Exporting Type Information for IPFIX Information Elements
draft-ietf-ipfix-exporting-type-01.txt

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Abstract

This document describes an extension to IPFIX to allow the encoding of IPFIX Information Model properties within an IPFIX Message stream, to allow the export of extended type information for enterprise-specific Information Elements. This format is designed to facilitate 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
§  Intellectual Property and Copyright Statements

1.  Introduction

The IPFIX protocol specification allows the creation of enterprise-specific Information Elements to easily extend the protocol to meet requirements which aren't covered by the existing Information Model. However, IPFIX Templates provide only the ability to export the size of the fields defined by these Information Elements; there is no mechanism to provide full type information for these Information Elements as is defined for the Information Elements in the IPFIX Information Model.

This 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 proposes a 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.

Note that the solution described in this draft is only for providing interoperability for enterprise specific information elements that are not yet standardized. The solution introduces overhead and does not lead to real interoperability as provided by standards. Therefore we highly recommend to standardize all new information elements by registering them with IANA. Standardization is straightforward. 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.

We assume that the proposed solution is mainly used in the following two situations: a) for information elements for very specific solutions or in very specific environments for which a standardization might not seem necessary because only few users are using it or b) temporarily for new information elements before they are standardized or to first investigate whether they become popular enough to become standardized.

It might happen that information elements previously described by the proposed exporting type information later become a standard information element. In some environments old and new version of the information element can coexist. A translation between information elements expressed by the described solution and standardized information elements is not necessary. Collectors will act in accordance to their capabilities and ignore messages that they do not support.

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. and N. Brownlee, “Architecture Model for IP Flow Information Export,” October 2003.) [I‑D.ietf‑ipfix‑arch] (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.

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 Information Element Type Options Template itself. 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,” October 2008.) [I‑D.ietf‑psamp‑info].

3.1.  informationElementDataType

Description:

A description of the storage type of an IPFIX information element. These correspond to 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 following values:

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

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,” October 1998.) [RFC2434] to modify.

Abstract Data Type:

unsigned8

ElementId:

TBD1

Status:

Proposed

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 string containing a human-readable description of an Information Element.

Abstract Data Type:

string

Data Type Semantics:

identifier

ElementId:

TBD2

Status:

Proposed

3.3.  informationElementName

Description:

A string containing the name of an Information Element.

Abstract Data Type:

string

Data Type Semantics:

identifier

ElementId:

TBD3

Status:

Proposed

3.4.  informationElementRangeBegin

Description:

Contains the inclusive low end of the range of acceptable values for an Information Element. Not valid and SHOULD be ignored by a Collecting Process unless informationElementRangeEnd is also available for the same Information Element.

Abstract Data Type:

unsigned64

Data Type Semantics:

quantity

ElementId:

TBD4

Status:

Proposed

3.5.  informationElementRangeEnd

Description:

Contains the inclusive high end of the range of acceptable values for an Information Element. Not valid and SHOULD be ignored by a Collecting Process unless informationElementRangeBegin is also available for the same Information Element.

Abstract Data Type:

unsigned64

Data Type Semantics:

quantity

ElementId:

TBD5

Status:

Proposed

3.6.  informationElementSemantics

Description:

A description of the semantics of an IPFIX information element. These correspond to 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 following values; the special value 0x00 (none) 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	none
0x01	quantity
0x02	totalCounter
0x03	deltaCounter
0x04	identifier
0x05	flags

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,” October 1998.) [RFC2434] to modify.

Abstract Data Type:

unsigned8

ElementId:

TBD6

Status:

Proposed

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 following values; 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

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,” October 1998.) [RFC2434] basis.

Abstract Data Type:

unsigned16

ElementId:

TBD7

Status:

Proposed

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 used to scope an informationElementID, as would appear in an IPFIX Template Record. This element can be used to scope properties to a specific Information Element. If the Enterprise ID bit of the corresponding Information Element is cleared (has the value 0), this IE should be set to 0. The presence of a non-zero value in this IE implies that the Enterprise ID bit of the corresponding Information Element is set (has the value 1).

Abstract Data Type:

unsigned32

Data Type Semantics:

identifier

ElementId:

TBD8

Status:

Proposed

Reference:

Section 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]

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 within a Transport Session, but 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. Conflicting semantic or type information MUST be ignored by a Collecting Process.

The template SHOULD contain the following Information Elements as defined in the PSAMP Information Model (Dietz, T., Claise, B., Aitken, P., Dressler, F., and G. Carle, “Information Model for Packet Sampling Exports,” October 2008.) [I‑D.ietf‑psamp‑info] and in this document, above:

3.10.  Data Type and Semantics Restrictions

Note that the informationElementSemantics values 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. Any informationElementSemantics value is valid for unsigned informationElementDataType values ("unsigned8", "unsigned16", "unsigned32", or "unsigned64"). Any informationElementSemantics value except flags is valid for signed informationElementDataType values ("signed8", "signed16", "signed32", or "signed64"). Any informationElementSemantics value except "identifier" or "flags" is valid for floating-point informationElementDataType values ("float32" or "float64"). Only the informationElementSemantics value "none" 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.

5.  IANA Considerations

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 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,” October 1998.) [RFC2434].

[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,” October 1998.) [RFC2434].

[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,” October 1998.) [RFC2434] 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 for the detailed technical review, 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, CERT (PEN 6871) private IE 14, 1 octet, the TCP flags on the first TCP packet in the flow.
• unionTCPFlags, CERT (PEN 6871) 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       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                            PEN 6871                           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| (unionTCPFlags)          15 |       Field Length =  1       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                            PEN 6871                           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|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         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                            PEN 6871                           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|           IE 14               |0x01 unsigned8 |0x05 flags     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   15 length   |                                               |
+-+-+-+-+-+-+-+-+                                               |
|                      "initialTCPFlags"                        |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                            PEN 6871                           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|           IE 15               |0x01 unsigned8 |0x05 flags     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   13 length   |                                               |
+-+-+-+-+-+-+-+-+        "unionTCPFlags"                        |
|                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Authors' Addresses

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