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Keywords: flow-based measurement
Internet Engineering Task Force (IETF) A. Kobayashi, Ed.
Request for Comments: 5982 NTT PF Lab.
Category: Informational B. Claise, Ed.
ISSN: 2070-1721 Cisco Systems, Inc.
August 2010
IP Flow Information Export (IPFIX) Mediation: Problem Statement
Abstract
Flow-based measurement is a popular method for various network
monitoring usages. The sharing of flow-based information for
monitoring applications having different requirements raises some
open issues in terms of measurement system scalability, flow-based
measurement flexibility, and export reliability that IP Flow
Information Export (IPFIX) Mediation may help resolve. This document
describes some problems related to flow-based measurement that
network administrators have been facing, and then it describes IPFIX
Mediation applicability examples along with the problems.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
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). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see 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/rfc5982.
Copyright Notice
Copyright (c) 2010 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
Kobayashi and Claise Informational [Page 1]
RFC 5982 IPFIX Mediation: Problem Statement August 2010
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.
Table of Contents
1. Introduction ....................................................3
2. Terminology and Definitions .....................................3
3. IPFIX/PSAMP Documents Overview ..................................5
3.1. IPFIX Documents Overview ...................................5
3.2. PSAMP Documents Overview ...................................5
4. Problem Statement ...............................................5
4.1. Coping with IP Traffic Growth ..............................6
4.2. Coping with Multipurpose Traffic Measurement ...............7
4.3. Coping with Heterogeneous Environments .....................7
4.4. Summary ....................................................7
5. Mediation Applicability Examples ................................8
5.1. Adjusting Flow Granularity .................................8
5.2. Collecting Infrastructure ..................................8
5.3. Correlation for Data Records ...............................9
5.4. Time Composition ...........................................9
5.5. Spatial Composition .......................................10
5.6. Data Record Anonymization .................................11
5.7. Data Retention ............................................11
5.8. IPFIX Export from a Branch Office .........................12
5.9. Distributing Data Record Types ............................13
5.10. Flow-Based Sampling and Selection ........................14
5.11. Interoperability between Legacy Protocols and IPFIX ......15
6. IPFIX Mediators' Implementation-Specific Problems ..............15
6.1. Loss of Original Exporter Information .....................15
6.2. Loss of Base Time Information .............................16
6.3. Transport Sessions Management .............................16
6.4. Loss of Options Template Information ......................16
6.5. Template ID Management ....................................17
6.6. Consideration for Network Topology ........................18
6.7. IPFIX Mediation Interpretation ............................18
6.8. Consideration for Aggregation .............................19
7. Summary and Conclusion .........................................20
8. Security Considerations ........................................20
9. Acknowledgements ...............................................21
10. References ....................................................22
10.1. Normative References .....................................22
10.2. Informative References ...................................22
Contributors ......................................................24
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1. Introduction
An advantage of flow-based measurement is that it allows monitoring
large amounts of traffic observed at distributed Observation Points.
While flow-based measurement can be applied to one of various
purposes and applications, it is difficult for flow-based measurement
to apply to multiple applications with very different requirements in
parallel. Network administrators need to adjust the parameters of
the metering devices to fulfill the requirements of every single
measurement application. Such configurations are often not supported
by the metering devices, either because of functional restrictions or
because of limited computational and memory resources, which inhibit
the metering of large amounts of traffic with the desired setup. IP
Flow Information Export (IPFIX) Mediation fills the gap between
restricted metering capabilities and the requirements of measurement
applications by introducing an intermediate device called the IPFIX
Mediator.
The IPFIX requirements defined in [RFC3917] mention examples of
intermediate devices located between Exporters and Collectors, such
as IPFIX proxies or concentrators. But, there are no documents
defining a generalized concept for such intermediate devices. This
document addresses that issue by defining IPFIX Mediation -- a
generalized intermediate device concept for IPFIX -- and examining in
detail the motivations behind its application.
This document is structured as follows: Section 2 describes the
terminology used in this document, Section 3 gives an IPFIX/Packet
Sampling (PSAMP) document overview, Section 4 introduces general
problems related to flow-based measurement, Section 5 describes some
applicability examples where IPFIX Mediation would be beneficial,
and, finally, Section 6 describes some problems an IPFIX Mediation
implementation might face.
2. Terminology and Definitions
The IPFIX-specific and PSAMP-specific terminology used in this
document is defined in [RFC5101] and [RFC5476], respectively. In
this document, as in [RFC5101] and [RFC5476], the first letter of
each IPFIX-specific and PSAMP-specific term is capitalized along with
the IPFIX Mediation-specific terms defined here.
In this document, we call "record stream" a stream of records
carrying flow- or packet-based information. The records may be
encoded as IPFIX Data Records or in any other format.
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Original Exporter
An Original Exporter is an IPFIX Device that hosts the Observation
Points where the metered IP packets are observed.
IPFIX Mediation
IPFIX Mediation is the manipulation and conversion of a record
stream for subsequent export using the IPFIX protocol.
The following terms are used in this document to describe the
architectural entities used by IPFIX Mediation.
Intermediate Process
An Intermediate Process takes a record stream as its input from
Collecting Processes, Metering Processes, IPFIX File Readers,
other Intermediate Processes, or other record sources; performs
some transformations on this stream, based upon the content of
each record, states maintained across multiple records, or other
data sources; and passes the transformed record stream as its
output to Exporting Processes, IPFIX File Writers, or other
Intermediate Processes, in order to perform IPFIX Mediation.
Typically, an Intermediate Process is hosted by an IPFIX Mediator.
Alternatively, an Intermediate Process may be hosted by an
Original Exporter.
IPFIX Mediator
An IPFIX Mediator is an IPFIX Device that provides IPFIX Mediation
by receiving a record stream from some data sources, hosting one
or more Intermediate Processes to transform that stream, and
exporting the transformed record stream into IPFIX Messages via an
Exporting Process. In the common case, an IPFIX Mediator receives
a record stream from a Collecting Process, but it could also
receive a record stream from data sources not encoded using IPFIX,
e.g., in the case of conversion from the NetFlow V9 protocol
[RFC3954] to the IPFIX protocol.
Note that the IPFIX Mediator is a generalization of the
concentrator and proxy elements envisioned in the IPFIX
requirements [RFC3917]. IPFIX Mediators running appropriate
Intermediate Processes provide the functionality specified
therein.
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3. IPFIX/PSAMP Documents Overview
IPFIX Mediation can be applied to Flow- or packet-based information.
The Flow-based information is encoded as IPFIX Flow Records by the
IPFIX protocol, and the packet-based information is extracted by some
packet selection techniques and then encoded as PSAMP Packet Reports
by the PSAMP protocol. Thus, this section describes relevant
documents for both protocols.
3.1. IPFIX Documents Overview
The IPFIX protocol [RFC5101] provides network administrators with
access to IP flow information. The architecture for the export of
measured IP flow information from an IPFIX Exporting Process to a
Collecting Process is defined in [RFC5470], per the requirements
defined in [RFC3917]. The IPFIX protocol [RFC5101] specifies how
IPFIX Data Records and Templates are carried via a number of
transport protocols from IPFIX Exporting Processes to IPFIX
Collecting Processes. IPFIX has a formal description of IPFIX
Information Elements, their names, types, and additional semantic
information, as specified in [RFC5102]. [RFC5815] specifies the
IPFIX Management Information Base. Finally, [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. The storage
of IPFIX Messages in a file is specified in [RFC5655].
3.2. PSAMP Documents Overview
The framework for packet selection and reporting [RFC5474] enables
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 and Filtering) standardized by PSAMP is described in
[RFC5475]. The PSAMP protocol [RFC5476] specifies the export of
packet information from a PSAMP Exporting Process to a Collector.
Like IPFIX, PSAMP has a formal description of its Information
Elements, their names, types, and additional semantic information.
The PSAMP information model is defined in [RFC5477]. [PSAMP-MIB]
describes the PSAMP Management Information Base.
4. Problem Statement
Network administrators generally face the problems of measurement
system scalability, Flow-based measurement flexibility, and export
reliability, even if some techniques, such as Packet Sampling,
Filtering, Data Records aggregation, and export replication, have
already been developed. The problems consist of adjusting some
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parameters of metering devices to resources of the measurement system
while fulfilling appropriate conditions: data accuracy, Flow
granularity, and export reliability. These conditions depend on two
factors.
o Measurement system capacity: This consists of the bandwidth of the
management network, the storage capacity, and the performances of
the collecting devices and exporting devices.
o Application requirements: Different applications, such as traffic
engineering, detecting traffic anomalies, and accounting, impose
different Flow Record granularities, and data accuracies.
The sustained growth of IP traffic has been overwhelming the
capacities of measurement systems. Furthermore, a large variety of
applications (e.g., Quality-of-Service (QoS) measurement, traffic
engineering, security monitoring) and the deployment of measurement
systems in heterogeneous environments have been increasing the demand
and complexity of IP traffic measurements.
4.1. Coping with IP Traffic Growth
Enterprise or service provider networks already have multiple 10 Gb/s
links, their total traffic exceeding 100 Gb/s. In the near future,
broadband users' traffic will increase by approximately 40% every
year according to [TRAFGRW]. When administrators monitor IP traffic
sustaining its growth at multiple Exporters, the amount of exported
Flow Records from Exporters could exceed the ability of a single
Collector.
To deal with this problem, current data reduction techniques (Packet
Sampling and Filtering in [RFC5475], and aggregation of measurement
data) have been generally implemented on Exporters. Note that Packet
Sampling leads to potential loss of small Flows. With both Packet
Sampling and aggregation techniques, administrators might no longer
be able to detect and investigate subtle traffic changes and
anomalies, as this requires detailed Flow information. With
Filtering, only a subset of the Data Records are exported.
Considering the potential drawbacks of Packet Sampling, Filtering,
and Data Records aggregation, there is a need for a large-scale
collecting infrastructure that does not rely on data reduction
techniques.
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4.2. Coping with Multipurpose Traffic Measurement
Different monitoring applications impose different requirements on
the monitoring infrastructure. Some of them require traffic
monitoring at a Flow level while others need information about
individual packets or just Flow aggregates.
To fulfill these diverse requirements, an Exporter would need to
perform various complex metering tasks in parallel, which is a
problem due to limited resources. Hence, it can be advantageous to
run the Exporter with a much simpler setup and to perform appropriate
post-processing of the exported Data Records at a later stage.
4.3. Coping with Heterogeneous Environments
Network administrators use IPFIX Devices and PSAMP Devices from
various vendors, various software versions, and various device types
(router, switch, or probe) in a single network domain. Even legacy
flow export protocols are still deployed in current networks. This
heterogeneous environment leads to differences in Metering Process
capabilities, Exporting Process capacity (export rate, cache memory,
etc.), and data format. For example, probes and switches cannot
retrieve some derived packet properties from a routing table.
To deal with this problem, the measurement system needs to mediate
the differences. However, equipping all collecting devices with this
absorption function is difficult.
4.4. Summary
Due to resource limitations of the measurement system, it is
important to use traffic data reduction techniques as early as
possible, e.g., at the Exporter. However, this implementation is
made difficult by the heterogeneous environment of exporting devices.
On the other hand, keeping data accuracy and Flow granularity to meet
the requirements of different monitoring applications requires a
scalable and flexible collecting infrastructure.
This implies that a new Mediation function is required in typical
Exporter-Collector architectures. Based on some applicability
examples, the next section shows the limitation of the typical
Exporter-Collector architecture model and the IPFIX Mediation
benefits.
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5. Mediation Applicability Examples
5.1. Adjusting Flow Granularity
The simplest set of Flow Keys is a fixed 5-tuple of protocol, source
and destination IP addresses, and source and destination port
numbers. A shorter set of Flow Keys, such as a triple, a double, or
a single property, (for example, network prefix, peering autonomous
system number, or BGP Next-Hop fields), creates more aggregated Flow
Records. This is especially useful for measuring router-level
traffic matrices in a core network domain and for easily adjusting
the performance of Exporters and Collectors.
Implementation analysis:
Implementations for this case depend on where Flow granularity is
adjusted. More suitable implementations use configurable Metering
Processes in Original Exporters. The cache in the Metering
Process can specify its own set of Flow Keys and extra fields.
The Original Exporter thus generates Flow Records of the desired
Flow granularity.
In the case where a Metering Process hosting no ability to change
the Flow Keys in Original Exporters creates Flow Records, or PSAMP
Packet Reports, an IPFIX Mediator can aggregate Data Records based
on a new set of Flow Keys. Even in the case of a Metering Process
hosting this ability, an IPFIX Mediator can further aggregate the
Flow Records.
5.2. Collecting Infrastructure
Increasing numbers of IPFIX Exporters, IP traffic growth, and the
variety of treatments expected to be performed on the Data Records
make it more and more difficult to implement all measurement
applications within a single Collector.
Implementation analysis:
To increase the collecting (e.g., the bandwidth capacity) and
processing capacity, distributed Collectors close to Exporters
need to be deployed. In such a case, those Collectors would
become IPFIX Mediators, re-exporting Data Records on demand to
centralized applications. To cope with the variety of measurement
applications, one possible implementation uses an Intermediate
Process deciding to which Collector(s) each record is exported.
More specific cases are described in Section 5.9.
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5.3. Correlation for Data Records
The correlation amongst Data Records or between Data Records and
metadata provides new metrics or information, including the
following.
o One-to-one correlation between Data Records
* One-way delay from the correlation of PSAMP Packet Reports from
different Exporters along a specific path. For example, one-
way delay is calculated from the correlation of two PSAMP
Packet Reports, including the packet digest and the arrival
time at the Observation Point. This scenario is described in
Section 6.2.1.2 of [RFC5475].
* Packet inter-arrival time from the correlation of sequential
PSAMP Packet Reports from an Exporter.
* Treatment from the correlation of Data Records with common
properties, observed at incoming/outgoing interfaces. Examples
are the rate-limiting ratio, the compression ratio, the
optimization ratio, etc.
o Correlation amongst Data Records
Average/maximum/minimum values from correlating multiple Data
Records. Examples are the average/maximum/minimum number of
packets of the measured Flows, the average/maximum/minimum one-way
delay, the average/maximum/minimum number of lost packets, etc.
o Correlation between Data Records and other metadata
Examples are some BGP attributes associated with Data Records, as
determined via routing table lookup.
Implementation analysis:
One possible implementation for this case uses an Intermediate
Process located between the Metering Processes and Exporting
Processes on the Original Exporter, or alternatively, a separate
IPFIX Mediator located between the Original Exporters and IPFIX
Collectors.
5.4. Time Composition
Time composition is defined as the aggregation of consecutive Data
Records with identical Flow Keys. It leads to the same output as
setting a longer active timeout on Original Exporters, with one
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advantage: the creation of new metrics such as average, maximum, and
minimum values from Flow Records with a shorter time interval enables
administrators to keep track of changes that might have happened
during the time interval.
Implementation analysis:
One possible implementation for this case uses an Intermediate
Process located between the Metering Processes and Exporting
Processes on the Original Exporter, or alternatively a separate
IPFIX Mediator located between the Original Exporters and IPFIX
Collectors.
5.5. Spatial Composition
Spatial composition is defined as the aggregation of Data Records in
a set of Observation Points within an Observation Domain, across
multiple Observation Domains from a single Exporter, or even across
multiple Exporters. The spatial composition is divided into four
types.
o Case 1: Spatial composition within one Observation Domain
For example, to measure the traffic for a single logical interface
in the case in which link aggregation [IEEE802.3ad] exists, Data
Records metered at physical interfaces belonging to the same trunk
can be merged.
o Case 2: Spatial composition across Observation Domains, but within
a single Original Exporter
For example, in the case in which link aggregation exists, Data
Records metered at physical interfaces belonging to the same trunk
grouping beyond the line card can be merged.
o Case 3: Spatial composition across Exporters
Data Records metered within an administrative domain, such as the
west area and east area of an ISP network, can be merged.
o Case 4: Spatial composition across administrative domains
Data Records metered across administrative domains, such as across
different customer networks or different ISP networks, can be
merged. For example, a unique Collector knows in which customer
network an Exporter exists, and then works out the traffic data
per customer based on the Exporter IP address.
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Implementation analysis:
One possible implementation for cases 1 and 2 uses an Intermediate
Process located between the Metering Processes and Exporting
Processes on the Original Exporter. A separate IPFIX Mediator
located between the Original Exporters and IPFIX Collectors is a
valid solution for cases 1, 2, 3, and 4.
5.6. Data Record Anonymization
IPFIX exports across administrative domains can be used to measure
traffic for wide-area traffic engineering or to analyze Internet
traffic trends, as described in the spatial composition across
administrative domains in the previous subsection. In such a case,
administrators need to adhere to privacy protection policies and
prevent access to confidential traffic measurements by other people.
Typically, anonymization techniques enable the provision of traffic
data to other people without violating these policies.
Generally, anonymization modifies a data set to protect the identity
of the people or entities described by the data set from being
disclosed. It also attempts to preserve sets of network traffic
properties useful for a given analysis while ensuring the data cannot
be traced back to the specific networks, hosts, or users generating
the traffic. For example, IP address anonymization is particularly
important for avoiding the identification of users, hosts, and
routers. As another example, when an ISP provides traffic monitoring
service to end customers, network administrators take care of
anonymizing interface index fields that could disclose any
information about the vendor or software version of the Exporters.
Implementation analysis:
One possible implementation for this case uses an anonymization
function at the Original Exporter. However, this increases the
load on the Original Exporter. A more flexible implementation
uses a separate IPFIX Mediator between the Original Exporter and
Collector.
5.7. Data Retention
Data retention refers to the storage of traffic data by service
providers and commercial organizations. Legislative regulations
often require that network operators retain both IP traffic data and
call detail records, in wired and wireless networks, generated by end
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users while using a service provider's services. The traffic data is
required for the purpose of the investigation, detection, and
prosecution of serious crime, if necessary. Data retention examples
relevant to IP networks are the following:
o Internet telephony (includes every multimedia session associated
with IP multimedia services)
o Internet email
o Internet access
Data retention, for these services in particular, requires a
measurement system with reliable export and huge storage, as the data
must be available for a long period of time, typically at least six
months.
Implementation analysis:
Regarding export reliability requirement, the most suitable
implementation uses the Stream Control Transmission Protocol
(SCTP) between the Original Exporter and Collector. If an
unreliable transport protocol such as UDP is used, a legacy
exporting device exports Data Records to a nearby IPFIX Mediator
through UDP, and then an IPFIX Mediator could reliably export them
to the IPFIX Collector through SCTP. If an unreliable transport
protocol such as UDP is used and if there is no IPFIX Mediator,
the legacy exporting device should duplicate the exports to
several Collectors to lower the probability of losing Flow
Records. However, it might result in network congestion, unless
dedicated export links are used.
Regarding huge storage requirements, the collecting infrastructure
is described in Section 5.2.
5.8. IPFIX Export from a Branch Office
Generally, in large enterprise networks, Data Records from branch
offices are gathered in a central office. However, in the long-
distance branch office case, the bandwidth for transporting IPFIX is
limited. Therefore, even if multiple Data Record types should be of
interest to the Collector (e.g., IPFIX Flow Records in both
directions, IPFIX Flow Records before and after WAN optimization
techniques, performance metrics associated with the IPFIX Flow
Records exported at regular intervals, etc.), the export bandwidth
limitation is an important factor to pay attention to.
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Implementation analysis:
One possible implementation for this case uses an IPFIX Mediator
located in a branch office. The IPFIX Mediator would aggregate
and correlate Data Records to cope with the export bandwidth
limitation.
5.9. Distributing Data Record Types
Recently, several networks have shifted towards integrated networks,
such as the pure IP and MPLS networks, which include IPv4, IPv6, and
VPN traffic. Data Record types (IPv4, IPv6, MPLS, and VPN) need to
be analyzed separately and from different perspectives for different
organizations. A single Collector handling all Data Record types
might become a bottleneck in the collecting infrastructure. Data
Records distributed based on their respective types can be exported
to the appropriate Collector, resulting in load distribution amongst
multiple Collectors.
Implementation analysis:
One possible implementation for this case uses replication of the
IPFIX Message in an Original Exporter for multiple IPFIX
Collectors. Each Collector then extracts the Data Record required
by its own applications. However, this replication increases the
load of the Exporting Process and the waste of bandwidth between
the Exporter and Collector.
A more sophisticated implementation uses an Intermediate Process
located between the Metering Processes and Exporting Processes in
an Original Exporter. The Intermediate Process determines to
which Collector a Data Record is exported, depending on certain
field values. If an Original Exporter does not have this
capability, it exports Data Records to a nearby separate IPFIX
Mediator, and then the IPFIX Mediator could distribute them to the
appropriate IPFIX Collectors.
For example, in the case of distributing a specific customer's
Data Records, an IPFIX Mediator needs to identify the customer
networks. The Route Distinguisher (RD), ingress interface,
peering Autonomous System (AS) number, or BGP Next-Hop, or simply
the network prefix may be evaluated to distinguish different
customer networks. In the following figure, the IPFIX Mediator
reroutes Data Records on the basis of the RD value. This system
enables each customer's traffic to be inspected independently.
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.---------.
|Traffic |
.---->|Collector|<==>Customer#A
| |#1 |
| '---------'
RD=100:1
.----------. .-----------. |
|IPFIX | |IPFIX |----' .---------.
|Exporter#1| |Mediator | RD=100:2 |Traffic |
| |------->| |--------->|Collector|<==>Customer#B
| | | | |#2 |
| | | |----. '---------'
'----------' '-----------' |
RD=100:3
| .---------.
| |Traffic |
'---->|Collector|<==>Customer#C
|#3 |
'---------'
Figure A. Distributing Data Records to Collectors
Using IPFIX Mediator
5.10. Flow-Based Sampling and Selection
Generally, the distribution of the number of packets per Flow seems
to be heavy tailed. Most types of Flow Records are likely to be
small Flows consisting of a small number of packets. The measurement
system is overwhelmed with a huge amount of these small Flows. If
statistics information of small Flows is exported as merged data by
applying a policy or threshold, the load on the Exporter is reduced.
Furthermore, if the Flow distribution is known, exporting only a
subset of the Data Records might be sufficient.
Implementation analysis:
One possible implementation for this case uses an Intermediate
Process located between the Metering Processes and Exporting
Processes on the Original Exporter, or alternatively a separate
IPFIX Mediator located between the Original Exporters and IPFIX
Collectors. A set of IPFIX Mediation functions, such as
Filtering, selecting, and aggregation, is used in the IPFIX
Mediator.
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5.11. Interoperability between Legacy Protocols and IPFIX
During the migration process from a legacy protocol such as NetFlow
[RFC3954] to IPFIX, both NetFlow exporting devices and IPFIX
Exporters are likely to coexist in the same network. Operators need
to continue measuring the traffic data from legacy exporting devices,
even after introducing IPFIX Collectors.
Implementation analysis:
One possible implementation for this case uses an IPFIX Mediator
that converts a legacy protocol to IPFIX.
6. IPFIX Mediators' Implementation-Specific Problems
6.1. Loss of Original Exporter Information
Both the Exporter IP address indicated by the source IP address of
the IPFIX Transport Session and the Observation Domain ID included in
the IPFIX Message header are likely to be lost during IPFIX
Mediation. In some cases, an IPFIX Mediator might drop the
information deliberately. In general, however, the Collector must
recognize the origin of the measurement information, such as the IP
address of the Original Exporter, the Observation Domain ID, or even
the Observation Point ID. Note that, if an IPFIX Mediator cannot
communicate the Original Exporter IP address, then the IPFIX
Collector will wrongly deduce that the IP address of the IPFIX
Mediator is that of the Original Exporter.
In the following figure, a Collector can identify two IP addresses:
192.0.2.3 (IPFIX Mediator) and 192.0.2.2 (Exporter#2), respectively.
The Collector, however, needs to somehow recognize both Exporter#1
and Exporter#2, which are the Original Exporters. The IPFIX Mediator
must be able to notify the Collector about the IP address of the
Original Exporter.
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.----------. .--------.
|IPFIX | |IPFIX |
|Exporter#1|--------->|Mediator|---+
| | | | |
'----------' '--------' | .---------.
IP:192.0.2.1 IP:192.0.2.3 '----->|IPFIX |
ODID:10 ODID:0 |Collector|
+------>| |
.----------. | '---------'
|IPFIX | |
|Exporter#2|-----------------------'
| |
'----------'
IP:192.0.2.2
ODID:20
Figure B. Loss of Original Exporter Information
6.2. Loss of Base Time Information
The Export Time field included in the IPFIX Message header represents
a reference timestamp for Data Records. Some IPFIX Information
Elements, described in [RFC5102], carry delta timestamps that
indicate the time difference from the value of the Export Time field.
If the Data Records include any delta time fields and the IPFIX
Mediator overwrites the Export Time field when sending IPFIX
Messages, the delta time fields become meaningless and, because
Collectors cannot recognize this situation, wrong time values are
propagated.
6.3. Transport Sessions Management
Maintaining relationships between the incoming Transport Sessions and
the outgoing ones depends on the Mediator's implementation. If an
IPFIX Mediator relays multiple incoming Transport Sessions to a
single outgoing Transport Session, and if the IPFIX Mediator shuts
down its outgoing Transport Session, Data Records of the incoming
Transport Sessions would not be relayed anymore. In the case of
resetting an incoming Transport Session, the behavior of the IPFIX
Mediator needs to be specified.
6.4. Loss of Options Template Information
In some cases, depending on the implementation of the IPFIX
Mediators, the information reported in the Data Records defined by
Options Templates could also be lost. If, for example, the Sampling
rate is not communicated from the Mediator to the Collector, the
Collector would miscalculate the traffic volume. This might lead to
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crucial problems. Even if an IPFIX Mediator were to simply relay
received Data Records defined by Options Templates, the values of its
scope fields could become meaningless in the content of a different
Transport Session. The minimal information to be communicated by an
IPFIX Mediator must be specified.
6.5. Template ID Management
The Template ID is unique on the basis of the Transport Session and
Observation Domain ID. If an IPFIX Mediator is not able to manage
the relationships amongst the Template IDs and the incoming Transport
Session information, and if the Template ID is used in the Options
Template scope, IPFIX Mediators would, for example, relay wrong
values in the scope field and in the Template Withdrawal Message.
The Collector would thus not be able to interpret the Template ID in
the Template Withdrawal Message and in the Options Template scope.
As a consequence, there is a risk that the Collector would then shut
down the IPFIX Transport Session.
For example, an IPFIX Mediator must maintain the state of the
incoming Transport Sessions in order to manage the Template ID on its
outgoing Transport Session correctly. Even if the Exporter Transport
Session re-initializes, the IPFIX Mediator must manage the
association of Template IDs in a specific Transport Session. In the
following figure, the IPFIX Mediator exports three Templates (256,
257, and 258), received from Exporter#3, Exporter#2, and Exporter#1,
respectively. If Exporter#1 re-initializes, and the Template ID
value 258 is now replaced with 256, the IPFIX Mediator must correctly
manage the new mapping of (incoming Transport Session, Template ID)
and (outgoing Transport Session, Template ID) without shutting down
its outgoing Transport Session.
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.----------. OLD: Template ID 258
|IPFIX | NEW: Template ID 256
|Exporter#1|----+
| | |
'----------' X
.----------. | .-----------. .----------.
|IPFIX | '---------->| | | |
|Exporter#2|--------------->|IPFIX |-------------->|IPFIX |
| |Template ID 257 |Mediator |Template ID 258| Collector|
'----------' +---------->| |Template ID 257| |
.----------. | '-----------'Template ID 256'----------'
|IPFIX | |
|Exporter#3|----'
| | Template ID 256
'----------'
Figure C. Relaying from Multiple Transport Sessions
to a Single Transport Session
6.6. Consideration for Network Topology
While IPFIX Mediation can be applied anywhere, caution should be
taken as to how to aggregate the counters, as there is a potential
risk of double counting. For example, if three Exporters export
PSAMP Packet Reports related to the same flow, the one-way delay can
be calculated, while summing up the number of packets and bytes does
not make sense. Alternatively, if three Exporters export Flow
Records entering an administrative domain, then the sum of the
packets and bytes is a valid operation. Therefore, the possible
function to be applied to Flow Records must take into consideration
the measurement topology. The information such as the network
topology, or at least the Observation Point and measurement
direction, is required for IPFIX Mediation.
6.7. IPFIX Mediation Interpretation
In some cases, the IPFIX Collector needs to recognize which specific
function(s) IPFIX Mediation has executed on the Data Records. The
IPFIX Collector cannot distinguish between time composition and
spatial composition, if the IPFIX Mediator does not export the
applied function. Some parameters related to the function also would
need to be exported. For example, in the case of time composition,
the active timeout of original Flow Records is required to interpret
the minimum/maximum counter correctly. In the case of spatial
composition, spatial area information on which Data Records is
aggregated is required.
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6.8. Consideration for Aggregation
Whether the aggregation is based on time or spatial composition,
caution should be taken regarding how to aggregate non-key fields in
IPFIX Mediation. The IPFIX information model [RFC5102] specifies
that the value of non-key fields, which are derived from fields of
packets or from packet treatment and for which the value may change
from packet to packet within a single Flow, is determined by the
first packet observed for the corresponding Flow, unless the
description of the Information Element explicitly specifies a
different semantics.
However, this simple rule might not be appropriate when aggregating
Flow Records that have different values in a non-key field. For
example, if Differentiated Services Code Point (DSCP) information is
to be exported, the following problem can be observed: if two Flows
with identical Flow Key values are measured at different Observation
Points, they may contain identical packets observed at different
locations in the network and at different points in time. On their
way from the first to the second Observation Point, the DSCP and
potentially some other packet fields may have changed. Hence, if the
Information Element ipDiffServCodePoint is included as a non-key
field, it can be useful to include the DSCP value observed at either
the first or the second Observation Point in the resulting Flow
Record, depending on the application.
Other potential solutions include removing the Information Element
ipDiffServCodePoint from the Data Record when re-exporting the
aggregate Flow Record, changing the Information Element
ipDiffServCodePoint from a non-key field to a Flow Key when
re-exporting the aggregated Flow Record, or assigning a non-valid
value for the Information Element to express to the Collector that
this Information Element is meaningless.
If Packet Sampling or Filtering is applied, the IPFIX Mediator must
report an adjusted PSAMP Configured Selection Fraction when
aggregating IPFIX Flow Records with different Sampling rates.
Finally, special care must be taken when aggregating Flow Records
resulting from different Sampling techniques such as Systematic
Count-Based Sampling and Random n-out-of-N Sampling, for example.
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7. Summary and Conclusion
This document describes the problems that network administrators have
been facing, the applicability of IPFIX Mediation to these problems,
and the problems related to the implementation of IPFIX Mediators.
To assist the operations of the Exporters and Collectors, this
document demonstrates that there exist various IPFIX Mediation
functions from which the administrators may select.
However, there are still some open issues with the use of IPFIX
Mediators. These issues stem from the fact that no standards
regarding IPFIX Mediation have been set. In particular, the minimum
information that should be communicated between Original Exporters
and Collectors, the mapping between different IPFIX Transport
Sessions, and the internal components of IPFIX Mediators should be
standardized.
8. Security Considerations
A flow-based measurement system must prevent potential security
threats: the disclosure of confidential traffic data, injection of
incorrect data, and unauthorized access to traffic data. These
security threats of the IPFIX protocol are covered by the Security
Considerations section in [RFC5101] and are still valid for IPFIX
Mediators.
A measurement system must also prevent the following security threats
related to IPFIX Mediation:
o Attacks against an IPFIX Mediator
IPFIX Mediators can be considered as a prime target for attacks,
as an alternative to IPFIX Exporters and Collectors. IPFIX
Proxies or Masquerading Proxies need to prevent unauthorized
access or denial-of-service (DoS) attacks from untrusted public
networks.
o Man-in-the-middle attack by untrusted IPFIX Mediator
The Exporter-Mediator-Collector structure model could be misused
for a man-in-the-middle attack.
o Configuration on IPFIX Mediation
An accidental misconfiguration and unauthorized access to
configuration data could lead to the crucial problem of disclosure
of confidential traffic data.
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o Unintentional exposure of end-user information
The probability of collecting fine-grained information on one
arbitrary end user increases with the number of Observation
Points. An IPFIX Mediator facing such a situation may have to
apply appropriate functions (e.g., anonymization or aggregation)
to the Data Records it produces.
o Multiple-tenancy policy on an IPFIX Mediator
An IPFIX Mediator handling traffic data from multiple tenants or
customers needs to protect those tenants or customers from one
another's traffic data. For example, an IPFIX Mediator needs to
identify the customer's identifier, e.g., ingress interface index,
network address range, VLAN ID, Media Access Control (MAC)
address, etc., when feeding the customer's traffic data to a
customer's own dedicated IPFIX Collector. If the IPFIX Mediator
cannot identify each customer's traffic data, it may need to drop
the Data Records. In addition, another technique to keep track of
a customer's identifier may be required when customer sites are
movable, e.g., in the case of a virtual machine moving to another
physical machine.
o Confidentiality protection via an IPFIX Mediator
To ensure security of Data Records in transit, transport of Data
Records should be confidential and integrity-protected, e.g., by
using Transport Layer Security (TLS) [RFC5246] or Datagram
Transport Layer Security (DTLS) [RFC4347]. However, an IPFIX
Collector cannot know whether received Data Records are
transported as encrypted data between an Original Exporter and an
IPFIX Mediator. If this information is required on the IPFIX
Collector, it must be encoded in the IPFIX Mediator.
o Certification for an Original Exporter
An IPFIX Collector communicating via an IPFIX Mediator cannot
verify the identity of an Original Exporter directly. If an
Original Exporter and an IPFIX Collector are located in different
administrative domains, an IPFIX Collector cannot trust its Data
Records. If this information is required on the IPFIX Collector,
it must be encoded in the IPFIX Mediator.
9. Acknowledgements
We would like to thank the following persons: Gerhard Muenz for
thorough, detailed review and significant contributions regarding the
improvement of whole sections; Keisuke Ishibashi for contributions
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during the initial phases of the document; Brian Trammell for
contributions regarding the improvement of the Terminology and
Definitions section; and Nevil Brownlee, Juergen Schoenwaelder, and
Motonori Shindo for their technical reviews and feedback.
10. References
10.1. Normative References
[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.
[RFC5476] Claise, B., Ed., Johnson, A., and J. Quittek, "Packet
Sampling (PSAMP) Protocol Specifications", RFC 5476,
March 2009.
10.2. Informative References
[IEEE802.3ad] IEEE Computer Society, "Link Aggregation", IEEE
Std 802.3ad-2000, March 2000.
[PSAMP-MIB] Dietz, T., Ed., Claise, B., and J. Quittek,
"Definitions of Managed Objects for Packet Sampling",
Work in Progress, July 2010.
[RFC3917] Quittek, J., Zseby, T., Claise, B., and S. Zander,
"Requirements for IP Flow Information Export (IPFIX)",
RFC 3917, October 2004.
[RFC3954] Claise, B., Ed., "Cisco Systems NetFlow Services
Export Version 9", RFC 3954, October 2004.
[RFC4347] Rescorla, E. and N. Modadugu, "Datagram Transport
Layer Security", RFC 4347, April 2006.
[RFC5102] Quittek, J., Bryant, S., Claise, B., Aitken, P., and
J. Meyer, "Information Model for IP Flow Information
Export", RFC 5102, January 2008.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer
Security (TLS) Protocol Version 1.2", RFC 5246, August
2008.
[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 5982 IPFIX Mediation: Problem Statement August 2010
[RFC5472] Zseby, T., Boschi, E., Brownlee, N., and B. Claise,
"IP Flow Information Export (IPFIX) Applicability",
RFC 5472, 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.
[RFC5475] Zseby, T., Molina, M., Duffield, N., Niccolini, S.,
and F. Raspall, "Sampling and Filtering Techniques for
IP Packet Selection", RFC 5475, March 2009.
[RFC5477] Dietz, T., Claise, B., Aitken, P., Dressler, F., and
G. Carle, "Information Model for Packet Sampling
Exports", RFC 5477, March 2009.
[RFC5655] Trammell, B., Boschi, E., Mark, L., Zseby, T., and A.
Wagner, "Specification of the IP Flow Information
Export (IPFIX) File Format", RFC 5655, October 2009.
[RFC5815] Dietz, T., Ed., Kobayashi, A., Claise, B., and G.
Muenz, "Definitions of Managed Objects for IP Flow
Information Export", RFC 5815, April 2010.
[TRAFGRW] Cho, K., Fukuda, K., Esaki, H., and A. Kato, "The
Impact and Implications of the Growth in Residential
User-to-User Traffic", SIGCOMM2006, pp. 207-218, Pisa,
Italy, September 2006.
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Contributors
Haruhiko Nishida
NTT Information Sharing Platform Laboratories
3-9-11 Midori-cho
Musashino-shi, Tokyo 180-8585
Japan
Phone: +81-422-59-3978
EMail: nishida.haruhiko@lab.ntt.co.jp
Christoph Sommer
University of Erlangen-Nuremberg
Department of Computer Science 7
Martensstr. 3
Erlangen 91058
Germany
Phone: +49 9131 85-27993
EMail: christoph.sommer@informatik.uni-erlangen.de
URI: http://www7.informatik.uni-erlangen.de/~sommer/
Falko Dressler
University of Erlangen-Nuremberg
Department of Computer Science 7
Martensstr. 3
Erlangen 91058
Germany
Phone: +49 9131 85-27914
EMail: dressler@informatik.uni-erlangen.de
URI: http://www7.informatik.uni-erlangen.de/~dressler/
Stephan Emile
France Telecom
2 Avenue Pierre Marzin
Lannion, F-22307
France
Fax: +33 2 96 05 18 52
EMail: emile.stephan@orange-ftgroup.com
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RFC 5982 IPFIX Mediation: Problem Statement August 2010
Authors' Addresses
Atsushi Kobayashi (editor)
NTT Information Sharing Platform Laboratories
3-9-11 Midori-cho
Musashino-shi, Tokyo 180-8585
Japan
Phone: +81-422-59-3978
EMail: akoba@nttv6.net
Benoit Claise (editor)
Cisco Systems, Inc.
De Kleetlaan 6a b1
Diegem 1831
Belgium
Phone: +32 2 704 5622
EMail: bclaise@cisco.com
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