Network Working Group                                         C. Huitema
Internet-Draft                                      Private Octopus Inc.
Intended status: Standards Track                            S. Dickinson
Expires: January 13, 2022                                     Sinodun IT
                                                               A. Mankin
                                                              Salesforce
                                                           July 12, 2021


          Specification of DNS over Dedicated QUIC Connections
                     draft-ietf-dprive-dnsoquic-03

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 January 13, 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



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   carefully, as they describe your rights 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 . . . . . . . . . . . . . . . . . . .   4
     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  . . . . . . . . . . . . . . . . . . .   6
     5.2.  Stream Mapping and Usage  . . . . . . . . . . . . . . . .   7
       5.2.1.  DNS Message IDs . . . . . . . . . . . . . . . . . . .   8
     5.3.  DoQ Error Codes . . . . . . . . . . . . . . . . . . . . .   8
       5.3.1.  Transaction Errors  . . . . . . . . . . . . . . . . .   8
       5.3.2.  Protocol Errors . . . . . . . . . . . . . . . . . . .   8
     5.4.  Connection Management . . . . . . . . . . . . . . . . . .   9
     5.5.  Connection Resume and 0-RTT . . . . . . . . . . . . . . .  10
     5.6.  Message Sizes . . . . . . . . . . . . . . . . . . . . . .  10
   6.  Implementation Requirements . . . . . . . . . . . . . . . . .  11
     6.1.  Authentication  . . . . . . . . . . . . . . . . . . . . .  11
     6.2.  Fall Back to Other Protocols on Connection Failure  . . .  11
     6.3.  Address Validation  . . . . . . . . . . . . . . . . . . .  11
     6.4.  Padding . . . . . . . . . . . . . . . . . . . . . . . . .  12
     6.5.  Connection Handling . . . . . . . . . . . . . . . . . . .  12
       6.5.1.  Connection Reuse  . . . . . . . . . . . . . . . . . .  12
       6.5.2.  Resource Management and Idle Timeout Values . . . . .  13
     6.6.  Processing Queries in Parallel  . . . . . . . . . . . . .  13
     6.7.  Zone transfer . . . . . . . . . . . . . . . . . . . . . .  14
     6.8.  Flow Control Mechanisms . . . . . . . . . . . . . . . . .  14
   7.  Implementation Status . . . . . . . . . . . . . . . . . . . .  14
     7.1.  Performance Measurements  . . . . . . . . . . . . . . . .  15
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   9.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  16
     9.1.  Privacy Issues With 0-RTT data  . . . . . . . . . . . . .  16
     9.2.  Privacy Issues With Session Resume  . . . . . . . . . . .  16
     9.3.  Traffic Analysis  . . . . . . . . . . . . . . . . . . . .  17
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
     10.1.  Registration of DoQ Identification String  . . . . . . .  17



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     10.2.  Reservation of Dedicated Port  . . . . . . . . . . . . .  17
       10.2.1.  Port number 784 for experimentations . . . . . . . .  18
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  18
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  19
     12.2.  Informative References . . . . . . . . . . . . . . . . .  20
     12.3.  URIs . . . . . . . . . . . . . . . . . . . . . . . . . .  21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  22

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

   o  the "stub to recursive resolver" scenario

   o  the "recursive resolver to authoritative nameserver" scenario and

   o  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.



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   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.

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.




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   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"
       [I-D.ietf-quic-recovery].

   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.

   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.






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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.  DSO is only applicable for DNS over
   TCP and DNS over TLS.  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.

   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,



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   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].

   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



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   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 (0x01):  The DoQ implementation encountered an
      protocol error and is forcibly aborting the connection.

5.3.1.  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 may issue a QUIC Stream Reset with error code
   DOQ_INTERNAL_ERROR.  The corresponding transaction MUST be abandoned.

5.3.2.  Protocol Errors

   Other error scenarios can occur due to malformed, incomplete or
   unexpected messages during a transaction.  These include (but are not
   limited to)

   o  a client or server receives a message with a non-zero Message ID




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   o  a client or server receives a STREAM FIN before receiving all the
      bytes for a message indicated in the 2-octet length field

   o  a client receives a STREAM FIN before receiving all the expected
      responses

   o  a server receives more than one query on a stream

   o  a client receives a different number of responses on a stream than
      expected (e.g. multiple responses to a query for an A record)

   o  an implementation receives a message containing the edns-tcp-
      keepalive EDNS(0) Option [RFC7828] (see Section 6.5.2)

   o  an implementation receives a message containing the EDNS(0)
      Padding Option [RFC7830] (see Section 6.4)

   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:

   o  idle timeout

   o  immediate close

   o  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.

   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



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   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.  Connection Resume and 0-RTT

   A client MAY take advantage of the connection resume mechanisms
   supported by QUIC transport [RFC9000] and QUIC TLS [RFC9001].
   Clients SHOULD consider potential privacy issues associated with
   session resume before deciding to use this mechanism.  These privacy
   issues are detailed in Section 9.2.

   When resuming a session, a client MAY take advantage of the 0-RTT
   mechanism supported by QUIC.  The 0-RTT mechanism MUST NOT be used to
   send data that is not "replayable" transactions.  For example, a
   client MAY transmit a Query as 0-RTT, but MUST NOT transmit an
   Update.

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 flow control mechanisms of QUIC control how much data can be sent
   by QUIC nodes at a given time.  The initial values of per stream flow
   control parameters is defined by two transport parameters:

   o  initial_max_stream_data_bidi_local: when set by the client,
      specifies the amount of data that servers can send on a "response"
      stream without waiting for a MAX_STREAM_DATA frame.



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   o  initial_max_stream_data_bidi_remote: when set by the server,
      specifies the amount of data that clients can send on a "query"
      stream without waiting for a MAX_STREAM_DATA frame.

   For better performance, it is RECOMMENDED that clients and servers
   set each of these two parameters to a value of 65535 or greater.

   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
   [I-D.ietf-dprive-xfr-over-tls].

   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
   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




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   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

   There are mechanisms specified for padding individual DNS messages in
   "The EDNS(0) Padding Option" [RFC7830] and for padding within QUIC
   packets (see Section 8.6 of the QUIC transport specification
   [RFC9000]).

   Implementations MUST NOT use DNS options for padding individual DNS
   messages, because QUIC transport MAY transmit multiple STREAM frames
   containing separate DNS messages in a single QUIC packet.  Instead,
   implementations SHOULD use QUIC PADDING frames 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].

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.





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   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:

   o  Concurrent Connections (Section 6.2.2)

   o  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).

   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.

   Clients that are willing to use QUIC's 0-RTT mechanism can
   reestablish connections and send transactions on the new connection
   with minimal delay overhead.  These clients MAY chose low values of
   the idle timer.

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

   [I-D.ietf-dprive-xfr-over-tls] 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:

   o  DoQ servers MUST be able to handle multiple concurrent IXFR
      requests on a single QUIC connection

   o  DoQ servers MUST be able to handle multiple concurrent AXFR
      requests on a single QUIC connection

   o  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 as specified in QUIC.

   Servers MAY use the "maximum stream ID" option of the QUIC transport
   to limit the number of streams opened by the client.  This mechanism
   will effectively limit the number of DNS queries that a client can
   send on a single DoQ connection.

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 [1] A DNS proxy library that
           supports all existing DNS protocols including DNS-over-TLS,
           DNS-over-HTTPS, DNSCrypt and DNS-over-QUIC (experimental).



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       2.  DNS Proxy [2] 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 [3] Includes DNS-over-QUIC
           server-side support.

       4.  dnslookup [4] Simple command line utility to make DNS
           lookups.  Supports all known DNS protocols: plain DNS, DoH,
           DoT, DoQ, DNSCrypt.

   2.  Quicdoq [5] Quicdoq is a simple open source implementation of
       DoQ.  It is written in C, based on Picoquic [6].

   3.  Flamethrower [7] is an open source DNS performance and functional
       testing utility written in C++ that has an experimental
       implementation of DoQ.

   4.  aioquic [8] 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 [9] indicates that it performs well
   compared to the other encrypted protocols, particularly in mobile
   environments.  Reasons given for this include that DoQ

   o  Uses less bandwidth due to a more efficient handshake (and due to
      less per message overhead when compared to DoH).

   o  Performs better in mobile environments due to the increased
      resilience to packet loss

   o  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].








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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 resume, which can provide
       linkability between successive client sessions.

   These issues are developed in Section 9.1 and Section 9.2.

9.1.  Privacy Issues With 0-RTT data

   The 0-RTT data can be replayed by adversaries.  That data may trigger
   queries by a recursive resolver to authoritative resolvers.
   Adversaries may be able to pick a time at which the recursive
   resolver outgoing traffic is observable, and thus find out what name
   was queried for in the 0-RTT data.

   This risk is in fact a subset of the general problem of observing the
   behavior of the recursive resolver discussed in "DNS Privacy
   Considerations" [RFC7626].  The attack is partially mitigated by
   reducing the observability of this traffic.  However, the risk is
   amplified for 0-RTT data, because the attacker might replay it at
   chosen times, several times.

   The recommendation for TLS 1.3 [RFC8446] is that the capability to
   use 0-RTT data should be turned off by default, and only enabled if
   the user clearly understands the associated risks.

   QUESTION: Should 0-RTT only be used with Opportunistic profiles (i.e.
   disabled by default for Strict only)?

9.2.  Privacy Issues With Session Resume

   The QUIC session resume mechanism reduces the cost of re-establishing
   sessions and enables 0-RTT data.  There is a linkability issue
   associated with session resume, if the same resume token is used
   several times, but this risk is mitigated by the mechanisms
   incorporated in QUIC and in TLS 1.3.  With these mechanisms, clients



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   and servers can cooperate to avoid linkability by third parties.
   However, the server will always be able to link the resumed session
   to the initial session.  This creates a virtual long duration
   session.  The series of queries in that session can be used by the
   server to identify the client.

   Enabling the server to link client sessions through session resume is
   probably not a large additional risk if the client's connectivity did
   not change between the sessions, since the two sessions can probably
   be correlated by comparing the IP addresses.  On the other hand, if
   the addresses did change, the client SHOULD consider whether the
   linkability risk exceeds the performance benefits.  This evaluation
   will obviously depend on the level of trust between client and
   server.

9.3.  Traffic Analysis

   Even though QUIC packets are encrypted, adversaries can gain
   information from observing packet lengths, in both queries and
   responses, as well as packet timing.  Many DNS requests are emitted
   by web browsers.  Loading a specific web page may require resolving
   dozen of DNS names.  If an application adopts a simple mapping of one
   query or response per packet, or "one QUIC STREAM frame per packet",
   then the succession of packet lengths may provide enough information
   to identify the requested site.

   Implementations SHOULD use the mechanisms defined in Section 6.4 to
   mitigate this attack.

10.  IANA Considerations

10.1.  Registration of DoQ Identification String

   This document creates a new registration for the identification of
   DoQ in the "Application Layer Protocol Negotiation (ALPN) Protocol
   IDs" registry [RFC7301].

   The "doq" string identifies DoQ:

       Protocol:                 DoQ
       Identification Sequence:  0x64 0x6F 0x71 ("doq")
       Specification:            This document

10.2.  Reservation of Dedicated Port

   Port 853 is currently reserved for 'DNS query-response protocol run
   over TLS/DTLS' [RFC7858].  However, the specification for DNS over
   DTLS (DoD) [RFC8094] is experimental, limited to stub to resolver,



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   and no implementations or deployments currently exist to our
   knowledge (even though several years have passed since the
   specification was published).

   This specification proposes to additionally reserve the use of port
   853 for DoQ.  Whilst [RFC8094] did not specify the use of an ALPN for
   DoD, DoQ requires the use of the "doq" ALPN and is therefore de-
   muxable from DoD.

   IANA is requested to add the following value to the "Service Name and
   Transport Protocol Port Number Registry" in the System Range.  The
   registry for that range requires IETF Review or IESG Approval
   [RFC6335].

      Service Name           dns-over-quic
      Port Number            853
      Transport Protocol(s)  UDP
      Assignee               IESG
      Contact                IETF Chair
      Description            DNS query-response protocol run over QUIC
      Reference              This document

10.2.1.  Port number 784 for experimentations

   (RFC EDITOR NOTE: THIS SECTION TO BE REMOVED BEFORE PUBLICATION)
   Early experiments MAY use port 784.  This port is marked in the IANA
   registry as unassigned.

   (Note that version in -02 of this draft experiments were directed to
   use port 8853.)

11.  Acknowledgements

   This document liberally borrows text from the HTTP-3 specification
   [I-D.ietf-quic-http] edited by Mike Bishop, and from the DoT
   specification [RFC7858] authored by Zi Hu, Liang Zhu, John Heidemann,
   Allison Mankin, Duane Wessels, and Paul Hoffman.

   The privacy issue with 0-RTT data and session resume were analyzed by
   Daniel Kahn Gillmor (DKG) in a message to the IETF "DPRIVE" working
   group [DNS0RTT].

   Thanks to Tony Finch for an extensive review of the initial version
   of this draft.  Reviews by Paul Hoffman and interoperability tests
   conducted by Stephane Bortzmeyer helped improve the definition of the
   protocol.





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12.  References

12.1.  Normative References

   [I-D.ietf-dnsop-rfc8499bis]
              Hoffman, P. and K. Fujiwara, "DNS Terminology", draft-
              ietf-dnsop-rfc8499bis-02 (work in progress), June 2021.

   [I-D.ietf-dprive-xfr-over-tls]
              Toorop, W., Dickinson, S., Sahib, S., Aras, P., and A.
              Mankin, "DNS Zone Transfer-over-TLS", draft-ietf-dprive-
              xfr-over-tls-12 (work in progress), May 2021.

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
              <https://www.rfc-editor.org/info/rfc1034>.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
              November 1987, <https://www.rfc-editor.org/info/rfc1035>.

   [RFC1995]  Ohta, M., "Incremental Zone Transfer in DNS", RFC 1995,
              DOI 10.17487/RFC1995, August 1996,
              <https://www.rfc-editor.org/info/rfc1995>.

   [RFC5936]  Lewis, E. and A. Hoenes, Ed., "DNS Zone Transfer Protocol
              (AXFR)", RFC 5936, DOI 10.17487/RFC5936, June 2010,
              <https://www.rfc-editor.org/info/rfc5936>.

   [RFC6891]  Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
              for DNS (EDNS(0))", STD 75, RFC 6891,
              DOI 10.17487/RFC6891, April 2013,
              <https://www.rfc-editor.org/info/rfc6891>.

   [RFC7301]  Friedl, S., Popov, A., Langley, A., and E. Stephan,
              "Transport Layer Security (TLS) Application-Layer Protocol
              Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301,
              July 2014, <https://www.rfc-editor.org/info/rfc7301>.

   [RFC7766]  Dickinson, J., Dickinson, S., Bellis, R., Mankin, A., and
              D. Wessels, "DNS Transport over TCP - Implementation
              Requirements", RFC 7766, DOI 10.17487/RFC7766, March 2016,
              <https://www.rfc-editor.org/info/rfc7766>.

   [RFC7828]  Wouters, P., Abley, J., Dickinson, S., and R. Bellis, "The
              edns-tcp-keepalive EDNS0 Option", RFC 7828,
              DOI 10.17487/RFC7828, April 2016,
              <https://www.rfc-editor.org/info/rfc7828>.



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   [RFC7830]  Mayrhofer, A., "The EDNS(0) Padding Option", RFC 7830,
              DOI 10.17487/RFC7830, May 2016,
              <https://www.rfc-editor.org/info/rfc7830>.

   [RFC7858]  Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
              and P. Hoffman, "Specification for DNS over Transport
              Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
              2016, <https://www.rfc-editor.org/info/rfc7858>.

   [RFC7873]  Eastlake 3rd, D. and M. Andrews, "Domain Name System (DNS)
              Cookies", RFC 7873, DOI 10.17487/RFC7873, May 2016,
              <https://www.rfc-editor.org/info/rfc7873>.

   [RFC8094]  Reddy, T., Wing, D., and P. Patil, "DNS over Datagram
              Transport Layer Security (DTLS)", RFC 8094,
              DOI 10.17487/RFC8094, February 2017,
              <https://www.rfc-editor.org/info/rfc8094>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8310]  Dickinson, S., Gillmor, D., and T. Reddy, "Usage Profiles
              for DNS over TLS and DNS over DTLS", RFC 8310,
              DOI 10.17487/RFC8310, March 2018,
              <https://www.rfc-editor.org/info/rfc8310>.

   [RFC8484]  Hoffman, P. and P. McManus, "DNS Queries over HTTPS
              (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
              <https://www.rfc-editor.org/info/rfc8484>.

   [RFC9000]  Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
              Multiplexed and Secure Transport", RFC 9000,
              DOI 10.17487/RFC9000, May 2021,
              <https://www.rfc-editor.org/info/rfc9000>.

   [RFC9001]  Thomson, M., Ed. and S. Turner, Ed., "Using TLS to Secure
              QUIC", RFC 9001, DOI 10.17487/RFC9001, May 2021,
              <https://www.rfc-editor.org/info/rfc9001>.

12.2.  Informative References

   [DNS0RTT]  Kahn Gillmor, D., "DNS + 0-RTT", Message to DNS-Privacy WG
              mailing list, April 2016, <https://www.ietf.org/mail-
              archive/web/dns-privacy/current/msg01276.html>.






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   [I-D.ietf-dprive-rfc7626-bis]
              Wicinski, T., "DNS Privacy Considerations", draft-ietf-
              dprive-rfc7626-bis-09 (work in progress), March 2021.

   [I-D.ietf-quic-http]
              Bishop, M., "Hypertext Transfer Protocol Version 3
              (HTTP/3)", draft-ietf-quic-http-34 (work in progress),
              February 2021.

   [I-D.ietf-quic-recovery]
              Iyengar, J. and I. Swett, "QUIC Loss Detection and
              Congestion Control", draft-ietf-quic-recovery-34 (work in
              progress), January 2021.

   [RFC6335]  Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
              Cheshire, "Internet Assigned Numbers Authority (IANA)
              Procedures for the Management of the Service Name and
              Transport Protocol Port Number Registry", BCP 165,
              RFC 6335, DOI 10.17487/RFC6335, August 2011,
              <https://www.rfc-editor.org/info/rfc6335>.

   [RFC7626]  Bortzmeyer, S., "DNS Privacy Considerations", RFC 7626,
              DOI 10.17487/RFC7626, August 2015,
              <https://www.rfc-editor.org/info/rfc7626>.

   [RFC7942]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", BCP 205,
              RFC 7942, DOI 10.17487/RFC7942, July 2016,
              <https://www.rfc-editor.org/info/rfc7942>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [RFC8467]  Mayrhofer, A., "Padding Policies for Extension Mechanisms
              for DNS (EDNS(0))", RFC 8467, DOI 10.17487/RFC8467,
              October 2018, <https://www.rfc-editor.org/info/rfc8467>.

   [RFC8490]  Bellis, R., Cheshire, S., Dickinson, J., Dickinson, S.,
              Lemon, T., and T. Pusateri, "DNS Stateful Operations",
              RFC 8490, DOI 10.17487/RFC8490, March 2019,
              <https://www.rfc-editor.org/info/rfc8490>.

12.3.  URIs

   [1] https://github.com/AdguardTeam/DnsLibs

   [2] https://github.com/AdguardTeam/dnsproxy



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   [3] https://github.com/AdguardTeam/coredns

   [4] https://github.com/ameshkov/dnslookup

   [5] https://github.com/private-octopus/quicdoq

   [6] https://github.com/private-octopus/picoquic

   [7] https://github.com/DNS-OARC/flamethrower/tree/dns-over-quic

   [8] https://github.com/aiortc/aioquic

   [9] https://adguard.com/en/blog/dns-over-quic.html

Authors' Addresses

   Christian Huitema
   Private Octopus Inc.
   427 Golfcourse Rd
   Friday Harbor  WA 98250
   U.S.A

   Email: huitema@huitema.net


   Sara Dickinson
   Sinodun IT
   Oxford Science Park
   Oxford  OX4 4GA
   U.K.

   Email: sara@sinodun.com


   Allison Mankin
   Salesforce

   Email: allison.mankin@gmail.com













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