idnits 2.17.00 (12 Aug 2021) /tmp/idnits30385/draft-ietf-doh-dns-over-https-04.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- ** The abstract seems to contain references ([1]), which it shouldn't. Please replace those with straight textual mentions of the documents in question. -- The document has examples using IPv4 documentation addresses according to RFC6890, but does not use any IPv6 documentation addresses. Maybe there should be IPv6 examples, too? Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == The document seems to lack the recommended RFC 2119 boilerplate, even if it appears to use RFC 2119 keywords -- however, there's a paragraph with a matching beginning. Boilerplate error? (The document does seem to have the reference to RFC 2119 which the ID-Checklist requires). -- The document date (March 21, 2018) is 1521 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Looks like a reference, but probably isn't: '1' on line 682 ** Obsolete normative reference: RFC 5246 (Obsoleted by RFC 8446) ** Obsolete normative reference: RFC 6961 (Obsoleted by RFC 8446) -- Obsolete informational reference (is this intentional?): RFC 7719 (Obsoleted by RFC 8499) Summary: 3 errors (**), 0 flaws (~~), 2 warnings (==), 4 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group P. Hoffman 3 Internet-Draft ICANN 4 Intended status: Standards Track P. McManus 5 Expires: September 22, 2018 Mozilla 6 March 21, 2018 8 DNS Queries over HTTPS 9 draft-ietf-doh-dns-over-https-04 11 Abstract 13 This document describes how to run DNS service over HTTP using 14 https:// URIs. 16 [[ There is a repository for this draft at https://github.com/dohwg/ 17 draft-ietf-doh-dns-over-https [1] ]]. 19 Status of This Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at https://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on September 22, 2018. 36 Copyright Notice 38 Copyright (c) 2018 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents 43 (https://trustee.ietf.org/license-info) in effect on the date of 44 publication of this document. Please review these documents 45 carefully, as they describe your rights and restrictions with respect 46 to this document. Code Components extracted from this document must 47 include Simplified BSD License text as described in Section 4.e of 48 the Trust Legal Provisions and are provided without warranty as 49 described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 54 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 55 3. Protocol Requirements . . . . . . . . . . . . . . . . . . . . 3 56 3.1. Non-requirements . . . . . . . . . . . . . . . . . . . . 4 57 4. The HTTP Request . . . . . . . . . . . . . . . . . . . . . . 4 58 4.1. DNS Wire Format . . . . . . . . . . . . . . . . . . . . . 5 59 4.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . 5 60 5. The HTTP Response . . . . . . . . . . . . . . . . . . . . . . 7 61 5.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 8 62 6. HTTP Integration . . . . . . . . . . . . . . . . . . . . . . 8 63 6.1. Cache Interaction . . . . . . . . . . . . . . . . . . . . 8 64 6.2. HTTP/2 . . . . . . . . . . . . . . . . . . . . . . . . . 9 65 6.3. Server Push . . . . . . . . . . . . . . . . . . . . . . . 10 66 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 67 7.1. Registration of application/dns-udpwireformat Media Type 10 68 8. Security Considerations . . . . . . . . . . . . . . . . . . . 12 69 9. Operational Considerations . . . . . . . . . . . . . . . . . 13 70 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13 71 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 72 11.1. Normative References . . . . . . . . . . . . . . . . . . 14 73 11.2. Informative References . . . . . . . . . . . . . . . . . 15 74 11.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 16 75 Appendix A. Previous Work on DNS over HTTP or in Other Formats . 16 76 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 78 1. Introduction 80 The Internet does not always provide end to end reachability for 81 native DNS. On-path network devices may spoof DNS responses, block 82 DNS requests, or just redirect DNS queries to different DNS servers 83 that give less-than-honest answers. These are also sometimes 84 delivered with poor performance or reduced feature sets. 86 Over time, there have been many proposals for using HTTP and HTTPS as 87 a substrate for DNS queries and responses. To date, none of those 88 proposals have made it beyond early discussion, partially due to 89 disagreement about what the appropriate formatting should be and 90 partially because they did not follow HTTP best practices. 92 This document defines a specific protocol for sending DNS [RFC1035] 93 queries and getting DNS responses over HTTP [RFC7540] using https:// 94 (and therefore TLS [RFC5246] security for integrity and 95 confidentiality). Each DNS query-response pair is mapped into a HTTP 96 request-response pair. 98 The described approach is more than a tunnel over HTTP. It 99 establishes default media formatting types for requests and responses 100 but uses normal HTTP content negotiation mechanisms for selecting 101 alternatives that endpoints may prefer in anticipation of serving new 102 use cases. In addition to this media type negotiation, it aligns 103 itself with HTTP features such as caching, redirection, proxying, 104 authentication, and compression. 106 The integration with HTTP provides a transport suitable for both 107 traditional DNS clients and native web applications seeking access to 108 the DNS. 110 Two primary uses cases were considered during this protocol's 111 development. They included preventing on-path devices from 112 interfering with DNS operations and allowing web applications to 113 access DNS information via existing browser APIs in a safe way 114 consistent with Cross Origin Resource Sharing (CORS) [CORS]. There 115 are certainly other uses for this work. 117 2. Terminology 119 A server that supports this protocol is called a "DNS API server" to 120 differentiate it from a "DNS server" (one that uses the regular DNS 121 protocol). Similarly, a client that supports this protocol is called 122 a "DNS API client". 124 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 125 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 126 "OPTIONAL" in this document are to be interpreted as described in BCP 127 14, RFC8174 [RFC8174] when, and only when, they appear in all 128 capitals, as shown here. 130 3. Protocol Requirements 132 The protocol described here bases its design on the following 133 protocol requirements: 135 o The protocol must use normal HTTP semantics. 137 o The queries and responses must be able to be flexible enough to 138 express every normal DNS query. 140 o The protocol must allow implementations to use HTTP's content 141 negotiation mechanism. 143 o The protocol must ensure interoperable media formats through a 144 mandatory to implement format wherein a query must be able to 145 contain future modifications to the DNS protocol including the 146 inclusion of one or more EDNS extensions (including those not yet 147 defined). 149 o The protocol must use a secure transport that meets the 150 requirements for HTTPS. 152 3.1. Non-requirements 154 o Supporting network-specific DNS64 [RFC6147] 156 o Supporting other network-specific inferences from plaintext DNS 157 queries 159 o Supporting insecure HTTP 161 o Supporting legacy HTTP versions 163 4. The HTTP Request 165 To make a DNS API query a DNS API client encodes a single DNS query 166 into an HTTP request using either the HTTP GET or POST method and the 167 other requirements of this section. The DNS API server defines the 168 URI used by the request. Configuration and discovery of the URI is 169 done out of band from this protocol. 171 When using the POST method the DNS query is included as the message 172 body of the HTTP request and the Content-Type request header 173 indicates the media type of the message. POST-ed requests are 174 smaller than their GET equivalents. 176 When using the GET method the URI path MUST contain a query parameter 177 name-value pair [QUERYPARAMETER] with the name of "ct" and a value 178 indicating the media-format used for the dns parameter. The value 179 may either be an explicit media type (e.g. ct=application/dns- 180 udpwireformat&dns=...) or it may be empty. An empty value indicates 181 the default application/dns-udpwireformat type (e.g. ct&dns=...). 183 When using the GET method the URI path MUST contain a query parameter 184 with the name of "dns". The value of the parameter is the content of 185 the request potentially encoded with base64url [RFC4648]. 186 Specifications that define media types for use with DOH, such as DNS 187 Wire Format Section 4.1 of this document, MUST indicate if the dns 188 parameter uses base64url encoding. 190 Using the GET method is friendlier to many HTTP cache 191 implementations. 193 The DNS API client SHOULD include an HTTP "Accept:" request header to 194 say what type of content can be understood in response. The client 195 MUST be prepared to process "application/dns-udpwireformat" 196 Section 4.1 responses but MAY process any other type it receives. 198 In order to maximize cache friendliness, DNS API clients using media 199 formats that include DNS ID, such as application/dns-udpwireformat, 200 SHOULD use a DNS ID of 0 in every DNS request. HTTP correlates 201 request and response, thus eliminating the need for the ID in a media 202 type such as application/dns-udpwireformat and the use of a varying 203 DNS ID can cause semantically equivalent DNS queries to be cached 204 separately. 206 DNS API clients can use HTTP/2 padding and compression in the same 207 way that other HTTP/2 clients use (or don't use) them. 209 4.1. DNS Wire Format 211 The data payload is the DNS on-the-wire format defined in [RFC1035]. 212 The format is for DNS over UDP. (Note that this is different than 213 the wire format used in [RFC7858]. 215 When using the GET method, the data payload MUST be encoded with 216 base64url [RFC4648] and then placed as a name value pair in the query 217 portion of the URI with name "dns". Padding characters for base64url 218 MUST NOT be included. 220 When using the POST method, the data payload MUST NOT be encoded and 221 is used directly as the HTTP message body. 223 DNS API clients using the DNS wire format MAY have one or more EDNS 224 extensions [RFC6891] in the request. 226 The media type is "application/dns-udpwireformat". 228 4.2. Examples 230 These examples use HTTP/2 style formatting from [RFC7540]. 232 These examples use a DNS API service located at 233 https://dnsserver.example.net/dns-query to resolve the IN A records. 235 The requests are represented as application/dns-udpwirefomat typed 236 bodies. 238 The first example request uses GET to request www.example.com 240 :method = GET 241 :scheme = https 242 :authority = dnsserver.example.net 243 :path = /dns-query?ct& (no space or CR) 244 dns=AAABAAABAAAAAAAAA3d3dwdleGFtcGxlA2NvbQAAAQAB 245 accept = application/dns-udpwireformat 247 The same DNS query for www.example.com, using the POST method would 248 be: 250 :method = POST 251 :scheme = https 252 :authority = dnsserver.example.net 253 :path = /dns-query 254 accept = application/dns-udpwireformat 255 content-type = application/dns-udpwireformat 256 content-length = 33 258 <33 bytes represented by the following hex encoding> 259 00 00 01 00 00 01 00 00 00 00 00 00 03 77 77 77 260 07 65 78 61 6d 70 6c 65 03 63 6f 6d 00 00 01 00 261 01 263 Finally, a GET based query for a.62characterlabel-makes-base64url- 264 distinct-from-standard-base64.example.com is shown as an example to 265 emphasize that the encoding alphabet of base64url is different than 266 regular base64 and that padding is omitted. 268 The DNS query is 94 bytes represented by the following hex encoding 270 00 00 01 00 00 01 00 00 00 00 00 00 01 61 3e 36 271 32 63 68 61 72 61 63 74 65 72 6c 61 62 65 6c 2d 272 6d 61 6b 65 73 2d 62 61 73 65 36 34 75 72 6c 2d 273 64 69 73 74 69 6e 63 74 2d 66 72 6f 6d 2d 73 74 274 61 6e 64 61 72 64 2d 62 61 73 65 36 34 07 65 78 275 61 6d 70 6c 65 03 63 6f 6d 00 00 01 00 01 277 :method = GET 278 :scheme = https 279 :authority = dnsserver.example.net 280 :path = /dns-query?ct& (no space or CR) 281 dns=AAABAAABAAAAAAAAAWE-NjJjaGFyYWN0ZXJsYWJl (no space or CR) 282 bC1tYWtlcy1iYXNlNjR1cmwtZGlzdGluY3QtZnJvbS1z (no space or CR) 283 dGFuZGFyZC1iYXNlNjQHZXhhbXBsZQNjb20AAAEAAQ 284 accept = application/dns-udpwireformat 286 5. The HTTP Response 288 An HTTP response with a 2xx status code ([RFC7231] Section 6.3) 289 indicates a valid DNS response to the query made in the HTTP request. 290 A valid DNS response includes both success and failure responses. 291 For example, a DNS failure response such as SERVFAIL or NXDOMAIN will 292 be the message in a successful 2xx HTTP response even though there 293 was a failure at the DNS layer. Responses with non-successful HTTP 294 status codes do not contain DNS answers to the question in the 295 corresponding request. Some of these non-successful HTTP responses 296 (e.g. redirects or authentication failures) could allow clients to 297 make new requests to satisfy the original question. 299 Different response media types will provide more or less information 300 from a DNS response. For example, one response type might include 301 the information from the DNS header bytes while another might omit 302 it. The amount and type of information that a media type gives is 303 solely up to the format, and not defined in this protocol. 305 At the time this is published, the response types are works in 306 progress. The only response type defined in this document is 307 "application/dns-udpwireformat", but it is possible that other 308 response formats will be defined in the future. 310 The DNS response for "application/dns-udpwireformat" in Section 4.1 311 MAY have one or more EDNS extensions, depending on the extension 312 definition of the extensions given in the DNS request. 314 Each DNS request-response pair is matched to one HTTP request- 315 response pair. The responses may be processed and transported in any 316 order using HTTP's multi-streaming functionality ([RFC7540] 317 Section 5}). 319 The Answer section of a DNS response can contain zero or more RRsets. 320 (RRsets are defined in [RFC7719].) According to [RFC2181], each 321 resource record in an RRset has Time To Live (TTL) freshness 322 information. Different RRsets in the Answer section can have 323 different TTLs, although it is only possible for the HTTP response to 324 have a single freshness lifetime. The HTTP response freshness 325 lifetime ([RFC7234] Section 4.2) should be coordinated with the RRset 326 with the smallest TTL in the Answer section of the response. 327 Specifically, the HTTP freshness lifetime SHOULD be set to expire at 328 the same time any of the DNS resource records in the Answer section 329 reach a 0 TTL. The response freshness lifetime MUST NOT be greater 330 than that indicated by the DNS resoruce record with the smallest TTL 331 in the response. 333 If the DNS response has no records in the Answer section, and the DNS 334 response has an SOA record in the Authority section, the response 335 freshness lifetime MUST NOT be greater than the MINIMUM field from 336 that SOA record. Otherwise, the HTTP response MUST set a freshness 337 lifetime ([RFC7234] Section 4.2) of 0 by using a mechanism such as 338 "Cache-Control: no-cache" ([RFC7234] Section 5.2.1.4). 340 A DNS API client that receives a response without an explicit 341 freshness lifetime MUST NOT assign that response a heuristic 342 freshness ([RFC7234] Section 4.2.2.) greater than that indicated by 343 the DNS Record with the smallest TTL in the response. 345 A DNS API server MUST be able to process application/dns- 346 udpwireformat request messages. 348 A DNS API server SHOULD respond with HTTP status code 415 349 (Unsupported Media Type) upon receiving a media type it is unable to 350 process. 352 This document does not change the definition of any HTTP response 353 codes or otherwise proscribe their use. 355 5.1. Example 357 This is an example response for a query for the IN A records for 358 "www.example.com" with recursion turned on. The response bears one 359 record with an address of 192.0.2.1 and a TTL of 128 seconds. 361 :status = 200 362 content-type = application/dns-udpwireformat 363 content-length = 64 364 cache-control = max-age=128 366 <64 bytes represented by the following hex encoding> 367 00 00 81 80 00 01 00 01 00 00 00 00 03 77 77 77 368 07 65 78 61 6d 70 6c 65 03 63 6f 6d 00 00 01 00 369 01 03 77 77 77 07 65 78 61 6d 70 6c 65 03 63 6f 370 6d 00 00 01 00 01 00 00 00 80 00 04 C0 00 02 01 372 6. HTTP Integration 374 This protocol MUST be used with the https scheme URI [RFC7230]. 376 6.1. Cache Interaction 378 A DOH API client may utilize a hierarchy of caches that include both 379 HTTP and DNS specific caches. HTTP cache entries may be bypassed 380 with HTTP mechanisms such as the "Cache-Control no-cache" directive; 381 however DNS caches do not have a similar mechanism. 383 A DOH response that was previously stored in an HTTP cache will 384 contain the [RFC7234] Age response header indicating the elapsed time 385 between when the entry was placed in the HTTP cache and the current 386 DOH response. DNS API clients should subtract this time from the DNS 387 TTL if they are re-sharing the information in a non HTTP context 388 (e.g. their own DNS cache) to determine the remaining time to live of 389 the DNS record. 391 HTTP revalidation (e.g. via If-None-Match request headers) of cached 392 DNS information may be of limited value to DOH as revalidation 393 provides only a bandwidth benefit and DNS transactions are normally 394 latency bound. Furthermore, the HTTP response headers that enable 395 revalidation (such as "Last-Modified" and "Etag") are often fairly 396 large when compared to the overall DNS response size, and have a 397 variable nature that creates constant pressure on the HTTP/2 398 compression dictionary [RFC7541]. Other types of DNS data, such as 399 zone transfers, may be larger and benefit more from revalidation. 400 DNS API servers may wish to consider whether providing these 401 validation enabling response headers is worthwhile. 403 The stale-while-revalidate and stale-if-error cache control 404 directives may be well suited to a DOH implementation when allowed by 405 server policy. Those mechanisms allow a client, at the server's 406 discretion, to reuse a cache entry that is no longer fresh under some 407 extenuating circumstances defined in [RFC5861]. 409 All HTTP servers, including DNS API servers, need to consider cache 410 interaction when they generate responses that are not globally valid. 411 For instance, if a DNS API server customized a response based on the 412 client's identity then it would not want to globally allow reuse of 413 that response. This could be accomplished through a variety of HTTP 414 techniques such as a Cache-Control max-age of 0, or perhaps by the 415 Vary response header. 417 6.2. HTTP/2 419 The minimum version of HTTP used by DOH SHOULD be HTTP/2 [RFC7540]. 421 The messages in classic UDP based DNS [RFC1035] are inherently 422 unordered and have low overhead. A competitive HTTP transport needs 423 to support reordering, parallelism, priority, and header compression 424 to achieve similar performance. Those features were introduced to 425 HTTP in HTTP/2 [RFC7540]. Earlier versions of HTTP are capable of 426 conveying the semantic requirements of DOH but may result in very 427 poor performance for many uses cases. 429 6.3. Server Push 431 Before using DOH response data for DNS resolution, the client MUST 432 establish that the HTTP request URI is a trusted service for the DOH 433 query. For HTTP requests initiated by the DNS API client this trust 434 is implicit in the selection of URI. For HTTP server push ([RFC7540] 435 Section 8.2) extra care must be taken to ensure that the pushed URI 436 is one that the client would have directed the same query to if the 437 client had initiated the request. This specification does not extend 438 DNS resolution privileges to URIs that are not recognized by the 439 client as trusted DNS API servers. 441 7. IANA Considerations 443 7.1. Registration of application/dns-udpwireformat Media Type 444 To: ietf-types@iana.org 445 Subject: Registration of MIME media type 446 application/dns-udpwireformat 448 MIME media type name: application 450 MIME subtype name: dns-udpwireformat 452 Required parameters: n/a 454 Optional parameters: n/a 456 Encoding considerations: This is a binary format. The contents are a 457 DNS message as defined in RFC 1035. The format used here is for DNS 458 over UDP, which is the format defined in the diagrams in RFC 1035. 460 Security considerations: The security considerations for carrying 461 this data are the same for carrying DNS without encryption. 463 Interoperability considerations: None. 465 Published specification: This document. 467 Applications that use this media type: 468 Systems that want to exchange full DNS messages. 470 Additional information: 472 Magic number(s): n/a 474 File extension(s): n/a 476 Macintosh file type code(s): n/a 478 Person & email address to contact for further information: 479 Paul Hoffman, paul.hoffman@icann.org 481 Intended usage: COMMON 483 Restrictions on usage: n/a 485 Author: Paul Hoffman, paul.hoffman@icann.org 487 Change controller: IESG 489 8. Security Considerations 491 Running DNS over HTTPS relies on the security of the underlying HTTP 492 transport. This mitigates classic amplication attacks for UDP-based 493 DNS. Implementations utilizing HTTP/2 benefit from the TLS profile 494 defined in [RFC7540] Section 9.2. 496 Session level encryption has well known weaknesses with respect to 497 traffic analysis which might be particularly acute when dealing with 498 DNS queries. HTTP/2 provides further advice about the use of 499 compression (Section 10.6 of [RFC7540]) and padding (Section 10.7 of 500 [RFC7540]). 502 The HTTPS connection provides transport security for the interaction 503 between the DNS API server and client, but does not inherently ensure 504 the authenticity of DNS data. A DNS API client may also perform full 505 DNSSEC validation of answers received from a DNS API server or it may 506 choose to trust answers from a particular DNS API server, much as a 507 DNS client might choose to trust answers from its recursive DNS 508 resolver. This capability might be affected by the response media 509 type. 511 Section 6.1 describes the interaction of this protocol with HTTP 512 caching. An adversary that can control the cache used by the client 513 can affect that client's view of the DNS. This is no different than 514 the security implications of HTTP caching for other protocols that 515 use HTTP. 517 A server that is acting both as a normal web server and a DNS API 518 server is in a position to choose which DNS names it forces a client 519 to resolve (through its web service) and also be the one to answer 520 those queries (through its DNS API service). An untrusted DNS API 521 server can thus easily cause damage by poisoning a client's cache 522 with names that the DNS API server chooses to poison. A client MUST 523 NOT trust a DNS API server simply because it was discovered, or 524 because the client was told to trust the DNS API server by an 525 untrusted party. Instead, a client MUST only trust DNS API server 526 that is configured as trustworthy. 528 A client can use DNS over HTTPS as one of multiple mechanisms to 529 obtain DNS data. If a client of this protocol encounters an HTTP 530 error after sending a DNS query, and then falls back to a different 531 DNS retrieval mechanism, doing so can weaken the privacy expected by 532 the user of the client. 534 9. Operational Considerations 536 Local policy considerations and similar factors mean different DNS 537 servers may provide different results to the same query: for instance 538 in split DNS configurations [RFC6950]. It logically follows that the 539 server which is queried can influence the end result. Therefore a 540 client's choice of DNS server may affect the responses it gets to its 541 queries. For example, in the case of DNS64 [RFC6147], the choice 542 could affect whether IPv6/IPv4 translation will work at all. 544 The HTTPS channel used by this specification establishes secure two 545 party communication between the DNS API client and the DNS API 546 server. Filtering or inspection systems that rely on unsecured 547 transport of DNS will not function in a DNS over HTTPS environment. 549 Many HTTPS implementations perform real time third party checks of 550 the revocation status of the certificates being used by TLS. If this 551 check is done as part of the DNS API server connection procedure and 552 the check itself requires DNS resolution to connect to the third 553 party a deadlock can occur. The use of an OCSP [RFC6960] server is 554 one example of how this can happen. DNS API servers SHOULD utilize 555 OCSP Stapling [RFC6961] to provide the client with certificate 556 revocation information that does not require contacting a third 557 party. 559 A DNS API client may face a similar bootstrapping problem when the 560 HTTP request needs to resolve the hostname portion of the DNS URI. 561 Just as the address of a traditional DNS nameserver cannot be 562 originally determined from that same server, a DOH client cannot use 563 its DOH server to initially resolve the server's host name into an 564 address. Alternative strategies a client might employ include making 565 the initial resolution part of the configuration, IP based URIs and 566 corresponding IP based certificates for HTTPS, or resolving the DNS 567 API server's hostname via traditional DNS or another DOH server while 568 still authenticating the resulting connection via HTTPS. 570 HTTP [RFC7230] is a stateless application level protocol and 571 therefore DOH implementations do not provide stateful ordering 572 guarantees between different requests. DOH cannot be used as a 573 transport for other protocols that require strict ordering. 575 10. Acknowledgments 577 Joe Hildebrand contributed lots of material for a different iteration 578 of this document. Helpful early comments were given by Ben Schwartz 579 and Mark Nottingham. 581 11. References 583 11.1. Normative References 585 [RFC1035] Mockapetris, P., "Domain names - implementation and 586 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 587 November 1987, . 589 [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data 590 Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006, 591 . 593 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 594 (TLS) Protocol Version 1.2", RFC 5246, 595 DOI 10.17487/RFC5246, August 2008, 596 . 598 [RFC6960] Santesson, S., Myers, M., Ankney, R., Malpani, A., 599 Galperin, S., and C. Adams, "X.509 Internet Public Key 600 Infrastructure Online Certificate Status Protocol - OCSP", 601 RFC 6960, DOI 10.17487/RFC6960, June 2013, 602 . 604 [RFC6961] Pettersen, Y., "The Transport Layer Security (TLS) 605 Multiple Certificate Status Request Extension", RFC 6961, 606 DOI 10.17487/RFC6961, June 2013, 607 . 609 [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 610 Protocol (HTTP/1.1): Message Syntax and Routing", 611 RFC 7230, DOI 10.17487/RFC7230, June 2014, 612 . 614 [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 615 Protocol (HTTP/1.1): Semantics and Content", RFC 7231, 616 DOI 10.17487/RFC7231, June 2014, 617 . 619 [RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, 620 Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching", 621 RFC 7234, DOI 10.17487/RFC7234, June 2014, 622 . 624 [RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext 625 Transfer Protocol Version 2 (HTTP/2)", RFC 7540, 626 DOI 10.17487/RFC7540, May 2015, 627 . 629 [RFC7541] Peon, R. and H. Ruellan, "HPACK: Header Compression for 630 HTTP/2", RFC 7541, DOI 10.17487/RFC7541, May 2015, 631 . 633 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 634 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 635 May 2017, . 637 11.2. Informative References 639 [CORS] "Cross-Origin Resource Sharing", n.d., 640 . 642 [QUERYPARAMETER] 643 "application/x-www-form-urlencoded Parsing", n.d., 644 . 647 [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS 648 Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997, 649 . 651 [RFC5861] Nottingham, M., "HTTP Cache-Control Extensions for Stale 652 Content", RFC 5861, DOI 10.17487/RFC5861, May 2010, 653 . 655 [RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van 656 Beijnum, "DNS64: DNS Extensions for Network Address 657 Translation from IPv6 Clients to IPv4 Servers", RFC 6147, 658 DOI 10.17487/RFC6147, April 2011, 659 . 661 [RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms 662 for DNS (EDNS(0))", STD 75, RFC 6891, 663 DOI 10.17487/RFC6891, April 2013, 664 . 666 [RFC6950] Peterson, J., Kolkman, O., Tschofenig, H., and B. Aboba, 667 "Architectural Considerations on Application Features in 668 the DNS", RFC 6950, DOI 10.17487/RFC6950, October 2013, 669 . 671 [RFC7719] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS 672 Terminology", RFC 7719, DOI 10.17487/RFC7719, December 673 2015, . 675 [RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., 676 and P. Hoffman, "Specification for DNS over Transport 677 Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May 678 2016, . 680 11.3. URIs 682 [1] https://github.com/dohwg/draft-ietf-doh-dns-over-https 684 Appendix A. Previous Work on DNS over HTTP or in Other Formats 686 The following is an incomplete list of earlier work that related to 687 DNS over HTTP/1 or representing DNS data in other formats. 689 The list includes links to the tools.ietf.org site (because these 690 documents are all expired) and web sites of software. 692 o https://tools.ietf.org/html/draft-mohan-dns-query-xml 694 o https://tools.ietf.org/html/draft-daley-dnsxml 696 o https://tools.ietf.org/html/draft-dulaunoy-dnsop-passive-dns-cof 698 o https://tools.ietf.org/html/draft-bortzmeyer-dns-json 700 o https://www.nlnetlabs.nl/projects/dnssec-trigger/ 702 Authors' Addresses 704 Paul Hoffman 705 ICANN 707 Email: paul.hoffman@icann.org 709 Patrick McManus 710 Mozilla 712 Email: pmcmanus@mozilla.com