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rfc:rfc3954

Network Working Group B. Claise, Ed. Request for Comments: 3954 Cisco Systems Category: Informational October 2004

          Cisco Systems NetFlow Services Export Version 9

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) The Internet Society (2004).

IESG Note

 This RFC documents the NetFlow services export protocol Version 9 as
 it was when submitted to the IETF as a basis for further work in the
 IPFIX WG.
 This RFC itself is not a candidate for any level of Internet
 Standard.  The IETF disclaims any knowledge of the fitness of this
 RFC for any purpose, and in particular notes that it has not had
 complete IETF review for such things as security, congestion control,
 or inappropriate interaction with deployed protocols.  The RFC Editor
 has chosen to publish this document at its discretion.

Abstract

 This document specifies the data export format for version 9 of Cisco
 Systems' NetFlow services, for use by implementations on the network
 elements and/or matching collector programs.  The version 9 export
 format uses templates to provide access to observations of IP packet
 flows in a flexible and extensible manner.  A template defines a
 collection of fields, with corresponding descriptions of structure
 and semantics.

Table of Contents

 1.   Introduction. . . . . . . . . . . . . . . . . . . . . . . . .  2
 2.   Terminology . . . . . . . . . . . . . . . . . . . . . . . . .  4
      2.1.  Terminology Summary Table . . . . . . . . . . . . . . .  6
 3.   NetFlow High-Level Picture on the Exporter. . . . . . . . . .  6
      3.1.  The NetFlow Process on the Exporter . . . . . . . . . .  6
      3.2.  Flow Expiration . . . . . . . . . . . . . . . . . . . .  7

Claise Informational [Page 1] RFC 3954 Cisco Systems NetFlow Services Export V9 October 2004

      3.3.  Transport Protocol. . . . . . . . . . . . . . . . . . .  7
 4.   Packet Layout . . . . . . . . . . . . . . . . . . . . . . . .  8
 5.   Export Packet Format. . . . . . . . . . . . . . . . . . . . .  9
      5.1.  Header Format . . . . . . . . . . . . . . . . . . . . .  9
      5.2.  Template FlowSet Format . . . . . . . . . . . . . . . . 11
      5.3.  Data FlowSet Format . . . . . . . . . . . . . . . . . . 13
 6.   Options . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
      6.1.  Options Template FlowSet Format . . . . . . . . . . . . 14
      6.2.  Options Data Record Format. . . . . . . . . . . . . . . 16
 7.   Template Management . . . . . . . . . . . . . . . . . . . . . 17
 8.   Field Type Definitions. . . . . . . . . . . . . . . . . . . . 18
 9.   The Collector Side. . . . . . . . . . . . . . . . . . . . . . 25
 10.  Security Considerations . . . . . . . . . . . . . . . . . . . 26
      10.1. Disclosure of Flow Information Data . . . . . . . . . . 26
      10.2. Forgery of Flow Records or Template Records . . . . . . 26
      10.3. Attacks on the NetFlow Collector. . . . . . . . . . . . 27
 11.  Examples. . . . . . . . . . . . . . . . . . . . . . . . . . . 27
      11.1. Packet Header Example . . . . . . . . . . . . . . . . . 28
      11.2. Template FlowSet Example. . . . . . . . . . . . . . . . 28
      11.3. Data FlowSet Example. . . . . . . . . . . . . . . . . . 29
      11.4. Options Template FlowSet Example. . . . . . . . . . . . 30
      11.5. Data FlowSet with Options Data Records Example. . . . . 30
 12.  References. . . . . . . . . . . . . . . . . . . . . . . . . . 31
      12.1. Normative References. . . . . . . . . . . . . . . . . . 31
      12.2. Informative References. . . . . . . . . . . . . . . . . 31
 13.  Authors . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
 14.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 31
 15.  Authors' Addresses. . . . . . . . . . . . . . . . . . . . . . 32
 16.  Full Copyright Statement. . . . . . . . . . . . . . . . . . . 33

1. Introduction

 Cisco Systems' NetFlow services provide network administrators with
 access to IP flow information from their data networks.  Network
 elements (routers and switches) gather flow data and export it to
 collectors.  The collected data provides fine-grained metering for
 highly flexible and detailed resource usage accounting.
 A flow is defined as a unidirectional sequence of packets with some
 common properties that pass through a network device.  These
 collected flows are exported to an external device, the NetFlow
 collector.  Network flows are highly granular; for example, flow
 records include details such as IP addresses, packet and byte counts,
 timestamps, Type of Service (ToS), application ports, input and
 output interfaces, etc.
 Exported NetFlow data is used for a variety of purposes, including
 enterprise accounting and departmental chargebacks, ISP billing, data

Claise Informational [Page 2] RFC 3954 Cisco Systems NetFlow Services Export V9 October 2004

 warehousing, network monitoring, capacity planning, application
 monitoring and profiling, user monitoring and profiling, security
 analysis, and data mining for marketing purposes.
 This document specifies NetFlow version 9.  It describes the
 implementation specifications both from network element and NetFlow
 collector points of view.  These specifications should help the
 deployment of NetFlow version 9 across different platforms and
 different vendors by limiting the interoperability risks.  The
 NetFlow export format version 9 uses templates to provide access to
 observations of IP packet flows in a flexible and extensible manner.
 A template defines a collection of fields, with corresponding
 descriptions of structure and semantics.
 The template-based approach provides the following advantages:
  1. New fields can be added to NetFlow flow records without

changing the structure of the export record format. With

       previous NetFlow versions, adding a new field in the flow
       record implied a new version of the export protocol format and
       a new version of the NetFlow collector that supported the
       parsing of the new export protocol format.
  1. Templates that are sent to the NetFlow collector contain the

structural information about the exported flow record fields;

       therefore, if the NetFlow collector does not understand the
       semantics of new fields, it can still interpret the flow
       record.
  1. Because the template mechanism is flexible, it allows the

export of only the required fields from the flows to the

       NetFlow collector.  This helps to reduce the exported flow data
       volume and provides possible memory savings for the exporter
       and NetFlow collector.  Sending only the required information
       can also reduce network load.
 The IETF IPFIX Working Group (IP Flow Information eXport) is
 developing a new protocol, based on the version 9 of Cisco Systems'
 NetFlow services.  Some enhancements in different domains (congestion
 aware transport protocol, built-in security, etc... ) have been
 incorporated in this new IPFIX protocol.  Refer to the IPFIX Working
 Group documents for more details.
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in BCP 14, RFC 2119
 [RFC2119].

Claise Informational [Page 3] RFC 3954 Cisco Systems NetFlow Services Export V9 October 2004

2. Terminology

 Various terms used in this document are described in this section.
 Note that the terminology summary table in Section 2.1 gives a quick
 overview of the relationships between some of the different terms
 defined.
 Observation Point
 An Observation Point is a location in the network where IP packets
 can be observed; for example, one or a set of interfaces on a network
 device like a router.  Every Observation Point is associated with an
 Observation Domain.
 Observation Domain
 The set of Observation Points that is the largest aggregatable set of
 flow information at the network device with NetFlow services enabled
 is termed an Observation Domain.  For example, a router line card
 composed of several interfaces with each interface being an
 Observation Point.
 IP Flow or Flow
 An IP Flow, also called a Flow, is defined as a set of IP packets
 passing an Observation Point in the network during a certain time
 interval.  All packets that belong to a particular Flow have a set of
 common properties derived from the data contained in the packet and
 from the packet treatment at the Observation Point.
 Flow Record
 A Flow Record provides information about an IP Flow observed at an
 Observation Point.  In this document, the Flow Data Records are also
 referred to as NetFlow services data and NetFlow data.
 Exporter
 A device (for example, a router) with the NetFlow services enabled,
 the Exporter monitors packets entering an Observation Point and
 creates Flows from these packets.  The information from these Flows
 is exported in the form of Flow Records to the NetFlow Collector.
 NetFlow Collector
 The NetFlow Collector receives Flow Records from one or more
 Exporters.  It processes the received Export Packet(s); that is, it
 parses and stores the Flow Record information.  Flow Records can be
 optionally aggregated before being stored on the hard disk.  The
 NetFlow Collector is also referred to as the Collector in this
 document.

Claise Informational [Page 4] RFC 3954 Cisco Systems NetFlow Services Export V9 October 2004

 Export Packet
 An Export Packet is a packet originating at the Exporter that carries
 the Flow Records of this Exporter and whose destination is the
 NetFlow Collector.
 Packet Header
 The Packet Header is the first part of an Export Packet.  The Packet
 Header provides basic information about the packet such as the
 NetFlow version, number of records contained within the packet, and
 sequence numbering.
 Template Record
 A Template Record defines the structure and interpretation of fields
 in a Flow Data Record.
 Flow Data Record
 A Flow Data Record is a data record that contains values of the Flow
 parameters corresponding to a Template Record.
 Options Template Record
 An Options Template Record defines the structure and interpretation
 of fields in an Options Data Record, including defining the scope
 within which the Options Data Record is relevant.
 Options Data Record
 The data record that contains values and scope information of the
 Flow measurement parameters, corresponding to an Options Template
 Record.
 FlowSet
 FlowSet is a generic term for a collection of Flow Records that have
 a similar structure.  In an Export Packet, one or more FlowSets
 follow the Packet Header.  There are three different types of
 FlowSets: Template FlowSet, Options Template FlowSet, and Data
 FlowSet.
 Template FlowSet
 A Template FlowSet is one or more Template Records that have been
 grouped together in an Export Packet.
 Options Template FlowSet
 An Options Template FlowSet is one or more Options Template Records
 that have been grouped together in an Export Packet.

Claise Informational [Page 5] RFC 3954 Cisco Systems NetFlow Services Export V9 October 2004

 Data FlowSet
 A Data FlowSet is one or more records, of the same type, that are
 grouped together in an Export Packet.  Each record is either a Flow
 Data Record or an Options Data Record previously defined by a
 Template Record or an Options Template Record.

2.1. Terminology Summary Table

 +------------------+---------------------------------------------+
 |                  |                    Contents                 |
 |                  +--------------------+------------------------+
 |     FlowSet      | Template  Record   |    Data Record         |
 +------------------+--------------------+------------------------+
 |                  |                    |  Flow Data Record(s)   |
 | Data FlowSet     |          /         |          or            |
 |                  |                    | Options Data Record(s) |
 +------------------+--------------------+------------------------+
 | Template FlowSet | Template Record(s) |           /            |
 +------------------+--------------------+------------------------+
 | Options Template | Options Template   |           /            |
 | FlowSet          | Record(s)          |                        |
 +------------------+--------------------+------------------------+
 A Data FlowSet is composed of an Options Data Record(s) or Flow Data
 Record(s).  No Template Record is included. A Template Record defines
 the Flow Data Record, and an Options Template Record defines the
 Options Data Record.
 A Template FlowSet is composed of Template Record(s).  No Flow or
 Options Data Record is included.
 An Options Template FlowSet is composed of Options Template
 Record(s).  No Flow or Options Data Record is included.

3. NetFlow High-Level Picture on the Exporter

3.1. The NetFlow Process on the Exporter

 The NetFlow process on the Exporter is responsible for the creation
 of Flows from the observed IP packets.  The details of this process
 are beyond the scope of this document.

Claise Informational [Page 6] RFC 3954 Cisco Systems NetFlow Services Export V9 October 2004

3.2. Flow Expiration

 A Flow is considered to be inactive if no packets belonging to the
 Flow have been observed at the Observation Point for a given timeout.
 If any packet is seen within the timeout, the flow is considered an
 active flow. A Flow can be exported under the following conditions:
    1. If the Exporter can detect the end of a Flow.  For example, if
       the FIN or RST bit is detected in a TCP [RFC793] connection,
       the Flow Record is exported.
    2. If the Flow has been inactive for a certain period of time.
       This inactivity timeout SHOULD be configurable at the Exporter,
       with a minimum value of 0 for an immediate expiration.
    3. For long-lasting Flows, the Exporter SHOULD export the Flow
       Records on a regular basis.  This timeout SHOULD be
       configurable at the Exporter.
    4. If the Exporter experiences internal constraints, a Flow MAY be
       forced to expire prematurely; for example, counters wrapping or
       low memory.

3.3. Transport Protocol

 To achieve efficiency in terms of processing at the Exporter while
 handling high volumes of Export Packets, the NetFlow Export Packets
 are encapsulated into UDP [RFC768] datagrams for export to the
 NetFlow Collector.  However, NetFlow version 9 has been designed to
 be transport protocol independent.  Hence, it can also operate over
 congestion-aware protocols such as SCTP [RFC2960].
 Note that the Exporter can export to multiple Collectors, using
 independent transport protocols.
 UDP [RFC768] is a non congestion-aware protocol, so when deploying
 NetFlow version 9 in a congestion-sensitive environment, make the
 connection between Exporter and NetFlow Collector through a dedicated
 link.  This ensures that any burstiness in the NetFlow traffic
 affects only this dedicated link.  When the NetFlow Collector can not
 be placed within a one-hop distance from the Exporter or when the
 export path from the Exporter to the NetFlow Collector can not be
 exclusively used for the NetFlow Export Packets, the export path
 should be designed so that it can always sustain the maximum
 burstiness of NetFlow traffic from the Exporter.  Note that the
 congestion can occur on the Exporter in case the export path speed is
 too low.

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4. Packet Layout

 An Export Packet consists of a Packet Header followed by one or more
 FlowSets.  The FlowSets can be any of the possible three types:
 Template, Data, or Options Template.
   +--------+-------------------------------------------+
   |        | +----------+ +---------+ +----------+     |
   | Packet | | Template | | Data    | | Options  |     |
   | Header | | FlowSet  | | FlowSet | | Template | ... |
   |        | |          | |         | | FlowSet  |     |
   |        | +----------+ +---------+ +----------+     |
   +--------+-------------------------------------------+
                       Export Packet
 A FlowSet ID is used to distinguish the different types of FlowSets.
 FlowSet IDs lower than 256 are reserved for special FlowSets, such as
 the Template FlowSet (ID 0) and the Options Template FlowSet (ID 1).
 The Data FlowSets have a FlowSet ID greater than 255.
 The format of the Template, Data, and Options Template FlowSets will
 be discussed later in this document.  The Exporter MUST code all
 binary integers of the Packet Header and the different FlowSets in
 network byte order (also known as the big-endian byte ordering).
 Following are some examples of export packets:
 1. An Export Packet consisting of interleaved Template, Data, and
    Options Template FlowSets.  Example: a newly created Template is
    exported as soon as possible.  So if there is already an Export
    Packet with a Data FlowSet that is being prepared for export, the
    Template and Option FlowSets are also interleaved with this
    information, subject to availability of space.
 Export Packet:
 +--------+--------------------------------------------------------+
 |        | +----------+ +---------+     +-----------+ +---------+ |
 | Packet | | Template | | Data    |     | Options   | | Data    | |
 | Header | | FlowSet  | | FlowSet | ... | Template  | | FlowSet | |
 |        | |          | |         |     | FlowSet   | |         | |
 |        | +----------+ +---------+     +-----------+ +---------+ |
 +--------+--------------------------------------------------------+
 2. An Export Packet consisting entirely of Data FlowSets.  Example:
    after the appropriate Template Records have been defined and
    transmitted to the NetFlow Collector device, the majority of
    Export Packets consists solely of Data FlowSets.

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 Export Packet:
 +--------+----------------------------------------------+
 |        | +---------+     +---------+      +---------+ |
 | Packet | | Data    | ... | Data    | ...  | Data    | |
 | Header | | FlowSet | ... | FlowSet | ...  | FlowSet | |
 |        | +---------+     +---------+      +---------+ |
 +--------+----------------------------------------------+
 3. An Export Packet consisting entirely of Template and Options
    Template FlowSets.  Example: the Exporter MAY transmit a packet
    containing Template and Options Template FlowSets periodically to
    help ensure that the NetFlow Collector has the correct Template
    Records and Options Template Records when the corresponding Flow
    Data records are received.
 Export Packet:
 +--------+-------------------------------------------------+
 |        | +----------+     +----------+      +----------+ |
 | Packet | | Template |     | Template |      | Options  | |
 | Header | | FlowSet  | ... | FlowSet  | ...  | Template | |
 |        | |          |     |          |      | FlowSet  | |
 |        | +----------+     +----------+      +----------+ |
 +--------+-------------------------------------------------+

5. Export Packet Format

5.1. Header Format

 The Packet Header format is specified as:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |       Version Number          |            Count              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                           sysUpTime                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                           UNIX Secs                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                       Sequence Number                         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                        Source ID                              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Claise Informational [Page 9] RFC 3954 Cisco Systems NetFlow Services Export V9 October 2004

 Packet Header Field Descriptions
 Version
       Version of Flow Record format exported in this packet.  The
       value of this field is 9 for the current version.
 Count
       The total number of records in the Export Packet, which is the
       sum of Options FlowSet records, Template FlowSet records, and
       Data FlowSet records.
 sysUpTime
       Time in milliseconds since this device was first booted.
 UNIX Secs
       Time in seconds since 0000 UTC 1970, at which the Export Packet
       leaves the Exporter.
 Sequence Number
       Incremental sequence counter of all Export Packets sent from
       the current Observation Domain by the Exporter.  This value
       MUST be cumulative, and SHOULD be used by the Collector to
       identify whether any Export Packets have been missed.
 Source ID
       A 32-bit value that identifies the Exporter Observation Domain.
       NetFlow Collectors SHOULD use the combination of the source IP
       address and the Source ID field to separate different export
       streams originating from the same Exporter.

Claise Informational [Page 10] RFC 3954 Cisco Systems NetFlow Services Export V9 October 2004

5.2. Template FlowSet Format

 One of the essential elements in the NetFlow format is the Template
 FlowSet.  Templates greatly enhance the flexibility of the Flow
 Record format because they allow the NetFlow Collector to process
 Flow Records without necessarily knowing the interpretation of all
 the data in the Flow Record.  The format of the Template FlowSet is
 as follows:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |       FlowSet ID = 0          |          Length               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |      Template ID 256          |         Field Count           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |        Field Type 1           |         Field Length 1        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |        Field Type 2           |         Field Length 2        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |             ...               |              ...              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |        Field Type N           |         Field Length N        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |      Template ID 257          |         Field Count           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |        Field Type 1           |         Field Length 1        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |        Field Type 2           |         Field Length 2        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |             ...               |              ...              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |        Field Type M           |         Field Length M        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |             ...               |              ...              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |        Template ID K          |         Field Count           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |             ...               |              ...              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Template FlowSet Field Descriptions
 FlowSet ID
       FlowSet ID value of 0 is reserved for the Template FlowSet.

Claise Informational [Page 11] RFC 3954 Cisco Systems NetFlow Services Export V9 October 2004

 Length
       Total length of this FlowSet.  Because an individual Template
       FlowSet MAY contain multiple Template Records, the Length value
       MUST be used to determine the position of the next FlowSet
       record, which could be any type of FlowSet.  Length is the sum
       of the lengths of the FlowSet ID, the Length itself, and all
       Template Records within this FlowSet.
 Template ID
       Each of the newly generated Template Records is given a unique
       Template ID.  This uniqueness is local to the Observation
       Domain that generated the Template ID.  Template IDs 0-255 are
       reserved for Template FlowSets, Options FlowSets, and other
       reserved FlowSets yet to be created.  Template IDs of Data
       FlowSets are numbered from 256 to 65535.
 Field Count
       Number of fields in this Template Record.   Because a Template
       FlowSet usually contains multiple Template Records, this field
       allows the Collector to determine the end of the current
       Template Record and the start of the next.
 Field Type
       A numeric value that represents the type of the field.  Refer
       to the "Field Type Definitions" section.
 Field Length
       The length of the corresponding Field Type, in bytes.  Refer to
       the "Field Type Definitions" section.

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5.3. Data FlowSet Format

 The format of the Data FlowSet is as follows:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   FlowSet ID = Template ID    |          Length               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   Record 1 - Field Value 1    |   Record 1 - Field Value 2    |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   Record 1 - Field Value 3    |             ...               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   Record 2 - Field Value 1    |   Record 2 - Field Value 2    |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   Record 2 - Field Value 3    |             ...               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   Record 3 - Field Value 1    |             ...               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |              ...              |            Padding            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Data FlowSet Field Descriptions
 FlowSet ID = Template ID
       Each Data FlowSet is associated with a FlowSet ID.  The FlowSet
       ID maps to a (previously generated) Template ID.  The Collector
       MUST use the FlowSet ID to find the corresponding Template
       Record and decode the Flow Records from the FlowSet.
 Length
       The length of this FlowSet.  Length is the sum of the lengths
       of the FlowSet ID, Length itself, all Flow Records within this
       FlowSet, and the padding bytes, if any.
 Record N - Field Value M
       The remainder of the Data FlowSet is a collection of Flow Data
       Record(s), each containing a set of field values.  The Type and
       Length of the fields have been previously defined in the
       Template Record referenced by the FlowSet ID or Template ID.
 Padding
       The Exporter SHOULD insert some padding bytes so that the
       subsequent FlowSet starts at a 4-byte aligned boundary.  It is
       important to note that the Length field includes the padding
       bytes.  Padding SHOULD be using zeros.

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 Interpretation of the Data FlowSet format can be done only if the
 Template FlowSet corresponding to the Template ID is available at the
 Collector.

6. Options

6.1. Options Template FlowSet Format

 The Options Template Record (and its corresponding Options Data
 Record) is used to supply information about the NetFlow process
 configuration or NetFlow process specific data, rather than supplying
 information about IP Flows.
 For example, the Options Template FlowSet can report the sample rate
 of a specific interface, if sampling is supported, along with the
 sampling method used.
 The format of the Options Template FlowSet follows.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |       FlowSet ID = 1          |          Length               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Template ID           |      Option Scope Length      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |        Option Length          |       Scope 1 Field Type      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Scope 1 Field Length      |               ...             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Scope N Field Length      |      Option 1 Field Type      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Option 1 Field Length     |             ...               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Option M Field Length     |           Padding             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Options Template FlowSet Field Definitions
 FlowSet ID = 1
       A FlowSet ID value of 1 is reserved for the Options Template.
 Length
       Total length of this FlowSet.  Each Options Template FlowSet
       MAY contain multiple Options Template Records.  Thus, the
       Length value MUST be used to determine the position of the next
       FlowSet record, which could be either a Template FlowSet or
       Data FlowSet.

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       Length is the sum of the lengths of the FlowSet ID, the Length
       itself, and all Options Template Records within this FlowSet
       Template ID.
 Template ID
       Template ID of this Options Template.  This value is greater
       than 255.
 Option Scope Length
       The length in bytes of any Scope field definition contained in
       the Options Template Record (The use of "Scope" is described
       below).
 Option Length
       The length (in bytes) of any options field definitions
       contained in this Options Template Record.
 Scope 1 Field Type
       The relevant portion of the Exporter/NetFlow process to which
       the Options Template Record refers.
       Currently defined values are:
          1 System
          2 Interface
          3 Line Card
          4 Cache
          5 Template
       For example, the NetFlow process can be implemented on a per-
       interface basis, so if the Options Template Record were
       reporting on how the NetFlow process is configured, the Scope
       for the report would be 2 (interface).  The associated
       interface ID would then be carried in the associated Options
       Data FlowSet.  The Scope can be limited further by listing
       multiple scopes that all must match at the same time.  Note
       that the Scope fields always precede the Option fields.
 Scope 1 Field Length
       The length (in bytes) of the Scope field, as it would appear in
       an Options Data Record.
 Option 1 Field Type
       A numeric value that represents the type of field that would
       appear in the Options Template Record.  Refer to the Field Type
       Definitions section.
 Option 1 Field Length
       The length (in bytes) of the Option field.

Claise Informational [Page 15] RFC 3954 Cisco Systems NetFlow Services Export V9 October 2004

 Padding
       The Exporter SHOULD insert some padding bytes so that the
       subsequent FlowSet starts at a 4-byte aligned boundary.  It is
       important to note that the Length field includes the padding
       bytes.  Padding SHOULD be using zeros.

6.2. Options Data Record Format

 The Options Data Records are sent in Data FlowSets, on a regular
 basis, but not with every Flow Data Record.  How frequently these
 Options Data Records are exported is configurable.  See the
 "Templates Management" section for more details.
 The format of the Data FlowSet containing Options Data Records
 follows.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |    FlowSet ID = Template ID   |          Length               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   Record 1 - Scope 1 Value    |Record 1 - Option Field 1 Value|
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |Record 1 - Option Field 2 Value|             ...               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   Record 2 - Scope 1 Value    |Record 2 - Option Field 1 Value|
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |Record 2 - Option Field 2 Value|             ...               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   Record 3 - Scope 1 Value    |Record 3 - Option Field 1 Value|
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |Record 3 - Option Field 2 Value|             ...               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |              ...              |            Padding            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Options Data Records of the Data FlowSet Field Descriptions
 FlowSet ID = Template ID
       A FlowSet ID precedes each group of Options Data Records within
       a Data FlowSet.  The FlowSet ID maps to a previously generated
       Template ID corresponding to this Options Template Record.  The
       Collector MUST use the FlowSet ID to map the appropriate type
       and length to any field values that follow.

Claise Informational [Page 16] RFC 3954 Cisco Systems NetFlow Services Export V9 October 2004

 Length
       The length of this FlowSet. Length is the sum of the lengths of
       the FlowSet ID, Length itself, all the Options Data Records
       within this FlowSet, and the padding bytes, if any.
 Record N - Option Field M Value
       The remainder of the Data FlowSet is a collection of Flow
       Records, each containing a set of scope and field values.  The
       type and length of the fields were previously defined in the
       Options Template Record referenced by the FlowSet ID or
       Template ID.
 Padding
       The Exporter SHOULD insert some padding bytes so that the
       subsequent FlowSet starts at a 4-byte aligned boundary.  It is
       important to note that the Length field includes the padding
       bytes.  Padding SHOULD be using zeros.
 The Data FlowSet format can be interpreted only if the Options
 Template FlowSet corresponding to the Template ID is available at the
 Collector.

7. Template Management

 Flow Data records that correspond to a Template Record MAY appear in
 the same and/or subsequent Export Packets.  The Template Record is
 not necessarily carried in every Export Packet.  As such, the NetFlow
 Collector MUST store the Template Record to interpret the
 corresponding Flow Data Records that are received in subsequent data
 packets.
 A NetFlow Collector that receives Export Packets from several
 Observation Domains from the same Exporter MUST be aware that the
 uniqueness of the Template ID is not guaranteed across Observation
 Domains.
 The Template IDs must remain constant for the life of the NetFlow
 process on the Exporter.  If the Exporter or the NetFlow process
 restarts for any reason, all information about Templates will be lost
 and new Template IDs will be created.  Template IDs are thus not
 guaranteed to be consistent across an Exporter or NetFlow process
 restart.
 A newly created Template record is assigned an unused Template ID
 from the Exporter.  If the template configuration is changed, the
 current Template ID is abandoned and SHOULD NOT be reused until the

Claise Informational [Page 17] RFC 3954 Cisco Systems NetFlow Services Export V9 October 2004

 NetFlow process or Exporter restarts.  If a Collector should receive
 a new definition for an already existing Template ID, it MUST discard
 the previous template definition and use the new one.
 If a configured Template Record on the Exporter is deleted, and re-
 configured with exactly the same parameters, the same Template ID
 COULD be reused.
 The Exporter sends the Template FlowSet and Options Template FlowSet
 under the following conditions:
 1. After a NetFlow process restarts, the Exporter MUST NOT send any
    Data FlowSet without sending the corresponding Template FlowSet
    and the required Options Template FlowSet in a previous packet or
    including it in the same Export Packet.  It MAY transmit the
    Template FlowSet and Options Template FlowSet, without any Data
    FlowSets, in advance to help ensure that the Collector will have
    the correct Template Record before receiving the first Flow or
    Options Data Record.
 2. In the event of configuration changes, the Exporter SHOULD send
    the new template definitions at an accelerated rate.  In such a
    case, it MAY transmit the changed Template Record(s) and Options
    Template Record(s), without any data, in advance to help ensure
    that the Collector will have the correct template information
    before receiving the first data.
 3. On a regular basis, the Exporter MUST send all the Template
    Records and Options Template Records to refresh the Collector.
    Template IDs have a limited lifetime at the Collector and MUST be
    periodically refreshed.  Two approaches are taken to make sure
    that Templates get refreshed at the Collector:
          * Every N number of Export Packets.
          * On a time basis, so every N number of minutes.
    Both options MUST be configurable by the user on the Exporter.
    When one of these expiry conditions is met, the Exporter MUST send
    the Template FlowSet and Options Template.
 4. In the event of a clock configuration change on the Exporter, the
    Exporter SHOULD send the template definitions at an accelerated
    rate.

8. Field Type Definitions

 The following table describes all the field type definitions that an
 Exporter MAY support.  The fields are a selection of Packet Header
 fields, lookup results (for example, the autonomous system numbers or
 the subnet masks), and properties of the packet such as length.

Claise Informational [Page 18] RFC 3954 Cisco Systems NetFlow Services Export V9 October 2004

 Field Type                Value Length  Description
                                 (bytes)
                                         Incoming counter with
                                         length N x 8 bits for the
 IN_BYTES                     1    N     number of bytes associated
                                         with an IP Flow. By default
                                         N is 4
                                         Incoming counter with
                                         length N x 8 bits for the
 IN_PKTS                      2    N     number of packets
                                         associated with an IP Flow.
                                         By default N is 4
 FLOWS                        3    N     Number of Flows
                                         that were aggregated;
                                         by default N is 4
 PROTOCOL                     4    1     IP protocol byte
                                         Type of service byte
 TOS                          5    1     setting when entering
                                         the incoming interface
                                         TCP flags; cumulative of
 TCP_FLAGS                    6    1     all the TCP flags seen in
                                         this Flow
                                         TCP/UDP source port number
 L4_SRC_PORT                  7    2     (for example, FTP, Telnet,
                                         or equivalent)
 IPV4_SRC_ADDR                8    4     IPv4 source address
                                         The number of contiguous
                                         bits in the source subnet
 SRC_MASK                     9    1     mask (i.e., the mask in
                                         slash notation)
                                         Input interface index.
 INPUT_SNMP                   10   N     By default N is 2, but
                                         higher values can be used
                                         TCP/UDP destination port
 L4_DST_PORT                  11   2     number (for example, FTP,
                                         Telnet, or equivalent)

Claise Informational [Page 19] RFC 3954 Cisco Systems NetFlow Services Export V9 October 2004

 IPV4_DST_ADDR                12   4     IPv4 destination address
                                         The number of contiguous
                                         bits in the destination
 DST_MASK                     13   1     subnet mask (i.e., the mask
                                         in slash notation)
                                         Output interface index.
 OUTPUT_SNMP                  14   N     By default N is 2, but
                                         higher values can be used
 IPV4_NEXT_HOP                15   4     IPv4 address of the next-
                                         hop router
                                         Source BGP autonomous
 SRC_AS                       16   N     system number where N could
                                         be 2 or 4. By default N is
                                         2
                                         Destination BGP autonomous
 DST_AS                       17   N     system number where N could
                                         be 2 or 4. By default N is
                                         2
 BGP_IPV4_NEXT_HOP            18   4     Next-hop router's IP
                                         address in the BGP domain
                                         IP multicast outgoing
                                         packet counter with length
 MUL_DST_PKTS                 19   N     N x 8 bits for packets
                                         associated with the IP
                                         Flow. By default N is 4
                                         IP multicast outgoing
                                         Octet (byte) counter with
                                         length N x 8 bits for the
 MUL_DST_BYTES                20   N     number of bytes associated
                                         with the IP Flow. By
                                         default N is 4
                                         sysUptime in msec at which
 LAST_SWITCHED                21   4     the last packet of this
                                         Flow was switched
                                         sysUptime in msec at which
 FIRST_SWITCHED               22   4     the first packet of this
                                         Flow was switched

Claise Informational [Page 20] RFC 3954 Cisco Systems NetFlow Services Export V9 October 2004

                                         Outgoing counter with
                                         length N x 8 bits for the
 OUT_BYTES                    23   N     number of bytes associated
                                         with an IP Flow. By
                                         default N is 4
                                         Outgoing counter with
                                         length N x 8 bits for the
 OUT_PKTS                     24   N     number of packets
                                         associated with an IP Flow.
                                         By default N is 4
 IPV6_SRC_ADDR                27   16    IPv6 source address
 IPV6_DST_ADDR                28   16    IPv6 destination address
 IPV6_SRC_MASK                29   1     Length of the IPv6 source
                                         mask in contiguous bits
                                         Length of the IPv6
 IPV6_DST_MASK                30   1     destination mask in
                                         contiguous bits
 IPV6_FLOW_LABEL              31   3     IPv6 flow label as per
                                         RFC 2460 definition
                                         Internet Control Message
 ICMP_TYPE                    32   2     Protocol (ICMP) packet
                                         type; reported as
                                         ICMP Type * 256 + ICMP code
 MUL_IGMP_TYPE                33   1     Internet Group Management
                                         Protocol (IGMP) packet type
                                         When using sampled NetFlow,
                                         the rate at which packets
 SAMPLING_INTERVAL            34   4     are sampled; for example, a
                                         value of 100 indicates that
                                         one of every hundred
                                         packets is sampled
                                         For sampled NetFlow
                                         platform-wide:
 SAMPLING_ALGORITHM           35   1     0x01 deterministic sampling
                                         0x02 random sampling
                                         Use in connection with
                                         SAMPLING_INTERVAL

Claise Informational [Page 21] RFC 3954 Cisco Systems NetFlow Services Export V9 October 2004

                                         Timeout value (in seconds)
 FLOW_ACTIVE_TIMEOUT          36   2     for active flow entries
                                         in the NetFlow cache
                                         Timeout value (in seconds)
 FLOW_INACTIVE_TIMEOUT        37   2     for inactive Flow entries
                                         in the NetFlow cache
                                         Type of Flow switching
 ENGINE_TYPE                  38   1     engine (route processor,
                                         linecard, etc...)
 ENGINE_ID                    39   1     ID number of the Flow
                                         switching engine
                                         Counter with length
                                         N x 8 bits for the number
 TOTAL_BYTES_EXP              40   N     of bytes exported by the
                                         Observation Domain. By
                                         default N is 4
                                         Counter with length
                                         N x 8 bits for the number
 TOTAL_PKTS_EXP               41   N     of packets exported by the
                                         Observation Domain. By
                                         default N is 4
                                         Counter with length
                                         N x 8 bits for the number
 TOTAL_FLOWS_EXP              42   N     of Flows exported by the
                                         Observation Domain. By
                                         default N is 4
 MPLS_TOP_LABEL_TYPE          46   1     MPLS Top Label Type:
                                         0x00 UNKNOWN
                                         0x01 TE-MIDPT
                                         0x02 ATOM
                                         0x03 VPN
                                         0x04 BGP
                                         0x05 LDP
                                         Forwarding Equivalent Class
 MPLS_TOP_LABEL_IP_ADDR       47   4     corresponding to the MPLS
                                         Top Label
 FLOW_SAMPLER_ID              48   1     Identifier shown
                                         in "show flow-sampler"

Claise Informational [Page 22] RFC 3954 Cisco Systems NetFlow Services Export V9 October 2004

                                         The type of algorithm used
                                         for sampling data:
 FLOW_SAMPLER_MODE            49   1     0x02 random sampling
                                         Use in connection with
                                         FLOW_SAMPLER_MODE
                                         Packet interval at which to
 FLOW_SAMPLER_RANDOM_INTERVAL 50   4     sample. Use in connection
                                         with FLOW_SAMPLER_MODE
                                         Type of Service byte
 DST_TOS                      55   1     setting when exiting
                                         outgoing interface
 SRC_MAC                      56   6     Source MAC Address
 DST_MAC                      57   6     Destination MAC Address
                                         Virtual LAN identifier
 SRC_VLAN                     58   2     associated with ingress
                                         interface
                                         Virtual LAN identifier
 DST_VLAN                     59   2     associated with egress
                                         interface
                                         Internet Protocol Version
                                         Set to 4 for IPv4, set to 6
 IP_PROTOCOL_VERSION          60   1     for IPv6. If not present in
                                         the template, then version
                                         4 is assumed
                                         Flow direction:
 DIRECTION                    61   1     0 - ingress flow
                                         1 - egress flow
 IPV6_NEXT_HOP                62   16    IPv6 address of the
                                         next-hop router
 BGP_IPV6_NEXT_HOP            63   16    Next-hop router in the BGP
                                         domain
                                         Bit-encoded field
 IPV6_OPTION_HEADERS          64   4     identifying IPv6 option
                                         headers found in the flow
 MPLS_LABEL_1                 70   3     MPLS label at position 1 in
                                         the stack

Claise Informational [Page 23] RFC 3954 Cisco Systems NetFlow Services Export V9 October 2004

 MPLS_LABEL_2                 71   3     MPLS label at position 2 in
                                         the stack
 MPLS_LABEL_3                 72   3     MPLS label at position 3 in
                                         the stack
 MPLS_LABEL_4                 73   3     MPLS label at position 4 in
                                         the stack
 MPLS_LABEL_5                 74   3     MPLS label at position 5 in
                                         the stack
 MPLS_LABEL_6                 75   3     MPLS label at position 6 in
                                         the stack
 MPLS_LABEL_7                 76   3     MPLS label at position 7 in
                                         the stack
 MPLS_LABEL_8                 77   3     MPLS label at position 8 in
                                         the stack
 MPLS_LABEL_9                 78   3     MPLS label at position 9 in
                                         the stack
 MPLS_LABEL_10                79   3     MPLS label at position 10
                                         in the stack
 The value field is a numeric identifier for the field type. The
 following value fields are reserved for proprietary field types: 25,
 26, 43 to 45, 51 to 54, and 65 to 69.
 When extensibility is required, the new field types will be added to
 the list.  The new field types have to be updated on the Exporter and
 Collector but the NetFlow export format would remain unchanged.
 Refer to the latest documentation at http://www.cisco.com for the
 newly updated list.
 In some cases the size of a field type is fixed by definition, for
 example PROTOCOL, or IPV4_SRC_ADDR.  However in other cases they are
 defined as a variant type.  This improves the memory efficiency in
 the collector and reduces the network bandwidth requirement between
 the Exporter and the Collector.  As an example, in the case IN_BYTES,
 on an access router it might be sufficient to use a 32 bit counter (N
 = 4), whilst on a core router a 64 bit counter (N = 8) would be
 required.
 All counters and counter-like objects are unsigned integers of size N
 * 8 bits.

Claise Informational [Page 24] RFC 3954 Cisco Systems NetFlow Services Export V9 October 2004

9. The Collector Side

 The Collector receives Template Records from the Exporter, normally
 before receiving Flow Data Records (or Options Data Records).  The
 Flow Data Records (or Options Data Records) can then be decoded and
 stored locally on the devices.  If the Template Records have not been
 received at the time Flow Data Records (or Options Data Records) are
 received, the Collector SHOULD store the Flow Data Records (or
 Options Data Records) and decode them after the Template Records are
 received.  A Collector device MUST NOT assume that the Data FlowSet
 and the associated Template FlowSet (or Options Template FlowSet) are
 exported in the same Export Packet.
 The Collector MUST NOT assume that one and only one Template FlowSet
 is present in an Export Packet.
 The life of a template at the Collector is limited to a fixed refresh
 timeout.  Templates not refreshed from the Exporter within the
 timeout are expired at the Collector.  The Collector MUST NOT attempt
 to decode the Flow or Options Data Records with an expired Template.
 At any given time the Collector SHOULD maintain the following for all
 the current Template Records and Options Template Records: Exporter,
 Observation Domain, Template ID, Template Definition, Last Received.
 Note that the Observation Domain is identified by the Source ID field
 from the Export Packet.
 In the event of a clock configuration change on the Exporter, the
 Collector SHOULD discard all Template Records and Options Template
 Records associated with that Exporter, in order for Collector to
 learn the new set of fields: Exporter, Observation Domain, Template
 ID, Template Definition, Last Received.
 Template IDs are unique per Exporter and per Observation Domain.
 If the Collector receives a new Template Record (for example, in the
 case of an Exporter restart) it MUST immediately override the
 existing Template Record.
 Finally, note that the Collector MUST accept padding in the Data
 FlowSet and Options Template FlowSet, which means for the Flow Data
 Records, the Options Data Records and the Template Records. Refer to
 the terminology summary table in Section 2.1.

Claise Informational [Page 25] RFC 3954 Cisco Systems NetFlow Services Export V9 October 2004

10. Security Considerations

 The NetFlow version 9 protocol was designed with the expectation that
 the Exporter and Collector would remain within a single private
 network.  However the NetFlow version 9 protocol might be used to
 transport Flow Records over the public Internet which exposes the
 Flow Records to a number of security risks.  For example an attacker
 might capture, modify or insert Export Packets.  There is therefore a
 risk that IP Flow information might be captured or forged, or that
 attacks might be directed at the NetFlow Collector.
 The designers of NetFlow Version 9 did not impose any
 confidentiality, integrity or authentication requirements on the
 protocol because this reduced the efficiency of the implementation
 and it was believed at the time that the majority of deployments
 would confine the Flow Records to private networks, with the
 Collector(s) and Exporter(s) in close proximity.
 The IPFIX protocol (IP Flow Information eXport), which has chosen the
 NetFlow version 9 protocol as the base protocol, addresses the
 security considerations discussed in this section.  See the security
 section of IPFIX requirement draft [RFC3917] for more information.

10.1. Disclosure of Flow Information Data

 Because the NetFlow Version 9 Export Packets are not encrypted, the
 observation of Flow Records can give an attacker information about
 the active flows in the network, communication endpoints and traffic
 patterns.  This information can be used both to spy on user behavior
 and to plan and conceal future attacks.
 The information that an attacker could derive from the interception
 of Flow Records depends on the Flow definition.  For example, a Flow
 Record containing the source and destination IP addresses might
 reveal privacy sensitive information regarding the end user's
 activities, whilst a Flow Record only containing the source and
 destination IP network would be less revealing.

10.2. Forgery of Flow Records or Template Records

 If Flow Records are used in accounting and/or security applications,
 there may be a strong incentive to forge exported Flow Records (for
 example to defraud the service provider, or to prevent the detection
 of an attack).  This can be done either by altering the Flow Records
 on the path between the Observer and the Collector, or by injecting
 forged Flow Records that pretend to be originated by the Exporter.

Claise Informational [Page 26] RFC 3954 Cisco Systems NetFlow Services Export V9 October 2004

 An attacker could forge Templates and/or Options Templates and
 thereby try to confuse the NetFlow Collector, rendering it unable to
 decode the Export Packets.

10.3. Attacks on the NetFlow Collector

 Denial of service attacks on the NetFlow Collector can consume so
 many resources from the machine that, the Collector is unable to
 capture or decode some NetFlow Export Packets.  Such hazards are not
 explicitly addressed by the NetFlow Version 9 protocol, although the
 normal methods used to protect a server from a DoS attack will
 mitigate the problem.

11. Examples

 Let us consider the example of an Export Packet composed of a
 Template FlowSet, a Data FlowSet (which contains three Flow Data
 Records), an Options Template FlowSet, and a Data FlowSet (which
 contains two Options Data Records).
 Export Packet:
 +--------+---------------------------------------------. . .
 |        | +--------------+ +-----------------------+
 | Packet | | Template     | | Data                  |
 | Header | | FlowSet      | | FlowSet               |   . . .
 |        | | (1 Template) | | (3 Flow Data Records) |
 |        | +--------------+ +-----------------------+
 +--------+---------------------------------------------. . .
     . . .+-------------------------------------------------+
          +------------------+ +--------------------------+ |
          | Options          | | Data                     | |
     . . .| Template FlowSet | | FlowSet                  | |
          | (1 Template)     | | (2 Options Data Records) | |
          +------------------+ +--------------------------+ |
     . . .--------------------------------------------------+

Claise Informational [Page 27] RFC 3954 Cisco Systems NetFlow Services Export V9 October 2004

11.1. Packet Header Example

 The Packet Header is composed of:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Version = 9               |          Count = 7            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                           sysUpTime                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                           UNIX Secs                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                       Sequence Number                         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                           Source ID                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

11.2. Template FlowSet Example

 We want to report the following Field Types:
 -  The source IP address (IPv4), so the length is 4
 -  The destination IP address (IPv4), so the length is 4
 -  The next-hop IP address (IPv4), so the length is 4
 -  The number of bytes of the Flow
 -  The number of packets of the Flow
 Therefore, the Template FlowSet is composed of the following:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |       FlowSet ID = 0          |      Length = 28 bytes        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |       Template ID 256         |       Field Count = 5         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     IP_SRC_ADDR = 8           |       Field Length = 4        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     IP_DST_ADDR = 12          |       Field Length = 4        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     IP_NEXT_HOP = 15          |       Field Length = 4        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |       IN_PKTS = 2             |       Field Length = 4        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |       IN_BYTES = 1            |       Field Length = 4        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Claise Informational [Page 28] RFC 3954 Cisco Systems NetFlow Services Export V9 October 2004

11.3. Data FlowSet Example

 In this example, we report the following three Flow Records:
 Src IP addr. | Dst IP addr. | Next Hop addr. | Packet | Bytes
              |              |                | Number | Number
 ---------------------------------------------------------------
 198.168.1.12 | 10.5.12.254  | 192.168.1.1    | 5009   | 5344385
 192.168.1.27 | 10.5.12.23   | 192.168.1.1    | 748    | 388934
 192.168.1.56 | 10.5.12.65   | 192.168.1.1    | 5      | 6534
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |       FlowSet ID = 256        |          Length = 64          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                          198.168.1.12                         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                          10.5.12.254                          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                          192.168.1.1                          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                             5009                              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                            5344385                            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                          192.168.1.27                         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                           10.5.12.23                          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                          192.168.1.1                          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                              748                              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                             388934                            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                          192.168.1.56                         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                           10.5.12.65                          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                           192.168.1.1                         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                               5                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                              6534                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Claise Informational [Page 29] RFC 3954 Cisco Systems NetFlow Services Export V9 October 2004

 Note that padding was not necessary in this example.

11.4. Options Template FlowSet Example

 Per line card (the Exporter is composed of two line cards), we want
 to report the following Field Types:
 - Total number of Export Packets
 - Total number of exported Flows
 The format of the Options Template FlowSet is as follows:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |       FlowSet ID = 1          |          Length = 24          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |       Template ID 257         |    Option Scope Length = 4    |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |       Option Length = 8       |  Scope 1 Field Type = 3       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   Scope 1 Field Length = 2    |   TOTAL_EXP_PKTS_SENT = 41    |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |       Field Length = 2        |     TOTAL_FLOWS_EXP = 42      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |       Field Length = 2        |           Padding             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

11.5. Data FlowSet with Options Data Records Example

 In this example, we report the following two records:
 Line Card ID | Export Packet| Export Flow
 ------------------------------------------
 Line Card 1  | 345          | 10201
 Line Card 2  | 690          | 20402

Claise Informational [Page 30] RFC 3954 Cisco Systems NetFlow Services Export V9 October 2004

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |    FlowSet ID = 257           |         Length = 16           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |             1                 |             345               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |           10201               |              2                |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |            690                |            20402              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

12. References

12.1. Normative References

 [RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

12.2. Informative References

 [RFC768]    Postel, J., "User Datagram Protocol", STD 6, RFC 768,
             August 1980.
 [RFC793]    Postel, J., "Transmission Control Protocol", STD 7, RFC
             793, September 1981.
 [RFC2960]   Stewart, R., Xie, Q., Morneault, K., Sharp, C.,
             Schwarzbauer, H., Taylor, T., Rytina, I., Kalla, M.,
             Zhang, L., and V. Paxson, "Stream Control Transmission
             Protocol", RFC 2960, October 2000.
 [RFC3917]   Quittek, J., Zseby, T., Claise, B., and S. Zander,
             "Requirements for IP Flow Information Export (IPFIX)",
             RFC 3917, October 2004.

13. Authors

 This document was jointly written by Vamsidhar Valluri, Martin
 Djernaes, Ganesh Sadasivan, and Benoit Claise.

14. Acknowledgments

 I would like to thank Pritam Shah, Paul Kohler, Dmitri Bouianovski,
 and Stewart Bryant for their valuable technical feedback.

Claise Informational [Page 31] RFC 3954 Cisco Systems NetFlow Services Export V9 October 2004

15. Authors' Addresses

 Benoit Claise (Editor)
 Cisco Systems
 De Kleetlaan 6a b1
 1831 Diegem
 Belgium
 Phone:  +32 2 704 5622
 EMail:  bclaise@cisco.com
 Ganesh Sadasivan
 Cisco Systems, Inc.
 3750 Cisco Way
 San Jose, CA 95134
 USA
 Phone:  +1 408 527-0251
 EMail:  gsadasiv@cisco.com
 Vamsi Valluri
 Cisco Systems, Inc.
 510 McCarthy Blvd.
 San Jose, CA 95035
 USA
 Phone:  +1 408 525-1835
 EMail:  vvalluri@cisco.com
 Martin Djernaes
 Cisco Systems, Inc.
 510 McCarthy Blvd.
 San Jose, CA 95035
 USA
 Phone:  +1 408 853-1676
 EMail:  djernaes@cisco.com

Claise Informational [Page 32] RFC 3954 Cisco Systems NetFlow Services Export V9 October 2004

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Claise Informational [Page 33]

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