On Forwarding 6LoWPAN Fragments over a Multi-Hop IPv6 Network
RFC 8930

Document Type RFC - Proposed Standard (November 2020; No errata)
Authors Thomas Watteyne  , Pascal Thubert  , Carsten Bormann 
Last updated 2020-11-23
Replaces draft-watteyne-6lo-minimal-fragment
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Stream WG state Submitted to IESG for Publication
Document shepherd Carles Gomez
Shepherd write-up Show (last changed 2019-11-28)
IESG IESG state RFC 8930 (Proposed Standard)
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Responsible AD Suresh Krishnan
Send notices to Carles Gomez <carlesgo@entel.upc.edu>, Erik Kline <ek.ietf@gmail.com>
IANA IANA review state Version Changed - Review Needed
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Internet Engineering Task Force (IETF)                  T. Watteyne, Ed.
Request for Comments: 8930                                Analog Devices
Category: Standards Track                                P. Thubert, Ed.
ISSN: 2070-1721                                            Cisco Systems
                                                              C. Bormann
                                                  Universit├Ąt Bremen TZI
                                                           November 2020

     On Forwarding 6LoWPAN Fragments over a Multi-Hop IPv6 Network

Abstract

   This document provides generic rules to enable the forwarding of an
   IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN) fragment
   over a route-over network.  Forwarding fragments can improve both
   end-to-end latency and reliability as well as reduce the buffer
   requirements in intermediate nodes; it may be implemented using RFC
   4944 and Virtual Reassembly Buffers (VRBs).

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8930.

Copyright Notice

   Copyright (c) 2020 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 and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction
   2.  Terminology
     2.1.  Requirements Language
     2.2.  Background
     2.3.  New Terms
   3.  Overview of 6LoWPAN Fragmentation
   4.  Limitations of Per-Hop Fragmentation and Reassembly
     4.1.  Latency
     4.2.  Memory Management and Reliability
   5.  Forwarding Fragments
   6.  Virtual Reassembly Buffer (VRB) Implementation
   7.  Security Considerations
   8.  IANA Considerations
   9.  References
     9.1.  Normative References
     9.2.  Informative References
   Acknowledgments
   Authors' Addresses

1.  Introduction

   The original 6LoWPAN fragmentation is defined in [RFC4944] for use
   over a single Layer 3 hop, though multiple Layer 2 hops in a mesh-
   under network is also possible, and was not modified by the update in
   [RFC6282]. 6LoWPAN operations including fragmentation depend on a
   link-layer security that prevents any rogue access to the network.

   In a route-over 6LoWPAN network, an IP packet is expected to be
   reassembled at each intermediate hop, uncompressed, pushed to Layer 3
   to be routed, and then compressed and fragmented again.  This
   document introduces an alternate approach called 6LoWPAN Fragment
   Forwarding (6LFF) whereby an intermediate node forwards a fragment
   (or the bulk thereof, MTU permitting) without reassembling if the
   next hop is a similar 6LoWPAN link.  The routing decision is made on
   the first fragment of the datagram, which has the IPv6 routing
   information.  The first fragment is forwarded immediately, and a
   state is stored to enable forwarding the next fragments along the
   same path.

   Done right, 6LoWPAN Fragment Forwarding techniques lead to more
   streamlined operations, less buffer bloat, and lower latency.  But it
   may be wasteful when fragments are missing, leading to locked
   resources and low throughput, and it may be misused to the point that
   the end-to-end latency of one packet falls behind that of per-hop
   reassembly.

   This specification provides a generic overview of 6LFF, discusses
   advantages and caveats, and introduces a particular 6LFF technique
   called "Virtual Reassembly Buffer" (VRB) that can be used while
   retaining the message formats defined in [RFC4944].  Basic
   recommendations such as the insertion of an inter-frame gap between
   fragments are provided to avoid the most typical caveats.

2.  Terminology

2.1.  Requirements Language

   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
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