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Internet Engineering Task Force                             S. D'Antonio
Internet-Draft                                      University of Napoli
Intended status: Standards Track                            "Parthenope"
Expires: December 1, 2013                                       T. Zseby
                                                         CAIDA/FhG FOKUS
                                                                C. Henke
                                          Tektronix Communication Berlin
                                                               L. Peluso
                                                    University of Napoli
                                                            May 30, 2013


                       Flow Selection Techniques
              draft-ietf-ipfix-flow-selection-tech-18.txt

Abstract

   Intermediate Flow Selection Process is the process of selecting a
   subset of Flows from all observed Flows.  The Intermediate Flow
   Selection Process may be located at an IPFIX Exporter, Collector, or
   within an IPFIX Mediator.  It reduces the effort of post-processing
   Flow data and transferring Flow Records.  This document describes
   motivations for using the Intermediate Flow Selection process and
   presents Intermediate Flow Selection techniques.  It provides an
   information model for configuring Intermediate Flow Selection Process
   techniques and discusses what information about an Intermediate Flow
   Selection Process should be exported.

Requirements Language

   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].

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
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   Drafts is at http://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."



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   This Internet-Draft will expire on December 1, 2013.

Copyright Notice

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   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.























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Table of Contents

   1.  Scope  . . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Difference between Intermediate Flow Selection Process and
       Packet Selection . . . . . . . . . . . . . . . . . . . . . . .  8
   4.  Difference between Intermediate Flow Selection Process and
       Intermediate Selection Process . . . . . . . . . . . . . . . .  9
   5.  Intermediate Flow Selection Process within the IPFIX
       Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 10
     5.1.  Intermediate Flow Selection Process in the Metering
           Process  . . . . . . . . . . . . . . . . . . . . . . . . . 12
     5.2.  Intermediate Flow Selection Process in the Exporting
           Process  . . . . . . . . . . . . . . . . . . . . . . . . . 12
     5.3.  Intermediate Flow Selection Process as a function of
           the IPFIX Mediator . . . . . . . . . . . . . . . . . . . . 12
   6.  Intermediate Flow Selection Process Techniques . . . . . . . . 12
     6.1.  Flow Filtering . . . . . . . . . . . . . . . . . . . . . . 13
       6.1.1.  Property Match Filtering . . . . . . . . . . . . . . . 13
       6.1.2.  Hash-based Flow Filtering  . . . . . . . . . . . . . . 14
     6.2.  Flow Sampling  . . . . . . . . . . . . . . . . . . . . . . 14
       6.2.1.  Systematic sampling  . . . . . . . . . . . . . . . . . 14
       6.2.2.  Random Sampling  . . . . . . . . . . . . . . . . . . . 15
     6.3.  Flow-state Dependent Intermediate Flow Selection
           Process  . . . . . . . . . . . . . . . . . . . . . . . . . 15
     6.4.  Flow-state Dependent Packet Selection  . . . . . . . . . . 16
   7.  Configuration of Intermediate Flow Selection Process
       Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     7.1.  Intermediate Flow Selection Process Parameters . . . . . . 18
     7.2.  Description of Flow-state Dependent Packet Selection . . . 20
   8.  Information Model for Intermediate Flow Selection Process
       Configuration and Reporting  . . . . . . . . . . . . . . . . . 21
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 22
     9.1.  Registration of Information Elements . . . . . . . . . . . 22
       9.1.1.  flowSelectorAlgorithm  . . . . . . . . . . . . . . . . 22
       9.1.2.  flowSelectedOctetDeltaCount  . . . . . . . . . . . . . 24
       9.1.3.  flowSelectedPacketDeltaCount . . . . . . . . . . . . . 25
       9.1.4.  flowSelectedFlowDeltaCount . . . . . . . . . . . . . . 25
       9.1.5.  selectorIDTotalFlowsObserved . . . . . . . . . . . . . 25
       9.1.6.  selectorIDTotalFlowsSelected . . . . . . . . . . . . . 26
       9.1.7.  samplingFlowInterval . . . . . . . . . . . . . . . . . 26
       9.1.8.  samplingFlowSpacing  . . . . . . . . . . . . . . . . . 27
       9.1.9.  flowSamplingTimeInterval . . . . . . . . . . . . . . . 27
       9.1.10. flowSamplingTimeSpacing  . . . . . . . . . . . . . . . 27
       9.1.11. hashFlowDomain . . . . . . . . . . . . . . . . . . . . 28
     9.2.  Registration of Object Identifier  . . . . . . . . . . . . 28
   10. Security and Privacy Considerations  . . . . . . . . . . . . . 29
   11. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 30



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   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 31
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 31
     12.2. Informative References . . . . . . . . . . . . . . . . . . 31
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 32















































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1.  Scope

   This document describes Intermediate Flow Selection Process
   techniques for network traffic measurements.  A Flow is defined as a
   set of packets with common properties as described in
   [I-D.ietf-ipfix-protocol-rfc5101bis].  An Intermediate Flow Selection
   Process can be executed to limit the resource demands for capturing,
   storing, exporting and post-processing of Flow Records.  It also can
   be used to select a particular set of Flows that are of interest to a
   specific application.  This document provides a categorization of
   Intermediate Flow Selection Process techniques and describes
   configuration and reporting parameters for them.

   This document also addresses configuration and reporting parameters
   for Flow-state Dependent Packet Selection as described in [RFC5475],
   although this technique is categorized as packet selection.  The
   reason is that Flow-state Dependent Packet Selection techniques often
   aim at the reduction of resources for Flow capturing and Flow
   processing.  Furthermore, these techniques were only briefly
   discussed in [RFC5475].  Therefore configuration and reporting
   considerations for Flow-state Dependent Packet Selection techniques
   have been included in this document.


2.  Terminology

   This document is consistent with the terminology introduced in
   [I-D.ietf-ipfix-protocol-rfc5101bis], [RFC5470], [RFC5475] and
   [RFC3917].  As in [I-D.ietf-ipfix-protocol-rfc5101bis] and [RFC5476],
   the first letter of each IPFIX-specific and PSAMP-specific term is
   capitalized along with the Intermediate Flow Selection Process
   specific terms defined here.

   * Packet Classification

      Packet Classification is a process by which packets are mapped to
      specific Flow Records based on packet properties or external
      properties (e.g. interface).  The properties (e.g. header
      information, packet content, AS number) make up the Flow Key. In
      case a Flow Record for a specific Flow Key value already exists
      the Flow Record is updated, otherwise a new Flow Record is
      created.

   * Intermediate Flow Selection Process

      An Intermediate Flow Selection Process is an Intermediate Process
      as in [RFC6183] that takes Flow Records as its input and selects a
      subset of this set as its output.  Intermediate Flow Selection



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      Process is a more general concept than Intermediate Selection
      Process as defined in [RFC6183].  While an Intermediate Selection
      Process selects Flow Records from a sequence based upon criteria-
      evaluated Flow Record values and passes only those Flow Records
      that match the criteria, an Intermediate Flow Selection Process
      selects Flow Records using selection criteria applicable to a
      larger set of Flow characteristics and information.

   * Flow Cache

      A Flow Cache is the set of Flow Records.

   * Flow Selection State

      An Intermediate Flow Selection Process maintains state information
      for use by the Flow Selector.  At a given time, the Flow Selection
      State may depend on Flows and packets observed at and before that
      time, as well as other variables.  Examples include:

        (i)   sequence number of packets and accounted Flow Records;

        (ii)  number of selected Flows;

        (iii) number of observed Flows;

        (iv)  current Flow Cache occupancy;

        (v)   Flow specific counters, lower and upper bounds;

        (vi)  Intermediate Flow Selection Process timeout intervals.

   * Flow Selector

      A Flow Selector defines the action of an Intermediate Flow
      Selection Process on a single Flow of its input.  The Flow
      Selector can make use of the following information in order to
      establish whether a Flow has to be selected or not:

        (i)   the content of the Flow Record;

        (ii)  any state information related to the Metering Process or
              Exporting Process;

        (iii) any Flow Selection State that may be maintained by the
              Intermediate Flow Selection Process.

   * Complete Flow




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      A Complete Flow consists of all the packets that enter the
      Intermediate Flow Selection Process within the Flow time-out
      interval, and which belong to the same Flow as defined by the Flow
      definition in [RFC5470].  For this definition only packets that
      arrive at the Intermediate Flow Selection Process are considered.

   * Flow Position

      Flow Position is the position of a Flow Record within the Flow
      Cache.

   * Flow Filtering

      Flow Filtering selects flows based on a deterministic function on
      the Flow Record content, Flow Selection State, external properties
      (e.g. ingress interface) or external events (e.g violated Access
      Control List).  If the relevant parts of the Flow Record content
      can already be observed at packet level (e.g.  Flow Keys from
      packet header fields) Flow Filtering can be performed at packet
      level by Property Match Filtering as described in [RFC5475].

   * Hash-based Flow Filtering

      Hash-based Flow Filtering is a deterministic Flow filter function
      that selects flows based on a Hash Function.  The Hash Function is
      calculated over parts of the Flow Record content or external
      properties which are called the Hash Domain.  If the hash value
      falls into a predefined Hash Selection Range the Flow is selected.

   * Flow-state Dependent Intermediate Flow Selection Process

      Flow-state Dependent Intermediate Flow Selection Process is a
      selection function that selects or drops Flows based on the
      current Flow Selection State.  The selection can be either
      deterministic, random or non-uniform random.

   * Flow-state Dependent Packet Selection

      Flow-state Dependent Packet Selection is a selection function that
      selects or drops packets based on the current Flow Selection
      State.  The selection can be either deterministic, random or non-
      uniform random.  Flow-state Dependent Packet Selection can be used
      to prefer the selection of packets belonging to specific Flows.
      For example the selection probability of packets belonging to
      Flows that are already within the Flow Cache may be higher than
      for packets that have not been recorded yet.

   * Flow Sampling



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      Flow Sampling selects flows based on Flow Record sequence or
      arrival times (e.g. entry in Flow Cache, arrival time at Exporter
      or Mediator).  The selection can be systematic (e.g. every n-th
      Flow) or based on a random function (e.g. select each Flow Record
      with probability p, or randomly select n out of N Flow Records).


3.  Difference between Intermediate Flow Selection Process and Packet
    Selection

   Intermediate Flow Selection Process differs from packet selection
   described in [RFC5475].  Packet selection techniques consider packets
   as the basic element and the parent population consists of all
   packets observed at an Observation Point.  In contrast to this the
   basic elements in Flow selection are the Flows.  The parent
   population consists of all observed Flows and the Intermediate Flow
   Selection Process operates on the Flows.  The major characteristics
   of Intermediate Flow Selection Process are the following:

   -       Intermediate Flow Selection Process takes Flows as basic
           elements.  For packet selection, packets are considered as
           basic elements.

   -       Intermediate Flow Selection Process typically takes place
           after Packet Classification, because the classification rules
           determine to which Flow a packet belongs.  Intermediate Flow
           Selection Process can be performed before Packet
           Classification.  In that case Intermediate Flow Selection
           Process is based on the Flow Key (also on a hash value over
           the Flow Key), but not based on characteristics that are only
           available after Packet Classification (e.g.  Flow size, Flow
           duration).  Packet selection can be applied before and after
           Packet Classification.  As an example, packet selection
           before Packet Classification can be random packet selection
           whereas packet selection after Packet Classification can be
           Flow-state Dependent Packet Selection (as described in
           [RFC5475])

   -       Intermediate Flow Selection Process operates on Complete
           Flows.  That means that after the Intermediate Flow Selection
           Process either all packets of the Flow are kept or all
           packets of the Flow are discarded.  That means that if the
           Intermediate Flow Selection Process is preceded by a packet
           selection process the Complete Flow consists only of the
           packets that were not discarded during the packet selection.

   There are some techniques that are difficult to unambiguously
   categorize into one of the categories.  Here some guidance is given



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   on how to categorize such techniques:

   -       Techniques that can be considered as both packet selection
           and Intermediate Flow Selection Process: some packet
           selection techniques result in the selection of Complete
           Flows and therefore can be considered as packet selection or
           as Intermediate Flow Selection Process at the same time.  An
           example is Property Match Filtering of all packets to a
           specific destination address.  If Flows are defined based on
           destination addresses, such a packet selection also results
           in a Intermediate Flow Selection Process and can be
           considered as packet selection or Intermediate Flow Selection
           Process.

   -       Flow-state Dependent Packet Selection: there exist techniques
           that select packets based on the Flow state, e.g. based on
           the number of already observed packets belonging to the Flow.
           Examples of these techniques from the literature are "Sample
           and Hold" [EsVa01] "Fast Filtered Sampling" [MSZC10] or the
           "Sticky Sampling" algorithm presented in [MaMo02].  Such
           techniques can be used to influence which Flows are captured
           (e.g. increase the selection of packets belonging to large
           Flows) and reduce the number of Flows that need to be stored
           in the Flow Cache.  Nevertheless, such techniques do not
           necessarily select Complete Flows, because they do not ensure
           that all packets of a selected Flow are captured.  Therefore
           Flow-state Dependent Packet Selection techniques that do not
           ensure that either all or no packets of a Flow are selected
           strictly speaking have to be considered as packet selection
           techniques and not as Intermediate Flow Selection Process
           techniques.


4.  Difference between Intermediate Flow Selection Process and
    Intermediate Selection Process

   Intermediate Flow Selection Process differs from Intermediate
   Selection Process since Intermediate Flow Selection Process uses
   selection criteria that apply to a larger set of Flow information and
   properties than those used by Intermediate Selection Process.  The
   typical function of an Intermediate Selection Process is Property
   Match Filtering that selects a Flow Record if the value of a specific
   field in the Flow Record matches a configured value or falls within a
   configured range.  This means that the selection criteria used by an
   Intermediate Selection Process are evaluated only on Flow Record
   values.  An Intermediate Flow Selection Process makes its decision on
   whether a Flow has to be selected or not by taking into account not
   only information related to the content of the Flow Record, but also



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   any Flow Selection State information or variable that can be used to
   select Flows in order to meet applications requirements or resource
   constraints (e.g.  Flow Cache occupancy, export link capacity).
   Examples are as flow counters, Intermediate Flow Selection Process
   timeout intervals, and Flow Record time information.


5.  Intermediate Flow Selection Process within the IPFIX Architecture

   An Intermediate Flow Selection Process can be deployed at any of
   three places within the IPFIX architecture.  As shown in Figure 1
   Intermediate Flow Selection Process can occur

   1.  in the Metering Process at the IPFIX Exporter

   2.  in the Exporting Process at the Collector

   3.  within a Mediator

































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      +===========================================+
      |  IPFIX Exporter        +----------------+ |
      |                        | Metering Proc. | |
      | +-----------------+    +----------------+ |
      | |    Metering     |    |  Intermediate  | |
      | |    Process      | or | Flow Selection | |
      | |                 |    |     Process    | |
      | +-----------------+----+----------------+ |
      | |           Exporting Process           | |
      | +----|-------------------------------|--+ |
      +======|===============================|====+
             |                               |
             |                               |
      +======|========================+      |
      |      |  Mediator              |      |
      |    +-V-------------------+    |      |
      |    | Collecting Process  |    |      |
      |    +---------------------+    |      |
      |    | Intermediate Flow   |    |      |
      |    | Selection Process   |    |      |
      |    +---------------------+    |      |
      |    |  Exporting Process  |    |      |
      |    +-|-------------------+    |      |
      +======|========================+      |
             |                               |
             |                               |
      +======|===============================|=====+
      |      |         Collector             |     |
      | +----V-------------------------------V-+   |
      | |         Collecting Process           |   |
      | +--------------------------------------+   |
      | | Intermediate Flow Selection Process  |   |
      | +--------------------------------------+   |
      | |           Exporting Process          |   |
      | +------------------------------|-------+   |
      +================================|===========+
                                       |
                                       |
                                       V
                                +------------------+
                                |       IPFIX      |
                                +------------------+

     Figure 1: Potential Intermediate Flow Selection Process locations

   In contrast to packet selection, Intermediate Flow Selection Process
   is always applied after the packets are classified into Flows.




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5.1.  Intermediate Flow Selection Process in the Metering Process

   Intermediate Flow Selection Process in the Metering process uses
   packet information to update the Flow Records in the Flow Cache.
   Intermediate Flow Selection Process before Packet Classification can
   be based on the Flow Key (also on a hash value over the Flow Key),
   but not based on characteristics that are only available after Packet
   Classification (e.g.  Flow size, Flow duration).  An Intermediate
   Flow Selection Process is here applied to reduce resources for all
   succeeding processes or to select specific Flows of interest in case
   such Flow characteristics are already observable at packet level
   (e.g.  Flows to specific IP addresses).  In contrast, Flow-state
   Dependent Packet Selection is a packet selection technique, because
   it does not necessarily select Complete Flows.

5.2.  Intermediate Flow Selection Process in the Exporting Process

   Intermediate Flow Selection Process in the Exporting Process works on
   Flow Records.  An Intermediate Flow Selection Process in the
   Exporting Process can therefore depend on Flow characteristics that
   are only visible after the classification of packets, such as Flow
   size and Flow duration.  The Exporting Process may implement policies
   for exporting only a subset of the Flow Records which have been
   stored in the system memory in order to unload Flow export and Flow
   post-processing.  An Intermediate Flow Selection Process in the
   Exporting Process may select only the subset of Flow Records which
   are of interest to the users application, or select only as many Flow
   Records as can be handled by the available resources (e.g. limited
   export link capacity).

5.3.  Intermediate Flow Selection Process as a function of the IPFIX
      Mediator

   As shown in Figure 1, Intermediate Flow Selection Process can be
   performed within an IPFIX Mediator [RFC6183].  The Intermediate Flow
   Selection Process takes Flow Record stream as its input and selects
   Flow Records from a sequence based upon criteria-evaluated record
   values.  The Intermediate Flow Selection Process can again apply an
   Intermediate Flow Selection Process technique to obtain Flows of
   interest to the application.  Further, the Intermediate Flow
   Selection Process can base its selection decision on the correlation
   of data from different IPFIX Exporters, e.g. by only selecting Flows
   that were at least recorded on two IPFIX Exporters.


6.  Intermediate Flow Selection Process Techniques

   An Intermediate Flow Selection Process technique selects either all



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   or none of the packets of a Flow, otherwise the technique has to be
   considered as packet selection.  A difference is recognized between
   Flow Filtering and Flow Sampling.

6.1.  Flow Filtering

   Flow Filtering is a deterministic function on the IPFIX Flow Record
   content.  If the relevant Flow characteristics are already observable
   at packet level (e.g.  Flow Keys), Flow Filtering can be applied
   before aggregation at packet level.  In order to be compliant with
   IPFIX, at least one of this document's Flow Filtering schemes MUST be
   implemented.

6.1.1.  Property Match Filtering

   Property Match Filtering is performed similarly to Property Match
   Filtering for packet selection described in [RFC5475].  The
   difference is that, instead of packet fields, Flow Record fields are
   here used to derive the selection decision.  Property Match Filtering
   is used to select a specific subset of the Flows that are of interest
   to a particular application (e.g. all Flows to a specific
   destination, all large Flows, etc.).  Properties on which the
   filtering is based can be Flow Keys, Flow Timestamps, or Per-Flow
   Counters described in [RFC5102].  Examples are the Flow size in
   bytes, the number of packets in the Flow, the observation time of the
   first or last packet, or the maximum packet length.  An example of
   Property Match Filtering is to select Flows with more than a
   threshold number of observed octets.  The selection criteria can be a
   specific value, a set of specific values, or an interval.  For
   example, a Flow is selected if destinationIPv4Address and the total
   number of packets of the Flow equal two predefined values.  An
   Intermediate Flow Selection Process using Property Match Filtering in
   the Metering Process relies on properties that are observable at the
   packet level (e.g.  Flow Key).  For example, a Flow is selected if
   sourceIPv4Address and sourceIPv4PrefixLength equal, respectively, two
   specific values.

   An Intermediate Flow Selection Process using Property Match Filtering
   in the Exporting Process is based on properties that are only visible
   after Packet Classification, such as Flow size and Flow duration.  An
   example is the selection of the largest Flows or a percentage of
   Flows with the longest lifetime.  Another example is to select and
   remove from the Flow Cache the Flow Record with the lowest Flow
   volume per current Flow life time, in case the Flow Cache is full.

   An Intermediate Flow Selection Process using Property Match Filtering
   within an IPFIX Mediator selects a Flow Record if the value of a
   specific field in the Flow Record equals a configured value or falls



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   within a configured range [RFC6183].

6.1.2.  Hash-based Flow Filtering

   Hash-based Flow Filtering uses a Hash Function h to map the Flow Key
   c onto a Hash Range R. A Flow is selected if the hash value h(c) is
   within the Hash Selection Range S, which is a subset of R. Hash-based
   Flow Filtering can be used to emulate a random sampling process but
   still enable the correlation between selected Flow subsets at
   different Observation Points.  Hash-based Flow Filtering is similar
   to Hash-based Packet Selection, and in fact is identical when Hash-
   based Packet Selection uses the Flow Key that defines the Flow as the
   hash input.  Nevertheless there may be the incentive to apply Hash-
   based Flow Filtering not on the packet level in the Metering Process,
   for example when the size of the selection range and therefore the
   sampling probability is dependent on the number of observed Flows.
   In case Hash-based Flow Filtering is used to select the same subset
   of flows at different Observation Points, the Hash Domain MUST only
   include parts of the Flow Record content thar are invariant on the
   Flow path.  Also refer to the according Trajectory Sampling
   Application Example on packet level in [RFC5475] that explains the
   hash-based filtering approach on packet level.

6.2.  Flow Sampling

   Flow Sampling operates on Flow Record sequence or arrival times.  It
   can use either a systematic or a random function for the Intermediate
   Flow Selection Process.  Flow Sampling usually aims at the selection
   of a representative subset of all Flows in order to estimate
   characteristics of the whole set (e.g. mean Flow size in the
   network).

6.2.1.  Systematic sampling

   Systematic sampling is a deterministic selection function.
   Systematic sampling may be a periodic selection of the N-th Flow
   Record which arrives at the Intermediate Flow Selection Process.
   Systematic sampling MAY be applied in the Metering Process.  An
   example would be to create, besides the Flow Cache of selected Flows,
   an additional data structure that saves the Flow Keys values of the
   Flows that are not selected.  The selection of a Flow would then be
   based on the first packet of a Flow.  Everytime a packet belonging to
   a new Flow (which is neither in the data structure of the selected or
   not selected Flows) arrives at the Observation Point, a counter is
   increased.  In case the counter is increased to a multiple of N a new
   Flow Cache entry is created, and in case the counter is not a
   multiple of N the Flow Key value is added to the data structure for
   not selected Flows.



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   Systematic sampling can also be time-based.  Time-based systematic
   sampling is applied by only creating Flows that are observed between
   time-based start and stop triggers.  The time interval may be applied
   at packet level in the Metering Process or after aggregation on Flow
   level, e.g. by selecting a Flow arriving at the Exporting Process
   every n seconds.

6.2.2.  Random Sampling

   Random Flow sampling is based on a random process which requires the
   calculation of random numbers.  One can differentiate between n-out-N
   and probabilistic Flow sampling.

6.2.2.1.  n-out-of-N Flow Sampling

   In n-out-of-N Sampling, n elements are selected out of the parent
   population that consists of N elements.  One example would be to
   generate n different random numbers in the range [1,N] and select all
   Flows that have a Flow Position equal to one of the random numbers.

6.2.2.2.  Probabilistic Flow Sampling

   In probabilistic Sampling, the decision whether or not a Flow is
   selected is made in accordance with a predefined selection
   probability.  For probabilistic Sampling, the Sample Size can vary
   for different trials.  The selection probability does not necessarily
   have to be the same for each Flow.  Therefore, a difference is
   recognized between uniform probabilistic sampling (with the same
   selection probability for all Flows) and non-uniform probabilistic
   sampling (where the selection probability can vary for different
   Flows).  For non-uniform probabilistic Flow Sampling the sampling
   probability may be adjusted according to the Flow Record content.  An
   example would be to increase the selection probability of large
   volume Flows over small volume Flows as described in the Smart
   Sampling technique [DuLT01].

6.3.  Flow-state Dependent Intermediate Flow Selection Process

   Flow-state Dependent Intermediate Flow Selection Process can be a
   deterministic or random Intermediate Flow Selection Process based on
   the Flow Record content and the Flow state which may be kept
   additionally for each of the Flows.  External processes may update
   counters, bounds and timers for each of the Flow Records and the
   Intermediate Flow Selection Process utilises this information for the
   selection decision.  A review of Flow-state Dependent Intermediate
   Flow Selection Process techniques that aim at the selection of the
   most frequent items by keeping additional Flow state information can
   be found in [CoHa08].  Flow-state Dependent Intermediate Flow



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   Selection Process can only be applied after packet aggregation, when
   a packet has been assigned to a Flow.  The Intermediate Flow
   Selection Process then decides based upon the Flow state for each
   Flow if it is kept in the Flow Cache or not.  Two Flow-state
   Dependent Intermediate Flow Selection Process Algorithms are here
   described:

   The frequent algorithm [KaPS03] is a technique that aims at the
   selection of all flows that at least exceed a 1/k fraction of the
   Observed Packet Stream.  The algorithm has only a Flow Cache of size
   k-1 and each Flow in the Flow Cache has an additional counter.  The
   counter is incremented each time a packet belonging to the Flow in
   the Flow Cache is observed.  In case the observed packet does not
   belong to any Flow all counters are decremented and if any of the
   Flow counters has a value of zero the Flow is replaced with a Flow
   formed from the new packet.

   Lossy counting is a selection technique that identifies all Flows
   whose packet count exceeds a certain percentage of the whole observed
   packet stream (e.g. 5% of all packets) with a certain estimation
   error e.  Lossy counting separates the observed packet stream in
   windows of size N=1/e, where N is an amount of consecutive packets.
   For each observed Flow an additional counter will be held in the Flow
   state.  The counter is incremented each time a packet belonging to
   the Flow is observed and all counters are decremented at the end of
   each window and all Flows with a counter of zero are removed from the
   Flow Cache.

6.4.  Flow-state Dependent Packet Selection

   Flow-state Dependent Packet Selection is not an Intermediate Flow
   Selection Process technique but a packet selection technique.
   Nevertheless configuration and reporting parameters for this
   technique will be described in this document.  An example is the
   "Sample and Hold" algorithm [EsVa01] that tries to prefer large
   volume Flows in the selection.  When a packet arrives it is selected
   when a Flow Record for this packet already exists.  In case there is
   no Flow Record, the packet is selected by a certain probability that
   is dependent on the packet size.


7.  Configuration of Intermediate Flow Selection Process Techniques

   This section describes the configuration parameters of the Flow
   selection techniques presented above.  It provides the basis for an
   information model to be adopted in order to configure the
   Intermediate Flow Selection Process within an IPFIX Device.  The
   information model with the Information Elements (IEs) for



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   Intermediate Flow Selection Process configuration is described
   together with the reporting IEs in section 8.  The following table
   gives an overview of the defined Intermediate Flow Selection Process
   techniques, where they can be applied and what their input parameters
   are.  Depending on where the Flow selection techniques are applied
   different input parameters can be configured.

   Overview of Intermediate Flow Selection Process Techniques:

   +-------------------+--------------------+--------------------------+
   | Location          | Selection          | Selection Input          |
   |                   | Technique          |                          |
   +-------------------+--------------------+--------------------------+
   | In the Metering   | Flow-state         | packet sampling          |
   | Process           | Dependent Packet   | probabilities, Flow      |
   |                   | Selection          | Selection State, packet  |
   |                   |                    | properties               |
   +-------------------+--------------------+--------------------------+
   | In the Metering   | Property Match     | Flow record IEs,         |
   | Process           | Flow Filtering     | Selection Interval       |
   +-------------------+--------------------+--------------------------+
   | In the Metering   | Hash-based Flow    | selection range, Hash    |
   | Process           | Filtering          | Function, Flow Key,      |
   |                   |                    | (seed)                   |
   +-------------------+--------------------+--------------------------+
   | In the Metering   | Time-based         | Flow Position (derived   |
   | Process           | Systematic Flow    | from arrival time of     |
   |                   | Sampling           | packets), Flow Selection |
   |                   |                    | State                    |
   +-------------------+--------------------+--------------------------+
   | In the Metering   | Sequence-based     | Flow Position (derived   |
   | Process           | Systematic Flow    | from packet position),   |
   |                   | Sampling           | Flow Selection State     |
   +-------------------+--------------------+--------------------------+
   | In the Metering   | Random Flow        | random number generator  |
   | Process           | Sampling           | or list and packet       |
   |                   |                    | position, Flow state     |
   +-------------------+--------------------+--------------------------+
   | In the Exporting  | Property Match     | Flow Record content,     |
   | Process/ within   | Flow Filtering     | filter function          |
   | the IPFIX         |                    |                          |
   | Mediator          |                    |                          |
   +-------------------+--------------------+--------------------------+
   | In the Exporting  | Hash-based Flow    | selection range, Hash    |
   | Process/ within   | Filtering          | Function, hash input     |
   | the IPFIX         |                    | (Flow Keys and other     |
   | Mediator          |                    | Flow properties)         |
   +-------------------+--------------------+--------------------------+



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   +-------------------+--------------------+--------------------------+
   | In the Exporting  | Flow-state         | Flow state parameters,   |
   | Process/ within   | Dependent          | random number generator  |
   | the IPFIX         | Intermediate Flow  | or list                  |
   | Mediator          | Selection Process  |                          |
   +-------------------+--------------------+--------------------------+
   | In the Exporting  | Time-based         | Flow arrival time, Flow  |
   | Process/ within   | Systematic Flow    | state                    |
   | the IPFIX         | Sampling           |                          |
   | Mediator          |                    |                          |
   +-------------------+--------------------+--------------------------+
   | In the Exporting  | Sequence-based     | Flow Position, Flow      |
   | Process/ within   | Systematic Flow    | state                    |
   | the IPFIX         | Sampling           |                          |
   | Mediator          |                    |                          |
   +-------------------+--------------------+--------------------------+
   | In the Exporting  | Random Flow        | random number generator  |
   | Process/ within   | Sampling           | or list and Flow         |
   | the IPFIX         |                    | Position, Flow state     |
   | Mediator          |                    |                          |
   +-------------------+--------------------+--------------------------+

    Table 1: Overview of Intermediate Flow Selection Process Techniques

7.1.  Intermediate Flow Selection Process Parameters

   This section defines what parameters are required to describe the
   most common Intermediate Flow Selection Process techniques.

   Intermediate Flow Selection Process Parameters:

   For Property Match Filtering:

   -   Information Element as specified in [iana-ipfix-assignments]):
       Specifies the Information Element which is used as the property
       in the filter expression.  Section 8 specifies the Information
       Elements that MUST be exported by an Intermediate Flow Selection
       Process using Property Match Filtering.

   -   Selection Value or Value Interval:
       Specifies the value or interval of the filter expression.
       Packets and Flow Records that have a value equal to the Selection
       Value or within the Interval will be selected.

   For Hash-based Flow Filtering:






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   -   Hash Domain:
       Specifies the bits from the packet or Flow which are taken as the
       hash input to the Hash Function.

   -   Hash Function:
       Specifies the name of the Hash Function that is used to calculate
       the hash value.  Possible Hash Functions are BOB [RFC5475], IPSX
       [RFC5475], CRC-32 [Bra75]

   -   Hash Selection Range:
       Flows that have a hash value within the Hash Selection Range are
       selected.  The Hash Selection Range can be a value interval or
       arbitrary hash values within the Hash Range of the Hash Function.

   -   Random Seed or Initializer Value:
       Some Hash Functions require an initializing value.  In order to
       make the selection decision more secure one can choose a random
       seed that configures the hash function.

   For Flow-state Dependent Intermediate Flow Selection Process:

   -   frequency threshold:
       Specifies the frequency threshold s for Flow-state Dependent Flow
       Selection techniques that try to find the most frequent items
       within a dataset.  All Flows which exceed the defined threshold
       will be selected.

   -   accuracy parameter:
       specifies the accuracy parameter e for techniques that deal with
       the frequent items problems.  The accuracy parameter defines the
       maximum error, i.e. no Flows that have a true frequency less than
       ( s - e) N are selected, where s is the frequency threshold and N
       is the total number of packets.

   The above list of parameters for Flow-state Dependent Flow Selection
   techniques is suitable for the presented frequent item and lossy
   counting algorithms.  Nevertheless a variety of techniques exist with
   very specific parameters which are not defined here.

   For Systematic time-based Flow Sampling:

   -   Interval length (in usec)
       Defines the length of the sampling interval during which Flows
       are selected.







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   -   Spacing (in usec)
       The spacing parameter defines the spacing in usec between the end
       of one sampling interval and the start of the next succeeding
       interval.

   For Systematic count-based Flow Sampling:

   -   Interval length
       Defines the number of Flows that are selected within the sampling
       interval.

   -   Spacing
       The spacing parameter defines the spacing in number of observed
       Flows between the end of one sampling interval and the start of
       the next succeeding interval.

   For random n-out-of-N Flow Sampling:

   -   Population Size N
       The Population Size N is the number of all Flows in the
       Population from which the sample is drawn.

   -   Sampling Size n
       The sampling size n is the number of Flows that are randomly
       drawn from the population N.

   For probabilistic Flow Sampling:

   -   Sampling probability p
       The sampling probability p defines the probability by which each
       of the observed Flows is selected.

7.2.  Description of Flow-state Dependent Packet Selection

   The configuration of Flow-state Dependent Packet Selection has not
   been described in [RFC5475] therefore the parameters are defined
   here:

   For Flow-state Dependent Packet Selection:

   -   packet selection probability per possible Flow state interval
       Defines multiple {Flow interval, packet selection probability}
       value pairs that configure the sampling probability depending on
       the current Flow state.







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   -   additional parameters
       For the configuration of Flow-state Dependent Packet Selection
       additional parameters or packet properties may be required, e.g.
       the packet size ([EsVa01])


8.  Information Model for Intermediate Flow Selection Process
    Configuration and Reporting

   This section specifies the Information Elements that MUST be exported
   by an Intermediate Flow Selection Process in order to support the
   interpretation of measurement results from Flow measurements.  The
   information is mainly used to report how many packets and Flows have
   been observed in total and how many of them were selected.  This
   helps for instance to calculate the Attained Selection Fraction (see
   also [RFC5476]), which is an important parameter to provide an
   accuracy statement.  The IEs can provide reporting information about
   Flow Records, packets or bytes.  The reported metrics are total
   number of elements and the number of selected elements.  From this
   the number of dropped elements can be derived.

   List of Intermediate Flow Selection Process Information Elements:

   +-----+--------------------------+------+---------------------------+
   | ID  | Name                     | ID   | Name                      |
   +-----+--------------------------+------+---------------------------+
   | 301 | selectionSequenceID      | 302  | selectorID                |
   +-----+--------------------------+------+---------------------------+
   | TBD | flowSelectorAlgorithm    | 1    | octetDeltaCount           |
   | 1   |                          |      |                           |
   +-----+--------------------------+------+---------------------------+
   | TBD | flowSelectedOctetDeltaCo | 2    | packetDeltaCount          |
   | 2   | unt                      |      |                           |
   +-----+--------------------------+------+---------------------------+
   | TBD | flowSelectedPacketDeltaC | 3    | originalFlowsPresent      |
   | 3   | ount                     |      |                           |
   +-----+--------------------------+------+---------------------------+
   | TBD | flowSelectedFlowDeltaCou | TBD5 | selectorIDTotalFlowsObser |
   | 4   | nt                       |      | ved                       |
   +-----+--------------------------+------+---------------------------+
   | TBD | selectorIDTotalFlowsSele | TBD7 | samplingFlowInterval      |
   | 6   | cted                     |      |                           |
   +-----+--------------------------+------+---------------------------+
   | TBD | samplingFlowSpacing      | 309  | samplingSize              |
   | 8   |                          |      |                           |
   +-----+--------------------------+------+---------------------------+
   | 310 | samplingPopulation       | 311  | samplingProbability       |
   +-----+--------------------------+------+---------------------------+



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   +-----+--------------------------+------+---------------------------+
   | TBD | flowSamplingTimeInterval | TBD1 | flowSamplingTimeSpacing   |
   | 9   |                          | 0    |                           |
   +-----+--------------------------+------+---------------------------+
   | 326 | digestHashValue          | TBD1 | hashFlowDomain            |
   |     |                          | 1    |                           |
   +-----+--------------------------+------+---------------------------+
   | 329 | hashOutputRangeMin       | 330  | hashOutputRangeMax        |
   +-----+--------------------------+------+---------------------------+
   | 331 | hashSelectedRangeMin     | 332  | hashSelectedRangeMax      |
   +-----+--------------------------+------+---------------------------+
   | 333 | hashDigestOutput         | 334  | hashInitialiserValue      |
   +-----+--------------------------+------+---------------------------+
   | 320 | absoluteError            | 321  | relativeError             |
   +-----+--------------------------+------+---------------------------+
   | 336 | upperCILimit             | 337  | lowerCILimit              |
   +-----+--------------------------+------+---------------------------+
   | 338 | confidenceLevel          |      |                           |
   +-----+--------------------------+------+---------------------------+

     Table 2: Intermediate Flow Selection Process Information Elements


9.  IANA Considerations

9.1.  Registration of Information Elements

   IANA will register the following IEs in the IPFIX Information
   Elements registry at http://www.iana.org/assignments/ipfix/ipfix.xml

   IANA Note: please replace TBD1, TBD2, TBD3, TBD4, TBD5, TBD6, TBD7,
   TBD8, TBD9, TBD10, TBD11 with the assigned values, throughout the
   document

9.1.1.  flowSelectorAlgorithm

   Description:

      This Information Element identifies the Intermediate Flow
      Selection Process technique (e.g., Filtering, Sampling) that is
      applied by the Intermediate Flow Selection Process.  Most of these
      techniques have parameters.  Its configuration parameter(s) MUST
      be clearly specified.  Further Information Elements are needed to
      fully specify packet selection with these methods and all their
      parameters.  Further method identifiers may be added to the list
      below.  It might be necessary to define new Information Elements
      to specify their parameters.  The flowSelectorAlgorithm registry
      is maintained by IANA.  New assignments for the registry will be



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      administered by IANA, on a First Come First Served basis
      [RFC5226], subject to Expert Review [RFC5226].  Please note that
      the purpose of the flow selection techniques described in this
      document is the improvement of measurement functions as defined in
      the Scope (Section 1).  Before adding new flow selector algorithms
      it should be checked what is their intended purpose and especially
      if those contradict with policies defined in [RFC2804].  The
      designated expert(s) should consult with the community if a
      request is received that runs counter to [RFC2804].  The registry
      can be updated when specifications of the new method(s) and any
      new Information Elements are provided.  The group of experts must
      double check the flowSelectorAlgorithm definitions and Information
      Elements with already defined flowSelectorAlgorithm and
      Information Elements for completeness, accuracy, and redundancy.
      Those experts will initially be drawn from the Working Group
      Chairs and document editors of the IPFIX and PSAMP Working Groups.
      The following Intermediate Flow Selection Process Techniques
      identifiers are defined here:

































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   +----+------------------------+--------------------------+
   | ID |        Technique         |      Parameters          |
   +----+------------------------+--------------------------+
   | 1  | Systematic count-based | flowSamplingInterval     |
   |    | Sampling               | flowSamplingSpacing      |
   +----+------------------------+--------------------------+
   | 2  | Systematic time-based  | flowSamplingTimeInterval |
   |    | Sampling               | flowSamplingTimeSpacing  |
   +----+------------------------+--------------------------+
   | 3  | Random n-out-of-N      | samplingSize             |
   |    | Sampling               | samplingPopulation       |
   +----+------------------------+--------------------------+
   | 4  | Uniform probabilistic  | samplingProbability      |
   |    | Sampling               |                          |
   +----+------------------------+--------------------------+
   | 5  | Property Match         | Information Element      |
   |    | Filtering              | Value Range              |
   +----+------------------------+--------------------------+
   |   Hash-based Filtering      | hashInitialiserValue     |
   +----+------------------------+ hashFlowDomain           |
   | 6  | using BOB              | hashSelectedRangeMin     |
   +----+------------------------+ hashSelectedRangeMax     |
   | 7  | using IPSX             | hashOutputRangeMin       |
   +----+------------------------+ hashOutputRangeMax       |
   | 8  | using CRC              |                          |
   +----+------------------------+--------------------------+
   | 9  | Flow-state Dependent   | No agreed Parameters     |
   |    | Intermediate Flow      |                          |
   |    | Selection Process      |                          |
   +----+------------------------+--------------------------+

              Intermediate Flow Selection Process Techniques

   Abstract Data Type: unsigned16

   ElementId: TBD1

   Data Type Semantics: identifier

   Status: Current

9.1.2.  flowSelectedOctetDeltaCount

   Description:

      This Information Element specifies the volume in octets of all
      Flows that are selected in the Intermediate Flow Selection Process
      since the previous report.



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   Abstract Data Type: unsigned64

   ElementId: TBD2

   Units: Octets

   Status: Current

9.1.3.  flowSelectedPacketDeltaCount

   Description:

      This Information Element specifies the volume in packets of all
      Flows that were selected in the Intermediate Flow Selection
      Process since the previous report.

   Abstract Data Type: unsigned64

   ElementId: TBD3

   Units: Packets

   Status: Current

9.1.4.  flowSelectedFlowDeltaCount

   Description:

      This Information Element specifies the number of Flows that were
      selected in the Intermediate Flow Selection Process since the last
      report.

   Abstract Data Type: unsigned64

   ElementId: TBD4

   Units: Flows

   Status: Current

9.1.5.  selectorIDTotalFlowsObserved

   Description:

      This Information Element specifies the total number of Flows
      observed by a Selector, for a specific value of SelectorId.  This
      Information Element should be used in an Options Template scoped
      to the observation to which it refers.  See Section 3.4.2.1 of the



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      IPFIX protocol document [I-D.ietf-ipfix-protocol-rfc5101bis].

   Abstract Data Type: unsigned64

   ElementId: TBD5

   Units: Flows

   Status: Current

9.1.6.  selectorIDTotalFlowsSelected

   Description:

      This Information Element specifies the total number of Flows
      selected by a Selector, for a specific value of SelectorId.  This
      Information Element should be used in an Options Template scoped
      to the observation to which it refers.  See Section 3.4.2.1 of the
      IPFIX protocol document [I-D.ietf-ipfix-protocol-rfc5101bis].

   Abstract Data Type: unsigned64

   ElementId: TBD6

   Units: Flows

   Status: Current

9.1.7.  samplingFlowInterval

   Description:

      This Information Element specifies the number of Flows that are
      consecutively sampled.  A value of 100 means that 100 consecutive
      Flows are sampled.  For example, this Information Element may be
      used to describe the configuration of a systematic count-based
      Sampling Selector.

   Abstract Data Type: unsigned64

   ElementId: TBD7

   Units: Flows

   Status: Current






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9.1.8.  samplingFlowSpacing

   Description:

      This Information Element specifies the number of Flows between two
      "samplingFlowInterval"s.  A value of 100 means that the next
      interval starts 100 Flows (which are not sampled) after the
      current "samplingFlowInterval" is over.  For example, this
      Information Element may be used to describe the configuration of a
      systematic count-based Sampling Selector.

   Abstract Data Type: unsigned64

   ElementId: TBD8

   Units: Flows

   Status: Current

9.1.9.  flowSamplingTimeInterval

   Description:

      This Information Element specifies the time interval in
      microseconds during which all arriving Flows are sampled.  For
      example, this Information Element may be used to describe the
      configuration of a systematic time-based Sampling Selector.

   Abstract Data Type: unsigned64

   ElementId: TBD9

   Units: microseconds

   Status: Current

9.1.10.  flowSamplingTimeSpacing

   Description:

      This Information Element specifies the time interval in
      microseconds between two "flowSamplingTimeInterval"s.  A value of
      100 means that the next interval starts 100 microseconds (during
      which no Flows are sampled) after the current
      "flowsamplingTimeInterval" is over.  For example, this Information
      Element may used to describe the configuration of a systematic
      time-based Sampling Selector.




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   Abstract Data Type: unsigned64

   ElementId: TBD10

   Units: microseconds

   Status: Current

9.1.11.  hashFlowDomain

   Description:

      This Information Element specifies the Information Elements that
      are used by the Hash-based Flow Selector as the Hash Domain.

   Abstract Data Type: unsigned16

   ElementId: TBD11

   Data Type Semantics: identifier

   Status: Current

9.2.  Registration of Object Identifier

   IANA will register the following OID in the IPFIX-SELECTOR-MIB
   Functions sub-registry at http://www.iana.org/assignments/smi-numbers
   according to the procedures set forth in [RFC6615]

   +---------+-----------------------+---------------------+-----------+
   | Decimal | Name                  | Description         | Reference |
   +---------+-----------------------+---------------------+-----------+
   |         | flowSelectorAlgorithm | This Object         | TBDx      |
   |         |                       | Identifier          | [RFCyyyy] |
   |         |                       | identifies the      |           |
   |         |                       | Intermediate Flow   |           |
   |         |                       | Selection Process   |           |
   |         |                       | technique (e.g.,    |           |
   |         |                       | Filtering,          |           |
   |         |                       | Sampling) that is   |           |
   |         |                       | applied by the      |           |
   |         |                       | Intermediate Flow   |           |
   |         |                       | Selection Process   |           |
   +---------+-----------------------+---------------------+-----------+

               Table 4: Object Identifiers to be registered

   IANA Note: please replace TBDx with the assigned value, throughout



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   the document.

   Editor's Note (to be removed prior to publication): the RFC editor is
   asked to replace "yyyy" in this document by the number of the RFC
   when the assignment has been made.


10.  Security and Privacy Considerations

   Flow data exported by Exporting Processes, and collected by
   Collecting Processes, can be sensitive for privacy reasons and need
   to be protected.  Privacy considerations for collected data are
   provided in [I-D.ietf-ipfix-protocol-rfc5101bis].

   Some of the described Intermediate Flow Selection Process techniques
   (e.g., flow sampling, hash-based flow filtering) aim at the selection
   of a representative subset of flows in order to estimate parameters
   of the population.  An adversary may have incentives to influence the
   selection of flows, for example to circumvent accounting or to avoid
   the detection of packets that are part of an attack.

   Security considerations concerning the choice of a Hash Function for
   Hash-based Packet Selection have been discussed in Section 6.2.3 of
   [RFC5475] and are also appropriate for Hash-based Flow Selection.
   [RFC5475] discusses the possibility to craft Packet Streams which are
   disproportionately selected or can be used to discover Hash Function
   parameters.  It also describes vulnerabilities of different Hash
   Functions to these attacks, and practices to minimize these
   vulnerabilities.

   For other sampling approaches an adversary can gain knowledge about
   the start and stop triggers in time-based systematic Sampling, e.g.,
   by sending test packets.  This knowledge might allow adversariess to
   modify their send schedule in a way that their packets are
   disproportionately selected or not selected.  For random Sampling, an
   input to the encryption process, like the Initialization Vector of
   the CBC (Cipher Block Chaining) mode, should be used to prevent that
   an advisory can predict the selection decision [Dw01].

   Further security threats can occur when Intermediate Flow Selection
   Process parameters are configured or communicated to other entities.
   The protocol(s) for the configuration and reporting of Intermediate
   Flow Selection Process parameters are out of scope of this document.
   Nevertheless, a set of initial requirements for future configuration
   and reporting protocols are stated below:

   1.  Protection against disclosure of configuration information:
       Intermediate Flow Selection Process configuration information



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       describes the Intermediate Flow Selection Process and its
       parameters.  This information can be useful to attackers.
       Attackers may craft packets that never fit the selection criteria
       in order to prevent Flows to be seen by the Intermediate Flow
       Selection Process.  They can also craft a lot of packets that fit
       the selection criteria and overload or bias subsequent processes.
       Therefore any transmission of configuration data (e.g., to
       configure a process or to report its actual status) should be
       protected by encryption.

   2.  Protection against modification of configuration information: if
       wrong configuration information is sent to the Intermediate Flow
       Selection Process, it can lead to a malfunction of the
       Intermediate Flow Selection Process.  Also if wrong configuration
       information is reported from the Intermediate Flow Selection
       Process to other processes it can lead to wrong estimations at
       subsequent processes.  Therefore any protocol that transmits
       configuration information should prevent that an attacker can
       modify configuration information.  Data integrity can be achieved
       by authenticating the data.

   3.  Protection against malicious nodes sending configuration
       information: the remote configuration of Intermediate Flow
       Selection Process techniques should be protected against access
       by unauthorized nodes.  This can be achieved by access control
       lists at the device that hosts the Intermediate Flow Selection
       Process (e.g.  IPFIX Exporter, IPFIX Mediator or IPFIX Collector)
       and by source authentication.  The reporting of configuration
       data from an Intermediate Flow Selection Process has to be
       protected in the same way.  That means that also protocols that
       report configuration data from the Intermediate Flow Selection
       Process to other processes need to protect against unauthorized
       nodes reporting configuration information.

   The security threats that originate from communicating configuration
   information to and from Intermediate Flow Selection Processes cannot
   be assessed solely with the information given in this document.  A
   further more detailed assessment of security threats is necessary
   when a specific protocol for the configuration or reporting
   configuration data is proposed.


11.  Acknowledgments

   We would like to thank the IPFIX group, especially Brian Trammell,
   Paul Aitken and Benoit Claise for fruitful discussions and for
   proofreading the document.




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12.  References

12.1.  Normative References

   [I-D.ietf-ipfix-protocol-rfc5101bis]
              Claise, B. and B. Trammell, "Specification of the IP Flow
              Information eXport (IPFIX) Protocol for the Exchange of
              Flow Information", draft-ietf-ipfix-protocol-rfc5101bis-07
              (work in progress), May 2013.

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

   [RFC5102]  Quittek, J., Bryant, S., Claise, B., Aitken, P., and J.
              Meyer, "Information Model for IP Flow Information Export",
              RFC 5102, January 2008.

   [RFC5475]  Zseby, T., Molina, M., Duffield, N., Niccolini, S., and F.
              Raspall, "Sampling and Filtering Techniques for IP Packet
              Selection", RFC 5475, March 2009.

   [RFC5476]  Claise, B., Johnson, A., and J. Quittek, "Packet Sampling
              (PSAMP) Protocol Specifications", RFC 5476, March 2009.

   [RFC6615]  Dietz, T., Kobayashi, A., Claise, B., and G. Muenz,
              "Definitions of Managed Objects for IP Flow Information
              Export", RFC 6615, June 2012.

12.2.  Informative References

   [Bra75]    Brayer, K., "Evaluation of 32 Degree Polynomials in Error
              Detection on the SATIN IV Autovon Error Patterns",
              National Technical Information Service p.74, August 1975.

   [CoHa08]   Cormode, G. and M. Hadjieleftheriou, "Finding frequent
              items in data streams", Journal, Proceedings of the Very
              Large DataBase Endowment VLDB Endowment, Volume 1 Issue 2,
              August 2008, August 2008.

   [DuLT01]   Duffield, N., Lund, C., and M. Thorup, "Charging from
              Sampled Network Usage", ACM Internet Measurement Workshop
              IMW 2001, San Francisco, USA, November 2001.

   [Dw01]     Dworkin, M., "Recommendation for Block Cipher Modes of
              Operation - Methods and Techniques", NIST Special
              Publication NIST Special Publication 800-38A 2001 Edition,
              December 2001.




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   [EsVa01]   Estan, C. and G,. Varghese, "New Directions in Traffic
              Measurement and Accounting: Focusing on the Elephants,
              Ignoring the Mice", ACM SIGCOMM Internet Measurement
              Workshop 2001, San Francisco (CA), November 2001.

   [KaPS03]   Karp, R., Papadimitriou, C., and S. S. Shenker, "A simple
              algorithm for finding frequent elements in sets and
              bags.", ACM Transactions on Database Systems, Volume 28,
              51-55, 2003, March 2003.

   [MSZC10]   Mai, J., Sridharan, A., Zang, H., and C. Chuah, "Fast
              Filtered Sampling", Computer Networks Volume 54, Issue 11,
              Pages 1885-1898, ISSN 1389-1286, January 2010.

   [MaMo02]   Manku, G. and R. Motwani, "Approximate Frequency Counts
              over Data Streams", Proceedings of the International
              Conference on Very large DataBases (VLDB) pages 346--357,
              2002, Hong Kong, China, 2002.

   [RFC2804]  IAB and IESG, "IETF Policy on Wiretapping", RFC 2804,
              May 2000.

   [RFC3917]  Quittek, J., Zseby, T., Claise, B., and S. Zander,
              "Requirements for IP Flow Information Export (IPFIX)",
              RFC 3917, October 2004.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC5470]  Sadasivan, G., Brownlee, N., Claise, B., and J. Quittek,
              "Architecture for IP Flow Information Export", RFC 5470,
              March 2009.

   [RFC6183]  Kobayashi, A., Claise, B., Muenz, G., and K. Ishibashi,
              "IP Flow Information Export (IPFIX) Mediation: Framework",
              RFC 6183, April 2011.

   [iana-ipfix-assignments]
              "IP Flow Information Export Information Elements", 2007,
              <http://www.iana.org/assignments/ipfix/ipfix.xml>.










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Authors' Addresses

   Salvatore D'Antonio
   University of Napoli "Parthenope"
   Centro Direzionale di Napoli Is. C4
   Naples  80143
   Italy

   Phone: +39 081 5476766
   Email: salvatore.dantonio@uniparthenope.it


   Tanja Zseby
   CAIDA/FhG FOKUS
   San Diego Supercomputer Center (SDSC)
   University of California, San Diego (UCSD)
   9500 Gilman Drive
   La Jolla  CA 92093-0505
   USA

   Email: tanja@caida.org


   Christian Henke
   Tektronix Communication Berlin
   Wohlrabedamm 32
   Berlin  13629
   Germany

   Phone: +49 17 2323 8717
   Email: christian.henke@tektronix.com


   Lorenzo Peluso
   University of Napoli
   Via Claudio 21
   Napoli  80125
   Italy

   Phone: +39 081 7683821
   Email: lorenzo.peluso@unina.it










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