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Versions: 00 01 02 03 04 05 06 07 08 09 RFC 5982

IPFIX Working Group                                    A. Kobayashi, Ed.
Internet-Draft                                               NTT PF Lab.
Intended status: Informational                            B. Claise, Ed.
Expires: April 19, 2010                              Cisco Systems, Inc.
                                                        October 16, 2009







                   IPFIX Mediation: Problem Statement
            draft-ietf-ipfix-mediators-problem-statement-06

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Copyright Notice

   Copyright (c) 2009 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 in effect on the date of
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   Please review these documents carefully, as they describe your rights
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Abstract

   Flow-based measurement is a popular method for various network
   monitoring usages.  The sharing of flow-based information for
   monitoring applications having different requirements raises some
   open issues in terms of measurement system scalability, flow-based
   measurement flexibility, and export reliability that IPFIX Mediation
   may help resolve.  This document describes the IPFIX Mediation
   applicability examples, along with some problems that network
   administrators have been facing.









































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  Terminology and Definitions  . . . . . . . . . . . . . . . . .  6
   3.  IPFIX/PSAMP Documents Overview . . . . . . . . . . . . . . . .  8
     3.1.  IPFIX Documents Overview . . . . . . . . . . . . . . . . .  8
     3.2.  PSAMP Documents Overview . . . . . . . . . . . . . . . . .  8
   4.  Problem Statement  . . . . . . . . . . . . . . . . . . . . . .  9
     4.1.  Coping with IP Traffic Growth  . . . . . . . . . . . . . .  9
     4.2.  Coping with Multipurpose Traffic Measurement . . . . . . . 10
     4.3.  Coping with Heterogeneous Environments . . . . . . . . . . 10
     4.4.  Summary  . . . . . . . . . . . . . . . . . . . . . . . . . 10
   5.  Mediation Applicability Examples . . . . . . . . . . . . . . . 11
     5.1.  Adjusting Flow Granularity . . . . . . . . . . . . . . . . 11
     5.2.  Hierarchical Collecting Infrastructure . . . . . . . . . . 11
     5.3.  Correlation for Data Records . . . . . . . . . . . . . . . 12
     5.4.  Time Composition . . . . . . . . . . . . . . . . . . . . . 12
     5.5.  Spatial Composition  . . . . . . . . . . . . . . . . . . . 13
     5.6.  Data Record Anonymization  . . . . . . . . . . . . . . . . 14
     5.7.  Data Retention . . . . . . . . . . . . . . . . . . . . . . 14
     5.8.  IPFIX Export from a Branch Office  . . . . . . . . . . . . 15
     5.9.  Distributing Data Records  . . . . . . . . . . . . . . . . 16
     5.10. Flow-based Sampling and Selection  . . . . . . . . . . . . 17
     5.11. Interoperability between Legacy Protocols and IPFIX  . . . 18
   6.  IPFIX Mediators Implementation Specific Problems . . . . . . . 19
     6.1.  Loss of Original Exporter Information  . . . . . . . . . . 19
     6.2.  Loss of Base Time Information  . . . . . . . . . . . . . . 19
     6.3.  Transport Sessions Management  . . . . . . . . . . . . . . 20
     6.4.  Loss of Options Template Information . . . . . . . . . . . 20
     6.5.  Template ID Management . . . . . . . . . . . . . . . . . . 20
     6.6.  Consideration for Network Topology . . . . . . . . . . . . 21
     6.7.  Exporting the Function Item  . . . . . . . . . . . . . . . 21
     6.8.  Consideration for Aggregation  . . . . . . . . . . . . . . 22
   7.  Summary and Conclusion . . . . . . . . . . . . . . . . . . . . 23
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 25
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 26
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 27
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 28
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 28
     11.2. Informative References . . . . . . . . . . . . . . . . . . 28
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 30










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1.  Introduction

   One advantage of Flow-based measurement results from easily offering
   the traffic monitoring of a huge amount of traffic.  While the usage
   is applied to any networks and to multiple measurement applications,
   network administrators need to optimize the resource of metering
   devices and of multiple measurement applications.  IP traffic growth
   and a wide variety of measurement application make the optimization
   further difficult.  To achieve system optimization, an intermediate
   device can generally be applied to the system platform.

   The IPFIX requirements defined in [RFC3917] mention examples of
   intermediate devices, such as IPFIX Proxies or Concentrators, there
   are no documents defining a generalized concept for such intermediate
   devices.  This document addresses that issue by defining IPFIX
   Mediation, a generalized intermediate device concept for IPFIX, and
   examining in detail the motivations behind its application.

   This document is structured as follows: section 2 describes the
   terminology used in this document, section 3 gives an IPFIX/PSAMP
   document overview, section 4 introduces general problems related to
   flow-based measurement, section 5 describes some applicability
   examples where IPFIX Mediations would be beneficial, and, finally,
   section 6 describes some problems an IPFIX Mediation implementation
   might face.


























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2.  Terminology and Definitions

   The IPFIX-specific and PSAMP-specific terminology used in this
   document is defined in [RFC5101] and [RFC5476], respectively.  In
   this document, as in [RFC5101] and [RFC5476], the first letter of
   each IPFIX-specific and PSAMP-specific term is capitalized along with
   the IPFIX Mediation-specific term defined here.

   In this document, we use the generic term "record stream" to denote a
   set of flow- or packet-based data records with their additional
   information that flows from data sources, whether encoded in IPFIX
   protocol as IPFIX Data Records, or non-IPFIX protocols.  In IPFIX
   protocol, we use the generic term Data Records for IPFIX Flow
   Records, PSAMP Packet Reports, and Data Records defined by Options
   Templates, unless an explicit distinction is required.

   Original Exporter

      An Original Exporter is an IPFIX Device that hosts the Observation
      Points where the metered IP packets are observed.

   IPFIX Mediation

      IPFIX Mediation is the manipulation and conversion of a record
      stream for subsequent export using the IPFIX protocol.

   The following terms are used in this document to describe the
   architectural entities used by IPFIX Mediation.

   Intermediate Process

      An Intermediate Process takes a record stream as its input from
      Collecting Processes, Metering Processes, IPFIX File Readers,
      other Intermediate Processes, or other record sources; performs
      some transformations on this stream, based upon the content of
      each record, states maintained across multiple records, or other
      data sources; and passes the transformed record stream as its
      output to Exporting Processes, IPFIX File Writers, or other
      Intermediate Processes, in order to perform IPFIX Mediation.
      Typically, an Intermediate Process is hosted by an IPFIX Mediator.
      Alternatively, an Intermediate Process may be hosted by an
      Original Exporter.

   IPFIX Mediator

      An IPFIX Mediator is an IPFIX Device that provides IPFIX Mediation
      by receiving a record stream from some data sources, hosting one
      or more Intermediate Processes to transform that stream, and



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      exporting the transformed record stream into IPFIX Messages via an
      Exporting Process.  In the common case, an IPFIX Mediator receives
      a record stream from a Collecting Process, but it could also
      receive a record stream from data sources not encoded using IPFIX,
      e.g., in the case of conversion from the NetFlow V9 protocol
      [RFC3954] to IPFIX protocol.

   Specific types of IPFIX Mediators are defined below.

   IPFIX Proxy

      An IPFIX Proxy is an IPFIX Mediator that converts a record stream
      for the purpose of protocol conversion.

   IPFIX Concentrator

      An IPFIX Concentrator is an IPFIX Mediator that receives a record
      stream from one or more Exporters and performs correlation,
      aggregation, and/or modification.

   IPFIX Distributor

      An IPFIX Distributor is an IPFIX Mediator that receives a record
      stream from one or more Exporters and exports each record to one
      or more Collectors, deciding to which Collector(s) to export each
      record depending on the decision of an Intermediate Process.

   IPFIX Masquerading Proxy

      An IPFIX Masquerading Proxy is an IPFIX Mediator that receives a
      record stream from one or more Exporters to screen out parts of
      records according to configured policies in order to protect the
      privacy of the network's end users or to retain sensitive data of
      the exporting organization.

















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3.  IPFIX/PSAMP Documents Overview

3.1.  IPFIX Documents Overview

   The IPFIX protocol [RFC5101] provides network administrators with
   access to IP flow information.  The architecture for the export of
   measured IP flow information from an IPFIX Exporting Process to a
   Collecting Process is defined in [RFC5470], per the requirements
   defined in [RFC3917].  The IPFIX protocol [RFC5101] specifies how
   IPFIX Data Records and Templates are carried via a number of
   transport protocols from IPFIX Exporting Processes to IPFIX
   Collecting Processes.  IPFIX has a formal description of IPFIX
   Information Elements, their names, types, and additional semantic
   information, as specified in [RFC5102].  [IPFIX-MIB] specifies the
   IPFIX Management Information Base.  Finally, [RFC5472] describes what
   types of applications can use the IPFIX protocol and how they can use
   the information provided.  It furthermore shows how the IPFIX
   framework relates to other architectures and frameworks.  The storage
   of IPFIX Messages in a file is specified in [IPFIX-FILE].

3.2.  PSAMP Documents Overview

   The framework for packet selection and reporting [RFC5474] enables
   network elements to select subsets of packets by statistical and
   other methods and to export a stream of reports on the selected
   packets to a Collector.  The set of packet selection techniques
   (sampling and filtering) standardized by PSAMP is described in
   [RFC5475].  The PSAMP protocol [RFC5476] specifies the export of
   packet information from a PSAMP Exporting Process to a Collector.
   Like IPFIX, PSAMP has a formal description of its Information
   Elements, their names, types, and additional semantic information.
   The PSAMP information model is defined in [RFC5477].  [PSAMP-MIB]
   describes the PSAMP Management Information Base.


















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4.  Problem Statement

   Network administrators generally face the problems of measurement
   system scalability, flow-based measurement flexibility, and export
   reliability, even if some techniques, such as Sampling, Filtering,
   Data Records aggregation and export replication, have already been
   developed.  The problems consist of optimizing the resources of the
   measurement system while fulfilling appropriate conditions: data
   accuracy, flow granularity, and export reliability.  These conditions
   depend on two factors.

   o  measurement system capacity:
      This consists of the bandwidth of the management network, the
      storage capacity, and the performances of the collecting devices
      and exporting devices.

   o  application requirements:
      Different applications, such as traffic engineering, detecting
      traffic anomalies, and accounting, etc., impose different Flow
      Record granularities, and data accuracies.

   The sustained growth of IP traffic has been overwhelming the
   measurement system capacities.  Furthermore, a large variety of
   applications (e.g., QoS measurement, traffic engineering, security
   monitoring) and the deployment of measurement system in heterogeneous
   environments have been increasing the demand and complexity of IP
   traffic measurements.

4.1.  Coping with IP Traffic Growth

   Enterprise or service provider networks already have multiple 10 Gb/s
   links, their total traffic exceeding 100 Gb/s.  In the near future,
   broadband users' traffic will increase by approximately 40% every
   year according to [TRAFGRW].  When operators monitor traffic of 500
   Gb/s with a packet sampling rate of 1/1000, the amount of exported
   Flow Records from Exporters could exceed 50 kFlows/s.  This value is
   beyond the ability of a single Collector.

   To deal with this problem, current data reduction techniques
   (Sampling and Filtering in [RFC5475], and aggregation of measurement
   data) have been generally implemented on Exporters.  Note that
   Sampling technique leads to potential loss of small Flows.  With both
   Sampling and aggregation techniques, administrators might no longer
   be able to detect and investigate subtle traffic changes and
   anomalies as this requires detailed Flow information.  With
   Filtering, only a subset of the Data Records are exported.

   Considering the potential drawbacks of Sampling, Filtering, and Data



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   Records aggregation, there is a need for a large-scale collecting
   infrastructure that does not rely on data reduction techniques.

4.2.  Coping with Multipurpose Traffic Measurement

   Different monitoring applications impose different requirements on
   the monitoring infrastructure.  Some of them require traffic
   monitoring at a Flow level while others need information about
   individual packets or just Flow aggregates.

   To fulfill these divers requirements, an Exporter would need to
   perform various complex metering tasks in parallel, which is a
   problem due to limited resources.  Hence, it can be advantageous to
   run the Exporter with a much simpler setup and to perform appropriate
   post-processing of the exported Data Records at a later stage.

4.3.  Coping with Heterogeneous Environments

   Network administrators use IPFIX Devices and PSAMP Devices from
   various vendors, various software versions, various device types
   (router, switch, or probe) in a single network domain.  Even legacy
   flow export protocols are still deployed in current network.  This
   heterogeneous environment leads to differences in Metering Process
   capabilities, Exporting Process capacity (export rate, cache memory,
   etc.), and data format.  For example, probes and switches cannot
   retrieve some derived packet properties in [RFC5102] from a routing
   table.

   To deal with this problem, the measurement system needs to mediate
   the differences.  However, equipping all collecting devices with this
   absorption function is difficult.

4.4.  Summary

   In optimizing the resources of a measurement system, it is important
   to use traffic data reduction techniques as early as possible, e.g.,
   at the Exporter.  However, this implementation is made difficult by
   heterogeneous environment of exporting devices.

   This implies that a new Mediation function is required in typical
   Exporter-Collector architectures.  Based on some applicability
   examples, the next section shows the limitation of the typical
   Exporter-Collector architecture model and the IPFIX Mediation
   benefits.







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5.  Mediation Applicability Examples

5.1.  Adjusting Flow Granularity

   A set of common properties of simplest Flow type is a fixed 5-tuple
   of protocol, source and destination IP addresses, and source and
   destination port numbers.  A shorter set of common properties, such
   as a triple, a double, or a single property, (for example network
   prefix, peering autonomous system number, or BGP Next-Hop fields),
   creates more aggregated Flow Records.  This is especially useful for
   measuring traffic exchange in an entire network domain and for easily
   adjusting the performance of Exporters and Collectors.

   Implementation analysis:

      Implementations for this case depend on where Flow granularity is
      adjusted.  More suitable implementations use configurable Metering
      Processes in Original Exporters.  The cache in the Metering
      Process can specify its own set of common properties (Flow Keys)
      and extra fields.  The Original Exporter thus creates directly
      aggregated Flow Records.

      In the case where the Original Exporter contains a Metering
      Process that creates fixed tuple Flow Records (no ability to
      change the Flow Keys), or PSAMP Packet Reports, an IPFIX
      Concentrator can aggregate Data Records based on a new set of Flow
      Keys.  Even in the case where the Original Exporter contains a
      Metering Process for which the Flow Keys can be configured, an
      IPFIX Concentrator can further aggregate the Flow Records.

5.2.  Hierarchical Collecting Infrastructure

   The increase of IPFIX Exporters, the increase of the traffic, and the
   variety of treatments expected to be performed over the Data Records
   is more and more difficult to handle within a single Collector.
   Hence to increase the collecting (e.g., the bandwidth capacity) and
   processing capacity, distributed Collectors must be deployed.  As a
   possible approach, a hierarchical structure is useful for increasing
   the measurement systems capacity, both in export bandwidth capacity
   and in collecting capacity.

   Implementation analysis:

      To cope with the increase of IPFIX Exporters and traffic, one
      possible implementation uses IPFIX Concentrators to build a
      hierarchical collection system.  To cope with the variety of
      treatments, one possible implementation uses IPFIX Distributors to
      build a distributed collection system.  More specific cases are



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      described in section 5.9.

5.3.  Correlation for Data Records

   The correlation amongst Data Records or between Data Record and meta
   data provides new metrics or information, including the following.

   o  One-to-one correlation between Data Records

      *  One way delay from the correlation of PSAMP Packet Reports from
         different Exporters along a specific path, packet inter-arrival
         time, etc.

      *  Treatment from the correlation of Data Records with the common
         properties, observed at incoming/outgoing interfaces.  Examples
         are the rate-limiting ratio, the compression ratio, the
         optimization ratio, etc.

   o  Correlation amongst Data Records

      Average/maximum/minimum values from correlating multiple Data
      Records.  Examples are the average/maximum/minimum number of
      packets of the measured Flows, the average/maximum/minimum one way
      delay, the average/maximum/minimum number of lost packets, etc.

   o  Correlation between Data Record and other meta data

      Examples are some BGP attributes associated with Data Record by
      looking up the routing table.

   Implementation analysis:

      One possible implementation for this case uses an IPFIX
      Concentrator located between the Metering Processes and Exporting
      Processes on the Original Exporter, or alternatively a separate
      IPFIX Concentrator located between the Original Exporters and
      IPFIX Collectors.

5.4.  Time Composition

   Time composition is defined as the aggregation of consecutive Data
   Records with common properties.  It leads to the same output as
   setting a longer active interval timer on Original Exporters with one
   advantage: the creation of new metrics such as average, maximum and
   minimum values from Flow Records with a shorter time interval enables
   administrators to keep track of changes that might have happened
   during the time interval.




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   Implementation analysis:

      One possible implementation for this case uses an IPFIX
      Concentrator located between the Metering Processes and Exporting
      Processes on the Original Exporter, or alternatively a separate
      IPFIX Concentrator located between the Original Exporters and
      IPFIX Collectors.

5.5.  Spatial Composition

   Spatial composition is defined as the aggregation of Data Records in
   a set of Observation Points within an Observation Domain, across
   multiple Observation Domains from a single Exporter, or even across
   multiple Exporters.  The spatial composition is divided into four
   types.

   o  Case 1: Spatial Composition within one Observation Domain

      For example, in the case where a link aggregation exists, Data
      Records metered at physical interfaces belonging to the same trunk
      can be merged.

   o  Case 2: Spatial Composition across Observation Domains, but within
      a single Exporter

      For example, in the case where a link aggregation exists, Data
      Records metered at physical interfaces belonging to a same trunk
      grouping beyond the line interface module can be merged.

   o  Case 3: Spatial Composition across Exporters

      Data Records metered within an administrative domain, such as the
      west area and east area of an ISP network, can be merged.

   o  Case 4: Spatial Composition across administrative domains

      Data Records metered across administrative domains, such as across
      different customer networks or different ISP networks, can be
      merged.

   Implementation analysis:

      One possible implementation for the cases 1 and 2 uses an IPFIX
      Concentrator located between the Metering Processes and Exporting
      Processes on the Original Exporter.  A separate IPFIX Concentrator
      located between the Original Exporters and IPFIX Collector is a
      valid solution for the cases 1, 2, 3, and 4.




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5.6.  Data Record Anonymization

   IPFIX exports across administrative domains can be used to measure
   traffic for wide-area traffic engineering or to analyze Internet
   traffic trends, as described in the spatial composition across
   administrative domains in the previous subsection.
   In such a case, administrators need to adhere to privacy protection
   policies and prevent access to confidential traffic measurements by
   other people.  Typically, anonymization techniques enables the
   provision of traffic data to other people without violating these
   policies.

   Generally, anonymization modifies a data set to protect the identity
   of the people or entities described by the data set from being
   disclosed.  It also attempts to preserve sets of network traffic
   properties useful for a given analysis while ensuring the data cannot
   be traced back to the specific networks, hosts, or users generating
   the traffic.  For example, IP address anonymization is particularly
   important for avoiding the identification of the users, hosts, and
   routers.  As another example, when ISP provides a traffic monitoring
   service to end customers by their own Exporters, even in case of
   exporting interface index fields, network administrators take care of
   anonymizing its fields to avoid disclosing the vulnerability.

   Implementation analysis:

      One possible implementation for this case uses an anonymization
      function at the Original Exporter.  However, this increases the
      load on the Original Exporter.  A more flexible implementation
      uses a separate IPFIX Masquerading Proxy between the Original
      Exporter and Collector.

5.7.  Data Retention

   Data retention refers to the storage of traffic data by service
   providers and commercial organizations.  Legislative regulations
   often require that network operators retain both IP traffic data and
   call detail records, in wired and wireless networks, generated by end
   users while using a service provider's services.  The traffic data is
   required for the purpose of the investigation, detection and
   prosecution of serious crime, if necessary.  Data retention services
   examples are the following:

   o  Fixed telephony (includes fixed voice calls, voicemail, and
      conference and data calls)

   o  Mobile telephony (includes mobile voice calls, voicemail,
      conference and data calls, SMS, and MMS)



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   o  Internet telephony (includes every multimedia session associated
      with IP multimedia services)

   o  Internet e-mail

   o  Internet access

   Data retention for Internet access services in particular requires a
   measurement system with reliable export and huge storage as the data
   must be available for a long period of time, typically at least six
   months.

   Implementation analysis:

      Regarding export reliability requirement, the most suitable
      implementation uses the SCTP transport protocol between the
      Original Exporter and Collector.  If an unreliable transport
      protocol such as UDP is used, a legacy exporting device exports
      Data Records to a nearby IPFIX Proxy through UDP, and then an
      IPFIX Proxy could reliably export them to the IPFIX Collector
      through SCTP.  If an unreliable transport protocol such as UDP is
      used and if there is no IPFIX Proxy, the legacy exporting device
      should duplicate the exports to several Collectors to lower the
      probability of loosing Flow Records.  However, it might result in
      network congestion, unless dedicated export links are used.

      Regarding huge storage requirement, one possible implementation
      adopts a distributed measurement system to increase the storage
      capacity, by locating Collectors closer to the Exporters.  In such
      a case, those Collectors would become IPFIX Mediators, re-
      exporting Data Records on demand to a centralized application.

5.8.  IPFIX Export from a Branch Office

   Generally, in large enterprise networks, Data Records from branch
   offices are gathered in a central office.  However, in the long
   distance branch office case, the bandwidth for transport IPFIX is
   limited.  Therefore, even if multiple Data Record types should be of
   interest to the Collector (e.g., IPFIX Flow Records in both
   directions, IPFIX Flow Records before and after WAN optimization
   techniques, performance metrics associated with the IPFIX Flow
   Records exported on regular interval, etc.), the export bandwidth
   limitation is an important factor to pay attention to.

   Implementation analysis:

      One possible implementation for this case uses an IPFIX
      Concentrator located in a branch office.  The IPFIX Concentrator



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      would aggregate and correlate Data Records to cope with the export
      bandwidth limitation.

5.9.  Distributing Data Records

   Recently, several networks have shifted towards integrated networks,
   such as the pure IP and MPLS networks, which includes IPv4, IPv6, and
   VPN traffic.  Data Record types (IPv4, IPv6, MPLS, and VPN) need to
   be analyzed separately and from different perspectives for different
   organizations.  A single Collector handling all Data Record types
   might become a bottleneck in the collecting infrastructure.  Data
   Records distributed based on their respective types can be exported
   to the appropriate Collector, resulting in the load distribution
   amongst multiple Collectors.

   Implementation analysis:

      One possible implementation for this case uses the replications of
      the IPFIX Message in an Original Exporter for multiple IPFIX
      Collectors.  Each Collector then extracts the Data Record required
      by its own applications.  However, the replication increases the
      load of the Exporting Process and the waste of the bandwidth
      between the Exporter and Collector.

      A more sophisticated implementation uses an IPFIX Distributor
      located between the Metering Processes and Exporting Processes in
      an Original Exporter.  The IPFIX Distributor determines to which
      Collector a Data Record is exported depending on certain field
      values.  If a Original Exporter does not have IPFIX Distributor
      capability, it exports Data Records to a nearby separate IPFIX
      Distributor, and then the IPFIX Distributor could distribute them
      to the appropriate IPFIX Collectors.

      For example, in the case of distributing a specific customer's
      Data Records, an IPFIX Distributor needs to identify the customer
      networks.  The Route Distinguisher (RD), ingress interface,
      peering AS number, or BGP Next-Hop, or simply the network prefix
      may be evaluated to distinguish different customer networks.  In
      the following figure, the IPFIX Distributor reroutes Data Records
      on the basis of the RD value.  This system enables each customer's
      traffic to be inspected independently.










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                                               .---------.
                                               |Traffic  |
                                         .---->|Collector|<==>Customer#A
                                         |     |#1       |
                                         |     '---------'
                                      RD=100:1
    .----------.        .-----------.    |
    |IPFIX     |        |IPFIX      |----'     .---------.
    |Exporter#1|        |Distributor| RD=100:2 |Traffic  |
    |          |------->|           |--------->|Collector|<==>Customer#B
    |          |        |           |          |#2       |
    |          |        |           |----.     '---------'
    '----------'        '-----------'    |
                                      RD=100:3
                                         |     .---------.
                                         |     |Traffic  |
                                         '---->|Collector|<==>Customer#C
                                               |#3       |
                                               '---------'

      Figure A: Distributing Data Records to Collectors using IPFIX
      Distributor

5.10.  Flow-based Sampling and Selection

   Generally, the distribution of the number of packets per Flow seems
   to be heavy-tailed.  Most types of Flow Records are likely to be
   small Flows consisting of a small number of packets.  The measurement
   system is overwhelmed with a huge amount of these small Flows.  If
   statistics information of small Flows is exported as merged data by
   applying a policy or threshold, the load on the Exporter is reduced.
   Furthermore, if the flow distribution is known, exporting only a
   subset of the Data Records might be sufficient.

   Implementation analysis:

      One possible implementation for this case uses an IPFIX
      Concentrator located between the Metering Processes and Exporting
      Processes on the Original Exporter, or alternatively a separate
      IPFIX Concentrator located between the Original Exporters and
      IPFIX Collectors.  A set of IPFIX Mediation functions, such as
      filtering, selecting and aggregation is used in the IPFIX
      Concentrator.








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5.11.  Interoperability between Legacy Protocols and IPFIX

   During the migration process from a legacy protocol such as NetFlow
   [RFC3954] to IPFIX, both NetFlow exporting devices and IPFIX
   Exporters are likely to coexist in the same network.  Operators need
   to continue measuring the traffic data from legacy exporting devices,
   even after introducing IPFIX Collectors.

   Implementation analysis:

      One possible implementation for this case uses an IPFIX Proxy that
      converts a legacy protocol to IPFIX.







































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6.  IPFIX Mediators Implementation Specific Problems

6.1.  Loss of Original Exporter Information

   Both the Exporter IP address indicated by the source IP address of
   the IPFIX Transport Session and the Observation Domain ID included in
   the IPFIX Message header are likely to be lost during IPFIX
   Mediation.  In some cases, a IPFIX Masquerading Proxy might drop the
   information deliberately.  In general, however, the Collector must
   recognize the origin of the measurement information, such as the IP
   address of the Original Exporter, the Observation Domain ID, or even
   the Observation Point ID.  Note that, if an IPFIX Mediator can not
   communicate the Original Exporter IP address, then the IPFIX
   Collector will wrongly deduce that the IP address of the IPFIX
   Mediator is that of the Original Exporter.

   In the following figure, a Collector can identify two IP addresses:
   10.1.1.3 (IPFIX Mediator) and 10.1.1.2 (Exporter#2), respectively.
   The Collector, however, needs to somehow recognize both Exporter#1
   and Exporter#2, which are the Original Exporters.  The IPFIX Mediator
   must be able to notify the Collector about the IP address of the
   Original Exporter.

   .----------.          .--------.
   |IPFIX     |          |IPFIX   |
   |Exporter#1|--------->|Mediator|---+
   |          |          |        |   |
   '----------'          '--------'   |      .---------.
   IP:10.1.1.1         IP:10.1.1.3    '----->|IPFIX    |
   ODID:10             ODID:0                |Collector|
                                      +----->|         |
   .----------.                       |      '---------'
   |IPFIX     |                       |
   |Exporter#2|-----------------------'
   |          |
   '----------'
   IP:10.1.1.2
   ODID:20

   Figure B: Loss of Original Exporter Information.

6.2.  Loss of Base Time Information

   The Export Time field included in the IPFIX Message header represents
   a reference timestamp for Data Records.  Some IPFIX Information
   Elements, described in [RFC5102], carry delta timestamps that
   indicate the time difference from the value of the Export Time field.
   If the Data Records include any delta time fields and the IPFIX



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   Mediator overwrites the Export Time field when sending IPFIX
   Messages, the delta time fields become meaningless and, because
   Collectors cannot recognize this situation, wrong time values are
   propagated.

6.3.  Transport Sessions Management

   Maintaining relationships between the incoming Transport Sessions and
   the outgoing ones depends on the Mediator's implementation.  If an
   IPFIX Mediator relays multiple incoming Transport Sessions to a
   single outgoing Transport Session, and if the IPFIX Mediators shuts
   down its outgoing Transport Session, Data Records of the incoming
   Transport Sessions would not be relayed any more.  In the case of
   resetting an incoming session, the behavior of the IPFIX Mediator
   needs to be specified.

6.4.  Loss of Options Template Information

   In some cases, depending on the implementation of the IPFIX
   Mediators, the information reported in the Data Records defined by
   Options Templates could also be lost.  If, for example, the Sampling
   rate is not communicated from the Mediator to the Collector, the
   Collector would miscalculate the traffic volume.  This might lead to
   crucial problems.  Even if an IPFIX Mediator was to simply relay
   received Data Records defined by Options Templates, the values of its
   scope fields could become meaningless in the content of a different
   Transport Sessions.  The minimal information to be communicated by an
   IPFIX Mediator must be specified.

6.5.  Template ID Management

   The Template ID is unique on the basis of the Transport Session and
   Observation Domain ID.  If an IPFIX Mediation is not able to manage
   the relations amongst the Template IDs and the incoming Transport
   Session information, and if the Template ID is used in the Options
   Template scope, IPFIX Mediators would, for example, relay wrong
   values in the scope field and in the Template Withdrawal Message.
   The Collector would thus not be able to interpret the Template ID in
   the Template Withdrawal Message and in the Options Template scope.
   As a consequence, there is a risk that the Collector would then shut
   down the IPFIX Transport Session.

   For example, an IPFIX Distributor must maintain the state of the
   incoming Transport Sessions in order to manage the Template ID on its
   outgoing Transport Session correctly.  Even if the Exporter Transport
   Session re-initializes, the IPFIX Distributor must manage the
   association of Template IDs in specific Transport Session.  In the
   following figure, the IPFIX Distributor exports three Templates (256,



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   257, and 258), received respectively from Exporter#3, Exporter#2, and
   Exporter#1.  If the Exporter#1 re-initializes, and the Template ID
   value 258 is now replaced with 256, the IPFIX Distributor must
   correctly manage the new mapping of (incoming Transport Session,
   Template ID) and (outgoing Transport Session, Template ID) without
   shutting down its outgoing Transport Session.


   .----------. OLD: Template ID 258
   |IPFIX     | NEW: Template ID 256
   |Exporter#1|----+
   |          |    |
   '----------'    X
   .----------.    |           .-----------.               .----------.
   |IPFIX     |    '---------->|           |               |          |
   |Exporter#2|--------------->|IPFIX      |-------------->|IPFIX     |
   |          |Template ID 257 |Distributor|Template ID 258| Collector|
   '----------'    +---------->|           |Template ID 257|          |
   .----------.    |           '-----------'Template ID 256'----------'
   |IPFIX     |    |
   |Exporter#3|----'
   |          | Template ID 256
   '----------'

   Figure C: Relaying from Multiple Transport Sessions to Single
   Transport Session.

6.6.  Consideration for Network Topology

   While IPFIX Mediation can be applied anywhere, caution should be
   taken as how to aggregate the counters, as there is a potential risk
   of double-counting.  For example, if three Exporters export PSAMP
   Packet Reports related to the same Flow, the one-way delay can be
   calculated, while summing up the number of packets and bytes does not
   make sense.  Alternatively, if three Exporters export Flow Records
   entering an administrative domain, then the sum of the packets and
   bytes is a valid operation.  Therefore, the possible function to be
   applied to Flow Records must take into consideration the measurement
   topology.  The information such as the network topology, or at least
   the Observation Point and measurement direction, is required for
   IPFIX Mediation.

6.7.  Exporting the Function Item

   In some case, the IPFIX Collector needs to recognize which specific
   function(s) the IPFIX Mediation has executed on the Data Records.
   The IPFIX Collector cannot distinguish between time composition,
   spatial composition, and Flow Key aggregation, if the IPFIX Mediator



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   does not export the applied function.  Some parameters related to the
   function also would need to be exported.  For example, in case of
   time composition, the active time of original Flow Records is
   required to interpret the minimum/maximum counter correctly.  In case
   of spatial composition, spatial area information on which Data
   Records is aggregated is required.

6.8.  Consideration for Aggregation

   Whether the aggregation is based on time or spatial composition,
   caution should be taken on how to aggregate non-key fields in IPFIX
   Mediation.  The IPFIX information model [RFC5102] specifies that the
   value of non-key fields, which are derived from fields of packets or
   from packet treatment and for which the value may change from packet
   to packet within a single Flow, is determined by the first packet
   observed for the corresponding Flow, unless the description of the
   Information Element explicitly specifies a different semantics.

   However, this simple rule might not be appropriate when aggregating
   Flow Records which have different values in a non-key field.  For
   example, if two Flows with identical Flow Key values are measured at
   different Observation Points, they may contain identical packets
   observed at different locations in the network and at different
   points in time.  On their way from the first to the second
   Observation Point, some of the packet fields, such as the DSCP, may
   have changed.  Hence, if the Information Element ipDiffServCodePoint
   is included as a non-key field, it can be useful to include the DSCP
   value observed at either the first or the second Observation Point in
   the resulting Flow Record, depending on the application.

   Other potential solutions include: removing the Information Element
   ipDiffServCodePoint from the Data Record when re-exporting the
   aggregate Flow Record, changing the Information Element
   ipDiffServCodePoint from a non key-field to a Flow Key when re-
   exporting the aggregated Flow Record, or assigning a non valid value
   for the Information Element to express to the Collector that this
   Information Element is meaningless.

   Furthermore, rules must be specify on how to aggregate the new
   Configured Selection Fraction an IPFIX Mediator should report when
   aggregating IPFIX Flow Records with different sampling rates.
   Finally, special care must be taken when aggregating Flow Records
   resulting from different Sampling techniques such as Systematic
   Count-Based Sampling and Random n-out-of-N Sampling for example.







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7.  Summary and Conclusion

   This document described the problems that network administrators have
   been facing, the applicability of IPFIX Mediation to these problems,
   and the problems related to the implementation of IPFIX Mediators.
   To assist the operations of the Exporters and Collectors, there are
   various IPFIX Mediations from which the administrators may select.
   Examples of the applicability of IPFIX Mediation are as follows.

   o  Regarding large-scale measurement system, IPFIX Concentrators or
      IPFIX Distributors help to achieve traffic analysis with high data
      accuracy and fine flow granularity even as IP traffic grows.  As
      IPFIX Mediation capabilities, Flow sampling, aggregation, and
      composition are effective.

   o  Regarding data retention, IPFIX Mediators enhance the export
      reliability, and the storage of the measurement system.

   o  Regarding the distribution of Data Records, IPFIX Distributors
      help to achieve multipurpose traffic analysis for different
      organizations, or help to achieve respective traffic analysis
      based on Data Record types(IPv4, IPv6, MPLS, and VPN).

   o  Regarding the IPFIX export across domains, IPFIX Masquerading
      Proxies help administrators to anonymize or filter Data Records,
      preventing privacy violations.

   o  Regarding interoperability, IPFIX Proxies provide interoperability
      between legacy protocols and IPFIX, even during the migration
      period to IPFIX.

   As a result, the IPFIX Mediation benefits become apparent.  However,
   there are still some open issues with the use of IPFIX Mediators.

   o  Both Observation Point and IPFIX Message header information, such
      as the Exporter IP address, Observation Domain ID, and Export Time
      field, might be lost.  This data should therefore be communicated
      between the Original Exporter and Collector via the IPFIX
      Mediator.

   o  IPFIX Mediators are required to manage Transport Sessions,
      Template IDs, and Observation Domain IDs.  Otherwise, anomalous
      IPFIX Messages could be created.

   o  Data Records defined by Options Templates, such as those reporting
      the Sampling rate and Sampling algorithm used, might be lost
      during IPFIX Mediation.  If a Collector is not informed of current
      Sampling rates, traffic information might become worthless.



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   These problems stem from the fact that no standards regarding IPFIX
   Mediation have been set.  In particular, the minimum set of
   information that should be communicated between Original Exporters
   and Collectors, the management between different IPFIX Transport
   Sessions, and the internal components of IPFIX Mediators should be
   standardized.













































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8.  Security Considerations

   A flow-based measurement system must prevent potential security
   threats: the disclosure of confidential traffic data, injection of
   incorrect data, and unauthorized access to traffic data.  These
   security threats of the IPFIX protocol are covered by the security
   considerations section in [RFC5101] and are still valid for IPFIX
   Mediators.

   And a measurement system must also prevent the following security
   threats related to IPFIX Mediation:

   o  Attacks against IPFIX Mediator

      IPFIX Mediators can be considered as a prime target for attacks,
      as an alternative to IPFIX Exporters and Collectors.  IPFIX
      Proxies or Masquerading Proxies need to prevent unauthorized
      access or denial-of-service (DoS) attacks from untrusted public
      networks.

   o  Man-in-the-middle attack by untrusted IPFIX Mediator

      The Exporter-Mediator-Collector structure model would increase the
      risk of the man-in-the-middle attack.

   o  Configuration on IPFIX Mediation

      In the case of IPFIX Distributors and IPFIX Masquerading Proxies,
      an accidental misconfiguration and unauthorized access to
      configuration data could lead to the crucial problem of disclosure
      of confidential traffic data.




















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9.  IANA Considerations

   This document has no actions for IANA.
















































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10.  Acknowledgements

   We would like to thank the following persons: Gerhard Muenz for the
   thorough detail review and significant contribution regarding the
   improvement of whole sections; Keisuke Ishibashi for contribution
   during the initial phases of the document; Brian Trammel for
   contribution regarding the improvement of terminologies section;
   Nevil Brownlee, Juergen Schoenwaelder, Motonori Shindo for the
   technical reviews and feedback.










































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11.  References

11.1.  Normative References

   [RFC5101]  Claise, B., "Specification of the IP Flow Information
              Export (IPFIX) Protocol for the Exchange of IP Traffic
              Flow Information", January 2008.

   [RFC5476]  Claise, B., "Packet Sampling (PSAMP) Protocol
              Specifications", March 2009.

11.2.  Informative References

   [IPFIX-FILE]
              Trammell, B., Boschi, E., Mark, L., Zseby, T., and A.
              Wagner, "Specification of the IPFIX File Format",
              draft-ietf-ipfix-file-05 (work in progress) , August 2009.

   [IPFIX-MIB]
              Dietz, T., Claise, B., and A. Kobayashi, "Definitions of
              Managed Objects for IP Flow Information Export",
              draft-ietf-ipfix-mib-07 (work in progress) , July 2009.

   [PSAMP-MIB]
              Dietz, T. and B. Claise, "Definitions of Managed Objects
              for Packet Sampling", draft-ietf-psamp-mib-06 (work in
              progress) , June 2006.

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

   [RFC3954]  Claise, B., "Cisco Systems NetFlow Services Export Version
              9", October 2004.

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

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

   [RFC5472]  Zseby, T., Boschi, E., Brownlee, N., and B. Claise, "IP
              Flow Information Export (IPFIX) Applicability",
              March 2009.

   [RFC5474]  Duffield, N., "A Framework for Packet Selection and
              Reporting", March 2009.



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

   [RFC5477]  Dietz, T., Claise, B., Aitken, P., Dressler, F., and G.
              Carle, "Information Model for Packet Sampling Exports",
              March 2009.

   [TRAFGRW]  Cho, K., Fukuda, K., Esaki, H., and A. Kato, "The Impact
              and Implications of the Growth in Residential User-to-User
              Traffic", SIGCOMM2006, pp. 207-218, Pisa, Italy, September
              2006. .







































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Authors' Addresses

   Atsushi Kobayashi
   NTT Information Sharing Platform Laboratories
   3-9-11 Midori-cho
   Musashino-shi, Tokyo  180-8585
   Japan

   Phone: +81-422-59-3978
   Email: akoba@nttv6.net


   Benoit Claise
   Cisco Systems, Inc.
   De Kleetlaan 6a b1
   Diegem  1831
   Belgium

   Phone: +32 2 704 5622
   Email: bclaise@cisco.com


   Haruhiko Nishida
   NTT Information Sharing Platform Laboratories
   3-9-11 Midori-cho
   Musashino-shi, Tokyo  180-8585
   Japan

   Phone: +81-422-59-3978
   Email: nishida.haruhiko@lab.ntt.co.jp


   Christoph Sommer
   University of Erlangen-Nuremberg
   Department of Computer Science 7
   Martensstr. 3
   Erlangen  91058
   Germany

   Phone: +49 9131 85-27993
   Email: christoph.sommer@informatik.uni-erlangen.de
   URI:   http://www7.informatik.uni-erlangen.de/~sommer/









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   Falko Dressler
   University of Erlangen-Nuremberg
   Department of Computer Science 7
   Martensstr. 3
   Erlangen  91058
   Germany

   Phone: +49 9131 85-27914
   Email: dressler@informatik.uni-erlangen.de
   URI:   http://www7.informatik.uni-erlangen.de/~dressler/


   Stephan Emile
   France Telecom
   2 avenue Pierre Marzin
   Lannion,   F-22307

   Fax:   +33 2 96 05 18 52
   Email: emile.stephan@orange-ftgroup.com
































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