CBOR M. S. Lenders Internet-Draft FU Berlin Intended status: Standards Track C. Bormann Expires: 14 September 2023 Universität Bremen TZI T. C. Schmidt HAW Hamburg M. Wählisch FU Berlin 13 March 2023 A Concise Binary Object Representation (CBOR) of DNS Messages draft-lenders-dns-cbor-02 Abstract This document specifies a compressed data format of DNS messages using the Concise Binary Object Representation [RFC8949]. The primary purpose is to keep DNS messages small in constrained networks. 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://anr-bmbf- pivot.github.io/draft-lenders-dns-cbor/draft-lenders-dns-cbor.html. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-lenders-dns-cbor/. Discussion of this document takes place on the CBOR Working Group mailing list (mailto:cbor@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/cbor/. Subscribe at https://www.ietf.org/mailman/listinfo/cbor/. Source for this draft and an issue tracker can be found at https://github.com/anr-bmbf-pivot/draft-lenders-dns-cbor. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Lenders, et al. Expires 14 September 2023 [Page 1] Internet-Draft dns+cbor March 2023 Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 14 September 2023. Copyright Notice Copyright (c) 2023 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights 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 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. CBOR Representations (application/dns+cbor) . . . . . . . . . 4 3.1. Domain Name Representation . . . . . . . . . . . . . . . 4 3.2. Standard DNS Resource Records (RRs) . . . . . . . . . . . 4 3.3. DNS Queries . . . . . . . . . . . . . . . . . . . . . . . 6 3.4. DNS Responses . . . . . . . . . . . . . . . . . . . . . . 7 3.5. EDNS(0) . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.6. Name and Address Compression with Packed CBOR . . . . . . 9 3.6.1. Table Setup . . . . . . . . . . . . . . . . . . . . . 11 4. Security Considerations . . . . . . . . . . . . . . . . . . . 11 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 5.1. Media Type Registration . . . . . . . . . . . . . . . . . 12 5.1.1. "application/dns+cbor" . . . . . . . . . . . . . . . 12 5.2. CoAP Content-Format Registration . . . . . . . . . . . . 13 5.2.1. "application/dns-cbor" . . . . . . . . . . . . . . . 13 5.2.2. "application/dns+cbor;packed=1" . . . . . . . . . . . 13 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 6.1. Normative References . . . . . . . . . . . . . . . . . . 13 6.2. Informative References . . . . . . . . . . . . . . . . . 14 Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 15 A.1. DNS Queries . . . . . . . . . . . . . . . . . . . . . . . 15 A.2. DNS Responses . . . . . . . . . . . . . . . . . . . . . . 16 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 17 B.1. Since [draft-lenders-dns-cbor-01] . . . . . . . . . . . . 17 Lenders, et al. Expires 14 September 2023 [Page 2] Internet-Draft dns+cbor March 2023 B.2. Since draft-lenders-dns-cbor-00 . . . . . . . . . . . . . 17 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 18 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18 1. Introduction In constrained networks [RFC7228], the link layer may restrict the payload sizes to only a few hundreds bytes. Encrypted DNS resolution, such as DNS over HTTPS (DoH) [RFC8484] or DNS over CoAP (DoC) [I-D.ietf-core-dns-over-coap], may lead to DNS message sizes that exceed this limit, even when implementing header compression such as 6LoWPAN IPHC [RFC6282] or SCHC [RFC8724], [RFC8824]. Although adoption layers such as 6LoWPAN [RFC4944] or SCHC [RFC8724] offer fragmentation to comply with small MTUs, fragmentation should be avoided in constrained networks, because fragmentation combined with high packet loss multiplies the loss. As such, a compression format for DNS messages is needed. This document specifies a compressed data format for DNS messages. DNS messages are encoded in Concise Binary Object Representation (CBOR) [RFC8949] and, additionally, unnecessary or redundant information is removed. To use the outcome of this specification in DoH and DoC, this document also specifies a Media Type header for DoH and a Content-Format option for DoC. 2. Terminology CBOR types (unsigned integer, byte string, text string, arrays, etc.) are used as defined in [RFC8949]. TBD DNS server and client. A DNS query is a message that queries DNS information from an upstream DNS resolver. The term "constrained networks" is used as defined in [RFC7228]. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. Lenders, et al. Expires 14 September 2023 [Page 3] Internet-Draft dns+cbor March 2023 3. CBOR Representations (application/dns+cbor) To keep overhead minimal, a DNS message is represented as CBOR arrays. All CBOR items used in this specification are of definite length. CBOR arrays that do not follow the length definitions of this or follow-up specifications, MUST be silently ignored. It is assumed that DNS query and DNS response are distinguished message types and that the query can be mapped to the response by the transport protocol of choice. To define the representation of binary objects we use the Concise Data Definition Language (CDDL) [RFC8610]. If, for any reason, a DNS message is not representable in the CBOR format specified in this document, a fallback to the another DNS message format, e.g., the classic DNS wire format, MUST always be possible. 3.1. Domain Name Representation Domain names are represented in their commonly known string format (e.g., "example.org", see Section 2.3.1 in [RFC1035]) and in IDNA encoding [RFC5890] as a text string. For the purpose of this document, domain names remain case-insensitive as specified in [RFC1035]. The representation of a domain name is defined in Figure 1. domain-name = tstr .regexp "([^.]+\.)*[^.]+" Figure 1: Domain Name Definition 3.2. Standard DNS Resource Records (RRs) DNS resource records are encoded either in their binary form as a byte string or as CBOR arrays containing 2 to 5 entries in the following order: 1. An optional name (as text string, see Section 3.1), 2. A TTL (as unsigned integer), 3. An optional record type (as unsigned integer), 4. An optional record class (as unsigned integer), and lastly 5. A record data entry (as unsigned integer, negative integer, byte string, or text string). Lenders, et al. Expires 14 September 2023 [Page 4] Internet-Draft dns+cbor March 2023 If the first item of the resource record is a text string, it is its name. If the name is elided, the name is derived from the question section of the message. For responses, the question section is either taken from the query (see Section 3.3) or provided with the response see Section 3.4. The query may be derived from the transport context. If the record type is elided, the record type from the question is assumed. If record class is elided, the record class from the question is assumed. When a record class is required, the record type MUST also be provided. The byte format of the record data as a byte string follows the wire format as specified in Section 3.3 [RFC1035] (or other specifications of the respective record type). Note that this format does not include the RDLENGTH field from [RFC1035] as this value is encoded in the length field of the CBOR byte string. If the record data represents a domain name (e.g., for CNAME or PTR records), the record data MAY be represented as a text string as specified in Section 3.1. This can save 1 byte of data, because the byte representation of DNS names requires both an additional byte to define the length of the first name component and well as a zero byte at the end of the name. With CBOR on the other hand only 1 byte is required to define type and length of the text string up until a string length of 23 characters. Likewise, if the record data is purely a numerical value, it can be expressed as either an unsigned or negative integer. The representation of a DNS resource records is defined in Figure 2. type-spec = ( record-type: uint, ? record-class: uint, ) rr = ( ? name: domain-name, ttl: uint, ? type-spec, rdata: int / bstr / domain-name, ) dns-rr = [rr] / bstr Figure 2: DNS Resource Record Definition Lenders, et al. Expires 14 September 2023 [Page 5] Internet-Draft dns+cbor March 2023 3.3. DNS Queries DNS queries are encoded as CBOR arrays containing up to 5 entries in the following order: 1. An optional transaction ID (as unsigned integer), 2. An optional flag field (as unsigned integer), 3. The question section (as array), 4. An optional authority section (as array), and 5. An optional additional section (as array) If the first item of the query is an array, it is the question section, if it is an unsigned integer, it is the transaction ID. If the transaction ID is present and followed by another unsigned integer, that item is a flag field and maps to the header flags in [RFC1035] and the "DNS Header Flags" IANA registry including the QR flag and the Opcode. It MUST be lesser than 2^16. If the transaction ID is elided, the value 0 is assumed, same for the flags. The transaction ID MUST be included and set to an unpredictable value lesser than 2^32, if the DNS transport can not ensure the prevention of DNS response spoofing. An example for such a transport is unencrypted DoC (see [I-D.ietf-core-dns-over-coap], Section 6). The question section is encoded as a CBOR array containing up to 3 entries: 1. The queried name (as text string, see Section 3.1), 2. An optional record type (as unsigned integer), and 3. An optional record class (as unsigned integer) If the record type is elided, record type AAAA as specified in [RFC3596] is assumed. If the record class is elided, record class IN as specified in [RFC1035] is assumed. When a record class is required, the record type MUST also be provided. Lenders, et al. Expires 14 September 2023 [Page 6] Internet-Draft dns+cbor March 2023 The remainder of the query is either empty or MUST consist of up to two arrays. The first array, if present, encodes the authority section of the query as an array of DNS resource records (see Section 3.2) The second array, if present, encodes the additional section of the query as an array of DNS resource records (see Section 3.2) The representation of a DNS query is defined in Figure 3. query-id-flags = ( id: uint .default 0, ? flags: uint .default 0, ) question-section = ( name: domain-name, ? type-spec, ) extra-sections = ( ? authority: [+ dns-rr], additional: [+ dns-rr], ) query-sections = ( ? query-id-flags, [question-section], ? extra-sections, ) dns-query = [query-sections] Figure 3: DNS Query Definition 3.4. DNS Responses DNS responses are encoded as a CBOR array containing up to 7 entries. 1. An optional transaction ID (as unsigned integer), 2. An optional flag field (as unsigned integer), 3. An optional question section (as array, encoded as described in Section 3.3) 4. The answer section (as array), 5. An optional authority section (as array), and 6. An optional additional section (as array) Lenders, et al. Expires 14 September 2023 [Page 7] Internet-Draft dns+cbor March 2023 If the CBOR array is a response to a query that contains a transaction ID, it MUST be included and set to the corresponding value present in the query. If it is not included, the transaction ID is implied to be 0. If the CBOR array is a response to a query for which the flags indicate that flags are set in the response, they MUST be set accordingly and thus included in the response. If the flags are not included, the flags are implied to be 0x8000 (everything unset except for the QR flag). If the response includes only 1 array, this is the DNS answer section represented as an array of one or more DNS Resource Records (see Section 3.2). If the response includes 2 arrays, the first entry is a question section and the second entry is an answer section. The question section is encoded like as specified in Section 3.3, the answer section is represented as an array of one or more DNS Resource Records (see Section 3.2). If the response includes 3 arrays, the first section is a question section, the second an answer section, and the third an additional section (TBD: back choice to favor additional section by empirical data). Again, the question section is encoded like a DNS query as specified in Section 3.3 and both answer and additional sections are represented each as an array of one or more DNS Resource Records (see Section 3.2). If the response includes 4 arrays, the first section is a question section, the second an answer section, the third an authority section, and the fourth an additional section (TBD: back by empirical data). They follow the specification of 3 arrays in the answer. The authority section is also represented as an array of one or more DNS Resource Records (see Section 3.2). Lenders, et al. Expires 14 September 2023 [Page 8] Internet-Draft dns+cbor March 2023 response-id-flags = ( id: uint .default 0, ? flags: uint .default 0x8000, ) response-sections = (( ? response-id-flags, answer: [+ dns-rr], ) // ( ? response-id-flags, question: [question-section], answer: [+ dns-rr], ? extra-sections, )) dns-response = [response-sections] Figure 4: DNS Response Definition 3.5. EDNS(0) TBD, do we need special formatting here? 3.6. Name and Address Compression with Packed CBOR If both DNS server and client support packed CBOR [I-D.ietf-cbor-packed], it MAY be used for name and address compression in DNS responses. A DNS client uses media type "application/dns+cbor;packed=1" to negotiate (see, e.g., [RFC9110] or [RFC7252], Section 5.5.4) with the DNS server if the server supports packed CBOR. If it does, it MAY request the response to be in packed CBOR (media type "applicaton/ dns+cbor;packed=1"). The server then SHOULD reply with the response in packed CBOR. The representation of DNS responses in packed CBOR differs, in that responses are now represented as a CBOR array of two arrays. The first array is a packing table that is used both as shared item table and argument table (see [I-D.ietf-cbor-packed], Section 2.1), the second is the compressed response. The representation of a packed DNS response is defined in Figure 5. compr-dns-response = any /TBD; how to express packed CBOR in CDDL?/ packed-dns-response = [[pack-table], compr-dns-response] pack-table = any Figure 5: Definition of DNS messages in packed CBOR Lenders, et al. Expires 14 September 2023 [Page 9] Internet-Draft dns+cbor March 2023 If an index in the packing table is referenced with shared item reference ([I-D.ietf-cbor-packed], Section 2.2) a decoder uses the packing table as a shared item table. If an index in the packing table is referenced as an argument ([I-D.ietf-cbor-packed], Sections 2.3 and 4), a decoder uses the packing table as an argument table. Discussion TBD: * For queries, as they are only one question, i.e. at most one value of each at most, compression is not necessary. * Address and name compression are mostly about affix compression (i.e. straight/inverse referencing) ==> For occasions were value is the affix (e.g., "example.org" in ANY example in Appendix A.2) use shared item referencing to argument table to safe bytes (no extra shared item table, no, e.g., 216(""), just simple(0)) - *Example:* Using Basic Packed CBOR ([I-D.ietf-cbor-packed], section 3.1): o 131 bytes (Basic Packed CBOR) o 200 bytes (plain CBOR, see Appendix A.2) o 194 bytes (wire-format) 113( [ ["_coap._udp.local", "example.org", 3600, 28, 2], [h'20010db800000000000000000000', simple(1)], [ [simple(1), 12, 1], [[simple(1), simple(0)]], [ [simple(1), simple(4), 217("ns1.")], [simple(1), simple(4), 217("ns2.")] ], [ [simple(0), simple(1), simple(3), 6(h'0001')], [simple(0), simple(1), simple(3), 6(h'0002')], [217("ns1."), simple(1), simple(3), 6(h'0035')], [217("ns2."), simple(1), simple(3), 6(h'3535')] ] ] ] ) Lenders, et al. Expires 14 September 2023 [Page 10] Internet-Draft dns+cbor March 2023 vs. application/dns+cbor;packed=1 (shared and argument table as one) 126 bytes: [ [ h'20010db800000000000000000000', "_coap._udp.local" "example.org", 3600, 28, 2 ], [ [simple(2), 12, 1], [[simple(3), simple(1)]], [ [simple(2), simple(5), 218("ns1.")], [simple(2), simple(5), 218("ns2.")] ], [ [simple(1), simple(3), simple(4), 6(h'0001')], [simple(1), simple(3), simple(4), 6(h'0002')], [218("ns1."), simple(3), simple(4), 6(h'0035')], [218("ns2."), simple(3), simple(4), 6(h'3535')] ] ] ] 3.6.1. Table Setup TBD How to construct the packing table, here's a sketch: * Find most often used prefix and values - Probably some threshold needed, to prevent, e.g., 1 byte prefixes filling valuable table space * Sort descending by number of occurrences and length - Long prefixes should take precedence for index 0 for Tag 6 usage 4. Security Considerations TODO Security 5. IANA Considerations Lenders, et al. Expires 14 September 2023 [Page 11] Internet-Draft dns+cbor March 2023 5.1. Media Type Registration This document registers a media type for the serialization format of DNS messages in CBOR. It follows the procedures specified in [RFC6838]. 5.1.1. "application/dns+cbor" Type name: application Subtype name: dns+cbor Required parameters: None Optional parameters: packed Encoding considerations: Must be encoded as using [RFC8949]. See [TBD-this-spec] for details. Security considerations: See Section 4 of this draft Interoperability considerations: TBD Published specification: [TBD-this-spec] Applications that use this media type: TBD DNS over X systems Fragment Identifier Considerations: TBD Additional information: Deprecated alias names for this type: N/A Magic number(s): N/A File extension(s): dnsc Macintosh file type code(s): none Person & email address to contact for further information: Martine S. Lenders m.lenders@fu-berlin.de (mailto:m.lenders@fu-berlin.de) Intended usage: COMMON Restrictions on Usage: None? Author: Martine S. Lenders m.lenders@fu-berlin.de (mailto:m.lenders@fu-berlin.de) Lenders, et al. Expires 14 September 2023 [Page 12] Internet-Draft dns+cbor March 2023 Change controller: Martine S. Lenders m.lenders@fu-berlin.de (mailto:m.lenders@fu-berlin.de) Provisional registrations? No 5.2. CoAP Content-Format Registration IANA is requested to assign CoAP Content-Format ID for the new DNS message media types in the "CoAP Content-Formats" sub-registry, within the "CoRE Parameters" registry [RFC7252], corresponding the "application/dns+cbor" media type specified in Section 5.1: 5.2.1. "application/dns-cbor" Media-Type: application/dns+cbor Encoding: - Id: TBD Reference: [TBD-this-spec] 5.2.2. "application/dns+cbor;packed=1" Media-Type: application/dns+cbor;packed=1 Encoding: - Id: TBD Reference: [TBD-this-spec] 6. References 6.1. Normative References [I-D.ietf-cbor-packed] Bormann, C., "Packed CBOR", Work in Progress, Internet- Draft, draft-ietf-cbor-packed-08, 23 January 2023, . [RFC1035] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, November 1987, . Lenders, et al. Expires 14 September 2023 [Page 13] Internet-Draft dns+cbor March 2023 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC3596] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi, "DNS Extensions to Support IP Version 6", STD 88, RFC 3596, DOI 10.17487/RFC3596, October 2003, . [RFC5890] Klensin, J., "Internationalized Domain Names for Applications (IDNA): Definitions and Document Framework", RFC 5890, DOI 10.17487/RFC5890, August 2010, . [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type Specifications and Registration Procedures", BCP 13, RFC 6838, DOI 10.17487/RFC6838, January 2013, . [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, June 2014, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data Definition Language (CDDL): A Notational Convention to Express Concise Binary Object Representation (CBOR) and JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610, June 2019, . [RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object Representation (CBOR)", STD 94, RFC 8949, DOI 10.17487/RFC8949, December 2020, . 6.2. Informative References [I-D.ietf-core-dns-over-coap] Lenders, M. S., Amsüss, C., Gündoğan, C., Schmidt, T. C., and M. Wählisch, "DNS over CoAP (DoC)", Work in Progress, Internet-Draft, draft-ietf-core-dns-over-coap-01, 24 October 2022, . Lenders, et al. Expires 14 September 2023 [Page 14] Internet-Draft dns+cbor March 2023 [RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, "Transmission of IPv6 Packets over IEEE 802.15.4 Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007, . [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, DOI 10.17487/RFC6282, September 2011, . [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for Constrained-Node Networks", RFC 7228, DOI 10.17487/RFC7228, May 2014, . [RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018, . [RFC8724] Minaburo, A., Toutain, L., Gomez, C., Barthel, D., and JC. Zuniga, "SCHC: Generic Framework for Static Context Header Compression and Fragmentation", RFC 8724, DOI 10.17487/RFC8724, April 2020, . [RFC8824] Minaburo, A., Toutain, L., and R. Andreasen, "Static Context Header Compression (SCHC) for the Constrained Application Protocol (CoAP)", RFC 8824, DOI 10.17487/RFC8824, June 2021, . [RFC9110] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Ed., "HTTP Semantics", STD 97, RFC 9110, DOI 10.17487/RFC9110, June 2022, . Appendix A. Examples A.1. DNS Queries A DNS query of the record AAAA in class IN for name "example.org" is represented in CBOR extended diagnostic notation (EDN) (see Section 8 in [RFC8949] and Appendix G in [RFC8610]) as follows: [["example.org"]] A query of an A record for the same name is represented as Lenders, et al. Expires 14 September 2023 [Page 15] Internet-Draft dns+cbor March 2023 [["example.org", 1]] A query of ANY record for that name is represented as [["example.org", 255, 255]] A.2. DNS Responses The responses to the examples provided in Appendix A.1 are shown below. We use the CBOR extended diagnostic notation (EDN) (see Section 8 in [RFC8949] and Appendix G in [RFC8610]). To represent an AAAA record with TTL 300 seconds for the IPv6 address 2001:db8::1, a minimal response to ["example.org"] could be [[[300, h'20010db8000000000000000000000001']]] In this case, the name is derived from the query. If the name or the context is required, the following response would also be valid: [[["example.org", 300, h'20010db8000000000000000000000001']]] If the query can not be mapped to the response for some reason, a response would look like: [["example.org"], [[300, h'20010db8000000000000000000000001']]] To represent a minimal response of an A record with TTL 3600 seconds for the IPv4 address 192.0.2.1, a minimal response to ["example.org", 1] could be [[300, h'c0000201']] Note that here also the 1 of record type A can be elided, as this record type is specified in the question section. Lastly, a response to ["example.org", 255, 255] could be Lenders, et al. Expires 14 September 2023 [Page 16] Internet-Draft dns+cbor March 2023 [ ["example.org", 12, 1], [[3600, "_coap._udp.local"]], [ [3600, 2, "ns1.example.org"], [3600, 2, "ns2.example.org"] ], [ [ "_coap._udp.local", 3600, 28, h'20010db8000000000000000000000001' ], [ "_coap._udp.local", 3600, 28, h'20010db8000000000000000000000002' ], [ "ns1.example.org", 3600, 28, h'20010db8000000000000000000000035' ], [ "ns2.example.org", 3600, 28, h'20010db8000000000000000000003535' ] ] ] This one advertises two local CoAP servers (identified by service name _coap._udp.local) at 2001:db8::1 and 2001:db8::2 and two nameservers for the example.org domain, ns1.example.org at 2001:db8::35 and ns2.example.org at 2001.db8::3535. Each of the transmitted records has a TTL of 3600 seconds. Appendix B. Change Log B.1. Since [draft-lenders-dns-cbor-01] * Update definitions to accommodate for TID and flags, as well as more sections in query * Clarify fallback to wire-format B.2. Since draft-lenders-dns-cbor-00 (https://datatracker.ietf.org/doc/html/draft-lenders-dns-cbor-00) * Add support for DNS transaction IDs * Name and Address compression utilizing CBOR-packed Lenders, et al. Expires 14 September 2023 [Page 17] Internet-Draft dns+cbor March 2023 * Minor fixes to CBOR EDN and CDDL Acknowledgments TODO acknowledge. * Carsten Bormann Authors' Addresses Martine Sophie Lenders Freie Universität Berlin Email: m.lenders@fu-berlin.de Carsten Bormann Universität Bremen TZI Email: cabo@tzi.org Thomas C. Schmidt HAW Hamburg Email: t.schmidt@haw-hamburg.de Matthias Wählisch Freie Universität Berlin Email: m.waehlisch@fu-berlin.de Lenders, et al. Expires 14 September 2023 [Page 18]