IPFIX Working Group E. Boschi Internet-Draft B. Trammell Intended status: Experimental Hitachi Europe Expires: July 16, 2009 January 12, 2009 IP Flow Anonymisation Support draft-boschi-ipfix-anon-02.txt Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. 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. This Internet-Draft will expire on July 16, 2009. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Abstract This document describes anonymisation techniques for IP flow data and the export of anonymised data using the IPFIX protocol. It provides Boschi & Trammell Expires July 16, 2009 [Page 1] Internet-Draft IP Flow Anonymisation Support January 2009 a categorization of common anonymisation schemes and defines the parameters needed to describe them. It provides guidelines for the implementation of anonymised data export and storage over IPFIX, and describes an Options-based method for anonymization metadata export within the IPFIX protocol, providing the basis for the definition of information models for configuring anonymisation techniques within an IPFIX Metering or Exporting Process, and for reporting the technique in use to an IPFIX Collecting Process. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. IPFIX Protocol Overview . . . . . . . . . . . . . . . . . 3 1.2. IPFIX Documents Overview . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Categorisation of Anonymisation Techniques . . . . . . . . . . 4 4. Anonymisation of IP Flow Data . . . . . . . . . . . . . . . . 6 4.1. IP Address Anonymisation . . . . . . . . . . . . . . . . . 7 4.1.1. Truncation . . . . . . . . . . . . . . . . . . . . . . 7 4.1.2. Random Permutation . . . . . . . . . . . . . . . . . . 7 4.1.3. Prefix-preserving Pseudonymisation . . . . . . . . . . 7 4.2. Timestamp Anonymisation . . . . . . . . . . . . . . . . . 8 4.2.1. Precision Degradation . . . . . . . . . . . . . . . . 8 4.2.2. Enumeration . . . . . . . . . . . . . . . . . . . . . 8 4.2.3. Random Time Shifts . . . . . . . . . . . . . . . . . . 8 4.3. Counter Anonymisation . . . . . . . . . . . . . . . . . . 8 4.3.1. Precision Degradation . . . . . . . . . . . . . . . . 9 4.3.2. Binning . . . . . . . . . . . . . . . . . . . . . . . 9 4.3.3. Random Noise Addition . . . . . . . . . . . . . . . . 9 4.4. Anonymisation of Other Flow Fields . . . . . . . . . . . . 9 5. Applying Anonymisation Techniques to IPFIX Export and Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 5.1. Arrangement of Processes in IPFIX Anonymisation . . . . . 10 5.2. IPFIX-Specific Anonymisation Guidelines . . . . . . . . . 11 5.2.1. Anonymisation of Header Data . . . . . . . . . . . . . 11 5.2.2. Anonymisation of Options Data . . . . . . . . . . . . 12 6. Parameters for the Description of Anonymisation Techniques . . 13 7. Anonymisation Metadata Support in IPFIX . . . . . . . . . . . 13 8. Security Considerations . . . . . . . . . . . . . . . . . . . 14 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 11.1. Normative References . . . . . . . . . . . . . . . . . . . 14 11.2. Informative References . . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15 Boschi & Trammell Expires July 16, 2009 [Page 2] Internet-Draft IP Flow Anonymisation Support January 2009 1. Introduction The standardisation of an IP flow information export protocol [RFC5101] and associated representations removes a technical barrier to the sharing of IP flow data across organizational boundaries and with network operations, security, and research communities for a wide variety of purposes. However, with wider dissemination comes greater risks to the privacy of the users of networks under measurement, and to the security of those networks. While it is not a complete solution to the issues posed by distribution of IP flow information, anonymisation is an important tool for the protection of privacy within network measurement infrastructures. This document presents a mechanism for representing anonymised data within IPFIX and guidelines for using it. It begins with a categorization of anonymisation techniques. It then describes applicability of each technique to commonly anonymisable fields of IP flow data, organized by information element data type and semantics as in [RFC5102]; enumerates the parameters required by each of the applicable anonymisation techniques; and provides guidelines for the use of each of these techniques in accordance with best practices in data protection. Finally, it specifies a mechanism for exporting anonymised data and binding anonymisation metadata to templates using IPFIX Options. 1.1. IPFIX Protocol Overview In the IPFIX protocol, { type, length, value } tuples are expressed in templates containing { type, length } pairs, specifying which { value } fields are present in data records conforming to the Template, giving great flexibility as to what data is transmitted. Since Templates are sent very infrequently compared with Data Records, this results in significant bandwidth savings. Various different data formats may be transmitted simply by sending new Templates specifying the { type, length } pairs for the new data format. See [RFC5101] for more information. The IPFIX information model [RFC5102] defines a large number of standard Information Elements which provide the necessary { type } information for Templates. The use of standard elements enables interoperability among different vendors' implementations. Additionally, non-standard enterprise-specific elements may be defined for private use. 1.2. IPFIX Documents Overview "Specification of the IPFIX Protocol for the Exchange of IP Traffic Flow Information" [RFC5101] and its associated documents define the Boschi & Trammell Expires July 16, 2009 [Page 3] Internet-Draft IP Flow Anonymisation Support January 2009 IPFIX Protocol, which provides network engineers and administrators with access to IP traffic flow information. "Architecture for IP Flow Information Export" [I-D.ietf-ipfix-architecture] defines the architecture for the export of measured IP flow information out of an IPFIX Exporting Process to an IPFIX Collecting Process, and the basic terminology used to describe the elements of this architecture, per the requirements defined in "Requirements for IP Flow Information Export" [RFC3917]. The IPFIX Protocol document [RFC5101] then covers the details of the method for transporting IPFIX Data Records and Templates via a congestion-aware transport protocol from an IPFIX Exporting Process to an IPFIX Collecting Process. "Information Model for IP Flow Information Export" [RFC5102] describes the Information Elements used by IPFIX, including details on Information Element naming, numbering, and data type encoding. Finally, "IPFIX Applicability" [I-D.ietf-ipfix-as] describes the various applications of the IPFIX protocol and their use of information exported via IPFIX, and relates the IPFIX architecture to other measurement architectures and frameworks. Additionally, the "Specification of the IPFIX File Format" [I-D.ietf-ipfix-file] describes a file format based upon the IPFIX Protocol for the storage of flow data. This document references the Protocol and Architecture documents for terminology, and extends the IPFIX Information Model to provide new Information Elements for anonymisation metadata. The anonymisation techniques described herein are equally applicable to the IPFIX Protocol and data stored in IPFIX Files. 2. Terminology Terms used in this document that are defined in the Terminology section of the IPFIX Protocol [RFC5101] document are to be interpreted as defined there. 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]. 3. Categorisation of Anonymisation Techniques Anonymisation modifies a data set in order to protect the identity of the people or entities described by the data set from disclosure. Boschi & Trammell Expires July 16, 2009 [Page 4] Internet-Draft IP Flow Anonymisation Support January 2009 With respect to network traffic data, anonymisation generally attempts to preserve some set of properties of the network traffic useful for a given application or applications, while ensuring the data cannot be traced back to the specific networks, hosts, or users generating the traffic. Anonymisation may be broadly classified according to two properties: recoverability and countability. All anonymisation techniques map the real space of identifiers or values into a separate, anonymised space, according to some function. A technique is said to be recoverable when the function used is invertible or can otherwise be reversed and a real identifier can be recovered from a given replacement identifier. Countability compares the dimension of the anonymised space (N) to the dimension of the real space (M), and denotes how the count of unique values is preserved by the anonymisation function. If the anonymised space is smaller than the real space, then the function is said to generalise the input, mapping more than one input point to each anonymous value (e.g., as with aggregation). By definition, generalisation is not recoverable. If the dimensions of the anonymised and real spaces are the same, such that the count of unique values is preserved, then the function is said to be a direct substitution function. If the dimension of the anonymised space is larger, such that each real value maps to a set of anonymised values, then the function is said to be a set substitution function. Note that with set substitution functions, the sets of anonymised values are not necessarily disjoint. Either direct or set substitution functions are said to be one-way if there exists no method for recovering the real data point from an anonymised one. This classification is summarised in the table below. +------------------------+-----------------+------------------------+ | Recoverability / | Recoverable | Non-recoverable | | Countability | | | +------------------------+-----------------+------------------------+ | N < M | N.A. | Generalisation | | N = M | Direct | One-way Direct | | | Substitution | Substitution | | N > M | Set | One-way Set | | | Substitution | Substitution | +------------------------+-----------------+------------------------+ Boschi & Trammell Expires July 16, 2009 [Page 5] Internet-Draft IP Flow Anonymisation Support January 2009 4. Anonymisation of IP Flow Data Due to the restricted semantics of IP flow data, there are a relatively limited set of specific anonymisation techniques available on flow data, though each falls into the broad categories above. Each type of field that may commonly appear in a flow record may have its own applicable specific techniques. While anonymisation is generally applied at the resolution of single fields within a flow record, attacks against anonymisation use entire flows and relationships between hosts and flows within a given data set. Therefore, fields which may not necessarily be identifying by themselves may be anonymised in order to increase the anonymity of the data set as a whole. Of all the fields in an IP flow record, only IP addresses directly identify entities in the real world. Each IP address is associated with an interface on a network host, and can potentially be identified with a single user. Additionally, IP addresses are structured identifiers; that is, partial IP address prefixes may be used to identify networks just as full IP addresses identify hosts. This makes anonymisation of IP addresses particularly important. Port numbers identify abstract entities (applications) as opposed to real-world entities, but they can be used to classify hosts and user behavior. Passive port fingerprinting, both of well-known and ephemeral ports, can be used to determine the operating system running on a host. Relative data volumes by port can also be used to determine the host's function (workstation, web server, etc.); this information can be used to identify hosts and users. While not identifiers in and of themselves, timestamps and counters can reveal the behavior of the hosts and users on a network. Any given network activity is recognizable by a pattern of relative time differences and data volumes in the associated sequence of flows, even without host address information. They can therefore be used to identify hosts and users. Timestamps and counters are also vulnerable to traffic injection attacks, where traffic with a known pattern is injected into a network under measurement, and this pattern is later identified in the anonymised data set. The simplest and most extreme form of anonymisation, which can be applied to any field of a flow record, is black-marker anonymisation, or complete deletion of a given field. Note that black-marker anonymisation is equivalent to simply not exporting the field(s) in question. While black-marker anonymisation completely protects the data in the Boschi & Trammell Expires July 16, 2009 [Page 6] Internet-Draft IP Flow Anonymisation Support January 2009 deleted fields from the risk of disclosure, it also reduces the utility of the anonymised data set as a whole. Techniques that retain some information while reducing (though not eliminating) the disclosure risk will be extensively discussed in the following sections; note that the techniques specifically applicable to IP addresses, timestamps, and counters will be discussed in separate sections. 4.1. IP Address Anonymisation The following table gives an overview of the schemes for IP address anonymization described in this document and their categorization. +-------------------------------+-------------------+---------------+ | Scheme | Action | Reversibility | +-------------------------------+-------------------+---------------+ | Truncation | Generalisation | N | | Random Permutation | Direct | Y/N | | | Substitution | | | Prefix-preserving | Direct | Y | | Pseudonymisation | Substitution | | +-------------------------------+-------------------+---------------+ Note that random permutations might be either reversible or not, depending on the function used. 4.1.1. Truncation Truncation removes "n" of the least significant bits from an IP address. Note that truncating 8 bits would replace an IP address with the corresponding class C network address. 4.1.2. Random Permutation Random permutation replaces each IP address with a unique address randomply selected from the set of possible IP addresses. The permutation function is implementable using a hash table to ensure uniqueness. 4.1.3. Prefix-preserving Pseudonymisation Prefix-preserving pseudonymisation preserves the structure of subnets at each level while anonymising IP addresses. If two real IP addresses match on a prefix of "n" bits, the two anonymised IP addresses will match on a prefix of "n" bits as well. Boschi & Trammell Expires July 16, 2009 [Page 7] Internet-Draft IP Flow Anonymisation Support January 2009 4.2. Timestamp Anonymisation [TODO: introductory text] +-----------------------+---------------------------+---------------+ | Scheme | Action | Reversibility | +-----------------------+---------------------------+---------------+ | Precision Degradation | Generalisation | N | | Enumeration | Direct or Set | Y | | | Substitution | | | Random Shifts | Direct Substitution | Y | +-----------------------+---------------------------+---------------+ 4.2.1. Precision Degradation Precision Degradation removes the most precise components of a timestamp, accounting all events occurring in each given interval (e.g. one millisecond for millisecond level degradation) as simultaneous. This has the effect of potentially collapsing many timestamps into one. With this technique time precision is reduced, and sequencing may be lost, but the information at which time the event occurred is preserved. 4.2.2. Enumeration Enumeration keeps the chronological order in which events occurred while eliminating time information. Timestamps are substituted by equidistant timestamps (or numbers) starting from an randomly chosen start value. 4.2.3. Random Time Shifts Random Time Shifts keep the information on how far apart two events are from each other. This is achieved by shifting all timestamps by the same random number. Note that random time shifts also preserve chronological order. 4.3. Counter Anonymisation Counters (such as packet and octet volumes per flow) are subject to fingerprinting and injection attacks against anonymisation, as timestamps are, but relative magnitudes of activity can be useful for certain analysis tasks. [TODO: more intro text] Boschi & Trammell Expires July 16, 2009 [Page 8] Internet-Draft IP Flow Anonymisation Support January 2009 +-----------------------+---------------------------+---------------+ | Scheme | Action | Reversibility | +-----------------------+---------------------------+---------------+ | Precision Degradation | Generalisation | N | | Binning | Generalisation | N | | Random noise addition | Direct or Set | N | | | Substitution | | +-----------------------+---------------------------+---------------+ 4.3.1. Precision Degradation As with precision degradation in timestamps, precision degradation of counters removes lower-order bits of the counters, treating all the counters in a given range as having the same value. Depending on the precision reduction, this loses information about the relationships between sizes of similarly-sized flows, but keeps relative magnitude information. 4.3.2. Binning Binning can be seen as a special case of precision degradation; the operation is identical, except for in precision degradation the counter ranges are uniform, and in binning they need not be. For example, a common counter binning scheme for packet counters could be to bin values 1-2 together, and 3-infinity together, thereby separating potentially completely-opened TCP connections from unopened ones. Binning schemes are generally chosen to keep precisely the amount of information required in a counter for a given analysis task 4.3.3. Random Noise Addition Random noise addition adds a random amount to a counter in each flow; this is used to keep relative magnitude information and minimize the disruption to size relationship information while avoiding fingerprinting attacks against anonymization. 4.4. Anonymisation of Other Flow Fields [TODO: as section 4.1] 5. Applying Anonymisation Techniques to IPFIX Export and Storage When exporting or storing anonymised flow data using IPFIX, certain interactions between the IPFIX Protocol and the anonymisation techniques in use must be considered; these are treated in the subsections below. Boschi & Trammell Expires July 16, 2009 [Page 9] Internet-Draft IP Flow Anonymisation Support January 2009 5.1. Arrangement of Processes in IPFIX Anonymisation Anonymisation may be applied to IPFIX data at three stages within a the collection infrastructure: on initial export, at a mediator, or after collection, as shown in Figure 1. Each of these locations has specific considerations and applicability. +--------------------+ | IPFIX File Storage | +--------------------+ ^ | (Anonymised after collection) | +=======================================+ | Collecting Process | +=======================================+ ^ ^ | (Anonymised at mediator) | | | +=============================+ | | Mediator | | +=============================+ | ^ | | (Anonymised on initial export) | | | +=======================================+ | Exporting Process | +=======================================+ Figure 1: Potential Anonymisation Locations Anonymisation is generally performed before the wider dissemination or repurposing of a flow data set, e.g., adapting operational measurement data for research. Therefore, direct anonymisation of flow data on initial export is only applicable in certain restricted circumstances: when the Exporting Process is "publishing" data to a Collecting Process directly, and the Exporting Process and Collecting Process are operated by different entities. Note that certain guidelines in Section 5.2.1 with respect to timestamp anonymisation may not apply in this case, as the Collecting Process may be able to deduce certain timing information from the time at which each Message is received. A much more flexible arrangement is to anonymise data within a Mediator [I-D.ietf-ipfix-mediators-framework]. Here, original data is sent to a Mediator, which performs the anonymisation function and re-exports the anonymised data. Such a Mediator could be located at Boschi & Trammell Expires July 16, 2009 [Page 10] Internet-Draft IP Flow Anonymisation Support January 2009 the administrative domain boundary of the initial Exporting Process operator, exporting anonymised data to other consumers outside the organisation. In this case, the original Exporter SHOULD use TLS as specified in [RFC5101] to secure the channel to the Mediator, and the Mediator should follow the guidelines in Section 5.2, to mitigate the risk of original data disclosure. When data is to be published as an anonymised data set in an IPFIX File [I-D.ietf-ipfix-file], the anonymisation may be done at the final Collecting Process before storage and dissemination, as well. In this case, the Collector should follow the guidelines in Section 5.2, especially as regards File-specific Options in Section 5.2.2 Note that anonymisation may occur at more than one location within a given collection infrastructure, to provide varying levels of anonymisation reversal risk and utility for specific purposes. 5.2. IPFIX-Specific Anonymisation Guidelines In implementing and deploying the anonymisation techniques described in this document, care must be taken that data structures supporting the operation of the protocol itself do not leak data that could be used to reverse the anonymisation applied to the flow data. Such data structures may appear in the header, or within the data stream itself, especially as options data. Each of these and their impact on specific anonymisation techniques is noted in a separate subsection below. 5.2.1. Anonymisation of Header Data Each IPFIX Message contains a Message Header; within this Message Header are contained two fields which may be used to break certain anonymisation techniques: the Export Time, and the Observation Domain ID Export of IPFIX Messages containing anonymised timestamp data where the original Export Time Message header has some relationship to the anonymised timestamps SHOULD anonymise the Export Time header field using an equivalent technique, if possible. Otherwise, relationships between export and flow time could be used to partially or totally reverse timestamp anonymisation. The similarity in size between an Observation Domain ID and an IPv4 address (32 bits) may lead to a temptation to use an IPv4 interface address on the Metering or Exporting Process as the Observation Domain ID. If this address bears some relation to the IP addresses in the flow data (e.g., shares a network prefix with internal Boschi & Trammell Expires July 16, 2009 [Page 11] Internet-Draft IP Flow Anonymisation Support January 2009 addresses) and the IP addresses in the flow data are anonymised in a structure-preserving way, then the Observation Domain ID may be used to break the IP address anonymisation. Use of an IPv4 interface address on the Metering or Exporting Process as the Observation Domain ID is NOT RECOMMENDED in this case. [EDITOR'S NOTE: We might want to see if anyone is actually doing this with IPFIX. The example comes from other network measurement tools (e.g. Argus) which default to using an IPv4 address as a sensor ID.] 5.2.2. Anonymisation of Options Data IPFIX uses the Options mechanism to export, among other things, metadata about exported flows and the flow collection infrastructure. As with the IPFIX Message Header, certain Options recommended in [RFC5101] and the IPFIX File Format [I-D.ietf-ipfix-file] containing flow timestamps and network addresses of Exporting and Collecting Processes may be used to break certain anonymisation techniques; care should be taken while using them with anonymised data export and storage. The Exporting Process Reliability Statistics Options Template, recommended in [RFC5101], contains an Exporting Process ID field, which may be an exportingProcessIPv4Address Information Element or an exportingProcessIPv6Address Information Element. If the Exporting Process address bears some relation to the IP addresses in the flow data (e.g., shares a network prefix with internal addresses) and the IP addresses in the flow data are anonymised in a structure- preserving way, then the Exporting Process address may be used to break the IP address anonymisation. Exporting Processes exporting anonymised data in this situation SHOULD mitigate the risk of attack either by omitting Options described by the Exporting Process Reliability Statistics Options Template, or by anonymising the Exporting Process address using a similar technique to that used to anonymise the IP addresses in the exported data. Similarly, the Export Session Details Options Template and Message Details Options Template specified for the IPFIX File Format [I-D.ietf-ipfix-file] may contain the exportingProcessIPv4Address Information Element or the exportingProcessIPv6Address Information Element to identify an Exporting Process from which a flow record was received, and the collectingProcessIPv4Address Information Element or the collectingProcessIPv6Address Information Element to identify the Collecting Process which received it. If the Exporting Process or Collecting Process address bears some relation to the IP addresses in the flow data (e.g., shares a network prefix with internal addresses) and the IP addresses in the flow data are anonymised in a structure- preserving way, then the Exporting Process or Collecting Process Boschi & Trammell Expires July 16, 2009 [Page 12] Internet-Draft IP Flow Anonymisation Support January 2009 address may be used to break the IP address anonymisation. Since these Options Templates are primarily intended for storing IPFIX Transport Session data for auditing, replay, and testing purposes, it is NOT RECOMMENDED that storage of anonymised data include these Options Templates in order to mitigate the risk of attack. The Message Details Options Template specified for the IPFIX File Format [I-D.ietf-ipfix-file] also contains the collectionTimeMilliseconds Information Element. As with the Export Time Message Header field, if the exported flow data contains anonymised timestamp information, and the collectionTimeMilliseconds Information Element in a given Message has some relationship to the anonymised timestamp information, then this relationship can be exploited to reverse the timestamp anonymisation. Since this Options Template is primarily intended for storing IPFIX Transport Session data for auditing, replay, and testing purposes, it is NOT RECOMMENDED that storage of anonymised data include this Options Template in order to mitigate the risk of attack. Since the Time Window Options Template specified for the IPFIX File Format [I-D.ietf-ipfix-file] refers to the timestamps within the flow data to provide partial table of contents information for an IPFIX File, care must be taken to ensure that Options described by this template are written using the anonymised timestamps instead of the original ones. 6. Parameters for the Description of Anonymisation Techniques [TODO: see corresponding section of draft-ietf-psamp-sample-tech for the proposed structure of this section.] 7. Anonymisation Metadata Support in IPFIX [TODO: Here we'll describe how the information specified above can be transmitted on the wire using an option template. The idea is to scope the option to the Template ID and for each field specify which are anonymised, providing info on the output characteristics of the technique, and which ones aren't.] [EDITOR'S NOTE: Multiple anon. techniques applied on an IE at the same time is indicated with multiple elements of the same type (in application order as in PSAMP)] [EDITOR'S NOTE: for blackmarking we'll recommend not to export the information at all following the data protection law principle that only necessary information should be exported.] Boschi & Trammell Expires July 16, 2009 [Page 13] Internet-Draft IP Flow Anonymisation Support January 2009 8. Security Considerations [TODO: write this section.] 9. IANA Considerations This document contains no actions for IANA. 10. Acknowledgments We thank Paul Aitken for his comments and insight, and the PRISM project for its support of this work. 11. References 11.1. Normative References [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. 11.2. Informative References [I-D.ietf-ipfix-as] Zseby, T., "IPFIX Applicability", draft-ietf-ipfix-as-12 (work in progress), July 2007. [I-D.ietf-ipfix-architecture] Sadasivan, G., "Architecture for IP Flow Information Export", draft-ietf-ipfix-architecture-12 (work in progress), September 2006. [I-D.ietf-ipfix-file] Trammell, B., Boschi, E., Mark, L., Zseby, T., and A. Wagner, "Specification of the IPFIX File Format", draft-ietf-ipfix-file-03 (work in progress), October 2008. [I-D.ietf-ipfix-mediators-framework] Kobayashi, A., Nishida, H., and B. Claise, "IPFIX Mediation: Framework", draft-ietf-ipfix-mediators-framework-01 (work in Boschi & Trammell Expires July 16, 2009 [Page 14] Internet-Draft IP Flow Anonymisation Support January 2009 progress), November 2008. [RFC3917] Quittek, J., Zseby, T., Claise, B., and S. Zander, "Requirements for IP Flow Information Export (IPFIX)", RFC 3917, October 2004. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. Authors' Addresses Elisa Boschi Hitachi Europe c/o ETH Zurich Gloriastrasse 35 8092 Zurich Switzerland Phone: +41 44 632 70 57 Email: elisa.boschi@hitachi-eu.com Brian Trammell Hitachi Europe c/o ETH Zurich Gloriastrasse 35 8092 Zurich Switzerland Phone: +41 44 632 70 13 Email: brian.trammell@hitachi-eu.com Boschi & Trammell Expires July 16, 2009 [Page 15]