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Versions: (draft-trammell-ipfix-ie-doctors) 00 01 02 03 04 05 06 07 RFC 7013

IPFIX Working Group                                          B. Trammell
Internet-Draft                                                ETH Zurich
Intended status: BCP                                           B. Claise
Expires: May 24, 2012                                Cisco Systems, Inc.
                                                       November 21, 2011


   Guidelines for Authors and Reviewers of IPFIX Information Elements
                   draft-ietf-ipfix-ie-doctors-00.txt

Abstract

   This document provides guidelines for the definition of IPFIX
   Information Elements for addition to the IANA IPFIX Information
   Element registry, in order to extend the applicability of the IPFIX
   protocol to new operations and management areas.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 24, 2012.

Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   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.



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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Intended Audience and Usage  . . . . . . . . . . . . . . .  3
     1.2.  Overview of relevant IPFIX documents . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  How to apply IPFIX . . . . . . . . . . . . . . . . . . . . . .  4
   4.  Defining new Information Elements  . . . . . . . . . . . . . .  6
     4.1.  Information Element naming . . . . . . . . . . . . . . . .  6
     4.2.  Information Element data types . . . . . . . . . . . . . .  7
     4.3.  Information Element numbering  . . . . . . . . . . . . . .  8
     4.4.  Ancillary Information Element properties . . . . . . . . .  8
     4.5.  Internal structure in Information Elements . . . . . . . .  9
     4.6.  Information Element multiplicity . . . . . . . . . . . . . 10
     4.7.  Enumerated Values and Subregistries  . . . . . . . . . . . 10
     4.8.  Reversibility as per RFC 5103  . . . . . . . . . . . . . . 10
     4.9.  Promotion of Enterprise-Specific Information Elements  . . 11
     4.10. Avoiding Bad Ideas in Information Element Design . . . . . 11
   5.  The Information Element Lifecycle  . . . . . . . . . . . . . . 12
     5.1.  The IE-DOCTORS process . . . . . . . . . . . . . . . . . . 12
     5.2.  Revising Information Elements  . . . . . . . . . . . . . . 13
     5.3.  Deprecating Information Elements . . . . . . . . . . . . . 14
     5.4.  Versioning the entire IANA Registry  . . . . . . . . . . . 15
   6.  Tool support for IE-DOCTORS Reviews  . . . . . . . . . . . . . 15
   7.  When not to define new Information Elements  . . . . . . . . . 16
     7.1.  Maximizing reuse of existing Information Elements  . . . . 16
     7.2.  Applying enterprise-specific Information Elements  . . . . 17
   8.  Applying IPFIX to non-Flow Applications  . . . . . . . . . . . 18
   9.  Writing Internet-Drafts for IPFIX Applications . . . . . . . . 18
     9.1.  Example Information Element Definition . . . . . . . . . . 19
     9.2.  Defining Recommended Templates . . . . . . . . . . . . . . 19
   10. A Textual Format for Specifying Information Elements and
       Templates  . . . . . . . . . . . . . . . . . . . . . . . . . . 20
     10.1. Information Element Specifiers . . . . . . . . . . . . . . 21
     10.2. Specifying Templates . . . . . . . . . . . . . . . . . . . 23
     10.3. Specifying IPFIX Structured Data . . . . . . . . . . . . . 23
   11. Security Considerations  . . . . . . . . . . . . . . . . . . . 24
   12. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 25
   13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 25
   14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
     14.1. Normative References . . . . . . . . . . . . . . . . . . . 25
     14.2. Informative References . . . . . . . . . . . . . . . . . . 26
   Appendix A.  Example Information Element Definitions . . . . . . . 27
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27







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1.  Introduction

   This document provides guidelines for the extension of the
   applicability of the IP Flow Information Export (IPFIX) protocol to
   network operations and management purposes outside the initial scope
   defined in "IPFIX Applicability Statement" [RFC5472].  These new
   applications are largely defined by creating new Information Elements
   beyond those in the IANA IPFIX Information Element Registry
   [iana-ipfix-assignments].  New applications may be further specified
   through additional RFCs defining and describing their usage.

   We intend this document to enable the expansion of the applicability
   of IPFIX to new areas by experts in the working group or area
   directorate concerned with the technical details of the protocol or
   application to be measured or managed using IPFIX.  This expansion
   would occur with the consultation of IPFIX experts informally called
   'IE-Doctors'.  It provides guidelines both for those defining new
   Information Elements as well as the IE-Doctors reviewing them.

1.1.  Intended Audience and Usage

   This document is meant for two separate audiences.  For IETF
   contributors extending the applicability of IPFIX, it provides a set
   of guidelines and best practices to be used in deciding which
   Information Elements are necessary for a given existing or new
   application, defining these Information Elements, and deciding
   whether an RFC should be published to further describe the
   application.  For the IPFIX experts appointed as IE-Doctors, and for
   IANA personnel changing the Information Element registry, it defines
   a set of acceptance criteria against which these proposed Information
   Elements should be evaluated.

   This document is not intended to guide the extension of the IPFIX
   protocol itself, e.g. through new export mechanisms, data types, or
   the like; these activities should be pursued through the publication
   of standards-track RFCs by the IPFIX Working Group.

   This document specifies additional practices beyond those appearing
   in the IANA Considerations sections of existing IPFIX documents,
   especially the Information Model [RFC5102].  The practices outlined
   in this document are intended to guide experts when making changes to
   the IANA registry under Expert Review as defined in [RFC5226].

1.2.  Overview of relevant IPFIX documents

   [RFC5101] defines the IPFIX Protocol, the IPFIX-specific terminology
   used by this document, and the data type encodings for each of the
   data types supported by IPFIX.



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   [RFC5102] defines the initial IPFIX Information Model, as well as
   procedures for extending the Information Model.  It states that new
   Information Elements may be added to the Information Model on Expert
   Review basis, and delegates the appointment of experts to an IESG
   Area Director.  This document is intended to further codify the best
   practices to be followed by these experts, in order to improve the
   efficiency of this process.

   [RFC5103] defines a method for exporting bidirectional flow
   information using IPFIX; this document should be followed when
   extending IPFIX to represent information about bidirectional network
   interactions in general.  Additionally, new Information Elements
   should be annotated for their reversibility or lack thereof as per
   this document.

   [RFC5610] defines a method for exporting information about
   Information Elements inline within IPFIX.  In doing so, it explicitly
   defines a set of restrictions on the use of data types and semantics
   which are implied in [RFC5101] and [RFC5102]; these restrictions MUST
   be observed in the definition of new Information Elements, as in
   Section 4.4.


2.  Terminology

   Capitalized terms used in this document that are defined in the
   Terminology section of [RFC5101] are to be interpreted as defined
   there.

   An "application", as used in this document, refers to a candidate
   protocol, task, or domain to which IPFIX export, collection, and/or
   storage is applied, beyond those within the IPFIX Applicability
   statement [RFC5472].  By this definition, PSAMP [RFC5476] was the
   first new IPFIX application after the publication of the IPFIX
   protocol [RFC5101].

   "IANA registry", as used in this document, unless otherwise noted,
   refers to the IANA IPFIX Information Element Registry
   [iana-ipfix-assignments].

   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 [RFC2119].


3.  How to apply IPFIX

   Though originally specified for the export of IP flow information,



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   the message format, template mechanism, and data model specified by
   IPFIX lead to it being applicable to a wide variety of network
   management situations.  In addition to flow information export, for
   which it was designed, and packet information export as specified by
   PSAMP [RFC5476], any application with the following characteristics
   is a good candidate for an IPFIX application:

   o  The application's data flow is fundamentally unidirectional.
      IPFIX is a "push" protocol, supporting only the export of
      information from a sender (an Exporting Process) to a receiver (a
      Collecting Process).  Request-response interactions are not
      supported by IPFIX.

   o  The application handles discrete event information, or information
      to be periodically reported.  IPFIX is particularly well suited to
      representing events, which can be scoped in time.

   o  The application handles information about network entities.
      IPFIX's information model is network-oriented, so network
      management applications have many opportunities for information
      model reuse.

   o  The application requires a small number of arrangements of data
      structures relative to the number of records it handles.  The
      template-driven self-description mechanism used by IPFIX excels at
      handling large volumes of identically structured data, compared to
      representations which define structure inline with data (such as
      XML).

   Most applications meeting these criteria can be supported over IPFIX.
   Once it's been determined that IPFIX is a good fit, the next step is
   determining which Information Elements are necessary to represent the
   information required by the application.  Especially for network-
   centric applications, the IPFIX Information Element registry may
   already contain all the necessary Information Elements (see
   Section 7.1 for guidelines on maximizing Information Element reuse).
   In this case, no additional work within the IETF is necessary: simply
   define Templates and start exporting.

   It is expected, however, that most applications will be able to reuse
   some existing Information Elements, but must define some additional
   Information Elements to support all their requirements; in this case,
   see Section 4 for best practices to be followed in defining
   Information Elements.

   Optionally, a Working Group or individual contributor may choose to
   publish an RFC detailing the new IPFIX application.  Such an RFC
   should contain discussion of the new application, the Information



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   Element definitions as in Section 4, as well as suggested Templates
   and examples of the use of those Templates within the new application
   as in Section 9.2.  Section 10 defines a compact textual Information
   Element notation to be used in describing these suggested Templates
   and/or the use of IPFIX Structured Data
   [I-D.ietf-ipfix-structured-data] within the new application.


4.  Defining new Information Elements

   In many cases, a new application will require nothing more than a new
   Information Element or set of Information Elements to be exportable
   using IPFIX.  An Information Element meeting the following criteria,
   as evaluated by appointed IPFIX experts, is eligible for inclusion in
   the Information Element registry:

   o  The Information Element MUST be sufficiently unique within the
      registry.  A proposed Information Element which is a substantial
      duplicate of an existing Information Element is to be represented
      using the existing Element.

   o  The Information Element SHOULD contain minimal internal structure;
      complex information should be represented with multiple simple
      Information Elements to be exported in parallel, as in
      Section 4.5.

   o  The Information Element SHOULD be generally applicable to the
      application at hand, which SHOULD be of general interest to the
      community.  Information Elements representing information about
      proprietary or nonstandard applications SHOULD be represented
      using enterprise-specific Information Elements as detailed in
      section 6.2 of [RFC5101].

   The definition of new Information Elements requires a descriptive
   name, a specification of the data type as one from the IPFIX Data
   Type Registry, and a human-readable description written in English.
   This section provides guidelines on each of these components of an
   Information Element definition, referring to existing documentation
   such as [RFC5102] as appropriate.

4.1.  Information Element naming

   Information Element Names should be defined in accordance with
   section 2.3 of [RFC5102]; the most important naming conventions are
   repeated here for convenience.






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   o  Names of Information Elements should be descriptive.

   o  Names of Information Elements MUST be unique within the IPFIX
      information model.

   o  Names of Information Elements start with non-capitalized letters.

   o  Composed names use capital letters for the first letter of each
      component (except for the first one).  All other letters are non-
      capitalized, even for acronyms.  Exceptions are made for acronyms
      containing non-capitalized letter, such as 'IPv4' and 'IPv6'.
      Examples are sourceMacAddress and destinationIPv4Address.

   In addition, new Information Elements pertaining to a specific
   protocol SHOULD name the protocol in the first word in order to ease
   searching by name (e.g. "sipMethod" for a SIP method, as would be
   used in a logging format for SIP based on IPFIX).  Similarly, new
   Information Elements pertaining to a specific application SHOULD name
   the application in the first word.

4.2.  Information Element data types

   IPFIX provides a set of data types covering most primitives used in
   network measurement and management applications.  The most
   appropriate data type should be chosen for the Information Element
   type, out of the IPFIX informationElementDataTypes subregistry at
   [iana-ipfix-assignments].

   Because IPFIX provides reduced-length encoding for Information
   Elements, unless an integral Information Element is derived from a
   fixed-width field in a measured protocol (e.g., tcpSequenceNumber,
   which is an unsigned32), it should be defined with the maximum
   possible width, generally signed64 or unsigned64.  Applications can
   then choose to use reduced-size encoding as defined in Section 6.2 of
   [RFC5101] in cases where fewer than 2^64 values are necessary.

   Information Elements representing time values should be exported with
   appropriate precision.  For example, a Information Element for a time
   measured at second-level precision should be defined as having a
   dateTimeSeconds data type, instead of dateTimeMilliseconds.

   The type of an Information Element should match the type of the data
   it represents.  More specifically, information that could be
   represented as a String, but which better matches one of the other
   data types (e.g. an integral type for a number or enumerated type, an
   address type for an address) MUST be represented by the best-matching
   type.




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   This document does NOT cover the addition of new Data Types or Data
   Type Semantics to the IPFIX Protocol.  As such changes have important
   interoperability considerations and require implementation on both
   Collecting and Exporting Processes, they require a Standards Action
   as per [RFC5610].  However, note that the set of primitive types
   provided by IPFIX are applicable to most any appropriate application,
   so extending the type system is generally not necessary.

4.3.  Information Element numbering

   In general, when adding newly registered Information Elements to the
   registry, IANA SHOULD assign the lowest available Information Element
   identifier (the value column in [iana-ipfix-assignments] in the range
   128-32767, noting that prior noncontiguous allocation may lead to
   unassigned Information Elements with lower Information Element
   identifiers than some presently assigned Information Elements.  This
   is the case with the PSAMP Information Model [RFC5477], which
   assigned a block of Information Elements identifiers starting at 300.

   Information Element identifiers in the range 1-128 MUST NOT be
   assigned unless the Information Element is compatible with the
   NetFlow v9 protocol as described in [RFC3954].  Such Information
   Elements may ONLY be requested by a NetFlow v9 expert, to be
   designated by the IESG to consult with IANA on NetFlow v9
   compatibility with IPFIX.

4.4.  Ancillary Information Element properties

   Information Elements to which special semantics apply SHOULD define
   these semantics with one of the values in the Information Element
   Semantics registry, as described in Section 3.2 of [RFC5102], subject
   to the restrictions given in Section 3.10 of [RFC5610]; essentially,
   the semantics and the type must be consistent.

   When defining Information Elements representing a dimensioned
   quantity or entity count, the units of that quantity SHOULD be
   defined in the units field.  This field takes its values from the
   IANA Information Element Units registry.  If an Information Element
   expresses a quantity in units not yet in this registry, then the unit
   must be added to the Units registry at the same time the Information
   Element is added to the Information Element registry.

   Additionally, when the range of values an Information Element can
   take is smaller than the range implied by its data type, the range
   SHOULD be defined within the Information Element registry.






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4.5.  Internal structure in Information Elements

   The definition of Information Elements with internal structure with
   the structure defined in the Description field is discouraged, except
   in the following cases:

   o  The Information Element is a direct copy of a structured entity in
      a measured protocol (e.g. the tcpControlBits Information Element
      for the flags byte from the TCP header)

   o  The Information Element represents a section of a packet of
      protocol entity, in raw form as captured from the wire (e.g. the
      mplsLabelStackSection Information Element for the MPLS label
      stack)

   o  The Information Element represents a set of flags which are
      tightly semantically related, where representing the flags as
      separate one-byte booleans would be inefficient, and which should
      always appear together in a data record (e.g., the
      anonymizationFlags Information Element for specifying optional
      features of anonymization techniques)

   In other cases, candidate Information Elements with internal
   structure SHOULD be decomposed into multiple primitive Information
   Elements to be used in parallel.  For more complicated semantics,
   where the structure is not identical from Data Records to Data
   Records, use the IPFIX Structured Data
   [I-D.ietf-ipfix-structured-data] extension instead.

   As an example of information element decomposition, consider an
   application-level identifier called an "endpoint", which represents a
   {host, port, protocol} tuple.  Instead of allocating an opaque,
   structured "source endpoint" Information Element, the source endpoint
   should be represented by three separate Information Elements: "source
   address", "source port", "transport protocol".  In this example, the
   required information elements already exist in the Information
   Element registry: sourceIPv4Address or sourceIPv6Address,
   sourceTransportPort, protocolIdentifier.  Indeed, as well as being
   good practice, this normalization down to non-structured Information
   Elements also increases opportunities for reuse as in Section 7.1.

   The decomposition of data with internal structure SHOULD avoid the
   definition of Information Elements with a meaning too specific to be
   generally useful, or that would result in either the export of
   meaningless data or a multitude of templates to handle different
   multiplicities.  More information on multiplicities is given in the
   following section.




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4.6.  Information Element multiplicity

   Some Information Elements may represent information with a
   multiplicity other than one; i.e., items that may occur multiple
   times within the data to be represented in a single IPFIX record.  In
   this case, there are several options, depending on the circumstances:

   o  In cases where the items have a natural order (e.g., the order in
      which they occur in the packet), and the multiplicity is constant,
      the information can be modeled by containing multiple instances of
      the Information Element representing a single item within the
      Template Record describing the Data Records.

   o  In cases where the items have a variable multiplicity, a basicList
      of the Information Element representing a single item can be used
      as in IPFIX Structured Data [I-D.ietf-ipfix-structured-data]
      extension.

   o  If the multiple-item structure is taken directly from bytes
      observed on the wire by the Metering Process or otherwise taken
      from the application being measured, the multiple-item structure
      can be exported as a variable-length octetArray Information
      Element holding the raw content.

   Specifically, new Information Element SHOULD NOT encode any
   multiplicity or ordinality information into the definition of the
   Information Element itself.

4.7.  Enumerated Values and Subregistries

   When defining an Information Element that takes an enumerated value
   from a set of values which may change in the future, this enumeration
   MUST be defined by an IANA registry or subregistry.  For situations
   where an existing registry defines the enumeration (e.g., the IANA
   Protocol Numbers registry for the protocolIdentifier Information
   Element), that registry MUST be used.  Otherwise, a new IPFIX
   subregistry must be defined for the enumerated value, to be modified
   subject to Expert Review [RFC5226].

4.8.  Reversibility as per RFC 5103

   [RFC5103] defines a method for exporting bidirectional flows using a
   special Private Enterprise Number to define reverse-direction
   variants of IANA Information Elements, and a set of criteria for
   determining whether an Information Element may be reversed using this
   method.  Since almost all Information Elements are reversible,
   [RFC5103] enumerates those which Information Elements which were
   defined at the time of its publication which are NOT reversible.



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   New non-reversible Information Elements SHOULD contain a note in the
   description stating that they are not reversible.

4.9.  Promotion of Enterprise-Specific Information Elements

   Some Information Elements may start their lifecycle outside the IANA
   registry as enterprise-specific Information Elements scoped to a
   Private Enterprise Number.  One stated goal of enterprise-specific
   Information Elements is pre-standards product delivery and
   experimentation; should these experiments be successful and the
   Information Elements generally useful, these SHOULD subsequently
   registered with IANA.

   In order to support transition from experimental registration to IANA
   registration, the IANA registry provides an optional "enterprise-
   specific IE reference" column for each Information Element.  In cases
   of promoted enterprise-specific Information Elements, this column in
   the registry SHOULD contain the private enterprise and Information
   Element numbers of the enterprise-specific version of the Information
   Element.

4.10.  Avoiding Bad Ideas in Information Element Design

   In general, the existence of a similarly-defined Information Element
   in the IANA registry sets a precedent which may be followed to
   determine whether a given proposed Information Element "fits" within
   the registry.  Indeed, the rules specified by this document could be
   interpreted to mean "make new Information Elements that look like
   existing Information Elements".  However, for reasons of history,
   there are several Information Elements within the IANA registry which
   do not follow best practices in Information Element design, and
   should be explicitly ignored when looking for guidance as to whether
   a new Information Element should be added.

   Before registering a new Information Element, it must be determined
   that it would be sufficiently unique within the registry.  This
   evaluation has not always been done in the past, and the existence of
   the Information Elements defined without this evaluation should not
   be taken as an example that such Information Element definition
   practices should be followed in the future.  Specific examples of
   such Information Elements include initiatorOctets and responderOctets
   (which duplicate octetDeltaCount and its reverse per [RFC5103]) and
   initiatorPackets and responderPackets (the same, for
   packetDeltaCount).

   As mentioned in Section 4.2, the type of an Information Element
   SHOULD match the type of data the Information Element represents.  An
   example of how not to do this is presented by the p2pTechnology,



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   tunnelTechnology, and encryptedTechnology Information Elements: these
   represent a three-state enumeration using a String.  The example set
   by these Information Elements SHOULD NOT be followed in the
   definition of new Information Elements.

   As mentioned in Section 4.6, an Information Element definition SHOULD
   NOT include any ordinality or multiplicity information.  The only
   example of this within the IANA registry the following list of
   assigned IPFIX Information Elements: mplsTopLabelStackSection,
   mplsLabelStackSection2, mplsLabelStackSection3,
   mplsLabelStackSection4, mplsLabelStackSection5,
   mplsLabelStackSection6 mplsLabelStackSection7,
   mplsLabelStackSection8, mplsLabelStackSection9, and
   mplsLabelStackSection10.  The only distinction between those almost-
   identical Information Elements is the position within the MPLS stack.
   This Information Element design pattern met an early requirement of
   the definition of IPFIX which was not carried forward into the final
   specification -- namely, that no semantic dependency was allowed
   between Information Elements in the same Record -- and as such SHOULD
   NOT be followed in the definition of new Information Elements.  In
   this case, since the size of the MPLS stack will vary from flow to
   flow, it should be exported using IPFIX Structured Data
   [I-D.ietf-ipfix-structured-data] where supported, as a basicList of
   MPLS label entries, or as a raw MPLS label stack using the variable-
   length mplsLabelStackSection Information Element.


5.  The Information Element Lifecycle

   Once an Information Element or set of Information Elements has been
   identified for a given application, Information Element
   specifications in accordance with Section 4 are submitted to IANA to
   follow the IE-DOCTORS process, as defined below.  This process is
   also used for other changes to the registry, such as deprecation or
   revision, as described later in this section.

5.1.  The IE-DOCTORS process

   Requests to change the IANA Information Element registry or a linked
   subregistry are submitted to IANA, which forwards the request to a
   designated group of experts (IE-DOCTORS) appointed by the IETF
   Operations Area Directors.  This group of experts reviews the request
   for compliance with this document, compliance with other applicable
   IPFIX-related RFCs, and consistency with the currently defined set of
   Information Elements.

   IE-DOCTORS reviewers should endeavor to complete referred reviews in
   a timely manner.  If the request is acceptable, the IE-DOCTORS



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   signify their approval to IANA, which changes the IANA Information
   Element registry.  If the request is not acceptable, the IE-DOCTORS
   can coordinate with the requestor to change the request to be
   compliant.  The IE-DOCTORS may also choose in exceptional
   circumstances to reject clearly frivolous or inappropriate change
   requests outright.

5.2.  Revising Information Elements

   The Information Element status field in the Information Element
   Registry is defined in [RFC5102] to allow Information Elements to be
   'current', 'deprecated' or 'obsolete'.  No Information Elements are
   as of this writing deprecated or obsolete, and [RFC5102] does not
   define any policy for using them.  Additionally, no policy is defined
   for revising Information Element registry entries or addressing
   errors therein.  To be certain, changes and deprecations within the
   Information Element registry are not encouraged, and should be
   avoided to the extent possible.  However, in recognition that change
   is inevitable, this section is intended to remedy this situation.

   The primary requirement in the definition of a policy for managing
   changes to existing Information Elements is avoidance of
   interoperability problems; IPFIX experts appointed to review changes
   to the Information Element Registry MUST work to maintain
   interoperability above all else.  Changes to Information Elements
   already in use may only be done in an interoperable way; necessary
   changes which cannot be done in a way to allow interoperability with
   unchanged implementations MUST result in deprecation.

   A change to an Information Element is held to be interoperable only
   when:

   o  it involves the correction of an error which is obviously only
      editorial; or

   o  it corrects an ambiguity in the Information Element's definition,
      which itself leads to non-interoperability (e.g., a prior change
      to ipv6ExtensionHeaders); or

   o  it expands the Information Element's data type without changing
      how it is represented (e.g., changing unsigned32 to unsigned64, as
      with a prior change to selectorId); or

   o  it defines a previously undefined or reserved enumerated value, or
      one or more previously reserved bits in an Information Element
      with flag semantics; or





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   o  it expands the set of permissible values in the Information
      Element's range; or

   o  it harmonizes with an external reference which was itself
      corrected.

   A non-interoperable Information Element change may also be made if it
   can be reasonably assumed in the eyes of the appointed experts that
   no unchanged implementation of the Information Element exists; this
   can be held to happen if a non-interoperable change to an Information
   Element defined shortly before is proposed to the IPFIX mailing list
   by the original proposer of the Information Element, and no objection
   is raised within a reasonable amount of time, to be defined by the
   expert reviewers.

   If a change is permissible, it is sent to IANA, which passes it to
   the appointed experts for review; if there is no objection to the
   change from any appointed expert, IANA makes the change in the
   Information Element Registry.  The requestor of the change is
   appended to the Requestor in the registry.

   Each Information Element in the IANA registry has a revision number,
   starting at zero.  Each change to an Information Element following
   this process increments the revision number by one.  Since any
   revision must be interoperable according to the criteria above, there
   is no need for the IANA registry to store information about old
   revisions.

5.3.  Deprecating Information Elements

   Changes that are not permissible by these criteria may only be
   handled by deprecation.  An Information Element MAY be deprecated and
   replaced when:

   o  the Information Element definition has an error or shortcoming
      which cannot be permissibly changed as above; or

   o  the deprecation harmonizes with an external reference which was
      itself deprecated through that reference's accepted deprecation
      method; or

   o  changes in the IPFIX Protocol or its extensions, or in community
      understanding thereof, allow the information represented by the
      Information Element to be represented in a more efficient or
      convenient way.  Deprecation in this circumstance additionally
      requires the assent of the IPFIX Working Group, and should be
      specified in the Internet Draft(s) defining the protocol change.




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   A request for deprecation is sent to IANA, which passes it to the IE-
   DOCTORS for review, as above.  When deprecating an Information
   Element, the Information Element description MUST be updated to
   explain the deprecation, as well as to refer to any new Information
   Elements created to replace the deprecated Information Element.  The
   revision number of an Information Element is incremented upon
   deprecation.

   Deprecated Information Elements SHOULD continue to be supported by
   Collecting Processes, but SHOULD NOT be exported by Exporting
   Processes.  The use of deprecated Information Elements SHOULD result
   in a log entry or human-readable warning at the Exporting and
   Collecting Processes.  After a period of time determined in the eyes
   of the IE-DOCTORS experts to be reasonable in order to allow deployed
   Exporting Processes to be updated to account for the deprecation, a
   deprecated Information Element may be made obsolete.  Obsolete
   Information Elements MUST NOT be supported by either Exporting or
   Collecting Processes.  The receipt of obsolete Information Elements
   SHOULD be logged by the Collecting Process.

   Names of deprecated Information Elements MUST NOT be reused.  Names
   of obsolete Information Elements MAY be reused, but this is NOT
   RECOMMENDED, as it may cause confusion among users.

5.4.  Versioning the entire IANA Registry

   Consider a typical Collector implementation, which regularly
   downloads the entire registry in order to be compliant with the
   latest of set of supported IEs.  While a registry revision number
   might seems advantageous for the Collector at first glance (avoiding
   the one by one comparison of all IE revisions), it is not necessary,
   as the IPFIX IANA registry specifies the date at which the registry
   was last updated in the "Last Updated" field.  For purposes of
   identifying the latest set of Information Element versions specified
   in registry, the last revision date of the Information Element
   registry (available in the registry XML source, or from the Last-
   Modified: header of [iana-ipfix-assignments]) SHOULD be used.


6.  Tool support for IE-DOCTORS Reviews

   [TODO: IE-DOCTORS reviews are likely to be hard.  Identify areas that
   could be supported by tools, and enumerate them here to assist tool
   authors.]







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7.  When not to define new Information Elements

   Also important in defining new applications is avoiding redundancy
   and clutter in the Information Element registry.  Here we provide
   guidelines for reuse of existing Information Elements, as well as
   guidelines on using enterprise-specific Information Elements instead
   of adding Information Elements in the registry.

7.1.  Maximizing reuse of existing Information Elements

   Whenever possible, new applications should prefer usage of existing
   IPFIX Information Elements to the creation of new Information
   Elements.  IPFIX already provides Information Elements for every
   common Layer 4 and Layer 3 packet header field in the IETF protocol
   suite, basic Layer 2 information, basic counters, timestamps and time
   ranges, and so on.  When defining a new Information Element similar
   to an existing one, reviewers shall ensure that the existing one is
   not applicable.

   Note that this guideline to maximize reuse does not imply that an
   Information Element that represents the same information from a
   packet as a existing Information Element should not be added to the
   registry.  For example, consider the ipClassOfService (Element ID 5),
   ipDiffServCodePoint (Element ID 98), and ipPrecedence (Element ID
   196) Information Elements.  These all represent subsets of the same
   field in an IP version 4 packet header, but different uses of these
   bits.  The representation in one or another of these Information
   Elements contains information in itself as to how the bits were
   interpreted by the Metering Process.

   On the other hand, simply changing the context in which an
   Information Element will be used is insufficient reason for the
   definition of a new Information Element.  For example, an extension
   of IPFIX to log detailed information about HTTP transactions
   alongside network-level information should not define
   httpClientAddress and httpServerAddress Information Elements,
   preferring instead the use of sourceIPv[46]Address and
   destinationIPv[46]Address.

   Applications dealing with bidirectional interactions should use
   Bidirectional Flow Support for IPFIX [RFC5103] to represent these
   interactions.

   Specifically, existing timestamp and time range Information Elements
   should be reused for any situation requiring simple time stamping of
   an event: for single observations, the observationTime* Information
   Elements from PSAMP are provided, and for events with a duration, the
   flowStart* and flowEnd* Information Elements suffice.  This



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   arrangement allows minimal generic time handling by existing
   Collecting Processes and analysis workflows.  New timestamp
   Information Elements should ONLY be defined for semantically distinct
   timing information (e.g., an IPFIX-exported record containing
   information about an event to be scheduled in the future).

   In all cases the use of absolute timestamp Information Elements (e.g.
   flowStartMilliseconds) is RECOMMENDED, as these Information Elements
   allow for maximum flexibility in processing with minimal overhead.
   Timestamps based on the export time header in the enclosing IPFIX
   Message (e.g. flowStartTimeDeltaMicroseconds) MAY be used if high-
   precision timing is important, export bandwidth or storage space is
   limited, timestamps comprise a relatively large fraction of record
   size, and the application naturally groups records into IPFIX
   Messages.  Timestamps based on information which must be exported in
   a separate Data Record defined by an Options Template (e.g.
   flowStartSysUpTime) MAY be used only in the context of an existing
   practice of using runtime-defined epochs for the given application.
   New applications SHOULD avoid these structures when possible.

7.2.  Applying enterprise-specific Information Elements

   IPFIX provides a mechanism for defining enterprise-specific
   Infomation Elements, as in Section 3.2 of [RFC5101].  These are
   scoped to a vendor's or organization's Structure of Management
   Information (SMI) Private Enterprise Number, and are under complete
   control of the organization assigning them.

   For situations in which interoperability is unimportant, new
   information SHOULD be exported using enterprise-specific Information
   Elements instead of adding new Information Elements to the registry.
   These situations include:

   o  export of implementation-specific information, or

   o  export of information derived in a commercially-sensitive or
      proprietary method, or

   o  export of information or meta-information specific to a
      commercially-sensitive or proprietary application.

   While work within the IETF generally does not fall into these
   categories, enterprise-specific Information Elements are also useful
   for pre-standardization testing of a new IPFIX application.  While
   performing initial development and interoperability testing of a new
   application, the Information Elements used by the application SHOULD
   NOT be submitted to IANA for inclusion in the registry.  Instead,
   these experimental Information Elements SHOULD be represented as



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   enterprise-specific until their definitions are finalized, then
   transitioned from enterprise-specific to IANA-defined upon
   finalization.  To support this transition, the IANA registry provides
   an experimental IE reference as defined in Section 4.9.


8.  Applying IPFIX to non-Flow Applications

   At the core of IPFIX is its definition of a Flow, a set of packets
   sharing some common properties crossing an observation point within a
   certain time window.  However, the reliance on this definition does
   not preclude the application of IPFIX to domains which are not
   obviously handling flow data according to it.  Most network
   management data collection tasks, those to which IPFIX is most
   applicable, have at their core the movement of packets from one place
   to another; by a liberal interpretation of the common properties
   defining the flow, then, almost any event handled by these can be
   held to concern data records conforming to the IPFIX definition of a
   Flow.

   Non-flow information defining associations or key-value pairs, on the
   other hand, are defined by IPFIX Options Templates.  Here, the
   Information Elements within an Options Template Record are divided
   into Scope Information Elements which define the key, and non-scope
   Informatin Elements which define the values associated with that key.
   Unlike Flows, Data Records defined by Options Template are not
   necessarily scoped in time; these Data Records are generally held to
   be in effect until a new set of values for a specific set of keys is
   exported.  While this mechanism is often used by IPFIX to export
   metadata about the collection infrastructure, it is applicable to any
   association information.

   An IPFIX application can mix Data Records described either type of
   template in an IPFIX Message or Message stream, and exploit
   relationships among the Flow Keys, values, and Scopes to create
   interrelated data structures.  See [RFC5473] for an example
   application of this.


9.  Writing Internet-Drafts for IPFIX Applications

   When a new application is complex enough to require additional
   clarification or specification as to the use of the defined
   Information Elements, this may be given in an Internet-Draft.
   Internet-Drafts for new IPFIX applications are best submitted to a
   Working Group with expertise in the area of the new application, or
   as independent submissions.




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   When defining new Information Elements in an Internet-Draft, the
   Internet-Draft SHOULD contain a section (or subsection) for each
   Information Element, which contains the attributes in Section 4 in
   human-readable form.  An example subsection is given below.  These
   Information Element descriptions SHOULD NOT assign Information
   Element numbers, instead using placeholder identifiers for these
   numbers (e.g.  "AAA", "BBB", "CCC", or "TBD1", "TBD2", "TBD3") and a
   note to IANA in the IANA Considerations section to replace those
   placeholders in the document with Information Element numbers when
   the numbers are assigned.  The use of these placeholder definitions
   allows references to the numbers in e.g. box-and-line diagrams or
   template definitions as in Section 10.

9.1.  Example Information Element Definition

   This is an example of an Information Element definition which would
   appear in an Internet-Draft.  The name appears in the section title.

   Description:   Description goes here.

   Data Type:   Data type goes here; obligatory

   Data Type Semantics:   Data type semantics, if any, go here; optional

   Units:   Units, if any, go here; optional

   Range:   Range, if not implied by the data type, goes here; optional

   References:   References to other RFCs or documents outside the IETF,
      in which additional information is given, or which are referenced
      by the description, go here; optional

   ElementId:   TBD1

9.2.  Defining Recommended Templates

   New IPFIX applications SHOULD NOT, in the general case, define fixed
   templates for export, as this throws away much of the flexibility
   afforded by IPFIX.  However, fixed template export is permissible in
   the case that the export implementation must operate in a resource
   constrained environment, and/or that the application is replacing an
   existing fixed-format binary export format in a maximally compatible
   way.  In any case, Collecting Processes for such applications SHOULD
   support reordered Templates or Templates with additional Information
   Elements.

   An Internet-Draft clarifying the use of new Information Elements
   SHOULD include any recommended Template or Options Template Records



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   necessary for supporting the application, as well as examples of
   records exported using these Template Records.  In defining these
   Template Records, such Internet-Drafts SHOULD mention, subject to
   rare exceptions as above:

   o  that the order of Information Elements within a Template is not
      significant;

   o  that Templates on the wire for the application may also contain
      additional Information Elements beyond those specified in the
      recommended Template;

   o  that a stream of IPFIX Messages supporting the application may
      also contain Data Records not described by the recommended
      Templates; and

   o  that any reader of IPFIX Messages supporting the application MUST
      accept these conditions.

   Definitions of recommended Template Records for flow-like
   information, where the Flow Key is well-defined, SHOULD indicate
   which of the Information Elements in the recommended Template are
   Flow Keys.

   Recommended Templates are defined, for example, in [RFC5476] for
   PSAMP packet reports (section 6.4) and extended packet reports
   (section 6.5).  Recommended Options Templates are defined extensively
   throughout the IPFIX documents, including in the protocol document
   itself [RFC5101] for exporting export statistics; in the file format
   [RFC5655] for exporting file metadata; and in Mediator intermediate
   process definitions such as [I-D.ietf-ipfix-anon] for intermediate
   process metadata.  The discussion in these examples is a good model
   for recommended template definitions.


10.  A Textual Format for Specifying Information Elements and Templates

   Example Templates given in existing IPFIX documents are generally
   expressed using bitmap diagrams of the respective Templates.  These
   are illustrative of the wire representation of simple Templates, but
   not particularly readable for more complicated recommended Templates,
   provide no support for rapid implementation of new Templates, and do
   not adequately convey the optional nature of ordering and additional
   Information Elements as above.  Therefore, we define a RECOMMENDED
   textual format for specifying Information Elements and Templates in
   Internet-Drafts in this section.

   Here we define a simple textual syntax for describing IPFIX



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   Information Elements and IPFIX Templates, with human readability,
   human writability, compactness, and ease of parser/generator
   implementation without requiring external XML support as design
   goals.  It is intended both for use in human communication (e.g., in
   new Internet-Drafts containing higher-level descriptions of IPFIX
   Templates, or describing sets of new IPFIX Information Elements for
   supporting new applications of the protocol) as well as at runtime by
   IPFIX implementations.

10.1.  Information Element Specifiers

   The basis of this format is the textual Information Element
   Specifier, or IESpec.  An IESpec contains each of the four important
   aspects of an Information Element: its name, its number, its type,
   and its size, separated by simple markup based on various types of
   brackets.  Fully-qualified IESpecs may be used to specify existing or
   new Information Elements within an Information Model, while either
   fully-qualified or partial IESpecs may be used to define fields in a
   Template.

   Bare words are used for Information Element names, and each aspect of
   information associated with an Information Element is associated with
   a type of brackets:

   o  () parentheses for Information Element numbers,

   o  <> angles for Information Element data types, and

   o  [] square brackets for Information Element sizes.

   o  {} curly braces contain an optional space-separated list of
      context identifiers to be associated with an Information Element,
      as described in more detail in Section 10.2

   The symbol + is reserved for Information Element nesting within
   structured data elements; these are described in and Section 10.3,
   respectively.

   Whitespace in IESpecs is insignificant; spaces can be added after
   each element in order, e.g., to align columns for better readability.

   The basic form of a fully-qualified IESpec for an IANA-registered
   Information Element is as follows:

   name(number)<type>[size]

   where 'name' is the name of the Information Element in UTF-8,
   'number' is the Information Element as a decimal integer, 'type' is



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   the name of the data type as in the IANA informationElementDataTypes
   registry, and 'size' is the length of the Information Element in
   octets as a decimal integer, where 65535 or the string 'v' signifies
   a variable-length Information Element. [size] may be omitted; in this
   case, the data type's native or default size is assumed.

   The basic form of a fully-qualified IESpec for an enterprise-specific
   Information Element is as follows:

   name(pen/number)<type>[size]

   where 'pen' is the Private Enterprise Number as a decimal integer.

   A fully-qualified IESpec is intended to express enough information
   about an Information Element to decode and display Data Records
   defined by Templates containing that Information Element.  Range,
   unit, semantic, and description information, as in [RFC5610], is not
   supported by this syntax.

   Example fully-qualified IESpecs follow:

      octetDeltaCount(1)<unsigned64>[8]

      octetDeltaCount(1)<unsigned64> (unsigned64 is natively 8 octets
      long)

      sourceIPv4Address(8)<ipv4Address>

      wlanSSID(146)<string>[v]

      sipRequestURI(35566/403)<string>[65535]

   A partial IESpec is any IESpec that is not fully-qualified; these are
   useful when defining templates.  A partial IESpec is assumed to take
   missing values from its canonical definition, for example, the IANA
   registry.  At minimum, a partial IESpec must contain a name, or a
   number.  Any name, number, or type information given with a partial
   IESpec must match the values given in the Information Model; however,
   size information in a partial IESpec overrides size information in
   the Information Model; in this way, IESpecs can be used to express
   reduced-length encoding for Information Elements.

   Example partial IESpecs follow:

   o  octetDeltaCount

   o  octetDeltaCount[4] (reduced-length encoding)




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   o  (1)

   o  (1)[4] (reduced length encoding; note that this is exactly
      equivalent to an Information Element specifier in a Template)

10.2.  Specifying Templates

   A Template can then be defined simply as an ordered, newline-
   separated sequence of IESpecs.  IESpecs in example Templates
   illustrating a new application of IPFIX SHOULD be fully-qualified.
   Flow Keys may be optionally annotated by appending the {key} context
   to the end of each Flow Key specifier.  A template counting packets
   and octets per five-tuple with millisecond precision in IESpec syntax
   is shown below.

   flowStartMilliseconds(152)<dateTimeMilliseconds>[8]
   flowEndMilliseconds(153)<dateTimeMilliseconds>[8]
   octetDeltaCount(1)<unsigned64>[8]
   packetDeltaCount(2)<unsigned64>[8]
   sourceIPv4Address(8)<ipv4Address>[4]{key}
   destinationIPv4Address(12)<ipv4Address>[4]{key}
   sourceTransportPort(7)<unsigned16>[2]{key}
   destinationTransportPort(11)<unsigned16>[2]{key}
   protocolIdentifier(4)<unsigned8>[1]{key}

   An Options Template is specified similarly.  Scope is specified
   appending the {scope} context to the end of each IESpec for a Scope
   IE.  Due to the way Information Elements are represented in Options
   Templates, all {scope} IESpecs must appear before any non-scope
   IESpec.  The Flow Key Options Template defined in section 4.4 of
   [RFC5101] in IESpec syntax is shown below:

   templateId(145)<unsigned16>[2]{scope}
   flowKeyIndicator(173)<unsigned64>[8]

10.3.  Specifying IPFIX Structured Data

   IESpecs can also be used to illustrate the structure of the
   information exported using the IPFIX Structured Data extension
   [I-D.ietf-ipfix-structured-data].  Here, the semantics of the
   structured data elements are specified using contexts, and the
   information elements within each structured data element follow the
   structured data element, prefixed with + to show they are contained
   therein.  Arbitrary nesting of structured data elements is possible
   by using multiple + signs in the prefix.  For example, a basic list
   of IP addresses with "one or more" semantics would be expressed using
   parially qualified IESpecs as follows:




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   basicList{oneOrMoreOf}
   +sourceIPv4Address(8)[4]

   And an example subTemplateList itself containing a basicList is shown
   below:

   subTemplateList{allOf}
   +basicList{oneOrMoreOf}
   ++sourceIPv4Address(8)[4]
   +destinationIPv4Address(12)[4]

   This describes a subTemplateMultilist containing all of the expressed
   set of source-destination pairs, where the source address itself
   could be one of any number in a basicList (e.g., in the case of SCTP
   multihoming).

   The contexts associable with structured data Information Elements are
   the semantics, as defined in section 4.4 of
   [I-D.ietf-ipfix-structured-data]; a structured data Information
   Element without any context is taken to have undefined semantics.
   More information on the application of structured data is available
   in [I-D.ietf-ipfix-structured-data].


11.  Security Considerations

   The security aspects of new Information Elements must be considered
   in order not to give a potential attacker too much information.  For
   example, the "A Framework for Packet Selection and Reporting"
   [RFC5474] concluded in section 12.3.2 that the hash functions private
   parameters should not exported within IPFIX.

   If some security considerations are specific to an Information
   Element, they MUST be mentioned in the Information Element
   description.  For example, the ipHeaderPacketSection in the IPFIX
   registry mentions: "This Information Element, which may have a
   variable length, carries a series of octets from the start of the IP
   header of a sampled packet.  With sufficient length, this element
   also reports octets from the IP payload, subject to [RFC2804].  See
   the Security Considerations section."

   These security considerations MAY also be stressed in an accompanying
   Internet-Draft, as in Section 9.  For example, the "Packet Sampling
   (PSAMP) Protocols Specification" [RFC5476] specifies: "In the basic
   Packet Report, a PSAMP Device exports some number of contiguous bytes
   from the start of the packet, including the packet header (which
   includes link layer, network layer and other encapsulation headers)
   and some subsequent bytes of the packet payload.  The PSAMP Device



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   SHOULD NOT export the full payload of conversations, as this would
   mean wiretapping [RFC2804].  The PSAMP Device MUST respect local
   privacy laws."


12.  IANA Considerations

   With respect to the management of the IPFIX Information Element
   registry and associated subregistries located at
   [iana-ipfix-assignments], this document defines a process for IANA in
   Section 5.1, and includes a set of guidelines for IANA for applying
   this process in Section 4, Section 5, and Section 7.

   In addition, in order to support more effective management of the
   Information Element lifecycle as defined in Section 5, it specifies
   the addition of three new columns for this registry:

   Revision:   a serial revision number for each Information Element,
      beginning at 0 for all presently existing and newly created
      Information Elements.

   Date:   the date at which the Information Element was created or last
      modified.

   Enterprise-specific reference:   for Information Elements which where
      deployed as enterprise-specific Information Elements for
      experimentation and testing, and subsequently registered in the
      IANA registry, specifies the private enterprise number (PEN) and
      IE number of the equivalent experimental IE.


13.  Acknowledgements

   The authors would like to acknowledge the FP7 PRISM and DEMONS
   projects for their material support of this work.


14.  References

14.1.  Normative References

   [RFC3954]  Claise, B., "Cisco Systems NetFlow Services Export Version
              9", RFC 3954, October 2004.

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




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

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

   [RFC5610]  Boschi, E., Trammell, B., Mark, L., and T. Zseby,
              "Exporting Type Information for IP Flow Information Export
              (IPFIX) Information Elements", RFC 5610, July 2009.

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

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

14.2.  Informative References

   [RFC2804]  IAB and IESG, "IETF Policy on Wiretapping", RFC 2804,
              May 2000.

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

   [RFC4181]  Heard, C., "Guidelines for Authors and Reviewers of MIB
              Documents", BCP 111, RFC 4181, September 2005.

   [RFC5153]  Boschi, E., Mark, L., Quittek, J., Stiemerling, M., and P.
              Aitken, "IP Flow Information Export (IPFIX) Implementation
              Guidelines", RFC 5153, April 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



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              in IP Flow Information Export (IPFIX) and Packet Sampling
              (PSAMP) Reports", RFC 5473, March 2009.

   [RFC5474]  Duffield, N., Chiou, D., Claise, B., Greenberg, A.,
              Grossglauser, M., and J. Rexford, "A Framework for Packet
              Selection and Reporting", RFC 5474, March 2009.

   [RFC5476]  Claise, B., 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.

   [RFC5655]  Trammell, B., Boschi, E., Mark, L., Zseby, T., and A.
              Wagner, "Specification of the IP Flow Information Export
              (IPFIX) File Format", RFC 5655, October 2009.

   [I-D.ietf-ipfix-structured-data]
              Claise, B., Dhandapani, G., Yates, S., and P. Aitken,
              "Export of Structured Data in IPFIX",
              draft-ietf-ipfix-structured-data-06 (work in progress),
              May 2011.

   [I-D.ietf-ipfix-anon]
              Boschi, E. and B. Trammell, "IP Flow Anonymization
              Support", draft-ietf-ipfix-anon-06 (work in progress),
              January 2011.

   [iana-ipfix-assignments]
              Internet Assigned Numbers Authority, "IP Flow Information
              Export Information Elements
              (http://www.iana.org/assignments/ipfix/ipfix.xml)".


Appendix A.  Example Information Element Definitions

   [TODO: we have examples of bad IEs in Section 4.10, but it would help
   to have some good ones.  Use examples from SIPCLF.]












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Authors' Addresses

   Brian Trammell
   Swiss Federal Institute of Technology Zurich
   Gloriastrasse 35
   8092 Zurich
   Switzerland

   Phone: +41 44 632 70 13
   Email: trammell@tik.ee.ethz.ch


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

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































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