Subject: [ipfix-req] [Fwd: Re: version 3 of IPFIX requirements]

From: Tanja Zseby <[email-masked]>
Date: Wed, 12 Jun 2002 18:21:25 +0200

Hi Jürgen,

 it seems that something went wrong when I did send my comments to the 
requirements draft :-( 
(maybe because I did sent it from at home... I did not get an error from 
my mailtool, but it might have been caused by an unlucky combination of 
my virus scanner and zone alarm... )

I had a lot of comments to the version. So I attached it again to this mail.
Maybe we can make further version and also include the comments that 
were send on the list during the last days ?
Also if there are further comments from others they would have a last 
chance to contribute and send comments. 

Regards
Tanja

-------- Original Message --------
Message-ID: <[email-masked]>
Date: Thu, 06 Jun 2002 23:04:14 +0200
From: Tanja Zseby <[email-masked]>
Organization: FhI FOKUS
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To: Juergen Quittek <[email-masked]>
CC: Benoit Claise <[email-masked]> , Tanja Zseby <[email-masked]> 
, Sebastian Zander <[email-masked]> , Georg Carle 
<[email-masked]> , "K.C. Norseth" <[email-masked]> , 
[email-masked] , [email-masked]
Subject: Re: version 3 of IPFIX requirements
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<4782386.1023358227@[192.168.102.164]>
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Dear Jürgen,

I read through the requirements draft and inserted my commnents in the 
document (marked with //TZS: ).
It is mainly minor rephrasing and some typos. I attached the edited 
document.
One major point is that I still  have problems with the beginning  of 
section 6.3. (data transfer). I know we already discussed this several 
times... Please have a look at the extendended comment and proposed 
changes for this section in the document.
Furthermore it would be good if somebody reads the security 
considerations. Until now I only got some minor comments from Carter and 
Sebastian ...

Regards
Tanja
P.S.: I really like the new section. with the pictures..

Juergen Quittek wrote:

> Dear all,
>
> Attached please find a new version of the IPFIX requirements
> draft based on our discussion on May 17. Please have a look
> at it and send comments until Saturday.
>
> I plan to submit the new version to the IETF on Monday, if we
> can agree on the draft until then.
>
> I have not yet read carefully the new security considerations.
> Also, the appendix with the application requirements table
> is still missing. I will include it over the weekend.
>
> Tanja or Sebastian, can one of you send me the source file
> of draft version 2?
>
> Cheers,
>
>    Juergen
>
>

-- 
Dipl.-Ing. Tanja Zseby			    	      	
FhI FOKUS/Global Networking			Email: [email-masked]	
Kaiserin-Augusta-Allee 31				Phone: +49-30-3463-7153
D-10589 Berlin, Germany				Fax:   +49-30-3463-8153
-------------------------------------------------------------------------------------- 
"Living on earth is expensive but it includes a free trip around the sun." (Anonymous)
--------------------------------------------------------------------------------------

Internet Draft                                                J. Quittek
Document: draft-ietf-ipfix-reqs-03.txt                   NEC Europe Ltd.
Expires: November 2002                                          T. Zseby
                                                               FhI FOKUS
                                                               B. Claise
                                                           Cisco Systems
                                                               S. Zander
                                                                G. Carle
                                                               FhI FOKUS
                                                            K.C. Norseth
                                                              Consultant

                                                                May 2002

              Requirements for IP Flow Information Export

                     <draft-ietf-ipfix-reqs-03.txt>

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of [RFC 2026]. Internet-Drafts are
   working documents of the Internet Engineering Task Force (IETF), its
   areas, and its working groups. Note that other groups may also
   distribute working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time. It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html

   Distribution of this document is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2001). All Rights Reserved.

Abstract

   This memo defines requirements for the export of measured IP flow
   information out of routers, traffic measurement probes and
   middleboxes.

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Table of Contents

   1 Introduction .................................................    2
   2 Terminology ..................................................    2
   2.1 IP Traffic Flow ............................................    2
   2.2 Observation Point ..........................................    3
   2.3 Metering Process ...........................................    3
   2.4 Flow Record ................................................    4
   2.5 Export Process .............................................    4
   2.6 Collecting Process .........................................    4
   3 Applications Requiring IP Flow Information Export ............    4
   3.1 Usage-based Accounting .....................................    5
   3.2 Traffic Profiling ..........................................    5
   3.3 Attack/Intrusion Detection .................................    6
   3.4 QoS Monitoring .............................................    6
   4 Distinguishing Flows .........................................    7
   4.1 Interfaces .................................................    7
   4.2 IP Header Fields ...........................................    7
   4.3 Transport Header Fields ....................................    8
   4.4 MPLS Label .................................................    8
   4.5 DiffServ Code Point ........................................    8
   4.6 Header Compression and Encryption ..........................    8
   5 Metering Process .............................................    8
   5.1 Reliability ................................................    8
   5.2 Sampling ...................................................    9
   5.3 Overload Behavior ..........................................    9
   5.4 Timestamps .................................................   10
   5.5 Time Synchronization .......................................   10
   5.6 Timeout ....................................................   10
   5.7 Ignore Port Copy ...........................................   10
   6 Data Export ..................................................   11
   6.1 Information Model ..........................................   11
   6.2 Data Model .................................................   12
   6.3 Data Transfer ..............................................   13
   6.3.1 Congestion Awareness .....................................   13
   6.3.2 Reliability ..............................................   13
   6.3.3 Security .................................................   13
   6.4 Push and Pull Mode Reporting ...............................   14
   6.5 Regular Reporting Interval .................................   14
   6.6 Notification on Specific Events ............................   14
   6.7 Anonymization ..............................................   14
   7 Configuration ................................................   14
   8 General Requirements .........................................   15
   8.1 Openness ...................................................   15
   8.2 Scalability Concerning the Number of Export Processes ......   15
   8.3 Several Collectors .........................................   15
   9 Special Device Considerations ................................   15
   10 Security Considerations .....................................   17
   10.1 Disclosure of Flow Information Data .......................   18
   10.2 Forgery of Flow Records ...................................   18

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   10.3 Denial of Service (DoS) Attacks ...........................   18
   11 Acknowledgments .............................................   19
   12 References ..................................................   19
   13 Authors' Addresses ..........................................   20
   14 Full Copyright Statement ....................................   21

1.  Introduction

   There are several applications that require flow-based IP traffic
   measurements. Such measurements could be performed by a router while
   forwarding the traffic, by a middlebox [RFC3234], or by a traffic
   measurement probe attached to a line or a monitored port. This memo
   defines requirements for exporting traffic flow information out of
   these boxes for further processing by applications located on other
   devices. In section 2 a selection of such applications is presented.
   The following sections list requirements derived from these
   applications.

   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 [RFC2119].

2.  Terminology

   The following terminology is used within this document:

2.1.  IP Traffic Flow

   There are several definitions of the term 'flow' being used by the
   Internet community. Within this document we use the following one:

   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 of packet header fields (e.g. destination IP
         address)

//TZS: I would remove the "of"
 
      2. one or more properties of the packet itself (e.g. packet
         length)

      3. one or more of fields derived from packet treatment (e.g. AS
         number)

   A packet is defined to belong to a flow if it completely satisfies
   all the defined properties of the flow.

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   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.
   Please note that the flow definition does not match a general
   application-level end-to-end stream. However, an application may
   derive properties of application-level streams by processing measured
   flow data.

2.2.  Observation Point

   The observation point is a location in the network where IP packets
   can be observed. Examples are 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.

   Please note that a coarse-grined observation point of one flow, for

//TZS: "grained"

   example a line card with several ports, may be the superset of
   several more fine-grained observation points of some other flows, for
   example the individual ports of the line card.

//TZS: "coarse-grained" observation point sounds a little bit strange for me. 
I propose to edit the last paragraph to:

   Please note that multiple observation points can exist at the same device 
   for the same physical location simultaneously. One observation point can 
   for instance represents the line card with all ports. Further observation 
   points on the same device can represent the individual ports of the line 
   card. 

2.3.  Metering Process

   The metering process generates flow records. Input to the process are
   IP packet headers observed at an 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 flows record to
   the export process, and deleting flow records.

   The sampling function and the classifying function may be applied
   more than once with different parameters. Figure 1 shows the sequence
   in which the functions are applied. Sampling is not illustrated in
   the figure, it may be applied before any other function.

//TZS: Isnt this also true for classification. I think we discussed this 
in Minneapolis. But I dont remember the outcome  :-(

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                           packet header capturing
                                     |
                                timestamping
                                     |
                                     v
                              +----->+
                              |      |
                              | classifying
                              |      |
                              +------+
                                     |
                          maintaining flow records
                                     |
                                     v

                 Figure 1: Functions of the metering process

2.4.  Flow Record

   A flow record contains information about a specific flow that was
   metered at an observation point. A flow record contains measured
   properties of the flow (e.g. the total number of bytes of all packets
   of the flow) and usually also characteristic properties of the flow
   (e.g. source IP address).

2.5.  Export Process

//TZS: As far as I remember we decided to use the term "exporting process" ?
(in the last teleconference) Then this has to be changed throughout the 
whole document.

   The export process sends flow records to one or more collectors.  The
   flow records are generated by one or more metering processes.

2.6.  Collecting Process

   The collecting process receives flow records from one or more export
   processes. The collecting process might store received flow record or
   further process them, but these actions are out of the scope of this
   document.

3.  Applications Requiring IP Flow Information Export

   The following list contains a selection of applications requiring IP
   flow information export. Because requirements for flow export listed
   in further sections below are derived from these applications, their
   selection is crucial. The goal of this requirements document is not
   to cover all possible applications with all their flow export
   requirements, but to cover applications which are considered to be of
   significant importance in today's or future IP networks, and for
   which requirements can be met with reasonable technical effort.

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   Please note, that the described applications can have a large number
   of differing implementations. Requirement details or the weighting of
   requirements could differ for specific implementations. Therefore we
   derive the requirements from the general functionality of the
   selected applications. Furthermore, the list of applications should
   lead to a better understanding of the requirements which is
   particularly important when designing or implementing a traffic flow
   measuring device.

3.1.  Usage-based Accounting

   Several new business models for selling IP service and IP-based
   services are currently under investigation. Beyond flat rate services
   which do not need accounting, accounting for these models can be
   based on time or volume. Accounting data can serve as input for
   billing systems. Accounting can be performed per user or per user
   group, it can be performed just for basic IP service or individually
   per high-level service and/or per content type delivered. For
   advanced/future services, accounting may also be performed per class
   of service, per application, per time of day, per used (label
   switched) path, etc.

3.2.  Traffic Profiling

   Traffic profiling is a process of characterizing IP flows and flow

//TZS: "the" instead of "a" process

   aggregates by using a model that represents key parameters of the
   flow such as flow duration, volume, time and burstiness. It is a
   prerequisite for network planning, network dimensioning, trend
   analysis, developing business models, and other activities. It
   heavily depends on the particular traffic profiling objective(s) what
   statistics and accuracy are required from the measurements. Typical
   information needed for traffic profiling are the distribution of used
   services and protocols in the network, the amount of packets of a
   specific type (e.g. percentage of IPv6 packets) and specific flow
   profiles.

   Since objectives for traffic profiling can vary, this application
   requires a high flexibility of the measurement infrastructure,
   especially regarding the options for measurement configuration and
   packet classification.

   Traffic Engineering (TE) comprises methods for measurement, modeling,
   characterization and control of a network. The goal of TE is the
   optimization of network resource utilization and traffic performance
   [RFC2702]. Since control and administrative reaction to measurement
   results requires access to the involved network nodes, TE mechanisms
   and the required measurement function usually are performed within
   one administrative domain. Typical parameters required for TE are
   link utilization, load between specific network nodes, number, size
   and entry/exit points of the active flows and routing information.

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3.3.  Attack/Intrusion Detection

   Capturing of flow information plays an important role for network
   security, both for detection of security violation, and for
   subsequent defense. In case of a Denial of Service (DOS) attack, flow
   monitoring can allow detection of unusual load situations or
   suspicious flows. In a second step, flow analysis can be performed in
   order to gather information about the attacking flows, and for
   deriving a defense strategy.

   Intrusion detection is a potentially more demanding application which
   would not only look at specific characteristics of flows, but that
   may also use a stateful packet flow analysis for detecting specific,
   suspicious activities, or unusually frequent activities. Such
   activities may be characterized by specific communication patterns,
   detectable by characteristic sequences of certain packet types.

3.4.  QoS Monitoring

   QoS monitoring is the non-intrusive (passive) measurement of quality
   parameters for single flows or traffic aggregates. In contrast to
   intrusive (active) measurements, non-intrusive measurements utilize
   the existing traffic in the network for QoS analysis. Since no test
   traffic is sent, non-intrusive measurements can only be applied in
   situations where the traffic of interest is already present in the
   network. One example application is the validation of QoS parameters
   negotiated in a service level specification (SLS).

   Non-intrusive measurements cannot provide the kind of controllable
   experiments that can be achieved with active measurements. On the
   other hand non-intrusive measurements do not suffer from undesired
   side effects caused by sending test traffic (e.g. additional load,
   potential differences in treatment of test traffic and real customer
   traffic)

   QoS monitoring often requires the correlation of data from multiple
   measurement instances  (e.g. for measuring one-way metrics). This
   requires proper clock synchronization of the involved measurement
   instances. For some measurements packet events at the different
   measurement points must be correlated. For this, the provisioning of
   post-processing functions (e.g. the generation of packet IDs) at the
   measurement instances would be useful. Furthermore, QoS monitoring
   can lead to a huge amount of measurement result data. Therefore it
   would highly benefit from mechanisms to reduce the measurement data,
   like aggregation of results and flow sampling.

//TZS: "sampling" instead of "flow sampling"

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4.  Distinguishing Flows

   Packets are mapped to flows by evaluating their properties. Packets
   with common properties are considered to belong to the same flow. A
   packet showing at least one difference in the set of properties is
   considered to belong to a different flow.

   The following subsections list a set of properties which a metering
   process MUST, SHOULD, or MAY be able to evaluate for mapping packets
   to flows. Please note that requiring the ability to evaluate a
   certain property does not imply that this property must be evaluated
   for each packet.

   In other words, meeting the IPFIX requirements means that the
   metering process in general must be able, via its configuration, to
   somehow support to distinguish flows via all the MUST fields, even if
   in certain circumstance/for certain applications, only a subset of
   the MUST fields is needed and only a subset of the MUST fields is
   effectively used to distinguish flows.

   Which combination of properties is used for distinguishing a flow in
   a particular measurement and how these properties are evaluated
   depends on the configuration of the metering process. The configured
   choice of evaluated properties strongly depends on the environment
   and purpose of the measurement and on the information required by the
   collector.

   For specific deployments, only a subset of the REQUIRED properties
   listed below can be used to distinguish flows, for example in order
   to aggregate the flow records and reduce the number of flow records
   exported. On the other hand, some other deployments will require
   distinguishing flows by some extra parameters, like for example the
   TTL field of the IP header or the BGP Autonomous Systems.

4.1.  Interfaces

   The metering process MUST be able to separate flows by the incoming
   interface or by the outgoing interface or by both of them.

4.2.  IP Header Fields

   The metering process MUST, SHOULD, or MAY be able to separate flows
   by the following fields of the IP header as indicated.

      1. source IP address (MUST)

      2. destination IP address (MUST)

      3. protocol type (TCP,UDP,ICMP,...) (MUST)

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      4. IP version number (SHOULD)
         This requirement only applies if the the observation point is
         located at a device is supporting more than one version of IP.

//TZS: "that supports" instead of "is supporting "

   For source address and destination address, separating by full match
   MUST be supported as well as separation by a partial match (for
   example subnet masking).

4.3.  Transport Header Fields

   The metering process MUST be able to separate flows by the port
   numbers of the transport header in case of TCP or UDP being used as
   transport protocol. Both, source and destination port number MUST be
   supported for distinguishing flows, individually as well as in
   combination.

4.4.  MPLS Label

   If the observation point is located at a device supporting
   Multiprotocol Label Switching (MPLS, see [RFC3031]) then the metering
   process MUST be able to separate flows by the MPLS label.

4.5.  DiffServ Code Point

   If the observation point is located at a device supporting
   Differentiated Services (DiffServ) then the metering process MUST be
   able to separate flows by the DiffServ Code Point (DSCP, see
   [RFC2474]).

4.6.  Header Compression and Encryption

   If header compression or encryption is used, the metering process
   might not be able to access all header fields. For packets with
   compressed or encrypted headers, the requirements stated in this
   section 4 MUST be met for observation points at end points of header
   compression or of packet encryption, but they do not need to be met
   for observation points between the end points.

5.  Metering Process

   The following are requirements for the metering process. All
   measurements MUST be conducted from the point of view of the
   observation point.

//TZS: What does the last sentence mean ?

5.1.  Reliability

   The metering process MUST either be reliable or missing reliability
   MUST be known and indicated. The metering process is reliable, if
   each packet passing the observation point is measured according to

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   the configuration of the metering process. If, e.g. due to some
   overload, not all passing packets can be included into the metering
   process, then the metering process MUST be able to detect this
   failure and to report about it.

5.2.  Sampling

   Sampling describes the systematic or random selection of a subset of
   elements (the sample) out of a set of elements (the parent
   population). Usually the purpose of applying sampling techniques is
   to estimate a parameter of the parent population by using only the
   elements of the subset. Sampling techniques can be applied for
   instance to select a subset of packets out of all packets of a flow
   or to select a subset of flows out of all flows on a link.  Sampling
   methods differ in their sampling strategy (e.g. systematic or random)
   and in the event that triggers the selection of an element. The
   selection of one packet can for instance be triggered by its arrival
   time (time-based sampling), by its position in the flow (count-based
   sampling) or by the packet content (content-based sampling).

   The metering process MAY support measuring traffic by packet
   sampling. If sampling is supported the sampling configuration MUST be
   well defined. The sampling configuration includes the samplng method
   and all its parameters.

   If the sampling configuration is changed during operation, the new
   sampling configuration with its parameters MUST be indicated to all
   collectors receiving the affected flow records.

//TZS: add sentence: "This includes the case when sampling is applied for 
the first time (configuration changed from "no sampling" to a sampling scheme)"
Alternatively: modify first sentence to "If sampling is applied or the sampling configuration is changed .."

   In case of any change in the sampling configuration, all flow records
   metered by the previous sampling configuration MUST be terminated and
   exported according to the export configuration. The metering process
   MUST not merge the flow records generated with the new sampling
   configuration with the flow records generated with the previous
   sampling configuration.

5.3.  Overload Behavior

   In case of an overload, for example lack of memory or processing
   power, the metering process MAY change in order to cope with the lack

//TZS: "may change its behavior"

   of resources. Possible reactions include:

      -  Reduce the number of flow accounts. This can be achieved by
         more coarse grained flow measurement or by a restriction of the
         flow accounts to a subset of the set of original ones.

      -  Switch to sampling packets before they are processed by the
         metering process or - if sampling is already performed - reduce
         the sampling rate.

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      -  Stop metering.

      -  Reducing the resource usage of competing processes on the same
         device.  Example: reducing the packet forwarding throughput

   Overload behavior is not restricted to the four options listed above.
   But in case the overload behavior has an impact on the metering
   process or the export process, the overload behavior MUST be clearly
   defined and the collector MUST be able to distinguish the flow
   records exported before and after the metering process behavior
   change: In case of any change of the meter's behavior, all flow
   records metered by the previous behavior MUST be terminated and
   exported according to the export configuration. The metering process
   MUST not merge the flow records generated with the new behavior with
   the flow records generated with the previous behavior.

5.4.  Timestamps

   The metering process MUST be able to generate timestamps for the
   first and the last observed packet of a flow. The timestamp
   accuricaty MUST be at least the one of the sysUpTime [RFC1213], which

//TZS: "accuracy" instead of "accuricaty"

   is one centisecond.

5.5.  Time Synchronization

   Metering processes and collectors SHOULD be time-synchronized with
   each other. Using NTP or GPS are possible ways of achieving this.
   However selecting a method for time synchronization is not in the
   scope of this document.

5.6.  Timeout

   The metering process MUST be able to detect flow timeout. A flow is

//TZS: "timeouts" instead of "timeout" ?

   considered to be timed out if no packet of this flow has been
   observed for a given timeout interval. The metering process MAY
   support means for detecting the end of a flow before a time out

//TZS: "timeout" instead of "time´out" ?

   occurs, for example by detecting the FIN or RST bits in a TCP
   connection. The procedure for detecting a flow timeout MUST be
   clearly defined.

5.7.  Ignore Port Copy

   The metering process MAY be able to ignore packets which are
   generated by a port copy function acting at the device where the
   observation point of a flow is located.

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6.  Data Export

   The following are requirements for exporting measured flow data out
   of the exporter. Beside requirements on the data transfer, we
   separate requirements concerning the information model from
   requirements concerning the data model. Furthermore, we list
   requirements on reporting times and events and on anonymization of
   records.

6.1.  Information Model

   The information model for the flow information export is the list of
   attributes of a flow to be contained in the report (including the
   semantics of the attributes).

   This section lists attributes an export process MUST or MAY be able
   to report. This does not imply that each exported flow records MUST
   contain all REQUIRED attributes, but that it MUST be possible to
   configure the device in a way that all of the REQUIRED attributes are
   transmitted from the export process to the colleting process for each
   measured flow.

   In other words, meeting the IPFIX requirements means that the export
   process in general must be able, via its configuration, to somehow
   support to report all the MUST fields, even if in certain
   circumstance or for certain applications, only a subset of the MUST
   fields is needed and only a subset of the MUST fields is effectively
   reported.

   Beyond that, the device might offer to report also further attributes

//TZS; remove "also"

   not mentioned here. A particular flow record may contain some of the
   "REQUIRED" attributes as well as some additional ones, for example
   covering future technologies.

   This document does not impose that the following attributes would

//TZS: "are" or "would be" instead of "would"

   reported for every single flow records, especially for repetitif

//TZS: "record" instead of "records"
//TZS: "repetitiv" instead of "repetitif"

   attributes. For example, if the observation point is the incoming
   packet stream at IP interface with the ifIndex value 3, then this

//TZS: "at the IP interface" or "at an IP interface"

   observstion point does not have to be exported as part of every

//TZS: "observation"

   single flow record. Exporting it just once might give sufficient
   information to the collecting process.

   The measuring device MUST be able to report the following attributes
   for each measured flow:

      1. IP version number
         This requirement only applies if the observation point is
         located at a device supporting more than one version of IP.
      2. source IP address
      3. destination IP address

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      4. IP protocol type (TCP,UDP,ICMP,...)
      5. source TCP/UDP port number
      6. destination TCP/UDP port number
      7. input interface (ifIndex)
         This requirement does not apply if the observation point is
         located at a probe device.
      8. output interface (ifIndex)
         This requirement does not apply if the observation point is
         located at a probe device. This requirement does not apply in
         case of multicast flow records.
      9. packet counter
         If a packet is fragmented, each fragment is counted as an
         individual packet.
     10. byte counter
         Which bytes of a packet are counted MUST be defined exactly.
     11. in case of IPv4: Type of Service
     10. in case of IPv6: Flow Label
     11. if BGP is supported at the observation point: BGP AS#
     12. if MPLS is supported at the observation point: MPLS label
     13. if DiffServ is supported at the observation point: DSCP
     14. timestamp of the first packet of the flow
     15. timestamp of the last packet of the flow
     16. if sampling is used: sampling configuration
     17. unique identifier of the observation point
     18. unique identifier of the export process

   The metering process MAY be able to report the following attributes
   for each measured flow:

     20. Time To Live
     21. IP header flags
     22. TCP header flags
     23. dropped packet counter at the observation point
         If a packet is fragmented, each fragment MUST be counted as an
         individual packet.
     24. fragmented packet counter
         counter of all packets for which the fragmented bit is set in
         the IP header
     25. multicast replication factor
         the number of outgoing packets originating from a single
         incoming multicast packet

//TZS: for MC maybe also all the outgoing IFs ?

6.2.  Data Model

   The data model describes how information is represented in flow
   records.

   The data model MUST be extensible for future attributes to be added.
   Even if a set of attributes is fixed in the flow record, the data
   model MUST provide a way of extending the record by configuration or

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   for certain implementations.

   The data model used for exporting flow information MAY be flexible
   concerning the flow attributes contained in flow records. A flexible
   record format would offer the possibility of defining records in a
   flexible (customizable) way regarding the number and type of
   contained attributes.

   The Data Model SHOULD be independent of the underlying transport
   protocol, i.e. the data transfer.

6.3.  Data Transfer

   Requirements for the data transfer include reliability and security
   requirements. These requirements do not apply to the measuring device
   alone, but also to the transport network. Consequently, the export
   process does not necessarily have to guarantee that all requirements
   are met. Particularly if the security requirements are already
   guaranteed by the network used for data transfer, then these
   requirements do not have to be considered anymore by the export
   process. Therefore, these requirements are OPTIONAL for the export
   process, although they may be REQUIRED for the data transfer as
   specified in the appendix.

//TZS: We already had a lot of discussions regarding this. But I still 
have problems with this formulation. What does this mean ? The requirements 
for an IPFIX protocol applied in a LAN or in an environment with IPsec differ
from the requirements for an IPFIX protocol in an environment without these
capabilities ? So we could get two different protocol specifications ? or optional
security features that can switch an IPFIX implementation from "standard-conformant"
to "not standard-conformant" if disabled in the wrong environment ?
I propose to remove everthing after the "Consequently,"  and substitute it by

"The exporting process can utilize existing security features provided by the transport 
network or by the exporting device  "

With this formulation we allow the utilization of existing capabilities but leave the 
responsibilities with the IPFIX implementor. This could mean for instance IPFIX encryption 
capabilities can be only switched off or left out if e.g. replaced by a connection to an 
IPsec implementation.

6.3.1.  Congestion Awareness

   For the data transfer, a congestion aware protocol MUST be supported.

6.3.2.  Reliability

   Absence of reliability, for example caused by export packet loss or
   export packet reordering, of the data transfer MUST be indicated.

   Please note that if an unreliable transport protocol is used,
   reliability can be provided by higher layers. In such a case only
   lack of overall reliability MUST be indicated. For example reordering
   could be dealt with by adding a sequence number to each packet.

6.3.3.  Security

   Confidentiality of flow specific data transferred from an export
   process to a collecting process SHOULD be ensured.

   Integrity of flow specific data transferred from an export process to
   a collecting process MUST be ensured.

   Authenticity of flow specific data transferred from an export process
   to a collecting process MUST be ensured.

   See more about Security in the "Security Considerations" section 10,

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   from which the 3 requirements above are deducted.

// TZS: substitute last sentence by "The security threats from which these 3 requirements are deducted 
are explained in the "Security Considerations" section 10,.

6.4.  Push and Pull Mode Reporting

   In general, there are two ways of deciding on reporting times: push
   mode and pull mode. In push mode, the export process decides without
   an external trigger on when to send a report on measured flows. In

//TZS: without the first "on" ? 

   pull mode, sending a report is triggered by an explicit request from
   a collector. The measuring device MUST support push mode reporting,
   it MAY support pull mode reporting.

6.5.  Regular Reporting Interval

   The export process SHOULD be capable of reporting measured traffic
   data regularly according to a given interval length.

6.6.  Notification on Specific Events

   The export process MAY be capable of sending notifications to a
   collecting process, if a specific event occurs. Such an event can be

//TZS: add "for instance"

   the arrival of the first packet of a new flow, or the termination of
   a flow after flow timeout.

6.7.  Anonymization

   The export process MAY be capable of anonymizing source and
   destination IP addresses in flow data before exporting them. It MAY
   support anonymization of port numbers and other fields. Please note
   that anonymization is not originally an application requirement, but
   derived from general requirements for treatment of traffic within a
   network.

7.  Configuration

   The metering process MUST provide a way of configuring traffic
   measurement. The following parameters of the metering process SHOULD
   be configurable:

      1. specification of the observation point, e.g. an interface or
         a list of interfaces to be monitored.
      2. specifications of flows to be metered
      3. flow timeouts

   The following parameters MAY be configurable:

      4. sampling method and parameters, if feature is supported
      5. overload behavior

   The export process MUST provide a way of configuring the data export.

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   The following parameters of the export process SHOULD be
   configurable:

      1. reporting data format
         Specifying the reporting data format SHOULD include a selection
         of attributes to be reported for each flow.
      2. the collecting process (or list of collecting processes) to
         which flows are reported 2. notifications to be sent to the
         collecting process(es) 3. flow anonymization, if the export
         process supports it

//TZS: numbering under 2. ? 

   If configuration is done remotely, security of the configuration

//TZS: "security for the transfer of configuration data"

   SHOULD be supported including confidentiality, integrity and
   authenticity. The means used for remote configuration are out of the
   scope of this document.

8.  General Requirements

8.1.  Openness

   IPFIX specifications SHOULD be open to future technologies. This
   includes extensibility of configuration of measurement and reporting.

   Openness is also required concerning the extensibility of the data
   model, as stated in section 6.2.

8.2.  Scalability Concerning the Number of Export Processes

   Data collection from hundreds of different export processes MUST be
   supported. The collecting process MUST be able to distinguish several
   hundred export processes by their identifiers.

8.3.  Several Collectors

   The export process MAY be able to export flow information to more
   than one collecting process.

9.  Special Device Considerations

   This document is intended to avoid constraining the architecture of

//TZS: "intends to"

   probes, routers, and other devices hosting observation points,
   metering processes, export processes, or collecting processes.  It

//TZS: "and/or"

   can be expected that typically observation point, metering process,
   and export process are co-located at a single device.  However, the
   requirements defined in this document do not exclude devices that
   derive from this configureation. Figure 2 shows some examples.

//TZS: "configuration"

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            +---+     +-----+     +---------+       +---------+
            | E-+->   |  E--+->   |    E----+->   <-+--E   E--+->
            | | |     |  |  |     |   /    |       |  |   |  |
            | M |     |  M  |     |  M   M  |       |  M   M  |
            | | |     | /| |     | /| /| |       | /| /| |
            | O |     | OOO |     | OOO OOO |       | OOO OOO |
            +---+     +-----+     +---------+       +---------+
            Probe      Basic        Complex          Multiple
                       Router       Router           Exporters

//TZS: I love these figures :-) Nevertheless, some elements in row 3 and 4 appear 
displaced in my editor

          +---+     +---+     +---+
          | E-+->   | E-+->   | E-+------------->---+
          | | |     | | |     | | | +---+         +-+-----+
          +-+-+     | M |     | M | | E-+------->-+-C-M-E-+->
            |       | | |     | | | | | | +---+   +-+-----+
          +-+-+     +-+-+     | O | | M | | E-+->---+
          | | |       |       +---+ | | | | | |
          | M |     +-+-+           | O | | M |
          | | |     | | |           +---+ | | |           +-----+
          | O |     | O |                 | O |        ->-+-C-E-+->
          +---+     +---+                 +---+           +-----+

         Protocol   Remote             Concentrator        Proxy
         Converter  Observation

                      Figure X: IPFIX-related Devices

   All examples are composed of one or more of the following elements:
   observation point (O), full or partial metering process (M), export
   process (E), collecting process (C).

   A very simple device is a probe. It contains on a single observation
   point, a single metering process, and a single export process.  For
   this device the observation domain contains a single observation
   point only.

   A basic router extends this structure by multiple observation point.
   Here an exported flow record may still have an observation domain
   containing a single observation point. But also Observation domains
   containing all observation points of the routers are possible.

//TZS: hmm... we avoided the term "observation domain" in the terminology 
section. I would prefer to avoid "observation domain" here, too...

   A more complex router may host more than one metering process, for
   example one per line card. Please note that an observation domain is
   restricted to the observation points connected to a single metering
   process. An observation domain containing all observation points of
   this router is not possible with this structure.

//TZS: only if I connect all observation points to one metering process ?

   Alternatively, a complex router may use different export processes
   for flow records generated by different metering processes.

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   A protocol converter makes use of a metering process that can be
   accessed only by another protocol than the one defined for IPFIX, for
   example the SNMP and the Meter MIB module [RFC2720]. Then the
   exporter receives flow record from a remote metering process and
   exports these records using the IPFIX protocol.

//TZS: " The other protocol together with the record conversion is then 
seen as the metering process that serves the exporting process"
Is this the correct interpretation ?

   Another choice is remote packet observation. Packet header captured
   at an observation point may be exported as raw data to a device
   hosting metering process and exproting process.

//TZS "exporting" aahh... here you use "exporting" So I remembered our
decision correctly (see comment at 2.5)

//TZS:  maybe add "In this case the whole device which exports the raw 
header data is considered as the observation point for the metering process"
Correct interpretation ?

   An intermediate structure between protocol converter and remote
   observation (not shown in the Figure) would be a split metering

//TZS:  "splitted" ? 

   process, for example performing timestaping and sampling at the
   device hosting the observation point and performing packet
   classification at another device hosting the export process.

   A concentrator receives flow records via the IPFIX protocol, merges
   them into higher aggregated flows and exports the resulting flows
   again using the IPFIX protocol. Please note that for the final flow
   records the observation domain potentially contains observation
   points at all first level devices. The metering process of the final
   flow records is composed by the (partial) metering processes at the
   first level devices and the partial metering process at the
   concentrator.

   Finally, a very simple IPFIX-related device is a proxy. It just
   receives flow records using the IPFIX protocol and sends them further
   using the same protocol. A proxy might be useful for traversing
   firewalls or other gateways.

10.  Security Considerations

   The future IPFIX protocol must be capable to transport data over the
   public Internet. Therefore it cannot be excluded that an attacker
   captures or modifies exchanged packets or inserts additional packets.

   This section describes security requirements for IPFIX.  It therefore
   also states the required security features for a future IPFIX
   protocol. 

//TZS: Ssubstitute first 2 sentences by "This document contains the the 
required security features for a future IPFIX protocol." 

   Like other requirements, the security requirements differ
   for the considered applications. The incentive to modify collected
   data for accounting or intrusion detection for instance is usually
   higher than the incentive to change data collected for traffic
   profiling. Therefore the required security features in this document
   are listed per application in the appendix.  The suggestion of
   concrete solutions for achieving the required security properties
   will be part of the IPFIX architecture and protocol description and
   is out of scope of this document. Furthermore, methods for remote
   configuration of the IPFIX processes are out of scope for IPFIX.
   Therefore, threads that are caused by data exchange for remote

//TZS: "threats" :-)

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   configuration are not considered here.

   The following potential security hazards for an IPFIX protocol can be
   identified: disclosure of IP flow information, forgery of flow
   records, and Denial of Service (DoS) attacks.

10.1.  Disclosure of Flow Information Data

   The content of data exchanged by the IPFIX protocol (e.g. IPFIX flow
   records) should be kept confidential between the involved parties
   (export process and colleting process). Observation of IPFIX flow
   records gives an attacker information about the active flows in the
   network, communication endpoints and traffic patterns. This
   information cannot only be used to spy out user behavior but also to
   plan and conceal future attacks. Therefore the requirements document
   recommends to ensure the confidentiality of the transferred data.
   This can be achieved for instance by encryption.

10.2.  Forgery of Flow Records

   Because of the potential uses of IPFIX flow records in accounting and
   security applications, there are strong incentives to forge exported
   IPFIX  flow records (e.g. to save money or prevent the detection of
   an attack). This can be done either by altering flow records on the
   path or by injecting forged flow records that pretend to be
   originated by the original export process. In order to make the IPFIX
   protocol resistant against such attacks this document requires to
   ensure authenticity and integrity for the IPFIX data transfer.

   Special caution is required if security applications rely on IPFIX
   data. With forged flow records it is possible to trick on security
   applications. It is for instance possible to pretend that a DoS
   attack happens without even launching a real attack.

   IPFIX flow records are used in accounting and security applications.
   This leads to strong incentives for attackers to forge exported IPFIX
   flow records (for example to save money or to prevent the detection
   of an attack). In order to make the IPFIX protocol resistant against
   such attacks, source authentication and integrity assurance must be
   provided for IPFIX data. These requirements are covered in the
   security requirements section of this document.

//TZS: substitute all 3 paragraphs by the following 3: 

   IPFIX flow records are used in accounting and security applications.
   This leads to strong incentives for attackers to forge exported IPFIX
   flow records (for example to save money or to prevent the detection
   of an attack). This can be done either by altering flow records on the
   path or by injecting forged flow records that pretend to be originated 
   by the original export process. 

   Special caution is required if security applications rely on IPFIX
   data. With forged flow records it is possible to trick on security
   applications. It is for instance possible to pretend that a DoS
   attack happens without even launching a real attack.

   In order to make the IPFIX protocol resistant against such attacks, 
   source authentication and integrity assurance must be provided for 
   IPFIX data. These requirements are covered in the security requirements 
   section (6.3.3) of this document.

10.3.  Denial of Service (DoS) Attacks

   DoS attacks on routers or other middleboxes that have the IPFIX
   protocol implemented would also affect the IPFIX protocol and impair
   the sending of IPFIX records. Nevertheless, since such hazards are
   not induced specifically by the IPFIX protocol the prevention of such
   attacks is out of scope of this document.

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   Nevertheless IPFIX itself also causes potential hazards for DoS
   attacks.  All processes that expect the reception of traffic can be
   target of a DoS attack. With the IPFIX export process this is only
   the case if it supports the pull mode (which can be an optional
   feature of the future IPFIX protocol according to this document). The
   collecting process always expects data and therefore can be flooded
   by forged flow records.

11.  Acknowledgments

   We like to thank all the people contributing to the requirements
   discussion on the mailing list for a lot of valuable comments.

12.  References

[RFC2026]   S. Bradner, "The Internet Standards Process -- Revision 3",
            RFC 2026, October 1996.

[RFC3234]   B. Carpenter, "Middleboxes: taxonomy and issues", RFC 3234,
            February 2002.

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

[RFC2702]   D. Awduche, J. Malcolm, J. Agogbua, M. O'Dell, J. McManus,
            "Requirements for Traffic Engineering Over MPLS", RFC 2702,
            September 1999.

[RFC3031]   E. Rosen, A. Viswanathan, R. Callon, "Multiprotocol Label
            Switching Architecture", RFC 3031, January 2001.

[RFC2474]   K. Nichols, S. Blake, F. Baker, D. Black, "Definition of the
            Differentiated Services Field (DS Field) in the IPv4 and
            IPv6 Headers", RFC 2474, December 1998.

[RFC1213]   K. McCloghrie, M. Rose. "Management Information Base for
            Network Management of TCP/IP-based internets: MIB-II", RFC
            1213, March 1991.

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13.  Authors' Addresses

     Juergen Quittek
     NEC Europe Ltd., Network Laboratories
     Adenauerplatz 6
     69115 Heidelberg
     Germany

     Phone: +49 6221 90511-15
     EMail: [email-masked]

     Tanja Zseby
     Fraunhofer Institute for Open Communication Systems (FOKUS)
     Kaiserin-Augusta-Allee 31
     10589 Berlin
     Germany

     Phone: +49 30 3463 7153
     Email: [email-masked]

     Benoit Claise
     Cisco Systems
     De Kleetlaan 6a b1
     1831 Diegem
     Belgium

     Phone: +32 2 704 5622
     Email: [email-masked]

     Sebastian Zander
     Fraunhofer Institute for Open Communication Systems (FOKUS)
     Kaiserin-Augusta-Allee 31
     10589 Berlin
     Germany

     Phone: +49 30 3463 7287
     Email: [email-masked]

     Georg Carle
     Fraunhofer Institute for Open Communication Systems (FOKUS)
     Kaiserin-Augusta-Allee 31
     10589 Berlin
     Germany

     Phone: +49 30 3463 7149
     Email: [email-masked]

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     K.C. Norseth
     Consultant
     934 S. Palos Verdes Dr.
     Kaysville, Utah 84037 USA

     Phone: 801.546.3316
     Email: [email-masked]

14.  Full Copyright Statement

   Copyright (C) The Internet Society (2001). All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the  purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
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   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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