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INFORMATIONAL
Errata Exist
Internet Engineering Task Force (IETF) A. Kobayashi
Request for Comments: 6183 NTT
Updates: 5470 B. Claise
Category: Informational Cisco Systems, Inc.
ISSN: 2070-1721 G. Muenz
TU Muenchen
K. Ishibashi
NTT
April 2011
IP Flow Information Export (IPFIX) Mediation: Framework
Abstract
This document describes a framework for IP Flow Information Export
(IPFIX) Mediation. This framework extends the IPFIX reference model
specified in RFC 5470 by defining the IPFIX Mediator components.
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/rfc6183.
Copyright Notice
Copyright (c) 2011 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 ..................................6
3.1. IPFIX Documents Overview ...................................6
3.2. PSAMP Documents Overview ...................................6
4. IPFIX Mediation Reference Model .................................7
5. IPFIX Mediation Functional Blocks ..............................12
5.1. Collecting Process ........................................12
5.2. Exporting Process .........................................13
5.3. Intermediate Process ......................................13
5.3.1. Data Record Expiration .............................14
5.3.2. Specific Intermediate Processes ....................14
6. Component Combination ..........................................20
6.1. Data-Based Collector Selection ............................20
6.2. Flow Selection and Aggregation ............................21
6.3. IPFIX File Writer/Reader ..................................22
7. Encoding for IPFIX Message Header ..............................22
8. Information Model ..............................................24
9. Security Considerations ........................................24
9.1. Avoiding Security Level Downgrade .........................25
9.2. Avoiding Security Level Upgrade ...........................25
9.3. Approximating End-to-End Assertions for IPFIX Mediators ...26
9.4. Multiple Tenancy ..........................................26
10. References ....................................................27
10.1. Normative References .....................................27
10.2. Informative References ...................................27
11. Acknowledgements ..............................................29
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1. Introduction
The IP Flow Information Export (IPFIX) architectural components in
[RFC5470] consist of IPFIX Devices and IPFIX Collectors communicating
using the IPFIX protocol. Due to the sustained growth of IP traffic
in heterogeneous network environments, this Exporter-Collector
architecture may lead to scalability problems. In addition, it does
not provide the flexibility required by a wide variety of measurement
applications. A detailed descriptions of these problems is given in
[RFC5982].
To fulfill application requirements with limited system resources,
the IPFIX architecture needs to introduce an intermediate entity
between Exporters and Collectors. From a data manipulation point of
view, this intermediate entity may provide the aggregation,
correlation, filtering, and modification of Flow Records and/or
Packet Sampling (PSAMP) Packet Reports to save measurement system
resources and to perform preprocessing tasks for the Collector. From
a protocol conversion point of view, this intermediate entity may
provide conversion into IPFIX, or conversion of IPFIX transport
protocols (e.g., from UDP to the Stream Control Transmission Protocol
(SCTP)) to improve the export reliability.
This document introduces a generalized concept for such intermediate
entities and describes the high-level architecture of IPFIX
Mediation, key IPFIX Mediation architectural components, and
characteristics of IPFIX Mediation.
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 describes a high-level reference model,
Section 5 describes functional features related to IPFIX Mediation,
Section 6 describes combinations of components along with some
application examples, Section 7 describes consideration points of the
encoding for IPFIX Message Headers, Section 8 describes the
Information Elements used in an IPFIX Mediator, and Section 9
describes the security issues raised by IPFIX Mediation.
2. Terminology and Definitions
The IPFIX-specific and PSAMP-specific terminology used in this
document is defined in [RFC5101] and [RFC5476], respectively. The
IPFIX-Mediation-specific terminology used in this document is defined
in [RFC5982]. However, as reading the problem statements document is
not a prerequisite to reading this framework document, the
definitions have been reproduced here along with additional
definitions. In this document, as in [RFC5101] and [RFC5476], the
first letter of each IPFIX-specific and PSAMP-specific term is
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capitalized along with the IPFIX-Mediation-specific terms defined
here. The use of the terms "must", "should", and "may" in this
document is informational only.
In this document, we use the term "record stream" to mean a stream of
records carrying flow-based or packet-based information. The records
may be encoded as IPFIX Data Records or in any other format.
Transport Session Information
The Transport Session Information contains information that allows
the identification of an individual Transport Session as defined
in [RFC5101]. If SCTP is used as transport protocol, the
Transport Session Information identifies the SCTP association. If
TCP or UDP is used as transport protocol, the Transport Session
Information corresponds to the 5-tuple {Exporter IP address,
Collector IP address, Exporter transport port, Collector transport
port, transport protocol}. The Transport Session Information may
include further details about how Transport Layer Security (TLS)
[RFC5246] or Datagram Transport Layer Security (DTLS) [RFC4347] is
used for encryption and authentication.
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.
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Specific Intermediate Processes are described below. However, this
is not an exhaustive list.
Intermediate Conversion Process
An Intermediate Conversion Process is an Intermediate Process that
transforms non-IPFIX into IPFIX or manages the relation among
Templates and states of incoming/outgoing transport sessions in
the case of transport protocol conversion (e.g., from UDP to
SCTP).
Intermediate Aggregation Process
An Intermediate Aggregation Process is an Intermediate Process
that aggregates records based upon a set of Flow Keys or functions
applied to fields from the record (e.g., data binning and subnet
aggregation).
Intermediate Correlation Process
An Intermediate Correlation Process is an Intermediate Process
that adds information to records, noting correlations among them,
or generates new records with correlated data from multiple
records (e.g., the production of bidirectional flow records from
unidirectional flow records).
Intermediate Selection Process
An Intermediate Selection Process is an Intermediate Process that
selects records from a sequence based upon criteria-evaluated
record values and passes only those records that match the
criteria (e.g., filtering only records from a given network to a
given Collector).
Intermediate Anonymization Process
An Intermediate Anonymization Process is an Intermediate Process
that transforms records in order to anonymize them, to protect the
identity of the entities described by the records (e.g., by
applying prefix-preserving pseudonymization of IP addresses).
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
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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.
3. IPFIX/PSAMP Documents Overview
IPFIX Mediation can be applied to flow-based 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]. The IPFIX Management
Information Base is defined in [RFC5815]. 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
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Elements, their names, types, and additional semantic information.
The PSAMP information model is defined in [RFC5477]. The PSAMP
Management Information Base is described in [PSAMP-MIB].
4. IPFIX Mediation Reference Model
Figure A shows the high-level IPFIX Mediation reference model as an
extension of the IPFIX reference model presented in [RFC5470]. This
figure covers the various possible scenarios that can exist in an
IPFIX measurement system.
+----------------+ +---------------+ +---------------+
| Collector 1 | | Collector 2 | | Collector N |
|[Collecting | |[Collecting | |[Collecting |
| Process(es)] | | Process(es)] |... | Process(es)] |
+----^-----------+ +---^--------^--+ +--------^------+
| / \ |
| / \ |
Flow Records Flow Records Flow Records Flow Records
| / \ |
+------+-------------+------+ +------+-----------+--------+
|IPFIX Mediator N+1 | |IPFIX Mediator Z |
|[Exporting Process(es)] | |[Exporting Process(es)] |
|[Intermediate Process(es)] | |[Intermediate Process(es)] |
|[Collecting Process(es)] |... |[Collecting Process(es)] |
+----^----------------^-----+ +------^----------------^---+
| | | |
Flow Records Flow Records Packet Reports record stream
| | | |
+------+------+ +------+-------+ +------+-------+ +-----+-----+
|IPFIX | |IPFIX Original| |PSAMP Original| |Other |
| Mediator 1 | | Exporter 1 | | Exporter 1 | | Source 1 |
|+-------------+ |+--------------+ |+--------------+ |+-----------+
+|IPFIX | +|IPFIX Original| +|PSAMP Original| +|Other |
| Mediator N | | Exporter N | | Exporter N | | Source N |
|[Exporting | |[Exporting | |[Exporting | | |
| Process(es)]| | Process(es)]| | Process(es)]| | |
|[Intermediate| |[Metering | |[Metering | | |
| Process(es)]| | Process(es)]| | Process(es)]| | |
|[Collecting | |[Observation | |[Observation | | |
| Process(es)]| | Point(s)]| | Point(s)]| | |
+------^------+ +-----^-^------+ +-----^-^------+ +-----------+
| | | | |
Flow Records Packets coming Packets coming
into Observation into Observation
Points Points
Figure A: IPFIX Mediation Reference Model Overview
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The functional components within each entity are indicated within
brackets []. An IPFIX Mediator receives IPFIX Flow Records or PSAMP
Packet Reports from other IPFIX Mediators, IPFIX Flow Records from
IPFIX Original Exporters, PSAMP Packet Reports from PSAMP Original
Exporters, and/or a record stream from other sources. The IPFIX
Mediator then exports IPFIX Flow Records and/or PSAMP Packet Reports
to one or multiple Collectors and/or other IPFIX Mediators.
Figure B shows the basic IPFIX Mediator component model. An IPFIX
Mediator contains one or more Intermediate Processes and one or more
Exporting Processes. Typically, it also contains a Collecting
Process but might contain several Collecting Processes, as described
in Figure B.
IPFIX (Data Records)
^
^ |
+------------------------|-|---------------------+
| IPFIX Mediator | | |
| | | |
| .---------------------|-+-------------------. |
| .----------------------+--------------------.| |
| | Exporting Process(es) |' |
| '----------------------^--------------------' |
| | | |
| .---------------------|-+-------------------. |
| .----------------------+--------------------.| |
| | Intermediate Process(es) |' |
| '----------------------^--------------------' |
| | | |
| .---------------------|-+-------------------. |
| .----------------------+--------------------.| |
| | Collecting Process(es) |' |
| '----------------------^--------------------' |
+------------------------|-|---------------------+
|
IPFIX (Data Records)
Figure B: Basic IPFIX Mediator Component Model
However, other data sources are also possible: an IPFIX Mediator can
receive a record stream from non-IPFIX protocols such as NetFlow
[RFC3954] exporter(s). This document does not make any particular
assumption on how a record stream is transferred to an IPFIX
Mediator. Figure C shows the IPFIX Mediator component model in the
case of IPFIX protocol conversion from non-IPFIX exporters.
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IPFIX (Data Records)
^
^ |
+------------------------|-|---------------------+
| IPFIX Mediator | | |
| .---------------------|-+-------------------. |
| .----------------------+--------------------.| |
| | Exporting Process(es) |' |
| '----------------------^--------------------' |
| .---------------------|-+-------------------. |
| .----------------------+--------------------.| |
| | Intermediate Process(es) |' |
| '----------------------^--------------------' |
+------------------------|-----------------------+
| record stream
+------------------------|-----------------------+
| Non-IPFIX exporter | |
| +-------------+----------+ |
| | | |
+----------|------------------------|------------+
| |
Packets coming into observation points
Figure C: IPFIX Mediator Component Model in IPFIX
Protocol Conversion
Alternatively, an Original Exporter may provide IPFIX Mediation by
hosting one or more Intermediate Processes. The component model in
Figure D adds Intermediate Process(es) to the IPFIX Device model
illustrated in [RFC5470]. In comparison with Figures 1 or 2 in
[RFC5470], the Intermediate Process is located between Exporting
Process(es) and IPFIX or PSAMP Metering Process(es).
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IPFIX (Data Records)
^ ^
+---------------------------|-|------------------------+
| Original Exporter | | |
| | | |
| .---------------------|-+-------------------. |
| .----------------------+--------------------.| |
| | Exporting Process(es) |' |
| '----------------------^--------------------' |
| | | |
| .---------------------|-+-------------------. |
| .----------------------+--------------------.| |
| | Intermediate Process(es) |' |
| '---------^-----------------------^---------' |
| | Data Records | |
| .----------+---------. .---------+----------. |
| | Metering Process 1 |...| Metering Process N | |
| '----------^---------' '---------^----------' |
| | | |
| .-----------+---------. .---------+-----------. |
| | Observation Point 1 |...| Observation Point N | |
| '-----------^---------' '---------^-----------' |
+--------------|-----------------------|---------------+
| |
Packets coming into Observation Points
Figure D: IPFIX Mediation Component Model at Original Exporter
In addition, an Intermediate Process may be collocated with an IPFIX
File Reader and/or Writer. Figure E shows an IPFIX Mediation
component model with an IPFIX File Writer and/or Reader.
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IPFIX (Data Records)
^
^ |
.----------------------|-+--------------------.
.-----------------------+---------------------.|
| IPFIX File Writer |'
'-----------------------^---------------------'
| |
.----------------------|-+--------------------.
.-----------------------+---------------------.|
| Intermediate Process(es) |'
'-----------------------^---------------------'
| |
.----------------------|-+--------------------.
.-----------------------+---------------------.|
| IPFIX File Reader |'
'-----------------------^---------------------'
|
IPFIX (Data Records)
Figure E: IPFIX Mediation Component Model Collocated
with IPFIX File Writer/Reader
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5. IPFIX Mediation Functional Blocks
Figure F shows a functional block diagram example in an IPFIX
Mediator that has different Intermediate Process types.
IPFIX IPFIX IPFIX
^ ^ ^
| | |
.------------. .-----+-------. .-----+-------. .------+------.
| IPFIX File | | Exporting | | Exporting | | Exporting |
| Writer | | Process 1 | | Process 2 |....| Process N |
'-----^-^----' '-----^-------' '-----^-------' '------^------'
| | | | |
| +-------------+ | |
: Flow Records / Packet Reports :
.------+-------. .-----+--------. .----+---------. .--------------.
| Intermediate | | Intermediate | | Intermediate | | Intermediate |
| Anonymization| | Correlation | | Aggregation | | Selection |
| Process N | | Process N | | Process N | | Process N |
'------|-------' '------|-------' '-----|-|------' '-------|------'
| +---------------+ | |
: : : :
.------+-------. .------+-------. .-------+------. .-------+------.
| Intermediate | | Intermediate | | Intermediate | | Intermediate |
| Selection | | Selection | | Selection | | Selection |
| Process 1 | | Process 2 | | Process 3 | | Process 4 |
'------|-|-----' '------|-------' '-----|--------' '-------|------'
| +--------------+ | +----------------+
| | | | |
: Flow Records / Packet Reports :
.------+------. .-------+-----. .-----+-+-----. .-----+------.
| Collecting | | Collecting | | Collecting | | IPFIX File |
| Process 1 | | Process 2 |...| Process N | | Reader |
'------^------' '------^------' '------^------' '------------'
| | |
Flow Records Flow Records Flow Records
Figure F: IPFIX Mediation Functional Block Diagram
5.1. Collecting Process
A Collecting Process in an IPFIX Mediator is not different from the
Collecting Process described in [RFC5101]. Additional functions in
an IPFIX Mediator include transmitting the set of Data Records and
Control Information to one or more components, i.e., Intermediate
Processes and other applications. In other words, a Collecting
Process may duplicate the set and transmit it to one or more
components in sequence or in parallel. In the case of an IPFIX
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Mediator, the Control Information described in [RFC5470] includes
IPFIX Message Header information and Transport Session Information
along with information about the Metering Process and the Exporting
Process in an Original Exporter, e.g., Sampling parameters.
5.2. Exporting Process
An Exporting Process in an IPFIX Mediator is not different from the
Exporting Process described in [RFC5101]. Additional functions in an
IPFIX Mediator may include the following:
o Receiving the trigger to transmit the Template Withdrawal Messages
from Intermediate Process(es) when relevant Templates become
invalid due to, for example, incoming session failure.
o Transmitting the origin (e.g., Observation Point, Observation
Domain ID, Original Exporter IP address, etc.) of the data in
additional Data Record fields or additional Data Records. The
parameters that represent the origin should be configurable.
5.3. Intermediate Process
An Intermediate Process is a key functional block for IPFIX
Mediation. Its typical functions include the following:
o Generating a new record stream from an input record stream
including context information (e.g., Observation Domain ID and
Transport Session Information) and transmitting it to other
components.
o Reporting statistics and interpretations for IPFIX Metering
Processes, PSAMP Metering Processes, and Exporting Processes from
an Original Exporter. See Section 4 of [RFC5101] and Section 6 of
[RFC5476] for relevant statistics data structures and
interpretations, respectively. Activation of this function should
be configurable.
o Maintaining the configurable relation between Collecting
Process(es)/Metering Process(es) and Exporting Process(es)/other
Intermediate Process(es).
o Maintaining database(s) of Data Records in the case of an
Intermediate Aggregation Process and an Intermediate Correlation
Process. The function has the Data Record expiration rules
described in the next subsection.
o Maintaining statistics on the Intermediate Process itself, such as
the number of input/output Data Records, etc.
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o Maintaining additional information about output record streams,
which includes information related to the Original Exporters,
Observation Domain, and administrative domain as well as some
configuration parameters related to each function.
In the case of an Intermediate Aggregation Process, Intermediate
Anonymization Process, and Intermediate Correlation Process, the
value of the "flowKeyIndicator" needs to be modified when modifying
the data structure defined by an original Template.
For example, an Intermediate Aggregation Process aggregating incoming
Flow Records composed of the sourceIPv4Address and
destinationIPv4Address Flow Keys into outgoing Flow Records with the
destinationIPv4Address Flow Key must modify the incoming
flowKeyIndicator to contain only the destinationIPv4Address.
5.3.1. Data Record Expiration
An Intermediate Aggregation Process and Intermediate Correlation
Process need to have expiration conditions to export cached Data
Records. In the case of the Metering Process in an Original
Exporter, these conditions are described in [RFC5470]. In the case
of the Intermediate Process, these conditions are as follows:
o If there are no input Data Records belonging to a cached Flow for
a certain time period, aggregated Flow Records will expire. This
time period should be configurable at the Intermediate Process.
o If the Intermediate Process experiences resource constraints
(e.g., lack of memory to store Flow Records), aggregated Flow
Records may prematurely expire.
o For long-running Flows, the Intermediate Process should cause the
Flow to expire on a regular basis or on the basis of an expiration
policy. This periodicity or expiration policy should be
configurable at the Intermediate Process.
In the case of an Intermediate Correlation Process, a cached Data
Record may be prematurely expired (and discarded) when no correlation
can be computed with newly received Data Records. For example, an
Intermediate Correlation Process computing one-way delay may discard
the cached Packet Report when no other matching Packet Report are
observed within a certain time period.
5.3.2. Specific Intermediate Processes
This section describes the functional blocks of specific Intermediate
Processes.
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5.3.2.1. Intermediate Conversion Process
When receiving a non-IPFIX record stream, the Intermediate Conversion
Process covers the following functions:
o Determining the IPFIX Information Element identifiers that
correspond to the fields of the non-IPFIX records (e.g.,
converting the NetFlow V9 protocol [RFC3954] to the IPFIX
Information Model [RFC5102]).
o Transforming the non-IPFIX records into Data Records, (Options)
Template Records, and/or Data Records defined by Options
Templates.
o Converting additional information (e.g., sampling rate, sampling
algorithm, and observation information) into appropriate fields in
the existing Data Records or into Data Records defined by new
Options Templates.
IPFIX transport protocol conversion can be used to enhance the export
reliability, for example, for data retention and accounting. In this
case, the Intermediate Conversion Process covers the following
functions:
o Relaying Data Records, (Options) Template Records, and Data
Records defined by Options Templates.
o Setting the trigger for the Exporting Process in order to export
IPFIX Template Withdrawal Messages relevant to the Templates when
Templates becomes invalid due to, for example, incoming session
failure. This case applies to SCTP and TCP Transport Sessions on
the outgoing side only.
o Maintaining the mapping information about Transport Sessions,
Observation Domain IDs, and Template IDs on the incoming and
outgoing sides in order to ensure the consistency of scope field
values of incoming and outgoing Data Records defined by Options
Templates and of Template IDs of incoming and outgoing IPFIX
Template Withdrawal Messages.
5.3.2.2. Intermediate Selection Process
An Intermediate Selection Process has analogous functions to the
PSAMP Selection Process described in [RFC5475]. The difference is
that the Intermediate Selection Process takes a record stream, e.g.,
Flow Records or Packet Reports, instead of observed packets as its
input.
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The typical function is property match filtering that retrieves a
record stream of interest. The function selects a Data Record if the
value of a specific field in the Data Record equals a configured
value or falls within a configured range.
5.3.2.3. Intermediate Aggregation Process
An Intermediate Aggregation Process covers the following functions:
o Merging a set of Data Records within a certain time period into
one Flow Record by summing up the counters where appropriate.
o Maintaining statistics and additional information about aggregated
Flow Records.
The statistics for an aggregated Flow Record may include the
number of original Data Records and the maximum and minimum values
of per-flow counters. Additional information may include an
aggregation time period, a new set of Flow Keys, and observation
location information involved in the Flow aggregation.
Observation location information can be tuples of (Observation
Point, Observation Domain ID, Original Exporter IP address) or
another identifier indicating the location where the measured
traffic has been observed.
o Aggregation of Data Records, which can be done in the following
ways:
* Spatial composition
With spatial composition, Data Records sharing common
properties are merged into one Flow Record within a certain
time period. One typical aggregation can be based on a new set
of Flow Keys. Generally, a set of common properties smaller
than an original set of Flow Keys results in a higher level of
aggregation. Another aggregation can be based on a set of
Observation Points within an Observation Domain, on a set of
Observation Domains within an Exporter, or on a set of
Exporters.
If some fields do not serve as Flow Keys or per-Flow counters,
their values may change from Data Records to Data Records
within an aggregated Flow Record. The Intermediate Aggregation
Process determines their values by the first Data Record
received, a specific Exporter IP address, or other appropriate
decisions.
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Furthermore, a new identifier indicating a group of observation
locations can be introduced, for example, to indicate PoPs
(Points of Presence) in a large network, or a logical interface
composed of physical interfaces with link aggregation.
* Temporal composition
With temporal composition, multiple Flow Records with identical
Flow Key values are merged into a single Flow Record of longer
Flow duration if they arrive within a certain time interval.
The main difference to spatial composition is that Flow Records
are only merged if they originate from the same Observation
Point and if the Flow Key values are identical. For example,
multiple Flow Records with a Flow duration of less than one
minute can be merged into a single Flow Record with more than
ten minutes Flow duration.
In addition, the Intermediate Aggregation Process with temporal
composition produces aggregated counters while reducing the
number of Flow Records on a Collector. Some specific non-key
fields, such as the minimumIpTotalLength/maximumIpTotalLength
or minimumTTL/maximumTTL, will contain the minimum and maximum
values for the new aggregated Flow.
Spatial and temporal composition can be combined in a single
Intermediate Aggregation Process. The Intermediate Aggregation
Process can be combined with the Intermediate Selection Process in
order to aggregate only a subset of the original Flow Records, for
example, Flow Records with small numbers of packets as described
in Section 6.2.
5.3.2.4. Intermediate Anonymization Process
An Intermediate Anonymization Process covers the following typical
functions:
o Deleting specified fields
The function deletes existing fields in accordance with some
instruction rules. Examples include hiding network topology
information and private information. In the case of feeding Data
Records to end customers, disclosing vulnerabilities is avoided by
deleting fields, e.g., "ipNextHopIP{v4|v6}Address",
"bgpNextHopIP{v4|v6}Address", "bgp{Next|Prev}AdjacentAsNumber",
and "mplsLabelStackSection", as described in [RFC5102].
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o Anonymizing values of specified fields
The function modifies the values of specified fields. Examples
include anonymizing customers' private information, such as IP
address and port number, in accordance with a privacy protection
policy. The Intermediate Anonymization Process may also report
anonymized fields and the anonymization method as additional
information.
5.3.2.5. Intermediate Correlation Process
An Intermediate Correlation Process can be viewed as a special case
of the Intermediate Aggregation Process, covering the following
typical functions:
o Producing new information including metrics, counters, attributes,
or packet property parameters by evaluating the correlation among
sets of Data Records or among Data Records and other meta data
after gathering sets of Data Records within a certain time period.
o Adding new fields into a Data Record or creating a new Data
Record.
A correlation of Data Records can be done in the following ways,
which can be implemented individually or in combinations.
o One-to-one correlation between Data Records, with the following
examples:
* One-way delay, Packet delay variation in [RFC5481]
The metrics come from the correlation of the timestamp value on
a pair of Packet Reports indicating an identical packet at
different Observation Points in the network.
* Packet inter-arrival time
The metrics come from the correlation of the timestamp value on
consecutive Packet Reports from a single Exporter.
* Rate-limiting ratio, compression ratio, optimization ratio,
etc.
The data values come from the correlation of Data Records
indicating an identical Flow observed on the incoming/outgoing
points of a WAN interface.
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o Correlation amongst Data Records, with the following examples:
* Bidirectional Flow composition
The method of exporting and representing a Bidirectional Flow
(Biflow) is described in [RFC5103]. The Bidirectional Flow
composition is a special case of Flow Key aggregation. The
Flow Records are merged into one Flow Record as Biflow if Non-
directional Key Fields match and the Directional Key Fields
match their reverse direction counterparts. The direction
assignment method to assign the Biflow Source and Destination
as additional information may be reported. In the case of an
Intermediate Aggregation Process, the direction may be assigned
arbitrarily (see [RFC5103], Section 5.3).
* Average/maximum/minimum for packets, bytes, one-way delay,
packet loss, etc.
The data values come from the correlation of multiple Data
Records gathered in a certain time interval.
o Correlation between Data Record and other meta data
Typical examples are derived packet property parameters described
in [RFC5102]. The parameters are retrieved based on the value of
the specified field in an input Data Record, compensating for
traditional exporting devices or probes that are unable to add
packet property parameters. Typical derived packet property
parameters are as follows:
* "bgpNextHop{IPv4|IPv6}Address" described in [RFC5102]
This value indicates the egress router of a network domain. It
is useful for making a traffic matrix that covers the whole
network domain.
* BGP community attributes
This attribute indicates tagging for routes of geographical and
topological information and source types (e.g., transit, peer,
or customer) as described in [RFC4384]. Therefore, network
administrators can monitor the geographically-based or source-
type-based traffic volume by correlating the attribute.
* "mplsVpnRouteDistinguisher" described in [RFC5102]
This value indicates the VPN customer's identification, which
cannot be extracted from the core router in MPLS networks.
Thanks to this correlation, network administrators can monitor
the customer-based traffic volume even on core routers.
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6. Component Combination
An IPFIX Mediator may be able to simultaneously support more than one
Intermediate Process. Multiple Intermediate Processes generally are
configured in the following ways.
o Parallel Intermediate Processes
A record stream is processed by multiple Intermediate Processes in
parallel to fulfill the requirements of different applications.
In this setup, every Intermediate Process receives a copy of the
entire record stream as its input.
o Serial Intermediate Processes
To execute flexible manipulation of a record stream, the
Intermediate Processes are connected serially. In that case, an
output record stream from one Intermediate Process forms an input
record stream for a succeeding Intermediate Process.
In addition to the combination of Intermediate Processes, the
combination of some components (Exporting Process, Collecting
Process, IPFIX File Writer and Reader) can be applied to provide
various data reduction techniques. This section shows some
combinations along with examples.
6.1. Data-Based Collector Selection
The combination of one or more Intermediate Selection Processes and
Exporting Processes can determine to which Collector input Data
Records are exported. Applicable examples include exporting Data
Records to a dedicated Collector on the basis of a customer or an
organization. For example, an Intermediate Selection Process selects
Data Records from a record stream on the basis of the peering
autonomous system number, and an Exporting Process sends them to a
dedicated Collector, as shown in the Figure G.
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.----------------------. .------------.
| Intermediate | | Exporting |
| Selection Process 1 | | Process 1 |
+--+--- Peering AS #10 ---+-->| +--> Collector 1
| '----------------------' '------------'
| .----------------------. .------------.
record | | Intermediate | | Exporting |
stream | | Selection Process 2 | | Process 2 |
-------+--+--- Peering AS #20 ---+-->| +--> Collector 2
| '----------------------' '------------'
| .----------------------. .------------.
| | Intermediate | | Exporting |
| | Selection Process 3 | | Process 3 |
+--+--- Peering AS #30 ---+-->| +--> Collector 3
'----------------------' '------------'
Figure G: Data-Based Collector Selection
6.2. Flow Selection and Aggregation
The combination of one or more Intermediate Selection Processes and
Intermediate Aggregation Processes can efficiently reduce the amount
of Flow Records. The combination structure is similar to the concept
of the Composite Selector described in [RFC5474]. For example, an
Intermediate Selection Process selects Flows consisting of a small
number of packets and then transmits them to an Intermediate
Aggregation Process. Another Intermediate Selection Process selects
other Flow Records and then transmits them to an Exporting Process,
as shown in Figure H. This results in aggregation on the basis of
the distribution of the number of packets per Flow.
.------------------. .--------------. .------------.
| Intermediate | | Intermediate | | Exporting |
| Selection | | Aggregation | | Process |
| Process 1 | | Process | | |
+-+ packetDeltaCount +->| +->| |
| | <= 5 | | | | |
record | '------------------' '--------------' | |
stream | .------------------. | |
-------+ | Intermediate | | |
| | Selection | | |
| | Process 2 | | |
+-+ packetDeltaCount +------------------->| |
| > 5 | | |
'------------------' '------------'
Figure H: Flow Selection and Aggregation Example
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6.3. IPFIX File Writer/Reader
An IPFIX File Writer [RFC5655] stores Data Records in a file system.
When Data Records include problematic Information Elements, an
Intermediate Anonymization Process can delete these fields before the
IPFIX File Writer handles them, as shown in Figure I.
.---------------. .---------------. .-------------.
| Collecting | | Intermediate | | IPFIX |
IPFIX | Process | | Anonymization | | File |
----->| +->| Process +->| Writer |
'---------------' '---------------' '-------------'
Figure I: IPFIX Mediation Example with IPFIX File Writer
In contrast, an IPFIX File Reader [RFC5655] retrieves stored Data
Records when administrators want to retrieve past Data Records from a
given time period. If the data structure of the Data Records from
the IPFIX File Reader is different from what administrators want, an
Intermediate Anonymization Process and Intermediate Correlation
Process can modify the data structure, as shown in Figure J.
.-------------. .---------------. .---------------. .-----------.
| IPFIX | | Intermediate | | Intermediate | | Exporting |
| File | | Anonymization | | Correlation | | Process |
| Reader +->| Process +->| Process +->| |
'-------------' '---------------' '---------------' '-----------'
Figure J: IPFIX Mediation Example with IPFIX File Reader
In the case where distributed IPFIX Mediators enable on-demand export
of Data Records that have been previously stored by a File Writer, a
collecting infrastructure with huge storage capacity for data
retention can be set up.
7. Encoding for IPFIX Message Header
The IPFIX Message Header [RFC5101] includes Export Time, Sequence
Number, and Observation Domain ID fields. This section describes
some consideration points for the IPFIX Message Header encoding in
the context of IPFIX Mediation.
Export Time
An IPFIX Mediator can set the Export Time in two ways.
* Case 1: keeping the field value of incoming Transport Sessions
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* Case 2: setting the time at which an IPFIX Message leaves the
IPFIX Mediator
Case 1 can be applied when an IPFIX Mediator operates as a proxy
at the IPFIX Message level rather than the Data Record level. In
case 2, the IPFIX Mediator needs to handle any delta timestamp
fields described in [RFC5102], such as
"flowStartDeltaMicroseconds" and "flowEndDeltaMicroseconds".
Sequence Number
In the case where an IPFIX Mediator relays IPFIX Messages from one
Transport Session to another Transport Session, the IPFIX Mediator
needs to handle the Sequence Number properly. In particular, the
Sequence Number in the outgoing session is not allowed to be re-
initialized, even when the incoming session shuts down and
restarts.
Observation Domain ID
According to [RFC5101], the Observation Domain ID in the IPFIX
Message Header is locally unique per Exporting Process. In
contrast to the Observation Domain ID used by an Original
Exporter, the Observation Domain ID used by an IPFIX Mediator does
not necessarily represent a set of Observation Points located at
the IPFIX Mediator itself.
An IPFIX Mediator may act as a proxy by relaying entire IPFIX
Messages. In this case, it may report information about the
Original Exporters by using the Observation Domain ID of the
outgoing Messages as the scope field in an Options Template
Record.
Otherwise, the IPFIX Mediator should have a function to export the
observation location information regarding the Original Exporter.
The information contains the IP addresses and Observation Domain
IDs used by the Original Exporters and some information about the
Transport Session, for example, the source port number, so that
different Exporting Processes on the same Original Exporter can be
identified. As far as privacy policy permits, an IPFIX Mediator
reports the information to an IPFIX Collector.
If information about a set of Original Exporters needs to be
reported, it can be useful to export it as Common Properties as
specified in [RFC5473]. The commonPropertiesID may then serve as
a scope for the set of Original Exporters. The Common Properties
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Withdrawal Message [RFC5473] can be used to indicate that an
incoming Transport Session from one of the Original Exporters was
closed.
8. Information Model
IPFIX Mediation reuses the general information models from [RFC5102]
and [RFC5477], and, depending on the Intermediate Processes type,
potentially Information Elements such as:
o Original Exporter IP address, Observation Domain ID, and source
port number about the Transport Session at the Original Exporter,
in the case where an IPFIX Mediator reports original observation
location information in Section 7. The Information Elements
contained in the Export Session Details Options Template in
[RFC5655] may be utilized for this purpose.
o Report on the applied IPFIX Mediation functions as described in
Section 6.7. in [RFC5982].
o Certificate of an Original Exporter in Section 9. The Information
Element exporterCertificate in [RFC5655] may be utilized for this
purpose.
9. Security Considerations
As Mediators act as both IPFIX Collecting Processes and Exporting
Processes, the Security Considerations for IPFIX [RFC5101] also apply
to Mediators. The Security Considerations for IPFIX Files [RFC5655]
also apply to IPFIX Mediators that write IPFIX Files or use them for
internal storage. In addition, there are a few specific
considerations that IPFIX Mediator implementations must take into
account.
By design, IPFIX Mediators are "men-in-the-middle": they intercede in
the communication between an Original Exporter (or another upstream
Mediator) and a downstream Collecting Process. TLS provides no way
to connect the session between the Mediator and the Original Exporter
to the session between the Mediator and the downstream Collecting
Process; indeed, this is by design. This has important implications
for the level of confidentiality provided across an IPFIX Mediator
and the ability to protect data integrity and Original Exporter
authenticity across a Mediator. In general, a Mediator should
maintain the same level of integrity and confidentiality protection
on both sides of the mediation operation, except in situations where
the Mediator is explicitly deployed as a gateway between trusted and
untrusted networks.
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Subsequent subsections deal with specific security issues raised by
IPFIX Mediation.
9.1. Avoiding Security Level Downgrade
An IPFIX Mediator that accepts IPFIX Messages over a Transport
Session protected by TLS [RFC5246] or DTLS [RFC4347] and that then
exports IPFIX Messages derived therefrom in cleartext is a
potentially serious vulnerability in an IPFIX infrastructure. The
concern here is that confidentiality protection may be lost across a
Mediator.
Therefore, an IPFIX Mediator that receives IPFIX Messages from an
upstream Exporting Process protected using TLS or DTLS must provide
for sending of IPFIX Messages resulting from the operation of the
Intermediate Process(es) to a downstream Collecting Process using TLS
or DTLS by default. It may be configurable to export records derived
from protected records in cleartext but only when application
requirements allow.
There are two common use cases for this. First, a Mediator
performing a transformation that leads to a reduction in the required
level of security (e.g., by removing all information requiring
confidentiality from the output records) may export records
downstream without confidentiality protection. Second, a mediator
that acts as a proxy between an external (untrusted) network and an
internal (trusted) network may export records without TLS when the
additional overhead of TLS is unnecessary (e.g., on a physically
protected network in the same locked equipment rack).
9.2. Avoiding Security Level Upgrade
There is a similar problem in the opposite direction: as an IPFIX
Mediator's signature on a TLS session to a downstream Collecting
Process acts as an implicit assertion of the trustworthiness of the
data within the session, a poorly deployed IPFIX Mediator could be
used to "legitimize" records derived from untrusted sources.
Unprotected sessions from the Original Exporter are generally
untrusted, because they could have been tampered with or forged by an
unauthorized third party. The concern here is that a Mediator could
be used to add inappropriate trust to external information whose
integrity cannot be guaranteed.
When specific deployment requirements allow, an IPFIX Mediator may
export signed IPFIX Messages containing records derived from records
received without integrity protection via TLS. One such deployment
consideration would be the reverse of the second case above: when the
Mediator acts as a proxy between an internal (trusted) and an
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external (untrusted) network and when the path from the Original
Exporter is protected using some other method and the overhead of a
TLS session is unnecessary.
In such cases, the IPFIX Mediator should notify the downstream
Collector about the missing protection of all or part of the original
record stream as part of the Transport Session Information.
9.3. Approximating End-to-End Assertions for IPFIX Mediators
Because the Transport Session between an IPFIX Mediator and an
Original Exporter is independent from the Transport Session between
the Mediator and the downstream Collecting Process, there is no
existing method via TLS to assert the identity of the original
Exporting Process downstream. However, an IPFIX Mediator, which
modifies the stream of IPFIX Messages sent to it, is by definition a
trusted entity in the infrastructure. Therefore, the IPFIX
Mediator's signature on an outgoing Transport Session can be treated
as an implicit assertion that the Original Exporter was positively
identified by the Mediator and that the source information it
received was trustworthy. However, as noted in the previous section,
IPFIX Mediators must in this circumstance take care not to provide an
inappropriate upgrade of trust.
If the X.509 certificates [RFC5280] used to protect a Transport
Session between an Original Exporter and an IPFIX Mediator are
required downstream, an IPFIX Mediator may export Transport Session
Information, including the exporterCertificate and the
collectorCertificate Information Elements, with the Export Session
Details Options Template defined in Section 8.1.3 of [RFC5655] or the
Message Details Options Template defined in Section 8.1.4 of
[RFC5655] in order to export this information downstream. However,
in this case, the IPFIX Mediator is making an implicit assertion that
the upstream session was properly protected and therefore trustworthy
or that the Mediator has otherwise been configured to trust the
information from the Original Exporter and, as such, must protect the
Transport Session to the downstream Collector using TLS or DTLS as
well.
9.4. Multiple Tenancy
Information from multiple sources may only be combined within a
Mediator when that Mediator is applied for that specific purpose
(e.g., spatial aggregation or concentration of records). In all
other cases, an IPFIX Mediator must provide for keeping traffic data
from multiple sources separate. Though the details of this are
application-specific, this generally entails separating Transport
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Sessions within the Mediator and associating them with information
related to the source or purpose, e.g., network or hardware address
range, virtual LAN tag, interface identifiers, and so on.
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.
[RFC5470] Sadasivan, G., Brownlee, N., Claise, B., and J. Quittek,
"Architecture for IP Flow Information Export", RFC 5470,
March 2009.
[RFC5476] Claise, B., Ed., Johnson, A., and J. Quittek, "Packet
Sampling (PSAMP) Protocol Specifications", RFC 5476,
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.
10.2. Informative References
[PSAMP-MIB] Dietz, T., Claise, B., and J. Quittek, "Definitions of
Managed Objects for Packet Sampling", Work in Progress,
March 2011.
[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.
[RFC4384] Meyer, D., "BGP Communities for Data Collection", BCP
114, RFC 4384, February 2006.
[RFC5102] Quittek, J., Bryant, S., Claise, B., Aitken, P., and J.
Meyer, "Information Model for IP Flow Information
Export", RFC 5102, January 2008.
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[RFC5103] Trammell, B. and E. Boschi, "Bidirectional Flow Export
Using IP Flow Information Export (IPFIX)", RFC 5103,
January 2008.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation
List (CRL) Profile", RFC 5280, May 2008.
[RFC5472] Zseby, T., Boschi, E., Brownlee, N., and B. Claise, "IP
Flow Information Export (IPFIX) Applicability", RFC 5472,
March 2009.
[RFC5473] Boschi, E., Mark, L., and B. Claise, "Reducing Redundancy
in IP Flow Information Export (IPFIX) and Packet Sampling
(PSAMP) Reports", RFC 5473, 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.
[RFC5481] Morton, A. and B. Claise, "Packet Delay Variation
Applicability Statement", RFC 5481, March 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.
[RFC5982] Kobayashi, A., Ed., and B. Claise, Ed., "IP Flow
Information Export (IPFIX) Mediation: Problem Statement",
RFC 5982, August 2010.
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11. Acknowledgements
We would like to thank the following persons: Brian Trammell for his
contribution regarding the improvement of the terminology section and
the security considerations section; Daisuke Matsubara, Tsuyoshi
Kondoh, Hiroshi Kurakami, and Haruhiko Nishida for their contribution
during the initial phases of the document; Nevil Brownlee and Juergen
Quittek for their technical reviews and feedback.
Authors' Addresses
Atsushi Kobayashi
Nippon Telegraph and Telephone East Corporation
26F 3-20-2, Nishi-shinjuku 3-chome
Shinjuku, Tokyo 163-8019
Japan
Phone: +81-3-5353-3636
EMail: akoba@orange.plala.or.jp
Benoit Claise
Cisco Systems, Inc.
De Kleetlaan 6a b1
Diegem 1831
Belgium
Phone: +32 2 704 5622
EMail: bclaise@cisco.com
Gerhard Muenz
Technische Universitaet Muenchen
Boltzmannstr. 3
Garching 85748
Germany
EMail: muenz@net.in.tum.de
URI: http://www.net.in.tum.de/~muenz
Keisuke Ishibashi
NTT Service Integration Platform Laboratories
3-9-11 Midori-cho
Musashino-shi 180-8585
Japan
Phone: +81-422-59-3407
EMail: ishibashi.keisuke@lab.ntt.co.jp
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