Network Working Group                                         C. Huitema
Internet-Draft                                      Private Octopus Inc.
Intended status: Standards Track                            S. Dickinson
Expires: 23 April 2022                                        Sinodun IT
                                                               A. Mankin
                                                              Salesforce
                                                         20 October 2021


                  DNS over Dedicated QUIC Connections
                     draft-ietf-dprive-dnsoquic-06

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
   packet loss recovery 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 23 April 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 . . . . . . . . . . . . . . . . . . .  10
       5.3.4.  Alternative error codes . . . . . . . . . . . . . . .  11
     5.4.  Connection Management . . . . . . . . . . . . . . . . . .  11
     5.5.  Session Resumption and 0-RTT  . . . . . . . . . . . . . .  12
     5.6.  Message Sizes . . . . . . . . . . . . . . . . . . . . . .  12
   6.  Implementation Requirements . . . . . . . . . . . . . . . . .  13
     6.1.  Authentication  . . . . . . . . . . . . . . . . . . . . .  13
     6.2.  Fallback to Other Protocols on Connection Failure . . . .  13
     6.3.  Address Validation  . . . . . . . . . . . . . . . . . . .  13
     6.4.  Padding . . . . . . . . . . . . . . . . . . . . . . . . .  14
     6.5.  Connection Handling . . . . . . . . . . . . . . . . . . .  15
       6.5.1.  Connection Reuse  . . . . . . . . . . . . . . . . . .  15
       6.5.2.  Resource Management . . . . . . . . . . . . . . . . .  15
       6.5.3.  Using 0-RTT and Session Resumption  . . . . . . . . .  16
       6.5.4.  Controlling Connection Migration For Privacy  . . . .  16
     6.6.  Processing Queries in Parallel  . . . . . . . . . . . . .  17
     6.7.  Zone transfer . . . . . . . . . . . . . . . . . . . . . .  17
     6.8.  Flow Control Mechanisms . . . . . . . . . . . . . . . . .  17
   7.  Implementation Status . . . . . . . . . . . . . . . . . . . .  18
     7.1.  Performance Measurements  . . . . . . . . . . . . . . . .  19
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  19
   9.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  19
     9.1.  Privacy Issues With 0-RTT data  . . . . . . . . . . . . .  20
     9.2.  Privacy Issues With Session Resumption  . . . . . . . . .  20



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     9.3.  Privacy Issues With Address Validation Tokens . . . . . .  21
     9.4.  Privacy Issues With Long Duration Sessions  . . . . . . .  22
     9.5.  Traffic Analysis  . . . . . . . . . . . . . . . . . . . .  22
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  22
     10.1.  Registration of DoQ Identification String  . . . . . . .  22
     10.2.  Reservation of Dedicated Port  . . . . . . . . . . . . .  23
       10.2.1.  Port number 784 for experimentations . . . . . . . .  23
     10.3.  Reservation of Extended DNS Error Code Too Early . . . .  23
     10.4.  DNS over QUIC Error Codes Registry . . . . . . . . . . .  24
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  25
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  26
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  26
     12.2.  Informative References . . . . . . . . . . . . . . . . .  28
   Appendix A.  The NOTIFY Service . . . . . . . . . . . . . . . . .  29
   Appendix B.  Notable Changes From Previous Versions . . . . . . .  30
     B.1.  Stream Mapping Incompatibility With Draft-02  . . . . . .  30
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  30

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.

   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




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   *  the "recursive resolver to authoritative nameserver" scenario and

   *  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" [RFC9076] 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 protocol-induced delays, with
   features such as:

   1.  Support for 0-RTT data during session resumption.

   2.  Support for advanced packet loss 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.  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.





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   These considerations are 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 does support server-initiated transactions within existing
   connections.  However DoQ as defined here does not meet the criteria
   for an applicable transport for DSO because it does not guarantee in-
   order delivery of messages, see Section 4.2 of [RFC8490].

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".








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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 there is a mutual agreement to use another
   port.

   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 there is a mutual agreement to use another port.

   In order to use a port other than TBD, both clients and servers would
   need a configuration option in their software.

   DoQ connections MUST NOT use UDP 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].

   In the stub to recursive scenario, the use of port 443 as a mutually
   agreed alternative port can be operationally beneficial, since port
   443 is less likely to be blocked than other ports.  Several
   mechanisms for stubs to discover recursives offering encrypted
   transports, including the use of custom ports, are the subject of
   ongoing work.

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 [RFC9000], the QUIC
   transport specification.

   DNS traffic follows a simple pattern in which the client sends a
   query, and the server provides one or more responses (multiple
   responses can 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].




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   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.

   Servers MAY defer processing of a query until the STREAM FIN has been
   indicated on the stream selected by the client.  Servers and clients
   MAY monitor the number of "dangling" streams for which the expected
   queries or responses have been received but not the STREAM FIN.
   Implementations MAY impose a limit on the number of such dangling
   streams.  If limits are encountered, implementations MAY close the
   connection.

5.2.1.  DNS Message IDs

   When sending queries over a QUIC connection, the DNS Message ID MUST
   be set to zero.

   This has implications for proxying DoQ message to and from other
   transports.  For example, proxies may have to manage the fact that
   DoQ can support a larger number of outstanding queries on a single
   connection than e.g., DNS over TCP because DoQ is not limited by the
   Message ID space.

   When forwarding a DNS message from DoQ over another transport, a DNS
   Message ID MUST be generated according to the rules of the protocol
   that is in use.  When forwarding a DNS message from another transport
   over DoQ, the Message ID MUST be set to zero.

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 (0x0):  No error.  This is used when the connection or
      stream needs to be closed, but there is no error to signal.



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   DOQ_INTERNAL_ERROR (0x1):  The DoQ implementation encountered an
      internal error and is incapable of pursuing the transaction or the
      connection.

   DOQ_PROTOCOL_ERROR (0x2):  The DoQ implementation encountered an
      protocol error and is forcibly aborting the connection.

   DOQ_REQUEST_CANCELLED (0x3):  A DoQ client uses this to signal that
      it wants to cancel an outstanding transaction.

   DOQ_EXCESSIVE_LOAD (0x4):  A DoQ implementation uses this to signal
      when closing a connection due to excessive load.

   DOQ_ERROR_RESERVED (0xd098ea5e):  Alternative error code used for
      tests.

   See Section 10.4 for details on registering new error codes.

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.

   Servers that receive STOP_SENDING act in accordance with Section 3.5
   of [RFC9000].  Servers MAY impose implementation limits on the total
   number or rate of request cancellations.  If limits are encountered,
   servers MAY close the connection.  In this case, servers wanting to
   help client debugging MAY use the error code DOQ_EXCESSIVE_LOAD.
   There is always a trade-off between helping good faith clients debug
   issues and allowing denial-of-service attackers to test server
   defenses, so depending on circumstances servers might very well chose
   to send different error codes.

   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.



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   If a server is incapable of sending a DNS response due to an internal
   error, it SHOULD issue a QUIC Stream Reset.  The error code SHOULD be
   set to 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

   *  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

   *  the client or server does not indicate the expected STREAM FIN
      after sending requests or responses (see Section 5.2).

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

   *  a client or a server attempts to open an unidirectional QUIC
      stream

   *  a server attempts to open a server-initiated bidirectional QUIC
      stream

   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 SHOULD use the DoQ error code
   DOQ_PROTOCOL_ERROR.



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   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.

5.3.4.  Alternative error codes

   This specification suggests specific error codes Section 5.3.1,
   Section 5.3.2, and Section 5.3.3.  These error codes are meant to
   facilitates investigation of failures and other incidents.  New error
   codes may be defined in future versions of DoQ, or registered as
   specified in Section 10.4.

   Because new error codes can be defined without negotiation, use of an
   error code in an unexpected context or receipt of an unknown error
   code MUST be treated as equivalent to DOQ_NO_ERROR.

   Implementations MAY wish to test the support for the error code
   extension mechanism by using error codes not listed in this document,
   or they MAY use DOQ_ERROR_RESERVED.

5.4.  Connection Management

   Section 10 of [RFC9000], the QUIC transport specification, 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
   [RFC9000], 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
   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.






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   Clients MAY discard their connections to the server before the idle
   timeout expires.  A client that has outstanding queries SHOULD close
   the connection explicitly using QUIC's CONNECTION_CLOSE mechanism and
   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 the
   in progress transaction on that connection MUST be abandoned.

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.  In this specification, only
   transactions that have an OPCODE of QUERY or NOTIFY are considered
   replayable and MAY be sent in 0-RTT data.  See Appendix A for a
   detailed discussion of why NOTIFY is included here.

   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.

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.



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   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].  [RFC8932]
   states that DNS privacy services SHOULD provide credentials that
   clients can use to authenticate the server.  Given this, and to align
   with the authentication model for DoH, DoQ stubs SHOULD use a Strict
   authentication profile.  Client authentication for the encrypted stub
   to recursive scenario is not described in any DNS RFC.

   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.  Fallback 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.  Timeouts, connection refusals, and QUIC handshake failures are
   valid indicators that a server does not support DoQ.  Clients SHOULD
   NOT attempt DoQ queries to a server that does not support DoQ 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 [RFC9000], the QUIC transport specification, 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.




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   DoQ implementations SHOULD consider configuring servers to use the
   Address Validation using Retry Packets procedure defined in
   Section 8.1.2 of [RFC9000], the QUIC transport specification.  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 [RFC9000], the QUIC
   transport specification.  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 9.5 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 [RFC9000], the QUIC transport specification.

   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].

   *  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].









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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 provides similar advice on
   connection handling for DoQ.

6.5.1.  Connection Reuse

   Historic implementations of DNS clients are known to open and close
   TCP connections for each DNS query.  To amortise connection setup
   costs, both clients and servers SHOULD support connection reuse by
   sending multiple queries and responses over a single persistent QUIC
   connection.

   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

   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 of [RFC7766], updated by
      Section 6.4 of [RFC9103])

   *  Security Considerations (Section 10 of [RFC7766])

   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 [RFC9000],
   the QUIC transport specification.  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].  By default, clients SHOULD NOT use
   session resumption if the client's connectivity has changed.

   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].

6.5.4.  Controlling Connection Migration For Privacy

   DoQ implementation might consider using the connection migration
   features defined in Section 9 of [RFC9000].  These features enable
   connections to continue operating as the client's connectivity
   changes.  As detailed in Section 9.4, these features trade off
   privacy for latency.  By default, clients SHOULD be configured to
   prioritise privacy and start new sessions if their connectivity
   changes.




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6.6.  Processing Queries in Parallel

   As specified in Section 7 of [RFC7766] "DNS Transport over TCP -
   Implementation Requirements", 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.

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



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   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.

   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).



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   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.

   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" [RFC9076] apply to DoQ.  The specific
   considerations provided there do not differ between DoT and DoQ, and
   are not discussed further here.  Similarly, "Recommendations for DNS
   Privacy Service Operators" [RFC8932] (which covers operational,
   policy, and security considerations for DNS privacy services) is also
   applicable to DoQ services.

   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.



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   2.  The 0-RTT mechanism relies on TLS session resumption, 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" [RFC9076].  The attack is partially mitigated by
   reducing the observability of this traffic.  The mandatory replay
   protection mechanisms in TLS 1.3 [RFC8446] limit but do not eliminate
   the risk of replay. 0-RTT packets can only be replayed within a
   narrow window, which is only wide enough to account for variations in
   clock skew and network transmission.

   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.  In our case,
   allowing 0-RTT data provides significant performance gains, and we
   are concerned that a recommendation to not use it would simply be
   ignored.  Instead, we provide a set of practical recommendations in
   Section 5.5 and Section 6.5.3.

   The prevention on allowing replayable transactions in 0-RTT data
   expressed in Section 5.5 blocks the most obvious risks of replay
   attacks, as it only allows for transactions that will not change the
   long term state of the server.

   The attacks described above apply to the stub resolver to recursive
   resolver scenario, but similar attacks might be envisaged in the
   recursive resolver to authoritative resolver scenario, and the same
   mitigations apply.

9.2.  Privacy Issues With Session Resumption

   The QUIC session resumption mechanism reduces the cost of re-
   establishing sessions and enables 0-RTT data.  There is a linkability
   issue associated with session resumption, if the same resumption
   token is used several times.  Attackers on path between client and
   server could observe repeated usage of the token and use that to
   track the client over time or over multiple locations.



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   The session resumption mechanism allows servers to correlate the
   resumed sessions with the initial sessions, and thus to track the
   client.  This creates a virtual long duration session.  The series of
   queries in that session can be used by the server to identify the
   client.  Servers can most probably do that already if the client
   address remains constant, but session resumption tickets also enable
   tracking after changes of the client's address.

   The recommendations in Section 6.5.3 are designed to mitigate these
   risks.  Using session tickets only once mitigates the risk of
   tracking by third parties.  Refusing to resume a session if addresses
   change mitigates the risk of tracking by the server.

   The privacy trade-offs here may be context specific.  Stub resolvers
   will have a strong motivation to prefer privacy over latency since
   they often change location.  However, recursive resolvers that use a
   small set of static IP addresses are more likely to prefer the
   reduced latency provided by session resumption and may consider this
   a valid reason to use resumption tickets even if the IP address
   changed between sessions.

   Encrypted zone transfer (RFC9103) explicitly does not attempt to hide
   the identity of the parties involved in the transfer, but at the same
   time such transfers are not particularly latency sensitive.  This
   means that applications supporting zone transfers may decide to apply
   the same protections as stub to recursive applications.

9.3.  Privacy Issues With Address Validation Tokens

   QUIC specifies address validation mechanisms in Section 8 of
   [RFC9000].  Use of an address validation token allows QUIC servers to
   avoid an extra RTT for new connections.  Address validation tokens
   are typically tied to an IP address.  QUIC clients normally only use
   these tokens when setting a new connection from a previously used
   address.  However, due to the prevalence of NAT, clients are not
   always aware that they are using a new address.  There is a
   linkability risk if clients mistakenly use address validation tokens
   after unknowingly moving to a new location.

   The recommendations in Section 6.5.3 mitigates this risk by tying the
   usage of the NEW_TOKEN to that of session resumption.










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9.4.  Privacy Issues With Long Duration Sessions

   A potential alternative to session resumption is the use of long
   duration sessions: if a session remains open for a long time, new
   queries can be sent without incurring connection establishment
   delays.  It is worth pointing out that the two solutions have similar
   privacy characteristics.  Session resumption may allow servers to
   keep track of the IP addresses of clients, but long duration sessions
   have the same effect.

   In particular, a DoQ implementation might take advantage of the
   connection migration features of QUIC to maintain a session even if
   the client's connectivity changes, for example if the client migrates
   from a Wi-Fi connection to a cellular network connection, and then to
   another Wi-Fi connection.  The server would be able to track the
   client location by monitoring the succession of IP addresses used by
   the long duration connection.

   The recommendation in Section 6.5.4 mitigates the privacy concerns
   related to long duration sessions using multiple client addresses.

9.5.  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")



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   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,
   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.  QUIC was designed to be able to co-exist with other
   protocols on the same port, including DTLS , see Section 17.2 of
   [RFC9000].

   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.)

10.3.  Reservation of Extended DNS Error Code Too Early

   IANA is requested to add the following value to the Extended DNS
   Error Codes registry [RFC8914]:



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   INFO-CODE:  TBD

   Purpose:  Too Early

   Reference:  This document

10.4.  DNS over QUIC Error Codes Registry

   IANA [SHALL add/has added] a registry for "DNS over QUIC Error Codes"
   on the "Domain Name System (DNS) Parameters" web page.

   The "DNS over QUIC Error Codes" registry governs a 62-bit space.
   This space is split into three regions that are governed by different
   policies:

   *  Permanent registrations for values between 0x00 and 0x3f (in
      hexadecimal; inclusive), which are assigned using Standards Action
      or IESG Approval as defined in Section 4.9 and Section 4.10 of
      [RFC8126]

   *  Permanent registrations for values larger than 0x3f, which are
      assigned using the Specification Required policy ([RFC8126])

   *  Provisonal registrations for values larger than 0x3f, which
      require Expert Review, as defined in Section 4.5 of [RFC8126].

   Provisional reservations share the range of values larger than 0x3f
   with some permanent registrations.  This is by design, to enable
   conversion of provisional registrations into permanent registrations
   without requiring changes in deployed systems.  (This design is
   aligned with the principles set in Section 22 of [RFC9000].)

   Registrations in this registry MUST include the following fields:

   Value:  The assigned codepoint.

   Status:  "Permanent" or "Provisional".

   Contact:  Contact details for the registrant.

   Notes:  Supplementary notes about the registration.

   In addition, permanent registrations MUST include:

   Error:  A short mnemonic for the parameter.

   Specification:  A reference to a publicly available specification for
      the value (optional for provisional registrations).



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   Description:  A brief description of the error code semantics, which
      MAY be a summary if a specification reference is provided.

   Provisional registrations of codepoints are intended to allow for
   private use and experimentation with extensions to DNS over QUIC.
   However, provisional registrations could be reclaimed and reassigned
   for another purpose.  In addition to the parameters listed above,
   provisional registrations MUST include:

   Date:  The date of last update to the registration.

   A request to update the date on any provisional registration can be
   made without review from the designated expert(s).

   The initial contents of this registry are shown in Table 1.

   +==========+=======================+================+===============+
   |Value     | Error                 |Description     | Specification |
   +==========+=======================+================+===============+
   |0x0       | DOQ_NO_ERROR          |No error        | Section 5.3   |
   +----------+-----------------------+----------------+---------------+
   |0x1       | DOQ_INTERNAL_ERROR    |Implementation  | Section 5.3   |
   |          |                       |error           |               |
   +----------+-----------------------+----------------+---------------+
   |0x2       | DOQ_PROTOCOL_ERROR    |Generic protocol| Section 5.3   |
   |          |                       |violation       |               |
   +----------+-----------------------+----------------+---------------+
   |0x3       | DOQ_REQUEST_CANCELLED |Request         | Section 5.3   |
   |          |                       |cancelled by    |               |
   |          |                       |client          |               |
   +----------+-----------------------+----------------+---------------+
   |0x4       | DOQ_EXCESSIVE_LOAD    |Closing a       | Section 5.3   |
   |          |                       |connection for  |               |
   |          |                       |excessive load  |               |
   +----------+-----------------------+----------------+---------------+
   |0xd098ea5e| DOQ_ERROR_RESERVED    |Alternative     | Section 5.3   |
   |          |                       |error code used |               |
   |          |                       |for tests       |               |
   +----------+-----------------------+----------------+---------------+

             Table 1: Initial DNS over QUIC Error Codes Entries

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.



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   The privacy issue with 0-RTT data and session resumption 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, and to Robert Evans for the discussion of 0-RTT
   privacy issues.  Reviews by Paul Hoffman and Martin Thomson and
   interoperability tests conducted by Stephane Bortzmeyer helped
   improve the definition of the protocol.

12.  References

12.1.  Normative References

   [I-D.ietf-dnsop-rfc8499bis]
              Hoffman, P. and K. Fujiwara, "DNS Terminology", Work in
              Progress, Internet-Draft, draft-ietf-dnsop-rfc8499bis-03,
              28 September 2021, <https://www.ietf.org/archive/id/draft-
              ietf-dnsop-rfc8499bis-03.txt>.

   [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>.






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   [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>.

   [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>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [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>.

   [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>.






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   [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>.

   [RFC8914]  Kumari, W., Hunt, E., Arends, R., Hardaker, W., and D.
              Lawrence, "Extended DNS Errors", RFC 8914,
              DOI 10.17487/RFC8914, October 2020,
              <https://www.rfc-editor.org/info/rfc8914>.

   [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>.

   [RFC9103]  Toorop, W., Dickinson, S., Sahib, S., Aras, P., and A.
              Mankin, "DNS Zone Transfer over TLS", RFC 9103,
              DOI 10.17487/RFC9103, August 2021,
              <https://www.rfc-editor.org/info/rfc9103>.

12.2.  Informative References

   [DNS0RTT]  Kahn Gillmor, D., "DNS + 0-RTT", Message to DNS-Privacy WG
              mailing list, 6 April 2016, <https://www.ietf.org/mail-
              archive/web/dns-privacy/current/msg01276.html>.

   [I-D.ietf-quic-http]
              Bishop, M., "Hypertext Transfer Protocol Version 3
              (HTTP/3)", Work in Progress, Internet-Draft, draft-ietf-
              quic-http-34, 2 February 2021,
              <https://www.ietf.org/archive/id/draft-ietf-quic-http-
              34.txt>.

   [RFC1996]  Vixie, P., "A Mechanism for Prompt Notification of Zone
              Changes (DNS NOTIFY)", RFC 1996, DOI 10.17487/RFC1996,
              August 1996, <https://www.rfc-editor.org/info/rfc1996>.

   [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>.





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   [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>.

   [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>.

   [RFC8932]  Dickinson, S., Overeinder, B., van Rijswijk-Deij, R., and
              A. Mankin, "Recommendations for DNS Privacy Service
              Operators", BCP 232, RFC 8932, DOI 10.17487/RFC8932,
              October 2020, <https://www.rfc-editor.org/info/rfc8932>.

   [RFC9002]  Iyengar, J., Ed. and I. Swett, Ed., "QUIC Loss Detection
              and Congestion Control", RFC 9002, DOI 10.17487/RFC9002,
              May 2021, <https://www.rfc-editor.org/info/rfc9002>.

   [RFC9076]  Wicinski, T., Ed., "DNS Privacy Considerations", RFC 9076,
              DOI 10.17487/RFC9076, July 2021,
              <https://www.rfc-editor.org/info/rfc9076>.

Appendix A.  The NOTIFY Service

   This appendix discusses why it is considered acceptable to send
   NOTIFY (see [RFC1996]) in 0-RTT data.

   Section 5.5 says "The 0-RTT mechanism SHOULD NOT be used to send DNS
   requests that are not "replayable" transactions".  This specification
   supports sending a NOTIFY in 0-RTT data because although a NOTIFY
   technically changes the state of the receiving server, the effect of
   replaying NOTIFYs has negligible impact in practice.

   NOTIFY messages prompt a secondary to either send an SOA query or an
   XFR request to the primary on the basis that a newer version of the
   zone is available.  It has long been recognized that NOTIFYs can be
   forged and, in theory, used to cause a secondary to send repeated
   unnecessary requests to the primary.  For this reason, most
   implementations have some form of throttling of the SOA/XFR queries
   triggered by the receipt of one or more NOTIFYs.






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   [RFC9103] describes the privacy risks associated with both NOTIFY and
   SOA queries and does not include addressing those risks within the
   scope of encrypting zone transfers.  Given this, the privacy benefit
   of using DoQ for NOTIFY is not clear - but for the same reason,
   sending NOTIFY as 0-RTT data has no privacy risk above that of
   sending it using cleartext DNS.

Appendix B.  Notable Changes From Previous Versions

   (RFC EDITOR NOTE: THIS SECTION TO BE REMOVED BEFORE PUBLICATION)

B.1.  Stream Mapping Incompatibility With Draft-02

   Versions prior to -02 of this specification proposed a simpler
   mapping scheme of queries and responses to QUIc stream, which omitted
   the 2 byte length field and supported only a single response on a
   given stream.  The more complex mapping in Section 5.2 was adopted to
   specifically cater for XFR support, however it breaks compatibility
   with earlier versions.

Authors' Addresses

   Christian Huitema
   Private Octopus Inc.
   427 Golfcourse Rd
   Friday Harbor,  WA 98250
   United States of America

   Email: huitema@huitema.net


   Sara Dickinson
   Sinodun IT
   Oxford Science Park
   Oxford
   OX4 4GA
   United Kingdom

   Email: sara@sinodun.com


   Allison Mankin
   Salesforce

   Email: allison.mankin@gmail.com






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