Network Working Group A. Clemm
Internet-Draft Huawei - Futurewei Technologies, Inc.
Intended status: Standards Track E. Voit
Expires: April 25, 2019 Cisco Systems
X. Liu
Volta Networks
I. Bryskin
T. Zhou
G. Zheng
Huawei
H. Birkholz
Fraunhofer SIT
October 22, 2018
Smart Filters for Push Updates
draft-clemm-netmod-push-smart-filters-01
Abstract
This document defines a YANG model for Smart Filters for push
updates. Smart Filters allow to filter push updates based on values
of pushed datastore nodes and/or state, such as previous updates.
Smart Filters provide an important building block for service
assurance and network automation.
This revision of the document is intended as a placeholder,
containing the problem statement of draft-clemm-netconf-push-smart-
filters-ps-00 that has recently expired. The YANG model itself still
needs to be defined.
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 April 25, 2019.
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Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Key Words . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Definitions and Acronyms . . . . . . . . . . . . . . . . . . 3
4. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3
5. Smart Filter Data Model . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
8. Normative References . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
YANG-Push [yang-push] allows client applications to subscribe to
continuous datastore updates without needing to poll. YANG-Push
subscriptions allow client applications to select which datastore
nodes are of interest. For this purpose, filters that act as node
selectors are offered. However, what is currently not supported are
filters that filter updates based on values, such as sending updates
only when the value falls within a certain range. Also not supported
are filters that would require additional state, such as sending
updates only when the value exceeds a certain threshold for the first
time but not again until the threshold is cleared. We refer to such
filters as "Smart Filters", with further subcategories of "smart
stateless filters" and "smart stateful filters", respectively.
Smart Filters involve more complex subscription and implementation
semantics than the simple selection filters that are currently
offered as part of YANG-Push. They involve post processing of
updates that goes beyond basic update generation for polling
avoidance and place additional intelligence at the server. Because
of this, Smart Filter functionality was not included in the YANG-Push
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specification, although it was recognized that YANG-Push could be
extended to include such functionality if needed. This is the
purpose of this specification.
Smart Filters facilitate service assurance, because they allow client
applications to focus on "outliers" and updates that signify
exceptions and conditions of interest have the biggest operational
significance. They save network resources by avoiding the need to
stream updates that would be discarded anyway, and allow applications
to scale better since larger networks imply a larger amount of Smart
Filtering operations delegated away from the application to the
network. Smart Filters also facilitate network automation as they
constitute an important ingredient to specify triggers for automated
actions.
2. Key Words
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.
3. Definitions and Acronyms
Datastore node: An instance of management information in a
datastore. Also known as "object".
Smart Filter: A filter that involves some processing, such as
comparing values or differentiating behavior depending on state.
TCA: Threshold Crossing Alert.
YANG-Push: A server capability that allows client applications to
subscribe to network management datastore updates.
4. Problem Statement
YANG-Push provides client applications with the ability to subscribe
to continuous updates from network management datastores, obviating
the need to perform polling and resulting in more robust and
efficient applications. However, many applications do not require
every update, only updates that are of certain interest.
For example, an update concerning interface utilization may be only
needed when a certain utilization level is breached. Sending
continuous updates when utilization is low might divert processing
resources away from updates regarding interfaces whose utilization
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level may reach a critical point that requires attention. Doing so
will require a filter based on an object value. Even sending
continuous updates when utilization is high may be too much and
counterproductive. It may be sufficient to send an update when a
threshold is breached to raise a flag of attention, but then not to
continue sending updates while the condition still persists but
simply let the client application know when the threshold is cleared.
This behavior cannot be accomplished simply by a value-based filter,
but requires additional state to be maintained (so that the server
has a memory whether or not the condition of a breached threshold has
already been reported in prior update cycles).
What is needed are "Smart Filters" that provide the ability to apply
filters based on object values, possibly also state state. Smart
Filters are useful for Service Assurance applications that need to
monitor operational data for values that fall outside normal
operational ranges. They are also useful for network automation, in
which automated actions are automatically triggered based on when
certain events in the network occur while certain conditions hold. A
YANG-Push subscription with a Smart Filter can in effect act as a
source for such events. Combined with an optional check for a
condition when an event is observed, this can serve as the basis of
action triggers.
Smart Filters for Push Updates will provide support for the following
features:
o Support for Smart Filter extensions to YANG-Push subscriptions.
The targeted model takes a "base" YANG-Push subscription and
subjects updates to an additional filtering stage that is based on
value.
o Support for selected stateful filters:
* This includes specifically support for generalized "threshold
crossing alert" filters, or filters that provide an update only
when a datastore node's value passes a filter for the first
time, and not again until the datastore node's value passes a
counter filter. In effect, the support involves attaching
filter and counter filter to a datastore node, including a
switch at the datastore node indicating which filter is in
effect, and providing a distinction in the update which filter
(e.g. onset of clear) was applied.
* It may include additional filters, such a "recent high water
mark" filters that allow to specify a time horizon until the
current high water mark clears. A recent high water mark
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filter sends an update to an object only if its new value is
greater than the last value that had been previously reported.
o In addition to new filters, support for features to make them
easier to use:
* Support for refined on-change update semantics that allow
client to distinguish whether datastore node values were
omitted or included because the datastore node was created or
deleted, or because the datastore node's value fell outside
filter range.
* Support for a heartbeat that indicates that a filter is still
in effect after a longer period of inactivity.
It is easy to conceive of filters that are very smart and powerful
yet also very complex. While filters as defined in YANG-Push may be
a tad too simple for the applications envisioned here, it is
important to keep filters still simple enough to ensure broad
implementation and support by networking devices. The purpose of
Smart Filters defined in this effort is to address the 90% of cases
that can be addressed using 10% of the complexity. Items like the
following will therefore be outside the scope:
o Filters that involve freely programmable logic.
o Filters that aggregate or otherwise process information over time.
An example would be filters that compute an aggregate over a time
series of data (e.g. a datastore node's average or top percentile
value)
o Filters that aggregate or compare values of several datastore
nodes (e.g. the maximum or average from datastore nodes in a
list).
5. Smart Filter Data Model
The following section contains an initial YANG data model for smart
filters. The model is at this point still incomplete and included as
a starting point only. At this point, the model defines a simple
threshold filter. When used with a subscription, objects that meet
the filter criterion (i.e. the threshold comparison) are included in
the update whereas any other object is filtered.
The model will be extended to define a full "smart threshold" model
in a later revision. This will add the feature of a hysteresis
threshold, i.e. a counter threshold that allows to define when a
crossed threshold should be cleared. The value of the hysteresis
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threshold can be set to a lower value than the threshold itself to
avoid unnecessary updates in case of oscillations). It will also add
a notion of state to remember whether a threshold crossing has
already been reported, to avoid repeated inclusion of objects in
updates that remain above their threshold. By including metadata,
clients will be able to distinguish between the violation and the
clearing of thresholds.
The model will furthermore be extended for smart filters that are not
threshold-related, such as the previously mentioned recent high water
marks.
<CODE BEGINS> file "ietf-smart-filter@2018-10-22.yang"
module ietf-smart-filter {
yang-version "1.1";
namespace "urn:ietf:params:xml:ns:yang:ietf-smart-filter";
prefix "sf";
import ietf-yang-types {
prefix yang;
reference
"RFC 6991: Common YANG Data Types";
}
import ietf-subscribed-notifications {
prefix sn;
reference
"draft-ietf-netconf-subscribed-notifications:
Customized Subscriptions to a Publisher's Event Streams
NOTE TO RFC Editor: Please replace above reference to
draft-ietf-netconf-subscribed-notifications with RFC number
when published (i.e. RFC xxxx).";
}
organization "IETF";
contact
"WG Web: <http://tools.ietf.org/wg/netconf/>
WG List: <mailto:netconf@ietf.org>
Editor: Alexander Clemm
<mailto:ludwig@clemm.org>
Editor: Eric Voit
<mailto:evoit@cisco.com>
Editor: Xufeng Liu
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<mailto:xufeng.liu.ietf@gmail.com>
Editor: Igor Bryskin
<mailto:igor.bryskin@huawei.com>
Editor: Tianran Zhou
<mailto:zhoutianran@huawei.com>
Editor: Guangying Zheng
<mailto:zhengguangying@huawei.com>
Editor: Henk Birkholz
<mailto:henk.birkholz@sit.fraunhofer.de>";
description
"This module contains YANG specifications for smart filter.
Copyright (c) 2018 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
draft-clemm-netmod-push-smart-filters-01; see the RFC itself
for full legal notices.
NOTE TO RFC EDITOR: Please replace above reference to
with RFC number when
published (i.e. RFC xxxx).";
revision 2018-10-22 {
description
"Initial revision.
NOTE TO RFC EDITOR:
(1)Please replace the above revision date to
the date of RFC publication when published.
(2) Please replace the date in the file name
(ietf-smart-filter@2018-10-22.yang) to the date of RFC
publication.
(3) Please replace the following reference to
draft-clemm-netmod-push-smart-filters-01 with RFC number when
published (i.e. RFC xxxx).";
reference
"draft-clemm-netmod-push-smart-filters-01";
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}
/*
* IDENTITIES
*/
/* Smart-filter type identities */
identity smart-filter {
description
"A base identity that represents the smart filter types. ";
}
identity smart-filter-threshold {
base smart-filter;
description
"An identity instance based on smart-filter, which support
filter the push data by fix threshold value.";
}
/*
* TYPE DEFINITIONS
*/
typedef sf-op-type {
type enumeration {
enum eq {
description "equal to";
}
enum gt {
description "greater than";
}
enum ge {
description "greater than or equal to";
}
enum lt {
description "less than";
}
enum le {
description "less than or equal to";
}
}
description "A boolean comparator for an object and a data value.
Include: eq, gt, ge, lt, le.";
}
/*
* GROUP DEFINITIONS
*/
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grouping sf-threshold{
description
"the group for threshold filter";
leaf filter-node {
if-feature "sn:xpath";
type yang:xpath1.0;
description
"This parameter contains an XPath expression identifying
the node of the target filter.";
}
leaf threshold-value {
type string;
description "threshold value";
}
leaf op-type {
type sf-op-type;
description "comparison operator";
}
}
//augment statements
augment "/sn:subscriptions/sn:subscription" {
description "add the smart filter container";
container smart-filter {
description "It concludes filter configurations";
choice filter-type {
description
"Select different smart filter";
case threshold-filter {
description
"threshold-filter";
uses sf-threshold;
}
}
}
}
}
<CODE ENDS>
6. IANA Considerations
RFC Ed.: In this section, replace all occurrences of 'XXXX' with the
actual RFC number (and remove this note).
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IANA is requested to assign a new URI from the IETF XML Registry
[RFC3688]. The following URI is suggested:
URI: urn:ietf:params:xml:ns:yang:ietf-smart-filter
Registrant Contact: The IESG.
XML: N/A; the requested URI is an XML namespace.
This document also requests a new YANG module name in the YANG Module
Names registry [RFC7950] with the following suggestion:
name: ietf-ioam
namespace: urn:ietf:params:xml:ns:yang:ietf-smart-filter
prefix: sf
reference: RFC XXXX
7. Security Considerations
The application of Smart Filters requires a certain amount of
processing resources at the server. An attacker could attempt to
attack a server by creating YANG-push subscriptions with a large
number of complex Smart Filters in an attempt to diminish server
resources. Server implementations can guard against such scenarios
in several ways. For one, they can implement NACM in order to
require proper authorization for requests to be made. Second, server
implementations can reject requests made for a a larger number of
Smart Filters than the implementation can reasonably sustain.
8. Normative References
[notif-sub]
Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard,
E., and A. Tripathy, "Custom Subscriptions to a
Publisher's Event Streams", June 2018,
<https://datatracker.ietf.org/doc/
draft-ietf-netconf-subscribed-notifications/>.
[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>.
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[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>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/info/rfc7950>.
[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>.
[RFC8072] Bierman, A., Bjorklund, M., and K. Watsen, "YANG Patch
Media Type", RFC 8072, DOI 10.17487/RFC8072, February
2017, <https://www.rfc-editor.org/info/rfc8072>.
[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>.
[yang-push]
Clemm, A., Voit, E., Gonzalez Prieto, A., Tripathy, A.,
Nilsen-Nygaard, E., Bierman, A., and B. Lengyel,
"Subscribing to YANG datastore push updates", July 2018,
<https://datatracker.ietf.org/doc/
draft-ietf-netconf-yang-push/>.
Authors' Addresses
Alexander Clemm
Huawei - Futurewei Technologies, Inc.
2330 Central Expressway
Santa Clara, CA 95050
USA
Email: ludwig@clemm.org
Eric Voit
Cisco Systems
Email: evoit@cisco.com
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Xufeng Liu
Volta Networks
Email: xufeng.liu.ietf@gmail.com
Igor Bryskin
Huawei
Email: igor.bryskin@huawei.com
Tianran Zhou
Huawei
Email: zhoutianran@huawei.com
Guangying Zheng
Huawei
Email: zhengguangying@huawei.com
Henk Birkholz
Fraunhofer SIT
Email: henk.birkholz@sit.fraunhofer.de
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