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IP Parcels
draft-templin-intarea-parcels-00

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Author Fred Templin
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draft-templin-intarea-parcels-00
Network Working Group                                 F. L. Templin, Ed.
Internet-Draft                              Boeing Research & Technology
Updates: RFC2675 (if approved)                          17 December 2021
Intended status: Standards Track                                        
Expires: 20 June 2022

                               IP Parcels
                    draft-templin-intarea-parcels-00

Abstract

   IP packets (both IPv4 and IPv6) are understood to contain a unit of
   data which becomes the retransmission unit in case of loss.  Upper
   layer protocols such as the Transmission Control Protocol (TCP)
   prepare data units known as "segments", with traditional arrangements
   including a single segment per packet.  This document presents a new
   construct known as the "IP Parcel" which permits a single packet to
   carry multiple segments.  The parcel can be opened at middleboxes on
   the path with the included segments broken out into individual
   packets, then rejoined into one or more repackaged parcels to be
   forwarded further toward the final destination.  Reordering of
   segments within parcels is unimportant; what matters is that the
   number of parcels delivered to the final destination should be kept
   to a minimum, and that loss or receipt of individual segments (and
   not parcel size) determines the retransmission unit.

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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   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 June 2022.

Copyright Notice

   Copyright (c) 2021 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
   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
   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.  Motivation  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  IP Parcel Formation . . . . . . . . . . . . . . . . . . . . .   4
   4.  Transmission of IP Parcels  . . . . . . . . . . . . . . . . .   5
   5.  Integrity . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   6.  Compatibility . . . . . . . . . . . . . . . . . . . . . . . .   6
   7.  RFC2675 Updates . . . . . . . . . . . . . . . . . . . . . . .   6
   8.  Implementation Status . . . . . . . . . . . . . . . . . . . .   7
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   10. Security Considerations . . . . . . . . . . . . . . . . . . .   7
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     12.1.  Normative References . . . . . . . . . . . . . . . . . .   7
     12.2.  Informative References . . . . . . . . . . . . . . . . .   8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   IP packets (both IPv4 [RFC0791] and IPv6 [RFC8200]) are understood to
   contain a unit of data which becomes the retransmission unit in case
   of loss.  Upper layer protocols such as the Transmission Control
   Protocol (TCP) [RFC0793] prepare data units known as "segments", with
   traditional arrangements including a single segment per packet.  This
   document presents a new construct known as the "IP Parcel" which
   permits a single packet to carry multiple segments.

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   Parcels are formed when an upper layer protocol entity (identified by
   the "5-tuple" source IP address/port number, destination IP address/
   port number and protocol number) prepares a buffer of data with the
   concatenation of up to 64 properly-formed segments that could stand
   alone if broken out into individual packets.  All segments except the
   final segment must be equal in size, while the final segment must not
   be larger than the others but may be smaller.  Each non-final segment
   must be no smaller than 576 and no larger than 65535 minus the length
   of the IP header plus extensions.  The upper layer protocol entity
   then delivers the buffer and non-final segment size to the IP layer,
   which appends the necessary headers to identify this as a parcel and
   not an ordinary packet.

   Each parcel can be opened at a first-hop middlebox on the path with
   the included segments broken out into individual packets, then
   rejoined into one or more parcels at a last-hop middlebox to be
   forwarded to the final destination.  Reordering of segments within
   parcels is unimportant; what matters is that the number of parcels
   delivered to the final destination should be kept to a minimum, and
   that loss or receipt of individual segments (and not parcel size)
   determines the retransmission unit.

   The following sections discuss rationale for creating and shipping
   parcels as well as the actual protocol constructs and procedures
   involved.  It is expected that the parcel concept may drive future
   innovation in application and data link design.

2.  Motivation

   Studies have shown that applications that send and receive large
   packets can realize greater performance due to reduced numbers of
   system calls and interrupts as well as larger atomic data copies
   between kernel and user space.  Within the network, large packets
   also result in reduced numbers of device interrupts and better
   network utilization in comparison with smaller packet sizes.

   The issue with sending large packets is that they are often lost at
   links with smaller Maximum Transmission Units (MTUs), and the
   resulting Packet Too Big (PTB) message may be lost somewhere in the
   path back to the original source.  This "Path MTU black hole"
   condition can cripple application performance unless also
   supplemented with robust path probing techniques, however the best
   case performance always occurs when no packets are lost due to size
   restrictions.

   These considerations therefore motivate a design where the maximum
   segment size should be no larger than 65535 minus IP header sizes,
   while parcels that carry the segments may themselves be significantly

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   larger.  Then, even if a middlebox needs to open the parcels to
   deliver individual segments further toward final hops, an important
   performance optimization for both the original source and final
   destination can be realized.

   An analogy: when an end user orders 50 small items from a major
   online retailer, the retailer does not ship the order in 50 separate
   small boxes.  Instead, the retailer puts as many of the small boxes
   as possible in one or a few larger boxes (or parcels) then puts the
   parcels on a semi-truck or airplane.  The parcels arrive at a
   regional distribution center where they may be further broken down
   into slightly smaller parcels that get delivered to the end user.
   But most often, the end user will only find one or a few parcels at
   his doorstep and not 50 individual boxes.

3.  IP Parcel Formation

   IP parcel formation is invoked by an upper layer protocol (identified
   by the 5-tuple as above) when it produces a data buffer containing
   the concatenation of up to 64 segments.  All non-final segments MUST
   be equal in length while the final segment MUST NOT be larger but MAY
   be smaller.  Each non-final segment MUST be no smaller than 576 and
   no larger than 65535 minus the length the IP header plus extensions.
   The application then presents the buffer and non-final segment size
   to the IP layer which appends an IP header (plus any extension
   headers) before presenting the parcel to lower layers.

   For IPv4, the IP layer prepares the parcel by appending an IPv4
   header with a Jumbo Payload option (identified by option code TBD)
   formed as follows:

   +--------+--------+--------+--------+--------+--------+
   |000(TBD)|00000110|       Jumbo Payload Length        |
   +--------+--------+--------+--------+--------+--------+

   where "Jumbo Payload Length" is a 32-bit unsigned integer value (in
   network byte order) set to the lengths of the IPv4 header plus all
   concatenated segments.  The IP layer next sets the IPv4 header DF bit
   to 1, then sets the IPv4 header Total Length field to the length of
   the IPv4 header plus the length of the first segment only.  Note that
   the IP layer can form true IPv4 jumbograms (as opposed to parcels) by
   instead setting the IPv4 header Total Length field to 0.

   For IPv6, the IP layer forms a parcel by appending an IPv6 header
   with a Jumbo Payload option [RFC2675] the same as for IPv4 above
   where "Jumbo Payload Length" is set to the lengths of the IPv6 Hop-
   by-Hop Options header and any other extension headers present plus
   all concatenated segments.  The IP layer next sets the IPv6 header

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   Payload Length field to the lengths of the IPv6 Hop-by-Hop Options
   header and any other extension headers present plus the length of the
   first segment only.  As with IPv4 the IP layer can form true IPv6
   jumbograms (as opposed to parcels) by instead setting the IPv6 header
   Payload Length field to 0.

4.  Transmission of IP Parcels

   The IP layer next presents the parcel to the next lower layer.  If
   the lower layer is the OMNI Adaptation Layer (OAL)
   [I-D.templin-6man-omni], the OAL source opens the parcel and forwards
   each segment as an individual IP packet.  These individual packets
   eventually arrive at the OAL destination which re-combines them into
   a new parcel or parcels then forwards them to the final destination.
   Details for OAL parcel forwarding are discussed in
   [I-D.templin-6man-omni].

   If the lower layer is a true data link layer interface, however, the
   IP layer instead forwards the parcel according to the path MTU to
   either the first middlebox that configures an OAL layer or the final
   destination itself, whichever comes first.  If the parcel is no
   larger than the path MTU, the IP layer simply forwards the parcel the
   same as it would an ordinary IP packet and processes any PTB messages
   that may be returned (but, see below for compatibility issues).  If
   the parcel is larger than 65535 (minus encapsulation headers) and
   also larger than the path MTU, the IP layer instead discards the
   parcel and returns a packet size error to the upper layer protocol.

   If the parcel is no larger than 65535 (minus encapsulation headers)
   but larger than the path MTU, the IP layer instead performs IP
   encapsulation with destination set to the IP address of the middlebox
   or final destination and (Payload Length / Total Length) set to the
   Jumbo Payload Length plus encapsulation header length then performs
   source-fragmentation by generating IP fragments destined for the
   middlebox or final destination.

   When the middlebox or final destination receives the fragments or
   whole parcels, it reassembles then discards the encapsulation headers
   if necessary then presents the parcel to the OAL in the middlebox
   case or the upper layer protocol in the final destination case.

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5.  Integrity

   Parcels can range in length from the size of the smallest single
   segment to as large as (64 * (2**16)) octets.  Although link layer
   integrity checks provide sufficient protection for sizes up to
   approximately 9KB, reliance on the presence of link-layer integrity
   checks may not be possible over links such as tunnels.  Moreover, the
   segment contents of a received parcel may arrive in an incomplete
   and/or rearranged order in relation to how they were sent.

   For these reasons, upper layers must include individual integrity
   checks with each segment included in the parcel with a strength
   compatible with the segment length.  The integrity must then be
   verified at the receiver on a per-segment basis, with any corrupted
   segments discarded and considered as a loss event.

6.  Compatibility

   Legacy networking gear that forwards parcels over ordinary data links
   may not recognize this new coding of the Jumbo Payload extension
   header and may act only on what is observed in the IPv4 Total Length
   or IPv6 Payload Length field.  In that case, the legacy gear would
   likely forward the first segment of the parcel only while truncating
   the remainder since only the length of the first segment is included
   in the header.

   In networks where compatibility is thought to be an issue, the
   original source can perform encapsulation on parcels uniformly
   whether or not fragmentation is required to ensure they are delivered
   to the OAL source or final destination (whichever comes first).  In
   the same way the OAL destination can uniformly perform encapsulation
   to ensure that parcels are delivered to the final destination.

7.  RFC2675 Updates

   Section 3 of [RFC2675] provides a list of certain conditions to be
   considered as errors.  In particular:

      error: IPv6 Payload Length != 0 and Jumbo Payload option present

      error: Jumbo Payload option present and Jumbo Payload Length <
      65,536

   Implementations that obey this specification ignore these conditions
   and do not consider them as errors.

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8.  Implementation Status

   TBD.

9.  IANA Considerations

   The IANA is instructed to allocate a new IP option code in the 'ip
   option numbers' registry for the IPv4 Jumbo Payload option.  The Copy
   and Class fields must both be set to 0, and the Number field must be
   set to 'TBD'.

10.  Security Considerations

   Communications networking security is necessary to preserve
   confidentiality, integrity and availability.

11.  Acknowledgements

   This work was inspired by ongoing AERO/OMNI/DTN investigations.  The
   concepts were further motivated through discussions on the intarea
   list.

   A considerable body of work over recent years has produced useful
   "segmentation offload" facilities available in widely-deployed
   implementations.

   .

12.  References

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>.

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, DOI 10.17487/RFC0793, September 1981,
              <https://www.rfc-editor.org/info/rfc793>.

   [RFC2675]  Borman, D., Deering, S., and R. Hinden, "IPv6 Jumbograms",
              RFC 2675, DOI 10.17487/RFC2675, August 1999,
              <https://www.rfc-editor.org/info/rfc2675>.

   [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>.

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12.2.  Informative References

   [I-D.templin-6man-aero]
              Templin, F. L., "Automatic Extended Route Optimization
              (AERO)", Work in Progress, Internet-Draft, draft-templin-
              6man-aero-37, 15 November 2021,
              <https://www.ietf.org/archive/id/draft-templin-6man-aero-
              37.txt>.

   [I-D.templin-6man-omni]
              Templin, F. L. and T. Whyman, "Transmission of IP Packets
              over Overlay Multilink Network (OMNI) Interfaces", Work in
              Progress, Internet-Draft, draft-templin-6man-omni-51, 15
              November 2021, <https://www.ietf.org/archive/id/draft-
              templin-6man-omni-51.txt>.

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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