IPv6 Extended Fragment Header for IPv4
draft-templin-intarea-ipid-ext2-11

Network Working Group                                 F. L. Templin, Ed.
Internet-Draft                              Boeing Research & Technology
Intended status: Standards Track                             6 July 2026
Expires: 7 January 2027

                 IPv6 Extended Fragment Header for IPv4
                   draft-templin-intarea-ipid-ext2-11

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 adapting the IPv6 Extended Fragment
   Header for IPv4.

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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   This Internet-Draft will expire on 7 January 2027.

Copyright Notice

   Copyright (c) 2026 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
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   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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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Relation to IPv6  . . . . . . . . . . . . . . . . . . . . . .   3
   3.  IPv6 Extended Fragment Header (EFH) for IPv4  . . . . . . . .   3
   4.  Destination Qualification and Path MTU  . . . . . . . . . . .   4
   5.  IPv4 Flow Label . . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Packet Too Big (PTB) Extensions . . . . . . . . . . . . . . .   4
   7.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   5
   8.  Implementation Status . . . . . . . . . . . . . . . . . . . .   5
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   10. Security Considerations . . . . . . . . . . . . . . . . . . .   5
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     12.1.  Normative References . . . . . . . . . . . . . . . . . .   6
     12.2.  Informative References . . . . . . . . . . . . . . . . .   6
   Appendix A.  Change Log . . . . . . . . . . . . . . . . . . . . .   7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   8

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].  This specification adapts the
   IPv6 Extended Fragment Header (EFH) [I-D.templin-6man-ipid-ext2] for
   Identification extension and to support an alternate fragmentation
   and reassembly service for IPv4.

   IPv4 packets that include the IPv6 EFH engage a "deep packet
   fragmentation" service that supports Identification, fragmentation
   and reassembly independently of any IPv4 header level services.  This
   may be useful for networks that engage fragmentation and reassembly
   at extreme data rates, or for cases when advanced packet
   Identification uniqueness assurance is critical.

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2.  Relation to IPv6

   Protocol extensions intended for IPv6 can often be applied in similar
   fashion as for IPv4 (and vice-versa).  The terminology used and the
   motivation for extending the Identification field for IPv4 is the
   same as for the IPv6 Extended Fragment Header (EFH) as specified in
   [I-D.templin-6man-ipid-ext2].  All normative aspects of the IPv6
   specification that can be applied for IPv4 apply also to this
   document.

3.  IPv6 Extended Fragment Header (EFH) for IPv4

   IPv4 end systems, intermediate systems and routers by default do not
   recognize the IP protocol numbers for IPv6 extension headers as these
   are typically used to support only IPv6 operations.  However,
   implementations of this specification are required to recognize IP
   protocol number 60 (IPv6 Destination Options header per [RFC8200]) as
   an applicable extension for IPv4.

   Implementations of this specification also recognize the IPv6 EFH
   Option [I-D.templin-6man-ipid-ext2] when it appears in an IPv6
   Destination Options Header following the IPv4 header.  Requirements
   for encapsulation of extension headers in IPv4 packets are introduced
   and discussed in [I-D.herbert-ipv4-eh].

   IPv4 sources insert an IPv6 Destination Option Header with an EFH
   option in an extension header chain beginning immediately after the
   IPv4 header (plus options) and ending immediately before the upper
   layer protocol header, e.g., TCP, UDP, etc.  The source then
   increments the IPv4 Total Length by the length of the extension
   headers, and sets the IPv4 Protocol field to the protocol number of
   the first extension header.  The source then sets the IPv6
   Destination Options Next Header field to the protocol number of the
   next extension header or the upper layer protocol number if there are
   no further extensions.

   The IPv4 source then applies EFH fragmentation if necessary the same
   as for the IPv6 procedures specified in [I-D.templin-6man-ipid-ext2].
   This will produce a sequence of fragment packets each containing a
   copy of the IPv4 header followed by any Per-Fragment headers up to
   and including the IPv6 Destination Options Header with EFH Option
   followed by the fragment payload.  The IPv4 source then forwards the
   fragment packets toward the final destination which processes them
   only if all nodes in the path pass IPv4 packets that include the IPv6
   Destination Options header.

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   Intermediate systems and IPv4 routers on the path forward the
   fragment packets if the next hop link MTU is sufficient.  A router
   may perform IPv4 fragmentation if a fragment packet is too large and
   the Don't Fragment (DF) flag is 0; otherwise, the router drops the
   packet and returns an ICMPv4 Fragmentation Needed message.

   When the fragment packets arrive at the IPv4 destination, it performs
   IPv4 reassembly if necessary followed by EFH reassembly under the
   same conditions specified for the IPv6 EFH in
   [I-D.templin-6man-ipid-ext2].

4.  Destination Qualification and Path MTU

   IPv4 intermediate systems, routers and destinations that do not
   recognize the IPv6 Destination Options Header with EFH Option
   appearing after the IPv4 header unconditionally drop the packet and
   SHOULD return an "ICMPv4 Destination Unreachable - Protocol
   Unreachable" message per [RFC0792].

   The source can therefore test whether the path up to and including
   the destination accepts the IPv6 Destination Options Header and EFH
   Option by occasionally sending "probe" packets of a given size that
   include them.  If the source receives an acknowledgement, it has
   assurance that the destination recognizes the protocol and that
   intermediate systems and routers at least forward the protocol
   messages without dropping; the source can instead consider receipt of
   an ICMPv4 Destination Unreachable (Protocol Unreachable) as an
   indication that a node in the path rejects the protocol.  The source
   should occasionally re-probe each destination in case routing
   redirects a flow to a different anycast destination.

5.  IPv4 Flow Label

   Destinations that return Fragmentation Report (FR) messages per
   [I-D.templin-6man-ipid-ext2] set the Flow Label field to the value
   included by the source of the packet that elicited the FR (an IPv4
   Flow Label option appears in [I-D.dreibholz-ipv4-flowlabel]).  When
   the source does not include an explicit Flow Label, the destination
   sets the field to 0.

6.  Packet Too Big (PTB) Extensions

   [I-D.templin-6man-ipid-ext2] specifies a new "Packet Too Big (PTB)"
   ICMP message Type plus Code values for PTB Soft Errors.  Intermediate
   systems and destination end systems return ICMPv4 PTB Soft Errors to
   the source under the same conditions specified for IPv6.

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7.  Requirements

   All nodes that process IPv4 packets with an IPv6 Destination Options
   Header including the EFH Option observe the requirements found in
   [I-D.templin-6man-ipid-ext2] in addition to the requirements found in
   this section.

   Sources SHOULD set DF to 0 and include a suitable IPv4 ID value for
   packets that include fragment payloads based on the 1024 octet
   minimum non-final EFH fragment size.  Sources MUST set DF to 1 and
   include any IPv4 ID value for all others.  An updated specification
   of the IPv4 ID field is found in [RFC6864].

   Sources MUST include at most one EFH in each IPv4 packet.
   Intermediate systems and destinations SHOULD silently drop packets
   with multiples.

   Destinations that accept flows using EFH Options MUST configure an
   EMTU_R of 65535 octets or larger.

8.  Implementation Status

   In progress.

9.  IANA Considerations

   This document has no requirements for IANA.

10.  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 IPv4
   reassembly integrity concerns [RFC4963] [RFC8900] and also provide an
   advanced degree of packet Identification uniqueness assurance.

   All other security aspects of the IPv6 Extended Fragment Header per
   [I-D.templin-6man-ipid-ext2] apply also to its use in IPv4.

11.  Acknowledgements

   This work was inspired by continued DTN performance studies.  Amanda
   Baber, Tom Herbert, Bob Hinden and Eric Vyncke offered useful
   insights that helped improve the document.

   Honoring life, liberty and the pursuit of happiness.

12.  References

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12.1.  Normative References

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791,
              DOI 10.17487/RFC0791, September 1981,
              <https://www.rfc-editor.org/info/rfc791>.

   [RFC0792]  Postel, J., "Internet Control Message Protocol", STD 5,
              RFC 792, DOI 10.17487/RFC792, September 1981,
              <https://www.rfc-editor.org/info/rfc792>.

   [RFC1191]  Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
              DOI 10.17487/RFC1191, November 1990,
              <https://www.rfc-editor.org/info/rfc1191>.

   [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>.

   [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>.

12.2.  Informative References

   [I-D.dreibholz-ipv4-flowlabel]
              Dreibholz, T., "An IPv4 Flowlabel Option", Work in
              Progress, Internet-Draft, draft-dreibholz-ipv4-flowlabel-
              43, 11 April 2026, <https://datatracker.ietf.org/doc/html/
              draft-dreibholz-ipv4-flowlabel-43>.

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   [I-D.herbert-ipv4-eh]
              Herbert, T., "IPv4 Extension Headers and Flow Label", Work
              in Progress, Internet-Draft, draft-herbert-ipv4-eh-03, 22
              February 2024, <https://datatracker.ietf.org/doc/html/
              draft-herbert-ipv4-eh-03>.

   [I-D.templin-6man-ipid-ext2]
              Templin, F. and T. Herbert, "IPv6 Extended Fragment Header
              (EFH)", Work in Progress, Internet-Draft, draft-templin-
              6man-ipid-ext2-27, 12 January 2026,
              <https://datatracker.ietf.org/doc/html/draft-templin-6man-
              ipid-ext2-27>.

   [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>.

   [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>.

   [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>.

Appendix A.  Change Log

   << RFC Editor - remove prior to publication >>

   Differences from version -10 to version -11:

   *  Removed citation of "eh-limits" draft.

   Differences from version -09 to version -10:

   *  Cited draft on IPv6 Flow Labels for IPv4 packets.

   Differences from version -07 to version -09:

   *  Clarified IPv4 DF bit setting requirements.

   *  Included section on IPv4 Flow Label.

   *  IPv4 router fragmentation considerations.

   Differences from version -06 to version -07:

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   *  Now using normal (extended) ICMPv4 messages for IPv4 PTB instead
      of OMNI-encapsulated ICMPv6.

   Differences from version -05 to version -06:

   *  Removed reference to RFC9268.

   *  Clarified setting of DF bit.

   Differences from earlier versions:

   *  First draft publication.

Author's Address

   Fred L. Templin (editor)
   Boeing Research & Technology
   P.O. Box 3707
   Seattle, WA 98124
   United States of America
   Email: fltemplin@acm.org

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