



Internet Engineering Task Force (IETF)                   P. Thubert, Ed.
Request for Comments: 9926                                 February 2026
Updates: 4861, 6550, 8505, 8928, 9010                                   
Category: Standards Track                                               
ISSN: 2070-1721


            Prefix Registration for IPv6 Neighbor Discovery

Abstract

   This document updates IPv6 Neighbor Discovery (RFC 4861) and IPv6
   Subnet Neighbor Discovery (RFC 8505, RFC 8928) to enable a node that
   owns or is directly connected to a prefix to register that prefix to
   neighbor routers.  The registration indicates that the registered
   prefix can be reached via the advertising node without a loop.  The
   unicast prefix registration allows the node to request one or more
   neighbor routers to redistribute the prefix in another routing domain
   regardless of the routing protocol used in that domain.  This
   document updates the Routing Protocol for Low-Power and Lossy
   Networks (RPL), as specified in RFCs 6550 and 9010, to enable a
   6LoWPAN Router (6LR) to inject the registered prefix in RPL.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9926.

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
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   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
   2.  Terminology
     2.1.  Requirements Language
     2.2.  Inherited Terms and Concepts
     2.3.  Acronyms and Initialisms
     2.4.  New Terms
   3.  Overview
   4.  Updating RFC 4861
   5.  Updating RFC 7400
   6.  Updating RFC 6550
   7.  Updating RFC 8505
     7.1.  New P-Field Value
     7.2.  New EARO Prefix Length Field and F flag
     7.3.  New EDAR Prefix Length Field
     7.4.  Updating the Registration Operation
   8.  Updating RFC 9010
   9.  Updating RFC 8928
   10. Updating RFC 8929
   11. Security Considerations
   12. Operational Considerations
     12.1.  Partially Upgraded Networks
     12.2.  Application to RPL-Based Route-Over LLNs
     12.3.  Application to a Shared Link
     12.4.  Application to a Hub Link with Stub Spokes
   13. IANA Considerations
     13.1.  Updated P-Field Registry
     13.2.  New 6LoWPAN Capability Bit
   14. Normative References
   15. Informative References
   Acknowledgments
   Author's Address

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.  Other design constraints (such as a limited memory capacity,
   duty cycling of the LLN devices, and low-power lossy transmissions)
   derive from that primary concern.  The radio (both transmitting or
   simply listening) is a major energy drain, and the LLN protocols must
   be adapted to allow the nodes to remain sleeping with the radio
   turned off at most times.

   Examples of LLNs include hub-and-spoke access links such as (Low-
   Power) Wi-Fi [IEEE80211] and Bluetooth (Low Energy) [IEEE802151],
   Mesh-Under networks where the routing operation is handled at Layer 2
   (L2), and route-over networks such as the Wi-SUN [WI-SUN] and 6TiSCH
   [RFC9030] mesh networks, which leverage 6LoWPAN [RFC4919] [RFC6282]
   and RPL [RFC6550] over [IEEE802154].

   LLNs and constrained devices are the original domain of application
   for 6LoWPAN protocols.  It is thus a foremost concern, when designing
   those protocols, to minimize energy spendings.  In non-LLN
   environments where lowering carbon emissions is also a priority, it
   could make sense to apply the 6LoWPAN designs and extend some of the
   6LoWPAN protocols.  The general design points include:

   *  Placing the protocol complexity in the less-constrained routers to
      simplify the host implementation and avoid expanding the control
      traffic to all nodes.

   *  Using host-triggered operations to enable transient disconnections
      with the routers, e.g., to conserve power (sleep), but also to
      cope with inconsistent connectivity.

   These points translate into:

   *  Stateful proactively built knowledge in the routers that is
      available at any point of time.

   *  Unicast host-to-router operations triggered by the host and its
      applications.

   *  Minimal use of asynchronous L2 broadcast operations that would
      keep the host awake and listening with no application-level need
      to do so.

   "RPL: IPv6 Routing Protocol for Low-Power and Lossy Networks"
   [RFC6550] provides IPv6 [RFC8200] routing services within such
   constraints.  To save signaling and routing state in constrained
   networks, the RPL routing is only performed along a Destination-
   Oriented Directed Acyclic Graph (DODAG) that is optimized to reach a
   Root node, as opposed to along the shortest path between two peers,
   whatever that would mean in each LLN.

   The classical Neighbor Discovery Protocol (NDP) [RFC4861] [RFC4862]
   was defined for serial links and shared transit media such as
   Ethernet at a time when L2 broadcast was cheap on those media, while
   memory for neighbor cache was expensive.  Thus, it was designed as a
   reactive protocol that relies on caching and multicast operations for
   the Duplicate Address Detection (DAD) and Address Resolution (AR),
   aka address discovery or address lookup, of IPv6 unicast addresses.
   Those multicast operations typically impact every node on-link when
   at most one is really targeted, which is a waste of energy, and imply
   that all nodes are awake to hear the request, which is inconsistent
   with power-saving (sleeping) modes.

   "Architecture and Framework for IPv6 over Non-Broadcast Access"
   [IPv6-over-NBMA] introduces an evolution of IPv6 ND towards a
   proactive AR method.  Because the IPv6 model for NBMA depends on a
   routing protocol to reach inside the subnet, the IPv6 ND extension
   for NBMA is referred to as Subnet Neighbor Discovery (SND).  SND is
   based on work done in the context of Internet of Things (IoT), known
   as 6LoWPAN ND.  As opposed to the classical IPv6 ND protocol, this
   evolution follows the energy conservation principles discussed above:

   *  The original 6LoWPAN ND, "Neighbor Discovery Optimization for IPv6
      over Low-Power Wireless Personal Area Networks (6LoWPANs)"
      [RFC6775], was introduced to avoid the excessive use of multicast
      messages and enable IPv6 ND for operations over energy-constrained
      nodes.  [RFC6775] changes the classical IPv6 ND model to
      proactively establish the Neighbor Cache Entry (NCE) associated to
      the unicast address of a 6LoWPAN Node (6LN) in the one or more
      6LoWPAN Routers (6LRs) that serve it.  To that effect, [RFC6775]
      defines a new Address Registration Option (ARO) that is placed in
      unicast Neighbor Solicitation (NS) and Neighbor Advertisement (NA)
      messages between the 6LN and the 6LRs.

   *  "Registration Extensions for IPv6 over Low-Power Wireless Personal
      Area Network (6LoWPAN) Neighbor Discovery>" [RFC8505] updates
      [RFC6775] into a generic Address Registration mechanism and is the
      foundation for Subnet Neighbor Discovery (SND).  SND introduces
      the Extended Address Registration Option (EARO) to enable the
      registering node to access services such as routing inside a
      subnet and ND proxy operations [RFC8929].  This provides a
      routing-protocol-agnostic method for a host to request that the
      router inject a unicast IPv6 address in the local routing protocol
      and provide return reachability for that address.

   *  "Listener Subscription for IPv6 Neighbor Discovery Multicast and
      Anycast Addresses" [RFC9685] updates [RFC8505] to enable a
      listener to subscribe to an IPv6 anycast or multicast address; the
      document also updates [RFC9010] to enable a 6LR to inject the
      anycast and multicast addresses in RPL.  Similarly, this
      specification updates [RFC8505] and [RFC9010] to add the
      capability for a 6LN to register unicast prefixes up to 120 bits
      long, as opposed to addresses, and to signal in a routing-
      protocol-independent fashion to a 6LR that it is expected to
      redistribute the prefixes.

   This specification updates the above registration and subscription
   methods to enable a node to register a unicast prefix to the routing
   system and get it injected in the routing protocol.  As with
   [RFC8505], the prefix registration is agnostic to the routing
   protocol in which the router injects the prefix, and the router is
   agnostic to the method that was used to allocate the prefix to the
   node.  The energy conservation principles in [RFC8505] are retained
   as well, meaning that the node does not have to send or expect
   asynchronous multicast messages.

   Please note that an energy-conserving node is not necessarily a
   router, so even when a node is advertising a prefix, it is a design
   choice not to use Router Advertisement (RA) messages that would make
   the node appear as a router to peer nodes.  From the design
   principles above, it is clearly a design choice not to leverage (1)
   broadcasts from or to the node or (2) complex state machines in the
   node.  It is also a design choice to use and extend the EARO as
   opposed to the Route Information Option (RIO) [RFC4191] because the
   RIO is not intended to inject routes in routing, and is lacking
   related control information like the R bit in the EARO.
   Additionally, an RA with RIO cannot be trusted for a safe injection
   in the routing protocol for the lack of the equivalent of the
   Registration Ownership Verifier (ROVR) [RFC8928] in the EARO.

2.  Terminology

2.1.  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.

2.2.  Inherited Terms and Concepts

   This document uses terms and concepts that are discussed in:

   *  "Neighbor Discovery for IP version 6 (IPv6)" [RFC4861] and

   *  "IPv6 Stateless Address Autoconfiguration" [RFC4862] for the
      Neighbor Solicitation operation,

   *  "Neighbor Discovery Optimization for IPv6 over Low-Power Wireless
      Personal Area Networks (6LoWPANs)" [RFC6775], as well as

   *  "Registration Extensions for IPv6 over Low-Power Wireless Personal
      Area Network (6LoWPAN) Neighbor Discovery" [RFC8505], and

   *  "RPL: IPv6 Routing Protocol for Low-Power and Lossy Networks"
      [RFC6550] for RPL, which is the routing protocol used in LLNs for
      SND.

2.3.  Acronyms and Initialisms

   This document uses the following abbreviations:

   6CIO:       6LoWPAN Capability Indication Option [RFC7400]
   6LBR:       6LoWPAN Border Router [RFC6775]
   6LN:        6LoWPAN Node [RFC6775]
   6LR:        6LoWPAN Router [RFC6775]
   ARO:        Address Registration Option [RFC6775]
   DAD:        Duplicate Address Detection [RFC4861]
   DAO:        Destination Advertisement Object [RFC6550]
   DODAG:      Destination-Oriented Directed Acyclic Graph
   EARO:       Extended Address Registration Option [RFC8505]
   EDAC:       Extended Duplicate Address Confirmation [RFC8505]
   EDAR:       Extended Duplicate Address Request [RFC8505]
   ESS:        Extended Service Set [IEEE80211]
   IPAM:       IP Address Management
   LLN:        Low-Power and Lossy Network
   LLA:        Link-Layer Address
   LoWPAN:     Low-Power Wireless Personal Area Network
   LR-WPAN:    Low-Rate Wireless Personal Area Network [IEEE802154]
   MAC:        Medium Access Control
   NA:         Neighbor Advertisement (message) [RFC4861]
   NBMA:       Non-Broadcast Multi-Access (full mesh)
   NCE:        Neighbor Cache Entry [RFC4861]
   ND:         Neighbor Discovery (protocol)
   NDP:        Neighbor Discovery Protocol
   NS:         Neighbor Solicitation (message) [RFC4861]
   ROVR:       Registration Ownership Verifier (pronounced "rover")
               [RFC8505]
   RPL:        IPv6 Routing Protocol for LLNs (pronounced "ripple")
               [RFC6550]
   RA:         Router Advertisement (message) [RFC4861]
   RS:         Router Solicitation (message) [RFC4861]
   RTO:        RPL Target Option [RFC6550]
   SLLAO:      Source Link-Layer Address Option [RFC4861]
   SND:        Subnet Neighbor Discovery (protocol)
   TID:        Transaction ID [RFC8505]
   TIO:        Transit Information Option [RFC6550]
   TLLAO:      Target Link-Layer Address Option [RFC4861]

2.4.  New Terms

   This document introduces the following term:

   Origin:  The node that issued the prefix advertisement, either in the
          form of a NS(EARO) or as a DAO(TIO, RTO)

3.  Overview

   This specification inherits from [RFC6550], [RFC8505], and [RFC9010]
   to register prefixes as opposed to addresses.

   The IPv6 ND operation is agnostic to the routing protocol used in the
   SND.  Route-over LLNs typically leverage RPL.  A RPL-based SND
   deployment consists of:

   *  one or more 6LBRs that act as RPL Root,

   *  intermediate routers down the RPL graph that propagate routing
      information on addresses and prefixes towards the Root,

   *  6LRs that are RPL-aware 6LNs and can leverage RPL directly to
      expose their addresses and prefixes, and

   *  6LNs that are the RPL-unaware destinations and need SND to obtain
      reachability over the RPL LLN for their addresses and, with this
      specification, their prefixes as well.

   The SND operation for prefixes inherits from that for unicast
   addresses, meaning that it is the same unless specified otherwise
   herein.  In particular, forwarding a packet happens as specified in
   Section 11 of [RFC6550], including loop avoidance and detection.
   However, in the case of multicast, multiple copies might be
   generated.

   [RFC8505] is a prerequisite to this specification.  A node that
   implements this MUST also implement [RFC8505].  This specification
   does not introduce a new option; it modifies existing options and
   updates the associated behaviors to enable the registration for
   prefixes as an extension to [RFC8505].

   This specification updates the P-Field introduced in [RFC9685] for
   use in EARO, DAR, and RTO, with the new value of 3 to indicate the
   registration of a prefix, as detailed in Section 7.2.  With this
   extension, the 6LN can now express its willingness to receive the
   traffic for all addresses in the range of a prefix, using the P-Field
   value of 3 in the EARO to signal that the registration is for such
   prefix.  Multiple 6LNs acting as border routers to the same external
   network or as access routers to the same subnet may register the same
   prefix to the same 6LR or to different 6LRs.

   If the R flag is set in the registration of one or more 6LNs for the
   same prefix, then, according to its redistribution policy, the 6LR
   MUST redistribute the prefix in the routing protocol(s) (e.g., RPL)
   that it participates in.  The duration of the redistribution is based
   on the longest registration lifetime across the non-expired received
   registrations for the prefix.`

   Examples of use cases where this specification may apply include
   virtual links, shared links, and hub links as shown in Sections 12.3
   and 12.4, respectively.  More generally, the 6LN may be a router
   running a different routing protocol in an external network, e.g., a
   stub network, and acting as a border router.  Using the prefix
   registration method enables decoupling the routing protocol in the
   6LN from the routing protocol that the 6LRs run in the main LLN and
   provide signaling to stimulate the redistribution.

4.  Updating RFC 4861

   [RFC4861] expects that the NS/NA exchange is for a unicast address,
   which is indicated in the Target Address field of the ND message.
   Section 5.5 of [RFC8505] extends [RFC4861] to signal the Registered
   Address in the Target Address field.

   This specification updates [RFC4861] by allowing a 6LN to advertise a
   prefix in the Target Address field when the NS or NA message is used
   for a registration, per Section 5.5 of [RFC8505].  In that case, the
   prefix length MUST be indicated in the EARO of the NS message,
   overloading the field that is used in the NA response for the Status.

   If the 6LN owns at least one IPv6 address that is derived from the
   registered prefix with a non-zero interface ID, then it MUST indicate
   one of these addresses in full in the Target Address field of the
   NS(EARO) message.  Else, it MUST indicate the prefix padded with
   zeros in the Target Address field.

5.  Updating RFC 7400

   This specification updates "6LoWPAN-GHC: Generic Header Compression
   for IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs)"
   [RFC7400] by defining a new capability bit for use in the 6CIO.
   [RFC7400] was already extended by [RFC8505] for use in IPv6 ND
   messages.

   The new "Registration for prefixes supported" (F) flag indicates to
   the 6LN that the 6LR (1) accepts IPv6 prefix registrations as
   specified in this document, (2) will ensure that packets for the
   addresses that match this prefix will be routed to the 6LNs that
   registered the prefix, and (3) will ensure that the route to the
   prefix will be redistributed if the R flag is set to 1.

   Figure 1 illustrates the F flag in its position (16, counting 0 to 47
   in network order in the 48-bit array).

    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      |   Length = 1  | Experimental  |X|A|D|L|B|P|E|G|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |F|                         Reserved                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 1: New Capability Bit in the 6CIO

   New Option Field:

   F:  1-bit flag, set to 1 to indicate "Registration for prefixes
      supported"

6.  Updating RFC 6550

   [RFC6550] uses the Path Sequence in the Transit Information Option
   (TIO) to retain only the freshest unicast route and remove stale
   ones, e.g., in the case of mobility.  [RFC9010] copies the TID from
   the EARO into the Path Sequence, and the ROVR field into the
   associated RPL Target Option (RTO).  This way, it is possible to
   identify both the registering node and the order of registration in
   RPL for each individual advertisement, so the most recent path and
   lifetime values are used.

   [RFC9685] requires the use of the ROVR field as the indication of the
   origin of a Target advertisement in the RPL DAO messages, as
   specified in Section 6.1 of [RFC9010].  For anycast and multicast
   advertisements (in NS or DAO messages), multiple origins may
   subscribe to the same address, in which case the multiple
   advertisements from the different or unknown origins are merged by
   the common parent.  In that case, the common parent becomes the
   origin of the merged advertisements and uses its own ROVR value.  On
   the other hand, a parent that propagates an advertisement from a
   single origin uses the original ROVR in the propagated RTO, as it
   does for unicast address advertisements, so the origin is recognized
   across multiple hops.

   This specification updates [RFC6550] to require that, for prefix
   routes, the Path Sequence is used between and only between
   advertisements for the same Target and from the same origin (i.e.,
   with the same ROVR value); in that case, only the freshest
   advertisement is retained.  However, the freshness comparison cannot
   apply if the origin is not determined (i.e., the origin did not
   support this specification).

   [RFC6550] uses the Path Lifetime in the TIO to indicate the remaining
   time for which the advertisement is valid for unicast route
   determination, and a Path Lifetime value of 0 invalidates that route.
   [RFC9010] maps the Address Registration lifetime in the EARO and the
   Path Lifetime in the TIO so they are comparable when both forms of
   advertisements are received.

   The RPL router that merges multiple advertisements for the same
   prefix MUST use and advertise the longest remaining lifetime across
   all the origins of the advertisements for that prefix.  When the
   lifetime expires, the router sends a no-path DAO message (i.e., the
   lifetime is 0) using the same value for the ROVR value as for the
   previous advertisements.  This value refers to either the single
   descendant that advertised the Target if there is only one or the
   router itself if there is more than one.

   Note that the Registration Lifetime, TID, and ROVR fields are also
   placed in the EDAR message, so the state created by EDAR is also
   comparable with that created upon an NS(EARO) or a DAO message.  For
   simplicity, the text below mentions only NS(EARO) but it also applies
   to EDAR.

7.  Updating RFC 8505

   This specification updates the EARO and EDAR messages to enable the
   registration of prefixes and updates the registration operation in
   the case of a prefix, in particular from the standpoint of the 6LR,
   e.g., to enable the registration of overlapping prefixes.

7.1.  New P-Field Value

   [RFC9685] defines a 2-bit P-Field with values 0 through 2 and
   reserves the value 3 for future use.  This specification defines the
   semantics of P-Field value 3.

   When the P-Field is set to 3, it indicates that the Registered
   Address represents a prefix rather than a single address.  Upon
   receiving an NS(EARO) message with the P-Field set to 3, the receiver
   MUST install a route to the indicated prefix via the source address
   of the NS(EARO) message.

   This specification assigns the value 3 to the P-Field, resulting in
   the following complete set of defined values:

             +=======+======================================+
             | Value | Meaning                              |
             +=======+======================================+
             | 0     | Registration for a Unicast Address   |
             +-------+--------------------------------------+
             | 1     | Registration for a Multicast Address |
             +-------+--------------------------------------+
             | 2     | Registration for an Anycast Address  |
             +-------+--------------------------------------+
             | 3     | Registration for a Unicast Prefix    |
             +-------+--------------------------------------+

                         Table 1: P-Field Values

7.2.  New EARO Prefix Length Field and F flag

   Section 4.1 of [RFC8505] defines the EARO as an extension to the ARO
   option defined in [RFC6775].

   The Status field is used only when the EARO is placed in an NA
   message.  This specification repurposes that field to carry the
   prefix length when the EARO is placed in an NS message as illustrated
   in Figure 2.  The prefix length is expressed as 7 bits, and the most
   significant bit of the field is reserved.  A 7-bit value of 0 is
   understood as a truncated 128, meaning that this registration is for
   an address as opposed to a prefix.  This approach is backward
   compatible with [RFC8505] and spans both addresses and prefixes.

   This specification adds a new F flag to signal that the Registered
   Prefix is topologically correct through the Registering Node.  This
   means that the Registering Node relays packets that are sourced in
   the Registered Prefix to the outside, in accordance with "Network
   Ingress Filtering: Defeating Denial of Service Attacks which employ
   IP Source Address Spoofing" [BCP38].  The receiver forwards packets
   to the Registering Node address when the source address of the
   packets derives from the Registered Prefix.  Note that to avoid
   loops, the receiver must be in the inside so packets sent by the
   sender towards the outside may never reach the receiver.  The notion
   of "inside" and "outside" are administratively defined, e.g.,
   "inside" is a particular L2 network such as an Ethernet fabric.

   When the F flag is not set, the Registering Node owns the prefix and
   will deliver packets to the destination if the destination address
   derives from the prefix.  Conversely, if the F flag is set, the
   Registering Node will forward traffic whose source address derives
   from the Registered Prefix into a network location (e.g., to an ISP
   Provider Edge) where this source address is topologically correct
   (e.g., derives from a prefix assigned by that ISP).  The F flag is
   encoded in the most significant bit of the EARO Status field when the
   Status field is used to transport a Prefix Length as shown in
   Figure 2.

      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      |     Length    |F|Prefix Length|    Opaque     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |r|C| P | I |R|T|     TID       |     Registration Lifetime     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
    ...                            ROVR                             ...
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 2: EARO Format for Use in NS Messages

   New and updated Option Fields:

   F: (Forwarding Flag)  A 1-bit flag.  When set to 1, it indicates that
      the sender expects other routers to forward packets to the sender
      when those packets are sourced from within the registered prefix.

   Prefix Length:  A 7-bit unsigned integer.  When the P-Field is set to
      3 and the EARO is included in an NS message, this field MUST
      contain a prefix length expressed in bits, with a value in the
      inclusive range of 16 to 120.  When the EARO is included in an NA
      message, this field MUST carry a status value, regardless of the
      setting of the P-Field.  In all other cases, this field is
      reserved; it MUST be set to zero by the sender and MUST be ignored
      by the receiver.

   r (reserved):  A 1-bit reserved field.  It MUST be set to zero by the
      sender and MUST be ignored by the receiver.

7.3.  New EDAR Prefix Length Field

   This specification adds the new value of 3 to the P-Field to signal
   that the Registered Address is a prefix.  When that is the case, the
   prefix is assumed to be at most 120 bits long, padded with zeros up
   to 120 bits, and the remaining byte is dedicated to one reserved bit
   and the Prefix Length.

   Figure 3 illustrates the EDAR message when the value of the P-Field
   is 3.  Figure 4 shows the response EDAC message, with the Status
   field and the echoed Prefix.

      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      |CodePfx|CodeSfx|          Checksum             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |P=3| Reserved  |     TID       |     Registration Lifetime     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
    ...                          ROVR                               ...
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     +                           Prefix                              +
     |                                                               |
     +              (up to 120 bits, padded with zeros)              +
     |                                                               |
     +                                               +-+-+-+-+-+-+-+-+
     |                                               |r|Prefix Length|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Options ...
     +-+-+-+-+-+-+-+-+-+-+-+-

                 Figure 3: EDAR Message Format with P == 3

      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      |CodePfx|CodeSfx|          Checksum             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Status     |     TID       |     Registration Lifetime     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
    ...                          ROVR                               ...
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     +                           Prefix                              +
     |                                                               |
     +              (up to 120 bits, padded with zeros)              +
     |                                                               |
     +                                               +-+-+-+-+-+-+-+-+
     |                                               |r|Prefix Length|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Options ...
     +-+-+-+-+-+-+-+-+-+-+-+-

                       Figure 4: EDAC Message Format

   New and updated EDAR/EDAC Message Fields:

   Prefix:  A 15-byte field that carries up to 120 bits of the prefix.
      If the prefix is shorter than 120 bits, the remaining bits MUST be
      padded with zeros.  The receiver MUST treat the padding as zeroed
      and MUST overwrite any unused bits with zeros before using the
      prefix.

   r (reserved):  A 1-bit reserved field.  It MUST be set to zero by the
      sender and MUST be ignored by the receiver.

   Prefix Length:  A 7-bit unsigned integer indicating the length of the
      prefix in bits.  The value MUST be in the inclusive range of 16 to
      120.

   The capability to place the P-Field and the contiguous "Reserved"
   field in the EDAR message is specified in Section 7.2 of [RFC9685].

   The capability to append ND options to the EDAR and EDAC messages is
   introduced in Section 3.1 of [RFC8929].

   All other fields follow the same definition as specified in
   [RFC8505].  The values for these fields and RFC references are
   maintained by IANA under the "Internet Control Message Protocol
   version 6 (ICMPv6) Parameters" [IANA.ICMP] registry group.

7.4.  Updating the Registration Operation

   With [RFC8505]:

   *  A router that expects to reboot may send a final RA message, upon
      which nodes should register elsewhere or redo the registration to
      the same router upon reboot.  In all other cases, a node reboot is
      silent.  When the node comes back to life, existing registration
      state might be lost if it was not safely stored, e.g., in
      persistent memory.

   *  Only unicast addresses can be registered.

   *  The 6LN must register all its Unique Local Addresses (ULAs) and
      Global Unicast Addresses (GUAs) with a NS(EARO).

   *  The 6LN may set the R flag in the EARO to obtain return
      reachability services from the 6LR, e.g., through ND proxy
      operations or by injecting the route in a route-over subnet.

   *  The 6LR maintains a registration state per Registered Address,
      including an NCE with the Link Layer Address (LLA) of the
      Registered Node (the 6LN here).

   The operation for registering prefixes is similar to that for
   addresses from the perspective of the 6LN, but shows important
   differences on the router side, which maintains a separate state for
   each origin and merges them in its own advertisements.  This
   specification adds the following behavior, similar to that introduced
   by [RFC9685] for multicast addresses:

   *  The EARO status indicating a "Registration Refresh Request"
      applies to prefixes as well.

      This status is used in asynchronous NA(EARO) messages to indicate
      to peer 6LNs that they are requested to reregister all addresses
      and prefixes that were previously registered to the originating
      node.  The NA message MAY be sent to a unicast or a multicast
      link-scope address and SHOULD be contained within the L2 range
      where nodes may effectively have registered/subscribed to this
      router, e.g., a radio broadcast domain to preserve energy and
      spectrum.

      A device that wishes to refresh its state, e.g., upon reboot if it
      may have lost some registration state, SHOULD send an asynchronous
      NA(EARO) with this new status value.  That asynchronous NA(EARO)
      SHOULD be sent to the all-nodes link-scope multicast address
      (ff02::1), and Target MUST be set to the link-local address that
      was exposed previously by this node to accept registrations, and
      the TID MUST be set to 0; the ROVR field MUST be set to all zeros
      and ignored by the receiver.

      In an environment with unreliable transmissions, the multicast
      NA(EARO) message may be resent in a fast sequence, in which case
      the TID is incremented each time.  A 6LN that has recently
      processed the NA(EARO) indicating a "Registration Refresh Request"
      ignores the additional NA(EARO) also indicating a "Registration
      Refresh Request" within the duration of the fast sequence.  That
      duration depends on the environment and has to be configured.  By
      default, it is 10 seconds.

   *  Registration for prefixes is now supported.  The value of 3 in the
      P-Field of the EARO and the EDAR message signals when the
      registration is for a prefix as opposed to an address.  DAD for
      prefixes and addresses becomes a prefix overlap match.  Whether
      overlapping addresses and prefixes may be registered is a network
      policy decision and out of scope.  The same prefix may be injected
      twice (multiple routes) as long as they use the same value of the
      ROVR.

      Overlaps may be desirable.  For instance, it may happen that a
      router or a proxy (see Section 10) registers a prefix or an
      aggregation while a host using an address from that prefix or a
      prefix from that aggregation also registers its piece.

      In case of an overlapping registration, the longest prefix match
      wins, meaning that if the network policy allows for overlapping
      registrations, then the routes for the registered prefixes are
      installed towards the node that registered with the longest prefix
      match, all the way to /128.

   *  If the 6LR acts as a border router to external prefixes or owns
      the prefixes entirely, it SHOULD register all those prefixes on
      all interfaces from which it might be needed to relay traffic to
      that prefix.  It MUST set the P-Field in the EARO to 3 for those
      prefixes and set the R flag to receive the traffic associated to
      the prefixes.  It MAY refrain from registering a prefix on one
      interface if that prefix is already successfully registered on
      another interface, or the router handled the EDAR/EDAC flow by
      itself, to ensure that the prefix ownership is known and validated
      by the 6LBR.  Additionally, if the router expects to receive
      traffic for that prefix on that interface, it needs to ensure that
      the prefix is advertised some other way, e.g., over a routing
      protocol such as RPL.

   *  The 6LN MAY set the R flag in the EARO to request the 6LR to
      redistribute the prefix on other links using a routing protocol.
      The 6LR MUST NOT reregister that prefix to yet another router
      unless loops are avoided some way, e.g., following a tree
      structure.

   *  The 6LR and the 6LBR are extended to accept more than one
      registration for the same prefix, since multiple 6LNs may register
      it.  The ROVR in the EARO identifies uniquely a registration
      within the namespace of the Registered Prefix.

   *  The 6LR MUST maintain a registration state per tuple (IPv6 prefix,
      prefix length, ROVR) for all registered prefixes.  It SHOULD
      notify the 6LBR with an EDAR message, unless it determined that
      the 6LBR is legacy and does not support this specification (see
      Section 5).  In turn, the 6LBR MUST maintain a registration state
      per tuple (IPv6 prefix, ROVR) for all prefixes.

8.  Updating RFC 9010

   With [RFC9010]:

   *  The 6LR injects only unicast routes in RPL.

   *  Upon a registration with the R flag set to 1 in the EARO, the 6LR
      injects the address in the RPL unicast support.

   *  Upon receiving a packet directed to a unicast address for which it
      has an active registration, the 6LR delivers the packet as a
      unicast L2 frame to the LLA of the node that registered the
      unicast address.

   This specification adds the following behavior:

   *  Upon a registration with the R flag set to 1 and the P-Field set
      to 3 in the EARO, the 6LR injects the prefix in RPL using a prefix
      RTO.  The P-Field in the RTP MUST be set to 3.

   *  Upon receiving a packet directed to an address that derives from a
      prefix for which it has at least one registration, the 6LR
      delivers a copy of the packet as a unicast L2 frame to the LLA of
      exactly one of the nodes that registered to that prefix, using the
      longest prefix match derivation to find the best 6LN.

9.  Updating RFC 8928

   "Address-Protected Neighbor Discovery for Low-Power and Lossy
   Networks" [RFC8928] was defined to protect the ownership of unicast
   IPv6 addresses that are registered with [RFC8505].

   With Address-Protected Neighbor Discovery (AP-ND) [RFC8928], it is
   possible for a node to autoconfigure a pair of public and private
   keys and use them to sign the registration of addresses that are
   either autoconfigured or obtained through other methods.

   The first-hop router (the 6LR) can then validate a registration and
   perform source address validation on packets coming from the sender
   node (the 6LN).

   As multiple nodes may register the same prefix, the method specified
   in [RFC8928] cannot be used with node-local autoconfigured keypairs,
   which protect a single ownership only.

   For a prefix, as for an anycast or a multicast address, it is still
   possible to leverage AP-ND [RFC8928] to enforce the right to
   register.  If AP-ND [RFC8928] is used, a keypair MUST be created and
   associated with the prefix before the prefix is deployed, and a ROVR
   MUST be generated from that keypair as specified in [RFC8928].  The
   prefix and the ROVR MUST then be installed in the 6LBR at the first
   registration, or by an external mechanism such as IP Address
   Management (IPAM) or DHCPv6 snooping prior to the first registration.
   This way, the 6LBR can recognize the prefix on the future
   registrations and validate the right to register based on the ROVR.

   The keypair MUST then be provisioned in each node that needs to
   register the prefix or a prefix within, so the node can follow the
   steps in [RFC8928] to register the prefix.

   Upon receiving an NA message with the status set to 5 "Validation
   Requested", the node that registered the address or prefix performs
   the proof of ownership based on that longest prefix match.

10.  Updating RFC 8929

   "IPv6 Backbone Router" [RFC8929] defines a proxy operation whereby a
   6LoWPAN Border Router (6LBR) may impersonate a 6LN when performing an
   address registration.  In that case, [RFC8505] messages are used as
   is, with one change that the SLLAO in the proxied NS(EARO) messages
   indicates the Registering Node (the 6LBR) as opposed to the
   Registered Node (the 6LN).  See Figure 5 of [RFC8929] for an example
   of proxy operation by the 6LBR, which generates an NS(EARO) upon
   receiving an EDAR message.

   This specification updates that proxy operation with the updates in
   [RFC9685] and defines the formats and content of the EARO, EDAR, and
   EDAC messages in order to support the P-Field and the signaling of
   prefixes.  The proxy MUST use the P-Field as received in the EDAR or
   NS(EARO) message to generate the proxied NS(EARO), and it MUST use
   the exact same prefix and prefix length as received in the case of a
   prefix registration.

11.  Security Considerations

   This specification updates [RFC8505], and the security considerations
   of that document also apply to this document.  In particular, the
   link layer SHOULD be sufficiently protected to prevent rogue access,
   else a rogue node with physical access to the network may inject
   packets and perform an attack from within.

   Section 9 leverages AP-ND [RFC8928] to prevent a rogue node from
   registering a unicast address that it does not own.  The mechanism
   could be extended to anycast and multicast addresses if the values of
   the ROVR they use are known in advance, but how this is done is not
   in scope for this specification.  One way would be to authorize in
   advance the ROVR of the valid users.  A less preferred way could be
   to synchronize the ROVR and TID values across the valid registering
   nodes as a preshared key material.

   In the latter case, it could be possible to update the keys
   associated to a prefix in all the 6LNs, but the flow is not clearly
   documented and may not complete in due time for all nodes in LLN use
   cases.  It may be simpler to install an all-new address with new keys
   over a period of time and switch the traffic to that address when the
   migration is complete.

12.  Operational Considerations

12.1.  Partially Upgraded Networks

   Devices may coexist while providing different support (i.e., only
   [RFC8505], both [RFC8505] and [RFC9685], or those two as well as this
   specification).  The following cases may occur:

   *  A legacy 6LN will not register prefixes, and the service will be
      the same when the network is upgraded.

   *  A legacy 6LR will not set the F flag in the 6CIO and an upgraded
      6LN will not register prefixes with that router, though it may
      with other 6LRs that do support this specification.

   *  Upon an EDAR message, a legacy 6LBR may not realize that the
      address being registered comes with a whole prefix, and return
      that it is duplicate in the EDAC status.  The 6LR MUST ignore a
      duplicate status in the EDAR for prefixes.

12.2.  Application to RPL-Based Route-Over LLNs

   This specification also updates [RFC6550] and [RFC9010] in the case
   of a route-over multilink subnet based on the RPL routing protocol,
   to add multicast ingress replication in Non-Storing Mode and anycast
   support in both Storing and Non-Storing modes.  A 6LR that implements
   the RPL extensions specified therein MUST also implement [RFC9010].

   Figure 5 illustrates the classical situation of an LLN as a single
   IPv6 subnet, with a 6LoWPAN Border Router (6LBR) that acts as Root
   for RPL operations and as Address Registrar for 6LoWPAN ND.

            .- -- .
         .-(        ).
        (   Internet   )
       (___.________.___)
                 |
      ---+-------+--
         |
       +--------+
       |  6LBR  |
       | (Root) |
       +--------+
       o   o  o  o
         o   o  o
    o  o  o       o  o  o
    o  o  o  LLN   o   +-------+
      o  o          o  |  6LR  | RPL Router
      o o    o   o     +-------+
      o  o    o  o          +-------+  RPL
             o              |  6LN  |  leaf
                            +-------+  L

     o : LLN node

                     Figure 5: RPL-Based Route-Over LLN

   A RPL leaf L acting as a 6LN registers its addresses and prefixes to
   a RPL router acting as a 6LR, using a L2 unicast NS message with an
   EARO as specified in [RFC8505] and [RFC9685].  Note that a RPL leaf
   acting as 6LN may still be a border router for another routing
   protocol, an access router for an IP link, or a virtual Router
   serving virtual machines or applications within the same physical
   node.  Note also that a RPL-aware Leaf would preferably leverage RPL
   directly to inject routes, to fully leverage the routing protocol.
   The registration state is periodically renewed by the Registering
   Node (the 6LN), before the lifetime indicated in the EARO expires (at
   the 6LR).  As for unicast IPv6 addresses, the 6LR uses an Extended
   Duplicate Address Request/Confirmation (EDAR/EDAC) exchange with the
   6LBR to notify the 6LBR of the presence of the listeners.  With this
   specification, a router that owns a prefix or provides reachability
   to an external prefix but is not a RPL router can also register those
   prefixes with the R flag set, to enable reachability to the prefix
   within the RPL domain.

12.3.  Application to a Shared Link

   A shared link is a situation where more than one prefix is deployed
   over an L2 link (say, a switched Ethernet fabric or a Wi-Fi Extended
   Service Set (ESS) federating multiple Access Points (APs)), and not
   necessarily all nodes are aware of all prefixes.  Figure 6 depicts
   such a situation, with two routers 6LR1 and 6LR2 that own respective
   prefixes P1:: and P2:: and expose those in their RA messages over the
   same link.  Note that the shared link maybe operated with any
   combination of NDP and SND as discussed in Section 7 of
   [IPv6-over-NBMA].

            .- -- .
         .-(        ).
        (   Internet   )
       (___.________.___)
             |
        +----+--+          +-------+
        | P1::a |          | P2::b |
        | 6LR1  |          | 6LR2  |
        +---+---+          +---+---+
            |                  |
     ----+--+------+---------+-+-------+---------+----
         |         |         |         |         |
      +--+--+   +--+--+   +--+--+   +--+--+   +--+--+
      |P1::c|   |P2::d|   |P2::e|   |P1::f|   |P1::g|
      +-----+   +-----+   +-----+   +-----+   +-----+

                           Figure 6: Shared Link

   Say that 6LR1 is the router providing access to the outside, and 6LR2
   is aware of 6LR1 as its default gateway.  With this specification,
   6LR2 registers P2:: to 6LR1, and 6LR1 installs a route to P2:: via
   6LR2.  This way, addresses that derive from P2:: can still be reached
   via 6LR1 and then 6LR2.  6LR2 may then leverage ICMP Redirect
   messages [RFC4861] to shorten the path between 6LR1 and the nodes
   that own those addresses.

   If P2 were delegated by 6LR1, e.g., using DHCPv6 [RFC9915], then the
   expectation is that 6LR1 aggregates P1:: and P2:: in its
   advertisements to the outside, and there is no need to set the R
   flag.  However, unless 6LR2 knows about such a situation, e.g.,
   through configuration, 6LR2 SHOULD set the R flag requesting 6LR1 to
   advertise P2:: so as to obtain reachability.

12.4.  Application to a Hub Link with Stub Spokes

   A hub link is a situation where stub links are deployed around a
   backbone and interconnected by routers.  Figure 7 depicts such a
   situation, with one router 6LR1 serving the hub link and at least one
   router like 6LR2 and 6LR3 providing connectivity from the stub links
   to the hub link.  In this example, say that there is one prefix on
   each link -- P1:: on the hub link, and P2:: and P3:: on the stub
   links.

      +-----+   +-----+   +-----+       +-----+
      |P2::s|   |P2::d|   |P2::e|       |P2::f|
      +--+--+   +--+--+   +--+--+       +--+--+
         |         |         |             |
     ----+----+----+---------+--STUB-LINK--+-----
              |
          +---+---+              +-------+
          | P2::r |              |       |        .- --..
          | 6LR2  |              | 6LR1  +---- .-(       ).
          | P1::b |              | P1::a |   (   Internet  )
          +---+---+              +---+---+  (___._______.___)
              |                      |              |
     -------+-+---------+--HUB-LINK--+-----+--      |
            |           |                  |        |
        +---+---+    +--+--+           +---+---+    |
        | P1::c |    |P1::n|           | P1::q |    |
        | 6LR3  |    +-----+           | 6LR4  +----+
        | P3::m |                      | P3::a |
        +---+---+                      +---+---+
            |                              |
     ----+--+------+---------+--STUB-LINK--+-+-----
         |         |         |               |
      +--+--+   +--+--+   +--+--+         +--+--+
      |P3::h|   |P3::i|   |P3::j|         |P3::k|
      +-----+   +-----+   +-----+         +-----+

                          Figure 7: Hub and Stubs

   As before, say that 6LR1 is the router providing access to the
   outside, and 6LR2 is aware of 6LR1 as its default gateway.  With this
   specification, 6LR2 registers P2:: to 6LR1, and 6LR1 installs a route
   to P2:: via 6LR2.  This way, nodes on the stub link behind 6LR2 that
   derive their addresses from P2:: can still be reached via 6LR1 and
   then 6LR2.  The same goes for 6LR3 and any other routers serving stub
   links.

   If P2 were delegated by 6LR1, then the expectation is that 6LR1
   aggregates P1:: and P2:: in its advertisements to the outside, and
   there is no need to set the R flag.  However, unless 6LR2 knows about
   such a situation, e.g., through configuration, 6LR2 SHOULD set the R
   flag requesting 6LR1 to advertise P2:: so as to obtain reachability.

   In this example, routers 6LR3 and 6LR4 both connect to the same stub
   link where subnet P3 is installed.  They may both register P3 to
   6LR1, and 6LR1 will apply its own load-balancing logic to use either
   of the routers.

13.  IANA Considerations

   IANA has made changes under the "Internet Control Message Protocol
   version 6 (ICMPv6) Parameters" [IANA.ICMP] and the "Routing Protocol
   for Low Power and Lossy Networks (RPL)" [IANA.RPL] registry groups,
   as follows.

13.1.  Updated P-Field Registry

   This specification updates the P-Field introduced in [RFC9685] to
   assign the value of 3, which is the only remaining unassigned value
   for the 2-bit field.  To that effect, IANA has updated the "P-Field
   Values" registry in the "Internet Control Message Protocol version 6
   (ICMPv6) Parameters" registry group as indicated in Table 2:

         +=======+===================================+===========+
         | Value | Meaning                           | Reference |
         +=======+===================================+===========+
         | 3     | Registration for a Unicast Prefix | RFC 9926  |
         +-------+-----------------------------------+-----------+

                         Table 2: New P-Field Value

13.2.  New 6LoWPAN Capability Bit

   IANA has made an addition to the "6LoWPAN Capability Bits"
   [IANA.ICMP.6CIO] registry in the "Internet Control Message Protocol
   version 6 (ICMPv6) Parameters" registry group as indicated in
   Table 3:

   IANA has fixed the description of bit 9 (the "A" flag defined in
   [RFC8928]).  It is not called "1" but "A".

     +=====+=============================================+===========+
     | Bit | Description                                 | Reference |
     +=====+=============================================+===========+
     | 9   | AP-ND Enabled (A bit)                       | [RFC8928] |
     +-----+---------------------------------------------+-----------+
     | 16  | Registration for prefixes supported (F bit) | RFC 9926  |
     +-----+---------------------------------------------+-----------+

                    Table 3: New 6LoWPAN Capability Bit

14.  Normative References

   [IANA.ICMP]
              IANA, "Internet Control Message Protocol version 6
              (ICMPv6) Parameters",
              <https://www.iana.org/assignments/icmpv6-parameters>.

   [IANA.ICMP.6CIO]
              IANA, "6LoWPAN Capability Bits",
              <https://www.iana.org/assignments/icmpv6-parameters>.

   [IANA.RPL] IANA, "Routing Protocol for Low Power and Lossy Networks
              (RPL)", <https://www.iana.org/assignments/rpl>.

   [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>.

   [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/info/rfc4861>.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862,
              DOI 10.17487/RFC4862, September 2007,
              <https://www.rfc-editor.org/info/rfc4862>.

   [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>.

   [RFC6775]  Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.
              Bormann, "Neighbor Discovery Optimization for IPv6 over
              Low-Power Wireless Personal Area Networks (6LoWPANs)",
              RFC 6775, DOI 10.17487/RFC6775, November 2012,
              <https://www.rfc-editor.org/info/rfc6775>.

   [RFC7400]  Bormann, C., "6LoWPAN-GHC: Generic Header Compression for
              IPv6 over Low-Power Wireless Personal Area Networks
              (6LoWPANs)", RFC 7400, DOI 10.17487/RFC7400, November
              2014, <https://www.rfc-editor.org/info/rfc7400>.

   [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>.

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/info/rfc8200>.

   [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>.

   [RFC8928]  Thubert, P., Ed., Sarikaya, B., Sethi, M., and R. Struik,
              "Address-Protected Neighbor Discovery for Low-Power and
              Lossy Networks", RFC 8928, DOI 10.17487/RFC8928, November
              2020, <https://www.rfc-editor.org/info/rfc8928>.

   [RFC8929]  Thubert, P., Ed., Perkins, C.E., and E. Levy-Abegnoli,
              "IPv6 Backbone Router", RFC 8929, DOI 10.17487/RFC8929,
              November 2020, <https://www.rfc-editor.org/info/rfc8929>.

   [RFC9010]  Thubert, P., Ed. and M. Richardson, "Routing for RPL
              (Routing Protocol for Low-Power and Lossy Networks)
              Leaves", RFC 9010, DOI 10.17487/RFC9010, April 2021,
              <https://www.rfc-editor.org/info/rfc9010>.

   [RFC9685]  Thubert, P., Ed., "Listener Subscription for IPv6 Neighbor
              Discovery Multicast and Anycast Addresses", RFC 9685,
              DOI 10.17487/RFC9685, November 2024,
              <https://www.rfc-editor.org/info/rfc9685>.

15.  Informative References

   [BCP38]    Best Current Practice 38,
              <https://www.rfc-editor.org/info/bcp38>.
              At the time of writing, this BCP comprises the following:

              Ferguson, P. and D. Senie, "Network Ingress Filtering:
              Defeating Denial of Service Attacks which employ IP Source
              Address Spoofing", BCP 38, RFC 2827, DOI 10.17487/RFC2827,
              May 2000, <https://www.rfc-editor.org/info/rfc2827>.

   [IEEE80211]
              IEEE, "IEEE Standard for Information Technology --
              Telecommunications and Information Exchange between
              Systems - Local and Metropolitan Area Networks -- Specific
              Requirements - Part 11: Wireless LAN Medium Access Control
              (MAC) and Physical Layer (PHY) Specifications", IEEE
              Std 802.11-2022, DOI 10.1109/IEEESTD.2021.9363693,
              <https://ieeexplore.ieee.org/document/9363693>.

   [IEEE802151]
              IEEE, "IEEE Standard for Telecommunications and
              Information Exchange Between Systems - LAN/MAN - Specific
              Requirements - Part 15: Wireless Medium Access Control
              (MAC) and Physical Layer (PHY) Specifications for Wireless
              Personal Area Networks (WPANs)", IEEE Std 802.15.1-2002,
              DOI 10.1109/IEEESTD.2002.93621,
              <https://ieeexplore.ieee.org/document/1016473>.

   [IEEE802154]
              IEEE, "IEEE Standard for Information technology -- Local
              and metropolitan area networks -- Specific requirements --
              Part 15.4: Wireless Medium Access Control (MAC) and
              Physical Layer (PHY) Specifications for Low Rate Wireless
              Personal Area Networks (WPANs)", IEEE Std 802.15.4-2006,
              DOI 10.1109/IEEESTD.2006.232110,
              <https://ieeexplore.ieee.org/document/1700009>.

   [IPv6-over-NBMA]
              Thubert, P. and M. Richardson, "Architecture and Framework
              for IPv6 over Non-Broadcast Access", Work in Progress,
              Internet-Draft, draft-ietf-6man-ipv6-over-wireless-09, 9
              November 2025, <https://datatracker.ietf.org/doc/html/
              draft-ietf-6man-ipv6-over-wireless-09>.

   [RFC4191]  Draves, R. and D. Thaler, "Default Router Preferences and
              More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191,
              November 2005, <https://www.rfc-editor.org/info/rfc4191>.

   [RFC4919]  Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6
              over Low-Power Wireless Personal Area Networks (6LoWPANs):
              Overview, Assumptions, Problem Statement, and Goals",
              RFC 4919, DOI 10.17487/RFC4919, August 2007,
              <https://www.rfc-editor.org/info/rfc4919>.

   [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>.

   [RFC9030]  Thubert, P., Ed., "An Architecture for IPv6 over the Time-
              Slotted Channel Hopping Mode of IEEE 802.15.4 (6TiSCH)",
              RFC 9030, DOI 10.17487/RFC9030, May 2021,
              <https://www.rfc-editor.org/info/rfc9030>.

   [RFC9915]  Mrugalski, T., Volz, B., Richardson, M., Jiang, S., and T.
              Winters, "Dynamic Host Configuration Protocol for IPv6
              (DHCPv6)", STD 102, RFC 9915, DOI 10.17487/RFC9915,
              January 2026, <https://www.rfc-editor.org/info/rfc9915>.

   [WI-SUN]   "Wi-SUN Alliance", <https://wi-sun.org/>.

Acknowledgments

   Many thanks to Dave Thaler and Dan Romascanu for their early reviews,
   Adnan Rashid for all his contributions, and Éric Vyncke for his in-
   depth AD review.  Many thanks as well to the reviewers of the IETF
   Last Call and IESG rounds: Dan Romascanu, Shuping Peng, Mohamed
   Boucadair, Paul Wouters, Ketan Talaulikar, Gunter Van de Velde, Mike
   Bishop, and Roman Danyliw.

Author's Address

   Pascal Thubert (editor)
   06330 Roquefort-les-Pins
   France
   Email: pascal.thubert@gmail.com
