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Network Working Group B. Claise, Ed. Request for Comments: 5101 Cisco Systems, Inc. Category: Standards Track January 2008

 Specification of the IP Flow Information Export (IPFIX) Protocol
          for the Exchange of IP Traffic Flow Information

Status of This Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Abstract

 This document specifies the IP Flow Information Export (IPFIX)
 protocol that serves for transmitting IP Traffic Flow information
 over the network.  In order to transmit IP Traffic Flow information
 from an Exporting Process to an information Collecting Process, a
 common representation of flow data and a standard means of
 communicating them is required.  This document describes how the
 IPFIX Data and Template Records are carried over a number of
 transport protocols from an IPFIX Exporting Process to an IPFIX
 Collecting Process.

Table of Contents

 1. Introduction ....................................................3
    1.1. IPFIX Documents Overview ...................................4
 2. Terminology .....................................................4
    2.1. Terminology Summary Table ..................................9
 3. IPFIX Message Format ...........................................10
    3.1. Message Header Format .....................................11
    3.2. Field Specifier Format ....................................13
    3.3. Set and Set Header Format .................................14
         3.3.1. Set Format .........................................14
         3.3.2. Set Header Format ..................................15
    3.4. Record Format .............................................16
         3.4.1. Template Record Format .............................16
         3.4.2. Options Template Record Format .....................18
                3.4.2.1. Scope .....................................19
                3.4.2.2. Options Template Record Format ............20
         3.4.3. Data Record Format .................................22
 4. Specific Reporting Requirements ................................23
    4.1. The Metering Process Statistics Option Template ...........23

Claise, et al. Standards Track [Page 1] RFC 5101 IPFIX Protocol Specification January 2008

    4.2. The Metering Process Reliability Statistics Option
         Template ..................................................24
    4.3. The Exporting Process Reliability Statistics
         Option Template ...........................................25
    4.4. The Flow Keys Option Template .............................26
 5. IPFIX Message Header "Export Time" and Flow Record Time ........27
 6. Linkage with the Information Model .............................28
    6.1. Encoding of IPFIX Data Types ..............................28
         6.1.1. Integral Data Types ................................28
         6.1.2. Address Types ......................................28
         6.1.3. float32 ............................................28
         6.1.4. float64 ............................................28
         6.1.5. boolean ............................................28
         6.1.6. string and octetarray ..............................28
         6.1.7. dateTimeSeconds ....................................29
         6.1.8. dateTimeMilliseconds ...............................29
         6.1.9. dateTimeMicroseconds ...............................29
         6.1.10.dateTimeNanoseconds.................................29
    6.2. Reduced Size Encoding of Integer and Float Types ..........29
 7. Variable-Length Information Element ............................30
 8. Template Management ............................................31
 9. The Collecting Process's Side ..................................34
 10. Transport Protocol ............................................36
    10.1. Transport Compliance and Transport Usage .................36
    10.2. SCTP .....................................................37
         10.2.1. Congestion Avoidance ..............................37
         10.2.2. Reliability .......................................37
         10.2.3. MTU ...............................................37
         10.2.4. Exporting Process .................................38
                10.2.4.1. Association Establishment ................38
                10.2.4.2. Association Shutdown .....................38
                10.2.4.3. Stream ...................................38
                10.2.4.4. Template Management ......................39
         10.2.5. Collecting Process ................................39
         10.2.6. Failover ..........................................39
    10.3. UDP ......................................................39
         10.3.1. Congestion Avoidance ..............................39
         10.3.2. Reliability .......................................40
         10.3.3. MTU ...............................................40
         10.3.4. Port Numbers ......................................40
         10.3.5. Exporting Process .................................40
         10.3.6. Template Management ...............................40
         10.3.7. Collecting Process ................................41
         10.3.8. Failover ..........................................42
    10.4. TCP ......................................................42
         10.4.1. Connection Management .............................42
                10.4.1.1. Connection Establishment .................42
                10.4.1.2. Graceful Connection Release ..............43

Claise, et al. Standards Track [Page 2] RFC 5101 IPFIX Protocol Specification January 2008

                10.4.1.3. Restarting Interrupted Connections .......43
                10.4.1.4. Failover .................................43
         10.4.2. Data Transmission .................................43
                10.4.2.1. IPFIX Message Encoding ...................43
                10.4.2.2. Template Management ......................44
                10.4.2.3. Congestion Handling and Reliability ......44
         10.4.3. Collecting Process ................................45
 11. Security Considerations .......................................46
    11.1. Applicability of TLS and DTLS ............................47
    11.2. Usage ....................................................48
    11.3. Authentication ...........................................48
    11.4. Protection against DoS Attacks ...........................48
    11.5. When DTLS or TLS Is Not an Option ........................50
    11.6. Logging an IPFIX Attack ..................................50
    11.7. Securing the Collector ...................................51
 12. IANA Considerations ...........................................51
 Appendix A. IPFIX Encoding Examples ...............................52
    A.1. Message Header Example.....................................52
    A.2. Template Set Examples......................................53
         A.2.1. Template Set Using IETF-Specified Information
                Elements ...........................................53
         A.2.2. Template Set Using Enterprise-Specific Information
                Elements ...........................................53
    A.3. Data Set Example ..........................................55
    A.4. Options Template Set Examples .............................56
         A.4.1. Options Template Set Using IETF-Specified
                Information Elements ...............................56
         A.4.2. Options Template Set Using Enterprise-Specific
                Information Elements ...............................56
         A.4.3. Options Template Set Using an Enterprise-Specific
                Scope ..............................................57
         A.4.4. Data Set Using an Enterprise-Specific Scope ........58
    A.5. Variable-Length Information Element Examples ..............59
         A.5.1. Example of Variable-Length Information Element
                with Length Inferior to 255 Octets .................59
         A.5.2. Example of Variable-Length Information Element
                with Length 255 to 65535 Octets ....................59
 References ........................................................59
    Normative References ...........................................59
    Informative References .........................................60
 Acknowledgments ...................................................61

1. Introduction

 A data network with IP traffic primarily consists of IP flows passing
 through the network elements.  It is often interesting, useful, or
 even required to have access to information about these flows that
 pass through the network elements for administrative or other

Claise, et al. Standards Track [Page 3] RFC 5101 IPFIX Protocol Specification January 2008

 purposes.  The IPFIX Collecting Process should be able to receive the
 flow information passing through multiple network elements within the
 data network.  This requires uniformity in the method of representing
 the flow information and the means of communicating the flows from
 the network elements to the collection point.  This document
 specifies the protocol to achieve these aforementioned requirements.
 This document specifies in detail the representation of different
 flows, the additional data required for flow interpretation, packet
 format, transport mechanisms used, security concerns, etc.

1.1. IPFIX Documents Overview

 The IPFIX protocol provides network administrators with access to IP
 flow information.  The architecture for the export of measured IP
 flow information out of an IPFIX Exporting Process to a Collecting
 Process is defined in [IPFIX-ARCH], per the requirements defined in
 [RFC3917].  This document specifies how IPFIX data records and
 templates are carried via a number of transport protocols from IPFIX
 Exporting Processes to IPFIX Collecting Processes.  IPFIX has a
 formal description of IPFIX Information Elements, their name, type
 and additional semantic information, as specified in [RFC5102].
 Finally, [IPFIX-AS] describes what type of applications can use the
 IPFIX protocol and how they can use the information provided.  It
 furthermore shows how the IPFIX framework relates to other
 architectures and frameworks.

2. Terminology

 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 RFC 2119 [RFC2119].
 The definitions of the basic terms like IP Traffic Flow, Exporting
 Process, Collecting Process, Observation Points, etc.  are
 semantically identical to those found in the IPFIX requirements
 document [RFC3917].  Some of the terms have been expanded for more
 clarity when defining the protocol.  Additional terms required for
 the protocol have also been defined.  Definitions in this document
 and in [IPFIX-ARCH] are equivalent, except that definitions that are
 only relevant to the IPFIX protocol only appear here.
 The terminology summary table in Section 2.1 gives a quick overview
 of the relationships between some of the different terms defined.

Claise, et al. Standards Track [Page 4] RFC 5101 IPFIX Protocol Specification January 2008

 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:
    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 [RFC3550]).
       2. one or more characteristics of the packet itself (e.g.,
          number of MPLS labels, etc...).

Claise, et al. Standards Track [Page 5] RFC 5101 IPFIX Protocol Specification January 2008

       3. one or more of fields derived from packet treatment (e.g.,
          next hop IP address, the output interface, etc...).
    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.  belong to the packet header (e.g., destination IP address),
    2.  are a property of the packet itself (e.g., packet length),
    3.  are derived from packet treatment (e.g., Autonomous System
        (AS) number),
    and that are used to define a Flow are termed Flow Keys.
 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).
 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.

Claise, et al. Standards Track [Page 6] RFC 5101 IPFIX Protocol Specification January 2008

 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.
 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.
 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.

Claise, et al. Standards Track [Page 7] RFC 5101 IPFIX Protocol Specification January 2008

 Message Header
    The Message Header is the first part of an IPFIX Message, which
    provides basic information about the message, such as the IPFIX
    version, length of the message, message sequence number, etc.
 Template Record
    A Template Record defines the structure and interpretation of
    fields in a Data Record.
 Data Record
    A Data Record is a record that contains values of the parameters
    corresponding to a Template Record.
 Options Template Record
    An Options Template Record is a Template Record that defines the
    structure and interpretation of fields in a Data Record, including
    defining how to scope the applicability of the Data Record.
 Set
    Set is a generic term for a collection of records that have a
    similar structure.  In an IPFIX Message, one or more Sets follow
    the Message Header.
    There are three different types of Sets: Template Set, Options
    Template Set, and Data Set.
 Template Set
    A Template Set is a collection of one or more Template Records
    that have been grouped together in an IPFIX Message.
 Options Template Set
    An Options Template Set is a collection of one or more Options
    Template Records that have been grouped together in an IPFIX
    Message.
 Data Set
    A Data Set is one or more Data Records, of the same type, that are
    grouped together in an IPFIX Message.  Each Data Record is
    previously defined by a Template Record or an Options Template
    Record.

Claise, et al. Standards Track [Page 8] RFC 5101 IPFIX Protocol Specification January 2008

 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 [RFC5102] 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.
 Transport Session
    In Stream Control Transmission Protocol (SCTP), the transport
    session is known as the SCTP association, which is uniquely
    identified by the SCTP endpoints [RFC4960]; in TCP, the transport
    session is known as the TCP connection, which is uniquely
    identified by the combination of IP addresses and TCP ports used.
    In UDP, the transport session is known as the UDP session, which
    is uniquely identified by the combination of IP addresses and UDP
    ports used.

2.1. Terminology Summary Table

 +------------------+---------------------------------------------+
 |                  |                 contents                    |
 |                  +--------------------+------------------------+
 |       Set        |      Template      |         record         |
 +------------------+--------------------+------------------------+
 |     Data Set     |          /         |     Data Record(s)     |
 +------------------+--------------------+------------------------+
 |   Template Set   | Template Record(s) |           /            |
 +------------------+--------------------+------------------------+
 | Options Template | Options Template   |           /            |
 |       Set        | Record(s)          |                        |
 +------------------+--------------------+------------------------+
 Figure A: Terminology Summary Table
 A Data Set is composed of Data Record(s).  No Template Record is
 included.  A Template Record or an Options Template Record defines
 the Data Record.
 A Template Set contains only Template Record(s).
 An Options Template Set contains only Options Template Record(s).

Claise, et al. Standards Track [Page 9] RFC 5101 IPFIX Protocol Specification January 2008

3. IPFIX Message Format

 An IPFIX Message consists of a Message Header, followed by one or
 more Sets.  The Sets can be any of the possible three types: Data
 Set, Template Set, or Options Template Set.
 The format of the IPFIX Message is shown in Figure B.
 +----------------------------------------------------+
 | Message Header                                     |
 +----------------------------------------------------+
 | Set                                                |
 +----------------------------------------------------+
 | Set                                                |
 +----------------------------------------------------+
   ...
 +----------------------------------------------------+
 | Set                                                |
 +----------------------------------------------------+
 Figure B: IPFIX Message Format
 The Exporter MUST code all binary integers of the Message Header and
 the different Sets in network-byte order (also known as the
 big-endian byte ordering).
 Following are some examples of IPFIX Messages:
 1. An IPFIX Message consisting of interleaved Template, Data, and
    Options Template Sets -- A newly created Template is exported as
    soon as possible.  So, if there is already an IPFIX Message with a
    Data Set that is being prepared for export, the Template and
    Option Template Sets are interleaved with this information,
    subject to availability of space.
 +--------+--------------------------------------------------------+
 |        | +----------+ +---------+     +-----------+ +---------+ |
 |Message | | Template | | Data    |     | Options   | | Data    | |
 | Header | | Set      | | Set     | ... | Template  | | Set     | |
 |        | |          | |         |     | Set       | |         | |
 |        | +----------+ +---------+     +-----------+ +---------+ |
 +--------+--------------------------------------------------------+
 Figure C: IPFIX Message, Example 1

Claise, et al. Standards Track [Page 10] RFC 5101 IPFIX Protocol Specification January 2008

 2. An IPFIX Message consisting entirely of Data Sets -- After the
    appropriate Template Records have been defined and transmitted to
    the Collecting Process, the majority of IPFIX Messages consist
    solely of Data Sets.
 +--------+----------------------------------------------+
 |        | +---------+     +---------+      +---------+ |
 |Message | | Data    |     | Data    |      | Data    | |
 | Header | | Set     | ... | Set     | ...  | Set     | |
 |        | +---------+     +---------+      +---------+ |
 +--------+----------------------------------------------+
 Figure D: IPFIX Message, Example 2
 3. An IPFIX Message consisting entirely of Template and Options
    Template Sets.
 +--------+-------------------------------------------------+
 |        | +----------+     +----------+      +----------+ |
 |Message | | Template |     | Template |      | Options  | |
 | Header | | Set      | ... | Set      | ...  | Template | |
 |        | |          |     |          |      | Set      | |
 |        | +----------+     +----------+      +----------+ |
 +--------+-------------------------------------------------+
 Figure E: IPFIX Message, Example 3

3.1. Message Header Format

 The format of the IPFIX Message Header is shown in Figure F.
  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          |            Length             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                           Export Time                         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                       Sequence Number                         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                    Observation Domain ID                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Figure F: IPFIX Message Header Format

Claise, et al. Standards Track [Page 11] RFC 5101 IPFIX Protocol Specification January 2008

 Message Header Field Descriptions:
 Version
    Version of Flow Record format exported in this message.  The value
    of this field is 0x000a for the current version, incrementing by
    one the version used in the NetFlow services export version 9
    [RFC3954].
 Length
    Total length of the IPFIX Message, measured in octets, including
    Message Header and Set(s).
 Export Time
    Time, in seconds, since 0000 UTC Jan 1, 1970, at which the IPFIX
    Message Header leaves the Exporter.
 Sequence Number
    Incremental sequence counter modulo 2^32 of all IPFIX Data Records
    sent on this PR-SCTP stream from the current Observation Domain by
    the Exporting Process.  Check the specific meaning of this field
    in the subsections of Section 10 when UDP or TCP is selected as
    the transport protocol.  This value SHOULD be used by the
    Collecting Process to identify whether any IPFIX Data Records have
    been missed.  Template and Options Template Records do not
    increase the Sequence Number.
 Observation Domain ID
    A 32-bit identifier of the Observation Domain that is locally
    unique to the Exporting Process.  The Exporting Process uses the
    Observation Domain ID to uniquely identify to the Collecting
    Process the Observation Domain that metered the Flows.  It is
    RECOMMENDED that this identifier also be unique per IPFIX Device.
    Collecting Processes SHOULD use the Transport Session and the
    Observation Domain ID field to separate different export streams
    originating from the same Exporting Process.  The Observation
    Domain ID SHOULD be 0 when no specific Observation Domain ID is
    relevant for the entire IPFIX Message, for example, when exporting
    the Exporting Process Statistics, or in case of a hierarchy of
    Collectors when aggregated Data Records are exported.

Claise, et al. Standards Track [Page 12] RFC 5101 IPFIX Protocol Specification January 2008

3.2. Field Specifier Format

 Vendors need the ability to define proprietary Information Elements,
 because, for example, they are delivering a pre-standards product, or
 the Information Element is, in some way, commercially sensitive.
 This section describes the Field Specifier format for both
 IETF-specified Information Elements [RFC5102] and enterprise-specific
 Information Elements.
 The Information Elements are identified by the Information Element
 identifier.  When the Enterprise bit is set to 0, the corresponding
 Information Element identifier will report an IETF-specified
 Information Element, and the Enterprise Number MUST NOT be present.
 When the Enterprise bit is set to 1, the corresponding Information
 Element identifier will report an enterprise-specific Information
 Element; the Enterprise Number MUST be present.  An example of this
 is shown in Section A.4.2.
 The Field Specifier format is shown in Figure G.
 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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |E|  Information Element ident. |        Field Length           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                      Enterprise Number                        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Figure G: Field Specifier Format
 Where:
 E
    Enterprise bit.  This is the first bit of the Field Specifier.  If
    this bit is zero, the Information Element Identifier identifies an
    IETF-specified Information Element, and the four-octet Enterprise
    Number field MUST NOT be present.  If this bit is one, the
    Information Element identifier identifies an enterprise-specific
    Information Element, and the Enterprise Number filed MUST be
    present.
 Information Element identifier
    A numeric value that represents the type of Information Element.
    Refer to [RFC5102].

Claise, et al. Standards Track [Page 13] RFC 5101 IPFIX Protocol Specification January 2008

 Field Length
    The length of the corresponding encoded Information Element, in
    octets.  Refer to [RFC5102].  The field length may be smaller than
    the definition in [RFC5102] if the reduced size encoding is used
    (see Section 6.2).  The value 65535 is reserved for variable-
    length Information Elements (see Section 7).
 Enterprise Number
    IANA enterprise number [PEN] of the authority defining the
    Information Element identifier in this Template Record.

3.3. Set and Set Header Format

 A Set is a generic term for a collection of records that have a
 similar structure.  There are three different types of Sets: Template
 Sets, Options Template Sets, and Data Sets.  Each of these Sets
 consists of a Set Header and one or more records.  The Set Format and
 the Set Header Format are defined in the following sections.

3.3.1. Set Format

 A Set has the format shown in Figure H.  The record types can be
 either Template Records, Options Template Records, or Data Records.
 The record types MUST NOT be mixed within a Set.
 +--------------------------------------------------+
 | Set Header                                       |
 +--------------------------------------------------+
 | record                                           |
 +--------------------------------------------------+
 | record                                           |
 +--------------------------------------------------+
  ...
 +--------------------------------------------------+
 | record                                           |
 +--------------------------------------------------+
 | Padding (opt.)                                   |
 +--------------------------------------------------+
 Figure H: Set Format
 The Set Field Definitions are as follows:
 Set Header
    The Set Header Format is defined in Section 3.3.2.

Claise, et al. Standards Track [Page 14] RFC 5101 IPFIX Protocol Specification January 2008

 Record
    One of the record Formats: Template Record, Options Template
    Record, or Data Record Format.
 Padding
    The Exporting Process MAY insert some padding octets, so that the
    subsequent Set starts at an aligned boundary.  For security
    reasons, the padding octet(s) MUST be composed of zero (0) valued
    octets.  The padding length MUST be shorter than any allowable
    record in this Set.  If padding of the IPFIX Message is desired in
    combination with very short records, then the padding Information
    Element 'paddingOctets' [RFC5102] can be used for padding records
    such that their length is increased to a multiple of 4 or 8
    octets.  Because Template Sets are always 4-octet aligned by
    definition, padding is only needed in case of other alignments
    e.g., on 8-octet boundaries.

3.3.2. Set Header Format

 Every Set contains a common header.  This header is defined in Figure
 I.
  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |          Set ID               |          Length               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Figure I: Set Header Format
 The Set Header Field Definitions are as follows:
 Set ID
    Set ID value identifies the Set.  A value of 2 is reserved for the
    Template Set.  A value of 3 is reserved for the Option Template
    Set.  All other values from 4 to 255 are reserved for future use.
    Values above 255 are used for Data Sets.  The Set ID values of 0
    and 1 are not used for historical reasons [RFC3954].
 Length
    Total length of the Set, in octets, including the Set Header, all
    records, and the optional padding.  Because an individual Set MAY
    contain multiple records, the Length value MUST be used to
    determine the position of the next Set.

Claise, et al. Standards Track [Page 15] RFC 5101 IPFIX Protocol Specification January 2008

3.4. Record Format

 IPFIX defines three record formats, defined in the next sections: the
 Template Record Format, the Options Template Record Format, and the
 Data Record Format.

3.4.1. Template Record Format

 One of the essential elements in the IPFIX record format is the
 Template Record.  Templates greatly enhance the flexibility of the
 record format because they allow the Collecting Process to process
 IPFIX Messages without necessarily knowing the interpretation of all
 Data Records.  A Template Record contains any combination of
 IANA-assigned and/or enterprise-specific Information Elements
 identifiers.
 The format of the Template Record is shown in Figure J.  It consists
 of a Template Record Header and one or more Field Specifiers.  The
 definition of the Field Specifiers is given in Figure G above.
 +--------------------------------------------------+
 | Template Record Header                           |
 +--------------------------------------------------+
 | Field Specifier                                  |
 +--------------------------------------------------+
 | Field Specifier                                  |
 +--------------------------------------------------+
  ...
 +--------------------------------------------------+
 | Field Specifier                                  |
 +--------------------------------------------------+
 Figure J: Template Record Format
 The format of the Template Record Header is shown in Figure K.
  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |      Template ID (> 255)      |         Field Count           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Figure K: Template Record Header Format

Claise, et al. Standards Track [Page 16] RFC 5101 IPFIX Protocol Specification January 2008

 The Template Record Header Field Definitions are as follows:
 Template ID
    Each of the newly generated Template Records is given a unique
    Template ID.  This uniqueness is local to the Transport Session
    and Observation Domain that generated the Template ID.  Template
    IDs 0-255 are reserved for Template Sets, Options Template Sets,
    and other reserved Sets yet to be created.  Template IDs of Data
    Sets are numbered from 256 to 65535.  There are no constraints
    regarding the order of the Template ID allocation.
 Field Count
    Number of fields in this Template Record.
 The example in Figure L shows a Template Set with mixed standard and
 enterprise-specific Information Elements.  It consists of a Set
 Header, a Template Header, and several Field Specifiers.

Claise, et al. Standards Track [Page 17] RFC 5101 IPFIX Protocol Specification January 2008

  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |          Set ID = 2           |          Length               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |      Template ID = 256        |         Field Count = N       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |1| Information Element id. 1.1 |        Field Length 1.1       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                    Enterprise Number  1.1                     |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |0| Information Element id. 1.2 |        Field Length 1.2       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |             ...               |              ...              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |1| Information Element id. 1.N |        Field Length 1.N       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                    Enterprise Number  1.N                     |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |      Template ID = 257        |         Field Count = M       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |0| Information Element id. 2.1 |        Field Length 2.1       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |1| Information Element id. 2.2 |        Field Length 2.2       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                    Enterprise Number  2.2                     |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |             ...               |              ...              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |1| Information Element id. 2.M |        Field Length 2.M       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                    Enterprise Number  2.M                     |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                          Padding (opt)                        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Figure L: Template Set Example
 Information Element Identifiers 1.2 and 2.1 are defined by the IETF
 (Enterprise bit = 0) and, therefore, do not need an Enterprise Number
 to identify them.

3.4.2. Options Template Record Format

 Thanks to the notion of scope, The Options Template Record gives the
 Exporter the ability to provide additional information to the
 Collector that would not be possible with Flow Records alone.

Claise, et al. Standards Track [Page 18] RFC 5101 IPFIX Protocol Specification January 2008

 One Options Template Record example is the "Flow Keys", which reports
 the Flow Keys for a Template, which is defined as the scope.  Another
 example is the "Template configuration", which reports the
 configuration sampling parameter(s) for the Template, which is
 defined as the scope.

3.4.2.1. Scope

 The scope, which is only available in the Options Template Set, gives
 the context of the reported Information Elements in the Data Records.
 Note that the IPFIX Message Header already contains the Observation
 Domain ID (the identifier of the Observation Domain).  If not zero,
 this Observation Domain ID can be considered as an implicit scope for
 the Data Records in the IPFIX Message.  The Observation Domain ID
 MUST be zero when the IPFIX Message contains Data Records with
 different Observation Domain ID values defined as scopes.
 Multiple Scope Fields MAY be present in the Options Template Record,
 in which case, the composite scope is the combination of the scopes.
 For example, if the two scopes are defined as "metering process" and
 "template", the combined scope is this Template for this Metering
 Process.  The order of the Scope Fields, as defined in the Options
 Template Record, is irrelevant in this case.  However, if the order
 of the Scope Fields in the Options Template Record is relevant, the
 order of the Scope Fields MUST be used.  For example, if the first
 scope defines the filtering function, while the second scope defines
 the sampling function, the order of the scope is important.  Applying
 the sampling function first, followed by the filtering function,
 would lead to potentially different Data Records than applying the
 filtering function first, followed by the sampling function.  In this
 case, the Collector deduces the function order by looking at the
 order of the scope in the Options Template Record.
 The scope is an Information Element specified in the IPFIX
 Information Model [RFC5102].  An IPFIX-compliant implementation of
 the Collecting Process SHOULD support this minimum set of Information
 Elements as scope: LineCardId, TemplateId, exporterIPv4Address,
 exporterIPv6Address, and ingressInterface.  Note that other
 Information Elements, such as meteringProcessId, exportingProcessId,
 observationDomainId, etc. are also valid scopes.  The IPFIX protocol
 doesn't prevent the use of any Information Elements for scope.
 However, some Information Element types don't make sense if specified
 as scope; for example, the counter Information Elements.
 Finally, note that the Scope Field Count MUST NOT be zero.

Claise, et al. Standards Track [Page 19] RFC 5101 IPFIX Protocol Specification January 2008

3.4.2.2. Options Template Record Format

 An Options Template Record contains any combination of IANA-assigned
 and/or enterprise-specific Information Elements identifiers.
 The format of the Options Template Record is shown in Figure M.  It
 consists of an Options Template Record Header and one or more Field
 Specifiers.  The definition of the Field Specifiers is given in
 Figure G above.
 +--------------------------------------------------+
 | Options Template Record Header                   |
 +--------------------------------------------------+
 | Field Specifier                                  |
 +--------------------------------------------------+
 | Field Specifier                                  |
 +--------------------------------------------------+
  ...
 +--------------------------------------------------+
 | Field Specifier                                  |
 +--------------------------------------------------+
 Figure M: Options Template Record Format
 The format of the Options Template Record Header is shown in Figure
 N.
  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Template ID (> 255)   |         Field Count           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |      Scope Field Count        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Figure N: Options Template Record Header Format
 The Options Template Record Header Field Definitions are as follows:
 Template ID
 Template ID of this Options Template Record.  This value is greater
 than 255.

Claise, et al. Standards Track [Page 20] RFC 5101 IPFIX Protocol Specification January 2008

 Field Count
 Number of all fields in this Options Template Record, including the
 Scope Fields.
 Scope Field Count
 Number of scope fields in this Options Template Record.  The Scope
 Fields are normal Fields except that they are interpreted as scope at
 the Collector.  The Scope Field Count MUST NOT be zero.
 The example in Figure O shows an Option Template Set with mixed IETF
 and enterprise-specific Information Elements.  It consists of a Set
 Header, an Option Template Header, and several Field Specifiers.
  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |          Set ID = 3           |          Length               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Template ID = 258     |         Field Count = N + M   |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Scope Field Count = N     |0|  Scope 1 Infor. Element Id. |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Scope 1 Field Length      |0|  Scope 2 Infor. Element Id. |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Scope 2 Field Length      |             ...               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |            ...                |1|  Scope N Infor. Element Id. |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Scope N Field Length      |   Scope N Enterprise Number ...
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ...  Scope N Enterprise Number   |1| Option 1 Infor. Element Id. |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |    Option 1 Field Length      |  Option 1 Enterprise Number ...
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ... Option 1 Enterprise Number   |              ...              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |             ...               |0| Option M Infor. Element Id. |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Option M Field Length     |      Padding (optional)       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Figure O: Option Template Set Example

Claise, et al. Standards Track [Page 21] RFC 5101 IPFIX Protocol Specification January 2008

3.4.3. Data Record Format

 The Data Records are sent in Data Sets.  The format of the Data
 Record is shown in Figure P.  It consists only of one or more Field
 Values.  The Template ID to which the Field Values belong is encoded
 in the Set Header field "Set ID", i.e., "Set ID" = "Template ID".
 +--------------------------------------------------+
 | Field Value                                      |
 +--------------------------------------------------+
 | Field Value                                      |
 +--------------------------------------------------+
  ...
 +--------------------------------------------------+
 | Field Value                                      |
 +--------------------------------------------------+
 Figure P: Data Record Format
 Note that Field Values do not necessarily have a length of 16 bits.
 Field Values are encoded according to their data type specified in
 [RFC5102].
 Interpretation of the Data Record format can be done only if the
 Template Record corresponding to the Template ID is available at the
 Collecting Process.
 The example in Figure Q shows a Data Set. It consists of a Set Header
 and several Field Values.

Claise, et al. Standards Track [Page 22] RFC 5101 IPFIX Protocol Specification January 2008

  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   Set 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    |   Record 3 - Field Value 2    |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   Record 3 - Field Value 3    |             ...               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |              ...              |      Padding (optional)       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Figure Q: Data Set, Containing Data Records

4. Specific Reporting Requirements

 Some specific Options Templates and Options Template Records are
 necessary to provide extra information about the Flow Records and
 about the Metering Process.
 The Option Template and Options Template Records defined in these
 subsections, which impose some constraints on the Metering Process
 and Exporting Process implementations, MAY be implemented.  If
 implemented, the specific Option Templates SHOULD be implemented as
 specified in these subsections.
 The minimum set of Information Elements is always specified in these
 Specific IPFIX Options Templates.  Nevertheless, extra Information
 Elements may be used in these specific Options Templates.

4.1. The Metering Process Statistics Option Template

 The Metering Process Statistics Option Template specifies the
 structure of a Data Record for reporting Metering Process statistics.
 It SHOULD contain the following Information Elements that are defined
 in [RFC5102]:

Claise, et al. Standards Track [Page 23] RFC 5101 IPFIX Protocol Specification January 2008

 observationDomainId
                         An identifier of an Observation Domain that
                         is locally unique to the Exporting Process.
                         This Information Element MUST be defined as a
                         Scope Field.
 exportedMessageTotalCount
                         The total number of IPFIX Messages that the
                         Exporting Process successfully sent to the
                         Collecting Process since the Exporting
                         Process re-initialization.
 exportedFlowTotalCount
                         The total number of Flow Records that the
                         Exporting Process successfully sent to the
                         Collecting Process since the Exporting
                         Process re-initialization.
 exportedOctetTotalCount
                         The total number of octets that the Exporting
                         Process successfully sent to the Collecting
                         Process since the Exporting Process re-
                         initialization.
 The Exporting Process SHOULD export the Data Record specified by the
 Metering Process Statistics Option Template on a regular basis or
 based on some export policy.  This periodicity or export policy
 SHOULD be configurable.
 Note that if several Metering Processes are available on the Exporter
 Observation Domain, the Information Element meteringProcessId MUST be
 specified as an additional Scope Field.

4.2. The Metering Process Reliability Statistics Option Template

 The Metering Process Reliability Option Template specifies the
 structure of a Data Record for reporting lack of reliability in the
 Metering Process.  It SHOULD contain the following Information
 Elements that are defined in [RFC5102]:
 observationDomainId
                         An identifier of an Observation Domain that
                         is locally unique to the Exporting Process.
                         This Information Element MUST be defined as a
                         Scope Field.

Claise, et al. Standards Track [Page 24] RFC 5101 IPFIX Protocol Specification January 2008

 ignoredPacketTotalCount
                         The total number of IP packets that the
                         Metering Process did not process.
 ignoredOctetTotalCount
                         The total number of octets in observed IP
                         packets that the Metering Process did not
                         process.
 time first ignored
                         The timestamp of the first IP packet that was
                         ignored by the Metering Process.  For this
                         timestamp, any of the "flowStart" timestamp
                         Information Elements flowStartMilliseconds,
                         flowStartMicroseconds, flowStartNanoseconds,
                         and flowStartDeltaMicroseconds can be used.
 time last ignored
                         The timestamp of the last IP packet that was
                         ignored by the Metering Process.  For this
                         timestamp, any of the "flowEnd" timestamp
                         Information Elements flowEndMilliseconds,
                         flowEndMicroseconds, flowEndNanoseconds, and
                         flowEndDeltaMicroseconds can be used.
 The Exporting Process SHOULD export the Data Record specified by the
 Metering Process Reliability Statistics Option Template on a regular
 basis or based on some export policy.  This periodicity or export
 policy SHOULD be configurable.
 Note that if several Metering Processes are available on the Exporter
 Observation Domain, the Information Element meteringProcessId MUST be
 specified as an additional Scope Field.

4.3. The Exporting Process Reliability Statistics Option Template

 The Exporting Process Reliability Option Template specifies the
 structure of a Data Record for reporting lack of reliability in the
 Exporting process.  It SHOULD contain the following Information
 Elements that are defined in [RFC5102]:
 Exporting Process ID
                      The identifier of the Exporting Process for
                      which lack of reliability is reported.  There
                      are three Information Elements specified in
                      [RFC5102] that can be used for this purpose:
                      exporterIPv4Address, exporterIPv6Address, or

Claise, et al. Standards Track [Page 25] RFC 5101 IPFIX Protocol Specification January 2008

                      exportingProcessId.  This Information Element
                      MUST be defined as a Scope Field.
 notSentFlowTotalCount
                      The total number of Flows that were generated by
                      the Metering Process and dropped by the Metering
                      Process or by the Exporting Process instead of
                      being sent to the Collecting Process.
 notSentPacketTotalCount
                      The total number of packets in Flow Records that
                      were generated by the Metering Process and
                      dropped by the Metering Process or by the
                      Exporting Process instead of being sent to the
                      Collecting Process.
 notSentOctetTotalCount
                      The total number of octets in packets in Flow
                      Records that were generated by the Metering
                      Process and dropped by the Metering Process or
                      by the Exporting Process instead of being sent
                      to the Collecting Process.
 time first flow dropped
                      The timestamp of the first Flow was dropped by
                      the Metering Process.  For this timestamp, any
                      of the "flowStart" timestamp Information
                      Elements flowStartMilliseconds,
                      flowStartMicroseconds, flowStartNanoseconds, and
                      flowStartDeltaMicroseconds can be used.
 time last flow dropped
                      The timestamp of the last IP packet that was
                      ignored by the Metering Process.  For this
                      timestamp, any of the "flowEnd" timestamp
                      Information Elements flowEndMilliseconds,
                      flowEndMicroseconds, flowEndNanoseconds, and
                      flowEndDeltaMicroseconds can be used.
 The Exporting Process SHOULD export the Data Record specified by the
 Exporting Process Reliability Statistics Option Template on a regular
 basis or based on some export policy.  This periodicity or export
 policy SHOULD be configurable.

4.4. The Flow Keys Option Template

 The Flow Keys Option Template specifies the structure of a Data
 Record for reporting the Flow Keys of reported Flows.  A Flow Keys

Claise, et al. Standards Track [Page 26] RFC 5101 IPFIX Protocol Specification January 2008

 Data Record extends a particular Template Record that is referenced
 by its templateId identifier.  The Template Record is extended by
 specifying which of the Information Elements contained in the
 corresponding Data Records describe Flow properties that serve as
 Flow Keys of the reported Flow.
 The Flow Keys Option Template SHOULD contain the following
 Information Elements that are defined in [RFC5102]:
 templateId              An identifier of a Template.  This
                         Information Element MUST be defined as a
                         Scope Field.
 flowKeyIndicator        Bitmap with the positions of the Flow Keys in
                         the Data Records.

5. IPFIX Message Header "Export Time" and Flow Record Time

 The IPFIX Message Header "Export Time" field is the time in seconds
 since 0000 UTC Jan 1, 1970, at which the IPFIX Message Header leaves
 the Exporter.  The time-related Information Elements specified in
 [RFC5102] MAY use this "Export Time" as base time and specify an
 offset relative to it, instead of using a common base time, such as
 0000 UTC Jan 1, 1970.  All Information Elements that do not have
 their base time defined by their data type MUST have the base time
 clearly specified in their description.
 For example, Data Records requiring a microsecond precision can
 export the flow start and end times with the flowStartMicroseconds
 and flowEndMicroseconds Information Elements [RFC5102], containing
 the time since 0000 UTC Jan 1, 1970.  An alternate solution is to
 export the flowStartDeltaMicroseconds and flowEndDeltaMicroseconds
 Information Elements [RFC5102] in the Data Record, which respectively
 report the flow start and end time offsets compared to the IPFIX
 Message Header "Export Time".  The latter solution lowers the export
 bandwidth requirement while it increases the load on the Exporter, as
 the Exporting Process must calculate the flowStartDeltaMicroseconds
 and flowEndDeltaMicroseconds of every single Data Record before
 exporting the IPFIX Message.
 It must be noted that using time-related Information Elements with
 offset times, compared to the IPFIX Message Header "Export Time",
 imposes some time constraints on the Data Records contained in the
 IPFIX Message.  In the example of flowStartDeltaMicroseconds and
 flowEndDeltaMicroseconds Information Elements [RFC5102], the Data
 Record must be exported within a maximum of 71 minutes after its
 creation.  Otherwise, the 32-bit counter would not be sufficient to
 contain the flow start time offset.

Claise, et al. Standards Track [Page 27] RFC 5101 IPFIX Protocol Specification January 2008

6. Linkage with the Information Model

 The Information Elements [RFC5102] MUST be sent in canonical format
 in network-byte order (also known as the big-endian byte ordering).

6.1. Encoding of IPFIX Data Types

 The following sections will define the encoding of the data types
 specified in [RFC5102].

6.1.1. Integral Data Types

 Integral data types -- octet, signed8, unsigned16, signed16,
 unsigned32, signed32, signed64, and unsigned64 -- MUST be encoded
 using the default canonical format in network-byte order.  Signed
 Integral data types are represented in two's complement notation.

6.1.2. Address Types

 Address types -- macAddress, ipv4Address, and ipv6Address -- MUST be
 encoded the same way as the integral data types.  The macAddress is
 treated as a 6-octet integer, the ipv4Address as a 4-octet integer,
 and the ipv6Address as a 16-octet integer.

6.1.3. float32

 The float32 data type MUST be encoded as an IEEE single-precision
 32-bit floating point-type, as specified in [IEEE.754.1985].

6.1.4. float64

 The float64 data type MUST be encoded as an IEEE double-precision
 64-bit floating point-type, as specified in [IEEE.754.1985].

6.1.5. boolean

 The boolean data type is specified according to the TruthValue in
 [RFC2579]: it is an integer with the value 1 for true and a value 2
 for false.  Every other value is undefined.  The boolean data type
 MUST be encoded in a single octet.

6.1.6. string and octetarray

 The data type string represents a finite length string of valid
 characters of the Unicode character encoding set.  The string data
 type MUST be encoded in UTF-8 format.  The string is sent as an array
 of octets using an Information Element of fixed or variable length.

Claise, et al. Standards Track [Page 28] RFC 5101 IPFIX Protocol Specification January 2008

 The length of the Information Element specifies the length of the
 octetarray.

6.1.7. dateTimeSeconds

 The data type dateTimeseconds represents a time value in units of
 seconds normalized to the GMT timezone.  It MUST be encoded in a
 32-bit integer containing the number of seconds since 0000 UTC Jan 1,
 1970.  The 32-bit integer allows the time encoding up to 136 years.

6.1.8. dateTimeMilliseconds

 The data type dateTimeMilliseconds represents a time value in units
 of milliseconds normalized to the GMT timezone.  It MUST be encoded
 in a 64-bit integer containing the number of milliseconds since 0000
 UTC Jan 1, 1970.

6.1.9. dateTimeMicroseconds

 The data type dateTimeMicroseconds represents a time value in units
 of microseconds normalized to the GMT timezone.  It MUST be encoded
 in a 64-bit integer, according to the NTP format given in [RFC1305].

6.1.10. dateTimeNanoseconds

 The data type of dateTimeNanoseconds represents a time value in units
 of nanoseconds normalized to the GMT time zone.  It MUST be encoded
 in a 64-bit integer, according to the NTP format given in [RFC1305].

6.2. Reduced Size Encoding of Integer and Float Types

 Information Elements containing integer, string, float, and
 octetarray types in the information model MAY be encoded using fewer
 octets than those implied by their type in the information model
 definition [RFC5102], based on the assumption that the smaller size
 is sufficient to carry any value the Exporter may need to deliver.
 This reduces the network bandwidth requirement between the Exporter
 and the Collector.  Note that the Information Element definitions
 [RFC5102] will always define the maximum encoding size.
 For instance, the information model [RFC5102] defines byteCount as an
 unsigned64 type, which would require 64 bits.  However, if the
 Exporter will never locally encounter the need to send a value larger
 than 4294967295, it may chose to send the value instead as an
 unsigned32.  For example, a core router would require an unsigned64
 byteCount, while an unsigned32 might be sufficient for an access
 router.

Claise, et al. Standards Track [Page 29] RFC 5101 IPFIX Protocol Specification January 2008

 This behavior is indicated by the Exporter by specifying a type size
 with a smaller length than that associated with the assigned type of
 the Information Element.  In the example above, the Exporter would
 place a length of 4 versus 8 in the Template.
 If reduced sizing is used, it MUST only be applied to the following
 integer types: unsigned64, signed64, unsigned32, signed32,
 unsigned16, and signed16.  The signed versus unsigned property of the
 reported value MUST be preserved.  The reduction in size can be to
 any number of octets smaller than the original type if the data value
 still fits, i.e., so that only leading zeroes are dropped.  For
 example, an unsigned64 can be reduced in size to 7, 6, 5, 4, 3, 2, or
 1 octet(s).
 Reduced sizing can also be used to reduce float64 to float32.  The
 float32 not only has a reduced number range, but due to the smaller
 mantissa, is also less precise.
 The reduced size encoding MUST NOT be applied to dateTimeMicroseconds
 or to dateTimeNanoseconds because these represent an inherent
 structure that would be destroyed by using less than the original
 number of bytes.

7. Variable-Length Information Element

 The IPFIX Template mechanism is optimized for fixed-length
 Information Elements [RFC5102].  Where an Information Element has a
 variable length, the following mechanism MUST be used to carry the
 length information for both the IETF and proprietary Information
 Elements.
 In the Template Set, the Information Element Field Length is recorded
 as 65535.  This reserved length value notifies the Collecting Process
 that length of the Information Element will be carried in the
 Information Element content itself.
 In most cases, the length of the Information Element will be less
 than 255 octets.  The following length-encoding mechanism optimizes
 the overhead of carrying the Information Element length in this
 majority case.  The length is carried in the octet before the
 Information Element, as shown in Figure R.

Claise, et al. Standards Track [Page 30] RFC 5101 IPFIX Protocol Specification January 2008

  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Length (< 255)|          Information Element                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                      ... continuing as needed                 |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Figure R: Variable-Length Information Element (length < 255 octets)
 If the length of the Information Element is greater than or equal to
 255 octets, the length is encoded into 3 octets before the
 Information Element.  The first octet is 255, and the length is
 carried in the second and third octets, as shown in Figure S.
  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |      255      |      Length (0 to 65535)      |       IE      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                      ... continuing as needed                 |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Figure S: Variable-Length Information Element (length 0 to 65535
 octets)
 The octets carrying the length (either the first or the first three
 octets) MUST NOT be included in the length of the Information
 Element.

8. Template Management

 This section describes Template Management when using SCTP and
 PR-SCTP as the transport protocol.  Any necessary changes to Template
 Management specifically related to TCP or UDP transport protocols are
 specified in Section 10.
 The Exporting Process assigns and maintains the Template IDs per SCTP
 association for the Exporter's Observation Domains.  A newly created
 Template Record is assigned an unused Template ID by the Exporting
 Process.
 If a specific Information Element is required by a Template, but is
 not available in observed packets, the Exporting Process MAY choose
 to export Flow Records without this Information Element in a Data
 Record defined by a new Template.

Claise, et al. Standards Track [Page 31] RFC 5101 IPFIX Protocol Specification January 2008

 If an Information Element is required more than once in a Template,
 the different occurrences of this Information Element SHOULD follow
 the logical order of their treatments by the Metering Process.  For
 example, if a selected packet goes through two hash functions, and if
 the two hash values are sent within a single Template, the first
 occurrence of the hash value should belong to the first hash function
 in the Metering Process.  For example, when exporting the two source
 IP addresses of an IPv4 in IPv4 packets, the first sourceIPv4Address
 Information Element occurrence should be the IPv4 address of the
 outer header, while the second occurrence should be the inner header
 one.
 Template Sets and Options Template Sets may be sent on any SCTP
 stream.  Template Sets and Options Template Sets MUST be sent
 reliably, using SCTP-ordered delivery.  As such, the Collecting
 Process MUST store the Template Record information for the duration
 of the SCTP association so that it can interpret the corresponding
 Data Records that are received in subsequent Data Sets.
 The Exporting Process SHOULD transmit the Template Set and Options
 Template Set in advance of any Data Sets that use that (Options)
 Template ID, to help ensure that the Collector has the Template
 Record before receiving the first Data Record.  Data Records that
 correspond to a Template Record MAY appear in the same and/or
 subsequent IPFIX Message(s).
 Different Observation Domains from the same SCTP association may use
 the same Template ID value to refer to different Templates.
 The Templates that are not used anymore SHOULD be deleted.  Before
 reusing a Template ID, the Template MUST be deleted.  In order to
 delete an allocated Template, the Template is withdrawn through the
 use of a Template Withdrawal Message.
 The Template Withdrawal Message MUST NOT be sent until sufficient
 time has elapsed to allow the Collecting Process to receive and
 process the last Data Record using this Template information.  This
 time MUST be configurable.  A suitable default value is 5 seconds
 after the last Data Record has been sent.
 The Template ID from a withdrawn Template MUST NOT be reused until
 sufficient time has elapsed to allow for the Collecting Process to
 receive and process the Template Withdrawal Message.
 A Template Withdrawal Message is a Template Record for that Template
 ID with a Field Count of 0.  The format of the Template Withdrawal
 Message is shown in Figure T.

Claise, et al. Standards Track [Page 32] RFC 5101 IPFIX Protocol Specification January 2008

  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |       Set ID = (2 or 3)       |          Length = 16          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |          Template ID N        |        Field Count = 0        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |          Template ID ...      |        Field Count = 0        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |          Template ID M        |        Field Count = 0        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Figure T: Template Withdrawal Message Format
 The Set ID field MUST contain the value 2 for Template Set Withdrawal
 and the value 3 for Options Template Set Withdrawal.  Multiple
 Template IDs MAY be withdrawn with a single Template Withdrawal
 Message, in that case, padding MAY be used.
 The Template Withdrawal Message withdraws the Template IDs for the
 Observation Domain ID specified in the IPFIX Message Header.
 The Template Withdrawal Message may be sent on any SCTP stream.  The
 Template Withdrawal Message MUST be sent reliably, using SCTP-ordered
 delivery.
 The Template Withdrawal Message MUST NOT contain new Template or
 Options Template Records.
 If the measurement parameters change such that a new Template is
 required, the Template MUST be withdrawn (using a Template Withdraw
 Message and a new Template definition) or an unused Template ID MUST
 be used.  Examples of the measurement changes are: a new sampling
 rate, a new Flow expiration process, a new filtering definition, etc.
 When the SCTP association shuts down or the Exporting Process
 restarts, all Template assignments are lost and Template IDs MUST be
 reassigned.
 If the Metering Process restarts, the Exporting Process MUST either
 reuse the previously assigned Template ID for each Template, or it
 MUST withdraw the previously issued Template IDs by sending Template
 Withdraw Message(s) before reusing them.
 A Template Withdrawal Message to withdraw all Templates for the
 Observation Domain ID specified in the IPFIX Message Header MAY be
 used.  Its format is shown in Figure U.

Claise, et al. Standards Track [Page 33] RFC 5101 IPFIX Protocol Specification January 2008

  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |             Set ID = 2        |          Length = 8           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Template ID = 2       |        Field Count = 0        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Figure U: All Data Templates Withdrawal Message Format
 A Template Withdrawal Message to withdraw all Options Templates for
 the Observation Domain ID specified in the IPFIX Message Header MAY
 be used.  Its format is shown in Figure V.
  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |             Set ID = 3        |          Length = 8           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Template ID = 3       |        Field Count = 0        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Figure V: All Options Templates Withdrawal Message Format
 When the SCTP association restarts, the Exporting Process MUST resend
 all the Template Records.

9. The Collecting Process's Side

 This section describes the Collecting Process when using SCTP and
 PR-SCTP as the transport protocol.  Any necessary changes to the
 Collecting Process specifically related to TCP or UDP transport
 protocols are specified in Section 10.
 The Collecting Process SHOULD listen for a new association request
 from the Exporting Process.  The Exporting Process will request a
 number of streams to use for export.  An Exporting Process MAY
 request and support more than one stream per SCTP association.
 If the Collecting Process receives a malformed IPFIX Message, it MUST
 reset the SCTP association, discard the IPFIX Message, and SHOULD log
 the error.  Note that non-zero Set padding does not constitute a
 malformed IPFIX Message.
 Template Sets and Option Template Sets are only sent once.  The
 Collecting Process MUST store the Template Record information for the
 duration of the association so that it can interpret the
 corresponding Data Records that are received in subsequent Data Sets.

Claise, et al. Standards Track [Page 34] RFC 5101 IPFIX Protocol Specification January 2008

 Template IDs are unique per SCTP association and per Observation
 Domain.  If the Collecting Process receives a Template that has
 already been received but that has not previously been withdrawn
 (i.e., a Template Record from the same Exporter Observation Domain
 with the same Template ID received on the SCTP association), then the
 Collecting Process MUST shut down the association.
 When an SCTP association is closed, the Collecting Process MUST
 discard all Templates received over that association and stop
 decoding IPFIX Messages that use those Templates.
 The Collecting Process normally receives Template Records from the
 Exporting Process before receiving Data Records.  The Data Records
 are then decoded and stored by the Collector.  If the Template
 Records have not been received at the time Data Records are received,
 the Collecting Process MAY store the Data Records for a short period
 of time and decode them after the Template Records are received.  A
 Collecting Process MUST NOT assume that the Data Set and the
 associated Template Set (or Options Template Set) are exported in the
 same IPFIX Message.
 The Collecting Process MUST note the Information Element identifier
 of any Information Element that it does not understand and MAY
 discard that Information Element from the Flow Record.
 The Collector MUST accept padding in Data Records and Template
 Records.  The padding size is the Set Length minus the size of the
 Set Header (4 octets for the Set ID and the Set Length), modulo the
 Record size deduced from the Template Record.
 The IPFIX protocol has a Sequence Number field in the Export header
 that increases with the number of IPFIX Data Records in the IPFIX
 Message.  A Collector may detect out-of-sequence, dropped, or
 duplicate IPFIX Messages by tracking the Sequence Number.  A
 Collector SHOULD provide a logging mechanism for tracking
 out-of-sequence IPFIX Messages.  Such out-of-sequence IPFIX Messages
 may be due to Exporter resource exhaustion where it cannot transmit
 messages at their creation rate, an Exporting Process reset,
 congestion on the network link between the Exporter and Collector,
 Collector resource exhaustion where it cannot process the IPFIX
 Messages at their arrival rate, out-of-order packet reception,
 duplicate packet reception, or an attacker injecting false messages.
 If a Collecting Process receives a Template Withdrawal Message, the
 Collecting Process MUST delete the corresponding Template Records
 associated with the specific SCTP association and specific
 Observation Domain, and stop decoding IPFIX Messages that use the
 withdrawn Templates.

Claise, et al. Standards Track [Page 35] RFC 5101 IPFIX Protocol Specification January 2008

 If the Collecting Process receives a Template Withdraw message for a
 Template Record it has not received before on this SCTP association,
 it MUST reset the SCTP association, discard the IPFIX Message, and
 SHOULD log the error as it does for malformed IPFIX Messages.
 A Collecting Process that receives IPFIX Messages from several
 Observation Domains on the same Transport Session MUST be aware that
 the uniqueness of the Template ID is not guaranteed across
 Observation Domains.
 The Collector MUST support the use of Templates containing multiple
 occurrences of the similar Information Elements.

10. Transport Protocol

 The IPFIX Protocol Specification has been designed to be transport
 protocol independent.  Note that the Exporter can export to multiple
 Collecting Processes using independent transport protocols.
 The IPFIX Message Header 16-bit Length field limits the length of an
 IPFIX Message to 65535 octets, including the header.  A Collecting
 Process MUST be able to handle IPFIX Message lengths of up to 65535
 octets.

10.1. Transport Compliance and Transport Usage

 We need to differentiate between what must be implemented (so that
 operators can interoperably deploy compliant implementations from
 different vendors) and what should or could be used in various
 operational environments.  We must also make sure that ALL
 implementations can operate in a congestion-aware and
 congestion-avoidance mode.
 SCTP [RFC4960] using the PR-SCTP extension specified in [RFC3758]
 MUST be implemented by all compliant implementations.  UDP [UDP] MAY
 also be implemented by compliant implementations.  TCP [TCP] MAY also
 be implemented by compliant implementations.
 PR-SCTP SHOULD be used in deployments where Exporters and Collectors
 are communicating over links that are susceptible to congestion.
 PR-SCTP is capable of providing any required degree of reliability.
 TCP MAY be used in deployments where Exporters and Collectors
 communicate over links that are susceptible to congestion, but
 PR-SCTP is preferred due to its ability to limit back pressure on
 Exporters and its message versus stream orientation.

Claise, et al. Standards Track [Page 36] RFC 5101 IPFIX Protocol Specification January 2008

 UDP MAY be used, although it is not a congestion-aware protocol.
 However, the IPFIX traffic between Exporter and Collector MUST run in
 an environment where IPFIX traffic has been provisioned for, or is
 contained through some other means.

10.2. SCTP

 This section describes how IPFIX can be transported over SCTP
 [RFC4960] using the PR-SCTP [RFC3758] extension.

10.2.1. Congestion Avoidance

 The SCTP transport protocol provides the required level of congestion
 avoidance by design.
 SCTP will detect congestion in the end-to-end path between the IPFIX
 Exporting Process and the IPFIX Collecting Process, and limit the
 transfer rate accordingly.  When an IPFIX Exporting Process has
 records to export, but detects that transmission by SCTP is
 temporarily impossible, it can either wait until sending is possible
 again, or it can decide to drop the record.  In the latter case, the
 dropped export data MUST be accounted for, so that the amount of
 dropped export data can be reported.

10.2.2. Reliability

 The SCTP transport protocol is by default reliable, but has the
 capability to deliver messages with partial reliability  [RFC3758].
 Using reliable SCTP messages for the IPFIX export is not in itself a
 guarantee that all Data Records will be delivered.  If there is
 congestion on the link from the Exporting Process to the Collecting
 Process, or if a significant number of retransmissions are required,
 the send queues on the Exporting Process may fill up; the Exporting
 Process MAY either suspend, export, or discard the IPFIX Messages.
 If Data Records are discarded the IPFIX Sequence Numbers used for
 export MUST reflect the loss of data.

10.2.3. MTU

 SCTP provides the required IPFIX Message fragmentation service based
 on path MTU discovery.

Claise, et al. Standards Track [Page 37] RFC 5101 IPFIX Protocol Specification January 2008

10.2.4. Exporting Process

10.2.4.1. Association Establishment

 The IPFIX Exporting Process SHOULD initiate an SCTP association with
 the IPFIX Collecting Process.  By default, the Collecting Process
 listens for connections on SCTP port 4739.  By default, the
 Collecting Process listens for secure connections on SCTP port 4740
 (refer to the Security Considerations section).  By default, the
 Exporting Process tries to connect to one of these ports.  It MUST be
 possible to configure both the Exporting and Collecting Processes to
 use a different SCTP port.
 The Exporting Process MAY establish more than one association
 (connection "bundle" in SCTP terminology) to the Collecting Process.
 An Exporting Process MAY support more than one active association to
 different Collecting Processes (including the case of different
 Collecting Processes on the same host).

10.2.4.2. Association Shutdown

 When an Exporting Process is shut down, it SHOULD shut down the SCTP
 association.
 When a Collecting Process no longer wants to receive IPFIX Messages,
 it SHOULD shut down its end of the association.  The Collecting
 Process SHOULD continue to receive and process IPFIX Messages until
 the Exporting Process has closed its end of the association.
 When a Collecting Process detects that the SCTP association has been
 abnormally terminated, it MUST continue to listen for a new
 association establishment.
 When an Exporting Process detects that the SCTP association to the
 Collecting Process is abnormally terminated, it SHOULD try to
 re-establish the association.
 Association timeouts SHOULD be configurable.

10.2.4.3. Stream

 An Exporting Process MAY request more than one SCTP stream per
 association.  Each of these streams may be used for the transmission
 of IPFIX Messages containing Data Sets, Template Sets, and/or Options
 Template Sets.

Claise, et al. Standards Track [Page 38] RFC 5101 IPFIX Protocol Specification January 2008

 Depending on the requirements of the application, the Exporting
 Process may send Data Sets with full or partial reliability, using
 ordered or out-of-order delivery, over any SCTP stream established
 during SCTP Association setup.
 An IPFIX Exporting Process MAY use any PR-SCTP Service Definition as
 per Section 4 of the PR-SCTP [RFC3758] specification when using
 partial reliability to transmit IPFIX Messages containing only Data
 Sets.
 However, Exporting Processes SHOULD mark such IPFIX Messages for
 retransmission for as long as resource or other constraints allow.

10.2.4.4. Template Management

 When the transport protocol is SCTP, the default Template Management
 described in Section 8 is used.

10.2.5. Collecting Process

 When the transport protocol is SCTP, the default Collector processing
 described in Section 9 is used.

10.2.6. Failover

 If the Collecting Process does not acknowledge the attempt by the
 Exporting Process to establish an association, the Exporting Process
 should retry using the SCTP exponential backoff feature.  The
 Exporter MAY log an alarm if the time to establish the association
 exceeds a specified threshold, configurable on the Exporter.
 If Collecting Process failover is supported by the Exporting Process,
 a second SCTP association MAY be opened in advance.

10.3. UDP

 This section describes how IPFIX can be transported over UDP [UDP].

10.3.1. Congestion Avoidance

 UDP has no integral congestion-avoidance mechanism.  Its use over
 congestion-sensitive network paths is therefore not recommended.  UDP
 MAY be used in deployments where Exporters and Collectors always
 communicate over dedicated links that are not susceptible to
 congestion, i.e., over provisioned links compared to the maximum
 export rate from the Exporters.

Claise, et al. Standards Track [Page 39] RFC 5101 IPFIX Protocol Specification January 2008

10.3.2. Reliability

 UDP is not a reliable transport protocol, and cannot guarantee
 delivery of messages.  IPFIX Messages sent from the Exporting Process
 to the Collecting Process using UDP may therefore be lost.  UDP MUST
 NOT be used unless the application can tolerate some loss of IPFIX
 Messages.
 The Collecting Process SHOULD deduce the loss and reordering of IPFIX
 Data Records by looking at the discontinuities in the IPFIX Sequence
 Number.  In the case of UDP, the IPFIX Sequence Number contains the
 total number of IPFIX Data Records sent for the UDP Transport Session
 prior to the receipt of this IPFIX Message, modulo 2^32.  A Collector
 SHOULD detect out-of-sequence, dropped, or duplicate IPFIX Messages
 by tracking the Sequence Number.  Templates sent from the Exporting
 Process to the Collecting Process using UDP as a transport MUST be
 re-sent at regular intervals, in case previous copies were lost.

10.3.3. MTU

 The maximum size of exported messages MUST be configured such that
 the total packet size does not exceed the path MTU.  If the path MTU
 is unknown, a maximum packet size of 512 octets SHOULD be used.

10.3.4. Port Numbers

 By default, the Collecting Process listens on the UDP port 4739.  By
 default, the Collecting Process listens for secure connections on UDP
 port 4740 (refer to the "Security Considerations" section).  By
 default, the Exporting Process tries to connect to one of these
 ports.  It MUST be possible to configure both the Exporting and
 Collecting Processes to use a different UDP port.

10.3.5. Exporting Process

 The Exporting Process MAY duplicate the IPFIX Message to the several
 Collecting Processes.

10.3.6. Template Management

 When IPFIX uses UDP as the transport protocol, Template Sets and
 Option Template Sets MUST be re-sent at regular intervals.  The
 frequency of the (Options) Template transmission MUST be
 configurable.  The default value for the frequency of the (Options)
 Template transmission is 10 minutes.  The Exporting Process SHOULD
 transmit the Template Set and Options Template Set in advance of any
 Data Sets that use that (Options) Template ID to help ensure that the

Claise, et al. Standards Track [Page 40] RFC 5101 IPFIX Protocol Specification January 2008

 Collector has the Template Record before receiving the first Data
 Record.
 In the event of configuration changes, the Exporting Process SHOULD
 send multiple copies of the new Template definitions, in different
 IPFIX Messages, at an accelerated rate.  In such a case, it SHOULD
 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.
 If the Option Template scope is defined in another Template, then
 both Templates SHOULD be sent in the same IPFIX Message.  For
 example, if a Flow Key Option Template (see Section 4.4) is sent in
 an Option Template, then the associated Template SHOULD be sent in
 the same IPFIX Message.
 Following a configuration change that can modify the interpretation
 of the Data Records (for example, a sampling rate change) a new
 Template ID MUST be used, and the old Template ID MUST NOT be reused
 until its lifetime (see Section 10.3.7) has expired.
 If UDP is selected as the transport protocol, the Template Withdraw
 Messages MUST NOT be used, as this method is inefficient due to the
 unreliable nature of UDP.

10.3.7. Collecting Process

 The Collecting Process MUST associate a lifetime with each Template
 (or another definition of an identifier considered unique within the
 Transport Session) received via UDP.  Templates (and similar
 definitions) not refreshed by the Exporting Process within the
 lifetime are expired at the Collecting Process.  If the Template (or
 other definition) is not refreshed before that lifetime has expired,
 the Collecting Process MUST discard that definition and any current
 and future associated Data Records.  In which case, an alarm MUST be
 logged.  The Collecting Process MUST NOT decode any further Data
 Records that are associated with the expired Template.  If a Template
 is refreshed with a Template Record that differs from the previously
 received Template Record, the Collecting Process SHOULD log a warning
 and replace the previously received Template Record with the new one.
 The Template lifetime at the Collecting Process MUST be at least 3
 times higher than the Template refresh timeout configured on the
 Exporting Process.
 Template IDs are unique per UDP session and per Observation Domain.
 At any given time, the Collecting Process SHOULD maintain the
 following for all the current Template Records and Options Template

Claise, et al. Standards Track [Page 41] RFC 5101 IPFIX Protocol Specification January 2008

 Records: <IPFIX Device, Exporter source UDP port, Observation Domain
 ID, Template ID, Template Definition, Last Received>.
 The Collecting Process SHOULD accept Data Records without the
 associated Template Record (or other definitions) required to decode
 the Data Record.  If the Template Records (or other definitions such
 as Common Properties) have not been received at the time Data Records
 are received, the Collecting Process SHOULD store the Data Records
 for a short period of time and decode them after the Template Records
 (or other definitions) are received.  The short period of time MUST
 be lower than the lifetime of definitions associated with identifiers
 considered unique within the UDP session.
 If the Collecting Process receives a malformed IPFIX Message, it MUST
 discard the IPFIX Message and SHOULD log the error.

10.3.8. Failover

 Because UDP is not a connection-oriented protocol, the Exporting
 Process is unable to determine from the transport protocol that the
 Collecting Process is no longer able to receive the IPFIX Messages.
 Therefore, it cannot invoke a failover mechanism.  However, the
 Exporting Process MAY duplicate the IPFIX Message to several
 Collecting Processes.

10.4. TCP

 This section describes how IPFIX can be transported over TCP [TCP].

10.4.1. Connection Management

10.4.1.1. Connection Establishment

 The IPFIX Exporting Process initiates a TCP connection to the
 Collecting Process.  By default, the Collecting Process listens for
 connections on TCP port 4739.  By default, the Collecting Process
 listens for secure connections on TCP port 4740 (refer to the
 Security Considerations section).  By default, the Exporting Process
 tries to connect to one of these ports.  It MUST be possible to
 configure both the Exporting Process and the Collecting Process to
 use a different TCP port.
 An Exporting Process MAY support more than one active connection to
 different Collecting Processes (including the case of different
 Collecting Processes on the same host).
 The Exporter MAY log an alarm if the time to establish the connection
 exceeds a specified threshold, configurable on the Exporter.

Claise, et al. Standards Track [Page 42] RFC 5101 IPFIX Protocol Specification January 2008

10.4.1.2. Graceful Connection Release

 When an Exporting Process is shut down, it SHOULD shut down the TCP
 connection.
 When a Collecting Process no longer wants to receive IPFIX Messages,
 it SHOULD close its end of the connection.  The Collecting Process
 SHOULD continue to read IPFIX Messages until the Exporting Process
 has closed its end.

10.4.1.3. Restarting Interrupted Connections

 When a Collecting Process detects that the TCP connection to the
 Exporting Process has terminated abnormally, it MUST continue to
 listen for a new connection.
 When an Exporting Process detects that the TCP connection to the
 Collecting Process has terminated abnormally, it SHOULD try to
 re-establish the connection.  Connection timeouts and retry schedules
 SHOULD be configurable.  In the default configuration, an Exporting
 Process MUST NOT attempt to establish a connection more frequently
 than once per minute.

10.4.1.4. Failover

 If the Collecting Process does not acknowledge the attempt by the
 Exporting Process to establish a connection, it will retry using the
 TCP exponential backoff feature.
 If Collecting Process failover is supported by the Exporting Process,
 a second TCP connection MAY be opened in advance.

10.4.2. Data Transmission

 Once a TCP connection is established, the Exporting Process starts
 sending IPFIX Messages to the Collecting Process.

10.4.2.1. IPFIX Message Encoding

 IPFIX Messages are sent over the TCP connection without any special
 encoding.  The Length field in the IPFIX Message Header defines the
 end of each IPFIX Message and thus the start of the next IPFIX
 Message.  This means that IPFIX Messages cannot be interleaved.
 In the case of TCP, the IPFIX Sequence Number contains the total
 number of IPFIX Data Records sent from this TCP connection, from the
 current Observation Domain by the Exporting Process, prior to the
 receipt of this IPFIX Message, modulo 2^32.

Claise, et al. Standards Track [Page 43] RFC 5101 IPFIX Protocol Specification January 2008

 If an Exporting Process exports data from multiple Observation
 Domains, it should be careful to choose IPFIX Message lengths
 appropriately to minimize head-of-line blocking between different
 Observation Domains.  Multiple TCP connections MAY be used to avoid
 head-of-line between different Observation Domains.

10.4.2.2. Template Management

 For each Template, the Exporting Process MUST send the Template
 Record before exporting Data Records that refer to that Template.
 Template IDs are unique per TCP connection and per Observation
 Domain.  A Collecting Process MUST record all Template and Options
 Template Records for the duration of the connection, as an Exporting
 Process is not required to re-export Template Records.
 When the TCP connection restarts, the Exporting Process MUST resend
 all the Template Records.
 When a TCP connection is closed, the Collecting Process MUST discard
 all Templates received over that connection and stop decoding IPFIX
 Messages that use those Templates.
 The Templates that are not used anymore SHOULD be deleted.  Before
 reusing a Template ID, the Template MUST be deleted.  In order to
 delete an allocated Template, the Template is withdrawn through the
 use of a Template Withdrawal Message over the TCP connection.
 If the Collecting Process receives a malformed IPFIX Message, it MUST
 reset the TCP connection, discard the IPFIX Message, and SHOULD log
 the error.

10.4.2.3. Congestion Handling and Reliability

 TCP ensures reliable delivery of data from the Exporting Process to
 the Collecting Process.  TCP also controls the rate at which data can
 be sent from the Exporting Process to the Collecting Process, using a
 mechanism that takes into account both congestion in the network and
 the capabilities of the receiver.
 Therefore, an IPFIX Exporting Process may not be able to send IPFIX
 Messages at the rate that the Metering Process generates it, either
 because of congestion in the network or because the Collecting
 Process cannot handle IPFIX Messages fast enough.  As long as
 congestion is transient, the Exporting Process can buffer IPFIX
 Messages for transmission.  But such buffering is necessarily
 limited, both because of resource limitations and because of

Claise, et al. Standards Track [Page 44] RFC 5101 IPFIX Protocol Specification January 2008

 timeliness requirements, so ongoing and/or severe congestion may lead
 to a situation where the Exporting Process is blocked.
 When an Exporting Process has Data Records to export but the
 transmission buffer is full, and it wants to avoid blocking, it can
 decide to drop some Data Records.  The dropped Data Records MUST be
 accounted for, so that the amount can later be exported.
 When an Exporting Process finds that the rate at which records should
 be exported is consistently higher than the rate at which TCP sending
 permits, it should provide back pressure to the Metering Processes.
 The Metering Process could then adapt by temporarily reducing the
 amount of data it generates, for example, using sampling or
 aggregation.

10.4.3. Collecting Process

 The Collecting Process SHOULD listen for a new TCP connection from
 the Exporting Process.
 If the Collecting Process receives a malformed IPFIX Message, it MUST
 reset the TCP connection, discard the IPFIX Message, and SHOULD log
 the error.  Note that non-zero Set padding does not constitute a
 malformed IPFIX Message.
 Template Sets and Option Template Sets are only sent once.  The
 Collecting Process MUST store the Template Record information for the
 duration of the connection so that it can interpret the corresponding
 Data Records that are received in subsequent Data Sets.
 Template IDs are unique per TCP connection and per Observation
 Domain.  If the Collecting Process receives a Template that has
 already been received but that has not previously been withdrawn
 (i.e., a Template Record from the same Exporter Observation Domain
 with the same Template ID received on the TCP connection), then the
 Collecting Process MUST shut down the connection.
 When a TCP connection is closed, the Collecting Process MUST discard
 all Templates received over that connection and stop decoding IPFIX
 Messages that use those Templates.
 If a Collecting Process receives a Template Withdrawal Message, the
 Collecting Process MUST delete the corresponding Template Records
 associated with the specific TCP connection and specific Observation
 Domain, and stop decoding IPFIX Messages that use the withdrawn
 Templates.

Claise, et al. Standards Track [Page 45] RFC 5101 IPFIX Protocol Specification January 2008

 If the Collecting Process receives a Template Withdrawal Message for
 a Template Record it has not received before on this TCP connection,
 it MUST reset the TCP association, discard the IPFIX Message, and
 SHOULD log the error as it does for malformed IPFIX Messages.

11. Security Considerations

 The security considerations for the IPFIX protocol have been derived
 from an analysis of potential security threats, as discussed in the
 "Security Considerations" section of IPFIX requirements [RFC3917].
 The requirements for IPFIX security are as follows:
 1. IPFIX must provide a mechanism to ensure the confidentiality of
    IPFIX data transferred from an Exporting Process to a Collecting
    Process, in order to prevent disclosure of Flow Records
    transported via IPFIX.
 2. IPFIX must provide a mechanism to ensure the integrity of IPFIX
    data transferred from an Exporting Process to a Collecting
    Process, in order to prevent the injection of incorrect data or
    control information (e.g., Templates) into an IPFIX Message
    stream.
 3. IPFIX must provide a mechanism to authenticate IPFIX Collecting
    and Exporting Processes, to prevent the collection of data from an
    unauthorized Exporting Process or the export of data to an
    unauthorized Collecting Process.
 Because IPFIX can be used to collect information for network
 forensics and billing purposes, attacks designed to confuse, disable,
 or take information from an IPFIX collection system may be seen as a
 prime objective during a sophisticated network attack.
 An attacker in a position to inject false messages into an IPFIX
 Message stream can either affect the application using IPFIX (by
 falsifying data), or the IPFIX Collecting Process itself (by
 modifying or revoking Templates, or changing options); for this
 reason, IPFIX Message integrity is important.
 The IPFIX Messages themselves may also contain information of value
 to an attacker, including information about the configuration of the
 network as well as end-user traffic and payload data, so care must be
 taken to confine their visibility to authorized users.  When an
 Information Element containing end-user payload information is
 exported, it SHOULD be transmitted to the Collecting Process using a
 means that secures its contents against eavesdropping.  Suitable
 mechanisms include the use of either a direct point-to-point
 connection or the use of an encryption mechanism.  It is the

Claise, et al. Standards Track [Page 46] RFC 5101 IPFIX Protocol Specification January 2008

 responsibility of the Collecting Process to provide a satisfactory
 degree of security for this collected data, including, if necessary,
 anonymization of any reported data.

11.1. Applicability of TLS and DTLS

 Transport Layer Security (TLS) [RFC4346] and Datagram Transport Layer
 Security (DTLS) [RFC4347] were designed to provide the
 confidentiality, integrity, and authentication assurances required by
 the IPFIX protocol, without the need for pre-shared keys.
 With the mandatory SCTP and PR-SCTP transport protocols for IPFIX,
 DTLS [RFC4347] MUST be implemented.  If UDP is selected as the IPFIX
 transport protocol, DTLS [RFC4347] MUST be implemented.  If TCP is
 selected as the IPFIX transport protocol, TLS [RFC4346] MUST be
 implemented.
 Note that DTLS is selected as the security mechanism for SCTP and
 PR-SCTP.  Though TLS bindings to SCTP are defined in [RFC3436], they
 require all communication to be over reliable, bidirectional streams,
 and require one TLS connection per stream.  This arrangement is not
 compatible with the rationale behind the choice of SCTP as an IPFIX
 transport protocol.
 Note that using DTLS [RFC4347] has a vulnerability, i.e., a true man
 in the middle may attempt to take data out of an association and fool
 the sender into thinking that the data was actually received by the
 peer.  In generic TLS for SCTP (and/or TCP), this is not possible.
 This means that the removal of a message may become hidden from the
 sender or receiver.  Another vulnerability of using PR-SCTP with DTLS
 is that someone could inject SCTP control information to shut down
 the SCTP association, effectively generating a loss of IPFIX Messages
 if those are buffered outside of the SCTP association.  In the
 future, techniques such as [dtls-for-sctp] could be used to overcome
 these vulnerabilities.
 When using DTLS over SCTP, the Exporting Process MUST ensure that
 each IPFIX Message is sent over the same SCTP stream that would be
 used when sending the same IPFIX Message directly over SCTP.  Note
 that DTLS may send its own control messages on stream 0 with full
 reliability; however, this will not interfere with the processing of
 stream 0 IPFIX Messages at the Collecting Process, because DTLS
 consumes its own control messages before passing IPFIX Messages up to
 the application layer.

Claise, et al. Standards Track [Page 47] RFC 5101 IPFIX Protocol Specification January 2008

11.2. Usage

 The IPFIX Exporting Process initiates the communication to the IPFIX
 Collecting Process, and acts as a TLS or DTLS client according to
 [RFC4346] and [RFC4347], while the IPFIX Collecting Process acts as a
 TLS or DTLS server.  The DTLS client opens a secure connection on the
 SCTP port 4740 of the DTLS server if SCTP or PR-SCTP is selected as
 the transport protocol.  The TLS client opens a secure connection on
 the TCP port 4740 of the TLS server if TCP is selected as the
 transport protocol.  The DTLS client opens a secure connection on the
 UDP port 4740 of the DTLS server if UDP is selected as the transport
 protocol.

11.3. Authentication

 IPFIX Exporting Processes and IPFIX Collecting Processes are
 identified by the fully qualified domain name of the interface on
 which IPFIX Messages are sent or received, for purposes of X.509
 client and server certificates as in [RFC3280].
 To prevent man-in-the-middle attacks from impostor Exporting or
 Collecting Processes, the acceptance of data from an unauthorized
 Exporting Process, or the export of data to an unauthorized
 Collecting Process, strong mutual authentication via asymmetric keys
 MUST be used for both TLS and DTLS.  Each of the IPFIX Exporting and
 Collecting Processes MUST verify the identity of its peer against its
 authorized certificates, and MUST verify that the peer's certificate
 matches its fully qualified domain name, or, in the case of SCTP, the
 fully qualified domain name of one of its endpoints.
 The fully qualified domain name used to identify an IPFIX Collecting
 Process or Exporting Process may be stored either in a subjectAltName
 extension of type dNSName, or in the most specific Common Name field
 of the Subject field of the X.509 certificate.  If both are present,
 the subjectAltName extension is given preference.
 Internationalized domain names (IDN) in either the subjectAltName
 extension of type dNSName or the most specific Common Name field of
 the Subject field of the X.509 certificate MUST be encoded using
 Punycode [RFC3492] as described in Section 4 of [RFC3490],
 "Conversion Operations".

11.4. Protection against DoS Attacks

 An attacker may mount a denial-of-service (DoS) attack against an
 IPFIX collection system either directly, by sending large amounts of
 traffic to a Collecting Process, or indirectly, by generating large
 amounts of traffic to be measured by a Metering Process.

Claise, et al. Standards Track [Page 48] RFC 5101 IPFIX Protocol Specification January 2008

 Direct denial-of-service attacks can also involve state exhaustion,
 whether at the transport layer (e.g., by creating a large number of
 pending connections), or within the IPFIX Collecting Process itself
 (e.g., by sending Flow Records pending Template or scope information,
 a large amount of Options Template Records, etc.).
 SCTP mandates a cookie-exchange mechanism designed to defend against
 SCTP state exhaustion denial-of-service attacks.  Similarly, TCP
 provides the "SYN cookie" mechanism to mitigate state exhaustion; SYN
 cookies SHOULD be used by any Collecting Process accepting TCP
 connections.  DTLS also provides cookie exchange to protect against
 DTLS server state exhaustion.
 The reader should note that there is no way to prevent fake IPFIX
 Message processing (and state creation) for UDP & SCTP communication.
 The use of TLS and DTLS can obviously prevent the creation of fake
 states, but they are themselves prone to state exhaustion attacks.
 Therefore, Collector rate limiting SHOULD be used to protect TLS &
 DTLS (like limiting the number of new TLS or DTLS session per second
 to a sensible number).
 IPFIX state exhaustion attacks can be mitigated by limiting the rate
 at which new connections or associations will be opened by the
 Collecting Process, the rate at which IPFIX Messages will be accepted
 by the Collecting Process, and adaptively limiting the amount of
 state kept, particularly records waiting on Templates.  These rate
 and state limits MAY be provided by a Collecting Process; if
 provided, the limits SHOULD be user configurable.
 Additionally, an IPFIX Collecting Process can eliminate the risk of
 state exhaustion attacks from untrusted nodes by requiring TLS or
 DTLS mutual authentication, causing the Collecting Process to accept
 IPFIX Messages only from trusted sources.
 With respect to indirect denial of service, the behavior of IPFIX
 under overload conditions depends on the transport protocol in use.
 For IPFIX over TCP, TCP congestion control would cause the flow of
 IPFIX Messages to back off and eventually stall, blinding the IPFIX
 system.  PR-SCTP improves upon this situation somewhat, as some IPFIX
 Messages would continue to be received by the Collecting Process due
 to the avoidance of head-of-line blocking by SCTP's multiple streams
 and partial reliability features, possibly affording some visibility
 of the attack.  The situation is similar with UDP, as some datagrams
 may continue to be received at the Collecting Process, effectively
 applying sampling to the IPFIX Message stream, implying that some
 forensics may be left.

Claise, et al. Standards Track [Page 49] RFC 5101 IPFIX Protocol Specification January 2008

 To minimize IPFIX Message loss under overload conditions, some
 mechanism for service differentiation could be used to prioritize
 IPFIX traffic over other traffic on the same link.  Alternatively,
 IPFIX Messages can be transported over a dedicated network.  In this
 case, care must be taken to ensure that the dedicated network can
 handle the expected peak IPFIX Message traffic.

11.5. When DTLS or TLS Is Not an Option

 The use of DTLS or TLS might not be possible in some cases due to
 performance issues or other operational concerns.
 Without TLS or DTLS mutual authentication, IPFIX Exporting Processes
 and Collecting Processes can fall back on using IP source addresses
 to authenticate their peers.  A policy of allocating Exporting
 Process and Collecting Process IP addresses from specified address
 ranges, and using ingress filtering to prevent spoofing, can improve
 the usefulness of this approach.  Again, completely segregating IPFIX
 traffic on a dedicated network, where possible, can improve security
 even further.  In any case, the use of open Collecting Processes
 (those that will accept IPFIX Messages from any Exporting Process
 regardless of IP address or identity) is discouraged.
 Modern TCP and SCTP implementations are resistant to blind insertion
 attacks (see [RFC1948], [RFC4960]); however, UDP offers no such
 protection.  For this reason, IPFIX Message traffic transported via
 UDP and not secured via DTLS SHOULD be protected via segregation to a
 dedicated network.

11.6. Logging an IPFIX Attack

 IPFIX Collecting Processes MUST detect potential IPFIX Message
 insertion or loss conditions by tracking the IPFIX Sequence Number,
 and SHOULD provide a logging mechanism for reporting out-of-sequence
 messages.  Note that an attacker may be able to exploit the handling
 of out-of-sequence messages at the Collecting Process, so care should
 be taken in handling these conditions.  For example, a Collecting
 Process that simply resets the expected Sequence Number upon receipt
 of a later Sequence Number could be temporarily blinded by deliberate
 injection of later Sequence Numbers.
 IPFIX Exporting and Collecting Processes SHOULD log any connection
 attempt that fails due to authentication failure, whether due to
 being presented an unauthorized or mismatched certificate during TLS
 or DTLS mutual authentication, or due to a connection attempt from an
 unauthorized IP address when TLS or DTLS is not in use.

Claise, et al. Standards Track [Page 50] RFC 5101 IPFIX Protocol Specification January 2008

 IPFIX Exporting and Collecting Processes SHOULD detect and log any
 SCTP association reset or TCP connection reset.

11.7. Securing the Collector

 The security of the Collector and its implementation is important to
 achieve overall security.  However, it is outside the scope of this
 document.

12. IANA Considerations

 IPFIX Messages 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.
 The IPFIX Version Number value of 10 is reserved for the IPFIX
 protocol specified in this document.  Set ID values of 0 and 1 are
 not used for historical reasons [RFC3954].  The Set ID value of 2 is
 reserved for the Template Set.  The Set ID value of 3 is reserved for
 the Option Template Set.  All other Set ID values from 4 to 255 are
 reserved for future use.  Set ID values above 255 are used for Data
 Sets.
 New assignments in either IPFIX Version Number or IPFIX Set ID
 assignments require a Standards Action [RFC2434], i.e., they are to
 be made via Standards Track RFCs approved by the IESG.

Claise, et al. Standards Track [Page 51] RFC 5101 IPFIX Protocol Specification January 2008

Appendix A. IPFIX Encoding Examples

 This appendix, which is a not a normative reference, contains IPFIX
 encoding examples.
 Let's consider the example of an IPFIX Message composed of a Template
 Set, a Data Set (which contains three Data Records), an Options
 Template Set and a Data Set (which contains 2 Data Records related to
 the previous Options Template Record).
 IPFIX Message:
 +--------+------------------------------------------. . .
 |        | +--------------+ +------------------+
 |Message | | Template     | | Data             |
 | Header | | Set          | | Set              |   . . .
 |        | | (1 Template) | | (3 Data Records) |
 |        | +--------------+ +------------------+
 +--------+------------------------------------------. . .
      . . .-------------------------------------------+
            +------------------+ +------------------+ |
            | Options          | | Data             | |
     . . .  | Template Set     | | Set              | |
            | (1 Template)     | | (2 Data Records) | |
            +------------------+ +------------------+ |
      . . .-------------------------------------------+

A.1. Message Header Example

 The Message 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 = 0x000a          |         Length = 152          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                          Export Time                          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                        Sequence Number                        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                     Observation Domain ID                     |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Claise, et al. Standards Track [Page 52] RFC 5101 IPFIX Protocol Specification January 2008

A.2. Template Set Examples

A.2.1. Template Set Using IETF-Specified Information Elements

 We want to report the following Information Elements:
  1. The IPv4 source IP address: sourceIPv4Address in [RFC5102],

with a length of 4 octets

  1. The IPv4 destination IP address: destinationIPv4Address in

[RFC5102], with a length of 4 octets

  1. The next-hop IP address (IPv4): ipNextHopIPv4Address in

[RFC5102], with a length of 4 octets

  1. The number of packets of the Flow: inPacketDeltaCount in

[RFC5102], with a length of 4 octets

  1. The number of octets of the Flow: inOctetDeltaCount in

[RFC5102], with a length of 4 octets

 Therefore, the Template Set will be 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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Set ID = 2            |      Length = 28 octets       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |       Template ID 256         |       Field Count = 5         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |0|    sourceIPv4Address = 8    |       Field Length = 4        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |0| destinationIPv4Address = 12 |       Field Length = 4        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |0|  ipNextHopIPv4Address = 15  |       Field Length = 4        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |0|   inPacketDeltaCount = 2    |       Field Length = 4        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |0|   inOctetDeltaCount =  1    |       Field Length = 4        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

A.2.2. Template Set Using Enterprise-Specific Information Elements

 We want to report the following Information Elements:
  1. The IPv4 source IP address: sourceIPv4Address in [RFC5102], with a

length of 4 octets

Claise, et al. Standards Track [Page 53] RFC 5101 IPFIX Protocol Specification January 2008

  1. The IPv4 destination IP address: destinationIPv4Address in

[RFC5102], with a length of 4 octets

  1. An enterprise-specific Information Element representing proprietary

information, with a type of 15 and a length of 4

  1. The number of packets of the Flow: inPacketDeltaCount in [RFC5102],

with a length of 4 octets

  1. The number of octets of the Flow: inOctetDeltaCount in [RFC5102],

with a length of 4 octets

 Therefore, the Template Set will be 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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Set ID = 2            |      Length = 32 octets       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |       Template ID 257         |       Field Count = 5         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |0|    sourceIPv4Address = 8    |       Field Length = 4        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |0| destinationIPv4Address = 12 |       Field Length = 4        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |1| Information Element Id. = 15|       Field Length = 4        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                       Enterprise number                       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |0|   inPacketDeltaCount = 2    |       Field Length = 4        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |0|   inOctetDeltaCount = 1     |       Field Length = 4        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Claise, et al. Standards Track [Page 54] RFC 5101 IPFIX Protocol Specification January 2008

A.3. Data Set Example

 In this example, we report the following three Flow Records:
 Src IP addr. | Dst IP addr.  | Next Hop addr. | Packet | Octets
              |               |                | Number | Number
 ------------------------------------------------------------------
 192.0.2.12   | 192.0.2.254   | 192.0.2.1      | 5009   | 5344385
 192.0.2.27   | 192.0.2.23    | 192.0.2.2      | 748    | 388934
 192.0.2.56   | 192.0.2.65    | 192.0.2.3      | 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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |          Set ID = 256         |          Length = 64          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                          192.0.2.12                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                          192.0.2.254                          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                          192.0.2.1                            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                             5009                              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                            5344385                            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                          192.0.2.27                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                          192.0.2.23                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                          192.0.2.2                            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                              748                              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                             388934                            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                          192.0.2.56                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                          192.0.2.65                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                          192.0.2.3                            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                               5                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                              6534                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Note that padding is not necessary in this example.

Claise, et al. Standards Track [Page 55] RFC 5101 IPFIX Protocol Specification January 2008

A.4. Options Template Set Examples

A.4.1. Options Template Set Using IETF-Specified Information Elements

 Per line card (the router being composed of two line cards), we want
 to report the following Information Elements:
  1. Total number of IPFIX Messages: exportedPacketCount [RFC5102], with

a length of 2 octets

  1. Total number of exported Flows: exportedFlowCount [RFC5102], with a

length of 2 octets

 The line card, which is represented by the lineCardId Information
 Element [RFC5102], is used as the Scope Field.
 Therefore, the Options Template Set will be:
  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Set ID = 3            |          Length = 24          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |       Template ID 258         |        Field Count = 3        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Scope Field Count = 1     |0|     lineCardId = 141        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   Scope 1 Field Length = 4    |0|  exportedPacketCount = 41   |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |       Field Length = 2        |0|   exportedFlowCount = 42    |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |       Field Length = 2        |           Padding             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

A.4.2. Options Template Set Using Enterprise-Specific Information

      Elements
 Per line card (the router being composed of two line cards), we want
 to report the following Information Elements:
  1. Total number of IPFIX Messages: exportedPacketCount [RFC5102],

with a length of 2 octets

  1. An enterprise-specific number of exported Flows, with a type of

42 and a length of 4 octets

 The line card, which is represented by the lineCardId Information
 Element [RFC5102], is used as the Scope Field.

Claise, et al. Standards Track [Page 56] RFC 5101 IPFIX Protocol Specification January 2008

 The format of the Options Template Set 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
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Set ID = 3            |          Length = 28          |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |       Template ID 259         |        Field Count = 3        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |     Scope Field Count = 1     |0|     lineCardId = 141        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |   Scope 1 Field Length = 4    |0|  exportedPacketCount = 41   |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |       Field Length = 2        |1|Information Element Id. = 42 |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |       Field Length = 4        |       Enterprise number     ...
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  ...      Enterprise number      |           Padding             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

A.4.3. Options Template Set Using an Enterprise-Specific Scope

 In this example, we want to export the same information as in the
 example in Section A.4.1:
  1. Total number of IPFIX Messages: exportedPacketCount [RFC5102],

with a length of 2 octets

  1. Total number of exported Flows: exportedFlowCount [RFC5102],

with a length of 2 octets

 But this time, the information pertains to a proprietary scope,
 identified by enterprise-specific Information Element number 123.

Claise, et al. Standards Track [Page 57] RFC 5101 IPFIX Protocol Specification January 2008

 The format of the Options Template Set is now 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
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Set ID = 3            |          Length = 28          |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |       Template ID 260         |        Field Count = 3        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |     Scope Field Count = 1     |1|Scope 1 Infor. El. Id. = 123 |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |    Scope 1 Field Length = 4   |       Enterprise Number      ...
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ...       Enterprise Number      |0|  exportedPacketCount = 41   |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |       Field Length = 2        |0|   exportedFlowCount = 42    |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |       Field Length = 2        |           Padding             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

A.4.4. Data Set Using an Enterprise-Specific Scope

 In this example, we report the following two Data Records:
 Line Card ID               | IPFIX Message  | Exported Flow Records
 -------------------------------------------------------------------
 Line Card 1 (lineCardId=1) | 345            | 10201
 Line Card 2 (lineCardId=2) | 690            | 20402
  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |      Set ID = 260             |         Length = 20           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                               1                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |             345               |            10201              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                               2                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |             690               |            20402              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Claise, et al. Standards Track [Page 58] RFC 5101 IPFIX Protocol Specification January 2008

A.5. Variable-Length Information Element Examples

A.5.1. Example of Variable-Length Information Element with Length

      Inferior to 255 Octets
  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |       5       |          5 octet Information Element          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

A.5.2. Example of Variable-Length Information Element with Length 255

      to 65535 Octets
  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |      255      |             1000              |    IE ...     |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                1000 octet Information Element                 |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 :                              ...                              :
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                             ... IE            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

References

Normative References

 [RFC1305]       Mills, D., "Network Time Protocol (Version 3)
                 Specification, Implementation and Analysis", RFC
                 1305, March 1992.
 [RFC2119]       Bradner, S., "Key words for use in RFCs to Indicate
                 Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC2434]       Narten, T. and H. Alvestrand, "Guidelines for Writing
                 an IANA Considerations Section in RFCs", BCP 26, RFC
                 2434, October 1998.
 [RFC3280]       Housley, R., Polk, W., Ford, W., and D. Solo,
                 "Internet X.509 Public Key Infrastructure Certificate
                 and Certificate Revocation List (CRL) Profile", RFC
                 3280, April 2002.

Claise, et al. Standards Track [Page 59] RFC 5101 IPFIX Protocol Specification January 2008

 [RFC3436]       Jungmaier, A., Rescorla, E., and M. Tuexen,
                 "Transport Layer Security over Stream Control
                 Transmission Protocol", RFC 3436, December 2002.
 [RFC3758]       Stewart, R., Ramalho, M., Xie, Q., Tuexen, M., and P.
                 Conrad, "Stream Control Transmission Protocol (SCTP)
                 Partial Reliability Extension", RFC 3758, May 2004.
 [RFC4346]       Dierks, T. and E. Rescorla, "The Transport Layer
                 Security (TLS) Protocol Version 1.1", RFC 4346, April
                 2006.
 [RFC4347]       Rescorla, E. and N. Modadugu, "Datagram Transport
                 Layer Security", RFC 4347, April 2006.
 [RFC3490]       Faltstrom, P., Hoffman, P., and A. Costello,
                 "Internationalizing Domain Names in Applications
                 (IDNA)", RFC 3490, March 2003.
 [RFC3492]       Costello, A., "Punycode: A Bootstring encoding of
                 Unicode for Internationalized Domain Names in
                 Applications (IDNA)", RFC 3492, March 2003.
 [RFC4960]       Stewart, R., Ed., "Stream Control Transmission
                 Protocol", RFC 4960, September 2007.
 [RFC5102]       Quittek, J., Bryant S., Claise, B., Aitken, P., and
                 J. Meyer, "Information Model for IP Flow Information
                 Export", RFC 5102, January 2008.
 [TCP]           Postel, J., "Transmission Control Protocol", STD 7,
                 RFC 793, September 1981.
 [UDP]           Postel, J., "User Datagram Protocol", STD 6, RFC 768,
                 August 1980.

Informative References

 [IPFIX-ARCH]    Sadasivan, G., Brownlee, N., Claise, B., and J.
                 Quittek, "Architecture Model for IP Flow Information
                 Export", Work in Progress, September 2006.
 [IPFIX-AS]      Zseby, T., Boschi, E., Brownlee, N., and B. Claise,
                 "IPFIX Applicability", Work in Progress, June 2007.
 [PEN]           IANA Private Enterprise Numbers registry
                 http://www.iana.org/assignments/enterprise-numbers.

Claise, et al. Standards Track [Page 60] RFC 5101 IPFIX Protocol Specification January 2008

 [RFC1948]       Bellovin, S., "Defending Against Sequence Number
                 Attacks", RFC 1948, May 1996.
 [RFC2579]       McCloghrie, K., Perkins, D., and J. Schoenwaelder,
                 "Textual Conventions for SMIv2", STD 58, RFC 2579,
                 April 1999.
 [RFC3917]       Quittek, J., Zseby, T., Claise, B., and S. Zander,
                 "Requirements for IP Flow Information Export
                 (IPFIX)", RFC 3917, October 2004.
 [RFC3550]       Schulzrinne, H., Casner, S., Frederick, R., and V.
                 Jacobson, "RTP: A Transport Protocol for Real-Time
                 Applications", STD 64, RFC 3550, July 2003.
 [RFC3954]       Claise, B., Ed., "Cisco Systems NetFlow Services
                 Export Version 9", RFC 3954, October 2004.
 [IEEE.754.1985] Institute of Electrical and Electronics Engineers,
                 "Standard for Binary Floating-Point Arithmetic", IEEE
                 Standard 754, August 1985.
 [dtls-for-sctp] Tuexen, M. and E. Rescola, "Datagram Transport Layer
                 Security for Stream Control Transmission Protocol",
                 Work in Progress, November 2007.

Acknowledgments

 We would like to thank the following persons: Ganesh Sadasivan for
 his significant contribution during the initial phases of the
 protocol specification; Juergen Quittek for the coordination job
 within IPFIX and PSAMP; Nevil Brownlee, Dave Plonka, Paul Aitken, and
 Andrew Johnson for the thorough reviews; Randall Stewart and Peter
 Lei for their SCTP expertise and contributions; Martin Djernaes for
 the first essay on the SCTP section; Michael Behringer and Eric
 Vyncke for their advice and knowledge in security; Michael Tuexen for
 his help regarding the DTLS section; Elisa Boschi for her
 contribution regarding the improvement of SCTP sections; Mark
 Fullmer, Sebastian Zander, Jeff Meyer, Maurizio Molina, Carter
 Bullard, Tal Givoly, Lutz Mark, David Moore, Robert Lowe, Paul
 Calato, and many more, for the technical reviews and feedback.

Claise, et al. Standards Track [Page 61] RFC 5101 IPFIX Protocol Specification January 2008

Authors' Addresses

 Benoit Claise
 Cisco Systems
 De Kleetlaan 6a b1
 1831 Diegem
 Belgium
 Phone: +32 2 704 5622
 EMail: bclaise@cisco.com
 Stewart Bryant
 Cisco Systems, Inc.
 250, Longwater,
 Green Park,
 Reading, RG2 6GB,
 United Kingdom
 Phone: +44 (0)20 8824-8828
 EMail: stbryant@cisco.com
 Simon Leinen
 SWITCH
 Werdstrasse 2
 P.O. Box
 CH-8021 Zurich
 Switzerland
 Phone: +41 44 268 1536
 EMail: simon.leinen@switch.ch
 Thomas Dietz
 NEC Europe Ltd.
 NEC Laboratories Europe
 Network Research Division
 Kurfuersten-Anlage 36
 69115 Heidelberg
 Germany
 Phone: +49 6221 4342-128
 EMail: Thomas.Dietz@nw.neclab.eu
 Brian H. Trammell
 CERT Network Situational Awareness
 Software Engineering Institute
 4500 Fifth Avenue
 Pittsburgh, PA 15213
 United States
 Phone: +1 412 268 9748
 EMail: bht@cert.org

Claise, et al. Standards Track [Page 62] RFC 5101 IPFIX Protocol Specification January 2008

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Claise, et al. Standards Track [Page 63]

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