draft-ietf-dnssd-push-15.txt   draft-ietf-dnssd-push-16.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: March 21, 2019 Apple Inc. Expires: May 9, 2019 Apple Inc.
September 17, 2018 November 5, 2018
DNS Push Notifications DNS Push Notifications
draft-ietf-dnssd-push-15 draft-ietf-dnssd-push-16
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
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at 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 March 21, 2019. This Internet-Draft will expire on May 9, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 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
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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 . . . . . . . . . . . . . . 19 6.3. DNS Push Notification Updates . . . . . . . . . . . . . . 19
6.3.1. PUSH Message . . . . . . . . . . . . . . . . . . . . 19 6.3.1. PUSH Message . . . . . . . . . . . . . . . . . . . . 19
6.4. DNS Push Notification UNSUBSCRIBE . . . . . . . . . . . . 22 6.4. DNS Push Notification UNSUBSCRIBE . . . . . . . . . . . . 22
6.4.1. UNSUBSCRIBE Request . . . . . . . . . . . . . . . . . 22 6.4.1. UNSUBSCRIBE Request . . . . . . . . . . . . . . . . . 22
6.5. DNS Push Notification RECONFIRM . . . . . . . . . . . . . 24 6.5. DNS Push Notification RECONFIRM . . . . . . . . . . . . . 24
6.5.1. RECONFIRM Request . . . . . . . . . . . . . . . . . . 24 6.5.1. RECONFIRM Request . . . . . . . . . . . . . . . . . . 24
6.5.2. RECONFIRM Response . . . . . . . . . . . . . . . . . 26 6.5.2. RECONFIRM Response . . . . . . . . . . . . . . . . . 26
6.6. Client-Initiated Termination . . . . . . . . . . . . . . 28 6.6. DNS Stateful Operations TLV Context Summary . . . . . . . 28
7. Security Considerations . . . . . . . . . . . . . . . . . . . 29 6.7. Client-Initiated Termination . . . . . . . . . . . . . . 29
7.1. Security Services . . . . . . . . . . . . . . . . . . . . 29 7. Security Considerations . . . . . . . . . . . . . . . . . . . 30
7.2. TLS Name Authentication . . . . . . . . . . . . . . . . . 29 7.1. Security Services . . . . . . . . . . . . . . . . . . . . 30
7.3. TLS Compression . . . . . . . . . . . . . . . . . . . . . 30 7.2. TLS Name Authentication . . . . . . . . . . . . . . . . . 30
7.4. TLS Session Resumption . . . . . . . . . . . . . . . . . 30 7.3. TLS Compression . . . . . . . . . . . . . . . . . . . . . 31
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30 7.4. TLS Session Resumption . . . . . . . . . . . . . . . . . 31
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 31 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 31 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 32
10.1. Normative References . . . . . . . . . . . . . . . . . . 31 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 33
10.2. Informative References . . . . . . . . . . . . . . . . . 33 10.1. Normative References . . . . . . . . . . . . . . . . . . 33
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 35 10.2. Informative References . . . . . . . . . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 37
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
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Supporting DNS Updates and DNS Push Notifications on the same server Supporting DNS Updates and DNS Push Notifications on the same server
is OPTIONAL. A DNS Push Notification server does NOT also have to is OPTIONAL. A DNS Push Notification server does NOT also have to
support DNS Update. support DNS Update.
DNS Updates and DNS Push Notifications may be handled on different DNS Updates and DNS Push Notifications may be handled on different
ports on the same target host, in which case they are not considered ports on the same target host, in which case they are not considered
to be the "same server" for the purposes of this specification, and to be the "same server" for the purposes of this specification, and
communications with these two ports are handled independently. communications with these two ports are handled independently.
Standard DNS Queries MAY be sent over a DNS Push Notification Standard DNS Queries MAY be sent over a DNS Push Notification
connection, provided that these are queries for names falling within connection. For any zone for which the server is authoritative, it
the server's zone (the <zone> in the "_dns-push-tls._tcp.<zone>" SRV MUST respond authoritatively for queries on names falling within that
record). The RD (Recursion Desired) bit MUST be zero. If a query is zone (e.g., the <zone> in the "_dns-push-tls._tcp.<zone>" SRV record)
received with the RD bit set, matching records for names falling both for DNS Push Notification queries and for normal DNS queries.
within the server's zones should be returned with the RA (Recursion For names for which the server is acting as a caching resolver, e.g.
Available) bit clear. If the query is for a name not in the server's when the server is the local resolver, for any query for which it
zone, an error with RCODE NOTAUTH (Not Authoritative) should be supports DNS Push Notifications, it MUST also support standard
returned. queries.
DNS Push Notification clients are NOT required to implement DNS DNS Push Notification clients are NOT required to implement DNS
Update Prerequisite processing. Prerequisites are used to perform Update Prerequisite processing. Prerequisites are used to perform
tentative atomic test-and-set type operations when a client updates tentative atomic test-and-set type operations when a client updates
records on a server, and that concept has no applicability when it records on a server, and that concept has no applicability when it
comes to an authoritative server unilaterally informing a client of comes to an authoritative server unilaterally informing a client of
changes to DNS records. changes to DNS records.
This DNS Push Notification specification includes support for DNS This DNS Push Notification specification includes support for DNS
classes, for completeness. However, in practice, it is anticipated classes, for completeness. However, in practice, it is anticipated
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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
showing the results to the user) and the subscription SHOULD be showing the results to the user) and the subscription SHOULD be
cancelled as soon as the need for that data ends (for example, when cancelled as soon as the need for that data ends (for example, when
the user dismisses that display). Implementations MAY want to the user dismisses that display). Implementations may want to
implement idle timeouts, so that if the user ceases interacting with implement idle timeouts, so that if the user ceases interacting with
the device, the display showing the result of the DNS Push the device, the subscription is cancelled.
Notification subscription is automatically dismissed after a certain
period of inactivity. For example, if a user presses the "Print"
button on their smartphone, and then leaves the phone showing the
printer discovery screen until the phone goes to sleep, then the
printer discovery screen should be automatically dismissed as the
device goes to sleep. If the user does still intend to print, this
will require them to press the "Print" button again when they wake
their phone up.
(b) A DNS Push Notification client SHOULD NOT routinely keep a DNS (b) A DNS Push Notification client SHOULD NOT routinely keep a DNS
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
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number of Push Notification subscriptions. This number will vary number of Push Notification subscriptions. This number will vary
from server to server and is based on physical machine from server to server and is based on physical machine
characteristics, network bandwidth, and operating system resource characteristics, network bandwidth, and operating system resource
allocation. After a client establishes a session to a DNS server, allocation. After a client establishes a session to a DNS server,
each subscription is individually accepted or rejected. Servers may each subscription is individually accepted or rejected. Servers may
employ various techniques to limit subscriptions to a manageable employ various techniques to limit subscriptions to a manageable
level. Correspondingly, the client is free to establish simultaneous level. Correspondingly, the client is free to establish simultaneous
sessions to alternate DNS servers that support DNS Push Notifications sessions to alternate DNS servers that support DNS Push Notifications
for the zone and distribute subscriptions at the client's discretion. for the zone and distribute subscriptions at the client's discretion.
In this way, both clients and servers can react to resource In this way, both clients and servers can react to resource
constraints. Token bucket rate limiting schemes are also effective constraints.
in providing fairness by a server across numerous client requests.
6. Protocol Operation 6. Protocol Operation
The DNS Push Notification protocol is a session-oriented protocol, The DNS Push Notification protocol is a session-oriented protocol,
and makes use of DNS Stateful Operations (DSO) [DSO]. and makes use of DNS Stateful Operations (DSO) [DSO].
For details of the DSO message format refer to the DNS Stateful For details of the DSO message format refer to the DNS Stateful
Operations specification [DSO]. Those details are not repeated here. Operations specification [DSO]. Those details are not repeated here.
DNS Push Notification clients and servers MUST support DSO, but (as DNS Push Notification clients and servers MUST support DSO. A single
stated in the DSO specification [DSO]) the server SHOULD NOT issue server can support DNS Queries, DNS Updates, and DNS Push
any DSO messages until after the client has first initiated an Notifications (using DSO) on the same TCP port.
acknowledged DSO message of its own. A single server can support DNS
Queries, DNS Updates, and DNS Push Notifications (using DSO) on the
same TCP port, and until the client has sent at least one DSO
message, the server does not know what kind of client has connected
to it. Once the client has indicated willingness to use DSO by
sending one of its own, either side of the session may then initiate
further DSO messages at any time.
A DNS Push Notification exchange begins with the client discovering A DNS Push Notification exchange begins with the client discovering
the appropriate server, using the procedure described in Section 6.1, the appropriate server, using the procedure described in Section 6.1,
and then making a TLS/TCP connection to it. and then making a TLS/TCP connection to it.
A typical DNS Push Notification client will immediately issue a DSO A typical DNS Push Notification client will immediately issue a DSO
Keepalive operation to request a session timeout or keepalive Keepalive operation to request a session timeout or keepalive
interval longer than the the 15-second default, but this is not interval longer than the the 15-second default, but this is not
required. A DNS Push Notification client MAY issue other requests on required. A DNS Push Notification client MAY issue other requests on
the session first, and only issue a DSO Keepalive operation later if the session first, and only issue a DSO Keepalive operation later if
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client to server. client to server.
6.1. Discovery 6.1. Discovery
The first step in DNS Push Notification subscription is to discover The first step in DNS Push Notification subscription is to discover
an appropriate DNS server that supports DNS Push Notifications for an appropriate DNS server that supports DNS Push Notifications for
the desired zone. the desired zone.
The client begins by opening a DSO Session to its normal configured The client begins by opening a DSO Session to its normal configured
DNS recursive resolver and requesting a Push Notification DNS recursive resolver and requesting a Push Notification
subscription. If this is successful, then the recursive resolver subscription. This connection is made to the default DNS-over-TLS
will make appropriate Push Notification subscriptions on the client's port as defined in DNS over TLS [RFC7858]. If this connection is
behalf, and the client will receive appropriate results. If the successful, then the recursive resolver will make appropriate Push
recursive resolver does not support Push Notification subscriptions, Notification subscriptions on the client's behalf, and the client
then it will return an error code, and the client should proceed to will receive appropriate results.
discover the appropriate server for direct communication. The client
MUST also determine which TCP port on the server is listening for
connections, which need not be (and often is not) the typical TCP
port 53 used for conventional DNS, or TCP port 853 used for DNS over
TLS [RFC7858].
The algorithm described here is an iterative algorithm, which starts In many contexts, the local recursive resolver will be able to handle
with the full name of the record to which the client wishes to push notifications for all zones that the client may need to follow.
subscribe. Successive SOA queries are then issued, trimming one In other cases, the client may require Push Notifications from more
label each time, until the closest enclosing authoritative server is than one zone, and those zones may be served by different servers.
discovered. There is also an optimization to enable the client to Therefore, it is assumed that the client may need to maintain
take a "short cut" directly to the SOA record of the closest connections to more than one DNS Push server.
enclosing authoritative server in many cases.
In some cases, the recursive resolver may not be able to get answers
for a particular zone. In this case, rather than returning SERVFAIL,
the resolver returns NOTAUTH. This signals the client that queries
for this zone can't be handled by the local caching resolver. For
that zone, the client SHOULD contact the zone's DNS Push server
itself, even if all other DNS Push queries can be handled by the
local resolver. This may be necessary in cases where the client is
connected to a VPN, for example, or where the client has a pre-
established trust relationship with the owner of the zone that allows
the client, but not the local resolver, to successfully get answers
for queries in that zone.
If the recursive resolver does not support Push Notification
subscriptions, then it will return an error code, DSONOTIMPL. This
occurs when the local resolver follows the procedure below and does
not find an SRV record indicating support for DNS Push Notifications.
In case of either failure, the client should proceed to discover the
appropriate server for direct communication. The client MUST also
determine which TCP port on the server is listening for connections,
which need not be (and often is not) the typical TCP port 53 used for
conventional DNS, or TCP port 853 used for DNS over TLS.
The discovery algorithm described here is an iterative algorithm,
which starts with the full name of the record to which the client
wishes to subscribe. Successive SOA queries are then issued,
trimming one label each time, until the closest enclosing
authoritative server is discovered. There is also an optimization to
enable the client to take a "short cut" directly to the SOA record of
the closest enclosing authoritative server in many cases.
1. The client begins the discovery by sending a DNS query to its 1. The client begins the discovery by sending a DNS query to its
local resolver, with record type SOA [RFC1035] for the record local resolver, with record type SOA [RFC1035] for the record
name to which it wishes to subscribe. As an example, suppose the name to which it wishes to subscribe. As an example, suppose the
client wishes to subscribe to PTR records with the name client wishes to subscribe to PTR records with the name
_ipp._tcp.foo.example.com (to discover Internet Printing Protocol _ipp._tcp.foo.example.com (to discover Internet Printing Protocol
(IPP) printers [RFC8010] [RFC8011] being advertised at (IPP) printers [RFC8010] [RFC8011] being advertised at
"foo.example.com"). The client begins by sending an SOA query "foo.example.com"). The client begins by sending an SOA query
for _ipp._tcp.foo.example.com to the local recursive resolver. for _ipp._tcp.foo.example.com to the local recursive resolver.
The goal is to determine the server authoritative for the name The goal is to determine the server authoritative for the name
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2. If the requested SOA record exists, it will be returned in the 2. If the requested SOA record exists, it will be returned in the
Answer section with a NOERROR response code, and the client has Answer section with a NOERROR response code, and the client has
succeeded in discovering the information it needs. (This text is succeeded in discovering the information it needs. (This text is
not placing any new requirements on DNS recursive resolvers. It not placing any new requirements on DNS recursive resolvers. It
is merely describing the existing operation of the DNS protocol is merely describing the existing operation of the DNS protocol
[RFC1034] [RFC1035].) [RFC1034] [RFC1035].)
3. If the requested SOA record does not exist, the client will get 3. If the requested SOA record does not exist, the client will get
back a NOERROR/NODATA response or an NXDOMAIN/Name Error back a NOERROR/NODATA response or an NXDOMAIN/Name Error
response. In either case, the local resolver SHOULD include the response. In either case, the local resolver would normally
SOA record for the zone of the requested name in the Authority include the SOA record for the zone of the requested name in the
Section. If the SOA record is received in the Authority Section, Authority Section. If the SOA record is received in the
then the client has succeeded in discovering the information it Authority Section, then the client has succeeded in discovering
needs. (This text is not placing any new requirements on DNS the information it needs. (This text is not placing any new
recursive resolvers. It is merely describing the existing requirements on DNS recursive resolvers. It is merely describing
operation of the DNS protocol regarding negative responses the existing operation of the DNS protocol regarding negative
[RFC2308].) responses [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 one label in it, the client sends a new SOA name has at least one label in it, the client sends a new SOA
query, and processing continues at step 2 above, repeating the query, and processing continues at step 2 above, repeating the
iterative search until either an SOA is received, or the query iterative search until either an SOA is received, or the query
name is empty. In the case of an empty name, this is a network name is empty. In the case of an empty name, this is a network
configuration error which should not happen and the client gives configuration error which should not happen and the client gives
up. The client may retry the operation at a later time, of the up. The client may retry the operation at a later time, of the
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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 then keepalive interval if necessary, a DNS Push Notification client then
indicates its desire to receive DNS Push Notifications for a given indicates its desire to receive DNS Push Notifications for a given
domain name by sending a SUBSCRIBE request over the established DSO domain name by sending a SUBSCRIBE request over the established DSO
session to the server. A SUBSCRIBE request is encoded in a DSO [DSO] session to the server. A SUBSCRIBE request is encoded in a DSO [DSO]
message. This specification defines a DSO TLV for DNS Push message. This specification defines a primary DSO TLV for DNS Push
Notification SUBSCRIBE Requests/Responses (tentatively DSO Type Code Notification SUBSCRIBE Requests (tentatively DSO Type Code 0x40).
0x40).
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 should immediately abort the connection with a TCP RST (or the client should immediately abort the connection with a TCP RST (or
equivalent for other protocols). equivalent for other protocols).
6.2.1. SUBSCRIBE Request 6.2.1. SUBSCRIBE Request
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subscription was accepted. Supported RCODEs are as follows: subscription was accepted. Supported RCODEs are as follows:
+-----------+-------+-----------------------------------------------+ +-----------+-------+-----------------------------------------------+
| Mnemonic | Value | Description | | Mnemonic | Value | Description |
+-----------+-------+-----------------------------------------------+ +-----------+-------+-----------------------------------------------+
| NOERROR | 0 | SUBSCRIBE successful. | | NOERROR | 0 | SUBSCRIBE successful. |
| FORMERR | 1 | Server failed to process request due to a | | FORMERR | 1 | Server failed to process request due to a |
| | | malformed request. | | | | malformed request. |
| SERVFAIL | 2 | Server failed to process request due to a | | SERVFAIL | 2 | Server failed to process request due to a |
| | | problem with the server. | | | | problem with the server. |
| NXDOMAIN | 3 | NOT APPLICABLE. DNS Push Notification servers |
| | | MUST NOT return NXDOMAIN errors in response |
| | | to SUBSCRIBE requests. |
| NOTIMP | 4 | Server does not implement DSO. | | NOTIMP | 4 | Server does not implement DSO. |
| REFUSED | 5 | Server refuses to process request for policy | | REFUSED | 5 | Server refuses to process request for policy |
| | | or security reasons. | | | | or security reasons. |
| NOTAUTH | 9 | Server is not authoritative for the requested | | NOTAUTH | 9 | Server is not authoritative for the requested |
| | | name. | | | | name. |
| DSOTYPENI | 11 | SUBSCRIBE operation not supported. | | DSOTYPENI | 11 | SUBSCRIBE operation not supported. |
+-----------+-------+-----------------------------------------------+ +-----------+-------+-----------------------------------------------+
SUBSCRIBE Response codes Table 1: SUBSCRIBE Response codes
This document specifies only these RCODE values for SUBSCRIBE This document specifies only these RCODE values for SUBSCRIBE
Responses. Servers sending SUBSCRIBE Responses SHOULD use one of Responses. Servers sending SUBSCRIBE Responses SHOULD use one of
these values. However, future circumstances may create situations these values. Note that NXDOMAIN is not a valid RCODE in response to
where other RCODE values are appropriate in SUBSCRIBE Responses, so a SUBSCRIBE Request. However, future circumstances may create
clients MUST be prepared to accept SUBSCRIBE Responses with any RCODE situations where other RCODE values are appropriate in SUBSCRIBE
value. Responses, so clients MUST be prepared to accept SUBSCRIBE Responses
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 (a) the client is (at least partially) misconfigured, (b) the means
server resources are exhausted, or (c) there is some other unknown
failure on the server. In any case, the client shouldn't retry the a. the client is (at least partially) misconfigured,
subscription right away. Either end can terminate the session, but b. the server resources are exhausted, or
the client may want to try this subscription again, or it may have c. there is some other unknown failure on the server.
other successful subscriptions that it doesn't want to abandon. If
the server sends a nonzero RCODE then it SHOULD append a Retry Delay In any case, the client shouldn't retry the subscription to this
TLV [DSO] to the response specifying a delay before the client server right away. If multiple SRV records were returned as
described in discovery Section 6.1, Paragraph 7, a subsequent server
can be tried immediately.
If the client has other successful subscriptions to this server,
these subscriptions can remain even though additional subscriptions
may be refused. Neither the client, nor the server are required to
close the connection, although, either end may choose to do so.
If the server sends a nonzero RCODE then it SHOULD append a Retry
Delay TLV [DSO] to the response specifying a delay before the client
attempts this operation again. Recommended values for the delay for attempts this operation again. Recommended values for the delay for
different RCODE values are given below. These recommended values different RCODE values are given below. These recommended values
apply both to the default values a server should place in the Retry apply both to the default values a server should place in the Retry
Delay TLV, and the default values a client should assume if the Delay TLV, and the default values a client should assume if the
server provides no Retry Delay TLV. server provides no Retry Delay TLV.
For RCODE = 1 (FORMERR) the delay may be any value selected by the For RCODE = 1 (FORMERR) the delay may be any value selected by the
implementer. A value of five minutes is RECOMMENDED, to reduce implementer. A value of five minutes is RECOMMENDED, to reduce
the risk of high load from defective clients. the risk of high load from defective clients.
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be one hour. Note that in such a case, a server that doesn't be one hour. Note that in such a case, a server that doesn't
implement DSO is unlikely to place a Retry Delay TLV in its implement DSO is unlikely to place a Retry Delay TLV in its
response, so this recommended value in particular applies to what response, so this recommended value in particular applies to what
a client should assume by default. a client should assume by default.
For RCODE = 5 (REFUSED), which occurs on a server that implements For RCODE = 5 (REFUSED), which occurs on a server that implements
DNS Push Notifications, but is currently configured to disallow DNS Push Notifications, but is currently configured to disallow
DNS Push Notifications, the retry delay may be any value selected DNS Push Notifications, the retry delay may be any value selected
by the implementer and/or configured by the operator. by the implementer and/or configured by the operator.
This is a misconfiguration, since this server is listed in a If the server being queried is not the local resolver, this is a
misconfiguration, since this server is listed in a
"_dns-push-tls._tcp.<zone>" SRV record, but the server itself is "_dns-push-tls._tcp.<zone>" SRV record, but the server itself is
not currently configured to support DNS Push Notifications. Since not currently configured to support DNS Push Notifications for
it is possible that the misconfiguration may be repaired at any that zone. Since it is possible that the misconfiguration may be
time, the retry delay should not be set too high. By default, a repaired at any time, the retry delay should not be set too high.
value of 5 minutes is RECOMMENDED. By default, a value of 5 minutes is RECOMMENDED.
For RCODE = 9 (NOTAUTH), which occurs on a server that implements For RCODE = 9 (NOTAUTH), which occurs on a server that implements
DNS Push Notifications, but is not configured to be authoritative DNS Push Notifications, but is not configured to be authoritative
for the requested name, the retry delay may be any value selected for the requested name, the retry delay may be any value selected
by the implementer and/or configured by the operator. by the implementer and/or configured by the operator.
This is a misconfiguration, since this server is listed in a This is a misconfiguration, since this server is listed in a
"_dns-push-tls._tcp.<zone>" SRV record, but the server itself is "_dns-push-tls._tcp.<zone>" SRV record, but the server itself is
not currently configured to support DNS Push Notifications for not currently configured to support DNS Push Notifications for
that zone. Since it is possible that the misconfiguration may be that zone. Since it is possible that the misconfiguration may be
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Similarly, when both an SRV and a TXT record are deleted from a given Similarly, when both an SRV and a TXT record are deleted from a given
name, and no other records of any kind exist for that name, the name, and no other records of any kind exist for that name, the
server SHOULD send a "delete all RRsets from a name" PUSH message, server SHOULD send a "delete all RRsets from a name" PUSH message,
not two separate "delete an RRset from a name" PUSH messages. not two separate "delete an RRset from a name" PUSH messages.
A server SHOULD combine multiple change notifications in a single A server SHOULD combine multiple change notifications in a single
PUSH message when possible, even if those change notifications apply PUSH message when possible, even if those change notifications apply
to different subscriptions. Conceptually, a PUSH 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 and decremented as The TTL of an added record is stored by the client. While the
time passes, with the caveat that for as long as a relevant subscription is active, the TTL is not decremented, because a change
subscription is active, the TTL does not decrement below 1 second. to the TTL would produce a new update. For as long as a relevant
For as long as a relevant subscription remains active, the client subscription remains active, the client SHOULD assume that when a
SHOULD assume that when a record goes away the server will notify it record goes away the server will notify it of that fact.
of that fact. Consequently, a client does not have to poll to verify Consequently, a client does not have to poll to verify that the
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 resumes and records are removed from the local cache when their aging for records covered by the subscription resumes and records are
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. The UNSUBSCRIBE message is encoded as a
DSO [DSO] unidirectional message. This specification defines a DSO DSO [DSO] unidirectional message. This specification defines a
TLV for DNS Push Notification UNSUBSCRIBE Requests/Responses primary unidirectional DSO TLV for DNS Push Notification UNSUBSCRIBE
(tentatively DSO Type Code 0x42). Requests (tentatively DSO Type Code 0x42).
A server MUST NOT initiate an UNSUBSCRIBE request. If a server does A server MUST NOT initiate an UNSUBSCRIBE request. If a server does
send an UNSUBSCRIBE request over a DSO session initiated by a client, send an UNSUBSCRIBE request over a DSO session initiated by a client,
this is a fatal error and the client should immediately abort the this is a fatal error and the client should immediately abort the
connection with a TCP RST (or equivalent for other protocols). connection with a TCP RST (or equivalent for other protocols).
6.4.1. UNSUBSCRIBE Request 6.4.1. UNSUBSCRIBE Request
An UNSUBSCRIBE request begins with the standard DSO 12-byte header An UNSUBSCRIBE request begins with the standard DSO 12-byte header
[DSO], followed by the UNSUBSCRIBE TLV. An UNSUBSCRIBE request [DSO], followed by the UNSUBSCRIBE TLV. An UNSUBSCRIBE request
skipping to change at page 24, line 33 skipping to change at page 24, line 33
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.
6.5.1. RECONFIRM Request 6.5.1. RECONFIRM Request
A RECONFIRM request begins with the standard DSO 12-byte header A RECONFIRM request begins with the standard DSO 12-byte header
[DSO], followed by the RECONFIRM TLV. A RECONFIRM request message is [DSO], followed by the primary DSO RECONFIRM TLV. A RECONFIRM
illustrated in Figure 4. request message is illustrated in Figure 4.
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 RECONFIRM response has not yet cancelled using UNSUBSCRIBE. In the RECONFIRM 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 The other header fields MUST be set as described in the DSO
skipping to change at page 26, line 35 skipping to change at page 26, line 35
reconfirmation request. Supported RCODEs are as follows: reconfirmation request. Supported RCODEs are as follows:
+-----------+-------+-----------------------------------------------+ +-----------+-------+-----------------------------------------------+
| Mnemonic | Value | Description | | Mnemonic | Value | Description |
+-----------+-------+-----------------------------------------------+ +-----------+-------+-----------------------------------------------+
| NOERROR | 0 | RECONFIRM accepted. | | NOERROR | 0 | RECONFIRM accepted. |
| FORMERR | 1 | Server failed to process request due to a | | FORMERR | 1 | Server failed to process request due to a |
| | | malformed request. | | | | malformed request. |
| SERVFAIL | 2 | Server failed to process request due to a | | SERVFAIL | 2 | Server failed to process request due to a |
| | | problem with the server. | | | | problem with the server. |
| NXDOMAIN | 3 | NOT APPLICABLE. DNS Push Notification servers |
| | | MUST NOT return NXDOMAIN errors in response |
| | | to RECONFIRM requests. |
| NOTIMP | 4 | Server does not implement DSO. | | NOTIMP | 4 | Server does not implement DSO. |
| REFUSED | 5 | Server refuses to process request for policy | | REFUSED | 5 | Server refuses to process request for policy |
| | | or security reasons. | | | | or security reasons. |
| NOTAUTH | 9 | Server is not authoritative for the requested | | NOTAUTH | 9 | Server is not authoritative for the requested |
| | | name. | | | | name. |
| DSOTYPENI | 11 | RECONFIRM operation not supported. | | DSOTYPENI | 11 | RECONFIRM operation not supported. |
+-----------+-------+-----------------------------------------------+ +-----------+-------+-----------------------------------------------+
RECONFIRM Response codes Table 2: RECONFIRM Response codes
This document specifies only these RCODE values for RECONFIRM This document specifies only these RCODE values for RECONFIRM
Responses. Servers sending RECONFIRM Responses SHOULD use one of Responses. Servers sending RECONFIRM Responses SHOULD use one of
these values. However, future circumstances may create situations these values. Note that NXDOMAIN is not a valid RCODE in response to
where other RCODE values are appropriate in RECONFIRM Responses, so a RECONFIRM Request. However, future circumstances may create
clients MUST be prepared to accept RECONFIRM Responses with any RCODE situations where other RCODE values are appropriate in RECONFIRM
value. Responses, so clients MUST be prepared to accept RECONFIRM Responses
with any other RCODE value.
Nonzero RCODE values signal some kind of error. Nonzero RCODE values signal some kind of error.
RCODE value FORMERR indicates a message format error, for example RCODE value FORMERR indicates a message format error, for example
TYPE or CLASS being ANY (255). TYPE or CLASS being ANY (255).
RCODE value SERVFAIL indicates that the server has exhausted its RCODE value SERVFAIL indicates that the server has exhausted its
resources or other serious problem occurred. resources or other serious problem occurred.
RCODE values NOTIMP indicates that the server does not support DSO, RCODE values NOTIMP indicates that the server does not support DSO,
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Nonzero RCODE values SERVFAIL, REFUSED and DSOTYPENI are benign from Nonzero RCODE values SERVFAIL, REFUSED and DSOTYPENI are benign from
the client's point of view. The client may log them to aid in the client's point of view. The client may log them to aid in
debugging, but otherwise they require no special action. debugging, but otherwise they require no special action.
Nonzero RCODE values other than these three indicate a serious Nonzero RCODE values other than these three indicate a serious
problem with the client. After sending an error response other than problem with the client. After sending an error response other than
one of these three, the server SHOULD send a DSO Retry Delay TLV to one of these three, the server SHOULD send a DSO Retry Delay TLV to
end the DSO session, as described in the DSO specification [DSO]. end the DSO session, as described in the DSO specification [DSO].
6.6. Client-Initiated Termination 6.6. DNS Stateful Operations TLV Context Summary
This document defines four new DSO TLVs. As suggested in [DSO],
Section 8.2, the valid contexts of these new TLV types are summarized
below.
The client TLV contexts are:
C-P: Client primary TLV
C-U: Client primary unidirectional TLV
C-A: Client additional TLV
CRP: Client response primary TLV
CRA: Client response additional TLV
+-------------+-----+-----+-----+-----+-----+
| TLV Type | C-P | C-U | C-A | CRP | CRA |
+-------------+-----+-----+-----+-----+-----+
| SUBSCRIBE | X | | | | |
| PUSH | | | | | |
| UNSUBSCRIBE | | X | | | |
| RECONFIRM | X | | | | |
+-------------+-----+-----+-----+-----+-----+
Table 3: DSO TLV Client Context Summary
The server TLV contexts are:
S-P: Server primary TLV
S-U: Server primary unidirectional TLV
S-A: Server additional TLV
SRP: Server response primary TLV
SRA: Server response additional TLV
+-------------+-----+-----+-----+-----+-----+
| TLV Type | S-P | S-U | S-A | SRP | SRA |
+-------------+-----+-----+-----+-----+-----+
| SUBSCRIBE | | | | | |
| PUSH | | X | | | |
| UNSUBSCRIBE | | | | | |
| RECONFIRM | | | | | |
+-------------+-----+-----+-----+-----+-----+
Table 4: DSO TLV Server Context Summary
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 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.
skipping to change at page 29, line 7 skipping to change at page 30, line 7
If a client has performed operations on this session that it would If a client has performed operations on this session that it would
not want lost (like DNS updates) then the client SHOULD do an orderly not want lost (like DNS updates) then the client SHOULD do an orderly
disconnect, sending a TLS close_notify followed by a TCP FIN. (In disconnect, sending a TLS close_notify followed by a TCP FIN. (In
the BSD Sockets API, sending a TCP FIN is achieved by calling the BSD Sockets API, sending a TCP FIN is achieved by calling
"shutdown(s,SHUT_WR)" and keeping the socket open until all remaining "shutdown(s,SHUT_WR)" and keeping the socket open until all remaining
data has been read from it.) data has been read from it.)
7. Security Considerations 7. Security Considerations
The Strict Privacy Usage Profile for DNS over TLS is strongly The Strict Privacy Usage Profile for DNS over TLS is REQUIRED for DNS
recommended for DNS Push Notifications as defined in "Usage Profiles Push Notifications as defined in "Usage Profiles for DNS over TLS and
for DNS over TLS and DNS over DTLS" [RFC8310]. The Opportunistic DNS over DTLS" [RFC8310]. Cleartext connections for DNS Push
Privacy Usage Profile is permissible as a way to support incremental Notifications are not permissible. Since this is a new protocol,
deployment of security capabilities. Cleartext connections for DNS transition mechanisms from the Opportunistic Privacy profile are
Push Notifications are not permissible. deemed unnecessary.
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 provided added
confidence that the SRV query has not been subverted. confidence that the SRV query has not been subverted.
skipping to change at page 30, line 32 skipping to change at page 31, line 32
In order to reduce the chances of compression-related attacks, TLS- In order to reduce the chances of compression-related attacks, TLS-
level compression SHOULD be disabled when using TLS versions 1.2 and level compression SHOULD be disabled when using TLS versions 1.2 and
earlier. In TLS 1.3 [RFC8446], TLS-level compression has been earlier. In TLS 1.3 [RFC8446], TLS-level compression has been
removed completely. removed completely.
7.4. TLS Session Resumption 7.4. TLS Session Resumption
TLS Session Resumption is permissible on DNS Push Notification TLS Session Resumption is permissible on DNS Push Notification
servers. The server may keep TLS state with Session IDs [RFC5246] or servers. The server may keep TLS state with Session IDs [RFC5246] or
operate in stateless mode by sending a Session Ticket [RFC5077] to operate in stateless mode by sending a Session Ticket [RFC5077] to
the client for it to store. However, once the DSO session is closed, the client for it to store. However, closing the TLS connection
any existing subscriptions will be dropped. When the TLS session is terminates the DSO session. When the TLS session is resumed, the DNS
resumed, the DNS Push Notification server will not have any Push Notification server will not have any subscription state and
subscription state and will proceed as with any other new DSO will proceed as with any other new DSO session. Use of TLS Session
session. Use of TLS Session Resumption allows a new TLS connection Resumption may allow a TLS connection to be set up more quickly, but
to be set up more quickly, but the client will still have to recreate the client will still have to recreate any desired subscriptions.
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 to be published in the IANA
Registry Service Types [RFC6335][ST] that is only applicable for the Registry Service Types [RFC6335][ST] that is only applicable for the
TCP protocol. TCP protocol.
+-----------------------+------+----------------------+-------------+
| Name | Port | Value | Definition |
+-----------------------+------+----------------------+-------------+
| DNS Push Notification | None | "_dns-push-tls._tcp" | Section 6.1 |
| Service Type | | | |
+-----------------------+------+----------------------+-------------+
Table 5: IANA Service Type Assignments
This document also defines four new DNS Stateful Operation TLV types This document also defines four new DNS Stateful Operation TLV types
to be recorded in the IANA DSO Type Code Registry. to be recorded in the IANA DSO Type Code Registry.
+----------------------------+----------------------+---------------+ +-------------+------------------------+---------------+
| Name | Value | Definition | | Name | Value | Definition |
+----------------------------+----------------------+---------------+ +-------------+------------------------+---------------+
| DNS Push Notifcation | "_dns-push-tls._tcp" | Section 6.1 | | SUBSCRIBE | TBA (tentatively 0x40) | Section 6.2 |
| Service Type | | | | PUSH | TBA (tentatively 0x41) | Section 6.3.1 |
| SUBSCRIBE | TBA (tentatively | Section 6.2 | | UNSUBSCRIBE | TBA (tentatively 0x42) | Section 6.4 |
| | 0x40) | | | RECONFIRM | TBA (tentatively 0x43) | Section 6.5.1 |
| PUSH | TBA (tentatively | Section 6.3.1 | +-------------+------------------------+---------------+
| | 0x41) | |
| UNSUBSCRIBE | TBA (tentatively | Section 6.4 |
| | 0x42) | |
| RECONFIRM | TBA (tentatively | Section 6.5.1 |
| | 0x43) | |
+----------------------------+----------------------+---------------+
Table 1: IANA Assignments Table 6: IANA DSO TLV Type Code Assignments
9. Acknowledgements 9. Acknowledgements
The authors would like to thank Kiren Sekar and Marc Krochmal for The authors would like to thank Kiren Sekar and Marc Krochmal for
previous work completed in this field. previous work completed in this field.
This draft has been improved due to comments from Ran Atkinson, Tim This draft has been improved due to comments from Ran Atkinson, Tim
Chown, Mark Delany, Ralph Droms, Bernie Volz, Jan Komissar, Manju Chown, Mark Delany, Ralph Droms, Bernie Volz, Jan Komissar, Manju
Shankar Rao, Markus Stenberg, Dave Thaler, Soraia Zlatkovic, Sara Shankar Rao, Markus Stenberg, Dave Thaler, Soraia Zlatkovic, Sara
Dickinson, and Andrew Sullivan. Dickinson, and Andrew Sullivan. Ted Lemon provided clarifying text
that was greatly appreciated.
10. References 10. References
10.1. Normative References 10.1. Normative References
[DSO] Bellis, R., Cheshire, S., Dickinson, J., Dickinson, S., [DSO] Bellis, R., Cheshire, S., Dickinson, J., Dickinson, S.,
Lemon, T., and T. Pusateri, "DNS Stateful Operations", Lemon, T., and T. Pusateri, "DNS Stateful Operations",
draft-ietf-dnsop-session-signal-14 (work in progress), draft-ietf-dnsop-session-signal-18 (work in progress),
August 2018. October 2018.
[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",
 End of changes. 34 change blocks. 
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