Controlling Network Enrollment in RPL networks
draft-ietf-roll-enrollment-priority-18

ROLL Working Group                                         M. Richardson
Internet-Draft                                  Sandelman Software Works
Intended status: Standards Track                            R. A. Jadhav
Expires: 22 January 2027                                     Huawei Tech
                                                              P. Thubert
                                                             Independent
                                                             K. Iwanicki
                                                    University of Warsaw
                                                            21 July 2026

             Controlling Network Enrollment in RPL networks
                 draft-ietf-roll-enrollment-priority-18

Abstract

   The Routing Protocol for Low-Power and Lossy Networks (RPL) manages
   the routing topology but lacks a mechanism to globally regulate how
   many new nodes, known as Pledges, can join a node in a 6TiSCH network
   at any given time.  Currently, Join Proxies (6LowPAN Routers) make
   local decisions about whether to facilitate a Pledge's enrollment
   based only on their immediate resources.

   This document introduces RPL extensions to ensure that enrollment
   remains orderly, prevents localized congestion at specific Join
   Proxies, and allows the network to stay within its operational
   capacity limits.

About This Document

   This note is to be removed before publishing as an RFC.

   Status information for this document may be found at
   https://datatracker.ietf.org/doc/draft-ietf-roll-enrollment-
   priority/.

   Discussion of this document takes place on the roll Working Group
   mailing list (mailto:roll@ietf.org), which is archived at
   https://mailarchive.ietf.org/arch/browse/roll/.  Subscribe at
   https://www.ietf.org/mailman/listinfo/roll/.

   Source for this draft and an issue tracker can be found at
   https://github.com/roll-wg/voucher.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

Richardson, et al.       Expires 22 January 2027                [Page 1]
Internet-Draft                 join-metric                     July 2026

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 22 January 2027.

Copyright Notice

   Copyright (c) 2026 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
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Motivation and Overview . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Protocol Definition . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Option Format . . . . . . . . . . . . . . . . . . . . . .   6
     3.2.  Option Processing . . . . . . . . . . . . . . . . . . . .   7
   4.  Operational Considerations  . . . . . . . . . . . . . . . . .   8
     4.1.  Incremental deployment Considerations . . . . . . . . . .   8
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

Richardson, et al.       Expires 22 January 2027                [Page 2]
Internet-Draft                 join-metric                     July 2026

1.  Introduction

   The adaption of the Time-Slotted Channel Hopping (TSCH) mode of
   [ieee802154] for use in 6TiSCH networks is described in [RFC7554].
   The security and onboarding framework for these networks, described
   in [RFC9031] and [RFC9032], allows a new node, known as a "Pledge",
   to utilize a nearby 6LowPAN Router as a Join Proxy.

   To facilitate discovery, [RFC9032] specifies extensions to the IEEE
   802.15.4 Enhanced Beacon that allow a Join Proxy to announce its
   presence, enabling Pledges to identify and select an appropriate
   entry point into the network.  Currently, Join Proxies make local
   decisions about whether to facilitate a Pledge's enrollment based
   only on their immediate resources.

   This document introduces Routing Protocol for Low-Power and Lossy
   Networks (RPL) extensions to ensure that enrollment remains orderly,
   prevents localized congestion at specific Join Proxies, and allows
   the network to stay within its operational capacity limits.

1.1.  Motivation and Overview

   Not every routing member of a mesh ought to announce itself as a
   _Join Proxy_. The constructed Destination Oriented Directed Acyclic
   Graph (DODAG) can become unbalanced if many nodes join in one part.
   This can be the result of optimization decisions based upon local
   information only.  If nodes could get more information about the
   global view, then they could make different choices that would result
   in more balanced resource usage.

   There are a variety of local metrics which a 6LowPAN Router (6LR)
   [RFC6066] can use to determine if it should provide the _Join Proxy_
   function.  These reasons include low available battery power, already
   high committed network bandwidth, and lack of available free memory
   for Neighbor Cache Entry (NCE) slots [RFC4861], Section 5.1.  An NCE
   is needed in order to maintain communication with the Pledge nodes
   trying to enroll.  See [RFC9898] and [RFC6583] for a deeper analysis
   of NCE exhaustion.

   In addition to the local per-node constraints, if the network around
   a 6LR is congested then adding more nodes to that part of the network
   would make the congestion worse.  The attachment might not even
   succeed if other non-local resources are in short supply.  For
   instance, in storing-mode and mixed [dao-projection] mode LLNs,
   routing table entries at other levels could become exhausted.

Richardson, et al.       Expires 22 January 2027                [Page 3]
Internet-Draft                 join-metric                     July 2026

   Enrollment of new nodes into the DODAG involves having the Join Proxy
   forward traffic from unknown nodes into the DODAG.  These unknown
   nodes are not yet known to be trustworthy, the introduction of a lot
   of traffic from could be part of a denial of service attack.

   This extension includes a mechanism to allow the network operator to
   send a signal that no new nodes are expected at that time, and for
   all join proxy operations to be turned off by forcing the minimum
   enrollment priority to the maximum (worst) value.

   The RPL Destination Information Object (DIO) option described here
   contains new metrics that propagate down the DODAG, informing each
   layer of the conditions in the DODAG above the node.

   This new metric, the minimum enrollment priority, is updated by each
   6LR to reflect conditions in that 6LR.  This metric is only increased
   based upon local conditions, and the new value is sent as within the
   DIO that this node emits.  Additionally, this new metric forms the
   basis for the proxy priority described in [RFC9032].
   Section Section 3.1 explains how these fields affect the Trickle
   Timer.

   The minimum enrollment priority value is derived from multiple
   constraining factors, for instance, the size of the DODAG, the
   occupancy of the bandwidth at the DODAG Root, the memory capacity at
   the Root, or an administrative decision.

   This minimum enrollment priority is used by each 6LR node to
   determine whether or not it will operate as a _Join Proxy_ for nodes
   that want to enroll.  For nodes which are already enrolled, but which
   need to reconnect to a DODAG, the DODAG Size information helps the
   node decide between different DODAGs which might be visible.

   This minimum enrollment priority expresses the ability of RPL DODAG
   globally to accept new joins: lower numerical priority values
   indicate increased ability to accept new child nodes.

   Moreover, when a RPL domain is composed of multiple DODAGs, a node at
   the edge of more than one such DODAG may join any of the DODAGs it
   sees.  It can also use this information to move between DODAGs in
   order to help keep the relative sizes balanced.  For this, the
   approximate knowledge of the size of the DODAGs is also an essential
   metric.  Depending on the network policy, the size of the DODAG may
   or may not affect the minimum enrollment priority.  Therefore, since
   making one proportional to the other would be limiting their value,
   the current size of the DODAG is advertised separately in the new
   option.

Richardson, et al.       Expires 22 January 2027                [Page 4]
Internet-Draft                 join-metric                     July 2026

   Updates to the option propagate through the network according to the
   trickle algorithm.  [RFC6206] Other than the minimum enrollment
   priority value, the contents of the option are generated at the DODAG
   Root, and are not changed.

   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.

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 6LR means 6LowPAN Router, and is defined in [RFC6606].  It
   refers to a router that forwards packets in a 6LowPAN network.

   The terms DAO, DODAG, DODAG root, DIO, trickle timer are from
   [RFC6550].  The lollipop counter function comes from [RFC6550],
   Section 7.2.

   The term (1)"Join" has been used in documents such as [RFC9031] to
   denote the activity of a new node authenticating itself to the
   network 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 authenticated 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 is now called (1)Join in other
   documents, and is called enrollment in this document.  However, the
   term _Join Proxy_ is retained with its (1)"Join" meaning from
   [RFC9031].

3.  Protocol Definition

   This document uses the extensions mechanism specified by [RFC6550].
   As explained in Section 4, no mechanism is needed to enable it.

Richardson, et al.       Expires 22 January 2027                [Page 5]
Internet-Draft                 join-metric                     July 2026

3.1.  Option Format

   The following option is defined for transmission in DIOs issued by
   the DODAG Root to be propagated within the DODAG.

       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 = TBD01  |Opt Length = 3 |Version Number |T| Min Priority|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Exp  |DODAGSz|
      +-+-+-+-+-+-+-+-+

   Type  To be assigned by IANA.

   Version Number  An 8-bit unsigned integer set by the DODAG root and
      denoting the version number of the contents of the option.  The
      version number is interpreted as a lollipop counter (see
      Section 7.2 of [RFC6550]).

   T  A bit indicating whether the particular version of the option is
      important in that adopting its contents should trigger a trickle
      timer [RFC6206], Section 4.2 reset at the node [RFC6550],
      Section 8.3

   Min Priority  The minimum enrollment priority.  This is a 7-bit field
      providing a base value for the Enhanced Beacon Join priority.  A
      value of 0x7f (127) is considered infinity, and this disables the
      _Join Proxy_ function entirely.

   Exp  A 4-bit unsigned integer indicating the power of 2 that defines
      the unit of the DODAG Size, such that (unit = 2^Exp).

   DODAGSz  A 4-bit unsigned integer expressing the size of the DODAG in
      units that depend on the Exp field.

   The DODAG Size is calculated as (DODAGSz * 2^Exp).

   The DODAG Size can be measured by the Root based on the DAO activity.
   In such a case, it represents the number of routes not the number of
   nodes, and can thus be used to infer the load only in a network where
   each node advertises roughly the same number of addresses and
   generates roughly the same amount of traffic.

   As the DODAG Size is always a multiple of a power of 2, when the
   actual size falls between two such values, the DODAG Root is to
   always round up.

Richardson, et al.       Expires 22 January 2027                [Page 6]
Internet-Draft                 join-metric                     July 2026

   In any case, the DODAG Size may slightly change between one DIO and
   the next, so the value transmitted is considered as an approximation.

   A 6LR node uses the contents of this option from whichever parent it
   selects as the basis for the option that it sends.  When that parent
   increments its minimum enrollment priority above the previous value
   that was seen, then this MUST be considered an "inconsistent" value
   for the purposes of the trickle timer.  A parent that decrements its
   minimum enrollment priority to a lower value MAY be considered
   "inconsistent", or a node MAY wait re-transmit according to the
   trickle timer's redundancy constant.  This is consistent with
   paragraph one of [RFC6550], Section 8.3, which considers lower Rank
   to be consistent.

3.2.  Option Processing

   The contents of the option MUST be generated by the DODAG Root.  A
   6LR MAY change only the Version Number (in lollipop fashion), and MAY
   increment the Min Priority, if it is less than 0x7f.

   Whenever the DODAG root changes the values of the minimum enrollment
   priority or DODAG Size in the option, it MUST also increment the
   value of Version Number.  Moreover, if the change is considered
   important (i.e., it is expected to propagate in the DODAG quickly),
   the DODAG Root MUST also set the T bit to 1; otherwise, it MUST set
   the bit to 0.

   Upon receiving the option, a 6LR first checks the value of the
   Version Number field in the option, _vr_, versus the value of the
   Version Number it has last adopted locally, _vl_.

   *  If _vl_ is greater than _vr_ (in the lollipop counter order), then
      the 6LR MUST ignore the received option.

   *  Otherwise, the 6LR MUST adopt the contents of the option (i.e.,
      the values of Version Number, Min Priority, DODAG Size, and the T
      bit) as its local ones.  Moreover, if _vl_ was smaller than _vr_
      (in the lollipop counter order) and the T bit in the received
      option was set, then the 6LR MUST reset its DIO trickle timer.

   A 6LR, which would otherwise be willing to act as a _Join Proxy_,
   will examine the locally adopted value of minimum enrollment priority
   and to that number add any additional local consideration (such as
   upstream congestion, number of NCE slots available, etc.).

   The maximum resulting value any 6LR can obtain this way is 0x7f.

Richardson, et al.       Expires 22 January 2027                [Page 7]
Internet-Draft                 join-metric                     July 2026

   The resulting minimum enrollment priority, if less than 0x7f, should
   enable the _Join Proxy_ function.

   Note that the calculated local value _vl_ does _not_ update the value
   _vr_ in the option.

4.  Operational Considerations

   The RPL ecosystem has not included a management protocols to date.  A
   future mechanisms, such as [I-D.ietf-roll-capabilities] could enable
   assessment and configuration of node features.  If/when such a thing
   became available, a node would still need to be connected before it
   configuration parameters could be adjusted.  Until such a mechanism
   becomes available, the only way an operator can change any defaults
   in the node is via a custom firmware load, or a vendor proprietary
   mechanism.  For instance, a vendor might do this via custom
   programming of a configuration section in memory using some kind of
   cable.  This kind of per-node tuning is very expensive to do, and
   runs counter to the goals of zero-touch mechanisms.

   RPL nodes therefore need to come with sensible defaults that allow a
   node to join a DODAG.  Many current deployments have been single
   vendor with consistent features and well-tested defaults.  However,
   even within such an environment, incremental deployment of firmware
   updates might still cause feature skew among nodes.

   Intermediate nodes in a DODAG might not be upgraded at the same time
   as nodes further down the leaf, and therefore might not support this
   new metric container.

   It is therefore necessary to consider how the lack of this metric
   container can be compensated for nodes further away from the root.

4.1.  Incremental deployment Considerations

   A 6LR that did not support this option would not act on it or
   propagate it in its DIO messages.  In effect, the 6LR's sub-tree
   below a node without support for this option could not receive any
   information about the DODAG size or minimum enrollment priority.  In
   the absence of of this metric, a 6LR will need to base decisions on
   how to act based upon information about local resources only.

   This document therefore establishes that a 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.  This half-way value has been chosen to allow for the best
   reaction.

Richardson, et al.       Expires 22 January 2027                [Page 8]
Internet-Draft                 join-metric                     July 2026

   A 6LR downstream of a 6LR where there was such an interruption in the
   metric could err in two directions:

   *  If the value implied by the base value of 0x40 was too low, then
      the 6LR might continue to attract enrollment traffic when none
      should have been collected.  This is a stressor for the network,
      but the similar behaviour would occur if no option existed.

   *  If the value implied by the base value of 0x40 was too high, then
      the 6LR might deflect enrollment traffic to other parts of the
      DODAG, possibly refusing any enrollment traffic at all.

   In order for this to happen, some significant congestion must exist
   in the sub-DODAG 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-DODAG of the DODAG simply winds up being more
   cautious than it needed to be.

   There is an additional possibility of having more than one
   interruption of information if multiple nodes in the DODAG were
   lacking a firmware update to enable this option.  Such alternation of
   the above two situations might introduce some pathology of cycles of
   accepting and then rejecting enrollment traffic: This is something an
   operator should consider if they incrementally deploy this option to
   an existing Low-power/Lossy-Network (LLN).

   In addition, due to these interruptions, an operator would be unable
   to turn off enrollment traffic by sending a maximum value enrollment
   priority to the sub-DODAG.  This situation is unfortunate, but
   without this option, the situation would occur all over the DODAG,
   rather than just in the sub-DODAG that the option did not reach.  So
   this problem is not a new problem.

5.  Security Considerations

   As per [RFC7416], RPL control frames either run over a secured layer
   2 or use the [RFC6550] Secure DIO methods at layer 3.  This option
   can be placed into either a "clear" (layer-2 secured) DIO or a
   layer-3 Secure DIO.

   In most deployments involving wireless technology, layer 2 is always
   encrypted using a layer-2 specific technology, and so privacy of this
   option is available.

Richardson, et al.       Expires 22 January 2027                [Page 9]
Internet-Draft                 join-metric                     July 2026

   However, a malicious node that was part of the RPL control plane
   (i.e., had been enrolled into the layer-2 security) would be able to
   see the values of this option and, based upon the observed minimal
   enrollment priority, could signal a confederate that it was a good
   time to send malicious join traffic.

   What is more, such 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; higher minimal priorities could cause the enrollment
   process to stall.

   The use of layer-2 or layer-3 security for RPL control messages
   prevents the two aforementioned attacks by non-participating nodes by
   preventing malicious nodes from becoming part of the control plane.

   Nevertheless, 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 re-keying provisions
   of [RFC9031] exist to permit an operator to remove such nodes from
   the network.

6.  IANA Considerations

   Please allocate a new entry, TBD01 from Registry RPL Control Message
   Options at https://www.iana.org/assignments/rpl/rpl.xhtml#control-
   message-options

   This entry should be called Minimum Enrollment Priority, and the
   reference should be to this document.

7.  Acknowledgements

   This has been reviewed by Charlie Perkins, Rifaat Shehk-Yusek, Dave
   Thaler, and Thomas Watteyne.

   Huimin She contributed text about expressing the DODAG size.  Ketan
   Talaulika was the responsible AD and provided many editorial
   improvements.

8.  References

8.1.  Normative References

Richardson, et al.       Expires 22 January 2027               [Page 10]
Internet-Draft                 join-metric                     July 2026

   [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/rfc/rfc2119>.

   [RFC6206]  Levis, P., Clausen, T., Hui, J., Gnawali, O., and J. Ko,
              "The Trickle Algorithm", RFC 6206, DOI 10.17487/RFC6206,
              March 2011, <https://www.rfc-editor.org/rfc/rfc6206>.

   [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/rfc/rfc6550>.

   [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/rfc/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/rfc/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/rfc/rfc9032>.

8.2.  Informative References

   [dao-projection]
              Thubert, P., Jadhav, R., and M. Richardson, "Root-
              initiated Routing State in RPL", Work in Progress,
              Internet-Draft, draft-ietf-roll-dao-projection-40, 11
              March 2025, <https://datatracker.ietf.org/doc/html/draft-
              ietf-roll-dao-projection-40>.

Richardson, et al.       Expires 22 January 2027               [Page 11]
Internet-Draft                 join-metric                     July 2026

   [I-D.ietf-roll-capabilities]
              Jadhav, R., Thubert, P., Richardson, M., and R. N. Sahoo,
              "RPL Capabilities", Work in Progress, Internet-Draft,
              draft-ietf-roll-capabilities-09, 9 November 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-roll-
              capabilities-09>.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              DOI 10.17487/RFC4861, September 2007,
              <https://www.rfc-editor.org/rfc/rfc4861>.

   [RFC6066]  Eastlake 3rd, D., "Transport Layer Security (TLS)
              Extensions: Extension Definitions", RFC 6066,
              DOI 10.17487/RFC6066, January 2011,
              <https://www.rfc-editor.org/rfc/rfc6066>.

   [RFC6583]  Gashinsky, I., Jaeggli, J., and W. Kumari, "Operational
              Neighbor Discovery Problems", RFC 6583,
              DOI 10.17487/RFC6583, March 2012,
              <https://www.rfc-editor.org/rfc/rfc6583>.

   [RFC6606]  Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem
              Statement and Requirements for IPv6 over Low-Power
              Wireless Personal Area Network (6LoWPAN) Routing",
              RFC 6606, DOI 10.17487/RFC6606, May 2012,
              <https://www.rfc-editor.org/rfc/rfc6606>.

   [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/rfc/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/rfc/rfc7554>.

   [RFC9898]  Xiao, X., Vasilenko, E., Metz, E., Mishra, G., and N.
              Buraglio, "Neighbor Discovery Considerations in IPv6
              Deployments", RFC 9898, DOI 10.17487/RFC9898, November
              2025, <https://www.rfc-editor.org/rfc/rfc9898>.

Authors' Addresses

Richardson, et al.       Expires 22 January 2027               [Page 12]
Internet-Draft                 join-metric                     July 2026

   Michael Richardson
   Sandelman Software Works
   Email: mcr+ietf@sandelman.ca

   Rahul Arvind Jadhav
   Huawei Tech
   Email: rahul.ietf@gmail.com

   Pascal Thubert
   Independent
   Email: pascal.thubert@gmail.com

   Konrad Iwanicki
   University of Warsaw
   Email: iwanicki@mimuw.edu.pl

Richardson, et al.       Expires 22 January 2027               [Page 13]