Internet Engineering Task Force (IETF) E. Voit

Internet Engineering Task Force (IETF) E. Voit
Request for Comments: 7923 A. Clemm
Category: Informational A. Gonzalez Prieto
ISSN: 2070-1721 Cisco Systems
June 2016

Requirements for Subscription to YANG Datastores

Abstract

This document provides requirements for a service that allows client
applications to subscribe to updates of a YANG datastore. Based on
criteria negotiated as part of a subscription, updates will be pushed
to targeted recipients. Such a capability eliminates the need for
periodic polling of YANG datastores by applications and fills a
functional gap in existing YANG transports (i.e., Network
Configuration Protocol (NETCONF) and RESTCONF). Such a service can
be summarized as a "pub/sub" service for YANG datastore updates.
Beyond a set of basic requirements for the service, various
refinements are addressed. These refinements include: periodicity of
object updates, filtering out of objects underneath a requested a
subtree, and delivery QoS guarantees.

Status of This Memo

This document is not an Internet Standards Track specification; it is
published for informational purposes.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 7841.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7923.

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RFC 7923 YANG Subscription Requirements June 2016

Copyright Notice

Copyright (c) 2016 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
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.

Table of Contents

1. Introduction ....................................................3
2. Business Drivers ................................................3
2.1. Pub/Sub in the Interface to the Routing System (I2RS) ......4
2.2. Pub/Sub Variants on Network Elements .......................5
2.3. Existing Generalized Pub/Sub Implementations ...............6
3. Terminology .....................................................6
4. Requirements ....................................................7
4.1. Assumptions for Subscriber Behavior ........................7
4.2. Subscription Service Requirements ..........................8
4.2.1. General .............................................8
4.2.2. Negotiation .........................................9
4.2.3. Update Distribution ................................10
4.2.4. Transport ..........................................11
4.2.5. Security Requirements ..............................11
4.2.6. Subscription QoS ...................................13
4.2.7. Filtering ..........................................14
4.2.8. Assurance and Monitoring ...........................15
5. Security Considerations ........................................15
6. References .....................................................16
6.1. Normative References ......................................16
6.2. Informative References ....................................16
Acknowledgments ...................................................17
Authors' Addresses ................................................18

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1. Introduction

Applications interacting with YANG datastores require capabilities
beyond the traditional client-server configuration of network
elements. One class of such applications are service-assurance
applications, which must maintain a continuous view of operational
data and state. Another class of applications are security
applications, which must continuously track changes made upon network
elements to ensure compliance with corporate policy.

Periodic fetching of data is not an adequate solution for
applications requiring frequent or prompt updates of remote object
state. Applying polling-based solutions here imposes a load on
networks, devices, and applications. Additionally, polling solutions
are brittle in the face of communication glitches, and have
limitations in their ability to synchronize and calibrate retrieval
intervals across a network. These limitations can be addressed by
including generic object subscription mechanisms within network
elements, and allowing these mechanisms to be applied in the context
of data that is conceptually contained in YANG datastores.

This document aggregates requirements for such subscription from a
variety of deployment scenarios.

2. Business Drivers

For decades, information delivery of current network state has been
accomplished either by fetching from operations interfaces, or via
dedicated, customized networking protocols. With the growth of
centralized orchestration infrastructures, imperative policy
distribution, and YANG's ascent as the dominant data modeling
language for use in programmatic interfaces to network elements, this
mixture of fetch plus custom networking protocols is no longer
sufficient. What is needed is a push mechanism that is able to
deliver object changes as they happen.

These push distribution mechanisms will not replace existing
networking protocols. Instead they will supplement these protocols,
providing different response time, peering, scale, and security
characteristics.

Push solutions will not displace all existing operations
infrastructure needs. And SNMP and MIBs will remain widely deployed
and the de facto choice for many monitoring solutions. But some
functions could be displaced. Arguably the biggest shortcoming of
SNMP for those applications concerns the need to rely on periodic
polling, because it introduces an additional load on the network and
devices, because it is brittle if polling cycles are missed, and

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because it is hard to synchronize and calibrate across a network. If
applications can only use polling type interaction patterns with YANG
datastores, similar issues can be expected.

2.1. Pub/Sub in the Interface to the Routing System (I2RS)

Various documents about the Interface to the Routing System (I2RS)
highlight the need to provide pub/sub capabilities between network
elements. From [RFC7921], there are references throughout the
document beginning in Section 6.2. Some specific examples include:

o Section 7.6 of [RFC7921] provides high-level pub/sub
(notification) guidance.

o Section 6.4.2 of [RFC7921] identifies "subscribing to an
information stream of route changes" and "receiving notifications
about peers coming up or going down".

o Section 6.3 of [RFC7921] notes that when Local Configuration
preempts I2RS, external notification might be necessary.

In addition, [USECASE] has relevant requirements. A small subset
includes:

o L-Data-REQ-12: The I2RS interface should support user
subscriptions to data with the following parameters: push of data
synchronously or asynchronously via registered subscriptions...

o L-DATA-REQ-07: The I2RS interface (protocol and instant messages
(IMs)) should allow a subscriber to select portions of the data
model.

o PI-REQ01: Monitor the available routes installed in the Routing
Information Base (RIB) of each forwarding device, including near
real-time notification of route installation and removal.

o BGP-REQ10: The I2RS client SHOULD be able to instruct the I2RS
agent(s) to notify the I2RS client when the BGP processes on an
associated routing system observe a route change to a specific set
of IP Prefixes and associated prefixes.... The I2RS agent should
be able to notify the client via the publish or subscribe
mechanism.

o IGP-REQ-07: The I2RS interface (protocol and IMs) should support a
mechanism where the I2RS Clients can subscribe to the I2RS Agent's
notification of critical node IGP events.

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o MPLS-LDP-REQ-03: The I2RS Agent notifications should allow an I2RS
client to subscribe to a stream of state changes regarding the LDP
sessions or LDP Label Switched Paths (LSPs) from the I2RS Agent.

o L-Data-REQ-01: I2RS must be able to collect large data sets from
the network with high frequency and resolution, and with minimal
impact to the device's CPU and memory.

Also, Section 7.4.3 of [RFC7922] includes this pub/sub requirement:

o I2RS agents MUST support publishing I2RS trace log information to
that feed as described in [this document]. Subscribers would then
receive a live stream of I2RS interactions in trace log format and
could flexibly choose to do a number of things with the log
messages.

2.2. Pub/Sub Variants on Network Elements

This document is intended to cover requirements beyond I2RS. Looking
at history, there are many examples of switching and routing
protocols that have done explicit or implicit pub/sub in the past.
In addition, new policy notification mechanisms that operate on
switches and routers are being specified now. A small subset of
current and past subscription mechanisms includes:

o Multicast topology establishment is accomplished before any
content delivery is made to endpoints (IGMP, PIM, etc.).

o Secure Automation and Continuous Monitoring (SACM) allows
subscription into devices, which may then push spontaneous changes
in their configured hardware and software [SACMREQ].

o In MPLS VPNs [RFC6513], a Customer Edge router exchanges PIM
control messages before Provider Edge (PE) Routing Adjacencies are
passed [RFC6513].

o After OSPF establishes its adjacencies, Link State Advertisement
will then commence [RFC2328].

Worthy of note in the examples above is the wide variety of
underlying transports. A generalized pub/sub mechanism, therefore
should be structured to support alternative transports. Based on
current I2RS requirements, NETCONF should be the initially supported
transport due to the need for connection-oriented/unicast
communication. Eventual support for multicast and broadcast
subscription update distribution will be needed as well.

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2.3. Existing Generalized Pub/Sub Implementations

TIBCO, RSS, Common Object Request Broker Architecture (CORBA), and
other technologies all show precursor pub/sub technologies. However,
there are new needs (described in Section 4 below) that these
technologies do not serve. We need a new pub/sub technology.

There are at least two widely deployed generalized pub/sub
implementations that come close to current needs: Extensible
Messaging and Presence Protocol (XMPP) [XEP-0060] and Data
Distribution Service (DDS) [OMG-DDS]. Both serve as proof-points
that a highly scalable distributed datastore implementation
connecting millions of edge devices is possible.

Because of these proof-points, we can be comfortable that the
underlying technologies can enable reusable generalized YANG object
distribution. Analysis will need to fully dimension the speed and
scale of such object distribution for various subtree sizes and
transport types.

3. 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 [RFC2119]. Although
this document is not a protocol specification, the use of this
language clarifies the instructions to protocol designers producing
solutions that satisfy the requirements set out in this document.

A Subscriber makes requests for set(s) of YANG object data.

A Publisher is responsible for distributing subscribed YANG object
data per the terms of a subscription. In general, a Publisher is the
owner of the YANG datastore that is subjected to the subscription.

A Receiver is the target to which a Publisher pushes updates. In
general, the Receiver and Subscriber will be the same entity. A
Subscription Service provides subscriptions to Subscribers of YANG
data.

A Subscription Service interacts with the Publisher of the YANG data
as needed to provide the data per the terms of the subscription.

A subscription request for one or more YANG subtrees (including
single leafs) is made by the Subscriber of a Publisher and is
targeted to a Receiver. A subscription may include constraints that
dictate how often or under what conditions YANG information updates
might be sent.

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A subscription is a contract between a Subscription Service and a
Subscriber that stipulates the data to be pushed and the associated
terms.

A datastore is defined in [RFC6241].

An Update provides object changes that have occurred within
subscribed YANG subtree(s). An Update must include the current
status of (data) node instances for which filtering has indicated
they have different status than previously provided. An Update may
include a bundled set of ordered/sequential changes for a given
object that have been made since the last update.

A Filter contains evaluation criteria, which are evaluated against
YANG object(s) within a subscription. There are two types of
Filters: Subtree Filters, which identify selected objects/nodes
published under a target data node, and object element and attribute
Filters where an object should only be published if it has properties
meeting specified Filter criteria.

4. Requirements

Many of the requirements within this section have been adapted from
the XMPP [XEP-0060] and DDS [OMG-DDS] requirements specifications.

4.1. Assumptions for Subscriber Behavior

This document provides requirements for the Subscription Service. It
does not define all the requirements for the Subscriber/Receiver.
However in order to frame the desired behavior of the Subscription
Service, it is important to specify key input constraints.

A Subscriber SHOULD avoid attempting to establish multiple
subscriptions pertaining to the same information, i.e., referring to
the same datastore YANG subtrees.

A Subscriber MAY provide subscription QoS criteria to the
Subscription Service; if the Subscription Service is unable to meet
those criteria, the subscription SHOULD NOT be established.

When a Subscriber and Receiver are the same entity and the transport
session is lost/terminated, the Subscriber MUST re-establish any
subscriptions it previously created via signaling over the transport
session. That is, there is no requirement for the life span of such
signaled subscriptions to extend beyond the life span of the
transport session.

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A Subscriber MUST be able to infer when a Subscription Service is no
longer active and when no more updates are being sent.

A Subscriber MAY check with a Subscription Service to validate the
existence and monitored subtrees of a subscription.

A Subscriber MUST be able to periodically lease and extend the lease
of a subscription from a Subscription Service.

4.2. Subscription Service Requirements

4.2.1. General

A Subscription Service MUST support the ability to create, renew,
time out, and terminate a subscription.

A Subscription Service MUST be able to support and independently
track multiple subscription requests by the same Subscriber.

A Subscription Service MUST be able to support an add/change/delete
of subscriptions to multiple YANG subtrees as part of the same
subscription request.

A Subscription Service MUST support subscriptions against operational
datastores, configuration datastores, or both.

A Subscription Service MUST be able support filtering so that the
subscribed updates under a target node might publish only operational
data, only configuration data, or both.

A subscription MAY include Filters as defined within a subscription
request, therefore the Subscription Service MUST publish only data
nodes that meet the Filter criteria within a subscription.

A Subscription Service MUST support the ability to subscribe to
periodic updates. The subscription period MUST be configurable as
part of the subscription request.

A Subscription Service SHOULD support the ability to subscribe to
updates on-change, i.e., whenever values of subscribed data objects
change.

For on-change updates, the Subscription Service MUST support a
dampening period that needs to be passed before the first or
subsequent on-change updates are sent. The dampening period SHOULD
be configurable as part of the subscription request.

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A Subscription Service MUST allow subscriptions to be monitored.
Specifically, a Subscription Service MUST at a minimum maintain
information about which subscriptions are being serviced, the terms
of those subscriptions (e.g., what data is being subscribed,
associated Filters, update policy -- on change, periodic), and the
overall status of the subscription -- e.g., active or suspended.

A Subscription Service MUST support the termination of a subscription
when requested by the Subscriber.

A Subscription Service SHOULD support the ability to suspend and to
resume a subscription on request of a client.

A Subscription Service MAY at its discretion revoke or suspend an
existing subscription. Reasons may include transitory resource
limitation, credential expiry, failure to reconfirm a subscription,
loss of connectivity with the Receiver, operator command-line
interface (CLI), and/or others. When this occurs, the Subscription
Service MUST notify the Subscriber and update the subscription
status.

A Subscription Service MAY offer the ability to modify a subscription
Filter. If such an ability is offered, the service MUST provide
subscribers with an indication telling at what point the modified
subscription goes into effect.

4.2.2. Negotiation

A Subscription Service MUST be able to negotiate the following terms
of a subscription:

o The policy, i.e., whether updates are on-change or periodic

o The interval, for periodic publication policy

o The on-change policy dampening period (if the on-change policy is
supported)

o Any Filters associated with a subtree subscription

A Subscription Service SHOULD be able to negotiate QoS criteria for a
subscription. Examples of subscription QoS criteria may include
reliability of the Subscription Service, reaction time between a
monitored YANG subtree/object change and a corresponding notification
push, and the Subscription Service's ability to support certain
levels of object liveliness.

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In cases where a subscription request cannot be fulfilled due to
insufficient platform resources, the Subscription Service SHOULD
include within its decline hints on criteria that would have been
acceptable when the subscription request was made. For example, if
periodic updates were requested with update intervals that were too
short for the specified data set, an alternative acceptable interval
period might be returned from the Publisher. If on-change updates
were requested with too aggressive a dampening period, then an
acceptable dampening period may be returned, or alternatively an
indication that only periodic updates are supported for the requested
object(s).

4.2.3. Update Distribution

For on-change updates, the Subscription Service MUST only send deltas
to the object data for which a change occurred. (Otherwise the
subscriber might not know what has actually undergone change.) The
updates for each object MUST include an indication of whether it was
removed, added, or changed.

When a Subscription Service is not able to send updates per its
subscription contract, the subscription MUST notify subscribers and
put the subscription into a state indicating that the subscription
was suspended by the service. When able to resume service,
subscribers need to be notified as well. If unable to resume
service, the Subscription Service MAY terminate the subscription and
notify Subscribers accordingly.

When a subscription with on-change updates is suspended and then
resumed, the first update SHOULD include updates of any changes that
occurred while the subscription was suspended, with the current
value. The Subscription Service MUST provide a clear indication when
this capability is not supported (because in this case, a client
application may have to synchronize state separately).

Multiple objects being pushed to a Subscriber, perhaps from different
subscriptions, SHOULD be bundled together into a single Update.

The sending of an Update MUST NOT be delayed beyond the Push Latency
of any enclosed object changes.

The sending of an Update MUST NOT be delayed beyond the dampening
period of any enclosed object changes.

The sending of an Update MUST NOT occur before the dampening period
expires for any enclosed object changes.

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A Subscription Service MAY, as an option, support a replay capability
so that a set of updates generated during a previous time internal
can be sent to a Receiver.

4.2.4. Transport

It is possible for updates coming from a Subscription Service to be
pushed over different types of transports such as NETCONF, RESTCONF,
and HTTP. Beyond existing transports, this Subscription Service will
be applicable for emerging protocols such as those being defined in
[USECASE]. The need for such transport flexibility drives the
following requirements:

o A Subscription Service SHOULD support different transports.

o A Subscription Service SHOULD support different encodings of a
payload.

o It MUST be possible for Receivers to associate the update with a
specific subscription.

o In the case of connection-oriented transport, when a transport
connection drops, the associated subscription SHOULD be
terminated. It is up the Subscriber to request a new
subscription.

4.2.5. Security Requirements

Some uses of this Subscription Service will push privacy-sensitive
updates and metadata. For privacy-sensitive deployments,
subscription information MUST be bound within secure, encrypted
transport-layer mechanisms. For example, if NETCONF is used as
transport, then [RFC7589] would be a valid option to secure the
transported information. The Subscription Service can also be used
with emerging privacy-sensitive deployment contexts as well. As an
example, deployments based on [USECASE] would apply these
requirements in conjunction with those documented within
[I2RS-ENV-SEC] and [I2RS-PROT-SEC] to secure ephemeral state
information being pushed from a network element.

As part of the subscription establishment, mutual authentication MUST
be used between the Subscriber and the Subscription Service.

Subscribers MUST NOT be able to pose as the original Subscription
Service.

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Versioning of any subscription protocols MUST be supported so that
the capabilities and behaviors expected of specific technology
implementations can be exposed.

A subscription could be used to attempt to retrieve information to
which a client has no authorized access. Therefore, it is important
that data being pushed based on subscriptions is authorized in the
same way that regular data retrieval operations are authorized. Data
being pushed to a client MUST be filtered accordingly, just like if
the data were being retrieved on demand. For Unicast transports, the
NETCONF Authorization Control Model applies.

Additions or changes within a subscribed subtree structure MUST be
validated against authorization methods before subscription updates,
including new subtree information, are pushed.

A loss of authenticated access to the target subtree or node SHOULD
be communicated to the Subscriber.

For any encrypted information exchanges, commensurate strength
security mechanisms MUST be available and SHOULD be used. This
includes all stages of the subscription and update push process.

Subscription requests, including requests to create, terminate,
suspend, and resume subscriptions MUST be properly authorized.

When the Subscriber and Receiver are different, the Receiver MUST be
able to terminate any subscription to it where objects are being
delivered over a Unicast transport.

A Subscription Service SHOULD decline a subscription request if it is
likely to deplete its resources. It is preferable to decline a
subscription when originally requested, rather than having to
terminate it prematurely later.

When the Subscriber and Receiver are different, and when the
underlying transport connection passes credentials as part of
transport establishment, then potentially pushed objects MUST be
excluded from a push update if that object doesn't have read access
visibility for that Receiver.

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4.2.6. Subscription QoS

A Subscription Service SHOULD be able to negotiate the following
subscription QoS parameters with a Subscriber: Dampening,
Reliability, Deadline, and Bundling.

A Subscription Service SHOULD be able to interpret subscription QoS
parameters, and only establish a subscription if it is possible to
meet the QoS needs of the provided QoS parameters.

4.2.6.1. Liveliness

A Subscription Service MUST be able to respond to requests to verify
the Liveliness of a subscription.

A Subscription Service MUST be able to report the currently monitored
Nodes of a subscription.

4.2.6.2. Dampening

A Subscription Service MUST be able to negotiate the minimum time
separation since the previous update before transmitting a subsequent
update for subscription. (Note: this is intended to confine the
visibility of volatility into something digestible by the receiver.)

4.2.6.3. Reliability

A Subscription Service MAY send Updates over Best Effort and Reliable
transports.

4.2.6.4. Coherence

For a particular subscription, every update to a subscribed object
MUST be sent to the Receiver in sequential order.

4.2.6.5. Presentation

The Subscription Service MAY have the ability to bundle a set of
discrete object notifications into a single publishable update for a
subscription. A bundle MAY include information on different Data
Nodes and/or multiple updates about a single Data Node.

For any bundled updates, the Subscription Service MUST provide
information for a Receiver to reconstruct the order and timing of
updates.

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4.2.6.6. Deadline

The Subscription Service MUST be able to push updates at a regular
cadence that corresponds with the Subscriber's specified start and
end timestamps. (Note: the regular cadence can drive one update, a
discrete quantity of updates, or an unbounded set of periodic
updates.)

4.2.6.7. Push Latency

The Subscription Service SHOULD be able to delay Updates on object
push for a configurable period per Subscriber.

It MUST be possible for an administrative entity to determine the
Push latency between object change in a monitored subtree and the
Subscription Service Push of the update transmission.

4.2.6.8. Relative Priority

The Subscription Service SHOULD support the relative prioritization
of subscriptions so that the dequeuing and discarding of push updates
can consider this if there is insufficient bandwidth between the
Publisher and the Receiver.

4.2.7. Filtering

If no filtering criteria are provided, or if filtering criteria are
met, updates for a subscribed object MUST be pushed, subject to the
QoS limits established for the subscription.

It MUST be possible for the Subscription Service to receive Filter(s)
from a Subscriber and apply them to the corresponding object(s)
within a subscription.

It MUST be possible to attach one or more Subtree and/or object
element and attribute Filters to a subscription. Mandatory Filter
types include:

o For character-based object properties, Filter values that are
exactly equal to a provided string, not equal to the string, or
containing a string.

o For numeric object properties, Filter values that are =, !=, <,
<=, >, or >= a provided number.

It SHOULD be possible for Filtering criteria to evaluate more than
one property of a particular subscribed object as well as apply
multiple Filters against a single object.

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It SHOULD be possible to establish query match criteria on additional
objects to be used in conjunction with Filtering criteria on a
subscribed object. (For example, if A has changed and B=1, then Push
A.) Query match capability may be done on objects within the
datastore even if those objects are not included within the
subscription. This of course assumes that the subscriber has read
access to those objects.

For on-change subscription updates, an object MUST pass a Filter
through a Filter if it has changed since the previous update. This
includes if the object has changed multiple times since the last
update, and if the value happens to be the exact same value as the
last one sent.

4.2.8. Assurance and Monitoring

It MUST be possible to fetch the state of a single subscription from
a Subscription Service.

It MUST be possible to fetch the state of all subscriptions of a
particular Subscriber.

It MUST be possible to fetch a list and status of all subscription
requests over a period of time. If there is a failure, some failure
reasons might include:

o Improper security credentials provided to access the target node;

o Target node referenced does not exist;

o Subscription type requested is not available upon the target node;

o Out of resources, or resources not available;

o Incomplete negotiations with the Subscriber.

5. Security Considerations

There are no additional security considerations beyond the
requirements listed in Section 4.2.5.

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6. References

6.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.

[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
<http://www.rfc-editor.org/info/rfc2328>.

[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,
<http://www.rfc-editor.org/info/rfc6241>.

[RFC6513] Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/
BGP IP VPNs", RFC 6513, DOI 10.17487/RFC6513, February
2012, <http://www.rfc-editor.org/info/rfc6513>.

[RFC7589] Badra, M., Luchuk, A., and J. Schoenwaelder, "Using the
NETCONF Protocol over Transport Layer Security (TLS) with
Mutual X.509 Authentication", RFC 7589,
DOI 10.17487/RFC7589, June 2015,
<http://www.rfc-editor.org/info/rfc7589>.

[RFC7921] Atlas, A., Halpern, J., Hares, S., Ward, D., and T.
Nadeau, "An Architecture for the Interface to the Routing
System", RFC 7921, DOI 10.17487/RFC7921, June 2016,
<http://www.rfc-editor.org/info/rfc7921>.

[RFC7922] Clarke, J., Salgueiro, G., and C. Pignataro, "Interface to
the Routing System (I2RS) Traceability: Framework and
Information Model", RFC 7922, DOI 10.17487/RFC7922, June
2016, <http://www.rfc-editor.org/info/rfc7922>.

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6.2. Informative References

[I2RS-ENV-SEC]
Migault, D., Ed., Halpern, J., and S. Hares, "I2RS
Environment Security Requirements", Work in Progress,
draft-ietf-i2rs-security-environment-reqs-01, April 2016.

[I2RS-PROT-SEC]
Hares, S., Migault, D., and J. Halpern, "I2RS Security
Related Requirements", Work in Progress, draft-ietf-i2rs-
protocol-security-requirements-06, May 2016.

[OMG-DDS] Object Management Group (OMG), "Data Distribution Service
for Real-time Systems, Version 1.2", January 2007,
<http://www.omg.org/spec/DDS/1.2/>.

[SACMREQ] Nancy, N. and L. Lorenzin, "Security Automation and
Continuous Monitoring (SACM) Requirements", Work in
Progress, draft-ietf-sacm-requirements-13, March 2016.

[USECASE] Hares, S. and M. Chen, "Summary of I2RS Use Case
Requirements", Work in Progress, draft-ietf-i2rs-usecase-
reqs-summary-02, March 2016.

[XEP-0060] Millard, P., Saint-Andre, P., and R. Meijer, "Publish-
Subscribe", XSF XEP-0060, July 2010,
<http://xmpp.org/extensions/xep-0060.html>.

Voit, et al. Informational [Page 17]

RFC 7923 YANG Subscription Requirements June 2016

Acknowledgments

We wish to acknowledge the helpful contributions, comments, and
suggestions that were received from Ambika Tripathy and Prabhakara
Yellai as well as the helpfulness of related end-to-end system
context info from Nancy Cam Winget, Ken Beck, and David McGrew.

Authors' Addresses

Eric Voit
Cisco Systems

Email: [email protected]

Alexander Clemm
Cisco Systems

Email: [email protected]

Alberto Gonzalez Prieto
Cisco Systems

Email: [email protected]

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