draft-ietf-dnssd-push-08.txt   draft-ietf-dnssd-push-09.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: January 9, 2017 Apple Inc. Expires: May 4, 2017 Apple Inc.
July 8, 2016 October 31, 2016
DNS Push Notifications DNS Push Notifications
draft-ietf-dnssd-push-08 draft-ietf-dnssd-push-09
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 January 9, 2017. This Internet-Draft will expire on May 4, 2017.
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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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 . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Transport . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4. Transport . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Client-Initiated Termination . . . . . . . . . . . . . . 7 5. State Considerations . . . . . . . . . . . . . . . . . . . . 6
4.2. Server-Initiated Termination . . . . . . . . . . . . . . 9 6. Protocol Operation . . . . . . . . . . . . . . . . . . . . . 7
5. State Considerations . . . . . . . . . . . . . . . . . . . . 11 6.1. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 8
6. Protocol Operation . . . . . . . . . . . . . . . . . . . . . 12 6.2. DNS Push Notification SUBSCRIBE . . . . . . . . . . . . . 10
6.1. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 13 6.2.1. SUBSCRIBE Request . . . . . . . . . . . . . . . . . . 11
6.2. DNS Push Notification SUBSCRIBE . . . . . . . . . . . . . 15 6.2.2. SUBSCRIBE Response . . . . . . . . . . . . . . . . . 14
6.3. DNS Push Notification UNSUBSCRIBE . . . . . . . . . . . . 20 6.3. DNS Push Notification Update Messages . . . . . . . . . . 18
6.4. DNS Push Notification Update Messages . . . . . . . . . . 21 6.3.1. PUSH Message format . . . . . . . . . . . . . . . . . 18
6.5. DNS RECONFIRM . . . . . . . . . . . . . . . . . . . . . . 24 6.4. DNS Push Notification UNSUBSCRIBE . . . . . . . . . . . . 21
6.6. DNS Push Notification Termination Message . . . . . . . . 25 6.4.1. UNSUBSCRIBE Request . . . . . . . . . . . . . . . . . 22
6.4.2. UNSUBSCRIBE Response . . . . . . . . . . . . . . . . 24
6.5. DNS Session Signaling Push Notification RECONFIRM . . . . 26
6.6. Client-Initiated Termination . . . . . . . . . . . . . . 28
7. Security Considerations . . . . . . . . . . . . . . . . . . . 28 7. Security Considerations . . . . . . . . . . . . . . . . . . . 28
7.1. Security Services . . . . . . . . . . . . . . . . . . . . 28 7.1. Security Services . . . . . . . . . . . . . . . . . . . . 29
7.2. TLS Name Authentication . . . . . . . . . . . . . . . . . 28 7.2. TLS Name Authentication . . . . . . . . . . . . . . . . . 29
7.3. TLS Compression . . . . . . . . . . . . . . . . . . . . . 29 7.3. TLS Compression . . . . . . . . . . . . . . . . . . . . . 30
7.4. TLS Session Resumption . . . . . . . . . . . . . . . . . 29 7.4. TLS Session Resumption . . . . . . . . . . . . . . . . . 30
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 29 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 30
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 30 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 31
10.1. Normative References . . . . . . . . . . . . . . . . . . 30 10.1. Normative References . . . . . . . . . . . . . . . . . . 31
10.2. Informative References . . . . . . . . . . . . . . . . . 31 10.2. Informative References . . . . . . . . . . . . . . . . . 32
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 33 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34
1. Introduction 1. Introduction
IMPORTANT NOTE: This document currently references the EDNS(0) TCP
Keepalive option [RFC7828]. As a result of discussions about this
document, the community came to the realization that DNS needs
explicit session-level signaling, to complement the current EDNS(0)
per-message signaling. As a result, work on DNS Session Signaling
[I-D.bellis-dnsop-session-signal] is underway, and this document will
be updated shortly to make use of those new Session Signaling
mechanisms once they are agreed.
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 DNS clients to subscribe to receive asynchronous notifications of
notifications of changes to RRSets of interest. It is immediately changes to RRSets of interest. It is immediately relevant in the
relevant in the case of DNS Service Discovery [RFC6763] but is not case of DNS Service Discovery [RFC6763] but is not limited to that
limited to that use case, and provides a general DNS mechanism for use case, and provides a general DNS mechanism for DNS record change
DNS record change notifications. Familiarity with the DNS protocol notifications. Familiarity with the DNS protocol and DNS packet
and DNS packet formats is assumed [RFC1034] [RFC1035] [RFC6895]. formats is assumed [RFC1034] [RFC1035] [RFC6895].
1.1. Requirements Language 1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
"Key words for use in RFCs to Indicate Requirement Levels" [RFC2119]. "Key words for use in RFCs to Indicate Requirement Levels" [RFC2119].
2. Motivation 2. Motivation
As the domain name system continues to adapt to new uses and changes As the domain name system continues to adapt to new uses and changes
in deployment, polling has the potential to burden DNS servers at in deployment, polling has the potential to burden DNS servers at
many levels throughout the network. Other network protocols have many levels throughout the network. Other network protocols have
successfully deployed a publish/subscribe model to state changes successfully deployed a publish/subscribe model to state changes
following the Observer design pattern. XMPP Publish-Subscribe following the Observer design pattern [obs]. XMPP Publish-Subscribe
[XEP0060] and Atom [RFC4287] are examples. While DNS servers are [XEP0060] and Atom [RFC4287] are examples. While DNS servers are
generally highly tuned and capable of a high rate of query/response generally highly tuned and capable of a high rate of query/response
traffic, adding a publish/subscribe model for tracking changes to DNS traffic, adding a publish/subscribe model for tracking changes to DNS
records can result in more timely notification of changes with records can result in more timely notification of changes with
reduced CPU usage and lower network traffic. reduced CPU usage and lower network traffic.
Multicast DNS [RFC6762] implementations always listen on a well known Multicast DNS [RFC6762] implementations always listen on a well known
link-local IP multicast group, and new services and updates are sent link-local IP multicast group, and new services and updates are sent
for all group members to receive. Therefore, Multicast DNS already for all group members to receive. Therefore, Multicast DNS already
has asynchronous change notification capability. However, when DNS has asynchronous change notification capability. However, when DNS
Service Discovery [RFC6763] is used across a wide area network using Service Discovery [RFC6763] is used across a wide area network using
Unicast DNS (possibly facilitated via a Hybrid Proxy Unicast DNS (possibly facilitated via a Hybrid Proxy
[I-D.ietf-dnssd-hybrid]) it would be beneficial to have an equivalent [I-D.ietf-dnssd-hybrid]) it would be beneficial to have an equivalent
capability for Unicast DNS, to allow clients to learn about DNS capability for Unicast DNS, to allow clients to learn about DNS
record changes in a timely manner without polling. record changes in a timely manner without polling.
DNS Long-Lived Queries (LLQ) [I-D.sekar-dns-llq] is an existing DNS Long-Lived Queries (LLQ) [I-D.sekar-dns-llq] is an existing
deployed solution to provide asynchronous change notifications. Even deployed solution to provide asynchronous change notifications. Even
though it can be used over TCP, LLQ is defined primarily as a UDP- though it can be used over TCP, LLQ is defined primarily as a UDP-
based protocol, and as such it defines its own equivalents of 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, flow control, and
builds on experience gained with the LLQ protocol, with an improved reliability. This document builds on experience gained with the LLQ
design that uses long-lived TCP connections instead of UDP (and protocol, with an improved design. Instead of using UDP, this
therefore doesn't need to duplicate existing TCP functionality), and specification uses long-lived TCP connections
adopts the syntax and semantics of DNS Update messages [RFC2136] [I-D.ietf-dnsop-session-signal], and therefore doesn't need to
instead of inventing a new vocabulary of messages to communicate DNS reinvent existing TCP functionality. Instead of inventing a new
zone changes. vocabulary of messages to communicate DNS zone changes, this
specification adopts the syntax and semantics of DNS Update messages
[RFC2136].
Because DNS Push Notifications impose a certain load on the DNS Push Notifications impose less load on the responding server than
responding server (though less load than rapid polling of that rapid polling would, but Push Notifications do still have a cost, so
server) DNS Push Notification clients SHOULD exercise restraint in DNS Push Notification clients MUST NOT recklessly create an excessive
issuing DNS Push Notification subscriptions. A subscription SHOULD number of 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 to the
that subscription to the user) and the subscription SHOULD be user) and the subscription SHOULD be cancelled as soon as the need
cancelled as soon as the need for that data ends (for example, when for that data ends (for example, when the user dismisses that
the user dismisses that display). Implementations MAY want to display). Implementations MAY want to implement idle timeouts, so
implement idle timeouts, so that if the user ceases interacting with that if the user ceases interacting with the device, the display
the device, the display showing the result of the DNS Push showing the result of the DNS Push Notification subscription is
Notification subscription is automatically dismissed after a certain automatically dismissed after a certain period of inactivity. For
period of inactivity. For example, if a user presses the "Print" example, if a user presses the "Print" button on their smartphone,
button on their phone, and then leaves the phone showing the printer and then leaves the phone showing the printer discovery screen until
discovery screen until the phone goes to sleep, then the printer the phone goes to sleep, then the printer discovery screen should be
discovery screen should be automatically dismissed as the device goes automatically dismissed as the device goes to sleep. If the user
to sleep. If the user does still intend to print, this will require does still intend to print, this will require them to press the
them to press the "Print" button again when they wake their phone up. "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.
Generally, a client SHOULD NOT keep a connection to a server open Generally, a client SHOULD NOT keep a connection to a server open
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of generating the correct change notifications for a name. of generating the correct change notifications for a name.
It may be a master, slave, or stealth name server [RFC1996]. It may be a master, slave, or stealth name server [RFC1996].
Consequently, the "_dns-push-tls._tcp.<zone>" SRV record for a Consequently, the "_dns-push-tls._tcp.<zone>" SRV record for a
zone MAY reference the same target host and port as that zone's 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 both DNS a client MAY use a single TCP connection to that server for both DNS
Updates and DNS Push Notification Queries. Updates and DNS Push Notification Queries.
Supporting DNS Updates and DNS Push Notifications on the same server Supporting DNS Updates and DNS Push Notifications on the same server
is OPTIONAL. A DNS Push Notification server is not REQUIRED to is OPTIONAL. A DNS Push Notification server does NOT also have to
support DNS Update. support DNS Update.
DNS Updates and DNS Push Notifications may be handled on different DNS Updates and DNS Push Notifications may be handled on different
ports on the same target host, in which case they are not considered ports on the same target host, in which case they are not considered
to be the "same server" for the purposes of this specification, and to be the "same server" for the purposes of this specification, and
communications with these two ports are handled independently. communications with these two ports are handled independently.
Standard DNS Queries MAY be sent over a DNS Push Notification Standard DNS Queries MAY be sent over a DNS Push Notification
connection, provided that these are queries for names falling within connection, provided that these are queries for names falling within
the server's zone (the <zone> in the "_dns-push-tls._tcp.<zone>" SRV the server's zone (the <zone> in the "_dns-push-tls._tcp.<zone>" SRV
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DNS Push Notification clients are NOT required to implement DNS DNS Push Notification clients are NOT required to implement DNS
Update Prerequisite processing. Prerequisites are used to perform Update Prerequisite processing. Prerequisites are used to perform
tentative atomic test-and-set type operations when a client updates tentative atomic test-and-set type operations when a client updates
records on a server, and that concept has no applicability when it records on a server, and that concept has no applicability when it
comes to an authoritative server informing a client of changes to DNS comes to an authoritative server informing a client of changes to DNS
records. records.
This DNS Push Notification specification includes support for DNS This DNS Push Notification specification includes support for DNS
classes, for completeness. However, in practice, it is anticipated classes, for completeness. However, in practice, it is anticipated
that for the foreseeable future the only DNS class in use will be DNS that for the foreseeable future the only DNS class in use will be DNS
class "IN", as it is today with existing DNS servers and clients. A class "IN", as is the reality today with existing DNS servers and
DNS Push Notification server MAY choose to implement only DNS class clients. A DNS Push Notification server MAY choose to implement only
"IN". 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 [RFC7766]. This requirement to use UDP has subsequently been relaxed [RFC7766].
In keeping with the more recent precedent, DNS Push Notification is In keeping with the more recent precedent, DNS Push Notification is
defined only for TCP. DNS Push Notification clients MUST use TLS defined only for TCP. DNS Push Notification clients MUST use TLS
over TCP. over TCP.
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. Flooding attacks
flooding attacks are possible with any protocol over TCP, are possible with any protocol, and a benefit of TCP is that there
implementers are encouraged to use industry best practices to guard are already established industry best practices to guard against SYN
against such attacks [IPJ.9-4-TCPSYN] [RFC4953]. flooding and similar attacks [IPJ.9-4-TCPSYN] [RFC4953].
Use of TCP also allows DNS Push Notifications to take advantage of
current and future developments in TCP, such as Multipath TCP (MPTCP)
[RFC6824], TCP Fast Open (TFO) [RFC7413], Tail Loss Probe (TLP)
[I-D.dukkipati-tcpm-tcp-loss-probe], and so on.
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. When a
client terminates an individual subscription (via UNSUBSCRIBE) or all
subscriptions on that connection (by closing the connection) it is
signaling 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, 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 continue to meet its keepalive obligations
[RFC7828] 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, 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.
When closing a connection, a client will generally do an abortive
disconnect, sending a TCP RST. This immediately discards all
remaining inbound and outbound data, which is appropriate if the
client no longer has any interest in this data. In the BSD sockets
API, sending a TCP RST is achieved by setting the SO_LINGER option
with a time of 0 seconds and then closing the socket.
If a client has performed operations on this connection that it would
not want lost (like DNS updates) then the client SHOULD do an orderly
disconnect, sending a TCP FIN. In the BSD sockets API, sending a TCP
FIN is achieved by calling "shutdown(s,SHUT_WR)" and keeping the
socket open until all remaining data has been read from it.
In the first SUBSCRIBE response on a connection, the server MUST
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 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.
Upon receiving an error response from the server, a client SHOULD NOT
close the connection. An error relating to one particular operation
on a connection does not necessarily imply that all other operations
on that connection have also failed, or that future operations will
fail. The client should assume that the server will make its own
decision about whether or not to close the connection, based on the
server's determination of whether the error condition pertains to
this particular operation, or would also apply to any subsequent
operations. If the server does not close the connection then the
client SHOULD continue to use that connection for subsequent
operations.
Upon receiving a Termination Message from the server (see below), a
client MUST immediately close the connection.
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 [RFC7828] (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
complete 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. The time before the server closes the connection is
intentionally 50% longer than the time before the client is required
to generate keepalive traffic, to allow for differences in clock rate
and network propagation delays.
[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, or may allow the connection to remain
open. For error conditions that only affect the single operation in
question, the server SHOULD return an error response to the client
and leave the connection open for further operations. For error
conditions that are likely to make all operations unsuccessful in the
immediate future, the server SHOULD return an error response to the
client and then close the connection with a TCP FIN.
If the server is overloaded and needs to shed load, it SHOULD 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
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
to resource constraints. Token bucket rate limiting schemes are also to resource constraints. Token bucket rate limiting schemes are also
effective in providing fairness by a server across numerous client effective in providing fairness by a server across numerous client
requests. requests.
6. Protocol Operation 6. Protocol Operation
The DNS Push Notification protocol is a session-oriented protocol,
and makes use of DNS Session Signaling
[I-D.ietf-dnsop-session-signal].
DNS Push Notification clients and servers MUST support DNS Session
Signaling, but the server must not issue any DNS Session Signaling
operations until after the client has first initiated a DNS Session
Signaling operation of its own. A single server can support DNS
Queries, DNS Updates, and DNS Push Notifications (using DNS Session
Signaling) on the same TCP port, and until the client has sent at
least one DNS Session Signaling operation the server does not know
what kind of client has connected to it. Once the client has
indicated willingness to use DNS Session Signaling operations by
sending one of its own, either side of the connection may then
initiate further Session Signaling operations at any time.
A DNS Push Notification exchange begins with the client discovering A DNS Push Notification exchange begins with the client discovering
the appropriate server, and then making a TLS/TCP connection to it. the appropriate server, using the procedure described in Section 6.1,
The client may then add and remove Push Notification subscriptions and then making a TLS/TCP connection to it.
over this connection. In accordance with the current set of active
subscriptions the server sends relevant asynchronous Push A typical DNS Push Notification client will immediately issue a DNS
Session Signaling Idle Timeout operation to request a session timeout
longer than the the 30-second default, but this is NOT REQUIRED. A
DNS Push Notification client MAY issue other requests on the
connection first, and only issue a DNS Session Signaling Idle Timeout
operation later if it determines that to be necessary.
Once the connection is made, the client may then add and remove Push
Notification subscriptions. In accordance with the current set of
active subscriptions the server sends relevant asynchronous Push
Notifications to the client. Note that a client MUST be prepared to Notifications to the client. Note that a client MUST be prepared to
receive (and silently ignore) Push Notifications for subscriptions it receive (and silently ignore) Push Notifications for subscriptions it
has previously removed, since there is no way to prevent the has previously removed, since there is no way to prevent the
situation where a Push Notification is in flight from server to situation where a Push Notification is in flight from server to
client while the client's UNSUBSCRIBE message cancelling that client while the client's UNSUBSCRIBE message cancelling that
subscription is simultaneously in flight from client to server. subscription is simultaneously in flight from client to server.
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
Push Notification server. A client SHOULD share a single TLS/TCP
connection for all requests to the same DNS Push Notification server.
This shared connection should be used for all DNS Queries and DNS
Push Notification Queries queries to that server, and for DNS Update
requests too when the "_dns-update-tls._tcp.<zone>" SRV record
indicates that the same server also handles DNS Update requests.
This is to reduce unnecessary load on the DNS Push Notification
server.
For the purposes here, the determination of "same server" is made by
inspecting the target hostname 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 hostname
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.
Note that the "same server" determination described here is made
using the target hostname given in the SRV record, not the IP
address(es) that the hostname resolves to. If two different target
hostnames happen to resolve to the same IP address(es), then the
client SHOULD NOT recognize these as the "same server" for the
purposes of using a single shared connection to that server. If an
administrator wishes to use a single server for multiple zones and/or
multiple roles (e.g., both DNS Push Notifications and DNS Updates),
and wishes to have clients use a single shared connection for
operations on that server, then the administrator MUST use the same
target hostname in the appropriate SRV records.
However, server implementers and operators should be aware that this
connection sharing may not be possible in all cases. A single client
device may be home to multiple independent client software instances
that don't know about each other, so a DNS Push Notification server
MUST be prepared to accept multiple connections from the same client
IP address. This is undesirable from an efficiency standpoint, but
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.
Clients SHOULD silently ignore unrecognized messages (both requests
and responses) over the TLS/TCP connection. For example, UNSUBSCRIBE
and RECONFIRM currently generate no response, but if future versions
of this specification change that, existing clients SHOULD silently
ignore these unexpected responses. This allows for backwards
compatibility with future enhancements.
6.1. Discovery 6.1. Discovery
The first step in DNS Push Notification subscription is to discover The first step in DNS Push Notification subscription is to discover
an appropriate DNS server that supports DNS Push Notifications for an appropriate DNS server that supports DNS Push Notifications for
the desired zone. The client MUST also determine which TCP port on the desired zone. The client MUST also determine which TCP port on
the server is listening for connections, which need not be (and often the server is listening for connections, which need not be (and often
is not) the typical TCP port 53 used for conventional DNS, or TCP is not) the typical TCP port 53 used for conventional DNS, or TCP
port 853 used for DNS over TLS [I-D.ietf-dprive-dns-over-tls]. port 853 used for DNS over TLS [RFC7858].
1. The client begins the discovery by sending a DNS query to the 1. The client begins the discovery by sending a DNS query to 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 response. If not, the local resolver SHOULD Section of the response. If not, the local resolver SHOULD
include the SOA record for the zone of the requested name in the include the SOA record for the zone of the requested name in the
Authority Section. Authority Section.
skipping to change at page 15, line 5 skipping to change at page 9, line 17
"weight" 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.
Each time a client makes a new DNS Push Notification subscription Each time a client makes a new DNS Push Notification subscription
connection, it SHOULD repeat the discovery process in order to connection, it SHOULD repeat the discovery process in order to
determine the preferred DNS server for subscriptions at that time. determine the preferred DNS server for subscriptions at that time.
Note that this repeated discovery step is typically very fast and
typically results in no queries on the network. The client device
MUST respect the DNS TTL values on records it receives, and store
them in its local cache with this lifetime. This means that, as long
as the DNS TTL values on the authoritative records were set to
reasonable values, repeated application of this discovery process can
be completed nearly instantaneously by the client, using only
locally-stored data.
6.2. DNS Push Notification SUBSCRIBE 6.2. DNS Push Notification SUBSCRIBE
A DNS Push Notification client indicates its desire to receive DNS After connecting, and requesting a longer idle timeout if necessary,
Push Notifications for a given domain name by sending a SUBSCRIBE a DNS Push Notification client then indicates its desire to receive
request over the established TCP connection to the server. A DNS Push Notifications for a given domain name by sending a SUBSCRIBE
SUBSCRIBE request is formatted identically to a conventional DNS request over the established TLS connection to the server. A
QUERY request [RFC1035], except that the opcode is SUBSCRIBE (6) SUBSCRIBE request is encoded in a DNS Session Signaling
instead of QUERY (0). If neither QTYPE nor QCLASS are ANY (255) then [I-D.ietf-dnsop-session-signal] message. This specification defines
this is a specific subscription to changes for the given name, type a new DNS Session Signaling TLV for DNS Push Notification SUBSCRIBE
and class. If one or both of QTYPE or QCLASS are ANY (255) then this Requests/Responses (tentatively Session Signaling Type Code 64).
subscription matches any type and/or any class, as appropriate.
NOTE: A little-known quirk of DNS is that in DNS QUERY requests, A server may not initiate a SUBSCRIBE request.
QTYPE and QCLASS 255 mean "ANY" not "ALL". They indicate that the
server should respond with ANY matching records of its choosing, not
necessarily ALL matching records. This can lead to some surprising
and unexpected results, were a query returns some valid answers but
not all of them, and makes QTYPE=ANY queries less useful than people
sometimes imagine.
When used in conjunction with DNS SUBSCRIBE, QTYPE and QCLASS 255 6.2.1. SUBSCRIBE Request
should be interpreted to mean "ALL", not "ANY". After accepting a
subscription where one or both of QTYPE or QCLASS are 255, the server
MUST send Push Notification Updates for ALL record changes that match
the subscription, not just some of them.
In a SUBSCRIBE request the DNS Header QR bit MUST be zero. A SUBSCRIBE request message begins with the standard DNS Session
If the QR bit is not zero the message is not a SUBSCRIBE request. Signaling 4-byte header [I-D.ietf-dnsop-session-signal], followed by
the SUBSCRIBE TLV.
The AA, TC, RD, RA, Z, AD, and CD bits, and the RCODE field, MUST be 1 1 1 1 1 1
zero on transmission, and MUST be silently ignored on reception. 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| MESSAGE ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|QR| Opcode | Z | RCODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| SSOP-TYPE (SUBSCRIBE) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| SSOP-LENGTH |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| |
\ QNAME \
\ \
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| QTYPE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| QCLASS |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
The ID field may be set to any value of the client's choosing, and Figure 1
the server MUST echo this value back in the response message. The
client is not required to select unique ID values; it is permissible
to use the same value (e.g., zero) for all operations. Since the
name, qtype, and qclass are sufficient to uniquely identify a
SUBSCRIBE operation on a connection, the name, qtype, and qclass in a
SUBSCRIBE response are sufficient to correlate a response with its
corresponding request. However, for convenience, the client may put
any value it chooses in the ID field of the SUBSCRIBE request, and
the server MUST echo that value back unchanged in the SUBSCRIBE
response. Note that the ID field of Push Notification Update
Messages is always zero, since a Push Notification Update Message
could potentially match more than one subscription, or could relate
to a subscription that the client has just cancelled with an
UNSUBSCRIBE message.
Like a DNS QUERY request, a SUBSCRIBE request MUST contain exactly The MESSAGE ID field MUST be set to a unique value, that the client
one question. Since SUBSCRIBE requests are sent over TCP, multiple is not using for any other active operation on this connection. For
SUBSCRIBE requests can be concatenated in a single TCP stream and the purposes here, a MESSAGE ID is in use on this connection if the
packed efficiently into TCP segments, so the ability to pack multiple client has used it in a request for which it has not yet received a
SUBSCRIBE operations into a single DNS message within that TCP stream response, or if if the client has used it for a subscription which it
would add extra complexity for little benefit. has not yet cancelled using UNSUBSCRIBE. In the SUBSCRIBE response
the server MUST echo back the MESSAGE ID value unchanged.
ANCOUNT MUST be zero, and the Answer Section MUST be empty. In a request the DNS Header QR bit MUST be zero.
Any records in the Answer Section MUST be silently ignored.
NSCOUNT MUST be zero, and the Authority Section MUST be empty. The DNS Header Opcode field holds the Session Signaling Opcode value
Any records in the Authority Section MUST be silently ignored. (tentatively 6).
ARCOUNT specifies the number of records in the Additional Data The Z bits MUST be zero on transmission, and MUST be silently ignored
Section. Typically this is zero, but it may be nonzero in some on reception.
cases, such as when the request includes an EDNS(0) OPT record.
The return code (RCODE) field MUST be set to 0 in a request.
In the SUBSCRIBE TLV the SSOP-TYPE is SUBSCRIBE (tentatively 64).
The SSOP-LENGTH is the length of the data that follows, which
specifies the name, type, and class of the record(s) being sought.
A SUBSCRIBE request MUST contain exactly one question. There is no
QCOUNT field to specify more than one question. Since SUBSCRIBE
requests are sent over TCP, multiple SUBSCRIBE requests can be
concatenated in a single TCP stream and packed efficiently into TCP
segments.
If accepted, the subscription will stay in effect until the client If accepted, the subscription will stay in effect until the client
revokes the subscription or until the connection between the client cancels the subscription using UNSUBSCRIBE or until the connection
and the server is closed. between the client and the server is closed.
SUBSCRIBE requests on a given connection MUST be unique. A client SUBSCRIBE requests on a given connection MUST be unique. A client
MUST NOT send a SUBSCRIBE message that duplicates the name, type and MUST NOT send a SUBSCRIBE message that duplicates the QNAME, QTYPE
class of an existing active subscription on that TLS/TCP connection. and QCLASS of an existing active subscription on that TLS/TCP
For the purpose of this matching, the established DNS case- connection. For the purpose of this matching, the established DNS
insensitivity for US-ASCII letters applies (e.g., "foo.com" and case-insensitivity for US-ASCII letters applies (e.g., "foo.com" and
"Foo.com" are the same). If a server receives such a duplicate "Foo.com" are the same). If a server receives such a duplicate
SUBSCRIBE message this is an error and the server MUST immediately SUBSCRIBE message this is an error and the server MUST immediately
close the TCP connection. 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 literal wildcard character ("*") in SUBSCRIBE message matches only a literal wildcard character ("*") in
the zone, and nothing else. the zone, and nothing else.
Aliasing is not supported. That is, a CNAME in a SUBSCRIBE message Aliasing is not supported. That is, a CNAME in a SUBSCRIBE message
matches only a literal CNAME record in the zone, and nothing else. matches only a literal CNAME record in the zone, and nothing else.
A client may SUBSCRIBE to records that are unknown to the server at A client may SUBSCRIBE to records that are unknown to the server at
the time of the request (providing that the name falls within one of the time of the request (providing that the name falls within one of
the zone(s) the server is responsible for) and this is not an error. the zone(s) the server is responsible for) and this is not an error.
The server MUST accept these requests and send Push Notifications if The server MUST accept these requests and send Push Notifications if
and when matches are found in the future. and when matching records are found in the future.
Since all SUBSCRIBE operations are implicitly long-lived operations, If neither QTYPE nor QCLASS are ANY (255) then this is a specific
the server MUST interpret a SUBSCRIBE request as if it contained an subscription to changes for the given QNAME, QTYPE and QCLASS. If
EDNS(0) TCP Keepalive option [RFC7828]. A client MUST NOT include an one or both of QTYPE or QCLASS are ANY (255) then this subscription
actual EDNS(0) TCP Keepalive option in the request, since it is matches any type and/or any class, as appropriate.
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 NOTE: A little-known quirk of DNS is that in DNS QUERY requests,
record where necessary to carry additional EDNS(0) information other QTYPE and QCLASS 255 mean "ANY" not "ALL". They indicate that the
than a TCP Keepalive option. server should respond with ANY matching records of its choosing, not
necessarily ALL matching records. This can lead to some surprising
and unexpected results, were a query returns some valid answers but
not all of them, and makes QTYPE=ANY queries less useful than people
sometimes imagine.
The presence of a SUBSCRIBE operation on a connection indicates to When used in conjunction with SUBSCRIBE, QTYPE and QCLASS 255 should
the server that the client fully implements EDNS(0) [RFC6891], and be interpreted to mean "ALL", not "ANY". After accepting a
can correctly understand any response that conforms to that subscription where one or both of QTYPE or QCLASS are 255, the server
specification. After receiving a SUBSCRIBE request, the server MAY MUST send Push Notification Updates for ALL record changes that match
include OPT record in any of its responses, as needed. the subscription, not just some of them.
6.2.2. SUBSCRIBE Response
Each SUBSCRIBE request generates exactly one SUBSCRIBE response from Each SUBSCRIBE request generates exactly one SUBSCRIBE response from
the server. the server.
In a SUBSCRIBE response the DNS Header QR bit MUST be one. A SUBSCRIBE response message begins with the standard DNS Session
If the QR bit is not one the message is not a SUBSCRIBE response. Signaling 4-byte header [I-D.ietf-dnsop-session-signal], possibly
followed by one or more optional modifier TLVs such as a Terminate
modifier TLV [I-D.ietf-dnsop-session-signal].
The AA, TC, RD, RA, Z, AD, and CD bits, MUST be zero on transmission, 1 1 1 1 1 1
and MUST be silently ignored on reception. 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| MESSAGE ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|QR| Opcode | Z | RCODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
The ID field MUST echo the value given in the ID field of the Figure 2
SUBSCRIBE request.
The Question Section MUST echo back the values provided by the client The MESSAGE ID field MUST echo the value given in the ID field of the
in the SUBSCRIBE request that generated this SUBSCRIBE response. SUBSCRIBE request. This is how the client knows which request is
being responded to.
ANCOUNT MUST be zero, and the Answer Section MUST be empty. In a response the DNS Header QR bit MUST be one.
Any records in the Answer Section MUST be silently ignored. If the QR bit is not one the message is not a response.
If the subscription was accepted and there are positive answers for
the requested name, type and class, then these positive answers MUST
be communicated to the client in an immediately following Push
Notification Update, not in the Answer Section of the SUBSCRIBE
response. This simplifying requirement is made so that there is only
a single way that information is communicated to a DNS Push
Notification client. Since a DNS Push Notification client has to
parse information received via Push Notification Updates anyway, it
is simpler if it does not also have to parse information received via
the Answer Section of a SUBSCRIBE response.
NSCOUNT MUST be zero, and the Authority Section MUST be empty. The DNS Header Opcode field holds the Session Signaling Opcode value
Any records in the Authority Section MUST be silently ignored. (tentatively 6).
ARCOUNT specifies the number of records in the Additional Data The Z bits MUST be zero on transmission, and MUST be silently ignored
Section, e.g., the EDNS(0) OPT record. on reception.
In the SUBSCRIBE response the RCODE indicates whether or not the In the SUBSCRIBE response the RCODE indicates whether or not the
subscription was accepted. Supported RCODEs are as follows: subscription was accepted. Supported RCODEs are as follows:
+----------+-------+------------------------------------------------+ +------------+-------+----------------------------------------------+
| Mnemonic | Value | Description | | Mnemonic | Value | Description |
+----------+-------+------------------------------------------------+ +------------+-------+----------------------------------------------+
| NOERROR | 0 | SUBSCRIBE successful. | | NOERROR | 0 | SUBSCRIBE successful. |
| FORMERR | 1 | Server failed to process request due to a | | FORMERR | 1 | Server failed to process request due to a |
| | | malformed request. | | | | malformed request. |
| SERVFAIL | 2 | Server failed to process request due to | | SERVFAIL | 2 | Server failed to process request due to |
| | | resource exhaustion. | | | | resource exhaustion. |
| NXDOMAIN | 3 | NOT APPLICABLE. DNS Push Notification MUST NOT | | NXDOMAIN | 3 | NOT APPLICABLE. DNS Push Notification |
| | | return NXDOMAIN errors in response to | | | | servers MUST NOT return NXDOMAIN errors in |
| | | SUBSCRIBE requests. | | | | response to SUBSCRIBE requests. |
| NOTIMP | 4 | Server does not implement DNS Push | | NOTIMP | 4 | Server does not recognize DNS Session |
| | | Notifications. | | | | Signaling Opcode. |
| REFUSED | 5 | Server refuses to process request for policy | | REFUSED | 5 | Server refuses to process request for policy |
| | | or security reasons. | | | | or security reasons. |
| NOTAUTH | 9 | Server is not authoritative for the requested | | NOTAUTH | 9 | Server is not authoritative for the |
| | | name. | | | | requested name. |
+----------+-------+------------------------------------------------+ | SSOPNOTIMP | 11 | SUBSCRIBE operation not supported. |
+------------+-------+----------------------------------------------+
SUBSCRIBE Response codes SUBSCRIBE Response codes
This document specifies only these RCODE values for SUBSCRIBE This document specifies only these RCODE values for SUBSCRIBE
Responses. Servers sending SUBSCRIBE Responses SHOULD use one of Responses. Servers sending SUBSCRIBE Responses SHOULD use one of
these values. However, future circumstances may create situations these values. However, future circumstances may create situations
where other RCODE values are appropriate in SUBSCRIBE Responses, so where other RCODE values are appropriate in SUBSCRIBE Responses, so
clients MUST be prepared to accept SUBSCRIBE Responses with any RCODE clients MUST be prepared to accept SUBSCRIBE Responses with any RCODE
value. value.
In the first SUBSCRIBE response on a connection, the server MUST If the server sends a nonzero RCODE in the SUBSCRIBE response, either
include an explicit EDNS(0) TCP Keepalive option. If the first the client is (at least partially) misconfigured or the server
SUBSCRIBE response does not include an explicit EDNS(0) TCP Keepalive resources are exhausted. In either case, the client shouldn't retry
option this is an error and the client MUST immediately close the TCP the subscription right away. Either end can terminate the
connection. In this case the client should act as if the response connection, but the client may want to try this subscription again or
contained an EDNS(0) TCP Keepalive option with a value of one hour, it may have other successful subscriptions that it doesn't want to
and not attempt any further DNS Push Notification requests to that abandon. If the server sends a nonzero RCODE then it SHOULD append a
server until one hour has passed. This situation may occur if a Terminate modifier TLV [I-D.ietf-dnsop-session-signal] to the
client connects to a server that doesn't implement DNS Push response specifying a delay before the client attempts this operation
Notifications at all, and it is important not to burden such servers again. Recommended values for the delay for different RCODE values
with continuous retries. are given below:
The server MAY include EDNS(0) TCP Keepalive options in subsequent
messages, if the idle timeout changes. If the client receives
subsequent messages that do not contain an explicit EDNS(0) TCP
Keepalive option then the idle timeout for that connection remains
unchanged at that time.
In an error response, with nonzero RCODE, the server MUST contain an
EDNS(0) TCP Keepalive option specifying the delay before the client
submits further requests to this server:
For RCODE = 1 (FORMERR) the delay may be any value selected by the For RCODE = 1 (FORMERR) the delay may be any value selected by the
implementer. A value of one minute is RECOMMENDED, to avoid high implementer. A value of five minutes is RECOMMENDED, to avoid
load from defective clients. high load from defective clients.
For RCODE = 2 (SERVFAIL), which occurs due to resource exhaustion, For RCODE = 2 (SERVFAIL), which occurs due to resource exhaustion,
the delay should be chosen according to the level of server the delay should be chosen according to the level of server
overload and the anticipated duration of that overload. By overload and the anticipated duration of that overload. By
default, a value of one minute is RECOMMENDED. default, a value of one minute is RECOMMENDED.
For RCODE = 4 (NOTIMP), which occurs on a server that doesn't For RCODE = 4 (NOTIMP), which occurs on a server that doesn't
implement DNS Push Notifications, it is unlikely that the server implement DNS Session Signaling [I-D.ietf-dnsop-session-signal],
will begin supporting DNS Push Notifications in the next few it is unlikely that the server will begin supporting DNS Session
minutes, so the retry delay SHOULD be one hour. Note that a Signaling in the next few minutes, so the retry delay SHOULD be
server that doesn't implement DNS Push Notifications will most one hour.
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 For RCODE = 5 (REFUSED), which occurs on a server that implements
DNS Push Notifications, but is currently configured to disallow DNS Push Notifications, but is currently configured to disallow
DNS Push Notifications, the retry delay may be any value selected DNS Push Notifications, the retry delay may be any value selected
by the implementer and/or configured by the operator. by the implementer and/or configured by the operator.
This is a misconfiguration, since this server is listed in a This is a misconfiguration, since this server is listed in a
"_dns-push-tls._tcp.<zone>" SRV record, but the server itself is "_dns-push-tls._tcp.<zone>" SRV record, but the server itself is
not currently configured to support DNS Push Notifications. Since not currently configured to support DNS Push Notifications. Since
it is possible that the misconfiguration may be repaired at any it is possible that the misconfiguration may be repaired at any
time, the retry delay should not be set too high. By default, a time, the retry delay should not be set too high. By default, a
skipping to change at page 20, line 5 skipping to change at page 17, line 5
DNS Push Notifications, but is not configured to be authoritative DNS Push Notifications, but is not configured to be authoritative
for the requested name, the retry delay may be any value selected for the requested name, the retry delay may be any value selected
by the implementer and/or configured by the operator. by the implementer and/or configured by the operator.
This is a misconfiguration, since this server is listed in a This is a misconfiguration, since this server is listed in a
"_dns-push-tls._tcp.<zone>" SRV record, but the server itself is "_dns-push-tls._tcp.<zone>" SRV record, but the server itself is
not currently configured to support DNS Push Notifications for not currently configured to support DNS Push Notifications for
that zone. Since it is possible that the misconfiguration may be that zone. Since it is possible that the misconfiguration may be
repaired at any time, the retry delay should not be set too high. repaired at any time, the retry delay should not be set too high.
By default, a value of 5 minutes is RECOMMENDED. By default, a value of 5 minutes is RECOMMENDED.
For RCODE = 11 (DNS Push SUBSCRIBE operation not supported), 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.
For other RCODE values, the retry delay should be set by the For other RCODE values, the retry delay should be set by the
server as appropriate for that error condition. By default, a server as appropriate for that error condition. By default, a
value of 5 minutes is RECOMMENDED. value of 5 minutes is RECOMMENDED.
For RCODE = 9 (NOTAUTH), the time delay applies to requests for other For RCODE = 9 (NOTAUTH), the time delay applies to requests for other
names falling within the same zone. Requests for names falling names falling within the same zone. Requests for names falling
within other zones are not subject to the delay. For all other within other zones are not subject to the delay. For all other
RCODEs the time delay applies to all subsequent requests to this RCODEs the time delay applies to all subsequent requests to this
server. server.
After sending an error response the server MAY close the TCP After sending an error response the server MAY allow the connection
connection with a FIN, or MAY allow it to remain open, depending on to remain open, or MAY send a DNS Push Notification Terminate Session
the nature of the error. Clients MUST correctly handle both cases. operation TLV and then close the TCP connection, as described in the
DNS Session Signaling specification [I-D.ietf-dnsop-session-signal].
6.3. DNS Push Notification UNSUBSCRIBE Clients MUST correctly handle both cases.
To cancel an individual subscription without closing the entire
connection, the client sends an UNSUBSCRIBE message over the
established TCP connection to the server. The UNSUBSCRIBE message is
formatted identically to the SUBSCRIBE message which created the
subscription, with the exact same name, type and class, except that
the opcode is UNSUBSCRIBE (7) instead of SUBSCRIBE (6).
A client MUST NOT send an UNSUBSCRIBE message that does not exactly
match the name, type and class of an existing active subscription on
that TLS/TCP connection. If a server receives such an UNSUBSCRIBE
message this is an error and the server MUST immediately close the
connection.
No response message is generated as a result of processing an
UNSUBSCRIBE message.
Having being successfully revoked with a correctly-formatted
UNSUBSCRIBE message, the previously referenced subscription is no
longer active and the server MAY discard the state associated with it
immediately, or later, at the server's discretion.
6.4. DNS Push Notification Update Messages 6.3. DNS Push Notification Update Messages
Once a subscription has been successfully established, the server Once a subscription has been successfully established, the server
generates Push Notification Updates to send to the client as generates PUSH messages to send to the client as appropriate. An
appropriate. An initial Push Notification Update will be sent initial PUSH message will be sent immediately in the case that the
immediately in the case that the answer set was non-empty at the answer set was non-empty at the moment the subscription was
moment the subscription was established. Subsequent changes to the established. Subsequent changes to the answer set are then
answer set are then communicated to the client in subsequent Push communicated to the client in subsequent PUSH messages.
Notification Updates.
The format of Push Notification Updates borrows from the existing DNS 6.3.1. PUSH Message format
Update [RFC2136] protocol, with some simplifications.
The following figure shows the existing DNS Update header format: A PUSH message begins with the standard DNS Session Signaling 4-byte
header [I-D.ietf-dnsop-session-signal], followed by the PUSH TLV.
The format of PUSH messages borrows from the existing DNS Update
[RFC2136] protocol, with some simplifications.
1 1 1 1 1 1 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 | | MESSAGE ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|QR| Opcode | Z | RCODE | |QR| Opcode | Z | RCODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ZOCOUNT | | SSOP-TYPE (PUSH) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| PRCOUNT | | SSOP-LENGTH |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| UPCOUNT | | UPCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ADCOUNT | | |
\ Resource Records... \
\ \
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Figure 1 Figure 3
For DNS Push Notifications the following rules apply: The MESSAGE ID field MUST be set to zero on transmission, and
silently ignored on reception. A PUSH message could potentially
match more than one subscription, or could relate to a subscription
that the client has just cancelled with an UNSUBSCRIBE message, so
the MESSAGE ID field serves no useful purpose.
The QR bit MUST be zero, and the Opcode MUST be UPDATE (5). In a PUSH message the DNS Header QR bit MUST be zero.
Messages received where this is not true are not Push Notification
Update Messages and should be silently ignored for the purposes of
Push Notification Update Message handling.
ID, the Z bits, and RCODE MUST be zero on transmission, The DNS Header Opcode field holds the Session Signaling Opcode value
and MUST be silently ignored on reception. (tentatively 6).
ZOCOUNT MUST be zero, and the Zone Section MUST be empty. The Z bits MUST be zero on transmission, and MUST be silently ignored
Any records in the Zone Section MUST be silently ignored. on reception.
PRCOUNT MUST be zero, and the Prerequisite Section MUST be empty. The return code (RCODE) field MUST be set to 0 in a request.
Any records in the Prerequisite Section MUST be silently ignored.
UPCOUNT specifies the number of records in the Update Section. In the PUSH message TLV the SSOP-TYPE is PUSH (tentatively 65). The
SSOP-LENGTH is the length of the SSOP-DATA that follows.
ADCOUNT specifies the number of records in the Additional Data The SSOP-DATA contains a two-byte count of the number of records that
Section. Typically this is zero, but it may be nonzero in some follow, followed by the records, in customary Resource Record format
cases, such as when the message includes an EDNS(0) OPT record. (as used in DNS Update [RFC2136] messages).
The Update Section contains the relevant change information for the The SSOP-DATA contains the relevant change information for the
client, formatted identically to a DNS Update [RFC2136]. To recap: client, formatted identically to a DNS Update [RFC2136]. To recap:
Delete all RRsets from a name: Delete all RRsets from a name:
TTL=0, CLASS=ANY, RDLENGTH=0, TYPE=ANY. TTL=0, CLASS=ANY, RDLENGTH=0, TYPE=ANY.
Delete an RRset from a name: Delete an RRset from a name:
TTL=0, CLASS=ANY, RDLENGTH=0; TTL=0, CLASS=ANY, RDLENGTH=0;
TYPE specifies the RRset being deleted. TYPE specifies the RRset being deleted.
Delete an individual RR from a name: Delete an individual RR from a name:
TTL=0, CLASS=NONE; TTL=0, CLASS=NONE;
TYPE, RDLENGTH and RDATA specifies the RR being deleted. TYPE, RDLENGTH and RDATA specifies the RR being deleted.
Add to an RRset: Add to an RRset:
TTL, CLASS, TYPE, RDLENGTH and RDATA specifies the RR being added. TTL, CLASS, TYPE, RDLENGTH and RDATA specifies the RR being added.
When processing the records received in a Push Notification Update When processing the records received in a PUSH Message, the receiving
Message, the receiving client MUST validate that the records being client MUST validate that the records being added or deleted
added or deleted correspond with at least one currently active correspond with at least one currently active subscription on that
subscription on that connection. Specifically, the record name MUST connection. Specifically, the record name MUST match the name given
match the name given in the SUBSCRIBE request, subject to the usual in the SUBSCRIBE request, subject to the usual established DNS case-
established DNS case-insensitivity for US-ASCII letters. If the insensitivity for US-ASCII letters. If the QTYPE in the SUBSCRIBE
QTYPE in the SUBSCRIBE request was not ANY (255) then the TYPE of the request was not ANY (255) then the TYPE of the record must match the
record must match the QTYPE given in the SUBSCRIBE request. If the QTYPE given in the SUBSCRIBE request. If the QCLASS in the SUBSCRIBE
QCLASS in the SUBSCRIBE request was not ANY (255) then the CLASS of request was not ANY (255) then the CLASS of the record must match the
the record must match the QCLASS given in the SUBSCRIBE request. If QCLASS given in the SUBSCRIBE request. If a matching active
a matching active subscription on that connection is not found, then subscription on that connection is not found, then that individual
that individual record addition/deletion is silently ignored. record addition/deletion is silently ignored. Processing of other
Processing of other additions and deletions in this message is not additions and deletions in this message is not affected. The TCP
affected. The TCP connection is not closed. This is to allow for connection is not closed. This is to allow for the unavoidable race
the race condition where a client sends an outbound UNSUBSCRIBE while condition where a client sends an outbound UNSUBSCRIBE while inbound
inbound Push Notification Updates for that subscription from the PUSH messages for that subscription from the server are still in
server are still in flight. flight.
In the case where a single change affects more than one active In the case where a single change affects more than one active
subscription, only one update is sent. For example, an update adding subscription, only one PUSH message is sent. For example, a PUSH
a given record may match both a SUBSCRIBE request with the same QTYPE message adding a given record may match both a SUBSCRIBE request with
and a different SUBSCRIBE request with QTYPE=ANY. It is not the case the same QTYPE and a different SUBSCRIBE request with QTYPE=ANY. It
that two updates are sent because the new record matches two active is not the case that two PUSH messages are sent because the new
subscriptions. record matches two active subscriptions.
The server SHOULD encode change notifications in the most efficient The server SHOULD encode change notifications in the most efficient
manner possible. For example, when three AAAA records are deleted manner possible. For example, when three AAAA records are deleted
from a given name, and no other AAAA records exist for that name, the from a given name, and no other AAAA records exist for that name, the
server SHOULD send a "delete an RRset from a name" update, not three server SHOULD send a "delete an RRset from a name" PUSH message, not
separate "delete an individual RR from a name" updates. Similarly, three separate "delete an individual RR from a name" PUSH messages.
when both an SRV and a TXT record are deleted from a given name, and Similarly, when both an SRV and a TXT record are deleted from a given
no other records of any kind exist for that name, the server SHOULD name, and no other records of any kind exist for that name, the
send a "delete all RRsets from a name" update, not two separate server SHOULD send a "delete all RRsets from a name" PUSH message,
"delete an RRset from a name" updates. not two separate "delete an RRset from a name" PUSH messages.
A server SHOULD combine multiple change notifications in a single A server SHOULD combine multiple change notifications in a single
Update Message when possible, even if those change notifications PUSH message when possible, even if those change notifications apply
apply to different subscriptions. Conceptually, a Push Notification to different subscriptions. Conceptually, a PUSH messages is a
Update Message is a connection-level concept, not a subscription- connection-level concept, not a subscription-level concept.
level concept.
Push Notification Update Messages MAY contain an EDNS(0) TCP
Keepalive option [RFC7828] 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 Reception of a PUSH message does not directly generate a response
generate a response back to the server. (Updates may indirectly back to the server. (Updates may indirectly generate other
generate other operations; e.g., a Push Notification Update Message operations; e.g., a Push Notification Update Message declaring the
declaring the appearance of a PTR record could lead to a query for appearance of a PTR record could lead to a query for the SRV record
the SRV record named in the rdata of that PTR record[RFC6763]. 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 ageing resumes and records are removed from the local cache
when their TTL reaches zero. when their TTL reaches zero.
6.5. DNS RECONFIRM 6.4. DNS Push Notification UNSUBSCRIBE
Sometimes, particularly when used with a Hybrid Proxy To cancel an individual subscription without closing the entire
[I-D.ietf-dnssd-hybrid], a DNS Zone may contain stale data. When a connection, the client sends an UNSUBSCRIBE message over the
client encounters data that it believe may be stale (e.g., an SRV established TCP connection to the server. The UNSUBSCRIBE message is
record referencing a target host+port that is not responding to encoded in a DNS Session Signaling [I-D.ietf-dnsop-session-signal]
connection requests) the client sends a DNS RECONFIRM message to message. This specification defines a new DNS Session Signaling TLV
request that the server re-verify that the data is still valid. For for DNS Push Notification UNSUBSCRIBE Requests/Responses (tentatively
a Hybrid Proxy, this causes it to issue new Multicast DNS requests to Session Signaling Type Code 66).
ascertain whether the target device is still present. For other
kinds of DNS server the RECONFIRM operation is currently undefined
and SHOULD be silently ignored.
A RECONFIRM request is formatted similarly to a conventional DNS A server may not initiate an UNSUBSCRIBE request.
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. 6.4.1. UNSUBSCRIBE 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 An UNSUBSCRIBE request message begins with the standard DNS Session
field, MUST be zero on transmission, and MUST be silently ignored on Signaling 4-byte header [I-D.ietf-dnsop-session-signal], followed by
reception. the UNSUBSCRIBE TLV.
Like a DNS QUERY request, a RECONFIRM request MUST contain exactly 1 1 1 1 1 1
one question. Since RECONFIRM requests are sent over TCP, multiple 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
RECONFIRM requests can be concatenated in a single TCP stream and +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
packed efficiently into TCP segments, so the ability to pack multiple | MESSAGE ID |
RECONFIRM operations into a single DNS message within that TCP stream +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
would add extra complexity for little benefit. |QR| Opcode | Z | RCODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| SSOP-TYPE (UNSUBSCRIBE) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| SSOP-LENGTH (0) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
ANCOUNT MUST be nonzero, and the Answer Section MUST contain the Figure 4
rdata for the record(s) that the client believes to be in doubt.
NSCOUNT MUST be zero, and the Authority Section MUST be empty. The MESSAGE ID field MUST match the value given in the ID field of an
Any records in the Authority Section MUST be silently ignored. active SUBSCRIBE request. This is how the server knows which
SUBSCRIBE request is being cancelled. After receipt of the
UNSUBSCRIBE request, the SUBSCRIBE request is no longer active. If a
server receives an UNSUBSCRIBE message where the MESSAGE ID does not
match the ID of an active SUBSCRIBE request this is an error and the
the server MUST return a response containing RCODE = 1 (FORMERR). In
the UNSUBSCRIBE response the server MUST echo back the MESSAGE ID
value unchanged. It is allowable for the client to issue an
UNSUBSCRIBE request for a previous SUBSCRIBE request for which the
client has not yet received a SUBSCRIBE response. This is to allow
for the case where a client starts and stops a subscription in less
than the round-trip time to the server. The client is NOT required
to wait for the SUBSCRIBE response before issuing the UNSUBSCRIBE
request.
ARCOUNT specifies the number of records in the Additional Data In a request the DNS Header QR bit MUST be zero.
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 The DNS Header Opcode field holds the Session Signaling Opcode value
SUBSCRIBE message matches only a wildcard ("*") in the zone, and (tentatively 6).
nothing else.
Aliasing is not supported. That is, a CNAME in a SUBSCRIBE message The Z bits MUST be zero on transmission, and MUST be silently ignored
matches only a CNAME in the zone, and nothing else. on reception.
No response message is generated as a result of processing a The return code (RCODE) field MUST be set to 0 in a request.
RECONFIRM message.
If the server receiving the RECONFIRM request determines that the In the UNSUBSCRIBE TLV the SSOP-TYPE is UNSUBSCRIBE (tentatively 66).
records are in fact no longer valid, then subsequent DNS Push
Notification Update Messages will be generated to inform interested
clients. Thus, one client discovering that a previously-advertised
printer is no longer present has the side effect of informing all
other interested clients that the printer in question is now gone.
6.6. DNS Push Notification Termination Message The SSOP-LENGTH is zero.
If a server is low on resources it MAY simply terminate a client 6.4.2. UNSUBSCRIBE Response
connection with a TCP RST. However, the likely behaviour of the
client may be simply to reconnect immediately, putting more burden on
the server. Therefore, a server SHOULD instead choose to shed client
load by (a) sending a DNS Push Notification Termination Message and
then (b) immediately closing the client connection with a TCP FIN
instead of RST, thereby facilitating reliable delivery of the
Termination Message. Upon successful reception of the Termination
Message the client is expected to close the connection. The server
SHOULD set a timer and, if the client has not closed the connection
within a reasonable time, the server SHOULD then terminate the TCP
connection with a TCP RST. The RECOMMENDED time the server should
wait before terminating the TCP connection with a TCP RST is ten
seconds.
The format of a Termination Message is similar to a Push Notification Each UNSUBSCRIBE request generates exactly one UNSUBSCRIBE response
Update. from the server.
The following figure shows the existing DNS Update header format: An UNSUBSCRIBE response message contains with the standard DNS
Session Signaling 4-byte header [I-D.ietf-dnsop-session-signal].
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 | | MESSAGE ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|QR| Opcode | Z | RCODE | |QR| Opcode | Z | RCODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ZOCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| PRCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| UPCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ADCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Figure 2 Figure 5
For Termination Messages the following rules apply: The MESSAGE ID field MUST echo the value given in the ID field of the
UNSUBSCRIBE request. This is how the client knows which request is
being responded to.
The QR bit MUST be zero, and the Opcode MUST be UPDATE (5). In a response the DNS Header QR bit MUST be one.
Messages received where this is not true are not Termination Messages If the QR bit is not one the message is not a response.
and should be silently ignored.
ID and the Z bits MUST be zero on transmission, The DNS Header Opcode field holds the Session Signaling Opcode value
and MUST be silently ignored on reception. (tentatively 6).
ZOCOUNT MUST be zero, and the Zone Section MUST be empty. The Z bits MUST be zero on transmission, and MUST be silently ignored
Any records in the Zone Section MUST be silently ignored. on reception.
PRCOUNT MUST be zero, and the Prerequisite Section MUST be empty. In the UNSUBSCRIBE response the RCODE indicates whether or not the
Any records in the Prerequisite Section MUST be silently ignored. unsubscribe request was successful. Supported RCODEs are as follows:
UPCOUNT MUST be zero, and the Update Section MUST be empty. +------------+-------+----------------------------------------------+
Any records in the Update Section MUST be silently ignored. | Mnemonic | Value | Description |
+------------+-------+----------------------------------------------+
| NOERROR | 0 | UNSUBSCRIBE successful. |
| FORMERR | 1 | Server failed to process request due to a |
| | | malformed request. |
| NOTIMP | 4 | Server does not recognize DNS Session |
| | | Signaling Opcode. |
| SSOPNOTIMP | 11 | UNSUBSCRIBE operation not supported. |
+------------+-------+----------------------------------------------+
ADCOUNT specifies the number of records in the Additional Data UNSUBSCRIBE Response codes
Section, e.g., the EDNS(0) OPT record..
The RCODE MUST contain a nonzero code giving the reason for This document specifies only these RCODE values for UNSUBSCRIBE
termination, as indicated below: Responses. Servers sending UNSUBSCRIBE Responses SHOULD use one of
these values. However, future circumstances may create situations
where other RCODE values are appropriate in UNSUBSCRIBE Responses, so
clients MUST be prepared to accept UNSUBSCRIBE Responses with any
RCODE value.
+----------+-------+------------------------------------------------+ Having being successfully revoked with a correctly-formatted
| Mnemonic | Value | Description | UNSUBSCRIBE message (resulting in a response with RCODE NOERROR) the
+----------+-------+------------------------------------------------+ previously referenced subscription is no longer active and the server
| SERVFAIL | 2 | The server is overloaded due to resource | MAY discard the state associated with it immediately, or later, at
| | | exhaustion. | the server's discretion.
| 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 Nonzero RCODE values signal some kind of error.
This document specifies only these two RCODE values for Termination RCODE value FORMERR indicates an incorrect MESSAGE ID or other
Messages. Servers sending Termination Messages SHOULD use one of message format error.
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 RCODE values NOTIMP and SSOPNOTIMP should not occur in practice.
[RFC7828]. 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 A server would only generate NOTIMP if it did not support Session
existing subscriptions (perhaps because it has been reconfigured and Signaling, and if the server does not support Session Signaling then
is no longer authoritative for those names) with a REFUSED (5) RCODE, it should not be possible for a client to have an active subscription
the EDNS(0) TCP Keepalive option's idle timeout MAY be zero, to cancel.
indicating that the client SHOULD attempt to re-establish its
subscriptions immediately.
In the case where a server is terminating a large number of Similarly, a server would only generate SSOPNOTIMP if it did not
connections at once (e.g., if the system is restarting) and the support Push Notifications, and if the server does not support Push
server doesn't want to be inundated with a flood of simultaneous Notifications then it should not be possible for a client to have an
retries, it SHOULD send different EDNS(0) TCP Keepalive values to active subscription to cancel.
each client. These adjustments MAY be selected randomly,
pseudorandomly, or deterministically (e.g., incrementing the time All nonzero RCODE values indicate a serious problem with the client.
value by one tenth of a second for each successive client, yielding a After sending an error response, the server SHOULD send a DNS Push
post-restart reconnection rate of ten clients per second). Notification Terminate Session operation TLV and then close the TCP
connection, as described in the DNS Session Signaling specification
[I-D.ietf-dnsop-session-signal].
6.5. DNS Session Signaling Push Notification RECONFIRM
Sometimes, particularly when used with a Hybrid Proxy
[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
record referencing a target host+port that is not responding to
connection requests) the client can send a RECONFIRM message to
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
ascertain whether the target device is still present. For other
types of DNS server, the RECONFIRM operation is currently undefined
and SHOULD be silently ignored.
A RECONFIRM request is formatted identically to a SUBSCRIBE request,
except that the TLV type is RECONFIRM (tentatively 67) instead of
SUBSCRIBE. Additionally, QTYPE MUST NOT be the value ANY (255) and
QCLASS MUST NOT be the value ANY (255).
Like all DNS Session Signaling [I-D.ietf-dnsop-session-signal]
requests, a RECONFIRM request MUST contain a unique MESSAGE ID, not
currently in use in this session.
A RECONFIRM request generates exactly one RECONFIRM response from the
server, formatted identically to a SUBSCRIBE response, which echoes
back the unique MESSAGE ID from the RECONFIRM request.
In the RECONFIRM response the RCODE indicates whether or not the
request was successful. Supported RCODEs are as follows:
+------------+-------+----------------------------------------------+
| Mnemonic | Value | Description |
+------------+-------+----------------------------------------------+
| NOERROR | 0 | RECONFIRM successful. |
| FORMERR | 1 | Server failed to process request due to a |
| | | malformed request. |
| NOTIMP | 4 | Server does not recognize DNS Session |
| | | Signaling Opcode. |
| SSOPNOTIMP | 11 | RECONFIRM operation not supported. |
+------------+-------+----------------------------------------------+
RECONFIRM Response codes
This document specifies only these RCODE values for RECONFIRM
Responses. Servers sending RECONFIRM Responses SHOULD use one of
these values. However, future circumstances may create situations
where other RCODE values are appropriate in RECONFIRM Responses, so
clients MUST be prepared to accept RECONFIRM Responses with any RCODE
value.
A correctly-formatted RECONFIRM message results in a response with
RCODE NOERROR.
Nonzero RCODE values signal some kind of error. If the server sends
a nonzero RCODE then it SHOULD append a Terminate modifier TLV
[I-D.ietf-dnsop-session-signal] to the response specifying a delay
before the client attempts this operation again. The RECOMMENDED
value for the delay is five minutes. For serious errors, after
sending the error response, the server SHOULD send a DNS Push
Notification Terminate Session operation TLV and then close the TCP
connection, as described in the DNS Session Signaling specification
[I-D.ietf-dnsop-session-signal].
If, after receiving a valid RECONFIRM request, the server determines
that the records are in fact no longer valid, then subsequent DNS
PUSH Messages will be generated to inform interested clients. Thus,
one client discovering that a previously-advertised printer is no
longer present has the side effect of informing all other interested
clients that the printer in question is now gone.
6.6. Client-Initiated Termination
An individual subscription is terminated by sending an UNSUBSCRIBE
TLV for that specific subscription, or all subscriptions can be
cancelled at once by the client closing the connection. When a
client terminates an individual subscription (via UNSUBSCRIBE) or all
subscriptions on that connection (by closing the connection) it is
signaling 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, 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 continue to meet its keepalive obligations
[I-D.ietf-dnsop-session-signal] 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, 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.
When closing a connection, a client will generally do an abortive
disconnect, sending a TCP RST. This immediately discards all
remaining inbound and outbound data, which is appropriate if the
client no longer has any interest in this data. In the BSD Sockets
API, sending a TCP RST is achieved by setting the SO_LINGER option
with a time of 0 seconds and then closing the socket.
If a client has performed operations on this connection that it would
not want lost (like DNS updates) then the client SHOULD do an orderly
disconnect, sending a TCP FIN. In the BSD Sockets API, sending a TCP
FIN is achieved by calling "shutdown(s,SHUT_WR)" and keeping the
socket open until all remaining data has been read from it.
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 29, line 11 skipping to change at page 30, line 7
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.
7.3. 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.
7.4. 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,
skipping to change at page 29, line 35 skipping to change at page 30, line 31
Use of TLS Session Resumption allows a new TLS connection to be set Use of TLS Session Resumption allows a new TLS connection to be set
up more quickly, but the client will still have to recreate any up more quickly, but the client will still have to recreate any
desired subscriptions. desired subscriptions.
8. IANA Considerations 8. IANA Considerations
This document defines the service name: "_dns-push-tls._tcp". This document defines the service name: "_dns-push-tls._tcp".
It is only applicable for the TCP protocol. It is only applicable for the TCP protocol.
This name is to be published in the IANA Service Name Registry. This name is to be published in the IANA Service Name Registry.
This document defines three DNS OpCodes: SUBSCRIBE with (tentative) This document defines three DNS Session Signaling TLV types:
value 6, UNSUBSCRIBE with (tentative) value 7, and RECONFIRM with SUBSCRIBE with (tentative) value 64, PUSH with (tentative) value 65,
(tentative) value 8. UNSUBSCRIBE with (tentative) value 66, and RECONFIRM with (tentative)
value 67.
9. Acknowledgements 9. Acknowledgements
The authors would like to thank Kiren Sekar and Marc Krochmal for The authors would like to thank Kiren Sekar and Marc Krochmal for
previous work completed in this field. previous work completed in this field.
This draft has been improved due to comments from Ran Atkinson, Tim This draft has been improved due to comments from Ran Atkinson, Tim
Chown, Mark Delany, Ralph Droms, Bernie Volz, Jan Komissar, Manju Chown, Mark Delany, Ralph Droms, Bernie Volz, Jan Komissar, Manju
Shankar Rao, Markus Stenberg, Dave Thaler, and Soraia Zlatkovic. Shankar Rao, Markus Stenberg, Dave Thaler, and Soraia Zlatkovic.
10. References 10. References
10.1. Normative References 10.1. Normative References
[I-D.bellis-dnsop-session-signal] [I-D.ietf-dnsop-session-signal]
Bellis, R., Cheshire, S., Marcon, J., Mankin, A., and T. Bellis, R., Cheshire, S., Dickinson, J., Dickinson, S.,
Pusateri, "DNS Session Signaling", draft-bellis-dnsop- Mankin, A., and T. Pusateri, "DNS Session Signaling",
session-signal-00 (work in progress), July 2016. draft-ietf-dnsop-session-signal-00 (work in progress),
August 2016.
[I-D.ietf-tls-tls13] [I-D.ietf-tls-tls13]
Rescorla, E., "The Transport Layer Security (TLS) Protocol Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", draft-ietf-tls-tls13-13 (work in progress), Version 1.3", draft-ietf-tls-tls13-18 (work in progress),
May 2016. October 2016.
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, DOI [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
10.17487/RFC0768, August 1980, DOI 10.17487/RFC0768, August 1980,
<http://www.rfc-editor.org/info/rfc768>. <http://www.rfc-editor.org/info/rfc768>.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC [RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
793, DOI 10.17487/RFC0793, September 1981, RFC 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",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<http://www.rfc-editor.org/info/rfc1034>. <http://www.rfc-editor.org/info/rfc1034>.
[RFC1035] Mockapetris, P., "Domain names - implementation and [RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <http://www.rfc-editor.org/info/rfc1035>. November 1987, <http://www.rfc-editor.org/info/rfc1035>.
[RFC1123] Braden, R., Ed., "Requirements for Internet Hosts - [RFC1123] Braden, R., Ed., "Requirements for Internet Hosts -
Application and Support", STD 3, RFC 1123, DOI 10.17487/ Application and Support", STD 3, RFC 1123,
RFC1123, October 1989, DOI 10.17487/RFC1123, October 1989,
<http://www.rfc-editor.org/info/rfc1123>. <http://www.rfc-editor.org/info/rfc1123>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ Requirement Levels", BCP 14, RFC 2119,
RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound, [RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound,
"Dynamic Updates in the Domain Name System (DNS UPDATE)", "Dynamic Updates in the Domain Name System (DNS UPDATE)",
RFC 2136, DOI 10.17487/RFC2136, April 1997, RFC 2136, DOI 10.17487/RFC2136, April 1997,
<http://www.rfc-editor.org/info/rfc2136>. <http://www.rfc-editor.org/info/rfc2136>.
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for [RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782, specifying the location of services (DNS SRV)", RFC 2782,
DOI 10.17487/RFC2782, February 2000, DOI 10.17487/RFC2782, February 2000,
<http://www.rfc-editor.org/info/rfc2782>. <http://www.rfc-editor.org/info/rfc2782>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/ (TLS) Protocol Version 1.2", RFC 5246,
RFC5246, August 2008, DOI 10.17487/RFC5246, August 2008,
<http://www.rfc-editor.org/info/rfc5246>. <http://www.rfc-editor.org/info/rfc5246>.
[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS) [RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)
Extensions: Extension Definitions", RFC 6066, DOI Extensions: Extension Definitions", RFC 6066,
10.17487/RFC6066, January 2011, DOI 10.17487/RFC6066, January 2011,
<http://www.rfc-editor.org/info/rfc6066>. <http://www.rfc-editor.org/info/rfc6066>.
[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>.
[RFC6895] Eastlake 3rd, D., "Domain Name System (DNS) IANA [RFC6895] Eastlake 3rd, D., "Domain Name System (DNS) IANA
Considerations", BCP 42, RFC 6895, DOI 10.17487/RFC6895, Considerations", BCP 42, RFC 6895, DOI 10.17487/RFC6895,
April 2013, <http://www.rfc-editor.org/info/rfc6895>. April 2013, <http://www.rfc-editor.org/info/rfc6895>.
[RFC7673] Finch, T., Miller, M., and P. Saint-Andre, "Using DNS- [RFC7673] Finch, T., Miller, M., and P. Saint-Andre, "Using DNS-
Based Authentication of Named Entities (DANE) TLSA Records Based Authentication of Named Entities (DANE) TLSA Records
with SRV Records", RFC 7673, DOI 10.17487/RFC7673, October with SRV Records", RFC 7673, DOI 10.17487/RFC7673, October
2015, <http://www.rfc-editor.org/info/rfc7673>. 2015, <http://www.rfc-editor.org/info/rfc7673>.
[RFC7766] Dickinson, J., Dickinson, S., Bellis, R., Mankin, A., and [RFC7766] Dickinson, J., Dickinson, S., Bellis, R., Mankin, A., and
D. Wessels, "DNS Transport over TCP - Implementation D. Wessels, "DNS Transport over TCP - Implementation
Requirements", RFC 7766, DOI 10.17487/RFC7766, March 2016, Requirements", RFC 7766, DOI 10.17487/RFC7766, March 2016,
<http://www.rfc-editor.org/info/rfc7766>. <http://www.rfc-editor.org/info/rfc7766>.
[RFC7828] Wouters, P., Abley, J., Dickinson, S., and R. Bellis, "The
edns-tcp-keepalive EDNS0 Option", RFC 7828, DOI 10.17487/
RFC7828, April 2016,
<http://www.rfc-editor.org/info/rfc7828>.
10.2. Informative References 10.2. Informative References
[I-D.dukkipati-tcpm-tcp-loss-probe]
Dukkipati, N., Cardwell, N., Cheng, Y., and M. Mathis,
"Tail Loss Probe (TLP): An Algorithm for Fast Recovery of
Tail Losses", draft-dukkipati-tcpm-tcp-loss-probe-01 (work
in progress), February 2013.
[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-03 (work in progress), Discovery", draft-ietf-dnssd-hybrid-03 (work in progress),
November 2015. February 2016.
[I-D.ietf-dprive-dns-over-tls]
Zi, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over TLS", draft-
ietf-dprive-dns-over-tls-09 (work in progress), March
2016.
[I-D.sekar-dns-llq] [I-D.sekar-dns-llq]
Sekar, K., "DNS Long-Lived Queries", draft-sekar-dns- Sekar, K., "DNS Long-Lived Queries", draft-sekar-dns-
llq-01 (work in progress), August 2006. llq-01 (work in progress), August 2006.
[IPJ.9-4-TCPSYN] [IPJ.9-4-TCPSYN]
Eddy, W., "Defenses Against TCP SYN Flooding Attacks", The Eddy, W., "Defenses Against TCP SYN Flooding Attacks", The
Internet Protocol Journal, Cisco Systems, Volume 9, Number Internet Protocol Journal, Cisco Systems, Volume 9,
4, December 2006. Number 4, December 2006.
[obs] "Observer Pattern", <https://en.wikipedia.org/wiki/
Observer_pattern>.
[RFC1996] Vixie, P., "A Mechanism for Prompt Notification of Zone [RFC1996] Vixie, P., "A Mechanism for Prompt Notification of Zone
Changes (DNS NOTIFY)", RFC 1996, DOI 10.17487/RFC1996, Changes (DNS NOTIFY)", RFC 1996, DOI 10.17487/RFC1996,
August 1996, <http://www.rfc-editor.org/info/rfc1996>. August 1996, <http://www.rfc-editor.org/info/rfc1996>.
[RFC4287] Nottingham, M., Ed. and R. Sayre, Ed., "The Atom [RFC4287] Nottingham, M., Ed. and R. Sayre, Ed., "The Atom
Syndication Format", RFC 4287, DOI 10.17487/RFC4287, Syndication Format", RFC 4287, DOI 10.17487/RFC4287,
December 2005, <http://www.rfc-editor.org/info/rfc4287>. December 2005, <http://www.rfc-editor.org/info/rfc4287>.
[RFC4953] Touch, J., "Defending TCP Against Spoofing Attacks", RFC [RFC4953] Touch, J., "Defending TCP Against Spoofing Attacks",
4953, DOI 10.17487/RFC4953, July 2007, RFC 4953, DOI 10.17487/RFC4953, July 2007,
<http://www.rfc-editor.org/info/rfc4953>. <http://www.rfc-editor.org/info/rfc4953>.
[RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig, [RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,
"Transport Layer Security (TLS) Session Resumption without "Transport Layer Security (TLS) Session Resumption without
Server-Side State", RFC 5077, DOI 10.17487/RFC5077, Server-Side State", RFC 5077, DOI 10.17487/RFC5077,
January 2008, <http://www.rfc-editor.org/info/rfc5077>. January 2008, <http://www.rfc-editor.org/info/rfc5077>.
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762, [RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
DOI 10.17487/RFC6762, February 2013, DOI 10.17487/RFC6762, February 2013,
<http://www.rfc-editor.org/info/rfc6762>. <http://www.rfc-editor.org/info/rfc6762>.
[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service [RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013, Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
<http://www.rfc-editor.org/info/rfc6763>. <http://www.rfc-editor.org/info/rfc6763>.
[RFC6824] Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
"TCP Extensions for Multipath Operation with Multiple
Addresses", RFC 6824, DOI 10.17487/RFC6824, January 2013,
<http://www.rfc-editor.org/info/rfc6824>.
[RFC7413] Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP
Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014,
<http://www.rfc-editor.org/info/rfc7413>.
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre, [RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer "Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <http://www.rfc-editor.org/info/rfc7525>. 2015, <http://www.rfc-editor.org/info/rfc7525>.
[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over Transport
Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2016, <http://www.rfc-editor.org/info/rfc7858>.
[XEP0060] Millard, P., Saint-Andre, P., and R. Meijer, "Publish- [XEP0060] Millard, P., Saint-Andre, P., and R. Meijer, "Publish-
Subscribe", XSF XEP 0060, July 2010. Subscribe", XSF XEP 0060, July 2010.
Authors' Addresses Authors' Addresses
Tom Pusateri Tom Pusateri
Seeking affiliation Seeking affiliation
Hilton Head Island, SC Hilton Head Island, SC
USA USA
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