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draft-ietf-dprive-dnsoquic-04.txt
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Network Working Group C. Huitema
Internet-Draft Private Octopus Inc.
Intended status: Standards Track S. Dickinson
Expires: 6 March 2022 Sinodun IT
A. Mankin
Salesforce
2 September 2021
Specification of DNS over Dedicated QUIC Connections
draft-ietf-dprive-dnsoquic-04
Abstract
This document describes the use of QUIC to provide transport privacy
for DNS. The encryption provided by QUIC has similar properties to
that provided by TLS, while QUIC transport eliminates the head-of-
line blocking issues inherent with TCP and provides more efficient
error corrections than UDP. DNS over QUIC (DoQ) has privacy
properties similar to DNS over TLS (DoT) specified in RFC7858, and
latency characteristics similar to classic DNS over UDP.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 6 March 2022.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
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and restrictions with respect to this document. Code Components
extracted from this document must include Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Key Words . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Document work via GitHub . . . . . . . . . . . . . . . . . . 4
4. Design Considerations . . . . . . . . . . . . . . . . . . . . 4
4.1. Provide DNS Privacy . . . . . . . . . . . . . . . . . . . 5
4.2. Design for Minimum Latency . . . . . . . . . . . . . . . 5
4.3. No Specific Middlebox Bypass Mechanism . . . . . . . . . 6
4.4. No Server Initiated Transactions . . . . . . . . . . . . 6
5. Specifications . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Connection Establishment . . . . . . . . . . . . . . . . 6
5.1.1. Draft Version Identification . . . . . . . . . . . . 6
5.1.2. Port Selection . . . . . . . . . . . . . . . . . . . 7
5.2. Stream Mapping and Usage . . . . . . . . . . . . . . . . 7
5.2.1. DNS Message IDs . . . . . . . . . . . . . . . . . . . 8
5.3. DoQ Error Codes . . . . . . . . . . . . . . . . . . . . . 8
5.3.1. Transaction Cancellation . . . . . . . . . . . . . . 9
5.3.2. Transaction Errors . . . . . . . . . . . . . . . . . 9
5.3.3. Protocol Errors . . . . . . . . . . . . . . . . . . . 9
5.4. Connection Management . . . . . . . . . . . . . . . . . . 10
5.5. Session Resumption and 0-RTT . . . . . . . . . . . . . . 11
5.6. Message Sizes . . . . . . . . . . . . . . . . . . . . . . 12
6. Implementation Requirements . . . . . . . . . . . . . . . . . 12
6.1. Authentication . . . . . . . . . . . . . . . . . . . . . 12
6.2. Fall Back to Other Protocols on Connection Failure . . . 12
6.3. Address Validation . . . . . . . . . . . . . . . . . . . 13
6.4. Padding . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.5. Connection Handling . . . . . . . . . . . . . . . . . . . 14
6.5.1. Connection Reuse . . . . . . . . . . . . . . . . . . 14
6.5.2. Resource Management and Idle Timeout Values . . . . . 14
6.5.3. Using 0-RTT and Session Resumption . . . . . . . . . 15
6.6. Processing Queries in Parallel . . . . . . . . . . . . . 15
6.7. Zone transfer . . . . . . . . . . . . . . . . . . . . . . 16
6.8. Flow Control Mechanisms . . . . . . . . . . . . . . . . . 16
7. Implementation Status . . . . . . . . . . . . . . . . . . . . 17
7.1. Performance Measurements . . . . . . . . . . . . . . . . 18
8. Security Considerations . . . . . . . . . . . . . . . . . . . 18
9. Privacy Considerations . . . . . . . . . . . . . . . . . . . 18
9.1. Privacy Issues With 0-RTT data . . . . . . . . . . . . . 19
9.2. Privacy Issues With Session Resumption . . . . . . . . . 20
9.3. Privacy Issues With New Tokens . . . . . . . . . . . . . 20
9.4. Traffic Analysis . . . . . . . . . . . . . . . . . . . . 21
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10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
10.1. Registration of DoQ Identification String . . . . . . . 21
10.2. Reservation of Dedicated Port . . . . . . . . . . . . . 21
10.2.1. Port number 784 for experimentations . . . . . . . . 22
10.3. Reservation of Extended DNS Error Code Too Early . . . . 22
10.4. DNS over QUIC Error Codes Registry . . . . . . . . . . . 22
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 24
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 24
12.1. Normative References . . . . . . . . . . . . . . . . . . 24
12.2. Informative References . . . . . . . . . . . . . . . . . 26
Appendix A. The NOTIFY service . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 28
1. Introduction
Domain Name System (DNS) concepts are specified in "Domain names -
concepts and facilities" [RFC1034]. The transmission of DNS queries
and responses over UDP and TCP is specified in "Domain names -
implementation and specification" [RFC1035]. This document presents
a mapping of the DNS protocol over the QUIC transport [RFC9000]
[RFC9001]. DNS over QUIC is referred here as DoQ, in line with "DNS
Terminology" [I-D.ietf-dnsop-rfc8499bis]. The goals of the DoQ
mapping are:
1. Provide the same DNS privacy protection as DNS over TLS (DoT)
[RFC7858]. This includes an option for the client to
authenticate the server by means of an authentication domain name
as specified in "Usage Profiles for DNS over TLS and DNS over
DTLS" [RFC8310].
2. Provide an improved level of source address validation for DNS
servers compared to classic DNS over UDP.
3. Provide a transport that is not constrained by path MTU
limitations on the size of DNS responses it can send.
4. Explore the characteristics of using QUIC as a DNS transport,
versus other solutions like DNS over UDP [RFC1035], DNS over TLS
(DoT) [RFC7858], or DNS over HTTPS (DoH) [RFC8484].
In order to achieve these goals, and to support ongoing work on
encryption of DNS, the scope of this document includes
* the "stub to recursive resolver" scenario
* the "recursive resolver to authoritative nameserver" scenario and
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* the "nameserver to nameserver" scenario (mainly used for zone
transfers (XFR) [RFC1995], [RFC5936]).
In other words, this document is intended to specify QUIC as a
general purpose transport for DNS.
The specific non-goals of this document are:
1. No attempt is made to evade potential blocking of DNS over QUIC
traffic by middleboxes.
2. No attempt to support server initiated transactions, which are
used only in DNS Stateful Operations (DSO) [RFC8490].
Specifying the transmission of an application over QUIC requires
specifying how the application's messages are mapped to QUIC streams,
and generally how the application will use QUIC. This is done for
HTTP in "Hypertext Transfer Protocol Version 3
(HTTP/3)"[I-D.ietf-quic-http]. The purpose of this document is to
define the way DNS messages can be transmitted over QUIC.
In this document, Section 4 presents the reasoning that guided the
proposed design. Section 5 specifies the actual mapping of DoQ.
Section 6 presents guidelines on the implementation, usage and
deployment of DoQ.
2. Key Words
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14 [RFC8174].
3. Document work via GitHub
(RFC EDITOR NOTE: THIS SECTION TO BE REMOVED BEFORE PUBLICATION)The
Github repository for this document is at https://github.com/huitema/
dnsoquic. Proposed text and editorial changes are very much welcomed
there, but any functional changes should always first be discussed on
the IETF DPRIVE WG (dns-privacy) mailing list.
4. Design Considerations
This section and its subsections present the design guidelines that
were used for DoQ. This section is informative in nature.
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4.1. Provide DNS Privacy
DoT [RFC7858] defines how to mitigate some of the issues described in
"DNS Privacy Considerations" [RFC7626] by specifying how to transmit
DNS messages over TLS. The "Usage Profiles for DNS over TLS and DNS
over DTLS" [RFC8310] specify Strict and Opportunistic Usage Profiles
for DoT including how stub resolvers can authenticate recursive
resolvers.
QUIC connection setup includes the negotiation of security parameters
using TLS, as specified in "Using TLS to Secure QUIC" [RFC9001],
enabling encryption of the QUIC transport. Transmitting DNS messages
over QUIC will provide essentially the same privacy protections as
DoT [RFC7858] including Strict and Opportunistic Usage Profiles
[RFC8310]. Further discussion on this is provided in Section 9.
4.2. Design for Minimum Latency
QUIC is specifically designed to reduce the delay between HTTP
queries and HTTP responses. This is achieved through three main
components:
1. Support for 0-RTT data during session resumption.
2. Support for advanced error recovery procedures as specified in
"QUIC Loss Detection and Congestion Control" [RFC9002].
3. Mitigation of head-of-line blocking by allowing parallel delivery
of data on multiple streams.
This mapping of DNS to QUIC will take advantage of these features in
three ways:
1. Optional support for sending 0-RTT data during session resumption
(the security and privacy implications of this are discussed in
later sections).
2. Long-lived QUIC connections over which multiple DNS transactions
are performed, generating the sustained traffic required to
benefit from advanced recovery features.
3. Fast resumption of QUIC connections to manage the disconnect-on-
idle feature of QUIC without incurring retransmission time-outs.
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4. Mapping of each DNS Query/Response transaction to a separate
stream, to mitigate head-of-line blocking. This enables servers
to respond to queries "out of order". It also enables clients to
process responses as soon as they arrive, without having to wait
for in order delivery of responses previously posted by the
server.
These considerations will be reflected in the mapping of DNS traffic
to QUIC streams in Section 5.2.
4.3. No Specific Middlebox Bypass Mechanism
The mapping of DoQ is defined for minimal overhead and maximum
performance. This means a different traffic profile than HTTP3 over
QUIC. This difference can be noted by firewalls and middleboxes.
There may be environments in which HTTP3 over QUIC will be able to
pass through, but DoQ will be blocked by these middle boxes.
4.4. No Server Initiated Transactions
As stated in Section 1, this document does not specify support for
server initiated transactions within established DoQ connections.
That is, only the initiator of the DoQ connection may send queries
over the connection.
DSO supports server-initiated transactions within existing
connections, however DSO is not applicable to DNS over HTTP since
HTTP has its own mechanism for managing sessions, and this is
incompatible with the DSO; the same is true for DoQ.
5. Specifications
5.1. Connection Establishment
DoQ connections are established as described in the QUIC transport
specification [RFC9000]. During connection establishment, DoQ
support is indicated by selecting the ALPN token "doq" in the crypto
handshake.
5.1.1. Draft Version Identification
(RFC EDITOR NOTE: THIS SECTION TO BE REMOVED BEFORE PUBLICATION) Only
implementations of the final, published RFC can identify themselves
as "doq". Until such an RFC exists, implementations MUST NOT
identify themselves using this string.
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Implementations of draft versions of the protocol MUST add the string
"-" and the corresponding draft number to the identifier. For
example, draft-ietf-dprive-dnsoquic-00 is identified using the string
"doq-i00".
5.1.2. Port Selection
By default, a DNS server that supports DoQ MUST listen for and accept
QUIC connections on the dedicated UDP port TBD (number to be defined
in Section 10), unless it has mutual agreement with its clients to
use a port other than TBD for DoQ. In order to use a port other than
TBD, both clients and servers would need a configuration option in
their software.
By default, a DNS client desiring to use DoQ with a particular server
MUST establish a QUIC connection to UDP port TBD on the server,
unless it has mutual agreement with its server to use a port other
than port TBD for DoQ. Such another port MUST NOT be port 53. This
recommendation against use of port 53 for DoQ is to avoid confusion
between DoQ and the use of DNS over UDP [RFC1035].
5.2. Stream Mapping and Usage
The mapping of DNS traffic over QUIC streams takes advantage of the
QUIC stream features detailed in Section 2 of the QUIC transport
specification [RFC9000].
DNS traffic follows a simple pattern in which the client sends a
query, and the server provides one or more responses (multiple can
responses occur in zone transfers).
The mapping specified here requires that the client selects a
separate QUIC stream for each query. The server then uses the same
stream to provide all the response messages for that query. In order
that multiple responses can be parsed, a 2-octet length field is used
in exactly the same way as the 2-octet length field defined for DNS
over TCP [RFC1035]. The practical result of this is that the content
of each QUIC stream is exactly the same as the content of a TCP
connection that would manage exactly one query.
All DNS messages (queries and responses) sent over DoQ connections
MUST be encoded as a 2-octet length field followed by the message
content as specified in [RFC1035].
The client MUST select the next available client-initiated
bidirectional stream for each subsequent query on a QUIC connection,
in conformance with the QUIC transport specification [RFC9000].
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The client MUST send the DNS query over the selected stream, and MUST
indicate through the STREAM FIN mechanism that no further data will
be sent on that stream.
The server MUST send the response(s) on the same stream and MUST
indicate, after the last response, through the STREAM FIN mechanism
that no further data will be sent on that stream.
Therefore, a single client initiated DNS transaction consumes a
single stream. This means that the client's first query occurs on
QUIC stream 0, the second on 4, and so on.
For completeness it is noted that versions prior to -02 of this
specification proposed a simpler mapping scheme which omitted the 2
byte length field and supported only a single response on a given
stream. The more complex mapping above was adopted to specifically
cater for XFR support, however it breaks compatibility with earlier
versions.
5.2.1. DNS Message IDs
When sending queries over a QUIC connection, the DNS Message ID MUST
be set to zero.
It is noted that this has implications for proxying DoQ message to
other transports in that a mapping of some form must be performed
(e.g., from DoQ connection/stream to unique Message ID).
5.3. DoQ Error Codes
The following error codes are defined for use when abruptly
terminating streams, aborting reading of streams, or immediately
closing connections:
DOQ_NO_ERROR (0x00): No error. This is used when the connection or
stream needs to be closed, but there is no error to signal.
DOQ_INTERNAL_ERROR (0x01): The DoQ implementation encountered an
internal error and is incapable of pursuing the transaction or the
connection.
DOQ_PROTOCOL_ERROR (0x02): The DoQ implementation encountered an
protocol error and is forcibly aborting the connection.
DOQ_REQUEST_CANCELLED (0x03): A DoQ client uses this to signal that
it wants to cancel an outstanding transaction.
See Section 10.4 for details on registering new error codes.
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5.3.1. Transaction Cancellation
In QUIC, sending STOP_SENDING requests that a peer cease transmission
on a stream. If a DoQ client wishes to cancel an outstanding
request, it MUST issue a QUIC Stop Sending with error code
DOQ_REQUEST_CANCELLED. This may be sent at any time but will be
ignored if the server has already sent the response. The
corresponding DNS transaction MUST be abandoned.
A server that receives STOP_SENDING MUST issue a RESET_STREAM with
error code DOQ_REQUEST_CANCELLED, unless it has already sent a
complete response in which case it MAY ignore the STOP_SENDING
request. Servers MAY limit the number of DOQ_REQUEST_CANCELLED
errors received on a connection before choosing to close the
connection.
Note that this mechanism provides a way for secondaries to cancel a
single zone transfer occurring on a given stream without having to
close the QUIC connection.
5.3.2. Transaction Errors
Servers normally complete transactions by sending a DNS response (or
responses) on the transaction's stream, including cases where the DNS
response indicates a DNS error. For example, a Server Failure
(SERVFAIL, [RFC1035]) SHOULD be notified to the client by sending
back a response with the Response Code set to SERVFAIL.
If a server is incapable of sending a DNS response due to an internal
error, it SHOULD issue a QUIC Stream Reset with error code
DOQ_INTERNAL_ERROR. The corresponding DNS transaction MUST be
abandoned. Clients MAY limit the number of unsolicited QUIC Stream
Resets received on a connection before choosing to close the
connection.
Note that this mechanism provides a way for primaries to abort a
single zone transfer occurring on a given stream without having to
close the QUIC connection.
5.3.3. Protocol Errors
Other error scenarios can occur due to malformed, incomplete or
unexpected messages during a transaction. These include (but are not
limited to)
* a client or server receives a message with a non-zero Message ID
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* a client or server receives a STREAM FIN before receiving all the
bytes for a message indicated in the 2-octet length field
* a client receives a STREAM FIN before receiving all the expected
responses
* a server receives more than one query on a stream
* a client receives a different number of responses on a stream than
expected (e.g. multiple responses to a query for an A record)
* a client receives a STOP_SENDING request
* an implementation receives a message containing the edns-tcp-
keepalive EDNS(0) Option [RFC7828] (see Section 6.5.2)
If a peer encounters such an error condition it is considered a fatal
error. It SHOULD forcibly abort the connection using QUIC's
CONNECTION_CLOSE mechanism, and use the DoQ error code
DOQ_PROTCOL_ERROR.
It is noted that the restrictions on use of the above EDNS(0) options
has implications for proxying message from TCP/DoT/DoH over DoQ.
5.4. Connection Management
Section 10 of the QUIC transport specification [RFC9000] specifies
that connections can be closed in three ways:
* idle timeout
* immediate close
* stateless reset
Clients and servers implementing DoQ SHOULD negotiate use of the idle
timeout. Closing on idle timeout is done without any packet
exchange, which minimizes protocol overhead. Per section 10.1 of the
QUIC transport specification, the effective value of the idle timeout
is computed as the minimum of the values advertised by the two
endpoints. Practical considerations on setting the idle timeout are
discussed in Section 6.5.2.
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Clients SHOULD monitor the idle time incurred on their connection to
the server, defined by the time spent since the last packet from the
server has been received. When a client prepares to send a new DNS
query to the server, it will check whether the idle time is
sufficient lower than the idle timer. If it is, the client will send
the DNS query over the existing connection. If not, the client will
establish a new connection and send the query over that connection.
Clients MAY discard their connection to the server before the idle
timeout expires. If they do that, they SHOULD close the connection
explicitly, using QUIC's CONNECTION_CLOSE mechanism, and use the DoQ
error code DOQ_NO_ERROR.
Clients and servers MAY close the connection for a variety of other
reasons, indicated using QUIC's CONNECTION_CLOSE. Client and servers
that send packets over a connection discarded by their peer MAY
receive a stateless reset indication. If a connection fails, all
queries in progress over the connection MUST be considered failed,
and a Server Failure (SERVFAIL, [RFC1035]) SHOULD be notified to the
initiator of the transaction.
5.5. Session Resumption and 0-RTT
A client MAY take advantage of the session resumption mechanisms
supported by QUIC transport [RFC9000] and QUIC TLS [RFC9001].
Clients SHOULD consider potential privacy issues associated with
session resumption before deciding to use this mechanism. These
privacy issues are detailed in Section 9.2 and Section 9.1, and the
implementation considerations are discussed in Section 6.5.3.
The 0-RTT mechanism SHOULD NOT be used to send DNS requests that are
not "replayable" transactions. Our analysis so far shows that such
replayable transactions can only be QUERY requests, although we may
need to also consider NOTIFY requests once the analysis of NOTIFY
services is complete, see Appendix A.
Servers MUST NOT execute non replayable transactions received in
0-RTT data. Servers MUST adopt one of the following behaviors:
* Queue the offending transaction and only execute it after the QUIC
handshake has been completed, as defined in section 4.1.1 of
[RFC9001].
* Reply to the offending transaction with a response code REFUSED
and an Extended DNS Error Code (EDE) "Too Early", see
Section 10.3.
* Close the connection with the error code DOQ_PROTOCOL_ERROR.
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For the zone transfer scenario, it would be possible to replay an XFR
QUERY that had been sent in 0-RTT data. However the authentication
mechanisms described in RFC9103 ("Zone transfer over TLS") will
ensure that the response is not sent by the primary until the
identity of the secondary has been verified i.e. the first behavior
listed above.
5.6. Message Sizes
DoQ Queries and Responses are sent on QUIC streams, which in theory
can carry up to 2^62 bytes. However, DNS messages are restricted in
practice to a maximum size of 65535 bytes. This maximum size is
enforced by the use of a two-octet message length field in DNS over
TCP [RFC1035] and DNS over TLS [RFC7858], and by the definition of
the "application/dns-message" for DNS over HTTP [RFC8484]. DoQ
enforces the same restriction.
The Extension Mechanisms for DNS (EDNS) [RFC6891] allow peers to
specify the UDP message size. This parameter is ignored by DoQ. DoQ
implementations always assume that the maximum message size is 65535
bytes.
6. Implementation Requirements
6.1. Authentication
For the stub to recursive resolver scenario, the authentication
requirements are the same as described in DoT [RFC7858] and "Usage
Profiles for DNS over TLS and DNS over DTLS" [RFC8310]. There is no
need to authenticate the client's identity in either scenario.
For zone transfer, the requirements are the same as described in
[RFC9103].
For the recursive resolver to authoritative nameserver scenario,
authentication requirements are unspecified at the time of writing
and are the subject on ongoing work in the DPRIVE WG.
6.2. Fall Back to Other Protocols on Connection Failure
If the establishment of the DoQ connection fails, clients MAY attempt
to fall back to DoT and then potentially clear text, as specified in
DoT [RFC7858] and "Usage Profiles for DNS over TLS and DNS over DTLS"
[RFC8310], depending on their privacy profile.
DNS clients SHOULD remember server IP addresses that don't support
DoQ, including timeouts, connection refusals, and QUIC handshake
failures, and not request DoQ from them for a reasonable period (such
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as one hour per server). DNS clients following an out-of-band key-
pinned privacy profile ([RFC7858]) MAY be more aggressive about
retrying DoQ connection failures.
6.3. Address Validation
Section 8 of the QUIC transport specification [RFC9000] defines
Address Validation procedures to avoid servers being used in address
amplification attacks. DoQ implementations MUST conform to this
specification, which limits the worst case amplification to a factor
3.
DoQ implementations SHOULD consider configuring servers to use the
Address Validation using Retry Packets procedure defined in section
8.1.2 of the QUIC transport specification [RFC9000]). This procedure
imposes a 1-RTT delay for verifying the return routability of the
source address of a client, similar to the DNS Cookies mechanism
[RFC7873].
DoQ implementations that configure Address Validation using Retry
Packets SHOULD implement the Address Validation for Future
Connections procedure defined in section 8.1.3 of the QUIC transport
specification [RFC9000]). This defines how servers can send NEW
TOKEN frames to clients after the client address is validated, in
order to avoid the 1-RTT penalty during subsequent connections by the
client from the same address.
6.4. Padding
Implementations SHOULD protect against the traffic analysis attacks
described in Section 9.4 by the judicious injection of padding. This
could be done either by padding individual DNS messages using the
EDNS(0) Padding Option [RFC7830] and by padding QUIC packets (see
Section 8.6 of the QUIC transport specification [RFC9000]).
In theory, padding at the QUIC level could result in better
performance for the equivalent protection, because the amount of
padding can take into account non-DNS frames such as acknowledgeemnts
or flow control updates, and also because QUIC packets can carry
multiple DNS messages. However, applications can only control the
amount of padding in QUIC packets if the implementation of QUIC
exposes adequate APIs. This leads to the following recommendation:
* if the implementation of QUIC exposes APIs to set a padding
policy, DNS over QUIC SHOULD use that API to align the packet
length to a small set of fixed sizes, aligned with the
recommendations of the "Padding Policies for Extension Mechanisms
for DNS (EDNS(0))" [RFC8467].
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* if padding at the QUIC level is not available or not used, DNS
over QUIC MUST ensure that all DNS queries and responses are
padded to a small set of fixed sizes, using the EDNS padding
extension as specified in "Padding Policies for Extension
Mechanisms for DNS (EDNS(0))" [RFC8467].
6.5. Connection Handling
"DNS Transport over TCP - Implementation Requirements" [RFC7766]
provides updated guidance on DNS over TCP, some of which is
applicable to DoQ. This section attempts to specify which and how
those considerations apply to DoQ.
6.5.1. Connection Reuse
Historic implementations of DNS clients are known to open and close
TCP connections for each DNS query. To avoid excess QUIC
connections, each with a single query, clients SHOULD reuse a single
QUIC connection to the recursive resolver.
In order to achieve performance on par with UDP, DNS clients SHOULD
send their queries concurrently over the QUIC streams on a QUIC
connection. That is, when a DNS client sends multiple queries to a
server over a QUIC connection, it SHOULD NOT wait for an outstanding
reply before sending the next query.
6.5.2. Resource Management and Idle Timeout Values
Proper management of established and idle connections is important to
the healthy operation of a DNS server. An implementation of DoQ
SHOULD follow best practices similar to those specified for DNS over
TCP [RFC7766], in particular with regard to:
* Concurrent Connections (Section 6.2.2)
* Security Considerations (Section 10)
Failure to do so may lead to resource exhaustion and denial of
service.
Clients that want to maintain long duration DoQ connections SHOULD
use the idle timeout mechanisms defined in Section 10.1 of the QUIC
transport specification [RFC9000]. Clients and servers MUST NOT send
the edns-tcp-keepalive EDNS(0) Option [RFC7828] in any messages sent
on a DoQ connection (because it is specific to the use of TCP/TLS as
a transport).
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This document does not make specific recommendations for timeout
values on idle connections. Clients and servers should reuse and/or
close connections depending on the level of available resources.
Timeouts may be longer during periods of low activity and shorter
during periods of high activity.
6.5.3. Using 0-RTT and Session Resumption
Using 0-RTT for DNS over QUIC has many compelling advantages.
Clients can establish connections and send queries without incurring
a connection delay. Servers can thus negotiate low values of the
connection timers, which reduces the total number of connections that
they need to manage. They can do that because the clients that use
0-RTT will not incur latency penalties if new connections are
required for a query.
Session resumption and 0-RTT data transmission create privacy risks
detailed in detailed in Section 9.2 and Section 9.1. The following
recommendations are meant to reduce the privacy risks while enjoying
the performance benefits of 0-RTT data, with the restriction
specified in Section 5.5.
Clients SHOULD use resumption tickets only once, as specified in
Appendix C.4 to [RFC8446]. Clients could receive address validation
tokens from the server using the NEW TOKEN mechanism; see section 8
of [RFC9000]. The associated tracking risks are mentioned in
Section 9.3. Clients SHOULD only use the address validation tokens
when they are also using session resumption, thus avoiding additional
tracking risks.
Servers SHOULD issue session resumption tickets with a sufficiently
long life time (e.g., 6 hours), so that clients are not tempted to
either keep connection alive or frequently poll the server to renew
session resumption tickets. Servers SHOULD implement the anti-replay
mechanisms specified in section 8 of [RFC8446].
6.6. Processing Queries in Parallel
As specified in Section 7 of "DNS Transport over TCP - Implementation
Requirements" [RFC7766], resolvers are RECOMMENDED to support the
preparing of responses in parallel and sending them out of order. In
DoQ, they do that by sending responses on their specific stream as
soon as possible, without waiting for availability of responses for
previously opened streams.
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6.7. Zone transfer
[RFC9103] specifies zone transfer over TLS (XoT) and includes updates
to [RFC1995] (IXFR), [RFC5936] (AXFR) and [RFC7766]. Considerations
relating to the re-use of XoT connections described there apply
analogously to zone transfers performed using DoQ connections. For
example:
* DoQ servers MUST be able to handle multiple concurrent IXFR
requests on a single QUIC connection
* DoQ servers MUST be able to handle multiple concurrent AXFR
requests on a single QUIC connection
* DoQ implementations SHOULD
- use the same QUIC connection for both AXFR and IXFR requests to
the same primary
- pipeline such requests (if they pipeline XFR requests in
general) and MAY intermingle them
- send the response(s) for each request as soon as they are
available i.e. responses MAY be sent intermingled
6.8. Flow Control Mechanisms
Servers and Clients manage flow control using the mechanisms defined
in section 4 of [RFC9000]. These mechanisms allow clients and
servers to specify how many streams can be created, how much data can
be sent on a stream, and how much data can be sent on the union of
all streams. For DNS over QUIC, controlling how many streams are
created allows servers to control how many new requests the client
can send on a given connection.
Flow control exists to protect endpoint resources. For servers,
global and per-stream flow control limits control how much data can
be sent by clients. The same mechanisms allow clients to control how
much data can be sent by servers. Values that are too small will
unnecessarily limit performance. Values that are too large might
expose endpoints to overload or memory exhaustion. Implementations
or deployments will need to adjust flow control limits to balance
these concerns. In particular, zone transfer implementations will
need to control these limits carefully to ensure both large and
concurrent zone transfers are well managed.
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Initial values of parameters control how many requests and how much
data can be sent by clients and servers at the beginning of the
connection. These values are specified in transport parameters
exchanged during the connection handshake. The parameter values
received in the initial connection also control how many requests and
how much data can be sent by clients using 0-RTT data in a resumed
connection. Using too small values of these initial parameters would
restrict the usefulness of allowing 0-RTT data.
7. Implementation Status
(RFC EDITOR NOTE: THIS SECTION TO BE REMOVED BEFORE PUBLICATION) This
section records the status of known implementations of the protocol
defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC7942].
1. AdGuard launched a DoQ recursive resolver service in December
2020. They have released a suite of open source tools that
support DoQ:
1. AdGuard C++ DNS libraries (https://github.com/AdguardTeam/
DnsLibs) A DNS proxy library that supports all existing DNS
protocols including DNS-over-TLS, DNS-over-HTTPS, DNSCrypt
and DNS-over-QUIC (experimental).
2. DNS Proxy (https://github.com/AdguardTeam/dnsproxy) A simple
DNS proxy server that supports all existing DNS protocols
including DNS-over-TLS, DNS-over-HTTPS, DNSCrypt, and DNS-
over-QUIC. Moreover, it can work as a DNS-over-HTTPS, DNS-
over-TLS or DNS-over-QUIC server.
3. CoreDNS fork for AdGuard DNS (https://github.com/AdguardTeam/
coredns) Includes DNS-over-QUIC server-side support.
4. dnslookup (https://github.com/ameshkov/dnslookup) Simple
command line utility to make DNS lookups. Supports all known
DNS protocols: plain DNS, DoH, DoT, DoQ, DNSCrypt.
2. Quicdoq (https://github.com/private-octopus/quicdoq) Quicdoq is a
simple open source implementation of DoQ. It is written in C,
based on Picoquic (https://github.com/private-octopus/picoquic).
3. Flamethrower (https://github.com/DNS-OARC/flamethrower/tree/dns-
over-quic) is an open source DNS performance and functional
testing utility written in C++ that has an experimental
implementation of DoQ.
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4. aioquic (https://github.com/aiortc/aioquic) is an implementation
of QUIC in Python. It includes example client and server for
DoQ.
7.1. Performance Measurements
To our knowledge, no benchmarking studies comparing DoT, DoH and DoQ
are published yet. However anecdotal evidence from the AdGuard DoQ
recursive resolver deployment (https://adguard.com/en/blog/dns-over-
quic.html) indicates that it performs well compared to the other
encrypted protocols, particularly in mobile environments. Reasons
given for this include that DoQ
* Uses less bandwidth due to a more efficient handshake (and due to
less per message overhead when compared to DoH).
* Performs better in mobile environments due to the increased
resilience to packet loss
* Can maintain connections as users move between mobile networks via
its connection management
8. Security Considerations
The security considerations of DoQ should be comparable to those of
DoT [RFC7858].
9. Privacy Considerations
The general considerations of encrypted transports provided in "DNS
Privacy Considerations" [I-D.ietf-dprive-rfc7626-bis] apply to DoQ.
The specific considerations provided there do not differ between DoT
and DoQ, and are not discussed further here.
QUIC incorporates the mechanisms of TLS 1.3 [RFC8446] and this
enables QUIC transmission of "0-RTT" data. This can provide
interesting latency gains, but it raises two concerns:
1. Adversaries could replay the 0-RTT data and infer its content
from the behavior of the receiving server.
2. The 0-RTT mechanism relies on TLS session resumption, which can
provide linkability between successive client sessions.