TUD Dresden University of Technology

Helmholtzstr. 10 Dresden D-01069 Germany martine.lenders@tu-dresden.de

christian@amsuess.com

NeuralAgent GmbH

Mies-van-der-Rohe-Straße 6 Munich D-80807 Germany cenk.gundogan@neuralagent.ai

HAW Hamburg

Berliner Tor 7 Hamburg D-20099 Germany t.schmidt@haw-hamburg.de

TUD Dresden University of Technology & Barkhausen Institut

Helmholtzstr. 10 Dresden D-01069 Germany m.waehlisch@tu-dresden.de

WIT CoRE CoRE CoAP DNS This document defines a protocol for exchanging DNS queries (OPCODE 0) over the Constrained Application Protocol (CoAP). These CoAP messages can be protected by (D)TLS-Secured CoAP or Object Security for Constrained RESTful Environments (OSCORE) to provide encrypted DNS message exchange for constrained devices in the Internet of Things (IoT).

Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at .

Copyright Notice Copyright (c) 2026 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents () in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.

Table of Contents

• .  Introduction
• .  Terminology and Conventions
• .  Selection of a DoC Server
  • .  Discovery by Resource Type
  • .  Discovery Using SVCB Resource Records or DNR
    • .  Examples
• .  Basic Message Exchange
  • .  The "application/dns-message" Content-Format
  • .  DNS Queries in CoAP Requests
    • .  Request Format
    • .  Support of CoAP Caching
    • .  Example
  • .  DNS Responses in CoAP Responses
    • .  Response Codes and Handling DNS and CoAP Errors
    • .  Support of CoAP Caching
    • .  Examples
• .  Interaction with Other CoAP and CoRE Features
  • .  DNS Push Notifications and CoAP Observe
  • .  OSCORE
  • .  Mapping DoC to DoH
• .  Considerations for Unprotected Use
• .  Security Considerations
• .  IANA Considerations
  • .  CoAP Content-Formats Registry
  • .  DNS SVBC Service Parameter Keys (SvcParamKeys) Registry
  • .  Resource Type (rt=) Link Target Attribute Values Registry
• .  Operational Considerations
  • .  Coexistence of Different DNS and CoAP Transports
  • .  Redirects
  • .  Proxy Hop Limit
  • .  Error Handling
  • .  DNS Extensions
• . References
  • .  Normative References
  • .  Informative References
• .  Evaluation
• Acknowledgments
• Authors' Addresses

Introduction This document defines DNS over CoAP (DoC), a protocol to send DNS queries and get DNS responses over the Constrained Application Protocol (CoAP) using OPCODE 0 (Query). Each DNS query-response pair is mapped into a CoAP message exchange. Each CoAP message can be secured by any combination of DTLS 1.2 or newer , TLS 1.3 or newer , or Object Security for Constrained RESTful Environments (OSCORE) to ensure message integrity and confidentiality. The application use case of DoC is inspired by DNS over HTTPS (DoH) . However, DoC aims for deployment in the constrained Internet of Things (IoT), which usually conflicts with the requirements introduced by HTTPS. Constrained IoT devices may be restricted in memory, power consumption, link-layer frame sizes, throughput, and latency. They may only have a handful kilobytes of both RAM and ROM. They may sleep for long durations of time, after which they need to refresh the named resources they know about. Name resolution in such scenarios must take into account link-layer frame sizes of only a few hundred bytes, bit rates in the magnitude of kilobits per second, and latencies of several seconds . In order not to be burdened by the resource requirements of TCP and HTTPS, constrained IoT devices could use DNS over DTLS . In contrast to DNS over DTLS, DoC can take advantage of CoAP features to mitigate drawbacks of datagram-based communication. These features include (1) block-wise transfer , which solves the Path MTU problem of DNS over DTLS (see ), (2) CoAP proxies, which provide an additional level of caching, and (3) reuse of data structures for application traffic and DNS information, which saves memory on constrained devices. To avoid the resource requirements of DTLS or TLS on top of UDP (e.g., introduced by DNS over DTLS or DNS over QUIC ), DoC allows for lightweight message protection based on OSCORE.

Basic DoC Architecture . FETCH coaps://[2001:db8::1]/ / / CoAP request +------+ [DNS query] +------+------+ DNS query .--------------. | DoC |-------------->| DoC | DNS |--- --- --- --->| DNS | |Client|<--------------|Server|Client|<--- --- --- ---| Infrastructure | +------+ CoAP response +------+------+ DNS response '--------------' [DNS response] \ / \ / '-----DNS over CoAP-----' '----DNS over UDP/HTTPS/QUIC/...---'

The most important components of DoC can be seen in : a DoC client tries to resolve DNS information by sending DNS queries carried within CoAP requests to a DoC server. That DoC server can be the authoritative name server for the queried record or a DNS client (i.e., a stub or recursive resolver) that resolves DNS information by using other DNS transports such as DNS over UDP , DNS over HTTPS , or DNS over QUIC when communicating with the upstream DNS infrastructure. Using that information, the DoC server then replies to the queries of the DoC client with DNS responses carried within CoAP responses. A DoC server MAY also serve as a DNSSEC validator to provide DNSSEC validation to the more constrained DoC clients. Note that this specification is distinct from DoH because the CoAP-specific FETCH method is used. A benefit of using this method is having the DNS query in the body such as when using the POST method, but with the same caching advantages of responses to requests that use the GET method. Having the DNS query in the body means that there is no need for extra base64 encoding, which would increase code complexity and message sizes. Also, this allows for the block-wise transfer of queries .

Terminology and Conventions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here. A server that provides the service specified in this document is called a "DoC server" to differentiate it from a classic "DNS server". A DoC server acts as either a DNS stub resolver or a DNS recursive resolver . As such, the DoC server communicates with an "upstream DNS infrastructure" or a single "upstream DNS server". A "DoC resource" is a CoAP resource at the DoC server that DoC clients can target in order to send a DNS query in a CoAP request. A client using the service specified in this document to retrieve the DNS information is called a "DoC client". The term "constrained nodes" is used as defined in . describes that Constrained RESTful Environments (CoRE) realize the Representational State Transfer (REST) architecture in a suitable form for such constrained nodes. A DoC server can provide Observe capabilities as defined in . As part of that, it administers a "list of observers". DoC clients using these capabilities are "observers" as defined in . A "notification" is a CoAP response message with an Observe option; see . The terms "payload" and "body" are used as defined in . Note that, when block-wise transfer is not used, the terms "payload" and "body" are to be understood as equal. In the examples in this document, the binary payload and resource records are shown in a hexadecimal representation as well as a human-readable format for better readability. However, in the actual message sent and received, they are encoded in the binary message format defined in .

Selection of a DoC Server While there is no path specified for the DoC resource, it is 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 server. Possible options to assure this could be (1) manual configuration of a Uniform Resource Identifier (URI) or Constrained Resource Identifier (CRI) or (2) automatic configuration, e.g., using a CoRE resource directory , DHCP or Router Advertisement options , or discovery of designated resolvers . Automatic configuration MUST only be done from a trusted source.

Discovery by Resource Type For discovery of the DoC resource through a link mechanism that allows describing a resource type (e.g., the Resource Type attribute in ), this document introduces the resource type "core.dns". It can be used to identify a generic DNS resolver that is available to the client.

Discovery Using SVCB Resource Records or DNR A DoC server can also be discovered using Service Binding (SVCB) Resource Records (RRs) resolved via another DNS service (e.g., provided by an unencrypted local resolver) or Discovery of Network-designated Resolvers (DNR) Service Parameters via DHCP or Router Advertisements. defines the Application-Layer Protocol Negotiation (ALPN) ID for CoAP over TLS servers and defines the ALPN ID for CoAP over DTLS servers. DoC servers that use only OSCORE and Ephemeral Diffie-Hellman Over COSE (EDHOC) (COSE stands for "Concise Binary Object Notation (CBOR) Object Signing and Encryption" ) to support security cannot be discovered using these SVCB RR or DNR mechanisms. Specifying an alternate discovery mechanism is out of the scope of this document. This document is not an SVCB mapping document for the CoAP schemes as defined in . A full SVCB mapping is specified in . It generalizes mechanisms for all CoAP services. This document introduces only the discovery of DoC services. This document specifies "docpath" as a single-valued Service Parameter Key (SvcParamKey) that is mandatory for DoC SVCB records. If the "docpath" SvcParamKey is absent, the service should not be considered a valid DoC service. 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 ABNF : docpath-segment = 1*255OCTET Note that this restricts the length of each docpath-segment to at most 255 octets. Paths with longer segments cannot be advertised with the "docpath" SvcParam and are thus NOT RECOMMENDED for the path to the DoC resource. The presentation format value of "docpath" SHALL be a comma-separated list () of 0 or more docpath-segments. The root path "/" is represented by 0 docpath-segments, i.e., an empty list. The same considerations apply for the "," and "\" characters in docpath-segments for zone-file implementations and the alpn-ids in an "alpn" SvcParam (). The wire-format value for "docpath" consists of 0 or more sequences of octets prefixed by their respective length as a single octet. We call this single octet the length octet. The length octet and the corresponding sequence form a length-value pair. These length-value pairs are concatenated to form the SvcParamValue. These pairs MUST exactly fill the SvcParamValue; otherwise, the SvcParamValue is malformed. Each such length-value pair represents one segment of the absolute path to the DoC resource. The root path "/" is represented by 0 length-value pairs, i.e., SvcParamValue length 0. Note that this format uses the same encoding as the "alpn" SvcParam, and 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-segment has a length between 0 and 23 octets, inclusive, it is easily transferred into the path representation in CRIs by masking each length octet with the CBOR text string major type 3 (0x60 as an octet; see ). Furthermore, it is easily transferable into a sequence of CoAP Uri-Path options by mapping each length octet into the Option Delta and Option Length of the corresponding CoAP Uri-Path option, provided the docpath-segments are all of a length between 0 and 12 octets (see ). Likewise, it can be transferred into a URI path-abempty form by replacing each length octet with the "/" character. None of the abovementioned prevent longer docpath-segments than the considered ones; they just make the translation harder as space is required for the longer delimiters, which in turn require octets to be moved. 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 SvcParams including "docpath". The construction algorithm for DoC requests is as follows, with the provided records in order of their priority. For the purposes of this algorithm, the DoC client is assumed to be SVCB-optional (see ).

• If the "alpn" SvcParam value for the service is "coap", a CoAP request for CoAP over TLS MUST be constructed . If it is "co", a CoAP request for CoAP over DTLS MUST be constructed . Any other SvcParamKeys specifying a transport are out of the scope of this document.
• The destination address for the request SHOULD be taken from additional information about the target. This may include (1) A or AAAA RRs associated with the target name and delivered with the SVCB RR (see ), (2) "ipv4hint" or "ipv6hint" SvcParams from the SVCB RR (see ), or (3) IPv4 or IPv6 addresses provided if DNR is used. As a fallback, an address MAY be queried for the target name of the SVCB record from another DNS service.
• The destination port for the request MUST be taken from the "port" SvcParam value, if present. Otherwise, take the default port of the CoAP transport, e.g., with regards to this specification, the default is TCP port 5684 for "coap" or UDP port 5684 for "co". This document introduces no limitations on the ports that can be used. If a malicious SVCB record allows its originator to influence message payloads, recommends placing such restrictions in the SVCB mapping document. The records used in this document only influence the Uri-Path option. That option is only sent in the plaintext of an encrypted (D)TLS channel and thus does not warrant any limitations.
• The request URI's hostname component MUST be the Authentication Domain Name (ADN) when obtained through DNR and MUST be the target name of the SVCB record when obtained through a _dns query (if AliasMode is used to the target name of the AliasMode record). This can be achieved efficiently by setting that name in TLS Server Name Indication (SNI) or by setting the Uri-Host option on each request.
• For each element in the CBOR sequence of the "docpath" SvcParam value, a Uri-Path option MUST be added to the request.
• If the request constructed this way receives a response, the same SVCB record MUST be used for construction of future DoC queries. If not, or if the endpoint becomes unreachable, the algorithm repeats with the SVCB RR or DNR Encrypted DNS option with the next highest Service Priority as a fallback (see Sections and of ).

A more generalized construction algorithm for any CoAP request can be found in .

Examples A typical SVCB resource record response for a DoC server at the root path "/" of the server looks like the following (the "docpath" SvcParam is the last 4 bytes 00 0a 00 00 in the binary): Resource record (binary): 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 6e 73 07 65 78 61 6d 70 6c 65 03 6f 72 67 00 00 01 00 03 02 63 6f 00 0a 00 00 Resource record (human-readable): _dns.example.org. 1576 IN SVCB 1 dns.example.org ( alpn=co docpath ) The root path is RECOMMENDED but not required. Here are two examples where the "docpath" represents paths of varying depth. First, "/dns" is provided in the following example (the last 8 bytes 00 0a 00 04 03 64 6e 73): Resource record (binary): 04 5f 64 6e 73 07 65 78 61 6d 70 6c 65 03 6f 72 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 01 00 03 02 63 6f 00 0a 00 04 03 64 6e 73 Resource record (human-readable): _dns.example.org. 85 IN SVCB 1 dns.example.org ( alpn=co docpath=dns ) Second, see an example for the path "/n/s" (the last 8 bytes 00 0a 00 04 01 6e 01 73): Resource record (binary): 04 5f 64 6e 73 07 65 78 61 6d 70 6c 65 03 6f 72 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 01 00 03 02 63 6f 00 0a 00 04 01 6e 01 73 Resource record (human-readable): _dns.example.org. 1643 IN SVCB 1 dns.example.org ( alpn=co docpath=n,s ) If the server also provides DNS over HTTPS, "dohpath" and "docpath" MAY coexist: Resource record (binary): 04 5f 64 6e 73 07 65 78 61 6d 70 6c 65 03 6f 72 67 00 00 40 00 01 00 00 01 ad 00 2c 00 01 03 64 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 64 6e 73 7d 00 0a 00 00 Resource record (human-readable): _dns.example.org. 429 IN SVCB 1 dns.example.org ( alpn=h3,co dohpath=/{?dns} docpath )

Basic Message Exchange

The "application/dns-message" Content-Format This document defines a CoAP Content-Format ID for the Internet media type "application/dns-message" to be the mnemonic 553, based on the port assignment of DNS. This media type is defined as in , i.e., a single DNS message encoded in the DNS on-the-wire format . Both DoC client and DoC server MUST be able to parse contents in the "application/dns-message" Content-Format. This document only specifies OPCODE 0 (Query) for DNS over CoAP messages. Future documents can provide considerations for additional OPCODEs or extend its specification (e.g., by describing whether other CoAP codes need to be used for which OPCODE). Unless another error takes precedence, a DoC server uses RCODE = 4, NotImp , in its response to a query with an OPCODE that it does not implement (see also ).

DNS Queries in CoAP Requests A DoC client encodes a single DNS query in one or more CoAP request messages that use the CoAP FETCH request method. Requests SHOULD include an Accept option to indicate the type of content that can be parsed in the response. Since CoAP provides reliability at the message layer (e.g., through Confirmable messages), the retransmission mechanism of the DNS protocol as defined in is not needed.

Request Format When sending a CoAP request, a DoC client MUST include the DNS query in the body of the CoAP request. As specified in , the type of content of the body MUST be indicated using the Content-Format option. This document specifies the usage of Content-Format "application/dns-message" (for details, see ).

Support of CoAP Caching The DoC client SHOULD set the ID field of the DNS header to 0 to enable a CoAP cache (e.g., a CoAP proxy en route) to respond to the same DNS queries with a cache entry. This ensures that the CoAP Cache-Key (see ) does not change when multiple DNS queries for the same DNS data, carried in CoAP requests, are issued. Apart from losing these caching benefits, there is no harm in not setting it to 0, e.g., when the query was received from somewhere else. In any instance, a DoC server MUST copy the ID from the query in its response to that query.

Example The following example illustrates the usage of a CoAP message to resolve "example.org. IN AAAA" based on the URI "coaps://[2001:db8::1]/". The CoAP body is encoded in the "application/dns-message" Content-Format. FETCH coaps://[2001:db8::1]/ Content-Format: 553 (application/dns-message) Accept: 553 (application/dns-message) Payload (binary): 00 00 01 00 00 01 00 00 00 00 00 00 07 65 78 61 6d 70 6c 65 03 6f 72 67 00 00 1c 00 01 Payload (human-readable): ;; ->>Header<<- opcode: QUERY, status: NOERROR, id: 0 ;; flags: rd; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;example.org. IN AAAA

DNS Responses in CoAP Responses Each DNS query-response pair is mapped to a CoAP request-response operation. DNS responses are provided in the body of the CoAP response, i.e., it is also possible to transfer them using block-wise transfer . A DoC server MUST be able to produce responses in the "application/dns-message" Content-Format (for details, see ) when requested. The use of the Accept option in the request is OPTIONAL. However, all DoC clients MUST be able to parse an "application/dns-message" response (see also ). Any response Content-Format other than "application/dns-message" MUST be indicated with the Content-Format option by the DoC server.

Response Codes and Handling DNS and CoAP Errors A DNS response indicates either success or failure in the RCODE of the DNS header (see ). It is RECOMMENDED that CoAP responses that carry a parsable DNS response use a 2.05 (Content) response code. CoAP responses using non-successful response codes MUST NOT contain a DNS response and MUST only be used for errors in the CoAP layer or when a request does not fulfill the requirements of the DoC protocol. Communication errors with an upstream DNS server (e.g., timeouts) MUST be indicated by including a DNS response with the appropriate RCODE in a successful CoAP response, i.e., using a 2.xx response code. When an error occurs at the CoAP layer, e.g., if an unexpected request method or an unsupported Content-Format in the request are used, the DoC server SHOULD respond with an appropriate CoAP error. A DoC client might try to repeat a non-successful exchange unless otherwise prohibited. The DoC client might also decide to repeat a non-successful exchange with a different URI, for instance, when the response indicates an unsupported Content-Format.

Support of CoAP Caching For reliability and energy-saving measures, content decoupling (such 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 refresh stale cache entries to reduce the number of large response messages. For cache validation, CoAP implementations regularly use hashing over the message content for ETag generation (see ). As such, the approach to guarantee the same cache key for DNS responses as proposed in DoH () is not sufficient and needs to be updated so that the TTLs in the response are more often the same regardless of query time. The DoC server MUST ensure that the sum of the Max-Age value of a CoAP response and any TTL in the DNS response is less than or equal to the corresponding TTL received from an upstream DNS server. This also includes the default Max-Age value of 60 seconds (see ) when no Max-Age option is provided. The 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 calculated TTLs for the associated records. To meet the requirement for DoC, the RECOMMENDED algorithm for a DoC 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 of that DNS response. This prevents expired records from unintentionally being served from an intermediate CoAP cache. Additionally, if the ETag for cache validation is based on the content of the response, it allows that ETag not to change. This then remains the case even if the TTL values are updated by an upstream DNS cache. If only one record set per DNS response is assumed, a simplification of this algorithm is to just set all TTLs in the response to 0 and set the TTLs at the DoC client to the value of the Max-Age option. If shorter caching periods are plausible, e.g., if the RCODE of the message indicates an error that should only be cached for a minimal duration, the value for the Max-Age option SHOULD be set accordingly. This value might be 0, but if the DoC server knows that the error will persist, greater values are also conceivable, depending on the projected duration of the error. The same applies for DNS responses that, for any reason, do not carry any records with a TTL.

Examples The following example illustrates the response to the query "example.org. IN AAAA record", with recursion turned on. Successful responses carry one answer record including the address 2001:db8:1:0:1:2:3:4 and TTL 79689. A successful response: 2.05 Content Content-Format: 553 (application/dns-message) Max-Age: 58719 Payload (human-readable): ;; ->>Header<<- opcode: QUERY, status: NOERROR, id: 0 ;; flags: qr rd ad; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;example.org. IN AAAA ;; ANSWER SECTION: ;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 case - is noted in the DNS response, the CoAP response still indicates success. 2.05 Content Content-Format: 553 (application/dns-message) Payload (human-readable): ;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 0 ;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;does.not.exist. IN AAAA As described in , a DoC server uses NotImp (RCODE = 4) if it does not support an OPCODE - in this case, it errors on a DNS Update (OPCODE = 5) for "example.org". 2.05 Content Content-Format: 553 (application/dns-message) Payload (human-readable): ;; ->>Header<<- opcode: UPDATE, status: NOTIMP, id: 0 ;; flags: qr ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0 ;; QUERY SECTION: ;example.org. IN AAAA When an error occurs at the CoAP layer, the DoC server responds with an appropriate CoAP error, for instance, 4.15 (Unsupported Content-Format) if the Content-Format option in the request was not set to "application/dns-message" and the Content-Format is not otherwise supported by the server. 4.15 Unsupported Content-Format [no payload]

Interaction with Other CoAP and CoRE Features

DNS Push Notifications and CoAP Observe DNS Push Notifications provide the capability to asynchronously notify clients about resource record changes. However, it results in additional overhead, which conflicts with constrained resources. This is the reason why it is RECOMMENDED to use CoAP Observe instead of DNS Push in the DoC domain. This is particularly useful if a short-lived record is requested frequently. The DoC server SHOULD provide Observe capabilities on its DoC resource and do as follows. 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 observers for that resource in accordance with . The DoC server MAY subscribe to DNS Push Notifications for that record. This involves sending a DNS Subscribe message (see ), instead of a classic DNS query to fetch the information on behalf of the DoC client. After the list of observers for a particular DNS query has become empty (by explicit or implicit cancellation of the observation as per ), and no other reason to subscribe to that request is present, the DoC server SHOULD cancel the corresponding subscription. This can involve sending a DNS Unsubscribe message or closing the session (see ). As there is no CoAP observer anymore from the perspective of the DoC server, a failure to unsubscribe or close the session cannot be communicated back to any DoC observer. As such, error handling (if any) needs to be resolved between the DoC server and the upstream DNS infrastructure. Whenever the DoC server receives a DNS Push message from the DNS infrastructure for an observed resource record, the DoC server sends an appropriate Observe notification response to the DoC client. A server that responds with notifications (i.e., sends the Observe option) needs to have the means of obtaining current resource records. This may happen through DNS Push or also by upstream polling or implicit circumstances (e.g., if the DoC server is the authoritative name server for the record and wants to notify about changes).

OSCORE It is RECOMMENDED to carry DNS messages protected using OSCORE between the DoC client and the DoC server. The establishment and maintenance of the OSCORE security context is out of the scope of this document. describes a method to allow cache retrieval of OSCORE responses and discusses the corresponding implications on message sizes and security properties.

Mapping DoC to DoH This document provides no specification on how to map between DoC and DoH, e.g., at a CoAP-to-HTTP proxy. Such a direct mapping is NOT RECOMMENDED: Rewriting the FETCH method () and TTL () as specified in this document would be non-trivial. It is RECOMMENDED to use a DNS forwarder to map between DoC and DoH, as would be the case for mapping between any other pair of DNS transports.

Considerations for Unprotected Use The use of DoC without confidentiality and integrity protection is NOT RECOMMENDED. Without secure communication, many possible attacks need to be evaluated in the context of the application's threat model. This includes known threats for unprotected DNS and CoAP (). While DoC does not use the random ID of the DNS header (see ), equivalent protection against off-path poisoning attacks is achieved by using random large token values for unprotected CoAP requests. If a DoC message is unprotected, it MUST use a random token with a length of at least 2 bytes to mitigate this kind of poisoning attack.

Security Considerations General CoAP security considerations () apply to DoC. DoC also inherits the security considerations of the protocols used for secure communication, e.g., OSCORE () as well as DTLS 1.2 or newer ( and ). Additionally, DoC uses request patterns that require the maintenance of long-lived security contexts. provides insights on what can be done when those are resumed from a new endpoint. Though DTLS v1.2 was obsoleted by DTLS v1.3 , there are many CoAP implementations that still use v1.2 at the time of writing. As such, this document also accounts for the usage of DTLS v1.2 even though newer versions are RECOMMENDED when using DTLS to secure CoAP. When using unprotected CoAP (see ), setting the ID of a DNS message to 0 as specified in opens the DNS cache of a DoC client to cache poisoning attacks via response spoofing. This document requires an unpredictable CoAP token in each DoC query from the client when CoAP is not secured to mitigate such an attack over DoC (see ). For secure communication via (D)TLS or OSCORE, an unpredictable ID to protect against spoofing is not necessary. Both (D)TLS and OSCORE offer mechanisms to harden against injecting spoofed responses in their protocol design. Consequently, the ID of the DNS message can be set to 0 without any concern in order to leverage the advantages of CoAP caching. A DoC client must be aware that the DoC server may communicate unprotected with the upstream DNS infrastructure, e.g., using DNS over UDP. DoC can only guarantee confidentiality and integrity of communication between parties for which the security context is exchanged. The DoC server may use another security context to communicate upstream with both confidentiality and integrity (e.g., DNS over QUIC ); however, while recommended, this is opaque to the DoC client on the protocol level. Record integrity can also be ensured upstream using DNSSEC . A DoC client may not be able to perform DNSSEC validation, e.g., due to code size constraints or the size of the responses. It may trust its DoC server to perform DNSSEC validation; how that trust is expressed is out of the scope of this document. For instance, a DoC client may be configured to use a particular credential by which it recognizes an eligible DoC server. That information can also imply trust in the DNSSEC validation by that DoC server.

IANA Considerations

CoAP Content-Formats Registry 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 ; this corresponds to the "application/dns-message" media type from the "Media Types" registry (see ). CoAP Content-Format ID

Content Type	ID	Reference
application/dns-message	553	and RFC 9953,

DNS SVBC Service Parameter Keys (SvcParamKeys) Registry IANA has added the following entry to the "DNS SVCB Service Parameter Keys (SvcParamKeys)" registry in the "DNS Service Bindings (SVCB)" registry group. The definition of this parameter can be found in . Value for SvcParamKeys

Number	Name	Meaning	Change Controller	Reference
10	docpath	DNS over CoAP resource path	IETF	RFC 9953,

Resource Type (rt=) Link Target Attribute Values Registry IANA has added "core.dns" to the "Resource Type (rt=) Link Target Attribute Values" registry in the "Constrained RESTful Environments (CoRE) Parameters" registry group. Resource Type (rt=) Link Target Attribute

Value	Description	Reference
core.dns	DNS over CoAP resource	RFC 9953,

Operational Considerations

Coexistence of Different DNS and CoAP Transports Many DNS transports may coexist on the DoC server, such as DNS over UDP , DNS over (D)TLS , DNS over HTTPS , or DNS over QUIC . In principle, transports employing channel or object security should be preferred. In constrained scenarios, DNS over CoAP is preferable to DNS over DTLS. The final decision regarding the preference, however, heavily depends on the use case and is therefore left to the implementers or users and is not defined in this document. CoAP supports Confirmable and Non-Confirmable messages to deploy different levels of reliability. However, this document does not enforce any of these message types, as the decision on which one is appropriate depends on the characteristics of the network where DoC is deployed.

Redirects 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 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 support redirection. Future specifications of CoAP redirect may need to consider the impact of different results between previous and new DNS servers.

Proxy Hop Limit Mistakes might lead to CoAP proxies forming infinite loops. Using the CoAP Hop-Limit option mitigates such loops.

Error Handling specifies that DNS operational errors should be reported back to a DoC client using the appropriate DNS RCODE. If a DoC client did not receive any successful DNS messages from a DoC server for a while, it might indicate that the DoC server lost connectivity to the upstream DNS infrastructure. The DoC client should handle this error case like a recursive resolver that lost connectivity to the upstream DNS infrastructure. In case of CoAP errors, the usual mechanisms for CoAP response codes apply.

DNS Extensions DNS extensions that are specific to the choice of transport, such as described in , are not applicable to DoC.

References Normative References In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. A Uniform Resource Identifier (URI) is a compact sequence of characters that identifies an abstract or physical resource. This specification defines the generic URI syntax and a process for resolving URI references that might be in relative form, along with guidelines and security considerations for the use of URIs on the Internet. The URI syntax defines a grammar that is a superset of all valid URIs, allowing an implementation to parse the common components of a URI reference without knowing the scheme-specific requirements of every possible identifier. This specification does not define a generative grammar for URIs; that task is performed by the individual specifications of each URI scheme. [STANDARDS-TRACK] Internet technical specifications often need to define a formal syntax. Over the years, a modified version of Backus-Naur Form (BNF), called Augmented BNF (ABNF), has been popular among many Internet specifications. The current specification documents ABNF. It balances compactness and simplicity with reasonable representational power. The differences between standard BNF and ABNF involve naming rules, repetition, alternatives, order-independence, and value ranges. This specification also supplies additional rule definitions and encoding for a core lexical analyzer of the type common to several Internet specifications. [STANDARDS-TRACK] This document specifies version 1.2 of the Datagram Transport Layer Security (DTLS) protocol. The DTLS protocol provides communications privacy for datagram protocols. The protocol allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery. The DTLS protocol is based on the Transport Layer Security (TLS) protocol and provides equivalent security guarantees. Datagram semantics of the underlying transport are preserved by the DTLS protocol. This document updates DTLS 1.0 to work with TLS version 1.2. [STANDARDS-TRACK] The Constrained Application Protocol (CoAP) is a specialized web transfer protocol for use with constrained nodes and constrained (e.g., low-power, lossy) networks. The nodes often have 8-bit microcontrollers with small amounts of ROM and RAM, while constrained networks such as IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs) often have high packet error rates and a typical throughput of 10s of kbit/s. The protocol is designed for machine- to-machine (M2M) applications such as smart energy and building automation. CoAP provides a request/response interaction model between application endpoints, supports built-in discovery of services and resources, and includes key concepts of the Web such as URIs and Internet media types. CoAP is designed to easily interface with HTTP for integration with the Web while meeting specialized requirements such as multicast support, very low overhead, and simplicity for constrained environments. The Constrained Application Protocol (CoAP) is a RESTful application protocol for constrained nodes and networks. The state of a resource on a CoAP server can change over time. This document specifies a simple protocol extension for CoAP that enables CoAP clients to "observe" resources, i.e., to retrieve a representation of a resource and keep this representation updated by the server over a period of time. The protocol follows a best-effort approach for sending new representations to clients and provides eventual consistency between the state observed by each client and the actual resource state at the server. The Constrained Application Protocol (CoAP) is a RESTful transfer protocol for constrained nodes and networks. Basic CoAP messages work well for small payloads from sensors and actuators; however, applications will need to transfer larger payloads occasionally -- for instance, for firmware updates. In contrast to HTTP, where TCP does the grunt work of segmenting and resequencing, CoAP is based on datagram transports such as UDP or Datagram Transport Layer Security (DTLS). These transports only offer fragmentation, which is even more problematic in constrained nodes and networks, limiting the maximum size of resource representations that can practically be transferred. Instead of relying on IP fragmentation, this specification extends basic CoAP with a pair of "Block" options for transferring multiple blocks of information from a resource representation in multiple request-response pairs. In many important cases, the Block options enable a server to be truly stateless: the server can handle each block transfer separately, with no need for a connection setup or other server-side memory of previous block transfers. Essentially, the Block options provide a minimal way to transfer larger representations in a block-wise fashion. A CoAP implementation that does not support these options generally is limited in the size of the representations that can be exchanged, so there is an expectation that the Block options will be widely used in CoAP implementations. Therefore, this specification updates RFC 7252. The methods defined in RFC 7252 for the Constrained Application Protocol (CoAP) only allow access to a complete resource, not to parts of a resource. In case of resources with larger or complex data, or in situations where resource continuity is required, replacing or requesting the whole resource is undesirable. Several applications using CoAP need to access parts of the resources. This specification defines the new CoAP methods, FETCH, PATCH, and iPATCH, which are used to access and update parts of a resource. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. The Constrained Application Protocol (CoAP), although inspired by HTTP, was designed to use UDP instead of TCP. The message layer of CoAP over UDP includes support for reliable delivery, simple congestion control, and flow control. Some environments benefit from the availability of CoAP carried over reliable transports such as TCP or Transport Layer Security (TLS). This document outlines the changes required to use CoAP over TCP, TLS, and WebSockets transports. It also formally updates RFC 7641 for use with these transports and RFC 7959 to enable the use of larger messages over a reliable transport. This document defines a protocol for sending DNS queries and getting DNS responses over HTTPS. Each DNS query-response pair is mapped into an HTTP exchange. This document defines Object Security for Constrained RESTful Environments (OSCORE), a method for application-layer protection of the Constrained Application Protocol (CoAP), using CBOR Object Signing and Encryption (COSE). OSCORE provides end-to-end protection between endpoints communicating using CoAP or CoAP-mappable HTTP. OSCORE is designed for constrained nodes and networks supporting a range of proxy operations, including translation between different transport protocols. Although an optional functionality of CoAP, OSCORE alters CoAP options processing and IANA registration. Therefore, this document updates RFC 7252. The Domain Name System (DNS) was designed to return matching records efficiently for queries for data that are relatively static. When those records change frequently, DNS is still efficient at returning the updated results when polled, as long as the polling rate is not too high. But, there exists no mechanism for a client to be asynchronously notified when these changes occur. This document defines a mechanism for a client to be notified of such changes to DNS records, called DNS Push Notifications. The presence of Constrained Application Protocol (CoAP) proxies may lead to infinite forwarding loops, which is undesirable. To prevent and detect such loops, this document specifies the Hop-Limit CoAP option. The Concise Binary Object Representation (CBOR) is a data format whose design goals include the possibility of extremely small code size, fairly small message size, and extensibility without the need for version negotiation. These design goals make it different from earlier binary serializations such as ASN.1 and MessagePack. This document obsoletes RFC 7049, providing editorial improvements, new details, and errata fixes while keeping full compatibility with the interchange format of RFC 7049. It does not create a new version of the format. This document specifies version 1.3 of the Datagram Transport Layer Security (DTLS) protocol. DTLS 1.3 allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery. The DTLS 1.3 protocol is based on the Transport Layer Security (TLS) 1.3 protocol and provides equivalent security guarantees with the exception of order protection / non-replayability. Datagram semantics of the underlying transport are preserved by the DTLS protocol. This document obsoletes RFC 6347. This document specifies the "SVCB" ("Service Binding") and "HTTPS" DNS resource record (RR) types to facilitate the lookup of information needed to make connections to network services, such as for HTTP origins. SVCB records allow a service to be provided from multiple alternative endpoints, each with associated parameters (such as transport protocol configuration), and are extensible to support future uses (such as keys for encrypting the TLS ClientHello). They also enable aliasing of apex domains, which is not possible with CNAME. The HTTPS RR is a variation of SVCB for use with HTTP (see RFC 9110, "HTTP Semantics"). By providing more information to the client before it attempts to establish a connection, these records offer potential benefits to both performance and privacy. The SVCB DNS resource record type expresses a bound collection of endpoint metadata, for use when establishing a connection to a named service. DNS itself can be such a service, when the server is identified by a domain name. This document provides the SVCB mapping for named DNS servers, allowing them to indicate support for encrypted transport protocols. This document defines Discovery of Designated Resolvers (DDR), a set of mechanisms for DNS clients to use DNS records to discover a resolver's encrypted DNS configuration. An Encrypted DNS Resolver discovered in this manner is referred to as a "Designated Resolver". These mechanisms can be used to move from unencrypted DNS to encrypted DNS when only the IP address of a resolver is known. These mechanisms are designed to be limited to cases where Unencrypted DNS Resolvers and their Designated Resolvers are operated by the same entity or cooperating entities. It can also be used to discover support for encrypted DNS protocols when the name of an Encrypted DNS Resolver is known. This document specifies new DHCP and IPv6 Router Advertisement options to discover encrypted DNS resolvers (e.g., DNS over HTTPS, DNS over TLS, and DNS over QUIC). Particularly, it allows a host to learn an Authentication Domain Name together with a list of IP addresses and a set of service parameters to reach such encrypted DNS resolvers. This RFC is the revised basic definition of The Domain Name System. It obsoletes RFC-882. This memo describes the domain style names and their used for host address look up and electronic mail forwarding. It discusses the clients and servers in the domain name system and the protocol used between them. This RFC is the revised specification of the protocol and format used in the implementation of the Domain Name System. It obsoletes RFC-883. This memo documents the details of the domain name client - server communication. Informative References The Domain Name System (DNS) is defined in literally dozens of different RFCs. The terminology used by implementers and developers of DNS protocols, and by operators of DNS systems, has changed in the decades since the DNS was first defined. This document gives current definitions for many of the terms used in the DNS in a single document. This document updates RFC 2308 by clarifying the definitions of "forwarder" and "QNAME". It obsoletes RFC 8499 by adding multiple terms and clarifications. Comprehensive lists of changed and new definitions can be found in Appendices A and B. This document describes the DNS Security Extensions (commonly called "DNSSEC") that are specified in RFCs 4033, 4034, and 4035, as well as a handful of others. One purpose is to introduce all of the RFCs in one place so that the reader can understand the many aspects of DNSSEC. This document does not update any of those RFCs. A second purpose is to state that using DNSSEC for origin authentication of DNS data is the best current practice. A third purpose is to provide a single reference for other documents that want to refer to DNSSEC. RISE AB When using the Constrained Application Protocol (CoAP), exchanged messages can be protected end-to-end also across untrusted intermediary proxies. This can be achieved with Object Security for Constrained RESTful Environments (OSCORE) or, in the case of group communication, with Group Object Security for Constrained RESTful Environments (Group OSCORE). However, this sidesteps the proxies' abilities to cache responses from the origin server(s). This document restores cacheability of end-end protected responses at proxies, by using Group OSCORE and introducing consensus requests, which any client in an OSCORE group can send to one server or multiple servers in the same group. Work in Progress Universität Bremen TZI RFC 7252 defines the Constrained Application Protocol (CoAP), along with a number of additional specifications, including RFC 7641, RFC 7959, RFC 8132, and RFC 8323. RFC 6690 defines the link format that is used in CoAP self-description documents. Some parts of the specification may be unclear or even contain errors that may lead to misinterpretations that may impair interoperability between different implementations. The present document provides corrections, additions, and clarifications to the RFCs cited; this document thus updates these RFCs. In addition, other clarifications related to the use of CoAP in other specifications, including RFC 7390 and RFC 8075, are also provided. Work in Progress Universität Bremen TZI Fraunhofer SIT The Constrained Resource Identifier (CRI) is a complement to the Uniform Resource Identifier (URI) that represents the URI components in Concise Binary Object Representation (CBOR) rather than as a sequence of characters. This approach simplifies parsing, comparison, and reference resolution in environments with severe limitations on processing power, code size, and memory size. This RFC updates RFC 7595 by adding a column on the "URI Schemes" registry. // (This "cref" paragraph will be removed by the RFC editor:) After // approval of -28 and nit fixes in -29, the present revision -30 // contains two more small fixes for nits that were uncovered in the // RPC intake process. Work in Progress TU Dresden, Germany Unaffiliated, Vienna, Austria Huawei Technologies, Munich, Germany TU Dresden, Germany HAW Hamburg, Hamburg, Germany TU Dresden &amp; Barkhausen Institut, Dresden, Germany Proceedings of the ACM on Networking, vol. 1, no. CoNEXT2, pp. 1-25 University of California, Irvine Ph.D. Dissertation, University of California, Irvine Although the DNS Security Extensions (DNSSEC) have been under development for most of the last decade, the IETF has never written down the specific set of threats against which DNSSEC is designed to protect. Among other drawbacks, this cart-before-the-horse situation has made it difficult to determine whether DNSSEC meets its design goals, since its design goals are not well specified. This note attempts to document some of the known threats to the DNS, and, in doing so, attempts to measure to what extent (if any) DNSSEC is a useful tool in defending against these threats. This memo provides information for the Internet community. This specification defines Web Linking using a link format for use by constrained web servers to describe hosted resources, their attributes, and other relationships between links. Based on the HTTP Link Header field defined in RFC 5988, the Constrained RESTful Environments (CoRE) Link Format is carried as a payload and is assigned an Internet media type. "RESTful" refers to the Representational State Transfer (REST) architecture. A well-known URI is defined as a default entry point for requesting the links hosted by a server. [STANDARDS-TRACK] The Internet Protocol Suite is increasingly used on small devices with severe constraints on power, memory, and processing resources, creating constrained-node networks. This document provides a number of basic terms that have been useful in the standardization work for constrained-node networks. Universität Bremen TZI Ericsson Universitat Politecnica de Catalunya The Internet Protocol Suite is increasingly used on small devices with severe constraints on power, memory, and processing resources, creating constrained-node networks. This document provides a number of basic terms that have been useful in research and standardization work for constrained-node networks. This document obsoletes RFC 7228. Work in Progress DNS messages between clients and servers may be received over either UDP or TCP. UDP transport involves keeping less state on a busy server, but can cause truncation and retries over TCP. Additionally, UDP can be exploited for reflection attacks. Using TCP would reduce retransmits and amplification. However, clients commonly use TCP only for retries and servers typically use idle timeouts on the order of seconds. This document defines an EDNS0 option ("edns-tcp-keepalive") that allows DNS servers to signal a variable idle timeout. This signalling encourages the use of long-lived TCP connections by allowing the state associated with TCP transport to be managed effectively with minimal impact on the DNS transaction time. This document describes the use of Transport Layer Security (TLS) to provide privacy for DNS. Encryption provided by TLS eliminates opportunities for eavesdropping and on-path tampering with DNS queries in the network, such as discussed in RFC 7626. In addition, this document specifies two usage profiles for DNS over TLS and provides advice on performance considerations to minimize overhead from using TCP and TLS with DNS. This document focuses on securing stub-to-recursive traffic, as per the charter of the DPRIVE Working Group. It does not prevent future applications of the protocol to recursive-to-authoritative traffic. DNS queries and responses are visible to network elements on the path between the DNS client and its server. These queries and responses can contain privacy-sensitive information, which is valuable to protect. This document proposes the use of Datagram Transport Layer Security (DTLS) for DNS, to protect against passive listeners and certain active attacks. As latency is critical for DNS, this proposal also discusses mechanisms to reduce DTLS round trips and reduce the DTLS handshake size. The proposed mechanism runs over port 853. This document specifies version 1.3 of the Transport Layer Security (TLS) protocol. TLS allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery. This document updates RFCs 5705 and 6066, and obsoletes RFCs 5077, 5246, and 6961. This document also specifies new requirements for TLS 1.2 implementations. Concise Binary Object Representation (CBOR) is a data format designed for small code size and small message size. There is a need to be able to define basic security services for this data format. This document defines the CBOR Object Signing and Encryption (COSE) protocol. This specification describes how to create and process signatures, message authentication codes, and encryption using CBOR for serialization. This specification additionally describes how to represent cryptographic keys using CBOR. This document, along with RFC 9053, obsoletes RFC 8152. This document describes the privacy issues associated with the use of the DNS by Internet users. It provides general observations about typical current privacy practices. It is intended to be an analysis of the present situation and does not prescribe solutions. This document obsoletes RFC 7626. In many Internet of Things (IoT) applications, direct discovery of resources is not practical due to sleeping nodes or networks where multicast traffic is inefficient. These problems can be solved by employing an entity called a Resource Directory (RD), which contains information about resources held on other servers, allowing lookups to be performed for those resources. The input to an RD is composed of links, and the output is composed of links constructed from the information stored in the RD. This document specifies the web interfaces that an RD supports for web servers to discover the RD and to register, maintain, look up, and remove information on resources. Furthermore, new target attributes useful in conjunction with an RD are defined. This document describes the use of QUIC to provide transport confidentiality for DNS. The encryption provided by QUIC has similar properties to those provided by TLS, while QUIC transport eliminates the head-of-line blocking issues inherent with TCP and provides more efficient packet-loss recovery than UDP. DNS over QUIC (DoQ) has privacy properties similar to DNS over TLS (DoT) specified in RFC 7858, and latency characteristics similar to classic DNS over UDP. This specification describes the use of DoQ as a general-purpose transport for DNS and includes the use of DoQ for stub to recursive, recursive to authoritative, and zone transfer scenarios. This document specifies Ephemeral Diffie-Hellman Over COSE (EDHOC), a very compact and lightweight authenticated Diffie-Hellman key exchange with ephemeral keys. EDHOC provides mutual authentication, forward secrecy, and identity protection. EDHOC is intended for usage in constrained scenarios, and a main use case is to establish an Object Security for Constrained RESTful Environments (OSCORE) security context. By reusing CBOR Object Signing and Encryption (COSE) for cryptography, Concise Binary Object Representation (CBOR) for encoding, and Constrained Application Protocol (CoAP) for transport, the additional code size can be kept very low. TUD Dresden University of Technology The Constrained Application Protocol (CoAP, [RFC7252]) is available over different transports (UDP, DTLS, TCP, TLS, WebSockets), but lacks a way to unify these addresses. This document provides terminology and provisions based on Web Linking [RFC8288] and Service Bindings (SVCB, [RFC9460]) to express alternative transports available to a device, and to optimize exchanges using these. Work in Progress

Evaluation The authors of this document presented the design, implementation, and analysis of DoC in their paper "Securing Name Resolution in the IoT: DNS over CoAP" .

Acknowledgments The authors of this document want to thank , , , , , , , , , , , , , , , , , , , and for their feedback and comments. This work was supported in parts by the German Federal Ministry of Research, Technology and Space (BMFTR) under the grant numbers 16KIS1386K (TU Dresden) and 16KIS1387 (HAW Hamburg) within the research project PIVOT and under the grant numbers 16KIS1694K (TU Dresden) and 16KIS1695 (HAW Hamburg) within the research project C-ray4edge.

Authors' Addresses TUD Dresden University of Technology

Helmholtzstr. 10 Dresden D-01069 Germany martine.lenders@tu-dresden.de

christian@amsuess.com

NeuralAgent GmbH

Mies-van-der-Rohe-Straße 6 Munich D-80807 Germany cenk.gundogan@neuralagent.ai

HAW Hamburg

Berliner Tor 7 Hamburg D-20099 Germany t.schmidt@haw-hamburg.de

TUD Dresden University of Technology & Barkhausen Institut

Helmholtzstr. 10 Dresden D-01069 Germany m.waehlisch@tu-dresden.de