| RFC 9595 | YANG Schema Item iDentifier (YANG SID) | June 2024 |
| Veillette, et al. | Standards Track | [Page] |
YANG Schema Item iDentifiers (YANG SIDs) are globally unique 63-bit unsigned integers used to identify YANG items, as a more compact method to identify YANG items that can be used for efficiency and in constrained environments (RFC 7228). This document defines the semantics, registration processes, and assignment processes for YANG SIDs for IETF-managed YANG modules. To enable the implementation of these processes, this document also defines a file format used to persist and publish assigned YANG SIDs.¶
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 (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.¶
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 equivalent to NETCONF [RFC6241] like [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 mechanism specified in this document. 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].¶
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]:¶
This specification also makes use of the following terminology:¶
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 deal 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.¶
As discussed in the Introduction, SIDs are intended as globally unique (unsigned) integers.¶
Specifically, this means that:¶
Any 63-bit unsigned integer either (1) is unassigned as a SID or (2) immutably maps to EXACTLY one YANG name. Only the transition from unassigned to that immutable mapping is defined.¶
This enables a recipient of a data structure employing SIDs to translate them into the globally meaningful YANG names that the existing encodings of YANG data such as YANG-XML [RFC7950] and YANG-JSON [RFC7951] employ today.¶
The term "YANG name" is not defined outside this document, and YANG has a complex system of names and entities that can have those names. Instead of defining the term technically, this set of objectives uses it in such a way that the overall objectives of YANG SID can be achieved.¶
A desirable objective is that:¶
Any YANG name in active use has one SID assigned.¶
This means that:¶
There should not be YANG names without SIDs assigned.¶
YANG names should not have multiple SIDs assigned.¶
These objectives are unattainable in full, because YANG names are not necessarily born with a SID assignment and because entirely autonomous entities might decide to assign SIDs for the same YANG name without communicating ("like ships in the night"). Note that as long as this autonomy is maintained, any single observer will have the impression that Objective 2 is attained. Only when entities that have acted autonomously start communicating will a deviation be observed.¶
YANG modules evolve (see Section 11 of [RFC7950] and Section 4.27 of [RFC8407]). The technical objectives listed above are states in terms that are independent of this evolution.¶
However, some modules are still in a very fluid state, and the assignment of permanent SIDs to the YANG names created in them is less desirable. This is true not only for new modules but also for emerging new revisions of existing stable modules.¶
The SID management system is independent of any module versioning.¶
A registration system is used in order to guarantee the uniqueness of SIDs. To be able to provide some autonomy in allocation (and avoid information disclosure where it is not desirable), 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.¶
In the YANG development process, we can discern a number of parties that are concerned with a YANG module:¶
The owner of the YANG module, i.e., the controller about its evolution.¶
The controller of the module namespace, specifically also of the prefixes that are in common use. (This is not a required party.)¶
An entity that supplies modules to module users. This can be an "official" entity (e.g., IANA for IETF modules) or an "unofficial" entity (e.g., the YANG Catalog [yangcatalog]). Not all repositories are in a position to act as a registry, i.e., as a permanent record for the information they supply; these repositories need to recur to module owners as a stable source.¶
An entity that uses a module, after obtaining it from the module controller or a module repository.¶
This set of parties needs to evolve to take on the additional roles that the SID assignment process requires:¶
An entity that assigns SIDs for a module. Objective 2 aims at having only one SID assigner for each module. SID assigners preferably stay the same over a module development process; however, this specification provides SID files to ensure an organized handover.¶
An entity that supplies a SID assigner with SID ranges that it can use in assigning SIDs for a module. (In this specification, there is a structure with mega-ranges and individual SID ranges; this is not relevant here.)¶
An entity that supplies SID assignments to SID users, usually in the form of a SID file.¶
The module user that uses the SIDs provided by a SID assigner for a YANG module. SID users need to find SID assigners (or at least their SID assignments).¶
During the introduction of SIDs, the distribution of the SID roles to the existing parties for a YANG module will evolve.¶
The desirable end state of this evolution is shown in Table 1.¶
| Role | Party |
|---|---|
| SID assigner | module developer |
| SID range registry | (as discussed in this specification) |
| SID repository | module repository |
| SID user | module user (naturally) |
This grouping of roles and parties puts the module developer in a position where it can achieve the objectives laid out in this section (a "type-1", "SID-guiding" module controller). (While a third party might theoretically assign additional SIDs and conflict with Objective 2, there is very little reason to do so if SID files are always provided by the module developer with the module.)¶
The rest of this section is concerned with the transition to this end state.¶
For existing modules, there is no SID file. The entity that stands in as the SID assigner is not specified. This situation has the highest potential for conflict with Objective 2.¶
Similarly, for new module development, the module owner may not have heard about SIDs or may not be interested in assigning them (e.g., because of lack of software or procedures within their organization).¶
For these two cases (which we will call "type-3", "SID-oblivious" module controllers), module repositories can act as a mediator, giving SID users access to a SID assigner that is carefully chosen to be a likely choice by other module repositories as well, maximizing the likelihood of achieving Objective 2.¶
If a module controller has heard about SIDs but is not assigning them yet, it can designate a SID assigner instead. This can lead to a stable, unique set of SID assignments being provided indirectly by a ("type-2", "SID-aware") module developer. Entities offering designated SID assigner services could make these available in an easy-to-use way, e.g., via a web interface.¶
The entity acting as a SID assigner minimally needs to record the SID range it uses for the SID assignment. If the SID range registry can record the module name and revision and if the assignment processes (including the software used) are stable, the SID assigner can theoretically reconstruct its assignments, but this could invite implementation bugs.¶
SID assigners attending to a module in development (not yet stable) need to decide whether SIDs for a new revision are reassigned from scratch ("clean slate") or use existing assignments from a previous revision as a base, only assigning new SIDs for new names. Once a module is declared stable, its SID assignments SHOULD be declared stable as well (except that, for existing YANG modules, some review may be needed before this is done).¶
This specification does not further discuss how mediating entities such as designated SID assigners or SID repositories could operate; instead, it supplies objectives for their operation.¶
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, in order 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 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 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' 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.¶
".sid" files are used to persist and publish SIDs assigned to the different YANG items in 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
+-- 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 this file. Encoding is performed in JSON [RFC8259] using the rules defined in [RFC7951]. This module imports 'ietf-yang-types' [RFC6991] and 'ietf-yang-structure-ext' [RFC8791]. It also references [RFC7950] and [RFC8407].¶
<CODE BEGINS> file "ietf-sid-file@2024-06-17.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
"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).";
revision 2024-06-17 {
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 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 '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 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 that are the result of new
processing or reported errata.";
}
leaf sid-file-status {
type enumeration {
enum unpublished {
description
"This .sid file is unpublished (RFC 8407) 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: Guidelines for Authors and
Reviewers of Documents Containing
YANG Data Models";
}
enum published {
description
"This .sid file is published, for a published YANG
module. 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 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 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>
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.¶
This document registers the following XML namespace URN in the "IETF XML Registry", following the format defined in [RFC3688]:¶
This document registers one YANG module in the "YANG Module Names" registry [RFC6020]:¶
The name of this registry is "YANG SID Mega-Range". This registry is used to record the delegation of the management of a block of SIDs to third parties (such as Standards Development Organizations (SDOs) or registrars).¶
Each entry in this registry must include:¶
The entry point (first SID) of the registered SID block.¶
The size of the registered SID block. The size SHOULD be one million (1 000 000) SIDs; it MAY exceptionally be a multiple of 1 000 000.¶
The policy of SID range allocations: Public, Private, or Both.¶
The contact information of the requesting organization, including the following:¶
The IANA policy for future additions to this registry is "Expert Review" [RFC8126].¶
An organization requesting to manage a YANG SID Range (and thus have an entry in the "YANG SID Mega-Range" registry) must ensure the following capacities:¶
The capacity to manage and operate a registry of YANG SID ranges. A registry of YANG SID ranges MUST provide the following information for all YANG SID Ranges allocated by the registry:¶
The entry point of the allocated YANG SID Range.¶
The size of the allocated YANG SID Range.¶
Type: Public or Private.¶
Public ranges MUST include at least a reference to the YANG module and ".sid" files for that YANG SID Range (e.g., compare Section 6.4.3 for the "IETF YANG SID" registry).¶
Private ranges MUST be marked as "Private".¶
A policy of allocation, which clearly identifies whether the YANG SID Range allocations would be Private, Public, or Both.¶
Technical capacity to provide or refer to ".sid" files in a way that meets the security objective of data integrity for these files (see also Section 5).¶
Technical capacity to ensure the sustained operation of the registry for a period of at least 5 years. If Private Registrations are allowed, the period must be at least 10 years.¶
If a size of the allocation beyond 1 000 000 is desired, the organization must demonstrate the sustainability of the technical approach for utilizing this size of allocation and how it does not negatively impact the overall usability of the SID allocation mechanisms; such allocations are preferably placed in the space above 4 295 000 000 (64-bit space).¶
For a first allocation to be provided, the requesting organization must demonstrate a functional registry infrastructure.¶
On one or more subsequent allocation requests, the organization must demonstrate the exhaustion of the prior range. These conditions need to be asserted by the assigned expert(s).¶
If such a request for an additional allocation is made within 3 years of the last allocation, the experts need to discuss this request on the CORE Working Group mailing list and consensus needs to be obtained before allocating a new Mega-Range.¶
This registry contains the following initial entry:¶
| Entry Point | Size | Allocation | Organization Name | URL |
|---|---|---|---|---|
| 0 | 1000000 | Public | IANA | <https://www.iana.org/> |
The first million SIDs assigned to IANA is subdivided as follows:¶
The range of 0 to 999 (size 1000) is subject to "IESG Approval" as defined in [RFC8126]; of these, SID value 0 has been reserved for implementations to internally signify the absence of a SID number and does not occur in interchange.¶
The ranges of 1000 to 59,999 (size 59,000) and 100,000 to 299,999 (size 200,000) are designated for YANG modules defined in RFCs.¶
The range of 60,000 to 99,999 (size 40,000) is reserved for experimental YANG modules. This range MUST NOT be used in operational deployments, since these SIDs are not globally unique which limit their interoperability. The IANA policy for this range is "Experimental Use" [RFC8126].¶
The range of 300,000 to 999,999 (size 700,000) is "Reserved" as defined in [RFC8126].¶
| Entry Point | Size | IANA Policy |
|---|---|---|
| 0 | 1,000 | IESG Approval |
| 1,000 | 59,000 | RFC Required |
| 60,000 | 40,000 | Experimental/Private Use |
| 100,000 | 200,000 | RFC Required |
| 300,000 | 700,000 | Reserved |
The size of the SID range allocated for a YANG module is recommended to be a multiple of 50 and to be at least 33% above the current number of YANG items. This headroom allows assignments within the same range of new YANG items introduced by subsequent revisions. The SID range size SHOULD NOT exceed 1000; a larger size may be requested by the authors if this recommendation is considered insufficient. It is important to note that an additional SID range can be allocated to an existing YANG module if the initial range is exhausted; this then just leads to a slightly less efficient representation.¶
If a SID range is allocated for an existing RFC through the "Expert Review" policy, the Reference field for the given allocation should point to the RFC that the YANG module is defined in.¶
If a SID range is required before publishing the RFC due to implementations needing stable SID values, early allocation as defined in [BCP100] can be employed for the "RFC Required" range (Section 2 of RFC 7120 [BCP100]).¶
During an RFC's publication process, IANA contacts the designated expert team ("the team"), who are responsible for delivering a final SID file for each module defined by the RFC. For a type-3 developer (SID-oblivious; see Section 2.4), the team creates a new SID file from each YANG module; see below. For a type-2 (SID-aware) developer, the team first obtains the existing draft SID file from a stable reference in the approved draft; for a type-1 (SID-guiding) developer, the team extracts the SID file from the approved draft.¶
The team uses a tool to generate a final SID file from each YANG module; the final SID file has all SID assignments set to "stable" and the SID file status set to "published". A published ".sid" file MUST NOT contain SID assignments with a status of "unstable".¶
For the cases other than type-3 (SID-oblivious), the team feeds the existing draft SID file as an input ("reference SID file") to the tool so that the changes resulting from regeneration are minimal. For YANG modules that are revisions of previously published modules, any existing published SID file needs to serve as a reference SID file for the tool, during generation of either the revised draft SID file (type-1, type-2) or the final SID file (type-3).¶
In any case, the team checks the generated file, including checking for validity as a SID file, for consistency with the SID range allocations, for full coverage of the YANG items in the YANG module, and for the best achievable consistency with the existing draft SID file.¶
The designated experts then give the SID file to IANA to publish in the "IETF YANG SID" registry (Section 6.5) along with the YANG module.¶
The ".sid" file MUST NOT be published as part of the RFC: the IANA registry is authoritative, and a link to it is to be inserted in the RFC. (Note that the present RFC is an exception to this rule, as the SID file also serves as an example for exposition.) RFCs that need SIDs assigned to their new modules for use in the text of the document, e.g., for examples, need to alert the RFC Editor in the draft text that this is the case. Such RFCs cannot be produced by type-3 (SID-oblivious) developers: the SIDs used in the text need to be assigned in the existing draft SID file, and the designated expert team needs to check that the assignments in the final SID file are consistent with the usage in the RFC text or that the approved draft text is changed appropriately.¶
Initial entries in this registry are as follows:¶
| Entry Point | Size | Module Name | Reference |
|---|---|---|---|
| 0 | 1 | (Reserved: not a valid SID) | RFC 9595 |
| 1000 | 100 | ietf-coreconf | [CORE-COMI] |
| 1100 | 50 | ietf-yang-types | [RFC6991] |
| 1150 | 50 | ietf-inet-types | [RFC6991] |
| 1200 | 50 | iana-crypt-hash | [RFC7317] |
| 1250 | 50 | ietf-netconf-acm | [RFC8341] |
| 1300 | 50 | ietf-sid-file | RFC 9595 |
| 1500 | 100 | ietf-interfaces | [RFC8343] |
| 1600 | 100 | ietf-ip | [RFC8344] |
| 1700 | 100 | ietf-system | [RFC7317] |
| 1800 | 400 | iana-if-type | [RFC7224] |
| 2400 | 50 | ietf-voucher | [RFC8366] |
| 2450 | 50 | ietf-constrained-voucher | [CONSTRAINED-VOUCHER] |
| 2500 | 50 | ietf-constrained-voucher-request | [CONSTRAINED-VOUCHER] |
For allocation, RFC publication of the YANG module is required as per [RFC8126]. The YANG module must be registered in the "YANG Module Names" registry according to the rules specified in Section 14 of [RFC6020].¶
The name of this registry is "IETF YANG SID". This registry is used to record the allocation of SIDs for individual YANG module items.¶
Each entry in this registry must include:¶
The YANG module name. This module name must be present in the "Name" column of the "YANG Module Names" registry.¶
A URI for the associated ".yang" file. This file link must be present in the "File" column of the "YANG Module Names" registry.¶
The URI for the ".sid" file that defines the allocation. The ".sid" file is stored by IANA.¶
The number of actually allocated SIDs in the ".sid" file.¶
The allocation policy is "Expert Review" [RFC8126]. The expert MUST ensure that the following conditions are met:¶
The ".sid" file has a valid structure:¶
The ".sid" file MUST be a valid JSON file following the structure of the module defined in this document.¶
The ".sid" file allocates individual SIDs ONLY in the YANG SID Ranges for this YANG module (as allocated in the "IETF YANG SID Range" registry):¶
All SIDs in this ".sid" file MUST be within the ranges allocated to this YANG module in the "IETF YANG SID Range" registry.¶
If another ".sid" file has already allocated SIDs for this YANG module (e.g., for older or newer versions of the YANG module), the YANG items are assigned the same SIDs as those in the other ".sid" file.¶
If there is an older version of the ".sid" file, all allocated SIDs from that version are still present in the current version of the ".sid" file.¶
Due to the difficulty in changing SID values during IETF document processing, it is expected that most documents will ask for SID range allocations using early allocations [BCP100]. The details of the early allocation to be requested, including the timeline envisioned, should be included in any working group adoption call. Prior to working group adoption, an Internet-Draft author can use the experimental SID range (as per Section 6.4.2) for their SID allocations or other values that do not create ambiguity with other SID uses (for example, they can use a range that comes from a non-IANA-managed registry of YANG SID mega-ranges).¶
After working group adoption, any modification of a ".sid" file is expected to be discussed on the mailing lists of the appropriate working groups. Specific attention should be paid to implementers' opinions after Working Group Last Call if a SID value is to change its meaning. In all cases, a ".sid" file and the SIDs associated with it are subject to change before the publication of an Internet-Draft as an RFC.¶
During the early use of SIDs, many existing, previously published YANG modules will not have SID allocations. For an allocation to be useful, the included YANG modules may also need to have SID allocations made, in a process that will generally be analogous to that in Section 6.4.3 for the type-3 (SID-oblivious) case.¶
The expert reviewer who performs the (early) allocation analysis will need to go through the list of included YANG modules and perform SID allocations for those modules as well.¶
If the document is a published RFC, then the allocation of SIDs for its referenced YANG modules is permanent. The expert reviewer provides the generated ".sid" file to IANA for registration.¶
If the document is an unprocessed Internet-Draft adopted in a working group, then an early allocation is performed for this document as well. Early allocations require approval by an IESG area director. An early allocation that requires additional allocations will list the other allocations in its description and will be cross-posted to the mailing lists of any other working groups concerned.¶
A YANG module that references a module in a document that has not yet been adopted by any working group will be unable to perform an early allocation for that other document until it is adopted by a working group. As described in [BCP100], an AD-sponsored document acts as if it had a working group. The approving AD may also exempt a document from this policy by agreeing to AD-sponsor the document.¶
At the end of the IETF process, all the dependencies of a given module for which SIDs are assigned should also have SIDs assigned. Those dependencies' assignments should be permanent (not early allocation).¶
A previously SID-allocated YANG module that changes its references to include a YANG module for which there is no SID allocation needs to repeat the early allocation process.¶
[BCP100] defines a time limit for the validity of early allocations, after which they expire unless they are renewed. Section 3.3 of RFC 7120 [BCP100] also says:¶
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 must not be considered to have expired while the document is under IESG consideration or is awaiting publication in the RFC Editor's queue after approval by the IESG.¶
At the time of writing, this registry does not contain any entries.¶
This document adds the following media type to the "Media Types" registry.¶
| Name | Template | Reference |
|---|---|---|
| yang-sid+json | application/yang-sid+json | RFC 9595 |
application¶
yang-sid+json¶
N/A¶
N/A¶
binary (UTF-8)¶
RFC 9595¶
Applications that need to obtain YANG SIDs to interchange YANG-modeled data in a concise and efficient representation.¶
The syntax and semantics of fragment identifiers specified for "application/yang-sid+json" is as specified for "application/json". (At publication of this document, there is no fragment identification syntax defined for "application/json".)¶
CORE WG mailing list (core@ietf.org) or IETF Applications and Real-Time Area (art@ietf.org)¶
COMMON¶
none¶
IETF¶
This document adds the following Content-Format to the "CoAP Content-Formats" registry within the "Constrained RESTful Environments (CoRE) Parameters" group of registries, where 260 has been assigned from the "IETF Review" (256-9999) range.¶
| Content Type | Content Coding | ID | Reference |
|---|---|---|---|
| application/yang-sid+json | - | 260 | RFC 9595 |
The following ".sid" file ('ietf-system@2014-08-06.sid') has been generated using the following YANG modules:¶
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"
}
]
}
}
The assignment of SIDs to YANG items SHOULD be automated. The recommended process to assign SIDs is as follows:¶
A tool extracts the different items defined for a specific YANG module.¶
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.¶
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.¶
If the number of items exceeds the SID range(s) allocated to a YANG module, an extra range is added for subsequent assignments.¶
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 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, only unassigned YANG items are processed. 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.¶
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 Range" 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.¶
The following activity diagram summarizes the creation of a YANG module and its associated ".sid" file.¶
The following activity diagram summarizes the update of a YANG module and its associated ".sid" 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@2023-10-27"
},
"content-data": { <replace this object>
"ietf-sid-file:sid-file" : {
"module-name": ...
}
}
}
}
¶
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.¶