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


   [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

Status of This Memo

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   This Internet-Draft will expire on October 27, 2020.

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   the Trust Legal Provisions and are provided without warranty as
   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",
   "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

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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

              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.

              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

              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.,

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

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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,

   [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,

   [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,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

7.2.  Informative References

              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.

              Richardson, M., "6tisch Secure Join protocol", draft-ietf-
              6tisch-dtsecurity-secure-join-01 (work in progress),
              February 2017.

              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

              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, <>.

   [RFC8366]  Watsen, K., Richardson, M., Pritikin, M., and T. Eckert,
              "A Voucher Artifact for Bootstrapping Protocols",
              RFC 8366, DOI 10.17487/RFC8366, May 2018,

Appendix A.  Change history

   version 00.

Author's Address

   Michael Richardson
   Sandelman Software Works


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