draft-ietf-6lo-minimal-fragment-06.txt   draft-ietf-6lo-minimal-fragment-07.txt 
6lo T. Watteyne, Ed. 6lo T. Watteyne, Ed.
Internet-Draft Analog Devices Internet-Draft Analog Devices
Intended status: Standards Track P. Thubert, Ed. Intended status: Standards Track P. Thubert, Ed.
Expires: 30 May 2020 Cisco Systems Expires: 31 May 2020 Cisco Systems
C. Bormann C. Bormann
Universitaet Bremen TZI Universitaet Bremen TZI
27 November 2019 28 November 2019
On Forwarding 6LoWPAN Fragments over a Multihop IPv6 Network On Forwarding 6LoWPAN Fragments over a Multihop IPv6 Network
draft-ietf-6lo-minimal-fragment-06 draft-ietf-6lo-minimal-fragment-07
Abstract Abstract
This document introduces the capability to forward 6LoWPAN fragments. This document introduces the capability to forward 6LoWPAN fragments.
This method reduces the latency and increases end-to-end reliability This method reduces the latency and increases end-to-end reliability
in route-over forwarding. It is the companion to using virtual in route-over forwarding. It is the companion to using virtual
reassembly buffers which is a pure implementation technique. reassembly buffers which is a pure implementation technique.
Status of This Memo Status of This Memo
skipping to change at page 1, line 36 skipping to change at page 1, line 36
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on 30 May 2020. This Internet-Draft will expire on 31 May 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Provisions Relating to IETF Documents (https://trustee.ietf.org/ Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document. license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components and restrictions with respect to this document. Code Components
extracted from this document must include Simplified BSD License text extracted from this document must include Simplified BSD License text
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provided without warranty as described in the Simplified BSD License. provided without warranty as described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Overview of 6LoWPAN Fragmentation . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Limits of Per-Hop Fragmentation and Reassembly . . . . . . . 5 2.1. BCP 14 . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Latency . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2. Referenced Work . . . . . . . . . . . . . . . . . . . . . 3
3.2. Memory Management and Reliability . . . . . . . . . . . . 5 2.3. New Terms . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Forwarding Fragments . . . . . . . . . . . . . . . . . . . . 6 3. Overview of 6LoWPAN Fragmentation . . . . . . . . . . . . . . 4
5. Virtual Reassembly Buffer (VRB) Implementation . . . . . . . 7 4. Limits of Per-Hop Fragmentation and Reassembly . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 4.1. Latency . . . . . . . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 4.2. Memory Management and Reliability . . . . . . . . . . . . 6
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9 5. Forwarding Fragments . . . . . . . . . . . . . . . . . . . . 7
9. Normative References . . . . . . . . . . . . . . . . . . . . 9 6. Virtual Reassembly Buffer (VRB) Implementation . . . . . . . 9
10. Informative References . . . . . . . . . . . . . . . . . . . 10 7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11
10. Normative References . . . . . . . . . . . . . . . . . . . . 11
11. Informative References . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction 1. Introduction
The original 6LoWPAN fragmentation is defined in [6LoWPAN] and it is The original 6LoWPAN fragmentation is defined in [RFC4944] and it is
implicitly defined for use over a single IP hop through possibly implicitly defined for use over a single IP hop through possibly
multiple Layer-2 (mesh-under) hops in a meshed 6LoWPAN Network. multiple Layer-2 (mesh-under) hops in a meshed 6LoWPAN Network.
Although [6LoWPAN-HC] updates [6LoWPAN], it does not redefine 6LoWPAN Although [RFC6282] updates [RFC4944], it does not redefine 6LoWPAN
fragmentation. fragmentation.
This means that over a Layer-3 (route-over) network, an IP packet is This means that over a Layer-3 (route-over) network, an IP packet is
expected to be reassembled at every hop at the 6LoWPAN sublayer, expected to be reassembled at every hop at the 6LoWPAN sublayer,
pushed to Layer-3 to be routed, and then fragmented again if the next pushed to Layer-3 to be routed, and then fragmented again if the next
hop is another similar 6LoWPAN link. This draft introduces an hop is another similar 6LoWPAN link. This draft introduces an
alternate approach called 6LoWPAN Fragment Forwarding (FF) whereby an alternate approach called 6LoWPAN Fragment Forwarding (FF) whereby an
intermediate node forwards a fragment as soon as it is received if intermediate node forwards a fragment as soon as it is received if
the next hop is a similar 6LoWPAN link. The routing decision is made the next hop is a similar 6LoWPAN link. The routing decision is made
on the first fragment, which has all the IPv6 routing information. on the first fragment, which has all the IPv6 routing information.
skipping to change at page 2, line 48 skipping to change at page 3, line 4
on the first fragment, which has all the IPv6 routing information. on the first fragment, which has all the IPv6 routing information.
The first fragment is forwarded immediately and a state is stored to The first fragment is forwarded immediately and a state is stored to
enable forwarding the next fragments along the same path. enable forwarding the next fragments along the same path.
Done right, 6LoWPAN Fragment Forwarding techniques lead to more Done right, 6LoWPAN Fragment Forwarding techniques lead to more
streamlined operations, less buffer bloat and lower latency. It may streamlined operations, less buffer bloat and lower latency. It may
be wasteful if some fragments are missing after the first one since be wasteful if some fragments are missing after the first one since
the first fragment will still continue till the 6LoWPAN endpoint that the first fragment will still continue till the 6LoWPAN endpoint that
will attempt to perform the reassembly, and may be misused to the will attempt to perform the reassembly, and may be misused to the
point that performances fall behind that of per-hop recomposition. point that performances fall behind that of per-hop recomposition.
This specification provides a generic overview of FF, discusses This specification provides a generic overview of FF, discusses
advantages and caveats, and introduces a particular 6LoWPAN Fragment advantages and caveats, and introduces a particular 6LoWPAN Fragment
Forwarding technique called Virtual Reassembly Buffer that can be Forwarding technique called Virtual Reassembly Buffer that can be
used while conserving the message formats defined in [6LoWPAN]. used while conserving the message formats defined in [RFC4944].
2. Overview of 6LoWPAN Fragmentation 2. Terminology
2.1. BCP 14
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119][RFC8174] when, and only when, they appear in all
capitals, as shown here.
2.2. Referenced Work
Past experience with fragmentation has shown that misassociated or
lost fragments can lead to poor network behavior and, occasionally,
trouble at application layer. The reader is encouraged to read "IPv4
Reassembly Errors at High Data Rates" [RFC4963] and follow the
references for more information. That experience led to the
definition of "Path MTU discovery" [RFC8201] (PMTUD) protocol that
limits fragmentation over the Internet.
"IP Fragmentation Considered Fragile" [FRAG-ILE] discusses security
threats that are linked to using IP fragmentation. The 6LoWPAN
fragmentation takes place underneath, but some issues described there
may still apply to 6LoWPAN fragments.
Readers are expected to be familiar with all the terms and concepts
that are discussed in "IPv6 over Low-Power Wireless Personal Area
Networks (6LoWPANs): Overview, Assumptions, Problem Statement, and
Goals" [RFC4919] and "Transmission of IPv6 Packets over IEEE 802.15.4
Networks" [RFC4944].
Quoting the "Multiprotocol Label Switching (MPLS) Architecture"
[RFC3031]: with MPLS, '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". 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.
2.3. New Terms
This specification uses the following terms:
6LoWPAN endpoints: The nodes in charge of generating or expanding a
6LoWPAN header from/to a full IPv6 packet. The 6LoWPAN endpoints
are the points where fragmentation and reassembly take place.
Compressed Form: This specification uses the generic term Compressed
Form to refer to the format of a datagram after the action of
[RFC6282] and possibly [RFC8138] for RPL [RFC6550] artifacts.
datagram_size: The size of the datagram in its Compressed Form
before it is fragmented. The datagram_size is expressed in a unit
that depends on the MAC layer technology, by default a byte.
datagram_tag: An identifier of a datagram that is locally unique to
the Layer-2 sender. Associated with the MAC address of the
sender, this becomes a globally unique identifier for the
datagram.
fragment_offset: The offset of a particular fragment of a datagram
in its Compressed Form. The fragment_offset is expressed in a
unit that depends on the MAC layer technology and is by default a
byte.
3. Overview of 6LoWPAN Fragmentation
We use Figure 1 to illustrate 6LoWPAN fragmentation. We assume node We use Figure 1 to illustrate 6LoWPAN fragmentation. We assume node
A forwards a packet to node B, possibly as part of a multi-hop route A forwards a packet to node B, possibly as part of a multi-hop route
between IPv6 source and destination nodes which are neither A nor B. between IPv6 source and destination nodes which are neither A nor B.
+---+ +---+ +---+ +---+
... ---| A |-------------------->| B |--- ... ... ---| A |-------------------->| B |--- ...
+---+ +---+ +---+ +---+
# (frag. 5) # (frag. 5)
skipping to change at page 3, line 27 skipping to change at page 5, line 6
+---------+ +---------+ +---------+ +---------+
| # ###| |### # | | # ###| |### # |
+---------+ +---------+ +---------+ +---------+
outgoing incoming outgoing incoming
fragmentation reassembly fragmentation reassembly
buffer buffer buffer buffer
Figure 1: Fragmentation at node A, reassembly at node B. Figure 1: Fragmentation at node A, reassembly at node B.
Node A starts by compacting the IPv6 packet using the header Node A starts by compacting the IPv6 packet using the header
compression mechanism defined in [6LoWPAN-HC]. If the resulting compression mechanism defined in [RFC6282]. If the resulting 6LoWPAN
6LoWPAN packet does not fit into a single Link-Layer frame, node A's packet does not fit into a single Link-Layer frame, node A's 6LoWPAN
6LoWPAN sublayer cuts it into multiple 6LoWPAN fragments, which it sublayer cuts it into multiple 6LoWPAN fragments, which it transmits
transmits as separate Link-Layer frames to node B. Node B's 6LoWPAN as separate Link-Layer frames to node B. Node B's 6LoWPAN sublayer
sublayer reassembles these fragments, inflates the compressed header reassembles these fragments, inflates the compressed header fields
fields back to the original IPv6 header, and hands over the full IPv6 back to the original IPv6 header, and hands over the full IPv6 packet
packet to its IPv6 layer. to its IPv6 layer.
In Figure 1, a packet forwarded by node A to node B is cut into nine In Figure 1, a packet forwarded by node A to node B is cut into nine
fragments, numbered 1 to 9 as follows: fragments, numbered 1 to 9 as follows:
* Each fragment is represented by the '#' symbol. * Each fragment is represented by the '#' symbol.
* Node A has sent fragments 1, 2, 3, 5, 6 to node B. * Node A has sent fragments 1, 2, 3, 5, 6 to node B.
* Node B has received fragments 1, 2, 3, 6 from node A. * Node B has received fragments 1, 2, 3, 6 from node A.
skipping to change at page 4, line 28 skipping to change at page 6, line 7
* a state indicating the fragments already received, * a state indicating the fragments already received,
* a datagram_size, * a datagram_size,
* a timer that allows discarding a partially reassembled packet * a timer that allows discarding a partially reassembled packet
after some timeout. after some timeout.
A fragmentation header is added to each fragment; it indicates what A fragmentation header is added to each fragment; it indicates what
portion of the packet that fragment corresponds to. Section 5.3 of portion of the packet that fragment corresponds to. Section 5.3 of
[6LoWPAN] defines the format of the header for the first and [RFC4944] defines the format of the header for the first and
subsequent fragments. All fragments are tagged with a 16-bit subsequent fragments. All fragments are tagged with a 16-bit
"datagram_tag", used to identify which packet each fragment belongs "datagram_tag", used to identify which packet each fragment belongs
to. Each datagram can be uniquely identified by the sender Link- to. Each datagram can be uniquely identified by the sender Link-
Layer addresses of the frame that carries it and the datagram_tag Layer addresses of the frame that carries it and the datagram_tag
that the sender allocated for this datagram. [6LoWPAN] also mandates that the sender allocated for this datagram. [RFC4944] also mandates
that the first fragment is sent first and with a particular format that the first fragment is sent first and with a particular format
that is different than that of the next fragments. Each fragment but that is different than that of the next fragments. Each fragment but
the first one can be identified within its datagram by the datagram- the first one can be identified within its datagram by the datagram-
offset. offset.
Node B's typical behavior, per [6LoWPAN], is as follows. Upon Node B's typical behavior, per [RFC4944], is as follows. Upon
receiving a fragment from node A with a datagram_tag previously receiving a fragment from node A with a datagram_tag previously
unseen from node A, node B allocates a buffer large enough to hold 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 the entire packet. The length of the packet is indicated in each
fragment (the datagram_size field), so node B can allocate the buffer fragment (the datagram_size field), so node B can allocate the buffer
even if the first fragment it receives is not fragment 1. As even if the first fragment it receives is not fragment 1. As
fragments come in, node B fills the buffer. When all fragments have fragments come in, node B fills the buffer. When all fragments have
been received, node B inflates the compressed header fields into an been received, node B inflates the compressed header fields into an
IPv6 header, and hands the resulting IPv6 packet to the IPv6 layer IPv6 header, and hands the resulting IPv6 packet to the IPv6 layer
which performs the route lookup. This behavior typically results in which performs the route lookup. This behavior typically results in
per-hop fragmentation and reassembly. That is, the packet is fully per-hop fragmentation and reassembly. That is, the packet is fully
reassembled, then (re)fragmented, at every hop. reassembled, then (re)fragmented, at every hop.
3. Limits of Per-Hop Fragmentation and Reassembly 4. Limits of Per-Hop Fragmentation and Reassembly
There are at least 2 limits to doing per-hop fragmentation and There are at least 2 limits to doing per-hop fragmentation and
reassembly. See [ARTICLE] for detailed simulation results on both reassembly. See [ARTICLE] for detailed simulation results on both
limits. limits.
3.1. Latency 4.1. Latency
When reassembling, a node needs to wait for all the fragments to be When reassembling, a node needs to wait for all the fragments to be
received before being able to generate the IPv6 packet, and possibly received before being able to generate the IPv6 packet, and possibly
forward it to the next hop. This repeats at every hop. forward it to the next hop. This repeats at every hop.
This may result in increased end-to-end latency compared to a case This may result in increased end-to-end latency compared to a case
where each fragment is forwarded without per-hop reassembly. where each fragment is forwarded without per-hop reassembly.
3.2. Memory Management and Reliability 4.2. Memory Management and Reliability
Constrained nodes have limited memory. Assuming a reassembly buffer Constrained nodes have limited memory. Assuming a reassembly buffer
for a 6LoWPAN MTU of 1280 bytes as defined in section 4 of [6LoWPAN], for a 6LoWPAN MTU of 1280 bytes as defined in section 4 of [RFC4944],
typical nodes only have enough memory for 1-3 reassembly buffers. typical nodes only have enough memory for 1-3 reassembly buffers.
To illustrate this we use the topology from Figure 2, where nodes A, To illustrate this we use the topology from Figure 2, where nodes A,
B, C and D all send packets through node E. We further assume that B, C and D all send packets through node E. We further assume that
node E's memory can only hold 3 reassembly buffers. node E's memory can only hold 3 reassembly buffers.
+---+ +---+ +---+ +---+
... --->| A |------>| B | ... --->| A |------>| B |
+---+ +---+\ +---+ +---+\
\ \
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... --->| C |------>| D | ... --->| C |------>| D |
+---+ +---+ +---+ +---+
Figure 2: Illustrating the Memory Management Issue. Figure 2: Illustrating the Memory Management Issue.
When nodes A, B and C concurrently send fragmented packets, all 3 When nodes A, B and C concurrently send fragmented packets, all 3
reassembly buffers in node E are occupied. If, at that moment, node 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 D also sends a fragmented packet, node E has no option but to drop
one of the packets, lowering end-to-end reliability. one of the packets, lowering end-to-end reliability.
4. Forwarding Fragments 5. Forwarding Fragments
A 6LoWPAN Fragment Forwarding technique makes the routing decision on A 6LoWPAN Fragment Forwarding technique makes the routing decision on
the first fragment, which is always the one with the IPv6 address of the first fragment, which is always the one with the IPv6 address of
the destination. Upon a first fragment, a forwarding node (e.g. node the destination. Upon a first fragment, a forwarding node (e.g. node
B in a A->B->C sequence) that does fragment forwarding MUST attempt B in a A->B->C sequence) that does fragment forwarding MUST attempt
to create a state and forward the fragment. This is an atomic to create a state and forward the fragment. This is an atomic
operation, and if the first fragment cannot be forwarded then the operation, and if the first fragment cannot be forwarded then the
state MUST be removed. When a forwarding node receives a fragment state MUST be removed. When a forwarding node receives a fragment
other than a first fragment, it MUST look up state based on the other than a first fragment, it MUST look up state based on the
source Link-Layer address and the datagram_tag in the received source Link-Layer address and the datagram_tag in the received
fragment. If no such state is found, the fragment MUST be dropped; fragment. If no such state is found, the fragment MUST be dropped;
otherwise the fragment MUST be forwarded using the information in the otherwise the fragment MUST be forwarded using the information in the
state found. Since the datagram_tag is uniquely associated to the state found. Since the datagram_tag is uniquely associated to the
source Link-Layer address of the fragment, the forwarding node MUST source Link-Layer address of the fragment, the forwarding node MUST
assign a new datagram_tag from its own namespace for the next hop and 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. rewrite the fragment header of each fragment with that datagram_tag.
Compared to Section 2, the conceptual reassembly buffer in node B now Compared to Section 3, the conceptual reassembly buffer in node B now
contains, assuming that node B is neither the source nor the final contains, assuming that node B is neither the source nor the final
destination: destination:
* a datagram_tag as received in the incoming fragments, associated * a datagram_tag as received in the incoming fragments, associated
to Link-Layer address of node A for which the received to Link-Layer address of node A for which the received
datagram_tag is unique, datagram_tag is unique,
* the Link-Layer address that node B uses as source to forward the * the Link-Layer address that node B uses as source to forward the
fragments fragments
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* a buffer for the remainder of a previous fragment left to be sent, * a buffer for the remainder of a previous fragment left to be sent,
* a timer that allows discarding the stale FF state after some * a timer that allows discarding the stale FF state after some
timeout. timeout.
A node that has not received the first fragment cannot forward the A node that has not received the first fragment cannot forward the
next fragments. This means that if node B receives a fragment, node next fragments. This means that if node B receives a fragment, node
A was in possession of the first fragment at some point. In order to A was in possession of the first fragment at some point. In order to
keep the operation simple, it makes sense to be consistent with keep the operation simple, it makes sense to be consistent with
[6LoWPAN] and enforce that the first fragment is always sent first. [RFC4944] and enforce that the first fragment is always sent first.
When that is done, if node B receives a fragment that is not the 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 this as an first and for which it has no state, then node B treats this as an
error and refrain from creating a state or attempting to forward. error and refrain from creating a state or attempting to forward.
This also means that node A should perform all its possible retries This also means that node A should perform all its possible retries
on the first fragment before it attempts to send the next fragments, 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 and that it should abort the datagram and release its state if it
fails to send the first fragment. fails to send the first fragment.
One benefit of Fragment Forwarding is that the memory that is used to One benefit of Fragment Forwarding is that the memory that is used to
store the packet is now distributed along the path, which limits the store the packet is now distributed along the path, which limits the
skipping to change at page 7, line 28 skipping to change at page 9, line 5
node C forwards the previous fragment to a node D at the same time node C forwards the previous fragment to a node D at the same time
and on the same frequency as node A sends the next fragment to node and on the same frequency as node A sends the next fragment to node
B, this may result in a hidden terminal problem at B whereby the B, this may result in a hidden terminal problem at B whereby the
transmission from C interferes with that from A unbeknownst of node transmission from C interferes with that from A unbeknownst of node
A. It results that consecutive fragments must be reasonably spaced A. It results that consecutive fragments must be reasonably spaced
in order to avoid the 2 forms of collision described above. A node in order to avoid the 2 forms of collision described above. A node
that has multiple packets or fragments to send via different next-hop that has multiple packets or fragments to send via different next-hop
routers may interleave the messages in order to alleviate those routers may interleave the messages in order to alleviate those
effects. effects.
5. Virtual Reassembly Buffer (VRB) Implementation 6. Virtual Reassembly Buffer (VRB) Implementation
Virtual Reassembly Buffer (VRB) is the implementation technique Virtual Reassembly Buffer (VRB) is the implementation technique
described in [LWIG-VRB] in which a forwarder does not reassemble each described in [LWIG-VRB] in which a forwarder does not reassemble each
packet in its entirety before forwarding it. packet in its entirety before forwarding it.
VRB overcomes the limits listed in Section 3. Nodes do not wait for VRB overcomes the limits listed in Section 4. Nodes do not wait for
the last fragment before forwarding, reducing end-to-end latency. the last fragment before forwarding, reducing end-to-end latency.
Similarly, the memory footprint of VRB is just the VRB table, Similarly, the memory footprint of VRB is just the VRB table,
reducing the packet drop probability significantly. reducing the packet drop probability significantly.
There are, however, limits: There are, however, limits:
Non-zero Packet Drop Probability: The abstract data in a VRB table Non-zero Packet Drop Probability: The abstract data in a VRB table
entry contains at a minimum the Link-Layer address of the entry contains at a minimum the Link-Layer address of the
predecessor and that of the successor, the datagram_tag used by predecessor and that of the successor, the datagram_tag used by
the predecessor and the local datagram_tag that this node will the predecessor and the local datagram_tag that this node will
skipping to change at page 8, line 28 skipping to change at page 10, line 5
The severity and occurrence of these limits depends on the Link-Layer The severity and occurrence of these limits depends on the Link-Layer
used. Whether these limits are acceptable depends entirely on the used. Whether these limits are acceptable depends entirely on the
requirements the application places on the network. requirements the application places on the network.
If the limits are present and not acceptable for the application, If the limits are present and not acceptable for the application,
future specifications may define new protocols to overcome these future specifications may define new protocols to overcome these
limits. One example is [FRAG-RECOV] which defines a protocol which limits. One example is [FRAG-RECOV] which defines a protocol which
allows fragment recovery. allows fragment recovery.
6. Security Considerations 7. Security Considerations
Secure joining and the Link-Layer security that it sets up protects Secure joining and the Link-Layer security that it sets up protects
against those attacks from network outsiders. against those attacks from network outsiders.
"IP Fragmentation Considered Fragile" [FRAG-ILE] discusses security "IP Fragmentation Considered Fragile" [FRAG-ILE] discusses security
threats that are linked to using IP fragmentation. The 6LoWPAN threats that are linked to using IP fragmentation. The 6LoWPAN
fragmentation takes place underneath, but some issues described there fragmentation takes place underneath, but some issues described there
may still apply to 6lo fragments. may still apply to 6lo fragments.
* Overlapping fragment attacks are possible with 6LoWPAN fragments * Overlapping fragment attacks are possible with 6LoWPAN fragments
skipping to change at page 9, line 23 skipping to change at page 10, line 48
* Attacks based on predictable fragment identification values are * Attacks based on predictable fragment identification values are
also possible but can be avoided. The datagram_tag SHOULD be also possible but can be avoided. The datagram_tag SHOULD be
assigned pseudo-randomly in order to defeat such attacks. assigned pseudo-randomly in order to defeat such attacks.
* Evasion of Network Intrusion Detection Systems (NIDS) leverages * Evasion of Network Intrusion Detection Systems (NIDS) leverages
ambiguity in the reassembly of the fragment. This sounds ambiguity in the reassembly of the fragment. This sounds
difficult and mostly useless in a 6LoWPAN network since the difficult and mostly useless in a 6LoWPAN network since the
fragmentation is not end-to-end. fragmentation is not end-to-end.
7. IANA Considerations 8. IANA Considerations
No requests to IANA are made by this document. No requests to IANA are made by this document.
8. Acknowledgments 9. Acknowledgments
The authors would like to thank Yasuyuki Tanaka, Ines Robles and Dave The authors would like to thank Carles Gomez Montenegro, Yasuyuki
Thaler for their in-depth review of this document and improvement Tanaka, Ines Robles and Dave Thaler for their in-depth review of this
suggestions. Also many thanks to Georgies Papadopoulos and Dominique document and improvement suggestions. Also many thanks to Georgies
Barthel for their own reviews. Papadopoulos and Dominique Barthel for their own reviews.
9. Normative References 10. Normative References
[6LoWPAN] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4 "Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007, Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007,
<https://www.rfc-editor.org/info/rfc4944>. <https://www.rfc-editor.org/info/rfc4944>.
[LWIG-VRB] Bormann, C. and T. Watteyne, "Virtual reassembly buffers [LWIG-VRB] Bormann, C. and T. Watteyne, "Virtual reassembly buffers
in 6LoWPAN", Work in Progress, Internet-Draft, draft-ietf- in 6LoWPAN", Work in Progress, Internet-Draft, draft-ietf-
lwig-6lowpan-virtual-reassembly-01, 11 March 2019, lwig-6lowpan-virtual-reassembly-01, 11 March 2019,
<https://tools.ietf.org/html/draft-ietf-lwig-6lowpan- <https://tools.ietf.org/html/draft-ietf-lwig-6lowpan-
virtual-reassembly-01>. virtual-reassembly-01>.
[FRAG-RECOV] [FRAG-RECOV]
Thubert, P., "6LoWPAN Selective Fragment Recovery", Work Thubert, P., "6LoWPAN Selective Fragment Recovery", Work
in Progress, Internet-Draft, draft-ietf-6lo-fragment- in Progress, Internet-Draft, draft-ietf-6lo-fragment-
recovery-07, 23 October 2019, recovery-07, 23 October 2019,
<https://tools.ietf.org/html/draft-ietf-6lo-fragment- <https://tools.ietf.org/html/draft-ietf-6lo-fragment-
recovery-07>. recovery-07>.
10. Informative References 11. Informative References
[6LoWPAN-HC] [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6
Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs):
Overview, Assumptions, Problem Statement, and Goals",
RFC 4919, DOI 10.17487/RFC4919, August 2007,
<https://www.rfc-editor.org/info/rfc4919>.
[RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly
Errors at High Data Rates", RFC 4963,
DOI 10.17487/RFC4963, July 2007,
<https://www.rfc-editor.org/info/rfc4963>.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031,
DOI 10.17487/RFC3031, January 2001,
<https://www.rfc-editor.org/info/rfc3031>.
[RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
DOI 10.17487/RFC6282, September 2011, DOI 10.17487/RFC6282, September 2011,
<https://www.rfc-editor.org/info/rfc6282>. <https://www.rfc-editor.org/info/rfc6282>.
[RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie,
"IPv6 over Low-Power Wireless Personal Area Network
(6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138,
April 2017, <https://www.rfc-editor.org/info/rfc8138>.
[RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed.,
"Path MTU Discovery for IP version 6", STD 87, RFC 8201,
DOI 10.17487/RFC8201, July 2017,
<https://www.rfc-editor.org/info/rfc8201>.
[RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
Low-Power and Lossy Networks", RFC 6550,
DOI 10.17487/RFC6550, March 2012,
<https://www.rfc-editor.org/info/rfc6550>.
[FRAG-ILE] Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O., [FRAG-ILE] Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O.,
and F. Gont, "IP Fragmentation Considered Fragile", Work and F. Gont, "IP Fragmentation Considered Fragile", Work
in Progress, Internet-Draft, draft-ietf-intarea-frag- in Progress, Internet-Draft, draft-ietf-intarea-frag-
fragile-17, 30 September 2019, fragile-17, 30 September 2019,
<https://tools.ietf.org/html/draft-ietf-intarea-frag- <https://tools.ietf.org/html/draft-ietf-intarea-frag-
fragile-17>. fragile-17>.
[ARTICLE] Tanaka, Y., Minet, P., and T. Watteyne, "6LoWPAN Fragment [ARTICLE] Tanaka, Y., Minet, P., and T. Watteyne, "6LoWPAN Fragment
Forwarding", IEEE Communications Standards Magazine , Forwarding", IEEE Communications Standards Magazine ,
2019. 2019.
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