rfc8930xml2.original.xml		rfc8930.xml
			<?xml version='1.0' encoding='utf-8'?>
			<rfc xmlns:xi="http://www.w3.org/2001/XInclude" version="3" category="std" conse
			nsus="true" docName="draft-ietf-6lo-minimal-fragment-15" indexInclude="true" ipr
			="trust200902" number="8930" prepTime="2020-11-16T16:17:37" scripts="Common,Lati
			n" sortRefs="true" submissionType="IETF" symRefs="true" tocDepth="3" tocInclude=
			"true" xml:lang="en">
			<link href="https://datatracker.ietf.org/doc/draft-ietf-6lo-minimal-fragment-1
			5" rel="prev"/>
			<link href="https://dx.doi.org/10.17487/rfc8930" rel="alternate"/>
			<link href="urn:issn:2070-1721" rel="alternate"/>
			<front>
			<title abbrev="Fragment Forwarding">On Forwarding 6LoWPAN Fragments over a M
			ulti-Hop IPv6 Network</title>
			<seriesInfo name="RFC" value="8930" stream="IETF"/>
			<author initials="T." surname="Watteyne" fullname="Thomas Watteyne" role="ed
			itor">
			<organization showOnFrontPage="true">Analog Devices</organization>
			<address>
			<postal>
			<street>32990 Alvarado-Niles Road, Suite 910</street>
			<city>Union City</city>
			<region>CA</region>
			<code>94587</code>
			<country>United States of America</country>
			</postal>
			<email>thomas.watteyne@analog.com</email>
			</address>
			</author>
			<author initials="P." surname="Thubert" fullname="Pascal Thubert" role="edit
			or">
			<organization abbrev="Cisco Systems" showOnFrontPage="true">Cisco Systems,
			Inc</organization>
			<address>
			<postal>
			<extaddr>Building D</extaddr>
			<street>45 Allee des Ormes - BP1200</street>
			<city>Mougins - Sophia Antipolis</city>
			<code>06254</code>
			<country>France</country>
			</postal>
			<phone>+33 497 23 26 34</phone>
			<email>pthubert@cisco.com</email>
			</address>
			</author>
			<author initials="C." surname="Bormann" fullname="Carsten Bormann">
			<organization showOnFrontPage="true">Universität Bremen TZI</organization>
			<address>
			<postal>
			<street>Postfach 330440</street>
			<city>Bremen</city>
			<code>D-28359</code>
			<country>Germany</country>
			</postal>
			<phone>+49-421-218-63921</phone>
			<email>cabo@tzi.org</email>
			</address>
			</author>
			<date month="11" year="2020"/>
			<area>Internet Area</area>
			<workgroup>6lo</workgroup>
			<keyword>6LoWPAN</keyword>
			<keyword>Fragment</keyword>
			<abstract pn="section-abstract">
			<t indent="0" pn="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).</t>
			</abstract>
			<boilerplate>
			<section anchor="status-of-memo" numbered="false" removeInRFC="false" toc=
			"exclude" pn="section-boilerplate.1">
			<name slugifiedName="name-status-of-this-memo">Status of This Memo</name
			>
			<t indent="0" pn="section-boilerplate.1-1">
			This is an Internet Standards Track document.
			</t>
			<t indent="0" pn="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.
			</t>
			<t indent="0" pn="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
			<eref target="https://www.rfc-editor.org/info/rfc8930" brackets="non
			e"/>.
			</t>
			</section>
			<section anchor="copyright" numbered="false" removeInRFC="false" toc="excl
			ude" pn="section-boilerplate.2">
			<name slugifiedName="name-copyright-notice">Copyright Notice</name>
			<t indent="0" pn="section-boilerplate.2-1">
			Copyright (c) 2020 IETF Trust and the persons identified as the
			document authors. All rights reserved.
			</t>
			<t indent="0" pn="section-boilerplate.2-2">
			This document is subject to BCP 78 and the IETF Trust's Legal
			Provisions Relating to IETF Documents
			(<eref target="https://trustee.ietf.org/license-info" brackets="none
			"/>) 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.
			</t>
			</section>
			</boilerplate>
			<toc>
			<section anchor="toc" numbered="false" removeInRFC="false" toc="exclude" p
			n="section-toc.1">
			<name slugifiedName="name-table-of-contents">Table of Contents</name>
			<ul bare="true" empty="true" indent="2" spacing="compact" pn="section-to
			c.1-1">
			<li pn="section-toc.1-1.1">
			<t indent="0" keepWithNext="true" pn="section-toc.1-1.1.1"><xref der
			ivedContent="1" format="counter" sectionFormat="of" target="section-1"/>.  <xref
			derivedContent="" format="title" sectionFormat="of" target="name-introduction">
			Introduction</xref></t>
			</li>
			<li pn="section-toc.1-1.2">
			<t indent="0" pn="section-toc.1-1.2.1"><xref derivedContent="2" form
			at="counter" sectionFormat="of" target="section-2"/>.  <xref derivedContent="" f
			ormat="title" sectionFormat="of" target="name-terminology">Terminology</xref></t
			>
			<ul bare="true" empty="true" indent="2" spacing="compact" pn="sectio
			n-toc.1-1.2.2">
			<li pn="section-toc.1-1.2.2.1">
			<t indent="0" keepWithNext="true" pn="section-toc.1-1.2.2.1.1"><
			xref derivedContent="2.1" format="counter" sectionFormat="of" target="section-2.
			1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-re
			quirements-language">Requirements Language</xref></t>
			</li>
			<li pn="section-toc.1-1.2.2.2">
			<t indent="0" keepWithNext="true" pn="section-toc.1-1.2.2.2.1"><
			xref derivedContent="2.2" format="counter" sectionFormat="of" target="section-2.
			2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-ba
			ckground">Background</xref></t>
			</li>
			<li pn="section-toc.1-1.2.2.3">
			<t indent="0" pn="section-toc.1-1.2.2.3.1"><xref derivedContent=
			"2.3" format="counter" sectionFormat="of" target="section-2.3"/>.  <xref derived
			Content="" format="title" sectionFormat="of" target="name-new-terms">New Terms</
			xref></t>
			</li>
			</ul>
			</li>
			<li pn="section-toc.1-1.3">
			<t indent="0" pn="section-toc.1-1.3.1"><xref derivedContent="3" form
			at="counter" sectionFormat="of" target="section-3"/>.  <xref derivedContent="" f
			ormat="title" sectionFormat="of" target="name-overview-of-6lowpan-fragmen">Overv
			iew of 6LoWPAN Fragmentation</xref></t>
			</li>
			<li pn="section-toc.1-1.4">
			<t indent="0" pn="section-toc.1-1.4.1"><xref derivedContent="4" form
			at="counter" sectionFormat="of" target="section-4"/>.  <xref derivedContent="" f
			ormat="title" sectionFormat="of" target="name-limitations-of-per-hop-frag">Limit
			ations of Per-Hop Fragmentation and Reassembly</xref></t>
			<ul bare="true" empty="true" indent="2" spacing="compact" pn="sectio
			n-toc.1-1.4.2">
			<li pn="section-toc.1-1.4.2.1">
			<t indent="0" pn="section-toc.1-1.4.2.1.1"><xref derivedContent=
			"4.1" format="counter" sectionFormat="of" target="section-4.1"/>.  <xref derived
			Content="" format="title" sectionFormat="of" target="name-latency">Latency</xref
			></t>
			</li>
			<li pn="section-toc.1-1.4.2.2">
			<t indent="0" pn="section-toc.1-1.4.2.2.1"><xref derivedContent=
			"4.2" format="counter" sectionFormat="of" target="section-4.2"/>.  <xref derived
			Content="" format="title" sectionFormat="of" target="name-memory-management-and-
			relia">Memory Management and Reliability</xref></t>
			</li>
			</ul>
			</li>
			<li pn="section-toc.1-1.5">
			<t indent="0" pn="section-toc.1-1.5.1"><xref derivedContent="5" form
			at="counter" sectionFormat="of" target="section-5"/>.  <xref derivedContent="" f
			ormat="title" sectionFormat="of" target="name-forwarding-fragments">Forwarding F
			ragments</xref></t>
			</li>
			<li pn="section-toc.1-1.6">
			<t indent="0" pn="section-toc.1-1.6.1"><xref derivedContent="6" form
			at="counter" sectionFormat="of" target="section-6"/>.  <xref derivedContent="" f
			ormat="title" sectionFormat="of" target="name-virtual-reassembly-buffer-v">Virtu
			al Reassembly Buffer (VRB) Implementation</xref></t>
			</li>
			<li pn="section-toc.1-1.7">
			<t indent="0" pn="section-toc.1-1.7.1"><xref derivedContent="7" form
			at="counter" sectionFormat="of" target="section-7"/>.  <xref derivedContent="" f
			ormat="title" sectionFormat="of" target="name-security-considerations">Security
			Considerations</xref></t>
			</li>
			<li pn="section-toc.1-1.8">
			<t indent="0" pn="section-toc.1-1.8.1"><xref derivedContent="8" form
			at="counter" sectionFormat="of" target="section-8"/>.  <xref derivedContent="" f
			ormat="title" sectionFormat="of" target="name-iana-considerations">IANA Consider
			ations</xref></t>
			</li>
			<li pn="section-toc.1-1.9">
			<t indent="0" pn="section-toc.1-1.9.1"><xref derivedContent="9" form
			at="counter" sectionFormat="of" target="section-9"/>.  <xref derivedContent="" f
			ormat="title" sectionFormat="of" target="name-references">References</xref></t>
			<ul bare="true" empty="true" indent="2" spacing="compact" pn="sectio
			n-toc.1-1.9.2">
			<li pn="section-toc.1-1.9.2.1">
			<t indent="0" pn="section-toc.1-1.9.2.1.1"><xref derivedContent=
			"9.1" format="counter" sectionFormat="of" target="section-9.1"/>.  <xref derived
			Content="" format="title" sectionFormat="of" target="name-normative-references">
			Normative References</xref></t>
			</li>
			<li pn="section-toc.1-1.9.2.2">
			<t indent="0" pn="section-toc.1-1.9.2.2.1"><xref derivedContent=
			"9.2" format="counter" sectionFormat="of" target="section-9.2"/>.  <xref derived
			Content="" format="title" sectionFormat="of" target="name-informative-references
			">Informative References</xref></t>
			</li>
			</ul>
			</li>
			<li pn="section-toc.1-1.10">
			<t indent="0" pn="section-toc.1-1.10.1"><xref derivedContent="" form
			at="none" sectionFormat="of" target="section-appendix.a"/><xref derivedContent="
			" format="title" sectionFormat="of" target="name-acknowledgments">Acknowledgment
			s</xref></t>
			</li>
			<li pn="section-toc.1-1.11">
			<t indent="0" pn="section-toc.1-1.11.1"><xref derivedContent="" form
			at="none" sectionFormat="of" target="section-appendix.b"/><xref derivedContent="
			" format="title" sectionFormat="of" target="name-authors-addresses">Authors' Add
			resses</xref></t>
			</li>
			</ul>
			</section>
			</toc>
			</front>
			<middle>
			<section anchor="Intro" numbered="true" removeInRFC="false" toc="include" pn
			="section-1">
			<name slugifiedName="name-introduction">Introduction</name>
			<t indent="0" pn="section-1-1">The original 6LoWPAN fragmentation is defin
			ed in <xref target="RFC4944" format="default" sectionFormat="of" derivedContent=
			"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 t
			he update in <xref target="RFC6282" format="default" sectionFormat="of" derivedC
			ontent="RFC6282"/>.
			6LoWPAN operations including fragmentation depend on a link-layer security that
			prevents any rogue access to the network.
			</t>
			<t indent="0" pn="section-1-2">
			In a route-over 6LoWPAN network, an IP packet is expected to be reassembled at e
			ach intermediate hop, uncompressed, pushed to Layer 3 to be routed, and then com
			pressed and fragmented again.
			This document introduces an alternate approach called 6LoWPAN Fragment Forwardin
			g (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, a
			nd a state is stored to enable forwarding the next fragments along the same path
			.
			</t>
			<t indent="0" pn="section-1-3">
			Done right, 6LoWPAN Fragment Forwarding techniques lead to more streamlined oper
			ations, less buffer bloat, and lower latency. But it may be wasteful when fragme
			nts are missing, leading to locked resources and low throughput, and it may be m
			isused to the point that the end-to-end latency of one packet falls behind that
			of per-hop reassembly.
			</t>
			<t indent="0" pn="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 <x
			ref target="RFC4944" format="default" sectionFormat="of" derivedContent="RFC4944
			"/>. Basic recommendations such as the insertion of an inter-frame gap between f
			ragments are provided to avoid the most typical caveats.
			</t>
			</section>
			<section numbered="true" removeInRFC="false" toc="include" pn="section-2">
			<name slugifiedName="name-terminology">Terminology</name>
			<section anchor="bcp" numbered="true" removeInRFC="false" toc="include" pn
			="section-2.1">
			<name slugifiedName="name-requirements-language">Requirements Language</
			name>
			<t indent="0" pn="section-2.1-1">
			The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>", "<bcp14>REQU
			IRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL NOT</bcp14>", "<bcp14>SHOUL
			D</bcp14>", "<bcp14>SHOULD NOT</bcp14>", "<bcp14>RECOMMENDED</bcp14>", "<bcp14>N
			OT RECOMMENDED</bcp14>",
			"<bcp14>MAY</bcp14>", and "<bcp14>OPTIONAL</bcp14>" in this document are to
			be interpreted as
			described in BCP 14 <xref target="RFC2119" format="default" sectionFormat="o
			f" derivedContent="RFC2119"/> <xref target="RFC8174" format="default" sectionFor
			mat="of" derivedContent="RFC8174"/>
			when, and only when, they appear in all capitals, as shown here.
			</t>
			</section>
			<section numbered="true" removeInRFC="false" toc="include" pn="section-2.2
			">
			<name slugifiedName="name-background">Background</name>
			<t indent="0" pn="section-2.2-1">
			Past experience with fragmentation, e.g., as described in <xref t
			arget="RFC4963" format="default" sectionFormat="of" derivedContent="RFC4963">"IP
			v4 Reassembly Errors at High Data Rates"</xref> and references therein, has sho
			wn 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 <xref target="RFC820
			1" format="default" sectionFormat="of" derivedContent="RFC8201">"Path
			MTU Discovery for IP version 6"</xref> protocol that limits fragmentatio
			n over the
			Internet.
			</t>
			<t indent="0" pn="section-2.2-2"><xref target="RFC8900" format="default"
			sectionFormat="of" derivedContent="RFC8900">"IP Fragmentation
			Considered Fragile"</xref> 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
			<xref target="security-considerations" format="default" sectionFormat="o
			f" derivedContent="Section 7"/>).
			</t>
			<t indent="0" pn="section-2.2-3">Readers are expected to be familiar wit
			h all the terms and concepts
			that are discussed in <xref target="RFC4919" format="default" section
			Format="of" derivedContent="RFC4919">"IPv6 over Low-Power
			Wireless Personal Area Networks (6LoWPANs): Overview, Assumptions,
			Problem Statement, and Goals"</xref> and <xref target="RFC4944" forma
			t="default" sectionFormat="of" derivedContent="RFC4944">
			"Transmission of IPv6 Packets over IEEE 802.15.4 Networks"</xref>.
			</t>
			<t indent="0" pn="section-2.2-4"><xref target="RFC3031" format="default"
			sectionFormat="of" derivedContent="RFC3031">"Multiprotocol Label Switching
			Architecture"</xref> states that with MPLS,</t>
			<blockquote pn="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.
			</blockquote>
			<t indent="0" pn="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.
			</t>
			</section>
			<section anchor="new" numbered="true" removeInRFC="false" toc="include" pn
			="section-2.3">
			<name slugifiedName="name-new-terms">New Terms</name>
			<t indent="0" pn="section-2.3-1">
			This specification uses the following terms:
			</t>
			<dl indent="3" newline="false" spacing="normal" pn="section-2.3-2">
			<dt pn="section-2.3-2.1">6LoWPAN Fragment Forwarding Endpoints:</dt>
			<dd pn="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.
			</dd>
			<dt pn="section-2.3-2.3">Compressed Form:</dt>
			<dd pn="section-2.3-2.4">
			This specification uses the generic term "compressed form" to refer t
			o
			the format of a datagram after the action of <xref target="RFC6282" form
			at="default" sectionFormat="of" derivedContent="RFC6282"/>
			and possibly <xref target="RFC8138" format="default" sectionFormat="of"
			derivedContent="RFC8138"/> for Routing Protocol for Low-Power and Lossy Network
			(RPL) <xref target="RFC6550" format="default" sectionFormat="of" derivedContent=
			"RFC6550"/>
			artifacts.
			</dd>
			<dt pn="section-2.3-2.5">Datagram_Size:</dt>
			<dd pn="section-2.3-2.6">
			The size of the datagram in its compressed form before it is fragmented.
			</dd>
			<dt pn="section-2.3-2.7">Datagram_Tag:</dt>
			<dd pn="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 glo
			bally
			unique identifier for the datagram within the duration of its transmissi
			on.
			</dd>
			<dt pn="section-2.3-2.9">Fragment_Offset:</dt>
			<dd pn="section-2.3-2.10">
			The offset of a fragment of a datagram in its compressed form.
			</dd>
			</dl>
			</section>
			</section>
			<section anchor="overview-of-6lowpan-fragmentation" numbered="true" removeIn
			RFC="false" toc="include" pn="section-3">
			<name slugifiedName="name-overview-of-6lowpan-fragmen">Overview of 6LoWPAN
			Fragmentation</name>
			<t indent="0" pn="section-3-1"><xref target="FIGperhop" format="default" s
			ectionFormat="of" derivedContent="Figure 1"/> illustrates 6LoWPAN fragmentation.
			We assume node A forwards a packet to node B, possibly as part of a multi-hop ro
			ute 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 an
			d the 6LoWPAN compression endpoints.</t>
			<figure anchor="FIGperhop" align="left" suppress-title="false" pn="figure-
			1">
			<name slugifiedName="name-fragmentation-at-node-a-and">Fragmentation at
			Node A, and Reassembly at Node B</name>
			<artwork align="left" pn="section-3-2.1">
			+---+ +---+
			... ---| A |--------------------&gt;| B |--- ...
			+---+ +---+
			# (frag. 5)
			123456789 123456789
			+---------+ +---------+
			| # ###| |### # |
			+---------+ +---------+
			outgoing incoming
			fragmentation reassembly
			buffer buffer
			</artwork>
			</figure>
			<t indent="0" pn="section-3-3">Typically, node A starts with an uncompress
			ed packet and compacts the IPv6 packet using the header compression mechanism de
			fined in <xref target="RFC6282" format="default" sectionFormat="of" derivedConte
			nt="RFC6282"/>.
			If the resulting 6LoWPAN packet does not fit into a single link-layer frame, nod
			e A's 6LoWPAN sub-layer cuts it into multiple 6LoWPAN fragments, which it transm
			its 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 pac
			ket to its IPv6 layer.</t>
			<t indent="0" pn="section-3-4">In <xref target="FIGperhop" format="default
			" sectionFormat="of" derivedContent="Figure 1"/>, a packet forwarded by node A t
			o node B is cut into nine fragments, numbered 1 to 9 as follows:</t>
			<ul bare="false" empty="false" indent="3" spacing="normal" pn="section-3-5
			">
			<li pn="section-3-5.1">Each fragment is represented by the '#' symbol.</
			li>
			<li pn="section-3-5.2">Node A has sent fragments 1, 2, 3, 5, and 6 to no
			de B.</li>
			<li pn="section-3-5.3">Node B has received fragments 1, 2, 3, and 6 from
			node A.</li>
			<li pn="section-3-5.4">Fragment 5 is still being transmitted at the link
			layer from node A to node B.</li>
			</ul>
			<t indent="0" pn="section-3-6">The reassembly buffer for 6LoWPAN is indexe
			d in node B by:</t>
			<ul bare="false" empty="false" indent="3" spacing="normal" pn="section-3-7
			">
			<li pn="section-3-7.1">a unique identifier of node A (e.g., node A's lin
			k-layer address).</li>
			<li pn="section-3-7.2">the Datagram_Tag chosen by node A for this fragme
			nted datagram.</li>
			</ul>
			<t indent="0" pn="section-3-8">Because it may be hard for node B to correl
			ate all possible link-layer addresses that node A may use (e.g., short versus lo
			ng addresses), node A must use the same link-layer address to send all the fragm
			ents of the same datagram to node B.
			</t>
			<t indent="0" pn="section-3-9">Conceptually, the reassembly buffer in node
			B contains:</t>
			<ul bare="false" empty="false" indent="3" spacing="normal" pn="section-3-1
			0">
			<li pn="section-3-10.1">a Datagram_Tag as received in the incoming fragm
			ents, associated
			with the interface and the link-layer address of node A for which the rece
			ived Datagram_Tag is unique,</li>
			<li pn="section-3-10.2">the actual packet data from the fragments receiv
			ed so far, in a form that makes it possible to detect when the whole packet has
			been received and can be processed or forwarded,</li>
			<li pn="section-3-10.3">a state indicating the fragments already receive
			d,</li>
			<li pn="section-3-10.4">a Datagram_Size, and</li>
			<li pn="section-3-10.5">a timer that allows discarding a partially reass
			embled packet after some timeout.</li>
			</ul>
			<t indent="0" pn="section-3-11">A fragmentation header is added to each fr
			agment; it indicates what portion of the packet that fragment corresponds to.
			<xref target="RFC4944" sectionFormat="of" section="5.3" format="default" derived
			Link="https://rfc-editor.org/rfc/rfc4944#section-5.3" derivedContent="RFC4944"/>
			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 pa
			cket each fragment belongs to.
			Each datagram can be uniquely identified by the sender link-layer addresses of t
			he frame that carries it and the Datagram_Tag that the sender allocated for this
			datagram.
			<xref target="RFC4944" format="default" sectionFormat="of" derivedContent="RFC49
			44"/> 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 f
			or the first one can be identified within its datagram by the datagram-offset.</
			t>
			<t indent="0" pn="section-3-12">Node B's typical behavior, per <xref targe
			t="RFC4944" format="default" sectionFormat="of" derivedContent="RFC4944"/>, is a
			s 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 no
			t the first fragment.
			As fragments come in, node B fills the buffer.
			When all fragments have been received, node B inflates the compressed header fie
			lds into an IPv6 header and hands the resulting IPv6 packet to the IPv6 layer, w
			hich performs the route lookup. This behavior typically results in per-hop fragm
			entation and reassembly.
			That is, the packet is fully reassembled, then (re-)fragmented, at every hop.</t
			>
			</section>
			<section anchor="SEClimits" numbered="true" removeInRFC="false" toc="include
			" pn="section-4">
			<name slugifiedName="name-limitations-of-per-hop-frag">Limitations of Per-
			Hop Fragmentation and Reassembly</name>
			<t indent="0" pn="section-4-1">There are at least two limitations to doing
			per-hop fragmentation and reassembly.
			See <xref target="ARTICLE" format="default" sectionFormat="of" derivedContent="A
			RTICLE"/> for detailed simulation results on both limitations.</t>
			<section anchor="latency" numbered="true" removeInRFC="false" toc="include
			" pn="section-4.1">
			<name slugifiedName="name-latency">Latency</name>
			<t indent="0" pn="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 pack
			et and possibly forwarding it to the next hop. This repeats at every hop.</t>
			<t indent="0" pn="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 rea
			ssembly.</t>
			</section>
			<section anchor="memory-management-and-reliability" numbered="true" remove
			InRFC="false" toc="include" pn="section-4.2">
			<name slugifiedName="name-memory-management-and-relia">Memory Management
			and Reliability</name>
			<t indent="0" pn="section-4.2-1">Constrained nodes have limited memory.
			Assuming a reassembly buffer for a 6LoWPAN MTU of 1280 bytes as defined in <xref
			target="RFC4944" sectionFormat="of" section="4" format="default" derivedLink="h
			ttps://rfc-editor.org/rfc/rfc4944#section-4" derivedContent="RFC4944"/>, typical
			nodes only have enough memory for 1-3 reassembly buffers.</t>
			<t indent="0" pn="section-4.2-2">To illustrate this, we use the topology
			from <xref target="FIGtopology" format="default" sectionFormat="of" derivedCont
			ent="Figure 2"/>, 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.</t>
			<figure anchor="FIGtopology" align="left" suppress-title="false" pn="fig
			ure-2">
			<name slugifiedName="name-illustrating-the-memory-man">Illustrating th
			e Memory Management Issue</name>
			<artwork align="left" pn="section-4.2-3.1">
			+---+ +---+
			... ---&gt;| A |------&gt;| B |
			+---+ +---+\
			\
			+---+ +---+
			| E |---&gt;| F | ...
			+---+ +---+
			/
			/
			+---+ +---+
			... ---&gt;| C |------&gt;| D |
			+---+ +---+
			</artwork>
			</figure>
			<t indent="0" pn="section-4.2-4">When nodes A, B, and C concurrently sen
			d 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.</t>
			</section>
			</section>
			<section anchor="ff" numbered="true" removeInRFC="false" toc="include" pn="s
			ection-5">
			<name slugifiedName="name-forwarding-fragments">Forwarding Fragments</name
			>
			<t indent="0" pn="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 <bcp14>MUST</bcp14> attempt to create a
			state and forward the fragment. This is an atomic operation, and if the first f
			ragment cannot be forwarded, then the state <bcp14>MUST</bcp14> be removed.
			</t>
			<t indent="0" pn="section-5-2">
			Since the Datagram_Tag is uniquely associated with the source link-layer address
			of the fragment, the forwarding node <bcp14>MUST</bcp14> assign a new Datagram_
			Tag from its own namespace for the next hop and rewrite the fragment header of e
			ach fragment with that Datagram_Tag.
			</t>
			<t indent="0" pn="section-5-3">
			When a forwarding node receives a fragment other than a first fragment, it <bcp1
			4>MUST</bcp14> look up state based on the source link-layer address and the Data
			gram_Tag in the received fragment. If no such state is found, the fragment <bcp1
			4>MUST</bcp14> be dropped; otherwise, the fragment <bcp14>MUST</bcp14> be forwar
			ded using the information in the state found.
			</t>
			<t indent="0" pn="section-5-4">
			Compared to <xref target="overview-of-6lowpan-fragmentation" format="default" se
			ctionFormat="of" derivedContent="Section 3"/>, the conceptual reassembly buffer
			in node B now contains the following, assuming that node B is neither the source
			nor the final destination:</t>
			<ul bare="false" empty="false" indent="3" spacing="normal" pn="section-5-5
			">
			<li pn="section-5-5.1">a Datagram_Tag as received in the incoming fragme
			nts, associated with the interface and the link-layer address of node A for whic
			h the received Datagram_Tag is unique.</li>
			<li pn="section-5-5.2">the link-layer address that node B uses as the so
			urce to forward the fragments.</li>
			<li pn="section-5-5.3"> the interface and the link-layer address of the
			next-hop C that is resolved on the first fragment.</li>
			<li pn="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.</
			li>
			<li pn="section-5-5.5">a buffer for the remainder of a previous fragment
			left to be sent.</li>
			<li pn="section-5-5.6">a timer that allows discarding the stale 6LFF sta
			te after some timeout.
			The duration of the timer should be longer than that which covers the reassemb
			ly at the receiving endpoint.
			</li>
			</ul>
			<t indent="0" pn="section-5-6">
			A node that has not received the first fragment cannot forward the next fragmen
			ts. This means that if node B receives a fragment, node A was in possession of t
			he first fragment at some point. To keep the operation simple and consistent wit
			h <xref target="RFC4944" format="default" sectionFormat="of" derivedContent="RFC
			4944"/>, the first fragment <bcp14>MUST</bcp14> always be sent first. When that
			is done, if node B receives a fragment that is not the first and for which it ha
			s 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 firs
			t fragment before it attempts to send the next fragments, and that it should abo
			rt the datagram and release its state if it fails to send the first fragment.
			</t>
			<t indent="0" pn="section-5-7">Fragment forwarding obviates some of the be
			nefits of the 6LoWPAN header compression <xref target="RFC6282" format="default"
			sectionFormat="of" derivedContent="RFC6282"/> 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 th
			e network as long as they do not interfere.
			An associated caveat is that on a half-duplex radio, if node A sends the next f
			ragment 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 <bcp14>MUST</bcp14> 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.
			</t>
			</section>
			<section anchor="virtual-reassembly-buffer-vrb-implementation" numbered="tru
			e" removeInRFC="false" toc="include" pn="section-6">
			<name slugifiedName="name-virtual-reassembly-buffer-v">Virtual Reassembly
			Buffer (VRB) Implementation</name>
			<t indent="0" pn="section-6-1">
			The VRB <xref target="I-D.ietf-lwig-6lowpan-virtual-reassembly" format="default"
			sectionFormat="of" derivedContent="LWIG-VRB"/> is a particular incarnation of a
			6LFF that can be implemented without a change to <xref target="RFC4944" format=
			"default" sectionFormat="of" derivedContent="RFC4944"/>.
			</t>
			<t indent="0" pn="section-6-2">VRB overcomes the limitations listed in <xr
			ef target="SEClimits" format="default" sectionFormat="of" derivedContent="Sectio
			n 4"/>.
			Nodes do not wait for the last fragment before forwarding, reducing end-to-end l
			atency.
			Similarly, the memory footprint of VRB is just the VRB table, reducing the packe
			t drop probability significantly.</t>
			<t indent="0" pn="section-6-3">However, there are other caveats:</t>
			<dl indent="3" newline="false" spacing="normal" pn="section-6-4">
			<dt pn="section-6-4.1">Non-zero Packet Drop Probability:</dt>
			<dd pn="section-6-4.2">
			The abstract data in a VRB table entry contains at a minimum the link-layer ad
			dress of the predecessor and the successor, the Datagram_Tag used by the predece
			ssor, and the local Datagram_Tag that this node will swap with it. The VRB may n
			eed to store a few octets from the last fragment that may not have fit within MT
			U 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 packet
			s than it has entries in its VRB table, packets are dropped.</dd>
			<dt pn="section-6-4.3">No Fragment Recovery:</dt>
			<dd pn="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 destin
			ation node can never construct the original IPv6 packet.</dd>
			<dt pn="section-6-4.5">No Per-Fragment Routing:</dt>
			<dd pn="section-6-4.6">
			All subsequent fragments follow the same sequence of hops from the source to t
			he 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 ef
			fect is that the first fragment must always be forwarded first.</dd>
			</dl>
			<t indent="0" pn="section-6-5">The severity and occurrence of these caveat
			s depend on the link layer used.
			Whether they are acceptable depends entirely on the requirements the application
			places on the network.</t>
			<t indent="0" pn="section-6-6">If the caveats are present and not acceptab
			le for the application, alternative specifications may define new protocols to o
			vercome them.
			One example is <xref target="RFC8931" format="default" sectionFormat="of" derive
			dContent="RFC8931"/>, which specifies a 6LFF technique that allows the end-to-en
			d fragment recovery between the 6LFF endpoints.</t>
			</section>
			<section anchor="security-considerations" numbered="true" removeInRFC="false
			" toc="include" pn="section-7">
			<name slugifiedName="name-security-considerations">Security Considerations
			</name>
			<t indent="0" pn="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.
			</t>
			<t indent="0" pn="section-7-2">Secure joining and the link-layer security
			that it sets up protects against those attacks from network outsiders.</t>
			<t indent="0" pn="section-7-3"><xref target="RFC8900" format="default" sec
			tionFormat="of" derivedContent="RFC8900">"IP Fragmentation Considered Fragile"</
			xref> discusses security threats and other caveats that are linked to using IP f
			ragmentation. The 6LoWPAN fragmentation takes place underneath the IP Layer, but
			some issues described there may still apply to 6LoWPAN fragments.</t>
			<ul bare="false" empty="false" indent="3" spacing="normal" pn="section-7-4
			">
			<li pn="section-7-4.1">Overlapping fragment attacks are possible with 6L
			oWPAN fragments, but there is no known firewall operation that would work on 6Lo
			WPAN fragments at the time of this writing, so the exposure is limited. An imple
			mentation of a firewall <bcp14>SHOULD NOT</bcp14> forward fragments but instead
			should recompose the IP packet, check it in the uncompressed form, and then forw
			ard it again as fragments if necessary. Overlapping fragments are acceptable as
			long as they contain the same payload. The firewall <bcp14>MUST</bcp14> drop the
			whole packet if overlapping fragments are encountered that result in different
			data at the same offset. </li>
			<li pn="section-7-4.2">Resource-exhaustion attacks are certainly possibl
			e 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 fr
			agments 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 no
			de suffers a lesser hit. This is because the VRB does not need to remember the f
			ull datagram as received so far but only possibly a few octets from the last fra
			gment that could not fit in it.
			An implementation <bcp14>MUST</bcp14> protect itself to keep the number of VR
			Bs within capacity and to ensure that old VRBs are protected by a timer of a rea
			sonable duration for the technology and destroyed upon timeout.</li>
			<li pn="section-7-4.3">Attacks based on predictable fragment identificat
			ion values are also possible but can be avoided. The Datagram_Tag <bcp14>SHOULD<
			/bcp14> 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.
			</li>
			<li pn="section-7-4.4">Evasion of Network Intrusion Detection Systems (N
			IDSs) leverages ambiguity in the reassembly of the fragment. This attack makes l
			ittle 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.</li>
			</ul>
			</section>
			<section anchor="iana-considerations" numbered="true" removeInRFC="false" to
			c="include" pn="section-8">
			<name slugifiedName="name-iana-considerations">IANA Considerations</name>
			<t indent="0" pn="section-8-1">This document has no IANA actions.</t>
			</section>
			</middle>
			<back>
			<displayreference target="I-D.ietf-lwig-6lowpan-virtual-reassembly" to="LWIG
			-VRB"/>
			<references pn="section-9">
			<name slugifiedName="name-references">References</name>
			<references pn="section-9.1">
			<name slugifiedName="name-normative-references">Normative References</na
			me>
			<reference anchor="RFC2119" target="https://www.rfc-editor.org/info/rfc2
			119" quoteTitle="true" derivedAnchor="RFC2119">
			<front>
			<title>Key words for use in RFCs to Indicate Requirement Levels</tit
			le>
			<author initials="S." surname="Bradner" fullname="S. Bradner">
			<organization showOnFrontPage="true"/>
			</author>
			<date year="1997" month="March"/>
			<abstract>
			<t indent="0">In many standards track documents several words are
			used to signify the requirements in the specification. These words are often ca
			pitalized. This document defines these words as they should be interpreted in IE
			TF documents. This document specifies an Internet Best Current Practices for th
			e Internet Community, and requests discussion and suggestions for improvements.<
			/t>
			</abstract>
			</front>
			<seriesInfo name="BCP" value="14"/>
			<seriesInfo name="RFC" value="2119"/>
			<seriesInfo name="DOI" value="10.17487/RFC2119"/>
			</reference>
			<reference anchor="RFC4919" target="https://www.rfc-editor.org/info/rfc4
			919" quoteTitle="true" derivedAnchor="RFC4919">
			<front>
			<title>IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs
			): Overview, Assumptions, Problem Statement, and Goals</title>
			<author initials="N." surname="Kushalnagar" fullname="N. Kushalnagar
			">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="G." surname="Montenegro" fullname="G. Montenegro">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="C." surname="Schumacher" fullname="C. Schumacher">
			<organization showOnFrontPage="true"/>
			</author>
			<date year="2007" month="August"/>
			<abstract>
			<t indent="0">This document describes the assumptions, problem sta
			tement, and goals for transmitting IP over IEEE 802.15.4 networks. The set of g
			oals enumerated in this document form an initial set only. This memo provides i
			nformation for the Internet community.</t>
			</abstract>
			</front>
			<seriesInfo name="RFC" value="4919"/>
			<seriesInfo name="DOI" value="10.17487/RFC4919"/>
			</reference>
			<reference anchor="RFC4944" target="https://www.rfc-editor.org/info/rfc4
			944" quoteTitle="true" derivedAnchor="RFC4944">
			<front>
			<title>Transmission of IPv6 Packets over IEEE 802.15.4 Networks</tit
			le>
			<author initials="G." surname="Montenegro" fullname="G. Montenegro">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="N." surname="Kushalnagar" fullname="N. Kushalnagar
			">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="J." surname="Hui" fullname="J. Hui">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="D." surname="Culler" fullname="D. Culler">
			<organization showOnFrontPage="true"/>
			</author>
			<date year="2007" month="September"/>
			<abstract>
			<t indent="0">This document describes the frame format for transmi
			ssion of IPv6 packets and the method of forming IPv6 link-local addresses and st
			atelessly autoconfigured addresses on IEEE 802.15.4 networks. Additional specifi
			cations include a simple header compression scheme using shared context and prov
			isions for packet delivery in IEEE 802.15.4 meshes. [STANDARDS-TRACK]</t>
			</abstract>
			</front>
			<seriesInfo name="RFC" value="4944"/>
			<seriesInfo name="DOI" value="10.17487/RFC4944"/>
			</reference>
			<reference anchor="RFC8174" target="https://www.rfc-editor.org/info/rfc8
			174" quoteTitle="true" derivedAnchor="RFC8174">
			<front>
			<title>Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words</ti
			tle>
			<author initials="B." surname="Leiba" fullname="B. Leiba">
			<organization showOnFrontPage="true"/>
			</author>
			<date year="2017" month="May"/>
			<abstract>
			<t indent="0">RFC 2119 specifies common key words that may be used
			in protocol specifications. This document aims to reduce the ambiguity by cla
			rifying that only UPPERCASE usage of the key words have the defined special mea
			nings.</t>
			</abstract>
			</front>
			<seriesInfo name="BCP" value="14"/>
			<seriesInfo name="RFC" value="8174"/>
			<seriesInfo name="DOI" value="10.17487/RFC8174"/>
			</reference>
			</references>
			<references pn="section-9.2">
			<name slugifiedName="name-informative-references">Informative References
			</name>
			<reference anchor="ARTICLE" target="https://ieeexplore.ieee.org/abstract
			/document/8771317" quoteTitle="true" derivedAnchor="ARTICLE">
			<front>
			<title>6LoWPAN Fragment Forwarding</title>
			<author initials="Y." surname="Tanaka" fullname="Yasuyuki Tanaka">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="P." surname="Minet" fullname="Pascale Minet">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="T." surname="Watteyne" fullname="Thomas Watteyne">
			<organization showOnFrontPage="true"/>
			</author>
			<date month="March" year="2019"/>
			</front>
			<seriesInfo name="IEEE Communications Standards Magazine" value="Vol.
			3, Issue 1, pp. 35-39"/>
			<seriesInfo name="DOI" value="10.1109/MCOMSTD.2019.1800029"/>
			</reference>
			<reference anchor="I-D.ietf-lwig-6lowpan-virtual-reassembly" quoteTitle=
			"true" target="https://tools.ietf.org/html/draft-ietf-lwig-6lowpan-virtual-reass
			embly-02" derivedAnchor="LWIG-VRB">
			<front>
			<title>Virtual reassembly buffers in 6LoWPAN</title>
			<author fullname="Carsten Bormann">
			<organization showOnFrontPage="true">Universitaet Bremen TZI</orga
			nization>
			</author>
			<author fullname="Thomas Watteyne">
			<organization showOnFrontPage="true">Analog Devices</organization>
			</author>
			<date month="March" day="9" year="2020"/>
			<abstract>
			<t indent="0"> When employing adaptation layer fragmentation in
			6LoWPAN, it may be
			beneficial for a forwarder not to have to reassemble each packet in
			its entirety before forwarding it.
			This has been always possible with the original fragmentation design
			of RFC 4944. Apart from a brief mention of the way to do this in
			Section 2.5.2 of the 6LoWPAN book, this has not been extensively
			described in the literature. The present document attempts to fill
			that gap.
			</t>
			</abstract>
			</front>
			<seriesInfo name="Internet-Draft" value="draft-ietf-lwig-6lowpan-virtu
			al-reassembly-02"/>
			<format type="TXT" target="https://www.ietf.org/internet-drafts/draft-
			ietf-lwig-6lowpan-virtual-reassembly-02.txt"/>
			<refcontent>Work in Progress</refcontent>
			</reference>
			<reference anchor="RFC3031" target="https://www.rfc-editor.org/info/rfc3
			031" quoteTitle="true" derivedAnchor="RFC3031">
			<front>
			<title>Multiprotocol Label Switching Architecture</title>
			<author initials="E." surname="Rosen" fullname="E. Rosen">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="A." surname="Viswanathan" fullname="A. Viswanathan
			">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="R." surname="Callon" fullname="R. Callon">
			<organization showOnFrontPage="true"/>
			</author>
			<date year="2001" month="January"/>
			<abstract>
			<t indent="0">This document specifies the architecture for Multipr
			otocol Label Switching (MPLS). [STANDARDS-TRACK]</t>
			</abstract>
			</front>
			<seriesInfo name="RFC" value="3031"/>
			<seriesInfo name="DOI" value="10.17487/RFC3031"/>
			</reference>
			<reference anchor="RFC4963" target="https://www.rfc-editor.org/info/rfc4
			963" quoteTitle="true" derivedAnchor="RFC4963">
			<front>
			<title>IPv4 Reassembly Errors at High Data Rates</title>
			<author initials="J." surname="Heffner" fullname="J. Heffner">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="M." surname="Mathis" fullname="M. Mathis">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="B." surname="Chandler" fullname="B. Chandler">
			<organization showOnFrontPage="true"/>
			</author>
			<date year="2007" month="July"/>
			<abstract>
			<t indent="0">IPv4 fragmentation is not sufficiently robust for us
			e under some conditions in today's Internet. At high data rates, the 16-bit IP
			identification field is not large enough to prevent frequent incorrectly assembl
			ed IP fragments, and the TCP and UDP checksums are insufficient to prevent the r
			esulting corrupted datagrams from being delivered to higher protocol layers. Th
			is note describes some easily reproduced experiments demonstrating the problem,
			and discusses some of the operational implications of these observations. This
			memo provides information for the Internet community.</t>
			</abstract>
			</front>
			<seriesInfo name="RFC" value="4963"/>
			<seriesInfo name="DOI" value="10.17487/RFC4963"/>
			</reference>
			<reference anchor="RFC6282" target="https://www.rfc-editor.org/info/rfc6
			282" quoteTitle="true" derivedAnchor="RFC6282">
			<front>
			<title>Compression Format for IPv6 Datagrams over IEEE 802.15.4-Base
			d Networks</title>
			<author initials="J." surname="Hui" fullname="J. Hui" role="editor">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="P." surname="Thubert" fullname="P. Thubert">
			<organization showOnFrontPage="true"/>
			</author>
			<date year="2011" month="September"/>
			<abstract>
			<t indent="0">This document updates RFC 4944, "Transmission of IPv
			6 Packets over IEEE 802.15.4 Networks". This document specifies an IPv6 header
			compression format for IPv6 packet delivery in Low Power Wireless Personal Area
			Networks (6LoWPANs). The compression format relies on shared context to allow c
			ompression of arbitrary prefixes. How the information is maintained in that sha
			red context is out of scope. This document specifies compression of multicast ad
			dresses and a framework for compressing next headers. UDP header compression is
			specified within this framework. [STANDARDS-TRACK]</t>
			</abstract>
			</front>
			<seriesInfo name="RFC" value="6282"/>
			<seriesInfo name="DOI" value="10.17487/RFC6282"/>
			</reference>
			<reference anchor="RFC6550" target="https://www.rfc-editor.org/info/rfc6
			550" quoteTitle="true" derivedAnchor="RFC6550">
			<front>
			<title>RPL: IPv6 Routing Protocol for Low-Power and Lossy Networks</
			title>
			<author initials="T." surname="Winter" fullname="T. Winter" role="ed
			itor">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="P." surname="Thubert" fullname="P. Thubert" role="
			editor">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="A." surname="Brandt" fullname="A. Brandt">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="J." surname="Hui" fullname="J. Hui">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="R." surname="Kelsey" fullname="R. Kelsey">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="P." surname="Levis" fullname="P. Levis">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="K." surname="Pister" fullname="K. Pister">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="R." surname="Struik" fullname="R. Struik">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="JP." surname="Vasseur" fullname="JP. Vasseur">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="R." surname="Alexander" fullname="R. Alexander">
			<organization showOnFrontPage="true"/>
			</author>
			<date year="2012" month="March"/>
			<abstract>
			<t indent="0">Low-Power and Lossy Networks (LLNs) are a class of n
			etwork in which both the routers and their interconnect are constrained. LLN ro
			uters typically operate with constraints on processing power, memory, and energy
			(battery power). Their interconnects are characterized by high loss rates, low
			data rates, and instability. LLNs are comprised of anything from a few dozen t
			o thousands of routers. Supported traffic flows include point-to-point (between
			devices inside the LLN), point-to-multipoint (from a central control point to a
			subset of devices inside the LLN), and multipoint-to-point (from devices inside
			the LLN towards a central control point). This document specifies the IPv6 Rou
			ting Protocol for Low-Power and Lossy Networks (RPL), which provides a mechanism
			whereby multipoint-to-point traffic from devices inside the LLN towards a centr
			al control point as well as point-to-multipoint traffic from the central control
			point to the devices inside the LLN are supported. Support for point-to-point
			traffic is also available. [STANDARDS-TRACK]</t>
			</abstract>
			</front>
			<seriesInfo name="RFC" value="6550"/>
			<seriesInfo name="DOI" value="10.17487/RFC6550"/>
			</reference>
			<reference anchor="RFC8138" target="https://www.rfc-editor.org/info/rfc8
			138" quoteTitle="true" derivedAnchor="RFC8138">
			<front>
			<title>IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN)
			Routing Header</title>
			<author initials="P." surname="Thubert" fullname="P. Thubert" role="
			editor">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="C." surname="Bormann" fullname="C. Bormann">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="L." surname="Toutain" fullname="L. Toutain">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="R." surname="Cragie" fullname="R. Cragie">
			<organization showOnFrontPage="true"/>
			</author>
			<date year="2017" month="April"/>
			<abstract>
			<t indent="0">This specification introduces a new IPv6 over Low-Po
			wer Wireless Personal Area Network (6LoWPAN) dispatch type for use in 6LoWPAN ro
			ute-over topologies, which initially covers the needs of Routing Protocol for Lo
			w-Power and Lossy Networks (RPL) data packet compression (RFC 6550). Using this
			dispatch type, this specification defines a method to compress the RPL Option (
			RFC 6553) information and Routing Header type 3 (RFC 6554), an efficient IP-in-I
			P technique, and is extensible for more applications.</t>
			</abstract>
			</front>
			<seriesInfo name="RFC" value="8138"/>
			<seriesInfo name="DOI" value="10.17487/RFC8138"/>
			</reference>
			<reference anchor="RFC8201" target="https://www.rfc-editor.org/info/rfc8
			201" quoteTitle="true" derivedAnchor="RFC8201">
			<front>
			<title>Path MTU Discovery for IP version 6</title>
			<author initials="J." surname="McCann" fullname="J. McCann">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="S." surname="Deering" fullname="S. Deering">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="J." surname="Mogul" fullname="J. Mogul">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="R." surname="Hinden" fullname="R. Hinden" role="ed
			itor">
			<organization showOnFrontPage="true"/>
			</author>
			<date year="2017" month="July"/>
			<abstract>
			<t indent="0">This document describes Path MTU Discovery (PMTUD) f
			or IP version 6. It is largely derived from RFC 1191, which describes Path MTU D
			iscovery for IP version 4. It obsoletes RFC 1981.</t>
			</abstract>
			</front>
			<seriesInfo name="STD" value="87"/>
			<seriesInfo name="RFC" value="8201"/>
			<seriesInfo name="DOI" value="10.17487/RFC8201"/>
			</reference>
			<reference anchor="RFC8900" target="https://www.rfc-editor.org/info/rfc8
			900" quoteTitle="true" derivedAnchor="RFC8900">
			<front>
			<title>IP Fragmentation Considered Fragile</title>
			<author initials="R." surname="Bonica" fullname="R. Bonica">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="F." surname="Baker" fullname="F. Baker">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="G." surname="Huston" fullname="G. Huston">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="R." surname="Hinden" fullname="R. Hinden">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="O." surname="Troan" fullname="O. Troan">
			<organization showOnFrontPage="true"/>
			</author>
			<author initials="F." surname="Gont" fullname="F. Gont">
			<organization showOnFrontPage="true"/>
			</author>
			<date year="2020" month="September"/>
			<abstract>
			<t indent="0">This document describes IP fragmentation and explain
			s how it introduces fragility to Internet communication.</t>
			<t indent="0">This document also proposes alternatives to IP fragm
			entation and provides recommendations for developers and network operators.</t>
			</abstract>
			</front>
			<seriesInfo name="BCP" value="230"/>
			<seriesInfo name="RFC" value="8900"/>
			<seriesInfo name="DOI" value="10.17487/RFC8900"/>
			</reference>
			<reference anchor="RFC8931" target="https://www.rfc-editor.org/info/rfc8
			931" quoteTitle="true" derivedAnchor="RFC8931">
			<front>
			<title>IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN)
			Selective Fragment Recovery</title>
			<author initials="P" surname="Thubert" fullname="Pascal Thubert" rol
			e="editor">
			<organization showOnFrontPage="true"/>
			</author>
			<date month="November" year="2020"/>
			</front>
			<seriesInfo name="RFC" value="8931"/>
			<seriesInfo name="DOI" value="10.17487/RFC8931"/>
			</reference>
			</references>
			</references>
			<section anchor="acknowledgments" numbered="false" toc="include" removeInRFC
			="false" pn="section-appendix.a">
			<name slugifiedName="name-acknowledgments">Acknowledgments</name>
			<t indent="0" pn="section-appendix.a-1">The authors would like to thank <c
			ontact fullname="Carles Gomez Montenegro"/>, <contact fullname="Yasuyuki Tanaka"
			/>, <contact fullname="Ines Robles"/>, and <contact fullname="Dave Thaler"/> for
			their in-depth review of this document and suggestions for improvement. Many th
			anks to <contact fullname="Georgios Papadopoulos"/> and <contact fullname="Domin
			ique Barthel"/> for their contributions during the WG activities. And many thank
			s as well to <contact fullname="Roman Danyliw"/>, <contact fullname="Barry Leiba
			"/>, <contact fullname="Murray Kucherawy"/>, <contact fullname="Derrell Piper"/>
			, <contact fullname="Sarah Banks"/>, <contact fullname="Joerg Ott"/>, <contact f
			ullname="Francesca Palombini"/>, <contact fullname="Mirja Kühlewind"/>, <contact
			fullname="Éric Vyncke"/>, and especially <contact fullname="Benjamin Kaduk"/> f
			or their constructive reviews through the IETF last call and IESG process.</t>
			</section>
			<section anchor="authors-addresses" numbered="false" removeInRFC="false" toc
			="include" pn="section-appendix.b">
			<name slugifiedName="name-authors-addresses">Authors' Addresses</name>
			<author initials="T." surname="Watteyne" fullname="Thomas Watteyne" role="
			editor">
			<organization showOnFrontPage="true">Analog Devices</organization>
			<address>
			<postal>
			<street>32990 Alvarado-Niles Road, Suite 910</street>
			<city>Union City</city>
			<region>CA</region>
			<code>94587</code>
			<country>United States of America</country>
			</postal>
			<email>thomas.watteyne@analog.com</email>
			</address>
			</author>
			<author initials="P." surname="Thubert" fullname="Pascal Thubert" role="ed
			itor">
			<organization abbrev="Cisco Systems" showOnFrontPage="true">Cisco System
			s, Inc</organization>
			<address>
			<postal>
			<extaddr>Building D</extaddr>
			<street>45 Allee des Ormes - BP1200</street>
			<city>Mougins - Sophia Antipolis</city>
			<code>06254</code>
			<country>France</country>
			</postal>
			<phone>+33 497 23 26 34</phone>
			<email>pthubert@cisco.com</email>
			</address>
			</author>
			<author initials="C." surname="Bormann" fullname="Carsten Bormann">
			<organization showOnFrontPage="true">Universität Bremen TZI</organizatio
			n>
			<address>
			<postal>
			<street>Postfach 330440</street>
			<city>Bremen</city>
			<code>D-28359</code>
			<country>Germany</country>
			</postal>
			<phone>+49-421-218-63921</phone>
			<email>cabo@tzi.org</email>
			</address>
			</author>
			</section>
			</back>
			</rfc>
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