Diff: rfc9665.original.xml

	rfc9665.original.xml	rfc9665.xml
	<?xml version="1.0" encoding="UTF-8"?>	<?xml version="1.0" encoding="UTF-8"?>

	<!DOCTYPE rfc SYSTEM "rfc2629-xhtml.ent">
	<rfc category="std" submissionType="IETF" docName="draft-ietf-dnssd-srp-25" ipr=	<!DOCTYPE rfc [
	"trust200902"	<!ENTITY nbsp " ">
	xmlns:xi="http://www.w3.org/2001/XInclude" version="3"	<!ENTITY zwsp "">
	scripts="Common,Latin" sortRefs="false" consensus="true"	<!ENTITY nbhy "‑">
	symRefs="true" tocDepth="4" tocInclude="true" xml:lang="en">	<!ENTITY wj "⁠">
		]>

		<rfc category="std" submissionType="IETF" docName="draft-ietf-dnssd-srp-latest"
		number="9665" ipr="trust200902" xmlns:xi="http://www.w3.org/2001/XInclude" obsol
		etes="" updates="" version="3" sortRefs="true" consensus="true" symRefs="true" t
		ocDepth="4" tocInclude="true" xml:lang="en">
	<front>	<front>

	<title abbrev='Service Registration Protocol'>Service Registration Protocol	<title abbrev="Service Registration Protocol">Service Registration Protocol
	for DNS-Based Service Discovery</title>	for DNS-Based Service Discovery</title>
	<author initials="T" surname="Lemon" fullname="Ted Lemon">	<seriesInfo name="RFC" value="9665"/>
		<author initials="T." surname="Lemon" fullname="Ted Lemon">
	<organization>Apple Inc.</organization>	<organization>Apple Inc.</organization>
	<address>	<address>
	<postal>	<postal>
	<street>One Apple Park Way</street>	<street>One Apple Park Way</street>
	<city>Cupertino</city>	<city>Cupertino</city>

	<region>California</region>	<region>CA</region>
	<code>95014</code>	<code>95014</code>

	<country>USA</country>	<country>United States of America</country>
	</postal>	</postal>
	<email>mellon@fugue.com</email>	<email>mellon@fugue.com</email>
	</address>	</address>
	</author>	</author>


	<author initials='S' surname='Cheshire' fullname='Stuart Cheshire'>	<author initials="S." surname="Cheshire" fullname="Stuart Cheshire">
	<organization>Apple Inc.</organization>	<organization>Apple Inc.</organization>
	<address>	<address>
	<postal>	<postal>
	<street>One Apple Park Way</street>	<street>One Apple Park Way</street>
	<city>Cupertino</city>	<city>Cupertino</city>

	<region>California</region>	<region>CA</region>
	<code>95014</code>	<code>95014</code>

	<country>USA</country>	<country>United States of America</country>
	</postal>	</postal>
	<phone>+1 408 974 3207</phone>	<phone>+1 408 974 3207</phone>
	<email>cheshire@apple.com</email>	<email>cheshire@apple.com</email>
	</address>	</address>
	</author>	</author>


	<date>March 4, 2024</date>	<date month="June" year="2025"/>
	<area>Internet</area>	<area>INT</area>
	<workgroup>Internet Engineering Task Force</workgroup>	<workgroup>dnssd</workgroup>
	<keyword>Multicast DNS</keyword>	<keyword>Multicast DNS</keyword>
	<keyword>DNS-Based Service Discovery</keyword>	<keyword>DNS-Based Service Discovery</keyword>
	<keyword>DNS Update</keyword>	<keyword>DNS Update</keyword>
	<keyword>SIG(0)</keyword>	<keyword>SIG(0)</keyword>

	<abstract>
	<t>

	The Service Registration Protocol for DNS-Based Service Discovery uses t
	he standard DNS Update mechanism to enable DNS-Based
	Service Discovery using only unicast packets. This makes it possible to
	deploy DNS Service Discovery without multicast,
	which greatly improves scalability and improves performance on networks
	where multicast service is not an optimal choice,
	particularly IEEE 802.11 (Wi&nbhy;Fi) and IEEE 802.15.4 networks. DNS&n
	bhy;SD Service registration
	uses public keys and SIG(0) to allow services to defend their registrati
	ons.


		<abstract>
		<t>The Service Registration Protocol (SRP) for DNS-based Service
		Discovery (DNS&nbhy;SD) uses the standard DNS Update mechanism to
		enable DNS&nbhy;SD using only unicast packets. This makes it possible
		to deploy DNS&nbhy;SD without multicast, which greatly improves
		scalability and improves performance on networks where multicast
		service is not an optimal choice, particularly IEEE 802.11
		(Wi-Fi) and IEEE 802.15.4 networks. DNS&nbhy;SD Service
		registration uses public keys and SIG(0) to allow services to defend
		their registrations.
	</t>	</t>
	</abstract>	</abstract>

	<note removeInRFC="true">
	<name>About This Document</name>
	<t>
	The latest revision of this draft can be found at <eref target="https://
	dnssd-wg.github.io/draft-ietf-dnssd-srp/draft-ietf-dnssd-srp.html"/>.
	Status information for this document may be found at <eref target="https
	://datatracker.ietf.org/doc/draft-ietf-dnssd-srp/"/>.
	</t>
	<t>
	Discussion of this document takes place on the
	DNS-SD Working Group mailing list (<eref target="mailto:dnssd@ietf.org"/
	>),
	which is archived at <eref target="https://mailarchive.ietf.org/arch/bro
	wse/dnssd/"/>.
	Subscribe at <eref target="https://www.ietf.org/mailman/listinfo/dnssd/"
	/>.
	</t>
	<t>Source for this draft and an issue tracker can be found at
	<eref target="https://github.com/dnssd-wg/draft-ietf-dnssd-srp"/>.</t>
	</note>
	</front>	</front>

	<middle>	<middle>

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

		DNS&nbhy;SD <xref target="RFC6763"/>
	<xref target="RFC6763">DNS-Based Service Discovery</xref> is a component	is a component of Zero Configuration Networking
	of Zero Configuration Networking	<xref target="RFC6760"/>
	<xref target="RFC6760"/> <xref target="ZC"/> <xref target="I-D.cheshire-	<xref target="ZC"/>
	dnssd-roadmap"/>.</t>	<xref target="I-D.cheshire-dnssd-roadmap"/>.</t>
	<t>
	This document describes an enhancement to <xref target="RFC6763">DNS-Bas
	ed Service Discovery</xref> (DNS&nbhy;SD) that
	allows servers to register the services they offer using the DNS protocol
	rather than using <xref target="RFC6762">Multicast
	DNS</xref> (mDNS). There is already a large installed base of DNS&nbhy;S
	D clients that can discover services using the DNS
	protocol (e.g. Android, Windows, Linux, Apple).</t>
	<t>	<t>

	This document is intended for three audiences: implementors of software	This document describes an enhancement to DNS&nbhy;SD that
	that provides services that should be advertised	allows servers to register the services they offer using the DNS protocol
	using DNS&nbhy;SD, implementors of DNS servers that will be used in cont	over unicast rather than using Multicast DNS (mDNS) <xref target="RFC6762
	exts where DNS&nbhy;SD registration is needed, and	"/>.
	administrators of networks where DNS&nbhy;SD service is required. The d	There is already a large installed base of DNS&nbhy;SD
	ocument is expected to provide sufficient	clients that can discover services using the DNS
	information to allow interoperable implementation of the registration pr	protocol (e.g., Android, Windows, Linux, Apple operating systems).</t>
	otocol.</t>
	<t>	<t>

	DNS-Based Service Discovery (DNS&nbhy;SD) allows services to advertise t	This document is intended for three audiences: Implementers of software
	he fact that they provide service, and to provide	that provides services that should be advertised
	the information required to access that service. DNS&nbhy;SD clients ca	using DNS&nbhy;SD, implementers of authoritative DNS servers that will
	n then discover the set of services of a particular	be used in contexts where DNS&nbhy;SD registration is needed, and
	type that are available. They can then select a service from among thos	administrators of networks where DNS&nbhy;SD service is required.
	e that are available and obtain the information	The document is expected to provide sufficient
	required to use it. Although DNS Service Discovery (DNS-SD) using the D	information to allow interoperable implementation
	NS protocol (as opposed to mDNS) can be more efficient and versatile, it is	of the Service Registration Protocol.</t>
	not common in practice, because of the difficulties associated with upda	<t>
	ting authoritative DNS services with service	DNS&nbhy;SD allows servers to publish the information required to access
	information.</t>	the services they provide. DNS&nbhy;SD clients can then discover the set
		of service instances of a particular type that are available. They can then
		select an instance from among those that are available and obtain the
		information required to use it. Although DNS&nbhy;SD using the DNS
		protocol can be more efficient and versatile than using mDNS, it is
		not common in practice because of the difficulties associated with
		updating authoritative DNS services with service information.</t>
	<t>	<t>

	Existing practice for updating DNS zones is to either manually enter new	The existing practice for updating DNS zones is either to enter new data
	data, or else use DNS Update	manually or to use DNS Update
	<xref target="RFC2136"/>. Unfortunately DNS Update requires either that t	<xref target="RFC2136"/>. Unfortunately, DNS Update requires either:</t>
	he authoritative DNS server automatically trust	<ul>
	updates, or else that the DNS Update requestor have some kind of shared s	<li>that the authoritative DNS server automatically trust
	ecret or public key that is known to the DNS server	updates or</li>
	and can be used to authenticate the update. Furthermore, DNS Update can	<li>that the DNS Update requester have some kind of shared secret
	be a fairly chatty process, requiring multiple	or public key that is known to the authoritative DNS server
	round trips with different conditional predicates to complete the update	and can be used to authenticate the update.</li></ul>
	process.</t>	<t>Furthermore, DNS Update can be a fairly chatty process, requiring mult
		iple
		roundtrips with different conditional predicates to complete the update p
		rocess.</t>
	<t>	<t>

	The Service Registration Protocol (SRP) adds a set of default heuristics	The Service Registration Protocol (SRP) adds a set of default
	for processing DNS updates that eliminates the need for DNS update	heuristics for processing DNS updates that eliminates the need for
	conditional predicates: instead, the SRP registrar (a DNS server that sup	conditional predicates.
	ports SRP updates) has a set of default predicates	Instead, the SRP registrar (an authoritative DNS server
	that are applied to the update, and the update either succeeds entirely,	that supports SRP Updates) has a set of default predicates
	or fails in a way that allows the requestor to know	that are applied to the update; and the update either succeeds entirely o
		r fails in a way that allows the requester to know
	what went wrong and construct a new update.</t>	what went wrong and construct a new update.</t>

	<t>	<t>

	SRP also adds a feature called First-Come, First-Served (FCFS) Naming, wh	SRP also adds a feature called "First Come, First Served Naming" (or "FCF
	ich allows the requestor to claim a name that is	S Naming"), which allows the requester to:</t>
	not yet in use, and, using SIG(0) <xref target="RFC2931"/>, to authentica	<ul><li>claim a name that is
	te both the initial claim and subsequent	not yet in use, and</li>
	updates. This prevents name conflicts, since a second SRP requestor attem	<li>authenticate, using SIG(0) <xref target="RFC2931"/>,
	pting to claim the same name will not possess the	both the initial claim
	SIG(0) key used by the first requestor to claim it, and so its claim will	(to ensure it has not been modified in transit)
	be rejected and the second requestor will have to	and subsequent updates
		(to ensure they come from the same entity that performed the initial clai
		m).</li></ul>

		<t>This prevents a new service instance from "stealing" a name that is al
		ready in use:
		A second SRP requester attempting to claim an existing name will not poss
		ess the
		SIG(0) key used by the first requester to claim it. Because of this, its
		claim will be rejected. This will force it to
	choose a new name.</t>	choose a new name.</t>

	<t>	<t>
	It is important to understand that "authenticate" here just means that we can tell that an update came from the same source	It is important to understand that "authenticate" here just means that we can tell that an update came from the same source
	as the original registration. We have not established trust. This has imp ortant implications for what we can and can't do	as the original registration. We have not established trust. This has imp ortant implications for what we can and can't do

	with data the client sends us. You will notice as you read this document	with data the SRP requester sends us.
	that we only support adding a very restricted set	You will notice as you read this document that
		we only support adding a very restricted set
	of records, and the content of those records is further constrained.</t>	of records, and the content of those records is further constrained.</t>

	<t>	<t>

	The reason for this is precisely that we have not established trust. So w	The reason for this is precisely that we have not established trust. So,
	e can only publish information that we feel safe in	we can only publish information that we feel safe in
	publishing even though we do not have any basis for trusting the requesto	publishing even though we do not have any basis for trusting the requeste
	r. We reason that mDNS <xref target="RFC6762"/>	r.
	allows arbitrary hosts on a single IP link to advertise services <xref ta	We reason that mDNS <xref target="RFC6762"/> allows
	rget="RFC6763"/>, relying on whatever service is	arbitrary hosts on a single IP link to advertise services
		<xref target="RFC6763"/>, relying on whatever service is
	advertised to provide authentication as a part of its protocol rather tha n in the service advertisement.</t>	advertised to provide authentication as a part of its protocol rather tha n in the service advertisement.</t>

	<t>	<t>
	This is considered reasonably safe because it requires physical presence on the network in order to advertise. An off-network	This is considered reasonably safe because it requires physical presence on the network in order to advertise. An off-network

	mDNS attack is simply not possible. Our goal with this specification is t o impose similar constraints. Because of this you will	mDNS attack is simply not possible. Our goal with this specification is t o impose similar constraints. Therefore, you will
	see in <xref target="add_validation"/> that a very restricted set of reco rds with a very restricted set of relationships are	see in <xref target="add_validation"/> that a very restricted set of reco rds with a very restricted set of relationships are
	allowed. You will also see in <xref target="source_validation"/> that we give advice on how to prevent off-network attacks.</t>	allowed. You will also see in <xref target="source_validation"/> that we give advice on how to prevent off-network attacks.</t>

	<t>	<t>
	This leads us to the disappointing observation that this protocol is not a mechanism for adding arbitrary information to	This leads us to the disappointing observation that this protocol is not a mechanism for adding arbitrary information to
	DNS zones. We have not evaluated the security properties of adding, for e xample, an SOA record, an MX record, or a CNAME	DNS zones. We have not evaluated the security properties of adding, for e xample, an SOA record, an MX record, or a CNAME

	record, and so these are forbidden. A future protocol specification might	record; therefore, these are forbidden.
	include analyses for other records, and extend	Future updates to this specification might include analyses for other rec
	the set of records that can be registered here. Or it might require estab	ords
	lishment of trust, and add an authorization model	and extend the set of records and/or record content that can be registere
	to the authentication model we now have. But this is work for a future do	d here.
	cument.</t>	Or it might require establishment of trust, and add an authorization mode
		l
		to the authentication model we now have.
		But that is work for a future document.</t>

	<t>	<t>

	Finally, SRP adds the concept of a 'lease,' similar to leases in Dynamic	Finally, SRP adds the concept of a "lease" <xref target="RFC9664"/>,
	Host Configuration Protocol	analogous to leases in DHCP <xref target="RFC2131"/> <xref
	<xref target="RFC8415"/>. The SRP registration itself has a lease which	target="RFC8415"/>. The SRP registration itself has a lease that may
	may be on the order of an hour; if the requestor	be on the order of two hours; if the requester does not renew the
	does not renew the lease before it has elapsed, the registration is remov	lease before it has elapsed, the registration is removed. The claim
	ed. The claim on the name can have a longer	on the name can have a longer lease so that another requester cannot
	lease, so that another requestor cannot claim the name, even though the r	immediately claim the name, even though the registration itself has
	egistration has expired.</t>	expired.</t>

	<t>	<t>

	The Service Registration Protocol for DNS&nbhy;SD (SRP), specified in th	The Service Registration Protocol for DNS&nbhy;SD
	is document, provides a reasonably secure mechanism	specified in this document provides a reasonably secure
	for publishing this information. Once published, these services can be	mechanism for publishing this information.
	readily discovered by DNS&nbhy;SD clients using	Once published, these services can be readily
		discovered by DNS&nbhy;SD clients using
	standard DNS lookups.</t>	standard DNS lookups.</t>
	<t>	<t>

	The DNS&nbhy;SD specification (<xref target="RFC6763" section="10" secti	Section <xref target="RFC6763" section="10" sectionFormat="bare"/>
	onFormat="comma"/>, “Populating the DNS with	of the DNS&nbhy;SD specification <xref target="RFC6763"/>
	Information”), briefly discusses ways that servers can publish their inf	briefly discusses ways that servers can advertise the services
	ormation in the DNS namespace. In the case of	they provide in the DNS namespace. In the case of
	mDNS, it allows servers to publish their information on the local link,	mDNS, it allows servers to advertise their services on the local link,
	using names in the ".local" namespace, which makes	using names in the "local." namespace, which makes
	their services directly discoverable by peers attached to that same loca l link.</t>	their services directly discoverable by peers attached to that same loca l link.</t>
	<t>	<t>

	RFC6763 also allows clients to discover services using <xref target="RFC	DNS&nbhy;SD <xref target="RFC6763"/> also allows clients to discover ser
	1035">the DNS protocol</xref>. This can be done by	vices
	having a system administrator manually configure service information in	by using the DNS protocol over traditional unicast <xref target="RFC1035
	the DNS, but manually populating DNS authoritative	"/>.
	server databases is costly and potentially error-prone, and requires a k	This can be done by
	nowledgeable network administrator. Consequently,	having a system administrator manually configure service information in
	although all DNS&nbhy;SD client implementations of which we are aware su	the DNS; however, manually populating DNS authoritative
	pport DNS&nbhy;SD using DNS queries, in practice it	server databases is costly and potentially error-prone and requires a kn
		owledgeable network administrator. Consequently,
		although all DNS&nbhy;SD client implementations of which we are
		aware support DNS&nbhy;SD using DNS queries, in practice it
	is used much less frequently than mDNS.</t>	is used much less frequently than mDNS.</t>
	<t>	<t>

	The <xref target="RFC8766">Discovery Proxy</xref> provides one way to au	The Discovery Proxy <xref target="RFC8766"/> provides one way to automat
	tomatically populate the DNS	ically populate the DNS
	namespace, but is only appropriate on networks where services are easily	namespace but is only appropriate on networks where services are easily
	advertised using mDNS. This document describes a	advertised using mDNS. The present document describes a
	solution more suitable for networks where multicast is inefficient, or w	solution more suitable for networks where multicast is inefficient,
	here sleepy devices are common, by supporting both	or where sleepy devices are common, by supporting the use of unicast
	offering of services, and discovery of services, using unicast.</t>	for both the offering of and the discovery of services.</t>
	</section>	</section>

	<section>	<section>
	<name>Conventions and Terminology Used in This Document</name>	<name>Conventions and Terminology Used in This Document</name>

	<t>	<t>
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOU	The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>", "<bcp14>REQU
	LD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED",	IRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL
	"MAY", and "OPTIONAL" in this document are to be interpreted as described	NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>", "<bcp14>
	in BCP 14 <xref target="RFC2119"/>	RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
	<xref target="RFC8174"/> when, and only when, they appear in all capital	"<bcp14>MAY</bcp14>", and "<bcp14>OPTIONAL</bcp14>" in this document are to
	s, as shown here.	be interpreted as
	</t>	described in BCP 14 <xref target="RFC2119"/> <xref target="RFC8174"/>
		when, and only when, they appear in all capitals, as shown here.
		</t>
		<t>Strictly speaking, fully qualified domain names end with a dot
		("."). In DNS zone files and other similar contexts, if the final dot
		is omitted, then a name may be treated incorrectly as relative to some
		other parent domain. This document follows the formal DNS convention,
		ending fully qualified domain names with a dot. When this document
		mentions domain names such as "local." and "default.service.arpa.",
		the final dot is part of the domain name; it is not a period
		indicating the end of the sentence.</t>
	</section>	</section>

	<section>	<section>
	<name>Service Registration Protocol</name>	<name>Service Registration Protocol</name>
	<t>	<t>

	Services that implement SRP use DNS Update <xref target="RFC2136"/> <xre	Services that implement SRP use DNS Update <xref target="RFC2136"/> with
	f target="RFC3007"/> to publish service information	SIG(0) <xref target="RFC3007"/> to publish service information
	in the DNS. Two variants exist, one for full-featured hosts, and one fo	in the DNS. Two variants exist: One for full-featured hosts and one for
	r devices designed for "Constrained-Node Networks"	devices designed for Constrained-Node Networks (CNNs)
	<xref target="RFC7228"/>. An SRP registrar is most likely an authoritati	<xref target="RFC7228"/>.
	ve DNS server, or else is updating an authoritative	An SRP registrar is most likely an authoritative DNS server
	DNS server. There is no requirement that the server that is receiving SRP	or is a source of data for one or more authoritative DNS servers.
	updates be the same server that is answering	There is no requirement that the authoritative DNS server that is
	queries that return records that have been registered.</t>	receiving SRP Updates be the same authoritative DNS server that is
		answering queries that return records that have been registered.
		For example, an SRP registrar could be the "hidden primary" that is
		the source of data for a fleet of secondary authoritative DNS servers.</
		t>
	<section>	<section>
	<name>Protocol Variants</name>	<name>Protocol Variants</name>
	<section>	<section>

	<name>Full-featured Hosts</name>	<name>Full-Featured Hosts</name>
	<t>	<t>

	Full-featured hosts either are configured manually with a registrati	Full-featured hosts either are configured manually with a registrati
	on domain, or discover the default registration	on domain or discover the default registration
	domain as described in <xref target="RFC6763" section="11" sectionFor	domain automatically using the Domain Enumeration process described i
	mat="of"/>. If this process does not produce a	n
	default registration domain, the Service Registration protocol is not	Section <xref target="RFC6763" section="11" sectionFormat="bare"/>
	discoverable on the local network using this	of the DNS&nbhy;SD specification <xref target="RFC6763"/>.
	mechanism. Other discovery mechanisms are possible, but are out of sc	If this process does not produce a
	ope for this document.</t>	default registration domain, the SRP registrar
		is not discoverable on the local network using this
		mechanism. Other discovery mechanisms are possible, but they are out
		of scope for this document.</t>
	<t>	<t>

	Manual configuration of the registration domain can be done either b	Configuration of the registration domain can be done either:</t>
	y querying the list of available registration	<ul><li>by querying the list of available registration
	domains ("r._dns&nbhy;sd._udp") and allowing the user to select one	domains ("r._dns&nbhy;sd._udp") and allowing the user to select one
	from the UI, or by any other means appropriate to	from the UI, or</li>
	the particular use case being addressed. Full-featured devices cons	<li>by any other means appropriate to
	truct the names of the SRV, TXT, and PTR records	the particular use case being addressed.</li></ul>
	describing their service(s) as subdomains of the chosen service regi	<t>Full-featured devices construct the names of the SRV, TXT, and PTR
	stration domain. For these names they then discover	records
	the zone apex of the closest enclosing DNS zone using SOA queries <x	describing their service or services as subdomains of the chosen ser
	ref target="RFC8765" section="6.1"/>. Having	vice registration domain. For these names, they then discover
		the zone apex of the closest enclosing DNS zone using SOA queries
		as described in
		Section <xref target="RFC8765" section="6.1" sectionFormat="bare"/>
		of the DNS Push Notification specification <xref target="RFC8765"/>.
		Having
	discovered the enclosing DNS zone, they query for the "_dnssd&nbhy;s rp._tcp.<zone>" SRV record to discover the	discovered the enclosing DNS zone, they query for the "_dnssd&nbhy;s rp._tcp.<zone>" SRV record to discover the

	server to which they can send SRP updates. Hosts that support SRP U pdates using TLS use the	SRP registrar to which they can send SRP Updates. Hosts that suppor t SRP Updates using TLS use the
	"_dnssd&nbhy;srp&nbhy;tls._tcp.<zone>" SRV record instead.</t>	"_dnssd&nbhy;srp&nbhy;tls._tcp.<zone>" SRV record instead.</t>
	<t>	<t>
	Examples of full-featured hosts include devices such as home computer s, laptops, powered peripherals with network	Examples of full-featured hosts include devices such as home computer s, laptops, powered peripherals with network

	connections such as printers, home routers, and even battery-operated devices such as mobile phones that have	connections (such as printers and home routers), and even battery-ope rated devices such as mobile phones that have
	long battery lives.	long battery lives.
	</t>	</t>
	</section>	</section>

	<section>	<section anchor="constrained_hosts">
	<name>Constrained Hosts</name>	<name>Constrained Hosts</name>
	<t>	<t>

	For devices designed for Constrained-Node Networks <xref target="RFC	For devices designed for CNNs <xref target="RFC7228"/>,
	7228"/> some simplifications are available. Instead of	some simplifications are available. Instead of
	being configured with (or discovering) the service registration doma	being configured with (or discovering) the service registration doma
	in, the special-use domain name (see	in,
	<xref target="RFC6761"/>) "default.service.arpa" is used. The detai	the special-use domain name <xref target="RFC6761"/> "default.servic
	ls of how SRP registrar(s) are discovered will be specific	e.arpa." is used.
	to the constrained network, and therefore we do not suggest a specif	The details of how SRP registrars are discovered will be specific
	ic mechanism here.</t>	to the constrained network; therefore, we do not suggest a specific
		mechanism here.</t>
	<t>	<t>

	SRP requestors on constrained networks are expected to receive from	SRP requesters on CNNs are expected to receive, from the network,
	the network a list of SRP registrars with which to register.	a list of SRP registrars with which to register. It is the
	It is the responsibility of a Constrained-Node Network supporting SR	responsibility of a CNN supporting SRP to provide at least one
	P to provide one or more registrar addresses. It is	registrar address and port. It is the responsibility of the
	the responsibility of the registrar supporting a Constrained-Node Ne	registrar supporting a CNN to handle the updates appropriately.
	twork to handle the updates appropriately. In some	In some network environments, updates may be accepted directly
	network environments, updates may be accepted directly into a local	into a local "default.service.arpa." zone, which has only local
	"default.service.arpa" zone, which has only local	visibility. In other network environments, updates for names
	visibility. In other network environments, updates for names ending	ending in "default.service.arpa." may be rewritten by the
	in "default.service.arpa" may be rewritten by the registrar	registrar to names with broader visibility. Domain name rewriting
	to names with broader visibility.</t>	should be performed as appropriate for the network environment in
		question. Some suggested techniques for how domain names can be
		translated from a locally scoped name to a domain name with larger
		scope can be found in the discussion of data translation for names
		in Multicast DNS answers in Section <xref target="RFC8766"
		section="5.5" sectionFormat="bare"/> of the Discovery Proxy
		specification <xref target="RFC8766"/>.</t>
	</section>	</section>
	<section>	<section>
	<name>Why two variants?</name>	<name>Why two variants?</name>
	<t>	<t>

	The reason for these different variants is that low-power devices th	The reason for these different variants is that low-power devices th
	at typically use Constrained-Node Networks may have	at typically use CNNs may have
	very limited battery storage. The series of DNS lookups required to	very limited battery capacity. The series of DNS lookups required t
	discover an SRP registrar and then communicate with	o discover an SRP registrar and then communicate with
	it will increase the energy required to advertise a service; for low -power devices, the additional flexibility this	it will increase the energy required to advertise a service; for low -power devices, the additional flexibility this
	provides does not justify the additional use of energy. It is also fairly typical of such networks that some network	provides does not justify the additional use of energy. It is also fairly typical of such networks that some network

	service information is obtained as part of the process of joining th e network, and so this can be relied upon to provide	service information is obtained as part of the process of joining th e network; thus, this can be relied upon to provide
	nodes with the information they need.</t>	nodes with the information they need.</t>
	<t>	<t>

	Networks that are not constrained networks can have more complicated	Networks that are not CNNs can have more complicated topologies at t
	topologies at the IP layer. Nodes connected	he IP layer. Nodes connected
	to such networks can be assumed to be able to do DNS-SD service regi	to such networks can be assumed to be able to do DNS&nbhy;SD
	stration domain discovery. Such networks are	service registration domain discovery. Such networks are
	generally able to provide registration domain discovery and routing. This creates the possibility of off-network	generally able to provide registration domain discovery and routing. This creates the possibility of off-network
	spoofing, where a device from a foreign network registers a service o n the local network in order to attack devices	spoofing, where a device from a foreign network registers a service o n the local network in order to attack devices

	on the local network. To prevent such spoofing, TCP is required for s	on the local network. To guard against off-path spoofing, TCP is requ
	uch networks.	ired for such networks.</t>
	</t>
	</section>	</section>
	</section>	</section>
	<section>	<section>
	<name>Protocol Details</name>	<name>Protocol Details</name>
	<t>	<t>

	We will discuss several parts to this process: how to know what to pub	We will discuss several parts to this process:</t>
	lish, how to know where to publish it (under what
	name), how to publish it, and how to secure its publication. In <xref
	target="maintenance"/>, we specify how to maintain
	the information once published.</t>


	<section>	<ul spacing="compact">
	<name>What to publish</name>	<li>how to know what to publish (<xref target="what"/>),</li>
		<li>how to know where to publish it (under what name) (<xref target="where"/>)
		,</li>
		<li>how to publish it (<xref target="how"/>),</li>
		<li>how to secure its publication (<xref target="how-to-secure"/>), and</li>
		<li>how to maintain
		the information once published (<xref target="maintenance"/>).</li></u
		l>

		<section anchor="what">
		<name>What to Publish</name>
	<t>	<t>

	SRP Updates are sent by SRP requestors to SRP registrars. Three typ es of instructions appear in an SRP update: Service	SRP Updates are sent by SRP requesters to SRP registrars. Three typ es of instructions appear in an SRP Update: Service
	Discovery instructions, Service Description instructions, and Host De scription instructions. These instructions are made	Discovery instructions, Service Description instructions, and Host De scription instructions. These instructions are made

	up of DNS Update RRs that are either adds or deletes. The types of re cords that are added, updated and removed in each	up of DNS Update Resource Records (RRs) that are either adds or delet es. The types of records that are added, updated, and removed in each
	of these instructions, as well as the constraints that apply to them, are described in <xref target="server_behavior"/>.	of these instructions, as well as the constraints that apply to them, are described in <xref target="server_behavior"/>.

	An SRP Update is a DNS Update message that is constructed so as to me	An SRP Update is a DNS Update message <xref target="RFC2136"/> that i
	et the constraints described in that section. The	s
		constructed so as to meet the constraints described in that section.
		The
	following is a brief overview of what is included in a typical SRP Up date:	following is a brief overview of what is included in a typical SRP Up date:
	</t>	</t>

	<ul spacing="compact">	<ul spacing="normal">

	<li>	<li>

	PTR Resource Record (RR) for services, which map from a generic se	Service Discovery PTR RR(s) for service(s), which map from a
	rvice type (or subtype) name to a specific	generic service type (or subtype(s)) to a specific
	Service Instance Name.</li>	service instance name <xref target="RFC6763"/>.</li>
	<li>	<li>

	For any Service Instance Name (<xref target="RFC6763" section="4.1"	For each service instance name, an SRV RR, one or more
	sectionFormat="comma"/>), an SRV RR, one or more	TXT RRs, and a KEY RR. Although, in principle, DNS&nbhy;SD
	TXT RRs, and a KEY RR. Although in principle DNS-SD Service Descrip	Service Description records can include other record types with
	tion records can include other record types with	the same service instance name, in practice, they rarely do.
	the same Service Instance Name, in practice they rarely do. SRP doe	Currently, SRP does not permit other record types. The KEY RR is us
	s not permit other record types. The KEY RR is used	ed
	to support FCFS naming, and has no specific meaning for DNS-SD look	to support FCFS Naming and has no specific meaning for DNS&nbhy;SD
	ups. SRV records for all services described in an	lookups. SRV records for all services described in an
	SRP update point to the same hostname.</li>	SRP Update point to the same hostname.</li>
	<li>	<li>

	There is never more than one hostname in a single SRP update. The h	There is always exactly one hostname in a single SRP Update.
	ostname has one or more address RRs (AAAA or A) and	A DNS Update containing more than one hostname is not an SRP Updat
	a KEY RR (used for FCFS naming). Depending on the use case, an SRP	e.
	requestor may be required to suppress some	The hostname has one or more address RRs (AAAA or A) and
		a KEY RR (used for FCFS Naming). Depending on the use case, an SRP
		requester may be required to suppress some
	addresses that would not be usable by hosts discovering the servic e through the SRP registrar. The exact address	addresses that would not be usable by hosts discovering the servic e through the SRP registrar. The exact address

	record suppression behavior required may vary for different types	record suppression behavior required may vary for different types
	of SRP requestors. An example of such advice can be	of SRP requesters.
	found in <xref target="RFC8766" section="5.5.2" sectionFormat="of"	Some suggested policies for suppressing unusable records can be fo
	/>.	und in
		Section <xref target="RFC8766" section="5.5.2" sectionFormat="bare
		"/>
		of the Discovery Proxy specification <xref target="RFC8766"/>.
	</li>	</li>
	</ul>	</ul>
	<t>	<t>

	<xref target="RFC6763"/> describes the details of what each of these	The DNS-Based Service Discovery specification
	types of RR mean, with the exception of	<xref target="RFC6763"/> describes the details of
	the KEY RR, which is defined in <xref target="RFC2539"/>. These RFCs	what each of these RR types mean, with the exception of
	should be considered the definitive source for	the KEY RR, which is defined in the
		specification for how to store Diffie-Hellman
		Keys in the DNS <xref target="RFC2539"/>.
		These specifications should be considered
		the definitive sources for
	information about what to publish; the reason for summarizing this h ere is to provide the reader with enough information	information about what to publish; the reason for summarizing this h ere is to provide the reader with enough information
	about what will be published that the service registration process c an be understood at a high level without first	about what will be published that the service registration process c an be understood at a high level without first

	learning the full details of DNS&nbhy;SD. Also, the "Service Instan	learning the full details of DNS&nbhy;SD.
	ce Name" is an important aspect of FCFS	Also, the "service instance name" is an important aspect of FCFS
	naming, which we describe later on in this document.</t>	Naming, which we describe later on in this document.</t>
	</section>	</section>


	<section>	<section anchor="where">
	<name>Where to publish it</name>	<name>Where to Publish It</name>
	<t>	<t>

	Multicast DNS uses a single namespace, ".local", which is valid on t	Multicast DNS (mDNS) uses a single namespace, "local.".
	he local link. This convenience is not available for	Subdomains of "local." are specific to the local link on which they
	DNS&nbhy;SD using the DNS protocol: services must exist in some spec	are advertised.
	ific DNS namespace that is chosen either by the	This convenience is not available for
	network operator, or automatically.</t>	DNS&nbhy;SD using the DNS protocol: Services must exist in
		some specific DNS namespace that is chosen either by the
		network operator or automatically.</t>
	<t>	<t>
	As described above, full-featured devices are responsible for knowin g the domain in which to register their services.	As described above, full-featured devices are responsible for knowin g the domain in which to register their services.

	Such devices MAY optionally support configuration of a registration d	Such devices <bcp14>MAY</bcp14> optionally support configuration of a
	omain by the operator of the device. However,	registration domain by the operator of the device. However,
	such devices MUST support registration domain discovery as described	such devices <bcp14>MUST</bcp14> support registration domain discover
	in <xref target="RFC6763" section="11" sectionFormat="of"/>,	y as described in
	"Discovery of Browsing and Registration Domains".	Section <xref target="RFC6763" section="11" sectionFormat="bare"/>
		of the DNS&nbhy;SD specification <xref target="RFC6763"/>.
	</t>	</t>
	<t>	<t>

	Devices made for Constrained-Node Networks register in the special u	Devices made for CNNs register in the
	se domain name <xref target="RFC6761"/>	special-use domain name <xref target="RFC6761"/>
	"default.service.arpa", and let the SRP registrar handle rewriting t	"default.service.arpa." and let the SRP registrar handle
	hat to a different domain if necessary.</t>	rewriting that to a different domain if necessary,
		as mentioned in <xref target="constrained_hosts"/>.</t>
	</section>	</section>


	<section>	<section anchor="how">
	<name>How to publish it</name>	<name>How to Publish It</name>
	<t>
	It is possible to issue a DNS Update that does several things at onc
	e; this means that it's possible to do all the work of
	adding a PTR resource record to the PTR RRset on the Service Name, a
	nd creating or updating the Service Instance Name and
	Host Description, in a single transaction.</t>
	<t>	<t>

	An SRP Update takes advantage of this: it is implemented as a single	It is possible to send a DNS Update message that does several things
	DNS Update message that contains a service's Service	at once:
	Discovery records, Service Description records, and Host Description	For example, it's possible in a single transaction
	records.</t>	to add or update a single Host Description
		while also adding or updating the RRs comprising the Service Descrip
		tion(s)
		for one or more service instance(s) available on that host
		and adding or updating the RRs comprising the Service Discovery inst
		ruction(s)
		for those service instance(s).</t>
	<t>	<t>

	Updates done according to this specification are somewhat different	An SRP Update takes advantage of this: It is implemented as a
	than regular DNS Updates as defined in	single DNS Update message that contains a service's Service
	<xref target="RFC2136"/>. The <xref target="RFC2136"/> update proces	Discovery records, Service Description records, and Host
	s can involve many update attempts: you might first	Description records.</t>
	attempt to add a name if it doesn't exist; if that fails, then in a s	<t>
	econd message you might update the name if it does	Updates done according to this specification are somewhat
	exist but matches certain preconditions. Because the registration pr	different from normal DNS Updates <xref target="RFC2136"/> where
	otocol uses a single transaction, some of this	the update process could involve many update attempts. The
		requester might first attempt to add a name if it doesn't exist;
		if that fails, then in a second message the requester might update
		the name if it does exist but matches certain
		preconditions. Because the Service Registration Protocol described
		in this document uses a single transaction, some of this
	adaptability is lost.</t>	adaptability is lost.</t>
	<t>	<t>
	In order to allow updates to happen in a single transaction, SRP Upd ates do not include update prerequisites. The	In order to allow updates to happen in a single transaction, SRP Upd ates do not include update prerequisites. The

	requirements specified in <xref target="server_behavior"/> are impli	requirements specified in <xref target="server_behavior"/> are impli
	cit in the processing of SRP Updates, and so there is	cit in the processing of SRP Updates; thus, there is
	no need for the SRP requestor to put in any explicit prerequisites.<	no need for the SRP requester to put in any explicit prerequisites.<
	/t>	/t>

	<section>	<section>

	<name>How the DNS&nbhy;SD Service Registration process differs from D NS Update as specified in RFC2136</name>	<name>How the DNS&nbhy;SD Service Registration Process Differs from D NS Update</name>
	<t>	<t>

	DNS&nbhy;SD Service Registration is based on standard RFC2136 DNS	DNS&nbhy;SD Service Registration uses the DNS Update specification
	Update, with some differences:</t>	<xref target="RFC2136"/>
	<ul spacing="compact">	with some additions:</t>
		<ul spacing="normal">
	<li>	<li>

	It implements first-come first-served name allocation, protected using SIG(0) <xref target="RFC2931"/>.</li>	It implements FCFS Naming, protected using SIG(0) <xref target="R FC2931"/>.</li>
	<li>	<li>
	It enforces policy about what updates are allowed.</li>	It enforces policy about what updates are allowed.</li>
	<li>	<li>

	It optionally performs rewriting of "default.service.arpa" to som e other domain.</li>	It optionally performs rewriting of "default.service.arpa." to so me other domain.</li>
	<li>	<li>
	It optionally performs automatic population of the address-to-nam e reverse mapping domains.</li>	It optionally performs automatic population of the address-to-nam e reverse mapping domains.</li>
	<li>	<li>
	An SRP registrar is not required to implement general DNS Update prerequisite processing.</li>	An SRP registrar is not required to implement general DNS Update prerequisite processing.</li>
	<li>	<li>

	Constrained-Node SRP requestors are allowed to send updates to th e generic domain "default.service.arpa."</li>	CNN SRP requesters are allowed to send updates to the generic dom ain "default.service.arpa.".</li>
	</ul>	</ul>
	</section>	</section>
	<section>	<section>
	<name>Retransmission Strategy</name>	<name>Retransmission Strategy</name>

	<t>The DNS protocol, including DNS updates, can operate over UDP or T	<t>The DNS protocol, including DNS updates, can operate over UDP
	CP. When using UDP, reliable	or TCP. For UDP updates from CNN devices, reliable transmission
	transmission must be guaranteed by retransmitting if a DNS UDP mess	must be guaranteed by retransmitting when a DNS UDP message is not
	age is not acknowledged in a	acknowledged in a reasonable interval. Section <xref
	reasonable interval. <xref target="RFC1035" section="4.2.1" section	target="RFC1035" section="4.2.1" sectionFormat="bare"/> of the DNS
	Format="of"/> provides some	specification <xref target="RFC1035"/> provides some guidance on
	guidance on this topic, as does <xref target="RFC1536" section="1"	this topic, as does Section <xref target="RFC1536" section="1"
	sectionFormat="of"/>.	sectionFormat="bare"/> of the IETF document describing common DNS
	<xref target="RFC8085" section="3.1.3" sectionFormat="of"/> also pr	implementation errors <xref target="RFC1536"/>. Section <xref
	ovides useful guidance that	target="RFC8085" section="3.1.3" sectionFormat="bare"/> of the UDP
	is particularly relevant to DNS.</t>	Usage Guidelines document <xref target="RFC8085"/> also provides
		useful guidance that is particularly relevant to DNS.</t>
	</section>	</section>

	<section>	<section>
	<name>Successive Updates</name>	<name>Successive Updates</name>

	<t>Service Registration Protocol does not require that every update c	<t>SRP does not require that every update contain the same informatio
	ontain the same information.	n.
	When an SRP requestor needs to send more than one SRP update to the	When an SRP requester needs to send more than one
	SRP registrar, it MUST send	SRP Update to the SRP registrar, it <bcp14>SHOULD</bcp14> combine
	these sequentially: until an earlier update has been successfully a	these into a single SRP Update,
	cknowledged, the requestor	when possible, subject to DNS message size limits and link-specific
	MUST NOT begin sending a subsequent update.</t>	size limits (e.g., an IEEE 802.15.4 network will perform poorly when a
		sked
		to deliver a packet larger than about 500 bytes).
		If the updates do not fit into a single SRP Update,
		then the SRP requester <bcp14>MUST</bcp14>
		send subsequent SRP Updates sequentially:
		Until an earlier SRP Update has been acknowledged,
		the requester <bcp14>MUST NOT</bcp14>
		send any subsequent SRP Updates.
		If a configuration change occurs while an outstanding
		SRP Update is in flight, the SRP registrar
		<bcp14>MUST</bcp14> defer sending a new SRP Update for
		that change until the previous SRP Update has completed.</t>
	</section>	</section>
	</section>	</section>

	<section anchor="how-to-secure">	<section anchor="how-to-secure">

	<name>How to secure it</name>	<name>How to Secure It</name>
	<t>	<t>

	DNS update as described in <xref target="RFC2136"/> is secured using	DNS Update messages can be secured using secret key transaction sign
	Secret Key Transaction Signatures,	atures (TSIG)
	<xref target="RFC8945"/>, which uses a secret key shared between the	<xref target="RFC8945"/>.
	DNS Update requestor (which issues the update) and	This approach uses a secret key shared between
	the server (which authenticates it). This model does not work for a	the DNS Update requester (which issues the update) and
	utomatic service registration.</t>	the authoritative DNS server (which authenticates it).
		This model does not work for automatic service registration.</t>
	<t>	<t>

	The goal of securing the DNS&nbhy;SD Registration Protocol is to pro	The goal of securing the DNS&nbhy;SD Registration Protocol
	vide the best possible security given the constraint	is to provide the best possible security given the constraint
	that service registration has to be automatic. It is possible to la yer more operational security on top of what we	that service registration has to be automatic. It is possible to la yer more operational security on top of what we

	describe here, but FCFS naming is already an improvement over the se curity of mDNS.</t>	describe here, but FCFS Naming is already an improvement over the se curity of mDNS.</t>

	<section anchor="fcfs">	<section anchor="fcfs">

	<name>First-Come First-Served Naming</name>	<name>FCFS Naming</name>
	<t>	<t>

	First-Come First-Serve naming provides a limited degree of securit	FCFS Naming provides a limited degree of security. A server that r
	y: a server that registers its service using	egisters its service using SRP
	DNS&nbhy;SD Registration protocol is given ownership of a name for	is given ownership of a name for an extended period of time based
	an extended period of time based on a lease	on a lease
	specific to the key used to authenticate the DNS Update, which may	specific to the key used to authenticate the SRP Update, which may
	be longer than the lease associated with the	be longer than the lease associated with the
	registered records. As long as the registration service remembers	registered RRs. As long as the registrar remembers the name
	the name and	and the public key corresponding to the private key used to regist
	the key used to register that name, no other server can add or upd	er RRs on that name,
	ate the information associated with that. If the	no other SRP requester can add or update the
	server fails to renew its service registration before the KEY leas	information associated with that name.
	e (<xref target="I-D.ietf-dnssd-update-lease"	If the SRP requester fails to renew its
	section="4"/>) expires, its name is no longer protected. FCFS nam	service registration before the KEY lease expires
	ing is used to protect both the Service Description	(Section <xref target="RFC9664" section="4" sectionFormat="bare"/>
		of the DNS Update Lease specification <xref target="RFC9664"/>)
		its name is no longer protected.
		FCFS Naming is used to protect both the Service Description
	and the Host Description.</t>	and the Host Description.</t>
	</section>	</section>
	</section>	</section>

	<section>	<section>

	<name>SRP Requestor Behavior</name>	<name>SRP Requester Behavior</name>
	<section>	<section>

	<name>Public/Private key pair generation and storage</name>	<name>Public/Private Key Pair Generation and Storage</name>
	<t>	<t>

	The requestor generates a public/private key pair (See <xref target	The requester generates a public/private key pair (<xref target="rs
	="rsa"/>). This key pair MUST be stored in stable	a"/>).
	storage; if there is no writable stable storage on the SRP requesto	This key pair <bcp14>MUST</bcp14> be stored in stable
	r, the SRP requestor MUST be pre-configured with a	storage; if there is no writable stable storage on the SRP requeste
	public/private key pair in read-only storage that can be used. Thi	r, the SRP requester <bcp14>MUST</bcp14> be preconfigured with a
	s key pair MUST be unique to the device. A device	public/private key pair in read-only storage.
	with rewritable storage SHOULD retain this key indefinitely. When	This key pair <bcp14>MUST</bcp14> be unique to the device.
	the device changes ownership, it may be appropriate	A device
		with rewritable storage <bcp14>SHOULD</bcp14> retain this key indef
		initely. When the device changes ownership, it may be appropriate
	for the former owner to erase the old key pair, which would then re quire the new owner to install a new	for the former owner to erase the old key pair, which would then re quire the new owner to install a new

	one. Therefore, the SRP requestor on the device SHOULD provide a me	one. Therefore, the SRP requester on the device <bcp14>SHOULD</bcp
	chanism to erase the key, for example as the	14> provide a mechanism to erase the key (for example, as the
	result of a "factory reset," and to generate a new key.</t>	result of a "factory reset") and to generate a new key.</t>
		<t>
		Note that when a new key is generated, this will prevent the
		device from registering with the name associated with the old
		key in the same domain where it had previously registered. So,
		implicit in the generation of a new key is the generation of a
		new name; this can be done either proactively when regenerating
		a key or only in the event that the SRP update produces a name conf
		lict.
		</t>
	<t>	<t>
	The policy described here for managing keys assumes that the keys a re only used for SRP. If a key that is used for SRP	The policy described here for managing keys assumes that the keys a re only used for SRP. If a key that is used for SRP

	is also used for other purposes, the policy described here is likel	is also used for other purposes, the policy described here is likel
	y to be insufficient. The policy stated here is NOT	y to be insufficient. The policy stated here is <bcp14>NOT
	RECOMMENDED in such a situation: a policy appropriate to the full s	RECOMMENDED</bcp14> in such a situation: a policy appropriate to th
	et of uses for the key must be chosen. Specifying	e full set of uses for the key must be chosen. Specifying
	such a policy is out of scope for this document.</t>	such a policy is out of scope for this document.</t>
	<t>	<t>

	When sending DNS updates, the requestor includes a KEY record conta	When sending DNS updates, the requester includes a KEY record conta
	ining the public portion of the key in each Host	ining the public portion of the key in each Host
	Description Instruction and each Service Description Instruction.	Description Instruction and each Service Description Instruction.
	Each KEY record MUST contain the same public key.	Each KEY record <bcp14>MUST</bcp14> contain the same public key.
	The update is signed using SIG(0), using the private key that corre sponds to the public key in the KEY record. The	The update is signed using SIG(0), using the private key that corre sponds to the public key in the KEY record. The

	lifetimes of the records in the update is set using the EDNS(0) Upd	lifetimes of the records in the update are
	ate Lease option	set using the EDNS(0) Update Lease option
	<xref target="I-D.ietf-dnssd-update-lease"/>.</t>	<xref target="RFC9664"/>.</t>
	<t>	<t>

	The format of the KEY resource record in the SRP Update is defined	The format of the KEY resource record in the SRP Update is
	in <xref target="RFC3445"/>. Because the KEY RR	defined in the IETF specification for DNSSEC Resource Records
	used in TSIG is not a zone-signing key, the flags field in the KEY	<xref target="RFC4034"/>. Because the KEY RR
	RR MUST be all zeroes.</t>	used in SIG(0) is not a zone-signing key, the flags field in the KE
		Y RR <bcp14>MUST</bcp14> be all zeroes.</t>
	<t>	<t>

	The KEY record in Service Description updates MAY be omitted for br evity; if it is omitted, the SRP registrar MUST behave	The KEY record in Service Description updates <bcp14>MAY</bcp14> be omitted for brevity; if it is omitted, the SRP registrar <bcp14>MUST</bcp14> be have
	as if the same KEY record that is given for the Host Description is also given for each Service Description for which	as if the same KEY record that is given for the Host Description is also given for each Service Description for which
	no KEY record is provided. Omitted KEY records are not used when c omputing the SIG(0) signature.</t>	no KEY record is provided. Omitted KEY records are not used when c omputing the SIG(0) signature.</t>
	</section>	</section>
	<section>	<section>
	<name>Name Conflict Handling</name>	<name>Name Conflict Handling</name>
	<t>	<t>

	Both Host Description RR adds and Service Description RR adds can h	"Add" operations for both Host Description RRs and
	ave names that result in name conflicts.	Service Description RRs can have names that result in name conflict
	Service Discovery record adds cannot have name conflicts. If any Ho	s.
	st Description or Service Description record	Service Discovery record "Add" operations
		cannot have name conflicts.
		If any Host Description or Service Description record
	is found by the SRP registrar to have a conflict with an existing n ame, the registrar will respond to the SRP Update	is found by the SRP registrar to have a conflict with an existing n ame, the registrar will respond to the SRP Update

	with a YXDomain RCODE (<xref target="RFC2136" section="2.2" section	with a YXDomain RCODE <xref target="RFC2136"/>, indicating that the
	Format="of"/>). In this case, the	desired name is already owned by a different SIG(0) key. In this ca
	requestor MUST choose a new name or give up.</t>	se, the
		SRP requester <bcp14>MUST</bcp14> choose a new name or give up.</t>
	<t>	<t>

	There is no specific requirement for how this is done; typically, h	There is no specific requirement for how the SRP
	owever, the requestor will append a number to the	requester should choose a new name. Typically,
	preferred name. This number could be sequentially increasing, or co	however, the requester will append a number to the
	uld be chosen randomly. One existing implementation	preferred name. This number could be sequentially increasing or cou
	attempts several sequential numbers before choosing randomly. So fo	ld be chosen randomly. One existing implementation
	r instance, it might try host.default.service.arpa,	attempts several sequential numbers before choosing randomly.
	then host-1.default.service.arpa, then host-2.default.service.arpa,	For instance, it might try host.default.service.arpa.,
	then host-31773.default.service.arpa.</t>	then host&nbhy;1.default.service.arpa.,
		then host&nbhy;2.default.service.arpa.,
		then host&nbhy;31773.default.service.arpa.</t>
	</section>	</section>

	<section>	<section anchor="lifetimes">
	<name>Record Lifetimes</name>	<name>Record Lifetimes</name>
	<t>	<t>

	The lifetime of the <xref target="RFC6763">DNS&nbhy;SD PTR, SRV, A,	The lifetime of the DNS&nbhy;SD PTR, SRV, A, AAAA, and TXT
	AAAA and TXT records</xref> uses the LEASE field	records <xref target="RFC6763"/> uses the LEASE field
	of the Update Lease option, and is typically set to two hours. Thi	of the Update Lease option and is typically set to two hours. Thus
	s means that if a device is disconnected from the	, if a device is disconnected from the
	network, it does not appear in the user interfaces of devices looki	network, it does not continue to appear for too long in the
	ng for services of that type for too long.</t>	user interfaces of devices looking for instances of that service ty
	<t>	pe.</t>
	The lifetime of the KEY records is set using the KEY-LEASE field of
	the Update Lease Option, and SHOULD be set to a
	much longer time, typically 14 days. The result of this is that ev
	en though a device may be temporarily unplugged,
	disappearing from the network for a few days, it makes a claim on i
	ts name that lasts much longer.</t>
	<t>	<t>

	This means that even if a device is unplugged from the network for	The lifetime of the KEY records is set using the KEY-LEASE field
	a few days, and its services are not available for	of the Update Lease Option and <bcp14>SHOULD</bcp14> be set to a
	that time, no other device can come along and claim its name the mo	much longer time, typically 14 days. The result being that even
	ment it disappears from the network. In the event	though a device may be temporarily disconnected or powered off
	that a device is unplugged from the network and permanently discard	-- disappearing from the network for a few days -- it makes a
	ed, then its name is eventually cleaned up and made	claim on its name that lasts much longer.</t>
	available for re-use.</t>	<t>Therefore, even if a device is disconnected from the network for a
		few days, and its services are not available for that time, no
		other device can come along and claim its name the moment it
		disappears from the network. In the event that a device is
		disconnected from the network and permanently discarded, then its
		name is eventually cleaned up and made available for reuse.</t>
	</section>	</section>
	<section>	<section>

	<name>Compression in SRV records</name>	<name>Compression in SRV Records</name>
	<t>
	Although <xref target="RFC2782"/> requires that the target name in
	the SRV record not be compressed, an SRP requestor
	MAY compress the target in the SRV record. The motivation for <em>n
	ot</em> compressing in <xref target="RFC2782"/>
	is not stated, but is assumed to be because a caching resolver that
	does not understand the format of the SRV record
	might store it as binary data and thus return an invalid pointer in
	response to a query. This does not apply in the
	case of SRP: an SRP registrar needs to understand SRV records in or
	der to validate the SRP Update. Compression of the
	target can save space in the SRP Update, so we want clients to be a
	ble to assume that the registrar will handle
	this. Therefore, SRP registrars MUST support compression of SRV RR
	targets.</t>
	<t>	<t>

	Note that this does not update <xref target="RFC2782"/>: DNS server	Although the original SRV specification <xref target="RFC2782"/>
	s still MUST NOT compress SRV record targets. The	requires that the target hostname in the RDATA of an SRV record
	requirement to accept compressed SRV records in updates only applie	not be compressed in DNS queries and responses, an SRP requester
	s to SRP registrars, and SRP registrars that are	<bcp14>MAY</bcp14> compress the target in the SRV record,
	also DNS servers still MUST NOT compress SRV record targets in DNS	since an SRP Update is neither a DNS query nor a DNS response.
	responses. We note also that	The motivation for <em>not</em> compressing
	<xref target="RFC6762"/> recomments that SRV records be compressed	is not stated in the SRV specification
	in mDNS messages, so <xref target="RFC2782"/> does	but is assumed to be because a recursive resolver
	not apply to mDNS messages.</t>	(caching server) that does not understand the format of the
		SRV record might store it as binary data without decoding a
		compression pointer embedded with the target hostname field
		and thus return nonsensical RDATA in response to a query.
		This concern does not apply in the
		case of SRP. An SRP registrar needs to understand SRV records in or
		der to validate the SRP Update. Compression of the
		target can save space in the SRP Update,
		so we want SRP requesters to be able to
		assume that the registrar will handle
		this. Therefore, SRP registrars <bcp14>MUST</bcp14> support compres
		sion of SRV RR targets.</t>
		<t>
		Note that this document does not update
		the SRV specification <xref target="RFC2782"/>:
		Authoritative DNS servers still <bcp14>MUST NOT</bcp14> compress SR
		V record targets.
		The requirement to accept compressed SRV records in updates only ap
		plies to SRP
		registrars. SRP registrars that are also authoritative DNS servers
		still
		<bcp14>MUST NOT</bcp14> compress SRV record targets in DNS response
		s.
		We note also that Multicast DNS <xref target="RFC6762"/>
		similarly compresses SRV records in mDNS messages.</t>
	<t>	<t>

	In addition, we note that an implementor of an SRP requestor might	In addition, we note that an implementer of an SRP requester
	update existing code that creates SRV records	might update existing code that creates SRV records or
	or compresses DNS messages so that it compresses the target of an S	compresses DNS messages so that it compresses the target of an
	RV record. Care must be taken if such code is	SRV record. Care must be taken if such code is used both in
	used both in requestors and in DNS servers that the code only compr	requesters and in authoritative DNS servers that the code only
	esses in the case where a requestor is generating	compresses SRV targets in the case where a requester is
	an SRP update.</t>	generating an SRP Update.</t>

	</section>	</section>
	<section anchor="remove">	<section anchor="remove">

	<name>Removing published services</name>	<name>Removing Published Services</name>
	<section anchor="zero-lease">	<section anchor="zero-lease">

	<name>Removing all published services</name>	<name>Removing All Published Services</name>
	<t>	<t>

	To remove all the services registered to a particular host, the S	To remove all the services registered to a particular hostname,
	RP requestor transmits an SRP update for that host	the SRP requester transmits an SRP Update for that hostname
	with an Update Lease option that has a LEASE value of zero. If th	with an Update Lease option that has a LEASE value of zero.
	e registration is to be permanently removed,	The SRP Update <bcp14>MUST</bcp14> contain
	KEY-LEASE SHOULD also be zero. Otherwise, it SHOULD be set to the	exactly one Host Description Instruction
	same value it had previously; this holds the name	that contains exactly one "Delete All RRsets From A Name" instruc
	in reserve for when the SRP requestor is once again able to provi	tion for the hostname
	de the service.</t>	and no "Add to an RRSet" instructions for that hostname.
		If the registration is to be permanently removed,
		KEY-LEASE <bcp14>SHOULD</bcp14> also be zero. Otherwise, it <bcp1
		4>SHOULD</bcp14> be set to the same value it had previously; this holds the name
		in reserve for when the SRP requester is once again able to provi
		de the service.</t>
	<t>	<t>

	SRP requestors are normally expected to remove all service instan	This method of removing services is intended for the case
	ces when removing a host. However, in some cases an SRP	where the requester is going offline and does not want
	requestor may not have retained sufficient state to know that som	any of its services to continue being advertised.
	e service instance is pointing to a host that it is
	removing. This method of removing services is intended for the c
	ase where the requestor is going offline and does
	not want its services advertised. Therefore, it is sufficient for
	the requestor to send the
	<xref target="hdi">Host Description Instruction</xref>.
	</t>	</t>

	<t>
	To support this, when removing services based on the lease time b	<t>To support this, when removing a hostname, an SRP registrar
	eing zero, an SRP registrar MUST remove all service	<bcp14>MUST</bcp14> remove all service instances pointing to
	instances pointing to a host when a host is removed, even if the	that hostname and all Service Discovery PTR records pointing to
	SRP requestor doesn't list them explicitly. If the	those service instances, even if the SRP requester doesn't list
	KEY lease time is nonzero, the SRP registrar MUST NOT delete the	them explicitly. If the KEY lease time is nonzero, the SRP
	KEY records for these SRP requestors.	registrar <bcp14>MUST NOT</bcp14> delete the KEY records for
		these service instances.
	</t>	</t>
	</section>	</section>
	<section>	<section>

	<name>Removing some published services</name>	<name>Removing Some Published Services</name>
	<t>
	In some use cases a requestor may need to remove some specific se
	rvice, without removing its other services. This can
	be accomplished in one of two ways. To simply remove a specific s
	ervice, the requestor sends a valid SRP Update where
	the <xref target="servdis">Service Discovery Instruction</xref> c
	ontains a single Delete an RR from an RRset
	(<xref target="RFC2136" section="2.5.4" sectionFormat="comma"/>)
	update that deletes the PTR record whose target is
	the service instance name. The <xref target="servdesc">Service De
	scription Instruction</xref> in this case contains
	a single Delete all RRsets from a Name (<xref target="RFC2136" se
	ction="2.5.3" sectionFormat="comma"/>) update to
	the service instance name.
	</t>
	<t>	<t>

	The second alternative is used when some service is being replace	In some use cases, a requester may need to remove a
	d by a different service with a different service	specific service instance without removing its other services.
	instance name. In this case, the old service is deleted as in the	For example, a device may
	first alternative. The new service is added, just	shut down its remote screen access (_rfb._tcp) service
	as it would be in an update that wasn't deleting the old service.	while retaining its command-line login (_ssh._tcp) service.
	Because both the removal of the old service and	This can be accomplished in one of two ways:</t>
	the add of the new service consist of a valid Service Discovery I
	nstruction and a valid Service Description	<ol type="1" spacing="normal">
	Instruction, the update as a whole is a valid SRP Update, and wil	<li>To simply remove a specific service instance, the requester
	l result in the old service being removed and the	sends
	new one added, or, to put it differently, in the old service bein	a valid SRP Update with a Service Description Instruction
	g replaced by the new service.	(<xref target="servdesc"/>) containing a single "Delete All
	</t>	RRsets From A Name" update to the service instance name.
		The SRP Update <bcp14>SHOULD</bcp14> include Service
		Discovery Instructions (<xref target="servdis"/>) consisting
		of "Delete An RR From An RRset" updates <xref
		target="RFC2136"/> that delete any Service Discovery PTR
		records whose target is the service instance name. However,
		even in the absence of such Service Discovery Instructions,
		the SRP registrar <bcp14>MUST</bcp14> delete any Service
		Discovery PTR records that point to the deleted service
		instance name.
		</li>
		<li>When deleting one service instance while simultaneously
		creating a new service instance with a different service
		instance name, an alternative is to perform both operations
		using a single SRP Update. In this case, the old service is
		deleted as in the first alternative. The new service is
		added, just as it would be in an update that wasn't deleting
		the old service. Because both the removal of the old service
		and the add of the new service consist of a valid Service
		Discovery Instruction and a valid Service Description
		Instruction, the update as a whole is a valid SRP Update and
		will result in the old service being removed and the new one
		added; or, to put it differently, the SRP Update will result
		in the old service being replaced by the new service.
		</li>
		</ol>

	<t>	<t>

	It is perhaps worth noting that if a service is being updated wit	It is perhaps worth noting that if a service is being updated wit
	hout the service instance name changing, that will	hout
	look very much like the second alternative above. The difference	the service instance name changing (for example, when only the ta
	is that because the target for the PTR record in	rget
	the Service Discovery Instruction is the same for both the Delete	port in the SRV record is being updated), then that SRP Update wi
	An RR From An RRset update and the Add To An RRSet	ll
	update, there is no way to tell whether they were intended to be	look very much like the second alternative above.
	one or two Instructions. The same would be true of	The PTR record in the Service Discovery Instruction will be the s
	the Service Description Instruction.	ame for
		both the "Delete An RR From An RRset" update and the "Add To An R
		Rset" update
		<xref target="RFC2136"/>.
		Since the removal of the old service and the addition
		of the new service are both valid SRP Update operations,
		the combined operation is a valid SRP Update operation.
		The SRP registrar does not need to include code to
		recognize this special case and does not need to
		take any special actions to handle it correctly.
	</t>	</t>
	<t>	<t>

	Whichever of these two alternatives is used, the host lease will	Whichever of these two alternatives is used, the hostname lease
	be updated with the lease time provided in the SRP	will be updated with the lease time provided in the SRP update.
	update. In neither of these cases is it permissible to delete the	In neither of these cases is it permissible to delete the hostnam
	host. All services must point to a host. If a host	e.
	is to be deleted, this must be done using the method described in	All services must point to a hostname. If a hostname
	<xref target="zero-lease"/>, which deletes the	is to be deleted, this must be done using the method
	host and all services that have that host as their target.	described in <xref target="zero-lease"/>, which deletes the
		hostname and all services that have that hostname as their target
		.
	</t>	</t>


	</section>	</section>
	</section>	</section>
	</section></section>	</section></section>

	<section anchor="server_behavior">	<section anchor="server_behavior">
	<name>Validation and Processing of SRP Updates</name>	<name>Validation and Processing of SRP Updates</name>
	<section anchor="add_validation">	<section anchor="add_validation">
	<name>Validation of DNS Update Add and Delete RRs</name>	<name>Validation of DNS Update Add and Delete RRs</name>
	<t>	<t>

	The SRP registrar first validates that the DNS Update is a syntactica	The SRP registrar first validates that the DNS Update message is a sy
	lly and semantically valid DNS Update according to	ntactically and semantically valid DNS Update message according to
	the rules specified in <xref target="RFC2136"/>.</t>	the usual DNS Update rules <xref target="RFC2136"/>.</t>
	<t>	<t>

	SRP Updates consist of a set of <em>instructions</em> that together a	SRP Updates consist of a set of <em>instructions</em>
	dd or remove one or more services. Each instruction	that together add or remove one or more services.
	consists of some combination of delete updates and add updates. When	Each <em>instruction</em> consists of
	an instruction contains a delete and an add, the	one or more delete update(s), or one or more add update(s),
	delete MUST precede the add.</t>	or some combination of both delete updates and add updates.</t>
	<t>	<t>
	The SRP registrar checks each instruction in the SRP Update to see th at it is either a Service Discovery Instruction, a	The SRP registrar checks each instruction in the SRP Update to see th at it is either a Service Discovery Instruction, a
	Service Description Instruction, or a Host Description Instruction. Order matters in DNS updates. Specifically,	Service Description Instruction, or a Host Description Instruction. Order matters in DNS updates. Specifically,

	deletes must precede adds for records that the deletes would affect;	deletes must precede adds for records that the deletes would affect;
	otherwise the add will have no effect. This is the	otherwise, the add will have no effect. This is the
	only ordering constraint; aside from this constraint, updates may app	only ordering constraint: Aside from this constraint, updates may app
	ear in whatever order is convenient when	ear in whatever order is convenient when
	constructing the update.</t>	constructing the update.</t>
	<t>	<t>

	Because the SRP Update is a DNS update, it MUST contain a single ques	Because the SRP Update is a DNS update, it <bcp14>MUST</bcp14> contai
	tion that indicates the zone to be updated.	n a single entry in the Zone Section (what would be the Question Section in a DN
	Every delete and update in an SRP Update MUST be within the zone that	S query or response) that indicates the zone to be updated. Every delete and upd
	is specified for the SRP Update.</t>	ate in an SRP Update <bcp14>MUST</bcp14> be within the zone that is specified fo
		r the SRP Update.</t>

	<section anchor="servdis">	<section anchor="servdis">
	<name>Service Discovery Instruction</name>	<name>Service Discovery Instruction</name>

	<t>An instruction is a Service Discovery Instruction if it contains< /t>	<t>An instruction is a Service Discovery Instruction if it:</t>
	<ul spacing="compact">	<ul spacing="compact">

	<li>exactly one "Add to an RRSet" (<xref target="RFC2136" section="	<li>consists of
	2.5.1" sectionFormat="comma"/>) or exactly one	exactly one "Add To An RRSet" or
	"Delete an RR from an RRSet" (<xref target="RFC2136" section="2.5	exactly one "Delete An RR From An RRSet"
	.4" sectionFormat="comma"/>) RR update,</li>	RR update
		(Section <xref target="RFC2136" section="2.5" sectionFormat="bare"/
		>
		of the DNS Update specification <xref target="RFC2136"/>),</li>
	<li>which updates a PTR RR,</li>	<li>which updates a PTR RR,</li>

	<li>the target of which is a Service Instance Name</li>	<li>the target of which is a service instance name</li>
	<li><t>for which name a Service Description Instruction is present in the SRP Update, and:</t>	<li><t>for which name a Service Description Instruction is present in the SRP Update, and:</t>
	<ul spacing="compact">	<ul spacing="compact">

	<li>if the RR Update is an "Add to an RRSet" instruction, that	<li>if the Service Discovery Instruction is an "Add To An RRSet
	Service Description Instruction contains an "Add to	" instruction,
	an RRset" RR update for the SRV RR describing that service an	that Service Description Instruction contains
	d no other "Delete from an RRset" instructions for	a "Delete All RRsets From A Name" instruction for that service
	that Service Instance Name; or</li>	instance name
	<li>if the RR Update is a "Delete an RR from an RRSet" instruct	followed by "Add To An RRset" instructions
	ion, that Service Description Instruction contains	for the SRV and TXT records describing that service; or</li>
	a "Delete from an RRset" RR update and no other "Add to an RR	<li>if the Service Discovery Instruction is a "Delete An RR
	set" instructions for that Service Instance	From An RRSet" instruction, that Service Description
	Name.</li></ul></li>	Instruction contains a "Delete All RRsets From A Name"
	<li>and contains no other add or delete RR updates for the same nam	instruction for that service instance name with no following
	e as the PTR RR Update.</li>	"Add To An RRset" instructions for the SRV and TXT records
		describing that service. An "Add to an RRset" instruction
		for the KEY record here is allowed but not
		implicit.</li></ul></li>
	</ul>	</ul>
	<t>	<t>

	Note that there can be more than one Service Discovery Instruction	Note that there can be more than one Service Discovery
	for the same name if the SRP requestor is	Instruction for the same service name
	advertising more than one service of the same type, or is changing	(the owner name of the Service Discovery PTR record)
	the target of a PTR RR. This is also true for SRP	if the SRP requester is advertising more than one instance
	subtypes (<xref target="RFC6763" section="7.1"/>). For each such PT	of the same service type or is changing the target of a PTR RR.
	R RR add or delete, the above constraints must be	When subtypes are being used
	met.</t>	(Section <xref target="RFC6763" section="7.1" sectionFormat="bare"/
		>
		of the DNS&nbhy;SD specification <xref target="RFC6763"/>),
		each subtype is a separate Service Discovery Instruction.
		For each such PTR RR add or delete, the above constraints must be m
		et.</t>
	</section>	</section>

	<section anchor="servdesc">	<section anchor="servdesc">
	<name>Service Description Instruction</name>	<name>Service Description Instruction</name>


	<t>An instruction is a Service Description Instruction if, for the a	<t>An instruction is a Service Description Instruction if, for the
	ppropriate Service Instance Name, the following are true:</t>	given service instance name, all of the following are true:</t>
	<ul spacing="compact">	<ul spacing="compact">
	<li>	<li>

	It contains exactly one "Delete all RRsets from a name" update fo	It contains exactly one "Delete All RRsets From A Name" update fo
	r the service instance name	r the service instance name
	(<xref target="RFC2136" section="2.5.3" sectionFormat="comma"/>),	(Section <xref target="RFC2136" section="2.5.3" sectionFormat="ba
	</li>	re"/>
	<li>	of the DNS Update specification <xref target="RFC2136"/>).</li>
	It contains zero or one "Add to an RRset" SRV RR,</li>
	<li>
	It contains zero or one "Add to an RRset" KEY RR that, if present
	, contains the public key corresponding to the private key
	that was used to sign the message (if present, the KEY MUST match
	the KEY RR given in the Host Description),</li>
	<li>	<li>

	It contains zero or more "Add to an RRset" TXT RRs,</li>	It contains zero or one "Add To An RRset" KEY RRs that, if presen
		t, contains the public key corresponding to the private key
		that was used to sign the message (if present, the KEY RR <bcp14>
		MUST</bcp14> match the KEY RR given in the Host Description).</li>
	<li>	<li>

	If there is one "Add to an RRset" SRV update, there MUST be at le ast one "Add to an RRset" TXT update.</li>	It contains zero or one "Add To An RRset" SRV RR.</li>
	<li>	<li>

	The target of the SRV RR Add, if present points to a hostname for	If an "Add To An RRSet" update for an SRV RR is present,
	which there is a Host Description Instruction in	there <bcp14>MUST</bcp14> be at least one "Add To An RRset"
		update for the corresponding TXT RR, and
		the target of the SRV RR <bcp14>MUST</bcp14> be the hostname give
		n in the Host Description Instruction in
	the SRP Update, or</li>	the SRP Update, or</li>
	<li>	<li>

	If there is no "Add to an RRset" SRV RR, then either:</li>	If there is no "Add To An RRset" update for an SRV RR, then
	<li><ul>	there <bcp14>MUST</bcp14> be no "Add To An RRset" updates for the
	<li>the name to which the "Delete all RRsets from a name" applies	corresponding TXT RR,
	does not exist, or</li>	and either:</li>
	<li>there is an existing KEY RR on that name, which matches the k	<li><ul spacing="compact">
	ey with which the SRP Update was	<li>the name to which the "Delete All RRsets From A Name" applies
		does not exist, or</li>
		<li>there is an existing KEY RR on that name that matches the key
		with which the SRP Update was
	signed.</li></ul></li>	signed.</li></ul></li>

	<li>
	No other resource records on the Service Instance Name are modifi
	ed.</li>
	</ul>	</ul>

	<t>An SRP registrar MUST correctly handle compressed names in the SRV	<t>Service Description Instructions do not add any other resource rec
	target.</t>	ords.</t>
		<t>An SRP registrar <bcp14>MUST</bcp14> correctly handle compressed n
		ames in the SRV target.</t>
	</section>	</section>

	<section anchor="hdi">	<section anchor="hdi">
	<name>Host Description Instruction</name>	<name>Host Description Instruction</name>


	<t>An instruction is a Host Description Instruction if, for the appr	<t>Every SRP Update always contains exactly one Host Description Ins
	opriate hostname, it contains</t>	truction.</t>
	<ul spacing="compact">
	<li>	<t>An instruction is a Host Description Instruction if, for the appr
	exactly one "Delete all RRsets from a name" RR,</li>	opriate hostname, it contains the following:</t>
		<ul spacing="normal">
	<li>	<li>

	one or more "Add to an RRset" RRs of type A and/or AAAA,</li>	exactly one "Delete All RRsets From A Name" RR</li>
	<li>	<li>

	exactly one "Add to an RRset" RR that adds a KEY RR that contains	exactly one "Add To An RRset" RR that adds a KEY RR that
	the public key corresponding to the private key	contains the public key corresponding to the private key that
	that was used to sign the message,</li>	was used to sign the message</li>
	<li>	<li>

	Host Description Instructions do not modify any other resource re	zero "Add To An RRset" operations (in the case of deleting a regi
	cords.</li>	stration)
	</ul>	or one or more "Add To An RRset" RRs of type A and/or AAAA
		(in the case of creating or updating a registration)</li>
		</ul>
	<t>	<t>

	A and/or AAAA records that are not of sufficient scope to be validl	Host Description Instructions do not add any other resource records
	y published in a DNS zone MAY be ignored by the	.</t>
	SRP registrar, which could result in a host description effectively	<t>
	containing zero reachable addresses even when it	A and/or AAAA records that are not of sufficient scope to be
		validly published in a DNS zone <bcp14>MAY</bcp14> be ignored by
		the SRP registrar, which could result in a Host Description
		effectively containing zero reachable addresses even when it
	contains one or more addresses.</t>	contains one or more addresses.</t>

	<t>	<t>

	For example, if a link-scope address or IPv4 autoconfiguration addr	For example, if an IPv4 link-local address <xref target="RFC3927"/>
	ess is provided by the SRP requestor, the SRP	or an IPv6 link-local address <xref target="RFC4862"/>
	registrar could not publish this in a DNS zone. However, in some si	is provided by the SRP requester, the SRP
	tuations, the registrar might make the records	registrar could elect not to publish this in a DNS zone.
	available through a mechanism such as an advertising proxy only on	However, in some situations, the registrar might make the records
	the specific link from which the SRP update	available through a mechanism such as an advertising proxy only on
	originated; in such a situation, locally-scoped records are still v	the specific link from which the SRP Update
	alid.</t>	originated. In such a situation, locally scoped records are still v
		alid.</t>
	</section>	</section>
	</section>	</section>


	<section>	<section anchor="validation">
	<name>Valid SRP Update Requirements</name>	<name>Valid SRP Update Requirements</name>
	<t>	<t>

	An SRP Update MUST contain exactly one Host Description Instruction.	An SRP Update <bcp14>MUST</bcp14> contain exactly one Host Descriptio
	In addition, there MUST NOT be any Service	n Instruction.
	Description Instruction to which no Service Discovery Instruction poi	Multiple Service Discovery updates and Service Description update
	nts. A DNS Update that contains any additional	s
	adds or deletes that cannot be identified as Service Discovery, Servi	may be combined into a single single SRP Update
	ce Description or Host Description Instructions is	along with a single Host Description update,
		as described in <xref target="how"/>.
		A DNS Update message that contains any additional
		adds or deletes that cannot be identified as Service Discovery, Servi
		ce Description, or Host Description Instructions is
	not an SRP Update. A DNS update that contains any prerequisites is no t an SRP Update.</t>	not an SRP Update. A DNS update that contains any prerequisites is no t an SRP Update.</t>

	<t>An SRP Update MUST include an EDNS(0) Update Lease option	<t>An SRP Update <bcp14>MUST</bcp14> include an EDNS(0) Update Lease op
	<xref target="I-D.ietf-dnssd-update-lease"/>. The LEASE time specifie	tion
	d in the Update Lease option MUST be less than	<xref target="RFC9664"/>.
		The LEASE time specified in the Update Lease
		option <bcp14>MUST</bcp14> be less than
	or equal to the KEY-LEASE time. A DNS update that does not include th e Update Lease option, or that includes a	or equal to the KEY-LEASE time. A DNS update that does not include th e Update Lease option, or that includes a

	KEY-LEASE value that is less than the LEASE value, is not an SRP upda	KEY-LEASE value that is less than the LEASE value, is not an SRP Upda
	te.</t>	te.</t>
	<t>When an SRP registrar receives a DNS Update that is not an SRP updat	<t>When an SRP registrar receives a DNS Update message that is not an S
	e, it MAY	RP
	process the update as regular RFC2136 updates, including access contr	update, it <bcp14>MAY</bcp14> process the update as normal DNS Update
	ol checks and constraint	<xref target="RFC2136"/>, including
	checks, if supported. Otherwise the SRP registrar MUST reject the DNS	access control checks and constraint checks, if supported. Otherwise,
	Update with the Refused RCODE.</t>	the SRP registrar <bcp14>MUST</bcp14> reject the DNS Update with the
		Refused RCODE.</t>
	<t>	<t>

	If the definitions of each of these instructions are followed careful	If the definitions of each of these instructions are followed
	ly and the update requirements are validated	carefully and the update requirements are validated correctly,
	correctly, many DNS Updates that look very much like SRP Updates neve	many DNS Update messages that look very much like SRP Updates
	rtheless will fail to validate. For example, a DNS	nevertheless will fail to validate. For example, a DNS update
	update that contains an Add to an RRset instruction for a Service Nam	that contains an "Add To An RRset" instruction for a Service Name
	e and an Add to an RRset instruction for a Service	and an "Add to an RRset" instruction for a service instance name
	Instance Name, where the PTR record added to the Service Name does no	where the PTR record added to the Service Name does not reference
	t reference the Service Instance Name, is not a	the service instance name is not a valid SRP Update but may be a
	valid SRP Update message, but may be a valid RFC2136 update.</t>	valid DNS Update.</t>
	</section>	</section>
	<section>	<section>

	<name>FCFS Name And Signature Validation</name>	<name>FCFS Name and Signature Validation</name>
	<t>	<t>

	Assuming that a DNS Update message has been validated with these cond	Assuming that the SRP registrar has confirmed that a DNS Update messa
	itions and is a valid SRP Update, the SRP registrar	ge
	checks that the name in the Host Description Instruction exists. If	is a valid SRP Update (<xref target="validation"/>), it
	so, then the registrar checks to see if the KEY	then checks that the name in the Host Description Instruction exists
		in the zone being updated. If so, then the registrar checks to see if the KEY
	record on that name is the same as the KEY record in the Host Descrip tion Instruction. The registrar performs the same	record on that name is the same as the KEY record in the Host Descrip tion Instruction. The registrar performs the same
	check for the KEY records in any Service Description Instructions. F or KEY records that were omitted from Service	check for the KEY records in any Service Description Instructions. F or KEY records that were omitted from Service
	Description Instructions, the KEY from the Host Description Instructi on is used. If any existing KEY record	Description Instructions, the KEY from the Host Description Instructi on is used. If any existing KEY record
	corresponding to a KEY record in the SRP Update does not match the KE Y record in the SRP Update (whether provided	corresponding to a KEY record in the SRP Update does not match the KE Y record in the SRP Update (whether provided

	or taken from the Host Description Instruction), then the SRP registr	or taken from the Host Description Instruction), then the SRP registr
	ar MUST reject the SRP Update with the YXDomain	ar
	RCODE.</t>	<bcp14>MUST</bcp14> reject the SRP Update with a YXDomain
		RCODE indicating that the desired name is already owned by a differen
		t SIG(0) key.
		This informs the SRP requester that it should select a different name
		and try again.</t>
	<t>	<t>

	Otherwise, the SRP registrar validates the SRP Update using SIG(0) ag	If the SRP Update is not in conflict with existing data in the zone b
	ainst the public key in the KEY record of the Host	eing updated, the SRP registrar validates the SRP Update using SIG(0) against th
	Description Instruction. If the validation fails, the registrar MUST	e public key in the KEY record of the Host
	reject the SRP Update with the Refused RCODE.	Description Instruction. If the validation fails,
	Otherwise, the SRP Update is considered valid and authentic, and is p	the SRP Update is malformed, and the registrar
	rocessed according to the method described in	<bcp14>MUST</bcp14> reject the SRP Update with the Refused RCODE.
	RFC2136.</t>	Otherwise, the SRP Update is considered valid and authentic and
		is processed as for a normal DNS Update <xref target="RFC2136"/>.</t>
	<t>	<t>

	KEY record updates omitted from Service Description Instruction are p	KEY record updates omitted from Service Description Instruction(s) ar
	rocessed as if they had been explicitly present:	e processed as if they had been explicitly present.
	every Service Description that is updated MUST, after the SRP Update	After the SRP Update has been applied, every Service Description that
	has been applied, have a KEY RR, and it must be the	is updated <bcp14>MUST</bcp14> have a KEY RR, which <bcp14>MUST</bcp14> have th
	same KEY RR that is present in the Host Description to which the Serv	e
	ice Description refers.</t>	same value as the KEY RR that is present in the Host Description to w
		hich the Service Description refers.</t>
	<t>	<t>

	<xref target="RFC3445"/> states that the flags field in the KEY RR MU	The IETF specification for
	ST be zero except for bit 7, which can	DNSSEC Resource Records <xref target="RFC4034"/>
	be one in the case of a zone key. However, the SRP registrar MUST NOT	states that the flags field in the KEY RR
	validate the flags field.</t>	<bcp14>MUST</bcp14> be zero except for bit 7, which can
		be one in the case of a zone key.
		SRP requesters implementing this version of the SRP specification
		<bcp14>MUST</bcp14> set the flags field in the KEY RR to all zeroes.
		SRP registrars implementing this version of the SRP specification
		<bcp14>MUST</bcp14> accept and store the flags field in the KEY RR
		as received, without checking or modifying its value.</t>
	</section>	</section>
	<section>	<section>
	<name>Handling of Service Subtypes</name>	<name>Handling of Service Subtypes</name>
	<t>	<t>

	SRP registrars MUST treat the update instructions for a service type and all its subtypes as atomic. That is, when a	SRP registrars <bcp14>MUST</bcp14> treat the update instructions for a service type and all its subtypes as atomic. That is, when a
	service and its subtypes are being updated, whatever information appe ars in the SRP Update is the entirety of	service and its subtypes are being updated, whatever information appe ars in the SRP Update is the entirety of
	information about that service and its subtypes. If any subtype appea red in a previous update but does not appear in	information about that service and its subtypes. If any subtype appea red in a previous update but does not appear in

	the current update, then the SRP registrar MUST remove that subtype.	the current update, then the SRP registrar <bcp14>MUST</bcp14> remove that subtype.
	</t>	</t>
	<t>	<t>

	Similarly, there is no mechanism for deleting subtypes. A delete of a	There is intentionally no mechanism for deleting a single subtype
	service deletes all of its subtypes. To delete an	individually. A delete of a service deletes all of its subtypes.
	individual subtype, an SRP Update must be constructed that contains t	To delete a single subtype individually, an SRP Update must
	he service type and all subtypes for that service	be constructed that contains the service type and all subtypes
	except for the one to be deleted.	for that service except for the subtype(s) to be deleted.
	</t>	</t>
	</section>	</section>
	<section>	<section>

	<name>SRP Update response</name>	<name>SRP Update Response</name>
	<t>	<t>

	The status that is returned depends on the result of processing the u	The status that is returned depends on the result of processing the u
	pdate, and can be either NoError, ServFail, Refused	pdate and can be either NoError, ServFail, Refused,
	or YXDomain: all other possible outcomes will already have been accou	or YXDomain. All other possible outcomes will already have been accou
	nted for when applying the constraints that	nted for when applying the constraints that
	qualify the update as an SRP Update. The meanings of these responses	qualify the update as an SRP Update. The meanings of these responses
	are explained in <xref target="RFC2136"	are explained in
	section="2.2"/>.</t>	Section <xref target="RFC2136" section="2.2" sectionFormat="bare"/>
		of the DNS Update specification <xref target="RFC2136"/>.</t>
	<t>	<t>

	In the case of a response other than NoError, <xref target="RFC2136"	In the case of a response other than NoError,
	section="3.8"/> specifies that the server is permitted	Section <xref target="RFC2136" section="3.8" sectionFormat="bare"/>
	to respond either with no RRs or to copy the RRs sent by the client	of the DNS Update specification <xref target="RFC2136"/>
	into the response. The SRP Requestor MUST NOT attempt	states that
		the authoritative DNS server is permitted
		to respond either with no RRs or to copy the RRs
		sent by the DNS Update client into the response.
		The SRP requester <bcp14>MUST NOT</bcp14> attempt
	to validate any RRs that are included in the response. It is possible that a future SRP extension may include per-RR	to validate any RRs that are included in the response. It is possible that a future SRP extension may include per-RR

	indications as to why the update failed, but at present this is not s	indications as to why the update failed, but
	pecified, so if a client were to attempt to validate	at the time of writing this is not specified.
	the RRs in the response, it might reject such a response, since it w	So, if an SRP requester were to attempt to validate
	ould contain RRs, but probably not a set of RRs	the RRs in the response, it might reject such a response, since it w
		ould contain RRs but probably not a set of RRs
	identical to what was sent in the SRP Update.</t>	identical to what was sent in the SRP Update.</t>
	</section>	</section>
	<section>	<section>
	<name>Optional Behavior</name>	<name>Optional Behavior</name>
	<t>	<t>

	The SRP registrar MAY add a Reverse Mapping (<xref target="RFC1035" s	The SRP registrar <bcp14>MAY</bcp14> add a Reverse Mapping PTR record
	ection="3.5"/>, <xref target="RFC3596" section="2.5"/>)	(described for IPv4 in Section
	that corresponds to the Host Description. This is not required becau	<xref target="RFC1035" section="3.5" sectionFormat="bare"/>
	se the Reverse Mapping serves no protocol function,	of the DNS specification <xref target="RFC1035"/>
	but it may be useful for debugging, e.g. in annotating network packet	and for IPv6 in Section
	traces or logs. In order for the registrar to do	<xref target="RFC3596" section="2.5" sectionFormat="bare"/>
	a reverse mapping update, it must be authoritative for the zone that	of the later document updating DNS for IPv6 <xref
	would need to be updated, or have credentials to do	target="RFC3596"/>) that corresponds to the Host Description.
	the update. The SRP requestor MAY also do a reverse mapping update i	This is optional: The reverse mapping PTR record serves no
	f it has credentials to do so.</t>	essential protocol function. One reason to provide reverse
	<t>	mappings is that they can be used to annotate logs and network
	The SRP registrar MAY apply additional criteria when accepting update	packet traces. In order for the registrar to do a reverse mapping
	s. In some networks, it may be possible to do	update, it must be authoritative for the zone that would need to
	out-of-band registration of keys, and only accept updates from pre-re	be updated or have credentials to do the update. The SRP
	gistered keys. In this case, an update for a key	requester <bcp14>MAY</bcp14> also do a reverse mapping update if
	that has not been registered SHOULD be rejected with the Refused RCOD	it has credentials to do so.</t>
	E.</t>
	<t>	<t>

	There are at least two benefits to doing this rather than simply usin	The SRP registrar <bcp14>MAY</bcp14> apply additional criteria when a
	g normal SIG(0) DNS updates. First, the same	ccepting updates. In some networks, it may be possible to do
	registration protocol can be used in both cases, so both use cases ca	out-of-band registration of keys and only accept updates from preregi
	n be addressed by the same SRP requestor	stered keys. In this case, an update for a key
	implementation. Second, the registration protocol includes maintenan	that has not been registered <bcp14>SHOULD</bcp14> be rejected with t
	ce functionality not present with normal DNS	he Refused RCODE.
	updates.</t>	When use of managed keys is desired,
		there are at least two benefits to doing this in conjunction with SRP
		rather than simply performing traditional DNS Updates using SIG(0) ke
		ys:</t>
		<ol><li>The same
		over-the-air registration protocol is used in both cases,
		so both use cases can be addressed by the same SRP requester
		implementation.</li>
		<li>The Service Registration Protocol includes
		maintenance functionality not present with normal DNS
		updates.</li></ol>
	<t>	<t>

	Note that the semantics of using SRP in this way are different than f	Note that the semantics of using SRP in this way
	or typical RFC2136 implementations: the KEY used	are different from the semantics of typical
	to sign the SRP Update only allows the SRP requestor to update record	implementations of DNS Update. The KEY used
	s that refer to its Host Description. RFC2136	to sign the SRP Update only allows the SRP requester to update record
	implementations do not normally provide a way to enforce a constraint	s that refer to its Host Description.
	of this type.</t>	Implementations of traditional DNS Update
		<xref target="RFC2136"/> do not normally provide
		a way to enforce a constraint of this type.</t>
	<t>	<t>
	The SRP registrar could also have a dictionary of names or name patte rns that are not permitted. If such a list is used,	The SRP registrar could also have a dictionary of names or name patte rns that are not permitted. If such a list is used,

	updates for Service Instance Names that match entries in the dictiona ry are rejected with a Refused RCODE.</t>	updates for service instance names that match entries in the dictiona ry are rejected with a Refused RCODE.</t>
	</section>	</section>
	</section>	</section>
	</section>	</section>

	<section>	<section>
	<name>TTL Consistency</name>	<name>TTL Consistency</name>
	<t>	<t>
	All RRs within an RRset are required to have the same TTL	All RRs within an RRset are required to have the same TTL

	(<xref target="RFC2181" section="5.2" sectionFormat="comma"> Clarificatio	(required by
	ns to the DNS Specification</xref>).	Section <xref target="RFC2181" section="5.2" sectionFormat="bare"/>
	In order to avoid inconsistencies, SRP places restrictions on TTLs sent b	of the DNS Clarifications document <xref target="RFC2181"/>).
	y requestors and requires that SRP registrars enforce	In order to avoid inconsistencies, SRP places restrictions on TTLs sent b
		y requesters and requires that SRP registrars enforce
	consistency.</t>	consistency.</t>
	<t>	<t>

	Requestors sending SRP Updates MUST use consistent TTLs in all RRs within	Requesters sending SRP Updates <bcp14>MUST</bcp14> use consistent
	the SRP Update.</t>	TTLs in all RRs within each RRset contained within an SRP Update.</t>
	<t>	<t>

	SRP registrars MUST check that the TTLs for all RRs within the SRP Update	SRP registrars <bcp14>MUST</bcp14> check that the TTLs for all RRs
	are the same. If they are not, the SRP	within each RRset contained within an SRP Update are the same.
	update MUST be rejected with a Refused RCODE.</t>	If they are not, the SRP
		update <bcp14>MUST</bcp14> be rejected with a Refused RCODE.</t>
	<t>	<t>

	Additionally, when adding RRs to an RRset, for example when processing Se rvice Discovery records, the SRP registrar MUST use the	Additionally, when adding RRs to an RRset (for example, when processing S ervice Discovery records), the SRP registrar <bcp14>MUST</bcp14> use the
	same TTL on all RRs in the RRset. How this consistency is enforced is up to the implementation.</t>	same TTL on all RRs in the RRset. How this consistency is enforced is up to the implementation.</t>
	<t>	<t>

	TTLs sent in SRP Updates are advisory: they indicate the SRP requestor's	TTLs sent in SRP Updates are advisory: they indicate the SRP requester's
	guess as to what a good TTL would be. SRP registrars may	guess as to what a good TTL would be. SRP registrars may
	override these TTLs. SRP registrars SHOULD ensure that TTLs are reasonab	override these TTLs. SRP registrars <bcp14>SHOULD</bcp14> ensure that TT
	le: neither too long nor too short. The TTL SHOULD NOT	Ls are reasonable: neither too long nor too short. The TTL <bcp14>SHOULD NOT</b
		cp14>
	ever be longer than the lease time (<xref target="stale"/>). Shorter TTL s will result in more frequent data refreshes;	ever be longer than the lease time (<xref target="stale"/>). Shorter TTL s will result in more frequent data refreshes;

	this increases latency on the DNS-SD client side, increases load on any c	this increases latency on the DNS&nbhy;SD client side, increases
	aching resolvers and on the authoritative server,	load on any caching resolvers and on the authoritative DNS server,
	and also increases network load, which may be an issue for constrained ne	and also increases network load, which may be an issue for CNNs. Longer
	tworks. Longer TTLs will increase the likelihood	TTLs will increase the likelihood
	that data in caches will be stale. TTL minimums and maximums SHOULD be c	that data in caches will be stale. TTL minimums and maximums <bcp14>SHOU
	onfigurable by the operator of the SRP registrar.	LD</bcp14> be configurable by the operator of the SRP registrar.
	</t>	</t>
	</section>	</section>

	<section anchor="maintenance">	<section anchor="maintenance">
	<name>Maintenance</name>	<name>Maintenance</name>
	<section anchor="stale">	<section anchor="stale">

	<name>Cleaning up stale data</name>	<name>Cleaning Up Stale Data</name>
	<t>Because the DNS&nbhy;SD registration protocol is automatic, and not ma	<t>Because the DNS&nbhy;SD Service Registration Protocol
	naged by humans,	is automatic and not managed by humans,
	some additional bookkeeping is required. When an update is constructe	some additional bookkeeping is required. When an update is constructe
	d by the SRP requestor,	d by the SRP requester,
	it MUST include an EDNS(0) Update Lease Option <xref target="I-D.ietf-	it <bcp14>MUST</bcp14> include an EDNS(0) Update Lease Option <xref ta
	dnssd-update-lease"/>.	rget="RFC9664"/>.
	The Update Lease Option contains two lease times: the Lease Time and t he KEY	The Update Lease Option contains two lease times: the Lease Time and t he KEY
	Lease Time.</t>	Lease Time.</t>


	<t>These leases are promises, similar to <xref target="RFC2131">DHCP leas	<t>Similar to DHCP leases <xref target="RFC2131"/>,
	es</xref>,	these leases are promises from the SRP requester that it will
	from the SRP requestor that it will send a new update for the service	send a new update for the service registration before the
	registration before the	lease time expires.
	lease time expires. The Lease time is chosen to represent the time af	The Lease time is chosen to represent the duration after the update
	ter the	during which the registered records other than the KEY record
	update during which the registered records other than the KEY record c	can be assumed to be valid.
	an be assumed	The KEY lease time represents the duration after the update
	to be valid. The KEY lease time represents the time after the update	during which the KEY record can be assumed to be valid.
	during	The reasoning behind the different lease times is discussed in
	which the KEY record can be assumed to be valid.</t>	Sections <xref target="fcfs" format="counter"/> and
		<xref target="lifetimes" format="counter"/>.</t>


	<t>The reasoning behind the different lease times is discussed in the sec	<t>SRP registrars may be configured with limits for these values.
	tion on FCFS naming	At the time of writing, a default limit of two hours for
	(<xref target="fcfs"/>). SRP registrars may be configured with limits	the Lease and 14 days for the SIG(0) KEY are thought to be good choice
	for these values. A default limit of two hours for	s. Devices with limited
	the Lease and 14 days for the SIG(0) KEY are currently thought to be g
	ood choices. Constrained devices with limited
	battery that wake infrequently are likely to request longer leases; re gistrars that support such devices may need to set	battery that wake infrequently are likely to request longer leases; re gistrars that support such devices may need to set

	higher limits. SRP requestors that are going to continue to use names	higher limits. SRP requesters that are going to
	on which they hold leases SHOULD update well before	continue to use names on which they hold leases
	the lease ends, in case the registrar is unavailable or under heavy lo	<bcp14>SHOULD</bcp14> refresh them well before
	ad.</t>	the lease ends in case the registrar is
		temporarily unavailable or under heavy load.</t>

	<t>	<t>

	The lease time applies specifically to the host. All service instances,	The lease time applies specifically to the hostname.
	and all service entries for such service	All service instances, and all service entries for such service
	instances, depend on the host. When the lease on a host expires, the ho	instances, depend on the hostname. When the lease on a
	st and all services that reference it MUST be	hostname expires, the hostname and all services that
	removed at the same time—it is never valid for a service instance	reference it <bcp14>MUST</bcp14> be removed at the same
	to remain when the host it references has been	time: It is never valid for a service instance to remain
	removed. If the KEY record for the host is to remain, the KEY record fo	when the hostname it references has been removed.
	r any services that reference it MUST also	If the KEY record for the hostname is to remain, the KEY record
	remain. However, the service PTR record MUST be removed, since it has n	for any services that reference it <bcp14>MUST</bcp14> also
	o key associated with it, and since it is never	remain. However, the Service Discovery PTR record <bcp14>MUST</bcp14>
	valid to have a service PTR record for which there is no service instan	be removed since it has no key associated with it and since it
	ce on the target of the PTR record.	is never valid to have a Service Discovery PTR record for which
		there is no service instance on the target of the PTR record.
	</t>	</t>

	<t>	<t>

	SRP registrars MUST also track a lease time per service instance. The r	SRP registrars <bcp14>MUST</bcp14> also track a lease time per service
	eason for doing this is that a requestor may	instance. The reason being that a requester may
	re-register a host with a different set of services, and not remember t	re-register a hostname with a different set of services and
	hat some different service instance had previously	not remember that some different service instance had previously
	been registered. In this case, when that service instance lease expires	been registered. In this case, when that service instance lease expires
	, the SRP registrar MUST remove the service	, the SRP registrar <bcp14>MUST</bcp14> remove the service
	instance (although the KEY record for the service instance SHOULD be re	instance,
	tained until the KEY lease on that service	and any associated Service Discovery PTR records pointing to that servi
	expires). This is beneficial because otherwise if the SRP requestor con	ce instance,
	tinues to renew the host, but never mentions the	(although the KEY record for the service instance
	stale service again, the stale service will continue to be advertised.	<bcp14>SHOULD</bcp14> be retained until the
		KEY lease on that service
		expires).
		This is beneficial because it avoids stale services continuing
		to be advertised after the SRP requester has forgotten about them.
	</t>	</t>


	<t>The SRP registrar MUST include an EDNS(0) Update Lease option in the	<t>The SRP registrar <bcp14>MUST</bcp14> include an EDNS(0) Update
	response if the lease time proposed by the requestor has been shortene	Lease option in the response. The requester <bcp14>MUST</bcp14> check
	d or lengthened by the registrar. The requestor	for the EDNS(0) Update Lease option in the response, and when deciding
	MUST check for the EDNS(0) Update Lease option in the response and MUS	when to renew its registration the requester <bcp14>MUST</bcp14> use
	T use the lease	the lease times from the Update Lease option in the response in place
	times from that option in place of the options that it sent to the reg	of the lease times that it originally requested from the registrar.
	istrar when	The times may be shorter or longer than those specified in the SRP
	deciding when to renew its registration. The times may be shorter or	Update. The SRP requester must honor them in either case.</t>
	longer than
	those specified in the SRP Update; the SRP requestor must honor them i
	n either case.</t>


	<t>SRP requestors SHOULD assume that each lease ends N seconds after the	<t>SRP requesters <bcp14>SHOULD</bcp14> assume that each lease ends N
	update was first	seconds after the update was first transmitted (where N is the granted le
	transmitted, where N is the lease duration. SRP Registrars SHOULD ass	ase
	ume that each lease	duration). SRP registrars <bcp14>SHOULD</bcp14> assume that each lease
	ends N seconds after the update that was successfully processed was re	ends N seconds after the update that was successfully processed was
	ceived. Because	received. Because the registrar will always receive the update after
	the registrar will always receive the update after the SRP requestor s	the SRP requester sent it, this avoids the possibility of
	ent it, this avoids the	a race condition where the SRP registrar prematurely removes
	possibility of misunderstandings.</t>	a service when the SRP requester thinks the lease has not yet expired.
		In addition, the SRP requester <bcp14>MUST</bcp14> begin attempting to re
		new
		its lease in advance of the expected expiration time, as required
		by the DNS Update Lease specification <xref target="RFC9664"/>,
		to accommodate the situation where the clocks on the SRP requester
		and the SRP registrar do not run at precisely the same rate.</t>


	<t>SRP registrars MUST reject updates that do not include an	<t>SRP registrars <bcp14>MUST</bcp14> reject updates that do not
	EDNS(0) Update Lease option. DNS authoritative servers that allow bot	include an EDNS(0) Update Lease option. DNS authoritative servers
	h SRP and non-SRP DNS updates MAY accept updates that don't include	that allow both SRP and non-SRP DNS updates <bcp14>MAY</bcp14> accept
	leases, but SHOULD differentiate between SRP Updates and	updates that don't include leases, but they <bcp14>SHOULD</bcp14>
	other updates, and MUST reject updates that would otherwise be SRP Upd	differentiate between SRP Updates and other updates and
	ates	<bcp14>MUST</bcp14> reject updates that would otherwise be SRP Updates
	if they do not include leases.</t>	if they do not include leases.</t>


	<t>Lease times have a completely different function than TTLs. On an aut	<t>The function of Lease times and the
	horitative	function of TTLs are completely different. On an
	DNS server, the TTL on a resource record is a constant: whenever that	authoritative DNS server, the TTL on a resource record is a
	RR is served in	constant. Whenever that RR is served in a DNS response, the TTL value
	a DNS response, the TTL value sent in the answer is the same. The lea	sent in the answer is the same. The lease time is never sent as a
	se time is never	TTL; its sole purpose is to determine when the authoritative DNS
	sent as a TTL; its sole purpose is to determine when the authoritative	server will delete stale records. It is not an error to send a DNS
	DNS server will	response with a TTL of M when the remaining time on the lease is
	delete stale records. It is not an error to send a DNS response with	less than M.</t>
	a TTL of 'n' when
	the remaining time on the lease is less than 'n'.</t>
	</section>	</section>
	</section>	</section>

	<section>	<section>
	<name>Security Considerations</name>	<name>Security Considerations</name>
	<section anchor="source_validation">	<section anchor="source_validation">
	<name>Source Validation</name>	<name>Source Validation</name>
	<t>SRP Updates have no authorization semantics other than	<t>SRP Updates have no authorization semantics other than

	FCFS. This means that if an attacker from outside of the administrati	"First Come, First Served" (FCFS).
	ve	Thus, if an attacker from outside the administrative
	domain of the SRP registrar knows the registrar's IP address, it can in	domain of the SRP registrar knows the registrar's IP address, it can, i
	principle send updates to the registrar	n principle, send updates to the registrar
	that will be processed successfully. SRP Registrars SHOULD therefore	that will be processed successfully. Therefore, SRP registrars <bcp14
	be configured to reject updates	>SHOULD</bcp14> be configured to reject updates
	from source addresses outside of the administrative domain of the regis trar.</t>	from source addresses outside of the administrative domain of the regis trar.</t>


	<t>For TCP updates, the initial SYN-SYN+ACK handshake prevents updates be	<t>For TCP updates, the initial SYN-SYN+ACK handshake prevents
	ing forged by an off-network attacker. In order to	updates being forged by an off-path attacker. In order to
	ensure that this handshake happens, SRP registrars relying on three-way	ensure that this handshake happens, SRP registrars relying on three-way
	-handshake validation MUST NOT accept TCP Fast Open	-handshake validation <bcp14>MUST NOT</bcp14> accept TCP Fast Open payloads
	<xref target="RFC7413"/> payloads. If the network infrastructure allow	<xref target="RFC7413"/>.
	s it, an SRP registrar MAY accept TCP Fast Open payloads if all such packets	If the network infrastructure allows it, an SRP registrar
		<bcp14>MAY</bcp14> accept TCP Fast Open payloads if all such packets
	are validated along the path, and the network is able to reject this ty pe of spoofing at all ingress points.</t>	are validated along the path, and the network is able to reject this ty pe of spoofing at all ingress points.</t>


	<t>For UDP updates from constrained devices, spoofing would have to be pr	<t>For UDP updates from CNN devices, spoofing would have to be prevented
	evented with appropriate source address filtration	with appropriate source address filtering
	on routers <xref target="RFC2827"/>. This would ordinarily be accomplis	on routers <xref target="RFC2827"/>.
	hed by measures such as are described in	This would ordinarily be accomplished by measures such as those describ
	<xref target="RFC7084" section="4.5" sectionFormat="of"/>. For example,	ed in
	a stub router <xref target="I-D.ietf-snac-simple"/>	Section <xref target="RFC7084" section="4.5" sectionFormat="bare"/>
	for a constrained network might only accept UDP updates from source add	of the IPv6 CE Router Requirements document <xref target="RFC7084"/>.
	resses known to be on-link on that stub network, and might	For example, a stub router <xref target="I-D.ietf-snac-simple"/>
		for a CNN might only accept UDP updates from source addresses known to
		be on-link on that stub network and might
	further validate that the UDP update was actually received on the stub network interface and not the interface connected to	further validate that the UDP update was actually received on the stub network interface and not the interface connected to
	the adjacent infrastructure link.</t>	the adjacent infrastructure link.</t>
	</section>	</section>
	<section>	<section>

	<name>Other DNS updates</name>	<name>Other DNS Updates</name>
	<t>Note that these rules only apply to the validation of SRP Updates.	<t>Note that these rules only apply to the validation of SRP Updates.

	A server that accepts updates from SRP	An authoritative DNS server that accepts updates from SRP
	requestors may also accept other DNS updates, and those DNS updates may	requesters may also accept other DNS Update messages, and those DNS Upd
	be validated	ate messages may be validated
	using different rules. However, in the case of a DNS server that acce	using different rules.
	pts SRP	However, in the case of an authoritative DNS server that accepts SRP
	updates, the intersection of the SRP Update rules and	updates, the intersection of the SRP Update rules and
	whatever other update rules are present must be considered very careful ly.</t>	whatever other update rules are present must be considered very careful ly.</t>


	<t>For example, a normal, authenticated DNS update to any RR that was add	<t>For example, a normal authenticated DNS update to any
	ed using SRP, but that is authenticated using a	RR that was added using SRP, but is authenticated using a
	different key, could be used to override a promise made by the SRP regi	different key, could be used to override a promise made by the SRP regi
	strar to an SRP requestor, by replacing all or part of	strar to an SRP requester by replacing all or part of
	the service registration information with information provided by an au	the service registration information with information provided by an au
	thenticated DNS update requestor. An implementation	thenticated DNS update requester. An implementation
	that allows both kinds of updates SHOULD NOT allow DNS Update requestor	that allows both kinds of updates <bcp14>SHOULD NOT</bcp14> allow DNS U
	s that are using different authentication and	pdate requesters that are using different authentication and
	authorization credentials to update records added by SRP requestors.</t	authorization credentials to update records added by SRP requesters.</t
	>	>
	</section>	</section>
	<section>	<section>

	<name>Risks of allowing arbitrary names to be registered in SRP updates</	<name>Risks of Allowing Arbitrary Names to be Registered in SRP Updates</
	name>	name>
	<t>It is possible to set up SRP updates for a zone that is used for non-D	<t>It is possible to set up SRP Updates for a zone
	NSSD services. For example, imagine that you set	that is also used for non-DNS&nbhy;SD records.
	up SRP service for example.com. SRP hosts can now register names like "	For example, imagine that you set
	www" or "mail" or "smtp" in this domain. In addition,	up SRP service for "example.com".
	SRP updates using FCFS naming can insert names that are obscene or offe	SRP requesters can now register names like "www"
	nsive into the zone. There is no simple solution to	or "mail" or "smtp" in this domain. In addition,
	these problems. We have two recommendations to address this problem, ho	SRP Updates using FCFS Naming can insert names that are obscene or offe
	wever:</t>	nsive into the zone. There is no simple solution to
	<ul spacing="compact">	these problems. However, we have two recommendations to address this pr
	<li>Do not provide SRP service in organization-level zones. Use subdoma	oblem:</t>
	ins of the organizational domain for DNS service	<ul spacing="normal">
	discovery. This does not prevent registering names as mentioned abov	<li>Do not provide SRP service in organization-level zones.
	e, but does ensure that genuinely important names	Use subdomains of the organizational domain for DNS&nbhy;SD.
	are not accidentally reserved for SRP clients. So for example, the zo	This does not prevent registering names as mentioned above
	ne "dnssd.example.com" could be used instead of	but does ensure that genuinely important names
	"example.com" for SRP updates. Because of the way that DNS browsing d	are not accidentally claimed by SRP requesters.
	omains are discovered, there is no need for the	So, for example, the zone "dnssd.example.com." could be used
	DNSSD discovery zone that is updated by SRP to have a user-friendly o	instead of "example.com." for SRP Updates. Because of the way that
	r important-sounding name.</li>	DNS-browsing domains are discovered, there is no need for the
		DNS&nbhy;SD discovery zone that is updated by SRP to
		have a user-friendly or important-sounding name.</li>

	<li>Configure a dictionary of names that are prohibited. Dictionaries o f common obscene and offensive names are no doubt	<li>Configure a dictionary of names that are prohibited. Dictionaries o f common obscene and offensive names are no doubt

	available, and can be augmented with a list of typical "special" name	available and can be augmented with a list of typical "special" names
	s like "www", "mail", "smtp" and so on. Lists of	like "www", "mail", "smtp", and so on. Lists of
	names are generally available, or can be constructed manually.</li>	names are generally available or can be constructed manually.
		Names rejected due to this should return a Refused
		RCODE, indicating to the SRP requester that it
		should not append or increment a number at the
		end of the name and then try again, since this
		would likely result in an infinite loop.
		If a name is considered unacceptable because it is
		obscene or offensive, adding a number on the end is
		unlikely to make the name acceptable.</li>
	</ul>	</ul>
	</section>	</section>
	<section>	<section>

	<name>Security of local service discovery</name>	<name>Security of Local Service Discovery</name>
	<t>Local links can be protected by managed services such as RA Guard <xre	<t>Local links can be protected by managed services such as RA Guard
	f target="RFC6105"/>, but multicast services like	<xref target="RFC6105"/>, but multicast services like DHCP <xref
	DHCP <xref target="RFC2131"/>, DHCPv6 <xref target="RFC8415"/> and IPv6	target="RFC2131"/>, DHCPv6 <xref target="RFC8415"/>, and IPv6 Neighbor
	Neighbor Discovery <xref target="RFC4861"/> are	Discovery <xref target="RFC4861"/> are, in most cases, not
	in most cases not authenticated and can't be controlled on unmanaged ne	authenticated and can't be controlled on unmanaged networks, such as
	tworks, such as home networks and small-office	home networks and small office networks where no network management
	networks where no network management staff are present. In such situati	staff are present. In such situations, the SRP service has
	ons, the SRP service has comparatively fewer	comparatively fewer potential security exposures and, hence, is not
	potential security exposures and hence is not the weak link. This is di	the weak link. This is discussed in more detail in <xref
	scussed in more detail in	target="how-to-secure"/>.</t>
	<xref target="how-to-secure"/>.</t>	<t>The fundamental protection for networks of this type is the user's
	<t>The fundamental protection for networks of this type is the user's cho	choice of what devices to add to the network. Work is being done in
	ice of what devices to add to the network. Work is	other working groups and standards bodies to improve the state of the
	being done in other working groups and standards bodies to improve the	art for network on-boarding and device isolation (e.g., Manufacturer
	state of the art for network on-boarding and device	Usage Descriptions <xref target="RFC8520"/> provide a means for
	isolation (e.g., <xref target="RFC8520"/> provides a means for constrai	constraining what behaviors are allowed for a device in an automatic
	ning what behaviors are allowed for a device in an	way), but such work is out of scope for this document.</t>
	automatic way), but such work is out of scope for this document.</t>
	</section>	</section>
	<section>	<section>
	<name>SRP Registrar Authentication</name>	<name>SRP Registrar Authentication</name>

	<t>This specification does not provide a mechanism for validating respons	<t>This specification does not provide a mechanism for validating respons
	es from SRP Registrars to	es from SRP registrars to
	SRP requestors. In principle, a KEY RR could be used by	SRP requesters. In principle, a KEY RR could be used by
	a non-constrained SRP requestor to validate responses from the registra	a non-CNN SRP requester to validate responses from the registrar, but t
	r, but this is not required,	his is not required,
	nor do we specify a mechanism for determining which key to use.</t>	nor do we specify a mechanism for determining which key to use.</t>
	<t>In addition, for DNS-over-TLS connections, out-of-band key pinning as described in	<t>In addition, for DNS-over-TLS connections, out-of-band key pinning as described in

	<xref target="RFC7858" section="4.2" sectionFormat="comma"/> could be u	Section <xref target="RFC7858" section="4.2" sectionFormat="bare"/>
	sed for authentication of the SRP registrar,	of the DNS-over-TLS specification <xref target="RFC7858"/>
	e.g. to prevent man-in-the-middle attacks. However the use of such keys	could be used for authentication of the SRP registrar,
	is impractical for an unmanaged service	e.g., to prevent man-in-the-middle attacks. However, the use of such ke
	registration protocol, and hence is out of scope for this document.</t>	ys is impractical for an unmanaged service
		registration protocol; hence, it is out of scope for this document.</t>
	</section>	</section>
	<section anchor="rsa">	<section anchor="rsa">
	<name>Required Signature Algorithm</name>	<name>Required Signature Algorithm</name>
	<t>	<t>

	For validation, SRP registrars MUST implement the ECDSAP256SHA256 signa	For validation, SRP registrars <bcp14>MUST</bcp14> implement the ECDSAP
	ture algorithm. SRP registrars SHOULD implement the	256SHA256 signature algorithm. SRP registrars <bcp14>SHOULD</bcp14> implement t
	algorithms specified in <xref target="RFC8624" section="3.1" sectionFor	he
	mat="comma"/>, in the validation column of the	algorithms that are listed in
	table, that are numbered 13 or higher and have a "MUST", "RECOMMENDED",	Section <xref target="RFC8624" section="3.1" sectionFormat="bare"/>
	or "MAY" designation in the validation column of	of the DNSSEC Cryptographic Algorithms specification <xref target="RFC8
		624"/>,
		in the validation column of the
		table, that are numbered 13 or higher and that have a "<bcp14>MUST</bcp
		14>", "<bcp14>RECOMMENDED</bcp14>", or "<bcp14>MAY</bcp14>" designation in the v
		alidation column of
	the table.	the table.

	SRP requestors MUST NOT assume that any algorithm numbered lower than 1 3 is	SRP requesters <bcp14>MUST NOT</bcp14> assume that any algorithm number ed lower than 13 is
	available for use in validating SIG(0) signatures.</t>	available for use in validating SIG(0) signatures.</t>
	</section>	</section>
	</section>	</section>
	<section>	<section>
	<name>Privacy Considerations</name>	<name>Privacy Considerations</name>
	<t>	<t>

	Because DNS-SD SRP Updates can be sent off-link, the privacy implications	Because DNS&nbhy;SD SRP Updates can be sent off-link,
	of SRP are different than for multicast DNS	the privacy implications of SRP are
	responses. Host implementations that are using TCP SHOULD also use TLS i	different from those for mDNS responses.
	f available. SRP Registrar implementations MUST offer	SRP Requester implementations that are using TCP <bcp14>SHOULD</bcp14>
	TLS support. The use of TLS with DNS is described in <xref target="RFC78	also use DNS-over-TLS <xref target="RFC7858"/> if available.
	58"/>. Because there is no mechanism for sharing	SRP registrar implementations <bcp14>MUST</bcp14> offer TLS support.
	keys, validation of DNS-over-TLS keys is not possible; DNS-over-TLS is us	Because there is no mechanism for sharing keys,
	ed only as described in	validation of DNS-over-TLS keys is not possible;
	<xref target="RFC7858" section="4.1" sectionFormat="comma"/>	DNS-over-TLS is used only for Opportunistic Privacy, as documented in
		Section <xref target="RFC7858" section="4.1" sectionFormat="bare"/>
		of the DNS-over-TLS specification <xref target="RFC7858"/>.
	</t>	</t>
	<t>	<t>

	Hosts that implement TLS support SHOULD NOT fall back to TCP; since SRP r	SRP requesters that are able to use TLS <bcp14>SHOULD NOT</bcp14>
	egistrars are required to support	fall back to TCP. Since all SRP registrars are required to support TLS,
	TLS, it is entirely up to the host implementation whether to use it.	whether to use TLS is entirely the decision of the SRP requester.
	</t>	</t>
	<t>	<t>

	Public keys can be used as identifiers to track hosts. SRP registrars MAY elect not to return KEY records for queries for	Public keys can be used as identifiers to track hosts. SRP registrars <bc p14>MAY</bcp14> elect not to return KEY records for queries for
	SRP registrations. To avoid DNSSEC validation failures, an SRP registrar that signs the zone for DNSSEC but refuses to return	SRP registrations. To avoid DNSSEC validation failures, an SRP registrar that signs the zone for DNSSEC but refuses to return

	a KEY record MUST NOT store the KEY record in the zone itself. Because th	a KEY record <bcp14>MUST NOT</bcp14> store the KEY record in the zone its
	e KEY record isn't in the zone, the nonexistance of	elf. Because the KEY record isn't in the zone, the nonexistence of
	the KEY record can be validated. If the zone is not signed, the server MA	the KEY record can be validated.
	Y instead return a negative non-error response	If the zone is not signed, the authoritative DNS server <bcp14>MAY</bcp14
	(either NXDOMAIN or no data).	>
		instead return a negative response (either NXDOMAIN or no data).
	</t>	</t>
	</section>	</section>

	<section>	<section>
	<name>Domain Name Reservation Considerations</name>	<name>Domain Name Reservation Considerations</name>
	<t>This section specifies considerations for systems involved in domain na me resolution when resolving queries for names	<t>This section specifies considerations for systems involved in domain na me resolution when resolving queries for names

	ending with '.service.arpa.'. Each item in this section addresses some a	ending with ".service.arpa.". Each item in this section addresses some a
	spect of the DNS or the process of resolving domain	spect of the DNS or the process of resolving domain
	names that would be affected by this special-use allocation. Detailed ex	names that would be affected by this special-use allocation.
	planations of these items can be found in Section 5	Detailed explanations of these items can be found in
	of <xref target="RFC6761"/>.</t>	Section <xref target="RFC6761" section="5" sectionFormat="bare"/>
		of the Special-Use Domain Names specification <xref target="RFC6761"/>.
		</t>
	<section>	<section>
	<name>Users</name>	<name>Users</name>

	<t>The current proposed use for 'service.arpa' does not require special k	<t>The current proposed use for "service.arpa." does not
	nowledge on the part of the user. While the	require special knowledge on the part of the user. While the
	'default.service.arpa.' subdomain is used as a generic name for registr	"default.service.arpa." subdomain is used as a generic name for registr
	ation, users are not expected to see this name in	ation, users are not expected to see this name in
	user interfaces. In the event that it does show up in a user interface,	user interfaces. In the event that it does show up in a user interface,
	it is just a domain name, and requires no special	it is just a domain name and requires no special
	treatment by the user. Users are not expected to see this name in user	treatment by the user.</t>
	interfaces, although it's certainly possible that
	they might. If they do, they are not expected to treat it specially.</t
	>
	</section>	</section>
	<section>	<section>
	<name>Application Software</name>	<name>Application Software</name>
	<t>	<t>

	Application software does not need to handle subdomains of 'service.arp	Application software does not need to handle
	a' specially. 'service.arpa' SHOULD NOT be treated	subdomains of "service.arpa." specially.
	as more trustworthy than any other insecure DNS domain, simply because	"service.arpa." <bcp14>SHOULD NOT</bcp14> be treated
	it is locally-served (or for any other reason). It	as more trustworthy than any other insecure DNS domain, simply because
	is not possible to register a PKI certificate for a subdomain of 'servi	it is locally served (or for any other reason). It
	ce.arpa.' because it is a locally-served domain	is not possible to register a PKI certificate for a subdomain of "servi
	name. So no such subdomain can be considered as uniquely identifying a	ce.arpa." because it is a locally served domain
	particular host, as would be required for such a	name. So, no such subdomain can be considered to be uniquely identifyin
	PKI cert to be issued. If a subdomain of 'service.arpa.' is returned by	g a particular host, as would be required for such a
	an API or entered in an input field of an	PKI certificate to be issued. If a subdomain of "service.arpa." is retu
		rned by an API or entered in an input field of an
	application, PKI authentication of the endpoint being identified by the name will not be possible. Alternative methods	application, PKI authentication of the endpoint being identified by the name will not be possible. Alternative methods
	and practices for authenticating such endpoints are out of scope for th is document.</t>	and practices for authenticating such endpoints are out of scope for th is document.</t>
	</section>	</section>
	<section>	<section>
	<name>Name Resolution APIs and Libraries</name>	<name>Name Resolution APIs and Libraries</name>

	<t>Name resolution APIs and libraries MUST NOT recognize names that end i	<t>Name resolution APIs and libraries <bcp14>MUST NOT</bcp14> recognize n
	n '.service.arpa.' as special and MUST NOT treat	ames that end in "service.arpa." as special and <bcp14>MUST NOT</bcp14> treat
	them as having special significance, except that it may be necessary th	them as having special significance, except that it may be
	at such APIs not bypass the locally configured	necessary that such APIs not bypass the locally discovered
	recursive resolvers.</t>	recursive resolvers.</t>

	<t>One or more IP addresses for recursive DNS servers will usually be sup	<t>One or more IP addresses for recursive resolvers will usually
	plied to the client through router advertisements	be supplied to the SRP requester through router advertisements
	or DHCP. For an administrative domain that uses subdomains of 'service	or DHCP. For an administrative domain that uses subdomains of "service
	.arpa.', the recursive resolvers provided by that	.arpa.", the recursive resolvers provided by that
	domain will be able to answer queries for subdomains of 'service.arpa.'	domain will be able to answer queries for subdomains of "service.arpa."
	; other (non-local) resolvers will not, or they	. Other (non-local) resolvers will not, or they
	will provide answers that are not correct within that administrative do main.</t>	will provide answers that are not correct within that administrative do main.</t>

	<t>A host that is configured to use a resolver other than one that has be	<t>A host that is configured to use a resolver other than one that has be
	en provided by the local network may be unable to	en provided by the local network may not be able to
	resolve, or may receive incorrect results for, subdomains of 'service.a	resolve or may receive incorrect results for subdomains of
	rpa.'. In order to avoid this, it is permissible	"service.arpa.". In order to avoid this, hosts <bcp14>SHOULD</bcp14> u
	that hosts use the resolvers that are locally provided for resolving 's	se the
	ervice.arpa.', even when they are configured to	resolvers that are locally provided for resolving "service.arpa." names
	use other resolvers.</t>	,
		even when they are configured to use other resolvers for other names.</
		t>
	</section>	</section>
	<section>	<section>

	<name>Caching DNS Servers</name>	<name>Recursive Resolvers</name>
	<t>There are three considerations for caching DNS servers that	<t>There are two considerations for recursive resolvers
	follow this specification:</t>	(also known as "caching DNS servers" or "recursive DNS servers") that
	<ol>	follow this specification:</t>
	<li>For correctness, recursive resolvers at sites using 'service.arpa.'	<ol spacing="normal">
	must in practice transparently support DNSSEC	<li>For correctness, recursive resolvers at sites using
	queries: queries for DNSSEC records and queries with the DNSSEC OK (	'service.arpa.' must, in practice, transparently support DNSSEC
	DO) bit set (<xref target="RFC4035" section="3.2.1"	queries: queries for DNSSEC records and queries with the DNSSEC OK
	sectionFormat="of"/>). DNSSEC validation is a Best Current Practice	(DO) bit set
	<xref target="RFC9364"/>: although validation is	(Section <xref target="RFC4035" section="3.2.1" sectionFormat="bare"/>
	not required, a caching recursive resolver that does not validate an	of the DNSSEC specification <xref target="RFC4035"/>).
	swers that can be validated may cache invalid data.
	This, in turn, would prevent validating stub resolvers from successf	DNSSEC validation <xref target="RFC9364"/>
	ully validating answers. Hence, as a practical	is a best current practice: Although validation is not required, a
	matter, recursive resolvers at sites using 'service.arpa' should do	caching recursive resolver that does not validate answers that can
	DNSSEC validation.</li>	be validated may cache invalid data. In turn, this would prevent
		validating stub resolvers from successfully validating
		answers. Hence, as a practical matter, recursive resolvers at sites
		using "service.arpa." should do DNSSEC validation.</li>
	<li>	<li>

	<t>Unless configured otherwise, recursive resolvers and DNS proxies M	<t>Unless configured otherwise, recursive resolvers and DNS
	UST behave as described in Locally Served Zones,	proxies <bcp14>MUST</bcp14> behave following
	<xref target="RFC6303" section="3" sectionFormat="of"/>. That is,	the rules prescribed for Iterative Resolvers in
	queries for 'service.arpa.' and subdomains of	Section <xref target="RFC6303" section="3" sectionFormat="bare"/>
	'service.arpa.' MUST NOT be forwarded, with one important exceptio	of the IETF Locally Served DNS Zones document <xref target="RFC6303"/
	n: a query for a DS record with the DO bit set MUST	>.
	return the correct answer for that question, including correct info	That is, queries for "service.arpa." and subdomains of
	rmation in the authority section that proves that	"service.arpa." <bcp14>MUST NOT</bcp14> be forwarded, with one
	the record is nonexistent.</t>	important exception: a query for a DS record with the DO bit set
	<t>So, for example, a query for the NS record for 'service.arpa.' M	<bcp14>MUST</bcp14> return the correct answer for that question,
	UST NOT result in that query being forwarded to an	including correct information in the authority section that proves
	upstream cache nor to the authoritative DNS server for '.arpa.'. H	that the record is nonexistent.</t>
	owever, as necessary to provide accurate	<t>So, for example, a query for the NS record for "service.arpa."
	authority information, a query for the DS record MUST result in for	<bcp14>MUST NOT</bcp14> result in that query being forwarded to an
	warding whatever queries are necessary;	upstream cache nor to the authoritative DNS server for ".arpa.".
	typically, this will just be a query for the DS record, since the n	However, to provide accurate authority information, a
	ecessary authority information will be included	query for the DS record <bcp14>MUST</bcp14> result in forwarding
	in the authority section of the response if the DO bit is set.</t>	whatever queries are necessary. Typically, this will just be a
		query for the DS record since the necessary authority information
		will be included in the authority section of the response if the
		DO bit is set.</t>
	</li>	</li>
	</ol>	</ol>
	</section>	</section>
	<section>	<section>
	<name>Authoritative DNS Servers</name>	<name>Authoritative DNS Servers</name>

	<t>No special processing of 'service.arpa.' is required for authoritative	<t>No special processing of "service.arpa." is required for authoritative
	DNS server implementations. It is possible that an	DNS server implementations. It is possible that an
	authoritative DNS server might attempt to check the authoritative serve	authoritative DNS server might attempt to check the authoritative DNS s
	rs for 'service.arpa.' for a delegation beneath that	ervers for "service.arpa." for a delegation beneath that
	name before answering authoritatively for such a delegated name. In su ch a case, because the name always has only local	name before answering authoritatively for such a delegated name. In su ch a case, because the name always has only local

	significance, there will be no such delegation in the 'service.arpa.' z	significance, there will be no such delegation in the "service.arpa." z
	one, and so the server would refuse to answer	one;
	authoritatively for such a zone. A server that implements this sort of	therefore, the authoritative DNS server would refuse to answer
	check MUST be configurable so that either it does	authoritatively for such a zone. An authoritative DNS server that impl
	not do this check for the 'service.arpa.' domain or it ignores the resu	ements
	lts of the check.</t>	this sort of check <bcp14>MUST</bcp14> be configurable so that either i
		t does
		not do this check for the "service.arpa." domain or it ignores the resu
		lts of the check.</t>
	</section>	</section>
	<section>	<section>
	<name>DNS Server Operators</name>	<name>DNS Server Operators</name>

	<t>DNS server operators MAY configure an authoritative server for 'servic	<t>DNS server operators <bcp14>MAY</bcp14> configure an authoritative DNS
	e.arpa.' for use with SRP. The operator for the	server for "service.arpa." for use with SRP. The operator for the
	DNS servers authoritative for 'service.arpa.' in the global DNS will co	DNS servers that are authoritative for "service.arpa." in the global DN
	nfigure any such servers as described in	S will configure any such DNS servers as described in
	<xref target="delegation"/>.</t>	<xref target="delegation"/>.</t>
	</section>	</section>
	<section>	<section>
	<name>DNS Registries/Registrars</name>	<name>DNS Registries/Registrars</name>

	<t>'service.arpa.' is a subdomain of the 'arpa' top-level domain, which i	<t>"service.arpa." is a subdomain of the "arpa." top-level domain,
	s operated by IANA under the authority of the	which is operated by IANA under the authority of the
	Internet Architecture Board according to the rules established in [RFC3	Internet Architecture Board (IAB) <xref target="RFC3172"/>.
	172]. There are no other DNS registrars for	There are no other DNS registrars for "arpa.".</t>
	'.arpa'.</t>
	</section>	</section>
	</section>	</section>

	<section anchor="delegation">	<section anchor="delegation">

	<name>Delegation of 'service.arpa.'</name>	<name>Delegation of "service.arpa."</name>
	<t>In order to be fully functional, the owner of the 'arpa.' zone must add	<t>
	a delegation of 'service.arpa.' in the '.arpa.'	The owner of the "arpa." zone, at the time of writing the IAB <xref targe
	zone <xref target="RFC3172"/>. This delegation is to be set up as was don	t="IAB-ARPA"/>,
	e for 'home.arpa', as a result of the	has added a delegation of "service.arpa."
	specification in <xref target="RFC8375" section="7" sectionFormat="of"/>.	in the "arpa." zone <xref target="RFC3172"/>,
	This is currently the responsibility of the IAB	following the guidance provided in
	<xref target="IAB-ARPA"/></t>	Section <xref target="RFC8375" section="7" sectionFormat="bare"/>
		of the "home.arpa." specification <xref target="RFC8375"/>.
		</t>
	</section>	</section>

	<section>	<section>
	<name>IANA Considerations</name>	<name>IANA Considerations</name>
	<section>	<section>

	<name>Registration and Delegation of 'service.arpa' as a Special-Use Doma	<name>Registration and Delegation of "service.arpa." as a Special-Use Dom
	in Name</name>	ain Name</name>
	<t>IANA is requested to record the domain name 'service.arpa.' in the Spe	<t>IANA has recorded the domain name "service.arpa." in the "Special-Use
	cial-Use Domain Names registry	Domain Names" registry
	<xref target="SUDN"/>. IANA is requested, with the approval of IAB, to	<xref target="SUDN"/>. IANA has implemented the delegation requested in
	implement the delegation requested in
	<xref target="delegation"/>.</t>	<xref target="delegation"/>.</t>


	<t>IANA is further requested to add a new entry to the "Transport-Indepen	</section>
	dent Locally-Served Zones" subregistry of	<section>
	the "Locally-Served DNS Zones" registry <xref target="LSDZ"/>. The ent	<name>Addition of "service.arpa." to the Locally-Served Zones Registry</n
	ry will be for the domain 'service.arpa.' with the	ame>
	description "DNS&nbhy;SD Service Registration Protocol Special-Use Doma	<t>IANA has also added a new entry to the "Transport-Independent Locally-
	in", listing this document as the reference.</t>	Served Zones Registry" registry of
		the "Locally-Served DNS Zones" group <xref target="LSDZ"/>.
		The entry is for the domain "SERVICE.ARPA." with the
		description "DNS&nbhy;SD Service Registration Protocol
		Special-Use Domain" and lists this document as the reference.</t>
	</section>	</section>

	<section anchor="subdomains">	<section anchor="subdomains">

	<name>Subdomains of 'service.arpa.'</name>	<name>Subdomains of "service.arpa."</name>
	<t>This document only makes use of the 'default.service.arpa' subdomain o
	f 'service.arpa.' Other subdomains are reserved for	<t>This document only makes use of the "default.service.arpa."
	future use by DNS-SD or related work. The IANA is requested to create a	subdomain of "service.arpa." Other subdomains are reserved for future
	registry, the "service.arpa Subdomain" registry.	use by DNS&nbhy;SD or related work. IANA has created the
	The IETF shall have change control for this registry. New entries may b	"service.arpa. Subdomain" registry <xref target="SUB"/>. The IETF has
	e added either as a result of Standards Action	change control for this registry. New entries may be added either as a
	<xref target="RFC8126" section="4.9"/> or with IESG approval <xref targ	result of Standards Action (Section <xref target="RFC8126"
	et="RFC8126" section="4.10"/>, provided that a	section="4.9" sectionFormat="bare"/> of the IANA Guidelines) or with
	specification exists <xref target="RFC8126" section="4.6"/>.	IESG Approval (Section <xref target="RFC8126" section="4.10"
	</t>	sectionFormat="bare"/> of the IANA Guidelines) <xref
		target="RFC8126"/>, provided that the values and their meanings are
		documented in a permanent and readily available public specification,
		in sufficient detail so that interoperability between independent
		implementations is possible. </t>
	<t>	<t>

	The IANA shall group the "service.arpa Subdomain" registry with the "Lo	IANA has grouped the "service.arpa. Subdomain" registry
	cally-Served DNS Zones" registry.	with the "Locally-Served DNS Zones" group.
	The registry shall be a table with three columns: the subdomain name (	The registry is a table with three columns: the subdomain name (expres
	expressed as a fully-qualified domain	sed as a fully qualified domain
	name), a brief description of how it is used, and a reference to the do cument that describes its use in detail.	name), a brief description of how it is used, and a reference to the do cument that describes its use in detail.
	</t>	</t>
	<t>	<t>

	This registry shall begin as the following table:	This initial contents of this registry are as follows:
	</t>	</t>
	<table>	<table>
	<thead>	<thead>
	<tr>	<tr>
	<th>Subdomain Name</th>	<th>Subdomain Name</th>
	<th>Description</th>	<th>Description</th>

	<th>reference</th>	<th>Reference</th>
	</tr>	</tr>
	</thead>	</thead>
	<tbody>	<tbody>
	<tr>	<tr>
	<td>default.service.arpa.</td>	<td>default.service.arpa.</td>

	<td>Default domain for SRP updates</td>	<td>Default domain for SRP Updates</td>
	<td>[THIS DOCUMENT]</td>	<td>RFC 9665</td>
	</tr>	</tr>
	</tbody>	</tbody>
	</table>	</table>
	</section>	</section>

	<section>	<section>

	<name>Service Name registrations</name>	<name>Service Name Registrations</name>
	<t>IANA is requested to add two new entries to the Service Names and Port	<t>IANA has added two new entries to the
	Numbers registry. The following sections	"Service Name and Transport Protocol Port Number Registry"
	contain tables with the fields required by <xref target="RFC6335" secti	<xref target="PORT"/>. The following subsections
	on="8.1.1" sectionFormat="of"/>.</t>	contain tables with the fields required by
	</section>	Section <xref target="RFC6335" section="8.1.1" sectionFormat="bare"/>
		of IANA's Procedures for Service Name allocation <xref target="RFC6335"
		/>.</t>

	<section>	<section>

	<name>'dnssd-srp' Service Name</name>	<name>"dnssd-srp" Service Name</name>

	<table>	<table>

	<thead><tr><td>Field Name</td><td>Value</td></tr></thead>	<thead><tr><th>Field Name</th><th>Value</th></tr></thead>
	<tbody>	<tbody>
	<tr><td> Service Name </td><td> dnssd-srp </td></tr>	<tr><td> Service Name </td><td> dnssd-srp </td></tr>

	<tr><td> Transport Protocol </td><td> TCP </td></tr>	<tr><td> Transport Protocol </td><td> tcp </td></tr>
	<tr><td> Assignee </td><td> IESG <iesg@ietf.org> </td></tr>	<tr><td> Assignee </td><td> IESG <iesg@ietf.org> </td></tr>
	<tr><td> Contact </td><td> IETF Chair <chair@ietf.org > </td></tr>	<tr><td> Contact </td><td> IETF Chair <chair@ietf.org > </td></tr>

	<tr><td> Description </td><td> DNS-SD Service Registration	<tr><td> Description </td><td> DNS&nbhy;SD Service Discovery
	</td></tr>	</td></tr>
	<tr><td> Reference </td><td> this document	<tr><td> Reference </td><td> RFC 9665
	</td></tr>	</td></tr>
	<tr><td> Port Number </td><td> None </td></tr>	<tr><td> Port Number </td><td> None </td></tr>
	<tr><td> Service Code </td><td> None </td></tr>	<tr><td> Service Code </td><td> None </td></tr>
	</tbody>	</tbody>
	</table>	</table>
	</section>	</section>
	<section>	<section>

	<name>'dnssd-srp-tls' Service Name</name>	<name>"dnssd-srp-tls" Service Name</name>
	<table>	<table>

	<thead><tr><td>Field Name</td><td>Value</td></tr></thead>	<thead><tr><th>Field Name</th><th>Value</th></tr></thead>
	<tbody>	<tbody>
	<tr><td> Service Name </td><td> dnssd-srp-tls </td></tr>	<tr><td> Service Name </td><td> dnssd-srp-tls </td></tr>

	<tr><td> Transport Protocol </td><td> TCP	<tr><td> Transport Protocol </td><td> tcp
	</td></tr>	</td></tr>
	<tr><td> Assignee </td><td> IESG	<tr><td> Assignee </td><td> IESG <iesg@ietf.org>
	</td></tr>	</td></tr>
	<tr><td> Contact </td><td> IETF Chair	<tr><td> Contact </td><td> IETF Chair <chair@ietf.org
	</td></tr>	> </td></tr>
	<tr><td> Description </td><td> DNS-SD Service Registration (	<tr><td> Description </td><td> DNS&nbhy;SD Service Discovery
	TLS) </td></tr>	(TLS) </td></tr>
	<tr><td> Reference </td><td> this document	<tr><td> Reference </td><td> RFC 9665
	</td></tr>	</td></tr>
	<tr><td> Port Number </td><td> None </td></tr>	<tr><td> Port Number </td><td> None </td></tr>
	<tr><td> Service Code </td><td> None </td></tr>	<tr><td> Service Code </td><td> None </td></tr>
	</tbody>	</tbody>
	</table>	</table>

	</section>	</section>
		</section>
	<section>	<section>
	<name>Anycast Address</name>	<name>Anycast Address</name>

	<t>IANA is requested to allocate an IPv6 Anycast address from the IPv6 Sp	<t>IANA has allocated an IPv6 anycast address from the
	ecial-Purpose Address Registry, similar to the Port	"IANA IPv6 Special-Purpose Address Registry" <xref target="IPv6"/>,
	Control Protocol anycast address, 2001:1::1. The value TBD is to be rep	similar to the Port
	laced with the actual allocation in the table that	Control Protocol <xref target="RFC6887"/>
	follows. The purpose of this allocation is to provide a fixed anycast a	anycast address <xref target="RFC7723"/>.
	ddress that can be commonly used as a destination for	The purpose of this allocation is to provide a fixed anycast
	SRP updates when no SRP registrar is explicitly configured. The values	address that can be commonly used as a destination for
	for the registry are:</t>	SRP Updates when no SRP registrar is explicitly configured. The initial
		values for the registry are as follows:</t>

	<table>	<table>
	<thead>	<thead>

	<tr><td>Attribute</td> <td>value</td></tr>	<tr><th>Attribute</th> <th>Value</th></tr>
	</thead>	</thead>
	<tbody>	<tbody>

	<tr><td>Address Block</td> <td>2001:1::TBD/128</td></t	<tr><td>Address Block</td> <td>2001:1::3/128</td></tr>
	r>	<tr><td>Name</td> <td>DNS&nbhy;SD Service Reg
	<tr><td>Name</td> <td>DNS-SD Service Registra	istration Protocol Anycast Address</td></tr>
	tion Protocol Anycast Address</td></tr>	<tr><td>RFC</td> <td>RFC 9665</td></tr>
	<tr><td>RFC</td> <td>[this document]</td></t	<tr><td>Allocation Date</td> <td>2024-04</td></tr>
	r>
	<tr><td>Allocation Date</td> <td>[date of allocation]</t
	d></tr>
	<tr><td>Termination Date</td> <td>N/A</td></tr>	<tr><td>Termination Date</td> <td>N/A</td></tr>
	<tr><td>Source</td> <td>True</td></tr>	<tr><td>Source</td> <td>True</td></tr>
	<tr><td>Destination</td> <td>True</td></tr>	<tr><td>Destination</td> <td>True</td></tr>
	<tr><td>Forwardable</td> <td>True</td></tr>	<tr><td>Forwardable</td> <td>True</td></tr>

	<tr><td>Global</td> <td>True</td></tr>	<tr><td>Globally Reachable</td> <td>True</td></
	<tr><td>Reserved-by-protocol</td> <td>False</td></tr>	tr>
		<tr><td>Reserved-by-Protocol</td> <td>False</td></tr>
	</tbody>	</tbody>
	</table>	</table>
	</section>	</section>
	</section>	</section>


	<section>
	<name>Implementation Status</name>
	<t>[Note to the RFC Editor: please remove this section prior to publicatio
	n.]</t>
	<t>
	This section records the status of known implementations of the protocol
	defined by this specification at the time of
	posting of this Internet-Draft, and is based on a proposal described in R
	FC 7942. The description of implementations in
	this section is intended to assist the IETF in its decision processes in
	progressing drafts to RFCs. Please note that the
	listing of any individual implementation here does not imply endorsement
	by the IETF. Furthermore, no effort has been spent
	to verify the information presented here that was supplied by IETF contri
	butors. This is not intended as, and must not be
	construed to be, a catalog of available implementations or their features
	. Readers are advised to note that other
	implementations may exist.
	</t>
	<t>
	According to RFC 7942, "this will allow reviewers and working groups to a
	ssign due consideration to documents that have the
	benefit of running code, which may serve as evidence of valuable experime
	ntation and feedback that have made the implemented
	protocols more mature. It is up to the individual working groups to use
	this information as they see fit".
	</t>
	<t>
	There are two known independent implementations of SRP requestors:
	</t>
	<ul>
	<li>SRP Client for OpenThread: https://github.com/openthread/openthread/p
	ull/6038</li>
	<li>mDNSResponder open source project: https://github.com/Abhayakara/mdns
	responder</li>
	</ul>
	<t>
	There are two related implementations of an SRP registrar. One acts as a
	DNS Update proxy, taking an SRP Update and applying it
	to the specified DNS zone using DNS update. The other acts as an Advertis
	ing Proxy
	<xref target="I-D.ietf-dnssd-advertising-proxy"/>. Both are included in t
	he mDNSResponder open source project mentioned above.
	</t>
	</section>

	<section>
	<name>Acknowledgments</name>
	<t>Thanks to <contact fullname="Toke Høiland-Jørgensen"/>, Jonathan Hui, E
	sko Dijk, Kangping Dong and Abtin Keshavarzian for
	their thorough technical reviews. Thanks to Kangping and Abtin as well fo
	r testing the document by doing an independent
	implementation. Thanks to Tamara Kemper for doing a nice developmental ed
	it, Tim Wattenberg for doing an SRP requestor
	proof-of-concept implementation at the Montreal Hackathon at IETF 102, an
	d Tom Pusateri for reviewing during the hackathon
	and afterwards. Thanks to Esko for a really thorough second last call rev
	iew. Thanks also to Nathan Dyck, Gabriel
	Montenegro, Kangping Dong, Martin Turon, and Michael Cowan for their deta
	iled second last call reviews. Thanks to Patrik
	Fältström, Dhruv Dhody, David Dong, Joey Salazar, Jean-Michel Combes, and
	Joerg Ott for their respective directorate
	reviews. Thanks to Paul Wouters for a <em>really</em> detailed IESG revie
	w! Thanks also to the other IESG members who
	provided comments or simply took the time to review the document.</t>
	</section>
	</middle>	</middle>

	<back>	<back>
	<displayreference target="I-D.cheshire-dnssd-roadmap" to="ROADMAP"/>	<displayreference target="I-D.cheshire-dnssd-roadmap" to="ROADMAP"/>

	<displayreference target="I-D.ietf-dnssd-advertising-proxy" to="AP"/>	<displayreference target="I-D.ietf-snac-simple" to="SNAC-SIMPLE"/>


	<!-- <displayreference target="I-D.ietf-dnssd-hybrid" to="I-D.ietf-dnssd-hyb rid"/> appears to not work in xml2rfc 2.6.2 -->
	<references>	<references>

		<name>References</name>
		<references>
	<name>Normative References</name>	<name>Normative References</name>

	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml3/reference.I-
	D.ietf-dnssd-update-lease.xml"/>	<!-- [I-D.ietf-dnssd-update-lease] companion document RFC 9664-->
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<reference anchor="RFC9664" target="https://www.rfc-editor.org/info/rfc966
	.1035.xml" />	4">
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<front>
	.1536.xml" />	<title>An EDNS(0) Option to Negotiate Leases on DNS Updates</title>
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<author fullname="Stuart Cheshire" initials="S." surname="Cheshire">
	.2119.xml" />	<organization>Apple Inc.</organization>
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	</author>
	.2136.xml" />	<author fullname="Ted Lemon" initials="T." surname="Lemon">
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<organization>Apple Inc</organization>
	.2181.xml" />	</author>
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<date month="June" year="2025"/>
	.2539.xml" />	</front>
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<seriesInfo name="RFC" value="9664"/>
	.2782.xml" />	<seriesInfo name="DOI" value="10.17487/RFC9664"/>
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	</reference>
	.2931.xml" />
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.103
	.3172.xml"/>	5.xml" />
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.153
	.3445.xml"/>	6.xml" />
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.211
	.3596.xml"/>	9.xml" />
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.213
	.4035.xml"/>	6.xml" />
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.218
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	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.253
	.6763.xml"/>	9.xml" />
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.278
	.7858.xml" />	2.xml" />
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.293
	.8085.xml" />	1.xml" />
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.317
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	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.359
	.8174.xml"/>	6.xml"/>
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.403
	.8375.xml"/>	4.xml"/>
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.403
	.8624.xml"/>	5.xml"/>
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.630
	.8765.xml" />	3.xml"/>
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.676
	.9364.xml" />	3.xml"/>
		<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.785
		8.xml" />
		<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.808
		5.xml" />
		<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.812
		6.xml"/>
		<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.817
		4.xml"/>
		<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.837
		5.xml"/>
		<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.862
		4.xml"/>
		<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.876
		5.xml" />
		<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.936
		4.xml" />
	</references>	</references>

	<references>	<references>
	<name>Informative References</name>	<name>Informative References</name>

	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.213
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	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.282
	.2827.xml" />	7.xml" />
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.300
	.3007.xml" />	7.xml" />
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.392
	.4861.xml" />	7.xml" />
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.486
	.6105.xml" />	1.xml" />
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.486
	.6335.xml" />	2.xml" />
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.610
	.6760.xml" />	5.xml" />
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.633
	.6761.xml" />	5.xml" />
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.676
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	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.676
	.7084.xml" />	1.xml" />
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.676
	.7228.xml" />	2.xml" />
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.688
	.7413.xml" />	7.xml" />
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.708
	.8415.xml" />	4.xml" />
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.772
	.8520.xml" />	3.xml" />
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.722
	.8766.xml" />	8.xml" />
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.741
	.8945.xml" />	3.xml" />
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml3/reference.I-	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.841
	D.cheshire-dnssd-roadmap.xml"/>	5.xml" />
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml3/reference.I-	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.852
	D.ietf-dnssd-advertising-proxy.xml"/>	0.xml" />
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	D.ietf-snac-simple.xml"/>	6.xml" />
		<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.894
		5.xml" />


	<reference anchor="SUDN" target="https://www.iana.org/assignments/special-	<!-- [I-D.cheshire-dnssd-roadmap] IESG state: Expired as of 06/05/25-->
	use-domain-names/special-use-domain-names.xhtml">	<xi:include href="https://datatracker.ietf.org/doc/bibxml3/reference.I-D.c
		heshire-dnssd-roadmap.xml"/>

		<!-- [I-D.ietf-snac-simple] IESG state: I-D Exists as of 06/05/25-->
		<xi:include href="https://datatracker.ietf.org/doc/bibxml3/reference.I-D.i
		etf-snac-simple.xml"/>

		<reference anchor="SUDN" target="https://www.iana.org/assignments/special-
		use-domain-names">
	<front>	<front>

	<title>Special-Use Domain Names Registry</title>	<title>Special-Use Domain Names</title>
	<author/>	<author>
	<date month="July" year="2012"/>	<organization>IANA</organization>
		</author>
	</front>	</front>
	</reference>	</reference>


	<reference anchor="LSDZ" target="https://www.iana.org/assignments/locally- served-dns-zones/locally-served-dns-zones.xhtml">	<reference anchor="LSDZ" target="https://www.iana.org/assignments/locally- served-dns-zones">
	<front>	<front>

	<title>Locally-Served DNS Zones Registry</title>	<title>Locally-Served DNS Zones</title>
	<author/>	<author>
	<date month="July" year="2011"/>	<organization>IANA</organization>
		</author>
		</front>
		</reference>

		<reference anchor="SUB" target="https://www.iana.org/assignments/locally-s
		erved-dns-zones/locally-served-dns-zones">
		<front>
		<title>service.arpa Subdomain</title>
		<author>
		<organization>IANA</organization>
		</author>
		</front>
		</reference>

		<reference anchor="PORT" target="https://www.iana.org/assignments/service-names-
		port-numbers">
		<front>
		<title>Service Name and Transport Protocol Port Number Registry</title
		>
		<author>
		<organization>IANA</organization>
		</author>
		</front>
		</reference>

		<reference anchor="IPv6" target="https://www.iana.org/assignments/iana-ipv
		6-special-registry">
		<front>
		<title>IANA IPv6 Special-Purpose Address Registry</title>
		<author>
		<organization>IANA</organization>
		</author>
	</front>	</front>
	</reference>	</reference>

	<reference anchor="IAB-ARPA" target="https://www.iab.org/documents/corresp ondence-reports-documents/2017-2/iab-statement-on-the-registration-of-special-us e-names-in-the-arpa-domain/">	<reference anchor="IAB-ARPA" target="https://www.iab.org/documents/corresp ondence-reports-documents/2017-2/iab-statement-on-the-registration-of-special-us e-names-in-the-arpa-domain/">
	<front>	<front>
	<title>Internet Architecture Board statement on the registration of sp ecial use names in the ARPA domain</title>	<title>Internet Architecture Board statement on the registration of sp ecial use names in the ARPA domain</title>
	<author/>	<author/>
	<date month="March" year="2017"/>	<date month="March" year="2017"/>
	</front>	</front>
	</reference>	</reference>

	<reference anchor="ZC">	<reference anchor="ZC">
	<front>	<front>
	<title>Zero Configuration Networking: The Definitive Guide</title>	<title>Zero Configuration Networking: The Definitive Guide</title>

	<author initials="S." surname="Cheshire" fullname="Stuart Cheshire"/>
	<author initials="D.H." surname="Steinberg" fullname="Daniel H. Steinb erg"/>	<author initials="D.H." surname="Steinberg" fullname="Daniel H. Steinb erg"/>

		<author initials="S." surname="Cheshire" fullname="Stuart Cheshire"/>
	<date year="2005" month="December"/>	<date year="2005" month="December"/>
	</front>	</front>

	<seriesInfo name="O'Reilly Media, Inc." value=""/>	<refcontent>O'Reilly Media, Inc.</refcontent>
	<seriesInfo name="ISBN" value="0-596-10100-7"/>	<seriesInfo name="ISBN" value="9780596101008"/>
	</reference>	</reference>

	</references>	</references>

		</references>

	<section>	<section>

	<name>Testing using standard RFC2136-compliant DNS servers</name>	<name>Using Standard Authoritative DNS Servers Compliant with RFC 2136 to Test SRP Requesters</name>
	<t>	<t>

	It may be useful to set up an authoritative DNS server for testing that	For testing, it may be useful to set up an
	does not implement SRP. This can be done by configuring the	authoritative DNS server that does not implement SRP.
	server to listen on the anycast address, or advertising it in the _dnssd	This can be done by configuring the
	&nbhy;srp._tcp.<zone> SRV and	authoritative DNS server to listen on the anycast address or by
	_dnssd&nbhy;srp&nbhy;tls._tcp.<zone> record. It must be configure	advertising it in the "_dnssd&nbhy;srp._tcp.<zone>" and
	d to be authoritative for	"_dnssd&nbhy;srp&nbhy;tls._tcp.<zone>" SRV records.
	"default.service.arpa", and to accept updates from hosts on local networ	It must be configured to be authoritative for
	ks for names under "default.service.arpa"	"default.service.arpa." and to accept updates from hosts
	without authentication, since such servers will not have support for FCF	on local networks for names under "default.service.arpa."
	S authentication (<xref target="fcfs"/>).</t>	without authentication since such authoritative DNS servers will not
		have support for FCFS authentication (<xref target="fcfs"/>).</t>
	<t>	<t>

	An authoritative DNS server configured in this way will be able to succe	An authoritative DNS server configured in this way will be able to succe
	ssfully accept and process SRP Updates from requestors that send SRP	ssfully accept and process SRP Updates from requesters that send SRP
	updates. However, no prerequisites will be applied, and this means that	updates. However, no prerequisites will be applied; this means
	the test server will accept internally	that the test authoritative DNS server will accept internally
	inconsistent SRP Updates, and will not stop two SRP Updates, sent by dif	inconsistent SRP Updates and will not stop two SRP Updates sent by diffe
	ferent services, that claim the same name(s),	rent services that claim the same name or names
	from overwriting each other.</t>	from overwriting each other.</t>
	<t>	<t>

	Since SRP Updates are signed with keys, validation of the SIG(0) algorit	Since SRP Updates are signed with keys, validation of the SIG(0) algorit
	hm used by the requestor can be done by manually	hm used by the requester can be done by manually
	installing the requestor's public key on the DNS server that will be rec	installing the requester's public key on the authoritative DNS server
	eiving the updates. The key can then be used to	that will be receiving the updates. The key can then be used to
	authenticate the SRP update, and can be used as a requirement for the up	authenticate the SRP Update and can be used as a requirement for the upd
	date. An example configuration for testing SRP	ate. An example configuration for testing SRP
	using BIND 9 is given in <xref target="bind-example"/>.</t>	using BIND 9 is given in <xref target="bind-example"/>.</t>
	</section>	</section>

	<section>	<section>

	<name>How to allow SRP requestors to update standard RFC2136-compliant ser vers</name>	<name>How to Allow SRP Requesters to Update Standard Servers Compliant wit h RFC 2136</name>
	<t>	<t>

	Ordinarily SRP Updates will fail when sent to an RFC 2136-compliant serv	Ordinarily, CNN SRP Updates sent to an authoritative DNS server
	er that does not implement SRP because the zone	that implements standard DNS Update <xref target="RFC2136"/> but not SRP
	being updated is "default.service.arpa", and no DNS server that is not a	will fail
	n SRP registrar would normally be configured to be	because the zone being updated is "default.service.arpa." and because
	authoritative for "default.service.arpa". Therefore, a requestor that s	no authoritative DNS server that is not an SRP registrar would normally
	ends an SRP Update can tell that the receiving server	be configured to be authoritative for "default.service.arpa.".
	does not support SRP, but does support RFC2136, because the RCODE will e	Therefore, a requester that sends an SRP Update can
	ither be NotZone, NotAuth or Refused, or because	tell that the receiving authoritative DNS server
	there is no response to the update request (when using the anycast addre	does not support SRP but does support
	ss)</t>	standard DNS Update <xref target="RFC2136"/>
		because the RCODE will either be NotZone, NotAuth, or Refused or because
		there is no response to the update request (when using the anycast addre
		ss).</t>
	<t>	<t>

	In this case a requestor MAY attempt to register itself using regular RF	In this case, a requester <bcp14>MAY</bcp14>
	C2136 DNS updates. To do so, it must discover the	attempt to register itself using
	default registration zone and the DNS server designated to receive updat	normal DNS updates <xref target="RFC2136"/>.
	es for that zone, as described earlier, using the	To do so, it must discover the
	_dns&nbhy;update._udp SRV record. It can then send the update to the po	default registration zone and the authoritative DNS server designated
	rt and host pointed to by the SRV record, and is	to receive updates for that zone, as described earlier, using the
		_dns&nbhy;update._udp SRV record. It can then send the update to the po
		rt and host pointed to by the SRV record, and it is
	expected to use appropriate prerequisites to avoid overwriting competing records. Such updates are out of scope for SRP,	expected to use appropriate prerequisites to avoid overwriting competing records. Such updates are out of scope for SRP,

	and a requestor that implements SRP MUST first attempt to use SRP to reg	and a requester that implements SRP <bcp14>MUST</bcp14>
	ister itself, and only attempt to use RFC2136	first attempt to use SRP to register itself and
	backwards compatibility if that fails. Although the owner name for the	only attempt to use backwards capability with
	SRV record specifies the UDP protocol for updates,	normal DNS Update <xref target="RFC2136"/>
	it is also possible to use TCP, and TCP SHOULD be required to prevent sp	if that fails.
	oofing.</t>	Although the owner name of the SRV record for
		DNS Update (_dns-update._udp) specifies UDP,
		it is also possible to use TCP, and TCP <bcp14>SHOULD</bcp14> be require
		d to prevent spoofing.</t>
	</section>	</section>

	<section anchor="bind-example">	<section anchor="bind-example">

	<name>Sample BIND9 configuration for default.service.arpa.</name>	<name>Sample BIND 9 Configuration for "default.service.arpa."</name>
	<figure title="Zone Configuration in named.conf"><artwork><![CDATA[
		<figure title="Zone Configuration in named.conf">
		<artwork align="center"><![CDATA[
	zone "default.service.arpa." {	zone "default.service.arpa." {
	type primary;	type primary;
	file "/etc/bind/primary/service.db";	file "/etc/bind/primary/service.db";
	allow-update { key demo.default.service.arpa.; };	allow-update { key demo.default.service.arpa.; };

	};	};]]></artwork>
	]]></artwork></figure>	</figure>
	<figure title="Example Zone file"><artwork><![CDATA[
	$ORIGIN .	<figure title="Example Zone File">
		<artwork align="center"><![CDATA[
	$TTL 57600 ; 16 hours	$TTL 57600 ; 16 hours

	default.service.arpa IN SOA ns3.default.service.arpa.	@ IN SOA ns postmaster (
	postmaster.default.service.arpa. (	2951053287 ; serial
	2951053287 ; serial	3600 ; refresh (1 hour)
	3600 ; refresh (1 hour)	1800 ; retry (30 minutes)
	1800 ; retry (30 minutes)	604800 ; expire (1 week)
	604800 ; expire (1 week)	3600 ; minimum (1 hour)
	3600 ; minimum (1 hour)	)
	)	NS ns
	NS ns3.default.service.arpa.	ns AAAA 2001:db8:0:2::1
	SRV 0 0 53 ns3.default.service.arpa.
	$ORIGIN default.service.arpa.
	$TTL 3600 ; 1 hour
	_ipps._tcp PTR demo._ipps._tcp
	$ORIGIN _ipps._tcp.default.service.arpa.
	demo TXT "0"
	SRV 0 0 9992 demo.default.service.arpa.
	$ORIGIN _udp.default.service.arpa.
	$TTL 3600 ; 1 hour
	_dns-update PTR ns3.default.service.arpa.
	$ORIGIN _tcp.default.service.arpa.
	_dnssd-srp PTR ns3.default.service.arpa.
	$ORIGIN default.service.arpa.
	$TTL 300 ; 5 minutes
	ns3 AAAA 2001:db8:0:1::1
	$TTL 3600 ; 1 hour	$TTL 3600 ; 1 hour

	demo AAAA 2001:db8:0:2::1
	KEY 0 3 13 (	; Autoconguration bootstrap records
	qweEmaaq0FAWok5//ftuQtZgiZoiFSUsm0srWREdywQU	_dnssd-srp._tcp SRV 0 0 53 ns
	9dpvtOhrdKWUuPT3uEFF5TZU6B4q1z1I662GdaUwqg==	_dnssd-srp-tls._tcp SRV 0 0 853 ns
	); alg = ECDSAP256SHA256 ; key id = 15008
	AAAA ::1	; Service Discovery Instruction
	]]></artwork></figure>	_ipps._tcp PTR demo._ipps._tcp

		; Service Description Instruction
		demo._ipps._tcp SRV 0 0 631 demohost
		TXT ""

		; Host Description Instruction
		demohost AAAA 2001:db8:0:2::2
		KEY 0 3 13 (
		qweEmaaq0FAWok5//ftuQtZgiZoiFSUsm0srWREdywQU
		9dpvtOhrdKWUuPT3uEFF5TZU6B4q1z1I662GdaUwqg==
		); alg = ECDSAP256SHA256 ; key id = 14495
		]]></artwork>
		</figure>

		</section>

		<section numbered="false">
		<name>Acknowledgments</name>
		<t>Thanks to <contact fullname="Toke Høiland-Jørgensen"/>, <contact
		fullname="Jonathan Hui"/>, <contact fullname="Esko Dijk"/>, <contact
		fullname="Kangping Dong"/>, and <contact fullname="Abtin Keshavarzian"/>
		for their thorough technical reviews. Thanks to <contact
		fullname="Kangping"/> and <contact fullname="Abtin"/> as well for
		testing the document by doing an independent implementation. Thanks to
		<contact fullname="Tamara Kemper"/> for doing a nice developmental edit,
		<contact fullname="Tim Wattenberg"/> for doing an SRP requester
		proof-of-concept implementation at the Montreal Hackathon at IETF 102,
		and <contact fullname="Tom Pusateri"/> for reviewing during the
		hackathon and afterwards. Thanks to <contact fullname="Esko"/> for a
		really thorough second Last Call review. Thanks also to <contact
		fullname="Nathan Dyck"/>, <contact fullname="Gabriel Montenegro"/>,
		<contact fullname="Kangping Dong"/>, <contact fullname="Martin Turon"/>,
		and <contact fullname="Michael Cowan"/> for their detailed second last
		call reviews. Thanks to <contact fullname="Patrik Fältström"/>, <contact
		fullname="Dhruv Dhody"/>, <contact fullname="David Dong"/>, <contact
		fullname="Joey Salazar"/>, <contact fullname="Jean-Michel Combes"/>, and
		<contact fullname="Joerg Ott"/> for their respective directorate
		reviews. Thanks to <contact fullname="Paul Wouters"/> for a
		<em>really</em> detailed IESG review! Thanks also to the other IESG
		members who provided comments or simply took the time to review the
		document.</t>
	</section>	</section>


	</back>	</back>

	</rfc>


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