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Network Working Group                                           A. Clemm
Internet-Draft                     Huawei - Futurewei Technologies, Inc.
Intended status: Informational                                   E. Voit
Expires: January 3, 2019                                   Cisco Systems
                                                                  X. Liu
                                                          Volta Networks
                                                              I. Bryskin
                                                                 T. Zhou
                                                                G. Zheng
                                                             H. Birkholz
                                                          Fraunhofer SIT
                                                            July 2, 2018

                     Smart Filters for Push Updates


   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 January 3, 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
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   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 . . . . . . . . . . . . . . . . . . . . .   5
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

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

2.  Key Words

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "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

   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

   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

   o  Filters that aggregate or compare values of several datastore
      nodes (e.g. the maximum or average from datastore nodes in a

5.  Smart Filter Data Model


6.  IANA Considerations


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

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   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

              Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard,
              E., and A. Tripathy, "Custom Subscriptions to a
              Publisher's Event Streams", June 2018,

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,

   [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,

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,

   [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>.

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   [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>.

              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,

Authors' Addresses

   Alexander Clemm
   Huawei - Futurewei Technologies, Inc.
   2330 Central Expressway
   Santa Clara,  CA 95050

   Email: ludwig@clemm.org

   Eric Voit
   Cisco Systems

   Email: evoit@cisco.com

   Xufeng Liu
   Volta Networks

   Email: xufeng.liu.ietf@gmail.com

   Igor Bryskin

   Email: igor.bryskin@huawei.com

   Tianran Zhou

   Email: zhoutianran@huawei.com

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   Guangying Zheng

   Email: zhengguangying@huawei.com

   Henk Birkholz
   Fraunhofer SIT

   Email: henk.birkholz@sit.fraunhofer.de

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