draft-ietf-dnssd-push-09.txt   draft-ietf-dnssd-push-10.txt 
Internet Engineering Task Force T. Pusateri Internet Engineering Task Force T. Pusateri
Internet-Draft Seeking affiliation Internet-Draft Seeking affiliation
Intended status: Standards Track S. Cheshire Intended status: Standards Track S. Cheshire
Expires: May 4, 2017 Apple Inc. Expires: September 14, 2017 Apple Inc.
October 31, 2016 March 13, 2017
DNS Push Notifications DNS Push Notifications
draft-ietf-dnssd-push-09 draft-ietf-dnssd-push-10
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 is relatively static. When efficiently for queries for data that is 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. But there exists no mechanism for a the updated results when polled. But there exists no mechanism
client to be asynchronously notified when these changes occur. This for a client to be asynchronously notified when these changes occur.
document defines a mechanism for a client to be notified of such This document defines a mechanism for a client to be notified
changes to DNS records, called DNS Push Notifications. of such changes to DNS records, called DNS Push Notifications.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://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 4, 2017. This Internet-Draft will expire on September 14, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2017 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
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Transport . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4. Transport . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5. State Considerations . . . . . . . . . . . . . . . . . . . . 6 5. State Considerations . . . . . . . . . . . . . . . . . . . . 8
6. Protocol Operation . . . . . . . . . . . . . . . . . . . . . 7 6. Protocol Operation . . . . . . . . . . . . . . . . . . . . . 9
6.1. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 8 6.1. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 10
6.2. DNS Push Notification SUBSCRIBE . . . . . . . . . . . . . 10 6.2. DNS Push Notification SUBSCRIBE . . . . . . . . . . . . . 12
6.2.1. SUBSCRIBE Request . . . . . . . . . . . . . . . . . . 11 6.2.1. SUBSCRIBE Request . . . . . . . . . . . . . . . . . . 13
6.2.2. SUBSCRIBE Response . . . . . . . . . . . . . . . . . 14 6.2.2. SUBSCRIBE Response . . . . . . . . . . . . . . . . . 15
6.3. DNS Push Notification Update Messages . . . . . . . . . . 18 6.3. DNS Push Notification Updates . . . . . . . . . . . . . . 18
6.3.1. PUSH Message format . . . . . . . . . . . . . . . . . 18 6.3.1. PUSH Message . . . . . . . . . . . . . . . . . . . . 19
6.4. DNS Push Notification UNSUBSCRIBE . . . . . . . . . . . . 21 6.3.2. PUSH Response . . . . . . . . . . . . . . . . . . . . 21
6.4.1. UNSUBSCRIBE Request . . . . . . . . . . . . . . . . . 22 6.4. DNS Push Notification UNSUBSCRIBE . . . . . . . . . . . . 22
6.4.1. UNSUBSCRIBE Request . . . . . . . . . . . . . . . . . 23
6.4.2. UNSUBSCRIBE Response . . . . . . . . . . . . . . . . 24 6.4.2. UNSUBSCRIBE Response . . . . . . . . . . . . . . . . 24
6.5. DNS Session Signaling Push Notification RECONFIRM . . . . 26 6.5. DNS Push Notification RECONFIRM . . . . . . . . . . . . . 26
6.6. Client-Initiated Termination . . . . . . . . . . . . . . 28 6.5.1. RECONFIRM Request . . . . . . . . . . . . . . . . . . 26
7. Security Considerations . . . . . . . . . . . . . . . . . . . 28 6.5.2. RECONFIRM Response . . . . . . . . . . . . . . . . . 28
7.1. Security Services . . . . . . . . . . . . . . . . . . . . 29 6.6. Client-Initiated Termination . . . . . . . . . . . . . . 30
7.2. TLS Name Authentication . . . . . . . . . . . . . . . . . 29 7. Security Considerations . . . . . . . . . . . . . . . . . . . 31
7.3. TLS Compression . . . . . . . . . . . . . . . . . . . . . 30 7.1. Security Services . . . . . . . . . . . . . . . . . . . . 31
7.4. TLS Session Resumption . . . . . . . . . . . . . . . . . 30 7.2. TLS Name Authentication . . . . . . . . . . . . . . . . . 31
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30 7.3. TLS Compression . . . . . . . . . . . . . . . . . . . . . 32
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 30 7.4. TLS Session Resumption . . . . . . . . . . . . . . . . . 32
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 31 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32
10.1. Normative References . . . . . . . . . . . . . . . . . . 31 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 32
10.2. Informative References . . . . . . . . . . . . . . . . . 32 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 33
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34 10.1. Normative References . . . . . . . . . . . . . . . . . . 33
10.2. Informative References . . . . . . . . . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 36
1. Introduction 1. Introduction
DNS records may be updated using DNS Update [RFC2136]. Other DNS records may be updated using DNS Update [RFC2136]. Other
mechanisms such as a Hybrid Proxy [I-D.ietf-dnssd-hybrid] can also mechanisms such as a Discovery Proxy [DisProx] can also generate
generate changes to a DNS zone. This document specifies a protocol changes to a DNS zone. This document specifies a protocol for DNS
for DNS clients to subscribe to receive asynchronous notifications of clients to subscribe to receive asynchronous notifications of changes
changes to RRSets of interest. It is immediately relevant in the to RRSets of interest. It is immediately relevant in the case of DNS
case of DNS Service Discovery [RFC6763] but is not limited to that Service Discovery [RFC6763] but is not limited to that use case, and
use case, and provides a general DNS mechanism for DNS record change provides a general DNS mechanism for DNS record change notifications.
notifications. Familiarity with the DNS protocol and DNS packet Familiarity with the DNS protocol and DNS packet formats is assumed
formats is assumed [RFC1034] [RFC1035] [RFC6895]. [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" [RFC2119]. "Key words for use in RFCs to Indicate Requirement Levels" [RFC2119].
2. Motivation 2. Motivation
skipping to change at page 3, line 30 skipping to change at page 4, line 23
generally highly tuned and capable of a high rate of query/response generally highly tuned and capable of a high rate of query/response
traffic, adding a publish/subscribe model for tracking changes to DNS traffic, adding a publish/subscribe model for tracking changes to DNS
records can result in more timely notification of changes with records can result in more timely notification of changes with
reduced CPU usage and lower network traffic. reduced CPU usage and lower network traffic.
Multicast DNS [RFC6762] implementations always listen on a well known Multicast DNS [RFC6762] implementations always listen on a well known
link-local IP multicast group, and new services and updates are sent link-local IP multicast group, and new services and updates are sent
for all group members to receive. Therefore, Multicast DNS already for all group members to receive. Therefore, Multicast DNS already
has asynchronous change notification capability. However, when DNS has asynchronous change notification capability. However, when DNS
Service Discovery [RFC6763] is used across a wide area network using Service Discovery [RFC6763] is used across a wide area network using
Unicast DNS (possibly facilitated via a Hybrid Proxy Unicast DNS (possibly facilitated via a Discovery Proxy [DisProx]) it
[I-D.ietf-dnssd-hybrid]) it would be beneficial to have an equivalent would be beneficial to have an equivalent capability for Unicast DNS,
capability for Unicast DNS, to allow clients to learn about DNS to allow clients to learn about DNS record changes in a timely manner
record changes in a timely manner without polling. without polling.
DNS Long-Lived Queries (LLQ) [I-D.sekar-dns-llq] is an existing
deployed solution to provide asynchronous change notifications. Even
though it can be used over TCP, LLQ is defined primarily as a UDP-
based protocol, and as such it defines its own equivalents of
existing TCP features like the three-way handshake, flow control, and
reliability. This document builds on experience gained with the LLQ
protocol, with an improved design. Instead of using UDP, this
specification uses long-lived TCP connections
[I-D.ietf-dnsop-session-signal], and therefore doesn't need to
reinvent existing TCP functionality. Instead of inventing a new
vocabulary of messages to communicate DNS zone changes, this
specification adopts the syntax and semantics of DNS Update messages
[RFC2136].
DNS Push Notifications impose less load on the responding server than
rapid polling would, but Push Notifications do still have a cost, so
DNS Push Notification clients MUST NOT recklessly create an excessive
number of Push Notification subscriptions. A subscription SHOULD
only be active when there is a valid reason to need live data (for
example, an on-screen display is currently showing the results to the
user) and the subscription SHOULD be cancelled as soon as the need
for that data ends (for example, when the user dismisses that
display). Implementations MAY want to implement idle timeouts, so
that if the user ceases interacting with the device, the display
showing the result of the DNS Push Notification subscription is
automatically dismissed after a certain period of inactivity. For
example, if a user presses the "Print" button on their smartphone,
and then leaves the phone showing the printer discovery screen until
the phone goes to sleep, then the printer discovery screen should be
automatically dismissed as the device goes to sleep. If the user
does still intend to print, this will require them to press the
"Print" button again when they wake their phone up.
A DNS Push Notification client MUST NOT routinely keep a DNS Push The DNS Long-Lived Queries (LLQ) [I-D.sekar-dns-llq] mechanism is an
Notification subscription active 24 hours a day 7 days a week just to existing deployed solution to provide asynchronous change
keep a list in memory up to date so that it will be really fast if notifications, used by Apple's Back to My Mac Service [RFC6281].
the user does choose to bring up an on-screen display of that data. Back to My Mac was designed in an era when the data centre operations
DNS Push Notifications are designed to be fast enough that there is staff asserted that it was impossible for a server to handle large
no need to pre-load a "warm" list in memory just in case it might be numbers of mostly-idle TCP connections, so LLQ had to defined as a
needed later. UDP-based protocol, effectively replicating much of TCP's connection
state management logic in user space, and creating its own poor
imitations of existing TCP features like the three-way handshake,
flow control, and reliability.
Generally, a client SHOULD NOT keep a connection to a server open This document builds on experience gained with the LLQ protocol, with
indefinitely if it has no active subscriptions on that connection. an improved design. Instead of using UDP, this specification uses
After 30 seconds with no active subscriptions the client SHOULD close TCP, and therefore doesn't need to reinvent existing TCP
the idle connection, and, if needed in the future, open a new functionality. Using TCP also gives long-lived low-traffic
connection. connections better longevity through NAT gateways without resorting
to excessive keepalive traffic [SessSig]. Instead of inventing a new
vocabulary of messages to communicate DNS zone changes as LLQ did,
this specification adopts the 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
skipping to change at page 6, line 5 skipping to change at page 6, line 8
comes to an authoritative server informing a client of changes to DNS comes to an authoritative server informing a client of changes to DNS
records. 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". DNS class "IN".
DNS Push Notifications impose less load on the responding server than
rapid polling would, but Push Notifications do still have a cost, so
DNS Push Notification clients MUST NOT recklessly create an excessive
number of Push Notification subscriptions. A subscription SHOULD
only be active when there is a valid reason to need live data (for
example, an on-screen display is currently showing the results to the
user) and the subscription SHOULD be cancelled as soon as the need
for that data ends (for example, when the user dismisses that
display). Implementations MAY want to implement idle timeouts, so
that if the user ceases interacting with the device, the display
showing the result of the DNS Push Notification subscription is
automatically dismissed after a certain period of inactivity. For
example, if a user presses the "Print" button on their smartphone,
and then leaves the phone showing the printer discovery screen until
the phone goes to sleep, then the printer discovery screen should be
automatically dismissed as the device goes to sleep. If the user
does still intend to print, this will require them to press the
"Print" button again when they wake their phone up.
A DNS Push Notification client MUST NOT routinely keep a DNS 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 choose
to bring up an on-screen display of that data, it can 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 just in
case it might be needed later.
Generally, as described in the DNS Session Signaling specification
[SessSig], a client MUST NOT keep a connection to a server open
indefinitely if it has no subscriptions (or other operations) active
on that connection. A client MAY close a connection as soon as it
becomes idle, and then if needed in the future, open a new connection
when required. Alternatively, a client MAY speculatively keep an
idle connection open for some time, subject to the constraint that it
MUST NOT keep a connection open that has been idle for more than the
session's idle timeout (15 seconds by default).
4. Transport 4. Transport
Implementations of DNS Update [RFC2136] MAY use either User Datagram Implementations of DNS Update [RFC2136] MAY use either User Datagram
Protocol (UDP) [RFC0768] or Transmission Control Protocol (TCP) Protocol (UDP) [RFC0768] or Transmission Control Protocol (TCP)
[RFC0793] as the transport protocol, in keeping with the historical [RFC0793] as the transport protocol, in keeping with the historical
precedent that DNS queries must first be sent over UDP [RFC1123]. precedent that DNS queries must first be sent over UDP [RFC1123].
This requirement to use UDP has subsequently been relaxed [RFC7766]. This requirement to use UDP has subsequently been relaxed [RFC7766].
In keeping with the more recent precedent, DNS Push Notification is In keeping with the more recent precedent, DNS Push Notification is
defined only for TCP. DNS Push Notification clients MUST use TLS defined only for TCP. DNS Push Notification clients MUST use TLS
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and DANE TLSA records [RFC7673] is strongly encouraged. See below in and DANE TLSA records [RFC7673] is strongly encouraged. See below in
Section 7.2 for details. Section 7.2 for details.
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
number of Push Notification subscriptions. This number will vary number of Push Notification subscriptions. This number will vary
from server to server and is based on physical machine from server to server and is based on physical machine
characteristics, network bandwidth, and operating system resource characteristics, network bandwidth, and operating system resource
allocation. After a client establishes a connection to a DNS server, allocation. After a client establishes a connection to a DNS server,
each record subscription is individually accepted or rejected. each subscription is individually accepted or rejected. Servers may
Servers may employ various techniques to limit subscriptions to a employ various techniques to limit subscriptions to a manageable
manageable level. Correspondingly, the client is free to establish level. Correspondingly, the client is free to establish simultaneous
simultaneous connections to alternate DNS servers that support DNS connections to alternate DNS servers that support DNS Push
Push Notifications for the zone and distribute record subscriptions Notifications for the zone and distribute subscriptions at its
at its discretion. In this way, both clients and servers can react discretion. In this way, both clients and servers can react to
to resource constraints. Token bucket rate limiting schemes are also resource constraints. Token bucket rate limiting schemes are also
effective in providing fairness by a server across numerous client effective in providing fairness by a server across numerous client
requests. requests.
6. Protocol Operation 6. Protocol Operation
The DNS Push Notification protocol is a session-oriented protocol, The DNS Push Notification protocol is a session-oriented protocol,
and makes use of DNS Session Signaling and makes use of DNS Session Signaling [SessSig].
[I-D.ietf-dnsop-session-signal].
For details of the DNS Session Signaling message format refer to the
DNS Session Signaling specification [SessSig]. Those details are not
repeated here.
DNS Push Notification clients and servers MUST support DNS Session DNS Push Notification clients and servers MUST support DNS Session
Signaling, but the server must not issue any DNS Session Signaling Signaling, but the server MUST NOT issue any DNS Session Signaling
operations until after the client has first initiated a DNS Session operations until after the client has first initiated a DNS Session
Signaling operation of its own. A single server can support DNS Signaling operation of its own. A single server can support DNS
Queries, DNS Updates, and DNS Push Notifications (using DNS Session Queries, DNS Updates, and DNS Push Notifications (using DNS Session
Signaling) on the same TCP port, and until the client has sent at Signaling) on the same TCP port, and until the client has sent at
least one DNS Session Signaling operation the server does not know least one DNS Session Signaling operation the server does not know
what kind of client has connected to it. Once the client has what kind of client has connected to it. Once the client has
indicated willingness to use DNS Session Signaling operations by indicated willingness to use DNS Session Signaling operations by
sending one of its own, either side of the connection may then sending one of its own, either side of the connection may then
initiate further Session Signaling operations at any time. initiate further Session Signaling operations at any time.
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 DNS A typical DNS Push Notification client will immediately issue a DNS
Session Signaling Idle Timeout operation to request a session timeout Session Signaling Keepalive operation to request a session timeout or
longer than the the 30-second default, but this is NOT REQUIRED. A keepalive interval longer than the the 15-second defaults, but this
DNS Push Notification client MAY issue other requests on the is NOT REQUIRED. A DNS Push Notification client MAY issue other
connection first, and only issue a DNS Session Signaling Idle Timeout requests on the connection first, and only issue a DNS Session
operation later if it determines that to be necessary. Signaling Keepalive operation later if it determines that to be
necessary.
Once the connection is made, the client may then add and remove Push Once the connection is made, the client may then add and remove Push
Notification subscriptions. In accordance with the current set of Notification subscriptions. In accordance with the current set of
active subscriptions the server sends relevant asynchronous Push active subscriptions the server sends relevant asynchronous Push
Notifications to the client. Note that a client MUST be prepared to Notifications to the client. Note that a client MUST be prepared to
receive (and silently ignore) Push Notifications for subscriptions it receive (and silently ignore) Push Notifications for subscriptions it
has previously removed, since there is no way to prevent the has previously removed, since there is no way to prevent the
situation where a Push Notification is in flight from server to situation where a Push Notification is in flight from server to
client while the client's UNSUBSCRIBE message cancelling that client while the client's UNSUBSCRIBE message cancelling that
subscription is simultaneously in flight from client to server. subscription is simultaneously in flight from client to server.
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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 client MUST also determine which TCP port on the desired zone. The client MUST also determine which TCP port on
the server is listening for connections, which need not be (and often the server is listening for connections, which need not be (and often
is not) the typical TCP port 53 used for conventional DNS, or TCP is not) the typical TCP port 53 used for conventional DNS, or TCP
port 853 used for DNS over TLS [RFC7858]. port 853 used for DNS over TLS [RFC7858].
1. The client begins the discovery by sending a DNS query to the 1. The client begins the discovery by sending a DNS query to its
local resolver with record type SOA [RFC1035] for the name of the local resolver, with record type SOA [RFC1035], for the domain
record it wishes to subscribe. name to which it wishes to subscribe.
2. If the SOA record exists, it MUST be returned in the Answer 2. If the SOA record exists, it MUST be returned in the Answer
Section of the response. If not, the local resolver SHOULD Section of the response. If not, the local resolver SHOULD
include the SOA record for the zone of the requested name in the include the SOA record for the zone of the requested name in the
Authority Section. Authority Section.
3. If no SOA record is returned, the client then strips off the 3. If no SOA record is returned, the client then strips off the
leading label from the requested name. If the resulting name has leading label from the requested name. If the resulting name has
at least one label in it, the client sends a new SOA query and at least one label in it, the client sends a new SOA query and
processing continues at step 2 above. If the resulting name is processing continues at step 2 above. If the resulting name is
empty (the root label) then this is a network configuration error empty (the root label) then this is a network configuration error
and the client gives up. The client MAY retry the operation at a and the client gives up. The client MAY retry the operation at a
later time. later time, of the client's choosing, such after a change in
network attachment.
4. Once the SOA is known (either by virtue of being seen in the 4. 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.
5. If the zone in question does not offer DNS Push Notifications 5. If the zone in question does not offer DNS Push Notifications
then SRV record MUST NOT exist and the SRV query will return a then SRV record MUST NOT exist and the SRV query will return a
negative answer. negative answer.
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connection, it SHOULD repeat the discovery process in order to connection, it SHOULD repeat the discovery process in order to
determine the preferred DNS server for subscriptions at that time. determine the preferred DNS server for subscriptions at that time.
Note that this repeated discovery step is typically very fast and Note that this repeated discovery step is typically very fast and
typically results in no queries on the network. The client device typically results in no queries on the network. The client device
MUST respect the DNS TTL values on records it receives, and store MUST respect the DNS TTL values on records it receives, and store
them in its local cache with this lifetime. This means that, as long them in its local cache with this lifetime. This means that, as long
as the DNS TTL values on the authoritative records were set to as the DNS TTL values on the authoritative records were set to
reasonable values, repeated application of this discovery process can reasonable values, repeated application of this discovery process can
be completed nearly instantaneously by the client, using only be completed nearly instantaneously by the client, using only
locally-stored data. locally-stored cached data.
6.2. DNS Push Notification SUBSCRIBE 6.2. DNS Push Notification SUBSCRIBE
After connecting, and requesting a longer idle timeout if necessary, After connecting, and requesting a longer idle timeout and/or
a DNS Push Notification client then indicates its desire to receive keepalive interval if necessary, a DNS Push Notification client then
DNS Push Notifications for a given domain name by sending a SUBSCRIBE indicates its desire to receive DNS Push Notifications for a given
request over the established TLS connection to the server. A domain name by sending a SUBSCRIBE request over the established TLS
SUBSCRIBE request is encoded in a DNS Session Signaling connection to the server. A SUBSCRIBE request is encoded in a DNS
[I-D.ietf-dnsop-session-signal] message. This specification defines Session Signaling [SessSig] message. This specification defines a
a new DNS Session Signaling TLV for DNS Push Notification SUBSCRIBE DNS Session Signaling TLV for DNS Push Notification SUBSCRIBE
Requests/Responses (tentatively Session Signaling Type Code 64). Requests/Responses (tentatively Session Signaling Type Code 0x40).
A server may not initiate a SUBSCRIBE request. A server MUST NOT initiate a SUBSCRIBE request.
6.2.1. SUBSCRIBE Request 6.2.1. SUBSCRIBE Request
A SUBSCRIBE request message begins with the standard DNS Session A SUBSCRIBE request message begins with the standard DNS Session
Signaling 4-byte header [I-D.ietf-dnsop-session-signal], followed by Signaling 12-byte header [SessSig], followed by the SUBSCRIBE TLV.
the SUBSCRIBE TLV. The SSOP-DATA for the the SUBSCRIBE TLV is as follows:
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 |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|QR| Opcode | Z | RCODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| SSOP-TYPE (SUBSCRIBE) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| SSOP-LENGTH |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| | | |
\ QNAME \ \ NAME \
\ \ \ \
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| QTYPE | | TYPE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| QCLASS | | CLASS |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Figure 1 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 connection. For is not using for any other active operation on this connection. For
the purposes here, a MESSAGE ID is in use on this connection if the the purposes here, a MESSAGE ID is in use on this connection 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 if the client has used it for a subscription which it response, or if 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.
In a request the DNS Header QR bit MUST be zero. In the SUBSCRIBE TLV the SSOP-TYPE is SUBSCRIBE (tentatively 0x40).
The SSOP-LENGTH is the length of the SSOP-DATA that follows, which
The DNS Header Opcode field holds the Session Signaling Opcode value
(tentatively 6).
The Z bits MUST be zero on transmission, and MUST be silently ignored
on reception.
The return code (RCODE) field MUST be set to 0 in a request.
In the SUBSCRIBE TLV the SSOP-TYPE is SUBSCRIBE (tentatively 64).
The SSOP-LENGTH is the length of the data that follows, which
specifies the name, type, and class of the record(s) being sought. specifies the name, type, and class of the record(s) being sought.
A SUBSCRIBE request MUST contain exactly one question. There is no A SUBSCRIBE request MUST contain exactly one question. The SUBSCRIBE
QCOUNT field to specify more than one question. Since SUBSCRIBE TLV has no QDCOUNT field to specify more than one question. Since
requests are sent over TCP, multiple SUBSCRIBE requests can be SUBSCRIBE requests are sent over TCP, multiple SUBSCRIBE request
concatenated in a single TCP stream and packed efficiently into TCP messages can be concatenated in a single TCP stream and packed
segments. 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 connection cancels the subscription using UNSUBSCRIBE or until the connection
between the client and the server is closed. between the client and the server is closed.
SUBSCRIBE requests on a given connection MUST be unique. A client SUBSCRIBE requests on a given connection MUST be unique. A client
MUST NOT send a SUBSCRIBE message that duplicates the QNAME, QTYPE MUST NOT send a SUBSCRIBE message that duplicates the NAME, TYPE and
and QCLASS of an existing active subscription on that TLS/TCP CLASS of an existing active subscription on that TLS/TCP connection.
connection. For the purpose of this matching, the established DNS For the purpose of this matching, the established DNS case-
case-insensitivity for US-ASCII letters applies (e.g., "foo.com" and insensitivity for US-ASCII letters applies (e.g., "foo.com" and
"Foo.com" are the same). If a server receives such a duplicate "Foo.com" are the same). If a server receives such a duplicate
SUBSCRIBE message this is an error and the server MUST immediately SUBSCRIBE message this is an error and the server MUST immediately
close the TCP connection. immediately terminate the connection with a TCP RST (or equivalent
for other protocols).
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 accept these requests and send Push Notifications if
and when matching records are found in the future. and when matching records are found in the future.
If neither QTYPE nor QCLASS 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 QNAME, QTYPE and QCLASS. If subscription to changes for the given NAME, TYPE and CLASS. If one
one or both of QTYPE or QCLASS are ANY (255) then this subscription or both of TYPE or CLASS are ANY (255) then this subscription matches
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
and unexpected results, were a query returns some valid answers but and unexpected results, were a query returns some valid answers but
not all of them, and makes QTYPE=ANY queries less useful than people not all of them, and makes QTYPE=ANY queries less useful than people
sometimes imagine. sometimes imagine.
When used in conjunction with SUBSCRIBE, QTYPE and QCLASS 255 should When used in conjunction with SUBSCRIBE, TYPE and CLASS 255 should be
be interpreted to mean "ALL", not "ANY". After accepting a interpreted to mean "ALL", not "ANY". After accepting a subscription
subscription where one or both of QTYPE or QCLASS are 255, the server where one or both of TYPE or CLASS are 255, the server MUST send Push
MUST send Push Notification Updates for ALL record changes that match Notification Updates for ALL record changes that match the
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 DNS Session A SUBSCRIBE response message begins with the standard DNS Session
Signaling 4-byte header [I-D.ietf-dnsop-session-signal], possibly Signaling 12-byte header [SessSig], possibly followed by one or more
followed by one or more optional modifier TLVs such as a Terminate optional Modifier TLVs, such as a Retry Delay Modifier TLV.
modifier TLV [I-D.ietf-dnsop-session-signal].
1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| MESSAGE ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|QR| Opcode | Z | RCODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Figure 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
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.
In a response the DNS Header QR bit MUST be one. A SUBSCRIBE response message MUST NOT contain a Session Signaling
If the QR bit is not one the message is not a response. Operation TLV. The Session Signaling Operation TLV is NOT copied
from the SUBSCRIBE request.
The DNS Header Opcode field holds the Session Signaling Opcode value
(tentatively 6).
The Z bits MUST be zero on transmission, and MUST be silently ignored
on reception.
In the SUBSCRIBE response the RCODE indicates whether or not the In the SUBSCRIBE response the RCODE indicates whether or not the
subscription was accepted. Supported RCODEs are as follows: subscription was accepted. Supported RCODEs are as follows:
+------------+-------+----------------------------------------------+ +------------+-------+----------------------------------------------+
| Mnemonic | Value | Description | | Mnemonic | Value | Description |
+------------+-------+----------------------------------------------+ +------------+-------+----------------------------------------------+
| NOERROR | 0 | SUBSCRIBE successful. | | NOERROR | 0 | SUBSCRIBE successful. |
| FORMERR | 1 | Server failed to process request due to a | | FORMERR | 1 | Server failed to process request due to a |
| | | malformed request. | | | | malformed request. |
skipping to change at page 16, line 12 skipping to change at page 16, line 12
clients MUST be prepared to accept SUBSCRIBE Responses with any RCODE clients MUST be prepared to accept SUBSCRIBE Responses with any RCODE
value. value.
If the server sends a nonzero RCODE in the SUBSCRIBE response, either If the server sends a nonzero RCODE in the SUBSCRIBE response, either
the client is (at least partially) misconfigured or the server the client is (at least partially) misconfigured or the server
resources are exhausted. In either case, the client shouldn't retry resources are exhausted. In either case, the client shouldn't retry
the subscription right away. Either end can terminate the the subscription right away. Either end can terminate the
connection, but the client may want to try this subscription again or connection, but the client may want to try this subscription again or
it may have other successful subscriptions that it doesn't want to it may have other successful subscriptions that it doesn't want to
abandon. If the server sends a nonzero RCODE then it SHOULD append a abandon. If the server sends a nonzero RCODE then it SHOULD append a
Terminate modifier TLV [I-D.ietf-dnsop-session-signal] to the Retry Delay Modifier TLV [SessSig] to the response specifying a delay
response specifying a delay before the client attempts this operation before the client attempts this operation again. Recommended values
again. Recommended values for the delay for different RCODE values for the delay for different RCODE values are given below:
are given below:
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 avoid implementer. A value of five minutes is RECOMMENDED, to reduce
high load from defective clients. the risk of high load from defective clients.
For RCODE = 2 (SERVFAIL), which occurs due to resource exhaustion, For RCODE = 2 (SERVFAIL), which occurs due to resource exhaustion,
the delay should be chosen according to the level of server the delay should be chosen according to the level of server
overload and the anticipated duration of that overload. By overload and the anticipated duration of that overload. By
default, a value of one minute is RECOMMENDED. default, a value of one minute is RECOMMENDED.
For RCODE = 4 (NOTIMP), which occurs on a server that doesn't For RCODE = 4 (NOTIMP), which occurs on a server that doesn't
implement DNS Session Signaling [I-D.ietf-dnsop-session-signal], implement DNS Session Signaling [SessSig], it is unlikely that the
it is unlikely that the server will begin supporting DNS Session server will begin supporting DNS Session Signaling in the next few
Signaling in the next few minutes, so the retry delay SHOULD be minutes, so the retry delay SHOULD be one hour.
one hour.
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.
This is a misconfiguration, since this server is listed in a This is a misconfiguration, since this server is listed in a
"_dns-push-tls._tcp.<zone>" SRV record, but the server itself is "_dns-push-tls._tcp.<zone>" SRV record, but the server itself is
not currently configured to support DNS Push Notifications. Since not currently configured to support DNS Push Notifications. Since
it is possible that the misconfiguration may be repaired at any it is possible that the misconfiguration may be repaired at any
time, the retry delay should not be set too high. By default, a time, the retry delay should not be set too high. By default, a
skipping to change at page 17, line 22 skipping to change at page 17, line 22
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.
After sending an error response the server MAY allow the connection After sending an error response the server MAY allow the connection
to remain open, or MAY send a DNS Push Notification Terminate Session to remain open, or MAY send a DNS Push Notification Retry Delay
operation TLV and then close the TCP connection, as described in the Operation TLV and then close the TCP connection, as described in the
DNS Session Signaling specification [I-D.ietf-dnsop-session-signal]. DNS Session Signaling specification [SessSig]. Clients MUST
Clients MUST correctly handle both cases. correctly handle both cases.
6.3. DNS Push Notification Update Messages 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. An generates PUSH messages to send to the client as appropriate. In the
initial PUSH message will be sent immediately in the case that the case that the answer set was non-empty at the moment the subscription
answer set was non-empty at the moment the subscription was was established, an initial PUSH message will be sent immediately
established. Subsequent changes to the answer set are then following the SUBSCRIBE Response. Subsequent changes to the answer
communicated to the client in subsequent PUSH messages. set are then communicated to the client in subsequent PUSH messages.
6.3.1. PUSH Message format
A PUSH message begins with the standard DNS Session Signaling 4-byte
header [I-D.ietf-dnsop-session-signal], followed by the PUSH TLV.
The format of PUSH messages borrows from the existing DNS Update
[RFC2136] protocol, with some simplifications.
1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| MESSAGE ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|QR| Opcode | Z | RCODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| SSOP-TYPE (PUSH) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| SSOP-LENGTH |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| UPCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| |
\ Resource Records... \
\ \
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Figure 3
The MESSAGE ID field MUST be set to zero on transmission, and
silently ignored on reception. A PUSH message could potentially
match more than one subscription, or could relate to a subscription
that the client has just cancelled with an UNSUBSCRIBE message, so
the MESSAGE ID field serves no useful purpose.
In a PUSH message the DNS Header QR bit MUST be zero.
The DNS Header Opcode field holds the Session Signaling Opcode value 6.3.1. PUSH Message
(tentatively 6).
The Z bits MUST be zero on transmission, and MUST be silently ignored A PUSH message begins with the standard DNS Session Signaling 12-byte
on reception. header [SessSig], followed by the PUSH TLV.
The return code (RCODE) field MUST be set to 0 in a request. The MESSAGE ID field MUST be set to a unique value, that the server
is not currently using for any other active outgoing request that it
has sent on this connection. The MESSAGE ID in the outgoing PUSH
message is selected by the server and has no relationship to the
MESSAGE ID in any of the client subscriptions it may relate to. In
the PUSH response the client MUST echo back the MESSAGE ID value
unchanged.
In the PUSH message TLV the SSOP-TYPE is PUSH (tentatively 65). The In the PUSH TLV the SSOP-TYPE is PUSH (tentatively 0x41). The SSOP-
SSOP-LENGTH is the length of the SSOP-DATA that follows. LENGTH is the length of the SSOP-DATA that follows, which specifies
the changes being communicated.
The SSOP-DATA contains a two-byte count of the number of records that The SSOP-DATA contains one or more Update records, in customary
follow, followed by the records, in customary Resource Record format Resource Record format, as used in DNS Update [RFC2136] messages. A
(as used in DNS Update [RFC2136] messages). PUSH Message MUST contain at least one Update record. If a PUSH
Message is received that contains no Update records this is a fatal
error, and the receiver MUST immediately terminate the connection
with a TCP RST (or equivalent for other protocols).
The SSOP-DATA contains the relevant change information for the The SSOP-DATA contains the relevant change information for the
client, formatted identically to a DNS Update [RFC2136]. To recap: client, formatted identically to a DNS Update [RFC2136]. To recap:
Delete all RRsets from a name: Delete all RRsets from a name:
TTL=0, CLASS=ANY, RDLENGTH=0, TYPE=ANY. TTL=0, CLASS=ANY, RDLENGTH=0, TYPE=ANY.
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.
skipping to change at page 19, line 39 skipping to change at page 19, line 51
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.
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
connection. Specifically, the record name MUST match the name given connection. Specifically, the record name MUST match the name given
in the SUBSCRIBE request, subject to the usual established DNS case- in the SUBSCRIBE request, subject to the usual established DNS case-
insensitivity for US-ASCII letters. If the QTYPE 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
QTYPE given in the SUBSCRIBE request. If the QCLASS 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
QCLASS given in the SUBSCRIBE request. If a matching active CLASS given in the SUBSCRIBE request. If a matching active
subscription on that connection is not found, then that individual subscription on that connection 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 TCP additions and deletions in this message is not affected. The TCP
connection is not closed. This is to allow for the unavoidable race connection is not closed. This is to allow for the unavoidable race
condition where a client sends an outbound UNSUBSCRIBE while inbound condition where a client sends an outbound UNSUBSCRIBE while inbound
PUSH messages for that subscription from the server are still in PUSH messages for that subscription from the server are still in
flight. flight.
In the case where a single change affects more than one active In the case where a single change affects more than one active
subscription, only one PUSH message is sent. For example, a PUSH subscription, only one PUSH message is sent. For example, a PUSH
message adding a given record may match both a SUBSCRIBE request with message adding a given record may match both a SUBSCRIBE request with
the same QTYPE and a different SUBSCRIBE request with QTYPE=ANY. It the same TYPE and a different SUBSCRIBE request with TYPE=ANY. It is
is not the case that two PUSH messages are sent because the new not the case that two PUSH messages are sent because the new record
record matches two active subscriptions. matches two active subscriptions.
The server SHOULD encode change notifications in the most efficient The server SHOULD encode change notifications in the most efficient
manner possible. For example, when three AAAA records are deleted manner possible. For example, when three AAAA records are deleted
from a given name, and no other AAAA records exist for that name, the from a given name, and no other AAAA records exist for that name, the
server SHOULD send a "delete an RRset from a name" PUSH message, not server SHOULD send a "delete an RRset from a name" PUSH message, not
three separate "delete an individual RR from a name" PUSH messages. three separate "delete an individual RR from a name" PUSH messages.
Similarly, when both an SRV and a TXT record are deleted from a given Similarly, when both an SRV and a TXT record are deleted from a given
name, and no other records of any kind exist for that name, the name, and no other records of any kind exist for that name, the
server SHOULD send a "delete all RRsets from a name" PUSH message, server SHOULD send a "delete all RRsets from a name" PUSH message,
not two separate "delete an RRset from a name" PUSH messages. not two separate "delete an RRset from a name" PUSH messages.
A server SHOULD combine multiple change notifications in a single A server SHOULD combine multiple change notifications in a single
PUSH message when possible, even if those change notifications apply PUSH message when possible, even if those change notifications apply
to different subscriptions. Conceptually, a PUSH messages is a to different subscriptions. Conceptually, a PUSH message is a
connection-level concept, not a subscription-level concept. connection-level mechanism, not a subscription-level mechanism.
Reception of a PUSH message does not directly generate a response Reception of a PUSH message by a client generates a PUSH response
back to the server. (Updates may indirectly generate other back to the server.
operations; e.g., a Push Notification Update Message declaring the
appearance of a PTR record could lead to a query for the SRV record
named in the rdata of that PTR record [RFC6763].)
The TTL of an added record is stored by the client and decremented as The TTL of an added record is stored by the client and decremented as
time passes, with the caveat that for as long as a relevant time passes, with the caveat that for as long as a relevant
subscription is active, the TTL does not decrement below 1 second. subscription is active, the TTL does not decrement below 1 second.
For as long as a relevant subscription remains active, the client For as long as a relevant subscription remains active, the client
SHOULD assume that when a record goes away the server will notify it SHOULD assume that when a record goes away the server will notify it
of that fact. Consequently, a client does not have to poll to verify of that fact. Consequently, a client does not have to poll to verify
that the record is still there. Once a subscription is cancelled that the record is still there. Once a subscription is cancelled
(individually, or as a result of the TCP connection being closed) (individually, or as a result of the TCP connection being closed)
record ageing resumes and records are removed from the local cache record ageing resumes and records are removed from the local cache
when their TTL reaches zero. when their TTL reaches zero.
6.3.2. PUSH Response
Each PUSH message generates exactly one PUSH response from the
receiver.
A PUSH response message begins with the standard DNS Session
Signaling 12-byte header [SessSig], possibly followed by one or more
optional Modifier TLVs, such as a Retry Delay Modifier TLV.
The MESSAGE ID field MUST echo the value given in the ID field of the
PUSH message.
A PUSH response message MUST NOT contain a Session Signaling
Operation TLV. The Session Signaling Operation TLV is NOT copied
from the PUSH message.
In a PUSH response the RCODE MUST be zero. Receiving a PUSH response
with a nonzero RCODE is a fatal error, and the receiver MUST
immediately terminate the connection with a TCP RST (or equivalent
for other protocols).
6.4. DNS Push Notification UNSUBSCRIBE 6.4. DNS Push Notification UNSUBSCRIBE
To cancel an individual subscription without closing the entire To cancel an individual subscription without closing the entire
connection, the client sends an UNSUBSCRIBE message over the connection, the client sends an UNSUBSCRIBE message over the
established TCP connection to the server. The UNSUBSCRIBE message is established TCP connection to the server. The UNSUBSCRIBE message is
encoded in a DNS Session Signaling [I-D.ietf-dnsop-session-signal] encoded in a DNS Session Signaling [SessSig] message. This
message. This specification defines a new DNS Session Signaling TLV specification defines a DNS Session Signaling TLV for DNS Push
for DNS Push Notification UNSUBSCRIBE Requests/Responses (tentatively Notification UNSUBSCRIBE Requests/Responses (tentatively Session
Session Signaling Type Code 66). Signaling Type Code 0x42).
A server may not initiate an UNSUBSCRIBE request. A server MUST NOT initiate an UNSUBSCRIBE request.
6.4.1. UNSUBSCRIBE Request 6.4.1. UNSUBSCRIBE Request
An UNSUBSCRIBE request message begins with the standard DNS Session An UNSUBSCRIBE request message begins with the standard DNS Session
Signaling 4-byte header [I-D.ietf-dnsop-session-signal], followed by Signaling 12-byte header [SessSig], followed by the UNSUBSCRIBE TLV.
the UNSUBSCRIBE TLV.
1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| MESSAGE ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|QR| Opcode | Z | RCODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| SSOP-TYPE (UNSUBSCRIBE) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| SSOP-LENGTH (0) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Figure 4 In the UNSUBSCRIBE TLV the SSOP-TYPE is UNSUBSCRIBE (tentatively
0x42). The SSOP-LENGTH is zero. There is no SSOP-DATA for
UNSUBSCRIBE.
The MESSAGE ID field MUST match the value given in the ID field of an The MESSAGE ID field MUST match the value given in the ID field of an
active SUBSCRIBE request. This is how the server knows which active SUBSCRIBE request. This is how the server knows which
SUBSCRIBE request is being cancelled. After receipt of the SUBSCRIBE request is being cancelled. After receipt of the
UNSUBSCRIBE request, the SUBSCRIBE request is no longer active. If a UNSUBSCRIBE request, the SUBSCRIBE request is no longer active. If a
server receives an UNSUBSCRIBE message where the MESSAGE ID does not server receives an UNSUBSCRIBE message where the MESSAGE ID does not
match the ID of an active SUBSCRIBE request this is an error and the match the ID of an active SUBSCRIBE request the server MUST return a
the server MUST return a response containing RCODE = 1 (FORMERR). In response containing RCODE = 3 (NXDOMAIN).
the UNSUBSCRIBE response the server MUST echo back the MESSAGE ID
value unchanged. It is allowable for the client to issue an
UNSUBSCRIBE request for a previous SUBSCRIBE request for which the
client has not yet received 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 the server. The client is NOT required
to wait for the SUBSCRIBE response before issuing the UNSUBSCRIBE
request.
In a request the DNS Header QR bit MUST be zero.
The DNS Header Opcode field holds the Session Signaling Opcode value
(tentatively 6).
The Z bits MUST be zero on transmission, and MUST be silently ignored
on reception.
The return code (RCODE) field MUST be set to 0 in a request.
In the UNSUBSCRIBE TLV the SSOP-TYPE is UNSUBSCRIBE (tentatively 66). It is allowable for the client to issue an UNSUBSCRIBE request for a
previous SUBSCRIBE request for which the client has not yet received
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
the server. The client is NOT required to wait for the SUBSCRIBE
response before issuing the UNSUBSCRIBE request. A consequence of
this is that if the client issues an UNSUBSCRIBE request for an as-
yet unacknowledged SUBSCRIBE request, and the SUBSCRIBE request is
subsequently unsuccessful for some reason, then when the UNSUBSCRIBE
request is eventually processed it will be an UNSUBSCRIBE request for
a nonexistent subscription, which will result NXDOMAIN response.
The SSOP-LENGTH is zero. Note that when the client issues an UNSUBSCRIBE request for an as-yet
unacknowledged SUBSCRIBE request, at that moment the client will have
two outstanding DNS Session Signaling operations with same MESSAGE
ID, a SUBSCRIBE request and an UNSUBSCRIBE request, which will both
receive responses, in that order. When the client has multiple
outstanding DNS Session Signaling operations with same MESSAGE ID,
care should be taken that when a DNS Session Signaling response
message is received for that MESSAGE ID, it is associated with the
*first* unacknowledged request.
6.4.2. UNSUBSCRIBE Response 6.4.2. UNSUBSCRIBE Response
Each UNSUBSCRIBE request generates exactly one UNSUBSCRIBE response Each UNSUBSCRIBE request generates exactly one UNSUBSCRIBE response
from the server. from the server.
An UNSUBSCRIBE response message contains with the standard DNS An UNSUBSCRIBE response message begins with the standard DNS Session
Session Signaling 4-byte header [I-D.ietf-dnsop-session-signal]. Signaling 12-byte header [SessSig], possibly followed by one or more
optional Modifier TLVs, such as a Retry Delay Modifier TLV.
1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| MESSAGE ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|QR| Opcode | Z | RCODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Figure 5
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
UNSUBSCRIBE request. This is how the client knows which request is UNSUBSCRIBE request. This is how the client knows which request is
being responded to. being responded to.
In a response the DNS Header QR bit MUST be one. An UNSUBSCRIBE response message MUST NOT contain a Session Signaling
If the QR bit is not one the message is not a response. Operation TLV. The Session Signaling Operation TLV is NOT copied
from the UNSUBSCRIBE request.
The DNS Header Opcode field holds the Session Signaling Opcode value
(tentatively 6).
The Z bits MUST be zero on transmission, and MUST be silently ignored
on reception.
In the UNSUBSCRIBE response the RCODE indicates whether or not the In the UNSUBSCRIBE response the RCODE indicates whether or not the
unsubscribe request was successful. Supported RCODEs are as follows: unsubscribe request was successful. Supported RCODEs are as follows:
+------------+-------+----------------------------------------------+ +------------+-------+----------------------------------------------+
| Mnemonic | Value | Description | | Mnemonic | Value | Description |
+------------+-------+----------------------------------------------+ +------------+-------+----------------------------------------------+
| NOERROR | 0 | UNSUBSCRIBE successful. | | NOERROR | 0 | UNSUBSCRIBE successful. |
| FORMERR | 1 | Server failed to process request due to a | | FORMERR | 1 | Server failed to process request due to a |
| | | malformed request. | | | | malformed request. |
| NXDOMAIN | 3 | Specified subscription does not exist. |
| NOTIMP | 4 | Server does not recognize DNS Session | | NOTIMP | 4 | Server does not recognize DNS Session |
| | | Signaling Opcode. | | | | Signaling Opcode. |
| SSOPNOTIMP | 11 | UNSUBSCRIBE operation not supported. | | SSOPNOTIMP | 11 | UNSUBSCRIBE operation not supported. |
+------------+-------+----------------------------------------------+ +------------+-------+----------------------------------------------+
UNSUBSCRIBE Response codes UNSUBSCRIBE Response codes
This document specifies only these RCODE values for UNSUBSCRIBE This document specifies only these RCODE values for UNSUBSCRIBE
Responses. Servers sending UNSUBSCRIBE Responses SHOULD use one of Responses. Servers sending UNSUBSCRIBE Responses SHOULD use one of
these values. However, future circumstances may create situations these values. However, future circumstances may create situations
skipping to change at page 25, line 20 skipping to change at page 25, line 5
RCODE value. RCODE value.
Having being successfully revoked with a correctly-formatted Having being successfully revoked with a correctly-formatted
UNSUBSCRIBE message (resulting in a response with RCODE NOERROR) the UNSUBSCRIBE message (resulting in a response with RCODE NOERROR) the
previously referenced subscription is no longer active and the server previously referenced subscription is no longer active and the server
MAY discard the state associated with it immediately, or later, at MAY discard the state associated with it immediately, or later, at
the server's discretion. the server's discretion.
Nonzero RCODE values signal some kind of error. Nonzero RCODE values signal some kind of error.
RCODE value FORMERR indicates an incorrect MESSAGE ID or other RCODE value FORMERR indicates a message format error.
message format error.
RCODE value NXDOMAIN indicates a MESSAGE ID that does not correspond
to any active subscription.
RCODE values NOTIMP and SSOPNOTIMP should not occur in practice. RCODE values NOTIMP and SSOPNOTIMP should not occur in practice.
A server would only generate NOTIMP if it did not support Session A server would only generate NOTIMP if it did not support Session
Signaling, and if the server does not support Session Signaling then Signaling, and if the server does not support Session Signaling then
it should not be possible for a client to have an active subscription it should not be possible for a client to have an active subscription
to cancel. to cancel.
Similarly, a server would only generate SSOPNOTIMP if it did not Similarly, a server would only generate SSOPNOTIMP if it did not
support Push Notifications, and if the server does not support Push support Push Notifications, and if the server does not support Push
Notifications then it should not be possible for a client to have an Notifications then it should not be possible for a client to have an
active subscription to cancel. active subscription to cancel.
All nonzero RCODE values indicate a serious problem with the client. Nonzero RCODE values other than NXDOMAIN indicate a serious problem
After sending an error response, the server SHOULD send a DNS Push with the client. After sending an error response other than
Notification Terminate Session operation TLV and then close the TCP NXDOMAIN, the server SHOULD send a DNS Session Signaling Retry Delay
connection, as described in the DNS Session Signaling specification Operation TLV and then close the TCP connection, as described in the
[I-D.ietf-dnsop-session-signal]. DNS Session Signaling specification [SessSig].
6.5. DNS Session Signaling Push Notification RECONFIRM 6.5. DNS Push Notification RECONFIRM
Sometimes, particularly when used with a Hybrid Proxy Sometimes, particularly when used with a Discovery Proxy [DisProx], a
[I-D.ietf-dnssd-hybrid], a DNS Zone may contain stale data. When a DNS Zone may contain stale data. When a client encounters data that
client encounters data that it believe may be stale (e.g., an SRV it believe may be stale (e.g., an SRV record referencing a target
record referencing a target host+port that is not responding to host+port that is not responding to connection requests) the client
connection requests) the client can send a RECONFIRM message to can send a RECONFIRM request to ask the server to re-verify that the
request that the server re-verify that the data is still valid. For data is still valid. For a Discovery Proxy, this causes it to issue
a Hybrid Proxy, this causes it to issue new Multicast DNS requests to new Multicast DNS requests to ascertain whether the target device is
ascertain whether the target device is still present. For other still present. For other types of DNS server, the RECONFIRM
types of DNS server, the RECONFIRM operation is currently undefined operation is currently undefined, and SHOULD result in a NOERROR
and SHOULD be silently ignored. response, but otherwise need not cause any action to occur. Frequent
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.
A RECONFIRM request is formatted identically to a SUBSCRIBE request, If, after receiving a valid RECONFIRM request, the server determines
except that the TLV type is RECONFIRM (tentatively 67) instead of that the disputed records are in fact no longer valid, then
SUBSCRIBE. Additionally, QTYPE MUST NOT be the value ANY (255) and subsequent DNS PUSH Messages will be generated to inform interested
QCLASS MUST NOT be the value ANY (255). clients. Thus, one client discovering that a previously-advertised
device (like a network printer) is no longer present has the side
effect of informing all other interested clients that the device in
question is now gone.
Like all DNS Session Signaling [I-D.ietf-dnsop-session-signal] 6.5.1. RECONFIRM Request
requests, a RECONFIRM request MUST contain a unique MESSAGE ID, not
currently in use in this session.
A RECONFIRM request generates exactly one RECONFIRM response from the A RECONFIRM request message begins with the standard DNS Session
server, formatted identically to a SUBSCRIBE response, which echoes Signaling 12-byte header [SessSig], followed by the RECONFIRM TLV.
back the unique MESSAGE ID from the RECONFIRM request. The SSOP-DATA for the the RECONFIRM TLV is as follows:
In the RECONFIRM response the RCODE indicates whether or not the 1 1 1 1 1 1
request was successful. Supported RCODEs are as follows: 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| |
\ NAME \
\ \
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| TYPE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| CLASS |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| RDLEN |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| |
\ RDATA \
\ \
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Figure 2
The MESSAGE ID field MUST be set to a unique value, that the client
is not using for any other active operation on this connection. For
the purposes here, a MESSAGE ID is in use on this connection if the
client has used it in a request for which it has not yet received a
response, or if if the client has used it for a subscription which it
has not yet cancelled using UNSUBSCRIBE. In the RECONFIRM response
the server MUST echo back the MESSAGE ID value unchanged.
In the RECONFIRM TLV the SSOP-TYPE is RECONFIRM (tentatively 0x43).
The SSOP-LENGTH is the length of the data that follows, which
specifies the name, type, class, and content of the record being
disputed.
A RECONFIRM request MUST contain exactly one record. The RECONFIRM
TLV has no count field to specify more than one record. Since
RECONFIRM requests are sent over TCP, multiple RECONFIRM request
messages can be concatenated in a single TCP stream and packed
efficiently into TCP segments.
TYPE MUST NOT be the value ANY (255) and CLASS MUST NOT be the value
ANY (255).
DNS wildcarding is not supported. That is, a wildcard ("*") in a
RECONFIRM message matches only a literal wildcard character ("*") in
the zone, and nothing else.
Aliasing is not supported. That is, a CNAME in a RECONFIRM message
matches only a literal CNAME record in the zone, and nothing else.
6.5.2. RECONFIRM Response
Each RECONFIRM request generates exactly one RECONFIRM response from
the server.
A RECONFIRM response message begins with the standard DNS Session
Signaling 12-byte header [SessSig], possibly followed by one or more
optional Modifier TLVs, such as a Retry Delay Modifier TLV.
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
being responded to.
A RECONFIRM response message MUST NOT contain a Session Signaling
Operation TLV. The Session Signaling Operation TLV is NOT copied
from the RECONFIRM request.
In the RECONFIRM response the RCODE confirms receipt of the
reconfirmation request. Supported RCODEs are as follows:
+------------+-------+----------------------------------------------+ +------------+-------+----------------------------------------------+
| Mnemonic | Value | Description | | Mnemonic | Value | Description |
+------------+-------+----------------------------------------------+ +------------+-------+----------------------------------------------+
| NOERROR | 0 | RECONFIRM successful. | | NOERROR | 0 | RECONFIRM accepted. |
| FORMERR | 1 | Server failed to process request due to a | | FORMERR | 1 | Server failed to process request due to a |
| | | malformed request. | | | | malformed request. |
| SERVFAIL | 2 | Server failed to process request due to |
| | | resource exhaustion. |
| NXDOMAIN | 3 | NOT APPLICABLE. DNS Push Notification |
| | | servers MUST NOT return NXDOMAIN errors in |
| | | response to RECONFIRM requests. |
| NOTIMP | 4 | Server does not recognize DNS Session | | NOTIMP | 4 | Server does not recognize DNS Session |
| | | Signaling Opcode. | | | | Signaling Opcode. |
| REFUSED | 5 | Server refuses to process request for policy |
| | | or security reasons. |
| NOTAUTH | 9 | Server is not authoritative for the |
| | | requested name. |
| SSOPNOTIMP | 11 | RECONFIRM operation not supported. | | SSOPNOTIMP | 11 | RECONFIRM operation not supported. |
+------------+-------+----------------------------------------------+ +------------+-------+----------------------------------------------+
RECONFIRM Response codes RECONFIRM Response codes
This document specifies only these RCODE values for RECONFIRM This document specifies only these RCODE values for RECONFIRM
Responses. Servers sending RECONFIRM Responses SHOULD use one of Responses. Servers sending RECONFIRM Responses SHOULD use one of
these values. However, future circumstances may create situations these values. However, future circumstances may create situations
where other RCODE values are appropriate in RECONFIRM Responses, so where other RCODE values are appropriate in RECONFIRM Responses, so
clients MUST be prepared to accept RECONFIRM Responses with any RCODE clients MUST be prepared to accept RECONFIRM Responses with any RCODE
value. value.
A correctly-formatted RECONFIRM message results in a response with Nonzero RCODE values signal some kind of error.
RCODE NOERROR.
Nonzero RCODE values signal some kind of error. If the server sends RCODE value FORMERR indicates a message format error, for example
a nonzero RCODE then it SHOULD append a Terminate modifier TLV TYPE or CLASS being ANY (255).
[I-D.ietf-dnsop-session-signal] to the response specifying a delay
before the client attempts this operation again. The RECOMMENDED
value for the delay is five minutes. For serious errors, after
sending the error response, the server SHOULD send a DNS Push
Notification Terminate Session operation TLV and then close the TCP
connection, as described in the DNS Session Signaling specification
[I-D.ietf-dnsop-session-signal].
If, after receiving a valid RECONFIRM request, the server determines RCODE value SERVFAIL indicates that the server is overloaded.
that the records are in fact no longer valid, then subsequent DNS
PUSH Messages will be generated to inform interested clients. Thus, RCODE values NOTIMP indicates that the server does not support
one client discovering that a previously-advertised printer is no Session Signaling, and Session Signaling is required for RECONFIRM
longer present has the side effect of informing all other interested requests.
clients that the printer in question is now gone.
RCODE value REFUSED indicates that the server supports RECONFIRM
requests but is currently not configured to accept them from this
client.
RCODE value NOTAUTH indicates that the server is not authoritative
for the requested name, and can do nothing to remedy the apparent
error. Note that there may be future cases in which a server is able
to pass on the RECONFIRM request to the ultimate source of the
information, and in these cases the server should return NOERROR.
RCODE value SSOPNOTIMP indicates that the server does not support
RECONFIRM requests.
Similarly, a server would only generate SSOPNOTIMP if it did not
support Push Notifications, and if the server does not support Push
Notifications then it should not be possible for a client to have an
active subscription to cancel.
Nonzero RCODE values SERVFAIL, REFUSED and SSOPNOTIMP are benign from
the client's point of view. The client may log them to aid in
debugging, but otherwise they require no special action.
Nonzero RCODE values other than these three indicate a serious
problem with the client. After sending an error response other than
one of these three, the server SHOULD send a DNS Session Signaling
Retry Delay Operation TLV and then close the TCP connection, as
described in the DNS Session Signaling specification [SessSig].
6.6. Client-Initiated Termination 6.6. Client-Initiated Termination
An individual subscription is terminated by sending an UNSUBSCRIBE An individual subscription is terminated by sending an UNSUBSCRIBE
TLV for that specific subscription, or all subscriptions can be TLV for that specific subscription, or all subscriptions can be
cancelled at once by the client closing the connection. When a cancelled at once by the client closing the connection. When a
client terminates an individual subscription (via UNSUBSCRIBE) or all client terminates an individual subscription (via UNSUBSCRIBE) or all
subscriptions on that connection (by closing the connection) it is subscriptions on that connection (by closing the connection) it is
signaling to the server that it is longer interested in receiving signaling to the server that it is longer interested in receiving
those particular updates. It is informing the server that the server those particular updates. It is informing the server that the server
may release any state information it has been keeping with regards to may release any state information it has been keeping with regards to
these particular subscriptions. these particular subscriptions.
After terminating its last subscription on a connection via After terminating its last subscription on a connection via
UNSUBSCRIBE, a client MAY close the connection immediately, or it may UNSUBSCRIBE, a client MAY close the connection immediately, or it may
keep it open if it anticipates performing further operations on that keep it open if it anticipates performing further operations on that
connection in the future. If a client wishes to keep an idle connection in the future. If a client wishes to keep an idle
connection open, it MUST continue to meet its keepalive obligations connection open, it MUST respect the maximum idle time required by
[I-D.ietf-dnsop-session-signal] or the server is entitled to close the server [SessSig].
the connection (see below).
If a client plans to terminate one or more subscriptions on a If a client plans to terminate one or more subscriptions on a
connection and doesn't intend to keep that connection open, then as connection and doesn't intend to keep that connection open, then as
an efficiency optimization it MAY instead choose to simply close the an efficiency optimization it MAY instead choose to simply close the
connection, which implicitly terminates all subscriptions on that connection, which implicitly terminates all subscriptions on that
connection. This may occur because the client computer is being shut connection. This may occur because the client computer is being shut
down, is going to sleep, the application requiring the subscriptions down, is going to sleep, the application requiring the subscriptions
has terminated, or simply because the last active subscription on has terminated, or simply because the last active subscription on
that connection has been cancelled. that connection has been cancelled.
skipping to change at page 30, line 29 skipping to change at page 32, line 33
resumed, the DNS Push Notification server will not have any resumed, the DNS Push Notification server will not have any
subscription state and will proceed as with any other new connection. subscription state and will proceed as with any other new connection.
Use of TLS Session Resumption allows a new TLS connection to be set Use of TLS Session Resumption allows a new TLS connection to be set
up more quickly, but the client will still have to recreate any up more quickly, but the client will still have to recreate any
desired subscriptions. desired subscriptions.
8. IANA Considerations 8. IANA Considerations
This document defines the service name: "_dns-push-tls._tcp". This document defines the service name: "_dns-push-tls._tcp".
It is only applicable for the TCP protocol. It is only applicable for the TCP protocol.
This name is to be published in the IANA Service Name Registry. This name is to be published in the IANA Service Name Registry
[RFC6335][SN].
This document defines three DNS Session Signaling TLV types: This document defines three DNS Session Signaling TLV types:
SUBSCRIBE with (tentative) value 64, PUSH with (tentative) value 65, SUBSCRIBE with (tentative) value 0x40 (64), PUSH with (tentative)
UNSUBSCRIBE with (tentative) value 66, and RECONFIRM with (tentative) value 0x41 (65), UNSUBSCRIBE with (tentative) value 0x42 (66), and
value 67. RECONFIRM with (tentative) value 0x43 (67).
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
Shankar Rao, Markus Stenberg, Dave Thaler, and Soraia Zlatkovic. Shankar Rao, Markus Stenberg, Dave Thaler, and Soraia Zlatkovic.
10. References 10. References
10.1. Normative References 10.1. Normative References
[I-D.ietf-dnsop-session-signal]
Bellis, R., Cheshire, S., Dickinson, J., Dickinson, S.,
Mankin, A., and T. Pusateri, "DNS Session Signaling",
draft-ietf-dnsop-session-signal-00 (work in progress),
August 2016.
[I-D.ietf-tls-tls13] [I-D.ietf-tls-tls13]
Rescorla, E., "The Transport Layer Security (TLS) Protocol Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", draft-ietf-tls-tls13-18 (work in progress), Version 1.3", draft-ietf-tls-tls13-18 (work in progress),
October 2016. October 2016.
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
DOI 10.17487/RFC0768, August 1980, DOI 10.17487/RFC0768, August 1980,
<http://www.rfc-editor.org/info/rfc768>. <http://www.rfc-editor.org/info/rfc768>.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, [RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
skipping to change at page 32, line 20 skipping to change at page 34, line 15
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, (TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008, DOI 10.17487/RFC5246, August 2008,
<http://www.rfc-editor.org/info/rfc5246>. <http://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,
<http://www.rfc-editor.org/info/rfc6066>. <http://www.rfc-editor.org/info/rfc6066>.
[RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
Cheshire, "Internet Assigned Numbers Authority (IANA)
Procedures for the Management of the Service Name and
Transport Protocol Port Number Registry", BCP 165,
RFC 6335, DOI 10.17487/RFC6335, August 2011,
<http://www.rfc-editor.org/info/rfc6335>.
[RFC6895] Eastlake 3rd, D., "Domain Name System (DNS) IANA [RFC6895] Eastlake 3rd, D., "Domain Name System (DNS) IANA
Considerations", BCP 42, RFC 6895, DOI 10.17487/RFC6895, Considerations", BCP 42, RFC 6895, DOI 10.17487/RFC6895,
April 2013, <http://www.rfc-editor.org/info/rfc6895>. April 2013, <http://www.rfc-editor.org/info/rfc6895>.
[RFC7673] Finch, T., Miller, M., and P. Saint-Andre, "Using DNS- [RFC7673] Finch, T., Miller, M., and P. Saint-Andre, "Using DNS-
Based Authentication of Named Entities (DANE) TLSA Records Based Authentication of Named Entities (DANE) TLSA Records
with SRV Records", RFC 7673, DOI 10.17487/RFC7673, October with SRV Records", RFC 7673, DOI 10.17487/RFC7673, October
2015, <http://www.rfc-editor.org/info/rfc7673>. 2015, <http://www.rfc-editor.org/info/rfc7673>.
[RFC7766] Dickinson, J., Dickinson, S., Bellis, R., Mankin, A., and [RFC7766] Dickinson, J., Dickinson, S., Bellis, R., Mankin, A., and
D. Wessels, "DNS Transport over TCP - Implementation D. Wessels, "DNS Transport over TCP - Implementation
Requirements", RFC 7766, DOI 10.17487/RFC7766, March 2016, Requirements", RFC 7766, DOI 10.17487/RFC7766, March 2016,
<http://www.rfc-editor.org/info/rfc7766>. <http://www.rfc-editor.org/info/rfc7766>.
[SessSig] Bellis, R., Cheshire, S., Dickinson, J., Dickinson, S.,
Mankin, A., and T. Pusateri, "DNS Session Signaling",
draft-ietf-dnsop-session-signal-02 (work in progress),
March 2017.
[SN] "Service Name and Transport Protocol Port Number
Registry", <http://www.iana.org/assignments/
service-names-port-numbers/>.
10.2. Informative References 10.2. Informative References
[DisProx] Cheshire, S., "Hybrid Unicast/Multicast DNS-Based Service
Discovery", draft-ietf-dnssd-hybrid-06 (work in progress),
March 2017.
[I-D.dukkipati-tcpm-tcp-loss-probe] [I-D.dukkipati-tcpm-tcp-loss-probe]
Dukkipati, N., Cardwell, N., Cheng, Y., and M. Mathis, Dukkipati, N., Cardwell, N., Cheng, Y., and M. Mathis,
"Tail Loss Probe (TLP): An Algorithm for Fast Recovery of "Tail Loss Probe (TLP): An Algorithm for Fast Recovery of
Tail Losses", draft-dukkipati-tcpm-tcp-loss-probe-01 (work Tail Losses", draft-dukkipati-tcpm-tcp-loss-probe-01 (work
in progress), February 2013. in progress), February 2013.
[I-D.ietf-dnssd-hybrid]
Cheshire, S., "Hybrid Unicast/Multicast DNS-Based Service
Discovery", draft-ietf-dnssd-hybrid-03 (work in progress),
February 2016.
[I-D.sekar-dns-llq] [I-D.sekar-dns-llq]
Sekar, K., "DNS Long-Lived Queries", draft-sekar-dns- Sekar, K., "DNS Long-Lived Queries", draft-sekar-dns-
llq-01 (work in progress), August 2006. llq-01 (work in progress), August 2006.
[IPJ.9-4-TCPSYN] [IPJ.9-4-TCPSYN]
Eddy, W., "Defenses Against TCP SYN Flooding Attacks", The Eddy, W., "Defenses Against TCP SYN Flooding Attacks", The
Internet Protocol Journal, Cisco Systems, Volume 9, Internet Protocol Journal, Cisco Systems, Volume 9,
Number 4, December 2006. Number 4, December 2006.
[obs] "Observer Pattern", <https://en.wikipedia.org/wiki/ [obs] "Observer Pattern", <https://en.wikipedia.org/wiki/
skipping to change at page 33, line 30 skipping to change at page 35, line 40
[RFC4953] Touch, J., "Defending TCP Against Spoofing Attacks", [RFC4953] Touch, J., "Defending TCP Against Spoofing Attacks",
RFC 4953, DOI 10.17487/RFC4953, July 2007, RFC 4953, DOI 10.17487/RFC4953, July 2007,
<http://www.rfc-editor.org/info/rfc4953>. <http://www.rfc-editor.org/info/rfc4953>.
[RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig, [RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,
"Transport Layer Security (TLS) Session Resumption without "Transport Layer Security (TLS) Session Resumption without
Server-Side State", RFC 5077, DOI 10.17487/RFC5077, Server-Side State", RFC 5077, DOI 10.17487/RFC5077,
January 2008, <http://www.rfc-editor.org/info/rfc5077>. January 2008, <http://www.rfc-editor.org/info/rfc5077>.
[RFC6281] Cheshire, S., Zhu, Z., Wakikawa, R., and L. Zhang,
"Understanding Apple's Back to My Mac (BTMM) Service",
RFC 6281, DOI 10.17487/RFC6281, June 2011,
<http://www.rfc-editor.org/info/rfc6281>.
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762, [RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
DOI 10.17487/RFC6762, February 2013, DOI 10.17487/RFC6762, February 2013,
<http://www.rfc-editor.org/info/rfc6762>. <http://www.rfc-editor.org/info/rfc6762>.
[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,
<http://www.rfc-editor.org/info/rfc6763>. <http://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
 End of changes. 86 change blocks. 
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