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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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-03) exists of draft-ietf-add-svcb-dns-00 == Outdated reference: A later version (-09) exists of draft-ietf-dnsop-svcb-https-07 == Outdated reference: A later version (-14) exists of draft-ietf-tls-esni-13 Summary: 0 errors (**), 0 flaws (~~), 5 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 ADD T. Pauly 3 Internet-Draft E. Kinnear 4 Intended status: Standards Track Apple Inc. 5 Expires: 4 April 2022 C.A. Wood 6 Cloudflare 7 P. McManus 8 Fastly 9 T. Jensen 10 Microsoft 11 1 October 2021 13 Discovery of Designated Resolvers 14 draft-ietf-add-ddr-03 16 Abstract 18 This document defines Discovery of Designated Resolvers (DDR), a 19 mechanism for DNS clients to use DNS records to discover a resolver's 20 encrypted DNS configuration. This mechanism can be used to move from 21 unencrypted DNS to encrypted DNS when only the IP address of a 22 resolver is known. This mechanism is designed to be limited to cases 23 where unencrypted resolvers and their designated resolvers are 24 operated by the same entity or cooperating entities. It can also be 25 used to discover support for encrypted DNS protocols when the name of 26 an encrypted resolver is known. 28 Discussion Venues 30 This note is to be removed before publishing as an RFC. 32 Discussion of this document takes place on the Adaptive DNS Discovery 33 Working Group mailing list (add@ietf.org), which is archived at 34 https://mailarchive.ietf.org/arch/browse/add/. 36 Source for this draft and an issue tracker can be found at 37 https://github.com/ietf-wg-add/draft-ietf-add-ddr. 39 Status of This Memo 41 This Internet-Draft is submitted in full conformance with the 42 provisions of BCP 78 and BCP 79. 44 Internet-Drafts are working documents of the Internet Engineering 45 Task Force (IETF). Note that other groups may also distribute 46 working documents as Internet-Drafts. The list of current Internet- 47 Drafts is at https://datatracker.ietf.org/drafts/current/. 49 Internet-Drafts are draft documents valid for a maximum of six months 50 and may be updated, replaced, or obsoleted by other documents at any 51 time. It is inappropriate to use Internet-Drafts as reference 52 material or to cite them other than as "work in progress." 54 This Internet-Draft will expire on 4 April 2022. 56 Copyright Notice 58 Copyright (c) 2021 IETF Trust and the persons identified as the 59 document authors. All rights reserved. 61 This document is subject to BCP 78 and the IETF Trust's Legal 62 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 63 license-info) in effect on the date of publication of this document. 64 Please review these documents carefully, as they describe your rights 65 and restrictions with respect to this document. Code Components 66 extracted from this document must include Simplified BSD License text 67 as described in Section 4.e of the Trust Legal Provisions and are 68 provided without warranty as described in the Simplified BSD License. 70 Table of Contents 72 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 73 1.1. Specification of Requirements . . . . . . . . . . . . . . 3 74 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 75 3. DNS Service Binding Records . . . . . . . . . . . . . . . . . 4 76 4. Discovery Using Resolver IP Addresses . . . . . . . . . . . . 5 77 4.1. Use of Designated Resolvers . . . . . . . . . . . . . . . 6 78 4.2. Authenticated Discovery . . . . . . . . . . . . . . . . . 6 79 4.3. Opportunistic Discovery . . . . . . . . . . . . . . . . . 7 80 5. Discovery Using Resolver Names . . . . . . . . . . . . . . . 7 81 6. Deployment Considerations . . . . . . . . . . . . . . . . . . 8 82 6.1. Caching Forwarders . . . . . . . . . . . . . . . . . . . 8 83 6.2. Certificate Management . . . . . . . . . . . . . . . . . 9 84 7. Security Considerations . . . . . . . . . . . . . . . . . . . 9 85 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 86 8.1. Special Use Domain Name "resolver.arpa" . . . . . . . . . 10 87 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 88 9.1. Normative References . . . . . . . . . . . . . . . . . . 10 89 9.2. Informative References . . . . . . . . . . . . . . . . . 11 90 Appendix A. Rationale for using SVCB records . . . . . . . . . . 12 91 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 93 1. Introduction 95 When DNS clients wish to use encrypted DNS protocols such as DNS- 96 over-TLS (DoT) [RFC7858] or DNS-over-HTTPS (DoH) [RFC8484], they 97 require additional information beyond the IP address of the DNS 98 server, such as the resolver's hostname, non-standard ports, or URL 99 paths. However, common configuration mechanisms only provide the 100 resolver's IP address during configuration. Such mechanisms include 101 network provisioning protocols like DHCP [RFC2132] and IPv6 Router 102 Advertisement (RA) options [RFC8106], as well as manual 103 configuration. 105 This document defines two mechanisms for clients to discover 106 designated resolvers using DNS server Service Binding (SVCB, 107 [I-D.ietf-dnsop-svcb-https]) records: 109 1. When only an IP address of an Unencrypted Resolver is known, the 110 client queries a special use domain name to discover DNS SVCB 111 records associated with one or more Encrypted Resolvers the 112 Unencrypted Resolver has designated for use when support for DNS 113 encryption is requested (Section 4). 115 2. When the hostname of an Encrypted Resolver is known, the client 116 requests details by sending a query for a DNS SVCB record. This 117 can be used to discover alternate encrypted DNS protocols 118 supported by a known server, or to provide details if a resolver 119 name is provisioned by a network (Section 5). 121 Both of these approaches allow clients to confirm that a discovered 122 Encrypted Resolver is designated by the originally provisioned 123 resolver. "Designated" in this context means that the resolvers are 124 operated by the same entity or cooperating entities; for example, the 125 resolvers are accessible on the same IP address, or there is a 126 certificate that claims ownership over both resolvers. 128 1.1. Specification of Requirements 130 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 131 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 132 "OPTIONAL" in this document are to be interpreted as described in BCP 133 14 [RFC2119] [RFC8174] when, and only when, they appear in all 134 capitals, as shown here. 136 2. Terminology 138 This document defines the following terms: 140 DDR: Discovery of Designated Resolvers. Refers to the mechanisms 141 defined in this document. 143 Designated Resolver: A resolver, presumably an Encrypted Resolver, 144 designated by another resolver for use in its own place. This 145 designation can be authenticated with TLS certificates. 147 Encrypted Resolver: A DNS resolver using any encrypted DNS 148 transport. This includes current mechanisms such as DoH and DoT 149 as well as future mechanisms. 151 Unencrypted Resolver: A DNS resolver using TCP or UDP port 53. 153 3. DNS Service Binding Records 155 DNS resolvers can advertise one or more Designated Resolvers that may 156 offer support over encrypted channels and are controlled by the same 157 entity. 159 When a client discovers Designated Resolvers, it learns information 160 such as the supported protocols, ports, and server name to use in 161 certificate validation. This information is provided in Service 162 Binding (SVCB) records for DNS Servers. The formatting of these 163 records, including the DNS-unique parameters such as "dohpath", are 164 defined by [I-D.ietf-add-svcb-dns]. 166 The following is an example of an SVCB record describing a DoH server 167 discovered by querying for _dns.example.net: 169 _dns.example.net 7200 IN SVCB 1 . ( 170 alpn=h2 dohpath=/dns-query{?dns} ) 172 The following is an example of an SVCB record describing a DoT server 173 discovered by querying for _dns.example.net: 175 _dns.example.net 7200 IN SVCB 1 dot.example.net ( 176 alpn=dot port=8530 ) 178 If multiple Designated Resolvers are available, using one or more 179 encrypted DNS protocols, the resolver deployment can indicate a 180 preference using the priority fields in each SVCB record 181 [I-D.ietf-dnsop-svcb-https]. 183 To avoid name lookup deadlock, Designated Resolvers SHOULD follow the 184 guidance in Section 10 of [RFC8484] regarding the avoidance of DNS- 185 based references that block the completion of the TLS handshake. 187 This document focuses on discovering DoH and DoT Designated 188 Resolvers. Other protocols can also use the format defined by 189 [I-D.ietf-add-svcb-dns]. However, if any protocol does not involve 190 some form of certificate validation, new validation mechanisms will 191 need to be defined to support validating designation as defined in 192 Section 4.2. 194 4. Discovery Using Resolver IP Addresses 196 When a DNS client is configured with an Unencrypted Resolver IP 197 address, it SHOULD query the resolver for SVCB records for 198 "dns://resolver.arpa" before making other queries. Specifically, the 199 client issues a query for _dns.resolver.arpa with the SVCB resource 200 record type (64) [I-D.ietf-dnsop-svcb-https]. 202 Because this query is for an SUDN, which no entity can claim 203 ownership over, the SVCB response MUST NOT use the "." value for the 204 TargetName. Instead, the domain name used for DoT or used to 205 construct the DoH template MUST be provided. 207 The following is an example of an SVCB record describing a DoH server 208 discovered by querying for _dns.resolver.arpa: 210 _dns.resolver.arpa 7200 IN SVCB 1 doh.example.net ( 211 alpn=h2 dohpath=/dns-query{?dns} ) 213 The following is an example of an SVCB record describing a DoT server 214 discovered by querying for _dns.resolver.arpa: 216 _dns.resolver.arpa 7200 IN SVCB 1 dot.example.net ( 217 alpn=dot port=8530 ) 219 If the recursive resolver that receives this query has one or more 220 Designated Resolvers, it will return the corresponding SVCB records. 221 When responding to these special queries for "dns://resolver.arpa", 222 the recursive resolver SHOULD include the A and AAAA records for the 223 name of the Designated Resolver in the Additional Answers section. 224 This will allow the DNS client to make queries over an encrypted 225 connection without waiting to resolve the Encrypted Resolver name per 226 [I-D.ietf-dnsop-svcb-https]. If no A/AAAA records or SVCB IP address 227 hints are included, clients will be forced to delay use of the 228 Encrypted Resolver until an additional DNS lookup for the A and AAAA 229 records can be made to the Unencrypted Resolver (or some other 230 resolver the DNS client has been configured to use). 232 If the recursive resolver that receives this query has no Designated 233 Resolvers, it SHOULD return NODATA for queries to the "resolver.arpa" 234 SUDN. 236 4.1. Use of Designated Resolvers 238 When a client discovers Designated Resolvers from an Unencrypted 239 Resolver IP address, it can choose to use these Designated Resolvers 240 either automatically, or based on some other policy, heuristic, or 241 user choice. 243 This document defines two preferred methods to automatically use 244 Designated Resolvers: 246 * Authenticated Discovery Section 4.2, for when a TLS certificate 247 can be used to validate the resolver's identity. 249 * Opportunistic Discovery Section 4.3, for when a resolver is 250 accessed using a non-public IP address. 252 A client MAY additionally use a discovered Designated Resolver 253 without either of these methods, based on implementation-specific 254 policy or user input. Details of such policy are out of scope of 255 this document. Clients SHOULD NOT automatically use a Designated 256 Resolver without some sort of validation, such as the two methods 257 defined in this document or a future mechanism. 259 4.2. Authenticated Discovery 261 Authenticated Discovery is a mechanism that allows automatic use of a 262 Designated Resolver that supports DNS encryption that performs a TLS 263 handshake. 265 In order to be considered an authenticated Designated Resolver, the 266 TLS certificate presented by the Designated Resolver MUST contain 267 both the domain name (from the SVCB answer) and the IP address of the 268 designating Unencrypted Resolver within the SubjectAlternativeName 269 certificate field. The client MUST check the SubjectAlternativeName 270 field for both the Unencrypted Resolver's IP address and the 271 advertised name of the Designated Resolver. If the certificate can 272 be validated, the client SHOULD use the discovered Designated 273 Resolver for any cases in which it would have otherwise used the 274 Unencrypted Resolver. If the Designated Resolver has a different IP 275 address than the Unencrypted Resolver and the TLS certificate does 276 not cover the Unencrypted Resolver address, the client MUST NOT 277 automatically use the discovered Designated Resolver. Additionally, 278 the client SHOULD suppress any further queries for Designated 279 Resolvers using this Unencrypted Resolver for the length of time 280 indicated by the SVCB record's Time to Live (TTL). 282 If the Designated Resolver and the Unencrypted Resolver share an IP 283 address, clients MAY choose to opportunistically use the Designated 284 Resolver even without this certificate check (Section 4.3). 286 If resolving the name of a Designated Resolver from an SVCB record 287 yields an IP address that was not presented in the Additional Answers 288 section or ipv4hint or ipv6hint fields of the original SVCB query, 289 the connection made to that IP address MUST pass the same TLS 290 certificate checks before being allowed to replace a previously known 291 and validated IP address for the same Designated Resolver name. 293 4.3. Opportunistic Discovery 295 There are situations where authenticated discovery of encrypted DNS 296 configuration over unencrypted DNS is not possible. This includes 297 Unencrypted Resolvers on non-public IP addresses such as those 298 defined in [RFC1918] whose identity cannot be confirmed using TLS 299 certificates. 301 Opportunistic Privacy is defined for DoT in Section 4.1 of [RFC7858] 302 as a mode in which clients do not validate the name of the resolver 303 presented in the certificate. A client MAY use information from the 304 SVCB record for "dns://resolver.arpa" with this "opportunistic" 305 approach (not validating the names presented in the 306 SubjectAlternativeName field of the certificate) as long as the IP 307 address of the Encrypted Resolver does not differ from the IP address 308 of the Unencrypted Resolver. This approach can be used for any 309 encrypted DNS protocol that uses TLS. 311 5. Discovery Using Resolver Names 313 A DNS client that already knows the name of an Encrypted Resolver can 314 use DDR to discover details about all supported encrypted DNS 315 protocols. This situation can arise if a client has been configured 316 to use a given Encrypted Resolver, or if a network provisioning 317 protocol (such as DHCP or IPv6 Router Advertisements) provides a name 318 for an Encrypted Resolver alongside the resolver IP address. 320 For these cases, the client simply sends a DNS SVCB query using the 321 known name of the resolver. This query can be issued to the named 322 Encrypted Resolver itself or to any other resolver. Unlike the case 323 of bootstrapping from an Unencrypted Resolver (Section 4), these 324 records SHOULD be available in the public DNS. 326 For example, if the client already knows about a DoT server 327 resolver.example.com, it can issue an SVCB query for 328 _dns.resolver.example.com to discover if there are other encrypted 329 DNS protocols available. In the following example, the SVCB answers 330 indicate that resolver.example.com supports both DoH and DoT, and 331 that the DoH server indicates a higher priority than the DoT server. 333 _dns.resolver.example.com 7200 IN SVCB 1 . ( 334 alpn=h2 dohpath=/dns-query{?dns} ) 335 _dns.resolver.example.com 7200 IN SVCB 2 . ( 336 alpn=dot ) 338 Often, the various supported encrypted DNS protocols will be 339 accessible using the same hostname. In the example above, both DoH 340 and DoT use the name resolver.example.com for their TLS certificates. 341 If a deployment uses a different hostname for one protocol, but still 342 wants clients to treat both DNS servers as designated, the TLS 343 certificates MUST include both names in the SubjectAlternativeName 344 fields. Note that this name verification is not related to the DNS 345 resolver that provided the SVCB answer. 347 For example, being able to discover a Designated Resolver for a known 348 Encrypted Resolver is useful when a client has a DoT configuration 349 for foo.resolver.example.com but is on a network that blocks DoT 350 traffic. The client can still send a query to any other accessible 351 resolver (either the local network resolver or an accessible DoH 352 server) to discover if there is a designated DoH server for 353 foo.resolver.example.com. 355 6. Deployment Considerations 357 Resolver deployments that support DDR are advised to consider the 358 following points. 360 6.1. Caching Forwarders 362 A DNS forwarder SHOULD NOT forward queries for "resolver.arpa" 363 upstream. This prevents a client from receiving an SVCB record that 364 will fail to authenticate because the forwarder's IP address is not 365 in the upstream resolver's Designated Resolver's TLS certificate SAN 366 field. A DNS forwarder which already acts as a completely blind 367 forwarder MAY choose to forward these queries when the operator 368 expects that this does not apply, either because the operator knows 369 the upstream resolver does have the forwarder's IP address in its TLS 370 certificate's SAN field or that the operator expects clients of the 371 unencrypted resolver to use the SVCB information opportunistically. 373 Operators who choose to forward queries for "resolver.arpa" upstream 374 should note that client behavior is never guaranteed and use of DDR 375 by a resolver does not communicate a requirement for clients to use 376 the SVCB record when it cannot be authenticated. 378 6.2. Certificate Management 380 Resolver owners that support authenticated discovery will need to 381 list valid referring IP addresses in their TLS certificates. This 382 may pose challenges for resolvers with a large number of referring IP 383 addresses. 385 7. Security Considerations 387 Since clients can receive DNS SVCB answers over unencrypted DNS, on- 388 path attackers can prevent successful discovery by dropping SVCB 389 packets. Clients should be aware that it might not be possible to 390 distinguish between resolvers that do not have any Designated 391 Resolver and such an active attack. To limit the impact of discovery 392 queries being dropped either maliciously or unintentionally, clients 393 can re-send their SVCB queries periodically. 395 While the IP address of the Unencrypted Resolver is often provisioned 396 over insecure mechanisms, it can also be provisioned securely, such 397 as via manual configuration, a VPN, or on a network with protections 398 like RA guard [RFC6105]. An attacker might try to direct Encrypted 399 DNS traffic to itself by causing the client to think that a 400 discovered Designated Resolver uses a different IP address from the 401 Unencrypted Resolver. Such a Designated Resolver might have a valid 402 certificate, but be operated by an attacker that is trying to observe 403 or modify user queries without the knowledge of the client or 404 network. 406 If the IP address of a Designated Resolver differs from that of an 407 Unencrypted Resolver, clients applying Authenicated Discovery 408 (Section 4.2) MUST validate that the IP address of the Unencrypted 409 Resolver is covered by the SubjectAlternativeName of the Designated 410 Resolver's TLS certificate. 412 Clients using Opportunistic Discovery (Section 4.3) MUST be limited 413 to cases where the Unencrypted Resolver and Designated Resolver have 414 the same IP address. 416 The constraints on validation of Designated Resolvers specified here 417 apply specifically to the automatic discovery mechanisms defined in 418 this document, which are referred to as Authenticated Discovery and 419 Opportunistic Discovery. Clients MAY use some other mechanism to 420 validate and use Designated Resolvers discovered using the DNS SVCB 421 record. However, use of such an alternate mechanism needs to take 422 into account the attack scenarios detailed here. 424 8. IANA Considerations 426 8.1. Special Use Domain Name "resolver.arpa" 428 This document calls for the creation of the "resolver.arpa" SUDN. 429 This will allow resolvers to respond to queries directed at 430 themselves rather than a specific domain name. While this document 431 uses "resolver.arpa" to return SVCB records indicating designated 432 encrypted capability, the name is generic enough to allow future 433 reuse for other purposes where the resolver wishes to provide 434 information about itself to the client. 436 The "resolver.arpa" SUDN is similar to "ipv4only.arpa" in that the 437 querying client is not interested in an answer from the authoritative 438 "arpa" name servers. The intent of the SUDN is to allow clients to 439 communicate with the Unencrypted Resolver much like "ipv4only.arpa" 440 allows for client-to-middlebox communication. For more context, see 441 the rationale behind "ipv4only.arpa" in [RFC8880]. 443 9. References 445 9.1. Normative References 447 [I-D.ietf-add-svcb-dns] 448 Schwartz, B., "Service Binding Mapping for DNS Servers", 449 Work in Progress, Internet-Draft, draft-ietf-add-svcb-dns- 450 00, 1 October 2021, 451 . 454 [I-D.ietf-dnsop-svcb-https] 455 Schwartz, B., Bishop, M., and E. Nygren, "Service binding 456 and parameter specification via the DNS (DNS SVCB and 457 HTTPS RRs)", Work in Progress, Internet-Draft, draft-ietf- 458 dnsop-svcb-https-07, 5 August 2021, 459 . 462 [RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G. 463 J., and E. Lear, "Address Allocation for Private 464 Internets", BCP 5, RFC 1918, DOI 10.17487/RFC1918, 465 February 1996, . 467 [RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., 468 and P. Hoffman, "Specification for DNS over Transport 469 Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May 470 2016, . 472 [RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS 473 (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018, 474 . 476 9.2. Informative References 478 [I-D.ietf-tls-esni] 479 Rescorla, E., Oku, K., Sullivan, N., and C. A. Wood, "TLS 480 Encrypted Client Hello", Work in Progress, Internet-Draft, 481 draft-ietf-tls-esni-13, 12 August 2021, 482 . 485 [I-D.schinazi-httpbis-doh-preference-hints] 486 Schinazi, D., Sullivan, N., and J. Kipp, "DoH Preference 487 Hints for HTTP", Work in Progress, Internet-Draft, draft- 488 schinazi-httpbis-doh-preference-hints-02, 13 July 2020, 489 . 492 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 493 Requirement Levels", BCP 14, RFC 2119, 494 DOI 10.17487/RFC2119, March 1997, 495 . 497 [RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor 498 Extensions", RFC 2132, DOI 10.17487/RFC2132, March 1997, 499 . 501 [RFC5507] IAB, Faltstrom, P., Ed., Austein, R., Ed., and P. Koch, 502 Ed., "Design Choices When Expanding the DNS", RFC 5507, 503 DOI 10.17487/RFC5507, April 2009, 504 . 506 [RFC6105] Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J. 507 Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105, 508 DOI 10.17487/RFC6105, February 2011, 509 . 511 [RFC8106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 512 "IPv6 Router Advertisement Options for DNS Configuration", 513 RFC 8106, DOI 10.17487/RFC8106, March 2017, 514 . 516 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 517 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 518 May 2017, . 520 [RFC8880] Cheshire, S. and D. Schinazi, "Special Use Domain Name 521 'ipv4only.arpa'", RFC 8880, DOI 10.17487/RFC8880, August 522 2020, . 524 Appendix A. Rationale for using SVCB records 526 This mechanism uses SVCB/HTTPS resource records 527 [I-D.ietf-dnsop-svcb-https] to communicate that a given domain 528 designates a particular Designated Resolver for clients to use in 529 place of an Unencrypted Resolver (using a SUDN) or another Encrypted 530 Resolver (using its domain name). 532 There are various other proposals for how to provide similar 533 functionality. There are several reasons that this mechanism has 534 chosen SVCB records: 536 * Discovering encrypted resolver using DNS records keeps client 537 logic for DNS self-contained and allows a DNS resolver operator to 538 define which resolver names and IP addresses are related to one 539 another. 541 * Using DNS records also does not rely on bootstrapping with higher- 542 level application operations (such as 543 [I-D.schinazi-httpbis-doh-preference-hints]). 545 * SVCB records are extensible and allow definition of parameter 546 keys. This makes them a superior mechanism for extensibility as 547 compared to approaches such as overloading TXT records. The same 548 keys can be used for discovering Designated Resolvers of different 549 transport types as well as those advertised by Unencrypted 550 Resolvers or another Encrypted Resolver. 552 * Clients and servers that are interested in privacy of names will 553 already need to support SVCB records in order to use Encrypted TLS 554 Client Hello [I-D.ietf-tls-esni]. Without encrypting names in 555 TLS, the value of encrypting DNS is reduced, so pairing the 556 solutions provides the largest benefit. 558 * Clients that support SVCB will generally send out three queries 559 when accessing web content on a dual-stack network: A, AAAA, and 560 HTTPS queries. Discovering a Designated Resolver as part of one 561 of these queries, without having to add yet another query, 562 minimizes the total number of queries clients send. While 563 [RFC5507] recommends adding new RRTypes for new functionality, 564 SVCB provides an extension mechanism that simplifies client 565 behavior. 567 Authors' Addresses 569 Tommy Pauly 570 Apple Inc. 571 One Apple Park Way 572 Cupertino, California 95014, 573 United States of America 575 Email: tpauly@apple.com 577 Eric Kinnear 578 Apple Inc. 579 One Apple Park Way 580 Cupertino, California 95014, 581 United States of America 583 Email: ekinnear@apple.com 585 Christopher A. Wood 586 Cloudflare 587 101 Townsend St 588 San Francisco, 589 United States of America 591 Email: caw@heapingbits.net 593 Patrick McManus 594 Fastly 596 Email: mcmanus@ducksong.com 598 Tommy Jensen 599 Microsoft 601 Email: tojens@microsoft.com