "application/dns -message" Content-Format.
This document only specifies OPCODE 0 (Query) for DNS over CoAP messages. This document only specifies OPCODE 0 (Query) for DNS over CoAP messages.
Future documents can provide considerations for additional OPCODEs or extend its spec ification (e.g. by describing whether other CoAP codes need to be used for which OPCO DE). Future documents can provide considerations for additional OPCODEs or extend its spec ification (e.g., by describing whether other CoAP codes need to be used for which OPC ODE).
Unless another error takes precedence, a DoC server uses RCODE = 4, NotImp {{-dns}}, in its response to a query with an OPCODE that it does not implement (see also {{sec: resp-examples}}). Unless another error takes precedence, a DoC server uses RCODE = 4, NotImp {{-dns}}, in its response to a query with an OPCODE that it does not implement (see also {{sec: resp-examples}}).
DNS Queries in CoAP Requests {#sec:queries} DNS Queries in CoAP Requests {#sec:queries}
---------------------------- ----------------------------
A DoC client encodes a single DNS query in one or more CoAP request A DoC client encodes a single DNS query in one or more CoAP request
messages that use the CoAP FETCH {{-coap-fetch}} request method. messages that use the CoAP FETCH {{-coap-fetch}} request method.
Requests SHOULD include an Accept option to indicate the type of content that can be parsed in the response. Requests SHOULD include an Accept option to indicate the type of content that can be parsed in the response.
Since CoAP provides reliability at the message layer (e.g., through Confirmable messa ges) the retransmission mechanism of the Since CoAP provides reliability at the message layer (e.g., through Confirmable messa ges), the retransmission mechanism of the
DNS protocol as defined in {{-dns}} is not needed. DNS protocol as defined in {{-dns}} is not needed.
### Request Format ### Request Format
When sending a CoAP request, a DoC client MUST include the DNS query in the body of t he CoAP request. When sending a CoAP request, a DoC client MUST include the DNS query in the body of t he CoAP request.
As specified in {{Section 2.3.1 of -coap-fetch}}, the type of content of the body MUS T be indicated using the Content-Format option. As specified in {{Section 2.3.1 of -coap-fetch}}, the type of content of the body MUS T be indicated using the Content-Format option.
This document specifies the usage of Content-Format "application/dns-message" (for de tails, see {{sec:content-format}}). This document specifies the usage of Content-Format "application/dns-message" (for de tails, see {{sec:content-format}}).
### Support of CoAP Caching {#sec:req-caching} ### Support of CoAP Caching {#sec:req-caching}
The DoC client SHOULD set the ID field of the DNS header to 0 to enable a CoAP cache <!--[rfced] We note that "Cache-Key" appears as "cache key" in RFC
(e.g., a CoAP proxy en-route) to respond to the same DNS queries with a cache entry. 8132. Would you like to match use in RFC 8132?
Original:
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.
Perhaps:
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.
-->
The DoC client SHOULD set the ID field of the DNS header 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 {{-coap-fetch, Section 2}}) does not change when multiple DNS queries for the same DNS data, carried in CoAP requests, are issue d. This ensures that the CoAP Cache-Key (see {{-coap-fetch, Section 2}}) does not change when multiple DNS queries for the same DNS data, carried in CoAP requests, are issue d.
Apart from losing these caching benefits, there is no harm it not setting it to 0, e. g., when the query was received from somewhere else. Apart from losing these caching benefits, there is no harm in not setting it to 0, e. g., when the query was received from somewhere else.
In any instance, a DoC server MUST copy the ID from the query in its response to that query. In any instance, a DoC server MUST copy the ID from the query in its response to that query.
### Example {#sec:req-examples} ### Example {#sec:req-examples}
The following example illustrates the usage of a CoAP message to 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 resolve "example.org. IN AAAA" based on the URI "coaps://\[2001:db8::1\]/". The
CoAP body is encoded in the "application/dns-message" Content-Format. CoAP body is encoded in the "application/dns-message" Content-Format.
FETCH coaps://[2001:db8::1]/ ~~~
Content-Format: 553 (application/dns-message) FETCH coaps://[2001:db8::1]/
Accept: 553 (application/dns-message) Content-Format: 553 (application/dns-message)
Payload (binary): Accept: 553 (application/dns-message)
00 00 01 00 00 01 00 00 00 00 00 00 07 65 78 61 Payload (binary):
6d 70 6c 65 03 6f 72 67 00 00 1c 00 01 00 00 01 00 00 01 00 00 00 00 00 00 07 65 78 61
6d 70 6c 65 03 6f 72 67 00 00 1c 00 01
Payload (human-readable): Payload (human-readable):
;; ->>Header<<- opcode: QUERY, status: NOERROR, id: 0 ;; ->>Header<<- opcode: QUERY, status: NOERROR, id: 0
;; flags: rd; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0 ;; flags: rd; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION: ;; QUESTION SECTION:
;example.org. IN AAAA ;example.org. IN AAAA
~~~
{: gi="sourcecode"}
DNS Responses in CoAP Responses DNS Responses in CoAP Responses
------------------------------- -------------------------------
Each DNS query-response pair is mapped to a CoAP request-response operation. Each DNS query-response pair is mapped to a CoAP request-response operation.
DNS responses are provided in the body of the CoAP response, i.e., it is also possibl e to transfer them using block-wise transfer {{-coap-blockwise}}. DNS responses are provided in the body of the CoAP response, i.e., it is also possibl e to transfer them using block-wise transfer {{-coap-blockwise}}.
A DoC server MUST be able to produce responses in the "application/dns-message" A DoC server MUST be able to produce responses in the "application/dns-message"
Content-Format (for details, see {{sec:content-format}}) when requested. Content-Format (for details, see {{sec:content-format}}) when requested.
The use of the Accept option in the request is optional. The use of the Accept option in the request is optional.
However, all DoC clients MUST be able to parse a "application/dns-message" response ( see also {{sec:content-format}}). However, all DoC clients MUST be able to parse an "application/dns-message" response (see also {{sec:content-format}}).
Any response Content-Format other than "application/dns-message" MUST be indicated wi th Any response Content-Format other than "application/dns-message" MUST be indicated wi th
the Content-Format option by the DoC server. the Content-Format option by the DoC server.
### Response Codes and Handling DNS and CoAP errors {#sec:resp-codes} ### Response Codes and Handling DNS and CoAP Errors {#sec:resp-codes}
A DNS response indicates either success or failure in the RCODE of the DNS header (se e {{-dns}}). A DNS response indicates either success or failure in the RCODE of the DNS header (se e {{-dns}}).
It is RECOMMENDED that CoAP responses that carry a parseable DNS response use a 2.05 (Content) response code. It is RECOMMENDED that CoAP responses that carry a parsable DNS response use a 2.05 ( Content) response code.
CoAP responses using non-successful response codes MUST NOT contain a DNS response CoAP responses using non-successful response codes MUST NOT contain a DNS response
and MUST only be used for errors in the CoAP layer or when a request does not and MUST only be used for errors in the CoAP layer or when a request does not
fulfill the requirements of the DoC protocol. fulfill the requirements of the DoC protocol.
Communication errors with an upstream DNS server (e.g., timeouts) MUST be indicated b y including a DNS response with the appropriate RCODE in a successful CoAP response, i.e., using a 2.xx response code. Communication errors with an upstream DNS server (e.g., timeouts) MUST be indicated b y including a DNS response with the appropriate RCODE in a successful CoAP response, i.e., using a 2.xx response code.
When an error occurs at the CoAP layer, e.g., if an unexpected request method or an u nsupported Content-Format in the request are used, the DoC server SHOULD respond with an appropriate CoAP error. When an error occurs at the CoAP layer, e.g., if an unexpected request method or an u nsupported Content-Format in the request are used, the DoC server SHOULD respond with an appropriate CoAP error.
A DoC client might try to repeat a non-successful exchange unless otherwise prohibite d. A DoC client might try to repeat a non-successful exchange unless otherwise prohibite d.
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. 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.
### Support of CoAP Caching {#sec:resp-caching} ### Support of CoAP Caching {#sec:resp-caching}
For reliability and energy saving measures, content decoupling (such as en-route cach ing on proxies) takes a far greater role than it does in HTTP. For reliability and energy-saving measures, content decoupling (such as en-route cach ing on proxies) takes a far greater role than it does in HTTP.
Likewise, CoAP makes it possible to use cache validation to refresh stale cache entri es to reduce the number of large response messages. Likewise, CoAP makes it possible to use cache validation to refresh stale cache entri es to reduce the number of large response messages.
For cache validation, CoAP implementations regularly use hashing over the message con tent for ETag generation (see {{-coap, Section 5.10.6}}). For cache validation, CoAP implementations regularly use hashing over the message con tent for ETag generation (see {{-coap, Section 5.10.6}}).
As such, the approach to guarantee the same cache key for DNS responses as proposed i n DoH ({{-doh, Section 5.1}}) is not sufficient and needs to be updated so that the T TLs in the response are more often the same regardless of query time. As such, the approach to guarantee the same cache key for DNS responses as proposed i n DoH ({{-doh, Section 5.1}}) is not sufficient and needs to be updated so that the T TLs in the response are more often the same regardless of query time.
The DoC server MUST ensure that the sum of the Max-Age value of a CoAP response and a ny TTL in the The DoC server MUST ensure that the sum of the Max-Age value of a CoAP response and a ny TTL in the
DNS response is less than or equal to the corresponding TTL received from an upstream DNS server. DNS response is less than or equal to the corresponding TTL received from an upstream DNS server.
This also includes the default Max-Age value of 60 seconds (see {{Section 5.10.5 of - coap}}) when no Max-Age option is provided. This also includes the default Max-Age value of 60 seconds (see {{Section 5.10.5 of - coap}}) when no Max-Age option is provided.
The DoC client MUST then add the Max-Age value of the carrying CoAP response to all T TLs in a DNS response on reception and use these calculated TTLs for the associated r ecords. The DoC client MUST then add the Max-Age value of the carrying CoAP response to all T TLs in a DNS response on reception and use these calculated TTLs for the associated r ecords.
The RECOMMENDED algorithm for a DoC server to meet the requirement for DoC is as foll ows: To meet the requirement for DoC, the RECOMMENDED algorithm for a DoC server is as fol lows:
Set the Max-Age option of a response to the minimum TTL of a DNS response and subtrac t this value from all TTLs of that DNS response. Set the Max-Age option of a response to the minimum TTL of a DNS response and subtrac t this value from all TTLs of that DNS response.
This prevents expired records unintentionally being served from an intermediate CoAP cache. This prevents expired records from unintentionally being served from an intermediate CoAP cache.
Additionally, if the ETag for cache validation is based on the content of the respons e, it allows that ETag not to change. Additionally, if the ETag for cache validation is based on the content of the respons e, it allows that ETag not to change.
This then remains the case even if the TTL values are updated by an upstream DNS cach e. This then remains the case even if the TTL values are updated by an upstream DNS cach e.
If only one record set per DNS response is assumed, a simplification of this algorith m is to just set all TTLs in the response to 0 and set the TTLs at the DoC client to the value of the Max-Age option. If only one record set per DNS response is assumed, a simplification of this algorith m is to just set all TTLs in the response to 0 and set the TTLs at the DoC client to the value of the Max-Age option.
If shorter caching periods are plausible, e.g., if the RCODE of the message indicates an error that should only be cached for a minimal duration, the value for the Max-Ag e option SHOULD be set accordingly. If shorter caching periods are plausible, e.g., if the RCODE of the message indicates an error that should only be cached for a minimal duration, the value for the Max-Ag e option SHOULD be set accordingly.
This value might be 0, but if the DoC server knows that the error will persist, great er values are also conceivable, depending on the projected duration of the error. This value might be 0, but if the DoC server knows that the error will persist, great er values are also conceivable, depending on the projected duration of the error.
The same applies for DNS responses that for any reason do not carry any records with a TTL. The same applies for DNS responses that, for any reason, do not carry any records wit h a TTL.
### Examples {#sec:resp-examples} ### Examples {#sec:resp-examples}
The following example illustrates the response to the query "example.org. IN The following example illustrates the response to the query "example.org. IN
AAAA record", with recursion turned on. Successful responses carry one answer AAAA record", with recursion turned on. Successful responses carry one answer
record including address 2001:db8:1:0:1:2:3:4 and TTL 79689. record including the address 2001:db8:1:0:1:2:3:4 and TTL 79689.
A successful response: A successful response:
2.05 Content ~~~
Content-Format: 553 (application/dns-message) 2.05 Content
Max-Age: 58719 Content-Format: 553 (application/dns-message)
Payload (human-readable): Max-Age: 58719
;; ->>Header<<- opcode: QUERY, status: NOERROR, id: 0 Payload (human-readable):
;; flags: qr rd ad; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0 ;; ->>Header<<- opcode: QUERY, status: NOERROR, id: 0
;; flags: qr rd ad; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION: ;; QUESTION SECTION:
;example.org. IN AAAA ;example.org. IN AAAA
;; ANSWER SECTION: ;; ANSWER SECTION:
;example.org. 79689 IN AAAA 2001:db8:1:0:1:2:3:4 ;example.org. 79689 IN AAAA 2001:db8:1:0:1:2:3:4
~~~
{: gi="sourcecode"}
When a DNS error &ndash; NxDomain (RCODE = 3) for "does.not.exist" in this case &ndas h; is noted in the DNS response, the CoAP response still indicates success. When a DNS error -- NxDomain (RCODE = 3) for "does.not.exist" in this case -- is note d in the DNS response, the CoAP response still indicates success.
2.05 Content ~~~
Content-Format: 553 (application/dns-message) 2.05 Content
Payload (human-readable): Content-Format: 553 (application/dns-message)
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 0 Payload (human-readable):
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0 ;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 0
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION: ;; QUESTION SECTION:
;does.not.exist. IN AAAA ;does.not.exist. IN AAAA
~~~
{: gi="sourcecode"}
As described in {{sec:content-format}}, a DoC server uses NotImp (RCODE = 4) if it do <!-- [rfced] Please review the text starting with "OPCODE—a DNS
es not support an OPCODE—a DNS Update (OPCODE = 5) for "example.org" in this case. Update ...". Should this be updated as follows or in some other way?
2.05 Content Original:
Content-Format: 553 (application/dns-message) As described in Section 4.1, a DoC server uses NotImp (RCODE = 4) if
Payload (human-readable): it does not support an OPCODE—a DNS Update (OPCODE = 5) for
;; ->>Header<<- opcode: UPDATE, status: NOTIMP, id: 0 "example.org" in this case.
;; flags: qr ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0
;; QUERY SECTION: Perhaps:
;example.org. IN AAAA As described in Section 4.1, a DoC server uses NotImp (RCODE = 4) if
it does not support an OPCODE - in this case, a DNS Update (OPCODE = 5) for
"example.org" is used.
-->
As described in {{sec:content-format}}, a DoC server uses NotImp (RCODE = 4) if it do
es not support an OPCODE-a DNS Update (OPCODE = 5) for "example.org" in this case.
~~~
2.05 Content
Content-Format: 553 (application/dns-message)
Payload (human-readable):
;; ->>Header<<- opcode: UPDATE, status: NOTIMP, id: 0
;; flags: qr ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0
;; QUERY SECTION:
;example.org. IN AAAA
~~~
{: gi="sourcecode"}
When an error occurs at the CoAP layer, the DoC server responds with When an error occurs at the CoAP layer, the DoC server responds with
an appropriate CoAP error, for instance 4.15 (Unsupported Content-Format) an appropriate CoAP error, for instance, 4.15 (Unsupported Content-Format)
if the Content-Format option in the request was not set to if the Content-Format option in the request was not set to
"application/dns-message" and the Content-Format is not otherwise supported by "application/dns-message" and the Content-Format is not otherwise supported by
the server. the server.
4.15 Unsupported Content-Format ~~~
[no payload] 4.15 Unsupported Content-Format
[no payload]
~~~
{: gi="sourcecode"}
Interaction with other CoAP and CoRE Features Interaction with Other CoAP and CoRE Features
============================================= =============================================
DNS Push Notifications and CoAP Observe DNS Push Notifications and CoAP Observe
--------------------------------------- ---------------------------------------
DNS Push Notifications {{-dns-push}} provides the capability to asynchronously notify clients about resource record changes. DNS Push Notifications {{-dns-push}} provide the capability to asynchronously notify clients about resource record changes.
However, it results in additional overhead, which conflicts with constrained resource s. However, it results in additional overhead, which conflicts with constrained resource s.
This is the reason why it is RECOMMENDED to use CoAP Observe {{-coap-observe}} instea d of DNS Push This is the reason why it is RECOMMENDED to use CoAP Observe {{-coap-observe}} instea d of DNS Push
in the DoC domain. in the DoC domain.
This is particularly useful if a short-lived record is requested frequently. This is particularly useful if a short-lived record is requested frequently.
The DoC server SHOULD provide Observe capabilities on its DoC resource and do as foll ows. The DoC server SHOULD provide Observe capabilities on its DoC resource and do as foll ows.
If a DoC clients wants to observe a resource record, a DoC server can respond with a If a DoC client wants to observe a resource record, a DoC server can respond with a n
notification otification
and add the client to its list of observers for that resource in accordance to {{-coa and add the client to its list of observers for that resource in accordance with {{-c
p-observe}}. oap-observe}}.
The DoC server MAY subscribe to DNS push notifications for that record. The DoC server MAY subscribe to DNS push notifications for that record.
This involves sending a DNS Subscribe message (see ({{Section 6.2 of -dns-push}}), This involves sending a DNS Subscribe message (see {{Section 6.2 of -dns-push}}),
instead of a classic DNS query to fetch the instead of a classic DNS query to fetch the
information on behalf of the DoC client. information on behalf of the DoC client.
<!--[rfced] Please clarify what "a failure to do so" refers to in the
following sentence.
Original:
As there is no CoAP observer anymore from the perspective of the
DoC server, a failure to do so cannot be communicated back to any
DoC observer.
-->
After the list of observers for a particular DNS query has become empty After the list of observers for a particular DNS query has become empty
(by explicit or implicit cancellation of the observation as per {{Section 3.6 of -coa p-observe}}), (by explicit or implicit cancellation of the observation as per {{Section 3.6 of -coa p-observe}}),
and no other reason to subscribe to that request is present, and no other reason to subscribe to that request is present,
the DoC server SHOULD cancel the corresponding subscription. the DoC server SHOULD cancel the corresponding subscription.
This can involve sending an DNS Unsubscribe message or closing the session (see {{Sec tion 6.4 of -dns-push}}). This can involve sending a DNS Unsubscribe message or closing the session (see {{Sect ion 6.4 of -dns-push}}).
As there is no CoAP observer anymore from the perspective of the DoC server, a failur e to do so cannot be communicated back to any DoC observer. As there is no CoAP observer anymore from the perspective of the DoC server, a failur e to do so cannot be communicated back to any DoC observer.
As such, error handling (if any) needs to be resolved between the DoC server and the upstream DNS infrastructure. As such, error handling (if any) needs to be resolved between the DoC server and the upstream DNS infrastructure.
Whenever the DoC server receives a DNS Push message from the DNS Whenever the DoC server receives a DNS Push message from the DNS
infrastructure for an observed resource record, the DoC server sends an appropriate O bserve notification response infrastructure for an observed resource record, the DoC server sends an appropriate O bserve notification response
to the DoC client. to the DoC client.
A server that responds with notifications (i.e., sends the Observe option) needs to h A server that responds with notifications (i.e., sends the Observe option) needs to h
ave means of obtaining current resource records. ave the means of obtaining current resource records.
This may happen through DNS Push, but also by upstream polling or implicit circumstan This may happen through DNS Push or also by upstream polling or implicit circumstance
ces (e.g., if the DoC server is the authoritative name server for the record and want s (e.g., if the DoC server is the authoritative name server for the record and wants
s to notify about changes). to notify about changes).
OSCORE OSCORE
------ ------
It is RECOMMENDED to carry DNS messages protected using OSCORE {{-oscore}} between th e DoC client It is RECOMMENDED to carry DNS messages protected using OSCORE {{-oscore}} between th e DoC client
and the DoC server. The establishment and maintenance of the OSCORE Security Context is out of the and the DoC server. The establishment and maintenance of the OSCORE security context is out of the
scope of this document. scope of this document.
{{-cachable-oscore}} describes a method to allow cache retrieval of OSCORE responses and discusses {{I-D.amsuess-core-cachable-oscore}} describes a method to allow cache retrieval of O SCORE responses and discusses
the corresponding implications on message sizes and security properties. the corresponding implications on message sizes and security properties.
Mapping DoC to DoH Mapping DoC to DoH
------------------ ------------------
This document provides no specification on how to map between DoC and DoH, e.g., at a This document provides no specification on how to map between DoC and DoH, e.g., at a
CoAP-to-HTTP-proxy; such a direct mapping is NOT RECOMMENDED: CoAP-to-HTTP proxy. Such a direct mapping is NOT RECOMMENDED:
rewriting the FETCH method ({{sec:queries}}) and the TTL rewriting ({{sec:resp-cachin Rewriting the FETCH method ({{sec:queries}}) and TTL ({{sec:resp-caching}}) as
g}}) as specified in this document would be non-trivial.
specified in this draft would be non-trivial.
It is RECOMMENDED to use a DNS forwarder to map between DoC and DoH, as would be the case for It is RECOMMENDED to use a DNS forwarder to map between DoC and DoH, as would be the case for
mapping between any other pair of DNS transports. mapping between any other pair of DNS transports.
Considerations for Unprotected Use {#sec:unprotected-coap} Considerations for Unprotected Use {#sec:unprotected-coap}
================================== ==================================
The use of DoC without confidentiality and integrity protection is NOT RECOMMENDED. The use of DoC without confidentiality and integrity protection is NOT RECOMMENDED.
Without secure communication, many possible attacks need to be evaluated in the conte xt of Without secure communication, many possible attacks need to be evaluated in the conte xt of
the application's threat model. the application's threat model.
This includes known threats for unprotected DNS {{-dns-threats}} {{-dns-privacy}} and CoAP {{Section 11 of -coap}}. This includes known threats for unprotected DNS {{-dns-threats}} {{-dns-privacy}} and CoAP ({{Section 11 of -coap}}).
While DoC does not use the random ID of the DNS header (see {{sec:req-caching}}), equ ivalent protection against off-path poisoning attacks is achieved by using random lar ge token values for unprotected CoAP requests. While DoC does not use the random ID of the DNS header (see {{sec:req-caching}}), equ ivalent protection against off-path poisoning attacks is achieved by using random lar ge token values for unprotected CoAP requests.
If a DoC message is unprotected it MUST use a random token of at least 2 bytes length If a DoC message is unprotected, it MUST use a random token with a length of at least
to mitigate this kind of poisoning attack. 2 bytes to mitigate this kind of poisoning attack.
Implementation Status
=====================
{::boilerplate rfc7942}
[^remove-impl-status]
[^remove-impl-status]: RFC Ed.: Please remove this section before publication. When d
eleting this
section, please also remove RFC7942 from the references of this document.
DoC Client
The authors of this document provide a [DoC client implementation available
in the IoT operating system RIOT][gcoap_dns].
Level of maturity:
: production
Version compatibility:
: draft-ietf-core-dns-over-coap-13
License:
: LGPL-2.1
Contact information:
: `Martine S. Lenders <martine.lenders@tu-dresden.de>`
Last update of this information:
: September 2024
DoC Server
The authors of this document provide a [DoC server implementation in
Python][aiodnsprox].
Level of maturity:
: production
Version compatibility:
: draft-ietf-core-dns-over-coap-13
License:
: MIT
Contact information:
: `Martine S. Lenders <martine.lenders@tu-dresden.de>`
Last update of this information:
: September 2024
Security Considerations Security Considerations
======================= =======================
General CoAP security considerations ({{RFC7252, Section 11}}) apply to DoC. General CoAP security considerations ({{RFC7252, Section 11}}) apply to DoC.
DoC also inherits the security considerations of the protocols used for secure commun ication, e.g., OSCORE ({{-oscore, Section 12}}) as well as DTLS 1.2 or newer ({{-dtls 12, Section 5}} {{-dtls13, Section 11}}). DoC also inherits the security considerations of the protocols used for secure commun ication, e.g., OSCORE ({{-oscore, Section 12}}) as well as DTLS 1.2 or newer ({{-dtls 12, Section 5}} and {{-dtls13, Section 11}}).
Additionally, DoC uses request patterns that require the maintenance of long-lived se curity Additionally, DoC uses request patterns that require the maintenance of long-lived se curity
contexts. contexts.
{{Section 2.6 of -core-corrclar}} provides insights on what can be done when those ar e resumed from a new endpoint. {{Section 2.6 of I-D.ietf-core-corr-clar}} provides insights on what can be done when those are resumed from a new endpoint.
Though DTLS v1.2 {{-dtls12}} was obsoleteted by DTLS v1.3 {{-dtls13}} there are still many CoAP Though DTLS v1.2 {{-dtls12}} was obsoleted by DTLS v1.3 {{-dtls13}}, there are many C oAP
implementations that still use v1.2 at the time of writing. implementations that still use v1.2 at the time of writing.
As such, this document also accounts for the usage of DTLS v1.2 even though newer ver sions are As such, this document also accounts for the usage of DTLS v1.2 even though newer ver sions are
RECOMMENDED when using DTLS to secure CoAP. RECOMMENDED when using DTLS to secure CoAP.
When using unprotected CoAP (see {{sec:unprotected-coap}}), setting the ID of a DNS m essage to 0 as When using unprotected CoAP (see {{sec:unprotected-coap}}), setting the ID of a DNS m essage to 0 as
specified in {{sec:req-caching}} opens the DNS cache of a DoC client to cache poisoni ng attacks specified in {{sec:req-caching}} opens the DNS cache of a DoC client to cache poisoni ng attacks
via response spoofing. via response spoofing.
This document requires an unpredictable CoAP token in each DoC query from the client when CoAP is This document requires an unpredictable CoAP token in each DoC query from the client when CoAP is
not secured to mitigate such an attack over DoC (see {{sec:unprotected-coap}}). not secured to mitigate such an attack over DoC (see {{sec:unprotected-coap}}).
For secure communication via (D)TLS or OSCORE, an unpredictable ID against spoofing i <!--[rfced] FYI: We added "to protect" to this sentence for
s not necessary. clarity. Please let us know if it changes the intended meaning.
Original:
For secure communication via (D)TLS or OSCORE, an unpredictable ID
against spoofing is not necessary.
Updated:
For secure communication via (D)TLS or OSCORE, an unpredictable ID
to protect against spoofing is not necessary.
-->
For secure communication via (D)TLS or OSCORE, an unpredictable ID to protect against
spoofing is not necessary.
Both (D)TLS and OSCORE offer mechanisms to harden against injecting spoofed responses in their protocol design. Both (D)TLS and OSCORE offer mechanisms to harden against injecting spoofed responses in their protocol design.
Consequently, the ID of the DNS message can be set to 0 without any concern in order to leverage the advantages of CoAP caching. Consequently, the ID of the DNS message can be set to 0 without any concern in order to leverage the advantages of CoAP caching.
A DoC client must be aware that the DoC server A DoC client must be aware that the DoC server
may communicate unprotected with the upstream DNS infrastructure, e.g., using DNS ove r UDP. may communicate unprotected with the upstream DNS infrastructure, e.g., using DNS ove r UDP.
DoC can only guarantee confidentiality and integrity of communication between parties for which the DoC can only guarantee confidentiality and integrity of communication between parties for which the
security context is exchanged. security context is exchanged.
The DoC server may use another security context to communicate upstream with both con fidentiality and integrity The DoC server may use another security context to communicate upstream with both con fidentiality and integrity
(e.g., DNS over QUIC {{-doq}}), but, while recommended, this is opaque to the DoC cli ent on the protocol level. (e.g., DNS over QUIC {{-doq}}); however, while recommended, this is opaque to the DoC client on the protocol level.
Record integrity can also be ensured upstream using DNSSEC {{-dnssec}}. Record integrity can also be ensured upstream using DNSSEC {{-dnssec}}.
A DoC client may not be able to perform DNSSEC validation, A DoC client may not be able to perform DNSSEC validation,
e.g., due to code size constraints, or due to the size of the responses. e.g., due to code size constraints or the size of the responses.
It may trust its DoC server to perform DNSSEC validation; It may trust its DoC server to perform DNSSEC validation;
how that trust is expressed is out of the scope of this document. how that trust is expressed is out of the scope of this document.
For instance, a DoC client may be, configured to use a particular credential by which it recognizes an eligible DoC server. For instance, a DoC client may be configured to use a particular credential by which it recognizes an eligible DoC server.
That information can also imply trust in the DNSSEC validation by that DoC server. That information can also imply trust in the DNSSEC validation by that DoC server.
IANA Considerations IANA Considerations
=================== ===================
[^replace-xxxx]
[^replace-xxxx]: RFC Ed.: throughout this section, please replace
RFC-XXXX with the RFC number of this specification and remove this
note.
This document has the following actions for IANA.
CoAP Content-Formats Registry CoAP Content-Formats Registry
----------------------------- -----------------------------
IANA is requested to assign a CoAP Content-Format ID for the "application/dns-message IANA has assigned a CoAP Content-Format ID for the "application/dns-message" media
" media type in the "CoAP Content-Formats" registry in the "Constrained RESTful Environments
type in the "CoAP Content-Formats" registry, within the "Constrained RESTful Environm (CoRE) Parameters"
ents (CoRE) Parameters" registry group {{-coap}}; this corresponds to the "application/dns-message" media
registry group {{-coap}}, corresponding to the "application/dns-message" media
type from the "Media Types" registry (see {{-doh}}). type from the "Media Types" registry (see {{-doh}}).
Content Type: application/dns-message | Content Type | ID | Reference |
| ------------ | -------- | ---------------------------------- |
Content Coding: - | application/dns-message | 553 | {{-doh}} and RFC 9953, {{sec:content-format}}
|
ID: 553 (suggested) {: #tab-coap-content-format title="CoAP Content-Format ID"}
Reference: {{-doh}} and \[RFC-XXXX\], {{sec:content-format}}
DNS Service Bindings (SVCB) Registry DNS SVBC Service Parameter Keys (SvcParamKeys) Registry
------------------------------------ ------------------------------------
IANA is requested to add the following entry to the "Service Parameter Keys (SvcParam Keys)" registry within the "DNS Service Bindings (SVCB)" registry group. IANA has added the following entry to the "DNS SVCB Service Parameter Keys (SvcParamK eys)" registry in the "DNS Service Bindings (SVCB)" registry group.
The definition of this parameter can be found in {{sec:doc-server-selection}}. The definition of this parameter can be found in {{sec:doc-server-selection}}.
| Number | Name | Meaning | Change Controller | Reference | | Number | Name | Meaning | Change Controller | Reference |
| ------- | -------------- | ---------------------------------- | ----------------- | --------------- | | ------- | -------------- | ---------------------------------- | ----------------- | --------------- |
| 10 (suggested) | docpath | DNS over CoAP resource path | IETF | \[RFC-XX | 10 | docpath | DNS over CoAP resource path | IETF | RFC 9953, {{sec:doc-
XX\], {{sec:doc-server-selection}} | server-selection}} |
{: #tab-svc-param-keys title="Values for SvcParamKeys"} {: #tab-svc-param-keys title="Value for SvcParamKeys"}
Resource Type (rt=) Link Target Attribute Values Registry Resource Type (rt=) Link Target Attribute Values Registry
--------------------------------------------------------- ---------------------------------------------------------
IANA is requested to add a new Resource Type (rt=) Link Target Attribute "core.dns" IANA has added "core.dns" to the "Resource Type (rt=) Link Target Attribute Values" r
to the "Resource Type (rt=) Link Target Attribute Values" registry within the "Constr egistry in the "Constrained RESTful Environments (CoRE) Parameters" registry group.
ained RESTful Environments (CoRE) Parameters" registry group.
Value: core.dns
Description: DNS over CoAP resource.
Reference: \[RFC-XXXX\], {{sec:doc-server-selection}} | Value | Description | Reference |
| ------------ | ------------ | --------------- |
| core.dns | DNS over CoAP resource | RFC 9953, {{sec:doc-server-selectio
n}} |
{: #tab-resource-type title="Resource Type (rt=) Link Target Attribute"}
Operational Considerations Operational Considerations
========================== ==========================
## Co-existence of different DNS and CoAP transports ## Coexistence of Different DNS and CoAP Transports
Many DNS transports may co-exist on the DoC server, such as DNS over UDP {{-dns}}, DN S over (D)TLS {{-dot}} {{-dodtls}}, DNS over HTTPS {{-doh}}, or DNS over QUIC {{-doq} }. Many DNS transports may coexist on the DoC server, such as DNS over UDP {{-dns}}, DNS over (D)TLS {{-dot}} {{-dodtls}}, DNS over HTTPS {{-doh}}, or DNS over QUIC {{-doq}} .
In principle, transports employing channel or object security should be preferred. In principle, transports employing channel or object security should be preferred.
In constrained scenarios, DNS over CoAP is preferable to DNS over DTLS. In constrained scenarios, DNS over CoAP is preferable to DNS over DTLS.
The final decision regarding the preference, however, heavily depends on the use case and is therefore left to the implementers or users and is not defined in this docume nt. The final decision regarding the preference, however, heavily depends on the use case and is therefore left to the implementers or users and is not defined in this docume nt.
CoAP supports Confirmable and Non-Confirmable messages {{-coap}} to deploy different levels of reliability. CoAP supports Confirmable and Non-Confirmable messages {{-coap}} to deploy different levels of reliability.
This document, however, does not enforce any of these message types, as the decision on which one is appropriate depends on the characteristics of the network where DoC i s deployed. However, this document does not enforce any of these message types, as the decision o n which one is appropriate depends on the characteristics of the network where DoC is deployed.
## Redirects ## Redirects
Application-layer redirects (e.g., HTTP) redirct a client to a new server. Application-layer redirects (e.g., HTTP) redirect a client to a new server.
In the case of DoC, this leads to a new DNS server. In the case of DoC, this leads to a new DNS server.
This new DNS server may provide different answers to the same DNS query than the prev ious DNS server. This new DNS server may provide different answers to the same DNS query than the prev ious DNS server.
At the time of writing, CoAP does not support redirection. At the time of writing, CoAP does not support redirection.
Future specifications of CoAP redirect may need to consider the impact of different r esults between previous and new DNS server. Future specifications of CoAP redirect may need to consider the impact of different r esults between previous and new DNS servers.
## Proxy Hop-Limit ## Proxy Hop Limit
Mistakes might lead to CoAP proxies forming infinite loops. Mistakes might lead to CoAP proxies forming infinite loops.
Using the CoAP Hop-Limit option {{-coap-hop-limit}} mitigates such loops. Using the CoAP Hop-Limit option {{-coap-hop-limit}} mitigates such loops.
## Error Handling ## Error Handling
{{sec:resp-codes}} specifies that DNS operational errors should be reported back to a DoC client {{sec:resp-codes}} specifies that DNS operational errors should be reported back to a DoC client
using the appropriate DNS RCODE. using the appropriate DNS RCODE.
If a DoC client did not receive any successful DNS message from a DoC server for a wh ile, it might If a DoC client did not receive any successful DNS messages from a DoC server for a w hile, it might
indicate that the DoC server lost connectivity to the upstream DNS infrastructure. indicate that the DoC server lost connectivity to the upstream DNS infrastructure.
The DoC client should handle this error case like a recursive resolver that lost conn ectivity to the upstream DNS infrastructure. The DoC client should handle this error case like a recursive resolver that lost conn ectivity to the upstream DNS infrastructure.
In case of CoAP errors, the usual mechanisms for CoAP response codes apply. In case of CoAP errors, the usual mechanisms for CoAP response codes apply.
## DNS Extensions ## DNS Extensions
DNS extensions that are specific to the choice of transport, such as {{?RFC7828}}, ar e not applicable to DoC. DNS extensions that are specific to the choice of transport, such as described in {{? RFC7828}}, are not applicable to DoC.
--- back --- back
Evaluation {#sec:evaluation} Evaluation {#sec:evaluation}
========== ==========
The authors of this document presented the design, implementation, and analysis of Do C in their The authors of this document presented the design, implementation, and analysis of Do C in their
paper "Securing Name Resolution in the IoT: DNS over CoAP" {{DoC-paper}}. paper "Securing Name Resolution in the IoT: DNS over CoAP" {{DoC-paper}}.
Change Log <!-- [rfced] FYI: We removed the change log, which included a
========== reference to RFC 2136. If RFC 2136 should be mentioned elsewhere in
the running text, please let us know.
[^remove-changelog] -->
[^remove-changelog]: RFC Ed.: Please remove this section before publication.
Since [draft-ietf-core-dns-over-coap-18]
- Address Address Mohamed Boucadair's COMMENT:
- Add Operational Considerations Section
- Make SVCB references normative
- Remove redundant requirement on parsing application/dns-message
- Remove contradicting statement and outdated reference about ALPN
- Add DNS client to Fig. 1
- Clarify recursion termination in the CoAP realm
- Clarify where addresses are coming from with DDR/DNR
- Address Gorry Fairhurst's follow-up DISCUSS:
- Refer to Observe terminology in Section 2
- Clarify registration
- Provide alternative observation examples
- Clarify that error handling is in the hands of the DoC server
Since [draft-ietf-core-dns-over-coap-17]
- Address Roman Danyliw's COMMENT:
- Remove unused RFC8742 reference
- Address Vladimír Čunát's DNSDIR review
- Address Éric Vyncke' COMMENT:
- Mention OPCODE 0 in Abstract and Introduction
- Reference to STD13 instead of RFC1035
- Provide extension pointers for future documents on other OPCODES
- Use only singular for example section if there is only one example
- Improvements on DNSSEC
- Hyphenate link-layer as modifier to frame
- Address Paul Wouters's DISCUSS and COMMENT:
- Remove unnecessary and confusing ad flag from query example
- Phrase full SVCB mapping sentence more neutrally
- Address Gorry Fairhurst's COMMENT:
- Add note (in addition to the `RFC Ed.:`) about paragraph removal
- Add references for "coap" and "co" ALPN to SvcParam algorithm
- Address Gorry's nits
- Address Gorry Fairhurst's DISCUSS:
- Update push notifications
- observation: Do not use normative language
- Address Orie Steele's COMMENT:
- Automatic configuration MUST only be done from a trusted source
- Remove confusing and unnecessary MAY
- Remove normative repeat of SvcParam algorithm by citing RFC 9461
- Fix wording around Accept option
- Address Deb Cooley's COMMENT:
- Group (D)TLS references
- Automatic configuration MUST only be done from a trusted source
- Fix wording about unpredictable ID and spoofing
- Remove confusing "e.g."
Since [draft-ietf-core-dns-over-coap-16]
- Mention TLS as possible protection mechanism in abstract and intro
- Fix representation format in the docpath examples
- Make docpath wire-format paragraph easier to parse
Since [draft-ietf-core-dns-over-coap-15]
- Address Genart and Artart review:
- Add editor's note about removing RFC7228 reference in case rfc7228bis comes out
before
publication
- Address minor nits
- Resolve less well-known abbreviations
- Name default ports for "coap" and "co"
- Add reasoning why we also consider DTLS v1.2 (RFC 6347)
- Add illustrative reference for ETag generation
- Address DNS SVCB SvcParamKeys IANA expert review:
- docpath: clarifications and examples
- Rework representation format and wire-format of "docpath"
- State that we don't do the full SVCB mapping
- Explicitly do not limit what port= can do.
- port limitations: We're not the SVCB mapping document
- Address Tsvart Review
- Prefer ADN for Uri-Host; don't prescribe *how* it is set
Since [draft-ietf-core-dns-over-coap-14]
- Remove superfluous and confusing step in SVCB to request algorithm
- Address AD review:
- Remove RFC8949 as CBOR diagnostic notation reference
- CoRE-specific FETCH method -> CoAP-specific FETCH method
- Remove double reference to BCP 219
- Fix wording and references around SVCB records and ALPN
- Move format description for examples to Terminology section
- Retitle section 5 to "Interaction with other CoAP and CoRE Features"
- Make prevention of poisoning attacks normative for unprotected CoAP
- Provide specs on if the SHOULD on ID=0 does not apply
- Make construction algorithm normative
- Add definition for CoRE
- General grammar, wording, and spelling cleanups
Since [draft-ietf-core-dns-over-coap-13]
- Address shepherd review
Since [draft-ietf-core-dns-over-coap-12]
- Address Esko's review
- Address Marcos's review
- Address Mikolai's review
Since [draft-ietf-core-dns-over-coap-10]
- Replace imprecise or wrong terms:
- disjunct => distinct
- unencrypted CoAP => unprotected CoAP
- security mode => confidential communication
- Pull in definition of CBOR sequences and their EDN
- Fix broken external section references
- Define terminology for "upstream DNS infrastructure" and "upstream DNS server"
- Fix wording on DNS error handling
- Clarify that any OpCode beyond 0 is not supported for now and remove now redundant
DNS Upgrade
section as a consequence
- Clarify that the DoC/DoH mapping is what is NOT RECOMMENDED
- Avoid use of undefined term “CoAP resource identifier”
- Discuss Max-Age option value in an error case
- Add human-readable format to examples
- General language check pass
Since [draft-ietf-core-dns-over-coap-09]
- Update SVCB SvcParamKey
- Update corr-clar reference
- Add reference to DNS Update [\[RFC2136\]](https://datatracker.ietf.org/doc/html/rfc
2136), clarify that it is currently not considered
- Add to security considerations: unprotected upstream DNS and DNSSEC
Since [draft-ietf-core-dns-over-coap-08]
- Update Cenk's Affiliation
Since [draft-ietf-core-dns-over-coap-07]
- Address IANA early review #1368678
- Update normative reference to CoAP over DTLS alpn SvcParam
- Add missing DTLSv1.2 reference
- Security considerations: Point into corr-clar-future
- Implementation Status: Update to current version
Since [draft-ietf-core-dns-over-coap-06]
- Add "docpath" SVCB ParamKey definition
- IANA fixes
+ Use new column names (see Errata 4954)
+ Add reference to RFC 8484 for application/dns-message Media Type
+ IANA: unify self references
Since [draft-ietf-core-dns-over-coap-05] <!--[rfced] We note that "draft-amsuess-core-cachable-oscore" is
- Add references to relevant SVCB/DNR RFCs and drafts expired and has been replaced by "draft-ietf-core-cacheable-oscore".
May we replace the current entry below with the entry for
"draft-ietf-core-cacheable-oscore"?
Since [draft-ietf-core-dns-over-coap-04] Current:
- Add note on cacheable OSCORE [I-D.amsuess-core-cachable-oscore]
- Address early IANA review Amsüss, C. and M. Tiloca, "Cacheable OSCORE", Work in Progress,
Internet-Draft, draft-amsuess-core-cachable-oscore-11, 6 July 2025,
<https://datatracker.ietf.org/doc/html/draft-amsuess-core-cachable-
oscore-11>.
Since [draft-ietf-core-dns-over-coap-03] Perhaps:
- Amended Introduction with short contextualization of constrained environments [CACHABLE-OSCORE]
- Add {{sec:evaluation}} on evaluation Amsüss, C. and M. Tiloca, "Cacheable OSCORE", Work in
Progress, Internet-Draft, draft-ietf-core-cacheable-
oscore-00, 22 September 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-core-
cacheable-oscore-00>.
-->
Since [draft-ietf-core-dns-over-coap-02] <!--[rfced] Sourcecode and artwork
- Move implementation details to Implementation Status (in accordance with {{RFC7942} a) Some lines in Figure 1 are too long for the TXT output. This figure is
}) marked as artwork, so it needs to have a width of 72 characters or less. How
- Recommend root path to keep the CoAP options small may we revise this figure to fit these parameters? We tested removing some
- Set Content-Format for application/dns-message to 553 space in the figure; please check out the following test files and let us know
- SVCB/DNR: Move to Server Selection Section but leave TBD based on DNSOP discussion if this would work (see TXT file for ascii art and HTML for SVG). If not, please
for now provide an updated figure.
- Clarify that DoC and DoH are distinct
- Clarify mapping between DoC and DoH
- Update considerations on unprotected use
- Don't call OSCORE end-to-end encrypted
Since [draft-ietf-core-dns-over-coap-01] Test files:
https://www.rfc-editor.org/authors/rfc9953test.md
https://www.rfc-editor.org/authors/rfc9953test.txt
https://www.rfc-editor.org/authors/rfc9953test.html
- Specify DoC server role in terms of DNS terminology b) We have updated the blocks in Sections 3.2, 3.2.1, 4.2.3, and 4.3.3 to be
- Clarify communication of DoC to DNS infrastructure is agnostic of the transport marked as sourcecode. We set the type for the block in Section 3.2 as "abnf"
- Add subsection on how to implement DNS Push in DoC (i.e., "~~~ abnf"). Please let us know if the type should be set for the other
- Add appendix on reference implementation sourcecode blocks. For example, should the ones in Section 3.2.1 be marked as
type "dns-rr"? If the current list of preferred values (see link below) does
not contain an applicable type, feel free to let us know. Also, it is
acceptable to leave the type not set.
Since [draft-ietf-core-dns-over-coap-00] List of sourcecode types:
https://www.rfc-editor.org/rpc/wiki/doku.php?id=sourcecode-types
- SVGify ASCII art c) The blocks in Section 4.3.3 are too long for the TXT output. We marked
- Move section on "DoC Server Considerations" (was Section 5.1) to its own draft these as sourcecode, so they should have a width of 69 characters or less. The
([draft-lenders-dns-cns]) long lines are currently 70 characters. Would moving all the lines with
- Replace layer violating statement for CON with statement of fact semicolons over to the left one space (in just this section or in all the
- Add security considerations on ID=0 sourcecode in the document) be a good solution? We tried this in the test
files listed above so you can see what the output will look like. Feel free to
offer other suggestions as well.
-->
Since [draft-lenders-dns-over-coap-04] <!--[rfced] Please review the "Inclusive Language" portion of the online
Style Guide <https://www.rfc-editor.org/styleguide/part2/#inclusive_language>
and let us know if any changes are needed. Updates of this nature typically
result in more precise language, which is helpful for readers.
- Removed change log of draft-lenders-dns-over-coap Note that our script did not flag any words in particular, but this should
still be reviewed as a best practice.
-->
# Acknowledgments # Acknowledgments
{:unnumbered} {:unnumbered}
The authors of this document want to thank Mike Bishop, Carsten Bormann, Mohamed Bouc adair, Deb Cooley, Vladimír Čunát, Roman Danyliw, Elwyn B. Davies, Esko Dijk, Gorry F airhurst, Thomas Fossati, Mikolai Gütschow, Todd Herr, Tommy Pauly, Jan Romann, Ben S chwartz, Orie Steele, Marco Tiloca, Éric Vyncke, Tim Wicinski, and Paul Wouters for t heir feedback and comments. The authors of this document want to thank {{{Mike Bishop}}}, {{{Carsten Bormann}}}, {{{Mohamed Boucadair}}}, {{{Deb Cooley}}}, {{{Vladimír Čunát}}}, {{{Roman Danyliw}}}, {{{Elwyn B. Davies}}}, {{{Esko Dijk}}}, {{{Gorry Fairhurst}}}, {{{Thomas Fossati}}}, {{{Mikolai Gütschow}}}, {{{Todd Herr}}}, {{{Tommy Pauly}}}, {{{Jan Romann}}}, {{{Ben Schwartz}}}, {{{Orie Steele}}}, {{{Marco Tiloca}}}, {{{Éric Vyncke}}}, {{{Tim Wicins ki}}}, and {{{Paul Wouters}}} for their feedback and comments.
[draft-ietf-core-dns-over-coap-18]: https://datatracker.ietf.org/doc/html/draft-ietf- core-dns-over-coap-18 [draft-ietf-core-dns-over-coap-18]: https://datatracker.ietf.org/doc/html/draft-ietf- core-dns-over-coap-18
[draft-ietf-core-dns-over-coap-17]: https://datatracker.ietf.org/doc/html/draft-ietf- core-dns-over-coap-17 [draft-ietf-core-dns-over-coap-17]: https://datatracker.ietf.org/doc/html/draft-ietf- core-dns-over-coap-17
[draft-ietf-core-dns-over-coap-16]: https://datatracker.ietf.org/doc/html/draft-ietf- core-dns-over-coap-16 [draft-ietf-core-dns-over-coap-16]: https://datatracker.ietf.org/doc/html/draft-ietf- core-dns-over-coap-16
[draft-ietf-core-dns-over-coap-15]: https://datatracker.ietf.org/doc/html/draft-ietf- core-dns-over-coap-15 [draft-ietf-core-dns-over-coap-15]: https://datatracker.ietf.org/doc/html/draft-ietf- core-dns-over-coap-15
[draft-ietf-core-dns-over-coap-14]: https://datatracker.ietf.org/doc/html/draft-ietf- core-dns-over-coap-14 [draft-ietf-core-dns-over-coap-14]: https://datatracker.ietf.org/doc/html/draft-ietf- core-dns-over-coap-14
[draft-ietf-core-dns-over-coap-13]: https://datatracker.ietf.org/doc/html/draft-ietf- core-dns-over-coap-13 [draft-ietf-core-dns-over-coap-13]: https://datatracker.ietf.org/doc/html/draft-ietf- core-dns-over-coap-13
[draft-ietf-core-dns-over-coap-12]: https://datatracker.ietf.org/doc/html/draft-ietf- core-dns-over-coap-12 [draft-ietf-core-dns-over-coap-12]: https://datatracker.ietf.org/doc/html/draft-ietf- core-dns-over-coap-12
[draft-ietf-core-dns-over-coap-10]: https://datatracker.ietf.org/doc/html/draft-ietf- core-dns-over-coap-10 [draft-ietf-core-dns-over-coap-10]: https://datatracker.ietf.org/doc/html/draft-ietf- core-dns-over-coap-10
[draft-ietf-core-dns-over-coap-09]: https://datatracker.ietf.org/doc/html/draft-ietf- core-dns-over-coap-09 [draft-ietf-core-dns-over-coap-09]: https://datatracker.ietf.org/doc/html/draft-ietf- core-dns-over-coap-09
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