ROLL Working Group M. Richardson
Internet-Draft Sandelman Software Works
Intended status: Informational April 25, 2020
Expires: October 27, 2020
Enabling secure network enrollment in RPL networks
draft-ietf-roll-enrollment-priority-02
Abstract
[I-D.ietf-6tisch-enrollment-enhanced-beacon] defines a method by
which a potential [I-D.ietf-6tisch-minimal-security] join 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 October 27, 2020.
Copyright Notice
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Protocol Definition . . . . . . . . . . . . . . . . . . . . . 3
2.1. Upwards compatibility . . . . . . . . . . . . . . . . . . 4
3. Security Considerations . . . . . . . . . . . . . . . . . . . 5
4. Privacy Considerations . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 7
Appendix A. Change history . . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
[RFC7554] describes the use of the time-slotted channel hopping
(TSCH) mode of [ieee802154]. [I-D.ietf-6tisch-minimal-security] and
[I-D.ietf-6tisch-dtsecurity-secure-join] describe mechanisms by which
a new node (the "pledge)" can use a friendly router as a Join Proxy.
[I-D.ietf-6tisch-enrollment-enhanced-beacon] 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.
The term (1)"Join" has been used in documents like
[I-D.ietf-6tisch-minimal-security] 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. This typically
involves a cryptographic authentication protocol in which a network
credential is provided.
In the context of the [RFC6550] RPL protocol, the term (2)"Join" has
an alternate 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. The term "Join"
has to do with 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 sometimes
used to describe this process. The term Join Proxy is retained with
it's meaning from [I-D.ietf-6tisch-minimal-security].
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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 Join
proxy neighbor cache slots.
There are other situations where the operator of the network would
like to selective enable or disable the enrollment process in a
particular DODAG.
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
[I-D.ietf-6tisch-enrollment-enhanced-beacon]) among all nodes in the
subtree of a congested link.
This document describes an RPL DIO option that can be used to
announce a minimum enrollment priority. Each potential Join Proxy
would this value as a base on which to add values relating to local
conditions. As explained in
[I-D.ietf-6tisch-enrollment-enhanced-beacon], higher values decrease
the likelyhood of an unenrolled node sending enrollment traffic via
this path.
A network operator can set this value to the maximum value allowed,
effectively disable all new enrollment traffic.
1.1. 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.
2. Protocol Definition
The following option is defined to transmission in the DIO issued by
the DODAG root. It may also be added by a router on part of the sub-
tree as a result of some (out of scope for this document) management
function.
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6LRs that see this DIO Option SHOULD increment their minimum
enrollment priority if they observe congestion on the channel used
for join traffic. The exact mechanism is a local decision, and may
be the subject for future work.
A 6LR which would otherwise be willing to act as a Join Proxy, will
examine the minimum priority field, and to that number, add any
additional local consideration (such as upstream congestion).
The Join Priority can only be increased by each each 6LR in value, to
the maximum value of 0x7f.
The resulting priority, if less than 0x7f should enable the Join
Proxy function.
0 1 2
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = TBD01|Opt Length = 1|R| min. priority |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.
Future work like [I-D.ietf-roll-capabilities] will enable collection
of capabilities such as this one in reports to the DODAG root.
2.1. 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.
6LRs that support this option, but whose parent does not send it
SHOULD assume a value of 0x40 as their base value. The nodes then
adjust this base value based upon their observed congestion, emitting
their adjusted DIO value to their children.
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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. * 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 unfortunately, but would be exactly the situation
without this option.
3. 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.
A malicious node (that was 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 behaviour.
Lower minimal priorities would cause downstream nodes to accept more
pledges than the network was expecting, and higher minimal priorities
cause the join process to stall.
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
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rekeying provisions of [I-D.ietf-6tisch-minimal-security] exist to
permit an operator to remove such nodes from the network.
4. Privacy Considerations
There are no new privacy issues caused by this extension.
5. IANA Considerations
Allocate a new number TBD01 from Registry RPL Control Message
Options. This entry should be called Minimum Enrollment Priority.
6. Acknowledgements
This has been reviewed by Pascal Thubert and Thomas Wattenye.
7. References
7.1. Normative References
[I-D.ietf-6tisch-enrollment-enhanced-beacon]
Dujovne, D. and M. Richardson, "IEEE 802.15.4 Information
Element encapsulation of 6TiSCH Join and Enrollment
Information", draft-ietf-6tisch-enrollment-enhanced-
beacon-14 (work in progress), February 2020.
[I-D.ietf-6tisch-minimal-security]
Vucinic, M., Simon, J., Pister, K., and M. Richardson,
"Constrained Join Protocol (CoJP) for 6TiSCH", draft-ietf-
6tisch-minimal-security-15 (work in progress), December
2019.
[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>.
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[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>.
[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>.
7.2. Informative References
[I-D.ietf-6tisch-architecture]
Thubert, P., "An Architecture for IPv6 over the TSCH mode
of IEEE 802.15.4", draft-ietf-6tisch-architecture-28 (work
in progress), October 2019.
[I-D.ietf-6tisch-dtsecurity-secure-join]
Richardson, M., "6tisch Secure Join protocol", draft-ietf-
6tisch-dtsecurity-secure-join-01 (work in progress),
February 2017.
[I-D.ietf-6tisch-terminology]
Palattella, M., Thubert, P., Watteyne, T., and Q. Wang,
"Terms Used in IPv6 over the TSCH mode of IEEE 802.15.4e",
draft-ietf-6tisch-terminology-10 (work in progress), March
2018.
[I-D.ietf-roll-capabilities]
Jadhav, R., Thubert, P., Richardson, M., and R. Sahoo,
"RPL Capabilities", draft-ietf-roll-capabilities-02 (work
in progress), March 2020.
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[RFC8137] Kivinen, T. and P. Kinney, "IEEE 802.15.4 Information
Element for the IETF", RFC 8137, DOI 10.17487/RFC8137, May
2017, <https://www.rfc-editor.org/info/rfc8137>.
[RFC8366] Watsen, K., Richardson, M., Pritikin, M., and T. Eckert,
"A Voucher Artifact for Bootstrapping Protocols",
RFC 8366, DOI 10.17487/RFC8366, May 2018,
<https://www.rfc-editor.org/info/rfc8366>.
Appendix A. Change history
version 00.
Author's Address
Michael Richardson
Sandelman Software Works
Email: mcr+ietf@sandelman.ca
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