rfc9926v2.txt   rfc9926.txt 
Internet Engineering Task Force (IETF) P. Thubert, Ed. Internet Engineering Task Force (IETF) P. Thubert, Ed.
Request for Comments: 9926 January 2026 Request for Comments: 9926 January 2026
Updates: 4861, 6550, 8505, 8928, 9010 Updates: 4861, 6550, 8505, 8928, 9010
Category: Standards Track Category: Standards Track
ISSN: 2070-1721 ISSN: 2070-1721
IPv6 Neighbor Discovery Prefix Registration Prefix Registration for IPv6 Neighbor Discovery
Abstract Abstract
This document updates IPv6 Neighbor Discovery (RFC 4861) and IPv6 This document updates IPv6 Neighbor Discovery (RFC 4861) and IPv6
Subnet Neighbor Discovery (RFC 8505, RFC 8928) to enable a node that 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 owns or is directly connected to a prefix to register that prefix to
neighbor routers. The registration indicates that the registered neighbor routers. The registration indicates that the registered
prefix can be reached via the advertising node without a loop. The prefix can be reached via the advertising node without a loop. The
unicast prefix registration allows the node to request one or more unicast prefix registration allows the node to request one or more
neighbor routers to redistribute the prefix in another routing domain neighbor routers to redistribute the prefix in another routing domain
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
2.2. Inherited Terms and Concepts 2.2. Inherited Terms and Concepts
This document uses terms and concepts that are discussed in: This document uses terms and concepts that are discussed in:
* "TLS User Mapping Extension" [RFC4861] and * "Neighbor Discovery for IP version 6 (IPv6)" [RFC4861] and
* "IPv6 Stateless Address Autoconfiguration" [RFC4862] for the * "IPv6 Stateless Address Autoconfiguration" [RFC4862] for the
Neighbor Solicitation operation, Neighbor Solicitation operation,
* "Neighbor Discovery Optimization for IPv6 over Low-Power Wireless * "Neighbor Discovery Optimization for IPv6 over Low-Power Wireless
Personal Area Networks (6LoWPANs)" [RFC6775], as well as Personal Area Networks (6LoWPANs)" [RFC6775], as well as
* "Registration Extensions for IPv6 over Low-Power Wireless Personal * "Registration Extensions for IPv6 over Low-Power Wireless Personal
Area Network (6LoWPAN) Neighbor Discovery" [RFC8505], and Area Network (6LoWPAN) Neighbor Discovery" [RFC8505], and
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DAO: Destination Advertisement Object [RFC6550] DAO: Destination Advertisement Object [RFC6550]
DODAG: Destination-Oriented Directed Acyclic Graph DODAG: Destination-Oriented Directed Acyclic Graph
EARO: Extended Address Registration Option [RFC8505] EARO: Extended Address Registration Option [RFC8505]
EDAC: Extended Duplicate Address Confirmation [RFC8505] EDAC: Extended Duplicate Address Confirmation [RFC8505]
EDAR: Extended Duplicate Address Request [RFC8505] EDAR: Extended Duplicate Address Request [RFC8505]
ESS: Extended Service Set [IEEE80211] ESS: Extended Service Set [IEEE80211]
IPAM: IP Address Management IPAM: IP Address Management
LLN: Low-Power and Lossy Network LLN: Low-Power and Lossy Network
LLA: Link-Layer Address LLA: Link-Layer Address
LoWPAN: Low-Power Wireless Personal Area Network LoWPAN: Low-Power Wireless Personal Area Network
LR-WPAN: Low-Rate Personal Area Network [IEEE802154] LR-WPAN: Low-Rate Wireless Personal Area Network [IEEE802154]
MAC: Medium Access Control MAC: Medium Access Control
NA: Neighbor Advertisement (message) [RFC4861] NA: Neighbor Advertisement (message) [RFC4861]
NBMA: Non-Broadcast Multi-Access (full mesh) NBMA: Non-Broadcast Multi-Access (full mesh)
NCE: Neighbor Cache Entry [RFC4861] NCE: Neighbor Cache Entry [RFC4861]
ND: Neighbor Discovery (protocol) ND: Neighbor Discovery (protocol)
NDP: Neighbor Discovery Protocol NDP: Neighbor Discovery Protocol
NS: Neighbor Solicitation (message) [RFC4861] NS: Neighbor Solicitation (message) [RFC4861]
ROVR: Registration Ownership Verifier (pronounced "rover") ROVR: Registration Ownership Verifier (pronounced "rover")
[RFC8505] [RFC8505]
RPL: IPv6 Routing Protocol for LLNs (pronounced "ripple") RPL: IPv6 Routing Protocol for LLNs (pronounced "ripple")
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RS: Router Solicitation (message) [RFC4861] RS: Router Solicitation (message) [RFC4861]
RTO: RPL Target Option [RFC6550] RTO: RPL Target Option [RFC6550]
SLLAO: Source Link-Layer Address Option [RFC4861] SLLAO: Source Link-Layer Address Option [RFC4861]
SND: Subnet Neighbor Discovery (protocol) SND: Subnet Neighbor Discovery (protocol)
TID: Transaction ID [RFC8505] TID: Transaction ID [RFC8505]
TIO: Transit Information Option [RFC6550] TIO: Transit Information Option [RFC6550]
TLLAO: Target Link-Layer Address Option [RFC4861] TLLAO: Target Link-Layer Address Option [RFC4861]
2.4. New Terms 2.4. New Terms
This document introduces the following terms: This document introduces the following term:
Origin: The node that issued the prefix advertisement, either in the Origin: The node that issued the prefix advertisement, either in the
form of a NS(EARO) or as a DAO(TIO, RTO) form of a NS(EARO) or as a DAO(TIO, RTO)
Merge: The action of receiving multiple anycast or multicast
advertisements, either (1) internally from self, (2) in the
form of a NS(EARO), or (3) as a DAO(TIO, RTO), and generating
a single DAO(TIO, RTO). The 6RPL router maintains a state per
origin for each advertised address, and merges the
advertisements for all subscriptions for the same address in a
single advertisement. A RPL router that merges then becomes
the origin of the merged advertisement and uses its own values
for the Path Sequence and ROVR fields.
3. Overview 3. Overview
This specification inherits from [RFC6550], [RFC8505], and [RFC9010] This specification inherits from [RFC6550], [RFC8505], and [RFC9010]
to register prefixes as opposed to addresses. to register prefixes as opposed to addresses.
An SND deployment consists of: 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, * one or more 6LBRs that act as RPL Root,
* intermediate routers down the RPL graph that propagate routing * intermediate routers down the RPL graph that propagate routing
information on addresses and prefixes towards the Root, information on addresses and prefixes towards the Root,
* 6LRs that are RPL-aware 6LNs and can leverage RPL directly to * 6LRs that are RPL-aware 6LNs and can leverage RPL directly to
expose their addresses and prefixes, and expose their addresses and prefixes, and
* 6LNs that are the RPL-unaware destinations and need SND to obtain * 6LNs that are the RPL-unaware destinations and need SND to obtain
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[RFC6550] uses the Path Lifetime in the TIO to indicate the remaining [RFC6550] uses the Path Lifetime in the TIO to indicate the remaining
time for which the advertisement is valid for unicast route time for which the advertisement is valid for unicast route
determination, and a Path Lifetime value of 0 invalidates that route. determination, and a Path Lifetime value of 0 invalidates that route.
[RFC9010] maps the Address Registration lifetime in the EARO and the [RFC9010] maps the Address Registration lifetime in the EARO and the
Path Lifetime in the TIO so they are comparable when both forms of Path Lifetime in the TIO so they are comparable when both forms of
advertisements are received. advertisements are received.
The RPL router that merges multiple advertisements for the same The RPL router that merges multiple advertisements for the same
prefix uses and advertises the longest remaining lifetime across all prefix uses and advertises the longest remaining lifetime across all
the origins of the advertisements for that prefix. When the lifetime the origins of the advertisements for that prefix. When the lifetime
expires, the router sends a no-path DAO (i.e., the lifetime is 0) expires, the router sends a no-path DAO message (i.e., the lifetime
using the same value for the ROVR value as for the previous is 0) using the same value for the ROVR value as for the previous
advertisements. This value refers to either the router itself or the advertisements. This value refers to either the single descendant
single descendant that advertised the Target. 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 Note that the Registration Lifetime, TID, and ROVR fields are also
placed in the EDAR message, so the state created by EDAR is 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 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 simplicity, the text below mentions only NS(EARO) but it also applies
to EDAR. to EDAR.
7. Updating RFC 8505 7. Updating RFC 8505
This specification updates the EARO and EDAR messages to enable the This specification updates the EARO and EDAR messages to enable the
 End of changes. 7 change blocks. 
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