NETCONF
Internet Engineering Task Force (IETF) E. Voit
Internet-Draft
Request for Comments: 8650 R. Rahman
Intended status:
Category: Standards Track E. Nilsen-Nygaard
Expires: December 13, 2019
ISSN: 2070-1721 Cisco Systems
A. Clemm
Huawei
Futurewei
A. Bierman
YumaWorks
June 11,
November 2019
Dynamic subscription Subscription to YANG Events and Datastores over RESTCONF
draft-ietf-netconf-restconf-notif-15
Abstract
This document provides a RESTCONF binding to the dynamic subscription
capability of both subscribed notifications and YANG-Push.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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(IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid the IETF community. It has
received public review and has been approved for a maximum publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of six months this document, any errata,
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 13, 2019.
https://www.rfc-editor.org/info/rfc8650.
Copyright Notice
Copyright (c) 2019 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
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
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Dynamic Subscriptions . . . . . . . . . . . . . . . . . . . . 3
3.1. Transport Connectivity . . . . . . . . . . . . . . . . . 4
3.2. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 4
3.3. RESTCONF RPCs and HTTP Status Codes . . . . . . . . . . . 4
3.4. Call Flow for Server-Sent Events . . . . . . . . . . . . 7
4. QoS Treatment . . . . . . . . . . . . . . . . . . . . . . . . 9
5. Notification Messages . . . . . . . . . . . . . . . . . . . . 10
6. YANG Tree . . . . . . . . . . . . . . . . . . . . . . . . . . 10
7. YANG module . . . . . . . . . . . . . . . . . . . . . . . . . 10 Module
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
9. Security Considerations . . . . . . . . . . . . . . . . . . . 12
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
11.1.
10.1. Normative References . . . . . . . . . . . . . . . . . . 13
11.2.
10.2. Informative References . . . . . . . . . . . . . . . . . 15
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 16
A.1. Dynamic Subscriptions . . . . . . . . . . . . . . . . . . 16
A.1.1. Establishing Dynamic Subscriptions . . . . . . . . . 16
A.1.2. Modifying Dynamic Subscriptions . . . . . . . . . . . 19
A.1.3. Deleting Dynamic Subscriptions . . . . . . . . . . . 21
A.2. Subscription State Notifications . . . . . . . . . . . . 21
A.2.1. subscription-modified . . . . . . . . . . . . . . . . 22 "subscription-modified"
A.2.2. subscription-completed, subscription-resumed, "subscription-completed", "subscription-resumed",
and
replay-complete . . . . . . . . . . . . . . . . . . . 22 "replay-completed"
A.2.3. subscription-terminated "subscription-terminated" and subscription-suspended . 22
"subscription-suspended"
A.3. Filter Example . . . . . . . . . . . . . . . . . . . . . 23
Appendix B. Changes between revisions . . . . . . . . . . . . . 24
Acknowledgments
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27
1. Introduction
Mechanisms to support event subscription and push YANG-Push are defined in
[I-D.draft-ietf-netconf-subscribed-notifications].
[RFC8639]. Enhancements to
[I-D.draft-ietf-netconf-subscribed-notifications] which [RFC8639] that enable YANG datastore
subscription and push YANG-Push are defined in
[I-D.ietf-netconf-yang-push]. [RFC8641]. This document
provides a transport specification for dynamic subscriptions over
RESTCONF [RFC8040]. Requirements for these mechanisms are captured
in [RFC7923].
The streaming of notifications encapsulating that encapsulate the resulting
information push is done via the mechanism described in section Section 6.3
of [RFC8040].
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.
The following terms use the definitions from
[I-D.draft-ietf-netconf-subscribed-notifications]: [RFC8639]: dynamic
subscription, event stream, notification message, publisher,
receiver, subscriber, and subscription.
Other terms reused include datastore, which is defined in [RFC8342],
and HTTP2 stream HTTP/2 stream, which maps to the definition of "stream" within
[RFC7540], Section 2.
[ note to the RFC Editor - please replace XXXX within this document
with the number of this document ]
3. Dynamic Subscriptions
This section provides specifics on how to establish and maintain
dynamic subscriptions over RESTCONF [RFC8040]. Subscribing to event
streams is accomplished in this way via RPCs defined within
[I-D.draft-ietf-netconf-subscribed-notifications]
[RFC8639], Section 2.4. The RPCs are done via RESTCONF POSTs. YANG
datastore subscription is accomplished via augmentations to
[I-D.draft-ietf-netconf-subscribed-notifications] [RFC8639]
as described within
[I-D.ietf-netconf-yang-push] [RFC8641], Section 4.4.
As described in [RFC8040] Section 6.3, 6.3 of [RFC8040], a GET needs to be made against performed
on a specific URI on the publisher. Subscribers cannot pre-determine predetermine
the URI against which a subscription might exist on a publisher, as
the URI will only exist after the "establish-subscription" RPC has
been accepted. Therefore, the POST for the "establish-subscription"
RPC replaces the GET request for the "location" leaf which that is used in
[RFC8040] to obtain the URI. The subscription URI will be determined
and sent as part of the response to the "establish-subscription" RPC,
and a subsequent GET to this URI will be done in order to start the
flow of notification messages back to the subscriber. A As specified
in Section 2.4.1 of [RFC8639], a subscription does not move to the
active state as per Section 2.4.1. of
[I-D.draft-ietf-netconf-subscribed-notifications] until the GET is received.
3.1. Transport Connectivity
For a dynamic subscription, where when a RESTCONF session doesn't already
exist, a new RESTCONF session is initiated from the subscriber.
As stated in Section 2.1 of [RFC8040], a subscriber MUST establish
the HTTP session over TLS [RFC8446] in order to secure the content in
transit.
Without the involvement of additional protocols, HTTP sessions by
themselves do not allow for a support quick recognition of when the loss of the
communication path has been lost with to the publisher. Where quick recognition of the
loss of a publisher is required, a subscriber SHOULD use a TLS
heartbeat [RFC6520], just from subscriber to publisher, to track HTTP
session continuity.
Loss of the heartbeat MUST result in the teardown of any subscription related
subscription-related TCP sessions between those endpoints being torn down. endpoints. A
subscriber can then attempt to re-establish the dynamic subscription
by using the procedure described in Section 3.4.
3.2. Discovery
Subscribers can learn what which event streams a RESTCONF server supports
by querying the "streams" container of ietf-subscribed-
notification.yang
notifications.yang in
[I-D.draft-ietf-netconf-subscribed-notifications]. [RFC8639]. Support for the "streams" container
of ietf-restconf-monitoring.yang in [RFC8040] is not required. In
the case when the RESTCONF binding specified by this document is used
to convey the "streams" container from ietf-
restconf-monitoring.yang ietf-restconf-monitoring.yang
(i.e., that feature is supported), any event streams contained
therein are also expected to be present in the "streams" container of
ietf-restconf-monitoring.yang.
Subscribers can learn what which datastores a RESTCONF server supports by
following Section 2 of [I-D.draft-ietf-netconf-nmda-restconf]. [RFC8527].
3.3. RESTCONF RPCs and HTTP Status Codes
Specific HTTP responses response codes as defined in [RFC7231] section Section 6 of [RFC7231]
will indicate the result of RESTCONF RPC requests with the publisher.
An HTTP status code of 200 is the proper response to any successful
RPC defined within [I-D.draft-ietf-netconf-subscribed-notifications] [RFC8639] or
[I-D.ietf-netconf-yang-push]. [RFC8641].
If a publisher fails to serve the RPC request for one of the reasons
indicated in [I-D.draft-ietf-netconf-subscribed-notifications] Section 2.4.6 of [RFC8639] or [I-D.ietf-netconf-yang-push] Appendix A, A of [RFC8641],
this will be indicated by an appropriate error code, as shown below,
transported in the HTTP response.
When an HTTP error code is returned, the RPC reply MUST include an
"rpc-error"
<rpc-error> element per [RFC8040] Section 7.1 of [RFC8040] with the following
parameter values:
o
* an "error-type" node of "application".
o
* an "error-tag" node with the whose value being is a string that corresponds to an
identity associated with the error. This "error-tag" will come
from one of two places. Either it places and will correspond to the error identities
either within
[I-D.draft-ietf-netconf-subscribed-notifications] section Section 2.4.6 of [RFC8639] for general subscription errors:
error identity uses error-tag HTTP Code
---------------------- -------------- ---------
dscp-unavailable invalid-value 400
encoding-unsupported invalid-value 400
filter-unsupported invalid-value 400
insufficient-resources resource-denied 409
no-such-subscription invalid-value 404
replay-unsupported operation-not-supported 501
Or this "error-tag" will correspond to the error identities
errors (Table 1) or within
[I-D.ietf-netconf-yang-push] Appendix A.1 of [RFC8641] for
subscription errors specific to YANG datastores:
error identity uses error-tag HTTP Code
---------------------- -------------- ---------
cant-exclude operation-not-supported 501
datastore-not-subscribable invalid-value 400
no-such-subscription-resync invalid-value 404
on-change-unsupported operation-not-supported 501
on-change-sync-unsupported operation-not-supported 501
period-unsupported invalid-value 400
update-too-big too-big 400
sync-too-big too-big 400
unchanging-selection operation-failed 500
o datastores (Table 2).
* an "error-app-tag" node with the whose value being is a string that corresponds
to an identity associated with the error, as defined in [I-D.draft-ietf-netconf-subscribed-notifications] section
Section 2.4.6 of [RFC8639] for general subscriptions, and [I-D.ietf-netconf-yang-push] subscriptions or
Appendix A.1, A.1 of [RFC8641] for datastore subscriptions. subscription errors specific to YANG
datastores. The tag to use depends on the RPC for which the error
occurred. Viable errors for different RPCs are as follows: found in Table 3.
+------------------------+-------------------------+-----------+
| Error identity | Uses "error-tag" | HTTP code |
+========================+=========================+===========+
| dscp-unavailable | invalid-value | 400 |
+------------------------+-------------------------+-----------+
| encoding-unsupported | invalid-value | 400 |
+------------------------+-------------------------+-----------+
| filter-unsupported | invalid-value | 400 |
+------------------------+-------------------------+-----------+
| insufficient-resources | resource-denied | 409 |
+------------------------+-------------------------+-----------+
| no-such-subscription | invalid-value | 404 |
+------------------------+-------------------------+-----------+
| replay-unsupported | operation-not-supported | 501 |
+------------------------+-------------------------+-----------+
Table 1: General Subscription Error Identities and
Associated "error-tag" Use
+-----------------------------+-------------------------+-----------+
| Error identity | Uses "error-tag" | HTTP |
| | | code |
+=============================+=========================+===========+
| cant-include | operation-not-supported | 501 |
+-----------------------------+-------------------------+-----------+
| datastore-not-subscribable | invalid-value | 400 |
+-----------------------------+-------------------------+-----------+
| no-such-subscription-resync | invalid-value | 404 |
+-----------------------------+-------------------------+-----------+
| on-change-unsupported | operation-not-supported | 501 |
+-----------------------------+-------------------------+-----------+
| on-change-sync-unsupported | operation-not-supported | 501 |
+-----------------------------+-------------------------+-----------+
| period-unsupported | invalid-value | 400 |
+-----------------------------+-------------------------+-----------+
| update-too-big | too-big | 400 |
+-----------------------------+-------------------------+-----------+
| sync-too-big | too-big | 400 |
+-----------------------------+-------------------------+-----------+
| unchanging-selection | operation-failed | 500 |
+-----------------------------+-------------------------+-----------+
Table 2: Datastore-Specific Error Identities and Associated
"error-tag" Use
+------------------------+--------------------------------+
| RPC select | Select an identity with a base
---------------------- ------------------------------ |
+========================+================================+
| establish-subscription | establish-subscription-error |
+------------------------+--------------------------------+
| modify-subscription | modify-subscription-error |
+------------------------+--------------------------------+
| delete-subscription | delete-subscription-error |
+------------------------+--------------------------------+
| kill-subscription | delete-subscription-error |
+------------------------+--------------------------------+
| resync-subscription | resync-subscription-error |
+------------------------+--------------------------------+
Table 3: RPC Errors and Associated Error Identities
Each error identity will be inserted as the "error-app-tag" using
JSON encoding following the form <modulename>:<identityname>. An
example of such a valid encoding would be "ietf-subscribed-
notifications:no-such-subscription".
In the case of error responses to an "establish-subscription" or "modify-
subscription" request
"modify-subscription" request, there is the option of including to include an "error-
info"
"error-info" node. This node may contain hints for parameter
settings that might lead to successful RPC requests in the future. Following are
Tables 4 and 5 show the yang-data structures which that may be returned:
establish-subscription returns returned.
+--------------+---------------------------------------------+
| Target: | Return hints in yang-data structure
---------------------- ------------------------------------
target: |
+==============+=============================================+
| event stream | establish-subscription-stream-error-info
target: |
+--------------+---------------------------------------------+
| datastore | establish-subscription-datastore-error-info
modify-subscription returns |
+--------------+---------------------------------------------+
Table 4: Optional "error-info" Node Hints for an
"establish-subscription" Request
+--------------+------------------------------------------+
| Target: | Returns hints in yang-data structure
---------------------- ------------------------------------
target: |
+==============+==========================================+
| event stream | modify-subscription-stream-error-info
target: |
+--------------+------------------------------------------+
| datastore | modify-subscription-datastore-error-info |
+--------------+------------------------------------------+
Table 5: Optional "error-info" Node Hints for an
"modify-subscription" Request
The yang-data included within "error-info" SHOULD NOT include the
optional leaf "reason", as such a leaf would be redundant with
information that is already placed within the "error-app-tag".
In case of an rpc error <rpc-error> as a result of a "delete-subscription", a
"kill-subscription", or a "resync-subscription" request, no
"error-info" "error-
info" needs to be included, as the "subscription-id" is the only RPC
input parameter parameter, and no hints regarding this RPC input parameters
need to be provided.
Note that "error-path" [RFC8040] does not need to be included with
the "rpc-error" <rpc-error> element, as subscription errors are generally
associated with the choice of RPC input parameters.
3.4. Call Flow for Server-Sent Events
The call flow for Server-Sent Events (SSE) is defined in Figure 1.
The logical connections denoted by (a) and (b) can be a TCP
connection or an HTTP2 HTTP/2 stream (if HTTP2 HTTP/2 is used, multiple HTTP2 HTTP/2
streams can be carried in one TCP connection). Requests to
[I-D.draft-ietf-netconf-subscribed-notifications] or
[I-D.ietf-netconf-yang-push] augmented RPCs as
defined in [RFC8639] or [RFC8641] are sent on a connection indicated
by (a). A successful "establish-subscription" will result in an RPC
response returned with both a subscription identifier which that uniquely
identifies a subscription, as well as a URI which that uniquely identifies
the location of subscription on the publisher (b). This URI is
defined via the "uri" leaf in the Data Model data model in Section 7.
An HTTP GET is then sent on a separate logical connection (b) to the
URI on the publisher. This signals the publisher to initiate the
flow of notification messages which that are sent in SSE [W3C-20150203] as
a response to the GET. There cannot be two or more simultaneous GET
requests on a subscription URI: any GET request received while there
is a current GET request on the same URI MUST be rejected with HTTP
error code 409.
As described in [RFC8040] Section 6.4, 6.4 of [RFC8040], RESTCONF servers SHOULD NOT
send the "event" or "id" fields in the SSE event notifications.
+--------------+ +--------------+
| Subscriber | | Publisher |
| | | |
| Logical | | Logical |
| Connection | | Connection |
| (a) (b) | | (a) (b) |
+--------------+ +--------------+
| RESTCONF POST (RPC:establish-subscription) |
|--------------------------------------------->|
| HTTP 200 OK (ID,URI)|
|<---------------------------------------------|
| |HTTP GET (URI) |
| |--------------------------------------------->|
| | HTTP 200 OK|
| |<---------------------------------------------|
| | SSE (notif-message)|
| |<---------------------------------------------|
| RESTCONF POST (RPC:modify-subscription) | |
|--------------------------------------------->| |
| | HTTP 200 OK| |
|<---------------------------------------------| |
| | SSE (subscription-modified)|
| |<------------------------------------------(c)|
| | SSE (notif-message)|
| |<---------------------------------------------|
| RESTCONF POST (RPC:delete-subscription) | |
|--------------------------------------------->| |
| | HTTP 200 OK| |
|<---------------------------------------------| |
| | | |
| | | |
(a) (b) (a) (b)
Figure 1: Dynamic Subscriptions with server-sent events Server-Sent Events
Additional requirements for dynamic subscriptions over SSE include:
o All
* A publisher MUST return all subscription state notifications from a publisher MUST be
returned in a
separate SSE message used by the subscription to which the state
change refers.
o
* Subscription RPCs MUST NOT use the connection currently providing
notification messages for that subscription.
o
* In addition to an RPC response for a "modify-subscription" RPC
traveling over (a), a "subscription-modified" state change
notification MUST be sent within (b). This allows the receiver to
know exactly when, within the stream of events, the new terms of
the subscription have been applied to the notification messages.
See arrow (c).
o
* In addition to any required access permissions (e.g., NACM), Network
Configuration Access Control Model (NACM)), the RPCs
modify-subscription, resync-subscription "modify-
subscription", "resync-subscription", and delete-subscription "delete-subscription"
SHOULD only be allowed by the same RESTCONF username [RFC8040]
which
that invoked establish-subscription. "establish-subscription". Such a restriction
generally serves to preserve users' privacy, but exceptions might
be made for administrators that may need to modify or delete other
users' subscriptions.
o
* The kill-subscription "kill-subscription" RPC can be invoked by any RESTCONF
username with the required administrative permissions.
A publisher MUST terminate a subscription in the following cases:
o
* Receipt of a "delete-subscription" or a "kill-subscription" RPC
for that subscription.
o subscription
* Loss of TLS heartbeat
A publisher MAY terminate a subscription at any time as stated in
[I-D.draft-ietf-netconf-subscribed-notifications]
Section 1.3 of [RFC8639].
4. QoS Treatment
Qos treatment for event streams is described in
[I-D.draft-ietf-netconf-subscribed-notifications] Section 2.3. 2.3 of
[RFC8639]. In addition, if HTTP2 HTTP/2 is used, the publisher MUST:
o take
* Take the "weighting" leaf node in
[I-D.draft-ietf-netconf-subscribed-notifications], [RFC8639] and copy it into the HTTP2
HTTP/2 stream weight, [RFC7540] section 5.3, Section 5.3 of [RFC7540], and
o take
* Take any existing subscription "dependency", as specified by the
"dependency" leaf node in
[I-D.draft-ietf-netconf-subscribed-notifications], [RFC8639], and use the
HTTP2 HTTP/2 stream for
the parent subscription as the HTTP2 HTTP/2 stream
dependency, [RFC7540] section 5.3.1, dependency (as
described in Section 5.3.1 of [RFC7540]) of the dependent
subscription.
o set
* Set the exclusive flag, [RFC7540] section 5.3.1, flag (Section 5.3.1 of [RFC7540]) to 0.
For dynamic subscriptions with the same DSCP Differentiated Services Code
Point (DSCP) value to a specific publisher, it is recommended that
the subscriber sends all URI GET requests on a common HTTP2 HTTP/2 session
(if HTTP2 HTTP/2 is used). Conversely, a subscriber can not cannot use a common HTTP2
HTTP/2 session for subscriptions with different DSCP values.
5. Notification Messages
Notification messages transported over RESTCONF will be encoded
according to [RFC8040], section Section 6.4.
6. YANG Tree
The YANG model module defined in Section 7 has one leaf augmented into that augments three
places
nodes of [I-D.draft-ietf-netconf-subscribed-notifications]. [RFC8639].
module: ietf-restconf-subscribed-notifications
augment /sn:establish-subscription/sn:output:
+--ro uri? inet:uri
augment /sn:subscriptions/sn:subscription:
+--ro uri? inet:uri
augment /sn:subscription-modified:
+--ro uri? inet:uri
7. YANG module Module
This module references
[I-D.draft-ietf-netconf-subscribed-notifications]. [RFC8639].
<CODE BEGINS> file
"ietf-restconf-subscribed-notifications@2019-01-11.yang" "ietf-restconf-subscribed-notifications@2019-10-15.yang"
module ietf-restconf-subscribed-notifications {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:"
+ "ietf-restconf-subscribed-notifications";
prefix rsn;
import ietf-subscribed-notifications {
prefix sn;
}
import ietf-inet-types {
prefix inet;
}
organization
"IETF NETCONF (Network Configuration) Working Group";
contact
"WG Web: <http:/tools.ietf.org/wg/netconf/> <https://datatracker.ietf.org/wg/netconf/>
WG List: <mailto:netconf@ietf.org>
Editor: Eric Voit
<mailto:evoit@cisco.com>
Editor: Alexander Clemm
<mailto:ludwig@clemm.org>
Editor: Reshad Rahman
<mailto:rrahman@cisco.com>";
description
"Defines RESTCONF as a supported transport for subscribed
event notifications.
Copyright (c) 2019 IETF Trust and the persons identified
as authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject to
the license terms contained in, the Simplified BSD License set
forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(https://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC XXXX; 8650; see the
RFC itself for full legal notices.";
revision 2019-01-11 2019-10-15 {
description
"Initial version";
reference
"RFC XXXX: RESTCONF Transport for Event Notifications"; 8650: Dynamic Subscription to YANG Events and Datastores
over RESTCONF";
}
grouping uri {
description
"Provides a reusable description of a URI.";
leaf uri {
type inet:uri;
config false;
description
"Location of a subscription specific subscription-specific URI on the publisher.";
}
}
augment "/sn:establish-subscription/sn:output" {
description
"This augmentation allows RESTCONF specific RESTCONF-specific parameters for a
response to a publisher's subscription request.";
uses uri;
}
augment "/sn:subscriptions/sn:subscription" {
description
"This augmentation allows RESTCONF specific RESTCONF-specific parameters to be
exposed for a subscription.";
uses uri;
}
augment "/sn:subscription-modified" {
description
"This augmentation allows RESTCONF specific RESTCONF-specific parameters to be
included as part of the notification that a subscription has
been modified.";
uses uri;
}
}
<CODE ENDS>
8. IANA Considerations
This document registers the following namespace URI in the "ns"
subregistry of the "IETF XML Registry" [RFC3688]:
URI: urn:ietf:params:xml:ns:yang:ietf-restconf-subscribed-
notifications
urn:ietf:params:xml:ns:yang:ietf-restconf-subscribed-notifications
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-restconf-subscribed-notifications
Namespace: urn:ietf:params:xml:ns:yang:ietf-restconf-subscribed-
notifications
urn:ietf:params:xml:ns:yang:ietf-restconf-subscribed-notifications
Prefix: rsn
Reference: RFC XXXX: RESTCONF Transport for Event Notifications 8650
9. Security Considerations
The YANG module specified in this document defines a schema for data
that is designed to be accessed via network management transports
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 [RFC8446].
The Network Configuration Access Control Model (NACM) [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.
The one new data node introduced in this YANG module may be
considered sensitive or vulnerable in some network environments. It
is thus important to control read access (e.g., via get, get-config,
or notification) to this data nodes. node. These are the subtrees and data
nodes and their sensitivity/vulnerability:
Container: "/subscriptions"
o
* "uri": leaf will show where subscribed resources might be located
on a publisher. Access control must be set so that only someone
with proper access permissions, i.e., the same RESTCONF [RFC8040]
user credentials which that invoked the corresponding "establish-
subscription", has the ability to access this resource.
The subscription URI is implementation specific and is encrypted via
the use of TLS. Therefore, even if an attacker succeeds in guessing
the subscription URI, a RESTCONF username [RFC8040] with the required
administrative permissions must be used to be able to access or
modify that subscription. It is recommended that the subscription
URI values not be easily predictable.
The access permission considerations for the RPCs modify-
subscription, resync-subscription, delete-subscription "modify-
subscription", "resync-subscription", "delete-subscription", and kill-
subscription
"kill-subscription" are described in Section 3.4.
If a buggy or compromised RESTCONF subscriber sends a number of
"establish-subscription" requests, then these subscriptions
accumulate and may use up system resources. In such a situation, the
publisher MAY also suspend or terminate a subset of the active
subscriptions from that RESTCONF subscriber in order to reclaim
resources and preserve normal operation for the other subscriptions.
10. Acknowledgments
We wish to acknowledge the helpful contributions, comments, and
suggestions that were received from: Ambika Prasad Tripathy, Alberto
Gonzalez Prieto, Susan Hares, Tim Jenkins, Balazs Lengyel, Kent
Watsen, Michael Scharf, Guangying Zheng, Martin Bjorklund, Qin Wu and
Robert Wilton.
11. References
11.1.
10.1. 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-21
(work in progress), January 2019.
[I-D.ietf-netconf-yang-push]
Clemm, A., Voit, E., Gonzalez Prieto, A., Prasad Tripathy,
A., Nilsen-Nygaard, E., Bierman, A., and B. Lengyel,
"Subscribing to YANG datastore push updates", draft-ietf-
netconf-yang-push-20 (work in progress), October 2018,
<https://datatracker.ietf.org/doc/
draft-ietf-netconf-yang-push/>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[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>.
[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>.
[RFC6520] Seggelmann, R., Tuexen, M., and M. Williams, "Transport
Layer Security (TLS) and Datagram Transport Layer Security
(DTLS) Heartbeat Extension", RFC 6520,
DOI 10.17487/RFC6520, February 2012,
<https://www.rfc-editor.org/info/rfc6520>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<https://www.rfc-editor.org/info/rfc7540>.
[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>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[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>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[W3C-20150203]
Hickson, I., "Server-Sent Events, World Wide Web
Consortium CR CR-eventsource-20121211", February 2015,
<https://www.w3.org/TR/2015/REC-eventsource-20150203/>.
11.2. Informative References
[I-D.draft-ietf-netconf-netconf-event-notifications]
Clemm, Alexander.,
[RFC8639] Voit, Eric., E., Clemm, A., Gonzalez Prieto, Alberto., A., Nilsen-Nygaard,
E., and A. Tripathy, "NETCONF support for
event notifications", May 2018,
<https://datatracker.ietf.org/doc/
draft-ietf-netconf-netconf-event-notifications/>.
[I-D.draft-ietf-netconf-nmda-restconf]
Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K., "Subscription to YANG Notifications",
RFC 8639, DOI 10.17487/RFC8639, September 2019,
<https://www.rfc-editor.org/info/rfc8639>.
[RFC8641] Clemm, A. and R. Wilton, "RESTCONF Extensions E. Voit, "Subscription to Support the Network
Management YANG Notifications
for Datastore Architecture", April 2018,
<https://datatracker.ietf.org/doc/
draft-ietf-netconf-nmda-restconf/>. Updates", RFC 8641, DOI 10.17487/RFC8641,
September 2019, <https://www.rfc-editor.org/info/rfc8641>.
[W3C-20150203]
Hickson, I., "Server-Sent Events", W3C Recommendation, 3
February 2015,
<https://www.w3.org/TR/2015/REC-eventsource-20150203/>.
Latest version available at <https://www.w3.org/TR/
eventsource/>.
10.2. Informative References
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014,
<https://www.rfc-editor.org/info/rfc7231>.
[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>.
[RFC7951] Lhotka, L., "JSON Encoding of Data Modeled with YANG",
RFC 7951, DOI 10.17487/RFC7951, August 2016,
<https://www.rfc-editor.org/info/rfc7951>.
[RFC8347] Liu, X., Ed., Kyparlis, A., Parikh, R., Lindem, A., and M.
Zhang, "A YANG Data Model for the Virtual Router
Redundancy Protocol (VRRP)", RFC 8347,
DOI 10.17487/RFC8347, March 2018,
<https://www.rfc-editor.org/info/rfc8347>.
[RFC8527] Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
and R. Wilton, "RESTCONF Extensions to Support the Network
Management Datastore Architecture", RFC 8527,
DOI 10.17487/RFC8527, March 2019,
<https://www.rfc-editor.org/info/rfc8527>.
[RFC8640] Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard,
E., and A. Tripathy, "Dynamic Subscription to YANG Events
and Datastores over NETCONF", RFC 8640,
DOI 10.17487/RFC8640, September 2019,
<https://www.rfc-editor.org/info/rfc8640>.
[XPATH] Clark, J. and S. DeRose, "XML Path Language (XPath)
Version 1.0", W3C Recommendation, 16 November 1999,
<http://www.w3.org/TR/1999/REC-xpath-19991116>. Latest
version available at <https://www.w3.org/TR/ xpath/>.
Appendix A. Examples
This section is non-normative. To allow easy comparison, this
section mirrors the functional examples shown with NETCONF over XML
within [I-D.draft-ietf-netconf-netconf-event-notifications]. [RFC8640]. In addition, HTTP2 HTTP/2 vs HTTP1.1 HTTP/1.1 headers are not
shown as the contents of the JSON encoded objects are identical
within.
The subscription URI values used in the examples in this section are
purely illustrative, and are not indicative of the expected usage
which
that is described in Section 9.
The DSCP values are only for example purposes and are all indicated
in decimal since the encoding is JSON [RFC7951].
A.1. Dynamic Subscriptions
A.1.1. Establishing Dynamic Subscriptions
The following figure shows two successful "establish-subscription"
RPC requests as per
[I-D.draft-ietf-netconf-subscribed-notifications]. [RFC8639]. The first request is given a
subscription identifier of 22, and the second, an identifier of 23.
+------------+ +-----------+
| Subscriber | | Publisher |
+------------+ +-----------+
| |
|establish-subscription |
|------------------------------>| (a)
| HTTP 200 OK, id#22, URI#1 |
|<------------------------------| (b)
|GET (URI#1) |
|------------------------------>| (c)
| HTTP 200 OK,notif-mesg (id#22)|
|<------------------------------|
| |
| |
|establish-subscription |
|------------------------------>|
| HTTP 200 OK, id#23, URI#2|
|<------------------------------|
|GET (URI#2) |
|------------------------------>|
| |
| |
| notif-mesg (id#22)|
|<------------------------------|
| HTTP 200 OK,notif-mesg (id#23)|
|<------------------------------|
| |
Figure 2: Multiple subscriptions Subscriptions over RESTCONF/HTTP
To provide examples of the information being transported, example
messages for interactions in Figure 2 are detailed below:
POST /restconf/operations
/ietf-subscribed-notifications:establish-subscription
{
"ietf-subscribed-notifications:input": {
"stream-xpath-filter": "/example-module:foo/",
"stream": "NETCONF",
"dscp": 10
}
}
Figure 3: establish-subscription request "establish-subscription" Request (a)
As the publisher was able to fully satisfy the request, the publisher
sends the subscription identifier of the accepted subscription, subscription and
the URI:
HTTP status code - 200
{
"id": 22,
"uri": "https://example.com/restconf/subscriptions/22"
}
Figure 4: establish-subscription success "establish-subscription" Success (b)
Upon receipt of the successful response, the subscriber does a GET to
the provided URI to start the flow of notification messages. When
the publisher receives this, the subscription is moved to the active
state (c).
GET /restconf/subscriptions/22
Figure 5: establish-subscription subsequent "establish-subscription" Subsequent POST
While not shown in Figure 2, if the publisher had not been able to
fully satisfy the request, or the subscriber has no authorization to
establish the subscription, the publisher would have sent an RPC
error response. For instance, if the "dscp" value of 10 asserted by
the subscriber in Figure 3 proved unacceptable, the publisher may
have returned:
HTTP status code - 400
{ "ietf-restconf:errors" : {
"error" : [
{
"error-type": "application",
"error-tag": "invalid-value",
"error-severity": "error",
"error-app-tag":
"ietf-subscribed-notifications:dscp-unavailable"
}
]
}
}
Figure 6: an unsuccessful establish subscription An Unsuccessful "establish-subscription"
The subscriber can use this information in future attempts to
establish a subscription.
A.1.2. Modifying Dynamic Subscriptions
An existing subscription may be modified. The following exchange
shows a negotiation of such a modification via several exchanges
between a subscriber and a publisher. This negotiation consists of a
failed RPC modification request/response, request/response followed by a successful
one.
+------------+ +-----------+
| Subscriber | | Publisher |
+------------+ +-----------+
| |
| notification message (id#23)|
|<-----------------------------|
| |
|modify-subscription (id#23) |
|----------------------------->| (d)
| HTTP 400 error (with hint)|
|<-----------------------------| (e)
| |
|modify-subscription (id#23) |
|----------------------------->|
| HTTP 200 OK |
|<-----------------------------|
| |
| notif-mesg (id#23)|
|<-----------------------------|
| |
Figure 7: Interaction model Model for successful subscription modification Successful Subscription Modification
If the subscription being modified in Figure 7 is a datastore
subscription as per [I-D.ietf-netconf-yang-push], [RFC8641], the modification request made in (d)
may look like that shown in Figure 8. As can be seen, the
modifications being attempted are the application of a new
xpath XML Path
Language (XPath) filter as well as the setting of a new periodic time
interval.
POST /restconf/operations
/ietf-subscribed-notifications:modify-subscription
{
"ietf-subscribed-notifications:input": {
"id": 23,
"ietf-yang-push:datastore-xpath-filter":
"/example-module:foo/example-module:bar",
"ietf-yang-push:periodic": {
"ietf-yang-push:period": 500
}
}
}
Figure 8: Subscription modification request Modification Request (c)
If the publisher can satisfy both changes, the publisher sends a
positive result for the RPC. If the publisher cannot satisfy either
of the proposed changes, the publisher sends an RPC error response
(e). The following is an example RPC error response for (e) which that
includes a hint. This hint is an alternative time period value which that
might have resulted in a successful modification:
HTTP status code - 400
{ "ietf-restconf:errors" : {
"error" : [
"error-type": "application",
"error-tag": "invalid-value",
"error-severity": "error",
"error-app-tag": "ietf-yang-push:period-unsupported",
"error-info": {
"ietf-yang-push":
"modify-subscription-datastore-error-info": {
"period-hint": 3000
}
}
]
}
}
Figure 9: Modify subscription failure "modify-subscription" Failure with Hint (e)
A.1.3. Deleting Dynamic Subscriptions
The following demonstrates deleting a subscription. This
subscription may have been to either a stream or a datastore.
POST /restconf/operations
/ietf-subscribed-notifications:delete-subscription
{
"delete-subscription": {
"id": "22"
}
}
Figure 10: Delete subscription "delete-subscription" Request
If the publisher can satisfy the request, the publisher replies with
success to the RPC request.
If the publisher cannot satisfy the request, the publisher sends an
error-rpc
<rpc-error> element indicating the modification didn't work.
Figure 11 shows a valid response for an existing valid subscription
identifier, but that subscription identifier was created on a
different transport session:
HTTP status code - 404
{
"ietf-restconf:errors" : {
"error" : [
"error-type": "application",
"error-tag": "invalid-value",
"error-severity": "error",
"error-app-tag":
"ietf-subscribed-notifications:no-such-subscription"
]
}
}
Figure 11: Unsuccessful delete subscription "delete-subscription"
A.2. Subscription State Notifications
A publisher will send subscription state notifications according to
the definitions within
[I-D.draft-ietf-netconf-subscribed-notifications]). [RFC8639].
A.2.1. subscription-modified "subscription-modified"
A "subscription-modified" encoded in JSON would look like:
{
"ietf-restconf:notification" : {
"eventTime": "2007-09-01T10:00:00Z",
"ietf-subscribed-notifications:subscription-modified": {
"id": 39,
"uri": "https://example.com/restconf/subscriptions/22"
"stream-xpath-filter": "/example-module:foo",
"stream": {
"ietf-netconf-subscribed-notifications" : "NETCONF"
}
}
}
}
Figure 12: subscription-modified subscription state notification "subscription-modified" Subscription State Notification
A.2.2. subscription-completed, subscription-resumed, "subscription-completed", "subscription-resumed", and replay-
complete "replay-
completed"
A "subscription-completed" notification would look like:
{
"ietf-restconf:notification" : {
"eventTime": "2007-09-01T10:00:00Z",
"ietf-subscribed-notifications:subscription-completed": {
"id": 39,
}
}
}
Figure 13: subscription-completed notification "subscription-completed" Notification in JSON
The "subscription-resumed" and "replay-complete" are virtually
identical, with "subscription-completed" simply being replaced by
"subscription-resumed" and "replay-complete".
A.2.3. subscription-terminated "subscription-terminated" and subscription-suspended "subscription-suspended"
A "subscription-terminated" would look like:
{
"ietf-restconf:notification" : {
"eventTime": "2007-09-01T10:00:00Z",
"ietf-subscribed-notifications:subscription-terminated": {
"id": 39,
"error-id": "suspension-timeout"
}
}
}
Figure 14: subscription-terminated subscription state notification "subscription-terminated" Subscription State Notification
The "subscription-suspended" is virtually identical, with
"subscription-terminated" simply being replaced by "subscription-
suspended".
A.3. Filter Example
This section provides an example which illustrate that illustrates the method of
filtering event record contents. The example is based on the YANG
notification "vrrp-protocol-error-event" as defined per the ietf-
vrrp.yang module within [RFC8347]. Event records based on this
specification which that are generated by the publisher might appear as:
data: {
data: "ietf-restconf:notification" : {
data: "eventTime" : "2018-09-14T08:22:33.44Z",
data: "ietf-vrrp:vrrp-protocol-error-event" : {
data: "protocol-error-reason" : "checksum-error"
data: }
data: }
data: }
Figure 15: RFC 8347 (VRRP) - Example Notification
Suppose a subscriber wanted to establish a subscription which that only
passes instances of event records where there is a "checksum-error"
as part of a VRRP Virtual Router Redundancy Protocol (VRRP) protocol
event. Also assume the publisher places such event records into the
NETCONF stream. To get a continuous series of matching event
records, the subscriber might request the application of an XPath
filter against the NETCONF stream. An "establish-subscription" RPC
to meet this objective might be:
POST /restconf/operations
/ietf-subscribed-notifications:establish-subscription
{
"ietf-subscribed-notifications:input": {
"stream": "NETCONF",
"stream-xpath-filter":
"/ietf-vrrp:vrrp-protocol-error-event[
protocol-error-reason='checksum-error']/",
}
}
Figure 16: Establishing a subscription error reason Subscription Error Reason via XPath
For more examples of XPath filters, see [XPATH].
Suppose the "establish-subscription" in Figure 16 was accepted. And
suppose later a subscriber decided they wanted to broaden this
subscription cover to all VRRP protocol events (i.e., not just those
with a "checksum error"). The subscriber might attempt to modify the
subscription in a way which that replaces the XPath filter with a subtree
filter which that sends all VRRP protocol events to a subscriber. Such a
"modify-subscription" RPC might look like:
POST /restconf/operations
/ietf-subscribed-notifications:modify-subscription
{
"ietf-subscribed-notifications:input": {
"stream": "NETCONF",
"stream-subtree-filter": {
"/ietf-vrrp:vrrp-protocol-error-event" : {}
}
}
}
Figure 17 17: Example "modify-subscription" RPC
For more examples of subtree filters, see [RFC6241], section 6.4.
Appendix B. Changes between revisions
(To be removed by RFC editor prior to publication)
v14 - v15
o Addressed review comments from Kent.
v13 - v14
o Addressed review comments from IESG.
v12 - v13
o Enhanced "error-tag" values based on SN review.
v11 - v12
o Added text in 3.2 for expected behavior when ietf-restconf-
monitoring.yang is also supported.
o Added section 2 to the reference to draft-ietf-netconf-nmda-
restconf.
o Replaced kill-subscription-error by delete-subscription-error in
section 3.3.
o Clarified vertical lines (a) and (b) in Figure 1 of section 3.4
o Section 3.4, 3rd bullet after Figure 1, replaced "must" with
"MUST".
o Modified text in section 3.4 regarding access to RPCs modify-
subscription, resync-subscription, delete-subscription and kill-
subscription.
o Section 4, first bullet for HTTP2: replaced dscp and priority with
weighting and weight.
o Section 6, added YANG tree diagram and fixed description of the
module.
o Section 7, fixed indentation of module description statement.
o Section 7, in YANG module changed year in copyright statement to
2019.
o Section 8, added text on how server protects access 6.4.
Acknowledgments
We wish to acknowledge the
subscription URI.
o Fixed outdated references and removed unused references.
o Fixed the instances of line too long.
o Fixed example in Figure 3.
v10 - v11
o Per Kent's request, added name attribute to artwork which need to
be extracted
v09 - v10
o Fixed typo for resync.
o Added text wrt RPC permissions helpful contributions, comments, and RESTCONF username.
v08 - v09
o Addressed comments
suggestions that were received during WGLC.
v07 - v08
o Aligned with RESTCONF mechanism.
o YANG model: removed augment of subscription-started, added
restconf transport.
o Tweaked Appendix A.1 to match draft-ietf-netconf-netconf-event-
notifications-13.
o Added Appendix A.3 for filter example.
v06 - v07
o Removed configured subscriptions.
o Subscription identifier renamed to id.
v05 - v06
o JSON examples updated by Reshad.
v04 - v05
o Error mechanisms updated to match embedded RESTCONF mechanisms
o Restructured format and sections of document.
o Added a YANG data model for HTTP specific parameters.
o Mirrored the examples from the NETCONF transport draft to allow
easy comparison.
v03 - v04
o Draft not fully synched to new version of subscribed-notifications
yet.
o References updated
v02 - v03
o Event notification reframed to notification message.
o Tweaks to wording/capitalization/format.
v01 - v02
o Removed sections now redundant with
[I-D.draft-ietf-netconf-subscribed-notifications] and
[I-D.ietf-netconf-yang-push] such as: mechanisms for subscription
maintenance, terminology definitions, stream discovery.
o 3rd party subscriptions are out-of-scope.
o SSE only used with RESTCONF and HTTP1.1 dynamic subscriptions
o Timeframes for event tagging are self-defined.
o Clean-up of wording, references to terminology, section numbers.
v00 - v01
o Removed the ability for more than one subscription to go to a
single HTTP2 stream.
o Updated call flows. Extensively.
o SSE only used with RESTCONF and HTTP1.1 dynamic subscriptions
o HTTP is not used to determine that a receiver has gone silent and
is not Receiving Event Notifications
o Many clean-ups of wording Ambika Prasad Tripathy, Alberto
Gonzalez Prieto, Susan Hares, Tim Jenkins, Balazs Lengyel, Kent
Watsen, Michael Scharf, Guangying Zheng, Martin Bjorklund, Qin Wu,
and terminology Robert Wilton.
Authors' Addresses
Eric Voit
Cisco Systems
Email: evoit@cisco.com
Reshad Rahman
Cisco Systems
Email: rrahman@cisco.com
Einar Nilsen-Nygaard
Cisco Systems
Email: einarnn@cisco.com
Alexander Clemm
Huawei
Futurewei
Email: ludwig@clemm.org
Andy Bierman
YumaWorks
Email: andy@yumaworks.com