YANG Schema Item iDentifier (YANG SID)

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This Internet-Draft will expire on 22 May 2022.¶

Copyright Notice

Copyright (c) 2021 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 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 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 'yang-data' extension.)¶
• 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 use only a subset of the assigned SIDs, for example, for protocols equivalent to NETCONF [RFC6241] like [I-D.ietf-core-comi] the transportation 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 Constrained YANG Module Library [I-D.ietf-core-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".¶

SIDs are assigned permanently. Items introduced by a new revision of a YANG module are added to the list of SIDs already assigned. Assignment of SIDs to YANG items are 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 process of YANG modules and associated SIDs. To enable the implementation of this registry, Section 4 defines a standard file format used to store and publish SIDs.¶

IETF managed YANG modules that need to allocate SIDs use the IANA mechanism specified in this document. YANG modules created by other parties allocate SID ranges using the IANA allocation mechanisms via Mega-Ranges (see Section 7.3); within the Mega-Range allocation, those other parties are free to make up their own mechanism.¶

At the time of writing, a tool for automated ".sid" file generation is available as part of the open-source project PYANG [PYANG].¶

2. Terminology and Notation

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.¶

The following terms are defined in [RFC7950]:¶

• action¶
• feature¶
• module¶
• notification¶
• RPC¶
• schema node¶
• schema tree¶
• submodule¶

The following term is defined in [RFC8040]:¶

• yang-data extension¶

This specification also makes use of the following terminology:¶

• item: A schema node, an identity, a module, or a feature defined using the YANG modeling language.¶
• schema-node path: A schema-node path is a string that identifies a schema node within the schema tree. A path consists of the list of consecutive schema node identifier(s) separated by slashes ("/"). Schema node identifier(s) are always listed from the top-level schema node up to the targeted schema node and could contain namespace information. (e.g. "/ietf-system:system-state/clock/current-datetime")¶
• Namespace-qualified form - a schema node identifier is prefixed with the name of the module in which the schema node is defined, separated from the schema node identifier by the colon character (":").¶
• YANG Schema Item iDentifier (YANG SID or simply SID): Unsigned integer used to identify different YANG items.¶

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 CORECONF [I-D.ietf-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 of their YANG module. The assignments can then be stored in a ".sid" file. For example on how this could be achieved, please refer to Appendix C.¶

Registration of the ".sid" file associated to a YANG module is optional but recommended to promote interoperability between devices and to 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 of the possibilities, please refer to the activity diagram on Figure 4 in Appendix C.¶

Each time a YANG module or one of its imported module(s) or included sub-module(s) is updated, a new ".sid" file MAY be created if the new or updated items will need SIDs. All the SIDs present in the previous version of the ".sid" file 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' as defined in Section 4. These extra SIDs are used for subsequent assignments.¶

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

4. ".sid" file format

".sid" files are used to persist and publish SIDs assigned to the different YANG items of a specific YANG module. It has the following structure.¶

module: ietf-sid-file

  structure sid-file:
    +-- module-name            yang:yang-identifier
    +-- module-revision?       revision-identifier
    +-- sid-file-version?      sid-file-version-identifier
    +-- 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]
       +-- namespace     enumeration
       +-- identifier    union
       +-- sid           sid

The following YANG module defines the structure of this file, encoding is performed in JSON [RFC8259] using the rules defined in [RFC7951]. It references ietf-yang-types defined in [RFC6991] and ietf-restconf defined in [RFC8040].¶

RFC Ed.: please update the date of the module and Copyright if needed and remove this note.¶

<CODE BEGINS> file "ietf-sid-file@2021-11-16.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:a@ackl.io>

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

  description
    "Copyright (c) 2021 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 Simplified 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 XXXX
     (https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself
     for full legal notices.

     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.

     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 YANG SID.";

  revision 2021-11-16 {
    description
      "Initial revision.";
    reference
      "[RFC XXXX] YANG Schema Item iDentifier (YANG SID)";
  }

  typedef revision-identifier {
    type string {
      pattern '\d{4}-\d{2}-\d{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 XXXX] 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:

       o  The leftmost (top-level) data node name is always in the
          namespace-qualified form.
       o  Any subsequent schema node name is in the
          namespace-qualified form if the node is defined in a module
          other than its parent node, and the simple form is used
          otherwise. No predicates are allowed.";
    reference
      "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 files.";

    container sid-file {
      description
        "A Wrapper container that together with the rc:yang-data
        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
       represente the file structure of a .sid files.";

    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 which are the result of new
        processing, or the result of reported errata.";
    }

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

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

      description
        "Information about the used revision during the .sid file
        generation of each YANG module that the module in
        'module-name' imported.";

      leaf module-name {
        type yang:yang-identifier;
        description
          "Name of the YANG module, dependency of 'module-name',
          for which revision information is provided.";
      }
      leaf module-revision {
        type revision-identifier;
        mandatory true;
        description
          "Revision of the YANG module, dependency of
          'module-name', for which revision information is
          provided.";
      }
    }

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

        - The YANG SID range first available value is entry-point
          and the last available value in the range is
          (entry-point + size - 1).
        - The YANG SID ranges specified by all assignment-rages
          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 defined 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 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. Content-Types

The following Content-Type has been defined in [I-D.ietf-core-yang-cbor]:¶

application/yang-data+cbor; id=sid:

This Content-Type represents a CBOR YANG document containing one or multiple data node values. Each data node is identified by its associated SID.¶

FORMAT: CBOR map of SID, instance-value¶

The message payload of Content-Type 'application/yang-data+cbor' is encoded using a CBOR map. Each entry within the CBOR map contains the data node identifier (i.e. SID) and the associated instance-value. Instance-values are encoded using the rules defined in Section 4 of [I-D.ietf-core-yang-cbor].¶

6. 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, as authoritative as the YANG modules that they are using.¶

7. IANA Considerations

Note that if a document is submitted for review to the IESG and at
the time of submission some early allocations are valid (not
expired), these allocations should not be expired while the document
is under IESG consideration or waiting in the RFC Editor's queue
after approval by the IESG.

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 [RFC8341])¶
• iana-crypt-hash@2014-08-06.yang (defined in [RFC7317])¶

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

{
  "ietf-sid-file:sid-file" : {
    "module-name": "ietf-system",
    "module-revision": "2014-08-06",
    "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"
      }
    ],
    "description": "Example sid file",
    "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/
                      current-datetime",
        "sid": 1716
      },
      {
        "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
      }
    ]
  }
}

For reconstructing the actual JSON file from this figure, all line breaks that occur in what would be JSON strings need to be removed, including any following blank space (indentation) on the line after the line break; in each such case, a single identifier without any embedded blank space results. This removal can be accomplished with this simple Ruby script:¶

@u = %{[^"\n]*}; @q = @u + '"'
puts ARGF.read.gsub(/^(#@q(#@q#@q)*#@u) *\n +(#@q)/, "\\1\\3")

Appendix B. SID auto generation

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' in descending order, 'identifier' 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 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" should reflect the revision numbers of each YANG module that the YANG module imports at the moment of the generation.¶

When updating a YANG module that is in active use, the existing SID assignments are maintained. (In contrast, when evolving an early 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 to allow 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 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 as 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 of ".sid" files can also be automated using the same method described above, only unassigned YANG items are processed at step #3. 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 should either be 0 or should not be present.¶

Note also that RPC or action "input" and "output" data nodes MUST always be assigned SID even if they don't contain data nodes. 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 "YANG SID Range Registry". If the YANG module is part of an IETF draft or RFC, the SID range need to be acquired from the "IETF YANG SID Range Registry" as defined in Section 7.4. For the other YANG modules, the authors can acquire a SID range from any "YANG SID Range Registry" of their choice.¶

Once the SID range is acquired, owners can use it to generate ".sid" file/s for their YANG module/s. It is recommended to leave some unallocated SIDs following the allocated range in each ".sid" file in order to allow better evolution of the YANG module 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.¶

Acknowledgments

The authors would like to thank Andy Bierman, Michael Richardson, 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.¶

Contributors

Authors' Addresses