Extending YANG modules at runtime

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Table of Contents

1. Introduction

In the process of revising [RFC8366] to accomodate needed extensions an effort was initially made to do this using augment (cite) and later augment-structure. [RFC8366] is a digitally signed voucher format used in onboarding of new devices. It is a file format that may be transmitted over CoAP, HTTP or via USB key, but it does not use RESTCONF. The contents of the file are not subject to negotiation as might be done with [RFC8528].¶

Rather than have each topic document define the relevant extensions needed, it turned out to be necessary to collect all the extensions necessary into a single revision to the YANG module, which is being produced as [I-D.ietf-anima-rfc8366bis].¶

[RFC8520] is like [RFC8366]: it is a file format. When [RFC8520] was defined, it anticipated that there would be future extensions, and defined a YANG leaf called "extensions" which is a list of subsequent YANG modules which are included. This is being used to define, for instance, [I-D.ietf-opsawg-ol].¶

When YANG is serialized to XML or JSON, the keys used in the attribute map are strings, and so it seems relatively straightforward for a human programmer to understand how to insert these new keys into the same attribute map. YANG however, is intended to be machine parseable, and [RFC9254] provides a way to serialize YANG to CBOR. While strings can be used if necessary, the preferred method is via YANG-SID values, allocated for instance, via [RFC9595]. It is not obvious how an extension mechanism as described by [RFC8520] can be efficiently encoded to CBOR, nor how YANG tooling should react to these ad-hoc extensions.¶

This document makes the [RFC8520] extension mechanism a generic mechanism that can be used by any YANG module, and explains how to efficiently encode this to CBOR using YANG-SID.¶

2. Terminology

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.¶

3. Protocol

4. Privacy Considerations

YYY¶

5. Security Considerations

ZZZ¶

6. IANA Considerations

7. Acknowledgements

Hello.¶

8. Changelog

9. References

Author's Address