Validating anydata in YANG Library context
draft-netana-nmop-yang-anydata-validation-01

NMOP                                                        A. Elhassany
Internet-Draft                                                   T. Graf
Intended status: Standards Track                                Swisscom
Expires: 23 April 2026                                   20 October 2025

               Validating anydata in YANG Library context
              draft-netana-nmop-yang-anydata-validation-01

Abstract

   This document describes a method to use YANG RFC 8525 and standard
   YANG validation rules in RFC 7950 to validate YANG data nodes that
   are children of an "anydata" data node.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on 23 April 2026.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Survey of existing use of "anydata" . . . . . . . . . . . . .   4
     3.1.  Documents that use "anydata" to operate on a datastore  .   4
     3.2.  To operate on YANG-like data  . . . . . . . . . . . . . .   5
   4.  Instantiated data node schema lookup  . . . . . . . . . . . .   5
   5.  Validating "anydata" Data Tree  . . . . . . . . . . . . . . .   5
   6.  Implementation Status . . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   Section 7.10 of [RFC7950] defines the "anydata" statement to
   represent an unknown set of YANG nodes for which the data model is
   not known at module design time.  However, Section 7.10 of [RFC7950]
   left the verification of the "anydata" tree open to become known
   through protocol signaling or other means.  Several IETF models,
   e.g., NETCONF Extensions for the NMDA [RFC8526], NMDA Datastores
   [RFC9144], Subscribed Notifications [RFC8639], YANG-Push [RFC8641],
   and RESTCONT [RFC8040], use "anydata" in their definitions.  Current
   YANG implementations accept syntactically valid YANG data nodes as
   children of an "anydata" node but do not check the data type of these
   data nodes against a YANG schema.

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   Unvalidated "anydata" subtrees prevents the automation of a YANG data
   processing chain.  This becomes a challenge for network operators
   collecting a large amount of YANG data, Big Data, from their
   networks.  For example, assume that YANG-Push [RFC8641] collects
   interface octet counters, YANG Interface Management [RFC8343], from
   thousands of network nodes and a network analytics component computes
   the total traffic volume across the network.  Suppose one of the
   nodes has a software defect and sends a YANG-Push notification with a
   large negative value for the interface octets counter.  In that case,
   the consumer without the ability to validate the "anydata" subtree
   will not be able to detect the error and will compute an incorrect
   total traffic volume, which could lead to inaccurate billing or
   capacity planning decisions.  Without the capability to validate the
   "anydata" subtree, the YANG data consumer is vulnerable to such
   errors, and troubleshooting such issues is challenging and time-
   consuming.

   YANG Schema Mount [RFC8528] allows mounting complete data models at
   implementation and run time.  While powerful, schema mount cannot
   address use cases where the user selects an arbitrary subset of an
   instantiated data tree, such as [RFC8641].  A current proposed
   approach, YANG Full Include [I-D.jouqui-netmod-yang-full-include],
   complements YANG Schema Mount and applies at design time, yet cannot
   address dynamic filtering of an instantiated YANG data tree.

   This document propeses using the [RFC8525] to define the context in
   which anydata trees are validated.  This would require the YANG
   tooling to implement additional flags that enables validating
   "anydata" subtrees in the context of a YANG Library.

   The validation of "anydata" subtrees is optional and allows a
   consumer of YANG messages to decide on how to process messages with
   "anydata" subtrees that do not conform to the expected schema.  For
   instance, a consumer might choose to ignore non-conforming messages,
   log them for further analysis, or trigger an alert to notify
   administrators of potential issues.  This allows the consumer to
   avoid catastrophic errors in large-scale production environments

1.1.  Requirements Language

   The key words "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.

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2.  Terminology

   This document uses the terminology defined in YANG [RFC7950] for
   schema node and schema tree but refines data node and data tree to be
   more precise.

   *  data node: A node in the schema tree that can be instantiated in a
      data tree.  One of container, leaf, leaf-list, list, anydata, and
      anyxml.  This document does not change how YANG handles anyxml
      data nodes.

   *  instantiated data node: an instantiated instance of a data node
      that contains before fully qualified name (module namespace +
      identifier) for the data node and the data modeled within YANG.

   *  data tree: a tree of data nodes (with no values).

   *  datastore: defined in YANG [RFC7950] and refined in Network
      Management Datastore Architecture (NMDA) [RFC8342] is realized as
      an instantiated data tree.

3.  Survey of existing use of "anydata"

   Several IETF models use "anydata" in their definitions.  The various
   IETF documents so far have used anydata to either operate on a
   datastore or to represent undefined YANG-like data.

3.1.  Documents that use "anydata" to operate on a datastore

   Documents are using "anydata" for one or more of the following four
   use-cases:

   1.  To represent a subtree filter NETCONF [RFC6241] for selecting an
       instantiated YANG data subtree from a given datastore NETCONF
       Extensions for the NMDA [RFC8526], NMDA Datastores [RFC9144], and
       YANG-Push [RFC8641].

   2.  To represent the output of either a subtree filter or XPATH query
       on a datastore NETCONF Extensions for the NMDA [RFC8526], NMDA
       Datastores [RFC9144], and YANG-Push [RFC8641].

   3.  To represent edit operations on an instantiated YANG data tree
       YANG Patch [RFC8072] and NMDA Datastores [RFC9144].

   4.  To store an instance of a YANG data tree YANG Instance Data
       [RFC9195].

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3.2.  To operate on YANG-like data

   There are currently only two documents that are using "anydata" to
   represent undefined YANG-like data.  The first one is Subscribed
   Notifications [RFC8639], which uses "anydata" to encode a filter on
   the stream of events without defining the source of these events.
   The second one is RESTCONF [RFC8040] to convey error information in
   the response body without defining the structure of this information.

4.  Instantiated data node schema lookup

   This document builds on the fact that when a YANG validator examines
   a node in an instantiated data tree, it can find the corresponding
   data node in a YANG schema.  For the existing YANG encodings, the
   following rules are defined to encode instantiated data nodes:

   *  In YANG XML encoding [RFC7950], The element's local name is the
      data node identifier, and its namespace is the module's XML
      namespace.

   *  In JSON encoding [RFC7951], each object member must be identical
      to the corresponding YANG data node identifier or namespace-
      qualified - the data node identifier is prefixed with the name of
      the module in which the data node is defined, separated from the
      data node identifier by the colon character (":").

   *  In CBOR [RFC9254] encoding, node should include information that
      would allow each node to be - identified in a stateless way, for
      instance, the SID number associated with the node, the SID delta
      from another SID in the application payload, the namespace-
      qualified name, or the instance-identifier.

   Given the encoding rules that maintain complete information to
   identify the corresponding data node for each instantiated data node,
   the YANG validator can easily find the schema for the data node in
   the YANG Library.

5.  Validating "anydata" Data Tree

   This document introduces two new YANG validation options: anydata-
   complete and anydata-candidate.  These two options align with
   Section 8.3.3 of [RFC7950], such that the complete validation
   validates the contents of the anydata subtree, which MUST obey all
   validation rules defined in the corresponding schema in the YANG
   Library.  The candidate does not apply the constraint checks.

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6.  Implementation Status

   Note to the RFC-Editor: Please remove this section before publishing.

   anydata-candidate validation is implemented for libyang and avaiable
   at https://github.com/ahassany/libyang/tree/anydata-strict-parsing

7.  IANA Considerations

   This memo includes no request to IANA.

8.  Security Considerations

   TBD

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,
              <https://www.rfc-editor.org/info/rfc7950>.

   [RFC7951]  Lhotka, L., "JSON Encoding of Data Modeled with YANG",
              RFC 7951, DOI 10.17487/RFC7951, August 2016,
              <https://www.rfc-editor.org/info/rfc7951>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8342]  Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              and R. Wilton, "Network Management Datastore Architecture
              (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018,
              <https://www.rfc-editor.org/info/rfc8342>.

   [RFC8525]  Bierman, A., Bjorklund, M., Schoenwaelder, J., Watsen, K.,
              and R. Wilton, "YANG Library", RFC 8525,
              DOI 10.17487/RFC8525, March 2019,
              <https://www.rfc-editor.org/info/rfc8525>.

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   [RFC9254]  Veillette, M., Ed., Petrov, I., Ed., Pelov, A., Bormann,
              C., and M. Richardson, "Encoding of Data Modeled with YANG
              in the Concise Binary Object Representation (CBOR)",
              RFC 9254, DOI 10.17487/RFC9254, July 2022,
              <https://www.rfc-editor.org/info/rfc9254>.

9.2.  Informative References

   [I-D.jouqui-netmod-yang-full-include]
              Quilbeuf, J., Claise, B., and T. Joubert, "YANG Full
              Embed", Work in Progress, Internet-Draft, draft-jouqui-
              netmod-yang-full-include-02, 5 July 2024,
              <https://datatracker.ietf.org/doc/html/draft-jouqui-
              netmod-yang-full-include-02>.

   [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,
              <https://www.rfc-editor.org/info/rfc6241>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <https://www.rfc-editor.org/info/rfc8040>.

   [RFC8072]  Bierman, A., Bjorklund, M., and K. Watsen, "YANG Patch
              Media Type", RFC 8072, DOI 10.17487/RFC8072, February
              2017, <https://www.rfc-editor.org/info/rfc8072>.

   [RFC8343]  Bjorklund, M., "A YANG Data Model for Interface
              Management", RFC 8343, DOI 10.17487/RFC8343, March 2018,
              <https://www.rfc-editor.org/info/rfc8343>.

   [RFC8526]  Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              and R. Wilton, "NETCONF Extensions to Support the Network
              Management Datastore Architecture", RFC 8526,
              DOI 10.17487/RFC8526, March 2019,
              <https://www.rfc-editor.org/info/rfc8526>.

   [RFC8528]  Bjorklund, M. and L. Lhotka, "YANG Schema Mount",
              RFC 8528, DOI 10.17487/RFC8528, March 2019,
              <https://www.rfc-editor.org/info/rfc8528>.

   [RFC8639]  Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard,
              E., and A. Tripathy, "Subscription to YANG Notifications",
              RFC 8639, DOI 10.17487/RFC8639, September 2019,
              <https://www.rfc-editor.org/info/rfc8639>.

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   [RFC8641]  Clemm, A. and E. Voit, "Subscription to YANG Notifications
              for Datastore Updates", RFC 8641, DOI 10.17487/RFC8641,
              September 2019, <https://www.rfc-editor.org/info/rfc8641>.

   [RFC9144]  Clemm, A., Qu, Y., Tantsura, J., and A. Bierman,
              "Comparison of Network Management Datastore Architecture
              (NMDA) Datastores", RFC 9144, DOI 10.17487/RFC9144,
              December 2021, <https://www.rfc-editor.org/info/rfc9144>.

   [RFC9195]  Lengyel, B. and B. Claise, "A File Format for YANG
              Instance Data", RFC 9195, DOI 10.17487/RFC9195, February
              2022, <https://www.rfc-editor.org/info/rfc9195>.

Acknowledgements

   The authors would like to thank Jean Quilbeuf, Benoit Claise, and
   Alex Huang Feng for their review and valuable comments.

Authors' Addresses

   Ahmed Elhassany
   Swisscom
   Binzring 17
   CH- Zurich 8045
   Switzerland
   Email: ahmed.elhassany@swisscom.com

   Thomas Graf
   Swisscom
   Binzring 17
   CH-8045 Zurich
   Switzerland
   Email: thomas.graf@swisscom.com

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