CoRE M. Veillette, Ed.
Internet-Draft Trilliant Networks Inc.
Intended status: Standards Track P. van der Stok, Ed.
Expires: January 10, 2020 consultant
A. Pelov
Acklio
A. Bierman
YumaWorks
I. Petrov, Ed.
Acklio
July 09, 2019
CoAP Management Interface
draft-ietf-core-comi-06
Abstract
This document describes a network management interface for
constrained devices and networks, called CoAP Management Interface
(CoMI). The Constrained Application Protocol (CoAP) is used to
access datastore and data node resources specified in YANG, or SMIv2
converted to YANG. CoMI uses the YANG to CBOR mapping and converts
YANG identifier strings to numeric identifiers for payload size
reduction. The complete solution composed of CoMI,
[I-D.ietf-core-yang-cbor] and [I-D.ietf-core-sid] is called CORECONF.
CORECONF extends the set of YANG based protocols, NETCONF and
RESTCONF, with the capability to manage constrained devices and
networks.
Note
Discussion and suggestions for improvement are requested, and should
be sent to yot@ietf.org.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 10, 2020.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. CoMI Architecture . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Major differences between RESTCONF and CoMI . . . . . . . 6
2.1.1. Differences due to CoAP and its efficient usage . . . 6
2.1.2. Differences due to the use of CBOR . . . . . . . . . 7
2.2. Compression of YANG identifiers . . . . . . . . . . . . . 7
2.3. Instance identifier . . . . . . . . . . . . . . . . . . . 8
2.4. Content-Formats . . . . . . . . . . . . . . . . . . . . . 8
2.5. Unified datastore . . . . . . . . . . . . . . . . . . . . 10
3. Example syntax . . . . . . . . . . . . . . . . . . . . . . . 11
4. CoAP Interface . . . . . . . . . . . . . . . . . . . . . . . 11
4.1. Using the 'k' Uri-Query option . . . . . . . . . . . . . 13
4.2. Data Retrieval . . . . . . . . . . . . . . . . . . . . . 14
4.2.1. Using the 'c' Uri-Query option . . . . . . . . . . . 14
4.2.2. Using the 'd' Uri-Query option . . . . . . . . . . . 15
4.2.3. GET . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.2.4. FETCH . . . . . . . . . . . . . . . . . . . . . . . . 18
4.3. Data Editing . . . . . . . . . . . . . . . . . . . . . . 19
4.3.1. Data Ordering . . . . . . . . . . . . . . . . . . . . 19
4.3.2. POST . . . . . . . . . . . . . . . . . . . . . . . . 19
4.3.3. PUT . . . . . . . . . . . . . . . . . . . . . . . . . 20
4.3.4. iPATCH . . . . . . . . . . . . . . . . . . . . . . . 21
4.3.5. DELETE . . . . . . . . . . . . . . . . . . . . . . . 22
4.4. Full datastore access . . . . . . . . . . . . . . . . . . 23
4.4.1. Full datastore examples . . . . . . . . . . . . . . . 23
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4.5. Event stream . . . . . . . . . . . . . . . . . . . . . . 24
4.5.1. Notify Examples . . . . . . . . . . . . . . . . . . . 25
4.5.2. The 'f' Uri-Query option . . . . . . . . . . . . . . 26
4.6. RPC statements . . . . . . . . . . . . . . . . . . . . . 27
4.6.1. RPC Example . . . . . . . . . . . . . . . . . . . . . 27
5. Use of Block-wise Transfers . . . . . . . . . . . . . . . . . 29
6. Application Discovery . . . . . . . . . . . . . . . . . . . . 29
6.1. YANG library . . . . . . . . . . . . . . . . . . . . . . 29
6.2. Resource Discovery . . . . . . . . . . . . . . . . . . . 30
6.2.1. Datastore Resource Discovery . . . . . . . . . . . . 30
6.2.2. Data node Resource Discovery . . . . . . . . . . . . 30
6.2.3. Event stream Resource Discovery . . . . . . . . . . . 31
7. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 31
8. Security Considerations . . . . . . . . . . . . . . . . . . . 35
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35
9.1. Resource Type (rt=) Link Target Attribute Values Registry 35
9.2. CoAP Content-Formats Registry . . . . . . . . . . . . . . 36
9.3. Media Types Registry . . . . . . . . . . . . . . . . . . 36
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 38
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 38
11.1. Normative References . . . . . . . . . . . . . . . . . . 38
11.2. Informative References . . . . . . . . . . . . . . . . . 40
Appendix A. ietf-comi YANG module . . . . . . . . . . . . . . . 40
Appendix B. ietf-comi .sid file . . . . . . . . . . . . . . . . 46
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 49
1. Introduction
The Constrained Application Protocol (CoAP) [RFC7252] is designed for
Machine to Machine (M2M) applications such as smart energy, smart
city and building control. Constrained devices need to be managed in
an automatic fashion to handle the large quantities of devices that
are expected in future installations. Messages between devices need
to be as small and infrequent as possible. The implementation
complexity and runtime resources need to be as small as possible.
This draft describes the CoAP Management Interface which uses CoAP
methods to access structured data defined in YANG [RFC7950]. This
draft is complementary to [RFC8040] which describes a REST-like
interface called RESTCONF, which uses HTTP methods to access
structured data defined in YANG.
The use of standardized data models specified in a standardized
language, such as YANG, promotes interoperability between devices and
applications from different manufacturers.
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CoMI and RESTCONF are intended to work in a stateless client-server
fashion. They use a single round-trip to complete a single editing
transaction, where NETCONF needs multiple round trips.
To promote small messges, CORECONF uses a YANG to CBOR mapping
[I-D.ietf-core-yang-cbor] and numeric identifiers [I-D.ietf-core-sid]
to minimize CBOR payloads and URI length.
1.1. 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.
The following terms are defined in the YANG data modelling language
[RFC7950]: action, anydata, anyxml, client, container, data model,
data node, identity, instance identifier, leaf, leaf-list, list,
module, RPC, schema node, server, submodule.
The following terms are defined in [RFC6241]: configuration data,
datastore, state data
The following term is defined in [I-D.ietf-core-sid]: YANG schema
item identifier (SID).
The following terms are defined in the CoAP protocol [RFC7252]:
Confirmable Message, Content-Format, Endpoint.
The following terms are defined in this document:
data node resource: a CoAP resource that models a YANG data node.
datastore resource: a CoAP resource that models a YANG datastore.
event stream resource: a CoAP resource used by clients to observe
YANG notifications.
notification instance: An instance of a schema node of type
notification, specified in a YANG module implemented by the
server. The instance is generated in the server at the occurrence
of the corresponding event and reported by an event stream.
list instance identifier: Handle used to identify a YANG data node
that is an instance of a YANG "list" specified with the values of
the key leaves of the list.
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single instance identifier: Handle used to identify a specific data
node which can be instantiated only once. This includes data
nodes defined at the root of a YANG module and data nodes defined
within a container. This excludes data nodes defined within a
list or any children of these data nodes.
instance-identifier: List instance identifier or single instance
identifier.
instance-value: The value assigned to a schema node instance.
Schema node values are serialized into the payload according to
the rules defined in section 4 of [I-D.ietf-core-yang-cbor].
2. CoMI Architecture
This section describes the CoMI architecture to use CoAP for reading
and modifying the content of datastore(s) used for the management of
the instrumented node.
+----------------------------------------------------------------+
| SMIv2 specification (optional) (2) |
+----------------------------------------------------------------+
|
V
+----------------------------------------------------------------+
| YANG specification (1) |
+----------------------------------------------------------------+
| |
Client V Server V
+----------------+ +-----------------------+
| Request |--> CoAP request(3) -->| Indication |
| Confirm |<-- CoAP response(3)<--| Response (4) |
| | | |
| |<==== Security (7) ===>|+---------------------+|
+----------------+ || Datastore(s) (5) ||
|+---------------------+|
|+---------------------+|
|| Event stream(s) (6) ||
|+---------------------+|
+-----------------------+
Figure 1: Abstract CoMI architecture
Figure 1 is a high-level representation of the main elements of the
CoMI management architecture. The different numbered components of
Figure 1 are discussed according to component number.
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(1) YANG specification: contains a set of named and versioned
modules.
(2) SMIv2 specification: Optional part that consists of a named
module which, specifies a set of variables and "conceptual
tables". There is an algorithm to translate SMIv2 specifications
to YANG specifications.
(3) CoAP request/response messages: The CoMI client sends request
messages to and receives response messages from the CoMI server.
(4) Request, Indication, Response, Confirm: Processes performed by
the CoMI clients and servers.
(5) Datastore: A resource used to access configuration data, state
data, RPCs and actions. A CoMI server may support a single
unified datastore or multiple datastores as those defined by
Network Management Datastore Architecture (NMDA) [RFC8342].
(6) Event stream: A resource used to get real time notifications. A
CoMI server may support multiple Event streams serving different
purposes such as normal monitoring, diagnostic, syslog, security
monitoring.
(7) Security: The server MUST prevent unauthorized users from
reading or writing any CoMI resources. CoMI relies on security
protocols such as DTLS [RFC6347] to secure CoAP communications.
2.1. Major differences between RESTCONF and CoMI
CoMI is a RESTful protocol for small devices where saving bytes to
transport counts. Contrary to RESTCONF, many design decisions are
motivated by the saving of bytes. Consequently, CoMI is not a
RESTCONF over CoAP protocol, but differs more significantly from
RESTCONF.
2.1.1. Differences due to CoAP and its efficient usage
o CoMI uses CoAP/UDP as transport protocol and CBOR as payload
format [I-D.ietf-core-yang-cbor]. RESTCONF uses HTTP/TCP as
transport protocol and JSON or XML as payload formats.
o CoMI uses the methods FETCH and iPATCH to access multiple data
nodes. RESTCONF uses instead the HTTP method PATCH and the HTTP
method GET with the "fields" Query parameter.
o RESTCONF uses the HTTP methods HEAD, and OPTIONS, which are not
supported by CoAP.
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o CoMI does not support "insert" query parameter (first, last,
before, after) and the "point" query parameter which are supported
by RESTCONF.
o CoMI does not support the "start-time" and "stop-time" query
parameters to retrieve past notifications.
o CoMI does not support the "filter" query parameters to observe a
specific set of notifications.
2.1.2. Differences due to the use of CBOR
o CoMI encodes YANG identifier strings as numbers, where RESTCONF
does not.
o CoMI also differ in the handling of default values, only 'report-
all' and 'trip' options are supported.
2.2. Compression of YANG identifiers
In the YANG specification, items are identified with a name string.
In order to significantly reduce the size of identifiers used in
CoMI, numeric identifiers are used instead of these strings. YANG
Schema Item iDentifier (SID) is defined in [I-D.ietf-core-yang-cbor]
section 2.1.
When used in a URI, SIDs are encoded in base64 using the URL and
Filename safe alphabet as defined by [RFC4648] section 5, without
padding. The last 6 bits encoded is always aligned with the least
significant 6 bits of the SID represented using an unsigned integer.
'A' characters (value 0) at the start of the resulting string are
removed.
SID in base64 = URLsafeChar[SID >> 60 & 0x3F] |
URLsafeChar[SID >> 54 & 0x3F] |
URLsafeChar[SID >> 48 & 0x3F] |
URLsafeChar[SID >> 42 & 0x3F] |
URLsafeChar[SID >> 36 & 0x3F] |
URLsafeChar[SID >> 30 & 0x3F] |
URLsafeChar[SID >> 24 & 0x3F] |
URLsafeChar[SID >> 18 & 0x3F] |
URLsafeChar[SID >> 12 & 0x3F] |
URLsafeChar[SID >> 6 & 0x3F] |
URLsafeChar[SID & 0x3F]
For example, SID 1721 is encoded as follow.
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URLsafeChar[1721 >> 60 & 0x3F] = URLsafeChar[0] = 'A'
URLsafeChar[1721 >> 54 & 0x3F] = URLsafeChar[0] = 'A'
URLsafeChar[1721 >> 48 & 0x3F] = URLsafeChar[0] = 'A'
URLsafeChar[1721 >> 42 & 0x3F] = URLsafeChar[0] = 'A'
URLsafeChar[1721 >> 36 & 0x3F] = URLsafeChar[0] = 'A'
URLsafeChar[1721 >> 30 & 0x3F] = URLsafeChar[0] = 'A'
URLsafeChar[1721 >> 24 & 0x3F] = URLsafeChar[0] = 'A'
URLsafeChar[1721 >> 18 & 0x3F] = URLsafeChar[0] = 'A'
URLsafeChar[1721 >> 12 & 0x3F] = URLsafeChar[0] = 'A'
URLsafeChar[1721 >> 6 & 0x3F] = URLsafeChar[26] = 'a'
URLsafeChar[1721 & 0x3F] = URLsafeChar[57] = '5'
The resulting base64 representation of SID 1721 is "a5"
2.3. Instance identifier
Instance identifiers are used to uniquely identify data node
instances within a datastore. This YANG built-in type is defined in
[RFC7950] section 9.13. An instance identifier is composed of the
data node identifier (i.e. a SID) and for data nodes within list(s)
the keys used to index within these list(s).
When part of a payload, instance identifiers are encoded in CBOR
based on the rules defined in [I-D.ietf-core-yang-cbor] section
6.13.1. When part of a URI, the SID is appended to the URI of the
targeted datastore, the keys are specified using the 'k' URI-Query as
defined in Section 4.1.
2.4. Content-Formats
CoMI uses Content-Formats based on the YANG to CBOR mapping specified
in [I-D.ietf-core-yang-cbor].
The following Content-formats are defined:
application/yang-data+cbor: This Content-Format represents a CBOR
YANG document containing one or multiple data node values. Each
data node is identified by its associated SID.
FORMAT: CBOR map of SID, instance-value
The message payload of Content-Format 'application/yang-data+cbor'
is encoded using a CBOR map. Each entry of this CBOR map is
composed of a key and a value. CBOR map keys are set to the SID
or SID deltas associated with the data nodes as defined in
[I-D.ietf-core-yang-cbor] section 4, CBOR map values are set to
the instance value as defined in [I-D.ietf-core-yang-cbor] section
4.
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application/yang-identifiers+cbor: This Content-Format represents a
CBOR YANG document containing a list of instance identifier used
to target specific data node instances within a datastore.
FORMAT: CBOR array of instance-identifier
The message payload of Content-Format 'application/yang-
identifiers+cbor' is encoded using a CBOR array. Each entry of
this CBOR array contain an instance identifier encoded as defined
in [I-D.ietf-core-yang-cbor] section 6.13.1.
application/yang-instances+cbor: This Content-Format represents a
CBOR YANG document containing a list of data node instances. Each
data node instance is identified by its associated instance
identifier.
FORMAT: CBOR array of CBOR map of instance-identifier, instance-
value
The message payload of Content-Format 'application/yang-
instances+cbor' is encoded using a CBOR array. Each entry within
this CBOR array contains a CBOR map carrying an instance
identifier and associated instance value. Instance identifiers
are encoded using the rules defined in [I-D.ietf-core-yang-cbor]
section 6.13.1, values are encoded using the rules defined in
[I-D.ietf-core-yang-cbor] section 4.
When present in an iPATCH request payload, this Content-Format
carry a list of data node instances to be replaced, created, or
deleted. For each data node instance D, for which the instance
identifier is the same as a data node instance I, in the targeted
datastore resource: the value of D replaces the value of I. When
the value of D is null, the data node instance I is removed. When
the targeted datastore resource does not contain a data node
instance with the same instance identifier as D, a new instance is
created with the same instance identifier and value as D.
The different Content-format usages are summarized in the table
below:
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+---------------+--------------+------------------------------------+
| Method | Resource | Content-Format |
+---------------+--------------+------------------------------------+
| GET response | data node | /application/yang-data+cbor |
| | | |
| PUT request | data node | /application/yang-data+cbor |
| | | |
| POST request | data node | /application/yang-data+cbor |
| | | |
| DELETE | data node | n/a |
| | | |
| GET response | datastore | /application/yang-data+cbor |
| | | |
| PUT request | datastore | /application/yang-data+cbor |
| | | |
| POST request | datastore | /application/yang-data+cbor |
| | | |
| FETCH request | datastore | /application/yang-identifiers+cbor |
| | | |
| FETCH | datastore | /application/yang-instances+cbor |
| response | | |
| | | |
| iPATCH | datastore | /application/yang-instances+cbor |
| request | | |
| | | |
| GET response | event stream | /application/yang-instances+cbor |
| | | |
| POST request | rpc, action | /application/yang-data+cbor |
| | | |
| POST response | rpc, action | /application/yang-data+cbor |
+---------------+--------------+------------------------------------+
2.5. Unified datastore
CoMI supports a simple datastore model consisting of a single unified
datastore. This datastore provides access to both configuration and
operational data. Configuration updates performed on this datastore
are reflected immediately or with a minimal delay as operational
data.
Alternatively, CoMI servers MAY implement a more complex datastore
model such as the Network Management Datastore Architecture (NMDA) as
defined by [RFC8342]. Each datastore supported is implemented as a
datastore resource.
Characteristics of the unified datastore are summarized in the table
below:
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+-------------+-----------------------------------------------------+
| Name | Value |
+-------------+-----------------------------------------------------+
| Name | unified |
| | |
| YANG | all modules |
| modules | |
| | |
| YANG nodes | all data nodes ("config true" and "config false") |
| | |
| Access | read-write |
| | |
| How applied | changes applied in place immediately or with a |
| | minimal delay |
| | |
| Protocols | CORECONF |
| | |
| Defined in | "ietf-comi" |
+-------------+-----------------------------------------------------+
3. Example syntax
CBOR is used to encode CoMI request and response payloads. The CBOR
syntax of the YANG payloads is specified in [RFC7049]. The payload
examples are notated in Diagnostic notation (defined in section 6 of
[RFC7049]) that can be automatically converted to CBOR.
SIDs in URIs are represented as a base64 number, SIDs in the payload
are represented as decimal numbers.
4. CoAP Interface
This note specifies a Management Interface. CoAP endpoints that
implement the CoMI management protocol, support at least one
discoverable management resource of resource type (rt): core.c.ds,
with example path: /c, where c is short-hand for CoMI. The path /c
is recommended, but not compulsory (see Section 6).
The mapping of YANG data node instances to CoMI resources is as
follows. Every data node of the YANG modules loaded in the CoMI
server represents a sub-resource of the datastore resource (e.g. /c/
sid). When multiple instances of a list exist, instance selection is
possible as described in Section 4.1, Section 4.2.3.1, and
Section 4.2.4.
CoMI also supports event stream resources used to observe
notification instances. Event stream resources can be discovered
using resource type (rt): core.c.ev.
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The description of the CoMI management interface is shown in the
table below:
+-------------+------------------+-----------+
| Function | Recommended path | rt |
+-------------+------------------+-----------+
| Datastore | /c | core.c.ds |
| | | |
| Data node | /c/SID | core.c.dn |
| | | |
| Event steam | /s | core.c.ev |
+-------------+------------------+-----------+
The path values in the table are the recommended ones. On discovery,
the server makes the actual path values known for these resources.
The methods used by CoMI are:
+-----------+-------------------------------------------------------+
| Operation | Description |
+-----------+-------------------------------------------------------+
| GET | Retrieve the datastore resource or a data node |
| | resource |
| | |
| FETCH | Retrieve specific data nodes within a datastore |
| | resource |
| | |
| POST | Create a datastore resource or a data node resource, |
| | invoke an RPC or action |
| | |
| PUT | Create or replace a datastore resource or a data node |
| | resource |
| | |
| iPATCH | Idem-potently create, replace, and delete data node |
| | resource(s) within a datastore resource |
| | |
| DELETE | Delete a datastore resource or a data node resource |
+-----------+-------------------------------------------------------+
There is one Uri-Query option for the GET, PUT, POST, and DELETE
methods.
+------------------+----------------------------------------+
| Uri-Query option | Description |
+------------------+----------------------------------------+
| k | Select an instance within YANG list(s) |
+------------------+----------------------------------------+
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This parameter is not used for FETCH and iPATCH, because their
request payloads support list instance selection.
4.1. Using the 'k' Uri-Query option
The "k" (key) parameter specifies a specific instance of a data node.
The SID in the URI is followed by the (?k=key1,key2,...). Where SID
identifies a data node, and key1, key2 are the values of the key
leaves that specify an instance. Lists can have multiple keys, and
lists can be part of lists. The order of key value generation is
given recursively by:
o For a given list, if a parent data node is a list, generate the
keys for the parent list first.
o For a given list, generate key values in the order specified in
the YANG module.
Key values are encoded using the rules defined in the following
table.
+-----------------------------+--------------------------------+
| YANG datatype | Uri-Query text content |
+-----------------------------+--------------------------------+
| uint8,uint16,unit32, uint64 | int2str(key) |
| | |
| int8, int16,int32, int64 | urlSafeBase64(CBORencode(key)) |
| | |
| decimal64 | urlSafeBase64(CBOR key) |
| | |
| string | key |
| | |
| boolean | "0" or "1" |
| | |
| enumeration | int2str(key) |
| | |
| bits | urlSafeBase64(CBORencode(key)) |
| | |
| binary | urlSafeBase64(key) |
| | |
| identityref | int2str(key) |
| | |
| union | urlSafeBase64(CBORencode(key)) |
| | |
| instance-identifier | urlSafeBase64(CBORencode(key)) |
+-----------------------------+--------------------------------+
In this table:
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o The method int2str() is used to convert an integer value to a
decimal string. For example, int2str(0x0123) return the string
"291".
o The method urlSafeBase64() is used to convert a binary string to
base64 using the URL and Filename safe alphabet as defined by
[RFC4648] section 5, without padding. For example,
urlSafeBase64(\xF9\x56\xA1\x3C) return the string "-VahPA".
o The method CBORencode() is used to convert a YANG value to CBOR as
specified in [I-D.ietf-core-yang-cbor] section 6.
The resulting key string is encoded in a Uri-Query as specified in
[RFC7252] section 6.5.
4.2. Data Retrieval
One or more data nodes can be retrieved by the client. The operation
is mapped to the GET method defined in section 5.8.1 of [RFC7252] and
to the FETCH method defined in section 2 of [RFC8132].
There are two additional Uri-Query options for the GET and FETCH
methods.
+-------------+-----------------------------------------------------+
| Uri-Query | Description |
| option | |
+-------------+-----------------------------------------------------+
| c | Control selection of configuration and non- |
| | configuration data nodes (GET and FETCH) |
| | |
| d | Control retrieval of default values. |
+-------------+-----------------------------------------------------+
4.2.1. Using the 'c' Uri-Query option
The 'c' (content) option controls how descendant nodes of the
requested data nodes will be processed in the reply.
The allowed values are:
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+-------+-----------------------------------------------------+
| Value | Description |
+-------+-----------------------------------------------------+
| c | Return only configuration descendant data nodes |
| | |
| n | Return only non-configuration descendant data nodes |
| | |
| a | Return all descendant data nodes |
+-------+-----------------------------------------------------+
This option is only allowed for GET and FETCH methods on datastore
and data node resources. A 4.02 (Bad Option) error is returned if
used for other methods or resource types.
If this Uri-Query option is not present, the default value is "a".
4.2.2. Using the 'd' Uri-Query option
The "d" (with-defaults) option controls how the default values of the
descendant nodes of the requested data nodes will be processed.
The allowed values are:
+-------+-----------------------------------------------------------+
| Value | Description |
+-------+-----------------------------------------------------------+
| a | All data nodes are reported. Defined as 'report-all' in |
| | section 3.1 of [RFC6243]. |
| | |
| t | Data nodes set to the YANG default are not reported. |
| | Defined as 'trim' in section 3.2 of [RFC6243]. |
+-------+-----------------------------------------------------------+
If the target of a GET or FETCH method is a data node that represents
a leaf that has a default value, and the leaf has not been given a
value by any client yet, the server MUST return the default value of
the leaf.
If the target of a GET method is a data node that represents a
container or list that has child resources with default values, and
these have not been given value yet,
The server MUST NOT return the child resource if d= 't'
The server MUST return the child resource if d= 'a'.
If this Uri-Query option is not present, the default value is 't'.
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4.2.3. GET
A request to read the values of a data node instance is sent with a
CoAP GET message. A base64-encoded instance-identifier in SID-form
is specified in the URI path prefixed with the example path /c.
FORMAT:
GET /c/instance-identifier
2.05 Content (Content-Format: application/yang-data+cbor)
CBOR map of SID, instance-value
The returned payload contains the CBOR encoding of the specified data
node instance value.
4.2.3.1. GET Examples
Using for example the current-datetime leaf from module ietf-system
[RFC7317], a request is sent to retrieve the value of 'system-
state/clock/current-datetime' specified in container system-state.
The SID of 'system-state/clock/current-datetime' is 1723, encoded in
base64 according to Section 2.2, yields a7. The response to the
request returns the CBOR map with the key set to the SID of the
requested data node (i.e. 1723) and the value encoded using a 'text
string' as defined in [I-D.ietf-core-yang-cbor] section 6.4.
REQ: GET example.com/c/a7
RES: 2.05 Content (Content-Format: application/yang-data+cbor)
{
1723 : "2014-10-26T12:16:31Z"
}
The next example represents the retrieval of a YANG container. In
this case, the CoMI client performs a GET request on the clock
container (SID = 1721; base64: a5). The container returned is
encoded using a CBOR map as specified by [I-D.ietf-core-yang-cbor]
section 4.2.
REQ: GET example.com/c/a5
RES: 2.05 Content (Content-Format: application/yang-data+cbor)
{
1721 : {
+2 : "2014-10-26T12:16:51Z", / current-datetime SID 1723 /
+1 : "2014-10-21T03:00:00Z" / boot-datetime SID 1722 /
}
}
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This example shows the retrieval of the /interfaces/interface YANG
list accessed using SID 1533 (base64: X9). The return payload is
encoded using a CBOR array as specified by [I-D.ietf-core-yang-cbor]
section 4.4.1 containing 2 instances.
REQ: GET example.com/c/X9
RES: 2.05 Content (Content-Format: application/yang-data+cbor)
{
1533 : [
{
+4 : "eth0", / name (SID 1537) /
+1 : "Ethernet adaptor", / description (SID 1534) /
+5 : 1880, / type, (SID 1538) identity /
/ ethernetCsmacd (SID 1880) /
+2 : true / enabled ( SID 1535) /
},
{
+4 : "eth1", / name (SID 1537) /
+1 : "Ethernet adaptor", / description (SID 1534) /
+5 : 1880, / type, (SID 1538) identity /
/ ethernetCsmacd (SID 1880) /
+2 : false / enabled ( SID 1535) /
}
]
}
To retrieve a specific instance within the /interfaces/interface YANG
list, the CoMI client adds the key of the targeted instance in its
CoAP request using the 'k' URI-Query. The return payload containing
the instance requested is encoded using a CBOR array as specified by
[I-D.ietf-core-yang-cbor] section 4.4.1.
REQ: GET example.com/c/X9?k="eth0"
RES: 2.05 Content (Content-Format: application/yang-data+cbor)
{
1533 : [
{
+4 : "eth0", / name (SID 1537) /
+1 : "Ethernet adaptor", / description (SID 1534) /
+5 : 1880, / type, (SID 1538) identity /
/ ethernetCsmacd (SID 1880) /
+2 : true / enabled ( SID 1535) /
}
]
}
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It is equally possible to select a leaf of a specific instance of a
list. The example below requests the description leaf (SID=1534,
base64: X-) within the interface list corresponding to the interface
name "eth0". The returned value is encoded in CBOR based on the
rules specified by [I-D.ietf-core-yang-cbor] section 6.4.
REQ: GET example.com/c/X-?k="eth0"
RES: 2.05 Content (Content-Format: application/yang-data+cbor)
{
1534 : "Ethernet adaptor"
}
4.2.4. FETCH
The FETCH is used to retrieve multiple data node instance values.
The FETCH request payload contains the list of instance identifier of
the data node instances requested.
The return response payload contains a list of data node instance
values in the same order as requested. A CBOR null is returned for
each data node requested by the client, not supported by the server
or not currently instantiated.
For compactness, indexes of the list instance identifiers returned by
the FETCH response SHOULD be elided, only the SID is provided. In
this case, the format of each entry within the CBOR array of the
FETCH response is identical to the format as a GET response.
FORMAT:
FETCH /c (Content-Format: application/yang-identifiers+cbor)
CBOR array of instance-identifier
2.05 Content (Content-Format: application/yang-instances+cbor)
CBOR array of CBOR map of instance-identifier, instance-value
4.2.4.1. FETCH examples
This example uses the current-datetime leaf from module ietf-system
[RFC7317] and the interface list from module ietf-interfaces
[RFC7223]. In this example the value of current-datetime (SID 1723)
and the interface list (SID 1533) instance identified with
name="eth0" are queried.
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REQ: FETCH /c (Content-Format: application/yang-identifiers+cbor)
[
1723, / current-datetime (SID 1723) /
[1533, "eth0"] / interface (SID 1533) with name = "eth0" /
]
RES: 2.05 Content (Content-Format: application/yang-instances+cbor)
[
{
1723 : "2014-10-26T12:16:31Z" / current-datetime (SID 1723) /
},
{
1533 : {
+4 : "eth0", / name (SID 1537) /
+1 : "Ethernet adaptor", / description (SID 1534) /
+5 : 1880, / type (SID 1538), identity /
/ ethernetCsmacd (SID 1880) /
+2 : true / enabled (SID 1535) /
}
}
]
4.3. Data Editing
CoMI allows datastore contents to be created, modified and deleted
using CoAP methods.
4.3.1. Data Ordering
A CoMI server SHOULD preserve the relative order of all user-ordered
list and leaf-list entries that are received in a single edit
request. These YANG data node types are encoded as CBOR arrays so
messages will preserve their order.
4.3.2. POST
The CoAP POST operation is used in CoMI for creation of data node
resources and the invocation of "ACTION" and "RPC" resources. Refer
to Section 4.6 for details on "ACTION" and "RPC" resources.
A request to create a data node resource is sent with a CoAP POST
message. The URI specifies the data node to be instantiated at the
exception of list instances. In this case, for compactness, the URI
specifies the list for which an instance is created.
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FORMAT:
POST /c/<instance identifier>
(Content-Format: application/yang-data+cbor)
CBOR map of SID, instance-value
2.01 Created
If the data node resource already exists, then the POST request MUST
fail and a "4.09 Conflict" response code MUST be returned
4.3.2.1. Post example
The example uses the interface list from module ietf-interfaces
[RFC7223]. This example creates a new list instance within the
interface list (SID = 1533):
REQ: POST /c/X9 (Content-Format: application/yang-data+cbor)
{
1533 : [
{
+4 : "eth5", / name (SID 1537) /
+1 : "Ethernet adaptor", / description (SID 1534) /
+5 : 1880, / type (SID 1538), identity /
/ ethernetCsmacd (SID 1880) /
+2 : true / enabled (SID 1535) /
}
]
}
RES: 2.01 Created
4.3.3. PUT
A data node resource instance is created or replaced with the PUT
method. A request to set the value of a data node instance is sent
with a CoAP PUT message.
FORMAT:
PUT /c/<instanceidentifier>
(Content-Format: application/yang-data+cbor)
CBOR map of SID, instance-value
2.01 Created
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4.3.3.1. PUT example
The example uses the interface list from module ietf-interfaces
[RFC7223]. Example updates the instance of the list interface (SID =
1533) with key name="eth0":
REQ: PUT /c/X9?k="eth0" (Content-Format: application/yang-data+cbor)
{
1533 : [
{
+4 : "eth0", / name (SID 1537) /
+1 : "Ethernet adaptor", / description (SID 1534) /
+5 : 1880, / type (SID 1538), identity /
/ ethernetCsmacd (SID 1880) /
+2 : true / enabled (SID 1535) /
}
]
}
RES: 2.04 Changed
4.3.4. iPATCH
One or multiple data node instances are replaced with the idempotent
CoAP iPATCH method [RFC8132].
There are no Uri-Query options for the iPATCH method.
The processing of the iPATCH command is specified by Content-Format
'application/yang-instances+cbor'. In summary, if the CBOR patch
payload contains a data node instance that is not present in the
target, this instance is added. If the target contains the specified
instance, the content of this instance is replaced with the value of
the payload. A null value indicates the removal of an existing data
node instance.
FORMAT:
iPATCH /c (Content-Format: application/yang-instances+cbor)
CBOR array of CBOR map of instance-identifier, instance-value
2.04 Changed
4.3.4.1. iPATCH example
In this example, a CoMI client requests the following operations:
o Set "/system/ntp/enabled" (SID 1755) to true.
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o Remove the server "tac.nrc.ca" from the "/system/ntp/server" (SID
1756) list.
o Add/set the server "NTP Pool server 2" to the list "/system/ntp/
server" (SID 1756).
REQ: iPATCH /c (Content-Format: application/yang-instances+cbor)
[
{
1755 : true / enabled (SID 1755) /
},
{
[1756, "tac.nrc.ca"] : null / server (SID 1756) /
},
{
1756 : { / server (SID 1756) /
+3 : "tic.nrc.ca", / name (SID 1759) /
+4 : true, / prefer (SID 1760) /
+5 : { / udp (SID 1761) /
+1 : "132.246.11.231" / address (SID 1762) /
}
}
}
]
RES: 2.04 Changed
4.3.5. DELETE
A data node resource is deleted with the DELETE method.
FORMAT:
Delete /c/<instance identifier>
2.02 Deleted
4.3.5.1. DELETE example
This example uses the interface list from module ietf-interfaces
[RFC7223]. This example deletes an instance of the interface list
(SID = 1533):
REQ: DELETE /c/X9?k="eth0"
RES: 2.02 Deleted
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4.4. Full datastore access
The methods GET, PUT, POST, and DELETE can be used to request,
replace, create, and delete a whole datastore respectively.
FORMAT:
GET /c
2.05 Content (Content-Format: application/yang-data+cbor)
CBOR map of SID, instance-value
FORMAT:
PUT /c (Content-Format: application/yang-data+cbor)
CBOR map of SID, instance-value
2.04 Changed
FORMAT:
POST /c (Content-Format: application/yang-data+cbor)
CBOR map of SID, instance-value
2.01 Created
FORMAT:
DELETE /c
2.02 Deleted
The content of the CBOR map represents the complete datastore of the
server at the GET indication of after a successful processing of a
PUT or POST request.
4.4.1. Full datastore examples
The example uses the interface list from module ietf-interfaces
[RFC7223] and the clock container from module ietf-system [RFC7317].
We assume that the datastore contains two modules ietf-system (SID
1700) and ietf-interfaces (SID 1500); they contain the 'interface'
list (SID 1533) with one instance and the 'clock' container (SID
1721). After invocation of GET, a CBOR map with data nodes from
these two modules is returned:
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REQ: GET /c
RES: 2.05 Content (Content-Format: application/yang-data+cbor)
{
1721 : { / Clock (SID 1721) /
+2: "2016-10-26T12:16:31Z", / current-datetime (SID 1723) /
+1: "2014-10-05T09:00:00Z" / boot-datetime (SID 1722) /
},
1533 : [
{ / interface (SID 1533) /
+4 : "eth0", / name (SID 1537) /
+1 : "Ethernet adaptor", / description (SID 1534) /
+5 : 1880, / type (SID 1538), identity: /
/ ethernetCsmacd (SID 1880) /
+2 : true / enabled (SID 1535) /
}
]
}
4.5. Event stream
Event notification is an essential function for the management of
servers. CoMI allows notifications specified in YANG [RFC5277] to be
reported to a list of clients. The recommended path of the default
event stream is /s. The server MAY support additional event stream
resources to address different notification needs.
Reception of notification instances is enabled with the CoAP Observe
[RFC7641] function. Clients subscribe to the notifications by
sending a GET request with an "Observe" option, specifying the /s
resource when the default stream is selected.
Each response payload carries one or multiple notifications. The
number of notifications reported, and the conditions used to remove
notifications from the reported list is left to implementers. When
multiple notifications are reported, they MUST be ordered starting
from the newest notification at index zero.
The format of notification contents is defined in
[I-D.ietf-core-yang-cbor] section 4.2.1. For notification without
any content, a null value is returned.
An example implementation is:
Every time an event is generated, the generated notification
instance is appended to the chosen stream(s). After an
aggregation period, which may be adjusted using an exclusion delay
and limited by the maximum number of notifications supported, the
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content of the instance is sent to all clients observing the
modified stream.
FORMAT:
GET /<stream-resource> Observe(0)
2.05 Content (Content-Format: application/yang-instances+cbor)
CBOR array of CBOR map of instance-identifier, instance-value
The array of data node instances may contain identical entries which
have been generated at different times.
4.5.1. Notify Examples
Let suppose the server generates the example-port-fault event as
defined below.
module example-port {
...
notification example-port-fault { // SID 60010
description
"Event generated if a hardware fault is detected";
leaf port-name { // SID 60011
type string;
}
leaf port-fault { // SID 60012
type string;
}
}
}
By executing a GET on the /s resource the client receives the
following response:
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REQ: GET /s Observe(0)
RES: 2.05 Content (Content-Format: application/yang-tree+cbor)
Observe(12)
[
{
60010 : { / example-port-fault (SID 60010) /
+1 : "0/4/21", / port-name (SID 60011) /
+2 : "Open pin 2" / port-fault (SID 60012) /
}
},
{
60010 : { / example-port-fault (SID 60010) /
+1 : "1/4/21", / port-name (SID 60011) /
+2 : "Open pin 5" / port-fault (SID 60012) /
}
}
]
In the example, the request returns a success response with the
contents of the last two generated events. Consecutively the server
will regularly notify the client when a new event is generated.
To check that the client is still alive, the server MUST send
Confirmable Message periodically. When the client does not confirm
the notification from the server, the server will remove the client
from the list of observers [RFC7641].
4.5.2. The 'f' Uri-Query option
The 'f' (filter) option is used to indicate which subset of all
possible notifications is of interest. If not present, all events
notifications supported by the event stream are reported.
When not supported by a CoMI server, this option shall be ignored,
all events notifications are reported independently of the presence
and content of the 'f' (filter) option.
When present, this option contains a comma separated list of
notification SIDs. For example, the following request returns
notifications 60010 and 60020.
REQ: GET /s?f=60010,60020 Observe(0)
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4.6. RPC statements
The YANG "action" and "RPC" statements specify the execution of a
Remote procedure Call (RPC) in the server. It is invoked using a
POST method to an "Action" or "RPC" resource instance.
The request payload contains the values assigned to the input
container when specified. The response payload contains the values
of the output container when specified. Both the input and output
containers are encoded in CBOR using the rules defined in
[I-D.ietf-core-yang-cbor] section 4.2.1.
The returned success response code is 2.05 Content.
FORMAT:
POST /c/<instance identifier>
(Content-Format: application/yang-data+cbor)
CBOR map of SID, instance-value
2.05 Content (Content-Format: application/yang-data+cbor)
CBOR map of SID, instance-value
4.6.1. RPC Example
The example is based on the YANG action "reset" as defined in
[RFC7950] section 7.15.3 and annotated below with SIDs.
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module example-server-farm {
yang-version 1.1;
namespace "urn:example:server-farm";
prefix "sfarm";
import ietf-yang-types {
prefix "yang";
}
list server { // SID 60000
key name;
leaf name { // SID 60001
type string;
}
action reset { // SID 60002
input {
leaf reset-at { // SID 60003
type yang:date-and-time;
mandatory true;
}
}
output {
leaf reset-finished-at { // SID 60004
type yang:date-and-time;
mandatory true;
}
}
}
}
}
This example invokes the 'reset' action (SID 60002, base64: Opq), of
the server instance with name equal to "myserver".
REQ: POST /c/Opq?k="myserver"
(Content-Format: application/yang-data+cbor)
{
60002 : {
+1 : "2016-02-08T14:10:08Z09:00" / reset-at (SID 60003) /
}
}
RES: 2.05 Content (Content-Format: application/yang-data+cbor)
{
60002 : {
+2 : "2016-02-08T14:10:08Z09:18" / reset-finished-at (SID 60004)/
}
}
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5. Use of Block-wise Transfers
The CoAP protocol provides reliability by acknowledging the UDP
datagrams. However, when large pieces of data need to be
transported, datagrams get fragmented, thus creating constraints on
the resources in the client, server and intermediate routers. The
block option [RFC7959] allows the transport of the total payload in
individual blocks of which the size can be adapted to the underlying
transport sizes such as: (UDP datagram size ~64KiB, IPv6 MTU of 1280,
IEEE 802.15.4 payload of 60-80 bytes). Each block is individually
acknowledged to guarantee reliability.
Notice that the Block mechanism splits the data at fixed positions,
such that individual data fields may become fragmented. Therefore,
assembly of multiple blocks may be required to process the complete
data field.
Beware of race conditions. Blocks are filled one at a time and care
should be taken that the whole data representation is sent in
multiple blocks sequentially without interruption. On the server,
values are changed, lists are re-ordered, extended or reduced. When
these actions happen during the serialization of the contents of the
resource, the transported results do not correspond with a state
having occurred in the server; or worse the returned values are
inconsistent. For example: array length does not correspond with the
actual number of items. It may be advisable to use Indefinite-length
CBOR arrays and maps, which are foreseen for data streaming purposes.
6. Application Discovery
Two application discovery mechanisms are supported by CoMI, the YANG
library data model as defined by [I-D.veillette-core-yang-library]
and the CORE resource discovery [RFC6690]. Implementers may choose
to implement one or the other or both.
6.1. YANG library
The YANG library data model [I-D.veillette-core-yang-library]
provides a high level description of the resources available. The
YANG library contains the list of modules, features and deviations
supported by the CoMI server. From this information, CoMI clients
can infer the list of data nodes supported and the interaction model
to be used to access them. This module also contains the list of
datastores implemented.
The location of the YANG library can be found by sending a GET
request to "/.well-known/core" including a resource type (RT)
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parameter with the value "core.c.yl". Upon success, the return
payload will contain the root resource of the YANG library module.
REQ: GET /.well-known/core?rt=core.c.yl
RES: 2.05 Content (Content-Format: application/link-format)
</c/kv>;rt="core.c.yl"
6.2. Resource Discovery
Even if the YANG library provides all the information needed for
application discovery once it is itself discovered, other types of
resources could be discovered using the implementation of Resource
discovery as defined by [RFC6690]. This can be desirable for a
seamless integration with other CoAP interfaces and services.
6.2.1. Datastore Resource Discovery
The presence and location of (path to) each datastore implemented by
the CoMI server can be discovered by sending a GET request to
"/.well-known/core" including a resource type (RT) parameter with the
value "core.c.ds".
Upon success, the return payload contains the list of datastore
resources.
Each datastore returned is further qualified using the "ds" Link-
Format attribute. This attribute is set to the SID assigned to the
datastore identity. When a unified datastore is implemented, the ds
attribute is set to 1029. For other examples of datastores, see the
Network Management Datastore Architecture (NMDA) [RFC7950].
link-extension = ( "ds" "=" sid ) )
; SID assigned to the datastore identity
sid = 1*DIGIT
For example:
REQ: GET /.well-known/core?rt=core.c.ds
RES: 2.05 Content (Content-Format: application/link-format)
</c>; rt="core.c.ds";ds= 1029
6.2.2. Data node Resource Discovery
The presence and location of (path to) each data node implemented by
the CoMI server are discovered by sending a GET request to "/.well-
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known/core" including a resource type (RT) parameter with the value
"core.c.dn".
Upon success, the return payload contains the SID assigned to each
data node and their location.
The example below shows the discovery of the presence and location of
data nodes. Data nodes '/ietf-system:system-state/clock/boot-
datetime' (SID 1722) and '/ietf-system:system-state/clock/current-
datetime' (SID 1723) are returned.
REQ: GET /.well-known/core?rt=core.c.dn
RES: 2.05 Content (Content-Format: application/link-format)
</c/a6>;rt="core.c.dn",
</c/a7>;rt="core.c.dn"
Without additional filtering, the list of data nodes may become
prohibitively long. Implementations MAY return a subset of this list
or can rely solely on the YANG library.
6.2.3. Event stream Resource Discovery
The presence and location of (path to) each event stream implemented
by the CoMI server are discovered by sending a GET request to
"/.well-known/core" including a resource type (RT) parameter with the
value "core.c.es".
Upon success, the return payload contains the list of event stream
resources.
For example:
REQ: GET /.well-known/core?rt=core.c.es
RES: 2.05 Content (Content-Format: application/link-format)
</s>;rt="core.c.es"
7. Error Handling
In case a request is received which cannot be processed properly, the
CoMI server MUST return an error response. This error response MUST
contain a CoAP 4.xx or 5.xx response code.
Errors returned by a CoMI server can be broken into two categories,
those associated to the CoAP protocol itself and those generated
during the validation of the YANG data model constrains as described
in [RFC7950] section 8.
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The following list of common CoAP errors should be implemented by
CoMI servers. This list is not exhaustive, other errors defined by
CoAP and associated RFCs may be applicable.
o Error 4.01 (Unauthorized) is returned by the CoMI server when the
CoMI client is not authorized to perform the requested action on
the targeted resource (i.e. data node, datastore, rpc, action or
event stream).
o Error 4.02 (Bad Option) is returned by the CoMI server when one or
more CoAP options are unknown or malformed.
o Error 4.04 (Not Found) is returned by the CoMI server when the
CoMI client is requesting a non-instantiated resource (i.e. data
node, datastore, rpc, action or event stream).
o Error 4.05 (Method Not Allowed) is returned by the CoMI server
when the CoMI client is requesting a method not supported on the
targeted resource. (e.g. GET on an rpc, PUT or POST on a data
node with "config" set to false).
o Error 4.08 (Request Entity Incomplete) is returned by the CoMI
server if one or multiple blocks of a block transfer request is
missing, see [RFC7959] for more details.
o Error 4.13 (Request Entity Too Large) may be returned by the CoMI
server during a block transfer request, see [RFC7959] for more
details.
o Error 4.15 (Unsupported Content-Format) is returned by the CoMI
server when the Content-Format used in the request does not match
those specified in section Section 2.4.
CoMI server MUST also enforce the different constraints associated to
the YANG data models implemented. These constraints are described in
[RFC7950] section 8. These errors are reported using the CoAP error
code 4.00 (Bad Request) and may have the following error container as
payload. The YANG definition and associated .sid file are available
in Appendix A and Appendix B. The error container is encoded using
the encoding rules of a YANG data template as defined in
[I-D.ietf-core-yang-cbor] section 5.
+--rw error!
+--rw error-tag identityref
+--rw error-app-tag? identityref
+--rw error-data-node? instance-identifier
+--rw error-message? string
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The following 'error-tag' and 'error-app-tag' are defined by the
ietf-comi YANG module, these tags are implemented as YANG identity
and can be extended as needed.
o error-tag 'operation-failed' is returned by the CoMI server when
the operation request cannot be processed successfully.
* error-app-tag 'malformed-message' is returned by the CoMI
server when the payload received from the CoMI client does not
contain a well-formed CBOR content as defined in [RFC7049]
section 3.3 or does not comply with the CBOR structure defined
within this document.
* error-app-tag 'data-not-unique' is returned by the CoMI server
when the validation of the 'unique' constraint of a list or
leaf-list fails.
* error-app-tag 'too-many-elements' is returned by the CoMI
server when the validation of the 'max-elements' constraint of
a list or leaf-list fails.
* error-app-tag 'too-few-elements' is returned by the CoMI server
when the validation of the 'min-elements' constraint of a list
or leaf-list fails.
* error-app-tag 'must-violation' is returned by the CoMI server
when the restrictions imposed by a 'must' statement are
violated.
* error-app-tag 'duplicate' is returned by the CoMI server when a
client tries to create a duplicate list or leaf-list entry.
o error-tag 'invalid-value' is returned by the CoMI server when the
CoMI client tries to update or create a leaf with a value encoded
using an invalid CBOR datatype or if the 'range', 'length',
'pattern' or 'require-instance' constrain is not fulfilled.
* error-app-tag 'invalid-datatype' is returned by the CoMI server
when CBOR encoding does not follow the rules set by or when the
value is incompatible with the YANG Built-In type (e.g. a value
greater than 127 for an int8, undefined enumeration)
* error-app-tag 'not-in-range' is returned by the CoMI server
when the validation of the 'range' property fails.
* error-app-tag 'invalid-length' is returned by the CoMI server
when the validation of the 'length' property fails.
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* error-app-tag 'pattern-test-failed' is returned by the CoMI
server when the validation of the 'pattern' property fails.
o error-tag 'missing-element' is returned by the CoMI server when
the operation requested by a CoMI client fails to comply with the
'mandatory' constraint defined. The 'mandatory' constraint is
enforced for leafs and choices, unless the node or any of its
ancestors have a 'when' condition or 'if-feature' expression that
evaluates to 'false'.
* error-app-tag 'missing-key' is returned by the CoMI server to
further qualify a missing-element error. This error is
returned when the CoMI client tries to create or list instance,
without all the 'key' specified or when the CoMI client tries
to delete a leaf listed as a 'key'.
* error-app-tag 'missing-input-parameter' is returned by the CoMI
server when the input parameters of an RPC or action are
incomplete.
o error-tag 'unknown-element' is returned by the CoMI server when
the CoMI client tries to access a data node of a YANG module not
supported, of a data node associated to an 'if-feature' expression
evaluated to 'false' or to a 'when' condition evaluated to
'false'.
o error-tag 'bad-element' is returned by the CoMI server when the
CoMI client tries to create data nodes for more than one case in a
choice.
o error-tag 'data-missing' is returned by the CoMI server when a
data node required to accept the request is not present.
* error-app-tag 'instance-required' is returned by the CoMI
server when a leaf of type 'instance-identifier' or 'leafref'
marked with require-instance set to 'true' refers to an
instance that does not exist.
* error-app-tag 'missing-choice' is returned by the CoMI server
when no nodes exist in a mandatory choice.
o error-tag 'error' is returned by the CoMI server when an
unspecified error has occurred.
For example, the CoMI server might return the following error.
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RES: 4.00 Bad Request (Content-Format: application/yang-data+cbor)
{
1024 : {
+4 : 1011, / error-tag (SID 1028) /
/ = invalid-value (SID 1011) /
+1 : 1018, / error-app-tag (SID 1025) /
/ = not-in-range (SID 1018) /
+2 : 1740, / error-data-node (SID 1026) /
/ = timezone-utc-offset (SID 1740) /
+3 : "maximum value exceeded" / error-message (SID 1027) /
}
}
8. Security Considerations
For secure network management, it is important to restrict access to
configuration variables only to authorized parties. CoMI re-uses the
security mechanisms already available to CoAP, this includes DTLS
[RFC6347] for protected access to resources, as well suitable
authentication and authorization mechanisms.
Among the security decisions that need to be made are selecting
security modes and encryption mechanisms (see [RFC7252]). This
requires a trade-off, as the NoKey mode gives no protection at all,
but is easy to implement, whereas the Certificate mode is quite
secure, but may be too complex for constrained devices.
In addition, mechanisms for authentication and authorization may need
to be selected in case NoKey is used.
9. IANA Considerations
9.1. Resource Type (rt=) Link Target Attribute Values Registry
This document adds the following resource type to the "Resource Type
(rt=) Link Target Attribute Values", within the "Constrained RESTful
Environments (CoRE) Parameters" registry.
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+-----------+---------------------+-----------+
| Value | Description | Reference |
+-----------+---------------------+-----------+
| core.c.ds | YANG datastore | RFC XXXX |
| | | |
| core.c.dn | YANG data node | RFC XXXX |
| | | |
| core.c.yl | YANG module library | RFC XXXX |
| | | |
| core.c.es | YANG event stream | RFC XXXX |
+-----------+---------------------+-----------+
// RFC Ed.: replace RFC XXXX with this RFC number and remove this
note.
9.2. CoAP Content-Formats Registry
This document adds the following Content-Format to the "CoAP Content-
Formats", within the "Constrained RESTful Environments (CoRE)
Parameters" registry.
+-----------------------------------+------------+------+-----------+
| Media Type | Content | ID | Reference |
| | Coding | | |
+-----------------------------------+------------+------+-----------+
| application/yang-data+cbor | | TBD1 | RFC XXXX |
| | | | |
| application/yang-identifiers+cbor | | TBD2 | RFC XXXX |
| | | | |
| application/yang-instances+cbor | | TBD3 | RFC XXXX |
+-----------------------------------+------------+------+-----------+
// RFC Ed.: replace TBD1, TBD2 and TBD3 with assigned IDs and remove
this note. // RFC Ed.: replace RFC XXXX with this RFC number and
remove this note.
9.3. Media Types Registry
This document adds the following media types to the "Media Types"
registry.
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+-----------------------+----------------------------+-----------+
| Name | Template | Reference |
+-----------------------+----------------------------+-----------+
| yang-data+cbor | application/yang-data+cbor | RFC XXXX |
| | | |
| yang-identifiers+cbor | application/ | RFC XXXX |
| | | |
| | yang-identifiers+cbor | |
| | | |
| yang-instances+cbor | application/ | RFC XXXX |
| | | |
| | yang-instances+cbor | |
+-----------------------+----------------------------+-----------+
Each of these media types share the following information:
o Subtype name: <as listed in table>
o Required parameters: N/A
o Optional parameters: N/A
o Encoding considerations: binary
o Security considerations: See the Security Considerations section
of RFC XXXX
o Interoperability considerations: N/A
o Published specification: RFC XXXX
o Applications that use this media type: CoMI
o Fragment identifier considerations: N/A
o Additional information:
* Deprecated alias names for this type: N/A
* Magic number(s): N/A
* File extension(s): N/A
* Macintosh file type code(s): N/A
o Person & email address to contact for further information:
iesg&ietf.org
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o Intended usage: COMMON
o Restrictions on usage: N/A
o Author: Michel Veillette, ietf&augustcellars.com
o Change Controller: IESG
o Provisional registration? No
// RFC Ed.: replace RFC XXXX with this RFC number and remove this
note.
10. Acknowledgements
We are very grateful to Bert Greevenbosch who was one of the original
authors of the CoMI specification.
Mehmet Ersue and Bert Wijnen explained the encoding aspects of PDUs
transported under SNMP. Carsten Bormann has given feedback on the
use of CBOR.
The draft has benefited from comments (alphabetical order) by Rodney
Cummings, Dee Denteneer, Esko Dijk, Michael van Hartskamp, Tanguy
Ropitault, Juergen Schoenwaelder, Anuj Sehgal, Zach Shelby, Hannes
Tschofenig, Michael Verschoor, and Thomas Watteyne.
11. References
11.1. Normative References
[I-D.ietf-core-sid]
Veillette, M., Pelov, A., and I. Petrov, "YANG Schema Item
iDentifier (SID)", draft-ietf-core-sid-07 (work in
progress), July 2019.
[I-D.ietf-core-yang-cbor]
Veillette, M., Petrov, I., and A. Pelov, "CBOR Encoding of
Data Modeled with YANG", draft-ietf-core-yang-cbor-10
(work in progress), April 2019.
[I-D.veillette-core-yang-library]
Veillette, M. and I. Petrov, "Constrained YANG Module
Library", draft-veillette-core-yang-library-04 (work in
progress), March 2019.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/info/rfc4648>.
[RFC5277] Chisholm, S. and H. Trevino, "NETCONF Event
Notifications", RFC 5277, DOI 10.17487/RFC5277, July 2008,
<https://www.rfc-editor.org/info/rfc5277>.
[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,
<https://www.rfc-editor.org/info/rfc6241>.
[RFC6243] Bierman, A. and B. Lengyel, "With-defaults Capability for
NETCONF", RFC 6243, DOI 10.17487/RFC6243, June 2011,
<https://www.rfc-editor.org/info/rfc6243>.
[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
October 2013, <https://www.rfc-editor.org/info/rfc7049>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>.
[RFC7641] Hartke, K., "Observing Resources in the Constrained
Application Protocol (CoAP)", RFC 7641,
DOI 10.17487/RFC7641, September 2015,
<https://www.rfc-editor.org/info/rfc7641>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/info/rfc7950>.
[RFC7959] Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in
the Constrained Application Protocol (CoAP)", RFC 7959,
DOI 10.17487/RFC7959, August 2016,
<https://www.rfc-editor.org/info/rfc7959>.
[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
<https://www.rfc-editor.org/info/rfc8040>.
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[RFC8132] van der Stok, P., Bormann, C., and A. Sehgal, "PATCH and
FETCH Methods for the Constrained Application Protocol
(CoAP)", RFC 8132, DOI 10.17487/RFC8132, April 2017,
<https://www.rfc-editor.org/info/rfc8132>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
11.2. Informative References
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
<https://www.rfc-editor.org/info/rfc6690>.
[RFC7223] Bjorklund, M., "A YANG Data Model for Interface
Management", RFC 7223, DOI 10.17487/RFC7223, May 2014,
<https://www.rfc-editor.org/info/rfc7223>.
[RFC7317] Bierman, A. and M. Bjorklund, "A YANG Data Model for
System Management", RFC 7317, DOI 10.17487/RFC7317, August
2014, <https://www.rfc-editor.org/info/rfc7317>.
[RFC8342] Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
and R. Wilton, "Network Management Datastore Architecture
(NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018,
<https://www.rfc-editor.org/info/rfc8342>.
Appendix A. ietf-comi YANG module
<CODE BEGINS> file "ietf-comi@2019-03-28.yang"
module ietf-comi {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-comi";
prefix comi;
import ietf-datastores {
prefix ds;
}
import ietf-restconf {
prefix rc;
description
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"This import statement is required to access
the yang-data extension defined in RFC 8040.";
reference "RFC 8040: RESTCONF Protocol";
}
organization
"IETF Core Working Group";
contact
"Michel Veillette
<mailto:michel.veillette@trilliantinc.com>
Alexander Pelov
<mailto:alexander@ackl.io>
Peter van der Stok
<mailto:consultancy@vanderstok.org>
Andy Bierman
<mailto:andy@yumaworks.com>";
description
"This module contains the different definitions required
by the CoMI protocol.";
revision 2019-03-28 {
description
"Initial revision.";
reference
"[I-D.ietf-core-comi] CoAP Management Interface";
}
identity unified {
base ds:datastore;
description
"Identifier of the unified configuration and operational
state datastore.";
}
identity error-tag {
description
"Base identity for error-tag.";
}
identity operation-failed {
base error-tag;
description
"Returned by the CoMI server when the operation request
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can't be processed successfully.";
}
identity invalid-value {
base error-tag;
description
"Returned by the CoMI server when the CoMI client tries to
update or create a leaf with a value encoded using an
invalid CBOR datatype or if the 'range', 'length',
'pattern' or 'require-instance' constrain is not
fulfilled.";
}
identity missing-element {
base error-tag;
description
"Returned by the CoMI server when the operation requested
by a CoMI client fails to comply with the 'mandatory'
constraint defined. The 'mandatory' constraint is
enforced for leafs and choices, unless the node or any of
its ancestors have a 'when' condition or 'if-feature'
expression that evaluates to 'false'.";
}
identity unknown-element {
base error-tag;
description
"Returned by the CoMI server when the CoMI client tries to
access a data node of a YANG module not supported, of a
data node associated with an 'if-feature' expression
evaluated to 'false' or to a 'when' condition evaluated
to 'false'.";
}
identity bad-element {
base error-tag;
description
"Returned by the CoMI server when the CoMI client tries to
create data nodes for more than one case in a choice.";
}
identity data-missing {
base error-tag;
description
"Returned by the CoMI server when a data node required to
accept the request is not present.";
}
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identity error {
base error-tag;
description
"Returned by the CoMI server when an unspecified error has
occurred.";
}
identity error-app-tag {
description
"Base identity for error-app-tag.";
}
identity malformed-message {
base error-app-tag;
description
"Returned by the CoMI server when the payload received
from the CoMI client don't contain a well-formed CBOR
content as defined in [RFC7049] section 3.3 or don't
comply with the CBOR structure defined within this
document.";
}
identity data-not-unique {
base error-app-tag;
description
"Returned by the CoMI server when the validation of the
'unique' constraint of a list or leaf-list fails.";
}
identity too-many-elements {
base error-app-tag;
description
"Returned by the CoMI server when the validation of the
'max-elements' constraint of a list or leaf-list fails.";
}
identity too-few-elements {
base error-app-tag;
description
"Returned by the CoMI server when the validation of the
'min-elements' constraint of a list or leaf-list fails.";
}
identity must-violation {
base error-app-tag;
description
"Returned by the CoMI server when the restrictions
imposed by a 'must' statement are violated.";
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}
identity duplicate {
base error-app-tag;
description
"Returned by the CoMI server when a client tries to create
a duplicate list or leaf-list entry.";
}
identity invalid-datatype {
base error-app-tag;
description
"Returned by the CoMI server when CBOR encoding is
incorect or when the value encoded is incompatible with
the YANG Built-In type. (e.g. value greater than 127
for an int8, undefined enumeration).";
}
identity not-in-range {
base error-app-tag;
description
"Returned by the CoMI server when the validation of the
'range' property fails.";
}
identity invalid-length {
base error-app-tag;
description
"Returned by the CoMI server when the validation of the
'length' property fails.";
}
identity pattern-test-failed {
base error-app-tag;
description
"Returned by the CoMI server when the validation of the
'pattern' property fails.";
}
identity missing-key {
base error-app-tag;
description
"Returned by the CoMI server to further qualify a
missing-element error. This error is returned when the
CoMI client tries to create or list instance, without all
the 'key' specified or when the CoMI client tries to
delete a leaf listed as a 'key'.";
}
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identity missing-input-parameter {
base error-app-tag;
description
"Returned by the CoMI server when the input parameters
of a RPC or action are incomplete.";
}
identity instance-required {
base error-app-tag;
description
"Returned by the CoMI server when a leaf of type
'instance-identifier' or 'leafref' marked with
require-instance set to 'true' refers to an instance
that does not exist.";
}
identity missing-choice {
base error-app-tag;
description
"Returned by the CoMI server when no nodes exist in a
mandatory choice.";
}
rc:yang-data comi-error {
container error {
description
"Optional payload of a 4.00 Bad Request CoAP error.";
leaf error-tag {
type identityref {
base error-tag;
}
mandatory true;
description
"The enumerated error-tag.";
}
leaf error-app-tag {
type identityref {
base error-app-tag;
}
description
"The application-specific error-tag.";
}
leaf error-data-node {
type instance-identifier;
description
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"When the error reported is caused by a specific data node,
this leaf identifies the data node in error.";
}
leaf error-message {
type string;
description
"A message describing the error.";
}
}
}
}
<CODE ENDS>
Appendix B. ietf-comi .sid file
{
"assignment-ranges": [
{
"entry-point": 1000,
"size": 100
}
],
"module-name": "ietf-comi",
"module-revision": "2019-03-28",
"items": [
{
"namespace": "module",
"identifier": "ietf-comi",
"sid": 1000
},
{
"namespace": "identity",
"identifier": "bad-element",
"sid": 1001
},
{
"namespace": "identity",
"identifier": "data-missing",
"sid": 1002
},
{
"namespace": "identity",
"identifier": "data-not-unique",
"sid": 1003
},
{
"namespace": "identity",
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"identifier": "duplicate",
"sid": 1004
},
{
"namespace": "identity",
"identifier": "error",
"sid": 1005
},
{
"namespace": "identity",
"identifier": "error-app-tag",
"sid": 1006
},
{
"namespace": "identity",
"identifier": "error-tag",
"sid": 1007
},
{
"namespace": "identity",
"identifier": "instance-required",
"sid": 1008
},
{
"namespace": "identity",
"identifier": "invalid-datatype",
"sid": 1009
},
{
"namespace": "identity",
"identifier": "invalid-length",
"sid": 1010
},
{
"namespace": "identity",
"identifier": "invalid-value",
"sid": 1011
},
{
"namespace": "identity",
"identifier": "malformed-message",
"sid": 1012
},
{
"namespace": "identity",
"identifier": "missing-choice",
"sid": 1013
},
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{
"namespace": "identity",
"identifier": "missing-element",
"sid": 1014
},
{
"namespace": "identity",
"identifier": "missing-input-parameter",
"sid": 1015
},
{
"namespace": "identity",
"identifier": "missing-key",
"sid": 1016
},
{
"namespace": "identity",
"identifier": "must-violation",
"sid": 1017
},
{
"namespace": "identity",
"identifier": "not-in-range",
"sid": 1018
},
{
"namespace": "identity",
"identifier": "operation-failed",
"sid": 1019
},
{
"namespace": "identity",
"identifier": "pattern-test-failed",
"sid": 1020
},
{
"namespace": "identity",
"identifier": "too-few-elements",
"sid": 1021
},
{
"namespace": "identity",
"identifier": "too-many-elements",
"sid": 1022
},
{
"namespace": "identity",
"identifier": "unified",
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"sid": 1029
},
{
"namespace": "identity",
"identifier": "unknown-element",
"sid": 1023
},
{
"namespace": "data",
"identifier": "/ietf-comi:error",
"sid": 1024
},
{
"namespace": "data",
"identifier": "/ietf-comi:error/error-app-tag",
"sid": 1025
},
{
"namespace": "data",
"identifier": "/ietf-comi:error/error-data-node",
"sid": 1026
},
{
"namespace": "data",
"identifier": "/ietf-comi:error/error-message",
"sid": 1027
},
{
"namespace": "data",
"identifier": "/ietf-comi:error/error-tag",
"sid": 1028
}
]
}
Authors' Addresses
Michel Veillette (editor)
Trilliant Networks Inc.
610 Rue du Luxembourg
Granby, Quebec J2J 2V2
Canada
Email: michel.veillette@trilliant.com
Veillette, et al. Expires January 10, 2020 [Page 49]
Internet-Draft CoMI July 2019
Peter van der Stok (editor)
consultant
Phone: +31-492474673 (Netherlands), +33-966015248 (France)
Email: consultancy@vanderstok.org
URI: www.vanderstok.org
Alexander Pelov
Acklio
2bis rue de la Chataigneraie
Cesson-Sevigne, Bretagne 35510
France
Email: a@ackl.io
Andy Bierman
YumaWorks
685 Cochran St.
Suite #160
Simi Valley, CA 93065
USA
Email: andy@yumaworks.com
Ivaylo Petrov (editor)
Acklio
1137A avenue des Champs Blancs
Cesson-Sevigne, Bretagne 35510
France
Email: ivaylo@ackl.io
Veillette, et al. Expires January 10, 2020 [Page 50]
