Network Working Group T. Zseby
Request for Comments: 5472 Fraunhofer FOKUS
Category: Informational E. Boschi
Hitachi Europe
N. Brownlee
CAIDA
B. Claise
Cisco Systems, Inc.
March 2009
IP Flow Information Export (IPFIX) Applicability
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
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Abstract
In this document, we describe the applicability of the IP Flow
Information eXport (IPFIX) protocol for a variety of applications.
We show how applications can use IPFIX, describe the relevant
Information Elements (IEs) for those applications, and present
opportunities and limitations of the protocol. Furthermore, we
describe relations of the IPFIX framework to other architectures and
frameworks.
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Table of Contents
1. Introduction ....................................................4
1.1. Terminology ................................................4
2. Applications of IPFIX ...........................................4
2.1. Accounting .................................................4
2.1.1. Example .............................................5
2.2. Traffic Profiling ..........................................7
2.3. Traffic Engineering ........................................8
2.4. Network Security ...........................................9
2.5. QoS Monitoring ............................................11
2.5.1. Correlating Events from Multiple
Observation Points .................................12
2.5.2. Examples ...........................................12
2.6. Inter-Domain Exchange of IPFIX Data .......................14
2.7. Export of Derived Metrics .................................14
2.8. Summary ...................................................15
3. Relation of IPFIX to Other Frameworks and Protocols ............16
3.1. IPFIX and IPv6 ............................................16
3.2. IPFIX and PSAMP ...........................................16
3.3. IPFIX and RMON ............................................16
3.4. IPFIX and IPPM ............................................18
3.5. IPFIX and AAA .............................................18
3.5.1. Connecting via a AAA Client ........................20
3.5.2. Connecting via an Application Specific
Module (ASM) .......................................21
3.6. IPFIX and RTFM ............................................21
3.6.1. Architecture .......................................21
3.6.2. Flow Definition ....................................22
3.6.3. Configuration and Management .......................22
3.6.4. Data Collection ....................................22
3.6.5. Data Model Details .................................23
3.6.6. Transport Protocol .................................23
3.6.7. Summary ............................................23
4. Limitations ....................................................24
4.1. Using IPFIX for Other Applications than Listed in
RFC 3917 ..................................................24
4.2. Using IPFIX for Billing (Reliability Limitations) .........24
4.3. Using a Different Transport Protocol than SCTP ............25
4.4. Push vs. Pull Mode ........................................25
4.5. Template ID Number ........................................26
4.6. Exporting Bidirectional Flow Information ..................26
4.7. Remote Configuration ......................................27
5. Security Considerations ........................................27
6. Acknowledgements ...............................................28
7. Normative References ...........................................28
8. Informative References .........................................28
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1. Introduction
The IPFIX protocol defines how IP Flow information can be exported
from routers, measurement probes, or other devices. IP Flow
information provides important input data for a variety of
applications. The IPFIX protocol is a general data transport
protocol that is easily extensible to suit the needs of such
applications. In this document, we describe how typical applications
can use the IPFIX protocol and show opportunities and limitations of
the protocol. Furthermore, we describe the relationship of IPFIX to
other frameworks and architectures. Although examples in this
document are shown for IPv4 only, the applicability statements apply
to IPv4 and IPv6. IPFIX provides appropriate Information Elements
for both IP versions.
1.1. Terminology
IPFIX-specific terminology used in this document is defined in
Section 2 of [RFC5101]. In this document, as in [RFC5101], the first
letter of each IPFIX-specific term is capitalized.
2. Applications of IPFIX
IPFIX data enables several critical applications. The IPFIX target
applications and the requirements that originate from those
applications are described in [RFC3917]. Those requirements were
used as basis for the design of the IPFIX protocol. This section
describes how these target applications can use the IPFIX protocol.
Considerations for using IPFIX for other applications than those
described in [RFC3917] can be found in Section 4.1.
2.1. Accounting
Usage-based accounting is one of the target applications for IPFIX as
defined in [RFC3917]. IPFIX records provide fine-grained measurement
results for highly flexible and detailed usage reporting. Such data
is used to realize usage-based accounting. Nevertheless, IPFIX does
not provide the reliability required by usage-based billing systems
as defined in [RFC2975] (see Section 4.2). The accounting scenarios
described in this document only provide limited reliability as
explained in Section 4.2 and should not be used in environments where
reliability as demanded by [RFC2975] is mandatory.
In order to realize usage-based accounting with IPFIX, the Flow
definition has to be chosen in accordance to the accounting purpose,
such as trend analysis, capacity planning, auditing, or billing and
cost allocation where some loss of data can be tolerated (see Section
4.2).
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Flows can be distinguished by various IEs (e.g., packet header
fields) from [RFC5102]. Due to the flexible IPFIX Flow definition,
arbitrary Flow-based accounting models can be realized without
extensions to the IPFIX protocol.
Accounting can, for instance, be based on individual end-to-end
Flows. In this case, it can be realized with a Flow definition
determined by the quintuple consisting of source address
(sourceIPv4Address), destination address (destinationIPv4Address),
protocol (protocolIdentifier), and port numbers (udpSourcePort,
udpDestinationPort). Another example is class-dependent accounting
(e.g., in a Diffserv network). In this case, Flows could be
distinguished just by the Diffserv codepoint (DSCP)
(ipDiffServCodePoint) and IP addresses (sourceIPv4Address,
destinationIPv4Address). The essential elements needed for
accounting are the number of transferred packets and bytes per Flow,
which can be represented by the per-flow counter IEs (e.g.,
packetTotalCount, octetTotalCount).
For accounting purposes, it would be advantageous to have the ability
to use IPFIX Flow Records as accounting input in an Authentication,
Authorization, and Accounting (AAA) infrastructure. AAA servers then
could provide the mapping between user and Flow information. Again
for such scenarios the limited reliability currently provided by
IPFIX has to be taken into account.
2.1.1. Example
Please note: As noted in [RFC3330], the address block 192.0.2.0/24
may be used for example addresses. In the example below, we use two
example networks. In order to be conformant to [RFC3330], we divide
the given address block into two networks by subnetting with a 25-bit
netmask (192.0.2.0/25) as follows:
Network A: 192.0.2.0 ... 192.0.2.127
Network B: 192.0.2.128 ... 192.0.2.255
Let's suppose someone needs to monitor the individual Flows in a
Diffserv network in order to compare traffic amount trend with the
terms outlined in a Service Level Agreement (SLA). Flows are
distinguished by source and destination address. The information to
export in this case is:
- IPv4 source IP address: sourceIPv4Address in [RFC5102], with a
length of 4 octets
- IPv4 destination IP address: destinationIPv4Address in
[RFC5102], with a length of 4 octets
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- DSCP: ipDiffServCodePoint in [RFC5102], with a length of 1 octet
- Number of octets of the Flow: octetDeltaCount in [RFC5102], with
a length of 4 octets
The Template set will look as follows:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Set ID = 2 | Length = 24 octets |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Template ID 256 | Field Count = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| sourceIPv4Address = 8 | Field Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| destinationIPv4Address = 12 | Field Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| ipDiffServCodePoint = 195 | Field Length = 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| octetDeltaCount = 1 | Field Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The information to be exported might be as listed in the following
example table:
Src. IP addr. | Dst. IP addr. | DSCP | Octets Number
--------------+---------------+--------+--------------
192.0.2.12 | 192.0.2.144 | 46 | 120868
192.0.2.24 | 192.0.2.156 | 46 | 310364
192.0.2.36 | 192.0.2.168 | 46 | 241239
In the example we use Diffserv codepoint 46, recommended for the
Expedited Forwarding Per Hop Behavior (EF PHB) in [RFC3246].
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The Flow Records will then look as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Set ID = 256 | Length = 43 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 192.0.2.12 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 192.0.2.144 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 46 | 120868 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | 192.0.2.24 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | 192.0.2.156 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | 46 | 310364 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | 192.0.2.36 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | 192.0.2.168 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | 46 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 241239 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2.2. Traffic Profiling
Measurement results reported in IPFIX records can provide useful
input for traffic profiling. IPFIX records captured over a long
period of time can be used to track and anticipate network growth and
usage. Such information is valuable for trend analysis and network
planning.
The parameters of interest are determined by the profiling
objectives. Example parameters for traffic profiling are Flow
duration, Flow volume, burstiness, the distribution of used services
and protocols, the amount of packets of a specific type, etc.
[RFC3917].
The distribution of services and protocols in use can be analyzed by
configuring appropriate Flows Keys for Flow discrimination.
Protocols can be distinguished by the protocolIdentifier IE.
Portnumbers (e.g., udpDestinationPort) often provide information
about services in use. Those Flow Keys are defined in [RFC5102]. If
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portnumbers are not sufficient for service discrimination, further
parts of the packet may be needed. Header fields can be expressed by
IEs from [RFC5102].
Packet payload can be reported by using the IE ipPayloadPacketSection
in [RFC5477].
The Flow duration can be calculated from the Flow Timestamp IEs
defined in [RFC5102] (e.g., flowEndMicroseconds -
flowStartMicroseconds). The number of packets and number of bytes of
a Flow are represented in the per-flow counter IEs (e.g.,
packetTotalCount, octetTotalCount). The burstiness of a Flow can be
calculated from the Flow volume measured at different time intervals.
2.3. Traffic Engineering
Traffic engineering aims at the optimization of network resource
utilization and traffic performance [RFC2702]. Typical parameters
are link utilization, load between specific network, nodes, number,
size and entry/exit points of active Flows, and routing information
[RFC3917].
The size of Flows in packets and bytes can be reported by the IEs
packetTotalCount and octetTotalCount. Utilization of a physical link
can be reported by using a coarse-grained Flow definition (e.g.,
based on identifier IEs such as egressInterface or ingressInterface)
and per-flow counter IEs (e.g., packetTotalCount, octetTotalCount)
defined in [RFC5102].
The load between specific network nodes can be reported in the same
way if one interface of a network node receives only traffic from
exactly one neighbor node (as is usually the case). If the ingress
interface is not sufficient for an unambiguous identification of the
neighbor node, sub-IP header fields IEs (like sourceMacAddress) can
be added as Flow Keys.
The IE observedFlowTotalCount provides the number of all Flows
exported for the Observation Domain since the last initialization of
the Metering Process [RFC5102]. If this IE is exported at subsequent
points in time, one can derive the number of active Flows in a
specific time interval from the difference of the reported counters.
The configured Flow termination criteria have to be taken into
account to interpret those numbers correctly.
Entry and exit points can be derived from Flow Records if Metering
Processes are installed at all edges of the network and results are
mapped in accordance to Flow Keys. For this and other analysis
methods that require the mapping of records from different
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Observation Points, the same Flow Keys should be used at all
Observation Points. The path that packets take through a network can
be investigated by using hash-based sampling techniques as described
in [DuGr00] and [RFC5475]. For this, IEs from [RFC5477] are needed.
Neither [RFC5102] nor [RFC5477] defines IEs suitable for exporting
routing information.
2.4. Network Security
Attack and intrusion detection are among the IPFIX target
applications described in [RFC3917]. Due to the enormous amount of
different network attack types, only general requirements could be
addressed in [RFC3917].
The number of metrics useful for attack detection is as diverse as
attack patterns themselves. Attackers adapt rapidly to circumvent
detection methods and try to hide attack patterns using slow or
stealth attacks. Furthermore, unusual traffic patterns are not
always caused by malicious activities. A sudden traffic increase may
be caused by legitimate users who seek access to a recently published
web content. Strange traffic patterns may also be caused by
misconfiguration.
IPFIX can export Flow information for arbitrary Flow definitions as
defined in [RFC5101]. Packet information can be exported with IPFIX
by using the additional Information Elements described in [RFC5477].
With this, theoretically all information about traffic in the network
at the IP layer and above is accessible. This data either can be
used directly to detect anomalies or can provide the basis for
further post-processing to generate more complex attack detection
metrics.
Depending on the attack type, different metrics are useful. A sudden
increase of traffic load can be a hint that an attack has been
launched. The overall traffic at an Observation Point can be
monitored using per-flow counter IEs like packetTotalCount or
octetTotalCount as described in Section 2.3. The number of active
Flows can be monitored by regular reporting of the
observedFlowTotalCount defined in [RFC5102].
A sudden increase of Flows from different sources to one destination
may be caused by an attack on a specific host or network node using
spoofed addresses. The number of Flows from or to specific networks
or hosts can be observed by using source and destination addresses as
Flow Keys and observing the number of active Flows as explained
above. Many Flows to the same machine, but on different ports, or
many Flows to the same port and different machines may be an
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indicator for vertical or horizontal port scanning activities. The
number of Flows to different ports can be reported by using the
portnumber Information Elements (udpSourcePort, udpDestinationPort,
tcpSourcePort, tcpDestinationPort) defined in [RFC5102] as Flow Keys.
An unusual ratio of TCP-SYN to TCP-FIN packets can refer to SYN-
flooding. The number of SYN and FIN packets in a Flow can be
reported with the IPFIX Information Elements tcpSynTotalCount and
tcpFinTotalCount defined in [RFC5102].
Worms may leave signatures in traffic patterns. Detecting such
events requires more detailed measurements and post-processing than
detecting simple changes in traffic volumes.
A difficult task is the separation of good from bad packets to
prepare and launch counteraction. This may require a deeper look
into packet content by using further header field IEs from [RFC5102]
and/or packet payloads from IE ipPayloadPacketSection in [RFC5477].
Furthermore, the amount of resources needed for measurement and
reporting increases with the level of granularity required to detect
an attack. Multi-step analysis techniques may be useful, e.g., to
launch an in-depth analysis (e.g., based on packet information) in
case the Flow information shows suspicious patterns. In order to
supervise traffic to a specific host or network node, it is useful to
apply filtering methods such as those described in [RFC5475].
Mapping the two directions of communication is often useful for
checking correct protocol behavior (see Section 4.6). A correlation
of IPFIX data from multiple Observation Points (see Section 2.5.1)
allows assessing the propagation of an attack and can help to locate
its source.
The integration of previous measurement results helps to review
traffic changes over time for detection of traffic anomalies and
provides the basis for forensic analysis. A standardized storage
format for IPFIX data would support the offline analysis of data from
different operators.
Nevertheless, capturing full packet traces at all Observation Points
in the network is not viable due to resource limitations and privacy
concerns. Therefore, metrics should be chosen wisely to allow a
solid detection with minimal resource consumption. Resources can be
saved, for instance, by using coarser-grained Flow definitions,
reporting pre-processed metrics (e.g., with additional Information
Elements), or deploying sampling methods.
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In many cases, only derived metrics provide sufficient evidence about
security incidents. For example, comparing the number of SYN and FIN
packets for a specific time interval can reveal an ongoing SYN
attack, which is not obvious from unprocessed packet and Flow data.
Further metrics like the cumulated sum of various counters,
distributions of packet attributes, or spectrum coefficients have
been used to identify a variety of attacks.
In order to detect attacks early, it is useful to process the data as
soon as possible in order to generate significant metrics for the
detection. Pre-processing of raw packet and Flow data already at the
measurement device can speed up the detection process and reduces the
amount of data that need to be exported. Furthermore, it is possible
to directly report derived metrics by defining appropriate
Information Elements. Immediate data export in case of a potential
incident is desired. IPFIX supports such source-triggered exporting
of information due to the push model approach. Nevertheless, further
exporting criteria have to be implemented to export IPFIX records
upon incident detection events and not only upon flow-end or fixed-
time intervals.
Intrusion detection would profit from the combination of IPFIX
functions with AAA functions (see Section 3.5). Such an
interoperation enables further means for attacker detection, advanced
defense strategies, and secure inter-domain cooperation.
2.5. QoS Monitoring
Quality of service (QoS) monitoring is one target application of the
IPFIX protocol [RFC3917]. QoS monitoring is the passive observation
of the transmission quality for single Flows or traffic aggregates in
the network. One example of its use is the validation of QoS
guarantees in service level agreements (SLAs). Typical QoS
parameters are loss [RFC2680], one-way [RFC2679] and round-trip delay
[RFC2681], and delay variation [RFC3393]. Whenever applicable, the
IP Performance Metrics (IPPM) definitions [RFC4148] should be used
when reporting QoS metrics.
The calculation of those QoS metrics requires per-packet processing.
Reporting packet information with IPFIX is possible by simply
considering a single packet as Flow. [RFC5101] also allows the
reporting of multiple identical Information Elements in one Flow
Record. Using this feature for reporting information about multiple
packets in one record would require additional agreement on semantics
regarding the order of Information Elements (e.g., which timestamp
belongs to which packet payload in a sequence of Information
Elements). [RFC5477] defines useful additional Information Elements
for exporting per-packet information with IPFIX.
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2.5.1. Correlating Events from Multiple Observation Points
Some QoS metrics require the correlation of data from multiple
Observation Points. For this, the clocks of the involved Metering
Processes must be synchronized. Furthermore, it is necessary to
recognize that the same packet was observed at different Observation
Points.
This can be done by capturing parts of the packet content (packet
header and/or parts of the payload) that do not change on the way to
the destination. Based on the packet content, it can be recognized
when the same packet arrived at another Observation Point. To reduce
the amount of measurement data, a unique packet ID can be calculated
from the packet content, e.g., by using a Cyclic Redundancy Check
(CRC) or hash function instead of transferring and comparing the
unprocessed content. Considerations on collision probability and
efficiency of using such packet IDs are described in [GrDM98],
[DuGr00], and [ZsZC01].
IPFIX allows the reporting of several IP and transport header fields
(see Sections 5.3 and 5.4 in [RFC5102]). Using only those fields for
packet recognition or ID generation can be sufficient in scenarios
where those header fields vary a lot among subsequent packets, where
a certain amount of packet ID collisions are tolerable, or where
packet IDs need to be unique only for a small time interval.
For including packet payload information, the Information Element
ipPayloadPacketSection defined in [RFC5477] can be used. The
Information Element ipHeaderPacketSection can also be used. However,
header fields that can change on the way from source to destination
have to be excluded from the packet ID generation because they may
differ at different Observation Points.
For reporting packet IDs generated by a CRC or hash function, the
Information Element digestHashValue defined in [RFC5477] can be used.
2.5.2. Examples
The following examples show which Information Elements need to be
reported by IPFIX to generate specific QoS metrics. As an
alternative, the metrics can be generated directly at the exporter
and IPFIX can be used to export the metrics (see Section 2.7).
2.5.2.1. RTT Measurements with Packet Pair Matching (Single-Point)
The passive measurement of round-trip time (RTT) can be performed by
using packet pair matching techniques as described in [Brow00]. For
the measurements, request/response packet pairs from protocols such
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as DNS, ICMP, SNMP or TCP (SYN/SYN_ACK, DATA/ACK) are utilized to
passively observe the RTT [Brow00]. This technique requires the
correlation of data from both directions.
Required Information Elements per packet (DNS example):
- Packet arrival time: observationTimeMicroseconds [RFC5477]
- DNS header: ipPayloadPacketSection [RFC5477]
Required functions:
- Recognition of request/response packet pairs
Remarks:
- Requires Information Elements from [RFC5477].
- observationTimeMicroseconds can be substituted by
flowStartMicroseconds [RFC5102] because a single packet can be
represented as a Flow.
- If time values with a finer granularity are needed,
observationTimeNanoseconds can be used.
2.5.2.2. One-Way Delay Measurements (Multi-Point)
Passive one-way delay measurements require the collection of data at
two Observation Points. As mentioned above, synchronized clocks are
needed to avoid time-differences at the involved Observation Points.
The recognition of packets at the second Observation Point can be
based on parts of the packet content directly. A more efficient way
is to use a packet ID (generated from packet content).
Required Information Elements per packet (with packet ID):
- Packet arrival time: observationTimeMicroseconds [RFC5477]
- Packet ID: digestHashValue [RFC5477]
Required functions:
- Packet ID generation
- Delay calculation (from arrival times at the two Observation
Points)
Remarks:
- Requires Information Elements from [RFC5477].
- observationTimeMicroseconds can be substituted by
flowStartMicroseconds [RFC5102], because a single packet can be
represented as a Flow.
- If time values with a finer granularity are needed,
observationTimeNanoseconds can be used.
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- The amount of content used for ID generation influences the number
of collisions (different packets that map to the same ID) that can
occur. Investigations on this and other considerations on packet
ID generation can be found in [GrDM98], [DuGr00], and [ZsZC01].
2.6. Inter-Domain Exchange of IPFIX Data
IPFIX data can be used to share information with neighbor providers.
A few recommendations should be considered if IPFIX records travel
over the public Internet, compared to its usage within a single
domain. First of all, security threat levels are higher if data
travels over the public Internet. Protection against disclosure or
manipulation of data is even more important than for intra-domain
usage. Therefore, Transport Layer Security (TLS) or Datagram
Transport Layer Security should be used as described in [RFC5101].
Furthermore, data transfer should be congestion-aware in order to
allow untroubled coexistence with other data Flows in public or
foreign networks. That means transport over Stream Control
Transmission Protocol (SCTP) or TCP is required.
Some ISPs are still reluctant to share information due to concerns
that competing ISPs might exploit network information from neighbor
providers to strengthen their own position in the market.
Nevertheless, technical needs have already triggered the exchange of
data in the past (e.g., exchange of routing information by BGP). The
need to provide inter-domain guarantees is one big incentive to
increase inter-domain cooperation. The necessity to defend networks
against current and future threats (denial-of-service attacks, worm
distributions, etc.) will hopefully increase the willingness to
exchange measurement data between providers.
2.7. Export of Derived Metrics
The IPFIX protocol is used to transport Flow and packet information
to provide the input for the calculation of a variety of metrics
(e.g., for QoS validation or attack detection). IPFIX can also be
used to transfer these metrics directly, e.g., if the metric
calculation is co-located with the Metering and Exporting Processes.
It doesn't matter which measurement and post-processing functions are
applied to generate a specific metric. IPFIX can be used to
transport the results from passive and active measurements and from
post-processing operations. For the reporting of derived metrics,
additional Information Elements need to be defined.
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For most QoS metrics like loss, delay, delay variation, etc.,
standard IPPM definitions exist. In case such metrics are reported
with IPFIX, the IPPM standard definition should be used.
2.8. Summary
The following table shows an overview of the Information Elements
required for the target applications described in [RFC3917]
(M-mandatory, R-recommended, O-optional).
| Application | [RFC5102] | [RFC5477] | additional IEs |
+-------------+------------+--------------+-----------------+
| Accounting | M | - | - |
+-------------+------------+--------------+-----------------+
| Traffic | M | O | - |
| Profiling | | | |
+-------------+------------+--------------+-----------------+
| Traffic | M | - | O |
| Engineering | | | (routing info) |
+-------------+------------+--------------+-----------------+
| Attack | M | R | R |
| Detection | | |(derived metrics)|
+-------------+------------+--------------+-----------------+
| QoS | M | M | O |
| Monitoring | |(most metrics)|(derived metrics)|
+-------------+------------+--------------+-----------------+
For accounting, the IEs in [RFC5102] are sufficient. As mentioned
above, IPFIX does not conform to the reliability requirements
demanded by [RFC2975] for usage-based billing systems (see Section
4.2). For traffic profiling, additional IEs from [RFC5477] can be
useful to gain more insight into the traffic. For traffic
engineering, Flow information from [RFC5102] is sufficient, but it
would profit from routing information, which could be exported by
IPFIX. Attack detection usually profits from further insight into
the traffic. This can be achieved with IEs from [RFC5477].
Furthermore, the reporting of derived metrics in additional IEs would
be useful. Most QoS metrics require the use of IEs from [RFC5477].
IEs from [RFC5477] are also useful for the mapping of results from
different Observation Points as described in Section 2.5.1.
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3. Relation of IPFIX to Other Frameworks and Protocols
3.1. IPFIX and IPv6
From the beginning, IPFIX has been designed for IPv4 and IPv6.
Therefore, IPFIX can be used in IPv4 and IPv6 networks without
limitations. The usage of IPFIX in IPv6 networks has two aspects:
- Generation and reporting of IPFIX records about IPv6 traffic
- Exporting IPFIX records over IPv6
The generation and reporting of IPFIX records about IPv6 traffic is
possible. Appropriate Information Elements for the reporting of IPv6
traffic are defined in [RFC5102]. Exporting IPFIX records over IPv6
is not explicitly addressed in [RFC5101]. Since IPFIX runs over a
transport protocol (SCTP, PR-SCTP, UDP, or TCP) and all potential
IPFIX transport protocols can run in IPv6 networks, one just needs to
provide the chosen transport protocol in the IPv6 network to run
IPFIX over IPv6.
3.2. IPFIX and PSAMP
PSAMP defines packet selection methods, their configuration at
routers and probes, and the reporting of packet information.
PSAMP uses IPFIX as a basis for exporting packet information
[RFC5476]. [RFC5477] describes further Information Elements for
exporting packet information and reporting configuration information.
The main difference between IPFIX and PSAMP is that IPFIX addresses
the export of Flow Records, whereas PSAMP addresses the export of
packet records. Furthermore, PSAMP explicitly addresses remote
configuration. It defines a MIB for the configuration of packet
selection processes. Remote configuration is not (yet) addressed in
IPFIX, but one could consider extending the PSAMP MIB to also allow
configuration of IPFIX processes.
3.3. IPFIX and RMON
Remote Monitoring (RMON) [RFC3577] is a widely used monitoring system
that gathers traffic data from RMON Agents in network devices. One
major difference between RMON and IPFIX is that RMON uses SNMP for
data export, whereas IPFIX defines its own push-oriented protocol.
RMON defines MIBs that contain the information to be exported. In
IPFIX, the data to be exported is defined as Information Elements.
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The most relevant MIBs for comparison with IPFIX are the Application
Performance Measurement MIB (APM-MIB) [RFC3729] and the Transport
Performance Metrics MIB (TPM-MIB) [RFC4150]. The APM-MIB has a
complex system for tracking user application performance, with
reporting about transactions and SLA threshold notification-trigger
configuration, and persistence across DHCP lease expirations. It
requires a full RMON2-MIB protocolDirTable implementation.
The APM-MIB reports the performance of transactions. A transaction
is a service-oriented term and describes the data exchange from the
transaction start (when a user requests a service) until its
completion. The performance parameters include response times,
throughput, streaming responsiveness, and availability of services.
The RMON transaction concept differs from the IPFIX Flow concept. A
Flow is a very generic term that allows one to group IP packets in
accordance with common properties. In contrast to this, the term
transaction is service-oriented and contains all data exchange
required for service completion.
In order to report such data with IPFIX, one would probably need a
specific combination of multiple Flows and the ability to map those
to the transaction. Due to the service-oriented focus of APM, the
required metrics also differ. For instance, the RMON APM requires a
metric for the responsiveness of services. Such metrics are not
addressed in IPFIX.
Furthermore, the APM-MIB allows the configuration of the transaction
type to be monitored, which is currently not addressed in IPFIX.
The APM MIB could be considered as an extension of the IPFIX Metering
Process where the application performance of a combination of
multiple Flows is measured. If appropriate, IEs would be defined in
the IPFIX information model and the IPFIX Device would support the
APM MIB data collection, the solutions could be complementary. That
means one could use IPFIX to export APM MIB transaction information.
The TPM-MIB breaks out the APM-MIB transactions into sub-application
level transactions. For instance, a web request is broken down into
DNS, TCP, and HTTP sub-transactions. Such sub-transactions can be
considered as bidirectional Flows. With an appropriate Flow
definition and the ability to map both directions of a Flow (see
Section 4.6), one could measure and report Flow characteristics of
such sub-application level transaction with IPFIX.
The TPM-MIB requires APM-MIB and RMON2-MIB.
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3.4. IPFIX and IPPM
The IPFIX protocol can be used to carry IPPM network performance
metrics or information that can be used to calculate those metrics
(see Sections 2.5 and 2.7 for details and references).
3.5. IPFIX and AAA
AAA defines a protocol and architecture for authentication,
authorization, and accounting for service usage [RFC2903]. The
DIAMETER protocol [RFC3588] is used for AAA communication, which is
needed for network access services (Mobile IP, NASREQ, and ROAMOPS).
The AAA architecture [RFC2903] provides a framework for extending AAA
support to other services. DIAMETER defines the exchange of messages
between AAA entities, e.g., between AAA clients at access devices and
AAA servers, and among AAA servers. DIAMETER is used for the
transfer of accounting records. In order to form accounting records
for usage-based accounting measurement, data from the network is
required. IPFIX defines a protocol to export such data from routers,
measurement probes, and other devices. Therefore, it looks promising
to connect those two architectures.
For all scenarios described here, one has to keep in mind that IPFIX
does not conform to the reliability requirements for usage-based
billing described in [RFC2975] (see Section 4.2). Using IPFIX
without reliability extensions together with AAA would result in
accounting scenarios that do not conform to usage-based billing
requirements described in [RFC2975].
As shown in Section 2.1, accounting applications can directly
incorporate an IPFIX Collecting Process to receive IPFIX records with
information about the transmitted volume. Nevertheless, if a AAA
infrastructure is in place, the cooperation between IPFIX and AAA
provides many valuable synergistic benefits. IPFIX records can
provide the input for AAA accounting functions and provide the basis
for the generation of DIAMETER accounting records. However, as
stated in Section 4.2, the use of IPFIX as described in [RFC5101] is
currently limited to situations where the purpose of the accounting
does not require reliability.
Further potential features include the mapping of a user ID to Flow
information (by using authentication information) or using the secure
authorized exchange of DIAMETER accounting records with neighbor
domains. The last feature is especially useful in roaming scenarios
where the user connects to a foreign network and the home provider
generates the invoice.
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Coupling an IPFIX Collecting Process with AAA functions also has high
potential for intrusion and attack detection. AAA controls network
access and maintains data about users and nodes. AAA functions can
help to identify the source of malicious traffic. Authorization
functions are able to deny access to suspicious users or nodes.
Therefore, coupling those functions with an IPFIX Collecting Process
can provide an efficient defense against network attacks.
Sharing IPFIX records (either directly or encapsulated in DIAMETER)
with neighbor providers allows an efficient inter-domain attack
detection. For this, it would be useful to allow remote
configuration of measurement and record generation in order to
provide information in the required granularity and accuracy. Since
remote configuration is currently not addressed in IPFIX, this would
require additional work. The AAA infrastructure itself may be used
to configure measurement functions in the network as proposed in
[RFC3334].
Furthermore, the transport of IPFIX records with DIAMETER would
require the translation of IPFIX Information Elements into DIAMETER
attribute value pairs (AVPs) defined in [RFC3588]. Since the
DIAMETER AVPs do not comprise all IPFIX Information Elements, it is
necessary to define new AVPs to transport them over DIAMETER.
Two possibilities exist to connect IPFIX and AAA:
- Connecting via a AAA Client
- Connecting via an Application Specific Module (ASM)
Both are explained in the following sections. The approaches only
require a few additional functions. They do not require any changes
to IPFIX or DIAMETER.
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3.5.1. Connecting via a AAA Client
One possibility of connecting IPFIX and AAA is to run a AAA client on
the IPFIX Collector. This client can generate DIAMETER accounting
messages and send them to a AAA server. The mapping of the Flow
information to a user ID can be done in the AAA server by using data
from the authentication process. DIAMETER accounting messages can be
sent to the accounting application or to other AAA servers (e.g., in
roaming scenarios).
+---------+ DIAMETER +---------+
| AAA-S |------------->| AAA-S |
+---------+ +---------+
^
| DIAMETER
|
|
+--+--------+--+
| | AAA-C | |
+ +--------+ |
| |
| Collector |
+--------------+
^
| IPFIX
|
+------------+
| Exporter |
+------------+
Figure 1: IPFIX Collector connects to AAA server via AAA client
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3.5.2. Connecting via an Application Specific Module (ASM)
Another possibility is to directly connect the IPFIX Collector with
the AAA server via an application specific module (ASM). Application
specific modules have been proposed by the IRTF AAA architecture
research group (AAARCH) in [RFC2903]. They act as an interface
between AAA server and service equipment. In this case, the IPFIX
Collector is part of the ASM. The ASM acts as an interface between
the IPFIX protocol and the input interface of the AAA server. The
ASM translates the received IPFIX data into an appropriate format for
the AAA server. The AAA server then can add information about the
user ID and generate a DIAMETER accounting record. This accounting
record can be sent to an accounting application or to other AAA
servers.
+---------+ DIAMETER +---------+
| AAA-S |------------->| AAA-S |
+---------+ +---------+
^
|
+------------------+
| ASM |
| +------------+ |
| | Collector | |
+------------------+
^
| IPFIX
|
+------------+
| Exporter |
+------------+
Figure 2: IPFIX connects to AAA server via ASM
3.6. IPFIX and RTFM
The Realtime Traffic Flow Measurement (RTFM) working group defined an
architecture for Flow measurement [RFC2722]. This section compares
the RTFM framework with the IPFIX framework.
3.6.1. Architecture
The RTFM architecture [RFC2722] is very similar to the IPFIX
architecture. It defines meter, meter reader, and a manager as
building blocks of the measurement architecture. The manager
configures the meter, and the meter reader collects data from the
meter. In RTFM, the building blocks communicate via SNMP.
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The IPFIX architecture [RFC5470] defines Metering, Exporting, and
Collecting Processes. IPFIX speaks about processes instead of
devices to clarify that multiple of those processes may be co-located
on the same machine.
These definitions do not contradict each other. One could see the
Metering Process as part of the meter, and the Collecting Process as
part of the meter reader.
One difference is that IPFIX currently does not define a managing
process because remote configuration was (at least initially) out of
scope for the working group.
3.6.2. Flow Definition
RTFM and IPFIX both consider Flows as a group of packets that share a
common set of properties. A Flow is completely specified by that set
of values, together with a termination criterion (like inactivity
timeout).
A difference is that RTFM defines Flows as bidirectional. An RTFM
meter matches packets from B to A and A to B as separate parts of a
single Flow, and it maintains two sets of packet and byte counters,
one for each direction.
IPFIX does not explicitly state whether Flows are uni- or
bidirectional. Nevertheless, Information Elements for describing
Flow properties were defined for only one direction in [RFC5102].
There are several solutions for reporting bidirectional Flow
information (see Section 4.6).
3.6.3. Configuration and Management
In RTFM, remote configuration is the only way to configure a meter.
This is done by using SNMP and a specific Meter MIB [RFC2720]. The
IPFIX group currently does not address IPFIX remote configuration.
IPFIX Metering Processes export the layout of data within their
Templates, from time to time. IPFIX Collecting Processes use that
Template information to determine how they should interpret the IPFIX
Flow data they receive.
3.6.4. Data Collection
One major difference between IPFIX and RTFM is the data collection
model. RTFM retrieves data in pull mode, whereas IPFIX uses a push
mode model to send data to Collecting Processes.
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An RTFM meter reader pulls data from a meter by using SNMP. SNMP
security on the meter determines whether a reader is allowed to pull
data from it. An IPFIX Exporting Process is configured to export
records to a specified list of IPFIX Collecting Processes. The
condition of when to send IPFIX records (e.g., Flow termination) has
to be configured in the Exporting or Metering Process.
3.6.5. Data Model Details
RTFM defines all its attributes in the RTFM Meter MIB [RFC2720].
IPFIX Information Elements are defined in [RFC5102].
RTFM uses continuously-incrementing 64-bit counters for the storage
of the number of packets of a Flow. The counters are never reset and
just wrap back to zero if the maximum value is exceeded. Flows can
be read at any time. The difference between counter readings gives
the counts for activity in the interval between readings.
IPFIX allows absolute (totalCounter) and relative counters
(deltaCounter) [RFC5102]. The totalCounter is never reset and just
wraps to zero if values are too large, exactly as the counters used
in RTFM. The deltaCounter is reset to zero when the associated Flow
Record is exported.
3.6.6. Transport Protocol
RTFM has a Standards-Track Meter MIB [RFC2720], which is used both to
configure a meter and to store metering results. The MIB provides a
way to read lists of attributes with a single Object Identifier
(called a 'package'), which reduces the SNMP overhead for Flow data
collection. SNMP, of course, normally uses UDP as its transport
protocol. Since RTFM requires a reliable Flow data transport system,
an RTFM meter reader must time out and resend unanswered SNMP
requests. Apart from being clumsy, this can limit the maximum data
transfer rate from meter to meter reader.
IPFIX is designed to work over a variety of different transport
protocols. SCTP [RFC4960] and PR-SCTP [RFC3758] are mandatory. UDP
and TCP are optional. In addition, the IPFIX protocol encodes data
much more efficiently than SNMP does, hence IPFIX has lower data
transport overheads than RTFM.
3.6.7. Summary
IPFIX exports Flow information in a push model by using SCTP, TCP, or
UDP. It currently does not address remote configuration. RTFM data
collection is using the pull model and runs over SNMP. RTFM
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addresses remote configuration, which also runs over SNMP. Both
frameworks allow a very flexible Flow definition, although RTFM is
based on a bidirectional Flow definition.
4. Limitations
The goal of this section is to show the limitations of IPFIX and to
give advice where not to use IPFIX or in which cases additional
considerations are required.
4.1. Using IPFIX for Other Applications than Listed in RFC 3917
IPFIX provides a generic export mechanism. Due to its Template-based
structure, it is a quite flexible protocol. Network operators and
users may want to use it for other applications than those described
in [RFC3917].
Apart from sending raw Flow information, it can be used to send per-
packet data, aggregated or post-processed data. For this, new
Templates and Information Elements can be defined if needed. Due to
its push mode operation, IPFIX is also suited to send network
initiated events like alarms and other notifications. It can be used
for exchanging information among network nodes to autonomously
improve network operation.
Nevertheless, the IPFIX design is based on the requirements that
originate only from the target applications stated in [RFC3917].
Using IPFIX for other purposes requires a careful checking of IPFIX
capabilities against application requirements. Only with this, one
can decide whether IPFIX is a suitable protocol to meet the needs of
a specific application.
4.2. Using IPFIX for Billing (Reliability Limitations)
The reliability requirements defined in [RFC3917] are not sufficient
to guarantee the level of reliability that is needed for usage-based
billing systems as described in [RFC2975]. In particular, IPFIX does
not support the following features required by [RFC2975]:
- Record loss: IPFIX allows the usage of different transport
protocols for the transfer of data records. Resilience against the
loss of IPFIX data records can be only provided if TCP or SCTP is
used for the transfer of data records.
- Network or device failures: IPFIX does allow the usage of multiple
Collectors for one Exporter, but it neither specifies nor demands
the use of multiple Collectors for the provisioning of fault
tolerance.
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- Detection and elimination of duplicate records: This is currently
not supported by IPFIX.
- Application layer acknowledgements: IPFIX does not support the
control of measurement and Exporting Processes by higher-level
applications. Application layer acknowledgements are necessary,
e.g., to inform the Exporter in case the application is not able to
process the data exported with IPFIX. Such acknowledgements are
not supported in IPFIX.
Further features like archival accounting and pre-authorization are
out of scope of the IPFIX specification but need to be realized in
billing system architectures as described in [RFC2975].
4.3. Using a Different Transport Protocol than SCTP
SCTP is the preferred protocol for IPFIX, i.e., a conforming
implementation must work over SCTP. Although IPFIX can also work
over TCP or UDP, both protocols have drawbacks [RFC5101]. Users
should make sure they have good reasons before using protocols other
than SCTP in a specific environment.
4.4. Push vs. Pull Mode
IPFIX works in push mode. That means IPFIX records are automatically
exported without the need to wait for a request. The responsibility
for initiating a data export lies with the Exporting Process.
Criteria for exporting data need to be configured at the Exporting
Process. Therefore, push mode has more benefits if the trigger for
data export is related to events at the Exporting Process (e.g., Flow
termination, memory shortage due to large amount of Flows, etc.). If
the protocol used pull mode, the Exporting Process would need to wait
for a request to send the data. With push mode, it can send data
immediately, e.g., before memory shortage would require a discarding
of data.
With push mode, one can prevent the overloading of resources at the
Exporting Process by simply exporting the information as soon as
certain thresholds are about to be exceeded. Therefore, exporting
criteria are often related to traffic characteristics (e.g., Flow
timeout) or resource limitations (e.g., size of Flow cache).
However, traffic characteristics are usually quite dynamic and often
impossible to predict. If they are used to trigger Flow export, the
exporting rate and the resource consumption for Flow export becomes
variable and unpredictable.
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Pull mode has advantages if the trigger for data export is related to
events at the Collecting Process (e.g., a specific application
requests immediate input).
In a pull mode, a request could simply be forwarded to the Exporting
Process. In a push mode, the exporting configuration must be changed
to trigger the export of the requested data. Furthermore, with pull
mode, one can prevent the overloading of the Collecting Process by
the arrival of more records than it can process.
Whether this is a relevant drawback depends on the flexibility of the
IPFIX configuration and how IPFIX configuration rules are
implemented.
4.5. Template ID Number
The IPFIX specification limits the different Template ID numbers that
can be assigned to the newly generated Template records in an
Observation Domain. In particular, Template IDs up to 255 are
reserved for Template or option sets (or other sets to be created)
and Template IDs from 256 to 65535 are assigned to data sets. In the
case of many exports requiring many different Templates, the set of
Template IDs could be exhausted.
4.6. Exporting Bidirectional Flow Information
Although IPFIX does not explicitly state that Flows are
unidirectional, Information Elements that describe Flow
characteristics are defined only for one direction in [RFC5102].
[RFC5101] allows the reporting of multiple identical Information
Elements in one Flow Record. With this, Information Elements for
forward and reverse directions can be reported in one Flow Record.
However, this is not sufficient. Using this feature for reporting
bidirectional Flow information would require an agreement on the
semantics of Information Elements (e.g., first counter is the counter
for the forward direction, the second counter for the reverse
direction).
Another option is to use two adjacent Flow Records to report both
directions of a bidirectional Flow separately. This approach
requires additional means for mapping those records and is quite
inefficient due to the redundant reporting of Flow Keys.
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4.7. Remote Configuration
Remote configuration was initially out of scope of the IPFIX working
group in order to concentrate on the protocol specification.
Therefore, there is currently no standardized way to configure IPFIX
processes remotely. Nevertheless, due to the broad need for this
feature, it is quite likely that solutions for this will be
standardized soon.
5. Security Considerations
This document describes the usage of IPFIX in various scenarios.
Security requirements for IPFIX target applications and security
considerations for IPFIX are addressed in [RFC3917] and [RFC5101].
Those requirements have to be met for the usage of IPFIX for all
scenarios described in this document. To our current knowledge, the
usage scenarios proposed in Section 2 do not induce further security
hazards.
The threat level to IPIFX itself may depend on the usage scenario of
IPFIX. The usage of IPFIX for accounting or attack detection may
increase the incentive to attack IPFIX itself. Nevertheless,
security considerations have to be taken into account in all
described scenarios.
As described in the security considerations in [RFC5101], security
incidents can become a threat to IPFIX processes themselves, even if
IPIFX is not the target of the attack. If an attack generates a
large amount of Flows (e.g., by sending packets with spoofed
addresses or simulating Flow termination), Exporting and Collecting
Processes may get overloaded by the immense amount of records that
are exported. A flexible deployment of packet or Flow sampling
methods can be useful to prevent the exhaustion of resources.
Section 3 of this document describes how IPFIX can be used in
combination with other technologies. New security hazards can arise
when two individually secure technologies or architectures are
combined. For the combination of AAA with IPFIX, an application
specific module (ASM) or an IPFIX Collector can function as a transit
point for the messages. One has to ensure that at this point the
applied security mechanisms (e.g., encryption of messages) are
maintained.
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6. Acknowledgements
We would like to thank the following people for their contributions,
discussions on the mailing list, and valuable comments:
Sebastian Zander
Robert Loewe
Reinaldo Penno
Lutz Mark
Andy Biermann
Part of the work has been developed in the research project 6QM,
co-funded with support from the European Commission.
7. Normative References
[RFC4148] Stephan, E., "IP Performance Metrics (IPPM) Metrics
Registry", BCP 108, RFC 4148, August 2005.
[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.
[RFC5477] Dietz, T., Claise, B., Aitken, P., Dressler, F., and G.
Carle, "Information Model for Packet Sampling Exports",
RFC 5477, March 2009.
8. Informative References
[Brow00] Brownlee, N., "Packet Matching for NeTraMet
Distributions",
RFC, FYI, BCP