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INFORMATIONAL

Internet Engineering Task Force (IETF)                 A. Kobayashi, Ed.
Request for Comments: 5982                                   NTT PF Lab.
Category: Informational                                   B. Claise, Ed.
ISSN: 2070-1721                                      Cisco Systems, Inc.
                                                             August 2010


    IP Flow Information Export (IPFIX) Mediation: Problem Statement

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 IP Flow
   Information Export (IPFIX) Mediation may help resolve.  This document
   describes some problems related to flow-based measurement that
   network administrators have been facing, and then it describes IPFIX
   Mediation applicability examples along with the problems.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc5982.

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
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must



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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................3
   2. Terminology and Definitions .....................................3
   3. IPFIX/PSAMP Documents Overview ..................................5
      3.1. IPFIX Documents Overview ...................................5
      3.2. PSAMP Documents Overview ...................................5
   4. Problem Statement ...............................................5
      4.1. Coping with IP Traffic Growth ..............................6
      4.2. Coping with Multipurpose Traffic Measurement ...............7
      4.3. Coping with Heterogeneous Environments .....................7
      4.4. Summary ....................................................7
   5. Mediation Applicability Examples ................................8
      5.1. Adjusting Flow Granularity .................................8
      5.2. Collecting Infrastructure ..................................8
      5.3. Correlation for Data Records ...............................9
      5.4. Time Composition ...........................................9
      5.5. Spatial Composition .......................................10
      5.6. Data Record Anonymization .................................11
      5.7. Data Retention ............................................11
      5.8. IPFIX Export from a Branch Office .........................12
      5.9. Distributing Data Record Types ............................13
      5.10. Flow-Based Sampling and Selection ........................14
      5.11. Interoperability between Legacy Protocols and IPFIX ......15
   6. IPFIX Mediators' Implementation-Specific Problems ..............15
      6.1. Loss of Original Exporter Information .....................15
      6.2. Loss of Base Time Information .............................16
      6.3. Transport Sessions Management .............................16
      6.4. Loss of Options Template Information ......................16
      6.5. Template ID Management ....................................17
      6.6. Consideration for Network Topology ........................18
      6.7. IPFIX Mediation Interpretation ............................18
      6.8. Consideration for Aggregation .............................19
   7. Summary and Conclusion .........................................20
   8. Security Considerations ........................................20
   9. Acknowledgements ...............................................21
   10. References ....................................................22
      10.1. Normative References .....................................22
      10.2. Informative References ...................................22
   Contributors ......................................................24







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1.  Introduction

   An advantage of flow-based measurement is that it allows monitoring
   large amounts 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.  IP
   Flow Information Export (IPFIX) Mediation fills the gap between
   restricted metering capabilities and the requirements of measurement
   applications by introducing an intermediate device called the 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/Packet
   Sampling (PSAMP) document overview, Section 4 introduces general
   problems related to flow-based measurement, Section 5 describes some
   applicability examples where IPFIX Mediation would be beneficial,
   and, finally, Section 6 describes some problems an IPFIX Mediation
   implementation might face.

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 terms 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.






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   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,
      e.g., in the case of conversion from the NetFlow V9 protocol
      [RFC3954] to the 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 as IPFIX Flow Records by the
   IPFIX protocol, and the packet-based information is extracted by some
   packet selection techniques and then encoded as PSAMP Packet Reports
   by the 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].  [RFC5815] 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.  Furthermore, it 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.

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



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   parameters of metering devices 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
   capacities of measurement systems.  Furthermore, a large variety of
   applications (e.g., Quality-of-Service (QoS) measurement, traffic
   engineering, security monitoring) and the deployment of measurement
   systems 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 a 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.

   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.








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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 diverse 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, and various device types
   (router, switch, or probe) in a single network domain.  Even legacy
   flow export protocols are still deployed in current networks.  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

   The 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 Exporters 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 Records and
   metadata 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 the correlation of two PSAMP
         Packet Reports, including the packet digest and the arrival
         time at the Observation Point.  This scenario is described in
         Section 6.2.1.2 of [RFC5475].

      *  Packet inter-arrival time from the correlation of sequential
         PSAMP Packet Reports from an 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 Records and other metadata

      Examples are some BGP attributes associated with Data Records, as
      determined via routing table lookup.

   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



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   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.

   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  Case 1: Spatial composition within one Observation Domain

      For example, to measure the traffic for a single logical interface
      in the case in which link aggregation [IEEE802.3ad] 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 Original Exporter

      For example, in the case in which link aggregation exists, Data
      Records metered at physical interfaces belonging to the same trunk
      grouping beyond the line card 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.  For example, a unique Collector knows in which customer
      network an Exporter exists, and then works out the traffic data
      per customer based on the Exporter IP address.




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   Implementation analysis:

      One possible implementation for 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 Collectors is a
      valid solution for 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 that 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






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   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 examples
   relevant to IP networks are the following:

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

   o  Internet email

   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 Stream Control Transmission Protocol
      (SCTP) 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 losing Flow
      Records.  However, it might result in network congestion, unless
      dedicated export links are used.

      Regarding huge storage requirements, 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 at regular intervals, etc.), the export bandwidth
   limitation is an important factor to pay attention to.





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   Implementation analysis:

      One possible implementation for this case uses an IPFIX Mediator
      located in a branch office.  The IPFIX Mediator would aggregate
      and correlate Data Records to cope with the export bandwidth
      limitation.

5.9.  Distributing Data Record Types

   Recently, several networks have shifted towards integrated networks,
   such as the pure IP and MPLS networks, which include 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 load distribution amongst
   multiple Collectors.

   Implementation analysis:

      One possible implementation for this case uses replication 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, this replication increases the
      load of the Exporting Process and the waste of 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 an 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 Autonomous System (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.

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.
















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      .----------.          .--------.
      |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
   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 Mediator shuts
   down its outgoing Transport Session, Data Records of the incoming
   Transport Sessions would not be relayed anymore.  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



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   crucial problems.  Even if an IPFIX Mediator were 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 Session.  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 Mediator is not able to manage
   the relationships 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 a specific Transport Session.  In the
   following figure, the IPFIX Mediator exports three Templates (256,
   257, and 258), received from Exporter#3, Exporter#2, and Exporter#1,
   respectively.  If 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.




















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   .----------. 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 a Single Transport Session

6.6.  Consideration for Network Topology

   While IPFIX Mediation can be applied anywhere, caution should be
   taken as to 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 cases, 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
   applied function.  Some parameters related to the function also would
   need to be exported.  For example, in the case of time composition,
   the active timeout of original Flow Records is required to interpret
   the minimum/maximum counter correctly.  In the case of spatial
   composition, spatial area information on which Data Records is
   aggregated is required.





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6.8.  Consideration for Aggregation

   Whether the aggregation is based on time or spatial composition,
   caution should be taken regarding 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 that 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 describes 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
   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.

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 a 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.




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   o  Unintentional exposure of end-user information

      The probability of collecting fine-grained information on one
      arbitrary end user increases with the number of Observation
      Points.  An IPFIX Mediator facing such a 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 those tenants or customers from one
      another's traffic data.  For example, an IPFIX Mediator needs to
      identify the customer's identifier, e.g., ingress interface index,
      network address range, VLAN ID, Media Access Control (MAC)
      address, etc., when feeding the customer's traffic data to a
      customer's own dedicated IPFIX Collector.  If the IPFIX Mediator
      cannot identify each customer's traffic data, it may need to drop
      the Data Records.  In addition, another technique to keep track of
      a customer's identifier may be required when customer sites are
      movable, e.g., in the case of a 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 confidential and integrity-protected, e.g., by
      using Transport Layer Security (TLS) [RFC5246] or Datagram
      Transport Layer Security (DTLS) [RFC4347].  However, an IPFIX
      Collector cannot 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 cannot
      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 cannot trust its Data
      Records.  If this information is required on the IPFIX Collector,
      it must be encoded in the IPFIX Mediator.

9.  Acknowledgements

   We would like to thank the following persons: Gerhard Muenz for
   thorough, detailed review and significant contributions regarding the
   improvement of whole sections; Keisuke Ishibashi for contributions



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   during the initial phases of the document; Brian Trammell for
   contributions regarding the improvement of the Terminology and
   Definitions section; and Nevil Brownlee, Juergen Schoenwaelder, and
   Motonori Shindo for their technical reviews and feedback.

10.  References

10.1.  Normative References

   [RFC5101]      Claise, B., Ed., "Specification of the IP Flow
                  Information Export (IPFIX) Protocol for the Exchange
                  of IP Traffic Flow Information", RFC 5101,
                  January 2008.

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

10.2.  Informative References

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

   [PSAMP-MIB]    Dietz, T., Ed., Claise, B., and J. Quittek,
                  "Definitions of Managed Objects for Packet Sampling",
                  Work in Progress, July 2010.

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

   [RFC3954]      Claise, B., Ed., "Cisco Systems NetFlow Services
                  Export Version 9", RFC 3954, October 2004.

   [RFC4347]      Rescorla, E. and N. Modadugu, "Datagram Transport
                  Layer Security", RFC 4347, April 2006.

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

   [RFC5246]      Dierks, T. and E. Rescorla, "The Transport Layer
                  Security (TLS) Protocol Version 1.2", RFC 5246, August
                  2008.

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



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   [RFC5472]      Zseby, T., Boschi, E., Brownlee, N., and B. Claise,
                  "IP Flow Information Export (IPFIX) Applicability",
                  RFC 5472, March 2009.

   [RFC5474]      Duffield, N., Ed., Chiou, D., Claise, B., Greenberg,
                  A., Grossglauser, M., and J. Rexford, "A Framework for
                  Packet Selection and Reporting", RFC 5474, March 2009.

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

   [RFC5477]      Dietz, T., Claise, B., Aitken, P., Dressler, F., and
                  G.  Carle, "Information Model for Packet Sampling
                  Exports", RFC 5477, March 2009.

   [RFC5655]      Trammell, B., Boschi, E., Mark, L., Zseby, T., and A.
                  Wagner, "Specification of the IP Flow Information
                  Export (IPFIX) File Format", RFC 5655, October 2009.

   [RFC5815]      Dietz, T., Ed., Kobayashi, A., Claise, B., and G.
                  Muenz, "Definitions of Managed Objects for IP Flow
                  Information Export", RFC 5815, April 2010.

   [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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Contributors

   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/


   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
   France

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







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Authors' Addresses

   Atsushi Kobayashi (editor)
   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 (editor)
   Cisco Systems, Inc.
   De Kleetlaan 6a b1
   Diegem  1831
   Belgium

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































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