Network Working Group B. Claise Internet-Draft J. Clarke Updates: 7950 (if approved) Cisco Systems, Inc. Intended status: Standards Track B. Lengyel Expires: June 18, 2018 Ericsson K. D'Souza AT&T December 15, 2017 New YANG Module Update Procedure draft-clacla-netmod-yang-model-update-03 Abstract This document specifies a new YANG module update procedure in case of backward-incompatible changes, as an alternative proposal to the YANG 1.1 specifications. This document updates RFC 7950. 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 June 18, 2018. Copyright Notice Copyright (c) 2017 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 Claise, et al. Expires June 18, 2018 [Page 1] Internet-Draft YANG Catalog December 2017 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. The Problems . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Slow Standardization . . . . . . . . . . . . . . . . . . 3 2.2. Some YANG Modules are Not Backward Compatible . . . . . . 3 2.3. Non-Backward Compatible Errors . . . . . . . . . . . . . 4 2.4. A Zoo of YANG Modules . . . . . . . . . . . . . . . . . . 4 2.5. YANG Modules Obsolete Relationship . . . . . . . . . . . 5 2.6. YANG Module Transition Strategy . . . . . . . . . . . . . 6 2.7. Need to Allow Non-Backward Compatible changes . . . . . . 6 2.8. Problematic Handling of Status Statement . . . . . . . . 7 2.9. No way to easily decide whether a change is Backward Compatible . . . . . . . . . . . . . . . . . . . . . . . 7 2.10. Early Warning about Removal . . . . . . . . . . . . . . . 8 3. The Solution . . . . . . . . . . . . . . . . . . . . . . . . 8 3.1. SEMVER Semantic Versioning . . . . . . . . . . . . . . . 9 3.2. Updates to YANG 1.1 status statement . . . . . . . . . . 11 3.3. Updating the YANG 1.1 Module Update rules . . . . . . . . 11 3.4. The Derived Semantic Version . . . . . . . . . . . . . . 11 3.5. Import by Semantic Version . . . . . . . . . . . . . . . 12 4. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 13 5. Semantic Version Extension YANG Module . . . . . . . . . . . 14 6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 16 7. Security Considerations . . . . . . . . . . . . . . . . . . . 16 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 9.1. Normative References . . . . . . . . . . . . . . . . . . 17 9.2. Informative References . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18 1. Introduction The YANG data modeling language [RFC7950] specifies strict rules for updating YANG modules (see section 11 "Updating a Module"). Citing a few of the relevant rules: 1. "As experience is gained with a module, it may be desirable to revise that module. However, changes to published modules are not allowed if they have any potential to cause interoperability problems between a client using an original specification and a server using an updated specification." 2. "Note that definitions contained in a module are available to be imported by any other module and are referenced in "import" Claise, et al. Expires June 18, 2018 [Page 2] Internet-Draft YANG Catalog December 2017 statements via the module name. Thus, a module name MUST NOT be changed. Furthermore, the "namespace" statement MUST NOT be changed, since all XML elements are qualified by the namespace." 3. "Otherwise, if the semantics of any previous definition are changed (i.e., if a non-editorial change is made to any definition other than those specifically allowed above), then this MUST be achieved by a new definition with a new identifier." 4. "deprecated indicates an obsolete definition, but it permits new/ continued implementation in order to foster interoperability with older/existing implementations." What are the consequences? 1. Ideally, the YANG module names should not be changed due the importance of not changing the automation code in case of import statements or service composition at the orchestration layer. 2. When the same YANG module name is kept, its new revision must be updated in a backward-compatible way. 3. While most of the non-backward compatible changes are prohibited, a client still does not know if a changed module is backward compatible, as a server may remove parts of a module after marking it deprecated or obsolete. 2. The Problems This section lists a series of problems, hopefully listed in a logical order, which leads to the solution in the next section. 2.1. Slow Standardization The conclusions drawn in the introduction lead to the logical conclusion that the standardized YANG modules have to be perfect on day one (at least the structure), which in turn might explain why all the IETF YANG modules take so long to standardize. Shooting for perfection (at least in structure) is obviously a noble goal, but if the perfect standard comes too late, it doesn't help the industry. 2.2. Some YANG Modules are Not Backward Compatible As we learn from our mistakes, we're going to face more and more backward-incompatible YANG modules. An example is the YANG data model for L3VPN service delivery [RFC8049], which, based on implementation experience, must be updated in a backward-incompatible way with draft-wu-l3sm-rfc8049bis [I-D.wu-l3sm-rfc8049bis]. Claise, et al. Expires June 18, 2018 [Page 3] Internet-Draft YANG Catalog December 2017 While Standards Development Organization (SDO) YANG modules are obviously better for the industry, we must recognize that many YANG modules are actually generated YANG modules (for example, from internal databases), also known as native YANG modules, or vendor modules [RFC8199]. From time to time, the new YANG modules are not backward-compatible. In such cases, it would be better to indicate how backward-compatible a given YANG module actually is. 2.3. Non-Backward Compatible Errors Sometimes small errors force us to make non-backward compatible updates. As an example imagine that we have a string with a complex pattern (e.g., an IP address). Let's assume the initial pattern incorrectly allows IP addresses to start with 355. In the next version this is corrected to disallow addresses starting with 355. Formally this is an non-backward compatible change as the value space of the string is decreased. In reality an IP address and the implementation behind it was never capable of handling an address starting with 355. So practically this is a backward compatible change, just like a correction of the description statement. Still current YANG rules would force a module name change. 2.4. A Zoo of YANG Modules Even if we focus on the IETF, we have to observe that many SDOs, opensource fora, and vendors develop YANG modules. This should be considered a success for an IETF developed technology. However, the operators are faced with this problem: how to select the YANG modules to take into account for their service developments. The site (and the YANG catalog that it provides: YANG module for yangcatalog.org, [I-D.clacla-netmod-model-catalog]) is an attempt to become a reference for all YANG modules available in the industry, for both YANG developers to search on what exists already) and for operators (to discover the more mature YANG models to automate services). This YANG catalog should not only contain pointers to the YANG modules themselves, but also contain metadata related to those YANG modules: What is the module type (service model or not?); what is the maturity level? (e.g., for the IETF: is this an RFC, a working group document or an individual draft?); is this module implemented?; who is the contact?; is there open-source code available? And we expect many more in the future. The industry has begun to understand that the metadata related to YANG models become equally important as the YANG models themselves. Claise, et al. Expires June 18, 2018 [Page 4] Internet-Draft YANG Catalog December 2017 The yangcatalog.org instantiation of the catalog provides a means for module authors and vendors implementing modules to upload their metadata, which is then searchable via an API, as well as using a variety of web-based tools. The instructions for contributing and searching for metadata can be found at . The issue is actually the number of YANG modules the operators are offered. At the time of writing this document, the number of unique YANG modules in the catalog is exactly 2596 (and that number keeps growing), while the IETF has standardized or is busy standardizing a small subset of those. Therefore, it's important to distinguish the relevant YANG modules with the pack and to understand the relationship between the YANG modules. 2.5. YANG Modules Obsolete Relationship So the operators use the yangcatalog.org to discover which YANG modules they can use NOW. They base their selection not only on the YANG module content, but also on the related metadata. When faced with the zoo of the YANG modules, it's difficult to understand the relationship between YANG modules. As an example: how could an operator discover that YANG-MODULE-B obsoletes YANG-MODULE-A? Indeed, both have different YANG module names. The only available information is an "obsolete" tag in the published RFC containing YANG-MODULE-B: this tag would point to YANG-MODULE-A. In the world of automation, going through a published RFC as a level of indirection to understand the YANG module obsolete relationship is a non-starter. Food for thought: the IETF should stop thinking that the metric for success is an RFC number, as opposed to the contained YANG module(s). We need an automatic way to discover that a YANG-MODULE-B obsoletes YANG-MODULE-A, so that YANG-MODULE-A should not be given any attention. The following example is not an automatic way. description "This YANG module defines a generic service configuration model for Layer 3 VPNs. This model is common across all vendor implementations. This obsoletes the RFC8049 YANG module, ietf-l3vpn-svc@2017-01-2"; revision 2017-09-14 { description "First revision of RFC8049."; reference "RFC xxxx: YANG Data Model for L3VPN Service Delivery"; Claise, et al. Expires June 18, 2018 [Page 5] Internet-Draft YANG Catalog December 2017 Along the same lines, while going through an out-of-band tool such as the yangcatalog.org in order to discover the obsolete relationship is a possible automatic way, it is not ideal. 2.6. YANG Module Transition Strategy Let's assume for a moment that we change the YANG module, with the specific example of ietf-routing, which some propose to update to ietf-routing-2. Here are all the ietf-routing dependent YANG modules (those modules that depend on ietf-routing) . So many YANG modules. Let's look at the difference for ietf-routing-2: . Changing the module name from ietf-routing to ietf-routing-2 implies that the we have to warn all draft authors of ietf-routing YANG dependent modules. First, to make sure they are aware of ietf- routing-2 (publishing a RFC8022bis mentioning in the module description that this module is not compatible with the NMDA architecture, and providing a pointer to ietf-routing-2 ... is not an automatic way... so barely useful). And second, to ask them to change their import (or service composition) to ietf-routing-2. Hopefully, in the ietf-routing case, most dependent YANG modules are part of the IETF, so the communication is a manageable. For the already existing dependent vendor modules the problem is worse. Changing the ietf-interfaces YANG module name would be a different challenge, as it's used throughout the industry: 2.7. Need to Allow Non-Backward Compatible changes As described in the previous sections, there is a need to allow non- backward compatible changes without changing a module's name. This would avoid many of the above problems. In most cases even after non-backward compatible updates a module should keep its name. However, for really major changes renaming the module is still the proper way to go: Claise, et al. Expires June 18, 2018 [Page 6] Internet-Draft YANG Catalog December 2017 when splitting a module into two separate modules when removing 80% of a module's schema when a standard module is moved from one organization to another (e.g., from ietf to ieee) when a company's name is changed and new versions of the module are renamed to reflect that Allowing non-backward compatible changes to happen without a module name change will decrease the number of separate modules to handle and will make it a trivial task to track these non-backward compatible changes. 2.8. Problematic Handling of Status Statement The current definition of deprecated and obsolete in [RFC7950] (as quoted below) is problematic and should be corrected. o "deprecated" indicates an obsolete definition, but it permits new/ continued implementation in order to foster interoperability with older/existing implementations. o "obsolete" means that the definition is obsolete and SHOULD NOT be implemented and/or can be removed from implementations. YANG is considered an interface contract between the server and the client. The current definitions of deprecated and obsolete mean that a schema node that is either deprecated or obsolete may or may not be implemented. The client has no way to find out which is the case except for by trying to write or read data at the leaf in question. This probing would need to be done for each separate data-node, which not a trivial thing to do. This "may or may not" is unacceptable in a contract. In effect, this works as if there would be an if-feature statement on each deprecated schema node where the server does not advertise whether the feature is supported or not. Why is it not advertised? 2.9. No way to easily decide whether a change is Backward Compatible A management system, SDN controller or any other user of a module should be capable of easily determining the compatibility between two module versions. Higher level logic for a network function, something that can not be implemented in a purely model driven way, is always dependent on a specific version of the module. If the client finds that the module has been updated on the network node, it has to decide if it tries to handle it as it handled the previous Claise, et al. Expires June 18, 2018 [Page 7] Internet-Draft YANG Catalog December 2017 version of the model or if it just stops, to avoid problems. To make this decision the client needs to know if the module was updated in a backward compatible way or not. This is not possible to decide today because of the following: o It is possible to change the semantic behavior of a data node, action or rpc while the YANG definition does not change (with the possible exception of the description statement). In such a case it is impossible to determine whether the change is backward compatible just by looking at the YANG statements. Its only the human model designer that can decide. o Problems with the status statement, Section 2.8 o Modelers might decide to violate YANG 1.1 update rules for some of the reasons above Finding status changes or violations of update rules need a line by line comparision of the old and new modules, no easy task. 2.10. Early Warning about Removal If a schema part is considered old/bad we need to be able to give advance warning that it will be removed. As this is an advance warning the part shall still be present and usable in the current revision; however, it will be removed in one of the next revisions. We need the advance warning to allow users of the module time enough to plan/execute migration away from the deprecated functionality. Often deprecation will be accompanied by information whether the functionality will just disappear or that there is an alternative, possibly more advanced solution that should be used. Vendors use such warnings often, but the NMDA related redesign of IETF modules is also an example where it would be useful. (As another example see the usage of deprecated in the Java programing language.) The current definition of the deprecated status does not serve this purpose as described in Section 2.8. The definition of "deprecated" in the status statement shall be changed to address this issue. 3. The Solution The solution is composed of four parts, a semantic versioning YANG extension, updates to the YANG 1.1. status statement and module update rules and the import by version statement. An optional additional check, validating the semantic versioning from a syntactic point of view, can either assist in determining the correct semantic Claise, et al. Expires June 18, 2018 [Page 8] Internet-Draft YANG Catalog December 2017 versioning values, or can help in determining the values for YANG modules that don't support this extension. 3.1. SEMVER Semantic Versioning The semantic versioning solution proposed here has already been proposed in [I-D.openconfig-netmod-model-catalog] (included here with the authors permission)which itself is based on [openconfigsemver]. The goal is to indicate the YANG module backwards (in)compatibility, following semver.org semantic versioning [semver]: "The SEMVER version number for the module is introduced. This is expressed as a semantic version number of the form: x.y.z o x is the MAJOR version. It is incremented when the new version of the specification is incompatible with previous versions. o y is the MINOR version. It is incremented when new functionality is added in a manner that is backward-compatible with previous versions. o z is the PATCH level. It is incremented when bug fixes are made in a backward-compatible manner. Along these lines, we propose the following YANG 1.1 extension for a more generic semantic version. The formal definition is found at the end of this document. extension module-version { argument "semver" { yin-element false; } } The extension would typically be used this way: Claise, et al. Expires June 18, 2018 [Page 9] Internet-Draft YANG Catalog December 2017 module yang-module-name { namespace "name-space"; prefix "prefix-name"; import ietf-semver { prefix "semver"; } description "to be completed"; revision 2017-10-30 { description "Change the module structure"; semver:module-version "2.0.0"; } revision 2017-07-30 { description "Added new feature XXX"; semver:module-version "1.2.0";"; } revision 2017-04-03 { description "Update copyright notice."; semver:module-version "1.0.1";; } revision 2017-04-03 { description "First release version."; semver:module-version "1.0.0";; } revision 2017-01-26 { description "Initial module for inet types"; semver:module-version "0.1.0";; } //YANG module definition starts here See also "Semantic Versioning and Structure for IETF Specifications" [I-D.claise-semver] for a mechanism to combine the semantic versioning, the github tools, and a potential change to the IETF process. Claise, et al. Expires June 18, 2018 [Page 10] Internet-Draft YANG Catalog December 2017 3.2. Updates to YANG 1.1 status statement RFC 7950 section 11, must be updated to change the definition of deprecated and obsolete. In both cases the client must be able to determine whether the relevant parts are implemented or not without probing. The following definition is proposed: o Deprecated schema nodes MUST still work as defined. The deprecated status serves only as a a warning that the schema node will be removed or obsoleted in the future. o Obsolete schema nodes MUST be removed from the implementation. Requests concerning these schema nodes MUST be rejected with: * error-tag: operation-failed * error-app-tag: obsolete element If there is a need to allow the server to decide whether a deprecated/obsolete schema part is implemented YANG already has a facility for that: the feature statement. Use it! 3.3. Updating the YANG 1.1 Module Update rules RFC 7950 section 11, must be updated to express: "As experience is gained with a module, it may be desirable to revise that module. Changes to published modules are allowed, even if they have some potential to cause interoperability problems, if the module-version YANG extension is used in the revision statement to clearly indicate the nature of the change." 3.4. The Derived Semantic Version The YANG catalog contains not only the most up-to-date YANG module revision of a given module, but keeps all previous revisions as well. With APIs in mind, it's important to understand whether different YANG module revisions are backward compatible (this is specifically imported for native YANG modules, i.e. the ones where generated-from = native), even for the YANG modules that don't support the YANG extension specified in this document. Two distinct leaves in the YANG module [I-D.clacla-netmod-model-catalog] contain this semver notation: o the semantic-version leaf contains the value embedded within a YANG module (if it is available). Claise, et al. Expires June 18, 2018 [Page 11] Internet-Draft YANG Catalog December 2017 o the derived-semantic-version leaf is established by examining the the YANG module themselves. As such derived-semantic-version only takes syntax into account as opposed to the meaning of various elements when it computes the semantic version. o The algorithm used to produce the derived-semantic-version is as follows: 1. Order all modules of the same name by revision from oldest to newest. Include module revisions that are not available, but which are defined in the revision statements in one of the available module versions. 2. If module A, revision N+1 has failed compilation, bump its derived semantic MAJOR version. For unavailable module versions assume non-backward compatible changes were done., thus bump its derived semantic MAJOR version. 3. Else, run "pyang --check-update-from" on module A, revision N and revision N+1 to see if backward-incompatible changes exist. 4. If backward-incompatible changes exist, bump module A, revision N+1's derived MAJOR semantic version. 5. If no backward-incompatible changes exist, compare the pyang trees of module A, revision N and revision N+1. 6. If there are structural differences (e.g., new nodes), bump module A, revision N+1's derived MINOR semantic version. 7. If no structural differences exist, bump module A, revision N+1's derived PATCH semantic version. Note that the absolute numbers in the semantic-version and derived- semantic-version are actually meaningless by themselves. That is, one must compare two different semver values for a given module to understand the compatibility between them. 3.5. Import by Semantic Version If a module is imported by another one, it is usually not specified which version of the imported module should be used. However not all versions may be acceptable. Today YANG 1.1 allows us to specify the revision date of the imported module, but that is too specific, as even a small spelling correction of the imported module results in a change to its revision date, thus making the module revision ineligible for import. Claise, et al. Expires June 18, 2018 [Page 12] Internet-Draft YANG Catalog December 2017 Using semantic versioning to indicate the acceptable imported module versions is much more flexible. o We might indicate that any compatible module-version after e.g. 3.1.0 is acceptable o We might indicate that any compatible module-version of the 3.1.0, 4.0.0 or 5.0.0 major versions is acceptable. Later depending on updates in the 6.0.0 series we might allow those revisions also to be imported. As an non-backward compatible change in the 6.0.0 line might just change a small part of the imported module, the non-backward compatible changes may or may not affect the importer. The module-version statement SHOULD be a substatement of the import statement. An import statement MUST NOT contain both a module- version and a revision substatement. The use of the revision substatement of import should be discouraged/deprecated. 4. Open Issues There are a number of open issues to be disccused. These include the following: o Do we need include-by-Semver? o Should IETF/IANA officially generate derived semantic versions for their own modules? As they are the owner of the modules it should be their responsibility, but how to document it? o There are cases where the module's name should be changed but we still want to formally document the connection between the old and the new module names. For these cases shall we introduce a new YANG extension statement o "replaces-module ietf-vlan;" ? o We could consider a new naming convention for module files. Today, module files are named using a module@revision.yang notation. We could consider a module%semver.yang variant. Re- using the '@' for version is not ideal, so another separator character should be used. In this manner, both version and revision could be used. o Taking another page from Openconfig, the notion of a module bundle could be considered. That is, there may need to be a way to enumerate modules that are part of a bundle and are known to Claise, et al. Expires June 18, 2018 [Page 13] Internet-Draft YANG Catalog December 2017 interoperate. This may not be as critical if a rich import-by- version is defined. While the issue is interesting, it will be not be handled in this document. o Similarly, the concept of a feature bundle should be considered. Typically, operators combine and test YANG modules to build value- add services. These bundles form releases for specific features or services, and it is critical to ensure as the modules evolve, the bundles can coherently evolve with them. While the issue is interesting, it will be not be handled in this document. o When we'll start using this new procedure for a new YANG module revision, will we have to update all the dependent YANG modules to start using this new procedure, along with the new import statement? Is this a moot point, as a new YANG module name would suffer from the same symptoms? We see no need for updating other dependent modules. It is a good idea to update them, as they will benefit from using SEMVER, however there is no specific need to update them. 5. Semantic Version Extension YANG Module The extension described in this module is defined in the YANG module below. file "ietf-semver@2017-12-15.yang" module ietf-semver { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-semver"; prefix semver; organization "IETF NETMOD (Network Modeling) Working Group"; contact "WG Web: WG List: Author: Benoit Claise Author: Joe Clarke Author: Kevin D'Souza Claise, et al. Expires June 18, 2018 [Page 14] Internet-Draft YANG Catalog December 2017 Author: Balazs Lengyel "; description "This module contains a definition for a YANG 1.1 extension to express the semantic version of YANG modules."; revision 2017-12-15 { description "Initial revision."; reference "draft-clacla-netmod-yang-model-update: New YANG Module Update Procedure"; semver:module-semver 0.1.1; } extension module-version { argument semver; description "The version number for the module revision it is used in. This is expressed as a semantic version string in the form: x.y.z where: * x corresponds to the major version, * y corresponds to a minor version, * z corresponds to a patch version. A major version number of 0 indicates that this model is still in development, and is potentially subject to change. Following a release of major version 1, all modules will increment major revision number where backwards incompatible changes to the model are made. The minor version is changed when features are added to the model that do not impact current clients use of the model. When major version is stepped, the minor version is reset to 0. The patch-level version is incremented when non-feature changes (such as bugfixes or clarifications to human-readable descriptions that do not impact model functionality) are made that maintain backwards compatibility. When major or minor version is stepped, the patch-level is reset to 0. The version number is stored in the module meta-data. By comparing the module-version between two revisions of a given module, one can know if revision N+1 is backwards compatible or not relative to revision N, as well as Claise, et al. Expires June 18, 2018 [Page 15] Internet-Draft YANG Catalog December 2017 whether or not new features have been added to revision N+1. If a module contains this extension it indicates that for this module the updated status and update rules as this described in RFC XXXX are used. The statement MUST only be a substatement of the revision, import or include statements. Zero or One module-version statement is allowed per parent statement. NO substatements are allowed. "; reference "http://semver.org/ : Semantic Versioning 2.0.0"; } augment /yanglib:modules-state/yanglib:module { leaf module-version { type string { pattern "[0-9]+.[0-9]+.[0-9]+"; } } } augment /yanglib:modules-state/yanglib:module/yanglib:submodule { leaf submodule-version { type string { pattern "[0-9]+.[0-9]+.[0-9]+"; } } } } 6. Contributors o Anees Shaikh, Google o Rob Shakir, Google 7. Security Considerations The document does not define any new protocol or data model. There are no security impacts. Claise, et al. Expires June 18, 2018 [Page 16] Internet-Draft YANG Catalog December 2017 8. IANA Considerations No IANA action is requested. 9. References 9.1. Normative References [RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016, . 9.2. Informative References [I-D.clacla-netmod-model-catalog] Clarke, J. and B. Claise, "YANG module for yangcatalog.org", draft-clacla-netmod-model-catalog-02 (work in progress), October 2017. [I-D.claise-semver] Claise, B., Barnes, R., and J. Clarke, "Semantic Versioning and Structure for IETF Specifications", draft- claise-semver-01 (work in progress), July 2017. [I-D.openconfig-netmod-model-catalog] Shaikh, A., Shakir, R., and K. D'Souza, "Catalog and registry for YANG models", draft-openconfig-netmod-model- catalog-02 (work in progress), March 2017. [I-D.wu-l3sm-rfc8049bis] Wu, Q., Litkowski, S., Tomotaki, L., and K. Ogaki, "YANG Data Model for L3VPN Service Delivery", draft-wu-l3sm- rfc8049bis-11 (work in progress), December 2017. [openconfigsemver] "Semantic Versioning for Openconfig Models", . [RFC8049] Litkowski, S., Tomotaki, L., and K. Ogaki, "YANG Data Model for L3VPN Service Delivery", RFC 8049, DOI 10.17487/RFC8049, February 2017, . [RFC8199] Bogdanovic, D., Claise, B., and C. Moberg, "YANG Module Classification", RFC 8199, DOI 10.17487/RFC8199, July 2017, . [semver] "Semantic Versioning 2.0.0", . Claise, et al. Expires June 18, 2018 [Page 17] Internet-Draft YANG Catalog December 2017 Authors' Addresses Benoit Claise Cisco Systems, Inc. De Kleetlaan 6a b1 1831 Diegem Belgium Phone: +32 2 704 5622 Email: bclaise@cisco.com Joe Clarke Cisco Systems, Inc. 7200-12 Kit Creek Rd Research Triangle Park, North Carolina United States of America Phone: +1-919-392-2867 Email: jclarke@cisco.com Balazs Lengyel Ericsson Magyar Tudosok Korutja 1117 Budapest Hungary Phone: +36-70-330-7909 Email: balazs.lengyel@ericsson.com Kevin D'Souza AT&T 200 S. Laurel Ave Middletown, NJ United States of America Email: kd6913@att.com Claise, et al. Expires June 18, 2018 [Page 18]