idnits 2.17.00 (12 Aug 2021) /tmp/idnits42956/draft-ietf-dprive-dnsoquic-04.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == The document seems to lack the recommended RFC 2119 boilerplate, even if it appears to use RFC 2119 keywords -- however, there's a paragraph with a matching beginning. Boilerplate error? (The document does seem to have the reference to RFC 2119 which the ID-Checklist requires). -- The document date (2 September 2021) is 260 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-03) exists of draft-ietf-dnsop-rfc8499bis-02 ** Downref: Normative reference to an Experimental RFC: RFC 8094 == Outdated reference: draft-ietf-dprive-rfc7626-bis has been published as RFC 9076 -- Obsolete informational reference (is this intentional?): RFC 7626 (Obsoleted by RFC 9076) Summary: 1 error (**), 0 flaws (~~), 4 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group C. Huitema 3 Internet-Draft Private Octopus Inc. 4 Intended status: Standards Track S. Dickinson 5 Expires: 6 March 2022 Sinodun IT 6 A. Mankin 7 Salesforce 8 2 September 2021 10 Specification of DNS over Dedicated QUIC Connections 11 draft-ietf-dprive-dnsoquic-04 13 Abstract 15 This document describes the use of QUIC to provide transport privacy 16 for DNS. The encryption provided by QUIC has similar properties to 17 that provided by TLS, while QUIC transport eliminates the head-of- 18 line blocking issues inherent with TCP and provides more efficient 19 error corrections than UDP. DNS over QUIC (DoQ) has privacy 20 properties similar to DNS over TLS (DoT) specified in RFC7858, and 21 latency characteristics similar to classic DNS over UDP. 23 Status of This Memo 25 This Internet-Draft is submitted in full conformance with the 26 provisions of BCP 78 and BCP 79. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF). Note that other groups may also distribute 30 working documents as Internet-Drafts. The list of current Internet- 31 Drafts is at https://datatracker.ietf.org/drafts/current/. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 This Internet-Draft will expire on 6 March 2022. 40 Copyright Notice 42 Copyright (c) 2021 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 47 license-info) in effect on the date of publication of this document. 48 Please review these documents carefully, as they describe your rights 49 and restrictions with respect to this document. Code Components 50 extracted from this document must include Simplified BSD License text 51 as described in Section 4.e of the Trust Legal Provisions and are 52 provided without warranty as described in the Simplified BSD License. 54 Table of Contents 56 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 57 2. Key Words . . . . . . . . . . . . . . . . . . . . . . . . . . 4 58 3. Document work via GitHub . . . . . . . . . . . . . . . . . . 4 59 4. Design Considerations . . . . . . . . . . . . . . . . . . . . 4 60 4.1. Provide DNS Privacy . . . . . . . . . . . . . . . . . . . 5 61 4.2. Design for Minimum Latency . . . . . . . . . . . . . . . 5 62 4.3. No Specific Middlebox Bypass Mechanism . . . . . . . . . 6 63 4.4. No Server Initiated Transactions . . . . . . . . . . . . 6 64 5. Specifications . . . . . . . . . . . . . . . . . . . . . . . 6 65 5.1. Connection Establishment . . . . . . . . . . . . . . . . 6 66 5.1.1. Draft Version Identification . . . . . . . . . . . . 6 67 5.1.2. Port Selection . . . . . . . . . . . . . . . . . . . 7 68 5.2. Stream Mapping and Usage . . . . . . . . . . . . . . . . 7 69 5.2.1. DNS Message IDs . . . . . . . . . . . . . . . . . . . 8 70 5.3. DoQ Error Codes . . . . . . . . . . . . . . . . . . . . . 8 71 5.3.1. Transaction Cancellation . . . . . . . . . . . . . . 9 72 5.3.2. Transaction Errors . . . . . . . . . . . . . . . . . 9 73 5.3.3. Protocol Errors . . . . . . . . . . . . . . . . . . . 9 74 5.4. Connection Management . . . . . . . . . . . . . . . . . . 10 75 5.5. Session Resumption and 0-RTT . . . . . . . . . . . . . . 11 76 5.6. Message Sizes . . . . . . . . . . . . . . . . . . . . . . 12 77 6. Implementation Requirements . . . . . . . . . . . . . . . . . 12 78 6.1. Authentication . . . . . . . . . . . . . . . . . . . . . 12 79 6.2. Fall Back to Other Protocols on Connection Failure . . . 12 80 6.3. Address Validation . . . . . . . . . . . . . . . . . . . 13 81 6.4. Padding . . . . . . . . . . . . . . . . . . . . . . . . . 13 82 6.5. Connection Handling . . . . . . . . . . . . . . . . . . . 14 83 6.5.1. Connection Reuse . . . . . . . . . . . . . . . . . . 14 84 6.5.2. Resource Management and Idle Timeout Values . . . . . 14 85 6.5.3. Using 0-RTT and Session Resumption . . . . . . . . . 15 86 6.6. Processing Queries in Parallel . . . . . . . . . . . . . 15 87 6.7. Zone transfer . . . . . . . . . . . . . . . . . . . . . . 16 88 6.8. Flow Control Mechanisms . . . . . . . . . . . . . . . . . 16 89 7. Implementation Status . . . . . . . . . . . . . . . . . . . . 17 90 7.1. Performance Measurements . . . . . . . . . . . . . . . . 18 91 8. Security Considerations . . . . . . . . . . . . . . . . . . . 18 92 9. Privacy Considerations . . . . . . . . . . . . . . . . . . . 18 93 9.1. Privacy Issues With 0-RTT data . . . . . . . . . . . . . 19 94 9.2. Privacy Issues With Session Resumption . . . . . . . . . 20 95 9.3. Privacy Issues With New Tokens . . . . . . . . . . . . . 20 96 9.4. Traffic Analysis . . . . . . . . . . . . . . . . . . . . 21 98 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 99 10.1. Registration of DoQ Identification String . . . . . . . 21 100 10.2. Reservation of Dedicated Port . . . . . . . . . . . . . 21 101 10.2.1. Port number 784 for experimentations . . . . . . . . 22 102 10.3. Reservation of Extended DNS Error Code Too Early . . . . 22 103 10.4. DNS over QUIC Error Codes Registry . . . . . . . . . . . 22 104 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 24 105 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 24 106 12.1. Normative References . . . . . . . . . . . . . . . . . . 24 107 12.2. Informative References . . . . . . . . . . . . . . . . . 26 108 Appendix A. The NOTIFY service . . . . . . . . . . . . . . . . . 27 109 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 28 111 1. Introduction 113 Domain Name System (DNS) concepts are specified in "Domain names - 114 concepts and facilities" [RFC1034]. The transmission of DNS queries 115 and responses over UDP and TCP is specified in "Domain names - 116 implementation and specification" [RFC1035]. This document presents 117 a mapping of the DNS protocol over the QUIC transport [RFC9000] 118 [RFC9001]. DNS over QUIC is referred here as DoQ, in line with "DNS 119 Terminology" [I-D.ietf-dnsop-rfc8499bis]. The goals of the DoQ 120 mapping are: 122 1. Provide the same DNS privacy protection as DNS over TLS (DoT) 123 [RFC7858]. This includes an option for the client to 124 authenticate the server by means of an authentication domain name 125 as specified in "Usage Profiles for DNS over TLS and DNS over 126 DTLS" [RFC8310]. 128 2. Provide an improved level of source address validation for DNS 129 servers compared to classic DNS over UDP. 131 3. Provide a transport that is not constrained by path MTU 132 limitations on the size of DNS responses it can send. 134 4. Explore the characteristics of using QUIC as a DNS transport, 135 versus other solutions like DNS over UDP [RFC1035], DNS over TLS 136 (DoT) [RFC7858], or DNS over HTTPS (DoH) [RFC8484]. 138 In order to achieve these goals, and to support ongoing work on 139 encryption of DNS, the scope of this document includes 141 * the "stub to recursive resolver" scenario 143 * the "recursive resolver to authoritative nameserver" scenario and 144 * the "nameserver to nameserver" scenario (mainly used for zone 145 transfers (XFR) [RFC1995], [RFC5936]). 147 In other words, this document is intended to specify QUIC as a 148 general purpose transport for DNS. 150 The specific non-goals of this document are: 152 1. No attempt is made to evade potential blocking of DNS over QUIC 153 traffic by middleboxes. 155 2. No attempt to support server initiated transactions, which are 156 used only in DNS Stateful Operations (DSO) [RFC8490]. 158 Specifying the transmission of an application over QUIC requires 159 specifying how the application's messages are mapped to QUIC streams, 160 and generally how the application will use QUIC. This is done for 161 HTTP in "Hypertext Transfer Protocol Version 3 162 (HTTP/3)"[I-D.ietf-quic-http]. The purpose of this document is to 163 define the way DNS messages can be transmitted over QUIC. 165 In this document, Section 4 presents the reasoning that guided the 166 proposed design. Section 5 specifies the actual mapping of DoQ. 167 Section 6 presents guidelines on the implementation, usage and 168 deployment of DoQ. 170 2. Key Words 172 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 173 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 174 document are to be interpreted as described in BCP 14 [RFC8174]. 176 3. Document work via GitHub 178 (RFC EDITOR NOTE: THIS SECTION TO BE REMOVED BEFORE PUBLICATION)The 179 Github repository for this document is at https://github.com/huitema/ 180 dnsoquic. Proposed text and editorial changes are very much welcomed 181 there, but any functional changes should always first be discussed on 182 the IETF DPRIVE WG (dns-privacy) mailing list. 184 4. Design Considerations 186 This section and its subsections present the design guidelines that 187 were used for DoQ. This section is informative in nature. 189 4.1. Provide DNS Privacy 191 DoT [RFC7858] defines how to mitigate some of the issues described in 192 "DNS Privacy Considerations" [RFC7626] by specifying how to transmit 193 DNS messages over TLS. The "Usage Profiles for DNS over TLS and DNS 194 over DTLS" [RFC8310] specify Strict and Opportunistic Usage Profiles 195 for DoT including how stub resolvers can authenticate recursive 196 resolvers. 198 QUIC connection setup includes the negotiation of security parameters 199 using TLS, as specified in "Using TLS to Secure QUIC" [RFC9001], 200 enabling encryption of the QUIC transport. Transmitting DNS messages 201 over QUIC will provide essentially the same privacy protections as 202 DoT [RFC7858] including Strict and Opportunistic Usage Profiles 203 [RFC8310]. Further discussion on this is provided in Section 9. 205 4.2. Design for Minimum Latency 207 QUIC is specifically designed to reduce the delay between HTTP 208 queries and HTTP responses. This is achieved through three main 209 components: 211 1. Support for 0-RTT data during session resumption. 213 2. Support for advanced error recovery procedures as specified in 214 "QUIC Loss Detection and Congestion Control" [RFC9002]. 216 3. Mitigation of head-of-line blocking by allowing parallel delivery 217 of data on multiple streams. 219 This mapping of DNS to QUIC will take advantage of these features in 220 three ways: 222 1. Optional support for sending 0-RTT data during session resumption 223 (the security and privacy implications of this are discussed in 224 later sections). 226 2. Long-lived QUIC connections over which multiple DNS transactions 227 are performed, generating the sustained traffic required to 228 benefit from advanced recovery features. 230 3. Fast resumption of QUIC connections to manage the disconnect-on- 231 idle feature of QUIC without incurring retransmission time-outs. 233 4. Mapping of each DNS Query/Response transaction to a separate 234 stream, to mitigate head-of-line blocking. This enables servers 235 to respond to queries "out of order". It also enables clients to 236 process responses as soon as they arrive, without having to wait 237 for in order delivery of responses previously posted by the 238 server. 240 These considerations will be reflected in the mapping of DNS traffic 241 to QUIC streams in Section 5.2. 243 4.3. No Specific Middlebox Bypass Mechanism 245 The mapping of DoQ is defined for minimal overhead and maximum 246 performance. This means a different traffic profile than HTTP3 over 247 QUIC. This difference can be noted by firewalls and middleboxes. 248 There may be environments in which HTTP3 over QUIC will be able to 249 pass through, but DoQ will be blocked by these middle boxes. 251 4.4. No Server Initiated Transactions 253 As stated in Section 1, this document does not specify support for 254 server initiated transactions within established DoQ connections. 255 That is, only the initiator of the DoQ connection may send queries 256 over the connection. 258 DSO supports server-initiated transactions within existing 259 connections, however DSO is not applicable to DNS over HTTP since 260 HTTP has its own mechanism for managing sessions, and this is 261 incompatible with the DSO; the same is true for DoQ. 263 5. Specifications 265 5.1. Connection Establishment 267 DoQ connections are established as described in the QUIC transport 268 specification [RFC9000]. During connection establishment, DoQ 269 support is indicated by selecting the ALPN token "doq" in the crypto 270 handshake. 272 5.1.1. Draft Version Identification 274 (RFC EDITOR NOTE: THIS SECTION TO BE REMOVED BEFORE PUBLICATION) Only 275 implementations of the final, published RFC can identify themselves 276 as "doq". Until such an RFC exists, implementations MUST NOT 277 identify themselves using this string. 279 Implementations of draft versions of the protocol MUST add the string 280 "-" and the corresponding draft number to the identifier. For 281 example, draft-ietf-dprive-dnsoquic-00 is identified using the string 282 "doq-i00". 284 5.1.2. Port Selection 286 By default, a DNS server that supports DoQ MUST listen for and accept 287 QUIC connections on the dedicated UDP port TBD (number to be defined 288 in Section 10), unless it has mutual agreement with its clients to 289 use a port other than TBD for DoQ. In order to use a port other than 290 TBD, both clients and servers would need a configuration option in 291 their software. 293 By default, a DNS client desiring to use DoQ with a particular server 294 MUST establish a QUIC connection to UDP port TBD on the server, 295 unless it has mutual agreement with its server to use a port other 296 than port TBD for DoQ. Such another port MUST NOT be port 53. This 297 recommendation against use of port 53 for DoQ is to avoid confusion 298 between DoQ and the use of DNS over UDP [RFC1035]. 300 5.2. Stream Mapping and Usage 302 The mapping of DNS traffic over QUIC streams takes advantage of the 303 QUIC stream features detailed in Section 2 of the QUIC transport 304 specification [RFC9000]. 306 DNS traffic follows a simple pattern in which the client sends a 307 query, and the server provides one or more responses (multiple can 308 responses occur in zone transfers). 310 The mapping specified here requires that the client selects a 311 separate QUIC stream for each query. The server then uses the same 312 stream to provide all the response messages for that query. In order 313 that multiple responses can be parsed, a 2-octet length field is used 314 in exactly the same way as the 2-octet length field defined for DNS 315 over TCP [RFC1035]. The practical result of this is that the content 316 of each QUIC stream is exactly the same as the content of a TCP 317 connection that would manage exactly one query. 319 All DNS messages (queries and responses) sent over DoQ connections 320 MUST be encoded as a 2-octet length field followed by the message 321 content as specified in [RFC1035]. 323 The client MUST select the next available client-initiated 324 bidirectional stream for each subsequent query on a QUIC connection, 325 in conformance with the QUIC transport specification [RFC9000]. 327 The client MUST send the DNS query over the selected stream, and MUST 328 indicate through the STREAM FIN mechanism that no further data will 329 be sent on that stream. 331 The server MUST send the response(s) on the same stream and MUST 332 indicate, after the last response, through the STREAM FIN mechanism 333 that no further data will be sent on that stream. 335 Therefore, a single client initiated DNS transaction consumes a 336 single stream. This means that the client's first query occurs on 337 QUIC stream 0, the second on 4, and so on. 339 For completeness it is noted that versions prior to -02 of this 340 specification proposed a simpler mapping scheme which omitted the 2 341 byte length field and supported only a single response on a given 342 stream. The more complex mapping above was adopted to specifically 343 cater for XFR support, however it breaks compatibility with earlier 344 versions. 346 5.2.1. DNS Message IDs 348 When sending queries over a QUIC connection, the DNS Message ID MUST 349 be set to zero. 351 It is noted that this has implications for proxying DoQ message to 352 other transports in that a mapping of some form must be performed 353 (e.g., from DoQ connection/stream to unique Message ID). 355 5.3. DoQ Error Codes 357 The following error codes are defined for use when abruptly 358 terminating streams, aborting reading of streams, or immediately 359 closing connections: 361 DOQ_NO_ERROR (0x00): No error. This is used when the connection or 362 stream needs to be closed, but there is no error to signal. 364 DOQ_INTERNAL_ERROR (0x01): The DoQ implementation encountered an 365 internal error and is incapable of pursuing the transaction or the 366 connection. 368 DOQ_PROTOCOL_ERROR (0x02): The DoQ implementation encountered an 369 protocol error and is forcibly aborting the connection. 371 DOQ_REQUEST_CANCELLED (0x03): A DoQ client uses this to signal that 372 it wants to cancel an outstanding transaction. 374 See Section 10.4 for details on registering new error codes. 376 5.3.1. Transaction Cancellation 378 In QUIC, sending STOP_SENDING requests that a peer cease transmission 379 on a stream. If a DoQ client wishes to cancel an outstanding 380 request, it MUST issue a QUIC Stop Sending with error code 381 DOQ_REQUEST_CANCELLED. This may be sent at any time but will be 382 ignored if the server has already sent the response. The 383 corresponding DNS transaction MUST be abandoned. 385 A server that receives STOP_SENDING MUST issue a RESET_STREAM with 386 error code DOQ_REQUEST_CANCELLED, unless it has already sent a 387 complete response in which case it MAY ignore the STOP_SENDING 388 request. Servers MAY limit the number of DOQ_REQUEST_CANCELLED 389 errors received on a connection before choosing to close the 390 connection. 392 Note that this mechanism provides a way for secondaries to cancel a 393 single zone transfer occurring on a given stream without having to 394 close the QUIC connection. 396 5.3.2. Transaction Errors 398 Servers normally complete transactions by sending a DNS response (or 399 responses) on the transaction's stream, including cases where the DNS 400 response indicates a DNS error. For example, a Server Failure 401 (SERVFAIL, [RFC1035]) SHOULD be notified to the client by sending 402 back a response with the Response Code set to SERVFAIL. 404 If a server is incapable of sending a DNS response due to an internal 405 error, it SHOULD issue a QUIC Stream Reset with error code 406 DOQ_INTERNAL_ERROR. The corresponding DNS transaction MUST be 407 abandoned. Clients MAY limit the number of unsolicited QUIC Stream 408 Resets received on a connection before choosing to close the 409 connection. 411 Note that this mechanism provides a way for primaries to abort a 412 single zone transfer occurring on a given stream without having to 413 close the QUIC connection. 415 5.3.3. Protocol Errors 417 Other error scenarios can occur due to malformed, incomplete or 418 unexpected messages during a transaction. These include (but are not 419 limited to) 421 * a client or server receives a message with a non-zero Message ID 422 * a client or server receives a STREAM FIN before receiving all the 423 bytes for a message indicated in the 2-octet length field 425 * a client receives a STREAM FIN before receiving all the expected 426 responses 428 * a server receives more than one query on a stream 430 * a client receives a different number of responses on a stream than 431 expected (e.g. multiple responses to a query for an A record) 433 * a client receives a STOP_SENDING request 435 * an implementation receives a message containing the edns-tcp- 436 keepalive EDNS(0) Option [RFC7828] (see Section 6.5.2) 438 If a peer encounters such an error condition it is considered a fatal 439 error. It SHOULD forcibly abort the connection using QUIC's 440 CONNECTION_CLOSE mechanism, and use the DoQ error code 441 DOQ_PROTCOL_ERROR. 443 It is noted that the restrictions on use of the above EDNS(0) options 444 has implications for proxying message from TCP/DoT/DoH over DoQ. 446 5.4. Connection Management 448 Section 10 of the QUIC transport specification [RFC9000] specifies 449 that connections can be closed in three ways: 451 * idle timeout 453 * immediate close 455 * stateless reset 457 Clients and servers implementing DoQ SHOULD negotiate use of the idle 458 timeout. Closing on idle timeout is done without any packet 459 exchange, which minimizes protocol overhead. Per section 10.1 of the 460 QUIC transport specification, the effective value of the idle timeout 461 is computed as the minimum of the values advertised by the two 462 endpoints. Practical considerations on setting the idle timeout are 463 discussed in Section 6.5.2. 465 Clients SHOULD monitor the idle time incurred on their connection to 466 the server, defined by the time spent since the last packet from the 467 server has been received. When a client prepares to send a new DNS 468 query to the server, it will check whether the idle time is 469 sufficient lower than the idle timer. If it is, the client will send 470 the DNS query over the existing connection. If not, the client will 471 establish a new connection and send the query over that connection. 473 Clients MAY discard their connection to the server before the idle 474 timeout expires. If they do that, they SHOULD close the connection 475 explicitly, using QUIC's CONNECTION_CLOSE mechanism, and use the DoQ 476 error code DOQ_NO_ERROR. 478 Clients and servers MAY close the connection for a variety of other 479 reasons, indicated using QUIC's CONNECTION_CLOSE. Client and servers 480 that send packets over a connection discarded by their peer MAY 481 receive a stateless reset indication. If a connection fails, all 482 queries in progress over the connection MUST be considered failed, 483 and a Server Failure (SERVFAIL, [RFC1035]) SHOULD be notified to the 484 initiator of the transaction. 486 5.5. Session Resumption and 0-RTT 488 A client MAY take advantage of the session resumption mechanisms 489 supported by QUIC transport [RFC9000] and QUIC TLS [RFC9001]. 490 Clients SHOULD consider potential privacy issues associated with 491 session resumption before deciding to use this mechanism. These 492 privacy issues are detailed in Section 9.2 and Section 9.1, and the 493 implementation considerations are discussed in Section 6.5.3. 495 The 0-RTT mechanism SHOULD NOT be used to send DNS requests that are 496 not "replayable" transactions. Our analysis so far shows that such 497 replayable transactions can only be QUERY requests, although we may 498 need to also consider NOTIFY requests once the analysis of NOTIFY 499 services is complete, see Appendix A. 501 Servers MUST NOT execute non replayable transactions received in 502 0-RTT data. Servers MUST adopt one of the following behaviors: 504 * Queue the offending transaction and only execute it after the QUIC 505 handshake has been completed, as defined in section 4.1.1 of 506 [RFC9001]. 508 * Reply to the offending transaction with a response code REFUSED 509 and an Extended DNS Error Code (EDE) "Too Early", see 510 Section 10.3. 512 * Close the connection with the error code DOQ_PROTOCOL_ERROR. 514 For the zone transfer scenario, it would be possible to replay an XFR 515 QUERY that had been sent in 0-RTT data. However the authentication 516 mechanisms described in RFC9103 ("Zone transfer over TLS") will 517 ensure that the response is not sent by the primary until the 518 identity of the secondary has been verified i.e. the first behavior 519 listed above. 521 5.6. Message Sizes 523 DoQ Queries and Responses are sent on QUIC streams, which in theory 524 can carry up to 2^62 bytes. However, DNS messages are restricted in 525 practice to a maximum size of 65535 bytes. This maximum size is 526 enforced by the use of a two-octet message length field in DNS over 527 TCP [RFC1035] and DNS over TLS [RFC7858], and by the definition of 528 the "application/dns-message" for DNS over HTTP [RFC8484]. DoQ 529 enforces the same restriction. 531 The Extension Mechanisms for DNS (EDNS) [RFC6891] allow peers to 532 specify the UDP message size. This parameter is ignored by DoQ. DoQ 533 implementations always assume that the maximum message size is 65535 534 bytes. 536 6. Implementation Requirements 538 6.1. Authentication 540 For the stub to recursive resolver scenario, the authentication 541 requirements are the same as described in DoT [RFC7858] and "Usage 542 Profiles for DNS over TLS and DNS over DTLS" [RFC8310]. There is no 543 need to authenticate the client's identity in either scenario. 545 For zone transfer, the requirements are the same as described in 546 [RFC9103]. 548 For the recursive resolver to authoritative nameserver scenario, 549 authentication requirements are unspecified at the time of writing 550 and are the subject on ongoing work in the DPRIVE WG. 552 6.2. Fall Back to Other Protocols on Connection Failure 554 If the establishment of the DoQ connection fails, clients MAY attempt 555 to fall back to DoT and then potentially clear text, as specified in 556 DoT [RFC7858] and "Usage Profiles for DNS over TLS and DNS over DTLS" 557 [RFC8310], depending on their privacy profile. 559 DNS clients SHOULD remember server IP addresses that don't support 560 DoQ, including timeouts, connection refusals, and QUIC handshake 561 failures, and not request DoQ from them for a reasonable period (such 562 as one hour per server). DNS clients following an out-of-band key- 563 pinned privacy profile ([RFC7858]) MAY be more aggressive about 564 retrying DoQ connection failures. 566 6.3. Address Validation 568 Section 8 of the QUIC transport specification [RFC9000] defines 569 Address Validation procedures to avoid servers being used in address 570 amplification attacks. DoQ implementations MUST conform to this 571 specification, which limits the worst case amplification to a factor 572 3. 574 DoQ implementations SHOULD consider configuring servers to use the 575 Address Validation using Retry Packets procedure defined in section 576 8.1.2 of the QUIC transport specification [RFC9000]). This procedure 577 imposes a 1-RTT delay for verifying the return routability of the 578 source address of a client, similar to the DNS Cookies mechanism 579 [RFC7873]. 581 DoQ implementations that configure Address Validation using Retry 582 Packets SHOULD implement the Address Validation for Future 583 Connections procedure defined in section 8.1.3 of the QUIC transport 584 specification [RFC9000]). This defines how servers can send NEW 585 TOKEN frames to clients after the client address is validated, in 586 order to avoid the 1-RTT penalty during subsequent connections by the 587 client from the same address. 589 6.4. Padding 591 Implementations SHOULD protect against the traffic analysis attacks 592 described in Section 9.4 by the judicious injection of padding. This 593 could be done either by padding individual DNS messages using the 594 EDNS(0) Padding Option [RFC7830] and by padding QUIC packets (see 595 Section 8.6 of the QUIC transport specification [RFC9000]). 597 In theory, padding at the QUIC level could result in better 598 performance for the equivalent protection, because the amount of 599 padding can take into account non-DNS frames such as acknowledgeemnts 600 or flow control updates, and also because QUIC packets can carry 601 multiple DNS messages. However, applications can only control the 602 amount of padding in QUIC packets if the implementation of QUIC 603 exposes adequate APIs. This leads to the following recommendation: 605 * if the implementation of QUIC exposes APIs to set a padding 606 policy, DNS over QUIC SHOULD use that API to align the packet 607 length to a small set of fixed sizes, aligned with the 608 recommendations of the "Padding Policies for Extension Mechanisms 609 for DNS (EDNS(0))" [RFC8467]. 611 * if padding at the QUIC level is not available or not used, DNS 612 over QUIC MUST ensure that all DNS queries and responses are 613 padded to a small set of fixed sizes, using the EDNS padding 614 extension as specified in "Padding Policies for Extension 615 Mechanisms for DNS (EDNS(0))" [RFC8467]. 617 6.5. Connection Handling 619 "DNS Transport over TCP - Implementation Requirements" [RFC7766] 620 provides updated guidance on DNS over TCP, some of which is 621 applicable to DoQ. This section attempts to specify which and how 622 those considerations apply to DoQ. 624 6.5.1. Connection Reuse 626 Historic implementations of DNS clients are known to open and close 627 TCP connections for each DNS query. To avoid excess QUIC 628 connections, each with a single query, clients SHOULD reuse a single 629 QUIC connection to the recursive resolver. 631 In order to achieve performance on par with UDP, DNS clients SHOULD 632 send their queries concurrently over the QUIC streams on a QUIC 633 connection. That is, when a DNS client sends multiple queries to a 634 server over a QUIC connection, it SHOULD NOT wait for an outstanding 635 reply before sending the next query. 637 6.5.2. Resource Management and Idle Timeout Values 639 Proper management of established and idle connections is important to 640 the healthy operation of a DNS server. An implementation of DoQ 641 SHOULD follow best practices similar to those specified for DNS over 642 TCP [RFC7766], in particular with regard to: 644 * Concurrent Connections (Section 6.2.2) 646 * Security Considerations (Section 10) 648 Failure to do so may lead to resource exhaustion and denial of 649 service. 651 Clients that want to maintain long duration DoQ connections SHOULD 652 use the idle timeout mechanisms defined in Section 10.1 of the QUIC 653 transport specification [RFC9000]. Clients and servers MUST NOT send 654 the edns-tcp-keepalive EDNS(0) Option [RFC7828] in any messages sent 655 on a DoQ connection (because it is specific to the use of TCP/TLS as 656 a transport). 658 This document does not make specific recommendations for timeout 659 values on idle connections. Clients and servers should reuse and/or 660 close connections depending on the level of available resources. 661 Timeouts may be longer during periods of low activity and shorter 662 during periods of high activity. 664 6.5.3. Using 0-RTT and Session Resumption 666 Using 0-RTT for DNS over QUIC has many compelling advantages. 667 Clients can establish connections and send queries without incurring 668 a connection delay. Servers can thus negotiate low values of the 669 connection timers, which reduces the total number of connections that 670 they need to manage. They can do that because the clients that use 671 0-RTT will not incur latency penalties if new connections are 672 required for a query. 674 Session resumption and 0-RTT data transmission create privacy risks 675 detailed in detailed in Section 9.2 and Section 9.1. The following 676 recommendations are meant to reduce the privacy risks while enjoying 677 the performance benefits of 0-RTT data, with the restriction 678 specified in Section 5.5. 680 Clients SHOULD use resumption tickets only once, as specified in 681 Appendix C.4 to [RFC8446]. Clients could receive address validation 682 tokens from the server using the NEW TOKEN mechanism; see section 8 683 of [RFC9000]. The associated tracking risks are mentioned in 684 Section 9.3. Clients SHOULD only use the address validation tokens 685 when they are also using session resumption, thus avoiding additional 686 tracking risks. 688 Servers SHOULD issue session resumption tickets with a sufficiently 689 long life time (e.g., 6 hours), so that clients are not tempted to 690 either keep connection alive or frequently poll the server to renew 691 session resumption tickets. Servers SHOULD implement the anti-replay 692 mechanisms specified in section 8 of [RFC8446]. 694 6.6. Processing Queries in Parallel 696 As specified in Section 7 of "DNS Transport over TCP - Implementation 697 Requirements" [RFC7766], resolvers are RECOMMENDED to support the 698 preparing of responses in parallel and sending them out of order. In 699 DoQ, they do that by sending responses on their specific stream as 700 soon as possible, without waiting for availability of responses for 701 previously opened streams. 703 6.7. Zone transfer 705 [RFC9103] specifies zone transfer over TLS (XoT) and includes updates 706 to [RFC1995] (IXFR), [RFC5936] (AXFR) and [RFC7766]. Considerations 707 relating to the re-use of XoT connections described there apply 708 analogously to zone transfers performed using DoQ connections. For 709 example: 711 * DoQ servers MUST be able to handle multiple concurrent IXFR 712 requests on a single QUIC connection 714 * DoQ servers MUST be able to handle multiple concurrent AXFR 715 requests on a single QUIC connection 717 * DoQ implementations SHOULD 719 - use the same QUIC connection for both AXFR and IXFR requests to 720 the same primary 722 - pipeline such requests (if they pipeline XFR requests in 723 general) and MAY intermingle them 725 - send the response(s) for each request as soon as they are 726 available i.e. responses MAY be sent intermingled 728 6.8. Flow Control Mechanisms 730 Servers and Clients manage flow control using the mechanisms defined 731 in section 4 of [RFC9000]. These mechanisms allow clients and 732 servers to specify how many streams can be created, how much data can 733 be sent on a stream, and how much data can be sent on the union of 734 all streams. For DNS over QUIC, controlling how many streams are 735 created allows servers to control how many new requests the client 736 can send on a given connection. 738 Flow control exists to protect endpoint resources. For servers, 739 global and per-stream flow control limits control how much data can 740 be sent by clients. The same mechanisms allow clients to control how 741 much data can be sent by servers. Values that are too small will 742 unnecessarily limit performance. Values that are too large might 743 expose endpoints to overload or memory exhaustion. Implementations 744 or deployments will need to adjust flow control limits to balance 745 these concerns. In particular, zone transfer implementations will 746 need to control these limits carefully to ensure both large and 747 concurrent zone transfers are well managed. 749 Initial values of parameters control how many requests and how much 750 data can be sent by clients and servers at the beginning of the 751 connection. These values are specified in transport parameters 752 exchanged during the connection handshake. The parameter values 753 received in the initial connection also control how many requests and 754 how much data can be sent by clients using 0-RTT data in a resumed 755 connection. Using too small values of these initial parameters would 756 restrict the usefulness of allowing 0-RTT data. 758 7. Implementation Status 760 (RFC EDITOR NOTE: THIS SECTION TO BE REMOVED BEFORE PUBLICATION) This 761 section records the status of known implementations of the protocol 762 defined by this specification at the time of posting of this 763 Internet-Draft, and is based on a proposal described in [RFC7942]. 765 1. AdGuard launched a DoQ recursive resolver service in December 766 2020. They have released a suite of open source tools that 767 support DoQ: 769 1. AdGuard C++ DNS libraries (https://github.com/AdguardTeam/ 770 DnsLibs) A DNS proxy library that supports all existing DNS 771 protocols including DNS-over-TLS, DNS-over-HTTPS, DNSCrypt 772 and DNS-over-QUIC (experimental). 774 2. DNS Proxy (https://github.com/AdguardTeam/dnsproxy) A simple 775 DNS proxy server that supports all existing DNS protocols 776 including DNS-over-TLS, DNS-over-HTTPS, DNSCrypt, and DNS- 777 over-QUIC. Moreover, it can work as a DNS-over-HTTPS, DNS- 778 over-TLS or DNS-over-QUIC server. 780 3. CoreDNS fork for AdGuard DNS (https://github.com/AdguardTeam/ 781 coredns) Includes DNS-over-QUIC server-side support. 783 4. dnslookup (https://github.com/ameshkov/dnslookup) Simple 784 command line utility to make DNS lookups. Supports all known 785 DNS protocols: plain DNS, DoH, DoT, DoQ, DNSCrypt. 787 2. Quicdoq (https://github.com/private-octopus/quicdoq) Quicdoq is a 788 simple open source implementation of DoQ. It is written in C, 789 based on Picoquic (https://github.com/private-octopus/picoquic). 791 3. Flamethrower (https://github.com/DNS-OARC/flamethrower/tree/dns- 792 over-quic) is an open source DNS performance and functional 793 testing utility written in C++ that has an experimental 794 implementation of DoQ. 796 4. aioquic (https://github.com/aiortc/aioquic) is an implementation 797 of QUIC in Python. It includes example client and server for 798 DoQ. 800 7.1. Performance Measurements 802 To our knowledge, no benchmarking studies comparing DoT, DoH and DoQ 803 are published yet. However anecdotal evidence from the AdGuard DoQ 804 recursive resolver deployment (https://adguard.com/en/blog/dns-over- 805 quic.html) indicates that it performs well compared to the other 806 encrypted protocols, particularly in mobile environments. Reasons 807 given for this include that DoQ 809 * Uses less bandwidth due to a more efficient handshake (and due to 810 less per message overhead when compared to DoH). 812 * Performs better in mobile environments due to the increased 813 resilience to packet loss 815 * Can maintain connections as users move between mobile networks via 816 its connection management 818 8. Security Considerations 820 The security considerations of DoQ should be comparable to those of 821 DoT [RFC7858]. 823 9. Privacy Considerations 825 The general considerations of encrypted transports provided in "DNS 826 Privacy Considerations" [I-D.ietf-dprive-rfc7626-bis] apply to DoQ. 827 The specific considerations provided there do not differ between DoT 828 and DoQ, and are not discussed further here. 830 QUIC incorporates the mechanisms of TLS 1.3 [RFC8446] and this 831 enables QUIC transmission of "0-RTT" data. This can provide 832 interesting latency gains, but it raises two concerns: 834 1. Adversaries could replay the 0-RTT data and infer its content 835 from the behavior of the receiving server. 837 2. The 0-RTT mechanism relies on TLS session resumption, which can 838 provide linkability between successive client sessions. 840 These issues are developed in Section 9.1 and Section 9.2. 842 9.1. Privacy Issues With 0-RTT data 844 The 0-RTT data can be replayed by adversaries. That data may trigger 845 queries by a recursive resolver to authoritative resolvers. 846 Adversaries may be able to pick a time at which the recursive 847 resolver outgoing traffic is observable, and thus find out what name 848 was queried for in the 0-RTT data. 850 This risk is in fact a subset of the general problem of observing the 851 behavior of the recursive resolver discussed in "DNS Privacy 852 Considerations" [RFC7626]. The attack is partially mitigated by 853 reducing the observability of this traffic. However, the risk is 854 amplified for 0-RTT data, because the attacker might replay it at 855 chosen times, several times. 857 The recommendation for TLS 1.3 [RFC8446] is that the capability to 858 use 0-RTT data should be turned off by default, and only enabled if 859 the user clearly understands the associated risks. In our case, 860 allowing 0-RTT data provides significant performance gains, and we 861 are concerned that a recommendation to not use it would simply be 862 ignored. Instead, we provide a set of practical recommendations in 863 Section 5.5 and Section 6.5.3. 865 The prevention on allowing replayable transactions in 0-RTT data 866 expressed in Section 5.5 blocks the most obvious risks of replay 867 attacks, as it only allows for transactions that will not change the 868 long term state of the server. 870 Attacks trying to assess the state of the cache are more powerful if 871 the attacker can choose the time at which the 0-RTT data will be 872 replayed. Such attacks are blocked if the server enforces single-use 873 tickets, or if the server implements a combination of Client Hello 874 recording and freshness checks, as specified in section 8 of 875 [RFC8446]. These blocking mechanisms rely on shared state between 876 all server instances in a server system. In the case of DNS over 877 QUIC, the protection against replay attacks on the DNS cache is 878 achieved if this state is shared between all servers that share the 879 same DNS cache. 881 The attacks described above apply to the stub resolver to recursive 882 resolver scenario, but similar attacks might be envisaged in the 883 recursive resolver to authoritative resolver scenario, and the same 884 mitigations apply. 886 9.2. Privacy Issues With Session Resumption 888 The QUIC session resumption mechanism reduces the cost of re- 889 establishing sessions and enables 0-RTT data. There is a linkability 890 issue associated with session resumption, if the same resumption 891 token is used several times. Attackers on path between client and 892 server could observe repeated usage of the token and use that to 893 track the client over time or over multiple locations. 895 The session resumption mechanism allows servers to correlate the 896 resumed sessions with the initial sessions, and thus to track the 897 client. This creates a virtual long duration session. The series of 898 queries in that session can be used by the server to identify the 899 client. Servers can most probably do that already if the client 900 address remains constant, but session resumption tickets also enable 901 tracking after changes of the client's address. 903 The recommendations in Section 6.5.3 are designed to mitigate these 904 risks. Using session tickets only once mitigates the risk of 905 tracking by third parties. Refusing to resume a session if addresses 906 change mitigates the risk of tracking by the server. 908 The privacy trade-offs here may be context specific. Stub resolvers 909 will have a strong motivation to prefer privacy over latency since 910 they often change location. However, recursive resolvers that use a 911 small set of static IP addresses are more likely to prefer the 912 reduced latency provided by session resumption and may consider this 913 a valid reason to use resumption tickets even if the IP address 914 changed between sessions. 916 Encrypted zone transfer (RFC9103) explicitly does not attempt to hide 917 the identity of the parties involved in the transfer, but at the same 918 time such transfers are not particularly latency sensitive. This 919 means that applications supporting zone transfers may decide to apply 920 the same protections as stub to recursive applications. 922 9.3. Privacy Issues With New Tokens 924 QUIC specifies address validation mechanisms in section 8 of 925 [RFC9000]. Use of an address validation token allows QUIC servers to 926 avoid an extra RTT for new connections. Address validation tokens 927 are typically tied to an IP address. QUIC clients normally only use 928 these tokens when setting a new connection from a previously used 929 address. However, due to the prevalence of NAT, clients are not 930 always aware that they are using a new address. There is a 931 linkability risk if clients mistakenly use address validation tokens 932 after unknowingly moving to a new location. 934 The recommendations in Section 6.5.3 mitigates this risk by tying the 935 usage of the NEW TOKEN to that of session resumption. 937 9.4. Traffic Analysis 939 Even though QUIC packets are encrypted, adversaries can gain 940 information from observing packet lengths, in both queries and 941 responses, as well as packet timing. Many DNS requests are emitted 942 by web browsers. Loading a specific web page may require resolving 943 dozen of DNS names. If an application adopts a simple mapping of one 944 query or response per packet, or "one QUIC STREAM frame per packet", 945 then the succession of packet lengths may provide enough information 946 to identify the requested site. 948 Implementations SHOULD use the mechanisms defined in Section 6.4 to 949 mitigate this attack. 951 10. IANA Considerations 953 10.1. Registration of DoQ Identification String 955 This document creates a new registration for the identification of 956 DoQ in the "Application Layer Protocol Negotiation (ALPN) Protocol 957 IDs" registry [RFC7301]. 959 The "doq" string identifies DoQ: 961 Protocol: DoQ 962 Identification Sequence: 0x64 0x6F 0x71 ("doq") 963 Specification: This document 965 10.2. Reservation of Dedicated Port 967 Port 853 is currently reserved for 'DNS query-response protocol run 968 over TLS/DTLS' [RFC7858]. However, the specification for DNS over 969 DTLS (DoD) [RFC8094] is experimental, limited to stub to resolver, 970 and no implementations or deployments currently exist to our 971 knowledge (even though several years have passed since the 972 specification was published). 974 This specification proposes to additionally reserve the use of port 975 853 for DoQ. QUIC was designed to be able to co-exist with other 976 protocols on the same port, including DTLS , see Section 17.2 in 977 [RFC9000]. 979 IANA is requested to add the following value to the "Service Name and 980 Transport Protocol Port Number Registry" in the System Range. The 981 registry for that range requires IETF Review or IESG Approval 982 [RFC6335]. 984 Service Name dns-over-quic 985 Port Number 853 986 Transport Protocol(s) UDP 987 Assignee IESG 988 Contact IETF Chair 989 Description DNS query-response protocol run over QUIC 990 Reference This document 992 10.2.1. Port number 784 for experimentations 994 (RFC EDITOR NOTE: THIS SECTION TO BE REMOVED BEFORE PUBLICATION) 995 Early experiments MAY use port 784. This port is marked in the IANA 996 registry as unassigned. 998 (Note that version in -02 of this draft experiments were directed to 999 use port 8853.) 1001 10.3. Reservation of Extended DNS Error Code Too Early 1003 IANA is requested to add the following value to the Extended DNS 1004 Error Codes registry [RFC8914]: 1006 INFO-CODE TBD 1007 Purpose Too Early 1008 Reference This document 1010 10.4. DNS over QUIC Error Codes Registry 1012 IANA [SHALL add/has added] a registry for "DNS over QUIC Error Codes" 1013 on the "Domain Name System (DNS) Parameters" web page. 1015 The "DNS over QUIC Error Codes" registry governs a 62-bit space. 1016 This space is split into three regions that are governed by different 1017 policies: 1019 * Permanent registrations for values between 0x00 and 0x3f (in 1020 hexadecimal; inclusive), which are assigned using Standards Action 1021 or IESG Approval as defined in Section 4.9 and 4.10 of [RFC8126] 1023 * Permanent registrations for values larger than 0x3f, which are 1024 assigned using the Specification Required policy ([RFC8126]) 1026 * Provisonal registrations for values larger than 0x3f, which 1027 require Expert Review, as defined in Section 4.5 of [RFC8126]. 1029 Provisional reservations share the range of values larger than 0x3f 1030 with some permanent registrations. This is by design, to enable 1031 conversion of provisional registrations into permanent registrations 1032 without requiring changes in deployed systems. (This design is 1033 aligned with the principles set in section 22 of [RFC9000].) 1035 Registrations in this registry MUST include the following fields: 1037 Value: The assigned codepoint. 1039 Status: "Permanent" or "Provisional". 1041 Contact: Contact details for the registrant. 1043 Notes: Supplementary notes about the registration. 1045 In addition, permanent registrations MUST include: 1047 Error: A short mnemonic for the parameter. 1049 Specification: A reference to a publicly available specification for 1050 the value (optional for provisional registrations). 1052 Description: A brief description of the error code semantics, which 1053 MAY be a summary if a specification reference is provided. 1055 Provisional registrations of codepoints are intended to allow for 1056 private use and experimentation with extensions to DNS over QUIC. 1057 However, provisional registrations could be reclaimed and reassigned 1058 for another purpose. In addition to the parameters listed above, 1059 provisional registrations MUST include: 1061 Date: The date of last update to the registration. 1063 A request to update the date on any provisional registration can be 1064 made without review from the designated expert(s). 1066 The initial contents of this registry are shown in Table 1. 1068 +=======+=======================+===================+===============+ 1069 | Value | Error | Description | Specification | 1070 +=======+=======================+===================+===============+ 1071 | 0x0 | DOQ_NO_ERROR | No error | Section 5.3 | 1072 +-------+-----------------------+-------------------+---------------+ 1073 | 0x1 | DOQ_INTERNAL_ERROR | Implementation | Section 5.3 | 1074 | | | error | | 1075 +-------+-----------------------+-------------------+---------------+ 1076 | 0x2 | DOQ_PROTOCOL_ERROR | Generic protocol | Section 5.3 | 1077 | | | violation | | 1078 +-------+-----------------------+-------------------+---------------+ 1079 | 0x3 | DOQ_REQUEST_CANCELLED | Request | Section 5.3 | 1080 | | | cancelled by | | 1081 | | | client | | 1082 +-------+-----------------------+-------------------+---------------+ 1084 Table 1: Initial DNS over QUIC Error Codes Entries 1086 11. Acknowledgements 1088 This document liberally borrows text from the HTTP-3 specification 1089 [I-D.ietf-quic-http] edited by Mike Bishop, and from the DoT 1090 specification [RFC7858] authored by Zi Hu, Liang Zhu, John Heidemann, 1091 Allison Mankin, Duane Wessels, and Paul Hoffman. 1093 The privacy issue with 0-RTT data and session resumption were 1094 analyzed by Daniel Kahn Gillmor (DKG) in a message to the IETF 1095 "DPRIVE" working group [DNS0RTT]. 1097 Thanks to Tony Finch for an extensive review of the initial version 1098 of this draft, and to Robert Evans for the discussion of 0-RTT 1099 privacy issues. Reviews by Paul Hoffman and Martin Thomson and 1100 interoperability tests conducted by Stephane Bortzmeyer helped 1101 improve the definition of the protocol. 1103 12. References 1105 12.1. Normative References 1107 [I-D.ietf-dnsop-rfc8499bis] 1108 Hoffman, P. and K. Fujiwara, "DNS Terminology", Work in 1109 Progress, Internet-Draft, draft-ietf-dnsop-rfc8499bis-02, 1110 24 June 2021, . 1113 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 1114 STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, 1115 . 1117 [RFC1035] Mockapetris, P., "Domain names - implementation and 1118 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 1119 November 1987, . 1121 [RFC1995] Ohta, M., "Incremental Zone Transfer in DNS", RFC 1995, 1122 DOI 10.17487/RFC1995, August 1996, 1123 . 1125 [RFC5936] Lewis, E. and A. Hoenes, Ed., "DNS Zone Transfer Protocol 1126 (AXFR)", RFC 5936, DOI 10.17487/RFC5936, June 2010, 1127 . 1129 [RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms 1130 for DNS (EDNS(0))", STD 75, RFC 6891, 1131 DOI 10.17487/RFC6891, April 2013, 1132 . 1134 [RFC7301] Friedl, S., Popov, A., Langley, A., and E. Stephan, 1135 "Transport Layer Security (TLS) Application-Layer Protocol 1136 Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301, 1137 July 2014, . 1139 [RFC7766] Dickinson, J., Dickinson, S., Bellis, R., Mankin, A., and 1140 D. Wessels, "DNS Transport over TCP - Implementation 1141 Requirements", RFC 7766, DOI 10.17487/RFC7766, March 2016, 1142 . 1144 [RFC7828] Wouters, P., Abley, J., Dickinson, S., and R. Bellis, "The 1145 edns-tcp-keepalive EDNS0 Option", RFC 7828, 1146 DOI 10.17487/RFC7828, April 2016, 1147 . 1149 [RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., 1150 and P. Hoffman, "Specification for DNS over Transport 1151 Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May 1152 2016, . 1154 [RFC7873] Eastlake 3rd, D. and M. Andrews, "Domain Name System (DNS) 1155 Cookies", RFC 7873, DOI 10.17487/RFC7873, May 2016, 1156 . 1158 [RFC8094] Reddy, T., Wing, D., and P. Patil, "DNS over Datagram 1159 Transport Layer Security (DTLS)", RFC 8094, 1160 DOI 10.17487/RFC8094, February 2017, 1161 . 1163 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1164 Writing an IANA Considerations Section in RFCs", BCP 26, 1165 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1166 . 1168 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1169 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1170 May 2017, . 1172 [RFC8310] Dickinson, S., Gillmor, D., and T. Reddy, "Usage Profiles 1173 for DNS over TLS and DNS over DTLS", RFC 8310, 1174 DOI 10.17487/RFC8310, March 2018, 1175 . 1177 [RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS 1178 (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018, 1179 . 1181 [RFC8914] Kumari, W., Hunt, E., Arends, R., Hardaker, W., and D. 1182 Lawrence, "Extended DNS Errors", RFC 8914, 1183 DOI 10.17487/RFC8914, October 2020, 1184 . 1186 [RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based 1187 Multiplexed and Secure Transport", RFC 9000, 1188 DOI 10.17487/RFC9000, May 2021, 1189 . 1191 [RFC9001] Thomson, M., Ed. and S. Turner, Ed., "Using TLS to Secure 1192 QUIC", RFC 9001, DOI 10.17487/RFC9001, May 2021, 1193 . 1195 [RFC9103] Toorop, W., Dickinson, S., Sahib, S., Aras, P., and A. 1196 Mankin, "DNS Zone Transfer over TLS", RFC 9103, 1197 DOI 10.17487/RFC9103, August 2021, 1198 . 1200 12.2. Informative References 1202 [DNS0RTT] Kahn Gillmor, D., "DNS + 0-RTT", Message to DNS-Privacy WG 1203 mailing list, 6 April 2016, . 1206 [I-D.ietf-dprive-rfc7626-bis] 1207 Wicinski, T., "DNS Privacy Considerations", Work in 1208 Progress, Internet-Draft, draft-ietf-dprive-rfc7626-bis- 1209 09, 9 March 2021, . 1212 [I-D.ietf-quic-http] 1213 Bishop, M., "Hypertext Transfer Protocol Version 3 1214 (HTTP/3)", Work in Progress, Internet-Draft, draft-ietf- 1215 quic-http-34, 2 February 2021, 1216 . 1219 [RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S. 1220 Cheshire, "Internet Assigned Numbers Authority (IANA) 1221 Procedures for the Management of the Service Name and 1222 Transport Protocol Port Number Registry", BCP 165, 1223 RFC 6335, DOI 10.17487/RFC6335, August 2011, 1224 . 1226 [RFC7626] Bortzmeyer, S., "DNS Privacy Considerations", RFC 7626, 1227 DOI 10.17487/RFC7626, August 2015, 1228 . 1230 [RFC7830] Mayrhofer, A., "The EDNS(0) Padding Option", RFC 7830, 1231 DOI 10.17487/RFC7830, May 2016, 1232 . 1234 [RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running 1235 Code: The Implementation Status Section", BCP 205, 1236 RFC 7942, DOI 10.17487/RFC7942, July 2016, 1237 . 1239 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 1240 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 1241 . 1243 [RFC8467] Mayrhofer, A., "Padding Policies for Extension Mechanisms 1244 for DNS (EDNS(0))", RFC 8467, DOI 10.17487/RFC8467, 1245 October 2018, . 1247 [RFC8490] Bellis, R., Cheshire, S., Dickinson, J., Dickinson, S., 1248 Lemon, T., and T. Pusateri, "DNS Stateful Operations", 1249 RFC 8490, DOI 10.17487/RFC8490, March 2019, 1250 . 1252 [RFC9002] Iyengar, J., Ed. and I. Swett, Ed., "QUIC Loss Detection 1253 and Congestion Control", RFC 9002, DOI 10.17487/RFC9002, 1254 May 2021, . 1256 Appendix A. The NOTIFY service 1258 This appendix discusses the issue of allowing NOTIFY to be sent in 1259 0-RTT data. 1261 Section Section 5.5 says "The 0-RTT mechanism SHOULD NOT be used to 1262 send DNS requests that are not "replayable" transactions", and 1263 suggests this is limited to OPCODE QUERY. It might also be viable to 1264 propose that NOTIFY should be permitted in 0-RTT data because 1265 although it technically changes the state of the receiving server, 1266 the effect of replaying NOTIFYs has negligible impact in practice. 1268 NOTIFY messages prompt a secondary to either send an SOA query or an 1269 XFR request to the primary on the basis that a newer version of the 1270 zone is available. It has long been recognized that NOTIFYs can be 1271 forged and, in theory, used to cause a secondary to send repeated 1272 unnecessary requests to the primary. For this reason, most 1273 implementations have some form of throttling of the SOA/XFR queries 1274 triggered by the receipt of one or more NOTIFYs. 1276 RFC9103 describes the privacy risks associated with both NOTIFY and 1277 SOA queries and does not include addressing those risks within the 1278 scope of encrypting zone transfers. Given this, the privacy benefit 1279 of using DoQ for NOTIFY is not clear - but for the same reason, 1280 sending NOTIFY as 0-RTT data has no privacy risk above that of 1281 sending it using cleartext DNS. 1283 Authors' Addresses 1285 Christian Huitema 1286 Private Octopus Inc. 1287 427 Golfcourse Rd 1288 Friday Harbor 1290 Email: huitema@huitema.net 1292 Sara Dickinson 1293 Sinodun IT 1294 Oxford Science Park 1295 Oxford 1297 Email: sara@sinodun.com 1299 Allison Mankin 1300 Salesforce 1302 Email: allison.mankin@gmail.com