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Versions: 00 01 02 03 04 05 06 07 08 09 rfc5982            Informational
IPFIX Working Group                                    A. Kobayashi, Ed.
Internet-Draft                                               NTT PF Lab.
Intended status: Informational                            B. Claise, Ed.
Expires: September 28, 2010                          Cisco Systems, Inc.
                                                          March 27, 2010







                   IPFIX Mediation: Problem Statement
            draft-ietf-ipfix-mediators-problem-statement-09

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 some problems related to
   flow-based measurement that network administrators have been facing,
   and then describes IPFIX Mediation applicability examples along with
   the problems.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on September 28, 2010.

Copyright Notice

   Copyright (c) 2010 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.



































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology and Definitions  . . . . . . . . . . . . . . . . .  5
   3.  IPFIX/PSAMP Documents Overview . . . . . . . . . . . . . . . .  7
     3.1.  IPFIX Documents Overview . . . . . . . . . . . . . . . . .  7
     3.2.  PSAMP Documents Overview . . . . . . . . . . . . . . . . .  7
   4.  Problem Statement  . . . . . . . . . . . . . . . . . . . . . .  8
     4.1.  Coping with IP Traffic Growth  . . . . . . . . . . . . . .  8
     4.2.  Coping with Multipurpose Traffic Measurement . . . . . . .  9
     4.3.  Coping with Heterogeneous Environments . . . . . . . . . .  9
     4.4.  Summary  . . . . . . . . . . . . . . . . . . . . . . . . .  9
   5.  Mediation Applicability Examples . . . . . . . . . . . . . . . 10
     5.1.  Adjusting Flow Granularity . . . . . . . . . . . . . . . . 10
     5.2.  Collecting Infrastructure  . . . . . . . . . . . . . . . . 10
     5.3.  Correlation for Data Records . . . . . . . . . . . . . . . 11
     5.4.  Time Composition . . . . . . . . . . . . . . . . . . . . . 11
     5.5.  Spatial Composition  . . . . . . . . . . . . . . . . . . . 12
     5.6.  Data Record Anonymization  . . . . . . . . . . . . . . . . 13
     5.7.  Data Retention . . . . . . . . . . . . . . . . . . . . . . 13
     5.8.  IPFIX Export from a Branch Office  . . . . . . . . . . . . 14
     5.9.  Distributing Data Records  . . . . . . . . . . . . . . . . 15
     5.10. Flow-based Sampling and Selection  . . . . . . . . . . . . 16
     5.11. Interoperability between Legacy Protocols and IPFIX  . . . 17
   6.  IPFIX Mediators Implementation Specific Problems . . . . . . . 18
     6.1.  Loss of Original Exporter Information  . . . . . . . . . . 18
     6.2.  Loss of Base Time Information  . . . . . . . . . . . . . . 18
     6.3.  Transport Sessions Management  . . . . . . . . . . . . . . 19
     6.4.  Loss of Options Template Information . . . . . . . . . . . 19
     6.5.  Template ID Management . . . . . . . . . . . . . . . . . . 19
     6.6.  Consideration for Network Topology . . . . . . . . . . . . 20
     6.7.  IPFIX Mediation Interpretation . . . . . . . . . . . . . . 20
     6.8.  Consideration for Aggregation  . . . . . . . . . . . . . . 21
   7.  Summary and Conclusion . . . . . . . . . . . . . . . . . . . . 22
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 23
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 25
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 26
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 27
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 27
     11.2. Informative References . . . . . . . . . . . . . . . . . . 27
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29










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1.  Introduction

   An advantage of flow-based measurement is that it allows monitoring
   large amount of traffic observed at distributed observation points.
   While flow-based measurement can be applied to one of various
   purposes and applications, it is difficult for flow-based measurement
   to apply to multiple applications with very different requirements in
   parallel.  Network administrators need to adjust the parameters of
   the metering devices to fulfill the requirements of every single
   measurement application.  Such configurations are often not supported
   by the metering devices, either because of functional restrictions or
   because of limited computational and memory resources, which inhibit
   the metering of large amounts of traffic with the desired setup.
   IPFIX Mediation fills the gap between restricted metering
   capabilities and the requirements of measurement applications by
   introducing an intermediate device called IPFIX Mediator.

   The IPFIX requirements defined in [RFC3917] mention examples of
   intermediate devices located between Exporters and Collectors, such
   as IPFIX proxies or concentrators.  But, 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 call "record stream" a stream of records
   carrying flow- or packet-based information.  The records may be
   encoded as IPFIX Data Records or in any other format.

   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
      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,



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      e.g., in the case of conversion from the NetFlow V9 protocol
      [RFC3954] to IPFIX protocol.

      Note that the IPFIX Mediator is a generalization of the
      concentrator and proxy elements envisioned in the IPFIX
      requirements [RFC3917].  IPFIX Mediators running appropriate
      Intermediate Processes provide the functionality specified
      therein.











































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3.  IPFIX/PSAMP Documents Overview

   IPFIX Mediation can be applied to flow- or packet-based information.
   The flow-based information is encoded by IPFIX protocol, and the
   packet-based information is extracted by some sampling techniques and
   then encoded by PSAMP protocol.  Thus, this section describes
   relevant documents for both protocols.

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 [RFC5655].

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 packet Sampling,
   Filtering, Data Records aggregation and export replication, have
   already been developed.  The problems consist of adjusting some
   parameters of metering device to 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, 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 administrators monitor IP traffic
   sustaining its growth at multiple Exporters, the amount of exported
   Flow Records from Exporters could exceed the ability of single
   Collector.

   To deal with this problem, current data reduction techniques (packet
   Sampling and Filtering in [RFC5475], and aggregation of measurement
   data) have been generally implemented on Exporters.  Note that packet
   Sampling leads to potential loss of small Flows.  With both packet
   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.




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   Considering the potential drawbacks of packet Sampling, Filtering,
   and Data 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 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

   Due to resource limitations of the 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 the heterogeneous environment of exporting devices.
   On the other hand, keeping data accuracy and flow granularity to meet
   the requirements of different monitoring applications requires a
   scalable and flexible collecting infrastructure.

   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 simplest set of Flow Keys is a fixed 5-tuple of protocol, source
   and destination IP addresses, and source and destination port
   numbers.  A shorter set of Flow Keys, 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 router-level
   traffic matrices in a core 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 Flow Keys and extra fields.
      The Original Exporter thus generates Flow Records of the desired
      Flow granularity.

      In the case where a Metering Process hosting no ability to change
      the Flow Keys in Original Exporter creates Flow Records, or PSAMP
      Packet Reports, an IPFIX Mediator can aggregate Data Records based
      on a new set of Flow Keys.  Even in the case of a Metering Process
      hosting this ability, an IPFIX Mediator can further aggregate the
      Flow Records.

5.2.  Collecting Infrastructure

   Increasing numbers of IPFIX Exporters, IP traffic growth, and the
   variety of treatments expected to be performed on the Data Records
   make it more and more difficult to implement all measurement
   applications within a single Collector.

   Implementation analysis:

      To increase the collecting (e.g., the bandwidth capacity) and
      processing capacity, distributed Collectors close to Exporters
      need to be deployed.  In such a case, those Collectors would
      become IPFIX Mediators, re-exporting Data Records on demand to
      centralized applications.  To cope with the variety of measurement
      applications, one possible implementation uses an Intermediate
      Process deciding to which Collector(s) each record is exported.
      More specific cases are described in section 5.9.





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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.  For example, one
         way delay is calculated from correlation of two PSAMP Packet
         Reports including the packet digest and the arrival time at
         Observation Point.  This cases are described in section 6.2.1.2
         in [RFC5475].

      *  Packet inter-arrival time from the correlation of sequential
         PSAMP Packet Reports from a Exporter.

      *  Treatment from the correlation of Data Records with 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 Intermediate
      Process located between the Metering Processes and Exporting
      Processes on the Original Exporter, or alternatively a separate
      IPFIX Mediator located between the Original Exporters and IPFIX
      Collectors.

5.4.  Time Composition

   Time composition is defined as the aggregation of consecutive Data
   Records with identical Flow Keys.  It leads to the same output as
   setting a longer active timeout on Original Exporters with one
   advantage: the creation of new metrics such as average, maximum and



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   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.

   Implementation analysis:

      One possible implementation for this case uses an Intermediate
      Process located between the Metering Processes and Exporting
      Processes on the Original Exporter, or alternatively a separate
      IPFIX Mediator 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  Cases 1: Spatial composition within one Observation Domain

      For example, to measure the traffic for a single logical interface
      in the case where link aggregation [IEEE802.3ad] exists, Data
      Records metered at physical interfaces belonging to the same trunk
      can be merged.

   o  Cases 2: Spatial composition across Observation Domains, but
      within a single Original Exporter

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

   o  Cases 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  Cases 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.  For example, an unique Collector knows in which customer
      network an Explorter exists, and then works out the traffic data
      per customer based on the Explorter IP address.





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   Implementation analysis:

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

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 enable 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 users, hosts, and
   routers.  As another example, when an ISP provides traffic monitoring
   service to end customers, network administrators take care of
   anonymizing interface index fields which could disclose any
   information about the vendor or software version of the Exporters.

   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 Mediator 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



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   prosecution of serious crime, if necessary.  Data retention examples
   relevant to IP networks are the following:

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

   o  Internet e-mail

   o  Internet access

   Data retention for these 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 Mediator through UDP, and then an
      IPFIX Mediator 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 Mediator, 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, the collecting infrastructure
      is described in section 5.2.

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 transporting 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 Mediator
      located in a branch office.  The IPFIX Mediator would aggregate



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

      For example, in the case of distributing a specific customer's
      Data Records, an IPFIX Mediator 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 Mediator 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|        |Mediator   | 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
      Mediator

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 Intermediate
      Process located between the Metering Processes and Exporting
      Processes on the Original Exporter, or alternatively a separate
      IPFIX Mediator 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
      Mediator.








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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 Mediator
      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, an IPFIX Mediator 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 cannot
   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:
   192.0.2.3 (IPFIX Mediator) and 192.0.2.2 (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:192.0.2.1        IP:192.0.2.3    '----->|IPFIX    |
   ODID:10             ODID:0                 |Collector|
                                      +------>|         |
   .----------.                       |       '---------'
   |IPFIX     |                       |
   |Exporter#2|-----------------------'
   |          |
   '----------'
   IP:192.0.2.2
   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 Transport 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 Mediator 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 Mediator must manage the
   association of Template IDs in specific Transport Session.  In the
   following figure, the IPFIX Mediator 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 Mediator 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 |Mediator   |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.  IPFIX Mediation Interpretation

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



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   applied function.  Some parameters related to the function also would
   need to be exported.  For example, in case of time composition, the
   active timeout 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 Differentiated Services Code Point (DSCP) information is
   to be exported, the following problem can be observed: 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, the DSCP and
   potentially some other packet fields 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.

   If packet Sampling or Filtering is applied, the IPFIX Mediator must
   report an adjusted PSAMP Configured Selection Fraction 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, this
   document demonstrates that there exist various IPFIX Mediation
   functions from which the administrators may select.

   However, there are still some open issues with the use of IPFIX
   Mediators.  These issues 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 mapping 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.

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

   o  Attacks against an 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 could be misused
      for man-in-the-middle attack.

   o  Configuration on IPFIX Mediation

      An accidental misconfiguration and unauthorized access to
      configuration data could lead to the crucial problem of disclosure
      of confidential traffic data.

   o  Unintentional exposure of end user information

      The probability to collect fine-grained information on one
      arbitrary end-user increases with the number of Observation
      Points.  An IPFIX Mediator facing such situation may have to apply
      appropriate functions (e.g. anonymization or aggregation) to the
      Data Records it produces.

   o  Multiple-tenancy policy on an IPFIX Mediator

      An IPFIX Mediator handling traffic data from multiple tenants or
      customers needs to protect from one another traffic data.  For
      example, an IPFIX Mediator needs to identify the customer's
      identifier, e.g., ingress interface index, network address range,
      VLAN ID, MAC address, and etc., when feeding customer's traffic
      data to a customer own dedicated IPFIX Collector.  If the IPFIX
      Mediator can not identify each customer's traffic data, it may



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      need to drop the Data Records.  In addition, another technique to
      keep track of customer's identifier may be required when customer
      site are movable, e.g., in the case of virtual machine moving to
      another physical machine.

   o  Confidentiality protection via an IPFIX Mediator

      To ensure security of Data Records in transit, transport of Data
      Records should be confidentiality and integrity-protected, e.g. by
      using Transport Layer Security (TLS) [RFC4346] or Datagram
      Transport Layer Security (DTLS) [RFC4347].  However, an IPFIX
      Collector can not know whether received Data Records are
      transported as encrypted data between an Original Exporter and an
      IPFIX Mediator.  If this information is required on the IPFIX
      Collector, it must be encoded in the IPFIX Mediator.

   o  Certification for an Original Exporter

      An IPFIX Collector communicating via an IPFIX Mediator can not
      verify the identity of an Original Exporter directly.  If an
      Original Exporter and an IPFIX Collector are located in different
      administrative domains, an IPFIX Collector can not trust its Data
      Records.  If this information is required on the IPFIX Collector,
      it must be encoded in the IPFIX Mediator.



























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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 Trammell 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

   [IEEE802.3ad]
              IEEE Computer Society, "Link Aggregation", IEEE Std
              802.3ad-2000 , March 2000.

   [IPFIX-MIB]
              Dietz, T., Kobayashi, A., Claise, B., and G. Muenz,
              "Definitions of Managed Objects for IP Flow Information
              Export", draft-ietf-ipfix-mib-10 (work in progress) ,
              January 2010.

   [PSAMP-MIB]
              Dietz, T., Claise, B., and J. Quittek, "Definitions of
              Managed Objects for Packet Sampling",
              draft-ietf-ipfix-psamp-mib-00 (work in progress) ,
              March 2010.

   [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.

   [RFC4346]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.1", April 2006.

   [RFC4347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security", April 2006.

   [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.



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   [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.

   [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.

   [RFC5655]  Trammell, B., Boschi, E., Mark, L., Zseby, T., and A.
              Wagner, "Specification of the IP Flow Information Export
              (IPFIX) File Format", October 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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