| Internet-Draft | Constrained YANG Module Library | June 2021 |
| Veillette & Petrov | Expires 16 December 2021 | [Page] |
This document describes a constrained version of the YANG library that provides information about the YANG modules, datastores, and datastore schemas used by a constrained network management server (e.g., a CORECONF server).¶
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.¶
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.¶
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."¶
This Internet-Draft will expire on 16 December 2021.¶
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 Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.¶
There is a need for a standard mechanism to expose which YANG modules, datastores and datastore schemas are in use by a constrained network management server. This document defines the YANG module 'ietf-constrained-yang-library' that provides this information.¶
YANG module 'ietf-constrained-yang-library' shares the same data model and objectives as 'ietf-yang-library', only datatypes and mandatory requirements have been updated to minimize its size to allow its implementation by Constrained Nodes and/or Constrained Networks as defined by [RFC7228]. To review the list of objectives and the proposed data model, please refer to [RFC8525] section 2 and 3.¶
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]: client, deviation, feature, module, submodule, and server.¶
The following term is defined in [I-D.ietf-core-sid]: YANG Schema Item iDentifier (SID).¶
The following terms are defined in [RFC8525]: YANG library and YANG library checksum.¶
The conceptual model of the YANG library is depicted in Figure 1.¶
+-----------+
| datastore |
+-----------+
|
| has a
V
+-----------+ +--------+ +------------+
| datastore | union of | module | consists of | modules + |
| schema |----------->| set |--------------->| submodules |
+-----------+ +--------+ +------------+
It's expected that most constrained network management servers have one datastore (e.g. a unified datastore). However, some servers may have multiples datastore as described by NMDA [RFC8342]. The YANG library data model supports both cases.¶
In this model, every datastore has an associated datastore schema, which is the union of module sets, which is a collection of modules. Multiple datastores may refer to the same datastore schema and individual datastore schemas may share module sets.¶
For each module, the YANG library provides:¶
YANG module namespace and location are also supported, but their implementation is not recommended for constrained servers.¶
The tree diagram of YANG module ietf-constrained-yang-library is provided below. This graphical representation of a YANG module is defined in [RFC8340].¶
module: ietf-constrained-yang-library
+--ro yang-library
+--ro module-set* [index]
| +--ro index uint8
| +--ro module* [identifier]
| | +--ro identifier sid:sid
| | +--ro revision? revision-identifier
| | +--ro namespace? inet:uri
| | +--ro location* inet:uri
| | +--ro submodule* [identifier]
| | | +--ro identifier sid:sid
| | | +--ro revision? revision-identifier
| | | +--ro location* inet:uri
| | +--ro feature* sid:sid
| | +--ro deviation* -> ../../module/identifier
| +--ro import-only-module* [identifier revision]
| +--ro identifier sid:sid
| +--ro revision union
| +--ro namespace? inet:uri
| +--ro location* inet:uri
| +--ro submodule* [identifier]
| +--ro identifier sid:sid
| +--ro revision? revision-identifier
| +--ro location* inet:uri
+--ro schema* [index]
| +--ro index uint8
| +--ro module-set* -> ../../module-set/index
+--ro datastore* [identifier]
| +--ro identifier ds:datastore-ref
| +--ro schema -> ../../schema/index
+--ro checksum binary
notifications:
+---n yang-library-update
+--ro checksum -> /yang-library/checksum
¶
The changes between the reference data model 'ietf-yang-library' and its constrained version 'ietf-constrained-yang-library' are listed below:¶
RFC Ed.: update the date below with the date of RFC publication and remove this note.¶
<CODE BEGINS> file "ietf-constrained-yang-library@2019-03-28.yang"
module ietf-constrained-yang-library {
yang-version 1.1;
namespace
"urn:ietf:params:xml:ns:yang:ietf-constrained-yang-library";
prefix "yanglib";
// RFC Ed.: update ietf-core-sid reference.
import ietf-sid-file {
prefix sid;
reference "RFC YYYY: YANG Schema Item iDentifier (SID)";
// RFC Editor: Please replace YYYY with RFC number of I-D.ietf-core-sid.
}
import ietf-inet-types {
prefix inet;
reference "RFC 6991: Common YANG Data Types.";
}
import ietf-datastores {
prefix ds;
reference
"RFC 8342: Network Management Datastore Architecture (NMDA).";
}
organization
"IETF CoRE Working Group";
contact
"WG Web: <http://datatracker.ietf.org/wg/core/>
WG List: <mailto:core@ietf.org>
Editor: Michel Veillette
<mailto:michel.veillette@trilliantinc.com>
Editor: Ivaylo Petrov
<mailto:ivaylo@ackl.io>";
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 provides information about the YANG modules,
datastores, and datastore schemas implemented by a
constrained network management server.";
// RFC Editor: Please replace XXXX with RFC number and remove this note
revision 2019-03-28 {
description
"Second revision.";
reference
"RFC XXXX: Constrained YANG Module Library";
// RFC Editor: Please replace XXXX with RFC number and remove this note
}
/*
* Typedefs
*/
typedef revision-identifier {
type binary {
length "4";
}
description
"Revision date encoded as a binary string, each nibble
representing a digit of the revision date. For example,
revision 2018-09-21 is encoded as 0x20 0x18 0x09 0x21.";
}
/*
* Groupings
*/
grouping module-identification-leafs {
description
"Parameters for identifying YANG modules and submodules.";
leaf identifier {
type sid:sid;
mandatory true;
description
"SID assigned to this module or submodule.";
}
leaf revision {
type revision-identifier;
description
"The YANG module or submodule revision date. If no
revision statement is present in the YANG module
or submodule, this leaf is not instantiated.";
}
}
grouping location-leaf-list {
description
"Common location leaf list parameter for modules and
submodules.";
leaf-list location {
type inet:uri;
description
"Contains a URL that represents the YANG schema resource
for this module or submodule.
This leaf is present in the model to keep the alignment
with 'ietf-yang-library'. Support of this leaf in
constrained devices is not necessarily required, nor
expected. It is recommended that clients used the module
or sub-module SID as the handle used to retrieve the
corresponding YANG module";
}
}
grouping implementation-parameters {
description
"Parameters for describing the implementation of a module.";
leaf-list feature {
type sid:sid;
description
"List of all YANG feature names from this module that are
supported by the server, regardless whether they are
defined in the module or any included submodule.";
}
leaf-list deviation {
type leafref {
path "../../module/identifier";
}
description
"List of all YANG deviation modules used by this server to
modify the conformance of the module associated with this
entry. Note that the same module can be used for
deviations for multiple modules, so the same entry MAY
appear within multiple 'module' entries.
This reference MUST NOT (directly or indirectly)
refer to the module being deviated.
Robust clients may want to make sure that they handle a
situation where a module deviates itself (directly or
indirectly) gracefully.";
}
}
grouping module-set-parameters {
description
"A set of parameters that describe a module set.";
leaf index {
type uint8;
description
"An arbitrary number assigned of the module set.";
}
list module {
key "identifier";
description
"An entry in this list represents a module implemented
by the server, as per RFC 7950 section 5.6.5, with a
particular set of supported features and deviations.";
reference
"RFC 7950: The YANG 1.1 Data Modeling Language.";
uses module-identification-leafs;
leaf namespace {
type inet:uri;
description
"The XML namespace identifier for this module.
This leaf is present in the model to keep the alignment
with 'ietf-yang-library'. Support of this leaf in
constrained devices is not required, nor expected.";
}
uses location-leaf-list;
list submodule {
key "identifier";
description
"Each entry represents one submodule within the parent
module.";
uses module-identification-leafs;
uses location-leaf-list;
}
uses implementation-parameters;
}
list import-only-module {
key "identifier revision";
description
"An entry in this list indicates that the server imports
reusable definitions from the specified revision of the
module, but does not implement any protocol accessible
objects from this revision.
Multiple entries for the same module name MAY exist.
This can occur if multiple modules import the same
module, but specify different revision-dates in the
import statements.";
leaf identifier {
type sid:sid;
description
"The YANG module name.";
}
leaf revision {
type union {
type revision-identifier;
type string {
length 0;
}
}
description
"The YANG module revision date.";
}
leaf namespace {
type inet:uri;
description
"The XML namespace identifier for this module.
This leaf is present in the model to keep the alignment
with 'ietf-yang-library'. Support of this leaf in
constrained devices is not required, nor expected.";
}
uses location-leaf-list;
list submodule {
key "identifier";
description
"Each entry represents one submodule within the
parent module.";
uses module-identification-leafs;
uses location-leaf-list;
}
}
}
grouping yang-library-parameters {
description
"The YANG library data structure is represented as a grouping
so it can be reused in configuration or another monitoring
data structure.";
list module-set {
key index;
description
"A set of modules that may be used by one or more schemas.
A module set does not have to be referentially complete,
i.e., it may define modules that contain import statements
for other modules not included in the module set.";
uses module-set-parameters;
}
list schema {
key "index";
description
"A datastore schema that may be used by one or more
datastores.
The schema must be valid and referentially complete,
i.e., it must contain modules to satisfy all used import
statements for all modules specified in the schema.";
leaf index {
type uint8;
description
"An arbitrary reference number assigned to the schema.";
}
leaf-list module-set {
type leafref {
path "../../module-set/index";
}
description
"A set of module-sets that are included in this schema.
If a non import-only module appears in multiple module
sets, then the module revision and the associated
features and deviations must be identical.";
}
}
list datastore {
key "identifier";
description
"A datastore supported by this server.
Each datastore indicates which schema it supports.
The server MUST instantiate one entry in this list
per specific datastore it supports.
Each datstore entry with the same datastore schema
SHOULD reference the same schema.";
leaf identifier {
type ds:datastore-ref;
description
"The identity of the datastore.";
}
leaf schema {
type leafref {
path "../../schema/index";
}
mandatory true;
description
"A reference to the schema supported by this datastore.
All non import-only modules of the schema are
implemented with their associated features and
deviations.";
}
}
}
/*
* Top-level container
*/
container yang-library {
config false;
description
"Container holding the entire YANG library of this server.";
uses yang-library-parameters;
leaf checksum {
type binary;
mandatory true;
description
"A server-generated checksum or digest of the contents of
the 'yang-library' tree. The server MUST change the
value of this leaf if the information represented by
the 'yang-library' tree, except 'yang-library/checksum',
has changed.";
}
}
/*
* Notifications
*/
notification yang-library-update {
description
"Generated when any YANG library information on the
server has changed.";
leaf checksum {
type leafref {
path "/yanglib:yang-library/yanglib:checksum";
}
mandatory true;
description
"Contains the YANG library checksum or digest for the
updated YANG library at the time the notification is
generated.";
}
}
}
<CODE ENDS>¶
This document registers one YANG module in the YANG Module Names registry [RFC7950].¶
name: ietf-constrained-yang-library¶
namespace: urn:ietf:params:xml:ns:yang:ietf-constrained-yang-library¶
prefix: lib¶
reference: RFC XXXX¶
// RFC Ed.: replace XXXX with RFC number and remove this note¶
This document registers the following XML namespace URN in the "IETF XML Registry", following the format defined in [RFC3688]:¶
URI: please assign urn:ietf:params:xml:ns:yang:ietf-constrained-yang-library¶
Registrant Contact: The IESG.¶
XML: N/A, the requested URI is an XML namespace.¶
Reference: RFC XXXX¶
// RFC Ed.: replace XXXX with RFC number and remove this note¶
The YANG module specified in this document defines a schema for data that is designed to be accessed via network management protocols such as NETCONF [RFC6241], RESTCONF [RFC8040] or CORECONF [I-D.ietf-core-comi]. The lowest NETCONF layer is the secure transport layer, and the mandatory-to-implement secure transport is Secure Shell (SSH) [RFC6242]. The lowest RESTCONF layer is HTTPS, and the mandatory-to-implement secure transport is TLS [RFC8446]. The lowest CORECONF layer is CoAP [RFC7252] and the mandatory-to-implement security transport is any one of DTLS [RFC6347] and OSCORE [RFC8613].¶
The Network Configuration Access Control Model (NACM) [RFC8341] provides the means to restrict access for particular NETCONF or RESTCONF users to a preconfigured subset of all available NETCONF or RESTCONF protocol operations and content.¶
Some of the readable data nodes in this YANG module may be considered sensitive or vulnerable in some network environments. It is thus important to control read access (e.g., via get, get-config, or notification) to these data nodes.¶
Specifically, the 'module' list may help an attacker to identify the server capabilities and server implementations with known bugs. Server vulnerabilities may be specific to particular modules, module revisions, module features, or even module deviations. This information is included in each module entry. For example, if a particular operation on a particular data node is known to cause a server to crash or significantly degrade device performance, then the module list information will help an attacker to identify server implementations with such a defect, in order to launch a denial of service attack on these devices.¶
The YANG module defined by this memo has been derived from an already existing YANG module, ietf-yang-library [RFC8525], we will like to thank the authors of this YANG module. A special thank also to Andy Bierman for his initial recommendations for the creation of this YANG module. The authors would also like to thank Tom Petch for his help during the development of this document and his useful comments during the review process.¶