NETMOD Working Group                                           L. Lhotka
Internet-Draft                                                    CZ.NIC
Intended status: Standards Track                           June 12,                      September 10, 2015
Expires: December 14, 2015 March 13, 2016

                JSON Encoding of Data Modeled with YANG
                     draft-ietf-netmod-yang-json-04
                     draft-ietf-netmod-yang-json-05

Abstract

   This document defines encoding rules for representing configuration,
   state data, RPC operation or action input and output parameters, and
   notifications defined using YANG as JavaScript Object Notation (JSON)
   text.

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   This Internet-Draft will expire on December 14, 2015. March 13, 2016.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology and Notation  . . . . . . . . . . . . . . . . . .   3
   3.  Validation  Properties of JSON-encoded
       Instance Data . . . . . . . . . the JSON Encoding . . . . . . . . . . . . . . .   4
   4.  Names and Namespaces  . . . . . . . . . . . . . . . . . . . .   4
   5.  Encoding of YANG Data Node Instances  . . . . . . . . . . . .   6
     5.1.  The "leaf" Data Node  . . . . . . . . . . . . . . . . . .   7
     5.2.  The "container" Data Node . . . . . . . . . . . . . . . .   7
     5.3.  The "leaf-list" Data Node . . . . . . . . . . . . . . . .   7
     5.4.  The "list" Data Node  . . . . . . . . . . . . . . . . . .   8
     5.5.  The "anydata" Data Node . . . . . . . . . . . . . . . . .   9
     5.6.  The "anyxml" Data Node  . . . . . . . . . . . . . . . . .  10
   6.  The Mapping of  Representing YANG Data Types to in JSON Values . . . . . . . . .  10
     6.1.  Numeric Types . . . . . . . . . . . . . . . . . . . . . .  10
     6.2.  The "string" Type . . . . . . . . . . . . . . . . . . . .  11
     6.3.  The "boolean" Type  . . . . . . . . . . . . . . . . . . .  11
     6.4.  The "enumeration" Type  . . . . . . . . . . . . . . . . .  11
     6.5.  The "bits" Type . . . . . . . . . . . . . . . . . . . . .  11
     6.6.  The "binary" Type . . . . . . . . . . . . . . . . . . . .  11
     6.7.  The "leafref" Type  . . . . . . . . . . . . . . . . . . .  11  12
     6.8.  The "identityref" Type  . . . . . . . . . . . . . . . . .  11  12
     6.9.  The "empty" Type  . . . . . . . . . . . . . . . . . . . .  12
     6.10. The "union" Type  . . . . . . . . . . . . . . . . . . . .  13
     6.11. The "instance-identifier" Type  . . . . . . . . . . . . .  13  14
   7.  I-JSON Compliance . . . . . . . . . . . . . . . . . . . . . .  14
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  15
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  15
     10.2.  Informative References . . . . . . . . . . . . . . . . .  16
   Appendix A.  A Complete Example . . . . . . . . . . . . . . . . .  16
   Appendix B.  Change Log . . . . . . . . . . . . . . . . . . . . .  18
     B.1.  Changes Between Revisions -04 and -05 . . . . . . . . . .  18
     B.2.  Changes Between Revisions -03 and -04 . . . . . . . . . .  18
     B.2.
     B.3.  Changes Between Revisions -02 and -03 . . . . . . . . . .  19
     B.3.
     B.4.  Changes Between Revisions -01 and -02 . . . . . . . . . .  19
     B.4.
     B.5.  Changes Between Revisions -00 and -01 . . . . . . . . . .  19
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  19  20

1.  Introduction

   The NETCONF protocol [RFC6241] uses XML [W3C.REC-xml-20081126] for
   encoding data in its Content Layer.  Other management protocols might
   want to use other encodings while still benefiting from using YANG
   [I-D.ietf-netmod-rfc6020bis] as the data modeling language.

   For example, the RESTCONF protocol [I-D.ietf-netconf-restconf]
   supports two encodings: XML (media type "application/yang.data+xml")
   and JSON (media type "application/yang.data+json).

   The specification of YANG 1.1 data modelling language
   [I-D.ietf-netmod-rfc6020bis] defines only XML encoding for data
   instances, i.e., contents of configuration datastores, state data,
   RFC
   RPC operation or action input and output parameters, and event
   notifications.  The aim of this document is to define rules for
   encoding the same data as JavaScript Object Notation (JSON)
   text [RFC7159].

   In order to achieve maximum interoperability while allowing
   implementations to use a variety of available JSON parsers, the JSON
   encoding rules follow, as much as possible, the constraints of the
   I-JSON restricted profile [RFC7493].  Section 7 discusses I-JSON
   conformance in more detail.

2.  Terminology and Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   The following terms are defined in [I-D.ietf-netmod-rfc6020bis]:

   o  action,

   o  anydata,

   o  anyxml,

   o  augment,

   o  container,

   o  data node,

   o  data tree,

   o  identity,

   o  instance identifier,

   o  leaf,

   o  leaf-list,

   o  list,

   o  module,

   o  RPC operation,
   o  submodule.

3.  Validation  Properties of JSON-encoded Instance Data

   Instance data validation as defined in [I-D.ietf-netmod-rfc6020bis],
   sec. 8.3.3, is only applicable to XML-encoded data.  For one,
   semantic constraints in "must" statements are expressed using
   XPath 1.0 [W3C.REC-xpath-19991116], which can be properly interpreted
   only in the XML context.

   This document and the corresponding "XML Mapping Rules" sections from
   [I-D.ietf-netmod-rfc6020bis] also define an implicit schema-driven
   mapping of JSON-encoded instances to XML-encoded instances (and vice
   versa). JSON Encoding

   This mapping is mostly straightforward.  In cases where
   doubts could arise, this document gives explicit instructions for
   mapping JSON-encoded instances to XML.

   In order to validate a JSON instance document, it needs first to be
   mapped, at least conceptually, to the corresponding XML instance
   document.  By definition, the defines JSON document is then valid if encoding for YANG data trees and only
   if the XML document their
   subtrees.  It is valid according to always assumed that the rules stated top-level structure in
   [I-D.ietf-netmod-rfc6020bis].

4.  Names and Namespaces JSON-
   encoded data is an object.

   Instances of YANG data nodes (leafs, containers, leaf-lists, lists,
   anydata and anyxml nodes) are always encoded as members of a JSON object,
   i.e., as name/value pairs.  This section  Section 4 defines how the name part is
   formed, and the following sections deal with the value part.

   Except in the cases specified below, the member name

   Unlike XML element content, JSON values carry partial type
   information (number, string, boolean).  The JSON encoding is identical to defined
   so that this information is never in conflict with the identifier data type of
   the corresponding YANG data node.  Every leaf or leaf-list.

   With the exception of anyxml and schema-less anydata nodes, it is
   possible to map a JSON-encoded data tree to XML encoding as defined
   in [I-D.ietf-netmod-rfc6020bis], and vice versa.  However, such name
   belongs
   conversions require the YANG data model to be available.

   In order to achieve maximum interoperability while allowing
   implementations to use a namespace which variety of existing JSON parsers, the JSON
   encoding rules follow, as much as possible, the constraints of the
   I-JSON restricted profile [RFC7493].  Section 7 discusses I-JSON
   conformance in more detail.

4.  Names and Namespaces

   An object member name MUST be in one of the following forms:

   o  simple - identical to the identifier of the corresponding YANG
      data node;

   o  namespace-qualified - the data node identifier is associated prefixed with
      the YANG name of the module where in which the corresponding data node is defined.  If defined, and
      separated by the colon character (":").

   The name of a module determines the namespace of all data node names
   defined in that module.  If a data node is defined in a submodule,
   then the namespace is determined by namespace-qualified member name uses the name of the main
   module to which the submodule belongs.

   If the namespace

   ABNF syntax [RFC5234] of a member name has to be explicitly specified, the
   module name SHALL be used as a prefix to the member's local name.
   Both parts of the member name SHALL be separated with a colon
   character (":").  Using ABNF [RFC5234], the namespace-qualified name
   can be expressed as is shown in Figure 1, where
   the production for "identifier" is defined in sec. 13 of
   [I-D.ietf-netmod-rfc6020bis].

           qualified-member-name

           member-name = identifier ":" [identifier ":"] identifier

             Figure 1: ABNF production for a qualified JSON member name.

   Names with namespace identifiers in the form shown in Figure 1 are

   A namespace-qualified member name MUST be used if for all members of a
   top-level JSON object, and only if then also whenever the namespaces of the parent
   data node belongs to a different
   namespace, which also includes all top-level YANG data nodes that
   have no and its parent node. node are different.  In all other cases, the
   simple form of the member name MUST be used.

   For example, consider the following YANG module:

   module foomod {

     namespace "http://example.com/foomod";

     prefix "foo";

     container top {
       leaf foo {
         type uint8;
       }
     }
   }

   If the data model consists only of this module, then the following is
   a valid JSON-encoded configuration:

   {
     "foomod:top": {
       "foo": 54
     }
   }

   Note that the member of the top-level container instance contains object uses the namespace
   identifier (module name) namespace-
   qualified name but the "foo" leaf doesn't because it is defined in
   the same module as its parent container. container "top".

   Now, assume the container "top" is augmented from another module,
   "barmod":

   module barmod {

     namespace "http://example.com/barmod";

     prefix "bar";

     import foomod {
       prefix "foo";
     }

     augment "/foo:top" {
       leaf bar {
         type boolean;
       }
     }
   }

   A valid JSON-encoded configuration containing both leafs may then
   look like this:

   {
     "foomod:top": {
       "foo": 54,
       "barmod:bar": true
     }
   }

   The name of the "bar" leaf is prefixed with the namespace identifier
   because its parent is defined in a different module, hence it belongs
   to another namespace. module.

   Explicit namespace identifiers are sometimes needed when encoding
   values of the "identityref" and "instances-identifier" types.  The
   same form of namespace-qualified name as shown in Figure 1 defined above is then used as well. used.
   See Sections 6.8 and 6.11 for details.

5.  Encoding of YANG Data Node Instances

   Every complete JSON instance document, such as a configuration
   datastore content, is an object.  Its members are instances of all
   top-level data nodes defined by the YANG data model.

   Character encoding MUST be UTF-8.

   Any data node instance is encoded as a name/value pair where the
   name is formed from the data node identifier using the rules of
   Section 4.  The value depends on the category of the data node as
   explained in the following subsections.

   Character encoding MUST be UTF-8.

5.1.  The "leaf" Data Node

   A leaf instance is encoded as a name/value pair where the value can
   be a string, number, literal "true" or "false", or the special array
   "[null]", depending on the type of the leaf (see Section 6 for the
   type encoding rules).

   Example: For the leaf node definition

   leaf foo {
     type uint8;
   }

   the following is a valid JSON-encoded instance:

   "foo": 123

5.2.  The "container" Data Node

   A container instance is encoded as a name/object pair.  The
   container's child data nodes are encoded as members of the object.

   Example: For the container definition

   container bar {
     leaf foo {
       type uint8;
     }
   }

   the following is a valid JSON-encoded instance:

   "bar": {
     "foo": 123
   }

5.3.  The "leaf-list" Data Node

   A leaf-list is encoded as a name/array pair, and the array elements
   are values of some scalar type, which can be a string, number,
   literal "true" or "false", or the special array "[null]", depending
   on the type of the leaf-list (see Section 6 for the type encoding
   rules).

   The ordering of array elements follows the same rules as the ordering
   of XML elements representing leaf-list entries in the XML encoding.
   Specifically, the "ordered-by" properties (sec. 7.7.7 in
   [I-D.ietf-netmod-rfc6020bis]) MUST be observed.

   Example: For the leaf-list definition

   leaf-list foo {
     type uint8;
   }

   the following is a valid JSON-encoded instance:

   "foo": [123, 0]

5.4.  The "list" Data Node

   A list instance is encoded as a name/array pair, and the array
   elements are JSON objects.

   The ordering of array elements follows the same rules as the ordering
   of XML elements representing list entries in the XML encoding.
   Specifically, the "ordered-by" properties (sec. 7.7.7 in
   [I-D.ietf-netmod-rfc6020bis]) MUST be observed.

   Unlike the XML encoding, where list keys are required to precede any
   other siblings within a list entry, and appear in the order specified
   by the data model, the order of members in a JSON-encoded list entry
   is arbitrary because JSON objects are fundamentally unordered
   collections of members.

   Example: For the list definition

   list bar {
     key foo;
     leaf foo {
       type uint8;
     }
     leaf baz {
       type string;
     }
   }

   the following is a valid JSON-encoded instance:

   "bar": [
     {
       "foo": 123,
       "baz": "zig"
     },
     {
       "baz": "zag",
       "foo": 0
     }
   ]

5.5.  The "anydata" Data Node

   Anydata data node is a new feature in YANG 1.1.  It serves as a
   container for data an unknown set of nodes that however appear as normal
   YANG-modeled data, except
   their data.  A data model is for anydata content may or may not a priori known.
   exist at run time.  In the latter case, no universal mapping between
   JSON- and XML-encoded instances is available.

   An anydata instance is thus encoded in the same way as a container,
   and its i.e.,
   as a value/object pair.  The requirement that anydata content is subject to can be
   modeled by YANG implies the following rules: rules for JSON text inside the
   object:

   o  It is a valid I-JSON message [RFC7493].

   o  Any  All object member name is either a YANG identifier as defined by names satisfy the
      "identifier" ABNF production in sec. 13 of
      [I-D.ietf-netmod-rfc6020bis], or two such identifiers separated by
      the colon character (":").  See also Section 4. Figure 1.

   o  Any JSON array contains either only unique scalar values (as a
      leaf-list, see Section 5.3), or only objects (as a list, see
      Section 5.4).

   o  The "null" value is only allowed in the single-element array
      "[null]" corresponding to the encoding of the "empty" type, see
      Section 6.9.

   If a data model for anydata content is not available, it may be
   impossible to map a JSON-encoded anydata instance to XML, and vice
   versa.  Note, however, that such a mapping is not needed for
   validation purposes (Section 3) because anydata contents are
   generally not subject to YANG-based validation (see sec. 7.10 in
   [I-D.ietf-netmod-rfc6020bis]).

   Example: for the anydata definition

   anydata data;

   the following is a valid JSON-encoded instance:

   "data": {
     "ietf-notification:notification": {
       "eventTime": "2014-07-29T13:43:01Z",
       "example-event:event": {
         "event-class: "fault",
         "reporting-entity": {
           "card": "Ethernet0"
         },
         "severity": "major"
       }
     }
   }

5.6.  The "anyxml" Data Node

   An anyxml instance is encoded as a JSON name/value pair which MUST
   satisfy I-JSON constraints.  Otherwise it is unrestricted, i.e., the
   value can be an object, array, number, string or one of the literals
   "true", "false" and "null".

   As in the case of anydata (Section 5.5), there

   There is no universal procedure for mapping JSON-encoded anyxml
   instances to XML, and vice versa.

   Example: For the anyxml definition

   anyxml bar;

   the following is a valid JSON-encoded instance:

   "bar": [true, null, true]

6.  The Mapping of  Representing YANG Data Types to in JSON Values

   The type of the JSON value in an instance of the leaf or leaf-list
   data node depends on the type of that data node as specified in the
   following subsections.

6.1.  Numeric Types

   A value of the types "int8", "int16", "int32", "uint8", "uint16" and
   "uint32" is represented as a JSON number.

   A value of the "int64", "uint64" or "decimal64" type is encoded represented
   as a JSON string whose contents content is the lexical representation of that
   numeric value the
   corresponding YANG type as specified in sections 9.2.1 and 9.3.1 of
   [I-D.ietf-netmod-rfc6020bis].

   For example, if the type of the leaf "foo" in Section 5.1 was
   "uint64" instead of "uint8", the instance would have to be encoded as

   "foo": "123"

   The special handling of 64-bit numbers follows from the I-JSON
   recommendation to encode numbers exceeding the IEEE 754-2008 double
   precision range as strings, see sec. 2.2 in [RFC7493].

6.2.  The "string" Type

   A "string" value encoded represented as a JSON string, subject to JSON string
   encoding rules.

6.3.  The "boolean" Type

   A "boolean" value is mapped to represented as the corresponding JSON literal
   name "true" or "false".

6.4.  The "enumeration" Type

   An "enumeration" value is mapped in the same way represented as a JSON string except
   that - one of the permitted values are defined
   names assigned by "enum" statements in YANG.
   See

   The representation is identical to the lexical representation of the
   "enumeration" type in XML, see sec. 9.6 in
   [I-D.ietf-netmod-rfc6020bis].

6.5.  The "bits" Type

   A "bits" value is mapped to represented as a JSON string - a space-separated
   sequence of names of bits that are set.  The permitted bit names are
   assigned by "bit" statements in YANG.

   The representation is identical to the lexical representation of this value in XML, i.e., space-separated names
   representing the individual bit values that are set.  See
   "bits" type, see sec. 9.7 in [I-D.ietf-netmod-rfc6020bis].

6.6.  The "binary" Type

   A "binary" value is mapped to represented as a JSON string - base64-encoding of
   arbitrary binary data.

   The representation is identical to the lexical representation of this value the
   "binary" type in XML, i.e., base64-encoded binary
   data.  See see sec. 9.8 in [I-D.ietf-netmod-rfc6020bis].

6.7.  The "leafref" Type

   A "leafref" value is mapped according to represented using the same rules as the type of
   the leaf being referred to. to which the leafref value refers.

6.8.  The "identityref" Type

   An "identityref" value is mapped to represented as a string representing - the name of an
   identity.  Its namespace MUST be expressed as shown in Figure 1 if
   it is different from  If the namespace of identity is defined in another module than the leaf
   node containing the identityref value, and MAY the namespace-qualified form
   (Section 4) MUST be expressed otherwise. used.  Otherwise, both the simple and namespace-
   qualified forms are permitted.

   For example, consider the following schematic module:

   module exmod {
     ...
     import ietf-interfaces {
       prefix if;
     }
     import iana-if-type {
       prefix ianaift;
     }
     ...
     leaf type {
       type identityref {
         base "if:interface-type";
       }
     }
   }

   A valid instance of the "type" leaf is then encoded as follows:

   "type": "iana-if-type:ethernetCsmacd"

   The namespace identifier "iana-if-type" must be present in this case
   because the "ethernetCsmacd" identity is not defined in the same
   module as the "type" leaf.

6.9.  The "empty" Type

   An "empty" value is mapped to represented as "[null]", i.e., an array with the
   "null" literal being its only element.  For the purposes of this
   document, "[null]" is treated as considered an atomic scalar value.

   This encoding of the "empty" type was chosen instead of using simply
   "null" in order to facilitate the use of empty leafs in common
   programming languages.  When used in languages where the "null" value of a boolean context, member is treated
   as if the "[null]"
   value, unlike "null", evaluates to true. member is not present.

   Example: For the leaf definition

   leaf foo {
     type empty;
   }

   a valid instance is

   "foo": [null]

6.10.  The "union" Type

   A value of the "union" type is encoded as the value of any of the
   member types.

   Unlike XML, JSON conveys part of the type information already in the
   encoding.

   When validating a value of the "union" type, this the type information
   conveyed by the JSON encoding MUST also be taken into account.

   For example, consider the following YANG definition:

   leaf bar {
     type union {
       type uint16;
       type string;
     }
   }

   In RESTCONF [I-D.ietf-netconf-restconf], it is fully acceptable possible to set the
   value of "bar" in the following way when using the
   "application/yang.data+xml" "application/
   yang.data+xml" media type:

   <bar>13.5</bar>

   because the value may be interpreted as a string, i.e., the second
   member type of the union.  When using the "application/
   yang.data+json" media type, however, this is an error:

   "bar": 13.5

   In this case, the JSON encoding indicates the value is supposed to be
   a number rather than a string.

6.11.  The "instance-identifier" Type

   An "instance-identifier" value is encoded as a string that is
   analogical to the lexical representation in XML encoding, see
   sec. 9.13.3 in [I-D.ietf-netmod-rfc6020bis].  However, the encoding
   of namespaces in instance-identifier values follows the rules stated
   in Section 4, namely:

   o  The namespace identifier is the module name where each data node
      is defined.

   o  The encoding of a node name with an explicit namespace is as shown
      in Figure 1.

   o  The leftmost (top-level) data node name is always prefixed with in the
      namespace identifier.
      namespace-qualified form.

   o  Any subsequent data node name has is in the namespace identifier if and only namespace-qualified form
      if the node is defined in another module than its parent node has a different namespace. node, and
      the simple form is used otherwise.  This rule also holds for node
      names appearing in predicates.

   For example,

   /ietf-interfaces:interfaces/interface[name='eth0']/ietf-ip:ipv4/ip

   is a valid instance-identifer value because the data nodes
   "interfaces", "interface" and "name" are defined in the module "ietf-
   interfaces", whereas "ipv4" and "ip" are defined in "ietf-ip".

   When translating an instance-identifier value from JSON to XML, the
   namespace identifier (YANG module name) in each component of the
   instance-identifier MUST be replaced by an XML namespace prefix that
   is associated with the namespace URI reference of the module in the
   scope of the element containing the instance-identifier value.

7.  I-JSON Compliance

   I-JSON [RFC7493] is a restricted profile of JSON that guarantees
   maximum interoperability for protocols that use JSON in their
   messages, no matter what JSON encoders/decoders are used in protocol
   implementations.  The encoding defined in this document therefore
   observes the I-JSON requirements and recommendations as closely as
   possible.

   In particular, the following properties are guaranteed:

   o  Character encoding is UTF-8.

   o  Member names within the same JSON object are always unique.

   o  The order of JSON object members is never relied upon.

   o  Numbers of any type supported by YANG can be exchanged reliably.
      See Section 6.1 for details.

   This

   The JSON encoding defined in this document deviates from I-JSON only
   in the encoding representation of values
   with the "binary" type.  It uses  In order to remain
   compatible with XML encoding, the base64 encoding scheme is used
   (Section 6.6), whereas I-JSON recommends base64url instead.
   Theoretically, values of the "binary" type might appear in URI
   references, such as Request-URI in RESTCONF, although in practice the
   cases where it is really needed should be extremely rare.

8.  Security Considerations

   This document defines an alternative encoding for data modeled in the
   YANG data modeling language.  As such, it doesn't contribute any new
   security issues beyond those discussed in sec. 16 of
   [I-D.ietf-netmod-rfc6020bis].

   JSON processing is rather different from XML, and JSON parsers may
   thus suffer from other types of vulnerabilities than their XML
   counterparts.  To minimize these new security risks, software on the
   receiving side SHOULD reject all messages that do not comply to the
   rules of this document and reply with an appropriate error message to
   the sender.

9.  Acknowledgments

   The author wishes to thank Andy Bierman, Martin Bjorklund, Dean
   Bogdanovic, Balazs Lengyel, Juergen Schoenwaelder and Phil Shafer for
   their helpful comments and suggestions.

10.  References

10.1.  Normative References

   [I-D.ietf-netmod-rfc6020bis]
              Bjorklund, M., "YANG - A Data Modeling Language for the
              Network Configuration Protocol (NETCONF)", draft-ietf-
              netmod-rfc6020bis-05
              netmod-rfc6020bis-06 (work in progress), May July 2015.

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

   [RFC5234]  Crocker, D. D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/
              RFC5234, January 2008. 2008,
              <http://www.rfc-editor.org/info/rfc5234>.

   [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. 2011,
              <http://www.rfc-editor.org/info/rfc6241>.

   [RFC7159]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March 2014.
              2014, <http://www.rfc-editor.org/info/rfc7159>.

   [RFC7493]  Bray, T., Ed., "The I-JSON Message Format", RFC 7493, DOI
              10.17487/RFC7493, March
              2015.

   [W3C.REC-xml-20081126]
              Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and
              F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth
              Edition)", World Wide Web Consortium Recommendation REC-
              xml-20081126, November 2008,
              <http://www.w3.org/TR/2008/REC-xml-20081126>. 2015,
              <http://www.rfc-editor.org/info/rfc7493>.

10.2.  Informative References

   [I-D.ietf-netconf-restconf]
              Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", draft-ietf-netconf-restconf-05 draft-ietf-netconf-restconf-07 (work in
              progress), June July 2015.

   [RFC7223]  Bjorklund, M., "A YANG Data Model for Interface
              Management", RFC 7223, DOI 10.17487/RFC7223, May 2014.

   [W3C.REC-xpath-19991116]
              Clark, J. and S. DeRose, "XML Path 2014,
              <http://www.rfc-editor.org/info/rfc7223>.

   [W3C.REC-xml-20081126]
              Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and
              F. Yergeau, "Extensible Markup Language (XPath)
              Version 1.0", (XML) 1.0 (Fifth
              Edition)", World Wide Web Consortium Recommendation
              REC-xpath-19991116, REC-
              xml-20081126, November 1999,
              <http://www.w3.org/TR/1999/REC-xpath-19991116>. 2008,
              <http://www.w3.org/TR/2008/REC-xml-20081126>.

Appendix A.  A Complete Example

   The JSON document shown below represents the same data as the reply
   to the NETCONF <get> request appearing in Appendix D of [RFC7223].
   The data model is a combination of two YANG modules: "ietf-
   interfaces" and "ex-vlan" (the latter is an example module from
   Appendix C of [RFC7223]).  The "if-mib" feature defined in the "ietf-
   interfaces" module is considered to be active.

   {
     "ietf-interfaces:interfaces": {
       "interface": [
         {
           "name": "eth0",
           "type": "iana-if-type:ethernetCsmacd",
           "enabled": false
         },
         {
           "name": "eth1",
           "type": "iana-if-type:ethernetCsmacd",
           "enabled": true,
           "ex-vlan:vlan-tagging": true
         },
         {
           "name": "eth1.10",
           "type": "iana-if-type:l2vlan",
           "enabled": true,
           "ex-vlan:base-interface": "eth1",
           "ex-vlan:vlan-id": 10
         },
         {
           "name": "lo1",
           "type": "iana-if-type:softwareLoopback",
           "enabled": true
         }
       ]
     },
     "ietf-interfaces:interfaces-state": {
       "interface": [
         {
           "name": "eth0",
           "type": "iana-if-type:ethernetCsmacd",
           "admin-status": "down",
           "oper-status": "down",
           "if-index": 2,
           "phys-address": "00:01:02:03:04:05",
           "statistics": {
             "discontinuity-time": "2013-04-01T03:00:00+00:00"
           }
         },
         {
           "name": "eth1",
           "type": "iana-if-type:ethernetCsmacd",
           "admin-status": "up",
           "oper-status": "up",
           "if-index": 7,
           "phys-address": "00:01:02:03:04:06",
           "higher-layer-if": [
             "eth1.10"
           ],
           "statistics": {
             "discontinuity-time": "2013-04-01T03:00:00+00:00"
           }
         },
         {
           "name": "eth1.10",
           "type": "iana-if-type:l2vlan",
           "admin-status": "up",
           "oper-status": "up",
           "if-index": 9,
           "lower-layer-if": [
             "eth1"
           ],
           "statistics": {
             "discontinuity-time": "2013-04-01T03:00:00+00:00"
           }
         },
         {
           "name": "eth2",
           "type": "iana-if-type:ethernetCsmacd",
           "admin-status": "down",
           "oper-status": "down",
           "if-index": 8,
           "phys-address": "00:01:02:03:04:07",
           "statistics": {
             "discontinuity-time": "2013-04-01T03:00:00+00:00"
           }
         },
         {
           "name": "lo1",
           "type": "iana-if-type:softwareLoopback",
           "admin-status": "up",
           "oper-status": "up",
           "if-index": 1,
           "statistics": {
             "discontinuity-time": "2013-04-01T03:00:00+00:00"
           }
         }
       ]
     }
   }

Appendix B.  Change Log

   RFC Editor: Remove this section upon publication as an RFC.

B.1.  Changes Between Revisions -04 and -05

   o  Removed section "Validation of JSON-encoded Instance Data" and
      other text about XML-JSON mapping.

   o  Added section "Properties of the JSON Encoding".

B.2.  Changes Between Revisions -03 and -04

   o  I-D.ietf-netmod-rfc6020bis is used as a normative reference
      instead of RFC 6020.

   o  Removed noncharacters as an I-JSON issue because it doesn't exist
      in YANG 1.1.

   o  Section about anydata encoding was added.

   o  Require I-JSON for anyxml encoding.

   o  Use ABNF for defining qualified name.

B.2.

B.3.  Changes Between Revisions -02 and -03

   o  Namespace encoding is defined without using RFC 2119 keywords.

   o  Specification for anyxml nodes was extended and clarified.

   o  Text about ordering of list entries was corrected.

B.3.

B.4.  Changes Between Revisions -01 and -02

   o  Encoding of namespaces in instance-identifiers was changed.

   o  Text specifying the order of array elements in leaf-list and list
      instances was added.

B.4.

B.5.  Changes Between Revisions -00 and -01

   o  Metadata encoding was moved to a separate I-D, draft-lhotka-
      netmod-yang-metadata.

   o  JSON encoding is now defined directly rather than via XML-JSON
      mapping.

   o  The rules for namespace encoding has changed.  This affect both
      node instance names and instance-identifiers.

   o  I-JSON-related changes.  The most significant is the string
      encoding of 64-bit numbers.

   o  When validating union type, the partial type info present in JSON
      encoding is taken into account.

   o  Added section about I-JSON compliance.

   o  Updated the example in appendix.

   o  Wrote Security Considerations.

   o  Removed IANA Considerations as there are none.

Author's Address

   Ladislav Lhotka
   CZ.NIC

   Email: lhotka@nic.cz