draft-ietf-6lo-minimal-fragment-10.txt   draft-ietf-6lo-minimal-fragment-11.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: 4 August 2020 Cisco Systems Expires: 10 August 2020 Cisco Systems
C. Bormann C. Bormann
Universitaet Bremen TZI Universitaet Bremen TZI
1 February 2020 7 February 2020
On Forwarding 6LoWPAN Fragments over a Multihop IPv6 Network On Forwarding 6LoWPAN Fragments over a Multihop IPv6 Network
draft-ietf-6lo-minimal-fragment-10 draft-ietf-6lo-minimal-fragment-11
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
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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 4 August 2020. This Internet-Draft will expire on 10 August 2020.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
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
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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 until the 6LoWPAN endpoint the first fragment will still continue until the 6LoWPAN endpoint
that will attempt to perform the reassembly, and may be misused to that will attempt to perform the reassembly, and may be misused to
the point that the end-to-end latency falls behind that of per-hop the point that the end-to-end latency falls behind that of per-hop
recomposition. This specification provides a generic overview of FF, recomposition.
discusses advantages and caveats, and introduces a particular 6LoWPAN
Fragment Forwarding technique called Virtual Reassembly Buffer that This specification provides a generic overview of FF, discusses
can be used while conserving the message formats defined in advantages and caveats, and introduces a particular 6LoWPAN Fragment
[RFC4944]. Forwarding technique called Virtual Reassembly Buffer that can be
used while conserving the message formats defined in [RFC4944].
2. Terminology 2. Terminology
2.1. BCP 14 2.1. BCP 14
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119][RFC8174] when, and only when, they appear in all 14 [RFC2119][RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
2.2. Referenced Work 2.2. Referenced Work
Past experience with fragmentation, e.g., as described in "IPv4 Past experience with fragmentation, e.g., as described in "IPv4
Reassembly Errors at High Data Rates" [RFC4963] and references Reassembly Errors at High Data Rates" [RFC4963] and references
therein, has shown that mis-associated or lost fragments can lead to therein, has shown that mis-associated or lost fragments can lead to
poor network behavior and, occasionally, trouble at application poor network behavior and, occasionally, trouble at the application
layer. That experience led to the definition of "Path MTU discovery" layer. That experience led to the definition of the "Path MTU
[RFC8201] (PMTUD) protocol that limits fragmentation over the discovery" [RFC8201] (PMTUD) protocol that limits fragmentation over
Internet. the Internet.
"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 6LoWPAN fragments. may still apply to 6LoWPAN fragments (as discussed in further details
in Section 7).
Readers are expected to be familiar with all the terms and concepts Readers are expected to be familiar with all the terms and concepts
that are discussed in "IPv6 over Low-Power Wireless Personal Area that are discussed in "IPv6 over Low-Power Wireless Personal Area
Networks (6LoWPANs): Overview, Assumptions, Problem Statement, and Networks (6LoWPANs): Overview, Assumptions, Problem Statement, and
Goals" [RFC4919] and "Transmission of IPv6 Packets over IEEE 802.15.4 Goals" [RFC4919] and "Transmission of IPv6 Packets over IEEE 802.15.4
Networks" [RFC4944]. Networks" [RFC4944].
Quoting the "Multiprotocol Label Switching (MPLS) Architecture" "Multiprotocol Label Switching (MPLS) Architecture" [RFC3031] says
[RFC3031]: with MPLS, 'packets are "labeled" before they are that with MPLS, 'packets are "labeled" before they are forwarded.'
forwarded'. At subsequent hops, there is no further analysis of the It goes on to say, "At subsequent hops, there is no further analysis
packet's network layer header. Rather, the label is used as an index of the packet's network layer header. Rather, the label is used as
into a table which specifies the next hop, and a new label". The an index into a table which specifies the next hop, and a new label".
MPLS technique is leveraged in the present specification to forward The MPLS technique is leveraged in the present specification to
fragments that actually do not have a network layer header, since the forward fragments that actually do not have a network layer header,
fragmentation occurs below IP. since the fragmentation occurs below IP.
2.3. New Terms 2.3. New Terms
This specification uses the following terms: This specification defines the following terms:
6LoWPAN endpoints: The nodes in charge of generating or expanding a 6LoWPAN endpoints: The 6LoWPAN endpoints are the first and last
6LoWPAN header from/to a full IPv6 packet. The 6LoWPAN endpoints nodes in an unbroken string of 6LoWPAN nodes. They are in charge
are the points where fragmentation and reassembly take place. of generating or expanding a 6LoWPAN header from/to a full IPv6
packet. They are also the points where the fragmentation and
reassembly operations take place.
Compressed Form: This specification uses the generic term Compressed Compressed Form: This specification uses the generic term Compressed
Form to refer to the format of a datagram after the action of Form to refer to the format of a datagram after the action of
[RFC6282] and possibly [RFC8138] for RPL [RFC6550] artifacts. [RFC6282] and possibly [RFC8138] for RPL [RFC6550] artifacts.
datagram_size: The size of the datagram in its Compressed Form datagram_size: The size of the datagram in its Compressed Form
before it is fragmented. The datagram_size is expressed in a unit before it is fragmented. The datagram_size is expressed in a unit
that depends on the MAC layer technology, by default a byte. that depends on the MAC layer technology, by default a byte.
datagram_tag: An identifier of a datagram that is locally unique to datagram_tag: An identifier of a datagram that is locally unique to
the Layer-2 sender. Associated with the MAC address of the the Layer-2 sender. Associated with the MAC address of the
sender, this becomes a globally unique identifier for the sender, this becomes a globally unique identifier for the
datagram. datagram.
fragment_offset: The offset of a particular fragment of a datagram fragment_offset: The offset of a fragment of a datagram in its
in its Compressed Form. The fragment_offset is expressed in a Compressed Form. The fragment_offset is expressed in a unit that
unit that depends on the MAC layer technology and is by default a depends on the MAC layer technology and is by default a byte.
byte.
3. Overview of 6LoWPAN Fragmentation 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 |--- ...
+---+ +---+ +---+ +---+
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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.
4. 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 limitations 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. limitations.
4.1. 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.
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and that is used when forwarding the fragments of the datagram and that is used when forwarding the fragments of the datagram
* 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. The duration of the timer should be longer than that timeout. The duration of the timer should be longer than that
which covers the reassembly at the receiving end point. which covers the reassembly at the receiving end point.
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. To keep the
keep the operation simple, it makes sense to be consistent with operation simple, it makes sense to be consistent with [RFC4944] and
[RFC4944] and enforce that the first fragment is always sent first. enforce that the first fragment is always sent first. When that is
When that is done, if node B receives a fragment that is not the done, if node B receives a fragment that is not the first and for
first and for which it has no state, then node B treats this as an which it has no state, then node B treats this as an error and
error and refrain from creating a state or attempting to forward. refrains from creating a state or attempting to forward. This also
This also means that node A should perform all its possible retries means that node A should perform all its possible retries on the
on the first fragment before it attempts to send the next fragments, first fragment before it attempts to send the next fragments, and
and that it should abort the datagram and release its state if it that it should abort the datagram and release its state if it fails
fails to send the first fragment. 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
buffer bloat effect. Multiple fragments may progress in parallel buffer bloat effect. Multiple fragments may progress in parallel
along the network as long as they do not interfere. An associated along the network as long as they do not interfere. An associated
caveat is that on a half duplex radio, if node A sends the next caveat is that on a half duplex radio, if node A sends the next
fragment at the same time as node B forwards the previous fragment to fragment at the same time as node B forwards the previous fragment to
a node C down the path then node B will miss the next fragment from a node C down the path then node B will miss the next fragment from
node A. If node C forwards the previous fragment to a node D at the node A. If 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 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 at B whereby to node B, this may result in a hidden terminal problem at B whereby
the transmission from C interferes with that from A unbeknownst of the transmission from C interferes with that from A unbeknownst of
node A. It results that consecutive fragments must be reasonably node A. It results that consecutive fragments must be reasonably
spaced in order to avoid the 2 forms of collision described above. A spaced to avoid the 2 forms of collision described above. A node
node that has multiple packets or fragments to send via different that has multiple packets or fragments to send via different next-hop
next-hop routers may interleave the messages in order to alleviate routers may interleave the messages in order to alleviate those
those effects. effects.
6. 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 4. Nodes do not wait for VRB overcomes the limitations listed in Section 4. Nodes do not wait
the last fragment before forwarding, reducing end-to-end latency. for 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 other caveats, however:
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
swap with it. The VRB may need to store a few octets from the swap with it. The VRB may need to store a few octets from the
last fragment that may not have fit within MTU and that will be last fragment that may not have fit within MTU and that will be
prepended to the next fragment. This yields a small footprint prepended to the next fragment. This yields a small footprint
that is 2 orders of magnitude smaller compared to needing a that is 2 orders of magnitude smaller compared to needing a
1280-byte reassembly buffer for each packet. Yet, the size of the 1280-byte reassembly buffer for each packet. Yet, the size of the
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entries in its VRB table, packets are dropped. entries in its VRB table, packets are dropped.
No Fragment Recovery: There is no mechanism in VRB for the node that No Fragment Recovery: There is no mechanism in VRB for the node that
reassembles a packet to request a single missing fragment. reassembles a packet to request a single missing fragment.
Dropping a fragment requires the whole packet to be resent. This Dropping a fragment requires the whole packet to be resent. This
causes unnecessary traffic, as fragments are forwarded even when causes unnecessary traffic, as fragments are forwarded even when
the destination node can never construct the original IPv6 packet. the destination node can never construct the original IPv6 packet.
No Per-Fragment Routing: All subsequent fragments follow the same No Per-Fragment Routing: All subsequent fragments follow the same
sequence of hops from the source to the destination node as the sequence of hops from the source to the destination node as the
first fragment, because the IP header is required to route the first fragment, because the IP header is required in order to
fragment and is only present in the first fragment. A side effect route the fragment and is only present in the first fragment. A
is that the first fragment must always be forwarded first. side effect is that the first fragment must always be forwarded
first.
The severity and occurrence of these limits depends on the Link-Layer The severity and occurrence of these caveats depends on the Link-
used. Whether these limits are acceptable depends entirely on the Layer used. Whether they 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 caveats 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 them. One
limits. One example is [FRAG-RECOV] which defines a protocol which example is [FRAG-RECOV] which defines a protocol which allows
allows fragment recovery. fragment recovery.
7. 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 6LoWPAN fragments. may still apply to 6LoWPAN fragments.
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necessary. necessary.
* Resource exhaustion attacks are certainly possible and a sensitive * Resource exhaustion attacks are certainly possible and a sensitive
issue in a constrained network. An attacker can perform a Denial- issue in a constrained network. An attacker can perform a Denial-
of-Service (DoS) attack on a node implementing VRB by generating a of-Service (DoS) attack on a node implementing VRB by generating a
large number of bogus first fragments without sending subsequent large number of bogus first fragments without sending subsequent
fragments. This causes the VRB table to fill up. When hop-by-hop 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 reassembly is used, the same attack can be more damaging if the
node allocates a full datagram_size for each bogus first fragment. node allocates a full datagram_size for each bogus first fragment.
With the VRB, the attack can be performed remotely on all nodes With the VRB, the attack can be performed remotely on all nodes
along a path, but each node suffers a lesser hit. this is because along a path, but each node suffers a lesser hit. This is because
the VRB does not need to remember the full datagram as received so 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 far but only possibly a few octets from the last fragment that
could not fit in it. An implementation MUST protect itself to could not fit in it. An implementation MUST protect itself to
keep the number of VRBs within capacity, and that old VRBs are keep the number of VRBs within capacity, and ensure that old VRBs
protected by a timer of a reasonable duration for the technology are protected by a timer of a reasonable duration for the
and destroyed upon timeout. technology and destroyed upon timeout.
* 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 is difficult
difficult and mostly useless in a 6LoWPAN network since the and mostly useless in a 6LoWPAN network since the fragmentation is
fragmentation is not end-to-end. not end-to-end.
8. IANA Considerations 8. IANA Considerations
No requests to IANA are made by this document. No requests to IANA are made by this document.
9. Acknowledgments 9. Acknowledgments
The authors would like to thank Carles Gomez Montenegro, Yasuyuki The authors would like to thank Carles Gomez Montenegro, Yasuyuki
Tanaka, Ines Robles and Dave Thaler for their in-depth review of this Tanaka, Ines Robles and Dave Thaler for their in-depth review of this
document and improvement suggestions. Also many thanks to Georgies document and improvement suggestions. Also many thanks to Georgios
Papadopoulos and Dominique Barthel for their own reviews, and to Papadopoulos and Dominique Barthel for their own reviews, and to
Sarah Banks, Joerg Ott and Francesca Palombini For their constructive Barry Leiba, Derrell Piper, Sarah Banks, Joerg Ott and Francesca
reviews through the IESG process. Palombini for their constructive reviews through the IETF last call
and IESG process.
10. Normative References 10. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, [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>.
11. Informative References
[RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6
over Low-Power Wireless Personal Area Networks (6LoWPANs): over Low-Power Wireless Personal Area Networks (6LoWPANs):
Overview, Assumptions, Problem Statement, and Goals", Overview, Assumptions, Problem Statement, and Goals",
RFC 4919, DOI 10.17487/RFC4919, August 2007, RFC 4919, DOI 10.17487/RFC4919, August 2007,
<https://www.rfc-editor.org/info/rfc4919>. <https://www.rfc-editor.org/info/rfc4919>.
11. Informative References
[RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly
Errors at High Data Rates", RFC 4963, Errors at High Data Rates", RFC 4963,
DOI 10.17487/RFC4963, July 2007, DOI 10.17487/RFC4963, July 2007,
<https://www.rfc-editor.org/info/rfc4963>. <https://www.rfc-editor.org/info/rfc4963>.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol [RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031, Label Switching Architecture", RFC 3031,
DOI 10.17487/RFC3031, January 2001, DOI 10.17487/RFC3031, January 2001,
<https://www.rfc-editor.org/info/rfc3031>. <https://www.rfc-editor.org/info/rfc3031>.
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