NETCONF E. Voit
Internet-Draft R. Rahman
Intended status: Standards Track E. Nilsen-Nygaard
Expires: August 18, 2019 Cisco Systems
A. Clemm
Huawei
A. Bierman
YumaWorks
February 14, 2019
Dynamic subscription to YANG Events and Datastores over RESTCONF
draft-ietf-netconf-restconf-notif-13
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.
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 August 18, 2019.
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
include Simplified BSD License text as described in Section 4.e of
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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 (SSE) . . . . . . . . . 7
4. QoS Treatment . . . . . . . . . . . . . . . . . . . . . . . . 9
5. Notification Messages . . . . . . . . . . . . . . . . . . . . 10
6. YANG Tree . . . . . . . . . . . . . . . . . . . . . . . . . . 10
7. YANG module . . . . . . . . . . . . . . . . . . . . . . . . . 10
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
9. Security Considerations . . . . . . . . . . . . . . . . . . . 12
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
11.1. Normative References . . . . . . . . . . . . . . . . . . 13
11.2. Informative References . . . . . . . . . . . . . . . . . 15
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 15
A.1. Dynamic Subscriptions . . . . . . . . . . . . . . . . . . 16
A.1.1. Establishing Dynamic Subscriptions . . . . . . . . . 16
A.1.2. Modifying Dynamic Subscriptions . . . . . . . . . . . 18
A.1.3. Deleting Dynamic Subscriptions . . . . . . . . . . . 20
A.2. Subscription State Notifications . . . . . . . . . . . . 21
A.2.1. subscription-modified . . . . . . . . . . . . . . . . 21
A.2.2. subscription-completed, subscription-resumed, and
replay-complete . . . . . . . . . . . . . . . . . . . 22
A.2.3. subscription-terminated and subscription-suspended . 22
A.3. Filter Example . . . . . . . . . . . . . . . . . . . . . 22
Appendix B. Changes between revisions . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27
1. Introduction
Mechanisms to support event subscription and push are defined in
[I-D.draft-ietf-netconf-subscribed-notifications]. Enhancements to
[I-D.draft-ietf-netconf-subscribed-notifications] which enable YANG
datastore subscription and push are defined in
[I-D.ietf-netconf-yang-push]. This document provides a transport
specification for dynamic subscriptions over RESTCONF [RFC8040].
Driving these requirements is [RFC7923].
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The streaming of notifications encapsulating the resulting
information push is done via the mechanism described in section 6.3
of [RFC8040].
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].
The following terms use the definitions from
[I-D.draft-ietf-netconf-subscribed-notifications]: dynamic
subscription, event stream, notification message, publisher,
receiver, subscriber, and subscription.
Other terms reused include datastore, which is defined in [RFC8342],
and HTTP2 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] 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] as described within
[I-D.ietf-netconf-yang-push] Section 4.4.
As described in [RFC8040] Section 6.3, a GET needs to be made against
a specific URI on the publisher. Subscribers cannot pre-determine
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 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 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.
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3.1. Transport Connectivity
For a dynamic subscription, where 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 [RFC5246] in order to secure the content in
transit.
Without the involvement of additional protocols, HTTP sessions by
themselves do not allow for a quick recognition of when the
communication path has been lost with the publisher. Where quick
recognition of the loss of a publisher is required, a subscriber
SHOULD use a TLS heartbeat [RFC6520], just from receiver to
publisher, to track HTTP session continuity.
Loss of the heartbeat MUST result in any subscription related TCP
sessions between those endpoints being torn down. A subscriber can
then attempt to re-establish the dynamic subscription by using the
procedure described in Section 3.
3.2. Discovery
Subscribers can learn what event streams a RESTCONF server supports
by querying the "streams" container of ietf-subscribed-
notification.yang in
[I-D.draft-ietf-netconf-subscribed-notifications]. Support for the
"streams" container of ietf-restconf-monitoring.yang in [RFC8040] is
not required. If it is supported, the event streams which are in the
"streams" container of ietf-subscribed-notifications.yang SHOULD also
be in the "streams" container of ietf-restconf-monitoring.yang.
Subscribers can learn what datastores a RESTCONF server supports by
following Section 2 of [I-D.draft-ietf-netconf-nmda-restconf].
3.3. RESTCONF RPCs and HTTP Status Codes
Specific HTTP responses codes as defined in [RFC7231] section 6 will
indicate the result of RESTCONF RPC requests with publisher. An HTTP
status code of 200 is the proper response to any successful RPC
defined within [I-D.draft-ietf-netconf-subscribed-notifications] or
[I-D.ietf-netconf-yang-push].
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 or [I-D.ietf-netconf-yang-push] Appendix A, this will
be indicated by "406" status code transported in the HTTP response.
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When a "406" status code is returned, the RPC reply MUST include an
"rpc-error" element per [RFC8040] Section 7.1 with the following
parameter values:
o an "error-type" node of "application".
o an "error-tag" node with the value being a string that corresponds
to an identity associated with the error. This "error-tag" will
come from one of two places. Either it will correspond to the
error identities within
[I-D.draft-ietf-netconf-subscribed-notifications] section 2.4.6
for general subscription errors:
error identity uses error-tag
---------------------- --------------
dscp-unavailable invalid-value
encoding-unsupported invalid-value
filter-unsupported invalid-value
insufficient-resources resource-denied
no-such-subscription invalid-value
replay-unsupported operation-not-supported
Or this "error-tag" will correspond to the error identities within
[I-D.ietf-netconf-yang-push] Appendix A.1 for subscription errors
specific to YANG datastores:
error identity uses error-tag
---------------------- --------------
cant-exclude operation-not-supported
datastore-not-subscribable invalid-value
no-such-subscription-resync invalid-value
on-change-unsupported operation-not-supported
on-change-sync-unsupported operation-not-supported
period-unsupported invalid-value
update-too-big too-big
sync-too-big too-big
unchanging-selection operation-failed
o an "error-app-tag" node with the value being a string that
corresponds to an identity associated with the error, as defined
in [I-D.draft-ietf-netconf-subscribed-notifications] section 2.4.6
for general subscriptions, and [I-D.ietf-netconf-yang-push]
Appendix A.1, for datastore subscriptions. The tag to use depends
on the RPC for which the error occurred. Viable errors for
different RPCs are as follows:
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RPC 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
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 case of error responses to an "establish-subscription" or "modify-
subscription" request there is the option of including an "error-
info" node. This node may contain hints for parameter settings that
might lead to successful RPC requests in the future. Following are
the yang-data structures which may be returned:
establish-subscription returns hints in yang-data structure
---------------------- ------------------------------------
target: event stream establish-subscription-stream-error-info
target: datastore establish-subscription-datastore-error-info
modify-subscription returns hints in yang-data structure
---------------------- ------------------------------------
target: event stream modify-subscription-stream-error-info
target: datastore modify-subscription-datastore-error-info
The yang-data included within "error-info" SHOULD NOT include the
optional leaf "error-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 as a result of a "delete-subscription", a
"kill-subscription", or a "resync-subscription" request, no
"error-info" needs to be included, as the "subscription-id" is
the only RPC input 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" element, as subscription errors are generally
associated with the choice of RPC input parameters.
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3.4. Call Flow for Server-Sent Events (SSE)
The call flow is defined in Figure 1. The logical connections
denoted by (a) and (b) can be a TCP connection or an HTTP2 stream
(multiple HTTP2 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 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
uniquely identifies a subscription, as well as a URI which uniquely
identifies the location of subscription on the publisher (b). This
URI is defined via the "uri" leaf the Data Model in Section 7.
An HTTP GET is then sent on a separate logical connection (b) to the
URI on the publisher. This initiates the publisher to initiate the
flow of notification messages which are sent in SSE [W3C-20150203] as
a response to the GET.
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+--------------+ +--------------+
| 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 with server-sent events
Additional requirements for dynamic subscriptions over SSE include:
o 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
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know exactly when 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), RPCs
modify-subscription, resync-subscription and delete-subscription
SHOULD only be allowed by the same RESTCONF username [RFC8040]
which invoked establish-subscription.
o The 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 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
4. QoS Treatment
To meet subscription quality of service promises, the publisher MUST
take any existing subscription "dscp" and apply it to the DSCP
marking in the IP header.
In addition, where HTTP2 transport is available to a notification
message queued for transport to a receiver, the publisher MUST:
o take any existing subscription "priority", as specified by the
"weighting" leaf node in
[I-D.draft-ietf-netconf-subscribed-notifications], and copy it
into the HTTP2 stream weight, [RFC7540] section 5.3, and
o take any existing subscription "dependency", as specified by the
"dependency" leaf node in
[I-D.draft-ietf-netconf-subscribed-notifications], and use the
HTTP2 stream for the parent subscription as the HTTP2 stream
dependency, [RFC7540] section 5.3.1, of the dependent
subscription.
o set the exclusive flag, [RFC7540] section 5.3.1, to 0.
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5. Notification Messages
Notification messages transported over RESTCONF will be encoded
according to [RFC8040], section 6.4.
6. YANG Tree
The YANG model defined in Section 7 has one leaf augmented into three
places of [I-D.draft-ietf-netconf-subscribed-notifications].
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
This module references
[I-D.draft-ietf-netconf-subscribed-notifications].
<CODE BEGINS> file
"ietf-restconf-subscribed-notifications@2019-01-11.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/>
WG List: <mailto:netconf@ietf.org>
Editor: Eric Voit
<mailto:evoit@cisco.com>
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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; see the RFC
itself for full legal notices.";
revision 2019-01-11 {
description
"Initial version";
reference
"RFC XXXX: RESTCONF Transport for Event Notifications";
}
grouping uri {
description
"Provides a reusable description of a URI.";
leaf uri {
type inet:uri;
config false;
description
"Location of a subscription specific URI on the publisher.";
}
}
augment "/sn:establish-subscription/sn:output" {
description
"This augmentation allows RESTCONF specific parameters for a
response to a publisher's subscription request.";
uses uri;
}
augment "/sn:subscriptions/sn:subscription" {
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description
"This augmentation allows RESTCONF specific parameters to be
exposed for a subscription.";
uses uri;
}
augment "/sn:subscription-modified" {
description
"This augmentation allows 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 "IETF XML
Registry" [RFC3688]:
URI: 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
Prefix: rsn
Reference: RFC XXXX: RESTCONF Transport for Event Notifications
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 [RFC5246].
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,
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or notification) to this data nodes. 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, and perhaps even HTTP session 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.
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. 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>.
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[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
DOI 10.17487/RFC3688, January 2004,
<https://www.rfc-editor.org/info/rfc3688>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>.
[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>.
[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>.
[W3C-20150203]
"Server-Sent Events, World Wide Web Consortium CR CR-
eventsource-20121211", February 2015,
<https://www.w3.org/TR/2015/REC-eventsource-20150203/>.
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11.2. Informative References
[I-D.draft-ietf-netconf-netconf-event-notifications]
Clemm, Alexander., Voit, Eric., Gonzalez Prieto, Alberto.,
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.,
and R. Wilton, "RESTCONF Extensions to Support the Network
Management Datastore Architecture", April 2018,
<https://datatracker.ietf.org/doc/
draft-ietf-netconf-nmda-restconf/>.
[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>.
[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>.
[XPATH] Clark, J. and S. DeRose, "XML Path Language (XPath)
Version 1.0", November 1999,
<http://www.w3.org/TR/1999/REC-xpath-19991116>.
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]. In
addition, HTTP2 vs HTTP1.1 headers are not shown as the contents of
the JSON encoded objects are identical within.
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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]. The first request
is given a subscription identifier of 22, 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 over RESTCONF/HTTP
To provide examples of the information being transported, example
messages for interactions in Figure 2 are detailed below:
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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 (a)
As publisher was able to fully satisfy the request, the publisher
sends the subscription identifier of the accepted subscription, and
the URI:
HTTP status code - 200
{
"id": "22",
"uri": "https://example.com/restconf/subscriptions/22"
}
Figure 4: establish-subscription success (b)
Upon receipt of the successful response, the subscriber does a GET
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 POST
While not shown in Figure 2, if the publisher had not been able to
fully satisfy the request, or 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:
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HTTP status code - 406
{ "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
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, followed by a successful
one.
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+------------+ +-----------+
| Subscriber | | Publisher |
+------------+ +-----------+
| |
| notification message (id#23)|
|<-----------------------------|
| |
|modify-subscription (id#23) |
|----------------------------->| (d)
| HTTP 406 error (with hint)|
|<-----------------------------| (e)
| |
|modify-subscription (id#23) |
|----------------------------->|
| HTTP 200 OK |
|<-----------------------------|
| |
| notif-mesg (id#23)|
|<-----------------------------|
| |
Figure 7: Interaction model for successful subscription modification
If the subscription being modified in Figure 7 is a datastore
subscription as per [I-D.ietf-netconf-yang-push], 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 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 (c)
If the publisher can satisfy both changes, the publisher sends a
positive result for the RPC. If the publisher cannot satisfy either
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of the proposed changes, the publisher sends an RPC error response
(e). The following is an example RPC error response for (e) which
includes a hint. This hint is an alternative time period value which
might have resulted in a successful modification:
HTTP status code - 406
{ "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 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
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 element indicating the modification didn't work. Figure 11
shows a valid response for existing valid subscription identifier,
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but that subscription identifier was created on a different transport
session:
HTTP status code - 406
{
"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
A.2. Subscription State Notifications
A publisher will send subscription state notifications according to
the definitions within
[I-D.draft-ietf-netconf-subscribed-notifications]).
A.2.1. 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
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A.2.2. subscription-completed, subscription-resumed, and replay-
complete
A "subscription-completed" would look like:
{
"ietf-restconf:notification" : {
"eventTime": "2007-09-01T10:00:00Z",
"ietf-subscribed-notifications:subscription-completed": {
"id": "39",
}
}
}
Figure 13: 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 and 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
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 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 are generated by the publisher might appear as:
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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 only
passes instances of event records where there is a "checksum-error"
as part of a 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 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 replaces the XPath filter with a subtree
filter which sends all VRRP protocol events to a subscriber. Such a
"modify-subscription" RPC might look like:
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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
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)
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.
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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 to 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 and RESTCONF username.
v08 - v09
o Addressed comments 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
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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.
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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 and terminology
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
Email: ludwig@clemm.org
Andy Bierman
YumaWorks
Email: andy@yumaworks.com
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