draft-ietf-dnssd-push-24.txt   draft-ietf-dnssd-push-25.txt 
Internet Engineering Task Force T. Pusateri Internet Engineering Task Force T. Pusateri
Internet-Draft Unaffiliated Internet-Draft Unaffiliated
Intended status: Standards Track S. Cheshire Intended status: Standards Track S. Cheshire
Expires: February 8, 2020 Apple Inc. Expires: April 15, 2020 Apple Inc.
August 7, 2019 October 13, 2019
DNS Push Notifications DNS Push Notifications
draft-ietf-dnssd-push-24 draft-ietf-dnssd-push-25
Abstract Abstract
The Domain Name System (DNS) was designed to return matching records The Domain Name System (DNS) was designed to return matching records
efficiently for queries for data that are relatively static. When efficiently for queries for data that are relatively static. When
those records change frequently, DNS is still efficient at returning those records change frequently, DNS is still efficient at returning
the updated results when polled, as long as the polling rate is not the updated results when polled, as long as the polling rate is not
too high. But there exists no mechanism for a client to be too high. But there exists no mechanism for a client to be
asynchronously notified when these changes occur. This document asynchronously notified when these changes occur. This document
defines a mechanism for a client to be notified of such changes to defines a mechanism for a client to be notified of such changes to
skipping to change at page 1, line 38 skipping to change at page 1, line 38
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 8, 2020. This Internet-Draft will expire on April 15, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 2, line 25 skipping to change at page 2, line 25
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. State Considerations . . . . . . . . . . . . . . . . . . . . 6 4. State Considerations . . . . . . . . . . . . . . . . . . . . 6
5. Transport . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5. Transport . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6. Protocol Operation . . . . . . . . . . . . . . . . . . . . . 8 6. Protocol Operation . . . . . . . . . . . . . . . . . . . . . 8
6.1. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 9 6.1. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 9
6.2. DNS Push Notification SUBSCRIBE . . . . . . . . . . . . . 13 6.2. DNS Push Notification SUBSCRIBE . . . . . . . . . . . . . 13
6.2.1. SUBSCRIBE Request . . . . . . . . . . . . . . . . . . 13 6.2.1. SUBSCRIBE Request . . . . . . . . . . . . . . . . . . 13
6.2.2. SUBSCRIBE Response . . . . . . . . . . . . . . . . . 16 6.2.2. SUBSCRIBE Response . . . . . . . . . . . . . . . . . 16
6.3. DNS Push Notification Updates . . . . . . . . . . . . . . 20 6.3. DNS Push Notification Updates . . . . . . . . . . . . . . 20
6.3.1. PUSH Message . . . . . . . . . . . . . . . . . . . . 20 6.3.1. PUSH Message . . . . . . . . . . . . . . . . . . . . 20
6.4. DNS Push Notification UNSUBSCRIBE . . . . . . . . . . . . 25 6.4. DNS Push Notification UNSUBSCRIBE . . . . . . . . . . . . 26
6.4.1. UNSUBSCRIBE Message . . . . . . . . . . . . . . . . . 25 6.4.1. UNSUBSCRIBE Message . . . . . . . . . . . . . . . . . 26
6.5. DNS Push Notification RECONFIRM . . . . . . . . . . . . . 27 6.5. DNS Push Notification RECONFIRM . . . . . . . . . . . . . 28
6.5.1. RECONFIRM Message . . . . . . . . . . . . . . . . . . 28 6.5.1. RECONFIRM Message . . . . . . . . . . . . . . . . . . 29
6.6. DNS Stateful Operations TLV Context Summary . . . . . . . 30 6.6. DNS Stateful Operations TLV Context Summary . . . . . . . 31
6.7. Client-Initiated Termination . . . . . . . . . . . . . . 31 6.7. Client-Initiated Termination . . . . . . . . . . . . . . 32
6.8. Client Fallback to Polling . . . . . . . . . . . . . . . 32 6.8. Client Fallback to Polling . . . . . . . . . . . . . . . 33
7. Security Considerations . . . . . . . . . . . . . . . . . . . 33 7. Security Considerations . . . . . . . . . . . . . . . . . . . 34
7.1. Security Services . . . . . . . . . . . . . . . . . . . . 33 7.1. Security Services . . . . . . . . . . . . . . . . . . . . 35
7.2. TLS Name Authentication . . . . . . . . . . . . . . . . . 34 7.2. TLS Name Authentication . . . . . . . . . . . . . . . . . 35
7.3. TLS Early Data . . . . . . . . . . . . . . . . . . . . . 34 7.3. TLS Early Data . . . . . . . . . . . . . . . . . . . . . 36
7.4. TLS Session Resumption . . . . . . . . . . . . . . . . . 35 7.4. TLS Session Resumption . . . . . . . . . . . . . . . . . 36
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 36 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 36 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 37
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 37 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 38
10.1. Normative References . . . . . . . . . . . . . . . . . . 37 10.1. Normative References . . . . . . . . . . . . . . . . . . 38
10.2. Informative References . . . . . . . . . . . . . . . . . 38 10.2. Informative References . . . . . . . . . . . . . . . . . 40
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 41 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 42
1. Introduction 1. Introduction
Domain Name System (DNS) records may be updated using DNS Update Domain Name System (DNS) records may be updated using DNS Update
[RFC2136]. Other mechanisms such as a Discovery Proxy [DisProx] can [RFC2136]. Other mechanisms such as a Discovery Proxy [DisProx] can
also generate changes to a DNS zone. This document specifies a also generate changes to a DNS zone. This document specifies a
protocol for DNS clients to subscribe to receive asynchronous protocol for DNS clients to subscribe to receive asynchronous
notifications of changes to RRsets of interest. It is immediately notifications of changes to RRsets of interest. It is immediately
relevant in the case of DNS Service Discovery [RFC6763] but is not relevant in the case of DNS Service Discovery [RFC6763] but is not
limited to that use case, and provides a general DNS mechanism for limited to that use case, and provides a general DNS mechanism for
skipping to change at page 4, line 19 skipping to change at page 4, line 19
many levels throughout the network. Other network protocols have many levels throughout the network. Other network protocols have
successfully deployed a publish/subscribe model following the successfully deployed a publish/subscribe model following the
Observer design pattern [obs]. XMPP Publish-Subscribe [XEP0060] and Observer design pattern [obs]. XMPP Publish-Subscribe [XEP0060] and
Atom [RFC4287] are examples. While DNS servers are generally highly Atom [RFC4287] are examples. While DNS servers are generally highly
tuned and capable of a high rate of query/response traffic, adding a tuned and capable of a high rate of query/response traffic, adding a
publish/subscribe model for tracking changes to DNS records can publish/subscribe model for tracking changes to DNS records can
deliver more timely notification of changes with reduced CPU usage deliver more timely notification of changes with reduced CPU usage
and lower network traffic. 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 address, and record changes are sent to link-local IP multicast group address, and changes are sent to that
that multicast group address for all group members to receive. multicast group address for all group members to receive. Therefore,
Therefore, Multicast DNS already has asynchronous change notification Multicast DNS already has asynchronous change notification
capability. However, when DNS Service Discovery [RFC6763] is used capability. When DNS Service Discovery [RFC6763] is used across a
across a wide area network using Unicast DNS (possibly facilitated wide area network using Unicast DNS (possibly facilitated via a
via a Discovery Proxy [DisProx]) it would be beneficial to have an Discovery Proxy [DisProx]) it would be beneficial to have an
equivalent capability for Unicast DNS, to allow clients to learn equivalent capability for Unicast DNS, to allow clients to learn
about DNS record changes in a timely manner without polling. about DNS record changes in a timely manner without polling.
The DNS Long-Lived Queries (LLQ) mechanism [LLQ] is an existing The DNS Long-Lived Queries (LLQ) mechanism [LLQ] is an existing
deployed solution to provide asynchronous change notifications, used deployed solution to provide asynchronous change notifications, used
by Apple's Back to My Mac [RFC6281] service introduced in Mac OS X by Apple's Back to My Mac [RFC6281] service introduced in Mac OS X
10.5 Leopard in 2007. Back to My Mac was designed in an era when the 10.5 Leopard in 2007. Back to My Mac was designed in an era when the
data center operations staff asserted that it was impossible for a data center operations staff asserted that it was impossible for a
server to handle large numbers of mostly-idle TCP connections, so LLQ server to handle large numbers of mostly-idle TCP connections, so LLQ
was defined as a UDP-based protocol, effectively replicating much of was defined as a UDP-based protocol, effectively replicating much of
TCP's connection state management logic in user space, and creating TCP's connection state management logic in user space, and creating
its own poor imitations of existing TCP features like the three-way its own imitation of existing TCP features like the three-way
handshake, flow control, and reliability. handshake, flow control, and reliability.
This document builds on experience gained with the LLQ protocol, with This document builds on experience gained with the LLQ protocol, with
an improved design. Instead of using UDP, this specification uses an improved design. Instead of using UDP, this specification uses
DNS Stateful Operations (DSO) [RFC8490] running over TLS over TCP, DNS Stateful Operations (DSO) [RFC8490] running over TLS over TCP,
and therefore doesn't need to reinvent existing TCP functionality. and therefore doesn't need to reinvent existing TCP functionality.
Using TCP also gives long-lived low-traffic connections better Using TCP also gives long-lived low-traffic connections better
longevity through NAT gateways without depending on the gateway to longevity through NAT gateways without depending on the gateway to
support NAT Port Mapping Protocol (NAT-PMP) [RFC6886] or Port Control support NAT Port Mapping Protocol (NAT-PMP) [RFC6886] or Port Control
Protocol (PCP) [RFC6887], or resorting to excessive keepalive Protocol (PCP) [RFC6887], or resorting to excessive keepalive
skipping to change at page 5, line 35 skipping to change at page 5, line 35
server" for the purposes of this specification, and communications server" for the purposes of this specification, and communications
with these two ports are handled independently. Supporting DNS with these two ports are handled independently. Supporting DNS
Updates and DNS Push Notifications on the same server is OPTIONAL. A Updates and DNS Push Notifications on the same server is OPTIONAL. A
DNS Push Notification server is not required to support DNS Update. DNS Push Notification server is not required to support DNS Update.
Standard DNS Queries MAY be sent over a DNS Push Notification (i.e., Standard DNS Queries MAY be sent over a DNS Push Notification (i.e.,
DSO) session. For any zone for which the server is authoritative, it DSO) session. For any zone for which the server is authoritative, it
MUST respond authoritatively for queries for names falling within MUST respond authoritatively for queries for names falling within
that zone (e.g., the "_dns-push-tls._tcp.<zone>" SRV record) both for that zone (e.g., the "_dns-push-tls._tcp.<zone>" SRV record) both for
normal DNS queries and for DNS Push Notification subscriptions. For normal DNS queries and for DNS Push Notification subscriptions. For
names for which the server is acting as a recursive resolver, e.g., names for which the server is acting as a recursive resolver (e.g.,
when the server is the local recursive resolver, for any query for when the server is the local recursive resolver) for any query for
which it supports DNS Push Notification subscriptions, it MUST also which it supports DNS Push Notification subscriptions, it MUST also
support standard queries. support standard queries.
DNS Push Notifications impose less load on the responding server than DNS Push Notifications impose less load on the responding server than
rapid polling would, but Push Notifications do still have a cost, so rapid polling would, but Push Notifications do still have a cost, so
DNS Push Notification clients MUST NOT recklessly create an excessive DNS Push Notification clients MUST NOT recklessly create an excessive
number of Push Notification subscriptions. Specifically: number of Push Notification subscriptions. Specifically:
(a) A subscription should only be active when there is a valid reason (a) A subscription should only be active when there is a valid reason
to need live data (for example, an on-screen display is currently to need live data (for example, an on-screen display is currently
skipping to change at page 6, line 18 skipping to change at page 6, line 18
Push Notification subscription active 24 hours a day, 7 days a week, Push Notification subscription active 24 hours a day, 7 days a week,
just to keep a list in memory up to date so that if the user does just to keep a list in memory up to date so that if the user does
choose to bring up an on-screen display of that data, it can be choose to bring up an on-screen display of that data, it can be
displayed really fast. DNS Push Notifications are designed to be displayed really fast. DNS Push Notifications are designed to be
fast enough that there is no need to pre-load a "warm" list in memory fast enough that there is no need to pre-load a "warm" list in memory
just in case it might be needed later. just in case it might be needed later.
Generally, as described in the DNS Stateful Operations specification Generally, as described in the DNS Stateful Operations specification
[RFC8490], a client must not keep a DSO session to a server open [RFC8490], a client must not keep a DSO session to a server open
indefinitely if it has no subscriptions (or other operations) active indefinitely if it has no subscriptions (or other operations) active
on that session. A client MAY close a DSO session immediately it on that session. A client may close a DSO session immediately it
becomes idle, and then if needed in the future, open a new session becomes idle, and then if needed in the future, open a new session
when required. Alternatively, a client MAY speculatively keep an when required. Alternatively, a client may speculatively keep an
idle DSO session open for some time, subject to the constraint that idle DSO session open for some time, subject to the constraint that
it must not keep a session open that has been idle for more than the it must not keep a session open that has been idle for more than the
session's idle timeout (15 seconds by default) [RFC8490]. session's idle timeout (15 seconds by default) [RFC8490].
Note that a DSO session which has an active DNS Push Notification Note that a DSO session that has an active DNS Push Notification
subscription is not considered idle, even if there is no traffic subscription is not considered idle, even if there is no traffic
flowing for an extended period of time. In this case the DSO flowing for an extended period of time. In this case the DSO
inactivity timeout does not apply, because the session is not inactivity timeout does not apply, because the session is not
inactive, but the keepalive interval does still apply, to ensure inactive, but the keepalive interval does still apply, to ensure
generation of sufficient messages to maintain state in middleboxes generation of sufficient messages to maintain state in middleboxes
(such at NAT gateways or firewalls) and for the client and server to (such at NAT gateways or firewalls) and for the client and server to
periodically verify that they still have connectivity to each other. periodically verify that they still have connectivity to each other.
This is described in Section 6.2 of the DSO specification [RFC8490]. This is described in Section 6.2 of the DSO specification [RFC8490].
4. State Considerations 4. State Considerations
skipping to change at page 7, line 19 skipping to change at page 7, line 19
(TCP) [RFC0793] as the transport protocol, in keeping with the (TCP) [RFC0793] as the transport protocol, in keeping with the
historical precedent that DNS queries must first be sent over UDP historical precedent that DNS queries must first be sent over UDP
[RFC1123]. This requirement to use UDP has subsequently been relaxed [RFC1123]. This requirement to use UDP has subsequently been relaxed
[RFC7766]. [RFC7766].
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 DNS defined only for TCP. DNS Push Notification clients MUST use DNS
Stateful Operations [RFC8490] running over TLS over TCP [RFC7858]. Stateful Operations [RFC8490] running over TLS over TCP [RFC7858].
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 which is a potential problem concerns of state overload at the server, which is a potential
with connectionless protocols using spoofed source addresses. All problem with connectionless protocols, which can be more vulnerable
to being exploited by attackers using spoofed source addresses. All
subscribers are guaranteed to be reachable by the server by virtue of subscribers are guaranteed to be reachable by the server by virtue of
the TCP three-way handshake. Flooding attacks are possible with any the TCP three-way handshake. Flooding attacks are possible with any
protocol, and a benefit of TCP is that there are already established protocol, and a benefit of TCP is that there are already established
industry best practices to guard against SYN flooding and similar industry best practices to guard against SYN flooding and similar
attacks [SYN] [RFC4953]. attacks [SYN] [RFC4953].
Use of TCP also allows DNS Push Notifications to take advantage of Use of TCP also allows DNS Push Notifications to take advantage of
current and future developments in TCP, such as Multipath TCP (MPTCP) current and future developments in TCP, such as Multipath TCP (MPTCP)
[RFC6824], TCP Fast Open (TFO) [RFC7413], RACK: a time-based fast [RFC6824], TCP Fast Open (TFO) [RFC7413], the TCP RACK fast loss
loss detection algorithm for TCP [I-D.ietf-tcpm-rack], and so on. detection algorithm [I-D.ietf-tcpm-rack], and so on.
Transport Layer Security (TLS) [RFC8446] is well understood, and used Transport Layer Security (TLS) [RFC8446] is well understood, and used
by many application-layer protocols running over TCP. TLS is by many application-layer protocols running over TCP. TLS is
designed to prevent eavesdropping, tampering, and message forgery. designed to prevent eavesdropping, tampering, and message forgery.
TLS is REQUIRED for every connection between a client subscriber and TLS is REQUIRED for every connection between a client subscriber and
server in this protocol specification. Additional security measures server in this protocol specification. Additional security measures
such as client authentication during TLS negotiation MAY also be such as client authentication during TLS negotiation may also be
employed to increase the trust relationship between client and employed to increase the trust relationship between client and
server. server.
6. Protocol Operation 6. Protocol Operation
The DNS Push Notification protocol is a session-oriented protocol, The DNS Push Notification protocol is a session-oriented protocol,
and makes use of DNS Stateful Operations (DSO) [RFC8490]. and makes use of DNS Stateful Operations (DSO) [RFC8490].
For details of the DSO message format refer to the DNS Stateful Oper- For details of the DSO message format refer to the DNS Stateful Oper-
ations specification [RFC8490]. Those details are not repeated here. ations specification [RFC8490]. Those details are not repeated here.
skipping to change at page 8, line 23 skipping to change at page 8, line 23
DNS Push Notification clients and servers MUST support DSO. A single DNS Push Notification clients and servers MUST support DSO. A single
server can support DNS Queries, DNS Updates, and DNS Push server can support DNS Queries, DNS Updates, and DNS Push
Notifications (using DSO) on the same TCP port. Notifications (using DSO) on the same TCP port.
A DNS Push Notification exchange begins with the client discovering A DNS Push Notification exchange begins with the client discovering
the appropriate server, using the procedure described in Section 6.1, the appropriate server, using the procedure described in Section 6.1,
and then making a TLS/TCP connection to it. and then making a TLS/TCP connection to it.
A typical DNS Push Notification client will immediately issue a DSO A typical DNS Push Notification client will immediately issue a DSO
Keepalive operation to request a session timeout and/or keepalive Keepalive operation to request a session timeout and/or keepalive
interval longer than the the 15-second default values, but this is interval longer than the 15-second default values, but this is not
not required. A DNS Push Notification client MAY issue other required. A DNS Push Notification client MAY issue other requests on
requests on the session first, and only issue a DSO Keepalive the session first, and only issue a DSO Keepalive operation later if
operation later if it determines that to be necessary. Sending it determines that to be necessary. Sending either a DSO Keepalive
either a DSO Keepalive operation or a Push Notification subscription operation or a Push Notification subscription request over the TLS/
request over the TLS/TCP connection to the server signals the TCP connection to the server signals the client's support of DSO and
client's support of DSO and serves to establish a DSO session. serves to establish a DSO session.
In accordance with the current set of active subscriptions, the In accordance with the current set of active subscriptions, the
server sends relevant asynchronous Push Notifications to the client. server sends relevant asynchronous Push Notifications to the client.
Note that a client MUST be prepared to receive (and silently ignore) Note that a client MUST be prepared to receive (and silently ignore)
Push Notifications for subscriptions it has previously removed, since Push Notifications for subscriptions it has previously removed, since
there is no way to prevent the situation where a Push Notification is there is no way to prevent the situation where a Push Notification is
in flight from server to client while the client's UNSUBSCRIBE in flight from server to client while the client's UNSUBSCRIBE
message cancelling that subscription is simultaneously in flight from message cancelling that subscription is simultaneously in flight from
client to server. client to server.
skipping to change at page 9, line 26 skipping to change at page 9, line 26
doesn't already have an active subscription for that name, type, and doesn't already have an active subscription for that name, type, and
class, then the recursive resolver will make a corresponding Push class, then the recursive resolver will make a corresponding Push
Notification subscription on the client's behalf. Results received Notification subscription on the client's behalf. Results received
are relayed to the client. This is closely analogous to how a client are relayed to the client. This is closely analogous to how a client
sends a normal DNS query to its configured DNS recursive resolver sends a normal DNS query to its configured DNS recursive resolver
which, if it doesn't already have appropriate answer(s) in its cache, which, if it doesn't already have appropriate answer(s) in its cache,
issues an upstream query to satisfy the request. issues an upstream query to satisfy the request.
In many contexts, the recursive resolver will be able to handle Push In many contexts, the recursive resolver will be able to handle Push
Notifications for all names that the client may need to follow. Use Notifications for all names that the client may need to follow. Use
of VPN tunnels and split-view DNS can create some additional of VPN tunnels and Private DNS [RFC8499] can create some additional
complexity in the client software here; the techniques to handle VPN complexity in the client software here; the techniques to handle VPN
tunnels and split-view DNS for DNS Push Notifications are the same as tunnels and Private DNS for DNS Push Notifications are the same as
those already used to handle this for normal DNS queries. those already used to handle this for normal DNS queries.
If the recursive resolver does not support DNS over TLS, or supports If the recursive resolver does not support DNS over TLS, or supports
DNS over TLS but is not listening on TCP port 853, or supports DNS DNS over TLS but is not listening on TCP port 853, or supports DNS
over TLS on TCP port 853 but does not support DSO on that port, then over TLS on TCP port 853 but does not support DSO on that port, then
the DSO Session session establishment will fail [RFC8490]. the DSO Session session establishment will fail [RFC8490].
If the recursive resolver does support DSO but not Push Notification If the recursive resolver does support DSO but not Push Notification
subscriptions, then it will return the DSO error code, DSOTYPENI subscriptions, then it will return the DSO error code DSOTYPENI (11).
(11).
In some cases, the recursive resolver may support DSO and Push In some cases, the recursive resolver may support DSO and Push
Notification subscriptions, but may not be able to subscribe for Push Notification subscriptions, but may not be able to subscribe for Push
Notifications for a particular name. In this case, the recursive Notifications for a particular name. In this case, the recursive
resolver should return SERVFAIL to the client. This includes being resolver should return SERVFAIL to the client. This includes being
unable to establish a connection to the zone's DNS Push Notification unable to establish a connection to the zone's DNS Push Notification
server or establishing a connection but receiving a non success server or establishing a connection but receiving a non success
response code. In some cases, where the client has a pre-established response code. In some cases, where the client has a pre-established
trust relationship with the owner of the zone (that is not handled trust relationship with the owner of the zone (that is not handled
via the usual mechanisms for VPN software) the client may handle via the usual mechanisms for VPN software) the client may handle
skipping to change at page 11, line 14 skipping to change at page 11, line 14
operation of the DNS protocol regarding negative responses operation of the DNS protocol regarding negative responses
[RFC2308].) [RFC2308].)
4. If the client receives a response containing no SOA record, then 4. If the client receives a response containing no SOA record, then
it proceeds with the iterative approach. The client strips the it proceeds with the iterative approach. The client strips the
leading label from the current query name, and if the resulting leading label from the current query name, and if the resulting
name has at least two labels in it, the client sends an SOA query name has at least two labels in it, the client sends an SOA query
for that new name, and processing continues at step 2 above, for that new name, and processing continues at step 2 above,
repeating the iterative search until either an SOA is received, repeating the iterative search until either an SOA is received,
or the query name consists of a single label, i.e., a Top Level or the query name consists of a single label, i.e., a Top Level
Domain (TLD). In the case of a single-label (TLD), this is a Domain (TLD). In the case of a single-label name (TLD), this is
network configuration error, which should not happen, and the a network configuration error, which should not happen, and the
client gives up. The client may retry the operation at a later client gives up. The client may retry the operation at a later
time, of the client's choosing, such after a change in network time, of the client's choosing, such after a change in network
attachment. attachment.
5. Once the SOA is known (either by virtue of being seen in the 5. Once the SOA is known (either by virtue of being seen in the
Answer Section, or in the Authority Section), the client sends a Answer Section, or in the Authority Section), the client sends a
DNS query with type SRV [RFC2782] for the record name DNS query with type SRV [RFC2782] for the record name
"_dns-push-tls._tcp.<zone>", where <zone> is the owner name of "_dns-push-tls._tcp.<zone>", where <zone> is the owner name of
the discovered SOA record. the discovered SOA record.
skipping to change at page 12, line 5 skipping to change at page 12, line 5
subscription requests. As described in the SRV specification subscription requests. As described in the SRV specification
[RFC2782], the server with the lowest "priority" is first [RFC2782], the server with the lowest "priority" is first
contacted. If more than one server has the same "priority", the contacted. If more than one server has the same "priority", the
"weight" 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 willing to probabilities of being selected. If a server is not willing to
accept a subscription request, or is not reachable within a accept a subscription request, or is not reachable within a
reasonable time, as determined by the client, then a subsequent reasonable time, as determined by the client, then a subsequent
server is to be contacted. 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, it
session, it SHOULD repeat the discovery process in order to determine SHOULD repeat the discovery process in order to determine the
the preferred DNS server for subscriptions at that time. However, preferred DNS server for that subscription at that time. If a client
the client device MUST respect the DNS TTL values on records it already has a DSO session with that DNS server the client SHOULD
receives, and store them in its local cache with this lifetime. This reuse that existing DSO session for the new subscription, otherwise,
a new DSO session is established. The client MUST respect the DNS
TTL values on records it receives while performing the discovery
process and store them in its local cache with this lifetime (as it
will generally be do anyway for all DNS queries it performs). This
means that, as long as the DNS TTL values on the authoritative means that, as long as the DNS TTL values on the authoritative
records are set to reasonable values, repeated application of this records are set to reasonable values, repeated application of the
discovery process can be completed nearly instantaneously by the discovery process can be completed nearly instantaneously by the
client, using only locally-stored cached data. client, using only locally-stored cached data.
6.2. DNS Push Notification SUBSCRIBE 6.2. DNS Push Notification SUBSCRIBE
After connecting, and requesting a longer idle timeout and/or After connecting, and requesting a longer idle timeout and/or
keepalive interval if necessary, a DNS Push Notification client keepalive interval if necessary, a DNS Push Notification client
then indicates its desire to receive DNS Push Notifications for then indicates its desire to receive DNS Push Notifications for
a given domain name by sending a SUBSCRIBE request to the server. a given domain name by sending a SUBSCRIBE request to the server.
A SUBSCRIBE request is encoded in a DSO message [RFC8490]. A SUBSCRIBE request is encoded in a DSO message [RFC8490].
skipping to change at page 13, line 25 skipping to change at page 13, line 25
DSO messages with the SUBSCRIBE TLV as the Primary TLV are permitted DSO messages with the SUBSCRIBE TLV as the Primary TLV are permitted
in TLS early data, provided that the precautions described in in TLS early data, provided that the precautions described in
Section 7.3 are followed. Section 7.3 are followed.
The entity that initiates a SUBSCRIBE request is by definition the The entity that initiates a SUBSCRIBE request is by definition the
client. A server MUST NOT send a SUBSCRIBE request over an existing client. A server MUST NOT send a SUBSCRIBE request over an existing
session from a client. If a server does send a SUBSCRIBE request session from a client. If a server does send a SUBSCRIBE request
over a DSO session initiated by a client, this is a fatal error and over a DSO session initiated by a client, this is a fatal error and
the client MUST forcibly abort the connection immediately. the client MUST forcibly abort the connection immediately.
Each SUBSCRIBE request generates exactly one SUBSCRIBE response from
the server. The entity that initiates a SUBSCRIBE response is by
definition the server. A client MUST NOT send a SUBSCRIBE response.
If a client does send a SUBSCRIBE response, this is a fatal error and
the server MUST forcibly abort the connection immediately.
6.2.1. SUBSCRIBE Request 6.2.1. SUBSCRIBE Request
A SUBSCRIBE request begins with the standard DSO 12-byte header A SUBSCRIBE request begins with the standard DSO 12-byte header
[RFC8490], followed by the SUBSCRIBE primary TLV. A SUBSCRIBE [RFC8490], followed by the SUBSCRIBE primary TLV. A SUBSCRIBE
request message is illustrated in Figure 1. request is illustrated in Figure 1.
The MESSAGE ID field MUST be set to a unique value, that the client The MESSAGE ID field MUST be set to a unique value, that the client
is not using for any other active operation on this DSO session. For is not using for any other active operation on this DSO session. For
the purposes here, a MESSAGE ID is in use on this session if the the purposes here, a MESSAGE ID is in use on this session if the
client has used it in a request for which it has not yet received a client has used it in a request for which it has not yet received a
response, or if the client has used it for a subscription which it response, or if the client has used it for a subscription which it
has not yet cancelled using UNSUBSCRIBE. In the SUBSCRIBE response has not yet cancelled using UNSUBSCRIBE. In the SUBSCRIBE response
the server MUST echo back the MESSAGE ID value unchanged. the server MUST echo back the MESSAGE ID value unchanged.
The other header fields MUST be set as described in the DSO spec- The other header fields MUST be set as described in the DSO spec-
ification [RFC8490]. The DNS OPCODE field contains the OPCODE value ification [RFC8490]. The DNS OPCODE field contains the OPCODE value
for DNS Stateful Operations (6). The four count fields MUST be zero, for DNS Stateful Operations (6). The four count fields must be zero,
and the corresponding four sections MUST be empty (i.e., absent). and the corresponding four sections must be empty (i.e., absent).
The DSO-TYPE is SUBSCRIBE (tentatively 0x40). The DSO-TYPE is SUBSCRIBE (tentatively 0x40).
The DSO-LENGTH is the length of the DSO-DATA that follows, which The DSO-LENGTH is the length of the DSO-DATA that follows, which
specifies the name, type, and class of the record(s) being sought. specifies the name, type, and class of the record(s) being sought.
1 1 1 1 1 1 1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \
| MESSAGE ID | \ | MESSAGE ID | \
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
|QR| OPCODE(6) | Z | RCODE | | |QR| OPCODE(6) | Z | RCODE | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| QDCOUNT (MUST BE ZERO) | | | QDCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > HEADER +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > HEADER
| ANCOUNT (MUST BE ZERO) | | | ANCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| NSCOUNT (MUST BE ZERO) | | | NSCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| ARCOUNT (MUST BE ZERO) | / | ARCOUNT (MUST BE ZERO) | /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ / +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /
| DSO-TYPE = SUBSCRIBE (tentatively 0x40) | | DSO-TYPE = SUBSCRIBE (tentatively 0x40) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| DSO-LENGTH (number of octets in DSO-DATA) | | DSO-LENGTH (number of octets in DSO-DATA) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \
| | \ \ NAME \ \
\ NAME \ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
\ \ | | TYPE | > DSO-DATA
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > DSO-DATA +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| TYPE | | | CLASS | /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /
| CLASS | /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /
Figure 1: SUBSCRIBE Request Figure 1: SUBSCRIBE Request
The DSO-DATA for a SUBSCRIBE request MUST contain exactly one NAME, The DSO-DATA for a SUBSCRIBE request MUST contain exactly one NAME,
TYPE, and CLASS. Since SUBSCRIBE requests are sent over TCP, TYPE, and CLASS. Since SUBSCRIBE requests are sent over TCP,
multiple SUBSCRIBE DSO request messages can be concatenated in a multiple SUBSCRIBE DSO request messages can be concatenated in a
single TCP stream and packed efficiently into TCP segments. single TCP stream and packed efficiently into TCP segments.
If accepted, the subscription will stay in effect until the client If accepted, the subscription will stay in effect until the client
cancels the subscription using UNSUBSCRIBE or until the DSO session cancels the subscription using UNSUBSCRIBE or until the DSO session
between the client and the server is closed. between the client and the server is closed.
SUBSCRIBE requests on a given session MUST be unique. A client MUST SUBSCRIBE requests on a given session MUST be unique. A client MUST
NOT send a SUBSCRIBE message that duplicates the NAME, TYPE and CLASS NOT send a SUBSCRIBE message that duplicates the NAME, TYPE and CLASS
of an existing active subscription on that DSO session. For the of an existing active subscription on that DSO session. For the
purpose of this matching, the established DNS case-insensitivity for purpose of this matching, the established DNS case-insensitivity for
US-ASCII letters applies (e.g., "example.com" and "Example.com" are US-ASCII letters [RFC0020] applies (e.g., "example.com" and
the same). If a server receives such a duplicate SUBSCRIBE message, "Example.com" are the same). If a server receives such a duplicate
this is a fatal error and the server MUST forcibly abort the SUBSCRIBE message, this is a fatal error and the server MUST forcibly
connection immediately. abort the connection immediately.
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 no other records matches only a literal CNAME record in the zone, and no other records
with the same owner name. with the same owner name.
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
skipping to change at page 16, line 7 skipping to change at page 16, line 7
people sometimes imagine. people sometimes imagine.
When used in conjunction with SUBSCRIBE, TYPE and CLASS 255 should be When used in conjunction with SUBSCRIBE, TYPE and CLASS 255 should be
interpreted to mean "ALL", not "ANY". After accepting a subscription interpreted to mean "ALL", not "ANY". After accepting a subscription
where one or both of TYPE or CLASS are 255, the server MUST send Push where one or both of TYPE or CLASS are 255, the server MUST send Push
Notification Updates for ALL record changes that match the Notification Updates for ALL record changes that match the
subscription, not just some of them. subscription, not just some of them.
6.2.2. SUBSCRIBE Response 6.2.2. SUBSCRIBE Response
Each SUBSCRIBE request generates exactly one SUBSCRIBE response from
the server.
A SUBSCRIBE response begins with the standard DSO 12-byte header A SUBSCRIBE response begins with the standard DSO 12-byte header
[RFC8490]. The QR bit in the header is set indicating it is a [RFC8490]. The QR bit in the header is set indicating it is a
response. The header MAY be followed by one or more optional TLVs, response. The header MAY be followed by one or more optional TLVs,
such as a Retry Delay TLV. such as a Retry Delay TLV. A SUBSCRIBE response is illustrated in
Figure 2.
The MESSAGE ID field MUST echo the value given in the MESSAGE ID The MESSAGE ID field MUST echo the value given in the MESSAGE ID
field of the SUBSCRIBE request. This is how the client knows which field of the SUBSCRIBE request. This is how the client knows which
request is being responded to. request is being responded to.
The other header fields MUST be set as described in the DSO spec-
ification [RFC8490]. The DNS OPCODE field contains the OPCODE value
for DNS Stateful Operations (6). The four count fields must be zero,
and the corresponding four sections must be empty (i.e., absent).
A SUBSCRIBE response message MUST NOT include a SUBSCRIBE TLV. If a A SUBSCRIBE response message MUST NOT include a SUBSCRIBE TLV. If a
client receives a SUBSCRIBE response message containing a SUBSCRIBE client receives a SUBSCRIBE response message containing a SUBSCRIBE
TLV then the response message is processed but the SUBSCRIBE TLV MUST TLV then the response message is processed but the SUBSCRIBE TLV MUST
be silently ignored. be silently ignored.
A client MUST NOT send a SUBSCRIBE response. If a client does send a
SUBSCRIBE message, with the QR bit set indicating that it is a
response, this is a fatal error and the server MUST forcibly abort
the connection immediately.
1 1 1 1 1 1 1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \
| MESSAGE ID | \ | MESSAGE ID | \
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
|QR| OPCODE(6) | Z | RCODE | | |QR| OPCODE(6) | Z | RCODE | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| QDCOUNT (MUST BE ZERO) | | | QDCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > HEADER +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > HEADER
| ANCOUNT (MUST BE ZERO) | | | ANCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| NSCOUNT (MUST BE ZERO) | | | NSCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| ARCOUNT (MUST BE ZERO) | / | ARCOUNT (MUST BE ZERO) | /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ / +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /
Figure 2: SUBSCRIBE Response Message Figure 2: SUBSCRIBE Response
In the SUBSCRIBE response the RCODE indicates whether or not the In the SUBSCRIBE response the RCODE indicates whether or not the
subscription was accepted. Supported RCODEs are as follows: subscription was accepted. Supported RCODEs are as follows:
+-----------+-------+-----------------------------------------------+ +-----------+-------+-----------------------------------------------+
| Mnemonic | Value | Description | | Mnemonic | Value | Description |
+-----------+-------+-----------------------------------------------+ +-----------+-------+-----------------------------------------------+
| NOERROR | 0 | SUBSCRIBE successful. | | NOERROR | 0 | SUBSCRIBE successful. |
| FORMERR | 1 | Server failed to process request due to a | | FORMERR | 1 | Server failed to process request due to a |
| | | malformed request. | | | | malformed request. |
skipping to change at page 17, line 37 skipping to change at page 17, line 37
Responses. Servers sending SUBSCRIBE Responses SHOULD use one of Responses. Servers sending SUBSCRIBE Responses SHOULD use one of
these values. Note that NXDOMAIN is not a valid RCODE in response to these values. Note that NXDOMAIN is not a valid RCODE in response to
a SUBSCRIBE Request. However, future circumstances may create a SUBSCRIBE Request. However, future circumstances may create
situations where other RCODE values are appropriate in SUBSCRIBE situations where other RCODE values are appropriate in SUBSCRIBE
Responses, so clients MUST be prepared to accept SUBSCRIBE Responses Responses, so clients MUST be prepared to accept SUBSCRIBE Responses
with any other RCODE value. with any other RCODE value.
If the server sends a nonzero RCODE in the SUBSCRIBE response, that If the server sends a nonzero RCODE in the SUBSCRIBE response, that
means: means:
a. the client is (at least partially) misconfigured, a. the client is (at least partially) misconfigured, or
b. the server resources are exhausted, or b. the server resources are exhausted, or
c. there is some other unknown failure on the server. c. there is some other unknown failure on the server.
In any case, the client shouldn't retry the subscription to this In any case, the client shouldn't retry the subscription to this
server right away. If multiple SRV records were returned as server right away. If multiple SRV records were returned as
described in Section 6.1, Paragraph 7, a subsequent server can be described in Section 6.1, Paragraph 7, a subsequent server MAY be
tried immediately. tried immediately.
If the client has other successful subscriptions to this server, If the client has other successful subscriptions to this server,
these subscriptions remain even though additional subscriptions may these subscriptions remain even though additional subscriptions may
be refused. Neither the client nor the server are required to close be refused. Neither the client nor the server are required to close
the connection, although, either end may choose to do so. the connection, although, either end may choose to do so.
If the server sends a nonzero RCODE then it SHOULD append a Retry If the server sends a nonzero RCODE then it SHOULD append a Retry
Delay TLV [RFC8490] to the response specifying a delay before the Delay TLV [RFC8490] to the response specifying a delay before the
client attempts this operation again. Recommended values for the client attempts this operation again. Recommended values for the
skipping to change at page 20, line 15 skipping to change at page 20, line 15
6.3. DNS Push Notification Updates 6.3. DNS Push Notification Updates
Once a subscription has been successfully established, the server Once a subscription has been successfully established, the server
generates PUSH messages to send to the client as appropriate. In the generates PUSH messages to send to the client as appropriate. In the
case that the answer set was already non-empty at the moment the case that the answer set was already non-empty at the moment the
subscription was established, an initial PUSH message will be sent subscription was established, an initial PUSH message will be sent
immediately following the SUBSCRIBE Response. Subsequent changes to immediately following the SUBSCRIBE Response. Subsequent changes to
the answer set are then communicated to the client in subsequent PUSH the answer set are then communicated to the client in subsequent PUSH
messages. messages.
A client MUST NOT send a PUSH message. If a client does send a PUSH
message, or a PUSH message is sent with the QR bit set indicating
that it is a response, this is a fatal error and the receiver MUST
forcibly abort the connection immediately.
6.3.1. PUSH Message 6.3.1. PUSH Message
A PUSH unidirectional message begins with the standard DSO 12-byte A PUSH unidirectional message begins with the standard DSO 12-byte
header [RFC8490], followed by the PUSH primary TLV. A PUSH message header [RFC8490], followed by the PUSH primary TLV. A PUSH message
is illustrated in Figure 3. is illustrated in Figure 3.
In accordance with the definition of DSO unidirectional messages, the In accordance with the definition of DSO unidirectional messages, the
MESSAGE ID field MUST be zero. There is no client response to a PUSH MESSAGE ID field MUST be zero. There is no client response to a PUSH
message. message.
The other header fields MUST be set as described in the DSO spec- The other header fields MUST be set as described in the DSO spec-
ification [RFC8490]. The DNS OPCODE field contains the OPCODE value ification [RFC8490]. The DNS OPCODE field contains the OPCODE value
for DNS Stateful Operations (6). The four count fields MUST be zero, for DNS Stateful Operations (6). The four count fields must be zero,
and the corresponding four sections MUST be empty (i.e., absent). and the corresponding four sections must be empty (i.e., absent).
A client MUST NOT send a PUSH message. If a client does send a PUSH
message, or a PUSH message is sent with the QR bit set indicating
that it is a response, this is a fatal error and the receiver MUST
forcibly abort the connection immediately.
The DSO-TYPE is PUSH (tentatively 0x41). The DSO-TYPE is PUSH (tentatively 0x41).
The DSO-LENGTH is the length of the DSO-DATA that follows, which The DSO-LENGTH is the length of the DSO-DATA that follows, which
specifies the changes being communicated. specifies the changes being communicated.
The DSO-DATA contains one or more change notifications. A PUSH The DSO-DATA contains one or more change notifications. A PUSH
Message MUST contain at least one change notification. If a PUSH Message MUST contain at least one change notification. If a PUSH
Message is received that contains no change notifications, this is a Message is received that contains no change notifications, this is a
fatal error, and the client MUST forcibly abort the connection fatal error, and the client MUST forcibly abort the connection
immediately. immediately.
The change notification records are formatted similarly to how DNS The change notification records are formatted similarly to how DNS
Resource Records are conventionally expressed in DNS messages, as Resource Records are conventionally expressed in DNS messages, as
illustrated in Figure 3, and are interpreted as described below. illustrated in Figure 3, and are interpreted as described below.
The TTL field holds an unsigned 32-bit integer [RFC2181]. If the TTL The TTL field holds an unsigned 32-bit integer [RFC2181]. If the TTL
is in the range 0 to 2,147,483,647 seconds (2^31 - 1, or 0x7FFFFFFF), is in the range 0 to 2,147,483,647 seconds (0 to 2^31 - 1, or
then a new DNS Resource Record with the given name, type, class and 0x7FFFFFFF), then a new DNS Resource Record with the given name,
RDATA is added. A TTL of 0 means that this record should be retained type, class and RDATA is added. Type and class MUST NOT be 255
for as long as the subscription is active, and should be discarded (ANY). If either type or class are 255 (ANY) this is a fatal error,
immediately the moment the subscription is cancelled. and the client MUST forcibly abort the connection immediately. A TTL
of 0 means that this record should be retained for as long as the
subscription is active, and should be discarded immediately the
moment the subscription is cancelled.
If the TTL has the value 0xFFFFFFFF, then the DNS Resource Record If the TTL has the value 0xFFFFFFFF, then the DNS Resource Record
with the given name, type, class and RDATA is removed. with the given name, type, class and RDATA is removed. Type and
class MUST NOT be 255 (ANY). If either type or class are 255 (ANY)
this is a fatal error, and the client MUST forcibly abort the
connection immediately.
If the TTL has the value 0xFFFFFFFE, then this is a 'collective' If the TTL has the value 0xFFFFFFFE, then this is a 'collective'
remove notification. For collective remove notifications RDLEN MUST remove notification. For collective remove notifications RDLEN MUST
be zero and consequently the RDATA MUST be empty. If a change be zero and consequently the RDATA MUST be empty. If a change
notification is received where TTL = 0xFFFFFFFE and RDLEN is not notification is received where TTL = 0xFFFFFFFE and RDLEN is not
zero, this is a fatal error, and the client MUST forcibly abort the zero, this is a fatal error, and the client MUST forcibly abort the
connection immediately. connection immediately.
There are three types of collective remove notification: There are three types of collective remove notification:
For collective remove notifications, if CLASS is not 255 (ANY) and For collective remove notifications, if CLASS is not 255 (ANY) and
TYPE is not 255 (ANY) then for the given name this deletes all TYPE is not 255 (ANY) then for the given name this removes all
records of the specified type in the specified class. records of the specified type in the specified class.
For collective remove notifications, if CLASS is not 255 (ANY) and For collective remove notifications, if CLASS is not 255 (ANY) and
TYPE is 255 (ANY) then for the given name this deletes all records of TYPE is 255 (ANY) then for the given name this removes all records of
all types in the specified class. all types in the specified class.
For collective remove notifications, if CLASS is 255 (ANY), then for For collective remove notifications, if CLASS is 255 (ANY), then for
the given name this deletes all records of all types in all classes. the given name this removes all records of all types in all classes.
In this case TYPE MUST be set to zero on transmission, and MUST be In this case TYPE MUST be set to zero on transmission, and MUST be
silently ignored on reception. silently ignored on reception.
Summary of change notification types: Summary of change notification types:
Delete all RRsets from a name, in all classes Remove all RRsets from a name, in all classes
TTL = 0xFFFFFFFE, RDLEN = 0, CLASS = 255 (ANY) TTL = 0xFFFFFFFE, RDLEN = 0, CLASS = 255 (ANY)
Delete all RRsets from a name, in given class: Remove all RRsets from a name, in given class:
TTL = 0xFFFFFFFE, RDLEN = 0, CLASS gives class, TYPE = 255 (ANY) TTL = 0xFFFFFFFE, RDLEN = 0, CLASS gives class, TYPE = 255 (ANY)
Delete specified RRset from a name, in given class: Remove specified RRset from a name, in given class:
TTL = 0xFFFFFFFE, RDLEN = 0 TTL = 0xFFFFFFFE, RDLEN = 0
CLASS and TYPE specify the RRset being deleted CLASS and TYPE specify the RRset being removed
Delete an individual RR from a name: Remove an individual RR from a name:
TTL = 0xFFFFFFFF TTL = 0xFFFFFFFF
CLASS, TYPE, RDLEN and RDATA specify the RR being deleted. CLASS, TYPE, RDLEN and RDATA specify the RR being removed
Add individual RR to a name Add individual RR to a name
TTL >= 0 and TTL <= 0x7FFFFFFF TTL >= 0 and TTL <= 0x7FFFFFFF
CLASS, TYPE, RDLEN, RDATA and TTL specify the RR being added. CLASS, TYPE, RDLEN, RDATA and TTL specify the RR being added
Note that it is valid for the RDATA of an added or removed DNS Note that it is valid for the RDATA of an added or removed DNS
Resource Record to be empty (zero length). For example, an Address Resource Record to be empty (zero length). For example, an Address
Prefix List Resource Record [RFC3123] may have empty RDATA. Prefix List Resource Record [RFC3123] may have empty RDATA.
Therefore, a change notification with RDLEN = 0 does not Therefore, a change notification with RDLEN = 0 does not
automatically indicate a remove notification. If RDLEN = 0 and TTL automatically indicate a remove notification. If RDLEN = 0 and TTL
is the in the range 0 - 0x7FFFFFFF, this change notification signals is the in the range 0 - 0x7FFFFFFF, this change notification signals
the addition of a record with the given name, type, class, and empty the addition of a record with the given name, type, class, and empty
RDATA. If RDLEN = 0 and TTL = 0xFFFFFFFF, this change notification RDATA. If RDLEN = 0 and TTL = 0xFFFFFFFF, this change notification
signals the removal specifically of that single record with the given signals the removal specifically of that single record with the given
skipping to change at page 23, line 9 skipping to change at page 24, line 5
DNS message length of 16,382 bytes, the change notifications MUST be DNS message length of 16,382 bytes, the change notifications MUST be
communicated in separate PUSH messages of up to 16,382 bytes each. communicated in separate PUSH messages of up to 16,382 bytes each.
DNS name compression becomes less effective for messages larger than DNS name compression becomes less effective for messages larger than
16,384 bytes, so little efficiency benefit is gained by sending 16,384 bytes, so little efficiency benefit is gained by sending
messages larger than this. messages larger than this.
If a client receives a PUSH message with a DNS message length larger If a client receives a PUSH message with a DNS message length larger
than 16,382 bytes, this is a fatal error, and the client MUST than 16,382 bytes, this is a fatal error, and the client MUST
forcibly abort the connection immediately. forcibly abort the connection immediately.
1 1 1 1 1 1 1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \
| MESSAGE ID (MUST BE ZERO) | \ | MESSAGE ID (MUST BE ZERO) | \
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
|QR| OPCODE(6) | Z | RCODE | | |QR| OPCODE(6) | Z | RCODE | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| QDCOUNT (MUST BE ZERO) | | | QDCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > HEADER +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > HEADER
| ANCOUNT (MUST BE ZERO) | | | ANCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| NSCOUNT (MUST BE ZERO) | | | NSCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| ARCOUNT (MUST BE ZERO) | / | ARCOUNT (MUST BE ZERO) | /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ / +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /
| DSO-TYPE = PUSH (tentatively 0x41) | | DSO-TYPE = PUSH (tentatively 0x41) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| DSO-LENGTH (number of octets in DSO-DATA) | | DSO-LENGTH (number of octets in DSO-DATA) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \
\ NAME \ \ \ NAME \ \
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| TYPE | | | TYPE | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| CLASS | | | CLASS | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| TTL | | | TTL | |
| (32-bit unsigned big-endian integer) | > DSO-DATA | (32-bit unsigned big-endian integer) | > DSO-DATA
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| RDLEN (16-bit unsigned big-endian integer) | | | RDLEN (16-bit unsigned big-endian integer) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
\ RDATA (sized as necessary) \ | \ RDATA (sized as necessary) \ |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
: NAME, TYPE, CLASS, TTL, RDLEN, RDATA : | : NAME, TYPE, CLASS, TTL, RDLEN, RDATA : |
: Repeated As Necessary : / : Repeated As Necessary : /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ / +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /
Figure 3: PUSH Message Figure 3: PUSH Message
When processing the records received in a PUSH Message, the receiving When processing the records received in a PUSH Message, the receiving
client MUST validate that the records being added or deleted client MUST validate that the records being added or removed
correspond with at least one currently active subscription on that correspond with at least one currently active subscription on that
session. Specifically, the record name MUST match the name given in session. Specifically, the record name MUST match the name given in
a SUBSCRIBE request, subject to the usual established DNS case- the SUBSCRIBE request, subject to the usual established DNS case-
insensitivity for US-ASCII letters. If the TYPE in the SUBSCRIBE insensitivity for US-ASCII letters. For individual additions and
request was not ANY (255) then the TYPE of the record must match the removals, if the TYPE in the SUBSCRIBE request was not ANY (255) then
TYPE given in the SUBSCRIBE request. If the CLASS in the SUBSCRIBE the TYPE of the record must match the TYPE given in the SUBSCRIBE
request was not ANY (255) then the CLASS of the record must match the request, and if the CLASS in the SUBSCRIBE request was not ANY (255)
CLASS given in the SUBSCRIBE request. If a matching active then the CLASS of the record must match the CLASS given in the
subscription on that session is not found, then that individual SUBSCRIBE request. For collective removals, at least one of the
record addition/deletion is silently ignored. Processing of other records being removed must match an active subscription. If a
additions and deletions in this message is not affected. The DSO matching active subscription on that session is not found, then that
session is not closed. This is to allow for the unavoidable race particular addition/removal record is silently ignored. Processing
condition where a client sends an outbound UNSUBSCRIBE while inbound of other additions and removal records in this message is not
PUSH messages for that subscription from the server are still in affected. The DSO session is not closed. This is to allow for the
flight. unavoidable race condition where a client sends an outbound
UNSUBSCRIBE while inbound PUSH messages for that subscription from
the server are still in flight.
In the case where a single change affects more than one active In the case where a single change affects more than one active
subscription, only one PUSH message is sent. For example, a PUSH subscription, only one PUSH message is sent. For example, a PUSH
message adding a given record may match both a SUBSCRIBE request with message adding a given record may match both a SUBSCRIBE request with
the same TYPE and a different SUBSCRIBE request with TYPE = 255 the same TYPE and a different SUBSCRIBE request with TYPE = 255
(ANY). It is not the case that two PUSH messages are sent because (ANY). It is not the case that two PUSH messages are sent because
the new record matches two active subscriptions. the new 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 removed
from a given name, and no other AAAA records exist for that name, the from a given name, and no other AAAA records exist for that name, the
server SHOULD send a "delete an RRset from a name" PUSH message, not server SHOULD send a "remove an RRset from a name" PUSH message, not
three separate "delete an individual RR from a name" PUSH messages. three separate "remove an individual RR from a name" PUSH messages.
Similarly, when both an SRV and a TXT record are deleted from a given Similarly, when both an SRV and a TXT record are removed from a given
name, and no other records of any kind exist for that name, the name, and no other records of any kind exist for that name, the
server SHOULD send a "delete all RRsets from a name" PUSH message, server SHOULD send a "remove all RRsets from a name" PUSH message,
not two separate "delete an RRset from a name" PUSH messages. not two separate "remove an RRset from a name" PUSH messages.
A server SHOULD combine multiple change notifications in a single A server SHOULD combine multiple change notifications in a single
PUSH message when possible, even if those change notifications apply PUSH message when possible, even if those change notifications apply
to different subscriptions. Conceptually, a PUSH message is a to different subscriptions. Conceptually, a PUSH message is a
session-level mechanism, not a subscription-level mechanism. session-level mechanism, not a subscription-level mechanism.
The TTL of an added record is stored by the client. While the The TTL of an added record is stored by the client. While the
subscription is active, the TTL is not decremented, because a change subscription is active, the TTL is not decremented, because a change
to the TTL would produce a new update. For as long as a relevant to the TTL would produce a new update. For as long as a relevant
subscription remains active, the client SHOULD assume that when a subscription remains active, the client SHOULD assume that when a
skipping to change at page 25, line 9 skipping to change at page 26, line 9
Consequently, a client does not have to poll to verify that the Consequently, a client does not have to poll to verify that the
record is still there. Once a subscription is cancelled record is still there. Once a subscription is cancelled
(individually, or as a result of the DSO session being closed) record (individually, or as a result of the DSO session being closed) record
aging for records covered by the subscription resumes and records are aging for records covered by the subscription resumes and records are
removed from the local cache when their TTL reaches zero. removed from the local cache when their TTL reaches zero.
6.4. DNS Push Notification UNSUBSCRIBE 6.4. DNS Push Notification UNSUBSCRIBE
To cancel an individual subscription without closing the entire DSO To cancel an individual subscription without closing the entire DSO
session, the client sends an UNSUBSCRIBE message over the established session, the client sends an UNSUBSCRIBE message over the established
DSO session to the server. The UNSUBSCRIBE message is encoded as a DSO session to the server.
DSO unidirectional message [RFC8490]. This specification defines a
primary unidirectional DSO TLV for DNS Push Notification UNSUBSCRIBE
Messages (tentatively DSO Type Code 0x42).
A server MUST NOT send an UNSUBSCRIBE message. If a server does send The entity that initiates an UNSUBSCRIBE message is by definition the
an UNSUBSCRIBE message over a DSO session initiated by a client, or client. A server MUST NOT send an UNSUBSCRIBE message over an
an UNSUBSCRIBE message is sent with the QR bit set indicating that it existing session from a client. If a server does send an UNSUBSCRIBE
is a response, this is a fatal error and the receiver MUST forcibly message over a DSO session initiated by a client, or an UNSUBSCRIBE
abort the connection immediately. message is sent with the QR bit set indicating that it is a response,
this is a fatal error and the receiver MUST forcibly abort the
connection immediately.
6.4.1. UNSUBSCRIBE Message 6.4.1. UNSUBSCRIBE Message
An UNSUBSCRIBE unidirectional message begins with the standard DSO An UNSUBSCRIBE unidirectional message begins with the standard DSO
12-byte header [RFC8490], followed by the UNSUBSCRIBE primary TLV. 12-byte header [RFC8490], followed by the UNSUBSCRIBE primary TLV.
An UNSUBSCRIBE message is illustrated in Figure 4. An UNSUBSCRIBE message is illustrated in Figure 4.
In accordance with the definition of DSO unidirectional messages, the In accordance with the definition of DSO unidirectional messages, the
MESSAGE ID field MUST be zero. There is no server response to an MESSAGE ID field MUST be zero. There is no server response to an
UNSUBSCRIBE message. UNSUBSCRIBE message.
The other header fields MUST be set as described in the DSO spec- The other header fields MUST be set as described in the DSO spec-
ification [RFC8490]. The DNS OPCODE field contains the OPCODE value ification [RFC8490]. The DNS OPCODE field contains the OPCODE value
for DNS Stateful Operations (6). The four count fields MUST be zero, for DNS Stateful Operations (6). The four count fields must be zero,
and the corresponding four sections MUST be empty (i.e., absent). and the corresponding four sections must be empty (i.e., absent).
The DSO-TYPE is UNSUBSCRIBE (tentatively 0x42). The DSO-TYPE is UNSUBSCRIBE (tentatively 0x42).
The DSO-LENGTH field contains the value 2, the length of the 2-octet The DSO-LENGTH field contains the value 2, the length of the 2-octet
MESSAGE ID contained in the DSO-DATA. MESSAGE ID contained in the DSO-DATA.
The DSO-DATA contains the value given in the MESSAGE ID field of an The DSO-DATA contains the value previously given in the MESSAGE ID
active SUBSCRIBE request. This is how the server knows which field of an active SUBSCRIBE request. This is how the server knows
SUBSCRIBE request is being cancelled. After receipt of the which SUBSCRIBE request is being cancelled. After receipt of the
UNSUBSCRIBE message, the SUBSCRIBE request is no longer active. UNSUBSCRIBE message, the SUBSCRIBE request is no longer active.
It is allowable for the client to issue an UNSUBSCRIBE message for a It is allowable for the client to issue an UNSUBSCRIBE message for a
previous SUBSCRIBE request for which the client has not yet received previous SUBSCRIBE request for which the client has not yet received
a SUBSCRIBE response. This is to allow for the case where a client a SUBSCRIBE response. This is to allow for the case where a client
starts and stops a subscription in less than the round-trip time to starts and stops a subscription in less than the round-trip time to
the server. The client is NOT required to wait for the SUBSCRIBE the server. The client is NOT required to wait for the SUBSCRIBE
response before issuing the UNSUBSCRIBE message. response before issuing the UNSUBSCRIBE message.
Consequently, it is possible for a server to receive an UNSUBSCRIBE Consequently, it is possible for a server to receive an UNSUBSCRIBE
skipping to change at page 27, line 17 skipping to change at page 28, line 17
Sometimes, particularly when used with a Discovery Proxy [DisProx], a Sometimes, particularly when used with a Discovery Proxy [DisProx], a
DNS Zone may contain stale data. When a client encounters data that DNS Zone may contain stale data. When a client encounters data that
it believes may be stale (e.g., an SRV record referencing a target it believes may be stale (e.g., an SRV record referencing a target
host+port that is not responding to connection requests) the client host+port that is not responding to connection requests) the client
can send a RECONFIRM message to ask the server to re-verify that the can send a RECONFIRM message to ask the server to re-verify that the
data is still valid. For a Discovery Proxy, this causes it to issue data is still valid. For a Discovery Proxy, this causes it to issue
new Multicast DNS queries to ascertain whether the target device is new Multicast DNS queries to ascertain whether the target device is
still present. How the Discovery Proxy causes these new Multicast still present. How the Discovery Proxy causes these new Multicast
DNS queries to be issued depends on the details of the underlying DNS queries to be issued depends on the details of the underlying
Multicast DNS implementation being used. For example, a Discovery Multicast DNS implementation being used. For example, a Discovery
Proxy built on Apple's dns_sd.h API responds to a DNS Push Proxy built on Apple's dns_sd.h API [SD-API] responds to a DNS Push
Notification RECONFIRM message by calling the underlying API's Notification RECONFIRM message by calling the underlying API's
DNSServiceReconfirmRecord() routine. DNSServiceReconfirmRecord() routine.
For other types of DNS server, the RECONFIRM operation is currently For other types of DNS server, the RECONFIRM operation is currently
undefined, and SHOULD result in a NOERROR response, but otherwise undefined, and SHOULD result in a NOERROR response, but otherwise
need not cause any action to occur. need not cause any action to occur.
Frequent use of RECONFIRM operations may be a sign of network Frequent use of RECONFIRM operations may be a sign of network
unreliability, or some kind of misconfiguration, so RECONFIRM unreliability, or some kind of misconfiguration, so RECONFIRM
operations MAY be logged or otherwise communicated to a human operations MAY be logged or otherwise communicated to a human
skipping to change at page 27, line 39 skipping to change at page 28, line 39
problems. problems.
If, after receiving a valid RECONFIRM message, the server determines If, after receiving a valid RECONFIRM message, the server determines
that the disputed records are in fact no longer valid, then that the disputed records are in fact no longer valid, then
subsequent DNS PUSH Messages will be generated to inform interested subsequent DNS PUSH Messages will be generated to inform interested
clients. Thus, one client discovering that a previously-advertised clients. Thus, one client discovering that a previously-advertised
device (like a network printer) is no longer present has the side device (like a network printer) is no longer present has the side
effect of informing all other interested clients that the device in effect of informing all other interested clients that the device in
question is now gone. question is now gone.
A server MUST NOT send a RECONFIRM message. If a server does send a The entity that initiates a RECONFIRM message is by definition the
RECONFIRM message over a DSO session initiated by a client, or a client. A server MUST NOT send a RECONFIRM message over an existing
RECONFIRM message is sent with the QR bit set indicating that it is a session from a client. If a server does send a RECONFIRM message
response, this is a fatal error and the receiver MUST forcibly abort over a DSO session initiated by a client, or a RECONFIRM message is
the connection immediately. sent with the QR bit set indicating that it is a response, this is a
fatal error and the receiver MUST forcibly abort the connection
immediately.
6.5.1. RECONFIRM Message 6.5.1. RECONFIRM Message
A RECONFIRM unidirectional message begins with the standard DSO A RECONFIRM unidirectional message begins with the standard DSO
12-byte header [RFC8490], followed by the RECONFIRM primary TLV. 12-byte header [RFC8490], followed by the RECONFIRM primary TLV.
A RECONFIRM message is illustrated in Figure 5. A RECONFIRM message is illustrated in Figure 5.
In accordance with the definition of DSO unidirectional messages, the In accordance with the definition of DSO unidirectional messages, the
MESSAGE ID field MUST be zero. There is no server response to a MESSAGE ID field MUST be zero. There is no server response to a
RECONFIRM message. RECONFIRM message.
The other header fields MUST be set as described in the DSO spec- The other header fields MUST be set as described in the DSO spec-
ification [RFC8490]. The DNS OPCODE field contains the OPCODE value ification [RFC8490]. The DNS OPCODE field contains the OPCODE value
for DNS Stateful Operations (6). The four count fields MUST be zero, for DNS Stateful Operations (6). The four count fields must be zero,
and the corresponding four sections MUST be empty (i.e., absent). and the corresponding four sections must be empty (i.e., absent).
The DSO-TYPE is RECONFIRM (tentatively 0x43). The DSO-TYPE is RECONFIRM (tentatively 0x43).
The DSO-LENGTH is the length of the data that follows, which The DSO-LENGTH is the length of the data that follows, which
specifies the name, type, class, and content of the record being specifies the name, type, class, and content of the record being
disputed. disputed.
The DSO-DATA for a RECONFIRM message MUST contain exactly one record. The DSO-DATA for a RECONFIRM message MUST contain exactly one record.
The DSO-DATA for a RECONFIRM message has no count field to specify The DSO-DATA for a RECONFIRM message has no count field to specify
more than one record. Since RECONFIRM messages are sent over TCP, more than one record. Since RECONFIRM messages are sent over TCP,
skipping to change at page 29, line 5 skipping to change at page 30, line 5
the zone, and nothing else. the zone, and nothing else.
Aliasing is not supported. That is, a CNAME in a RECONFIRM message Aliasing is not supported. That is, a CNAME in a RECONFIRM message
matches only a literal CNAME record in the zone, and no other records matches only a literal CNAME record in the zone, and no other records
with the same owner name. with the same owner name.
Note that there is no RDLEN field, since the length of the RDATA can Note that there is no RDLEN field, since the length of the RDATA can
be inferred from DSO-LENGTH, so an additional RDLEN field would be be inferred from DSO-LENGTH, so an additional RDLEN field would be
redundant. redundant.
1 1 1 1 1 1 1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \
| MESSAGE ID | \ | MESSAGE ID (MUST BE ZERO) | \
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
|QR| OPCODE(6) | Z | RCODE | | |QR| OPCODE(6) | Z | RCODE | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| QDCOUNT (MUST BE ZERO) | | | QDCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > HEADER +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > HEADER
| ANCOUNT (MUST BE ZERO) | | | ANCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| NSCOUNT (MUST BE ZERO) | | | NSCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| ARCOUNT (MUST BE ZERO) | / | ARCOUNT (MUST BE ZERO) | /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ / +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /
| DSO-TYPE = RECONFIRM (tentatively 0x43) | | DSO-TYPE = RECONFIRM (tentatively 0x43) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| DSO-LENGTH (number of octets in DSO-DATA) | | DSO-LENGTH (number of octets in DSO-DATA) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \
\ NAME \ \ \ NAME \ \
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| TYPE | | | TYPE | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > DSO-DATA +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > DSO-DATA
| CLASS | | | CLASS | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
\ RDATA \ / \ RDATA \ /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ / +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /
Figure 5: RECONFIRM Message Figure 5: RECONFIRM Message
6.6. DNS Stateful Operations TLV Context Summary 6.6. DNS Stateful Operations TLV Context Summary
This document defines four new DSO TLVs. As suggested in Section 8.2 This document defines four new DSO TLVs. As recommended in
of the DNS Stateful Operations specification [RFC8490], the valid Section 8.2 of the DNS Stateful Operations specification [RFC8490],
contexts of these new TLV types are summarized below. the valid contexts of these new TLV types are summarized below.
The client TLV contexts are: The client TLV contexts are:
C-P: Client request message, primary TLV C-P: Client request message, primary TLV
C-U: Client unidirectional message, primary TLV C-U: Client unidirectional message, primary TLV
C-A: Client request or unidirectional message, additional TLV C-A: Client request or unidirectional message, additional TLV
CRP: Response back to client, primary TLV CRP: Response back to client, primary TLV
CRA: Response back to client, additional TLV CRA: Response back to client, additional TLV
+-------------+-----+-----+-----+-----+-----+ +-------------+-----+-----+-----+-----+-----+
skipping to change at page 31, line 12 skipping to change at page 32, line 12
Table 3: DSO TLV Server Context Summary Table 3: DSO TLV Server Context Summary
6.7. Client-Initiated Termination 6.7. Client-Initiated Termination
An individual subscription is terminated by sending an UNSUBSCRIBE An individual subscription is terminated by sending an UNSUBSCRIBE
TLV for that specific subscription, or all subscriptions can be TLV for that specific subscription, or all subscriptions can be
cancelled at once by the client closing the DSO session. When a cancelled at once by the client closing the DSO session. When a
client terminates an individual subscription (via UNSUBSCRIBE) or all client terminates an individual subscription (via UNSUBSCRIBE) or all
subscriptions on that DSO session (by ending the session) it is subscriptions on that DSO session (by ending the session) it is
signaling to the server that it is longer interested in receiving signaling to the server that it is no longer interested in receiving
those particular updates. It is informing the server that the server those particular updates. It is informing the server that the server
may release any state information it has been keeping with regards to may release any state information it has been keeping with regards to
these particular subscriptions. these particular subscriptions.
After terminating its last subscription on a session via UNSUBSCRIBE, After terminating its last subscription on a session via UNSUBSCRIBE,
a client MAY close the session immediately, or it may keep it open if a client MAY close the session immediately, or it may keep it open if
it anticipates performing further operations on that session in the it anticipates performing further operations on that session in the
future. If a client wishes to keep an idle session open, it MUST future. If a client wishes to keep an idle session open, it MUST
respect the maximum idle time required by the server [RFC8490]. respect the maximum idle time required by the server [RFC8490].
skipping to change at page 33, line 38 skipping to change at page 34, line 38
client-server security or end-to-end security. However, client-server security or end-to-end security. However,
recommendations for security in particular deployment scenarios are recommendations for security in particular deployment scenarios are
outside the scope of this document. outside the scope of this document.
DNSSEC is RECOMMENDED for the authentication of DNS Push Notification DNSSEC is RECOMMENDED for the authentication of DNS Push Notification
servers. TLS alone does not provide complete security. TLS servers. TLS alone does not provide complete security. TLS
certificate verification can provide reasonable assurance that the certificate verification can provide reasonable assurance that the
client is really talking to the server associated with the desired client is really talking to the server associated with the desired
host name, but since the desired host name is learned via a DNS SRV host name, but since the desired host name is learned via a DNS SRV
query, if the SRV query is subverted then the client may have a query, if the SRV query is subverted then the client may have a
secure connection to a rogue server. DNSSEC can provided added secure connection to a rogue server. DNSSEC can provide added
confidence that the SRV query has not been subverted. confidence that the SRV query has not been subverted.
7.1. Security Services 7.1. Security Services
It is the goal of using TLS to provide the following security It is the goal of using TLS to provide the following security
services: services:
Confidentiality: All application-layer communication is encrypted Confidentiality: All application-layer communication is encrypted
with the goal that no party should be able to decrypt it except with the goal that no party should be able to decrypt it except
the intended receiver. the intended receiver.
Data integrity protection: Any changes made to the communication in Data integrity protection: Any changes made to the communication in
transit are detectable by the receiver. transit are detectable by the receiver.
Authentication: An end-point of the TLS communication is Authentication: An end-point of the TLS communication is
authenticated as the intended entity to communicate with. authenticated as the intended entity to communicate with.
Anti-replay protection: TLS provides for the detection of and Anti-replay protection: TLS provides for the detection of and
prevention against messages sent previously over a TLS connection prevention against messages sent previously over a TLS connection
(such as DNS Push Notifications). Prior messages cannot be re- (such as DNS Push Notifications). If prior messages are re-sent
sent at a later time as a form of a man-in-the-middle attack. at a later time as a form of a man-in-the-middle attack then the
receiver will detect this and reject the replayed messages.
Deployment recommendations on the appropriate key lengths and cypher Deployment recommendations on the appropriate key lengths and cypher
suites are beyond the scope of this document. Please refer to TLS suites are beyond the scope of this document. Please refer to TLS
Recommendations [RFC7525] for the best current practices. Keep in Recommendations [BCP195] for the best current practices. Keep in
mind that best practices only exist for a snapshot in time and mind that best practices only exist for a snapshot in time and
recommendations will continue to change. Updated versions or errata recommendations will continue to change. Updated versions or errata
may exist for these recommendations. may exist for these recommendations.
7.2. TLS Name Authentication 7.2. TLS Name Authentication
As described in Section 6.1, the client discovers the DNS Push As described in Section 6.1, the client discovers the DNS Push
Notification server using an SRV lookup for the record name Notification server using an SRV lookup for the record name
"_dns-push-tls._tcp.<zone>". The server connection endpoint SHOULD "_dns-push-tls._tcp.<zone>". The server connection endpoint SHOULD
then be authenticated using DANE TLSA records for the associated SRV then be authenticated using DANE TLSA records for the associated SRV
skipping to change at page 35, line 12 skipping to change at page 36, line 28
With TLS early data there are no guarantees of non-replay between With TLS early data there are no guarantees of non-replay between
connections. If packets are duplicated and delayed in the network, connections. If packets are duplicated and delayed in the network,
the later arrivals could be mistaken for new subscription requests. the later arrivals could be mistaken for new subscription requests.
Generally this is not a major concern, since the amount of state Generally this is not a major concern, since the amount of state
generated on the server for these spurious subscriptions is small and generated on the server for these spurious subscriptions is small and
short-lived, since the TCP connection will not complete the three-way short-lived, since the TCP connection will not complete the three-way
handshake. Servers MAY choose to implement rate-limiting measures handshake. Servers MAY choose to implement rate-limiting measures
that are activated when the server detects an excessive number of that are activated when the server detects an excessive number of
spurious subscription requests. spurious subscription requests.
For further guidance please see Section 2.3, Section 8, and For further guidance please see discussion of zero round-trip data
Appendix E.5 of the TLS 1.3 specification [RFC8446]. (Section 2.3, Section 8, and Appendix E.5) in the TLS 1.3
specification, [RFC8446].
7.4. TLS Session Resumption 7.4. TLS Session Resumption
TLS Session Resumption is permissible on DNS Push Notification TLS Session Resumption [RFC8446] is permissible on DNS Push
servers. The server may keep TLS state with Session IDs [RFC8446] or Notification servers. However, closing the TLS connection terminates
operate in stateless mode by sending a Session Ticket [RFC5077] to the DSO session. When the TLS session is resumed, the DNS Push
the client for it to store. However, closing the TLS connection Notification server will not have any subscription state and will
terminates the DSO session. When the TLS session is resumed, the DNS proceed as with any other new DSO session. Use of TLS Session
Push Notification server will not have any subscription state and
will proceed as with any other new DSO session. Use of TLS Session
Resumption may allow a TLS connection to be set up more quickly, but Resumption may allow a TLS connection to be set up more quickly, but
the client will still have to recreate any desired subscriptions. the client will still have to recreate any desired subscriptions.
8. IANA Considerations 8. IANA Considerations
This document defines a new service name to be published in the IANA This document defines a new service name, only applicable for the TCP
Registry Service Types [RFC6335][ST] that is only applicable for the protocol, to be recorded in the IANA Service Type Registry
TCP protocol. [RFC6335][SRVTYPE].
+-----------------------+------+----------------------+-------------+ +-----------------------+------+----------------------+-------------+
| Name | Port | Value | Definition | | Name | Port | Value | Definition |
+-----------------------+------+----------------------+-------------+ +-----------------------+------+----------------------+-------------+
| DNS Push Notification | None | "_dns-push-tls._tcp" | Section 6.1 | | DNS Push Notification | None | "_dns-push-tls._tcp" | Section 6.1 |
| Service Type | | | | | Service Type | | | |
+-----------------------+------+----------------------+-------------+ +-----------------------+------+----------------------+-------------+
Table 4: IANA Service Type Assignments Table 4: IANA Service Type Assignments
This document also defines four new DNS Stateful Operation TLV types This document defines four new DNS Stateful Operation TLV types to be
to be recorded in the IANA DSO Type Code Registry. recorded in the IANA DSO Type Code Registry [RFC8490][DSOTYPE].
+-------------+------------+---------+-----------------+------------+ +-------------+------------+--------+-----------------+-------------+
| Name | Value | Early | Status | Definition | | Name | Value | Early | Status | Definition |
| | | Data | | | | | | Data | | |
+-------------+------------+---------+-----------------+------------+ +-------------+------------+--------+-----------------+-------------+
| SUBSCRIBE | TBA (0x40) | OK | Standards Track | Section | | SUBSCRIBE | TBA (0x40) | OK | Standards Track | Section 6.2 |
| | | | | 6.2 | | PUSH | TBA (0x41) | NO | Standards Track | Section 6.3 |
| PUSH | TBA (0x41) | NO | Standards Track | Section | | UNSUBSCRIBE | TBA (0x42) | NO | Standards Track | Section 6.4 |
| | | | | 6.3 | | RECONFIRM | TBA (0x43) | NO | Standards Track | Section 6.5 |
| UNSUBSCRIBE | TBA (0x42) | NO | Standards Track | Section | +-------------+------------+--------+-----------------+-------------+
| | | | | 6.4 |
| RECONFIRM | TBA (0x43) | NO | Standards Track | Section |
| | | | | 6.5 |
+-------------+------------+---------+-----------------+------------+
Table 5: IANA DSO TLV Type Code Assignments Table 5: IANA DSO TLV Type Code Assignments
This document defines no new DNS OPCODEs or RCODEs. This document defines no new DNS OPCODEs or RCODEs.
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.
skipping to change at page 37, line 9 skipping to change at page 38, line 9
Rescorla, Michael Richardson, David Schinazi, Manju Shankar Rao, Rescorla, Michael Richardson, David Schinazi, Manju Shankar Rao,
Robert Sparks, Markus Stenberg, Andrew Sullivan, Michael Sweet, Dave Robert Sparks, Markus Stenberg, Andrew Sullivan, Michael Sweet, Dave
Thaler, Brian Trammell, Bernie Volz, Eric Vyncke, Christopher Wood, Thaler, Brian Trammell, Bernie Volz, Eric Vyncke, Christopher Wood,
Liang Xia, and Soraia Zlatkovic. Ted Lemon provided clarifying text Liang Xia, and Soraia Zlatkovic. Ted Lemon provided clarifying text
that was greatly appreciated. that was greatly appreciated.
10. References 10. References
10.1. Normative References 10.1. Normative References
[DSOTYPE] "DSO Type Code Registry",
<https://www.iana.org/assignments/dns-parameters/>.
[RFC0020] Cerf, V., "ASCII format for network interchange", STD 80,
RFC 20, DOI 10.17487/RFC0020, October 1969,
<https://www.rfc-editor.org/info/rfc20>.
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
DOI 10.17487/RFC0768, August 1980, DOI 10.17487/RFC0768, August 1980,
<https://www.rfc-editor.org/info/rfc768>. <https://www.rfc-editor.org/info/rfc768>.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, [RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981, RFC 793, DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/rfc793>. <https://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,
skipping to change at page 38, line 26 skipping to change at page 39, line 36
[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, <https://www.rfc-editor.org/info/rfc7673>. 2015, <https://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,
<https://www.rfc-editor.org/info/rfc7766>. <https://www.rfc-editor.org/info/rfc7766>.
[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, <https://www.rfc-editor.org/info/rfc7858>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8310] Dickinson, S., Gillmor, D., and T. Reddy, "Usage Profiles
for DNS over TLS and DNS over DTLS", RFC 8310,
DOI 10.17487/RFC8310, March 2018,
<https://www.rfc-editor.org/info/rfc8310>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>. <https://www.rfc-editor.org/info/rfc8446>.
[RFC8490] Bellis, R., Cheshire, S., Dickinson, J., Dickinson, S., [RFC8490] Bellis, R., Cheshire, S., Dickinson, J., Dickinson, S.,
Lemon, T., and T. Pusateri, "DNS Stateful Operations", Lemon, T., and T. Pusateri, "DNS Stateful Operations",
RFC 8490, DOI 10.17487/RFC8490, March 2019, RFC 8490, DOI 10.17487/RFC8490, March 2019,
<https://www.rfc-editor.org/info/rfc8490>. <https://www.rfc-editor.org/info/rfc8490>.
[ST] "Service Name and Transport Protocol Port Number [SRVTYPE] "Service Name and Transport Protocol Port Number
Registry", <http://www.iana.org/assignments/ Registry", <http://www.iana.org/assignments/service-names-
service-names-port-numbers/>. port-numbers/>.
10.2. Informative References 10.2. Informative References
[BCP195] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, May 2015,
<http://www.rfc-editor.org/info/bcp195>.
[DisProx] Cheshire, S., "Discovery Proxy for Multicast DNS-Based [DisProx] Cheshire, S., "Discovery Proxy for Multicast DNS-Based
Service Discovery", draft-ietf-dnssd-hybrid-10 (work in Service Discovery", draft-ietf-dnssd-hybrid-10 (work in
progress), March 2019. progress), March 2019.
[I-D.ietf-tcpm-rack] [I-D.ietf-tcpm-rack]
Cheng, Y., Cardwell, N., Dukkipati, N., and P. Jha, "RACK: Cheng, Y., Cardwell, N., Dukkipati, N., and P. Jha, "RACK:
a time-based fast loss detection algorithm for TCP", a time-based fast loss detection algorithm for TCP",
draft-ietf-tcpm-rack-05 (work in progress), April 2019. draft-ietf-tcpm-rack-05 (work in progress), April 2019.
[LLQ] Cheshire, S. and M. Krochmal, "DNS Long-Lived Queries", [LLQ] Cheshire, S. and M. Krochmal, "DNS Long-Lived Queries",
skipping to change at page 39, line 27 skipping to change at page 41, line 5
<https://www.rfc-editor.org/info/rfc3123>. <https://www.rfc-editor.org/info/rfc3123>.
[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, <https://www.rfc-editor.org/info/rfc4287>. December 2005, <https://www.rfc-editor.org/info/rfc4287>.
[RFC4953] Touch, J., "Defending TCP Against Spoofing Attacks", [RFC4953] Touch, J., "Defending TCP Against Spoofing Attacks",
RFC 4953, DOI 10.17487/RFC4953, July 2007, RFC 4953, DOI 10.17487/RFC4953, July 2007,
<https://www.rfc-editor.org/info/rfc4953>. <https://www.rfc-editor.org/info/rfc4953>.
[RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,
"Transport Layer Security (TLS) Session Resumption without
Server-Side State", RFC 5077, DOI 10.17487/RFC5077,
January 2008, <https://www.rfc-editor.org/info/rfc5077>.
[RFC6281] Cheshire, S., Zhu, Z., Wakikawa, R., and L. Zhang, [RFC6281] Cheshire, S., Zhu, Z., Wakikawa, R., and L. Zhang,
"Understanding Apple's Back to My Mac (BTMM) Service", "Understanding Apple's Back to My Mac (BTMM) Service",
RFC 6281, DOI 10.17487/RFC6281, June 2011, RFC 6281, DOI 10.17487/RFC6281, June 2011,
<https://www.rfc-editor.org/info/rfc6281>. <https://www.rfc-editor.org/info/rfc6281>.
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762, [RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
DOI 10.17487/RFC6762, February 2013, DOI 10.17487/RFC6762, February 2013,
<https://www.rfc-editor.org/info/rfc6762>. <https://www.rfc-editor.org/info/rfc6762>.
[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service [RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
skipping to change at page 40, line 14 skipping to change at page 41, line 36
[RFC6887] Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R., and [RFC6887] Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R., and
P. Selkirk, "Port Control Protocol (PCP)", RFC 6887, P. Selkirk, "Port Control Protocol (PCP)", RFC 6887,
DOI 10.17487/RFC6887, April 2013, DOI 10.17487/RFC6887, April 2013,
<https://www.rfc-editor.org/info/rfc6887>. <https://www.rfc-editor.org/info/rfc6887>.
[RFC7413] Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP [RFC7413] Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP
Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014, Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014,
<https://www.rfc-editor.org/info/rfc7413>. <https://www.rfc-editor.org/info/rfc7413>.
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <https://www.rfc-editor.org/info/rfc7525>.
[RFC7719] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS [RFC7719] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", RFC 7719, DOI 10.17487/RFC7719, December Terminology", RFC 7719, DOI 10.17487/RFC7719, December
2015, <https://www.rfc-editor.org/info/rfc7719>. 2015, <https://www.rfc-editor.org/info/rfc7719>.
[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, <https://www.rfc-editor.org/info/rfc7858>.
[RFC8010] Sweet, M. and I. McDonald, "Internet Printing [RFC8010] Sweet, M. and I. McDonald, "Internet Printing
Protocol/1.1: Encoding and Transport", STD 92, RFC 8010, Protocol/1.1: Encoding and Transport", STD 92, RFC 8010,
DOI 10.17487/RFC8010, January 2017, DOI 10.17487/RFC8010, January 2017,
<https://www.rfc-editor.org/info/rfc8010>. <https://www.rfc-editor.org/info/rfc8010>.
[RFC8011] Sweet, M. and I. McDonald, "Internet Printing [RFC8011] Sweet, M. and I. McDonald, "Internet Printing
Protocol/1.1: Model and Semantics", STD 92, RFC 8011, Protocol/1.1: Model and Semantics", STD 92, RFC 8011,
DOI 10.17487/RFC8011, January 2017, DOI 10.17487/RFC8011, January 2017,
<https://www.rfc-editor.org/info/rfc8011>. <https://www.rfc-editor.org/info/rfc8011>.
[RFC8310] Dickinson, S., Gillmor, D., and T. Reddy, "Usage Profiles [RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
for DNS over TLS and DNS over DTLS", RFC 8310, Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
DOI 10.17487/RFC8310, March 2018, January 2019, <https://www.rfc-editor.org/info/rfc8499>.
<https://www.rfc-editor.org/info/rfc8310>.
[SD-API] "dns_sd.h API",
<https://opensource.apple.com/source/mDNSResponder/
mDNSResponder-878.70.2/mDNSShared/dns_sd.h.auto.html>.
[SYN] Eddy, W., "Defenses Against TCP SYN Flooding Attacks", The [SYN] Eddy, W., "Defenses Against TCP SYN Flooding Attacks", The
Internet Protocol Journal, Cisco Systems, Volume 9, Internet Protocol Journal, Cisco Systems, Volume 9,
Number 4, December 2006. Number 4, December 2006.
[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
 End of changes. 79 change blocks. 
289 lines changed or deleted 310 lines changed or added

This html diff was produced by rfcdiff 1.47. The latest version is available from http://tools.ietf.org/tools/rfcdiff/