draft-ietf-dnssd-push-18.txt		draft-ietf-dnssd-push-19.txt
	Internet Engineering Task Force T. Pusateri		Internet Engineering Task Force T. Pusateri
	Internet-Draft Unaffiliated		Internet-Draft Unaffiliated
	Intended status: Standards Track S. Cheshire		Intended status: Standards Track S. Cheshire
	Expires: September 12, 2019 Apple Inc.		Expires: September 25, 2019 Apple Inc.
	March 11, 2019		March 24, 2019
	DNS Push Notifications		DNS Push Notifications
	draft-ietf-dnssd-push-18		draft-ietf-dnssd-push-19
	Abstract		Abstract
	The Domain Name System (DNS) was designed to return matching records		The Domain Name System (DNS) was designed to return matching records
	efficiently for queries for data that are relatively static. When		efficiently for queries for data that are relatively static. When
	those records change frequently, DNS is still efficient at returning		those records change frequently, DNS is still efficient at returning
	the updated results when polled, as long as the polling rate is not		the updated results when polled, as long as the polling rate is not
	too high. But there exists no mechanism for a client to be		too high. But there exists no mechanism for a client to be
	asynchronously notified when these changes occur. This document		asynchronously notified when these changes occur. This document
	defines a mechanism for a client to be notified of such changes to		defines a mechanism for a client to be notified of such changes to
	skipping to change at page 1, line 38 ¶		skipping to change at page 1, line 38 ¶
	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 September 12, 2019.		This Internet-Draft will expire on September 25, 2019.
	Copyright Notice		Copyright Notice
	Copyright (c) 2019 IETF Trust and the persons identified as the		Copyright (c) 2019 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 4, line 41 ¶		skipping to change at page 4, line 41 ¶
	10.5 Leopard in 2007. Back to My Mac was designed in an era when the		10.5 Leopard in 2007. Back to My Mac was designed in an era when the
	data center operations staff asserted that it was impossible for a		data center operations staff asserted that it was impossible for a
	server to handle large numbers of mostly-idle TCP connections, so LLQ		server to handle large numbers of mostly-idle TCP connections, so LLQ
	was defined as a UDP-based protocol, effectively replicating much of		was defined as a UDP-based protocol, effectively replicating much of
	TCP's connection state management logic in user space, and creating		TCP's connection state management logic in user space, and creating
	its own poor imitations of existing TCP features like the three-way		its own poor imitations of existing TCP features like the three-way
	handshake, flow control, and reliability.		handshake, flow control, and reliability.
	This document builds on experience gained with the LLQ protocol, with		This document builds on experience gained with the LLQ protocol, with
	an improved design. Instead of using UDP, this specification uses		an improved design. Instead of using UDP, this specification uses
	DNS Stateful Operations (DSO) [DSO] running over TLS over TCP, and		DNS Stateful Operations (DSO) [RFC8490] running over TLS over TCP,
	therefore doesn't need to reinvent existing TCP functionality. Using		and therefore doesn't need to reinvent existing TCP functionality.
	TCP also gives long-lived low-traffic connections better longevity		Using TCP also gives long-lived low-traffic connections better
	through NAT gateways without depending on the gateway to support NAT		longevity through NAT gateways without depending on the gateway to
	Port Mapping Protocol (NAT-PMP) [RFC6886] or Port Control Protocol		support NAT Port Mapping Protocol (NAT-PMP) [RFC6886] or Port Control
	(PCP) [RFC6887], or resorting to excessive keepalive traffic.		Protocol (PCP) [RFC6887], or resorting to excessive keepalive
			traffic.
	3. Overview		3. Overview
	A DNS Push Notification client subscribes for Push Notifications for		A DNS Push Notification client subscribes for Push Notifications for
	a particular RRSet by connecting to the appropriate Push Notification		a particular RRSet by connecting to the appropriate Push Notification
	server for that RRSet, and sending DSO message(s) indicating the		server for that RRSet, and sending DSO message(s) indicating the
	RRSet(s) of interest. When the client loses interest in receiving		RRSet(s) of interest. When the client loses interest in receiving
	further updates to these records, it unsubscribes.		further updates to these records, it unsubscribes.
	The DNS Push Notification server for a DNS zone is any server capable		The DNS Push Notification server for a DNS zone is any server capable
	skipping to change at page 6, line 27 ¶		skipping to change at page 6, line 27 ¶
	(b) A DNS Push Notification client SHOULD NOT routinely keep a DNS		(b) A DNS Push Notification client SHOULD NOT routinely keep a DNS
	Push Notification subscription active 24 hours a day, 7 days a week,		Push Notification subscription active 24 hours a day, 7 days a week,
	just to keep a list in memory up to date so that if the user does		just to keep a list in memory up to date so that if the user does
	choose to bring up an on-screen display of that data, it can be		choose to bring up an on-screen display of that data, it can be
	displayed really fast. DNS Push Notifications are designed to be		displayed really fast. DNS Push Notifications are designed to be
	fast enough that there is no need to pre-load a "warm" list in memory		fast enough that there is no need to pre-load a "warm" list in memory
	just in case it might be needed later.		just in case it might be needed later.
	Generally, as described in the DNS Stateful Operations specification		Generally, as described in the DNS Stateful Operations specification
	[DSO], a client must not keep a session to a server open indefinitely		[RFC8490], a client must not keep a session to a server open
	if it has no subscriptions (or other operations) active on that		indefinitely if it has no subscriptions (or other operations) active
	session. A client MAY close a session as soon as it becomes idle,		on that session. A client MAY close a session as soon as it becomes
	and then if needed in the future, open a new session when required.		idle, and then if needed in the future, open a new session when
	Alternatively, a client MAY speculatively keep an idle session open		required. Alternatively, a client MAY speculatively keep an idle
	for some time, subject to the constraint that it MUST NOT keep a		session open for some time, subject to the constraint that it MUST
	session open that has been idle for more than the session's idle		NOT keep a session open that has been idle for more than the
	timeout (15 seconds by default) [DSO].		session's idle timeout (15 seconds by default) [RFC8490].
	4. Transport		4. Transport
	Other DNS operations like DNS Update [RFC2136] MAY use either User		Other DNS operations like DNS Update [RFC2136] MAY use either User
	Datagram Protocol (UDP) [RFC0768] or Transmission Control Protocol		Datagram Protocol (UDP) [RFC0768] or Transmission Control Protocol
	(TCP) [RFC0793] as the transport protocol, in keeping with the		(TCP) [RFC0793] as the transport protocol, in keeping with the
	historical precedent that DNS queries must first be sent over UDP		historical precedent that DNS queries must first be sent over UDP
	[RFC1123]. This requirement to use UDP has subsequently been relaxed		[RFC1123]. This requirement to use UDP has subsequently been relaxed
	[RFC7766].		[RFC7766].
	In keeping with the more recent precedent, DNS Push Notification is		In keeping with the more recent precedent, DNS Push Notification is
	defined only for TCP. DNS Push Notification clients MUST use DNS		defined only for TCP. DNS Push Notification clients MUST use DNS
	Stateful Operations (DSO) [DSO] running over TLS over TCP [RFC7858].		Stateful Operations [RFC8490] running over TLS over TCP [RFC7858].
	Connection setup over TCP ensures return reachability and alleviates		Connection setup over TCP ensures return reachability and alleviates
	concerns of state overload at the server through anonymous		concerns of state overload at the server through anonymous
	subscriptions. All subscribers are guaranteed to be reachable by the		subscriptions. All subscribers are guaranteed to be reachable by the
	server by virtue of the TCP three-way handshake. Flooding attacks		server by virtue of the TCP three-way handshake. Flooding attacks
	are possible with any protocol, and a benefit of TCP is that there		are possible with any protocol, and a benefit of TCP is that there
	are already established industry best practices to guard against SYN		are already established industry best practices to guard against SYN
	flooding and similar attacks [SYN] [RFC4953].		flooding and similar attacks [SYN] [RFC4953].
	Use of TCP also allows DNS Push Notifications to take advantage of		Use of TCP also allows DNS Push Notifications to take advantage of
	skipping to change at page 9, line 8 ¶		skipping to change at page 9, line 8 ¶
	employ various techniques to limit subscriptions to a manageable		employ various techniques to limit subscriptions to a manageable
	level. Correspondingly, the client is free to establish simultaneous		level. Correspondingly, the client is free to establish simultaneous
	sessions to alternate DNS servers that support DNS Push Notifications		sessions to alternate DNS servers that support DNS Push Notifications
	for the zone and distribute subscriptions at the client's discretion.		for the zone and distribute subscriptions at the client's discretion.
	In this way, both clients and servers can react to resource		In this way, both clients and servers can react to resource
	constraints.		constraints.
	6. Protocol Operation		6. Protocol Operation
	The DNS Push Notification protocol is a session-oriented protocol,		The DNS Push Notification protocol is a session-oriented protocol,
	and makes use of DNS Stateful Operations (DSO) [DSO].		and makes use of DNS Stateful Operations (DSO) [RFC8490].
	For details of the DSO message format refer to the DNS Stateful		For details of the DSO message format refer to the DNS Stateful Oper-
	Operations specification [DSO]. Those details are not repeated here.		ations specification [RFC8490]. Those details are not repeated here.
	DNS Push Notification clients and servers MUST support DSO. A single		DNS Push Notification clients and servers MUST support DSO. A single
	server can support DNS Queries, DNS Updates, and DNS Push		server can support DNS Queries, DNS Updates, and DNS Push
	Notifications (using DSO) on the same TCP port.		Notifications (using DSO) on the same TCP port.
	A DNS Push Notification exchange begins with the client discovering		A DNS Push Notification exchange begins with the client discovering
	the appropriate server, using the procedure described in Section 6.1,		the appropriate server, using the procedure described in Section 6.1,
	and then making a TLS/TCP connection to it.		and then making a TLS/TCP connection to it.
	A typical DNS Push Notification client will immediately issue a DSO		A typical DNS Push Notification client will immediately issue a DSO
	skipping to change at page 10, line 36 ¶		skipping to change at page 10, line 36 ¶
	In many contexts, the recursive resolver will be able to handle Push		In many contexts, the recursive resolver will be able to handle Push
	Notifications for all names that the client may need to follow. Use		Notifications for all names that the client may need to follow. Use
	of VPN tunnels and split-view DNS can create some additional		of VPN tunnels and split-view DNS can create some additional
	complexity in the client software here; the techniques to handle VPN		complexity in the client software here; the techniques to handle VPN
	tunnels and split-view DNS for DNS Push Notifications are the same as		tunnels and split-view DNS for DNS Push Notifications are the same as
	those already used to handle this for normal DNS queries.		those already used to handle this for normal DNS queries.
	If the recursive resolver does not support DNS over TLS, or does		If the recursive resolver does not support DNS over TLS, or does
	support DNS over TLS but is not listening on TCP port 853, or does		support DNS over TLS but is not listening on TCP port 853, or does
	support DNS over TLS on TCP port 853 but does not support DSO on that		support DNS over TLS on TCP port 853 but does not support DSO on that
	port, then the DSO Session session establishment will fail [DSO].		port, then the DSO Session session establishment will fail [RFC8490].
	If the recursive resolver does support DSO but not Push Notification		If the recursive resolver does support DSO but not Push Notification
	subscriptions, then it will return the DSO error code, DSOTYPENI		subscriptions, then it will return the DSO error code, DSOTYPENI
	(11).		(11).
	In some cases, the recursive resolver may support DSO and Push		In some cases, the recursive resolver may support DSO and Push
	Notification subscriptions, but may not be able to subscribe for Push		Notification subscriptions, but may not be able to subscribe for Push
	Notifications for a particular name. In this case, the recursive		Notifications for a particular name. In this case, the recursive
	resolver should return an informative error code to the client so		resolver should return an informative error code to the client so
	that the client can make an informed decision how to handle the		that the client can make an informed decision how to handle the
	skipping to change at page 14, line 8 ¶		skipping to change at page 14, line 8 ¶
	the client device MUST respect the DNS TTL values on records it		the client device MUST respect the DNS TTL values on records it
	receives, and store them in its local cache with this lifetime. This		receives, and store them in its local cache with this lifetime. This
	means that, as long as the DNS TTL values on the authoritative		means that, as long as the DNS TTL values on the authoritative
	records were set to reasonable values, repeated application of this		records were set to reasonable values, repeated application of this
	discovery process can be completed nearly instantaneously by the		discovery process can be completed nearly instantaneously by the
	client, using only locally-stored cached data.		client, using only locally-stored cached data.
	6.2. DNS Push Notification SUBSCRIBE		6.2. DNS Push Notification SUBSCRIBE
	After connecting, and requesting a longer idle timeout and/or		After connecting, and requesting a longer idle timeout and/or
	keepalive interval if necessary, a DNS Push Notification client then		keepalive interval if necessary, a DNS Push Notification client
	indicates its desire to receive DNS Push Notifications for a given		then indicates its desire to receive DNS Push Notifications for
	domain name by sending a SUBSCRIBE request to the server. A		a given domain name by sending a SUBSCRIBE request to the server.
	SUBSCRIBE request is encoded in a DSO message [DSO]. This		A SUBSCRIBE request is encoded in a DSO message [RFC8490].
	specification defines a primary DSO TLV for DNS Push Notification		This specification defines a primary DSO TLV for DNS Push
	SUBSCRIBE Requests (tentatively DSO Type Code 0x40).		Notification SUBSCRIBE Requests (tentatively DSO Type Code 0x40).
	The entity that initiates a SUBSCRIBE request is by definition the		The entity that initiates a SUBSCRIBE request is by definition the
	client. A server MUST NOT send a SUBSCRIBE request over an existing		client. A server MUST NOT send a SUBSCRIBE request over an existing
	session from a client. If a server does send a SUBSCRIBE request		session from a client. If a server does send a SUBSCRIBE request
	over a DSO session initiated by a client, this is a fatal error and		over a DSO session initiated by a client, this is a fatal error and
	the client should immediately abort the connection with a TCP RST (or		the client should immediately abort the connection with a TCP RST (or
	equivalent for other protocols).		equivalent for other protocols).
	6.2.1. SUBSCRIBE Request		6.2.1. SUBSCRIBE Request
	A SUBSCRIBE request begins with the standard DSO 12-byte header		A SUBSCRIBE request begins with the standard DSO 12-byte header
	[DSO], followed by the SUBSCRIBE primary TLV. A SUBSCRIBE request		[RFC8490], followed by the SUBSCRIBE primary TLV. A SUBSCRIBE
	message is illustrated in Figure 1.		request message is illustrated in Figure 1.
	The MESSAGE ID field MUST be set to a unique value, that the client		The MESSAGE ID field MUST be set to a unique value, that the client
	is not using for any other active operation on this DSO session. For		is not using for any other active operation on this DSO session. For
	the purposes here, a MESSAGE ID is in use on this session if the		the purposes here, a MESSAGE ID is in use on this session if the
	client has used it in a request for which it has not yet received a		client has used it in a request for which it has not yet received a
	response, or if the client has used it for a subscription which it		response, or if the client has used it for a subscription which it
	has not yet cancelled using UNSUBSCRIBE. In the SUBSCRIBE response		has not yet cancelled using UNSUBSCRIBE. In the SUBSCRIBE response
	the server MUST echo back the MESSAGE ID value unchanged.		the server MUST echo back the MESSAGE ID value unchanged.
	The other header fields MUST be set as described in the DSO		The other header fields MUST be set as described in the DSO spec-
	specification [DSO]. The DNS OPCODE field contains the OPCODE value		ification [RFC8490]. The DNS OPCODE field contains the OPCODE value
	for DNS Stateful Operations (6). The four count fields MUST be zero,		for DNS Stateful Operations (6). The four count fields MUST be zero,
	and the corresponding four sections MUST be empty (i.e., absent).		and the corresponding four sections MUST be empty (i.e., absent).
	The DSO-TYPE is SUBSCRIBE (tentatively 0x40).		The DSO-TYPE is SUBSCRIBE (tentatively 0x40).
	The DSO-LENGTH is the length of the DSO-DATA that follows, which		The DSO-LENGTH is the length of the DSO-DATA that follows, which
	specifies the name, type, and class of the record(s) being sought.		specifies the name, type, and class of the record(s) being sought.
	1 1 1 1 1 1		1 1 1 1 1 1
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5		0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
	skipping to change at page 17, line 11 ¶		skipping to change at page 17, line 11 ¶
	where one or both of TYPE or CLASS are 255, the server MUST send Push		where one or both of TYPE or CLASS are 255, the server MUST send Push
	Notification Updates for ALL record changes that match the		Notification Updates for ALL record changes that match the
	subscription, not just some of them.		subscription, not just some of them.
	6.2.2. SUBSCRIBE Response		6.2.2. SUBSCRIBE Response
	Each SUBSCRIBE request generates exactly one SUBSCRIBE response from		Each SUBSCRIBE request generates exactly one SUBSCRIBE response from
	the server.		the server.
	A SUBSCRIBE response begins with the standard DSO 12-byte header		A SUBSCRIBE response begins with the standard DSO 12-byte header
	[DSO], possibly followed by one or more optional TLVs, such as a		[RFC8490], possibly followed by one or more optional TLVs, such as a
	Retry Delay TLV.		Retry Delay TLV.
	The MESSAGE ID field MUST echo the value given in the ID field of the		The MESSAGE ID field MUST echo the value given in the ID field of the
	SUBSCRIBE request. This is how the client knows which request is		SUBSCRIBE request. This is how the client knows which request is
	being responded to.		being responded to.
	A SUBSCRIBE response message MUST NOT include a SUBSCRIBE TLV. If a		A SUBSCRIBE response message MUST NOT include a SUBSCRIBE TLV. If a
	client receives a SUBSCRIBE response message containing a SUBSCRIBE		client receives a SUBSCRIBE response message containing a SUBSCRIBE
	TLV then the response message is processed but the SUBSCRIBE TLV MUST		TLV then the response message is processed but the SUBSCRIBE TLV MUST
	be silently ignored.		be silently ignored.
	skipping to change at page 18, line 23 ¶		skipping to change at page 18, line 23 ¶
	server right away. If multiple SRV records were returned as		server right away. If multiple SRV records were returned as
	described in Section 6.1, Paragraph 7, a subsequent server can be		described in Section 6.1, Paragraph 7, a subsequent server can be
	tried immediately.		tried immediately.
	If the client has other successful subscriptions to this server,		If the client has other successful subscriptions to this server,
	these subscriptions remain even though additional subscriptions may		these subscriptions remain even though additional subscriptions may
	be refused. Neither the client nor the server are required to close		be refused. Neither the client nor the server are required to close
	the connection, although, either end may choose to do so.		the connection, although, either end may choose to do so.
	If the server sends a nonzero RCODE then it SHOULD append a Retry		If the server sends a nonzero RCODE then it SHOULD append a Retry
	Delay TLV [DSO] to the response specifying a delay before the client		Delay TLV [RFC8490] to the response specifying a delay before the
	attempts this operation again. Recommended values for the delay for		client attempts this operation again. Recommended values for the
	different RCODE values are given below. These recommended values		delay for different RCODE values are given below. These recommended
	apply both to the default values a server should place in the Retry		values apply both to the default values a server should place in the
	Delay TLV, and the default values a client should assume if the		Retry Delay TLV, and the default values a client should assume if the
	server provides no Retry Delay TLV.		server provides no Retry Delay TLV.
	For RCODE = 1 (FORMERR) the delay may be any value selected by the		For RCODE = 1 (FORMERR) the delay may be any value selected by the
	implementer. A value of five minutes is RECOMMENDED, to reduce		implementer. A value of five minutes is RECOMMENDED, to reduce
	the risk of high load from defective clients.		the risk of high load from defective clients.
	For RCODE = 2 (SERVFAIL) the delay should be chosen according to		For RCODE = 2 (SERVFAIL) the delay should be chosen according to
	the level of server overload and the anticipated duration of that		the level of server overload and the anticipated duration of that
	overload. By default, a value of one minute is RECOMMENDED. If a		overload. By default, a value of one minute is RECOMMENDED. If a
	more serious server failure occurs, the delay may be longer in		more serious server failure occurs, the delay may be longer in
	accordance with the specific problem encountered.		accordance with the specific problem encountered.
	For RCODE = 4 (NOTIMP), which occurs on a server that doesn't		For RCODE = 4 (NOTIMP), which occurs on a server that doesn't
	implement DNS Stateful Operations [DSO], it is unlikely that the		implement DNS Stateful Operations [RFC8490], it is unlikely that
	server will begin supporting DSO in the next few minutes, so the		the server will begin supporting DSO in the next few minutes, so
	retry delay SHOULD be one hour. Note that in such a case, a		the retry delay SHOULD be one hour. Note that in such a case, a
	server that doesn't implement DSO is unlikely to place a Retry		server that doesn't implement DSO is unlikely to place a Retry
	Delay TLV in its response, so this recommended value in particular		Delay TLV in its response, so this recommended value in particular
	applies to what a client should assume by default.		applies to what a client should assume by default.
	For RCODE = 5 (REFUSED), which occurs on a server that implements		For RCODE = 5 (REFUSED), which occurs on a server that implements
	DNS Push Notifications, but is currently configured to disallow		DNS Push Notifications, but is currently configured to disallow
	DNS Push Notifications, the retry delay may be any value selected		DNS Push Notifications, the retry delay may be any value selected
	by the implementer and/or configured by the operator.		by the implementer and/or configured by the operator.
	If the server being queried is listed in a		If the server being queried is listed in a
	skipping to change at page 19, line 47 ¶		skipping to change at page 19, line 47 ¶
	For RCODE = 9 (NOTAUTH), the time delay applies to requests for other		For RCODE = 9 (NOTAUTH), the time delay applies to requests for other
	names falling within the same zone. Requests for names falling		names falling within the same zone. Requests for names falling
	within other zones are not subject to the delay. For all other		within other zones are not subject to the delay. For all other
	RCODEs the time delay applies to all subsequent requests to this		RCODEs the time delay applies to all subsequent requests to this
	server.		server.
	After sending an error response the server MAY allow the session to		After sending an error response the server MAY allow the session to
	remain open, or MAY send a DNS Push Notification Retry Delay		remain open, or MAY send a DNS Push Notification Retry Delay
	Operation TLV instructing the client to close the session, as		Operation TLV instructing the client to close the session, as
	described in the DSO specification [DSO]. Clients MUST correctly		described in the DSO specification [RFC8490]. Clients MUST correctly
	handle both cases.		handle both cases.
	6.3. DNS Push Notification Updates		6.3. DNS Push Notification Updates
	Once a subscription has been successfully established, the server		Once a subscription has been successfully established, the server
	generates PUSH messages to send to the client as appropriate. In the		generates PUSH messages to send to the client as appropriate. In the
	case that the answer set was already non-empty at the moment the		case that the answer set was already non-empty at the moment the
	subscription was established, an initial PUSH message will be sent		subscription was established, an initial PUSH message will be sent
	immediately following the SUBSCRIBE Response. Subsequent changes to		immediately following the SUBSCRIBE Response. Subsequent changes to
	the answer set are then communicated to the client in subsequent PUSH		the answer set are then communicated to the client in subsequent PUSH
	messages.		messages.
	6.3.1. PUSH Message		6.3.1. PUSH Message
	A PUSH unidirectional message begins with the standard DSO 12-byte		A PUSH unidirectional message begins with the standard DSO 12-byte
	header [DSO], followed by the PUSH primary TLV. A PUSH message is		header [RFC8490], followed by the PUSH primary TLV. A PUSH message
	illustrated in Figure 2.		is illustrated in Figure 2.
	In accordance with the definition of DSO unidirectional messages, the		In accordance with the definition of DSO unidirectional messages, the
	MESSAGE ID field MUST be zero. There is no client response to a PUSH		MESSAGE ID field MUST be zero. There is no client response to a PUSH
	message.		message.
	The other header fields MUST be set as described in the DSO		The other header fields MUST be set as described in the DSO spec-
	specification [DSO]. The DNS OPCODE field contains the OPCODE value		ification [RFC8490]. The DNS OPCODE field contains the OPCODE value
	for DNS Stateful Operations (6). The four count fields MUST be zero,		for DNS Stateful Operations (6). The four count fields MUST be zero,
	and the corresponding four sections MUST be empty (i.e., absent).		and the corresponding four sections MUST be empty (i.e., absent).
	The DSO-TYPE is PUSH (tentatively 0x41).		The DSO-TYPE is PUSH (tentatively 0x41).
	The DSO-LENGTH is the length of the DSO-DATA that follows, which		The DSO-LENGTH is the length of the DSO-DATA that follows, which
	specifies the changes being communicated.		specifies the changes being communicated.
	The DSO-DATA contains one or more change notifications. A PUSH		The DSO-DATA contains one or more change notifications. A PUSH
	Message MUST contain at least one change notification. If a PUSH		Message MUST contain at least one change notification. If a PUSH
	Message is received that contains no change notifications, this is a		Message is received that contains no change notifications, this is a
	fatal error, and the receiver MUST immediately terminate the		fatal error, and the receiver MUST immediately terminate the
	connection with a TCP RST (or equivalent for other protocols). The		connection with a TCP RST (or equivalent for other protocols).
	change notifications are formatted similarly to how DNS Resource
	Records are conventionally expressed in DNS messages, and are
	interpreted as described below.
	If the signed 32-bit TTL is in the range 0 to 604,800 seconds (one		The change notification records are formatted similarly to how DNS
	week), then a new DNS Resource Record with the given name, type,		Resource Records are conventionally expressed in DNS messages, as
	class and RDATA is added. The maximum record lifetime supported in a		illustrated in Figure 2, and are interpreted as described below.
	PUSH Message is one week. In the event that the DNS record in
	question has an actual TTL greater than one week, the TTL is reported
	in the PUSH Message as being one week. A TTL of 0 means that this
	record should be retained for as long as the subscription is active,
	and should be discarded immediately the moment the subscription is
	cancelled.
	If the signed 32-bit TTL has the value -1, then the DNS Resource		The TTL field holds an unsigned 32-bit integer [RFC2181]. If the TTL
	Record with the given name, type, class and RDATA is removed.		is in the range 0 to 2,147,483,647 seconds (2^31 - 1, or 0x7FFFFFFF),
			then a new DNS Resource Record with the given name, type, class and
			RDATA is added. A TTL of 0 means that this record should be retained
			for as long as the subscription is active, and should be discarded
			immediately the moment the subscription is cancelled.
	If the signed 32-bit TTL has the value -2, then this is a		If the TTL has the value 0xFFFFFFFF, then the DNS Resource Record
	'collective' remove notification. For collective remove		with the given name, type, class and RDATA is removed.
	notifications RDLEN MUST be zero and consequently the RDATA MUST be
	empty. If a change notification is received where TTL = -2 and RDLEN		If the TTL has the value 0xFFFFFFFE, then this is a 'collective'
	is not zero, this is a fatal error, and the receiver MUST immediately		remove notification. For collective remove notifications RDLEN MUST
			be zero and consequently the RDATA MUST be empty. If a change
			notification is received where TTL = 0xFFFFFFFE and RDLEN is not
			zero, this is a fatal error, and the receiver MUST immediately
	terminate the connection with a TCP RST (or equivalent for other		terminate the connection with a TCP RST (or equivalent for other
	protocols). There are three types of collective remove notification:		protocols). There are three types of collective remove notification:
	For collective remove notifications, if CLASS is ANY, then for the		For collective remove notifications, if CLASS is 255 (ANY), then for
	given name this deletes all records of all types in all classes. In		the given name this deletes all records of all types in all classes.
	this case TYPE MUST be set to ANY on tranmission, and MUST be		In this case TYPE MUST be set to zero on transmission, and MUST be
	silently ignored on reception.		silently ignored on reception.
	For collective remove notifications, if CLASS is not ANY and TYPE is		For collective remove notifications, if CLASS is not 255 (ANY) and
	is ANY then for the given name this deletes all records of all types		TYPE is 255 (ANY) then for the given name this deletes all records of
	in the specified class.		all types in the specified class.
	For collective remove notifications, if CLASS is not ANY and TYPE is		For collective remove notifications, if CLASS is not 255 (ANY) and
	is not ANY then for the given name this deletes all records of the		TYPE is not 255 (ANY) then for the given name this deletes all
	specified type in the specified class.		records of the specified type in the specified class.
	Summary of change notification types:		Summary of change notification types:
	Delete all RRsets from a name, in all classes		Delete all RRsets from a name, in all classes
	TTL=-2, RDLENGTH=0, TYPE=ANY, CLASS=ANY		TTL=0xFFFFFFFE, RDLENGTH=0, CLASS=255 (ANY)
	Delete all RRsets from a name, in given class:		Delete all RRsets from a name, in given class:
	TTL=-2, RDLENGTH=0, TYPE=ANY		TTL=0xFFFFFFFE, RDLENGTH=0, CLASS specifies class, TYPE=255 (ANY)
	CLASS specifies class (usually class "IN")
	Delete specified RRset from a name, in given class:		Delete specified RRset from a name, in given class:
	TTL=-2, RDLENGTH=0		TTL=0xFFFFFFFE, RDLENGTH=0
	CLASS and TYPE specify the RRset being deleted		CLASS and TYPE specify the RRset being deleted
	Delete an individual RR from a name:		Delete an individual RR from a name:
	TTL=-1		TTL=0xFFFFFFFF
	CLASS, TYPE, RDLENGTH and RDATA specify the RR being deleted.		CLASS, TYPE, RDLENGTH and RDATA specify the RR being deleted.
	Add individual RR to a name		Add individual RR to a name
	TTL>=0		TTL>=0
	CLASS, TYPE, RDLENGTH, RDATA and TTL specify the RR being added.		CLASS, TYPE, RDLENGTH, RDATA and TTL specify the RR being added.
	Note that it is valid for the RDATA of an added or removed DNS		Note that it is valid for the RDATA of an added or removed DNS
	Resource Record to be empty (zero length). For example, an Address		Resource Record to be empty (zero length). For example, an Address
	Prefix List Resource Record [RFC3123] may have empty RDATA.		Prefix List Resource Record [RFC3123] may have empty RDATA.
	Therefore, a change notification with RDLEN=0 does not automatically		Therefore, a change notification with RDLEN=0 does not automatically
	indicate a remove notification. If RDLEN=0 and TTL >= 0, this change		indicate a remove notification. If RDLEN=0 and TTL is the in the
	notification signals the addition of a record with the given name,		range 0 - 0x7FFFFFFF, this change notification signals the addition
	type, class, and empty RDATA. If RDLEN=0 and TTL = -1, this change		of a record with the given name, type, class, and empty RDATA. If
	notification signals the removal specifically of that single record		RDLEN=0 and TTL = 0xFFFFFFFF, this change notification signals the
	with the given name, type, class, and empty RDATA.		removal specifically of that single record with the given name, type,
			class, and empty RDATA.
			If the TTL is any value other than 0xFFFFFFFF, 0xFFFFFFFE, or a value
			in the range 0 - 0x7FFFFFFF, then the receiver SHOULD silently ignore
			this particular change notification record. The connection is not
			terminated and other valid change notification records within this
			PUSH message are processed as usual.
	For efficiency, when generating a PUSH message, a server SHOULD		For efficiency, when generating a PUSH message, a server SHOULD
	include as many change notifications as it has immediately available		include as many change notifications as it has immediately available
	to send, rather than sending each change notification as a separate		to send, rather than sending each change notification as a separate
	DSO message. Once it has exhausted the list of change notifications		DSO message. Once it has exhausted the list of change notifications
	immediately available to send, a server SHOULD then send the PUSH		immediately available to send, a server SHOULD then send the PUSH
	message immediately, rather than waiting to see if additional change		message immediately, rather than waiting to see if additional change
	notifications become available.		notifications become available.
	For efficiency, when generating a PUSH message, a server SHOULD use		For efficiency, when generating a PUSH message, a server SHOULD use
	standard DNS name compression, with offsets relative to the beginning		standard DNS name compression, with offsets relative to the beginning
	of the DNS message [RFC1035]. When multiple change notifications in		of the DNS message [RFC1035]. When multiple change notifications in
	a single PUSH message have the same owner name, this name compression		a single PUSH message have the same owner name, this name compression
	can yield significant savings. Name compression should be performed		can yield significant savings. Name compression should be performed
	as specified in Section 18.14 of the Multicast DNS specification		as specified in Section 18.14 of the Multicast DNS specification
	[RFC6762], namely, owner names should always be compressed, and names		[RFC6762], namely, owner names should always be compressed, and names
	appearing within only the RDATA of the following DNS types should be		appearing within RDATA should be compressed for only the RR types
	compressed:		listed below:
	NS, CNAME, PTR, DNAME, SOA, MX, AFSDB, RT, KX, RP, PX, SRV, NSEC		NS, CNAME, PTR, DNAME, SOA, MX, AFSDB, RT, KX, RP, PX, SRV, NSEC
	Servers MAY generate PUSH messages up to a DNS message length of		Servers may generate PUSH messages up to a maximum DNS message length
	16,382 bytes, counting from the start of the DSO 12-byte header.		of 16,382 bytes, counting from the start of the DSO 12-byte header.
	Including the two-byte length prefix that is used to frame DNS over a		Including the two-byte length prefix that is used to frame DNS over a
	byte stream like TLS, this makes a total of 16,384 bytes. Servers		byte stream like TLS, this makes a total of 16,384 bytes. Servers
	SHOULD NOT generate PUSH messages larger than this. Where the		MUST NOT generate PUSH messages larger than this. Where the
	immediately available change notifications are sufficient to exceed a		immediately available change notifications are sufficient to exceed a
	DNS message length of 16,382 bytes, the change notifications SHOULD		DNS message length of 16,382 bytes, the change notifications MUST be
	be communicated in separate PUSH messages of up to 16,382 bytes each.		communicated in separate PUSH messages of up to 16,382 bytes each.
	DNS name compression becomes less effective for messages larger than		DNS name compression becomes less effective for messages larger than
	16,384 bytes, so little efficiency benefit is gained by sending		16,384 bytes, so little efficiency benefit is gained by sending
	messages larger than this.		messages larger than this.
	If a client receives a PUSH message with a DNS message length larger		If a client receives a PUSH message with a DNS message length larger
	than 16,382 bytes, the this is a fatal error, and the receiver MUST		than 16,382 bytes, the this is a fatal error, and the receiver MUST
	immediately terminate the connection with a TCP RST (or equivalent		immediately terminate the connection with a TCP RST (or equivalent
	for other protocols).		for other protocols).
	1 1 1 1 1 1		1 1 1 1 1 1
	skipping to change at page 23, line 31 ¶		skipping to change at page 23, line 33 ¶
	+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+		+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
	| DSO-LENGTH (number of octets in DSO-DATA) |		| DSO-LENGTH (number of octets in DSO-DATA) |
	+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \		+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \
	\ NAME \ \		\ NAME \ \
	+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |		+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
	| TYPE | |		| TYPE | |
	+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |		+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
	| CLASS | |		| CLASS | |
	+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |		+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
	| TTL | |		| TTL | |
	| (32-bit signed big-endian integer) | > DSO-DATA		| (32-bit unsigned big-endian integer) | > DSO-DATA
	+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |		+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
	| RDLEN | |		| RDLEN | |
	+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |		+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
	\ RDATA (sized as necessary) \ |		\ RDATA (sized as necessary) \ |
	+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |		+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
	: NAME, TYPE, CLASS, TTL, RDLEN, RDATA : |		: NAME, TYPE, CLASS, TTL, RDLEN, RDATA : |
	: Repeated As Necessary : /		: Repeated As Necessary : /
	+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /		+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /
	Figure 2: PUSH Message		Figure 2: PUSH Message
	skipping to change at page 24, line 15 ¶		skipping to change at page 24, line 18 ¶
	record addition/deletion is silently ignored. Processing of other		record addition/deletion is silently ignored. Processing of other
	additions and deletions in this message is not affected. The DSO		additions and deletions in this message is not affected. The DSO
	session is not closed. This is to allow for the unavoidable race		session is not closed. This is to allow for the unavoidable race
	condition where a client sends an outbound UNSUBSCRIBE while inbound		condition where a client sends an outbound UNSUBSCRIBE while inbound
	PUSH messages for that subscription from the server are still in		PUSH messages for that subscription from the server are still in
	flight.		flight.
	In the case where a single change affects more than one active		In the case where a single change affects more than one active
	subscription, only one PUSH message is sent. For example, a PUSH		subscription, only one PUSH message is sent. For example, a PUSH
	message adding a given record may match both a SUBSCRIBE request with		message adding a given record may match both a SUBSCRIBE request with
	the same TYPE and a different SUBSCRIBE request with TYPE=ANY. It is		the same TYPE and a different SUBSCRIBE request with TYPE=ANY (255).
	not the case that two PUSH messages are sent because the new record		It is not the case that two PUSH messages are sent because the new
	matches two active subscriptions.		record matches two active subscriptions.
	The server SHOULD encode change notifications in the most efficient		The server SHOULD encode change notifications in the most efficient
	manner possible. For example, when three AAAA records are deleted		manner possible. For example, when three AAAA records are deleted
	from a given name, and no other AAAA records exist for that name, the		from a given name, and no other AAAA records exist for that name, the
	server SHOULD send a "delete an RRset from a name" PUSH message, not		server SHOULD send a "delete an RRset from a name" PUSH message, not
	three separate "delete an individual RR from a name" PUSH messages.		three separate "delete an individual RR from a name" PUSH messages.
	Similarly, when both an SRV and a TXT record are deleted from a given		Similarly, when both an SRV and a TXT record are deleted from a given
	name, and no other records of any kind exist for that name, the		name, and no other records of any kind exist for that name, the
	server SHOULD send a "delete all RRsets from a name" PUSH message,		server SHOULD send a "delete all RRsets from a name" PUSH message,
	not two separate "delete an RRset from a name" PUSH messages.		not two separate "delete an RRset from a name" PUSH messages.
	skipping to change at page 25, line 10 ¶		skipping to change at page 25, line 10 ¶
	record is still there. Once a subscription is cancelled		record is still there. Once a subscription is cancelled
	(individually, or as a result of the DSO session being closed) record		(individually, or as a result of the DSO session being closed) record
	aging for records covered by the subscription resumes and records are		aging for records covered by the subscription resumes and records are
	removed from the local cache when their TTL reaches zero.		removed from the local cache when their TTL reaches zero.
	6.4. DNS Push Notification UNSUBSCRIBE		6.4. DNS Push Notification UNSUBSCRIBE
	To cancel an individual subscription without closing the entire DSO		To cancel an individual subscription without closing the entire DSO
	session, the client sends an UNSUBSCRIBE message over the established		session, the client sends an UNSUBSCRIBE message over the established
	DSO session to the server. The UNSUBSCRIBE message is encoded as a		DSO session to the server. The UNSUBSCRIBE message is encoded as a
	DSO unidirectional message [DSO]. This specification defines a		DSO unidirectional message [RFC8490]. This specification defines a
	primary unidirectional DSO TLV for DNS Push Notification UNSUBSCRIBE		primary unidirectional DSO TLV for DNS Push Notification UNSUBSCRIBE
	Messages (tentatively DSO Type Code 0x42).		Messages (tentatively DSO Type Code 0x42).
	A server MUST NOT initiate an UNSUBSCRIBE message. If a server does		A server MUST NOT initiate an UNSUBSCRIBE message. If a server does
	send an UNSUBSCRIBE message over a DSO session initiated by a client,		send an UNSUBSCRIBE message over a DSO session initiated by a client,
	this is a fatal error and the client should immediately abort the		this is a fatal error and the client should immediately abort the
	connection with a TCP RST (or equivalent for other protocols).		connection with a TCP RST (or equivalent for other protocols).
	6.4.1. UNSUBSCRIBE Message		6.4.1. UNSUBSCRIBE Message
	An UNSUBSCRIBE unidirectional message begins with the standard DSO		An UNSUBSCRIBE unidirectional message begins with the standard DSO
	12-byte header [DSO], followed by the UNSUBSCRIBE primary TLV. An		12-byte header [RFC8490], followed by the UNSUBSCRIBE primary TLV.
	UNSUBSCRIBE message is illustrated in Figure 3.		An UNSUBSCRIBE message is illustrated in Figure 3.
	In accordance with the definition of DSO unidirectional messages, the		In accordance with the definition of DSO unidirectional messages, the
	MESSAGE ID field MUST be zero. There is no server response to an		MESSAGE ID field MUST be zero. There is no server response to an
	UNSUBSCRIBE message.		UNSUBSCRIBE message.
	The other header fields MUST be set as described in the DSO		The other header fields MUST be set as described in the DSO spec-
	specification [DSO]. The DNS OPCODE field contains the OPCODE value		ification [RFC8490]. The DNS OPCODE field contains the OPCODE value
	for DNS Stateful Operations (6). The four count fields MUST be zero,		for DNS Stateful Operations (6). The four count fields MUST be zero,
	and the corresponding four sections MUST be empty (i.e., absent).		and the corresponding four sections MUST be empty (i.e., absent).
	The DSO-TYPE is UNSUBSCRIBE (tentatively 0x42).		The DSO-TYPE is UNSUBSCRIBE (tentatively 0x42).
	The DSO-LENGTH field contains the value 2, the length of the 2-octet		The DSO-LENGTH field contains the value 2, the length of the 2-octet
	MESSAGE ID contained in the DSO-DATA.		MESSAGE ID contained in the DSO-DATA.
	The DSO-DATA contains the value given in the MESSAGE ID field of an		The DSO-DATA contains the value given in the MESSAGE ID field of an
	active SUBSCRIBE request. This is how the server knows which		active SUBSCRIBE request. This is how the server knows which
	skipping to change at page 28, line 8 ¶		skipping to change at page 28, line 8 ¶
	that the disputed records are in fact no longer valid, then		that the disputed records are in fact no longer valid, then
	subsequent DNS PUSH Messages will be generated to inform interested		subsequent DNS PUSH Messages will be generated to inform interested
	clients. Thus, one client discovering that a previously-advertised		clients. Thus, one client discovering that a previously-advertised
	device (like a network printer) is no longer present has the side		device (like a network printer) is no longer present has the side
	effect of informing all other interested clients that the device in		effect of informing all other interested clients that the device in
	question is now gone.		question is now gone.
	6.5.1. RECONFIRM Message		6.5.1. RECONFIRM Message
	A RECONFIRM unidirectional message begins with the standard DSO		A RECONFIRM unidirectional message begins with the standard DSO
	12-byte header [DSO], followed by the RECONFIRM primary TLV. A		12-byte header [RFC8490], followed by the RECONFIRM primary TLV.
	RECONFIRM message is illustrated in Figure 4.		A RECONFIRM message is illustrated in Figure 4.
	In accordance with the definition of DSO unidirectional messages, the		In accordance with the definition of DSO unidirectional messages, the
	MESSAGE ID field MUST be zero. There is no server response to a		MESSAGE ID field MUST be zero. There is no server response to a
	RECONFIRM message.		RECONFIRM message.
	The other header fields MUST be set as described in the DSO		The other header fields MUST be set as described in the DSO spec-
	specification [DSO]. The DNS OPCODE field contains the OPCODE value		ification [RFC8490]. The DNS OPCODE field contains the OPCODE value
	for DNS Stateful Operations (6). The four count fields MUST be zero,		for DNS Stateful Operations (6). The four count fields MUST be zero,
	and the corresponding four sections MUST be empty (i.e., absent).		and the corresponding four sections MUST be empty (i.e., absent).
	The DSO-TYPE is RECONFIRM (tentatively 0x43).		The DSO-TYPE is RECONFIRM (tentatively 0x43).
	The DSO-LENGTH is the length of the data that follows, which		The DSO-LENGTH is the length of the data that follows, which
	specifies the name, type, class, and content of the record being		specifies the name, type, class, and content of the record being
	disputed.		disputed.
	1 1 1 1 1 1		1 1 1 1 1 1
	skipping to change at page 30, line 8 ¶		skipping to change at page 30, line 8 ¶
	DNS wildcarding is not supported. That is, a wildcard ("*") in a		DNS wildcarding is not supported. That is, a wildcard ("*") in a
	RECONFIRM message matches only a literal wildcard character ("*") in		RECONFIRM message matches only a literal wildcard character ("*") in
	the zone, and nothing else.		the zone, and nothing else.
	Aliasing is not supported. That is, a CNAME in a RECONFIRM message		Aliasing is not supported. That is, a CNAME in a RECONFIRM message
	matches only a literal CNAME record in the zone, and nothing else.		matches only a literal CNAME record in the zone, and nothing else.
	6.6. DNS Stateful Operations TLV Context Summary		6.6. DNS Stateful Operations TLV Context Summary
	This document defines four new DSO TLVs. As suggested in Section 8.2		This document defines four new DSO TLVs. As suggested in Section 8.2
	of the DNS Stateful Operations specification [DSO], the valid		of the DNS Stateful Operations specification [RFC8490], the valid
	contexts of these new TLV types are summarized below.		contexts of these new TLV types are summarized below.
	The client TLV contexts are:		The client TLV contexts are:
	C-P: Client request message, primary TLV		C-P: Client request message, primary TLV
	C-U: Client unidirectional message, primary TLV		C-U: Client unidirectional message, primary TLV
	C-A: Client request or unidirectional message, additional TLV		C-A: Client request or unidirectional message, additional TLV
	CRP: Response back to client, primary TLV		CRP: Response back to client, primary TLV
	CRA: Response back to client, additional TLV		CRA: Response back to client, additional TLV
	skipping to change at page 31, line 21 ¶		skipping to change at page 31, line 21 ¶
	subscriptions on that DSO session (by ending the session) it is		subscriptions on that DSO session (by ending the session) it is
	signaling to the server that it is longer interested in receiving		signaling to the server that it is longer interested in receiving
	those particular updates. It is informing the server that the server		those particular updates. It is informing the server that the server
	may release any state information it has been keeping with regards to		may release any state information it has been keeping with regards to
	these particular subscriptions.		these particular subscriptions.
	After terminating its last subscription on a session via UNSUBSCRIBE,		After terminating its last subscription on a session via UNSUBSCRIBE,
	a client MAY close the session immediately, or it may keep it open if		a client MAY close the session immediately, or it may keep it open if
	it anticipates performing further operations on that session in the		it anticipates performing further operations on that session in the
	future. If a client wishes to keep an idle session open, it MUST		future. If a client wishes to keep an idle session open, it MUST
	respect the maximum idle time required by the server [DSO].		respect the maximum idle time required by the server [RFC8490].
	If a client plans to terminate one or more subscriptions on a session		If a client plans to terminate one or more subscriptions on a session
	and doesn't intend to keep that session open, then as an efficiency		and doesn't intend to keep that session open, then as an efficiency
	optimization it MAY instead choose to simply close the session, which		optimization it MAY instead choose to simply close the session, which
	implicitly terminates all subscriptions on that session. This may		implicitly terminates all subscriptions on that session. This may
	occur because the client computer is being shut down, is going to		occur because the client computer is being shut down, is going to
	sleep, the application requiring the subscriptions has terminated, or		sleep, the application requiring the subscriptions has terminated, or
	simply because the last active subscription on that session has been		simply because the last active subscription on that session has been
	cancelled.		cancelled.
	skipping to change at page 33, line 6 ¶		skipping to change at page 33, line 6 ¶
	recommendations will continue to change. Updated versions or errata		recommendations will continue to change. Updated versions or errata
	may exist for these recommendations.		may exist for these recommendations.
	7.2. TLS Name Authentication		7.2. TLS Name Authentication
	As described in Section 6.1, the client discovers the DNS Push		As described in Section 6.1, the client discovers the DNS Push
	Notification server using an SRV lookup for the record name		Notification server using an SRV lookup for the record name
	"_dns-push-tls._tcp.<zone>". The server connection endpoint SHOULD		"_dns-push-tls._tcp.<zone>". The server connection endpoint SHOULD
	then be authenticated using DANE TLSA records for the associated SRV		then be authenticated using DANE TLSA records for the associated SRV
	record. This associates the target's name and port number with a		record. This associates the target's name and port number with a
	trusted TLS certificate [RFC7673]. This procedure uses the TLS Sever		trusted TLS certificate [RFC7673]. This procedure uses the TLS
	Name Indication (SNI) extension [RFC6066] to inform the server of the		Server Name Indication (SNI) extension [RFC6066] to inform the server
	name the client has authenticated through the use of TLSA records.		of the name the client has authenticated through the use of TLSA
	Therefore, if the SRV record passes DNSSEC validation and a TLSA		records. Therefore, if the SRV record passes DNSSEC validation and a
	record matching the target name is useable, an SNI extension must be		TLSA record matching the target name is useable, an SNI extension
	used for the target name to ensure the client is connecting to the		must be used for the target name to ensure the client is connecting
	server it has authenticated. If the target name does not have a		to the server it has authenticated. If the target name does not have
	usable TLSA record, then the use of the SNI extension is optional.		a usable TLSA record, then the use of the SNI extension is optional.
	See Usage Profiles for DNS over TLS and DNS over DTLS [RFC8310] for		See Usage Profiles for DNS over TLS and DNS over DTLS [RFC8310] for
	more information on authenticating domain names.		more information on authenticating domain names.
	7.3. TLS Session Resumption		7.3. TLS Session Resumption
	TLS Session Resumption is permissible on DNS Push Notification		TLS Session Resumption is permissible on DNS Push Notification
	servers. The server may keep TLS state with Session IDs [RFC8446] or		servers. The server may keep TLS state with Session IDs [RFC8446] or
	operate in stateless mode by sending a Session Ticket [RFC5077] to		operate in stateless mode by sending a Session Ticket [RFC5077] to
	the client for it to store. However, closing the TLS connection		the client for it to store. However, closing the TLS connection
	terminates the DSO session. When the TLS session is resumed, the DNS		terminates the DSO session. When the TLS session is resumed, the DNS
	skipping to change at page 34, line 31 ¶		skipping to change at page 34, line 31 ¶
	This draft has been improved due to comments from Ran Atkinson, Tim		This draft has been improved due to comments from Ran Atkinson, Tim
	Chown, Mark Delany, Ralph Droms, Bernie Volz, Jan Komissar, Manju		Chown, Mark Delany, Ralph Droms, Bernie Volz, Jan Komissar, Manju
	Shankar Rao, Markus Stenberg, Dave Thaler, Soraia Zlatkovic, Sara		Shankar Rao, Markus Stenberg, Dave Thaler, Soraia Zlatkovic, Sara
	Dickinson, and Andrew Sullivan. Ted Lemon provided clarifying text		Dickinson, and Andrew Sullivan. Ted Lemon provided clarifying text
	that was greatly appreciated.		that was greatly appreciated.
	10. References		10. References
	10.1. Normative References		10.1. Normative References
	[DSO] Bellis, R., Cheshire, S., Dickinson, J., Dickinson, S.,
	Lemon, T., and T. Pusateri, "DNS Stateful Operations",
	draft-ietf-dnsop-session-signal-18 (work in progress),
	October 2018.
	[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,		[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
	DOI 10.17487/RFC0768, August 1980,		DOI 10.17487/RFC0768, August 1980,
	<https://www.rfc-editor.org/info/rfc768>.		<https://www.rfc-editor.org/info/rfc768>.
	[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,		[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
	RFC 793, DOI 10.17487/RFC0793, September 1981,		RFC 793, DOI 10.17487/RFC0793, September 1981,
	<https://www.rfc-editor.org/info/rfc793>.		<https://www.rfc-editor.org/info/rfc793>.
	[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",		[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
	STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,		STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
	skipping to change at page 35, line 20 ¶		skipping to change at page 35, line 15 ¶
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119,		Requirement Levels", BCP 14, RFC 2119,
	DOI 10.17487/RFC2119, March 1997,		DOI 10.17487/RFC2119, March 1997,
	<https://www.rfc-editor.org/info/rfc2119>.		<https://www.rfc-editor.org/info/rfc2119>.
	[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>.
	[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for		[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
	specifying the location of services (DNS SRV)", RFC 2782,		specifying the location of services (DNS SRV)", RFC 2782,
	DOI 10.17487/RFC2782, February 2000,		DOI 10.17487/RFC2782, February 2000,
	<https://www.rfc-editor.org/info/rfc2782>.		<https://www.rfc-editor.org/info/rfc2782>.
	[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)		[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)
	Extensions: Extension Definitions", RFC 6066,		Extensions: Extension Definitions", RFC 6066,
	DOI 10.17487/RFC6066, January 2011,		DOI 10.17487/RFC6066, January 2011,
	<https://www.rfc-editor.org/info/rfc6066>.		<https://www.rfc-editor.org/info/rfc6066>.
	skipping to change at page 36, line 13 ¶		skipping to change at page 36, line 9 ¶
	<https://www.rfc-editor.org/info/rfc7766>.		<https://www.rfc-editor.org/info/rfc7766>.
	[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC		[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
	2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,		2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
	May 2017, <https://www.rfc-editor.org/info/rfc8174>.		May 2017, <https://www.rfc-editor.org/info/rfc8174>.
	[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol		[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
	Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,		Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
	<https://www.rfc-editor.org/info/rfc8446>.		<https://www.rfc-editor.org/info/rfc8446>.
			[RFC8490] Bellis, R., Cheshire, S., Dickinson, J., Dickinson, S.,
			Lemon, T., and T. Pusateri, "DNS Stateful Operations",
			RFC 8490, DOI 10.17487/RFC8490, March 2019,
			<https://www.rfc-editor.org/info/rfc8490>.
	[ST] "Service Name and Transport Protocol Port Number		[ST] "Service Name and Transport Protocol Port Number
	Registry", <http://www.iana.org/assignments/		Registry", <http://www.iana.org/assignments/
	service-names-port-numbers/>.		service-names-port-numbers/>.
	10.2. Informative References		10.2. Informative References
	[DisProx] Cheshire, S., "Discovery Proxy for Multicast DNS-Based		[DisProx] Cheshire, S., "Discovery Proxy for Multicast DNS-Based
	Service Discovery", draft-ietf-dnssd-hybrid-08 (work in		Service Discovery", draft-ietf-dnssd-hybrid-10 (work in
	progress), March 2018.		progress), March 2019.
	[I-D.dukkipati-tcpm-tcp-loss-probe]		[I-D.dukkipati-tcpm-tcp-loss-probe]
	Dukkipati, N., Cardwell, N., Cheng, Y., and M. Mathis,		Dukkipati, N., Cardwell, N., Cheng, Y., and M. Mathis,
	"Tail Loss Probe (TLP): An Algorithm for Fast Recovery of		"Tail Loss Probe (TLP): An Algorithm for Fast Recovery of
	Tail Losses", draft-dukkipati-tcpm-tcp-loss-probe-01 (work		Tail Losses", draft-dukkipati-tcpm-tcp-loss-probe-01 (work
	in progress), February 2013.		in progress), February 2013.
	[LLQ] Sekar, K., "DNS Long-Lived Queries", draft-sekar-dns-		[LLQ] Cheshire, S. and M. Krochmal, "DNS Long-Lived Queries",
	llq-01 (work in progress), August 2006.		draft-sekar-dns-llq-03 (work in progress), March 2019.
	[obs] "Observer Pattern",		[obs] "Observer Pattern",
	<https://en.wikipedia.org/wiki/Observer_pattern>.		<https://en.wikipedia.org/wiki/Observer_pattern>.
	[RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS		[RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS
	NCACHE)", RFC 2308, DOI 10.17487/RFC2308, March 1998,		NCACHE)", RFC 2308, DOI 10.17487/RFC2308, March 1998,
	<https://www.rfc-editor.org/info/rfc2308>.		<https://www.rfc-editor.org/info/rfc2308>.
	[RFC3123] Koch, P., "A DNS RR Type for Lists of Address Prefixes		[RFC3123] Koch, P., "A DNS RR Type for Lists of Address Prefixes
	(APL RR)", RFC 3123, DOI 10.17487/RFC3123, June 2001,		(APL RR)", RFC 3123, DOI 10.17487/RFC3123, June 2001,
End of changes. 50 change blocks.
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