This document is obsolete. Please
refer to RFC 8525.
Internet Engineering Task Force (IETF) A. Bierman Request for Comments: 7895 YumaWorks Category: Standards Track M. Bjorklund ISSN: 2070-1721 Tail-f Systems K. Watsen Juniper Networks June 2016
YANG Module Library
Abstract
This document describes a YANG library that provides information about all the YANG modules used by a network management server (e.g., a Network Configuration Protocol (NETCONF) server). Simple caching mechanisms are provided to allow clients to minimize retrieval of this information.
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 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, 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 standard mechanisms to identify the YANG modules and submodules that are in use by a server that implements YANG data models. If a large number of YANG modules are utilized by the server, then the YANG library contents needed can be relatively large. This information changes very infrequently, so it is important that clients be able to cache the YANG library contents and easily identify whether their cache is out of date.
YANG library information can be different on every server and can change at runtime or across a server reboot.
If the server implements multiple protocols to access the YANG- defined data, each such protocol has its own conceptual instantiation of the YANG library.
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: Each YANG module and submodule within the library has a revision. This is derived from the most recent revision statement within the module or submodule. If no such revision statement exists, the module's or submodule's revision is the zero-length string.
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o submodule list: The name and 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 used for deviation statements MUST be identified.
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 "ietf-yang-library" module provides information about the YANG library used by a server. This module is defined using YANG version 1, but it supports the description of YANG modules written in any revision of YANG.
Following is 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:uri
This mandatory leaf contains a unique implementation-specific identifier representing 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 is no requirement that the same set always results in the same "module- set-id" value.
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This leaf allows a client to fetch the module list 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-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]. Thus, 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.
This mandatory list contains one entry for each YANG data model module supported by the server. There MUST be an entry in this list for each revision of each YANG module that is used by the server. It is possible for multiple revisions of the same module to be imported, in addition to an entry for the revision that is implemented by the server.
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.";
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.";
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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;
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} 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; } } }
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."; } }
The YANG module defined in this memo is designed to be accessed via 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] provides the means to restrict access for particular NETCONF users to a pre-configured subset of all available NETCONF 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:
o /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
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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.
[YANG1.1] Bjorklund, M., "The YANG 1.1 Data Modeling Language", Work in Progress, draft-ietf-netmod-rfc6020bis-12, April 2016.
Acknowledgements
Contributions to this material by Andy Bierman are based upon work supported by the Space & Terrestrial Communications Directorate (S&TCD) under Contract No. W15P7T-13-C-A616. Any opinions, findings, conclusions, or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the Space & Terrestrial Communications Directorate (S&TCD).