Diff: rfc9762.original.xml

	rfc9762.original.xml	rfc9762.xml

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	<rfc	<rfc xmlns:xi="http://www.w3.org/2001/XInclude" category="std" docName="draft-ie
	xmlns:xi="http://www.w3.org/2001/XInclude"	tf-6man-pio-pflag-12" number="9762" ipr="trust200902" obsoletes="" updates="4861
	category="std"	, 4862" submissionType="IETF" xml:lang="en" version="3" tocInclude="true" sortR
	docName="draft-ietf-6man-pio-pflag-12"	efs="true" symRefs="true" consensus="true">
	ipr="trust200902"
	obsoletes=""
	updates="4861,4862"
	submissionType="IETF"
	xml:lang="en"
	version="3">
	<front>	<front>

	<title abbrev="pio-p-flag">Signaling DHCPv6 Prefix per Client Availability to Ho	<title abbrev="PIO P Flag">Using Router Advertisements to
	sts</title>	Signal the Availability of DHCPv6 Prefix Delegation to Clients</title>
	<seriesInfo name="Internet-Draft" value="draft-ietf-6man-pio-pflag-12"/>	<seriesInfo name="RFC" value="9762"/>

	<author initials="L." surname="Colitti" fullname="Lorenzo Colitti">	<author initials="L." surname="Colitti" fullname="Lorenzo Colitti">
	<organization>Google</organization>	<organization>Google</organization>
	<address>	<address>
	<postal>	<postal>
	<street>Shibuya 3-21-3</street>	<street>Shibuya 3-21-3</street>
	<country>Japan</country>	<country>Japan</country>
	</postal>	</postal>
	<email>lorenzo@google.com</email>	<email>lorenzo@google.com</email>
	</address>	</address>
	</author>	</author>
	<author fullname="Jen Linkova" initials="J" surname="Linkova">	<author fullname="Jen Linkova" initials="J" surname="Linkova">
	<organization>Google</organization>	<organization>Google</organization>
	<address>	<address>
	<postal>	<postal>

	<!-- Reorder these if your country does things differently -->
	<street>1 Darling Island Rd</street>	<street>1 Darling Island Rd</street>
	<city>Pyrmont</city>	<city>Pyrmont</city>
	<region>NSW</region>	<region>NSW</region>
	<code>2009</code>	<code>2009</code>

	<country>AU</country>	<country>Australia</country>
	</postal>	</postal>
	<email>furry13@gmail.com</email>	<email>furry13@gmail.com</email>
	<email>furry@google.com</email>	<email>furry@google.com</email>
	</address>	</address>
	</author>	</author>
	<author fullname="Xiao Ma" initials="X" role="editor" surname="Ma">	<author fullname="Xiao Ma" initials="X" role="editor" surname="Ma">
	<organization>Google</organization>	<organization>Google</organization>
	<address>	<address>
	<postal>	<postal>
	<street>Shibuya 3-21-3</street>	<street>Shibuya 3-21-3</street>
	<country>Japan</country>	<country>Japan</country>
	</postal>	</postal>
	<email>xiaom@google.com</email>	<email>xiaom@google.com</email>
	</address>	</address>
	</author>	</author>
	<author fullname="David 'equinox' Lamparter" initials="D" surname="Lamparter">	<author fullname="David 'equinox' Lamparter" initials="D" surname="Lamparter">
	<organization>NetDEF, Inc.</organization>	<organization>NetDEF, Inc.</organization>
	<address>	<address>
	<postal>	<postal>

	<city>San Jose</city>	<city>Leipzig</city>
	<country>USA</country>	<code>04229</code>
		<country>Germany</country>
	</postal>	</postal>
	<email>equinox@diac24.net</email>	<email>equinox@diac24.net</email>
	<email>equinox@opensourcerouting.org</email>	<email>equinox@opensourcerouting.org</email>
	</address>	</address>
	</author>	</author>


	<date year="2024"/>	<date year="2025" month="April"/>
	<area>Internet</area>
	<workgroup>IPv6 Maintenance</workgroup>	<area>INT</area>
		<workgroup>6man</workgroup>

	<keyword>ipv6</keyword>	<keyword>ipv6</keyword>
	<keyword>slaac</keyword>	<keyword>slaac</keyword>
	<keyword>pio</keyword>	<keyword>pio</keyword>
	<keyword>dhcpv6-pd</keyword>	<keyword>dhcpv6-pd</keyword>

	<abstract>	<abstract>
	<t>	<t>

	This document defines a "P" flag in the Prefix Information Option (PIO) of IPv6	This document defines the P flag in the Prefix Information Option (PIO) of
	Router Advertisements (RAs).	IPv6 Router Advertisements (RAs). The flag is used to indicate that the
	The flag is used to indicate that the network prefers that clients use the RFC96	network prefers that clients use the deployment model in RFC 9663
	63 deployment model instead of using individual adresses in the on-link prefix a	instead of using individual addresses in the on-link prefix assigned using
	ssigned using Stateless Address Autoconfiguration (SLAAC) or DHCPv6 address assi	Stateless Address Autoconfiguration (SLAAC) or DHCPv6 address assignment.
	gnment.
	</t>	</t>
	<t>	<t>

	This document updates RFC4862 to indicate that the Autonomous flag in a PIO need	This document updates RFC 4862 to indicate that the Autonomous flag in a PIO
	s to be ignored if the PIO has the P flag set.	needs to be ignored if the PIO has the P flag set. It also updates RFC 4861
	It also updates RFC4861 to specify that the P flag indicates DHCPv6 Prefix Deleg	to specify that the P flag indicates DHCPv6 prefix delegation support for
	ation support for clients.	clients.
	</t>	</t>

	</abstract>	</abstract>

	</front>	</front>

	<middle>	<middle>

	<section>	<section>
	<name>Introduction</name>	<name>Introduction</name>
	<t>	<t>

	<xref target="RFC9663"/> documents an IPv6 address assignment model where IPv6 d	<xref target="RFC9663"/> documents an IPv6 address assignment model where IPv6 d
	evices obtain dedicated prefixes from the network via DHCPv6 Prefix Delegation (	evices obtain dedicated prefixes from the network via DHCPv6 prefix delegation (
	DHCPv6-PD, <xref target="RFC8415"/>).	DHCPv6-PD) <xref target="RFC8415"/>. This model provides devices with a large IP
	This model provides devices with large IPv6 address space they can use to create	v6 address space they can use to create addresses for communication, individuall
	addresses for communication, individually number virtual machines (VM)s or cont	y number virtual machines (VMs) or containers, or extend the network to downstre
	ainers, or extend the network to downstream devices. It also provides scalabilit	am devices. It also provides scalability benefits on large networks because netw
	y benefits on large networks because network infrastructure devices do not need	ork infrastructure devices do not need to maintain per-address state, such as IP
	to maintain per-address state, such as IPv6 neighbor cache, Source Address Valid	v6 neighbor cache, Source Address Validation Improvement (SAVI) <xref target="RF
	ation Improvement (SAVI, <xref target="RFC7039"/>) mappings, Virtual eXtensible	C7039"/> mappings, Virtual eXtensible Local Area Network (VXLAN) <xref target="
	Local Area Network (VXLAN, <xref target="RFC7348"/>) routes, etc.	RFC7348"/> routes, etc.
	</t>	</t>
	<t>	<t>

	On networks with fewer devices, however, this model may not be appropriate, beca	On networks with fewer devices, however, this model may not be appropriate, be
	use scaling to support multiple individual IPv6 addresses per device is less of	cause scaling to support multiple individual IPv6 addresses per device is less o
	a concern. Also, many home networks currently offer prefix delegation but assume	f a concern. Also, many home networks currently offer prefix delegation but assu
	that a limited number of specialized devices and/or applications will require d	me that a limited number of specialized devices and/or applications will require
	elegated prefixes, and thus do not allocate enough address space to offer prefix	delegated prefixes and thus do not allocate enough address space to offer prefi
	es to every device that connects to the network. For example, if clients enable	xes to every device that connects to the network.
	<xref target="RFC9663"/> on a home network that only receives a /60 from the ISP	For example, if clients assume the <xref target="RFC9663"/> deployment model o
	, and each client obtains a /64 prefix, then the network will run out of prefixe	n a home network that only receives a /60 from the ISP and each client obtains a
	s after 15 devices have been connected.	/64 prefix, then the network will run out of prefixes after 15 devices have bee
		n connected.
	</t>	</t>
	<t>	<t>

	Therefore, to safely roll out <xref target="RFC9663"/> implementations on the cl ient side, it is necessary to have a mechanism for the network to signal to the client which address assignment method is preferred.	Therefore, to safely roll out the support of the deployment model defined in <xr ef target="RFC9663"/> on the client side, it is necessary to have a mechanism fo r the network to signal to the client which address assignment method is preferr ed.
	</t>	</t>

	<t>	<t>
	</t>	</t>

	</section>	</section>

	<section>	<section>
	<name>Requirements Language</name>	<name>Requirements Language</name>

	<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL",	<t>The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>", "<bcp
	"SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT	14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>",
	RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be	"<bcp14>SHALL NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NO
		T</bcp14>", "<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT
		RECOMMENDED</bcp14>", "<bcp14>MAY</bcp14>", and "<bcp14>OPTIONAL</bcp1
		4>" in this document are to be
	interpreted as described in BCP 14 <xref target="RFC2119"/>	interpreted as described in BCP 14 <xref target="RFC2119"/>
	<xref target="RFC8174"/> when, and only when, they appear in	<xref target="RFC8174"/> when, and only when, they appear in
	all capitals, as shown here.</t>	all capitals, as shown here.</t>
	</section>	</section>


	<section>	<section>
	<name>Terminology</name>	<name>Terminology</name>
	<t>
	Node: a device that implements IPv6, <xref target=
	"RFC8200"/>.
	</t>
	<t>
	Host: any node that is not a router, <xref target=
	"RFC8200"/>.
	</t>
	<t>
	Client: a node which connects to a network and acquires addresses. The node may
	wish to obtain addresses for its own use, or may be a router that wishes to exte
	nd the network to its physical or virtual subsystems, or both. It may be either
	a host or a router as defined by <xref target="RFC8200"/>.
	</t>
	<t>
	DHCPv6-PD: DHCPv6 (<xref target="RFC8415"/>) mechanism to delegate IPv6 prefixes
	to clients.
	</t>
	<t>
	DHCPv6 IA_NA: Identity Association for Non-temporary Addresses (Section 21.4 of
	<xref target="RFC8415"/>).
	</t>
	<t>
	DHCPv6 IA_PD: Identity Association for Prefix Delegation (Section 21.21 of <xref
	target="RFC8415"/>).
	</t>
	<t>
	ND: Neighbor Discovery, <xref target="RFC4861"/>.
	</t>


	<t>	<dl spacing="normal" newline="false">
	On-link address: an address that is assigned to an interface on a specified link	<dt>Node:</dt><dd>a device that implements IPv6 <xref target="RFC8200"
	(<xref target="RFC4861"/>).	/></dd>
	</t>	<dt>Host:</dt><dd>any node that is not a router <xref target="RFC8200"
	<t>	/></dd>
	On-link prefix: a prefix that is assigned to a specified link.	<dt>Client:</dt><dd>a node that connects to a network and acquires
	</t>	addresses. The node may wish to obtain addresses for its own use, or it
	<t>	may be a router that wishes to extend the network to its physical or
	Off-link: the opposite of "on-link" (see <xref target="RFC4861"/>).	virtual subsystems, or both. It may be either a host or a router as
	</t>	defined by <xref target="RFC8200"/>.</dd>
	<t>
	PIO: Prefix Information Option, <xref target="RFC4862"/>.
	</t>
	<t>
	SLAAC: IPv6 Stateless Address Autoconfiguration, <xref tar
	get="RFC4862"/>.
	</t>


	</section>	<dt>DHCPv6-PD:</dt><dd>DHCPv6 Prefix Delegation <xref target="RFC8415"/
		>; a mechanism to delegate IPv6 prefixes to clients.</dd>
		<dt>DHCPv6 IA_NA:</dt><dd>Identity Association for Non-temporary Addres
		ses (<xref section="21.4" sectionFormat="of" target="RFC8415"/>)</dd>
		<dt>DHCPv6 IA_PD:</dt><dd>Identity Association for Prefix Delegation (<
		xref section="21.21" sectionFormat="of" target="RFC8415"/>)</dd>
		<dt>ND:</dt><dd>Neighbor Discovery <xref target="RFC4861"/></dd>
		<dt>On-link address:</dt><dd>an address that is assigned to an interfac
		e on a specified link <xref target="RFC4861"/></dd>
		<dt>On-link prefix:</dt><dd>a prefix that is assigned to a specified li
		nk</dd>
		<dt>Off-link:</dt><dd>the opposite of "on-link" (see <xref target="RFC4
		861"/>)</dd>
		<dt>PIO:</dt><dd>Prefix Information Option <xref target="RFC4862"/></dd
		>
		<dt>RA:</dt><dd>Router Advertisement <xref target="RFC4861"/></dd>
		<dt>SLAAC:</dt><dd>Stateless Address Autoconfiguration <xref target="R
		FC4862"/></dd>
		</dl>
		</section>

	<section anchor="rationale">	<section anchor="rationale">
	<name>Rationale</name>	<name>Rationale</name>
	<t>	<t>
	The network administrator might want to indicate to clients that requesting a pr efix via DHCPv6-PD and using that prefix for address assignment (see <xref targe t="RFC9663"/>) should be preferred over using individual addresses from the on-l ink prefix.	The network administrator might want to indicate to clients that requesting a pr efix via DHCPv6-PD and using that prefix for address assignment (see <xref targe t="RFC9663"/>) should be preferred over using individual addresses from the on-l ink prefix.

	The information is passed to the client via a P flag in the Prefix Information O ption (PIO). The reason for it being a PIO flag is as follows:	The information is passed to the client via a P flag in the PIO. The reasons for it being a PIO flag are as follows:
	</t>	</t>
	<ul>	<ul>

	<li>	<li>
	The information must be contained in the Router Advertisement because it must be	The information must be contained in the RA because it must be available to the
	available to the client before it decides to form IPv6 addresses from the PIO p	client before it decides to form IPv6 addresses from the PIO prefix using SLAAC.
	refix using SLAAC. Otherwise, the client might use SLAAC to form IPv6 addresses	Otherwise, the client might use SLAAC to form IPv6 addresses from the PIO provi
	from the PIO provided and start using them, even if a unique per-client prefix i	ded and start using them, even if a unique per-client prefix is available via DH
	s available via DHCPv6-PD.	CPv6-PD.
	Forming addresses via SLAAC is suboptimal because if the client later acquires a	Forming addresses via SLAAC is suboptimal because if the client later acquires a
	prefix using DHCPv6-PD, it can either use both the prefix and SLAAC addresses,	prefix using DHCPv6-PD, it can either 1) use both the prefix and SLAAC addresse
	reducing the scalability benefits of using DHCPv6-PD, or can remove the SLAAC ad	s, reducing the scalability benefits of using DHCPv6-PD, or 2) remove the SLAAC
	dresses, which would be disruptive for applications that are using them.	addresses, which would be disruptive for applications that are using them.

	</li>	</li>


	<li>	<li>

	This information is specific to the particular prefix being announced. For examp	This information is specific to the particular prefix being announced. For
	le, a network administrator might want clients to assign global addresses from d	example, a network administrator might want clients to assign global addresses
	elegated prefixes, but use the PIO prefix to form Unique Local Unicast (ULA, <xr	from delegated prefixes but form Unique Local IPv6
	ef target="RFC4193"/>) addresses.	Unicast Addresses <xref target="RFC4193"/> from another PIO in the RA using SLAA
	Also, in a multihoming situation, one upstream network might choose to assign pr	C. Also, in a multihoming situation,
	efixes via prefix delegation, and another via PIOs.	one upstream network might choose to assign prefixes via prefix delegation and
		another via PIOs.

	</li>	</li>
	</ul>	</ul>

	<t>	<t>

	Note that setting the 'P' flag in a PIO expresses the network operator's prefere nce as to whether clients should attempt using DHCPv6-PD instead of performing i ndividual address configuration on the prefix.	Note that setting the P flag in a PIO expresses the network operator's preferenc e that clients should attempt using DHCPv6-PD instead of performing individual a ddress configuration on the prefix.
	For clients that honor this preference by requesting prefix delegation, the actu al delegated prefix will necessarily be a prefix different from the one from the PIO.	For clients that honor this preference by requesting prefix delegation, the actu al delegated prefix will necessarily be a prefix different from the one from the PIO.
	</t>	</t>

	</section>	</section>

	<section anchor="flag-over">	<section anchor="flag-over">
	<name>P Flag Overview</name>	<name>P Flag Overview</name>
	<t>	<t>

	The P flag (also called DHCPv6-PD preferred flag) is a 1-bit PIO flag, located a fter the R flag (<xref target="RFC6275"/>).	The P flag (also called the DHCPv6-PD Preferred Flag) is a 1-bit PIO flag, locat ed after the R flag <xref target="RFC6275"/>.


	The presence of a PIO with the P flag set indicates that the network prefers tha t clients use Prefix Delegation instead of acquiring individual addresses via SL AAC or DHCPv6 address assignment. This implies that the network has a DHCPv6 ser ver capable of making DHCPv6 Prefix Delegations to every device on the network, as described in <xref target="RFC9663"/>.</t>	The presence of a PIO with the P flag set indicates that the network prefers tha t clients use prefix delegation instead of acquiring individual addresses via SL AAC or DHCPv6 address assignment. This implies that the network has a DHCPv6 ser ver capable of making DHCPv6 prefix delegations to every device on the network, as described in <xref target="RFC9663"/>.</t>

	<t>	<t>

	The resulting format of the Prefix Information Option is as follows (see Figure 1):	<xref target="fig_pio_new"/> shows the resulting format of the PIO.
	</t>	</t>

	<figure align="center" anchor="fig_pio_new">	<figure align="center" anchor="fig_pio_new">
	<artwork align="center"><![CDATA[	<artwork align="center"><![CDATA[

	0 1 2 3	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1	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 \| Prefix Length \|L\|A\|R\|P\| Rsvd1 \|	\| Type \| Length \| Prefix Length \|L\|A\|R\|P\| Rsvd1 \|
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| Valid Lifetime \|	\| Valid Lifetime \|
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| Preferred Lifetime \|	\| Preferred Lifetime \|
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| Reserved2 \|	\| Reserved2 \|
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| \|	\| \|
	+ +	+ +
	\| \|	\| \|
	+ Prefix +	+ Prefix +
	\| \|	\| \|
	+ +	+ +
	\| \|	\| \|
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

	]]></artwork>	]]></artwork>

	</figure>	-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
		</figure>

	<t>	<t>

	The P flag is independent of the value of the M and O flags in the Router Advert	The P flag is independent of the value of the M and O flags in the RA.
	isement.	If the network desires to delegate prefixes to devices that support DHCPv6 prefi
	If the network desires to delegate prefixes to devices that support DHCPv6 Prefi	x delegation but do not support the P flag, it <bcp14>SHOULD</bcp14> also set th
	x Delegation but do not support the P flag, it SHOULD also set the M or O bits i	e M or O bits in the RA to 1, because some devices, such as Customer Edge (CE) r
	n the RA to 1, because some devices, such as <xref target="RFC7084"/> Customer E	outers <xref target="RFC7084"/>, might not initiate DHCPv6 prefix delegation if
	dge (CE) routers, might not initiate DHCPv6 Prefix Delegation if both the M and	both the M and O bits are set to zero.
	O bits are set to zero.
	</t>	</t>
	</section>	</section>

	<section anchor="Router">	<section anchor="Router">

	<name>Router Behaviour</name>	<name>Router Behavior</name>
	<t>	<t>

	Routers SHOULD set the P flag to zero by default, unless explicitly configured b	Routers <bcp14>SHOULD</bcp14> set the P flag to zero by default, unless explicit
	y the administrator, and SHOULD allow the operator to set the P flag value for a	ly configured by the administrator, and <bcp14>SHOULD</bcp14> allow the operator
	ny given prefix advertised in a PIO.	to set the P flag value for any given prefix advertised in a PIO.
	Routers MUST allow the P flag to be configured separately from the A flag. In p	Routers <bcp14>MUST</bcp14> allow the P flag to be configured separately from th
	articular, enabling or disabling the P flag MUST not trigger automatic changes i	e A flag.
	n the A flag value set by the router.	In particular, enabling or disabling the P flag <bcp14>MUST NOT</bcp14> trigger
		automatic changes in the A flag value set by the router.
	</t>	</t>
	</section>	</section>
	<section anchor="client">	<section anchor="client">

	<name>Client Behaviour</name>	<name>Client Behavior</name>
	<section>	<section>
	<name>Processing the P Flag</name>	<name>Processing the P Flag</name>
	<t>	<t>

	This specification only applies to clients which support DHCPv6 Prefix Delegatio	This specification only applies to clients that support DHCPv6 prefix delegation
	n.	.
	Clients which do not support DHCPv6 prefix delegation MUST ignore the P flag.	Clients that do not support DHCPv6 prefix delegation <bcp14>MUST</bcp14> ignore
	The P flag is meaningless for link-local prefixes and any Prefix Information Opt	the P flag.
	ion containing	The P flag is meaningless for link-local prefixes, and any PIO containing
	the link-local prefix MUST be ignored as specified in <xref target="RFC4862" sec	the link-local prefix <bcp14>MUST</bcp14> be ignored as specified in <xref targe
	tion="5.5.3"/>.	t="RFC4862" section="5.5.3"/>.
	In the following text, all prefixes are assumed not to be link-local.	In the following text, all prefixes are assumed not to be link-local.
	</t>	</t>

	<t>	<t>

	For each interface, the client MUST keep a list of every prefix that was receive	For each interface, the client <bcp14>MUST</bcp14> keep a list of every prefix t
	d	hat was received
	from a PIO with the P flag set and currently has a non-zero Preferred Lifetime.	from a PIO with the P flag set and currently has a non-zero preferred lifetime.
	The list affects the behaviour of the DHCPv6 client as follows:	The list affects the behavior of the DHCPv6 client as follows:
	</t>	</t>
	<ul>	<ul>

	<li>When a prefix's Preferred Lifetime becomes zero, either because the Preferre	<li>When a prefix's preferred lifetime becomes zero, either because the preferre
	d	d
	Lifetime expires or because the client receives a PIO for the prefix with a zero	lifetime expires or because the client receives a PIO for the prefix with a zero
	Preferred Lifetime, the prefix MUST be removed from the list.	preferred lifetime, the prefix <bcp14>MUST</bcp14> be removed from the list.
	</li>	</li>

	<li>When the length of the list increases to one, the client SHOULD start reques ting	<li>When the length of the list increases to one, the client <bcp14>SHOULD</bcp1 4> start requesting
	prefixes via DHCPv6 prefix delegation unless it is already doing so.</li>	prefixes via DHCPv6 prefix delegation unless it is already doing so.</li>

	<li>When the length of the list decreases to zero, the client SHOULD stop reques ting	<li>When the length of the list decreases to zero, the client <bcp14>SHOULD</bcp 14> stop requesting
	or renewing prefixes via DHCPv6 prefix delegation if it has no other reason to d o so.	or renewing prefixes via DHCPv6 prefix delegation if it has no other reason to d o so.
	The lifetimes of any prefixes already obtained via DHCPv6 are unaffected.</li>	The lifetimes of any prefixes already obtained via DHCPv6 are unaffected.</li>
	<li>	<li>
	If the client has already received delegated prefix(es) from one or more	If the client has already received delegated prefix(es) from one or more

	servers, then any time a prefix is added to or removed from the list, the client MUST	servers, then any time a prefix is added to or removed from the list, the client <bcp14>MUST</bcp14>
	consider this to be a change in configuration information as	consider this to be a change in configuration information as

	described in <xref target="RFC8415" section="18.2.12"/>. In that case the client MUST perform	described in <xref target="RFC8415" section="18.2.12"/>. In that case, the clien t <bcp14>MUST</bcp14> perform
	a REBIND, unless the list is now empty.	a REBIND, unless the list is now empty.
	This is in addition to performing a REBIND in the other cases required by that	This is in addition to performing a REBIND in the other cases required by that

	section. Issuing a REBIND allows the client to obtain new prefixes if necessary,	section. Issuing a REBIND allows the client to obtain new prefixes if necessary,
	for example	for example,
	when the network is being renumbered. It also refreshes state related to the	when the network is being renumbered. It also refreshes the state related to the
	delegated prefix(es).	delegated prefix(es).
	</li>	</li>
	</ul>	</ul>
	<t>	<t>

	When a client requests a prefix via DHCPv6-PD, it MUST use the prefix length hin t (<xref target="RFC8415" section="18.2.4"/>) to request a prefix that is short enough to form addresses via SLAAC.</t>	When a client requests a prefix via DHCPv6-PD, it <bcp14>MUST</bcp14> use the pr efix length hint (<xref target="RFC8415" section="18.2.4"/>) to request a prefix that is short enough to form addresses via SLAAC.</t>


	<t>In order to achieve the scalability benefits of using DHCPv6-PD, the client S	<t>In order to achieve the scalability benefits of using DHCPv6-PD, the client
	HOULD prefer	<bcp14>SHOULD</bcp14> prefer to form addresses from the delegated prefix
	to form addresses from the delegated prefix instead of using individual addresse	instead of using individual addresses in the on-link prefix(es). Therefore,
	s in the	when the client requests a prefix using DHCPv6-PD, the client <bcp14>SHOULD
	on-link prefix(es). Therefore, when the client requests a prefix using DHCPv6-PD	NOT</bcp14> use SLAAC to obtain IPv6 addresses from PIOs with the P and A bits
	, the client	set. Similarly, if all PIOs processed by the client have the P bit set, the
	SHOULD NOT use SLAAC to obtain IPv6 addresses from PIOs with the P and A bits se	client <bcp14>SHOULD NOT</bcp14> request individual IPv6 addresses from
	t.	DHCPv6, i.e., it <bcp14>SHOULD NOT</bcp14> include any IA_NA options in
	Similarly, if all PIOs processed by the client have the P bit set, the client SH	Solicit messages <xref target="RFC8415"/>. The client <bcp14>MAY</bcp14>
	OULD NOT request individual IPv6 addresses from DHCPv6, i.e., it SHOULD NOT incl	continue to use addresses that are already configured.
	ude any IA_NA options in SOLICIT (<xref target="RFC8415"/>) messages.
	The client MAY continue to use addresses that are already configured.
	</t>	</t>


	<t>If the client does not obtain any suitable prefixes via DHCPv6-PD that are su itable for SLAAC, it MAY choose to disable further processing of the P flag on t hat interface, allowing the client to fall back to other address assignment mech anisms, such as forming addresses via SLAAC (if the PIO has the A flag set to 1) and/or requesting individual addresses via DHCPv6.</t>	<t>If the client does not obtain any suitable prefixes via DHCPv6-PD that are su itable for SLAAC, it <bcp14>MAY</bcp14> choose to disable further processing of the P flag on that interface, allowing the client to fall back to other address assignment mechanisms, such as forming addresses via SLAAC (if the PIO has the A flag set to 1) and/or requesting individual addresses via DHCPv6.</t>
	</section>	</section>

	<section anchor="received">	<section anchor="received">
	<name>	<name>
	Using Delegated Prefix(es)	Using Delegated Prefix(es)
	</name>	</name>

	<t>	<t>

	If the delegated prefix is too long to be used for SLAAC, the cli	If the delegated prefix is too long to be used for SLAAC, the cli
	ent MUST ignore it, as Section 7 of <xref target="RFC9663"/> requires the networ	ent <bcp14>MUST</bcp14> ignore it, as <xref section="7" sectionFormat="of" targe
	k to provide a SLAAC-suitable prefix to clients.	t="RFC9663"/> requires the network to provide a SLAAC-suitable prefix to clients
	If the prefix is shorter than required for SLAAC, the client SHOULD accep	.
	t it, allocate one or more longer prefix suitable for SLAAC and use the prefixes	If the prefix is shorter than required for SLAAC, the client <bcp14>SHOUL
	as described below.	D</bcp14> accept it, allocate one or more longer prefixes suitable for SLAAC, an
		d use the prefixes as described below.
	</t>	</t>
	<t>	<t>
	For every accepted prefix:	For every accepted prefix:
	</t>	</t>

	<ul>	<ul>
	<li>	<li>

	The client MAY form as many IPv6 addresses from the prefix as it chooses.	The client <bcp14>MAY</bcp14> form as many IPv6 addresses from the prefix as it chooses.
	</li>	</li>
	<li>	<li>

	The client MAY use the prefix to provide IPv6 addresses to internal components s uch as virtual machines or containers.	The client <bcp14>MAY</bcp14> use the prefix to provide IPv6 addresses to intern al components such as VMs or containers.
	</li>	</li>
	<li>	<li>

	The client MAY use the prefix to allow devices directly connected to it to obtai n IPv6 addresses. For example, the client MAY route traffic for that prefix to t he interface and send a Router Advertisement containing a PIO for the prefix on the interface. That interface MUST NOT be the interface the prefix is obtained f rom. If the client advertises the prefix on an interface, and it has formed addr esses from the prefix, then it MUST act as though the addresses were assigned to that interface for the purposes of Neighbour Discovery and Duplicate Address De tection.	The client <bcp14>MAY</bcp14> use the prefix to allow devices directly connected to it to obtain IPv6 addresses. For example, the client <bcp14>MAY</bcp14> rout e traffic for that prefix to the interface and send a RA containing a PIO for th e prefix on the interface. That interface <bcp14>MUST NOT</bcp14> be the interfa ce the prefix is obtained from. If the client advertises the prefix on an interf ace and it has formed addresses from the prefix, then it <bcp14>MUST</bcp14> act as though the addresses were assigned to that interface for the purposes of Nei ghbor Discovery and Duplicate Address Detection.
	</li>	</li>
	</ul>	</ul>


	<t>The client MUST NOT send or forward packets with destination addresses within a delegated prefix to the interface that it obtained the prefix on, as this can cause a routing loop. This problem will not occur if the client has assigned th e prefix to another interface. Another way the client can prevent this problem i s to add to its routing table a high-metric discard route for the delegated pref ix.	<t>The client <bcp14>MUST NOT</bcp14> send or forward packets with destination a ddresses within a delegated prefix to the interface that it obtained the prefix on, as this can cause a routing loop. This problem will not occur if the client has assigned the prefix to another interface. Another way the client can prevent this problem is to add to its routing table a high-metric discard route for the delegated prefix.
	</t>	</t>

	</section>	</section>

	<section anchor="p0">	<section anchor="p0">

	<name>Absence of PIOs with P bit set</name>	<name>Absence of PIOs with the P Bit Set</name>
	<t>	<t>
	The P bit is purely a positive indicator, telling nodes that DHCPv6	The P bit is purely a positive indicator, telling nodes that DHCPv6

	Prefix Delegation is available and the network prefers that nodes use it,	prefix delegation is available and the network prefers that nodes use it,
	even if they do not have any other reason to run a Prefix Delegation client.	even if they do not have any other reason to run a prefix delegation client.
	The absence of any PIOs with the P bit does not carry any kind of signal to	The absence of any PIOs with the P bit does not carry any kind of signal to

	the opposite, and MUST NOT be processed to mean that DHCPv6-PD is absent. In	the opposite and <bcp14>MUST NOT</bcp14> be processed to mean that DHCPv6-PD is absent. In
	particular, nodes that run DHCPv6-PD due to explicit configuration or by default	particular, nodes that run DHCPv6-PD due to explicit configuration or by default

	(e.g., to extend the network) MUST NOT disable DHCPv6-PD on the absence of PIOs	(e.g., to extend the network) <bcp14>MUST NOT</bcp14> disable DHCPv6-PD on the a
	with the P bit set. A very common example of this are CE routers as described	bsence of PIOs
		with the P bit set.
		A very common example of this are CE routers as described
	by <xref target="RFC7084"/>.	by <xref target="RFC7084"/>.
	</t>	</t>
	</section>	</section>

	<section anchor="onlink">	<section anchor="onlink">

	<name>On-link Communication</name>	<name>On-Link Communication</name>
	<t>	<t>

	When the network delegates unique prefixes to clients, each client will consider	When the network delegates unique prefixes to clients, each client will consider
	other client's destination addresses to be off-link, because those addresses ar	other client's destination addresses to be off-link, because those addresses ar
	e from the delegated prefixes and are not within any on-link prefix. When a clie	e from the delegated prefixes and are not within any on-link prefix. When a clie
	nt sends traffic to another client, packets will initially be sent to the defaul	nt sends traffic to another client, packets will initially be sent to the defaul
	t router. The router may respond with an ICMPv6 redirect message (Section 4.5 of	t router. The router may respond with an ICMPv6 redirect message (<xref section=
	[RFC4861]). If the client receives and accepts the redirect, then traffic can f	"4.5" sectionFormat="of" target="RFC4861"/>). If the client receives and accepts
	low directly from device to device. Therefore, hosts supporting the P flag SHOUL	the redirect, then traffic can flow directly from device to device. Therefore,
	D process redirects unless configured otherwise.	hosts supporting the P flag <bcp14>SHOULD</bcp14> process redirects unless confi
	Hosts which do not process ICMPv6 redirects, and routers, which do not act on IC	gured otherwise.
	MPv6 redirects, may experience higher latency while communicating to prefixes de	Hosts that do not process ICMPv6 redirects, and routers that do not act on ICMPv
	legated to other clients on the same link.	6 redirects, may experience higher latency while communicating to prefixes deleg
		ated to other clients on the same link.
	</t>	</t>
	</section>	</section>

	<section anchor="addrselect">	<section anchor="addrselect">
	<name>Source Address Selection</name>	<name>Source Address Selection</name>
	<t>	<t>

	For the purpose of source address selection <xref target="RFC6724"/>, if the hos	For the purpose of source address selection <xref target="RFC6724"/>, if the h
	t creates any addresses from a delegated prefix, it SHOULD treat those addresses	ost creates any addresses from a delegated prefix, it <bcp14>SHOULD</bcp14> trea
	as if they were assigned to the interface on which the prefix was received. Thi	t those addresses as if they were assigned to the interface on which the prefix
	s includes placing them in the candidate set, and associating them with the outg	was received.
	oing interface when implementing Rule 5 of the source address selection algorith	This includes placing them in the candidate set and associating them with the
	m.	outgoing interface when implementing Rule 5 of the source address selection algo
		rithm <xref target="RFC6724"/>.
	</t>	</t>
	</section>	</section>

	</section>	</section>

	<section anchor="mhoming">	<section anchor="mhoming">
	<name>	<name>
	Multihoming	Multihoming
	</name>	</name>

	<t>	<t>

	In multi-prefix multihoming, the host generally needs to associate the prefix wi th the router that advertised it (see for example, <xref target="RFC6724"/> Rule 5.5). If the host supports Rule 5.5, then it SHOULD associate each prefix with the link-local address of the DHCPv6 server or relay from which it received the REPLY packet.	In multi-prefix multihoming, the host generally needs to associate the prefix wi th the router that advertised it (for example, see Rule 5.5 in <xref target="RFC 6724"/>). If the host supports Rule 5.5, then it <bcp14>SHOULD</bcp14> associate each prefix with the link-local address of the DHCPv6 server or relay from whic h it received the REPLY packet.
	When receiving multiple REPLYs carrying the same prefix from distinct	When receiving multiple REPLYs carrying the same prefix from distinct

	link-local addresses, the host SHOULD associate that prefix with all of these	link-local addresses, the host <bcp14>SHOULD</bcp14> associate that prefix with all of these
	addresses. This can commonly happen in networks with redundant routers and	addresses. This can commonly happen in networks with redundant routers and
	DHCPv6 servers or relays.	DHCPv6 servers or relays.

	</t>	</t>

	</section>	</section>

	<section anchor="rfcchanges">	<section anchor="rfcchanges">
	<name>	<name>

	Modifications to RFC-Mandated Behaviour	Modifications to RFC-Mandated Behavior
	</name>

	<section>
	<name>
	Changes to RFC4861
	</name>
	<t>
	This document makes the following changes to Section 4.2 of <xref target="RFC486
	1"/>:
	</t>

	<t>
	OLD TEXT:
	</t>
	<t>
	====
	</t>
	<t>
	Note: If neither M nor O flags are set, this indicates that no information is av
	ailable via DHCPv6.
	</t>
	<t>
	====
	</t>

	<t>
	NEW TEXT:
	</t>
	<t>
	====
	</t>
	<t>
	Note: If none of M, O, or P (draft-ietf-6man-pio-pflag) flags are set, this indi
	cates that no information is available via DHCPv6.
	</t>
	<t>
	====
	</t>

	</section>
	<section>
	<name>
	Changes to RFC4862
	</name>	</name>

	<t>
	This document makes the following changes to Section 5.5.3 of <xref target="RFC4
	862"/>:
	</t>

	<t>
	OLD TEXT:
	</t>
	<t>
	===
	</t>

	<t>


	For each Prefix-Information option in the Router Advertisement:	<section>
	</t>	<name>Changes to RFC 4861</name>
		<t>This document makes the following changes to <xref section="4.2" secti
	<t>	onFormat="of" target="RFC4861"/>:</t>

	a) If the Autonomous flag is not set, silently ignore the Prefix
	Information option.
	</t>
	<t>
	b) If the prefix is the link-local prefix, silently ignore the Prefix Informat
	ion option.
	</t>
	<t>
	c) If the preferred lifetime is greater than the valid lifetime, silently ignor
	e the Prefix Information option. A node MAY wish to log a system management err
	or in this case.
	</t>
	<t>
	d) If the prefix advertised is not equal to the prefix of an
	address configured by stateless autoconfiguration already in the
	list of addresses associated with the interface (where "equal"
	means the two prefix lengths are the same and the first prefix-
	length bits of the prefixes are identical), and if the Valid
	Lifetime is not 0, form an address (and add it to the list) by
	combining the advertised prefix with an interface identifier of
	the link as follows:
	</t>


	<t>	<!-- [rfced] *AD and authors - There is an open erratum report against RFC
	===	4861 regarding the text that is being updated in Section 9.1 of this
	</t>	document. Are any updates needed?
	<t>
	NEW TEXT:
	</t>
	<t>
	===
	</t>
	<t>
	For each Prefix-Information option in the Router Advertisement:
	</t>


	<t>	See https://www.rfc-editor.org/errata/eid8055.
	a) If the P flag is set, and the node implements draft-ietf-6man-pio-pflag, it S	-->
	HOULD treat the Autonomous flag as if it was unset, and use prefix delegation to
	obtain addresses as described in draft-ietf-6man-pio-pflag.
	</t>


	<t>	<t>OLD TEXT:</t>
		<blockquote>Note: If neither M nor O flags are set, this indicates that
		no information is available via DHCPv6.</blockquote>


	b) If the Autonomous flag is not set, silently ignore the Prefix	<t>NEW TEXT:</t>
	Information option.	<blockquote>Note: If the M, O, or P (RFC 9762)
	</t>	flags are not set, this indicates that no information is available via
	<t>	DHCPv6.</blockquote>
	c) If the prefix is the link-local prefix, silently ignore the Prefix Informat
	ion option.
	</t>
	<t>
	d) If the preferred lifetime is greater than the valid lifetime, silently ignor
	e the Prefix Information option. A node MAY wish to log a system management err
	or in this case.
	</t>
	<t>
	e) If the prefix advertised is not equal to the prefix of an
	address configured by stateless autoconfiguration already in the
	list of addresses associated with the interface (where "equal"
	means the two prefix lengths are the same and the first prefix-
	length bits of the prefixes are identical), and if the Valid
	Lifetime is not 0, form an address (and add it to the list) by
	combining the advertised prefix with an interface identifier of
	the link as follows:
	</t>


	<t>	</section>
	===	<section>
	</t>	<name>Changes to RFC 4862</name>
		<t>This document makes the following changes to <xref section="5.5.3" sec
		tionFormat="of" target="RFC4862"/>:</t>


	</section>	<t>OLD TEXT:</t>
		<blockquote><t>For each Prefix-Information option in the Router Advertise
		ment:</t>
		<ol type="%c)">
		<li>If the Autonomous flag is not set, silently ignore the Prefix Inform
		ation option.</li>
		<li>If the prefix is the link-local prefix, silently ignore the Prefix I
		nformation option.</li>
		<li>If the preferred lifetime is greater than the valid lifetime,
		silently ignore the Prefix Information option. A node
		<bcp14>MAY</bcp14> wish to log a system management error in this
		case.</li>
		<li>If the prefix advertised is not equal to the prefix of an address
		configured by stateless autoconfiguration already in the list of
		addresses associated with the interface (where "equal" means the two
		prefix lengths are the same and the first prefix-length bits of the
		prefixes are identical), and if the Valid Lifetime is not 0, form an
		address (and add it to the list) by combining the advertised prefix
		with an interface identifier of the link as follows:</li>
		</ol>
		</blockquote>


		<t>NEW TEXT:</t>
		<blockquote><t>For each Prefix Information Option in the Router Advertise
		ment:</t>
		<ol type="%c)">
		<li>If the P flag is set and the node implements
		RFC 9762, it <bcp14>SHOULD</bcp14> treat the
		Autonomous flag as if it was unset and use prefix delegation to
		obtain addresses as described in RFC 9762.</li>
		<li>If the Autonomous flag is not set, silently ignore the Prefix Inform
		ation Option.</li>
		<li>If the prefix is the link-local prefix, silently ignore the
		Prefix Information Option.</li>
		<li>If the preferred lifetime is greater than the valid lifetime,
		silently ignore the Prefix Information Option. A node
		<bcp14>MAY</bcp14> wish to log a system management error in this
		case.</li>
		<li>If the prefix advertised is not equal to the prefix of an address
		configured by stateless autoconfiguration already in the list of
		addresses associated with the interface (where "equal" means the two
		prefix lengths are the same and the first prefix-length bits of the
		prefixes are identical) and if the Valid Lifetime is not 0, form an
		address (and add it to the list) by combining the advertised prefix
		with an interface identifier of the link as follows:</li>
		</ol>
		</blockquote>
		</section>
	</section>	</section>

	<section anchor="Security">	<section anchor="Security">

	<!-- All drafts are required to have a security considerations section. Se e RFC 3552 for a guide. -->
	<name>Security Considerations</name>	<name>Security Considerations</name>

	<t>	<t> The mechanism described in this document relies on the information
	The mechanism described in this document relies on the information provid	provided in the RA and therefore shares the same
	ed in the Router Advertisement and therefore shares the same security model as S	security model as SLAAC. If the network does not implement RA-Guard
	LAAC.	<xref target="RFC6105"/>, an attacker might send RAs containing the PIO
	If the network does not implement RA Guard <xref target="RFC6105"/>, an a	used by the network, set the P flag to 1, and force hosts to ignore the A
	ttacker might send RAs containing the PIO used by the network, set the P flag to	flag. In the absence of DHCPv6-PD infrastructure, hosts would either
	1 and force hosts to ignore the A flag.	obtain no IPv6 addresses or, if they fall back to other IPv6 address
	In the absence of DHCPv6-PD infrastructure, hosts would either obtain no	assignment mechanisms such as SLAAC and IA_NA, would experience delays
	IPv6 addresses or, if they fall back to other IPv6 address assignment mechanisms	in obtaining IPv6 addresses. If the network does not support
	such as SLAAC and IA_NA, would experience delays in obtaining IPv6 addresses. I	DHCPv6-Shield <xref target="RFC7610"/>, the attacker could also run a
	f the network does not support DHCPv6-Shield <xref target="RFC7610"/>, the attac	rogue DHCPv6 server, providing the host with invalid prefixes or other
	ker could also run a rogue DHCPv6 server, providing the host with invalid prefix	invalid configuration information.</t>
	es or other invalid configuration information.	<t>The attacker might force hosts to oscillate between DHCPv6-PD and
	</t>	PIO-based SLAAC by sending the same set of PIOs with and then without the
	<t>	P flag
	The attacker might force hosts to oscillate between DHCPv6-PD	set. That would cause the clients to issue REBIND requests, increasing
	and PIO-based SLAAC by sending the same set of PIOs with and then w/o P flag se	the load on the DHCP infrastructure. However, <xref section="14.1" sectio
	t.	nFormat="of"
	That would cause the clients to issue REBIND requests, increa	target="RFC8415"/> requires that DHCPv6-PD clients rate-limit
	sing the load on the DHCP infrastructure.	transmitted DHCPv6 messages.</t>
	However, Section 14.1 of <xref target="RFC8415"/> requires th	<t>It should be noted that if the network allows rogue RAs to be sent,
	at DHCPv6-PD clients rate limit transmitted DHCPv6 messages.	the attacker would be able to disrupt hosts connectivity anyway, so this
	</t>	document doesn't introduce any fundamentally new security
		considerations.</t>
	<t>	<t>Security considerations inherent to the PD-per-device model are
	It should be noted that if the network allows rogue RAs to be	documented in <xref section="15" sectionFormat="of" target="RFC9663"/>.</t
	sent, the attacker would be able to disrupt hosts connectivity anyway, so this	>
	document doesn't introduce any fundamentally new security considerations.
	</t>
	<t>
	Security considerations inherent to the PD-per-device model are docu
	mented in Section 15 of <xref target="RFC9663"/>.
	</t>
	</section>	</section>

	<section anchor="privacy">	<section anchor="privacy">
	<name>Privacy Considerations</name>	<name>Privacy Considerations</name>
	<t>	<t>

	The privacy implications of implementing the P flag and using DHCPv6-PD to assig	The privacy implications of implementing the P flag and using DHCPv6-PD to assig
	n prefixes to hosts are similar to privacy implications of using DHCPv6 for assi	n prefixes to hosts are similar to the privacy implications of using DHCPv6 for
	gning individual addresses.	assigning individual addresses.
	If the DHCPv6 infrastructure assigns the same prefix to the same client, then an	If the DHCPv6 infrastructure assigns the same prefix to the same client, then an
	observer might be able to identify clients based on the highest 64 bits of the	observer might be able to identify clients based on the highest 64 bits of the
	client's address. Those implications and recommended countermeasures are discuss	client's address. Those implications and recommended countermeasures are discuss
	ed in Section 13 of <xref target="RFC9663"/>.</t>	ed in <xref section="13" sectionFormat="of" target="RFC9663"/>.</t>
	<t>	<t>

	Implementing the P flag support on a host / receiving side enables DHCPv 6 on that host.	Implementing the P flag support on a host and receiving side enables DHC Pv6 on that host.
	Sending DHCPv6 packets may reveal some minor additional information about the h ost,	Sending DHCPv6 packets may reveal some minor additional information about the h ost,

	most prominently the hostname. This is not a new concern and would apply for any network which uses DHCPv6 and sets 'M' flag in Router Advertisements.	most prominently the hostname. This is not a new concern and would apply for any network that uses DHCPv6 and sets the M flag in RAs.
	</t>	</t>
	<t>	<t>
	No privacy considerations result from supporting the P flag on the sende r side.	No privacy considerations result from supporting the P flag on the sende r side.
	</t>	</t>
	</section>	</section>

	<section anchor="IANA">	<section anchor="IANA">

	<!-- All drafts are required to have an IANA considerations section. See RFC 8126 for a guide.-->
	<name>IANA Considerations</name>	<name>IANA Considerations</name>

	<t>This memo requests that IANA allocate bit 3 from the "IPv6 Neighbor	<t>IANA has made the following allocation in the "IPv6 Neighbor Discovery
	Discovery Prefix Information Option Flags" registry created by	Prefix Information Option Flags" registry <xref target="RFC8425"/>:
	<xref target="RFC8425"/> for use as the P flag as described in this	</t>
	document. The following entry should be appended:</t>	<table>
	<table>
	<thead>	<thead>
	<tr><th>PIO Option Bit</th><th>Description</th><th>Reference</th></tr>	<tr><th>PIO Option Bit</th><th>Description</th><th>Reference</th></tr>
	</thead>	</thead>
	<tbody>	<tbody>

	<tr><td>3</td><td>P - DHCPv6-PD preferred flag</td><td>[THIS DOCUMENT] </td></tr>	<tr><td>3</td><td>P - DHCPv6-PD Preferred Flag</td><td>RFC 9762</td></ tr>
	</tbody>	</tbody>
	</table>	</table>
	</section>	</section>


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	<xi:include href="https://www.rfc-editor.org/refs/bibxml/reference.RFC.4 861.xml"/>	<xi:include href="https://www.rfc-editor.org/refs/bibxml/reference.RFC.4 861.xml"/>
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	<xi:include href="https://www.rfc-editor.org/refs/bibxml/reference.RFC.8 415.xml"/>	<xi:include href="https://www.rfc-editor.org/refs/bibxml/reference.RFC.8 415.xml"/>
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	<xi:include href="https://www.rfc-editor.org/refs/bibxml/reference. RFC.4193.xml"/>	<xi:include href="https://www.rfc-editor.org/refs/bibxml/reference. RFC.4193.xml"/>
	<xi:include href="https://www.rfc-editor.org/refs/bibxml/reference. RFC.6105.xml"/>	<xi:include href="https://www.rfc-editor.org/refs/bibxml/reference. RFC.6105.xml"/>
	<xi:include href="https://www.rfc-editor.org/refs/bibxml/reference. RFC.6275.xml"/>	<xi:include href="https://www.rfc-editor.org/refs/bibxml/reference. RFC.6275.xml"/>

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	</references>	</references>


	<section anchor="Acknowledgements" numbered="false">	<section anchor="Acknowledgements" numbered="false">
	<name>Acknowledgements</name>	<name>Acknowledgements</name>

	<t>	<t>Thanks to <contact fullname="Nick Buraglio"/>, <contact
	Thanks to Nick Buraglio, Brian Carpenter, Tim Chown, David Farmer, Fernando Gont	fullname="Brian Carpenter"/>, <contact fullname="Tim Chown"/>, <contact
	, Susan Hares, Dirk Von Hugo, Mahesh Jethanandani, Suresh Krishnan, Ted Lemon, A	fullname="David Farmer"/>, <contact fullname="Fernando Gont"/>, <contact
	ndrew McGregor, Erik Nordmark, Tomek Mrugalski, Michael Richardson, John Scudder	fullname="Susan Hares"/>, <contact fullname="Mahesh Jethanandani"/>,
	, Ole Trøan, Eric Vyncke and Timothy Winters for the discussions, reviews, the i	<contact fullname="Suresh Krishnan"/>, <contact fullname="Ted Lemon"/>,
	nput and all contributions.	<contact fullname="Andrew McGregor"/>, <contact fullname="Tomek
	</t>	Mrugalski"/>, <contact fullname="Erik Nordmark"/>, <contact
		fullname="Michael Richardson"/>, <contact fullname="John Scudder"/>,
		<contact fullname="Ole Trøan"/>, <contact fullname="Dirk Von Hugo"/>,
		<contact fullname="Éric Vyncke"/> and <contact fullname="Timothy
		Winters"/> for the discussions, reviews, input, and
		contributions.</t>
	</section>	</section>


	</back>	</back>
	</rfc>	</rfc>

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