RFC 7895
YANG Module Library
RFC 7895: YANG Module Library 💖
Okay bestie, here's the paperwork first 📋 This is RFC 7895, titled YANG Module Library, a Standards Track document dated June 2016. Its ISSN is 2070-1721. The authors are A. Bierman (YumaWorks), M. Bjorklund (Tail-f Systems), and K. Watsen (Juniper Networks). The title block doesn't list anything it obsoletes or updates 🦋
Abstract 🌸
Okay so this doc describes a YANG library that tells you about every YANG module a network management server uses (like a Network Configuration Protocol (NETCONF) server) 🖥️ It also has simple caching tricks so clients don't have to keep re-downloading all that info. Main character energy for efficiency ✨
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 got public review and was approved for publication by the Internet Engineering Steering Group (IESG). If you want more info on Internet Standards, check Section 2 of RFC 7841 💅
Info about the current status of this document, any errata, and how to give feedback is at http://www.rfc-editor.org/info/rfc7895 🔗
Copyright Notice ©️
Copyright (c) 2016 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 (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, because 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 they are provided without warranty as described in the Simplified BSD License 🫶
Table of Contents 📚
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Tree Diagrams . . . . . . . . . . . . . . . . . . . . . . 3
2. YANG Module Library . . . . . . . . . . . . . . . . . . . . . 4
2.1. modules-state . . . . . . . . . . . . . . . . . . . . . . 4
2.1.1. modules-state/module-set-id . . . . . . . . . . . . . 4
2.1.2. modules-state/module . . . . . . . . . . . . . . . . 5
2.2. YANG Library Module . . . . . . . . . . . . . . . . . . . 5
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
3.1. YANG Module Registry . . . . . . . . . . . . . . . . . . 11
4. Security Considerations . . . . . . . . . . . . . . . . . . . 11
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.1. Normative References . . . . . . . . . . . . . . . . . . 12
5.2. Informative References . . . . . . . . . . . . . . . . . 12
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 131. Introduction ✨
Okay so there's a real need for standard ways to identify the YANG modules and submodules a server uses when it implements YANG data models 🧚 If the server uses a huge pile of YANG modules, the YANG library contents can get pretty big. The info barely changes, so it's super important that clients can cache the YANG library contents and quickly tell whether their cache is outdated 💅
YANG library info can be different on every server, and it can change at runtime or across a server reboot 🔄
If the server implements multiple protocols to access the YANG-defined data, each protocol gets its own conceptual instantiation of the YANG library 🦋
For each YANG module in the library, a client application needs the following info to fully use the YANG data modeling language:
- name: The name of the YANG module.
- revision: Each YANG module and submodule in the library has a revision. It's derived from the most recent revision statement inside the module or submodule. If there's no such revision statement, the module's or submodule's revision is the zero-length string.
- submodule list: The name and revision of each submodule used by the module MUST be identified.
- feature list: The name of each YANG feature supported by the server MUST be identified.
- deviation list: The name of each YANG module used for deviation statements MUST be identified.
1.1. Terminology 🎀
The keywords "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]. 🌈
The following terms are defined in [RFC6241]:
- client
- server
The following terms are defined in [YANG1.1]:
- module
- submodule
The following terms are used within this document:
- YANG library: A collection of YANG modules and submodules used by a server.
1.2. Tree Diagrams 🌳
This doc uses a simplified picture of the data model. Here's what the symbols mean:
- Brackets "[" and "]" enclose list keys.
- Abbreviations before data node names: "rw" means configuration data (read-write), and "ro" means state data (read-only).
- Symbols after data node names: "?" means an optional node, "!" means a presence container, and "*" denotes a list and leaf-list.
- Parentheses enclose choice and case nodes, and case nodes are also marked with a colon (":").
- Ellipsis ("...") stands for contents of subtrees that aren't shown.
2. YANG Module Library 💜
The "ietf-yang-library" module gives you info about the YANG library a server uses. This module is defined using YANG version 1, but it supports describing YANG modules written in any revision of YANG 👑
Here's the YANG Tree Diagram for the "ietf-yang-library" module:
+--ro modules-state
+--ro module-set-id string
+--ro module* [name revision]
+--ro name yang:yang-identifier
+--ro revision union
+--ro schema? inet:uri
+--ro namespace inet:uri
+--ro feature* yang:yang-identifier
+--ro deviation* [name revision]
| +--ro name yang:yang-identifier
| +--ro revision union
+--ro conformance-type enumeration
+--ro submodule* [name revision]
+--ro name yang:yang-identifier
+--ro revision union
+--ro schema? inet:uri2.1. modules-state 🧁
This mandatory container holds the identifiers for the YANG data model modules the server supports.
2.1.1. modules-state/module-set-id 🔑
This mandatory leaf holds a unique, implementation-specific identifier for the current set of modules and submodules on a specific server. The value of this leaf MUST change whenever the set of modules and submodules in the YANG library changes. There's no requirement that the same set always gives the same module-set-id value 🤷♀️
This leaf lets a client fetch the module list once, cache it, and only refetch it if the value of this leaf has changed 💖
If the value of this leaf changes, the server also generates a yang-library-change notification, with the new value of module-set-id 🔔
Note that for a NETCONF server that implements YANG 1.1 [YANG1.1], a change of the module-set-id value results in a new value for the :yang-library capability defined in [YANG1.1]. So if such a server implements NETCONF notifications [RFC5277] and the notification netconf-capability-change [RFC6470], a netconf-capability-change notification is generated whenever the module-set-id changes 🦋
2.1.2. modules-state/module 📦
This mandatory list contains one entry for each YANG data model module the server supports. There MUST be an entry in this list for each revision of each YANG module that the server uses. It's possible for multiple revisions of the same module to be imported, in addition to an entry for the revision that the server implements 🌸
2.2. YANG Library Module 💖
Okay bestie, this is the main event 🎀 The "ietf-yang-library" module is the monitoring info that tells you which YANG modules and submodules a server is actually running. Think of it as the server's full wardrobe check 👗
It leans on the "ietf-yang-types" and "ietf-inet-types" modules from [RFC6991] for some of its type definitions ✨
Here's the whole thing, no cuts 💅
<CODE BEGINS> file "ietf-yang-library@2016-06-21.yang"
module ietf-yang-library {
namespace "urn:ietf:params:xml:ns:yang:ietf-yang-library";
prefix "yanglib";
import ietf-yang-types {
prefix yang;
}
import ietf-inet-types {
prefix inet;
}
organization
"IETF NETCONF (Network Configuration) Working Group";
contact
"WG Web: <https://datatracker.ietf.org/wg/netconf/>
WG List: <mailto:netconf@ietf.org>
WG Chair: Mehmet Ersue
<mailto:mehmet.ersue@nsn.com>
WG Chair: Mahesh Jethanandani
<mailto:mjethanandani@gmail.com>
Editor: Andy Bierman
<mailto:andy@yumaworks.com>
Editor: Martin Bjorklund
<mailto:mbj@tail-f.com>
Editor: Kent Watsen
<mailto:kwatsen@juniper.net>";
description
"This module contains monitoring information about the YANG
modules and submodules that are used within a YANG-based
server.
Copyright (c) 2016 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
(http://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC 7895; see
the RFC itself for full legal notices.";
revision 2016-06-21 {
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
*/
grouping module-list {
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 {
description
"Common parameters for YANG modules and submodules.";
leaf name {
type yang:yang-identifier;
description
"The YANG module or submodule name.";
}
leaf revision {
type union {
type revision-identifier;
type string { length 0; }
}
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.";
}
}
grouping schema-leaf {
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";
description
"Each entry represents one revision of one module
currently supported by the server.";
uses common-leafs;
uses schema-leaf;
leaf namespace {
type inet:uri;
mandatory true;
description
"The XML namespace identifier for this module.";
}
leaf-list feature {
type yang:yang-identifier;
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";
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;
}
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;
description
"Indicates the type of conformance the server is claiming
for the YANG module identified by this entry.";
}
list submodule {
key "name revision";
description
"Each entry represents one submodule within the
parent module.";
uses common-leafs;
uses schema-leaf;
}
}
}
/*
* Operational state data nodes
*/
container modules-state {
config false;
description
"Contains YANG module monitoring information.";
leaf module-set-id {
type string;
mandatory true;
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;
}
/*
* Notifications
*/
notification yang-library-change {
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;
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>The vibe here is pure family tree 🌳 You get modules, their submodules, and deviations, all sorted by name and revision. Notice how the yang-library-change notification points right back at module-set-id, so the whole thing stays linked together 🦋
3. IANA Considerations 🌷
3.1. YANG Module Registry 📚
This document registers one URI in the "IETF XML Registry" [RFC3688]. Following the format in RFC 3688, the following registration has been made:
URI: urn:ietf:params:xml:ns:yang:ietf-yang-library
Registrant Contact: The NETCONF WG of the IETF.
XML: N/A, the requested URI is an XML namespace.This document also registers one YANG module in the "YANG Module Names" registry [RFC6020]:
name: ietf-yang-library
namespace: urn:ietf:params:xml:ns:yang:ietf-yang-library
prefix: yanglib
reference: RFC 78954. Security Considerations 🔐
Okay, this part is serious, so lock in 🔒 The YANG module in this memo is designed to be accessed through the NETCONF protocol [RFC6241]. The lowest NETCONF layer is the secure transport layer, and the mandatory-to-implement secure transport is SSH [RFC6242]. The NETCONF access control model [RFC6536] gives you the tools to restrict particular NETCONF users to a pre-set subset of the available NETCONF protocol operations and content 🛡️
Some of the readable data nodes in this YANG module may be sensitive or vulnerable depending on the network environment, so it's super important to control read access to them (for example, via get, get-config, or notification). Here are the subtrees and data nodes, with their sensitivity or vulnerability:
/modules-state/module: The module list used in a server implementation may help an attacker identify the server capabilities and server implementations with known bugs. Although some of this information may be available to all 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. 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 identify server implementations with such a defect, in order to launch a denial-of-service attack on the device 💀
5. References 📖
5.1. Normative References
okay bestie, these are the must-reads 📚 if you want the full picture you NEED these. they're the stuff the spec is literally built on 💅
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
DOI 10.17487/RFC3688, January 2004,
<http://www.rfc-editor.org/info/rfc3688>.
[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC6020, October 2010,
<http://www.rfc-editor.org/info/rfc6020>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<http://www.rfc-editor.org/info/rfc6241>.
[RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure
Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
<http://www.rfc-editor.org/info/rfc6242>.
[RFC6536] Bierman, A. and M. Bjorklund, "Network Configuration
Protocol (NETCONF) Access Control Model", RFC 6536,
DOI 10.17487/RFC6536, March 2012,
<http://www.rfc-editor.org/info/rfc6536>.
[RFC6991] Schoenwaelder, J., Ed., "Common YANG Data Types",
RFC 6991, DOI 10.17487/RFC6991, July 2013,
<http://www.rfc-editor.org/info/rfc6991>.5.2. Informative References
these ones are more like bonus reading 🌸 super useful for context, not strictly required to get the vibe of the spec
[RFC5277] Chisholm, S. and H. Trevino, "NETCONF Event
Notifications", RFC 5277, DOI 10.17487/RFC5277, July 2008,
<http://www.rfc-editor.org/info/rfc5277>.
[RFC6470] Bierman, A., "Network Configuration Protocol (NETCONF)
Base Notifications", RFC 6470, DOI 10.17487/RFC6470,
February 2012, <http://www.rfc-editor.org/info/rfc6470>.
[YANG1.1] Bjorklund, M., "The YANG 1.1 Data Modeling Language", Work
in Progress, draft-ietf-netmod-rfc6020bis-12, April 2016.Acknowledgements ✨
okay the people who made this possible 🫶 Andy Bierman's contributions to this material were based on work supported by the Space & Terrestrial Communications Directorate (S&TCD) under Contract No. W15P7T-13-C-A616. the vibes here are very "funded research gets a shoutout" 🎀 also, any opinions, findings, conclusions, or recommendations in this material belong to the author(s) and don't necessarily reflect the views of the S&TCD. just so everyone knows whose hot takes are whose 💅
Authors' Addresses 🦋
here's who to slide into the DMs (well, email) 💌
Andy Bierman
YumaWorks
Email: andy@yumaworks.com
Martin Bjorklund
Tail-f Systems
Email: mbj@tail-f.com
Kent Watsen
Juniper Networks
Email: kwatsen@juniper.net📦 where this page comes from
- ietf: rfc7895 2016-06
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms