Network Working Group A. Bierman Internet-Draft YumaWorks Intended status: Standards Track M. Bjorklund Expires: August 23, 2018 Tail-f Systems K. Watsen Juniper Networks February 19, 2018 YANG Data Extensions draft-ietf-netmod-yang-data-ext-00 Abstract This document describes YANG mechanisms for defining abstract data structures with YANG. It is intended to replace and extend the "yang-data" extension statement defined in RFC 8040. Status of This Memo 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 http://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 August 23, 2018. Copyright Notice Copyright (c) 2018 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 Bierman, et al. Expires August 23, 2018 [Page 1] Internet-Draft YANG Data Extensions February 2018 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 1.1.1. NMDA . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1.2. YANG . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Restrictions on Conceptual YANG Data . . . . . . . . . . 4 2.2. YANG Data Extensions Module . . . . . . . . . . . . . . . 4 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 3.1. YANG Module Registry . . . . . . . . . . . . . . . . . . 9 4. Security Considerations . . . . . . . . . . . . . . . . . . . 9 5. Normative References . . . . . . . . . . . . . . . . . . . . 9 Appendix A. Open Issues . . . . . . . . . . . . . . . . . . . . 9 A.1. uses-yang-data . . . . . . . . . . . . . . . . . . . . . 9 A.2. error-info . . . . . . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 1. Introduction There is a need for standard mechanisms to allow the definition of abstract data that is not intended to be implemented as configuration or operational state. The "yang-data" extension statement from RFC 8040 [RFC8040] is defined for this purpose, however it is limited in its functionality. The intended use of the "yang-data" extension is to model all or part of a protocol message, such as the "errors" definition in ietf- restconf.yang [RFC8040], or the contents of a file. However, protocols are often layered such that the header or payload portions of the message can be extended by external documents. The YANG statements that model a protocol need to support this extensibility that is already found in that protocol. This document defines a new YANG extension statement called "augment-yang-data", which allows abstract data structures to be augmented from external modules, similar to the existing YANG "augment" statement. Note that "augment" cannot be used to augment a yang data structure since a YANG compiler or other tool is not required to understand the "yang-data" extension. The "yang-data" extension from [RFC8040] has been copied here and updated to be more flexible. There is no longer a requirement for the "yang-data" statement to result in exactly one container object. There is no longer an assumption that a yang data structure can only Bierman, et al. Expires August 23, 2018 [Page 2] Internet-Draft YANG Data Extensions February 2018 be used as a top-level abstraction, instead of nested within some other data structure. 1.1. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. The following terms are used within this document: o yang data structure: A data structure defined with the "yang-data" statement. 1.1.1. NMDA The following terms are defined in the Network Management Datastore Architecture (NMDA) [I-D.ietf-netmod-revised-datastores]. and are not redefined here: o configuration o operational state 1.1.2. YANG The following terms are defined in [RFC7950]: o absolute-schema-nodeid o container o data definition statement o data node o leaf o leaf-list o list 2. Definitions Bierman, et al. Expires August 23, 2018 [Page 3] Internet-Draft YANG Data Extensions February 2018 2.1. Restrictions on Conceptual YANG Data This document places restrictions on the "yang-data" external statements that can be used with the "yang-data" and "augment-yang-data" extensions. The conceptual data definitions are considered to be in the same identifier namespace as defined in section 6.2.1 of [RFC7950]. In particular, bullet 7: All leafs, leaf-lists, lists, containers, choices, rpcs, actions, notifications, anydatas, and anyxmls defined (directly or through a "uses" statement) within a parent node or at the top level of the module or its submodules share the same identifier namespace. This means that conceptual data defined with the "yang-data" or "augment-yang-data" statements cannot have the same local-name as sibling nodes from regular YANG data definition statements or other "yang-data" or "augment-yang-data" statements. This does not mean a yang data structure has to be used as a top- level protocol message or other top-level data structure. A yang data structure does not have to result in a single container. 2.2. YANG Data Extensions Module The "ietf-yang-data-ext" module defines the "augment-yang-data" extension to augment conceptual data already defined with the "yang-data" extension. The RESTCONF "yang-data" extension has been moved to this document and updated. RFC Ed.: update the date below with the date of RFC publication and remove this note. file "ietf-yang-data-ext@2018-02-19.yang" module ietf-yang-data-ext { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-yang-data-ext"; prefix "yd"; organization "IETF NETMOD (NETCONF Data Modeling Language) Working Group"; contact "WG Web: WG List: Author: Andy Bierman Bierman, et al. Expires August 23, 2018 [Page 4] Internet-Draft YANG Data Extensions February 2018 Author: Martin Bjorklund Author: Kent Watsen "; description "This module contains conceptual YANG specifications for defining abstract 'yang-data' data structures. Copyright (c) 2017 - 2018 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)."; revision 2018-02-19 { description "Initial revision."; reference "RFC XXXX: YANG Data Extensions."; } extension yang-data { argument name { yin-element true; } description "This extension is used to specify a YANG data template which represents conceptual data defined in YANG. It is intended to describe hierarchical data independent of protocol context or specific message encoding format. Data definition statements within a yang-data extension specify the generic syntax for the specific YANG data template, whose name is the argument of the yang-data extension statement. Note that this extension does not define a media-type. A specification using this extension MUST specify the message encoding rules, including the content media type. The mandatory 'name' parameter value identifies the YANG Bierman, et al. Expires August 23, 2018 [Page 5] Internet-Draft YANG Data Extensions February 2018 data template that is being defined. It contains the template name. This parameter is only used for readability purposes. There are no mechanisms to reuse yang-data by its template name value. This extension is ignored unless it appears as a top-level statement. It MUST contain data definition statements that result in a set of data definition statements. If the yang data template is intended to be used as a top-level structure, then the yang data template needs to result in a single container, so an instance of the YANG data template can thus be translated into an XML instance document, whose top-level element corresponds to the top-level container. The module name and namespace value for the YANG module using the extension statement is assigned to each of the data definition statements resulting from the yang data template. The name of each data definition statement resulting from a yang data template is assigned to a top-level identifier name in the data node identifier namespace, according to RFC 7950, section 6.2.1. The sub-statements of this extension MUST follow the 'data-def-stmt' rule in the YANG ABNF. The XPath document root is the extension statement itself, such that the child nodes of the document root are represented by the data-def-stmt sub-statements within this extension. This conceptual document is the context for the following YANG statements: - must-stmt - when-stmt - path-stmt - min-elements-stmt - max-elements-stmt - mandatory-stmt - unique-stmt - ordered-by - instance-identifier data type The following data-def-stmt sub-statements are constrained when used within a yang-data-resource extension statement. - The list-stmt is not required to have a key-stmt defined. - The if-feature-stmt is ignored if present. - The config-stmt is ignored if present. Bierman, et al. Expires August 23, 2018 [Page 6] Internet-Draft YANG Data Extensions February 2018 - The available identity values for any 'identityref' leaf or leaf-list nodes is limited to the module containing this extension statement, and the modules imported into that module. "; } extension augment-yang-data { argument path { yin-element true; } description "This extension is used to specify an augmentation to conceptual data defined with the 'yang-data' statement. It is intended to describe hierarchical data independent of protocol context or specific message encoding format. This statement has almost the same structure as the 'augment-stmt'. Data definition statements within this statement specify the semantics and generic syntax for the additional data to be added to the specific YANG data template, identified by the 'path' argument. The mandatory 'path' parameter value identifies the YANG conceptual data node that is being augmented, represented as an absolute-schema-nodeid string. This extension is ignored unless it appears as a top-level statement. The sub-statements of this extension MUST follow the 'data-def-stmt' rule in the YANG ABNF. The module name and namespace value for the YANG module using the extension statement is assigned to instance document data conforming to the data definition statements within this extension. The XPath document root is the augmented extension statement itself, such that the child nodes of the document root are represented by the data-def-stmt sub-statements within the augmented yang-data statement. The context node of the augment-yang-data statement is derived in the same way as the 'augment' statement, as defined in section 6.4.1 of [RFC7950]. This conceptual node is considered the context node for the following YANG statements: - must-stmt Bierman, et al. Expires August 23, 2018 [Page 7] Internet-Draft YANG Data Extensions February 2018 - when-stmt - path-stmt - min-elements-stmt - max-elements-stmt - mandatory-stmt - unique-stmt - ordered-by - instance-identifier data type The following data-def-stmt sub-statements are constrained when used within a augment-yang-data extension statement. - The list-stmt is not required to have a key-stmt defined. - The if-feature-stmt is ignored if present. - The config-stmt is ignored if present. - The available identity values for any 'identityref' leaf or leaf-list nodes is limited to the module containing this extension statement, and the modules imported into that module. Example: foo.yang { import yang-data-ext { prefix yd; } yd:yang-data foo-data { container foo-con { } } } bar.yang { import yang-data-ext { prefix yd; } import foo { prefix foo; } yd:augment-yang-data /foo:foo-con { leaf add-leaf1 { type int32; } leaf add-leaf2 { type string; } } } "; } } Bierman, et al. Expires August 23, 2018 [Page 8] Internet-Draft YANG Data Extensions February 2018 3. IANA Considerations 3.1. YANG Module Registry TBD 4. Security Considerations This document defines YANG extensions that are used to define conceptual YANG data. It does not introduce any new vulnerabilities beyond those specified in YANG 1.1 [RFC7950]. 5. Normative References [I-D.ietf-netmod-revised-datastores] Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K., and R. Wilton, "Network Management Datastore Architecture", draft-ietf-netmod-revised-datastores-05 (work in progress), October 2017. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016, . [RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017, . Appendix A. Open Issues A.1. uses-yang-data Is there a need for a separate grouping and uses mechanism for yang- data? Currently only real grouping-stmt and uses-stmt are used. A.2. error-info Is there a need for a special-purpose extension to define yang-data for the contents of the node in NETCONF and RESTCONF responses? This node is defined with anyxml so there is no way for a YANG tool to use real schema nodes, based on the RPC operation being requested or the error-app-tag that is being returned. Bierman, et al. Expires August 23, 2018 [Page 9] Internet-Draft YANG Data Extensions February 2018 Authors' Addresses 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 Bierman, et al. Expires August 23, 2018 [Page 10]