draft-ietf-dnssd-push-03.txt   draft-ietf-dnssd-push-04.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 8, 2016 Apple Inc. Expires: July 14, 2016 Apple Inc.
November 5, 2015 January 11, 2016
DNS Push Notifications DNS Push Notifications
draft-ietf-dnssd-push-03 draft-ietf-dnssd-push-04
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 for a
client to be asynchronously notified when these changes occur. This client to be asynchronously notified when these changes occur. This
document defines a mechanism for a client to be notified of such document defines a mechanism for a client to be notified of such
changes to DNS records, called DNS Push Notifications. changes to DNS records, called DNS Push Notifications.
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at 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 8, 2016. This Internet-Draft will expire on July 14, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Transport . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4. Transport . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. State Considerations . . . . . . . . . . . . . . . . . . . . 6 5. State Considerations . . . . . . . . . . . . . . . . . . . . 6
6. Protocol Operation . . . . . . . . . . . . . . . . . . . . . 7 6. Protocol Operation . . . . . . . . . . . . . . . . . . . . . 7
6.1. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 7 6.1. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 8
6.2. DNS Push Notification SUBSCRIBE . . . . . . . . . . . . . 9 6.2. DNS Push Notification SUBSCRIBE . . . . . . . . . . . . . 9
6.3. DNS Push Notification UNSUBSCRIBE . . . . . . . . . . . . 12 6.3. DNS Push Notification UNSUBSCRIBE . . . . . . . . . . . . 12
6.4. DNS Push Notification Update Messages . . . . . . . . . . 13 6.4. DNS Push Notification Update Messages . . . . . . . . . . 13
6.5. DNS RECONFIRM . . . . . . . . . . . . . . . . . . . . . . 16 6.5. DNS RECONFIRM . . . . . . . . . . . . . . . . . . . . . . 16
6.6. DNS Push Notification Termination Message . . . . . . . . 18 6.6. DNS Push Notification Termination Message . . . . . . . . 17
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19 7. Security Considerations . . . . . . . . . . . . . . . . . . . 18
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 7.1. Security Services . . . . . . . . . . . . . . . . . . . . 18
9. Security Considerations . . . . . . . . . . . . . . . . . . . 19 7.2. TLS Name Authentication . . . . . . . . . . . . . . . . . 19
9.1. Security Services . . . . . . . . . . . . . . . . . . . . 19 7.3. TLS Compression . . . . . . . . . . . . . . . . . . . . . 19
9.2. TLS Name Authentication . . . . . . . . . . . . . . . . . 20 7.4. TLS Session Resumption . . . . . . . . . . . . . . . . . 19
9.3. TLS Compression . . . . . . . . . . . . . . . . . . . . . 20 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
9.4. TLS Session Resumption . . . . . . . . . . . . . . . . . 20 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 21 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
10.1. Normative References . . . . . . . . . . . . . . . . . . 21 10.1. Normative References . . . . . . . . . . . . . . . . . . 20
10.2. Informative References . . . . . . . . . . . . . . . . . 22 10.2. Informative References . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
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 Hybrid Proxy [I-D.ietf-dnssd-hybrid] can also
generate changes to a DNS zone. This document specifies a protocol generate changes to a DNS zone. This document specifies a protocol
for Unicast DNS clients to subscribe to receive asynchronous for Unicast DNS clients to subscribe to receive asynchronous
notifications of changes to RRSets of interest. It is immediately notifications of changes to RRSets of interest. It is immediately
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based protocol, and as such it defines its own equivalents of based protocol, and as such it defines its own equivalents of
existing TCP features like the three-way handshake. This document existing TCP features like the three-way handshake. This document
builds on experience gained with the LLQ protocol, with an improved builds on experience gained with the LLQ protocol, with an improved
design that uses long-lived TCP connections instead of UDP (and design that uses long-lived TCP connections instead of UDP (and
therefore doesn't need to duplicate existing TCP functionality), and therefore doesn't need to duplicate existing TCP functionality), and
adopts the syntax and semantics of DNS Update messages [RFC2136] adopts the syntax and semantics of DNS Update messages [RFC2136]
instead of inventing a new vocabulary of messages to communicate DNS instead of inventing a new vocabulary of messages to communicate DNS
zone changes. zone changes.
Because DNS Push Notifications impose a certain load on the Because DNS Push Notifications impose a certain load on the
responding server (though less load that rapid polling of that responding server (though less load than rapid polling of that
server) DNS Push Notification clients SHOULD exercise restraint in server) DNS Push Notification clients SHOULD exercise restraint in
issuing DNS Push Notification subscriptions. A subscription SHOULD issuing DNS Push Notification subscriptions. A subscription SHOULD
only be active when there is a valid reason to need live data (for only be active when there is a valid reason to need live data (for
example, an on-screen display is currently showing the results of example, an on-screen display is currently showing the results of
that subscription to the user) and the subscription SHOULD be that subscription to the user) and the subscription SHOULD be
cancelled as soon as the need for that data ends (for example, when cancelled as soon as the need for that data ends (for example, when
the user dismisses that display). the user dismisses that display).
A DNS Push Notification client MUST not routinely keep a DNS Push 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 Notification subscription active 24 hours a day 7 days a week just to
keep a list in memory up to date so that it will be really fast if keep a list in memory up to date so that it will be really fast if
the user does choose to bring up an on-screen display of that data. the user does choose to bring up an on-screen display of that data.
DNS Push Notifications are designed to be fast enough that there is 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 no need to pre-load a "warm" list in memory just in case it might be
needed later. needed later.
3. Overview 3. Overview
The existing DNS Update protocol [RFC2136] provides a mechanism for The existing DNS Update protocol [RFC2136] provides a mechanism for
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Transport Layer Security (TLS) [RFC5246] is well understood and Transport Layer Security (TLS) [RFC5246] is well understood and
deployed across many protocols running over TCP. It is designed to deployed across many protocols running over TCP. It is designed to
prevent eavesdropping, tampering, or message forgery. TLS is prevent eavesdropping, tampering, or message forgery. TLS is
REQUIRED for every connection between a client subscriber and server REQUIRED for every connection between a client subscriber and server
in this protocol specification. Additional security measures such as in this protocol specification. Additional security measures such as
client authentication during TLS negotiation MAY also be employed to client authentication during TLS negotiation MAY also be employed to
increase the trust relationship between client and server. increase the trust relationship between client and server.
Additional authentication of the SRV target using DNSSEC verification Additional authentication of the SRV target using DNSSEC verification
and DANE TLSA records [RFC7673] is strongly encouraged. See below in and DANE TLSA records [RFC7673] is strongly encouraged. See below in
Section 9.2 for details. Section 7.2 for details.
5. State Considerations 5. State Considerations
Each DNS Push Notification server is capable and 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 record subscription is individually accepted or rejected.
Servers may employ various techniques to limit subscriptions to a Servers may employ various techniques to limit subscriptions to a
manageable level. Correspondingly, the client is free to establish manageable level. Correspondingly, the client is free to establish
simultaneous connections to alternate DNS servers that support DNS simultaneous connections to alternate DNS servers that support DNS
Push Notifications for the zone and distribute record subscriptions Push Notifications for the zone and distribute record subscriptions
at its discretion. In this way, both clients and servers can react at its discretion. In this way, both clients and servers can react
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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
A DNS Push Notification exchange begins with the client discovering A DNS Push Notification exchange begins with the client discovering
the appropriate server, and then making a TLS/TCP connection to it. the appropriate server, and then making a TLS/TCP connection to it.
The client may then add and remove Push Notification subscriptions The client may then add and remove Push Notification subscriptions
over this connection. In accordance with the current set of active over this connection. In accordance with the current set of active
subscriptions the server sends relevant asynchronous Push subscriptions the server sends relevant asynchronous Push
Notifications to the client. The exchange terminates when either end Notifications to the client. Note that a client MUST be prepared to
receive (and silently discard) Push Notifications for subscriptions
it has previously removed, since there is no way to prevent the
situation where a Push Notification is in flight from server to
client while the client's UNSUBSCRIBE message cancelling that
subscription is simultaneously in flight from client to server.
The exchange between client and server terminates when either end
closes the TCP connection with a TCP FIN or RST. closes the TCP connection with a TCP FIN or RST.
A client SHOULD NOT make multiple TLS/TCP connections to the same DNS A client SHOULD NOT make multiple TLS/TCP connections to the same DNS
Push Notification server. A client SHOULD share a single TLS/TCP Push Notification server. A client SHOULD share a single TLS/TCP
connection for all requests to the same DNS Push Notification server. connection for all requests to the same DNS Push Notification server.
This shared connection should be used for all DNS Queries and DNS This shared connection should be used for all DNS Queries and DNS
Push Notification Queries queries to that server, and for DNS Update Push Notification Queries queries to that server, and for DNS Update
requests too when the "_dns-update-tls._tcp.<zone>" SRV record requests too when the "_dns-update-tls._tcp.<zone>" SRV record
indicates that the same server also handles DNS Update requests. indicates that the same server also handles DNS Update requests.
This is to reduce unnecessary load on the DNS Push Notification This is to reduce unnecessary load on the DNS Push Notification
server. server.
For the purposes here, the determination of "same server" is made by
inspecting the target host and port, regardless of the name being
queried, or what zone if falls within. A given server may support
Push Notifications (and possibly DNS Updates too) for multiple DNS
zones. When a client discovers that the DNS Push Notification server
(and/or DNS Update server) for several different names (including
names that fall within different zones) is the same target host and
port, the client SHOULD use a single shared TCP connection for all
relevant operations on those names. A client SHOULD NOT open
multiple TCP connections to the same target host and port just
because the names being queried (or updated) happen to fall within
different zones.
However, a single client device may be home to multiple independent However, a single client device may be home to multiple independent
client software instances that don't know about each other, so a DNS client software instances that don't know about each other, so a DNS
Push Notification server MUST be prepared to accept multiple Push Notification server MUST be prepared to accept multiple
connections from the same client IP address. This is undesirable connections from the same client IP address. This is undesirable
from an efficiency stanpoint, but may be unavoidable in some from an efficiency stanpoint, but may be unavoidable in some
situations, so a DNS Push Notification server MUST be prepared to situations, so a DNS Push Notification server MUST be prepared to
accept multiple connections from the same client IP address. accept multiple connections from the same client IP address.
6.1. Discovery 6.1. Discovery
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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.
6. If the zone in question is set up to offer DNS Push Notifications 6. If the zone in question is set up to offer DNS Push Notifications
then this SRV record MUST exist. The SRV "target" contains the then this SRV record MUST exist. The SRV "target" contains the
name of the server providing DNS Push Notifications for the zone. name of the server providing DNS Push Notifications for the zone.
The port number on which to contact the server is in the SRV The port number on which to contact the server is in the SRV
record "port" field. The address(es) of the target host MAY be record "port" field. The address(es) of the target host MAY be
included in the Additional Section, however, the address records included in the Additional Section, however, the address records
SHOULD be authenticated before use as described below in SHOULD be authenticated before use as described below in
Section 9.2 [RFC7673]. Section 7.2 [RFC7673].
7. More than one SRV record may be returned. In this case, the 7. More than one SRV record may be returned. In this case, the
"priority" and "weight" values in the returned SRV records are "priority" and "weight" values in the returned SRV records are
used to determine the order in which to contact the servers for used to determine the order in which to contact the servers for
subscription requests. As described in the SRV specification subscription requests. As described in the SRV specification
[RFC2782], the server with the lowest "priority" is first [RFC2782], the server with the lowest "priority" is first
contacted. If more than one server has the same "priority", the contacted. If more than one server has the same "priority", the
"weight" is indicates the weighted probability that the client "weight" is indicates the weighted probability that the client
should contact that server. Higher weights have higher should contact that server. Higher weights have higher
probabilities of being selected. If a server is not reachable or probabilities of being selected. If a server is not reachable or
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close the TCP connection. close the TCP connection.
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 wildcard ("*") in the zone, and SUBSCRIBE message matches only a wildcard ("*") in the zone, and
nothing else. 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 CNAME in the zone, and nothing else. matches only a CNAME 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 and this is not an error. The server MUST the time of the request (providing that the name falls within one of
accept these requests and send Push Notifications if and when matches the zone(s) the server is responsible for) and this is not an error.
are found in the future. The server MUST accept these requests and send Push Notifications if
and when matches are found in the future.
Since all SUBSCRIBE operations are implicitly long-lived operations, Since all SUBSCRIBE operations are implicitly long-lived operations,
the server MUST interpret a SUBSCRIBE request as if it contained an the server MUST interpret a SUBSCRIBE request as if it contained an
EDNS0 TCP Keepalive option [I-D.ietf-dnsop-edns-tcp-keepalive]. A EDNS0 TCP Keepalive option [I-D.ietf-dnsop-edns-tcp-keepalive]. A
client MUST NOT include an actual EDNS0 TCP Keepalive option in the client MUST NOT include an actual EDNS0 TCP Keepalive option in the
request, since it is automatic, and implied by the semantics of request, since it is automatic, and implied by the semantics of
SUBSCRIBE. If a server receives a SUBSCRIBE request this is an error SUBSCRIBE. If a server receives a SUBSCRIBE request that does
and the server MUST immediately close the TCP connection. In a contain an actual EDNS0 TCP Keepalive option this is an error and the
SUBSCRIBE response the server MUST include an EDNS0 TCP Keepalive server MUST immediately close the TCP connection. In a SUBSCRIBE
option specifying the idle timeout so that the client knows the response the server MUST include an EDNS0 TCP Keepalive option
frequency of keepalives it must generate to keep the connection specifying the idle timeout so that the client knows the frequency of
alive. If the client receives a SUBSCRIBE response that does not keepalives it must generate to keep the connection alive. If the
contain an EDNS0 TCP Keepalive option this is an error and the client client receives a SUBSCRIBE response that does not contain an EDNS0
MUST immediately close the TCP connection. TCP Keepalive option this is an error and the client MUST immediately
close the TCP connection.
6.3. DNS Push Notification UNSUBSCRIBE 6.3. 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
formatted identically to the SUBSCRIBE message which created the formatted identically to the SUBSCRIBE message which created the
subscription, with the exact same name, type and class, except that subscription, with the exact same name, type and class, except that
the opcode is UNSUBSCRIBE (7) instead of SUBSCRIBE (6). the opcode is UNSUBSCRIBE (7) instead of SUBSCRIBE (6).
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ADCOUNT MUST be zero, and the Additional Data Section MUST be empty. ADCOUNT MUST be zero, and the Additional Data Section MUST be empty.
Any records in the Additional Data Section MUST be silently ignored. Any records in the Additional Data Section MUST be silently ignored.
The RCODE MUST contain a code giving the reason for termination. The RCODE MUST contain a code giving the reason for termination.
[Codes to be determined.] The Termination Message MUST contain an [Codes to be determined.] The Termination Message MUST contain an
EDNS0 TCP Keepalive option [I-D.ietf-dnsop-edns-tcp-keepalive] where EDNS0 TCP Keepalive option [I-D.ietf-dnsop-edns-tcp-keepalive] where
the idle timeout indicates the time the client SHOULD wait before the idle timeout indicates the time the client SHOULD wait before
attempting to reconnect. attempting to reconnect.
7. Acknowledgements 7. Security Considerations
The authors would like to thank Kiren Sekar and Marc Krochmal for
previous work completed in this field. This draft has been improved
due to comments from Ran Atkinson.
8. IANA Considerations
This document defines the service name: "_dns-push-tls._tcp".
It is only applicable for the TCP protocol.
This name is to be published in the IANA Service Name Registry.
This document defines two DNS OpCodes: SUBSCRIBE with (tentative)
value 6 and UNSUBSCRIBE with (tentative) value 7.
9. Security Considerations
TLS support is mandatory in DNS Push Notifications. There is no TLS support is REQUIRED in DNS Push Notifications. There is no
provision for opportunistic encryption using a mechanism like provision for opportunistic encryption using a mechanism like
"STARTTLS". "STARTTLS".
9.1. Security Services DNSSEC is RECOMMENDED for DNS Push Notifications. TLS alone does not
provide complete security. TLS certificate verification can provide
reasonable assurance that the client is really talking to the server
associated with the desired host name, but since the desired host
name is learned via a DNS SRV query, if the SRV query is subverted
then the client may have a secure connection to a rogue server.
DNSSEC can provided added confidence that the SRV query has not been
subverted.
7.1. Security Services
It is the goal of using TLS to provide the following security It is the goal of using TLS to provide the following security
services: services:
Confidentiality All application-layer communication is encrypted Confidentiality All application-layer communication is encrypted
with the goal that no party should be able to decrypt it except with the goal that no party should be able to decrypt it except
the intended receiver. the intended receiver.
Data integrity protection Any changes made to the communication in Data integrity protection Any changes made to the communication in
transit are detectable by the receiver. transit are detectable by the receiver.
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Authentication An end-point of the TLS communication is Authentication An end-point of the TLS communication is
authenticated as the intended entity to communicate with. authenticated as the intended entity to communicate with.
Deployment recommendations on the appropriate key lengths and cypher Deployment recommendations on the appropriate key lengths and cypher
suites are beyond the scope of this document. Please refer to TLS suites are beyond the scope of this document. Please refer to TLS
Recommendations [RFC7525] for the best current practices. Keep in Recommendations [RFC7525] for the best current practices. Keep in
mind that best practices only exist for a snapshot in time and mind that best practices only exist for a snapshot in time and
recommendations will continue to change. Updated versions or errata recommendations will continue to change. Updated versions or errata
may exist for these recommendations. may exist for these recommendations.
9.2. TLS Name Authentication 7.2. TLS Name Authentication
As described in Section 6.1, the client discovers the DNS Push As described in Section 6.1, the client discovers the DNS Push
Notification server using an SRV lookup for the record name Notification server using an SRV lookup for the record name
"_dns-push-tls._tcp.<zone>". The server connection endpoint SHOULD "_dns-push-tls._tcp.<zone>". The server connection endpoint SHOULD
then be authenticated using DANE TLSA records for the associated SRV then be authenticated using DANE TLSA records for the associated SRV
record. This associates the target's name and port number with a record. This associates the target's name and port number with a
trusted TLS certificate [RFC7673]. This procedure uses the TLS Sever trusted TLS certificate [RFC7673]. This procedure uses the TLS Sever
Name Indication (SNI) extension [RFC6066] to inform the server of the Name Indication (SNI) extension [RFC6066] to inform the server of the
name the client has authenticated through the use of TLSA records. name the client has authenticated through the use of TLSA records.
Therefore, if the SRV record passes DNSSEC validation and a TLSA Therefore, if the SRV record passes DNSSEC validation and a TLSA
record matching the target name is useable, an SNI extension MUST be record matching the target name is useable, an SNI extension MUST be
used for the target name to ensure the client is connecting to the used for the target name to ensure the client is connecting to the
server it has authenticated. If the target name does not have a server it has authenticated. If the target name does not have a
usable TLSA record, then the use of the SNI extension is optional. usable TLSA record, then the use of the SNI extension is optional.
9.3. TLS Compression 7.3. TLS Compression
In order to reduce the chances of compression related attacks, TLS- In order to reduce the chances of compression related attacks, TLS-
level compression SHOULD be disabled when using TLS versions 1.2 and level compression SHOULD be disabled when using TLS versions 1.2 and
earlier. In the draft version of TLS 1.3 [I-D.ietf-tls-tls13], TLS- earlier. In the draft version of TLS 1.3 [I-D.ietf-tls-tls13], TLS-
level compression has been removed completely. level compression has been removed completely.
9.4. TLS Session Resumption 7.4. TLS Session Resumption
TLS Session Resumption is permissible on DNS Push Notification TLS Session Resumption is permissible on DNS Push Notification
servers. The server may keep TLS state with Session IDs [RFC5246] or servers. The server may keep TLS state with Session IDs [RFC5246] or
operate in stateless mode by sending a Session Ticket [RFC5077] to operate in stateless mode by sending a Session Ticket [RFC5077] to
the client for it to store. However, once the connection is closed, the client for it to store. However, once the connection is closed,
any existing subscriptions will be dropped. When the TLS session is any existing subscriptions will be dropped. When the TLS session is
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
up more quickly, but the client will still have to recreate any
desired subscriptions.
8. IANA Considerations
This document defines the service name: "_dns-push-tls._tcp".
It is only applicable for the TCP protocol.
This name is to be published in the IANA Service Name Registry.
This document defines three DNS OpCodes: SUBSCRIBE with (tentative)
value 6, UNSUBSCRIBE with (tentative) value 7, and RECONFIRM with
(tentative) value 8.
9. Acknowledgements
The authors would like to thank Kiren Sekar and Marc Krochmal for
previous work completed in this field.
This draft has been improved due to comments from Ran Atkinson, Mark
Delany, and Markus Stenberg.
10. References 10. References
10.1. Normative References 10.1. Normative References
[I-D.ietf-dnsop-5966bis] [I-D.ietf-dnsop-5966bis]
Dickinson, J., Dickinson, S., Bellis, R., Mankin, A., and Dickinson, J., Dickinson, S., Bellis, R., Mankin, A., and
D. Wessels, "DNS Transport over TCP - Implementation D. Wessels, "DNS Transport over TCP - Implementation
Requirements", draft-ietf-dnsop-5966bis-04 (work in Requirements", draft-ietf-dnsop-5966bis-05 (work in
progress), November 2015. progress), December 2015.
[I-D.ietf-dnsop-edns-tcp-keepalive] [I-D.ietf-dnsop-edns-tcp-keepalive]
Wouters, P., Abley, J., Dickinson, S., and R. Bellis, "The Wouters, P., Abley, J., Dickinson, S., and R. Bellis, "The
edns-tcp-keepalive EDNS0 Option", draft-ietf-dnsop-edns- edns-tcp-keepalive EDNS0 Option", draft-ietf-dnsop-edns-
tcp-keepalive-04 (work in progress), October 2015. tcp-keepalive-05 (work in progress), January 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-tls13-10 (work in progress), Version 1.3", draft-ietf-tls-tls13-11 (work in progress),
October 2015. December 2015.
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, DOI [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, DOI
10.17487/RFC0768, August 1980, 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, RFC [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC
793, DOI 10.17487/RFC0793, September 1981, 793, DOI 10.17487/RFC0793, September 1981,
<http://www.rfc-editor.org/info/rfc793>. <http://www.rfc-editor.org/info/rfc793>.
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities", [RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
 End of changes. 25 change blocks. 
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