Internet DRAFT - draft-ietf-roll-turnon-rfc8138
draft-ietf-roll-turnon-rfc8138
ROLL P. Thubert, Ed.
Internet-Draft L. Zhao
Updates: 8138 (if approved) Cisco Systems
Intended status: Standards Track 18 December 2020
Expires: 21 June 2021
A RPL DODAG Configuration Option for the 6LoWPAN Routing Header
draft-ietf-roll-turnon-rfc8138-18
Abstract
This document updates RFC 8138 by defining a bit in the RPL DODAG
Configuration Option to indicate whether compression is used within
the RPL Instance, and specify the behavior of RFC 8138-capable nodes
when the bit is set and unset.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 21 June 2021.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. References . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Glossary . . . . . . . . . . . . . . . . . . . . . . . . 3
2.3. Requirements Language . . . . . . . . . . . . . . . . . . 4
3. Extending RFC 6550 . . . . . . . . . . . . . . . . . . . . . 4
4. Updating RFC 8138 . . . . . . . . . . . . . . . . . . . . . . 5
5. Transition Scenarios . . . . . . . . . . . . . . . . . . . . 5
5.1. Coexistence . . . . . . . . . . . . . . . . . . . . . . . 6
5.2. Inconsistent State While Migrating . . . . . . . . . . . 6
5.3. Rolling Back . . . . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
9. Normative References . . . . . . . . . . . . . . . . . . . . 8
10. Informative References . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
The design of Low Power and Lossy Networks (LLNs) is generally
focused on saving energy, which is the most constrained resource of
all. The routing optimizations in the "Routing Protocol for Low
Power and Lossy Networks" [RFC6550] (RPL) such as routing along a
Destination-Oriented Directed Acyclic Graph (DODAG) to a Root Node
and the associated routing header compression and forwarding
technique specified in [RFC8138] derive from that primary concern.
Enabling [RFC8138] on a running network requires a Flag Day where the
network is upgraded and rebooted. Otherwise, if acting as a Leaf, a
node that does not support the compression would fail to communicate;
if acting as a router it would drop the compressed packets and black-
hole a portion of the network. This specification enables a hot
upgrade where a live network is migrated. During the migration, the
compression remains inactive, until all nodes are upgraded.
This document complements [RFC8138] and signals whether it should be
used within a RPL DODAG with a new flag in the RPL DODAG
Configuration Option. The setting of this new flag is controlled by
the Root and propagates as is in the whole network as part of the
normal RPL signaling.
The flag is cleared to maintain the compression inactive during the
migration phase. When the migration is complete (e.g., as known by
network management and/or inventory), the flag is set and the
compression is globally activated in the whole DODAG.
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2. Terminology
2.1. References
The terminology used in this document is consistent with and
incorporates that described in "Terms Used in Routing for Low-Power
and Lossy Networks (LLNs)" [RFC7102]. Other terms in use in LLNs are
found in "Terminology for Constrained-Node Networks" [RFC7228].
"RPL", the "RPL Packet Information" (RPI), and "RPL Instance"
(indexed by a RPLInstanceID) are defined in "RPL: IPv6 Routing
Protocol for Low-Power and Lossy Networks" [RFC6550]. The RPI is the
abstract information that RPL defines to be placed in data packets,
e.g., as the RPL Option [RFC6553] within the IPv6 Hop-By-Hop Header.
By extension the term "RPI" is often used to refer to the RPL Option
itself. The DODAG Information Solicitation (DIS), Destination
Advertisement Object (DAO) and DODAG Information Object (DIO)
messages are also specified in [RFC6550].
This document uses the terms RPL-Unaware Leaf (RUL) and RPL-Aware
Leaf (RAL) consistently with "Using RPI Option Type, Routing Header
for Source Routes and IPv6-in-IPv6 encapsulation in the RPL Data
Plane" [USEofRPLinfo]. The term RPL-Aware Node (RAN) refers to a
node that is either a RAL or a RPL Router. A RAN manages the
reachability of its addresses and prefixes by injecting them in RPL
by itself. In contrast, a RUL leverages "Registration Extensions for
IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN) Neighbor
Discovery" [RFC8505] to obtain reachability services from its parent
router(s) as specified in "Routing for RPL Leaves" [UNAWARE-LEAVES].
2.2. Glossary
This document often uses the following acronyms:
6LoWPAN: IPv6 over Low-Power Wireless Personal Area Network
6LoRH: 6LoWPAN Routing Header
DIO: DODAG Information Object (a RPL message)
DODAG: Destination-Oriented Directed Acyclic Graph
LLN: Low-Power and Lossy Network
RPL: IPv6 Routing Protocol for Low-Power and Lossy Networks
SubDAG: A DODAG rooted at a node which is a child of that node and a
subset of a larger DAG
MOP: RPL Mode of Operation
RPI: RPL Packet Information
RAL: RPL-Aware Leaf
RAN: RPL-Aware Node
RUL: RPL-Unaware Leaf
SRH: Source Routing Header
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2.3. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119][RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Extending RFC 6550
The DODAG Configuration Option is defined in Section 6.7.6 of
[RFC6550]. Its purpose is extended to distribute configuration
information affecting the construction and maintenance of the DODAG,
as well as operational parameters for RPL on the DODAG, through the
DODAG. As shown in Figure 1, the Option was originally designed with
4 bit positions reserved for future use as Flags.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 0x04 |Opt Length = 14| | |T| |A| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
<- Flags ->
Figure 1: DODAG Configuration Option (Partial View)
This specification defines a new flag "Enable RFC8138 Compression"
(T). The "T" flag is set to turn-on the use of [RFC8138] within the
DODAG. The "T" flag is encoded in position 2 of the reserved Flags
in the DODAG Configuration Option (counting from bit 0 as the most
significant bit) and set to 0 in legacy implementations as specified
respectively in Sections 20.14 and 6.7.6 of [RFC6550].
Section 4.3 of [USEofRPLinfo] updates [RFC6550] to indicate that the
definition of the Flags applies to Mode of Operation (MOP) values
zero (0) to six (6) only. For a MOP value of 7, [RFC8138] MUST be
used on Links where 6LoWPAN Header Compression [RFC6282] applies and
MUST NOT be used otherwise.
The RPL DODAG Configuration Option is typically placed in a DODAG
Information Object (DIO) message. The DIO message propagates down
the DODAG to form and then maintain its structure. The DODAG
Configuration Option is copied unmodified from parents to children.
[RFC6550] states that "Nodes other than the DODAG Root MUST NOT
modify this information when propagating the DODAG Configuration
option". Therefore, a legacy parent propagates the "T" flag as set
by the Root, and when the "T" flag is set, it is transparently
flooded to all the nodes in the DODAG.
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4. Updating RFC 8138
A node SHOULD generate packets in the compressed form using [RFC8138]
if and only if the "T" flag is set. This behavior can be overridden
by configuration or network management. Overriding may be needed
e.g., to turn on the compression in a network where all nodes support
[RFC8138] but the Root does not support this specification and cannot
set the "T" flag, or to disable it locally in case of a problem.
The decision to use [RFC8138] is made by the originator of the packet
depending on its capabilities and its knowledge of the state of the
"T" flag. A router encapsulating a packet is the originator of the
resulting packet and is responsible for compressing the outer headers
with [RFC8138], but it MUST leave the encapsulated packet as is.
An external target [USEofRPLinfo] is not expected to support
[RFC8138]. In most cases, packets to and from an external target are
tunneled back and forth between the border router (referred to as
6LR) that serves the external target and the Root, regardless of the
MOP used in the RPL DODAG. The inner packet is typically not
compressed with [RFC8138], so for outgoing packets, the border router
just needs to decapsulate the (compressed) outer header and forward
the (uncompressed) inner packet towards the external target.
A router MUST uncompress a packet that is to be forwarded to an
external target. Otherwise, the router MUST forward the packet in
the form that the source used, either compressed or uncompressed.
A RUL [UNAWARE-LEAVES] is both a leaf and an external target. A RUL
does not participate in RPL and depends on the parent router to
obtain connectivity. In the case of a RUL, forwarding towards an
external target actually means delivering the packet.
5. Transition Scenarios
A node that supports [RFC8138] but not this specification can only be
used in a homogeneous network. Enabling the [RFC8138] compression
without a turn-on signaling method requires a "flag day"; by which
time all nodes must be upgraded, and at which point the network can
be rebooted with the [RFC8138] compression turned on.
The intent for this specification is to perform a migration once and
for all without the need for a flag day. In particular it is not the
intention to undo the setting of the "T" flag. Though it is possible
to roll back (see Section 5.3), the roll back operation SHOULD be
complete before the network operator adds nodes that do not support
[RFC8138].
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5.1. Coexistence
A node that supports this specification can operate in a network with
the [RFC8138] compression turned on or off with the "T" flag set
accordingly and in a network in transition from off to on or on to
off (see Section 5.2).
A node that does not support [RFC8138] can interoperate with nodes
that do in a network with [RFC8138] compression turned off. If the
compression is turned on, all the RPL-Aware Nodes are expected to be
able to handle compressed packets in the compressed form. A node
that cannot do so may remain connected to the network as a RUL as
described in [UNAWARE-LEAVES].
5.2. Inconsistent State While Migrating
When the "T" flag is turned on by the Root, the information slowly
percolates through the DODAG as the DIO gets propagated. Some nodes
will see the flag and start sourcing packets in the compressed form
while other nodes in the same RPL DODAG are still not aware of it.
In non-storing mode, the Root will start using [RFC8138] with a
Source Routing Header 6LoRH (SRH-6LoRH) that routes all the way to
the parent router or to the leaf.
To ensure that a packet is forwarded across the RPL DODAG in the form
in which it was generated, it is required that all the RPL nodes
support [RFC8138] at the time of the switch.
Setting the "T" flag is ultimately the responsibility of the Network
Administrator. The expectation is that the network management or
upgrading tools in place enable the Network Administrator to know
when all the nodes that may join a DODAG were migrated. In the case
of a RPL instance with multiple Roots, all nodes that participate to
the RPL Instance may potentially join any DODAG. The network MUST be
operated with the "T" flag unset until all nodes in the RPL Instance
are upgraded to support this specification.
5.3. Rolling Back
When turning [RFC8138] compression off in the network, the Network
Administrator MUST wait until all nodes have converged to the "T"
flag unset before allowing nodes that do not support the compression
in the network. To that effect, whether the compression is active in
a node SHOULD be exposed the node's management interface.
Nodes that do not support [RFC8138] SHOULD NOT be deployed in a
network where the compression is turned on. If that is done, the
node can only operate as a RUL.
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6. IANA Considerations
This specification updates the Registry that was created for
[RFC6550] as the registry for "DODAG Configuration Option Flags" and
updated as the registry for "DODAG Configuration Option Flags for MOP
0..6" by [USEofRPLinfo], by allocating one new Flag as follows:
+---------------+---------------------------------+-----------+
| Bit Number | Capability Description | Reference |
+---------------+---------------------------------+-----------+
| 2 (suggested) | Turn on RFC8138 Compression (T) | THIS RFC |
+---------------+---------------------------------+-----------+
Table 1: New DODAG Configuration Option Flag
IANA is requested to add [this document] as a reference for MOP 7 in
the RPL Mode of Operation registry.
7. Security Considerations
It is worth noting that in RPL [RFC6550], every node in the LLN that
is RPL-aware and has access to the RPL domain can inject any RPL-
based attack in the network, more in [RFC7416]. This document
applies typically to an existing deployment and does not change its
security requirements and operations. It is assumed that the
security mechanisms as defined for RPL are followed.
Setting the "T" flag before all routers are upgraded may cause a loss
of packets. The new bit is protected as the rest of the
configuration so this is just one of the many attacks that can happen
if an attacker manages to inject a corrupted configuration.
Setting and unsetting the "T" flag may create inconsistencies in the
network but as long as all nodes are upgraded to [RFC8138] support
they will be able to forward both forms. The source is responsible
for selecting whether the packet is compressed or not, and all
routers must use the format that the source selected. So the result
of an inconsistency is merely that both forms will be present in the
network, at an additional cost of bandwidth for packets in the
uncompressed form.
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An attacker may unset the "T" flag to force additional energy
consumption of child or descendant nodes in its subDAG. Conversely
it may set the "T" flag, so that nodes located downstream would
compress when that it is not desired, potentially resulting in the
loss of packets. In a tree structure, the attacker would be in
position to drop the packets from and to the attacked nodes. So the
attacks above would be more complex and more visible than simply
dropping selected packets. The downstream node may have other
parents and see both settings, which could raise attention.
8. Acknowledgments
The authors wish to thank Murray Kucherawy, Meral Shirazipour, Barry
Leiba, Tirumaleswar Reddy, Nagendra Kumar Nainar, Stewart Bryant,
Carles Gomez, Eric Vyncke, Roman Danyliw, and especially Benjamin
Kaduk, Alvaro Retana, Dominique Barthel and Rahul Jadhav for their
in-depth reviews and constructive suggestions.
Also many thanks to Michael Richardson for being always helpful and
responsive when need comes.
9. Normative References
[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>.
[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>.
[RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and
Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January
2014, <https://www.rfc-editor.org/info/rfc7102>.
[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>.
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[RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C.
Perkins, "Registration Extensions for IPv6 over Low-Power
Wireless Personal Area Network (6LoWPAN) Neighbor
Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018,
<https://www.rfc-editor.org/info/rfc8505>.
[UNAWARE-LEAVES]
Thubert, P. and M. Richardson, "Routing for RPL Leaves",
Work in Progress, Internet-Draft, draft-ietf-roll-unaware-
leaves-27, 17 December 2020, <https://tools.ietf.org/html/
draft-ietf-roll-unaware-leaves-27>.
10. Informative References
[RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
DOI 10.17487/RFC6282, September 2011,
<https://www.rfc-editor.org/info/rfc6282>.
[RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low-
Power and Lossy Networks (RPL) Option for Carrying RPL
Information in Data-Plane Datagrams", RFC 6553,
DOI 10.17487/RFC6553, March 2012,
<https://www.rfc-editor.org/info/rfc6553>.
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014,
<https://www.rfc-editor.org/info/rfc7228>.
[RFC7416] Tsao, T., Alexander, R., Dohler, M., Daza, V., Lozano, A.,
and M. Richardson, Ed., "A Security Threat Analysis for
the Routing Protocol for Low-Power and Lossy Networks
(RPLs)", RFC 7416, DOI 10.17487/RFC7416, January 2015,
<https://www.rfc-editor.org/info/rfc7416>.
[USEofRPLinfo]
Robles, I., Richardson, M., and P. Thubert, "Using RPI
Option Type, Routing Header for Source Routes and IPv6-in-
IPv6 encapsulation in the RPL Data Plane", Work in
Progress, Internet-Draft, draft-ietf-roll-useofrplinfo-42,
12 November 2020, <https://tools.ietf.org/html/draft-ietf-
roll-useofrplinfo-42>.
Authors' Addresses
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Pascal Thubert (editor)
Cisco Systems, Inc
Building D
45 Allee des Ormes - BP1200
06254 MOUGINS - Sophia Antipolis
France
Phone: +33 497 23 26 34
Email: pthubert@cisco.com
Li Zhao
Cisco Systems, Inc
Xinsi Building
No. 926 Yi Shan Rd
SHANGHAI
200233
China
Email: liz3@cisco.com
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