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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 DNSOP Working Group B. Schwartz 3 Internet-Draft Google 4 Intended status: Standards Track M. Bishop 5 Expires: December 14, 2020 E. Nygren 6 Akamai Technologies 7 June 12, 2020 9 Service binding and parameter specification via the DNS (DNS SVCB and 10 HTTPS RRs) 11 draft-ietf-dnsop-svcb-https-00 13 Abstract 15 This document specifies the "SVCB" and "HTTPS" DNS resource record 16 (RR) types to facilitate the lookup of information needed to make 17 connections for origin resources, such as for HTTPS URLs. SVCB 18 records allow an origin to be served from multiple network locations, 19 each with associated parameters (such as transport protocol 20 configuration and keys for encrypting the TLS ClientHello). They 21 also enable aliasing of apex domains, which is not possible with 22 CNAME. The HTTPS RR is a variation of SVCB for HTTPS and HTTP 23 origins. By providing more information to the client before it 24 attempts to establish a connection, these records offer potential 25 benefits to both performance and privacy. 27 TO BE REMOVED: This proposal is inspired by and based on recent DNS 28 usage proposals such as ALTSVC, ANAME, and ESNIKEYS (as well as long 29 standing desires to have SRV or a functional equivalent implemented 30 for HTTP). These proposals each provide an important function but 31 are potentially incompatible with each other, such as when an origin 32 is load-balanced across multiple hosting providers (multi-CDN). 33 Furthermore, these each add potential cases for adding additional 34 record lookups in addition to AAAA/A lookups. This design attempts 35 to provide a unified framework that encompasses the key functionality 36 of these proposals, as well as providing some extensibility for 37 addressing similar future challenges. 39 TO BE REMOVED: This document is being collaborated on in Github at: 40 https://github.com/MikeBishop/dns-alt-svc [1]. The most recent 41 working version of the document, open issues, etc. should all be 42 available there. The authors (gratefully) accept pull requests. 44 Status of This Memo 46 This Internet-Draft is submitted in full conformance with the 47 provisions of BCP 78 and BCP 79. 49 Internet-Drafts are working documents of the Internet Engineering 50 Task Force (IETF). Note that other groups may also distribute 51 working documents as Internet-Drafts. The list of current Internet- 52 Drafts is at https://datatracker.ietf.org/drafts/current/. 54 Internet-Drafts are draft documents valid for a maximum of six months 55 and may be updated, replaced, or obsoleted by other documents at any 56 time. It is inappropriate to use Internet-Drafts as reference 57 material or to cite them other than as "work in progress." 59 This Internet-Draft will expire on December 14, 2020. 61 Copyright Notice 63 Copyright (c) 2020 IETF Trust and the persons identified as the 64 document authors. All rights reserved. 66 This document is subject to BCP 78 and the IETF Trust's Legal 67 Provisions Relating to IETF Documents 68 (https://trustee.ietf.org/license-info) in effect on the date of 69 publication of this document. Please review these documents 70 carefully, as they describe your rights and restrictions with respect 71 to this document. Code Components extracted from this document must 72 include Simplified BSD License text as described in Section 4.e of 73 the Trust Legal Provisions and are provided without warranty as 74 described in the Simplified BSD License. 76 Table of Contents 78 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 79 1.1. Goals of the SVCB RR . . . . . . . . . . . . . . . . . . 5 80 1.2. Overview of the SVCB RR . . . . . . . . . . . . . . . . . 6 81 1.3. Parameter for Encrypted ClientHello . . . . . . . . . . . 7 82 1.4. Terminology . . . . . . . . . . . . . . . . . . . . . . . 7 83 2. The SVCB record type . . . . . . . . . . . . . . . . . . . . 7 84 2.1. Presentation format . . . . . . . . . . . . . . . . . . . 8 85 2.1.1. Presentation format for SvcFieldValue key=value pairs 8 86 2.2. SVCB RDATA Wire Format . . . . . . . . . . . . . . . . . 9 87 2.3. SVCB owner names . . . . . . . . . . . . . . . . . . . . 10 88 2.4. SvcRecordType . . . . . . . . . . . . . . . . . . . . . . 11 89 2.5. SVCB records: AliasForm . . . . . . . . . . . . . . . . . 11 90 2.6. SVCB records: ServiceForm . . . . . . . . . . . . . . . . 12 91 2.6.1. Special handling of "." for SvcDomainName in 92 ServiceForm . . . . . . . . . . . . . . . . . . . . . 12 93 2.6.2. SvcFieldPriority . . . . . . . . . . . . . . . . . . 13 94 3. Client behavior . . . . . . . . . . . . . . . . . . . . . . . 13 95 3.1. Handling resolution failures . . . . . . . . . . . . . . 14 96 3.2. Clients using a Proxy . . . . . . . . . . . . . . . . . . 14 98 4. DNS Server Behavior . . . . . . . . . . . . . . . . . . . . . 15 99 4.1. Authoritative servers . . . . . . . . . . . . . . . . . . 15 100 4.2. Recursive resolvers . . . . . . . . . . . . . . . . . . . 15 101 4.3. General requirements . . . . . . . . . . . . . . . . . . 16 102 5. Performance optimizations . . . . . . . . . . . . . . . . . . 16 103 5.1. Optimistic pre-connection and connection reuse . . . . . 16 104 5.2. Generating and using incomplete responses . . . . . . . . 17 105 5.3. Structuring zones for performance . . . . . . . . . . . . 17 106 6. Initial SvcParamKeys . . . . . . . . . . . . . . . . . . . . 18 107 6.1. "alpn" and "no-default-alpn" . . . . . . . . . . . . . . 18 108 6.2. "port" . . . . . . . . . . . . . . . . . . . . . . . . . 19 109 6.3. "echconfig" . . . . . . . . . . . . . . . . . . . . . . . 20 110 6.4. "ipv4hint" and "ipv6hint" . . . . . . . . . . . . . . . . 20 111 7. Using SVCB with HTTPS and HTTP . . . . . . . . . . . . . . . 21 112 7.1. Owner names for HTTPS RRs . . . . . . . . . . . . . . . . 21 113 7.2. Relationship to Alt-Svc . . . . . . . . . . . . . . . . . 22 114 7.2.1. ALPN usage . . . . . . . . . . . . . . . . . . . . . 22 115 7.2.2. Untrusted channel . . . . . . . . . . . . . . . . . . 22 116 7.2.3. TTL and granularity . . . . . . . . . . . . . . . . . 23 117 7.3. Interaction with Alt-Svc . . . . . . . . . . . . . . . . 23 118 7.4. Requiring Server Name Indication . . . . . . . . . . . . 23 119 7.5. HTTP Strict Transport Security . . . . . . . . . . . . . 24 120 7.6. HTTP-based protocols . . . . . . . . . . . . . . . . . . 24 121 8. SVCB/HTTPS RR parameter for ECH configuration . . . . . . . . 25 122 8.1. Client behavior . . . . . . . . . . . . . . . . . . . . . 25 123 8.2. Deployment considerations . . . . . . . . . . . . . . . . 25 124 9. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 26 125 9.1. Protocol enhancements . . . . . . . . . . . . . . . . . . 26 126 9.2. Apex aliasing . . . . . . . . . . . . . . . . . . . . . . 26 127 9.3. Parameter binding . . . . . . . . . . . . . . . . . . . . 27 128 9.4. Non-HTTPS uses . . . . . . . . . . . . . . . . . . . . . 27 129 10. Interaction with other standards . . . . . . . . . . . . . . 27 130 11. Security Considerations . . . . . . . . . . . . . . . . . . . 28 131 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28 132 12.1. New registry for Service Parameters . . . . . . . . . . 28 133 12.1.1. Procedure . . . . . . . . . . . . . . . . . . . . . 28 134 12.1.2. Initial contents . . . . . . . . . . . . . . . . . . 29 135 12.2. Registry updates . . . . . . . . . . . . . . . . . . . . 30 136 13. Acknowledgments and Related Proposals . . . . . . . . . . . . 31 137 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 31 138 14.1. Normative References . . . . . . . . . . . . . . . . . . 31 139 14.2. Informative References . . . . . . . . . . . . . . . . . 34 140 14.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 35 141 Appendix A. Comparison with alternatives . . . . . . . . . . . . 35 142 A.1. Differences from the SRV RR type . . . . . . . . . . . . 35 143 A.2. Differences from the proposed HTTP record . . . . . . . . 35 144 A.3. Differences from the proposed ANAME record . . . . . . . 35 145 A.4. Comparison with separate RR types for AliasForm and 146 ServiceForm . . . . . . . . . . . . . . . . . . . . . . . 36 147 Appendix B. Change history . . . . . . . . . . . . . . . . . . . 36 148 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 38 150 1. Introduction 152 The SVCB and HTTPS RRs provide clients with complete instructions for 153 access to an origin. This information enables improved performance 154 and privacy by avoiding transient connections to a sub-optimal 155 default server, negotiating a preferred protocol, and providing 156 relevant public keys. 158 For example, when clients need to make a connection to fetch 159 resources associated with an HTTPS URI, they currently resolve only A 160 and/or AAAA records for the origin hostname. This is adequate for 161 services that use basic HTTPS (fixed port, no QUIC, no [ECH]). Going 162 beyond basic HTTPS confers privacy, performance, and operational 163 advantages, but it requires the client to learn additional 164 information, and it is highly desirable to minimize the number of 165 round-trips and lookups required to learn this additional 166 information. 168 The SVCB and HTTPS RRs also help when the operator of an origin 169 wishes to delegate operational control to one or more other domains, 170 e.g. delegating the origin resource "https://example.com" to a 171 service operator endpoint at "svc.example.net". While this case can 172 sometimes be handled by a CNAME, that does not cover all use-cases. 173 CNAME is also inadequate when the service operator needs to provide a 174 bound collection of consistent configuration parameters through the 175 DNS (such as network location, protocol, and keying information). 177 This document first describes the SVCB RR as a general-purpose 178 resource record that can be applied directly and efficiently to a 179 wide range of services (Section 2). The HTTPS RR is then defined as 180 a special case of SVCB that improves efficiency and convenience for 181 use with HTTPS (Section 7) by avoiding the need for an [Attrleaf] 182 label (Section 7.1). Other protocols with similar needs may follow 183 the pattern of HTTPS and assign their own SVCB-compatible RR types. 185 All behaviors described as applying to the SVCB RR also apply to the 186 HTTPS RR unless explicitly stated otherwise. Section 7 describes 187 additional behaviors specific to the HTTPS RR. Apart from Section 7 188 and introductory examples, much of this document refers only to the 189 SVCB RR, but those references should be taken to apply to SVCB, 190 HTTPS, and any future SVCB-compatible RR types. 192 The SVCB RR has two forms: 1) the "Alias Form" simply delegates 193 operational control for a resource; 2) the "Service Form" binds 194 together configuration information for a service endpoint. The 195 Service Form provides additional key=value parameters within each 196 RDATA set. 198 TO BE REMOVED: If we use this for providing configuration for DNS 199 authorities, it is likely we'd specify a distinct "NS2" RR type that 200 is an instantiation of SVCB for authoritative nameserver delegation 201 and parameter specification, similar to HTTPS. See 202 [I-D.draft-tapril-ns2-00] as one example. 204 1.1. Goals of the SVCB RR 206 The goal of the SVCB RR is to allow clients to resolve a single 207 additional DNS RR in a way that: 209 o Provides service endpoints authoritative for the service, along 210 with parameters associated with each of these endpoints. 212 o Does not assume that all alternative service endpoints have the 213 same parameters or capabilities, or are even operated by the same 214 entity. This is important as DNS does not provide any way to tie 215 together multiple RRs for the same name. For example, if 216 www.example.com is a CNAME alias that switches between one of 217 three CDNs or hosting environments, successive queries for that 218 name may return records that correspond to different environments. 220 o Enables CNAME-like functionality at a zone apex (such as 221 "example.com") for participating protocols, and generally enables 222 delegation of operational authority for an origin within the DNS 223 to an alternate name. 225 Additional goals specific to HTTPS RRs and the HTTPS use-case 226 include: 228 o Connect directly to [HTTP3] (QUIC transport) alternative service 229 endpoints 231 o Obtain the [ECH] keys associated with an alternative service 232 endpoint 234 o Support non-default TCP and UDP ports 236 o Address a set of long-standing issues due to HTTP(S) clients not 237 implementing support for SRV records, as well as due to a 238 limitation that a DNS name can not have both CNAME and NS RRs (as 239 is the case for zone apex names) 241 o Provide an HSTS-like indication signaling for the duration of the 242 DNS RR TTL that the HTTPS scheme should be used instead of HTTP 243 (see Section 7.5). 245 1.2. Overview of the SVCB RR 247 This subsection briefly describes the SVCB RR in a non-normative 248 manner. (As mentioned above, this all applies equally to the HTTPS 249 RR which shares the same encoding, format, and high-level semantics.) 251 The SVCB RR has two forms: AliasForm, which aliases a name to another 252 name, and ServiceForm, which provides connection information bound to 253 a service endpoint domain. Placing both forms in a single RR type 254 allows clients to fetch the relevant information with a single query. 256 The SVCB RR has two mandatory fields and one optional. The fields 257 are: 259 1. SvcFieldPriority: The priority of this record (relative to 260 others, with lower values preferred). A value of 0 indicates 261 AliasForm. (Described in Section 2.6.2.) 263 2. SvcDomainName: The domain name of either the alias target (for 264 AliasForm) or the alternative service endpoint (for ServiceForm). 266 3. SvcFieldValue (optional): A list of key=value pairs describing 267 the alternative service endpoint for the domain name specified in 268 SvcDomainName (only used in ServiceForm and otherwise ignored). 269 Described in Section 2.1.1. 271 Cooperating DNS recursive resolvers will perform subsequent record 272 resolution (for SVCB, A, and AAAA records) and return them in the 273 Additional Section of the response. Clients must either use 274 responses included in the additional section returned by the 275 recursive resolver or perform necessary SVCB, A, and AAAA record 276 resolutions. DNS authoritative servers may attach in-bailiwick SVCB, 277 A, AAAA, and CNAME records in the Additional Section to responses for 278 a SVCB query. 280 When in the ServiceForm, the SvcFieldValue of the SVCB RR provides an 281 extensible data model for describing network endpoints that are 282 authoritative for the origin, along with parameters associated with 283 each of these endpoints. 285 For the HTTPS use-case, the HTTPS RR enables many of the benefits of 286 [AltSvc] without waiting for a full HTTP connection initiation 287 (multiple roundtrips) before learning of the preferred alternative, 288 and without necessarily revealing the user's intended destination to 289 all entities along the network path. 291 1.3. Parameter for Encrypted ClientHello 293 This document also defines a parameter for Encrypted ClientHello 294 [ECH] keys. See Section 8. 296 1.4. Terminology 298 For consistency with [AltSvc], we adopt the following definitions: 300 o An "origin" is an information source as in [RFC6454]. For 301 services other than HTTPS, the exact definition will need to be 302 provided by the document mapping that service onto the SVCB RR. 304 o The "origin server" is the server that the client would reach when 305 accessing the origin in the absence of the SVCB record or an HTTPS 306 Alt-Svc. 308 o An "alternative service" is a different server that can serve the 309 origin over a specified protocol. 311 For example within HTTPS, the origin consists of a scheme (typically 312 "https"), a hostname, and a port (typically "443"). 314 Additional DNS terminology intends to be consistent with [DNSTerm]. 316 SVCB is a contraction of "service binding". The SVCB RR, HTTPS RR, 317 and future RR types that share SVCB's format and registry are 318 collectively known as SVCB-compatible RR types. 320 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 321 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 322 "OPTIONAL" in this document are to be interpreted as described in BCP 323 14 [RFC2119] [RFC8174] when, and only when, they appear in all 324 capitals, as shown here. 326 2. The SVCB record type 328 The SVCB DNS resource record (RR) type (RR type ???) is used to 329 locate endpoints that can service an origin. There is special 330 handling for the case of "https" origins. 332 The algorithm for resolving SVCB records and associated address 333 records is specified in Section 3. 335 2.1. Presentation format 337 The presentation format of the record is: 339 Name TTL IN SVCB SvcFieldPriority SvcDomainName SvcFieldValue 341 The SVCB record is defined specifically within the Internet ("IN") 342 Class ([RFC1035]). SvcFieldPriority is a number in the range 343 0-65535, SvcDomainName is a domain name (absolute or relative), and 344 SvcFieldValue is a set of key=value pairs present for the 345 ServiceForm. Each key SHALL appear at most once in an SvcFieldValue. 346 The SvcFieldValue is empty for the AliasForm. 348 2.1.1. Presentation format for SvcFieldValue key=value pairs 350 In ServiceForm, the SvcFieldValue consists of zero or more elements 351 separated by whitespace. Each element represents a key=value pair. 353 Keys are IANA-registered SvcParamKeys (Section 12.1) with both a 354 case-insensitive string representation and a numeric representation 355 in the range 0-65535. Registered key names should only contain 356 characters from the ranges "a"-"z", "0"-"9", and "-". In ABNF 357 [RFC5234], 359 ALPHA-LC = %x61-7A ; a-z 360 key = 1*(ALPHA-LC / DIGIT / "-") 361 display-key = 1*(ALPHA / DIGIT / "-") 363 Values are in a format specific to the SvcParamKey. Their definition 364 should specify both their presentation format and wire encoding 365 (e.g., domain names, binary data, or numeric values). The initial 366 keys and formats are defined in Section 6. 368 The presentation format for SvcFieldValue is a whitespace-separated 369 list of key=value pairs. When the value is omitted, or both the 370 value and the "=" are omitted, the presentation value is the empty 371 string. 373 ; basic-visible is VCHAR minus DQUOTE, ";", "(", ")", and "\". 374 basic-visible = %x21 / %x23-27 / %2A-3A / %x3C-5B / %x5D-7E 375 escaped-char = "\" (VCHAR / WSP) 376 contiguous = 1*(basic-visible / escaped-char) 377 quoted-string = DQUOTE *(contiguous / WSP) DQUOTE 378 value = quoted-string / contiguous 379 pair = display-key "=" value 380 element = display-key / pair 381 The value format is intended to match the definition of in [RFC1035] Section 5.1. (Unlike , the 383 length of a value is not limited to 255 characters.) 385 Unrecognized keys are represented in presentation format as 386 "keyNNNNN" where NNNNN is the numeric value of the key type without 387 leading zeros. In presentation format, values corresponding to 388 unrecognized keys SHALL be represented in wire format, using decimal 389 escape codes (e.g. \255) when necessary. 391 When decoding values of unrecognized keys in the presentation format: 393 o a character other than "\" represents its ASCII value in wire 394 format. 396 o the character "\" followed by three decimal digits, up to 255, 397 represents an octet in the wire format. 399 o the character "\" followed by any allowed character, except a 400 decimal digit, represents the subsequent character's ASCII value. 402 Elements in presentation format MAY appear in any order, but keys 403 MUST NOT be repeated. 405 2.2. SVCB RDATA Wire Format 407 The RDATA for the SVCB RR consists of: 409 o a 2 octet field for SvcFieldPriority as an integer in network byte 410 order. 412 o the uncompressed, fully-qualified SvcDomainName, represented as a 413 sequence of length-prefixed labels as in Section 3.1 of [RFC1035]. 415 o the SvcFieldValue byte string, consuming the remainder of the 416 record (so smaller than 65535 octets and constrained by the RDATA 417 and DNS message sizes). 419 AliasForm is defined by SvcFieldPriority being 0. 421 When SvcFieldValue is non-empty (ServiceForm), it contains a series 422 of SvcParamKey=SvcParamValue pairs, represented as: 424 o a 2 octet field containing the SvcParamKey as an integer in 425 network byte order. (See Section 12.1.2 for the defined values.) 427 o a 2 octet field containing the length of the SvcParamValue as an 428 integer between 0 and 65535 in network byte order (but constrained 429 by the RDATA and DNS message sizes). 431 o an octet string of this length whose contents are in a format 432 determined by the SvcParamKey. 434 SvcParamKeys SHALL appear in increasing numeric order. 436 Clients MUST consider an RR malformed if 438 o the parser reaches the end of the RDATA while parsing an 439 SvcFieldValue. 441 o SvcParamKeys are not in strictly increasing numeric order. 443 o the SvcParamValue for an SvcParamKey does not have the expected 444 format. 446 Note that the second condition implies that there are no duplicate 447 SvcParamKeys. 449 If any RRs are malformed, the client MUST reject the entire RRSet and 450 fall back to non-SVCB connection establishment. 452 TODO: decide if we want special handling for any SvcParamKey ranges? 453 For example: range for greasing; experimental range; range-of- 454 mandatory-to-use-the-RR vs range of ignore-just-param-if-unknown. 456 2.3. SVCB owner names 458 When querying the SVCB RR, an origin is translated into a QNAME by 459 prepending the hostname with a label indicating the scheme, prefixed 460 with an underscore, resulting in a domain name like 461 "_examplescheme.api.example.com.". 463 Protocol mapping documents MAY specify additional underscore-prefixed 464 labels to be prepended. For schemes that specify a port 465 (Section 3.2.3 of [URI]), one reasonable possibility is to prepend 466 the indicated port number (or the default if no port number is 467 specified). We term this behavior "Port Prefix Naming", and use it 468 in the examples throughout this document. 470 See Section 7.1 for the HTTPS RR behavior. 472 When a prior CNAME or SVCB record has aliased to a SVCB record, each 473 RR shall be returned under its own owner name. 475 Note that none of these forms alter the origin or authority for 476 validation purposes. For example, clients MUST continue to validate 477 TLS certificate hostnames based on the origin host. 479 As an example, the owner of example.com could publish this record 481 _8443._foo.api.example.com. 7200 IN SVCB 0 svc4.example.net. 483 to indicate that "foo://api.example.com:8443" is aliased to 484 "svc4.example.net". The owner of example.net, in turn, could publish 485 this record 487 svc4.example.net. 7200 IN SVCB 3 svc4.example.net. ( 488 alpn="bar" port="8004" echconfig="..." ) 490 to indicate that these services are served on port number 8004, which 491 supports the protocol "bar" and its associated transport in addition 492 to the default transport protocol for "foo://". 494 (Parentheses are used to ignore a line break ([RFC1035] 495 Section 5.1).) 497 2.4. SvcRecordType 499 The SvcRecordType is indicated by the SvcFieldPriority, and defines 500 the form of the SVCB RR. When SvcFieldPriority is 0, the SVCB 501 SvcRecordType is defined to be in AliasForm. Otherwise, the SVCB 502 SvcRecordType is defined to be in ServiceForm. 504 Within a SVCB RRSet, all RRs should have the same SvcRecordType. If 505 an RRSet contains a record in AliasForm, the client MUST ignore any 506 records in the set with ServiceForm. 508 2.5. SVCB records: AliasForm 510 When SvcRecordType is AliasForm, the SVCB record is to be treated 511 similar to a CNAME alias pointing to SvcDomainName. SVCB RRSets 512 SHOULD only have a single resource record in this form. If multiple 513 are present, clients or recursive resolvers SHOULD pick one at 514 random. 516 The AliasForm's primary purpose is to allow aliasing at the zone 517 apex, where CNAME is not allowed. For example, if an operator of 518 https://example.com wanted to point HTTPS requests to a service 519 operating at svc.example.net, they would publish a record such as: 521 example.com. 3600 IN SVCB 0 svc.example.net. 523 In AliasForm, SvcDomainName MUST be the name of a domain that has 524 SVCB, AAAA, or A records. It MUST NOT be equal to the owner name, as 525 this would cause a loop. 527 Note that the SVCB record's owner name MAY be the canonical name of a 528 CNAME record, and the SvcDomainName MAY be the owner of a CNAME 529 record. Clients and recursive resolvers MUST follow CNAMEs as 530 normal. 532 To avoid unbounded alias chains, clients and recursive resolvers MUST 533 impose a limit on the total number of SVCB aliases they will follow 534 for each resolution request. This limit MUST NOT be zero, i.e. 535 implementations MUST be able to follow at least one AliasForm record. 536 The exact value of this limit is left to implementations. 538 For compatibility and performance, zone owners SHOULD NOT configure 539 their zones to require following multiple AliasForm records. 541 As legacy clients will not know to use this record, service operators 542 will likely need to retain fallback AAAA and A records alongside this 543 SVCB record, although in a common case the target of the SVCB record 544 might offer better performance, and therefore would be preferable for 545 clients implementing this specification to use. 547 Note that SVCB AliasForm RRs do not alias to RR types other than 548 address records (AAAA and A), CNAMEs, and ServiceForm SVCB records. 549 For example, an AliasForm SVCB record does not alias to an HTTPS RR, 550 nor vice-versa. 552 2.6. SVCB records: ServiceForm 554 When SvcRecordType is the ServiceForm, the combination of 555 SvcDomainName and SvcFieldValue parameters within each resource 556 record associates an alternative service location with its connection 557 parameters. 559 Each protocol scheme that uses SVCB MUST define a protocol mapping 560 that explains how SvcFieldValues are applied for connections of that 561 scheme. Unless specified otherwise by the protocol mapping, clients 562 MUST ignore SvcFieldValue parameters that they do not recognize. 564 2.6.1. Special handling of "." for SvcDomainName in ServiceForm 566 For ServiceForm SVCB RRs, if SvcDomainName has the value "." 567 (represented in the wire format as a zero-length label), then the 568 owner name of this record MUST be used as the effective 569 SvcDomainName. 571 For example, in the following example "svc2.example.net" is the 572 effective SvcDomainName: 574 www.example.com. 7200 IN HTTPS 0 svc.example.net. 575 svc.example.net. 7200 IN CNAME svc2.example.net. 576 svc2.example.net. 7200 IN HTTPS 1 . port=8002 echconfig="..." 577 svc2.example.net. 300 IN A 192.0.2.2 578 svc2.example.net. 300 IN AAAA 2001:db8::2 580 2.6.2. SvcFieldPriority 582 As RRs within an RRSet are explicitly unordered collections, the 583 SvcFieldPriority value serves to indicate priority. SVCB RRs with a 584 smaller SvcFieldPriority value SHOULD be given preference over RRs 585 with a larger SvcFieldPriority value. 587 When receiving an RRSet containing multiple SVCB records with the 588 same SvcFieldPriority value, clients SHOULD apply a random shuffle 589 within a priority level to the records before using them, to ensure 590 uniform load-balancing. 592 3. Client behavior 594 An SVCB-aware client resolves an origin HOST by attempting to 595 determine the preferred SvcFieldValue and IP addresses for its 596 service, using the following procedure: 598 1. Issue parallel AAAA/A and SVCB queries for the name HOST. The 599 answers for these may or may not include CNAME pointers before 600 reaching one or more of these records. 602 2. If a SVCB record of AliasForm SvcRecordType is returned for HOST, 603 clients MUST loop back to step 1 replacing HOST with 604 SvcDomainName, subject to chain length limits and loop detection 605 heuristics (see Section 3.1). 607 3. If one or more SVCB records of ServiceForm SvcRecordType are 608 returned for HOST, clients should select the highest-priority 609 option with acceptable parameters, and resolve AAAA and/or A 610 records for its SvcDomainName if they are not already available. 611 These are the preferred SvcFieldValue and IP addresses. If the 612 connection fails, the client MAY try to connect using values from 613 a lower-priority record. If none of the options succeed, the 614 client SHOULD connect to the origin server directly. 616 4. If a SVCB record for HOST does not exist, the received AAAA and/ 617 or A records are the preferred IP addresses and there is no 618 SvcFieldValue. 620 This procedure does not rely on any recursive or authoritative server 621 to comply with this specification or have any awareness of SVCB. 623 When selecting between AAAA and A records to use, clients may use an 624 approach such as [HappyEyeballsV2]. 626 Some important optimizations are discussed in Section 5 to avoid 627 additional latency in comparison to ordinary AAAA/A lookups. 629 3.1. Handling resolution failures 631 If a SVCB query results in a SERVFAIL error, transport error, or 632 timeout, and DNS exchanges between the client and the recursive 633 resolver are cryptographically protected (e.g. using TLS [RFC7858] or 634 HTTPS [RFC8484]), the client MUST NOT fall back to non-SVCB 635 connection establishment. This ensures that an active attacker 636 cannot mount a downgrade attack by denying the user access to the 637 SVCB information. 639 A SERVFAIL error can occur if the domain is DNSSEC-signed, the 640 recursive resolver is DNSSEC-validating, and the attacker is between 641 the recursive resolver and the authoritative DNS server. A transport 642 error or timeout can occur if an active attacker between the client 643 and the recursive resolver is selectively dropping SVCB queries or 644 responses, based on their size or other observable patterns. 646 Similarly, if the client enforces DNSSEC validation on A/AAAA 647 responses, it MUST NOT fall back to non-SVCB connection establishment 648 if the SVCB response fails to validate. 650 If the client is unable to complete SVCB resolution due to its chain 651 length limit, the client SHOULD fall back to non-SVCB connection, as 652 if the origin's SVCB record did not exist. 654 3.2. Clients using a Proxy 656 Clients using a domain-oriented transport proxy like HTTP CONNECT 657 ([RFC7231] Section 4.3.6) or SOCKS5 ([RFC1928]) SHOULD disable SVCB 658 support if performing SVCB queries would violate the client's privacy 659 intent. 661 If the client can safely perform SVCB queries (e.g. via the proxy or 662 an affiliated resolver), the client SHOULD follow the standard SVCB 663 resolution process, selecting the highest priority option that is 664 compatible with the client and the proxy. The client SHOULD provide 665 the final SvcDomainName and port to the proxy, which will perform any 666 required A and AAAA lookups. 668 Providing the proxy with the final SvcDomainName has several 669 benefits: 671 o It allows the client to use the SvcFieldValue, if present, which 672 is only usable with a specific SvcDomainName. The SvcFieldValue 673 may include information that enhances performance (e.g. alpn) and 674 privacy (e.g. echconfig). 676 o It allows the origin to delegate the apex domain. 678 o It allows the proxy to select between IPv4 and IPv6 addresses for 679 the server according to its configuration, and receive addresses 680 based on its network geolocation. 682 4. DNS Server Behavior 684 4.1. Authoritative servers 686 When replying to a SVCB query, authoritative DNS servers SHOULD 687 return A, AAAA, and SVCB records (as well as any relevant CNAME or 688 [DNAME] records) in the Additional Section for any in-bailiwick 689 SvcDomainNames. 691 4.2. Recursive resolvers 693 Recursive resolvers that are aware of SVCB SHOULD ensure that the 694 client can execute the procedure in Section 3 without issuing a 695 second round of queries, by incorporating all the necessary 696 information into a single response. For the initial SVCB record 697 query, this is just the normal response construction process (i.e. 698 unknown RR type resolution under [RFC3597]). For followup 699 resolutions performed during this procedure, we define incorporation 700 as adding all Answer and Additional RRs to the Additional section, 701 and all Authority RRs to the Authority section, without altering the 702 response code. 704 Upon receiving a SVCB query, recursive resolvers SHOULD start with 705 the standard resolution procedure, and then follow this procedure to 706 construct the full response to the stub resolver: 708 1. Incorporate the results of SVCB resolution. If the chain length 709 limit has been reached, terminate successfully (i.e. a NOERROR 710 response). 712 2. If any of the resolved SVCB records are in AliasForm, choose an 713 AliasForm record at random, and resolve SVCB, A, and AAAA records 714 for its SvcDomainName. 716 * If any SVCB records are resolved, go to step 1. 718 * Otherwise, incorporate the results of A and AAAA resolution, 719 and terminate. 721 3. All the resolved SVCB records are in ServiceForm. Resolve A and 722 AAAA queries for each SvcDomainName (or for the owner name if 723 SvcDomainName is "."), incorporate all the results, and 724 terminate. 726 In this procedure, "resolve" means the resolver's ordinary recursive 727 resolution procedure, as if processing a query for that RRSet. This 728 includes following any aliases that the resolver would ordinarily 729 follow (e.g. CNAME, [DNAME]). 731 4.3. General requirements 733 All DNS servers SHOULD treat the SvcFieldValue portion of the SVCB RR 734 as opaque and SHOULD NOT try to alter their behavior based on its 735 contents. 737 When responding to a query that includes the DNSSEC OK bit 738 ([RFC3225]), DNSSEC-capable recursive and authoritative DNS servers 739 MUST accompany each RRSet in the Additional section with the same 740 DNSSEC-related records that they would send when providing that RRSet 741 as an Answer (e.g. RRSIG, NSEC, NSEC3). 743 5. Performance optimizations 745 For optimal performance (i.e. minimum connection setup time), clients 746 SHOULD issue address (AAAA and/or A) and SVCB queries simultaneously, 747 and SHOULD implement a client-side DNS cache. Responses in the 748 Additional section of a SVCB response SHOULD be placed in cache 749 before performing any followup queries. With these optimizations in 750 place, and conforming DNS servers, using SVCB does not add network 751 latency to connection setup. 753 5.1. Optimistic pre-connection and connection reuse 755 If an address response arrives before the corresponding SVCB 756 response, the client MAY initiate a connection as if the SVCB query 757 returned NODATA, but MUST NOT transmit any information that could be 758 altered by the SVCB response until it arrives. For example, a TLS 759 ClientHello can be altered by the "echconfig" value of a SVCB 760 response (Section 6.3). Clients implementing this optimization 761 SHOULD wait for 50 milliseconds before starting optimistic pre- 762 connection, as per the guidance in [HappyEyeballsV2]. 764 An SVCB record is consistent with a connection if the client would 765 attempt an equivalent connection when making use of that record. If 766 a SVCB record is consistent with an active or in-progress connection 767 C, the client MAY prefer that record and use C as its connection. 768 For example, suppose the client receives this SVCB RRSet for a 769 protocol that uses TLS over TCP: 771 _1234._bar.example.com. 300 IN SVCB 1 svc1.example.net ( 772 echconfig="111..." ipv6hint=2001:db8::1 port=1234 ... ) 773 SVCB 2 svc2.example.net ( 774 echconfig="222..." ipv6hint=2001:db8::2 port=1234 ... ) 776 If the client has an in-progress TCP connection to 777 "[2001:db8::2]:1234", it MAY proceed with TLS on that connection 778 using "echconfig="222..."", even though the other record in the RRSet 779 has higher priority. 781 If none of the SVCB records are consistent with any active or in- 782 progress connection, clients must proceed as described in Step 3 of 783 the procedure in Section 3. 785 5.2. Generating and using incomplete responses 787 When following the procedure in Section 4.2, recursive resolvers MAY 788 terminate the procedure early and produce a reply that omits some of 789 the associated RRSets. This is REQUIRED when the chain length limit 790 is reached (Section 4.2 step 1), but might also be appropriate when 791 the maximum response size is reached, or when responding before fully 792 chasing dependencies would improve performance. When omitting 793 certain RRSets, recursive resolvers SHOULD prioritize information 794 from higher priority ServiceForm records over lower priority 795 ServiceForm records. 797 As discussed in Section 3, clients MUST be able to fetch additional 798 information that is required to use a SVCB record, if it is not 799 included in the initial response. As a performance optimization, if 800 some of the SVCB records in the response can be used without 801 requiring additional DNS queries, the client MAY prefer those 802 records, regardless of their priorities. 804 5.3. Structuring zones for performance 806 To avoid a delay for clients using a nonconforming recursive 807 resolver, domain owners SHOULD use a single SVCB record whose 808 SvcDomainName is "." if possible. This will ensure that the required 809 address records are already present in the client's DNS cache as part 810 of the responses to the address queries that were issued in parallel. 812 6. Initial SvcParamKeys 814 A few initial SvcParamKeys are defined here. These keys are useful 815 for HTTPS, and most are applicable to other protocols as well. 817 6.1. "alpn" and "no-default-alpn" 819 The "alpn" and "no-default-alpn" SvcParamKeys together indicate the 820 set of Application Layer Protocol Negotation (ALPN) protocol 821 identifiers [ALPN] and associated transport protocols supported by 822 this service endpoint. 824 As with [AltSvc], the ALPN protocol identifier is used to identify 825 the application protocol and associated suite of protocols supported 826 by the endpoint (the "protocol suite"). Clients filter the set of 827 ALPN identifiers to match the protocol suites they support, and this 828 informs the underlying transport protocol used (such as QUIC-over-UDP 829 or TLS-over-TCP). 831 ALPNs are identified by their registered "Identification Sequence" 832 (alpn-id), which is a sequence of 1-255 octets. 834 alpn-id = 1*255(OCTET) 836 The presentation value of "alpn" is a comma-separated list of one or 837 more "alpn-id"s. Any commas present in the protocol-id are escaped 838 by a backslash: 840 escaped-octet = %x00-2b / "\," / %x2d-5b / "\\" / %x5D-FF 841 escaped-id = 1*(escaped-octet) 842 alpn-value = escaped-id *("," escaped-id) 844 The wire format value for "alpn" consists of at least one ALPN 845 identifier ("alpn-id") prefixed by its length as a single octet, and 846 these length-value pairs are concatenated to form the SvcParamValue. 847 These pairs MUST exactly fill the SvcParamValue; otherwise, the 848 SvcParamValue is malformed. 850 For "no-default-alpn", the presentation and wire format values MUST 851 be empty. 853 Each scheme that uses this SvcParamKey defines a "default set" of 854 supported ALPNs, which SHOULD NOT be empty. To determine the set of 855 protocol suites supported by an endpoint (the "ALPN set"), the client 856 parses the set of ALPN identifiers in the "alpn" parameter, and then 857 adds the default set unless the "no-default-alpn" SvcParamKey is 858 present. The presence of a value in the alpn set indicates that this 859 service endpoint, described by SvcDomainName and the other parameters 860 (e.g. "port") offers service with the protocol suite associated with 861 the ALPN ID. 863 ALPN IDs that do not uniquely identify a protocol suite (e.g. an ID 864 that can be used with both TLS and DTLS) are not compatible with this 865 SvcParamKey and MUST NOT be included in the ALPN set. 867 Clients SHOULD NOT attempt connection to a service endpoint whose 868 ALPN set does not contain any compatible protocol suites. To ensure 869 consistency of behavior, clients MAY reject the entire SVCB RRSet and 870 fall back to basic connection establishment if all of the RRs 871 indicate "no-default-alpn", even if connection could have succeeded 872 using a non-default alpn. 874 For compatibility with clients that require default transports, zone 875 operators SHOULD ensure that at least one RR in each RRSet supports 876 the default transports. 878 Clients MUST include an "application_layer_protocol_negotiation" 879 extension in their ClientHello with a ProtocolNameList that includes 880 at least one ID from the ALPN set. Clients SHOULD also include any 881 other values that they support and could negotiate on that connection 882 with equivalent or better security properties. For example, if the 883 ALPN set only contains "http/1.1", the client could include 884 "http/1.1" and "h2" in the ProtocolNameList. 886 Once the client has formulated the ClientHello, protocol negotiation 887 on that connection proceeds as specified in [ALPN], without regard to 888 the SVCB ALPN set. To preserve the security guarantees of this 889 process, clients MUST consolidate all compatible ALPN IDs into a 890 single ProtocolNameList. 892 6.2. "port" 894 The "port" SvcParamKey defines the TCP or UDP port that should be 895 used to contact this alternative service. If this key is not 896 present, clients SHALL use the origin server's port number. 898 The presentation format of the SvcParamValue is a numeric value 899 between 0 and 65535 inclusive. Any other values (e.g. the empty 900 value) are syntax errors. 902 The wire format of the SvcParamValue is the corresponding 2 octet 903 numeric value in network byte order. 905 If a port-restricting firewall is in place between some client and 906 the service endpoint, changing the port number might cause that 907 client to lose access to the service, so operators should exercise 908 caution when using this SvcParamKey to specify a non-default port. 910 6.3. "echconfig" 912 The SvcParamKey to enable Encrypted ClientHello (ECH) is "echconfig". 913 Its value is defined in Section 8. It is applicable to most TLS- 914 based protocols. 916 When publishing a record containing an "echconfig" parameter, the 917 publisher MUST ensure that all IP addresses of SvcDomainName 918 correspond to servers that have access to the corresponding private 919 key or are authoritative for the public name. (See Section 7.2.2 of 920 [ECH] for more details about the public name.) This yields an 921 anonymity set of cardinality equal to the number of ECH-enabled 922 server domains supported by a given client-facing server. Thus, even 923 with an encrypted ClientHello, an attacker who can enumerate the set 924 of ECH-enabled domains supported by a client-facing server can guess 925 the correct SNI with probability at least 1/K, where K is the size of 926 this ECH-enabled server anonymity set. This probability may be 927 increased via traffic analysis or other mechanisms. 929 6.4. "ipv4hint" and "ipv6hint" 931 The "ipv4hint" and "ipv6hint" keys convey IP addresses that clients 932 MAY use to reach the service. If A and AAAA records for 933 SvcDomainName are locally available, the client SHOULD ignore these 934 hints. Otherwise, clients SHOULD perform A and/or AAAA queries for 935 SvcDomainName as in Section 3, and clients SHOULD use the IP address 936 in those responses for future connections. Clients MAY opt to 937 terminate any connections using the addresses in hints and instead 938 switch to the addresses in response to the SvcDomainName query. 939 Failure to use A and/or AAAA response addresses could negatively 940 impact load balancing or other geo-aware features and thereby degrade 941 client performance. 943 The wire format for each parameter is a sequence of IP addresses in 944 network byte order. Like an A or AAAA RRSet, the list of addresses 945 represents an unordered collection, and clients SHOULD pick addresses 946 to use in a random order. An empty list of addresses is invalid. 948 When selecting between IPv4 and IPv6 addresses to use, clients may 949 use an approach such as [HappyEyeballsV2]. When only "ipv4hint" is 950 present, IPv6-only clients may synthesize IPv6 addresses as specified 951 in [RFC7050] or ignore the "ipv4hint" key and wait for AAAA 952 resolution (Section 3). Recursive resolvers MUST NOT perform DNS64 953 ([RFC6147]) on parameters within a SVCB record. For best 954 performance, server operators SHOULD include an "ipv6hint" parameter 955 whenever they include an "ipv4hint" parameter. 957 The presentation format for each parameter is a comma-separated list 958 of IP addresses in standard textual format [RFC5952]. 960 These parameters are intended to minimize additional connection 961 latency when a recursive resolver is not compliant with the 962 requirements in Section 4, and SHOULD NOT be included if most clients 963 are using compliant recursive resolvers. When SvcDomainName is ".", 964 server operators SHOULD NOT include these hints, because they are 965 unlikely to convey any performance benefit. 967 7. Using SVCB with HTTPS and HTTP 969 Use of any protocol with SVCB requires a protocol-specific mapping 970 specification. This section specifies the mapping for HTTPS and 971 HTTP. 973 To enable special handling for the HTTPS and HTTP use-cases, the 974 HTTPS RR type is defined as a SVCB-compatible RR type, specific to 975 the https and http schemes. Clients MUST NOT perform SVCB queries or 976 accept SVCB responses for "https" or "http" schemes. 978 The HTTPS RR wire format and presentation format are identical to 979 SVCB, and both share the SvcParamKey registry. SVCB semantics apply 980 equally to HTTPS RRs unless specified otherwise. 982 All the SvcParamKeys defined in Section 6 are permitted for use in 983 HTTPS RRs. The default set of ALPN IDs is the single value 984 "http/1.1". 986 The presence of an HTTPS RR for an origin also indicates that all 987 HTTP resources are available over HTTPS, as discussed in Section 7.5. 988 This allows HTTPS RRs to apply to pre-existing "http" scheme URLs, 989 while ensuring that the client uses a secure and authenticated HTTPS 990 connection. 992 The HTTPS RR parallels the concepts introduced in the HTTP 993 Alternative Services proposed standard [AltSvc]. Clients and servers 994 that implement HTTPS RRs are NOT REQUIRED to implement Alt-Svc. 996 7.1. Owner names for HTTPS RRs 998 The HTTPS RR uses Port Prefix Naming (Section 2.3), with one 999 modification: if the scheme is "https" and the port is 443, then the 1000 client's original QNAME is equal to the origin hostname, without any 1001 prefix labels. 1003 By removing the [Attrleaf] labels used in SVCB, this construction 1004 enables offline DNSSEC signing of wildcard domains, which are 1005 commonly used with HTTPS. Reusing the origin hostname also allows 1006 the targets of existing CNAME chains (e.g. CDN hosts) to start 1007 returning HTTPS RR responses without requiring origin domains to 1008 configure and maintain an additional delegation. 1010 Following of HTTPS RR AliasForm and CNAME aliases is unchanged from 1011 SVCB. 1013 Clients always convert "http" URLs to "https" before performing an 1014 HTTPS RR query using the process described in Section 7.5, so domain 1015 owners MUST NOT publish HTTPS RRs with a prefix of "_http". 1017 Note that none of these forms alter the HTTPS origin or authority. 1018 For example, clients MUST continue to validate TLS certificate 1019 hostnames based on the origin host. 1021 7.2. Relationship to Alt-Svc 1023 Publishing a ServiceForm HTTPS RR in DNS is intended to be similar to 1024 transmitting an Alt-Svc field value over HTTPS, and receiving an 1025 HTTPS RR is intended to be similar to receiving that field value over 1026 HTTPS. However, there are some differences in the intended client 1027 and server behavior. 1029 7.2.1. ALPN usage 1031 Unlike Alt-Svc Field Values, HTTPS RRs can contain multiple ALPN IDs, 1032 and clients are encouraged to offer additional ALPNs that they 1033 support (subject to security constraints). 1035 TO BE REMOVED: The ALPN semantics in [AltSvc] are ambiguous, and 1036 problematic in some interpretations. We should update [AltSvc] to 1037 give it well-defined semantics that match HTTPS RRs. 1039 7.2.2. Untrusted channel 1041 SVCB does not require or provide any assurance of authenticity. 1042 (DNSSEC signing and verification, which would provide such assurance, 1043 are OPTIONAL.) The DNS resolution process is treated as an untrusted 1044 channel that learns only the QNAME, and is prevented from mounting 1045 any attack beyond denial of service. 1047 Alt-Svc parameters that cannot be safely received in this model MUST 1048 NOT have a corresponding defined SvcParamKey. For example, there is 1049 no SvcParamKey corresponding to the Alt-Svc "persist" parameter, 1050 because this parameter is not safe to accept over an untrusted 1051 channel. 1053 7.2.3. TTL and granularity 1055 There is no SvcParamKey corresponding to the Alt-Svc "ma" (max age) 1056 parameter. Instead, server operators encode the expiration time in 1057 the DNS TTL. 1059 The appropriate TTL value will typically be similar to the "ma" value 1060 used for Alt-Svc, but may vary depending on the desired efficiency 1061 and agility. Some DNS caches incorrectly extend the lifetime of DNS 1062 records beyond the stated TTL, so server operators cannot rely on 1063 HTTPS RRs expiring on time. Shortening the TTL to compensate for 1064 incorrect caching is NOT RECOMMENDED, as this practice impairs the 1065 performance of correctly functioning caches and does not guarantee 1066 faster expiration from incorrect caches. Instead, server operators 1067 SHOULD maintain compatibility with expired records until they observe 1068 that nearly all connections have migrated to the new configuration. 1070 Sending Alt-Svc over HTTP allows the server to tailor the Alt-Svc 1071 Field Value specifically to the client. When using an HTTPS RR, 1072 groups of clients will necessarily receive the same SvcFieldValue. 1073 Therefore, HTTPS RRs are not suitable for uses that require single- 1074 client granularity. 1076 7.3. Interaction with Alt-Svc 1078 Clients that do not implement support for Encrypted ClientHello MAY 1079 skip the HTTPS RR query if a usable Alt-Svc value is available in the 1080 local cache. If Alt-Svc connection fails, these clients SHOULD fall 1081 back to the HTTPS RR client connection procedure (Section 3). 1083 For clients that implement support for ECH, the interaction between 1084 HTTPS RRs and Alt-Svc is described in Section 8.1. 1086 This specification does not alter the DNS queries performed when 1087 connecting to an Alt-Svc hostname (typically A and/or AAAA only). 1089 7.4. Requiring Server Name Indication 1091 Clients MUST NOT use an HTTPS RR response unless the client supports 1092 TLS Server Name Indication (SNI) and indicate the origin name when 1093 negotiating TLS. This supports the conservation of IP addresses. 1095 Note that the TLS SNI (and also the HTTP "Host" or ":authority") will 1096 indicate the origin, not the SvcDomainName. 1098 7.5. HTTP Strict Transport Security 1100 By publishing an HTTPS RR, the server operator indicates that all 1101 useful HTTP resources on that origin are reachable over HTTPS, 1102 similar to HTTP Strict Transport Security [HSTS]. When an HTTPS RR 1103 is present for an origin, all "http" scheme requests for that origin 1104 SHOULD logically be redirected to "https". 1106 Prior to making an "http" scheme request, the client SHOULD perform a 1107 lookup to determine if any HTTPS RRs exist for that origin. To do 1108 so, the client SHOULD construct a corresponding "https" URL as 1109 follows: 1111 1. Replace the "http" scheme with "https". 1113 2. If the "http" URL explicitly specifies port 80, specify port 443. 1115 3. Do not alter any other aspect of the URL. 1117 This construction is equivalent to Section 8.3 of [HSTS], point 5. 1119 If an HTTPS RR query for this "https" URL returns any HTTPS RRs 1120 (AliasForm or ServiceForm), the client SHOULD act as if it has 1121 received an HTTP "307 Temporary Redirect" redirect to this "https" 1122 URL. Because HTTPS RRs are received over an often insecure channel 1123 (DNS), clients MUST NOT place any more trust in this signal than if 1124 they had received a 307 redirect over cleartext HTTP. 1126 When making an "https" scheme request to an origin with an HTTPS RR, 1127 either directly or via the above redirect, the client SHOULD 1128 terminate the connection if there are any errors with the underlying 1129 secure transport, such as errors in certificate validation. This 1130 aligns with Section 8.4 and Section 12.1 of [HSTS]. 1132 7.6. HTTP-based protocols 1134 We define an "HTTP-based protocol" as one that involves connecting to 1135 an "http:" or "https:" URL. When implementing an HTTP-based 1136 protocol, clients that use HTTPS RRs for HTTP SHOULD also use it for 1137 this URL. For example, clients that support HTTPS RRs and implement 1138 the altered [WebSocket] opening handshake from [FETCH] SHOULD use 1139 HTTPS RRs for the "requestURL". 1141 An HTTP-based protocol MAY define its own SVCB mapping. Such 1142 mappings MAY be defined to take precedence over HTTPS RRs. 1144 8. SVCB/HTTPS RR parameter for ECH configuration 1146 The SVCB "echconfig" parameter is defined for conveying the ECH 1147 configuration of an alternative service. In wire format, the value 1148 of the parameter is an ECHConfigs vector [ECH], including the 1149 redundant length prefix. In presentation format, the value is 1150 encoded in [base64]. 1152 When ECH is in use, the TLS ClientHello is divided into an 1153 unencrypted "outer" and an encrypted "inner" ClientHello. The outer 1154 ClientHello is an implementation detail of ECH, and its contents are 1155 controlled by the ECHConfig in accordance with [ECH]. The inner 1156 ClientHello is used for establishing a connection to the service, so 1157 its contents may be influenced by other SVCB parameters. For 1158 example, the requirements on the ProtocolNameList in Section 6.1 1159 apply only to the inner ClientHello. Similarly, it is the inner 1160 ClientHello whose Server Name Indication identifies the origin. 1162 8.1. Client behavior 1164 The general client behavior specified in Section 3 permits clients to 1165 retry connection with a less preferred alternative if the preferred 1166 option fails, including falling back to a direct connection if all 1167 SVCB options fail. This behavior is not suitable for ECH, because 1168 fallback would negate the privacy benefits of ECH. Accordingly, ECH- 1169 capable clients SHALL implement the following behavior for connection 1170 establishment. 1172 1. Perform connection establishment using HTTPS RRs as described in 1173 Section 3, but do not fall back to the origin's A/AAAA records. 1174 If all the HTTPS RRs have an "echconfig" key, and they all fail, 1175 terminate connection establishment. 1177 2. If the client implements Alt-Svc, try to connect using any 1178 entries from the Alt-Svc cache. 1180 3. Fall back to the origin's A/AAAA records if necessary. 1182 As a latency optimization, clients MAY prefetch DNS records for later 1183 steps before they are needed. 1185 8.2. Deployment considerations 1187 An HTTPS RRSet containing some RRs with "echconfig" and some without 1188 is vulnerable to a downgrade attack. This configuration is NOT 1189 RECOMMENDED. Zone owners who do use such a mixed configuration 1190 SHOULD mark the RRs with "echconfig" as more preferred (i.e. smaller 1191 SvcFieldPriority) than those without, in order to maximize the 1192 likelihood that ECH will be used in the absence of an active 1193 adversary. 1195 9. Examples 1197 9.1. Protocol enhancements 1199 Consider a simple zone of the form 1201 simple.example. 300 IN A 192.0.2.1 1202 AAAA 2001:db8::1 1204 The domain owner could add this record 1206 simple.example. 7200 IN HTTPS 1 . alpn=h3 ... 1208 to indicate that simple.example uses HTTPS, and supports QUIC in 1209 addition to HTTPS over TCP (an implicit default). The record could 1210 also include other information (e.g. non-standard port, ECH 1211 configuration). 1213 9.2. Apex aliasing 1215 Consider a zone that is using CNAME aliasing: 1217 $ORIGIN aliased.example. ; A zone that is using a hosting service 1218 ; Subdomain aliased to a high-performance server pool 1219 www 7200 IN CNAME pool.svc.example. 1220 ; Apex domain on fixed IPs because CNAME is not allowed at the apex 1221 @ 300 IN A 192.0.2.1 1222 IN AAAA 2001:db8::1 1224 With HTTPS RRs, the owner of aliased.example could alias the apex by 1225 adding one additional record: 1227 @ 7200 IN HTTPS 0 pool.svc.example. 1229 With this record in place, HTTPS-RR-aware clients will use the same 1230 server pool for aliased.example and www.aliased.example. (They will 1231 also upgrade to HTTPS on aliased.example.) Non-HTTPS-RR-aware 1232 clients will just ignore the new record. 1234 Similar to CNAME, HTTPS RRs have no impact on the origin name. When 1235 connecting, clients will continue to treat the authoritative origins 1236 as "https://www.aliased.example" and "https://aliased.example", 1237 respectively, and will validate TLS server certificates accordingly. 1239 9.3. Parameter binding 1241 Suppose that svc.example's default server pool supports HTTP/2, and 1242 it has deployed HTTP/3 on a new server pool with a different 1243 configuration. This can be expressed in the following form: 1245 $ORIGIN svc.example. ; A hosting provider. 1246 pool 7200 IN HTTPS 1 h3pool alpn=h2,h3 echconfig="123..." 1247 HTTPS 2 . alpn=h2 echconfig="abc..." 1248 pool 300 IN A 192.0.2.2 1249 AAAA 2001:db8::2 1250 h3pool 300 IN A 192.0.2.3 1251 AAAA 2001:db8::3 1253 This configuration is entirely compatible with the "Apex aliasing" 1254 example, whether the client supports HTTPS RRs or not. If the client 1255 does support HTTPS RRs, all connections will be upgraded to HTTPS, 1256 and clients will use HTTP/3 if they can. Parameters are "bound" to 1257 each server pool, so each server pool can have its own protocol, ECH 1258 configuration, etc. 1260 9.4. Non-HTTPS uses 1262 For services other than HTTPS, the SVCB RR and an [Attrleaf] label 1263 will be used. For example, to reach an example resource of 1264 "baz://api.example.com:8765", the following Alias Form SVCB record 1265 would be used to delegate to "svc4-baz.example.net." which in-turn 1266 could return AAAA/A records and/or SVCB records in ServiceForm. 1268 _8765._baz.api.example.com. 7200 IN SVCB 0 svc4-baz.example.net. 1270 HTTPS RRs use similar [Attrleaf] labels if the origin contains a non- 1271 default port. 1273 10. Interaction with other standards 1275 This standard is intended to reduce connection latency and improve 1276 user privacy. Server operators implementing this standard SHOULD 1277 also implement TLS 1.3 [RFC8446] and OCSP Stapling [RFC6066], both of 1278 which confer substantial performance and privacy benefits when used 1279 in combination with SVCB records. 1281 To realize the greatest privacy benefits, this proposal is intended 1282 for use over a privacy-preserving DNS transport (like DNS over TLS 1283 [RFC7858] or DNS over HTTPS [RFC8484]). However, performance 1284 improvements, and some modest privacy improvements, are possible 1285 without the use of those standards. 1287 Any specification for use of SVCB with a protocol MUST have an entry 1288 for its scheme under the SVCB RR type in the IANA DNS Underscore 1289 Global Scoped Entry Registry [Attrleaf]. The scheme SHOULD have an 1290 entry in the IANA URI Schemes Registry [RFC7595]. The scheme SHOULD 1291 have a defined specification for use with SVCB. 1293 11. Security Considerations 1295 SVCB/HTTPS RRs are intended for distribution over untrusted channels, 1296 and clients are REQUIRED to verify that the alternative service is 1297 authoritative for the origin (similar to Section 2.1 of [AltSvc]). 1298 Therefore, DNSSEC signing and validation are OPTIONAL for publishing 1299 and using SVCB and HTTPS RRs. 1301 Clients MUST ensure that their DNS cache is partitioned for each 1302 local network, or flushed on network changes, to prevent a local 1303 adversary in one network from implanting a forged DNS record that 1304 allows them to track users or hinder their connections after they 1305 leave that network. 1307 12. IANA Considerations 1309 12.1. New registry for Service Parameters 1311 The "Service Binding (SVCB) Parameter Registry" defines the namespace 1312 for parameters, including string representations and numeric 1313 SvcParamKey values. This registry is shared with other SVCB- 1314 compatible RR types, such as the HTTPS RR. 1316 ACTION: create and include a reference to this registry. 1318 12.1.1. Procedure 1320 A registration MUST include the following fields: 1322 o Name: Service parameter key name 1324 o SvcParamKey: Service parameter key numeric identifier (range 1325 0-65535) 1327 o Meaning: a short description 1329 o Pointer to specification text 1331 SvcParamKey values to be added to this namespace have different 1332 policies ([RFC5226], Section 4.1) based on their range: 1334 +-------------+-------------------------+ 1335 | SvcParamKey | IANA Policy | 1336 +-------------+-------------------------+ 1337 | 0-255 | Standards Action | 1338 | | | 1339 | 256-32767 | Expert Review | 1340 | | | 1341 | 32768-65280 | First Come First Served | 1342 | | | 1343 | 65280-65534 | Private Use | 1344 | | | 1345 | 65535 | Standards Action | 1346 +-------------+-------------------------+ 1348 Apart from the initial contents, the SvcParamKey name MUST NOT start 1349 with "key". 1351 12.1.2. Initial contents 1353 The "Service Binding (SVCB) Parameter Registry" shall initially be 1354 populated with the registrations below: 1356 +-------------+-----------------+----------------------+------------+ 1357 | SvcParamKey | NAME | Meaning | Reference | 1358 +-------------+-----------------+----------------------+------------+ 1359 | 0 | (no name) | Reserved for | (This | 1360 | | | internal use | document) | 1361 | | | | | 1362 | 1 | alpn | Additional supported | (This | 1363 | | | protocols | document) | 1364 | | | | | 1365 | 2 | no-default-alpn | No support for | (This | 1366 | | | default protocol | document) | 1367 | | | | | 1368 | 3 | port | Port for alternative | (This | 1369 | | | service | document) | 1370 | | | | | 1371 | 4 | ipv4hint | IPv4 address hints | (This | 1372 | | | | document) | 1373 | | | | | 1374 | 5 | echconfig | Encrypted | (This | 1375 | | | ClientHello info | document) | 1376 | | | | | 1377 | 6 | ipv6hint | IPv6 address hints | (This | 1378 | | | | document) | 1379 | | | | | 1380 | 65280-65534 | keyNNNNN | Private Use | (This | 1381 | | | | document) | 1382 | | | | | 1383 | 65535 | key65535 | Reserved | (This | 1384 | | | | document) | 1385 +-------------+-----------------+----------------------+------------+ 1387 TODO: do we also want to reserve a range for greasing? 1389 12.2. Registry updates 1391 Per [RFC6895], please add the following entries to the data type 1392 range of the Resource Record (RR) TYPEs registry: 1394 +-------+------------------------------------------+----------------+ 1395 | TYPE | Meaning | Reference | 1396 +-------+------------------------------------------+----------------+ 1397 | SVCB | Service Location and Parameter Binding | (This | 1398 | | | document) | 1399 | | | | 1400 | HTTPS | HTTPS Service Location and Parameter | (This | 1401 | | Binding | document) | 1402 +-------+------------------------------------------+----------------+ 1403 Per [Attrleaf], please add the following entry to the DNS Underscore 1404 Global Scoped Entry Registry: 1406 +---------+------------+-----------------+-----------------+ 1407 | RR TYPE | _NODE NAME | Meaning | Reference | 1408 +---------+------------+-----------------+-----------------+ 1409 | HTTPS | _https | HTTPS SVCB info | (This document) | 1410 +---------+------------+-----------------+-----------------+ 1412 13. Acknowledgments and Related Proposals 1414 There have been a wide range of proposed solutions over the years to 1415 the "CNAME at the Zone Apex" challenge proposed. These include 1416 [I-D.draft-bellis-dnsop-http-record-00], 1417 [I-D.draft-ietf-dnsop-aname-03], and others. 1419 Thank you to Ian Swett, Ralf Weber, Jon Reed, Martin Thomson, Lucas 1420 Pardue, Ilari Liusvaara, Tim Wicinski, Tommy Pauly, Chris Wood, David 1421 Benjamin, and others for their feedback and suggestions on this 1422 draft. 1424 14. References 1426 14.1. Normative References 1428 [ALPN] Friedl, S., Popov, A., Langley, A., and E. Stephan, 1429 "Transport Layer Security (TLS) Application-Layer Protocol 1430 Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301, 1431 July 2014, . 1433 [Attrleaf] 1434 Crocker, D., "DNS Scoped Data Through "Underscore" Naming 1435 of Attribute Leaves", draft-ietf-dnsop-attrleaf-16 (work 1436 in progress), November 2018. 1438 [base64] Josefsson, S., "The Base16, Base32, and Base64 Data 1439 Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006, 1440 . 1442 [DNAME] Rose, S. and W. Wijngaards, "DNAME Redirection in the 1443 DNS", RFC 6672, DOI 10.17487/RFC6672, June 2012, 1444 . 1446 [ECH] Rescorla, E., Oku, K., Sullivan, N., and C. Wood, "TLS 1447 Encrypted Client Hello", draft-ietf-tls-esni-07 (work in 1448 progress), June 2020. 1450 [HappyEyeballsV2] 1451 Schinazi, D. and T. Pauly, "Happy Eyeballs Version 2: 1452 Better Connectivity Using Concurrency", RFC 8305, 1453 DOI 10.17487/RFC8305, December 2017, 1454 . 1456 [HSTS] Hodges, J., Jackson, C., and A. Barth, "HTTP Strict 1457 Transport Security (HSTS)", RFC 6797, 1458 DOI 10.17487/RFC6797, November 2012, 1459 . 1461 [HTTP3] Bishop, M., "Hypertext Transfer Protocol Version 3 1462 (HTTP/3)", draft-ietf-quic-http-20 (work in progress), 1463 April 2019. 1465 [RFC1035] Mockapetris, P., "Domain names - implementation and 1466 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 1467 November 1987, . 1469 [RFC1928] Leech, M., Ganis, M., Lee, Y., Kuris, R., Koblas, D., and 1470 L. Jones, "SOCKS Protocol Version 5", RFC 1928, 1471 DOI 10.17487/RFC1928, March 1996, 1472 . 1474 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1475 Requirement Levels", BCP 14, RFC 2119, 1476 DOI 10.17487/RFC2119, March 1997, 1477 . 1479 [RFC3225] Conrad, D., "Indicating Resolver Support of DNSSEC", 1480 RFC 3225, DOI 10.17487/RFC3225, December 2001, 1481 . 1483 [RFC3597] Gustafsson, A., "Handling of Unknown DNS Resource Record 1484 (RR) Types", RFC 3597, DOI 10.17487/RFC3597, September 1485 2003, . 1487 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 1488 IANA Considerations Section in RFCs", RFC 5226, 1489 DOI 10.17487/RFC5226, May 2008, 1490 . 1492 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 1493 Specifications: ABNF", STD 68, RFC 5234, 1494 DOI 10.17487/RFC5234, January 2008, 1495 . 1497 [RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6 1498 Address Text Representation", RFC 5952, 1499 DOI 10.17487/RFC5952, August 2010, 1500 . 1502 [RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS) 1503 Extensions: Extension Definitions", RFC 6066, 1504 DOI 10.17487/RFC6066, January 2011, 1505 . 1507 [RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van 1508 Beijnum, "DNS64: DNS Extensions for Network Address 1509 Translation from IPv6 Clients to IPv4 Servers", RFC 6147, 1510 DOI 10.17487/RFC6147, April 2011, 1511 . 1513 [RFC6454] Barth, A., "The Web Origin Concept", RFC 6454, 1514 DOI 10.17487/RFC6454, December 2011, 1515 . 1517 [RFC7050] Savolainen, T., Korhonen, J., and D. Wing, "Discovery of 1518 the IPv6 Prefix Used for IPv6 Address Synthesis", 1519 RFC 7050, DOI 10.17487/RFC7050, November 2013, 1520 . 1522 [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 1523 Protocol (HTTP/1.1): Semantics and Content", RFC 7231, 1524 DOI 10.17487/RFC7231, June 2014, 1525 . 1527 [RFC7595] Thaler, D., Ed., Hansen, T., and T. Hardie, "Guidelines 1528 and Registration Procedures for URI Schemes", BCP 35, 1529 RFC 7595, DOI 10.17487/RFC7595, June 2015, 1530 . 1532 [RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., 1533 and P. Hoffman, "Specification for DNS over Transport 1534 Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May 1535 2016, . 1537 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1538 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1539 May 2017, . 1541 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 1542 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 1543 . 1545 [RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS 1546 (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018, 1547 . 1549 [WebSocket] 1550 Fette, I. and A. Melnikov, "The WebSocket Protocol", 1551 RFC 6455, DOI 10.17487/RFC6455, December 2011, 1552 . 1554 14.2. Informative References 1556 [AltSvc] Nottingham, M., McManus, P., and J. Reschke, "HTTP 1557 Alternative Services", RFC 7838, DOI 10.17487/RFC7838, 1558 April 2016, . 1560 [DNSTerm] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS 1561 Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499, 1562 January 2019, . 1564 [FETCH] "Fetch Living Standard", May 2020, 1565 . 1567 [I-D.draft-bellis-dnsop-http-record-00] 1568 Bellis, R., "A DNS Resource Record for HTTP", draft- 1569 bellis-dnsop-http-record-00 (work in progress), November 1570 2018. 1572 [I-D.draft-ietf-dnsop-aname-03] 1573 Finch, T., Hunt, E., Dijk, P., Eden, A., and W. Mekking, 1574 "Address-specific DNS aliases (ANAME)", draft-ietf-dnsop- 1575 aname-03 (work in progress), April 2019. 1577 [I-D.draft-tapril-ns2-00] 1578 April, T., "Parameterized Nameserver Delegation with NS2 1579 and NS2T", draft-tapril-ns2-00 (work in progress), March 1580 2020. 1582 [RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for 1583 specifying the location of services (DNS SRV)", RFC 2782, 1584 DOI 10.17487/RFC2782, February 2000, 1585 . 1587 [RFC6895] Eastlake 3rd, D., "Domain Name System (DNS) IANA 1588 Considerations", BCP 42, RFC 6895, DOI 10.17487/RFC6895, 1589 April 2013, . 1591 [URI] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 1592 Resource Identifier (URI): Generic Syntax", STD 66, 1593 RFC 3986, DOI 10.17487/RFC3986, January 2005, 1594 . 1596 14.3. URIs 1598 [1] https://github.com/MikeBishop/dns-alt-svc 1600 Appendix A. Comparison with alternatives 1602 The SVCB and HTTPS RR types closely resemble, and are inspired by, 1603 some existing record types and proposals. A complaint with all of 1604 the alternatives is that web clients have seemed unenthusiastic about 1605 implementing them. The hope here is that by providing an extensible 1606 solution that solves multiple problems we will overcome the inertia 1607 and have a path to achieve client implementation. 1609 A.1. Differences from the SRV RR type 1611 An SRV record [RFC2782] can perform a similar function to the SVCB 1612 record, informing a client to look in a different location for a 1613 service. However, there are several differences: 1615 o SRV records are typically mandatory, whereas clients will always 1616 continue to function correctly without making use of SVCB. 1618 o SRV records cannot instruct the client to switch or upgrade 1619 protocols, whereas SVCB can signal such an upgrade (e.g. to 1620 HTTP/2). 1622 o SRV records are not extensible, whereas SVCB and HTTPS RRs can be 1623 extended with new parameters. 1625 A.2. Differences from the proposed HTTP record 1627 Unlike [I-D.draft-bellis-dnsop-http-record-00], this approach is 1628 extensible to cover Alt-Svc and Encrypted ClientHello use-cases. 1629 Like that proposal, this addresses the zone apex CNAME challenge. 1631 Like that proposal, it remains necessary to continue to include 1632 address records at the zone apex for legacy clients. 1634 A.3. Differences from the proposed ANAME record 1636 Unlike [I-D.draft-ietf-dnsop-aname-03], this approach is extensible 1637 to cover Alt-Svc and ECH use-cases. This approach also does not 1638 require any changes or special handling on either authoritative or 1639 master servers, beyond optionally returning in-bailiwick additional 1640 records. 1642 Like that proposal, this addresses the zone apex CNAME challenge for 1643 clients that implement this. 1645 However, with this SVCB proposal, it remains necessary to continue to 1646 include address records at the zone apex for legacy clients. If 1647 deployment of this standard is successful, the number of legacy 1648 clients will fall over time. As the number of legacy clients 1649 declines, the operational effort required to serve these users 1650 without the benefit of SVCB indirection should fall. Server 1651 operators can easily observe how much traffic reaches this legacy 1652 endpoint, and may remove the apex's address records if the observed 1653 legacy traffic has fallen to negligible levels. 1655 A.4. Comparison with separate RR types for AliasForm and ServiceForm 1657 Abstractly, functions of AliasForm and ServiceForm are independent, 1658 so it might be tempting to specify them as separate RR types. 1659 However, this would result in a serious performance impairment, 1660 because clients cannot rely on their recursive resolver to follow 1661 SVCB aliases (unlike CNAME). Thus, clients would have to issue 1662 queries for both RR types in parallel, potentially at each step of 1663 the alias chain. Recursive resolvers that implement the 1664 specification would, upon receipt of a ServiceForm query, emit both a 1665 ServiceForm and an AliasForm query to the authoritative. Thus, 1666 splitting the RR type would double, or in some cases triple, the load 1667 on clients and servers, and would not reduce implementation 1668 complexity. 1670 Appendix B. Change history 1672 o draft-ietf-dnsop-svcb-https-00 1674 * Rename HTTPSSVC RR to HTTPS RR 1676 * Rename "an SVCB" to "a SVCB" 1678 * Removed "design considerations and open issues" section and 1679 some other "to be removed" text 1681 o draft-ietf-dnsop-svcb-httpssvc-03 1683 * Revised chain length limit requirements 1685 * Revised IANA registry rules for SvcParamKeys 1686 * Require HTTPS clients to implement SNI 1688 * Update terminology for Encrypted ClientHello 1690 * Clarifications: non-default ports, transport proxies, HSTS 1691 procedure, WebSocket behavior, wire format, IP hints, inner/ 1692 outer ClientHello with ECH 1694 * Various textual and ABNF corrections 1696 o draft-ietf-dnsop-svcb-httpssvc-02 1698 * All changes to Alt-Svc have been removed 1700 * Expanded and reorganized examples 1702 * Priority zero is now the definition of AliasForm 1704 * Repeated SvcParamKeys are no longer allowed 1706 * The "=" sign may be omitted in a key=value pair if the value is 1707 also empty 1709 * In the wire format, SvcParamKeys must be in sorted order 1711 * New text regarding how to handle resolution timeouts 1713 * Expanded description of recursive resolver behavior 1715 * Much more precise description of the intended ALPN behavior 1717 * Match the HSTS specification's language on HTTPS enforcement 1719 * Removed 'esniconfig=""' mechanism and simplified ESNI 1720 connection logic 1722 o draft-ietf-dnsop-svcb-httpssvc-01 1724 * Reduce the emphasis on conversion between HTTPSSVC and Alt-Svc 1726 * Make the "untrusted channel" concept more precise. 1728 * Make SvcFieldPriority = 0 the definition of AliasForm, instead 1729 of a requirement. 1731 o draft-ietf-dnsop-svcb-httpssvc-00 1732 * Document an optimization for optimistic pre-connection. (Chris 1733 Wood) 1735 * Relax IP hint handling requirements. (Eric Rescorla) 1737 o draft-nygren-dnsop-svcb-httpssvc-00 1739 * Generalize to an SVCB record, with special-case handling for 1740 Alt-Svc and HTTPS separated out to dedicated sections. 1742 * Split out a separate HTTPSSVC record for the HTTPS use-case. 1744 * Remove the explicit SvcRecordType=0/1 and instead make the 1745 AliasForm vs ServiceForm be implicit. This was based on 1746 feedback recommending against subtyping RR type. 1748 * Remove one optimization. 1750 o draft-nygren-httpbis-httpssvc-03 1752 * Change redirect type for HSTS-style behavior from 302 to 307 to 1753 reduce ambiguities. 1755 o draft-nygren-httpbis-httpssvc-02 1757 * Remove the redundant length fields from the wire format. 1759 * Define a SvcDomainName of "." for SvcRecordType=1 as being the 1760 HTTPSSVC RRNAME. 1762 * Replace "hq" with "h3". 1764 o draft-nygren-httpbis-httpssvc-01 1766 * Fixes of record name. Replace references to "HTTPSVC" with 1767 "HTTPSSVC". 1769 o draft-nygren-httpbis-httpssvc-00 1771 * Initial version 1773 Authors' Addresses 1775 Ben Schwartz 1776 Google 1778 Email: bemasc@google.com 1779 Mike Bishop 1780 Akamai Technologies 1782 Email: mbishop@evequefou.be 1784 Erik Nygren 1785 Akamai Technologies 1787 Email: erik+ietf@nygren.org