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Re: [IPFIX] WG last call on draft-ietf-ipfix-mediators-problem-statement-06




Hi,

Here is my review of draft-ietf-ipfix-mediators-problem-statement-06.

The main content is ok. Some parts of the text still need revision.

I'm not sure if we need to define Mediator types like IPFIX Proxy, IPFIX Concentrator, IPFIX Distributor, IPFIX Masquerading Proxy in the terminology section. Why not just talk about IPFIX Mediators?

Regards,
Gerhard



Abstract

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

Shouldn't it be the other way round:
- first problems
- then applicability examples
?

1.  Introduction

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

Sorry, I can only guess what this paragraph is supposed to say.
Please rewrite in a better understandable and readable way.

BTW, I would be careful with terms like "optimize" and "optimization".


   The IPFIX requirements defined in [RFC3917] mention examples of
   intermediate devices, such as IPFIX Proxies or Concentrators, there

missing conjunction, such as "but", "yet", or something like that

The term "intermediate" or "intermediate device" does not appear in RFC3917. So, explain why you call these devices like this.
(For example, because they are located between Exporters and Collectors.)

   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.


2.  Terminology and Definitions

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

   In this document, we use the generic term "record stream" to denote a

I would not call "record stream" a "term" unless it appears in the list below with capitalized first letter.

   set of flow- or packet-based data records with their additional

I would not say that the records are flow-based or packet-based. They contain flow or packet information.

   information that flows from data sources, whether encoded in IPFIX
   protocol as IPFIX Data Records, or non-IPFIX protocols.  In IPFIX
   protocol, we use the generic term Data Records for IPFIX Flow
   Records, PSAMP Packet Reports, and Data Records defined by Options
   Templates, unless an explicit distinction is required.

Do we need the last sentence?

   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 IPFIX protocol.

   Specific types of IPFIX Mediators are defined below.

   IPFIX Proxy

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

   IPFIX Concentrator

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

   IPFIX Distributor

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

   IPFIX Masquerading Proxy

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

Do we really need these four terms?
I think that they can be removed. As Brian said, it is difficult to classify IPFIX Mediators according to these types.
All later occurrences of these terms can be replaced by "IPFIX Mediator".


4.  Problem Statement

   Network administrators generally face the problems of measurement
   system scalability, flow-based measurement flexibility, and export
   reliability, even if some techniques, such as Sampling, Filtering,
   Data Records aggregation and export replication, have already been
   developed.  The problems consist of optimizing the resources of the

How can you "optimize the resources"?

   measurement system while fulfilling appropriate conditions: data
   accuracy, flow granularity, and export reliability.  These conditions
   depend on two factors.

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

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

remove "etc."

      Record granularities, and data accuracies.

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

4.1.  Coping with IP Traffic Growth

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

This paragraph describes the situation today. Are we sure that these numbers are still valid next year? Maybe we are then able to process 50kFlows/s.
I would remove all these figures.

   To deal with this problem, current data reduction techniques
   (Sampling and Filtering in [RFC5475], and aggregation of measurement

"packet Sampling and Filtering"?

   data) have been generally implemented on Exporters.  Note that
   Sampling technique leads to potential loss of small Flows.  With both

"packet Sampling leads to..."

   Sampling and aggregation techniques, administrators might no longer
   be able to detect and investigate subtle traffic changes and
   anomalies as this requires detailed Flow information.  With
   Filtering, only a subset of the Data Records are exported.

   Considering the potential drawbacks of Sampling, Filtering, and Data
   Records aggregation, there is a need for a large-scale collecting
   infrastructure that does not rely on data reduction techniques.

Hm, I do not see this problem if a Collector receives data from a single Exporter. You should say that these problems arise if multiple Exporters send data to a single Collector.

4.2.  Coping with Multipurpose Traffic Measurement

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

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

4.3.  Coping with Heterogeneous Environments

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

remove "in [RFC5102]"

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

4.4.  Summary

   In optimizing the resources of a measurement system, it is important

I still do not understand what "optimize the resources" is supposed to mean.

   to use traffic data reduction techniques as early as possible, e.g.,
   at the Exporter.  However, this implementation is made difficult by
   heterogeneous environment of exporting devices.

Please revise the entire paragraph above. It only talks about data reduction. I do not think that this is the core of mediation.

   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.


5.  Mediation Applicability Examples

5.1.  Adjusting Flow Granularity

   A set of common properties of simplest Flow type is a fixed 5-tuple
   of protocol, source and destination IP addresses, and source and

As you talk about "Flow Keys", you should use this term and not invent a new one!

   destination port numbers.  A shorter set of common properties, such
   as a triple, a double, or a single property, (for example network
   prefix, peering autonomous system number, or BGP Next-Hop fields),
   creates more aggregated Flow Records.  This is especially useful for
   measuring traffic exchange in an entire network domain and for easily

What do you mean by "traffic exchange in an entire network domain"?

   adjusting the performance of Exporters and Collectors.

   Implementation analysis:

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

IMO, "aggregated Flow Record" is non-sense. If you look at the definition of "Flow", you see that this is a normal Flow Record. I would say that the Original Exporter generates Flow Records of the desired Flow granularity.

      In the case where the Original Exporter contains a Metering
      Process that creates fixed tuple Flow Records (no ability to

Replace "fixed tuple Flow Records" by correct IPFIX language.

      change the Flow Keys), or PSAMP Packet Reports, an IPFIX
      Concentrator can aggregate Data Records based on a new set of Flow
      Keys.  Even in the case where the Original Exporter contains a
      Metering Process for which the Flow Keys can be configured, an
      IPFIX Concentrator can further aggregate the Flow Records.

5.2.  Hierarchical Collecting Infrastructure

   The increase of IPFIX Exporters, the increase of the traffic, and the
   variety of treatments expected to be performed over the Data Records

over => on

   is more and more difficult to handle within a single Collector.
   Hence to increase the collecting (e.g., the bandwidth capacity) and
   processing capacity, distributed Collectors must be deployed.  As a
   possible approach, a hierarchical structure is useful for increasing

I don't understand how the collecting and processing capacity increases thanks to a hierarchical structure.

The capacity increases because I implement more resources in the network, e.g. more Collectors.

   the measurement systems capacity, both in export bandwidth capacity
   and in collecting capacity.

   Implementation analysis:

      To cope with the increase of IPFIX Exporters and traffic, one

"number of IPFIX Exporters" (only IPFIX?)

      possible implementation uses IPFIX Concentrators to build a
      hierarchical collection system.  To cope with the variety of
      treatments, one possible implementation uses IPFIX Distributors to
      build a distributed collection system.  More specific cases are
      described in section 5.9.


5.3.  Correlation for Data Records

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

   o  One-to-one correlation between Data Records

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

"packet inter-arrival times from the correlation of PSAMP Packet Reports generated by a single Exporter, etc."

      *  Treatment from the correlation of Data Records with the common

remove "the" in front of "common"

         properties, observed at incoming/outgoing interfaces.  Examples
         are the rate-limiting ratio, the compression ratio, the
         optimization ratio, etc.

   o  Correlation amongst Data Records

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

   o  Correlation between Data Record and other meta data

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

   Implementation analysis:

      One possible implementation for this case uses an IPFIX
      Concentrator located between the Metering Processes and Exporting

IPFIX Concentrator => Intermediate Process

      Processes on the Original Exporter, or alternatively a separate
      IPFIX Concentrator located between the Original Exporters and
      IPFIX Collectors.

5.4.  Time Composition

   Time composition is defined as the aggregation of consecutive Data
   Records with common properties.  It leads to the same output as

applies to Flow Records only?
common properties => Flow Keys?

   setting a longer active interval timer on Original Exporters with one

active timeouts?

   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.

Hm, changes can be much better detected by looking at the short-lived values directly instead of looking at the long-term average, maximum, or minimum.


   Implementation analysis:

      One possible implementation for this case uses an IPFIX
      Concentrator located between the Metering Processes and Exporting

Intermediate Process

      Processes on the Original Exporter, or alternatively a separate
      IPFIX Concentrator located between the Original Exporters and
      IPFIX Collectors.

5.5.  Spatial Composition

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

   o  Case 1: Spatial Composition within one Observation Domain

      For example, in the case where a link aggregation exists, Data

remove "a"

      Records metered at physical interfaces belonging to the same trunk
      can be merged.

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

Original Exporter?

      For example, in the case where a link aggregation exists, Data

remove "a"

      Records metered at physical interfaces belonging to a same trunk
      grouping beyond the line interface module can be merged.

"line card"?


   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.

Are more cases thinkable?
If yes, I would call the above "cases" "examples".

   Implementation analysis:

      One possible implementation for the cases 1 and 2 uses an IPFIX
      Concentrator located between the Metering Processes and Exporting

Intermediate Process

      Processes on the Original Exporter.  A separate IPFIX Concentrator
      located between the Original Exporters and IPFIX Collector is a
      valid solution for the cases 1, 2, 3, and 4.


5.6.  Data Record Anonymization

   IPFIX exports across administrative domains can be used to measure
   traffic for wide-area traffic engineering or to analyze Internet
   traffic trends, as described in the spatial composition across
   administrative domains in the previous subsection.
   In such a case, administrators need to adhere to privacy protection
   policies and prevent access to confidential traffic measurements by
   other people.  Typically, anonymization techniques enables the

enable

   provision of traffic data to other people without violating these
   policies.

   Generally, anonymization modifies a data set to protect the identity
   of the people or entities described by the data set from being
   disclosed.  It also attempts to preserve sets of network traffic
   properties useful for a given analysis while ensuring the data cannot
   be traced back to the specific networks, hosts, or users generating
   the traffic.  For example, IP address anonymization is particularly
   important for avoiding the identification of the users, hosts, and

remove second "the"

   routers.  As another example, when ISP provides a traffic monitoring

an ISP

   service to end customers by their own Exporters, even in case of
   exporting interface index fields, network administrators take care of
   anonymizing its fields to avoid disclosing the vulnerability.

Why does an interface represent a vulnerability?

   Implementation analysis:

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




5.10.  Flow-based Sampling and Selection

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

   Implementation analysis:

      One possible implementation for this case uses an IPFIX
      Concentrator located between the Metering Processes and Exporting

Intermediate Process

      Processes on the Original Exporter, or alternatively a separate
      IPFIX Concentrator located between the Original Exporters and
      IPFIX Collectors.  A set of IPFIX Mediation functions, such as
      filtering, selecting and aggregation is used in the IPFIX
      Concentrator.


6.  IPFIX Mediators Implementation Specific Problems

6.1.  Loss of Original Exporter Information

   Both the Exporter IP address indicated by the source IP address of
   the IPFIX Transport Session and the Observation Domain ID included in
   the IPFIX Message header are likely to be lost during IPFIX
   Mediation.  In some cases, a IPFIX Masquerading Proxy might drop the

a => an

   information deliberately.  In general, however, the Collector must
   recognize the origin of the measurement information, such as the IP
   address of the Original Exporter, the Observation Domain ID, or even
   the Observation Point ID.  Note that, if an IPFIX Mediator can not

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

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

   Figure B: Loss of Original Exporter Information.

6.2.  Loss of Base Time Information

   The Export Time field included in the IPFIX Message header represents
   a reference timestamp for Data Records.  Some IPFIX Information
   Elements, described in [RFC5102], carry delta timestamps that
   indicate the time difference from the value of the Export Time field.
   If the Data Records include any delta time fields and the IPFIX
   Mediator overwrites the Export Time field when sending IPFIX
   Messages, the delta time fields become meaningless and, because
   Collectors cannot recognize this situation, wrong time values are
   propagated.

6.3.  Transport Sessions Management

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

Transport Session

   needs to be specified.


6.7.  Exporting the Function Item

   In some case, the IPFIX Collector needs to recognize which specific
   function(s) the IPFIX Mediation has executed on the Data Records.

remove first "the"

   The IPFIX Collector cannot distinguish between time composition,
   spatial composition, and Flow Key aggregation, if the IPFIX Mediator

What is "Flow Key aggregation"? Is this a good expression?
Usually, some Flow Key fields are just dropped or replaced by non-key fields.

   does not export the applied function.  Some parameters related to the
   function also would need to be exported.  For example, in case of
   time composition, the active time of original Flow Records is

"active timeout"?

   required to interpret the minimum/maximum counter correctly.  In case
   of spatial composition, spatial area information on which Data
   Records is aggregated is required.

6.8.  Consideration for Aggregation

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

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

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

   Furthermore, rules must be specify on how to aggregate the new
   Configured Selection Fraction an IPFIX Mediator should report when

What about:
"If packet Sampling or Filtering is applied, the IPFIX Mediator must report an adjusted PSAMP Configured Selection Fraction when aggregating..."

   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.


7.  Summary and Conclusion

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

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

Sampling and aggregation reduce the accuracy or granularity.
Correlation seems to be appropriate.

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

   o  Regarding the distribution of Data Records, IPFIX Distributors
      help to achieve multipurpose traffic analysis for different
      organizations, or help to achieve respective traffic analysis

remove "respective"?

      based on Data Record types(IPv4, IPv6, MPLS, and VPN).

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

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

even => for example

      period to IPFIX.

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

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

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

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

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


There is a lot of repetition in this section.

8.  Security Considerations

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

   And a measurement system must also prevent the following security

remove "And"

   threats related to IPFIX Mediation:

   o  Attacks against IPFIX Mediator

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

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

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

"would increase the risk of..." => "could be misused for man-in-the-middle attacks"

   o  Configuration on IPFIX Mediation

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

--
Dipl.-Ing. Gerhard Münz
Chair for Network Architectures and Services (I8)
Technische Universität München - Department of Informatics
Boltzmannstr. 3, 85748 Garching bei München, Germany
Phone:  +49 89 289-18008       Fax: +49 89 289-18033
E-mail: muenz at net.in.tum.de    WWW: http://www.net.in.tum.de/~muenz


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