One document matched: draft-trammell-ipfix-ie-doctors-03.xml
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<front>
<title abbrev="IPFIX IE-DOCTORS">
Guidelines for Authors and Reviewers of IPFIX Information Elements
</title>
<author initials="B." surname="Trammell" fullname="Brian Trammell">
<organization abbrev="ETH Zurich">
Swiss Federal Institute of Technology Zurich
</organization>
<address>
<postal>
<street>Gloriastrasse 35</street>
<city>8092 Zurich</city>
<country>Switzerland</country>
</postal>
<phone>+41 44 632 70 13</phone>
<email>trammell@tik.ee.ethz.ch</email>
</address>
</author>
<author initials="B." surname="Claise" fullname="Benoit Claise">
<organization abbrev="Cisco Systems, Inc.">
Cisco Systems, Inc.
</organization>
<address>
<postal>
<street>De Kleetlaan 6a b1</street>
<city>1831 Diagem</city>
<country>Belgium</country>
</postal>
<phone>+32 2 704 5622</phone>
<email>bclaise@cisco.com</email>
</address>
</author>
<date month="October" day="28" year="2011"/>
<area>Operations</area>
<workgroup>IPFIX Working Group</workgroup>
<abstract>
<t>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.</t>
</abstract>
</front>
<middle>
<section title="Introduction" anchor="sec-intro">
<t> 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 <xref target="RFC5472">"IPFIX Applicability
Statement"</xref>. These new applications are largely defined by
creating new Information Elements beyond those in the <xref
target="iana-ipfix-assignments">IANA IPFIX Information Element
Registry</xref>. New applications may be further specified through
additional RFCs defining and describing their usage.</t>
<t>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.</t>
<section title="Intended Audience and Usage" anchor="sec-audience">
<t>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.</t>
<t>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.</t>
<t>This document specifies additional practices beyond those
appearing in the IANA Considerations sections of existing IPFIX
documents, especially the <xref target="RFC5102">Information
Model</xref>. The practices outlined in this document are intended
to guide experts when making changes to the IANA registry under
Expert Review as defined in <xref target="RFC5226"/>.</t>
</section>
<section title="Overview of relevant IPFIX documents">
<t><xref target="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.</t>
<t><xref target="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.
</t>
<t><xref target="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.</t>
<t><xref target="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 <xref
target="RFC5101"/> and <xref target="RFC5102"/>; these
restrictions MUST be observed in the definition of new Information
Elements, as in <xref target="sec-ie-semantics"/>.</t>
</section>
</section>
<section title="Terminology" anchor="terminology-section">
<t>Capitalized terms used in this document that are defined in the
Terminology section of <xref target="RFC5101"/> are to be interpreted
as defined there.</t>
<t>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 <xref
target="RFC5472">IPFIX Applicability statement</xref>. By this
definition, <xref target="RFC5476">PSAMP</xref> was the first new
IPFIX application after the publication of the IPFIX protocol <xref
target="RFC5101"/>.</t>
<t>"IANA registry", as used in this document, unless otherwise noted,
refers to the <xref target="iana-ipfix-assignments">IANA IPFIX
Information Element Registry</xref>.</t>
<t>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 <xref
target="RFC2119"/>.</t>
</section>
<section title="How to apply IPFIX" anchor="sec-howto">
<t>Though originally specified for the export of IP flow information,
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
<xref target="RFC5476">PSAMP</xref>, any application with the
following characteristics is a good candidate for an IPFIX
application:</t>
<t><list style="symbols">
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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).</t>
</list></t>
<t>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 <xref
target="sec-ie-reuse"/> for guidelines on maximizing Information
Element reuse). In this case, no additional work within the IETF is
necessary: simply define Templates and start exporting.</t>
<t>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 <xref target="sec-iedef"/> for best practices to be
followed in defining Information Elements.</t>
<t>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
Element definitions as in <xref target="sec-iedef"/>, as well as
suggested Templates and examples of the use of those Templates within
the new application as in <xref target="sec-templates"/>. <xref
target="sec-iespec"/> defines a compact textual Information Element
notation to be used in describing these suggested Templates and/or the
use of <xref target="I-D.ietf-ipfix-structured-data">IPFIX Structured
Data</xref> within the new application.</t>
</section>
<section title="Defining new Information Elements" anchor="sec-iedef">
<t>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:</t>
<t><list style="symbols">
<t>The Information Element MUST be sufficiently unique within the
registry. A proposed Information Elements which is a substantial
duplicate of an exiting Information Element is to be represented
using the existing Element.</t>
<t>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
<xref target="sec-ie-structure"/>.</t>
<t>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 <xref target="RFC5101"/>.</t>
</list></t>
<t>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 <xref target="RFC5102"/> as appropriate.</t>
<section title="Information Element naming" anchor="ie-names">
<t>Information Element Names should be defined in accordance with
section 2.3 of <xref target="RFC5102"/>; the most important naming
conventions are repeated here for convenience.</t>
<t><list style="symbols">
<t>Names of Information Elements should be descriptive.</t>
<t>Names of Information Elements MUST be unique within the
IPFIX information model.</t>
<t>Names of Information Elements start with non-capitalized
letters.</t>
<t>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.</t>
</list></t>
<t>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.</t>
</section>
<section title="Information Element data types" anchor="sec-ie-types">
<t>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
<xref target="iana-ipfix-assignments"/>.</t>
<t>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 <xref target="RFC5101"/> in cases where fewer than 2^64 values
are necessary.</t>
<t>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.</t>
<t>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 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, even if the data was represented using a
different type in the source (i.e., 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.)</t>
<t>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 <xref target="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.</t>
</section>
<section title="Information Element numbering">
<t>In general, when adding newly registered Information Elements
to the registry, IANA SHOULD assign the lowest available
Information Element identifier (the value column in <xref
target="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 <xref target="RFC5477">PSAMP Information
Model</xref>, which assigned a block of Information Elements
identifiers starting at 300.</t>
<t>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 <xref target="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.</t>
</section>
<section title="Ancillary Information Element properties"
anchor="sec-ie-semantics">
<t>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 <xref target="RFC5102"/>, subject to the restrictions given
in Section 3.10 of <xref target="RFC5610"/>; essentially, the
semantics and the type must be consistent.</t>
<t>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.</t>
<t>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.</t>
</section>
<section title="Internal structure in Information Elements" anchor="sec-ie-structure">
<t>The definition of Information Elements with
internal structure with the structure defined in the Description
field is discouraged, except in the following cases:</t>
<t><list style="symbols">
<t>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)</t>
<t>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)</t>
<t>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)</t>
</list></t>
<t>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 <xref
target="I-D.ietf-ipfix-structured-data">IPFIX Structured
Data</xref> extension instead.</t>
<t>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 <xref
target="sec-ie-reuse"/>.</t>
<t>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.</t>
</section>
<section title="Information Element multiplicity" anchor="sec-ie-multiplicity">
<t>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:</t>
<t><list style="symbols">
<t>As specified in section 8 of <xref target="RFC5101"/>: "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 containing
multiple instances of the Information Element representing a
single item within the Template Record describing the Data
Records.</t>
<t>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 <xref
target="I-D.ietf-ipfix-structured-data">IPFIX Structured
Data</xref> extension.</t>
<t>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.</t>
</list></t>
<t>Specifically, new Information Element SHOULD NOT encode any
multiplicity or ordinality information into the definition of the
Information Element itself.</t>
</section>
<section title="Enumerated Values and Subregistries" anchor="ie-subregistries">
<t>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 <xref
target="RFC5226">Expert Review</xref>.</t>
</section>
<section title="Reversibility as per RFC 5103" anchor="ie-reversibility">
<t><xref target="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, <xref target="RFC5103"/>
enumerates those which Information Elements which were defined at
the time of its publication which are NOT reversible.</t>
<t>New non-reversible Information Elements SHOULD contain a note
in the description stating that they are not reversible. </t>
</section>
<section title="Promotion of Enterprise-Specific Information Elements" anchor="ie-promotion">
<t>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.</t>
<t>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.</t>
</section>
<section title="Avoiding Bad Ideas in Information Element Design" anchor="ie-dont-do-this">
<t>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.</t>
<t>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 <xref
target="RFC5103"/>) and initiatorPackets and responderPackets (the
same, for packetDeltaCount).</t>
<t>As mentioned in <xref target="sec-ie-types"/>, 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.</t>
<t>As mentioned in <xref target="sec-ie-multiplicity"/>, 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 <xref
target="I-D.ietf-ipfix-structured-data">IPFIX Structured Data</xref>
where supported, as a basicList of MPLS label entries, or as a raw
MPLS label stack using the variable-length mplsLabelStackSection
Information Element.</t>
</section>
</section>
<section title="The Information Element Lifecycle" anchor="sec-lifecycle">
<t>Once an Information Element or set of Information Elements has been
identified for a given application, Information Element specifications
in accordance with <xref target="sec-iedef"/> 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.</t>
<section title="The IE-DOCTORS process" anchor="sec-process">
<t>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.</t>
<t>IE-DOCTORS reviewers 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 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.</t>
</section>
<section title="Revising Information Elements" anchor="sec-revision">
<t>The Information Element status field in the Information Element
Registry is defined in <xref target="RFC5102"/> to allow Information
Elements to be 'current', 'deprecated' or 'obsolete'. No Information
Elements are as of this writing deprecated or obsolete, and <xref
target="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.</t>
<t>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.</t>
<t>A change to an Information Element is held to be interoperable only
when:</t>
<t><list style="symbols">
<t>it involves the correction of an error which is obviously only
editorial; or</t>
<t>it corrects an ambiguity in the Information Element's
definition, which itself leads to non-interoperability (e.g., a
prior change to ipv6ExtensionHeaders); or</t>
<t>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</t>
<t>it defines a previously undefined or reserved enumerated value,
or one or more previously reserved bits in an Information Element
with flag semantics; or</t>
<t>it expands the set of permissible values in the Information
Element's range; or</t>
<t>it harmonizes with an external reference which was itself
corrected.</t>
</list></t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
</section>
<section title="Deprecating Information Elements" anchor="sec-deprecation">
<t>Changes that are not permissible by these criteria may only be
handled by deprecation. An Information Element MAY be deprecated and
replaced when:</t>
<t><list style="symbols">
<t>the Information Element definition has an error or shortcoming
which cannot be permissibly changed as above; or</t>
<t>the deprecation harmonizes with an external reference which was
itself deprecated through that reference's accepted deprecation
method; or</t>
<t>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.</t>
</list></t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
</section>
<section title="Versioning the entire IANA Registry">
<t>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 <xref
target="iana-ipfix-assignments"/>) SHOULD be used.</t>
</section>
</section>
<section title="When not to define new Information Elements" anchor="sec-noie">
<t>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.</t>
<section title="Maximizing reuse of existing Information Elements" anchor="sec-ie-reuse">
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>Applications dealing with bidirectional interactions should use
<xref target="RFC5103">Bidirectional Flow Support for IPFIX</xref>
to represent these interactions.</t>
<t>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 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).</t>
<t>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.</t>
</section>
<section title="Applying enterprise-specific Information Elements" anchor="ie-enterprise">
<t>IPFIX provides a mechanism for defining enterprise-specific
Infomation Elements, as in Section 3.2 of <xref
target="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.</t>
<t>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:</t>
<t><list style="symbols">
<t>export of implementation-specific information, or</t>
<t>export of information derived in a commercially-sensitive
or proprietary method, or</t>
<t>export of information or meta-information specific to a
commercially-sensitive or proprietary application.</t>
</list></t>
<t>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 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
<xref target="ie-promotion"/>.</t>
</section>
</section>
<section title="Applying IPFIX to non-Flow Applications" anchor="sec-nonflow">
<t>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.</t>
<t>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.</t>
<t>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
<xref target="RFC5473"/> for an example application of this.</t>
</section>
<section title="Writing Internet-Drafts for IPFIX Applications" anchor="sec-draft">
<t>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.</t>
<t>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 <xref
target="sec-iedef"/> 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 <xref target="sec-iespec"/>.</t>
<section title="Example Information Element Definition">
<t>This is an example of an Information Element definition which would appear in an Internet-Draft. The name appears in the section title.</t>
<t><list style="hanging">
<t hangText="Description: ">
Description goes here.
</t>
<t hangText="Data Type: ">Data type goes here; obligatory</t>
<t hangText="Data Type Semantics: ">Data type semantics, if any, go here; optional</t>
<t hangText="Units: ">Units, if any, go here; optional</t>
<t hangText="Range: ">Range, if not implied by the data type, goes here; optional</t>
<t hangText="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</t>
<t hangText="ElementId: ">TBD1</t>
</list></t>
</section>
<section title="Defining Recommended Templates" anchor="sec-templates">
<t>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.</t>
<t>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 as above:</t>
<t><list style="symbols">
<t>that the order of Information Elements within a Template is
not significant;</t>
<t>that Templates on the wire for the application may also
contain additional Information Elements beyond those specified
in the recommended Template;</t>
<t>that a stream of IPFIX Messages supporting the application
may also contain Data Records not described by the recommended
Templates; and</t>
<t>that any reader of IPFIX Messages supporting the
application MUST accept these conditions.</t>
</list></t>
<t>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.</t>
<t>Recommended Templates are defined, for example, in <xref
target="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 <xref target="RFC5101">the protocol document
itself</xref> for exporting export statistics; in the <xref
target="RFC5655">file format</xref> for exporting file metadata;
and in Mediator intermediate process definitions such as <xref
target="I-D.ietf-ipfix-anon"/> for intermediate process metadata.
The discussion in these examples is a good model for recommended
template definitions.</t>
</section>
</section>
<section title="A Textual Format for Specifying Information Elements and
Templates" anchor="sec-iespec">
<t>The examples given above are all 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.</t>
<t>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 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.</t>
<section title="Information Element Specifiers">
<t>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.</t>
<t>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:</t>
<t><list style="symbols">
<t>() parentheses for Information Element numbers,</t>
<t><> angles for Information Element data types, and</t>
<t>[] square brackets for Information Element sizes.</t>
<t>{} curly braces contain an optional space-separated list of
context identifiers to be associated with an Information
Element, as described in more detail in <xref
target="sec-iespec-templates"/></t>
</list></t>
<t>The symbol + is reserved for Information Element nesting within
structured data elements; these are described in and <xref
target="sec-iespec-structured"/>, respectively.</t>
<t>Whitespace in IESpecs is insignificant; spaces can be added
after each element in order, e.g., to align columns for better
readability.</t>
<t>The basic form of a fully-qualified IESpec for an
IANA-registered Information Element is as follows:</t>
<t>name(number)<type>[size]</t>
<t>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.</t>
<t>The basic form of a fully-qualified IESpec for an
enterprise-specific Information Element is as follows:</t>
<t>name(pen/number)<type>[size]</t>
<t>where 'pen' is the Private Enterprise Number as a decimal
integer.</t>
<t>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
<xref target="RFC5610"/>, is not supported by this syntax.</t>
<t>Example fully-qualified IESpecs follow:</t>
<t><list>
<t>octetDeltaCount(1)<unsigned64>[8]</t>
<t>octetDeltaCount(1)<unsigned64> (unsigned64 is natively 8 octets long)</t>
<t>sourceIPv4Address(8)<ipv4Address></t>
<t>wlanSSID(146)<string>[v]</t>
<t>sipRequestURI(35566/403)<string>[65535]</t>
</list></t>
<t>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.</t>
<t>Example partial IESpecs follow:</t>
<t><list style="symbols">
<t>octetDeltaCount</t>
<t>octetDeltaCount[4] (reduced-length encoding)</t>
<t>(1)</t>
<t>(1)[4] (reduced length encoding; note that this is exactly equivalent to an Information Element specifier in a Template)</t>
</list></t>
</section>
<section title="Specifying Templates" anchor="sec-iespec-templates">
<t>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.</t>
<artwork><![CDATA[
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}
]]></artwork>
<t>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 <xref target="RFC5101"/> in IESpec syntax is shown
below:</t>
<artwork><![CDATA[
templateId(145)<unsigned16>[2]{scope}
flowKeyIndicator(173)<unsigned64>[8]
]]></artwork>
</section>
<section title="Specifying IPFIX Structured Data" anchor="sec-iespec-structured">
<t>IESpecs can also be used to illustrate the structure of the
information exported using the <xref
target="I-D.ietf-ipfix-structured-data">IPFIX Structured Data
extension</xref>. 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:</t>
<artwork><![CDATA[
basicList{oneOrMoreOf}
+sourceIPv4Address(8)[4]
]]></artwork>
<t>And an example subTemplateList itself containing a basicList is
shown below:</t>
<artwork><![CDATA[
subTemplateList{allOf}
+basicList{oneOrMoreOf}
++sourceIPv4Address(8)[4]
+destinationIPv4Address(12)[4]
]]></artwork>
<t>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).</t>
<t>The contexts associable with structured data Information
Elements are the semantics, as defined in section 4.4 of <xref
target="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 <xref
target="I-D.ietf-ipfix-structured-data"/>.</t>
</section>
</section>
<section title="Security Considerations" anchor="security-section">
<t>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" <xref
target="RFC5474"/> concluded in section 12.3.2 that the hash functions
private parameters should not exported within IPFIX. </t>
<t>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 <xref
target="RFC2804"/>. See the Security Considerations section." </t>
<t> These security considerations MAY also be stressed in an
accompanying Internet-Draft, as in <xref target="sec-draft"/>. For
example, the "Packet Sampling (PSAMP) Protocols Specification" <xref
target="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 SHOULD NOT export the
full payload of conversations, as this would mean wiretapping <xref
target="RFC2804"/>. The PSAMP Device MUST respect local privacy laws."
</t>
</section>
<section title="IANA Considerations" anchor="iana-section">
<t>With respect to the management of the IPFIX Information Element
registry and associated subregistries located at <xref
target="iana-ipfix-assignments"/>, this document defines a process for
IANA in <xref target="sec-process"/>, and includes a set of guidelines
for IANA for applying this process in <xref target="sec-iedef"/>, <xref
target="sec-lifecycle"/>, and <xref target="sec-noie"/>.</t>
<t>In addition, in order to support more effective management of the
Information Element lifecycle as defined in <xref
target="sec-lifecycle"/>, it specifies the addition of three new columns
for this registry:</t>
<t><list style="hanging">
<t hangText="Revision: ">a serial revision number for each
Information Element, beginning at 0 for all presently existing and
newly created Information Elements.</t>
<t hangText="Date: ">the date at which the Information Element was
created or last modified.</t>
<t hangText="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.</t>
</list></t>
</section>
<section title="Acknowledgements">
<t>The authors would like to acknowledge the FP7 PRISM and DEMONS
projects for their material support of this work.</t>
</section>
<!-- <section title="Open Issues">
<list style="symbols">
<t>TBD: refer to the Draft Standards version of RFC5101 and
RFC5102, once these are written.</t>
<t>TBD: Do we want the IE-Doctors to be a formal directorate under
the OPS area? What can we take from the experience of PMOL? This
should be handled in discussions with IANA, the IESG, and the
IPFIX WG.</t>
<t>add examples everywhere (including sipclf)</t>
</list>
</section> -->
</middle>
<back>
<references title="Normative References">
<?rfc include="reference.RFC.3954" ?>
<?rfc include="reference.RFC.5101" ?>
<?rfc include="reference.RFC.5102" ?>
<?rfc include="reference.RFC.5103" ?>
<?rfc include="reference.RFC.5610" ?>
<?rfc include="reference.RFC.2119" ?>
<?rfc include="reference.RFC.5226" ?>
</references>
<references title="Informative References">
<?rfc include="reference.RFC.2804" ?>
<?rfc include="reference.RFC.3917" ?>
<?rfc include="reference.RFC.4181" ?>
<?rfc include="reference.RFC.5153" ?>
<?rfc include="reference.RFC.5470" ?>
<?rfc include="reference.RFC.5471" ?>
<?rfc include="reference.RFC.5472" ?>
<?rfc include="reference.RFC.5473" ?>
<?rfc include="reference.RFC.5474" ?>
<?rfc include="reference.RFC.5476" ?>
<?rfc include="reference.RFC.5477" ?>
<?rfc include="reference.RFC.5655" ?>
<?rfc include="reference.I-D.ietf-ipfix-structured-data" ?>
<?rfc include="reference.I-D.ietf-ipfix-anon" ?>
<reference anchor='iana-ipfix-assignments'>
<front>
<title>IP Flow Information Export Information Elements (http://www.iana.org/assignments/ipfix/ipfix.xml)</title>
<author surname="Internet Assigned Numbers Authority"/>
</front>
</reference>
</references>
</back>
</rfc>
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