CBOR Encoding of Data Modeled with YANGTrilliant Networks Inc.610 Rue du LuxembourgGranbyQuebecJ2J 2V2Canada+14503750556michel.veillette@trilliantinc.comAcklio2bis rue de la ChataigneraieCesson-SevigneBretagne35510Francea@ackl.ioTridonic GmbH & Co KGFarbergasse 15DornbirnVorarlberg6850Austria+43664808926169abhinav.somaraju@tridonic.comLandis+Gyr30000 Mill Creek AveSuite 100AlpharettaGA30022US++16782581292randy.turner@landisgyr.comhttp://www.landisgyr.com/Acklio2bis rue de la châtaigneraieCesson-SévignéBretagne35510Franceana@ackl.io
Applications and Real-Time Area (art)
Internet Engineering Task ForceCBORThis document defines encoding rules for serializing configuration data, state data, RPC input and RPC output, Action input, Action output and notifications defined within YANG modules using the Concise Binary Object Representation (CBOR) .The specification of the YANG 1.1 data modelling language defines only an XML encoding for data instances, i.e. contents of configuration datastores, state data, RPC inputs and outputs, action inputs and outputs, and event notifications.A new set of encoding rules has been defined to allow the use of the same data models in environments based on the JavaScript Object Notation (JSON) Data Interchange Format . This is accomplished in the JSON Encoding of Data Modeled with YANG specification .The aim of this document is to define a set of encoding rules for the Concise Binary Object Representation (CBOR) . The resulting encoding is more compact compared to XML and JSON and more suitable for Constrained Nodes and/or Constrained Networks as defined by .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 .The following terms are defined in :actionanydataanyxmldata nodedata treemodulenotificationRPCschema nodeschema treesubmoduleThe following terms are defined in :member namename of an identityThe following term is defined in :YANG hashThis specification also makes use of the following terminology:child: A schema node defined within a collection such as a container, a list, a case, a notification, an RPC input, an RPC output, an action input, an action output.delta : Difference between the SID assigned to the current schema node and the SID assigned to the parent.parent: The collection in which a schema node is defined.structured identifier or SID: Unsigned integer used to identify different YANG items.Within this document, CBOR binary contents are represented using an equivalent textual form called CBOR diagnostic notation as defined in section 6. This notation is used strictly for documentation purposes and is never used in the data serialization.CBOR contentCBOR typeDiagnostic notationExampleCBOR encodingUnsigned integer0Decimal digits12318 7bNegative integer1Decimal digits prefixed by a minus sign-12338 7aByte string2Hexadecimal value enclosed between single quotes and prefixed by an ‘h’h’f15c’42 f15cText string3String of Unicode characters enclosed between double quotes“txt”63 747874Array4Comma-separated list of values within square brackets[ 1, 2 ]82 01 02Map5Comma-separated list of key : value pairs within curly braces{ 1: 123, 2: 456 }a2 01187b 021901c8Boolean7/20falsefalsef47/21truetruef5Null7/22nullnullf6Not assigned7/23undefinedundefinedf7Within this document, comments are allowed in CBOR diagnostic notation. Any characters after a Pound sign (‘#’) outside of a string, up to the end of the line, are treated as a comment.This document defines CBOR encoding rules for YANG schema trees and their subtrees.Basic schema nodes such as leaf, leaf-list, list, anydata and anyxml can be encoded standalone. In this case, only the value of this schema node is encoded in CBOR. Identification of this value need to be provided by some external means when needed.A collection such as container, list instance, notification, RPC input, RPC output, action input and action output is serialized using a CBOR map in which each child schema node is encoded using a key and a value. This specification supports three type of keys; SID as defined in [I-D.somaraju-core-sid], member names as defined in and YANG hash as defined by . Each of these key type is encoded using a specific CBOR type which allows their interpretation during the deserialization process. The end user of this mapping specification can mandate the use of a specific key type or a specific subset of key types.In order to minimize the size of the encoded data, the proposed mapping does not make use of any meta-information beyond those natively supported by CBOR. For instance, CBOR tags are not used for any of the proposed mapping. It is expected that entities generating and decoding CBOR contents have enough knowledge about the information processed in order to perform the expected task without the need of such extra meta-information. The CoAP Content-Format Option, or an HTTP Content-Type header field, conveys that the data is YANG-encoded CBOR in the first place.Schema node instances defined using the YANG modeling language are encoded using CBOR based on the rules defined in this section. We assume that the reader is
already familiar with both YANG and CBOR .Leafs MUST be encoded based on the encoding rules specified in .Collections such as containers, list instances, notifications, RPC inputs, RPC outputs, action inputs and action outputs MUST be encoded using a CBOR map data item (major type 5). A map is comprised of pairs of data items, with each data item consisting of a key and a value. This specification supports three type of keys; SID as defined in [I-D.somaraju-core-sid], member names as defined in and YANG hash as defined by .SIDs as keysKeys implemented using SIDs MUST be encoded using a CBOR unsigned integer (major type 0) and set to the delta value of the associated SID. Delta values are computed as follows:The delta value is equal to the SID of the current schema node minus the SID of the parent schema node. When no parent exists in the context of use of this container, the delta is set to the SID of the current schema node (a parent with SID equal to zero is assumed).Delta values may result in a negative number, clients and servers MUST support negative deltas.Member names as keysKeys implemented using member names MUST be encoded using a CBOR text string data item (major type 3). A namespace-qualified member name MUST be used for all members of a top-level collection, and then also whenever the namespaces of the schema node and its parent are different. In all other cases, the simple form of the member name MUST be used. Member names and namespaces are defined in section 4.YANG hashes as keysKeys implemented using YANG hashes MUST be encoded using a CBOR byte string data item (major type 2).Values MUST be encoded using the appropriate rules defined in and .Definition example :SIDs exampleThis example is encoded using the SIDs defined in [I-D.somaraju-core-sid] Appendix C.CBOR diagnostic notation:CBOR encoding:Member names exampleCBOR diagnostic notation:CBOR encoding:YANG Hashes exampleCBOR diagnostic notation:CBOR encoding:A leaf-list MUST be encoded using a CBOR array data item (major type 4).
Each entry of this array MUST be encoded using the rules defined by the YANG type specified.Definition example :CBOR diagnostic notation: [ “ietf.org”, “ieee.org” ]CBOR encoding: 82 68 696574662e6f7267 68 696565652e6f7267A list MUST be encoded using a CBOR array data item (major type 4). Each entry of this array is encoded using a CBOR map data item (major type 5) based on the same rules as a YANG container, see .Definition example :SIDs exampleSIDs used in this example are defined in [I-D.somaraju-core-sid] Appendix C. It is important to note that the protocol or method using this mapping may carry a parent SID or may have the knowledge of this parent SID based on its context. In these cases, delta encoding can be performed based on this parent SID which minimizes the size of the encoded data.CBOR diagnostic notation:CBOR encoding:Member names exampleCBOR diagnostic notation:CBOR encoding:YANG hashes exampleCBOR diagnostic notation:CBOR encoding:An anydata serves as a container for an arbitrary set of schema nodes that otherwise appear as normal YANG-modeled data. An anydata instance is encoded using the same rules as a container, i.e., CBOR map. The requirement that anydata content can be modeled by YANG implies the following:Keys MUST be set to valid SIDs, member names or YANG hashes. This rule applies to the key of the anydata node and the key of any inner schema node.The CBOR array MUST contain either unique scalar values (as a leaf-list, see ), or maps (as a list, see ).Values MUST follow the encoding rules of one of the datatypes listed in .An anyxml instance is encoded as a CBOR key/value pair. The key of the anyxml schema node MUST be a valid SID, member name or YANG hash but the value is unrestricted, i.e., the value can be any CBOR encoded content.Leafs of type uint8, uint16, uint32 and uint64 MUST be encoded using a CBOR
unsigned integer data item (major type 0).Definition example :CBOR diagnostic notation: 1280CBOR encoding: 19 0500Leafs of type int8, int16, int32 and int64 MUST be encoded using either CBOR
unsigned integer (major type 0) or CBOR signed integer (major type 1), depending
on the actual value.Definition example :CBOR diagnostic notation: -300CBOR encoding: 39 012bLeafs of type decimal64 MUST be encoded using either CBOR unsigned integer
(major type 0) or CBOR signed integer (major type 1), depending on the actual
value. The position of the decimal point is defined by the fraction-digits YANG statement and is not available in the CBOR encoding.Definition example :CBOR diagnostic notation: 257 (Represents decimal value 2.57)CBOR encoding: 19 0101Leafs of type string MUST be encoded using a CBOR text string data item (major
type 3).Definition example :CBOR diagnostic notation: “eth0”CBOR encoding: 64 65746830Leafs of type boolean MUST be encoded using a CBOR true (major type 7, additional
information 21) or false data item (major type 7, additional information
20).Definition example :CBOR diagnostic notation: trueCBOR encoding: f5Leafs of type enumeration MUST be encoded using a CBOR unsigned integer data
item (major type 0).Definition example :CBOR diagnostic notation: 3 (Represents enumeration value “testing”)CBOR encoding: 03Leafs of type bits MUST be encoded using a CBOR byte string data item (major
type 2). Bits position 0 to 7 are assigned to the first byte within the byte
string, bits 8 to 15 to the second byte, and subsequent bytes are assigned
similarly. Within each byte, bits are assigned from least to most significant.Definition example :CBOR diagnostic notation: h’05’ (Represents bits disable-nagle and 10-Mb-only set)CBOR encoding: 41 05Leafs of type binary MUST be encoded using a CBOR byte string data item (major
type 2).Definition example:CBOR diagnostic notation: h’1f1ce6a3f42660d888d92a4d8030476e’CBOR encoding: 50 1f1ce6a3f42660d888d92a4d8030476eLeafs of type leafref MUST be encoded using the rules of the schema node referenced
by the “path” YANG statement.Definition example :CBOR diagnostic notation: “eth1”CBOR encoding: 64 65746831This specification supports two approaches for encoding identityref, a SID as defined in [I-D.somaraju-core-sid] or a name as defined in section 6.8.SIDs as identityrefSIDs are globally unique and may be used as identityref. This approach is both compact and simple to implement. When SIDs are used, identityref MUST be encoded using a CBOR unsigned integer data item (major type 0) and set to a SID allocated from a registered SID range.Name as identityrefAlternatively, an identityref may be encoded using a name as defined in section 6.8. When names are used, identityref MUST be encoded using a CBOR text string data item (major type 3). If the identity is defined in another module than the leaf node containing the identityref value, the namespace-qualified form MUST be used. Otherwise, both the simple and namespace-qualified forms are permitted.Definition example :SIDs as identityrefAssuming that the identity “iana-if-type:ethernetCsmacd” has been assigned to the SID value 1179.CBOR diagnostic notation: 1179CBOR encoding: 19 049bName as identityrefCBOR diagnostic notation: “iana-if-type:ethernetCsmacd”CBOR encoding: 78 1b 69616e612d69662d747970653a65746865726e657443736d616364Leafs of type empty MUST be encoded using the CBOR null value (major type
7, additional information 22).Definition example :CBOR diagnostic notation: nullCBOR encoding: f6Leafs of type union MUST be encoded using the rules associated with one of
the types listed.Definition example :CBOR diagnostic notation: “2001:db8:a0b:12f0::1”CBOR encoding: 74 323030313a6462383a6130623a313266303a3a31This specification supports three approaches for encoding an instance-identifier, one based on SIDs as defined in [I-D.somaraju-core-sid], one based on names as defined in section 6.13 and one based on YANG hashes as defined in .SIDs as instance-identifierSIDs uniquely identify a data node. For a single instance data node, the SID is sufficient to identify this instance. For a multi-instance data node, a SID is combined with the list key(s) to identify each instance of this data node within the YANG list(s).Single instance data nodes MUST be encoded using a CBOR unsigned integer data item (major type 0) and set to the targeted data node SID.Multi-instances data nodes MUST be encoded using a CBOR array data item (major type 4) containing the following entries:The first entry MUST be encoded as a CBOR unsigned integer data item (major type 0) and set to the targeted data node SID.The following entries MUST contain the value of each key required to identify the instance of the targeted data node. These keys MUST be ordered as defined in the “key” YANG statement, starting from top level list, and follow by each of the subordinate list(s).When SIDs identify a YANG list, the presence of the key(s) for this list is optional. When the key(s) are present, the targeted instance within this list is selected. When the key(s) are absent, the entire YANG list is selected.Names as instance-identifierThe use of names as instance-identifier is defined in section 6.11. The resulting xpath MUST be encoded using a CBOR text string data item (major type 3).YANG hashes as instance-identifierWhen YANG hashes are used, xpath can be compressed based on the method defined by sections 4.1.4.1 and 4.1.4.2.Definition example :First example based on SIDIn this example, a field of type instance-identifier identifies the data node “/system/contact” (SID 1728).CBOR encoding:First example based on nameSame example as above based on names.CBOR encoding:First example based on YANG hashSame example assuming data node “/system/contact” is associated to YANG hash 0x09b06d17 or “JsG0X” in base64.CBOR diagnostic notation:CBOR encoding:Definition example :Second example based on SIDIn this example, a field of type instance-identifier identify the data node “/system/authentication/user/authorized-key/key-data” (SID 1721) for the user name “bob” and the authorized-key name “admin”.CBOR diagnostic notation:CBOR encoding:Second example based on nameSame example as above based on names.CBOR diagnostic notation:CBOR encoding:Second example based on YANG hashSame example assuming data node “/ietf-system:system/authentication/user/authorized-key/key-data” is associated to YANG hash 0x0d6e7afb or “Nbnr7” in base64.CBOR diagnostic notation:CBOR encoding:Third example based on SIDThis third example identify an instance within the list “/system/authentication/user” (SID 1717) corresponding to the user name “jack”.CBOR diagnostic notation:CBOR encoding:Third example based on nameSame example as above based on names.CBOR diagnostic notation:CBOR encoding:Third example based on YANG hashSame example assuming data node “/ietf-system:system/authentication/user” is associated to YANG hash 0x2677c6c1 or “md8bB” in base64.CBOR diagnostic notation:CBOR encoding:The security considerations of and apply.This document defines an alternative encoding for data modeled in the YANG data modeling language. As such, this encoding does not contribute any new security issues in addition of those identified for the specific protocol or context for which it is used.To minimize 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.This document has been largely inspired by the extensive works done by Andy Bierman and Peter van der Stok on . has also been a critical input to this work. The authors would like to thank the authors and contributors to these two drafts.The authors would also like to acknowledge the review, feedback, and comments from Ladislav Lhotka and Juergen Schoenwaelder.The YANG 1.1 Data Modeling LanguageYANG is a data modeling language used to model configuration data, state data, remote procedure calls, and notifications for network management protocols like the Network Configuration Protocol (NETCONF).Key words for use in RFCs to Indicate Requirement LevelsIn many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.Concise Binary Object Representation (CBOR)The Concise Binary Object Representation (CBOR) is a data format whose design goals include the possibility of extremely small code size, fairly small message size, and extensibility without the need for version negotiation. These design goals make it different from earlier binary serializations such as ASN.1 and MessagePack.JSON Encoding of Data Modeled with YANGThis document defines encoding rules for representing configuration data, state data, parameters of RPC operations or actions, and notifications defined using YANG as JavaScript Object Notation (JSON) text.CoAP Management InterfaceThis document describes a network management interface for constrained devices, called CoMI. CoMI is an adaptation of the RESTCONF protocol for use in constrained devices and networks. The Constrained Application Protocol (CoAP) is used to access management data resources specified in YANG, or SMIv2 converted to YANG. CoMI use the YANG to CBOR mapping and encodes YANG names to reduce payload size. Note Discussion and suggestions for improvement are requested, and should be sent to core@ietf.org.The JavaScript Object Notation (JSON) Data Interchange FormatJavaScript Object Notation (JSON) is a lightweight, text-based, language-independent data interchange format. It was derived from the ECMAScript Programming Language Standard. JSON defines a small set of formatting rules for the portable representation of structured data.This document removes inconsistencies with other specifications of JSON, repairs specification errors, and offers experience-based interoperability guidance.A YANG Data Model for Interface ManagementThis document defines a YANG data model for the management of network interfaces. It is expected that interface-type-specific data models augment the generic interfaces data model defined in this document. The data model includes configuration data and state data (status information and counters for the collection of statistics).Terminology for Constrained-Node NetworksThe Internet Protocol Suite is increasingly used on small devices with severe constraints on power, memory, and processing resources, creating constrained-node networks. This document provides a number of basic terms that have been useful in the standardization work for constrained-node networks.A YANG Data Model for IP ManagementThis document defines a YANG data model for management of IP implementations. The data model includes configuration data and state data.A YANG Data Model for System ManagementThis document defines a YANG data model for the configuration and identification of some common system properties within a device containing a Network Configuration Protocol (NETCONF) server. This document also includes data node definitions for system identification, time-of-day management, user management, DNS resolver configuration, and some protocol operations for system management.