Extended TCP Options and IPv6 Extension Headers IPFIX Information Elements

1.1. Issues with ipv6ExtensionHeaders Information Element

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

• Cover the full extension headers' range (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 [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 139, 140, 253, and 254.¶

• 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., [I-D.ietf-6man-eh-limits]). The specification of the ipv6ExtensionHeaders Information Element does not 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 which 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 extension headers length.¶

Section 3 addresses these issues. Also, ipv6ExtensionHeaders IPFIX IE is deprecated in favor of the new IEs defined in this document.¶

1.2. Issues with tcpOptions Information Element

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

• Describe how some observed TCP option 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 Experimental Identifiers (ExIDs) that are carried in shared TCP options (Kind=253 or 254) [RFC6994].¶

• Optimize the encoding.¶

Section 4 addresses these issues. Also, tcpOptions IE is deprecated in favor of the new IEs defined in this document.¶

3.1. ipv6ExtensionHeaderType Information Element

Name:

ipv6ExtensionHeaderType¶

ElementID:

TBD1¶

Description:

Type of an IPv6 extension header observed in packets of this Flow.¶

Abstract Data Type:

unsigned8¶

Data Type Semantics:

identifier¶

Additional Information:

See [IANA-EH] for assigned extension header types.¶

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

Reference:

This-Document¶

3.2. ipv6ExtensionHeaderCount Information Element

Name:

ipv6ExtensionHeaderCount¶

ElementID:

TBD2¶

Description:

The number of consecutive occurrences of a same extension header type in a Flow.¶

The type of the extension header is provided in the ipv6ExtensionHeaderType Information Element.¶

Abstract Data Type:

unsigned8¶

Data Type Semantics:

totalCounter¶

Additional Information:

See [IANA-EH] for assigned extension header types.¶

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

Reference:

This-Document¶

3.3. ipv6ExtensionHeadersFull Information Element

Name:

ipv6ExtensionHeadersFull¶

ElementID:

TBD3¶

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 [NEW_IPFIX_IPv6EH_SUBREGISTRY]. Bit 0 corresponds to the least-significant bit in the ipv6ExtensionHeadersFull IE while bit 255 corresponds to the most-significant bit 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" (59) 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.¶

Several extension header chains may be observed in a Flow. These extension headers MAY be aggregated in one single ipv6ExtensionHeadersFull Information Element or be exported in separate ipv6ExtensionHeadersFull IEs, one for each extension header chain.¶

Abstract Data Type:

unsigned256¶

Data Type Semantics:

flags¶

Additional Information:

See the assigned bits to each IPv6 extension header type in [NEW_IPFIX_IPv6EH_SUBREGISTRY].¶

See [IANA-EH] for assigned extension header types.¶

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

Reference:

This-Document¶

• Note to the RFC Editor: Please replace [NEW_IPFIX_IPv6EH_SUBREGISTRY] with the link to the "ipv6ExtensionHeaders Bits" registry (Section 8.4).¶

3.4. ipv6ExtensionHeaderTypeCountList Information Element

Name:

ipv6ExtensionHeaderTypeCountList¶

ElementID:

TBD4¶

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 Information Element echoes the order of extension headers and number of consecutive occurrences of the same extension header type in a Flow.¶

This Information Element is a subTemplateList of ipv6ExtensionHeaderType and ipv6ExtensionHeaderCount Information Elements.¶

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

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

• the count of Hop-by-Hop Options header,¶

• the occurrences of the Destination Options header that are observed before the Fragment header,¶

• the occurrences of the Fragment header, and¶

• the occurrences of the Destination Options header that are observed right after the Fragment header.¶

Abstract Data Type:

subTemplateList¶

Data Type Semantics:

list¶

Additional Information:

See the assigned IPv6 extension header types in [IANA-EH].¶

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

Reference:

This-Document¶

3.5. ipv6ExtensionHeadersLimit Information Element

Name:

ipv6ExtensionHeadersLimit¶

ElementID:

TBD5¶

Description:

When set to "false", this Information Element indicates that the exported extension headers 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 Information Element 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:

This-Document¶

3.6. ipv6ExtensionHeadersChainLength Information Element

Name:

ipv6ExtensionHeadersChainLength¶

ElementID:

TBD6¶

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 are often dropped in the Internet.¶

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 length of all extension headers of the chain. Exporting such information might help identifying root causes of performance degradation, including packet drops.¶

If several extension header chains are observed in a Flow, each header chain length 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:

This-Document¶

4.1. tcpOptionsFull Information Element

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

Name:

tcpOptionsFull¶

ElementID:

TBD7¶

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 support that option and without requiring updating a mapping table.¶

Abstract Data Type:

unsigned256¶

Data Type Semantics:

flags¶

Additional Information:

See the assigned TCP option Kinds at [IANA-TCP].¶

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

Reference:

This-Document¶

4.2. tcpSharedOptionExID16 Information Element

Name:

tcpSharedOptionExID16¶

ElementID:

TBD8¶

Description:

Any observed 2-byte Experiments IDs (ExIDs) in a shared TCP option (Kind=253 or 254) in a Flow. The information is encoded in a set of 16-bit fields. Each 16-bit field carries an observed 2-byte ExID in a shared option.¶

Abstract Data Type:

octetArray¶

Data Type Semantics:

identifier¶

Additional Information:

See assigned ExIDs at [IANA-TCP-EXIDs].¶

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

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

Reference:

This-Document¶

4.3. tcpSharedOptionExID32 Information Element

Name:

tcpSharedOptionExID32¶

ElementID:

TBD9¶

Description:

Any observed 4-byte Experiments IDs (ExIDs) in a shared TCP option (Kind=253 or 254) in a Flow. The information is encoded in a set of 32-bit fields. Each 32-bit field carries an observed 4-byte ExID in a shared option.¶

Abstract Data Type:

octetArray¶

Data Type Semantics:

identifier¶

Additional Information:

See assigned ExIDs at [IANA-TCP-EXIDs].¶

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

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

Reference:

This-Document¶

5.1. IPv6 Extension Headers

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

If an implementation determines that an observed packet of a Flow includes an extension header that it does not support, then the exact observed code of that extension header will be echoed in the ipv6ExtensionHeaderTypeCountList IE (Section 3.4). How an implementation disambiguates between unknown upper-layer protocols vs. extension headers is not IPFIX-specific. Readers may refer, for example, to Section 2.2 of [RFC8883] for a behavior of an intermediate node that encounters an unknown Next Header type. It is out of the scope of this document to discuss those considerations.¶

The ipv6ExtensionHeadersFull Information Element SHOULD NOT be exported if ipv6ExtensionHeaderTypeCountList Information Element is also present because of the overlapping scopes between these two IEs. If both IEs are present, then ipv6ExtensionHeaderTypeCountList Information Element takes precedence.¶

The ipv6ExtensionHeadersLimit IE (Section 3.5) may or may not be present when the ipv6ExtensionHeadersChainLength IE (Section 3.6) is also present as these IEs are targeting distinct properties of extension headers handling.¶

5.2. TCP Options

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

Implementations of tcpSharedOptionExID16 and tcpSharedOptionExID32 IEs are assumed to be provided with a list of valid Experiment IDs [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 it is 2- or 4-byte length.¶

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

6.1. IPv6 Extension Headers

Figure 1 provides an example of reported values in an ipv6ExtensionHeadersFull IE for an IPv6 Flow in which only the IPv6 Destination Options header is observed. One octet is sufficient to report these observed options. Concretely, the ipv6ExtensionHeadersFull IE will be set to 0x01. 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 2 provides another example of reported values in an ipv6ExtensionHeadersFull IE for an IPv6 Flow in which the IPv6 Hop-by-Hop Options, Routing, and Destination Options headers are observed. One octet is sufficient to report these observed options. Concretely, the ipv6ExtensionHeadersFull IE will be set to 0x23.¶

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|1|0|0|0|1|1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+-+-+-+-+-+-+

6.2. TCP Options

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 3 shows an example of reported values in a tcpOptionsFull IE for a TCP Flow in which End of Option List, Maximum Segment Size, and Window Scale options are observed. One octet is sufficient to report these observed options. Concretely, the tcpOptionsFull IE will be set to 0x0D.¶

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|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+-+-+-+-+-+-+

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 RMDA protocol) [RFC7609] are observed. As shown in Figure 4, two TCP shared IEs will be used to report these observed ExIDs:¶

1. The tcpSharedOptionExID16 IE set to 0x348454E to report observed 2-byte ExIDs: HOST_ID and TCP-ENO ExIDs.¶

2. The tcpSharedOptionExID32 IE set to 0xE2D4C3D9 to report the only observed 4-byte ExID.¶

tcpSharedOptionExID16 IE:

MSB                                                          LSB
                     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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|              0x0348           |             0x454E            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

tcpSharedOptionExID32 IE:

MSB                                                          LSB
                     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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                           0xE2D4C3D9                          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

8.1. Deprecate ipv6ExtensionHeaders and tcpOptions Information Elements

This document requests IANA to update the "IPFIX Information Elements" registry under the "IP Flow Information Export (IPFIX) Entities" registry group [IANA-IPFIX] as follows:¶

• Update the ipv6ExtensionHeaders IE (64) entry by marking it as deprecated in favor of the ipv6ExtensionHeadersFull IE defined in this document. This note should also be echoed in the "Additional Information" of this IE.¶

• Update the tcpOptions IE (209) entry by marking it as deprecated in favor of the tcpOptionsFull IE defined in this document. This note should also be echoed in the "Additional Information" of this IE.¶

IANA is also requested to update the reference of ipv6ExtensionHeaders IE (64) and tcpOptions IE (209) to point to this document.¶

8.2. New IPFIX Information Elements

This document requests IANA to add the following new IPFIX IEs to the "IPFIX Information Elements" registry under the "IP Flow Information Export (IPFIX) Entities" registry group [IANA-IPFIX]:¶

8.3. New IPFIX Information Element Data Type

This document requests IANA to add 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]:¶

The type "unsigned256" represents a non-negative integer value in the range of '0' to '2^256 - 1'. This type MUST be encoded per Section 6.1.1 of [RFC7011]. Reduced-Size encoding (Section 6.2 of [RFC7011]) applies to this data type.¶

8.4. IPFIX Subregistry for IPv6 Extension Headers

This document requests IANA to create a new registry entitled "ipv6ExtensionHeaders Bits" under 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 "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 is requested to add the following note to [IANA-EH]:¶

• Note:

  When a new code is assigned to an IPv6 Extension Header, the next available free bit in [NEW_IPFIX_IPv6EH_SUBREGISTRY] is selected for this new Extension Header. [NEW_IPFIX_IPv6EH_SUBREGISTRY] is updated accordingly. Modifications to existing registrations must be mirrored in [NEW_IPFIX_IPv6EH_SUBREGISTRY].¶

• Note to the RFC Editor: Please replace [NEW_IPFIX_IPv6EH_SUBREGISTRY] with the link used by IANA for this new registry.¶

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