IP Flow Information Export WG G. Sadasivan
(ipfix) Cisco Systems, Inc.
Internet-Draft N. Brownlee
Expires: November 30, 2004 CAIDA | The University of Auckland
B. Claise
Cisco Systems, Inc.
J. Quittek
NEC Europe Ltd.
June 2004
Architecture for IP Flow Information Export
draft-ietf-ipfix-architecture-03
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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This Internet-Draft will expire on November 30, 2004.
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This memo defines the IPFIX architecture for the selective monitoring
of network traffic flows, and for the export of measured IP flow
information from an IPFIX device to a Collector, as per the
requirements set out in the IPFIX Requirements document.
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Table of Contents
1. Changes/Issues from the -02 Draft . . . . . . . . . . . . . 4
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Examples of Flows . . . . . . . . . . . . . . . . . . . . . 9
6. IPFIX reference Model . . . . . . . . . . . . . . . . . . . 11
7. IPFIX Functional and Logical blocks . . . . . . . . . . . . 13
7.1 Metering Process . . . . . . . . . . . . . . . . . . . . . 13
7.1.1 Observation Point . . . . . . . . . . . . . . . . . . 13
7.1.2 Selection Criteria for Packets . . . . . . . . . . . . 13
7.2 Observation Domain . . . . . . . . . . . . . . . . . . . . 15
7.3 Flow Recording Process . . . . . . . . . . . . . . . . . . 15
7.4 Exporting Process . . . . . . . . . . . . . . . . . . . . 15
8. Overview of the IPFIX Protocol . . . . . . . . . . . . . . . 16
8.1 Encoding Flow Data Information . . . . . . . . . . . . . . 17
8.2 Encoding Control Information . . . . . . . . . . . . . . . 17
8.3 Exporting Control Information . . . . . . . . . . . . . . 17
8.4 Export Error Handling . . . . . . . . . . . . . . . . . . 18
8.5 Flow Expiration and Export . . . . . . . . . . . . . . . . 19
8.6 Selection Criteria of flows for export . . . . . . . . . . 19
9. IPFIX Protocol Details . . . . . . . . . . . . . . . . . . . 20
9.1 The IPFIX basis protocol . . . . . . . . . . . . . . . . . 20
9.2 The Collecting Process . . . . . . . . . . . . . . . . . . 22
9.3 IPFIX Protocol on the Collecting Process . . . . . . . . . 23
9.4 Support for Applications . . . . . . . . . . . . . . . . . 23
10. Export Models . . . . . . . . . . . . . . . . . . . . . . . 23
10.1 Export with Reliable Control Connection . . . . . . . . 23
10.2 Collector Failure Detection and Recovery . . . . . . . . 24
10.3 Collector Redundancy . . . . . . . . . . . . . . . . . . 25
11. IPFIX flow collection for Special Traffic . . . . . . . . . 25
12. IPFIX flow collection from Special Devices . . . . . . . . . 25
13. Security Considerations . . . . . . . . . . . . . . . . . . 26
13.1 Data security . . . . . . . . . . . . . . . . . . . . . 26
13.1.1 No security . . . . . . . . . . . . . . . . . . . . 27
13.1.2 Authentication-only . . . . . . . . . . . . . . . . 27
13.1.3 Encryption . . . . . . . . . . . . . . . . . . . . . 27
13.2 IPFIX end point authentication . . . . . . . . . . . . . 28
14. IPFIX overload . . . . . . . . . . . . . . . . . . . . . . . 28
14.1 Denial of service (DoS) attack prevention . . . . . . . 28
14.1.1 Network under attack . . . . . . . . . . . . . . . . 28
14.1.2 Generic DoS attack on the IPFIX system . . . . . . . 28
14.1.3 IPFIX specific DoS attack . . . . . . . . . . . . . 29
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . 29
16. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 29
17. References . . . . . . . . . . . . . . . . . . . . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 30
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Intellectual Property and Copyright Statements . . . . . . . 32
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1. Changes/Issues from the -02 Draft
Flow Aggregates:
Are an optional part of the Flow Recording Process. That means
that aggregate flows will need to be exported, e.g. an Exporting
Process could send aggregate flows to one Collector, and the
individual flows which comprise the aggregate to another. I've
added text to point this out.
Packet Selection functions:
I've rewritten these sections so as to make it clearer what they
actually do, and to point out that the selected packets may be
subdivided further into actual Flows, each of which gets exported.
Selective Export:
I've taken this out of the draft because it doesn't seem useful,
and it adds unnecessary complexity to the IPFIX system.
Given that one configures an IPFIX device to select and/or sample
only those packets which are of interest, surely one would always
want to export them?
Flow Expiration:
The text says "inactivity timeout 0 means immediate expiration."
That would break long-running flows into a sequence of
single-packet flows - do we really want that? I've added text to
explain this.
MUST vs SHOULD:
I've changed SHOULD to MUST in some places, where that seems more
sensible to me. Comments to the IPFIX list please!
Editorial:
I've changed lots of the wording to improve readability, and added
explanations to make descriptions clearer.
2. Introduction
There are several applications e.g., usage-based accounting, traffic
profiling, traffic engineering, attack/intrusion detection, QoS
monitoring, that require flow-based IP traffic measurements. It is
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therefore important to have a standard way of exporting information
related to IP flows. This document defines an architecture for IP
traffic flow monitoring, measuring and exporting. It provides a
high-level description of the key components and their functions.
3. Scope
This document defines the architecture for IPFIX. Its main
objectives are to:
o Describe the key architectural components of IPFIX.
o Define the architectural requirements, e.g., Recovery, Security,
etc., for the IPFIX system.
o Describe the characteristics of the IPFIX (flow export) protocol.
Note that the IPFIX system does not provide for remote configuration
of an IPFIX device. Instead, IPFIX devices are configured locally by
Network Operations Staff.
4. Terminology
The definition of the basic terms like IP Traffic Flow, Exporting
Process, Collecting Process, Observation Point, etc. are
semantically identical with those found in the IPFIX requirements
document IPFIX-REQS [1]. Some of the terms have been expanded for
more clarity when defining the protocol. Additional terms required
for the architecture have also been defined. For the same terms
defined in both this document and IPFIX-PROTO [4] the definitions are
identical with IPFIX-PROTO [4].
* Observation Point
An Observation Point is a location in the network where IP packets
can be observed. Examples include: a line to which a probe is
attached, a shared medium, such as an Ethernet-based LAN, a single
port of a router, or a set of interfaces (physical or logical) of
a router.
Note that one Observation Point may be a superset of several other
Observation Points. For example one Observation Point can be an
entire line card. That would be the superset of the individual
Observation Points at the line card's interfaces.
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* Observation Domain
The set of Observation Points which is the largest aggregatable
set of flow information at the Metering Process is termed an
Observation Domain. Each Observation Domain presents itself using
a unique ID to the Exporting Process to identify the IPFIX
messages it generates. For example, a router line card may be
composed of several interfaces with each interface being an
Observation Point. Every Observation Point is associated with an
Observation Domain.
* IP Traffic Flow or Flow
There are several definitions of the term 'flow' being used by the
Internet community. Within the context of IPFIX we use the
following definition:
A flow is defined as a set of IP packets passing an observation
point in the network during a certain time interval. All packets
belonging to a particular flow have a set of common properties.
Each property is defined as the result of applying a function to
the values of:
1. One or more packet header field (e.g. destination IP
address), transport header field (e.g. destination port
number), or application header field (e.g. RTP header fields
[RFC1889])
2. One or more characteristics of the packet itself (e.g. number
of MPLS labels)
3. One or more fields derived from packet treatment (e.g. next
hop IP address, output interface)
A packet is said to belong to a flow if it completely satisfies
all the defined properties of the flow.
This definition covers the range from a flow containing all
packets observed at a network interface to a flow consisting of
just a single packet between two applications with a specific
sequence number.
* Flow Key
Each of the fields which
1. Belong to the packet header (e.g. destination IP address)
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2. Are a property of the packet itself (e.g. packet length)
3. Are derived from packet treatment (e.g. AS number)
and which are used to define a Flow are termed Flow Keys.
* Flow Type
A function F() which would take as input a set of Flow Keys, and
produce as output one or more Flows depending on the combination
of values for the set of Flow Keys, is termed a Flow Type. In
other words, a Flow Type F() maps sets of Flow Key values to
Flows.
* Flow Record
A Flow Record contains information about a specific Flow that was
observed at an Observation Point. A Flow Record contains measured
properties of the Flow (e.g. the total number of bytes for all
the Flow's packets) and usually characteristic properties of the
Flow (e.g. source IP address).
* Metering Process
A Metering Process generates Flow Records. Input to the process
are packets observed at an Observation Point, and packet treatment
at the Observation Point. The Metering Process consists of a set
of functions that includes packet header capturing, timestamping,
sampling, classifying, and maintaining Flow Records. The
maintenance of Flow Records may include creating new records,
updating existing ones, computing Flow statistics, deriving
further Flow properties, detecting Flow expiration, passing Flow
Records to the Exporting Process, and deleting Flow Records.
* Exporting Process
An Exporting Process sends Flow Records to one or more Collecting
Processes. The Flow Records are generated by one or more Metering
Processes.
* IPFIX Device
An IPFIX device hosts at least one Observation Point, a Metering
Process and an Exporting Process. Typically, corresponding
Observation Point(s), Metering Process(es) and Exporting
Process(es) are co-located at such a device, for example at a
router.
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* IPFIX Node
An IPFIX node is a host that implements the IPFIX protocol, i.e.
it contains an Exporting Process or a Collecting Process or both.
* Collecting Process
A Collecting Process receives Flow Records from one or more
Exporting Processes. The Collecting Process might process or
store received Flow Records, but such actions are out of scope for
this document.
* Collector
A device which hosts one or more Collecting Processes is termed a
Collector.
* Flow Recording Process
The Flows generated from the metering device(s) in an Observation
Domain MAY be collected into one or more databases before
exporting. This functional block, in addition to maintaining the
Flow database(s) MAY do Flow aggregation, maintain aggregate
statistics etc. This block is optional for an IPFIX device.
* Template
A Template is an ordered list (e.g. of <type, length> pairs),
used to completely identify the structure and semantics of a
particular set of information that needs to be communicated from
an IPFIX Device to a Collector. Each template is uniquely
identifiable by some means, e.g. by using a Template ID.
* Control Information, Data Stream
The information that needs to be exported from the IPFIX device
can be classified into the following categories:
Control Information
This includes the Flow type definition, selection criteria for
packets within the Flow sent by the Exporting Process, and any
IPFIX protocol messages (e.g. keepalives). The 'control'
stream carries all the information needed for the end-points to
understand the IPFIX protocol, and specifically for the
receiver (collector) to understand and interpret the data sent
by the sender (exporter).
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Data Stream
This includes data records carrying the field values for the
various observed Flows at each of the Observation Points.
IPFIX Message
An IPFIX Message is a message originating at the Exporting
Process that carries the IPFIX records of this Exporting
Process and whose destination is the Collecting Process. An
IPFIX Message is encapsulated within a transport layer header.
5. Examples of Flows
Some examples of flows are listed below:
Example 1: To create flows, the different fields to distinguish flows
are defined. The different combination of the field values creates
unique flows. If the keys are defined as {source IP address,
destination IP address, DSCP}, then all of these are different flows.
1. {192.1.40.1, 171.6.23.5, 4}
2. {192.1.40.23, 171.6.23.67, 4}
3. {192.1.40.23, 171.6.23.67, 2}
4. {198.20.9.200, 171.6.23.67, 4}
Example 2: To create flows, a match function can be applied to all
the packets that pass through an Observation Point, in order to
aggregate some values. This could be done by defining the keys as
{source IP address, destination IP address, DSCP} as in example 1
above, and applying the function which masks the least significant 8
bits of the source IP address and destination IP address (i.e. the
result is a /24 address). The four flows from example 1 would now be
aggregated into three flows by merging the flows 1. and 2. into a
single flow.
1. {192.1.40.0/24, 171.6.23.0/24, 4}
2. {192.1.40.0/24, 171.6.23.0/24, 2}
3. {198.20.9.0/24, 171.6.23.0/24, 4}
Example 3: To create flows, a filter defined by some field values can
be applied on all packets that pass the Observation Point, in order
to select only certain flows. The filter is defined by choosing
fixed values for specific fields from the packet.
All the packets that go from a customer network 192.1.40.0/24 to
another customer network 171.6.23.0/24 with DSCP value of 4 define a
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flow. All other combinations don't define a flow and are not taken
into account. The three flows from example 2 would now be reduced to
one flow, by filtering away the second and the third flow.
{192.1.40.0/24, 171.6.23.0/24, 4}.
The above example can be thought of as a function F() taking as input
{source IP address, destination IP address, DSCP}. The function
selects only the packets which satisfy all three of the following
conditions:
1. Mask out the least significant 8 bits of source IP address, match
against 192.1.40.0.
2. Mask out the least significant 8 bits of destination IP address,
match against 171.6.23.0.
3. DSCP value equal to 4.
Depending on the values of {source IP address, destination IP
address, DSCP} of the different observed packets, the metering
process function F() would choose/filter/aggregate different sets of
packets, which would create different flows. For example, various
combination of values of {source IP address, destination IP address,
DSCP}, F(source IP address, destination IP address, DSCP) would
result in the definition of one or more flows. The function F() is
referred to as a Flow Type.
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6. IPFIX reference Model
The figure below shows the reference model for IPFIX. This figure
covers the various possible scenarios that can exist in an IPFIX
system.
+----------------+ +----------------+
|[*Application 1]| ..|[*Application n]|
+--------+-------+ +-------+--------+
^ ^
~ ~
+~~~~~~~~~~+~~~~~~~~+
^
~
+------------------------+ +-------+------------------+
|IPFIX Device(1) | | Collector(1) |
|[Exporting Process(es)] |<----------->| [Collecting Process(es)] |
+------------------------+ +--------------------------+
.... ....
+------------------------+ +---------------------------+
|IPFIX Device(i) | | Collector(j) |
|[Obsv Point(s)] |<---------->| [Collecting Process(es)] |
|[Metering Process(es)] | +---->| [*Application(s)] |
|[Exporting Process(es)] | | +---------------------------+
+------------------------+ .
.... . ....
+------------------------+ | +--------------------------+
|IPFIX Device(m) | | | Collector(n) |
|[Obsv Point(s)] |<-----+---->| [Collecting Process(es)] |
|[Metering Process(es)] | | [*Application(s)] |
|[Exporting Process(es)] | +--------------------------+
+------------------------+
The various functional components are indicated within brackets [].
The functional components within [*] are not part of the IPFIX
framework. The interfaces shown by "<-->" are defined by the IPFIX
framework but those shown by "<~~>" are not.
The figure below shows a typical IPFIX device.
+--------------------------------------------------+
| IPFIX Device |
| +------------------------+ (*) +-----+ |
| | Flow Recording Process +----+---------> | |
| | | | | E | |
| +------------------------+ | | | |
| ^ ^ | | x | |
| |(*) |(*) | | | |
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| +---......--+------------+ | p | |
| | | | | |
| +----+----+ +----+----+ | o | |
| |Metering | |Metering | | | |
| |Process 1| |Process N| | r | |
| |(Packet | |(Packet | | | |
| | Level) | | Level) | | t | |
| +---------+ +---------+ | | |
| ^ ^ | i | |
|+-------+-----------------------+-------+ | | |
|| | Observation Domain 1 | | | n | |
|| +-----+------+ +-----+------+| | | |
|| |Obsv Point 1| ... |Obsv Point M|| | g | |
|| +------------+ +------------+| | | |
Packets|+-------^-------------------------^-----+ | | |Export
--->---+--------+----------.....----------+ | | |Packet to
In | | +------->
| ........ | | |Collector(s)
| +------------------------+ (*) | P | |
| | Flow Recording Process +----+---------> | |
| | | | | r | |
| +------------------------+ | | | |
| ^ ^ | | o | |
| |(*) | (*) | | | |
| +--- ... ---+------------+ | c | |
| | | | | |
| +----+----+ +----+----+ | e | |
| |Metering | |Metering | | | |
| |Process 1| |Process N| | s | |
| +---------+ +---------+ | | |
| ^ ^ | s | |
|+-------+-----------------------+-------+ | | |
|| | Observation Domain K | | | | |
|| +-----+------+ +-----+------+| | | |
|| |Obsv Point 1| ... |Obsv Point M|| | | |
|| +------------+ +------------+| | | |
Packets|+-------^-------------------------^-----+ +-----+ |
--->---+--------+---------- ... ----------+ |
In | |
+--------------------------------------------------+
In the above figure the IPFIX components are shown in rectangular
boxes. The interface shown by (*) is applicable only if the optional
flow recording process is present. Otherwise the metering
process(es) at the packet level interface directly with the exporting
function. Note that in case of multiple Observation Domains, a
unique ID per Observation Domain must be transmitted as a parameter
to the exporting function. The exporting process includes IPFIX
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protocol and underlying transport layer.
7. IPFIX Functional and Logical blocks
7.1 Metering Process
Every observation point in an IPFIX device, participating in flow
measurements, MUST be associated with at least one metering process.
Every packet coming into an observation point goes into each of the
metering processes associated with the observation point. Broadly,
each metering process extracts the packet headers that come into an
observation point, does timestamping and classifies the packet into
flow(s) based on the selection criteria.
Collecting Processes use a Flow Record's Template ID to interpret
that record's Flow Keys. To allow this, an IPFIX exporter MUST
ensure that an IPFIX collector knows the Template ID for each
incoming Flow Record. To interpret incoming Flow Records, an IPFIX
collector MAY also need to know the Flow Type, i.e. the function F()
that was used by the Metering Process for each Flow.
In addition to Flow Type, an IPFIX collector MAY also use the
following supplementary information to interpret the flow records
further:
o Observation Point
o Selection Criteria for Packets
7.1.1 Observation Point
A Flow Record can be better analyzed if the Observation Point from
which it was measured is known. As such it is RECOMMENDED that
exporters send this information to collectors as well as Flow
Records. In cases where there is a single observation point or where
the observation point information is not relevant, the metering
process MAY choose not to add this to the flow records.
7.1.2 Selection Criteria for Packets
A measurement device MAY define rules so that only certain packets
within an incoming stream of packets are chosen for measurement at an
observation point. This MAY be done by one of the two methods
defined below or a combination of them. A combination of each of
these methods can be adopted to select the packets, i.e. one can
define a set of methods {F1, S1, F2, S2, S3} executed in a specified
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sequence at an observation point to select flows of a particular
type.
7.1.2.1 Filter Functions, Fi
A Filter Function selects only those incoming packets that satisfy a
function on fields defined by the packet header fields, fields
obtained while doing the packet processing, or properties of the
packet itself.
Example: Mask/Match of the fields that define a filter. A filter
might be defined as {Protocol == TCP, Destination Port between 80 and
120}.
Several such filters could be used in any sequence to select packets.
Note that packets selected by a (sequence of) filter functions may be
further classified by their Flow Type, i.e. the selected packets may
belong to several Flows, all of which are exported.
7.1.2.2 Sampling Functions, Si
A Sampling Function determines which packets within a stream of
incoming packets is selected for measurement, i.e. packets that
satisfy the sampling criteria for this Metering Process.
Example: Sample every 100th packet that was received at an
observation point and collect the flow information for a particular
flow type. Choosing all the packets is a special case where the
sampling rate is 1:1.
The figure below shows the operations which MAY be applied as part of
a typical metering process.
packet header capturing
|
timestamping
|
v
+----->+
| |
| sampling Si (1:1 in case of no sampling)
| |
| filtering Fi (select all when no criteria)
| |
+------+
|
v
Flows
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Note that filtering and sampling functions may also be used in an
exporting process to select flows to be exported.
7.2 Observation Domain
The Observation Domain is a logical block that presents a single
identity for a group of Observation Points within an IPFIX device.
Each {Observation point, Metering Process} MUST belong to a single
Observation Domain. An IPFIX device could have multiple Observation
Domains each of which has a subset of the total set of Observation
Points in it. Each Observation Domain MUST carry a unique ID within
the context of an IPFIX device. One exporting process MAY serve
multiple Observation Domains. In such a case the exporting process
uses this unique ID to distinguish export packets among the different
Observation Domains. The same concept is also used at the collecting
process to identify packets from different Observation Domains within
the same IPFIX device.
7.3 Flow Recording Process
The Flow Recording Process is a functional block which manages all
the flows generated from an Observation Domain. The typical
functions of a Flow Recording Process MAY include:
o Maintain database(s) of all the flows from an Observation Domain.
This includes creating new records, updating existing ones,
computing flow statistics, deriving further flow properties,
adding non-flow-specific information (in some cases fields like AS
numbers, router state, etc.)
o Maintain aggregate statistics like flows generated, flows exported
etc. Aggregate flows could be exported to one collector while the
aggregate's component flows were being exported to a different
collector.
It is not mandatory that every IPFIX device use a Flow Recording
Process. Instead the flows generated by the metering process can be
sent directly to the exporting process.
7.4 Exporting Process
The Exporting Process is the functional block that contains one or
more instances of the IPFIX protocol. On one side it interfaces with
Metering/Flow Recording Process to get flow records, while on the
other side the Exporting Process talks to a collecting process on the
collector(s).
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8. Overview of the IPFIX Protocol
An IPFIX Device consists of a set of co-operating processes that
implement the functional blocks described above, together with a
supervisor process that provides management and oversight of the
IPFIX system and its operation.
Alternatively, an IPFIX Device can be viewed simply as a network
entity which implements the IPFIX protocol. At the IPFIX device, the
protocol functionality resides in the exporting process. The IPFIX
protocol gets flows from a flow recording process or directly from
the metering process, and carries them to the collector(s).
At a high level, the IPFIX protocol at an IPFIX device does the
following ..
Maintain rules for:
1. Selection and sampling of the packets arriving at each
observation point
2. Expiring Flows which have become inactive.
3. Picking and sending control information and flow records.
4. Encoding control and flow record information based on the IPFIX
Information Model IPFIX-INFO [3].
5. IPFIX device overload handling.
Perform the following tasks:
1. Encode control information into templates.
2. Encode Flows observed at the observation points into flow
records.
3. Packetize the selected templates and flow records into IPFIX
export packets.
4. Use the underlying transport layer to send control and data
packets to the collector.
5. Handle export errors and timeouts.
6. Handle IPFIX device overload.
For details of the IPFIX protocol please refer to IPFIX-PROTO [4].
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8.1 Encoding Flow Data Information
The following rules provide guidelines to be followed while encoding
the flow data information:
o A flow data record MUST contain enough information so that the
collecting process can identify the corresponding <Per-flow
control information, Configuration control information>.
o All fields MUST be encoded in network byte order.
o The exporter MUST encode a given field based on the encoding
standards prescribed by IPFIX-PROTO [4].
8.2 Encoding Control Information
The following rules provide guidelines to be followed while encoding
the control information:
o Per-flow control information SHOULD be encoded such that it can
capture the structure and semantics of the corresponding flow data
for each of the flows exported by the IPFIX device.
o Configuration control information SHOULD be encoded such that it
can capture the structure and semantics of the corresponding
configuration data. The configuration data which is also control
information SHOULD carry additional information on the Observation
Domain within which the configuration takes effect. For example,
sampling using the same sampling algorithm, say 1 in 100 packets,
is configured on two observation points O1 and O2. The
configuration in this case MAY be encoded as <ID, configuration
domain (O1,O2), sampling algorithm, interval (1 in 100)>, where ID
uniquely identifies this configuration.
o There SHOULD be provisions to encode fixed length and variable
length fields
o All fields MUST be encoded in network byte order.
o The exporter MUST encode a given field based on the encoding
standards prescribed by IPFIX-PROTO [4].
8.3 Exporting Control Information
The Control Information is used by the collecting process to:
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o Decode and interpret flow records.
o Understand the state of the exporting process.
Sending control information from the exporting process in a timely
and reliable manner is critical to the proper functioning of the
IPFIX collecting process. The following approaches MAY be taken for
the export of control information.
1. Send all the control information pertaining to flow records prior
to sending the flow records themselves. This includes any
incremental changes to the definition of the flow records.
2. Notify on a near real time basis the state of the IPFIX device to
the collecting process. This includes all changes such as a
configuration change that affects the flow behavior, changes to
exporting process resources that alter export rates, etc., which
the collector needs to be aware of.
3. Since it is vital that a collecting process maintains accurate
knowledge of the exporter's state, the export of the control
information SHOULD be done such that that it reaches the
collector reliably. One way to achieve this would be to send the
control information over a reliable transport.
8.4 Export Error Handling
This section describes some of the errors that may be encountered by
an IPFIX Export Process because of problems in exporting data, or
because feedback is received by an IPFIX device from other entities
in the export path towards the collector. Such errors include:
o Unavailability of resources, e.g. packet buffers for IPFIX export
packets.
o Errors detected in the underlying transport layer.
The protocol MAY choose to take one or more of the following actions:
o Buffer the flow records until the error condition gets corrected.
o Drop flow records for one or more flows based on some rules, i.e.
decrease the flow's sampling rate. In such a case a record of
what action is taken MUST be maintained, e.g. n flow records of a
flow were dropped.
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8.5 Flow Expiration and Export
A flow is considered to be inactive if no packets of this flow have
been observed at the observation point for a given timeout interval.
The flow MAY be expired and exported under the following conditions:
1. If the Metering Process can deduce the end of a Flow. The Flow
SHOULD be exported when the end of the Flow is detected. For
example: flow generated by TCP type of traffic where the FIN or
RST bits indicate the end of the flow.
2. If the Flow has been inactive for a certain period of time. This
inactivity timeout SHOULD be configurable at the Metering
Process, with a minimum value of 0 seconds for immediate
expiration. (However, note that a zero timeout would break a
long-running flow into a sequence of single-packet flows.)
3. For long-running flows, the Exporting Process MAY export the flow
records on regular basis. Some of the reasons for doing this
could be:
1. Reporting for periodic accounting information.
2. Avoiding counter wrapping.
4. When a long-running flow is exported, the flow MAY still be
maintained in the IPFIX device so that for the incoming packets
that continue to come on the same flow, a new flow does not get
created in the flow recording data base.
5. In some cases flows MAY be exported as they are generated. This
can be useful when real time processing of flow records is
required.
6. If the IPFIX device experiences resource constraints, a flow MAY
be prematurely expired (e.g. lack of memory to store flow data)
7. In some cases flows the exporting process MAY choose not to
export the generated flow as is. For example, this happens if a
set of flows are aggregated into coarser flows.
8.6 Selection Criteria of flows for export
There MAY be additional rules defined within the context observation
domain so that only certain flows records are picked up for export.
This MAY be done by either one or a combination of Si, Fi, as
described in the section on "Selection Criteria for Packets".
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Example: Only the flow records which meet the following selection
criteria are exported.
1. All flow records whose destination IP address matches {20.3.1.5}.
2. Every other (.i.e. sampling rate 1 in 2) flow record whose
destination IP address matches {160.0.1.30}.
9. IPFIX Protocol Details
When the IPFIX Working Group was chartered there were existing common
practices in the area of flow export, for example NetFlow, CRANE,
LFAP, RTFM, etc. IPFIX's charter required the Working Group to
consider those existing practices, and select the one that was the
closest fit to the IPFIX requirements IPFIX-REQS [1]. Additions or
modifications would then be made to the selected protocol to fit it
exactly into the IPFIX architecture.
9.1 The IPFIX basis protocol
The working group went through an extensive evaluation of the various
existing protocols that were available, weighing the level of
compliance with the requirements, and finally selected NetFlow V9
with minor modification as the basis for the IPFIX protocol
IPFIX-EVAL [2]. The following is a brief description of the selected
IPFIX basis protocol; details of the IPFIX protocol proper are given
in IPFIX-PROTO [4].
This protocol is template based. A template in terms of NetFlow V9
is a collection of fields with corresponding descriptions of their
structures and their semantics which is in strict conformance with
IPFIX architecture.
This approach provides the following advantages:
o Using the template mechanism, new fields can be added to IPFIX
flow records without changing the structure of the export record
format.
o Templates that are sent to the collecting process carry structural
information about the exported flow record fields. Therefore, if
the collector does not understand the semantics of new fields it
can ignore them, but still interpret the flow record.
o Because the template mechanism is flexible, it allows the export
of only the required fields from the flows to the collecting
process. This helps to reduce the exported flow data volume and
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possibly provide memory savings at the Exporting Process and
Collecting Process. Sending only the required information can
also reduce network load.
The figure below shows the functions performed in sequence by the
various functional blocks in an IPFIX device.
Packet(s) coming into Observation Point(s)
| |
v v
+----------------+-------------------------+ +-----+-------+
| Metering Process on an | | |
| Observation Point | | |
| packet header capturing | | |
| | | | Metering |
| timestamping | | Process |
| | | | on an |
| +----->+ | | Observation |
| | | | | Point |
| | sampling Si (1:1 in case of no | | |
| | | sampling) | | |
| | classifying Fi (select all when | | |
| | | no criteria) | | |
| +------+ | | |
| | | | |
+--------+---------------------------------+ +-----+-------+
| |
Flows (identified by observation domain) Flows
+----... +----------+...
| v
| +-------------------------------------+-------------+
| | Flow Recording Process(*) |
| | +----------------------+ +------------------+ |
| | | Flow data base |<----|Provide non-flow | |
| | | (includes flows | | information (e.g.| |
| | | from all obsv | | router state) | |
| | | points in an obsv | +------------------+ |...
| | | domain) | |
| | +----------------------+<----+------------------+|
| | +-------------------------+ |Maintain aggregate| |
| | |Aggregate flow records(*)| | statistics | |
| | +-------------------------+ +------------------+ |
| +---------------------------------+-----------------+
| |
| Flow Database (identified by observation domain)
| +------------------...
| |
| |
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v v
+----------+------------------------------------+--------------------+
| | Exporting Process | |
| | +------------------->|
|+---------+------------------------------------------------------+ |
|| v IPFIX Protocol | |
||+------------------------------+ +----------------------------+| |
|||Rules for | |Functions || |
|||-Picking & sending templates | |-Packetize selected control || |
|||-Picking & sending data recrds|->| & data information into || |
|||-Timing out flows | | IPFIX export packet. ||->|
|||-Encoding template & data | |-Handle export errors || |
|||-Selecting flows for export(*)| |-Handle timeouts & overloads|| |
||+------------------------------+ +----------------------------+| |
|| | |
|+----------------------------+-----------------------------------+ |
| | |
| +------------------------------------->|
| IPFIX exported packet |
| | |
|+----------------------------+------------------------------------+ |
|| Anonymize export packet(*) | |
|+----------------------------+------------------------------------+ |
| | |
|+----------------------------+------------------------------------+ |
|| Transport Protocol | |
|+----------------------------+------------------------------------+ |
| | |
+-----------------------------+--------------------------------------+
|
v
IPFIX export packet to collector.
(*) indicates that the block is optional.
9.2 The Collecting Process
A Collecting Process is a subsystem that interacts with one or more
IPFIX devices. The functions of the collecting process MUST include:
o Identifying, accepting and decoding export packets from different
<Exporting Process, Observation Domain> pairs.
o Running the IPFIX protocol.
o Storing the control information and flow records received from
IPFIX device.
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o Notifying the IPFIX device of the Collector's status and problems.
At a high level, the IPFIX protocol at the collecting process:
1. Receives and stores the control information.
2. Decodes and stores the flow records using the control
information.
3. May optionally monitor the status of the collecting process and
execute a failover should any problem arise.
9.3 IPFIX Protocol on the Collecting Process
The Collecting process is responsible for:
1. Receiving and decoding flow records from the IPFIX devices.
2. Indicating flow record losses to the exporting IPFIX device and/
or IPFIX users.
3. Optionally notifying status and overload conditions to the IPFIX
device.
Complete details of the IPFIX protocol are given in IPFIX-PROTO [4].
9.4 Support for Applications
Applications that use the information collected by IPFIX may be
Billing or Intrusion Detection sub-systems, etc. These applications
may be an integral part of the collecting process or they may be
co-located with the collecting process. The way by which these
applications interface with IPFIX system to get the desired
information is out of scope for this document.
10. Export Models
10.1 Export with Reliable Control Connection
As mentioned in the IPFIX-REQS [1] document, an IPFIX device MUST be
able to transport its control information and data stream over a
congestion-aware transport protocol. If the network in which the
IPFIX device and collecting process are located does not guarantee
reliability, at least the control information SHOULD be exported over
a reliable transport. There could be network security concerns
between IPFIX device and collecting process. To avoid re-inventing
the wheel, and to reduce the complexity of the flow export protocol,
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one or a combination of the following methods MAY be adopted so as to
achieve security:
o IP Authentication Header MAY be used when the threat environment
requires stronger integrity protection, but does not require
confidentiality.
o IP Encapsulating Security Payload (ESP) MAY be used to provide
confidentiality and integrity.
o If the transport protocol used is TCP, the TCP MD5 signature
option MAY be used to protect against spoofed TCP segments.
o If the transport protocol used is TCP, TLS MAY be used to provide
integrity, authenticity and confidentiality.
The data stream MAY be exported over a reliable or unreliable
transport protocol.
10.2 Collector Failure Detection and Recovery
The transport connection (in the case of a connection oriented
protocol) is pre-configured between the IPFIX device and the
collector. The IPFIX protocol does not provide any mechanism for
configuring the Metering or Exporting processes.
Once connected, an IPFIX Collector receives control information and
uses that information to interpret flow records. The IPFIX device
SHOULD set a keepalive (e.g. the keepalive timeout in the case of
TCP, the HEARTBEAT interval in the case of SCTP, or an IPFIX protocol
level keepalive if any) to a sufficiently low value so that it can
quickly detect a collector failure.
Collector failure refers to the crash or restart of the Collecting
Process, or of the collector itself. A collector failure is detected
at the IPFIX device by the break in control connection (depending on
the transport protocol - the connection timeout mechanisms differ).
On detecting a keepalive timeout, the IPFIX device SHOULD stop
sending the flow export data to the collector and try to reestablish
the transport connection. This is valid for a single collector
scenario. If there are multiple collectors for the same IPFIX
device, the IPFIX device opens control connections to each of the
collectors. However, data gets sent only to one of the collectors
which is chosen as the primary.
There could be one or more collectors configured as secondary and a
priority assigned to them. The primary collector crash is detected
at the IPFIX device by the break in control connection (depending on
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the transport protocol - the connection timeout mechanisms differ).
On detecting loss of connectivity, the IPFIX device opens a data
stream with the secondary collector of the next highest priority.
That collector now becomes the primary. The maximum export data loss
would be the amount of data exported in the time between when the
loss of connectivity to the collector happened, and the time at which
this was detected by the IPFIX device.
10.3 Collector Redundancy
Since the IPFIX protocol requires a congestion-aware transport,
achieving redundancy using multicast is not an option. Multiple
<control information, data stream> pairs could be set up, each to a
different collector from the same IPFIX device. The control and data
information would then be replicated on each of the control
information and data streams.
11. IPFIX flow collection for Special Traffic
An IPFIX device could be doing one or more of generating, receiving,
altering special types of traffic which are listed below.
Tunnel traffic:
The IPFIX device could be the head, midpoint or endpoint of a
tunnel. In such cases the IPFIX could be handling GRE, IPinIP or
UTI traffic.
VPN traffic:
The IPFIX device could be a Provider Edge Device which receives
traffic from customer sites belonging to different Virtual Private
Networks.
In the cases above, there should be clear guidelines as to:
o How and when to classify the packets as flows in the IPFIX device.
o If multiple encapsulations are used to define flows, how to convey
the same fields (e.g. IP address) in different layers.
o How to differentiate flows based on different private domains.
For example, overlapping IP addresses in Layer-3 VPNs
12. IPFIX flow collection from Special Devices
IPFIX could be implemented on devices which perform one or more of
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the following special services:
o Explicitly drop packets. For example a device which provides
firewall service drops packets based on some administrative
policy.
o Alter the values of fields used as IPFIX flow keys of interest.
For example a device which provides NAT service can change source
or(and) destination IP address.
In the cases above, there should be clear guidelines as to:
o How and when to classify the packets as flows in the IPFIX device.
o What extra information be exported so that the collector can make
a clear interpretation of the received flow records.
13. Security Considerations
IP flow information can be used for various purposes, such as usage
accounting, traffic profiling, traffic engineering, and intrusion
detection. The security requirement may differ significantly for
such applications. To be able to satisfy the security needs of
various IPFIX users, an IPFIX system MUST provide different levels of
security protection.
13.1 Data security
IPFIX data comprises control information and data stream generated by
the IPFIX device.
The IPFIX data may exist in both the IPFIX device and the collector.
In addition, the data is also transferred on the wire from the IPFIX
device to the collector when it is exported. To provide security,
the data SHOULD be protected from common network attacks.
The protection of IPFIX data within the end system (IPFIX device and
collector) is out of scope for this document. It is assumed that the
end system operator will provide adequate security for the IPFIX
data.
The IPFIX architecture MUST allow different levels of protection to
the IPFIX data on the wire. Wherever security functions are required
it is recommended that users should leverage lower layers using
either IPSEC or TLS, if these can successfully satisfy the security
requirement of IPFIX data protection.
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To protect the data on the wire, three levels of granularity SHOULD
be supported ..
13.1.1 No security
Security may not be required when the transport between the IPFIX
device and the collector is perceived as safe. This option allows
the protocol to run most efficiently without extra overhead and an
IPFIX system MUST support it.
13.1.2 Authentication-only
Authentication-only protection provides IPFIX users with the
assurance of data integrity and authenticity. The data exchanged
between the IPFIX device and the collector is protected by an
authentication signature. Any modification of the IPFIX data will be
detected by the recipient, resulting in discarding of the received
data. However, the authentication-only option doesn't offer data
confidentiality.
The IPFIX user SHOULD avoid use authentication-only when sensitive or
confidential information is being exchanged. An IPFIX solution
SHOULD support this option. The authentication-only option SHOULD
provide replay attack protection. Some means to achieve this level
of security are:
o TCP with MD5 options.
o IP Authentication Header
13.1.3 Encryption
Data encryption provides the best protection for IPFIX data. The
IPFIX data is encrypted at the sender and only the intended recipient
can decrypt and have access to the data. This option MUST be used
when the transport between the IPFIX device and the collector are
unsafe and the IPFIX data needs to be protected. It is recommended
that the underlying transport layer's security functions be used for
this purpose. Some means to achieve this level of security are:
o Encapsulating Security Payload.
o Transport Layer Security Protocol
The data encryption option adds overhead to the IPFIX data transfer.
It may limit the rate that an exporter can report its flow to the
collector due to the resource requirement for running encryption.
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13.2 IPFIX end point authentication
It is important to make sure that the IPFIX device is talking to the
"right" collector rather than to a masquerading collector. The same
logic also holds true from the collector point of view, i.e. it may
want to make sure it is collecting the flow information from the
"right" IPFIX device. An IPFIX system SHOULD allow the end point
authentication capability so that either one-way or mutual
authentication can be performed between the IPFIX device and
collector.
The IPFIX architecture SHOULD use any existing transport protection
protocols such as TLS or IPSEC to fulfill the authentication
requirement.
14. IPFIX overload
An IPFIX device could become overloaded under various conditions.
This may be because of exhaustion of internal resources used for flow
generation and/or export. Such overloading may cause loss of data
from the exporting process, either from lack of export bandwidth
(possibly caused by an unusually high number of observed flows) or
from network congestion in the path from exporter to collector.
IPFIX collectors SHOULD be able to detect the loss of exported flow
data, and SHOULD at least record the number of lost flow data
records.
14.1 Denial of service (DoS) attack prevention
Since one of the potential usages for IPFIX is for intrusion
detection, it is important for the IPFIX architecture to support some
kind of DoS resistance.
14.1.1 Network under attack
The Network itself may be under attack, resulting in an overwhelming
number of IPFIX messages. An IPFIX system SHOULD try to capture as
much information as possible. However, when a large number of IPFIX
messages are generated in a short period of time, the IPFIX system
may become overloaded.
14.1.2 Generic DoS attack on the IPFIX system
The IPFIX system may subject to generic DoS attacks, just as any
system on any open network. These types of attacks are not IPFIX
specific. Preventing and responding to such types of attacks are out
of the scope of this document.
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14.1.3 IPFIX specific DoS attack
There are some specific attacks on the IPFIX portion of the IPFIX
device or Collector.
o The attacker could pound the Collector with spoofed IPFIX export
packets. One way to solve this problem is to periodically
synchronize the sequence numbers of the flow records between the
exporting and collecting processes.
o The attacker could provide false reports to the IPFIX device by
sending spoofed control packets.
The problems mentioned above can be solved to a large extent if the
control packets are encrypted both ways.
15. IANA Considerations
The IPFIX protocol will need an IP port number assigned by IANA, and
the various fields described in the IPFIX Information Model will need
a set of identifying numbers.
Full IANA considerations are given in the IPFIX Information Model
IPFIX-INFO [3] and IPFIX Protocol IPFIX-PROTO [4] documents.
16. Acknowledgements
The document editors wish to thank all the people contributing to the
discussion of this document on the mailing list, and the design teams
for many valuable comments. In particular, the following made
significant contributions:
Tanja Zseby
Paul Calato
Dave Plonka
Jeffrey Meyer
Benoit Claise
Ganesh Sadasivan
K.C.Norseth
Vamsi Valluri
Cliff Wang
Ram Gopal
Jc Martin
Carter Bullard
Juergen Quittek
Reinaldo Penno
Nevil Brownlee
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Simon Leinen
Kevin Zhang
17 References
[1] Quittek, J., Zseby, T. and B. Claise, "Requirements for IP Flow
Information Export", (work in progress), Internet Draft,
draft-ietf-ipfix-reqs-16.txt, June 2004.
[2] Leinen, S., "Evaluation of Candidate Protocols for IP Flow
Information Export", (work in progress), Internet Draft,
draft-leinen-ipfix-eval-contrib-03.txt, May 2004.
[3] Quittek, J., Meyer, J. and P. Calato, "IPFIX: Information
Model", (work in progress), Internet Draft,
draft-ietf-ipfix-info-03.txt, February 2004.
[4] Fulmer, M., Claise, B., Calato, P. and R. Penno, "IPFIX:
Protocol", (work in progress), Internet Draft,
draft-ietf-ipfix-protocol-03.txt, January 2004.
Authors' Addresses
Ganesh Sadasivan
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134
USA
Phone: +1 408 527-0251
EMail: gsadasiv@cisco.com
Nevil Brownlee
CAIDA | The University of Auckland
Private Bag 92019
Auckland
New Zealand
Phone: +64 9 373 7599 x8941
EMail: n.brownlee@auckland.ac.nz
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Benoit Claise
Cisco Systems, Inc.
De Kleetlaan 6a b1
1831 Diegem
Belgium
Phone: +32 2 704 5622
EMail: bclaise@cisco.com
Juergen Quittek
NEC Europe Ltd.
Adenauerplatz 6
69225 Heidelberg
Germany
Phone: +49 6221 90511-15
EMail: quittek@ccrle.nec.de
URI:
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