





Network Working Group                                       G. Sadasivan
Request for Comments: 5470                                Rohati Systems
Category: Informational                                      N. Brownlee
                                      CAIDA | The University of Auckland
                                                               B. Claise
                                                     Cisco Systems, Inc.
                                                              J. Quittek
                                                                     NEC
                                                              March 2009


              Architecture for IP Flow Information Export

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents in effect on the date of
   publication of this document (http://trustee.ietf.org/license-info).
   Please review these documents carefully, as they describe your rights
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   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Abstract

   This memo defines the IP Flow Information eXport (IPFIX) architecture
   for the selective monitoring of IP Flows, and for the export of
   measured IP Flow information from an IPFIX Device to a Collector.




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Table of Contents

   1. Introduction ....................................................3
      1.1. Document Scope .............................................3
      1.2. IPFIX Documents Overview ...................................3
   2. Terminology .....................................................4
   3. Examples of Flows ...............................................8
   4. IPFIX Reference Model ..........................................10
   5. IPFIX Functional and Logical Blocks ............................12
      5.1. Metering Process ..........................................12
           5.1.1. Flow Expiration ....................................12
           5.1.2. Flow Export ........................................13
      5.2. Observation Point .........................................13
      5.3. Selection Criteria for Packets ............................13
           5.3.1. Sampling Functions, Si .............................14
           5.3.2. Filter Functions, Fi ...............................15
      5.4. Observation Domain ........................................15
      5.5. Exporting Process .........................................15
      5.6. Collecting Process ........................................16
      5.7. Summary ...................................................17
   6. Overview of the IPFIX Protocol .................................18
      6.1. Information Model Overview ................................19
      6.2. Flow Records ..............................................19
      6.3. Control Information .......................................20
      6.4. Reporting Responsibilities ................................21
   7. IPFIX Protocol Details .........................................21
      7.1. The IPFIX Basis Protocol ..................................21
      7.2. IPFIX Protocol on the Collecting Process ..................22
      7.3. Support for Applications ..................................22
   8. Export Models ..................................................23
      8.1. Export with Reliable Control Connection ...................23
      8.2. Collector Failure Detection and Recovery ..................23
      8.3. Collector Redundancy ......................................24
   9. IPFIX Flow Collection in Special Situations ....................24
   10. Security Considerations .......................................25
      10.1. Data Security ............................................25
           10.1.1. Host-Based Security ...............................26
           10.1.2. Authentication-Only ...............................26
           10.1.3. Encryption ........................................26
      10.2. IPFIX End-Point Authentication ...........................27
      10.3. IPFIX Overload ...........................................27
           10.3.1. Denial-of-Service (DoS) Attack Prevention .........27
   11. IANA Considerations ...........................................28
      11.1. Numbers Used in the Protocol .............................28
      11.2. Numbers Used in the Information Model ....................29
   12. Acknowledgements ..............................................29





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   13. References ....................................................30
      13.1. Normative References .....................................30
      13.2. Informative References ...................................30

1.  Introduction

   There are several applications, e.g., usage-based accounting, traffic
   profiling, traffic engineering, attack/intrusion detection, quality-
   of-service (QoS) monitoring, that require Flow-based IP traffic
   measurements.  It is therefore important to have a standard way of
   exporting information related to IP Flows.  This document defines an
   architecture for IP traffic Flow monitoring, measuring, and
   exporting.  It provides a high-level description of an IPFIX Device's
   key components and their functions.

1.1.  Document Scope

   This document defines the architecture for IPFIX.  Its main
   objectives are to:

   o  Describe the key IPFIX architectural components, consisting of (at
      least) IPFIX Devices and Collectors communicating using the IPFIX
      protocol.

   o  Define the IPFIX architectural requirements, e.g., recovery,
      security, etc.

   o  Describe the characteristics of the IPFIX protocol.

1.2.  IPFIX Documents Overview

   The IPFIX protocol provides network administrators with access to IP
   Flow information.  This document specifies the architecture for the
   export of measured IP Flow information from an IPFIX Exporting
   Process to a Collecting Process, per the requirements defined in RFC
   3917 [1].  The IPFIX protocol document, RFC 5101 [3], specifies how
   IPFIX data records and templates are carried via a congestion-aware
   transport protocol, from IPFIX Exporting Process to IPFIX Collecting
   Process.  IPFIX has a formal description of IPFIX information
   elements (fields), their name, type, and additional semantic
   information, as specified in RFC 5102 [2].  Finally, RFC 5472 [4]
   describes what type 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.

   Note that the IPFIX system does not provide for remote configuration
   of an IPFIX device.  Instead, implementors must provide an effective
   way to configure their IPFIX devices.



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2.  Terminology

   The definitions of basic IPFIX terms such as IP Traffic Flow,
   Exporting Process, Collecting Process, Observation Point, etc., are
   semantically identical with those found in the IPFIX requirements
   document, RFC 3917 [1].  Some of the terms have been expanded for
   more clarity when defining the protocol.  Additional definitions
   required for the architecture have also been defined.  For terms that
   are defined here and in RFC 5101 [3], the definitions are equivalent
   in both documents.

   * Observation Point

      An Observation Point is a location in the network where IP packets
      can be observed.  Examples include: a line to which a probe is
      attached, a shared medium, such as an Ethernet-based LAN, a single
      port of a router, or a set of interfaces (physical or logical) of
      a router.

      Note that every Observation Point is associated with an
      Observation Domain (defined below), and that one Observation Point
      may be a superset of several other Observation Points.  For
      example, one Observation Point can be an entire line card.  That
      would be the superset of the individual Observation Points at the
      line card's interfaces.

   * Observation Domain

      An Observation Domain is the largest set of Observation Points for
      which Flow information can be aggregated by a Metering Process.
      For example, a router line card may be an Observation Domain if it
      is composed of several interfaces, each of which is an Observation
      Point.  In the IPFIX Message it generates, the Observation Domain
      includes its Observation Domain ID, which is unique per Exporting
      Process.  That way, the Collecting Process can identify the
      specific Observation Domain from the Exporter that sends the IPFIX
      Messages.  Every Observation Point is associated with an
      Observation Domain.  It is recommended that Observation Domain IDs
      also be unique per IPFIX Device.

   * IP Traffic Flow or Flow

      There are several definitions of the term 'flow' being used by the
      Internet community.  Within the context of IPFIX we use the
      following definition:






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      A Flow is defined as a set of IP packets passing an Observation
      Point in the network during a certain time interval.  All packets
      belonging to a particular Flow have a set of common properties.
      Each property is defined as the result of applying a function to
      the values of:

      1.  one or more packet header fields (e.g., destination IP
          address), transport header fields (e.g., destination port
          number), or application header fields (e.g., RTP header fields
          [5]).

      2.  one or more characteristics of the packet itself (e.g., number
          of MPLS labels)

      3.  one or more fields derived from packet treatment (e.g., next
          hop IP address, output interface)

      A packet is defined as belonging to a Flow if it completely
      satisfies all the defined properties of the Flow.

      This definition covers the range from a Flow containing all
      packets observed at a network interface to a Flow consisting of
      just a single packet between two applications.  It includes
      packets selected by a sampling mechanism.

   * Flow Key

      Each of the fields that:

      1.  belongs to the packet header (e.g., destination IP address),

      2.  is a property of the packet itself (e.g., packet length),

      3.  is derived from packet treatment (e.g., Autonomous System (AS)
          number), and

      4.  is used to define a Flow

      is termed a Flow Key.

   * Flow Record

      A Flow Record contains information about a specific Flow that was
      observed at an Observation Point.  A Flow Record contains measured
      properties of the Flow (e.g., the total number of bytes for all
      the Flow's packets) and usually characteristic properties of the
      Flow (e.g., source IP address).




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   * Metering Process

      The Metering Process generates Flow Records.  Inputs to the
      process are packet headers and characteristics observed at an
      Observation Point, and packet treatment at the Observation Point
      (for example, the selected output interface).

      The Metering Process consists of a set of functions that includes
      packet header capturing, timestamping, sampling, classifying, and
      maintaining Flow Records.

      The maintenance of Flow Records may include creating new records,
      updating existing ones, computing Flow statistics, deriving
      further Flow properties, detecting Flow expiration, passing Flow
      Records to the Exporting Process, and deleting Flow Records.

   * Exporting Process

      The Exporting Process sends Flow Records to one or more Collecting
      Processes.  The Flow Records are generated by one or more Metering
      Processes.

   * Exporter

      A device that hosts one or more Exporting Processes is termed an
      Exporter.

   * IPFIX Device

      An IPFIX Device hosts at least one Exporting Process.  It may host
      further Exporting Processes and arbitrary numbers of Observation
      Points and Metering Processes.

   * Collecting Process

      A Collecting Process receives Flow Records from one or more
      Exporting Processes.  The Collecting Process might process or
      store received Flow Records, but such actions are out of scope for
      this document.

   * Collector

      A device that hosts one or more Collecting Processes is termed a
      Collector.







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   * Template

      A Template is an ordered sequence of <type, length> pairs used to
      completely specify the structure and semantics of a particular set
      of information that needs to be communicated from an IPFIX Device
      to a Collector.  Each Template is uniquely identifiable by means
      of a Template ID.

   * Control Information, Data Stream

      The information that needs to be exported from the IPFIX Device
      can be classified into the following categories:

      Control Information

         This includes the Flow definition, selection criteria for
         packets within the Flow sent by the Exporting Process, and
         templates describing the data to be exported.  Control
         Information carries all the information needed for the end-
         points to understand the IPFIX protocol, and specifically for
         the Collector to understand and interpret the data sent by the
         sending Exporter.

      Data Stream

         This includes Flow Records carrying the field values for the
         various observed Flows at each of the Observation Points.

   * IPFIX Message

      An IPFIX Message is a message originating at the Exporting Process
      that carries the IPFIX records of this Exporting Process and whose
      destination is a Collecting Process.  An IPFIX Message is
      encapsulated at the transport layer.

   * Information Element

      An Information Element is a protocol and encoding-independent
      description of an attribute that may appear in an IPFIX Record.
      The IPFIX information model, RFC 5102 [2], defines the base set of
      Information Elements for IPFIX.  The type associated with an
      Information Element indicates constraints on what it may contain
      and also determines the valid encoding mechanisms for use in
      IPFIX.







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3.  Examples of Flows

   Some examples of Flows are listed below.  In the IPv4 examples, we
   use interface addresses in three different 26-bit (/26) subnets.  In
   the IPv6 examples, we use 'mac addr-nn' in the low-order 64 bits to
   indicate the IEEE MAC (Media Access Control) address of host
   interface nn.

   Example 1: Flow Keys define the different fields by which Flows are
   distinguished.  The different combination of their field values
   creates unique Flows.  If {source IP address, destination IP address,
   DSCP} are Flow Keys, then all of these are different Flows:

     1. {192.0.2.1,   192.0.2.65, 4}
     2. {192.0.2.23,  192.0.2.67, 4}
     3. {192.0.2.23,  192.0.2.67, 2}
     4. {192.0.2.129, 192.0.2.67, 4}

     5. {2001:DB8::0:mac-addr-01, 2001:DB8::1:mac-addr-11, 4}
     6. {2001:DB8::0:mac-addr-02, 2001:DB8::1:mac-addr-13, 4}
     7. {2001:DB8::0:mac-addr-02, 2001:DB8::1:mac-addr-13, 2}
     8. {2001:DB8::2:mac-addr-21, 2001:DB8::1:mac-addr-13, 4}

   Example 2: A mask function can be applied to all the packets that
   pass through an Observation Point, in order to aggregate some values.
   This could be done by defining the set of Flow Keys as {source IP
   address, destination IP address, DSCP} as in Example 1 above, and
   applying functions that mask out the source and destination IP
   addresses (least significant 6 bits for IPv4, 64 bits for IPv6).  The
   eight Flows from Example 1 would now be aggregated into six Flows by
   merging the Flows 1+2 and 5+6 into single Flows:

     1. {192.0.2.0/26,   192.0.2.64/26, 4}
     2. {192.0.2.0/26,   192.0.2.64/26, 2}
     3. {192.0.2.128/26, 192.0.2.64/26, 4}

     4. {2001:DB8::0/64, 2001:DB8::1/64, 4}
     5. {2001:DB8::0/64, 2001:DB8::1/64, 2}
     6. {2001:DB8::2/64, 2001:DB8::1/64, 4}

   Example 3: A filter defined by some Flow Key values can be applied on
   all packets that pass the Observation Point, in order to select only
   certain Flows.  The filter is defined by choosing fixed values for
   specific Keys from the packet.

   All the packets that go from a customer network 192.0.2.0/26 to
   another customer network 192.0.2.64/26 with DSCP value of 4 define a
   Flow.  All other combinations don't define a Flow and are not taken



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   into account.  The three Flows from Example 2 would now be reduced to
   one Flow by filtering out Flows 2 and 3, leaving only Flow 1,
   {192.0.2.0/26, 192.0.2.64/26, 4}.

   Similarly, for the IPv6 packets in the examples above, one could
   filter out Flows 5 and 6 to leave Flow 4.

   The above examples can be thought of as a function F() taking as
   input {source IP address, destination IP address, DSCP}.  The
   function selects only the packets that satisfy all three of the
   following conditions:

   1.  Mask out the least significant 6 bits of source IP address, match
       against 192.0.2.0.

   2.  Mask out the least significant 6 bits of destination IP address,
       match against 192.0.2.64.

   3.  Only accept DSCP value equal to 4.

   Depending on the values of {source IP address, destination IP
   address, DSCP} of the different observed packets, the Metering
   Process function F() would choose/filter/aggregate different sets of
   packets, which would create different Flows.  For example, for
   various combinations of values of {source IP address, destination IP
   address, DSCP}, F(source IP address, destination IP address, DSCP)
   would result in the definition of one or more Flows.
























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4.  IPFIX Reference Model

   The figure below shows the reference model for IPFIX.  This figure
   covers the various possible scenarios that can exist in an IPFIX
   system.

                             +----------------+     +----------------+
                             |[*Application 1]| ... |[*Application n]|
                             +--------+-------+     +-------+--------+
                                      ^                     ^
                                      |                     |
                                      + = = = = -+- = = = = +
                                                 ^
                                                 |
   +------------------------+            +-------+------------------+
   |IPFIX Exporter          |            | Collector(1)             |
   |[Exporting Process(es)] |<---------->| [Collecting Process(es)] |
   +------------------------+            +--------------------------+
           ....                                  ....
   +------------------------+           +---------------------------+
   |IPFIX Device(i)         |           | Collector(j)              |
   |[Observation Point(s)]  |<--------->| [Collecting Process(es)]  |
   |[Metering Process(es)]  |     +---->| [*Application(s)]         |
   |[Exporting Process(es)] |     |     +---------------------------+
   +------------------------+     .
          ....                    .              ....
   +------------------------+     |     +--------------------------+
   |IPFIX Device(m)         |     |     | Collector(n)             |
   |[Observation Point(s)]  |<----+---->| [Collecting Process(es)] |
   |[Metering Process(es)]  |           | [*Application(s)]        |
   |[Exporting Process(es)] |           +--------------------------+
   +------------------------+

   The various functional components are indicated within brackets [].
   The functional components within [*] are not part of the IPFIX
   architecture.  The interfaces shown by "<----->" are defined by the
   IPFIX architecture, but those shown by "<= = = =>" are not.

                      Figure 1: IPFIX Reference Model












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   The figure below shows a typical IPFIX Device where the IPFIX
   components are shown in rectangular boxes.

           +--------------------------------------------------+
           |                 IPFIX Device                     |
           |                                          +-----+ |
           |        +------- ... ------------+--------->    | |
           |        |                        |        |     | |
           |   +----+----+              +----+----+   |     | |
           |   |Metering |              |Metering |   |  E  | |
           |   |Process 1|              |Process N|   |  x  | |
           |   +---------+              +---------+   |  p  | |
           |        ^                        ^        |  o  | |
           | +------+--------+     +---------+------+ |  r  | |
           | | Obsv Domain 1 |     | Obsv Domain N  | |  t  | |
           | |+-----+-------+|     |+-------+------+| |  i  | |
           | ||Obsv Pt 1..j || ... ||Obsv Pt j+1..M|| |  n  | |
           | |+-------------+|     |+--------------+| |  g  | | Export
   Packets | +------^--------+     +---------^------+ |     | | packets
   --->----+--------+---------- ... ---------+        |     | |   to
      In   |                                          |     +--------->
           |        . . . . .                         |     | |Collector
           |                                          |     | |
           |        +------ ... -------------+--------->    | |
           |        |                        |        |     | |
           |   +----+----+              +----+----+   |  P  | |
           |   |Metering |              |Metering |   |  r  | |
           |   |Process 1|              |Process N|   |  o  | |
           |   +---------+              +---------+   |  c  | |
           |        ^                        ^        |  e  | |
           | +------+--------+     +---------+------+ |  s  | |
           | | Obsv Domain 1 |     | Obsv Domain N  | |  s  | |
           | |+-----+-------+|     |+-------+------+| |     | |
           | ||Obsv Pt 1..k || ... ||Obsv Pt k+1..M|| |     | |
           | |+-------------+|     |+--------------+| |     | |
   Packets | +------^--------+     +---------^------+ +-----+ |
   --->----+--------+---------- ... ---------+                |
      In   |                                                  |
           +--------------------------------------------------+

                          Figure 2: IPFIX Device










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5.  IPFIX Functional and Logical Blocks

5.1.  Metering Process

   Every Observation Point in an IPFIX Device, participating in Flow
   measurements, must be associated with at least one Metering Process.
   Every packet coming into an Observation Point goes into each of the
   Metering Processes associated with the Observation Point.  Broadly,
   each Metering Process observes the packets that pass an Observation
   Point, does timestamping, and classifies the packets into Flow(s)
   based on the selection criteria.

   The Metering Process is a functional block that manages all the Flows
   generated from an Observation Domain.  The typical functions of a
   Metering Process may include:

   o  Maintaining database(s) of all the Flow Records from an
      Observation Domain.  This includes creating new Flow Records,
      updating existing ones, computing Flow Records statistics,
      deriving further Flow properties, and adding non-Flow-specific
      information based on the packet treatment (in some cases, fields
      like AS numbers, router state, etc.)

   o  Maintaining statistics about the Metering Process itself, such as
      Flow Records generated, packets observed, etc.

5.1.1.  Flow Expiration

   A Flow is considered to have expired under the following conditions:

   1.  If no packets belonging to the Flow have been observed for a
       certain period of time.  This time period should be configurable
       at the Metering Process, with a minimum value of 0 seconds for
       immediate expiration.  Note that a zero timeout would report a
       Flow as a sequence of single-packet Flows.

   2.  If the IPFIX Device experiences resource constraints, a Flow may
       be prematurely expired (e.g., lack of memory to store Flow
       Records).

   3.  For long-running Flows, the Metering Process should expire the
       Flow on a regular basis or based on some expiration policy.  This
       periodicity or expiration policy should be configurable at the
       Metering Process.  When a long-running Flow is expired, its Flow
       Record may still be maintained by the Metering Process so that
       the Metering Process does not need to create a new Flow Record
       for further observed packets of the same Flow.




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5.1.2.  Flow Export

   The Exporting Process decides when and whether to export an expired
   Flow.  A Flow can be exported because it expired for any of the
   reasons mentioned in Section 5.1.1, "Flow Expiration".  For example:
   the Exporting Process exports a portion of the expired Flows every
   'x' seconds.

   For long-lasting Flows, the Exporting Process should export the Flow
   Records on a regular basis or based on some export policy.  This
   periodicity or export policy should be configurable at the Exporting
   Process.

5.2.  Observation Point

   A Flow Record can be better analysed if the Observation Point from
   which it was measured is known.  As such, it is recommended that
   IPFIX Devices send this information to Collectors.  In cases where
   there is a single Observation Point or where the Observation Point
   information is not relevant, the Metering Process may choose not to
   add the Observation Point information to the Flow Records.

5.3.  Selection Criteria for Packets

   A Metering Process may define rules so that only certain packets
   within an incoming stream of packets are chosen for measurement at an
   Observation Point.  This may be done by one of the two methods
   defined below or a combination of them, in either order.  A
   combination of each of these methods can be adopted to select the
   packets, i.e., one can define a set of methods {F1, S1, F2, S2, S3}
   executed in a specified sequence at an Observation Point to select
   particular Flows.

   The figure below shows the operations that may be applied as part of
   a typical Metering Process.
















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                 +---------------------------+
                 |  packet header capturing  |
                 +---------------------------+
                              |
                              v
                 +---------------------------+
                 |       timestamping        |
                 +---------------------------+
                              |
                              v
            +---------------> +
            |                 |
            |                 v
            |    +----------------------------------------------+
            |    |   sampling Si (1:1 in case of no sampling)   |
            |    +----------------------------------------------+
            |                 |
            |                 v
            |    +----------------------------------------------+
            |    |  filtering Fi (select all when no criteria)  |
            |    +----------------------------------------------+
            |                 |
            |                 v
            +-----------------+
                              |
                              v
                 +---------------------------+
                 |          Flows            |
                 +---------------------------+

                 Figure 3: Selection Criteria for Packets

   Note that packets could be selected before or after any IP
   processing, i.e., before there is any IP checksum validation, IP
   filtering, etc., or after one or more of these steps.  This has an
   impact on what kinds of traffic (or erroneous conditions) IPFIX can
   observe.  It is recommended that packets are selected after their
   checksums have been verified.

5.3.1.  Sampling Functions, Si

   A sampling function determines which packets within a stream of
   incoming packets are selected for measurement, i.e., packets that
   satisfy the sampling criteria for this Metering Process.

   Example: sample every 100th packet that was received at an
   Observation Point.




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   Choosing all the packets is a special case where the sampling rate is
   1:1.

5.3.2.  Filter Functions, Fi

   A Filter Function selects only those incoming packets that satisfy a
   function on fields defined by the packet header fields, fields
   obtained while doing the packet processing, or properties of the
   packet itself.

   Example: Mask/Match of the fields that define a filter.  A filter
   might be defined as {Protocol == TCP, Destination Port < 1024}.

   Several such filters could be used in any sequence to select packets.
   Note that packets selected by a (sequence of) filter functions may be
   further classified by other filter functions, i.e., the selected
   packets may belong to several Flows, any or all of which are
   exported.

5.4.  Observation Domain

   The Observation Domain is a logical block that presents a single
   identity for a group of Observation Points within an IPFIX Device.
   Each {Observation Point, Metering Process} pair belongs to a single
   Observation Domain.  An IPFIX Device could have multiple Observation
   Domains, each of which has a subset of the total set of Observation
   Points in it.  Each Observation Domain must carry a unique ID within
   the context of an IPFIX Device.  Note that in the case of multiple
   Observation Domains, a unique ID per Observation Domain must be
   transmitted as a parameter to the Exporting Function.  That unique ID
   is referred to as the IPFIX Observation Domain ID.

5.5.  Exporting Process

   The Exporting Process is the functional block that sends data to one
   or more IPFIX Collectors using the IPFIX protocol.  On one side, the
   Exporting Process interfaces with Metering Process(es) to get Flow
   Records; while on the other side, it talks to a Collecting Process on
   the Collector(s).

   There may be additional rules defined within an Observation Domain so
   that only certain Flow Records are exported.  This may be done by
   either one or a combination of Si and Fi, as described in
   Section 5.3, "Selection Criteria for Packets".

   Example: Only the Flow Records that meet the following selection
   criteria are exported:




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   1.  All Flow Records whose destination IP address matches
       {192.0.33.5}.

   2.  Every other (i.e., sampling rate 1 in 2) Flow Record whose
       destination IP address matches {192.0.11.30}.

5.6.  Collecting Process

   Collecting Processes use a Flow Record's Template ID to interpret
   that Flow Record's Information Elements.  To allow this, an IPFIX
   Exporter must ensure that an IPFIX Collector knows the Template ID
   for each incoming Flow Record.  To interpret incoming Flow Records,
   an IPFIX Collector may also need to know the function F() that was
   used by the Metering Process for each Flow.

   The functions of the Collecting Process must include:

   o  Identifying, accepting, and decoding the IPFIX Messages from
      different <Exporting Process, Observation Domain> pairs.

   o  Storing the Control Information and Flow Records received from an
      IPFIX Device.

   At a high level, the Collecting Process:

   1.  Receives and stores the Control Information.

   2.  Decodes and stores the Flow Records using the Control
       Information.






















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5.7.  Summary

   The figure below shows the functions performed in sequence by the
   various functional blocks in an IPFIX Device.

                    Packet(s) coming into Observation Point(s)
                      |                                   |
                      v                                   v
     +----------------+-------------------------+   +-----+-------+
     |          Metering Process on an          |   |             |
     |             Observation Point            |   |             |
     |                                          |   |             |
     |   packet header capturing                |   |             |
     |        |                                 |...| Metering    |
     |   timestamping                           |   | Process N   |
     |        |                                 |   |             |
     | +----->+                                 |   |             |
     | |      |                                 |   |             |
     | |   sampling Si (1:1 in case of no       |   |             |
     | |      |          sampling)              |   |             |
     | |   filtering Fi (select all when        |   |             |
     | |      |          no criteria)           |   |             |
     | +------+                                 |   |             |
     |        |                                 |   |             |
     |        |        Timing out Flows         |   |             |
     |        |    Handle resource overloads    |   |             |
     +--------|---------------------------------+   +-----|-------+
              |                                           |
      Flow Records (identified by Observation Domain)  Flow Records
              |                                           |





















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              +---------+---------------------------------+
                        |
   +--------------------|----------------------------------------------+
   |                    |     Exporting Process                        |
   |+-------------------|-------------------------------------------+  |
   ||                   v       IPFIX Protocol                      |  |
   ||+-----------------------------+  +----------------------------+|  |
   |||Rules for                    |  |Functions                   ||  |
   ||| Picking/sending Templates   |  |-Packetise selected Control ||  |
   ||| Picking/sending Flow Records|->|  & data Information into   ||  |
   ||| Encoding Template & data    |  |  IPFIX export packets.     ||  |
   ||| Selecting Flows to export(*)|  |-Handle export errors       ||  |
   ||+-----------------------------+  +----------------------------+|  |
   |+----------------------------+----------------------------------+  |
   |                             |                                     |
   |                    exported IPFIX Messages                        |
   |                             |                                     |
   |                +------------+-----------------+                   |
   |                |  Anonymise export packet(*)  |                   |
   |                +------------+-----------------+                   |
   |                             |                                     |
   |                +------------+-----------------+                   |
   |                |       Transport  Protocol    |                   |
   |                +------------+-----------------+                   |
   |                             |                                     |
   +-----------------------------+-------------------------------------+
                                 |
                                 v
                    IPFIX export packet to Collector

   (*) indicates that the block is optional.

                 Figure 4: IPFIX Device functional blocks

6.  Overview of the IPFIX Protocol

   An IPFIX Device consists of a set of cooperating processes that
   implement the functional blocks described in the previous section.
   Alternatively, an IPFIX Device can be viewed simply as a network
   entity that implements the IPFIX protocol.  At the IPFIX Device, the
   protocol functionality resides in the Exporting Process.  The IPFIX
   Exporting Process gets Flow Records from a Metering Process, and
   sends them to the Collector(s).

   At a high level, an IPFIX Device performs the following tasks:

   1.  Encodes Control Information into Templates.




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   2.  Encodes packets observed at the Observation Points into Flow
       Records.

   3.  Packetises the selected Templates and Flow Records into IPFIX
       Messages.

   4.  Sends IPFIX Messages to the Collector.

   The IPFIX protocol communicates information from an IPFIX Exporter to
   an IPFIX Collector.  That information includes not only Flow Records,
   but also information about the Metering Process.  Such information
   (referred to as Control Information) includes details of the data
   fields in Flow Records.  It may also include statistics from the
   Metering Process, such as the number of packets lost (i.e., not
   metered).

   For details of the IPFIX protocol, please refer to RFC 5101 [3].

6.1.  Information Model Overview

   The IP Flow Information eXport (IPFIX) protocol serves for
   transmitting information related to measured IP traffic over the
   Internet.  The protocol specification in RFC 5101 [3] defines how
   Information Elements are transmitted.  For Information Elements, it
   specifies the encoding of a set of basic data types.  However, the
   list of fields that can be transmitted by the protocol, such as Flow
   attributes (source IP address, number of packets, etc.) and
   information about the Metering and Exporting Process (packet
   Observation Point, sampling rate, Flow timeout interval, etc.), is
   not specified in RFC 5101 [3].  Instead, it is defined in the IPFIX
   information model in RFC 5102 [2].

   The information model provides a complete description of the
   properties of every IPFIX Information Element.  It does this by
   specifying each element's name, Field Type, data type, etc., and
   providing a description of each element.  Element descriptions give
   the semantics of the element, i.e., say how it is derived from a Flow
   or other information available within an IPFIX Device.

6.2.  Flow Records

   The following rules provide guidelines to be followed while encoding
   the Flow Records information:

   A Flow Record contains enough information so that the Collecting
   Process can identify the corresponding <Per-Flow Control Information,
   Configuration Control Information>.




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   The Exporting Process encodes a given Information Element (as
   specified in RFC 5102 [2]), based on the encoding standards
   prescribed by RFC 5101 [3].

6.3.  Control Information

   The following rules provide guidelines to be followed while encoding
   the Control Information:

   o  Per-Flow Control Information should be encoded such that the
      Collecting Process can capture the structure and semantics of the
      corresponding Flow data for each of the Flow Records exported by
      the IPFIX Device.

   o  Configuration Control Information is conveyed to a Collector so
      that its Collecting Process can capture the structure and
      semantics of the corresponding configuration data.  The
      configuration data, which is also Control Information, should
      carry additional information on the Observation Domain within
      which the configuration takes effect.

   For example, sampling using the same sampling algorithm, say 1 in 100
   packets, is configured on two Observation Points O1 and O2.  The
   configuration in this case may be encoded as {ID, observation points
   (O1,O2), sampling algorithm, interval (1 in 100)}, where ID is the
   Observation Domain ID for the domain containing O1 and O2.  The
   Observation Domain ID uniquely identifies this configuration, and
   must be sent within the Flow Records in order to be able to match the
   right configuration control information.

   The Control Information is used by the Collecting Process to:

   o  Decode and interpret Flow Records.

   o  Understand the state of the Exporting Process.

   Sending Control Information from the Exporting Process in a timely
   and reliable manner is critical to the proper functioning of the
   IPFIX Collecting Process.  The following approaches may be taken for
   the export of Control Information:

   1.  Send all the Control Information pertaining to Flow Records prior
       to sending the Flow Records themselves.  This includes any
       incremental changes to the definition of the Flow Records.







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   2.  Notify, on a near real-time basis, the state of the IPFIX Device
       to the Collecting Process.  This includes all changes such as a
       configuration change that affects the Flow behaviour, changes to
       Exporting Process resources that alter export rates, etc., which
       the Collector needs to be aware of.

   3.  Since it is vital that a Collecting Process maintains accurate
       knowledge of the Exporter's state, the export of the Control
       Information should be done such that it reaches the Collector
       reliably.  One way to achieve this is to send the Control
       Information over a reliable transport.

6.4.  Reporting Responsibilities

   From time to time, an IPFIX Device may not be able to observe all the
   packets reaching one of its Observation Points.  This could occur if
   a Metering Process finds itself temporarily short of resources.  For
   example, it might run out of packet buffers for IPFIX export.

   In such situations, the IPFIX Device should attempt to count the
   number of packet losses that have occurred, and report them to its
   Collector(s).  If it is not possible to count losses accurately,
   e.g., when transport layer (i.e., non-IPFIX) errors are detected, the
   IPFIX Device should report this fact, and perhaps indicate the time
   period during which some packets might not have been observed.

7.  IPFIX Protocol Details

   When the IPFIX Working Group was chartered, there were existing
   common practices in the area of Flow export, for example, NetFlow,
   CRANE (Common Reliable Accounting for Network Element), LFAP (Light-
   weight Flow Admission Protocol), RTFM (Real-time Traffic Flow
   Measurement), etc.  IPFIX's charter required the Working Group to
   consider those existing practices, and select the one that was the
   closest fit to the IPFIX requirements in RFC 3917 [1].  Additions or
   modifications would then be made to the selected protocol to fit it
   exactly into the IPFIX architecture.

7.1.  The IPFIX Basis Protocol

   The Working Group went through an extensive evaluation of the various
   existing protocols that were available, weighing the level of
   compliance with the requirements, and selected one of the candidates
   as the basis for the IPFIX protocol.  For more details of the
   evaluation process, please see RFC 3955 [6].






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   In the basis protocol, Flow Records are defined by Templates, where a
   Template is an ordered set of the Information Elements appearing in a
   Flow Record, together with their field sizes within those records.

   This approach provides the following advantages:

   o  Using the Template mechanism, new fields can be added to IPFIX
      Flow Records without changing the structure of the export record
      format.

   o  Templates that are sent to the Collecting Process carry structural
      information about the exported Flow Record fields.  Therefore, if
      the Collector does not understand the semantics of new fields, it
      can ignore them, but still interpret the Flow Record.

   o  Because the template mechanism is flexible, it allows the export
      of only the required fields from the Flows to the Collecting
      Process.  This helps to reduce the exported Flow data volume and
      possibly provide memory savings at the Exporting Process and
      Collecting Process.  Sending only the required information can
      also reduce network load.

7.2.  IPFIX Protocol on the Collecting Process

   The Collecting Process is responsible for:

   1.  Receiving and decoding Flow Records from the IPFIX Devices.

   2.  Reporting on the loss of Flow Records sent to the Collecting
       Process by an IPFIX Exporting Process.

   Complete details of the IPFIX protocol are given in RFC 5101 [3].

7.3.  Support for Applications

   Applications that use the information collected by IPFIX may be
   Billing or Intrusion Detection sub-systems, etc.  These applications
   may be an integral part of the Collecting Process, or they may be co-
   located with the Collecting Process.  The way by which these
   applications interface with IPFIX systems to get the desired
   information is out of scope for this document.










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8.  Export Models

8.1.  Export with Reliable Control Connection

   As mentioned in RFC 3917 [1], an IPFIX Device must be able to
   transport its Control Information and Data Stream over a congestion-
   aware transport protocol.

   If the network in which the IPFIX Device and Collecting Process are
   located does not guarantee reliability, at least the Control
   Information should be exported over a reliable transport.  The Data
   Stream may be exported over a reliable or unreliable transport
   protocol.

   Possible transport protocols include:

   o  SCTP: Supports reliable and unreliable transport.

   o  TCP: Provides reliable transport only.

   o  UDP: Provides unreliable transport only.  Network operators would
      need to avoid congestion by keeping traffic within their own
      administrative domains.  For example, one could use a dedicated
      network (or Ethernet link) to carry IPFIX traffic from Exporter to
      Collector.

8.2.  Collector Failure Detection and Recovery

   The transport connection (in the case of a connection-oriented
   protocol) is pre-configured between the IPFIX Device and the
   Collector.  The IPFIX protocol does not provide any mechanism for
   configuring the Exporting and Collecting Processes.

   Once connected, an IPFIX Collector receives Control Information and
   uses that information to interpret Flow Records.  The IPFIX Device
   should set a keepalive (e.g., the keepalive timeout in the case of
   TCP, the HEARTBEAT interval in the case of SCTP) to a sufficiently
   low value so that it can quickly detect a Collector failure.  Note,
   however, that extremely short keepalive intervals can incorrectly
   abort the connection during transient periods of congestion.  They
   can also cause some level of additional network load during otherwise
   idle periods.

   Collector failure refers to the crash or restart of the Collecting
   Process or of the Collector itself.  A Collector failure is detected
   at the IPFIX Device by the break in the connection-oriented transport
   protocol session; depending on the transport protocol, the connection
   timeout mechanisms differ.  On detecting a keepalive timeout in a



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   single Collector scenario, the IPFIX Device should stop sending Flow
   Records to the Collector and try to reestablish the transport
   connection.  If Collecting Process failover is supported by the
   Exporting Process, backup session(s) may be opened in advance, and
   Control Information sent to the failover Collecting Process.

   There could be one or more secondary Collectors with priority
   assigned to them.  The primary Collector crash is detected at the
   IPFIX Device.  On detecting loss of connectivity, the IPFIX Device
   opens a Data Stream with the secondary Collector of the next highest
   priority.  If that secondary was not opened in advance, both the
   Control Information and Data Stream must be sent to it.  That
   Collector might then become the primary, or the Exporting Process
   might try to reestablish the original session.

8.3.  Collector Redundancy

   Configuring redundant Collectors is an alternative to configuring
   backup Collectors.  In this model, all Collectors simultaneously
   receive the Control Information and Data Streams.  Multiple {Control
   Information, Data Stream} pairs could be sent, each to a different
   Collector, from the same IPFIX Device.  Since the IPFIX protocol
   requires a congestion-aware transport, achieving redundancy using
   multicast is not an option.

9.  IPFIX Flow Collection in Special Situations

   An IPFIX Device can generate, receive, and/or alter two special types
   of traffic, which are listed below.

   Tunnel traffic:

      The IPFIX Device could be the head, midpoint, or end-point of a
      tunnel.  In such cases, the IPFIX Device could be handling Generic
      Routing Encapsulation (GRE) [8], IPinIP [7], or Layer Two
      Tunneling Protocol version 3 [9] traffic.

   VPN traffic:

      The IPFIX Device could be a provider-edge device that receives
      traffic from customer sites belonging to different Virtual Private
      Networks.

   Similarly, IPFIX could be implemented on devices which perform one or
   more of the following special services:






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   o  Explicitly drop packets.  For example, a device that provides
      firewall service drops packets based on some administrative
      policy.

   o  Alter the values of fields used as IPFIX Flow Keys of interest.
      For example, a device that provides NAT service can change the
      source and/or destination IP address.

   In cases such as those listed above, there should be clear guidelines
   as to:

   o  How and when to classify the packets as Flows in the IPFIX Device.

   o  If multiple encapsulations are used to define Flows, how to convey
      the same fields (e.g., IP address) in different layers.

   o  How to differentiate Flows based on different private domains.
      For example, overlapping IP addresses in Layer-3 VPNs.

   o  What extra information needs to be exported so that the Collector
      can make a clear interpretation of the received Flow Records.

10.  Security Considerations

   Flow information can be used for various purposes, such as usage-
   based accounting, traffic profiling, traffic engineering, and
   intrusion detection.  The security requirements may differ
   significantly for such applications.  To be able to satisfy the
   security needs of various IPFIX users, an IPFIX system must provide
   different levels of security protection.

10.1.  Data Security

   IPFIX data comprises Control Information and Data Streams generated
   by the IPFIX Device.

   The IPFIX data may exist in both the IPFIX Device and the Collector.
   In addition, the data is also transferred on the wire from the IPFIX
   Device to the Collector when it is exported.  To provide security,
   the data should be protected from common network attacks.

   The protection of IPFIX data within the end system (IPFIX Device and
   Collector) is out of scope for this document.  It is assumed that the
   end system operator will provide adequate security for the IPFIX
   data.






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   The IPFIX architecture must allow different levels of protection to
   the IPFIX data on the wire.  Wherever security functions are
   required, it is recommended that users should leverage lower layers
   using either TLS or DTLS (Datagram Transport Layer Security), if
   these can successfully satisfy the security requirement of IPFIX data
   protection.

   To protect the data on the wire, three levels of granularity should
   be supported; these are described in the following subsections.

10.1.1.  Host-Based Security

   Security may not be required when the transport between the IPFIX
   Device and the Collector is perceived as safe.  This option allows
   the protocol to run most efficiently without extra overhead, and an
   IPFIX system must support it.

10.1.2.  Authentication-Only

   Authentication-only protection provides IPFIX users with the
   assurance of data integrity and authenticity.  The data exchanged
   between the IPFIX Device and the Collector is protected by an
   authentication signature.  Any modification of the IPFIX data will be
   detected by the recipient, resulting in the discarding of the
   received data.  However, the authentication-only option doesn't offer
   data confidentiality.

   The IPFIX user should not use authentication-only when sensitive or
   confidential information is being exchanged.  An IPFIX solution
   should support this option.  The authentication-only option should
   provide replay attack protection.  Some means to achieve this level
   of security are:

   o  Encapsulating Security Payload (with a null encryption algorithm)

   o  Transport Layer Security (with a null encryption algorithm)

   o  IP Authentication Header

10.1.3.  Encryption

   Data encryption provides the best protection for IPFIX data.  The
   IPFIX data is encrypted at the sender, and only the intended
   recipient can decrypt and have access to the data.  This option must
   be used when the transport between the IPFIX Device and the Collector
   is unsafe, and the IPFIX data needs to be protected.  It is





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   recommended that the underlying transport layer's security functions
   be used for this purpose.  Some means to achieve this level of
   security are:

   o  Encapsulating Security Payload

   o  Transport Layer Security Protocol

   The data encryption option adds overhead to the IPFIX data transfer.
   It may limit the rate that an Exporter can report its Flow Records to
   the Collector, due to the resource requirement for running
   encryption.

10.2.  IPFIX End-Point Authentication

   It is important to make sure that the IPFIX Device is talking to the
   "right" Collector rather than to a masquerading Collector.  The same
   logic also holds true from the Collector's point of view, i.e., it
   may want to make sure it is collecting the Flow Records from the
   "right" IPFIX Device.  An IPFIX system should allow the end-point
   authentication capability so that either one-way or mutual
   authentication can be performed between the IPFIX Device and
   Collector.

   The IPFIX architecture should use any existing transport protection
   protocols, such as TLS, to fulfil the authentication requirement.

10.3.  IPFIX Overload

   An IPFIX Device could become overloaded under various conditions.
   This may be because of exhaustion of internal resources used for Flow
   generation and/or export.  Such overloading may cause loss of data
   from the Exporting Process, either from lack of export bandwidth
   (possibly caused by an unusually high number of observed Flows) or
   from network congestion in the path from Exporter to Collector.

   IPFIX Collectors should be able to detect the loss of exported Flow
   Records, and should at least record the number of lost Flow Records.

10.3.1.  Denial-of-Service (DoS) Attack Prevention

   Since one of the potential usages for IPFIX is for intrusion
   detection, it is important for the IPFIX architecture to support some
   kind of DoS resistance.







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10.3.1.1.  Network under Attack

   The network itself may be under attack, resulting in an overwhelming
   number of IPFIX Messages.  An IPFIX system should try to capture as
   much information as possible.  However, when a large number of IPFIX
   Messages are generated in a short period of time, the IPFIX system
   may become overloaded.

10.3.1.2.  Generic DoS Attack on the IPFIX Device and Collector

   The IPFIX Device and Collector may be subject to generic DoS attacks,
   just as any system on any open network.  These types of attacks are
   not IPFIX specific.  Preventing and responding to such types of
   attacks are out of the scope of this document.

10.3.1.3.  IPFIX-Specific DoS Attack

   There are some specific attacks on the IPFIX portion of the IPFIX
   Device or Collector:

   o  The attacker could overwhelm the Collector with spoofed IPFIX
      Export packets.  One way to solve this problem is to periodically
      synchronise the sequence numbers of the Flow Records between the
      Exporting and Collecting Processes.

   o  The attacker could provide false reports to the Collector by
      sending spoofed packets.

   The problems mentioned above can be solved to a large extent if the
   control packets are encrypted both ways, thereby providing more
   information that the Collector could use to identify and ignore
   spoofed data packets.

11.  IANA Considerations

   The IPFIX Architecture, as set out in this document, has two sets of
   assigned numbers, as outlined in the following subsections.

11.1.  Numbers Used in the Protocol

   IPFIX Messages, as described in RFC 5101 [3], use two fields with
   assigned values.  These are the IPFIX Version Number, indicating
   which version of the IPFIX Protocol was used to export an IPFIX
   Message, and the IPFIX Set ID, indicating the type for each set of
   information within an IPFIX Message.






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   Values for the IPFIX Version Number and the IPFIX Set ID, together
   with the considerations for assigning them, are defined in RFC 5101
   [3].

11.2.  Numbers Used in the Information Model

   Fields of the IPFIX protocol carry information about traffic
   measurement.  They are modelled as elements of the IPFIX information
   model RFC 5102 [2].  Each Information Element describes a field that
   may appear in an IPFIX Message.  Within an IPFIX Message, the field
   type is indicated by its Field Type.

   Values for the IPFIX Information Element IDs, together with the
   considerations for assigning them, are defined in RFC 5102 [2].

12.  Acknowledgements

   The document editors wish to thank all the people contributing to the
   discussion of this document on the mailing list, and the design teams
   for many valuable comments.  In particular, the following made
   significant contributions:

      Tanja Zseby
      Paul Calato
      Dave Plonka
      Jeffrey Meyer
      K.C.Norseth
      Vamsi Valluri
      Cliff Wang
      Ram Gopal
      Jc Martin
      Carter Bullard
      Reinaldo Penno
      Simon Leinen
      Kevin Zhang
      Paul Aitken
      Brian Trammell

      Special thanks to Dave Plonka for the multiple thorough reviews.












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13.  References

13.1.  Normative References

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

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

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

   [4]  Zseby, T., Boschi, E., Brownlee, N., and B. Claise, "IPFIX
        Applicability", RFC 5472, March 2009.

13.2.  Informative References

   [5]  Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson,
        "RTP: A Transport Protocol for Real-Time Applications", STD 64,
        RFC 3550, July 2003.

   [6]  Leinen, S., "Evaluation of Candidate Protocols for IP Flow
        Information Export (IPFIX)", RFC 3955, October 2004.

   [7]  Simpson, W., "IP in IP Tunneling", RFC 1853, October 1995.

   [8]  Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. Traina,
        "Generic Routing Encapsulation (GRE)", RFC 2784, March 2000.

   [9]  Lau, J., Townsley, M., and I. Goyret, "Layer Two Tunneling
        Protocol - Version 3 (L2TPv3)", RFC 3931, March 2005.

















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Authors' Addresses

   Ganesh Sadasivan
   Rohati Systems
   1192 Borregas Ave.
   Sunnyvale, CA  94089
   USA

   EMail: gsadasiv@rohati.com


   Nevil Brownlee
   CAIDA | The University of Auckland
   Private Bag 92019
   Auckland  1142
   New Zealand

   Phone: +64 9 373 7599 x88941
   EMail: n.brownlee@auckland.ac.nz


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

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


   Juergen Quittek
   NEC Laboratories Europe, NEC Europe Ltd.
   Kurfuersten-Anlage 36
   Heidelberg  69115
   Germany

   Phone: +49 6221 4342-115
   EMail: quittek@nw.neclab.eu
   URI:   http://www.neclab.eu/











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