Summary

  • RFC 9911 is an IETF Proposed Standard from December 2025 and obsoletes RFC 6991.
  • It revises both ietf-yang-types and ietf-inet-types while retaining their namespaces and module names.
  • The practical change is revision-aware: accepted values, canonical representations, patterns, and descriptions may differ even when a dependent model still appears to import a familiar module.
  • Adoption and implementation behavior remain unknown; no universal rollout or blanket incompatibility should be inferred.

The mechanism matters more than the label. A module can remain recognizable to tooling and engineers while its revision statement points to a different contract. RFC 9911 adds date/time and duration types, language-tag and protocol-number types, link-local address types, address-and-prefix types, host-name, and email-address types. It also aligns yang-identifier with YANG 1.1 and corrects or improves multiple pattern and description statements.

The date/time detail is operationally important. Under the semantics incorporated from RFC 9557, Z and +00:00 both express UTC, but they do not assert the same thing: +00:00 asserts UTC as the local reference point, while Z indicates UTC without that assertion. A parser, canonicalizer, or serializer that normalizes both forms indiscriminately can erase information that a consumer may use.

The revised patterns deserve the same caution. A value accepted under RFC 6991 is not automatically invalid under RFC 9911, and the packet does not establish which stored values fail in any particular deployment. The right question is whether the exact imported revision changes the value space or its canonical form for a field your model uses. Descriptions can also alter engineering assumptions even where machine validation is unchanged. RFC 9911 records equivalence, or non-equivalence, with several SMIv2 textual conventions; that is useful evidence, not a promise of identical behavior in every implementation.

Revision-aware evidence ledger

Question Evidence and boundary
What changed? RFC 9911 revises the two common modules, adds typedefs, aligns yang-identifier with YANG 1.1, and updates patterns and descriptions.
What stayed familiar? Namespaces and module names remain; a new revision date is published. This does not guarantee semantic compatibility.
What is known about status? IETF Proposed Standard, December 2025; RFC 9911 obsoletes RFC 6991.
What remains unknown? Deployed adoption, client revision pinning, and which existing datastore values fail under revised patterns.
What must not be inferred? No universal adoption, no blanket incompatibility, and no vendor-specific migration behavior without evidence.

Sources