Internet Engineering Task Force (IETF)                         B. Claise
Request for Comments: 6313                                 G. Dhandapani
Updates: 5102                                                  P. Aitken
Category: Standards Track                                       S. Yates
ISSN: 2070-1721                                      Cisco Systems, Inc.
                                                               July 2011

Export of Structured Data in IP Flow Information Export (IPFIX)

Abstract

   This document specifies an extension to the IP Flow Information
   Export (IPFIX) protocol specification in RFC 5101 and the IPFIX
   information model specified in RFC 5102 to support hierarchical
   structured data and lists (sequences) of Information Elements in data
   records.  This extension allows definition of complex data structures
   such as variable-length lists and specification of hierarchical
   containment relationships between Templates.  Finally, the semantics
   are provided in order to express the relationship among multiple list
   elements in a structured data record.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6313.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of

the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.

   1. Overview ........................................................5
      1.1. IPFIX Documents Overview ...................................5
      1.2. Relationship between IPFIX and PSAMP .......................6
   2. Introduction ....................................................6
      2.1. The IPFIX Track ............................................7
      2.2. The IPFIX Limitations ......................................8
      2.3. Structured Data Use Cases ..................................8
      2.4. Specifications Summary ....................................11
   3. Terminology ....................................................11
      3.1. New Terminology ...........................................12
      3.2. Conventions Used in This Document .........................12
   4. Linkage with the IPFIX Information Model .......................12
      4.1. New Abstract Data Types ...................................12
           4.1.1. basicList ..........................................12
           4.1.2. subTemplateList ....................................12
           4.1.3. subTemplateMultiList ...............................12
      4.2. New Data Type Semantic ....................................13
           4.2.1. List ...............................................13
      4.3. New Information Elements ..................................13
           4.3.1. basicList ..........................................13
           4.3.2. subTemplateList ....................................13
           4.3.3. subTemplateMultiList ...............................13
      4.4. New Structured Data Type Semantics ........................13
           4.4.1. undefined ..........................................14
           4.4.2. noneOf .............................................14
           4.4.3. exactlyOneOf .......................................14
           4.4.4. oneOrMoreOf ........................................15
           4.4.5. allOf ..............................................16
           4.4.6. ordered ............................................16
      4.5. Encoding of IPFIX Data Types ..............................16
           4.5.1. basicList ..........................................17
           4.5.2. subTemplateList ....................................19
           4.5.3. subTemplateMultiList ...............................21
   5. Structured Data Format .........................................25
      5.1. Length Encoding Considerations ............................25
      5.2. Recursive Structured Data .................................26
      5.3. Structured Data Information Elements Applicability
           in Options Template Sets ..................................26
      5.4. Usage Guidelines for Equivalent Data Representations ......27
      5.5. Padding ...................................................29
      5.6. Semantic ..................................................29
   6. Template Management ............................................33
   7. The Collecting Process's Side ..................................33

   8. Defining New Information Elements Based on the New
      Abstract Data Types ............................................34
   9. Structured Data Encoding Examples ..............................34
      9.1. Encoding a Multicast Data Record with basicList ...........35
      9.2. Encoding a Load-Balanced Data Record with a basicList .....37
      9.3. Encoding subTemplateList ..................................38
      9.4. Encoding subTemplateMultiList .............................41
      9.5. Encoding an Options Template Set Using Structured Data ....46
   10. Relationship with the Other IPFIX Documents ...................51
      10.1. Relationship with Reducing Redundancy ....................51
           10.1.1. Encoding Structured Data Element Using
                   Common Properties .................................51
           10.1.2. Encoding Common Properties Elements with
                   Structured Data Information Element ...............51
      10.2. Relationship with Guidelines for IPFIX Testing ...........53
      10.3. Relationship with IPFIX Mediation Function ...............54
   11. IANA Considerations ...........................................54
      11.1. New Abstract Data Types ..................................54
           11.1.1. basicList .........................................54
           11.1.2. subTemplateList ...................................54
           11.1.3. subTemplateMultiList ..............................55
      11.2. New Data Type Semantics ..................................55
           11.2.1. list ..............................................55
      11.3. New Information Elements .................................55
           11.3.1. basicList .........................................55
           11.3.2. subTemplateList ...................................56
           11.3.3. subTemplateMultiList ..............................56
      11.4. New Structured Data Semantics ............................56
           11.4.1. undefined .........................................56
           11.4.2. noneOf ............................................57
           11.4.3. exactlyOneOf ......................................57
           11.4.4. oneOrMoreOf .......................................57
           11.4.5. allOf .............................................57
           11.4.6. ordered ...........................................58
   12. Security Considerations .......................................58
   13. References ....................................................58
      13.1. Normative References .....................................58
      13.2. Informative References ...................................58
   14. Acknowledgements ..............................................59
   Appendix A. Additions to XML Specification of IPFIX
               Information Elements and Abstract Data Types ..........60
   Appendix B. Encoding IPS Alert Using Structured Data
               Information Elements ..................................65

Table of Figures

  Figure 1:  basicList Encoding ......................................17
  Figure 2:  basicList Encoding with Enterprise Number ...............18
  Figure 3:  Variable-Length basicList Encoding (Length < 255 Octets) 18
  Figure 4:  Variable-Length basicList Encoding (Length 0 to 65535
             Octets) .................................................19
  Figure 5:  subTemplateList Encoding ................................19
  Figure 6:  Variable-Length subTemplateList Encoding
             (Length < 255 Octets) ...................................20
  Figure 7:  Variable-Length subTemplateList Encoding
             (Length 0 to 65535 Octets) ..............................21
  Figure 8:  subTemplateMultiList Encoding ...........................21
  Figure 9:  Variable-Length subTemplateMultiList Encoding
             (Length < 255 Octets) ...................................23
  Figure 10: Variable-Length subTemplateMultiList Encoding
             (Length 0 to 65535 Octets) ..............................24
  Figure 11: Encoding basicList, Template Record .....................35
  Figure 12: Encoding basicList, Data Record, Semantic allOf .........36
  Figure 13: Encoding basicList, Data Record with Variable-Length
             Elements, Semantic allOf ................................37
  Figure 14: Encoding basicList, Data Record, Semantic exactlyOneOf ..38
  Figure 15: Encoding subTemplateList, Template for One-Way Delay
             Metrics .................................................39
  Figure 16: Encoding subTemplateList, Template Record ...............40
  Figure 17: Encoding subTemplateList, Data Set ......................40
  Figure 18: Encoding subTemplateMultiList, Template for Filtering
             Attributes ..............................................44
  Figure 19: Encoding subTemplateMultiList, Template for Sampling
             Attributes ..............................................44
  Figure 20: Encoding subTemplateMultiList, Template for Flow Record .45
  Figure 21: Encoding subTemplateMultiList, Data Set .................45
  Figure 22: PSAMP SSRI to Be encoded ................................48
  Figure 23: Options Template Record for PSAMP SSRI Using
             subTemplateMultiList ....................................48
  Figure 24: PSAMP SSRI, Template Record for interface ...............49
  Figure 25: PSAMP SSRI, Template Record for linecard ................49
  Figure 26: PSAMP SSRI, Template Record for linecard and interface ..49
  Figure 27: Example of a PSAMP SSRI Data Record, Encoded Using a
             subTemplateMultiList ...................................50
  Figure 28: Common and Specific Properties Exported Together
             [RFC5473] ..............................................51
  Figure 29: Common and Specific Properties Exported Separately
             According to [RFC5473] .................................52
  Figure 30: Common and Specific Properties Exported with Structured
             Data Information Element ...............................52
  Figure 31: Encoding IPS Alert, Template for Target ................67
  Figure 32: Encoding IPS Alert, Template for Attacker ..............68

  Figure 33: Encoding IPS Alert, Template for Participant ...........68
  Figure 34: Encoding IPS Alert, Template for IPS Alert .............69
  Figure 35: Encoding IPS Alert, Data Set ...........................69

1. Overview

1.1. IPFIX Documents Overview

   The IPFIX protocol [RFC5101] provides network administrators with
   access to IP Flow information.

   The architecture for the export of measured IP Flow information out
   of an IPFIX Exporting Process to a Collecting Process is defined in
   the IPFIX architecture [RFC5470], per the requirements defined in RFC
   3917 [RFC3917].

   The IPFIX architecture [RFC5470] specifies how IPFIX Data Records and
   Templates are carried via a congestion-aware transport protocol 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 the
   IPFIX information model [RFC5102].

   In order to gain a level of confidence in the IPFIX implementation,
   probe the conformity and robustness, and allow interoperability, the
   guidelines for IPFIX testing [RFC5471] present a list of tests for
   implementers of compliant Exporting Processes and Collecting
   Processes.

   The Bidirectional Flow Export [RFC5103] specifies a method for
   exporting bidirectional flow (biflow) information using the IP Flow
   Information Export (IPFIX) protocol, representing each biflow using a
   single Flow Record.

   "Reducing Redundancy in IP Flow Information Export (IPFIX) and Packet
   Sampling (PSAMP) Reports" [RFC5473] specifies a bandwidth-saving
   method for exporting Flow or packet information, by separating
   information common to several Flow Records from information specific
   to an individual Flow Record: common Flow information is exported
   only once.

1.2. Relationship between IPFIX and PSAMP

   The specification in this document applies to the IPFIX protocol
   specifications [RFC5101].  All specifications from [RFC5101] apply
   unless specified otherwise in this document.

   The Packet Sampling (PSAMP) protocol [RFC5476] specifies the export
   of packet information from a PSAMP Exporting Process to a PSAMP
   Collecting Process.  Like IPFIX, PSAMP has a formal description of
   its information elements, their name, type, and additional semantic
   information.  The PSAMP information model is defined in [RFC5477].

   As the PSAMP protocol specifications [RFC5476] are based on the IPFIX
   protocol specifications, the specifications in this document are also
   valid for the PSAMP protocol.

   Indeed, the major difference between IPFIX and PSAMP is that the
   IPFIX protocol exports Flow Records while the PSAMP protocol exports
   Packet Reports.  From a pure export point of view, IPFIX will not
   distinguish a Flow Record composed of several packets aggregated
   together from a Flow Record composed of a single packet.  So the
   PSAMP export can be seen as a special IPFIX Flow Record containing
   information about a single packet.

2. Introduction

   While collecting the interface counters every five minutes has proven
   to be useful in the past, more and more granular information is
   required from network elements for a series of applications:
   performance assurance, capacity planning, security, billing, or
   simply monitoring.  However, the amount of information has become so
   large that, when dealing with highly granular information such as
   Flow information, a push mechanism (as opposed to a pull mechanism,
   such as Simple Network Management Protocol (SNMP)) is the only
   solution for routers whose primary function is to route packets.
   Indeed, polling short-lived Flows via SNMP is not an option: high-end
   routers can support hundreds of thousands of Flows simultaneously.
   Furthermore, in order to reduce the export bandwidth requirements,
   the network elements have to integrate mediation functions to
   aggregate the collected information, both in space (typically, from
   different linecards or different Exporters) and in time.

   Typically, it would be beneficial if access routers could export Flow
   Records, composed of the counters before and after an optimization
   mechanism on the egress interface, instead of exporting two Flow
   Records with identical tuple information.

   In terms of aggregation in time, let us imagine that, for performance
   assurance, the network management application must receive the
   performance metrics associated with a specific Flow, every
   millisecond.  Since the performance metrics will be constantly
   changing, there is a new dimension to the Flow definition: we are not
   dealing anymore with a single Flow lasting a few seconds or a few
   minutes, but with a multitude of one millisecond sub-flows for which
   the performance metrics are reported.

   Which current protocol is suitable for these requirements: push
   mechanism, highly granular information, and huge number of similar
   records? IPFIX, as specified in RFC 5101 would give part of the
   solution.

2.1. The IPFIX Track

   The IPFIX working group has specified a protocol to export Flow
   information [RFC5101].  This protocol is designed to export
   information about IP traffic Flows and related measurement data,
   where a Flow is defined by a set of key attributes (e.g., source and
   destination IP address, source and destination port).

   The IPFIX protocol specification [RFC5101] specifies that traffic
   measurements for Flows are exported using a TLV (type, length, value)
   format.  The information is exported using a Template Record that is
   sent once to export the {type, length} pairs that define the data
   format for the Information Elements in a Flow.  The Data Records
   specify values for each Flow.

   Based on the requirements for IP Flow Information Export (IPFIX)
   [RFC3917], the IPFIX protocol has been optimized to export Flow-
   related information.  However, thanks to its Template mechanism, the
   IPFIX protocol can export any type of information, as long as the
   relevant Information Element is specified in the IPFIX information
   model [RFC5102], registered with IANA [IANA-IPFIX], or specified as
   an enterprise-specific Information Element.  For each Information
   Element, the IPFIX information model [RFC5102] defines a numeric
   identifier, an abstract data type, an encoding mechanism for the data
   type, and any semantic constraints.  Only basic, single-valued data
   types, e.g., numbers, strings, and network addresses, are currently
   supported.

2.2. The IPFIX Limitations

   The IPFIX protocol specification [RFC5101] does not support the
   encoding of hierarchical structured data and arbitrary-length lists
   (sequences) of Information Elements as fields within a Template
   Record.  As it is currently specified, a Data Record is a "flat" list
   of single-valued attributes.  However, it is a common data modeling
   requirement to compose complex hierarchies of data types, with
   multiple occurrences, e.g., 0..* cardinality allowed for instances of
   each Information Element in the hierarchy.

   A typical example is the MPLS label stack entries model.  An early
   NetFlow implementation used two Information Elements to represent the
   MPLS label stack entry: a "label stack entry position" followed by a
   "label stack value".  However, several drawbacks were discovered.
   Firstly, the Information Elements in the Template Record had to be
   imposed so that the position would always precede the value.
   However, some encoding optimizations are based on the permutation of
   Information Element order.  Secondly, a new semantic intelligence,
   not described in the information model, had to be hard-coded in the
   Collecting Process: the label value at the position "X" in the stack
   is contained in the "label stack value" Information Element following
   by a "label stack entry position" Information Element containing the
   value "X".  Therefore, this model was abandoned.

   The selected solution in the IPFIX information model [RFC5102] is a
   long series of Information Elements: mplsTopLabelStackSection,
   mplsLabelStackSection2, mplsLabelStackSection3,
   mplsLabelStackSection4, mplsLabelStackSection5,
   mplsLabelStackSection6, mplsLabelStackSection7,
   mplsLabelStackSection8, mplsLabelStackSection9,
   mplsLabelStackSection10.  While this model removes any ambiguity, it
   overloads the IPFIX information model with repetitive information.
   Furthermore, if mplsLabelStackSection11 is required, IANA
   [IANA-IPFIX] will not be able to assign the new Information Element
   next to the other ones in the registry, which might cause some
   confusion.

2.3. Structured Data Use Cases

   Clearly, the MPLS label stack entries issue can best be solved by
   using a real structured data type composed of ("label stack entry
   position", "label stack value") pairs, potentially repeated multiple
   times in Flow Records, since this would be the most efficient from an
   information model point of view.

   Some more examples enter the same category: how to encode the list of
   output interfaces in a multicast Flow, how to encode the list of BGP
   Autonomous Systems (AS) in a BGP Flow, how to encode the BGP
   communities in a BGP Flow, etc.

   The one-way delay passive measurement, which is described in the
   IPFIX applicability [RFC5472], is yet another example that would
   benefit from a structured data encoding.  Assuming synchronized
   clocks, the Collector can deduce the one-way delay between two
   Observation Points from the following two Information Elements,
   collected from two different Observation Points:

       - Packet arrival time: observationTimeMicroseconds [RFC5477]
       - Packet ID: digestHashValue [RFC5477]

   In practice, this implies that many pairs of
   (observationTimeMicroseconds, digestHashValue) must be exported for
   each Observation Point, even if Hash-Based Filtering [RFC5475] is
   used.  On top of that information, if the requirement is to
   understand the one-way delay per application type, the 5-tuple
   (source IP address, destination IP address, protocol, source port,
   destination port) would need to be added to every Flow Record.
   Instead of exporting this repetitive 5-tuple, as part of every single
   Flow Record a Flow Record composed of a structured data type such as
   the following would save a lot of bandwidth:

      5-tuple
                { observationTimeMicroseconds 1, digestHashValue 1 }
                { observationTimeMicroseconds 2, digestHashValue 2 }
                { observationTimeMicroseconds 3, digestHashValue 3 }
                { ...  , ... }

   As a last example, here is a more complex case of hierarchical
   structured data encoding.  Consider the example scenario of an IPS
   (Intrusion Prevention System) alert data structure containing
   multiple participants, where each participant contains multiple
   attackers and multiple targets, with each target potentially composed
   of multiple applications, as depicted below:

      alert
          signatureId
          protocolIdentifier
          riskRating
          participant 1
              attacker 1
                  sourceIPv4Address
                  applicationId
              ...
              attacker N
                  sourceIPv4Address
                  applicationId
              target 1
                  destinationIPv4Address
                  applicationId 1
                  ...
                  applicationId n
              ...
              target N
                  destinationIPv4Address
                  applicationId 1
                  ...
                  applicationId n
          participant 2
              ...

   To export this information in IPFIX, the data would need to be
   flattened (thus, losing the hierarchical relationships) and a new
   IPFIX Template created for each alert, according to the number of
   applicationId elements in each target, the number of targets and
   attackers in each participant, and the number of participants in each
   alert.  Clearly, each Template will be unique to each alert, and a
   large amount of CPU, memory, and export bandwidth will be wasted
   creating, exporting, maintaining, and withdrawing the Templates.  See
   Appendix B for a specific example related to this case study.

2.4. Specifications Summary

   This document specifies an IPFIX extension to support hierarchical
   structured data and variable-length lists by defining three new
   Information Elements and three corresponding new abstract data types
   called basicList, subTemplateList, and subTemplateMultiList.  These
   are defined in Sections 4.1 and 4.3.

   The three Structured Data Information Elements carry some semantic
   information so that the Collecting Process can understand the
   relationship between the different list elements.  The semantic in
   the Structured Data Information Elements is provided in order to
   express the relationship among the multiple top-level list elements.
   As an example, if a list is composed of the elements (A,B,C), the
   semantic expresses the relationship among A, B, and C, regardless of
   whether A, B, and C are individual elements or a list of elements.

   It is important to note that whereas the Information Elements and
   abstract data types defined in the IPFIX information model [RFC5102]
   represent single values, these new abstract data types are structural
   in nature and primarily contain references to other Information
   Elements and to Templates.  By referencing other Information Elements
   and Templates from an Information Element's data content, it is
   possible to define complex data structures such as variable-length
   lists and to specify hierarchical containment relationships between
   Templates.  Therefore, this document prefers the more generic "Data
   Record" term to the "Flow Record" term.

   This document specifies three new abstract data types, which are
   basic blocks to represent structured data.  However, this document
   does not comment on all possible combinations of basicList,
   subTemplateList, and subTemplateMultiList.  Neither does it limit the
   possible combinations.

3. Terminology

   IPFIX-specific terminology used in this document is defined in
   Section 2 of the IPFIX protocol specification [RFC5101] and Section 3
   of the PSAMP protocol specification [RFC5476].  As in [RFC5101],
   these IPFIX-specific terms have the first letter of a word
   capitalized when used in this document.

3.1. New Terminology

   Structured Data Information Element

      One of the Information Elements supporting structured data, i.e.,
      the basicList, subTemplateList, or subTemplateMultiList
      Information Elements specified in Section 4.3.

3.2. Conventions Used in This Document

   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].

4. Linkage with the IPFIX Information Model

   As in the IPFIX protocol specification [RFC5101], the new Information
   Elements specified in Section 4.3 MUST be sent in canonical format in
   network-byte order (also known as the big-endian byte ordering).

4.1. New Abstract Data Types

This document specifies three new abstract data types, as described
below.

4.1.1. basicList

   The type "basicList" represents a list of zero or more instances of
   any Information Element, primarily used for single-valued data types.
   Examples include a list of port numbers, a list of interface indexes,
   a list of AS in a BGP AS-PATH, etc.

4.1.2. subTemplateList

   The type "subTemplateList" represents a list of zero or more
   instances of a structured data type, where the data type of each list
   element is the same and corresponds with a single Template Record.
   Examples include a structured data type composed of multiple pairs of
   ("MPLS label stack entry position", "MPLS label stack value"), a
   structured data type composed of performance metrics, and a
   structured data type composed of multiple pairs of IP address, etc.

4.1.3. subTemplateMultiList

   The type "subTemplateMultiList" represents a list of zero or more
   instances of a structured data type, where the data type of each list
   element can be different and corresponds with different Template
   definitions.  Examples include a structured data type composed of

multiple access-list entries, where entries can be composed of
different criteria types.

4.2. New Data Type Semantic

   This document specifies a new data type semantic, in addition to the
   ones specified in Section 3.2 of the IPFIX information model
   [RFC5102], as described below.

4.2.1. List

   A list represents an arbitrary-length sequence of zero or more
   structured data Information Elements, either composed of regular
   Information Elements or composed of data conforming to a Template
   Record.

4.3. New Information Elements

This document specifies three new Information Elements, as described
below.

4.3.1. basicList

   A basicList specifies a generic Information Element with a basicList
   abstract data type as defined in Section 4.1.1 and list semantics as
   defined in Section 4.2.1.  Examples include a list of port numbers, a
   list of interface indexes, etc.

4.3.2. subTemplateList

   A subTemplateList specifies a generic Information Element with a
   subTemplateList abstract data type as defined in Section 4.1.2 and
   list semantics as defined in Section 4.2.1.

4.3.3. subTemplateMultiList

   A subTemplateMultiList specifies a generic Information Element with a
   subTemplateMultiList abstract data type as defined in Section 4.1.3
   and list semantics as defined in Section 4.2.1.

4.4. New Structured Data Type Semantics

   Structured data type semantics are provided in order to express the
   relationship among multiple list elements in a Structured Data
   Information Element.  These structured data type semantics require a
   new IPFIX subregistry, as specified in the "IANA Considerations"
   section.  The semantics are specified in the following subsections.

4.4.1. undefined

   The "undefined" structured data type semantic specifies that the
   semantic of list elements is not specified and that, if a semantic
   exists, then it is up to the Collecting Process to draw its own
   conclusions.  The "undefined" structured data type semantic, which is
   the default value, is used when no other structured data type
   semantic applies.

   For example, a mediator that wants to translate IPFIX [RFC5101] into
   the export of structured data according to the specifications in this
   document doesn't know what the semantic is; it can only guess, as the
   IPFIX specifications [RFC5101] does not contain any semantic.
   Therefore, the mediator should use the "undefined" semantic.

4.4.2. noneOf

   The "noneOf" structured data type semantic specifies that none of the
   elements are actual properties of the Data Record.

   For example, a mediator might want to report to a Collector that a
   specific Flow is suspicious, but that it checked already that this
   Flow does not belong to the attack type 1, attack type 2, or attack
   type 3.  So this Flow might need some further inspection.  In such a
   case, the mediator would report the Flow Record with a basicList
   composed of (attack type 1, attack type 2, attack type 3) and the
   respective structured data type semantic of "noneOf".

   Another example is a router that monitors some specific BGP AS-PATHs
   and reports if a Flow belongs to any of them.  If the router wants to
   export that a Flow does not belong to any of the monitored BGP AS-
   PATHs, the router reports a Data Record with a basicList composed of
   (BGP AS-PATH 1, BGP AS-PATH 2, BGP AS-PATH 3) and the respective
   structured data type semantic of "noneOf".

4.4.3. exactlyOneOf

   The "exactlyOneOf" structured data type semantic specifies that only
   a single element from the structured data is an actual property of
   the Data Record.  This is equivalent to a logical XOR operation.

   For example, if a Flow record contains a basicList of outgoing
   interfaces with the "exactlyOneOf" semantic, then it implies that the
   reported Flow only egressed from a single interface, although the
   Flow Record lists all of the possible outgoing interfaces.  This is a
   typical example of a per destination load-balancing.

   Another example is a mediator that must aggregate Data Records from
   different Observation Points and report an aggregated Observation
   Point.  However, the different Observation Points can be specified by
   different Information Element types depending on the Exporter.  For
   example:

      Exporter1 Observation Point is characterized by the
      exporterIPv4Address, so a specific Exporter can be represented.

      Exporter2 Observation Point is characterized by the
      exporterIPv4Address and a basicList of ingressInterface, so the
      Exporting Process can express that the observations were made on a
      series of input interfaces.

      Exporter3 Observation Point is characterized by the
      exporterIPv4Address and a specific lineCardId, so the Exporting
      Process can express that the observation was made on a specific
      linecard.

   If the mediator models the three different types of Observation
   Points with the three Template Records below:

      Template Record 1: exporterIPv4Address
      Template Record 2: exporterIPv4Address, basicList of
                         ingressInterface
      Template Record 3: exporterIPv4Address, lineCardId

   then it can represent the aggregated Observation Point with a
   subTemplateMultiList and the semantic "exactlyOneOf".  The aggregated
   Observation Point is modeled with the Data Records corresponding to
   either Template Record 1, Template Record 2, or Template Record 3 but
   not more than one of these.  This implies that the Flow was observed
   at exactly one of the Observation Points reported.

4.4.4. oneOrMoreOf

   The "oneOrMoreOf" structured data type semantic specifies that one or
   more elements from the list in the structured data are actual
   properties of the Data Record.  This is equivalent to a logical OR
   operation.

   Consider an example where a mediator must report an aggregated Flow
   (e.g., by aggregating IP addresses from IP prefixes), with an
   aggregated Observation Point.  However, the different Observation
   Points can be specified by different Information Element types as
   described in Section 4.4.2.

   If the mediator models the three different types of Observation
   Points with the three Template Records below:

          Template Record 1: exporterIPv4Address
          Template Record 2: exporterIPv4Address, basicList of
                             ingressInterface
          Template Record 3: exporterIPv4Address, lineCardId

   then it can represent the aggregated Observation Point with a
   subTemplateMultiList and the semantic "oneOrMoreOf".  The aggregated
   Observation Point is modeled with the Data Records corresponding to
   either Template Record 1, Template Record 2, or Template Record 3.
   This implies that the Flow was observed on at least one of the
   Observation Points reported, and potentially on multiple Observation
   Points.

4.4.5. allOf

   The "allOf" structured data type semantic specifies that all of the
   list elements from the structured data are actual properties of the
   Data Record.

   For example, if a Record contains a basicList of outgoing interfaces
   with the "allOf" semantic, then the observed Flow is typically a
   multicast Flow where each packet in the Flow has been replicated to
   each outgoing interface in the basicList.

4.4.6. ordered

   The "ordered" structured data type semantic specifies that elements
   from the list in the structured data are ordered.

   For example, an Exporter might want to export the AS10 AS20 AS30 AS40
   BGP AS-PATH.  In such a case, the Exporter would report a basicList
   composed of (AS10, AS20, AS30, AS40) and the respective structured
   data type semantic of "ordered".

4.5. Encoding of IPFIX Data Types

   The following subsections define the encoding of the abstract data
   types defined in Section 4.1.  These data types may be encoded using
   either fixed- or variable-length Information Elements, as discussed
   in Section 5.1.  Like in the IPFIX specifications [RFC5101], all
   lengths are specified in octets.

4.5.1. basicList

   The basicList Information Element defined in Section 4.3.1 represents
   a list of zero or more instances of an Information Element and is
   encoded 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Semantic    |0|          Field ID           |   Element...  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | ...Length     |           basicList Content ...               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 1: basicList Encoding

   Semantic

      The Semantic field indicates the relationship among the different
      Information Element values within this Structured Data Information
      Element.  Refer to IANA's "IPFIX Structured Data Types Semantics"
      registry.

   Field ID

      Field ID is the Information Element identifier of the Information
      Element(s) contained in the list.

   Element Length

      Per Section 7 of [RFC5101], the Element Length field indicates the
      length, in octets, of each list element specified by Field ID, or
      contains the value 0xFFFF if the length is encoded as a variable-
      length Information Element at the start of the basicList Content.

      Effectively, the Element Length field is part of the header, so
      even in the case of a zero-element list, it MUST NOT be omitted.

   basicList Content

      A Collecting Process decodes list elements from the basicList
      Content until no further data remains.  A field count is not
      included but can be derived when the Information Element is
      decoded.

   Note that in the diagram above, Field ID is shown with the Enterprise
   bit (most significant bit) set to 0.  Instead, if the Enterprise bit
   is set to 1, a four-byte Enterprise Number MUST be encoded
   immediately after the Element Length as shown below.  See the "Field
   Specifier Format" section in the IPFIX protocol [RFC5101] for
   additional information.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Semantic   |1|         Field ID            |   Element...  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | ...Length     |               Enterprise Number ...           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      ...      |              basicList Content ...            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 2: basicList Encoding with Enterprise Number

   Also, note that if a basicList has zero elements, the encoded data
   contains the Semantic field, Field ID, the Element Length field, and
   the four-byte Enterprise Number (if present), while the basicList
   Content is empty.

   If the basicList is encoded as a variable-length Information Element
   in less than 255 octets, it MAY be encoded with the Length field per
   Section 7 of [RFC5101] as shown in Figure 3.  However, the three-byte
   length encoding, as shown in Figure 4, is RECOMMENDED (see Section
   5.1).

    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)|   Semantic    |0|          Field ID           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Element Length        | basicList Content ...         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        Figure 3: Variable-Length basicList Encoding
                      (Length < 255 Octets)

   If the basicList is encoded as a variable-length Information Element
   in 255 or more octets, it MUST be encoded with the Length field per
   Section 7 of [RFC5101] 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      255      |      Length (0 to 65535)      |   Semantic    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|          Field ID           |        Element Length         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      basicList Content ...                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Figure 4: Variable-Length basicList Encoding
                  (Length 0 to 65535 Octets)

4.5.2. subTemplateList

   The subTemplateList Information Element represents a list of zero or
   more Data Records corresponding to a specific Template.  Because the
   Template Record referenced by a subTemplateList Information Element
   can itself contain other subTemplateList Information Elements, and
   because these Template Record references are part of the Information
   Elements content in the Data Record, it is possible to represent
   complex hierarchical data structures.  The following diagram shows
   how a subTemplateList Information Element is encoded within a Data
   Record:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Semantic    |         Template ID           |     ...       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                subTemplateList Content    ...                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 5: subTemplateList Encoding

   Semantic

      The Semantic field indicates the relationship among the different
      Data Records within this Structured Data Information Element.

   Template ID

      The Template ID field contains the ID of the Template used to
      encode and decode the subTemplateList Content.

   subTemplateList Content

      subTemplateList Content consists of zero or more instances of Data
      Records corresponding to the Template ID specified in the Template
      ID field.  A Collecting Process decodes the subTemplateList
      Content until no further data remains.  A record count is not
      included but can be derived when the subTemplateList is decoded.
      Encoding and decoding are performed recursively if the specified
      Template itself contains Structured Data Information Elements as
      described here.

   Note that, if a subTemplateList has zero elements, the encoded data
   contains only the Semantic field and the Template ID field, while the
   subTemplateList Content is empty.

   If the subTemplateList is encoded as a variable-length Information
   Element in less than 255 octets, it MAY be encoded with the Length
   field per Section 7 of [RFC5101] as shown in Figure 6.  However, the
   three-byte length encoding, as shown in Figure 7, is RECOMMENDED (see
   Section 5.1).

    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)|   Semantic    |         Template ID           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                subTemplateList Content    ...                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Figure 6: Variable-Length subTemplateList Encoding
                       (Length < 255 Octets)

   If the subTemplateList is encoded as a variable-length Information
   Element in 255 or more octets, it MUST be encoded with the Length
   field per Section 7 of [RFC5101] 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      255      |      Length (0 to 65535)      |   Semantic    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Template ID           | subTemplateList Content ...   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Figure 7: Variable-Length subTemplateList Encoding
                    (Length 0 to 65535 Octets)

4.5.3. subTemplateMultiList

   Whereas each element in a subTemplateList Information Element
   corresponds to a single Template, it is sometimes useful for a list
   to contain elements corresponding to different Templates.  To support
   this case, each top-level element in a subTemplateMultiList
   Information Element carries a Template ID, Length, and zero or more
   Data Records corresponding to the Template ID.  The following diagram
   shows how a subTemplateMultiList Information Element is encoded
   within a Data Record.  Note that the encoding following the Semantic
   field is consistent with the Set Header specified in [RFC5101].

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Semantic   |         Template ID X         |Data Records...|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | ... Length X  |        Data Record X.1 Content ...            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      ...      |        Data Record X.2 Content ...            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      ...      |        Data Record X.L Content ...            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      ...      |         Template ID Y         |Data Records...|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   | ... Length Y  |        Data Record  Y.1 Content ...           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      ...      |        Data Record Y.2 Content ...            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      ...      |        Data Record Y.M Content ...            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      ...      |         Template ID Z         |Data Records...|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | ... Length Z  |        Data Record Z.1 Content ...            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      ...      |        Data Record Z.2 Content ...            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      ...      |        Data Record Z.N Content ...            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      ...      |
   +-+-+-+-+-+-+-+-+

                Figure 8: subTemplateMultiList Encoding

   Semantic

      The Semantic field indicates the top-level relationship among the
      series of Data Records corresponding to the different Template
      Records within this Structured Data Information Element.

   Template ID

      Unlike the subTemplateList Information Element, each element of
      the subTemplateMultiList contains a Template ID that specifies the
      encoding of the following Data Records.

   Data Records Length

      This is the total length of the Data Records encoding for the
      Template ID previously specified, including the two bytes for the
      Template ID and the two bytes for the Data Records Length field
      itself.

   Data Record X.M

      The Data Record X.M consists of the Mth Data Record of the
      Template Record X.  A Collecting Process decodes the Data Records
      according to Template Record X until no further data remains,
      according to the Data Records Length X.  Further Template IDs and
      Data Records may then be decoded according to the overall
      subTemplateMultiList length.  A record count is not included but
      can be derived when the Element Content is decoded.  Encoding and
      decoding are performed recursively if the specified Template
      itself contains Structured Data Information Elements as described
      here.

   In the exceptional case of zero instances in the
   subTemplateMultiList, no data is encoded, only the Semantic field and
   Template ID field(s), and the Data Record Length field is set to
   zero.

   If the subTemplateMultiList is encoded as a variable-length
   Information Element in less than 255 octets, it MAY be encoded with
   the Length field per Section 7 of [RFC5101] as shown in Figure 9.
   However, the three-byte length encoding, as shown in Figure 10, is
   RECOMMENDED (see Section 5.1).

    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)|    Semantic   |         Template ID X         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Data Records Length X    |  Data Record X.1 Content ...  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             ...               |   Data Record X.2 Content ... |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             ...               |   Data Record X.L Content ... |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   |             ...               |         Template ID Y         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Data Records Length Y    |   Data Record Y.1 Content ... |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             ...               |   Data Record Y.2 Content ... |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             ...               |   Data Record Y.M Content ... |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             ...               |         Template ID Z         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Data Records Length Z    |   Data Record Z.1 Content ... |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             ...               |   Data Record Z.2 Content ... |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             ...               |   Data Record Z.N Content ... |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             ...               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Figure 9: Variable-Length subTemplateMultiList Encoding
                      (Length < 255 Octets)

   If the subTemplateMultiList is encoded as a variable-length
   Information Element in 255 or more octets, it MUST be encoded with
   the Length field per Section 7 of [RFC5101] 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      255      |      Length (0 to 65535)      |   Semantic    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Template ID X         |    Data Records Length X      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Data Record X.1 Content ...                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Data Record X.2 Content ...                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Data Record X.L Content ...                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Template ID Y         |    Data Records Length Y      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Data Record  Y.1 Content ...                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Data Record Y.2 Content ...                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Data Record Y.M Content ...                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Template ID Z         |    Data Records Length Z      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Data Record Z.1 Content ...               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Data Record Z.2 Content ...               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Data Record Z.N Content ...               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Figure 10: Variable-Length subTemplateMultiList Encoding
                        (Length 0 to 65535 Octets)

5. Structured Data Format

5.1. Length Encoding Considerations

The new Structured Data Information Elements represent a list that
potentially carries complex hierarchical and repeated data.

   When the encoding of a Structured Data Information Element has a
   fixed length (because, for example, it contains the same number of
   fixed-length elements, or if the permutations of elements in the list
   always produces the same total length), the element length can be
   encoded in the corresponding Template Record.

   However, when representing variable-length data, hierarchical data,
   and repeated data with variable element counts, where the number and
   length of elements can vary from record to record, we RECOMMEND that
   the Information Elements are encoded using the variable-length
   encoding described in Section 7 of [RFC5101], with the length carried
   before the Structured Data Information Element encoding.

   Because of the complex and repeated nature of the data, it is
   potentially difficult for the Exporting Process to efficiently know
   in advance the exact encoding size.  In this case, the Exporting
   Process may encode the available data starting at a fixed offset and
   fill in the final length afterwards.  Therefore, the three-byte
   length encoding is RECOMMENDED for variable-length Information
   Elements in all Template Records containing a Structured Data
   Information Element, even if the encoded length can be less than 255
   bytes, because the starting offset of the data is known in advance.

   When encoding such data, an Exporting Process MUST take care to not
   exceed the maximum allowed IPFIX message length of 65535 bytes as
   specified in [RFC5101].

5.2. Recursive Structured Data

   It is possible to define recursive relationships between IPFIX
   structured data instances, for example, when representing a tree
   structure.  The simplest case of this might be a basicList, where
   each element is itself a basicList, or a subTemplateList where one of
   the fields of the referenced Template is itself a subTemplateList
   referencing the same Template.  Also, the Exporting Process MUST take
   care when encoding recursively-defined structured data not to exceed
   the maximum allowed length of an IPFIX Message (as noted in Length
   Encoding Considerations).

5.3. Structured Data Information Elements Applicability in Options
Template Sets

   Structured Data Information Elements MAY be used in Options Template
   Sets.

   As an example, consider a mediation function that must aggregate Data
   Records from multiple Observation Point types:

      Router 1, (interface 1)
      Router 2, (linecard A)
      Router 3, (linecard B)
      Router 4, (linecard C, interface 2)

   In order to encode the PSAMP Selection Sequence Report Interpretation
   [RFC5476], the mediation function must express this combination of
   Observation Points as a single new Observation Point.  Recall from
   [RFC5476] that the PSAMP Selection Sequence Report Interpretation
   consists of the following fields:

     Scope:     selectionSequenceId
     Non-Scope: one Information Element mapping the Observation Point
                selectorId (one or more)

   Without structured data, there is clearly no way to express the
   complex aggregated Observation Point as "one Information Element
   mapping the Observation Point".  However, the desired result may be
   easily achieved using the structured data types.  Refer to Section
   9.5. for an encoding example related to this case study.

   Regarding the scope in the Options Template Record, the IPFIX
   specification [RFC5101] mentions that "the IPFIX protocol doesn't
   prevent the use of any Information Elements for scope".  Therefore, a
   Structured Data Information Element MAY be used as scope in an
   Options Template Set.

   Extending the previous example, the mediation function could export a
   given name for this complex aggregated Observation Point:

      Scope: Aggregated Observation Point (structured data)
      Non-Scope: a new Information Element containing the name

5.4. Usage Guidelines for Equivalent Data Representations

   Because basicList, subTemplateList, and subTemplateMultiList are all
   lists, in several cases, there is more than one way to represent what
   is effectively the same data structure.  However, in some cases, one
   approach has an advantage over the other, e.g., more compact, uses
   fewer resources, and is therefore preferred over an alternate
   representation.

   A subTemplateList can represent the same simple list of single-valued
   Information Elements as a basicList, if the Template referenced by
   the subTemplateList contains only one single-valued Information
   Element.  Although the encoding is more compact than a basicList by
   two bytes, using a subTemplateList, in this case, requires a new

   Template per Information Element.  The basicList requires no
   additional Template and is therefore RECOMMENDED in this case.

   Although a subTemplateMultiList with one Element can represent the
   contents of a subTemplateList, the subTemplateMultiList carries two
   additional bytes (Element Length).  It is also potentially useful to
   a Collecting Process to know in advance that a subTemplateList
   directly indicates that list element types are consistent.  The
   subTemplateList Information Element is therefore RECOMMENDED in this
   case.

   The Semantic field in a subTemplateMultiList indicates the top-level
   relationship among the series of Data Records corresponding to the
   different Template Records, within this Structured Data Information
   Element.  If a semantic is required to describe the relationship
   among the different Data Records corresponding to a single Template
   ID within the subTemplateMultiList, then an encoding based on a
   basicList of subTemplateLists should be used; refer to Section 5.6
   for more information.  Alternatively, if a semantic is required to
   describe the relationship among all Data Records within a
   subTemplateMultiList (regardless of the Template Record), an encoding
   based on a subTemplateMultiList with one Data Record corresponding to
   a single Template ID can be used.

   Note that the referenced Information Element(s) in the Structured
   Data Information Elements can be taken from the IPFIX information
   model [RFC5102], the PSAMP information model [RFC5477], any of the
   Information Elements defined in the IANA IPFIX registry [IANA-IPFIX],
   or enterprise-specific Information Elements.

   If a Template Record contains a subTemplateList as the only field, a
   Set encoding as specified in the IPFIX protocol specifications
   [RFC5101] should be considered, unless:

   - A relationship among multiple list elements must be exported, in
     which case, the semantic from the IPFIX Structured Data Information
     Element can convey this relationship.

   - The Exporting Process wants to convey the number of elements in the
     list, even in the special cases of zero or one element in the list.
     Indeed, the case of an empty list cannot be represented with the
     IPFIX protocol specifications [RFC5101].  In the case of a single
     element list, the Template Record specified in the IPFIX protocol
     specification [RFC5101] could be used.  However, on the top of the
     Template Record with the subTemplateList to export multiple list
     elements, this supplementary Template would impose some extra

     management, both on the Exporting Process and on the Collecting
     Process, which might have to correlate the information from two
     Template Records.

   Similarly, if a Template Record contains a subTemplateMultiList as
   the only field, an IPFIX Message as described in the IPFIX protocol
   specification [RFC5101] should be considered, unless:

   - A relationship among top-level list elements must be exported, in
     which case, the semantic from the IPFIX Structured Data Information
     Element can convey this relationship.

   - The Exporting Process wants to convey the number of Data Records
     corresponding to every Template in the subTemplateMultiList.

5.5. Padding

   The Exporting Process MAY insert some padding octets in structured
   data field values in a Data Record by including the 'paddingOctets'
   Information Element as described in [RFC5101], Section 3.3.1.  The
   paddingOctets Information Element can be included in a Template
   Record referenced by a structured data Information Element for this
   purpose.

5.6. Semantic

   Semantic interpretations of received Data Records at or beyond the
   Collecting Process remain explicitly undefined, unless that data is
   transmitted using this extension with explicit structured data type
   semantic information.

   It is not the Exporter's role to check the validity of the semantic
   representation of Data Records.

   More complex semantics can be expressed as a combination of the
   Semantic Data Information Elements specified in this document.

   For example, the export of the AS10 AS20 AS30 AS40 {AS50,AS60} BGP
   AS-PATH would be reported as a basicList of two elements, each
   element being a basicList of BGP AS, with the top-level structured
   data type semantic of "ordered".  The first element would contain a
   basicList composed of (AS10,AS20,AS30,AS40) and the respective
   structured data type semantic of "ordered", while the second element
   would contain a basicList composed of (AS50, AS60) and the respective
   structured data type semantic of "exactlyOneOf".  A high-level Data
   Record diagram would be represented as:

        BGP AS-PATH = (basicList, ordered,

            (basicList, ordered, AS10,AS20,AS30,AS40),

            (basicList, exactlyOneOf, AS50, AS60)

        )

   If a semantic is required to describe the relationship among the
   different Data Records corresponding to a single Template ID within
   the subTemplateMultiList, then an encoding based on a basicList of
   subTemplateLists should be used, as shown in the next case study.

    Case study 1:

   In this example, an Exporter monitoring security attacks must export
   a list of security events consisting of attackers and targets.  For
   the sake of the example, assume that the Collector can differentiate
   the attacker (which is expressed using source fields) from the target
   (which is expressed using destination fields).  Imagine that
   attackers A1 or A2 may attack targets T1 and T2.

   The first case uses a subTemplateMultiList composed of two Template
   Records, one representing the attacker and one representing the
   target, each of them containing an IP address and a port.

        Attacker Template Record = (src IP address, src port)

        Target Template Record = (dst IP address, dst port)

   A high-level Data Record diagram would be represented as:

         Alert = (subTemplateMultiList, allOf,

            (Attacker Template Record, A1, A2),

            (Target Template Record, T1, T2)

         )

   The Collecting Process can only conclude that the list of attackers
   (A1, A2) and the list of targets (T1, T2) are present, without
   knowing the relationship amongst attackers and targets.  The
   Exporting Process would have to explicitly call out the relationship
   amongst attackers and targets as the top-level semantic offered by
   the subTemplateMultiList isn't sufficient.

   The only proper encoding for the previous semantic (i.e., attacker A1
   or A2 may attack target T1 and T2) uses a basicList of
   subTemplateLists and is represented as follows:

        Attacker Template Record = (src IP address, src port)

        Target Template Record = (dst IP address, dst port)

        Alert = (basicList, allOf,

              (subTemplateList, exactlyOneOf, attacker A1, A2)

              (subTemplateList, allOf, target T1, T2)

        )

    Case study 2:

   In this example, an Exporter monitoring security attacks must export
   a list of attackers and targets.  For the sake of the example, assume
   that the Collector can differentiate the attacker (which is expressed
   using source fields) from the target (which is expressed using
   destination fields).  Imagine that attacker A1 or A2 is attacking
   target T1, while attacker A3 is attacking targets T2 and T3.  The
   first case uses a subTemplateMultiList that contains Data Records
   corresponding to two Template Records, one representing the attacker
   and one representing the target, each of them containing an IP
   address and a port.

        Attacker Template Record = (src IP address, src port)
        Target Template Record = (dst IP address, dst port)

   A high-level Data Record diagram would be represented as:

         Alert = (subTemplateMultiList, allOf,

            (Attacker Template Record, A1, A2, A3),

            (Target Template Record, T1, T2, T3)

         )

   The Collecting Process can only conclude that the list of attackers
   (A1, A2, A3), and the list of targets (T1, T2, T3) are present,
   without knowing the relationship amongst attackers and targets.

   The second case could use a Data Record definition composed of the
   following:

         Alert = (subTemplateMultiList, allOf,

            (Attacker Template Record, A1, A2),

            (Target Template Record, T1),

            (Attacker Template Record, A3),

            (Target Template Record, T2, T3)

         )

   With the above representation, the Collecting Process can infer that
   the alert consists of the list of attackers (A1, A2), target (T1),
   attacker (A3), and list of targets (T2, T3).  From the sequence in
   which attackers and targets are encoded, the Collector can possibly
   deduce that some relationship exists among (A1, A2, T1) and (A2, T1,
   T2) but cannot understand what it is exactly.  So, there is a need
   for the Exporting Process to explicitly define the relationship
   between the attackers, and targets and the top-level semantic of the
   subTemplateMultiList is not sufficient.

   The only proper encoding for the previous semantic (i.e., attacker A1
   or A2 attacks target T1, attacker A3 attacks targets T2 and T3) uses
   a basicList of subTemplateLists and is represented as follows:

        Participant P1 =

        (basicList, allOf,

              (subTemplateList, exactlyOneOf, attacker A1, A2)

              (subTemplateList, undefined, target T1)

        )

        Participant P2 =

        (basicList, allOf,

              (subTemplateList, undefined, attacker A3,

              (subTemplateList, allOf, targets T2, T3)

        )

   The security alert is represented as a subTemplateList of
   participants.

        Alert =

           (subTemplateList, allOf, Participant P1, Participant P2)

   Note that, in the particular case of a single element in a Structured
   Data Information Element, the Semantic field is actually not very
   useful since it specifies the relationship among multiple elements.
   Any choice of allOf, exactlyOneOf, or OneOrMoreOf would provide the
   same result semantically.  Therefore, in case of a single element in
   a Structured Data Information Element, the default "undefined"
   semantic SHOULD be used.

6. Template Management

   This section introduces some more specific Template management and
   Template Withdrawal Message-related specifications compared to the
   IPFIX protocol specification [RFC5101].

   First of all, the Template ID uniqueness is unchanged compared to
   [RFC5101]; the uniqueness is local to the Transport Session and
   Observation Domain that generated the Template ID.  In other words,
   the Set ID used to export the Template Record does not influence the
   Template ID uniqueness.

   While [RFC5101] mentions that "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", this rule MAY be ignored within
   Structured Data Information Elements.

   As specified in [RFC5101], Templates that are not used anymore SHOULD
   be deleted.  Deleting a Template implies that it MUST NOT be used
   within subTemplateList and subTemplateMultiList anymore.  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.

7. The Collecting Process's Side

   This section introduces some more specific specifications to the
   Collection Process compared to Section 9 in the IPFIX protocol
   [RFC5101].

   As opposed to the IPFIX specification in [RFC5101], IPFIX Messages
   with IPFIX Structured Data Information Elements change the IPFIX

   concept from the Collector's point of view as the data types are
   present in the Data Records rather than in the Template Records.  For
   example, a basicList Information Element in a Template Record doesn't
   specify the list element data type; this information is contained in
   the Data Record.  For example, in case of a subTemplateMultiList, the
   Collecting Process must refer to the included Template Records in the
   middle of the Data Record decode.

   As described in [RFC5101], a 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.  Therefore, a Collection Process that does not support
   the extension specified in this document can ignore the Structured
   Data Information Elements in a Data Record, or it can ignore Data
   Records containing these new Structured Data Information Elements
   while continuing to process other Data Records.

   If the structured data contains the "undefined" structured data type
   semantic, the Collecting Process MAY attempt to draw its own
   conclusion in terms of the semantic contained in the Data Record.

8. Defining New Information Elements Based on the New Abstract Data
Types

   This document specifies three new abstract data types: basicList,
   subTemplateList, and subTemplateMultiList.  As specified in
   [RFC5102], the specification of new IPFIX Information Elements uses
   the Template specified in Section 2.1 of [RFC5102].  This Template
   mentioned existing and future the data types: "One of the types
   listed in Section 3.1 of this document or in a future extension of
   the information model".  So new Information Elements can be specified
   based on the three new abstract data types.

   The authors anticipate the creation of both enterprise-specific and
   IANA Information Elements based on the IPFIX structured data types.
   For example, bgpPathList, bgpSequenceList, and bgpSetList, of
   abstract types and semantics basicList/ordered, basicList/ordered,
   and basicList/exactlyOneOf respectively, would define the complete
   semantic of the list.  This specification doesn't specify any new
   Information Elements beyond the ones in Section 4.3.

9. Structured Data Encoding Examples

   The following examples are created solely for the purpose of
   illustrating how the extensions proposed in this document are
   encoded.

9.1. Encoding a Multicast Data Record with basicList

   Consider encoding a multicast Data Record containing the following
   data:

   ---------------------------------------------------------------
    Ingress If | Source IP   | Destination IP  | Egress Interfaces
   ---------------------------------------------------------------
         9       192.0.2.201      233.252.0.1         1, 4, 8
   ---------------------------------------------------------------

   Template Record for the multicast Flows, with the Template ID 256:

    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 = 24 octets       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Template ID = 256       |       Field Count = 4         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|    ingressInterface = 10    |       Field Length = 4        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|   sourceIPv4Address = 8     |       Field Length = 4        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0| DestinationIPv4Address = 12 |       Field Length = 4        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|       basicList = 291       |     Field Length = 0xFFFF     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 11: Encoding basicList, Template Record

   The list of outgoing interfaces is represented as a basicList with
   semantic allOf, and the Length of the list is chosen to be encoded in
   three bytes even though it may be less than 255 octets.

   The Data Set is represented 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 = 256         |          Length = 36          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     ingressInterface = 9                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               sourceIPv4Address = 192.0.2.201                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             DestinationIPv4Address = 233.252.0.1              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      255      |        List Length = 17       | semantic=allOf|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | egressInterface FieldId = 14  |egressInterface Field Length=4 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                egressInterface value 1 = 1                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                egressInterface value 2 = 4                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                egressInterface value 3 = 8                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        Figure 12: Encoding basicList, Data Record, Semantic allOf

   In the example above, the basicList contains fixed-length elements.
   To illustrate how variable-length elements would be encoded, the same
   example is shown below with variable-length interface names in the
   basicList instead:

    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 = 44          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     ingressInterface = 9                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               sourceIPv4Address = 192.0.2.201                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             DestinationIPv4Address = 233.252.0.1              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      255      |        List Length = 25       | semantic=allOf|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0| InterfaceName FieldId = 82  | InterfaceName Field Len=0xFFFF|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Length = 5   |      'F'      |      'E'      |      '0'      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     '/'       |      '0'      |  Length = 7   |      'F'      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     'E'       |      '1'      |      '0'      |      '/'      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     '1'       |      '0'      |  Length = 5   |      'F'      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     'E'       |      '2'      |     '/'       |      '2'      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Figure 13: Encoding basicList, Data Record with Variable-Length
                       Elements, Semantic allOf

9.2. Encoding a Load-Balanced Data Record with a basicList

   Consider encoding a load-balanced Data Record containing the
   following data:

   ---------------------------------------------------------------
    Ingress If | Source IP   | Destination IP  | Egress Interfaces
   ---------------------------------------------------------------
         9       192.0.2.201      233.252.0.1         1, 4, 8
   ---------------------------------------------------------------

   So the Data Record egressed from either interface 1, 4, or 8.  The
   Data Set is represented 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 = 256         |          Length = 36          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     ingressInterface = 9                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               sourceIPv4Address = 192.0.2.201                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             DestinationIPv4Address = 233.252.0.1              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      255      |        List Length = 17       |sem=exactlyOne |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | egressInterface FieldId = 14  |egressInterface Field Length=4 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                egressInterface value 1 = 1                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                egressInterface value 2 = 4                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                egressInterface value 3 = 8                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Note: sem=exactlyOne represents semantic=exactlyOneOf

     Figure 14: Encoding basicList, Data Record, Semantic exactlyOneOf

9.3. Encoding subTemplateList

   As explained in Section 2.2, multiple pairs of
   (observationTimeMicroseconds, digestHashValue) must be collected from
   two different Observation Points to passively compute the one-way
   delay across the network.  This data can be exported with an
   optimized Data Record that consists of the following attributes:

       5-tuple
                 { observationTimeMicroseconds 1, digestHashValue 1 }
                 { observationTimeMicroseconds 2, digestHashValue 2 }
                 { observationTimeMicroseconds 3, digestHashValue 3 }
                 { ...  , ... }

   A subTemplateList is best suited for exporting the list of
   (observationTimeMicroseconds, digestHashValue).  For illustration
   purposes, the number of elements in the list is 5; in practice, it
   could be more.

   ------------------------------------------------------------------
   srcIP     | dstIP      | src   | dst  |proto| one-way delay
             |            | Port  | Port |     |   metrics
   ------------------------------------------------------------------
   192.0.2.1  192.0.2.105   1025     80     6    Time1, 0x0x91230613
                                                 Time2, 0x0x91230650
                                                 Time3, 0x0x91230725
                                                 Time4, 0x0x91230844
                                                 Time5, 0x0x91230978
   ------------------------------------------------------------------

   The following Template is defined for exporting the one-way delay
   metrics:

    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 = 16 octets       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Template ID = 257       |       Field Count = 2         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0| observationTimeMicroSec=324 |       Field Length = 8        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|   digestHashValue = 326     |       Field Length = 4        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Figure 15: Encoding subTemplateList, Template for One-Way Delay
                                 Metrics

   The Template Record for the Optimized Data Record 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 = 2            |      Length = 32 octets       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Template ID = 258       |       Field Count = 6         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|   sourceIPv4Address = 8     |       Field Length = 4        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0| destinationIPv4Address = 12 |       Field Length = 4        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|  sourceTransportPort = 7    |       Field Length = 2        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0| destinationTransportPort= 11|       Field Length = 2        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0| protocolIdentifier = 4      |       Field Length = 1        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|  subTemplateList = 292      |     Field Length = 0xFFFF     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 16: Encoding subTemplateList, Template Record

   The list of (observationTimeMicroseconds, digestHashValue) is
   exported as a subTemplateList with semantic allOf.  The Length of the
   subTemplateList is chosen to be encoded in three bytes even though it
   may be less than 255 octets.

   The Data Record is represented 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 = 258          |      Length = 83 octets       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                sourceIPv4Address = 192.0.2.1                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              destinationIPv4Address = 192.0.2.105             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | sourceTransportPort = 1025    | destinationTransportPort = 80 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Protocol = 6  |      255      | one-way metrics list len = 63 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | semantic=allOf|       TemplateID = 257        | TimeValue1    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 ... octets 2-5 of TimeValue1                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   |          ... octets 6-8 of TimeValue1         |digestHashVal1=|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                ... 0x0x91230613               | TimeValue2    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 ... octets 2-5 of TimeValue2                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          ... octets 6-8 of TimeValue2         |digestHashVal2=|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                ... 0x0x91230650               | TimeValue3    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 ... octets 2-5 of TimeValue3                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          ... octets 6-8 of TimeValue3         |digestHashVal3=|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                ... 0x0x91230725               | TimeValue4    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 ... octets 2-5 of TimeValue4                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          ... octets 6-8 of TimeValue4         |digestHashVal4=|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                ... 0x0x91230844               | TimeValue5    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 ... octets 2-5 of TimeValue5                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          ... octets 6-8 of TimeValue5         |digestHashVal5=|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                ... 0x0x91230978               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 17: Encoding subTemplateList, Data Set

9.4. Encoding subTemplateMultiList

   As explained in Section 4.5.3, a subTemplateMultiList is used to
   export a list of mixed-type content where each top-level element
   corresponds to a different Template Record.

   To illustrate this, consider the Data Record with the following
   attributes:

        5-tuple (Flow Keys), octetCount, packetCount
                  attributes for filtering
                       selectorId,
                       selectorAlgorithm
                  attributes for sampling
                       selectorId,
                       selectorAlgorithm,
                       samplingPacketInterval,
                       samplingPacketSpace

   This example demonstrates that the Selector Report Interpretation
   [RFC5476] can be encoded with the subTemplateMultiList.  More
   specifically, the example describes Property Match Filtering Selector
   Report Interpretation [RFC5476] used for filtering purposes, and the
   Systemic Count-Based Sampling as described in Section 6.5.2.1 of
   [RFC5476].  Some traffic will be filtered according to match
   properties configured, some will be sampled, some will be filtered
   and sampled, and some will not be filtered or sampled.

   A subTemplateMultiList is best suited for exporting this variable
   data.  A Template is defined for filtering attributes and another
   Template is defined for sampling attributes.  A Data Record can
   contain data corresponding to either of the Templates, both of them,
   or neither of them.

   Consider the example below where the following Data Record contains
   both filtering and sampling attributes.

   Key attributes of the Data Record:

   ------------------------------------------------------------------
   srcIP      | dstIP     | src  | dst  | proto | octetCount | packet
              |           | Port | Port |       |            | Count
   ------------------------------------------------------------------
   2001:DB8::1 2001:DB8::2  1025    80      6       108000      120
   ------------------------------------------------------------------

   Filtering attributes:

   -------------------------------------------
   selectorId  | selectorAlgorithm
   -------------------------------------------
      100         5 (Property Match Filtering)
   -------------------------------------------

   Sampling attributes:

   For Systemic Count-Based Sampling as defined in Section 6.5.2.1 of
   [RFC5476] the required algorithm-specific Information Elements are:

         samplingPacketInterval: number of packets selected in a row
         samplingPacketSpace:    number of packets between selections

   Example of a simple 1-out-of-100 systematic count-based Selector
   definition, where the samplingPacketInterval is 1 and the
   samplingPacketSpace is 99.

   --------------------------------------------------------------
   selectorId | selectorAlgorithm        | sampling | sampling
              |                          | Packet   | Packet
              |                          | Interval | Space
   --------------------------------------------------------------
      15        1 (Count-Based Sampling)      1         99
   --------------------------------------------------------------

   To represent the Data Record, the following Template Records are
   defined:

       Template for filtering attributes: 259
        Template for sampling attributes: 260
        Template for Flow Record: 261

        Flow record (261)
            |  (sourceIPv6Address)
            |  (destinationIPv6Address)
            |  (sourceTransportPort)
            |  (destinationTransportPort)
            |  (protocolIdentifier)
            |  (octetTotalCount)
            |  (packetTotalCount)
            |
            +------ filtering attributes (259)
            |          (selectorId)
            |          (selectorAlgorithm)
            |
            +------ sampling attributes (260)
            |          (selectorId)
            |          (selectorAlgorithm)
            |          (samplingPacketInterval)
            |          (samplingPacketSpace)

   The following Template Record is defined for filtering attributes:

    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 = 16          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Template ID = 259        |        Field Count = 2        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|    selectorId = 302         |        Field Length = 4       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0| selectorAlgorithm = 304     |        Field Length = 1       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Figure 18: Encoding subTemplateMultiList, Template for Filtering
                               Attributes

   The Template for sampling attributes is defined 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 = 2           |          Length = 24          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Template ID = 260        |        Field Count = 4        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|    selectorId = 302         |        Field Length = 4       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|  selectorAlgorithm = 304    |        Field Length = 1       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0| samplingPacketInterval = 305|        Field Length = 1       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0| samplingPacketSpace = 306   |        Field Length = 1       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Figure 19: Encoding subTemplateMultiList, Template for Sampling
                               Attributes

   Note that while selectorAlgorithm is defined as unsigned16, and
   samplingPacketInterval and samplingPacketSpace are defined as
   unsigned32, they are compressed down to 1 octet here as allowed by
   Reduced Size Encoding in Section 6.2 of the IPFIX protocol
   specifications [RFC5101].

   Template for the Flow Record is defined as shown below:

    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 = 40          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Template ID = 261        |        Field Count = 8        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|   sourceIPv6Address = 27    |       Field Length = 16       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0| destinationIPv6Address = 28 |       Field Length = 16       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0| sourceTransportPort = 7     |       Field Length = 2        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0| destinationTransportPort=11 |       Field Length = 2        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0| protocolIdentifier = 4      |       Field Length = 1        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|   octetTotalCount = 85      |       Field Length = 4        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|   packetTotalCount = 86     |       Field Length = 4        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0| subTemplateMultiList = 293  |     Field Length = 0XFFFF     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Figure 20: Encoding subTemplateMultiList, Template for Flow Record

   A subTemplateMultiList with semantic allOf is used to export the
   filtering and sampling attributes.  The Length field of the
   subTemplateMultiList is chosen to be encoded in three bytes even
   though it may be less than 255 octets.

   The Data Record is encoded 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 = 261            |          Length = 73          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      sourceIPv6Address =        ...           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          2001:DB8::1                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   |                   destinationIPv6Address =      ...           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          2001:DB8::2                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  sourceTransportPort = 1025   | destinationTransportPort = 80 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | protocol = 6  |        octetTotalCount = 108000               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     ...       |        packetTotalCount = 120                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     ...       |      255      | Attributes List Length = 21   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |semantic=allOf | Filtering Template ID = 259   |Filtering Attr |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | ...Length = 9 |              selectorId = ...                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | ...  100      |selectorAlg = 5|  Sampling Template ID = 260   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Sampling Attributes Length=11 |         selectorId = ...      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  ...         15               |selectorAlg = 1|  Interval = 1 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Space = 99    |
   +-+-+-+-+-+-+-+-+

           Figure 21: Encoding subTemplateMultiList, Data Set

9.5. Encoding an Options Template Set Using Structured Data

   As described in Section 5.3, consider a mediation function that must
   aggregate Data Records from different Observation Points.

   Say Observation Point 1 consists of one or more interfaces,
   Observation Points 2 and 3 consist of one or more linecards, and
   Observation Point 4 consists of one or more interfaces and one or
   more linecards.  Without structured data, a Template would have to be
   defined for every possible combination to interpret the data
   corresponding to each of the Observation Points.  However, with
   structured data, a basicList can be used to encode the list of
   interfaces and another basicList can be used to encode the list of
   linecards.

   For the sake of simplicity, each Observation Point shown below has
   the IP address corresponding to the Router and an <interface> or
   <linecard> or <linecard and interface>.  This can very well be
   extended to include a list of interfaces and a list of linecards
   using basicLists as explained above.

      Observation Point 1: Router 1, (interface 1)
      Observation Point 2: Router 2, (linecard A)
      Observation Point 3: Router 3, (linecard B)
      Observation Point 4: Router 4, (linecard C, interface 2)

   The mediation function wishes to express this as a single Observation
   Point, in order to encode the PSAMP Selection Sequence Report
   Interpretation (SSRI).  Recall from [RFC5476] that the PSAMP
   Selection Sequence Report Interpretation consists of the following
   fields:

     Scope:     selectionSequenceId
     Non-Scope: one Information Element mapping the
                Observation Point
                selectorId (one or more)

   For example, the Observation Point detailed above may be encoded in a
   PSAMP Selection Sequence Report Interpretation as shown below:

    Selection Sequence 7 (Filter->Sampling):
     Observation Point: subTemplateMultiList.
      Router 1 (IP address = 192.0.2.11), (interface 1)
      Router 2 (IP address = 192.0.2.12), (linecard A)
      Router 3 (IP address = 192.0.2.13), (linecard B)
      Router 4 (IP address = 192.0.2.14), (linecard C, interface 2)
      selectorId: 5 (Filter, match IPv4SourceAddress 192.0.2.1)
      selectorId: 10 (Sampler, Random 1 out-of ten)

   The following Templates are defined to represent the PSAMP SSRI:
   Template for representing PSAMP SSRI: 262
   Template for representing interface: 263
   Template for representing linecard: 264
   Template for representing linecard and interface: 265

    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 = 16          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Template ID = 263      |         Field Count = 2       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|   exporterIPv4Address = 8   |        Field Length = 4       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|   ingressInterface = 10     |        Field Length = 4       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 24: PSAMP SSRI, Template Record for interface

    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 = 16          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Template ID = 264      |         Field Count = 2       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|   exporterIPv4Address = 8   |         Field Length = 4      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|      lineCardId = 141       |         Field Length = 4      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

          Figure 25: PSAMP SSRI, Template Record for linecard

    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 = 20          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Template ID = 265      |         Field Count = 3       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|   exporterIPv4Address = 8   |       Field Length = 4        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|      lineCardId = 141       |        Field Length = 4       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|    ingressInterface = 10    |        Field Length = 4       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Figure 26: PSAMP SSRI, Template Record for linecard and interface

   The PSAMP SSRI Data Set is represented 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 = 262         |           Length = 68         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    selectionSequenceId = 7                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      255      | Observation Point List Len=49 |semantic=allOf |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     OP1 Template ID = 263     |        OP1 Length = 12        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Router 1 exporterIPv4Address = 192.0.2.11             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  OP1 ingressInterface = 1                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   OP2&OP3 Template ID = 264   |    OP2 & OP3 Length = 20      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Router 2 exporterIPv4Address = 192.0.2.12             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      OP2 lineCardId = A                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Router 3 exporterIPv4Address = 192.0.2.13             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      OP3 lineCardId = B                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     OP4 Template ID = 265     |         OP4 Length = 16       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Router 4 exporterIPv4Address = 192.0.2.14             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      OP4 lineCardId = C                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   OP4 ingressInterface = 2                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         selectorId = 5                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         selectorId = 10                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Figure 27: Example of a PSAMP SSRI Data Record, Encoded Using a
                         subTemplateMultiList

   Note that the Data Record above contains multiple instances of
   Template 264 to represent Observation Point 2 (Router2, linecard A)
   and Observation Point 3 (Router3, linecard B).  Instead, if a single
   Observation Point had both linecard A and linecard B, a basicList
   would be used to represent the list of linecards.

10. Relationship with the Other IPFIX Documents

10.1. Relationship with Reducing Redundancy

   "Reducing Redundancy in IP Flow Information Export (IPFIX) and Packet
   Sampling (PSAMP) Reports" [RFC5473] describes a bandwidth saving
   method for exporting Flow or packet information using the IP Flow
   Information Export (IPFIX) protocol.

   It defines the commonPropertiesID Information Element for exporting
   Common Properties.

10.1.1. Encoding Structured Data Element Using Common Properties

   When Structured Data Information Elements contain repeated elements,
   these elements may be replaced with a commonPropertiesID Information
   Element as specified in [RFC5473].  The replaced elements may include
   the basicList, subTemplateList, and subTemplateMultiList Information
   Elements.

   This technique might help reducing the bandwidth requirements for the
   export.  However, a detailed analysis of the gain has not been done;
   refer to Section 8.3 of [RFC5473] for further considerations.

10.1.2. Encoding Common Properties Elements with Structured Data
Information Element

   Structured Data Information Element MAY be used to define a list of
   commonPropertiesID, as a replacement for the specifications in
   [RFC5473].

   Indeed, the example in Figures 1 and 2 of [RFC5473] can be encoded
   with the specifications in this document.

   +----------------+-------------+---------------------------+
   | sourceAddressA | sourcePortA |     <Flow1 information>   |
   +----------------+-------------+---------------------------+
   | sourceAddressA | sourcePortA |     <Flow2 information>   |
   +----------------+-------------+---------------------------+
   | sourceAddressA | sourcePortA |     <Flow3 information>   |
   +----------------+-------------+---------------------------+
   | sourceAddressA | sourcePortA |     <Flow4 information>   |
   +----------------+-------------+---------------------------+
   |      ...       |     ...     |            ...            |
   +----------------+-------------+---------------------------+

   Figure 28: Common and Specific Properties Exported Together
                              [RFC5473]

   +------------------------+-----------------+-------------+
   | index for properties A | sourceAddressA  | sourcePortA |
   +------------------------+-----------------+-------------+
   |          ...           |      ...        |     ...     |
   +------------------------+-----------------+-------------+

   +------------------------+---------------------------+
   | index for properties A |     <Flow1 information>   |
   +------------------------+---------------------------+
   | index for properties A |     <Flow2 information>   |
   +------------------------+---------------------------+
   | index for properties A |     <Flow3 information>   |
   +------------------------+---------------------------+
   | index for properties A |     <Flow4 information>   |
   +------------------------+---------------------------+

   Figure 29: Common and Specific Properties Exported Separately
                     According to [RFC5473]

   +----------------+-------------+---------------------------+
   | sourceAddressA | sourcePortA |     <Flow1 information>   |
   +----------------+-------------+---------------------------+
                                  |     <Flow2 information>   |
                                  +---------------------------+
                                  |     <Flow3 information>   |
                                  +---------------------------+
                                  |     <Flow4 information>   |
                                  +---------------------------+
                                  |            ...            |
                                  +---------------------------+

    Figure 30: Common and Specific Properties Exported with
                 Structured Data Information Element

   The example in Figure 28 could be encoded with a basicList if the
   <Flow information> represents a single Information Element, with a
   subTemplateList if the <Flow information> represents a Template
   Record, or with a subTemplateMultiList if the <Flow information> is
   composed of different Template Records.

   Using Structured Data Information Elements as a replacement for the
   techniques specified in "Reducing Redundancy in IP Flow Information
   Export (IPFIX) and Packet Sampling (PSAMP) Reports" [RFC5473] offers
   the advantage that a single Template Record is defined.  Hence, the
   Collector's job is simplified in terms of Template management and
   combining Template/Options Template Records.

   However, it must be noted that using Structured Data Information
   Elements as a replacement for the techniques specified in "Reducing
   Redundancy in IP Flow Information Export (IPFIX) and Packet Sampling
   (PSAMP) Reports" only applies to simplified cases.  For example, the
   "Multiple Data Reduction" (Section 7.1 [RFC5473]) might be too
   complex to encode with Structured Data Information Elements.

10.2. Relationship with Guidelines for IPFIX Testing

   [RFC5471] presents a list of tests for implementers of IP Flow
   Information Export (IPFIX) compliant Exporting Processes and
   Collecting Processes.

   Although [RFC5471] doesn't define any structured data element
   specific tests, the Structured Data Information Elements can be used
   in many of the [RFC5471] tests.

   The [RFC5471] series of test could be useful because the document
   specifies that every Information Element type should be tested.
   However, not all cases from this document are tested in [RFC5471].

   The following sections are especially noteworthy:

3.2.1. Transmission of Template with Fixed-Size Information
Elements

         - each data type should be used in at least one test.  The new
           data types specified in Section 4.1 should be included in
           this test.

3.2.2. Transmission of Template with Variable-Length Information
Elements

         - this test should be expanded to include Data Records
           containing variable length basicList, subTemplateList, and
           subTemplateMultiList Information Elements.

3.3.1. Enterprise-Specific Information Elements

         - this test should include the export of basicList,
           subTemplateList, and subTemplateMultiList Information
           Elements containing Enterprise-specific Information Elements,
           e.g., see the example in Figure 2.

3.3.3. Multiple Instances of the Same Information Element in One
Template

         - this test should verify that multiple instances of the
           basicList, subTemplateList, and subTemplateMultiList
           Information Elements are accepted.

3.5. Stress/Load Tests

         - since the structured data types defined here allow modeling
           of complex data structures, they may be useful for stress
           testing both Exporting Processes and Collecting Processes.

10.3. Relationship with IPFIX Mediation Function

   The Structured Data Information Elements would be beneficial for the
   export of aggregated Data Records in mediation function, as was
   demonstrated with the example of the aggregated Observation Point in
   Section 5.3.

11. IANA Considerations

   This document specifies several new IPFIX abstract data types, a new
   IPFIX Data Type Semantic, and several new Information Elements.

   Two new IPFIX registries have been created, and the existing IPFIX
   Information Element registry has been updated as detailed below.

11.1. New Abstract Data Types

   Section 4.1 of this document specifies several new IPFIX abstract
   data types.  Per Section 6 of the IPFIX information model [RFC5102],
   new abstract data types can be added to the IPFIX information model
   in the IPFIX Information Element Data Types registry.

   Abstract data types that have been added to the IPFIX Information
   Element Data Types registry are listed below.

11.1.1. basicList

The type "basicList" represents a list of any Information Element
used for single-valued data types.

11.1.2. subTemplateList

   The type "subTemplateList" represents a list of a structured data
   type, where the data type of each list element is the same and
   corresponds with a single Template Record.

11.1.3. subTemplateMultiList

   The type "subTemplateMultiList" represents a list of structured data
   types, where the data types of the list elements can be different and
   correspond with different Template definitions.

11.2. New Data Type Semantics

   Section 4.2 of this document specifies a new IPFIX Data Type
   Semantic.  Per Section 3.2 of the IPFIX information model [RFC5102],
   new data type semantics can be added to the IPFIX information model.
   Therefore, the IANA IPFIX informationElementSemantics registry
   [IANA-IPFIX], which contains all the data type semantics from Section
   3.2 of [RFC5102], has been augmented with the "list" value below.

11.2.1. list

A list is a structured data type, being composed of a sequence of
elements, e.g., Information Element, Template Record.

11.3. New Information Elements

   Section 4.3 of this document specifies several new Information
   Elements that have been created in the IPFIX Information Element
   registry [IANA-IPFIX].

   New Information Elements that have been added to the IPFIX
   Information Element registry are listed below.

11.3.1. basicList

   Name: basicList
   Description:
   Specifies a generic Information Element with a basicList abstract
   data type.  Examples include a list of port numbers, and a list of
   interface indexes.
   Abstract Data Type: basicList
   Data Type Semantics: list
   ElementId: 291
   Status: current

11.3.2. subTemplateList

   Name: subTemplateList
   Description:
   Specifies a generic Information Element with a subTemplateList
   abstract data type.
   Abstract Data Type: subTemplateList
   Data Type Semantics: list
   ElementId: 292
   Status: current

11.3.3. subTemplateMultiList

   Name: subTemplateMultiList
   Description:
   Specifies a generic Information Element with a
   subTemplateMultiList abstract data type.
   Abstract Data Type: subTemplateMultiList
   Data Type Semantics: list
   ElementId: 293
   Status: current

11.4. New Structured Data Semantics

   Section 4.4 of this document specifies a series of new IPFIX
   structured data type semantics, which is expressed as an 8-bit value.
   This requires the creation of a new "IPFIX Structured Data Types
   Semantics" IPFIX subregistry [IANA-IPFIX].

   Entries may be added to this subregistry subject to a Standards
   Action [RFC5226].  Initially, this registry includes all the
   structured data type semantics listed below.

11.4.1. undefined

   Name: undefined

   Description: The "undefined" structured data type semantic specifies
   that the semantic of list elements is not specified and that, if a
   semantic exists, then it is up to the Collecting Process to draw its
   own conclusions.  The "undefined" structured data type semantic is
   the default structured data type semantic.

   Value: 0xFF

   Reference: RFC 6313

11.4.2. noneOf

   Name: noneOf

   Description: The "noneOf" structured data type semantic specifies
   that none of the elements are actual properties of the Data Record.

   Value: 0x00

   Reference: RFC 6313

11.4.3. exactlyOneOf

   Name: exactlyOneOf

   Description: The "exactlyOneOf" structured data type semantic
   specifies that only a single element from the structured data is an
   actual property of the Data Record.  This is equivalent to a logical
   XOR operation.

   Value: 0x01

   Reference: RFC 6313

11.4.4. oneOrMoreOf

   Name: oneOrMoreOf

   Description: The "oneOrMoreOf" structured data type semantic
   specifies that one or more elements from the list in the structured
   data are actual properties of the Data Record.  This is equivalent to
   a logical OR operation.

   Value: 0x02

   Reference: RFC 6313

11.4.5. allOf

   Name: allOf

   Description: The "allOf" structured data type semantic specifies that
   all of the list elements from the structured data are actual
   properties of the Data Record.

   Value: 0x03

   Reference: RFC 6313

11.4.6. ordered

   Name: ordered Description: The "ordered" structured data type
   semantic specifies that elements from the list in the structured data
   are ordered.

   Value: 0x04

   Reference: RFC 6313

12. Security Considerations

   The addition of complex data types necessarily complicates the
   implementation of the Collector.  This could easily result in new
   security vulnerabilities (e.g., buffer overflows); this creates
   additional risk in cases where either Datagram Transport Layer
   Security (DTLS) is not used or if the Observation Point and Collector
   belong to different trust domains.  Otherwise, the same security
   considerations as for the IPFIX protocol [RFC5101] and the IPFIX
   information model [RFC5102] apply.

13. References

13.1. Normative References

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

   [RFC5101]    Claise, B., Ed., "Specification of the IP Flow
                Information Export (IPFIX) Protocol for the Exchange of
                IP Traffic Flow Information", RFC 5101, January 2008.

   [RFC5102]    Quittek, J., Bryant, S., Claise, B., Aitken, P., and J.
                Meyer, "Information Model for IP Flow Information
                Export", RFC 5102, January 2008.

   [RFC5226]    Narten, T. and H. Alvestrand, "Guidelines for Writing an
                IANA Considerations Section in RFCs", BCP 26, RFC 5226,
                May 2008.

13.2. Informative References

   [RFC3917]    Quittek, J., Zseby, T., Claise, B., and S. Zander,
                "Requirements for IP Flow Information Export (IPFIX)",
                RFC 3917, October 2004.

   [RFC5103]    Trammell, B. and E. Boschi, "Bidirectional Flow Export
                Using IP Flow Information Export (IPFIX)", RFC 5103,
                January 2008.

   [RFC5470]    Sadasivan, G., Brownlee, N., Claise, B., and J. Quittek,
                "Architecture for IP Flow Information Export", RFC 5470,
                March 2009.

   [RFC5471]    Schmoll, C., Aitken, P., and B. Claise, "Guidelines for
                IP Flow Information Export (IPFIX) Testing", RFC 5471,
                March 2009.

   [RFC5472]    Zseby, T., Boschi, E., Brownlee, N., and B. Claise, "IP
                Flow Information Export (IPFIX) Applicability", RFC
                5472, March 2009.

   [RFC5473]    Boschi, E., Mark, L., and B. Claise, "Reducing
                Redundancy in IP Flow Information Export (IPFIX) and
                Packet Sampling (PSAMP) Reports", RFC 5473, March 2009.

   [RFC5475]    Zseby, T., Molina, M., Duffield, N., Niccolini, S., and
                F. Raspall, "Sampling and Filtering Techniques for IP
                Packet Selection", RFC 5475, March 2009.

   [RFC5476]    Claise, B., Ed., Johnson, A., and J. Quittek, "Packet
                Sampling (PSAMP) Protocol Specifications", RFC 5476,
                March 2009.

   [RFC5477]    Dietz, T., Claise, B., Aitken, P., Dressler, F., and G.
                Carle, "Information Model for Packet Sampling Exports",
                RFC 5477, March 2009.

   [IANA-IPFIX] IANA, "IP Flow Information Export (IPFIX) Entities",
                <http://www.iana.org/>.

14. Acknowledgements

   The authors would like to thank Zhipu Jin, Nagaraj Varadharajan,
   Brian Trammel, Atsushi Kobayashi, and Rahul Patel for their feedback,
   and Gerhard Muenz, for proofreading the document.

Appendix A. Additions to XML Specification of IPFIX Information
Elements and Abstract Data Types

   This appendix contains additions to the machine-readable description
   of the IPFIX information model coded in XML in Appendices A and B in
   [RFC5102].  Note that this appendix is of informational nature, while
   the text in Section 4 (generated from this appendix) is normative.

   The following field definitions are appended to the IPFIX information
   model in Appendix A of [RFC5102].

   <field name="basicList"
           dataType="basicList"
           group="structured-data"
           dataTypeSemantics="List"
           elementId="291" applicability="all" status="current">
      <description>
        <paragraph>
           Represents a list of zero or more instances of
           any Information Element, primarily used for
           single-valued data types.  Examples include a list of port
           numbers, list of interface indexes, and a list of AS in a
           BGP AS-PATH.
        </paragraph>
      </description>
    </field>

    <field name="subTemplateList"
           dataType="subTemplateList"
           group="structured-data"
           dataTypeSemantics="List"
           elementId="292" applicability="all" status="current">
      <description>
        <paragraph>
           Represents a list of zero or more instances of a
           structured data type, where the data type of each list
           element is the same and corresponds with a single
           Template Record.  Examples include a structured data type
           composed of multiple pairs of ("MPLS label stack entry
           position", "MPLS label stack value"), a structured data
           type composed of performance metrics, and a structured data
           type composed of multiple pairs of IP address.
        </paragraph>
      </description>
    </field>

    <field name="subTemplateMultiList"
           dataType="subTemplateMultiList"
           group="structured-data"
           dataTypeSemantics="List"
           elementId="293" applicability="all" status="current">
      <description>
        <paragraph>
          Represents a list of zero or more instances of
          structured data types, where the data type of each list
          element can be different and corresponds with
          different Template definitions.  Examples include, a
          structured data type composed of multiple access-list
          entries, where entries can be composed of different
          criteria types.
        </paragraph>
      </description>
    </field>

   The following structured data type semantic definitions are appended
   to the IPFIX information model in Appendix A of [RFC5102].

   <structuredDataTypeSemantics>
     <structuredDataTypeSemantic name="undefined" value="255">
       <description>
         <paragraph>
          The "undefined" structured data type semantic specifies
          that the semantic of list elements is not specified and
          that, if a semantic exists, then it is up to the
          Collecting Process to draw its own conclusions.  The
          "undefined" structured data type semantic is the default
          structured data type semantic.
         </paragraph>
       </description>
     </structuredDataTypeSemantic>

     <structuredDataTypeSemantic name="noneOf" value="0">
       <description>
         <paragraph>
          The "noneOf" structured data type semantic specifies
          that none of the elements are actual properties of the
          Data Record.
         </paragraph>
       </description>
     </structuredDataTypeSemantic>

     <structuredDataTypeSemantic name="exactlyOneOf" value="1">
       <description>
         <paragraph>
          The "exactlyOneOf" structured data type semantic
          specifies that only a single element from the structured
          data is an actual property of the Data Record.  This is
          equivalent to a logical XOR operation.
         </paragraph>
       </description>
     </structuredDataTypeSemantic>

     <structuredDataTypeSemantic name="oneOrMoreOf" value="2">
       <description>
         <paragraph>
          The "oneOrMoreOf" structured data type semantic
          specifies that one or more elements from the list in the
          structured data are actual properties of the Data
          Record.  This is equivalent to a logical OR operation.
         </paragraph>
       </description>
     </structuredDataTypeSemantic>

     <structuredDataTypeSemantic name="allOf" value="3">
       <description>
         <paragraph>
          The "allOf" structured data type semantic specifies that
          all of the list elements from the structured data are
          actual properties of the Data Record.
         </paragraph>
       </description>
     </structuredDataTypeSemantic>

     <structuredDataTypeSemantic name="ordered" value="4">
       <description>
         <paragraph>
          The "ordered" structured data type semantic specifies
          that elements from the list in the structured data are
          ordered.
         </paragraph>
       </description>
     </structuredDataTypeSemantic>
   </structuredDataTypeSemantics>

   The following schema definitions are appended to the abstract data
   types defined in Appendix B of [RFC5102].  This schema and its
   namespace are registered by IANA at
   http://www.iana.org/assignments/xml-registry/schema/ipfix.xsd.

<simpleType name="dataType">
   <restriction base="string">
     <enumeration value="basicList">
       <annotation>
         <documentation>
           Represents a list of zero or more instances of
           any Information Element, primarily used for
           single-valued data types.  Examples include a list of port
           numbers, a list of interface indexes, and a list of AS in a
           BGP AS-PATH.
         </documentation>
       </annotation>
     </enumeration>
     <enumeration value="subTemplateList">
       <annotation>
         <documentation>
           Represents a list of zero or more instances of a
           structured data type, where the data type of each list
           element is the same and corresponds with a single
           Template Record.  Examples include a structured data type
           composed of multiple pairs of ("MPLS label stack entry
           position", "MPLS label stack value"), a structured
           data type composed of performance metrics, and a
           structured data type composed of multiple pairs of IP
           address.
         </documentation>
       </annotation>
     </enumeration>
     <enumeration value="subTemplateMultiList">
       <annotation>
         <documentation>
           Represents a list of zero or more instances of
           structured data types, where the data type of each
           list element can be different and corresponds with
           different Template definitions.  An example is a
           structured data type composed of multiple
           access-list entries, where entries can be
           composed of different criteria types.
         </documentation>
       </annotation>
     </enumeration>
   </restriction>
</simpleType>

<simpleType name="dataTypeSemantics">
   <restriction base="string">
     <enumeration value="List">
       <annotation>
         <documentation>
           Represents an arbitrary-length sequence of structured
           data elements, either composed of regular Information
           Elements or composed of data conforming to a Template
           Record.
         </documentation>
       </annotation>
     </enumeration>
   </restriction>
</simpleType>

<complexType name="structuredDataTypeSemantics">
   <sequence>
     <element name="structuredDataTypeSemantic"
              minOccurs="1" maxOccurs="unbounded">
       <complexType>
         <sequence>
           <element name="description" type="text"/>
         </sequence>
         <attribute name="name" type="string" use="required"/>
         <attribute name="value" type="unsignedByte" use="required"/>
       </complexType>
     </element>
   </sequence>
</complexType>

<element name="structuredDataTypeSemantics"
          type="structuredDataTypeSemantics">
   <annotation>
     <documentation>
       Structured data type semantics express the relationship
       among multiple list elements in a structured data
       Information Element.
     </documentation>
   </annotation>
</element>

Appendix B. Encoding IPS Alert Using Structured Data Information
Elements

   In this section, an IPS alert example is used to demonstrate how
   complex data and multiple levels of hierarchy can be encoded using
   Structured Data Information Elements.  Also, this example
   demonstrates how a basicList of subTemplateLists can be used to
   represent semantics at multiple levels in the hierarchy.

   An IPS alert consists of the following mandatory attributes:
   signatureId, protocolIdentifier, and riskRating.  It can also contain
   zero or more participants, and each participant can contain zero or
   more attackers and zero or more targets.  An attacker contains the
   attributes sourceIPv4Address and applicationId, and a target contains
   the attributes destinationIPv4Address and applicationId.

   Note that the signatureId and riskRating Information Element fields
   are created for these examples only; the Field IDs are shown as N/A.
   The signatureId helps to uniquely identify the IPS signature that
   triggered the alert.  The riskRating identifies the potential risk,
   on a scale of 0-100 (100 being most serious), of the traffic that
   triggered the alert.

   Consider the example described in case study 2 of Section 5.6. The
   IPS alert contains participants encoded as a subTemplateList with
   semantic allOf.  Each participant uses a basicList of
   subTemplateLists to represent attackers and targets.  For the sake of
   simplicity, the alert has two participants P1 and P2.  In participant
   P1, attacker A1 or A2 attacks target T1.  In participant P2, attacker
   A3 attacks targets T2 and T3.

   Participant P1:

        (basicList, allOf,

              (subTemplateList, exactlyOneOf, attacker A1, A2)

              (subTemplateList, undefined, target T1)

        )

   Participant P2:

        (basicList, allOf,

              (subTemplateList, undefined, attacker A3,
              (subTemplateList, allOf, targets T2, T3)

        )

   Alert :

           (subTemplateList, allOf, Participant P1, Participant P2)

    ------------------------------------------------------------------
          |        |        |             participant
    sigId |protocol| risk   |      attacker   |      target
          |   Id   | Rating |    IP   | appId |    IP      | appId
    ------------------------------------------------------------------
    1003     17      10      192.0.2.3  103    192.0.2.103    3001
                             192.0.2.4  104

                             192.0.2.5  105    192.0.2.104    4001
                                               192.0.2.105    5001
    ------------------------------------------------------------------

    Participant P1 contains:
    Attacker A1: (IP, appId)=(192.0.2.3, 103)
    Attacker A2: (IP, appId)=(192.0.2.4, 104)
    Target T1: (IP, appId)= (192.0.2.103, 3001)

    Participant P2 contains:
    Attacker A3: (IP, appId) = (192.0.2.5, 105)
    Target T2: (IP, appId)= (192.0.2.104, 4001)
    Target T3: (IP, appId)= (192.0.2.105, 5001)

    To represent an alert, the following Templates are defined:
    Template for target (268)
    Template for attacker (269)

    Template for participant (270)
    Template for alert (271)

         alert (271)
         |  (signatureId)
         |  (protocolIdentifier)
         |  (riskRating)
         |
         +------- participant (270)
                  |
                  +------- attacker (269)
                  |           (sourceIPv4Address)
                  |           (applicationId)
                  |
                  +------- target (268)
                           |  (destinationIPv4Address)
                           |  (applicationId)

   Note that the attackers are always composed of a single
   applicationId, while the targets typically have multiple
   applicationIds; for the sake of simplicity, this example shows only
   one applicationId in the target.

   Template Record for target, with the Template ID 268:

    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 = 16 octets       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |       Template ID = 268       |       Field Count = 2         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0| destinationIPv4Address = 12 |       Field Length = 4        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0|       applicationId = 95    |       Field Length = 4        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 31: Encoding IPS Alert, Template for Target

    Template Record for attacker, with the Template ID 269:

     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 = 16 octets       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |       Template ID = 269       |       Field Count = 2         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0|    sourceIPv4Address = 8    |       Field Length = 4        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0|     applicationId = 95      |       Field Length = 4        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 32: Encoding IPS Alert, Template for Attacker

    Template Record for participant, with the Template ID 270:

     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 = 12 octets       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |       Template ID = 270       |       Field Count = 1         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0|       basicList = 291       |     Field Length = 0xFFFF     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

          Figure 33: Encoding IPS Alert, Template for Participant

   The Template Record for the participant has one basicList Information
   Element, which is a list of subTemplateLists of attackers and
   targets.

   Template Record for IPS alert, with the Template ID 271:

     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 = 24 octets       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |       Template ID = 271       |       Field Count = 4         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0|    signatureId = N/A        |       Field Length = 2        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0|   protocolIdentifier = 4    |       Field Length = 1        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0|     riskRating = N/A        |       Field Length = 1        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0|     subTemplateList = 292   |     Field Length = 0xFFFF     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 34: Encoding IPS Alert, Template for IPS Alert

   The subTemplateList in the alert Template Record contains a list of
   participants.

   The Length of basicList and subTemplateList are encoded in three
   bytes even though they may be less than 255 octets.

   The Data Set is represented 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 = 271         |         Length = 102          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |      signatureId = 1003       | protocolId=17 | riskRating=10 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |      255      |participant List Length  = 91  |semantic=allOf |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | participant Template ID = 270 |     255       | P1 List Len = |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |      41       | semantic=allOf|    P1 List Field ID = 292     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | P1 List Field ID Len = 0xFFFF |      255      |P1 attacker ...|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | List Len = 19 |sem=exactlyOne | P1 attacker Template ID = 269 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          P1 attacker A1 sourceIPv4Address = 192.0.2.3         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |               P1 attacker A1 applicationId = 103              |

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          P1 attacker A2 sourceIPv4Address = 192.0.2.4         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |               P1 attacker A2 applicationId = 104              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |      255      | P1 target List Len = 11       | sem=undefined |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  P1 target Template ID = 268  | P1 target T1 destinationIPv4  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | ... Address = 192.0.2.103     |P1 target T1 applicationId =...|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | ...       3001                |      255      | P2 List Len = |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | ...  41       | semantic=allOf|    P2 List Field ID = 292     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | P2 List Field ID Len = 0xFFFF |      255      |P2 attacker ...|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | List Len = 11 | sem=undefined | P2 attacker Template ID = 269 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          P2 attacker A3 sourceIPv4Address = 192.0.2.5         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |               P2 attacker A3 applicationId = 105              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |      255      |    P2 target List Len = 19    |semantic=allOf |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  P2 target Template ID = 268  | P2 target T2 destinationIPv4  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | ... Address = 192.0.2.104     |P2 target T2 applicationId =...|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | ...       4001                | P2 target T3 destinationIPv4  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | ... Address = 192.0.2.105     |P2 target T3 applicationId =...|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | ...       5001                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

          Note: sem=exactlyOne represents semantic=exactlyOneOf

                  Figure 35: Encoding IPS Alert, Data Set

Authors' Addresses

   Benoit Claise
   Cisco Systems, Inc.
   De Kleetlaan 6a b1
   Diegem 1813
   Belgium

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

   Gowri Dhandapani
   Cisco Systems, Inc.
   13615 Dulles Technology Drive
   Herndon, Virginia 20171
   United States

   Phone: +1 408 853 0480
   EMail: gowri@cisco.com

   Paul Aitken
   Cisco Systems, Inc.
   96 Commercial Quay
   Commercial Street
   Edinburgh, EH6 6LX
   United Kingdom

   Phone: +44 131 561 3616
   EMail: paitken@cisco.com

   Stan Yates
   Cisco Systems, Inc.
   7100-8 Kit Creek Road
   PO Box 14987
   Research Triangle Park, North Carolina 27709-4987
   United States

   Phone: +1 919 392 8044
   EMail: syates@cisco.com