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 https://www.rfc-editor.org/info/rfc9595.¶

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

Some of the items defined in YANG [RFC7950] require the use of a unique identifier. In both the Network Configuration Protocol (NETCONF) [RFC6241] and RESTCONF [RFC8040], these identifiers are implemented using names. To allow the implementation of data models defined in YANG in constrained devices [RFC7228] and constrained networks, a more compact method to identify YANG items is required. This compact identifier, called the YANG Schema Item iDentifier or YANG SID (or simply SID in this document and when the context is clear), is encoded using a 63-bit unsigned integer. The limitation to 63-bit unsigned integers allows SIDs to be manipulated more easily on platforms that might otherwise lack 64-bit unsigned arithmetic. The loss of a single bit of range is not significant, given the size of the remaining space.¶

The following items are identified using SIDs:¶

• identities¶

• data nodes (note: including those nodes defined by the 'rc:yang-data' extension [RFC8040] and the 'sx:structure' extension [RFC8791])¶

• remote procedure calls (RPCs) and associated input(s) and output(s)¶

• actions and associated input(s) and output(s)¶

• notifications and associated information¶

• YANG modules and features¶

It is possible that some protocols will use only a subset of the assigned SIDs; for example, for protocols other than NETCONF [RFC6241] that provide access to YANG-modeled data, such as [CORE-COMI], the transport of YANG module SIDs might be unnecessary. Other protocols might need to be able to transport this information -- for example, protocols related to discovery such as the Constrained YANG Module Library [YANG-LIBRARY].¶

SIDs are globally unique integers. A registration system is used in order to guarantee their uniqueness. SIDs are registered in blocks called "SID ranges". Once they are considered "stable", SIDs are assigned permanently. Items introduced by a new revision of a YANG module are added to the list of SIDs already assigned. This is discussed in more detail in Section 2.¶

The assignment of SIDs to YANG items is usually automated as discussed in Appendix B, which also discusses some cases where manual interventions may be appropriate.¶

Section 3 provides more details about the registration processes for YANG modules and associated SIDs. To enable the implementation of these processes, Section 4 defines a standard file format used to store and publish SIDs.¶

IETF-managed YANG modules that need to allocate SIDs will use the IANA mechanisms specified in this document. See Section 6 for details. YANG modules created by other parties allocate SID ranges using the IANA allocation mechanisms via Mega-Ranges (see Section 6.3); within the Mega-Range allocation, those other parties are free to make up their own mechanism.¶

Among other uses, YANG SIDs are particularly useful for obtaining a compact encoding for YANG-CBOR [RFC9254]. At the time of writing, a tool for automated ".sid" file generation is available as part of the open-source project PYANG [PYANG].¶

2. Objectives

The overriding objective of the SID assignment and registration system is to ensure global interoperability of protocols that employ SIDs in order to communicate about data modeled in YANG. This objective poses certain requirements on the stability of SIDs while at the same time not hindering active evolution of the YANG modules the SIDs are intended to support.¶

Additional objectives include:¶

• enabling the developer of a YANG module to also be the originating entity for the SIDs pertaining to that module.¶

• making it easy for YANG developers to obtain SIDs.¶

• enabling other developers to define SIDs for a module where the developer of the module is not interested in assigning the SIDs.¶

• keeping an assignment regime that keeps short SIDs (2..4 bytes) readily available for the applications that would benefit from them while at the same time employing the vast 63-bit SID space to facilitate permissionless actions.¶

• enabling multiple entities to provide services that support the assignment of SIDs.¶

• maintaining some locality in the assignment of SIDs so the efficiencies of the SID delta mechanism can be fully employed.¶

• enabling various software components to operate in terms of SIDs without having complete information about other parties in the communication process.¶

While IANA ultimately maintains the registries that govern SIDs for IETF-defined modules, various support tools (such as, at the time of writing, the YANG Catalog [yangcatalog]) need to provide the support to enable SID assignment and use for modules still in IETF development. Developers of open-source or proprietary YANG modules also need to be able to serve as such entities autonomously, possibly forming alliances independent of the IETF, while still fitting in the overall SID number space managed by IANA. Obviously, this process has a number of parallels to the management of IP addresses but is also very different.¶

3. ".sid" File Lifecycle

YANG is a language designed to model data accessed using one of the compatible protocols (e.g., NETCONF [RFC6241], RESTCONF [RFC8040], and the CoAP Management Interface (CORECONF) [CORE-COMI]). A YANG module defines hierarchies of data, including configuration, state data, RPCs, actions, and notifications.¶

Many YANG modules are not created in the context of constrained applications. YANG modules can be implemented using NETCONF [RFC6241] or RESTCONF [RFC8040] without the need to assign SIDs.¶

As needed, authors of YANG modules can assign SIDs to their YANG modules. In order to do that, they should first obtain a SID range from a registry and use that range to assign or generate SIDs to items in their YANG module. The assignments can then be stored in a ".sid" file. For an example of how this could be achieved, please refer to Appendix C.¶

Items introduced by a new revision of a YANG module are added to the list of SIDs already assigned. When this is done during the development of a new protocol document, it may be necessary to make provisional assignments. They may get changed, revised, or withdrawn during the development of a new standard. These provisional assignments are marked with a status of "unstable", so that they can be removed and the SID number possibly reassigned for a different YANG schema name/path later in the development process. When the specification is advanced to a final document, the assignment is marked with a status of "stable". During a period of development starting from a published specification, two variants of the ".sid" file should be made available by the tooling involved in that development: (1) a "published" ".sid" file with the existing stable SID assignments only (which the development effort should keep stable), as well as (2) an "unpublished" ".sid" file that also contains the unstable SID assignments.¶

Registration of the ".sid" file associated with a YANG module is optional but recommended; doing so will promote interoperability between devices and avoid duplicate allocation of SIDs to a single YANG module. Different registries might have different requirements for the registration and publication of the ".sid" files. For a diagram of one possible scenario, please refer to the activity diagram shown in Figure 4 in Appendix C.¶

Each time a YANG module, one or more of its imported modules, or one or more of its included submodules are updated, a new ".sid" file MAY be created if the new or updated items will need SIDs. All the SIDs present in a previous version of the ".sid" file that was in active use MUST be present in the new version as well. The creation of this new version of the ".sid" file SHOULD be performed using an automated tool.¶

If a new revision requires more SIDs than initially allocated, a new SID range MUST be added to the 'assignment-range' item as defined in Section 4. These extra SIDs are used for subsequent assignments.¶

For an example of this update process, see the activity diagram shown in Figure 5 in Appendix C.¶

4. ".sid" File Format

".sid" files are used to persist and publish SIDs assigned to the different YANG items in a specific YANG module.¶

The following tree diagram [BCP215] provides an overview of the data model:¶

module: ietf-sid-file

  structure sid-file:
    +-- module-name            yang:yang-identifier
    +-- module-revision?       revision-identifier
    +-- sid-file-version?      sid-file-version-identifier
    +-- sid-file-status?       enumeration
    +-- description?           string
    +-- dependency-revision*   [module-name]
    |  +-- module-name         yang:yang-identifier
    |  +-- module-revision     revision-identifier
    +-- assignment-range*      [entry-point]
    |  +-- entry-point         sid
    |  +-- size                uint64
    +-- item*                  [namespace identifier]
       +-- status?             enumeration
       +-- namespace           enumeration
       +-- identifier          union
       +-- sid                 sid

The following YANG module defines the structure of ".sid" files. Encoding is performed in JSON [STD90] using the rules defined in [RFC7951]. This module imports 'ietf-yang-types' [RFC6991] and 'ietf-yang-structure-ext' [RFC8791]. It also references [STD68], [RFC7950], and [BCP216].¶

<CODE BEGINS> file "ietf-sid-file@2024-07-31.yang"

module ietf-sid-file {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-sid-file";
  prefix sid;

  import ietf-yang-types {
    prefix yang;
    reference
      "RFC 6991: Common YANG Data Types";
  }
  import ietf-yang-structure-ext {
    prefix sx;
    reference
      "RFC 8791: YANG Data Structure Extensions";
  }

  organization
    "IETF CORE Working Group";

  contact
    "WG Web:   <https://datatracker.ietf.org/wg/core/>

     WG List:  <mailto:core@ietf.org>

     Editor:   Michel Veillette
               <mailto:michel.veillette@trilliant.com>

     Editor:   Andy Bierman
               <mailto:andy@yumaworks.com>

     Editor:   Alexander Pelov
               <mailto:alexander.pelov@imt-atlantique.fr>

     Editor:   Ivaylo Petrov
               <mailto:ivaylopetrov@google.com>";

  description
    "This module defines the structure of the '.sid' files.

     Each '.sid' file contains the mapping between each
     string identifier defined by a YANG module and a
     corresponding numeric value called a YANG SID.

     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 (RFC 2119) (RFC 8174) when, and only when,
     they appear in all capitals, as shown here.

     Copyright (c) 2024 IETF Trust and the persons identified as
     authors of the code.  All rights reserved.

     Redistribution and use in source and binary forms, with or
     without modification, is permitted pursuant to, and subject to
     the license terms contained in, the Revised BSD License set
     forth in Section 4.c of the IETF Trust's Legal Provisions
     Relating to IETF Documents
     (https://trustee.ietf.org/license-info).

     This version of this YANG module is part of RFC 9595; see
     the RFC itself for full legal notices.";

  revision 2024-07-31 {
    description
      "Initial revision.";
    reference
      "RFC 9595: YANG Schema Item iDentifier (YANG SID)";
  }

  typedef revision-identifier {
    type string {
      pattern '[0-9]{4}-[0-9]{2}-[0-9]{2}';
    }
    description
      "Represents a date in YYYY-MM-DD format.";
  }

  typedef sid-file-version-identifier {
    type uint32;
    description
      "Represents the version of a '.sid' file.";
  }

  typedef sid {
    type uint64 {
      range "0..9223372036854775807";
    }
    description
      "YANG Schema Item iDentifier.";
    reference
      "RFC 9595: YANG Schema Item iDentifier (YANG SID)";
  }

  typedef schema-node-path {
    type string {
      pattern
        '/[a-zA-Z_][a-zA-Z0-9\-_.]*:[a-zA-Z_][a-zA-Z0-9\-_.]*' +
        '(/[a-zA-Z_][a-zA-Z0-9\-_.]*(:[a-zA-Z_][a-zA-Z0-9\-_.]*)?)*';
    }
    description
      "A schema-node path is an absolute YANG schema-node
       identifier as defined by the YANG ABNF rule
       'absolute-schema-nodeid', except that module names are used
       instead of prefixes.

       This string additionally follows the following rules:

       -  The leftmost (top-level) data node name is always in the
          namespace-qualified form.
       -  Any subsequent schema-node name is in the
          namespace-qualified form if the node is defined in a
          module other than its parent node.  Otherwise, the
          simple form is used.  No predicates are allowed.";
    reference
      "RFC 5234 (STD 68): Augmented BNF for Syntax Specifications:
                          ABNF
       RFC 7950: The YANG 1.1 Data Modeling Language,
                 Section 6.5: Schema Node Identifier";
  }

  sx:structure sid-file {
    uses sid-file-contents;
  }

  grouping sid-file {
    description
      "A grouping that contains a YANG container
       representing the file structure of a '.sid' file.";

    container sid-file {
      description
        "A wrapper container that together with the 'sx:structure'
         extension marks the YANG data structures inside as not
         being intended to be implemented as part of a
         configuration datastore or as an operational state within
         the server.";
      uses sid-file-contents;
    }
  }

  grouping sid-file-contents {
    description
      "A grouping that defines the contents of a container that
       represents the file structure of a '.sid' file.";

    leaf module-name {
      type yang:yang-identifier;
      mandatory true;
      description
        "Name of the YANG module associated with this
         '.sid' file.";
    }

    leaf module-revision {
      type revision-identifier;
      description
        "Revision of the YANG module associated with this '.sid'
         file.
         This leaf is not present if no revision statement is
         defined in the YANG module.";
    }

    leaf sid-file-version {
      type sid-file-version-identifier;
      default 0;
      description
        "Optional leaf that specifies the version number of the
         '.sid' file.  '.sid' files and the version sequence are
         specific to a given YANG module revision.  This number
         starts at zero when there is a new YANG module revision
         and increases monotonically.  This number can distinguish
         updates to the '.sid' file - for instance, as the result
         of new processing or reported errata.";
    }

    leaf sid-file-status {
      type enumeration {
        enum unpublished {
          description
            "This '.sid' file is unpublished (BCP 216) and is
             also called a work-in-progress or workfile.
             This may be when it accompanies an unpublished YANG
             module or when only the '.sid' file itself is
             unpublished.
             The 'item' list MAY contain entries with a status
             value of 'unstable'.";
          reference
            "RFC 8407 (BCP 216): Guidelines for Authors and
                                 Reviewers of Documents Containing
                                 YANG Data Models";
        }
        enum published {
          description
            "This '.sid' file is published.  This status
             applies to '.sid' files for published YANG modules.
             The 'item' list MUST NOT contain entries with a
             status value of 'unstable'.";
        }
      }
      default "published";
      description
        "Optional leaf that specifies the status of the
         '.sid' file.";
    }

    leaf description {
      type string;
      description
        "Free-form meta-information about the generated file.  It
         might include a '.sid' file generation tool and time,
         among other things.";
    }

    list dependency-revision {
      key "module-name";

      description
        "Information about the revision used during the
         '.sid' file generation of each dependency, i.e., each
         YANG module that the YANG module associated with this
         '.sid' file imported.";

      leaf module-name {
        type yang:yang-identifier;
        description
          "YANG module name of this dependency.";
      }
      leaf module-revision {
        type revision-identifier;
        mandatory true;
        description
          "Revision of the YANG module of this dependency.";
      }
    }

    list assignment-range {
      key "entry-point";
      description
        "YANG-SID Range(s) allocated to the YANG module
         identified by 'module-name' and 'module-revision'.

         -  The first available value in the YANG-SID Range is
            'entry-point', and the last available value in the
            range is ('entry-point' + size - 1).
         -  The YANG-SID Ranges specified by all
            'assignment-range' entries MUST NOT overlap.";

      leaf entry-point {
        type sid;
        description
          "Lowest YANG SID available for assignment.";
      }

      leaf size {
        type uint64;
        mandatory true;
        description
          "Number of YANG SIDs available for assignment.";
      }
    }

    list item {
      key "namespace identifier";
      unique "sid";

      description
        "Each entry within this list defines the mapping between
         a YANG item string identifier and a YANG SID.  This list
         MUST include a mapping entry for each YANG item defined
         by the YANG module identified by 'module-name' and
         'module-revision'.";

      leaf status {
        type enumeration {
          enum stable {
            value 0;
            description
              "This SID allocation has been published as the
               stable allocation for the given namespace and
               identifier.";
          }
          enum unstable {
            value 1;
            description
              "This SID allocation has been done during a
               development process; it is not yet stable.";
          }
          enum obsolete {
            value 2;
            description
              "This SID allocation is no longer in use.  It is
               recorded to avoid reallocation of its SID value.";
          }
        }
        default "stable";
        description
          "The status field contains information about the
           stability of the allocation.  For each specific SID
           value, over time it can only transition from
           'unstable' to 'stable', and possibly from 'stable' to
           'obsolete'.";
      }

      leaf namespace {
        type enumeration {
          enum module {
            value 0;
            description
              "All module and submodule names share the same
               global module identifier namespace.";
          }
          enum identity {
            value 1;
            description
              "All identity names defined in a module and its
               submodules share the same identity identifier
               namespace.";
          }
          enum feature {
            value 2;
            description
              "All feature names defined in a module and its
               submodules share the same feature identifier
               namespace.";
          }
          enum data {
            value 3;
            description
              "The namespace for all data nodes, as defined in
               YANG.";
          }
        }
        description
          "Namespace of the YANG item for this mapping entry.";
      }

      leaf identifier {
        type union {
          type yang:yang-identifier;
          type schema-node-path;
        }
        description
          "String identifier of the YANG item for this mapping
           entry.

           If the corresponding 'namespace' field is 'module',
           'feature', or 'identity', then this field MUST
           contain a valid YANG identifier string.

           If the corresponding 'namespace' field is 'data',
           then this field MUST contain a valid schema-node
           path.";
      }

      leaf sid {
        type sid;
        mandatory true;
        description
          "YANG SID assigned to the YANG item for this mapping
           entry.";
      }
    }
  }
}

<CODE ENDS>

5. Security Considerations

This document defines a new type of identifier used to encode data that are modeled in YANG [RFC7950]. This new identifier maps semantic concepts to integers, and if the source of this mapping is not trusted, then new security risks might occur if an attacker can control the mapping.¶

At the time of writing, it is expected that the ".sid" files will be processed by a software developer, within a software development environment. Developers are advised to only import ".sid" files from authoritative sources. IANA is the authoritative source for IETF-managed YANG modules.¶

Conceptually, ".sid" files could be processed by less-constrained target systems such as network management systems. Such systems need to take extra care to make sure that they are only processing ".sid" files from authoritative sources that are as authoritative as the YANG modules that they are using.¶

".sid" files are identified with and can employ dereferenceable identifiers, i.e., identifiers that could lead implementations in certain situations to automatically perform remote access, the target of which is indicated at least partially by those identifiers. This can give an attacker information from and/or control over such accesses, which can have security and privacy implications. Please also see Sections 6 and 7 of [DEREF-ID] for further considerations that may be applicable.¶

6. IANA Considerations

Appendix A. ".sid" File Example

The following ".sid" file ('ietf-system@2014-08-06.sid') has been generated using the following YANG modules:¶

• 'ietf-system@2014-08-06.yang' (defined in [RFC7317])¶

• 'ietf-yang-types@2013-07-15.yang' (defined in [RFC6991])¶

• 'ietf-inet-types@2013-07-15.yang' (defined in [RFC6991])¶

• 'ietf-netconf-acm@2018-02-14.yang' (defined in [STD91])¶

• 'iana-crypt-hash@2014-08-06.yang' (defined in [RFC7317])¶

For purposes of exposition, per [RFC8792], line breaks have been introduced below in some JSON strings that represent overly long identifiers.¶

=============== NOTE: '\' line wrapping per RFC 8792 ================

{
  "ietf-sid-file:sid-file": {
    "module-name": "ietf-system",
    "module-revision": "2014-08-06",
    "description": "Example '.sid' file",
    "dependency-revision": [
      {
        "module-name": "ietf-yang-types",
        "module-revision": "2013-07-15"
      },
      {
        "module-name": "ietf-inet-types",
        "module-revision": "2013-07-15"
      },
      {
        "module-name": "ietf-netconf-acm",
        "module-revision": "2018-02-14"
      },
      {
        "module-name": "iana-crypt-hash",
        "module-revision": "2014-08-06"
      }
    ],
    "assignment-range": [
      {
        "entry-point": "1700",
        "size": "100"
      }
    ],
    "item": [
      {
        "namespace": "module",
        "identifier": "ietf-system",
        "sid": "1700"
      },
      {
        "namespace": "identity",
        "identifier": "authentication-method",
        "sid": "1701"
      },
      {
        "namespace": "identity",
        "identifier": "local-users",
        "sid": "1702"
      },
      {
        "namespace": "identity",
        "identifier": "radius",
        "sid": "1703"
      },
      {
        "namespace": "identity",
        "identifier": "radius-authentication-type",
        "sid": "1704"
      },
      {
        "namespace": "identity",
        "identifier": "radius-chap",
        "sid": "1705"
      },
      {
        "namespace": "identity",
        "identifier": "radius-pap",
        "sid": "1706"
      },
      {
        "namespace": "feature",
        "identifier": "authentication",
        "sid": "1707"
      },
      {
        "namespace": "feature",
        "identifier": "dns-udp-tcp-port",
        "sid": "1708"
      },
      {
        "namespace": "feature",
        "identifier": "local-users",
        "sid": "1709"
      },
      {
        "namespace": "feature",
        "identifier": "ntp",
        "sid": "1710"
      },
      {
        "namespace": "feature",
        "identifier": "ntp-udp-port",
        "sid": "1711"
      },
      {
        "namespace": "feature",
        "identifier": "radius",
        "sid": "1712"
      },
      {
        "namespace": "feature",
        "identifier": "radius-authentication",
        "sid": "1713"
      },
      {
        "namespace": "feature",
        "identifier": "timezone-name",
        "sid": "1714"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:set-current-datetime",
        "sid": "1715"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:set-current-datetime/input",
        "sid": "1775"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:set-current-datetime/input/\
                                                   current-datetime",
        "sid": "1776"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system",
        "sid": "1717"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system-restart",
        "sid": "1718"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system-shutdown",
        "sid": "1719"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system-state",
        "sid": "1720"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system-state/clock",
        "sid": "1721"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system-state/clock/boot-datetime\
                                                                   ",
        "sid": "1722"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system-state/clock/current-\
                                                           datetime",
        "sid": "1723"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system-state/platform",
        "sid": "1724"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system-state/platform/machine",
        "sid": "1725"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system-state/platform/os-name",
        "sid": "1726"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system-state/platform/os-release\
                                                                   ",
        "sid": "1727"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system-state/platform/os-version\
                                                                   ",
        "sid": "1728"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/authentication",
        "sid": "1729"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/authentication/user",
        "sid": "1730"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/authentication/user-\
                                               authentication-order",
        "sid": "1731"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/authentication/user/\
                                                     authorized-key",
        "sid": "1732"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/authentication/user/\
                                           authorized-key/algorithm",
        "sid": "1733"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/authentication/user/\
                                            authorized-key/key-data",
        "sid": "1734"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/authentication/user/\
                                                authorized-key/name",
        "sid": "1735"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/authentication/user/name",
        "sid": "1736"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/authentication/user/\
                                                           password",
        "sid": "1737"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/clock",
        "sid": "1738"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/clock/timezone-name",
        "sid": "1739"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/clock/timezone-utc-offset\
                                                                   ",
        "sid": "1740"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/contact",
        "sid": "1741"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/dns-resolver",
        "sid": "1742"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/dns-resolver/options",
        "sid": "1743"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/dns-resolver/options/\
                                                           attempts",
        "sid": "1744"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/dns-resolver/options/\
                                                            timeout",
        "sid": "1745"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/dns-resolver/search",
        "sid": "1746"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/dns-resolver/server",
        "sid": "1747"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/dns-resolver/server/name",
        "sid": "1748"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/dns-resolver/server/udp-\
                                                            and-tcp",
        "sid": "1749"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/dns-resolver/server/udp-\
                                                    and-tcp/address",
        "sid": "1750"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/dns-resolver/server/udp-\
                                                       and-tcp/port",
        "sid": "1751"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/hostname",
        "sid": "1752"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/location",
        "sid": "1753"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/ntp",
        "sid": "1754"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/ntp/enabled",
        "sid": "1755"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/ntp/server",
        "sid": "1756"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/ntp/server/association-\
                                                               type",
        "sid": "1757"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/ntp/server/iburst",
        "sid": "1758"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/ntp/server/name",
        "sid": "1759"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/ntp/server/prefer",
        "sid": "1760"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/ntp/server/udp",
        "sid": "1761"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/ntp/server/udp/address",
        "sid": "1762"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/ntp/server/udp/port",
        "sid": "1763"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/radius",
        "sid": "1764"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/radius/options",
        "sid": "1765"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/radius/options/attempts",
        "sid": "1766"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/radius/options/timeout",
        "sid": "1767"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/radius/server",
        "sid": "1768"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/radius/server/\
                                                authentication-type",
        "sid": "1769"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/radius/server/name",
        "sid": "1770"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/radius/server/udp",
        "sid": "1771"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/radius/server/udp/address\
                                                                   ",
        "sid": "1772"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/radius/server/udp/\
                                                authentication-port",
        "sid": "1773"
      },
      {
        "namespace": "data",
        "identifier": "/ietf-system:system/radius/server/udp/shared-\
                                                             secret",
        "sid": "1774"
      }
    ]
  }
}

Appendix B. SID Autogeneration

The assignment of SIDs to YANG items SHOULD be automated. The recommended process to assign SIDs is as follows:¶

1. A tool extracts the different items defined for a specific YANG module.¶

2. The list of items is sorted in alphabetical order. 'namespace' entries are sorted in descending order, and 'identifier' entries are sorted in ascending order. The 'namespace' and 'identifier' formats are described in the YANG module 'ietf-sid-file' defined in Section 4.¶

3. SIDs are assigned sequentially from the entry point up to the size of the registered SID range. This approach is recommended to minimize the serialization overhead, especially when the delta between a reference SID and the current SID is used by protocols aiming to reduce message size.¶

4. If the number of items exceeds the SID range(s) allocated to a YANG module, an extra range is added for subsequent assignments.¶

5. The 'dependency-revision' list item should reflect the revision numbers of each YANG module that the YANG module imports at the moment of file generation.¶

When updating a YANG module that is in active use, the existing SID assignments are maintained. (In contrast, when evolving an early version of an Internet-Draft that has not yet been adopted by a community of developers, SID assignments are often better done from scratch after a revision.) If the name of a schema node changes but the data remain structurally and semantically similar to what was previously available under an old name, the SID that was used for the old name MAY continue to be used for the new name. If the meaning of an item changes, a new SID MAY be assigned to it; this is particularly useful for allowing the new SID to identify the new structure or semantics of the item. If the YANG data type changes in a new revision of a published module such that the resulting CBOR encoding is changed, then implementations will be aided significantly if a new SID is assigned. Note that these decisions are generally at the discretion of the YANG module author, who should decide if the benefits of a manual intervention are worth the deviation from automatic assignment.¶

In the case of an update to an existing ".sid" file, an additional step is needed that increments the ".sid" file version number. If there was no version number in the previous version of the ".sid" file, 0 is assumed to be the version number of the old version of the ".sid" file and the version number is 1 for the new ".sid" file. Apart from that, changes to ".sid" files can also be automated using the same method as that described above, except that in step #3, previous SID assignments are kept, only previously unassigned YANG items are processed, and these are assigned previously unassigned SIDs. Already-existing items in the ".sid" file should not be given new SIDs.¶

Note that ".sid" file versions are specific to a YANG module revision. For each new YANG module or each new revision of an existing YANG module, the version number of the initial ".sid" file either (1) should be 0 or (2) should not be present.¶

Note also that RPC or action "input" and "output" YANG items MUST always be assigned SIDs even if they don't contain further YANG items. The reason for this requirement is that other modules can augment the given module and those SIDs might be necessary.¶

Appendix C. ".sid" File Lifecycle

Before assigning SIDs to their YANG modules, YANG module authors must acquire a SID range from a registry of YANG-SID Ranges. If the YANG module is part of an IETF Internet-Draft or RFC, the SID range needs to be acquired from the "IETF YANG-SID Ranges" registry as defined in Section 6.4. For the other YANG modules, the authors can choose to acquire a SID range from any registry of YANG-SID Ranges.¶

Once the SID range is acquired, owners can use it to generate one or more ".sid" files for their YANG module or modules. It is recommended to leave some unallocated SIDs following the allocated range in each ".sid" file in order to allow better evolution of the owners' YANG modules in the future. Generation of ".sid" files should be performed using an automated tool. Note that ".sid" files can only be generated for YANG modules and not for submodules.¶

Appendix D. Keeping a ".sid" File in a YANG Instance Data File

[RFC9195] defines a format for "YANG instance data". This essentially leads to an encapsulation of the instance data within some metadata envelope.¶

If a ".sid" file needs to be stored in a YANG instance data file, this can be achieved by embedding the value of the ".sid" file as the value of the content-data member in the following template and copying over the second-level members as indicated with the angle brackets:¶

{
  "ietf-yang-instance-data:instance-data-set": {
    "name": "<module-name>@<module-revision>.sid",
    "description":  ["<description>"],
    "content-schema": {
      "module": "ietf-sid-file@2024-06-17"
    },
    "content-data": {  <replace this object>
      "ietf-sid-file:sid-file" : {
        "module-name": ...
      }
    }
  }
}

Acknowledgments

The authors would like to thank Andy Bierman, Abhinav Somaraju, Peter van der Stok, Laurent Toutain, and Randy Turner for their help during the development of this document and their useful comments during the review process. Special thanks go to the IESG members who supplied very useful comments during the IESG processing phase, in particular to Benjamin Kaduk and Rob Wilton, and to Francesca Palombini as responsible AD.¶

Contributors

Authors' Addresses