| 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
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.
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.
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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.
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.
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 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.
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.
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 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:
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:
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 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
<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";
}
/*
* 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
*/
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>
RFC Ed.: In this section, replace all occurrences of 'XXXX' with the actual RFC number (and remove this note).
IANA is requested to assign a new URI from the IETF XML Registry. 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 with the following suggestion:
name: ietf-ioam
namespace: urn:ietf:params:xml:ns:yang:ietf-smart-filter
prefix: sf
reference: RFC XXXX
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.