draft-ietf-dnssd-push-05.txt   draft-ietf-dnssd-push-06.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: August 1, 2016 Apple Inc. Expires: September 22, 2016 Apple Inc.
January 29, 2016 March 21, 2016
DNS Push Notifications DNS Push Notifications
draft-ietf-dnssd-push-05 draft-ietf-dnssd-push-06
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 August 1, 2016. This Internet-Draft will expire on September 22, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2016 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
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to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
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 . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Transport . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4. Transport . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. State Considerations . . . . . . . . . . . . . . . . . . . . 6 4.1. Client-Initiated Termination . . . . . . . . . . . . . . 7
6. Protocol Operation . . . . . . . . . . . . . . . . . . . . . 7 4.2. Server-Initiated Termination . . . . . . . . . . . . . . 7
6.1. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 8 5. State Considerations . . . . . . . . . . . . . . . . . . . . 9
6.2. DNS Push Notification SUBSCRIBE . . . . . . . . . . . . . 10 6. Protocol Operation . . . . . . . . . . . . . . . . . . . . . 10
6.3. DNS Push Notification UNSUBSCRIBE . . . . . . . . . . . . 13 6.1. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 11
6.4. DNS Push Notification Update Messages . . . . . . . . . . 14 6.2. DNS Push Notification SUBSCRIBE . . . . . . . . . . . . . 13
6.5. DNS RECONFIRM . . . . . . . . . . . . . . . . . . . . . . 17 6.3. DNS Push Notification UNSUBSCRIBE . . . . . . . . . . . . 18
6.6. DNS Push Notification Termination Message . . . . . . . . 18 6.4. DNS Push Notification Update Messages . . . . . . . . . . 19
7. Security Considerations . . . . . . . . . . . . . . . . . . . 19 6.5. DNS RECONFIRM . . . . . . . . . . . . . . . . . . . . . . 22
7.1. Security Services . . . . . . . . . . . . . . . . . . . . 19 6.6. DNS Push Notification Termination Message . . . . . . . . 24
7.2. TLS Name Authentication . . . . . . . . . . . . . . . . . 20 7. Security Considerations . . . . . . . . . . . . . . . . . . . 26
7.3. TLS Compression . . . . . . . . . . . . . . . . . . . . . 20 7.1. Security Services . . . . . . . . . . . . . . . . . . . . 26
7.4. TLS Session Resumption . . . . . . . . . . . . . . . . . 20 7.2. TLS Name Authentication . . . . . . . . . . . . . . . . . 27
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 7.3. TLS Compression . . . . . . . . . . . . . . . . . . . . . 27
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 21 7.4. TLS Session Resumption . . . . . . . . . . . . . . . . . 27
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 21 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
10.1. Normative References . . . . . . . . . . . . . . . . . . 21 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 28
10.2. Informative References . . . . . . . . . . . . . . . . . 23 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24 10.1. Normative References . . . . . . . . . . . . . . . . . . 28
10.2. Informative References . . . . . . . . . . . . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31
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
relevant in the case of DNS Service Discovery [RFC6763] but is not relevant in the case of DNS Service Discovery [RFC6763] but is not
limited to that use case and provides a general DNS mechanism for DNS limited to that use case, and provides a general DNS mechanism for
record change notifications. Familiarity with the DNS protocol and DNS record change notifications. Familiarity with the DNS protocol
DNS packet formats is assumed [RFC1034] [RFC1035] [RFC6195]. and DNS packet formats is assumed [RFC1034] [RFC1035] [RFC6195].
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
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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 than 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). 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 phone, 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 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
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. Adopting this resource record sets (RRSets) on the zone's server.
existing syntax and semantics for DNS Push Notifications allows for
messages going in the other direction, from server to client, to
communicate changes to a zone. The client first must subscribe for
Push Notifications by connecting to the server and sending DNS
message(s) indicating the RRSet(s) of interest. When the client
loses interest in updates to these records, it unsubscribes.
The DNS Push Notification server for a zone is any server capable of This specification adopts a simplified subset of these existing
generating the correct change notifications for a name. It may be a syntax and semantics, and uses them for DNS Push Notification
master, slave, or stealth name server [RFC1996]. Consequently, the messages going in the opposite direction, from server to client, to
"_dns-push-tls._tcp.<zone>" SRV record for a <zone> MAY reference the communicate changes to a zone. The client subscribes for Push
same target host and port as that zone's Notifications by connecting to the server and sending DNS message(s)
indicating the RRSet(s) of interest. When the client loses interest
in updates to these records, it unsubscribes.
The DNS Push Notification server for a zone is any server capable
of generating the correct change notifications for a name.
It may be a master, slave, or stealth name server [RFC1996].
Consequently, the "_dns-push-tls._tcp.<zone>" SRV record for a
zone MAY reference the same target host and port as that zone's
"_dns-update-tls._tcp.<zone>" SRV record. When the same target host "_dns-update-tls._tcp.<zone>" SRV record. When the same target host
and port is offered for both DNS Updates and DNS Push Notifications, and port is offered for both DNS Updates and DNS Push Notifications,
a client MAY use a single TCP connection to that server for DNS a client MAY use a single TCP connection to that server for both DNS
Updates, DNS Queries, and DNS Push Notification Queries. Updates and DNS Push Notification Queries.
Supporting DNS Updates and DNS Push Notifications on the same server
is OPTIONAL. A DNS Push Notification server is not REQUIRED to
support DNS Update.
DNS Updates and DNS Push Notifications may be handled on different
ports on the same target host, in which case they are not considered
to be the "same server" for the purposes of this specification, and
communications with these two ports are handled independently.
Standard DNS Queries MAY be sent over a DNS Push Notification
connection, provided that these are queries for names falling within
the server's zone (the <zone> in the "_dns-push-tls._tcp.<zone>" SRV
record). The RD (Recursion Desired) bit MUST be zero.
DNS Push Notification clients are NOT required to implement DNS DNS Push Notification clients are NOT required to implement DNS
Update Prerequisite processing. Prerequisites are used to perform Update Prerequisite processing. Prerequisites are used to perform
tentative atomic test-and-set type operations on the server, and that tentative atomic test-and-set type operations when a client updates
concept has no application when it comes to an authoritative server records on a server, and that concept has no applicability when it
informing a client of changes to DNS records. comes to an authoritative server informing a client of changes to DNS
records.
This DNS Push Notification specification includes support for DNS
classes, for completeness. However, in practice, it is anticipated
that for the foreseeable future the only DNS class in use will be DNS
class "IN", as it is today with existing DNS servers and clients. A
DNS Push Notification server MAY choose to implement only DNS class
"IN".
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 This requirement to use UDP has subsequently been relaxed
[RFC5966][I-D.ietf-dnsop-5966bis]. Following that precendent, DNS [RFC5966][I-D.ietf-dnsop-5966bis].
Push Notification is defined only for TCP. DNS Push Notification
clients MUST use TLS over TCP.
Either end of the TCP connection can terminate all of the
subscriptions on that connection by simply closing the connection
abruptly with a TCP FIN or RST. (An individual subscription is
terminated by sending an UNSUBSCRIBE message for that specific
subscription.)
If a client closes the connection, it is signaling that it is no
longer interested in receiving updates to any of the records it has
subscribed. It is informing the server that the server may release
all state information it has been keeping with regards to this
client. This may occur because the client computer has been
disconnected from the network, has gone to sleep, or the application
requiring the records has terminated.
If a server closes the connection, it is informing the client that it In keeping with the more recent precedent, DNS Push Notification is
can no longer provide updates for the subscribed records. This may defined only for TCP. DNS Push Notification clients MUST use TLS
occur because the server application software or operating system is over TCP.
restarting, the application terminated unexpectedly, the server is
undergoing maintenance procedures, or the server is overloaded and
can no longer provide the information to all the clients that wish to
receive it. The client can try to re-subscribe at a later time or
connect to another server supporting DNS Push Notifications for the
zone.
Connection setup over TCP ensures return reachability and alleviates Connection setup over TCP ensures return reachability and alleviates
concerns of state overload at the server through anonymous concerns of state overload at the server through anonymous
subscriptions. All subscribers are guaranteed to be reachable by the subscriptions. All subscribers are guaranteed to be reachable by the
server by virtue of the TCP three-way handshake. Because TCP SYN server by virtue of the TCP three-way handshake. Because TCP SYN
flooding attacks are possible with any protocol over TCP, flooding attacks are possible with any protocol over TCP,
implementers are encouraged to use industry best practices to guard implementers are encouraged to use industry best practices to guard
against such attacks [IPJ.9-4-TCPSYN] [RFC4953]. against such attacks [IPJ.9-4-TCPSYN] [RFC4953].
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 7.2 for details. Section 7.2 for details.
A DNS Push Notification session begins with a client connecting to a
DNS Push Notification server. Over that connection the client then
issues DNS operation requests, such as SUBSCRIBE.
4.1. Client-Initiated Termination
An individual subscription is terminated by sending an UNSUBSCRIBE
message for that specific subscription, or all subscriptions can be
cancelled at once by the client closing the connection with a TCP
RST. When a client terminates an individual subscription (via
UNSUBSCRIBE) or all subscriptions on that connection (by closing the
connection) it is signalling to the server that it is longer
interested in receiving those particular updates. It is informing
the server that the server may release any state information it has
been keeping with regards to these particular subscriptions.
After terminating its last subscription on a connection via
UNSUBSCRIBE, a client MAY close the connection immediately with a TCP
FIN, or it may keep it open if it anticipates performing further
operations on that connection in the future. If a client wishes to
keep an idle connection open, it MUST meet its keepalive obligations
[I-D.ietf-dnsop-edns-tcp-keepalive] or the server is entitled to
close the connection (see below).
If a client plans to terminate one or more subscriptions on a
connection and doesn't intend to keep that connection open, then as
an efficiency optimization it MAY instead choose to simply close the
connection with a TCP RST, which implicitly terminates all
subscriptions on that connection. This may occur because the client
computer is being shut down, is going to sleep, the application
requiring the subscriptions has terminated, or simply because the
last active subscription on that connection has been cancelled.
4.2. Server-Initiated Termination
If a client makes a connection and then fails to send any DNS message
that uses EDNS(0) TCP Keepalive [I-D.ietf-dnsop-edns-tcp-keepalive]
(either SUBSCRIBE, where Keepalive is implicit, or some other DNS
message, with an explicit an EDNS(0) TCP Keepalive option) then after
30 seconds of inactivity the server SHOULD close the connection. If
no data has been sent on the connection the server MAY abort the
connection with a TCP RST. If data has been sent on the connection
then the server SHOULD close the connection gracefully with a TCP FIN
so that the data is reliably delivered.
In the response to the first successful SUBSCRIBE, the included
EDNS(0) TCP Keepalive option specifies the idle timeout so that the
client knows the frequency of traffic it must generate to keep the
connection alive. If the idle timeout for that connection changes,
then the server communicates this by placing an updated EDNS(0) TCP
Keepalive option in a subsequent message to the client.
At both servers and clients, the generation or reception of any
request, response, update, or keepalive message resets the keepalive
timer for that connection.
In the absence of any requests, responses, or update messages on a
connection, a client MUST generate keepalive traffic before the idle
timeout expires, or the server is entitled to close the connection.
If a client disconnects from the network abruptly, without closing
its connection, the server learns of this after failing to receive
further traffic from that client. If no requests, responses, update
messages or keepalive traffic occurs on a connection for 1.5 times
the idle timeout, then this indicates that the client is probably no
longer on the network, and the server SHOULD abort the connection
with a TCP RST.
[We need to discuss the nature of "the required keepalives". Are
they TCP-layer keepalives? DNS-layer keepalives? There is currently
no DNS-layer keepalive or 'no-op' operation defined. What would that
operation be? A DNS QUERY containing zero questions? A DNS
SUBSCRIBE containing zero questions? An "empty" DNS message over the
TCP connection (just a pair of zero bytes, signifying a zero-length
message)? One benefit of TCP-layer keepalives is that they transmit
fewer bytes, and involve less software overhead for processing those
bytes. Another benefit is that it is more feasible to implement
these in networking offload hardware, which can allow devices to meet
their TCP keepalive obligations while sleeping. This is particularly
important for battery-powered devices like mobile phones and tablets.
On the other hand, using TCP-layer keepalives requires an API for a
client to tell the networking stack at what frequency to perform TCP-
layer keepalives, and an API for a server to request the networking
stack to inform it when TCP-layer keepalives are not received by the
required deadline. TCP-layer keepalives also only verify liveness of
the remote networking stack, whereas DNS-layer keepalives provide
higher assurance of liveness of the remote server application
software -- though this a limited benefit, since there is no reason
to expect that DNS Push Notification server software will routinely
become wedged and unresponsive.]
After sending an error response to a client, the server MAY close the
connection with a TCP FIN.
If the server is overloaded and needs to shed load, it MAY send a
Termination Message to the client and close the connection with a TCP
FIN.
Apart from the cases described above, a server MUST NOT close a
connection with a DNS Push Notification client, except in
extraordinary error conditions. Closing the connection is the
client's responsibility, to be done at the client's discretion, when
it so chooses. A DNS Push Notification server only closes a DNS Push
Notification connection under exceptional circumstances, such as when
the server application software or underlying operating system is
restarting, the server application terminated unexpectedly (perhaps
due to a bug that makes it crash), or the server is undergoing
maintenance procedures. When possible, a DNS Push Notification
server SHOULD send a Termination Message (Section 6.6 ) informing the
client of the reason for the connection being closed.
After a connection is closed by the server, the client SHOULD try to
reconnect, to that server, or to another server supporting DNS Push
Notifications for the zone. If reconnecting to the same server, and
there was a Termination Message or error response containing a
EDNS(0) TCP Keepalive option, the client MUST respect the indicated
delay before attempting to reconnect.
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 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
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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. Note that a client MUST be prepared to Notifications to the client. Note that a client MUST be prepared to
receive (and silently discard) Push Notifications for subscriptions receive (and silently ignore) Push Notifications for subscriptions it
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.
The exchange between client and server terminates when either end 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.
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address(es) that the hostname resolves to. If two different target address(es) that the hostname resolves to. If two different target
hostnames happen to resolve to the same IP address(es), then the hostnames happen to resolve to the same IP address(es), then the
client SHOULD NOT recognize these as the "same server" for the client SHOULD NOT recognize these as the "same server" for the
purposes of using a single shared connection to that server. If an purposes of using a single shared connection to that server. If an
administrator wishes to use a single server for multiple zones and/or administrator wishes to use a single server for multiple zones and/or
multiple roles (e.g., both DNS Push Notifications and DNS Updates), multiple roles (e.g., both DNS Push Notifications and DNS Updates),
and wishes to have clients use a single shared connection for and wishes to have clients use a single shared connection for
operations on that server, then the administrator MUST use the same operations on that server, then the administrator MUST use the same
target hostname in the appropriate SRV records. target hostname in the appropriate SRV records.
However, a single client device may be home to multiple independent However, server implementers and operators should be aware that this
client software instances that don't know about each other, so a DNS connection sharing may not be possible in all cases. A single client
Push Notification server MUST be prepared to accept multiple device may be home to multiple independent client software instances
connections from the same client IP address. This is undesirable that don't know about each other, so a DNS Push Notification server
from an efficiency stanpoint, but may be unavoidable in some MUST be prepared to accept multiple connections from the same client
situations, so a DNS Push Notification server MUST be prepared to IP address. This is undesirable from an efficiency standpoint, but
accept multiple connections from the same client IP address. may be unavoidable in some situations, so a DNS Push Notification
server MUST be prepared to accept multiple connections from the same
client IP address.
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. is not) the typical TCP port 53 used for conventional DNS.
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 the
local resolver with record type SOA [RFC1035] for the name of the local resolver with record type SOA [RFC1035] for the name of the
record it wishes to subscribe. record 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 reply. If not, the server SHOULD include the SOA Section of the reply. If not, the local resolver SHOULD include
record for the zone of the requested name in the Authority the SOA record for the zone of the requested name in the
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.
4. Once the SOA is known, the client sends a DNS query with type SRV 4. Once the SOA is known, the client sends a DNS query with type SRV
skipping to change at page 9, line 17 skipping to change at page 12, line 20
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 7.2 [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" 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
is not willing to accept a subscription request, then a is not willing to accept a subscription request, then a
subsequent server is to be contacted. subsequent server is to be contacted.
If a server closes a DNS Push Notification subscription connection, Each time a client makes a new DNS Push Notification subscription
the client SHOULD repeat the discovery process in order to determine connection, it SHOULD repeat the discovery process in order to
the preferred DNS server for subscriptions at that time. determine the preferred DNS server for subscriptions at that time.
6.2. DNS Push Notification SUBSCRIBE 6.2. DNS Push Notification SUBSCRIBE
A DNS Push Notification client indicates its desire to receive DNS A DNS Push Notification client indicates its desire to receive DNS
Push Notifications for a given domain name by sending a SUBSCRIBE Push Notifications for a given domain name by sending a SUBSCRIBE
request over the established TCP connection to the server. A request over the established TCP connection to the server. A
SUBSCRIBE request is formatted identically to a conventional DNS SUBSCRIBE request is formatted identically to a conventional DNS
QUERY request [RFC1035], except that the opcode is SUBSCRIBE (6) QUERY request [RFC1035], except that the opcode is SUBSCRIBE (6)
instead of QUERY (0). If neither QTYPE nor QCLASS are ANY (255) then instead of QUERY (0). If neither QTYPE nor QCLASS are ANY (255) then
this is a specific subscription to changes for the given name, type this is a specific subscription to changes for the given name, type
skipping to change at page 10, line 37 skipping to change at page 13, line 37
packed efficiently into TCP segments, so the ability to pack multiple packed efficiently into TCP segments, so the ability to pack multiple
SUBSCRIBE operations into a single DNS message within that TCP stream SUBSCRIBE operations into a single DNS message within that TCP stream
would add extra complexity for little benefit. would add extra complexity for little benefit.
ANCOUNT MUST be zero, and the Answer Section MUST be empty. ANCOUNT MUST be zero, and the Answer Section MUST be empty.
Any records in the Answer Section MUST be silently ignored. Any records in the Answer Section MUST be silently ignored.
NSCOUNT MUST be zero, and the Authority Section MUST be empty. NSCOUNT MUST be zero, and the Authority Section MUST be empty.
Any records in the Authority Section MUST be silently ignored. Any records in the Authority Section MUST be silently ignored.
ARCOUNT MUST be zero, and the Additional Section MUST be empty. ARCOUNT specifies the number of records in the Additional Data
Any records in the Additional Section MUST be silently ignored. Section. Typically this is zero, but it may be nonzero in some
cases, such as when the request includes an EDNS(0) OPT record.
Each SUBSCRIBE request generates exactly one SUBSCRIBE response from If accepted, the subscription will stay in effect until the client
the server. revokes the subscription or until the connection between the client
and the server is closed.
In the SUBSCRIBE response the RCODE indicates whether or not the SUBSCRIBE requests on a given connection MUST be unique. A client
subscription was accepted. Supported RCODEs are as follows: MUST NOT send a SUBSCRIBE message that duplicates the name, type and
class of an existing active subscription on that TLS/TCP connection.
For the purpose of this matching, the established DNS case-
insensitivity for US-ASCII letters applies (e.g., "foo.com" and
"Foo.com" are the same). If a server receives such a duplicate
SUBSCRIBE message this is an error and the server MUST immediately
close the TCP connection.
+----------+-------+------------------------------------------------+ DNS wildcarding is not supported. That is, a wildcard ("*") in a
| Mnemonic | Value | Description | SUBSCRIBE message matches only a literal wildcard character ("*") in
+----------+-------+------------------------------------------------+ the zone, and nothing else.
| NOERROR | 0 | SUBSCRIBE successful |
| FORMERR | 1 | Server failed to process request due to a |
| | | malformed request |
| SERVFAIL | 2 | Server failed to process request due to |
| | | resource exhaustion |
| NOTIMP | 4 | Server does not implement DNS Push |
| | | Notifications |
| REFUSED | 5 | Server refuses to process request for policy |
| | | or security reasons |
+----------+-------+------------------------------------------------+
Table 1: Response codes Aliasing is not supported. That is, a CNAME in a SUBSCRIBE message
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
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 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,
the server MUST interpret a SUBSCRIBE request as if it contained an
EDNS(0) TCP Keepalive option [I-D.ietf-dnsop-edns-tcp-keepalive]. A
client MUST NOT include an actual EDNS(0) TCP Keepalive option in the
request, since it is automatic, and implied by the semantics of
SUBSCRIBE. If a server receives a SUBSCRIBE request that does
contain an actual EDNS(0) TCP Keepalive option this is an error and
the server MUST immediately close the TCP connection.
A SUBSCRIBE operation MAY include an explicit EDNS(0) [RFC6891] OPT
record where necessary to carry additional information.
The presence of a SUBSCRIBE operation on a connection indicates to
the server that the client fully implements EDNS(0) [RFC6891], and
can correctly understand any response that conforms to that
specification. After receiving a SUBSCRIBE request, the server MAY
include OPT record in any of its responses, as needed.
Each SUBSCRIBE request generates exactly one SUBSCRIBE response from
the server.
In a SUBSCRIBE response the DNS Header QR bit MUST be one. In a SUBSCRIBE response the DNS Header QR bit MUST be one.
If the QR bit is not one the message is not a SUBSCRIBE response. If the QR bit is not one the message is not a SUBSCRIBE response.
The AA, TC, RD, RA, Z, AD, and CD bits, and the ID field, MUST be The AA, TC, RD, RA, Z, AD, and CD bits, and the ID field, MUST be
zero on transmission, and MUST be silently ignored on reception. zero on transmission, and MUST be silently ignored on reception.
The Question Section MUST echo back the values provided by the client The Question Section MUST echo back the values provided by the client
in the SUBSCRIBE request that generated this SUBSCRIBE response. in the SUBSCRIBE request that generated this SUBSCRIBE response.
skipping to change at page 11, line 52 skipping to change at page 15, line 33
response. This simplifying requirement is made so that there is only response. This simplifying requirement is made so that there is only
a single way that information is communicated to a DNS Push a single way that information is communicated to a DNS Push
Notification client. Since a DNS Push Notification client has to Notification client. Since a DNS Push Notification client has to
parse information received via Push Notification Updates anyway, it parse information received via Push Notification Updates anyway, it
is simpler if it does not also have to parse information received via is simpler if it does not also have to parse information received via
the Answer Section of a SUBSCRIBE response. the Answer Section of a SUBSCRIBE response.
NSCOUNT MUST be zero, and the Authority Section MUST be empty. NSCOUNT MUST be zero, and the Authority Section MUST be empty.
Any records in the Authority Section MUST be silently ignored. Any records in the Authority Section MUST be silently ignored.
ARCOUNT MUST be zero, and the Additional Section MUST be empty. ARCOUNT specifies the number of records in the Additional Data
Section, e.g., the EDNS(0) OPT record.
Any records in the Additional Section MUST be silently ignored. In the SUBSCRIBE response the RCODE indicates whether or not the
subscription was accepted. Supported RCODEs are as follows:
If accepted, the subscription will stay in effect until the client +----------+-------+------------------------------------------------+
revokes the subscription or until the connection between the client | Mnemonic | Value | Description |
and the server is closed. +----------+-------+------------------------------------------------+
| NOERROR | 0 | SUBSCRIBE successful. |
| FORMERR | 1 | Server failed to process request due to a |
| | | malformed request. |
| SERVFAIL | 2 | Server failed to process request due to |
| | | resource exhaustion. |
| NXDOMAIN | 3 | NOT APPLICABLE. DNS Push Notification MUST NOT |
| | | return NXDOMAIN errors in response to |
| | | SUBSCRIBE requests. |
| NOTIMP | 4 | Server does not implement DNS Push |
| | | Notifications. |
| REFUSED | 5 | Server refuses to process request for policy |
| | | or security reasons. |
| NOTAUTH | 9 | Server is not authoritative for the requested |
| | | name. |
+----------+-------+------------------------------------------------+
SUBSCRIBE requests on a given connection MUST be unique. A client SUBSCRIBE Response codes
MUST NOT send a SUBSCRIBE message that duplicates the name, type and
class of an existing active subscription on that TLS/TCP connection.
For the purpose of this matching, the established DNS case-
insensitivity for US-ASCII letters applies (e.g., "foo.com" and
"Foo.com" are the same). If a server receives such a duplicate
SUBSCRIBE message this is an error and the server MUST immediately
close the TCP connection.
DNS wildcarding is not supported. That is, a wildcard ("*") in a This document specifies only these RCODE values for SUBSCRIBE
SUBSCRIBE message matches only a wildcard ("*") in the zone, and Responses. Servers sending SUBSCRIBE Responses SHOULD use one of
nothing else. these values. However, future circumstances may create situations
where other RCODE values are appropriate in SUBSCRIBE Responses, so
clients MUST be prepared to accept SUBSCRIBE Responses with any RCODE
value.
Aliasing is not supported. That is, a CNAME in a SUBSCRIBE message In the first SUBSCRIBE response on a connection, the server MUST
matches only a CNAME in the zone, and nothing else. include an explicit EDNS(0) TCP Keepalive option. If the first
SUBSCRIBE response does not include an explicit EDNS(0) TCP Keepalive
option this is an error and the client MUST immediately close the TCP
connection. In this case the client should act as if the response
contained an EDNS(0) TCP Keepalive option with a value of one hour,
and not attempt any further DNS Push Notification requests to that
server until one hour has passed. This situation may occur if a
client connects to a server that doesn't implement DNS Push
Notifications at all, and it is important not to burden such servers
with continuous retries.
A client may SUBSCRIBE to records that are unknown to the server at The server MAY include EDNS(0) TCP Keepalive options in subsequent
the time of the request (providing that the name falls within one of messages, if the idle timeout changes. If the client receives
the zone(s) the server is responsible for) and this is not an error. subsequent messages that do not contain an explicit EDNS(0) TCP
The server MUST accept these requests and send Push Notifications if Keepalive option then the idle timeout for that connection remains
and when matches are found in the future. unchanged at that time.
Since all SUBSCRIBE operations are implicitly long-lived operations, In an error response, with nonzero RCODE, the server MUST contain an
the server MUST interpret a SUBSCRIBE request as if it contained an EDNS(0) TCP Keepalive option specifying the delay before the client
EDNS0 TCP Keepalive option [I-D.ietf-dnsop-edns-tcp-keepalive]. A tries again:
client MUST NOT include an actual EDNS0 TCP Keepalive option in the
request, since it is automatic, and implied by the semantics of For RCODE = 1 (FORMERR) the delay may be any value selected by the
SUBSCRIBE. If a server receives a SUBSCRIBE request that does implementer. A value of one minute is RECOMMENDED, to avoid high
contain an actual EDNS0 TCP Keepalive option this is an error and the load from defective clients.
server MUST immediately close the TCP connection. In a SUBSCRIBE
response the server MUST include an EDNS0 TCP Keepalive option For RCODE = 2 (SERVFAIL), which occurs due to resource exhaustion,
specifying the idle timeout so that the client knows the frequency of the delay should be chosen according to the level of server
keepalives it must generate to keep the connection alive. If the overload and the anticipated duration of that overload. By
client receives a SUBSCRIBE response that does not contain an EDNS0 default, a value of one minute is RECOMMENDED.
TCP Keepalive option this is an error and the client MUST immediately
close the TCP connection. For RCODE = 4 (NOTIMP), which occurs on a server that doesn't
implement DNS Push Notifications, it is unlikely that the server
will begin supporting DNS Push Notifications in the next few
minutes, so the retry delay SHOULD be one hour. Note that a
server that doesn't implement DNS Push Notifications will most
likely not implement this retry delay mechanism using the EDNS(0)
TCP Keepalive option either, and in this case the client will fall
back to the case described above specifying how to handle
SUBSCRIBE responses that do not contain an EDNS(0) TCP Keepalive
option.
For RCODE = 5 (REFUSED), which occurs on a server that implements
DNS Push Notifications, but is currently configured to disallow
DNS Push Notifications, the retry delay may be any value selected
by the implementer and/or configured by the operator.
This is a misconfiguration, since this server is listed in a
"_dns-push-tls._tcp.<zone>" SRV record, but the server itself is
not currently configured to support DNS Push Notifications. Since
it is possible that the misconfiguration may be repaired at any
time, the retry delay should not be set too high. By default, a
value of 5 minutes is RECOMMENDED.
For RCODE = 9 (NOTAUTH), which occurs on a server that implements
DNS Push Notifications, but is not configured to be authoritative
for the requested name, the retry delay may be any value selected
by the implementer and/or configured by the operator.
This is a misconfiguration, since this server is listed in a
"_dns-push-tls._tcp.<zone>" SRV record, but the server itself is
not currently configured to support DNS Push Notifications for
that zone. Since it is possible that the misconfiguration may be
repaired at any time, the retry delay should not be set too high.
By default, a value of 5 minutes is RECOMMENDED.
For other RCODE values, the retry delay should be set by the
server as appropriate for that error condition. By default, a
value of 5 minutes is RECOMMENDED.
After sending an error response the server MAY close the TCP
connection with a FIN, or MAY allow it to remain open. Clients MUST
correctly handle both cases.
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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ID, the Z bits, and RCODE MUST be zero on transmission, ID, the Z bits, and RCODE MUST be zero on transmission,
and MUST be silently ignored on reception. and MUST be silently ignored on reception.
ZOCOUNT MUST be zero, and the Zone Section MUST be empty. ZOCOUNT MUST be zero, and the Zone Section MUST be empty.
Any records in the Zone Section MUST be silently ignored. Any records in the Zone Section MUST be silently ignored.
PRCOUNT MUST be zero, and the Prerequisite Section MUST be empty. PRCOUNT MUST be zero, and the Prerequisite Section MUST be empty.
Any records in the Prerequisite Section MUST be silently ignored. Any records in the Prerequisite Section MUST be silently ignored.
ADCOUNT MUST be zero, and the Additional Data Section MUST be empty. UPCOUNT specifies the number of records in the Update Section.
Any records in the Additional Data Section MUST be silently ignored.
ADCOUNT specifies the number of records in the Additional Data
Section. Typically this is zero, but it may be nonzero in some
cases, such as when the message includes an EDNS(0) OPT record.
The Update Section contains the relevant change information for the The Update Section 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.
Delete an individual RR from a name: Delete an individual RR from a name:
TTL=0, CLASS=NONE; TTL=0, CLASS=NONE;
TYPE, RDLENGTH and RDATA specifies the RR being deleted. TYPE, RDLENGTH and RDATA specifies the RR being deleted.
Add an individual RR to a name: 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.
Upon reception of a Push Notification Update Message, the client When processing the records received in a Push Notification Update
receiving the message MUST validate that the records being added or Message, the receiving client MUST validate that the records being
deleted correspond with at least one currently active subscription on added or deleted correspond with at least one currently active
that connection. Specifically, the record name MUST match the name subscription on that connection. Specifically, the record name MUST
given in the SUBSCRIBE request, subject to the usual established DNS match the name given in the SUBSCRIBE request, subject to the usual
case-insensitivity for US-ASCII letters. If the QTYPE was not ANY established DNS case-insensitivity for US-ASCII letters. If the
(255) then the TYPE of the record must match the QTYPE given in the QTYPE in the SUBSCRIBE request was not ANY (255) then the TYPE of the
SUBSCRIBE request. If the QCLASS was not ANY (255) then the CLASS of record must match the QTYPE given in the SUBSCRIBE request. If the
QCLASS in the SUBSCRIBE request was not ANY (255) then the CLASS of
the record must match the QCLASS given in the SUBSCRIBE request. If the record must match the QCLASS given in the SUBSCRIBE request. If
a matching active subscription on that connection is not found, then a matching active subscription on that connection is not found, then
that individual record addition/deletion is silently ignored. that individual record addition/deletion is silently ignored.
Processing of other additions and deletions in this message is not Processing of other additions and deletions in this message is not
affected. The TCP connection is not closed. This is to allow for affected. The TCP connection is not closed. This is to allow for
the race condition where a client sends an outbound UNSUBSCRIBE while the race condition where a client sends an outbound UNSUBSCRIBE while
inbound Push Notification Updates for that subscription from the inbound Push Notification Updates for that subscription from the
server are still in flight. server are still in 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
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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" update, not three server SHOULD send a "delete an RRset from a name" update, not three
separate "delete an individual RR from a name" updates. Similarly, separate "delete an individual RR from a name" updates. Similarly,
when both an SRV and a TXT record are deleted from a given name, and 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 server SHOULD no other records of any kind exist for that name, the server SHOULD
send a "delete all RRsets from a name" update, not two separate send a "delete all RRsets from a name" update, not two separate
"delete an RRset from a name" updates. "delete an RRset from a name" updates.
All Push Notification Update Messages MUST contain an EDNS0 TCP A server SHOULD combine multiple change notifications in a single
Keepalive option [I-D.ietf-dnsop-edns-tcp-keepalive] specifying the Update Message when possible, even if those change notifications
idle timeout so that the client knows the frequency of keepalives it apply to different subscriptions. Conceptually, a Push Notification
must generate to keep the connection alive. If the client receives a Update Message is a connection-level concept, not a subscription-
Push Notification Update Message that does not contain an EDNS0 TCP level concept.
Keepalive option this is an error and the client MUST immediately
close the TCP connection.
Reception of a Push Notification Update Message results in no Push Notification Update Messages MAY contain an EDNS(0) TCP
response back to the server. Keepalive option [I-D.ietf-dnsop-edns-tcp-keepalive] if the idle
timeout has changed since the last time the server sent an EDNS(0)
TCP Keepalive option on this connection.
In the event that the server wishes to inform a client of a new idle
timeout for the connection, the server MAY combine that with the next
message it sends to the client, or the server MAY send an empty Push
Notification Update Message (zero records in the Update Section) to
carry the EDNS(0) TCP Keepalive option. Clients MUST correctly
receive and process the EDNS(0) TCP Keepalive option in both cases.
Reception of a Push Notification Update Message does not directly
generate a response back to the server. (Updates may indirectly
generate other 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 aging resumes and records are removed from the local cache record aging resumes and records are removed from the local cache
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Sometimes, particularly when used with a Hybrid Proxy Sometimes, particularly when used with a Hybrid Proxy
[I-D.ietf-dnssd-hybrid], a DNS Zone may contain stale data. When a [I-D.ietf-dnssd-hybrid], a DNS Zone may contain stale data. When a
client encounters data that it believe may be stale (e.g., an SRV client encounters data that it believe may be stale (e.g., an SRV
record referencing a target host+port that is not responding to record referencing a target host+port that is not responding to
connection requests) the client sends a DNS RECONFIRM message to connection requests) the client sends a DNS RECONFIRM message to
request that the server re-verify that the data is still valid. For request that the server re-verify that the data is still valid. For
a Hybrid Proxy, this causes it to issue new Multicast DNS requests to a Hybrid Proxy, this causes it to issue new Multicast DNS requests to
ascertain whether the target device is still present. For other ascertain whether the target device is still present. For other
kinds of DNS server the RECONFIRM operation is currently undefined kinds of DNS server the RECONFIRM operation is currently undefined
and should be sliently ignored. A RECONFIRM request is formatted and SHOULD be silently ignored.
similarly to a conventional DNS QUERY request [RFC1035], except that
the opcode is RECONFIRM (8) instead of QUERY (0). QTYPE MUST NOT be A RECONFIRM request is formatted similarly to a conventional DNS
the value ANY (255). QCLASS MUST NOT be the value ANY (255). QUERY request [RFC1035], except that the opcode is RECONFIRM (8)
instead of QUERY (0). QTYPE MUST NOT be the value ANY (255). QCLASS
MUST NOT be the value ANY (255).
In a RECONFIRM request the DNS Header QR bit MUST be zero. In a RECONFIRM request the DNS Header QR bit MUST be zero.
If the QR bit is not zero the message is not a RECONFIRM request. If the QR bit is not zero the message is not a RECONFIRM request.
The AA, TC, RD, RA, Z, AD, and CD bits, the ID field, and the RCODE The AA, TC, RD, RA, Z, AD, and CD bits, the ID field, and the RCODE
field, MUST be zero on transmission, and MUST be silently ignored on field, MUST be zero on transmission, and MUST be silently ignored on
reception. reception.
Like a DNS QUERY request, a RECONFIRM request MUST contain exactly Like a DNS QUERY request, a RECONFIRM request MUST contain exactly
one question. Since RECONFIRM requests are sent over TCP, multiple one question. Since RECONFIRM requests are sent over TCP, multiple
skipping to change at page 17, line 41 skipping to change at page 22, line 43
packed efficiently into TCP segments, so the ability to pack multiple packed efficiently into TCP segments, so the ability to pack multiple
RECONFIRM operations into a single DNS message within that TCP stream RECONFIRM operations into a single DNS message within that TCP stream
would add extra complexity for little benefit. would add extra complexity for little benefit.
ANCOUNT MUST be nonzero, and the Answer Section MUST contain the ANCOUNT MUST be nonzero, and the Answer Section MUST contain the
rdata for the record(s) that the client believes to be in doubt. rdata for the record(s) that the client believes to be in doubt.
NSCOUNT MUST be zero, and the Authority Section MUST be empty. NSCOUNT MUST be zero, and the Authority Section MUST be empty.
Any records in the Authority Section MUST be silently ignored. Any records in the Authority Section MUST be silently ignored.
ARCOUNT MUST be zero, and the Additional Section MUST be empty. ARCOUNT specifies the number of records in the Additional Data
Any records in the Additional Section MUST be silently ignored. Section. Typically this is zero, but it may be nonzero in some
cases, such as when the request includes an EDNS(0) OPT record.
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.
No response message is generated as a result of processing a No response message is generated as a result of processing a
RECONFIRM message. RECONFIRM message.
skipping to change at page 18, line 15 skipping to change at page 24, line 8
If the server receiving the RECONFIRM request determines that the If the server receiving the RECONFIRM request determines that the
records are in fact no longer valid, then subsequent DNS Push records are in fact no longer valid, then subsequent DNS Push
Notification Update Messages will be generated to inform interested Notification Update Messages will be generated to inform interested
clients. Thus, one client discovering that a previously-advertised clients. Thus, one client discovering that a previously-advertised
printer is no longer present has the side effect of informing all printer is no longer present has the side effect of informing all
other interested clients that the printer in question is now gone. other interested clients that the printer in question is now gone.
6.6. DNS Push Notification Termination Message 6.6. DNS Push Notification Termination Message
If a server is low on resources it MAY simply terminate a client If a server is low on resources it MAY simply terminate a client
connection with a TCP RST. However, the likely behavour of the connection with a TCP RST. However, the likely behaviour of the
client may be simply to reconnect immediately, putting more burden on client may be simply to reconnect immediately, putting more burden on
the server. Therefore, a server MAY instead choose to shed client the server. Therefore, a server SHOULD instead choose to shed client
load by (a) sending a DNS Push Notification Termination Message and load by (a) sending a DNS Push Notification Termination Message and
then (b) closing the client connection with a TCP FIN instead of RST, then (b) immediately closing the client connection with a TCP FIN
thereby facilitating reliable delivery of the Termination Message. instead of RST, thereby facilitating reliable delivery of the
Termination Message.
The format of a Termination Message is similar to a Push Notification The format of a Termination Message is similar to a Push Notification
Update. Update.
The following figure shows the existing DNS Update header format: The following figure shows the existing DNS Update header format:
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
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ID | | ID |
skipping to change at page 19, line 14 skipping to change at page 25, line 8
ZOCOUNT MUST be zero, and the Zone Section MUST be empty. ZOCOUNT MUST be zero, and the Zone Section MUST be empty.
Any records in the Zone Section MUST be silently ignored. Any records in the Zone Section MUST be silently ignored.
PRCOUNT MUST be zero, and the Prerequisite Section MUST be empty. PRCOUNT MUST be zero, and the Prerequisite Section MUST be empty.
Any records in the Prerequisite Section MUST be silently ignored. Any records in the Prerequisite Section MUST be silently ignored.
UPCOUNT MUST be zero, and the Update Section MUST be empty. UPCOUNT MUST be zero, and the Update Section MUST be empty.
Any records in the Update Section MUST be silently ignored. Any records in the Update Section MUST be silently ignored.
ADCOUNT MUST be zero, and the Additional Data Section MUST be empty. ADCOUNT specifies the number of records in the Additional Data
Any records in the Additional Data Section MUST be silently ignored. Section, e.g., the EDNS(0) OPT record..
The RCODE MUST contain a code giving the reason for termination. The RCODE MUST contain a nonzero code giving the reason for
[Codes to be determined.] The Termination Message MUST contain an termination, as indicated below:
EDNS0 TCP Keepalive option [I-D.ietf-dnsop-edns-tcp-keepalive] where
the idle timeout indicates the time the client SHOULD wait before +----------+-------+------------------------------------------------+
attempting to reconnect. | Mnemonic | Value | Description |
+----------+-------+------------------------------------------------+
| SERVFAIL | 2 | The server is overloaded due to resource |
| | | exhaustion. |
| REFUSED | 5 | The server has been reconfigured and is no |
| | | longer accepting DNS Push Notification |
| | | requests for one or more of the currently |
| | | subscribed names. |
+----------+-------+------------------------------------------------+
Termination Response codes
This document specifies only these two RCODE values for Termination
Messages. Servers sending Termination Messages SHOULD use one of
these two values. However, future circumstances may create
situations where other RCODE values are appropriate in Termination
Messages, so clients MUST be prepared to accept Termination Messages
with any RCODE value. In particular, a Termination Message with
RCODE value zero (NOERROR) is still a Termination Message and should
be treated as such.
The Termination Message MUST contain an EDNS(0) TCP Keepalive option
[I-D.ietf-dnsop-edns-tcp-keepalive]. The client MUST wait for the
time indicated in the EDNS(0) TCP Keepalive option's idle timeout
before attempting any new connections to this server. A client that
receives a Termination Message without an EDNS(0) TCP Keepalive
option SHOULD treat it as equivalent to a TCP Keepalive option with a
zero timeout value.
In the case where the server is rejecting some, but not all, of the
existing subscriptions (perhaps because it has been reconfigured and
is no longer authoritative for those names) with a REFUSED (5) RCODE,
the EDNS(0) TCP Keepalive option's idle timeout MAY be zero,
indicating that the client SHOULD attempt to re-establish its
subscriptions immediately.
In the case where a server is terminating a large number of
connections at once (e.g., if the system is restarting) and the
server doesn't want to be inundated with a flood of simultaneous
retries, it SHOULD send different EDNS(0) TCP Keepalive values to
each client. These adjustments MAY be selected randomly,
pseudorandomly, or deterministically (e.g., incrementing the time
value by one for each successive client, yielding a post-restart
reconnection rate of ten clients per second).
7. Security Considerations 7. Security Considerations
TLS support is REQUIRED 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".
DNSSEC is RECOMMENDED for DNS Push Notifications. TLS alone does not DNSSEC is RECOMMENDED for DNS Push Notifications. TLS alone does not
provide complete security. TLS certificate verification can provide provide complete security. TLS certificate verification can provide
reasonable assurance that the client is really talking to the server reasonable assurance that the client is really talking to the server
skipping to change at page 19, line 43 skipping to change at page 26, line 31
name is learned via a DNS SRV query, if the SRV query is subverted 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. then the client may have a secure connection to a rogue server.
DNSSEC can provided added confidence that the SRV query has not been DNSSEC can provided added confidence that the SRV query has not been
subverted. subverted.
7.1. Security Services 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.
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.
7.2. TLS Name Authentication 7.2. TLS Name Authentication
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This document defines three DNS OpCodes: SUBSCRIBE with (tentative) This document defines three DNS OpCodes: SUBSCRIBE with (tentative)
value 6, UNSUBSCRIBE with (tentative) value 7, and RECONFIRM with value 6, UNSUBSCRIBE with (tentative) value 7, and RECONFIRM with
(tentative) value 8. (tentative) value 8.
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, Mark This draft has been improved due to comments from Ran Atkinson, Tim
Delany, Manju Shankar Rao, and Markus Stenberg. Chown, Mark Delany, Ralph Droms, Bernie Holz, Jan Komissar, Manju
Shankar Rao, Markus Stenberg, and Dave Thaler.
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-06 (work in Requirements", draft-ietf-dnsop-5966bis-06 (work in
progress), January 2016. progress), January 2016.
[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-05 (work in progress), January 2016. tcp-keepalive-06 (work in progress), February 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-tls13-11 (work in progress), Version 1.3", draft-ietf-tls-tls13-11 (work in progress),
December 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>.
skipping to change at page 23, line 9 skipping to change at page 29, line 47
[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS) [RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)
Extensions: Extension Definitions", RFC 6066, DOI Extensions: Extension Definitions", RFC 6066, DOI
10.17487/RFC6066, January 2011, 10.17487/RFC6066, January 2011,
<http://www.rfc-editor.org/info/rfc6066>. <http://www.rfc-editor.org/info/rfc6066>.
[RFC6195] Eastlake 3rd, D., "Domain Name System (DNS) IANA [RFC6195] Eastlake 3rd, D., "Domain Name System (DNS) IANA
Considerations", RFC 6195, DOI 10.17487/RFC6195, March Considerations", RFC 6195, DOI 10.17487/RFC6195, March
2011, <http://www.rfc-editor.org/info/rfc6195>. 2011, <http://www.rfc-editor.org/info/rfc6195>.
[RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
for DNS (EDNS(0))", STD 75, RFC 6891, DOI 10.17487/
RFC6891, April 2013,
<http://www.rfc-editor.org/info/rfc6891>.
[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>.
10.2. Informative References 10.2. Informative References
[I-D.ietf-dnssd-hybrid] [I-D.ietf-dnssd-hybrid]
Cheshire, S., "Hybrid Unicast/Multicast DNS-Based Service Cheshire, S., "Hybrid Unicast/Multicast DNS-Based Service
Discovery", draft-ietf-dnssd-hybrid-02 (work in progress), Discovery", draft-ietf-dnssd-hybrid-03 (work in progress),
November 2015. November 2015.
[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, Number Internet Protocol Journal, Cisco Systems, Volume 9, Number
4, December 2006. 4, December 2006.
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