Internet DRAFT - draft-ietf-netconf-subscribed-notifications
draft-ietf-netconf-subscribed-notifications
NETCONF E. Voit
Internet-Draft Cisco Systems
Intended status: Standards Track A. Clemm
Expires: November 9, 2019 Huawei
A. Gonzalez Prieto
Microsoft
E. Nilsen-Nygaard
A. Tripathy
Cisco Systems
May 8, 2019
Subscription to YANG Event Notifications
draft-ietf-netconf-subscribed-notifications-26
Abstract
This document defines a YANG data model and associated mechanisms
enabling subscriber-specific subscriptions to a publisher's event
streams. Applying these elements allows a subscriber to request for
and receive a continuous, custom feed of publisher generated
information.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on November 9, 2019.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.3. Solution Overview . . . . . . . . . . . . . . . . . . . . 5
1.4. Relationship to RFC 5277 . . . . . . . . . . . . . . . . 6
2. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1. Event Streams . . . . . . . . . . . . . . . . . . . . . . 7
2.2. Event Stream Filters . . . . . . . . . . . . . . . . . . 8
2.3. QoS . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.4. Dynamic Subscriptions . . . . . . . . . . . . . . . . . . 9
2.5. Configured Subscriptions . . . . . . . . . . . . . . . . 17
2.6. Event Record Delivery . . . . . . . . . . . . . . . . . . 25
2.7. Subscription state change notifications . . . . . . . . . 26
2.8. Subscription Monitoring . . . . . . . . . . . . . . . . . 31
2.9. Advertisement . . . . . . . . . . . . . . . . . . . . . . 32
3. YANG Data Model Trees . . . . . . . . . . . . . . . . . . . . 32
3.1. Event Streams Container . . . . . . . . . . . . . . . . . 32
3.2. Filters Container . . . . . . . . . . . . . . . . . . . . 33
3.3. Subscriptions Container . . . . . . . . . . . . . . . . . 33
4. Data Model . . . . . . . . . . . . . . . . . . . . . . . . . 35
5. Considerations . . . . . . . . . . . . . . . . . . . . . . . 62
5.1. IANA Considerations . . . . . . . . . . . . . . . . . . . 62
5.2. Implementation Considerations . . . . . . . . . . . . . . 63
5.3. Transport Requirements . . . . . . . . . . . . . . . . . 64
5.4. Security Considerations . . . . . . . . . . . . . . . . . 65
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 68
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 69
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7.1. Normative References . . . . . . . . . . . . . . . . . . 69
7.2. Informative References . . . . . . . . . . . . . . . . . 70
Appendix A. Example Configured Transport Augmentation . . . . . 71
Appendix B. Changes between revisions . . . . . . . . . . . . . 73
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 79
1. Introduction
This document defines a YANG data model and associated mechanisms
enabling subscriber-specific subscriptions to a publisher's event
streams. Effectively this enables a 'subscribe then publish'
capability where the customized information needs and access
permissions of each target receiver are understood by the publisher
before subscribed event records are marshaled and pushed. The
receiver then gets a continuous, custom feed of publisher generated
information.
While the functionality defined in this document is transport-
agnostic, transports like NETCONF [RFC6241] or RESTCONF [RFC8040] can
be used to configure or dynamically signal subscriptions, and there
are bindings defined for subscribed event record delivery for NETCONF
within [I-D.draft-ietf-netconf-netconf-event-notifications], and for
RESTCONF within [I-D.draft-ietf-netconf-restconf-notif].
The YANG model in this document conforms to the Network Management
Datastore Architecture defined in [RFC8342].
1.1. Motivation
Various limitations in [RFC5277] are discussed in [RFC7923].
Resolving these issues is the primary motivation for this work. Key
capabilities supported by this document include:
o multiple subscriptions on a single transport session
o support for dynamic and configured subscriptions
o modification of an existing subscription in progress
o per-subscription operational counters
o negotiation of subscription parameters (through the use of hints
returned as part of declined subscription requests)
o subscription state change notifications (e.g., publisher driven
suspension, parameter modification)
o independence from transport
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1.2. 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.
Client: defined in [RFC8342].
Configuration: defined in [RFC8342].
Configuration datastore: defined in [RFC8342].
Configured subscription: A subscription installed via configuration
into a configuration datastore.
Dynamic subscription: A subscription created dynamically by a
subscriber via a remote procedure call.
Event: An occurrence of something that may be of interest. Examples
include a configuration change, a fault, a change in status, crossing
a threshold, or an external input to the system.
Event occurrence time: a timestamp matching the time an originating
process identified as when an event happened.
Event record: A set of information detailing an event.
Event stream: A continuous, chronologically ordered set of events
aggregated under some context.
Event stream filter: Evaluation criteria which may be applied against
event records within an event stream. Event records pass the filter
when specified criteria are met.
Notification message: Information intended for a receiver indicating
that one or more events have occurred.
Publisher: An entity responsible for streaming notification messages
per the terms of a subscription.
Receiver: A target to which a publisher pushes subscribed event
records. For dynamic subscriptions, the receiver and subscriber are
the same entity.
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Subscriber: A client able to request and negotiate a contract for the
generation and push of event records from a publisher. For dynamic
subscriptions, the receiver and subscriber are the same entity.
Subscription: A contract with a publisher, stipulating which
information one or more receivers wish to have pushed from the
publisher without the need for further solicitation.
All YANG tree diagrams used in this document follow the notation
defined in [RFC8340].
1.3. Solution Overview
This document describes a transport agnostic mechanism for
subscribing to and receiving content from an event stream within a
publisher. This mechanism is through the use of a subscription.
Two types of subscriptions are supported:
1. Dynamic subscriptions, where a subscriber initiates a
subscription negotiation with a publisher via a Remote Procedure
Call (RPC). If the publisher is able to serve this request, it
accepts it, and then starts pushing notification messages back to
the subscriber. If the publisher is not able to serve it as
requested, then an error response is returned. This response MAY
include hints at subscription parameters that, had they been
present, may have enabled the dynamic subscription request to be
accepted.
2. Configured subscriptions, which allow the management of
subscriptions via a configuration so that a publisher can send
notification messages to a receiver. Support for configured
subscriptions is optional, with its availability advertised via a
YANG feature.
Additional characteristics differentiating configured from dynamic
subscriptions include:
o The lifetime of a dynamic subscription is bound by the transport
session used to establish it. For connection-oriented stateful
transports like NETCONF, the loss of the transport session will
result in the immediate termination of any associated dynamic
subscriptions. For connectionless or stateless transports like
HTTP, a lack of receipt acknowledgment of a sequential set of
notification messages and/or keep-alives can be used to trigger a
termination of a dynamic subscription. Contrast this to the
lifetime of a configured subscription. This lifetime is driven by
relevant configuration being present within the publisher's
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applied configuration. Being tied to configuration operations
implies configured subscriptions can be configured to persist
across reboots, and implies a configured subscription can persist
even when its publisher is fully disconnected from any network.
o Configured subscriptions can be modified by any configuration
client with write permission on the configuration of the
subscription. Dynamic subscriptions can only be modified via an
RPC request made by the original subscriber, or a change to
configuration data referenced by the subscription.
Note that there is no mixing-and-matching of dynamic and configured
operations on a single subscription. Specifically, a configured
subscription cannot be modified or deleted using RPCs defined in this
document. Similarly, a dynamic subscription cannot be directly
modified or deleted by configuration operations. It is however
possible to perform a configuration operation which indirectly
impacts a dynamic subscription. By changing value of a pre-
configured filter referenced by an existing dynamic subscription, the
selected event records passed to a receiver might change.
Also note that transport-specific specifications based on this
specification MUST detail the lifecycle of dynamic subscriptions, as
well as the lifecycle of configured subscriptions (if supported).
A publisher MAY terminate a dynamic subscription at any time.
Similarly, it MAY decide to temporarily suspend the sending of
notification messages for any dynamic subscription, or for one or
more receivers of a configured subscription. Such termination or
suspension is driven by internal considerations of the publisher.
1.4. Relationship to RFC 5277
This document is intended to provide a superset of the subscription
capabilities initially defined within [RFC5277]. Especially when
extending an existing [RFC5277] implementation, it is important to
understand what has been reused and what has been replaced. Key
relationships between these two documents include:
o this document defines a transport independent capability,
[RFC5277] is specific to NETCONF.
o the data model in this document is used instead of the data model
in Section 3.4 of [RFC5277] for the new operations.
o the RPC operations in this draft replace the operation "create-
subscription" defined in [RFC5277], section 4.
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o the <notification> message of [RFC5277], Section 4 is used.
o the included contents of the "NETCONF" event stream are identical
between this document and [RFC5277].
o a publisher MAY implement both the Notification Management Schema
and RPCs defined in [RFC5277] and this new document concurrently.
o unlike [RFC5277], this document enables a single transport session
to intermix notification messages and RPCs for different
subscriptions.
o A subscription "stop-time" can be specified as part of a
notification replay. This supports an analogous capability to the
stopTime parameter of [RFC5277]. However in this specification, a
"stop-time" parameter can also be applied without replay.
2. Solution
Per the overview provided in Section 1.3, this section details the
overall context, state machines, and subsystems which may be
assembled to allow the subscription of events from a publisher.
2.1. Event Streams
An event stream is a named entity on a publisher which exposes a
continuously updating set of YANG defined event records. An event
record is an instantiation of a "notification" YANG statement. If
the "notification" is defined as a child to a data node, the
instantiation includes the hierarchy of nodes that identifies the
data node in the datastore (see Section 7.16.2 of [RFC7950]). Each
event stream is available for subscription. It is out of the scope
of this document to identify a) how event streams are defined (other
than the NETCONF stream), b) how event records are defined/generated,
and c) how event records are assigned to event streams.
There is only one reserved event stream name within this document:
"NETCONF". The "NETCONF" event stream contains all NETCONF event
record information supported by the publisher, except where an event
record has explicitly been excluded from the stream. Beyond the
"NETCONF" stream, implementations MAY define additional event
streams.
As YANG defined event records are created by a system, they may be
assigned to one or more streams. The event record is distributed to
a subscription's receiver(s) where: (1) a subscription includes the
identified stream, and (2) subscription filtering does not exclude
the event record from that receiver.
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Access control permissions may be used to silently exclude event
records from within an event stream for which the receiver has no
read access. As an example of how this might be accomplished, see
[RFC8341] section 3.4.6. Note that per Section 2.7 of this document,
subscription state change notifications are never filtered out.
If no access control permissions are in place for event records on an
event stream, then a receiver MUST be allowed access to all the event
records. If subscriber permissions change during the lifecycle of a
subscription and event stream access is no longer permitted, then the
subscription MUST be terminated.
Event records MUST NOT be delivered to a receiver in a different
order than they were placed onto an event stream.
2.2. Event Stream Filters
This document defines an extensible filtering mechanism. The filter
itself is a boolean test which is placed on the content of an event
record. A 'false' filtering result causes the event record to be
excluded from delivery to a receiver. A filter never results in
information being stripped from within an event record prior to that
event record being encapsulated within a notification message. The
two optional event stream filtering syntaxes supported are [XPATH]
and subtree [RFC6241].
If no event stream filter is provided within a subscription, all
event records on an event stream are to be sent.
2.3. QoS
This document provides for several Quality of Service (QoS)
parameters. These parameters indicate the treatment of a
subscription relative to other traffic between publisher and
receiver. Included are:
o A "dscp" marking to differentiate prioritization of notification
messages during network transit.
o A "weighting" so that bandwidth proportional to this weighting can
be allocated to this subscription relative to other subscriptions.
o a "dependency" upon another subscription.
If the publisher supports the "dscp" feature, then a subscription
with a "dscp" leaf MUST result in a corresponding [RFC2474] DSCP
marking being placed within the IP header of any resulting
notification messages and subscription state change notifications. A
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publisher MUST respect the DSCP markings for subscription traffic
egressing that publisher.
Different DSCP code points require different transport connections.
As a result where TCP is used, a publisher which supports the "dscp"
feature must ensure that a subscription's notification messages are
returned within a single TCP transport session where all traffic
shares the subscription's "dscp" leaf value. Where this cannot be
guaranteed, any "establish subscription" RPC request SHOULD be
rejected with a "dscp-unavailable" error.
For the "weighting" parameter, when concurrently dequeuing
notification messages from multiple subscriptions to a receiver, the
publisher MUST allocate bandwidth to each subscription proportionally
to the weights assigned to those subscriptions. "Weighting" is an
optional capability of the publisher; support for it is identified
via the "qos" feature.
If a subscription has the "dependency" parameter set, then any
buffered notification messages containing event records selected by
the parent subscription MUST be dequeued prior to the notification
messages of the dependent subscription. If notification messages
have dependencies on each other, the notification message queued the
longest MUST go first. If a "dependency" included within an RPC
references a subscription which does not exist or is no longer
accessible to that subscriber, that "dependency" MUST be silently
removed. "Dependency" is an optional capability of the publisher;
support for it is identified via the "qos" feature.
"Dependency" and "weight" parameters will only be respected and
enforced between subscriptions that share the same "dscp" leaf value.
There are additional types over publisher capacity overload which
this specification does not address within its scope. For example,
the prioritization of which subscriptions have precedence when the
publisher CPU is overloaded is not discussed. As a result,
implementation choices will need to be made to address such
considerations.
2.4. Dynamic Subscriptions
Dynamic subscriptions are managed via protocol operations (in the
form of [RFC7950], Section 7.14 RPCs) made against targets located
within the publisher. These RPCs have been designed extensibly so
that they may be augmented for subscription targets beyond event
streams. For examples of such augmentations, see the RPC
augmentations within [I-D.ietf-netconf-yang-push]'s YANG model.
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2.4.1. Dynamic Subscription State Model
Below is the publisher's state machine for a dynamic subscription.
Each state is shown in its own box. It is important to note that
such a subscription doesn't exist at the publisher until an
"establish-subscription" RPC is accepted. The mere request by a
subscriber to establish a subscription is insufficient for that
subscription to be externally visible. Start and end states are
depicted to reflect subscription creation and deletion events.
.........
: start :
:.......:
|
establish-subscription
|
| .-------modify-subscription--------.
v v |
.-----------. .-----------.
.--------. | receiver |--insufficient CPU, b/w-->| receiver |
modify- '| active | | suspended |
subscription | |<----CPU, b/w sufficient--| |
---------->'-----------' '-----------'
| |
delete/kill-subscription delete/kill-
| subscription
v |
......... |
: end :<---------------------------------'
:.......:
Figure 1: Publisher's state for a dynamic subscription
Of interest in this state machine are the following:
o Successful "establish-subscription" or "modify-subscription" RPCs
put the subscription into the active state.
o Failed "modify-subscription" RPCs will leave the subscription in
its previous state, with no visible change to any streaming
updates.
o A "delete-subscription" or "kill-subscription" RPC will end the
subscription, as will the reaching of a "stop-time".
o A publisher may choose to suspend a subscription when there is
insufficient CPU or bandwidth available to service the
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subscription. This is notified to a subscriber with a
"subscription-suspended" subscription state change notification.
o A suspended subscription may be modified by the subscriber (for
example in an attempt to use fewer resources). Successful
modification returns the subscription to the active state.
o Even without a "modify-subscription" request, a publisher may
return a subscription to the active state should the resource
constraints become sufficient again. This is announced to the
subscriber via the "subscription-resumed" subscription state
change notification.
2.4.2. Establishing a Dynamic Subscription
The "establish-subscription" RPC allows a subscriber to request the
creation of a subscription.
The input parameters of the operation are:
o A "stream" name which identifies the targeted event stream against
which the subscription is applied.
o An event stream filter which may reduce the set of event records
pushed.
o Where the transport used by the RPC supports multiple encodings,
an optional "encoding" for the event records pushed. If no
"encoding" is included, the encoding of the RPC MUST be used.
o An optional "stop-time" for the subscription. If no "stop-time"
is present, notification messages will continue to be sent until
the subscription is terminated.
o An optional "replay-start-time" for the subscription. The
"replay-start-time" MUST be in the past and indicates that the
subscription is requesting a replay of previously generated
information from the event stream. For more on replay, see
Section 2.4.2.1. Where there is no "replay-start-time", the
subscription starts immediately.
If the publisher can satisfy the "establish-subscription" request, it
replies with an identifier for the subscription, and then immediately
starts streaming notification messages.
Below is a tree diagram for "establish-subscription". All objects
contained in this tree are described within the included YANG model
within Section 4.
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+---x establish-subscription
+---w input
| +---w (target)
| | +--:(stream)
| | +---w (stream-filter)?
| | | +--:(by-reference)
| | | | +---w stream-filter-name
| | | | stream-filter-ref
| | | +--:(within-subscription)
| | | +---w (filter-spec)?
| | | +--:(stream-subtree-filter)
| | | | +---w stream-subtree-filter? <anydata>
| | | | {subtree}?
| | | +--:(stream-xpath-filter)
| | | +---w stream-xpath-filter?
| | | yang:xpath1.0 {xpath}?
| | +---w stream stream-ref
| | +---w replay-start-time?
| | yang:date-and-time {replay}?
| +---w stop-time?
| | yang:date-and-time
| +---w dscp? inet:dscp
| | {dscp}?
| +---w weighting? uint8
| | {qos}?
| +---w dependency?
| | subscription-id {qos}?
| +---w encoding? encoding
+--ro output
+--ro id subscription-id
+--ro replay-start-time-revision? yang:date-and-time
{replay}?
Figure 2: establish-subscription RPC tree diagram
A publisher MAY reject the "establish-subscription" RPC for many
reasons as described in Section 2.4.6. The contents of the resulting
RPC error response MAY include details on input parameters which if
considered in a subsequent "establish-subscription" RPC, may result
in a successful subscription establishment. Any such hints MUST be
transported within a yang-data "establish-subscription-stream-error-
info" container included within the RPC error response.
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yang-data establish-subscription-stream-error-info
+--ro establish-subscription-stream-error-info
+--ro reason? identityref
+--ro filter-failure-hint? string
Figure 3: establish-subscription RPC yang-data tree diagram
2.4.2.1. Requesting a replay of event records
Replay provides the ability to establish a subscription which is also
capable of passing event records generated in the recent past. In
other words, as the subscription initializes itself, it sends any
event records within the target event stream which meet the filter
criteria, which have an event time which is after the "replay-start-
time", and which have an event time before the "stop-time" should
this "stop-time" exist. The end of these historical event records is
identified via a "replay-completed" subscription state change
notification. Any event records generated since the subscription
establishment may then follow. For a particular subscription, all
event records will be delivered in the order they are placed into the
event stream.
Replay is an optional feature which is dependent on an event stream
supporting some form of logging. This document puts no restrictions
on the size or form of the log, where it resides within the
publisher, or when event record entries in the log are purged.
The inclusion of a "replay-start-time" within an "establish-
subscription" RPC indicates a replay request. If the "replay-start-
time" contains a value that is earlier than what a publisher's
retained history supports, then if the subscription is accepted, the
actual publisher's revised start time MUST be set in the returned
"replay-start-time-revision" object.
A "stop-time" parameter may be included in a replay subscription.
For a replay subscription, the "stop-time" MAY be earlier than the
current time, but MUST be later than the "replay-start-time".
If the given "replay-start-time" is later than the time marked within
any event records retained within the replay buffer, then the
publisher MUST send a "replay-completed" notification immediately
after a successful establish-subscription RPC response.
If an event stream supports replay, the "replay-support" leaf is
present in the "/streams/stream" list entry for the event stream. An
event stream that does support replay is not expected to have an
unlimited supply of saved notifications available to accommodate any
given replay request. To assess the timeframe available for replay,
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subscribers can read the leafs "replay-log-creation-time" and
"replay-log-aged-time". See Figure 18 for the YANG tree, and
Section 4 for the YANG model describing these elements. The actual
size of the replay log at any given time is a publisher specific
matter. Control parameters for the replay log are outside the scope
of this document.
2.4.3. Modifying a Dynamic Subscription
The "modify-subscription" operation permits changing the terms of an
existing dynamic subscription. Dynamic subscriptions can be modified
any number of times. Dynamic subscriptions can only be modified via
this RPC using a transport session connecting to the subscriber. If
the publisher accepts the requested modifications, it acknowledges
success to the subscriber, then immediately starts sending event
records based on the new terms.
Subscriptions created by configuration cannot be modified via this
RPC. However configuration may be used to modify objects referenced
by the subscription (such as a referenced filter).
Below is a tree diagram for "modify-subscription". All objects
contained in this tree are described within the included YANG model
within Section 4.
+---x modify-subscription
+---w input
+---w id
| subscription-id
+---w (target)
| +--:(stream)
| +---w (stream-filter)?
| +--:(by-reference)
| | +---w stream-filter-name
| | stream-filter-ref
| +--:(within-subscription)
| +---w (filter-spec)?
| +--:(stream-subtree-filter)
| | +---w stream-subtree-filter? <anydata>
| | {subtree}?
| +--:(stream-xpath-filter)
| +---w stream-xpath-filter?
| yang:xpath1.0 {xpath}?
+---w stop-time?
yang:date-and-time
Figure 4: modify-subscription RPC tree diagram
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If the publisher accepts the requested modifications on a currently
suspended subscription, the subscription will immediately be resumed
(i.e., the modified subscription is returned to the active state.)
The publisher MAY immediately suspend this newly modified
subscription through the "subscription-suspended" notification before
any event records are sent.
If the publisher rejects the RPC request, the subscription remains as
prior to the request. That is, the request has no impact whatsoever.
Rejection of the RPC for any reason is indicated by via RPC error as
described in Section 2.4.6. The contents of such a rejected RPC MAY
include hints on inputs which (if considered) may result in a
successfully modified subscription. These hints MUST be transported
within a yang-data "modify-subscription-stream-error-info" container
inserted into the RPC error response.
Below is a tree diagram for "modify-subscription-RPC-yang-data". All
objects contained in this tree are described within the included YANG
model within Section 4.
yang-data modify-subscription-stream-error-info
+--ro modify-subscription-stream-error-info
+--ro reason? identityref
+--ro filter-failure-hint? string
Figure 5: modify-subscription RPC yang-data tree diagram
2.4.4. Deleting a Dynamic Subscription
The "delete-subscription" operation permits canceling an existing
subscription. If the publisher accepts the request, and the
publisher has indicated success, the publisher MUST NOT send any more
notification messages for this subscription.
Below is a tree diagram for "delete-subscription". All objects
contained in this tree are described within the included YANG model
within Section 4.
+---x delete-subscription
+---w input
+---w id subscription-id
Figure 6: delete-subscription RPC tree diagram
Dynamic subscriptions can only be deleted via this RPC using a
transport session connecting to the subscriber. Configured
subscriptions cannot be deleted using RPCs.
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2.4.5. Killing a Dynamic Subscription
The "kill-subscription" operation permits an operator to end a
dynamic subscription which is not associated with the transport
session used for the RPC. A publisher MUST terminate any dynamic
subscription identified by the "id" parameter in the RPC request, if
such a subscription exists.
Configured subscriptions cannot be killed using this RPC. Instead,
configured subscriptions are deleted as part of regular configuration
operations. Publishers MUST reject any RPC attempt to kill a
configured subscription.
Below is a tree diagram for "kill-subscription". All objects
contained in this tree are described within the included YANG model
within Section 4.
+---x kill-subscription
+---w input
+---w id subscription-id
Figure 7: kill-subscription RPC tree diagram
2.4.6. RPC Failures
Whenever an RPC is unsuccessful, the publisher returns relevant
information as part of the RPC error response. Transport level error
processing MUST be done before RPC error processing described in this
section. In all cases, RPC error information returned will use
existing transport layer RPC structures, such as those seen with
NETCONF in [RFC6241] Appendix A, or with RESTCONF in [RFC8040]
Section 7.1. These structures MUST be able to encode subscription
specific errors identified below and defined within this document's
YANG model.
As a result of this variety, how subscription errors are encoded
within an RPC error response is transport dependent. Following are
valid errors which can occur for each RPC:
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establish-subscription modify-subscription
---------------------- -------------------
dscp-unavailable filter-unsupported
encoding-unsupported insufficient-resources
filter-unsupported no-such-subscription
insufficient-resources
replay-unsupported
delete-subscription kill-subscription
---------------------- ----------------------
no-such-subscription no-such-subscription
To see a NETCONF based example of an error response from above, see
[I-D.draft-ietf-netconf-netconf-event-notifications], Figure 10.
There is one final set of transport independent RPC error elements
included in the YANG model. These are three yang-data structures
which enable the publisher to provide to the receiver that error
information which does not fit into existing transport layer RPC
structures. These three yang-data structures are:
1. "establish-subscription-stream-error-info": This MUST be returned
with the leaf "reason" populated if an RPC error reason has not
been placed elsewhere within the transport portion of a failed
"establish-subscription" RPC response. This MUST be sent if
hints on how to overcome the RPC error are included.
2. "modify-subscription-stream-error-info": This MUST be returned
with the leaf "reason" populated if an RPC error reason has not
been placed elsewhere within the transport portion of a failed
"modify-subscription" RPC response. This MUST be sent if hints
on how to overcome the RPC error are included.
3. "delete-subscription-error-info": This MUST be returned with the
leaf "reason" populated if an RPC error reason has not been
placed elsewhere within the transport portion of a failed
"delete-subscription" or "kill-subscription" RPC response.
2.5. Configured Subscriptions
A configured subscription is a subscription installed via
configuration. Configured subscriptions may be modified by any
configuration client with the proper permissions. Subscriptions can
be modified or terminated via configuration at any point of their
lifetime. Multiple configured subscriptions MUST be supportable over
a single transport session.
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Configured subscriptions have several characteristics distinguishing
them from dynamic subscriptions:
o persistence across publisher reboots,
o persistence even when transport is unavailable, and
o an ability to send notification messages to more than one receiver
(note that receivers are unaware of the existence of any other
receivers.)
On the publisher, supporting configured subscriptions is optional and
advertised using the "configured" feature. On a receiver of a
configured subscription, support for dynamic subscriptions is
optional. However if replaying missed event records is required for
a configured subscription, support for dynamic subscription is highly
recommended. In this case, a separate dynamic subscription can be
established to retransmit the missing event records.
In addition to the subscription parameters available to dynamic
subscriptions described in Section 2.4.2, the following additional
parameters are also available to configured subscriptions:
o A "transport" which identifies the transport protocol to use to
connect with all subscription receivers.
o One or more receivers, each intended as the destination for event
records. Note that each individual receiver is identifiable by
its "name".
o Optional parameters to identify where traffic should egress a
publisher:
* A "source-interface" which identifies the egress interface to
use from the publisher. Publisher support for this is optional
and advertised using the "interface-designation" feature.
* A "source-address" address, which identifies the IP address to
stamp on notification messages destined for the receiver.
* A "source-vrf" which identifies the Virtual Routing and
Forwarding (VRF) instance on which to reach receivers. This
VRF is a network instance as defined within [RFC8529].
Publisher support for VRFs is optional and advertised using the
"supports-vrf" feature.
If none of the above parameters are set, notification messages
MUST egress the publisher's default interface.
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A tree diagram describing these parameters is shown in Figure 20
within Section 3.3. All parameters are described within the YANG
model in Section 4.
2.5.1. Configured Subscription State Model
Below is the state machine for a configured subscription on the
publisher. This state machine describes the three states (valid,
invalid, and concluded), as well as the transitions between these
states. Start and end states are depicted to reflect configured
subscription creation and deletion events. The creation or
modification of a configured subscription initiates an evaluation by
the publisher to determine if the subscription is in valid or invalid
states. The publisher uses its own criteria in making this
determination. If in the valid state, the subscription becomes
operational. See (1) in the diagram below.
.........
: start :-.
:.......: |
create .---modify-----.----------------------------------.
| | | |
V V .-------. ....... .---------.
.----[evaluate]--no--->|invalid|-delete->: end :<-delete-|concluded|
| '-------' :.....: '---------'
|-[evaluate]--no-(2). ^ ^ ^
| ^ | | | |
yes | '->unsupportable delete stop-time
| modify (subscription- (subscription- (subscription-
| | terminated*) terminated*) concluded*)
| | | | |
(1) | (3) (4) (5)
| .---------------------------------------------------------------.
'-->| valid |
'---------------------------------------------------------------'
Legend:
dotted boxes: subscription added or removed via configuration
dashed boxes: states for a subscription
[evaluate]: decision point on whether the subscription is supportable
(*): resulting subscription state change notification
Figure 8: Publisher state model for a configured subscription
A subscription in the valid state may move to the invalid state in
one of two ways. First, it may be modified in a way which fails a
re-evaluation. See (2) in the diagram. Second, the publisher might
determine that the subscription is no longer supportable. This could
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be for reasons of an unexpected but sustained increase in an event
stream's event records, degraded CPU capacity, a more complex
referenced filter, or other subscriptions which have usurped
resources. See (3) in the diagram. No matter the case, a
"subscription-terminated" notification is sent to any receivers in an
active or suspended state. A subscription in the valid state may
also transition to the concluded state via (5) if a configured stop
time has been reached. In this case, a "subscription-concluded"
notification is sent to any receivers in active or suspended states.
Finally, a subscription may be deleted by configuration (4).
When a subscription is in the valid state, a publisher will attempt
to connect with all receivers of a configured subscription and
deliver notification messages. Below is the state machine for each
receiver of a configured subscription. This receiver state machine
is fully contained within the state machine of the configured
subscription, and is only relevant when the configured subscription
is in the valid state.
.-----------------------------------------------------------------.
| valid |
| .----------. .------------. |
| | receiver |---timeout---------------->| receiver | |
| |connecting|<----------------reset--(c)|disconnected| |
| | |<-transport '------------' |
| '----------' loss,reset------------------------------. |
| (a) | | |
| subscription- (b) (b) |
| started* .--------. .---------. |
| '----->| |(d)-insufficient CPU,------->| | |
| |receiver| buffer overflow |receiver | |
| subscription-| active | |suspended| |
| modified* | |<----CPU, b/w sufficient,-(e)| | |
| '---->'--------' subscription-modified* '---------' |
'-----------------------------------------------------------------'
Legend:
dashed boxes which include the word 'receiver' show the possible
states for an individual receiver of a valid configured subscription.
* indicates a subscription state change notification
Figure 9: Receiver state for a configured subscription on a Publisher
When a configured subscription first moves to the valid state, the
"state" leaf of each receiver is initialized to the connecting state.
If transport connectivity is not available to any receiver and there
are any notification messages to deliver, a transport session is
established (e.g., through [RFC8071]). Individual receivers are
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moved to the active state when a "subscription-started" subscription
state change notification is successfully passed to that receiver
(a). Event records are only sent to active receivers. Receivers of
a configured subscription remain active if both transport
connectivity can be verified to the receiver, and event records are
not being dropped due to a publisher buffer capacity being reached.
The result is that a receiver will remain active on the publisher as
long as events aren't being lost, or the receiver cannot be reached.
In addition, a configured subscription's receiver MUST be moved to
the connecting state if the receiver is reset via the "reset" action
(b), (c). For more on reset, see Section 2.5.5. If transport
connectivity cannot be achieved while in the connecting state, the
receiver MAY be moved to the disconnected state.
A configured subscription's receiver MUST be moved to the suspended
state if there is transport connectivity between the publisher and
receiver, but notification messages are failing to be delivered due
to publisher buffer capacity being reached, or notification messages
are not able to be generated for that receiver due to insufficient
CPU (d). This is indicated to the receiver by the "subscription-
suspended" subscription state change notification.
A configured subscription receiver MUST be returned to the active
state from the suspended state when notification messages are able to
be generated, bandwidth is sufficient to handle the notification
messages, and a receiver has successfully been sent a "subscription-
resumed" or "subscription-modified" subscription state change
notification (e). The choice as to which of these two subscription
state change notifications is sent is determined by whether the
subscription was modified during the period of suspension.
Modification of a configured subscription is possible at any time. A
"subscription-modified" subscription state change notification will
be sent to all active receivers, immediately followed by notification
messages conforming to the new parameters. Suspended receivers will
also be informed of the modification. However this notification will
await the end of the suspension for that receiver (e).
The mechanisms described above are mirrored in the RPCs and
notifications within the document. It should be noted that these
RPCs and notifications have been designed to be extensible and allow
subscriptions into targets other than event streams. For instance,
the YANG module defined in Section 5 of [I-D.ietf-netconf-yang-push]
augments "/sn:modify-subscription/sn:input/sn:target".
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2.5.2. Creating a Configured Subscription
Configured subscriptions are established using configuration
operations against the top-level "subscriptions" subtree.
Because there is no explicit association with an existing transport
session, configuration operations MUST include additional parameters
beyond those of dynamic subscriptions. These parameters identify
each receiver, how to connect with that receiver, and possibly
whether the notification messages need to come from a specific egress
interface on the publisher. Receiver specific transport connectivity
parameters MUST be configured via transport specific augmentations to
this specification. See Section 2.5.7 for details.
After a subscription is successfully established, the publisher
immediately sends a "subscription-started" subscription state change
notification to each receiver. It is quite possible that upon
configuration, reboot, or even steady-state operations, a transport
session may not be currently available to the receiver. In this
case, when there is something to transport for an active
subscription, transport specific call-home operations will be used to
establish the connection. When transport connectivity is available,
notification messages may then be pushed.
With active configured subscriptions, it is allowable to buffer event
records even after a "subscription-started" has been sent. However
if events are lost (rather than just delayed) due to replay buffer
capacity being reached, a new "subscription-started" must be sent.
This new "subscription-started" indicates an event record
discontinuity.
To see an example of subscription creation using configuration
operations over NETCONF, see Appendix A of
[I-D.draft-ietf-netconf-netconf-event-notifications].
2.5.3. Modifying a Configured Subscription
Configured subscriptions can be modified using configuration
operations against the top-level "subscriptions" subtree.
If the modification involves adding receivers, added receivers are
placed in the connecting state. If a receiver is removed, the
subscription state change notification "subscription-terminated" is
sent to that receiver if that receiver is active or suspended.
If the modification involves changing the policies for the
subscription, the publisher sends to currently active receivers a
"subscription-modified" notification. For any suspended receivers, a
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"subscription-modified" notification will be delayed until the
receiver is resumed. (Note: in this case, the "subscription-
modified" notification informs the receiver that the subscription has
been resumed, so no additional "subscription-resumed" need be sent.
Also note that if multiple modifications have occurred during the
suspension, only the "subscription-modified" notification describing
the latest one need be sent to the receiver.)
2.5.4. Deleting a Configured Subscription
Subscriptions can be deleted through configuration against the top-
level "subscriptions" subtree.
Immediately after a subscription is successfully deleted, the
publisher sends to all receivers of that subscription a subscription
state change notification stating the subscription has ended (i.e.,
"subscription-terminated").
2.5.5. Resetting a Configured Subscription Receiver
It is possible that a configured subscription to a receiver needs to
be reset. This is accomplished via the "reset" action within the
YANG model at "/subscriptions/subscription/receivers/receiver/reset".
This action may be useful in cases where a publisher has timed out
trying to reach a receiver. When such a reset occurs, a transport
session will be initiated if necessary, and a new "subscription-
started" notification will be sent. This action does not have any
effect on transport connectivity if the needed connectivity already
exists.
2.5.6. Replay for a Configured Subscription
It is possible to do replay on a configured subscription. This is
supported via the configuration of the "configured-replay" object on
the subscription. The setting of this object enables the streaming
of the buffered event records for the subscribed event stream. All
buffered event records which have been retained since the last
publisher restart will be sent to each configured receiver.
Replay of events records created since restart is useful. It allows
event records generated before transport connectivity establishment
to be passed to a receiver. Setting the restart time as the earliest
configured replay time precludes possibility of resending of event
records logged prior to publisher restart. It also ensures the same
records will be sent to each configured receiver, regardless of the
speed of transport connectivity establishment to each receiver.
Finally, establishing restart as the earliest potential time for
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event records to be included within notification messages, a well-
understood timeframe for replay is defined.
As a result, when any configured subscription receivers become
active, buffered event records will be sent immediately after the
"subscription-started" notification. If the publisher knows the last
event record sent to a receiver, and the publisher has not rebooted,
the next event record on the event stream which meets filtering
criteria will be the leading event record sent. Otherwise, the
leading event record will be the first event record meeting filtering
criteria subsequent to the latest of three different times: the
"replay-log-creation-time", "replay-log-aged-time", or the most
recent publisher boot time. The "replay-log-creation-time" and
"replay-log-aged-time" are discussed in Section 2.4.2.1. The most
recent publisher boot time ensures that duplicate event records are
not replayed from a previous time the publisher was booted.
It is quite possible that a receiver might want to retrieve event
records from an event stream prior to the latest boot. If such
records exist where there is a configured replay, the publisher MUST
send the time of the event record immediately preceding the "replay-
start-time" within the "replay-previous-event-time" leaf. Through
the existence of the "replay-previous-event-time", the receiver will
know that earlier events prior to reboot exist. In addition, if the
subscriber was previously receiving event records with the same
subscription "id", the receiver can determine if there was a time gap
where records generated on the publisher were not successfully
received. And with this information, the receiver may choose to
dynamically subscribe to retrieve any event records placed into the
event stream before the most recent boot time.
All other replay functionality remains the same as with dynamic
subscriptions as described in Section 2.4.2.1.
2.5.7. Transport Connectivity for a Configured Subscription
This specification is transport independent. However supporting a
configured subscription will often require the establishment of
transport connectivity. And the parameters used for this transport
connectivity establishment are transport specific. As a result, the
YANG model defined within Section 4 is not able to directly define
and expose these transport parameters.
It is necessary for an implementation to support the connection
establishment process. To support this function, the YANG model does
include a node where transport specific parameters for a particular
receiver may be augmented. This node is
"/subscriptions/subscription/receivers/receiver". By augmenting
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transport parameters from this node, system developers are able to
incorporate the YANG objects necessary to support the transport
connectivity establishment process.
The result of this is the following requirement. A publisher
supporting the feature "configured" MUST also support least one YANG
model which augments transport connectivity parameters on
"/subscriptions/subscription/receivers/receiver". For an example of
such an augmentation, see Appendix A.
2.6. Event Record Delivery
Whether dynamic or configured, once a subscription has been set up,
the publisher streams event records via notification messages per the
terms of the subscription. For dynamic subscriptions, notification
messages are sent over the session used to establish the
subscription. For configured subscriptions, notification messages
are sent over the connections specified by the transport and each
receiver of a configured subscription.
A notification message is sent to a receiver when an event record is
not blocked by either the specified filter criteria or receiver
permissions. This notification message MUST include an "eventTime"
object as defined per [RFC5277] Section 4. This "eventTime" MUST be
at the top level of YANG structured event record.
The following example within [RFC7950] section 7.16.3 is an example
of a compliant message:
<notification
xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
<eventTime>2007-09-01T10:00:00Z</eventTime>
<link-failure xmlns="http://acme.example.com/system">
<if-name>so-1/2/3.0</if-name>
<if-admin-status>up</if-admin-status>
<if-oper-status>down</if-oper-status>
</link-failure>
</notification>
Figure 10: subscribed notification message
[RFC5277] Section 2.2.1 states that a notification message is to be
sent to a subscriber which initiated a "create-subscription". With
this specification, this [RFC5277] statement should be more broadly
interpreted to mean that notification messages can also be sent to a
subscriber which initiated an "establish-subscription", or a
configured receiver which has been sent a "subscription-started".
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When a dynamic subscription has been started or modified, with
"establish-subscription" or "modify-subscription" respectively, event
records matching the newly applied filter criteria MUST NOT be sent
until after the RPC reply has been sent.
When a configured subscription has been started or modified, event
records matching the newly applied filter criteria MUST NOT be sent
until after the "subscription-started" or "subscription-modified"
notifications has been sent, respectively.
2.7. Subscription state change notifications
In addition to sending event records to receivers, a publisher MUST
also send subscription state change notifications when events related
to subscription management have occurred.
Subscription state change notifications are unlike other
notifications in that they are never included in any event stream.
Instead, they are inserted (as defined in this section) within the
sequence of notification messages sent to a particular receiver.
subscription state change notifications cannot be dropped or filtered
out, they cannot be stored in replay buffers, and they are delivered
only to impacted receivers of a subscription. The identification of
subscription state change notifications is easy to separate from
other notification messages through the use of the YANG extension
"subscription-state-notif". This extension tags a notification as a
subscription state change notification.
The complete set of subscription state change notifications is
described in the following subsections.
2.7.1. subscription-started
This notification indicates that a configured subscription has
started, and event records may be sent. Included in this
subscription state change notification are all the parameters of the
subscription, except for the receiver(s) transport connection
information and origin information indicating where notification
messages will egress the publisher. Note that if a referenced filter
from the "filters" container has been used within the subscription,
the notification still provides the contents of that referenced
filter under the "within-subscription" subtree.
Note that for dynamic subscriptions, no "subscription-started"
notifications are ever sent.
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Below is a tree diagram for "subscription-started". All objects
contained in this tree are described within the included YANG model
within Section 4.
+---n subscription-started {configured}?
+--ro id
| subscription-id
+--ro (target)
| +--:(stream)
| +--ro (stream-filter)?
| | +--:(by-reference)
| | | +--ro stream-filter-name
| | | stream-filter-ref
| | +--:(within-subscription)
| | +--ro (filter-spec)?
| | +--:(stream-subtree-filter)
| | | +--ro stream-subtree-filter? <anydata>
| | | {subtree}?
| | +--:(stream-xpath-filter)
| | +--ro stream-xpath-filter? yang:xpath1.0
| | {xpath}?
| +--ro stream stream-ref
| +--ro replay-start-time?
| | yang:date-and-time {replay}?
| +--ro replay-previous-event-time?
| yang:date-and-time {replay}?
+--ro stop-time?
| yang:date-and-time
+--ro dscp? inet:dscp
| {dscp}?
+--ro weighting? uint8 {qos}?
+--ro dependency?
| subscription-id {qos}?
+--ro transport? transport
| {configured}?
+--ro encoding? encoding
+--ro purpose? string
{configured}?
Figure 11: subscription-started notification tree diagram
2.7.2. subscription-modified
This notification indicates that a subscription has been modified by
configuration operations. It is delivered directly after the last
event records processed using the previous subscription parameters,
and before any event records processed after the modification.
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Below is a tree diagram for "subscription-modified". All objects
contained in this tree are described within the included YANG model
within Section 4.
+---n subscription-modified
+--ro id
| subscription-id
+--ro (target)
| +--:(stream)
| +--ro (stream-filter)?
| | +--:(by-reference)
| | | +--ro stream-filter-name
| | | stream-filter-ref
| | +--:(within-subscription)
| | +--ro (filter-spec)?
| | +--:(stream-subtree-filter)
| | | +--ro stream-subtree-filter? <anydata>
| | | {subtree}?
| | +--:(stream-xpath-filter)
| | +--ro stream-xpath-filter? yang:xpath1.0
| | {xpath}?
| +--ro stream stream-ref
| +--ro replay-start-time?
| yang:date-and-time {replay}?
+--ro stop-time?
| yang:date-and-time
+--ro dscp? inet:dscp
| {dscp}?
+--ro weighting? uint8 {qos}?
+--ro dependency?
| subscription-id {qos}?
+--ro transport? transport
| {configured}?
+--ro encoding? encoding
+--ro purpose? string
{configured}?
Figure 12: subscription-modified notification tree diagram
A publisher most often sends this notification directly after the
modification of any configuration parameters impacting a configured
subscription. But it may also be sent at two other times:
1. Where a configured subscription has been modified during the
suspension of a receiver, the notification will be delayed until
the receiver's suspension is lifted. In this situation, the
notification indicates that the subscription has been both
modified and resumed.
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2. A "subscription-modified" subscription state change notification
MUST be sent if the contents of the filter identified by the
subscription's "stream-filter-ref" leaf has changed. This state
change notification is to be sent for a filter change impacting
any active receiver of a configured or dynamic subscription.
2.7.3. subscription-terminated
This notification indicates that no further event records for this
subscription should be expected from the publisher. A publisher may
terminate the sending event records to a receiver for the following
reasons:
1. Configuration which removes a configured subscription, or a
"kill-subscription" RPC which ends a dynamic subscription. These
are identified via the reason "no-such-subscription".
2. A referenced filter is no longer accessible. This is identified
by "filter-unavailable".
3. The event stream referenced by a subscription is no longer
accessible by the receiver. This is identified by "stream-
unavailable".
4. A suspended subscription has exceeded some timeout. This is
identified by "suspension-timeout".
Each of the reasons above correspond one-to-one with a "reason"
identityref specified within the YANG model.
Below is a tree diagram for "subscription-terminated". All objects
contained in this tree are described within the included YANG model
within Section 4.
+---n subscription-terminated
+--ro id subscription-id
+--ro reason identityref
Figure 13: subscription-terminated notification tree diagram
Note: this subscription state change notification MUST be sent to a
dynamic subscription's receiver when the subscription ends
unexpectedly. The cases when this might happen are when a "kill-
subscription" RPC is successful, or when some other event not
including the reaching the subscription's "stop-time" results in a
publisher choosing to end the subscription.
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2.7.4. subscription-suspended
This notification indicates that a publisher has suspended the
sending of event records to a receiver, and also indicates the
possible loss of events. Suspension happens when capacity
constraints stop a publisher from serving a valid subscription. The
two conditions where is this possible are:
1. "insufficient-resources" when a publisher is unable to produce
the requested event stream of notification messages, and
2. "unsupportable-volume" when the bandwidth needed to get generated
notification messages to a receiver exceeds a threshold.
These conditions are encoded within the "reason" object. No further
notification will be sent until the subscription resumes or is
terminated.
Below is a tree diagram for "subscription-suspended". All objects
contained in this tree are described within the included YANG model
within Section 4.
+---n subscription-suspended
+--ro id subscription-id
+--ro reason identityref
Figure 14: subscription-suspended notification tree diagram
2.7.5. subscription-resumed
This notification indicates that a previously suspended subscription
has been resumed under the unmodified terms previously in place.
Subscribed event records generated after the issuance of this
subscription state change notification may now be sent.
Below is the tree diagram for "subscription-resumed". All objects
contained in this tree are described within the included YANG model
within Section 4.
+---n subscription-resumed
+--ro id subscription-id
Figure 15: subscription-resumed notification tree diagram
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2.7.6. subscription-completed
This notification indicates that a subscription that includes a
"stop-time" has successfully finished passing event records upon the
reaching of that time.
Below is a tree diagram for "subscription-completed". All objects
contained in this tree are described within the included YANG model
within Section 4.
+---n subscription-completed {configured}?
+--ro id subscription-id
Figure 16: subscription-completed notification tree diagram
2.7.7. replay-completed
This notification indicates that all of the event records prior to
the current time have been passed to a receiver. It is sent before
any notification message containing an event record with a timestamp
later than (1) the "stop-time" or (2) the subscription's start time.
If a subscription contains no "stop-time", or has a "stop-time" that
has not been reached, then after the "replay-completed" notification
has been sent, additional event records will be sent in sequence as
they arise naturally on the publisher.
Below is a tree diagram for "replay-completed". All objects
contained in this tree are described within the included YANG model
within Section 4.
+---n replay-completed {replay}?
+--ro id subscription-id
Figure 17: replay-completed notification tree diagram
2.8. Subscription Monitoring
In the operational state datastore, the container "subscriptions"
maintains the state of all dynamic subscriptions, as well as all
configured subscriptions. Using datastore retrieval operations, or
subscribing to the "subscriptions" container
[I-D.ietf-netconf-yang-push] allows the state of subscriptions and
their connectivity to receivers to be monitored.
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Each subscription in the operational state datastore is represented
as a list element. Included in this list are event counters for each
receiver, the state of each receiver, as well as the subscription
parameters currently in effect. The appearance of the leaf
"configured-subscription-state" indicates that a particular
subscription came into being via configuration. This leaf also
indicates if the current state of that subscription is valid,
invalid, and concluded.
To understand the flow of event records within a subscription, there
are two counters available for each receiver. The first counter is
"sent-event-records" which shows the quantity of events actually
identified for sending to a receiver. The second counter is
"excluded-event-records" which shows event records not sent to
receiver. "excluded-event-records" shows the combined results of
both access control and per-subscription filtering. For configured
subscriptions, counters are reset whenever the subscription is
evaluated to valid (see (1) in Figure 8).
Dynamic subscriptions are removed from the operational state
datastore once they expire (reaching stop-time) or when they are
terminated. While many subscription objects are shown as
configurable, dynamic subscriptions are only included within the
operational state datastore and as a result are not configurable.
2.9. Advertisement
Publishers supporting this document MUST indicate support of the YANG
model "ietf-subscribed-notifications" within the YANG library of the
publisher. In addition if supported, the optional features "encode-
xml", "encode-json", "configured" "supports-vrf", "qos", "xpath",
"subtree", "interface-designation", "dscp", and "replay" MUST be
indicated.
3. YANG Data Model Trees
This section contains tree diagrams for nodes defined in Section 4.
For tree diagrams of subscription state change notifications, see
Section 2.7. For the tree diagrams for the RPCs, see Section 2.4.
3.1. Event Streams Container
A publisher maintains a list of available event streams as
operational data. This list contains both standardized and vendor-
specific event streams. This enables subscribers to discover what
streams a publisher supports.
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+--ro streams
+--ro stream* [name]
+--ro name string
+--ro description string
+--ro replay-support? empty {replay}?
+--ro replay-log-creation-time yang:date-and-time
| {replay}?
+--ro replay-log-aged-time? yang:date-and-time
{replay}?
Figure 18: Stream Container tree diagram
Above is a tree diagram for the "streams" container. All objects
contained in this tree are described within the included YANG model
within Section 4.
3.2. Filters Container
The "filters" container maintains a list of all subscription filters
that persist outside the life-cycle of a single subscription. This
enables pre-defined filters which may be referenced by more than one
subscription.
+--rw filters
+--rw stream-filter* [name]
+--rw name string
+--rw (filter-spec)?
+--:(stream-subtree-filter)
| +--rw stream-subtree-filter? <anydata> {subtree}?
+--:(stream-xpath-filter)
+--rw stream-xpath-filter? yang:xpath1.0 {xpath}?
Figure 19: Filter Container tree diagram
Above is a tree diagram for the filters container. All objects
contained in this tree are described within the included YANG model
within Section 4.
3.3. Subscriptions Container
The "subscriptions" container maintains a list of all subscriptions
on a publisher, both configured and dynamic. It can be used to
retrieve information about the subscriptions which a publisher is
serving.
+--rw subscriptions
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+--rw subscription* [id]
+--rw id
| subscription-id
+--rw (target)
| +--:(stream)
| +--rw (stream-filter)?
| | +--:(by-reference)
| | | +--rw stream-filter-name
| | | stream-filter-ref
| | +--:(within-subscription)
| | +--rw (filter-spec)?
| | +--:(stream-subtree-filter)
| | | +--rw stream-subtree-filter? <anydata>
| | | {subtree}?
| | +--:(stream-xpath-filter)
| | +--rw stream-xpath-filter?
| | yang:xpath1.0 {xpath}?
| +--rw stream stream-ref
| +--ro replay-start-time?
| | yang:date-and-time {replay}?
| +--rw configured-replay? empty
| {configured,replay}?
+--rw stop-time?
| yang:date-and-time
+--rw dscp? inet:dscp
| {dscp}?
+--rw weighting? uint8 {qos}?
+--rw dependency?
| subscription-id {qos}?
+--rw transport? transport
| {configured}?
+--rw encoding? encoding
+--rw purpose? string
| {configured}?
+--rw (notification-message-origin)? {configured}?
| +--:(interface-originated)
| | +--rw source-interface?
| | if:interface-ref {interface-designation}?
| +--:(address-originated)
| +--rw source-vrf?
| | -> /ni:network-instances/network-instance/name
| | {supports-vrf}?
| +--rw source-address?
| inet:ip-address-no-zone
+--ro configured-subscription-state? enumeration
| {configured}?
+--rw receivers
+--rw receiver* [name]
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+--rw name string
+--ro sent-event-records?
| yang:zero-based-counter64
+--ro excluded-event-records?
| yang:zero-based-counter64
+--ro state enumeration
+---x reset {configured}?
+--ro output
+--ro time yang:date-and-time
Figure 20: Subscriptions tree diagram
Above is a tree diagram for the subscriptions container. All objects
contained in this tree are described within the included YANG model
within Section 4.
4. Data Model
This module imports typedefs from [RFC6991], [RFC8343], and
[RFC8040], and it references [RFC8529], [XPATH], [RFC6241],
[RFC7049], [RFC7540], [RFC7951] , [RFC7950] and [RFC8259].
[ note to the RFC Editor - please replace XXXX within this YANG model
with the number of this document ]
[ note to the RFC Editor - please replace the two dates within the
YANG module with the date of publication ]
<CODE BEGINS> file "ietf-subscribed-notifications@2019-05-06.yang"
module ietf-subscribed-notifications {
yang-version 1.1;
namespace
"urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications";
prefix sn;
import ietf-inet-types {
prefix inet;
reference
"RFC 6991: Common YANG Data Types";
}
import ietf-interfaces {
prefix if;
reference
"RFC 8343: A YANG Data Model for Interface Management";
}
import ietf-netconf-acm {
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prefix nacm;
reference
"RFC 8341: Network Configuration Access Control Model";
}
import ietf-network-instance {
prefix ni;
reference
"RFC 8529: YANG Model for Network Instances";
}
import ietf-restconf {
prefix rc;
reference
"RFC 8040: RESTCONF Protocol";
}
import ietf-yang-types {
prefix yang;
reference
"RFC 6991: Common YANG Data Types";
}
organization "IETF NETCONF (Network Configuration) Working Group";
contact
"WG Web: <http:/tools.ietf.org/wg/netconf/>
WG List: <mailto:netconf@ietf.org>
Author: Alexander Clemm
<mailto:ludwig@clemm.org>
Author: Eric Voit
<mailto:evoit@cisco.com>
Author: Alberto Gonzalez Prieto
<mailto:alberto.gonzalez@microsoft.com>
Author: Einar Nilsen-Nygaard
<mailto:einarnn@cisco.com>
Author: Ambika Prasad Tripathy
<mailto:ambtripa@cisco.com>";
description
"Contains a YANG specification for subscribing to event records
and receiving matching content within notification messages.
Copyright (c) 2018 IETF Trust and the persons identified as authors
of the code. All rights reserved.
Redistribution and use in source and binary forms, with or without
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modification, is permitted pursuant to, and subject to the license
terms contained in, the Simplified BSD License set forth in Section
4.c of the IETF Trust's Legal Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC XXXX; see the RFC
itself for full legal notices.";
revision 2019-05-06 {
description
"Initial version";
reference
"RFC XXXX:Subscription to YANG Event Notifications";
}
/*
* FEATURES
*/
feature configured {
description
"This feature indicates that configuration of subscriptions is
supported.";
}
feature dscp {
description
"This feature indicates that a publisher supports the ability to
set the DiffServ Code Point (DSCP) value in outgoing packets.";
}
feature encode-json {
description
"This feature indicates that JSON encoding of notification
messages is supported.";
}
feature encode-xml {
description
"This feature indicates that XML encoding of notification
messages is supported.";
}
feature interface-designation {
description
"This feature indicates a publisher supports sourcing all
receiver interactions for a configured subscription from a single
designated egress interface.";
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}
feature qos {
description
"This feature indicates a publisher supports absolute
dependencies of one subscription's traffic over another, as well
as weighted bandwidth sharing between subscriptions. Both of
these are Quality of Service (QoS) features which allow
differentiated treatment of notification messages between a
publisher and a specific receiver.";
}
feature replay {
description
"This feature indicates that historical event record replay is
supported. With replay, it is possible for past event records to
be streamed in chronological order.";
}
feature subtree {
description
"This feature indicates support for YANG subtree filtering.";
reference "RFC 6241, Section 6.";
}
feature supports-vrf {
description
"This feature indicates a publisher supports VRF configuration
for configured subscriptions. VRF support for dynamic
subscriptions does not require this feature.";
reference "RFC XXXY, Section 6.";
}
feature xpath {
description
"This feature indicates support for XPath filtering.";
reference "http://www.w3.org/TR/1999/REC-xpath-19991116";
}
/*
* EXTENSIONS
*/
extension subscription-state-notification {
description
"This statement applies only to notifications. It indicates that
the notification is a subscription state change notification.
Therefore it does not participate in a regular event stream and
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does not need to be specifically subscribed to in order to be
received. This statement can only occur as a substatement to the
YANG 'notification' statement. This statement is not for use
outside of this YANG module.";
}
/*
* IDENTITIES
*/
/* Identities for RPC and Notification errors */
identity delete-subscription-error {
description
"Problem found while attempting to fulfill either a
'delete-subscription' RPC request or a 'kill-subscription'
RPC request.";
}
identity establish-subscription-error {
description
"Problem found while attempting to fulfill an
'establish-subscription' RPC request.";
}
identity modify-subscription-error {
description
"Problem found while attempting to fulfill a
'modify-subscription' RPC request.";
}
identity subscription-suspended-reason {
description
"Problem condition communicated to a receiver as part of a
'subscription-suspended' notification.";
}
identity subscription-terminated-reason {
description
"Problem condition communicated to a receiver as part of a
'subscription-terminated' notification.";
}
identity dscp-unavailable {
base establish-subscription-error;
if-feature "dscp";
description
"The publisher is unable mark notification messages with a
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prioritization information in a way which will be respected
during network transit.";
}
identity encoding-unsupported {
base establish-subscription-error;
description
"Unable to encode notification messages in the desired format.";
}
identity filter-unavailable {
base subscription-terminated-reason;
description
"Referenced filter does not exist. This means a receiver is
referencing a filter which doesn't exist, or to which they do not
have access permissions.";
}
identity filter-unsupported {
base establish-subscription-error;
base modify-subscription-error;
description
"Cannot parse syntax within the filter. This failure can be from
a syntax error, or a syntax too complex to be processed by the
publisher.";
}
identity insufficient-resources {
base establish-subscription-error;
base modify-subscription-error;
base subscription-suspended-reason;
description
"The publisher has insufficient resources to support the
requested subscription. An example might be that allocated CPU
is too limited to generate the desired set of notification
messages.";
}
identity no-such-subscription {
base modify-subscription-error;
base delete-subscription-error;
base subscription-terminated-reason;
description
"Referenced subscription doesn't exist. This may be as a result of
a non-existent subscription id, an id which belongs to another
subscriber, or an id for configured subscription.";
}
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identity replay-unsupported {
base establish-subscription-error;
if-feature "replay";
description
"Replay cannot be performed for this subscription. This means the
publisher will not provide the requested historic information
from the event stream via replay to this receiver.";
}
identity stream-unavailable {
base subscription-terminated-reason;
description
"Not a subscribable event stream. This means the referenced event
stream is not available for subscription by the receiver.";
}
identity suspension-timeout {
base subscription-terminated-reason;
description
"Termination of previously suspended subscription. The publisher
has eliminated the subscription as it exceeded a time limit for
suspension.";
}
identity unsupportable-volume {
base subscription-suspended-reason;
description
"The publisher does not have the network bandwidth needed to get
the volume of generated information intended for a receiver.";
}
/* Identities for encodings */
identity configurable-encoding {
description
"If a transport identity derives from this identity, it means
that it supports configurable encodings. An example of a
configurable encoding might be a new identity such as
'encode-cbor'. Such an identity could use
'configurable-encoding' as its base. This would allow a
dynamic subscription encoded in JSON [RFC-8259] to request
notification messages be encoded via CBOR [RFC-7049]. Further
details for any specific configurable encoding would be
explored in a transport document based on this specification.";
}
identity encoding {
description
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"Base identity to represent data encodings";
}
identity encode-xml {
base encoding;
if-feature "encode-xml";
description
"Encode data using XML as described in RFC 7950";
reference
"RFC 7950 - The YANG 1.1 Data Modeling Language";
}
identity encode-json {
base encoding;
if-feature "encode-json";
description
"Encode data using JSON as described in RFC 7951";
reference
"RFC 7951 - JSON Encoding of Data Modeled with YANG";
}
/* Identities for transports */
identity transport {
description
"An identity that represents the underlying mechanism for
passing notification messages.";
}
/*
* TYPEDEFs
*/
typedef encoding {
type identityref {
base encoding;
}
description
"Specifies a data encoding, e.g. for a data subscription.";
}
typedef stream-filter-ref {
type leafref {
path "/sn:filters/sn:stream-filter/sn:name";
}
description
"This type is used to reference an event stream filter.";
}
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typedef stream-ref {
type leafref {
path "/sn:streams/sn:stream/sn:name";
}
description
"This type is used to reference a system-provided event stream.";
}
typedef subscription-id {
type uint32;
description
"A type for subscription identifiers.";
}
typedef transport {
type identityref {
base transport;
}
description
"Specifies transport used to send notification messages to a
receiver.";
}
/*
* GROUPINGS
*/
grouping stream-filter-elements {
description
"This grouping defines the base for filters applied to event
streams.";
choice filter-spec {
description
"The content filter specification for this request.";
anydata stream-subtree-filter {
if-feature "subtree";
description
"Event stream evaluation criteria encoded in the syntax of a
subtree filter as defined in RFC 6241, Section 6.
The subtree filter is applied to the representation of
individual, delineated event records as contained within the
event stream.
If the subtree filter returns a non-empty node set, the
filter matches the event record, and the event record is
included in the notification message sent to the receivers.";
reference "RFC 6241, Section 6.";
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}
leaf stream-xpath-filter {
if-feature "xpath";
type yang:xpath1.0;
description
"Event stream evaluation criteria encoded in the syntax of
an XPath 1.0 expression.
The XPath expression is evaluated on the representation of
individual, delineated event records as contained within
the event stream.
The result of the XPath expression is converted to a
boolean value using the standard XPath 1.0 rules. If the
boolean value is 'true', the filter matches the event
record, and the event record is included in the notification
message sent to the receivers.
The expression is evaluated in the following XPath context:
o The set of namespace declarations is the set of prefix
and namespace pairs for all YANG modules implemented
by the server, where the prefix is the YANG module
name and the namespace is as defined by the
'namespace' statement in the YANG module.
If the leaf is encoded in XML, all namespace
declarations in scope on the 'stream-xpath-filter'
leaf element are added to the set of namespace
declarations. If a prefix found in the XML is
already present in the set of namespace declarations,
the namespace in the XML is used.
o The set of variable bindings is empty.
o The function library is the core function library, and
the XPath functions defined in section 10 in RFC 7950.
o The context node is the root node.";
reference
"http://www.w3.org/TR/1999/REC-xpath-19991116
RFC 7950, Section 10.";
}
}
}
grouping update-qos {
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description
"This grouping describes Quality of Service information
concerning a subscription. This information is passed to lower
layers for transport prioritization and treatment";
leaf dscp {
if-feature "dscp";
type inet:dscp;
default "0";
description
"The desired network transport priority level. This is the
priority set on notification messages encapsulating the
results of the subscription. This transport priority is
shared for all receivers of a given subscription.";
}
leaf weighting {
if-feature "qos";
type uint8 {
range "0 .. 255";
}
description
"Relative weighting for a subscription. Larger weights get
more resources. Allows an underlying transport layer perform
informed load balance allocations between various
subscriptions";
reference
"RFC-7540, section 5.3.2";
}
leaf dependency {
if-feature "qos";
type subscription-id;
description
"Provides the 'subscription-id' of a parent subscription which
has absolute precedence should that parent have push updates
ready to egress the publisher. In other words, there should be
no streaming of objects from the current subscription if
the parent has something ready to push.
If a dependency is asserted via configuration or via RPC, but
the referenced 'subscription-id' does not exist, the
dependency is silently discarded. If a referenced
subscription is deleted this dependency is removed.";
reference
"RFC-7540, section 5.3.1";
}
}
grouping subscription-policy-modifiable {
description
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"This grouping describes all objects which may be changed
in a subscription.";
choice target {
mandatory true;
description
"Identifies the source of information against which a
subscription is being applied, as well as specifics on the
subset of information desired from that source.";
case stream {
choice stream-filter {
description
"An event stream filter can be applied to a subscription.
That filter will come either referenced from a global list,
or be provided within the subscription itself.";
case by-reference {
description
"Apply a filter that has been configured separately.";
leaf stream-filter-name {
type stream-filter-ref;
mandatory true;
description
"References an existing event stream filter which is to
be applied to an event stream for the subscription.";
}
}
case within-subscription {
description
"Local definition allows a filter to have the same
lifecycle as the subscription.";
uses stream-filter-elements;
}
}
}
}
leaf stop-time {
type yang:date-and-time;
description
"Identifies a time after which notification messages for a
subscription should not be sent. If 'stop-time' is not
present, the notification messages will continue until the
subscription is terminated. If 'replay-start-time' exists,
'stop-time' must be for a subsequent time. If
'replay-start-time' doesn't exist, 'stop-time' when established
must be for a future time.";
}
}
grouping subscription-policy-dynamic {
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description
"This grouping describes the only information concerning a
subscription which can be passed over the RPCs defined in this
model.";
uses subscription-policy-modifiable {
augment target/stream {
description
"Adds additional objects which can be modified by RPC.";
leaf stream {
type stream-ref {
require-instance false;
}
mandatory true;
description
"Indicates the event stream to be considered for
this subscription.";
}
leaf replay-start-time {
if-feature "replay";
type yang:date-and-time;
config false;
description
"Used to trigger the replay feature for a dynamic
subscription, with event records being selected needing to
be at or after the start at the time specified. If
'replay-start-time' is not present, this is not a replay
subscription and event record push should start
immediately. It is never valid to specify start times that
are later than or equal to the current time.";
}
}
}
uses update-qos;
}
grouping subscription-policy {
description
"This grouping describes the full set of policy information
concerning both dynamic and configured subscriptions, with the
exclusion of both receivers and networking information specific
to the publisher such as what interface should be used to
transmit notification messages.";
uses subscription-policy-dynamic;
leaf transport {
if-feature "configured";
type transport;
description
"For a configured subscription, this leaf specifies the
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transport used to deliver messages destined to all receivers
of that subscription.";
}
leaf encoding {
when 'not(../transport) or derived-from(../transport,
"sn:configurable-encoding")';
type encoding;
description
"The type of encoding for notification messages. For a
dynamic subscription, if not included as part of an establish-
subscription RPC, the encoding will be populated with the
encoding used by that RPC. For a configured subscription, if
not explicitly configured the encoding with be the default
encoding for an underlying transport.";
}
leaf purpose {
if-feature "configured";
type string;
description
"Open text allowing a configuring entity to embed the
originator or other specifics of this subscription.";
}
}
/*
* RPCs
*/
rpc establish-subscription {
description
"This RPC allows a subscriber to create (and possibly negotiate)
a subscription on its own behalf. If successful, the
subscription remains in effect for the duration of the
subscriber's association with the publisher, or until the
subscription is terminated. In case an error occurs, or the
publisher cannot meet the terms of a subscription, an RPC error
is returned, the subscription is not created. In that case, the
RPC reply's 'error-info' MAY include suggested parameter
settings that would have a higher likelihood of succeeding in a
subsequent 'establish-subscription' request.";
input {
uses subscription-policy-dynamic;
leaf encoding {
type encoding;
description
"The type of encoding for the subscribed data. If not
included as part of the RPC, the encoding MUST be set by the
publisher to be the encoding used by this RPC.";
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}
}
output {
leaf id {
type subscription-id;
mandatory true;
description
"Identifier used for this subscription.";
}
leaf replay-start-time-revision {
if-feature "replay";
type yang:date-and-time;
description
"If a replay has been requested, this represents the
earliest time covered by the event buffer for the requested
event stream. The value of this object is the
'replay-log-aged-time' if it exists. Otherwise it is the
'replay-log-creation-time'. All buffered event records
after this time will be replayed to a receiver. This
object will only be sent if the starting time has been
revised to be later than the time requested by the
subscriber.";
}
}
}
rc:yang-data establish-subscription-stream-error-info {
container establish-subscription-stream-error-info {
description
"If any 'establish-subscription' RPC parameters are
unsupportable against the event stream, a subscription is not
created and the RPC error response MUST indicate the reason
why the subscription failed to be created. This yang-data MAY
be inserted as structured data within a subscription's RPC
error response to indicate the failure reason. This yang-data
MUST be inserted if hints are to be provided back to the
subscriber.";
leaf reason {
type identityref {
base establish-subscription-error;
}
description
"Indicates the reason why the subscription has failed to
be created to a targeted event stream.";
}
leaf filter-failure-hint {
type string;
description
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"Information describing where and/or why a provided filter
was unsupportable for a subscription. The syntax and
semantics of this hint are implementation-specific.";
}
}
}
rpc modify-subscription {
description
"This RPC allows a subscriber to modify a dynamic subscription's
parameters. If successful, the changed subscription
parameters remain in effect for the duration of the
subscription, until the subscription is again modified, or until
the subscription is terminated. In case of an error or an
inability to meet the modified parameters, the subscription is
not modified and the original subscription parameters remain in
effect. In that case, the RPC error MAY include 'error-info'
suggested parameter hints that would have a high likelihood of
succeeding in a subsequent 'modify-subscription' request. A
successful 'modify-subscription' will return a suspended
subscription to an 'active' state.";
input {
leaf id {
type subscription-id;
mandatory true;
description
"Identifier to use for this subscription.";
}
uses subscription-policy-modifiable;
}
}
rc:yang-data modify-subscription-stream-error-info {
container modify-subscription-stream-error-info {
description
"This yang-data MAY be provided as part of a subscription's RPC
error response when there is a failure of a
'modify-subscription' RPC which has been made against an event
stream. This yang-data MUST be used if hints are to be
provided back to the subscriber.";
leaf reason {
type identityref {
base modify-subscription-error;
}
description
"Information in a 'modify-subscription' RPC error response
which indicates the reason why the subscription to an event
stream has failed to be modified.";
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}
leaf filter-failure-hint {
type string;
description
"Information describing where and/or why a provided filter
was unsupportable for a subscription. The syntax and
semantics of this hint are implementation-specific.";
}
}
}
rpc delete-subscription {
description
"This RPC allows a subscriber to delete a subscription that
was previously created from by that same subscriber using the
'establish-subscription' RPC.
If an error occurs, the server replies with an 'rpc-error' where
the 'error-info' field MAY contain an
'delete-subscription-error-info' structure.";
input {
leaf id {
type subscription-id;
mandatory true;
description
"Identifier of the subscription that is to be deleted.
Only subscriptions that were created using
'establish-subscription' from the same origin as this RPC
can be deleted via this RPC.";
}
}
}
rpc kill-subscription {
nacm:default-deny-all;
description
"This RPC allows an operator to delete a dynamic subscription
without restrictions on the originating subscriber or underlying
transport session.
If an error occurs, the server replies with an 'rpc-error' where
the 'error-info' field MAY contain an
'delete-subscription-error-info' structure.";
input {
leaf id {
type subscription-id;
mandatory true;
description
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"Identifier of the subscription that is to be deleted. Only
subscriptions that were created using
'establish-subscription' can be deleted via this RPC.";
}
}
}
rc:yang-data delete-subscription-error-info {
container delete-subscription-error-info {
description
"If a 'delete-subscription' RPC or a 'kill-subscription' RPC
fails, the subscription is not deleted and the RPC error
response MUST indicate the reason for this failure. This
yang-data MAY be inserted as structured data within a
subscription's RPC error response to indicate the failure
reason.";
leaf reason {
type identityref {
base delete-subscription-error;
}
mandatory true;
description
"Indicates the reason why the subscription has failed to be
deleted.";
}
}
}
/*
* NOTIFICATIONS
*/
notification replay-completed {
sn:subscription-state-notification;
if-feature "replay";
description
"This notification is sent to indicate that all of the replay
notifications have been sent.";
leaf id {
type subscription-id;
mandatory true;
description
"This references the affected subscription.";
}
}
notification subscription-completed {
sn:subscription-state-notification;
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if-feature "configured";
description
"This notification is sent to indicate that a subscription has
finished passing event records, as the 'stop-time' has been
reached.";
leaf id {
type subscription-id;
mandatory true;
description
"This references the gracefully completed subscription.";
}
}
notification subscription-modified {
sn:subscription-state-notification;
description
"This notification indicates that a subscription has been
modified. Notification messages sent from this point on will
conform to the modified terms of the subscription. For
completeness, this subscription state change notification
includes both modified and non-modified aspects of a
subscription.";
leaf id {
type subscription-id;
mandatory true;
description
"This references the affected subscription.";
}
uses subscription-policy {
refine "target/stream/stream-filter/within-subscription" {
description
"Filter applied to the subscription. If the
'stream-filter-name' is populated, the filter within the
subscription came from the 'filters' container. Otherwise it
is populated in-line as part of the subscription.";
}
}
}
notification subscription-resumed {
sn:subscription-state-notification;
description
"This notification indicates that a subscription that had
previously been suspended has resumed. Notifications will once
again be sent. In addition, a 'subscription-resumed' indicates
that no modification of parameters has occurred since the last
time event records have been sent.";
leaf id {
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type subscription-id;
mandatory true;
description
"This references the affected subscription.";
}
}
notification subscription-started {
sn:subscription-state-notification;
if-feature "configured";
description
"This notification indicates that a subscription has started and
notifications are beginning to be sent.";
leaf id {
type subscription-id;
mandatory true;
description
"This references the affected subscription.";
}
uses subscription-policy {
refine "target/stream/replay-start-time" {
description
"Indicates the time that a replay is using for the streaming
of buffered event records. This will be populated with the
most recent of the following: the event time of the previous
event record sent to a receiver, the
'replay-log-creation-time', the 'replay-log-aged-time',
or the most recent publisher boot time.";
}
refine "target/stream/stream-filter/within-subscription" {
description
"Filter applied to the subscription. If the
'stream-filter-name' is populated, the filter within the
subscription came from the 'filters' container. Otherwise it
is populated in-line as part of the subscription.";
}
augment "target/stream" {
description
"This augmentation adds additional parameters specific to a
subscription-started notification.";
leaf replay-previous-event-time {
when "../replay-start-time";
if-feature "replay";
type yang:date-and-time;
description
"If there is at least one event in the replay buffer prior
to 'replay-start-time', this gives the time of the event
generated immediately prior to the 'replay-start-time'.
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If a receiver previously received event records for this
configured subscription, it can compare this time to the
last event record previously received. If the two are not
the same (perhaps due to a reboot), then a dynamic replay
can be initiated to acquire any missing event records.";
}
}
}
}
notification subscription-suspended {
sn:subscription-state-notification;
description
"This notification indicates that a suspension of the
subscription by the publisher has occurred. No further
notifications will be sent until the subscription resumes.
This notification shall only be sent to receivers of a
subscription; it does not constitute a general-purpose
notification.";
leaf id {
type subscription-id;
mandatory true;
description
"This references the affected subscription.";
}
leaf reason {
type identityref {
base subscription-suspended-reason;
}
mandatory true;
description
"Identifies the condition which resulted in the suspension.";
}
}
notification subscription-terminated {
sn:subscription-state-notification;
description
"This notification indicates that a subscription has been
terminated.";
leaf id {
type subscription-id;
mandatory true;
description
"This references the affected subscription.";
}
leaf reason {
type identityref {
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base subscription-terminated-reason;
}
mandatory true;
description
"Identifies the condition which resulted in the termination .";
}
}
/*
* DATA NODES
*/
container streams {
config false;
description
"This container contains information on the built-in event
streams provided by the publisher.";
list stream {
key "name";
description
"Identifies the built-in event streams that are supported by
the publisher.";
leaf name {
type string;
description
"A handle for a system-provided event stream made up of a
sequential set of event records, each of which is
characterized by its own domain and semantics.";
}
leaf description {
type string;
description
"A description of the event stream, including such
information as the type of event records that are available
within this event stream.";
}
leaf replay-support {
if-feature "replay";
type empty;
description
"Indicates that event record replay is available on this
event stream.";
}
leaf replay-log-creation-time {
when "../replay-support";
if-feature "replay";
type yang:date-and-time;
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mandatory true;
description
"The timestamp of the creation of the log used to support the
replay function on this event stream. This time might be
earlier than the earliest available information contained in
the log. This object is updated if the log resets for some
reason.";
}
leaf replay-log-aged-time {
when "../replay-support";
if-feature "replay";
type yang:date-and-time;
description
"The timestamp associated with last event record which has
been aged out of the log. This timestamp identifies how far
back into history this replay log extends, if it doesn't
extend back to the 'replay-log-creation-time'. This object
MUST be present if replay is supported and any event records
have been aged out of the log.";
}
}
}
container filters {
description
"This container contains a list of configurable filters
that can be applied to subscriptions. This facilitates
the reuse of complex filters once defined.";
list stream-filter {
key "name";
description
"A list of pre-configured filters that can be applied to
subscriptions.";
leaf name {
type string;
description
"An name to differentiate between filters.";
}
uses stream-filter-elements;
}
}
container subscriptions {
description
"Contains the list of currently active subscriptions, i.e.
subscriptions that are currently in effect, used for
subscription management and monitoring purposes. This includes
subscriptions that have been setup via RPC primitives as well as
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subscriptions that have been established via configuration.";
list subscription {
key "id";
description
"The identity and specific parameters of a subscription.
Subscriptions within this list can be created using a control
channel or RPC, or be established through configuration.
If configuration operations or the 'kill-subscription' RPC are
used to delete a subscription, a 'subscription-terminated'
message is sent to any active or suspended receivers.";
leaf id {
type subscription-id;
description
"Identifier of a subscription; unique within a publisher";
}
uses subscription-policy {
refine "target/stream/stream" {
description
"Indicates the event stream to be considered for this
subscription. If an event stream has been removed,
and no longer can be referenced by an active subscription,
send a 'subscription-terminated' notification with
'stream-unavailable' as the reason. If a configured
subscription refers to a non-existent event stream, move
that subscription to the 'invalid' state.";
}
refine "transport" {
description
"For a configured subscription, this leaf specifies the
transport used to deliver messages destined to all
receivers of that subscription. This object is mandatory
for subscriptions in the configuration datastore. This
object is not mandatory for dynamic subscriptions within
the operational state datastore. The object should not
be present for dynamic subscriptions.";
}
augment "target/stream" {
description
"Enables objects to added to a configured stream
subscription";
leaf configured-replay {
if-feature "configured";
if-feature "replay";
type empty;
description
"The presence of this leaf indicates that replay for the
configured subscription should start at the earliest time
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in the event log, or at the publisher boot time, which
ever is later.";
}
}
}
choice notification-message-origin {
if-feature "configured";
description
"Identifies the egress interface on the publisher from which
notification messages are to be sent.";
case interface-originated {
description
"When notification messages to egress a specific,
designated interface on the publisher.";
leaf source-interface {
if-feature "interface-designation";
type if:interface-ref;
description
"References the interface for notification messages.";
}
}
case address-originated {
description
"When notification messages are to depart from a publisher
using specific originating address and/or routing context
information.";
leaf source-vrf {
if-feature "supports-vrf";
type leafref {
path "/ni:network-instances/ni:network-instance/ni:name";
}
description
"VRF from which notification messages should egress a
publisher.";
}
leaf source-address {
type inet:ip-address-no-zone;
description
"The source address for the notification messages. If a
source VRF exists, but this object doesn't, a publisher's
default address for that VRF must be used.";
}
}
}
leaf configured-subscription-state {
if-feature "configured";
type enumeration {
enum valid {
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value 1;
description
"Subscription is supportable with current parameters.";
}
enum invalid {
value 2;
description
"The subscription as a whole is unsupportable with its
current parameters.";
}
enum concluded {
value 3;
description
"A subscription is inactive as it has hit a stop time,
it no longer has receivers in the 'receiver active' or
'receiver suspended' state, but not yet been
removed from configuration.";
}
}
config false;
description
"The presence of this leaf indicates that the subscription
originated from configuration, not through a control channel
or RPC. The value indicates the system established state
of the subscription.";
}
container receivers {
description
"Set of receivers in a subscription.";
list receiver {
key "name";
min-elements 1;
description
"A host intended as a recipient for the notification
messages of a subscription. For configured subscriptions,
transport specific network parameters (or a leafref to
those parameters) may augmentated to a specific receiver
within this list.";
leaf name {
type string;
description
"Identifies a unique receiver for a subscription.";
}
leaf sent-event-records {
type yang:zero-based-counter64;
config false;
description
"The number of event records sent to the receiver. The
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count is initialized when a dynamic subscription is
established, or when a configured receiver
transitions to the valid state.";
}
leaf excluded-event-records {
type yang:zero-based-counter64;
config false;
description
"The number of event records explicitly removed either
via an event stream filter or an access control filter so
that they are not passed to a receiver. This count is
set to zero each time 'sent-event-records' is
initialized.";
}
leaf state {
type enumeration {
enum active {
value 1;
description
"Receiver is currently being sent any applicable
notification messages for the subscription.";
}
enum suspended {
value 2;
description
"Receiver state is 'suspended', so the publisher
is currently unable to provide notification messages
for the subscription.";
}
enum connecting {
value 3;
if-feature "configured";
description
"A subscription has been configured, but a
'subscription-started' subscription state change
notification needs to be successfully received before
notification messages are sent.
If the 'reset' action is invoked for a receiver of an
active configured subscription, the state must be
moved to 'connecting'.";
}
enum disconnected {
value 4;
if-feature "configured";
description
"A subscription has failed in sending a subscription
started state change to the receiver.
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Additional attempts at connection attempts are not
currently being made.";
}
}
config false;
mandatory true;
description
"Specifies the state of a subscription from the
perspective of a particular receiver. With this info it
is possible to determine whether a publisher is
currently generating notification messages intended for
that receiver.";
}
action reset {
if-feature "configured";
description
"Allows the reset of this configured subscription
receiver to the 'connecting' state. This enables the
connection process to be re-initiated.";
output {
leaf time {
type yang:date-and-time;
mandatory true;
description
"Time a publisher returned the receiver to a
'connecting' state.";
}
}
}
}
}
}
}
}
<CODE ENDS>
5. Considerations
5.1. IANA Considerations
This document registers the following namespace URI in the "IETF XML
Registry" [RFC3688]:
URI: urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications
Registrant Contact: The IESG.
XML: N/A; the requested URI is an XML namespace.
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This document registers the following YANG module in the "YANG Module
Names" registry [RFC6020]:
Name: ietf-subscribed-notifications
Namespace: urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications
Prefix: sn
Reference: draft-ietf-netconf-ietf-subscribed-notifications-11.txt
(RFC form)
5.2. Implementation Considerations
To support deployments including both configured and dynamic
subscriptions, it is recommended to split the subscription "id"
domain into static and dynamic halves. That way it eliminates the
possibility of collisions if the configured subscriptions attempt to
set a subscription-id which might have already been dynamically
allocated. A best practice is to use lower half the "id" object's
integer space when that "id" is assigned by an external entity (such
as with a configured subscription). This leaves the upper half of
subscription integer space available to be dynamically assigned by
the publisher.
If a subscription is unable to marshal a series of filtered event
records into transmittable notification messages, the receiver should
be suspended with the reason "unsupportable-volume".
For configured subscriptions, operations are against the set of
receivers using the subscription "id" as a handle for that set. But
for streaming updates, subscription state change notifications are
local to a receiver. In this specification it is the case that
receivers get no information from the publisher about the existence
of other receivers. But if a network operator wants to let the
receivers correlate results, it is useful to use the subscription
"id" across the receivers to allow that correlation. Note that due
to the possibility of different access control permissions per
receiver, each receiver may actually get a different set of event
records.
For configured replay subscriptions, the receiver is protected from
duplicated events being pushed after a publisher is rebooted.
However it is possible that a receiver might want to acquire event
records which failed to be delivered just prior to the reboot.
Delivering these event records be accomplished by leveraging the
"eventTime" from the last event record received prior to the receipt
of a "subscription-started" subscription state change notification.
With this "eventTime" and the "replay-start-time" from the
"subscription-started" notification, an independent dynamic
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subscription can be established which retrieves any event records
which may have been generated but not sent to the receiver.
5.3. Transport Requirements
This section provides requirements for any subscribed notification
transport supporting the solution presented in this document.
The transport selected by the subscriber to reach the publisher MUST
be able to support multiple "establish-subscription" requests made
within the same transport session.
For both configured and dynamic subscriptions the publisher MUST
authenticate a receiver via some transport level mechanism before
sending any event records for which they are authorized to see. In
addition, the receiver MUST authenticate the publisher at the
transport level. The result is mutual authentication between the
two.
A secure transport is highly recommended. Beyond this, the publisher
MUST ensure that the receiver has sufficient authorization to perform
the function they are requesting against the specific subset of
content involved.
A specific transport specification built upon this document may or
may not choose to require the use of the same logical channel for the
RPCs and the event records. However the event records and the
subscription state change notifications MUST be sent on the same
transport session to ensure the properly ordered delivery.
A specific transport specification MUST identity any encoding
supported. Where a configured subscription's transport allows
different encodings, the specification MUST identify the default
encoding.
A subscriber which includes a "dscp" leaf within an "establish-
subscription" request will need to understand and consider what the
corresponding DSCP value represents within the domain of the
publisher.
Additional transport requirements will be dictated by the choice of
transport used with a subscription. For an example of such
requirements with NETCONF transport, see
[I-D.draft-ietf-netconf-netconf-event-notifications].
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5.4. Security Considerations
The YANG module specified in this document defines a schema for data
that is designed to be accessed via network management transports
such as NETCONF [RFC6241] or RESTCONF [RFC8040]. The lowest NETCONF
layer is the secure transport layer, and the mandatory-to-implement
secure transport is Secure Shell (SSH) [RFC6242]. The lowest
RESTCONF layer is HTTPS, and the mandatory-to-implement secure
transport is TLS [RFC5246].
The NETCONF Access Control Model (NACM) [RFC8341] provides the means
to restrict access for particular NETCONF or RESTCONF users to a
preconfigured subset of all available NETCONF or RESTCONF operations
and content.
With configured subscriptions, one or more publishers could be used
to overwhelm a receiver. To counter this, notification messages
SHOULD NOT be sent to any receiver which does not support this
specification. Receivers that do not want notification messages need
only terminate or refuse any transport sessions from the publisher.
When a receiver of a configured subscription gets a new
"subscription-started" message for a known subscription where it is
already consuming events, it may indicate that an attacker has done
something that has momentarily disrupted receiver connectivity. To
acquire events lost during this interval, the receiver SHOULD
retrieve any event records generated since the last event record was
received. This can be accomplished by establishing a separate
dynamic replay subscription with the same filtering criteria with the
publisher, assuming the publisher supports the "replay" feature.
For dynamic subscriptions, implementations need to protect against
malicious or buggy subscribers which may send a large number
"establish-subscription" requests, thereby using up system resources.
To cover this possibility operators SHOULD monitor for such cases
and, if discovered, take remedial action to limit the resources used,
such as suspending or terminating a subset of the subscriptions or,
if the underlying transport is session based, terminate the
underlying transport session.
The replay mechanisms described in Section 2.4.2.1 and Section 2.5.6
provides access to historical event records. By design, the access
control model that protects these records could enable subscribers to
view data to which they were not authorized at the time of
collection.
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Using DNS names for configured subscription receiver "name" lookup
can cause situations where the name resolves unexpectedly differently
on the publisher, so the recipient would be different than expected.
An attacker that can cause the publisher to use an incorrect time can
induce message replay by setting the time in the past, and introduce
a risk of message loss by setting the time in the future.
There are a number of data nodes defined in this YANG module that are
writable/creatable/deletable (i.e., config true, which is the
default). These data nodes may be considered sensitive or vulnerable
in some network environments. Write operations (e.g., edit-config)
to these data nodes without proper protection can have a negative
effect on network operations. These are the subtrees and data nodes
where there is a specific sensitivity/vulnerability:
Container: "/filters"
o "stream-subtree-filter": updating a filter could increase the
computational complexity of all referencing subscriptions.
o "stream-xpath-filter": updating a filter could increase the
computational complexity of all referencing subscriptions.
Container: "/subscriptions"
The following considerations are only relevant for configuration
operations made upon configured subscriptions:
o "configured-replay": can be used to send a large number of event
records to a receiver.
o "dependency": can be used to force important traffic to be queued
behind less important updates.
o "dscp": if unvalidated, can result in the sending of traffic with
a higher priority marking than warranted.
o "id": can overwrite an existing subscription, perhaps one
configured by another entity.
o "name": adding a new key entry can be used to attempt to send
traffic to an unwilling receiver.
o "replay-start-time": can be used to push very large logs, wasting
resources.
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o "source-address": the configured address might not be able to
reach a desired receiver.
o "source-interface": the configured interface might not be able to
reach a desired receiver.
o "source-vrf": can place a subscription into a virtual network
where receivers are not entitled to view the subscribed content.
o "stop-time": could be used to terminate content at an inopportune
time.
o "stream": could set a subscription to an event stream containing
no content permitted for the targeted receivers.
o "stream-filter-name": could be set to a filter which is irrelevant
to the event stream.
o "stream-subtree-filter": a complex filter can increase the
computational resources for this subscription.
o "stream-xpath-filter": a complex filter can increase the
computational resources for this subscription.
o "weighting": placing a large weight can overwhelm the dequeuing of
other subscriptions.
Some of the readable data nodes in this YANG module may be considered
sensitive or vulnerable in some network environments. It is thus
important to control read access (e.g., via get, get-config, or
notification) to these data nodes. These are the subtrees and data
nodes and their sensitivity/vulnerability:
Container: "/streams"
o "name": if access control is not properly configured, can expose
system internals to those who should have no access to this
information.
o "replay-support": if access control is not properly configured,
can expose logs to those who should have no access.
Container: "/subscriptions"
o "excluded-event-records": leaf can provide information about
filtered event records. A network operator should have
permissions to know about such filtering. Improper configuration
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could provide a receiver with information leakage consisting of
the dropping of event records.
o "subscription": different operational teams might have a desire to
set varying subsets of subscriptions. Access control should be
designed to permit read access to just the allowed set.
Some of the RPC operations in this YANG module may be considered
sensitive or vulnerable in some network environments. It is thus
important to control access to these operations. These are the
operations and their sensitivity/vulnerability:
RPC: all
o If a malicious or buggy subscriber sends an unexpectedly large
number of RPCs, the result might be an excessive use of system
resources on the publisher just to determine that these
subscriptions should be declined. In such a situation,
subscription interactions MAY be terminated by terminating the
transport session.
RPC: "delete-subscription"
o No special considerations.
RPC: "establish-subscription"
o Subscriptions could overload a publisher's resources. For this
reason, publishers MUST ensure that they have sufficient resources
to fulfill this request or otherwise reject the request.
RPC: "kill-subscription"
o The "kill-subscription" RPC MUST be secured so that only
connections with administrative rights are able to invoke this
RPC.
RPC: "modify-subscription"
o Subscriptions could overload a publisher's resources. For this
reason, publishers MUST ensure that they have sufficient resources
to fulfill this request or otherwise reject the request.
6. Acknowledgments
For their valuable comments, discussions, and feedback, we wish to
acknowledge Andy Bierman, Tim Jenkins, Martin Bjorklund, Kent Watsen,
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Balazs Lengyel, Robert Wilton, Sharon Chisholm, Hector Trevino, Susan
Hares, Michael Scharf, and Guangying Zheng.
7. References
7.1. Normative References
[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>.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474,
DOI 10.17487/RFC2474, December 1998,
<https://www.rfc-editor.org/info/rfc2474>.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
DOI 10.17487/RFC3688, January 2004,
<https://www.rfc-editor.org/info/rfc3688>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>.
[RFC5277] Chisholm, S. and H. Trevino, "NETCONF Event
Notifications", RFC 5277, DOI 10.17487/RFC5277, July 2008,
<https://www.rfc-editor.org/info/rfc5277>.
[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC6020, October 2010,
<https://www.rfc-editor.org/info/rfc6020>.
[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>.
[RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure
Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
<https://www.rfc-editor.org/info/rfc6242>.
[RFC6991] Schoenwaelder, J., Ed., "Common YANG Data Types",
RFC 6991, DOI 10.17487/RFC6991, July 2013,
<https://www.rfc-editor.org/info/rfc6991>.
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[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>.
[RFC7951] Lhotka, L., "JSON Encoding of Data Modeled with YANG",
RFC 7951, DOI 10.17487/RFC7951, August 2016,
<https://www.rfc-editor.org/info/rfc7951>.
[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>.
[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>.
[RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration
Access Control Model", STD 91, RFC 8341,
DOI 10.17487/RFC8341, March 2018,
<https://www.rfc-editor.org/info/rfc8341>.
[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>.
[RFC8343] Bjorklund, M., "A YANG Data Model for Interface
Management", RFC 8343, DOI 10.17487/RFC8343, March 2018,
<https://www.rfc-editor.org/info/rfc8343>.
[RFC8529] Berger, L., Hopps, C., Lindem, A., Bogdanovic, D., and X.
Liu, "YANG Data Model for Network Instances", RFC 8529,
DOI 10.17487/RFC8529, March 2019,
<https://www.rfc-editor.org/info/rfc8529>.
[XPATH] Clark, J. and S. DeRose, "XML Path Language (XPath)
Version 1.0", November 1999,
<http://www.w3.org/TR/1999/REC-xpath-19991116>.
7.2. Informative References
[I-D.draft-ietf-netconf-netconf-event-notifications]
Clemm, Alexander., Voit, Eric., Gonzalez Prieto, Alberto.,
Nilsen-Nygaard, E., and A. Tripathy, "NETCONF support for
event notifications", May 2019,
<https://datatracker.ietf.org/doc/
draft-ietf-netconf-netconf-event-notifications/>.
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[I-D.draft-ietf-netconf-restconf-notif]
Voit, Eric., Clemm, Alexander., Tripathy, A., Nilsen-
Nygaard, E., and Alberto. Gonzalez Prieto, "Restconf and
HTTP transport for event notifications", May 2019,
<https://datatracker.ietf.org/doc/
draft-ietf-netconf-restconf-notif/>.
[I-D.ietf-netconf-yang-push]
Clemm, Alexander., Voit, Eric., Gonzalez Prieto, Alberto.,
Tripathy, A., Nilsen-Nygaard, E., Bierman, A., and B.
Lengyel, "YANG Datastore Subscription", May 2019,
<https://datatracker.ietf.org/doc/
draft-ietf-netconf-yang-push/>.
[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>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<https://www.rfc-editor.org/info/rfc7540>.
[RFC7923] Voit, E., Clemm, A., and A. Gonzalez Prieto, "Requirements
for Subscription to YANG Datastores", RFC 7923,
DOI 10.17487/RFC7923, June 2016,
<https://www.rfc-editor.org/info/rfc7923>.
[RFC8071] Watsen, K., "NETCONF Call Home and RESTCONF Call Home",
RFC 8071, DOI 10.17487/RFC8071, February 2017,
<https://www.rfc-editor.org/info/rfc8071>.
[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/info/rfc8259>.
[RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
<https://www.rfc-editor.org/info/rfc8340>.
Appendix A. Example Configured Transport Augmentation
This appendix provides a non-normative example of how the YANG model
defined in Section 4 may be enhanced to incorporate the configuration
parameters needed to support the transport connectivity process.
This example is not intended to be a complete transport model. In
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this example, connectivity via an imaginary transport type of "foo"
is explored. For more on the overall need, see Section 2.5.7.
The YANG model defined in this section contains two main elements.
First is a transport identity "foo". This transport identity allows
a configuration agent to define "foo" as the selected type of
transport for a subscription. Second is a YANG case augmentation
"foo" which is made to the "/subscriptions/subscription/receivers/
receiver" node of Section 4. Within this augmentation are the
transport configuration parameters "address" and "port" which are
necessary to make the connect to the receiver.
module example-foo-subscribed-notifications {
yang-version 1.1;
namespace
"urn:example:foo-subscribed-notifications";
prefix fsn;
import ietf-subscribed-notifications {
prefix sn;
}
import ietf-inet-types {
prefix inet;
}
description
"Defines 'foo' as a supported type of configured transport for
subscribed event notifications.";
identity foo {
base sn:transport;
description
"Transport type 'foo' is available for use as a configured
subscription transport protocol for subscribed notifications.";
}
augment
"/sn:subscriptions/sn:subscription/sn:receivers/sn:receiver" {
when 'derived-from(../../../transport, "fsn:foo")';
description
"This augmentation makes 'foo' specific transport parameters
available for a receiver.";
leaf address {
type inet:host;
mandatory true;
description
"Specifies the address to use for messages destined to a
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receiver.";
}
leaf port {
type inet:port-number;
mandatory true;
description
"Specifies the port number to use for messages destined to a
receiver.";
}
}
}
Figure 21: Example Transport Augmentation for the fictitious protocol
foo
This example YANG model for transport "foo" will not be seen in a
real world deployment. For a real world deployment supporting an
actual transport technology, a similar YANG model must be defined.
Appendix B. Changes between revisions
(To be removed by RFC editor prior to publication)
v25 - v26
o Tweaks from Alissa Cooper's review, and Benjamin Kaduk's discuss.
o Magnus' review help refine the words on several 'overload'
considerations. And a couple of QoS requirements were clarified.
o Note on interpreting RFC-5277 so that notification messages can
follow establish-subscription RPCs.
o draft-ietf-rtgwg-ni-model updated to RFC-8529
v24 - v25
o Replay security consideration added based on Roman Danyliw's
discuss
o Spelling fixes, acronyms expanded
o Tweaks and updates based Benjamin Kaduk's comments. This includes
the adding of clarifying security considerations, a couple of
claifications in the YANG definitions, and ensuring a fuller set
of transport specification requirements are defined in 5.3.
v23 - v24
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o Per Benjamin Kaduk's discuss, adjusted IPR to pre5378Trust200902
o Tweaks from Chris Lonvick's IESG review. This includes moving a
paragraph from Security Considerations into a sentence within
Implementation Considerations.
o Tweaks from Wesley Eddy DSCP description
v22 - v23
o During the YANG Doctor review, feature dscp support was refined to
avoid the out-of-order delivery of packets in a single TCP
session.
v21 - v22
o YANG Dr definition clarifications. This includes refined text on:
(a) stop-time can be used without replay, (b) a separate dynamic
subscription for replay, (c) subscription state change
notifications can't be dropped, more details on "enum concluded"
and (d) more text on configurable-encoding leaf (which adds two
informative references). There also was one minor tweak in the
YANG model. The stream description leaf had "mandatory true"
removed.
v20 - v21
o Editorial change in Section 1.3 requested by Qin's Shepherd review
of NETCONF-Notif and RESTCONF-Notif. Basically extra text was
added further describing that dynamic subscriptions can have state
change notifications.
v18 - v20
o XPath-stream-filter YANG object definition updated based on NETMOD
discussions.
v17 - v18
o Transport optional in YANG model.
o Modify subscription must come from the originator of the
subscription. (Text got dropped somewhere previously.)
o Title change.
v16 - v17
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o YANG renaming: Subscription identifier renamed to id. Counters
renamed. Filters id made into name.
o Text tweaks.
v15 - v16
o Mandatory empty case "transport" removed.
o Appendix case turned from "netconf" to "foo".
v14 - v15
o Text tweaks.
o Mandatory empty case "transport" added for transport parameters.
This includes a new section and an appendix explaining it.
v13 - v14
o Removed the 'address' leaf.
o Replay is now of type 'empty' for configured.
v12 - v13
o Tweaks from Kent's comments
o Referenced in YANG model updated per Tom Petch's comments
o Added leaf replay-previous-event-time
o Renamed the event counters, downshifted the subscription states
v11 - v12
o Tweaks from Kent's, Tim's, and Martin's comments
o Clarified dscp text, and made its own feature
o YANG model tweaks alphabetizing, features.
v10 - v11
o access control filtering of events in streams included to match
RFC5277 behavior
o security considerations updated based on YANG template.
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o dependency QoS made non-normative on HTTP2 QoS
o tree diagrams referenced for each figure using them
o reference numbers placed into state machine figures
o broke configured replay into its own section
o many tweaks updates based on LC and YANG doctor reviews
o trees and YANG model reconciled were deltas existed
o new feature for interface originated.
o dscp removed from the qos feature
o YANG model updated in a way which collapses groups only used once
so that they are part of the 'subscriptions' container.
o alternative encodings only allowed for transports which support
them.
v09 - v10
o Typos and tweaks
v08 - v09
o NMDA model supported. Non NMDA version at https://github.com/
netconf-wg/rfc5277bis/
o Error mechanism revamped to match to embedded implementations.
o Explicitly identified error codes relevant to each RPC/
Notification
v07 - v08
o Split YANG trees to separate document subsections.
o Clarified configured state machine based on Balazs comments, and
moved it into the configured subscription subsections.
o Normative reference to Network Instance model for VRF
o One transport for all receivers of configured subscriptions.
o QoS section moved in from yang-push
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v06 - v07
o Clarification on state machine for configured subscriptions.
v05 - v06
o Made changes proposed by Martin, Kent, and others on the list.
Most significant of these are stream returned to string (with the
SYSLOG identity removed), intro section on 5277 relationship, an
identity set moved to an enumeration, clean up of definitions/
terminology, state machine proposed for configured subscriptions
with a clean-up of subscription state options.
o JSON and XML become features. Also Xpath and subtree filtering
become features
o Terminology updates with event records, and refinement of filters
to just event stream filters.
o Encoding refined in establish-subscription so it takes the RPC's
encoding as the default.
o Namespaces in examples fixed.
v04 - v05
o Returned to the explicit filter subtyping of v00
o stream object changed to 'name' from 'stream'
o Cleaned up examples
o Clarified that JSON support needs notification-messages draft.
v03 - v04
o Moved back to the use of RFC5277 one-way notifications and
encodings.
v03 - v04
o Replay updated
v02 - v03
o RPCs and Notification support is identified by the Notification
2.0 capability.
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o Updates to filtering identities and text
o New error type for unsupportable volume of updates
o Text tweaks.
v01 - v02
o Subscription status moved under receiver.
v00 - v01
o Security considerations updated
o Intro rewrite, as well as scattered text changes
o Added Appendix A, to help match this to related drafts in progress
o Updated filtering definitions, and filter types in yang file, and
moved to identities for filter types
o Added Syslog as an event stream
o HTTP2 moved in from YANG-Push as a transport option
o Replay made an optional feature for events. Won't apply to
datastores
o Enabled notification timestamp to have different formats.
o Two error codes added.
v01 5277bis - v00 subscribed notifications
o Kill subscription RPC added.
o Renamed from 5277bis to Subscribed Notifications.
o Changed the notification capabilities version from 1.1 to 2.0.
o Extracted create-subscription and other elements of RFC5277.
o Error conditions added, and made specific in return codes.
o Simplified yang model structure for removal of 'basic' grouping.
o Added a grouping for items which cannot be statically configured.
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o Operational counters per receiver.
o Subscription-id and filter-id renamed to identifier
o Section for replay added. Replay now cannot be configured.
o Control plane notification renamed to subscription state change
notification
o Source address: Source-vrf changed to string, default address
option added
o In yang model: 'info' changed to 'policy'
o Scattered text clarifications
v00 - v01 of 5277bis
o YANG Model changes. New groupings for subscription info to allow
restriction of what is changeable via RPC. Removed notifications
for adding and removing receivers of configured subscriptions.
o Expanded/renamed definitions from event server to publisher, and
client to subscriber as applicable. Updated the definitions to
include and expand on RFC 5277.
o Removal of redundancy with other drafts
o Many other clean-ups of wording and terminology
Authors' Addresses
Eric Voit
Cisco Systems
Email: evoit@cisco.com
Alexander Clemm
Huawei
Email: ludwig@clemm.org
Alberto Gonzalez Prieto
Microsoft
Email: alberto.gonzalez@microsoft.com
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Einar Nilsen-Nygaard
Cisco Systems
Email: einarnn@cisco.com
Ambika Prasad Tripathy
Cisco Systems
Email: ambtripa@cisco.com
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