rfc9953.original   rfc9953.txt 
CoRE M. S. Lenders Internet Engineering Task Force (IETF) M. S. Lenders
Internet-Draft TU Dresden Request for Comments: 9953 TU Dresden
Intended status: Standards Track C. Amsüss Category: Standards Track C. Amsüss
Expires: 20 March 2026 ISSN: 2070-1721
C. Gündoğan C. Gündoğan
NeuralAgent GmbH NeuralAgent GmbH
T. C. Schmidt T. C. Schmidt
HAW Hamburg HAW Hamburg
M. Wählisch M. Wählisch
TU Dresden & Barkhausen Institut TU Dresden & Barkhausen Institut
16 September 2025 March 2026
DNS over CoAP (DoC) DNS over the Constrained Application Protocol (DoC)
draft-ietf-core-dns-over-coap-20
Abstract Abstract
This document defines a protocol for exchanging DNS queries (OPCODE This document defines a protocol for exchanging DNS queries (OPCODE
0) over the Constrained Application Protocol (CoAP). These CoAP 0) over the Constrained Application Protocol (CoAP). These CoAP
messages can be protected by (D)TLS-Secured CoAP (CoAPS) or Object messages can be protected by (D)TLS-Secured CoAP (CoAPS) or Object
Security for Constrained RESTful Environments (OSCORE) to provide Security for Constrained RESTful Environments (OSCORE) to provide
encrypted DNS message exchange for constrained devices in the encrypted DNS message exchange for constrained devices in the
Internet of Things (IoT). Internet of Things (IoT).
About This Document
This note is to be removed before publishing as an RFC.
The latest revision of this draft can be found at https://core-
wg.github.io/draft-dns-over-coap/draft-ietf-core-dns-over-coap.html.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-ietf-core-dns-over-coap/.
Discussion of this document takes place on the CoRE Working Group
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Source for this draft and an issue tracker can be found at
https://github.com/core-wg/draft-dns-over-coap.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on 20 March 2026. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9953.
Copyright Notice Copyright Notice
Copyright (c) 2025 IETF Trust and the persons identified as the Copyright (c) 2026 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction
2. Terminology and Conventions . . . . . . . . . . . . . . . . . 5 2. Terminology and Conventions
3. Selection of a DoC Server . . . . . . . . . . . . . . . . . . 6 3. Selection of a DoC Server
3.1. Discovery by Resource Type . . . . . . . . . . . . . . . 7 3.1. Discovery by Resource Type
3.2. Discovery using SVCB Resource Records or DNR . . . . . . 7 3.2. Discovery Using SVCB Resource Records or DNR
3.2.1. Examples . . . . . . . . . . . . . . . . . . . . . . 9 3.2.1. Examples
4. Basic Message Exchange . . . . . . . . . . . . . . . . . . . 11 4. Basic Message Exchange
4.1. The "application/dns-message" Content-Format . . . . . . 11 4.1. The "application/dns-message" Content-Format
4.2. DNS Queries in CoAP Requests . . . . . . . . . . . . . . 11 4.2. DNS Queries in CoAP Requests
4.2.1. Request Format . . . . . . . . . . . . . . . . . . . 11 4.2.1. Request Format
4.2.2. Support of CoAP Caching . . . . . . . . . . . . . . . 12 4.2.2. Support of CoAP Caching
4.2.3. Example . . . . . . . . . . . . . . . . . . . . . . . 12 4.2.3. Example
4.3. DNS Responses in CoAP Responses . . . . . . . . . . . . . 12 4.3. DNS Responses in CoAP Responses
4.3.1. Response Codes and Handling DNS and CoAP errors . . . 13 4.3.1. Response Codes and Handling DNS and CoAP Errors
4.3.2. Support of CoAP Caching . . . . . . . . . . . . . . . 13 4.3.2. Support of CoAP Caching
4.3.3. Examples . . . . . . . . . . . . . . . . . . . . . . 14 4.3.3. Examples
5. Interaction with other CoAP and CoRE Features . . . . . . . . 15 5. Interaction with Other CoAP and CoRE Features
5.1. DNS Push Notifications and CoAP Observe . . . . . . . . . 15 5.1. DNS Push Notifications and CoAP Observe
5.2. OSCORE . . . . . . . . . . . . . . . . . . . . . . . . . 16 5.2. OSCORE
5.3. Mapping DoC to DoH . . . . . . . . . . . . . . . . . . . 16 5.3. Mapping DoC to DoH
6. Considerations for Unprotected Use
6. Considerations for Unprotected Use . . . . . . . . . . . . . 17 7. Security Considerations
7. Implementation Status . . . . . . . . . . . . . . . . . . . . 17 8. IANA Considerations
7.1. DoC Client . . . . . . . . . . . . . . . . . . . . . . . 17 8.1. CoAP Content-Formats Registry
7.2. DoC Server . . . . . . . . . . . . . . . . . . . . . . . 18 8.2. DNS SVBC Service Parameter Keys (SvcParamKeys) Registry
8. Security Considerations . . . . . . . . . . . . . . . . . . . 18 8.3. Resource Type (rt=) Link Target Attribute Values Registry
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 9. Operational Considerations
9.1. CoAP Content-Formats Registry . . . . . . . . . . . . . . 19 9.1. Coexistence of Different DNS and CoAP Transports
9.2. DNS Service Bindings (SVCB) Registry . . . . . . . . . . 20 9.2. Redirects
9.3. Resource Type (rt=) Link Target Attribute Values 9.3. Proxy Hop Limit
Registry . . . . . . . . . . . . . . . . . . . . . . . . 20 9.4. Error Handling
10. Operational Considerations . . . . . . . . . . . . . . . . . 20 9.5. DNS Extensions
10.1. Co-existence of different DNS and CoAP transports . . . 20 10. References
10.2. Redirects . . . . . . . . . . . . . . . . . . . . . . . 21 10.1. Normative References
10.3. Proxy Hop-Limit . . . . . . . . . . . . . . . . . . . . 21 10.2. Informative References
10.4. Error Handling . . . . . . . . . . . . . . . . . . . . . 21 Appendix A. Evaluation
10.5. DNS Extensions . . . . . . . . . . . . . . . . . . . . . 21 Acknowledgments
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 21 Authors' Addresses
11.1. Normative References . . . . . . . . . . . . . . . . . . 21
11.2. Informative References . . . . . . . . . . . . . . . . . 24
Appendix A. Evaluation . . . . . . . . . . . . . . . . . . . . . 26
Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 27
B.1. Since draft-ietf-core-dns-over-coap-18 . . . . . . . . . 27
B.2. Since draft-ietf-core-dns-over-coap-17 . . . . . . . . . 27
B.3. Since draft-ietf-core-dns-over-coap-16 . . . . . . . . . 29
B.4. Since draft-ietf-core-dns-over-coap-15 . . . . . . . . . 29
B.5. Since draft-ietf-core-dns-over-coap-14 . . . . . . . . . 30
B.6. Since draft-ietf-core-dns-over-coap-13 . . . . . . . . . 30
B.7. Since draft-ietf-core-dns-over-coap-12 . . . . . . . . . 30
B.8. Since draft-ietf-core-dns-over-coap-10 . . . . . . . . . 31
B.9. Since draft-ietf-core-dns-over-coap-09 . . . . . . . . . 31
B.10. Since draft-ietf-core-dns-over-coap-08 . . . . . . . . . 32
B.11. Since draft-ietf-core-dns-over-coap-07 . . . . . . . . . 32
B.12. Since draft-ietf-core-dns-over-coap-06 . . . . . . . . . 32
B.13. Since draft-ietf-core-dns-over-coap-05 . . . . . . . . . 32
B.14. Since draft-ietf-core-dns-over-coap-04 . . . . . . . . . 33
B.15. Since draft-ietf-core-dns-over-coap-03 . . . . . . . . . 33
B.16. Since draft-ietf-core-dns-over-coap-02 . . . . . . . . . 33
B.17. Since draft-ietf-core-dns-over-coap-01 . . . . . . . . . 33
B.18. Since draft-ietf-core-dns-over-coap-00 . . . . . . . . . 34
B.19. Since draft-lenders-dns-over-coap-04 . . . . . . . . . . 34
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34
1. Introduction 1. 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
[STD13] queries and get DNS responses over the Constrained [STD13] queries and get DNS responses over the Constrained
Application Protocol (CoAP) [RFC7252] using OPCODE 0 (Query). Each Application Protocol (CoAP) [RFC7252] using OPCODE 0 (Query). Each
DNS query-response pair is mapped into a CoAP message exchange. Each DNS query-response pair is mapped into a CoAP message exchange. Each
CoAP message can be secured by DTLS 1.2 or newer [RFC6347] [RFC9147] CoAP message can be secured by DTLS 1.2 or newer [RFC6347] [RFC9147]
as well as Object Security for Constrained RESTful Environments as well as Object Security for Constrained RESTful Environments
(OSCORE) [RFC8613] but also TLS 1.3 or newer [RFC8323] [RFC8446] to (OSCORE) [RFC8613] and TLS 1.3 or newer [RFC8323] [RFC8446] to ensure
ensure message integrity and confidentiality. message integrity and confidentiality.
The application use case of DoC is inspired by DNS over HTTPS The application use case of DoC is inspired by DNS over HTTPS (DoH)
[RFC8484] (DoH). DoC, however, aims for deployment in the [RFC8484]. However, DoC aims for deployment in the constrained
constrained Internet of Things (IoT), which usually conflicts with Internet of Things (IoT), which usually conflicts with the
the requirements introduced by HTTPS. Constrained IoT devices may be requirements introduced by HTTPS. Constrained IoT devices may be
restricted in memory, power consumption, link-layer frame sizes, restricted in memory, power consumption, link-layer frame sizes,
throughput, and latency. They may only have a handful kilobytes of throughput, and latency. They may only have a handful kilobytes of
both RAM and ROM. They may sleep for long durations of time, after both RAM and ROM. They may sleep for long durations of time, after
which they need to refresh the named resources they know about. Name which they need to refresh the named resources they know about. Name
resolution in such scenarios must take into account link layer frame resolution in such scenarios must take into account link-layer frame
sizes of only a few hundred bytes, bit rates in the magnitude of sizes of only a few hundred bytes, bit rates in the magnitude of
kilobits per second, and latencies of several seconds [RFC7228] kilobits per second, and latencies of several seconds [RFC7228]
[I-D.ietf-iotops-7228bis] [RFC7228bis].
// RFC Ed.: Please remove the [RFC7228] 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 In order not to be burdened by the resource requirements of TCP and
HTTPS, constrained IoT devices could use DNS over DTLS [RFC8094]. In HTTPS, constrained IoT devices could use DNS over DTLS [RFC8094]. In
contrast to DNS over DTLS, DoC can take advantage of CoAP features to contrast to DNS over DTLS, DoC can take advantage of CoAP features to
mitigate drawbacks of datagram-based communication. These features mitigate drawbacks of datagram-based communication. These features
include: block-wise transfer [RFC7959], which solves the Path MTU include (1) block-wise transfer [RFC7959], which solves the Path MTU
problem of DNS over DTLS (see [RFC8094], Section 5); CoAP proxies, problem of DNS over DTLS (see [RFC8094], Section 5), (2) CoAP
which provide an additional level of caching; re-use of data proxies, which provide an additional level of caching, and (3) reuse
structures for application traffic and DNS information, which saves of data structures for application traffic and DNS information, which
memory on constrained devices. saves memory on constrained devices.
To avoid the resource requirements of DTLS or TLS on top of UDP To avoid the resource requirements of DTLS or TLS on top of UDP
(e.g., introduced by DNS over DTLS [RFC8094] or DNS over QUIC (e.g., introduced by DNS over DTLS [RFC8094] or DNS over QUIC
[RFC9250]), DoC allows for lightweight message protection based on [RFC9250]), DoC allows for lightweight message protection based on
OSCORE. OSCORE.
. 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/...----'
Figure 1: Basic DoC architecture Figure 1: Basic DoC Architecture
The most important components of DoC can be seen in Figure 1: a DoC The most important components of DoC can be seen in Figure 1: a DoC
client tries to resolve DNS information by sending DNS queries client tries to resolve DNS information by sending DNS queries
carried within CoAP requests to a DoC server. That DoC server can be carried within CoAP requests to a DoC server. That DoC server can be
the authoritive name server for the queried record or a DNS client the authoritative name server for the queried record or a DNS client
(i.e., a stub or recursive resolver) that resolves DNS information by (i.e., a stub or recursive resolver) that resolves DNS information by
using other DNS transports such as DNS over UDP [STD13], DNS over using other DNS transports such as DNS over UDP [STD13], DNS over
HTTPS [RFC8484], or DNS over QUIC [RFC9250] when communicating with HTTPS [RFC8484], or DNS over QUIC [RFC9250] when communicating with
the upstream DNS infrastructure. Using that information, the DoC the upstream DNS infrastructure. Using that information, the DoC
server then replies to the queries of the DoC client with DNS server then replies to the queries of the DoC client with DNS
responses carried within CoAP responses. A DoC server MAY also serve responses carried within CoAP responses. A DoC server MAY also serve
as DNSSEC validator to provide DNSSEC validation to the more 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- Note that this specification is distinct from DoH because the CoAP-
specific FETCH method [RFC8132] is used. This has the benefit of specific FETCH method [RFC8132] is used. A benefit of using this
having the DNS query in the body as when using the POST method, but method is having the DNS query in the body such as when using the
still with the same caching advantages of responses to requests that POST method, but with the same caching advantages of responses to
use the GET method. Having the DNS query in the body means that we requests that use the GET method. Having the DNS query in the body
do not need extra base64 encoding, which would increase code means that there is no need for extra base64 encoding, which would
complexity and message sizes. Also, this allows for the block-wise increase code complexity and message sizes. Also, this allows for
transfer of queries [RFC7959]. the block-wise transfer of queries [RFC7959].
2. Terminology and Conventions 2. Terminology and Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
A server that provides the service specified in this document is A server that provides the service specified in this document is
called a "DoC server" to differentiate it from a classic "DNS called a "DoC server" to differentiate it from a classic "DNS
server". A DoC server acts either as a DNS stub resolver or a DNS server". A DoC server acts as either a DNS stub resolver or a DNS
recursive resolver [BCP219]. As such, the DoC server communicates recursive resolver [BCP219]. As such, the DoC server communicates
with an "upstream DNS infrastructure" or a single "upstream DNS with an "upstream DNS infrastructure" or a single "upstream DNS
server". A "DoC resource" is a CoAP resource [RFC7252] at the DoC server". A "DoC resource" is a CoAP resource [RFC7252] at the DoC
server that DoC clients can target to send a DNS query in a CoAP server that DoC clients can target in order to send a DNS query in a
request. 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 the
DNS information is called a "DoC client". DNS information is called a "DoC client".
The term "constrained nodes" is used as defined in [RFC7228]. The term "constrained nodes" is used as defined in [RFC7228].
[RFC6690] describes that "Constrained RESTful Environments (CoRE)" [RFC6690] describes that Constrained RESTful Environments (CoRE)
realize the Representational State Transfer (REST) architecture realize the Representational State Transfer (REST) architecture
[REST] in a suitable form for such constrained nodes. [REST] in a suitable form for such constrained nodes.
A DoC server can provide Observe capabilities as defined in A DoC server can provide Observe capabilities as defined in
[RFC7641], Section 1.2. As part of that, it administers a "list of [RFC7641], Section 1.2. As part of that, it administers a "list of
observers". DoC clients using these capabilities are "observers" as observers". DoC clients using these capabilities are "observers" as
defined in [RFC7641], Section 1.2 in that case. A "notification" is defined in [RFC7641], Section 1.2. A "notification" is a CoAP
a CoAP response message with an Observe option, see [RFC7641], response message with an Observe option; see [RFC7641], Section 4.2.
Section 4.2.
The terms "payload" and "body" are used as defined in [RFC7959], The terms "payload" and "body" are used as defined in [RFC7959],
Section 2. Note that, when block-wise transfer is not used, the Section 2. Note that, when block-wise transfer is not used, the
terms "payload" and "body" are to be understood as equal. terms "payload" and "body" are to be understood as equal.
For better readability, in the examples in this document the binary In the examples in this document, the binary payload and resource
payload and resource records are shown in a hexadecimal records are shown in a hexadecimal representation as well as a human-
representation as well as a human-readable format. In the actual readable format for better readability. However, in the actual
message sent and received, however, they are encoded in the binary message sent and received, they are encoded in the binary message
message format defined in [STD13]. format defined in [STD13].
3. Selection of a DoC Server 3. Selection of a DoC Server
While there is no path specified for the DoC resource, it is While there is no path specified for the DoC resource, it is
RECOMMENDED to use the root path "/" to keep the CoAP requests small. RECOMMENDED to use the root path "/" to keep the CoAP requests small.
The DoC client needs to know the DoC server and the DoC resource at 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 the DoC server. Possible options to assure this could be (1) manual
configuration of a Uniform Resource Identifier (URI) [RFC3986] or configuration of a Uniform Resource Identifier (URI) [RFC3986] or
Constrained Resource Identifier (CRI) [I-D.ietf-core-href], or Constrained Resource Identifier (CRI) [CRI] or (2) automatic
automatic configuration, e.g., using a CoRE resource directory configuration, e.g., using a CoRE resource directory [RFC9176], DHCP
[RFC9176], DHCP or Router Advertisement options [RFC9463], or or Router Advertisement options [RFC9463], or discovery of designated
discovery of designated resolvers [RFC9462]. Automatic configuration resolvers [RFC9462]. Automatic configuration MUST only be done from
MUST only be done from a trusted source. a trusted source.
3.1. Discovery by Resource Type 3.1. Discovery by Resource Type
For discovery of the DoC resource through a link mechanism that For discovery of the DoC resource through a link mechanism that
allows describing a resource type (e.g., the Resource Type attribute allows describing a resource type (e.g., the Resource Type attribute
in [RFC6690]), this document introduces the resource type "core.dns". in [RFC6690]), this document introduces the resource type "core.dns".
It can be used to identify a generic DNS resolver that is available It can be used to identify a generic DNS resolver that is available
to the client. to the client.
3.2. Discovery using SVCB Resource Records or DNR 3.2. Discovery Using SVCB Resource Records or DNR
A DoC server can also be discovered using Service Binding (SVCB) A DoC server can also be discovered using Service Binding (SVCB)
Resource Records (RR) [RFC9460] [RFC9461] resolved via another DNS Resource Records (RRs) [RFC9460] [RFC9461] resolved via another DNS
service (e.g., provided by an unencrypted local resolver) or service (e.g., provided by an unencrypted local resolver) or
Discovery of Network-designated Resolvers (DNR) Service Parameters Discovery of Network-designated Resolvers (DNR) Service Parameters
[RFC9463] via DHCP or Router Advertisements. [RFC8323] defines the [RFC9463] via DHCP or Router Advertisements. [RFC8323] defines the
Application-Layer Protocol Negotiation (ALPN) ID for CoAP over TLS Application-Layer Protocol Negotiation (ALPN) ID for CoAP over TLS
servers and [I-D.ietf-core-coap-dtls-alpn] defines the ALPN ID for servers and [PRE-RFC9952] defines the ALPN ID for CoAP over DTLS
CoAP over DTLS servers. DoC servers that use only OSCORE [RFC8613] servers. DoC servers that use only OSCORE [RFC8613] and Ephemeral
and Ephemeral Diffie-Hellman Over COSE (EDHOC) [RFC9528] (with COSE Diffie-Hellman Over COSE (EDHOC) [RFC9528] (COSE stands for "Concise
abbreviating "Concise Binary Object Notation (CBOR) Object Signing Binary Object Notation (CBOR) Object Signing and Encryption"
and Encryption" [RFC9052]) to support security cannot be discovered [RFC9052]) to support security cannot be discovered using these SVCB
using these SVCB RR or DNR mechanisms. Specifying an alternate RR or DNR mechanisms. Specifying an alternate discovery mechanism is
discovery mechanism is out of scope of this document. out of the scope of this document.
This document is not an SVCB mapping document for the CoAP schemes as This document is not an SVCB mapping document for the CoAP schemes as
defined in Section 2.4.3 of [RFC9460]. A full SVCB mapping is defined in Section 2.4.3 of [RFC9460]. A full SVCB mapping is
specified in [I-D.ietf-core-transport-indication]. It generalizes specified in [TRANSPORT-IND]. It generalizes mechanisms for all CoAP
mechanisms for all CoAP services. This document introduces only the services. This document introduces only the discovery of DoC
discovery of DoC services. services.
This document specifies "docpath" as a single-valued SvcParamKey that This document specifies "docpath" as a single-valued Service
is mandatory for DoC SVCB records. If the "docpath" SvcParamKey is Parameter Key (SvcParamKey) that is mandatory for DoC SVCB records.
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 The docpath is divided up into segments of the absolute path to the
DoC resource (docpath-segment), each a sequence of 1-255 octets. In DoC resource (docpath-segment), each a sequence of 1-255 octets. In
ABNF [RFC5234]: ABNF [RFC5234]:
docpath-segment = 1*255OCTET docpath-segment = 1*255OCTET
Note that this restricts the length of each docpath-segment to at Note that this restricts the length of each docpath-segment to at
most 255 octets. Paths with longer segments cannot be advertised most 255 octets. Paths with longer segments cannot be advertised
with the "docpath" SvcParam and are thus NOT RECOMMENDED for the path with the "docpath" SvcParam and are thus NOT RECOMMENDED for the path
to the DoC resource. to the DoC resource.
The presentation format value of "docpath" SHALL be a comma-separated The presentation format value of "docpath" SHALL be a comma-separated
list (Appendix A.1 of [RFC9460]) of 0 or more docpath-segments. The list (Appendix A.1 of [RFC9460]) of 0 or more docpath-segments. The
root path "/" is represented by 0 docpath-segments, i.e., an empty root path "/" is represented by 0 docpath-segments, i.e., an empty
list. The same considerations for the "," and "" characters in list. The same considerations apply for the "," and "" characters in
docpath-segments for zone-file implementations as for the alpn-ids in docpath-segments for zone-file implementations and the alpn-ids in an
an "alpn" SvcParam apply (Section 7.1.1 of [RFC9460]). "alpn" SvcParam (Section 7.1.1 of [RFC9460]).
The wire-format value for "docpath" consists of 0 or more sequences The wire-format value for "docpath" consists of 0 or more sequences
of octets prefixed by their respective length as a single octet. We of octets prefixed by their respective length as a single octet. We
call this single octet the length octet. The length octet and the call this single octet the length octet. The length octet and the
corresponding sequence form a length-value pair. These length-value corresponding sequence form a length-value pair. These length-value
pairs are concatenated to form the SvcParamValue. These pairs MUST pairs are concatenated to form the SvcParamValue. These pairs MUST
exactly fill the SvcParamValue; otherwise, the SvcParamValue is exactly fill the SvcParamValue; otherwise, the SvcParamValue is
malformed. Each such length-value pair represents one segment of the malformed. Each such length-value pair represents one segment of the
absolute path to the DoC resource. The root path "/" is represented absolute path to the DoC resource. The root path "/" is represented
by 0 length-value pairs, i.e., SvcParamValue length 0. by 0 length-value pairs, i.e., SvcParamValue length 0.
Note that this format uses the same encoding as the "alpn" SvcParam Note that this format uses the same encoding as the "alpn" SvcParam,
and can reuse the decoders and encoders for that SvcParam with the and it can reuse the decoders and encoders for that SvcParam with the
adaption that a length of zero is allowed. As long as each docpath- adaption that a length of zero is allowed. As long as each docpath-
segment is of length 0 and 24 octets, it is easily transferred into 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 the path representation in CRIs [CRI] by masking each length octet
length octet with the CBOR text string major type 3 (0x60 as an with the CBOR text string major type 3 (0x60 as an octet; see
octet, see [RFC8949]). Furthermore, it is easily transferable into a [RFC8949]). Furthermore, it is easily transferable into a sequence
sequence of CoAP Uri-Path options by mapping each length octet into of CoAP Uri-Path options by mapping each length octet into the Option
the Option Delta and Option Length of the corresponding CoAP Uri-Path Delta and Option Length of the corresponding CoAP Uri-Path option,
option, provided the docpath-segments are all of a length between 0 provided the docpath-segments are all of a length between 0 and 12
and 12 octets (see [RFC7252], Section 3.1). Likewise, it can be octets (see [RFC7252], Section 3.1). Likewise, it can be transferred
transferred into a URI path-abempty form by replacing each length into a URI path-abempty form by replacing each length octet with the
octet with the "/" character None of the abovementioned prevent "/" character None of the abovementioned prevent longer docpath-
longer docpath-segments than the considered, they just make the segments than the considered, they just make the translation harder,
translation harder, as they require to make space for the longer as they require to make space for the longer delimiters, in turn
delimiters, in turn requiring to move octets. requiring to move octets.
To use the service binding from an SVCB RR or DNR Encrypted DNS To use the service binding from an SVCB RR or DNR Encrypted DNS
option, the DoC client MUST send a DoC request constructed from the option, the DoC client MUST send a DoC request constructed from the
SvcParams including "docpath". The construction algorithm for DoC SvcParams including "docpath". The construction algorithm for DoC
requests is as follows, going through the provided records in order requests is as follows, going through the provided records in order
of their priority. For the purposes of this algorithm, the DoC of their priority. For the purposes of this algorithm, the DoC
client is assumed to be SVCB-optional (see Section 3 of [RFC9460]). client is assumed to be SVCB-optional (see Section 3 of [RFC9460]).
* If the "alpn" SvcParam value for the service is "coap", a CoAP * If the "alpn" SvcParam value for the service is "coap", a CoAP
request for CoAP over TLS MUST be constructed [RFC8323]. If it is request for CoAP over TLS MUST be constructed [RFC8323]. If it is
"co", a CoAP request for CoAP over DTLS MUST be constructed "co", a CoAP request for CoAP over DTLS MUST be constructed
[I-D.ietf-core-coap-dtls-alpn]. Any other SvcParamKeys specifying [PRE-RFC9952]. Any other SvcParamKeys specifying a transport are
a transport are out of the scope of this document. out of the scope of this document.
* The destination address for the request SHOULD be taken from * The destination address for the request SHOULD be taken from
additional information about the target. This may include (1) A additional information about the target. This may include (1) A
or AAAA RRs associated with the target name and delivered with the or AAAA RRs associated with the target name and delivered with the
SVCB RR (see [RFC9462]), (2) "ipv4hint" or "ipv6hint" SvcParams SVCB RR (see [RFC9462]), (2) "ipv4hint" or "ipv6hint" SvcParams
from the SVCB RR (see [RFC9461]), or (3) from IPv4 or IPv6 from the SVCB RR (see [RFC9461]), or (3) from IPv4 or IPv6
addresses provided if DNR [RFC9463] is used. As a fallback, an addresses provided if DNR [RFC9463] is used. As a fallback, an
address MAY be queried for the target name of the SVCB record from address MAY be queried for the target name of the SVCB record from
another DNS service. another DNS service.
* The destination port for the request MUST be taken from the "port" * The destination port for the request MUST be taken from the "port"
SvcParam value, if present. Otherwise, take the default port of SvcParam value, if present. Otherwise, take the default port of
the CoAP transport, e.g., with regards to this specification TCP the CoAP transport, e.g., with regards to this specification, the
port 5684 for "coap" or UDP port 5684 for "co". This document default is TCP port 5684 for "coap" or UDP port 5684 for "co".
introduces no limitations on the ports that can be used. If a This document introduces no limitations on the ports that can be
malicious SVCB record allows its originator to influence message used. If a malicious SVCB record allows its originator to
payloads, Section 12 of [RFC9460] recommends placing such influence message payloads, Section 12 of [RFC9460] recommends
restrictions in the SVCB mapping document. The records used in placing such restrictions in the SVCB mapping document. The
this document only infuence the Uri-Path option. That option is records used in this document only influence the Uri-Path option.
only sent in the plaintext of an encrytped (D)TLS channel, and That option is only sent in the plaintext of an encrypted (D)TLS
thus does not warrant any limitations. channel and thus does not warrant any limitations.
* The request URI's hostname component MUST be the Authentication * The request URI's hostname component MUST be the Authentication
Domain Name (ADN) when obtained through DNR and MUST be the target Domain Name (ADN) when obtained through DNR and MUST be the target
name of the SVCB record when obtained through a _dns query (if name of the SVCB record when obtained through a _dns query (if
AliasMode is used, to the target name of the AliasMode record). AliasMode is used to the target name of the AliasMode record).
This can be achieved efficiently by setting that name in TLS This can be achieved efficiently by setting that name in TLS
Server Name Indication (SNI) [RFC8446], or by setting the Uri-Host Server Name Indication (SNI) [RFC8446] or by setting the Uri-Host
option on each request. option on each request.
* For each element in the CBOR sequence of the "docpath" SvcParam * For each element in the CBOR sequence of the "docpath" SvcParam
value, a Uri-Path option MUST be added to the request. value, a Uri-Path option MUST be added to the request.
* If the request constructed this way receives a response, the same * If the request constructed this way receives a response, the same
SVCB record MUST be used for construction of future DoC queries. SVCB record MUST be used for construction of future DoC queries.
If not, or if the endpoint becomes unreachable, the algorithm If not, or if the endpoint becomes unreachable, the algorithm
repeats with the SVCB RR or DNR Encrypted DNS option with the next 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 highest Service Priority as a fallback (see Sections 2.4.1 and 3
of [RFC9460]). of [RFC9460]).
A more generalized construction algorithm for any CoAP request can be A more generalized construction algorithm for any CoAP request can be
found in [I-D.ietf-core-transport-indication]. found in [TRANSPORT-IND].
3.2.1. Examples 3.2.1. Examples
// RFC Ed.: Since the number for "docpath" was not assigned at the
// time of writing, we used the hex ff 0a (in decimal 65290; from the
// private use range of SvcParamKeys) throughout this section.
// Before publication, please replace ff 0a with the hexadecimal
// representation of the final value assigned by IANA in this
// section. Please remove this paragraph after that.
A typical SVCB resource record response for a DoC server at the root A typical SVCB resource record response for a DoC server at the root
path "/" of the server looks like the following (the "docpath" path "/" of the server looks like the following (the "docpath"
SvcParam is the last 4 bytes ff 0a 00 00 in the binary): SvcParam is the last 4 bytes 00 0a 00 00 in the binary):
Resource record (binary): Resource record (binary):
04 5f 64 6e 73 07 65 78 61 6d 70 6c 65 03 6f 72 04 5f 64 6e 73 07 65 78 61 6d 70 6c 65 03 6f 72
67 00 00 40 00 01 00 00 06 28 00 1e 00 01 03 64 67 00 00 40 00 01 00 00 06 28 00 1e 00 01 03 64
6e 73 07 65 78 61 6d 70 6c 65 03 6f 72 67 00 00 6e 73 07 65 78 61 6d 70 6c 65 03 6f 72 67 00 00
01 00 03 02 63 6f ff 0a 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 )
The root path is RECOMMENDED but not required. Here are two examples The root path is RECOMMENDED but not required. Here are two examples
where the "docpath" represents paths of varying depth. First, "/dns" where the "docpath" represents paths of varying depth. First, "/dns"
is provided in the following example (the last 8 bytes ff 0a 00 04 03 is provided in the following example (the last 8 bytes 00 0a 00 04 03
64 6e 73): 64 6e 73):
Resource record (binary): Resource record (binary):
04 5f 64 6e 73 07 65 78 61 6d 70 6c 65 03 6f 72 04 5f 64 6e 73 07 65 78 61 6d 70 6c 65 03 6f 72
67 00 00 40 00 01 00 00 00 55 00 22 00 01 03 64 67 00 00 40 00 01 00 00 00 55 00 22 00 01 03 64
6e 73 07 65 78 61 6d 70 6c 65 03 6f 72 67 00 00 6e 73 07 65 78 61 6d 70 6c 65 03 6f 72 67 00 00
01 00 03 02 63 6f ff 0a 00 04 03 64 6e 73 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 )
Second, an examples for the path "/n/s" (the last 8 bytes ff 0a 00 04 Second, see an example for the path "/n/s" (the last 8 bytes 00 0a 00
01 6e 01 73): 04 01 6e 01 73):
Resource record (binary): Resource record (binary):
04 5f 64 6e 73 07 65 78 61 6d 70 6c 65 03 6f 72 04 5f 64 6e 73 07 65 78 61 6d 70 6c 65 03 6f 72
67 00 00 40 00 01 00 00 06 6b 00 22 00 01 03 64 67 00 00 40 00 01 00 00 06 6b 00 22 00 01 03 64
6e 73 07 65 78 61 6d 70 6c 65 03 6f 72 67 00 00 6e 73 07 65 78 61 6d 70 6c 65 03 6f 72 67 00 00
01 00 03 02 63 6f ff 0a 00 04 01 6e 01 73 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 )
If the server also provides DNS over HTTPS, "dohpath" and "docpath" If the server also provides DNS over HTTPS, "dohpath" and "docpath"
MAY co-exist: MAY coexist:
Resource record (binary): Resource record (binary):
04 5f 64 6e 73 07 65 78 61 6d 70 6c 65 03 6f 72 04 5f 64 6e 73 07 65 78 61 6d 70 6c 65 03 6f 72
67 00 00 40 00 01 00 00 01 ad 00 2b 00 01 03 64 67 00 00 40 00 01 00 00 01 ad 00 2b 00 01 03 64
6e 73 07 65 78 61 6d 70 6c 65 03 6f 72 67 00 00 6e 73 07 65 78 61 6d 70 6c 65 03 6f 72 67 00 00
01 00 06 02 68 33 02 63 6f 00 07 00 07 2f 7b 3f 01 00 06 02 68 33 02 63 6f 00 07 00 07 2f 7b 3f
64 6e 73 7d ff 0a 00 00 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 )
4. Basic Message Exchange 4. Basic Message Exchange
4.1. The "application/dns-message" Content-Format 4.1. The "application/dns-message" Content-Format
This document defines a CoAP Content-Format identifier for the This document defines a CoAP Content-Format ID for the Internet media
Internet media type "application/dns-message" to be the mnemonic 553 type "application/dns-message" to be the mnemonic 553, based on the
— based on the port assignment of DNS. This media type is defined as port assignment of DNS. This media type is defined as in Section 6
in Section 6 of [RFC8484], i.e., a single DNS message encoded in the of [RFC8484], i.e., a single DNS message encoded in the DNS on-the-
DNS on-the-wire format [STD13]. Both DoC client and DoC server MUST wire format [STD13]. Both DoC client and DoC server MUST be able to
be able to parse contents in the "application/dns-message" Content- parse contents in the "application/dns-message" Content-Format. This
Format. This document only specifies OPCODE 0 (Query) for DNS over document only specifies OPCODE 0 (Query) for DNS over CoAP messages.
CoAP messages. Future documents can provide considerations for Future documents can provide considerations for additional OPCODEs or
additional OPCODEs or extend its specification (e.g. by describing extend its specification (e.g., by describing whether other CoAP
whether other CoAP codes need to be used for which OPCODE). Unless codes need to be used for which OPCODE). Unless another error takes
another error takes precedence, a DoC server uses RCODE = 4, NotImp precedence, a DoC server uses RCODE = 4, NotImp [STD13], in its
[STD13], in its response to a query with an OPCODE that it does not response to a query with an OPCODE that it does not implement (see
implement (see also Section 4.3.3). also Section 4.3.3).
4.2. DNS Queries in CoAP Requests 4.2. DNS Queries in CoAP Requests
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 [RFC8132] request method. Requests messages that use the CoAP FETCH [RFC8132] request method. Requests
SHOULD include an Accept option to indicate the type of content that SHOULD include an Accept option to indicate the type of content that
can be parsed in the response. can be parsed in the response.
Since CoAP provides reliability at the message layer (e.g., through Since CoAP provides reliability at the message layer (e.g., through
Confirmable messages) the retransmission mechanism of the DNS Confirmable messages), the retransmission mechanism of the DNS
protocol as defined in [STD13] is not needed. protocol as defined in [STD13] is not needed.
4.2.1. Request Format 4.2.1. Request Format
When sending a CoAP request, a DoC client MUST include the DNS query When sending a CoAP request, a DoC client MUST include the DNS query
in the body of the CoAP request. As specified in Section 2.3.1 of in the body of the CoAP request. As specified in Section 2.3.1 of
[RFC8132], the type of content of the body MUST be indicated using [RFC8132], the type of content of the body MUST be indicated using
the Content-Format option. This document specifies the usage of the Content-Format option. This document specifies the usage of
Content-Format "application/dns-message" (for details, see Content-Format "application/dns-message" (for details, see
Section 4.1). Section 4.1).
4.2.2. Support of CoAP Caching 4.2.2. Support of CoAP Caching
The DoC client SHOULD set the ID field of the DNS header to 0 to 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 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 same DNS queries with a cache entry. This ensures that the CoAP
Cache-Key (see [RFC8132], Section 2) does not change when multiple Cache-Key (see [RFC8132], Section 2) does not change when multiple
DNS queries for the same DNS data, carried in CoAP requests, are DNS queries for the same DNS data, carried in CoAP requests, are
issued. Apart from losing these caching benefits, there is no harm issued. Apart from losing these caching benefits, there is no harm
it not setting it to 0, e.g., when the query was received from 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 somewhere else. In any instance, a DoC server MUST copy the ID from
the query in its response to that query. the query in its response to that query.
4.2.3. Example 4.2.3. Example
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 resolve "example.org. IN AAAA" based on the URI
"coaps://[2001:db8::1]/". The CoAP body is encoded in the "coaps://[2001:db8::1]/". The CoAP body is encoded in the
"application/dns-message" Content-Format. "application/dns-message" Content-Format.
skipping to change at page 12, line 47 skipping to change at line 498
4.3. DNS Responses in CoAP Responses 4.3. DNS Responses in CoAP Responses
Each DNS query-response pair is mapped to a CoAP request-response Each DNS query-response pair is mapped to a CoAP request-response
operation. DNS responses are provided in the body of the CoAP operation. DNS responses are provided in the body of the CoAP
response, i.e., it is also possible to transfer them using block-wise response, i.e., it is also possible to transfer them using block-wise
transfer [RFC7959]. A DoC server MUST be able to produce responses transfer [RFC7959]. A DoC server MUST be able to produce responses
in the "application/dns-message" Content-Format (for details, see in the "application/dns-message" Content-Format (for details, see
Section 4.1) when requested. The use of the Accept option in the Section 4.1) when requested. The use of the Accept option in the
request is optional. However, all DoC clients MUST be able to parse request is optional. However, all DoC clients MUST be able to parse
a "application/dns-message" response (see also Section 4.1). Any an "application/dns-message" response (see also Section 4.1). Any
response Content-Format other than "application/dns-message" MUST be response Content-Format other than "application/dns-message" MUST be
indicated with the Content-Format option by the DoC server. indicated with the Content-Format option by the DoC server.
4.3.1. Response Codes and Handling DNS and CoAP errors 4.3.1. Response Codes and Handling DNS and CoAP Errors
A DNS response indicates either success or failure in the RCODE of A DNS response indicates either success or failure in the RCODE of
the DNS header (see [STD13]). It is RECOMMENDED that CoAP responses the DNS header (see [STD13]). It is RECOMMENDED that CoAP responses
that carry a parseable DNS response use a 2.05 (Content) response that carry a parsable DNS response use a 2.05 (Content) response
code. code.
CoAP responses using non-successful response codes MUST NOT contain a 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 DNS response and MUST only be used for errors in the CoAP layer or
when a request does not fulfill the requirements of the DoC protocol. when a request does not fulfill the requirements of the DoC protocol.
Communication errors with an upstream DNS server (e.g., timeouts) Communication errors with an upstream DNS server (e.g., timeouts)
MUST be indicated by including a DNS response with the appropriate MUST be indicated by including a DNS response with the appropriate
RCODE in a successful CoAP response, i.e., using a 2.xx response 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 code. When an error occurs at the CoAP layer, e.g., if an unexpected
request method or an unsupported Content-Format in the request are request method or an unsupported Content-Format in the request are
used, the DoC server SHOULD respond with an appropriate CoAP error. used, the DoC server SHOULD respond with an appropriate CoAP error.
A DoC client might try to repeat a non-successful exchange unless A DoC client might try to repeat a non-successful exchange unless
otherwise prohibited. The DoC client might also decide to repeat a otherwise prohibited. The DoC client might also decide to repeat a
non-successful exchange with a different URI, for instance, when the non-successful exchange with a different URI, for instance, when the
response indicates an unsupported Content-Format. response indicates an unsupported Content-Format.
4.3.2. Support of CoAP Caching 4.3.2. Support of CoAP Caching
For reliability and energy saving measures, content decoupling (such For reliability and energy-saving measures, content decoupling (such
as en-route caching on proxies) takes a far greater role than it does as en-route caching on proxies) takes a far greater role than it does
in HTTP. Likewise, CoAP makes it possible to use cache validation to in HTTP. Likewise, CoAP makes it possible to use cache validation to
refresh stale cache entries to reduce the number of large response refresh stale cache entries to reduce the number of large response
messages. For cache validation, CoAP implementations regularly use messages. For cache validation, CoAP implementations regularly use
hashing over the message content for ETag generation (see [RFC7252], hashing over the message content for ETag generation (see [RFC7252],
Section 5.10.6). As such, the approach to guarantee the same cache Section 5.10.6). As such, the approach to guarantee the same cache
key for DNS responses as proposed in DoH ([RFC8484], Section 5.1) is key for DNS responses as proposed in DoH ([RFC8484], Section 5.1) is
not sufficient and needs to be updated so that the TTLs in the not sufficient and needs to be updated so that the TTLs in the
response are more often the same regardless of query time. 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 The DoC server MUST ensure that the sum of the Max-Age value of a
CoAP response and any TTL in the DNS response is less than or equal CoAP response and any TTL in the DNS response is less than or equal
to the corresponding TTL received from an upstream DNS server. This to the corresponding TTL received from an upstream DNS server. This
also includes the default Max-Age value of 60 seconds (see also includes the default Max-Age value of 60 seconds (see
Section 5.10.5 of [RFC7252]) when no Max-Age option is provided. The Section 5.10.5 of [RFC7252]) when no Max-Age option is provided. The
DoC client MUST then add the Max-Age value of the carrying CoAP DoC client MUST then add the Max-Age value of the carrying CoAP
response to all TTLs in a DNS response on reception and use these response to all TTLs in a DNS response on reception and use these
calculated TTLs for the associated records. calculated TTLs for the associated records.
The RECOMMENDED algorithm for a DoC server to meet the requirement To meet the requirement for DoC, the RECOMMENDED algorithm for a DoC
for DoC is as follows: Set the Max-Age option of a response to the server is as follows: Set the Max-Age option of a response to the
minimum TTL of a DNS response and subtract this value from all TTLs minimum TTL of a DNS response and subtract this value from all TTLs
of that DNS response. This prevents expired records unintentionally of that DNS response. This prevents expired records from
being served from an intermediate CoAP cache. Additionally, if the unintentionally being served from an intermediate CoAP cache.
ETag for cache validation is based on the content of the response, it Additionally, if the ETag for cache validation is based on the
allows that ETag not to change. This then remains the case even if content of the response, it allows that ETag not to change. This
the TTL values are updated by an upstream DNS cache. If only one then remains the case even if the TTL values are updated by an
record set per DNS response is assumed, a simplification of this upstream DNS cache. If only one record set per DNS response is
algorithm is to just set all TTLs in the response to 0 and set the assumed, a simplification of this algorithm is to just set all TTLs
TTLs at the DoC client to the value of the Max-Age option. 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 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 message indicates an error that should only be cached for a minimal
duration, the value for the Max-Age option SHOULD be set accordingly. duration, the value for the Max-Age option SHOULD be set accordingly.
This value might be 0, but if the DoC server knows that the error This value might be 0, but if the DoC server knows that the error
will persist, greater values are also conceivable, depending on the will persist, greater values are also conceivable, depending on the
projected duration of the error. The same applies for DNS responses projected duration of the error. The same applies for DNS responses
that for any reason do not carry any records with a TTL. that, for any reason, do not carry any records with a TTL.
4.3.3. Examples 4.3.3. Examples
The following example illustrates the response to the query The following example illustrates the response to the query
"example.org. IN AAAA record", with recursion turned on. Successful "example.org. IN AAAA record", with recursion turned on. Successful
responses carry one answer record including address responses carry one answer record including the address
2001:db8:1:0:1:2:3:4 and TTL 79689. 2001:db8:1:0:1:2:3:4 and TTL 79689.
A successful response: A successful response:
2.05 Content 2.05 Content
Content-Format: 553 (application/dns-message) Content-Format: 553 (application/dns-message)
Max-Age: 58719 Max-Age: 58719
Payload (human-readable): Payload (human-readable):
;; ->>Header<<- opcode: QUERY, status: NOERROR, id: 0 ;; ->>Header<<- opcode: QUERY, status: NOERROR, id: 0
;; flags: qr rd ad; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 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
When a DNS error – NxDomain (RCODE = 3) for "does.not.exist" in this When a DNS error -- NxDomain (RCODE = 3) for "does.not.exist" in this
case – is noted in the DNS response, the CoAP response still case -- is noted in the DNS response, the CoAP response still
indicates success. indicates success.
2.05 Content 2.05 Content
Content-Format: 553 (application/dns-message) Content-Format: 553 (application/dns-message)
Payload (human-readable): Payload (human-readable):
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 0 ;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 0
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 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
As described in Section 4.1, a DoC server uses NotImp (RCODE = 4) if As described in Section 4.1, a DoC server uses NotImp (RCODE = 4) if
it does not support an OPCODE—a DNS Update (OPCODE = 5) for it does not support an OPCODE-a DNS Update (OPCODE = 5) for
"example.org" in this case. "example.org" in this case.
2.05 Content 2.05 Content
Content-Format: 553 (application/dns-message) Content-Format: 553 (application/dns-message)
Payload (human-readable): Payload (human-readable):
;; ->>Header<<- opcode: UPDATE, status: NOTIMP, id: 0 ;; ->>Header<<- opcode: UPDATE, status: NOTIMP, id: 0
;; flags: qr ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0 ;; flags: qr ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0
;; QUERY SECTION: ;; QUERY SECTION:
;example.org. IN AAAA ;example.org. IN AAAA
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- an appropriate CoAP error, for instance, 4.15 (Unsupported Content-
Format) if the Content-Format option in the request was not set to Format) if the Content-Format option in the request was not set to
"application/dns-message" and the Content-Format is not otherwise "application/dns-message" and the Content-Format is not otherwise
supported by the server. supported by the server.
4.15 Unsupported Content-Format 4.15 Unsupported Content-Format
[no payload] [no payload]
5. Interaction with other CoAP and CoRE Features 5. Interaction with Other CoAP and CoRE Features
5.1. DNS Push Notifications and CoAP Observe 5.1. DNS Push Notifications and CoAP Observe
DNS Push Notifications [RFC8765] provides the capability to DNS Push Notifications [RFC8765] provide the capability to
asynchronously notify clients about resource record changes. asynchronously notify clients about resource record changes.
However, it results in additional overhead, which conflicts with However, it results in additional overhead, which conflicts with
constrained resources. This is the reason why it is RECOMMENDED to constrained resources. This is the reason why it is RECOMMENDED to
use CoAP Observe [RFC7641] instead of DNS Push in the DoC domain. use CoAP Observe [RFC7641] instead of DNS Push in the DoC domain.
This is particularly useful if a short-lived record is requested This is particularly useful if a short-lived record is requested
frequently. The DoC server SHOULD provide Observe capabilities on frequently. The DoC server SHOULD provide Observe capabilities on
its DoC resource and do as follows. its DoC resource and do as follows.
If a DoC clients wants to observe a resource record, a DoC server can If a DoC client wants to observe a resource record, a DoC server can
respond with a notification and add the client to its list of respond with a notification and add the client to its list of
observers for that resource in accordance to [RFC7641]. The DoC observers for that resource in accordance with [RFC7641]. The DoC
server MAY subscribe to DNS push notifications for that record. This server MAY subscribe to DNS push notifications for that record. This
involves sending a DNS Subscribe message (see (Section 6.2 of involves sending a DNS Subscribe message (see Section 6.2 of
[RFC8765]), instead of a classic DNS query to fetch the information [RFC8765]), instead of a classic DNS query to fetch the information
on behalf of the DoC client. on behalf of the DoC client.
After the list of observers for a particular DNS query has become After the list of observers for a particular DNS query has become
empty (by explicit or implicit cancellation of the observation as per empty (by explicit or implicit cancellation of the observation as per
Section 3.6 of [RFC7641]), and no other reason to subscribe to that Section 3.6 of [RFC7641]), and no other reason to subscribe to that
request is present, the DoC server SHOULD cancel the corresponding request is present, the DoC server SHOULD cancel the corresponding
subscription. This can involve sending an DNS Unsubscribe message or subscription. This can involve sending a DNS Unsubscribe message or
closing the session (see Section 6.4 of [RFC8765]). As there is no closing the session (see Section 6.4 of [RFC8765]). As there is no
CoAP observer anymore from the perspective of the DoC server, a CoAP observer anymore from the perspective of the DoC server, a
failure to do so cannot be communicated back to any DoC observer. As failure to do so cannot be communicated back to any DoC observer. As
such, error handling (if any) needs to be resolved between the DoC such, error handling (if any) needs to be resolved between the DoC
server and the upstream DNS infrastructure. 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 infrastructure for an observed resource record, the DoC server sends
an appropriate Observe notification response to the DoC client. an appropriate Observe notification response to the DoC client.
A server that responds with notifications (i.e., sends the Observe A server that responds with notifications (i.e., sends the Observe
option) needs to have means of obtaining current resource records. option) needs to have the means of obtaining current resource
This may happen through DNS Push, but also by upstream polling or records. This may happen through DNS Push or also by upstream
implicit circumstances (e.g., if the DoC server is the authoritative polling or implicit circumstances (e.g., if the DoC server is the
name server for the record and wants to notify about changes). authoritative name server for the record and wants to notify about
changes).
5.2. OSCORE 5.2. OSCORE
It is RECOMMENDED to carry DNS messages protected using OSCORE It is RECOMMENDED to carry DNS messages protected using OSCORE
[RFC8613] between the DoC client and the DoC server. The [RFC8613] between the DoC client and the DoC server. The
establishment and maintenance of the OSCORE Security Context is out establishment and maintenance of the OSCORE security context is out
of the scope of this document. of the scope of this document.
[I-D.amsuess-core-cachable-oscore] describes a method to allow cache [CACHABLE-OSCORE] describes a method to allow cache retrieval of
retrieval of OSCORE responses and discusses the corresponding OSCORE responses and discusses the corresponding implications on
implications on message sizes and security properties. message sizes and security properties.
5.3. Mapping DoC to DoH 5.3. Mapping DoC to DoH
This document provides no specification on how to map between DoC and 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 DoH, e.g., at a CoAP-to-HTTP proxy. Such a direct mapping is NOT
RECOMMENDED: rewriting the FETCH method (Section 4.2) and the TTL RECOMMENDED: Rewriting the FETCH method (Section 4.2) and TTL
rewriting (Section 4.3.2) as specified in this draft would be non- (Section 4.3.2) as specified in this document would be non-trivial.
trivial. It is RECOMMENDED to use a DNS forwarder to map between DoC It is RECOMMENDED to use a DNS forwarder to map between DoC and DoH,
and DoH, as would be the case for mapping between any other pair of as would be the case for mapping between any other pair of DNS
DNS transports. transports.
6. Considerations for Unprotected Use 6. Considerations for Unprotected Use
The use of DoC without confidentiality and integrity protection is The use of DoC without confidentiality and integrity protection is
NOT RECOMMENDED. Without secure communication, many possible attacks NOT RECOMMENDED. Without secure communication, many possible attacks
need to be evaluated in the context of the application's threat need to be evaluated in the context of the application's threat
model. This includes known threats for unprotected DNS [RFC3833] model. This includes known threats for unprotected DNS [RFC3833]
[RFC9076] and CoAP Section 11 of [RFC7252]. While DoC does not use [RFC9076] and CoAP (Section 11 of [RFC7252]). While DoC does not use
the random ID of the DNS header (see Section 4.2.2), equivalent the random ID of the DNS header (see Section 4.2.2), equivalent
protection against off-path poisoning attacks is achieved by using protection against off-path poisoning attacks is achieved by using
random large token values for unprotected CoAP requests. If a DoC random large token values for unprotected CoAP requests. If a DoC
message is unprotected it MUST use a random token of at least 2 bytes message is unprotected, it MUST use a random token with a length of
length to mitigate this kind of poisoning attack. at least 2 bytes to mitigate this kind of poisoning attack.
7. Implementation Status
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC7942].
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may
exist.
According to [RFC7942], "this will allow reviewers and working groups
to assign due consideration to documents that have the benefit of
running code, which may serve as evidence of valuable experimentation
and feedback that have made the implemented protocols more mature.
It is up to the individual working groups to use this information as
they see fit".
// RFC Ed.: Please remove this section before publication. When
// deleting this section, please also remove RFC7942 from the
// references of this document.
7.1. DoC Client
The authors of this document provide a DoC client implementation
available in the IoT operating system RIOT (https://doc.riot-os.org/
group__net__gcoap__dns.html).
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
7.2. DoC Server
The authors of this document provide a DoC server implementation in
Python (https://github.com/anr-bmbf-pivot/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
8. Security Considerations 7. Security Considerations
General CoAP security considerations ([RFC7252], Section 11) apply to General CoAP security considerations ([RFC7252], Section 11) apply to
DoC. DoC also inherits the security considerations of the protocols DoC. DoC also inherits the security considerations of the protocols
used for secure communication, e.g., OSCORE ([RFC8613], Section 12) used for secure communication, e.g., OSCORE ([RFC8613], Section 12)
as well as DTLS 1.2 or newer ([RFC6347], Section 5 [RFC9147], as well as DTLS 1.2 or newer ([RFC6347], Section 5 and [RFC9147],
Section 11). Additionally, DoC uses request patterns that require Section 11). Additionally, DoC uses request patterns that require
the maintenance of long-lived security contexts. Section 2.6 of the maintenance of long-lived security contexts. Section 2.6 of
[I-D.ietf-core-corr-clar] provides insights on what can be done when [CoAP-CORR-CLAR] provides insights on what can be done when those are
those are resumed from a new endpoint. resumed from a new endpoint.
Though DTLS v1.2 [RFC6347] was obsoleteted by DTLS v1.3 [RFC9147] Though DTLS v1.2 [RFC6347] was obsoleted by DTLS v1.3 [RFC9147],
there are still many CoAP implementations that still use v1.2 at the there are many CoAP implementations that still use v1.2 at the time
time of writing. As such, this document also accounts for the usage of writing. As such, this document also accounts for the usage of
of DTLS v1.2 even though newer versions are RECOMMENDED when using DTLS v1.2 even though newer versions are RECOMMENDED when using DTLS
DTLS to secure CoAP. to secure CoAP.
When using unprotected CoAP (see Section 6), setting the ID of a DNS When using unprotected CoAP (see Section 6), setting the ID of a DNS
message to 0 as specified in Section 4.2.2 opens the DNS cache of a message to 0 as specified in Section 4.2.2 opens the DNS cache of a
DoC client to cache poisoning attacks via response spoofing. This DoC client to cache poisoning attacks via response spoofing. This
document requires an unpredictable CoAP token in each DoC query from document requires an unpredictable CoAP token in each DoC query from
the client when CoAP is not secured to mitigate such an attack over the client when CoAP is not secured to mitigate such an attack over
DoC (see Section 6). DoC (see Section 6).
For secure communication via (D)TLS or OSCORE, an unpredictable ID For secure communication via (D)TLS or OSCORE, an unpredictable ID to
against spoofing is not necessary. Both (D)TLS and OSCORE offer protect against spoofing is not necessary. Both (D)TLS and OSCORE
mechanisms to harden against injecting spoofed responses in their offer mechanisms to harden against injecting spoofed responses in
protocol design. Consequently, the ID of the DNS message can be set their protocol design. Consequently, the ID of the DNS message can
to 0 without any concern in order to leverage the advantages of CoAP be set to 0 without any concern in order to leverage the advantages
caching. of CoAP caching.
A DoC client must be aware that the DoC server may communicate A DoC client must be aware that the DoC server may communicate
unprotected with the upstream DNS infrastructure, e.g., using DNS unprotected with the upstream DNS infrastructure, e.g., using DNS
over UDP. DoC can only guarantee confidentiality and integrity of over UDP. DoC can only guarantee confidentiality and integrity of
communication between parties for which the security context is communication between parties for which the security context is
exchanged. The DoC server may use another security context to exchanged. The DoC server may use another security context to
communicate upstream with both confidentiality and integrity (e.g., communicate upstream with both confidentiality and integrity (e.g.,
DNS over QUIC [RFC9250]), but, while recommended, this is opaque to DNS over QUIC [RFC9250]); however, while recommended, this is opaque
the DoC client on the protocol level. Record integrity can also be to the DoC client on the protocol level. Record integrity can also
ensured upstream using DNSSEC [BCP237]. be ensured upstream using DNSSEC [BCP237].
A DoC client may not be able to perform DNSSEC validation, e.g., due 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. It to code size constraints or the size of the responses. It may trust
may trust its DoC server to perform DNSSEC validation; how that trust its DoC server to perform DNSSEC validation; how that trust is
is expressed is out of the scope of this document. For instance, a expressed is out of the scope of this document. For instance, a DoC
DoC client may be, configured to use a particular credential by which client may be configured to use a particular credential by which it
it recognizes an eligible DoC server. That information can also recognizes an eligible DoC server. That information can also imply
imply trust in the DNSSEC validation by that DoC server. trust in the DNSSEC validation by that DoC server.
9. IANA Considerations
// 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.
9.1. CoAP Content-Formats Registry
IANA is requested to assign a CoAP Content-Format ID for the 8. IANA Considerations
"application/dns-message" media type in the "CoAP Content-Formats"
registry, within the "Constrained RESTful Environments (CoRE)
Parameters" registry group [RFC7252], corresponding to the
"application/dns-message" media type from the "Media Types" registry
(see [RFC8484]).
Content Type: application/dns-message 8.1. CoAP Content-Formats Registry
Content Coding: - IANA has assigned a CoAP Content-Format ID for the "application/dns-
message" media type in the "CoAP Content-Formats" registry in the
"Constrained RESTful Environments (CoRE) Parameters" registry group
[RFC7252]; this corresponds to the "application/dns-message" media
type from the "Media Types" registry (see [RFC8484]).
ID: 553 (suggested) +=========================+=====+===================+
Reference: [RFC8484] and [RFC-XXXX], Section 4.1 | Content Type | ID | Reference |
+=========================+=====+===================+
| application/dns-message | 553 | [RFC8484] and RFC |
| | | 9953, Section 4.1 |
+-------------------------+-----+-------------------+
9.2. DNS Service Bindings (SVCB) Registry Table 1: CoAP Content-Format ID
IANA is requested to add the following entry to the "Service 8.2. DNS SVBC Service Parameter Keys (SvcParamKeys) Registry
Parameter Keys (SvcParamKeys)" registry within the "DNS Service
Bindings (SVCB)" registry group. The definition of this parameter
can be found in Section 3.
+=============+=========+===============+============+=============+ IANA has added the following entry to the "DNS SVCB Service Parameter
| Number | Name | Meaning | Change | Reference | Keys (SvcParamKeys)" registry in the "DNS Service Bindings (SVCB)"
| | | | Controller | | registry group. The definition of this parameter can be found in
+=============+=========+===============+============+=============+ Section 3.
| 10 | docpath | DNS over CoAP | IETF | [RFC-XXXX], |
| (suggested) | | resource path | | Section 3 |
+-------------+---------+---------------+------------+-------------+
Table 1: Values for SvcParamKeys +========+=========+===============+===================+===========+
| Number | Name | Meaning | Change Controller | Reference |
+========+=========+===============+===================+===========+
| 10 | docpath | DNS over CoAP | IETF | RFC 9953, |
| | | resource path | | Section 3 |
+--------+---------+---------------+-------------------+-----------+
9.3. Resource Type (rt=) Link Target Attribute Values Registry Table 2: Value for SvcParamKeys
IANA is requested to add a new Resource Type (rt=) Link Target 8.3. Resource Type (rt=) Link Target Attribute Values Registry
Attribute "core.dns" to the "Resource Type (rt=) Link Target
Attribute Values" registry within the "Constrained RESTful
Environments (CoRE) Parameters" registry group.
Value: core.dns IANA has added "core.dns" to the "Resource Type (rt=) Link Target
Attribute Values" registry in the "Constrained RESTful Environments
(CoRE) Parameters" registry group.
Description: DNS over CoAP resource. +==========+========================+=====================+
| Value | Description | Reference |
+==========+========================+=====================+
| core.dns | DNS over CoAP resource | RFC 9953, Section 3 |
+----------+------------------------+---------------------+
Reference: [RFC-XXXX], Section 3 Table 3: Resource Type (rt=) Link Target Attribute
10. Operational Considerations 9. Operational Considerations
10.1. Co-existence of different DNS and CoAP transports 9.1. Coexistence of Different DNS and CoAP Transports
Many DNS transports may co-exist on the DoC server, such as DNS over Many DNS transports may coexist on the DoC server, such as DNS over
UDP [STD13], DNS over (D)TLS [RFC7858] [RFC8094], DNS over HTTPS UDP [STD13], DNS over (D)TLS [RFC7858] [RFC8094], DNS over HTTPS
[RFC8484], or DNS over QUIC [RFC9250]. In principle, transports [RFC8484], or DNS over QUIC [RFC9250]. In principle, transports
employing channel or object security should be preferred. In employing channel or object security should be preferred. In
constrained scenarios, DNS over CoAP is preferable to DNS over DTLS. constrained scenarios, DNS over CoAP is preferable to DNS over DTLS.
The final decision regarding the preference, however, heavily depends The final decision regarding the preference, however, heavily depends
on the use case and is therefore left to the implementers or users on the use case and is therefore left to the implementers or users
and is not defined in this document. and is not defined in this document.
CoAP supports Confirmable and Non-Confirmable messages [RFC7252] to CoAP supports Confirmable and Non-Confirmable messages [RFC7252] to
deploy different levels of reliability. This document, however, does deploy different levels of reliability. However, this document does
not enforce any of these message types, as the decision on which one not enforce any of these message types, as the decision on which one
is appropriate depends on the characteristics of the network where is appropriate depends on the characteristics of the network where
DoC is deployed. DoC is deployed.
10.2. Redirects 9.2. Redirects
Application-layer redirects (e.g., HTTP) redirct a client to a new 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. This 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 new DNS server may provide different answers to the same DNS query
than the previous DNS server. At the time of writing, CoAP does not than the previous DNS server. At the time of writing, CoAP does not
support redirection. Future specifications of CoAP redirect may need support redirection. Future specifications of CoAP redirect may need
to consider the impact of different results between previous and new to consider the impact of different results between previous and new
DNS server. DNS servers.
10.3. Proxy Hop-Limit 9.3. Proxy Hop Limit
Mistakes might lead to CoAP proxies forming infinite loops. Using Mistakes might lead to CoAP proxies forming infinite loops. Using
the CoAP Hop-Limit option [RFC8768] mitigates such loops. the CoAP Hop-Limit option [RFC8768] mitigates such loops.
10.4. Error Handling 9.4. Error Handling
Section 4.3.1 specifies that DNS operational errors should be Section 4.3.1 specifies that DNS operational errors should be
reported back to a DoC client using the appropriate DNS RCODE. If a reported back to a DoC client using the appropriate DNS RCODE. If a
DoC client did not receive any successful DNS message from a DoC DoC client did not receive any successful DNS messages from a DoC
server for a while, it might indicate that the DoC server lost server for a while, it might indicate that the DoC server lost
connectivity to the upstream DNS infrastructure. The DoC client connectivity to the upstream DNS infrastructure. The DoC client
should handle this error case like a recursive resolver that lost should handle this error case like a recursive resolver that lost
connectivity to the upstream DNS infrastructure. In case of CoAP connectivity to the upstream DNS infrastructure. In case of CoAP
errors, the usual mechanisms for CoAP response codes apply. errors, the usual mechanisms for CoAP response codes apply.
10.5. DNS Extensions 9.5. DNS Extensions
DNS extensions that are specific to the choice of transport, such as DNS extensions that are specific to the choice of transport, such as
[RFC7828], are not applicable to DoC. described in [RFC7828], are not applicable to DoC.
11. References 10. References
11.1. Normative References 10.1. Normative References
[I-D.ietf-core-coap-dtls-alpn] [PRE-RFC9952]
Lenders, M. S., Amsüss, C., Schmidt, T. C., and M. Lenders, M. S., Amsüss, C., Schmidt, T. C., and M.
Wählisch, "ALPN ID Specification for CoAP over DTLS", Work Wählisch, "The Application-Layer Protocol Negotiation
in Progress, Internet-Draft, draft-ietf-core-coap-dtls- (ALPN) ID Specification for the Constrained Application
alpn-05, 11 August 2025, Protocol (CoAP) over DTLS", RFC PRE-9952, DOI
<https://datatracker.ietf.org/doc/html/draft-ietf-core- 10.17487/PRE-RFC9952, March 2026,
coap-dtls-alpn-05>. <https://www.rfc-editor.org/info/rfc9952>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005, RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/rfc/rfc3986>. <https://www.rfc-editor.org/info/rfc3986>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008, DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/rfc/rfc5234>. <https://www.rfc-editor.org/info/rfc5234>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/rfc/rfc6347>. January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252, Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014, DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/rfc/rfc7252>. <https://www.rfc-editor.org/info/rfc7252>.
[RFC7641] Hartke, K., "Observing Resources in the Constrained [RFC7641] Hartke, K., "Observing Resources in the Constrained
Application Protocol (CoAP)", RFC 7641, Application Protocol (CoAP)", RFC 7641,
DOI 10.17487/RFC7641, September 2015, DOI 10.17487/RFC7641, September 2015,
<https://www.rfc-editor.org/rfc/rfc7641>. <https://www.rfc-editor.org/info/rfc7641>.
[RFC7959] Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in [RFC7959] Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in
the Constrained Application Protocol (CoAP)", RFC 7959, the Constrained Application Protocol (CoAP)", RFC 7959,
DOI 10.17487/RFC7959, August 2016, DOI 10.17487/RFC7959, August 2016,
<https://www.rfc-editor.org/rfc/rfc7959>. <https://www.rfc-editor.org/info/rfc7959>.
[RFC8132] van der Stok, P., Bormann, C., and A. Sehgal, "PATCH and [RFC8132] van der Stok, P., Bormann, C., and A. Sehgal, "PATCH and
FETCH Methods for the Constrained Application Protocol FETCH Methods for the Constrained Application Protocol
(CoAP)", RFC 8132, DOI 10.17487/RFC8132, April 2017, (CoAP)", RFC 8132, DOI 10.17487/RFC8132, April 2017,
<https://www.rfc-editor.org/rfc/rfc8132>. <https://www.rfc-editor.org/info/rfc8132>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8323] Bormann, C., Lemay, S., Tschofenig, H., Hartke, K., [RFC8323] Bormann, C., Lemay, S., Tschofenig, H., Hartke, K.,
Silverajan, B., and B. Raymor, Ed., "CoAP (Constrained Silverajan, B., and B. Raymor, Ed., "CoAP (Constrained
Application Protocol) over TCP, TLS, and WebSockets", Application Protocol) over TCP, TLS, and WebSockets",
RFC 8323, DOI 10.17487/RFC8323, February 2018, RFC 8323, DOI 10.17487/RFC8323, February 2018,
<https://www.rfc-editor.org/rfc/rfc8323>. <https://www.rfc-editor.org/info/rfc8323>.
[RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS [RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS
(DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018, (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
<https://www.rfc-editor.org/rfc/rfc8484>. <https://www.rfc-editor.org/info/rfc8484>.
[RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz, [RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
"Object Security for Constrained RESTful Environments "Object Security for Constrained RESTful Environments
(OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019, (OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019,
<https://www.rfc-editor.org/rfc/rfc8613>. <https://www.rfc-editor.org/info/rfc8613>.
[RFC8765] Pusateri, T. and S. Cheshire, "DNS Push Notifications", [RFC8765] Pusateri, T. and S. Cheshire, "DNS Push Notifications",
RFC 8765, DOI 10.17487/RFC8765, June 2020, RFC 8765, DOI 10.17487/RFC8765, June 2020,
<https://www.rfc-editor.org/rfc/rfc8765>. <https://www.rfc-editor.org/info/rfc8765>.
[RFC8768] Boucadair, M., Reddy.K, T., and J. Shallow, "Constrained [RFC8768] Boucadair, M., Reddy.K, T., and J. Shallow, "Constrained
Application Protocol (CoAP) Hop-Limit Option", RFC 8768, Application Protocol (CoAP) Hop-Limit Option", RFC 8768,
DOI 10.17487/RFC8768, March 2020, DOI 10.17487/RFC8768, March 2020,
<https://www.rfc-editor.org/rfc/rfc8768>. <https://www.rfc-editor.org/info/rfc8768>.
[RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object [RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", STD 94, RFC 8949, Representation (CBOR)", STD 94, RFC 8949,
DOI 10.17487/RFC8949, December 2020, DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/rfc/rfc8949>. <https://www.rfc-editor.org/info/rfc8949>.
[RFC9147] Rescorla, E., Tschofenig, H., and N. Modadugu, "The [RFC9147] Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version Datagram Transport Layer Security (DTLS) Protocol Version
1.3", RFC 9147, DOI 10.17487/RFC9147, April 2022, 1.3", RFC 9147, DOI 10.17487/RFC9147, April 2022,
<https://www.rfc-editor.org/rfc/rfc9147>. <https://www.rfc-editor.org/info/rfc9147>.
[RFC9460] Schwartz, B., Bishop, M., and E. Nygren, "Service Binding [RFC9460] Schwartz, B., Bishop, M., and E. Nygren, "Service Binding
and Parameter Specification via the DNS (SVCB and HTTPS and Parameter Specification via the DNS (SVCB and HTTPS
Resource Records)", RFC 9460, DOI 10.17487/RFC9460, Resource Records)", RFC 9460, DOI 10.17487/RFC9460,
November 2023, <https://www.rfc-editor.org/rfc/rfc9460>. November 2023, <https://www.rfc-editor.org/info/rfc9460>.
[RFC9461] Schwartz, B., "Service Binding Mapping for DNS Servers", [RFC9461] Schwartz, B., "Service Binding Mapping for DNS Servers",
RFC 9461, DOI 10.17487/RFC9461, November 2023, RFC 9461, DOI 10.17487/RFC9461, November 2023,
<https://www.rfc-editor.org/rfc/rfc9461>. <https://www.rfc-editor.org/info/rfc9461>.
[RFC9462] Pauly, T., Kinnear, E., Wood, C. A., McManus, P., and T. [RFC9462] Pauly, T., Kinnear, E., Wood, C. A., McManus, P., and T.
Jensen, "Discovery of Designated Resolvers", RFC 9462, Jensen, "Discovery of Designated Resolvers", RFC 9462,
DOI 10.17487/RFC9462, November 2023, DOI 10.17487/RFC9462, November 2023,
<https://www.rfc-editor.org/rfc/rfc9462>. <https://www.rfc-editor.org/info/rfc9462>.
[RFC9463] Boucadair, M., Ed., Reddy.K, T., Ed., Wing, D., Cook, N., [RFC9463] Boucadair, M., Ed., Reddy.K, T., Ed., Wing, D., Cook, N.,
and T. Jensen, "DHCP and Router Advertisement Options for and T. Jensen, "DHCP and Router Advertisement Options for
the Discovery of Network-designated Resolvers (DNR)", the Discovery of Network-designated Resolvers (DNR)",
RFC 9463, DOI 10.17487/RFC9463, November 2023, RFC 9463, DOI 10.17487/RFC9463, November 2023,
<https://www.rfc-editor.org/rfc/rfc9463>. <https://www.rfc-editor.org/info/rfc9463>.
[STD13] Internet Standard 13, [STD13] Internet Standard 13,
<https://www.rfc-editor.org/info/std13>. <https://www.rfc-editor.org/info/std13>.
At the time of writing, this STD comprises the following: At the time of writing, this STD comprises the following:
Mockapetris, P., "Domain names - concepts and facilities", Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/info/rfc1034>. <https://www.rfc-editor.org/info/rfc1034>.
Mockapetris, P., "Domain names - implementation and Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>. November 1987, <https://www.rfc-editor.org/info/rfc1035>.
11.2. Informative References 10.2. Informative References
[BCP219] Best Current Practice 219, [BCP219] Best Current Practice 219,
<https://www.rfc-editor.org/info/bcp219>. <https://www.rfc-editor.org/info/bcp219>.
At the time of writing, this BCP comprises the following: At the time of writing, this BCP comprises the following:
Hoffman, P. and K. Fujiwara, "DNS Terminology", BCP 219, Hoffman, P. and K. Fujiwara, "DNS Terminology", BCP 219,
RFC 9499, DOI 10.17487/RFC9499, March 2024, RFC 9499, DOI 10.17487/RFC9499, March 2024,
<https://www.rfc-editor.org/info/rfc9499>. <https://www.rfc-editor.org/info/rfc9499>.
[BCP237] Best Current Practice 237, [BCP237] Best Current Practice 237,
<https://www.rfc-editor.org/info/bcp237>. <https://www.rfc-editor.org/info/bcp237>.
At the time of writing, this BCP comprises the following: At the time of writing, this BCP comprises the following:
Hoffman, P., "DNS Security Extensions (DNSSEC)", BCP 237, Hoffman, P., "DNS Security Extensions (DNSSEC)", BCP 237,
RFC 9364, DOI 10.17487/RFC9364, February 2023, RFC 9364, DOI 10.17487/RFC9364, February 2023,
<https://www.rfc-editor.org/info/rfc9364>. <https://www.rfc-editor.org/info/rfc9364>.
[DoC-paper] [CACHABLE-OSCORE]
Lenders, M., Amsüss, C., Gündogan, C., Nawrocki, M.,
Schmidt, T., and M. Wählisch, "Securing Name Resolution in
the IoT: DNS over CoAP", Association for Computing
Machinery (ACM), Proceedings of the ACM on Networking vol.
1, no. CoNEXT2, pp. 1-25, DOI 10.1145/3609423, September
2023, <https://doi.org/10.1145/3609423>.
[I-D.amsuess-core-cachable-oscore]
Amsüss, C. and M. Tiloca, "Cacheable OSCORE", Work in Amsüss, C. and M. Tiloca, "Cacheable OSCORE", Work in
Progress, Internet-Draft, draft-amsuess-core-cachable- Progress, Internet-Draft, draft-amsuess-core-cachable-
oscore-11, 6 July 2025, oscore-11, 6 July 2025,
<https://datatracker.ietf.org/doc/html/draft-amsuess-core- <https://datatracker.ietf.org/doc/html/draft-amsuess-core-
cachable-oscore-11>. cachable-oscore-11>.
[I-D.ietf-core-corr-clar] [CoAP-CORR-CLAR]
Bormann, C., "Constrained Application Protocol (CoAP): Bormann, C., "Constrained Application Protocol (CoAP):
Corrections and Clarifications", Work in Progress, Corrections and Clarifications", Work in Progress,
Internet-Draft, draft-ietf-core-corr-clar-02, 20 June Internet-Draft, draft-ietf-core-corr-clar-03, 22 December
2025, <https://datatracker.ietf.org/doc/html/draft-ietf- 2025, <https://datatracker.ietf.org/doc/html/draft-ietf-
core-corr-clar-02>. core-corr-clar-03>.
[I-D.ietf-core-href] [CRI] Bormann, C. and H. Birkholz, "Constrained Resource
Bormann, C. and H. Birkholz, "Constrained Resource
Identifiers", Work in Progress, Internet-Draft, draft- Identifiers", Work in Progress, Internet-Draft, draft-
ietf-core-href-24, 30 August 2025, ietf-core-href-30, 21 November 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-core-
href-24>.
[I-D.ietf-core-transport-indication]
Amsüss, C. and M. S. Lenders, "CoAP Transport Indication",
Work in Progress, Internet-Draft, draft-ietf-core-
transport-indication-09, 7 July 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-core- <https://datatracker.ietf.org/doc/html/draft-ietf-core-
transport-indication-09>. href-30>.
[I-D.ietf-iotops-7228bis] [DoC-paper]
Bormann, C., Ersue, M., Keränen, A., and C. Gomez, Lenders, M., Amsüss, C., Gündogan, C., Nawrocki, M.,
"Terminology for Constrained-Node Networks", Work in Schmidt, T., and M. Wählisch, "Securing Name Resolution in
Progress, Internet-Draft, draft-ietf-iotops-7228bis-02, 7 the IoT: DNS over CoAP", Proceedings of the ACM on
July 2025, <https://datatracker.ietf.org/doc/html/draft- Networking, vol. 1, no. CoNEXT2, pp. 1-25,
ietf-iotops-7228bis-02>. DOI 10.1145/3609423, September 2023,
<https://doi.org/10.1145/3609423>.
[REST] Fielding, R., "Architectural Styles and the Design of [REST] Fielding, R., "Architectural Styles and the Design of
Network-based Software Architectures", Ph.D. Dissertation, Network-based Software Architectures", Ph.D. Dissertation,
University of California, Irvine, 2000, University of California, Irvine, 2000,
<https://www.ics.uci.edu/~fielding/pubs/dissertation/ <https://www.ics.uci.edu/~fielding/pubs/dissertation/
fielding_dissertation.pdf>. fielding_dissertation.pdf>.
[RFC3833] Atkins, D. and R. Austein, "Threat Analysis of the Domain [RFC3833] Atkins, D. and R. Austein, "Threat Analysis of the Domain
Name System (DNS)", RFC 3833, DOI 10.17487/RFC3833, August Name System (DNS)", RFC 3833, DOI 10.17487/RFC3833, August
2004, <https://www.rfc-editor.org/rfc/rfc3833>. 2004, <https://www.rfc-editor.org/info/rfc3833>.
[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link [RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Format", RFC 6690, DOI 10.17487/RFC6690, August 2012, Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
<https://www.rfc-editor.org/rfc/rfc6690>. <https://www.rfc-editor.org/info/rfc6690>.
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228, Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014, DOI 10.17487/RFC7228, May 2014,
<https://www.rfc-editor.org/rfc/rfc7228>. <https://www.rfc-editor.org/info/rfc7228>.
[RFC7228bis]
Bormann, C., Ersue, M., Keränen, A., and C. Gomez,
"Terminology for Constrained-Node Networks", Work in
Progress, Internet-Draft, draft-ietf-iotops-7228bis-04, 2
March 2026, <https://datatracker.ietf.org/doc/html/draft-
ietf-iotops-7228bis-04>.
[RFC7828] Wouters, P., Abley, J., Dickinson, S., and R. Bellis, "The [RFC7828] Wouters, P., Abley, J., Dickinson, S., and R. Bellis, "The
edns-tcp-keepalive EDNS0 Option", RFC 7828, edns-tcp-keepalive EDNS0 Option", RFC 7828,
DOI 10.17487/RFC7828, April 2016, DOI 10.17487/RFC7828, April 2016,
<https://www.rfc-editor.org/rfc/rfc7828>. <https://www.rfc-editor.org/info/rfc7828>.
[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., [RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over Transport and P. Hoffman, "Specification for DNS over Transport
Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2016, <https://www.rfc-editor.org/rfc/rfc7858>. 2016, <https://www.rfc-editor.org/info/rfc7858>.
[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205,
RFC 7942, DOI 10.17487/RFC7942, July 2016,
<https://www.rfc-editor.org/rfc/rfc7942>.
[RFC8094] Reddy, T., Wing, D., and P. Patil, "DNS over Datagram [RFC8094] Reddy, T., Wing, D., and P. Patil, "DNS over Datagram
Transport Layer Security (DTLS)", RFC 8094, Transport Layer Security (DTLS)", RFC 8094,
DOI 10.17487/RFC8094, February 2017, DOI 10.17487/RFC8094, February 2017,
<https://www.rfc-editor.org/rfc/rfc8094>. <https://www.rfc-editor.org/info/rfc8094>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/rfc/rfc8446>. <https://www.rfc-editor.org/info/rfc8446>.
[RFC9052] Schaad, J., "CBOR Object Signing and Encryption (COSE): [RFC9052] Schaad, J., "CBOR Object Signing and Encryption (COSE):
Structures and Process", STD 96, RFC 9052, Structures and Process", STD 96, RFC 9052,
DOI 10.17487/RFC9052, August 2022, DOI 10.17487/RFC9052, August 2022,
<https://www.rfc-editor.org/rfc/rfc9052>. <https://www.rfc-editor.org/info/rfc9052>.
[RFC9076] Wicinski, T., Ed., "DNS Privacy Considerations", RFC 9076, [RFC9076] Wicinski, T., Ed., "DNS Privacy Considerations", RFC 9076,
DOI 10.17487/RFC9076, July 2021, DOI 10.17487/RFC9076, July 2021,
<https://www.rfc-editor.org/rfc/rfc9076>. <https://www.rfc-editor.org/info/rfc9076>.
[RFC9176] Amsüss, C., Ed., Shelby, Z., Koster, M., Bormann, C., and [RFC9176] Amsüss, C., Ed., Shelby, Z., Koster, M., Bormann, C., and
P. van der Stok, "Constrained RESTful Environments (CoRE) P. van der Stok, "Constrained RESTful Environments (CoRE)
Resource Directory", RFC 9176, DOI 10.17487/RFC9176, April Resource Directory", RFC 9176, DOI 10.17487/RFC9176, April
2022, <https://www.rfc-editor.org/rfc/rfc9176>. 2022, <https://www.rfc-editor.org/info/rfc9176>.
[RFC9250] Huitema, C., Dickinson, S., and A. Mankin, "DNS over [RFC9250] Huitema, C., Dickinson, S., and A. Mankin, "DNS over
Dedicated QUIC Connections", RFC 9250, Dedicated QUIC Connections", RFC 9250,
DOI 10.17487/RFC9250, May 2022, DOI 10.17487/RFC9250, May 2022,
<https://www.rfc-editor.org/rfc/rfc9250>. <https://www.rfc-editor.org/info/rfc9250>.
[RFC9528] Selander, G., Preuß Mattsson, J., and F. Palombini, [RFC9528] Selander, G., Preuß Mattsson, J., and F. Palombini,
"Ephemeral Diffie-Hellman Over COSE (EDHOC)", RFC 9528, "Ephemeral Diffie-Hellman Over COSE (EDHOC)", RFC 9528,
DOI 10.17487/RFC9528, March 2024, DOI 10.17487/RFC9528, March 2024,
<https://www.rfc-editor.org/rfc/rfc9528>. <https://www.rfc-editor.org/info/rfc9528>.
[TRANSPORT-IND]
Amsüss, C. and M. S. Lenders, "CoAP Transport Indication",
Work in Progress, Internet-Draft, draft-ietf-core-
transport-indication-09, 7 July 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-core-
transport-indication-09>.
Appendix A. Evaluation Appendix A. Evaluation
The authors of this document presented the design, implementation, The authors of this document presented the design, implementation,
and analysis of DoC in their paper "Securing Name Resolution in the and analysis of DoC in their paper "Securing Name Resolution in the
IoT: DNS over CoAP" [DoC-paper]. IoT: DNS over CoAP" [DoC-paper].
Appendix B. Change Log
// RFC Ed.: Please remove this section before publication.
B.1. Since draft-ietf-core-dns-over-coap-18
(https://datatracker.ietf.org/doc/html/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
B.2. Since draft-ietf-core-dns-over-coap-17
(https://datatracker.ietf.org/doc/html/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."
B.3. Since draft-ietf-core-dns-over-coap-16
(https://datatracker.ietf.org/doc/html/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
B.4. Since draft-ietf-core-dns-over-coap-15
(https://datatracker.ietf.org/doc/html/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
B.5. Since draft-ietf-core-dns-over-coap-14
(https://datatracker.ietf.org/doc/html/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
B.6. Since draft-ietf-core-dns-over-coap-13
(https://datatracker.ietf.org/doc/html/draft-ietf-core-dns-over-
coap-13)
* Address shepherd review
B.7. Since draft-ietf-core-dns-over-coap-12
(https://datatracker.ietf.org/doc/html/draft-ietf-core-dns-over-
coap-12)
* Address Esko's review
* Address Marcos's review
* Address Mikolai's review
B.8. Since draft-ietf-core-dns-over-coap-10
(https://datatracker.ietf.org/doc/html/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
B.9. Since draft-ietf-core-dns-over-coap-09
(https://datatracker.ietf.org/doc/html/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/rfc2136), clarify that it
is currently not considered
* Add to security considerations: unprotected upstream DNS and
DNSSEC
B.10. Since draft-ietf-core-dns-over-coap-08
(https://datatracker.ietf.org/doc/html/draft-ietf-core-dns-over-
coap-08)
* Update Cenk's Affiliation
B.11. Since draft-ietf-core-dns-over-coap-07
(https://datatracker.ietf.org/doc/html/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
B.12. Since draft-ietf-core-dns-over-coap-06
(https://datatracker.ietf.org/doc/html/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
B.13. Since draft-ietf-core-dns-over-coap-05
(https://datatracker.ietf.org/doc/html/draft-ietf-core-dns-over-
coap-05)
* Add references to relevant SVCB/DNR RFCs and drafts
B.14. Since draft-ietf-core-dns-over-coap-04
(https://datatracker.ietf.org/doc/html/draft-ietf-core-dns-over-
coap-04)
* Add note on cacheable OSCORE
* Address early IANA review
B.15. Since draft-ietf-core-dns-over-coap-03
(https://datatracker.ietf.org/doc/html/draft-ietf-core-dns-over-
coap-03)
* Amended Introduction with short contextualization of constrained
environments
* Add Appendix A on evaluation
B.16. Since draft-ietf-core-dns-over-coap-02
(https://datatracker.ietf.org/doc/html/draft-ietf-core-dns-over-
coap-02)
* Move implementation details to Implementation Status (in
accordance with [RFC7942])
* Recommend root path to keep the CoAP options small
* Set Content-Format for application/dns-message to 553
* SVCB/DNR: Move to Server Selection Section but leave TBD based on
DNSOP discussion for now
* 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
B.17. Since draft-ietf-core-dns-over-coap-01
(https://datatracker.ietf.org/doc/html/draft-ietf-core-dns-over-
coap-01)
* Specify DoC server role in terms of DNS terminology
* Clarify communication of DoC to DNS infrastructure is agnostic of
the transport
* Add subsection on how to implement DNS Push in DoC
* Add appendix on reference implementation
B.18. Since draft-ietf-core-dns-over-coap-00
(https://datatracker.ietf.org/doc/html/draft-ietf-core-dns-over-
coap-00)
* SVGify ASCII art
* Move section on "DoC Server Considerations" (was Section 5.1) to
its own draft (draft-lenders-dns-cns
(https://datatracker.ietf.org/doc/draft-lenders-dns-cns/))
* Replace layer violating statement for CON with statement of fact
* Add security considerations on ID=0
B.19. Since draft-lenders-dns-over-coap-04
(https://datatracker.ietf.org/doc/html/draft-lenders-dns-over-
coap-04)
* Removed change log of draft-lenders-dns-over-coap
Acknowledgments Acknowledgments
The authors of this document want to thank Mike Bishop, Carsten The authors of this document want to thank Mike Bishop, Carsten
Bormann, Mohamed Boucadair, Deb Cooley, Vladimír Čunát, Roman Bormann, Mohamed Boucadair, Deb Cooley, Vladimír Čunát, Roman
Danyliw, Elwyn B. Davies, Esko Dijk, Gorry Fairhurst, Thomas Danyliw, Elwyn B. Davies, Esko Dijk, Gorry Fairhurst, Thomas Fossati,
Fossati, Mikolai Gütschow, Todd Herr, Tommy Pauly, Jan Romann, Ben Mikolai Gütschow, Todd Herr, Tommy Pauly, Jan Romann, Ben Schwartz,
Schwartz, Orie Steele, Marco Tiloca, Éric Vyncke, Tim Wicinski, and Orie Steele, Marco Tiloca, Éric Vyncke, Tim Wicinski, and Paul
Paul Wouters for their feedback and comments. Wouters for their feedback and comments.
Authors' Addresses Authors' Addresses
Martine Sophie Lenders Martine Sophie Lenders
TUD Dresden University of Technology TUD Dresden University of Technology
Helmholtzstr. 10 Helmholtzstr. 10
D-01069 Dresden D-01069 Dresden
Germany Germany
Email: martine.lenders@tu-dresden.de Email: martine.lenders@tu-dresden.de
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