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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 M. Shore 5 Expires: October 12, 2017 Fastly 6 A. Mankin 7 Salesforce 8 S. Dickinson 9 Sinodun IT 10 J. Iyengar 11 Google 12 April 10, 2017 14 Specification of DNS over QUIC 15 draft-huitema-quic-dnsoquic-00 17 Abstract 19 This document describes the use of QUIC to provide transport privacy 20 for DNS. The encryption provided by QUIC has similar properties to 21 that provided by TLS, while QUIC transport eliminates the head-of- 22 line blocking issues inherent with TCP and provides more efficient 23 error corrections than UDP. DNS over QUIC has privacy properties 24 similar to DNS over TLS specified in RFC7858, and performance similar 25 to classic DNS over UDP. 27 Status of This Memo 29 This Internet-Draft is submitted in full conformance with the 30 provisions of BCP 78 and BCP 79. 32 Internet-Drafts are working documents of the Internet Engineering 33 Task Force (IETF). Note that other groups may also distribute 34 working documents as Internet-Drafts. The list of current Internet- 35 Drafts is at http://datatracker.ietf.org/drafts/current/. 37 Internet-Drafts are draft documents valid for a maximum of six months 38 and may be updated, replaced, or obsoleted by other documents at any 39 time. It is inappropriate to use Internet-Drafts as reference 40 material or to cite them other than as "work in progress." 42 This Internet-Draft will expire on October 12, 2017. 44 Copyright Notice 46 Copyright (c) 2017 IETF Trust and the persons identified as the 47 document authors. All rights reserved. 49 This document is subject to BCP 78 and the IETF Trust's Legal 50 Provisions Relating to IETF Documents 51 (http://trustee.ietf.org/license-info) in effect on the date of 52 publication of this document. Please review these documents 53 carefully, as they describe your rights and restrictions with respect 54 to this document. Code Components extracted from this document must 55 include Simplified BSD License text as described in Section 4.e of 56 the Trust Legal Provisions and are provided without warranty as 57 described in the Simplified BSD License. 59 Table of Contents 61 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 62 2. Key Words . . . . . . . . . . . . . . . . . . . . . . . . . . 4 63 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 64 4. Design Considerations . . . . . . . . . . . . . . . . . . . . 4 65 4.1. Scope is Limited to the Stub to Resolver Scenario . . . . 4 66 4.2. Provide DNS Privacy . . . . . . . . . . . . . . . . . . . 5 67 4.3. Design for Minimum Latency . . . . . . . . . . . . . . . 5 68 4.4. Development of QUIC Protocols and API . . . . . . . . . . 6 69 4.5. No Specific Middlebox Bypass Mechanism . . . . . . . . . 6 70 5. Specifications . . . . . . . . . . . . . . . . . . . . . . . 7 71 5.1. Connection Establishment . . . . . . . . . . . . . . . . 7 72 5.1.1. Draft Version Identification . . . . . . . . . . . . 7 73 5.1.2. Port Selection . . . . . . . . . . . . . . . . . . . 7 74 5.2. Stream Mapping and Usage . . . . . . . . . . . . . . . . 8 75 5.2.1. Server Initiated Transactions . . . . . . . . . . . . 8 76 5.2.2. Stream Reset . . . . . . . . . . . . . . . . . . . . 9 77 5.3. Closing the DNS over QUIC Connection . . . . . . . . . . 9 78 5.4. Connection Resume and 0-RTT . . . . . . . . . . . . . . . 9 79 6. Implementation Requirements . . . . . . . . . . . . . . . . . 10 80 6.1. Authentication . . . . . . . . . . . . . . . . . . . . . 10 81 6.2. Fall Back to Other Protocols on Connection Failure . . . 10 82 6.3. Response Sizes . . . . . . . . . . . . . . . . . . . . . 10 83 6.4. DNS Message IDs . . . . . . . . . . . . . . . . . . . . . 10 84 6.5. Padding . . . . . . . . . . . . . . . . . . . . . . . . . 11 85 6.6. Connection Handling . . . . . . . . . . . . . . . . . . . 11 86 6.6.1. Connection Reuse . . . . . . . . . . . . . . . . . . 11 87 6.6.2. Connection Close . . . . . . . . . . . . . . . . . . 11 88 6.6.3. Idle Timeouts . . . . . . . . . . . . . . . . . . . . 12 89 7. Security Considerations . . . . . . . . . . . . . . . . . . . 12 90 8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 12 91 8.1. Privacy Issues With 0RTT data . . . . . . . . . . . . . . 13 92 8.2. Privacy Issues With Session Resume . . . . . . . . . . . 13 93 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 94 9.1. Registration of DNS over QUIC Identification String . . . 14 95 9.2. Reservation of Dedicated Port . . . . . . . . . . . . . . 14 96 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14 97 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 15 98 11.1. Normative References . . . . . . . . . . . . . . . . . . 15 99 11.2. Informative References . . . . . . . . . . . . . . . . . 16 100 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18 102 1. Introduction 104 Domain Name System (DNS) concepts are specified in [RFC1034]. This 105 document presents a mapping of the DNS protocol [RFC1035] over QUIC 106 transport [I-D.ietf-quic-transport]. The goals of this mapping are: 108 1. Provide the same DNS privacy protection as DNS over TLS 109 [RFC7858]. This includes to option for the client to 110 authenticate the server by means of an authentication domain name 111 [I-D.ietf-dprive-dtls-and-tls-profiles]. 113 2. Provide an improved level of source address validation for DNS 114 servers compared to DNS over UDP [RFC1035]. 116 3. Provide a transport that is not constrained by path MTU 117 limitations on the size of DNS responses it can send. 119 4. Explore the potential performance gains of using QUIC as a DNS 120 transport, versus other solutions like DNS over UDP [RFC1035] or 121 DNS over TLS [RFC7858]. 123 5. Participate in the definition of QUIC protocols and API, by 124 outlining a use case for QUIC different from HTTP over QUIC 125 [I-D.ietf-quic-http]. 127 In order to achieve these goals, the focus is limited to the "stub to 128 recursive resolver" scenario also addressed by [RFC7858], that is the 129 protocol described here works for queries and responses between stub 130 clients and recursive servers. The specific non-goals are: 132 1. No attempt is made to support zone transfers [RFC5936], as these 133 are not relevant to the stub to recursive resolver scenario. 135 2. No attempt is made to evade potential blocking of DNS over QUIC 136 traffic by middleboxes. 138 Users interested in zone transfers should continue using TCP based 139 solutions, and users interested in evading middleboxes should 140 consider using solutions like DNS over HTTPS or DNS over HTTP over 141 QUIC (TODO: References required). 143 Specifying the transmission of an application over QUIC requires to 144 specify how the application messages are mapped to QUIC streams, and 145 generally how the application will use QUIC. This is done for HTTP 146 in [I-D.ietf-quic-http]. The purpose of this document is to define 147 the way DNS can be transmitted over QUIC. 149 In this document, Section 4 presents the reasoning that guided the 150 proposed design. Section 5 specifies the actual mapping of DNS over 151 QUIC. Section 6 presents guidelines on the implementation, usage and 152 deployment of DNS over QUIC. 154 2. Key Words 156 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 157 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 158 document are to be interpreted as described in [RFC2119]. 160 3. Terminology 162 The term DNS/QUIC is used interchangeably with 'DNS over QUIC' 163 throughout this document. 165 TODO: Make this usage more consistent. 167 4. Design Considerations 169 This section and its subsection present the design guidelines that 170 were used for the proposed mapping of DNS over QUIC. This section is 171 informative in nature. 173 4.1. Scope is Limited to the Stub to Resolver Scenario 175 Usage scenarios for the DNS protocol can be broadly classified in 176 three groups: stub to recursive resolver, recursive resolver to 177 authoritative server, and server to server. This design focuses only 178 on the "stub to recursive resolver" scenario following the approach 179 taken in [RFC7858] and [I-D.ietf-dprive-dtls-and-tls-profiles]. 181 QUESTION: Should this document specify any aspects of configuration 182 of discoverability differently to DNS over TLS? 184 No attempt is made to address the recursive to authoritative 185 scenarios. Authoritative resolvers are discovered dynamically 186 through NS records. It is noted that at the time of writing work is 187 ongoing in the DPRIVE working group to attempt to address the 188 analogous problem for DNS over TLS [I-D.bortzmeyer-dprive-step-2]. 189 In the absence of an agreed way for authoritative to signal support 190 for QUIC transport, recursive resolvers would have to resort to some 191 trial and error process. At this stage of QUIC deployment, this 192 would be mostly errors, and does not seem attractive. This could 193 change in the future. 195 The DNS protocol is also used for zone transfers. In the zone 196 transfer scenario ([RFC5936]), the client emits a single AXFR query, 197 and the server responds with a series of AXFR responses. This 198 creates a unique profile, in which a query results in several 199 responses. Supporting that profile would complicate the mapping of 200 DNS queries over QUIC streams. Zone transfers are not used in the 201 stub to recursive scenario that is the focus here, and seem to be 202 currently well served by the DNS over TCP. There is no attempt to 203 support them in this proposed mapping of DNS to QUIC. 205 4.2. Provide DNS Privacy 207 DNS privacy considerations are described in [RFC7626]. [RFC7858] 208 defines how to mitigate some of these issues by transmitting DNS 209 messages over TLS and TCP and [I-D.ietf-dprive-dtls-and-tls-profiles] 210 specifies Strict and Opportunistic profiles for DNS over TLS 211 including how stub resolvers can authenticate recursive resolvers. 213 QUIC connection setup includes the negotiation of security parameters 214 using TLS, as specified in [I-D.ietf-quic-tls], enabling encryption 215 of the QUIC transport. Transmitting DNS messages over QUIC will 216 provide essentially the same privacy protections as [RFC7858] and 217 [I-D.ietf-dprive-dtls-and-tls-profiles]. Further discussion on this 218 is provided in Section 8. 220 4.3. Design for Minimum Latency 222 QUIC is specifically designed to reduce the delay between HTTP 223 queries and HTTP responses. This is achieved through three main 224 components: 226 1. Support for 0-RTT data during session resume. 228 2. Support for advanced error recovery procedures as specified in 229 [I-D.ietf-quic-recovery]. 231 3. Mitigation of head-of-line blocking by allowing parallel delivery 232 of data on multiple streams. 234 The mapping of DNS to QUIC will take advantage of these features in 235 three ways: 237 1. Optional support for sending 0-RTT data during session resume 238 (the security and privacy implications of this are discussed in 239 later sections). 241 2. Long-lived QUIC connections over which multiple DNS transactions 242 are performed, generating the sustained traffic required to 243 benefit from advanced recovery features. 245 3. Mapping of each DNS Query/Response transaction to a separate 246 stream, to mitigate head-of-line blocking. 248 These considerations will be reflected in the mapping of DNS traffic 249 to QUIC streams in Section 5.2. 251 4.4. Development of QUIC Protocols and API 253 QUIC is defined as a layered protocol, with application specific 254 mapping layered on top of the generic QUIC transport. The only 255 mapping defined at this stage is HTTP over QUIC [I-D.ietf-quic-http]. 256 Adding a different mapping for a different application contributes to 257 the development of QUIC. 259 In the HTTP over QUIC mappings, the stream number 3 is used for 260 control messages, in which client or server announce their intent to 261 send headers and bodies of requests and responses and specify the 262 number of the streams that will carry these headers and response. 263 The advantage is that client and server can then schedule processing 264 of the requests and responses according to various policies and 265 priorities, and can tightly control the usage of streams. This comes 266 at the cost of some complexity, and also some performance since the 267 control stream is exposed to head-of-line blocking. 269 In this document a different design is deliberately explored, in 270 which there is no control stream. Clients and servers can initiate 271 queries as determined by the DNS application logic, opening new 272 streams as necessary. This provides for maximum parallelism between 273 queries, as noted in Section 4.3. It also places constraints on the 274 API. Instead of merely listening for control messages on a control 275 stream, client and servers will have to be notified of the opening of 276 a new stream by their peer. Instead of orderly closing the control 277 stream, client and server will have to use orderly connection closure 278 mechanisms and manage the potential loss of data if closing on one 279 end conflicts with opening of a stream on the other end. 281 4.5. No Specific Middlebox Bypass Mechanism 283 Being different from HTTP over QUIC is a design choice. The 284 advantage is that the mapping can be defined for minimal overhead and 285 maximum performance. The downside is that the difference can be 286 noted by firewalls and middleboxes. There may be environments in 287 which HTTP over QUIC will be allowed, but DNS over QUIC will be 288 disallowed and blocked by these middle boxes. 290 It is recognised that this might be a problem, but there is currently 291 no indication on how widespread that problem might be. It might be 292 that the problem will be so acute that the only realistic solution 293 would be to communicate with independent recursive resolvers using 294 DNS over HTTPS, or maybe DNS over HTTP over QUIC. Or it might be 295 that the problem is rare enough and the performance gains significant 296 enough that the correct solution is to use DNS over QUIC most of the 297 time, and to fall back on DNS over HTTPS some of the time. 298 Measurements and experimentations will inform that decision. In 299 between, we believe that a clean design is most likely to inform the 300 QUIC development, as explained in Section 4.4. 302 5. Specifications 304 5.1. Connection Establishment 306 DNS/QUIC connections are established as described in 307 [I-D.ietf-quic-transport]. During connection establishment, DNS/QUIC 308 support is indicated by selecting the ALPN token "dq" in the crypto 309 handshake. 311 5.1.1. Draft Version Identification 313 *RFC Editor's Note:* Please remove this section prior to publication 314 of a final version of this document. 316 Only implementations of the final, published RFC can identify 317 themselves as "dq". Until such an RFC exists, implementations MUST 318 NOT identify themselves using this string. 320 Implementations of draft versions of the protocol MUST add the string 321 "-" and the corresponding draft number to the identifier. For 322 example, draft-huitema-quic-dnsoquic-00 is identified using the 323 string "dq-h00". 325 5.1.2. Port Selection 327 By default, a DNS server that supports DNS/QUIC MUST listen for and 328 accept QUIC connections on the dedicated UDP port TBD (number to be 329 defined in Section 9, unless it has mutual agreement with its clients 330 to use a port other than TBD for DNS over QUIC. In order to use a 331 port other than TBD, both clients and servers would need a 332 configuration option in their software. 334 By default, a DNS client desiring to use DNS over QUIC with a 335 particular server MUST establish a QUIC connection to UDP port TBD on 336 the server, unless it has mutual agreement with its server to use a 337 port other than port TBD for DNS over QUIC. Such another port MUST 338 NOT be port 53 or port 853. This recommendation against use of port 339 53 for DNS over QUIC is to avoid confusion between DNS over QUIC and 340 DNS over UDP as specified in [RFC1035]. Similarly, using port 853 341 would cause confusion between DNS over QUIC and DNS over DTLS as 342 specified in [RFC8094]. 344 5.2. Stream Mapping and Usage 346 The mapping of DNS traffic over QUIC streams takes advantage of the 347 QUIC stream features detailed in Section 10 of 348 [I-D.ietf-quic-transport]. 350 The stub to resolver DNS traffic follows a simple pattern in which 351 the client sends a query, and the server provides a response. This 352 design specifies that for each subsequent query on a QUIC connection 353 the client MUST select the next available client stream, in 354 conformance with Section 10.2 of [I-D.ietf-quic-transport]. 356 The client MUST send the DNS query over the selected stream, and MUST 357 indicate through the STREAM FIN mechanism that no further data will 358 be sent on that stream. 360 The server MUST send the response on the same stream, and MUST 361 indicate through the STREAM FIN mechanism mechanism that no further 362 data will be sent on that stream. 364 Therefore a single client initiated DNS transaction consumes a single 365 stream. This means that the client's first query occurs on QUIC 366 stream 3, the second on 5, and so on. 368 DNS query and responses are formatted as specified in [RFC1035]. In 369 contrast with DNS over TCP [RFC7766] and DNS over TLS [RFC7858], 370 these messages are sent without a two bytes length field prepended. 372 5.2.1. Server Initiated Transactions 374 There are planned traffic patterns in which a server sends 375 unsolicited queries to a client, such as for example PUSH messages 376 defined in [I-D.ietf-dnssd-push]. When a server wishes to send such 377 queries it MUST select the next available server stream, in 378 conformance with Section 10.2 of [I-D.ietf-quic-transport]. 380 The server MUST send the DNS query over the selected stream, and MUST 381 indicate through the STREAM FIN mechanism that no further data will 382 be sent on that stream. 384 The client MUST send the response on the same stream, and MUST 385 indicate through the STREAM FIN mechanism mechanism that no further 386 data will be sent on that stream. 388 Therefore a single server initiated DNS transaction consumes a single 389 stream. This means that the servers's first query occurs on QUIC 390 stream 2, the second on 4, and so on. 392 5.2.2. Stream Reset 394 Stream transmission may be abandoned by either party, using the 395 stream "reset" facility. A stream reset indicates that one party is 396 unwilling to continue processing the transaction associated with the 397 stream. The corresponding transaction MUST be abandoned. A Server 398 Failure (SERVFAIL, [RFC1035]) SHOULD be notified to the initiator of 399 the transaction. 401 5.3. Closing the DNS over QUIC Connection 403 QUIC connections are closed using the CONNECTION_CLOSE mechanisms 404 specified in [I-D.ietf-quic-transport]. Connections can be closed at 405 the initiative of either the client or the server (also see 406 Section 6.6.2). The party initiating the connection closure SHOULD 407 use the QUIC GOAWAY mechanism to initiate a graceful shutdown of a 408 connection. 410 The transactions corresponding to stream number higher than indicated 411 in the GO AWAY frames MUST be considered failed. Similarly, if 412 streams are still open when the CONNECTION_CLOSE is received, the 413 corresponding transactions MUST be considered failed. In both cases, 414 a Server Failure (SERVFAIL, [RFC1035]) SHOULD be notified to the 415 initiator of the transaction. 417 5.4. Connection Resume and 0-RTT 419 A stub resolver MAY take advantage of the connection resume 420 mechanisms supported by QUIC transport [I-D.ietf-quic-transport] and 421 QUIC TLS [I-D.ietf-quic-tls]. Stub resolvers SHOULD consider 422 potential privacy issues associated with session resume before 423 deciding to use this mechanism. These privacy issues are detailed in 424 Section 8.2. 426 When resuming a session, a stub resolver MAY take advantage of the 427 0-RTT mechanism supported by QUIC. The 0-RTT mechanism MUST NOT be 428 used to send data that is not "replayable" transactions. For 429 example, a stub resolver MAY transmit a Query as 0-RTT, but MUST NOT 430 transmit an Update. 432 6. Implementation Requirements 434 6.1. Authentication 436 For the stub to recursive resolver scenario, the authentication 437 requirements are the same as described in [RFC7858] and 438 [I-D.ietf-dprive-dtls-and-tls-profiles]. There is no need to 439 authenticate the client's identity in either scenario. 441 6.2. Fall Back to Other Protocols on Connection Failure 443 If the establishment of the DNS over QUIC connection fails, clients 444 SHOULD attempt to fall back to DNS over TLS and then potentially 445 clear text, as specified in [RFC7858] and 446 [I-D.ietf-dprive-dtls-and-tls-profiles], depending on their privacy 447 profile. 449 DNS clients SHOULD remember server IP addresses that don't support 450 DNS over QUIC, including timeouts, connection refusals, and QUIC 451 handshake failures, and not request DNS over QUIC from them for a 452 reasonable period (such as one hour per server). DNS clients 453 following an out-of-band key-pinned privacy profile ([RFC7858]) MAY 454 be more aggressive about retrying DNS over QUIC connection failures. 456 6.3. Response Sizes 458 DNS over QUIC does not suffer from the limitation on the size of 459 responses that can be delivered as DNS over UDP [RFC1035] does, since 460 large responses will be sent in separate STREAM frames in separate 461 packets. 463 QUESTION: However this raises a new issue because the responses sent 464 over QUIC can be significantly larger than those sent over TCP 465 (65,635 bytes). According to [I-D.ietf-quic-transport] "The largest 466 offset delivered on a stream - the sum of the re-constructed offset 467 and data length - MUST be less than 2^64". Should a specific limit 468 be applied for DNS over QUIC responses or not? 470 6.4. DNS Message IDs 472 QUESTION: Should we include the restrictions 'When sending multiple 473 queries over a QUIC connection, clients MUST NOT reuse the DNS 474 Message ID of an in-flight query on that connection in order to avoid 475 Message ID collisions.' 477 And similarly for 'Clients MUST match outstanding queries using the 478 Message ID and if the response contains a question section, the 479 client MUST match the QNAME, QCLASS, and QTYPE fields.'. In other 480 words should we involve the stream ID in message matching or not? 482 6.5. Padding 484 There are mechanisms specified for both padding individual DNS 485 messages [RFC7830], [I-D.ietf-dprive-padding-policy] and padding 486 within QUIC packets (see Section 8.6 of [I-D.ietf-quic-transport]), 487 which may contain multiple frames. 489 QUESTION: What should the padding guidelines be here? 491 6.6. Connection Handling 493 [RFC7766] provides updated guidance on DNS over TCP much of which is 494 applicable to DNS over QUIC. This section attempts to specify how 495 those considerations apply to DNS over QUIC. 497 6.6.1. Connection Reuse 499 Historic implementations of DNS stub resolvers are known to open and 500 close TCP connections for each DNS query. To avoid excess QUIC 501 connections, each with a single query, clients SHOULD reuse a single 502 QUIC connection to the recursive resolver. 504 In order to achieve performance on par with UDP, DNS clients SHOULD 505 send their queries concurrently over the QUIC streams on a QUIC 506 connection. That is, when a DNS client sends multiple queries to a 507 server over a QUIC connection, it SHOULD NOT wait for an outstanding 508 reply before sending the next query. 510 6.6.2. Connection Close 512 In order to amortize QUIC and TLS connection setup costs, clients and 513 servers SHOULD NOT immediately close a QUIC connection after each 514 response. Instead, clients and servers SHOULD reuse existing QUIC 515 connections for subsequent queries as long as they have sufficient 516 resources. In some cases, this means that clients and servers may 517 need to keep idle connections open for some amount of time. 519 Under normal operation DNS clients typically initiate connection 520 closing on idle connections; however, DNS servers can close the 521 connection if the idle timeout set by local policy is exceeded. 522 Also, connections can be closed by either end under unusual 523 conditions such as defending against an attack or system failure/ 524 reboot. 526 Clients and servers that keep idle connections open MUST be robust to 527 termination of idle connection by either party. As with current DNS 528 over TCP, DNS servers MAY close the connection at any time (perhaps 529 due to resource constraints). As with current DNS over TCP, clients 530 MUST handle abrupt closes and be prepared to reestablish connections 531 and/or retry queries. 533 6.6.3. Idle Timeouts 535 Proper management of established and idle connections is important to 536 the healthy operation of a DNS server. An implementor of DNS over 537 QUIC SHOULD follow best practices for DNS over TCP, as described in 538 [RFC7766]. Failure to do so may lead to resource exhaustion and 539 denial of service. 541 This document does not make specific recommendations for timeout 542 values on idle connections. Clients and servers should reuse and/or 543 close connections depending on the level of available resources. 544 Timeouts may be longer during periods of low activity and shorter 545 during periods of high activity. Current work in this area may also 546 assist DNS over TLS clients and servers in selecting useful timeout 547 values [RFC7828] [I-D.ietf-dnsop-session-signal] [TDNS]. 549 TODO: Clarify what timers (idle timeouts, response timeouts) apply at 550 the stream level and at the connection level. 552 TODO: QUIC provides an efficient mechanism for resuming connections, 553 including the possibility of sending 0-RTT data. Does that change 554 the tradeoff? Is it plausible to use shorter timers than specified 555 for TCP? 557 7. Security Considerations 559 The security considerations of DNS over QUIC should be comparable to 560 those of DNS over TLS [RFC7858]. 562 8. Privacy Considerations 564 DNS over QUIC is specifically designed to protect the DNS traffic 565 between stub and resolver from observations by third parties, and 566 thus protect the privacy of queries from the stub. However, the 567 recursive resolver has full visibility of the stub's traffic, and 568 could be used as an observation point, as discussed in [RFC7626]. 569 These considerations do not differ between DNS over TLS and DNS over 570 QUIC and are not discussed further here. 572 QUIC incorporates the mechanisms of TLS 1.3 [I-D.ietf-tls-tls13] and 573 this enables QUIC transmission of "Zero RTT" data. This can provide 574 interesting latency gains, but it raises two concerns: 576 1. Adversaries could replay the zero-RTT data and infer its content 577 from the behavior of the receiving server. 579 2. The zero-RTT mechanism relies on TLS resume, which can provide 580 linkability between successive client sessions. 582 These issues are developed in Section 8.1 and Section 8.2. 584 8.1. Privacy Issues With 0RTT data 586 The zero-RTT data can be replayed by adversaries. That data may 587 triggers a query by a recursive resolver to an authoritative 588 resolvers. Adversaries may be able to pick a time at which the 589 recursive resolver outgoing traffic is observable, and thus find out 590 what name was queried for in the 0-RTT data. 592 This risk is in fact a subset of the general problem of observing the 593 behavior of the recursive resolver discussed in [RFC7626]. The 594 attack is partially mitigated by reducing the observability of this 595 traffic. However, the risk is amplified for 0-RTT data, because the 596 attacker might replay it at chosen times, several times. 598 The recommendation in [I-D.ietf-tls-tls13] is that the capability to 599 use 0-RTT data should be turned off by default, on only enabled if 600 the user clearly understands the associated risks. 602 QUESTION: Should 0-RTT only be used with Opportunistic profiles (i.e. 603 disabled by default for Strict only)? 605 8.2. Privacy Issues With Session Resume 607 The QUIC session resume mechanism reduces the cost of reestablishing 608 sessions and enables zero-RTT data. There is a linkability issue 609 associated with session resume, if the same resume token is used 610 several times, but this risk is mitigated by the mechanisms 611 incorporated in QUIC and in TLS 1.3. With these mechanisms, clients 612 and servers can cooperate to avoid linkability by third parties. 613 However, the server will always be able to link the resumed session 614 to the initial session. This creates a virtual long duration 615 session. The series of queries in that session can be used by the 616 server to identify the client. 618 Enabling the server to link client sessions through session resume is 619 probably not a large additional risk if the client's connectivity did 620 not change between the sessions, since the two sessions can probably 621 be correlated by comparing the IP addresses. On the other hand, if 622 the addresses did change, the client SHOULD consider whether the 623 linkability risk exceeds the privacy benefits. This evaluation will 624 obviously depend on the level of trust between stub and recursive. 626 9. IANA Considerations 628 9.1. Registration of DNS over QUIC Identification String 630 This document creates a new registration for the identification of 631 DNS over QUIC in the "Application Layer Protocol Negotiation (ALPN) 632 Protocol IDs" registry established in [RFC7301]. 634 The "dq" string identifies DNS over QUIC: 636 Protocol: DNS over QUIC 638 Identification Sequence: 0x64 0x71 ("dq") 640 Specification: This document 642 9.2. Reservation of Dedicated Port 644 IANA is required to add the following value to the "Service Name and 645 Transport Protocol Port Number Registry" in the System Range. The 646 registry for that range requires IETF Review or IESG Approval 647 [RFC6335], and such a review was requested using the early allocation 648 process [RFC7120] for the well-known UDP port in this document. 649 Since port 853 is reserved for 'DNS query-response protocol run over 650 TLS' consideration is requested for reserving port 953 for 'DNS 651 query-response 652 protocol run over QUIC'. 654 Service Name domain-s 655 Transport Protocol(s) TCP/UDP 656 Assignee IESG 657 Contact IETF Chair 658 Description DNS query-response protocol run over QUIC 659 Reference This document 661 10. Acknowledgements 663 This document liberally borrows text from [I-D.ietf-quic-http] edited 664 by Mike Bishop, and from [RFC7858] authored by Zi Hu, Liang Zhu, John 665 Heidemann, Allison Mankin, Duane Wessels, and Paul Hoffman. 667 The privacy issue with 0-RTT data and session resume were analyzed by 668 Daniel Kahn Gillmor (DKG) in a message to the IETF "DPRIV" working 669 group [DNS0RTT]. 671 Thanks to our wide cast of supporters. 673 11. References 675 11.1. Normative References 677 [I-D.ietf-dprive-dtls-and-tls-profiles] 678 Dickinson, S., Gillmor, D., and T. Reddy, "Authentication 679 and (D)TLS Profile for DNS-over-(D)TLS", draft-ietf- 680 dprive-dtls-and-tls-profiles-08 (work in progress), 681 January 2017. 683 [I-D.ietf-quic-tls] 684 Thomson, M. and S. Turner, "Using Transport Layer Security 685 (TLS) to Secure QUIC", draft-ietf-quic-tls-02 (work in 686 progress), March 2017. 688 [I-D.ietf-quic-transport] 689 Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed 690 and Secure Transport", draft-ietf-quic-transport-02 (work 691 in progress), March 2017. 693 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 694 STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, 695 . 697 [RFC1035] Mockapetris, P., "Domain names - implementation and 698 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 699 November 1987, . 701 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 702 Requirement Levels", BCP 14, RFC 2119, 703 DOI 10.17487/RFC2119, March 1997, 704 . 706 [RFC7301] Friedl, S., Popov, A., Langley, A., and E. Stephan, 707 "Transport Layer Security (TLS) Application-Layer Protocol 708 Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301, 709 July 2014, . 711 11.2. Informative References 713 [DNS0RTT] Kahn Gillmor, D., "DNS + 0-RTT", Message DNS-Privacy WG 714 mailing list, April 2016, . 717 [I-D.bortzmeyer-dprive-step-2] 718 Bortzmeyer, S., "Next step for DPRIVE: resolver-to-auth 719 link", draft-bortzmeyer-dprive-step-2-05 (work in 720 progress), December 2016. 722 [I-D.ietf-dnsop-session-signal] 723 Bellis, R., Cheshire, S., Dickinson, J., Dickinson, S., 724 Mankin, A., and T. Pusateri, "DNS Session Signaling", 725 draft-ietf-dnsop-session-signal-02 (work in progress), 726 March 2017. 728 [I-D.ietf-dnssd-push] 729 Pusateri, T. and S. Cheshire, "DNS Push Notifications", 730 draft-ietf-dnssd-push-10 (work in progress), March 2017. 732 [I-D.ietf-dprive-padding-policy] 733 Mayrhofer, A., "Padding Policy for EDNS(0)", draft-ietf- 734 dprive-padding-policy-00 (work in progress), December 735 2016. 737 [I-D.ietf-quic-http] 738 Bishop, M., "Hypertext Transfer Protocol (HTTP) over 739 QUIC", draft-ietf-quic-http-02 (work in progress), March 740 2017. 742 [I-D.ietf-quic-recovery] 743 Iyengar, J. and I. Swett, "QUIC Loss Detection and 744 Congestion Control", draft-ietf-quic-recovery-02 (work in 745 progress), March 2017. 747 [I-D.ietf-tls-tls13] 748 Rescorla, E., "The Transport Layer Security (TLS) Protocol 749 Version 1.3", draft-ietf-tls-tls13-19 (work in progress), 750 March 2017. 752 [RFC5936] Lewis, E. and A. Hoenes, Ed., "DNS Zone Transfer Protocol 753 (AXFR)", RFC 5936, DOI 10.17487/RFC5936, June 2010, 754 . 756 [RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S. 757 Cheshire, "Internet Assigned Numbers Authority (IANA) 758 Procedures for the Management of the Service Name and 759 Transport Protocol Port Number Registry", BCP 165, 760 RFC 6335, DOI 10.17487/RFC6335, August 2011, 761 . 763 [RFC7120] Cotton, M., "Early IANA Allocation of Standards Track Code 764 Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January 765 2014, . 767 [RFC7626] Bortzmeyer, S., "DNS Privacy Considerations", RFC 7626, 768 DOI 10.17487/RFC7626, August 2015, 769 . 771 [RFC7766] Dickinson, J., Dickinson, S., Bellis, R., Mankin, A., and 772 D. Wessels, "DNS Transport over TCP - Implementation 773 Requirements", RFC 7766, DOI 10.17487/RFC7766, March 2016, 774 . 776 [RFC7828] Wouters, P., Abley, J., Dickinson, S., and R. Bellis, "The 777 edns-tcp-keepalive EDNS0 Option", RFC 7828, 778 DOI 10.17487/RFC7828, April 2016, 779 . 781 [RFC7830] Mayrhofer, A., "The EDNS(0) Padding Option", RFC 7830, 782 DOI 10.17487/RFC7830, May 2016, 783 . 785 [RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., 786 and P. Hoffman, "Specification for DNS over Transport 787 Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May 788 2016, . 790 [RFC8094] Reddy, T., Wing, D., and P. Patil, "DNS over Datagram 791 Transport Layer Security (DTLS)", RFC 8094, 792 DOI 10.17487/RFC8094, February 2017, 793 . 795 [TDNS] Zhu, L., Hu, Z., Heidemann, J., Wessels, D., Mankin, A., 796 and N. Somaiya, "Connection-Oriented DNS to Improve 797 Privacy and Security", 2015 IEEE Symposium on Security and 798 Privacy (SP), DOI 10.1109/SP.2015.18, 799 . 801 Authors' Addresses 803 Christian Huitema 804 Private Octopus Inc. 805 Friday Harbor WA 98250 806 U.S.A 808 Email: huitema@huitema.net 810 Melinda Shore 811 Fastly 813 Email: mshore@fastly.com 815 Allison Mankin 816 Salesforce 818 Email: amankin@salesforce.com 820 Sara Dickinson 821 Sinodun IT 822 Magdalen Centre 823 Oxford Science Park 824 Oxford OX4 4GA 825 U.K. 827 Email: sara@sinodun.com 829 Jana Iyengar 830 Google 832 Email: jri@google.com