Network Working Group F. L. Templin, Ed. Internet-Draft Boeing Research & Technology Intended status: Experimental T. Herbert Expires: 20 November 2025 Unaffiliated 19 May 2025 IPv6 Extended Fragment Header (EFH) draft-templin-6man-ipid-ext2-13 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 Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. 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 20 November 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 Templin & Herbert Expires 20 November 2025 [Page 1] Internet-Draft IPv6 Extended Fragment Header (EFH) May 2025 and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are 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. IPv6 Destination Reassembly . . . . . . . . . . . . . . . . . 8 7. Destination Qualification and Path MTU . . . . . . . . . . . 8 8. Packet Size Issues . . . . . . . . . . . . . . . . . . . . . 8 9. Fragmentation Reports and Retransmissions . . . . . . . . . . 9 10. Multicast and Anycast . . . . . . . . . . . . . . . . . . . . 11 11. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 11 12. Implementation Status . . . . . . . . . . . . . . . . . . . . 12 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 13.1. IPv6 Parameters . . . . . . . . . . . . . . . . . . . . 12 13.2. ICMPv6 Parameters . . . . . . . . . . . . . . . . . . . 13 13.3. ICMP Parameters . . . . . . . . . . . . . . . . . . . . 13 14. Security Considerations . . . . . . . . . . . . . . . . . . . 14 15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14 16. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 16.1. Normative References . . . . . . . . . . . . . . . . . . 14 16.2. Informative References . . . . . . . . . . . . . . . . . 15 Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18 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). Templin & Herbert Expires 20 November 2025 [Page 2] Internet-Draft IPv6 Extended Fragment Header (EFH) May 2025 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". Templin & Herbert Expires 20 November 2025 [Page 3] Internet-Draft IPv6 Extended Fragment Header (EFH) May 2025 The term "Fragmentation Report (FR)" refers to an alternate option type encoding of the EFH option used to report per-flow 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 with segment sizes that exceed the path MTU was similarly proven using the HDTN and ION-DTN LTP implementations which engage IP fragmentation and reassembly. Templin & Herbert Expires 20 November 2025 [Page 4] Internet-Draft IPv6 Extended Fragment Header (EFH) May 2025 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 enable a duplicate packet detection service where the network remembers recent Identification values for a flow 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 for a flow as potential spurious transmissions. The standard IPv6 Fragment Header also carried forward the cumbersome 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. Templin & Herbert Expires 20 November 2025 [Page 5] Internet-Draft IPv6 Extended Fragment Header (EFH) May 2025 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 (64 bits) -+-+-+-+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Option Type 8-bit value '100[TBD1]'. Opt Data Len 8-bit value 10. NH-Actual the actual value of the original Destination Options Next Header prior to fragmentation. M/P/Index a 6-bit "Index" field that identifies the ordinal index for each fragment payload, preceded by a 1-bit "(M)ore Fragments" flag and a 1-bit "(P)robe" flag. 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. The Identification field is 8 octets (64 bits) in length and 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. Templin & Herbert Expires 20 November 2025 [Page 6] Internet-Draft IPv6 Extended Fragment Header (EFH) May 2025 For improved efficiency, sources often send packets that include full IPv6 headers (including the full EFH) 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, Flow Label, Identification)-tuple to ensure that fragmentation is adaptive on a per-flow basis. 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. Templin & Herbert Expires 20 November 2025 [Page 7] Internet-Draft IPv6 Extended Fragment Header (EFH) May 2025 6. 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, Flow Label, 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. 7. 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 10). 8. 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 flow path MTU 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 9. The responsive packet can be a NULL packet (e.g., one with Next Header set to No Next Header) or a live data packet with the IP Source and Destination addresses reversed. Templin & Herbert Expires 20 November 2025 [Page 8] Internet-Draft IPv6 Extended Fragment Header (EFH) May 2025 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 for a given flow, it can begin returning authentic IP packets with Fragmentation Report options to the source (see: Section 9) 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. 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). 9. 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 Templin & Herbert Expires 20 November 2025 [Page 9] Internet-Draft IPv6 Extended Fragment Header (EFH) May 2025 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. 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]). Templin & Herbert Expires 20 November 2025 [Page 10] Internet-Draft IPv6 Extended Fragment Header (EFH) May 2025 10. 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. 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. 11. Requirements Normative aspects of standard IPv6 fragmentation and reassembly [RFC8200] apply also to the IPv6 EFH except where this document specifies differences. Templin & Herbert Expires 20 November 2025 [Page 11] Internet-Draft IPv6 Extended Fragment Header (EFH) May 2025 Sources and Destinations MUST apply EFH fragmentation and reassembly according to the 4-tuple (Source, Destination, Flow Label, Identification). Inclusion of the Flow Label ensures that the path MTU for each flow is adaptive independently of all other flows. 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 per flow reassembly congestion. 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 9. 12. Implementation Status In progress. 13. IANA Considerations 13.1. 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]. Templin & Herbert Expires 20 November 2025 [Page 12] Internet-Draft IPv6 Extended Fragment Header (EFH) May 2025 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. 13.2. 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 13.3. 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) Templin & Herbert Expires 20 November 2025 [Page 13] Internet-Draft IPv6 Extended Fragment Header (EFH) May 2025 14. 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. 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 (e.g., per the algorithms found in [RFC7739]) 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. 15. 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. 16. References 16.1. Normative References [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, DOI 10.17487/RFC0791, September 1981, . [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - Communication Layers", STD 3, RFC 1122, DOI 10.17487/RFC1122, October 1989, . Templin & Herbert Expires 20 November 2025 [Page 14] Internet-Draft IPv6 Extended Fragment Header (EFH) May 2025 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [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, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", STD 86, RFC 8200, DOI 10.17487/RFC8200, July 2017, . [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, . 16.2. 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, . [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, . [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-omni3-57, 21 April 2025, . Templin & Herbert Expires 20 November 2025 [Page 15] Internet-Draft IPv6 Extended Fragment Header (EFH) May 2025 [I-D.templin-6man-parcels2] Templin, F., "IPv6 Parcels and Advanced Jumbos (AJs)", Work in Progress, Internet-Draft, draft-templin-6man- parcels2-24, 16 April 2025, . [I-D.templin-dtn-ltpfrag] Templin, F., "LTP Performance Maximization", Work in Progress, Internet-Draft, draft-templin-dtn-ltpfrag-17, 23 May 2024, . [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, . [RFC4302] Kent, S., "IP Authentication Header", RFC 4302, DOI 10.17487/RFC4302, December 2005, . [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC 4303, DOI 10.17487/RFC4303, December 2005, . [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly Errors at High Data Rates", RFC 4963, DOI 10.17487/RFC4963, July 2007, . [RFC6437] Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme, "IPv6 Flow Label Specification", RFC 6437, DOI 10.17487/RFC6437, November 2011, . [RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field", RFC 6864, DOI 10.17487/RFC6864, February 2013, . [RFC7739] Gont, F., "Security Implications of Predictable Fragment Identification Values", RFC 7739, DOI 10.17487/RFC7739, February 2016, . Templin & Herbert Expires 20 November 2025 [Page 16] Internet-Draft IPv6 Extended Fragment Header (EFH) May 2025 [RFC8799] Carpenter, B. and B. Liu, "Limited Domains and Internet Protocols", RFC 8799, DOI 10.17487/RFC8799, July 2020, . [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, . [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, . [RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based Multiplexed and Secure Transport", RFC 9000, DOI 10.17487/RFC9000, May 2021, . [RFC9293] Eddy, W., Ed., "Transmission Control Protocol (TCP)", STD 7, RFC 9293, DOI 10.17487/RFC9293, August 2022, . Appendix A. Change Log << RFC Editor - remove prior to publication >> 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. 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: Templin & Herbert Expires 20 November 2025 [Page 17] Internet-Draft IPv6 Extended Fragment Header (EFH) May 2025 * 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 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 Templin & Herbert Expires 20 November 2025 [Page 18] Internet-Draft IPv6 Extended Fragment Header (EFH) May 2025 Email: tom@herbertland.com Templin & Herbert Expires 20 November 2025 [Page 19]