NETCONF A. Clemm
Internet-Draft Huawei
Intended status: Standards Track E. Voit
Expires: September 1, 2017 A. Gonzalez Prieto
A. Tripathy
E. Nilsen-Nygaard
Cisco Systems
A. Bierman
YumaWorks
B. Lengyel
Ericsson
February 28, 2017
Subscribing to YANG datastore push updates
draft-ietf-netconf-yang-push-05
Abstract
This document defines a subscription and push mechanism for YANG
datastores. This mechanism allows subscriber applications to request
updates from a YANG datastore, which are then pushed by the publisher
to a receiver per a subscription policy, without requiring additional
subscriber requests.
Status of This Memo
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Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Definitions and Acronyms . . . . . . . . . . . . . . . . . . 5
3. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Subscription Model . . . . . . . . . . . . . . . . . . . 6
3.2. Negotiation of Subscription Policies . . . . . . . . . . 7
3.3. On-Change Considerations . . . . . . . . . . . . . . . . 8
3.4. Data Encodings . . . . . . . . . . . . . . . . . . . . . 9
3.5. YANG object filters . . . . . . . . . . . . . . . . . . . 10
3.6. Push Data Stream and Transport Mapping . . . . . . . . . 10
3.7. Subscription management . . . . . . . . . . . . . . . . . 14
3.8. Other considerations . . . . . . . . . . . . . . . . . . 15
4. A YANG data model for management of datastore push
subscriptions . . . . . . . . . . . . . . . . . . . . . . . . 19
4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 19
4.2. Filters . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.3. Subscription configuration . . . . . . . . . . . . . . . 26
4.4. Notifications . . . . . . . . . . . . . . . . . . . . . . 27
4.5. RPCs . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5. YANG module . . . . . . . . . . . . . . . . . . . . . . . . . 34
6. Security Considerations . . . . . . . . . . . . . . . . . . . 47
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 47
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 47
8.1. Normative References . . . . . . . . . . . . . . . . . . 47
8.2. Informative References . . . . . . . . . . . . . . . . . 48
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Appendix A. Technologies to be considered for future iterations 49
A.1. Proxy YANG Subscription when the Subscriber and Receiver
are different . . . . . . . . . . . . . . . . . . . . . . 49
A.2. OpState and Filters . . . . . . . . . . . . . . . . . . . 49
A.3. Splitting push updates . . . . . . . . . . . . . . . . . 50
A.4. Potential Subscription Parameters . . . . . . . . . . . . 50
Appendix B. Issues that are currently being worked and resolved 51
Appendix C. Changes between revisions . . . . . . . . . . . . . 51
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 52
1. Introduction
YANG [RFC7950] was originally designed for the Netconf protocol
[RFC6241] which focused on configuration data. However, YANG can be
used to model both configuration and operational data. It is
therefore reasonable to expect YANG datastores will increasingly be
used to support applications that care about about both.
For example, service assurance applications will need to be aware of
any remote updates to configuration and operational objects. Rapid
awareness of object changes will enable such things as validating and
maintaining cross-network integrity and consistency, or monitoring
state and key performance indicators of remote devices.
Traditional approaches to remote visibility have been built on
polling. With polling, data is periodically explicitly retrieved by
a client from a server to stay up-to-date. However, there are issues
associated with polling-based management:
o It introduces additional load on network, devices, and
applications. Each polling cycle requires a separate yet arguably
redundant request that results in an interrupt, requires parsing,
consumes bandwidth.
o It lacks robustness. Polling cycles may be missed, requests may
be delayed or get lost, often particularly in cases when the
network is under stress and hence exactly when the need for the
data is the greatest.
o Data may be difficult to calibrate and compare. Polling requests
may undergo slight fluctuations, resulting in intervals of
different lengths which makes data hard to compare. Likewise,
pollers may have difficulty issuing requests that reach all
devices at the same time, resulting in offset polling intervals
which again make data hard to compare.
A more effective alternative to polling is when an application can
request to be automatically updated on current relevant content of a
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datastore. If such a request is accepted, interesting updates will
subsequently be pushed from that datastore.
Dependence on polling-based management is typically considered an
important shortcoming of applications that rely on MIBs polled using
SNMP [RFC1157]. However, without a provision to support a push-based
alternative, there is no reason to believe that management
applications that operate on YANG datastores will be any more
effective, as they would follow the same request/response pattern.
While YANG allows the definition of push notifications, such
notifications generally indicate the occurrence of certain well-
specified event conditions, such as the onset of an alarm condition
or the occurrence of an error. A capability to subscribe to and
deliver such pre-defined event notifications has been defined in
[RFC5277]. In addition, configuration change notifications have been
defined in [RFC6470]. These change notifications pertain only to
configuration information, not to operational state, and convey the
root of the subtree to which changes were applied along with the
edits, but not the modified data nodes and their values.
Furthermore, while delivery of updates using notifications is a
viable option, some applications desire the ability to stream updates
using other transports.
Accordingly, there is a need for a service that allows applications
to dynamically subscribe to updates of a YANG datastore and that
allows the publisher to push those updates, possibly using one of
several delivery mechanisms. Additionally, support for subscriptions
configured directly on the publisher are also useful when dynamic
signaling is undesirable or unsupported. The requirements for such a
service are documented in [RFC7923].
This document proposes a solution. The solution builds on top of the
NETCONF WG's Subscribed Notifications draft [I-D:netconf-sub-notif].
At its core, the solution defined here suppliments that work by
introducing datastore push update mechanisms, and providing
corresponding extensions to the event subscription model. The
document also includes YANG data model augmentations which extend the
model and RPCs defined within [I-D:netconf-sub-notif].
Key capabilities worth highlighting include:
o Additions to event subscription mechanisms which allow clients to
subscribe to datastore updates. The subscription allows clients
to specify which data they are interested in, what types of
updates (e.g., create, delete, modify), and to provide filter
criteria that data must meet for updates to be sent. Furthermore,
subscriptions can specify a policy that directs when updates are
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provided. For example, a client may request to be updated
periodically in certain intervals, or whenever data changes occur.
o Format and contents of the YANG push updates themselves.
o The ability for a publisher to push back on requested subscription
parameters. Because not every publisher may support every
requested update policy for every piece of data, it is necessary
for a publisher to be able to indicate whether or not it is
capable of supporting a requested subscription, and possibly allow
to hints at subscription parameters which might have succeeded.
o Subscription parameters which allow the specification of QoS
extensions to address prioritization between independent streams
of updates.
2. Definitions and Acronyms
Many of the terms in this document are defined in
[I-D:netconf-sub-notif]. Please see that document for these
definitions.
Data node: An instance of management information in a YANG datastore.
Data node update: A data item containing the current value/property
of a Data node at the time the data node update was created.
Data record: A record containing a set of one or more data node
instances and their associated values.
Datastore: A conceptual store of instantiated management information,
with individual data items represented by data nodes which are
arranged in hierarchical manner.
Datastream: A continuous stream of data records, each including a set
of updates, i.e. data node instances and their associated values.
Data subtree: An instantiated data node and the data nodes that are
hierarchically contained within it.
Push-update stream: A conceptual data stream of a datastore that
streams the entire datastore contents continuously and perpetually.
Update: A data item containing the current value of a data node.
Update notification: An Event Notification including those data node
update(s) to be pushed in order to meet the obligations of a single
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Subscription. All included data node updates must reflect the state
of a Datastore at a snapshot in time.
Update record: A representation of a data node update as a data
record. An update record can be included as part of an update
stream. It can also be logged for retrieval. In general, an update
record will include the value/property of a data node. It may also
include information about the type of data node update, i.e. whether
the data node was modified/updated, or newly created, or deleted.
Update trigger: A mechanism, as specified by a Subscription Policy,
that determines when a data node update is to be communicated. (e.g.,
a change trigger, invoked when the value of a data node changes or a
data node is created or deleted, or a time trigger, invoked after the
laps of a periodic time interval.)
YANG object filter: A filter that contains evaluation criteria which
are evaluated against YANG objects of a subscription. An update is
only published if the object meets the specified filter criteria.
YANG-Push: The subscription and push mechanism for YANG datastores
that is specified in this document.
3. Solution Overview
This document specifies a solution for a push update subscription
service. This solution supports the dynamic as well as configured
subscriptions to information updates from YANG datastores. A
subscription might target exposed operational and/or configuration
YANG objects on a device. YANG objects are subsequently pushed from
the publisher to the receiver per the terms of the subscription.
3.1. Subscription Model
YANG-push subscriptions are defined using a data model that is itself
defined in YANG. This model augments the event subscription model
defined in [I-D:netconf-sub-notif] and introduces new capabilities
that allow subscribers to specify what to include in an update
notification and what triggers such an update notification.
o Enhancements to filters. Specifically the filter must at least
identify at least one targeted yang data node/subtree. The filter
may also define additional yang nodes/subtrees to include or
exclude. The publisher must only send to the receiver those data
node updates that can traverse applied filter. Filters can be
specified "inline" as part of the subscription, or can be
configured separately and referenced by a subscription in order to
facilitate reuse of complex filters.
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o A subscription policy definition regarding the update trigger when
to send new update notifications.
* For periodic subscriptions, the trigger is defined by two
parameters that defines the interval with which updates are to
be pushed. These parameters are the period/interval of
reporting duration, and an anchor time which can be used to
calculate at which times updates needs to be assembled and
sent.
* For on-change subscriptions, the trigger occurs whenever a
change in the subscribed information is detected. On-change
subscriptions have more complex semantics that can be guided by
additional parameters. Please refer also to Section 3.3.
+ One parameter specifiing the dampening period. This period
is the interval which must pass before a successive update
notification for the same Subscription is sent. Note that
the dampening period applies to the set of all data nodes
within a single subscription. This means that on the first
change of an object, an update notification containing that
object is sent either immediately or at the end of a
dampening period already in effect.
+ Another parameter allowing the restriction of the types of
changes for which updates are sent (changes to object
values, object creation or deletion events).
+ A third parameter specifing whether or not a complete push-
update with all the subscribed data should be sent at the
beginning of a subscription. Such a push provides the
receiver the current state, and establish the frame of
reference for subsequent updates.
o Anydata encoding for the contents of periodic and on-change push
updates.
The subscription data model is described via augmentations to
[I-D:netconf-sub-notif] later in this specification. It is
conceivable that additional subscription parameters might be
interesting. Augmentations to the subscription data model may be
used for this.
3.2. Negotiation of Subscription Policies
A dynamic subscription request SHOULD be declined based on
publisher's assessment that it may be unable to provide a filtered
update notifications that would meet the terms of the request. But a
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subscriber may quickly follow up with a new subscription request
using different parameters.
Random guessing at different parameters should be discouraged.
Therefore to minimize the number of subscription iterations between
subscriber and publisher, dynamic subscriptions must support a simple
negotiation between subscribers and publishers for subscription
parameters. This negotiation is limited to either an establish or
modify subscription request, followed by no-success response. The
no-success message, where available SHOULD include in the returned
error information parameters. The returned parameters provide
information that, when followed, increase the likelihood of success
for subsequent requests. However, there are no guarantee that
subsequent requests for this subscriber will in fact be accepted.
Negotiable parameters which may be returned from a publisher beyond
those from [I-D:netconf-sub-notif] include: hints at acceptable time
intervals, size estimates forn the number or objects which would be
returned from a filter, and the names of targeted objects not found
in the publisher's YANG tree.
3.3. On-Change Considerations
On-change subscriptions allow subscribers to subscribe to updates
whenever changes to objects occur. As such, on-change subscriptions
are of particular interest for data that changes relatively
infrequently, yet that require applications to be notified with
minimal delay when changes do occur.
On-change subscriptions tend to be more difficult to implement than
periodic subscriptions. Specifically, on-change subscriptions may
involve a notion of state to see if a change occurred between past
and current state, or the ability to tap into changes as they occur
in the underlying system. Accordingly, on-change subscriptions may
not be supported by all implementations or for every object.
When an on-change subscription is requested for a datastream with a
given subtree filter, where not all objects support on-change update
triggers, only the objects supporting on-change will be provided.
For more on how objects are so marked, see Section 3.8.5
Any updates for an on-change subscription will include only supported
objects for which a change was detected and which met the filtering
criteria. To avoid flooding receivers with repeated updates for
fast-changing objects, or objects with oscillating values, an on-
change subscription allows for the definition of a dampening period.
Once an update for a given object is sent, no other updates for this
particular subscription are sent until the end of the dampening
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period. Values sent at the end of the dampening period are the
current values of all changed objects which are current at the time
the dampening period expires. Changed objects includes those which
were deleted or newly created during that dampening period.
On-change subscriptions can be refined to let users subscribe only to
certain types of changes, for example, only to object creations and
deletions, but not to modifications of object values.
3.4. Data Encodings
Subscribed data is encoded in either XML or JSON format. A publisher
MUST support XML encoding and MAY support JSON encoding.
It is conceivable that additional encodings may be supported as
options in the future. This can be accomplished by augmenting the
subscription data model with additional identity statements used to
refer to requested encodings.
3.4.1. Periodic Subscriptions
In a periodic subscription, the data included as part of an update
corresponds to data that could have been simply retrieved using a get
operation and is encoded in the same way. XML encoding rules for
data nodes are defined in [RFC7950]. JSON encoding rules are defined
in [RFC7951]. This encoding is valid JSON, but also has special
encoding rules to identify module namespaces and provide consistent
type processing of YANG data.
3.4.2. On-Change Subscriptions
In an on-change subscription, updates need to indicate not only
values of changed data nodes but also the types of changes that
occurred since the last update, such as whether data nodes were newly
created since the last update or whether they were merely modified,
as well as which data nodes were deleted.
Encoding rules for data in on-change updates correspond to how data
would be encoded in a YANG-patch operation as specified in [RFC8072].
The "YANG-patch" would in this case be applied to the earlier state
reported by the preceding update, to result in the now-current state
of YANG data. Of course, contrary to a YANG-patch operation, the
data is sent from the publisher to the receiver and is not restricted
to configuration data.
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3.5. YANG object filters
Subscriptions can specify filters for subscribed data. The following
filters are supported:
o subtree-filter: A subtree filter specifies a subtree that the
subscription refers to. When specified, updates will only concern
data nodes from this subtree. Syntax and semantics correspond to
that specified for [RFC6241] section 6.
o xpath-filter: An XPath filter specifies an XPath expression
applied to the data in an update, assuming XML-encoded data.
Only a single filter can be applied to a subscription at a time.
It is conceivable for implementations to support other filters. For
example, an on-change filter might specify that changes in values
should be sent only when the magnitude of the change since previous
updates exceeds a certain threshold. It is possible to augment the
subscription data model with additional filter types.
3.6. Push Data Stream and Transport Mapping
Pushing data based on a subscription could be considered analogous to
a response to a data retrieval request, e.g., a "get" request.
However, contrary to such a request, multiple responses to the same
request may get sent over a longer period of time.
An applicable mechanism is that of a notification. There are however
some specifics that need to be considered. Contrary to other
notifications that are associated with alarms and unexpected event
occurrences, update notifications are solicited, i.e. tied to a
particular subscription which triggered the notification.
A push update notification contains several parameters:
o A subscription correlator, referencing the name of the
subscription on whose behalf the notification is sent.
o Data nodes containing a representation of the datastore subtree(s)
containing the updates. In all cases, the subtree(s) are filtered
per access control rules to contain only data that the subscriber
is authorized to see. For on-change subscriptions, the subtree
may only contain the data nodes which have changed since the start
of the previous dampening interval.
This document introduces two generic notifications: "push-update" and
"push-change-update". Those notifications may be encapsulated on a
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transport (e.g., NETCONF or HTTP) to carry data records with updates
of datastore contents as specified by a subscription. It is possible
also map notifications to other transports and encodings and use the
same subscription model; however, the definition of such mappings is
outside the scope of this document.
A push-update notification defines a complete update of the datastore
per the terms of a subscription. This type of notification is used
for continuous updates of periodic subscriptions. A push-update
notification can also used be for the on-change subscriptions in two
cases. First it will be used as the initial push-update if there is
a need to synchronize the receiver at the start of a new
subscription. It also may be sent if the publisher later chooses to
resynch a previously synched on-change subscription. The push-update
record contains a data snippet that contains an instantiated subtree
with the subscribed contents. The content of the update notification
is equivalent to the contents that would be obtained had the same
data been explicitly retrieved using e.g., a Netconf "get"-operation,
with the same filters applied.
The contents of the push-update notification conceptually represents
the union of all data nodes in the yang modules supported by the
publisher. However, in a YANG data model, it is not practical to
model the precise data contained in the updates as part of the
notification. To capture this data, a single parameter that can
encapsulate the full set of subscribed datastore contents is used,
not parameters that represent data nodes one at a time.
A push-change-update notification is the most common type of update
for on-change subscriptions. The update record in this case contains
a data snippet that indicates the full set of changes that data nodes
have undergone since the last notification of YANG objects. In other
words, this indicates which data nodes have been created, deleted, or
have had changes to their values. The format of the data snippet
follows YANG-patch [RFC8072], i.e. the same format that would be used
with a YANG-patch operation to apply changes to a data tree,
indicating the creates, deletes, and modifications of data nodes.
Please note that as the update can include a mix of configuration and
operational data
The following is an example of push notification. It contains an
update for subscription 1011, including a subtree with root foo that
contains a leaf, bar:
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2015-03-09T19:14:56Z
1011
2015-03-09T19:14:56.233Z
some_string
Figure 1: Push example
The following is an example of an on-change notification. It
contains an update for subscription 89, including a new value for a
leaf called beta, which is a child of a top-level container called
alpha:
2015-03-09T19:14:56Z
89
2015-03-09T19:14:56.233Z
1500
Figure 2: Push example for on change
The equivalent update when requesting json encoding:
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2015-03-09T19:14:56Z
89
2015-03-09T19:14:56.233Z
{
"ietf-yang-patch:yang-patch": {
"patch-id": [
null
],
"edit": [
{
"edit-id": "edit1",
"operation": "merge",
"target": "/alpha/beta",
"value": {
"beta": 1500
}
}
]
}
}
Figure 3: Push example for on change with JSON
When the beta leaf is deleted, the publisher may send
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2015-03-09T19:14:56Z
89
2015-03-09T19:14:56.233Z
Figure 4: 2nd push example for on change update
3.7. Subscription management
A [I-D:netconf-sub-notif] subscription needs enhancment to support
YANG Push subscription negotiation. Specifically, these enhancements
are needed to signal to the subscriber why an attempt has failed.
A subscription can be rejected for multiple reasons, including the
lack of authorization to establish a subscription, the lack of read
authorization on the requested data node, or the inability of the
publisher to provide a stream with the requested semantics. In such
cases, no subscription is established. Instead, the subscription-
result with the failure reason is returned as part of the RPC
response. In addition, a set of alternative subscription parameters
MAY be returned that would likely have resulted in acceptance of the
subscription request, which the subscriber may try for a future
subscription attempt.
It should be noted that a rejected subscription does not result in
the generation of an rpc-reply with an rpc-error element, as neither
the specification of YANG-push specific errors nor the specification
of additional data parameters to be returned in an error case are
supported as part of a YANG data model.
For instance, for the following request:
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push-update
500
encode-xml
Figure 5: Establish-Subscription example
the publisher might return:
error-insufficient-resources
2000
Figure 6: Error response example
3.8. Other considerations
3.8.1. Authorization
A receiver of subscription data may only be sent updates for which
they have proper authorization. Data that is being pushed therefore
needs to be subjected to a filter that applies all corresponding
rules applicable at the time of a specific pushed update, silently
removing any non-authorized data from subtrees.
The authorization model for data in YANG datastores is described in
the Netconf Access Control Model [RFC6536]. However, some
clarifications to that RFC are needed so that the desired access
control behavior is applied to pushed updates.
One of these clarifications is that a subscription may only be
established if the receiver has read access to every data node
specifically named within the subscription filter.
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+-------------+ +-------------+
subscription | protocol | | target |
request --> | operation | -------------> | data node |
| allowed? | datastore | access |
+-------------+ or state | allowed? |
data access +-------------+
Figure 7: Access control for subscription
Likewise if a receiver no longer has read access permission to a data
node named/targeted within a filter, the subscription must be
abnormally terminated (with loss of access permission as the reason
provided).
Another clarification to [RFC6536] is that each of the individual
nodes in a pushed update must also go through access control
filtering. This includes new nodes added since the last update
notification, as well as existing nodes. For each of these read
access must be verified. The methods of doing this efficiently are
left to implementation.
+-------------+ +-------------------+
subscription | data node | yes | |
update --> | access | ---> | add data node |
| allowed? | | to update message |
+-------------+ +-------------------+
Figure 8: Access control for push updates
If there are read access control changes applied under the data node
named/targeted within a filter, no notifications indicating the fact
that this has occurred should be provided.
3.8.2. Robustness and reliability considerations
Particularly in the case of on-change push updates, it is important
that push updates do not get lost.
Update notifications will typically traverse a secure and reliable
transport. Notifications will not be reordered, and will also
contain a time stamp. Despite these protections for on-change, it is
possible that complete update notifications get lost. For this
reason, update sequence numbers for push-change-updates may be
included in a subscription so that an application can determine if an
update has been lost.
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At the same time, it is conceivable that under certain circumstances,
a publisher will recognize that it is unable to include within an
update notification the full set of objects desired per the terms of
a subscription. In this case, the publisher must take one or more of
the following actions.
o A publisher must set the updates-not-sent flag on any update
notification which is known to be missing information.
o It may choose to suspend and resume a subscription as per
[I-D:netconf-sub-notif].
o When resuming an on-change subscription, the publisher should
generate a complete patch from the previous update notification.
If this is not possible and the synch-on-start option is
configured, then the full datastore contents may be sent instead
(effectively replacing the previous contents). If neither of
these are possible, then an updates-not-sent flag must be included
on the next push-change-update.
3.8.3. Update size and fragmentation considerations
Depending on the subscription, the volume of updates can become quite
large. Additionally, based on the platform, it is possible that
push-updates for a single subscription are best sent independently
from different line-cards. Therefore, it may not always be practical
to send the entire update in a single chunk. Implementations of
push-update MAY therefore choose, at their discretion, to "chunk"
updates and break them out into several push-update notifications.
In this case the updates-not-sent flag will indicate that no single
push-update is complete. Push-change-updates may also be chunked as
long as none of the changed objects in the separate pushes are state-
entangled.
3.8.4. Implementation considerations
Implementation specifics are outside the scope of this specification.
That said,it should be noted that monitoring of operational state
changes inside a system can be associated with significant
implementation challenges.
Even periodic retrieval and push of operational counters may consume
considerable system resources. In addition the on-change push of
small amounts of configuration data may, depending on the
implementation, require invocation of APIs, possibly on an object-by-
object basis, possibly involving additional internal interrupts, etc.
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For those reasons, it is important for an implementation to
understand what subscriptions it can or cannot support. It is far
preferable to decline a subscription request then to accept such a
request when it cannot be met.
Whether or not a subscription can be supported will in general be
determined by a combination of several factors, including the
subscription policy (on-change or periodic, with on-change in general
being the more challenging of the two), the period in which to report
changes (1 second periods will consume more resources than 1 hour
periods), the amount of data in the subtree that is being subscribed
to, and the number and combination of other subscriptions that are
concurrently being serviced.
When providing access control to every node in a pushed update, it is
possible to make and update efficient access control filters for an
update. These filters can be set upon subscription and applied
against a stream of updates. These filters need only be updated when
(a) there is a new node added/removed from the subscribed tree with
different permissions than its parent, or (b) read access permissions
have been changed on nodes under the target node for the subscriber.
3.8.5. Identifying on-change notifiable YANG objects
In some cases, a publisher supporting on-change notifications may not
be able to push updates for some object types on-change. Reasons for
this might be that the value of the data node changes frequently
(e.g., a received-octets-counter), that small object changes are
frequent and meaningless (e.g., a temperature gauge changing 0.1
degrees), or that the implementation is not capable of on-change
notification of an object type.
Support for on-change notification is usually specific to the
individual YANG model and/or implementation so it is possible to
define in design time. System integrators need this information
(without reading any data from a live node).
The default assumption is that no data nodes support on-change
notification. Schema nodes and subtrees that support on-change
notifications MUST be marked as such with the YANG extension
notifiable-on-change.
If the model designer wants to add the notifiable-on-change statement
to an existing module, but wants to avoid modifying the text of the
existing module, the notifiable-on-change statement may be added
using deviation statements.
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extension notifiable-on-change {
Indicates whether changes to the data node are reportable in
on-change subscriptions.
The statement MUST only be a substatement of the leaf, leaf-list,
container, list, anyxml, anydata statements. Zero or One
notifiable-on-change statement is allowed per parent statement. NO
substatements are allowed.
The argument is a boolean value indicating whether on-change
notifications are supported. If notifiable-on-change is not
specified, the default is the same as the parent data node's
value. For top level data nodes the default value is false.";
argument value;
}
Figure 9: Notifiable Extension
When an on-change subscription is established data-nodes marked with
notifiable-on-change false; will be automatically filtered out. This
also means that authorization checks need be performed on them.
deviation /sys:system/sys:system-time {
deviate add {
yp:notifiable-on-change false;
}
}
Figure 10: Deviation Example
4. A YANG data model for management of datastore push subscriptions
4.1. Overview
The YANG data model for datastore push subscriptions is depicted in
the following figure. Following Yang tree convention in the
depiction, brackets enclose list keys, "rw" means configuration, "ro"
operational state data, "?" designates optional nodes, "*" designates
nodes that can have multiple instances. Parantheses with a name in
the middle enclose choice and case nodes. A "+" at the end of a line
indicates that the line is to be concatenated with the subsequent
line. New YANG tree notation is the i] which indicates that the node
in that line has been brought in / imported from another model, and
an (a) which indicates this is the specific imported node augmented.
In the figure below, all have been imported from 5277bis. The model
consists mostly of augmentations to RPCs and notifications defined in
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the data model for subscriptions for event notifications of
[I-D:netconf-sub-notif].
(Note: the yp indicates augmentations from yang push above and
beyond the event-notifications model)
module: ietf-subscribed-notifications
+--ro streams
| +--ro stream* stream
+--rw filters
| +--rw filter* [identifier]
| +--rw identifier filter-id
| +--rw (filter-type)?
| +--:(by-reference)
| | +--rw filter-ref? filter-ref
| +--:(event-filter)
| | +--rw filter?
| +--:(yp:update-filter)
| +--rw (yp:update-filter)?
| +--:(yp:subtree)
| | +--rw yp:subtree-filter?
| +--:(yp:xpath)
| +--rw yp:xpath-filter? yang:xpath1.0
+--rw subscription-config {configured-subscriptions}?
| +--rw subscription* [identifier]
| +--rw identifier subscription-id
| +--rw stream? stream
| +--rw encoding? encoding
| +--rw stop-time? yang:date-and-time
| +--rw (filter-type)?
| | +--:(by-reference)
| | | +--rw filter-ref? filter-ref
| | +--:(event-filter)
| | | +--rw filter?
| | +--:(yp:update-filter)
| | +--rw (yp:update-filter)?
| | +--:(yp:subtree)
| | | +--rw yp:subtree-filter?
| | +--:(yp:xpath)
| | +--rw yp:xpath-filter? yang:xpath1.0
| +--rw receivers
| | +--rw receiver* [address]
| | +--rw address inet:host
| | +--rw port inet:port-number
| | +--rw protocol? transport-protocol
| +--rw (notification-origin)?
| | +--:(interface-originated)
| | | +--rw source-interface? if:interface-ref
| | +--:(address-originated)
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| | +--rw source-vrf? string
| | +--rw source-address? inet:ip-address-no-zone
| +--rw (yp:update-trigger)?
| | +--:(yp:periodic)
| | | +--rw yp:period yang:timeticks
| | | +--rw yp:anchor-time? yang:date-and-time
| | +--:(yp:on-change) {on-change}?
| | +--rw yp:dampening-period yang:timeticks
| | +--rw yp:no-synch-on-start? empty
| | +--rw yp:excluded-change* change-type
| +--rw yp:dscp? inet:dscp
| +--rw yp:weighting? uint8
| +--rw yp:dependency? sn:subscription-id
+--ro subscriptions
+--ro subscription* [identifier]
+--ro identifier subscription-id
+--ro configured-subscription?
| empty {configured-subscriptions}?
+--ro stream? stream
+--ro encoding? encoding
+--ro replay-start-time? yang:date-and-time
+--ro stop-time? yang:date-and-time
+--ro (filter-type)?
| +--:(by-reference)
| | +--ro filter-ref? filter-ref
| +--:(event-filter)
| | +--ro filter?
| +--:(yp:update-filter)
| +--ro (yp:update-filter)?
| +--:(yp:subtree)
| | +--ro yp:subtree-filter?
| +--:(yp:xpath)
| +--ro yp:xpath-filter? yang:xpath1.0
+--ro (notification-origin)?
| +--:(interface-originated)
| | +--ro source-interface? if:interface-ref
| +--:(address-originated)
| +--ro source-vrf? string
| +--ro source-address? inet:ip-address-no-zone
+--ro receivers
| +--ro receiver* [address]
| +--ro address inet:host
| +--ro port inet:port-number
| +--ro protocol? transport-protocol
| +--ro pushed-notifications? yang:counter64
| +--ro excluded-notifications? yang:counter64
+--ro subscription-status? subscription-status
+--ro (yp:update-trigger)?
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| +--:(yp:periodic)
| | +--ro yp:period yang:timeticks
| | +--ro yp:anchor-time? yang:date-and-time
| +--:(yp:on-change) {on-change}?
| +--ro yp:dampening-period yang:timeticks
| +--ro yp:no-synch-on-start? empty
| +--ro yp:excluded-change* change-type
+--ro yp:dscp? inet:dscp
+--ro yp:weighting? uint8
+--ro yp:dependency? sn:subscription-id
rpcs:
+---x establish-subscription
| +---w input
| | +---w stream? stream
| | +---w encoding? encoding
| | +---w replay-start-time? yang:date-and-time
| | +---w stop-time? yang:date-and-time
| | +---w (filter-type)?
| | | +--:(by-reference)
| | | | +---w filter-ref? filter-ref
| | | +--:(event-filter)
| | | | +---w filter?
| | | +--:(yp:update-filter)
| | | +---w (yp:update-filter)?
| | | +--:(yp:subtree)
| | | | +---w yp:subtree-filter?
| | | +--:(yp:xpath)
| | | +---w yp:xpath-filter? yang:xpath1.0
| | +---w (yp:update-trigger)?
| | | +--:(yp:periodic)
| | | | +---w yp:period yang:timeticks
| | | | +---w yp:anchor-time? yang:date-and-time
| | | +--:(yp:on-change) {on-change}?
| | | +---w yp:dampening-period yang:timeticks
| | | +---w yp:no-synch-on-start? empty
| | | +---w yp:excluded-change* change-type
| | +---w yp:dscp? inet:dscp
| | +---w yp:weighting? uint8
| | +---w yp:dependency? sn:subscription-id
| +--ro output
| +--ro subscription-result subscription-result
| +--ro (result)?
| +--:(no-success)
| | +--ro filter-failure? string
| | +--ro replay-start-time-hint? yang:date-and-time
| | +--ro yp:period-hint? yang:timeticks
| | +--ro yp:error-path? string
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| | +--ro yp:object-count-estimate? uint32
| | +--ro yp:object-count-limit? uint32
| | +--ro yp:kilobytes-estimate? uint32
| | +--ro yp:kilobytes-limit? uint32
| +--:(success)
| +--ro identifier subscription-id
+---x modify-subscription
| +---w input
| | +---w identifier? subscription-id
| | +---w stop-time? yang:date-and-time
| | +---w (filter-type)?
| | | +--:(by-reference)
| | | | +---w filter-ref? filter-ref
| | | +--:(event-filter)
| | | | +---w filter?
| | | +--:(yp:update-filter)
| | | +---w (yp:update-filter)?
| | | +--:(yp:subtree)
| | | | +---w yp:subtree-filter?
| | | +--:(yp:xpath)
| | | +---w yp:xpath-filter? yang:xpath1.0
| | +---w (yp:update-trigger)?
| | +--:(yp:periodic)
| | | +---w yp:period yang:timeticks
| | | +---w yp:anchor-time? yang:date-and-time
| | +--:(yp:on-change) {on-change}?
| | +---w yp:dampening-period yang:timeticks
| +--ro output
| +--ro subscription-result subscription-result
| +--ro (result)?
| +--:(no-success)
| +--ro filter-failure? string
| +--ro yp:period-hint? yang:timeticks
| +--ro yp:error-path? string
| +--ro yp:object-count-estimate? uint32
| +--ro yp:object-count-limit? uint32
| +--ro yp:kilobytes-estimate? uint32
| +--ro yp:kilobytes-limit? uint32
+---x delete-subscription
| +---w input
| | +---w identifier subscription-id
| +--ro output
| +--ro subscription-result subscription-result
+---x kill-subscription
+---w input
| +---w identifier subscription-id
+--ro output
+--ro subscription-result subscription-result
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notifications:
+---n replay-complete
| +--ro identifier subscription-id
+---n notification-complete
| +--ro identifier subscription-id
+---n subscription-started
| +--ro identifier subscription-id
| +--ro stream? stream
| +--ro encoding? encoding
| +--ro replay-start-time? yang:date-and-time
| +--ro stop-time? yang:date-and-time
| +--ro (filter-type)?
| | +--:(by-reference)
| | | +--ro filter-ref? filter-ref
| | +--:(event-filter)
| | | +--ro filter?
| | +--:(yp:update-filter)
| | +--ro (yp:update-filter)?
| | +--:(yp:subtree)
| | | +--ro yp:subtree-filter?
| | +--:(yp:xpath)
| | +--ro yp:xpath-filter? yang:xpath1.0
| +--ro (yp:update-trigger)?
| | +--:(yp:periodic)
| | | +--ro yp:period yang:timeticks
| | | +--ro yp:anchor-time? yang:date-and-time
| | +--:(yp:on-change) {on-change}?
| | +--ro yp:dampening-period yang:timeticks
| | +--ro yp:no-synch-on-start? empty
| | +--ro yp:excluded-change* change-type
| +--ro yp:dscp? inet:dscp
| +--ro yp:weighting? uint8
| +--ro yp:dependency? sn:subscription-id
+---n subscription-resumed
| +--ro identifier subscription-id
+---n subscription-modified
| +--ro identifier subscription-id
| +--ro stream? stream
| +--ro encoding? encoding
| +--ro replay-start-time? yang:date-and-time
| +--ro stop-time? yang:date-and-time
| +--ro (filter-type)?
| | +--:(by-reference)
| | | +--ro filter-ref? filter-ref
| | +--:(event-filter)
| | | +--ro filter?
| | +--:(yp:update-filter)
| | +--ro (yp:update-filter)?
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| | +--:(yp:subtree)
| | | +--ro yp:subtree-filter?
| | +--:(yp:xpath)
| | +--ro yp:xpath-filter? yang:xpath1.0
| +--ro (yp:update-trigger)?
| | +--:(yp:periodic)
| | | +--ro yp:period yang:timeticks
| | | +--ro yp:anchor-time? yang:date-and-time
| | +--:(yp:on-change) {on-change}?
| | +--ro yp:dampening-period yang:timeticks
| | +--ro yp:no-synch-on-start? empty
| | +--ro yp:excluded-change* change-type
| +--ro yp:dscp? inet:dscp
| +--ro yp:weighting? uint8
| +--ro yp:dependency? sn:subscription-id
+---n subscription-terminated
| +--ro identifier subscription-id
| +--ro error-id subscription-errors
| +--ro filter-failure? string
+---n subscription-suspended
+--ro identifier subscription-id
+--ro error-id subscription-errors
+--ro filter-failure? string
module: ietf-yang-push
notifications:
+---n push-update
| +--ro subscription-id sn:subscription-id
| +--ro time-of-update? yang:date-and-time
| +--ro updates-not-sent? empty
| +--ro datastore-contents?
+---n push-change-update {on-change}?
+--ro subscription-id sn:subscription-id
+--ro time-of-update? yang:date-and-time
+--ro updates-not-sent? empty
+--ro datastore-changes?
Figure 11: Model structure
Selected components of the model are summarized in the following
subsections.
4.2. Filters
Filters can be supported via a reference to an entry in the filter
container, or via direct embedding within a subscription itself.
When a reference is used, it becomes possible to configure filters
independently of the lifecycle of a subscription. This facilitates
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the reuse of filter definitions, which can be important in case of
complex filter conditions. Referenced filters can also allow an
implementation to avoid evaluating filter acceptability during a
dynamic subscription request.
Whether referenced or in-line, filters used for yang-push must be of
case update-filters, and must follow the syntax and semantics of RFC
6241. It is not expected that implementations will support
comprehensive XPATH syntax and boundless complexity. It will be up
to implementations to describe what is viable, but the goal is to
provide equivalent capabilities to what is available with a GET.
Yang-push implementations must reject dynamic subscriptions or
suspend configured subscriptions if they include filters which are
unsupportable on a platform.
It is conceivable that other types of filters will be introduced for
yang-push in the future. To support such filter types, additional
filter cases can augment the data model.
4.3. Subscription configuration
Both configured and dynamic subscriptions are represented within the
list subscription-config. Each subscription has own list elements.
New and enhanced parameters extending the basic subscription data
model in [I-D:netconf-sub-notif] include:
o An update filter identifying yang nodes of interest. Filter
contents are specified via a reference to an existing filter, or
via an in-line definition for only that subscription. The case
statement differentates the options.
o For periodic subscriptions, triggered updates will occur at the
boundaries of a specified time interval. The periodic parameters
which define this interval include:
* a "period" which defines duration between period push updates.
* an "anchor-time". Update intervals always fall on the points
in time that are a multiple of a period after the anchor time.
If anchor time is not provided, then the anchor time must be
set for when the initial push update can be sent.
o When used in conjunction with period, the boundaries of periodic
update periods may be calculated.
o For on-change subscriptions, assuming the dampening period has
completed, triggered occurs whenever a change in the subscribed
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information is detected. On-change subscriptions have more
complex semantics that is guided by its own set of parameters:
* a "dampening-period" specifies the interval that must pass
before a successive update for the subscription is sent. The
first time a change is detected, the update is sent
immediately. If a subsequent change is detected, another
update is only sent once the dampening period has passed for
this subscription has passed.
* an "excluded-change" flag which allows restriction of the types
of changes for which updates should be sent (changes to object
values, object creation or deletion events).
* a "no-synch-on-start" flag which specifies whether a complete
update with all the subscribed data should be sent at the
beginning of a subscription.
o Optional qos parameters to indicate the treatment of a
susbcription relative to other traffic between publisher and
receiver. These include:
* A "dscp" QoS marking which should be stamped on packets to show
network QoS treatment.
* A "weighting" so that bandwidth proportional to this weighting
can be allocated to this subscription relative to others for
that receiver.
* a "dependency" upon another subscription. No push should be
sent until all updates for the referenced subscription have
been queued and sent.
o A subscription's weighting should work identically to stream
dependency weighting as described within RFC 7540, section 5.3.2.
o A subscription's dependency should work identically to stream
dependency as described within RFC 7540, sections 5.3.1, 5.3.3,
and 5.3.4. If a dependency is attempted via an RPC, but the
referenced subscription does not exist, the dependency will be
removed.
4.4. Notifications
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4.4.1. Monitoring and OAM Notifications
OAM notifications and mechanism are with one exception reused from
[I-D:netconf-sub-notif].
The one excpetion is the excluded-notifications object is not
applicable for yang-push. This is because discarded notifications
for datastore does not have meaning in this context, and should
always be zero.
4.4.2. Update Notifications
The data model introduces two YANG notifications for the actual
updates themselves.
Notification "push-update" is used to send a complete snapshot of the
data that has been subscribed to, with all YANG object filters
applied. The notification is used for periodic subscription updates
in a periodic subscription.
The notification can also be used in an on-change subscription for
the purposes of allowing a receiver to "synch" on a complete set of
susbcribed datastore contents. This will be done the start of an on-
change subscription, unless no-synch-on-start is specified for that
subscription. In addition, this notification MAY be used during the
subscription. This might be a useful thing to do if change updates
were not sent as expected (as indicated by the "updates-not-sent"
flag, or an identification of loss in pushed updates), or for general
resynchronization of a datastore extract at longer period intervals
(such as once per day) to mitigate the possibility of any
application-dependent synchronization drift. A mandatory requirement
defining when to sending a push-update notification in conjunction
with on-change subscription is not asserted in this specification
beyond synch-on-start. However an on-change receiver must be able to
handle an unsolicited push-update as a state synchonization reset.
The format and syntax of the contained update notification data
corresponds to the format and syntax of data that would be returned
in a corresponding get operation with the same filter parameters
applied.
Notification "push-change-update" is used to send data updates for
changes that have occurred in the subscribed data. This notification
is used only in conjunction with on-change subscriptions.
The data updates are encoded analogous to the syntax of a
corresponding yang-patch operation. It corresponds to the data that
would be contained in a yang-patch operation applied to the YANG
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datastore at the previous update, to result in the current state (and
applying it also to operational data).
If the application detects a discontinuity in the updates it is
pushing, the notification can include a flag "updates-not-sent".
This is a flag which indicates that not all changes which have
occurred since the last update are actually included with this
update. In other words, the publisher has failed to fulfill its full
subscription obligations, for example in cases where it was not able
to keep up with a change burst. To facilitate synchronization, a
publisher MAY subsequently send a push-update containing a full
snapshot of subscribed data.
4.5. RPCs
YANG-Push subscriptions are established, modified, and deleted using
RPCs augmented from [I-D:netconf-sub-notif].
4.5.1. Establish-subscription RPC
The subscriber sends an establish-subscription RPC with the
parameters in section 3.1. An example might look like:
500
encode-xml
Figure 12: Establish-subscription RPC
The publisher must respond explicitly positively (i.e., subscription
accepted) or negatively (i.e., subscription rejected) to the request.
Positive responses include the subscription-id of the accepted
subscription. In that case a publisher may respond:
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ok
52
Figure 13: Establish-subscription positive RPC response
A subscription can be rejected for multiple reasons, including the
lack of authorization to establish a subscription, the lack of read
authorization on the requested data node, or the inability of the
publisher to provide a stream with the requested semantics.
When the requester is not authorized to read the requested data node,
the returned information indicates the node is unavailable. For
instance, if the above request was unauthorized to read node "ex:foo"
the publisher may return:
subtree-unavailable
/ex:foo
Figure 14: Establish-subscription access denied response
If a request is rejected because the publisher is not able to serve
it, the publisher SHOULD include in the returned error what
subscription parameters would have been accepted for the request.
However, there are no guarantee that subsequent requests for this
subscriber or others will in fact be accepted.
For example, for the following request:
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push-update
10
encode-xml
Figure 15: Establish-subscription request example 2
A publisher that cannot serve on-change updates but periodic updates
might return the following:
period-unsupported
100
Figure 16: Establish-subscription error response example 2
4.5.2. Modify-subscription RPC
The subscriber may send a modify-subscription PRC for a subscription
previously established using RPC The subscriber may change any
subscription parameters by including the new values in the modify-
subscription RPC. Parameters not included in the rpc should remain
unmodified. For illustration purposes we include an exchange example
where a subscriber modifies the period of the subscription.
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push-update
1011
250
Figure 17: Modify subscription request
The publisher must respond explicitly positively (i.e., subscription
accepted) or negatively (i.e., subscription rejected) to the request.
Positive responses include the subscription-id of the accepted
subscription. In that case a publisher may respond:
ok
Figure 18: Modify subscription response
If the subscription modification is rejected, the publisher must send
a response like it does for an establish-subscription and maintain
the subscription as it was before the modification request. A
subscription may be modified multiple times.
A configured subscription cannot be modified using modify-
subscription RPC. Instead, the configuration needs to be edited as
needed.
4.5.3. Delete-subscription RPC
To stop receiving updates from a subscription and effectively delete
a subscription that had previously been established using an
establish-subscription RPC, a subscriber can send a delete-
subscription RPC, which takes as only input the subscription-id. For
example:
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1011
ok
Figure 19: Delete subscription
Configured subscriptions cannot be deleted via RPC, but have to be
removed from the configuration.
4.5.4. YANG Module Synchronization
In order to fully support datastore replication, the receiver needs
to know the YANG module library that is in use by server that is
being replicated. The YANG 1.0 module library information is sent by
a NETCONF server in the NETCONF 'hello' message. For YANG 1.1
modules and all modules used with the RESTCONF [RFC8040] protocol,
this information is provided by the YANG Library module (ietf-yang-
library.yang from [RFC7895]. The YANG library information is
important for the receiver to reproduce the set of object definitions
used by the replicated datastore.
The YANG library includes a module list with the name, revision,
enabled features, and applied deviations for each YANG module
implemented by the publisher. The receiver is expected to know the
YANG library information before starting a subscription. The
"/modules-state/module-set-id" leaf in the "ietf-yang-library" module
can be used to cache the YANG library information.
The set of modules, revisions, features, and deviations can change at
run-time (if supported by the server implementation). In this case,
the receiver needs to be informed of module changes before data nodes
from changed modules can be processed correctly. The YANG library
provides a simple "yang-library-change" notification that informs the
client that the library has changed somehow. The receiver then needs
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to re-read the entire YANG library data for the replicated server in
order to detect the specific YANG library changes. The "ietf-
netconf-notifications" module defined in [RFC6470] contains a
"netconf-capability-change" notification that can identify specific
module changes. For example, the module URI capability of a newly
loaded module will be listed in the "added-capability" leaf-list, and
the module URI capability of an removed module will be listed in the
"deleted-capability" leaf-list.
5. YANG module
file "ietf-yang-push@2017-02-08.yang"
module ietf-yang-push {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-yang-push";
prefix yp;
import ietf-inet-types {
prefix inet;
}
import ietf-yang-types {
prefix yang;
}
import ietf-subscribed-notifications {
prefix sn;
}
organization "IETF";
contact
"WG Web:
WG List:
WG Chair: Mahesh Jethanandani
WG Chair: Mehmet Ersue
Editor: Alexander Clemm
Editor: Eric Voit
Editor: Alberto Gonzalez Prieto
Editor: Ambika Prasad Tripathy
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Editor: Einar Nilsen-Nygaard
Editor: Andy Bierman
Editor: Balazs Lengyel
";
description
"This module contains conceptual YANG specifications
for YANG push.";
revision 2017-02-08 {
description
"Updates to simplify modify-subscription, add anchor-time";
reference
"YANG Datastore Push, draft-ietf-netconf-yang-push-05";
}
feature on-change {
description
"This feature indicates that on-change updates are
supported.";
}
/*
* IDENTITIES
*/
/* Additional errors for subscription operations */
identity period-unsupported {
base sn:error;
description
"Requested time period is too short. This can be for both
periodic and on-change dampening.";
}
identity qos-unsupported {
base sn:error;
description
"Subscription QoS parameters not supported on this platform.";
}
identity dscp-unavailable {
base sn:error;
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description
"Requested DSCP marking not allocatable.";
}
identity on-change-unsupported {
base sn:error;
description
"On-change not supported.";
}
identity synch-on-start-unsupported {
base sn:error;
description
"On-change synch-on-start not supported.";
}
identity synch-on-start-datatree-size {
base sn:error;
description
"Synch-on-start would push a datatree which exceeds size limit.";
}
identity reference-mismatch {
base sn:error;
description
"Mismatch in filter key and referenced yang subtree.";
}
identity subtree-unavailable {
base sn:error;
description
"Referenced yang subtree doesn't exist, or is a node where read
access is not permitted.";
}
identity datatree-size {
base sn:error;
description
"Resulting push updates would exceed size limit.";
}
/* Additional types of streams */
identity yang-push {
base sn:stream;
description
"A conceptual datastream consisting of all datastore updates,
including operational and configuration data.";
}
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identity custom-stream {
base sn:stream;
description
"A conceptual datastream for datastore updates with custom
updates as defined by a user.";
}
/* Additional transport option */
identity http2 {
base sn:transport;
description
"HTTP2 notifications as a transport";
}
/*
* TYPE DEFINITIONS
*/
typedef filter-id {
type uint32;
description
"A type to identify filters which can be associated with a
subscription.";
}
typedef change-type {
type enumeration {
enum "create" {
description
"A new data node was created";
}
enum "delete" {
description
"A data node was deleted";
}
enum "modify" {
description
"The value of a data node has changed";
}
}
description
"Specifies different types of changes that may occur to a
datastore.";
}
grouping update-filter {
description
"This groupings defines filters for push updates for a
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datastore tree. The filters define which updates are of
interest in a push update subscription. Mixing and matching
of multiple filters does not occur at the level of this
grouping. When a push-update subscription is created, the
filter can be a regular subscription filter, or one of the
additional filters that are defined in this grouping.";
choice update-filter {
description
"Define filters regarding which data nodes to include
in push updates";
case subtree {
description
"Subtree filter.";
anyxml subtree-filter {
description
"Subtree-filter used to specify the data nodes targeted
for subscription within a subtree, or subtrees, of a
conceptual YANG datastore. Objects matching the filter
criteria will traverse the filter. The syntax follows
the subtree filter syntax specified in RFC 6241.";
reference "RFC 6241 section 6";
}
}
case xpath {
description
"XPath filter";
leaf xpath-filter {
type yang:xpath1.0;
description
"Xpath defining the data items of interest.";
}
}
}
}
grouping update-policy-modifiable {
description
"This grouping describes the datastore specific subscription
conditions that can be changed during the lifetime of the
subscription.";
choice update-trigger {
description
"Defines necessary conditions for sending an event to
the subscriber.";
case periodic {
description
"The agent is requested to notify periodically the current
values of the datastore as defined by the filter.";
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leaf period {
type yang:timeticks;
mandatory true;
description
"Duration of time which should occur between periodic
push updates. Where the anchor of a start-time is
available, the push will include the objects and their
values which exist at an exact multiple of timeticks
aligning to this start-time anchor.";
}
leaf anchor-time {
type yang:date-and-time;
description
"Designates a timestamp from which the series of periodic
push updates are computed. The next update will take place
at the next period interval from the anchor time. For
example, for an anchor time at the top of a minute and a
period interval of a minute, the next update will be sent
at the top of the next minute.";
}
}
case on-change {
if-feature "on-change";
description
"The agent is requested to notify changes in values in the
datastore subset as defined by a filter.";
leaf dampening-period {
type yang:timeticks;
mandatory true;
description
"Minimum amount of time that needs to have passed since the
last time an update was provided for the subscription.";
}
}
}
}
grouping update-policy {
description
"This grouping describes the datastore specific subscription
conditions of a subscription.";
uses update-policy-modifiable {
augment "update-trigger/on-change" {
description
"Includes objects not modifiable once subscription is
established.";
leaf no-synch-on-start {
type empty;
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description
"This leaf acts as a flag that determines behavior at the
start of the subscription. When present, synchronization
of state at the beginning of the subscription is outside
the scope of the subscription. Only updates about changes
that are observed from the start time, i.e. only push-
change-update notifications are sent. When absent (default
behavior), in order to facilitate a receiver's
synchronization, a full update is sent when the
subscription starts using a push-update notification, just
like in the case of a periodic subscription. After that,
push-change-update notifications only are sent unless the
Publisher chooses to resynch the subscription again.";
}
leaf-list excluded-change {
type change-type;
description
"Use to restrict which changes trigger an update.
For example, if modify is excluded, only creation and
deletion of objects is reported.";
}
}
}
}
grouping update-qos {
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 {
type inet:dscp;
default "0";
description
"The push update's IP packet transport priority. This is made
visible across network hops to receiver. The transport
priority is shared for all receivers of a given
subscription.";
}
leaf weighting {
type uint8 {
range "0 .. 255";
}
description
"Relative weighting for a subscription. Allows an underlying
transport layer perform informed load balance allocations
between various subscriptions";
reference
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"RFC-7540, section 5.3.2";
}
leaf dependency {
type sn:subscription-id;
description
"Provides the Subscription ID of a parent subscription which has
absolute priority 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 of the
parent has something ready to push.";
reference
"RFC-7540, section 5.3.1";
}
}
grouping update-error-hints {
description
"Allow return additional negotiation hints that apply
specifically to push updates.";
leaf period-hint {
type yang:timeticks;
description
"Returned when the requested time period is too short. This hint
can assert an viable period for both periodic push cadence and
on-change dampening.";
}
leaf error-path {
type string;
description
"Reference to a YANG path which is associated with the error
being returned.";
}
leaf object-count-estimate {
type uint32;
description
"If there are too many objects which could potentially be
returned by the filter, this identifies the estimate of the
number of objects which the filter would potentially pass.";
}
leaf object-count-limit {
type uint32;
description
"If there are too many objects which could be returned by the
filter, this identifies the upper limit of the publisher's
ability to service for this subscription.";
}
leaf kilobytes-estimate {
type uint32;
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description
"If the returned information could be beyond the capacity of the
publisher, this would identify the data size which could result
from this filter.";
}
leaf kilobytes-limit {
type uint32;
description
"If the returned information would be beyond the capacity of the
publisher, this identifies the upper limit of the publisher's
ability to service for this subscription.";
}
}
augment "/sn:establish-subscription/sn:input" {
description
"Define additional subscription parameters that apply
specifically to push updates";
uses update-policy;
uses update-qos;
}
augment "/sn:establish-subscription/sn:input/"+
"sn:filter-type" {
description
"Add push filters to selection of filter types.";
case update-filter {
description
"Additional filter options for push subscription.";
uses update-filter;
}
}
augment "/sn:establish-subscription/sn:output/"+
"sn:result/sn:no-success" {
description
"Add push datastore error info and hints to RPC output.";
uses update-error-hints;
}
augment "/sn:modify-subscription/sn:input" {
description
"Define additional subscription parameters that apply
specifically to push updates.";
uses update-policy-modifiable;
}
augment "/sn:modify-subscription/sn:input/"+
"sn:filter-type" {
description
"Add push filters to selection of filter types.";
case update-filter {
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description
"Additional filter options for push subscription.";
uses update-filter;
}
}
augment "/sn:modify-subscription/sn:output/"+
"sn:result/sn:no-success" {
description
"Add push datastore error info and hints to RPC output.";
uses update-error-hints;
}
notification push-update {
description
"This notification contains a push update, containing data
subscribed to via a subscription. This notification is sent for
periodic updates, for a periodic subscription. It can also be
used for synchronization updates of an on-change subscription.
This notification shall only be sent to receivers of a
subscription; it does not constitute a general-purpose
notification.";
leaf subscription-id {
type sn:subscription-id;
mandatory true;
description
"This references the subscription because of which the
notification is sent.";
}
leaf time-of-update {
type yang:date-and-time;
description
"This leaf contains the time of the update.";
}
leaf updates-not-sent {
type empty;
description
"This is a flag which indicates that not all data nodes
subscribed to are included with this update. In other words,
the publisher has failed to fulfill its full subscription
obligations. This may lead to intermittent loss of
synchronization of data at the client. Synchronization at the
client can occur when the next push-update is received.";
}
anydata datastore-contents {
description
"This contains the updated data. It constitutes a snapshot
at the time-of-update of the set of data that has been
subscribed to. The format and syntax of the data
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corresponds to the format and syntax of data that would be
returned in a corresponding get operation with the same
filter parameters applied.";
}
}
notification push-change-update {
if-feature "on-change";
description
"This notification contains an on-change push update. This
notification shall only be sent to the receivers of a
subscription; it does not constitute a general-purpose
notification.";
leaf subscription-id {
type sn:subscription-id;
mandatory true;
description
"This references the subscription because of which the
notification is sent.";
}
leaf time-of-update {
type yang:date-and-time;
description
"This leaf contains the time of the update, i.e. the time at
which the change was observed.";
}
leaf updates-not-sent {
type empty;
description
"This is a flag which indicates that not all changes which
have occurred since the last update are included with this
update. In other words, the publisher has failed to
fulfill its full subscription obligations, for example in
cases where it was not able to keep up with a change burst.
To facilitate synchronization, a publisher MAY subsequently
send a push-update containing a full snapshot of subscribed
data. Such a push-update might also be triggered by a
subscriber requesting an on-demand synchronization.";
}
anydata datastore-changes {
description
"This contains datastore contents that has changed since the
previous update, per the terms of the subscription. Changes
are encoded analogous to the syntax of a corresponding yang-
patch operation, i.e. a yang-patch operation applied to the
YANG datastore implied by the previous update to result in the
current state (and assuming yang-patch could also be applied to
operational data).";
}
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}
augment "/sn:subscription-started" {
description
"This augmentation adds push subscription parameters to the
notification that a subscription has started and data updates are
beginning to be sent. This notification shall only be sent to
receivers of a subscription; it does not constitute a general-
purpose notification.";
uses update-policy;
uses update-qos;
}
augment "/sn:subscription-started/sn:filter-type" {
description
"This augmentation allows to include additional update filters
options to be included as part of the notification that a
subscription has started.";
case update-filter {
description
"Additional filter options for push subscription.";
uses update-filter;
}
}
augment "/sn:subscription-modified" {
description
"This augmentation adds push subscription parameters to the
notification that a subscription has been modified. This
notification shall only be sent to receivers of a subscription;
it does not constitute a general-purpose notification.";
uses update-policy;
uses update-qos;
}
augment "/sn:subscription-modified/sn:filter-type" {
description
"This augmentation allows to include additional update
filters options to be included as part of the notification
that a subscription has been modified.";
case update-filter {
description
"Additional filter options for push subscription.";
uses update-filter;
}
}
augment "/sn:filters/sn:filter/"+
"sn:filter-type" {
description
"This container adds additional update filter options to the list
of configurable filters that can be applied to subscriptions.
This facilitates the reuse of complex filters once defined.";
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case update-filter {
uses update-filter;
}
}
augment "/sn:subscription-config/sn:subscription" {
description
"Contains the list of subscriptions that are configured,
as opposed to established via RPC or other means.";
uses update-policy;
uses update-qos;
}
augment "/sn:subscription-config/sn:subscription/"+
"sn:filter-type" {
description
"Add push filters to selection of filter types.";
case update-filter {
uses update-filter;
}
}
augment "/sn:subscriptions/sn:subscription" {
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, e.g. establish-subscription, delete-subscription,
and modify-subscription, as well as subscriptions that
have been established via configuration.";
uses update-policy;
uses update-qos;
}
augment "/sn:subscriptions/sn:subscription/"+
"sn:filter-type" {
description
"Add push filters to selection of filter types.";
case update-filter {
description
"Additional filter options for push subscription.";
uses update-filter;
}
}
}
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6. Security Considerations
Subscriptions could be used to attempt to overload publishers of YANG
datastores. For this reason, it is important that the publisher has
the ability to decline a subscription request if it would deplete its
resources. In addition, a publisher needs to be able to suspend an
existing subscription when needed. When this occur, the subscription
status is updated accordingly and the receivers are notified.
Likewise, requests for subscriptions need to be properly authorized.
A subscription could be used to retrieve data in subtrees that a
receiver has no authorized access to. Therefore it is important that
data pushed based on subscriptions is authorized in the same way that
regular data retrieval operations are. Data being pushed to a
receiver needs therefore to be filtered accordingly, just like if the
data were being retrieved on-demand. The Netconf Authorization
Control Model applies.
A subscription could be configured on another receiver's behalf, with
the goal of flooding that receiver with updates. One or more
publishers could be used to overwhelm a receiver which doesn't even
support subscriptions. Receivers which do not want pushed data need
only terminate or refuse any transport sessions from the publisher.
In addition, the Netconf Authorization Control Model SHOULD be used
to control and restrict authorization of subscription configuration.
For both configured and dynamic subscriptions it is essential to
authenticate and authorize that receiver via some transport level
mechanism before sending any push updates.
7. Acknowledgments
For their valuable comments, discussions, and feedback, we wish to
acknowledge Tim Jenkins, Kent Watsen, Susan Hares, Yang Geng, Peipei
Guo, Michael Scharf, Sharon Chisholm, and Guangying Zheng.
8. References
8.1. Normative References
[I-D:netconf-sub-notif]
Clemm, A., Gonzalez Prieto, A., Voit, E., Tripathy, A.,
and E. Nilsen-Nygaard, "Subscribing to YANG-Defined Event
Notifications", draft-ietf-netconf-subscribed-
notifications-00 (work in progress), February 2017.
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[RFC6470] Bierman, A., "Network Configuration Protocol (NETCONF)
Base Notifications", RFC 6470, DOI 10.17487/RFC6470,
February 2012, .
[RFC6536] Bierman, A. and M. Bjorklund, "Network Configuration
Protocol (NETCONF) Access Control Model", RFC 6536,
DOI 10.17487/RFC6536, March 2012,
.
[RFC7895] Bierman, A., Bjorklund, M., and K. Watsen, "YANG Module
Library", RFC 7895, DOI 10.17487/RFC7895, June 2016,
.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
.
[RFC7951] Lhotka, L., "JSON Encoding of Data Modeled with YANG",
RFC 7951, DOI 10.17487/RFC7951, August 2016,
.
[RFC8072] Bierman, A., Bjorklund, M., and K. Watsen, "YANG Patch
Media Type", RFC 8072, DOI 10.17487/RFC8072, February
2017, .
8.2. Informative References
[RFC1157] Case, J., "A Simple Network Management Protocol (SNMP)",
RFC 1157, May 1990.
[RFC5277] Chisholm, S. and H. Trevino, "NETCONF Event
Notifications", RFC 5277, July 2008.
[RFC6241] Enns, R., Bjorklund, M., Schoenwaelder, J., and A.
Bierman, "Network Configuration Protocol (NETCONF)",
RFC 6241, June 2011.
[RFC7923] Voit, E., Clemm, A., and A. Gonzalez Prieto, "Requirements
for Subscription to YANG Datastores", RFC 7923, June 2016.
[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
.
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Appendix A. Technologies to be considered for future iterations
A.1. Proxy YANG Subscription when the Subscriber and Receiver are
different
The properties of Dynamic and Configured Subscriptions can be
combined to enable deployment models where the Subscriber and
Receiver are different. Such separation can be useful with some
combination of:
o An operator does not want the subscription to be dependent on the
maintenance of transport level keep-alives. (Transport
independence provides different scalability characteristics.)
o There is not a transport session binding, and a transient
Subscription needs to survive in an environment where there is
unreliable connectivity with the Receiver and/or Subscriber.
o An operator wants the Publisher to include highly restrictive
capacity management and Subscription security mechanisms outside
of domain of existing operational or programmatic interfaces.
To build a Proxy Subscription, first the necessary information must
be signaled as part of the . Using this set
of Subscriber provided information; the same process described within
section 3 will be followed.
After a successful establishment, if the Subscriber wishes to track
the state of Receiver subscriptions, it may choose to place a
separate on-change Subscription into the "Subscriptions" subtree of
the YANG Datastore on the Publisher.
A.2. OpState and Filters
Currently there are ongoing discusssions to revise the concept of
datastores, allowing for proper handling and distinction of intended
versus applied configurations and extending the notion of a datastore
to operational data. When finalized, the new concept may open up the
possibility for new types of subscription filters, for example,
targeting specific datastores and targeting (potentially) differences
in datatrees across different datastores.
Likewise, it is conceivable that filters are defined that apply to
metadata, such as data nodes for which metadata has been defined that
meets a certain criteria.
Defining any such subscription filters at this point would be highly
speculative in nature. However, it should be noted that
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corresponding extensions may be defined in future specifications.
Any such extensions will be straightforward to accommodate by
introducing a model that defines new filter types, and augmenting the
new filter type into the subscription model.
A.3. Splitting push updates
Push updates may become fairly large and extend across multiple
subsystems in a YANG-Push Server. As a result, it conceivable to not
combine all updates into a single update message, but to split
updates into multiple separate update messages. Such splitting could
occur along multiple criteria: limiting the number of data nodes
contained in a single update, grouping updates by subtree, grouping
updates by internal subsystems (e.g., by line card), or grouping them
by other criteria.
Splitting updates bears some resemblance to fragmenting packets. In
effect, it can be seen as fragmenting update messages at an
application level. However, from a transport perspective, splitting
of update messages is not required as long as the transport does not
impose a size limitation or provides its own fragmentation mechanism
if needed. We assume this to be the case for YANG-Push. In the case
of NETCONF, RESTCONF, HTTP/2, no limit on message size is imposed.
In case of other transports, any message size limitations need to be
handled by the corresponding transport mapping.
There may be some scenarios in which splitting updates might still
make sense. For example, if updates are collected from multiple
independent subsystems, those updates could be sent separately
without need for combining. However, if updates were to be split,
other issues arise. Examples include indicating the number of
updates to the receiver, dinstinguishing a missed fragment from a
missed update, and the ordering with which updates are received.
Proper addressing those issues would result in considerable
complexity, while resulting in only very limited gains. In addition,
if a subscription is found to result in updates that are too large, a
publisher can always reject the request for a subscription while the
subscriber is always free to break a subscription up into multiple
subscriptions.
A.4. Potential Subscription Parameters
A possible is the introduction of an additional parameter "changes-
only" for periodic subscription. Including this flag would results
in sending at the end of each period an update containing only
changes since the last update (i.e. a change-update as in the case of
an on-change subscription), not a full snapshot of the subscribed
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information. Such an option might be interesting in case of data
that is largely static and bandwidth-constrained environments.
Appendix B. Issues that are currently being worked and resolved
(To be removed by RFC editor prior to publication)
Issue #6: Data plane notifications and layered headers. Specifically
how do we want to enable standard header unificiation and bundle
support vs. the data plane notifications currently defined.
Appendix C. Changes between revisions
(To be removed by RFC editor prior to publication)
v04 to v05
o Referenced based subscription document changed to Subscribed
Notifications from 5277bis.
o Getting operational data from filters
o Extension notifiable-on-change added
o New appendix on potential futures. Moved text into there from
several drafts.
o Subscription configuration section now just includes changed
parameters from Subscribed Notifications
o Subscription monitoring moved into Subscribed Notifications
o New error and hint mechanisms included in text and in the yang
model.
o Updated examples based on the error definitions
o Groupings updated for consistency
o Text updates throughout
v03 to v04
o Updates-not-sent flag added
o Not notifiable extension added
o Dampening period is for whole subscription, not single objects
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o Moved start/stop into rfc5277bis
o Client and Server changed to subscriber, publisher, and receiver
o Anchor time for periodic
o Message format for synchronization (i.e. synch-on-start)
o Material moved into 5277bis
o QoS parameters supported, by not allowed to be modified by RPC
o Text updates throughout
Authors' Addresses
Alexander Clemm
Huawei
Email: ludwig@clemm.org
Eric Voit
Cisco Systems
Email: evoit@cisco.com
Alberto Gonzalez Prieto
Cisco Systems
Email: albertgo@cisco.com
Ambika Prasad Tripathy
Cisco Systems
Email: ambtripa@cisco.com
Einar Nilsen-Nygaard
Cisco Systems
Email: einarnn@cisco.com
Clemm, et al. Expires September 1, 2017 [Page 52]
Internet-Draft YANG-Push February 2017
Andy Bierman
YumaWorks
Email: andy@yumaworks.com
Balazs Lengyel
Ericsson
Email: balazs.lengyel@ericsson.com
Clemm, et al. Expires September 1, 2017 [Page 53]