Internet DRAFT - draft-ietf-dhc-v6only
draft-ietf-dhc-v6only
Dynamic Host Configuration L. Colitti
Internet-Draft J. Linkova
Updates: 2563 (if approved) Google
Intended status: Standards Track M. Richardson
Expires: February 14, 2021 Sandelman
T. Mrugalski
ISC
August 13, 2020
IPv6-Only-Preferred Option for DHCPv4
draft-ietf-dhc-v6only-08
Abstract
This document specifies a DHCPv4 option to indicate that a host
supports an IPv6-only mode and is willing to forgo obtaining an IPv4
address if the network provides IPv6 connectivity. It also updates
RFC2563 to specify the DHCPv4 server behavior when the server
receives a DHCPDISCOVER not containing the Auto-Configure option but
containing the new option defined in this document.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 14, 2021.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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carefully, as they describe your rights and restrictions with respect
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Reasons to Signal IPv6-Only Support in DHCPv4 Packets . . . . 5
3. IPv6-Only Preferred Option . . . . . . . . . . . . . . . . . 5
3.1. Option format . . . . . . . . . . . . . . . . . . . . . . 6
3.2. DHCPv4 Client Behavior . . . . . . . . . . . . . . . . . 6
3.3. DHCPv4 Server Behavior . . . . . . . . . . . . . . . . . 8
3.3.1. Interaction with RFC2563 . . . . . . . . . . . . . . 9
3.4. Constants and Configuration Variables . . . . . . . . . . 10
4. IPv6-Only Transition Technologies Considerations . . . . . . 10
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
6. Security Considerations . . . . . . . . . . . . . . . . . . . 12
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
8.1. Normative References . . . . . . . . . . . . . . . . . . 12
8.2. Informative References . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
One of the biggest challenges of deploying IPv6-only LANs is that
such networks might contain rather heterogeneous collection of hosts.
While some hosts are capable of operating in IPv6-only mode (either
because the OS and all applications are IPv6-only capable or because
the host has some form of 464XLAT [RFC6877] deployed), others might
still have IPv4 dependencies and need IPv4 addresses to operate
properly. To incrementally rollout IPv6-only, network operators
might need to provide IPv4 on demand whereby a host receives an IPv4
address if it needs it, while IPv6-only capable hosts (such as modern
mobile devices) are not allocated IPv4 addresses. Traditionally that
goal is achieved by placing IPv6-only capable devices into a
dedicated IPv6-only network segment or WiFi SSID, while dual-stack
devices reside in another network with IPv4 and DHCPv4 enabled.
However such an approach has a number of drawbacks, including but not
limited to:
o Doubling the number of network segments leads to operational
complexity and performance impact, for instance due to high memory
utilization caused by an increased number of ACL entries.
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o Placing a host into the correct network segment is problematic.
For example, in the case of 802.11 Wi-Fi the user might select the
wrong SSID. In the case of wired 802.1x authentication the
authentication server might not have all the information required
to make the correct decision and choose between an IPv6-only and a
dual-stack VLAN.
It would be beneficial for IPv6 deployment if operators could
implement IPv6-mostly (or IPv4-on-demand) segments where IPv6-only
hosts co-exist with legacy dual-stack devices. The trivial solution
of disabling IPv4 stack on IPv6-only capable hosts is not feasible as
those clients must be able to operate on IPv4-only networks as well.
While IPv6-only capable devices might use a heuristic approach to
learning if the network provides IPv6-only functionality and stop
using IPv4 if it does, such an approach might be practically
undesirable. One important reason is that when a host connects to a
network, it does not know if the network is IPv4-only, dual-stack or
IPv6-only. To ensure that the connectivity over whatever protocol is
present becomes available as soon as possible the host usually starts
configuring both IPv4 and IPv6 immediately. If hosts were to delay
requesting IPv4 until IPv6 reachability is confirmed, that would
penalize IPv4-only and dual-stack networks, which does not seem
practical. Requesting IPv4 and then releasing it later, after IPv6
reachability is confirmed, might cause user-visible errors as it
would be disruptive for applications which have started using the
assigned IPv4 address already. Instead it would be useful to have a
mechanism which would allow a host to indicate that its request for
an IPv4 address is optional and a network to signal that IPv6-only
functionality (such as NAT64, [RFC6146]) is available. The proposed
solution is to introduce a new DHCPv4 option which a client uses to
indicate that it does not need an IPv4 address if the network
provides IPv6-only connectivity (as NAT64 and DNS64). If the
particular network segment provides IPv4-on-demand such clients would
not be supplied with IPv4 addresses, while on IPv4-only or dual-stack
segments without NAT64 services IPv4 addresses will be provided.
[RFC2563] introduces the Auto-Configure DHCPv4 option and describes
DHCPv4 servers behavior if no address is chosen for a host. This
document updates [RFC2563] to modify the server behavior if the
DHCPOFFER contains the IPv6-only Preferred option.
1.1. 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.
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1.2. Terminology
Dual-stack network or device: a network or device which has both
versions of the Internet Protocol (IPv4 and IPv6) enabled and
operational.
IPv6-only capable host: a host which does not require an IPv4 address
and can operate on IPv6-only networks. More precisely, IPv6-only
capability is specific to a given interface of the host: if some
application on a host require IPv4 and 464XLAT CLAT [RFC6877] is only
enabled on one interface, the host is IPv6-only capable if connected
to a NAT64 network via that interface. This document implies that
IPv6-only capable hosts reach IPv4-only destinations via a NAT64
service provided by the network. Section 4 discusses hypothetical
scenarios of other transition technologies being used.
IPv4-requiring host: a host which is not IPv6-only capable and can
not operate in an IPv6-only network providing NAT64 service.
IPv4-on-demand: a deployment scenario where end hosts are expected to
operate in IPv6-only mode by default and IPv4 addresses can be
assigned to some hosts if those hosts explicitly opt-in to receiving
IPv4 addresses.
IPv6-mostly network: a network which provides NAT64 (possibly with
DNS64) service as well as IPv4 connectivity and allows coexistence of
IPv6-only, dual-stack and IPv4-only hosts on the same segment. Such
deployment scenario allows operators to incrementally turn off IPv4
on end hosts, while still providing IPv4 to devices which require
IPv4 to operate. But, IPv6-only capable devices need not be assigned
IPv4 addresses.
IPv6-only mode: a mode of operation when a host acts as an IPv6-only
capable host and does not have IPv4 addresses assigned (except that
IPv4 link-local addresses [RFC3927] may have been configured).
IPv6-only network: a network which does not provide routing
functionality for IPv4 packets. Such networks may or may not allow
intra-LAN IPv4 connectivity. IPv6-only network usually provides
access to IPv4-only resources via NAT64 [RFC6146].
NAT64: Network Address and Protocol Translation from IPv6 Clients to
IPv4 Servers [RFC6146].
RA: Router Advertisement, a message used by IPv6 routers to advertise
their presence together with various link and Internet parameters
[RFC4861].
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DNS64: a mechanism for synthesizing AAAA records from A records
[RFC6147].
Network attachment event: A Link Up event, as described by [RFC4957]
which results in a host detecting an available network.
Disabling IPv4 stack on the host interface: the host behavior when
the host:
o does not send any IPv4 packets from that interface,
o drops all IPv4 packets received on that interface and
o does not forward any IPv4 packets to that interface.
2. Reasons to Signal IPv6-Only Support in DHCPv4 Packets
For networks which contain a mix of both IPv6-only capable hosts and
IPv4-requiring hosts, and which utilize DHCPv4 for configuring the
IPv4 network stack on hosts, it seems natural to leverage the same
protocol to signal that IPv4 is discretional on a given segment. An
ability to remotely disable IPv4 on a host can be seen as a new
denial-of-service attack vector. The proposed approach limits the
attack surface to DHCPv4-related attacks without introducing new
vulnerable elements.
Another benefit of using DHCPv4 for signaling is that IPv4 will be
disabled only if both the client and the server indicate IPv6-only
capability. It allows IPv6-only capable hosts to turn off IPv4 only
upon receiving an explicit signal from the network and operate in
dual-stack or IPv4-only mode otherwise. In addition, the proposed
mechanism does not introduce any additional delays to the process of
configuring IP stack on hosts. If the network does not support IPv6-
only/IPv4-on-demand mode, an IPv6-only capable host would configure
an IPv4 address as quickly as on any other host.
Being a client/server protocol, DHCPv4 allows IPv4 to be selectively
disabled on a per-host basis on a given network segment. Coexistence
of IPv6-only, dual-stack and even IPv4-only hosts on the same LAN
would not only allow network administrators to preserve scarce IPv4
addresses but would also drastically simplify incremental deployment
of IPv6-only networks, positively impacting IPv6 adoption.
3. IPv6-Only Preferred Option
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3.1. Option format
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Length | Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value (contd) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: IPv6-Only Preferred Option Format
Fields:
Code: 8-bit identifier of the IPv6-Only Preferred option code as
assigned by IANA: TBD.
The client includes the Code in the Parameter Request List in
DHCPDISCOVER and DHCPREQUEST messages as described in
Section 3.2.
Length: 8-bit unsigned integer. The length of the option excluding
the Code and Length Fields. The server MUST set the length
field to 4. The client MUST ignore the IPv6-Only Preferred
option if the length field value is not 4.
Value: 32-bit unsigned integer.
The number of seconds the client should disable DHCPv4 for
(V6ONLY_WAIT configuration variable).
If the server pool is explicitly configured with a
V6ONLY_WAIT timer the server MUST set the field to that
configured value. Otherwise the server MUST set it to zero.
The client MUST process that field as described in
Section 3.2.
The client never sets this field as it never sends the full
option but includes the option code in the Parameter Request
List as described in Section 3.2.
3.2. DHCPv4 Client Behavior
A DHCPv4 client SHOULD allow a device administrator to configure
IPv6-only preferred mode either for a specific interface (to indicate
that the device is IPv6-only capable if connected to a NAT64 network
via that interface) or for all interfaces. If only a specific
interface is configured as IPv6-only capable the DHCPv4 client MUST
NOT consider the host to be an IPv6-only capable for the purpose of
sending/receiving DHCPv4 packets over any other interfaces.
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The DHCPv4 client on an IPv4-requiring host MUST NOT include the
IPv6-only Preferred option in the Parameter Request List of any
DHCPv4 packets and MUST ignore that option in packets received from
DHCPv4 servers.
DHCPv4 clients running on IPv6-only capable hosts SHOULD include the
IPv6-only Preferred option code in the Parameter Request List in
DHCPDISCOVER and DHCPREQUEST messages for interfaces so enabled and
follow the processing as described below on a per enabled interface
basis.
If the client did not include the IPv6-only Preferred option code in
the Parameter Request List option in the DHCPDISCOVER or DHCPREQUEST
message it MUST ignore the IPv6-only Preferred option in any messages
received from the server.
If the client includes the IPv6-only Preferred option in the
Parameter Request List and the DHCPOFFER message from the server
contains a valid IPv6-only Preferred option, the client SHOULD NOT
request the IPv4 address provided in the DHCPOFFER. If the IPv6-only
Preferred option returned by the server contains a value greater or
equal to MIN_V6ONLY_WAIT, the client SHOULD set the V6ONLY_WAIT timer
to that value. Otherwise, the client SHOULD set the V6ONLY_WAIT
timer to MIN_V6ONLY_WAIT. The client SHOULD stop the DHCPv4
configuration process for V6ONLY_WAIT seconds or until a network
attachment event, whichever happens first. The host MAY disable the
IPv4 stack completely on the affected interface for V6ONLY_WAIT
seconds or until the network attachment event, whichever happens
first.
The IPv6-only Preferred option SHOULD be included in the Parameter
Request List option in DHCPREQUEST messages (after receiving a
DHCPOFFER without this option, for a INIT-REBOOT, or when renewing or
rebinding a leased address). If the DHCPv4 server responds with a
DHCPACK that includes the IPv6-only Preferred option, the client
behaviour depends on the client's state. If the client is in the
INIT-REBOOT state it SHOULD stop the DHCPv4 configuration process or
disable IPv4 stack completely for V6ONLY_WAIT seconds or until the
network event, whichever happens first. It also MAY send a
DHCPRELEASE message. If the client is in any other state it SHOULD
continue to use the assigned IPv4 address until further DHCPv4
reconfiguration events.
If the client includes the IPv6-only Preferred option in the
Parameter Request List and the server responds with DHCPOFFER message
without a valid IPv6-only Preferred option, the client MUST proceed
as normal with a DHCPREQUEST.
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If the client waits for multiple DHCPOFFER responses and selects one
of them, it MUST follow the processing for the IPv6-only Preferred
option based on the selected response. A client MAY use the presence
of the IPv6-only Preferred option as a selection criteria.
When an IPv6-only capable client receives the IPv6-Only Preferred
option from the server, the client MAY configurean IPv4 link-local
address [RFC3927]. In that case IPv6-only capable devices might
still be able to communicate over IPv4 to other devices on the link.
The Auto-Configure Option [RFC2563] can be used to control IPv4 link-
local addresses autoconfiguration. Section 3.3.1 discusses the
interaction between the IPv6-only Preferred and the Auto-Configure
options.
3.3. DHCPv4 Server Behavior
The DHCPv4 server SHOULD be able to configure all or individual pools
to include the IPv6-only preferred option in DHCPv4 responses if the
client included the option code in the Parameter Request List option.
The DHCPv4 server MAY have a configuration option to specify the
V6ONLY_WAIT timer for all or individual IPv6-mostly pools.
The server MUST NOT include the IPv6-only Preferred option in the
DHCPOFFER or DHCPACK message if the YIADDR field in the message does
not belong to a pool configured as IPv6-mostly. The server MUST NOT
include the IPv6-only Preferred option in the DHCPOFFER or DHCPACK
message if the option was not present in the Parameter Request List
sent by the client.
If the IPv6-only Preferred option is present in the Parameter Request
List received from the client and the corresponding DHCPv4 pool is
explicitly configured as belonging to an IPv6-mostly network segment,
the server MUST include the IPv6-only Preferred option when
responding with the DHCPOFFER or DHCPACK message. If the server
responds with the IPv6-only Preferred option and the V6ONLY_WAIT
timer is configured for the pool, the server MUST copy the configured
value to the IPv6-only Preferred option value field. Otherwise it
MUST set the field to zero. The server SHOULD NOT assign an address
from the pool. Instead it SHOULD return 0.0.0.0 as the offered
address. Alternatively, if offering 0.0.0.0 is not feasible, for
example due to some limitations of the server or the network
infrastructure, the server MAY include an available IPv4 address from
the pool into the DHCPOFFER as per recommendations in [RFC2131]. In
this case, the offered address MUST be a valid address that is not
committed to any other client. Because the client is not expected
ever to request this address, the server SHOULD NOT reserve the
address and SHOULD NOT verify its uniqueness. If the client then
issues a DHCPREQUEST for the address, the server MUST process it per
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[RFC2131], including replying with a DHCPACK for the address if in
the meantime it has not been committed to another client.
If a client includes both a Rapid-Commit option [RFC4039] and
IPv6-Only Preferred option in the DHCPDISCOVER message the server
SHOULD NOT honor the Rapid-Commit option if the response would
contain the IPv6-only Preferred option to the client. It SHOULD
instead respond with a DHCPOFFER as indicated above.
If the server receives a DHCPREQUEST containing the IPv6-only
Preferred option for the address from a pool configured as
IPv6-mostly, the server MUST process it per [RFC2131].
3.3.1. Interaction with RFC2563
[RFC2563] defines an Auto-Configure DHCPv4 option to disable IPv4
link-local address configuration for IPv4 clients. Clients can
support both, neither or just one of IPv6-Only Preferred and Auto-
Configure options. If a client sends both IPv6-Only Preferred and
Auto-Configure options the network administrator can prevent the host
from configuring an IPv4 link-local address on an IPv6-mostly
network. To achieve this the server needs to send DHCPOFFER which
contains a 'yiaddr' of 0x00000000, and the Auto-Configure flag saying
"DoNotAutoConfigure".
However special care should be taken in a situation when a server
supports both options and receives just IPv6-Only Preferred option
from a client. Section 2.3 of [RFC2563] states that if no address is
chosen for the host (which would be the case for IPv6-only capable
clients on IPv6-mostly network) then: "If the DHCPDISCOVER does not
contain the Auto-Configure option, it is not answered." Such
behavior would be undesirable for clients supporting the IPv6-Only
Preferred option without supporting the Auto-Configure option as they
would not receive any response from the server and would keep asking,
instead of disabling DHCPv4 for V6ONLY_WAIT seconds. Therefore the
following update is made to Section 2.3 of [RFC2563]"
OLD TEXT:
---
However, if no address is chosen for the host, a few additional steps
MUST be taken.
If the DHCPDISCOVER does not contain the Auto-Configure option, it is
not answered.
---
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NEW TEXT:
---
However, if no address is chosen for the host, a few additional steps
MUST be taken.
If the DHCPDISCOVER does not contain the Auto-Configure option and
the IPv6-Only Preferred option is not present, it is not answered.
If the DHCPDISCOVER does not contain the Auto-Configure option but
contains the IPv6-Only Preferred option, the processing rules for the
IPv6-Only Preferred option apply.
---
3.4. Constants and Configuration Variables
V6ONLY_WAIT The time for which the client SHOULD stop the DHCPv4
configuration process. The value MUST NOT be less
than MIN_V6ONLY_WAIT seconds. Default: 1800 seconds
MIN_V6ONLY_WAIT The lower boundary for V6ONLY_WAIT. Value: 300
seconds
4. IPv6-Only Transition Technologies Considerations
Until IPv6 adoption in the Internet reaches 100%, communication
between an IPv6-only host and IPv4-only destination requires some
form of transition mechanism deployed in the network. At the time of
writing, the only such mechanism that is widely supported by end
hosts is NAT64 [RFC6146] (either with or without 464XLAT). Therefore
the IPv6-only Preferred option is only sent by hosts capable of
operating on NAT64 networks. In a typical deployment scenario, a
network administrator would not configure the DHCPv4 server to return
the IPv6-only Preferred option unless the network provides NAT64
service.
Hypothetically, it is possible for multiple transition technologies
to coexist. In such scenario some form of negotiation would be
required between a client and a server to ensure that the transition
technology supported by the client is the one the network provides.
However it seems unlikely that any new transition technology would
arise and be widely adopted in any foreseeable future. Therefore
adding support for non-existing technologies seems to be suboptimal
and the proposed mechanism implies that NAT64 is used to facilitate
connectivity between IPv6 and IPv4. In the unlikely event that a new
transition mechanism becomes widely deployed, the applicability of
the IPv6-Only-Preferred option to that mechanism will depend on the
nature of the new mechanism. If the new mechanism is designed in
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such a way that it's fully transparent for hosts that support NAT64
and the IPv6-Only-Preferred option, then the option can continue to
be used with the new mechanism. If the new mechanism is not
compatible with NAT64, and implementation on the host side is
required to support it, then a new DHCPv4 option needs to be defined.
It should be also noted that declaring a host (technically, a host
interface) IPv6-only capable is a policy decision. For example,
o An operating system vendor may make such decision and configure
their DHCPv4 clients to send the IPv6-Only Preferred option by
default if the OS has 464XLAT CLAT [RFC6877] enabled.
o An enterprise network administrator may provision the corporate
hosts as IPv6-only capable if all applications users are supposed
to run have been tested in an IPv6-only environment (or if 464XLAT
CLAT is enabled on the devices).
o IoT devices may be shipped in IPv6-only capable mode if they are
designed to connect to IPv6-enabled cloud destination only.
5. IANA Considerations
The IANA is requested to assign a new DHCPv4 Option code for the
IPv6-Only Preferred option from the BOOTP Vendor Extensions and
DHCPv4 Options registry, located at https://www.iana.org/assignments/
bootp-dhcp-parameters/bootp-dhcp-parameters.xhtml#options . If
possible, please assign option code 108.
+-----------+-----------+--------+----------+-----------------------+
| Tag | Name | Data | Meaning | Reference |
| | | Length | | |
+-----------+-----------+--------+----------+-----------------------+
| TBD | IPv6-only | 4 | Number | draft-ietf-dhc-v6only |
| (proposed | Preferred | | of | |
| value: | option | | seconds | |
| 108) | | | to | |
| | | | disable | |
| | | | DHCPv4 | |
| | | | for | |
+-----------+-----------+--------+----------+-----------------------+
Table 1
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6. Security Considerations
An attacker might send a spoofed DHCPOFFER containing IPv6-only
Preferred option with the value field set to a large number, such as
0xffffffff, effectively disabling DHCPv4 on clients supporting the
option. If the network is IPv4-only such clients would lose
connectivity, while on a dual-stack network without NAT64 service
only connectivity to IPv4-only destinations would be affected. The
recovery would require triggering a network attachment event.
However it should be noted that if the network does not provide
protection from a rogue DHCPv4 server the similar attack vector can
be executed by offering an invalid address and setting the Lease Time
option value field to 0xffffffff. The latter attack would affect all
hosts, not just hosts that support the IPv6-only Preferred option.
Therefore the security measures against rogue DHCPv4 servers would be
sufficient to prevent the attacks specific to IPv6-only Preferred
option. Additionally such attacks can only be executed if the victim
prefers the rogue DHCPOFFER over the legitimate ones. Therefore for
the attack to be successful the attacker needs to know the selection
criteria used by the client and to be able to make its rogue offer
more preferable.
It should be noted that disabling IPv4 on a host upon receiving the
IPv6-only Preferred option from the DHCPv4 server protects the host
from IPv4-related attacks and therefore could be considered a
security feature as it reduces the attack surface.
7. Acknowledgements
Thanks to the following people (in alphabetical order) for their
review and feedback: Mohamed Boucadair, Martin Duke, Russ Housley,
Sheng Jiang, Benjamin Kaduk, Murray Kucherawy, Ted Lemon, Roy
Marples, Bjorn Mork, Alvaro Retana, Peng Shuping, Pascal Thubert,
Bernie Volz, Eric Vyncke, Robert Wilton. Authors would like to thank
Bob Hinden and Brian Carpenter for the initial idea of signaling
IPv6-only capability to hosts. Special thanks to Erik Kline, Mark
Townsley and Maciej Zenczykowski for the discussion which led to the
idea of signalling IPv6-only capability over DHCPv4.
8. References
8.1. 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>.
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[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, DOI 10.17487/RFC2131, March 1997,
<https://www.rfc-editor.org/info/rfc2131>.
[RFC2563] Troll, R., "DHCP Option to Disable Stateless Auto-
Configuration in IPv4 Clients", RFC 2563,
DOI 10.17487/RFC2563, May 1999,
<https://www.rfc-editor.org/info/rfc2563>.
[RFC3927] Cheshire, S., Aboba, B., and E. Guttman, "Dynamic
Configuration of IPv4 Link-Local Addresses", RFC 3927,
DOI 10.17487/RFC3927, May 2005,
<https://www.rfc-editor.org/info/rfc3927>.
[RFC4039] Park, S., Kim, P., and B. Volz, "Rapid Commit Option for
the Dynamic Host Configuration Protocol version 4
(DHCPv4)", RFC 4039, DOI 10.17487/RFC4039, March 2005,
<https://www.rfc-editor.org/info/rfc4039>.
[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>.
8.2. 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>.
[RFC4957] Krishnan, S., Ed., Montavont, N., Njedjou, E., Veerepalli,
S., and A. Yegin, Ed., "Link-Layer Event Notifications for
Detecting Network Attachments", RFC 4957,
DOI 10.17487/RFC4957, August 2007,
<https://www.rfc-editor.org/info/rfc4957>.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
April 2011, <https://www.rfc-editor.org/info/rfc6146>.
[RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van
Beijnum, "DNS64: DNS Extensions for Network Address
Translation from IPv6 Clients to IPv4 Servers", RFC 6147,
DOI 10.17487/RFC6147, April 2011,
<https://www.rfc-editor.org/info/rfc6147>.
Colitti, et al. Expires February 14, 2021 [Page 13]
Internet-Draft IPv6-Only-Preferred Option for DHCPv4 August 2020
[RFC6877] Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT:
Combination of Stateful and Stateless Translation",
RFC 6877, DOI 10.17487/RFC6877, April 2013,
<https://www.rfc-editor.org/info/rfc6877>.
Authors' Addresses
Lorenzo Colitti
Google
Shibuya 3-21-3
Shibuya, Tokyo 150-0002
JP
Email: lorenzo@google.com
Jen Linkova
Google
1 Darling Island Rd
Pyrmont, NSW 2009
AU
Email: furry@google.com
Michael C. Richardson
Sandelman Software Works
Email: mcr+ietf@sandelman.ca
URI: http://www.sandelman.ca/
Tomek Mrugalski
Internet Systems Consortium, Inc.
950 Charter Street
Redwood City, CA 94063
USA
Email: tomasz.mrugalski@gmail.com
Colitti, et al. Expires February 14, 2021 [Page 14]
