Internet Engineering Task Force S. D'Antonio
Internet-Draft University of Napoli
Intended status: Standards Track "Parthenope"
Expires: January 12, 2012 T. Zseby
Fraunhofer Institute FOKUS
C. Henke
Technische Universitat Berlin
L. Peluso
University of Napoli
July 11, 2011
Flow Selection Techniques
draft-ietf-ipfix-flow-selection-tech-07.txt
Abstract
Flow selection is the process of selecting a subset of flows from all
flows observed at an observation point. Flow selection reduces the
effort of post-processing flow data and transferring Flow Records.
This document describes motivations for flow selection and presents
flow selection techniques. It provides an information model for
configuring flow selection techniques and discusses what information
about a flow selection process should be exported.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on January 12, 2012.
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Table of Contents
1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Difference between Flow Selection and Packet Selection . . . . 7
4. Flow selection as a Function in the IPFIX Architecture . . . . 8
4.1. Flow selection during the Metering Process . . . . . . . . 10
4.2. Flow selection during the Exporting Process . . . . . . . 10
4.3. Flow selection as a function of the IPFIX Mediator . . . . 10
5. Flow Selection Techniques . . . . . . . . . . . . . . . . . . 11
5.1. Flow Filtering . . . . . . . . . . . . . . . . . . . . . . 11
5.1.1. Property Match Filtering . . . . . . . . . . . . . . . 11
5.1.2. Hash-based Flow Filtering . . . . . . . . . . . . . . 11
5.2. Flow Sampling . . . . . . . . . . . . . . . . . . . . . . 12
5.2.1. Systematic sampling . . . . . . . . . . . . . . . . . 12
5.2.2. Random sampling . . . . . . . . . . . . . . . . . . . 12
5.3. Flow-state Dependent Flow Selection . . . . . . . . . . . 13
5.4. Flow-state Dependent Packet Selection . . . . . . . . . . 13
6. Configuration of Flow Selection Techniques . . . . . . . . . . 14
6.1. Description of Flow Selection Techniques . . . . . . . . . 15
6.2. Description of Flow-state Dependent Packet Selection . . . 17
7. Information Model for Flow Selection Reporting . . . . . . . . 17
7.1. fsFlowRecordTotalCount . . . . . . . . . . . . . . . . . . 18
7.2. fsFlowRecordSelectedCount . . . . . . . . . . . . . . . . 19
7.3. fsPacketTotalCount . . . . . . . . . . . . . . . . . . . . 19
7.4. fsPacketSelectedCount . . . . . . . . . . . . . . . . . . 19
7.5. fsOctetTotalCount . . . . . . . . . . . . . . . . . . . . 19
7.6. fsOctetSelectedCount . . . . . . . . . . . . . . . . . . . 20
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
9. Security Considerations . . . . . . . . . . . . . . . . . . . 20
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
10.1. Normative References . . . . . . . . . . . . . . . . . . . 21
10.2. Informative References . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22
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1. Scope
This document describes flow selection techniques for network traffic
measurements. A flow is defined as a set of packets with common
properties as described in [RFC5101]. Flow selection can be done to
limit the resource demands for capturing, storing, exporting and
post-processing of Flow Records. It also can be used to select a
particular set of flows that are of interest to a specific
application. This document provides a categorization of flow
selection techniques and describes configuration and reporting
parameters for them. In order to be compliant with this document, at
least one of the flow selection schemes MUST be implemented. That
means that the configuration parameters as well as the reporting
Information Elements for this particular scheme MUST be supported.
This document also addresses configuration and reporting parameters
for flow-state dependent packet selection as described in [RFC5475],
although this technique is categorized as packet selection. The
reason is, that flow-state dependent packet selection techniques
often aim at the reduction of resources for flow capturing and flow
processing. Furthermore, they were only briefly discussed in
[RFC5475]. Therefore we included configuration and reporting
considerations for such techniques in this document.
2. Terminology
This document is consistent with the terminology introduced in
[RFC5101], [RFC5470], [RFC5475] and [RFC3917]. As in [RFC5101] and
[RFC5476], the first letter of each IPFIX-specific and PSAMP-specific
term is capitalized along with the flow selection specific terms
defined here.
* Packet Classification
Packet Classification is a process by which packets are mapped to
specific Flow Records based on packet properties or external
properties (e.g. interface). The properties make up the Flow Key
(e.g. header information, packet content, AS number). In case a
Flow Record for a specific Flow Key already exists the Flow Record
is updated, otherwise a new Flow Record is created.
* Packet Aggregation Process
In the IPFIX Metering Process the Packet Aggregation Process
aggregates packet data into flow data and forms the Flow Records.
After the aggregation step only the aggregated flow information is
available. Information about individual packets is lost.
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* Flow Selection Process
A Flow Selection Process takes Flow Records as its input and
selects a subset of this set as its output. A Flow Selection
Process MAY run on several instances within the IPFIX
architecture. A Flow Selection Process MAY be part of an IPFIX
Metering Process, Exporting Process or as an Intermediate
Selection Process as defined for the IPFIX Mediator [RFC6183].
* Flow Selection State
A Flow Selection Process SHOULD maintain state information for use
by the Flow Selector. At a given time, the Flow Selection State
may depend on flows and packets observed at and before that time,
as well as other variables. Examples include:
(i) sequence number of packets and accounted Flow Records;
(ii) number of selected flows;
(iii) number of observed flows;
(iv) current flow cache occupancy;
(v) flow specific counters, lower und upper bounds
(vi) flow selection timeout intervals
* Flow Selector
A Flow Selector defines the action of a Flow Selection Process on
a single flow of its input. The Flow Selector can make use of the
following information in order to establish whether a flow has to
be selected or not:
(i) the content of the Flow Record;
(ii) any state information related to the Metering Process or
Exporting Process;
(iii) any Flow Selection State that may be maintained by the
Flow Selection Process.
* Complete Flow
A Complete Flow consists of all packets within the flow time-out
interval that enter the Flow Selection Process and belong to the
same flow as defined by the flow definition in [RFC5470]. For
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this definition only packets that arrive at the Flow Selection
Process are considered. That means, packets that are not observed
at the Flow Selection Process because of prior packet selection or
packet loss are not considered as belonging to the Complete Flow.
* Flow Filtering
Flow Filtering selects flows based on a deterministic function on
the Flow Record content, flow state, external properties (e.g.
ingress interface) or external events (e.g violated Access Control
List). If the relevant parts of the Flow Record content can be
already observed at packet level (e.g. Flow Keys from packet
header fields) Flow Filtering can be performed at packet level by
Property Match Filtering as described in [RFC5475].
* Hash-based Flow Filtering
Hash-based Flow Filtering is a deterministic flow filter function
that selects flows based on a Hash Function which is calculated
over parts of the Flow Record content or external properties. If
the hash value falls into a predefined Hash Selection Range the
flow is selected.
* Flow-state Dependent Flow Selection
Flow-state Dependent Flow Selection is a selection function that
selects or drops flows based on the current flow state. The
selection can be either deterministic, random or non-uniform
random.
* Flow-state Dependent Packet Selection
Flow-state Dependent Packet Selection is a selection function that
selects or drops packets based on the current flow state. The
selection can be either deterministic, random or non-uniform
random. Flow-state Dependent Packet Selection can be used to
prefer the selection of packets belonging to specific flows (e.g.
large or small flows).
* Flow Sampling
Flow Sampling selects flows based on Flow Record sequence or
arrival times (e.g. entry in flow cache, arrival time at Exporter
or Mediator). The selection can be systematic (e.g. every n-th
flow) or based on a random function (e.g. select each Flow Record
with probability p, or randomly select n out of N Flow Records).
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3. Difference between Flow Selection and Packet Selection
Flow selection differs from packet selection described in [RFC5475].
Packet selection techniques consider packets as basic element and the
parent population consists of all packets observed at an observation
point. In contrast to this the basic elements in flow selection are
the flows. The parent population consists of all observed flows and
the selection process operates on the flows. The major
characteristics of flow selection are the following:
- Flow selection takes flows as basic elements. For packet
selection, packets are considered as basic elements.
- Flow selection can only take place after Packet
Classification, because the classification rules determine to
which flow a packet belongs. Packet selection can be applied
before and after Packet Classification.
- Flow selection operates on Complete Flows. That means that
after the Flow Selection Process either all packets of the
flow are kept or all packets of the flow are discarded. All
packets of the flow here means all packets that enter the
Flow Selection Process. That means that if the flow
selection is preceded by a packet selection process the
Complete Flow consists only of the packets that were not
discarded during the packet selection.
There are some techniques that are difficult to unambiguously
categorize into one of the categories. Here we give some guidance
how to categorize such techniques:
- Techniques that can be considered as both packet and flow
selection: some packet selection techniques result in the
selection of Complete Flows and therefore can be considered
as packet or as flow selection at the same time. An example
is Property Match Filtering of all packets to a specific
destination address. If flows are defined based on
destination addresses, such a packet selection also results
in a flow selection and can be considered as packet or flow
selection.
- Flow-state Dependent Packet Selection (as described in
[RFC5475]): there exist techniques that select packets based
on the flow state, e.g. based on the number of already
observed packets belonging to the flow. Examples of these
techniques from the literature are "Sample and Hold" [EsVa01]
"Fast Filtered Sampling" [MSZC10] or the "Sticky Sampling"
algorithm presented in [MaMo02]. Such techniques can be used
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to influence which flows are captured (e.g. increase the
selection of packets belonging to large flows) and reduce the
number of flows that need to be stored in the flow cache.
Nevertheless, such techniques do not necessarily select
Complete Flows, because they do not ensure that all packets
of a selected flow are captured. Therefore Flow-state
Dependent Packet Selection methods that do not ensure that
either all or no packets of a flow are selected strictly
speaking have to be considered as packet selection techniques
and not as flow selection techniques.
4. Flow selection as a Function in the IPFIX Architecture
Figure 1 shows the IPFIX reference model as defined in [RFC5470] and
shows the Packet Classification and Packet Aggregation Process in the
Metering Process.
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Packet(s) coming in to Observation Point(s)
| |
v v
+----------------+---------------------------+ +-----+-------+
| Metering Process | | |
| | | |
| packet header capturing | | |
| | |...| Metering |
| timestamping | | Process N |
| | | | |
| packet sampling | | |
| | | | |
| (packet classification) | | |
| | | | |
| packet filtering* | | |
| | | | |
| (packet aggregation)* | | |
| | | | |
+--------|-----------------------------------+ +-----|-------+
Flow Records Flow Records
| |
+----------------------+----------------------+
|
+----------------------|-----------------+
| Exporting Process* |
+----------------------+-----------------+
| IPFIX (Flow Records)
v
+-------------------------|-----------------------+
| IPFIX Mediator | |
| v |
| Collecting Process(es) |
| | |
| Intermediate Flow Selection Process (*) |
| | |
| Exporting Process(es) |
+-------------------------|-----------------------+
v
IPFIX
(*) indicates where flow selection can take place.
Figure 1: Flow selection in the IPFIX Architecture
In contrast to packet selection, flow selection is always applied
after the packets are classified into flows. Flows can be selected
at different stages of the measurement chain:
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1. during the Metering Process
2. during Exporting Process
3. during an Intermediate Selection Process on a Mediator
4.1. Flow selection during the Metering Process
In the Packet Aggregation Process the packet information is used to
update the Flow Records in the flow cache. Flow selection that is
applied before aggregation equals a packet selection process. The
flow still consists of individual packets. Those are then selected
based on the classification information, i.e. based on the flow they
belong to. Flow selection before aggregation can be based on the
fields of the Flow Key (also on a hash value over these fields), but
not based on characteristics that are only available after packet
aggregation (e.g. flow size, flow duration). Flow selection during
the Metering Process is applied to reduce resources for all
succeeding processes or to select specific flows of interest in case
such flow characteristics are already observable at packet level
(e.g. flows to specific IP addresses). In contrast, Flow-state
Dependent Packet Selection is a packet selection method, because it
does not necessarily select Complete Flows.
4.2. Flow selection during the Exporting Process
The Flow Selection Process at the Exporter is similar to an
Intermediate Selection Process as described in [RFC6183] and works on
Flow records. Flow selection during the Exporting Process can
therefore also depend on flow characteristics that are only visible
after the aggregation of packets, such as flow size and flow
duration. The Exporting Process may implement policies for exporting
only a subset of the Flow Records which have been stored in the
system memory in order to unload flow export and flow postprocessing.
Flow selection during the Exporting Process may select only the
subset of Flow Records which are of interest to the users
application, or select only as many Flow Records as can be handled by
the available resources (e.g. limited flow cache size and export link
capacity).
4.3. Flow selection as a function of the IPFIX Mediator
As shown in Figure 1, flow selection can be performed as an
Intermediate Process within an IPFIX Mediator [RFC6183]. The
Intermediate Selection Process takes Flow Record stream as its input
and selects a flow record stream. The Intermediate Selection Process
can again apply a flow selection technique to obtain flows of
interest to the application. Further the Intermediate Selection
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Process can base its selection decision on the correlation of data
from different observation points, e.g. by only selecting flows that
were at least recorded on two observation points.
5. Flow Selection Techniques
A flow selection technique selects either all or none of the packets
of a flow, otherwise the technique has to be considered as packet
selection. We distinguish between Flow Filtering and Flow Sampling.
5.1. Flow Filtering
Flow Filtering is a deterministic function on the IPFIX Flow Record
content. In case that the relevant flow characteristics are already
observable at packet level (e.g. Flow Keys) Flow Filtering can be
applied before aggregation at packet level.
5.1.1. Property Match Filtering
Flow Filtering can be done similarly to Property Match Filtering for
packet selection described in [RFC5475]. The difference is that,
instead of packet fields, Flow Record fields are here used to derive
the selection decision. Property Match Filtering is typically used
to select a specific subset of the flows that are of interest to a
particular application (e.g. all flows to a specific destination, all
large flows, etc.). Properties on which the filtering is based can
be for example Flow Keys, the flow size in bytes, the number of
packets in the flow, the observation time of the first or last
packet, or the maximum packet length. The selection criteria can be
a specific value or an interval. Property Match Filtering can be
applied during the Metering Process if the properties are already
observable at the packet level (e.g. Flow Key fields).
There are content-based Property Match Filtering techniques that
require a computation on the current flow cache. An example is the
selection of the k largest flows or a percentage of flows with the
longest lifetime. This type of Property Match Filtering is also used
in flow selection techniques that react to external events (e.g.
resource constraint). For example in case the flow cache is full,
the Flow Record with the lowest flow volume per current flow life
time is deleted.
5.1.2. Hash-based Flow Filtering
Hash-based Flow Filtering uses a Hash Function h to map the Flow Key
c onto a Hash Range R. A flow is selected if the hash value h(c) is
within the Hash Selection Range S, which is a subset of R. Hash-based
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Flow Filtering can be used to emulate a random sampling process but
still enable the correlation between selected flow subset at
different observation points. Hash-based Flow Filtering is similar
to Hash-based Packet Selection, and in fact is identical when Hash-
based Packet Selection uses the Flow Key that defines the flow as the
hash input. Nevertheless there MAY be the incentive to apply Hash-
based Flow Filtering not on the packet level during the Metering
Process, for example when the size of the selection range and
therefore the sampling probability is dependent on the number of
observed flows.
5.2. Flow Sampling
Flow Sampling operates on Flow Record sequence or arrival times. It
can use either a systematic or a random function for the selection
process. Flow Sampling usually aims at the selection of a
representative subset of all flows in order to estimate
characteristics of the whole set (e.g. mean flow size in the
network).
5.2.1. Systematic sampling
Systematic sampling is a deterministic selection function.
Systematic sampling may be a periodic selection of the k-th Flow
Record which arrives at the Exporting or Intermediate Selection
Process. Systematic sampling can also be applied during the Metering
Process. An example would be to use an additional data structure
that saves the Flow Keys of the non-selected flows.
Systematic sampling can also be time-based. Systematic sampling is
applied by only creating flows that are observed between time-based
start and stop triggers. The time interval may be applied at packet
level during the Metering Process or after aggregation on flow level,
e.g. by selecting a flow arriving at the Exporting Process every k
seconds.
5.2.2. Random sampling
Random flow sampling is based on a random process which requires the
calculation of random numbers. One can differentiate between n-out-N
and probabilistic flow sampling. The sampling probability of
individual Flows Records MAY be adjusted according to the Flow Record
content or external events like the available export resources. Non-
uniform random sampling approaches can be applied similar to the ones
defined in [RFC5475]. An example would be to increase the selection
probability of large volume flows over small volume flows as
described in the Smart Sampling technique [DuLT01]. Random flow
sampling can also be applied before the Packet Aggregation Process
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when additional flow state about non selected flows is kept.
5.3. Flow-state Dependent Flow Selection
Flow-state Dependent Flow Selection can be a deterministic or random
flow selection process based on the Flow Record content and the flow
state which may be kept additionally for each of the flows. External
processes may update counters, bounds and timers for each of the Flow
Records and the Flow Selection Process utilises this information for
the selection decision. A review of Flow-state Dependent Flow
Selection techniques that aim at the selection of the most frequent
items by keeping additional flow state information can be found in
[CoHa08]. Flow-state Dependent Flow Selection can only be applied
after packet aggregation, when a packet has been assigned to a flow.
The selection process then decides based upon the flow state for each
flow if it is kept in the flow cache or not. Two Flow State
Dependent Flow Selection are here described:
The frequent algorithm [KaPS03] is a technique that aims at the
selection of all flows that at least exceed a 1/k fraction of the
observed packet stream. The algorithm has only a flow cache of size
k-1 and each flow in the cache has an additional counter. The
counter is incremented each time a packet belonging to the flow in
the flow cache is observed. In case the observed packet does not
belong to any flow all counters are decremented and if any of the
flow counters has a value of zero the flow is replaced with a flow
formed from the new packet.
Lossy counting is a selection technique that identifies all flows
whose packet count exceeds a certain percentage of the whole observed
packet stream (e.g. 5% of all packets) with a certain estimation
error e. Lossy counting separates the observed packet stream in
windows of size N=1/e, where N is an amount of consecutive packets.
For each observed flow an additional counter will be held in the flow
state. The counter is incremented each time a packet belonging to
the flow is observed and all counters are decremented at the end of
each window and all flows with a counter of zero will be removed from
the flow cache.
5.4. Flow-state Dependent Packet Selection
Flow-state Dependent Packet Selection is not a flow selection
technique but a packet selection technique. Nevertheless we will
describe configuration and reporting parameters for this technique in
this document. An example is the "Sample and Hold" algorithm
[EsVa01] that tries to prefer large volume flows in the selection.
When a packet arrives it is selected when a Flow Record for this
packet already exists. In case there is no Flow Record, the packet
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is selected by a certain probability that is dependent on the packet
size.
6. Configuration of Flow Selection Techniques
This section describes the configuration parameters of the flow
selection techniques presented above. It provides the basis of an
information model to be adopted in order to configure the Flow
Selection Process within an IPFIX Device. The following table gives
an overview of the defined selection techniques, where they can be
applied and what their input parameters are. Dependent on where the
flow selection techniques are applied different input parameters can
be configured.
Overview of Flow Selection Techniques:
+------------------+-----------------+------------------------------+
| Location | Selection | Selection Input |
| | Method | |
+------------------+-----------------+------------------------------+
| During the | Flow-state | packet sampling |
| Metering Process | Dependent | probabilities, flow state, |
| based on Packets | Packet | packet properties |
| | Selection | |
+------------------+-----------------+------------------------------+
| | Property Match | Flow Key fields, filter |
| | Flow Filtering | function |
+------------------+-----------------+------------------------------+
| | Hash-based Flow | selection range, Hash |
| | Filtering | Function, Flow Key |
+------------------+-----------------+------------------------------+
| | Time-based | flow position (derived from |
| | Systematic Flow | arrival time of packets), |
| | Sampling | flow state |
+------------------+-----------------+------------------------------+
| | Sequence-based | flow position (derived from |
| | Systematic Flow | packet position), flow state |
| | Sampling | |
+------------------+-----------------+------------------------------+
| | Random Flow | random number generator or |
| | Sampling | list and packet position, |
| | | flow state |
+------------------+-----------------+------------------------------+
| Exporting / | Property Match | Flow Record content, filter |
| Intermediate | Flow Filtering | function |
| Selection | | |
| Process | | |
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| | Hash-based Flow | selection range, Hash |
| | Filtering | Function, hash input (Flow |
| | | Keys and other flow |
| | | properties) |
+------------------+-----------------+------------------------------+
| | Flow-state | flow state parameters, |
| | Dependent Flow | random number generator or |
| | Selection | list |
+------------------+-----------------+------------------------------+
| | Time-based | flow arrival time, flow |
| | Systematic Flow | state |
| | Sampling | |
+------------------+-----------------+------------------------------+
| | Sequence-based | flow position, flow state |
| | Systematic Flow | |
| | Sampling | |
+------------------+-----------------+------------------------------+
| | Random Flow | random number generator or |
| | Sampling | list and flow position, flow |
| | | state |
+------------------+-----------------+------------------------------+
6.1. Description of Flow Selection Techniques
In this section, we define what parameters are required to describe
the most common Flow Selection techniques.
Flow Selection Parameters:
For Property Match Filtering:
- Information Element (from [RFC5102]):
Specifies the Information Element which is used as the property
in the filter expression.
- Selection Value or Value Interval:
Specifies the value or interval of the filter expression.
Packets and Flow Record that have a value equal to the Selection
Value or within the Interval will be selected.
For Hash-based Flow Filtering:
- Hash Domain:
Specifies the bits from packet (IPv4 or IPv6) which are taken as
the hash input to the Hash Function.
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- Hash Function:
Specifies the name of the Hash Function that is used to calculate
the hash value. Possible Hash Functions are BOB, IPSX, CRC-32
- Hash Selection Range:
Flows that have a hash value within the Hash Selection Range are
selected. The Hash Selection Range can be a value interval or
arbitrary hash values within the Hash Range of the Hash Function.
- Random Seed or Initializer Value:
Some Hash Functions require an initializing value. In order to
make the selection decision more secure one can choose a random
seed that configures the hash function.
For Flow-state Dependent Flow Selection:
- frequency threshold:
Specifies the frequency threshold s for flow state dependent flow
selection techniques that try to find the most frequent items
within a dataset. All flows which exceed the defined threshold
will be selected.
- accuracy parameter:
specifies the accuracy parameter e for techniques that deal with
the frequent items problems. The accuracy paramter defines the
maximum error, i.e. no flows that have a true frequency less than
(s- e) N is selected, where s is the frequency threshold and N is
the total number of packets.
The above list of parameters for Flow-state Dependent Flow Selection
techniques is suitable for the presented frequent item and lossy
counting algorithm. Nevertheless there exist a variety of techniques
with very specific parameters which are not defined here.
For Systematic time-based Flow Sampling:
- Interval length (in usec)
Defines the length of the sampling interval during which flows
are selected.
- Spacing (in usec)
The spacing parameter defines the spacing in usec between the end
of one sampling interval and the start of the next succeeding
interval.
For Systematic count-based Flow Sampling:
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- Interval length
Defines the number of flows that are selected within the sampling
interval.
- Spacing
The spacing parameter defines the spacing in number of observed
flows between the end of one sampling interval and the start of
the next succeeding interval.
For random n-out-of-N Flow Sampling:
- Population Size N
The Population Size N is the number of all flows in the
Population from which the sample is drawn.
- Sample size n
The sample size n is the number of flows that are randomly drawn
from the population N.
For probabilistic Flow Sampling:
- Sampling probability p
The sampling probability p defines the probability by which each
of the observed flows is selected.
6.2. Description of Flow-state Dependent Packet Selection
The configuration of Flow-state Dependent Packet Selection has not
been described in [RFC5475] therefore the parameters are defined
here:
For Flow-state Dependent Packet Selection:
- packet selection probability per possible flow state interval
Defines multiple [flow interval, packet selection probability]
value pairs that configure the sampling probability dependent on
the current flow state.
- additional parameters
For the configuration of flow state dependent packet selection
additional parameters or packet properties may be required for
the configuration, e.g. the packet size ([EsVa01])
7. Information Model for Flow Selection Reporting
In this section we describe Information Elements (IEs) that SHOULD be
exported by a flow selection process in order to support the
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interpretation of measurement results from flow measurements where
only some flows are selected. The information is mainly used to
report how many packets and flows have been observed in total and how
many of them were selected. This helps for instance to calculate the
Attained Selection Fraction, which is an important parameter to
provide an accuracy statement. The IEs can provide reporting
information about Flow Records, packets or bytes. The reported
metrics are number of total and the number of selected elements.
From this the number of dropped elements can be derived. All
counters SHOULD be exported and reset when a new measurement interval
starts. Additional IEs may be useful for future flow selection
techniques. Those can be defined additionally if needed.
List of additional Flow Selection Information Elements:
+------+---------------------------+
| ID | Name |
+------+---------------------------+
| TBD1 | fsFlowRecordTotalCount |
+------+---------------------------+
| TBD2 | fsFlowRecordSelectedCount |
+------+---------------------------+
| TBD3 | fsPacketTotalCount |
+------+---------------------------+
| TBD4 | fsPacketSelectedCount |
+------+---------------------------+
| TBD5 | fsOctetTotalCount |
+------+---------------------------+
| TBD6 | fsOctetSelectedCount |
+------+---------------------------+
7.1. fsFlowRecordTotalCount
Description:
This Information Element specifies the current number of all Flow
Records that form the parent population as input to the Flow
Selection Process.
Abstract Data Type: unsigned64
ElementId: TBD1
Units: Flows
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7.2. fsFlowRecordSelectedCount
Description:
This Information Element specifies the current number of Flow
Records that were selected during the Flow Selection Process.
Abstract Data Type: unsigned64
ElementId: TBD2
Units: Flows
7.3. fsPacketTotalCount
Description:
This Information Element specifies the current number of packets
in all flows that form the parent population as input to the Flow
Selection Process.
Abstract Data Type: unsigned64
ElementId: TBD7
Units: Packets
7.4. fsPacketSelectedCount
Description:
This Information Element specifies the current number packets in
all flows that were selected during the Flow Selection Process.
Abstract Data Type: unsigned64
ElementId: TBD8
Units: Packets
7.5. fsOctetTotalCount
Description:
This Information Element specifies the current number of all bytes
in all flows that form the parent population as input to the Flow
Selection Process.
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Abstract Data Type: unsigned64
ElementId: TBD9
Units: Octets
7.6. fsOctetSelectedCount
Description:
This Information Element specifies the current number of bytes in
all flows that were selected during the Flow Selection Process.
Abstract Data Type: unsigned64
ElementId: TBD10
Units: Octets
8. IANA Considerations
This document introduces several new Information Elements as an
extension to the IPFIX information model. Values TBD1-TBD10 in
section 7 of this document should be replaced with the assigned
numbers by IANA.
9. Security Considerations
In this section security issues concerning an IPFIX Device performing
flow selection are pointed out. In case the flow selection function
is activated an IPFIX Device might be exposed to security threats.
Since flow selection implies analysing flow packets, associating them
to a specific traffic flow and selecting Flow Records, a malicious
user who was able to gain control of an IPFIX Device might access
both packet and flow data, thus violating their confidentiality.
Furthermore, the intruder might be attracted by the possibility of
altering the Flow Selection Process by modifying the criteria used to
select Flow Records. In this case, the IPFIX Device would export
flow data which are different from the ones that the Collector
expects to receive.
It is apparent that these security threats can be mitigated by
authenticating entities that interact with the IPFIX Device and
keeping information for flow selection configuration confidential.
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10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
10.2. Informative References
[CoHa08] Cormode, G. and M. Hadjieleftheriou, "Finding frequent
items in data streams", Journal, Proceedings of the Very
Large DataBase Endowment VLDB Endowment, Volume 1 Issue 2,
August 2008, August 2008.
[DuLT01] Duffield, N., Lund, C., and M. Thorup, "Charging from
Sampled Network Usage", ACM Internet Measurement Workshop
IMW 2001, San Francisco, USA, November 2001.
[EsVa01] Estan, C. and G,. Varghese, "New Directions in Traffic
Measurement and Accounting: Focusing on the Elephants,
Ignoring the Mice", ACM SIGCOMM Internet Measurement
Workshop 2001, San Francisco (CA), November 2001.
[KaPS03] Karp, R., Papadimitriou, C., and S. S. Shenker, "A simple
algorithm for finding frequent elements in sets and
bags.", ACM Transactions on Database Systems, Volume 28,
51-55, 2003, March 2003.
[MSZC10] Mai, J., Sridharan, A., Zang, H., and C. Chuah, "Fast
Filtered Sampling", Computer Networks Volume 54, Issue 11,
Pages 1885-1898, ISSN 1389-1286, January 2010.
[MaMo02] Manku, G. and R. Motwani, "Approximate Frequency Counts
over Data Streams", Proceedings of the Internation
Conference on Very large DataBases (VLDB) pages 346--357,
2002, Hong Kong, China, 2002.
[RFC3917] Quittek, J., Zseby, T., Claise, B., and S. Zander,
"Requirements for IP Flow Information Export (IPFIX)",
RFC 3917, October 2004.
[RFC5101] Claise, B., "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.
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[RFC5470] Sadasivan, G., Brownlee, N., Claise, B., and J. Quittek,
"Architecture for IP Flow Information Export", RFC 5470,
March 2009.
[RFC5475] Zseby, T., Molina, M., Duffield, N., Niccolini, S., and F.
Raspall, "Sampling and Filtering Techniques for IP Packet
Selection", RFC 5475, March 2009.
[RFC5476] Claise, B., Johnson, A., and J. Quittek, "Packet Sampling
(PSAMP) Protocol Specifications", RFC 5476, March 2009.
[RFC6183] Kobayashi, A., Claise, B., Muenz, G., and K. Ishibashi,
"IP Flow Information Export (IPFIX) Mediation: Framework",
RFC 6183, April 2011.
Authors' Addresses
Salvatore D'Antonio
University of Napoli "Parthenope"
Centro Direzionale di Napoli Is. C4
Naples 80143
Italy
Phone: +39 081 5476766
Email: salvatore.dantonio@uniparthenope.it
Tanja Zseby
Fraunhofer Institute FOKUS
Kaiserin-Augusta-Allee 31
Berlin 10589
Germany
Phone: +49 30 3463 7153
Email: tanja.zseby@fokus.fraunhofer.de
Christian Henke
Technische Universitat Berlin
Strasse des 17. Juni 135
Berlin 10623
Germany
Phone: +49 30 3463 7366
Email: c.henke@tu-berlin.de
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Lorenzo Peluso
University of Napoli
Via Claudio 21
Napoli 80125
Italy
Phone: +39 081 7683821
Email: lorenzo.peluso@unina.it
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