NETCONF A. Clemm
Internet-Draft Huawei
Intended status: Standards Track E. Voit
Expires: June 25, 2018 Cisco Systems
A. Gonzalez Prieto
VMware
A. Tripathy
E. Nilsen-Nygaard
Cisco Systems
A. Bierman
YumaWorks
B. Lengyel
Ericsson
December 22, 2017
YANG Datastore Subscription
draft-ietf-netconf-yang-push-12
Abstract
Via the mechanism described in this document, subscriber applications
may request a continuous, customized stream of updates from a YANG
datastore. Providing such visibility into changes made upon YANG
configuration and operational objects enables new capabilities based
on the remote mirroring of configuration and operational state.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 25, 2018.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Definitions and Acronyms . . . . . . . . . . . . . . . . . . 4
3. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Subscription Model . . . . . . . . . . . . . . . . . . . 4
3.2. Negotiation of Subscription Policies . . . . . . . . . . 6
3.3. On-Change Considerations . . . . . . . . . . . . . . . . 6
3.4. Promise-Theory Considerations . . . . . . . . . . . . . . 8
3.5. Data Encodings . . . . . . . . . . . . . . . . . . . . . 8
3.6. Datastore Selection . . . . . . . . . . . . . . . . . . . 9
3.7. Streaming Updates . . . . . . . . . . . . . . . . . . . . 10
3.8. Subscription Management . . . . . . . . . . . . . . . . . 12
3.9. Receiver Authorization . . . . . . . . . . . . . . . . . 14
3.10. On-change Notifiable YANG objects . . . . . . . . . . . . 15
3.11. Other Considerations . . . . . . . . . . . . . . . . . . 16
4. A YANG data model for management of datastore push
subscriptions . . . . . . . . . . . . . . . . . . . . . . . . 17
4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 17
4.2. Subscription configuration . . . . . . . . . . . . . . . 25
4.3. YANG Notifications . . . . . . . . . . . . . . . . . . . 26
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4.4. YANG RPCs . . . . . . . . . . . . . . . . . . . . . . . . 27
5. YANG module . . . . . . . . . . . . . . . . . . . . . . . . . 32
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 47
7. Security Considerations . . . . . . . . . . . . . . . . . . . 47
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 48
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 48
9.1. Normative References . . . . . . . . . . . . . . . . . . 48
9.2. Informative References . . . . . . . . . . . . . . . . . 49
Appendix A. Changes between revisions . . . . . . . . . . . . . 49
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 52
1. Introduction
Traditional approaches to remote visibility have been built on
polling. With polling, data is periodically requested and retrieved
by a client from a server to stay up-to-date. However, there are
issues associated with polling-based management:
o Polling incurs significant latency. This latency prohibits many
application types.
o Polling cycles may be missed, requests may be delayed or get lost,
often when the network is under stress and the need for the data
is the greatest.
o Polling requests may undergo slight fluctuations, resulting in
intervals of different lengths. The resulting data is difficult
to calibrate and compare.
o For applications that monitor for changes, many remote polling
cycles place ultimately fruitless load on the network, devices,
and applications.
A more effective alternative to polling is for an application to
receive automatic and continuous updates from a targeted subset of a
datastore. Accordingly, there is a need for a service that allows
applications to subscribe to updates from a datastore and that
enables the publisher to push and in effect stream those updates.
The requirements for such a service have been documented in
[RFC7923].
This document defines a corresponding solution that is built on top
of "Custom Subscription to Event Streams"
[I-D.draft-ietf-netconf-subscribed-notifications]. Supplementing
that work are YANG data model augmentations, extended RPCs, and new
datastore specific update notifications. Transport options for
[I-D.draft-ietf-netconf-subscribed-notifications] will work
seamlessly with this solution.
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2. Definitions and Acronyms
The terms below supplement those defined in
[I-D.draft-ietf-netconf-subscribed-notifications]. In addition, the
term "datastore" is defined in
[I-D.draft-ietf-netmod-revised-datastores].
Datastore node: An instance of management information in a datastore.
Also known as "object".
Datastore node update: A data item containing the current value/
property of a datastore node at the time the datastore node update
was created.
Datastore subtree: An instantiated datastore node and the datastore
nodes that are hierarchically contained within it.
Update record: A representation datastore node update(s) resulting
from the application of a selection filter for a subscription. An
update record will include the value/property of one or more
datastore nodes at a point in time. It may contain the update type
for each datastore node (e.g., add, change, delete). Also included
may be metadata/headers such as a subscription identifier.
Selection filter: Evaluation and/or selection criteria, which may be
applied against a targeted set of objects.
Update trigger: A mechanism that determines when an update record
needs to be generated.
YANG-Push: The subscription and push mechanism for 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 datastores. Subscriptions
specify when notification messages should be sent and what data to
include in update records. 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 enhances the subscription model defined
in [I-D.draft-ietf-netconf-subscribed-notifications] with
capabilities that allow subscribers to subscribe to datastore node
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updates, specifically to specify the triggers defining when to
generate update records as well as what to include in an update
record. Key enhancements include:
o Specification of selection filters which identify targeted YANG
datastore nodes and/or subtrees within a datastore for which
updates are to be pushed.
o An encoding (using anydata) for the contents of periodic and on-
change push updates.
o Specification of update policies contain conditions which trigger
the generation and pushing of new update records. There are two
types of triggers for subscriptions: periodic and on-change.
* For periodic subscriptions, the trigger is specified by two
parameters that define when updates are to be pushed. These
parameters are the period interval with which to report
updates, and an anchor time which can be used to calculate at
which point in time updates need to be assembled and sent.
* For on-change subscriptions, a trigger occurs whenever a change
in the subscribed information is detected. Included are
additional parameters such as:
+ Dampening period: In an on-change subscription, detected
object changes should be sent as quickly as possible.
However it may be undesirable to send a rapid series of
object changes. Such behavior has the potential to exhaust
of resources in the publisher or receiver. In order to
protect against that, a dampening period MAY be used to
specify the interval which must pass before successive
update records for the same subscription are generated for a
receiver. The dampening period collectively applies to the
set of all datastore nodes selected by a single subscription
and sent to a single receiver. This means that when there
is a change to one or more subscribed objects, an update
record containing those objects is created either
immediately when no dampening period is in effect, or at the
end of a dampening period. If multiple changes to a single
object occur during a dampening period, only the value that
is in effect is included as part of the update record. The
dampening period goes into effect every time an update
record completes assembly.
+ Change type: This parameter can be used to reduce the types
of datastore changes for which updates are sent (e.g., you
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might only send when an object is created or deleted, but
not when an object value changes).
+ No Synch on start: defines whether or not a complete push-
update of all subscribed data will be sent at the beginning
of a subscription. Such early synchronization establishes
the frame of reference for subsequent updates.
3.2. Negotiation of Subscription Policies
A dynamic subscription request SHOULD be declined if a publisher's
assessment is that it may be unable to provide update records meeting
the terms of the request. In this case, a subscriber may quickly
follow up with a new subscription request using different parameters.
Random guessing at different parameters by a subscriber is to be
discouraged. Therefore, in order to minimize the number of
subscription iterations between subscriber and publisher, dynamic
subscriptions supports a simple negotiation between subscribers and
publishers for subscription parameters. This negotiation is in the
form of a no-success response to a failed establish or modify
subscription request. The no-success message SHOULD include in the
returned error response information that, when considered, increases
the likelihood of success for subsequent requests. However, there
are no guarantees that subsequent requests for this subscriber will
be accepted.
[I-D.draft-ietf-netconf-subscribed-notifications] contains several
negotiable subscription parameters. Additional yang-push negotiation
information defined in this specification includes hints at
acceptable time intervals, size estimates for the number or objects
which would be returned from a filter, and the location of an error
in a provided filter.
3.3. On-Change Considerations
On-change subscriptions allow subscribers to receive updates whenever
changes to targeted objects occur. As such, on-change subscriptions
are particularly effective for data that changes infrequently, yet
for which applications need to be quickly notified whenever a change
does occur with minimal delay.
On-change subscriptions tend to be more difficult to implement than
periodic subscriptions. Accordingly, on-change subscriptions may not
be supported by all implementations or for every object.
Whether or not to accept or reject on-change subscription requests
when the scope of the subscription contains objects for which on-
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change is not supported is up to the publisher implementation. A
publisher MAY accept an on-change subscription even when the scope of
the subscription contains objects for which on-change is not
supported. In that case, updates are sent only for those objects
within the scope that do support on-change updates whereas other
objects are excluded from update records, whether or not their values
actually change. In order for a subscriber to determine whether
objects support on-change subscriptions, objects are marked
accordingly on a publisher. Accordingly, when subscribing, it is the
responsibility of the subscriber to ensure it is aware of which
objects support on-change and which do not. For more on how objects
are so marked, see Section 3.10.
Alternatively, a publisher MAY decide to simply reject an on-change
subscription in case the scope of the subscription contains objects
for which on-change is not supported. In case of a configured
subscription, the subscription MAY be suspended.
To avoid flooding receivers with repeated updates for subscriptions
containing fast-changing objects, or objects with oscillating values,
an on-change subscription allows for the definition of a dampening
period. Once an update record for a given object is generated, no
other updates for this particular subscription will be created until
the end of the dampening 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 include those which were deleted or newly created during that
dampening period. If an object has returned to its original value
(or even has been created and then deleted) during the dampening-
period, the last change will still be sent. This will indicate churn
is occurring on that object.
On-change subscriptions can be refined to let users subscribe only to
certain types of changes. For example, a subscriber might only want
object creations and deletions, but not modifications of object
values.
Putting it all together, following is the conceptual process for
creating an push-change-update notification:
1. Just before a change, or at the start of a dampening period,
evaluate any filtering and any access control rules. The result
is a set "A" of datastore nodes and subtrees.
2. Just after a change, or at the end of a dampening period,
evaluate any filtering and any (possibly new) access control
rules. The result is a set "B" of datastore nodes and subtrees.
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3. Construct a YANG patch record for going from A to B. If the
record is non-empty, send it to the receiver.
Note: In cases where a subscriber wants to have separate dampening
periods for different objects, multiple subscriptions with different
objects in a selection filter can be created.
3.4. Promise-Theory Considerations
A subscription to updates from a datastore is intended to obviate the
need for polling. However, in order to do so, it is critical that
subscribers can rely on the subscription and have confidence that
they will indeed receive the subscribed updates without having to
worry updates being silently dropped. In other words, a subscription
constitutes a promise on the side of the publisher to provide the
receivers with updates per the terms of the subscription.
Now, there are many reasons why a publisher may at some point no
longer be able to fulfill the terms of the subscription, even if the
subscription had been entered into with good faith. For example, the
volume of data objects may be larger than anticipated, the interval
may prove too short to send full updates in rapid succession, or an
internal problem may prevent objects from being collected. If for
some reason the publisher of a subscription is not able to keep its
promise, receivers MUST be notified immediately and reliably. The
publisher MAY also suspend the subscription.
A publisher SHOULD reject a request for a subscription if it is
unlikely that the publisher will be able fulfill the terms of that
subscription request. In such cases, it is preferable to have a
subscriber request a less resource intensive subscription than to
deal with frequently degraded behavior.
3.5. Data Encodings
3.5.1. Periodic Subscriptions
In a periodic subscription, the data included as part of an update
corresponds to data that could have been read using a retrieval
operation over that subscription's transport.
3.5.2. On-Change Subscriptions
In an on-change subscription, updates need to indicate not only
values of changed datastore nodes but also the types of changes that
occurred since the last update. Therefore encoding rules for data in
on-change updates will generally follow YANG-patch operation as
specified in [RFC8072]. The YANG-patch will describe what needs to
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be applied to the earlier state reported by the preceding update, to
result in the now-current state. Note that contrary to [RFC8072],
objects encapsulated are not restricted to configuration objects
only.
However a patch must be able to do more than just describe the delta
from the previous state to the current state. As per Section 3.3, it
must also be able to identify if transient changes have occurred on
an object during a dampening period. To support this, it is valid to
encode a YANG patch operation so that its application would result in
a no change between the previous and current state. This indicates
that some churn has occurred on the object. An example of this would
be a patch that does a "create" operation for a datastore node where
the receiver believes one already exists, or a "merge" operation
which replaces a previous value with the same value. Note that this
means that the "create" and "delete" errors described in [RFC8072]
section 2.5 are not errors, and are valid operations with YANG push.
3.6. Datastore Selection
A subscription must specify both the selection filters and the
datastore against which these selection filters will be applied.
This information is used to choose and subsequently push data from
the publisher's datastore to the receivers.
Only a single selection filter can be applied to a subscription at a
time. The following selection filter types are included in the yang-
push data model, and may be applied against a datastore:
o subtree: A subtree selection filter identifies one or more
datastore subtrees. When specified, update records will only come
from the datastore nodes of selected datastore subtree(s). The
syntax and semantics correspond to that specified for [RFC6241]
section 6.
o xpath: An xpath selection filter is an XPath expression that
returns a node set. When specified, updates will only come from
the selected data nodes.
These filters are intended to be used as selectors that define which
objects are within the scope of a subscription. A publisher MUST
support at least one type of selection filter.
Selection filters are not intended to be used for property value
filtering for non-key objects. Supporting non-key property value
filtering so would have a number of implications that would result in
significant complexity. While it is possible to define extensions in
the future that will support selection filtering based on values,
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this is not supported in this version of yang-push and a publisher
MAY reject a subscription request that contains a filter for object
values.
Xpath itself provides powerful filtering constructs, and care must be
used in filter definition. As an example, consider an xpath filter
with a boolean result; such a result will not provide an easily
interpretable subset of a datastore. Beyond the boolean example, it
is quite possible to define an xpath filter where results are easy
for an application to mis-interpret. Consider an xpath filter which
only passes a datastore object when an interface is up. It is up to
the receiver to understand implications of the presence or absence of
objects in each update.
When the set of selection filtering criteria is applied for periodic
subscription, all selected datastore nodes for which a receiver has
access are provided to a receiver. If the same filtering criteria is
applied to an on-change subscription, only the subset of those
datastore nodes supporting on-change are provided. A datastore node
which doesn't support on-change is never sent as part of an on-change
subscription's "push-update" or "push-change-update".
3.7. Streaming Updates
Contrary to traditional data retrieval requests, datastore
subscription enables an unbounded series of update records to be
streamed over time. Two generic YANG notifications for update
records have been defined for this: "push-update" and "push-change-
update".
A "push-update" notification defines a complete, filtered update of
the datastore per the terms of a subscription. This type of YANG
notification is used for continuous updates of periodic
subscriptions. A "push-update" notification can also be used 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 an on-change subscription. The
"push-update" update record contains a data snippet that contains an
instantiated datastore subtree with the subscribed contents. The
content of the update record 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.
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 set of changes that datastore nodes
have undergone since the last notification message. In other words,
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this indicates which datastore nodes have been created, deleted, or
have had changes to their values. In cases where multiple changes
have occurred and the object has not been deleted, the object's most
current value is reported. (In other words, for each object, only
one change is reported, not its entire history. Doing so would
defeat the purpose of the dampening period.)
These new "push-update" or "push-change-update" are encoded and
placed within notification messages, and ultimately queued for egress
over the specified transport.
The following is an example of a notification message for a
subscription tracking the operational status of a single Ethernet
port (per [RFC7223]). This notification message is encoded XML over
NETCONF as per [I-D.draft-ietf-netconf-netconf-event-notifications].
2017-10-25T08:00:11.22Z
1011
eth0
up
Figure 1: Push example
The following is an example of an on-change notification message for
the same subscription.
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2017-10-25T08:22:33.44Z
89
1
edit1
merge
/ietf-interfaces:interfaces-state
eth0
down
Figure 2: Push example for on change
Of Note in the above example is the 'patch-id' with a value of '1'.
Per [RFC8072], the 'patch-id' is an arbitrary string. With YANG
Push, the publisher SHOULD put into the 'patch-id' a counter starting
at '1' which increments with every 'push-change-update' generated for
a subscription. If used as a counter, this counter MUST be reset to
'1' anytime a resynchronization occurs (i.e., with the sending of a
'push-update'). Also if used as a counter, the counter MUST be reset
to '1' the after passing a maximum value of '99999'. Such a
mechanism allows easy identification of lost or out-of-sequence
update records.
3.8. Subscription Management
The RPCs defined within
[I-D.draft-ietf-netconf-subscribed-notifications] have been enhanced
to support datastore subscription negotiation. Included in these
enhancements are error codes which can indicate why a datastore
subscription attempt has failed.
A datastore subscription can be rejected for multiple reasons. This
includes a too large subtree request, or the inability of the
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publisher push update records as frequently as requested. In such
cases, no subscription is established. Instead, the subscription-
result with the failure reason is returned as part of the RPC
response. As part of this response, a set of alternative
subscription parameters MAY be returned that would likely have
resulted in acceptance of the subscription request. The subscriber
may consider these as part of future subscription attempts.
For instance, for the following request:
ds:operational
/ex:foo
500
Figure 3: Establish-Subscription example
the publisher might return:
yp:period-unsupported
2000
Figure 4: Error response example
As can be seen above the rejected subscription does not result in the
generation of an rpc-reply with an rpc-error element. YANG-push
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specific errors and negotiation hints part are returned as part of
normal RPC operations.
3.9. Receiver Authorization
A receiver of subscription data MUST only be sent updates for which
they have proper authorization. A publisher MUST ensure that no non-
authorized data is included in push updates. To do so, it needs to
apply all corresponding checks applicable at the time of a specific
pushed update and if necessary silently remove any non-authorized
data from datastore subtrees. This enables YANG data pushed based on
subscriptions to be authorized equivalently to a regular data
retrieval (get) operation.
A publisher MUST allow for the possibility that a subscription's
selection filter references non-existent or access-protected data.
Such support permits a receiver the ability to monitor the entire
lifecyle of some datastore tree. In this case, all "push-update"
notifications must be sent empty, and no "push-change-update"
notifications will be sent until some data becomes visible for a
receiver.
A publisher MAY choose reject an establish-subscription request which
selects non-existent or access-protected data. In addition, a
publisher MAY choose to terminate a dynamic subscription or suspend a
configured receiver when the authorization privileges of a receiver
change, or the access controls for subscribed objects change. Such a
capability enables the publisher to avoid having to support a
continuous, and total filtering of an entire subscription's content.
In these cases above, the error identity "data-unavailable" SHOULD be
returned. This reduces the possibility of leakage of access
controlled objects.
The conceptual authorization model for datastores is the NETCONF
Access Control Model [RFC6536bis], Section 3.2.4. A clarification to
this is that each of the individual nodes in a resulting update
record MUST also have applied access control to resulting pushed
messages. This includes validating that read access is ok for any
nodes newly selected since the last update record for each receiver.
+-----------------+ +--------------------+
push-update or --> | datastore node | yes | add datastore node |
push-change-update | access allowed? | ---> | to update message |
+-----------------+ +--------------------+
Figure 5: Access control for push updates
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If read access into previously accessible nodes has been lost due to
a receiver permissions change, this SHOULD be reported as a patch
"delete" operation for on-change subscriptions. If not capable of
handling such receiver permission changes with such a "delete",
publisher implementations MUST force dynamic subscription re-
establishment or configured subscription re-initialization so that
appropriate filtering is installed.
3.10. 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 datastore node changes frequently
(e.g., [RFC7223]'s in-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 for a particular object.
Support for on-change notification is specific to the individual YANG
model and/or implementation, and is useful to define in design time.
System integrators need this information (without reading any data
from a live node).
The default assumption is that no datastore nodes support on-change
notification. Schema nodes and subtrees that support on-change
notifications MUST be marked by accordingly with the YANG extension
"notifiable-on-change". This extension is defined in the data model
below.
When an on-change subscription is established, data-nodes are
automatically excluded unless they are marked with notifiable-on-
change as true. This also means that authorization checks SHALL NOT
be performed on them. A subscriber can identify which nodes may be
included in on-change updates by retrieving the datastore nodes in
the subscription's scope and checking for which notifiable-on-change
is marked as true.
In theory, adding "notifiable-on-change" markings can be done within
corresponding YANG models. But a more extensible way to avoid having
to modify existing module definitions is to add "notifiable-on-
change" markings within separate module deviations. This means that
when a YANG model designer wants to add a "notifiable-on-change"
marking to nodes of an existing module without modifying the module
definitions, a new module is introduced that contains deviation
statements which add "notifiable-on-change" statements as applicable.
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deviation /sys:system/sys:system-time {
deviate add {
yp:notifiable-on-change false;
}
}
Figure 6: Deviation Example
3.11. Other Considerations
3.11.1. Robustness and reliability
Particularly in the case of on-change updates, it is important that
these updates do not get lost. Or in case the loss of an update is
unavoidable, it is critical that the receiver is notified
accordingly.
Update records for a single subscription MAY NOT be resequenced prior
to transport.
It is conceivable that under certain circumstances, a publisher will
recognize that it is unable to include within an update record 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
record which is known to be missing information.
o It MAY choose to suspend a subscription as per
[I-D.draft-ietf-netconf-subscribed-notifications].
o When resuming an on-change subscription, the publisher SHOULD
generate a complete patch from the previous update record. If
this is not possible and the "no-synch-on-start" option is not
present for the subscription, then the full datastore contents MAY
be sent via a "push-update" 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".
Note: It is perfectly acceptable to have a series of "push-change-
update" notifications (and even "push update" notifications) serially
queued at the transport layer awaiting transmission. It is not
required to merge pending update messages. I.e., the dampening
period applies to update record creation, not transmission.
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3.11.2. Publisher capacity
It is far preferable to decline a subscription request than to accept
such a request when it cannot be met.
Whether or not a subscription can be supported will be determined by
a combination of several factors such as the subscription trigger
(on-change or periodic), the period in which to report changes (one
second periods will consume more resources than one hour periods),
the amount of data in the datastore subtree that is being subscribed
to, and the number and combination of other subscriptions that are
concurrently being serviced.
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. Parentheses with a name in
the middle enclose choice and case nodes. New schema objects defined
here (i.e., beyond those from
[I-D.draft-ietf-netconf-subscribed-notifications]) are identified
with "yp".
module: ietf-subscribed-notifications
+--rw streams
| +--rw stream* [name]
| +--rw name string
| +--rw description string
| +--rw replay-support? empty {replay}?
| +--rw replay-log-creation-time? yang:date-and-time {replay}?
| +--rw replay-log-aged-time? yang:date-and-time {replay}?
+--rw filters
| +--rw stream-filter* [identifier]
| | +--rw identifier filter-id
| | +--rw (filter-spec)?
| | +--:(stream-subtree-filter)
| | | +--rw stream-subtree-filter? {subtree}?
| | +--:(stream-xpath-filter)
| | +--rw stream-xpath-filter? yang:xpath1.0 {xpath}?
| +--rw yp:selection-filter* [identifier]
| +--rw yp:identifier sn:filter-id
| +--rw (yp:filter-spec)?
| +--:(yp:datastore-subtree-filter)
| | +--rw yp:datastore-subtree-filter? {sn:subtree}?
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| +--:(yp:datastore-xpath-filter)
| +--rw yp:datastore-xpath-filter?
| yang:xpath1.0 {sn:xpath}?
+--rw subscription-config {configured}?
| +--rw subscription* [identifier]
| +--rw identifier subscription-id
| +--rw purpose? string
| +--rw protocol transport {configured}?
| +--rw encoding encoding
| +--rw (target)
| | +--:(stream)
| | | +--rw (stream-filter)?
| | | | +--:(by-reference)
| | | | | +--rw stream-filter-ref stream-filter-ref
| | | | +--:(within-subscription)
| | | | +--rw (filter-spec)?
| | | | +--:(stream-subtree-filter)
| | | | | +--rw stream-subtree-filter? {subtree}?
| | | | +--:(stream-xpath-filter)
| | | | +--rw stream-xpath-filter?
| | | | yang:xpath1.0 {sn:xpath}?
| | | +--rw stream? stream-ref
| | | +--rw replay-start-time? yang:date-and-time {replay}?
| | +--:(yp:datastore)
| | +--rw yp:datastore identityref
| | +--rw (yp:selected-content)?
| | +--:(yp:by-reference)
| | | +--rw yp:selection-filter-ref selection-filter-ref
| | +--:(yp:within-subscription)
| | +--rw (yp:filter-spec)?
| | +--:(yp:datastore-subtree-filter)
| | | +--rw yp:datastore-subtree-filter?
| | {sn:subtree}?
| | +--:(yp:datastore-xpath-filter)
| | +--rw yp:datastore-xpath-filter?
| | yang:xpath1.0 {sn:xpath}?
| +--rw stop-time? yang:date-and-time
| +--rw dscp? inet:dscp {qos}?
| +--rw weighting? uint8 {qos}?
| +--rw dependency? sn:subscription-id {qos}?
| +--rw (notification-message-origin)?
| | +--:(interface-originated)
| | | +--rw source-interface? if:interface-ref
| | +--:(address-originated)
| | +--rw source-vrf? -> /ni:network-instances/
| | network-instance/name {supports-vrf}?
| | +--rw source-address? inet:ip-address-no-zone
| +--rw receivers
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| | +--rw receiver* [address port]
| | +--rw address inet:host
| | +--rw port inet:port-number
| +--rw (yp:update-trigger)
| +--:(yp:periodic)
| | +--rw yp:periodic!
| | +--rw yp:period yang:timeticks
| | +--rw yp:anchor-time? yang:date-and-time
| +--:(yp:on-change) {on-change}?
| +--rw yp:on-change!
| +--rw yp:dampening-period? yang:timeticks
| +--rw yp:no-synch-on-start? empty
| +--rw yp:excluded-change* change-type
+--ro subscriptions
+--ro subscription* [identifier]
+--ro identifier subscription-id
+--ro configured-subscription-state? enumeration {configured}?
+--ro purpose? string {configured}?
+--ro protocol transport {configured}?
+--ro encoding encoding
+--ro (target)
| +--:(stream)
| | +--ro (stream-filter)?
| | | +--:(by-reference)
| | | | +--ro stream-filter-ref stream-filter-ref
| | | +--:(within-subscription)
| | | +--ro (filter-spec)?
| | | +--:(stream-subtree-filter)
| | | | +--ro stream-subtree-filter? {subtree}?
| | | +--:(stream-xpath-filter)
| | | +--ro stream-xpath-filter?
| | | yang:xpath1.0 {sn:xpath}?
| | +--ro stream? stream-ref
| | +--ro replay-start-time? yang:date-and-time {replay}?
| +--:(yp:datastore)
| +--ro yp:datastore identityref
| +--ro (yp:selected-content)?
| +--:(yp:by-reference)
| | +--ro yp:selection-filter-ref selection-filter-ref
| +--:(yp:within-subscription)
| +--ro (yp:filter-spec)?
| +--:(yp:datastore-subtree-filter)
| | +--ro yp:datastore-subtree-filter?
| {sn:subtree}?
| +--:(yp:datastore-xpath-filter)
| +--ro yp:datastore-xpath-filter?
| yang:xpath1.0 {sn:xpath}?
+--ro stop-time? yang:date-and-time
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+--ro dscp? inet:dscp {qos}?
+--ro weighting? uint8 {qos}?
+--ro dependency? sn:subscription-id {qos}?
+--ro (notification-message-origin)?
| +--:(interface-originated)
| | +--ro source-interface? if:interface-ref
| +--:(address-originated)
| +--ro source-vrf? -> /ni:network-instances/
| | network-instance/name {supports-vrf}?
| +--ro source-address? inet:ip-address-no-zone
+--ro receivers
| +--ro receiver* [address port]
| +--ro address inet:host
| +--ro port inet:port-number
| +--ro pushed-notifications? yang:counter64
| +--ro excluded-notifications? yang:counter64
| +--ro status enumeration
| +---x reset
| +--ro output
| +--ro time yang:date-and-time
+--ro (yp:update-trigger)
+--:(yp:periodic)
| +--ro yp:periodic!
| +--ro yp:period yang:timeticks
| +--ro yp:anchor-time? yang:date-and-time
+--:(yp:on-change) {on-change}?
+--ro yp:on-change!
+--ro yp:dampening-period? yang:timeticks
+--ro yp:no-synch-on-start? empty
+--ro yp:excluded-change* change-type
rpcs:
+---x establish-subscription
| +---w input
| | +---w encoding? encoding
| | +---w (target)
| | | +--:(stream)
| | | | +---w (stream-filter)?
| | | | | +--:(by-reference)
| | | | | | +---w stream-filter-ref stream-filter-ref
| | | | | +--:(within-subscription)
| | | | | +---w (filter-spec)?
| | | | | +--:(stream-subtree-filter)
| | | | | | +---w stream-subtree-filter? {subtree}?
| | | | | +--:(stream-xpath-filter)
| | | | | +---w stream-xpath-filter?
| | | | | yang:xpath1.0 {sn:xpath}?
| | | | +---w stream? stream-ref
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| | | | +---w replay-start-time? yang:date-and-time {replay}?
| | | +--:(yp:datastore)
| | | +---w yp:datastore identityref
| | | +---w (yp:selected-content)?
| | | +--:(yp:by-reference)
| | | | +---w yp:selection-filter-ref selection-filter-ref
| | | +--:(yp:within-subscription)
| | | +---w (yp:filter-spec)?
| | | +--:(yp:datastore-subtree-filter)
| | | | +---w yp:datastore-subtree-filter?
| | | | {sn:subtree}?
| | | +--:(yp:datastore-xpath-filter)
| | | +---w yp:datastore-xpath-filter?
| | | yang:xpath1.0 {sn:xpath}?
| | +---w stop-time? yang:date-and-time
| | +---w dscp? inet:dscp {qos}?
| | +---w weighting? uint8 {qos}?
| | +---w dependency? sn:subscription-id {qos}?
| | +---w (yp:update-trigger)
| | +--:(yp:periodic)
| | | +---w yp:periodic!
| | | +---w yp:period yang:timeticks
| | | +---w yp:anchor-time? yang:date-and-time
| | +--:(yp:on-change) {on-change}?
| | +---w yp:on-change!
| | +---w yp:dampening-period? yang:timeticks
| | +---w yp:no-synch-on-start? empty
| | +---w yp:excluded-change* change-type
| +--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
| | +--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 (target)
| | | +--:(stream)
| | | | +---w (stream-filter)?
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| | | | +--:(by-reference)
| | | | | +---w stream-filter-ref stream-filter-ref
| | | | +--:(within-subscription)
| | | | +---w (filter-spec)?
| | | | +--:(stream-subtree-filter)
| | | | | +---w stream-subtree-filter? {subtree}?
| | | | +--:(stream-xpath-filter)
| | | | +---w stream-xpath-filter?
| | | | yang:xpath1.0 {sn:xpath}?
| | | +--:(yp:datastore)
| | | +---w (yp:selected-content)?
| | | +--:(yp:by-reference)
| | | | +---w yp:selection-filter-ref selection-filter-ref
| | | +--:(yp:within-subscription)
| | | +---w (yp:filter-spec)?
| | | +--:(yp:datastore-subtree-filter)
| | | | +---w yp:datastore-subtree-filter?
| | | | {sn:subtree}?
| | | +--:(yp:datastore-xpath-filter)
| | | +---w yp:datastore-xpath-filter?
| | | yang:xpath1.0 {sn:xpath}?
| | +---w stop-time? yang:date-and-time
| | +---w (yp:update-trigger)
| | +--:(yp:periodic)
| | | +---w yp:periodic!
| | | +---w yp:period yang:timeticks
| | | +---w yp:anchor-time? yang:date-and-time
| | +--:(yp:on-change) {on-change}?
| | +---w yp: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
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| +---w identifier subscription-id
+--ro output
+--ro subscription-result subscription-result
notifications:
+---n replay-completed {replay}?
| +--ro identifier subscription-id
+---n subscription-completed
| +--ro identifier subscription-id
+---n subscription-started {configured}?
| +--ro identifier subscription-id
| +--ro protocol transport {configured}?
| +--ro encoding encoding
| +--ro (target)
| | +--:(stream)
| | | +--ro (stream-filter)?
| | | | +--:(by-reference)
| | | | | +--ro stream-filter-ref stream-filter-ref
| | | | +--:(within-subscription)
| | | | +--ro (filter-spec)?
| | | | +--:(stream-subtree-filter)
| | | | | +--ro stream-subtree-filter? {subtree}?
| | | | +--:(stream-xpath-filter)
| | | | +--ro stream-xpath-filter?
| | | | yang:xpath1.0 {sn:xpath}?
| | | +--ro stream? stream-ref
| | | +--ro replay-start-time? yang:date-and-time {replay}?
| | +--:(yp:datastore)
| | +--ro yp:datastore identityref
| | +--ro (yp:selected-content)?
| | +--:(yp:by-reference)
| | | +--ro yp:selection-filter-ref selection-filter-ref
| | +--:(yp:within-subscription)
| | +--ro (yp:filter-spec)?
| | +--:(yp:datastore-subtree-filter)
| | | +--ro yp:datastore-subtree-filter?{sn:subtree}?
| | +--:(yp:datastore-xpath-filter)
| | +--ro yp:datastore-xpath-filter?
| | yang:xpath1.0 {sn:xpath}?
| +--ro stop-time? yang:date-and-time
| +--ro dscp? inet:dscp {qos}?
| +--ro weighting? uint8 {qos}?
| +--ro dependency? sn:subscription-id {qos}?
| +--ro (yp:update-trigger)
| +--:(yp:periodic)
| | +--ro yp:periodic!
| | +--ro yp:period yang:timeticks
| | +--ro yp:anchor-time? yang:date-and-time
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| +--:(yp:on-change) {on-change}?
| +--ro yp:on-change!
| +--ro yp:dampening-period? yang:timeticks
| +--ro yp:no-synch-on-start? empty
| +--ro yp:excluded-change* change-type
+---n subscription-resumed
| +--ro identifier subscription-id
+---n subscription-modified
| +--ro identifier subscription-id
| +--ro protocol transport {configured}?
| +--ro encoding encoding
| +--ro (target)
| | +--:(stream)
| | | +--ro (stream-filter)?
| | | | +--:(by-reference)
| | | | | +--ro stream-filter-ref stream-filter-ref
| | | | +--:(within-subscription)
| | | | +--ro (filter-spec)?
| | | | +--:(stream-subtree-filter)
| | | | | +--ro stream-subtree-filter? {subtree}?
| | | | +--:(stream-xpath-filter)
| | | | +--ro stream-xpath-filter?
| | | | yang:xpath1.0 {sn:xpath}?
| | | +--ro stream? stream-ref
| | | +--ro replay-start-time? yang:date-and-time {replay}?
| | +--:(yp:datastore)
| | +--ro yp:datastore identityref
| | +--ro (yp:selected-content)?
| | +--:(yp:by-reference)
| | | +--ro yp:selection-filter-ref selection-filter-ref
| | +--:(yp:within-subscription)
| | +--ro (yp:filter-spec)?
| | +--:(yp:datastore-subtree-filter)
| | | +--ro yp:datastore-subtree-filter?{sn:subtree}?
| | +--:(yp:datastore-xpath-filter)
| | +--ro yp:datastore-xpath-filter?
| | yang:xpath1.0 {sn:xpath}?
| +--ro stop-time? yang:date-and-time
| +--ro dscp? inet:dscp {qos}?
| +--ro weighting? uint8 {qos}?
| +--ro dependency? sn:subscription-id {qos}?
| +--ro (yp:update-trigger)
| +--:(yp:periodic)
| | +--ro yp:periodic!
| | +--ro yp:period yang:timeticks
| | +--ro yp:anchor-time? yang:date-and-time
| +--:(yp:on-change) {on-change}?
| +--ro yp:on-change!
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| +--ro yp:dampening-period? yang:timeticks
| +--ro yp:no-synch-on-start? empty
| +--ro yp:excluded-change* change-type
+---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
rpcs:
+---x resynch-subscription {on-change}?
+---w input
| +---w identifier sn:subscription-id
+--ro output
+--ro subscription-result sn:subscription-result
notifications:
+---n push-update
| +--ro subscription-id? sn:subscription-id
| +--ro updates-not-sent? empty
| +--ro datastore-contents?
+---n push-change-update {on-change}?
+--ro subscription-id? sn:subscription-id
+--ro updates-not-sent? empty
+--ro datastore-changes?
Figure 7: Model structure
Selected components of the model are summarized below.
4.2. Subscription configuration
Both configured and dynamic subscriptions are represented within the
list subscription. But only configured subscriptions are listed
within list subscription-config. In both lists, each subscription
has own list elements. New and enhanced parameters extending the
basic subscription data model in
[I-D.draft-ietf-netconf-subscribed-notifications] include:
o The targeted datastore from which the selection is being made.
The potential datastores include those from
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[I-D.draft-ietf-netmod-revised-datastores]. A platform may also
choose to support a custom datastore.
o A selection filter identifying yang nodes of interest within a
datastore. Filter contents are specified via a reference to an
existing filter, or via an in-line definition for only that
subscription. Referenced filters allows an implementation to
avoid evaluating filter acceptability during a dynamic
subscription request. The case statement differentiates the
options.
o For periodic subscriptions, triggered updates will occur at the
boundaries of a specified time interval. These boundaries many be
calculated from the periodic parameters:
* 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" from an "anchor-time".
If "anchor-time" is not provided, then the "anchor-time" MUST
be set with the creation time of the initial update record.
o For on-change subscriptions, assuming any dampening period has
completed, triggering occurs whenever a change in the subscribed
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. If no
dampening period is in effect, 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.
* an "excluded-change" flag which allows restriction of the types
of changes for which updates should be sent (e.g., only add to
an update record on object creation).
* a "no-synch-on-start" flag which specifies whether a complete
update with all the subscribed data is to be sent at the
beginning of a subscription.
4.3. YANG Notifications
4.3.1. State Change Notifications
Subscription state notifications and mechanism are reused from
[I-D.draft-ietf-netconf-subscribed-notifications]. Some have been
augmented to include the datastore specific objects.
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4.3.2. Notifications for Subscribed Content
Along with the subscribed content, there are other objects which
might be part of a "push-update" or "push-change-update"
A "subscription-id" MUST be transported along with the subscribed
contents. An [RFC5277] Section 4 one-way notification MAY be used
for encoding updates. Where it is, the relevant "subscription-id"
MUST be encoded as the first element within each "push-update" or
"push-change-update". This allows a receiver to differentiate which
subscription resulted in a particular push.
A "time-of-update" which represents the time an update record
snapshot was generated. A receiver MAY assume that a publisher's
objects have these pushed values at this point in time.
An "updates-not-sent" object. This object 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 a
datastore was unable to providing the full set of datastore nodes to
a publisher process.) To facilitate re-synchronization of on-change
subscriptions, a publisher MAY subsequently send a "push-update"
containing a full selection snapshot of subscribed data.
4.4. YANG RPCs
YANG-Push subscriptions are established, modified, and deleted using
RPCs augmented from
[I-D.draft-ietf-netconf-subscribed-notifications].
4.4.1. Establish-subscription RPC
The subscriber sends an establish-subscription RPC with the
parameters in section 3.1. An example might look like:
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ds:operational
500
Figure 8: 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 "identifier" of the accepted
subscription. In that case a publisher MAY respond:
ok
52
Figure 9: Establish-subscription positive RPC response
A subscription can be rejected for multiple reasons, including the
lack of authorization to establish a subscription, no capacity to
serve the subscription at the publisher, or the inability of the
publisher to select datastore content at the requested cadence.
If a request is rejected because the publisher is not able to serve
it, the publisher SHOULD include in the returned error hints ar what
subscription parameters might have been accepted for the request.
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However, there are no guarantee that subsequent requests using this
info will in fact be accepted.
For example, for the following request:
ds:operational
/ex:foo
10
Figure 10: Establish-subscription request example 2
a publisher that cannot serve on-change updates but periodic updates
might return the following:
yp:period-unsupported
100
Figure 11: Establish-subscription error response example 2
4.4.2. Modify-subscription RPC
The subscriber MAY invoke the "modify-subscription" RPC for a
subscription it previously established. The subscriber will include
newly desired values in the "modify-subscription" RPC. Parameters
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not included MUST remain unmodified. Below is an example where a
subscriber attempts to modify the "period" of a subscription.
1011
ds:operational
/ex:bar
250
Figure 12: Modify subscription request
The publisher MUST respond explicitly positively or negatively to the
request. A response to a successful modification might look like:
ok
Figure 13: 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.
Responses MAY include hints. 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.
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4.4.3. 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's
"identifier".
Configured subscriptions cannot be deleted via RPC, but have to be
removed from the configuration. This RPC is identical to the RPC
from [I-D.draft-ietf-netconf-subscribed-notifications].
4.4.4. Resynch-subscription RPC
This RPC is only applicable only for on-change subscriptions
previously been established using an "establish-subscription" RPC.
On receipt, a publisher must either reply "ok" and quickly follow
with a "push-update", or send an appropriate error such as "on-
change-synch-unsupported". For example:
1011
sn:ok
Resynch subscription
4.4.5. YANG Module Synchronization
To make subscription requests, the subscriber needs to know the YANG
module library available on the publisher. 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]. This YANG
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library information is important for the receiver to reproduce the
set of object definitions used within the publisher.
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 publisher implementation). In this
case, the receiver needs to be informed of module changes before
datastore nodes from changed modules can be processed correctly. The
YANG library provides a simple "yang-library-change" notification
that informs the subscriber that the library has changed. The
receiver then needs to re-read the entire YANG library data for the
replicated publisher 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.yang"
module ietf-yang-push {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-yang-push";
prefix yp;
import ietf-yang-types {
prefix yang;
}
import ietf-subscribed-notifications {
prefix sn;
}
import ietf-datastores {
prefix ds;
}
organization "IETF";
contact
"WG Web:
WG List:
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Editor: Alexander Clemm
Editor: Eric Voit
Editor: Alberto Gonzalez Prieto
Editor: Ambika Prasad Tripathy
Editor: Einar Nilsen-Nygaard
Editor: Andy Bierman
Editor: Balazs Lengyel
";
description
"This module contains YANG specifications for YANG push.";
revision 2017-12-20 {
description
"Initial revision.";
reference
"draft-ietf-netconf-yang-push-12";
}
/*
* EXTENSIONS
*/
extension notifiable-on-change {
argument "value";
description
"Indicates whether changes to the datastore 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
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specified, the default is the same as the parent datastore node's
value. For top level datastore nodes the default value is false.";
}
/*
* FEATURES
*/
feature on-change {
description
"This feature indicates that on-change triggered subscriptions
are supported.";
}
/*
* IDENTITIES
*/
/* Error type identities for datastore subscription */
identity period-unsupported {
base sn:error;
description
"Requested time period is too short. This can be for both
periodic and on-change dampening.";
}
identity on-change-unsupported {
base sn:error;
description
"On-change is not supported for any objects which are selectable
by this filter.";
}
identity on-change-synch-unsupported {
base sn:error;
description
"Neither synch on start nor resynchonization are supported for
this subscription. This error will be used for two reasons. First
if an 'establish-subscription' RPC doesn't include
'no-synch-on-start', yet the publisher can't support sending a
'push update' for this subscription for reasons other that
'on-change-unsupported' or 'result-too-big'. And second, if the
'resynch-subscription' RPC is invoked either for an existing
periodic subscription, or for an on-change subscription which
can't support resynchronization.";
}
identity data-unavailable {
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base sn:error;
description
"Referenced datatree node or subtree doesn't exist, or read
access is not permitted.";
}
identity result-too-big {
base sn:error;
description
"Resulting periodic or on-change push updates may exceed a size
limit during normal conditions.";
}
identity synchronization-size {
base sn:error;
description
"The resulting synch-on-start or resynchronization would push a
datatree which exceeds size limit for a one-time update.";
}
identity datastore-not-subscribable {
base sn:error;
description
"This is not a subscribable datastore.";
}
/*
* TYPE DEFINITIONS
*/
typedef change-type {
type enumeration {
enum "create" {
description
"Create a new data resource if it does not already exist. If
it already exists, replace.";
}
enum "delete" {
description
"Delete a data resource if it already exists. If it does not
exists, take no action.";
}
enum "insert" {
description
"Insert a new user-ordered data resource";
}
enum "merge" {
description
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"merge the edit value with the target data resource; create
if it does not already exist";
}
enum "move" {
description
"Reorder the target data resource";
}
enum "replace" {
description
"Replace the target data resource with the edit value";
}
enum "remove" {
description
"Remove a data resource if it already exists ";
}
}
description
"Specifies different types of datastore changes.";
reference
"RFC 8072 section 2.5, with a delta that it is valid for a
receiver to process an update record which performs a create
operation on a datastore node the receiver believes exists, or to
process a delete on a datastore node the receiver believes is
missing.";
}
typedef selection-filter-ref {
type leafref {
path "/sn:filters/yp:selection-filter/yp:identifier";
}
description
"This type is used to reference a selection filter.";
}
/*
* GROUP DEFINITIONS
*/
grouping datastore-criteria {
description
"A grouping to define criteria for which selected objects from
a targeted datastore should be included in push updates.";
leaf datastore {
type identityref {
base ds:datastore;
}
mandatory true;
description
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"Datastore from which to retrieve data.";
}
uses selection-filter-objects;
}
grouping selection-filter-types {
description
"This grouping defines a selector for objects from a
datastore.";
choice filter-spec {
description
"The content filter specification for this request.";
anydata datastore-subtree-filter {
if-feature "sn:subtree";
description
"This parameter identifies the portions of the
target datastore to retrieve.";
}
leaf datastore-xpath-filter {
if-feature "sn:xpath";
type yang:xpath1.0;
description
"This parameter contains an XPath expression identifying the
portions of the target datastore to retrieve.
If the expression returns a node-set, all nodes in the
node-set are selected by the filter. Otherwise, if the
expression does not return a node-set, the filter
doesn't select any nodes.
The expression is evaluated in the following XPath context:
o The set of namespace declarations are those in scope on
the 'xpath-filter' leaf element.
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 of the target
datastore.";
}
}
}
grouping selection-filter-objects {
description
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"This grouping defines a selector for objects from a
datastore.";
choice selected-content {
description
"The source of the selection filter applied to the subscription.
This will come either referenced from a global list, or be
provided within the subscription itself.";
case by-reference {
description
"Incorporate a filter that has been configured separately.";
leaf selection-filter-ref {
type selection-filter-ref;
mandatory true;
description
"References an existing selection filter which is to be
applied to the subscription.";
}
}
case within-subscription {
description
"Local definition allows a filter to have the same lifecycle
as the subscription.";
uses selection-filter-types;
}
}
}
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 {
when "../yp:target/yp:datastore/yp:datastore";
mandatory true;
description
"Defines necessary conditions for sending an event record to
the subscriber.";
case periodic {
container periodic {
presence "indicates an periodic subscription";
description
"The publisher is requested to notify periodically the
current values of the datastore as defined by the selection
filter.";
leaf period {
type yang:timeticks;
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mandatory true;
description
"Duration of time which should occur between periodic
push updates. Where the anchor-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 before or after which a series of
periodic push updates are determined. The next update
will take place at a whole multiple interval from the
anchor time. For example, for an anchor time is set for
the top of a particular minute and a period interval of a
minute, updates will be sent at the top of every minute
this subscription is active.";
}
}
}
case on-change {
if-feature "on-change";
container on-change {
presence "indicates an on-change subscription";
description
"The publisher is requested to notify changes in values in
the datastore subset as defined by a selection filter.";
leaf dampening-period {
type yang:timeticks;
default 0;
description
"Specifies the minimum interval between the assembly of
successive update records for a single receiver of a
subscription. Whenever subscribed objects change, and a
dampening period interval (which may be zero) has elapsed
since the previous update record creation for a receiver,
then any subscribed objects and properties which have
changed since the previous update record will have their
current values marshalled and placed into a new update
record.";
}
}
}
}
}
grouping update-policy {
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description
"This grouping describes the datastore specific subscription
conditions of a subscription.";
uses update-policy-modifiable {
augment "update-trigger/on-change/on-change" {
description
"Includes objects not modifiable once subscription is
established.";
leaf no-synch-on-start {
type empty;
description
"The presence of this object restricts an on-change
subscription from sending push-update notifications. When
present, pushing a full selection per the terms of the
selection filter MUST NOT be done for this subscription.
Only updates about changes, 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 are exclusively sent unless the publisher
chooses to resynch the subscription via a new push-update
notification.";
}
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-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 {
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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 selection 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
selection filter, this identifies the upper limit of the
publisher's ability to service for this subscription.";
}
leaf kilobytes-estimate {
type uint32;
description
"If the returned information could be beyond the capacity of
the publisher, this would identify the data size which could
result from this selection 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.";
}
}
/*
* RPCs
*/
rpc resynch-subscription {
if-feature "on-change";
description
"This RPC allows a subscriber of an active on-change
subscription to request a full push of objects in there current
state. A successful result would be the set of YANG objects
equivalent to a Get using the existing selection criteria. This
request may only come from the same subscriber using the
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establish-subscription RPC.";
input {
leaf identifier {
type sn:subscription-id;
mandatory true;
description
"Identifier of the subscription that is to be resynched.";
}
}
output {
leaf subscription-result {
type sn:subscription-result;
mandatory true;
description
"Indicates whether the request for the subscription resynch
has been accepted, or why it has been denied.";
}
}
}
/*
* DATA NODES
*/
augment "/sn:establish-subscription/sn:input" {
when "sn:target/yp:datastore/yp:datastore";
description
"This augmentation adds additional subscription parameters that
apply specifically to datastore updates to RPC input.";
uses update-policy;
}
augment "/sn:establish-subscription/sn:input/sn:target" {
description
"This augmentation adds the datastore as a valid parameter object
for the subscription to RPC input. This provides a target for
the filter.";
case datastore {
uses datastore-criteria;
}
}
augment "/sn:establish-subscription/sn:output/"+
"sn:result/sn:no-success" {
description
"This augmentation adds datastore specific error info
and hints to RPC output.";
uses update-error-hints;
}
augment "/sn:modify-subscription/sn:input" {
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description
"This augmentation adds additional subscription parameters
specific to datastore updates.";
uses update-policy-modifiable;
}
augment "/sn:modify-subscription/sn:input/sn:target" {
description
"This augmentation adds the datastore as a valid parameter object
for the subscription to RPC input. This provides a target for
the filter.";
case datastore {
uses selection-filter-objects;
}
}
augment "/sn:modify-subscription/sn:output/"+
"sn:result/sn:no-success" {
description
"This augmentation adds 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;
description
"This references the subscription which drove the notification
to be sent.";
}
leaf updates-not-sent {
type empty;
description
"This is a flag which indicates that not all datastore nodes
subscribed to are included with this update. In other words,
the publisher has failed to fulfill its full subscription
obligations, and despite its best efforts is providing an
incomplete set of objects.";
}
anydata datastore-contents {
description
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"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
corresponds to the format and syntax of data that would be
returned in a corresponding get operation with the same
selection 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;
description
"This references the subscription which drove the notification
to be sent.";
}
leaf updates-not-sent {
type empty;
description
"The presence of this object indicates 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.";
}
anydata datastore-changes {
description
"This contains the set of datastore changes needed
to update a remote datastore starting at the time of 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
datastore implied by the previous update to result in the
current state.";
reference
"RFC 8072 section 2.5, with a delta that it is ok to receive
ability create on an existing node, or receive a delete on a
missing node.";
}
}
augment "/sn:subscription-started" {
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description
"This augmentation adds many datastore specific objects to
the notification that a subscription has started.";
uses update-policy;
}
augment "/sn:subscription-started/sn:target" {
description
"This augmentation allows the datastore to be included as part
of the notification that a subscription has started.";
case datastore {
uses datastore-criteria {
refine "selected-content/within-subscription" {
description
"Specifies where the selection filter, and where came from
within the subscription and then populated within this
notification. If the 'selection-filter-ref' is populated,
the filter within the subscription came from the 'filters'
container. Otherwise it is populated in-line as part of the
subscription itself.";
}
}
}
}
augment "/sn:filters" {
description
"This augmentation allows the datastore to be included as part
of the selection filtering criteria for a subscription.";
list selection-filter {
key "identifier";
description
"A list of pre-positioned filters that can be applied
to datastore subscriptions.";
leaf identifier {
type sn:filter-id;
description
"An identifier to differentiate between selection filters.";
}
uses selection-filter-types;
}
}
augment "/sn:subscription-modified" {
description
"This augmentation adds many datastore specific objects to
the notification that a subscription has been modified.";
uses update-policy;
}
augment "/sn:subscription-modified/sn:target" {
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description
"This augmentation allows the datastore to be included as part
of the notification that a subscription has been modified.";
case datastore {
uses datastore-criteria {
refine "selected-content/within-subscription" {
description
"Specifies where the selection filter, and where came from
within the subscription and then populated within this
notification. If the 'selection-filter-ref' is populated,
the filter within the subscription came from the 'filters'
container. Otherwise it is populated in-line as part of the
subscription itself.";
}
}
}
}
augment "/sn:subscription-config/sn:subscription" {
description
"This augmentation adds many datastore specific objects
which can be configured as opposed to established via RPC.";
uses update-policy;
}
augment "/sn:subscription-config/sn:subscription/sn:target" {
description
"This augmentation adds the datastore to the selection filtering
criteria for a subscription.";
case datastore {
uses datastore-criteria;
}
}
augment "/sn:subscriptions/sn:subscription" {
yp:notifiable-on-change true;
description
"This augmentation adds many datastore specific objects to a
subscription.";
uses update-policy;
}
augment "/sn:subscriptions/sn:subscription/sn:target" {
description
"This augmentation allows the datastore to be included as part
of the selection filtering criteria for a subscription.";
case datastore {
uses datastore-criteria;
}
}
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/* YANG Parser Pyang crashing on syntax below, due to fixed bug
https://github.com/mbj4668/pyang/issues/300
deviation "/sn:subscriptions/sn:subscription/sn:receivers/"
+ "sn:receiver/sn:pushed-notifications" {
deviate add {
yp:notifiable-on-change false;
}
}
deviation "/sn:subscriptions/sn:subscription/sn:receivers/"
+ "sn:receiver/sn:excluded-notifications" {
deviate add {
yp:notifiable-on-change false;
}
}
YANG Parser Pyang crashing on syntax above */
}
6. IANA Considerations
This document registers the following namespace URI in the "IETF XML
Registry" [RFC3688]:
URI: urn:ietf:params:xml:ns:yang:ietf-yang-push
Registrant Contact: The IESG.
XML: N/A; the requested URI is an XML namespace.
This document registers the following YANG module in the "YANG Module
Names" registry [RFC6020]:
Name: ietf-yang-push
Namespace: urn:ietf:params:xml:ns:yang:ietf-yang-push
Prefix: yp
Reference: draft-ietf-netconf-yang-push-12.txt (RFC form)
7. Security Considerations
All security considerations from
[I-D.draft-ietf-netconf-subscribed-notifications] are relevant for
datastores. In addition there are specific security considerations
for receivers defined in Section 3.9
If the access control permissions on subscribed YANG nodes change
during the lifecycle of a subscription, a publisher MUST either
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transparently conform to the new access control permissions, or must
terminate or restart the subscriptions so that new access control
permissions are re-established.
The NETCONF Authorization Control Model SHOULD be used to restrict
the delivery of YANG nodes for which the receiver has no access.
8. Acknowledgments
For their valuable comments, discussions, and feedback, we wish to
acknowledge Tim Jenkins, Kent Watsen, Susan Hares, Yang Geng, Peipei
Guo, Michael Scharf, Martin Bjorklund, and Guangying Zheng.
9. References
9.1. Normative References
[I-D.draft-ietf-netconf-subscribed-notifications]
Voit, E., Clemm, A., Gonzalez Prieto, A., Tripathy, A.,
and E. Nilsen-Nygaard, "Custom Subscription to Event
Streams", draft-ietf-netconf-subscribed-notifications-06
(work in progress), October 2017.
[I-D.draft-ietf-netmod-revised-datastores]
Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
and R. Wilton, "Network Management Datastore
Architecture", draft-ietf-netmod-revised-datastores-04
(work in progress), August 2017.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
DOI 10.17487/RFC3688, January 2004,
.
[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC6020, October 2010,
.
[RFC6470] Bierman, A., "Network Configuration Protocol (NETCONF)
Base Notifications", RFC 6470, DOI 10.17487/RFC6470,
February 2012, .
[RFC6536bis]
Bierman, A. and M. Bjorklund, "Network Configuration
Protocol (NETCONF) Access Control Model", draft-ietf-
netconf-rfc6536bis-05 (work in progress), September 2017.
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[RFC7895] Bierman, A., Bjorklund, M., and K. Watsen, "YANG Module
Library", RFC 7895, DOI 10.17487/RFC7895, June 2016,
.
[RFC8072] Bierman, A., Bjorklund, M., and K. Watsen, "YANG Patch
Media Type", RFC 8072, DOI 10.17487/RFC8072, February
2017, .
9.2. Informative References
[I-D.draft-ietf-netconf-netconf-event-notifications]
Gonzalez Prieto, A., Clemm, A., Voit, E., Nilsen-Nygaard,
E., and A. Tripathy, "NETCONF Support for Event
Notifications", September 2017.
[RFC5277] Chisholm, S. and H. Trevino, "NETCONF Event
Notifications", RFC 5277, DOI 10.17487/RFC5277, July 2008,
.
[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,
.
[RFC7223] Bjorklund, M., "A YANG Data Model for Interface
Management", RFC 7223, DOI 10.17487/RFC7223, May 2014,
.
[RFC7923] Voit, E., Clemm, A., and A. Gonzalez Prieto, "Requirements
for Subscription to YANG Datastores", RFC 7923,
DOI 10.17487/RFC7923, June 2016,
.
[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
.
Appendix A. Changes between revisions
(To be removed by RFC editor prior to publication)
v11 - v12
o Included Martin's review clarifications.
o QoS moved to subscribed-notifications
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o time-of-update removed as it is redundant with RFC5277's
eventTime, and other times from notification-messages.
v10 - v11
o Promise model reference added.
o Error added for no-such-datastore
o Inherited changes from subscribed notifications (such as optional
feature definitions).
o scrubbed the examples for proper encodings
v09 - v10
o Returned to the explicit filter subtyping of v00-v05
o identityref to ds:datastore made explicit
o Returned ability to modify a selection filter via RPC.
v08 - v09
o Minor tweaks cleaning up text, removing appendicies, and making
reference to revised-datastores.
o Subscription-id optional in push updates, except when encoded in
RFC5277, Section 4 one-way notification.
o Finished adding the text descibing the resynch subscription RPC.
o Removed relationships to other drafts and future technology
appendicies as this work is being explored elsewhere.
o Deferred the multi-line card issue to new drafts
o Simplified the NACM interactions.
v07 - v08
o Updated YANG models with minor tweaks to accommodate changes of
ietf-subscribed-notifications.
v06 - v07
o Clarifying text tweaks.
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o Clarification that filters act as selectors for subscribed
datastore nodes; support for value filters not included but
possible as a future extension
o Filters don't have to be matched to existing YANG objects
v05 - v06
o Security considerations updated.
o Base YANG model in [subscribe] updated as part of move to
identities, YANG augmentations in this doc matched up
o Terms refined and text updates throughout
o Appendix talking about relationship to other drafts added.
o Datastore replaces stream
o Definitions of filters improved
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
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o Updates-not-sent flag added
o Not notifiable extension added
o Dampening period is for whole subscription, not single objects
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
VMware
Email: agonzalezpri@vmware.com
Ambika Prasad Tripathy
Cisco Systems
Email: ambtripa@cisco.com
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Einar Nilsen-Nygaard
Cisco Systems
Email: einarnn@cisco.com
Andy Bierman
YumaWorks
Email: andy@yumaworks.com
Balazs Lengyel
Ericsson
Email: balazs.lengyel@ericsson.com
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