draft-sctl-service-registration-01.txt		draft-sctl-service-registration-02.txt
	Internet Engineering Task Force S. Cheshire		Internet Engineering Task Force S. Cheshire
	Internet-Draft Apple Inc.		Internet-Draft Apple Inc.
	Intended status: Informational T. Lemon		Intended status: Informational T. Lemon
	Expires: January 3, 2019 Nibbhaya Consulting		Expires: January 15, 2019 Nibbhaya Consulting
	July 2, 2018		July 14, 2018
	Service Registration Protocol for DNS-Based Service Discovery		Service Registration Protocol for DNS-Based Service Discovery
	draft-sctl-service-registration-01		draft-sctl-service-registration-02
	Abstract		Abstract
	The DNS-SD Service Registration Protocol uses the standard DNS Update		The DNS-SD Service Registration Protocol uses the standard DNS Update
	mechanism to enable DNS-Based Service Discovery using only unicast		mechanism to enable DNS-Based Service Discovery using only unicast
	packets. This eliminates the dependency on Multicast DNS as the		packets. This eliminates the dependency on Multicast DNS as the
	foundation layer, which greatly improves scalability and improves		foundation layer, which greatly improves scalability and improves
	performance on networks where multicast service is not an optimal		performance on networks where multicast service is not an optimal
	choice, particularly 802.11 (WiFi) and 802.15 (IoT) networks. DNS-SD		choice, particularly 802.11 (Wi-Fi) and 802.15.4 (IoT) networks.
	Service registration uses public keys and SIG(0) to allow services to		DNS-SD Service registration uses public keys and SIG(0) to allow
	defend their registrations against attack.		services to defend their registrations against attack.
	Status of This Memo		Status of This Memo
	This Internet-Draft is submitted in full conformance with the		This Internet-Draft is submitted in full conformance with the
	provisions of BCP 78 and BCP 79.		provisions of BCP 78 and BCP 79.
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at https://datatracker.ietf.org/drafts/current/.		Drafts is at https://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on January 3, 2019.		This Internet-Draft will expire on January 15, 2019.
	Copyright Notice		Copyright Notice
	Copyright (c) 2018 IETF Trust and the persons identified as the		Copyright (c) 2018 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(https://trustee.ietf.org/license-info) in effect on the date of		(https://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	skipping to change at page 2, line 14 ¶		skipping to change at page 2, line 14 ¶
	to this document. Code Components extracted from this document must		to this document. Code Components extracted from this document must
	include Simplified BSD License text as described in Section 4.e of		include Simplified BSD License text as described in Section 4.e of
	the Trust Legal Provisions and are provided without warranty as		the Trust Legal Provisions and are provided without warranty as
	described in the Simplified BSD License.		described in the Simplified BSD License.
	1. Introduction		1. Introduction
	DNS-Based Service Discovery [RFC6763] is a component of Zero		DNS-Based Service Discovery [RFC6763] is a component of Zero
	Configuration Networking [RFC6760] [ZC] [I-D.cheshire-dnssd-roadmap].		Configuration Networking [RFC6760] [ZC] [I-D.cheshire-dnssd-roadmap].
			This document describes an enhancement to DNS-Based Service Discovery
			[RFC6763] that allows services to automatically register their
			services using the DNS protocol rather than using mDNS. There is
			already a large installed base of DNS-SD clients that can do service
			discovery using the DNS protocol. This extension makes it much
			easier to take advantage of this existing functionality.
			This document is intended for three audiences: implementors of
			software that provides services that should be advertised using DNS-
			SD, implementors of DNS servers that will be used in contexts where
			DNS-SD registration is needed, and administrators of networks where
			DNS-SD service is required. The document is intended to provide
			sufficient information to allow interoperable implementation of the
			registration protocol.
	DNS-Based Service Discovery (DNS-SD) allows services to advertise the		DNS-Based Service Discovery (DNS-SD) allows services to advertise the
	fact that they provide service, and to provide the information		fact that they provide service, and to provide the information
	required to access that service. Clients can then discover the set		required to access that service. Clients can then discover the set
	of services of a particular type that are available. They can then		of services of a particular type that are available. They can then
	select a service from among those that are available and obtain the		select a service from among those that are available and obtain the
	information required to use it.		information required to use it.
	The DNS-SD Service Registration protocol, described in this document,		The DNS-SD Service Registration protocol, described in this document,
	provides a reasonably secure mechanism for publishing this		provides a reasonably secure mechanism for publishing this
	information: what services are offered, and how to use them. Once		information. Once published, these services can be readily
	published, these services can be readily discovered by clients using		discovered by clients using standard DNS lookups.
	standard DNS lookups.
	In the DNS-Based Service Discovery specification [RFC6763] Section 10		In the DNS-Based Service Discovery specification [RFC6763] Section 10
	"Populating the DNS with Information" briefly discusses ways that		"Populating the DNS with Information" briefly discusses ways that
	services can publish their information in the DNS namespace. In the		services can publish their information in the DNS namespace. In the
	case of Multicast DNS [RFC6762], allows clients to directly query		case of Multicast DNS [RFC6762], it allows services to publish their
	services on the local link for names in the ".local" namespace.		information on the local link, using names in the ".local" namespace,
			which makes their services directly discoverable by peers attached to
			that same local link.
	RFC6763 also allows clients to discover services using the DNS		RFC6763 also allows clients to discover services using the DNS
	protocol [RFC1035]; this is done either by having a system		protocol [RFC1035]. This can be done by having a system
	administrator manually configure service information in the DNS, or		administrator manually configure service information in the DNS, but
	by using a Discovery Proxy [I-D.ietf-dnssd-hybrid], which performs		manually populating DNS authoritative server databases is costly and
	mDNS queries on behalf clients issuing queries using DNS. This		potentially error-prone, and requires a knowledgable network
	eliminats the "link local" limitation of mDNS, but provides no		administrator. Consequently, although all DNS-SD client
	additional security, and still relies on multicast.		implementations of which we are aware support DNS-SD using DNS
			queries, in practice it is used much less frequently than mDNS. The
	Manual configuration of DNS servers is costly and failure-prone, and		Discovery Proxy [I-D.ietf-dnssd-hybrid] provides one way to
	requires a knowledgable network administrator. Consequently,		automatically populate the DNS namespace, but is only appropriate on
	although all DNS-SD implementations of which we are aware support it,		networks where services are already advertised using mDNS. This
	it is much less frequently used than mDNS. This document describes a		document describes a solution more suitable for networks where
	solution: a way to provide DNS-SD using DNS that can be as automatic		multicast is inefficient, or undesirable for other reasons, by
	as multicast DNS, but with better performance, scalability and		supporting both offering of services, and discovery of services,
	security.		using unicast.
	2. Service Registration Protocol		2. Service Registration Protocol
	Services using the DNS-SD Service Registration Protocol use DNS		Services that implement the DNS-SD Service Registration Protocol use
	Update [RFC2136] [RFC3007] to publish service information in the DNS.		DNS Update [RFC2136] [RFC3007] to publish service information in the
			DNS. Two variants exist, one for full-featured devices, and one for
			devices designed for "Constrained-Node Networks" [RFC7228].
			Full-featured devices are either configured manually, or use the
			"dr._dns-sd._udp" query [RFC6763] to learn the default registration
			domain from the network. Using the chosen service registration
			domain, full-featured devices construct the names of the SRV, TXT,
			and PTR records describing their service(s). For these names they
			then discover the zone apex of the closest enclosing DNS zone using
			SOA queries [I-D.ietf-dnssd-push]. Having discovered the enclosing
			DNS zone, they query for the "_dns-update._udp<zone>" SRV record to
			discover the server to which they should send DNS updates.
			For devices designed for "Constrained-Node Networks" [RFC7228] some
			simplifications are used. Instead of being configured with (or
			discovering) the service registration domain, the (proposed) special
			use domain name [RFC6761] "services.arpa" is used. Instead of
			learning the server to which they should send DNS updates, a fixed
			IPv6 anycast address is used (value TBD). It is the responsibility
			of a "Constrained-Node Network" supporting DNS-SD Service
			Registration Protocol to provide appropriate anycast routing to
			deliver the DNS updates to the appropriate server. It is the
			responsibility of the DNS-SD Service Registration server on a
			"Constrained-Node Network" to handle the updates appropriately. In
			some network environments, updates may be accepted directly into a
			local "services.arpa" zone, which has only local visibility. In
			other network environments, updates for names ending in
			"services.arpa" may be rewritten internally to names with broader
			visibility.
			The reason for these different assumptions is that "Constrained-Node
			Networks" generally require special egress support, and Anycast
			packets captured at the "Constrained-Node Network" egress can be
			assumed to have originated locally. Low-power devices that typically
			use "Constrained-Node Networks" may have very limited battery power.
			The additional DNS lookups required to discover a registration server
			and then communicate with it will increase the power required to
			advertise a service; for low-power devices, the additional
			flexibility this provides does not justify the additional use of
			power.
			General networks have the potential to have more complicated
			topologies at the Internet layer, which makes anycast routing more
			difficult. Such networks may or may not have the infrastructure
			required to route anycast to a server that can process it. However,
			they can be assumed to be able to provide registration domain
			discovery and routing. By requiring the use of TCP, the possibility
			of off-network spoofing is eliminated.
	We will discuss several parts to this process: how to know what to		We will discuss several parts to this process: how to know what to
	publish, how to know where to publish it (under what name), how to		publish, how to know where to publish it (under what name), how to
	publish it, how to secure its publication, and how to maintain the		publish it, how to secure its publication, and how to maintain the
	information once published.		information once published.
	2.1. What to publish		2.1. What to publish
	RFC 6763 describes the details of what is to be published. In		We refer to the message that services using the DNSSD Registration
	general terms, a service will have a name under which it offers		Protocol send as a Registration. Three types of updates appear in a
	services ([RFC6763] section 4.1.1) and one or more service names		Registration: Service Discovery records, Service Description records,
	under which that instance name appears ([RFC6763] section 4.1.2).		and Host Description records.
	The full details of how this works are described in section 4 of that
	document in its entirety. A service publishes its contact
	information using an SRV record on the Service Instance Name. It can
	also publish TXT records with additional information about the
	service; this is discussed in section 6 of RFC 6763.
	RFC 6763 is the definitive source for information about what to		o Service Discovery records are one or more PTR RRs, mapping from
	publish; the reason for mentioning it here is that the reader may		the generic service type (or subtype) to the specific Service
	prefer to have an overview of the whole service registration process		Instance Name.
	before digging into the details. Also, the "Service Instance Name"
	is an important aspect of first-come, first-serve naming, which we		o Service Description records are exactly one SRV RR, and one or
	describe later on in this document.		more TXT RRs, both with the same name, the Service Instance Name
			([RFC6763] section 4.1). In principle Service Description records
			can include other record types, with the same Service Instance
			Name, though in practice they rarely do. The Service Instance
			Name MUST be referenced by one or more Service Discovery PTR
			records, unless it is a placeholder service registration for an
			intentionally non-discoverable service name.
			o The Host Description records for a service are a KEY RR, used to
			claim exclusive ownership of the service registration, and one or
			more RRs of type A or AAAA, giving the IPv4 or IPv6 address(es) of
			the host where the service resides.
			RFC 6763 describes the details of what each of these types of updates
			contains and is the definitive source for information about what to
			publish; the reason for mentioning it here is to provide the reader
			with enough information about what will be published that the service
			registration process can be understood at a high level without first
			learning the full details of DNS-SD. Also, the "Service Instance
			Name" is an important aspect of first-come, first-serve naming, which
			we describe later on in this document.
	2.2. Where to publish it		2.2. Where to publish it
	Multicast DNS uses a single namespace, ".local", which is valid on		Multicast DNS uses a single namespace, ".local", which is valid on
	the local link. This convenience is not available for DNS-SD using		the local link. This convenience is not available for DNS-SD using
	the DNS protocol: the portion of the DNS namespace in which services		the DNS protocol: services must exist in some specific unicast
	on the local network are to be published must be discovered by the		namespace.
	service before it can register itself.
	Names published using DNS-SD service registration will be published		As described above, full-featured devices are responsible for knowing
	under some name other than .local. However, the process of		in what domain they should register their services. Devices made for
	discovering what that name is is complicated, and for any given		"Constrained-Node Networks" register in the (proposed) special use
	network it should always be the case that there will be just one		domain name [RFC6761] "services.arpa", and let the DNS-SD Service
	namespace in which registered names will be published. Rather than		Registration server handle rewriting that to a different domain if
	requiring the service to discover this name before issuing a		necessary.
	registration, the service SHOULD simply use the name ".local." The
	DNS server that receives the registration request will rewrite all
	instances of the terminal label ".local" to use the local
	registration domain name. The response to the DNS Update being used
	to register the service will contain the rewritten names, instead of
	".local". Subsequent updates should still use the ".local" domain
	and not the registration domain, since the registration domain may
	change over time or when the service is physically moved to a new
	network.
	2.3. How to publish it		2.3. How to publish it
	DNS Updates are very flexible. As a consequence, it is possible to		It is possible to issue a DNS Update that does several things at
	do the entire registration in a single DNS message. The update		once; this means that it's possible to do all the work of adding a
	consists of two elements. The first updates the Service Name by		PTR resource record to the PTR RRset on the Service Name if it
	adding a PTR record pointing to the Service Instance Name. The		already exists, or creating one if it doesn't, and creating or
	second updates the Service Instance Name. The second creates or		updating the Service Instance Name and Host Description in a single
	updates the Service Instance Name update adds an SRV record and a KEY		transaction.
	record, and optionally adds a TXT record with extra information about
	the service. The contents of the KEY record are described in the
	section on First-Come First-Served Naming (Section 2.4.1). The
	update is signed using the private key that corresponds to the public
	key in the KEY record, using the SIG(0) protocol [RFC2931].
	The update may be rejected. If the chosen service instance name is		A Registration is therefore implemented as a single DNS Update
	not permitted, or is already taken, the update will be returned with		message that contains a service's Service Discovery records, Service
	the error code YXDOMAIN. In this case, the service will need to		Description records, and Host Description records.
	choose a new instance name and try again.
			Updates done according to this specification are somewhat different
			than regular DNS Updates as defined in RFC2136. RFC2136 assumes that
			updating is a fairly heavyweight process, so you might first attempt
			to add a name if it doesn't exist, and then in a second message
			update the name if it does exist but matches certain preconditions.
			Because the registration protocol uses a single transaction, some of
			this adaptability is lost.
			In order to allow updates to happen in a single transaction,
			Registrations do not include update constraints. The constraints
			specified in Section 2.4.2 are implicit in the processing of
			Registrations, and so there is no need for the service sending the
			Registration to put in any explicit constraints.
			2.3.1. How DNS-SD Service Registration differs from standard RFC2136
			DNS Update
			DNS-SD Service Registration is based on standard RFC2136 DNS Update,
			with some differences:
			o It implements first-come first-served name allocation, protected
			using SIG(0).
			o It enforces policy about what updates are allowed.
			o It optionally performs rewriting of "services.arpa" to some other
			domain.
			o It optionally performs automatic population of the address-to-name
			reverse mapping domains.
			o A DNS-SD Service Registration server is not required to implement
			general DNS Update prerequsite processing.
			o Simplified clients are allowed to send updates to an anycast
			address, for names ending in "services.arpa"
			2.3.2. Testing using standard RFC2136-compliant servers
			It may be useful to set up a DNS server for testing that does not
			implement the Registration protocol. This can be done by configuring
			the server to listen on the anycast address, or advertising it in the
			_dns-update._udp SRV record. It must be configured to be
			authoritative for "services.arpa", and to accept updates from hosts
			on local networks for names under "services.arpa" without
			authentication.
			A server configured in this way will be able to successfully accept
			and process Registrations from services that send Registrations.
			However, no constraints will be applied, and this means that the test
			server will accept internally inconsistent Registrations, and will
			not stop two Registrations, sent by different services, that claim
			the same name(s), from overwriting each other.
			2.3.3. How to allow services to update standard RFC2136-compliant
			servers
			Ordinarily Registrations will fail when sent to any non-Registration
			Protocol server because the zone being updated is "services.arpa",
			and no DNS server that is not a Registration Protocol server should
			normally be configured to be authoritative for "services.arpa".
			Therefore, a service that sends a Registration can tell that the
			receiving server does not support the Registration Protocol, but does
			support 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 address)
			In this case a service MAY attempt to register itself using regular
			RFC2136 DNS updates. To do so, it must discover default registration
			zone and the DNS server designated to receive updates for that zone,
			as described earlier using the _dns-update._udp SRV record. It can
			then make the update using the port and host pointed to by the SRV
			record, and should use appropriate constraints to avoid overwriting
			competing records. Such updates are out of scope for the DNSSD
			Registration Protocol, and a service that implements the DNSSD
			Registration Protocol MUST first attempt to use the Registration
			Protocol to register itself, and should only attempt to use RFC2136
			backwards compatibility if that fails.
	2.4. How to secure it		2.4. How to secure it
	Traditional DNS update is secured using the TSIG protocol, which uses		Traditional DNS update is secured using the TSIG protocol, which uses
	a secret key shared between the client (which issues the update) and		a secret key shared between the client (which issues the update) and
	the server (which authenticates it). This model does not work for		the server (which authenticates it). This model does not work for
	automatic service registration.		automatic service registration.
	The goal of securing the DNS-SD Registration Protocol is to provide		The goal of securing the DNS-SD Registration Protocol is to provide
	the best possible security given the constraint that service		the best possible security given the constraint that service
	skipping to change at page 5, line 13 ¶		skipping to change at page 8, line 15 ¶
	or update the information associated with that Service Instance Name.		or update the information associated with that Service Instance Name.
	2.4.1.1. Service Behavior		2.4.1.1. Service Behavior
	The service generates a public/private key pair. This key pair MUST		The service generates a public/private key pair. This key pair MUST
	be stored in stable storage; if there is no writable stable storage		be stored in stable storage; if there is no writable stable storage
	on the client, the client MUST be pre-configured with a public/		on the client, the client MUST be pre-configured with a public/
	private key pair that can be used.		private key pair that can be used.
	When sending DNS updates, the service includes a KEY record		When sending DNS updates, the service includes a KEY record
	containing the public portion of the key, which is stored as an RRset		containing the public portion of the key in each Host Description
	under the Service Instance Name. It is permissible for a device that		update. The update is signed using SIG(0), using the private key
	offers more than one service under more than one Service Instance		that corresponds to the public key in the KEY record. The lifetimes
	Name to use the same KEY on each such name.		of the records in the update is set using the EDNS(0) Update Lease
			option.
	The update is signed using SIG(0), using the private key that
	corresponds to the public key in the KEY record.
	The lifetime of the DNS-SD PTR, SRV and TXT records [RFC6763] is		The lifetime of the DNS-SD PTR, SRV, A, AAAA and TXT records
	typically set to two hours. This means that if a device is		[RFC6763] is typically set to two hours. This means that if a device
	disconnected from the network, it does not appear in the user		is disconnected from the network, it does not appear in the user
	interfaces of devices looking for services of that type for too long.		interfaces of devices looking for services of that type for too long.
	However, the lifetime of its DNS SIG(0) public key should be set to a		However, the lifetime of its KEY record should be set to a much
	much longer time, typically 14 days. The result of this is that even		longer time, typically 14 days. The result of this is that even
	though a device may be temporarily unplugged, disappearing from the		though a device may be temporarily unplugged, disappearing from the
	network for a few days, it makes a claim on its name that lasts much		network for a few days, it makes a claim on its name that lasts much
	longer.		longer.
	This way, even if a device is unplugged from the network for a few		This way, even if a device is unplugged from the network for a few
	days, and its services are not available for that time, no other		days, and its services are not available for that time, no other
	rogue device can come along and immediately claim its name the moment		rogue device can come along and immediately claim its name the moment
	it disappears from the network, and yet the name is eventually		it disappears from the network. In the event that a device is
	cleaned up and made available for re-use.		unplugged from the network and permanently discarded, then its name
			is eventually cleaned up and made available for re-use.
	2.4.1.2. Registration Server Behavior		2.4.2. Registration Server Behavior
	The Registration server checks that the DNS update contains a Service		The Registration server checks each update in the Registration to see
	Instance Name. In principle, each name in the update should be		that it contains a Service Discovery update, a Service Description
	evaluated as a candidate Service Instance Name. However, some names		update, and a Host Description update.
	will obviously be Service Names, and these can be skipped when
	evaluating candidates. In order for a candidate to actually be a
	service instance name, the following conditions must be true:
	o There is at least one name that turns out NOT to be a Service		An update is a Service Discovery update if it contains
	Instance Name for which there is a PTR RRset update that includes
	a record pointing to the candidate.
	o The candidate includes an SRV record		o exactly one RRset update,
	o The candidate includes a KEY record		o which is for a PTR RR,
			o which points to a Service Instance Name
			o for which an update is present in the Registration.
	If an update does not contain a valid Service Instance Name, or if it		An update is a Service Description update if, for the appropriate
	contains an update to a PTR RRset that references a name that is not		Service Instance Name, it contains
	the Service Instance Name being updated, the update is rejected with
	the NOTAUTH RCODE.
	If an update contains an SRV record that contains an IP address other		o exactly one "Delete all RRsets from a name" update,
	than the IP address from which the update was recieved, the update is		o exactly one SRV RRset update,
	rejected with the NOTAUTH RCODE.		o one or more TXT RRset updates,
			o and the target of the SRV record update references a hostname for
			which there is a Host Description update in the Registration.
	Once each name for which there are updates in the DNS Update has been		An update is a Host Description update if, for the appropriate
	considered as a candidate, it should be the case that only one name		hostname, it contains
	is actually a possible Service Instance Name. If more than one name
	is still a possible candidate, then the DNS Update is rejected with
	the FORMERR RCODE.
	If there is only one candidate, then the server checks to see if that		o exactly one "Delete all RRsets from a name" update,
	name already exists. If it does already exist, then the server		o A or AAAA RR update(s)
	checks to see if the KEY record on the name is the same as the one in		o a KEY RR update that adds a KEY RR that contains the public key
	the update for that name. If it is not, then the DNS Update is		corresponding to the private key that was used to sign the
	rejected with the YXDOMAIN RCODE.		message,
			o there is a Service Instance Name update in the Registration that
			updates an SRV RR so that it points to the hostname being updated
			by this update.
	Otherwise, the server validates the update using SIG(0). If the		A Registration MUST include at least one Service Name update, at
	validation fails, the update is rejected with NOTAUTH. Otherwise,		least one Service Description update, and exactly one Host
	the update is evaluated according to the rules described in RFC2136		Description update. An update message that does not is not a
	for processing DNS updates, and whatever the correct result is is		Registration. An update message that contains any other updates, or
	returned.		any update constraints, is not a Registration. Such messages should
			either be processed as regular RFC2136 updates, including access
			control checks and constraint checks, if supported, or else rejected
			with RCODE=REFUSED.
			Note that if the definitions of each of these update types are
			followed carefully, this means that many things that look very much
			like Registrations nevertheless are not. For example, a Registration
			that contains an update to a Service Name and an update to a Service
			Instance Name, where the Service Name does not reference the Service
			Instance Name, is not a valid Registration message, but may be a
			valid RFC2136 update.
			Assuming that an update message has been validated with these
			conditions and is a valid Registration, the server checks that the
			name in the Host Description update exists. If so, then the server
			checks to see if the KEY record on the name is the same as the KEY
			record in the update. If it is not, then the server MUST reject the
			Registration with the YXDOMAIN RCODE.
			Otherwise, the server validates the update using SIG(0) on the public
			key in the KEY record of the Host Description update. If the
			validation fails, the server MUST reject the rejectration rejected
			with the REFUSED RCODE. Otherwise, the update is considered valid
			and authentic, and is processed according to the method described in
			RFC2136. The status that is returned depends on the result of
			processing the update.
			The server MAY add a Reverse Mapping that corresponds to the Host
			Description. This is not required because the Reverse Mapping serves
			no protocol function, but it may be useful for debugging, e.g. in
			annotating network packet traces or logs.
	The server MAY apply additional criteria when accepting updates. In		The server MAY apply additional criteria when accepting updates. In
	some networks, it may be possible to do out-of-band registration of		some networks, it may be possible to do out-of-band registration of
	keys, and only accept updates from pre-registered keys. In this		keys, and only accept updates from pre-registered keys. In this
	case, an update for a key that has not been registered should be		case, an update for a key that has not been registered should be
	rejected using NOTAUTH.		rejected with the REFUSED RCODE.
	There are at least two benefits to doing this rather than simply		There are at least two benefits to doing this rather than simply
	using normal SIG(0) DNS updates. First, the same registration		using normal SIG(0) DNS updates. First, the same registration
	protocol can be used in both cases, so both use cases can be		protocol can be used in both cases, so both use cases can be
	addressed by the same implementation. Second, the registration		addressed by the same service implementation. Second, the
	protocol includes maintenance functionality not present with normal		registration protocol includes maintenance functionality not present
	DNS updates.		with normal DNS updates.
			Note that the semantics of using the Registration Protocol in this
			way are different than for typical RFC2136 implementations: the KEY
			used to sign the update in the Registration Protocol only allows the
			client to update records that refer to its Host Description. RFC2136
			implementations do not normally provide a way to enforce a constraint
			of this type.
	The server may also have a dictionary of names or name patterns that		The server may also have a dictionary of names or name patterns that
	are not permitted. If such a list is used, updates for Service		are not permitted. If such a list is used, updates for Service
	Instance Names that match entries in the dictionary are rejected with		Instance Names that match entries in the dictionary are rejected with
	YXDOMAIN.		YXDOMAIN.
	2.5. Maintenance		2.5. TTL Consistency
	2.5.1. Cleaning up stale data		All RRs within an RRset are required to have the same TTL
			(Clarifications to the DNS Specification [RFC2181], Section 5.2). In
			order to avoid inconsistencies, the Registration Protocol places
			restrictions on TTLs sent by services and requires that Registration
			Protocol Servers enforce consistency.
			Services sending Registrations MUST use consistent TTLs in all RRs
			within the Registration.
			Registration Protocol servers MUST check that the TTLs for all RRs
			within the Registration are the same. If they are not, the
			Registration MUST be rejected with a REFUSED RCODE.
			Additionally, when adding RRs to an RRset, for example when
			processing Service Discovery records, the server MUST use the same
			TTL on all RRs in the RRset. How this consistency is enforced is up
			to the implementation.
			2.6. Maintenance
			2.6.1. Cleaning up stale data
	Because the DNS-SD registration protocol is automatic, and not		Because the DNS-SD registration protocol is automatic, and not
	managed by humans, some additional bookkeeping is required. When an		managed by humans, some additional bookkeeping is required. When an
	update is constructed by the client, it MUST include include an		update is constructed by the client, it MUST include include an
	EDNS(0) Update Lease option and an EDNS(0) Instance Lease option.		EDNS(0) Update Lease Option [I-D.sekar-dns-ul]. The Update Lease
			Option contains two lease times: the Update Lease Time and the
			Instance Lease Time.
	These leases are promises, similar to DHCP leases [RFC2131], from the		These leases are promises, similar to DHCP leases [RFC2131], from the
	client that it will send a new update for the service registration		client that it will send a new update for the service registration
	before the lease time expires. The Update Lease time is chosen to		before the lease time expires. The Update Lease time is chosen to
	represent the time after the update during which the registered		represent the time after the update during which the registered
	records other than the KEY record should be assumed to be valid. The		records other than the KEY record should be assumed to be valid. The
	Instance Lease time represents the time after the update during which		Instance Lease time represents the time after the update during which
	the KEY record should be assumed to be valid.		the KEY record should be assumed to be valid.
	The reasoning behind the different lease times is discussed in the		The reasoning behind the different lease times is discussed in the
	section on first-come, first-served naming Section 2.4.1. DNS-SD		section on first-come, first-served naming Section 2.4.1. DNS-SD
	Registration Protocol servers may be configured with limits for these		Registration Protocol servers may be configured with limits for these
	values. A default limit of two hours for the Update Lease and 30		values. A default limit of two hours for the Update Lease and 14
	days for the Instance Lease are currently thought to be good choices.		days for the SIG(0) KEY are currently thought to be good choices.
	Clients that are going to continue to use names on which they hold		Clients that are going to continue to use names on which they hold
	leases should update well before the lease ends, in case the		leases should update well before the lease ends, in case the
	registration service is unavailable or under heavy load.		registration service is unavailable or under heavy load.
			The Registration Protocol server MUST include an EDNS(0) Update Lease
			option in the response if the lease time proposed by the service has
			been shortened. The service MUST check for the EDNS(0) Update Lease
			option in the response and MUST use the lease times from that option
			in place of the options that it sent to the server when deciding when
			to update its registration.
	Clients should assume that each lease ends N seconds after the update		Clients should assume that each lease ends N seconds after the update
	was first transmitted, where N is the number included in the option.		was first transmitted, where N is the lease duration. Servers should
	Servers should assume that each lease ends N seconds after the update		assume that each lease ends N seconds after the update that was
	that was successfully processed was received. Because the server		successfully processed was received. Because the server will always
	will always receive the update after the client sent it, this avoids		receive the update after the client sent it, this avoids the
	the possibility of misunderstandings.		possibility of misunderstandings.
	DNS-SD Registration Protocol servers SHOULD reject updates that do		DNS-SD Registration Protocol servers MUST reject updates that do not
	not include a DNS update lease time. Dual-use servers may accept		include an EDNS(0) Update Lease option. Dual-use servers MAY accept
	updates that don't include leases, but SHOULD differentiate between		updates that don't include leases, but SHOULD differentiate between
	DNS-SD registration protocol updates and other updates, and SHOULD		DNS-SD registration protocol updates and other updates, and MUST
	reject updates that are known to be DNS-SD registration protocol		reject updates that are known to be DNS-SD Registration Protocol
	updates if they do not include leases.		updates if they do not include leases.
	2.5.2. Sleep Proxy		2.6.2. Sleep Proxy
	Another use of Service Registration Protocol is for devices that		Another use of Service Registration Protocol is for devices that
	sleep to reduce power consumption.		sleep to reduce power consumption.
	In this case, in addition to the DNS Update Lease option		In this case, in addition to the DNS Update Lease option
	[I-D.sekar-dns-ul] described above, the device includes an EDNS(0)		[I-D.sekar-dns-ul] described above, the device includes an EDNS(0)
	OWNER Option [I-D.cheshire-edns0-owner-option].		OWNER Option [I-D.cheshire-edns0-owner-option].
	The DNS Update Lease option constitutes a promise by the device that		The EDNS(0) Update Lease option constitutes a promise by the device
	it will wake up before this time elapses, to renew its records and		that it will wake up before this time elapses, to renew its
	thereby demonstrate that it is still attached to the network. If it		registration and thereby demonstrate that it is still attached to the
	fails to renew the records by this time, that indicates that it is no		network. If it fails to renew the registration by this time, that
	longer attached to the network, and its records should be deleted.		indicates that it is no longer attached to the network, and its
			registration (except for the KEY in the Host Description) should be
			deleted.
	The EDNS(0) OWNER Option indicates that the device will be asleep,		The EDNS(0) OWNER Option indicates that the device will be asleep,
	and will not be receptive to normal network traffic. When a DNS		and will not be receptive to normal network traffic. When a DNS
	server receives a DNS Update with an EDNS(0) OWNER Option, that		server receives a DNS Update with an EDNS(0) OWNER Option, that
	signifies that the DNS server should act as a proxy for any IPv4 or		signifies that the Registration Protocol server should set up a proxy
	IPv6 address records in the DNS Update message. This means that the		for any IPv4 or IPv6 address records in the DNS Update message. This
	DNS server should send ARP or ND messages claiming ownership of the		proxy should send ARP or ND messages claiming ownership of the IPv4
	IPv4 and/or IPv6 addresses in the records in question. In addition,		and/or IPv6 addresses in the records in question. In addition, proxy
	the DNS server should answer future ARP or ND requests for those IPv4		should answer future ARP or ND requests for those IPv4 and/or IPv6
	and/or IPv6 addresses, claiming ownership of them. When the DNS		addresses, claiming ownership of them. When the DNS server receives
	server receives a TCP SYN or UDP packet addressed to one of the IPv4		a TCP SYN or UDP packet addressed to one of the IPv4 or IPv6
	or IPv6 addresses for which it proxying, it should then wake up the		addresses for which it proxying, it should then wake up the sleeping
	sleeping device using the information in the EDNS(0) OWNER Option.		device using the information in the EDNS(0) OWNER Option. At present
	At present version 0 of the OWNER Option specifies the "Wake-on-LAN		version 0 of the OWNER Option specifies the "Wake-on-LAN Magic
	Magic Packet" that needs to be sent; future versions could be		Packet" that needs to be sent; future versions could be extended to
	extended to specify other wakeup mechanisms.		specify other wakeup mechanisms.
			Note that although the authoritative DNS server that implements the
			DNSSD Service Registration Protocol function need not be on the same
			link as the sleeping host, the Sleep Proxy must be on the same link.
	3. Security Considerations		3. Security Considerations
	DNS-SD Service Registration Protocol updates have no authorization		DNS-SD Service Registration Protocol updates have no authorization
	semantics other than first-come, first-served. This means that if an		semantics other than first-come, first-served. This means that if an
	attacker from outside of the administrative domain of the server		attacker from outside of the administrative domain of the server
	knows the server's IP address, it can in principle send updates to		knows the server's IP address, it can in principle send updates to
	the server that will be processed successfully. Servers should		the server that will be processed successfully. Servers should
	therefore be configured to reject updates from source addresses		therefore be configured to reject updates from source addresses
	outside of the administrative domain of the server.		outside of the administrative domain of the server.
			For Anycast updates, this validation must be enforced by every router
			that connects the CDN to the unconstrained portion of the network.
			For TCP updates, the initial SYN-SYN+ACK handshake prevents updates
			being forged from off-network. In order to ensure that this
			handshake happens, Service Discovery Protocol servers MUST NOT accept
			0-RTT TCP payloads.
	Note that these rules only apply to the validation of DNS-SD		Note that these rules only apply to the validation of DNS-SD
	registration protocol updates. A server that accepts updates from		registration protocol updates. A server that accepts updates from
	DNS-SD registration protocol clients may also accept other DNS		DNS-SD registration protocol clients may also accept other DNS
	updates, and those DNS updates may be validated using different		updates, and those DNS updates may be validated using different
	rules. However, in the case of a DNS service that accepts automatic		rules. However, in the case of a DNS service that accepts automatic
	updates, the intersection of the DNS-SD service registration update		updates, the intersection of the DNS-SD service registration update
	rules and whatever other update rules are present must be considered		rules and whatever other update rules are present must be considered
	very carefully.		very carefully.
			For example, a normal, authenticated RFC2136 update to any RR that
			was added using the Registration protocol, but that is authenticated
			using a different key, could be used to override a promise made by
			the registration protocol, by replacing all or part of the service
			registration information with information provided by a different
			client. An implementation that allows both kinds of updates should
			not allow updates to records added by Registrations using different
			authentication and authorization credentials.
	4. Privacy Considerations		4. Privacy Considerations
	5. References		5. Acknowledgments
	5.1. Normative References
			Thanks to Toke Hoeiland-Joergensen for a thorough technical review,
			to Tamara Kemper for doing a nice developmental edit, Tim Wattenberg
			for doing a service implementation at the Montreal Hackathon at IETF
			102, and [...] more reviewers to come, hopefully.
			6. References
			6.1. Normative References
	[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service		[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
	Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,		Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
	<https://www.rfc-editor.org/info/rfc6763>.		<https://www.rfc-editor.org/info/rfc6763>.
	5.2. Informative References		[I-D.sekar-dns-ul]
			Sekar, K., "Dynamic DNS Update Leases", draft-sekar-dns-
			ul-01 (work in progress), August 2006.
			6.2. Informative References
			[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
			STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
			<https://www.rfc-editor.org/info/rfc1034>.
	[RFC1035] Mockapetris, P., "Domain names - implementation and		[RFC1035] Mockapetris, P., "Domain names - implementation and
	specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,		specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
	November 1987, <https://www.rfc-editor.org/info/rfc1035>.		November 1987, <https://www.rfc-editor.org/info/rfc1035>.
	[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",		[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
	RFC 2131, DOI 10.17487/RFC2131, March 1997,		RFC 2131, DOI 10.17487/RFC2131, March 1997,
	<https://www.rfc-editor.org/info/rfc2131>.		<https://www.rfc-editor.org/info/rfc2131>.
	[RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound,		[RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound,
	"Dynamic Updates in the Domain Name System (DNS UPDATE)",		"Dynamic Updates in the Domain Name System (DNS UPDATE)",
	RFC 2136, DOI 10.17487/RFC2136, April 1997,		RFC 2136, DOI 10.17487/RFC2136, April 1997,
	<https://www.rfc-editor.org/info/rfc2136>.		<https://www.rfc-editor.org/info/rfc2136>.
			[RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS
			Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997,
			<https://www.rfc-editor.org/info/rfc2181>.
	[RFC2931] Eastlake 3rd, D., "DNS Request and Transaction Signatures		[RFC2931] Eastlake 3rd, D., "DNS Request and Transaction Signatures
	( SIG(0)s )", RFC 2931, DOI 10.17487/RFC2931, September		( SIG(0)s )", RFC 2931, DOI 10.17487/RFC2931, September
	2000, <https://www.rfc-editor.org/info/rfc2931>.		2000, <https://www.rfc-editor.org/info/rfc2931>.
	[RFC3007] Wellington, B., "Secure Domain Name System (DNS) Dynamic		[RFC3007] Wellington, B., "Secure Domain Name System (DNS) Dynamic
	Update", RFC 3007, DOI 10.17487/RFC3007, November 2000,		Update", RFC 3007, DOI 10.17487/RFC3007, November 2000,
	<https://www.rfc-editor.org/info/rfc3007>.		<https://www.rfc-editor.org/info/rfc3007>.
			[RFC3152] Bush, R., "Delegation of IP6.ARPA", BCP 49, RFC 3152,
			DOI 10.17487/RFC3152, August 2001,
			<https://www.rfc-editor.org/info/rfc3152>.
	[RFC6760] Cheshire, S. and M. Krochmal, "Requirements for a Protocol		[RFC6760] Cheshire, S. and M. Krochmal, "Requirements for a Protocol
	to Replace the AppleTalk Name Binding Protocol (NBP)",		to Replace the AppleTalk Name Binding Protocol (NBP)",
	RFC 6760, DOI 10.17487/RFC6760, February 2013,		RFC 6760, DOI 10.17487/RFC6760, February 2013,
	<https://www.rfc-editor.org/info/rfc6760>.		<https://www.rfc-editor.org/info/rfc6760>.
			[RFC6761] Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
			RFC 6761, DOI 10.17487/RFC6761, February 2013,
			<https://www.rfc-editor.org/info/rfc6761>.
	[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,		[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
	DOI 10.17487/RFC6762, February 2013,		DOI 10.17487/RFC6762, February 2013,
	<https://www.rfc-editor.org/info/rfc6762>.		<https://www.rfc-editor.org/info/rfc6762>.
			[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
			Constrained-Node Networks", RFC 7228,
			DOI 10.17487/RFC7228, May 2014,
			<https://www.rfc-editor.org/info/rfc7228>.
	[I-D.ietf-dnssd-hybrid]		[I-D.ietf-dnssd-hybrid]
	Cheshire, S., "Discovery Proxy for Multicast DNS-Based		Cheshire, S., "Discovery Proxy for Multicast DNS-Based
	Service Discovery", draft-ietf-dnssd-hybrid-08 (work in		Service Discovery", draft-ietf-dnssd-hybrid-08 (work in
	progress), March 2018.		progress), March 2018.
	[I-D.sekar-dns-ul]		[I-D.ietf-dnssd-push]
	Sekar, K., "Dynamic DNS Update Leases", draft-sekar-dns-		Pusateri, T. and S. Cheshire, "DNS Push Notifications",
	ul-01 (work in progress), August 2006.		draft-ietf-dnssd-push-14 (work in progress), March 2018.
	[I-D.cheshire-dnssd-roadmap]		[I-D.cheshire-dnssd-roadmap]
	Cheshire, S., "Service Discovery Road Map", draft-		Cheshire, S., "Service Discovery Road Map", draft-
	cheshire-dnssd-roadmap-01 (work in progress), March 2018.		cheshire-dnssd-roadmap-01 (work in progress), March 2018.
	[I-D.cheshire-edns0-owner-option]		[I-D.cheshire-edns0-owner-option]
	Cheshire, S. and M. Krochmal, "EDNS0 OWNER Option", draft-		Cheshire, S. and M. Krochmal, "EDNS0 OWNER Option", draft-
	cheshire-edns0-owner-option-01 (work in progress), July		cheshire-edns0-owner-option-01 (work in progress), July
	2017.		2017.
	skipping to change at page 10, line 19 ¶		skipping to change at page 16, line 4 ¶
	[I-D.cheshire-edns0-owner-option]		[I-D.cheshire-edns0-owner-option]
	Cheshire, S. and M. Krochmal, "EDNS0 OWNER Option", draft-		Cheshire, S. and M. Krochmal, "EDNS0 OWNER Option", draft-
	cheshire-edns0-owner-option-01 (work in progress), July		cheshire-edns0-owner-option-01 (work in progress), July
	2017.		2017.
	[ZC] Cheshire, S. and D. Steinberg, "Zero Configuration		[ZC] Cheshire, S. and D. Steinberg, "Zero Configuration
	Networking: The Definitive Guide", O'Reilly Media, Inc. ,		Networking: The Definitive Guide", O'Reilly Media, Inc. ,
	ISBN 0-596-10100-7, December 2005.		ISBN 0-596-10100-7, December 2005.
	Authors' Addresses		Authors' Addresses
	Stuart Cheshire		Stuart Cheshire
	Apple Inc.		Apple Inc.
	1 Infinite Loop		One Apple Park Way
	Cupertino, California 95014		Cupertino, California 95014
	USA		USA
	Phone: +1 408 974 3207		Phone: +1 408 974 3207
	Email: cheshire@apple.com		Email: cheshire@apple.com
	Ted Lemon		Ted Lemon
	Nibbhaya Consulting		Nibbhaya Consulting
	P.O. Box 958		P.O. Box 958
	Brattleboro, Vermont 05302		Brattleboro, Vermont 05302
End of changes. 52 change blocks.
	168 lines changed or deleted		428 lines changed or added
This html diff was produced by rfcdiff 1.47. The latest version is available from http://tools.ietf.org/tools/rfcdiff/