draft-ietf-dnssd-push-16.txt   draft-ietf-dnssd-push-17.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: May 9, 2019 Apple Inc. Expires: September 10, 2019 Apple Inc.
November 5, 2018 March 9, 2019
DNS Push Notifications DNS Push Notifications
draft-ietf-dnssd-push-16 draft-ietf-dnssd-push-17
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
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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 May 9, 2019. This Internet-Draft will expire on September 10, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2018 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
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
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
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Transport . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4. Transport . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5. State Considerations . . . . . . . . . . . . . . . . . . . . 8 5. State Considerations . . . . . . . . . . . . . . . . . . . . 8
6. Protocol Operation . . . . . . . . . . . . . . . . . . . . . 9 6. Protocol Operation . . . . . . . . . . . . . . . . . . . . . 9
6.1. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 10 6.1. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 10
6.2. DNS Push Notification SUBSCRIBE . . . . . . . . . . . . . 13 6.2. DNS Push Notification SUBSCRIBE . . . . . . . . . . . . . 14
6.2.1. SUBSCRIBE Request . . . . . . . . . . . . . . . . . . 13 6.2.1. SUBSCRIBE Request . . . . . . . . . . . . . . . . . . 14
6.2.2. SUBSCRIBE Response . . . . . . . . . . . . . . . . . 16 6.2.2. SUBSCRIBE Response . . . . . . . . . . . . . . . . . 17
6.3. DNS Push Notification Updates . . . . . . . . . . . . . . 19 6.3. DNS Push Notification Updates . . . . . . . . . . . . . . 20
6.3.1. PUSH Message . . . . . . . . . . . . . . . . . . . . 19 6.3.1. PUSH Message . . . . . . . . . . . . . . . . . . . . 20
6.4. DNS Push Notification UNSUBSCRIBE . . . . . . . . . . . . 22 6.4. DNS Push Notification UNSUBSCRIBE . . . . . . . . . . . . 23
6.4.1. UNSUBSCRIBE Request . . . . . . . . . . . . . . . . . 22 6.4.1. UNSUBSCRIBE Request . . . . . . . . . . . . . . . . . 23
6.5. DNS Push Notification RECONFIRM . . . . . . . . . . . . . 24 6.5. DNS Push Notification RECONFIRM . . . . . . . . . . . . . 25
6.5.1. RECONFIRM Request . . . . . . . . . . . . . . . . . . 24 6.5.1. RECONFIRM Request . . . . . . . . . . . . . . . . . . 25
6.5.2. RECONFIRM Response . . . . . . . . . . . . . . . . . 26 6.5.2. RECONFIRM Response . . . . . . . . . . . . . . . . . 28
6.6. DNS Stateful Operations TLV Context Summary . . . . . . . 28 6.6. DNS Stateful Operations TLV Context Summary . . . . . . . 30
6.7. Client-Initiated Termination . . . . . . . . . . . . . . 29 6.7. Client-Initiated Termination . . . . . . . . . . . . . . 31
7. Security Considerations . . . . . . . . . . . . . . . . . . . 30 7. Security Considerations . . . . . . . . . . . . . . . . . . . 32
7.1. Security Services . . . . . . . . . . . . . . . . . . . . 30 7.1. Security Services . . . . . . . . . . . . . . . . . . . . 32
7.2. TLS Name Authentication . . . . . . . . . . . . . . . . . 30 7.2. TLS Name Authentication . . . . . . . . . . . . . . . . . 32
7.3. TLS Compression . . . . . . . . . . . . . . . . . . . . . 31 7.3. TLS Session Resumption . . . . . . . . . . . . . . . . . 33
7.4. TLS Session Resumption . . . . . . . . . . . . . . . . . 31 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 33
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 34
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 32 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 34
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 33 10.1. Normative References . . . . . . . . . . . . . . . . . . 34
10.1. Normative References . . . . . . . . . . . . . . . . . . 33 10.2. Informative References . . . . . . . . . . . . . . . . . 36
10.2. Informative References . . . . . . . . . . . . . . . . . 34 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 38
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 37
1. Introduction 1. Introduction
Domain Name System (DNS) records may be updated using DNS Update Domain Name System (DNS) records may be updated using DNS Update
[RFC2136]. Other mechanisms such as a Discovery Proxy [DisProx] can [RFC2136]. Other mechanisms such as a Discovery Proxy [DisProx] can
also generate changes to a DNS zone. This document specifies a also generate changes to a DNS zone. This document specifies a
protocol for DNS clients to subscribe to receive asynchronous protocol for DNS clients to subscribe to receive asynchronous
notifications of changes to RRSets of interest. It is immediately notifications of changes to RRSets of interest. It is immediately
relevant in the case of DNS Service Discovery [RFC6763] but is not relevant in the case of DNS Service Discovery [RFC6763] but is not
limited to that use case, and provides a general DNS mechanism for limited to that use case, and provides a general DNS mechanism for
DNS record change notifications. Familiarity with the DNS protocol DNS record change notifications. Familiarity with the DNS protocol
and DNS packet formats is assumed [RFC1034] [RFC1035] [RFC6895]. and DNS packet formats is assumed [RFC1034] [RFC1035] [RFC6895].
1.1. Requirements Language 1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
"Key words for use in RFCs to Indicate Requirement Levels", when, and BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
only when, they appear in all capitals, as shown here [RFC2119] capitals, as shown here. These words may also appear in this
[RFC8174]. document in lower case as plain English words, absent their normative
meanings.
2. Motivation 2. Motivation
As the domain name system continues to adapt to new uses and changes As the domain name system continues to adapt to new uses and changes
in deployment, polling has the potential to burden DNS servers at in deployment, polling has the potential to burden DNS servers at
many levels throughout the network. Other network protocols have many levels throughout the network. Other network protocols have
successfully deployed a publish/subscribe model following the successfully deployed a publish/subscribe model following the
Observer design pattern [obs]. XMPP Publish-Subscribe [XEP0060] and Observer design pattern [obs]. XMPP Publish-Subscribe [XEP0060] and
Atom [RFC4287] are examples. While DNS servers are generally highly Atom [RFC4287] are examples. While DNS servers are generally highly
tuned and capable of a high rate of query/response traffic, adding a tuned and capable of a high rate of query/response traffic, adding a
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multicast group address for all group members to receive. Therefore, multicast group address for all group members to receive. Therefore,
Multicast DNS already has asynchronous change notification Multicast DNS already has asynchronous change notification
capability. However, when DNS Service Discovery [RFC6763] is used capability. However, when DNS Service Discovery [RFC6763] is used
across a wide area network using Unicast DNS (possibly facilitated across a wide area network using Unicast DNS (possibly facilitated
via a Discovery Proxy [DisProx]) it would be beneficial to have an via a Discovery Proxy [DisProx]) it would be beneficial to have an
equivalent capability for Unicast DNS, to allow clients to learn equivalent capability for Unicast DNS, to allow clients to learn
about DNS record changes in a timely manner without polling. about DNS record changes in a timely manner without polling.
The DNS Long-Lived Queries (LLQ) mechanism [LLQ] is an existing The DNS Long-Lived Queries (LLQ) mechanism [LLQ] is an existing
deployed solution to provide asynchronous change notifications, used deployed solution to provide asynchronous change notifications, used
by Apple's Back to My Mac Service [RFC6281] introduced in Mac OS X by Apple's Back to My Mac [RFC6281] service introduced in Mac OS X
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) [DSO] running over TLS over TCP, and
therefore doesn't need to reinvent existing TCP functionality. Using therefore doesn't need to reinvent existing TCP functionality. Using
TCP also gives long-lived low-traffic connections better longevity TCP also gives long-lived low-traffic connections better longevity
through NAT gateways without resorting to excessive keepalive through NAT gateways without depending on the gateway to support NAT
traffic. Instead of inventing a new vocabulary of messages to Port Mapping Protocol (NAT-PMP) [RFC6886] or Port Control Protocol
communicate DNS zone changes as LLQ did, this specification borrows (PCP) [RFC6887], or resorting to excessive keepalive traffic.
the established syntax and semantics of DNS Update messages Instead of inventing a new vocabulary of messages to communicate DNS
[RFC2136]. zone changes as LLQ did, this specification borrows the established
syntax and semantics of DNS Update messages [RFC2136].
3. Overview 3. Overview
The existing DNS Update protocol [RFC2136] provides a mechanism for The existing DNS Update protocol [RFC2136] provides a mechanism for
clients to add or delete individual resource records (RRs) or entire clients to add or delete individual resource records (RRs) or entire
resource record sets (RRSets) on the zone's server. resource record sets (RRSets) on the zone's server.
This specification adopts a simplified subset of these existing This specification adopts a simplified subset of these existing
syntax and semantics, and uses them for DNS Push Notification syntax and semantics, and uses them for DNS Push Notification
messages going in the opposite direction, from server to client, to messages going in the opposite direction, from server to client, to
communicate changes to a zone. The client subscribes for Push communicate changes to a name's records. The client subscribes for
Notifications by connecting to the server and sending DNS message(s) Push Notifications by connecting to the server and sending DNS
indicating the RRSet(s) of interest. When the client loses interest message(s) indicating the RRSet(s) of interest. When the client
in receiving further updates to these records, it unsubscribes. loses interest in receiving further updates to these records, it
unsubscribes.
The DNS Push Notification server for a zone is any server capable of The DNS Push Notification server for a zone is any server capable of
generating the correct change notifications for a name. It may be a generating the correct change notifications for a name. It may be a
primary, secondary, or stealth name server [RFC7719]. Consequently, primary, secondary, or stealth name server [RFC7719]. Consequently,
the "_dns-push-tls._tcp.<zone>" SRV record for a zone MAY reference the "_dns-push-tls._tcp.<zone>" SRV record for a zone MAY reference
the same target host and port as that zone's the same target host and port as that zone's
"_dns-update-tls._tcp.<zone>" SRV record. When the same target host "_dns-update-tls._tcp.<zone>" SRV record. When the same target host
and port is offered for both DNS Updates and DNS Push Notifications, and port is offered for both DNS Updates and DNS Push Notifications,
a client MAY use a single TCP connection to that server for both DNS a client MAY use a single TCP connection to that server for both DNS
Updates and DNS Push Notification Subscriptions. Updates and DNS Push Notification Subscriptions.
Supporting DNS Updates and DNS Push Notifications on the same server Supporting DNS Updates and DNS Push Notifications on the same server
is OPTIONAL. A DNS Push Notification server does NOT also have to is OPTIONAL. A DNS Push Notification server is NOT REQUIRED also to
support DNS Update. support DNS Update.
DNS Updates and DNS Push Notifications may be handled on different DNS Updates and DNS Push Notifications may be handled on different
ports on the same target host, in which case they are not considered ports on the same target host, in which case they are not considered
to be the "same server" for the purposes of this specification, and to be the "same server" for the purposes of this specification, and
communications with these two ports are handled independently. communications with these two ports are handled independently.
Standard DNS Queries MAY be sent over a DNS Push Notification Standard DNS Queries MAY be sent over a DNS Push Notification (i.e.,
connection. For any zone for which the server is authoritative, it DSO) session. For any zone for which the server is authoritative, it
MUST respond authoritatively for queries on names falling within that MUST respond authoritatively for queries on names falling within that
zone (e.g., the <zone> in the "_dns-push-tls._tcp.<zone>" SRV record) zone (e.g., the <zone> in the "_dns-push-tls._tcp.<zone>" SRV record)
both for DNS Push Notification queries and for normal DNS queries. both for normal DNS queries and for DNS Push Notification
For names for which the server is acting as a caching resolver, e.g. subscriptions. For names for which the server is acting as a
when the server is the local resolver, for any query for which it recursive resolver, e.g. when the server is the local recursive
supports DNS Push Notifications, it MUST also support standard resolver, for any query for which it supports DNS Push Notification
queries. subscriptions, it MUST also support standard queries.
DNS Push Notification clients are NOT required to implement DNS DNS Push Notification clients are NOT required to implement DNS
Update Prerequisite processing. Prerequisites are used to perform Update Prerequisite processing. Prerequisites are used to perform
tentative atomic test-and-set type operations when a client updates tentative atomic test-and-set type operations when a client updates
records on a server, and that concept has no applicability when it records on a server, and that concept has no applicability when it
comes to an authoritative server unilaterally informing a client of comes to an authoritative server unilaterally informing a client of
changes to DNS records. changes to DNS records.
This DNS Push Notification specification includes support for DNS This DNS Push Notification specification includes support for DNS
classes, for completeness. However, in practice, it is anticipated classes, for completeness. However, in practice, it is anticipated
that for the foreseeable future the only DNS class in use will be DNS that for the foreseeable future the only DNS class in use will be DNS
class "IN", as is the reality today with existing DNS servers and class "IN", as is the reality today with existing DNS servers and
clients. A DNS Push Notification server MAY choose to implement only clients. A DNS Push Notification server MAY choose to implement only
DNS class "IN". If messages are received for a class other than DNS class "IN". If messages are received for a class other than
"IN", and that class is not supported, an error with RCODE NOTIMPL "IN", and that class is not supported, an error with RCODE NOTIMPL
(Not Implemented) should be returned. (Not Implemented) should be returned.
DNS Push Notifications impose less load on the responding server than DNS Push Notifications impose less load on the responding server than
rapid polling would, but Push Notifications do still have a cost, so rapid polling would, but Push Notifications do still have a cost, so
DNS Push Notification clients must not recklessly create an excessive DNS Push Notification clients MUST NOT recklessly create an excessive
number of Push Notification subscriptions. Specifically: number of Push Notification subscriptions. Specifically:
(a) A subscription should only be active when there is a valid reason (a) A subscription should only be active when there is a valid reason
to need live data (for example, an on-screen display is currently to need live data (for example, an on-screen display is currently
showing the results to the user) and the subscription SHOULD be showing the results to the user) and the subscription SHOULD be
cancelled as soon as the need for that data ends (for example, when cancelled as soon as the need for that data ends (for example, when
the user dismisses that display). Implementations may want to the user dismisses that display). In the case of a device like a
implement idle timeouts, so that if the user ceases interacting with smartphone which, after some period of inactivity, goes to sleep or
the device, the subscription is cancelled. otherwise darkens its screen, it should cancel its subscriptions when
darkening the screen (since the user cannot see any changes in the
display anyway) and reinstate its subscriptions when re-awakening
from display sleep.
(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 [DSO], a client must not keep a session to a server open indefinitely
if it has no subscriptions (or other operations) active on that if it has no subscriptions (or other operations) active on that
session. A client MAY close a session as soon as it becomes idle, session. A client MAY close a session as soon as it becomes idle,
and then if needed in the future, open a new session when required. and then if needed in the future, open a new session when required.
Alternatively, a client MAY speculatively keep an idle session open Alternatively, a client MAY speculatively keep an idle session open
for some time, subject to the constraint that it MUST NOT keep a for some time, subject to the constraint that it MUST NOT keep a
session open that has been idle for more than the session's idle session open that has been idle for more than the session's idle
timeout (15 seconds by default). timeout (15 seconds by default) [DSO].
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].
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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
current and future developments in TCP, such as Multipath TCP (MPTCP) current and future developments in TCP, such as Multipath TCP (MPTCP)
[RFC6824], TCP Fast Open (TFO) [RFC7413], Tail Loss Probe (TLP) [RFC6824], TCP Fast Open (TFO) [RFC7413], Tail Loss Probe (TLP)
[I-D.dukkipati-tcpm-tcp-loss-probe], and so on. [I-D.dukkipati-tcpm-tcp-loss-probe], and so on.
Transport Layer Security (TLS) [RFC5246] is well understood and Transport Layer Security (TLS) [RFC8446] is well understood and
deployed across many protocols running over TCP. It is designed to deployed across many protocols running over TCP. It is designed to
prevent eavesdropping, tampering, and message forgery. TLS is prevent eavesdropping, tampering, and message forgery. TLS is
REQUIRED for every connection between a client subscriber and server REQUIRED for every connection between a client subscriber and server
in this protocol specification. Additional security measures such as in this protocol specification. Additional security measures such as
client authentication during TLS negotiation MAY also be employed to client authentication during TLS negotiation MAY also be employed to
increase the trust relationship between client and server. increase the trust relationship between client and server.
5. State Considerations 5. State Considerations
Each DNS Push Notification server is capable of handling some finite Each DNS Push Notification server is capable of handling some finite
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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
Keepalive operation to request a session timeout or keepalive Keepalive operation to request a session timeout and/or keepalive
interval longer than the the 15-second default, but this is not interval longer than the the 15-second default values, but this is
required. A DNS Push Notification client MAY issue other requests on not required. A DNS Push Notification client MAY issue other
the session first, and only issue a DSO Keepalive operation later if requests on the session first, and only issue a DSO Keepalive
it determines that to be necessary. However, Push Notification operation later if it determines that to be necessary. Sending
subscriptions can also be used to establish the DSO session. either a DSO Keepalive operation or a Push Notification subscription
over the TLS/TCP connection to the server signals the client's
support of DSO and serves to establish a DSO session.
In accordance with the current set of active subscriptions, the In accordance with the current set of active subscriptions, the
server sends relevant asynchronous Push Notifications to the client. server sends relevant asynchronous Push Notifications to the client.
Note that a client MUST be prepared to receive (and silently ignore) Note that a client MUST be prepared to receive (and silently ignore)
Push Notifications for subscriptions it has previously removed, since Push Notifications for subscriptions it has previously removed, since
there is no way to prevent the situation where a Push Notification is there is no way to prevent the situation where a Push Notification is
in flight from server to client while the client's UNSUBSCRIBE in flight from server to client while the client's UNSUBSCRIBE
message cancelling that subscription is simultaneously in flight from message cancelling that subscription is simultaneously in flight from
client to server. client to server.
6.1. Discovery 6.1. Discovery
The first step in DNS Push Notification subscription is to discover The first step in DNS Push Notification subscription is to discover
an appropriate DNS server that supports DNS Push Notifications for an appropriate DNS server that supports DNS Push Notifications for
the desired zone. the desired zone.
The client begins by opening a DSO Session to its normal configured The client begins by opening a DSO Session to its normal configured
DNS recursive resolver and requesting a Push Notification DNS recursive resolver and requesting a Push Notification
subscription. This connection is made to the default DNS-over-TLS subscription. This connection is made to TCP port 853, the default
port as defined in DNS over TLS [RFC7858]. If this connection is port for DNS-over-TLS DNS over TLS [RFC7858]. If the request for a
successful, then the recursive resolver will make appropriate Push Push Notification subscription is successful, then the recursive
Notification subscriptions on the client's behalf, and the client resolver will make a corresponding Push Notification subscription on
will receive appropriate results. the client's behalf (if the recursive resolver doesn't already have
an active subscription for that name, type, and class), and pass on
any results it receives back to the client. This is closely
analogous to how a client sends normal DNS queries to its configured
DNS recursive resolver, which issues queries on the client's behalf
(if the recursive resolver doesn't already have appropriate answer(s)
in its cache), and passes on any results it receives back to the
client.
In many contexts, the local recursive resolver will be able to handle In many contexts, the recursive resolver will be able to handle Push
push notifications for all zones that the client may need to follow. Notifications for all names that the client may need to follow. Use
In other cases, the client may require Push Notifications from more of VPN tunnels and split-view DNS can create some additional
than one zone, and those zones may be served by different servers. complexity in the client software here; the techniques to handle VPN
Therefore, it is assumed that the client may need to maintain tunnels and split-view DNS for DNS Push Notifications are the same as
connections to more than one DNS Push server. those already used to handle this for normal DNS queries.
In some cases, the recursive resolver may not be able to get answers If the recursive resolver does not support DNS over TLS, or does
for a particular zone. In this case, rather than returning SERVFAIL, support DNS over TLS but is not listening on TCP port 853, or does
the resolver returns NOTAUTH. This signals the client that queries support DNS over TLS on TCP port 853 but does not support DSO on that
for this zone can't be handled by the local caching resolver. For port, then the DSO Session session establishment will fail [DSO].
that zone, the client SHOULD contact the zone's DNS Push server
itself, even if all other DNS Push queries can be handled by the
local resolver. This may be necessary in cases where the client is
connected to a VPN, for example, or where the client has a pre-
established trust relationship with the owner of the zone that allows
the client, but not the local resolver, to successfully get answers
for queries in that zone.
If the recursive resolver does not support Push Notification If the recursive resolver does support DSO but not Push Notification
subscriptions, then it will return an error code, DSONOTIMPL. This subscriptions, then it will return the DSO error code, DSOTYPENI
occurs when the local resolver follows the procedure below and does (11).
not find an SRV record indicating support for DNS Push Notifications.
In case of either failure, the client should proceed to discover the In some cases, the recursive resolver may support DSO and Push
Notification subscriptions, but may not be able to subscribe for Push
Notifications for a particular name. In this case, the recursive
resolver should return an informative error code to the client so
that the client can make an informed decision how to handle the
error. If the recursive resolver is unable to establish a connection
to the zone's DNS Push Notification server (perhaps because the
required SRV record does not exist) the recursive resolver should
return SERVFAIL. If the recursive resolver is able to establish a
connection to the zone's DNS Push Notification server and some other
error code is then received, the recursive resolver should pass on
this received error code back to the client. In some cases, where
the client has a pre-established trust relationship with the owner of
the zone (that is not handled via the usual mechanisms for VPN
software) the client may handle these failures by contacting the
zone's DNS Push server directly.
In any of the cases described above where the client fails to
establish a DNS Push Notification subscription via its configured
recursive resolver, the client should proceed to discover the
appropriate server for direct communication. The client MUST also appropriate server for direct communication. The client MUST also
determine which TCP port on the server is listening for connections, determine which TCP port on the server is listening for connections,
which need not be (and often is not) the typical TCP port 53 used for which need not be (and often is not) the typical TCP port 53 used for
conventional DNS, or TCP port 853 used for DNS over TLS. conventional DNS, or TCP port 853 used for DNS over TLS.
The discovery algorithm described here is an iterative algorithm, The discovery algorithm described here is an iterative algorithm,
which starts with the full name of the record to which the client which starts with the full name of the record to which the client
wishes to subscribe. Successive SOA queries are then issued, wishes to subscribe. Successive SOA queries are then issued,
trimming one label each time, until the closest enclosing trimming one label each time, until the closest enclosing
authoritative server is discovered. There is also an optimization to authoritative server is discovered. There is also an optimization to
skipping to change at page 11, line 17 skipping to change at page 11, line 35
1. The client begins the discovery by sending a DNS query to its 1. The client begins the discovery by sending a DNS query to its
local resolver, with record type SOA [RFC1035] for the record local resolver, with record type SOA [RFC1035] for the record
name to which it wishes to subscribe. As an example, suppose the name to which it wishes to subscribe. As an example, suppose the
client wishes to subscribe to PTR records with the name client wishes to subscribe to PTR records with the name
_ipp._tcp.foo.example.com (to discover Internet Printing Protocol _ipp._tcp.foo.example.com (to discover Internet Printing Protocol
(IPP) printers [RFC8010] [RFC8011] being advertised at (IPP) printers [RFC8010] [RFC8011] being advertised at
"foo.example.com"). The client begins by sending an SOA query "foo.example.com"). The client begins by sending an SOA query
for _ipp._tcp.foo.example.com to the local recursive resolver. for _ipp._tcp.foo.example.com to the local recursive resolver.
The goal is to determine the server authoritative for the name The goal is to determine the server authoritative for the name
_ipp._tcp.foo.example.com. The DNS zone containing the name _ipp._tcp.foo.example.com. The closest enclosing DNS zone
_ipp._tcp.foo.example.com could be example.com, or containing the name _ipp._tcp.foo.example.com could be
foo.example.com, or _tcp.foo.example.com, or even example.com, or foo.example.com, or _tcp.foo.example.com, or even
_ipp._tcp.foo.example.com. The client does not know in advance _ipp._tcp.foo.example.com. The client does not know in advance
where the closest enclosing zone cut occurs, which is why it uses where the closest enclosing zone cut occurs, which is why it uses
the procedure described here to discover this information. the iterative procedure described here to discover this
information.
2. If the requested SOA record exists, it will be returned in the 2. If the requested SOA record exists, it will be returned in the
Answer section with a NOERROR response code, and the client has Answer section with a NOERROR response code, and the client has
succeeded in discovering the information it needs. (This text is succeeded in discovering the information it needs.
not placing any new requirements on DNS recursive resolvers. It (This language is not placing any new requirements on DNS
is merely describing the existing operation of the DNS protocol recursive resolvers. This text merely describes the existing
[RFC1034] [RFC1035].) operation of the DNS protocol [RFC1034] [RFC1035].)
3. If the requested SOA record does not exist, the client will get 3. If the requested SOA record does not exist, the client will get
back a NOERROR/NODATA response or an NXDOMAIN/Name Error back a NOERROR/NODATA response or an NXDOMAIN/Name Error
response. In either case, the local resolver would normally response. In either case, the local resolver would normally
include the SOA record for the zone of the requested name in the include the SOA record for the closest enclosing zone of the
Authority Section. If the SOA record is received in the requested name in the Authority Section. If the SOA record is
Authority Section, then the client has succeeded in discovering received in the Authority Section, then the client has succeeded
the information it needs. (This text is not placing any new in discovering the information it needs.
requirements on DNS recursive resolvers. It is merely describing (This language is not placing any new requirements on DNS
the existing operation of the DNS protocol regarding negative recursive resolvers. This text merely describes the existing
responses [RFC2308].) operation of the DNS protocol regarding negative responses
[RFC2308].)
4. If the client receives a response containing no SOA record, then 4. If the client receives a response containing no SOA record, then
it proceeds with the iterative approach. The client strips the it proceeds with the iterative approach. The client strips the
leading label from the current query name and if the resulting leading label from the current query name and if the resulting
name has at least one label in it, the client sends a new SOA name has at least one label in it, the client sends an SOA query
query, and processing continues at step 2 above, repeating the for that new name, and processing continues at step 2 above,
iterative search until either an SOA is received, or the query repeating the iterative search until either an SOA is received,
name is empty. In the case of an empty name, this is a network or the query name consists of a single label, i.e., a Top Level
configuration error which should not happen and the client gives Domain (TLD). In the case of a single-label TLD, this is a
up. The client may retry the operation at a later time, of the network configuration error which should not happen and the
client's choosing, such after a change in network attachment. client gives up. The client may retry the operation at a later
time, of the client's choosing, such after a change in network
attachment.
5. Once the SOA is known (either by virtue of being seen in the 5. Once the SOA is known (either by virtue of being seen in the
Answer Section, or in the Authority Section), the client sends a Answer Section, or in the Authority Section), the client sends a
DNS query with type SRV [RFC2782] for the record name DNS query with type SRV [RFC2782] for the record name
"_dns-push-tls._tcp.<zone>", where <zone> is the owner name of "_dns-push-tls._tcp.<zone>", where <zone> is the owner name of
the discovered SOA record. the discovered SOA record.
6. If the zone in question is set up to offer DNS Push Notifications 6. If the zone in question is set up to offer DNS Push Notifications
then this SRV record MUST exist. (If this SRV record does not then this SRV record MUST exist. (If this SRV record does not
exist then the zone is not correctly configured for DNS Push exist then the zone is not correctly configured for DNS Push
skipping to change at page 13, line 10 skipping to change at page 14, line 10
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 then
indicates its desire to receive DNS Push Notifications for a given indicates its desire to receive DNS Push Notifications for a given
domain name by sending a SUBSCRIBE request over the established DSO domain name by sending a SUBSCRIBE request to the server. A
session to the server. A SUBSCRIBE request is encoded in a DSO [DSO] SUBSCRIBE request is encoded in a DSO message [DSO]. This
message. This specification defines a primary DSO TLV for DNS Push specification defines a primary DSO TLV for DNS Push Notification
Notification SUBSCRIBE Requests (tentatively DSO Type Code 0x40). 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 TLV. A SUBSCRIBE request message is [DSO], followed by the SUBSCRIBE primary TLV. A SUBSCRIBE request
illustrated in Figure 1. 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 session. For the is not using for any other active operation on this DSO session. For
purposes here, a MESSAGE ID is in use on this session if the client the purposes here, a MESSAGE ID is in use on this session if the
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
specification [DSO]. The DNS Opcode is the DSO Opcode. The four specification [DSO]. The DNS OPCODE field contains the OPCODE value
count fields MUST be zero, and the corresponding four sections MUST for DNS Stateful Operations (6). The four count fields MUST be zero,
be empty (i.e., absent). and the corresponding four sections MUST be empty (i.e., absent).
The DSO-TYPE is SUBSCRIBE. The DSO-LENGTH is the length of the DSO- The DSO-TYPE is SUBSCRIBE (tentatively 0x40).
DATA that follows, which specifies the name, type, and class of the
record(s) being sought. 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.
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
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \
| MESSAGE ID | \ | MESSAGE ID | \
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
|QR| Opcode | Z | RCODE | | |QR| OPCODE(6) | Z | RCODE | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| QDCOUNT (MUST BE ZERO) | | | QDCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > HEADER +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > HEADER
| ANCOUNT (MUST BE ZERO) | | | ANCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| NSCOUNT (MUST BE ZERO) | | | NSCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| ARCOUNT (MUST BE ZERO) | / | ARCOUNT (MUST BE ZERO) | /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ / +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /
| DSO-TYPE = SUBSCRIBE | | DSO-TYPE = SUBSCRIBE (tentatively 0x40) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| DSO-LENGTH (number of octets in DSO-DATA) | | DSO-LENGTH (number of octets in DSO-DATA) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \
| | \ | | \
\ NAME \ | \ NAME \ |
\ \ | \ \ |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > DSO-DATA +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > DSO-DATA
| TYPE | | | TYPE | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| CLASS | / | CLASS | /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ / +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /
Figure 1: SUBSCRIBE Request Figure 1: SUBSCRIBE Request
The DSO-DATA for a SUBSCRIBE request MUST contain exactly one NAME, The DSO-DATA for a SUBSCRIBE request MUST contain exactly one NAME,
Type, and CLASS. Since SUBSCRIBE requests are sent over TCP, TYPE, and CLASS. Since SUBSCRIBE requests are sent over TCP,
multiple SUBSCRIBE request messages can be concatenated in a single multiple SUBSCRIBE DSO request messages can be concatenated in a
TCP stream and packed efficiently into TCP segments. single TCP stream and packed efficiently into TCP segments.
If accepted, the subscription will stay in effect until the client If accepted, the subscription will stay in effect until the client
cancels the subscription using UNSUBSCRIBE or until the DSO session cancels the subscription using UNSUBSCRIBE or until the DSO session
between the client and the server is closed. between the client and the server is closed.
SUBSCRIBE requests on a given session MUST be unique. A client MUST SUBSCRIBE requests on a given session MUST be unique. A client MUST
NOT send a SUBSCRIBE message that duplicates the NAME, TYPE and CLASS NOT send a SUBSCRIBE message that duplicates the NAME, TYPE and CLASS
of an existing active subscription on that DSO session. For the of an existing active subscription on that DSO session. For the
purpose of this matching, the established DNS case-insensitivity for purpose of this matching, the established DNS case-insensitivity for
US-ASCII letters applies (e.g., "example.com" and "Example.com" are US-ASCII letters applies (e.g., "example.com" and "Example.com" are
skipping to change at page 15, line 15 skipping to change at page 16, line 15
DNS wildcarding is not supported. That is, a wildcard ("*") in a DNS wildcarding is not supported. That is, a wildcard ("*") in a
SUBSCRIBE message matches only a literal wildcard character ("*") in SUBSCRIBE 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 SUBSCRIBE message Aliasing is not supported. That is, a CNAME in a SUBSCRIBE 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.
A client may SUBSCRIBE to records that are unknown to the server at A client may SUBSCRIBE to records that are unknown to the server at
the time of the request (providing that the name falls within one of the time of the request (providing that the name falls within one of
the zone(s) the server is responsible for) and this is not an error. the zone(s) the server is responsible for) and this is not an error.
The server MUST accept these requests and send Push Notifications if The server MUST NOT return NXDOMAIN in this case. The server MUST
and when matching records are found in the future. accept these requests and send Push Notifications if and when
matching records are found in the future.
If neither TYPE nor CLASS are ANY (255) then this is a specific If neither TYPE nor CLASS are ANY (255) then this is a specific
subscription to changes for the given NAME, TYPE and CLASS. If one subscription to changes for the given NAME, TYPE and CLASS. If one
or both of TYPE or CLASS are ANY (255) then this subscription matches or both of TYPE or CLASS are ANY (255) then this subscription matches
any type and/or any class, as appropriate. any type and/or any class, as appropriate.
NOTE: A little-known quirk of DNS is that in DNS QUERY requests, NOTE: A little-known quirk of DNS is that in DNS QUERY requests,
QTYPE and QCLASS 255 mean "ANY" not "ALL". They indicate that the QTYPE and QCLASS 255 mean "ANY" not "ALL". They indicate that the
server should respond with ANY matching records of its choosing, not server should respond with ANY matching records of its choosing, not
necessarily ALL matching records. This can lead to some surprising necessarily ALL matching records. This can lead to some surprising
skipping to change at page 16, line 10 skipping to change at page 17, line 10
interpreted to mean "ALL", not "ANY". After accepting a subscription interpreted to mean "ALL", not "ANY". After accepting a subscription
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 message begins with the standard DSO 12-byte A SUBSCRIBE response begins with the standard DSO 12-byte header
header [DSO], possibly followed by one or more optional TLVs, such as [DSO], possibly followed by one or more optional TLVs, such as a
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 17, line 6 skipping to change at page 18, line 6
This document specifies only these RCODE values for SUBSCRIBE This document specifies only these RCODE values for SUBSCRIBE
Responses. Servers sending SUBSCRIBE Responses SHOULD use one of Responses. Servers sending SUBSCRIBE Responses SHOULD use one of
these values. Note that NXDOMAIN is not a valid RCODE in response to these values. Note that NXDOMAIN is not a valid RCODE in response to
a SUBSCRIBE Request. However, future circumstances may create a SUBSCRIBE Request. However, future circumstances may create
situations where other RCODE values are appropriate in SUBSCRIBE situations where other RCODE values are appropriate in SUBSCRIBE
Responses, so clients MUST be prepared to accept SUBSCRIBE Responses Responses, so clients MUST be prepared to accept SUBSCRIBE Responses
with any other RCODE value. with any other RCODE value.
If the server sends a nonzero RCODE in the SUBSCRIBE response, that If the server sends a nonzero RCODE in the SUBSCRIBE response, that
means means:
a. the client is (at least partially) misconfigured, a. the client is (at least partially) misconfigured,
b. the server resources are exhausted, or b. the server resources are exhausted, or
c. there is some other unknown failure on the server. c. there is some other unknown failure on the server.
In any case, the client shouldn't retry the subscription to this In any case, the client shouldn't retry the subscription to this
server right away. If multiple SRV records were returned as server right away. If multiple SRV records were returned as
described in discovery Section 6.1, Paragraph 7, a subsequent server described in Section 6.1, Paragraph 7, a subsequent server can be
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 can remain even though additional subscriptions these subscriptions remain even though additional subscriptions may
may be refused. Neither the client, nor the server are required to be refused. Neither the client nor the server are required to close
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 [DSO] to the response specifying a delay before the client
attempts this operation again. Recommended values for the delay for attempts this operation again. Recommended values for the delay for
different RCODE values are given below. These recommended values different RCODE values are given below. These recommended values
apply both to the default values a server should place in the Retry apply both to the default values a server should place in the Retry
Delay TLV, and the default values a client should assume if the 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 DSO [DSO], it is unlikely that the server will begin implement DNS Stateful Operations [DSO], it is unlikely that the
supporting DSO in the next few minutes, so the retry delay SHOULD server will begin supporting DSO in the next few minutes, so the
be one hour. Note that in such a case, a server that doesn't retry delay SHOULD be one hour. Note that in such a case, a
implement DSO is unlikely to place a Retry Delay TLV in its server that doesn't implement DSO is unlikely to place a Retry
response, so this recommended value in particular applies to what Delay TLV in its response, so this recommended value in particular
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 not the local resolver, this is a If the server being queried is listed in a
misconfiguration, since this server is listed in a "_dns-push-tls._tcp.<zone>" SRV record for the zone, then this is
"_dns-push-tls._tcp.<zone>" SRV record, but the server itself is a misconfiguration, since this server is being advertised as
not currently configured to support DNS Push Notifications for supporting DNS Push Notifications for this zone, but the server
that zone. Since it is possible that the misconfiguration may be itself is not currently configured to perform that task. Since it
repaired at any time, the retry delay should not be set too high. is possible that the misconfiguration may be repaired at any time,
By default, a value of 5 minutes is RECOMMENDED. the retry delay should not be set too high. By default, a value
of 5 minutes is RECOMMENDED.
For RCODE = 9 (NOTAUTH), which occurs on a server that implements For RCODE = 9 (NOTAUTH), which occurs on a server that implements
DNS Push Notifications, but is not configured to be authoritative DNS Push Notifications, but is not configured to be authoritative
for the requested name, the retry delay may be any value selected for the requested name, 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.
This is a misconfiguration, since this server is listed in a If the server being queried is listed in a
"_dns-push-tls._tcp.<zone>" SRV record, but the server itself is "_dns-push-tls._tcp.<zone>" SRV record for the zone, then this is
not currently configured to support DNS Push Notifications for a misconfiguration, since this server is being advertised as
that zone. Since it is possible that the misconfiguration may be supporting DNS Push Notifications for this zone, but the server
repaired at any time, the retry delay should not be set too high. itself is not currently configured to perform that task. Since it
By default, a value of 5 minutes is RECOMMENDED. is possible that the misconfiguration may be repaired at any time,
the retry delay should not be set too high. By default, a value
of 5 minutes is RECOMMENDED.
For RCODE = 11 (DSOTYPENI), which occurs on a server that doesn't For RCODE = 11 (DSOTYPENI), which occurs on a server that
implement DNS Push Notifications, it is unlikely that the server implements DSO but doesn't implement DNS Push Notifications, it is
will begin supporting DNS Push Notifications in the next few unlikely that the server will begin supporting DNS Push
minutes, so the retry delay SHOULD be one hour. Notifications in the next few minutes, so the retry delay SHOULD
be one hour.
For other RCODE values, the retry delay should be set by the For other RCODE values, the retry delay should be set by the
server as appropriate for that error condition. By default, a server as appropriate for that error condition. By default, a
value of 5 minutes is RECOMMENDED. value of 5 minutes is RECOMMENDED.
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.
skipping to change at page 19, line 9 skipping to change at page 20, line 9
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 [DSO]. 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 non-empty at the moment the subscription case that the answer set was already non-empty at the moment the
was established, an initial PUSH message will be sent immediately subscription was established, an initial PUSH message will be sent
following the SUBSCRIBE Response. Subsequent changes to the answer immediately following the SUBSCRIBE Response. Subsequent changes to
set are then communicated to the client in subsequent PUSH messages. the answer set are then communicated to the client in subsequent PUSH
messages.
6.3.1. PUSH Message 6.3.1. PUSH Message
A PUSH message begins with the standard DSO 12-byte header [DSO], A PUSH unidirectional message begins with the standard DSO 12-byte
followed by the PUSH TLV. A PUSH message is illustrated in Figure 2. header [DSO], followed by the PUSH primary TLV. A PUSH message 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 also be set as described in the DSO The other header fields MUST be set as described in the DSO
specification [DSO]. The DNS Opcode is the DSO Opcode. The four specification [DSO]. The DNS OPCODE field contains the OPCODE value
count fields MUST be zero, and the corresponding four sections MUST for DNS Stateful Operations (6). The four count fields MUST be zero,
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-LENGTH is the The DSO-TYPE is PUSH (tentatively 0x41).
length of the DSO-DATA that follows, which specifies the changes
being communicated. The DSO-LENGTH is the length of the DSO-DATA that follows, which
specifies the changes being communicated.
The DSO-DATA contains one or more Update records. A PUSH Message The DSO-DATA contains one or more Update records. A PUSH Message
MUST contain at least one Update record. If a PUSH Message is MUST contain at least one Update record. If a PUSH Message is
received that contains zero Update records, this is a fatal error, received that contains zero Update records, this is a fatal error,
and the receiver MUST immediately terminate the connection with a TCP and the receiver MUST immediately terminate the connection with a TCP
RST (or equivalent for other protocols). The Update records are RST (or equivalent for other protocols). The Update records are
formatted in the customary way for Resource Records in DNS messages. formatted in the customary way for Resource Records in DNS messages.
Update records in a PUSH Message are interpreted according to the Update records in a PUSH Message are interpreted according to the
same rules as for DNS Update [RFC2136] messages, namely: same rules as for DNS Update [RFC2136] messages, namely:
skipping to change at page 20, line 4 skipping to change at page 21, line 7
Delete an RRset from a name: Delete an RRset from a name:
TTL=0, CLASS=ANY, RDLENGTH=0; TTL=0, CLASS=ANY, RDLENGTH=0;
TYPE specifies the RRset being deleted. TYPE specifies the RRset being deleted.
Delete an individual RR from a name: Delete an individual RR from a name:
TTL=0, CLASS=NONE; TTL=0, CLASS=NONE;
TYPE, RDLENGTH and RDATA specifies the RR being deleted. TYPE, RDLENGTH and RDATA specifies the RR being deleted.
Add to an RRset: Add to an RRset:
TTL, CLASS, TYPE, RDLENGTH and RDATA specifies the RR being added. TTL, CLASS, TYPE, RDLENGTH and RDATA specifies the RR being added.
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
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \
| MESSAGE ID (MUST BE ZERO) | \ | MESSAGE ID (MUST BE ZERO) | \
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
|QR| Opcode | Z | RCODE | | |QR| OPCODE(6) | Z | RCODE | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| QDCOUNT (MUST BE ZERO) | | | QDCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > HEADER +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > HEADER
| ANCOUNT (MUST BE ZERO) | | | ANCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| NSCOUNT (MUST BE ZERO) | | | NSCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| ARCOUNT (MUST BE ZERO) | / | ARCOUNT (MUST BE ZERO) | /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ / +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /
| DSO-TYPE = PUSH | | DSO-TYPE = PUSH (tentatively 0x41) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| DSO-LENGTH (number of octets in DSO-DATA) | | DSO-LENGTH (number of octets in DSO-DATA) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \
\ NAME \ \ \ NAME \ \
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| TYPE | | | TYPE | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| CLASS | | | CLASS | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| TTL | | | TTL | |
skipping to change at page 20, line 49 skipping to change at page 21, line 51
: 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
When processing the records received in a PUSH Message, the receiving When processing the records received in a PUSH Message, the receiving
client MUST validate that the records being added or deleted client MUST validate that the records being added or deleted
correspond with at least one currently active subscription on that correspond with at least one currently active subscription on that
session. Specifically, the record name MUST match the name given in session. Specifically, the record name MUST match the name given in
the SUBSCRIBE request, subject to the usual established DNS case- a SUBSCRIBE request, subject to the usual established DNS case-
insensitivity for US-ASCII letters. If the TYPE in the SUBSCRIBE insensitivity for US-ASCII letters. If the TYPE in the SUBSCRIBE
request was not ANY (255) then the TYPE of the record must match the request was not ANY (255) then the TYPE of the record must match the
TYPE given in the SUBSCRIBE request. If the CLASS in the SUBSCRIBE TYPE given in the SUBSCRIBE request. If the CLASS in the SUBSCRIBE
request was not ANY (255) then the CLASS of the record must match the request was not ANY (255) then the CLASS of the record must match the
CLASS given in the SUBSCRIBE request. If a matching active CLASS given in the SUBSCRIBE request. If a matching active
subscription on that session is not found, then that individual subscription on that session is not found, then that individual
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
skipping to change at page 22, line 10 skipping to change at page 23, 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 [DSO] unidirectional message. This specification defines a DSO unidirectional message [DSO]. This specification defines a
primary unidirectional DSO TLV for DNS Push Notification UNSUBSCRIBE primary unidirectional DSO TLV for DNS Push Notification UNSUBSCRIBE
Requests (tentatively DSO Type Code 0x42). Requests (tentatively DSO Type Code 0x42).
A server MUST NOT initiate an UNSUBSCRIBE request. If a server does A server MUST NOT initiate an UNSUBSCRIBE request. If a server does
send an UNSUBSCRIBE request over a DSO session initiated by a client, send an UNSUBSCRIBE request 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 Request 6.4.1. UNSUBSCRIBE Request
An UNSUBSCRIBE request begins with the standard DSO 12-byte header An UNSUBSCRIBE request begins with the standard DSO 12-byte header
[DSO], followed by the UNSUBSCRIBE TLV. An UNSUBSCRIBE request [DSO], followed by the UNSUBSCRIBE primary TLV. An UNSUBSCRIBE
message is illustrated in Figure 3. request message is illustrated in Figure 3.
The MESSAGE ID field MUST be zero. There is no server response to a In accordance with the definition of DSO unidirectional messages, the
MESSAGE ID field MUST be zero. There is no server response to a
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
specification [DSO]. The DNS Opcode is the DSO Opcode. The four specification [DSO]. The DNS OPCODE field contains the OPCODE value
count fields MUST be zero, and the corresponding four sections MUST for DNS Stateful Operations (6). The four count fields MUST be zero,
be empty (i.e., absent). and the corresponding four sections MUST be empty (i.e., absent).
In the UNSUBSCRIBE TLV the DSO-TYPE is UNSUBSCRIBE. The DSO-LENGTH The DSO-TYPE is UNSUBSCRIBE (tentatively 0x42).
is 2 octets.
The DSO-DATA contains the MESSAGE ID field of the value given in the The DSO-LENGTH field contains the value 2, the length of the 2-octet
ID field of an active SUBSCRIBE request. This is how the server MESSAGE ID contained in the DSO-DATA.
knows which SUBSCRIBE request is being cancelled. After receipt of
the UNSUBSCRIBE request, the SUBSCRIBE request is no longer active. The DSO-DATA contains the value given in the MESSAGE ID field of an
active SUBSCRIBE request. This is how the server knows which
SUBSCRIBE request is being cancelled. After receipt of the
UNSUBSCRIBE request, the SUBSCRIBE request is no longer active.
It is allowable for the client to issue an UNSUBSCRIBE request for a It is allowable for the client to issue an UNSUBSCRIBE request for a
previous SUBSCRIBE request for which the client has not yet received previous SUBSCRIBE request for which the client has not yet received
a SUBSCRIBE response. This is to allow for the case where a client a SUBSCRIBE response. This is to allow for the case where a client
starts and stops a subscription in less than the round-trip time to starts and stops a subscription in less than the round-trip time to
the server. The client is NOT required to wait for the SUBSCRIBE the server. The client is NOT required to wait for the SUBSCRIBE
response before issuing the UNSUBSCRIBE request. response before issuing the UNSUBSCRIBE request.
Consequently, it is possible for a server to receive an UNSUBSCRIBE
request that does not match any currently active subscription. This
can occur when a client sends a SUBSCRIBE request, which subsequently
fails and returns an error code, but the client sent an UNSUBSCRIBE
request before it became aware that the SUBSCRIBE request had failed.
Because of this, servers MUST silently ignore UNSUBSCRIBE requests
that do not match any currently active subscription.
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
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \
| MESSAGE ID (MUST BE ZERO) | \ | MESSAGE ID (MUST BE ZERO) | \
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
|QR| Opcode | Z | RCODE | | |QR| OPCODE(6) | Z | RCODE | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| QDCOUNT (MUST BE ZERO) | | | QDCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > HEADER +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > HEADER
| ANCOUNT (MUST BE ZERO) | | | ANCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| NSCOUNT (MUST BE ZERO) | | | NSCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| ARCOUNT (MUST BE ZERO) | / | ARCOUNT (MUST BE ZERO) | /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ / +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /
| DSO-TYPE = UNSUBSCRIBE | | DSO-TYPE = UNSUBSCRIBE (tentatively 0x42) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| DSO-LENGTH (2 octets) | | DSO-LENGTH (2) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \
| SUBSCRIBE MESSAGE ID | > DSO-DATA | SUBSCRIBE MESSAGE ID | > DSO-DATA
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ / +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /
Figure 3: UNSUBSCRIBE Request Figure 3: UNSUBSCRIBE Request
6.5. DNS Push Notification RECONFIRM 6.5. DNS Push Notification RECONFIRM
Sometimes, particularly when used with a Discovery Proxy [DisProx], a Sometimes, particularly when used with a Discovery Proxy [DisProx], a
DNS Zone may contain stale data. When a client encounters data that DNS Zone may contain stale data. When a client encounters data that
it believe may be stale (e.g., an SRV record referencing a target it believes may be stale (e.g., an SRV record referencing a target
host+port that is not responding to connection requests) the client host+port that is not responding to connection requests) the client
can send a RECONFIRM request to ask the server to re-verify that the can send a RECONFIRM request to ask the server to re-verify that the
data is still valid. For a Discovery Proxy, this causes it to issue data is still valid. For a Discovery Proxy, this causes it to issue
new Multicast DNS requests to ascertain whether the target device is new Multicast DNS requests to ascertain whether the target device is
still present. For other types of DNS server, the RECONFIRM still present. How the Discovery Proxy causes these new Multicast
operation is currently undefined, and SHOULD result in a NOERROR DNS requests to be issued depends on the details of the underlying
response, but otherwise need not cause any action to occur. Frequent Multicast DNS being used. For example, a Discovery Proxy built on
RECONFIRM operations may be a sign of network unreliability, or some Apple's dns_sd.h API responds to a DNS Push Notification RECONFIRM
kind of misconfiguration, so RECONFIRM operations MAY be logged or message by calling the underlying API's DNSServiceReconfirmRecord()
otherwise communicated to a human administrator to assist in routine.
detecting, and remedying, such network problems.
For other types of DNS server, the RECONFIRM operation is currently
undefined, and SHOULD result in a NOERROR response, but otherwise
need not cause any action to occur.
Frequent use of RECONFIRM operations may be a sign of network
unreliability, or some kind of misconfiguration, so RECONFIRM
operations MAY be logged or otherwise communicated to a human
administrator to assist in detecting, and remedying, such network
problems.
If, after receiving a valid RECONFIRM request, the server determines If, after receiving a valid RECONFIRM request, the server determines
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 Request 6.5.1. RECONFIRM Request
A RECONFIRM request begins with the standard DSO 12-byte header A RECONFIRM request begins with the standard DSO 12-byte header
[DSO], followed by the primary DSO RECONFIRM TLV. A RECONFIRM [DSO], followed by the RECONFIRM primary TLV. A RECONFIRM request
request message is illustrated in Figure 4. message is illustrated in Figure 4.
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 RECONFIRM response has not yet cancelled using UNSUBSCRIBE. In the RECONFIRM 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
specification [DSO]. The DNS Opcode is the DSO Opcode. The four specification [DSO]. The DNS OPCODE field contains the OPCODE value
count fields MUST be zero, and the corresponding four sections MUST for DNS Stateful Operations (6). The four count fields MUST be zero,
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-LENGTH is the The DSO-TYPE is RECONFIRM (tentatively 0x43).
length of the data that follows, which specifies the name, type,
class, and content of the record being disputed. The DSO-LENGTH is the length of the data that follows, which
specifies the name, type, class, and content of the record being
disputed.
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
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \
| MESSAGE ID | \ | MESSAGE ID | \
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
|QR| Opcode | Z | RCODE | | |QR| OPCODE(6) | Z | RCODE | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| QDCOUNT (MUST BE ZERO) | | | QDCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > HEADER +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > HEADER
| ANCOUNT (MUST BE ZERO) | | | ANCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| NSCOUNT (MUST BE ZERO) | | | NSCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| ARCOUNT (MUST BE ZERO) | / | ARCOUNT (MUST BE ZERO) | /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ / +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /
| DSO-TYPE = RECONFIRM | | DSO-TYPE = RECONFIRM (tentatively 0x43) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| DSO-LENGTH (number of octets in DSO-DATA) | | DSO-LENGTH (number of octets in DSO-DATA) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \
\ NAME \ \ \ NAME \ \
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| TYPE | | | TYPE | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > DSO-DATA +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > DSO-DATA
| CLASS | | | CLASS | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
\ RDATA \ / \ RDATA \ /
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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.
6.5.2. RECONFIRM Response 6.5.2. RECONFIRM Response
Each RECONFIRM request generates exactly one RECONFIRM response from Each RECONFIRM request generates exactly one RECONFIRM response from
the server. the server.
A RECONFIRM response message begins with the standard DSO 12-byte A RECONFIRM response begins with the standard DSO 12-byte header
header [DSO], possibly followed by one or more optional TLVs, such as [DSO], possibly followed by one or more optional TLVs, such as a
a Retry Delay TLV. For suggested values for the Retry Delay TLV, see Retry Delay TLV. For suggested values for the Retry Delay TLV, see
Section 6.2.2. Section 6.2.2.
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
RECONFIRM request. This is how the client knows which request is RECONFIRM request. This is how the client knows which request is
being responded to. being responded to.
A RECONFIRM response message MUST NOT include a DSO RECONFIRM TLV. A RECONFIRM response message MUST NOT include a DSO RECONFIRM TLV.
If a client receives a RECONFIRM response message containing a If a client receives a RECONFIRM response message containing a
RECONFIRM TLV then the response message is processed but the RECONFIRM TLV then the response message is processed but the
RECONFIRM TLV MUST be silently ignored. RECONFIRM TLV MUST be silently ignored.
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the client's point of view. The client may log them to aid in the client's point of view. The client may log them to aid in
debugging, but otherwise they require no special action. debugging, but otherwise they require no special action.
Nonzero RCODE values other than these three indicate a serious Nonzero RCODE values other than these three indicate a serious
problem with the client. After sending an error response other than problem with the client. After sending an error response other than
one of these three, the server SHOULD send a DSO Retry Delay TLV to one of these three, the server SHOULD send a DSO Retry Delay TLV to
end the DSO session, as described in the DSO specification [DSO]. end the DSO session, as described in the DSO specification [DSO].
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 [DSO], This document defines four new DSO TLVs. As suggested in Section 8.2
Section 8.2, the valid contexts of these new TLV types are summarized of the DNS Stateful Operations specification [DSO], the valid
below. contexts of these new TLV types are summarized below.
The client TLV contexts are: The client TLV contexts are:
C-P: Client primary TLV C-P: Client request message, primary TLV
C-U: Client primary unidirectional TLV C-U: Client unidirectional message, primary TLV
C-A: Client additional TLV C-A: Client request or unidirectional message, additional TLV
CRP: Client response primary TLV CRP: Response back to client, primary TLV
CRA: Client response additional TLV CRA: Response back to client, additional TLV
+-------------+-----+-----+-----+-----+-----+ +-------------+-----+-----+-----+-----+-----+
| TLV Type | C-P | C-U | C-A | CRP | CRA | | TLV Type | C-P | C-U | C-A | CRP | CRA |
+-------------+-----+-----+-----+-----+-----+ +-------------+-----+-----+-----+-----+-----+
| SUBSCRIBE | X | | | | | | SUBSCRIBE | X | | | | |
| PUSH | | | | | | | PUSH | | | | | |
| UNSUBSCRIBE | | X | | | | | UNSUBSCRIBE | | X | | | |
| RECONFIRM | X | | | | | | RECONFIRM | X | | | | |
+-------------+-----+-----+-----+-----+-----+ +-------------+-----+-----+-----+-----+-----+
Table 3: DSO TLV Client Context Summary Table 3: DSO TLV Client Context Summary
The server TLV contexts are: The server TLV contexts are:
S-P: Server primary TLV S-P: Server request message, primary TLV
S-U: Server primary unidirectional TLV S-U: Server unidirectional message, primary TLV
S-A: Server additional TLV S-A: Server request or unidirectional message, additional TLV
SRP: Server response primary TLV SRP: Response back to server, primary TLV
SRA: Server response additional TLV SRA: Response back to server, additional TLV
+-------------+-----+-----+-----+-----+-----+ +-------------+-----+-----+-----+-----+-----+
| TLV Type | S-P | S-U | S-A | SRP | SRA | | TLV Type | S-P | S-U | S-A | SRP | SRA |
+-------------+-----+-----+-----+-----+-----+ +-------------+-----+-----+-----+-----+-----+
| SUBSCRIBE | | | | | | | SUBSCRIBE | | | | | |
| PUSH | | X | | | | | PUSH | | X | | | |
| UNSUBSCRIBE | | | | | | | UNSUBSCRIBE | | | | | |
| RECONFIRM | | | | | | | RECONFIRM | | | | | |
+-------------+-----+-----+-----+-----+-----+ +-------------+-----+-----+-----+-----+-----+
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If a client has performed operations on this session that it would If a client has performed operations on this session that it would
not want lost (like DNS updates) then the client SHOULD do an orderly not want lost (like DNS updates) then the client SHOULD do an orderly
disconnect, sending a TLS close_notify followed by a TCP FIN. (In disconnect, sending a TLS close_notify followed by a TCP FIN. (In
the BSD Sockets API, sending a TCP FIN is achieved by calling the BSD Sockets API, sending a TCP FIN is achieved by calling
"shutdown(s,SHUT_WR)" and keeping the socket open until all remaining "shutdown(s,SHUT_WR)" and keeping the socket open until all remaining
data has been read from it.) data has been read from it.)
7. Security Considerations 7. Security Considerations
The Strict Privacy Usage Profile for DNS over TLS is REQUIRED for DNS The Strict Privacy Usage Profile for DNS over TLS is REQUIRED for DNS
Push Notifications as defined in "Usage Profiles for DNS over TLS and Push Notifications [RFC8310]. Cleartext connections for DNS Push
DNS over DTLS" [RFC8310]. Cleartext connections for DNS Push
Notifications are not permissible. Since this is a new protocol, Notifications are not permissible. Since this is a new protocol,
transition mechanisms from the Opportunistic Privacy profile are transition mechanisms from the Opportunistic Privacy profile are
deemed unnecessary. unnecessary.
Also, see Section 9 of the DNS over (D)TLS Usage Profiles document
[RFC8310] for additional recommendations for various versions of TLS
usage.
DNSSEC is RECOMMENDED for the authentication of DNS Push Notification DNSSEC is RECOMMENDED for the authentication of DNS Push Notification
servers. TLS alone does not provide complete security. TLS servers. TLS alone does not provide complete security. TLS
certificate verification can provide reasonable assurance that the certificate verification can provide reasonable assurance that the
client is really talking to the server associated with the desired client is really talking to the server associated with the desired
host name, but since the desired host name is learned via a DNS SRV host name, but since the desired host name is learned via a DNS SRV
query, if the SRV query is subverted then the client may have a query, if the SRV query is subverted then the client may have a
secure connection to a rogue server. DNSSEC can provided added secure connection to a rogue server. DNSSEC can provided added
confidence that the SRV query has not been subverted. confidence that the SRV query has not been subverted.
skipping to change at page 31, line 11 skipping to change at page 33, line 14
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 Sever
Name Indication (SNI) extension [RFC6066] to inform the server of the Name Indication (SNI) extension [RFC6066] to inform the server of the
name the client has authenticated through the use of TLSA records. name the client has authenticated through the use of TLSA records.
Therefore, if the SRV record passes DNSSEC validation and a TLSA Therefore, if the SRV record passes DNSSEC validation and a TLSA
record matching the target name is useable, an SNI extension must be record matching the target name is useable, an SNI extension must be
used for the target name to ensure the client is connecting to the used for the target name to ensure the client is connecting to the
server it has authenticated. If the target name does not have a server it has authenticated. If the target name does not have a
usable TLSA record, then the use of the SNI extension is optional. 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. Also note that a more information on authenticating domain names.
DNS Push server is an authoritative server and a DNS Push client is a
standard DNS client. While the terminology in Usage Profiles for DNS
over TLS and DNS over DTLS [RFC8310] explicitly states it does not
apply to authoritative servers, it does in this case apply to DNS
Push Notification clients and servers.
7.3. TLS Compression
In order to reduce the chances of compression-related attacks, TLS-
level compression SHOULD be disabled when using TLS versions 1.2 and
earlier. In TLS 1.3 [RFC8446], TLS-level compression has been
removed completely.
7.4. 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 [RFC5246] 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
Push Notification server will not have any subscription state and Push Notification server will not have any subscription state and
will proceed as with any other new DSO session. Use of TLS Session will proceed as with any other new DSO session. Use of TLS Session
Resumption may allow a TLS connection to be set up more quickly, but Resumption may allow a TLS connection to be set up more quickly, but
the client will still have to recreate any desired subscriptions. the client will still have to recreate any desired subscriptions.
8. IANA Considerations 8. IANA Considerations
skipping to change at page 32, line 23 skipping to change at page 34, line 5
+-----------------------+------+----------------------+-------------+ +-----------------------+------+----------------------+-------------+
| DNS Push Notification | None | "_dns-push-tls._tcp" | Section 6.1 | | DNS Push Notification | None | "_dns-push-tls._tcp" | Section 6.1 |
| Service Type | | | | | Service Type | | | |
+-----------------------+------+----------------------+-------------+ +-----------------------+------+----------------------+-------------+
Table 5: IANA Service Type Assignments Table 5: IANA Service Type Assignments
This document also defines four new DNS Stateful Operation TLV types This document also defines four new DNS Stateful Operation TLV types
to be recorded in the IANA DSO Type Code Registry. to be recorded in the IANA DSO Type Code Registry.
+-------------+------------------------+---------------+ +-------------+------------------------+-------------+
| Name | Value | Definition | | Name | Value | Definition |
+-------------+------------------------+---------------+ +-------------+------------------------+-------------+
| SUBSCRIBE | TBA (tentatively 0x40) | Section 6.2 | | SUBSCRIBE | TBA (tentatively 0x40) | Section 6.2 |
| PUSH | TBA (tentatively 0x41) | Section 6.3.1 | | PUSH | TBA (tentatively 0x41) | Section 6.3 |
| UNSUBSCRIBE | TBA (tentatively 0x42) | Section 6.4 | | UNSUBSCRIBE | TBA (tentatively 0x42) | Section 6.4 |
| RECONFIRM | TBA (tentatively 0x43) | Section 6.5.1 | | RECONFIRM | TBA (tentatively 0x43) | Section 6.5 |
+-------------+------------------------+---------------+ +-------------+------------------------+-------------+
Table 6: IANA DSO TLV Type Code Assignments Table 6: IANA DSO TLV Type Code Assignments
9. Acknowledgements 9. Acknowledgements
The authors would like to thank Kiren Sekar and Marc Krochmal for The authors would like to thank Kiren Sekar and Marc Krochmal for
previous work completed in this field. previous work completed in this field.
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
skipping to change at page 34, line 5 skipping to change at page 35, line 25
[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>.
[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>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>.
[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>.
[RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S. [RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
Cheshire, "Internet Assigned Numbers Authority (IANA) Cheshire, "Internet Assigned Numbers Authority (IANA)
Procedures for the Management of the Service Name and Procedures for the Management of the Service Name and
Transport Protocol Port Number Registry", BCP 165, Transport Protocol Port Number Registry", BCP 165,
RFC 6335, DOI 10.17487/RFC6335, August 2011, RFC 6335, DOI 10.17487/RFC6335, August 2011,
skipping to change at page 36, line 5 skipping to change at page 37, line 23
[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>.
[RFC6824] Ford, A., Raiciu, C., Handley, M., and O. Bonaventure, [RFC6824] Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
"TCP Extensions for Multipath Operation with Multiple "TCP Extensions for Multipath Operation with Multiple
Addresses", RFC 6824, DOI 10.17487/RFC6824, January 2013, Addresses", RFC 6824, DOI 10.17487/RFC6824, January 2013,
<https://www.rfc-editor.org/info/rfc6824>. <https://www.rfc-editor.org/info/rfc6824>.
[RFC6886] Cheshire, S. and M. Krochmal, "NAT Port Mapping Protocol
(NAT-PMP)", RFC 6886, DOI 10.17487/RFC6886, April 2013,
<https://www.rfc-editor.org/info/rfc6886>.
[RFC6887] Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R., and
P. Selkirk, "Port Control Protocol (PCP)", RFC 6887,
DOI 10.17487/RFC6887, April 2013,
<https://www.rfc-editor.org/info/rfc6887>.
[RFC7413] Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP [RFC7413] Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP
Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014, Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014,
<https://www.rfc-editor.org/info/rfc7413>. <https://www.rfc-editor.org/info/rfc7413>.
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre, [RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer "Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <https://www.rfc-editor.org/info/rfc7525>. 2015, <https://www.rfc-editor.org/info/rfc7525>.
skipping to change at page 37, line 17 skipping to change at page 38, line 39
Tom Pusateri Tom Pusateri
Unaffiliated Unaffiliated
Raleigh, NC 27608 Raleigh, NC 27608
USA USA
Phone: +1 919 867 1330 Phone: +1 919 867 1330
Email: pusateri@bangj.com Email: pusateri@bangj.com
Stuart Cheshire Stuart Cheshire
Apple Inc. Apple Inc.
1 Infinite Loop One Apple Park Way
Cupertino, CA 95014 Cupertino, CA 95014
USA USA
Phone: +1 408 974 3207 Phone: +1 (408) 996-1010
Email: cheshire@apple.com Email: cheshire@apple.com
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