NETCONF A. Clemm
Internet-Draft Huawei
Intended status: Standards Track E. Voit
Expires: December 2, 2018 Cisco Systems
A. Gonzalez Prieto
VMware
A. Tripathy
E. Nilsen-Nygaard
Cisco Systems
A. Bierman
YumaWorks
B. Lengyel
Ericsson
May 31, 2018
YANG Datastore Subscription
draft-ietf-netconf-yang-push-16
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 datastore nodes 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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 2, 2018.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Definitions and Acronyms . . . . . . . . . . . . . . . . . . 4
3. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Subscription Model . . . . . . . . . . . . . . . . . . . 5
3.2. Negotiation of Subscription Policies . . . . . . . . . . 6
3.3. On-Change Considerations . . . . . . . . . . . . . . . . 7
3.4. Reliability Considerations . . . . . . . . . . . . . . . 8
3.5. Data Encodings . . . . . . . . . . . . . . . . . . . . . 9
3.6. Defining the Selection with a Datastore . . . . . . . . . 10
3.7. Streaming Updates . . . . . . . . . . . . . . . . . . . . 11
3.8. Subscription Management . . . . . . . . . . . . . . . . . 13
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 . . . . . . . . . . . . . . . 22
4.3. YANG Notifications . . . . . . . . . . . . . . . . . . . 23
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4.4. YANG RPCs . . . . . . . . . . . . . . . . . . . . . . . . 24
5. YANG module . . . . . . . . . . . . . . . . . . . . . . . . . 29
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 45
7. Security Considerations . . . . . . . . . . . . . . . . . . . 45
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 46
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 46
9.1. Normative References . . . . . . . . . . . . . . . . . . 47
9.2. Informative References . . . . . . . . . . . . . . . . . 47
Appendix A. Appendix A: Subscription Errors . . . . . . . . . . 48
A.1. RPC Failures . . . . . . . . . . . . . . . . . . . . . . 48
A.2. Notifications of Failure . . . . . . . . . . . . . . . . 50
Appendix B. Changes between revisions . . . . . . . . . . . . . 50
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 54
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
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datastore specific update notifications. Transport options for
[I-D.draft-ietf-netconf-subscribed-notifications] will work
seamlessly with this solution.
2. Definitions and Acronyms
This document uses the terminology defined in [RFC7950], [RFC8341],
and [RFC8342]. In addition, the following terms are introduced:
o Datastore node: An instance of a data node in a datastore. In the
context of this document sometimes also referred to as "object".
o Datastore node update: A data item containing the current value of
a datastore node at the time the datastore node update was
created.
o Datastore subscription: A subscription to updates regarding
contents of a datastore.
o Datastore subtree: An instantiated datastore node and the
datastore nodes that are hierarchically contained within it.
o On-change subscription: A datastore subscription with updates that
are triggered when changes in subscribed datastore nodes are
detected.
o Periodic subscription: A datastore subscription with updates that
are triggered periodically according to some time interval.
o Selection filter: Evaluation and/or selection criteria, which may
be applied against a targeted set of objects.
o Update record: A representation of one or more datastore node
updates. In addition, an update record may contain which type of
update led to the datastore node update (e.g., whether the
datastore node was added, changed, deleted). Also included in the
update record may be other metadata, such as a subscription
identifier of the subscription as part of which the update record
was generated.
o Update trigger: A mechanism that determines when an update record
needs to be generated.
o YANG-Push: The subscription and push mechanism for datastore
updates that is specified in this document.
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3. Solution Overview
This document specifies a solution that provides subscription service
for updates from a datastore. This solution supports dynamic as well
as configured subscriptions to updates of datastore nodes.
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
updates, specifically to specify the update 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 Specification of update policies contain conditions which trigger
the generation and pushing of new update records. There are two
types of subscriptions, distinguished by how updates are
triggered: periodic and on-change.
* For periodic subscriptions, the update 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, an update 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
datastore node changes should be sent as quickly as
possible. However, it may be undesirable to send a rapid
series of datastore node 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
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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 datastore node occur during
a dampening period, only the value that is in effect at the
time the update record is created is included. 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
might only send when a datastore node is created or deleted,
but not when a datastore node 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.
o An encoding (using anydata) for the contents of periodic and on-
change push 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 an "establish-subscription" or "modify-subscription" rpc
request. In this case, a subscriber may quickly follow up with a new
rpc 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
subscription supports a simple negotiation between subscribers and
publishers for subscription parameters. This negotiation is in the
form of supplemental information which may be inserted within error
responses to a failed rpc request. This returned error response
information, when considered, should increase the likelihood of
success for subsequent rpc requests. Such hints include suggested
periodic time intervals, acceptable dampening periods, and size
estimates for the number or objects which would be returned from a
proposed selection filter. However, there are no guarantees that
subsequent requests which consider these hints will be accepted.
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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 datastore node.
Whether or not to accept or reject on-change subscription requests
when the scope of the subscription contains objects for which on-
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 datastore node 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 a datastore node 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 datastore node.
On-change subscriptions can be refined to let users subscribe only to
certain types of changes. For example, a subscriber might only want
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datastore node creations and deletions, but not modifications of
datastore node 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.
3. Construct a YANG patch record for going from A to B.
4. If there were any changes made between A and B which canceled
each other out, insert into the YANG patch record the last change
made for any datastore node which otherwise wouldn't have
appeared.
5. If the resulting patch 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. Reliability 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 about 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. For this
reason, the solution that is defined in this document mandates that a
publisher notifies receivers immediately and reliably whenever it
encounters a situation in which it is unable to keep the terms of the
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subscription, and provides the publisher with the option to suspend
the subscription in such a case.
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.
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
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.
A publisher will indicate a change to the effect that a value of a
datstore node has been updated by indicating a "replace" operation
(applied to the datastore node) in the patch. When a new datastore
node was created (other than an element in a list), a publisher will
indicate a "create" operation in the patch. When a datastore node
was deleted (other than an element in a list), the publisher
indicates this by a "delete". When a new list element was created or
removed, the publisher indicates it by an "insert" or "remove",
respectively.
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 a
datastore node during a dampening period. To support this, it is
valid to encode a YANG patch operation so that its application would
result in no change between the previous and current state. This
indicates that some churn has occurred on the datastore node. 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
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"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. Defining the Selection with a Datastore
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. An rpc request proposing a new selection filter MUST remove
any existing filter. 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 datastore 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.
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 misinterpret. Consider an XPath filter which
only passes a datastore node 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 a
periodic subscription, all selected datastore nodes to which a
receiver has access are provided to that receiver. If the same
filtering criteria is applied to an on-change subscription, only the
subset of those datastore nodes supporting on-change is provided. A
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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 an instantiated datastore
subtree with all of 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 a datastore
retrieval operation using the same transport 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
the set of changes that datastore nodes have undergone since the last
notification message. In other words, 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
datastore node has not been deleted, the datastore node's most
current value is reported. (In other words, for each datastore node,
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].
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<notification xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
<eventTime>2017-10-25T08:00:11.22Z</eventTime>
<push-update xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push">
<subscription-id>1011</subscription-id>
<datastore-contents>
<interfaces-state xmlns="urn:ietf:params:xml:ns:yang:ietf-interfaces">
<interface>
<name>eth0</name>
<oper-status>up</oper-status>
</interface>
</interfaces-state>
</datastore-contents>
</push-update>
</notification>
Figure 1: Push example
The following is an example of an on-change notification message for
the same subscription.
<notification xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
<eventTime>2017-10-25T08:22:33.44Z</eventTime>
<push-change-update xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push">
<subscription-id>89</subscription-id>
<datastore-changes>
<yang-patch xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-patch">
<patch-id>1</patch-id>
<edit>
<edit-id>edit1</edit-id>
<operation>merge</operation>
<target>/ietf-interfaces:interfaces-state</target>
<value>
<interfaces-state xmlns="http://foo.com/ietf-interfaces">
<interface>
<name>eth0</name>
<oper-status>down</oper-status>
</interface>
</interfaces-state>
</value>
</edit>
</yang-patch>
</datastore-changes>
</push-change-update>
</notification>
Figure 2: Push example for on change
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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 '4294967295' (i.e.
maximum value that can be represented using uint32 data type). 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. Also, new error codes
have been added that are able to indicate why a datastore
subscription attempt has failed, along with new yang-data that MAY be
used to include details on input parameters that might result in a
successful subsequent RPC invocation.
The establishment or modification of a datastore subscription can be
rejected for multiple reasons. This includes a too large subtree
request, or the inability of the publisher to 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.
In the case of a rejected request for an establishment of a datastore
subscription, the hints MUST be transported within a yang-data
"establish-subscription-datastore-error-info" container inserted into
the RPC error response, in lieu of the "establish-subscription-
stream-error-info" that is inserted in case of a stream subscription.
Below is a tree diagram for "establish-subscription-datastore-error-
info". All tree diagrams used in this document follow the notation
defined in [RFC8340]
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yang-data establish-subscription-datastore-error-info
+--ro establish-subscription-datasore-error-info
+--ro reason? identityref
+--ro period-hint? yang:timeticks
+--ro filter-failure-hint? string
+--ro object-count-estimate? uint32
+--ro object-count-limit? uint32
+--ro kilobytes-estimate? uint32
+--ro kilobytes-limit? uint32
Figure 3: Tree diagram for establish-subscription-datastore-error-
info
Similarly, in the case of a rejected request for modification of a
datastore subscription, the hints MUST be transported within a yang-
data "modify-subscription-datastore-error-info" container inserted
into the RPC error response, in lieu of the "modify-subscription-
stream-error-info" that is inserted in case of a stream subscription.
Below is a tree diagram for "modify-subscription-datastore-error-
info".
yang-data modify-subscription-datastore-error-info
+--ro modify-subscription-datasore-error-info
+--ro reason? identityref
+--ro period-hint? yang:timeticks
+--ro filter-failure-hint? string
+--ro object-count-estimate? uint32
+--ro object-count-limit? uint32
+--ro kilobytes-estimate? uint32
+--ro kilobytes-limit? uint32
Figure 4: Tree diagram for modify-subscription-datastore-error-info
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
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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 "unchanging-selection"
SHOULD be returned. This reduces the possibility of leakage of
access controlled objects.
Each "push-update" and "push-change-update" MUST have access control
applied. This includes validating that read access is permitted for
any new objects selected since the last notification message was sent
to a particular each receiver. To accomplish this, implementations
SHOULD support the conceptual authorization model of [RFC8342],
specifically section 3.2.4.
+-----------------+ +--------------------+
push-update or --> | datastore node | yes | add datastore node |
push-change-update | access allowed? | ---> | to update message |
+-----------------+ +--------------------+
Figure 5: Updated [rfc6536bis] access control for push updates
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 datastore nodes 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
datastore node changes are frequent and meaningless (e.g., a
temperature gauge changing 0.1 degrees), or that the implementation
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is not capable of on-change notification for a particular datastore
node.
In those cases, it will be important for client applications to have
a way to identify for which objects on-change notifications are
supported and for which ones they are not supported. Otherwise
client applications will have no way of knowing whether they can
indeed rely on their on-change subscription to provide them with the
change updates that they are interested in. In other words, if
implementations do not provide a solution and do not support
comprehensive on-change notifiability, clients of those
implementations will have no way of knowing what their on-change
subscription actually covers.
Implementations are therefore strongly advised to provide a solution
to this problem. It is expected that such a solution will be
standardized at some point in the future. In the meantime and until
this occurs, implementations will be expected to provide their own
solution.
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 MUST 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 "incomplete-update" 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
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previous contents). If neither of these are possible, then an
"incomplete-update" 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.
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 update
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. The tree diagram follows the notiation defined
in [RFC8340]. New schema objects defined here (i.e., beyond those
from [I-D.draft-ietf-netconf-subscribed-notifications]) are
identified with "yp". For the reader's convenience, in order to
compact the tree representation, some nodes that are defined in ietf-
subscribed-notifications and that are not essential to the
understanding of the data model defined here have been removed. This
is indicated by "..." in the diagram where applicable.
module: ietf-subscribed-notifications
...
+--rw filters
| ...
| +--rw yp:selection-filter* [identifier]
| +--rw yp:identifier sn:filter-id
| +--rw (yp:filter-spec)?
| +--:(yp:datastore-subtree-filter)
| | +--rw yp:datastore-subtree-filter? <anydata>
| | {sn:subtree}?
| +--:(yp:datastore-xpath-filter)
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| +--rw yp:datastore-xpath-filter? yang:xpath1.0
| {sn:xpath}?
+--rw subscriptions
+--rw subscription* [identifier]
| ...
+--rw (target)
| +--:(stream)
| | ...
| +--:(yp:datastore)
| +--rw yp:datastore identityref
| +--rw (yp:selection-filter)?
| +--:(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?
| | <anydata> {sn:subtree}?
| +--:(yp:datastore-xpath-filter)
| +--rw yp:datastore-xpath-filter?
| yang:xpath1.0 {sn:xpath}?
| ...
+--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
rpcs:
+---x establish-subscription
| +---w input
| | ...
| | +---w (target)
| | | +--:(stream)
| | | | ...
| | | +--:(yp:datastore)
| | | +---w yp:datastore identityref
| | | +---w (yp:selection-filter)?
| | | +--:(yp:by-reference)
| | | | +---w yp:selection-filter-ref
| | | | selection-filter-ref
| | | +--:(yp:within-subscription)
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| | | +---w (yp:filter-spec)?
| | | +--:(yp:datastore-subtree-filter)
| | | | +---w yp:datastore-subtree-filter?
| | | | <anydata> {sn:subtree}?
| | | +--:(yp:datastore-xpath-filter)
| | | +---w yp:datastore-xpath-filter?
| | | yang:xpath1.0 {sn:xpath}?
| | | ...
| | +---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 identifier subscription-id
+---x modify-subscription
| +---w input
| ...
| +---w (target)
| | ...
| | +--:(yp:datastore)
| | +---w (yp:selection-filter)?
| | +--:(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?
| | | <anydata> {sn:subtree}?
| | +--:(yp:datastore-xpath-filter)
| | +---w yp:datastore-xpath-filter?
| | yang:xpath1.0 {sn:xpath}?
| | ...
| +---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
+---x delete-subscription
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| ...
+---x kill-subscription
...
yang-data (for placement into rpc error responses)
...
notifications:
+---n replay-completed {replay}?
| ...
+---n subscription-completed
| ...
+---n subscription-started {configured}?
| | ...
| +--ro (target)
| | ...
| | +--:(yp:datastore)
| | +--ro yp:datastore identityref
| | +--ro (yp:selection-filter)?
| | +--:(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?
| | <anydata> {sn:subtree}?
| | +--:(yp:datastore-xpath-filter)
| | +--ro yp:datastore-xpath-filter?
| | yang:xpath1.0 {sn:xpath}?
| ...
| +--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
+---n subscription-resumed
| ...
+---n subscription-modified
| ...
| +--ro (target)
| | | ...
| | +--:(yp:datastore)
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| | +--ro yp:datastore identityref
| | +--ro (yp:selection-filter)?
| | +--:(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?
| | | <anydata> {sn:subtree}?
| | +--:(yp:datastore-xpath-filter)
| | +--ro yp:datastore-xpath-filter?
| | yang:xpath1.0 {sn:xpath}?
| ...
| +--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
+---n subscription-terminated
| ...
+---n subscription-suspended
...
module: ietf-yang-push
rpcs:
+---x resynch-subscription {on-change}?
+---w input
+---w identifier sn:subscription-id
yang-data: (for placement into rpc error responses)
+-- resynch-subscription-error
| +--ro reason? identityref
| +--ro period-hint? timeticks
| +--ro filter-failure-hint? string
| +--ro object-count-estimate? uint32
| +--ro object-count-limit? uint32
| +--ro kilobytes-estimate? uint32
| +--ro kilobytes-limit? uint32
+-- establish-subscription-error-datastore
| +--ro reason? identityref
| +--ro period-hint? timeticks
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| +--ro filter-failure-hint? string
| +--ro object-count-estimate? uint32
| +--ro object-count-limit? uint32
| +--ro kilobytes-estimate? uint32
| +--ro kilobytes-limit? uint32
+-- modify-subscription-error-datastore
+--ro reason? identityref
+--ro period-hint? timeticks
+--ro filter-failure-hint? string
+--ro object-count-estimate? uint32
+--ro object-count-limit? uint32
+--ro kilobytes-estimate? uint32
+--ro kilobytes-limit? uint32
notifications:
+---n push-update
| +--ro subscription-id? sn:subscription-id
| +--ro incomplete-update? empty
| +--ro datastore-contents? <anydata>
+---n push-change-update {on-change}?
+--ro subscription-id? sn:subscription-id
+--ro incomplete-update? empty
+--ro datastore-changes? <anydata>
Figure 6: 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". New 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 [RFC8341]. 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.
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o For periodic subscriptions, triggered updates will occur at the
boundaries of a specified time interval. These boundaries can be
calculated from the periodic parameters:
* a "period" which defines the duration between 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 datastore node 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]. Notifications
"subscription-started" and "subscription-modified" have been
augmented to include the datastore specific objects.
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"
notification.
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"
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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 "incomplete-update" leaf. This leaf 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:
<netconf:rpc message-id="101"
xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
<establish-subscription
xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications"
xmlns:yp="urn:ietf:params:xml:ns:yang:ietf-yang-push">
<yp:datastore>
<yp:source xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
ds:operational
</yp:source>
<xpath-filter
xmlns:ex="http://example.com/sample-data/1.0"
select="/ex:foo"/>
</yp:datastore>
<yp:periodic>
<yp:period>500</yp:period>
</yp:periodic>
</establish-subscription>
</netconf:rpc>
Figure 7: Establish-subscription RPC
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A positive response includes the "identifier" of the accepted
subscription. In that case a publisher MAY respond:
<rpc-reply message-id="101"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<subscription-result
xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications">
ok
</subscription-result>
<identifier
xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications">
52
</identifier>
</rpc-reply>
Figure 8: 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 which
help a subscriber understand subscription parameters might have been
accepted for the request. These hints would be included within the
yang-data structure "establish-subscription-error-datastore".
However even with these hints, there are no guarantee that subsequent
requests will in fact be accepted.
The specific parameters to be returned in as part of the RPC error
response depend on the specific transport that is used to manage the
subscription. In the case of NETCONF
[I-D.draft-ietf-netconf-netconf-event-notifications], when a
subscription request is rejected, the NETCONF RPC reply MUST include
an "rpc-error" element with the following elements:
o "error-type" of "application".
o "error-tag" of "operation-failed".
o Optionally, an "error-severity" of "error" (this MAY but does not
have to be included).
o "error-app-tag" with the value being a string that corresponds to
an identity with a base of "establish-subscription-error".
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o Optionally, "error-info" containing XML-encoded data with hints
for parameter settings that might result in future RPC success per
yang-data definition "establish-subscription-error-datastore".
For example, for the following request:
<netconf:rpc message-id="101"
xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
<establish-subscription
xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications"
xmlns:yp="urn:ietf:params:xml:ns:yang:ietf-yang-push">
<yp:datastore
xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
ds:operational
</yp:datastore>
<yp:datastore-xpath-filter netconf:type="xpath"
xmlns:ex="http://example.com/sample-data/1.0">
/ex:foo
</yp:datastore-xpath-filter>
<yp:on-change>
<yp:dampening-period>100</yp:dampening-period>
</yp:on-change>
</establish-subscription>
</netconf:rpc>
Figure 9: Establish-subscription request example 2
a publisher that cannot serve on-change updates but periodic updates
might return the following:
<rpc-reply message-id="101"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<rpc-error>
<error-type>application</error-type>
<error-tag>operation-failed</error-tag>
<error-severity>error</error-severity>
<error-app-tag>
on-change-unsupported
</error-message>
<error-path
xmlns:yp="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications">
/yp:periodic/yp:period
</error-path>
</rpc-error>
</rpc-reply>
Figure 10: Establish-subscription error response example 2
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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
not included MUST remain unmodified. Below is an example where a
subscriber attempts to modify the "period" of a subscription.
<netconf:rpc message-id="102"
xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
<modify-subscription
xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications"
xmlns:yp="urn:ietf:params:xml:ns:yang:ietf-yang-push">
<identifier>1011</identifier>
<yp:datastore
xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
ds:operational
</yp:datastore>
<yp:datastore-xpath-filter
netconf:type="xpath" xmlns:ex="http://example.com/sample-data/1.0">
/ex:bar
</yp:datastore-xpath-filter>
<yp:periodic>
<yp:period>250</yp:period>
</yp:periodic>
</modify-subscription>
</netconf:rpc>
Figure 11: Modify subscription request
The publisher MUST respond explicitly positively or negatively to the
request. If the subscription modification is rejected, the
subscription is maintained as it was before the modification request.
In addition, the publisher MUST send an rpc error response. This rpc
error response may contain hints encapsulated within the yang-data
structure "modify-subscription-error-datastore". A subscription MAY
be modified multiple times.
The specific parameters to be returned in as part of the RPC error
response depend on the specific transport that is used to manage the
subscription. In the case of NETCONF
[I-D.draft-ietf-netconf-netconf-event-notifications], when a
subscription request is rejected, the NETCONF RPC reply MUST include
an "rpc-error" element with the following elements:
o "error-type" of "application".
o "error-tag" of "operation-failed".
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o Optionally, an "error-severity" of "error" (this MAY but does not
have to be included).
o "error-app-tag" with the value being a string that corresponds to
an identity with a base of "modify-subscription-error".
o "error-path" pointing to the data node or parameter that caused
the rejection.
o Optionally, "error-info" containing XML-encoded data with hints
for parameter settings that might result in future RPC success per
yang-data definition "modify-subscription-error-datastore".
A configured subscription cannot be modified using "modify-
subscription" RPC. Instead, the configuration needs to be edited as
needed.
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". This RPC is unmodified 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 established using an "establish-subscription" RPC. For
example:
<netconf:rpc message-id="103"
xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
<resynch-subscription
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push"
xmlns:sn="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications">
<identifier>1011</identifier>
</resynch-subscription>
</netconf:rpc>
Resynch subscription
On receipt, a publisher must either accept the request and quickly
follow with a "push-update", or send an appropriate error within an
rpc error response. Within an error response, the publisher may
include supplemental information about the reasons within the yang-
data structure "resynch-subscription-error".
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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
library information is important for the receiver to reproduce the
set of data node 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
<CODE BEGINS> file "ietf-yang-push@2018-05-31.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 {
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prefix ds;
}
import ietf-restconf {
prefix rc;
}
organization
"IETF";
contact
"WG Web: <http://tools.ietf.org/wg/netconf/>
WG List: <mailto:netconf@ietf.org>
Editor: Alexander Clemm
<mailto:ludwig@clemm.org>
Editor: Eric Voit
<mailto:evoit@cisco.com>
Editor: Alberto Gonzalez Prieto
<mailto:agonzalezpri@vmware.com>
Editor: Ambika Prasad Tripathy
<mailto:ambtripa@cisco.com>
Editor: Einar Nilsen-Nygaard
<mailto:einarnn@cisco.com>
Editor: Andy Bierman
<mailto:andy@yumaworks.com>
Editor: Balazs Lengyel
<mailto:balazs.lengyel@ericsson.com>";
description
"This module contains YANG specifications for YANG push.";
revision 2018-05-31 {
description
"Initial revision.";
reference "draft-ietf-netconf-yang-push-16";
}
/*
* FEATURES
*/
feature on-change {
description
"This feature indicates that on-change triggered subscriptions
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are supported.";
}
/*
* IDENTITIES
*/
/* Error type identities for datastore subscription */
identity resynch-subscription-error {
description
"Problem found while attempting to fulfill an
'resynch-subscription' RPC request. ";
}
identity cant-exclude {
base sn:establish-subscription-error;
description
"Unable to remove the set of 'excluded-changes'. This means the
publisher is unable to restrict 'push-change-update's to just
the change types requested for this subscription.";
}
identity datastore-not-subscribable {
base sn:establish-subscription-error;
base sn:subscription-terminated-reason;
description
"This is not a subscribable datastore.";
}
identity no-such-subscription-resynch {
base resynch-subscription-error;
description
"Referenced subscription doesn't exist. This may be as a result
of a non-existent subscription ID, an ID which belongs to
another subscriber, or an ID for configured subscription.";
}
identity on-change-unsupported {
base sn:establish-subscription-error;
description
"On-change is not supported for any objects which are selectable
by this filter.";
}
identity on-change-synch-unsupported {
base sn:establish-subscription-error;
description
"Neither synch on start nor resynchronization are supported for
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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 than
'on-change-unsupported' or 'synchronization-size'. 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 period-unsupported {
base sn:establish-subscription-error;
base sn:modify-subscription-error;
base sn:subscription-suspended-reason;
description
"Requested time period is too short. This can be for both
periodic and on-change subscriptions (with or without
dampening.) Hints suggesting alternative periods may be
returned as supplemental information.";
}
identity result-too-big {
base sn:establish-subscription-error;
base sn:modify-subscription-error;
base sn:subscription-suspended-reason;
description
"Periodic or on-change push update datatrees exceed a maximum
size limit. Hints on estimated size of what was too big may
be returned as supplemental information.";
}
identity synchronization-size {
base sn:establish-subscription-error;
base sn:modify-subscription-error;
base resynch-subscription-error;
base sn:subscription-suspended-reason;
description
"Synch-on-start or resynchronization datatree exceeds a maximum
size limit. Hints on estimated size of what was too big may be
returned as supplemental information.";
}
identity unchanging-selection {
base sn:establish-subscription-error;
base sn:modify-subscription-error;
base sn:subscription-terminated-reason;
description
"Selection filter is unlikely to ever select datatree nodes.
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This means that based on the subscriber's current access
rights, the publisher recognizes that the selection filter is
unlikely to ever select datatree nodes which change. Examples
for this might be that node or subtree doesn't exist, read
access is not permitted for a receiver, or static objects that
only change at reboot have been chosen.";
}
/*
* TYPE DEFINITIONS
*/
typedef change-type {
type enumeration {
enum create {
description
"A change that refers to the creation of a new data node.";
}
enum delete {
description
"A change that refers to the deletion of a data node.";
}
enum insert {
description
"A change that refers to the insertion of a new
user-ordered data node.";
}
enum merge {
description
"A change that refers to a merging of a new value with a
target data node.";
}
enum move {
description
"A change that refers to a reordering of the target data
node";
}
enum replace {
description
"A change that refers to a replacement of the target data
node's value.";
}
enum remove {
description
"A change that refers to the removal of a data node.";
}
}
description
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"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:filter-id";
}
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
"Datastore from which to retrieve data.";
}
uses selection-filter-objects;
}
grouping selection-filter-types {
description
"This grouping defines the types of selectors 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.";
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}
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 'datastore-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
"This grouping defines a selector for objects from a
datastore.";
choice selection-filter {
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.";
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}
}
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 {
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;
mandatory true;
description
"Duration of time which should occur between periodic
push updates.";
}
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 {
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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 {
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.
After that, push-change-update notifications are
exclusively sent unless the publisher chooses to resynch
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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 hints {
description
"Parameters associated with some error for a subscription made
upon a datastore.";
leaf period-hint {
type yang:timeticks;
description
"Returned when the requested time period is too short. This
hint can assert a viable period for either a periodic push
cadence or an on-change dampening interval.";
}
leaf filter-failure-hint {
type string;
description
"Information describing where and/or why a provided filter
was unsupportable for a subscription.";
}
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
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"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.
A successful invocation results in a push-update of all
datastore objects that the subscriber is permitted to access.
This RPC can only be invoked on the same session on which the
subscription was established (using an establish-subscription
RPC). In case of an error, a resynch-subscription-error is
sent as part of an error response.";
input {
leaf identifier {
type sn:subscription-id;
mandatory true;
description
"Identifier of the subscription that is to be resynched.";
}
}
}
rc:yang-data resynch-subscription-error {
container resynch-subscription-error {
description
"If a 'resynch-subscription' RPC fails, the subscription is
not resynched and the RPC error response MUST indicate the
reason for this failure. This yang-data MAY be inserted as
structured data within a subscription's RPC error response
to indicate the failure reason.";
leaf reason {
type identityref {
base resynch-subscription-error;
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}
mandatory true;
description
"Indicates the reason why the publisher has declined a
request for subscription resynchronization.";
}
uses hints;
}
}
augment "/sn:establish-subscription/sn:input" {
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 target
for the subscription to RPC input.";
case datastore {
description
"Information specifying the parameters of an request for a
datastore subscription.";
uses datastore-criteria;
}
}
rc:yang-data establish-subscription-datastore-error-info {
container establish-subscription-datastore-error-info {
description
"If any 'establish-subscription' RPC parameters are
unsupportable against the datastore, a subscription is not
created and the RPC error response MUST indicate the reason
why the subscription failed to be created. This yang-data MAY
be inserted as structured data within a subscription's RPC
error response to indicate the failure reason. This
yang-data MUST be inserted if hints are to be provided back
to the subscriber.";
leaf reason {
type identityref {
base sn:establish-subscription-error;
}
description
"Indicates the reason why the subscription has failed to
be created to a targeted datastore.";
}
uses hints;
}
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}
augment "/sn:modify-subscription/sn:input" {
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 target
for the subscription to RPC input.";
case datastore {
description
"Information specifying the parameters of an request for a
datastore subscription.";
uses selection-filter-objects;
}
}
rc:yang-data modify-subscription-datastore-error-info {
container modify-subscription-datastore-error-info {
description
"This yang-data MAY be provided as part of a subscription's RPC
error response when there is a failure of a
'modify-subscription' RPC which has been made against a
datastore. This yang-data MUST be used if hints are to be
provides back to the subscriber.";
leaf reason {
type identityref {
base sn:modify-subscription-error;
}
description
"Indicates the reason why the subscription has failed to
be modified.";
}
uses hints;
}
}
/*
* NOTIFICATIONS
*/
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
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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 that would be subscribable as part of the NETCONF
event stream by any receiver.";
leaf subscription-id {
type sn:subscription-id;
description
"This references the subscription which drove the notification
to be sent.";
}
leaf incomplete-update {
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
"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 snapshot corresponds to the same
snapshot 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 incomplete-update {
type empty;
description
"The presence of this object indicates not all changes which
have occurred since the last update are included with this
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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 of the
target datastore starting at the time of the
previous update, per the terms of the subscription.
The datastore changes are encoded per RFC 8027
(YANG Patch).";
}
}
augment "/sn:subscription-started" {
description
"This augmentation adds 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 "selection-filter/within-subscription" {
description
"Specifies the selection filter and where it originated
from. 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-modified" {
description
"This augmentation adds datastore-specific objects to
the notification that a subscription has been modified.";
uses update-policy;
}
augment "/sn:subscription-modified/sn:target" {
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 {
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refine "selection-filter/within-subscription" {
description
"Specifies where the selection filter, and where it 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.";
}
}
}
}
/*
* DATA NODES
*/
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 "filter-id";
description
"A list of pre-configured filters that can be applied
to datastore subscriptions.";
leaf filter-id {
type string;
description
"An identifier to differentiate between selection filters.";
}
uses selection-filter-types;
}
}
augment "/sn:subscriptions/sn:subscription" {
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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}
<CODE ENDS>
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-16.txt (RFC form)
7. Security Considerations
The YANG module specified in this document defines a schema for data
that is designed to be accessed via network management protocols such
as NETCONF [RFC6241] or RESTCONF [RFC8040]. The lowest NETCONF layer
is the secure transport layer, and the mandatory-to-implement secure
transport is Secure Shell (SSH) [RFC6242]. The lowest RESTCONF layer
is HTTPS, and the mandatory-to-implement secure transport is TLS
[RFC5246].
The NETCONF access control model [RFC8341] provides the means to
restrict access for particular NETCONF or RESTCONF users to a
preconfigured subset of all available NETCONF or RESTCONF protocol
operations and content.
There are a number of data nodes defined in this YANG module that are
writable/creatable/deletable (i.e., config true, which is the
default). These data nodes may be considered sensitive or vulnerable
in some network environments. Write operations (e.g., edit-config)
to these data nodes without proper protection can have a negative
effect on network operations. These are the subtrees and data nodes
and their sensitivity/vulnerability:
First, it should be noted that the YANG module augments the YANG
module from [I-D.draft-ietf-netconf-subscribed-notifications].
All security considerations that are listed there are relevant
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also for datastore subscriptions. In the following, we focus on
the data nodes that are newly introduced here.
Subtree "selection-filter" under container "filters": This subtree
allows to specify which objects or subtrees to include in a
datastore subscription. An attacker could attempt to modify the
filter. For example, the filter might be modified to result in
very few objects being filtered in order to attempt to overwhelm
the receiver. Alternatively, the filter might be modified to
result in certain objects to be excluded from updates, in order to
have certain changes go unnoticed.
Subtree "datastore" in choice "target" in list "subscription":
Analogous to "selection filter", an attacker might attempt to
modify the objects being filtered in order to overwhelm a receiver
with a larger volume of datastore node updates than expected, or
to have certain changes go unnoticed.
Choice "update-trigger" in list "subscription": By modifying the
update trigger, an attacker might alter the updates that are being
sent in order to confuse a receiver, to withhold certain updates
to be sent to the receiver, and/or to overwhelm a receiver. For
example, an attacker might modify the period with which updates
are reported for a periodic subscription, or it might modify the
dampening period for an on-change subscription, resulting in
greater delay of successive updates (potentially affecting
responsiveness of applications that depend on the updates) or in a
high volume of updates (to exhaust receiver resources).
RPC "resynch-subscription": This RPC allows a subscriber of an on-
change subscription to request a full push of objects in the
subscription's scope. This can result in a large volume of data.
An attacker could attempt to use this RPC to exhaust resources on
the server to generate the data, and attempt to overwhelm a
receiver with the resulting data volume.
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
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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-12
(work in progress), April 2018.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
DOI 10.17487/RFC3688, January 2004,
<https://www.rfc-editor.org/info/rfc3688>.
[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC6020, October 2010,
<https://www.rfc-editor.org/info/rfc6020>.
[RFC6470] Bierman, A., "Network Configuration Protocol (NETCONF)
Base Notifications", RFC 6470, DOI 10.17487/RFC6470,
February 2012, <https://www.rfc-editor.org/info/rfc6470>.
[RFC7895] Bierman, A., Bjorklund, M., and K. Watsen, "YANG Module
Library", RFC 7895, DOI 10.17487/RFC7895, June 2016,
<https://www.rfc-editor.org/info/rfc7895>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/info/rfc7950>.
[RFC8072] Bierman, A., Bjorklund, M., and K. Watsen, "YANG Patch
Media Type", RFC 8072, DOI 10.17487/RFC8072, February
2017, <https://www.rfc-editor.org/info/rfc8072>.
[RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration
Access Control Model", STD 91, RFC 8341,
DOI 10.17487/RFC8341, March 2018,
<https://www.rfc-editor.org/info/rfc8341>.
[RFC8342] Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
and R. Wilton, "Network Management Datastore Architecture
(NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018,
<https://www.rfc-editor.org/info/rfc8342>.
9.2. Informative References
[bergstra2014]
Bergstra, J. and M. Burgess, "Promise Theory, Createspace
Independent Publishers, ISBN-13 9781495437779", 2014.
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[I-D.draft-ietf-netconf-netconf-event-notifications]
Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard,
E., and A. Tripathy, "NETCONF Support for Event
Notifications", May 2018.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>.
[RFC5277] Chisholm, S. and H. Trevino, "NETCONF Event
Notifications", RFC 5277, DOI 10.17487/RFC5277, July 2008,
<https://www.rfc-editor.org/info/rfc5277>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<https://www.rfc-editor.org/info/rfc6241>.
[RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure
Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
<https://www.rfc-editor.org/info/rfc6242>.
[RFC7223] Bjorklund, M., "A YANG Data Model for Interface
Management", RFC 7223, DOI 10.17487/RFC7223, May 2014,
<https://www.rfc-editor.org/info/rfc7223>.
[RFC7923] Voit, E., Clemm, A., and A. Gonzalez Prieto, "Requirements
for Subscription to YANG Datastores", RFC 7923,
DOI 10.17487/RFC7923, June 2016,
<https://www.rfc-editor.org/info/rfc7923>.
[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
<https://www.rfc-editor.org/info/rfc8040>.
[RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
<https://www.rfc-editor.org/info/rfc8340>.
Appendix A. Appendix A: Subscription Errors
A.1. RPC Failures
Rejection of an RPC for any reason is indicated by via RPC error
response from the publisher. Valid RPC errors returned include both
existing transport layer RPC error codes, such as those seen with
NETCONF in [RFC6241], as well as subscription specific errors such as
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those defined within the YANG model. As a result, how subscription
errors are encoded within an RPC error response is transport
dependent.
References to specific identities within the either the subscribed-
notifications YANG model or the yang-push YANG model may be returned
as part of the error responses resulting from failed attempts at
datastore subscription. Following are valid errors per RPC (note:
throughout this section the prefix 'sn' indicates an item imported
from the subscribed-notifications.yang model):
establish-subscription modify-subscription
---------------------- -------------------
cant-exclude sn:filter-unsupported
datastore-not-subscribable sn:insufficient-resources
sn:dscp-unavailable sn:no-such-subscription
sn:filter-unsupported period-unsupported
sn:insufficient-resources result-too-big
on-change-unsupported synchronization-size
on-change-synch-unsupported unchanging-selection
period-unsupported
result-too-big resynch-subscription
synchronization-size --------------------
unchanging-selection no-such-subscription-resynch
synchronization-size
delete-subscription kill-subscription
---------------------- -----------------
sn:no-such-subscription sn:no-such-subscription
There is one final set of transport independent RPC error elements
included in the YANG model. These are the following four yang-data
structures for failed datastore subscriptions:
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1. yang-data establish-subscription-error-datastore
This MUST be returned if information identifying the reason for an
RPC error has not been placed elsewhere within the transport
portion of a failed "establish-subscription" RPC response. This
MUST be sent if hints are included.
2. yang-data modify-subscription-error-datastore
This MUST be returned if information identifying the reason for an
RPC error has not been placed elsewhere within the transport
portion of a failed "modifiy-subscription" RPC response. This
MUST be sent if hints are included.
3. yang-data sn:delete-subscription-error
This MUST be returned if information identifying the reason for an
RPC error has not been placed elsewhere within the transport
portion of a failed "delete-subscription" or "kill-subscription"
RPC response.
4. yang-data resynch-subscription-error
This MUST be returned if information identifying the reason for an
RPC error has not been placed elsewhere within the transport
portion of a failed "resynch-subscription" RPC response.
A.2. Notifications of Failure
A subscription may be unexpectedly terminated or suspended
independent of any RPC or configuration operation. In such cases,
indications of such a failure MUST be provided. To accomplish this,
the following types of error identities may be returned within the
corresponding subscription state change notification:
subscription-terminated subscription-suspended
----------------------- ----------------------
datastore-not-subscribable sn:insufficient-resources
sn:filter-unavailable period-unsupported
sn:no-such-subscription result-too-big
sn:suspension-timeout synchronization-size
unchanging-selection
Appendix B. Changes between revisions
(To be removed by RFC editor prior to publication)
v15 - v16
o Updated security considerations.
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o Updated references.
o Addressed comments from last call review, specifically comments
received from Martin Bjorklund.
v14 - v15
o Minor text fixes. Includes a fix to on-change update calculation
to cover churn when a object changes to and from a value during a
dampening period.
v13 - v14
o Minor text fixes.
v12 - v13
o Hint negotiation models now show error examples.
o yang-data structures for rpc errors.
v11 - v12
o Included Martin's review clarifications.
o QoS moved to subscribed-notifications
o time-of-update removed as it is redundant with RFC5277's
eventTime, and other times from notification-messages.
o Error model moved to match existing implementations
o On-change notifiable removed, how to do this is implementation
specific.
o NMDA model supported. Non NMDA version at https://github.com/
netconf-wg/yang-push/
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
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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.
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
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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
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)
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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
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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