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<!DOCTYPE html>
<html lang="en" class="RFC">
<head>
<meta charset="utf-8">
<meta content="Common,Latin" name="scripts">
<meta content="initial-scale=1.0" name="viewport">
<title>RFC 8930: On Forwarding 6LoWPAN Fragments over a Multi-Hop IPv6 Network</title>
<meta content="Thomas Watteyne" name="author">
<meta content="Pascal Thubert" name="author">
<meta content="Carsten Bormann" name="author">
<meta content="
       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). 
    " name="description">
<meta content="xml2rfc 3.5.0" name="generator">
<meta content="6LoWPAN" name="keyword">
<meta content="Fragment" name="keyword">
<meta content="8930" name="rfc.number">
<!-- Generator version information:
  xml2rfc 3.5.0
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<link href="rfc8930.xml" rel="alternate" type="application/rfc+xml">
<link href="#copyright" rel="license">
<style type="text/css">/*

  NOTE: Changes at the bottom of this file overrides some earlier settings.

  Once the style has stabilized and has been adopted as an official RFC style,
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*/

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}
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<link href="https://dx.doi.org/10.17487/rfc8930" rel="alternate">
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<table class="ears">
<thead><tr>
<td class="left">RFC 8930</td>
<td class="center">Fragment Forwarding</td>
<td class="right">November 2020</td>
</tr></thead>
<tfoot><tr>
<td class="left">Watteyne, et al.</td>
<td class="center">Standards Track</td>
<td class="right">[Page]</td>
</tr></tfoot>
</table>
<div id="external-metadata" class="document-information"></div>
<div id="internal-metadata" class="document-information">
<dl id="identifiers">
<dt class="label-stream">Stream:</dt>
<dd class="stream">Internet Engineering Task Force (IETF)</dd>
<dt class="label-rfc">RFC:</dt>
<dd class="rfc"><a href="https://www.rfc-editor.org/rfc/rfc8930" class="eref">8930</a></dd>
<dt class="label-category">Category:</dt>
<dd class="category">Standards Track</dd>
<dt class="label-published">Published:</dt>
<dd class="published">
<time datetime="2020-11" class="published">November 2020</time>
    </dd>
<dt class="label-issn">ISSN:</dt>
<dd class="issn">2070-1721</dd>
<dt class="label-authors">Authors:</dt>
<dd class="authors">
<div class="author">
      <div class="author-name">T. Watteyne, <span class="editor">Ed.</span>
</div>
<div class="org">Analog Devices</div>
</div>
<div class="author">
      <div class="author-name">P. Thubert, <span class="editor">Ed.</span>
</div>
<div class="org">Cisco Systems</div>
</div>
<div class="author">
      <div class="author-name">C. Bormann</div>
<div class="org">Universität Bremen TZI</div>
</div>
</dd>
</dl>
</div>
<h1 id="rfcnum">RFC 8930</h1>
<h1 id="title">On Forwarding 6LoWPAN Fragments over a Multi-Hop IPv6 Network</h1>
<section id="section-abstract">
      <h2 id="abstract"><a href="#abstract" class="selfRef">Abstract</a></h2>
<p id="section-abstract-1">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).<a href="#section-abstract-1" class="pilcrow">¶</a></p>
</section>
<div id="status-of-memo">
<section id="section-boilerplate.1">
        <h2 id="name-status-of-this-memo">
<a href="#name-status-of-this-memo" class="section-name selfRef">Status of This Memo</a>
        </h2>
<p id="section-boilerplate.1-1">
            This is an Internet Standards Track document.<a href="#section-boilerplate.1-1" class="pilcrow">¶</a></p>
<p id="section-boilerplate.1-2">
            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.<a href="#section-boilerplate.1-2" class="pilcrow">¶</a></p>
<p id="section-boilerplate.1-3">
            Information about the current status of this document, any
            errata, and how to provide feedback on it may be obtained at
            <span><a href="https://www.rfc-editor.org/info/rfc8930">https://www.rfc-editor.org/info/rfc8930</a></span>.<a href="#section-boilerplate.1-3" class="pilcrow">¶</a></p>
</section>
</div>
<div id="copyright">
<section id="section-boilerplate.2">
        <h2 id="name-copyright-notice">
<a href="#name-copyright-notice" class="section-name selfRef">Copyright Notice</a>
        </h2>
<p id="section-boilerplate.2-1">
            Copyright (c) 2020 IETF Trust and the persons identified as the
            document authors. All rights reserved.<a href="#section-boilerplate.2-1" class="pilcrow">¶</a></p>
<p id="section-boilerplate.2-2">
            This document is subject to BCP 78 and the IETF Trust's Legal
            Provisions Relating to IETF Documents
            (<span><a href="https://trustee.ietf.org/license-info">https://trustee.ietf.org/license-info</a></span>) 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.<a href="#section-boilerplate.2-2" class="pilcrow">¶</a></p>
</section>
</div>
<div id="toc">
<section id="section-toc.1">
        <a href="#" onclick="scroll(0,0)" class="toplink">▲</a><h2 id="name-table-of-contents">
<a href="#name-table-of-contents" class="section-name selfRef">Table of Contents</a>
        </h2>
<nav class="toc"><ul class="toc ulEmpty compact">
<li class="toc ulEmpty compact" id="section-toc.1-1.1">
            <p id="section-toc.1-1.1.1" class="keepWithNext"><a href="#section-1" class="xref">1</a>.  <a href="#name-introduction" class="xref">Introduction</a><a href="#section-toc.1-1.1.1" class="pilcrow">¶</a></p>
</li>
          <li class="toc ulEmpty compact" id="section-toc.1-1.2">
            <p id="section-toc.1-1.2.1"><a href="#section-2" class="xref">2</a>.  <a href="#name-terminology" class="xref">Terminology</a><a href="#section-toc.1-1.2.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty compact">
<li class="toc ulEmpty compact" id="section-toc.1-1.2.2.1">
                <p id="section-toc.1-1.2.2.1.1" class="keepWithNext"><a href="#section-2.1" class="xref">2.1</a>.  <a href="#name-requirements-language" class="xref">Requirements Language</a><a href="#section-toc.1-1.2.2.1.1" class="pilcrow">¶</a></p>
</li>
              <li class="toc ulEmpty compact" id="section-toc.1-1.2.2.2">
                <p id="section-toc.1-1.2.2.2.1" class="keepWithNext"><a href="#section-2.2" class="xref">2.2</a>.  <a href="#name-background" class="xref">Background</a><a href="#section-toc.1-1.2.2.2.1" class="pilcrow">¶</a></p>
</li>
              <li class="toc ulEmpty compact" id="section-toc.1-1.2.2.3">
                <p id="section-toc.1-1.2.2.3.1"><a href="#section-2.3" class="xref">2.3</a>.  <a href="#name-new-terms" class="xref">New Terms</a><a href="#section-toc.1-1.2.2.3.1" class="pilcrow">¶</a></p>
</li>
            </ul>
</li>
          <li class="toc ulEmpty compact" id="section-toc.1-1.3">
            <p id="section-toc.1-1.3.1"><a href="#section-3" class="xref">3</a>.  <a href="#name-overview-of-6lowpan-fragmen" class="xref">Overview of 6LoWPAN Fragmentation</a><a href="#section-toc.1-1.3.1" class="pilcrow">¶</a></p>
</li>
          <li class="toc ulEmpty compact" id="section-toc.1-1.4">
            <p id="section-toc.1-1.4.1"><a href="#section-4" class="xref">4</a>.  <a href="#name-limitations-of-per-hop-frag" class="xref">Limitations of Per-Hop Fragmentation and Reassembly</a><a href="#section-toc.1-1.4.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty compact">
<li class="toc ulEmpty compact" id="section-toc.1-1.4.2.1">
                <p id="section-toc.1-1.4.2.1.1"><a href="#section-4.1" class="xref">4.1</a>.  <a href="#name-latency" class="xref">Latency</a><a href="#section-toc.1-1.4.2.1.1" class="pilcrow">¶</a></p>
</li>
              <li class="toc ulEmpty compact" id="section-toc.1-1.4.2.2">
                <p id="section-toc.1-1.4.2.2.1"><a href="#section-4.2" class="xref">4.2</a>.  <a href="#name-memory-management-and-relia" class="xref">Memory Management and Reliability</a><a href="#section-toc.1-1.4.2.2.1" class="pilcrow">¶</a></p>
</li>
            </ul>
</li>
          <li class="toc ulEmpty compact" id="section-toc.1-1.5">
            <p id="section-toc.1-1.5.1"><a href="#section-5" class="xref">5</a>.  <a href="#name-forwarding-fragments" class="xref">Forwarding Fragments</a><a href="#section-toc.1-1.5.1" class="pilcrow">¶</a></p>
</li>
          <li class="toc ulEmpty compact" id="section-toc.1-1.6">
            <p id="section-toc.1-1.6.1"><a href="#section-6" class="xref">6</a>.  <a href="#name-virtual-reassembly-buffer-v" class="xref">Virtual Reassembly Buffer (VRB) Implementation</a><a href="#section-toc.1-1.6.1" class="pilcrow">¶</a></p>
</li>
          <li class="toc ulEmpty compact" id="section-toc.1-1.7">
            <p id="section-toc.1-1.7.1"><a href="#section-7" class="xref">7</a>.  <a href="#name-security-considerations" class="xref">Security Considerations</a><a href="#section-toc.1-1.7.1" class="pilcrow">¶</a></p>
</li>
          <li class="toc ulEmpty compact" id="section-toc.1-1.8">
            <p id="section-toc.1-1.8.1"><a href="#section-8" class="xref">8</a>.  <a href="#name-iana-considerations" class="xref">IANA Considerations</a><a href="#section-toc.1-1.8.1" class="pilcrow">¶</a></p>
</li>
          <li class="toc ulEmpty compact" id="section-toc.1-1.9">
            <p id="section-toc.1-1.9.1"><a href="#section-9" class="xref">9</a>.  <a href="#name-references" class="xref">References</a><a href="#section-toc.1-1.9.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty compact">
<li class="toc ulEmpty compact" id="section-toc.1-1.9.2.1">
                <p id="section-toc.1-1.9.2.1.1"><a href="#section-9.1" class="xref">9.1</a>.  <a href="#name-normative-references" class="xref">Normative References</a><a href="#section-toc.1-1.9.2.1.1" class="pilcrow">¶</a></p>
</li>
              <li class="toc ulEmpty compact" id="section-toc.1-1.9.2.2">
                <p id="section-toc.1-1.9.2.2.1"><a href="#section-9.2" class="xref">9.2</a>.  <a href="#name-informative-references" class="xref">Informative References</a><a href="#section-toc.1-1.9.2.2.1" class="pilcrow">¶</a></p>
</li>
            </ul>
</li>
          <li class="toc ulEmpty compact" id="section-toc.1-1.10">
            <p id="section-toc.1-1.10.1"><a href="#section-appendix.a" class="xref"></a><a href="#name-acknowledgments" class="xref">Acknowledgments</a><a href="#section-toc.1-1.10.1" class="pilcrow">¶</a></p>
</li>
          <li class="toc ulEmpty compact" id="section-toc.1-1.11">
            <p id="section-toc.1-1.11.1"><a href="#section-appendix.b" class="xref"></a><a href="#name-authors-addresses" class="xref">Authors' Addresses</a><a href="#section-toc.1-1.11.1" class="pilcrow">¶</a></p>
</li>
        </ul>
</nav>
</section>
</div>
<div id="Intro">
<section id="section-1">
      <h2 id="name-introduction">
<a href="#section-1" class="section-number selfRef">1. </a><a href="#name-introduction" class="section-name selfRef">Introduction</a>
      </h2>
<p id="section-1-1">The original 6LoWPAN fragmentation is defined in <span>[<a href="#RFC4944" class="xref">RFC4944</a>]</span> 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 <span>[<a href="#RFC6282" class="xref">RFC6282</a>]</span>.
6LoWPAN operations including fragmentation depend on a link-layer security that prevents any rogue access to the network.<a href="#section-1-1" class="pilcrow">¶</a></p>
<p id="section-1-2">
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.<a href="#section-1-2" class="pilcrow">¶</a></p>
<p id="section-1-3">

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.<a href="#section-1-3" class="pilcrow">¶</a></p>
<p id="section-1-4">
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 <span>[<a href="#RFC4944" class="xref">RFC4944</a>]</span>. Basic recommendations such as the insertion of an inter-frame gap between fragments are provided to avoid the most typical caveats.<a href="#section-1-4" class="pilcrow">¶</a></p>
</section>
</div>
<section id="section-2">
      <h2 id="name-terminology">
<a href="#section-2" class="section-number selfRef">2. </a><a href="#name-terminology" class="section-name selfRef">Terminology</a>
      </h2>
<div id="bcp">
<section id="section-2.1">
        <h3 id="name-requirements-language">
<a href="#section-2.1" class="section-number selfRef">2.1. </a><a href="#name-requirements-language" class="section-name selfRef">Requirements Language</a>
        </h3>
<p id="section-2.1-1">
    The key words "<span class="bcp14">MUST</span>", "<span class="bcp14">MUST NOT</span>", "<span class="bcp14">REQUIRED</span>", "<span class="bcp14">SHALL</span>", "<span class="bcp14">SHALL NOT</span>", "<span class="bcp14">SHOULD</span>", "<span class="bcp14">SHOULD NOT</span>", "<span class="bcp14">RECOMMENDED</span>", "<span class="bcp14">NOT RECOMMENDED</span>",
    "<span class="bcp14">MAY</span>", and "<span class="bcp14">OPTIONAL</span>" in this document are to be interpreted as
    described in BCP 14 <span>[<a href="#RFC2119" class="xref">RFC2119</a>]</span> <span>[<a href="#RFC8174" class="xref">RFC8174</a>]</span> 
    when, and only when, they appear in all capitals, as shown here.<a href="#section-2.1-1" class="pilcrow">¶</a></p>
</section>
</div>
<section id="section-2.2">
        <h3 id="name-background">
<a href="#section-2.2" class="section-number selfRef">2.2. </a><a href="#name-background" class="section-name selfRef">Background</a>
        </h3>
<p id="section-2.2-1">
   
 Past experience with fragmentation, e.g., as described in <span><a href="#RFC4963" class="xref">"IPv4 Reassembly Errors at High Data Rates"</a> [<a href="#RFC4963" class="xref">RFC4963</a>]</span> and references therein,  has shown that misassociated or lost
        fragments can lead to poor network behavior and, occasionally, trouble
        at the application layer.
 That experience led to the definition of the <span><a href="#RFC8201" class="xref">"Path
        MTU Discovery for IP version 6"</a> [<a href="#RFC8201" class="xref">RFC8201</a>]</span> protocol that limits fragmentation over the
        Internet.<a href="#section-2.2-1" class="pilcrow">¶</a></p>
<p id="section-2.2-2"><span><a href="#RFC8900" class="xref">"IP Fragmentation
        Considered Fragile"</a> [<a href="#RFC8900" class="xref">RFC8900</a>]</span> discusses security threats that are linked to
        using IP fragmentation. The 6LoWPAN fragmentation takes place underneath the IP Layer,
        but some issues described there may still apply to 6LoWPAN fragments
        (as discussed in further details in
        <a href="#security-considerations" class="xref">Section 7</a>).<a href="#section-2.2-2" class="pilcrow">¶</a></p>
<p id="section-2.2-3">Readers are expected to be familiar with all the terms and concepts
     that are discussed in <span><a href="#RFC4919" class="xref">"IPv6 over Low-Power
     Wireless Personal Area Networks (6LoWPANs): Overview, Assumptions,
     Problem Statement, and Goals"</a> [<a href="#RFC4919" class="xref">RFC4919</a>]</span> and <span><a href="#RFC4944" class="xref">"Transmission of IPv6 Packets over IEEE 802.15.4 Networks"</a> [<a href="#RFC4944" class="xref">RFC4944</a>]</span>.<a href="#section-2.2-3" class="pilcrow">¶</a></p>
<p id="section-2.2-4"><span><a href="#RFC3031" class="xref">"Multiprotocol Label Switching
        Architecture"</a> [<a href="#RFC3031" class="xref">RFC3031</a>]</span> states that with MPLS,<a href="#section-2.2-4" class="pilcrow">¶</a></p>
<blockquote id="section-2.2-5">
        packets are "labeled" before
        they are forwarded. At subsequent hops, there is
        no further analysis of the packet's network layer header.  Rather, the
        label is used as an index into a table which specifies the next hop,
        and a new label.<a href="#section-2.2-5" class="pilcrow">¶</a>
</blockquote>
<p id="section-2.2-6">The MPLS
        technique is leveraged in the present specification to forward
        fragments that actually
        do not have a network-layer header, since the fragmentation occurs below
        IP.<a href="#section-2.2-6" class="pilcrow">¶</a></p>
</section>
<div id="new">
<section id="section-2.3">
        <h3 id="name-new-terms">
<a href="#section-2.3" class="section-number selfRef">2.3. </a><a href="#name-new-terms" class="section-name selfRef">New Terms</a>
        </h3>
<p id="section-2.3-1">
    This specification uses the following terms:<a href="#section-2.3-1" class="pilcrow">¶</a></p>
<span class="break"></span><dl class="dlParallel" id="section-2.3-2">
          <dt id="section-2.3-2.1">6LoWPAN Fragment Forwarding Endpoints:</dt>
          <dd style="margin-left: 1.5em" id="section-2.3-2.2">
     The 6LFF endpoints are the first and last nodes in an unbroken string
        of 6LFF nodes. They are also the only points
        where the fragmentation and reassembly operations take place.<a href="#section-2.3-2.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-2.3-2.3">Compressed Form:</dt>
          <dd style="margin-left: 1.5em" id="section-2.3-2.4">
     This specification uses the generic term "compressed form" to refer to
        the format of a datagram after the action of <span>[<a href="#RFC6282" class="xref">RFC6282</a>]</span>
        and possibly <span>[<a href="#RFC8138" class="xref">RFC8138</a>]</span> for Routing Protocol for Low-Power and Lossy Network (RPL) <span>[<a href="#RFC6550" class="xref">RFC6550</a>]</span>
        artifacts.<a href="#section-2.3-2.4" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-2.3-2.5">Datagram_Size:</dt>
          <dd style="margin-left: 1.5em" id="section-2.3-2.6">
        The size of the datagram in its compressed form before it is fragmented.<a href="#section-2.3-2.6" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-2.3-2.7">Datagram_Tag:</dt>
          <dd style="margin-left: 1.5em" id="section-2.3-2.8">
        An identifier of a datagram that is locally unique to the Layer 2 sender.
        Associated with the link-layer address of the sender, this becomes a globally
        unique identifier for the datagram within the duration of its transmission.<a href="#section-2.3-2.8" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-2.3-2.9">Fragment_Offset:</dt>
          <dd style="margin-left: 1.5em" id="section-2.3-2.10">
        The offset of a fragment of a datagram in its compressed form.<a href="#section-2.3-2.10" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
</dl>
</section>
</div>
</section>
<div id="overview-of-6lowpan-fragmentation">
<section id="section-3">
      <h2 id="name-overview-of-6lowpan-fragmen">
<a href="#section-3" class="section-number selfRef">3. </a><a href="#name-overview-of-6lowpan-fragmen" class="section-name selfRef">Overview of 6LoWPAN Fragmentation</a>
      </h2>
<p id="section-3-1"><a href="#FIGperhop" class="xref">Figure 1</a> illustrates 6LoWPAN fragmentation.
We assume node A forwards a packet to node B, possibly as part of a multi-hop route between 6LoWPAN Fragment Forwarding endpoints, which may be neither A nor B, though 6LoWPAN may compress the IP header better when they are both the 6LFF and the 6LoWPAN compression endpoints.<a href="#section-3-1" class="pilcrow">¶</a></p>
<span id="name-fragmentation-at-node-a-and"></span><div id="FIGperhop">
<figure id="figure-1">
        <div class="artwork art-text alignLeft" id="section-3-2.1">
<pre>
               +---+                     +---+
        ... ---| A |--------------------&gt;| B |--- ...
               +---+                     +---+
                              # (frag. 5)

             123456789                 123456789
            +---------+               +---------+
            |   #  ###|               |###  #   |
            +---------+               +---------+
               outgoing                incoming
          fragmentation                reassembly
                 buffer                buffer
</pre>
</div>
<figcaption><a href="#figure-1" class="selfRef">Figure 1</a>:
<a href="#name-fragmentation-at-node-a-and" class="selfRef">Fragmentation at Node A, and Reassembly at Node B</a>
        </figcaption></figure>
</div>
<p id="section-3-3">Typically, node A starts with an uncompressed packet and compacts the IPv6 packet using the header compression mechanism defined in <span>[<a href="#RFC6282" class="xref">RFC6282</a>]</span>.
If the resulting 6LoWPAN packet does not fit into a single link-layer frame, node A's 6LoWPAN sub-layer cuts it into multiple 6LoWPAN fragments, which it transmits as separate link-layer frames to node B.
Node B's 6LoWPAN sub-layer reassembles these fragments, inflates the compressed header fields back to the original IPv6 header, and hands over the full IPv6 packet to its IPv6 layer.<a href="#section-3-3" class="pilcrow">¶</a></p>
<p id="section-3-4">In <a href="#FIGperhop" class="xref">Figure 1</a>, a packet forwarded by node A to node B is cut into nine fragments, numbered 1 to 9 as follows:<a href="#section-3-4" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-3-5.1">Each fragment is represented by the '#' symbol.<a href="#section-3-5.1" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-3-5.2">Node A has sent fragments 1, 2, 3, 5, and 6 to node B.<a href="#section-3-5.2" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-3-5.3">Node B has received fragments 1, 2, 3, and 6 from node A.<a href="#section-3-5.3" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-3-5.4">Fragment 5 is still being transmitted at the link layer from node A to node B.<a href="#section-3-5.4" class="pilcrow">¶</a>
</li>
      </ul>
<p id="section-3-6">The reassembly buffer for 6LoWPAN is indexed in node B by:<a href="#section-3-6" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-3-7.1">a unique identifier of node A (e.g., node A's link-layer address).<a href="#section-3-7.1" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-3-7.2">the Datagram_Tag chosen by node A for this fragmented datagram.<a href="#section-3-7.2" class="pilcrow">¶</a>
</li>
      </ul>
<p id="section-3-8">Because it may be hard for node B to correlate all possible link-layer addresses that node A may use (e.g., short versus long addresses), node A must use the same link-layer address to send all the fragments of the same datagram to node B.<a href="#section-3-8" class="pilcrow">¶</a></p>
<p id="section-3-9">Conceptually, the reassembly buffer in node B contains:<a href="#section-3-9" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-3-10.1">a Datagram_Tag as received in the incoming fragments, associated
      with the interface and the link-layer address of node A for which the received Datagram_Tag is unique,<a href="#section-3-10.1" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-3-10.2">the actual packet data from the fragments received so far, in a form that makes it possible to detect when the whole packet has been received and can be processed or forwarded,<a href="#section-3-10.2" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-3-10.3">a state indicating the fragments already received,<a href="#section-3-10.3" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-3-10.4">a Datagram_Size, and<a href="#section-3-10.4" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-3-10.5">a timer that allows discarding a partially reassembled packet after some timeout.<a href="#section-3-10.5" class="pilcrow">¶</a>
</li>
      </ul>
<p id="section-3-11">A fragmentation header is added to each fragment; it indicates what portion of the packet that fragment corresponds to.
<span><a href="https://www.rfc-editor.org/rfc/rfc4944#section-5.3" class="relref">Section 5.3</a> of [<a href="#RFC4944" class="xref">RFC4944</a>]</span> defines the format of the header for the first and subsequent fragments.
All fragments are tagged with a 16-bit "Datagram_Tag", used to identify which packet each fragment belongs to.
Each datagram can be uniquely identified by the sender link-layer addresses of the frame that carries it and the Datagram_Tag that the sender allocated for this datagram.
<span>[<a href="#RFC4944" class="xref">RFC4944</a>]</span> also mandates that the first fragment is sent first and with a particular format that is different than that of the next fragments. Each fragment except for the first one can be identified within its datagram by the datagram-offset.<a href="#section-3-11" class="pilcrow">¶</a></p>
<p id="section-3-12">Node B's typical behavior, per <span>[<a href="#RFC4944" class="xref">RFC4944</a>]</span>, is as follows.
Upon receiving a fragment from node A with a Datagram_Tag previously unseen from node A, node B allocates a buffer large enough to hold the entire packet.
The length of the packet is indicated in each fragment (the Datagram_Size field), so node B can allocate the buffer even if the fragment it receives first is not the first fragment.
As fragments come in, node B fills the buffer.
When all fragments have been received, node B inflates the compressed header fields into an IPv6 header and hands the resulting IPv6 packet to the IPv6 layer, which performs the route lookup. This behavior typically results in per-hop fragmentation and reassembly.
That is, the packet is fully reassembled, then (re-)fragmented, at every hop.<a href="#section-3-12" class="pilcrow">¶</a></p>
</section>
</div>
<div id="SEClimits">
<section id="section-4">
      <h2 id="name-limitations-of-per-hop-frag">
<a href="#section-4" class="section-number selfRef">4. </a><a href="#name-limitations-of-per-hop-frag" class="section-name selfRef">Limitations of Per-Hop Fragmentation and Reassembly</a>
      </h2>
<p id="section-4-1">There are at least two limitations to doing per-hop fragmentation and reassembly.
See <span>[<a href="#ARTICLE" class="xref">ARTICLE</a>]</span> for detailed simulation results on both limitations.<a href="#section-4-1" class="pilcrow">¶</a></p>
<div id="latency">
<section id="section-4.1">
        <h3 id="name-latency">
<a href="#section-4.1" class="section-number selfRef">4.1. </a><a href="#name-latency" class="section-name selfRef">Latency</a>
        </h3>
<p id="section-4.1-1">When reassembling, a node needs to wait for all the fragments to be received before being able to re-form the IPv6 packet and possibly forwarding it to the next hop. This repeats at every hop.<a href="#section-4.1-1" class="pilcrow">¶</a></p>
<p id="section-4.1-2">This may result in increased end-to-end latency compared to a case where each fragment is forwarded without per-hop reassembly.<a href="#section-4.1-2" class="pilcrow">¶</a></p>
</section>
</div>
<div id="memory-management-and-reliability">
<section id="section-4.2">
        <h3 id="name-memory-management-and-relia">
<a href="#section-4.2" class="section-number selfRef">4.2. </a><a href="#name-memory-management-and-relia" class="section-name selfRef">Memory Management and Reliability</a>
        </h3>
<p id="section-4.2-1">Constrained nodes have limited memory. Assuming a reassembly buffer for a 6LoWPAN MTU of 1280 bytes as defined in <span><a href="https://www.rfc-editor.org/rfc/rfc4944#section-4" class="relref">Section 4</a> of [<a href="#RFC4944" class="xref">RFC4944</a>]</span>, typical nodes only have enough memory for 1-3 reassembly buffers.<a href="#section-4.2-1" class="pilcrow">¶</a></p>
<p id="section-4.2-2">To illustrate this, we use the topology from <a href="#FIGtopology" class="xref">Figure 2</a>, where nodes A, B, C, and D all send packets through node E.
We further assume that node E's memory can only hold 3 reassembly buffers.<a href="#section-4.2-2" class="pilcrow">¶</a></p>
<span id="name-illustrating-the-memory-man"></span><div id="FIGtopology">
<figure id="figure-2">
          <div class="artwork art-text alignLeft" id="section-4.2-3.1">
<pre>
               +---+       +---+
       ... ---&gt;| A |------&gt;| B |
               +---+       +---+\
                                 \
                                 +---+    +---+
                                 | E |---&gt;| F | ...
                                 +---+    +---+
                                 /
                                /
               +---+       +---+
       ... ---&gt;| C |------&gt;| D |
               +---+       +---+
</pre>
</div>
<figcaption><a href="#figure-2" class="selfRef">Figure 2</a>:
<a href="#name-illustrating-the-memory-man" class="selfRef">Illustrating the Memory Management Issue</a>
          </figcaption></figure>
</div>
<p id="section-4.2-4">When nodes A, B, and C concurrently send fragmented packets, all three reassembly buffers in node E are occupied.
If, at that moment, node D also sends a fragmented packet, node E has no option but to drop one of the packets, lowering end-to-end reliability.<a href="#section-4.2-4" class="pilcrow">¶</a></p>
</section>
</div>
</section>
</div>
<div id="ff">
<section id="section-5">
      <h2 id="name-forwarding-fragments">
<a href="#section-5" class="section-number selfRef">5. </a><a href="#name-forwarding-fragments" class="section-name selfRef">Forwarding Fragments</a>
      </h2>
<p id="section-5-1">
A 6LoWPAN Fragment Forwarding technique makes the routing decision on the first fragment, which is always the one with the IPv6 address of the destination. Upon receiving a first fragment, a forwarding node (e.g., node B in an A-&gt;B-&gt;C sequence) that does fragment forwarding <span class="bcp14">MUST</span> attempt to create a state and forward the fragment. This is an atomic operation, and if the first fragment cannot be forwarded, then the state <span class="bcp14">MUST</span> be removed.<a href="#section-5-1" class="pilcrow">¶</a></p>
<p id="section-5-2">
Since the Datagram_Tag is uniquely associated with the source link-layer address of the fragment, the forwarding node <span class="bcp14">MUST</span> assign a new Datagram_Tag from its own namespace for the next hop and rewrite the fragment header of each fragment with that Datagram_Tag.<a href="#section-5-2" class="pilcrow">¶</a></p>
<p id="section-5-3">

When a forwarding node receives a fragment other than a first fragment, it <span class="bcp14">MUST</span> look up state based on the source link-layer address and the Datagram_Tag in the received fragment. If no such state is found, the fragment <span class="bcp14">MUST</span> be dropped; otherwise, the fragment <span class="bcp14">MUST</span> be forwarded using the information in the state found.<a href="#section-5-3" class="pilcrow">¶</a></p>
<p id="section-5-4">
Compared to <a href="#overview-of-6lowpan-fragmentation" class="xref">Section 3</a>, the conceptual reassembly buffer in node B now contains the following, assuming that node B is neither the source nor the final destination:<a href="#section-5-4" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-5-5.1">a Datagram_Tag as received in the incoming fragments, associated with the interface and the link-layer address of node A for which the received Datagram_Tag is unique.<a href="#section-5-5.1" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-5-5.2">the link-layer address that node B uses as the source to forward the fragments.<a href="#section-5-5.2" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-5-5.3"> the interface and the link-layer address of the next-hop C that is resolved on the first fragment.<a href="#section-5-5.3" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-5-5.4">a Datagram_Tag that node B uniquely allocated for this datagram and that is used when forwarding the fragments of the datagram.<a href="#section-5-5.4" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-5-5.5">a buffer for the remainder of a previous fragment left to be sent.<a href="#section-5-5.5" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-5-5.6">a timer that allows discarding the stale 6LFF state after some timeout.
  The duration of the timer should be longer than that which covers the reassembly at the receiving endpoint.<a href="#section-5-5.6" class="pilcrow">¶</a>
</li>
      </ul>
<p id="section-5-6">
 A node that has not received the first fragment cannot forward the next fragments. This means that if node B receives a fragment, node A was in possession of the first fragment at some point. To keep the operation simple and consistent with <span>[<a href="#RFC4944" class="xref">RFC4944</a>]</span>, the first fragment <span class="bcp14">MUST</span> always be sent first. When that is done, if node B receives a fragment that is not the first and for which it has no state, then node B treats it as an error and refrains from creating a state or attempting to forward.
 This also means that node A should perform all its possible retries on the first fragment before it attempts to send the next fragments, and that it should abort the datagram and release its state if it fails to send the first fragment.<a href="#section-5-6" class="pilcrow">¶</a></p>
<p id="section-5-7">Fragment forwarding obviates some of the benefits of the 6LoWPAN header compression <span>[<a href="#RFC6282" class="xref">RFC6282</a>]</span> in intermediate hops. In return, the memory used to store the packet is distributed along the path, which limits the buffer-bloat effect. Multiple fragments may progress simultaneously along the network as long as they do not interfere.
 An associated caveat is that on a half-duplex radio, if node A sends the next fragment at the same time as node B forwards the previous fragment to node C down the path, then node B will miss it.

 If node C forwards the previous fragment to node D at the same time and on the same frequency as node A sends the next fragment to node B, this may result in a hidden terminal problem. In that case, the transmission from node C interferes at node B with that from node A, unbeknownst to node A.

 Consecutive fragments of a same datagram <span class="bcp14">MUST</span> be separated with an inter-frame gap that allows one fragment to progress beyond the next hop and beyond the interference domain before the next shows up. This can be achieved by interleaving packets or fragments sent via different next-hop routers.<a href="#section-5-7" class="pilcrow">¶</a></p>
</section>
</div>
<div id="virtual-reassembly-buffer-vrb-implementation">
<section id="section-6">
      <h2 id="name-virtual-reassembly-buffer-v">
<a href="#section-6" class="section-number selfRef">6. </a><a href="#name-virtual-reassembly-buffer-v" class="section-name selfRef">Virtual Reassembly Buffer (VRB) Implementation</a>
      </h2>
<p id="section-6-1">
The VRB <span>[<a href="#I-D.ietf-lwig-6lowpan-virtual-reassembly" class="xref">LWIG-VRB</a>]</span> is a particular incarnation of a 6LFF that can be implemented without a change to <span>[<a href="#RFC4944" class="xref">RFC4944</a>]</span>.<a href="#section-6-1" class="pilcrow">¶</a></p>
<p id="section-6-2">VRB overcomes the limitations listed in <a href="#SEClimits" class="xref">Section 4</a>.
Nodes do not wait for the last fragment before forwarding, reducing end-to-end latency.
Similarly, the memory footprint of VRB is just the VRB table, reducing the packet drop probability significantly.<a href="#section-6-2" class="pilcrow">¶</a></p>
<p id="section-6-3">However, there are other caveats:<a href="#section-6-3" class="pilcrow">¶</a></p>
<span class="break"></span><dl class="dlParallel" id="section-6-4">
        <dt id="section-6-4.1">Non-zero Packet Drop Probability:</dt>
        <dd style="margin-left: 1.5em" id="section-6-4.2">
  The abstract data in a VRB table entry contains at a minimum the link-layer address of the predecessor and the successor, the Datagram_Tag used by the predecessor, and the local Datagram_Tag that this node will swap with it. The VRB may need to store a few octets from the last fragment that may not have fit within MTU and that will be prepended to the next fragment.
This yields a small footprint that is 2 orders of magnitude smaller, compared to needing a 1280-byte reassembly buffer for each packet.
Yet, the size of the VRB table necessarily remains finite.
In the extreme case where a node is required to concurrently forward more packets than it has entries in its VRB table, packets are dropped.<a href="#section-6-4.2" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
<dt id="section-6-4.3">No Fragment Recovery:</dt>
        <dd style="margin-left: 1.5em" id="section-6-4.4">
  There is no mechanism in VRB for the node that reassembles a packet to request a single missing fragment.
Dropping a fragment requires the whole packet to be resent.
This causes unnecessary traffic, as fragments are forwarded even when the destination node can never construct the original IPv6 packet.<a href="#section-6-4.4" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
<dt id="section-6-4.5">No Per-Fragment Routing:</dt>
        <dd style="margin-left: 1.5em" id="section-6-4.6">
  All subsequent fragments follow the same sequence of hops from the source to the destination node as the first fragment, because the IP header is required in order to route the fragment and is only present in the first fragment. A side effect is that the first fragment must always be forwarded first.<a href="#section-6-4.6" class="pilcrow">¶</a>
</dd>
      <dd class="break"></dd>
</dl>
<p id="section-6-5">The severity and occurrence of these caveats depend on the link layer used.
Whether they are acceptable depends entirely on the requirements the application places on the network.<a href="#section-6-5" class="pilcrow">¶</a></p>
<p id="section-6-6">If the caveats are present and not acceptable for the application, alternative specifications may define new protocols to overcome them.
One example is <span>[<a href="#RFC8931" class="xref">RFC8931</a>]</span>, which specifies a 6LFF technique that allows the end-to-end fragment recovery between the 6LFF endpoints.<a href="#section-6-6" class="pilcrow">¶</a></p>
</section>
</div>
<div id="security-considerations">
<section id="section-7">
      <h2 id="name-security-considerations">
<a href="#section-7" class="section-number selfRef">7. </a><a href="#name-security-considerations" class="section-name selfRef">Security Considerations</a>
      </h2>
<p id="section-7-1">
   An attacker can perform a Denial-of-Service (DoS) attack on a node
   implementing VRB by generating a large number of bogus "fragment 1"
   fragments without sending subsequent fragments.  This causes the VRB
   table to fill up.  Note that the VRB does not need to remember the
   full datagram as received so far but only possibly a few octets from
   the last fragment that could not fit in it.  It is expected that an
   implementation protects itself to keep the number of VRBs within
   capacity, and that old VRBs are protected by a timer of a reasonable
   duration for the technology and destroyed upon timeout.<a href="#section-7-1" class="pilcrow">¶</a></p>
<p id="section-7-2">Secure joining and the link-layer security that it sets up protects against those attacks from network outsiders.<a href="#section-7-2" class="pilcrow">¶</a></p>
<p id="section-7-3"><span><a href="#RFC8900" class="xref">"IP Fragmentation Considered Fragile"</a> [<a href="#RFC8900" class="xref">RFC8900</a>]</span> discusses security threats and other caveats that are linked to using IP fragmentation. The 6LoWPAN fragmentation takes place underneath the IP Layer, but some issues described there may still apply to 6LoWPAN fragments.<a href="#section-7-3" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-7-4.1">Overlapping fragment attacks are possible with 6LoWPAN fragments, but there is no known firewall operation that would work on 6LoWPAN fragments at the time of this writing, so the exposure is limited. An implementation of a firewall <span class="bcp14">SHOULD NOT</span> forward fragments but instead should recompose the IP packet, check it in the uncompressed form, and then forward it again as fragments if necessary. Overlapping fragments are acceptable as long as they contain the same payload. The firewall <span class="bcp14">MUST</span> drop the whole packet if overlapping fragments are encountered that result in different data at the same offset.<a href="#section-7-4.1" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-7-4.2">Resource-exhaustion attacks are certainly possible and a sensitive issue in a constrained network. An attacker can perform a DoS attack on a node implementing VRB by generating a large number of bogus first fragments without sending subsequent fragments. This causes the VRB table to fill up. When hop-by-hop reassembly is used, the same attack can be more damaging if the node allocates a full Datagram_Size for each bogus first fragment. With the VRB, the attack can be performed remotely on all nodes along a path, but each node suffers a lesser hit. This is because the VRB does not need to remember the full datagram as received so far but only possibly a few octets from the last fragment that could not fit in it.
   An implementation <span class="bcp14">MUST</span> protect itself to keep the number of VRBs within capacity and to ensure that old VRBs are protected by a timer of a reasonable duration for the technology and destroyed upon timeout.<a href="#section-7-4.2" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-7-4.3">Attacks based on predictable fragment identification values are also possible but can be avoided. The Datagram_Tag <span class="bcp14">SHOULD</span> be assigned pseudorandomly in order to reduce the risk of such attacks. A larger size of the
   Datagram_Tag makes the guessing more difficult and reduces the chances of an
   accidental reuse while the original packet is still in flight, at the expense of more space in each frame.
   Nonetheless, some level of risk remains because an
      attacker that is able to authenticate to and send traffic on the
      network can guess a valid Datagram_Tag value, since there are only
      a limited number of possible values.<a href="#section-7-4.3" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-7-4.4">Evasion of Network Intrusion Detection Systems (NIDSs) leverages ambiguity in the reassembly of the fragment. This attack makes little sense in the context of this specification since the fragmentation happens within the Low-Power and Lossy Network (LLN), meaning that the intruder should already be inside to perform the attack.

   NIDS systems would probably not be installed within the LLN either but
   rather at a bottleneck at the exterior edge of the network.<a href="#section-7-4.4" class="pilcrow">¶</a>
</li>
      </ul>
</section>
</div>
<div id="iana-considerations">
<section id="section-8">
      <h2 id="name-iana-considerations">
<a href="#section-8" class="section-number selfRef">8. </a><a href="#name-iana-considerations" class="section-name selfRef">IANA Considerations</a>
      </h2>
<p id="section-8-1">This document has no IANA actions.<a href="#section-8-1" class="pilcrow">¶</a></p>
</section>
</div>
<section id="section-9">
      <h2 id="name-references">
<a href="#section-9" class="section-number selfRef">9. </a><a href="#name-references" class="section-name selfRef">References</a>
      </h2>
<section id="section-9.1">
        <h3 id="name-normative-references">
<a href="#section-9.1" class="section-number selfRef">9.1. </a><a href="#name-normative-references" class="section-name selfRef">Normative References</a>
        </h3>
<dl class="references">
<dt id="RFC2119">[RFC2119]</dt>
        <dd>
<span class="refAuthor">Bradner, S.</span>, <span class="refTitle">"Key words for use in RFCs to Indicate Requirement Levels"</span>, <span class="seriesInfo">BCP 14</span>, <span class="seriesInfo">RFC 2119</span>, <span class="seriesInfo">DOI 10.17487/RFC2119</span>, <time datetime="1997-03" class="refDate">March 1997</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc2119">https://www.rfc-editor.org/info/rfc2119</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC4919">[RFC4919]</dt>
        <dd>
<span class="refAuthor">Kushalnagar, N.</span><span class="refAuthor">, Montenegro, G.</span><span class="refAuthor">, and C. Schumacher</span>, <span class="refTitle">"IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): Overview, Assumptions, Problem Statement, and Goals"</span>, <span class="seriesInfo">RFC 4919</span>, <span class="seriesInfo">DOI 10.17487/RFC4919</span>, <time datetime="2007-08" class="refDate">August 2007</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc4919">https://www.rfc-editor.org/info/rfc4919</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC4944">[RFC4944]</dt>
        <dd>
<span class="refAuthor">Montenegro, G.</span><span class="refAuthor">, Kushalnagar, N.</span><span class="refAuthor">, Hui, J.</span><span class="refAuthor">, and D. Culler</span>, <span class="refTitle">"Transmission of IPv6 Packets over IEEE 802.15.4 Networks"</span>, <span class="seriesInfo">RFC 4944</span>, <span class="seriesInfo">DOI 10.17487/RFC4944</span>, <time datetime="2007-09" class="refDate">September 2007</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc4944">https://www.rfc-editor.org/info/rfc4944</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8174">[RFC8174]</dt>
      <dd>
<span class="refAuthor">Leiba, B.</span>, <span class="refTitle">"Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words"</span>, <span class="seriesInfo">BCP 14</span>, <span class="seriesInfo">RFC 8174</span>, <span class="seriesInfo">DOI 10.17487/RFC8174</span>, <time datetime="2017-05" class="refDate">May 2017</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8174">https://www.rfc-editor.org/info/rfc8174</a>&gt;</span>. </dd>
<dd class="break"></dd>
</dl>
</section>
<section id="section-9.2">
        <h3 id="name-informative-references">
<a href="#section-9.2" class="section-number selfRef">9.2. </a><a href="#name-informative-references" class="section-name selfRef">Informative References</a>
        </h3>
<dl class="references">
<dt id="ARTICLE">[ARTICLE]</dt>
        <dd>
<span class="refAuthor">Tanaka, Y.</span><span class="refAuthor">, Minet, P.</span><span class="refAuthor">, and T. Watteyne</span>, <span class="refTitle">"6LoWPAN Fragment Forwarding"</span>, <span class="refContent">IEEE Communications Standards Magazine, Vol. 3, Issue 1, pp. 35-39</span>, <span class="seriesInfo">DOI 10.1109/MCOMSTD.2019.1800029</span>, <time datetime="2019-03" class="refDate">March 2019</time>, <span>&lt;<a href="https://ieeexplore.ieee.org/abstract/document/8771317">https://ieeexplore.ieee.org/abstract/document/8771317</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="I-D.ietf-lwig-6lowpan-virtual-reassembly">[LWIG-VRB]</dt>
        <dd>
<span class="refAuthor">Bormann, C.</span><span class="refAuthor"> and T. Watteyne</span>, <span class="refTitle">"Virtual reassembly buffers in 6LoWPAN"</span>, <span class="refContent">Work in Progress</span>, <span class="seriesInfo">Internet-Draft, draft-ietf-lwig-6lowpan-virtual-reassembly-02</span>, <time datetime="2020-03-09" class="refDate">9 March 2020</time>, <span>&lt;<a href="https://tools.ietf.org/html/draft-ietf-lwig-6lowpan-virtual-reassembly-02">https://tools.ietf.org/html/draft-ietf-lwig-6lowpan-virtual-reassembly-02</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC3031">[RFC3031]</dt>
        <dd>
<span class="refAuthor">Rosen, E.</span><span class="refAuthor">, Viswanathan, A.</span><span class="refAuthor">, and R. Callon</span>, <span class="refTitle">"Multiprotocol Label Switching Architecture"</span>, <span class="seriesInfo">RFC 3031</span>, <span class="seriesInfo">DOI 10.17487/RFC3031</span>, <time datetime="2001-01" class="refDate">January 2001</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc3031">https://www.rfc-editor.org/info/rfc3031</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC4963">[RFC4963]</dt>
        <dd>
<span class="refAuthor">Heffner, J.</span><span class="refAuthor">, Mathis, M.</span><span class="refAuthor">, and B. Chandler</span>, <span class="refTitle">"IPv4 Reassembly Errors at High Data Rates"</span>, <span class="seriesInfo">RFC 4963</span>, <span class="seriesInfo">DOI 10.17487/RFC4963</span>, <time datetime="2007-07" class="refDate">July 2007</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc4963">https://www.rfc-editor.org/info/rfc4963</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC6282">[RFC6282]</dt>
        <dd>
<span class="refAuthor">Hui, J., Ed.</span><span class="refAuthor"> and P. Thubert</span>, <span class="refTitle">"Compression Format for IPv6 Datagrams over IEEE 802.15.4-Based Networks"</span>, <span class="seriesInfo">RFC 6282</span>, <span class="seriesInfo">DOI 10.17487/RFC6282</span>, <time datetime="2011-09" class="refDate">September 2011</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6282">https://www.rfc-editor.org/info/rfc6282</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC6550">[RFC6550]</dt>
        <dd>
<span class="refAuthor">Winter, T., Ed.</span><span class="refAuthor">, Thubert, P., Ed.</span><span class="refAuthor">, Brandt, A.</span><span class="refAuthor">, Hui, J.</span><span class="refAuthor">, Kelsey, R.</span><span class="refAuthor">, Levis, P.</span><span class="refAuthor">, Pister, K.</span><span class="refAuthor">, Struik, R.</span><span class="refAuthor">, Vasseur, JP.</span><span class="refAuthor">, and R. Alexander</span>, <span class="refTitle">"RPL: IPv6 Routing Protocol for Low-Power and Lossy Networks"</span>, <span class="seriesInfo">RFC 6550</span>, <span class="seriesInfo">DOI 10.17487/RFC6550</span>, <time datetime="2012-03" class="refDate">March 2012</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6550">https://www.rfc-editor.org/info/rfc6550</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8138">[RFC8138]</dt>
        <dd>
<span class="refAuthor">Thubert, P., Ed.</span><span class="refAuthor">, Bormann, C.</span><span class="refAuthor">, Toutain, L.</span><span class="refAuthor">, and R. Cragie</span>, <span class="refTitle">"IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN) Routing Header"</span>, <span class="seriesInfo">RFC 8138</span>, <span class="seriesInfo">DOI 10.17487/RFC8138</span>, <time datetime="2017-04" class="refDate">April 2017</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8138">https://www.rfc-editor.org/info/rfc8138</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8201">[RFC8201]</dt>
        <dd>
<span class="refAuthor">McCann, J.</span><span class="refAuthor">, Deering, S.</span><span class="refAuthor">, Mogul, J.</span><span class="refAuthor">, and R. Hinden, Ed.</span>, <span class="refTitle">"Path MTU Discovery for IP version 6"</span>, <span class="seriesInfo">STD 87</span>, <span class="seriesInfo">RFC 8201</span>, <span class="seriesInfo">DOI 10.17487/RFC8201</span>, <time datetime="2017-07" class="refDate">July 2017</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8201">https://www.rfc-editor.org/info/rfc8201</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8900">[RFC8900]</dt>
        <dd>
<span class="refAuthor">Bonica, R.</span><span class="refAuthor">, Baker, F.</span><span class="refAuthor">, Huston, G.</span><span class="refAuthor">, Hinden, R.</span><span class="refAuthor">, Troan, O.</span><span class="refAuthor">, and F. Gont</span>, <span class="refTitle">"IP Fragmentation Considered Fragile"</span>, <span class="seriesInfo">BCP 230</span>, <span class="seriesInfo">RFC 8900</span>, <span class="seriesInfo">DOI 10.17487/RFC8900</span>, <time datetime="2020-09" class="refDate">September 2020</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8900">https://www.rfc-editor.org/info/rfc8900</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8931">[RFC8931]</dt>
      <dd>
<span class="refAuthor">Thubert, P., Ed.</span>, <span class="refTitle">"IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN) Selective Fragment Recovery"</span>, <span class="seriesInfo">RFC 8931</span>, <span class="seriesInfo">DOI 10.17487/RFC8931</span>, <time datetime="2020-11" class="refDate">November 2020</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8931">https://www.rfc-editor.org/info/rfc8931</a>&gt;</span>. </dd>
<dd class="break"></dd>
</dl>
</section>
</section>
<div id="acknowledgments">
<section id="section-appendix.a">
      <h2 id="name-acknowledgments">
<a href="#name-acknowledgments" class="section-name selfRef">Acknowledgments</a>
      </h2>
<p id="section-appendix.a-1">The authors would like to thank <span class="contact-name">Carles Gomez Montenegro</span>, <span class="contact-name">Yasuyuki Tanaka</span>, <span class="contact-name">Ines Robles</span>, and <span class="contact-name">Dave Thaler</span> for their in-depth review of this document and suggestions for improvement. Many thanks to <span class="contact-name">Georgios Papadopoulos</span> and <span class="contact-name">Dominique Barthel</span> for their contributions during the WG activities. And many thanks as well to <span class="contact-name">Roman Danyliw</span>, <span class="contact-name">Barry Leiba</span>, <span class="contact-name">Murray Kucherawy</span>, <span class="contact-name">Derrell Piper</span>, <span class="contact-name">Sarah Banks</span>, <span class="contact-name">Joerg Ott</span>, <span class="contact-name">Francesca Palombini</span>, <span class="contact-name">Mirja Kühlewind</span>, <span class="contact-name">Éric Vyncke</span>, and especially <span class="contact-name">Benjamin Kaduk</span> for their constructive reviews through the IETF last call and IESG process.<a href="#section-appendix.a-1" class="pilcrow">¶</a></p>
</section>
</div>
<div id="authors-addresses">
<section id="section-appendix.b">
      <h2 id="name-authors-addresses">
<a href="#name-authors-addresses" class="section-name selfRef">Authors' Addresses</a>
      </h2>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Thomas Watteyne (<span class="role">editor</span>)</span></div>
<div dir="auto" class="left"><span class="org">Analog Devices</span></div>
<div dir="auto" class="left"><span class="street-address">32990 Alvarado-Niles Road, Suite 910</span></div>
<div dir="auto" class="left">
<span class="locality">Union City</span>, <span class="region">CA</span> <span class="postal-code">94587</span>
</div>
<div dir="auto" class="left"><span class="country-name">United States of America</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:thomas.watteyne@analog.com" class="email">thomas.watteyne@analog.com</a>
</div>
</address>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Pascal Thubert (<span class="role">editor</span>)</span></div>
<div dir="auto" class="left"><span class="org">Cisco Systems, Inc</span></div>
<div dir="auto" class="left"><span class="extended-address">Building D</span></div>
<div dir="auto" class="left"><span class="street-address">45 Allee des Ormes - BP1200</span></div>
<div dir="auto" class="left">
<span class="postal-code">06254</span> <span class="locality">Mougins - Sophia Antipolis</span>
</div>
<div dir="auto" class="left"><span class="country-name">France</span></div>
<div class="tel">
<span>Phone:</span>
<a href="tel:+33%20497%2023%2026%2034" class="tel">+33 497 23 26 34</a>
</div>
<div class="email">
<span>Email:</span>
<a href="mailto:pthubert@cisco.com" class="email">pthubert@cisco.com</a>
</div>
</address>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Carsten Bormann</span></div>
<div dir="auto" class="left"><span class="org">Universität Bremen TZI</span></div>
<div dir="auto" class="left"><span class="street-address">Postfach 330440</span></div>
<div dir="auto" class="left">
<span class="postal-code">D-28359</span> <span class="locality">Bremen</span>
</div>
<div dir="auto" class="left"><span class="country-name">Germany</span></div>
<div class="tel">
<span>Phone:</span>
<a href="tel:+49-421-218-63921" class="tel">+49-421-218-63921</a>
</div>
<div class="email">
<span>Email:</span>
<a href="mailto:cabo@tzi.org" class="email">cabo@tzi.org</a>
</div>
</address>
</section>
</div>
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