6lo Working Group L. Iannone
Internet-Draft D. Lou
Intended status: Standards Track Huawei
Expires: 7 January 2027 A. Rashid
6 July 2026
Generic Address Assignment Option for 6LoWPAN Neighbor Discovery
draft-ietf-6lo-nd-gaao-10
Abstract
This document specifies a new extension to the IPv6 Neighbor
Discovery in Low Power and Lossy Networks (LLNs), enabling a node to
request to be assigned an address or a prefix from neighbor routers.
Such mechanism allows to algorithmically assign addresses and
prefixes to nodes in a 6LoWPAN deployment.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 7 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
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Algorithmic and Distributed Address Assignment . . . . . 3
1.2. Limitations of DHCPv6 in Constrained LLNs . . . . . . . . 4
1.3. Generic Address Assignment Option (GAAO) . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Requirements Notation . . . . . . . . . . . . . . . . . . 5
2.2. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . 5
2.3. Definition of Terms . . . . . . . . . . . . . . . . . . . 6
3. Algorithmically Assigned Addresses and Prefixes . . . . . . . 6
4. Generic Address Assignment Option Format . . . . . . . . . . 8
5. Messages Sequence and Processing . . . . . . . . . . . . . . 10
5.1. Request Phase . . . . . . . . . . . . . . . . . . . . . . 10
5.2. Explicit Registration Phase (Optional) . . . . . . . . . 11
5.3. Message Exchange Optimization . . . . . . . . . . . . . . 12
5.3.1. GAAO with Address Registration . . . . . . . . . . . 13
5.3.2. GAAO with Router Discovery . . . . . . . . . . . . . 13
5.4. Error Conditions . . . . . . . . . . . . . . . . . . . . 14
6. Signaling GAAO Support . . . . . . . . . . . . . . . . . . . 15
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
7.1. IPv6 Neighbor Discovery (ND) Option Types . . . . . . . . 15
7.2. 6LoWPAN Capability Bits . . . . . . . . . . . . . . . . . 16
7.3. GAAO Error code . . . . . . . . . . . . . . . . . . . . . 16
7.4. Address Assignment Function Registry . . . . . . . . . . 16
8. Security Considerations . . . . . . . . . . . . . . . . . . . 17
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 17
References . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Normative References . . . . . . . . . . . . . . . . . . . . . 18
Informative References . . . . . . . . . . . . . . . . . . . . 19
Appendix A. Analytical comparison of GAAO and DHCPv6 . . . . . . 21
A.1. DHCPv6 Message Structure . . . . . . . . . . . . . . . . 22
A.2. GAAO Structure . . . . . . . . . . . . . . . . . . . . . 23
A.3. DHCPv6 vs GAAO Address Configuration . . . . . . . . . . 23
A.3.1. 6LoWPAN MTU Constraint . . . . . . . . . . . . . . . 24
A.4. Energy Consumption . . . . . . . . . . . . . . . . . . . 24
A.5. Multicast Inefficiency . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25
1. Introduction
Low Power and Lossy Networks (LLNs) require adaptations of Internet
protocols to operate efficiently under constraints such as limited
energy, low data rates, constrained memory, and duty-cycled radio
operation. In many LLN deployments, the wireless interface is the
dominant source of energy consumption. As a result, protocol design
must minimize transmissions, idle listening, and the number of nodes
involved in control-plane operations.
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IPv6 Neighbor Discovery (ND) was optimized for LLNs in [RFC6775] and
later extended by [RFC8505], [RFC8929], [RFC9010], and [RFC9685].
These specifications reduce multicast usage, limit control-plane
participation, and introduce explicit address registration mechanisms
to better support energy-constrained and duty-cycled devices.
1.1. Algorithmic and Distributed Address Assignment
Recent work has demonstrated the benefits of algorithmically
structured addressing in constrained networks (e.g., [RFC9453],
[I-D.ietf-6lo-path-aware-semantic-addressing], [SHENOY21], [BLESS22],
[RIDOUX05]). Such approaches can simplify routing, reduce forwarding
state, and improve scalability. These schemes often require routers
to assign addresses or prefixes according to a distributed Address
Assignment Function (AAF).
Existing mechanisms do not provide a standardized way, within the
optimized ND framework defined by [RFC8505], for a 6LoWPAN Node (6LN)
to explicitly request an address or prefix from a neighboring 6LoWPAN
Router (6LR).
In general IPv6 networks, address and prefix assignment are well
supported by Stateless Address Auto-Configuration (SLAAC) [RFC4862]
and DHCPv6 [RFC9915]. However, these mechanisms do not fully align
with the architectural and operational goals of RFC8505-based 6LoWPAN
deployments, particularly in scenarios requiring:
* Strict minimization of multicast traffic,
* Avoidance of centralized infrastructure,
* Localized control-plane interactions,
* Algorithmically structured address assignment to support routing
optimizations.
This document does not attempt to replace SLAAC or DHCPv6 in general
IPv6 networks. Instead, it addresses specifically 6LoWPAN LLNs
operating under RFC8505-based Neighbor Discovery optimizations, where
nodes may need to request addresses or prefixes, usually
algorithmically generated, directly from neighboring routers without
introducing a centralized infrastructure (e.g. DHCPv6). In
scenarios where a global centralized coordination of address and
prefixes assignment is necessary, DHCPv6 remains the recommended
solution.
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1.2. Limitations of DHCPv6 in Constrained LLNs
DHCPv6 relies on a client-server model and typically uses multicast
(e.g., Solicit messages sent to FF02::1:2). While DHCPv6 is
efficient in traditional IPv6 networks, including support for long
lifetimes and reduced renewal frequency, its architectural model does
not align with the distributed, strictly localized control-plane
design promoted by RFC8505-based 6LoWPAN Neighbor Discovery.
In IEEE 802.15.4 [IEEE802154] and similar LLNs, IPv6 multicast is
commonly mapped to link-layer broadcast ([RASHID24], [SELIEM17]).
Such broadcasts cause all nodes on the channel to wake up and process
the frame. In duty-cycled networks, this increases:
* Radio wake-ups,
* Idle listening time,
* Channel contention,
* Overall energy consumption.
Furthermore, DHCPv6 requires a reachable server, often via relay
agents, which may introduce multi-hop control paths and centralized
state management. In lossy multi-hop LLNs, longer control paths
increase failure probability and recovery cost. Further analysis is
presented in {SEC:Appendix}.
1.3. Generic Address Assignment Option (GAAO)
This document specifies a new neighbor discovery option, the Generic
Address Assignment Option (GAAO), that enables a node to request an
address or prefix directly from a neighboring router using
RFC8505-based ND messages. The mechanism:
* Operates strictly at 1-hop,
* Avoids introducing a centralized infrastructure,
* Aligns with RFC8505 registration procedures,
* Supports distributed algorithmic address assignment.
GAAO complements the Extended Address Registration Option (EARO)
defined in [RFC8505] and its extensions, integrating address/prefix
assignment into the existing optimized ND framework for 6LoWPAN.
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2. Terminology
2.1. Requirements Notation
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. Acronyms
This document assumes familiarity with the terminology defined in
[RFC6775] and [RFC8505]. In particular for the following acronyms:
*6CIO*: Capability Indication Option
*6LBR*: 6LoWPAN Border Router
*6LN*: 6LoWPAN Node
*6LoWPAN*: IPv6 over Low-Power Wireless Personal Area Network
*6LR*: 6LoWPAN Router
*AAF*: Address Assignment Function
*ARO*: Address Registration Option
*EARO*: Extended Address Registration Option
*GAAO*: Generic Address Assignment Option
*IID*: Interface IDentifier
*LLN*: Low-Power and Lossy Network
*NA*: Neighbor Advertisement
*ND*: Neighbor Discovery
*NS*: Neighbor Solicitation
*PfxLen*: Prefix Length
*RA*: Router Advertisement
*RS*: Router Solicitation
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*SLAAC*: Stateless Address Auto-Configuration
*SLLAO*: Source Link-Layer Address Option
*TLLAO*: Target Link-Layer Address Option
2.3. Definition of Terms
*Address Assignment Function (AAF):* The Address Assignment Function
(AAF) is an implementation of the algorithm used by 6LRs/6LBR to
assign an address/prefix to requesting nodes. In order to avoid
addressing issues, only one AAF is used in a deployment. An AAF
assigns either addresses or prefixes but not both. This allows in
certain cases to indicate whether a node is requesting an address
or a prefix.
*GAAO:* Generic Address Assignment Option defined in this
specification (Section 4).
3. Algorithmically Assigned Addresses and Prefixes
The IPv6 address assignment model within a local domain relies on
randomly generated Interface Identifiers (IIDs). These can be
assigned in two ways: a centralized approach using DHCPv6
([RFC9915]), which guarantees collision-free addresses, or a
decentralized approach using SLAAC ([RFC4862]). In the latter case,
additional mechanisms are required to ensure address uniqueness and
security, including Duplicate Address Detection (DAD) [RFC4862],
Cryptographically Generated Addresses (CGA) [RFC3972], and Secure
Neighbor Discovery (SEND) [RFC3971]. However, there is a third
approach for address assignment, which is distributed and collision-
free: algorithmically generated addresses (e.g., [SHENOY21],
[BLESS22], [RIDOUX05], [ERIKSSON04]).
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The Address Assignment Function (AAF) will work as a decentralized
and distributed fashion. The AAF is used to assign addresses and
prefixes to nodes as they join a network. To ensure consistency, all
6LoWPAN Nodes (6LNs), 6LoWPAN Routers (6LRs), and 6LoWPAN Border
Routers (6LBRs) MUST use the same AAF within a given network
instance. When a node needs an address/prefix, it first selects a
neighboring 6LR/6LBR from those that responded to its initial Router
Solicitation (RS) with a Router Advertisement (RA), as specified in
[RFC6775]. The node then sends an explicit request for an address/
prefix to the chosen 6LR/6LBR (see Section 5 for details about
messages sequence and processing). The 6LR/6LBR assigns the address/
prefix based on the AAF. Depending on the specific technology and
algorithm in use, the 6LR/6LBR will either implicitly register this
assignment to the requesting 6LN, or will indicate to the 6LN that an
explicit registration of the assigned address/prefix is necessary to
confirm its use. The overall process is illustrated in Figure 1.
STEP
6LN 6LR/6LBR
| |
1. | Address/Prefix Request | \
| --------------------------> | \
| | + Request Phase
2. | Address/Prefix Offer | /
| <-------------------------- | /
| |
3. | Address/Prefix Acceptance | \
| --------------------------> | \
| | + Optional Explicit
4. | Address/Prefix Confirmation | / Registration Phase
| <-------------------------- | /
| |
Figure 1: Address/Prefix assignment sequence.
The optional registration phase (steps 3 and 4) is implemented using
the address/prefix registration procedures defined in [RFC8505],
[RFC9685], or [RFC9926]. In this phase, an Extended Address
Registration Option (EARO) and SLLAO are used to register an address/
prefix, which, in this context, is not self-generated. However, to
initiate the process--specifically steps 1 and 2, a new Generic
Address Assignment Option is required and proposed in this document.
Because no existing mechanism can be readily used for this purpose.
The remainder of this document first defines the format of this
option (see Section 4), followed by a revised sequence and processing
of Address/Prefix assignment messages (see Section 5).
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4. Generic Address Assignment Option Format
In order for a 6LN to request the assignment of an address or prefix,
GAAO message is used. The format of the GAAO message is 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 | Status | Opaque |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R|C|Rsvd | PfxLen | AAF | Assignment Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Registration Ownership Verifier (ROVR) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Address/Prefix |
| (128 bits) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Generic Address Assignment Option (GAAO) format.
Generic Address Assignment Option Fields:
*Type:* TBD
*Length:* 8-bit unsigned integer. The length of the option in units
of 8 bytes. This field is set to 1 plus the size of the ROVR
field when there is no address/prefix appended to the option. Its
value is augmented by 2 (16 bytes) when an address/prefix is
appended to the option.
*Status:* As defined in [RFC8505].
*Opaque:* As defined in [RFC8505].
*R:* 1-bit flag for explicit Registration being requested. It MUST
be initialized to 0 in Neighbor Solicitation (NS) messages by the
requester and MUST be ignored by the receiver. The 6LR/6LBR
replying to the request with an Neighbor Advertisement (NA)
message MAY set this bit to indicate that it requests a
confirmation that the address/prefix is accepted and will be used.
When the 6LR/6LBR sets the R-flag in a NA(GAAO) message, it
indicates that no registration state has been created and that the
requester MUST explicitly register the received address/prefix to
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the same 6LR/6LBR using the procedures defined in [RFC8505],
[RFC9926], and [RFC9685], according to the type of the assigned
address/prefix. When the 6LR/6LBR does not set this R-flag, it
implicitly indicates that the assigned address/prefix has been
also registered and state created as specified in [RFC8505],
[RFC9926], and [RFC9685], according to the type of the assigned
address/prefix. In the event that the 6LN does not want to use
the allocated address/prefix, it can de-register the allocation by
sending an NS(EARO) setting registration lifetime to zero, as
defined in [RFC8505].
*C:* 1-bit flag for Crypto-ID used for ROVR as defined in [RFC8928]
and [RFC9927]. This flag MUST be set when the ROVR field contains
a Crypto-ID.
*Reserved:* 3-bit reserved field for future use. It MUST be
initialized to 0 by the sender and MUST be ignored by the
receiver.
*PfxLen:* 7-bit unsigned integer. It indicates the length in bits
of the address/prefix carried in the option.
*AAF:* 4-bit unsigned integer. Describes the Address Assignment
Function (AAF), i.e. the algorithm, used to assign the address/
prefix. 0 is a special value indicating that the field is not
used. In an NS(GAAO) message, it is RECOMMENDED to set this field
to 0 to indicate there is no preference on how the address/prefix
is assigned. However, a 6LN MAY use a value different from 0,
meaning that it is requested to use a specific known AAF to assign
the address/prefix (see also Section 5.4). Section 7.4 describes
possible values of this field.
*Assignment Lifetime:* 16-bit unsigned integer, expressed in
minutes. In an NS(GAAO) message, the field expresses a desired
lifetime. It MAY be set to zero, indicating no particular desired
lifetime. In NA(GAAO) message it expresses the granted lifetime.
A node MUST NOT use the address/prefix after expiration of the
lifetime. Address/prefix lifetime SHOULD be configurable
according to the AAF in use and as mitigation of certain attacks
(see Section 8).
*ROVR:* As defined in [RFC8505] and extended in [RFC8928] and
[RFC9927].
*Address/Prefix:* 128-bit IPv6 address/prefix. This field MAY be
present in NS(GAAO) request messages to indicate the prefix from
which the address or sub-prefix has to be derived. If not present
in an NS(GAAO) message, it means that the address returned in an
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NA(GAAO) message is implicitly used on the interface used to send
the request. This field MUST be present in NA(GAAO) messages that
return a successful address/prefix allocation, but MUST NOT be
present in case of error. When the field is used return a prefix,
the leftmost bits are used for its encoding according to the
length field, the remaining bits are set to zero.
5. Messages Sequence and Processing
When a node bootstraps, it typically does multicast a RS message and
receives one or more unicast RA messages from neighbor 6LRs. The
node MAY choose one or more 6LRs from which to request address(es) or
prefix(es). A node MAY perform a request at any time, not
necessarily at boot time, using NS and NA messages.
5.1. Request Phase
When the node requests an address/prefix, the node will go through
the following steps:
1. The node will issue an NS(GAAO) message to obtain the address/
prefix. In this initial address request, GAAO Status field MUST
be set to 0. Opaque, ROVR, and C-flag are set according to the
local configuration. R-Flag MUST be set to 0. The AAF field
SHOULD be set to zero unless by configuration there is a
preference for the assignment algorithm. The Assignment Lifetime
field MAY be set to the desired lifetime, or zero otherwise. The
Address/Prefix field MAY be present to indicate the prefix from
which the address or sub-prefix has to be derived. In this case
the PfxLen field MUST be set accordingly. If the Address/Prefix
field is not present, the PfxLen field MUST be set to 0.
2. Assuming no errors occur, the node will receive an NA(GAAO)
message where all fields have been copied back except for:
* *Pfxlen:* Now indicating the actual length of the prefix. For
address assignments this field MUST be set to 64.
* *R:* The R-bit is set if the 6LR requests an explicit
registration.
* *AAF:* It is the algorithm, used to assign the address/prefix.
If the node is a 6LR it MUST use the same AAF to generate
addresses/prefixes to requesting neighbor nodes.
* *Assignment Lifetime:* The maximum lifetime of the assigned
address/prefix.
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The message sequence is depicted in Figure 3.
STEP
6LN 6LR/6LBR
| |
| ===== RS-RA Transaction Completed ====== |
| |
| |
| Address/Prefix Request |
1. | ---------------------------------------> |
| NS (GAAO) |
| |
| Address/Prefix Offer |
2. | <--------------------------------------- |
| NA (GAAO) |
| |
Figure 3: Address/Prefix assignment message sequence.
5.2. Explicit Registration Phase (Optional)
Depending on the algorithm in use and the underlying technology, the
address/prefix assignment procedure terminates after these two
messages. This may be sufficient for instance in deployments where
the link-layer offers reliable packet delivery. The use of this
option is done by configuration. Documents defining AAFs MUST
explicitly state whether this phase remains optional or is mandatory
due to factors specific to the proposed algorithm.
If the R-flag is set in the received NA(GAAO) message, the 6LN MUST
register with the obtained address/prefix by following the procedures
in [RFC8505], [RFC9685], or [RFC9926] depending on the type of
address/prefix. When setting the R-flag, and as for [RFC4861], the
6LR is expect to receive a registration within RETRANS_TIMER
multiplied by MAX_UNICAST_SOLICIT. If no registration is received
within this amount of time the 6LR will consider that address/prefix
is not in use by the requesting 6LN.
The complete sequence of actions is depicted in Figure 4.
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STEP
6LN 6LR/6LBR
| |
| ====== RS-RA Transaction Completed ====== |
| |
| Address/Prefix Request |
1. | -------------------------------------------> |
| NS(GAAO) |
| |
| Address/Prefix Offer |
2. | <------------------------------------------- |
| NA(GAAO) |
| |
| Address/Prefix Registration Request |
3. | -------------------------------------------> |
| NS(EARO + SLLAO) |
| |
...
Procedure According to [RFC8505], [RFC9685],
or [RFC9926] depending on the type
of address.
...
| |
| Address/Prefix Registration Response |
4. | <------------------------------------------- |
| NA(EARO with Status + SLLAO) |
| |
Figure 4: Address/Prefix assignment message sequence with explicit
registration.
[RFC8505], [RFC9685], and [RFC9926], define how nodes keep address/
prefix registering state so to maintain addressing in case of reboot.
When needed, in order to use this feature with GAAO, after reboot the
registration phase MUST be used to perform an explicit registration
and continue using the address/prefix. However, when using GAAO, and
when preforming the re-registering, if a "Registration Refresh
Request" or "Invalid Registration" Status value is returned, the node
MUST restart from the top with the initial Request Phase.
5.3. Message Exchange Optimization
There are two ways to optimize the prefix/address Request Phase: GAAO
with Address Registration and GAAO with Router Discovery.
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5.3.1. GAAO with Address Registration
Prefix/address Registration utilize NS/NA transactions for the link-
local address registration [RFC8505]. In this specification, for
prefix/address Request procedure utilizes an additional NS/NA
transaction. To minimize the number of transactions, GAAO MAY be
used together with the EARO option during address registration phase.
This piggybacking approach provides flexibility and maintains
compatibility with existing specifications [RFC8505]. In response
the NA message will contain GAAO. Figure 5 illustrates the GAAO
piggybacked within a link-layer address registration request and
response.
STEP
6LN 6LR/6LBR
| |
| Address Registration Request |
1. | ---------------------------------------> |
| NS(EARO + SLLAO + GAAO) |
| |
| Address Registration Response |
2. | <--------------------------------------- |
| NA(EARO with Status + SLLAO + GAAO) |
| |
Figure 5: GAAO piggybacking with link-layer Address Registration.
5.3.2. GAAO with Router Discovery
Another optimization for prefix/address requests can be performed
during the bootstrapping phase of a 6LN. The GAAO MAY be included in
the initial RS message, thereby implicitly indicating that the node
supports this specification. Similarly, 6LR/6LBR that support this
specification MUST include a prefix/address offer in a GAAO appended
to the corresponding RA message, as depicted in Figure 6.
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STEP
6LN 6LR/6LBR
| |
| RS message |
1. | ---------------------------------------> |
| (6CIO + SLLAO + GAAO) |
| |
| RA message |
2. | <--------------------------------------- |
| (PIO + 6CIO + ABRO + SLLAO + GAAO) |
| |
Figure 6: GAAO piggybacking with Router Discovery.
A 6LR/6LBR that does not support GAAO will simply ignore this option,
and the corresponding RA message will not include a GAAO. This
behavior implicitly signals that the feature is not supported.
5.4. Error Conditions
GAAO Status field uses same Status values defined in [RFC6775] and
[RFC8505], further revised in [RFC9010], for error reporting. This
specification introduces a new Status value when the AAF in GAAO in
an NS message is not in use in the 6LoWPAN network, as follows (see
also Section 7):
*AAF Not Used:* The AAF in GAAO in the NS message is not in use in
the 6LoWPAN network.
This status MUST be used when a node requesting an address/prefix did
put an AAF value, in the corresponding field, which is not in use in
the 6LoWPAN network. When the node receives this status back it
SHOULD perform one of the following actions:
* Re-issue the same request without specifying an AAF, meaning set
the AAF field to 0. The 6LR will return the AAF in use in the
6LoWPAN network and employed to generate the returned address/
prefix. If the requesting node does not support the returned AAF
it does not participate in the AAF-based 6LoWPAN network and does
not use the proposed address/prefix.
* Re-issue the same request with a different AAF. The 6LoWPAN
network is not using the requested AAF but may be using a
different one. Note that such an approach may lead to repeated
requests that may consume bandwidth and energy.
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* Do nothing and do not participate in the AAF-based 6LoWPAN
network.
The action to be used is selected by configuration. When nodes fail
to participate in the AAF-based 6LoWPAN network they MAY still use a
different mechanism (e.g., [RFC8505]) to configure addresses/
prefixes.
6. Signaling GAAO Support
This specification defines a new capability bit, named M-flag, for
use in the 6CIO as defined by [RFC7400] ("6LoWPAN-GHC: Generic Header
Compression for IPv6 over Low-Power Wireless Personal Area
Networks"). A 6LN that supports this specification MUST set the
M-flag in RS and RA messages.
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 | Reserved |X|A|D|L|B|P|E|G|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|F|M| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: New GAAO Capability Bit in the 6CIO.
*M:* 1-bit flag. The node supports managed addresses/prefixes via
the Generic Address Assignment Capability.
7. IANA Considerations
This section provides guidance to the Internet Assigned Numbers
Authority (IANA) regarding registration of values related to the GAAO
specification, in accordance with BCP 26 [RFC8126].
7.1. IPv6 Neighbor Discovery (ND) Option Types
IANA is requested to make an addition to the "IPv6 Neighbor Discovery
Option Formats" registry under the heading "Internet Control Message
Protocol version 6 (ICMPv6) Parameters" as indicated in Table 1:
+======+===================================+=================+
| Type | Description | Reference |
+======+===================================+=================+
| TBD | Generic Address Assignment Option | [This Document] |
+------+-----------------------------------+-----------------+
Table 1: New Generic Address Assignment Option.
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7.2. 6LoWPAN Capability Bits
IANA is requested to make an addition to the "6LoWPAN Capability
Bits" registry under the registry group "Internet Control Message
Protocol version 6 (ICMPv6) Parameters" as indicated in Table 2:
+=====+============================+===========+
| Bit | Description | Reference |
+=====+============================+===========+
| TBD | M-Flag for Generic Address | [This |
| | Assignment Capability | Document] |
+-----+----------------------------+-----------+
Table 2: New 6LoWPAN Capability Bit.
7.3. GAAO Error code
IANA is requested to make an addition to the "Address Registration
Option Status Values" registry under the registry group "Internet
Control Message Protocol version 6 (ICMPv6) Parameters" as indicated
in Table 3:
+================+==============+=================+
| Value | Description | Reference |
+================+==============+=================+
| 13 (Suggested) | AAF Not Used | [This Document] |
+----------------+--------------+-----------------+
Table 3: New Address Registration Option Status
Field Value.
7.4. Address Assignment Function Registry
IANA is asked to create a registry group named "Generic Address
Assignment Option".
Such registry group should be populated with an octet registry named
"Address Assignment Function" and used to identify the used AAF. The
registry is populated as shown in Table 4:
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+=========+================================+===========+
| Value | AAF Name | Reference |
+=========+================================+===========+
| 0x0 | No AAF. This can be used only | [This |
| | in NS message to indicate that | Document] |
| | no specific AAF is demanded. | |
+---------+--------------------------------+-----------+
| 0x1-0xE | Un-assigned | |
+---------+--------------------------------+-----------+
| 0xF | Experimental Use. Used for | [This |
| | experimental purposes during | Document] |
| | implementation of new AAFs. | |
+---------+--------------------------------+-----------+
Table 4: Allocation Function Sub-registry
Values can be assigned by IANA on a "First Come, First Served" basis
according to [RFC8126].
8. Security Considerations
This document extends [RFC8505], which already extended [RFC6775], as
such the security considerations of both documents apply to this
specification. In particular, the link layer SHOULD provide
sufficient protection to prevent potential attacks. Recommendations
listed in Section 7 of [RFC8505] SHOULD be applied as well to this
specification.
Depending on the AAF in use, the number of available addresses may
encounter limitations. A rouge node may leverage on this knowledge
to carry out address exhaustion attacks by impersonating different
nodes and performing multiple requests. To mitigate such risks the
recommendation about the lifetime and number of addresses per node
described in Section 7 of [RFC8505] remains valid.
Acknowledgements
This document received many comments and help from community people.
The authors would like to thank all of them. Thanks as well to Joel
Halpern (GENART) and Brian Haberman (INTDIR) for their reviews that
helped to spot overlooked points in the definition of the GAAO
mechanism. Thanks to Pascal Thubert for his help in making this
specification more integrated with existing specifications. Thanks
to Carles Gomez Montenegro for his very thorough shepherd review.
Thanks to Lorenzo Colitti for helping clarifying the scope of GAAO
with respect to DHCPv6.
References
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Normative References
[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>.
[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>.
[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/rfc/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/rfc/rfc7400>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/rfc/rfc8126>.
[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>.
[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/rfc/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/rfc/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/rfc/rfc8929>.
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[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/rfc/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/rfc/rfc9685>.
[RFC9926] Thubert, P., Ed., "Prefix Registration for IPv6 Neighbor
Discovery", RFC 9926, DOI 10.17487/RFC9926, February 2026,
<https://www.rfc-editor.org/rfc/rfc9926>.
[RFC9927] Thubert, P. and A. Rashid, "Fixing the C-Flag in the
Extended Address Registration Option (EARO)", RFC 9927,
DOI 10.17487/RFC9927, February 2026,
<https://www.rfc-editor.org/rfc/rfc9927>.
Informative References
[BLESS22] Bless, R., Zitterbart, M., Despotovic, Z., and A. Hecker,
"KIRA: Distributed Scalable ID-based Routing with Fast
Forwarding", 2022 IFIP Networking Conference (IFIP
Networking) pp. 1-9,
DOI 10.23919/ifipnetworking55013.2022.9829816, June 2022,
<https://doi.org/10.23919/
ifipnetworking55013.2022.9829816>.
[ERIKSSON04]
Eriksson, J., Faloutsos, M., and S. Krishnamurthy,
"Scalable ad hoc routing: the case for dynamic
addressing", IEEE INFOCOM 2004 vol. 2, pp. 1108-1119,
DOI 10.1109/infcom.2004.1356997, February 2005,
<https://doi.org/10.1109/infcom.2004.1356997>.
[FOURTY12] Fourty, N., van den Bossche, A., and T. Val, "An advanced
study of energy consumption in an IEEE 802.15.4 based
network: Everything but the truth on 802.15.4 node
lifetime", Computer Communications vol. 35, no. 14, pp.
1759-1767, DOI 10.1016/j.comcom.2012.05.008, August 2012,
<https://doi.org/10.1016/j.comcom.2012.05.008>.
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[I-D.ietf-6lo-path-aware-semantic-addressing]
Iannone, L., Li, G., Lou, D., Liu, P., and P. Thubert,
"Path-Aware Semantic Addressing (PASA) for Low power and
Lossy Networks", Work in Progress, Internet-Draft, draft-
ietf-6lo-path-aware-semantic-addressing-14, 1 July 2026,
<https://datatracker.ietf.org/doc/html/draft-ietf-6lo-
path-aware-semantic-addressing-14>.
[IEEE802154]
"IEEE Standard for Low-Rate Wireless Networks",
IEEE standard, DOI 10.1109/ieeestd.2016.7460875, April
2016, <https://doi.org/10.1109/ieeestd.2016.7460875>.
[OZTOPRAK24]
Oztoprak, A., Hassanpour, R., Ozkan, A., and K. Oztoprak,
"Security Challenges, Mitigation Strategies, and Future
Trends in Wireless Sensor Networks: A Review", ACM
Computing Surveys vol. 57, no. 4, pp. 1-29,
DOI 10.1145/3706583, December 2024,
<https://doi.org/10.1145/3706583>.
[RASHID24] Rashid, A. and T. Pecorella, "Is 6LoWPAN-ND necessary?
(Spoiler alert: Yes)", Computer Networks vol. 250, pp.
110535, DOI 10.1016/j.comnet.2024.110535, August 2024,
<https://doi.org/10.1016/j.comnet.2024.110535>.
[RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971,
DOI 10.17487/RFC3971, March 2005,
<https://www.rfc-editor.org/rfc/rfc3971>.
[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, DOI 10.17487/RFC3972, March 2005,
<https://www.rfc-editor.org/rfc/rfc3972>.
[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/rfc/rfc4862>.
[RFC9119] Perkins, C., McBride, M., Stanley, D., Kumari, W., and JC.
Zuniga, "Multicast Considerations over IEEE 802 Wireless
Media", RFC 9119, DOI 10.17487/RFC9119, October 2021,
<https://www.rfc-editor.org/rfc/rfc9119>.
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[RFC9453] Hong, Y., Gomez, C., Choi, Y., Sangi, A., and S.
Chakrabarti, "Applicability and Use Cases for IPv6 over
Networks of Resource-constrained Nodes (6lo)", RFC 9453,
DOI 10.17487/RFC9453, September 2023,
<https://www.rfc-editor.org/rfc/rfc9453>.
[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/rfc/rfc9915>.
[RIDOUX05] Ridoux, J., Fladenmuller, A., Viniotis, Y., and K.
Salamatian, "Trellis-Based Virtual Regular Addressing
Structures in Self-organized Networks", Lecture Notes in
Computer Science pp. 511-522, DOI 10.1007/11422778_41,
2005, <https://doi.org/10.1007/11422778_41>.
[SELIEM17] Seliem, M., Elsayed, K., and A. Khattab, "Optimized
neighbor discovery for 6LoWPANs: Implementation and
performance evaluation", Computer Communications vol. 112,
pp. 73-92, DOI 10.1016/j.comcom.2017.08.013, November
2017, <https://doi.org/10.1016/j.comcom.2017.08.013>.
[SHENOY21] Shenoy, N., Chandraiah, S., and P. Willis, "A Structured
Approach to Routing in the Internet", 2021 IEEE 22nd
International Conference on High Performance Switching and
Routing (HPSR) pp. 1-6,
DOI 10.1109/hpsr52026.2021.9481818, June 2021,
<https://doi.org/10.1109/hpsr52026.2021.9481818>.
Appendix A. Analytical comparison of GAAO and DHCPv6
While DHCPv6 is the standard for managed addressing in traditional
Ethernet or Wi-Fi networks, it is rarely used in 6LoWPAN (IPv6 over
Low-Power Wireless Personal Area Networks) for several critical
reasons rooted in efficiency and resource constraints. [RFC9119]
considers that the use of multicast transmissions over IEEE 802
wireless technologies may create issues related to:
* Reliability;
* Lower and variable data rate
* Capacity and impact on interference
* Power-save effects on multicast
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Hence, the intensive use of multicast may be not optimal. [RFC9119]
lists DHCPv6 [RFC9915] among the protocols that make an extensive use
of multicast. Neighbor Discovery is also listed, as multicast
optimization in this protocol is one of the reasons that lead to the
6LowPAN protocol stack development (c.f. [RFC6775] and [RFC8505]).
An extensive study comparing [RFC4861] and [RFC6775], showing the
efficiency of the former in 6LowPAN deployments, can be found in
[SELIEM17].
In rare cases, Stateless DHCPv6 is used in 6LoWPAN just to pass
"Other" information (like DNS server addresses or NTP servers) if the
Router Advertisements don't provide them. However, for actual
Address Assignment, it is almost non-existent in the field. Hence,
in 6LowPAN deployments the use of DHCPv6 entails to run an additional
service on the 6LRs beside the 6LowPAN ND. Running an additional
service will have impact on memory and battery lifetime. GAAO
requires only that the implementation supports the GAAO option, as it
is part of the the 6LowPAN ND already present and running, hence,
preserving the efficiency of [RFC6775] as shown in [SELIEM17].
A.1. DHCPv6 Message Structure
A typical DHCPv6 exchange involves four messages:
1. Solicit (from 6LN to server)
2. Advertise (from server to 6LN)
3. Request (from 6LN to server)
4. Reply (from server to 6LN)
Message payload (not including link/IPv6/UDP headers):
* Solicit: 30 bytes (minimal size - typical 80 to 150 bytes)
* Advertise: 32 bytes (minimal size - typical 100 to 180 bytes)
* Request: 48 bytes (minimal size - typical 80 to 150 bytes)
* Reply: 32 bytes (minimal size - typical 100 to 200 bytes)
Size of a minimal exchange: 142 bytes.
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DHCPv6 needs dedicated messages which may be multicast (depending on
the message type) and may span several links depending on where the
server is placed. As such, channel access and headers' overhead
cannot be shared with other messages. In a simple deployment with
the server directly accessible four different messages are necessary
with the first one being multicast.
A.2. GAAO Structure
A typical GAAO exchange involves two pass two options:
1. GAAO in NS (from 6LN to 6LR)
2. GAAO in NA (from 6LR to 6LN)
Option size: - *GAAO option* (32 bytes in NS messages and 40 bytes on
NA messages)
Size of a typical exchange: 72 bytes single hop.
GAAO does not need to be tramistted on dedicated messages. It can be
piggy-backed on ND messages carrying other options, hence sharing the
channel access and headers' overhead with these other options. If
not piggy-backed the exchange requires two unicast messages.
A.3. DHCPv6 vs GAAO Address Configuration
From an abstract point of view, for a 6LN to obtain an address
several, messages needs to be exchanged, as summarized in Table 5.
+========+=================+==================+====================+
| | Bytes Exchanged | Unicast messages | Multicast Messages |
+========+=================+==================+====================+
| DHCPv6 | 142 | 3 | 1 |
+--------+-----------------+------------------+--------------------+
| GAAO | 72 | 2 | 0 |
+--------+-----------------+------------------+--------------------+
Table 5: Number, type, and size of messages to configure an
address on a 6LN.
In generic and realistic 6LowPAN deployments, the GAAO option can be
piggy-backed on other ND messages, hence sharing header's and channel
access overhead, and it is just transmitted 1-hop away. DHCPv6,
cannot share such overhead with other data, specific packets needs to
be send per each message. Additionally, unicast messages may span
several hops, since the DHCPv6 server is usually deployed on the
6LBR, consuming network reesources (e.g., energy, network bandwidth)
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and experiencing higher latency. The multicast message may even
trigger a (ressource expensive) network wide broadcast, as explained
in Appendix A.5.
Addresses renewal bares similar cost for both DHCPv6 and GAAO, as it
consists on a two unicast messages. GAAO having a slightly smaller
message length, assuming DHCPv6 packets use the minimal size. The
difference lays in the fact that the DHCPv6 messages span several
hops, to reach the DHCPv6 server, hence consuming more ressources
(e.g., energy, network bandwidth, etc...). In case of dense and
noisy environment, with higher likelyhood of packet losses, this may
lead to nodes not being able to renew the DHCPv6 address lease, and
the node needing to restart address request using the the multicast-
based 4-packets exchange.
A.3.1. 6LoWPAN MTU Constraint
6LowPAN deployments may have very small MTU limits. For instance,
IEEE 802.15.4 frame size is only 127 bytes (max PHY layer payload).
Assuming that DHCPv6 is configured to use the bare minimal options,
there should be no MTU issues neither for DHCPv6 nor GAAO. If the
minimal conditions is not respected the fragmentation may be needed
for DHCPv6 large messages, increasing delay and energy consumption.
GAAO has a fixed size, hence the only consequence is that is better
to piggy-back with other options only if the MTU is respected.
A.4. Energy Consumption
Since DHCPv6 has to deliver almost twise the number of bytes compared
to GAAO, in terms of pure energy/byte consumption DHCPv6 uses almost
double the energy. Because the number of messages is also doubled,
there is an additional overhead due to 6LN accessing the channel four
times, with nodes staying awake longer which in turn consumes more
energy. Any communication pattern that forces many nodes to wake up
and receive packets (such as broadcast or multicast) has a
disproportionately large impact on battery lifetime [FOURTY12].
A.5. Multicast Inefficiency
It should stress that the unicast messages are all 1-hop, while the
multicast messages must be distributed to the whole network
[RASHID24]. Furthermore, multicast in 6LoWPAN is inefficient due to
the actual lack of multicast support at lower layers, which is
emulated either via broadcast or via unicast floods. Broadcast is
generally less energy-efficient than unicast for targeted
communication because it sends packets to all nodes, including those
not interested in the data, no ACKs are used, so retransmissions for
reliability must be handled at higher layers, potentially increasing
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energy usage, and all nodes must wake up and process the broadcast
packet, even if they are not the intended recipients ([FOURTY12],
[OZTOPRAK24]). Unicast floods, may increase reliability, however,
depending on the topology it may lead to higher latency and increased
energy consumption.
Authors' Addresses
Luigi Iannone
Huawei Technologies France S.A.S.U.
18, Quai du Point du Jour
92100 Boulogne-Billancourt
France
Email: luigi.iannone@huawei.com
David Lou
Huawei Technologies Duesseldorf GmbH
Riesstrasse 25
80992 Munich
Germany
Email: zhe.lou@huawei.com
Adnan Rashid
Email: adnanrashidpk@gmail.com
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