Internet-Draft anydata validation March 2024
Elhassany Expires 2 September 2024 [Page]
Intended Status:
Standards Track
A. Elhassany

Validating anydata in YANG Library context


This document describes a method to use yang-library to validate YANG data nodes with type anydata.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on 2 September 2024.

Table of Contents

1. Introduction

YANG [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, YANG [RFC7950] left the verification of the "anydata" tree open to be done using external means. Several IETF models, e.g., [RFC7895], [RFC8526], [RFC9144], [RFC8639], [RFC8641], and [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 semantics of these data nodes against a YANG schema. This creates a real problem for any consumer of these models when validating all leaves of the YANG data tree.

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 YANG PUSH [RFC8641]. A current proposed approach, YANG Full Include 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.

In this document we propese using YANG Library [RFC7895] to define the context in which anydata trees are validated. This would require the YANG tooling to implement an optional flag that enables a a flag for validating "anydata" subtrees in the context of a YANG library.

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.

2. Terminology

We use the terminology defined in YANG [RFC7950] for schema node and schema tree but refine data node and data tree to be more precise.

3. Validating "anydata" Data Tree

The current YANG encodings, XML, JSON, and CBOR, encode instantiated data nodes with fully qualified name using the module's namespace and a local name. The module's namespace can be either explicit or assumed from a default namespace defined in the top data tree.

This document introduces a new YANG validation option: anydata-subtree-validation. In this mode, a YANG data parser MUST accept a YANG library as input along the YANG data file. When this option is enabled, any instantiated data node (NodeB) that is a child of anydata node (NodeA) is accepted to be valid only if (i) the qualified name of the node NodeB is found in one of the data trees defined by the YANG library AND (ii) the instantiated data tree rooted by NodeB is valid incomplete instantiated data tree according to the data node of NodeB.

The first condition ensures the completeness of the YANG library, and no subtree can be included as a child of anydata node unless a schema is defined for all the children of anydata subtree and specified in the YANG library. The second condition applies a regular YANG validation against the subtree of anydata, considering that the subtree of anydata could be generated using an XPath [RFC8641] or a subtree filter [RFC6241]. Thus, the validator MUST consider this subtree incomplete and ignore any missing leaves.

4. IANA Considerations

This memo includes no request to IANA.

5. Security Considerations


6. References

6.1. Normative References

Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <>.
Bierman, A., Bjorklund, M., and K. Watsen, "YANG Module Library", RFC 7895, DOI 10.17487/RFC7895, , <>.
Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, , <>.
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <>.

6.2. Informative References

Joubert, T., Quilbeuf, J., and B. Claise, "YANG Full Include", Work in Progress, Internet-Draft, draft-jouqui-netmod-yang-full-include-00, , <>.
Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., and A. Bierman, Ed., "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, , <>.
Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, , <>.
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, , <>.
Bjorklund, M. and L. Lhotka, "YANG Schema Mount", RFC 8528, DOI 10.17487/RFC8528, , <>.
Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard, E., and A. Tripathy, "Subscription to YANG Notifications", RFC 8639, DOI 10.17487/RFC8639, , <>.
Clemm, A. and E. Voit, "Subscription to YANG Notifications for Datastore Updates", RFC 8641, DOI 10.17487/RFC8641, , <>.
Clemm, A., Qu, Y., Tantsura, J., and A. Bierman, "Comparison of Network Management Datastore Architecture (NMDA) Datastores", RFC 9144, DOI 10.17487/RFC9144, , <>.


The authors would like to thank Jean Quilbeuf and Thomas Graf for their review and valuable comments.

Author's Address

Ahmed Elhassany
Binzring 17
CH- Zuerich 8045