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IETF RFC 8525
Last modified on Thursday, March 7th, 2019
 Permanent link to RFC 8525
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Internet Engineering Task Force (IETF) A. Bierman
Request for Comments: 8525 YumaWorks
Obsoletes: 7895 M. Bjorklund
Category: Standards Track Tail-f Systems
ISSN: 2070-1721 J. Schoenwaelder
Jacobs University
K. Watsen
Watsen Networks
R. Wilton
Cisco Systems
March 2019
YANG Library
 Abstract
This document describes a YANG library that provides information
about the YANG modules, datastores, and datastore schemas used by a
network management server. Simple caching mechanisms are provided to
allow clients to minimize retrieval of this information. This
version of the YANG library supports the Network Management Datastore
Architecture (NMDA) by listing all datastores supported by a network
management server and the schema that is used by each of these
datastores.
This document obsoletes RFC 7895.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/RFC 8525.
Bierman, et al. Standards Track PAGE 1 
RFC 8525 YANG Library March 2019
Copyright Notice
Copyright (c) 2019 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.
Table of Contents
1. Introduction ....................................................3
1.1. Terminology ................................................4
2. Objectives ......................................................5
3. YANG Library Data Model .........................................6
4. YANG Library YANG Module ........................................8
5. IANA Considerations ............................................20
6. Security Considerations ........................................21
7. References .....................................................22
7.1. Normative References ......................................22
7.2. Informative References ....................................23
Appendix A. Summary of Changes from RFC 7895 .....................25
Appendix B. Example YANG Library Instance for a Basic Server .....25
Appendix C. Example YANG Library Instance for an Advanced Server .27
Authors' Addresses ................................................32
Bierman, et al. Standards Track PAGE 2
RFC 8525 YANG Library March 2019
1. Introduction
There is a need for a standard mechanism to expose which YANG modules
[RFC 7950], datastores [RFC 8342], and datastore schemas [RFC 8342] are
in use by a network management server.
This document defines the YANG module "ietf-yang-library" that
provides this information. This version of the YANG library is
compatible with the Network Management Datastore Architecture (NMDA)
[RFC 8342]. The previous version of the YANG library, defined in
[RFC 7895], is not compatible with the NMDA since it assumes that all
datastores have exactly the same schema. This is not necessarily
true in the NMDA since dynamic configuration datastores may have
their own datastore schema. Furthermore, the operational state
datastore may support non-configurable YANG modules in addition to
the YANG modules supported by conventional configuration datastores.
The old YANG library definitions have been retained (for backwards-
compatibility reasons), but the definitions have been marked as
deprecated. For backwards compatibility, an NMDA-supporting server
SHOULD populate the deprecated "/modules-state" tree in a backwards-
compatible manner. The new "/yang-library" tree will be ignored by
legacy clients but will provide all the data needed for NMDA-aware
clients (which will ignore the "/modules-state" tree). The
recommended approach to populate "/modules-state" is to report the
YANG modules with "config true" data nodes that are configurable via
conventional configuration datastores and the YANG modules with
"config false" data nodes that are returned via a Network
Configuration Protocol (NETCONF) <get> operation or equivalent.
The YANG library information can be different on every server, and it
can change at runtime or across a server reboot. If a server
implements multiple network management protocols to access the
server's datastores, then each such protocol may have its own
conceptual instantiation of the YANG library.
If a large number of YANG modules are utilized by a server, then the
YANG library contents can be relatively large. Since the YANG
library contents change very infrequently, it is important that
clients be able to cache the YANG library contents and easily
identify whether their cache is out of date.
Bierman, et al. Standards Track PAGE 3
RFC 8525 YANG Library March 2019
1.1. Terminology
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.
The following terms are defined in [RFC 7950]:
o module
o submodule
o data node
This document uses the phrase "implement a module" as defined in
Section 5.6.5 of [RFC 7950].
The following terms are defined in [RFC 8342]:
o datastore
o datastore schema
o configuration
o conventional configuration datastore
o operational state
o operational state datastore
o dynamic configuration datastore
o client
o server
The following terms are used within this document:
o YANG library: A collection of YANG modules, submodules,
datastores, and datastore schemas used by a server.
o YANG library content identifier: A server-generated identifier of
the contents of the YANG library.
Tree diagrams in this document use the notation defined in [RFC 8340].
Bierman, et al. Standards Track PAGE 4
RFC 8525 YANG Library March 2019
2. Objectives
The following information is needed by a client application (for each
YANG module in the library) to fully utilize the YANG data modeling
language:
o name: The name of the YANG module.
o revision: If defined in the YANG module or submodule, the revision
is derived from the most recent revision statement within the
module or submodule.
o submodule list: The name and (if defined) revision of each
submodule used by the module must be identified.
o feature list: The name of each YANG feature supported by the
server must be identified.
o deviation list: The name of each YANG module with deviation
statements affecting a given YANG module must be identified.
In addition, the following information is needed by a client
application for each datastore supported by a server:
o identity: The YANG identity for the datastore.
o schema: The schema (i.e., the set of modules) implemented by the
datastore.
In order to select one out of several possible designs for the YANG
library data model, the following criteria were used:
1. The information must be efficient for a client to consume. Since
the size of the YANG library can be quite large, it should be
possible for clients to cache the YANG library information.
2. A dynamic configuration datastore must be able to implement a
module or feature that is not implemented in the conventional
configuration datastores.
3. It must be possible to not implement a module or feature in
<operational>, even if it is implemented in some other datastore.
This is required for transition purposes; a server that wants to
implement <operational> should not have to implement all modules
at once.
Bierman, et al. Standards Track PAGE 5
RFC 8525 YANG Library March 2019
4. A given module can only be implemented in one revision in all
datastores. If a module is implemented in more than one
datastore, the same revision is implemented in all these
datastores.
5. Multiple revisions can be used for import, if import-by revision
is used.
6. It must be possible to use the YANG library by schema mount
[RFC 8528].
3. YANG Library Data Model
The "ietf-yang-library" YANG module provides information about the
modules, submodules, datastores, and datastore schemas supported by a
server. All data nodes in the "ietf-yang-library" module are "config
false" and thus only accessible in the operational state datastore.
+-----------+
| datastore |
+-----------+
|
| has a
V
+-----------+ +--------+ +------------+
| datastore | union of | module | consists of | modules + |
| schema |----------->| set |--------------->| submodules |
+-----------+ +--------+ +------------+
Figure 1
The conceptual model of the YANG library is depicted in Figure 1.
Following the NMDA, every datastore has an associated datastore
schema. A datastore schema is a union of module sets, and every
module set is a collection of modules and submodules, including the
modules and submodules used for imports. Note that multiple
datastores may refer to the same datastore schema. Furthermore, it
is possible for individual datastore schemas to share module sets. A
common use case is the operational state datastore schema, which is a
superset of the schema used by conventional configuration datastores.
Below is the YANG tree diagram for the "ietf-yang-library" module,
excluding the deprecated "/modules-state" tree:
Bierman, et al. Standards Track PAGE 6
RFC 8525 YANG Library March 2019
module: ietf-yang-library
+--ro yang-library
+--ro module-set* [name]
| +--ro name string
| +--ro module* [name]
| | +--ro name yang:yang-identifier
| | +--ro revision? revision-identifier
| | +--ro namespace inet:uri
| | +--ro location* inet:uri
| | +--ro submodule* [name]
| | | +--ro name yang:yang-identifier
| | | +--ro revision? revision-identifier
| | | +--ro location* inet:uri
| | +--ro feature* yang:yang-identifier
| | +--ro deviation* -> ../../module/name
| +--ro import-only-module* [name revision]
| +--ro name yang:yang-identifier
| +--ro revision union
| +--ro namespace inet:uri
| +--ro location* inet:uri
| +--ro submodule* [name]
| +--ro name yang:yang-identifier
| +--ro revision? revision-identifier
| +--ro location* inet:uri
+--ro schema* [name]
| +--ro name string
| +--ro module-set* -> ../../module-set/name
+--ro datastore* [name]
| +--ro name ds:datastore-ref
| +--ro schema -> ../../schema/name
+--ro content-id string
notifications:
+---n yang-library-update
+--ro content-id -> /yang-library/content-id
The "/yang-library" container holds the entire YANG library. The
container has the following child nodes:
o The "/yang-library/module-set" contains entries representing
module sets. The list "/yang-library/module-set/module"
enumerates the modules that belong to the module set. A module is
listed together with its submodules (if any), a set of features,
and any deviation modules. The list "/yang-library/module-set/
import-only-module" lists all modules (and their submodules) used
only for imports. The assignment of a module to a module set is
Bierman, et al. Standards Track PAGE 7
RFC 8525 YANG Library March 2019
at the server's discretion. This revision of the YANG library
attaches no semantics as to which module set a module is listed
in.
o The "/yang-library/schema" list contains an entry for each
datastore schema supported by the server. All conventional
configuration datastores use the same "schema" list entry. A
dynamic configuration datastore may use a different datastore
schema from the conventional configuration datastores and hence
may require a separate "schema" entry. A "schema" entry has a
leaf-list of references to entries in the "module-set" list. The
schema consists of the union of all modules in all referenced
module sets.
o The "/yang-library/datastore" list contains one entry for each
datastore supported by the server, and it identifies the datastore
schema associated with a datastore via a reference to an entry in
the "schema" list. Each supported conventional configuration
datastore has a separate entry, pointing to the same "schema" list
element.
o The "/yang-library/content-id" leaf contains the YANG library
content identifier, which is an implementation-specific identifier
representing the current information in the YANG library on a
specific server. The value of this leaf MUST change whenever the
information in the YANG library changes. There is no requirement
that the same information always result in the same "content-id"
value. This leaf allows a client to fetch all schema information
once, cache it, and only refetch it if the value of this leaf has
been changed. If the value of this leaf changes, the server also
generates a "yang-library-update" notification.
Note that for a NETCONF server implementing the NETCONF extensions to
support the NMDA [RFC 8526], a change of the YANG library content
identifier results in a new value for the :yang-library:1.1
capability defined in [RFC 8526]. Thus, if such a server implements
NETCONF notifications [RFC 5277] and the "netconf-capability-change"
notification [RFC 6470], a "netconf-capability-change" notification is
generated whenever the YANG library content identifier changes.
4. YANG Library YANG Module
The "ietf-yang-library" YANG module imports definitions from the
"ietf-yang-types" and "ietf-inet-types" modules defined in [RFC 6991]
and from the "ietf-datastores" module defined in [RFC 8342]. While
the YANG module is defined using YANG version 1.1, the YANG library
supports YANG modules written in any version of YANG.
Bierman, et al. Standards Track PAGE 8
RFC 8525 YANG Library March 2019
<CODE BEGINS> file "ietf-yang-library@2019-01-04.yang"
module ietf-yang-library {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-yang-library";
prefix yanglib;
import ietf-yang-types {
prefix yang;
reference
"RFC 6991: Common YANG Data Types";
}
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 NETCONF (Network Configuration) Working Group";
contact
"WG Web: <https://datatracker.ietf.org/wg/netconf/>
WG List: <mailto:netconf@ietf.org>
Author: Andy Bierman
<mailto:andy@yumaworks.com>
Author: Martin Bjorklund
<mailto:mbj@tail-f.com>
Author: Juergen Schoenwaelder
<mailto:j.schoenwaelder@jacobs-university.de>
Author: Kent Watsen
<mailto:kent+ietf@watsen.net>
Author: Robert Wilton
<mailto:rwilton@cisco.com>";
description
"This module provides information about the YANG modules,
datastores, and datastore schemas used by a network
management server.
Bierman, et al. Standards Track PAGE 9
RFC 8525 YANG Library March 2019
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) 2019 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 8525; see
the RFC itself for full legal notices.";
revision 2019-01-04 {
description
"Added support for multiple datastores according to the
Network Management Datastore Architecture (NMDA).";
reference
"RFC 8525: YANG Library";
}
revision 2016-04-09 {
description
"Initial revision.";
reference
"RFC 7895: YANG Module Library";
}
/*
* Typedefs
*/
typedef revision-identifier {
type string {
pattern '\d{4}-\d{2}-\d{2}';
}
description
"Represents a specific date in YYYY-MM-DD format.";
}
/*
* Groupings
*/
Bierman, et al. Standards Track PAGE 10
RFC 8525 YANG Library March 2019
grouping module-identification-leafs {
description
"Parameters for identifying YANG modules and submodules.";
leaf name {
type yang:yang-identifier;
mandatory true;
description
"The YANG module or submodule name.";
}
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 leaf-list parameter for the locations of 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 will only be present if there is a URL
available for retrieval of the schema for this entry.";
}
}
grouping module-implementation-parameters {
description
"Parameters for describing the implementation of a module.";
leaf-list feature {
type yang:yang-identifier;
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/name";
}
Bierman, et al. Standards Track PAGE 11
RFC 8525 YANG Library March 2019
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 name {
type string;
description
"An arbitrary name of the module set.";
}
list module {
key "name";
description
"An entry in this list represents a module implemented by the
server, as per Section 5.6.5 of RFC 7950, 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;
mandatory true;
description
"The XML namespace identifier for this module.";
}
uses location-leaf-list;
list submodule {
key "name";
description
"Each entry represents one submodule within the
parent module.";
uses module-identification-leafs;
uses location-leaf-list;
}
Bierman, et al. Standards Track PAGE 12
RFC 8525 YANG Library March 2019
uses module-implementation-parameters;
}
list import-only-module {
key "name 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 name {
type yang:yang-identifier;
description
"The YANG module name.";
}
leaf revision {
type union {
type revision-identifier;
type string {
length "0";
}
}
description
"The YANG module revision date.
A zero-length string is used if no revision statement
is present in the YANG module.";
}
leaf namespace {
type inet:uri;
mandatory true;
description
"The XML namespace identifier for this module.";
}
uses location-leaf-list;
list submodule {
key "name";
description
"Each entry represents one submodule within the
parent module.";
uses module-identification-leafs;
uses location-leaf-list;
}
}
}
Bierman, et al. Standards Track PAGE 13
RFC 8525 YANG Library March 2019
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 "name";
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 "name";
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 name {
type string;
description
"An arbitrary name of the schema.";
}
leaf-list module-set {
type leafref {
path "../../module-set/name";
}
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 "name";
description
"A datastore supported by this server.
Each datastore indicates which schema it supports.
Bierman, et al. Standards Track PAGE 14
RFC 8525 YANG Library March 2019
The server MUST instantiate one entry in this list per
specific datastore it supports.
Each datastore entry with the same datastore schema SHOULD
reference the same schema.";
leaf name {
type ds:datastore-ref;
description
"The identity of the datastore.";
}
leaf schema {
type leafref {
path "../../schema/name";
}
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 content-id {
type string;
mandatory true;
description
"A server-generated identifier 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/content-id', has
changed.";
}
}
/*
* Notifications
*/
notification yang-library-update {
Bierman, et al. Standards Track PAGE 15
RFC 8525 YANG Library March 2019
description
"Generated when any YANG library information on the
server has changed.";
leaf content-id {
type leafref {
path "/yanglib:yang-library/yanglib:content-id";
}
mandatory true;
description
"Contains the YANG library content identifier for the updated
YANG library at the time the notification is generated.";
}
}
/*
* Legacy groupings
*/
grouping module-list {
status deprecated;
description
"The module data structure is represented as a grouping
so it can be reused in configuration or another monitoring
data structure.";
grouping common-leafs {
status deprecated;
description
"Common parameters for YANG modules and submodules.";
leaf name {
type yang:yang-identifier;
status deprecated;
description
"The YANG module or submodule name.";
}
leaf revision {
type union {
type revision-identifier;
type string {
length "0";
}
}
status deprecated;
description
"The YANG module or submodule revision date.
A zero-length string is used if no revision statement
is present in the YANG module or submodule.";
}
Bierman, et al. Standards Track PAGE 16
RFC 8525 YANG Library March 2019
}
grouping schema-leaf {
status deprecated;
description
"Common schema leaf parameter for modules and submodules.";
leaf schema {
type inet:uri;
description
"Contains a URL that represents the YANG schema
resource for this module or submodule.
This leaf will only be present if there is a URL
available for retrieval of the schema for this entry.";
}
}
list module {
key "name revision";
status deprecated;
description
"Each entry represents one revision of one module
currently supported by the server.";
uses common-leafs {
status deprecated;
}
uses schema-leaf {
status deprecated;
}
leaf namespace {
type inet:uri;
mandatory true;
status deprecated;
description
"The XML namespace identifier for this module.";
}
leaf-list feature {
type yang:yang-identifier;
status deprecated;
description
"List of YANG feature names from this module that are
supported by the server, regardless of whether they are
defined in the module or any included submodule.";
}
list deviation {
key "name revision";
status deprecated;
Bierman, et al. Standards Track PAGE 17
RFC 8525 YANG Library March 2019
description
"List of YANG deviation module names and revisions
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.
The deviation module MUST be present in the 'module'
list, with the same name and revision values.
The 'conformance-type' value will be 'implement' for
the deviation module.";
uses common-leafs {
status deprecated;
}
}
leaf conformance-type {
type enumeration {
enum implement {
description
"Indicates that the server implements one or more
protocol-accessible objects defined in the YANG module
identified in this entry. This includes deviation
statements defined in the module.
For YANG version 1.1 modules, there is at most one
'module' entry with conformance type 'implement' for a
particular module name, since YANG 1.1 requires that
at most one revision of a module is implemented.
For YANG version 1 modules, there SHOULD NOT be more
than one 'module' entry for a particular module
name.";
}
enum import {
description
"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 'module' 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.";
}
}
mandatory true;
Bierman, et al. Standards Track PAGE 18
RFC 8525 YANG Library March 2019
status deprecated;
description
"Indicates the type of conformance the server is claiming
for the YANG module identified by this entry.";
}
list submodule {
key "name revision";
status deprecated;
description
"Each entry represents one submodule within the
parent module.";
uses common-leafs {
status deprecated;
}
uses schema-leaf {
status deprecated;
}
}
}
}
/*
* Legacy operational state data nodes
*/
container modules-state {
config false;
status deprecated;
description
"Contains YANG module monitoring information.";
leaf module-set-id {
type string;
mandatory true;
status deprecated;
description
"Contains a server-specific identifier representing
the current set of modules and submodules. The
server MUST change the value of this leaf if the
information represented by the 'module' list instances
has changed.";
}
uses module-list {
status deprecated;
}
}
/*
* Legacy notifications
Bierman, et al. Standards Track PAGE 19
RFC 8525 YANG Library March 2019
*/
notification yang-library-change {
status deprecated;
description
"Generated when the set of modules and submodules supported
by the server has changed.";
leaf module-set-id {
type leafref {
path "/yanglib:modules-state/yanglib:module-set-id";
}
mandatory true;
status deprecated;
description
"Contains the module-set-id value representing the
set of modules and submodules supported at the server
at the time the notification is generated.";
}
}
}
<CODE ENDS>
5. IANA Considerations
RFC 7895 previously registered one URI in the "IETF XML Registry"
[RFC 3688]. This document takes over this registration entry made by
RFC 7895 and changes the Registrant Contact to the IESG according to
Section 4 of [RFC 3688].
URI: urn:ietf:params:xml:ns:yang:ietf-yang-library
Registrant Contact: The IESG.
XML: N/A, the requested URI is an XML namespace.
This document registers a YANG module in the "YANG Module Names"
registry [RFC 6020]:
name: ietf-yang-library
namespace: urn:ietf:params:xml:ns:yang:ietf-yang-library
prefix: yanglib
reference: RFC 8525
Bierman, et al. Standards Track PAGE 20
RFC 8525 YANG Library March 2019
6. Security Considerations
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 [RFC 6241] or RESTCONF [RFC 8040]. The lowest NETCONF layer
is the secure transport layer, and the mandatory-to-implement secure
transport is Secure Shell (SSH) [RFC 6242]. The lowest RESTCONF layer
is HTTPS, and the mandatory-to-implement secure transport is TLS
[RFC 8446].
The Network Configuration Access Control Model (NACM) [RFC 8341]
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. These are the subtrees and data
nodes and their sensitivity/vulnerability:
The "/yang-library" subtree of the YANG library may help an attacker
identify the server capabilities and server implementations with
known bugs since the set of YANG modules supported by a server may
reveal the kind of device and the manufacturer of the device.
Although some of this information may be available to all NETCONF
users via the NETCONF <hello> message (or similar messages in other
management protocols), this YANG module potentially exposes
additional details that could be of some assistance to an attacker.
Server vulnerabilities may be specific to particular modules, module
revisions, module features, or even module deviations. 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 identify server
implementations with such a defect, in order to launch a denial-of-
service attack on the device.
Bierman, et al. Standards Track PAGE 21
RFC 8525 YANG Library March 2019
7. References
7.1. Normative References
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC 2119, March 1997,
<https://www.rfc-editor.org/info/RFC 2119>.
[RFC 3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
DOI 10.17487/RFC 3688, January 2004,
<https://www.rfc-editor.org/info/RFC 3688>.
[RFC 6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC 6020, October 2010,
<https://www.rfc-editor.org/info/RFC 6020>.
[RFC 6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC 6241, June 2011,
<https://www.rfc-editor.org/info/RFC 6241>.
[RFC 6242] Wasserman, M., "Using the NETCONF Protocol over Secure
Shell (SSH)", RFC 6242, DOI 10.17487/RFC 6242, June 2011,
<https://www.rfc-editor.org/info/RFC 6242>.
[RFC 6991] Schoenwaelder, J., Ed., "Common YANG Data Types",
RFC 6991, DOI 10.17487/RFC 6991, July 2013,
<https://www.rfc-editor.org/info/RFC 6991>.
[RFC 7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC 7950, August 2016,
<https://www.rfc-editor.org/info/RFC 7950>.
[RFC 8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", RFC 8040, DOI 10.17487/RFC 8040, January 2017,
<https://www.rfc-editor.org/info/RFC 8040>.
[RFC 8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC 8174,
May 2017, <https://www.rfc-editor.org/info/RFC 8174>.
[RFC 8341] Bierman, A. and M. Bjorklund, "Network Configuration
Access Control Model", STD 91, RFC 8341,
DOI 10.17487/RFC 8341, March 2018,
<https://www.rfc-editor.org/info/RFC 8341>.
Bierman, et al. Standards Track PAGE 22
RFC 8525 YANG Library March 2019
[RFC 8342] Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
and R. Wilton, "Network Management Datastore Architecture
(NMDA)", RFC 8342, DOI 10.17487/RFC 8342, March 2018,
<https://www.rfc-editor.org/info/RFC 8342>.
[RFC 8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC 8446, August 2018,
<https://www.rfc-editor.org/info/RFC 8446>.
7.2. Informative References
[RFC 5277] Chisholm, S. and H. Trevino, "NETCONF Event
Notifications", RFC 5277, DOI 10.17487/RFC 5277, July 2008,
<https://www.rfc-editor.org/info/RFC 5277>.
[RFC 6470] Bierman, A., "Network Configuration Protocol (NETCONF)
Base Notifications", RFC 6470, DOI 10.17487/RFC 6470,
February 2012, <https://www.rfc-editor.org/info/RFC 6470>.
[RFC 7895] Bierman, A., Bjorklund, M., and K. Watsen, "YANG Module
Library", RFC 7895, DOI 10.17487/RFC 7895, June 2016,
<https://www.rfc-editor.org/info/RFC 7895>.
[RFC 8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
BCP 215, RFC 8340, DOI 10.17487/RFC 8340, March 2018,
<https://www.rfc-editor.org/info/RFC 8340>.
[RFC 8343] Bjorklund, M., "A YANG Data Model for Interface
Management", RFC 8343, DOI 10.17487/RFC 8343, March 2018,
<https://www.rfc-editor.org/info/RFC 8343>.
[RFC 8344] Bjorklund, M., "A YANG Data Model for IP Management",
RFC 8344, DOI 10.17487/RFC 8344, March 2018,
<https://www.rfc-editor.org/info/RFC 8344>.
[RFC 8345] Clemm, A., Medved, J., Varga, R., Bahadur, N.,
Ananthakrishnan, H., and X. Liu, "A YANG Data Model for
Network Topologies", RFC 8345, DOI 10.17487/RFC 8345, March
2018, <https://www.rfc-editor.org/info/RFC 8345>.
[RFC 8348] Bierman, A., Bjorklund, M., Dong, J., and D. Romascanu, "A
YANG Data Model for Hardware Management", RFC 8348,
DOI 10.17487/RFC 8348, March 2018,
<https://www.rfc-editor.org/info/RFC 8348>.
Bierman, et al. Standards Track PAGE 23
RFC 8525 YANG Library March 2019
[RFC 8349] Lhotka, L., Lindem, A., and Y. Qu, "A YANG Data Model for
Routing Management (NMDA Version)", RFC 8349,
DOI 10.17487/RFC 8349, March 2018,
<https://www.rfc-editor.org/info/RFC 8349>.
[RFC 8526] Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
and R. Wilton, "NETCONF Extensions to Support the Network
Management Datastore Architecture", RFC 8526,
DOI 10.17487/RFC 8526, March 2019,
<https://www.rfc-editor.org/info/RFC 8526>.
[RFC 8528] Bjorklund, M. and L. Lhotka, "YANG Schema Mount",
RFC 8528, DOI 10.17487/RFC 8528, March 2019,
<https://www.rfc-editor.org/info/RFC 8528>.
Bierman, et al. Standards Track PAGE 24
RFC 8525 YANG Library March 2019
Appendix A. Summary of Changes from RFC 7895
This document changes [RFC 7895] in the following ways:
o Renamed document title from "YANG Module Library" to "YANG
Library".
o Added a new top-level "/yang-library" container to hold the entire
YANG library providing information about module sets, schemas, and
datastores.
o Refactored the "/modules-state" container into a new
"/yang-library/module-set" list.
o Added a new "/yang-library/schema" list and a new "/yang-library/
datastore" list.
o Added a set of new groupings as replacements for the deprecated
groupings.
o Added a "yang-library-update" notification as a replacement for
the deprecated "yang-library-change" notification.
o Deprecated the "/modules-state" tree.
o Deprecated the "/module-list" grouping.
o Deprecated the "/yang-library-change" notification.
Appendix B. Example YANG Library Instance for a Basic Server
The following example shows the YANG library of a basic server
implementing the "ietf-interfaces" [RFC 8343] and "ietf-ip" [RFC 8344]
modules in the <running>, <startup>, and <operational> datastores and
the "ietf-hardware" [RFC 8348] module in the <operational> datastore.
Newline characters in leaf values are added for formatting reasons.
<yang-library
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-library"
xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
<module-set>
<name>config-modules</name>
<module>
<name>ietf-interfaces</name>
<revision>2018-02-20</revision>
<namespace>
Bierman, et al. Standards Track PAGE 25
RFC 8525 YANG Library March 2019
urn:ietf:params:xml:ns:yang:ietf-interfaces
</namespace>
</module>
<module>
<name>ietf-ip</name>
<revision>2018-02-22</revision>
<namespace>
urn:ietf:params:xml:ns:yang:ietf-ip
</namespace>
</module>
<import-only-module>
<name>ietf-yang-types</name>
<revision>2013-07-15</revision>
<namespace>
urn:ietf:params:xml:ns:yang:ietf-yang-types
</namespace>
</import-only-module>
<import-only-module>
<name>ietf-inet-types</name>
<revision>2013-07-15</revision>
<namespace>
urn:ietf:params:xml:ns:yang:ietf-inet-types
</namespace>
</import-only-module>
</module-set>
<module-set>
<name>state-modules</name>
<module>
<name>ietf-hardware</name>
<revision>2018-03-13</revision>
<namespace>
urn:ietf:params:xml:ns:yang:ietf-hardware
</namespace>
</module>
<import-only-module>
<name>ietf-inet-types</name>
<revision>2013-07-15</revision>
<namespace>
urn:ietf:params:xml:ns:yang:ietf-inet-types
</namespace>
</import-only-module>
<import-only-module>
<name>ietf-yang-types</name>
<revision>2013-07-15</revision>
<namespace>
urn:ietf:params:xml:ns:yang:ietf-yang-types
</namespace>
Bierman, et al. Standards Track PAGE 26
RFC 8525 YANG Library March 2019
</import-only-module>
<import-only-module>
<name>iana-hardware</name>
<revision>2018-03-13</revision>
<namespace>
urn:ietf:params:xml:ns:yang:iana-hardware
</namespace>
</import-only-module>
</module-set>
<schema>
<name>config-schema</name>
<module-set>config-modules</module-set>
</schema>
<schema>
<name>state-schema</name>
<module-set>config-modules</module-set>
<module-set>state-modules</module-set>
</schema>
<datastore>
<name>ds:startup</name>
<schema>config-schema</schema>
</datastore>
<datastore>
<name>ds:running</name>
<schema>config-schema</schema>
</datastore>
<datastore>
<name>ds:operational</name>
<schema>state-schema</schema>
</datastore>
<content-id>75a43df9bd56b92aacc156a2958fbe12312fb285</content-id>
</yang-library>
Appendix C. Example YANG Library Instance for an Advanced Server
The following example extends the example in Appendix B by using
modules from [RFC 8345] and [RFC 8349] to illustrate a slightly more
advanced server that:
o Has a module with features only enabled in <operational>; the
"ietf-routing" module is supported in <running>, <startup>, and
<operational>, but the "multiple-ribs" and "router-id" features
are only enabled in <operational>. Hence, the "router-id" leaf
may be read but not configured.
Bierman, et al. Standards Track PAGE 27
RFC 8525 YANG Library March 2019
o Supports a dynamic configuration datastore "example-ds-ephemeral",
with only the "ietf-network" and "ietf-network-topology" modules
configurable via a notional dynamic configuration protocol.
o Shows an example of datastore-specific deviations. The
"example-vendor-hardware-deviations" module is included in the
schema for <operational> to remove data nodes that cannot be
supported by the server.
o Shows how module-sets can be used to organize related modules
together.
Newline characters in leaf values are added for formatting reasons.
<yang-library
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-library"
xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores"
xmlns:ex-ds-eph="urn:example:ds-ephemeral">
<module-set>
<name>config-state-modules</name>
<module>
<name>ietf-interfaces</name>
<revision>2018-02-20</revision>
<namespace>
urn:ietf:params:xml:ns:yang:ietf-interfaces
</namespace>
</module>
<module>
<name>ietf-ip</name>
<revision>2018-02-22</revision>
<namespace>
urn:ietf:params:xml:ns:yang:ietf-ip
</namespace>
</module>
<module>
<name>ietf-routing</name>
<revision>2018-03-13</revision>
<namespace>
urn:ietf:params:xml:ns:yang:ietf-routing
</namespace>
</module>
<import-only-module>
<name>ietf-yang-types</name>
<revision>2013-07-15</revision>
<namespace>
urn:ietf:params:xml:ns:yang:ietf-yang-types
</namespace>
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RFC 8525 YANG Library March 2019
</import-only-module>
<import-only-module>
<name>ietf-inet-types</name>
<revision>2013-07-15</revision>
<namespace>
urn:ietf:params:xml:ns:yang:ietf-inet-types
</namespace>
</import-only-module>
</module-set>
<module-set>
<name>config-only-modules</name>
<module>
<name>ietf-routing</name>
<revision>2018-03-13</revision>
<namespace>
urn:ietf:params:xml:ns:yang:ietf-routing
</namespace>
</module>
</module-set>
<module-set>
<name>dynamic-config-state-modules</name>
<module>
<name>ietf-network</name>
<revision>2018-02-26</revision>
<namespace>
urn:ietf:params:xml:ns:yang:ietf-network
</namespace>
</module>
<module>
<name>ietf-network-topology</name>
<revision>2018-02-26</revision>
<namespace>
urn:ietf:params:xml:ns:yang:ietf-network-topology
</namespace>
</module>
<import-only-module>
<name>ietf-inet-types</name>
<revision>2013-07-15</revision>
<namespace>
urn:ietf:params:xml:ns:yang:ietf-inet-types
</namespace>
</import-only-module>
</module-set>
<module-set>
<name>state-only-modules</name>
Bierman, et al. Standards Track PAGE 29
RFC 8525 YANG Library March 2019
<module>
<name>ietf-hardware</name>
<revision>2018-03-13</revision>
<namespace>
urn:ietf:params:xml:ns:yang:ietf-hardware
</namespace>
<deviation>example-vendor-hardware-deviations</deviation>
</module>
<module>
<name>ietf-routing</name>
<revision>2018-03-13</revision>
<namespace>
urn:ietf:params:xml:ns:yang:ietf-routing
</namespace>
<feature>multiple-ribs</feature>
<feature>router-id</feature>
</module>
<module>
<name>example-vendor-hardware-deviations</name>
<revision>2018-01-31</revision>
<namespace>
urn:example:example-vendor-hardware-deviations
</namespace>
</module>
<import-only-module>
<name>ietf-inet-types</name>
<revision>2013-07-15</revision>
<namespace>
urn:ietf:params:xml:ns:yang:ietf-inet-types
</namespace>
</import-only-module>
<import-only-module>
<name>ietf-yang-types</name>
<revision>2013-07-15</revision>
<namespace>
urn:ietf:params:xml:ns:yang:ietf-yang-types
</namespace>
</import-only-module>
<import-only-module>
<name>iana-hardware</name>
<revision>2018-03-13</revision>
<namespace>
urn:ietf:params:xml:ns:yang:iana-hardware
</namespace>
</import-only-module>
</module-set>
<schema>
Bierman, et al. Standards Track PAGE 30
RFC 8525 YANG Library March 2019
<name>config-schema</name>
<module-set>config-state-modules</module-set>
<module-set>config-only-modules</module-set>
</schema>
<schema>
<name>dynamic-config-schema</name>
<module-set>dynamic-config-state-modules</module-set>
</schema>
<schema>
<name>state-schema</name>
<module-set>config-state-modules</module-set>
<module-set>dynamic-config-state-modules</module-set>
<module-set>state-only-modules</module-set>
</schema>
<datastore>
<name>ds:startup</name>
<schema>config-schema</schema>
</datastore>
<datastore>
<name>ds:running</name>
<schema>config-schema</schema>
</datastore>
<datastore>
<name>ex-ds-eph:ds-ephemeral</name>
<schema>dynamic-config-schema</schema>
</datastore>
<datastore>
<name>ds:operational</name>
<schema>state-schema</schema>
</datastore>
<content-id>14782ab9bd56b92aacc156a2958fbe12312fb285</content-id>
</yang-library>
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RFC 8525 YANG Library March 2019
Authors' Addresses
Andy Bierman
YumaWorks
Email: andy@yumaworks.com
Martin Bjorklund
Tail-f Systems
Email: mbj@tail-f.com
Juergen Schoenwaelder
Jacobs University
Email: j.schoenwaelder@jacobs-university.de
Kent Watsen
Watsen Networks
Email: kent+ietf@watsen.net
Robert Wilton
Cisco Systems
Email: rwilton@cisco.com
Bierman, et al. Standards Track PAGE 32
RFC TOTAL SIZE: 57003 bytes
PUBLICATION DATE: Thursday, March 7th, 2019
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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