Internet Engineering Task Force (IETF) M. Boucadair

Internet Engineering Task Force (IETF) M. Boucadair
Request for Comments: 9740 Orange
Category: Standards Track B. Claise
ISSN: 2070-1721 Huawei
March 2025

New IPFIX Information Elements for TCP Options and IPv6 Extension
Headers

Abstract

This document specifies new IP Flow Information Export (IPFIX)
Information Elements (IEs) to solve issues with existing
ipv6ExtensionHeaders and tcpOptions IPFIX IEs, especially the ability
to export any observed IPv6 extension headers or TCP options.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9740.

Copyright Notice

Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved.

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Provisions Relating to IETF Documents
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Table of Contents

1. Introduction
1.1. Issues with ipv6ExtensionHeaders Information Element
1.2. Issues with tcpOptions Information Element
2. Conventions and Definitions
3. Information Elements for IPv6 Extension Headers
3.1. ipv6ExtensionHeaderType Information Element
3.2. ipv6ExtensionHeaderCount Information Element
3.3. ipv6ExtensionHeadersFull Information Element
3.4. ipv6ExtensionHeaderTypeCountList Information Element
3.5. ipv6ExtensionHeadersLimit Information Element
3.6. ipv6ExtensionHeadersChainLength Information Element
3.7. ipv6ExtensionHeaderChainLengthList Information Element
4. Information Elements for TCP Options
4.1. tcpOptionsFull Information Element
4.2. tcpSharedOptionExID16 Information Element
4.3. tcpSharedOptionExID32 Information Element
4.4. tcpSharedOptionExID16List Information Element
4.5. tcpSharedOptionExID32List Information Element
5. Implementation and Operational Considerations
6. Examples
6.1. IPv6 Extension Headers
6.2. TCP Options
6.2.1. Reduced-Size Encoding
6.2.2. Shared Options
7. Security Considerations
8. IANA Considerations
8.1. Deprecate ipv6ExtensionHeaders and tcpOptions Information
Elements
8.2. IPFIX Information Elements
8.3. IPFIX Information Element Data Type
8.3.1. unsigned256
8.4. IPFIX Registry for IPv6 Extension Headers
8.4.1. Initial Values
8.4.2. Guidelines for the Designated Experts
9. References
9.1. Normative References
9.2. Informative References
Acknowledgments
Authors' Addresses

1. Introduction

This document specifies new IP Flow Information Export (IPFIX)
[RFC7011] Information Elements (IEs) to solve a set of issues
encountered with the specifications of two IEs --
ipv6ExtensionHeaders (to export IPv6 extension headers) and
tcpOptions (to export TCP options) [IANA-IPFIX]. More details about
these issues are provided in the following subsections.

This document deprecates the ipv6ExtensionHeaders and tcpOptions
IPFIX IEs that were initially defined in [RFC5102].

Note that [RFC7012] obsoletes [RFC5102] and specifies that
[IANA-IPFIX] is the normative reference for these IEs.

1.1. Issues with ipv6ExtensionHeaders Information Element

The specification of the ipv6ExtensionHeaders IPFIX IE (64) does not:

* Cover the full extension headers' range defined in the IPv6
specification (Section 4 of [RFC8200]).

* Specify the procedure to follow when all bits are exhausted.

* Specify a means to export the order and the number of occurrences
of a given extension header.

* Specify how to automatically update the IANA IPFIX registry
[IANA-IPFIX] when a new value is assigned in the IPv6 Extension
Header Types registry [IANA-EH]. Only a frozen set of extension
headers can be exported using the ipv6ExtensionHeaders IE. For
example, the ipv6ExtensionHeaders IE can't report some IPv6 EHs,
specifically EHs for the Host Identity Protocol (139), Shim6
Protocol (140), or extension headers for experimentation and
testing.

* Specify whether the exported values match the full enclosed values
or only up to a limit imposed by hardware or software (e.g.,
Section 1.1 of [RFC8883]). Note that some implementations may not
be able to export all observed extension headers in a Flow because
of a hardware or software limit (see, e.g., [EH-LIMITS]).

* Discuss whether it covers all enclosed extension headers or only
up to a limit.

* Specify how to report the length of IPv6 extension headers.

* Optimize the encoding.

* Explain the reasoning for reporting values that do not correspond
to extension headers (e.g., "Unknown Layer 4 header" or "Payload
compression header").

* Specify how to report extension header chains or aggregate lengths
of extension headers.

Section 3 addresses these issues.

This specification deprecates the ipv6ExtensionHeaders IPFIX IE in
favor of the new IEs defined in this document.

1.2. Issues with tcpOptions Information Element

The specification of the tcpOptions IPFIX IE (209) does not:

* Describe how some observed TCP options in a Flow can be exported
using IPFIX. Only TCP options having a Kind <= 63 can be exported
in a tcpOptions IE.

* Allow reporting the observed Experiment Identifiers (ExIDs) that
are carried in shared Experimental TCP options (Kind=253 or 254)
[RFC6994].

* Optimize the encoding.

Section 4 addresses these issues.

This specification deprecates the tcpOptions IE in favor of the new
IEs defined in this document.

2. Conventions and Definitions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.

This document uses the IPFIX-specific terminology (Information
Element, Template Record, Flow, etc.) defined in Section 2 of
[RFC7011]. As in the base IPFIX specification [RFC7011], these
IPFIX-specific terms have the first letter of a word capitalized.

Also, the document uses the terms defined in the IPv6 [RFC8200] and
TCP [RFC9293] specifications.

In addition, the document makes use of the following terms:

Extension header chain: Refers to the chain of extension headers
that are present in an IPv6 packet.

This term should not be confused with the IPv6 header chain, which
includes the IPv6 header, zero or more IPv6 extension headers, and
zero or a single Upper-Layer Header.

Flow with varying extension header chains: Refers to a Flow where
distinct extension header chains are observed. Concretely,
different packets in such a Flow will have a different sequence of
extension header type codes.

3. Information Elements for IPv6 Extension Headers

3.1. ipv6ExtensionHeaderType Information Element

Name: ipv6ExtensionHeaderType

ElementID: 513

Description: Type of an IPv6 extension header observed in at least
one packet of this Flow.

Abstract Data Type: unsigned8

Data Type Semantics: identifier

Additional Information: See the "IPv6 Extension Header Types"
registry at [IANA-EH].

See Section 4 of [RFC8200] for the general definition of IPv6
extension headers.

Reference: RFC 9740

3.2. ipv6ExtensionHeaderCount Information Element

Name: ipv6ExtensionHeaderCount

ElementID: 514

Description: The number of consecutive occurrences of the same
extension header type in a Flow.

This IE is reported, e.g., in the ipv6ExtensionHeaderTypeCountList
IE.

The type of the extension header is provided in the
ipv6ExtensionHeaderType IE.

Abstract Data Type: unsigned8

Data Type Semantics: totalCounter

Additional Information: See the "IPv6 Extension Header Types"
registry at [IANA-EH].

See Section 4 of [RFC8200] for the general definition of IPv6
extension headers.

Reference: RFC 9740

3.3. ipv6ExtensionHeadersFull Information Element

Name: ipv6ExtensionHeadersFull

ElementID: 515

Description: IPv6 extension headers observed in packets of this
Flow. The information is encoded in a set of bit fields. For
each IPv6 extension header, there is a bit in this set. The bit
is set to 1 if any observed packet of this Flow contains the
corresponding IPv6 extension header. Otherwise, if no observed
packet of this Flow contains the respective IPv6 extension header,
the value of the corresponding bit is 0.

The IPv6 extension header associated with each bit is provided in
[IANA-IPFIX-IPv6EH]. Bit 0 corresponds to the least significant
bit (LSB) in the ipv6ExtensionHeadersFull IE, while bit 255
corresponds to the most significant bit (MSB) of the IE. In doing
so, few octets will be needed to encode common IPv6 extension
headers when observed in a Flow.

The "No Next Header" (bit 2) value (Section 4.7 of [RFC8200]) is
used if there is no upper-layer header in an IPv6 packet. Even if
the value is not considered as an extension header as such, the
corresponding bit is set in the ipv6ExtensionHeadersFull IE
whenever that value is encountered in the Flow.

Extension headers observed in a Flow with varying extension header
chains MUST NOT be grouped in the ipv6ExtensionHeadersFull IE if
the ipv6ExtensionHeaderChainLengthList IE is also present.

If the ipv6ExtensionHeaderChainLengthList IE is not present, then
extension headers observed in a Flow with varying extension header
chains MAY be grouped in one single ipv6ExtensionHeadersFull IE or
be exported in separate ipv6ExtensionHeadersFull IEs, one for each
extension header chain.

The ipv6ExtensionHeadersFull IE MUST NOT be exported if
ipv6ExtensionHeaderTypeCountList IE is also present because of the
overlapping scopes of these two IEs.

The value of ipv6ExtensionHeadersFull IE may be encoded in fewer
octets per the guidelines in Section 6.2 of [RFC7011].

Abstract Data Type: unsigned256

Data Type Semantics: flags

Additional Information: See the "IPFIX ipv6ExtensionHeaders Bits"
registry at [IANA-IPFIX-IPv6EH].

See the "IPv6 Extension Header Types" registry at [IANA-EH].

See Section 4 of [RFC8200] for the general definition of IPv6
extension headers.

The ipv6ExtensionHeadersFull IE deprecates the
ipv6ExtensionHeaders IE (64) that was initially defined in
[RFC5102].

[RFC7012] obsoletes [RFC5102] and specifies that [IANA-IPFIX] is
the normative reference for the ipv6ExtensionHeaders IE (64).

Reference: RFC 9740

3.4. ipv6ExtensionHeaderTypeCountList Information Element

Name: ipv6ExtensionHeaderTypeCountList

ElementID: 516

Description: As per Section 4.1 of [RFC8200], IPv6 nodes must accept
and attempt to process extension headers occurring any number of
times in the same packet. This IE echoes the order of extension
headers and number of consecutive occurrences of the same
extension header type in a Flow.

This IE is a subTemplateList of ipv6ExtensionHeaderType and
ipv6ExtensionHeaderCount IEs.

Each header chain in a Flow with varying extension header chains
MUST be exported in a separate IE.

The same extension header type may appear several times in an
ipv6ExtensionHeaderTypeCountList IE. For example, if an IPv6
packet of a Flow includes a Hop-by-Hop Options header, a
Destination Options header, a Fragment header, and a Destination
Options header, the ipv6ExtensionHeaderTypeCountList IE will
report:

* the count of Hop-by-Hop Options headers,

* the occurrences of the Destination Options headers that are
observed before a Fragment header,

* the occurrences of the Fragment headers, and

* the occurrences of the Destination Options headers that are
observed right after a Fragment header.

If an implementation determines that an observed packet of a Flow
includes an extension header (including an extension header that
it does not support), then the exact observed code of that
extension header MUST be echoed in the
ipv6ExtensionHeaderTypeCountList IE. How an implementation
disambiguates between unknown upper-layer protocols vs. extension
headers is not IPFIX-specific. Refer, for example, to Section 2.2
of [RFC8883] for a behavior of an intermediate node that
encounters an unknown Next Header type.

Abstract Data Type: subTemplateList

Data Type Semantics: list

Additional Information: See the "IPv6 Extension Header Types"
registry at [IANA-EH].

See Section 4 of [RFC8200] for the general definition of IPv6
extension headers.

Reference: RFC 9740

3.5. ipv6ExtensionHeadersLimit Information Element

Name: ipv6ExtensionHeadersLimit

ElementID: 517

Description: When set to "false", this IE indicates that the
exported extension header information (e.g.,
ipv6ExtensionHeadersFull or ipv6ExtensionHeaderTypeCountList) does
not match the full enclosed extension headers, but only up to a
limit that is typically set by hardware or software.

When set to "true", this IE indicates that the exported extension
header information matches the full enclosed extension headers.

Abstract Data Type: boolean

Data Type Semantics: default

Additional Information: See Section 4 of [RFC8200] for the general
definition of IPv6 extension headers.

See [RFC8883] for an example of IPv6 packet processing due to
limits on extension headers.

Reference: RFC 9740

3.6. ipv6ExtensionHeadersChainLength Information Element

Name: ipv6ExtensionHeadersChainLength

ElementID: 518

Description: In theory, there are no limits on the number of IPv6
extension headers that may be present in a packet other than the
path MTU. However, it was regularly reported that IPv6 packets
with extension headers were often dropped in the Internet (e.g.,
[RFC7872]).

As discussed in Section 1.2 of [RFC8883], some hardware devices
implement a parsing buffer of a fixed size to process packets,
including all the headers. When the aggregate length of headers
of an IPv6 packet exceeds that size, the packet will be discarded
or deferred to a slow path.

The ipv6ExtensionHeadersChainLength IE is used to report, in
octets, the length of an extension header chain observed in a
Flow. The length is the sum of the lengths of all extension
headers of the chain. Exporting such information might help
identifying root causes of performance degradation, including
packet drops.

Each header chain length of a Flow with varying extension header
chains MUST be exported in a separate
ipv6ExtensionHeadersChainLength IE.

Abstract Data Type: unsigned32

Data Type Semantics: identifier

Units: octets

Additional Information: See Section 4 of [RFC8200] for the general
definition of IPv6 extension headers.

See [RFC9098] for an overview of operational implications of IPv6
packets with extension headers.

Reference: RFC 9740

3.7. ipv6ExtensionHeaderChainLengthList Information Element

Name: ipv6ExtensionHeaderChainLengthList

ElementID: 519

Description: This IE is used to report the chains and their lengths
as observed in a Flow with varying extension header chains.

This IE is a subTemplateList of ipv6ExtensionHeadersFull and
ipv6ExtensionHeadersChainLength IEs.

If several extension header chains are observed in a Flow, each
header chain MUST be exported in a separate
ipv6ExtensionHeaderChainLengthList IE.

Abstract Data Type: subTemplateList

Data Type Semantics: list

Additional Information: See the "IPv6 Extension Header Types"
registry at [IANA-EH].

See Section 4 of [RFC8200] for the general definition of IPv6
extension headers.

Reference: RFC 9740

4. Information Elements for TCP Options

4.1. tcpOptionsFull Information Element

This section specifies a new IE to cover the full TCP options range.

Name: tcpOptionsFull

ElementID: 520

Description: TCP options in packets of this Flow. The information
is encoded in a set of bit fields. For each TCP option, there is
a bit in this set. The bit is set to 1 if any observed packet of
this Flow contains the corresponding TCP option. Otherwise, if no
observed packet of this Flow contains the respective TCP option,
the value of the corresponding bit is 0.

Options are mapped to bits according to their option numbers. TCP
option Kind 0 corresponds to the least significant bit in the
tcpOptionsFull IE, while Kind 255 corresponds to the most
significant bit of the IE. This approach allows an observer to
export any observed TCP option even if it does not support that
option and without requiring updating a mapping table.

The value of tcpOptionsFull IE may be encoded in fewer octets per
the guidelines in Section 6.2 of [RFC7011].

The presence of tcpSharedOptionExID16List or
tcpSharedOptionExID32List IEs is an indication that a shared TCP
option (Kind=253 or 254) is observed in a Flow. The presence of
tcpSharedOptionExID16List or tcpSharedOptionExID32List IEs takes
precedence over setting the corresponding bits in the
tcpOptionsFull IE for the same Flow. In order to optimize the use
of the reduced-size encoding in the presence of
tcpSharedOptionExID16List or tcpSharedOptionExID32List IEs, the
Exporter MUST NOT set to 1 the shared TCP options (Kind=253 or
254) of the tcpOptionsFull IE that is reported for the same Flow.

Abstract Data Type: unsigned256

Data Type Semantics: flags

Additional Information: See the "TCP Option Kind Numbers" registry
at [IANA-TCP].

See [RFC9293] for the general definition of TCP options.

The tcpOptionsFull IE deprecates the tcpOptions IE (209) that was
initially defined in [RFC5102].

[RFC7012] obsoletes [RFC5102] and specifies that [IANA-IPFIX] is
the normative reference for the tcpOptions IE (209).

Reference: RFC 9740

4.2. tcpSharedOptionExID16 Information Element

Name: tcpSharedOptionExID16

ElementID: 521

Description: Reports an observed 2-byte ExID in a shared TCP option
(Kind=253 or 254) in a Flow.

A basicList of tcpSharedOptionExID16 is used to report
tcpSharedOptionExID16List values.

Abstract Data Type: unsigned16

Data Type Semantics: identifier

Additional Information: See the "TCP Experimental Option Experiment
Identifiers (TCP ExIDs)" registry at [IANA-TCP-ExIDs].

See [RFC9293] for the general definition of TCP options.

See [RFC6994] for the shared use of experimental TCP Options.

Reference: RFC 9740

4.3. tcpSharedOptionExID32 Information Element

Name: tcpSharedOptionExID32

ElementID: 522

Description: Reports an observed 4-byte ExID in a shared TCP option
(Kind=253 or 254) in a Flow.

A basicList of tcpSharedOptionExID32 is used to report
tcpSharedOptionExID32List values.

Abstract Data Type: unsigned32

Data Type Semantics: identifier

Additional Information: See the "TCP Experimental Option Experiment
Identifiers (TCP ExIDs)" registry at [IANA-TCP-ExIDs].

See [RFC9293] for the general definition of TCP options.

See [RFC6994] for the shared use of experimental TCP Options.

Reference: RFC 9740

4.4. tcpSharedOptionExID16List Information Element

Name: tcpSharedOptionExID16List

ElementID: 523

Description: Reports observed 2-byte ExIDs in shared TCP options
(Kind=253 or 254) in a Flow.

A basicList of tcpSharedOptionExID16 IEs in which each
tcpSharedOptionExID16 IE carries an observed 2-byte ExID in a
shared option.

Abstract Data Type: basicList

Data Type Semantics: list

Additional Information: See the "TCP Experimental Option Experiment
Identifiers (TCP ExIDs)" registry at [IANA-TCP-ExIDs].

See [RFC9293] for the general definition of TCP options.

See [RFC6994] for the shared use of experimental TCP Options.

Reference: RFC 9740

4.5. tcpSharedOptionExID32List Information Element

Name: tcpSharedOptionExID32List

ElementID: 524

Description: Reports observed 4-byte ExIDs in shared TCP options
(Kind=253 or 254) in a Flow.

A basicList of tcpSharedOptionExID32 IEs in which each
tcpSharedOptionExID32 IE carries an observed 4-byte ExID in a
shared option.

Abstract Data Type: basicList

Data Type Semantics: list

Additional Information: See the "TCP Experimental Option Experiment
Identifiers (TCP ExIDs)" registry at [IANA-TCP-ExIDs].

See [RFC9293] for the general definition of TCP options.

See [RFC6994] for the shared use of experimental TCP Options.

Reference: RFC 9740

5. Implementation and Operational Considerations

Implementations of tcpSharedOptionExID16, tcpSharedOptionExID32,
tcpSharedOptionExID16List, and tcpSharedOptionExID32List IEs are
assumed to be provided with a list of valid ExIDs [IANA-TCP-ExIDs].
How that list is maintained is implementation-specific. Absent that
list, an implementation can't autonomously determine whether an ExID
is present and, if so, whether its length is 2 or 4 bytes.

If a TCP Flow contains packets with a mix of 2-byte and 4-byte ExIDs,
the same Template Record is used with both tcpSharedOptionExID16 and
tcpSharedOptionExID32 IEs.

6. Examples

This section provides a few examples to illustrate the use of some
IEs defined in this document.

6.1. IPv6 Extension Headers

Figure 1 provides an example of EH/bit mappings in an
ipv6ExtensionHeadersFull IE for an IPv6 Flow in which only the IPv6
Destination Options (0) header is observed. The bits are set
following the table provided in Section 8.4.1.

MSB LSB
1 25
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 ... 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+-+-+-+-+-+-+
|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0| |0|0|0|0|0|0|0|1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+-+-+-+-+-+-+

Figure 1: Example of EH/Bit Mappings in the
ipv6ExtensionHeadersFull IE

The leading zeros are dropped per the reduced-size encoding guidance.
One octet is thus sufficient to send these observed options on the
wire. Concretely, the ipv6ExtensionHeadersFull IE will be set to
0x01 (Figure 2).

MSB LSB
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|0|0|0|0|0|0|0|1|
+-+-+-+-+-+-+-+-+

Figure 2: Example A of ipv6ExtensionHeadersFull IE with Reduced-
Size Encoding

Figure 3 provides another example of reported values in an
ipv6ExtensionHeadersFull IE for an IPv6 Flow in which the Destination
Options (0), IPv6 Hop-by-Hop Options (1), and Routing (5) headers are
observed. One octet is sufficient to report these observed options.
Concretely, the ipv6ExtensionHeadersFull IE will be set to 0x23.

MSB LSB
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|0|0|1|0|0|0|1|1|
+-+-+-+-+-+-+-+-+

Figure 3: Example B of ipv6ExtensionHeadersFull IE with Reduced-
Size Encoding

Let us now consider an IPv6 Flow in which the following EH chain is
observed: Routing (5), Mobility (7), and Authentication (9) header.
Figure 4 shows the ipv6ExtensionHeadersFull IE (0x02A0) to report
this individual chain.

MSB LSB
1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0|0|0|0|0|1|0|1|0|1|0|0|0|0|0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 4: Example of ipv6ExtensionHeadersFull IE Reported for an
Extension Header Chain

6.2. TCP Options

6.2.1. Reduced-Size Encoding

Given TCP Kind allocation practices and the option mapping defined in
Section 4.1, fewer octets are likely to be used for Flows with common
TCP options.

Figure 5 shows an example of Kind/bit mappings in a tcpOptionsFull IE
for a TCP Flow in which End of Option List (0), Maximum Segment Size
(2), and Window Scale (3) options are observed.

MSB LSB
1 25
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 ... 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+-+-+-+-+-+-+
|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0| |0|0|0|0|1|1|0|1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+-+-+-+-+-+-+

Figure 5: Example of TCP Options / Bit Mappings in a
tcpOptionsFull IE

One octet is sufficient to report these observed options.
Concretely, the tcpOptionsFull IE will be set to 0x0D (Figure 6).

MSB LSB
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|0|0|0|0|1|1|0|1|
+-+-+-+-+-+-+-+-+

Figure 6: Example of tcpOptionsFull IE with Reduced-Size Encoding

6.2.2. Shared Options

Let us consider a TCP Flow in which shared options with ExIDs 0x0348
(HOST_ID) [RFC7974], 0x454E (TCP-ENO) [RFC8547], and 0xE2D4C3D9
(Shared Memory Communications over RDMA protocol) [RFC7609] are
observed. Figure 7 shows an excerpt of the Data Set encoding with a
focus on the tcpSharedOptionExID16 and tcpSharedOptionExID32 IEs.
The meaning of the fields is defined in [RFC6313].

MSB LSB
0 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
: ... :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 255 | List Length = 9 |semantic=allof |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|tcpSharedOptionExID16 = 521 | Field Length = 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x0348 | 0x454E |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 255 | List Length = 9 |semantic=allof |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|tcpSharedOptionExID32 = 522 | Field Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0xE2D4C3D9 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: ... :

Figure 7: Example of TCP Shared IEs

7. Security Considerations

IPFIX security considerations are discussed in Section 11 of
[RFC7011].

ipv6ExtensionHeadersChainLength and ipv6ExtensionHeadersLimit IEs can
be exploited by an unauthorized observer as a means to deduce the
processing capabilities of nodes. Section 8 of [RFC7012] discusses
the required measures to guarantee the integrity and confidentiality
of the exported information.

This document does not add new security considerations for exporting
IEs other than those already discussed in Section 8 of [RFC7012].

8. IANA Considerations

8.1. Deprecate ipv6ExtensionHeaders and tcpOptions Information Elements

IANA has updated the "IPFIX Information Elements" registry under the
"IP Flow Information Export (IPFIX) Entities" registry group
[IANA-IPFIX] as follows:

* The ipv6ExtensionHeaders IE (64) entry has been marked as
deprecated in favor of the ipv6ExtensionHeadersFull IE defined in
this document. This note is echoed in the "Additional
Information" of the ipv6ExtensionHeaders IE.

* The tcpOptions IE (209) entry has been marked as deprecated in
favor of the tcpOptionsFull IE defined in this document. This
note is echoed in the "Additional Information" of the tcpOptions
IE.

* The following has been added to the "Additional Information" of
both the ipv6ExtensionHeaders and tcpOptions IEs:

- This Information Element was initially specified in [RFC5102].

- [RFC7012] has obsoleted [RFC5102] and specifies that
[IANA-IPFIX] is the normative reference for this Information
Element.

Also, IANA has updated the reference of ipv6ExtensionHeaders IE (64)
and tcpOptions IE (209) to point to this document.

8.2. IPFIX Information Elements

IANA has added the following new IPFIX IEs to the "IPFIX Information
Elements" registry under the "IP Flow Information Export (IPFIX)
Entities" registry group [IANA-IPFIX]:

+===========+====================================+===============+
| ElementID | Name | Specification |
+===========+====================================+===============+
| 513 | ipv6ExtensionHeaderType | Section 3.1 |
| | | of RFC 9740 |
+-----------+------------------------------------+---------------+
| 514 | ipv6ExtensionHeaderCount | Section 3.2 |
| | | of RFC 9740 |
+-----------+------------------------------------+---------------+
| 515 | ipv6ExtensionHeadersFull | Section 3.3 |
| | | of RFC 9740 |
+-----------+------------------------------------+---------------+
| 516 | ipv6ExtensionHeaderTypeCountList | Section 3.4 |
| | | of RFC 9740 |
+-----------+------------------------------------+---------------+
| 517 | ipv6ExtensionHeadersLimit | Section 3.5 |
| | | of RFC 9740 |
+-----------+------------------------------------+---------------+
| 518 | ipv6ExtensionHeadersChainLength | Section 3.6 |
| | | of RFC 9740 |
+-----------+------------------------------------+---------------+
| 519 | ipv6ExtensionHeaderChainLengthList | Section 3.7 |
| | | of RFC 9740 |
+-----------+------------------------------------+---------------+
| 520 | tcpOptionsFull | Section 4.1 |
| | | of RFC 9740 |
+-----------+------------------------------------+---------------+
| 521 | tcpSharedOptionExID16 | Section 4.2 |
| | | of RFC 9740 |
+-----------+------------------------------------+---------------+
| 522 | tcpSharedOptionExID32 | Section 4.3 |
| | | of RFC 9740 |
+-----------+------------------------------------+---------------+
| 523 | tcpSharedOptionExID16List | Section 4.4 |
| | | of RFC 9740 |
+-----------+------------------------------------+---------------+
| 524 | tcpSharedOptionExID32List | Section 4.5 |
| | | of RFC 9740 |
+-----------+------------------------------------+---------------+

Table 1: New IPFIX Information Elements

8.3. IPFIX Information Element Data Type

IANA has added the following new abstract data type to the "IPFIX
Information Element Data Types" registry under the "IP Flow
Information Export (IPFIX) Entities" registry group [IANA-IPFIX]:

+=======+=============+===========+
| Value | Description | Reference |
+=======+=============+===========+
| 23 | unsigned256 | RFC 9740 |
+-------+-------------+-----------+

Table 2: New IPFIX Information
Element Data Type

8.3.1. unsigned256

The type "unsigned256" represents a non-negative integer value in the
range of '0' to '2^256 - 1'. Similar to Section 6.1.1 of [RFC7011],
this type MUST be encoded using the default canonical format in
network byte order.

Reduced-size encoding (Section 6.2 of [RFC7011]) applies to this data
type. The reduction in size can be to any number of octets smaller
than the unsigned256 type if the data value still fits, i.e., so that
only leading zeros are dropped.

8.4. IPFIX Registry for IPv6 Extension Headers

IANA has created a new registry entitled "IPFIX ipv6ExtensionHeaders
Bits" in the IANA IPFIX registry group [IANA-IPFIX].

When a new code is assigned to an IPv6 EH in [IANA-EH], the next
available free bit is selected by IANA for this EH from the "IPFIX
ipv6ExtensionHeaders Bits" registry, and the registry is updated with
the details that mirror the assigned EH. The "Label" mirrors the
"keyword" of an EH as indicated in [IANA-Protocols], while the
"Protocol Number" mirrors the "Protocol Number" in [IANA-EH]. IANA
has added the following note to [IANA-EH]:

Note: When a new code is assigned to an IPv6 Extension Header, the
next available free bit in [IANA-IPFIX-IPv6EH] is selected for
this new Extension Header. [IANA-IPFIX-IPv6EH] is updated
accordingly. Modifications to existing registrations must be
mirrored in [IANA-IPFIX-IPv6EH].

Otherwise, the registration policy for the registry is Expert Review
(Section 4.5 of [RFC8126]). See more details in Section 8.4.2.

8.4.1. Initial Values

The initial values of this registry are provided in Table 3.

+=======+=======+==========+=========================+===========+
| Bit | Label | Protocol | Description | Reference |
| | | Number | | |
+=======+=======+==========+=========================+===========+
| 0 | DST | 60 | Destination Options for | RFC 9740 |
| | | | IPv6 | |
+-------+-------+----------+-------------------------+-----------+
| 1 | HOP | 0 | IPv6 Hop-by-Hop Options | RFC 9740 |
+-------+-------+----------+-------------------------+-----------+
| 2 | NoNxt | 59 | No Next Header for IPv6 | RFC 9740 |
+-------+-------+----------+-------------------------+-----------+
| 3 | UNK | | Unknown extension or | RFC 9740 |
| | | | transport header | |
+-------+-------+----------+-------------------------+-----------+
| 4 | FRA0 | 44 | Fragment header - first | RFC 9740 |
| | | | fragment | |
+-------+-------+----------+-------------------------+-----------+
| 5 | RH | 43 | Routing header | RFC 9740 |
+-------+-------+----------+-------------------------+-----------+
| 6 | FRA1 | 44 | Fragmentation header - | RFC 9740 |
| | | | not first fragment | |
+-------+-------+----------+-------------------------+-----------+
| 7 | MOB | 135 | Mobility Header | RFC 9740 |
+-------+-------+----------+-------------------------+-----------+
| 8 | ESP | 50 | Encapsulating Security | RFC 9740 |
| | | | Payload | |
+-------+-------+----------+-------------------------+-----------+
| 9 | AH | 51 | Authentication Header | RFC 9740 |
+-------+-------+----------+-------------------------+-----------+
| 10 | HIP | 139 | Host Identity Protocol | RFC 9740 |
+-------+-------+----------+-------------------------+-----------+
| 11 | SHIM6 | 140 | Shim6 Protocol | RFC 9740 |
+-------+-------+----------+-------------------------+-----------+
| 12 | | 253 | Use for experimentation | RFC 9740 |
| | | | and testing | |
+-------+-------+----------+-------------------------+-----------+
| 13 | | 254 | Use for experimentation | RFC 9740 |
| | | | and testing | |
+-------+-------+----------+-------------------------+-----------+
| 14 to | | | Unassigned | |
| 255 | | | | |
+-------+-------+----------+-------------------------+-----------+

Table 3: Initial Values of the "IPFIX ipv6ExtensionHeaders
Bits" Registry

8.4.2. Guidelines for the Designated Experts

It is suggested that multiple designated experts be appointed for
registry change requests.

Designated experts are solicited only for changes that are not
covered by the automatic mirroring described above. For example, a
registration may request two bits for a new EH to cover specific
behaviors or uses of that EH.

Criteria that should be applied by the designated experts include
determining whether the proposed registration duplicates existing
entries, whether the exception to the automatic mirroring procedure
is justified, and whether the registration description is clear and
fits the purpose of this registry.

Within the review period, the designated experts will either approve
or deny the registration request, communicating this decision to the
IANA. Denials should include an explanation and, if applicable,
suggestions as to how to make the request successful.

9. References

9.1. Normative References

[IANA-EH] IANA, "IPv6 Extension Header Types",
<https://www.iana.org/assignments/ipv6-parameters>.

[IANA-IPFIX]
IANA, "IP Flow Information Export (IPFIX) Entities",
<https://www.iana.org/assignments/ipfix>.

[IANA-IPFIX-IPv6EH]
IANA, "IPFIX ipv6ExtensionHeaders Bits",
<https://www.iana.org/assignments/ipfix>.

[IANA-Protocols]
IANA, "Protocol Numbers",
<https://www.iana.org/assignments/protocol-numbers>.

[IANA-TCP] IANA, "TCP Option Kind Numbers",
<https://www.iana.org/assignments/tcp-parameters>.

[IANA-TCP-ExIDs]
IANA, "TCP Experimental Option Experiment Identifiers (TCP
ExIDs)",
<https://www.iana.org/assignments/tcp-parameters>.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.

[RFC6313] Claise, B., Dhandapani, G., Aitken, P., and S. Yates,
"Export of Structured Data in IP Flow Information Export
(IPFIX)", RFC 6313, DOI 10.17487/RFC6313, July 2011,
<https://www.rfc-editor.org/info/rfc6313>.

[RFC6994] Touch, J., "Shared Use of Experimental TCP Options",
RFC 6994, DOI 10.17487/RFC6994, August 2013,
<https://www.rfc-editor.org/info/rfc6994>.

[RFC7011] Claise, B., Ed., Trammell, B., Ed., and P. Aitken,
"Specification of the IP Flow Information Export (IPFIX)
Protocol for the Exchange of Flow Information", STD 77,
RFC 7011, DOI 10.17487/RFC7011, September 2013,
<https://www.rfc-editor.org/info/rfc7011>.

[RFC7012] Claise, B., Ed. and B. Trammell, Ed., "Information Model
for IP Flow Information Export (IPFIX)", RFC 7012,
DOI 10.17487/RFC7012, September 2013,
<https://www.rfc-editor.org/info/rfc7012>.

[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.

[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.

[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.

[RFC9293] Eddy, W., Ed., "Transmission Control Protocol (TCP)",
STD 7, RFC 9293, DOI 10.17487/RFC9293, August 2022,
<https://www.rfc-editor.org/info/rfc9293>.

9.2. Informative References

[EH-LIMITS]
Herbert, T., "Limits on Sending and Processing IPv6
Extension Headers", Work in Progress, Internet-Draft,
draft-ietf-6man-eh-limits-19, 27 February 2025,
<https://datatracker.ietf.org/api/v1/doc/document/draft-
ietf-6man-eh-limits/>.

[RFC5102] Quittek, J., Bryant, S., Claise, B., Aitken, P., and J.
Meyer, "Information Model for IP Flow Information Export",
RFC 5102, DOI 10.17487/RFC5102, January 2008,
<https://www.rfc-editor.org/info/rfc5102>.

[RFC7609] Fox, M., Kassimis, C., and J. Stevens, "IBM's Shared
Memory Communications over RDMA (SMC-R) Protocol",
RFC 7609, DOI 10.17487/RFC7609, August 2015,
<https://www.rfc-editor.org/info/rfc7609>.

[RFC7872] Gont, F., Linkova, J., Chown, T., and W. Liu,
"Observations on the Dropping of Packets with IPv6
Extension Headers in the Real World", RFC 7872,
DOI 10.17487/RFC7872, June 2016,
<https://www.rfc-editor.org/info/rfc7872>.

[RFC7974] Williams, B., Boucadair, M., and D. Wing, "An Experimental
TCP Option for Host Identification", RFC 7974,
DOI 10.17487/RFC7974, October 2016,
<https://www.rfc-editor.org/info/rfc7974>.

[RFC8547] Bittau, A., Giffin, D., Handley, M., Mazieres, D., and E.
Smith, "TCP-ENO: Encryption Negotiation Option", RFC 8547,
DOI 10.17487/RFC8547, May 2019,
<https://www.rfc-editor.org/info/rfc8547>.

[RFC8883] Herbert, T., "ICMPv6 Errors for Discarding Packets Due to
Processing Limits", RFC 8883, DOI 10.17487/RFC8883,
September 2020, <https://www.rfc-editor.org/info/rfc8883>.

[RFC9098] Gont, F., Hilliard, N., Doering, G., Kumari, W., Huston,
G., and W. Liu, "Operational Implications of IPv6 Packets
with Extension Headers", RFC 9098, DOI 10.17487/RFC9098,
September 2021, <https://www.rfc-editor.org/info/rfc9098>.

Acknowledgments

Thanks to Paul Aitken, Éric Vyncke, and Joe Touch for the reviews and
comments. Special thanks to Andrew Feren for sharing data about
scans of IPFIX data he collected.

Thanks to Wesley Eddy for the tsvart review, Yingzhen Qu for the
opsdir review, Dirk Von Hugo for intdir review, Joel Halpern for the
genart review, and Tero Kivinen for the secdir review.

Thanks to Thomas Graf for the Shepherd review.

Thanks to Mahesh Jethanandani for the AD review.

Thanks to Éric Vyncke, Erik Kline, Roman Danyliw, and Zaheduzzaman
Sarker for the IESG review.

Authors' Addresses

Mohamed Boucadair
Orange
Email: [email protected]

Benoit Claise
Huawei
Email: [email protected]