Internet Engineering Task Force (IETF) W. Kumari

Internet Engineering Task Force (IETF) W. Kumari
Request for Comments: 9686 Google, LLC
Category: Standards Track S. Krishnan
ISSN: 2070-1721 Cisco Systems, Inc.
R. Asati
Independent
L. Colitti
J. Linkova
Google, LLC
S. Jiang
BUPT
December 2024

Registering Self-Generated IPv6 Addresses Using DHCPv6

Abstract

This document defines a method to inform a DHCPv6 server that a
device has one or more self-generated or statically configured
addresses.

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/rfc9686.

Copyright Notice

Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
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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. Conventions and Definitions
3. Registration Mechanism Overview
4. DHCPv6 Address Registration Procedure
4.1. DHCPv6 Address Registration Option
4.2. DHCPv6 Address Registration Request Message
4.2.1. Server Message Processing
4.3. DHCPv6 Address Registration Acknowledgement
4.4. Signaling Address Registration Support
4.5. Retransmission
4.6. Registration Expiry and Refresh
4.6.1. SLAAC Addresses
4.6.2. Statically Assigned Addresses
4.6.3. Transmitting Refreshes
5. Client Configuration
6. Security Considerations
7. Privacy Considerations
8. IANA Considerations
9. References
9.1. Normative References
9.2. Informative References
Acknowledgements
Contributors
Authors' Addresses

1. Introduction

It is very common operational practice, especially in enterprise
networks, to use IPv4 DHCP logs for troubleshooting or forensics
purposes. An example of this includes a help desk dealing with a
ticket such as "The CEO's laptop cannot connect to the printer"; if
the Media Access Control (MAC) address of the printer is known (for
example, from an inventory system), the printer's IPv4 address can be
retrieved from the DHCP log or lease table and the printer can be
pinged to determine if it is reachable. Another common example is a
security operations team discovering suspicious events in outbound
firewall logs and then consulting DHCP logs to determine which
employee's laptop had that IPv4 address at that time so that they can
quarantine it and remove the malware.

This operational practice relies on the DHCP server knowing the IP
address assignments. This works quite well for IPv4 addresses, as
most addresses are either assigned by DHCP [RFC2131] or statically
configured by the network operator. For IPv6, however, this practice
is much harder to implement, as devices often self-configure IPv6
addresses via Stateless Address Autoconfiguration (SLAAC) [RFC4862].

This document provides a mechanism for a device to inform the DHCPv6
server that the device has a self-configured IPv6 address (or has a
statically configured address), and thus provides parity with IPv4 by
making DHCPv6 infrastructure aware of self-assigned IPv6 addresses.

2. Conventions and Definitions

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.

3. Registration Mechanism Overview

The DHCPv6 protocol is used as the address registration protocol and
a DHCPv6 server performs the role of an address registration server.
This document introduces a new Address Registration
(OPTION_ADDR_REG_ENABLE) option, which indicates that the server
supports the registration mechanism. Before registering any
addresses, the client MUST determine whether the network supports
address registration. It can do this by including the Address
Registration option code in the Option Request option (see
Section 21.7 of [RFC8415]) of the Information-Request, Solicit,
Request, Renew, or Rebind messages it sends to the server as part of
the regular stateless or stateful DHCPv6 configuration process. If
the server supports address registration, it includes an Address
Registration option in its Advertise or Reply messages. To avoid
undesired multicast traffic, if the DHCPv6 infrastructure does not
support (or is not willing to receive) any address registration
information, the client MUST NOT register any addresses using the
mechanism in this specification. Otherwise, the client registers
addresses as described below.

After successfully assigning a self-generated or statically
configured valid IPv6 address [RFC4862] on one of its interfaces, a
client implementing this specification multicasts an ADDR-REG-INFORM
message (see Section 4.2) in order to inform the DHCPv6 server that
this self-generated address is in use. Each ADDR-REG-INFORM message
contains a DHCPv6 Identity Association (IA) Address option [RFC8415]
to specify the address being registered.

The address registration mechanism overview is shown in Figure 1.

+--------+ +------------------+ +---------------+
| CLIENT | | FIRST-HOP ROUTER | | DHCPv6 SERVER |
+--------+ +---------+--------+ +-------+-------+
| SLAAC | |
|<--------------------> | |
| | |
| |
| src: link-local address |
| --------------------------------------------> |
| INFORMATION-REQUEST or SOLICIT/... |
| - OPTION REQUEST OPTION |
| -- OPTION_ADDR_REG_ENABLE |
| |
| ... |
| |
| |
|<--------------------------------------------- |
| REPLY or ADVERTISE MESSAGE |
| - OPTION_ADDR_REG_ENABLE |
| |
| |
| src: address being registered |
| --------------------------------------------> |
| ADDR-REG-INFORM MESSAGE |Register/
| |log addresses
| |
| |
| <-------------------------------------------- |
| ADDR-REG-REPLY MESSAGE |
| |

Figure 1: Address Registration Procedure Overview

4. DHCPv6 Address Registration Procedure

4.1. DHCPv6 Address Registration Option

The Address Registration option (OPTION_ADDR_REG_ENABLE) indicates
that the server supports the mechanism described in this document.
The format of the Address Registration option is described as
follows:

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| option-code | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 2: DHCPv6 Address Registration Option

option-code: OPTION_ADDR_REG_ENABLE (148)

option-len: 0

If a client has the address registration mechanism enabled, it MUST
include this option in all Option Request options that it sends.

A server that is configured to support the address registration
mechanism MUST include this option in Advertise and Reply messages if
the client message it is replying to contained this option in the
Option Request option.

4.2. DHCPv6 Address Registration Request Message

The DHCPv6 client sends an ADDR-REG-INFORM message to inform that an
IPv6 address is assigned to the client's interface. The format of
the ADDR-REG-INFORM message is described as follows:

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-type | transaction-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. options .
. (variable) .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 3: DHCPv6 ADDR-REG-INFORM Message

msg-type: Identifies the DHCPv6 message type; set to ADDR-REG-INFORM
(36).

transaction-id: The transaction ID for this message exchange.

options: The options carried in this message.

The client MUST generate a transaction ID as described in [RFC8415]
and insert this value in the transaction-id field.

The client MUST include the Client Identifier option [RFC8415] in the
ADDR-REG-INFORM message.

The ADDR-REG-INFORM message MUST NOT contain the Server Identifier
option and MUST contain exactly one IA Address option containing the
address being registered. The valid-lifetime and preferred-lifetime
fields in the option MUST match the current Valid Lifetime and
Preferred Lifetime of the address being registered.

The ADDR-REG-INFORM message is dedicated for clients to initiate an
address registration request toward an address registration server.
Consequently, clients MUST NOT put any Option Request option(s) in
the ADDR-REG-INFORM message. Clients MAY include other options, such
as the Client FQDN option [RFC4704].

The client sends the DHCPv6 ADDR-REG-INFORM message to the
All_DHCP_Relay_Agents_and_Servers multicast address (ff02::1:2). The
client MUST send separate messages for each address being registered.

Unlike other types of messages, which are sent from the link-local
address of the client, the ADDR-REG-INFORM message MUST be sent from
the address being registered. This is primarily for "fate sharing"
purposes; for example, if the network implements some form of Layer 2
security to prevent a client from spoofing other clients' MAC
addresses, this prevents an attacker from spoofing ADDR-REG-INFORM
messages.

On clients with multiple interfaces, the client MUST only send the
packet on the network interface that has the address being
registered, even if it has multiple interfaces with different
addresses. If the same address is configured on multiple interfaces,
then the client MUST send the ADDR-REG-INFORM message each time the
address is configured on an interface that did not previously have it
and refresh each registration independently from the others.

The client MUST only send the ADDR-REG-INFORM message for valid
addresses [RFC4862] of global scope [RFC4007]. This includes Unique
Local Addresses (ULAs), which are defined in [RFC4193] to have global
scope. This also includes statically assigned addresses of global
scope (such addresses are considered to be valid indefinitely). The
client MUST NOT send the ADDR-REG-INFORM message for addresses
configured by DHCPv6.

The client SHOULD NOT send the ADDR-REG-INFORM message unless it has
received a Router Advertisement (RA) message with either the M or O
flags set to 1.

Clients MUST discard any received ADDR-REG-INFORM messages.

4.2.1. Server Message Processing

Servers MUST discard any ADDR-REG-INFORM messages that meet any of
the following conditions:

* the message does not include a Client Identifier option;

* the message includes a Server Identifier option;

* the message does not include the IA Address option, or the IP
address in the IA Address option does not match the source address
of the original ADDR-REG-INFORM message sent by the client. The
source address of the original message is the source IP address of
the packet if it is not relayed or is the peer-address field of
the innermost Relay-forward message if it is relayed; or

* the message includes an Option Request option.

If the message is not discarded, the address registration server
SHOULD verify that the address being registered is "appropriate to
the link" as defined by [RFC8415] or within a prefix delegated to the
client via DHCPv6 for Prefix Delegation (DHCPv6-PD) (see Section 6.3
of [RFC8415]). If the address being registered fails this
verification, the server MUST drop the message and SHOULD log this
fact. If the message passes the verification, the server:

* MUST log the address registration information (as is done normally
for clients to which it has assigned an address), unless it is
configured not to do so. The server SHOULD log the client DHCP
Unique Identifier (DUID) and the link-layer address, if available.
The server MAY log any other information.

* SHOULD register a binding between the provided Client Identifier
and IPv6 address in its database, if no binding exists. The
lifetime of the binding is equal to the Valid Lifetime of the
address reported by the client. If there is already a binding
between the registered address and the same client, the server
MUST update its lifetime. If there is already a binding between
the registered address and another client, the server SHOULD log
the fact and update the binding.

* SHOULD mark the address as unavailable for use and not include it
in future Advertise messages.

* MUST send back an ADDR-REG-REPLY message to ensure the client does
not retransmit.

If a client is multihomed (i.e., connected to multiple administrative
domains, each operating its own DHCPv6 infrastructure), the
requirement to verify that the registered address is appropriate for
the link or belongs to a delegated prefix ensures that each DHCPv6
server only registers bindings for addresses from the given
administrative domain.

As mentioned in Section 4.2, although a client "MUST NOT send the
ADDR-REG-INFORM message for addresses configured by DHCPv6", if a
server does receive such a message, it SHOULD log and discard it.

DHCPv6 relay agents and switches that relay address registration
messages directly from clients MUST include the client's link-layer
address in the relayed message using the Client Link-Layer Address
option [RFC6939] if they would do so for other DHCPv6 client messages
such as Solicit, Request, and Rebind.

4.3. DHCPv6 Address Registration Acknowledgement

The server MUST acknowledge receipt of a valid ADDR-REG-INFORM
message by sending back an ADDR-REG-REPLY message. The format of the
ADDR-REG-REPLY message is described as follows:

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-type | transaction-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. options .
. (variable) .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 4: DHCPv6 ADDR-REG-REPLY Message

msg-type: Identifies the DHCPv6 message type; set to ADDR-REG-REPLY
(37).

transaction-id: The transaction ID for this message exchange.

options: The options carried in this message.

If the ADDR-REG-INFORM message that the server is replying to was not
relayed, then the IPv6 destination address of the message MUST be the
address being registered. If the ADDR-REG-INFORM message was
relayed, then the server MUST construct the Relay-reply message as
specified in Section 19.3 of [RFC8415].

The server MUST copy the transaction-id from the ADDR-REG-INFORM
message to the transaction-id field of the ADDR-REG-REPLY.

The ADDR-REG-REPLY message MUST contain an IA Address option for the
address being registered. The option MUST be identical to the one in
the ADDR-REG-INFORM message that the server is replying to.

Servers MUST ignore any received ADDR-REG-REPLY messages.

Clients MUST discard any ADDR-REG-REPLY messages that meet any of the
following conditions:

* the IPv6 destination address does not match the address being
registered;

* the IA Address option does not match the address being registered;

* the address being registered is not assigned to the interface
receiving the message; or

* the transaction-id does not match the transaction-id the client
used in the corresponding ADDR-REG-INFORM message.

The ADDR-REG-REPLY message only indicates that the ADDR-REG-INFORM
message has been received and that the client should not retransmit
it. The ADDR-REG-REPLY message MUST NOT be considered to be any
indication of the address validity and MUST NOT be required for the
address to be usable. DHCPv6 relays, or other devices that snoop
ADDR-REG-REPLY messages, MUST NOT add or alter any forwarding or
security state based on the ADDR-REG-REPLY message.

4.4. Signaling Address Registration Support

To avoid undesired multicast traffic, the client MUST NOT register
addresses using this mechanism unless the DHCPv6 infrastructure
supports address registration. The client can discover this by
including the OPTION_ADDR_REG_ENABLE option in the Option Request
options that it sends. If the client receives and processes an
Advertise or Reply message with the OPTION_ADDR_REG_ENABLE option, it
concludes that the DHCPv6 infrastructure supports address
registration. When the client detects address registration support,
it MUST start the registration process (unless configured not to do
so) and MUST immediately register any addresses that are already in
use. Once the client starts the registration process, it MUST NOT
stop registering addresses until it disconnects from the link, even
if subsequent Advertise or Reply messages do not contain the
OPTION_ADDR_REG_ENABLE option.

The client MUST discover whether the DHCPv6 infrastructure supports
address registration every time it connects to a network or when it
detects it has moved to a new link, without utilizing any prior
knowledge about address registration support on that network or link.
This client behavior allows networks to progressively roll out
support for the Address Registration option across the DHCPv6
infrastructure without causing clients to frequently stop and restart
address registration if some of the network's DHCPv6 servers support
it and some do not.

A client with multiple interfaces MUST discover address registration
support for each interface independently. The client MUST NOT send
address registration messages on a given interface unless the client
has discovered that the interface is connected to a network that
supports address registration.

4.5. Retransmission

To reduce the effects of packet loss on registration, the client MUST
retransmit the registration message. Retransmissions SHOULD follow
the standard retransmission logic specified by Section 15 of
[RFC8415] with the following default parameters for the initial
retransmission time (IRT) and maximum retransmission count (MRC):

* IRT 1 sec

* MRC 3

The client SHOULD allow these parameters to be configured by the
administrator.

To comply with Section 16.1 of [RFC8415], the client MUST leave the
transaction ID unchanged in retransmissions of an ADDR-REG-INFORM
message. When the client retransmits the registration message, the
lifetimes in the packet MUST be updated so that they match the
current lifetimes of the address.

If an ADDR-REG-REPLY message is received for the address being
registered, the client MUST stop retransmission.

4.6. Registration Expiry and Refresh

The client MUST refresh registrations to ensure that the server is
always aware of which addresses are still valid. The client SHOULD
perform refreshes as described below.

4.6.1. SLAAC Addresses

For an address configured using SLAAC, a function
AddrRegRefreshInterval(address) is defined as 80% of the address's
current Valid Lifetime. When calculating this value, the client
applies a multiplier of AddrRegDesyncMultiplier to avoid
synchronization with other clients, which could cause a large number
of registration messages to reach the server at the same time.
AddrRegDesyncMultiplier is a random value uniformly distributed
between 0.9 and 1.1 (inclusive) and is chosen by the client when it
starts the registration process, to ensure that refreshes for
addresses with the same lifetime are coalesced (see below).

Whenever the client registers or refreshes an address, it calculates
a NextAddrRegRefreshTime for that address as AddrRegRefreshInterval
seconds in the future but does not schedule any refreshes.

Whenever the network changes the Valid Lifetime of an existing
address by more than 1%, for example, by sending a Prefix Information
Option (PIO) [RFC4861] with a new Valid Lifetime, the client
calculates a new AddrRegRefreshInterval. The client schedules a
refresh for min(now + AddrRegRefreshInterval,
NextAddrRegRefreshTime). If the refresh would be scheduled in the
past, then the refresh occurs immediately.

Justification: This algorithm ensures that refreshes are not sent too
frequently while ensuring that the server never believes that the
address has expired when it has not. Specifically, after every
registration:

* If the network never changes the lifetime of an address (e.g., if
no further PIOs are received, or if all PIO lifetimes decrease in
step with the passage of time), then no refreshes occur.
Refreshes are not necessary, because the address expires at the
time the server expects it to expire.

* Any time the network changes the lifetime of an address (i.e.,
changes the time at which the address will expire), the client
ensures that a refresh is scheduled, so that server will be
informed of the new expiry.

* Because AddrRegDesyncMultiplier is at most 1.1, the refresh never
occurs later than a point 88% between the time when the address
was registered and the time when the address will expire. This
allows the client to retransmit the registration for up to 12% of
the original interval before it expires. This may not be possible
if the network sends a Router Advertisement (RA) [RFC4861] very
close to the time when the address would have expired. In this
case, the client refreshes immediately, which is the best it can
do.

* The 1% tolerance ensures that the client will not refresh or
reschedule refreshes if the Valid Lifetime experiences minor
changes due to transmission delays or clock skew between the
client and the router(s) sending the RA.

* AddrRegRefreshCoalesce (Section 4.6.3) allows battery-powered
clients to wake up less often. In particular, it allows the
client to coalesce refreshes for multiple addresses formed from
the same prefix, such as the stable and privacy addresses. Higher
values will result in fewer wakeups but may result in more network
traffic, because if a refresh is sent early, then the next RA
received will cause the client to immediately send a refresh
message.

* In typical networks, the lifetimes in periodic RAs either contain
constant values or values that decrease over time to match another
lifetime, such as the lifetime of a prefix delegated to the
network. In both these cases, this algorithm will refresh on the
order of once per address lifetime, which is similar to the number
of refreshes that are necessary using stateful DHCPv6.

* Because refreshes occur at least once per address lifetime, the
network administrator can control the address refresh frequency by
appropriately setting the Valid Lifetime in the PIO.

4.6.2. Statically Assigned Addresses

A statically assigned address has an infinite Valid Lifetime that is
not affected by RAs. Therefore, whenever the client registers or
refreshes a statically assigned address, the next refresh is
scheduled for StaticAddrRegRefreshInterval seconds in the future.
The default value of StaticAddrRegRefreshInterval is 4 hours. This
ensures static addresses are still refreshed periodically, but
refreshes for static addresses do not cause excessive multicast
traffic. The StaticAddrRegRefreshInterval interval SHOULD be
configurable.

4.6.3. Transmitting Refreshes

When a refresh is performed, the client MAY refresh all addresses
assigned to the interface that are scheduled to be refreshed within
the next AddrRegRefreshCoalesce seconds. The value of
AddrRegRefreshCoalesce is implementation dependent, and a suggested
default is 60 seconds.

Registration refresh packets MUST be retransmitted using the same
logic as used for initial registrations (see Section 4.5).

The client MUST generate a new transaction ID when refreshing the
registration.

When a Client-Identifier-to-IPv6-address binding expires, the server
MUST remove it and consider the address as available for use.

The client MAY choose to notify the server when an address is no
longer being used (e.g., if the client is disconnecting from the
network, the address lifetime expired, or the address is being
removed from the interface). To indicate that the address is not
being used anymore, the client MUST set the preferred-lifetime and
valid-lifetime fields of the IA Address option in the ADDR-REG-INFORM
message to zero. If the server receives a message with a valid-
lifetime of zero, it MUST act as if the address has expired.

5. Client Configuration

DHCP clients SHOULD allow the administrator to disable sending ADDR-
REG-INFORM messages. Sending the messages SHOULD be enabled by
default.

6. Security Considerations

An attacker may attempt to register a large number of addresses in
quick succession in order to overwhelm the address registration
server and/or fill up log files. Similar attack vectors exist today,
e.g., an attacker can DoS the server with messages containing spoofed
DHCP Unique Identifiers (DUIDs) [RFC8415].

If a network is using First-Come, First-Served Source Address
Validation Improvement (FCFS SAVI) [RFC6620], then the DHCPv6 server
can trust that the ADDR-REG-INFORM message was sent by the legitimate
holder of the address. This prevents a client from registering an
address configured on another client.

One of the use cases for the mechanism described in this document is
to identify sources of malicious traffic after the fact. Note,
however, that as the device itself is responsible for informing the
DHCPv6 server that it is using an address, a malicious or compromised
device can simply choose to not send the ADDR-REG-INFORM message.
This is an informational, optional mechanism and is designed to aid
in troubleshooting and forensics. On its own, it is not intended to
be a strong security access mechanism. In particular, the ADDR-REG-
INFORM message MUST NOT be used for authentication and authorization
purposes, because in addition to the reasons above, the packets
containing the message may be dropped.

7. Privacy Considerations

If the network doesn't have Multicast Listener Discovery (MLD)
snooping enabled, then IPv6 link-local multicast traffic is
effectively transmitted as broadcast. In such networks, an on-link
attacker listening to DHCPv6 messages might obtain information about
IPv6 addresses assigned to the client. As ADDR-REG-INFORM messages
contain unique identifiers such as the client's DUID, the attacker
may be able to track addresses being registered and map them to the
same client, even if the client uses randomized MAC addresses. This
privacy consideration is not specific to the proposed mechanism.
Section 4.3 of [RFC7844] discusses using the DUID for device tracking
in DHCPv6 environments and provides mitigation recommendations.

In general, hiding information about the specific IPv6 address from
on-link observers should not be considered a security measure, as
such information is usually disclosed via Duplicate Address Detection
[RFC4862] to all nodes anyway, if MLD snooping is not enabled.

If MLD snooping is enabled, an attacker might be able to join the
All_DHCP_Relay_Agents_and_Servers multicast address (ff02::1:2) group
to listen for address registration messages. However, the same
result can be achieved by joining the All Routers Address (ff02::2)
group and listen to gratuitous neighbor advertisement messages
[RFC9131]. It should be noted that this particular scenario shares
the fate with DHCPv6 address assignment: if an attacker can join the
All_DHCP_Relay_Agents_and_Servers multicast group, they would be able
to monitor all DHCPv6 messages sent from the client to DHCPv6 servers
and relays and therefore obtain the information about addresses being
assigned via DHCPv6. Layer 2 isolation allows mitigating this threat
by blocking on-link peer-to-peer communication between nodes.

8. IANA Considerations

This document introduces the following entities, which have been
allocated in the "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)" registry group defined at <http://www.iana.org/assignments/
dhcpv6-parameters>. These include:

* One new DHCPv6 option, described in Section 4.1, which has been
allocated in the "Option Codes" registry:

Value: 148
Description: OPTION_ADDR_REG_ENABLE
Client ORO: Yes
Singleton Option: Yes
Reference: RFC 9686

* Two new DHCPv6 messages, which have been allocated in the "Message
Types" registry (for more information, see Sections 4.2 and 4.3,
respectively, for each DHCPv6 message):

Value: 36
Description: ADDR-REG-INFORM
Reference: RFC 9686

Value: 37
Description: ADDR-REG-REPLY
Reference: RFC 9686

9. References

9.1. 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/info/rfc2119>.

[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, DOI 10.17487/RFC2131, March 1997,
<https://www.rfc-editor.org/info/rfc2131>.

[RFC4007] Deering, S., Haberman, B., Jinmei, T., Nordmark, E., and
B. Zill, "IPv6 Scoped Address Architecture", RFC 4007,
DOI 10.17487/RFC4007, March 2005,
<https://www.rfc-editor.org/info/rfc4007>.

[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,
<https://www.rfc-editor.org/info/rfc4193>.

[RFC4704] Volz, B., "The Dynamic Host Configuration Protocol for
IPv6 (DHCPv6) Client Fully Qualified Domain Name (FQDN)
Option", RFC 4704, DOI 10.17487/RFC4704, October 2006,
<https://www.rfc-editor.org/info/rfc4704>.

[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>.

[RFC6939] Halwasia, G., Bhandari, S., and W. Dec, "Client Link-Layer
Address Option in DHCPv6", RFC 6939, DOI 10.17487/RFC6939,
May 2013, <https://www.rfc-editor.org/info/rfc6939>.

[RFC7844] Huitema, C., Mrugalski, T., and S. Krishnan, "Anonymity
Profiles for DHCP Clients", RFC 7844,
DOI 10.17487/RFC7844, May 2016,
<https://www.rfc-editor.org/info/rfc7844>.

[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>.

[RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
Richardson, M., Jiang, S., Lemon, T., and T. Winters,
"Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 8415, DOI 10.17487/RFC8415, November 2018,
<https://www.rfc-editor.org/info/rfc8415>.

[RFC9131] Linkova, J., "Gratuitous Neighbor Discovery: Creating
Neighbor Cache Entries on First-Hop Routers", RFC 9131,
DOI 10.17487/RFC9131, October 2021,
<https://www.rfc-editor.org/info/rfc9131>.

9.2. Informative References

[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>.

[RFC6620] Nordmark, E., Bagnulo, M., and E. Levy-Abegnoli, "FCFS
SAVI: First-Come, First-Served Source Address Validation
Improvement for Locally Assigned IPv6 Addresses",
RFC 6620, DOI 10.17487/RFC6620, May 2012,
<https://www.rfc-editor.org/info/rfc6620>.

Acknowledgements

Many thanks to Bernie Volz for the significant review and feedback,
as well as Hermin Anggawijaya, Carlos Jesus Bernardos, Brian
Carpenter, Stuart Cheshire, Roman Danyliw, Alan DeKok, James
Guichard, James Guichard, Erik Kline, Mallory Knodel, Murray
Kucherawy, David Lamparter, Ted Lemon, Eric Levy-Abegnoli, Aditi
Patange, Jim Reid, Michael Richardson, Patrick Rohr, John Scudder,
Mark Smith, Gunter Van de Velde, Eric Vyncke, Timothy Winters, and
Peter Yee for their feedback, comments, and guidance. We apologize
if we inadvertently forgot to acknowledge anyone's contributions.

Contributors

Gang Chen
China Mobile
53A, Xibianmennei Ave.
Xuanwu District
Beijing
China
Email: [email protected]

Authors' Addresses

Warren Kumari
Google, LLC
Email: [email protected]

Suresh Krishnan
Cisco Systems, Inc.
Email: [email protected]

Rajiv Asati
Independent
Email: [email protected]

Lorenzo Colitti
Google, LLC
Shibuya 3-21-3,
Japan
Email: [email protected]

Jen Linkova
Google, LLC
1 Darling Island Rd
Pyrmont 2009
Australia
Email: [email protected]

Sheng Jiang
Beijing University of Posts and Telecommunications
No. 10 Xitucheng Road
Beijing
Haidian District, 100083
China
Email: [email protected]