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draft-ietf-netconf-subscribed-notifications-08.txt
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PRE-SUBMISSION WORKING COPY DEC 7th 2017
NETCONF E. Voit
Internet-Draft Cisco Systems
Intended status: Standards Track A. Clemm
Expires: May 26, 2018 Huawei
A. Gonzalez Prieto
VMWare
E. Nilsen-Nygaard
A. Tripathy
Cisco Systems
November 22, 2017
Custom Subscription to Event Streams
draft-ietf-netconf-subscribed-notifications-08
Abstract
This document defines capabilities and operations for the customized
establishment of subscriptions upon a publisher's event streams.
Also defined are delivery mechanisms for instances of the resulting
notification messages. Effectively this allows a subscriber to
request and receive a continuous, custom feed of publisher generated
information.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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 May 26, 2018.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
1.3. Solution Overview . . . . . . . . . . . . . . . . . . . . 4
1.4. Relationship to RFC-5277 . . . . . . . . . . . . . . . . 5
2. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Event Streams . . . . . . . . . . . . . . . . . . . . . . 6
2.2. Event Stream Filters . . . . . . . . . . . . . . . . . . 7
2.3. QoS . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.4. Dynamic Subscriptions . . . . . . . . . . . . . . . . . . 7
2.5. Configured Subscriptions . . . . . . . . . . . . . . . . 13
2.6. Event Record Delivery . . . . . . . . . . . . . . . . . . 17
2.7. Subscription State Notifications . . . . . . . . . . . . 18
2.8. Subscription Monitoring . . . . . . . . . . . . . . . . . 21
2.9. Advertisement . . . . . . . . . . . . . . . . . . . . . . 22
3. YANG Data Model Trees . . . . . . . . . . . . . . . . . . . . 22
3.1. Event Streams Container . . . . . . . . . . . . . . . . . 22
3.2. Event Stream Filters Container . . . . . . . . . . . . . 23
3.3. Subscriptions Container . . . . . . . . . . . . . . . . . 23
3.4. Subscription-config Container . . . . . . . . . . . . . . 24
4. Data Model . . . . . . . . . . . . . . . . . . . . . . . . . 25
5. Considerations . . . . . . . . . . . . . . . . . . . . . . . 49
5.1. Implementation Considerations . . . . . . . . . . . . . . 49
5.2. IANA Considerations . . . . . . . . . . . . . . . . . . . 50
5.3. Security Considerations . . . . . . . . . . . . . . . . . 50
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 51
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 51
7.1. Normative References . . . . . . . . . . . . . . . . . . 51
7.2. Informative References . . . . . . . . . . . . . . . . . 52
Appendix A. Changes between revisions . . . . . . . . . . . . . 53
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 56
1. Introduction
This document defines capabilities and operations for the customized
establishment of subscriptions upon system generated event streams.
Effectively this enables a "subscribe then publish" capability where
the customized information needs of each target receiver are
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understood by the publisher before subscribed event records are
marshalled and pushed. The receiver then gets a continuous, custom
feed of publisher generated information.
While the functionality defined in this document is transport-
agnostic, protocols like NETCONF [RFC6241] or RESTCONF [RFC8040] can
be used to configure or dynamically signal subscriptions, and there
are bindings defined for subscribed event record delivery for NETCONF
within [I-D.draft-ietf-netconf-netconf-event-notifications], and for
HTTP2 or HTTP1.1 within [I-D.draft-ietf-netconf-restconf-notif].
1.1. Motivation
There are various [RFC5277] limitations, many of which have been
exposed in [RFC7923] which needed to be solved. Key capabilities
supported by this document include:
o multiple subscriptions on a single transport session
o support for dynamic and statically configured subscriptions
o modification of an existing subscription
o operational counters and instrumentation
o negotiation of subscription parameters (through the use of hints
returned as part of declined subscription requests)
o state change notifications (e.g., publisher driven suspension,
parameter modification)
o independence from transport protocol
1.2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Configured subscription: A subscription installed via a configuration
interface which persists across reboots.
Dynamic subscription: A subscription agreed between subscriber and
publisher created via an establish-subscription RPC.
Event: An occurrence of something that may be of interest. (e.g., a
configuration change, a fault, a change in status, crossing a
threshold, or an external input to the system.)
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Event record: A set of information detailing an event.
NACM: NETCONF Access Control Model.
Notification message: A set of transport encapsulated information
intended for a receiver indicating that one or more event(s) have
occurred. A notification message may include event records.
Publisher: An entity responsible for streaming notification messages
per the terms of a Subscription.
Receiver: A target to which a publisher pushes subscribed event
records. For dynamic subscriptions, the receiver and subscriber are
the same entity.
Stream (also referred to as "event stream"): A continuous ordered set
of events aggregated under some context.
Stream filter: Evaluation criteria which may be applied against a
event records within a stream. Event records pass the filter when
specified criteria are met.
Subscribed event records: Event records which have met the terms of
the subscription. This include terms (such as security checks)
enforced by the publisher.
Subscriber: An entity able to request and negotiate a contract for
the generation and push of event records from a publisher.
Subscription: A contract with a publisher, stipulating which
information one or more receivers wish to have pushed from the
publisher without the need for further solicitation.
1.3. Solution Overview
This document describes a transport agnostic mechanism for
subscribing to and receiving content from a stream instantiated
within a publisher. This mechanism is through the use of a
subscription.
Two types of subscriptions are supported:
1. Dynamic subscriptions, where a subscriber initiates a
subscription negotiation with a publisher via RPC. If the
publisher wants to serve this request, it accepts it, and then
starts pushing notification messages. If the publisher does not
wish to serve it as requested, then an error response is
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returned. This response MAY include hints at subscription
parameters which would have been accepted.
2. Configured subscriptions, which allow the management of
subscriptions via a configuration interface so that a publisher
can send notification messages to configured receiver(s).
Support for this capability is optional.
Additional characteristics differentiating configured from dynamic
subscriptions include:
o The lifetime of a dynamic subscription is bounded by the transport
session used to establish it. For connection-oriented stateful
transport like NETCONF, the loss of the transport session will
result in the immediate termination of associated dynamic
subscriptions. For connectionless or stateless transports like
HTTP, it is the lack of receipt acknowledgement of a sequential
set of notification messages and/or keep-alives which will
terminate dynamic subscriptions. The lifetime of a configured
subscription is driven by relevant configuration being present on
the running configuration. This implies configured subscriptions
persist across reboots, and persist even when transport is
unavailable.
o Configured subscriptions can be modified by any configuration
client with write permission on the configuration of the
subscription. Dynamic subscriptions can only be modified via an
RPC request made upon the original subscribing transport session.
Note that there is no mixing-and-matching of dynamic and configured
operations on a single subscriptions. Specifically, a configured
subscription cannot be modified or deleted using RPCs defined in this
document. Similarly, a subscription established via RPC cannot be
modified through configuration operations.
The publisher MAY decide to terminate a dynamic subscription at any
time. Similarly, it MAY decide to temporarily suspend the sending of
notification messages for any dynamic subscription, or for one or
more receivers of a configured subscription. Such termination or
suspension is driven by internal considerations of the publisher.
1.4. Relationship to RFC-5277
This document is intended to provide a superset of the subscription
capabilities initially defined within [RFC5277]. Especially when
extending an existing [RFC5277] implementation, it is important to
understand what has been reused and what has been replaced. Key
relationships between these two documents include:
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o the data model in this document replaces the data model in
[RFC5277].
o the RPC operations in this draft replaces the symmetrical
operations of [RFC5277], section 4.
o the one way operation of [RFC5277] is still used. However this
operation will no longer be required with the availability of
[I.D.draft-ietf-netconf-notification-messages].
o the definition and contents of the NETCONF stream are identical
between this document and [RFC5277].
o a publisher MAY implement both the data model and RPCs defined in
[RFC5277] and this new document concurrently, in order to support
old clients. However the use of both alternatives on a single
transport session is prohibited.
2. Solution
2.1. Event Streams
An event stream is a named entity on a publisher which exposes a
continuously updating set of event records. Each event stream is
available for subscription. It is out of the scope of this document
to identify a) how streams are defined, b) how event records are
defined/generated, and c) how event records are assigned to streams.
There is only one reserved event stream within this document:
NETCONF. The NETCONF event stream contains all NETCONF XML event
record information supported by the publisher, except for where it
has been explicitly indicated that this the event record MUST be
excluded from the NETCONF stream. Beyond NETCONF, implementations
are free to add additional event streams.
As event records are created by a system, they may be assigned to one
or more streams. The event record is distributed to subscription's
receiver(s) where: (1) a subscription includes the identified stream,
and (2) subscription filtering does not exclude the event record from
that receiver.
If access control permissions are in use to secure publisher content,
then for event records to be sent to a receiver, that receiver MUST
be allowed access to all the event records on the stream. If
subscriber permissions change during the lifecycle of a subscription,
then the subscription MUST be continued or terminated accordingly.
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2.2. Event Stream Filters
This document defines an extensible filtering mechanism. Two
optional stream filtering syntaxes supported are [XPATH] and subtree
[RFC6241]. A subset of information is never stripped from within the
event record.
If no stream filter is provided within a subscription, all event
records on a stream are to be sent.
2.3. QoS
This document provides an optional feature describing QoS parameters.
These parameters indicate the treatment of a subscription relative to
other traffic between publisher and receiver. Included are:
o A "dscp" QoS marking to differentiate transport QoS behavior.
Where provided, this marking MUST be stamped on notification
messages.
o A "weighting" so that bandwidth proportional to this weighting can
be allocated to this subscription relative to other subscriptions
destined for that receiver.
o a "dependency" upon another subscription. Notification messages
MUST NOT be sent prior to other notification messages containing
update record(s) for the referenced subscription.
A subscription's weighting MUST work identically to stream dependency
weighting as described within RFC 7540, section 5.3.2.
A subscription's dependency MUST work identically to stream
dependency as described within [RFC7540], sections 5.3.1, 5.3.3, and
5.3.4. If a dependency is attempted via an RPC, but the referenced
subscription does not exist, the dependency will be silently removed.
2.4. Dynamic Subscriptions
Dynamic subscriptions are managed via RPC, and are made against
targets located within the publisher. These RPCs have been designed
extensibly so that they may be augmented for subscription targets
beyond event streams.
2.4.1. Dynamic Subscription State Model
Below is the state machine of a subscription for the publisher of a
dynamic subscription. It is important to note that such a
subscription doesn't exist at the publisher until it an "establish-
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subscription" RPC is accepted. The mere request by a subscriber to
establish a subscription is insufficient for that asserted
subscription to be externally visible.
.-------.
| start |
'-------'
|
establish-subscription
|
| .------modify-subscription-------.
v v '
.-----------. .-----------.
.--------. | |-subscription-suspended->| |
modify- '| active | | suspended |
subscription | |<--subscription-resumed--| |
---------->'-----------' '-----------'
| |
delete/kill-subscription delete/kill-
| subscription
v |
.-------. |
| end |<-------------------------------'
'-------'
Figure 1: Dynamic subscription states
Of interest in this state machine are the following:
o Successful establish or modify RPCs put the subscription into an
active state.
o Failed modify RPCs will leave the subscription in its previous
state, with no visible change to any streaming updates.
o A delete or kill RPC will end the subscription.
o Suspend and resume state changes are driven by internal process
and prioritization. There are no direct controls over suspend and
resume other than modifying a subscription
2.4.2. Establishing a Subscription
The "establish-subscription" operation allows a subscriber to request
the creation of a subscription via RPC. It MUST be possible to
support multiple establish subscription RPC requests made within the
same transport session.
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The input parameters of the operation are:
o A stream name which identifies the targeted stream of events
against which the subscription is applied.
o A stream filter which may reduce the set of event records pushed.
o An optional encoding for the event records pushed. Note: If no
encoding is included, the encoding of the RPC MUST be used.
o An optional stop time for the subscription. If no stop-time is
present, notification messages will continue to be sent until the
subscription is terminated.
o An optional start time which indicates that this subscription is
requesting a replay of previously generated information from the
event stream. For more on replay, see Section 2.4.2.1
If the publisher can satisfy the "establish-subscription" request, it
provides an identifier for the subscription, and immediately starts
streaming notification messages. If the subscriber has no
authorization to establish the subscription, transport protocol
specific replies are used to indicate an authorization error. If an
RPC request is properly framed, but publisher cannot satisfy the
"establish-subscription" request, the publisher MUST send a negative
"subscription-result" element describing the reason for the failure.
Optionally, the "subscription-result" MAY be accompanied by one or
more hints on alternative inputs which would have resulted in an
accepted subscription.
"establish-subscription" requests MUST fail if a filter with invalid
or unsupportable syntax is provided, or if a non-existent stream is
referenced.
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+---x establish-subscription
+---w input
| +---w encoding? encoding
| +---w (target)
| | +--:(stream)
| | +---w (stream-filter)?
| | | +--:(by-reference)
| | | | +---w stream-filter-ref stream-filter-ref
| | | +--:(within-subscription)
| | | +---w (filter-spec)?
| | | +--:(stream-subtree-filter)
| | | | +---w stream-subtree-filter? {subtree}?
| | | +--:(stream-xpath-filter)
| | | +---w stream-xpath-filter?
| | | yang:xpath1.0 {xpath}?
| | +---w stream stream
| | +---w replay-start-time? yang:date-and-time {replay}?
| +---w stop-time? yang:date-and-time
| +---w dscp? inet:dscp {qos}?
| +---w weighting? uint8 {qos}?
| +---w dependency? sn:subscription-id {qos}?
+--ro output
+--ro subscription-result subscription-result
+--ro (result)?
+--:(no-success)
| +--ro filter-failure? string
| +--ro replay-start-time-hint? yang:date-and-time
+--:(success)
+--ro identifier subscription-id
Figure 2: establish-subscription RPC
2.4.2.1. Replay Subscription
Replay provides the ability to establish a subscription which is also
capable of passing recently generated event records. In other words,
as the subscription initializes itself, it sends any previously
generated content from within target event stream which meets the
filter and timeframe criteria. These historical event records would
then be followed by event records generated after the subscription
has been established. All event records will be delivered in the
order generated.
Replay is an optional feature which is dependent on an event stream
supporting some form of logging. Replay puts no restrictions on the
size or form of the log, or where it resides within the device.
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The inclusion of a replay-start-time within an "establish-
subscription" RPC indicates a replay request. If the "replay-start-
time" contains a value that is earlier than content stored within the
publisher's replay buffer, then the subscription MUST be rejected,
and the leaf "replay-start-time-hint" MUST be set in the reply.
If a "stop-time" parameter is included, it MAY also be earlier than
the current time and MUST be later than the "replay-start-time". The
publisher MUST NOT accept a "replay-start-time" for a future time.
If the "replay-start-time" is later than any information stored in
the replay buffer, then the publisher MUST send a "replay-completed"
notification immediately after the "subscription-started"
notification.
If a stream supports replay, the "replay-support" leaf is present in
the "/streams/stream" list entry for the stream. An event stream
that does support replay is not expected to have an unlimited supply
of saved notifications available to accommodate any given replay
request. To assess the availability of replay, subscribers can
perform a get on "replay-log-creation-time" and "replay-log-aged-
time". See Figure 10 for the tree describing these elements. The
actual size of the replay log at any given time is a publisher
specific matter. Control parameters for the replay log are outside
the scope of this document.
2.4.3. Modifying a Subscription
The "modify-subscription" operation permits changing the terms of an
existing dynamic subscription previously established on that
transport session via "establish-subscription". Dynamic
subscriptions can be modified one or multiple times. If the
publisher accepts the requested modifications, it replies with "ok"
in the "subscription-result", then immediately starts sending event
records based on the new terms. If the publisher rejects the
request, the subscription remains as prior to the request. That is,
the request has no impact whatsoever. The contents of a such a
rejected modification MAY include one or more hints on alternative
inputs which would have resulted in a successfully modified
subscription.
If the publisher accepts the requested modifications on a currently
suspended subscription, the subscription will immediately be resumed
(i.e., the modified subscription is returned to an active status.)
The publisher MAY immediately suspend this newly modified
subscription through the "subscription-suspended" notification before
any event records are sent.
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+---x modify-subscription
+---w input
| +---w identifier? subscription-id
| +---w (target)
| | +--:(stream)
| | +---w (stream-filter)?
| | +--:(by-reference)
| | | +---w stream-filter-ref stream-filter-ref
| | +--:(within-subscription)
| | +---w (filter-spec)?
| | +--:(stream-subtree-filter)
| | | +---w stream-subtree-filter? {subtree}?
| | +--:(stream-xpath-filter)
| | +---w stream-xpath-filter?
| | yang:xpath1.0 {xpath}?
| +---w stop-time? yang:date-and-time
+--ro output
+--ro subscription-result subscription-result
+--ro (result)?
+--:(no-success)
+--ro filter-failure? string
Figure 3: modify-subscription RPC
Dynamic subscriptions established via RPC can only be modified via
RPC using the same transport session used to establish that
subscription. Subscriptions created by configuration operations
cannot be modified via this RPC.
2.4.4. Deleting a Subscription
The "delete-subscription" operation permits canceling an existing
subscription previously established on that transport session. If
the publisher accepts the request, and the publisher has indicated
this success via an "ok" in the "subscription-result", the publisher
MUST NOT send any more notification messages for this subscription.
If the publisher rejects the request, the request has no impact
whatsoever on any subscription.
+---x delete-subscription
+---w input
| +---w identifier subscription-id
+--ro output
+--ro subscription-result subscription-result
Figure 4: delete-subscription RPC
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Dynamic subscriptions can only be deleted via this RPC using the same
transport session previously used for subscription establishment.
Configured subscriptions cannot be deleted using RPCs.
2.4.5. Killing a Subscription
The "kill-subscription" operation permits an operator to end a
dynamic subscription which is not associated the transport session
used for the RPC. This operation MUST be secured so that only
connections with sufficiently privileged access rights are able to
invoke this RPC. A publisher MUST terminate any dynamic subscription
identified by RPC request. An operator may find subscription
identifiers which may be used with "kill-subscription" by searching
for the IP address of a receiver within
"subscriptions\subscription\receivers\receiver\address".
Configured subscriptions cannot be killed using this RPC. Instead,
configured subscriptions are deleted as part of regular configuration
operations. Publishers MUST reject any RPC attempt to kill a
configured subscription.
The tree structure of "kill-subscription" is almost identical to
"delete-subscription", with only the name of the RPC changing.
2.5. Configured Subscriptions
A configured subscription is a subscription installed via a
configuration interface. Configured subscriptions may be modified by
any configuration client with the proper permissions. Subscriptions
can be modified or terminated via the configuration interface at any
point of their lifetime.
Configured subscriptions have several characteristics distinguishing
them from dynamic subscriptions:
o persistence across reboots,
o persistence even when transport is unavailable, and
o an ability to send notification messages to more than one receiver
(note that receivers never provided information about other
receivers of the same subscription.)
Supporting configured subscriptions is optional and advertised using
the "configured" feature.
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In addition to subscription parameters available to dynamic
subscriptions as described in Section 2.4.2, the following additional
parameters are also available to configured subscriptions:
o One or more receiver IP addresses (and corresponding ports)
intended as the destination for notification messages.
o Optional parameters to identify an egress interface, a host IP
address, a VRF (as defined by the network instance name within
[I-D.draft-ietf-rtgwg-ni-model]), or an IP address plus VRF out of
which notification messages are to be pushed from the publisher.
Where any of this info is not explicitly included, or where just
the VRF is provided, notification messages MUST egress the
publisher's default interface towards that receiver.
2.5.1. Configured Subscription State Model
Below is the state machine for the publisher for a configured
subscriptions. When a subscription is first created, the operational
status of each receiver is initially set to connecting. Individual
are receivers are moved to an active status when a "subscription-
started" state change notification is successfully passed to that
receiver. Configured subscription receivers remain active if
transport connectivity is not lost, and event records are not being
dropped due to buffer overflow. A configured subscription's receiver
MUST be moved connecting if transport connectivity is lost.
A configured subscription's receiver MUST be moved to a suspended
state if there is transport connectivity between the publisher and
receiver, but notification messages are not being generated. A
configured subscription receiver MUST be returned to an active state
from the suspended state when notification messages are again being
generated and a receiver has successfully been sent a "subscription-
resumed" or a "subscription-modified".
Modification of a configured subscription is possible when there are
suspended receivers. However individual suspended receivers are not
notified via a "subscription-modified" until the subscription
resumes.
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.-------.
| start |
'-------'
|
create
.-----. |
modify \ v
| .---------------------------------------------------------------.
| | Subscription subscription .----------. |
'->| .---started------| receiver | |
| | |connecting|<--transport-. |
| | .-transport->| | loss | |
| V | loss '----------' | |
| .--------. .---------. |
| |receiver|--subscription-suspended--->|receiver | |
|subscription-| active | |suspended| |
| modified | |<--subscription-resumed,----| | |
| '---->'--------' subscription-modified '---------' |
'---------------------------------------------------------------'
|
delete
|
v
.-------.
| end |
'-------'
Figure 5: Configured subscription state and receiver status
The interaction model described within this section is mirrored in
the RPCs and Notifications later in the document. It should be noted
that these RPCs and Notifications have been designed to be extensible
and allow subscriptions into targets other than event streams.
[I-D.ietf-netconf-yang-push] provides an example of such an
extension.
2.5.2. Creating a Configured Subscription
Configured subscriptions are established using configuration
operations against the top-level subtree "subscription-config".
There are two key differences between the new RPCs defined in this
document and configuration operations for subscription creation.
Firstly, configuration operations install a subscription without
question, while the RPCs are designed to the support negotiation and
rejection of requests. Secondly, while the RPCs mandate that the
subscriber establishing the subscription is the only receiver of the
notification messages, configuration operations permit specifying
receivers independent of any tracked subscriber. Because there is no
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explicit association with an existing transport session,
configuration operations require additional parameters beyond those
of dynamic subscriptions to indicate receivers, and possibly whether
the notification messages need to come from a specific egress
interface on the publisher.
After a subscription is successfully created, the publisher
immediately sends a "subscription-started" state change notification
to each receiver. It is quite possible that upon configuration,
reboot, or even steady-state operations, a transport session may not
be currently available to the receiver. In this case, when there is
something to transport for an active subscription, transport specific
call-home operations will be used to establish the connection. When
transport connectivity is available, notification messages may then
be pushed.
With active configured subscriptions, it is allowable to buffer event
records even after a "subscription-started" has been sent. However
if events are lost (rather than just delayed) due to replay buffer
overflow, a new "subscription-started" must be sent. This new
"subscription-started" indicates an event record discontinuity.
To see an example at subscription creation using configuration
operations over NETCONF, see Appendix A of
[I-D.draft-ietf-netconf-netconf-event-notifications].
Note that is possible to configure replay on a configured
subscription. This capability is to allow a configured subscription
to exist on a system so that event records generated during boot can
be buffered and pushed as soon as the transport session is
established.
2.5.3. Modifying a Configured Subscription
Configured subscriptions can be modified using configuration
operations against the top-level subtree "subscription-config".
If the modification involves adding and/or removing receivers, those
modified receivers are sent state change notifications indicating
they have been added (i.e, "subscription-started") or removed (i.e.,
"subscription-terminated".)
If the modification involved changing the policies for the
subscription, the publisher sends to currently active receivers a
"subscription-modified" notification. For any suspended receviers, a
"subscription-modified" notification will be delayed until the
receiver is resumed. (Note: in this case, the "subscription-
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modified" notification informs the receiver that the subscription has
been resumed, so no additional "subscription-resumed" need be sent.)
2.5.4. Deleting a Configured Subscription
Subscriptions can be deleted using configuration operations against
the top-level subtree "subscription-config".
Immediately after a subscription is successfully deleted, the
publisher sends to all receivers of that subscription a state change
notification stating the subscription has ended (i.e., "subscription-
terminated").
2.6. Event Record Delivery
Whether dynamic or configured, once a subscription has been set up,
the publisher streams event records via notification messages per the
terms of the subscription. For dynamic subscriptions set up via RPC
operations, notification messages are sent over the session used to
establish the subscription. For configured subscriptions,
notification messages are sent over the connections specified by the
transport, plus receiver IP address and port configured.
A notification message is sent to a receiver when an event record is
able to traverse the specified filter criteria. This notification
message MUST be encoded as one-way notification element of [RFC5277],
Section 4. The following example within [RFC7950] section 7.16.3 is
an example of a compliant message:
<notification
xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
<eventTime>2007-09-01T10:00:00Z</eventTime>
<link-failure xmlns="http://acme.example.com/system">
<if-name>so-1/2/3.0</if-name>
<if-admin-status>up</if-admin-status>
<if-oper-status>down</if-oper-status>
</link-failure>
</notification>
Figure 6: subscribed notification message
This [RFC5277] section 4 one-way operation has the drawback of not
including useful header information such as a subscription
identifier. When using this mechanism, it is left up to
implementations or augmentations to this document to determine which
event records belong to which subscription.
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These drawbacks, along with other useful common headers and the
ability to bundle multiple event records together is being explored
within [I.D.draft-ietf-netconf-notification-messages]. When the
notification-messages is supported, this document will be updated to
indicate support.
2.7. Subscription State Notifications
In addition to subscribed event records, a publisher will send
subscription state notifications to indicate to receivers that an
event related to the subscription management has occurred.
Subscription state notifications are unlike other notifications which
might be found in the event stream. They cannot be filtered out, and
they are delivered only to directly impacted receiver(s) of a
subscription. The identification of subscription state notifications
is easy to separate from other notification messages through the use
of the YANG extension "subscription-state-notif". This extension
tags a notification as subscription state notification.
The complete set of subscription state notifications is described in
the following subsections.
2.7.1. subscription-started
This notification indicates that a configured subscription has
started, and event records may be sent. Included in this state
change notification are all the parameters of the subscription,
except for the receiver(s) addressing information and origin
information indicating where notification messages will egress the
publisher. Note that if a referenced filter from the "filters"
container has been used within the subscription, the notification
will include the contents of that referenced under the "within-
subscription" subtree.
Note that for dynamic subscriptions, no "subscription-started"
notifications are ever sent.