Internet Engineering Task Force (IETF) B. Claise

Internet Engineering Task Force (IETF) B. Claise
Request for Comments: 6526 P. Aitken
Category: Standards Track A. Johnson
ISSN: 2070-1721 Cisco Systems, Inc.
G. Muenz
TU Muenchen
March 2012

IP Flow Information Export (IPFIX) Per
Stream Control Transmission Protocol (SCTP) Stream

Abstract

This document specifies an extension to the specifications in RFC
5101, IP Flow Information Export (IPFIX), when using the Partial
Reliability extension of SCTP (PR-SCTP, Partial Reliability Stream
Control Transmission Protocol).

When implemented at both the Exporting Process and Collecting
Process, this method offers several advantages, such as the ability
to calculate Data Record losses for PR-SCTP per Template, immediate
export of Template Withdrawal Messages, immediate reuse of Template
IDs within an SCTP stream, reduced likelihood of Data Record loss,
and reduced demands on the Collecting Process. When implemented in
only the Collecting Process or Exporting Process, then normal IPFIX
behavior will be seen without all of the additional benefits.

Status of This Memo

This is an Internet Standards Track document.

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

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6526.

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Copyright Notice

Copyright (c) 2012 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. Relationship with IPFIX and PSAMP ..........................4
1.2. Applicability ..............................................5
1.3. Limitations ................................................5
2. Terminology .....................................................6
2.1. Conventions Used in This Document ..........................6
2.2. IPFIX Documents Overview ...................................6
2.3. PSAMP Documents Overview ...................................7
3. IPFIX Protocol Specifications: Limitations and Improvements .....7
3.1. Data Record Loss Calculated Per Template ...................7
3.1.1. IPFIX Protocol Specifications: Limitation ...........7
3.1.2. IPFIX Export Per SCTP Stream: Advantage .............8
3.2. Immediate Template Withdrawal and Reuse ....................8
3.2.1. IPFIX Protocol Specifications: Limitation ...........8
3.2.2. IPFIX Export Per SCTP Stream: Advantages ............9
3.3. Requirement for Data Set Buffering .........................9
3.3.1. IPFIX Protocol Specifications: Limitation ...........9
3.3.2. IPFIX Export Per SCTP Stream: Advantages ...........10
4. Specifications .................................................10
4.1. New Information Element ...................................10
4.2. Template Management .......................................11
4.3. SCTP ......................................................12
4.4. Template Withdrawal Message ...............................13
4.5. The Collecting Process's Side .............................14
4.5.1. SCTP ...............................................14
4.5.2. Enabling the Per-SCTP-Stream Extension .............14
4.5.3. Disabling the Per-SCTP-Stream Extension ............15
4.5.4. Calculating Data Record Loss Per Template ..........16
5. Resource Impact ................................................16
6. Examples .......................................................17
7. IANA Considerations ............................................20
8. Security Considerations ........................................21
9. References .....................................................21
9.1. Normative References ......................................21
9.2. Informative References ....................................21
10. Acknowledgments ...............................................22

1. Introduction

The IPFIX protocol [RFC5101] has the goal of exporting Flow
information. This protocol is designed to export information about
IP traffic Flows and related measurement data, where a Flow is
defined by a set of key attributes (e.g., source and destination IP
address, source and destination port, etc.). However, thanks to its
Template mechanism, the IPFIX protocol can export any type of

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information, as long as the relevant Information Element is specified
in the IPFIX information model [RFC5102], registered with IANA
[IANA], or specified as an enterprise-specific Information Element.

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

The IPFIX protocol [RFC5101] is flexible: It foresees the usage of
multiple SCTP streams per association; it allows the transmission of
Data Sets, Template Sets, and/or Options Template Sets on any SCTP
stream; it offers full and partially reliable export of Data Sets; it
specifies both ordered and out-of-order delivery of Data Sets.
However, due to bandwidth restrictions and packet losses in the
network as well as resource constraints on the Exporter and Collector
(e.g., limited buffer sizes), it is not always possible to export all
Data Sets in a reliable way.

This document specifies a method for exporting a Template Record and
its associated Data Sets in a single SCTP stream, limiting each
Template ID to a single SCTP stream if possible, and imposing
in-order transmission.

This method offers several advantages over IPFIX export as specified
in [RFC5101], such as the ability to calculate Data Record losses for
PR-SCTP per Template, immediate export of Template Withdrawal
Messages, immediate reuse of Template IDs within an SCTP stream,
reduced likelihood of Data Record loss, and reduced demands on the
Collecting Process.

1.1. Relationship with IPFIX and PSAMP

The specifications in this document apply to the IPFIX protocol
specifications [RFC5101]. However, they only apply to the SCTP
transport protocol [RFC4960] option of the IPFIX protocol
specifications (see Section 10 of [RFC5101]), specifically if the
Partial Reliability extension [RFC3758] is used. All specifications
from [RFC5101] apply, unless specified otherwise in this document.

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

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1.2. Applicability

The specifications contained in this document are applicable to cases
where application requirements include knowing how many Data Records
of a certain type (i.e., from a certain Template) were lost. A
typical example is a router exporting billing records, where the
Exporting Process cannot afford to export all the Flow Records
reliably, due to limited resources to buffer a large number of Flow
Records. Such a situation may occur if Data Sets are generated at a
higher rate at the Exporter than can be transferred to the Collector
because of bandwidth limitations in the network or slow reception at
the Collector.

To be more precise, the specification applicability is the case where
multiple Templates are simultaneously active within a single SCTP
Transport Session and the calculation of the Data Record loss for a
particular Template is required. Indeed, with the current IPFIX
specifications [RFC5101], if an IPFIX Message is lost (UDP or SCTP
partially reliable), it is not possible to determine to which
Template(s) the lost Data Records belong.

Exporting Processes following the specifications in this document
will interoperate with existing Collecting Processes that comply with
[RFC5101]; no changes are required at the Collecting Process to
receive data from an Exporting Process compliant with this method.
However, Collecting Processes may implement additional support for
per-stream export specified in this document in order to realize all
the benefits of the approach specified herein. Since the
specifications in this document mandate in-order transmission of
(Options) Templates and associated Data Records, late arrival of
(Options) Templates at the Collecting Process is avoided, which means
that there are no Data Records that need to be dropped or buffered.

1.3. Limitations

When multiple Templates are required, this method requires multiple
SCTP streams in the association between the Exporting Process and
Collecting Process, ideally one stream per Template. To properly
handle the transmission of additional Templates during the Transport
Session, additional SCTP streams are sometimes required. These SCTP
streams can only be added within the existing SCTP association if the
specifications in [RFC6525] are supported.

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2. Terminology

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

Note that, in this document, "(Options) Template" is used to refer to
Templates and Options Templates. Unless otherwise specified,
"Template" alone refers to Templates exclusive of Options Templates.

Template Reuse Delay

The time the Exporting Process needs to wait after sending the
last Data Set described by a given Template before sending a
Template Withdrawal Message for the Template. A suitable default
value is 5 seconds, as specified in [RFC5101].

2.1. Conventions Used in This Document

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].

2.2. IPFIX Documents Overview

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

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

The IPFIX architecture [RFC5470] specifies how IPFIX Data Records and
Templates are carried via a congestion-aware transport protocol from
IPFIX Exporting Processes to IPFIX Collecting Processes.

IPFIX has a formal description of IPFIX Information Elements, their
names, their types, and additional semantic information, as specified
in the IPFIX information model [RFC5102].

Finally, the IPFIX applicability statement [RFC5472] describes what
types of applications can use the IPFIX protocol and how they can use
the information provided. Furthermore, it shows how the IPFIX
framework relates to other architectures and frameworks.

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2.3. PSAMP Documents Overview

The document "A Framework for Packet Selection and Reporting"
[RFC5474] describes the Packet Sampling (PSAMP) framework for network
elements to select subsets of packets by statistical and other
methods, and to export a stream of reports on the selected packets to
a Collector.

The set of packet selection techniques (sampling, filtering, and
hashing) supported by PSAMP are described in "Sampling and Filtering
Techniques for IP Packet Selection" [RFC5475].

The PSAMP protocol [RFC5476] specifies the export of packet
information from a PSAMP Exporting Process to a PSAMP Collecting
Process. Like IPFIX, PSAMP has a formal description of its
Information Elements, their names, their types, and additional
semantic information. The PSAMP information model is defined in
[RFC5477].

3. IPFIX Protocol Specifications: Limitations and Improvements

For three specific topics ("Data Record Loss Calculated Per
Template", "Immediate Template Withdrawal and Reuse", and
"Requirement for Data Set Buffering"), this section explains the
limitations of the IPFIX protocol specifications on the one hand, and
the advantages of the method specified in this document on the other.

3.1. Data Record Loss Calculated Per Template

3.1.1. IPFIX Protocol Specifications: Limitation

Section 6.3.2 of [RFC3917], "Requirements for IP Flow Information
Export" discusses the data transfer reliability issues:

Loss of flow records during the data transfer from the Exporting
Process to the Collecting Process must be indicated at the
Collecting Process.

However, in some cases, it may be important to know how many Data
Records of a certain type were lost (e.g., in the case of billing),
and IPFIX does not conventionally provide this information.

A Collecting Process can detect out-of-sequence, dropped, or
duplicate IPFIX Messages by tracking the Sequence Number [RFC5101].
Note that the Sequence Number field in the IPFIX Message header
increases with the number of IPFIX Data Records within the SCTP
stream, so loss will be detected per stream.

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The IPFIX protocol specifications [RFC5101] specify that Data Records
defined by any Template may be sent on any SCTP stream. As such, if
there is more than one Template defined within the whole SCTP
association, then there is no way of knowing with which Template any
lost Data Record is associated. This is true, no matter what
convention the Exporting Process uses to send Data Records on
different SCTP streams, as the protocol makes no guarantees.

Note that a workaround allowed by the IPFIX specifications in
[RFC5101] is to use only one Template Record per SCTP Transport
Session, at the cost of multiplying the number of SCTP Transport
Sessions when multiple Template Records are required.

3.1.2. IPFIX Export Per SCTP Stream: Advantage

Using the specifications in this document, it is guaranteed that any
lost Data Records will be associated only with the Templates that are
defined on that SCTP stream. By defining only one Template per SCTP
stream, it is ensured that any loss is associated with that single
Template. So, by exporting each Template and its corresponding Data
Records in a separate SCTP stream from other Templates and Data
Records, the loss pertaining to each specific Template can be deduced
from the Sequence Number field in the IPFIX Message headers.

3.2. Immediate Template Withdrawal and Reuse

3.2.1. IPFIX Protocol Specifications: Limitation

A Collecting Process must have received the Template Record
associated with the Data Records to be able to decode the information
in the Data Records. [RFC5101] specifies the following:

The Exporting Process SHOULD transmit the Template Set and Options
Template Set in advance of any Data Sets that use that (Options)
Template ID, to help ensure that the Collecting Process has the
Template Record before receiving the first Data Record.

The fact that the Collecting Process cannot decode the Data Records
without the corresponding Template Record may result in Data Records
being discarded by the Collecting Process, as specified in [RFC5101]:

The Collecting Process normally receives Template Records from the
Exporting Process before receiving Data Records. The Data Records
are then decoded and stored by the Collector. If the Template
Records have not been received at the time Data Records are
received, the Collecting Process MAY store the Data Records for a
short period of time and decode them after the Template Records
are received.

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3.2.2. IPFIX Export Per SCTP Stream: Advantages

By exporting each Template Record and the corresponding Data Records
within a single SCTP stream and imposing in-order transmission, the
Template Record will always arrive before the associated Data
Records. Therefore, there is no risk that the Collecting Process
discards Data Records while waiting for the Template Record to
arrive.

Furthermore, when reusing a Template ID within an SCTP stream, the
Template Withdrawal Message will be guaranteed to arrive before the
new definition of the Template, and therefore the Template Record may
be sent directly after the Template Withdrawal Message. In other
words, the Template Reuse Delay restriction (5 seconds by default, as
specified in [RFC5101]) does not need to be applied to Template ID
reuse within the same SCTP stream.

Another advantage of the new specifications in this document is a
reduced load on the Collecting Process. Indeed, the Collecting
Process doesn't have to store the Data Records while waiting for the
Template Record, as the transmission order is always guaranteed.
This way, extra reliability of the Data Records is achieved without
extra burden on the Collecting Process.

3.3. Requirement for Data Set Buffering

3.3.1. IPFIX Protocol Specifications: Limitation

The fact that the protocol specifications in [RFC5101] are flexible
in terms of SCTP stream(s) on which the Template Set, Options
Template Set, and corresponding Data Sets are exported implies that
the (Options) Template Record might be exported on a different SCTP
stream than the corresponding Data Records. This might cause Data
Record loss in the Collecting Process, as ordered transmission across
SCTP streams is not guaranteed.

For example, a Template Record may be blocked pending reliable
transmission on one SCTP stream while the corresponding Data Records
may be transmitted immediately in another SCTP stream. Also, due to
different levels of SCTP stream congestion, it is possible that even
if the Template Record and corresponding Data Records are sent
reliably, Data Records sent on a different SCTP stream than the
Template Record might still arrive before the Template Record.

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3.3.2. IPFIX Export Per SCTP Stream: Advantages

By exporting each Template Record and all corresponding Data Records
within a single SCTP stream, and imposing in-order transmission, the
issue of ordered transmission across multiple SCTP streams is
avoided.

By exporting all corresponding Data Records within the same ordered
SCTP stream as the Template Record, each SCTP stream is independent
and self-contained, and the interaction between SCTP streams is
limited to that of the Options Template and associated Data Records
sent in different streams. This has several advantageous
consequences, including order preservation that does not result in
the blocking of unrelated data, and load reduction on the Collecting
Process (as the Template Records are guaranteed to be delivered
before the associated Data Records, there is no need for the
buffering of Data Sets that correspond with Templates that are
missing).

4. Specifications

This section specifies Exporting Process and Collecting Process
behavior different from that in [RFC5101] in order to realize the
benefits of per-stream export. Note that Exporting Processes
following these specifications will interoperate with [RFC5101]-
compliant Collecting Processes, but that Collecting Processes will
have to follow additional non-interoperable specifications to realize
the full benefits of the technique. These new specifications, which
add to those in [RFC5101], are described with the key words defined
in [RFC2119].

4.1. New Information Element

dataRecordsReliability

Description:
The export reliability of Data Records, within this SCTP
stream, for the element(s) in the Options Template scope. A
typical example of an element for which the export reliability
will be reported is the Template ID, as specified in the Data
Records Reliability Options Template. A value of 'True' means
that the Exporting Process MUST send any Data Records
associated with the element(s) reliably within this SCTP
stream. A value of 'False' means that the Exporting Process
MAY send any Data Records associated with the element(s)
unreliably within this SCTP stream.

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Abstract Data Type: boolean
Data Type Semantics: identifier
ElementId: 276
Status: current

Per Section 6.1.5 of [RFC5101], the boolean data type is encoded as a
single octet, with the value of 1 for True and the value of 2 for
False.

4.2. Template Management

To take advantage of per-stream export, Exporting Processes MUST
follow the specification in this section in addition to Section 8,
"Template Management", of [RFC5101].

As specified in [RFC5101], Template Sets and Options Template Sets
MUST be sent reliably.

Any Data Sets associated with a Template Record MUST be sent on the
same SCTP stream on which the Template Record was sent.

The Data Records Reliability Options Template is used to explicitly
inform the Collecting Process which Templates will be used in each
SCTP stream and whether each set of associated Data Records will be
sent reliably or unreliably. After defining a Template ID and before
sending any associated Data Records on an SCTP stream, the Exporting
Process MUST notify the Collecting Process of its intention to send
those Data Records reliably or unreliably within that SCTP stream.
It does this by sending a Data Record defined by the Data Records
Reliability Options Template for the Template associated with the
Data Records to be sent. If it does not, then the Collecting Process
MUST disable this extension for the SCTP association. The one
exception to this rule is that the Data Records associated with the
Data Records Reliability Options Template don't require an explicit
notification, as these MUST always be sent reliably.

The Data Records Reliability Options Template MUST contain the
following Information Elements:

Scope: Template ID
Non-scope: dataRecordsReliability

After sending a value of 'True' for the dataRecordsReliability
Element, the Exporting Process MUST send any Data Records associated
with the currently defined Template ID reliably within this SCTP
stream. After sending a value of 'False' for the

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dataRecordsReliability Element, the Exporting Process MAY send any
Data Records associated with the Template ID unreliably within this
SCTP stream.

If the Exporting Process wants to change the Data Records Reliability
value (from reliable to unreliable, or vice versa) for Data Records
on an SCTP stream, the Template MUST be withdrawn, and a new Template
MUST be used.

The Data Records Reliability Options Template MAY contain other
non-scope Information Elements associated with the (Options)
Template.

When an Options Template (including the Data Records Reliability
Options Template) and associated Data Records are sent in the same
SCTP stream, the first associated Data Record can follow the Options
Template immediately. When the Options Template and associated Data
Records are sent in different SCTP streams, the Exporting Process
SHOULD transmit the Options Template in advance of any Data Sets that
use it, to help ensure that the Collector has received the Options
Template Record before receiving the first associated Data Record.

It is RECOMMENDED that the Exporting Process only sends a single
Template and corresponding Data Sets within a single SCTP stream in
order to enable calculation of the potential Data Record loss for
this Template. The Exporting Process MAY group related (Options)
Templates and their associated Data Records within a single SCTP
stream so that loss statistics are calculated for the group of
Templates that are being sent unreliably within the SCTP stream.
This is suitable in cases where there are only slight variations
among the Templates in a group (e.g., the omission of unavailable
fields for export efficiency) and may be necessary if the SCTP
association does not support enough SCTP streams to export each
Template in its own SCTP stream.

If an SCTP stream contains a mixture of Data Records defined by
Template Records and by Options Template Records, the Data Records
defined by the Options Template Records SHOULD be sent reliably so
that the Collecting Process does not consider any loss to be
associated with the Options Data Records.

4.3. SCTP

To take advantage of per-stream export, Exporting Processes MUST
manage SCTP streams according to the specification in this section,
in addition to Section 10.2.4.3, "Stream", of [RFC5101].

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PR-SCTP [RFC3758] MUST be implemented by all compliant
implementations.

All IPFIX Messages in an SCTP stream MUST be sent in order.

As specified in [RFC5101], depending on the requirements of the
application, the Exporting Process may send Data Sets with full or
partial reliability.

If the Exporting Process is required to export a new Template Record
but there are no more free SCTP streams available, it SHOULD attempt
to increase the number of outbound SCTP streams to which it is able
to send, per [RFC6525]. Alternatively, the Exporting Process MAY add
the Template Set and Data Records to an existing SCTP stream at the
cost of diluting the granularity of any Data Record loss attribution.
An alternative that may result in the loss of Flow Records (for
example, due to lack of buffering on the Exporter) is to restart the
SCTP association with an increased number of SCTP streams.

4.4. Template Withdrawal Message

To take advantage of per-stream export, Exporting Processes MUST send
Template Withdrawal Messages according to the specification in this
section, in addition to Section 8, "Template Management", of
[RFC5101].

As specified in [RFC5101], Templates that are no longer in use SHOULD
be deleted. Before reusing a Template ID, the Template MUST be
deleted. In order to delete an allocated Template, the Template is
withdrawn through the use of a Template Withdrawal Message.

The Template Withdrawal Message MUST be sent on the same SCTP stream
as the associated Template Record.

The Template Withdrawal Message MUST be sent reliably, using SCTP-
ordered delivery per [RFC5101]. As all IPFIX Messages are sent in
order within an SCTP stream (per the specifications in this
document), the IPFIX Message containing the Template Withdrawal
Message will not arrive at the Collecting Process before any
associated and previously sent Data Record. As a consequence, no
Data Records will be lost due to delayed arrival at the Collecting
Process.

The Template ID from a withdrawn Template MAY be reused on the same
SCTP stream immediately after the Template Withdrawal Message is
sent. This case is equivalent to the use of a Template Reuse Delay
value of 0.

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After reusing the Template ID, the Exporting Process MUST send a Data
Record associated with the Data Records Reliability Options Template
to specify the reliability level of the Data Records associated with
the new Template.

If the Template ID is to be reused on a different SCTP stream, the
new Template Record MUST NOT be sent before the Template Reuse Delay
interval.

A Template Withdrawal Message to withdraw all Templates for the
Observation Domain ID specified in the IPFIX Message header MUST NOT
be used.

Multiple Template IDs MAY be withdrawn with a single Template
Withdrawal Message under the condition that all the Template IDs in
the Template Withdrawal Message are used on the same SCTP stream as
the Template Withdrawal Message.

4.5. The Collecting Process's Side

Collecting Processes must operate in a fashion slightly contrary to
[RFC5101] in order to realize the full benefits of per-stream export.
However, the specification in this section contains a mechanism that
allows per-stream-capable Collecting Processes to selectively enable
per-stream export, in order to ensure interoperability of per-stream-
capable Collecting Processes with Exporting Processes that do not
implement per-stream export.

4.5.1. SCTP

As specified in [RFC5101], the Collecting Process SHOULD listen for a
new association request from the Exporting Process. The Exporting
Process will request a number of SCTP streams to use for export.

A Collecting Process SHOULD support the procedure for the addition of
an SCTP stream specified in [RFC6525].

4.5.2. Enabling the Per-SCTP-Stream Extension

In IPFIX, there is no explicit notification of the Exporting
Process's capabilities. There is also no return channel for the
Collecting Process to communicate its capabilities.

When the Exporting Process is sending according to the per-SCTP-
stream extension, the first Data Record received by the Collecting
Process will be associated with the Data Records Reliability Options

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Template. In this case, the Collecting Process enables the extension
for this Transport Session. Otherwise, the Collecting Process MUST
NOT enable the extension for this Transport Session.

The Collecting Process MUST accept other non-scope Information
Elements in the Data Records Reliability Options Template.

4.5.3. Disabling the Per-SCTP-Stream Extension

Nothing prevents an implementation that does not meet the
specification of the per-SCTP-stream extension from sending a
Template that looks like a dataRecordsReliability Options Template.
Therefore, a Collecting Process MUST detect if the Exporting Process
fails to meet the specification fully. If any of the conditions
below is met, the Exporting Process does not properly use the
per-SCTP-stream extension, and the Collecting Process MUST log an
error message and disable this extension for the SCTP association.

1. A Data Record is received before the appropriate Data Record
associated with the Data Records Reliability Options Template
has been received on the same SCTP stream (see Section 4.2).
Note: Data Records associated with the Data Records Reliability
Options Template are an exception to this rule.

2. A Data Record associated with a Data Records Reliability
Options Template is received on an SCTP stream for a
(non-Options) Template that was defined on a different SCTP
stream.

3. A second Data Record associated with the Data Records
Reliability Options Template is received for the same (Options)
Template.

4. A Data Record or a Template Withdrawal Message is associated
with a Template that was defined on a different SCTP stream.

5. Loss of Data Records is detected within a stream where a Data
Record associated with the Data Records Reliability Options
Template indicating unreliable transmission for any Template
has not been received.

6. A message is received with the SCTP U(nordered) flag set to 1
(i.e., the message was sent unordered), even if it is processed
in order.

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4.5.4. Calculating Data Record Loss Per Template

As specified in [RFC5101], the IPFIX protocol has a Sequence Number
field in the IPFIX Message header that increases with the number of
IPFIX Data Records in the IPFIX Message. A Collecting Process may
detect out-of-sequence, dropped, or duplicate IPFIX Messages by
tracking the Sequence Number.

When one or more sequential IPFIX Messages are considered lost, the
number of lost Data Records is equal to the Sequence Number of the
first IPFIX Message Header following the lost packets (S2) minus the
Sequence Number of the first lost IPFIX Message (S1). The Sequence
Number of the first lost IPFIX Message can be calculated as the
Sequence Number of the last IPFIX Message before the sequence of lost
IPFIX Messages (S0) plus the number of Data Records in that IPFIX
Message (N0).

S1 = S0 + N0
loss = (S2 - S1) (mod(2^32))
= (S2 - (S0 + N0)) (mod(2^32))

Note that modulo 2^32 arithmetic is required, since the Sequence
Number may wrap within the series of lost IPFIX Messages. If less
than 2^32 Data Records are lost in a sequence (which can be assumed
in practice), the above equation returns the exact number of lost
Data Records.

Note that using an unsigned32 type for the loss would automatically
take care of the mod(2^32) operation.

As this Sequence Number is incremented per SCTP stream, the loss of
Data Records sent in that SCTP stream can be calculated in the case
of partially reliable export. This loss can be attributed to the
Data Records sent for the (Options) Template(s) whose records are
being sent unreliably within that SCTP stream.

5. Resource Impact

Although adding the new SCTP streams requires a message exchange, it
is more lightweight to set up additional SCTP streams than to set up
a new SCTP association, since the only overhead of adding SCTP
stream(s) to an existing SCTP association is the addition of 16-24
more bytes (allocated in the SCTP association, a single time),
whereas setting up a new SCTP association requires more overhead.

In terms of throughput impact, the fact that these specifications
discourage multiplexing Templates and Data Records of different
Template IDs may lead to a slightly larger IPFIX Message overhead.

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RFC 6526 IPFIX Per SCTP Stream March 2012

If the Data Record rate is low for a specific Template (and hence a
specific SCTP stream), the Exporting Process might not be able to
fill the IPFIX Messages with Data Records associated with other
Templates. In such a situation, there is a potential overhead due to
additional IPFIX Message headers and SCTP chunk headers.

Finally, with respect to the processing overhead on the Exporter, a
lot of state information must be stored when a large number of SCTP
streams are used within an SCTP association. However, no comparison
of the performance impact of multiple streams within an SCTP
association versus opening the same number of independent SCTP
associations is available.

6. Examples

Figure 1 shows an example where SCTP stream 10 carries a Template
Record with Template ID 257 transmitted with full reliability (FR),
together with associated Data Records transmitted with partial
reliability (PR). The Data Records Reliability Options Template with
Template ID 256 is transmitted with full reliability. Its
corresponding Data Set contains one Data Record.

Record 1:

o Scope: Template ID = 257
o Non-scope: dataRecordsReliability = False

+--------+ +---------+ +--------+
| | | | | |
stream 10 ----| Data | . . . | Data |---| Data |---...
| 257 | | 257 | | 256 |
| PR| | PR| | FR|
+--------+ +---------+ +--------+

+----------+ +-------------+
| | | Reliability |
| | | Options |
...---| Template |-------| Template |------>
| 257 | | 256 |
| FR| | FR|
+----------+ +-------------+

Figure 1

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Note that Template 257 will always be processed before the Data
Records by the Collecting Process, because all IPFIX Messages are
sent in order within an SCTP stream. Therefore, the job of the
Collecting Process is simplified. Furthermore, the Data Record loss
for Template 257 can easily be calculated by the Collecting Process.

If an Options Template is necessary to understand the content of a
Data Record (i.e., the scope in the Options Template Record is an
Information Element contained in the Data Record or associated with
the Data Record), the Options Template Record should be sent in the
same SCTP stream, as displayed in Figure 2.

+--------+ +--------+ +--------+
| | | | | |
stream 20 ----| Data |...| Data |-----| Data |--- ...
| 260 | | 260 | | 259 |
| PR| | PR| | FR|
+--------+ +--------+ +--------+

+--------+ +----------+
| | | |
...---| Data |-------| Template |---...
| 258 | | 260 |
| FR| | FR|
+--------+ +----------+

+----------+ +-------------+
| Options | | Reliability |
| Template | | Options |
...---| |-------| Template |------>
| 259 | | 258 |
| FR| | FR|
+----------+ +-------------+

Figure 2

Figure 2 shows an example where SCTP stream 20 carries the following:

- a Data Records Reliability Options Template with Template ID 258,
transmitted with full reliability.

- an Options Template Record with Template ID 259, transmitted with
full reliability. This Options Template Record contains
additional information related to the subsequent Data Records
based on Template ID 260. Typical examples are the Common
Properties information [RFC5473] or the Selector Report
Interpretation [RFC5476].

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RFC 6526 IPFIX Per SCTP Stream March 2012

- a Template Record with Template ID 260, transmitted with full
reliability.

- a Data Set specified by the Reliability Options Template with
Template ID 258, transmitted with full reliability.

The Data Set contains three Data Records:

Record 1:
o Scope: Template ID = 258
o Non-scope: dataRecordsReliability = True

Record 2:
o Scope: Template ID = 259
o Non-scope: dataRecordsReliability = True

Record 3:
o Scope: Template ID = 260
o Non-scope: dataRecordsReliability = False

These Data Records inform the Collecting Process that the Data
Records for Template IDs 258 and 259 are sent reliably, while the
Data Records for Template ID 260 are not. Note that the first
Data Record associated with the Data Record Reliability Options
Template (Template ID 258) is not required and can be omitted.

- a Data Record specified by Template ID 259, transmitted with full
reliability.

- a Data Record specified by Template ID 260, transmitted with
partial reliability.

If the Collecting Process observes some Data Record loss using the
Sequence Number, the loss can only stem from the Data Records
associated with Template ID 260, as these are the only Data Records
not exported reliably. Therefore, the calculation of loss per
Template ID 260 is possible.

Note that Options Templates 258, 259, and 260 will always arrive
before their associated Data Records, respectively, because all IPFIX
Messages must be sent in order within an SCTP stream.

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RFC 6526 IPFIX Per SCTP Stream March 2012

Figure 3 shows an example where SCTP stream 30 carries a Template
Record with Template ID 262 transmitted with full reliability, an
associated Data Record transmitted with full reliability, and a
Template Withdrawal Message, followed by a redefinition of Template
ID 262, and finally the Data Record associated with the new Template
transmitted with partial reliability. The Template Withdrawal
Message and the new definition of Template ID 262 are sent
immediately, without waiting for the Template Reuse Delay interval.

+--------+ +----------+ +----------+
| | |Data | | |
stream 30 ... ---| Data |...| 261 |-----| Template |---
| 262 | |tmpID: 262| | 262 |
| PR| |dRR: False| | FR|
+--------+ +----------+ +----------+

+----------+ +--------+ +----------+
| Template | | | | Data |
...| Withdraw |-----| Data |-------| 261 |---...
| 262 | | 262 | |tmpID: 262|
| FR| | FR| |dRR: True|
+----------+ +--------+ +----------+

+----------+ +-------------+
| | | Reliability |
| Template | | Options |
...---| |-------| Template |------>
| 262 | | 261 |
| FR| | FR|
+----------+ +-------------+

dRR: Data Records Reliability

Figure 3

The second Data Record associated with the Data Records Reliability
Options Template shows that the Data Records associated with the
newly specified Template ID 262 will be sent unreliably.

7. IANA Considerations

According to the process defined in [RFC5102], IANA has allocated the
dataRecordsReliability Information Element (defined in Section 4.1)
in the "IPFIX Information Elements" registry [IANA].

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8. Security Considerations

The same security considerations as for the IPFIX protocol [RFC5101]
apply.

9. References

9.1. Normative References

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

[RFC3758] Stewart, R., Ramalho, M., Xie, Q., Tuexen, M., and P.
Conrad, "Stream Control Transmission Protocol (SCTP)
Partial Reliability Extension", RFC 3758, May 2004.

[RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol",
RFC 4960, September 2007.

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

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

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

[RFC6525] Stewart, R., Tuexen, M., and P. Lei, "Stream Control
Transmission Protocol (SCTP) Stream Reconfiguration",
RFC 6525, February 2012.

9.2. Informative References

[IANA] IPFIX Information Elements Registry,
<http://www.iana.org/assignments/ipfix>.

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

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

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RFC 6526 IPFIX Per SCTP Stream March 2012

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

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

10. Acknowledgments

The authors would like to thank Brian Trammell for his expert
feedback and continuous effort to improve the specifications; Elisa
Boschi for her thorough reading; Randall Stewart, Peter Lei, and
Michael Tuexen for their SCTP-related feedback and expertise; and
Tobias Limmer.

Claise, et al. Standards Track [Page 22]

RFC 6526 IPFIX Per SCTP Stream March 2012

Authors' Addresses

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

Phone: +32 2 704 5622
EMail: [email protected]

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

Phone: +44 131 561 3616
EMail: [email protected]

Andrew Johnson
Cisco Systems, Inc.
96 Commercial Quay
Commercial Street
Edinburgh, EH6 6LX, United Kingdom

Phone: +44 131 561 3641
EMail: [email protected]

Gerhard Muenz
Technische Universitaet Muenchen
Department of Informatics - I8
Boltzmannstr. 3
Garching D-85748
DE

EMail: [email protected]
URI: http://www.net.in.tum.de/~muenz

Claise, et al. Standards Track [Page 23]