Exporting Type Information for IPFIX Information Elements
draft-ietf-ipfix-exporting-type-04.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 November 21, 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 in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document.

Abstract

This document describes an extension to the IP Flow Information Export (IPFIX) protocol, which is used to represent and transmit data from IP flow measurement devices for collection, storage and analysis, to allow the encoding of IPFIX Information Model properties within an IPFIX Message stream. This enables the export of extended type information for enterprise-specific Information Elements, and the storage of such information within IPFIX Files, facilitating interoperability and reusability among a wide variety of applications and tools.

Table of Contents

1.  Introduction
    1.1.  IPFIX Documents Overview
2.  Terminology
3.  Type Information Export
    3.1.  informationElementDataType
    3.2.  informationElementDescription
    3.3.  informationElementName
    3.4.  informationElementRangeBegin
    3.5.  informationElementRangeEnd
    3.6.  informationElementSemantics
    3.7.  informationElementUnits
    3.8.  privateEnterpriseNumber
    3.9.  Information Element Type Options Template
    3.10.  Data Type and Semantics Restrictions
4.  Security Considerations
5.  IANA Considerations
6.  Acknowledgements
7.  References
    7.1.  Normative References
    7.2.  Informative References
Appendix A.  Examples
§  Authors' Addresses

1.  Introduction

IP Flow Information Export (IPFIX) provides a template mechanism for the flexible description of Data Records, by defining a record as a collection of Information Elements defined in an IANA registry, However, these Templates provide limited information about the type of described data; indeed, they encode only the size of the fields defined by these Information Elements. There presently exists no mechanism to provide full type information for these Information Elements, as is defined for the Information Elements in the IPFIX Information Model.

This especially limits the interoperability of enterprise-specific Information Elements. It is not possible to use analysis tools on IPFIX records containing these partially defined Information Elements that have not been developed with a priori knowledge of their types, since such tools will not be able to decode them; these tools can only treat and store them as opaque octet arrays. However, if richer information is available, additional operations such as efficient storage, display, and limited analysis of records containing enterprise-specific Information Elements become possible, even for Collecting Processes that had not been specifically developed to understand them.

This document defines a general mechanism to encode the full set of properties available for the definition of Information Elements within the IPFIX Information Model inline within an IPFIX Message stream using IPFIX Options. This mechanism may be used to fully define type information for Information Elements used within a message stream, without resort to an external reference or reliance on out-of-band configuration, thereby improving the interoperability of enterprise-specific Information Elements.

Note that the solution described in this draft is not intended as a replacement for registration with IANA of generally useful Information Elements. It introduces overhead and does not lead to real interoperability as provided by standardization. Therefore we highly recommend to standardize all new generally useful Information Elements by registering them with IANA. Standardization is straightforward, and the type information that needs to be specified in order to support the proposed solution provides a perfect basis for the description required for standardizing the Information Element.

It might happen that an Information Element previously described by the mechanism in this document later becomes an IANA-registered, standard Information Element. In such environments old and new versions of the Information Element can coexist. A translation between Information Elements expressed by the described solution and standardized Information Elements is therefore not necessary, and is out of scope for this document.

1.1.  IPFIX Documents Overview

"Specification of the IPFIX Protocol for the Exchange of IP Traffic Flow Information" (Claise, B., “Specification of the IP Flow Information Export (IPFIX) Protocol for the Exchange of IP Traffic Flow Information,” January 2008.) [RFC5101] (informally, the IPFIX Protocol document) 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" (Sadasivan, G., Brownlee, N., Claise, B., and J. Quittek, “Architecture for IP Flow Information Export,” March 2009.) [RFC5470] (the IPFIX Architecture document) 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" (Quittek, J., Zseby, T., Claise, B., and S. Zander, “Requirements for IP Flow Information Export (IPFIX),” October 2004.) [RFC3917]. The IPFIX Protocol document [RFC5101] (Claise, B., “Specification of the IP Flow Information Export (IPFIX) Protocol for the Exchange of IP Traffic Flow Information,” January 2008.) 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" (Quittek, J., Bryant, S., Claise, B., Aitken, P., and J. Meyer, “Information Model for IP Flow Information Export,” January 2008.) [RFC5102] (informally, the IPFIX Information Model document) describes the Information Elements used by IPFIX, including details on Information Element naming, numbering, and data type encoding.

This document references the Protocol and Architecture documents for terminology and extends the IPFIX Information Model to provide new Information Elements for the representation of Information Element properties. It draws data type definitions and data type semantics definitions from the Information Model; the encodings of these data types are defined in [RFC5101] (Claise, B., “Specification of the IP Flow Information Export (IPFIX) Protocol for the Exchange of IP Traffic Flow Information,” January 2008.).

2.  Terminology

Terms used in this document that are defined in the Terminology section of the IPFIX Protocol (Claise, B., “Specification of the IP Flow Information Export (IPFIX) Protocol for the Exchange of IP Traffic Flow Information,” January 2008.) [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 (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.) [RFC2119].

3.  Type Information Export

This section describes the mechanism used to encode Information Element type information within an IPFIX Message stream. This mechanism consists of an Options Template Record used to define Information Element type records, and a set of Information Elements required by these type records. We first specify the necessary Information Elements, followed by the structure of the Options Template describing the type records.

Note that Information Element type records require one Information Element, informationElementId, that is defined in the PSAMP Information Model (Dietz, T., Claise, B., Aitken, P., Dressler, F., and G. Carle, “Information Model for Packet Sampling Exports,” March 2009.) [RFC5477]. This Information Element supports references only to IANA-defined Information Elements; the privateEnterpriseNumber Information Element is required alongside informationElementId to describe enterprise-specific Information Elements.

3.1.  informationElementDataType

Description:

A description of the abstract data type of an IPFIX information element. These are taken from the abstract data types defined in section 3.1 of the IPFIX Information Model (Quittek, J., Bryant, S., Claise, B., Aitken, P., and J. Meyer, “Information Model for IP Flow Information Export,” January 2008.) [RFC5102]; see that section for more information on the types described below. This field may take the values defined in Table 1 (IE Data Type values) below.

---

Value	Description
0x00	octetArray
0x01	unsigned8
0x02	unsigned16
0x03	unsigned32
0x04	unsigned64
0x05	signed8
0x06	signed16
0x07	signed32
0x08	signed64
0x09	float32
0x0A	float64
0x0B	boolean
0x0C	macAddress
0x0D	string
0x0E	dateTimeSeconds
0x0F	dateTimeMilliseconds
0x10	dateTimeMicroseconds
0x11	dateTimeNanoseconds
0x12	ipv4Address
0x13	ipv6Address

Table 1: IE Data Type values

---

These types are registered in the IANA IPFIX Information Element Data Type subregistry. This subregistry is intended to assign numbers for type names, not to provide a mechanism for adding data types to the IPFIX Protocol, and as such requires a Standards Action (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008.) [RFC5226] to modify.

Abstract Data Type:

unsigned8

ElementId:

TBD1

Status:

current

Reference:

Section 3.1 of the IPFIX Information Model (Quittek, J., Bryant, S., Claise, B., Aitken, P., and J. Meyer, “Information Model for IP Flow Information Export,” January 2008.) [RFC5102]

3.2.  informationElementDescription

Description:

A UTF-8 (Yergeau, F., “UTF-8, a transformation format of ISO 10646,” November 2003.) [RFC3629] encoded Unicode string containing a human-readable description of an Information Element. The content of the informationElementDescription MAY be annotated with one or more language tags (Phillips, A. and M. Davis, “Tags for Identifying Languages,” September 2006.) [RFC4646], encoded in-line (Whistler, K. and G. Adams, “Language Tagging in Unicode Plain Text,” January 1999.) [RFC2482] within the UTF-8 string, in order to specify the language in which the description is written. Language tags SHOULD be kept as simple as possible; it is NOT RECOMMENDED for an Exporting Process to export a language tag with any subtags other than the primary language subtag. Description text in multiple languages MAY tag each section with its own language tag; in this case, the description information in each language SHOULD have equivalent meaning. In the absence of any language tag, the "i-default" (Alvestrand, H., “IETF Policy on Character Sets and Languages,” January 1998.) [RFC2277] language SHOULD be assumed. See the Security Considerations section for notes on string handling for Information Element type records.

Abstract Data Type:

string

ElementId:

TBD2

Status:

current

3.3.  informationElementName

Description:

A UTF-8 (Yergeau, F., “UTF-8, a transformation format of ISO 10646,” November 2003.) [RFC3629] encoded Unicode string containing the name of an Information Element, intended as a simple identifier. See the Security Considerations section for notes on string handling for Information Element type records.

Abstract Data Type:

string

ElementId:

TBD3

Status:

current

3.4.  informationElementRangeBegin

Description:

Contains the inclusive low end of the range of acceptable values for an Information Element.

Abstract Data Type:

unsigned64

Data Type Semantics:

quantity

ElementId:

TBD4

Status:

current

3.5.  informationElementRangeEnd

Description:

Contains the inclusive high end of the range of acceptable values for an Information Element.

Abstract Data Type:

unsigned64

Data Type Semantics:

quantity

ElementId:

TBD5

Status:

current

3.6.  informationElementSemantics

Description:

A description of the semantics of an IPFIX Information Element. These are taken from the data type semantics defined in section 3.2 of the IPFIX Information Model (Quittek, J., Bryant, S., Claise, B., Aitken, P., and J. Meyer, “Information Model for IP Flow Information Export,” January 2008.) [RFC5102]; see that section for more information on the types described below. This field may take the values in Table 2 (IE Semantics values) below; the special value 0x00 (default) is used to note that no semantics apply to the field; it cannot be manipulated by a Collecting Process or File Reader that does not understand it a priori.

---

Value	Description
0x00	default
0x01	quantity
0x02	totalCounter
0x03	deltaCounter
0x04	identifier
0x05	flags

Table 2: IE Semantics values

---

These semantics are registered in the IANA IPFIX Information Element Semantics subregistry. This subregistry is intended to assign numbers for semantics names, not to provide a mechanism for adding semantics to the IPFIX Protocol, and as such requires a Standards Action (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008.) [RFC5226] to modify.

Abstract Data Type:

unsigned8

ElementId:

TBD6

Status:

current

Reference:

Section 3.2 of the IPFIX Information Model (Quittek, J., Bryant, S., Claise, B., Aitken, P., and J. Meyer, “Information Model for IP Flow Information Export,” January 2008.) [RFC5102]

3.7.  informationElementUnits

Description:

A description of the units of an IPFIX Information Element. These correspond to the units implicitly defined in the Information Element definitions in section 5 of the IPFIX Information Model (Quittek, J., Bryant, S., Claise, B., Aitken, P., and J. Meyer, “Information Model for IP Flow Information Export,” January 2008.) [RFC5102]; see that section for more information on the types described below. This field may take the values in Table 3 (IE Units values) below; the special value 0x00 (none) is used to note that the field is unitless.

---

Value	Name	Notes
0x0000	none
0x0001	bits
0x0002	octets
0x0003	packets
0x0004	flows
0x0005	seconds
0x0006	milliseconds
0x0007	microseconds
0x0008	nanoseconds
0x0009	4-octet words	for IPv4 header length
0x000A	messages	for reliability reporting
0x000B	hops	for TTL
0x000C	entries	for MPLS label stack

Table 3: IE Units values

---

These types are registered in the IANA IPFIX Information Element Units subregistry; new types may be added on a First Come First Served (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008.) [RFC5226] basis.

Abstract Data Type:

unsigned16

ElementId:

TBD7

Status:

current

Reference:

Section 5 of the IPFIX Information Model (Quittek, J., Bryant, S., Claise, B., Aitken, P., and J. Meyer, “Information Model for IP Flow Information Export,” January 2008.) [RFC5102]

3.8.  privateEnterpriseNumber

Description:

A private enterprise number, as assigned by IANA. Within the context of an Information Element Type record, this element can be used along with the informationElementId element to scope properties to a specific Information Element. To export type information about an IANA-assigned Information Element, set the privateEnterpriseNumber to 0, or do not export the privateEnterpriseNumber in the type record. To export type information about an enterprise-specific Information Element, export the enterprise number in privateEnterpriseNumber, and export the Information Element number with the Enterprise bit cleared in informationElementId. The Enterprise bit in the associated informationElementId Information Element MUST be ignored by the Collecting Process.

Abstract Data Type:

unsigned32

Data Type Semantics:

identifier

ElementId:

TBD8

Status:

current

Reference:

Sections 3.2 and 3.4.1 of the IPFIX Protocol (Claise, B., “Specification of the IP Flow Information Export (IPFIX) Protocol for the Exchange of IP Traffic Flow Information,” January 2008.) [RFC5101]; section 8.2.3 of the PSAMP Information Model (Dietz, T., Claise, B., Aitken, P., Dressler, F., and G. Carle, “Information Model for Packet Sampling Exports,” March 2009.) [RFC5477].

3.9.  Information Element Type Options Template

The Information Element Type Options Template attaches type information to Information Elements used within Template Records, as scoped to an Observation Domain within a Transport Session. This provides a mechanism for representing an IPFIX Information Model inline within an IPFIX Message stream. Data Records described by this template are referred to as Information Element type records.

In deployments in which interoperability across vendor implementations of IPFIX is important, an Exporting Process exporting data using Templates containing enterprise-specific Information Elements SHOULD export an Information Element type record for each enterprise-specific Information Element it exports. Collecting Processes MAY use these type records to improve handling of unknown enterprise-specific Information Elements. Exporting Processes using enterprise-specific Information Elements to implement proprietary features MAY omit type records for those Information Elements.

Information Element type records MUST be handled by Collecting Processes as scoped to the Transport Session in which they are sent; this facility is not intended to provide a method for the permanent definition of Information Elements.

Similarly, for security reasons, type information for a given Information Element MUST NOT be re-defined by Information Element type records, and a Collecting Process MUST NOT allow an Information Element type record to replace its own internal definition of an Information Element. Information Element type records SHOULD NOT be duplicated in a given Observation Domain within a Transport Session. Once an Information Element type record has been exported for a given Information Element within a given Transport Session, all subsequent type records for that Information Element MUST be identical. Information Elements for which a Collecting Process receives conflicting semantic or type information MUST be ignored.

Note that while this template MAY be used to export information about any Information Element, including those registered with IANA, Exporting Processes SHOULD NOT export any type records that could be reasonably assumed to duplicate type information available at the Collecting Process. This mechanism is not intended as a replacement for Exporting and Collecting Processes keeping up to date with changes to the IANA registry; such an update mechanism is out of scope for this document.

The template SHOULD contain the Information Elements in Table 4 (IE Type Options), below, as defined in the PSAMP Information Model (Dietz, T., Claise, B., Aitken, P., Dressler, F., and G. Carle, “Information Model for Packet Sampling Exports,” March 2009.) [RFC5477] and in this document, above.

3.10.  Data Type and Semantics Restrictions

Note that the informationElementSemantics values defined in section 3.2 of [RFC5102] (Quittek, J., Bryant, S., Claise, B., Aitken, P., and J. Meyer, “Information Model for IP Flow Information Export,” January 2008.) are primarily intended to differentiate semantic interpretation of numeric values, and that not all combinations of the informationElementDataType and informationElementSemantics Information Elements are valid; e.g., a counter cannot be encoded as an IPv4 address. The following are acceptable values of informationElementSemantics:

• Any value is valid for unsigned informationElementDataType values ("unsigned8", "unsigned16", "unsigned32", or "unsigned64").
• Any value except "flags" is valid for signed informationElementDataType values ("signed8", "signed16", "signed32", or "signed64").
• Any value except "identifier" or "flags" is valid for floating-point informationElementDataType values ("float32" or "float64").
• Only "default" is valid for all other other informationElementDataType values ("octetArray", "boolean", "macAddress", "string", "dateTimeSeconds", "dateTimeMilliseconds", "dateTimeMicroseconds", "dateTimeNanoseconds", "ipv4Address", or "ipv6Address").

Information Element type records containing invalid combinations of informationElementSemantics and informationElementDataType MUST NOT be sent by Exporting Processes, and MUST be ignored by Collecting Processes.

Future standards actions that modify the Information Element Data Type subregistry or the Information Element Semantics subregistry should contain a Data Type and Semantics Restrictions sections such as this one to define allowable combinations of type and semantics information.

4.  Security Considerations

The same security considerations as for the IPFIX Protocol (Claise, B., “Specification of the IP Flow Information Export (IPFIX) Protocol for the Exchange of IP Traffic Flow Information,” January 2008.) [RFC5101] apply.

Attention must be paid to the handling of Information Element type records at the Collecting Process. Type information precedence rules defined above (a Collecting Process' current knowledge overrides type records; types are not redefinable during a session) are designed to minimize the opportunity for an attacker to maliciously redefine the data model.

Note that Information Element type records may contain two strings describing Information Elements: informationElementName and informationElementDescription. IPFIX strings on the wire are length-prefixed and UTF-8 (Yergeau, F., “UTF-8, a transformation format of ISO 10646,” November 2003.) [RFC3629] encoded, most often within an IPFIX variable-length Information Element, which mitigates the risk of unterminated-string attacks against IPFIX Collecting Processes. However, care should still be taken when handling strings within the type system of the Collecting Process.

First, Collecting Processes should pay particular attention to buffer sizes converting between length-prefixed and null-terminated strings. Exporting Processes MUST NOT export, and Collecting Processes MUST ignore, any informationElementName or informationElementDescription content which contains null characters (U+0000) in order to ensure buffer and string lengths are consistent.

Also, note that there is no limit to IPFIX string length beyond that inherent in the protocol. The maximum IPFIX string length is 65512 octets (maximum message length (65535), minus message header (16), minus set header (4), minus long variable length field (3)). Specifically, although the informationElementName of all IANA Information Elements at the time of this writing is less than about 40 octets, and the informationElementDescription is less than 4096 octets, either of these Information Elements may contain strings up to 65512 octets long.

5.  IANA Considerations

This document specifies the creation of several new IPFIX Information Elements in the IPFIX Information Element registry as defined in section 3 above. IANA has assigned the following Information Element numbers for their respective Information Elements as specified below:

• Information Element Number TBD1 for the informationElementDataType Information Element
• Information Element Number TBD2 for the informationElementDescription Information Element
• Information Element Number TBD3 for the informationElementName Information Element
• Information Element Number TBD4 for the informationElementRangeBegin Information Element
• Information Element Number TBD5 for the informationElementRangeEnd Information Element
• Information Element Number TBD6 for the informationElementSemantics Information Element
• Information Element Number TBD7 for the informationElementUnits Information Element
• Information Element Number TBD8 for the privateEnterpriseNumber Information Element
• [NOTE for IANA: The text TBD1, TBD2, TBD3, TBD4, TBD5, TBD6, TBD7, and TBD8 should be replaced with the respective assigned Information Element numbers where they appear in this document.]

IANA has created an Information Element Data Type subregistry for the values defined for the informationElementSemantics Information Element. Entries may be added to this subregistry subject to a Standards Action (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008.) [RFC5226].

[NOTE for IANA: Please create a new Information Element Data Type subregistry as specified in the paragraph above, with values taken from section 3.1 of this document.]

IANA has created an Information Element Semantics subregistry for the values defined for the informationElementSemantics Information Element. Entries may be added to this subregistry subject to a Standards Action (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008.) [RFC5226].

[NOTE for IANA: Please create a new Information Element Semantics subregistry as specified in the paragraph above, with values taken from section 3.6 of this document.]

IANA has created an Information Element Units subregistry for the values defined for the informationElementUnits Information Element. Entries may be added to this subregistry on an Expert Review (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008.) [RFC5226] basis.

[NOTE for IANA: Please create a new Information Element Units subregistry as specified in the paragraph above, with values taken from section 3.7 of this document.]

6.  Acknowledgements

Thanks to Paul Aitken and Gerhard Muenz for the detailed reviews, and to David Moore for first raising this issue to the IPFIX mailing list.

7.  References

7.1. Normative References

7.2. Informative References

Appendix A.  Examples

The following example illustrates how the type information extension mechanism defined in this document may be used to describe the semantics of enterprise-specific Information Elements. The Information Elements used in this example are as follows:

• initialTCPFlags, an example private IE 14, 1 octet, the TCP flags on the first TCP packet in the flow.
• unionTCPFlags, an example private IE 15, 1 octet, the union of the TCP flags on all packets after the first TCP packet in the flow.

An Exporting Process exporting flows containing these Information Elements might use a Template like the following:

                     1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          Set ID = 2           |          Length =  52         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|      Template ID = 256        |        Field Count = 9        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| flowStartSeconds        150 |       Field Length =  4       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| sourceIPv4Address         8 |       Field Length =  4       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| destinationIPv4Address   12 |       Field Length =  4       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| sourceTransportPort       7 |       Field Length =  2       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| destinationTransportPort 11 |       Field Length =  2       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| octetTotalCount          85 |       Field Length =  4       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| (initialTCPFlags)        14 |       Field Length =  1       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                  Private Enterprise Number                    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| (unionTCPFlags)          15 |       Field Length =  1       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                  Private Enterprise Number                    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| protocolIdentifier        4 |       Field Length =  1       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

However, a Collecting Process receiving Data Sets described by this Template can only treat the enterprise-specific Information Elements as opaque octets; specifically, there is no hint to the collector that they contain flag information. To use the type information extension mechanism to address this problem, the Exporting Process would first export the Information Element Type Options Template described in section 3.9 above:

                     1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          Set ID = 3           |          Length =  26         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|      Template ID = 257        |        Field Count = 4        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|    Scope Field Count = 2      |0| priv.EnterpriseNumber  TBD8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|       Field Length = 4        |0| informationElementId    303 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|       Field Length = 2        |0| inf.El.DataType        TBD1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|       Field Length = 1        |0| inf.El.Semantics       TBD6 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|       Field Length = 1        |0| inf.El.Name            TBD3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Field Length = 65536      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Then, the Exporting Process would then export two records described by the Example Information Element Type Options Template to describe the enterprise-specific Information Elements:

                     1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          Set ID = 257         |          Length =  50         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                  Private Enterprise Number                    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|X|         IE 14               |0x01 unsigned8 |0x05 flags     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   15 length   |                                               |
+-+-+-+-+-+-+-+-+                                               |
|                      "initialTCPFlags"                        |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                  Private Enterprise Number                    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|X|         IE 15               |0x01 unsigned8 |0x05 flags     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   13 length   |                                               |
+-+-+-+-+-+-+-+-+        "unionTCPFlags"                        |
|                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Authors' Addresses