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draft-ietf-netconf-subscribed-notifications-13.txt
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PRE-DRAFT: April 26 2018
*************************
NETCONF E. Voit
Internet-Draft Cisco Systems
Intended status: Standards Track A. Clemm
Expires: October 28, 2018 Huawei
A. Gonzalez Prieto
VMWare
E. Nilsen-Nygaard
A. Tripathy
Cisco Systems
April 26, 2018
Customized Subscriptions to a Publisher's Event Streams
draft-ietf-netconf-subscribed-notifications-13
Abstract
This document defines a YANG data model and associated mechanisms
enabling subscriber-specific subscriptions to a publisher's event
streams. Applying these elements allows a subscriber to request for
and receive a continuous, custom feed of publisher generated
information.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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 October 28, 2018.
Copyright Notice
Copyright (c) 2018 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
(https://trustee.ietf.org/license-info) in effect on the date of
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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 . . . . . . . . . . . . . . . . . . . . 5
1.4. Relationship to RFC-5277 . . . . . . . . . . . . . . . . 6
2. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1. Event Streams . . . . . . . . . . . . . . . . . . . . . . 7
2.2. Event Stream Filters . . . . . . . . . . . . . . . . . . 8
2.3. QoS . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.4. Dynamic Subscriptions . . . . . . . . . . . . . . . . . . 9
2.5. Configured Subscriptions . . . . . . . . . . . . . . . . 17
2.6. Event Record Delivery . . . . . . . . . . . . . . . . . . 24
2.7. Subscription State Notifications . . . . . . . . . . . . 25
2.8. Subscription Monitoring . . . . . . . . . . . . . . . . . 30
2.9. Advertisement . . . . . . . . . . . . . . . . . . . . . . 31
3. YANG Data Model Trees . . . . . . . . . . . . . . . . . . . . 31
3.1. Event Streams Container . . . . . . . . . . . . . . . . . 31
3.2. Filters Container . . . . . . . . . . . . . . . . . . . . 32
3.3. Subscriptions Container . . . . . . . . . . . . . . . . . 32
4. Data Model . . . . . . . . . . . . . . . . . . . . . . . . . 33
5. Considerations . . . . . . . . . . . . . . . . . . . . . . . 60
5.1. Implementation Considerations . . . . . . . . . . . . . . 60
5.2. IANA Considerations . . . . . . . . . . . . . . . . . . . 60
5.3. Transport Considerations . . . . . . . . . . . . . . . . 61
5.4. Security Considerations . . . . . . . . . . . . . . . . . 61
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 64
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 64
7.1. Normative References . . . . . . . . . . . . . . . . . . 64
7.2. Informative References . . . . . . . . . . . . . . . . . 66
Appendix A. Changes between revisions . . . . . . . . . . . . . 67
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 71
1. Introduction
This document defines a YANG data model and associated mechanisms
enabling subscriber-specific subscriptions to a publisher's event
streams. Effectively this enables a 'subscribe then publish'
capability where the customized information needs and access
permissions of each target receiver are understood by the publisher
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before subscribed event records are marshaled and pushed. The
receiver then gets a continuous, custom feed of publisher generated
information.
While the functionality defined in this document is transport-
agnostic, transports like NETCONF [RFC6241] or RESTCONF [RFC8040] can
be used to configure or dynamically signal subscriptions, and there
are bindings defined for subscribed event record delivery for NETCONF
within [I-D.draft-ietf-netconf-netconf-event-notifications], and for
HTTP2 or HTTP1.1 within [I-D.draft-ietf-netconf-restconf-notif].
The YANG model in this document conforms to the Network Management
Datastore Architecture defined in [RFC8342].
1.1. Motivation
Various limitations in [RFC5277] are discussed in [RFC7923].
Resolving these issues is the primary motivation for this work. Key
capabilities supported by this document include:
o multiple subscriptions on a single transport session
o support for dynamic and configured subscriptions
o modification of an existing subscription in progress
o per-subscription operational counters
o negotiation of subscription parameters (through the use of hints
returned as part of declined subscription requests)
o subscription state change notifications (e.g., publisher driven
suspension, parameter modification)
o independence from transport
1.2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Configuration: defined in [RFC8342].
Configuration datastore: defined in [RFC8342].
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Configured subscription: A subscription installed via configuration
into a configuration datastore.
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. Examples
include a configuration change, a fault, a change in status, crossing
a threshold, or an external input to the system.
Event occurrence time: a timestamp matching the time an originating
process identified as when an event happened.
Event record: A set of information detailing an event.
Event stream: A continuous, chronologically ordered set of events
aggregated under some context.
Event stream filter: Evaluation criteria which may be applied against
event records within an event stream. Event records pass the filter
when specified criteria are met.
Notification message: Information intended for a receiver indicating
that one or more event(s) have occurred.
Publisher: An entity responsible for streaming notification messages
per the terms of a subscription.
Receiver: A target to which a publisher pushes subscribed event
records. For dynamic subscriptions, the receiver and subscriber are
the same entity.
Subscriber: An entity able to request and negotiate a contract for
the generation and push of event records from a publisher. For
dynamic subscriptions, the receiver and subscriber are the same
entity.
Subscription: A contract with a publisher, stipulating which
information one or more receivers wish to have pushed from the
publisher without the need for further solicitation.
All YANG tree diagrams used in this document follow the notation
defined in [I-D.ietf-netmod-yang-tree-diagrams].
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1.3. Solution Overview
This document describes a transport agnostic mechanism for
subscribing to and receiving content from an event stream within a
publisher. This mechanism is through the use of a subscription.
Two types of subscriptions are supported:
1. Dynamic subscriptions, where a subscriber initiates a
subscription negotiation with a publisher via an RPC. If the
publisher is able to serve this request, it accepts it, and then
starts pushing notification messages back to the subscriber. If
the publisher is not able to serve it as requested, then an error
response is returned. This response MAY include hints at
subscription parameters that, had they been present, would have
enabled the dynamic subscription request to be accepted.
2. Configured subscriptions, which allow the management of
subscriptions via a configuration so that a publisher can send
notification messages to configured receiver(s). Support for
configured subscriptions is optional, with its availability
advertised via a YANG feature.
Additional characteristics differentiating configured from dynamic
subscriptions include:
o The lifetime of a dynamic subscription is bound by the transport
session used to establish it. For connection-oriented stateful
transports like NETCONF, the loss of the transport session will
result in the immediate termination of any associated dynamic
subscriptions. For connectionless or stateless transports like
HTTP, a lack of receipt acknowledgment of a sequential set of
notification messages and/or keep-alives can be used to trigger a
termination of a dynamic subscription. Contrast this to the
lifetime of a configured subscription. This lifetime is driven by
relevant configuration being present within the publisher's
applied configuration. Being tied to configuration operations
implies configured subscriptions can be configured to persist
across reboots, and implies a configured subscription can persist
even when its publisher is fully disconnected from any network.
o Configured subscriptions can be modified by any configuration
client with write permission on the configuration of the
subscription. Dynamic subscriptions can only be modified via an
RPC request made by the original subscriber, or a change to
configuration data referenced by the subscription.
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Note that there is no mixing-and-matching of dynamic and configured
operations on a single subscription. Specifically, a configured
subscription cannot be modified or deleted using RPCs defined in this
document. Similarly, a subscription established via RPC cannot be
modified through configuration operations. Also note that transport
specific transport drafts based on this specification MUST detail the
life cycles of both dynamic and configured subscriptions.
A publisher MAY terminate a dynamic subscription at any time.
Similarly, it MAY decide to temporarily suspend the sending of
notification messages for any dynamic subscription, or for one or
more receivers of a configured subscription. Such termination or
suspension is driven by internal considerations of the publisher.
1.4. Relationship to RFC-5277
This document is intended to provide a superset of the subscription
capabilities initially defined within [RFC5277]. Especially when
extending an existing [RFC5277] implementation, it is important to
understand what has been reused and what has been replaced. Key
relationships between these two documents include:
o this document defines a transport independent capability,
[RFC5277] is specific to NETCONF.
o the data model in this document is used instead of the data model
in Section 3.4 of [RFC5277] for the new operations.
o the RPC operations in this draft replaces the operation "create-
subscription" defined in [RFC5277], section 4.
o the one way operation of [RFC5277], Section 4 is used.
o the included contents of the "NETCONF" event stream are identical
between this document and [RFC5277].
o a publisher MAY implement both the Notification Management Schema
and RPCs defined in [RFC5277] and this new document concurrently,
in order to support old clients. However the use of both
alternatives on a single transport session is prohibited.
o unlike [RFC5277], this document enables a single transport session
to intermix of notification messages and RPCs for different
subscriptions.
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2. Solution
Per the overview provided in Section 1.3, this section details the
overall context, state machines, and subsystems which may be
assembled to allow the subscription of events from a publisher.
2.1. Event Streams
An event stream is a named entity on a publisher which exposes a
continuously updating set of 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 (other than the NETCONF
stream), b) how event records are defined/generated, and c) how event
records are assigned to streams.
There is only one reserved event stream name within this document:
"NETCONF". The "NETCONF" event stream contains all NETCONF XML event
record information supported by the publisher, except for the
subscription state notifications described in Section 2.7. Among
these included NETCONF XML event records are individual YANG 1.1
notifications described in section 7.16 of [RFC7950]. Each of these
YANG 1.1 notifications will be treated as a distinct event record.
Beyond the "NETCONF" stream, implementations MAY define 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 a subscription's
receiver(s) where: (1) a subscription includes the identified stream,
and (2) subscription filtering does not exclude the event record from
that receiver.
Access control permissions may be used to silently exclude event
records from within an event stream for which the receiver has no
read access. As an example of how this might be accomplished, see
[RFC8341] section 3.4.6. Note that per Section 2.7 of this document,
subscription state change notifications are never filtered out.
If no access control permissions are in place for event records on an
event stream, then a receiver MUST be allowed access to all the event
records. If subscriber permissions change during the lifecycle of a
subscription and event stream access is no longer permitted, then the
subscription MUST be terminated.
Event records MUST NOT be delivered to a receiver in a different
order than they were placed onto an event stream.
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2.2. Event Stream Filters
This document defines an extensible filtering mechanism. The filter
itself is a boolean test which is placed on the content of an event
record. A 'false' filtering result causes the event message to be
excluded from delivery to a receiver. A filter never results in
information being stripped from within an event record prior to that
event record being encapsulated within a notification message. The
two optional event stream filtering syntaxes supported are [XPATH]
and subtree [RFC6241].
If no event stream filter is provided within a subscription, all
event records on an event stream are to be sent.
2.3. QoS
This document provide for several QoS parameters. These parameters
indicate the treatment of a subscription relative to other traffic
between publisher and receiver. Included are:
o A "dscp" marking to differentiate prioritization of notification
messages during network transit.
o A "weighting" so that bandwidth proportional to this weighting can
be allocated to this subscription relative to other subscriptions
destined for that receiver.
o a "dependency" upon another subscription.
If the publisher supports the "dscp" feature, then a subscription
with a "dscp" leaf MUST result in a corresponding [RFC2474] DSCP
marking being placed within the IP header of any resulting
notification messages and subscription state change notifications.
For the "weighting" parameter, when concurrently dequeuing
notification messages from multiple subscriptions to a receiver, the
publisher MUST allocate bandwidth to each subscription proportionally
to the weights assigned to those subscriptions. "Weighting" is an
optional capability of the publisher; support for it is identified
via the "QoS" feature.
If a subscription has the "dependency" parameter set, then any
buffered notification messages containing event records selected by
the parent subscription MUST be dequeued prior to the notification
messages of the dependent subscription. If notification messages
have dependencies on each other, the notification message queued the
longest MUST go first. If a "dependency" included within an RPC
references a subscription which does not exist or is no longer
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accessible to that subscriber, that "dependency" MUST be silently
removed. "Dependency" is an optional capability of the publisher;
support for it is identified via the "QoS" feature.
2.4. Dynamic Subscriptions
Dynamic subscriptions are managed via protocol operations (in the
form of [RFC7950], Section 7.14 RPCs) made against targets located
within the publisher. These RPCs have been designed extensibly so
that they may be augmented for subscription targets beyond event
streams. For examples of such augmentations, see the RPC
augmentations within [I-D.ietf-netconf-yang-push]'s YANG model.
2.4.1. Dynamic Subscription State Model
Below is the publisher's state machine for a dynamic subscription.
Each state is shown in its own box. It is important to note that
such a subscription doesn't exist at the publisher until an
"establish-subscription" RPC is accepted. The mere request by a
subscriber to establish a subscription is insufficient for that
subscription to be externally visible. States that are reflected in
the YANG model appear in upper-case letters; in addition, start and
end states are depicted to reflect subscription creation and deletion
events.
.........
: start :
:.......:
|
establish-subscription
|
| .-------modify-subscription--------.
v v |
.-----------. .-----------.
.--------. | receiver |--insufficient CPU, b/w-->| receiver |
modify- '| ACTIVE | | SUSPENDED |
subscription | |<----CPU, b/w sufficient--| |
---------->'-----------' '-----------'
| |
delete/kill-subscription delete/kill-
| subscription
v |
......... |
: end :<---------------------------------'
:.......:
Figure 1: Publisher's state for a dynamic subscription
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Of interest in this state machine are the following:
o Successful "establish-subscription" or "modify-subscription" RPCs
put the subscription into the active state.
o Failed "modify-subscription" RPCs will leave the subscription in
its previous state, with no visible change to any streaming
updates.
o A delete or kill RPC will end the subscription, as will the
reaching of a "stop-time".
o A publisher may choose to suspend a subscription when there is
insufficient CPU or bandwidth available to service the
subscription. This is notified to a subscriber with a
"subscription-suspended" state change notification.
o A suspended subscription may be modified by the subscriber (for
example in an attempt to use fewer resources). Successful
modification returns the subscription to an active state.
o Even without a "modify-subscription" request, a publisher may
return a subscription to the active state should the resource
constraints become sufficient again. This is announced to the
subscriber via the "subscription-resumed" subscription state
change notification.
2.4.2. Establishing a Dynamic Subscription
The "establish-subscription" RPC allows a subscriber to request the
creation of a subscription. The transport selected by the subscriber
to reach the publisher MUST be able to support multiple "establish-
subscription" requests made within the same transport session.
The input parameters of the operation are:
o A "stream" name which identifies the targeted event stream against
which the subscription is applied.
o An event stream filter which may reduce the set of event records
pushed.
o Where the transport used by the RPC supports multiple encodings,
an optional "encoding" for the event records pushed. Note: If no
"encoding" is included, the encoding of the RPC MUST be used.
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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" for the subscription. The "start-time"
MUST be in the past and indicates that the subscription is
requesting a replay of previously generated information from the
event stream. For more on replay, see Section 2.4.2.1. Where
there is no "start-time", the subscription starts immediately.
If the publisher can satisfy the "establish-subscription" request, it
replies with an identifier for the subscription, and then immediately
starts streaming notification messages.
Below is a tree diagram for "establish-subscription". All objects
contained in this tree are described within the included YANG model
within Section 4.
+---x establish-subscription
+---w input
| +---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? <anydata>
| | | | {subtree}?
| | | +--:(stream-xpath-filter)
| | | +---w stream-xpath-filter?
| | | yang:xpath1.0 {xpath}?
| | +---w stream stream-ref
| | +---w replay-start-time? yang:date-and-time
| | {replay}?
| +---w stop-time? yang:date-and-time
| +---w dscp? inet:dscp {dscp}?
| +---w weighting? uint8 {qos}?
| +---w dependency? subscription-id {qos}?
| +---w encoding? encoding
+--ro output
+--ro identifier subscription-id
+--ro replay-start-time-revision? yang:date-and-time
{replay}?
Figure 2: establish-subscription RPC tree diagram
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A publisher MAY reject the "establish-subscription" RPC for many
reasons as described in Section 2.4.6. The contents of the resulting
RPC error response MAY include details on input parameters which if
considered in a subsequent "establish-subscription" RPC, may result
in a successful subscription establishment. Any such hints MUST be
transported within a yang-data "establish-subscription-stream-error-
info" container included within the RPC error response.
yang-data establish-subscription-stream-error-info
+--ro establish-subscription-stream-error-info
+--ro reason? identityref
+--ro filter-failure-hint? string
Figure 3: establish-subscription RPC yang-data tree diagram
2.4.2.1. Requesting a replay of event records
Replay provides the ability to establish a subscription which is also
capable of passing recently generated event records. In other words,
as the subscription initializes itself, it sends any previously
generated content from within the target event stream which meets the
filter and timeframe criteria. The end of these historical event
records is identified via a "replay-completed" state change
notification. Any event records generated since the subscription
establishment may then follow. For a particular subscription, all
event records will be delivered in the order they are placed into the
stream.
Replay is an optional feature which is dependent on an event stream
supporting some form of logging. This document puts no restrictions
on the size or form of the log, where it resides within the
publisher, or when event record entries in the log are purged.
The inclusion of a "replay-start-time" within an "establish-
subscription" RPC indicates a replay request. If the "replay-start-
time" contains a value that is earlier than what a publisher's
retained history supports, then if the subscription is accepted, the
actual publisher's revised start time MUST be set in the returned
"replay-start-time-revision" object.
A "stop-time" parameter may be included in a replay subscription.
For a replay subscription, the "stop-time" MAY be earlier than the
current time, but MUST be later than the "replay-start-time".
If the time the replay starts is later than the time marked within
any event records retained within the replay buffer, then the
publisher MUST send a "replay-completed" notification immediately
after a successful establish-subscription RPC response.
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If an event 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 timeframe available for replay,
subscribers can read the leafs "replay-log-creation-time" and
"replay-log-aged-time". See Figure 18 for the YANG tree, and
Section 4 for the YANG model describing these elements. The actual
size of the replay log at any given time is a publisher specific
matter. Control parameters for the replay log are outside the scope
of this document.
2.4.3. Modifying a Dynamic Subscription
The "modify-subscription" operation permits changing the terms of an
existing dynamic subscription established on that transport session
via "establish-subscription". Dynamic subscriptions can be modified
any number of times. If the publisher accepts the requested
modifications, it acknowledges success to the subscriber, then
immediately starts sending event records based on the new terms.
Subscriptions created by configuration cannot be modified via this
RPC. However configuration may be used to modify objects referenced
by the subscription (such as a referenced filter).
Below is a tree diagram for "modify-subscription". All objects
contained in this tree are described within the included YANG model
within Section 4.
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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? <anydata>
| | {subtree}?
| +--:(stream-xpath-filter)
| +---w stream-xpath-filter?
| yang:xpath1.0 {xpath}?
+---w stop-time? yang:date-and-time
Figure 4: modify-subscription RPC tree diagram
If the publisher accepts the requested modifications on a currently
suspended subscription, the subscription will immediately be resumed
(i.e., the modified subscription is returned to the ACTIVE state.)
The publisher MAY immediately suspend this newly modified
subscription through the "subscription-suspended" notification before
any event records are sent.
If the publisher rejects the RPC request, the subscription remains as
prior to the request. That is, the request has no impact whatsoever.
Rejection of the RPC for any reason is indicated by via RPC error as
described in Section 2.4.6. The contents of such a rejected RPC MAY
include hints on inputs which (if considered) may result in a
successfully modified subscription. These hints MUST be transported
within a yang-data "modify-subscription-stream-error-info" container
inserted into the RPC error response.
Below is a tree diagram for "modify-subscription-RPC-yang-data". All
objects contained in this tree are described within the included YANG
model within Section 4.
yang-data modify-subscription-stream-error-info
+--ro modify-subscription-stream-error-info
+--ro reason? identityref
+--ro filter-failure-hint? string
Figure 5: modify-subscription RPC yang-data tree diagram
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2.4.4. Deleting a Dynamic Subscription
The "delete-subscription" operation permits canceling an existing
subscription established on that transport session. If the publisher
accepts the request, and the publisher has indicated success, the
publisher MUST NOT send any more notification messages for this
subscription. If the delete request matches a known subscription
established on the same transport session, then it MUST be deleted;
otherwise it MUST be rejected with no changes to the publisher.
Below is a tree diagram for "delete-subscription". All objects
contained in this tree are described within the included YANG model
within Section 4.
+---x delete-subscription
+---w input
+---w identifier subscription-id
Figure 6: delete-subscription RPC tree diagram
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 Dynamic Subscription
The "kill-subscription" operation permits an operator to end a
dynamic subscription which is not associated with the transport
session used for the RPC. A publisher MUST terminate any dynamic
subscription identified by 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.
Below is a tree diagram for "kill-subscription". All objects
contained in this tree are described within the included YANG model
within Section 4.
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+---x kill-subscription
+---w input
+---w identifier subscription-id
Figure 7: kill-subscription RPC tree diagram
2.4.6. RPC Failures
Whenever an RPC is unsuccessful, the publisher returns relevant
information as part of the RPC error response. Transport level error
processing MUST be done before RPC error processing described in this
section. In all cases, RPC error information returned will use
existing transport layer RPC structures, such as those seen with
NETCONF in [RFC6241] Appendix A, or with RESTCONF in [RFC8040]
Section 7.1. These structures MUST be able to encode subscription
specific errors identified below and defined within this document's
YANG model.
As a result of this mixture, how subscription errors are encoded
within an RPC error response is transport dependent. Following are
valid errors which can occur for each RPC:
establish-subscription modify-subscription
---------------------- -------------------
dscp-unavailable filter-unsupported
filter-unsupported insufficient-resources
history-unavailable no-such-subscription
insufficient-resources
replay-unsupported
delete-subscription kill-subscription
---------------------- ----------------------
no-such-subscription no-such-subscription
To see a NETCONF based example of an error response from above, see
[I-D.draft-ietf-netconf-netconf-event-notifications], Figure 10.
There is one final set of transport independent RPC error elements
included in the YANG model. These are the following three yang-data
structures for failed event stream subscriptions:
1. "establish-subscription-stream-error-info": This MUST be returned
if an RPC error reason has not been placed elsewhere within the
transport portion of a failed "establish-subscription" RPC
response. This MUST be sent if hints on how to overcome the RPC
error are included.
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2. "modify-subscription-stream-error-info": This MUST be returned if
an RPC error reason has not been placed elsewhere within the
transport portion of a failed "modify-subscription" RPC response.
This MUST be sent if hints on how to overcome the RPC error are
included.
3. "delete-subscription-error-info": This MUST be returned if an RPC
error reason has not been placed elsewhere within the transport
portion of a failed "delete-subscription" or "kill-subscription"
RPC response.
2.5. Configured Subscriptions
A configured subscription is a subscription installed via
configuration. Configured subscriptions may be modified by any
configuration client with the proper permissions. Subscriptions can
be modified or terminated via configuration at any point of their
lifetime.
Configured subscriptions have several characteristics distinguishing
them from dynamic subscriptions:
o persistence across publisher reboots,
o persistence even when transport is unavailable, and
o an ability to send notification messages to more than one receiver
(note that receivers are unaware of the existence of any other
receivers.)
Supporting configured subscriptions is optional and advertised using
the "configured" feature.
In addition to the subscription parameters available to dynamic
subscriptions described in Section 2.4.2, the following additional
parameters are also available to configured subscriptions:
o A "transport" which identifies the transport protocol to use to
connect with all subscription receivers.
o One or more receivers, each with an "address", where each address
is intended as the destination for event records.
o Optional parameters to identify where traffic should egress a
publisher:
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* A "source-interface" which identifies the egress interface to
use from the publisher. Publisher support for this is optional
and advertised using the "interface-designation" feature.
* A "source-address" address, which identifies the IP address to
stamp on notification messages destined for the receiver.
* A "source-vrf" which identifies the VRF on which to reach
receivers. This VRF is a network instance as defined within
[I-D.draft-ietf-rtgwg-ni-model]. Publisher support for VRFs is
optional and advertised using the "supports-vrf" feature.
If none of the above parameters are set, notification messages
MUST egress the publisher's default interface.
A tree diagram describing these parameters is shown in Figure 20
within Section 3.3. All parameters are described within the YANG
model in Section 4.
2.5.1. Configured Subscription State Model
Below is the state machine for a configured subscription on the
publisher. This state machine describes the three states (VALID,
INVALID, and CONCLUDED), as well as the transitions between these
states. Start and end states are depicted to reflect configured
subscription creation and deletion events. The creation or
modification of a configured subscription initiates an evaluation by
the publisher to determine if the subscription is in VALID or INVALID
states. The publisher uses its own criteria in making this
determination. If in the VALID state, the subscription becomes
operational. See (1) in the diagram below.