1. Introduction

This section preserves the RFC text for common YANG data types, including YANG modules, typedefs, patterns, ranges, units, revision statements, namespaces, IANA registry updates, and normative requirements.

Original RFC Text

1.  Introduction

   YANG [RFC7950] is a data modeling language used to model
   configuration and state data manipulated by the Network Configuration
   Protocol (NETCONF) [RFC6241].  The YANG language supports a small set
   of built-in data types and provides mechanisms to derive other types
   from the built-in types.

   This document defines a collection of common data types.  The
   definitions are organized into two YANG modules:

   *  The "ietf-yang-types" module defines generally useful data types
      such as types for counters and gauges, types related to date and
      time, and types for common string values (e.g., UUIDs, dotted-quad
      notation, and language tags).

   *  The "ietf-inet-types" module defines data types relevant for the
      Internet Protocol suite such as types related to IP addresses,
      types for domain name, host name, URI, and email, and types for
      values in common protocol fields (e.g., port numbers).

   The initial version of these YANG modules was published as [RFC6021].
   The first revision of [RFC6021], published as [RFC6991], added
   several type definitions to the YANG modules.  This second revision
   adds further new type definitions and addresses Erratum IDs 4076
   [Err4076] and 5105 [Err5105].  Furthermore, the yang-identifier
   definition has been aligned with YANG 1.1 [RFC7950], and some pattern
   statements have been improved.  For further details, see the revision
   statements of the YANG modules in Sections 3 and 4.  A brief overview
   of all types and when they were introduced can be found in Section 2.
   Additional type definitions may be added in the future by submitting
   proposals to the NETMOD Working Group.

   This document uses the YANG terminology defined in Section 3 of
   [RFC7950].

   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.