Network Working Group M. Bjorklund Internet-Draft Tail-f Systems Updates: 6241, 7950 (if approved) J. Schoenwaelder Intended status: Standards Track Jacobs University Expires: September 2, 2018 P. Shafer K. Watsen Juniper Networks R. Wilton Cisco Systems March 1, 2018 NETCONF Extensions to Support the Network Management Datastore Architecture draft-ietf-netconf-nmda-netconf-04 Abstract This document extends the NETCONF protocol defined in RFC 6241 in order to support the Network Management Datastore Architecture defined in I-D.ietf-netmod-revised-datastores. This document updates both RFC 6241 and RFC 7950. The update to RFC 6241 adds new operations and , and augments existing operations , , and . The update to RFC 7950 requires the usage of I-D.ietf-netconf-rfc7895bis by NETCONF servers implementing the Network Management Datastore Architecture. REF Editor: please replace "I-D.ietf-netmod-revised-datastores" and "I-D.ietf-netconf-rfc7895bis" above with their final RFC assignments. 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 September 2, 2018. Bjorklund, et al. Expires September 2, 2018 [Page 1] Internet-Draft March 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 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 1.2. Tree Diagrams . . . . . . . . . . . . . . . . . . . . . . 3 2. Datastore and YANG Library Requirements . . . . . . . . . . . 3 3. NETCONF Extensions . . . . . . . . . . . . . . . . . . . . . 4 3.1. New NETCONF Operations . . . . . . . . . . . . . . . . . 4 3.1.1. The Operation . . . . . . . . . . . . . . 4 3.1.2. The Operation . . . . . . . . . . . . . . 8 3.2. Augmentations to NETCONF Operations . . . . . . . . . . . 9 4. NETCONF Datastores YANG Module . . . . . . . . . . . . . . . 9 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 6. Security Considerations . . . . . . . . . . . . . . . . . . . 18 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 7.1. Normative References . . . . . . . . . . . . . . . . . . 19 7.2. Informative References . . . . . . . . . . . . . . . . . 20 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20 1. Introduction This document extends the NETCONF protocol defined in [RFC6241] in order to support the Network Management Datastore Architecture (NMDA) defined in [I-D.ietf-netmod-revised-datastores]. This document updates [RFC6241] in order to enable NETCONF clients to interact with all the datastores supported by a server implementing the NMDA. The update both adds new operations and , and augments existing operations , , and . This document also updates [RFC7950] in order to enable NETCONF clients to both discover which datastores are supported by the Bjorklund, et al. Expires September 2, 2018 [Page 2] Internet-Draft March 2018 NETCONF server, as well as determine which modules are supported in each datastore. The update requires NETCONF servers implementing the NMDA to support [I-D.ietf-netconf-rfc7895bis]. 1.1. Terminology This document uses the terminology defined by the NMDA [I-D.ietf-netmod-revised-datastores]. The following term is defined in [I-D.ietf-netconf-rfc7895bis]: o YANG library checksum 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] [RFC8174] when, and only when, they appear in all capitals, as shown here. 1.2. Tree Diagrams Tree diagrams used in this document follow the notation defined in [I-D.ietf-netmod-yang-tree-diagrams]. 2. Datastore and YANG Library Requirements RFC Ed.: Update 201X-XX-XX below with correct date. An NMDA-compliant NETCONF server MUST support the operational state datastore and it MUST implement at least revision 201X-XX-XX of the "ietf-yang-library" module defined in [I-D.ietf-netconf-rfc7895bis]. The server MUST advertise the following capability in the message (line breaks and whitespaces are used for formatting reasons only): urn:ietf:params:netconf:capability:yang-library:1.1? revision=&checksum= The parameter "revision" has the same value as the revision date of the "ietf-yang-library" module implemented by the server. This parameter MUST be present. The parameter "checksum" contains the YANG library checksum [I-D.ietf-netconf-rfc7895bis]. This parameter MUST be present. Bjorklund, et al. Expires September 2, 2018 [Page 3] Internet-Draft March 2018 With this mechanism, a client can cache the supported modules for a server and only update the cache if the "checksum" value in the message changes. This document updates [RFC7950], Section 5.6.4, to allow servers to advertise the capability :yang-library:1.1 instead of :yang- library:1.0, and to implement the subtree "/yang-library" [I-D.ietf-netconf-rfc7895bis] instead of "/modules-state". 3. NETCONF Extensions This section describes the NETCONF extensions needed to support the NMDA. These changes are defined in a new YANG ([RFC7950]) module "ietf-netconf-nmda". These changes include the use of source and target parameters based on the "datastore" identity defined in the "ietf-datastores" module [I-D.ietf-netmod-revised-datastores]. The use of identities allows future expansion in a way that the choice-based strategy from the original operations (e.g., , ) does not. 3.1. New NETCONF Operations Two new operations and are defined in this document in order to support the NMDA. These operations are similar to the and operations but they can work on an extensible set of datastores. 3.1.1. The Operation The operation retrieves data from a specific NMDA datastore. This operation is similar to NETCONF's operation defined in [RFC6241], but it adds the flexibility to select the source datastore. Bjorklund, et al. Expires September 2, 2018 [Page 4] Internet-Draft March 2018 +---x get-data +---w input | +---w datastore ds:datastore-ref | +--(filter-spec)? | | +--:(subtree-filter) | | | +---w subtree-filter? | | +--:(xpath-filter) | | +---w xpath-filter? yang:xpath1.0 {nc:xpath}? | +---w config-filter? boolean | +--(origin-filters)? {origin}? | | +--:(origin-filter) | | | +---w origin-filter* or:origin-ref | | +--:(negated-origin-filter) | | +---w negated-origin-filter* or:origin-ref | +---w max-depth? union | +---w with-origin? empty {origin}? | +---w with-defaults? with-defaults-mode +--ro output +--ro data? The "datastore" parameter indicates the datastore which is the source of the data to be retrieved. This is a datastore identity. The operation accepts a content filter parameter, similar to the "filter" parameter of , but using explicit nodes for subtree filtering ("subtree-filter") and XPath filtering ("xpath-filter"). The "config-filter" parameter can be used to retrieve only "config true" or "config false" nodes. The "origin-filter" parameter, which can be present multiple times, selects nodes matching any of the given values. The "negated-origin-filter", which can be present multiple times, selects nodes that do not match all given values. The "origin-filter" and "negated-origin-filter" parameters cannot be used together. The "max-depth" parameter can be used by the client to limit the number of sub-tree levels that are returned in the reply. 3.1.1.1. With-defaults interactions If the "with-defaults" capability is supported by the server, then the "with-defaults" parameter, defined in [RFC6243], is supported for operations that target conventional configuration datastores. Bjorklund, et al. Expires September 2, 2018 [Page 5] Internet-Draft March 2018 The "with-defaults" parameter is optional to support for operations that target . The associated capability to indicate a server's support is identified with the URI: urn:ietf:params:netconf:capability:with-operational-defaults:1.0 If the "with-defaults" parameter is supported for operations on , then all retrieval modes specified in either the 'basic-mode' or 'also-supported' parameters of the "with-defaults" capability are permitted. The behavior of the "with-defaults" parameter for is defined as below: o If no "with-defaults" parameter is specified, or if it is set to "explicit", "report-all", or "report-all-tagged", then the "in use" values, as defined in [I-D.ietf-netmod-revised-datastores] section 5.3, are returned from the operational state datastore, even if a node happens to have a default statement in the YANG module, and this default value is being used by the server. If the "with-defaults" parameter is set to "report-all-tagged", any values that match the schema default are tagged with additional metadata, as described in [RFC6243] section 3.4. o If the "with-defaults" parameter is set to "trim", all "in use" values are returned, except that the output is filtered to exclude any values that match the default defined in the YANG schema. Support for "with-defaults" in operations on any datastore not defined in [I-D.ietf-netmod-revised-datastores] SHOULD be defined by the specification for the datastore. 3.1.1.2. Origin Metadata Attribute The operation defines a parameter named "with-origin", which if present, requests that the server includes "origin" metadata annotations in its response, as detailed in the NMDA. This parameter is only valid for the operational state datastore and any datastores with identities derived from the "operational" identity. Otherwise, if an invalid datastore is specified then an error is returned, as specified in "ietf-netconf-nmda" (see Section 4). Note that "origin" metadata annotations are not included in a response unless a client explicitly requests them. Data in the operational state datastore can come from multiple sources. The server should return the most accurate value for the "origin" metadata annotation as possible, indicating the source of the operational value, as specified in Section 5.3.4 of [I-D.ietf-netmod-revised-datastores]. Bjorklund, et al. Expires September 2, 2018 [Page 6] Internet-Draft March 2018 When encoding the origin metadata annotation for a hierarchy of returned nodes, the annotation may be omitted for a child node when the value matches that of the parent node, as described in the "ietf-origin" YANG module [I-D.ietf-netmod-revised-datastores]. The "with-origin" parameter is optional to support. It is identified with the feature "origin". 3.1.1.3. Example: Retrieving an entire subtree from The following example shows the version of the example shown in Section 7.1 of [RFC6241]. ds:running root superuser Charlie Root 1 1 Bjorklund, et al. Expires September 2, 2018 [Page 7] Internet-Draft March 2018 3.1.2. The Operation The operation changes the contents of a writable datastore, similar to the operation defined in [RFC6241], but with additional flexibility in naming the target datastore. If an operation is invoked on a non-writable datastore, then an error is returned, as specified in "ietf-netconf-nmda" (see Section 4). +---x edit-data +---w input +---w datastore ds:datastore-ref +---w default-operation? enumeration +--(edit-content) +--:(config) | +---w config? +--:(url) +---w url? inet:uri {nc:url}? The "datastore" parameter is a datastore identity that indicates the desired target datastore where changes should be made. The "default-operation" parameter is a copy of the "default-operation" parameter of the operation. The "edit-content" choice mirrors the "edit-content" choice of the operation. Note, however, that the "config" element in the "edit-content" choice of uses "anydata" (introduced in YANG 1.1) while the "config" element in the "edit-content" choice of used "anyxml". The operation does not support the "error-option" and the "test-option" parameters that were part of the operation. The error behaviour of corresponds to the "error-option" "rollback-on-error". If the "with-defaults" capability is supported by the server, the semantics of editing modes is the same as for , as described in section 4.5.2 of [RFC6243]. Semantics for "with-defaults" in operations on any non conventional configuration datastores SHOULD be defined by the specification for the datastore. Bjorklund, et al. Expires September 2, 2018 [Page 8] Internet-Draft March 2018 3.1.2.1. Example: Setting a leaf of an interface in The following example shows the version of the first example in Section 7.2 of [RFC6241], setting the MTU to 1500 on an interface named "Ethernet0/0" in the running configuration datastore. ds:running Ethernet0/0 1500 The other examples shown in Section 7.2 can be translated to examples in a similar way. 3.2. Augmentations to NETCONF Operations Several of the operations defined in the base NETCONF YANG module "ietf-netconf" [RFC6241] may be used with new datastores. Hence, the , , and operations are augmented with a new "datastore" leaf that can select the desired datastore. If a , , or operation is not supported on a particular datastore then an error is returned, as specified in "ietf-netconf-nmda" (see Section 4). 4. NETCONF Datastores YANG Module This module imports definitions from [RFC6991], [RFC6241], [RFC6243], and [I-D.ietf-netmod-revised-datastores]. Bjorklund, et al. Expires September 2, 2018 [Page 9] Internet-Draft March 2018 RFC Ed.: update the date below with the date of RFC publication and remove this note. file "ietf-netconf-nmda@2018-02-28.yang" module ietf-netconf-nmda { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-netconf-nmda"; prefix ncds; 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; // RFC Ed.: update the reference below with the actual RFC number reference "RFC XXXX: Network Management Datastore Architecture."; } import ietf-origin { prefix or; // RFC Ed.: update the reference below with the actual RFC number reference "RFC XXXX: Network Management Datastore Architecture."; } import ietf-netconf { prefix nc; reference "RFC 6241: Network Configuration Protocol (NETCONF)"; } import ietf-netconf-with-defaults { prefix ncwd; reference "RFC 6243: With-defaults Capability for NETCONF."; } organization "IETF NETCONF Working Group"; contact "WG Web: WG List: Author: Martin Bjorklund Author: Juergen Schoenwaelder Bjorklund, et al. Expires September 2, 2018 [Page 10] Internet-Draft March 2018 Author: Phil Shafer Author: Kent Watsen Author: Rob Wilton "; description "This YANG module defines a set of NETCONF operations to support the Network Management Datastore Architecture (NMDA). Copyright (c) 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). This version of this YANG module is part of RFC XXXX (http://www.rfc-editor.org/info/rfcxxxx); see the RFC itself for full legal notices."; // RFC Ed.: update the date below with the date of RFC publication // and remove this note. // RFC Ed.: replace XXXX with actual RFC number and remove this // note. revision 2018-02-28 { description "Initial revision."; reference "RFC XXXX: NETCONF Extensions to Support the Network Management Datastore Architecture"; } feature origin { description "Indicates that the server supports the 'origin' annotation."; reference "RFC XXXX: Network Management Datastore Architecture"; } feature with-defaults { Bjorklund, et al. Expires September 2, 2018 [Page 11] Internet-Draft March 2018 description "NETCONF :with-defaults capability; If the server advertises the :with-defaults capability for a session, then this feature must also be enabled for that session. Otherwise, this feature must not be enabled."; reference "RFC 6243: With-defaults Capability for NETCONF, section 4; and RFC XXXX: NETCONF Extensions to Support the Network Management Datastore Architecture, section 3.1.1.1."; } rpc get-data { description "Retrieve data from an NMDA datastore. The content returned by get-data must satisfy all filters, i.e., the filter criteria are logically ANDed. The 'with-origin' parameter is only valid for an operational datastore. If 'with-origin' is used with an invalid datastore, then the server MUST return an element with an value of 'invalid-value'. The 'with-defaults' parameter only applies to the operational datastore if the NETCONF :with-defaults and :with-operational-defaults capabilities are both advertised. If the 'with-defaults' parameter is present in a request for which it is not supported, then the server MUST return an element with an value of 'invalid-value'."; input { leaf datastore { type ds:datastore-ref; mandatory true; description "Datastore from which to retrieve data. If the datastore is not supported by the server, then the server MUST return an element with an value of 'invalid-value'."; } choice filter-spec { description "The content filter specification for this request."; anydata subtree-filter { description Bjorklund, et al. Expires September 2, 2018 [Page 12] Internet-Draft March 2018 "This parameter identifies the portions of the target datastore to retrieve."; reference "RFC 6241: Network Configuration Protocol, Section 6."; } leaf xpath-filter { if-feature nc:xpath; type yang:xpath1.0; description "This parameter contains an XPath expression identifying the portions of the target datastore to retrieve. If the expression returns a node-set, all nodes in the node-set are selected by the filter. Otherwise, if the expression does not return a node-set, then the get-data operation fails. The expression is evaluated in the following XPath context: o The set of namespace declarations are those in scope on the 'xpath-filter' leaf element. o The set of variable bindings is empty. o The function library is the core function library, and the XPath functions defined in section 10 in RFC 7950. o The context node is the root node of the target datastore."; } } leaf config-filter { type boolean; description "Filter for nodes with the given value for their 'config' property."; } choice origin-filters { when 'derived-from-or-self(datastore, "ds:operational")'; if-feature origin; description "Filters based on the 'origin' annotation."; leaf-list origin-filter { type or:origin-ref; Bjorklund, et al. Expires September 2, 2018 [Page 13] Internet-Draft March 2018 description "Filter based on the 'origin' annotation. A node matches the filter if its 'origin' annotation is derived from or equal to any of the given filter values."; } leaf-list negated-origin-filter { type or:origin-ref; description "Filter based on the 'origin' annotation. A node matches the filter if its 'origin' annotation is not derived from and not equal to all of the given filter values."; } } leaf max-depth { type union { type uint16 { range "1..65535"; } type enumeration { enum "unbounded"; } } default "unbounded"; description "For each node selected by the filter, this parameter selects how many conceptual sub-tree levels should be returned in the reply. If the depth is 1, the reply includes just the selected nodes but no children. If the depth is 'unbounded', all descendant nodes are included."; } leaf with-origin { when 'derived-from-or-self(../datastore, "ds:operational")'; if-feature origin; type empty; description "If this parameter is present, the server will return the 'origin' annotation for the nodes that has one."; } uses ncwd:with-defaults-parameters { if-feature with-defaults; } } output { anydata data { Bjorklund, et al. Expires September 2, 2018 [Page 14] Internet-Draft March 2018 description "Copy of the source datastore subset which matched the filter criteria (if any). An empty data container indicates that the request did not produce any results."; } } } rpc edit-data { description "Edit data in an NMDA datastore. If an error condition occurs such that an error severity element is generated, the server will stop processing the operation and restore the specified configuration to its complete state at the start of this operation."; input { leaf datastore { type ds:datastore-ref; mandatory true; description "Datastore which is the target of the edit-data operation. If the target datastore is not writable, or is not supported by the server, then the server MUST return an element with an value of 'invalid-value'."; } leaf default-operation { type enumeration { enum "merge" { description "The default operation is merge."; } enum "replace" { description "The default operation is replace."; } enum "none" { description "There is no default operation."; } } default "merge"; description "The default operation to use."; Bjorklund, et al. Expires September 2, 2018 [Page 15] Internet-Draft March 2018 } choice edit-content { mandatory true; description "The content for the edit operation."; anydata config { description "Inline config content."; } leaf url { if-feature nc:url; type inet:uri; description "URL based config content."; } } } } /* * Augment the lock and unlock operations with a * "datastore" parameter. */ augment "/nc:lock/nc:input/nc:target/nc:config-target" { description "Add NMDA Datastore as target."; leaf datastore { type ds:datastore-ref; description "Datastore to lock. The lock operation is only supported on writable datastores. If the lock operation is not supported by the server on the specified target datastore, then the server MUST return an element with an value of 'invalid-value'."; } } augment "/nc:unlock/nc:input/nc:target/nc:config-target" { description "Add NMDA Datastore as target."; leaf datastore { type ds:datastore-ref; description "Datastore to unlock. Bjorklund, et al. Expires September 2, 2018 [Page 16] Internet-Draft March 2018 The unlock operation is only supported on writable datastores. If the unlock operation is not supported by the server on the specified target datastore, then the server MUST return an element with an value of 'invalid-value'."; } } /* * Augment the validate operation with a * "datastore" parameter. */ augment "/nc:validate/nc:input/nc:source/nc:config-source" { description "Add NMDA Datastore as source."; leaf datastore { type ds:datastore-ref; description "Datastore to validate. The validate operation is supported only on configuration datastores. If the validate operation is not supported by the server on the specified target datastore, then the server MUST return an element with an value of 'invalid-value'."; } } } 5. IANA Considerations This document registers two capability identifier URNs in the "Network Configuration Protocol (NETCONF) Capability URNs" registry: Bjorklund, et al. Expires September 2, 2018 [Page 17] Internet-Draft March 2018 Index Capability Identifier --------------------- :yang-library urn:ietf:params:netconf:capability:yang-library:1.1 :with-operational-defaults urn:ietf:params:netconf:capability:with-operational-defaults:1.0 This document registers a 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-netconf-nmda 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 [RFC6020]. name: ietf-netconf-nmda namespace: urn:ietf:params:xml:ns:yang:ietf-netconf-nmda prefix: ncds reference: RFC XXXX 6. Security Considerations The YANG module defined in this document extends the base operations of the NETCONF [RFC6241] protocol. The lowest NETCONF layer is the secure transport layer and the mandatory-to-implement secure transport is Secure Shell (SSH) [RFC6242]. The network configuration access control model [I-D.ietf-netconf-rfc6536bis] provides the means to restrict access for particular NETCONF users to a preconfigured subset of all available NETCONF protocol operations and content. The security considerations for the base NETCONF protocol operations (see Section 9 of [RFC6241]) apply to the new NETCONF and operations defined in this document. 7. References Bjorklund, et al. Expires September 2, 2018 [Page 18] Internet-Draft March 2018 7.1. Normative References [I-D.ietf-netconf-rfc6536bis] Bierman, A. and M. Bjorklund, "Network Configuration Access Control Module", draft-ietf-netconf-rfc6536bis-09 (work in progress), December 2017. [I-D.ietf-netconf-rfc7895bis] Bierman, A., Bjorklund, M., Schoenwaelder, J., Watsen, K., and R. Wilton, "YANG Library", draft-ietf-netconf- rfc7895bis-05 (work in progress), February 2018. [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-10 (work in progress), January 2018. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ RFC2119, March 1997, . [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004, . [RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, October 2010, . [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, . [RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011, . [RFC6243] Bierman, A. and B. Lengyel, "With-defaults Capability for NETCONF", RFC 6243, DOI 10.17487/RFC6243, June 2011, . [RFC6991] Schoenwaelder, J., Ed., "Common YANG Data Types", RFC 6991, DOI 10.17487/RFC6991, July 2013, . Bjorklund, et al. Expires September 2, 2018 [Page 19] Internet-Draft March 2018 [RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . 7.2. Informative References [I-D.ietf-netmod-yang-tree-diagrams] Bjorklund, M. and L. Berger, "YANG Tree Diagrams", draft- ietf-netmod-yang-tree-diagrams-06 (work in progress), February 2018. Authors' Addresses Martin Bjorklund Tail-f Systems Email: mbj@tail-f.com Juergen Schoenwaelder Jacobs University Email: j.schoenwaelder@jacobs-university.de Phil Shafer Juniper Networks Email: phil@juniper.net Kent Watsen Juniper Networks Email: kwatsen@juniper.net Robert Wilton Cisco Systems Email: rwilton@cisco.com Bjorklund, et al. Expires September 2, 2018 [Page 20]