ROLL Working Group M. Richardson
Internet-Draft Sandelman Software Works
Intended status: Standards Track R.A. Jadhav
Expires: 1 September 2022 Huawei Tech
P. Thubert
H. She
Cisco Systems
28 February 2022
Controlling Secure Network Enrollment in RPL networks
draft-ietf-roll-enrollment-priority-06
Abstract
[RFC9032] defines a method by which a potential [RFC9031] enrollment
proxy can announce itself as a available for new Pledges to enroll on
a network. The announcement includes a priority for enrollment.
This document provides a mechanism by which a RPL DODAG root can
disable enrollment announcements, or adjust the base priority for
enrollment operation.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 1 September 2022.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Please review these documents carefully, as they describe your rights
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and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Motivation and Overview . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Protocol Definition . . . . . . . . . . . . . . . . . . . . . 4
3.1. Option Format . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Upwards compatibility . . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 6
5. Privacy Considerations . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 8
Appendix A. Change history . . . . . . . . . . . . . . . . . . . 8
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
[RFC7554] describes the use of the time-slotted channel hopping
(TSCH) mode of [ieee802154]. [RFC9031] and [RFC9032] describe
mechanisms by which a new node (the "pledge") can use a friendly
router as a Join Proxy. [RFC9032] describes an extension to the
802.15.4 Enhanced Beacon that is used by a Join Proxy to announce its
existence such that Pledges can find them.
1.1. Motivation and Overview
It has become clear that not every routing member of the mesh ought
to announce itself as a _Join Proxy_. There are a variety of local
reasons by which a 6LR might not want to provide the _Join Proxy_
function. They include available battery power, already committed
network bandwidth, and also total available memory available for
Neighbor Cache Entry slots.
There are other situations where the operator of the network would
like to selectively enable or disable the enrollment process in a
particular DODAG.
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As the enrollment process involves permitting unencrypted traffic
into the best effort part of a (TSCH) network, it would be better to
have the enrollment process off when no new nodes are expected.
A network operator might also be able to recognize when certain parts
of the network are overloaded and can not accomodate additional
enrollment traffic, and it would like to adjust the enrollment
priority (the proxy priority field of [RFC9032]) among all nodes in
the subtree of a congested link.
It may derive from multiple constraining factors, e.g., the size of
the DODAG, the occupancy of the bandwidth at the Root, the memory
capacity at the DODAG Root, or an administrative decision.
Each potential _Join Proxy_ would utilize this value as a base on
which to add values relating to local conditions such as its Rank and
number of pending joins, which would degrade even further the
willingness to take more joins.
When a RPL domain is composed of multiple DODAGs, nodes at the edge
of 2 DODAGs may not only join either DODAG but also move from one to
the other in order to keep their relative sizes balanced. For this,
the approximate knowledge of size of the DODAG is an essential
metric. Depending on the network policy, the size of the DODAG may
or may not affect the minimum enrollment priority. It would be
limiting its value to enforce that one is proportional to the other.
This is why the current size of the DODAG is advertised separately in
the new option.
As explained in [RFC9032], higher values decrease the likelihood of
an unenrolled node sending enrollment traffic via this path.
A network operator can set this value to the maximum value allowed,
effectively disabling all new enrollment traffic.
Updates to the option propagate through the network according to the
trickle algorithm. The contents of the option are generated at the
DODAG Root and do not change at any hop. If the contents represent
an update that is considered important (e.g., quickly disabling any
enrollments), the option can trigger trickle timer resets at the
nodes to speed up its propagation.
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2. Terminology
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.
The term (1)"Join" has been used in documents like [RFC9031] to
denote the activity of a new node authenticating itself to the
network in order to obtain authorization to become a member of the
network.
In the context of the [RFC6550] RPL protocol, the term (2)"Join" has
an alternative meaning: that of a node (already authenticating to the
network, and already authorized to be a member of the network),
deciding which part of the RPL DODAG to attach to. This term "Join"
has to do with preferred parent selection processes.
In order to avoid the ambiguity of this term, this document refers to
the process (1)"Join" as enrollment, leaving the term "Join" to mean
(2)"Join". The term "onboarding" (or IoT Onboarding) is increasingly
used to describe what was called enrollment in other documents.
However, the term _Join Proxy_ is retained with its meaning from
[RFC9031].
3. Protocol Definition
This document uses the extensions mechanism designed into [RFC6550].
No mechanism is needed to enable it.
3.1. Option Format
The resulting priority, if less than 0x7f should enable the _Join
Proxy_ function.
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 |Opt Length = 3 | exp | DODAG_Size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R| min priority|
+-+-+-+-+-+-+-+-+
Type to be assigned by IANA.
exp a 4 bit unsigned integer, indicating the power of 2 that defines
the unit of the DODAG Size, such that (unit=2^exp).
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DODAG_Size a 12 bit unsigned integer, expressing the size of the
DODAG in units that depend on the exp field. The size of the
DODAG is computed as (DAG_Size*2^exp).
min.priority a 7 bit field which provides a base value for the
Enhanced Beacon Join priority. A value of 0x7f (127) disables the
_Join Proxy_ function entirely.
R a reserved bit that SHOULD be set to 0 by senders, and MUST be
ignored by receivers. This reserved bit SHOULD be copied to
options created.
This document uses the extensions mechanism designed into [RFC6550].
It does not need any mechanism to enable it.
The size of the DODAG is measured by the Root based one the DAO
activity. It represents a number of routes not a number of nodes,
and can only be used to infer a load in a homogeneous network where
each node advertises the same number of addresses and generates
roughly the same amount of traffic. The size may slightly change
between a DIO and the next, so the value transmitted MUST be
considered as an approximation.
Future work like [I-D.ietf-roll-capabilities] will enable collection
of capabilities such as this one in reports to the DODAG root.
3.2. Upwards compatibility
A 6LR which did not support this option would not act on it, or copy
it into it's DIO messages. Children and grandchildren nodes would
therefore not receive any telemetry via that path, and need to assume
a default value.
A 6LR which did not support this option would not act on it or
propagate it in its DIO messages. In effect, the 6LR's children and
grandchildren nodes could not receive any telemetry via that path.
Therefore, 6LRs that support this option but do not receive it via
any path SHOULD assume a default value of 0x40 as their base value
for the Enhanced Beacon Join Priority.
A 6LR downstream of a 6LR where there was an interruption in the
telemetry could err in two directions:
* if the value implied by the base value of 0x40 was too low, then a
6LR might continue to attract enrollment traffic when none should
have been collected. This is a stressor for the network, but this
would also be what would occur without this option at all.
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* if the value implied by the base value of 0x40 was too high, then
a 6LR might deflect enrollment traffic to other parts of the DODAG
tree, possibly refusing any enrollment traffic at all. In order
for this to happen, some significant congestion must be seen in
the sub-tree where the implied 0x40 was introduced.
The 0x40 is only the half-way point, so if such an amount of
congestion was present, then this sub-tree of the DODAG simply winds
up being more cautious than it needed to be.
It is possible that the temporal alternation of the above two
situations might introduce cycles of accepting and then rejecting
enrollment traffic. This is something an operator should consider if
when they incrementally deploy this option to an existing LLN. In
addition, an operator would be unable to turn off enrollment traffic
by sending a maximum value enrollment priority to the sub-tree. This
situation is unfortunate, but without this option, the the situation
would occur all over the DODAG, rather than just in the sub-tree
where the option was omitted.
4. Security Considerations
As per [RFC7416], RPL control frames either run over a secured layer
2, or use the [RFC6550] Secure DIO methods. This option can be
placed into either a "clear" (layer-2 secured) DIO, or a layer-3
Secure DIO. As such this option will have both integrity and
confidentiality mechanisms applied to it.
A malicious node (that was part of the RPL control plane) could see
these options and could, based upon the observed minimal enrollment
priority signal a confederate that it was a good time to send
malicious join traffic.
Such as a malicious node, being already part of the RPL control
plane, could also send DIOs with a different minimal enrollment
priority which would cause downstream mesh routers to change their
_Join Proxy_ behavior.
Lower minimal priorities would cause downstream nodes to accept more
pledges than the network was expecting, and higher minimal priorities
cause the enrollment process to stall.
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The use of layer-2 or layer-3 security for RPL control messages
prevents the above two attacks, by preventing malicious nodes from
becoming part of the control plane. A node that is attacked and has
malware placed on it creates vulnerabilities in the same way such an
attack on any node involved in Internet routing protocol does. The
rekeying provisions of [RFC9031] exist to permit an operator to
remove such nodes from the network easily.
5. Privacy Considerations
There are no new privacy issues caused by this extension.
6. IANA Considerations
Allocate a new number TBD01 from Registry RPL Control Message
Options. This entry should be called Minimum Enrollment Priority.
7. Acknowledgements
This has been reviewed by Konrad Iwanicki and Thomas Watteyne.
8. References
8.1. Normative References
[ieee802154]
IEEE standard for Information Technology, ., "IEEE Std.
802.15.4, Part. 15.4: Wireless Medium Access Control (MAC)
and Physical Layer (PHY) Specifications for Low-Rate
Wireless Personal Area Networks", n.d.,
<http://standards.ieee.org/findstds/
standard/802.15.4-2015.html>.
[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>.
[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>.
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[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>.
[RFC7554] Watteyne, T., Ed., Palattella, M., and L. Grieco, "Using
IEEE 802.15.4e Time-Slotted Channel Hopping (TSCH) in the
Internet of Things (IoT): Problem Statement", RFC 7554,
DOI 10.17487/RFC7554, May 2015,
<https://www.rfc-editor.org/info/rfc7554>.
[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>.
[RFC9031] Vučinić, M., Ed., Simon, J., Pister, K., and M.
Richardson, "Constrained Join Protocol (CoJP) for 6TiSCH",
RFC 9031, DOI 10.17487/RFC9031, May 2021,
<https://www.rfc-editor.org/info/rfc9031>.
[RFC9032] Dujovne, D., Ed. and M. Richardson, "Encapsulation of
6TiSCH Join and Enrollment Information Elements",
RFC 9032, DOI 10.17487/RFC9032, May 2021,
<https://www.rfc-editor.org/info/rfc9032>.
8.2. Informative References
[I-D.ietf-roll-capabilities]
Jadhav, R. A., Thubert, P., Richardson, M., and R. N.
Sahoo, "RPL Capabilities", Work in Progress, Internet-
Draft, draft-ietf-roll-capabilities-09, 9 November 2021,
<https://www.ietf.org/archive/id/draft-ietf-roll-
capabilities-09.txt>.
Appendix A. Change history
version 00.
Contributors
Authors' Addresses
Michael Richardson
Sandelman Software Works
Email: mcr+ietf@sandelman.ca
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Rahul Arvind Jadhav
Huawei Tech
Email: rahul.ietf@gmail.com
Pascal Thubert
Cisco Systems
Email: pthubert@cisco.com
Huimin She
Cisco Systems
Email: hushe@cisco.com
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