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Internet Engineering Task Force (IETF) B. Trammell
Request for Comments: 7013 ETH Zurich
BCP: 184 B. Claise
Category: Best Current Practice Cisco Systems, Inc.
ISSN: 2070-1721 September 2013
Guidelines for Authors and Reviewers of
IP Flow Information Export (IPFIX) Information Elements
Abstract
This document provides guidelines for how to write definitions of new
Information Elements for the IP Flow Information Export (IPFIX)
protocol. It provides instructions on using the proper conventions
for Information Elements to be registered in the IANA IPFIX
Information Element registry, and provides guidelines for expert
reviewers to evaluate new registrations.
Status of This Memo
This memo documents an Internet Best Current Practice.
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
BCPs 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/rfc7013.
Copyright Notice
Copyright (c) 2013 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 .......................4
2. Terminology .....................................................4
3. How to Apply IPFIX ..............................................5
4. Defining New Information Elements ...............................6
4.1. Information Element Naming .................................7
4.2. Information Element Data Types .............................7
4.3. Information Element Numbering ..............................8
4.4. Ancillary Information Element Properties ...................9
4.5. Internal Structure in Information Elements .................9
4.6. Information Element Multiplicity ..........................10
4.7. Enumerated Values and Subregistries .......................11
4.8. Reversibility as per RFC 5103 .............................11
4.9. Avoiding Bad Ideas in Information Element Design ..........11
5. The Information Element Life Cycle .............................13
5.1. The Process for Review by the IE-DOCTORS ..................13
5.2. Revising Information Elements .............................14
5.3. Deprecating Information Elements ..........................15
6. When Not to Define New Information Elements ....................16
6.1. Maximizing Reuse of Existing Information Elements .........16
6.2. Applying Enterprise-Specific Information Elements .........18
7. Information Element Definition Checklist .......................18
8. Applying IPFIX to Non-Flow Applications ........................21
9. Writing Internet-Drafts for IPFIX Applications .................21
9.1. Example Information Element Definition ....................22
9.2. Defining Recommended Templates ............................22
10. A Textual Format for Specifying Information Elements
and Templates .................................................23
10.1. Information Element Specifiers ...........................24
10.2. Specifying Templates .....................................26
10.3. Specifying IPFIX Structured Data .........................27
11. Security Considerations .......................................27
12. Acknowledgments ...............................................28
13. References ....................................................29
13.1. Normative References .....................................29
13.2. Informative References ...................................29
Appendix A. Example Information Element Definitions ...............31
A.1. sipResponseStatus ..........................................31
A.2. duplicatePacketDeltaCount ..................................31
A.3. ambientTemperature .........................................32
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1. Introduction
This document provides guidelines for the definition of new IPFIX
Information Elements beyond those currently in the IANA IPFIX
Information Element Registry [IANA-IPFIX]. Given the self-describing
nature of the data export format used by IPFIX, the definition of new
Information Elements is often sufficient to allow the application of
IPFIX to new network measurement and management use cases.
We intend this document to enable the application of IPFIX to new
areas by experts in the IETF Working Group or Area Directorate, the
IETF community, or organization external to the IETF, concerned with
the technical details of the protocol or application to be measured
or managed using IPFIX. This expansion occurs 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.
This document essentially codifies two meta-guidelines: (1) "define
new Information Elements that look like existing Information
Elements" and (2) "don't define Information Elements unless you need
to".
1.1. Intended Audience and Usage
This document is meant for two separate audiences. For those
defining new Information Elements, it provides specifications and
best practices to be used in deciding which Information Elements are
necessary for a given existing or new application, instructions for
writing the definitions for these Information Elements, and
information on the supporting documentation required for the new
application (up to and including the publication of one or more RFCs
describing it). For the IPFIX experts appointed as IE-DOCTORS, and
for IANA personnel changing the IANA IPFIX Information Element
Registry [IANA-IPFIX], 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 within the IPFIX Working Group.
This document, together with [RFC7012], defines the procedures for
management of the IANA IPFIX Information Element Registry
[IANA-IPFIX]. The practices outlined in this document are intended
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to guide experts when reviewing additions or changes to the
Information Elements in the registry under Expert Review (as defined
in [RFC5226]).
1.2. Overview of Relevant IPFIX Documents
[RFC7011] 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.
[RFC7012] defines the basis of the IPFIX Information Model, referring
to [IANA-IPFIX] for the specific Information Element definitions. It
states that new Information Elements may be added to the Information
Model on the basis of Expert Review, delegates the appointment of
experts to an IESG Area Director, and refers to this document for
details on the extension process. 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, implied in [RFC7011] and [RFC7012], on
the use of data types and semantic; 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 [RFC7011] 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. By this definition, the IPFIX applicability
statement [RFC5472] defined the initial applications of IPFIX, and
Packet Sampling (PSAMP) [RFC5476] was the first new IPFIX application
after the publication of the IPFIX protocol itself.
"IANA IE registry", as used in this document, unless otherwise noted,
refers to the IANA IPFIX Information Element Registry [IANA-IPFIX].
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3. How to Apply IPFIX
Though originally specified for the export of IP Flow information,
the message format, template mechanism, and data model specified by
IPFIX led 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 that define structure inline with data (such as
XML).
Most applications meeting these criteria can be supported over IPFIX.
Once it has 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 IANA IE registry may already contain all
the necessary Information Elements (see Section 6.1 for guidelines on
maximizing Information Element reuse). In this case, no 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 may need to 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.
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Optionally, a Working Group or individual contributor may choose to
write an Internet-Draft for publication as an RFC, detailing the new
IPFIX application. Such an RFC should contain discussion of the new
application, the Information 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 [RFC6313] 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 the IE-DOCTORS, is eligible for inclusion in the IANA
IE registry:
o The Information Element must be unique within the registry, and
its description must represent a substantially different meaning
from that of any existing Information Element. An existing
Information Element that can be reused for a given purpose should
be reused.
o The Information Element should contain as little internal
structure as possible. Instead of representing complex
information by overlaying internal structure on a simple data type
such as octetArray, such information should be represented with
multiple simple Information Elements to be exported in parallel or
using IPFIX Structured Data [RFC6313], as in Section 4.5. The
internal structure of a proposed IE may be evaluated by the IE-
DOCTORS with an eye toward interoperability and/or backward
compatibility with existing methods of exporting similar data on a
case-by-case basis.
o Information Elements representing information about proprietary or
nonstandard applications should not be registered in the IANA IE
registry. These can be represented using enterprise-specific
Information Elements as detailed in Section 3.2 of [RFC7011],
instead.
The definition of new Information Elements requires a descriptive
name, a specification of the data type from the IPFIX Data Type
subregistry in the IANA IE registry (defined in [RFC7012] as itself
extensible via Standards Action as per [RFC5226]), and a human-
readable description written in English. This section provides
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guidelines on each of these components of an Information Element
definition, referring to existing documentation such as [RFC7012] as
appropriate.
4.1. Information Element Naming
As the name of an Information Element is the first thing a potential
implementor will use when determining whether it is suitable for a
given application, it is important to be as precise and descriptive
as possible. Names of Information Elements:
o must be chosen carefully to describe the use of the Information
Element within the context in which it will be used.
o must be unique within the IANA IE registry.
o start with lowercase letters.
o use capital letters for the first letter of each component except
for the first one (aka "camel case"). All other letters are
lowercase, even for acronyms. Exceptions are made for acronyms
containing a mixture of lowercase and capital letters, 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, IPFIX informationElementDataTypes subregistry at [IANA-IPFIX].
This subregistry may be extended from time to time by a Standards
Action [RFC5226], as defined in [RFC5610].
Information Elements representing an integral value with a natural
width should be defined with the appropriate integral data type.
This applies especially to values taken directly from fixed-width
fields in a measured protocol. For example, tcpControlBits, the TCP
flags byte, is an unsigned8, and tcpSequenceNumber is an unsigned32.
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Information Elements representing counters or identifiers should be
defined as signed64 or unsigned64, as appropriate, to maximize the
range of values available; applications can use reduced-size encoding
as defined in Section 6.2 of [RFC7011] in cases where fewer than 2^64
values are necessary.
Information Elements representing time values must be defined with
appropriate precision. For example, an Information Element for a
time measured at second-level precision should be defined as having a
dateTimeSeconds data type, instead of dateTimeMilliseconds.
Information Elements of type string or octetArray that have length
constraints (fixed length, minimum and/or maximum length) must note
these constraints in their description.
The type of an Information Element must match the type of the data it
represents. More specifically, information that could be represented
as a string but that 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,
even if the data was represented using a different type in the
source. For example, an IPFIX application that exports Options
Template Records mapping IP addresses to additional information about
each host from an external database must use Information Elements of
an address type to represent the addresses, even if the source
database represented these as strings.
Strings and octetArrays must not be used to encode data that would be
more properly represented using multiple Information Elements and/or
IPFIX Structured Data [RFC6313]; see Section 4.5 for more.
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 almost any appropriate
application, so extending the type system is generally not necessary.
4.3. Information Element Numbering
Each Information Element has a unique identifier in the IANA
registry.
When adding newly registered Information Elements to the IANA IE
registry, IANA should assign the lowest available Information Element
identifier (the value column in [IANA-IPFIX]) in the range 128-32767.
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Information Elements with identifiers in the range 1-127 are reserved
for compatibility with corresponding fields in NetFlow version 9, as
described in [RFC3954].
4.4. Ancillary Information Element Properties
Information Elements to which special semantics apply should refer to
one of the values in the Information Element Semantics subregistry of
the IANA IE registry, as described in Section 3.2 of [RFC7012],
subject to the restrictions given in Section 3.10 of [RFC5610]; in
other words, 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 subregistry of the IANA IE registry.
If an Information Element expresses a quantity in units not yet in
this subregistry, then the unit must be added to the Units
subregistry at the same time the Information Element is added to the
IANA IE registry. Note that the Units subregistry as defined in
[RFC5610] is maintained on an Expert Review basis.
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's entry in the IANA
IE registry.
4.5. Internal Structure in Information Elements
The definition of Information Elements with an internal structure
that is defined in the Description field is not recommended, except
in the following cases:
1. 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).
2. 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).
3. The Information Element represents a set of flags that are
tightly semantically related, where representing the flags as
separate one-byte booleans would be inefficient, and that should
always appear together in a data record (e.g., the
anonymizationFlags Information Element for specifying optional
features of anonymization techniques).
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4. The Information Element contains internal structure by reference
to an external data type or specification containing internal
structure (e.g., a MIME type or URL), for interoperability and
backward-compatibility purposes.
Additional exceptions to the above list should be made through
publication of an RFC.
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 Record to Data Record,
or where there is semantic dependency between multiple decomposed
primitive Information Elements, use the IPFIX Structured Data
[RFC6313] 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 IANA IE 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 6.1.
The decomposition of data with internal structure should avoid the
definition of Information Elements that have a meaning too specific
to be generally useful or that would result in a multitude of
templates to handle different multiplicities. More information on
multiplicities is given in the following section.
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:
1. As specified in Section 8 of [RFC7011]: "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." In other
words, in cases where the items have a natural order (e.g., the
order in which they occur in the packet), and the multiplicity is
the same for each record, the information can be modeled by
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containing multiple instances of the Information Element
representing a single item within the Template Record describing
the Data Records.
2. In cases where the items have a variable multiplicity, a
basicList of the Information Element representing a single item
can be used as in the IPFIX Structured Data [RFC6313] extension.
3. 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 (e.g., a TCP options stack),
the multiple-item structure can be exported as a variable-length
octetArray Information Element holding the raw content.
Specifically, a 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 that may change in the future, this enumeration
must be defined by an IANA IE 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
subregistry of the IANA IPFIX registry 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 Information Elements that were defined at
the time of its publication that are NOT reversible.
New non-reversible Information Elements must contain a note in the
description stating that they are not reversible.
4.9. Avoiding Bad Ideas in Information Element Design
In general, the existence of a similarly defined Information Element
in the IANA IE registry sets a precedent that may be followed to
determine whether a given proposed Information Element "fits" within
the registry. Indeed, the rules specified by this document could be
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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 IE registry
that do not follow best practices in Information Element design.
These Information Elements are not necessarily so flawed so as to
require deprecation, but they should be explicitly ignored when
looking for guidance as to whether a new Information Element should
be added. Here we provide a set of representative examples taken
from the IANA IE registry; in general, entries in the IANA IE
registry that do not follow the guidelines in this document should
not be used as examples for new Information Element definitions.
Before registering a new Information Element, it must be determined
that it would be sufficiently unique within the IANA IE 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,
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 IE 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 that 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
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Flow, it should be exported using IPFIX Structured Data [RFC6313]
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 Life Cycle
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 process for review by the IE-DOCTORS, as defined below.
This process is also used for other changes to the IANA IE registry,
such as deprecation or revision, as described later in this section.
5.1. The Process for Review by the IE-DOCTORS
Requests to change the IANA IE registry or a linked subregistry are
submitted to IANA, which forwards the request to a designated group
of experts (IE-DOCTORS) appointed by the IESG; these are the
reviewers called for by the Expert Review [RFC5226] policy defined
for the IANA IE registry by [RFC7012]. The IE-DOCTORS review the
request for such things as compliance with this document, compliance
with other applicable IPFIX-related RFCs, and consistency with the
currently defined set of Information Elements.
Authors are expected to review compliance with the specifications in
this document to check their submissions before sending them to IANA.
The IE-DOCTORS should endeavor to complete referred reviews in a
timely manner. If the request is acceptable, the IE-DOCTORS signify
their approval to IANA, which changes the IANA IE 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.
This process should not in any way be construed as allowing the IE-
DOCTORS to overrule IETF consensus. Specifically, Information
Elements in the IANA IE registry that were added with IETF consensus
require IETF consensus for revision or deprecation.
Decisions by the IE-DOCTORS may be appealed as in Section 7 of
[RFC5226].
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5.2. Revising Information Elements
The Information Element status field in the IANA IE registry is
defined in [RFC7012] to allow Information Elements to be 'current' or
'deprecated'. No Information Elements are as of this writing
deprecated. [RFC5102] additionally specified an 'obsolete' status;
however, this has been removed on revision as it served no
operational purpose.
In addition, no policy is defined for revising IANA IE registry
entries or addressing errors therein. To be certain, changes and
deprecations within the IANA IE 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.
Changes are initiated by sending a new Information Element definition
to IANA, as in Section 5.1, for an already-existing Information
Element.
The primary requirement in the definition of a policy for managing
changes to existing Information Elements is avoidance of
interoperability problems; IE-DOCTORS 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 that 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:
1. it involves the correction of an error that is obviously only
editorial; or
2. it corrects an ambiguity in the Information Element's definition,
which itself leads to non-interoperability severe enough to
prevent the Information Element's usage as originally defined
(e.g., a prior change to ipv6ExtensionHeaders); or
3. 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
4. it corrects missing information in the Information Element's
definition without changing its meaning (e.g., the explicit
definition of 'quantity' semantics for numeric Information
Elements without a Data Type Semantics value); or
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5. it defines a previously undefined or reserved enumerated value,
or one or more previously reserved bits in an Information Element
with flag semantics; or
6. it expands the set of permissible values in the Information
Element's range; or
7. it harmonizes with an external reference that was itself
corrected.
If a change is deemed permissible by the IE-DOCTORS, IANA makes the
change in the IANA IE registry. The requestor of the change is
appended to the requestor in the registry.
Each Information Element in the IANA IE 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 IE registry to store information about
old revisions.
When a revised Information Element is accepted into the registry, the
date of acceptance of the most recent revision is placed into the
revision Date column of the registry for that Information Element.
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:
1. the Information Element definition has an error or shortcoming
that cannot be permissibly changed as in Section 5.2; or
2. the deprecation harmonizes with an external reference that was
itself deprecated through that reference's accepted deprecation
method; or
3. 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 requires a
Standards Action.
A request for deprecation is sent to IANA, which passes it to the IE-
DOCTORS for review, as in Section 5.1. When deprecating an
Information Element, the Information Element description in the IANA
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IE registry 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, and the revision Date updated, as with any revision.
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.
Names and elementIDs of deprecated Information Elements must not be
reused.
6. When Not to Define New Information Elements
Due to the relatively limited number space of Information Elements in
the IANA IE registry, and the fact that the difficulty of managing
and understanding the registry increases with its size, avoiding
redundancy and clutter in the registry is important in defining new
applications. New Information Elements should not be added to the
IANA IE registry unless there is an intent to implement and deploy
applications using them; research or experimental applications should
use enterprise-specific Information Elements as in Section 6.2
instead.
The subsections below 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 IANA IE registry.
6.1. 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 should 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 an existing Information Element should not be added to the
IANA IE registry. For example, consider the ipClassOfService
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(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.
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
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 that 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.
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6.2. Applying Enterprise-Specific Information Elements
IPFIX provides a mechanism for defining enterprise-specific
Information Elements, as in Section 3.2 of [RFC7011]. 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 IANA IE
registry. These situations include:
o export of implementation-specific information, or
o export of information supporting research or experiments within a
single organization or closed community, 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 IANA IE registry.
Instead, these experimental Information Elements should be
represented as enterprise-specific until their definitions are
finalized.
As this document contains best practices for defining new Information
Elements, organizations using enterprise-specific Information
Elements are advised to follow the guidelines set forth here even if
not submitting Information Elements for inclusion in the IANA IE
registry.
7. Information Element Definition Checklist
The following three checklists, condensed from the rest of this
document, can be used when defining and reviewing Information
Elements; they refer back to the section of this document from which
they are taken. These checklists are intended for the definition of
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new Information Elements; revision should follow the process defined
in Section 5.2, and deprecation should follow the process defined in
Section 5.3.
Though many of the considerations in this document require the
subjective judgement of Information Element authors, reviewers, and
IANA, certain parts of the process may be made simpler through tool
support. Items on these checklists that could be easily automated or
assisted by tools are annotated with "(tool support)". Other items
on these checklists require some level of subjective judgement;
checks for semantic uniqueness may additionally be supported by
textual analysis of descriptions in the future.
Checklist 1 contains conditions that must be met by all proposed
Information Elements:
1. The name must be unique within the IANA IE registry, and the name
of any current or deprecated Information Element must not be
reused. (Section 4.1) (tool support)
2. The description must be sufficiently semantically unique within
the IANA IE registry, representing a substantially different
meaning from any current or deprecated Information Element.
(Section 4)
3. The name must start with a lowercase letter. (Section 4.1) (tool
support)
4. Names composed of more than one word must use capital letters for
the first letter of each component except for the first one; all
other letters are lowercase, even for acronyms. Exceptions are
made for acronyms containing a mixture of lowercase and capital
letters, such as 'IPv4' and 'IPv6'. (Section 4.1) (tool support)
5. The data type must match the type of the data being represented.
(Section 4.2)
6. Data type semantics must be appropriate for the data type.
(Section 4.4) (tool support)
7. The Information Element identifier assigned by IANA must be
unique. (Section 4.3) (tool support)
8. The Information Element must be reviewed for the potential of
information leakage or other misuse that could reduce the
security of the measured system; security considerations specific
to the Information Element must be discussed in the description
or in a supporting RFC. (Section 11)
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Checklist 2 contains conditions that must be met by proposed
Information Elements with certain properties, as noted:
1. Time values must be defined with appropriate precision.
(Section 4.2)
2. Strings and octet arrays with length restrictions must note those
length restrictions in their descriptions. (Section 4.2)
3. Enumerations must refer to an IANA IE registry or subregistry, or
a registry maintained by an external standards organization. If
no suitable registry or subregistry exists, a new subregistry of
the IPFIX Information Element registry must be created for the
enumeration, to be modified subject to Expert Review [RFC5226].
(Section 4.7)
Checklist 3 contains conditions that should be met by proposed
Information Elements:
1. The name of an Information Element pertaining to a specific
protocol or application should contain the name of the protocol
or application as the first word. (Section 4.1)
2. Information Elements representing integral values should use a
data type for the appropriate width for the value.
(Section 4.2)
3. Information Elements representing counters or identifiers should
be represented as signed64 or unsigned64, unless they are
naturally represented with narrower integral types, as
appropriate. (Section 4.2)
4. An Information Element should not contain internal structure,
subject to the exceptions in Section 4.5; candidate Information
Elements with internal structure should be decomposed into
multiple Information Elements. (Section 4.5)
5. An Information Element should not contain multiplicity or
ordinality information within the definition of the Information
Element itself. (Section 4.6)
6. Data type semantics should be defined, if appropriate.
(Section 4.4) (tool support)
7. Units should be defined, if appropriate, with new units added to
the Information Element Units subregistry if necessary.
(Section 4.4) (tool support)
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8. Ranges should be defined, if appropriate. (Section 4.4) (tool
support)
9. Non-reversible Information Elements (see [RFC5103]) should note
non-reversibility in the description. (Section 4.8)
10. Information Elements to be registered with IANA should be
intended for implementation and deployment on production
networks.
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 that are not
obviously handling Flow data according to this definition. 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 that define the key and non-scope
Information Elements that define the values associated with that key.
Unlike Flows, Data Records defined by Options Templates 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.
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Internet-Drafts for new IPFIX applications are best submitted to a
Working Group with expertise in the area of the new application, or
to the Independent Submission stream.
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., "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 that would
appear in an Internet-Draft. The name appears in the section title.
Description: Description goes here.; obligatory
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: ElementId, if known, or "TBD" if it will be assigned by
IANA and filled in at publication time.
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
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way. In any case, Collecting Processes for such applications should
support the collection Templates with Information Elements in any
order, 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
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:
1. that the order of different Information Elements within a
Template is not significant;
2. that Templates on the wire for the application may also contain
additional Information Elements beyond those specified in the
recommended Template;
3. that a stream of IPFIX Messages supporting the application may
also contain Data Records not described by the recommended
Templates; and
4. 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 6.4.1) and extended packet reports
(Section 6.4.2). Recommended Options Templates are defined
extensively throughout the IPFIX documents, including in the protocol
document itself [RFC7011] for exporting export statistics; in the
file format [RFC5655] for exporting file metadata; and in
intermediate process definitions such as [RFC6235] 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
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Information Elements. 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
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 for use both 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 <> angle brackets 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 Elements nesting within
structured data elements; these are described in Section 10.3.
Whitespace in IESpecs is insignificant; spaces can be added after
each element in order, e.g., to align columns for better readability.
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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
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 in the IANA IE 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-size encoding for Information Elements.
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Example partial IESpecs follow:
o octetDeltaCount
o octetDeltaCount[4] (reduced-size encoding)
o (1)
o (1)[4] (reduced-size 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 5-tuple with millisecond precision in IESpec syntax is
shown in Figure 1.
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}
Figure 1: Sample Flow Template in IESpec Syntax
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
[RFC7011] in IESpec syntax is shown in Figure 2.
templateId(145)<unsigned16>[2]{scope}
flowKeyIndicator(173)<unsigned64>[8]
Figure 2: Flow Key Options Template in IESpec Syntax
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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
[RFC6313]. 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 partially qualified IESpecs as
shown in Figure 3.
basicList{oneOrMoreOf}
+sourceIPv4Address(8)[4]
Figure 3: Sample basicList in IESpec Syntax
And an example subTemplateList itself containing a basicList is shown
in Figure 4.
subTemplateList{allOf}
+basicList{oneOrMoreOf}
++sourceIPv4Address(8)[4]
+destinationIPv4Address(12)[4]
Figure 4: Sample subTemplateList in IESpec Syntax
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 [RFC6313]; 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 [RFC6313].
11. Security Considerations
The IE-DOCTORS must evaluate the security aspects of new Information
Elements in light of the information they could provide to support
potential attacks against the measured network or entities about
which information is exported. Specific security aspects to evaluate
include whether the exported information contains personally
identifiable information, or information that should be kept
confidential about the described entities (e.g., partial payload, or
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configuration information that could be exploited). This is not to
say that such Information Elements should not be defined, but there
must be an evaluation of the security risk versus the utility of the
exported information for the intended application. For example, "A
Framework for Packet Selection and Reporting" [RFC5474] concluded in
Section 12.3.2 that the hash function's private parameters should not
be exported within IPFIX.
Security considerations specific to an Information Element must be
addressed in the Security Considerations section of the Internet-
Draft describing the Information Element, or in the Information
Element description itself in case the Information Element is not
defined in an Internet-Draft. Information Elements with specific
security considerations should be described in an Internet-Draft.
For example, the ipHeaderPacketSection in the IPFIX IE 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". Another example can be seen in the "Packet
Sampling (PSAMP) Protocols Specification" [RFC5476]: "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
SHOULD NOT export the full payload of conversations, as this would
mean wiretapping [RFC2804]. The PSAMP Device MUST respect local
privacy laws."
12. Acknowledgments
Thanks to Paul Aitken, Andrew Feren, Dan Romascanu, and David
Harrington for their reviews and feedback. Thanks as well to Roni
Even and Yoav Nir for their area reviews; and to Pete Resnick, Adrian
Farrel, Stephen Farrell, Stewart Bryant, and Barry Leiba for their
contributions during IESG discussions. This work is materially
supported by the European Union Seventh Framework Programme under
grant agreement 257315 (DEMONS).
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13. References
13.1. Normative References
[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.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC6313] Claise, B., Dhandapani, G., Aitken, P., and S. Yates,
"Export of Structured Data in IP Flow Information Export
(IPFIX)", RFC 6313, July 2011.
[RFC7011] Claise, B., Ed., Trammell, B., Ed., and P. Aitken,
"Specification of the IP Flow Information Export (IPFIX)
Protocol for the Exchange of Flow Information", STD 77,
RFC 7011, September 2013.
[RFC7012] Claise, B., Ed. and B. Trammell, Ed., "Information Model
for IP Flow Information Export (IPFIX)", RFC 7012,
September 2013.
13.2. Informative References
[RFC2804] IAB IESG, "IETF Policy on Wiretapping", RFC 2804, May
2000.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[RFC3954] Claise, B., "Cisco Systems NetFlow Services Export Version
9", RFC 3954, October 2004.
[RFC5102] Quittek, J., Bryant, S., Claise, B., Aitken, P., and J.
Meyer, "Information Model for IP Flow Information Export",
RFC 5102, January 2008.
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[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.
[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.
[RFC5560] Uijterwaal, H., "A One-Way Packet Duplication Metric", RFC
5560, May 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.
[RFC6235] Boschi, E. and B. Trammell, "IP Flow Anonymization
Support", RFC 6235, May 2011.
[IANA-IPFIX]
IANA, "IP Flow Information Export (IPFIX) Entities",
<http://www.iana.org/assignments/ipfix>.
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Appendix A. Example Information Element Definitions
This section contains a few example Information Element definitions
as they would appear in an Internet-Draft. Note the conformance of
these examples to the guidelines in Section 4.
The sipResponseStatus Information Element (Appendix A.1) illustrates
the addition of an Information Element representing Layer 7
application information, with a reference to the registry containing
the allowable values. The duplicatePacketDeltaCount Information
Element (Appendix A.2) illustrates the addition of a new metric, with
a reference to the RFC defining the metric. The ambientTemperature
Information Element (Appendix A.3) illustrates the addition of a new
measured value outside the area of traditional networking
applications.
A.1. sipResponseStatus
Description: The SIP Response code as an integer, as in the
Response Codes registry at http://www.iana.org/assignments/sip-
parameters defined in [RFC3261] and amended in subsequent RFCs.
The presence of this Information Element in a SIP Message record
marks it as describing a SIP response; if absent, the record
describes a SIP request.
Data Type: unsigned16
Data Type Semantics: identifier
References: [RFC3261]
ElementId: TBD1
Replaces Enterprise-Specific Element: 35566 / 412
A.2. duplicatePacketDeltaCount
Description: The number of uncorrupted and identical additional
copies of each individual packet in the Flow arriving at the
destination since the previous Data Record for this Flow (if any),
as measured at the Observation Point. This is measured as the
Type-P-one-way-packet-duplication metric defined in Section 3 of
[RFC5560].
Data Type: unsigned64
Data Type Semantics: deltaCounter
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Units: packets
References: [RFC5560]
ElementId: TBD2
A.3. ambientTemperature
Description: An ambient temperature observed by measurement
equipment at an Observation Point, positioned such that it
measures the temperature of the surroundings (i.e., not including
any heat generated by the measuring or measured equipment),
expressed in degrees Celsius.
Data Type: float
Units: degrees Celsius
Range: -273.15 - +inf
ElementId: TBD3
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 Diegem
Belgium
Phone: +32 2 704 5622
EMail: bclaise@cisco.com
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