Concise Binary Object Representation Maintenance and ExtensionsC. Bormann Internet-Draft Universität Bremen TZI Intended status: Standards Track M. Matejka Expires: 24 August 2024 CZ.NIC 21 February 2024 Stand-in Tags for YANG-CBOR draft-bormann-cbor-yang-standin-00 Abstract YANG (RFC 7950) is a data modeling language used to model configuration data, state data, parameters and results of Remote Procedure Call (RPC) operations or actions, and notifications. YANG-CBOR (RFC 9254) defines encoding rules for YANG in the Concise Binary Object Representation (CBOR) (RFC 8949). While the overall structure of YANG-CBOR is encoded in an efficient, binary format, YANG itself has its roots in XML and therefore traditionally encodes some information such as date/times and IP addresses/prefixes in a verbose text form. This document defines how to use existing CBOR tags for this kind of information in YANG-CBOR as a "stand-in" for the text-based information that would be found in the original form of YANG-CBOR. About This Document This note is to be removed before publishing as an RFC. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-bormann-cbor-yang-standin/. Discussion of this document takes place on the CBOR (Concise Binary Object Representation Maintenance and Extensions) 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/cabo/yang-standin. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Bormann & Matejka Expires 24 August 2024 [Page 1] Internet-Draft Stand-in Tags for YANG-CBOR February 2024 Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 24 August 2024. Copyright Notice Copyright (c) 2024 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. Conventions and Definitions . . . . . . . . . . . . . . . . . 3 3. Stand-In Tags . . . . . . . . . . . . . . . . . . . . . . . . 4 3.1. ietf-yang-types: Tag 1 (Date/Time) and Tag 100 (Date) . . 4 3.2. ietf-inet-types: Tags 54 and 52 (IP addresses and prefixes) . . . . . . . . . . . . . . . . . . . . . . . . 5 3.3. Union handling . . . . . . . . . . . . . . . . . . . . . 8 4. Using Stand-In Tags . . . . . . . . . . . . . . . . . . . . . 8 4.1. Defining Stand-In Usage in Schema . . . . . . . . . . . . 8 4.2. Original stand-ins . . . . . . . . . . . . . . . . . . . 9 4.3. Legacy Round Trip . . . . . . . . . . . . . . . . . . . . 9 5. Negotiation . . . . . . . . . . . . . . . . . . . . . . . . . 9 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 7.1. stand-in tags? . . . . . . . . . . . . . . . . . . . . . 10 7.2. media-type parameters . . . . . . . . . . . . . . . . . . 10 8. Normative References . . . . . . . . . . . . . . . . . . . . 10 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 Bormann & Matejka Expires 24 August 2024 [Page 2] Internet-Draft Stand-in Tags for YANG-CBOR February 2024 1. Introduction (see abstract) 2. Conventions and Definitions The terminology of [RFC9254] applies. Legacy representation: The (often text-based) representation for a YANG data item as used in YANG-XML, YANG-JSON, and (unchanged) YANG-CBOR. Stand-in tag: A CBOR tag that can supply the information that is equivalent to a legacy representation in a more efficient format (e.g., using binary data). Encoder: The party which generates (sends) CBOR data described by YANG. Intermediate Encoder: An encoder which isn't the original author of the data, converting it from legacy representation. Decoder: The party which receives and parses CBOR data described by YANG. Intermediate Decoder: A decoder which isn't the final recipient of the data, converting it to legacy representation. Data Transfer: A series of actions, generally beginning by data origination, encoding, continuing by optional intermediate transcoding, sending and receiving, and finally decoding and consuming. Round Trip: Part of a data transfer between an encoder generating CBOR data with stand-in tags and a decoder parsing the data. Legacy Round Trip: A Round Trip where the encoder is an intermediate encoder or the decoder is an intermediate decoder and any of these converts from or to the legacy representation. Unambiguous Round Trip: A Legacy Round Trip that provides exactly the same legacy representation (not just semantically equivalent). The stand-in tag is also said to "unambiguously stand in" for the legacy representation. Bormann & Matejka Expires 24 August 2024 [Page 3] Internet-Draft Stand-in Tags for YANG-CBOR February 2024 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 3. Stand-In Tags This document defines two sets of stand-in tags. Where information starts out in a legacy representation, these tags are only used when an Unambiguous Round Trip can be achieved. 3.1. ietf-yang-types: Tag 1 (Date/Time) and Tag 100 (Date) Section 3 of [I-D.schoenw-netmod-rfc6991-bis] defines the following types in ietf-yang-types: +=============+========+==================================+========+ | YANG type | base | specification | stand- | | | type | | in | +=============+========+==================================+========+ | date-and- | string | [RFC6021] | tag 1 | | time | | | | +-------------+--------+----------------------------------+--------+ | date-with- | string | [I-D.schoenw-netmod-rfc6991-bis] | (none) | | zone-offset | | | | +-------------+--------+----------------------------------+--------+ | date-no- | string | [I-D.schoenw-netmod-rfc6991-bis] | tag | | zone | | | 100 | +-------------+--------+----------------------------------+--------+ Table 1: Legacy representations in ietf-yang-types Tag 1 (Section 3.4.2 of RFC 8949 [STD94]) can unambiguously stand in for all date-and-time values that: * do not specify a time zone (note that [I-D.schoenw-netmod-rfc6991-bis] uses the legacy "-00:00" format for time-zone-free date-times) * are not an inserted leap second (23:59:60 or 23:59:61) * do not have trailing zeroes in the fractional part of the seconds. * do not have fractional parts of the seconds with a precision that cannot be represented in floating-point tag content in a tag 1. All other date-and-time values stay in legacy representation. Bormann & Matejka Expires 24 August 2024 [Page 4] Internet-Draft Stand-in Tags for YANG-CBOR February 2024 Tag 1 uses an integer tag content for all date-and-time values without fractional seconds and a floating-point tag content for values that have fractional seconds given. Tag 100 [RFC8943] can unambiguously stand in for all date-no-zone values. 3.2. ietf-inet-types: Tags 54 and 52 (IP addresses and prefixes) Section 4 of [I-D.schoenw-netmod-rfc6991-bis] defines in ietf-inet- types: Bormann & Matejka Expires 24 August 2024 [Page 5] Internet-Draft Stand-in Tags for YANG-CBOR February 2024 +=============+============+================================+======+ |YANG type |base type |specification |stand-| | | | |in | +=============+============+================================+======+ |ip-address |union |[RFC6021] |(see | | | | |union)| +-------------+------------+--------------------------------+------+ |ipv6-address |string |[RFC6021] |tag 54| +-------------+------------+--------------------------------+------+ |ipv4-address |string |[RFC6021] |tag 52| +-------------+------------+--------------------------------+------+ |ip-address- |union |RFC 6991 |(see | |no-zone | | |union)| +-------------+------------+--------------------------------+------+ |ipv6-address-|ipv6-address|RFC 6991 |tag 54| |no-zone | | | | +-------------+------------+--------------------------------+------+ |ipv4-address-|ipv4-address|RFC 6991 |tag 52| |no-zone | | | | +-------------+------------+--------------------------------+------+ |ip-address- |union |[I-D.schoenw-netmod-rfc6991-bis]|(see | |link-local | | |union)| +-------------+------------+--------------------------------+------+ |ipv6-address-|ipv6-address|[I-D.schoenw-netmod-rfc6991-bis]|tag 54| |link-local | | | | +-------------+------------+--------------------------------+------+ |ipv4-address-|ipv4-address|[I-D.schoenw-netmod-rfc6991-bis]|tag 52| |link-local | | | | +-------------+------------+--------------------------------+------+ |ip-prefix |union |[RFC6021] |(see | | | | |union)| +-------------+------------+--------------------------------+------+ |ipv6-prefix |string |[RFC6021] |tag 54| +-------------+------------+--------------------------------+------+ |ipv4-prefix |string |[RFC6021] |tag 52| +-------------+------------+--------------------------------+------+ |ip-address- |union |[I-D.schoenw-netmod-rfc6991-bis]|(see | |and-prefix | | |union)| +-------------+------------+--------------------------------+------+ |ipv6-address-|string |[I-D.schoenw-netmod-rfc6991-bis]|tag 54| |and-prefix | | | | +-------------+------------+--------------------------------+------+ |ipv4-address-|string |[I-D.schoenw-netmod-rfc6991-bis]|tag 52| |and-prefix | | | | +-------------+------------+--------------------------------+------+ Table 2: Legacy representations in ietf-yang-types Bormann & Matejka Expires 24 August 2024 [Page 6] Internet-Draft Stand-in Tags for YANG-CBOR February 2024 An intermediate encoder MAY normalize IPv6 addresses and prefixes that do not comply with [RFC5952] but can be converted into the stand-in representation. For example, IPv6 address written as 2001:db8:: is the same as 2001:0db8::0:0 and both would be converted to 54(h'20010db8000000000000000000000000'), anyway only the first one complies with [RFC5952]. The encoder MAY refuse to convert the latter one. If the schema specifies ip-prefix, an intermediate encoder MAY normalize prefixes with non-zero bits after the prefix end. For example, if the legacy representation of ipv6-prefix is 2001:db8:1::/40, the encoder may either refuse it as malformed or convert it to 2001:db8::/40 and represent as 54([40, h'20010db8']). The encoder implementation should be clear about which normalizations are employed and how. Adapted examples from [RFC9164]: Stand-in representation of IPv6 address 2001:db8:1234:deed:beef:cafe:face:feed is 54(h'20010db81234deedbeefcafefacefeed'). CBOR encoding of stand-in (19 bytes): cbor-pretty D8 36 # tag(54) 50 # bytes(16) 20010DB81234DEEDBEEFCAFEFACEFEED CBOR encoding of legacy representation (40 bytes): cbor-pretty 78 26 # text(38) 323030313A6462383A313233343A646565643A62 6565663A636166653A666163653A66656564 Stand-in representation of IPv6 prefix 2001:db8:1234::/48 is 54([48, h'20010db81234']). CBOR encoding of stand-in (12 bytes): cbor-pretty D8 36 # tag(54) 82 # array(2) 18 30 # unsigned(48) 46 # bytes(6) 20010DB81234 # " \u0001\r\xB8\u00124" CBOR encoding of legacy representation (19 bytes): cbor-pretty 72 # text(18) 323030313A6462383A313233343A3A2F3438 # "2001:db8:1234::/48" Bormann & Matejka Expires 24 August 2024 [Page 7] Internet-Draft Stand-in Tags for YANG-CBOR February 2024 Stand-in representation of IPv6 link-local address fe80::0202:02ff:ffff:fe03:0303/64%eth0 is 54([h'fe8000000000020202fffffffe030303', 64, 'eth0']). CBOR encoding of stand-in (27 bytes): cbor-pretty D8 36 # tag(54) 83 # array(3) 50 # bytes(16) FE8000000000020202FFFFFFFE030303 18 40 # unsigned(64) 44 # bytes(4) 65746830 # "eth0" CBOR encoding of legacy representation (40 bytes): cbor-pretty 78 26 # text(38) 666538303A3A303230323A303266663A66666666 3A666530333A303330332F36342565746830 TO DO: adapt more examples from [RFC9164] TO DO: Check how the unions in [RFC6021] and [I-D.schoenw-netmod-rfc6991-bis] interact with this. E.g., the union ip-address needs to be parsed to decide between tag 54 and tag 52. 3.3. Union handling When the schema specifies a union data type for a node, there are additional requirements on the encoder and decoder. An encoder which is fully aware of data semantics MUST use the appropriate data type, even though it isn't formally specified by the schema. If an intermediate encoder doesn't fully understand the data semantics, it needs to find out which type the data actually is to choose the right stand-in. If more types are possible, it MAY choose any of these which allow for an Unambiguous Round Trip, otherwise it SHOULD keep the legacy representation. If a decoder receives data for a union-typed node, it MUST accept any data type of the union, even though it may violate additional constraints outside the schema. 4. Using Stand-In Tags 4.1. Defining Stand-In Usage in Schema TO DO: formally define the YANG extension Bormann & Matejka Expires 24 August 2024 [Page 8] Internet-Draft Stand-in Tags for YANG-CBOR February 2024 4.2. Original stand-ins The simplest situation is when no intermediate encoders and decoders are involved in the data transfer, therefore the round trip is not legacy. In this case, no conversions are involved and data is validated using the schema extension from the previous section. 4.3. Legacy Round Trip Producing a stand-in MUST be triggered by schema usage. Intermediate encoders MUST NOT encode stand-ins when no schema is available. It's generally not recommended to do a legacy round trip where both the encoder and decoder are converting from and to the legacy representation. 5. Negotiation Introducing stand-in tags in YANG-CBOR requires some form of consent between the producer and the consumer of YANG-CBOR information: * A producer that creates YANG-CBOR containing stand-in tags needs to know whether the consumer supports stand-in tags, and, possibly, which specific stand-in tags it supports. We speak about the _capability_ of a consumer to consume stand-in tags. A producer MUST NOT employ stand-in tags unless it knows about the capabilities of the consumer. A consumer SHOULD indicate its capabilities for consuming stand-in tags. * A consumer may not want to implement certain legacy text-based representations where more efficient (and easy to implement) stand-in tags are available. This places a _requirement_ on the producer (which needs to have the _capability_ to produce YANG- CBOR where those stand-in tags are used, in place of legacy representations). A producer MUST NOT employ legacy representations where stand-in tags are _required_ by the consumer. A consumer that has requirements for only receiving stand-in tags in place of legacy representations, MUST indicate this to the producer. ISSUE: Where do we put those two aspects of negotiation? * NETCONF negotiation * yang-library * media-type parameters Bormann & Matejka Expires 24 August 2024 [Page 9] Internet-Draft Stand-in Tags for YANG-CBOR February 2024 * ? 6. Security Considerations TODO Security 7. IANA Considerations 7.1. stand-in tags? ISSUE: Do we want to have a separate registry for stand-in tags? They already are CBOR tags and thus in the in the registry, but might get lost in the bulk of that (and are only identified as YANG-CBOR stand-in Tags in the specification). 7.2. media-type parameters ISSUE: Should the use of stand-in tags be mentioned in the various YANG-CBOR-based media types (as a media type parameter)? Compare how application/yang-data+cbor can use id=name/id=sid to indicate another encoding decision. 8. Normative References [I-D.schoenw-netmod-rfc6991-bis] Schönwälder, J., "Common YANG Data Types", Work in Progress, Internet-Draft, draft-schoenw-netmod-rfc6991- bis-01, 11 March 2019, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6 Address Text Representation", RFC 5952, DOI 10.17487/RFC5952, August 2010, . [RFC6021] Schoenwaelder, J., Ed., "Common YANG Data Types", RFC 6021, DOI 10.17487/RFC6021, October 2010, . Bormann & Matejka Expires 24 August 2024 [Page 10] Internet-Draft Stand-in Tags for YANG-CBOR February 2024 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8943] Jones, M., Nadalin, A., and J. Richter, "Concise Binary Object Representation (CBOR) Tags for Date", RFC 8943, DOI 10.17487/RFC8943, November 2020, . [RFC9164] Richardson, M. and C. Bormann, "Concise Binary Object Representation (CBOR) Tags for IPv4 and IPv6 Addresses and Prefixes", RFC 9164, DOI 10.17487/RFC9164, December 2021, . [RFC9254] Veillette, M., Ed., Petrov, I., Ed., Pelov, A., Bormann, C., and M. Richardson, "Encoding of Data Modeled with YANG in the Concise Binary Object Representation (CBOR)", RFC 9254, DOI 10.17487/RFC9254, July 2022, . [STD94] Bormann, C. and P. Hoffman, "Concise Binary Object Representation (CBOR)", STD 94, RFC 8949, December 2020. Acknowledgments TODO acknowledge. Authors' Addresses Carsten Bormann Universität Bremen TZI Postfach 330440 D-28359 Bremen Germany Phone: +49-421-218-63921 Email: cabo@tzi.org Maria Matejka CZ.NIC Milesovska 1136/5 13000 Praha Czechia Email: maria.matejka@nic.cz, mq@jmq.cz Bormann & Matejka Expires 24 August 2024 [Page 11]