Network Working Group F. L. Templin, Ed.
Internet-Draft Boeing Research & Technology
Intended status: Experimental T. Herbert
Expires: 5 December 2025 Unaffiliated
3 June 2025
IPv6 Extended Fragment Header (EFH)
draft-templin-6man-ipid-ext2-17
Abstract
The Internet Protocol, version 4 (IPv4) header includes a 16-bit
Identification field in all packets, but this length is too small to
ensure reassembly integrity even at moderate data rates in modern
networks. Even for Internet Protocol, version 6 (IPv6), the 32-bit
Identification field included when a Fragment Header is present may
be smaller than desired for some applications. This specification
addresses these limitations by defining an IPv6 Extended Fragment
Header (EFH) that includes a 64-bit Identification with efficient
fragmentation and reassembly procedures.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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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."
This Internet-Draft will expire on 5 December 2025.
Copyright Notice
Copyright (c) 2025 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 (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
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and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. IPv6 Extended Fragment Header (EFH) . . . . . . . . . . . . . 5
5. IPv6 Source Fragmentation . . . . . . . . . . . . . . . . . . 7
6. Intermediate System Fragmentation . . . . . . . . . . . . . . 8
7. IPv6 Destination Reassembly . . . . . . . . . . . . . . . . . 8
8. Destination Qualification and Path MTU . . . . . . . . . . . 9
9. Packet Size Issues . . . . . . . . . . . . . . . . . . . . . 9
10. Fragmentation Reports and Retransmissions . . . . . . . . . . 10
11. Multicast and Anycast . . . . . . . . . . . . . . . . . . . . 11
12. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 12
13. Implementation Status . . . . . . . . . . . . . . . . . . . . 13
14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
14.1. IPv6 Parameters . . . . . . . . . . . . . . . . . . . . 13
14.2. ICMPv6 Parameters . . . . . . . . . . . . . . . . . . . 14
14.3. ICMP Parameters . . . . . . . . . . . . . . . . . . . . 14
15. Security Considerations . . . . . . . . . . . . . . . . . . . 14
16. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15
17. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
17.1. Normative References . . . . . . . . . . . . . . . . . . 15
17.2. Informative References . . . . . . . . . . . . . . . . . 16
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
The Internet Protocol, version 4 (IPv4) header includes a 16-bit
Identification in all packets [RFC0791], but this length is too small
to ensure reassembly integrity even at moderate data rates in modern
networks [RFC4963][RFC6864][RFC8900]. For Internet Protocol, version
6 (IPv6), the Identification field is only present in packets that
include a Fragment Header [RFC8200], but even its standard length of
32 bits may be too small for some applications. Standard IP
fragmentation is also subject to numerous performance and security
issues that indicate a need for a more robust service. This
specification therefore defines a new fragmentation service that
addresses these issues through the introduction of an IPv6 Extended
Fragment Header (EFH).
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The IPv6 EFH employs a fragmentation/reassembly algorithm based on an
ordinal fragment index in combination with the non-final fragment
payload size instead of a 13-bit integer encoding an 8-octet offset.
In this arrangement, both fragmentation and reassembly are greatly
simplified allowing for efficient implementations. These
improvements are based on an ample minimum fragment payload size made
possible by the 1280 octet IPv6 minimum MTU.
The IPv6 EFH is needed for networks that engage fragmentation and
reassembly at extreme data rates, or for cases when advanced packet
Identification uniqueness assurance is critical. (Placement of the
IPv6 EFH in a Destination Options header may also make the option
less prone to network filtering.) This specification further defines
a messaging service for adaptive realtime response to loss and
congestion related to fragmentation/reassembly. Together, these
extensions support robust fragmentation and reassembly services as
well as packet Identification uniqueness for IPv6.
The IPv6 EFH 64-bit Identification concept is similar to the Extended
Sequence Number (ESN) framework found in IPsec AH [RFC4302] and ESP
[RFC4303]. In both cases, nodes can apply header compression to
transmit only the least significant bits while retaining the most
significant bits in cache memory.
2. Terminology
The terms "Maximum Transmission Unit (MTU)", "Effective MTU to
Receive (EMTU_R)", "Effective MTU to Send (EMTU_S)" and "Maximum
Segment Lifetime (MSL)" from standard Internetworking terminology
apply [RFC1122]. The term "Maximum Receive Unit (MRU)" is equivalent
to EMTU_R, and the term "maximum datagram lifetime (MDL)" (see:
[RFC0791][RFC6864]) is equivalent to MSL.
The term "Packet Too Big (PTB)" refers to an ICMPv6 "Packet Too Big"
message [RFC8201][RFC4443] or a new ICMPv4 "PTB" message type defined
in this document (see: IANA Considerations).
The term "flow" refers to a sequence of packets sent from a
particular source to a particular unicast, anycast or multicast
destination that a node desires to label as a flow [RFC6437].
The term "Extended Fragment Header (EFH)" refers to a new IPv6
Destination Option defined in this document. The EFH is included in
a Destination Options header as the final Per-Fragment header, while
the remainder of the packet that follows the Per-Fragment headers is
known as the "fragment payload".
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The term "Fragmentation Report (FR)" refers to an alternate option
type encoding of the EFH option used to report reassembly conditions.
Destinations may include the FR in return packets to EFH fragment
sources.
The Automatic Extended Route Optimization (AERO)
[I-D.templin-6man-aero3] and Overlay Multilink Network Interface
(OMNI) [I-D.templin-6man-omni3] services employ the IPv6 EFH for
secure adaptation layer encapsulation and fragmentation. New packet
types termed "IP Parcels and Advanced Jumbos (AJs)" are specified in
[I-D.templin-6man-parcels2].
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.
3. Motivation
Upper layer protocols can achieve greater performance by configuring
segment sizes that exceed the path Maximum Transmission Unit (MTU).
When the segment size exceeds the path MTU, lower layer IP
fragmentation is a natural consequence. However, the 4-octet
(32-bit) Identification field of the Fragment Header may be too small
to ensure reassembly integrity at sufficiently high data rates,
especially when the source resets the starting sequence number often
to maintain an unpredictable profile [RFC7739]. This specification
therefore proposes to fortify the IPv6 Identification by extending
its length.
Performance increases for upper layer protocols that use larger
segment sizes was historically observed for NFS over UDP, and can
still be readily observed today for TCP and the Delay Tolerant
Network (DTN) Licklider Transmission Protocol (LTP) - see:
[I-D.templin-dtn-ltpfrag]. The performance testbed included a pair
of modern high-performance workstations with 100Gbps Ethernet cards
connected via a point-to-point link and running a modern public
domain linux release. TCP performance using the public domain
'iperf3' tool was proven to increase when larger user buffer sizes
are used even if they exceed the path MTU and invoke a service known
as Generic Segment/Receive Offload (GSO/GRO). LTP performance
improvement with segment sizes that exceed the path MTU was similarly
proven using the HDTN and ION-DTN LTP implementations when IP
fragmentation and reassembly were invoked.
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In addition to accommodating higher data rates in the presence of
fragmentation and reassembly, extending the IPv6 Identification can
enable other important services. For example, an extended
Identification can support a duplicate packet detection service where
the network remembers recent Identification values to aid detection
of potential duplicates. When an encapsulation source includes an
IPv6 EFH, the extended Identification can also serve as a sequence
number that allows each encapsulation destination to exclude any
packets with values outside of the current sequence number window as
potential spurious transmissions.
The standard IPv6 Fragment Header also carried forward the awkward
fragmentation parameters found in IPv4 including a 13-bit quadword
Fragment Offset value, no restrictions on fragment-by-fragment
payload sizes and no limits on numbers of fragments produced. In
contrast, the IPv6 EFH service mandates same-sized fragments, forbids
tiny fragments, places a conservative limit on the maximum number of
fragments and eliminates any possibilities for fragment overlap.
These factors ensure a more secure and performance-optimized
fragmentation and reassembly service.
An optimized IP fragmentation and reassembly service using an
extended Identification can provide a useful tool for performance
maximization and path MTU robustness in the Internet. This document
therefore presents a means to extend the IPv6 Identification in a
more efficient fragmentation and reassembly specification to better
support these services through the introduction of an IPv6 Extended
Fragment Header (EFH).
4. IPv6 Extended Fragment Header (EFH)
For a conventional 4-octet IPv6 Identification, the source can simply
include a standard IPv6 Fragment Header as specified in [RFC8200]
with the Fragment Offset field and M flag set either to values
appropriate for a fragmented packet or the value 0 for an
unfragmented packet. The source then includes a 4-octet
Identification value for the packet.
For an extended Identification, advanced fragmentation and reassembly
procedures and/or for paths that drop packets including the standard
IPv6 Fragment Header, this specification permits the source to
instead include an IPv6 EFH. The source includes the IPv6 EFH in a
Destination Options header positioned as the final IPv6 Per-Fragment
Header. The remainder of the packet beyond the Destination Option
header beginning with any Extension and Upper Layer Headers for the
first fragment (or protocol data for non-first fragments) is known as
the fragment payload.
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The Destination Options header that includes the EFH option therefore
appears in each fragment in the same position where the standard
Fragment Header would normally appear while the Fragment Header
itself is omitted - see Sections 4.1 and 4.5 of [RFC8200].
The IPv6 EFH Destination Option is formatted as shown in Figure 1:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Opt Data Len | NH-Actual |M|P| Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+- Identification (32/64 bits) -+-+-+-+
~ ~
+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+
Option Type 8-bit value '100[TBD1]'.
Opt Data Len 8-bit value 6 for a 32-bit Identification
or 10 for a 64-bit Identification.
NH-Actual the actual value of the original Destination
Options Next Header prior to fragmentation.
M/P/Index "(M)ore Fragments" and "(P)robe" flags
followed by a 6-bit "Index" that identifies
the ordinal index for each fragment payload.
Identification an 8-octet (64 bit) unsigned integer
Identification, in network byte order.
Figure 1: IPv6 EFH Destination Option
The IPv6 EFH Destination Option is therefore identified as an Option
Type with the low-order 5 bits set to TBD1 (see: IANA Considerations)
and with the third-highest-order bit (i.e., "chg") set to 0. The
highest-order 2 bits (i.e., "act") are set to '10' so that
destinations that do not recognize the option will drop the packet or
fragment and (possibly) also return an ICMPv6 Parameter Problem
message. When Opt Data Len is 10, the Identification field is 8
octets (64 bits) in length. A Destination Options header that
includes the option may appear either in an unfragmented IPv6 packet
or in one for which IPv6 fragmentation is applied.
In a compressed form, the source sets Opt Data Len to the value 6
(i.e., instead of 10) and includes only the 4 least significant
octets of the (8-octet) Identification. The source can engage this
compressed form after it has already published the 4 most significant
octets to establish state in any intermediate systems and the
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destination end system. Nodes that have cached the 4 most
significant octets regard the Identification as a full 8 octet value
for the purpose of packet filtering and reassembly; otherwise, they
regard the 4 most significant octets as 0.
For improved efficiency, sources often send packets that include full
IPv6 headers (including the EFH extension) only as initial packets of
a flow while including greatly compressed headers in subsequent
packets. When a flow becomes stale, the source can send additional
full header packets to refresh flow state until header compression
can resume. The AERO/OMNI service is an example where the EFH is
subject to efficient header compression.
5. IPv6 Source Fragmentation
IPv6 fragmentation using the EFH is conducted in a manner similar to
standard IPv6 fragmentation (see: Section 4.5 of [RFC8200]) with the
following exceptions.
When the source performs fragmentation using the IPv6 EFH, it creates
fragments of the same packet based on the (Source, Destination,
Identification)-tuple. The source SHOULD produce the smallest number
of fragments possible within current path MTU constraints and MUST
produce no more than 64 fragments per packet. The fragment payload
of each non-final fragment following the Destination Options header
MUST NOT be smaller than 1024 octets, allowing for up to 256 octets
of Per-Fragment headers plus any lower-layer IP encapsulations within
the 1280 octet IPv6 minimum path MTU. Each non-final fragment
payload MUST be equal in length, while the final fragment payload MAY
be smaller and MUST NOT be larger.
For each of the F fragments produced during fragmentation, the source
writes an ordinal index number beginning with 0 in the "Index" field
for the first fragment and increasing by 1 for each successive non-
first fragment while setting the "M" flag accordingly. Specifically,
the source sets (Index, M) to (0, 1) for the first fragment, (1, 1)
for the second, (2, 1) for the third, etc., up to and including
((F-1), 0) for the final fragment.
For each fragment produced during fragmentation, the source inserts a
Destination Options header including the IPv6 EFH option as the final
Per-Fragment header. The source then caches the Destination Options
header Next Header value in the NH-Actual field and (for each non-
first fragment) resets the Next Header field to "No Next Header".
Intermediate systems that forward non-first fragments prepared in
this way will therefore ignore the fragment payload that follows (by
virtue of the "No Next Header" setting) unless they are configured to
more deeply inspect the data content.
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6. Intermediate System Fragmentation
Unlike IPv4, fragmentation in IPv6 is performed only by source nodes,
not by routers along a packet's delivery path [RFC8200]. However,
the standard IPv6 Fragment Header has no protocol provisions to
prevent intermediate systems from performing further fragmentation on
individual packets processed in isolation and the destination would
still reassemble correctly the same as for fragments produced by the
source.
For packets that include an IPv6 EFH, any fragmentation by an
intermediate system would cause malformed fragments to arrive at the
destination and therefore spoil any in-progress reassemblies. An
intermediate system could instead perform the onerous task of
(virtual) reassembly of all fragments of the same packet before
applying re-fragmentation, but this might not scale well in all
environments.
Draft version -12 of the IPv6 EHF specification included an "in case
of emergency break glass" service that allowed intermediate systems
to re-fragment individual packets without requiring (virtual)
reassembly. The service would support assured delivery even during
path MTU change events, but would also provide opportunity for
intermediate system misuse resulting in degraded performance. The
service has therefore been removed pending an open investigation on
intermediate system behavior.
7. IPv6 Destination Reassembly
IPv6 reassembly using the EFH is conducted in a similar manner as for
standard IPv6 reassembly (see: Section 4.5 of [RFC8200]) with the
following exceptions.
When the destination receives original EFH fragments with the same
(Source, Destination, Identification)-tuple, it reassembles by
concatenating the payloads of consecutive fragments in ascending
ordinal Index numbers, i.e., ordinal 0, followed by 1, followed by 2,
etc. until all fragments are concatenated. In the process, the
destination discards any non-final fragments with fragment payload
lengths less than 1024 octets or with fragment payload lengths that
differ from the others.
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8. Destination Qualification and Path MTU
Destinations that do not recognize the IPv6 EFH option drop the
packet and may also return a Code 2 ICMPv6 Parameter Problem message
[RFC4443]. (ICMPv6 messages may be lost on the return path and/or
manufactured by an adversary, however, and therefore provide only an
advisory indication.)
The source can then test whether destinations recognize the IPv6 EFH
option by occasionally sending "probe" packets/fragments that include
the option. The source has assurance that a destination recognizes
the option if it receives acknowledgments; otherwise, it may receive
Code 2 ICMPv6 Parameter Problem messages as hints that a destination
does not recognize the option. The source should re-probe the path
occasionally in case routing redirects a flow to a different anycast
destination or in case a multicast group membership changes (see:
Section 11).
9. Packet Size Issues
When the source node sends fragment payloads larger than the minimum
size of 1024 octets using the IPv6 EFH option, it should probe the
path MTU for each flow occasionally per [RFC8899] by setting the P
flag to 1 in probe first fragments, i.e., those with Index set to 0.
When the destination receives a probe fragment for a particular flow
(i.e., one with P set to 1 and Index set to 0), it returns a
responsive packet that includes a Fragmentation Report (FR)
Destination Option per Section 10. The responsive packet can be any
authentic return IP packet with the IP Source and Destination
addresses reversed.
The source can then perform source fragmentation using the IPv6 EFH
option with the fragment payload size advanced to the size of the
probe.
If the destination experiences reassembly congestion, it can begin
returning authentic IP packets with Fragmentation Report options to
the source (see: Section 10) and with MRU set to a reduced size.
When the source receives the messages, it should temporarily reduce
the size of its future transmissions for the flow but may resume
using larger sizes if the FR messages subside.
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If the source is an encapsulation ingress, it also returns a
translated PTB message with a corresponding soft error Code to the
original source per [RFC2473]. If the source regards the packet as
lost, it sets the Code to "Soft Error (loss); otherwise, it sets the
Code to "Soft Error (no loss)". For IPv4, the source uses a new
ICMPv4 PTB message Type TBD2 and with a corresponding soft error Code
(see: IANA Considerations).
10. Fragmentation Reports and Retransmissions
End systems that recognize the IPv6 EFH also recognize an IPv6
Fragmentation Report (FR) Option that uses option type TBD1 the same
as for the EFH itself but with the act/change bits set to '000' and
formatted as shown below:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Opt Data Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flow Label (20 bits) | MRU (11 bits) |L|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+- Identification (64 bits) -+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
+~+~+~+~ Bitmap (64 bits when present) ~+~+~+~+
~ ~
+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+~+
Figure 2: IPv6 Fragmentation Report Option
The destination end system includes the IPv6 FR option in a return
packet to the source to report receipt of a probe, reassembly
congestion conditions and/or fragment loss. Any return packet (i.e.,
one with the IP Source and Destination Addresses from the packet that
triggered the FR reversed) can be used to carry the option,
especially if it includes identifying parameters and/or
authentication signatures.
The destination sets Flow Label to the 20-bit Flow Label
corresponding to this reassembly. The destination then sets MRU to
the most significant 11 bits of the recommended 16-bit maximum
reassembly size under current congestion conditions. When the 11
transmitted MRU bits are all-1's, the 5 untransmitted bits are also
interpreted as all-1's; otherwise, they are interpreted as all-0's.
The destination then includes the full 8 octet (64-bit)
Identification even if the invoking packet included only the 4 least
significant octets.
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If all fragments of the packet have arrived the destination sets Opt
Data Len to 12, sets (L)oss to 0 and omits the Bitmap field. If the
destination has abandoned reassembly for this packet, it instead sets
L to 1. If some fragments are missing and might benefit from
retransmissions, the destination instead sets Opt Data Len to 20 and
includes a 64-bit Bitmap field with Bitmap(i) (for i=0 to 63) set to
1 for each ordinal fragment index it has received for this reassembly
and set to 0 for all others.
When the source receives authentic IP packets with the IPv6 FR
option, it matches the Identification with one of its recent
transmissions for the corresponding flow. If the recent transmission
was a probe, the source can advance the fragment size for the flow to
the probe size. The source should also reduce, maintain or increase
the size of its continued packet transmissions for the flow if
necessary according to the advertised MRU.
If the FR option further includes a Bitmap, the source can retransmit
any missing ordinal fragments if it still has them in its cache
provided the delay would not interfere with upper layer protocol
retransmissions. When the source receives IPv6 FRs that advertise a
larger MRU (or when it ceases to receive IPv6 FRs), it can begin to
increase its packet sizes. This ensures that the packet size is
adaptive for a given flow.
Note: the IPv6 FR option may appear in the same Destination Options
header that includes an IPv6 EFH option. Their bounded sizes permit
both options to appear without exceeding recommended limits (see:
[I-D.ietf-6man-eh-limits]).
11. Multicast and Anycast
In addition to unicast flows, similar considerations apply for flows
in which the Destination Address is multicast or anycast. Unless the
source and all candidate destinations are members of a limited domain
network [RFC8799] for which all nodes recognize the IPv6 EFH, some
destinations may recognize the option while others drop packets
containing the option and may return a Code 2 ICMPv6 Parameter
Problem message [RFC4443].
When a source sends packets/fragments with IPv6 EFH options to a
multicast group, the packets/fragments may be replicated in the
network such that a single transmission may reach N destinations over
as many as N different paths. Some destinations may then return IPv6
packets with IPv6 FR options if they experience congestion and/or
loss, while other destinations may return Code 2 ICMPv6 Parameter
Problem messages if they do not recognize the IPv6 EFH option.
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While the source receives authentic PTB messages or authentic IP
packets with IPv6 FR options, it should reduce the sizes of the
packets/fragments it sends to the flow multicast group even if only
one or a few paths or destinations are currently experiencing
congestion. This means that transmissions to a multicast group for a
given flow will converge to the performance characteristics of the
lowest common denominator group member destinations and/or paths.
While the source receives ICMPv6 Parameter Problem messages and/or
otherwise detects that some multicast group members do not recognize
the IPv6 EFH option, it must determine whether the benefits for group
members that recognize the option outweigh the drawbacks of service
denial for those that do not.
When a source sends packets/fragments with IPv6 EFH options to an
anycast address, routing may direct initial fragments of the same
packet to a first destination while directing the remaining fragments
to other destinations that configure the same address. These wayward
fragments will simply result in incomplete reassemblies at each such
anycast destination which will soon purge the fragments from the
reassembly buffer. The source will eventually retransmit, and all
resulting fragments should eventually reach a single reassembly
target.
12. Requirements
Normative aspects of standard IPv6 fragmentation and reassembly
[RFC8200] apply also to the IPv6 EFH except where this document
specifies differences.
Sources and Destinations MUST apply EFH fragmentation and reassembly
according to the 3-tuple (Source, Destination, Identification). This
means that all flows share the same Identification number space for
the purpose of fragmentation and reassembly, but path MTU feedback is
on a per-flow basis.
Destinations that accept flows using IPv6 EFH options MUST configure
an EMTU_R of 65535 octets or larger. Destinations MAY advertise
"soft" temporary EMTU_R reductions in FR messages during periods of
loss/congestion, but MUST continue to honor the "hard" upper limit.
The source SHOULD therefore respond to FR messages from the
destination by sending EFH fragments at rates that will minimize
reassembly congestion.
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Sources MUST NOT include more than one IPv6 Standard or Extended
Fragment Header in each IPv6 packet/fragment, and destinations MUST
silently drop packets/fragments with multiples. If the source
includes an IPv6 EFH, it MUST appear in a Destination Options header
that appears as the final Per-Fragment header before the fragment
payload.
Sources that include an IPv6 EFH option MUST perform fragmentation
such that at most 64 fragments are produced and all non-final
fragments include equal-length fragment payloads no smaller than 1024
octets. The final fragment MAY be smaller and MUST NOT be larger.
Sources that include the IPv6 EFH option in packet transmissions MUST
also recognize the IPv6 FR option in return packets as specified in
Section 10.
13. Implementation Status
In progress.
14. IANA Considerations
14.1. IPv6 Parameters
The IANA is requested to assign a new IPv6 Destination Option type in
the "Destination Options and Hop-by-Hop Options" table of the
https://www.iana.org/assignments/ipv6-parameters/ registry group
(registration procedures IESG Approval, IETF Review or Standards
Action). The option type should appear in 2 consecutive table
entries.
The first entry sets "act" to '00', "chg" to '0', "rest" to TBD1,
"Description" to "IPv6 Fragmentation Report" and "Reference" to this
document [RFCXXXX].
The second entry sets "act" to '10', "chg" to '0', "rest" to TBD1,
"Description" to "IPv6 Extended Fragment Header" and "Reference" to
this document [RFCXXXX].
Both table entries finally set "Hex Value" to the 2-digit hexadecimal
value corresponding to the 8-bit concatenation of act/chg/rest.
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14.2. ICMPv6 Parameters
The IANA is instructed to assign new Code values in the "ICMPv6 Code
Fields: Type 2 - Packet Too Big" registry in the
https://www.iana.org/assignments/icmpv6-parameters registry group
(registration procedure is Standards Action or IESG Approval). The
registry entries should appear as follows:
Code Name Reference
--- ---- ---------
0 PTB Hard Error [RFC4443]
1 (suggested) PTB Soft Error (loss) [RFCXXXX]
2 (suggested) PTB Soft Error (no loss) [RFCXXXX]
Figure 3: ICMPv6 Code Fields: Type 2 - Packet Too Big Values
14.3. ICMP Parameters
The IANA is instructed to assign a new Type number TBD2 in the "ICMP
Type Numbers" registry in the https://www.iana.org/assignments/icmp-
parameters registry group (registration procedures IESG Approval or
Standards Action). The entry should set "Type" to TBD2, "Name" to
"Packet Too Big (PTB)" and "Reference" to [RFCXXXX] (i.e., this
document).
The IANA is further instructed to create a new table titled: "Type
TBD2 - Packet Too Big (PTB)" in the "Code Fields" registry, with
registration procedures IESG Approval or Standards Action. The table
should have the following initial format:
Code Name Reference
--- ---- ---------
0 Reserved [RFCXXXX]
1 (suggested) PTB Soft Error (loss) [RFCXXXX]
2 (suggested) PTB Soft Error (no loss) [RFCXXXX]
Figure 4: Type TBD2 - Packet Too Big (PTB)
15. Security Considerations
All aspects of IP security apply equally to this document, which does
not introduce any new vulnerabilities. Moreover, when employed
correctly the mechanisms in this document robustly address known IP
reassembly integrity concerns [RFC4963] and also provide an advanced
degree of packet Identification uniqueness assurance.
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All security aspects of [RFC7739], including the algorithms for
selecting fragment identification values, apply also to the IPv6 EFH.
In particular, the source should reset its starting Identification
value frequently to maintain an unpredictable profile.
All normative security guidance on IPv6 fragmentation found in
[RFC8200] (e.g., processing of tiny first fragments, overlapping
fragments, etc.) applies also to the fragments generated under the
IPv6 EFH.
IPsec AH [RFC4302] and ESP [RFC4303] define an Extended Sequence
Number (ESN) that is analogous to the 64-bit Identification specified
for the IPv6 EFH option. Nodes that employ the IPv6 EFH can use the
Identification value as a sequence number to improve security in the
same fashion as for IPsec AH/ESP ESNs.
16. Acknowledgements
This work was inspired by continued DTN performance studies. Amanda
Baber, Bob Hinden, Christian Huitema, Mark Smith and Eric Vyncke
offered useful insights that helped improve the document.
Honoring life, liberty and the pursuit of happiness.
17. References
17.1. Normative References
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<https://www.rfc-editor.org/info/rfc791>.
[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122,
DOI 10.17487/RFC1122, October 1989,
<https://www.rfc-editor.org/info/rfc1122>.
[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>.
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006,
<https://www.rfc-editor.org/info/rfc4443>.
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[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>.
[RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed.,
"Path MTU Discovery for IP version 6", STD 87, RFC 8201,
DOI 10.17487/RFC8201, July 2017,
<https://www.rfc-editor.org/info/rfc8201>.
17.2. Informative References
[I-D.ietf-6man-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/doc/html/draft-ietf-6man-eh-
limits-19>.
[I-D.templin-6man-aero3]
Templin, F., "Automatic Extended Route Optimization
(AERO)", Work in Progress, Internet-Draft, draft-templin-
6man-aero3-44, 21 April 2025,
<https://datatracker.ietf.org/doc/html/draft-templin-6man-
aero3-44>.
[I-D.templin-6man-omni3]
Templin, F., "Transmission of IP Packets over Overlay
Multilink Network (OMNI) Interfaces", Work in Progress,
Internet-Draft, draft-templin-6man-omni3-59, 23 May 2025,
<https://datatracker.ietf.org/doc/html/draft-templin-6man-
omni3-59>.
[I-D.templin-6man-parcels2]
Templin, F., "IPv6 Parcels and Advanced Jumbos (AJs)",
Work in Progress, Internet-Draft, draft-templin-6man-
parcels2-27, 21 May 2025,
<https://datatracker.ietf.org/doc/html/draft-templin-6man-
parcels2-27>.
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[I-D.templin-dtn-ltpfrag]
Templin, F., "LTP Performance Maximization", Work in
Progress, Internet-Draft, draft-templin-dtn-ltpfrag-17, 23
May 2024, <https://datatracker.ietf.org/doc/html/draft-
templin-dtn-ltpfrag-17>.
[KENT87] Kent, C. and J. Mogul, ""Fragmentation Considered
Harmful", SIGCOMM '87: Proceedings of the ACM workshop on
Frontiers in computer communications technology, DOI
10.1145/55482.55524, http://www.hpl.hp.com/techreports/
Compaq-DEC/WRL-87-3.pdf.", August 1987.
[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473,
December 1998, <https://www.rfc-editor.org/info/rfc2473>.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
DOI 10.17487/RFC4302, December 2005,
<https://www.rfc-editor.org/info/rfc4302>.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, DOI 10.17487/RFC4303, December 2005,
<https://www.rfc-editor.org/info/rfc4303>.
[RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly
Errors at High Data Rates", RFC 4963,
DOI 10.17487/RFC4963, July 2007,
<https://www.rfc-editor.org/info/rfc4963>.
[RFC6437] Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
"IPv6 Flow Label Specification", RFC 6437,
DOI 10.17487/RFC6437, November 2011,
<https://www.rfc-editor.org/info/rfc6437>.
[RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field",
RFC 6864, DOI 10.17487/RFC6864, February 2013,
<https://www.rfc-editor.org/info/rfc6864>.
[RFC7739] Gont, F., "Security Implications of Predictable Fragment
Identification Values", RFC 7739, DOI 10.17487/RFC7739,
February 2016, <https://www.rfc-editor.org/info/rfc7739>.
[RFC8799] Carpenter, B. and B. Liu, "Limited Domains and Internet
Protocols", RFC 8799, DOI 10.17487/RFC8799, July 2020,
<https://www.rfc-editor.org/info/rfc8799>.
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[RFC8899] Fairhurst, G., Jones, T., Tüxen, M., Rüngeler, I., and T.
Völker, "Packetization Layer Path MTU Discovery for
Datagram Transports", RFC 8899, DOI 10.17487/RFC8899,
September 2020, <https://www.rfc-editor.org/info/rfc8899>.
[RFC8900] Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O.,
and F. Gont, "IP Fragmentation Considered Fragile",
BCP 230, RFC 8900, DOI 10.17487/RFC8900, September 2020,
<https://www.rfc-editor.org/info/rfc8900>.
[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/info/rfc9000>.
[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>.
Appendix A. Change Log
<< RFC Editor - remove prior to publication >>
Differences from draft version -16 to -17:
* Clarifications on option fields and formats.
Differences from draft version -15 to -16:
* Included option to transmit only the 4 least significant octets of
the Identification when the most significant octets have been
transmitted recently.
Differences from draft version -13 to -15:
* Walked back requirement to include Flow Label in reassembly.
* Statement on intermediate system fragmentation (-14).
Differences from draft version -12 to -13:
* Removed intermediate system (sub-)fragmentation features.
* Removed non-normative discussions about GSO/GRO and Fragmentation
Considered Harmful/Fragile.
* Aligned fragment probing with Fragmentation Report messaging.
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Differences from draft version -11 to -12:
* Under "Motivation", added specific justifications for including a
new fragmentation and reassembly algorithm.
* Requirements for "hard" and "soft" EMTU_R limits discussed.
* General cleanup.
Differences from draft version -09 to -11:
* Discussed implications of ULPs that include security
encapsulations such as TLS/SSL.
* Additional discussion of flow loss profiles.
* Added "D" flag to prevent intermediate systems from fragmenting.
Differences from draft version -08 to -09:
* Added note on header compression.
Differences from draft version -07 to -08:
* Added section on "Relation to GSO/GRO".
* Removed requirement citing a non-normative reference.
Differences from draft version -06 to -07:
* Introduced ICMP PTB Soft Errors.
Differences from draft version -05 to -06:
* Introduced ICMPv6 PTB "Probe Reply" message to support fragment
based RFC8899 path probing.
* Numerous supporting revisions to Fragmentation Report message.
* Removed stale references.
Differences from earlier versions:
* First draft publication.
Authors' Addresses
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Fred L. Templin (editor)
Boeing Research & Technology
P.O. Box 3707
Seattle, WA 98124
United States of America
Email: fltemplin@acm.org
Tom Herbert
Unaffiliated
San Jose, CA
United States of America
Email: tom@herbertland.com
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