Network Working Group R. Shakir
Internet-Draft A. Shaikh
Intended status: Informational P. Borman
Expires: September 14, 2017 M. Hines
C. Lebsack
C. Morrow
Google
March 13, 2017
gRPC Network Management Interface (gNMI)
draft-openconfig-rtgwg-gnmi-spec-00
Abstract
This document describes the gRPC Network Management Interface (gNMI),
a network management protocol based on the gRPC RPC framework. gNMI
supports retrieval and manipuation of state from network elements
where the data is represented by a tree structure, and addressable by
paths. The gNMI service defines operations for configuration
management, operational state retrieval, and bulk data collection via
streaming telemtry.
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 http://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
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 September 14, 2017.
Copyright Notice
Copyright (c) 2017 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
(http://trustee.ietf.org/license-info) in effect on the date of
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publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Common Message Types and Encodings . . . . . . . . . . . . . 4
2.1. Reusable Notification Message Format . . . . . . . . . . 4
2.2. Common Data Types . . . . . . . . . . . . . . . . . . . . 5
2.2.1. Timestamps . . . . . . . . . . . . . . . . . . . . . 5
2.2.2. Paths . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2.3. Node Values . . . . . . . . . . . . . . . . . . . . . 6
2.3. Encoding Data in an Update Message . . . . . . . . . . . 6
2.3.1. JSON and JSON_IETF . . . . . . . . . . . . . . . . . 6
2.3.2. Bytes . . . . . . . . . . . . . . . . . . . . . . . . 9
2.3.3. Protobuf . . . . . . . . . . . . . . . . . . . . . . 9
2.3.4. ASCII . . . . . . . . . . . . . . . . . . . . . . . . 9
2.4. Use of Data Schema Paths . . . . . . . . . . . . . . . . 9
2.4.1. Path Prefixes . . . . . . . . . . . . . . . . . . . . 9
2.4.2. Path Aliases . . . . . . . . . . . . . . . . . . . . 10
2.4.3. Interpretation of Paths Used in RPCs . . . . . . . . 11
2.5. Error handling . . . . . . . . . . . . . . . . . . . . . 12
2.6. Schema Definition Models . . . . . . . . . . . . . . . . 13
2.6.1. The ModelData message . . . . . . . . . . . . . . . . 13
3. Service Definition . . . . . . . . . . . . . . . . . . . . . 14
3.1. Session Security, Authentication and RPC Authorization . 14
3.2. Capability Discovery . . . . . . . . . . . . . . . . . . 15
3.2.1. The CapabilityRequest message . . . . . . . . . . . . 15
3.2.2. The CapabilityResponse message . . . . . . . . . . . 15
3.3. Retrieving Snapshots of State Information . . . . . . . . 16
3.3.1. The GetRequest Message . . . . . . . . . . . . . . . 16
3.3.2. The GetResponse message . . . . . . . . . . . . . . . 17
3.3.3. Considerations for using Get . . . . . . . . . . . . 18
3.4. Modifying State . . . . . . . . . . . . . . . . . . . . . 18
3.4.1. The SetRequest Message . . . . . . . . . . . . . . . 19
3.4.2. The SetResponse Message . . . . . . . . . . . . . . . 20
3.4.3. Transactions . . . . . . . . . . . . . . . . . . . . 20
3.4.4. Modes of Update: Replace versus Update . . . . . . . 21
3.4.5. Modifying Paths Identified by Attributes . . . . . . 21
3.4.6. Deleting Configuration . . . . . . . . . . . . . . . 22
3.4.7. Error Handling . . . . . . . . . . . . . . . . . . . 23
3.5. Subscribing to Telemetry Updates . . . . . . . . . . . . 24
3.5.1. Managing Subscriptions . . . . . . . . . . . . . . . 26
3.5.2. Sending Telemetry Updates . . . . . . . . . . . . . . 32
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4.1. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Appendix A. Appendix: Current Protobuf Message and Service
Specification . . . . . . . . . . . . . . . . . . . 36
Appendix B. Appendix: Current Outstanding Issues/Future Features 36
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 36
1. Introduction
This document defines a gRPC [1]-based protocol for the modification
and retrieval of configuration from a network element, as well as the
control and generation of telemetry streams from a network element to
a data collection system. The intention is that a single gRPC
service definition can cover both configuration and telemetry -
allowing a single implementation on the network element, as well as a
single NMS element to interact with the device via telemetry and
configuration RPCs.
All messages within the gRPC service definition are defined as
protocol buffers [2] (specifically proto3). gRPC service definitions
are expected to be described using the relevant features of the
protobuf IDL. A reference protobuf definition is maintained in
[REFERENCE-PROTO] [3]. The current, authoritative version of this
specification is available at [GNMI-SPEC] [4].
The service defined within this document is assumed to carry payloads
that contain data instances of OpenConfig [5] YANG schemas, but can
be used for any data with the following characteristics:
1. structure can be represented by a tree structure where nodes can
be uniquely identified by a path consisting of node names, or
node names coupled with attributes;
2. values can be serialised into a scalar object.
Currently, values may be serialised to a scalar object through
encoding as a JSON string, a byte-array, or a serialised protobuf
object - although the definition of new serialisations is possible.
Throughout this specification the following terminology is used:
o _Telemetry_ - refers to streaming data relating to underlying
characteristics of the device - either operational state or
configuration.
o _Configuration_ - elements within the data schema which are read/
write and can be manipulated by the client.
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o _Target_ - the device within the protocol which acts as the owner
of the data that is being manipulated or reported on. Typically
this will be a network device.
o _Client_ - the device or system using the protocol described in
this document to query/modify data on the target, or act as a
collector for streamed data. Typically this will be a network
management system.
2. Common Message Types and Encodings
2.1. Reusable Notification Message Format
When a target wishes to communicate data relating to the state of its
internal database to an interested client, it does so via means of a
common "Notification" message. Notification messages are reused in
other higher-layer messages for various purposes. The exact use of
the Notification message is described on a per-RPC basis.
The fields of the Notification message are as follows:
o "timestamp" - The time at which the data was collected by the
device from the underlying source, or the time that the target
generated the Notification message (in the case that the data does
not reflect an underlying data source). This value is always
represented according to the definition in Section 2.2.1.
o "prefix" - a prefix which is applied to all path fields (encoded
as per Section 2.2.2) included in the "Notification" message. The
paths expressed within the message are formed by the concatenation
of "prefix + path". The "prefix" always precedes the "path"
elements. Further semantics of prefixes are described in
Section 2.4.1.
o "alias"- a string providing an alias for the prefix specified
within the notification message. The encoding of an alias, and
the procedure for their creation is described in Section 2.4.2"."
o "update" - a list of update messages that indicate changes in the
underlying data of the target. Both modification and creation of
data is expressed through the update message.
* An "Update" message has two subfields:
+ "path" - a path encoded as per Section 2.2.2.
+ "value" - a value encoded as per Section 2.2.3.
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* The set of paths that are specified within the list of updates
MUST be unique. In this context, the path is defined to be the
fully resolved path (including the prefix). In the case that
there is a duplicate path specified within an update, only the
final update should be processed by the receiving entity.
o "delete" - a list of paths (encoded as per Section 2.2.2) that
indicate the deletion of data nodes on the target.
The creator of a Notification message MUST include the "timestamp"
field. All other fields are optional.
2.2. Common Data Types
2.2.1. Timestamps
Timestamp values MUST be represented as the number of nanoseconds
since the Unix epoch (January 1st 1970 00:00:00 UTC). The value MUST
be encoded as a signed 64-bit integer ("int64").
2.2.2. Paths
Paths are represented according to gNMI Path Conventions [6], a
simplified form of XPATH. Rather than utilising a single string to
represent the path - with the "/" character separating each element
of the path, the path is represented by an ordered list of strings,
starting at the root node, and ending at the most specific path
element.
A path is represented by the "Path" message with the following
fields:
o "element" -- a set of path elements, encoded as strings (see
examples below).
o "origin" - field which MAY be used to disambiguate the path if
necessary. For example, the origin may be used to indicate which
organization defined the schema to which the path belongs.
Each "Path" element should correspond to a node in the data tree.
For example, the path "/a/b/c/d" is encoded as:
path: <
element: "a"
element: "b"
element: "c"
element: "d"
>
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Where attributes are to be specified, these are encoded alongside the
node name within the path element, for example a node specified by
"/a/e[key=k1]/f/g" would have the path encoded as:
path: <
element: "a"
element: "e[key=k1]"
element: "f"
element: "g"
>
The root node ("/") is indicated by encoding a single path element
which is an empty string, as per the following example:
path: <
element: ""
>
Paths (defined to be the concatenation of the "Prefix" and "Path"
within the message) specified within a message MUST be absolute - no
messages with relative paths should be generated.
2.2.3. Node Values
The value of a data node is encoded as a two-field message:
o "bytes" - an arbitrary series of bytes which indicates the value
of the node referred to within the message context.
o "type" - a field indicating the type of data contained in the
bytes field. Currently defined types are:
2.3. Encoding Data in an Update Message
2.3.1. JSON and JSON_IETF
The "JSON" type indicates that the value included within the "bytes"
field of the node value message is encoded as a JSON string. This
format utilises the specification in RFC7159 [7]. Additional types
(e.g., "JSON_IETF") are utilised to indicate specific additional
characteristics of the encoding of the JSON data (particularly where
they relate to serialisation of YANG-modeled data).
For any JSON encoding:
o In the case that the data item at the specified path is a leaf
node (i.e., has no children) the value of that leaf is encoded
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directly - i.e., the "bare" value is specified (i.e., a JSON
object is not required, and a bare JSON value is included).
o Where the data item referred to has child nodes, the value field
contains a serialised JSON entity (object or array) corresponding
to the referenced item.
Using the following example data tree:
root +
|
+-- a +
|
+-- b[name=b1] +
|
+-- c +
|
+-- d (string)
+-- e (uint32)
The following serialisations would be used (note that the examples
below follow the conventions for textproto, and Golang-style
backticks are used for string literals that would otherwise require
escaping):
For "/a/b[name=b1]/c/d":
update: <
path: <
element: "a"
element: "b[name=b1]"
element: "c"
element: "d"
>
value: <
value: "AStringValue"
type: JSON
>
>
For "/a/b[name=b1]/c/e":
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update: <
path: <
element: "a"
element: "b[name=b1]"
element: "c"
element: "e"
>
value: <
Value: 10042 // decoded byte array
type: JSON
>
>
For "/a/b[name=b1]/c":
update: <
path: <
element: "a"
element: "b[name=b1]"
element: "c"
>
value: <
value: { "d": "AStringValue", "e": 10042 }
type: JSON
>
>
For "/a" :
update: <
path: <
element: "a"
>
value: <
value: `{ "b": [
{
"name": "b1",
"c": {
"d": "AStringValue",
"e": 10042
}
}
]
}`
type: JSON_IETF
>
>
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Note that all JSON values MUST be valid JSON. That is to say, whilst
a value or object may be included in the message, the relevant
quoting according to the JSON specification in RFC7159 [8] must be
used. This results in quoted string values, and unquoted number
values.
"JSON_IETF" encoded data MUST conform with the rules for JSON
serialisation described in RFC7951 [9]. Data specified with a type
of JSON MUST be valid JSON, but no additional constraints are placed
upon it. An implementation MUST NOT serialise data with mixed "JSON"
and "JSON_IETF" encodings.
Both the client and target MUST support the JSON encoding as a
minimum.
2.3.2. Bytes
The "BYTES" type indicates that the contents of the "bytes" field of
the message contains a byte sequence whose semantics is opaque to the
protocol.
2.3.3. Protobuf
The "PROTOBUF" type indicates that the contents of the "bytes" field
of the message contains a serialised protobuf message. Note that in
the case that the sender utilises this type, the receiver must
understand the schema (and hence the type of protobuf message that is
serialised) in order to decode the value. Such agreement is not
guaranteed by the protocol and hence must be established out-of-band.
2.3.4. ASCII
The "ASCII" type indicates that the contents of the "bytes" field of
the message contains system-formatted ASCII encoded text. For
configuration data, for example, this may consist of semi-structured
CLI configuration data formatted according to the target platform.
The gNMI protocol does not define the format of the text - this must
be established out-of-band.
2.4. Use of Data Schema Paths
2.4.1. Path Prefixes
In a number of messages, a prefix can be specified to reduce the
lengths of path fields within the message. In this case, a "prefix"
field is specified within a message - comprising of a valid path
encoded according to Section Section 2.2.2 In the case that a prefix
is specified, the absolute path is comprised of the concatenation of
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the list of path elements representing the prefix and the list of
path elements in the "path" field.
For example, again considering the data tree shown in
Section Section 2.3.1 if a "Notification" message updating values, a
prefix could be used to refer to the "/a/b[name=b1]/c/d" and
"/a/b[name=b1]/c/e"data nodes:
notification: <
timestamp: (timestamp) // timestamp as int64
prefix: <
element: "a"
element: "b[name=b1]"
element: "c"
>
update: <
path: <
element: "d"
>
value: <
value: "AStringValue"
type: JSON
>
>
update: <
path: <
element: "e"
>
value: <
value: 10042 // converted to int representation
type: JSON
>
>
>
2.4.2. Path Aliases
In some cases, a client or target MAY desire to utilises aliases for
a particular path - such that subsequent messages can be compressed
by utilising the alias, rather than using a complete representation
of the path. Doing so reduces total message length, by ensuring that
redundant information can be removed.
Support for path aliases MAY be provided by a target. In a case
where a target does not support aliases, the maximum message length
SHOULD be considered, especially in terms of bandwidth utilisation,
and the efficiency of message generation.
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A path alias is encoded as a string. In order to avoid valid data
paths clashing with aliases (e.g., "a" in the above example), an
alias name MUST be prefixed with a "#" character.
The means by which an alias is created is defined on a per-RPC basis.
In order to delete an alias, the alias name is sent with the path
corresponding to the alias empty.
Aliases MUST be specified as a fully expanded path, and hence MUST
NOT reference other aliases within their definition, such that a
single alias lookup is sufficient to resolve the absolute path.
2.4.3. Interpretation of Paths Used in RPCs
When a client specifies a path within an RPC message which indicates
a read, or retrieval of data, the path MUST be interpreted such that
it refers to the node directly corresponding with the path *and* all
its children. The path refers to the direct node and all descendent
branches which originate from the node, recursively down to each leaf
element. If specific nodes are expected to be excluded then an RPC
MAY provide means to filter nodes, such as regular-expression based
filtering, lists of excluded paths, or metadata-based filtering
(based on annotations of the data schema being manipulated, should
such annotations be available and understood by both client and
target).
For example, consider the following data tree:
root +
|
+-- childA +
| |
| +-- leafA1
| +-- leafA2
| +-- childA3 --+
| |
| +-- leafA31
| +-- leafA32
|
+-- childB +
|
+-- leafB1
+-- leafB2
A path referring to "root" (which is represented by a Path consisting
of a single element specifying an empty string) should result in the
nodes "childA" and "childB" and all of their children ("leafA1,
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leafA2, leafB1, leafB2, childA3, leafA31" and "leafA32") being
considered by the relevant operation.
In the case that the RPC is modifying the state of data (i.e., a
write operation), such recursion is not required - rather the
modification operation should be considered to be targeted at the
node within the schema that is specified by the path, and the value
should be deserialized such that it modifies the content of any child
nodes if required to do so.
2.5. Error handling
Where the client or target wishes to indicate an error, an "Error"
message is generated. Errors MUST be represented by a canonical gRPC
error code (Java [10], Golang [11], C++ [12]) . The entity generating
the error MUST specify a free-text string which indicates the context
of the error, allowing the receiving entity to generate log entries
that allow a human operator to understand the exact error that
occurred, and its context. Each RPC defines the meaning of the
relevant canonical error codes within the context of the operation it
performs.
The canonical error code that is chosen MUST consider the expected
behavior of the client on receipt of the message. For example, error
codes which indicate that a client may subsequently retry SHOULD only
be used where retrying the RPC is expected to result in a different
outcome.
A re-usable "Error" message MUST be used when sending errors in
response to an RPC operation. This message has the following fields:
o "code" - an unsigned 32-bit integer value corresponding to the
canonical gRPC error code.
o "message"- a human-readable string describing the error condition
in more detail. This string is not expected to be machine-
parsable, but rather provide contextual information which may be
passed to upstream systems.
o "data"- an arbitrary sequence of bytes (encoded as
"[proto.Any](https://github.com/google/protobuf/blob/master/src/
google/protobuf/any.proto)") which provides further contextual
information relating to the error.
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2.6. Schema Definition Models
The data tree supported by the target is expected to be defined by a
set of schemas. The definition and format of these models is out of
scope of this specification (YANG-modeled data is one example). In
the case that such schema definitions are used, the client should be
able to determine the models that are supported by the target, so
that it can generate valid modifications to the data tree, and
interpret the data returned by "Get" and "Subscribe" RPC calls.
Additionally, the client may wish to restrict the set of models that
are utilised by the target so that it can validate the data returned
to it against a specific set of data models. This is particularly
relevant where the target may otherwise add new values to restricted
value data elements (e.g., those representing an enumerated type), or
augment new data elements into the data tree.
In order to allow the client to restrict the set of data models to be
used when interacting with the target, the client MAY discover the
set of models that are supported by the target using the
"Capabilities" RPC described in Section 3.2. For subsequent "Get"
and "Subscribe" RPCs, the client MAY specify the models to be used by
the target. The set of models to use is expressed as a "ModelData"
message, as specified in Section 2.6.1.
If the client specifies a set of models in a "Get" or "Subscribe"
RPC, the target MUST NOT utilize data tree elements that are defined
in schema modules outside the specified set. In addition, where
there are data tree elements that have restricted value sets (e.g.,
enumerated types), and the set is extended by a module which is
outside of the set, such values MUST NOT be used in data instances
that are sent to the client. Where there are other elements of the
schema that depend on the existence of such enumerated values, the
target MUST NOT include such values in data instances sent to the
client.
2.6.1. The ModelData message
The "ModelData" message describes a specific model that is supported
by the target and used by the client. The fields of the "ModelData"
message identify a data model registered in a model catalog, as
described in [MODEL_CATALOG_DOC] [13] (the schema of the catalog
itself - expressed in YANG - is described in [MODEL_CATALOG_YANG
[14]]). Each model specified by a "ModelData" message may refer to a
specific schema module, a bundle of modules, or an augmentation or
deviation, as described by the catalog entry.
Each "ModelData" message contains the following fields:
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o "name" - name of the model expressed as a string.
o "organization" - the organization publishing the model, expressed
as a string.
o "version" - the supported (or requested) version of the model,
expressed as a string which represents the semantic version of the
catalog entry.
The combination of "name", "organization", and "version" uniquely
identifies an entry in the model catalog.
3. Service Definition
A single gRPC service is defined - future revisions of this
specification MAY result in additional services being introduced, and
hence an implementation MUST NOT make assumptions that limit to a
single service definition.
The service consists of the following RPCs:
o "Capabilities" - defined in Section 3.2 and used by the client and
target as an initial handshake to exchange capability information
o "Get" - defined in Section 3.3, used to retrieve snapshots of the
data on the target by the client.
o "Set" - defined in Section 3.4 and used by the client to modify
the state of the target.
o "Subscribe" - defined in Section 3.5 and used to control
subscriptions to data on the target by the client.
3.1. Session Security, Authentication and RPC Authorization
The session between the client and server MUST be encrypted using TLS
- and a target or client MUST NOT fall back to unencrypted channels.
New connections are mutually authenticated -- each entity validates
the X.509 certificate of the remote entity to ensure that the remote
entity is both known, and authorized to connect to the local system.
If the target is expected to authenticate an RPC operation, the
client MUST supply a username and password in the metadata of the RPC
message (e.g., "SubscribeRequest", "GetRequest" or "SetRequest"). If
the client supplies username/password credentials, the target MUST
authenticate the RPC per its local authentication functionality.
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Authorization is also performed per-RPC by the server, through
validating client-provided metadata. The client MAY include the
appropriate AAA metadata, which MUST contain a username, and MAY
include a password in the context of each RPC call it generates. If
the client includes both username and password, the target MUST
authenticate and authorize the request. If the client only supplies
the username, the target MUST authorize the RPC request.
A more detailed discussion of the requirements for authentication and
encryption used for gNMI is in [GNMI-AUTH] [15].
3.2. Capability Discovery
A client MAY discover the capabilities of the target using the
"Capabilities" RPC. The "CapabilityRequest" message is sent by the
client to interrogate the target. The target MUST reply with a
"CapabilityResponse" message that includes its gNMI service version,
the versioned data models it supports, and the supported data
encodings. This information is used in subsequent RPC messages from
the client to indicate the set of models that the client will use
(for "Get", "Subscribe" as described in Section 2.6) , and the
encoding to be used for the data.
When the client does not specify the models it is using, the target
SHOULD use all data schema modules that it supports when considering
the data tree to be addressed. If the client does not specify the
encoding in an RPC message, it MUST send JSON encoded values (the
default encoding).
3.2.1. The CapabilityRequest message
The "CapabilityRequest" message is sent by the client to request
capability information from the target. The "CapabilityRequest"
message carries no additional fields.
3.2.2. The CapabilityResponse message
The "CapabilityResponse" message has the following fields:
o "supported_models" - a set of "ModelData" messages (as defined in
Section 2.6.1) describing each of the models supported by the
target
o "supported_encodings" - an enumeration field describing the data
encodings supported by the target, as described in Section 2.3.
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o "gNMI_version" - the semantic version of the gNMI service
supported by the target, specified as a string. The version
should be interpreted as per [OPENCONFIG-SEMVER [16]].
3.3. Retrieving Snapshots of State Information
In some cases, a client may require a snapshot of the state that
exists on the target. In such cases, a client desires some subtree
of the data tree to be serialized by the target and transmitted to
it. It is expected that the values that are retrieved (whether
writeable by the client or not) are collected immediately and
provided to the client.
The "Get" RPC provides an interface by which a client can request a
set of paths to be serialized and transmitted to it by the target.
The client sends a "GetRequest" message to the target, specifying the
data that is to be retrieved. The fields of the "GetRequest" message
are described in Section 3.3.1.
Upon reception of a "GetRequest", the target serializes the requested
paths, and returns a "GetResponse" message. The target MUST reflect
the values of the specified leaves at a particular collection time,
which MAY be different for each path specified within the
"GetRequest" message.
The target closes the channel established by the "Get" RPC following
the transmission of the "GetResponse" message.
3.3.1. The GetRequest Message
The "GetRequest" message contains the following fields:
o "prefix" - a path (specified as per Section 2.2.2), and used as
described in Section 2.4.1. The prefix is applied to all paths
within the "GetRequest" message.
o "path" - a set of paths (expressed as per Section 2.2.2) for which
the client is requesting a data snapshot from the target. The
path specified MAY utilize wildcards. In the case that the path
specified is not valid, the target MUST populate the "error" field
of the "GetResponse" message indicating an error code of
"InvalidArgument" and SHOULD provide information about the invalid
path in the error message.
o "type" - the type of data that is requested from the target. The
valid values for type are described below.
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o "encoding" - the encoding that the target should utilise to
serialise the subtree of the data tree requested. The type MUST
be one of the encodings specified in Section 2.3. If the
"Capabilities" RPC has been utilised, the client SHOULD use an
encoding advertised as supported by the target. If the encoding
is not specified, JSON MUST be used. If the target does not
support the specified encoding, the target MUST populate the error
field of the "GetResponse" message, specifying an error of
"InvalidArgument". The error message MUST indicate that the
specified encoding is unsupported.
o "use_models" - a set of "ModelData" messages (defined in
Section 2.6.1) indicating the schema definition modules that
define the data elements that should be returned in response to
the Get RPC call. The semantics of the "use_models" field are
defined in Section 2.6.
Since the data tree stored by the target may consist of different
types of data (e.g., values that are operational in nature, such as
protocol statistics) - the client MAY specify that a subset of values
in the tree are of interest. In order for such filtering to be
implemented, the data schema on the target MUST be annotated in a
manner which specifies the type of data for individual leaves, or
subtrees of the data tree.
The types of data currently defined are:
o "CONFIG" - specified to be data that the target considers to be
read/write. If the data schema is described in YANG, this
corresponds to the "config true" set of leaves on the target.
o "STATE" - specified to be the read-only data on the target. If
the data schema is described in YANG, "STATE" data is the "config
false" set of leaves on the target.
o "OPERATIONAL" - specified to be the read-only data on the target
that is related to software processes operating on the device, or
external interactions of the device.
If the "type" field is not specified, the target MUST return CONFIG,
STATE and OPERATIONAL data fields in the tree resulting from the
client's query.
3.3.2. The GetResponse message
The "GetResponse" message consists of:
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o "notification" - a set of "Notification" messages, as defined in
Section 2.1. The target MUST generate a "Notification" message
for each path specified in the client's "GetRequest", and hence
MUST NOT collapse data from multiple paths into a single
"Notification" within the response. The "timestamp" field of the
"Notification" message MUST be set to the time at which the
target's snapshot of the relevant path was taken.
o "error" - an "Error" message encoded as per the specification in
Section 2.5, used to indicate errors in the "GetRequest" received
by the target from the client.
3.3.3. Considerations for using Get
The "Get" RPC is intended for clients to retrieve relatively small
sets of data as complete objects, for example a part of the
configuration. Such requests are not expected to put a significant
resource burden on the target. Since the target is expected to
return the entire snapshot in the "GetResponse" message, "Get" is not
well-suited for retrieving very large data sets, such as the full
contents of the routing table, or the entire component inventory.
For such operations, the "Subscribe" RPC is the recommended
mechanism, e.g. using the "ONCE" mode as described in Section 3.5.
Another consideration for "Get" is that the timestamp returned is
associated with entire set of data requested, although individual
data items may have been sampled by the target at different times.
If the client requires higher accuracy for individual data items, the
"Subscribe" RPC is recommended to request a telemetry stream (see
Section 3.5.2).
3.4. Modifying State
Modifications to the state of the target are made through the "Set"
RPC. A client sends a "SetRequest" message to the target indicating
the modifications it desires.
A target receiving a "SetRequest" message processes the operations
specified within it - which are treated as a transaction (see
Section 3.4.3). The server MUST process deleted paths (within the
"delete" field of the "SetRequest"), followed by paths to be replaced
(within the "replace" field), and finally updated paths (within the
"update" field). The order of the replace and update fields MUST be
treated as significant within a single "SetRequest" message. If a
single path is specified multiple times for a single operation (i.e.,
within "update" or "replace"), then the state of the target MUST
reflect the application of all of the operations in order, even if
they overwrite each other.
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In response to a "SetRequest", the target MUST respond with a
"SetResponse" message. For each operation specified in the
"SetRequest" message, an "UpdateResult" message MUST be included in
the response field of the "SetResponse". The order in which the
operations are applied MUST be maintained such that "UpdateResult"
messages can be correlated to the "SetRequest" operations. In the
case of a failure of an operation, the "error" field of the
"UpdateResult" message MUST be populated with an "Error" message as
per the specification in Section 2.5. In addition, the "error" field
of the "SetResponse" message MUST be populated with an error message
indicating the success or failure of the set of operations within the
"SetRequest" message (again using the error handling behavior defined
in Section 2.5).
3.4.1. The SetRequest Message
A "SetRequest" message consists of the following fields:
o "prefix" - specified as per Section 2.4.1. The prefix specified
is applied to all paths defined within other fields of the
message.
o "delete" - A set of paths, specified as per Section 2.2.2, which
are to be removed from the data tree. A specification of the
behavior of a delete is defined in Section 3.4.6.
o "replace" - A set of "Update" messages indicating elements of the
data tree whose content is to be replaced.
o "update" - A set of "Update" messages indicating elements of the
data tree whose content is to be updated.
The semantics of "updating" versus "replacing" content are defined in
Section 3.4.4
A re-usable "Update" message is utilised to indicate changes to paths
where a new value is required. The "Update" message contains two
fields:
o "path" - a path encoded as per Section 2.2.2 indicating the path
of the element to be modified.
o "value" - a value encoded as per Section 2.2.3 indicating the
value applied to the specified node. The semantics of how the
node is updated is dependent upon the context of the update
message, as specified in Section 3.4.4.
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3.4.2. The SetResponse Message
A "SetResponse" consists of the following fields:
o "prefix" - specified as per Section 2.4.1. The prefix specified
is applied to all paths defined within other fields of the
message.
o "message" - an error message as specified in Section 2.5. The
target SHOULD specify a "message" in the case that the update was
successfully applied, in which case an error code of "OK (0)"
"MUST" be specified. In cases where an update was not
successfully applied, the contents of the error message MUST be
specified as per Section 2.5.
o "response" - containing a list of responses, one per operation
specified within the "SetRequest" message. Each response consists
of an "UpdateResult" message with the following fields:
* "timestamp" - a timestamp (encoded as per Section 2.2.1) at
which the set request message was accepted by the system.
* "path" - the path (encoded as per Section 2.2.2) specified
within the "SetRequest". In the case that a common prefix was
not used within the "SetRequest", the target MAY specify a
"prefix" to reduce repetition of path elements within multiple
"UpdateResult" messages in the "request" field.
* "op" - the operation corresponding to the path. This value
MUST be one of "DELETE", "REPLACE", or "UPDATE".
* "message" - an error message (as specified in Section 2.5).
This field follows the same rules as the message field within
the "SetResponse" message specified above.
3.4.3. Transactions
All changes to the state of the target that are included in an
individual "SetRequest" message are considered part of a transaction.
That is, either all modifications within the request are applied, or
the target MUST rollback the state changes to reflect its state
before any changes were applied. The state of the target MUST NOT
appear to be changed until such time as all changes have been
accepted successfully. Hence, telemetry update messages MUST NOT
reflect a change in state until such time as the intended
modifications have been accepted.
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As per the specification in Section 3.4, within an individual
transaction ("SetRequest") the order of operations is "delete",
"replace", "update".
As the scope of a "transaction" is a single "SetRequest" message, a
client desiring a set of changes to be applied together MUST ensure
that they are encapsulated within a single "SetRequest" message.
3.4.4. Modes of Update: Replace versus Update
Changes to read-write values on the target are applied based on the
"replace" and "update" fields of the "SetRequest" message.
For both replace and update operations, if the path specified does
not exist, the target MUST create the data tree element and populate
it with the data in the "Update" message, provided the path is valid
according to the data tree schema. If invalid values are specified,
the target MUST cease processing updates within the "SetRequest"
method, return the data tree to the state prior to any changes, and
return a "SetResponse" message indicating the error encountered.
For "replace" operations, the behavior regarding omitted data
elements in the "Update" depends on whether they refer to non-default
values (i.e., set by a previous "SetRequest"), or unmodified
defaults. When the "replace" operation omits values that have been
previously set, they MUST be treated as deleted from the data tree.
Otherwise, omitted data elements MUST be created with their default
values on the target.
For "update" operations, only the value of those data elements that
are specified explicitly should be treated as changed.
3.4.5. Modifying Paths Identified by Attributes
The path convention defined in Section 2.2.2 allows nodes in the data
tree to be identified by a unique set of node names (e.g.,"/a/b/c/d")
or paths that consist of node names coupled with attributes (e.g.,
"/a/e[key=10]"). In the case where where a node name plus attribute
name is required to uniquely identify an element (i.e., the path
within the schema represents a list, map, or array), the following
considerations apply:
o In the case that multiple attribute values are required to
uniquely address an element - e.g., "/a/f[k1=10][k2=20]"- and a
replace or update operation's path specifies a subset of the
attributes (e.g., "/a/f[k1=10]") then this MUST be considered an
error by the target system - and an error code of"InvalidArgument
(3)" specified.
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o Where the path specified refers to a node which itself represents
the collection of objects (list, map, or array) a replace
operation MUST remove all collection entries that are not supplied
in the value provided in the "SetRequest". An update operation
MUST be considered to add new entries to the collection if they do
not exist.
o In the case that key values are specified both as attributes of a
node, and as their own elements within the data tree, update or
replace operations that modify instances of the key in conflicting
ways MUST be considered an error. The target MUST return an error
code of "InvalidArgument (3)".
For example, consider a tree corresponding to the examples above, as
illustrated below.
root +
|
+ a --+
|
+-- f[k1=10][k2=20] --+
| |
| +-- k1 = 10
| +-- k2 = 20
|
+-- f[k1=10][k2=21] --+
|
+-- k1 = 10
+-- k2 = 21
In this case, nodes "k1" and "k2" are standalone nodes within the
schema, but also correspond to attribute values for the node ""f"".
In this case, an update or replace message specifying a path of "/a/
f[k1=10][k2=20]" setting the value of "k1" to 100 MUST be considered
erroneous, and an error code of "InvalidArgument (3)" specified.
3.4.6. Deleting Configuration
Where a path is contained within the "delete" field of the
"SetRequest" message, it should be removed from the target's data
tree. In the case that the path specified is to an element that has
children, these children MUST be recursively deleted. If a wildcard
path is utilised, the wildcards MUST be expanded by the target, and
the corresponding elements of the data tree deleted. Such wildcards
MUST support paths specifying a subset of attributes required to
identify entries within a collection (list, array, or map) of the
data schema.
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In the case that a path specifies an element within the data tree
that does not exist, these deletes MUST be silently accepted.
3.4.7. Error Handling
When a client issues a "SetRequest", and the target is unable to
apply the specified changes, an error MUST be reported to the client.
The error is specified in multiple places:
o Within a "SetResponse" message, the error field indicates the
completion status of the entire transaction.
o With a "UpdateResult" message, where the error field indicates the
completion status of the individual operation.
The target MUST specify the "message" field within a "SetResponse"
message such that the overall status of the transaction is reflected.
In the case that no error occurs, the target MUST complete this field
specifying the "OK (0)" canonical error code.
In the case that any operation within the "SetRequest" message fails,
then (as per Section 3.4.3), the target MUST NOT apply any of the
specified changes, and MUST consider the transaction as failed. The
target SHOULD set the "message" field of the "SetResponse" message to
an error message with the code field set to "Aborted (10)", and MUST
set the "message" field of the "UpdateResult" corresponding to the
failed operation to an "Error" message indicating failure. In the
case that the processed operation is not the only operation within
the "SetRequest" the target MUST set the "message" field of the
"UpdateResult" messages for all other operations, setting the code
field to "Aborted (10)".
For the operation that the target is unable to process, the "message"
field MUST be set to a specific error code indicating the reason for
failure based on the following mappings to canonical gRPC error
codes:
o When the client has specified metadata requiring authentication
(see Section 3.1), and the authentication fails - "Unauthenticated
(16)".
o When the client does not have permission to modify the path
specified by the operation - "PermissionDenied (7)".
o When the operation specifies a path that cannot be parsed by the
target - "InvalidArgument (3)". In this case, the "message" field
of the "Error" message specified SHOULD specify human-readable
text indicating that the path could not be parsed.
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o When the operation is an update or replace operation that
corresponds to a path that is not valid - "NotFound (5)". In this
case the "message" field of the "Error" message specified SHOULD
specify human-readable text indicating the path that was invalid.
o When the operation is an update or replace operation that includes
an invalid value within the "Update" message specified -
"InvalidArgument (3)". This error SHOULD be used in cases where
the payload specifies scalar values that do not correspond to the
correct schema type, and in the case that multiple values are
specified using a particular encoding (e.g., JSON) which cannot be
decoded by the target.
3.5. Subscribing to Telemetry Updates
When a client wishes to receive updates relating to the state of data
instances on a target, it creates a subscription via the "Subscribe"
RPC. A subscription consists of one or more paths, with a specified
subscription mode. The mode of each subscription determines the
triggers for updates for data sent from the target to the client.
All requests for new subscriptions are encapsulated within a
"SubscribeRequest" message - which itself has a mode which describes
the longevity of the subscription. A client may create a
subscription which has a dedicated stream to return one-off data
("ONCE"); a subscription that utilizes a stream to periodically
request a set of data ("POLL"); or a long-lived subscription that
streams data according to the triggers specified within the
individual subscription's mode ("STREAM").
The target generates messages according to the type of subscription
that has been created, at the frequency requested by the client. The
methods to create subscriptions are described in Section 3.5.1.
Subscriptions are created for a set of paths - which cannot be
modified throughout the lifetime of the subscription. In order to
cancel a subscription, the client closes the gRPC channel over which
the "Subscribe" RPC was initiated, or terminates the entire gRPC
session.
Subscriptions are fundamentally a set of independent update messages
relating to the state of the data tree. That is, it is not possible
for a client requesting a subscription to assume that the set of
update messages received represent a snapshot of the data tree at a
particular point in time. Subscriptions therefore allow a client to:
o Receive ongoing updates from a target which allow synchronization
between the client and target for the state of elements within the
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data tree. In this case (i.e., a "STREAM" subscription), a client
creating a subscription receives an initial set of updates,
terminated by a message indicating that initial synchronisation
has completed, and then receives subsequent updates indicating
changes to the initial state of those elements.
o Receive a single view (polled, or one-off) for elements of the
data tree on a per-data element basis according to the state that
they are in at the time that the message is transmitted. This can
be more resource efficient for both target and client than a
"GetRequest" for large subtrees within the data tree. The target
does not need to coalesce values into a single snapshot view, or
create an in-memory representation of the subtree at the time of
the request, and subsequently transmit this entire view to the
client.
Based on the fact that subsequent update messages are considered to
be independent, and to ensure that the efficiencies described above
can be achieved, by default a target MUST NOT aggregate values within
an update message.
In some cases, however, elements of the data tree may be known to
change together, or need to be interpreted by the subscriber
together. Such data MUST be explicitly marked in the schema as being
eligible to be aggregated when being published. Additionally, the
subscribing client MUST explicitly request aggregation of eligible
schema elements for the subscription - by means of the
"allow_aggregation" flag within a "SubscriptionList" message. For
elements covered by a subscription that are not explicitly marked
within the schema as being eligible for aggregation the target MUST
NOT coalesce these values, regardless of the value of the
"allow_aggregation" flag.
When aggregation is not permitted by the client or the schema each
update message MUST contain a (key, value) pair - where the key MUST
be a path to a single leaf element within the data tree (encoded
according to Section 2.2.2). The value MUST encode only the value of
the leaf specified. In most cases, this will be a scalar value
(i.e., a JSON value if a JSON encoding is utilised), but in some
cases, where an individual leaf element within the schema represents
an object, it MAY represent a set of values (i.e., a JSON or Protobuf
object).
Where aggregation is permitted by both the client and schema, each
update message MUST contain a key value pair, where the key MUST be
the path to the element within the data tree which is explicitly
marked as being eligible for aggregation. The value MUST be an
object which encodes the children of the data tree element specified.
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For JSON, the value is therefore a JSON object, and for Protobuf is a
series of binary-encoded Protobuf messages.
3.5.1. Managing Subscriptions
3.5.1.1. The SubscribeRequest Message
A "SubscribeRequest" message is sent by a client to request updates
from the target for a specified set of paths.
The fields of the "SubscribeRequest" are as follows:
o A group of fields, only one of which may be specified, which
indicate the type of operation that the "SubscribeRequest" relates
to. These are:
* "subscribe" - a "SubscriptionList" message specifying a new set
of paths that the client wishes to subscribe to.
* "poll"- a "Poll" message used to specify (on an existing
channel) that the client wishes to receive a polled update for
the paths specified within the subscription. The semantics of
the "Poll" message are described in Section 3.5.1.5.3.
* "aliases" - used by a client to define (on an existing channel)
a new path alias (as described in Section 2.4.2). The use of
the aliases message is described in Section 3.5.1.6.
In order to create a new subscription (and its associated channel) a
client MUST send a "SubscribeRequest" message, specifying the
"subscribe" field. The "SubscriptionList" may create a one-off
subscription, a poll-only subscription, or a streaming subscription.
In the case of ONCE subscriptions, the channel between client and
target MUST be closed following the initial response generation.
Subscriptions are set once, and subsequently not modified by a
client. If a client wishes to subscribe to additional paths from a
target, it MUST do so by sending an additional "Subscribe" RPC call,
specifying a new "SubscriptionList" message. In order to end an
existing subscription, a client simply closes the gRPC channel that
relates to that subscription. If a channel is initiated with a
"SubscribeRequest" message that does not specify a "SubscriptionList"
message with the "request" field, the target MUST consider this an
error. If an additional "SubscribeRequest" message specifying a
"SubscriptionList" is sent via an existing channel, the target MUST
respond to this message with "SubscribeResponse" message indicating
an error message, with a contained error message indicating an error
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code of "InvalidArgument (4)"; existing subscriptions on other gRPC
channels MUST not be modified or terminated.
If a client initiates a "Subscribe" RPC with a "SubscribeRequest"
message which does not contain a "SubscriptionList" message, this is
an error. A "SubscribeResponse" message with the contained "error"
message indicating a error code of "InvalidArgument" MUST be sent.
The error text SHOULD indicate that an out-of-order operation was
requested on a non-existent subscription. The target MUST
subsequently close the channel.
3.5.1.2. The SubscriptionList Message
A "SubscriptionList" message is used to indicate a set of paths for
which common subscription behavior are required. The fields of the
message are:
o "subscription" - a set of "Subscription" messages that indicate
the set of paths associated with the subscription list.
o "mode" - the type of subscription that is being created. This may
be "ONCE" (described in Section 3.5.1.5.1); "STREAM" (described in
Section 3.5.1.5.2); or "POLL" (described in Section 3.5.1.5.3).
The default value for the mode field is "STREAM".
o "prefix"- a common prefix that is applied to all paths specified
within the message as per the definition in Section 2.4.1. The
default prefix is null.
o "use_aliases"- a boolean flag indicating whether the client
accepts target aliases via the subscription channel. In the case
that such aliases are accepted, the logic described in
Section 2.4.2 is utilised. By default, path aliases created by
the target are not supported.
o "qos" - a field describing the packet marking that is to be
utilised for the responses to the subscription that is being
created. This field has a single sub-value, "marking", which
indicates the DSCP value as a 32-bit unsigned integer. If the
"qos" field is not specified, the device should export telemetry
traffic using its default DSCP marking for management-plane
traffic.
o "allow_aggregation" - a boolean value used by the client to allow
schema elements that are marked as eligible for aggregation to be
combined into single telemetry update messages. By default,
aggregation MUST NOT be used.
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o "use_models" - a "ModelData" message (as specified in
Section 2.6.1) specifying the schema definition modules that the
target should use when creating a subscription. When specified,
the target MUST only consider data elements within the defined set
of schema models as defined in Section 2.6. When "use_models" is
not specified, the target MUST consider all data elements that are
defined in all schema modules that it supports.
A client generating a "SubscriptionList" message MUST include the
"subscription" field - which MUST be a non-empty set of
"Subscription" messages, all other fields are optional.
3.5.1.3. The Subscription Message
A "Subscription" message generically describes a set of data that is
to be subscribed to by a client. It contains a "path", specified as
per the definition in Section 2.2.2.
There is no requirement for the path that is specified within the
message to exist within the current data tree on the server. Whilst
the path within the subscription SHOULD be a valid path within the
set of schema modules that the target supports, subscribing to any
syntactically valid path within such modules MUST be allowed. In the
case that a particular path does not (yet) exist, the target MUST NOT
close the channel, and instead should continue to monitor for the
existence of the path, and transmit telemetry updates should it exist
in the future. The target MAY send a "SubscribeResponse" message
populating the error field with "NotFound (5)" to inform the client
that the path does not exist at the time of subscription creation.
For "POLL" and "STREAM" subscriptions, a client may optionally
specify additional parameters within the "Subscription" message. The
semantics of these additional fields are described in the relevant
section of this document.
3.5.1.4. The SubscribeResponse Message
A "SubscribeResponse" message is transmitted by a target to a client
over an established channel created by the "Subscribe" RPC. The
message contains the following fields:
o A set of fields referred to as the "response" fields, only one of
which can be specified per "SubscribeResponse" message:
* "update" - a "Notification" message providing an update value
for a subscribed data entity as described in Section 3.5.2.
The "update" field is also utilised when a target wishes to
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create an alias within a subscription, as described in
Section 3.5.2.2.
* "sync_response" - a boolean field indicating that a particular
set of data values has been transmitted, used for "POLL" and
"STREAM" subscriptions.
* "error" - an "Error" message transmitted to indicate an error
has occurred within a particular "Subscribe" RPC call.
3.5.1.5. Creating Subscriptions
3.5.1.5.1. ONCE Subscriptions
A subscription operating in the "ONCE" mode acts as a single request/
response channel. The target creates the relevant update messages,
transmits them, and subsequently closes the channel.
In order to create a one-off subscription, a client sends a
"SubscribeRequest" message to the target. The "subscribe" field
within this message specifies a "SubscriptionList" with the mode
field set to "ONCE". Updates corresponding to the subscription are
generated as per the semantics described in Section 3.5.2.
Following the transmission of all updates which correspond to data
items within the set of paths specified within the subscription list,
a "SubscribeResponse" message with the "sync_response" field set to
"true" MUST be transmitted, and the channel over which the
"SubscribeRequest" was received MUST be closed.
3.5.1.5.2. STREAM Subscriptions
Stream subscriptions are long-lived subscriptions which continue to
transmit updates relating to the set of paths that are covered within
the subscription indefinitely.
A "STREAM" subscription is created by sending a "SubscribeRequest"
message with the subscribe field containing a "SubscriptionList"
message with the type specified as "STREAM". Each entry within the
"Subscription" message is specified with one of the following
"modes":
o On Change ("ON_CHANGE") - when a subscription is defined to be "on
change", data updates are only sent when the value of the data
item changes. A heartbeat interval MAY be specified along with an
"on change" subscription - in this case, the value of the data
item(s) MUST be re-sent once per heartbeat interval regardless of
whether the value has changed or not.
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o Sampled ("SAMPLE") - a subscription that is defined to be sampled
MUST be specified along with a "sample_interval" encoded as an
unsigned 64-bit integer representing nanoseconds. The value of
the data item(s) is sent once per sample interval to the client.
If the target is unable to support the desired "sample_interval"
it MUST reject the subscription by returning a "SubscribeResponse"
message with the error field set to an error message indicating
the "InvalidArgument (3)" error code. If the "sample_interval" is
set to 0, the target MUST create the subscription and send the
data with the lowest interval possible for the target.
* Optionally, the "suppress_redundant" field of the
"Subscription" message may be set for a sampled subscription.
In the case that it is set to "true", the target SHOULD NOT
generate a telemetry update message unless the value of the
path being reported on has changed since the last update was
generated. Updates MUST only be generated for those individual
leaf nodes in the subscription that have changed. That is to
say that for a subscription to "/a/b" - where there are leaves
"c" and "d" branching from the "b" node - if the value of "c"
has changed, but "d" remains unchanged, an update for "d" MUST
NOT be generated, whereas an update for "c" MUST be generated.
* A "heartbeat_interval" MAY be specified to modify the behavior
of "suppress_redundant" in a sampled subscription. In this
case, the target MUST generate one telemetry update per
heartbeat interval, regardless of whether the
"suppress_redundant" flag is set to "true". This value is
specified as an unsigned 64-bit integer in nanoseconds.
o Target Defined "(TARGET_DEFINED)" - when a client creates a
subscription specifying the target defined mode, the target SHOULD
determine the best type of subscription to be created on a per-
leaf basis. That is to say, if the path specified within the
message refers to some leaves which are event driven (e.g., the
changing of state of an entity based on an external trigger) then
an "ON_CHANGE" subscription may be created, whereas if other data
represents counter values, a "SAMPLE" subscription may be created.
3.5.1.5.3. POLL Subscriptions
Polling subscriptions are used for on-demand retrieval of statistics
via long-lived channels. A poll subscription relates to a certain
set of subscribed paths, and is initiated by sending a
"SubscribeRequest" message with encapsulated "SubscriptionList".
"Subscription" messages contained within the "SubscriptionList"
indicate the set of paths that are of interest to the polling client.
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To retrieve data from the target, a client sends a "SubscribeRequest"
message to the target, containing a "poll" field, specified to be an
empty "Poll" message. On reception of such a message, the target
MUST generate updates for all the corresponding paths within the
"SubscriptionList". Updates MUST be generated according to
Section 3.5.2.
3.5.1.6. Client-defined Aliases within a Subscription
When a client wishes to create an alias that a target should use for
a path, the client should send a "SubscribeRequest" message
specifying the "aliases" field. The "aliases" field consists of an
"AliasList" message. An "AliasList" specifies a list of aliases,
each of which consists of:
o "path" - the target path for the alias - encoded as per
Section 2.2.2.
o "alias" - the (client-defined) alias for the path, encoded as per
Section 2.4.2.
Where a target is unable to support a client-defined alias it SHOULD
respond with a "SubscribeResponse" message with the error field
indicating an error of the following types:
o "InvalidArgument (3)" where the specified alias is not acceptable
to the target.
o "AlreadyExists (6)" where the alias defined is a duplicate of an
existing alias for the client.
o "ResourceExhausted (8)" where the target has insufficient memory
or processing resources to support the alias.
o "Unknown (2)" in all other cases.
Thus, for a client to create an alias corresponding to the
path"/a/b/c/d[id=10]/e" with the name "shortPath", it sends a
"SubscribeRequest" message with the following fields specified:
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subscriberequest: <
aliases: <
alias: <
path: <
element: "a"
element: "b"
element: "c"
element: "d[id=10]"
element: "e"
>
alias: "#shortPath"
>
>
>
If the alias is acceptable to the target, subsequent updates are
transmitted using the "#shortPath" alias in the same manner as
described in Section 3.5.2.2.
3.5.2. Sending Telemetry Updates
3.5.2.1. Bundling of Telemetry Updates
Since multiple "Notification" messages can be included in the update
field of a "SubscribeResponse" message, it is possible for a target
to bundle messages such that fewer messages are sent to the client.
The advantage of such bundling is clearly to reduce the number of
bytes on the wire (caused by message overhead). Since "Notification"
messages contain the timestamp at which an event occurred, or a
sample was taken, such bundling does not affect the sample accuracy
to the client. However, bundling does have a negative impact on the
freshness of the data in the client - and on the client's ability to
react to events on the target.
Since it is not possible for the target to infer whether its clients
are sensitive to the latency introduced by bundling, if a target
implements optimizations such that multiple "Notification" messages
are bundled together, it MUST provide an ability to disable this
functionality within the configuration of the gNMI service.
Additionally, a target SHOULD provide means by which the operator can
control the maximum number of updates that are to be bundled into a
single message, This configuration is expected to be implemented out-
of-band to the gNMI protocol itself.
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3.5.2.2. Target-defined Aliases within a Subscription
Where the "use_aliases" field of a "SubscriptionList" message has
been set to "true", a target MAY create aliases for paths within a
subscription. A target-defined alias MUST be created separately from
an update to the corresponding data item(s).
To create a target-defined alias, a "SubscribeResponse" message is
generated with the "update" field set to a "Notification" message.
The "Notification" message specifies the aliased path within the
"prefix" field, and a non-null "alias" field, specified according to
Section 2.4.2.
Thus, a target wishing to create an alias relating to the path "/a/b/
c[id=10]" and subsequently update children of the "c[id=10]"entity
must:
1. Generate a "SubscribeResponse" message and transmit it over the
channel to the client:
subscriberesponse: <
update: <
timestamp: (timestamp)
prefix: <
element: "a"
element: "b"
element: "c[id=10]"
>
alias: "#42"
>
>
1. Subsequently, this alias can be used to provide updates for the
"child1" leaf corresponding to "/a/b/c[id=10]/child1":
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subscriberesponse: <
update: <
timestamp: (timestamp)
prefix: <
element: "#42"
>
update: <
path: <
element: "child1"
>
value: <
value: 102 // integer representation
type: JSON_IETF
>
>
>
>
3.5.2.3. Sending Telemetry Updates
When an update for a subscribed telemetry path is to be sent, a
"SubscribeResponse" message is sent from the target to the client, on
the channel associated with the subscription. The "update" field of
the message contains a "Notification" message as per the description
in Section 2.1. The "timestamp" field of the "Notification" message
MUST be set to the time at which the value of the path that is being
updated was collected.
Where a leaf node's value has changed, or a new node has been
created, an "Update" message specifying the path and value for the
updated data item MUST be appended to the "update" field of the
message.
Where a node within the subscribed paths has been removed, the
"delete" field of the "Notification" message MUST have the path of
the node that has been removed appended to it.
When the target has transmitted the initial updates for all paths
specified within the subscription, a "SubscribeResponse" message with
the "sync_response" field set to "true" MUST be transmitted to the
client to indicate that the initial transmission of updates has
concluded. This provides an indication to the client that all of the
existing data for the subscription has been sent at least once. For
"STREAM" subscriptions, such messages are not required for subsequent
updates. For "POLL" subscriptions, after each set of updates for
individual poll request, a "SubscribeResponse" message with the
"sync_response" field set to "true" MUST be generated.
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4. References
4.1. URIs
[1] http://grpc.io
[2] https://developers.google.com/protocol-buffers/
[3] https://github.com/openconfig/reference/blob/master/rpc/gnmi/
gnmi.proto
[4] https://github.com/openconfig/reference/blob/master/rpc/gnmi/
gnmi-specification.md
[5] http://www.openconfig.net/
[6] https://github.com/openconfig/reference/blob/master/rpc/gnmi/
gnmi-path-conventions.md
[7] https://tools.ietf.org/html/rfc7159
[8] https://tools.ietf.org/html/rfc7159
[9] https://tools.ietf.org/html/rfc7951
[10] http://www.grpc.io/grpc-java/javadoc/index.html
[11] https://godoc.org/google.golang.org/grpc/codes#Code
[12] http://www.grpc.io/grpc/cpp/classgrpc_1_1_status.html
[13] https://datatracker.ietf.org/doc/draft-openconfig-netmod-model-
catalog/
[14] https://tools.ietf.org/html/draft-openconfig-netmod-model-
catalog-01
[15] https://github.com/openconfig/reference/blob/master/rpc/gnmi/
gnmi-authentication.md
[16] http://www.openconfig.net/documentation/semantic-versioning/
[17] https://github.com/openconfig/reference/blob/master/rpc/gnmi/
gnmi.proto
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Appendix A. Appendix: Current Protobuf Message and Service
Specification
The latest Protobuf IDL gNMI specification is found at [17].
Appendix B. Appendix: Current Outstanding Issues/Future Features
o Ability for the client to exclude paths from a subscription or
get.
o "Dial out" for the target to register with an NMS and publish pre-
configured subscriptions.
Authors' Addresses
Rob Shakir
Google, Inc.
1600 Amphitheatre Parkway
Mountain View, CA 94043
Email: robjs@google.com
Anees Shaikh
Google
1600 Amphitheatre Pkwy
Mountain View, CA 94043
US
Email: aashaikh@google.com
Paul Borman
Google
1600 Amphitheatre Pkwy
Mountain View, CA 94043
US
Email: borman@google.com
Marcus Hines
Google
1600 Amphitheatre Pkwy
Mountain View, CA 94043
US
Email: hines@google.com
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Carl Lebsack
Google
1600 Amphitheatre Pkwy
Mountain View, CA 94043
US
Email: csl@google.com
Chris Morrow
Google
Email: christopher.morrow@gmail.com
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