]> Hitachi Europe

c/o ETH Zurich Gloriastrasse 35 8092 Zurich Switzerland +41 44 632 70 13 brian.trammell@hitachi-eu.com

Hitachi Europe

c/o ETH Zurich Gloriastrasse 35 8092 Zurich Switzerland +41 44 632 70 57 elisa.boschi@hitachi-eu.com

Fraunhofer IFAM

Weiner Str. 12 38259 Bremen Germany +49 421 2246206 lutz.mark@ifam.fraunhofer.de

Fraunhofer Institute for Open Communication Systems

Kaiserin-Augusta-Allee 31 10589 Berlin Germany +49 30 3463 7153 tanja.zseby@fokus.fraunhofer.de

ETH Zurich

Gloriastrasse 35 8092 Zurich Switzerland +41 44 632 70 04 arno@wagner.name

Operations IPFIX Working Group This document describes a file format for the storage of flow data based upon the IPFIX Protocol. It proposes a set of requirements for flat-file, binary flow data file formats, then specifies the IPFIX File format to meet these requirements based upon IPFIX Messages. This IPFIX File format is designed to facilitate interoperability and reusability among a wide variety of flow storage, processing, and analysis tools.

This document specifies a file format based upon IPFIX, designed to facilitate interoperability and reusability among a wide variety of flow storage, processing, and analysis tools. It begins with an overview of the IPFIX File format, and a quick summary of how IPFIX Files work in . The detailed specification of the IPFIX File format appears in ; this section includes general specifications for IPFIX File Readers and IPFIX File Writers and specific recommendations for common situations in which they are used. The format makes use of the IPFIX Options mechanism for additional file metadata, in order to avoid requiring any protocol extensions, and to minimize the effort required to adapt IPFIX implementations to use the file format; a detailed definition of the Options Templates used for storage metadata appears in . and provide specific recommendations for error resilience during long-term storage and integration of IPFIX File data with other formats. contains a detailed example IPFIX File. These sections are intended to give additional information to implementors of IPFIX Files. The IPFIX File format was designed to be applicable to a wide variety of flow storage situations; the motivation behind its creation is described in . The document outlines of the set of requirements the format is designed to meet in , and explores the applicability of such a format to various specific application areas in . These sections are intended to give background on the development of IPFIX Files.

"Specification of the IPFIX Protocol for the Exchange of IP Traffic Flow Information" and its associated documents define the IPFIX Protocol, which provides network engineers and administrators with access to IP traffic flow information. "Architecture for IP Flow Information Export" 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". 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" describes the Information Elements used by IPFIX, including details on Information Element naming, numbering, and data type encoding. "IPFIX Applicability" 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. In addition, "Exporting Type Information for IPFIX Information Elements" specifies a method for encoding Information Model properties within an IPFIX Message stream. This document references and the architecture document for terminology, defines IPFIX File Writer and IPFIX File Reader in terms of the IPFIX Exporting Processes and IPFIX Collecting Process definitions from , and extends the IPFIX Information Model defined in to provide new Information Elements for IPFIX File metadata. It uses the method described in "Exporting Type Information for IPFIX Information Elements" document to support the self-description of IPFIX Files containing enterprise-specific Information Elements.

This section defines terminology related to the IPFIX File Format. In addition, terms used in this document that are defined in the Terminology section of are to be interpreted as defined there. An IPFIX File is a serialized stream of IPFIX Messages; this stream may be stored on a filesystem or transported using any technique customarily used for files. Any IPFIX Message stream that would be considered valid when transported one or more of the specified IPFIX transports (SCTP, TCP, or UDP) as defined in is considered an IPFIX File. However, this document extends that definition with recommendations on the construction of IPFIX Files that meet the requirements identified in . An IPFIX File Reader is a process which reads IPFIX Files from a filesystem. An IPFIX File Reader operates as an IPFIX Collecting Process as specified in , except as modified by this document. An IPFIX File Writer is a process which writes IPFIX Files to a filesystem. An IPFIX File Writer operates as an IPFIX Exporting Process as specified in , except as modified by this document. 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 .

An IPFIX File is simply a data stream containing one or more IPFIX Messages serialized to some filesystem. Though any set of valid IPFIX Messages can be serialized into an IPFIX File, the specification includes guidelines designed to ease storage and retrieval of flow data using the IPFIX File format. IPFIX Files contain only IPFIX Messages; any file metadata such as checksums or export session details are stored using Options within the IPFIX Message. This design has several advantages, including complete compatibility with the IPFIX Protocol on the wire and free manipulability of IPFIX Files through concatenation, appending, and splitting (on IPFIX Message boundaries). A schematic of a typical IPFIX File is shown below:

There is a wide variety of applications for the file-based storage of IP flow data, across a continuum of time scales. Tools used in the analysis of flow data and creation of analysis products often use files as a convenient unit of work, with an ephemeral lifetime. A set of flows relevant to a security investigation may be stored in a file for the duration of that investigation, and further exchanged among incident handlers via email or within an external incident handling workflow application. Sets of flow data relevant to Internet measurement research may be published as files, much as libpcap packet trace files are, to provide common datasets for the repeatability of research efforts; these files would have lifetimes measured in months or years. Operational flow measurement systems also have a need for long-term, archival storage of flow data, either as a primary flow data repository, or as a backing tier for online storage in a relational database management system (RDBMS). The variety of applications of flow data, and the variety of presently deployed storage approaches, indicates the need for a standard approach to flow storage with applicability across the continuum of time scales over which flow data is stored. A storage format based around flat files would best address the variety of storage requirements. While much work has been done on structured storage via RDBMS, relational database systems are not a good basis for format standardization owing to the fact that their internal data structures are generally private to a single implementation and subject to change for internal reasons. Also, there are a wide variety of operations available on flat files, and external tools and standards can be leveraged to meet file-based flow storage requirements. Further, flow data is often not very semantically complicated, and is managed in very high volume; therefore, an RDBMS-based flow storage system would not benefit much from the advantages of relational database technology. The simplest way to create a new file format is simply to serialize some internal data model to disk, with either textual or binary representation of data elements, and some framing strategy for delimiting fields and records. "Ad-hoc" file formats such as this have several important disadvantages. They impose the semantics of the data model from which they are derived on the file format, and as such, they are difficult to extend, describe, and standardize. Indeed, one de facto standard for the storage of flow data is one of these ad-hoc formats. A common method of storing data collected via Cisco NetFlow is to serialize a stream of raw NetFlow datagrams into files. These NetFlow PDU files consist of a collection of header-prefixed blocks (corresponding to the datagrams as received on the wire) containing fixed-length binary flow records. NetFlow V5, V7, and V8 data may be mixed within a given file, as the header on each datagram defines the NetFlow version of the records following. While this NetFlow PDU file format has all the disadvantages of an ad-hoc format, and is not extensible to data models other than that defined by Cisco NetFlow, it is at least reasonably well-understood due to its ubiquity. Over the past decade XML markup has emerged as a new "universal" representation format for structured data. It is intended to be human-readable; indeed, that is one reason for its rapid adoption. However XML has limited usefulness for representing network flow data. Network flow data has a simple, repetitive, non-hierarchical structure that does not benefit much from XML. An XML representation of flow data would be an essentially flat list of the attributes and their values for each flow record. The XML approach to data encoding is very heavyweight when compared to binary flow encoding. XML's use of start- and end-tags, and plain-text encoding of the actual values, leads to significant inefficiency in encoding size. Typical network traffic datasets can contain millions or billions of flows per hour of traffic represented. Any increase in storage size per record can have dramatic impact on flow data storage and transfer sizes. While data compression algorithms can partially remove the redundancy introduced by XML encoding, they introduce additional overhead of their own. A further problem is that XML processing tools require a full XML parser. XML parsers are fully general and therefore complex, resource-intensive and relatively slow, introducing significant processing time overhead for large network-flow datasets. In contrast, parsers for typical binary flow data encodings are simply structured, since they only need to parse a very small header and then have complete knowledge of all following fields for the particular flow. These can then be read in a very efficient linear fashion. This leads us to propose the IPFIX Message format as the basis for a new flow data file format. The IPFIX working group, in defining the IPFIX Protocol, has already defined an information model and data formatting rules for representation of flow data. Especially at shorter time scales, when a file is a unit of data interchange, the filesystem may be viewed as simply another IPFIX Message transport between processes. This format is especially well suited to representing flow data, as it was designed specifically for flow data export; it is easily extensible unlike ad-hoc serialization, and compact unlike XML. In addition, IPFIX is an IETF standard for the export and collection of flow data; using a common format for storage and analysis at the collection side allows implementors to use substantially the same information model and data formatting implementation for transport as well as storage.

In this section, we outline a proposed set of requirements for any persistent storage format for flow data. First and foremost, a flow data file format should support storage across the continuum of time scales important to flow storage applications. Each of the requirements enumerated in the sections below is broadly applicable to flow storage applications, though each may be more important at certain time scales. For each, we first identify the requirement, then explain how the IPFIX Message format addresses it, or briefly outline the changes that must be made in order for an IPFIX-based file format to meet the requirement.

Due to the wide variety of flow attributes collected by different network flow attribute measurement systems, the ideal flow storage format will not impose a single data model or a specific record type on the flows it stores. The file format must be flexible and extensible; that is, it must support the definition of multiple record types within the file itself, and must be able to support new field types for data within the records in a graceful way. IPFIX provides record format flexibility through the use of Templates to describe each Data Record, through the use of an IANA Registry to define its Information Elements, and through the use of enterprise-specific Information Elements.

Archived data may be read at a time in the future where any external reference to the meaning of the data may be lost. The ideal flow storage format should be self-describing; that is, a process reading flow data from storage should be able to properly interpret the stored flows without reference to anything other than standard sources (e.g., the standards document describing the file format) and the stored flow data itself. The IPFIX Message format is partially self-describing; that is, IPFIX Templates containing only IANA-assigned Information Elements can be completely interpreted according to the IPFIX Information Model without additional external data. However, Templates containing private information elements lack detailed type and semantic information; a Collecting Process receiving Data Records described by a Template containing enterprise-specific Information Elements it does not understand can only treat the data contained within those Information Elements as octet arrays. To be fully self-describing, enterprise-specific Information Elements must be additionally described via IPFIX Options according to the Information Element Type Options Template defined in "Exporting Type Information for IPFIX Information Elements".

Regardless of the representation format, flow data describing traffic on real networks tends to be highly compressible. Compression tends to improve the scalability of flow collection systems, by reducing the disk storage and I/O bandwidth requirement for a given workload. The ideal flow storage format should support applications which wish to leverage this fact by supporting compression of stored data. The IPFIX Message format has no support for data compression, as the IPFIX protocol was designed for speed and simplicity of export. Of course, any flat file is readily compressible using a wide variety of external data compression tools, formats, and algorithms; therefore, this requirement can be met externally. However, a couple of simple optimizations can be made by File Writers to increase the integrity and usability of compressed IPFIX data; these are outlined in .

Binary, record stream oriented file formats natively support only one form of searching, sequential scan in file order. By choosing the order of records in a file carefully (e.g., by flow end time), a file can be indexed by a single key. Beyond this, properly addressing indexing is an application-specific problem, as it inherently involves tradeoffs between storage complexity and retrieval speed, and requirements vary widely based on time scales and the types of queries used from site to site. However, a generic standard flow storage format may provide limited direct support for indexing and searching. The ideal flow storage format will support a limited table of contents facility noting that the records in a file contain data relating only to certain keys or values of keys, in order to keep multi-file search implementations from having to scan a file for data it does not contain. The IPFIX Message format has no direct support for indexing. However, the technique described in "Reducing Redundancy in IPFIX and PSAMP Reports" can be used to describe the contents of a file in a limited way. Additionally, as flow data is often sorted and divided by time, the start and end time of the flows in a file may be declared using the File Time Window Options Template defined in .

When storing flow data for archival purposes, it is important to ensure that hardware or software faults do not introduce errors into the data over time. The ideal flow storage format will support the detection and correction of encoding-level errors in the data. Note that more advanced error correction is best handled at a layer below that addressed by this document. Error correction is a topic well addressed by the storage industry in general (e.g. by RAID and other technologies), and by specifying a flow storage format based upon files, we can leverage these features to meet this requirement. However, the ideal flow storage format will be resilient against errors, providing an internal facility for the detection of errors and the ability to isolate errors to as few data records as possible. Note that this requirement interacts with the choice of data compression or encryption algorithm. The use of block compression algorithms can serve to isolate errors to a single compression block, unlike stream compressors, which may fail to resynchronize after a single bit error, invalidating the entire message stream. Similarly, the use of a stream cipher can serve to isolate errors in the plaintext without amplifying them as, for example, a cipher in CBC mode can. See the "Recommended Compression Error Resilience Strategy" and "Recommended Encryption Error Resilience Strategy" sections below for more on this interaction. The IPFIX Message format does not support data integrity assurance. It is assumed that advanced error correction will be provided externally. For simple error detection support, checksums may be attached to messages via IPFIX Options according to the Message Checksum Options Template defined in .

Archival storage of flow data may also require assurance that no unauthorized entity can read or modify the stored data. Asymmetric-key cryptography can be applied to this problem, by signing flow data with the private key of the creator, and encrypting it with the public keys of those authorized to read it. The ideal flow storage format will support the encryption and signing of flow data. As with error correction, this problem has been addressed well at a layer below that addressed by this document. Instead of specifying a particular choice of encryption technology, we can leverage the fact that existing cryptographic technologies work quite well on data stored in files to meet this requirement. Beyond support for the use of TLS for transport over TCP or DTLS for transport over SCTP or UDP, both of which provide transient authentication and confidentiality, the IPFIX protocol does not support this requirement directly. It is assumed that this requirement will be met externally.

To ensure the privacy of individuals and organizations at the endpoints of communications represented by flow records, it is often necessary to obfuscate or anonymize stored and exported flow data. The ideal flow storage format will provide for a notation that a given information element on a given record type represents anonymized, rather than real, data. The IPFIX Protocol presently has no support for anonymization notation. It should be noted that anonymization is one of the requirements given for IPFIX in . The decision to qualify this requirement with 'MAY' and not 'MUST' in the requirements document, and its subsequent lack of specification in the current version of the IPFIX protocol, is due to the fact that anonymization algorithms are still an open area of research, and that there currently exist no standardized methods for anonymization. No support is presently defined in or this IPFIX-based File Format for anonymization, as anonymization notation is an area of open work for the IPFIX working group.

Certain use cases for archival flow storage require the storage of collection infrastructure details alongside the data itself. These details include information about how and when data was received, and where it was received from, and are useful for auditing as well as for the replaying received data for testing purposes. The IPFIX Protocol contains no direct support for auditability and replayability, though the IPFIX Information Model does define various Information Elements required to represent collection infrastructure details. These details may be stored in IPFIX Files using the Export Session Details Options Template defined in and the Message Details Options Template defined in .

The ideal standard flow storage format will not have a significant negative impact on the performance of the application generating or processing flow data stored in the format. This is a non-functional requirement, but it is important to note that a standard that implies a significant performance penalty is unlikely to be widely implemented and adopted. An examination of the IPFIX Protocol would seem to suggest that implementations of it are not particularly prone to slowness; indeed, a template-based data representation is more easily subject to optimization for common cases than representations that embed structural information directly in the data stream (e.g. XML). However, a full analysis of the impact of using IPFIX Messages as a basis for flow data storage on read/write performance will require more implementation experience and performance measurement.

This section describes the specific applicability of IPFIX Files to various use cases. IPFIX Files are particularly useful in a flow collection and processing infrastructure using IPFIX for flow export. We explore the applicability and provide guidelines for using IPFIX files for the storage of flow data collected by IPFIX Collecting Processes and NetFlow V9 collectors, the testing of IPFIX Collecting Processes, and diagnostics of IPFIX Devices.

IPFIX Files can naturally be used to store flow data collected by an IPFIX Collecting Process; indeed, this was one of the primary initial motivations behind the file format described within this document. Using IPFIX Files as such provides a single, standard, well-understood encoding to be used for flow data on disk and on the wire, and allows IPFIX implementations to leverage substantially the same code for flow export and flow storage. In addition, the storage of single Transport Sessions in IPFIX Files is particularly important for network measurement research, allowing repeatability of experiments by providing a format for the storage and exchange of IPFIX flow trace data much as the libpcap format is used for experiments on packet trace data.

Although the IPFIX protocol is based on the Cisco Netflow Services, Version 9 (NetFlow V9) protocol, the two have diverged since work began on IPFIX. However, since the NetFlow V9 information model is a compatible subset of the IPFIX information model, it is possible to use IPFIX files to store collected NetFlow V9 flow data. This approach may be particularly useful in multi-vendor, multi-protocol collection infrastructures using both NetFlow V9 and IPFIX to export flow data. The applicability of IPFIX Files to this use case is outlined in .

IPFIX Files can be used to store IPFIX Messages for the testing of IPFIX Collecting Processes. A variety of test cases may be stored in IPFIX Files. First, IPFIX data collected in real network environments and stored in an IPFIX File can be used as input to check the behavior of new or extended implementations of IPFIX Collectors. Furthermore, IPFIX Files can be used to validate the operation of a given IPFIX Collecting Process in a new environment, i.e., to test with recorded IPFIX data from the target network before installing the Collecting Process in the network. The IPFIX File format can also be used to store artificial, non-compliant reference messages for specific Collecting Process test cases. Examples for such test cases are sets of IPFIX records with undefined Information Elements, Data Records described by missing Templates, or incorrectly framed Messages or Data Sets. Representative error handling test cases are defined in "IPFIX Testing". Furthermore, fast replay of IPFIX Messages stored in a file can be used for stress/load tests (e.g., high rate of incoming Data Records, large Templates with high Information Element counts), as described in "IPFIX Testing". The provisioning and use of a set of reference files for testing simplifies the performance of tests and increases the comparability of test results.

As an IPFIX File can be used store any collection of flows, the format may also be used for dumping and storing various types of flow data for IPFIX Device diagnostics (e.g., the open flow cache of a Metering Process or the flow backlog of an Exporting or Collecting Process at the time of a process reset or crash). File-based storage is preferable to remote transmission in such error-recovery situations.

Any valid serialized IPFIX Message stream MUST be accepted by a File Reader as a valid IPFIX File. In this way, the filesystem is simply treated as another IPFIX transport alongside SCTP, TCP, and UDP, albeit a potentially high-latency transport, as the File Reader and File Writer do not necessarily run at the same time. This section specifies the detailed actions of File Readers and File Writers in handling IPFIX Files, and further specifies actions of File Writers in specific use cases. Unless otherwise specified herein, IPFIX File Writers MUST behave as IPFIX Exporting Processes, and IPFIX File Readers MUST behave as IPFIX Collecting Processes, where appropriate.

An IPFIX File Reader MUST act as an IPFIX Collecting Process as specified in , except as modified by this document. An IPFIX File Reader MUST accept as valid any serialized IPFIX Message stream that would be considered valid by one or more of the other defined IPFIX transport layers. Practically, this means that the union of IPFIX Template management features supported by SCTP, TCP, and UDP MUST be supported in IPFIX Files. File Readers MUST: accept IPFIX Messages containing Template Sets, Options Template Sets, and Data Sets within the same message, as with IPFIX over TCP or UDP; accept Template Sets that define Templates already defined within the File, as may occur with retransmission of Templates when using IPFIX over UDP as described in section 10.3.6 of ; resolve any conflict between a resent definition and a previous definition by assuming that the new Template replaces the old, as consistent with Template expiration and ID reuse when using UDP at the IPFIX transport protocol; and accept Template Withdrawals as described in section 8 of , provided that the Template to be withdrawn is defined, as is the case with IPFIX over TCP and SCTP. Considering the filesystem-as-transport view, in the general case an IPFIX File SHOULD be treated as containing a single Transport Session as defined by . However, some applications may benefit from the ability to treat a collection of IPFIX Files as a single Transport Session; see especially below. A File Reader MAY be configurable to treat a collection of Files as a single Transport Session. However, a File Reader MUST NOT treat a single IPFIX File as containing multiple Transport Sessions. If an IPFIX File uses the technique described in "Reducing Redundancy in IPFIX and PSAMP Reports" AND all of the non-Options Templates in the File contain the commonPropertiesId Information Element, a File Reader MAY assume the set of commonPropertiesId definitions provides a complete table of contents for the File for searching purposes.

An IPFIX File Writer MUST act as an IPFIX Exporting Process as specified in , except as modified by this document. This section contains specifications for IPFIX File Writers in all situations; specifications and recommendations for specific File Writer use cases are found in below. File Writers SHOULD store the Templates and Options required to decode the data within the File in the File itself, unless modified by the requirements of a specific use case in a subsection of . In this way, a single IPFIX File generally contains a single notional Transport Session as defined by . File Writers SHOULD emit each Template Set or Options Template Set to appear in the File before any Data Set described by the Templates within that Set, to ensure the File Reader can decode every Data Set without waiting to process subsequent Templates or Options Templates. File Writers SHOULD emit Data Records described by Options Templates to appear in the File before any Data Records which depend on the scopes defined by those options. File Writers SHOULD use Template Withdrawals to withdraw Templates if Template IDs need to be reused. Template Withdrawals SHOULD NOT be used unless necessary to reuse Template IDs. File Writers SHOULD write IPFIX Messages within an IPFIX File in ascending Export Time order. File Writers MAY write Data Records to an IPFIX File in any order. However, File Writers that write flow records to an IPFIX File in flowStartTime or flowEndTime order SHOULD be consistent in this ordering within each File.

The specifications in this section apply to specific situations. Each section below extends or modifies the base File Writer specification in . Considerations for collocation of a File Writer with IPFIX Collecting Processes and Metering Processes are given, as are specific guidelines for using IPFIX Files for archival storage, or as documents. Also covered are the use of IPFIX Files in the testing and diagnostics of IPFIX Devices.

When collocating a File Writer with an IPFIX Collecting Process for archival storage of collected data in IPFIX Files as described in , the following recommendations may improve the usefulness of the stored data. The simplest way for a File Writer to store the data collected in a single Transport Session is to simply write the incoming IPFIX Messages to an IPFIX File as they are collected. This approach has several drawbacks. First, if the original Exporting Process did not conform to the recommendations in with respect to Template and Data Record ordering, the written file can be difficult to use later; in this case, File Writers MAY reorder records as received in order to ensure that Templates appear before the Data Records they describe. A File Writer collocated with a Collecting Process that starts writing data from a running Transport Session SHOULD write all the Templates currently active within that Transport Session before writing any Data Records described by them. Also, the resulting IPFIX Files will lack information about the IPFIX Transport Session used to export them, such as the network addresses of the Exporting and Collecting Processes and the protocols used to transport them. In this case, if information about the Transport Session is required, the File Writer SHOULD store a single IPFIX Transport Session in an IPFIX File and SHOULD record information about the Transport Session using the Export Session Details Options Template described in . Additional per-Message information MAY be recorded by the File Writer using the Message Details Options Template described in . Per-Message information includes the time at which each IPFIX Message was received at the Collecting Process, and can be used to resend IPFIX Messages while keeping the original measurement plane traffic profile. When collocating a File Writer with a Collecting Process, the Export Time of each Message SHOULD be the Export Time of the Message received by the Collecting Process containing the first Data Record in the Message. Note that File Writers storing IPFIX data collected from an IPFIX Collecting Process using SCTP as the transport protocol SHOULD interleave messages from multiple streams in order to preserve Export Time order, and SHOULD reorder the written messages as necessary to ensure that each Template Set or Options Template Set appears in the File before any Data Set described by the Templates within that Set. Template reordering MUST preserve the sequence of Template Sets with Template Withdrawals in order to ensure consistency of Templates. Note that when adding additional information to IPFIX Messages received from Collecting Processes (e.g. Message Checksum Options, Message Detail Options), the File Writer SHOULD extend the length of the Message for the additional data if possible; otherwise, the Message SHOULD be split into two approximately equal-size Messages aligned on a Data Set or Template Set boundary from the original Message if possible; otherwise, the Message SHOULD be split into approximately two equal size Messages aligned on a Data Record boundary. Note that, since the MSS or MTU of most network links (1500-9000 for common Ethernets) is smaller than the maximum IPFIX Message size (65536) within an IPFIX File, it is expected that message length extension will suffice in most circumstances.

Note that File Writers may also be collocated directly with IPFIX Metering Processes, for writing measured information directly to disk without intermediate IPFIX Exporting or Collecting Processes. This arrangement may be particularly useful when providing data to an analysis environment with an IPFIX File based workflow, or when testing Metering Processes during development. When collocating a File Writer with a Metering Process, note that Information Elements associated with Exporting or Collecting Processes are meaningless, and SHOULD NOT appear in the Export Session Details Options Template described in or the Message Details Options Template described in . When collocating a File Writer with an Metering Process, the Export Time of each Message SHOULD be the time at which the first Data Record in the Message was received from the Metering Process.

While in the general case File Writers should store one Transport Session per IPFIX File, some applications storing large collections of data over long periods of time may benefit from the ability to treat a collection of IPFIX Files as a single Transport Session. A File Writer MAY be configurable to write data from a single Transport Session into multiple IPFIX Files; however, File Writers supporting such a configuration option MUST provide a configuration option to support one-file-per-session behavior for interoperability purposes. File Writers compressing or encrypting archival data and File Readers reading compressed or encrypted archival data SHOULD follow the recommendations in .

When IPFIX Files are used as documents, to store a set of flows relevant to query, investigation, or other common context, or for the publication of traffic datasets relevant to network research, each File MUST be readable as a single Transport Session, self-contained and making no reference to metadata stored in separate Files, in order to ensure interoperability. When writing Files to be used as documents, File Writers MAY emit the special Data Records described by Options Templates before any other Data Records in the File in the following order to ease the inspection and use of documents by File Readers: Time Window records described by the File Time Window Options Template as defined in below; followed by Information Element Type Records as described in "Exporting Type Information for IPFIX Information Elements"; followed by commonPropertiesId definitions as described in "Reducing Redundancy in IPFIX and PSAMP Reports"; followed by Export Session details records described by the Export Session Details Options Template as defined in below. The Export Time of each Message within a File used as a document SHOULD be the time at which the Message was written by the File Writer. If an IPFIX File used as a document uses the technique described in "Reducing Redundancy in IPFIX and PSAMP Reports" AND all of the non-Options Templates in the File contain the commonPropertiesId Information Element, a File Reader MAY assume the set of commonPropertiesId definitions provides a complete table of contents for the File for searching purposes.

IPFIX Files can be used for testing IPFIX Collecting Processes in two ways. First, IPFIX Files can be used to store specific flow data for regression and stress testing of Collectors; there are no special considerations for IPFIX Files used in this way. Second, IPFIX Files are useful for storing reference messages which do not comply to the IPFIX Protocol in order to test the error handling and recovery behavior of Collectors. Of course, IPFIX Files intended to be used in this application necessarily MAY violate any of the specifications in this document or in , and such Files MUST NOT be transmitted to Collecting Processes or given as input File Readers not under test. Note that an extremely simple IPFIX Exporting Process may be crafted for testing purposes by simply reading an IPFIX File and transmitting it directly to a Collecting Process. Similarly, an extremely simple Collecting Process may be crafted for testing purposes by simply accepting connections and/or IPFIX Messages from Exporting Processes and writing the session's message stream to an IPFIX File.

IPFIX Files can be used in the debugging of devices which use flow data as internal state, as a common format for the representation of flow tables. In such situations, the opaqueOctets information element can be used to store additional non-IPFIX encoded, non-flow information (e.g., stack backtraces, process state, etc.) within the IPFIX File as in ; the IPFIX flow table information could also be embedded in a larger proprietary diagnostic format using delimiters as in

This section defines the Options Templates used for IPFIX File metadata, and the Information Elements they require.

The following Options Templates allow IPFIX Message streams to meet the requirements outlined above without extension to the message format or protocol. They are defined in terms of existing Information Elements defined in , the Information Elements defined in "Exporting Type Information for IPFIX Information Elements", as well as Information Elements defined in . IPFIX File Readers and Writers SHOULD support these Options Templates as defined below. In addition, IPFIX File Readers and Writers SHOULD support the Options Templates defined in "Exporting Type Information for IPFIX Information Elements" in order to support self-description of enterprise-specific Information Elements.

The Message Checksum Options Template specifies the structure of a Data Record for attaching an MD5 message checksum to an IPFIX Message. An MD5 message checksum as described MAY be used if data integrity is important to the application. The described Data Record MUST appear only once per IPFIX Message, but MAY appear anywhere within the Message. This Options Template SHOULD contain the following Information Elements: IE Description messageScope [scope] A marker denoting this Option applies to the whole IPFIX Message; content is ignored. This Information Element MUST be defined as a Scope Field. messageMD5Checksum The MD5 checksum of the containing IPFIX Message.

The File Time Window Options Template specifies the structure of a Data Record for attaching a time window to an IPFIX File; this Data Record is referred to as a time window record. A time window record defines the earliest flow start time and the latest flow end time of the flow records within a File. One and only one time window record MAY appear within an IPFIX File if the time window information is available; a File Writer MUST NOT write more than one time window record to an IPFIX File. A File Writer that writes a time window record to a File MUST NOT write any Flow with a start time before the beginning of the window or an end time after the end of the window to that File. This Options Template SHOULD contain the following Information Elements: IE Description sessionScope [scope] A marker denoting this Option applies to the whole IPFIX Transport Session (i.e., the IPFIX File in the common case); content is ignored. This Information Element MUST be defined as a Scope Field. minFlowStart* Exactly one of minFlowStartSeconds, minFlowStartMilliseconds, minFlowStartMicroseconds, or minFlowStartNanoseconds; SHOULD match the precision of the accompanying maxFlowEnd* Information Element. The start time of the earliest flow in the Transport Session (i.e., File). maxFlowEnd* Exactly one of maxFlowEndSeconds, maxFlowEndMilliseconds, maxFlowEndMicroseconds, or maxFlowEndNanoseconds; SHOULD match the precision of the accompanying minFlowStart* Information Element. The end time of the latest flow in the Transport Session (i.e., File).

The Export Session Details Options Template specifies the structure of a Data Record for recording the details of an IPFIX Transport Session in an IPFIX File. It is intended for use in storing a single complete IPFIX Transport Session in a single IPFIX File. The described Data Record SHOULD appear only once in a given IPFIX File. This Options Template SHOULD contain at least the following Information Elements, subject to applicability as noted on each Information Element: IE Description sessionScope [scope] A marker denoting this Option applies to the whole IPFIX Transport Session (i.e., the IPFIX File in the common case); content is ignored. This Information Element MUST be defined as a Scope Field. exporterIPv4Address IPv4 address of the IPFIX Exporting Process from which the Messages in this Transport Session were received. Present only for Exporting Processes with an IPv4 interface. For multi-homed SCTP associations, this SHOULD be the primary path endpoint address of the Exporting Process. exporterIPv6Address IPv6 address of the IPFIX Exporting Process from which the Messages in this Transport Session were received. Present only for Exporting Processes with an IPv6 interface. For multi-homed SCTP associations, this SHOULD be the primary path endpoint address of the Exporting Process. exporterTransportPort The source port from which the Messages in this Transport Session were received. collectorIPv4Address IPv4 address of the IPFIX Collecting Process which received the Messages in this Transport Session. Present only for Collecting Processes with an IPv4 interface. For multi-homed SCTP associations, this SHOULD be the primary path endpoint address of the Collecting Process. collectorIPv6Address IPv6 address of the IPFIX Collecting Process which received the Messages in this Transport Session. Present only for Collecting Processes with an IPv6 interface. For multi-homed SCTP associations, this SHOULD be the primary path endpoint address of the Collecting Process. collectorTransportPort The destination port on which the Messages in this Transport Session were received. collectorTransportProtocol The IP Protocol Identifier of the transport protocol used to transport Messages within this Transport Session. collectorProtocolVersion The version of the export protocol used to transport Messages within this Transport Session. Applicable only in mixed NetFlow V9-IPFIX collection environments when storing NetFlow V9 data in IPFIX Messages, as in minExportSeconds The Export Time of the first Message in the Transport Session. maxExportSeconds The Export Time of the last Message in the Transport Session.

The Message Details Options Template specifies the structure of a Data Record for attaching additional export details to an IPFIX Message. These details include the time at which a message was received and information about the export and collection infrastructure used to transport the Message. This Options Template also allows the storage of the export session metadata provided the Export Session Details Options Template, for storing information from multiple Transport Sessions in the same IPFIX File. This Options Template SHOULD contain at least the following Information Elements, subject to applicability as noted for each Information Element. Note that when used in conjunction with the Export Session Details Options Template, when storing a single complete IPFIX Transport Session in an IPFIX File, this Options Template SHOULD contain only the messageScope and collectionTimeMilliseconds Information Elements, and the exportSctpStreamId Information Element for Messages transported via SCTP. IE Description messageScope [scope] A marker denoting this Option applies to the whole IPFIX message; content is ignored. This Information Element MUST be defined as a Scope Field. collectionTimeMilliseconds The absolute time at which this Message was received by the IPFIX Collecting Process. exporterIPv4Address IPv4 address of the IPFIX Exporting Process from which this Message was received. Present only for Exporting Processes with an IPv4 interface, and if this information is not available via the Export Session Details Options Template. For multi-homed SCTP associations, this SHOULD be the primary path endpoint address of the Exporting Process. exporterIPv6Address IPv6 address of the IPFIX Exporting Process this Message was received. Present only for Exporting Processes with an IPv6 interface, and if this information is not available via the Export Session Details Options Template. For multi-homed SCTP associations, this SHOULD be the primary path endpoint address of the Exporting Process. exporterTransportPort The source port from which this Message received. Present only if this information is not available via the Export Session Details Options Template. collectorIPv4Address IPv4 address of the IPFIX Collecting Process which received this Message. Present only for Collecting Processes with an IPv4 interface, and if this information is not available via the Export Session Details Options Template. For multi-homed SCTP associations, this SHOULD be the primary path endpoint address of the Collecting Process. collectorIPv6Address IPv6 address of the IPFIX Collecting Process which received this Message. Present only for Collecting Processes with an IPv6 interface, and if this information is not available via the Export Session Details Options Template. For multi-homed SCTP associations, this SHOULD be the primary path endpoint address of the Collecting Process. collectorTransportPort The destination port on which this Message was received. Present only if this information is not available via the Export Session Details Options Template. collectorTransportProtocol The IP Protocol Identifier of the transport protocol used to transport this Message. Present only if this information is not available via the Export Session Details Options Template. collectorProtocolVersion The version of the export protocol used to transport this Message. Present only if necessary and if this information is not available via the Export Session Details Options Template. exportSctpStreamId The SCTP stream used to transport this Message. Present only if the Message was transported via SCTP.

The following Information Elements are used by the Options Templates in to allow IPFIX Message streams to meet the requirements outlined above without extension of the protocol. IPFIX File Readers and Writers SHOULD support these Information Elements as defined below. In addition, IPFIX File Readers and Writers SHOULD support the Information Elements defined in "Exporting Type Information for IPFIX Information Elements" in order to support full self-description of Information Elements.

The absolute timestamp at which the data within the scope containing this Information Element was received by a Collecting Process. This Information Element SHOULD be bound to its containing IPFIX Message via IPFIX Options and the messageScope Information Element, as defined below. dateTimeMilliseconds TBD1 current

The value of the SCTP Stream Identifier used by the Exporting Process for exporting IPFIX Message data. This is carried in the Stream Identifier field of the header of the SCTP DATA chunk containing the IPFIX Message(s). unsigned16 identifier TBD2 current

The absolute Export Time of the latest IPFIX Message within the scope containing this Information Element. This Information Element SHOULD be bound to its containing IPFIX Transport Session via IPFIX Options and the sessionScope Information Element. dateTimeSeconds TBD3 current seconds

The latest absolute timestamp of the last packet within any Flow within the scope containing this Information Element, rounded up to the microsecond if necessary. This Information Element SHOULD be bound to its containing IPFIX Transport Session via IPFIX Options and the sessionScope Information Element. This Information Element SHOULD be used only in Transport Sessions containing Flow Records with microsecond-precision (or better) timestamp Information Elements. dateTimeMicroeconds TBD11 current microseconds

The latest absolute timestamp of the last packet within any Flow within the scope containing this Information Element, rounded up to the millisecond if necessary. This Information Element SHOULD be bound to its containing IPFIX Transport Session via IPFIX Options and the sessionScope Information Element. This Information Element SHOULD be used only in Transport Sessions containing Flow Records with millisecond-precision (or better) timestamp Information Elements. dateTimeMilliseconds TBD12 current milliseconds

The latest absolute timestamp of the last packet within any Flow within the scope containing this Information Element. This Information Element SHOULD be bound to its containing IPFIX Transport Session via IPFIX Options and the sessionScope Information Element. This Information Element SHOULD be used only in Transport Sessions containing Flow Records with nanosecond-precision timestamp Information Elements. dateTimeNanoseconds TBD13 current nanoseconds

The latest absolute timestamp of the last packet within any Flow within the scope containing this Information Element, rounded up to the second if necessary. This Information Element SHOULD be bound to its containing IPFIX Transport Session via IPFIX Options and the sessionScope Information Element. dateTimeSeconds TBD4 current seconds

The MD5 checksum of the IPFIX Message containing this record. This Information Element SHOULD be bound to its containing IPFIX Message via an options record and the messageScope Information Element, as defined below, and SHOULD appear only once in a given IPFIX Message. To calculate the value of this Information Element, first buffer the containing IPFIX Message, setting the value of this Information Element to all zeroes. Then caluclate the MD5 checksum of the resulting buffer as defined in , place the resulting value in this Information Element, and export the buffered message. octetArray (16 bytes) TBD5 current RFC 1321, The MD5 Message-Digest Algorithm

The presence of this Information Element as scope in an Options Template signifies that the options described by the Template apply to the IPFIX Message that contains them. It is defined for general purpose message scoping of options, and proposed specifically to allow the attachment a checksum to a message via IPFIX Options. The value of this Information Element MUST be written as 0 by the File Writer or Exporting Process. The value of this Information Element MUST be ignored by the File Reader or the Collecting Process. octet TBD6 current

The absolute Export Time of the earliest IPFIX Message within the scope containing this Information Element. This Information Element SHOULD be bound to its containing IPFIX Transport Session via an options record and the sessionScope Information Element. dateTimeSeconds TBD7 current seconds

The earliest absolute timestamp of the first packet within any Flow within the scope containing this Information Element, rounded down to the microsecond if necessary. This Information Element SHOULD be bound to its containing IPFIX Transport Session via an options record and the sessionScope Information Element. This Information Element SHOULD be used only in Transport Sessions containing Flow Records with microsecond-precision (or better) timestamp Information Elements. dateTimeMicroseconds TBD14 current microseconds

The earliest absolute timestamp of the first packet within any Flow within the scope containing this Information Element, rounded down to the millisecond if necessary. This Information Element SHOULD be bound to its containing IPFIX Transport Session via an options record and the sessionScope Information Element. This Information Element SHOULD be used only in Transport Sessions containing Flow Records with millisecond-precision (or better) timestamp Information Elements. dateTimeMilliseconds TBD15 current milliseconds

The earliest absolute timestamp of the first packet within any Flow within the scope containing this Information Element. This Information Element SHOULD be bound to its containing IPFIX Transport Session via an options record and the sessionScope Information Element. This Information Element SHOULD be used only in Transport Sessions containing Flow Records with nanosecond-precision timestamp Information Elements. dateTimeNanoseconds TBD16 current nanoseconds

The earliest absolute timestamp of the first packet within any Flow within the scope containing this Information Element, rounded down to the second if necessary. This Information Element SHOULD be bound to its containing IPFIX Transport Session via an options record and the sessionScope Information Element. dateTimeSeconds TBD8 current seconds

This Information Element is used to encapsulate non-IPFIX data into an IPFIX Message stream, for the purpose of allowing a non-IPFIX data processor to store a data stream inline within an IPFIX File. A Collecting Process or File Writer MUST NOT try to interpret this binary data. This Information Element differs from paddingOctets as its contents are meaningful in some non-IPFIX context, while the contents of paddingOctets MUST be 0x00 and are intended only for Information Element alignment. octet TBD9 current

The presence of this Information Element as scope in an Options Template signifies that the options described by the Template apply to the IPFIX Transport Session that contains them. Note that as all options are implicitly scoped to Transport Session and Observation Domain, this Information Element is equivalent to a "null" scope. It is defined for general purpose session scoping of options, and proposed specifically to allow the attachment of time window to an IPFIX File via IPFIX Options. The value of this Information Element MUST be written as 0 by the File Writer or Exporting Process. The value of this Information Element MUST be ignored by the File Reader or the Collecting Process. octet TBD10 current

This section describes recommended methods for making IPFIX Files resilient to errors during storage. It is intended primarily for applications using IPFIX Files for long-term archival storage of flow data.

Note that, since any file may be compressed and decompressed with a variety of widely available tools implementing a variety of compression standards (both specified and de facto), compression of IPFIX File data can be accomplished externally. However, compression at the file level is not particularly resilient to errors; in the worst case, a single bit error in a stream-compressed file may result in the loss of the entire file. To limit the impact of errors on the recoverability of compressed data, we recommend the use of block compression where possible. Ideally, the block compression algorithm should support the identification and isolation of blocks containing errors; bzip2 is an example of such a block compressor. Since the block boundary of a block-compressed IPFIX File may fall in the middle of an IPFIX Message, resynchronization of an IPFIX Message stream by a File Reader after a compression error requires some care. The beginning of an IPFIX Message may be identified by its header signature (the Version field of the Message Header, 0x00 0x0A, followed by a 16-bit Message Length), but simply searching for the first occurance of the Version field is insufficient, since these two bytes may occur in valid IPFIX Template or Data Sets. Therefore, we propose the following algorithm for File Readers to resynchronize an IPFIX Message Stream after skipping a compressed block containing errors: Search after the error for the first occurrence of the octet string 0x00, 0x0A (the IPFIX Message Header Version field.) Treat this field as the beginning of a candidate IPFIX Message. Read the two bytes following the Version field as a Message Length, and seek to that offset from the beginning of the candidate IPFIX Message. If the first two octets after the candidate IPFIX Message are 0x00, 0x0A (i.e., the IPFIX Message Header Version field of the next message in the stream), or if end-of-file is reached precisely at the end of the candidate IPFIX Message, presume that the candidate IPFIX Message is valid, and begin reading the IPFIX File from the start of the candidate IPFIX Message. If not, or if the seek reaches end-of-file or another block containing errors before finding the end of the candidate message, go back to step 1, starting the search two bytes from the start of the candidate IPFIX Message. The algorithm above will improperly identify a non-message as a message approximately 1 in 2^32 times, assuming random IPFIX data. It may be expanded to consider multiple candidate IPFIX Messages in order to increase reliability. In applications (e.g. archival storage) in which error resilience is very important, File Writers SHOULD use block compression algorithms, and MAY attempt to align IPFIX Messages within compression blocks to ease resynchronization after errors, if such is supported by the chosen block compressor. File Readers SHOULD use the resynchronization algorithm above to minimize data loss due to compression errors.

File-level encryption has error resilience issues similar to file-level compression. Single bit errors in the encrypted data stream can result in unreadability of the entire remaining file, dependent on the encryption method used. The use of CBC (Cipher Block Chaining) mode, which suffers from this low error resilience, is relatively common. In applications (e.g. archival storage) in which error resilience is very important, File Writers SHOULD use a stream cipher, for example a block cipher in OFB (Output Feedback) mode (often referred to as stream mode) instead of modes like CBC when encrypting, since errors are not amplified by stream ciphers: A single-bit error in the ciphertext results in a single bit error in the plaintext. Alternatively File Writers SHOULD use any other cipher which can resynchronize after bit errors. An example is a block cipher in CBC mode that is reinitialized after a specific amount of data has been encrypted. The maximum data loss per bit-error is then up to the next reinitialization point. In this case, File Writers SHOULD also use the Message Checksum Options Template to attach a checksum to each IPFIX Message in the IPFIX File, in order to support the recognition of errors in the decrypted data.

This section describes methods for integrating IPFIX File data with other file formats.

At times it may be useful to export or store non-IPFIX data inline in an IPFIX File or Message stream. To do this cleanly, this data must be encapsulated into IPFIX Messages so that an IPFIX File Reader or Collecting Process can handle it without any need to interpret it. At the same time, this data must not be changed during transmission or storage. The opaqueOctets Information Element as defined in is provided for this encapsulation. Processing the encapsulated non-IPFIX data is left to a separate processing mechanisms that can identify encapsulated non-IPFIX data in an IPFIX message stream, but need not have any other IPFIX handling capability, except the ability to skip over all IPFIX messages that do not encapsulate non-IPFIX data. The Message Checksum Options Template, described in may be used as a uniform mechanism to identify errors within encapsulated data. Note that this mechanism can only encapsulate data objects up to 65,515 octets in length. If the space available in one IPFIX Message is not enough for the amount of data to be encapsulated, then the data must be broken into smaller segments that are encapsulated into consecutive IPFIX Messages. Any additional structuring or semantics of the raw data is outside the scope of IPFIX and must be implemented within the encapsulated binary data itself. Furthermore, the raw encapsulated data cannot be assumed by an IPFIX File Reader to have any specific format.

Consequently, it may also be useful to reverse the encapsulation, that is, to export or store IPFIX data inline within a non-IPFIX file or data stream. This makes sense when the other file format is not compatible with the encapsulation described above in . Generally speaking, the encapsulation here will be specific to the format of the containing file. For example, IPFIX Files may be embedded in XML elements using hex or Base64 encoding, or in raw binary files using start and end delimiters or some form of run-length encoding. As there are as many potential encapsulations here as there are potential file formats, the specifics of each are out of scope for this specification.

The IPFIX File format itself does not directly introduce security issues. Rather it is used to store information which may for privacy or business reasons be considered sensitive. The file format must therefore provide appropriate procedures to guarantee the integrity and confidentiality of the stored information. The underlying protocol used to exchange the information that will be stored using the format proposed in this document must as well apply appropriate procedures to guarantee the integrity and confidentiality of the exported information. Such issues are addressed in . Implementors of IPFIX File Writers which store data taken from an IPFIX Collecting Process using TLS or DTLS for transport security should note that IPFIX Files may present a potential breach of confidentiality if IPFIX data collected using TLS or DTLS is stored in unencrypted files, and should consider providing an external file encryption option to mitigate this risk.

This document specifies the creation of several new IPFIX Information Elements in the IPFIX Information Element registry located at http://www.iana.org/assignments/ipfix, as defined in above. IANA has assigned the following Information Element numbers for their respective Information Elements as specified below: Information Element number TBD1 for the collectionTimeMilliseconds Information Element. Information Element number TBD2 for the exportSctpStreamId Information Element. Information Element number TBD3 for the maxExportSeconds Information Element. Information Element number TBD11 for the maxFlowEndMicroseconds Information Element. Information Element number TBD12 for the maxFlowEndMilliseconds Information Element. Information Element number TBD13 for the maxFlowEndNanoseconds Information Element. Information Element number TBD4 for the maxFlowEndSeconds Information Element. Information Element number TBD5 for the messageMD5Checksum Information Element. Information Element number TBD6 for the messageScope Information Element. Information Element number TBD7 for the minExportSeconds Information Element. Information Element number TBD14 for the minFlowStartMicroseconds Information Element. Information Element number TBD15 for the minFlowStartMilliseconds Information Element. Information Element number TBD16 for the minFlowStartNanoseconds Information Element. Information Element number TBD8 for the minFlowStartSeconds Information Element. Information Element number TBD9 for the opaqueOctets Information Element. Information Element number TBD10 for the sessionScope Information Element. [NOTE for IANA: The text TBDn should be replaced with the respective assigned Information Element numbers where they appear in this document.]

Thanks to Maurizio Molina, Tom Kosnar, and Andreas Kind for technical assistance with the requirements for a standard flow storage format. Thanks to Benoit Claise, Paul Aitken, Andrew Johnson, and Gerhard Muenz for their reviews and feedback.

&rfc5101; &rfc5102; &draftIpfixET; &rfc1321; &draftIpfixArch; &draftIpfixAS; &draftIpfixRR; &draftIpfixTesting; &rfc3954; &rfc3917; &rfc2119;

In this section we will explore an example IPFIX File which demonstrates the various features of the IPFIX File format. This File contains flow records described by a single Template. This File also contains a File Time Window record to note the start and end time of the data, and an Export Session Details record to record collection infrastructure information. Each Message within this File also contains a Message Checksum record, as this File may be externally encrypted and/or stored as an archive. The structure of this File is shown in .

The Template describing the data records contains a flow start timestamp, an IPv4 5-tuple, and packet and octet total counts. The Template Set defining this is as shown in below:

This is followed by an Options Template Set containing the Options Templates required to read the File: the File Time Window Options Template defined in above, the Export Session Details Options Template defined in above, and the Message Checksum Options Template defined in above. This Options Template Set is shown in and below:

Following the Templates required to decode the File is the supplemental IPFIX Options information used to describe the File's contents and type information. First comes the File Time Window record; it notes that the File contains data from 9 October 2007 between 00:01:13 and 23:56:27 UTC, and appears as in :

This is followed by information about how the data in the File was collected, in the Export Session Details record. This record notes that the session stored in this File was sent via SCTP from an exporter at 192.0.2.30 port 32769 to an collector at 192.0.2.40 port 4739, and contains messages exported between 00:01:57 and 23:57:12 UTC on 9 October 2007; it is represented in its Data Set as in :

Each IPFIX Message within the File is completed with a Message Checksum record; the structure of this record within its Data Set is as in :

After the Templates and supplemental Options information comes the data itself. The first record of an example Data Set is shown with its message and set headers in :

Bringing together the examples above and adding message headers as appropriate, a hex dump of the first 317 bytes of the example Gile constructed above would appear as in the annotated below. [EDITOR'S NOTE: In this figure, xx refers to unassigned IANA IE numbers as in the IANA Considerations section above; cs refers to message checksum bytes that depend on the rest of the message contents. These will have to be replaced if we keep this example once the IE numbers are assigned.]

16:|00 02 00 28 01 00 00 08 00 96 00 04 00 08 00 04 [^ data template set --> 32: 00 0C 00 04 00 07 00 02 00 0B 00 02 00 04 00 01 48: 00 55 00 04 00 56 00 04|00 03 00 50 01 01 00 03 [^ opt template set --> 64: 00 01 xx xx 00 01 xx xx 00 04 xx xx 00 04 01 03 80: 00 02 00 01 xx xx 00 01 xx xx 00 10 01 02 00 09 96: 00 01 xx xx 00 01 00 82 00 04 00 D3 00 04 00 D9 112: 00 02 00 D8 00 02 00 D7 00 01 00 D0 00 01 xx xx 128: 00 04 xx xx 00 04 00 00|01 03 00 18 00 cs cs cs [^ checksum record --> 144: cs cs cs cs cs cs cs cs cs cs cs cs cs 00 00 00 176:|00 0A 00 50 47 0A B6 E5 00 00 00 01 00 00 00 01 [^ second message header (length 80 bytes) --> 192:|01 01 00 0E 00 47 0A B6 B9 47 0C 07 1B 00|01 02 [^ time window rec -> [ session detail rec ^ --> 208: 00 1C 00 C0 00 02 1E 0C 00 02 1F 80 01 12 83 84 224: 0A 47 0A B6 E5 47 0C 07 48 00|01 03 00 18 00 cs [ message checksum rec ^ --> 240: cs cs cs cs cs cs cs cs cs cs cs cs cs cs cs 00 256:|00 0A 05 10 47 0A B6 E5 00 00 00 06 00 00 00 01 [^ third message header (length 1296 bytes) --> 272:|01 00 04 E6|47 0A B6 B9 C0 00 02 02 C0 00 02 03 [^ set hdr ][^ first data rec --> 288: 80 02 00 50 06 00 00 46 50 00 00 00 41 ]]>

As the IPFIX Message format is nearly a superset of the NetFlow V9 packet format, IPFIX Files can be used for store NetFlow V9 data relatively easily. This section describes a method for doing so. The differences between the two protocols are outlined in below. A simple, lightweight, message-for-message translation method for transforming V9 Packets into IPFIX Messages for storage within IPFIX Files is described in . An example of this translation method is given in .

With a few caveats, the IPFIX Protocol is a superset of the NetFlow V9 protocol, having evolved from it largely through a process of feature addition to bring it into compliance with the IPFIX Requirements and the needs of stakeholders within the IPFIX Working Group. This appendix outlines the differences between the two protocols. It is informative only, and presented as an exploration of the two protocols to motivate the usage of IPFIX Files to store V9-collected flow data.

Both NetFlow V9 and IPFIX use streams of messages prefixed by a message header, though the message header differs significantly between the two. Note that in NetFlow V9 terminology, these messages are called packets, and messages must be delimited by datagram boundaries. IPFIX does not have this constraint. The header formats are detailed below:

The IPFIX Version Number MUST be 10, while the NetFlow V9 Version Number MUST be 9. The Count field in the NetFlow V9 packet header counts records in the message (including Data and Template Records), while the Length field in the IPFIX Message Header counts octets in the message. Note that this implies that NetFlow V9 collectors must rely on datagram boundaries or some other external delimeter; or otherwise must completely consume a message before finding its end. System uptime in milliseconds is exported in the NetFlow V9 packet header. This field is not present in the IPFIX Message Header, and must be exported using an IPFIX Option if required. Aside from being called UNIX Secs in the NetFlow V9 packet header specification, the export time in seconds since 1 January 1970 at 0000 UTC appears in both NetFlow V9 and IPFIX message headers. The NetFlow V9 Sequence Number counts packets, while the IPFIX Sequence Number counts records in Data Sets. Both are scoped to Observation Domain. Similarly, the NetFlow V9 sourceID has become the IPFIX Observation Domain ID.

Set headers are identical between NetFlow V9 and IPFIX; that is, each Set (FlowSet in NetFlow V9 terminology) is prefixed by a 4-byte set header containing the Set ID and the length of the set in octets. Note that the special Set IDs are different between IPFIX and NetFlow V9. IPFIX Template Sets are identified by Set ID 2, while NetFlow V9 Template FlowSets are identified by Set ID 0. Similarly, IPFIX Options Template Sets are identified by Set ID 3, while NetFlow V9 Options Template FlowSets are identified by Set ID 1. Both protocols reserve Set IDs 0-255, and use Set IDs 256-65535 for Data Sets (or FlowSets, in NetFlow V9 terminology).

Template FlowSets in NetFlow V9 support a subset of functionality of those in IPFIX. Specifically, NetFlow V9 does not have any support for vendor-specific Information Elements as IPFIX does, so there is no enterprise bit or facility for associating a private enterprise number with an information element. NetFlow V9 also does not support variable-length fields. Options Template FlowSets in NetFlow V9 are similar to Options Template Sets in IPFIX in the same way.

The NetFlow V9 field type definitions are a compatible subset of, and have evolved in concert with, the IPFIX Information Model. IPFIX Information Element identifiers in the range 1-127 are defined by the IPFIX Information Model to be compatible with the corresponding NetFlow V9 field types.

NetFlow V9 has no concept of a Transport Session as in IPFIX, as NetFlow V9 was designed with a connectionless transport in mind. Template IDs are therefore scoped to an Exporting Process lifetime (i.e., an Exporting Process instance between restarts). There is no facility in NetFlow V9 as in IPFIX for Template withdrawal or Template ID reuse. Template retransmission at the Exporter works as in UDP-based IPFIX Exporting Processes.

In practice, though NetFlow V9 is designed to be transport-independent, it is transported only over UDP. There is no facility as in IPFIX for full connection-oriented transport without datagram boundaries, due to the use of a record count field as opposed to a message length field in the packet header. There is no support in NetFlow V9 for transport layer security via TLS or DTLS.

This appendix describes a method for transforming NetFlow V9 Packets into IPFIX Messages, which can be used to store NetFlow V9 data in IPFIX Files. A process transforming NetFlow V9 Packets into IPFIX Messages must handle the fact that NetFlow V9 Packets and IPFIX Messages are framed differently, that sequence numbering works differently, and that the NetFlow V9 field type definitions are only compatible with the IPFIX Information Model below Information Element identifier 128. For each incoming NetFlow V9 packet, the transformation process must: Verify that the Version field of the packet header is 9. Verify that the Sequence Number field of the packet header is valid. Scan the packet to: verify that it contains no Templates with field types outside the range 1-127; verify that it contains no FlowSets with Set IDs between 2 and 255 inclusive; verify that it contains the number of records in FlowSets, Template FlowSets, and Options Template FlowSets declared in the Count field of the packet header; and count the number of records in Data FlowSets for calculating the IPFIX Sequence Number. Calculate a Sequence Number for each IPFIX Observation Domain by storing the last Sequence Number sent for each Observation Domain plus the count of records in Data FlowSets in the previous step to be sent as the Sequence Number for the IPFIX Message following this one within that Observation Domain. Generate a new IPFIX Message Header with: a Version field of 10; a Length field with the number of octets in the IPFIX Message, generally available by subtracting 4 from the length of the NetFlow V9 packet as returned from the transport layer (accounting for the difference in message header lengths); the Sequence Number calculated for this message by the Sequence Number calculation step; and Export Time and Observation Domain ID taken from the UNIX secs and Source ID fields of the NetFlow V9 packet header, respectively. Copy each FlowSet from the Netflow V9 packet to the IPFIX Message after the header. Replace Set ID 0 with Set ID 2 for Template Sets, and Set ID 1 with Set ID 3 for Options Template Sets. Note that this process loses system uptime information; if such information is required, the transformation process will have to export that information using IPFIX Options. This may require a more sophisticated transformation process structure.

The following two figures show a single NetFlow V9 packet with templates and the corresponding IPFIX Message, exporting a single flow record representing 60,303 octets sent from 192.0.2.2 to 192.0.2.3. This would be the 3rd packet exported in Observation Domain 33 from the NetFlow V9 exporter, containing records starting with the 12th record (packet and record sequence numbers count from 0). The ** symbol in the IPFIX example shows those fields that required modification from the NetFlow V9 packet by the transformation process.