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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group S. Bortzmeyer 3 Internet-Draft AFNIC 4 Obsoletes: 7816 (if approved) R. Dolmans 5 Intended status: Standards Track NLnet Labs 6 Expires: September 7, 2020 P. Hoffman 7 ICANN 8 March 6, 2020 10 DNS Query Name Minimisation to Improve Privacy 11 draft-ietf-dnsop-rfc7816bis-03 13 Abstract 15 This document describes techniques called "QNAME minimisation" to 16 improve DNS privacy, where the DNS resolver no longer always sends 17 the full original QNAME to the upstream name server. This document 18 obsoletes RFC 7816. 20 This document is part of the IETF DNSOP (DNS Operations) Working 21 Group. The source of the document, as well as a list of open issues, 22 is at 24 NOTE FOR THE DNSOP WORKING GROUP: There is still much work to be done 25 in this draft. Future versions of this draft will contain 26 descriptions of different minimisation implementation choices that 27 have been made since the RFC 7816 first came out, as well as 28 deployment experience. 30 Status of This Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at https://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on September 7, 2020. 47 Copyright Notice 49 Copyright (c) 2020 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (https://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the Simplified BSD License. 62 Table of Contents 64 1. Introduction and Background . . . . . . . . . . . . . . . . . 2 65 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 66 2. Description of QNAME Minimisation . . . . . . . . . . . . . . 3 67 2.1. Algorithm to Perform Aggressive Method QNAME Minimisation 5 68 3. QNAME Minimisation Examples . . . . . . . . . . . . . . . . . 5 69 4. Limit number of queries . . . . . . . . . . . . . . . . . . . 6 70 5. Operational Considerations . . . . . . . . . . . . . . . . . 7 71 6. Performance Considerations . . . . . . . . . . . . . . . . . 9 72 7. Alternative Methods for QNAME Minimisation . . . . . . . . . 10 73 8. Results of the Experimentation . . . . . . . . . . . . . . . 10 74 9. Security Considerations . . . . . . . . . . . . . . . . . . . 10 75 10. Implementation Status . . . . . . . . . . . . . . . . . . . . 11 76 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 77 11.1. Normative References . . . . . . . . . . . . . . . . . . 12 78 11.2. Informative References . . . . . . . . . . . . . . . . . 13 79 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 14 80 Changes from RFC 7816 . . . . . . . . . . . . . . . . . . . . . . 14 81 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 83 1. Introduction and Background 85 The problem statement for this document and its predecessor [RFC7816] 86 is described in [I-D.bortzmeyer-dprive-rfc7626-bis]. The terminology 87 ("QNAME", "resolver", etc.) is defined in 88 [I-D.ietf-dnsop-terminology-bis]. This specific solution is not 89 intended to fully solve the DNS privacy problem; instead, it should 90 be viewed as one tool amongst many. 92 QNAME minimisation follows the principle explained in Section 6.1 of 93 [RFC6973]: the less data you send out, the fewer privacy problems 94 you have. 96 Before QNAME minimisation, when a resolver received the query "What 97 is the AAAA record for www.example.com?", it sent to the root 98 (assuming a resolver whose cache is empty) the very same question. 99 Sending the full QNAME to the authoritative name server was a 100 tradition, not a protocol requirement. In a conversation with the 101 author in January 2015, Paul Mockapetris explained that this 102 tradition comes from a desire to optimise the number of requests, 103 when the same name server is authoritative for many zones in a given 104 name (something that was more common in the old days, where the same 105 name servers served .com and the root) or when the same name server 106 is both recursive and authoritative (something that is strongly 107 discouraged now). Whatever the merits of this choice at this time, 108 the DNS is quite different now. 110 QNAME minimisation is compatible with the current DNS system and 111 therefore can easily be deployed. Because it is only a change to the 112 way that the resolver operates, it does not change the protocol. The 113 behaviour suggested here (minimising the amount of data sent in 114 QNAMEs from the resolver) is allowed by Section 5.3.3 of [RFC1034] or 115 Section 7.2 of [RFC1035]. 117 1.1. Terminology 119 A "cold" cache is one that is empty, having literally no entries in 120 it. A "warm" cache is one that has some entries in it. 122 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 123 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 124 "OPTIONAL" in this document are to be interpreted as described in BCP 125 14 [RFC2119] [RFC8174] when, and only when, they appear in all 126 capitals, as shown here. 128 2. Description of QNAME Minimisation 130 The idea behind QNAME minimisation is to minimise the amount of 131 privacy sensitive data sent from the DNS resolver to the 132 authoritative name server. This section describes the RECOMMENDED 133 way to do QNAME minimisation -- the way that maximises privacy 134 benefits. That algorithm is summarized in Section 2.1. 136 When a resolver is not able to answer a query from cache it has to 137 send a query to an authoritative nameserver. Traditionally these 138 queries would contain the full QNAME and the original QTYPE as 139 received in the client query. The full QNAME and original QTYPE are 140 only needed at the nameserver that is authoritative for the record 141 requested by the client. All other nameservers queried while 142 resolving the query only need to receive enough of the QNAME to be 143 able to answer with a delegation. The QTYPE in these queries is not 144 relevant, as the nameserver is not authoritative to answer with the 145 records the client is looking for. Sending the full QNAME and 146 original QTYPE to these nameservers therefore exposes more privacy 147 sensitive data than necessary to resolve the client's request. A 148 resolver that implements QNAME minimisation changes the QNAME and 149 QTYPE in queries to authoritative nameserver that are not known to be 150 responsible for the original QNAME. These request are done with: 152 o a QTYPE selected by the resolver to hide the original QTYPE 154 o the QNAME that is the original QNAME, stripped to just one label 155 more than the longest matching domain name for which the 156 nameserver is known to be authoritative 158 This method is called the "aggressive method" in this document 159 because the resolver won't expose the original QTYPE to nameservers 160 that are not known to be responsible for the desired name. This 161 method is the safest from a privacy point of view, and is thus the 162 RECOMMENDED method for this document. Other methods are described in 163 Section 7. 165 The QTYPE to use while minimising queries can be any possible data 166 TYPE RRTYPE (rfc6895 #3.1) for which the authority always lies below 167 the zone cut (i.e. not DS, NSEC, NSEC3, OPT, TSIG, TKEY, ANY, MAILA, 168 MAILB, AXFR, and IXFR), as long as there is no relation between the 169 incoming QTYPE and the selection of the QTYPE to use while 170 minimising. A good candidate is to always use the A QTYPE as this is 171 the least likely to give issues at DNS software and middleboxes that 172 do not properly support all QTYPEs. The QTYPE=A queries will also 173 blend into traffic from non-minimising resolvers, making it in some 174 cases harder to observe that the resolving has QNAME minimisation 175 enabled. 177 The minimising resolver works perfectly when it knows the zone cut 178 (zone cuts are described in Section 6 of [RFC2181]). But zone cuts 179 do not necessarily exist at every label boundary. In the name 180 www.foo.bar.example, it is possible that there is a zone cut between 181 "foo" and "bar" but not between "bar" and "example". So, assuming 182 that the resolver already knows the name servers of example, when it 183 receives the query "What is the AAAA record of www.foo.bar.example?", 184 it does not always know where the zone cut will be. To find the 185 zone cut, it will query the example name servers for a record for 186 bar.example. It will get a non-referral answer, it has to query the 187 example name servers again with one more label, and so on. 188 (Section 2.1 describes this algorithm in deeper detail.) 190 2.1. Algorithm to Perform Aggressive Method QNAME Minimisation 192 This algorithm performs name resolution with aggressive method QNAME 193 minimisation in the presence of zone cuts that are not yet known. 195 Although a validating resolver already has the logic to find the 196 zone cuts, implementers of other resolvers may want to use this 197 algorithm to locate the zone cuts. 199 (0) If the query can be answered from the cache, do so; otherwise, 200 iterate as follows: 202 (1) Get the closest delegation point that can be used for QNAME from 203 the cache. This is the NS RRset with the owner matching the most 204 labels with the QNAME. The QNAME will be equal to or a subdomain 205 of this NS RRset. Call this ANCESTOR. 207 (2) Initialise CHILD to the same as ANCESTOR. 209 (3) If CHILD is the same as the QNAME, resolve the original query 210 using ANCESTOR's name servers, and finish. 212 (4) Otherwise, add a label from the QNAME to the start of CHILD. 214 (5) Look for a negative cache entry for the NS RRset at CHILD. If 215 this entry is for an NXDOMAIN and the resolver has support for 216 RFC8020 the NXDOMAIN can be used in response to the original 217 query, and stop. If the entry is for a NOERROR/NODATA answer go 218 back to step 3 220 (6) Query for CHILD with the minimised QTYPE using ANCESTOR's 221 name servers. The response can be: 223 (6a) A referral. Cache the NS RRset from the authority section, 224 and go back to step 1. 226 (6b) A NOERROR answer. Cache this answer, and go back to step 3. 228 (6c) An NXDOMAIN answer. Return an NXDOMAIN answer in response 229 to the original query, and stop. 231 3. QNAME Minimisation Examples 233 For example, a resolver receives a request to resolve 234 foo.bar.baz.example. Assume that the resolver already knows that 235 ns1.nic.example is authoritative for .example, and that the resolver 236 does not know a more specific authoritative name server. It will 237 send the query QTYPE=NS, QNAME=baz.example to ns1.nic.example. 239 Here are more detailed examples of queries with the aggressive method 240 of QNAME minimisation: 242 Cold cache, traditional resolution algorithm without QNAME 243 minimisation, request for A record of a.b.example.org: 245 QTYPE QNAME TARGET NOTE 246 A a.b.example.org root nameserver 247 A a.b.example.org org nameserver 248 A a.b.example.org example.org nameserver 250 Cold cache, aggressive QNAME minimisation method, request for A 251 record of a.b.example.org, using NS QTYPE to hide the original QTYPE: 253 QTYPE QNAME TARGET NOTE 254 NS org root nameserver 255 NS example.org org nameserver 256 NS b.example.org example.org nameserver 257 NS a.b.example.org example.org nameserver "a" may be delegated 258 A a.b.example.org example.org nameserver 260 Warm cache with only org delegation known, (example.org's NS RRset is 261 not known), aggressive QNAME minimisation method, request for A 262 record of a.b.example.org, using NS QTYPE to hide the original QTYPE: 264 QTYPE QNAME TARGET NOTE 265 NS example.org org nameserver 266 NS b.example.org example.org nameserver 267 NS a.b.example.org example.org nameserver "a" may be delegated 268 A a.b.example.org example.org nameserver 270 4. Limit number of queries 272 When using QNAME minimisation the number of labels in the received 273 QNAME can influence the number of queries sent from the resolver. 274 This opens an attack vector and can decrease performance. Resolvers 275 supporting QNAME minimisation should implement a mechanism to limit 276 the number of outgoing queries per user request. 278 Take for example an incoming QNAME with many labels, like 279 www.host.group.department.example.com, where 280 host.group.department.example.com is hosted on example.com's 281 name servers). Assume a resolver that knows only the name servers of 282 example.com. Without QNAME minimisation, it would send these 283 example.com name servers a query for 284 www.host.group.department.example.com and immediately get a specific 285 referral or an answer, without the need for more queries to probe for 286 the zone cut. For such a name, a cold resolver with QNAME 287 minimisation will, depending on how QNAME minimisation is 288 implemented, send more queries, one per label. Once the cache is 289 warm, there will be no difference with a traditional resolver. 290 Actual testing is described in [Huque-QNAME-Min]. Such deep domains 291 are especially common under ip6.arpa. 293 This behaviour can be exploited by sending queries with a large 294 number of labels in the QNAME that will be answered using a wildcard 295 record. Take for example a record for *.example.com, hosted on 296 example.com's name servers. An incoming query containing a QNAME 297 with more than 100 labels, ending in example.com, will result in a 298 query per label. By using random labels the attacker can bypass the 299 caching and always require the resolver to send many queries 300 upstream. Note that RFC8198 can limit this attack in some cases. 302 One mechanism to reduce this attack vector is by sending more than 303 one label per iteration for QNAMEs with a large number of labels. To 304 do this a maximum number of QNAME minimisation iterations has to be 305 selected (MAX_MINIMISE_COUNT), a good value is 10. Optionally a 306 value for the number of queries that should only have one label 307 appended can be selected (MINIMISE_ONE_LAB), a good value is 4. The 308 assumption here is that the number of labels on delegations higher in 309 the hierarchy are rather small, therefore not exposing too may labels 310 early on has the most privacy benefit. 312 When a resolver needs to send out a query if will look for the 313 closest known delegation point in its cache. The number of QNAME 314 minimisation iterations is the difference between this closest 315 nameserver and the incoming QNAME. The first MINIMISE_ONE_LAB 316 iterations will be handles as described in Section 2. The number of 317 labels that are not exposed yet now need to be divided over the 318 iterations that are left (MAX_MINIMISE_COUNT - MINIMISE_ONE_LAB). 319 The remainder of the division should be added to the last iterations. 320 For example, when resolving a QNAME with 18 labels, the number of 321 labels added per iteration are: 1,1,1,1,2,2,2,2,3,3. 323 5. Operational Considerations 325 TODO may be remove the whole section now that it is no longer 326 experimental? 328 QNAME minimisation is legal, since the original DNS RFCs do not 329 mandate sending the full QNAME. So, in theory, it should work 330 without any problems. However, in practice, some problems may occur 331 (see [Huque-QNAME-Min] for an analysis and [Huque-QNAME-Discuss] for 332 an interesting discussion on this topic). 334 Note that the aggressive method described in this document prevents 335 authoritative servers other than the server for a full name from 336 seeing information about the relative use of the various QTYPEs. 337 That information may be interesting for researchers (for instance, if 338 they try to follow IPv6 deployment by counting the percentage of AAAA 339 vs. A queries). 341 Some broken name servers do not react properly to QTYPE=NS requests. 342 For instance, some authoritative name servers embedded in load 343 balancers reply properly to A queries but send REFUSED to NS queries. 344 This behaviour is a protocol violation, and there is no need to stop 345 improving the DNS because of such behaviour. However, QNAME 346 minimisation may still work with such domains, since they are only 347 leaf domains (no need to send them NS requests). Such a setup breaks 348 more than just QNAME minimisation. It breaks negative answers, since 349 the servers don't return the correct SOA, and it also breaks anything 350 dependent upon NS and SOA records existing at the top of the zone. 352 Another way to deal with such incorrect name servers would be to try 353 with QTYPE=A requests (A being chosen because it is the most common 354 and hence a QTYPE that will always be accepted, while a QTYPE NS may 355 ruffle the feathers of some middleboxes). Instead of querying 356 name servers with a query "NS example.com", a resolver could use 357 "A _.example.com" and see if it gets a referral. TODO this is what 358 Unbound does 360 A problem can also appear when a name server does not react properly 361 to ENTs (Empty Non-Terminals). If ent.example.com has no resource 362 records but foobar.ent.example.com does, then ent.example.com is an 363 ENT. Whatever the QTYPE, a query for ent.example.com must return 364 NODATA (NOERROR / ANSWER: 0). However, some name servers incorrectly 365 return NXDOMAIN for ENTs. If a resolver queries only 366 foobar.ent.example.com, everything will be OK, but if it implements 367 QNAME minimisation, it may query ent.example.com and get an NXDOMAIN. 368 See also Section 3 of [DNS-Res-Improve] for the other bad 369 consequences of this bad behaviour. 371 A possible solution, currently implemented in Knot or Unbound, is to 372 retry with the full query when you receive an NXDOMAIN. It works, 373 but it is not ideal for privacy. 375 Other practices that do not conform to the DNS protocol standards may 376 pose a problem: there is a common DNS trick used by some web hosters 377 that also do DNS hosting that exploits the fact that the DNS protocol 378 (pre-DNSSEC) allows certain serious misconfigurations, such as parent 379 and child zones disagreeing on the location of a zone cut. 380 Basically, they have a single zone with wildcards for each TLD, like: 382 *.example. 60 IN A 192.0.2.6 384 (They could just wildcard all of "*.", which would be sufficient. It 385 is impossible to tell why they don't do it.) 387 This lets them have many web-hosting customers without having to 388 configure thousands of individual zones on their name servers. They 389 just tell the prospective customer to point their NS records at the 390 hoster's name servers, and the web hoster doesn't have to provision 391 anything in order to make the customer's domain resolve. NS queries 392 to the hoster will therefore not give the right result, which may 393 endanger QNAME minimisation (it will be a problem for DNSSEC, too). 395 TODO report by Akamai about why they return erroneous responses 396 https://mailarchive.ietf.org/arch/msg/dnsop/ 397 XIX16DCe2ln3ZnZai723v32ZIjE 399 TODO what to do if the resolver forwards? Unbound disables QNAME 400 minimisation in that case, since the forwarder will see everything, 401 anyway. What should a minimising resolver do when forwading the 402 request to a forwarder, not to an authoritative name server? Send 403 the full qname? Minimises? (But how since the resolver does not 404 know the zone cut?) 406 The administrators of the forwarders, and of the authoritative 407 name servers, will get less data, which will reduce the utility of 408 the statistics they can produce (such as the percentage of the 409 various QTYPEs). 411 DNS administrators are reminded that the data on DNS requests that 412 they store may have legal consequences, depending on your 413 jurisdiction (check with your local lawyer). 415 6. Performance Considerations 417 The main goal of QNAME minimisation is to improve privacy by sending 418 less data. However, it may have other advantages. For instance, if 419 a resolver sends a root name server queries for A.example followed by 420 B.example followed by C.example, the result will be three NXDOMAINs, 421 since .example does not exist in the root zone. When using QNAME 422 minimisation, the resolver would send only one question (for .example 423 itself) to which they could answer NXDOMAIN, thus opening up a 424 negative caching opportunity in which the full resolver could know a 425 priori that neither B.example nor C.example could exist. Thus, in 426 this common case, the total number of upstream queries under QNAME 427 minimisation could be counterintuitively less than the number of 428 queries under the traditional iteration (as described in the DNS 429 standard). TODO mention [RFC8020]? And [RFC8198], the latter 430 depending on DNSSEC? 432 QNAME minimisation may also improve lookup performance for TLD 433 operators. For a TLD that is delegation-only, a two-label QNAME 434 query may be optimal for finding the delegation owner name, depending 435 on the way domain matching is implemented. 437 QNAME minimisation can increase the number of queries based on the 438 incoming QNAME. This is described in Section 4. 440 7. Alternative Methods for QNAME Minimisation 442 One useful optimisation may be, in the spirit of the HAMMER idea 443 [HAMMER], The resolver can probe in advance for the introduction of 444 zone cuts where none previously existed to confirm their continued 445 absence or to discover them. 447 To reduce the number of queries (an issue described in Section 6), a 448 resolver could always use full name queries when the cache is cold 449 and then to move to the aggressive method of QNAME minimisation when 450 the cache is warm. (Precisely defining what is "warm" or "cold" is 451 left to the implementer). This will decrease the privacy for initial 452 queries but will guarantee no degradation of performance. 454 Another possible algorithm, not fully studied at this time, could be 455 to "piggyback" on the traditional resolution code. At startup, it 456 sends traditional full QNAMEs and learns the zone cuts from the 457 referrals received, then switches to NS queries asking only for the 458 minimum domain name. This leaks more data but could require fewer 459 changes in the existing resolver codebase. 461 8. Results of the Experimentation 463 TODO various experiences from actual deployments, problems heard. 464 TODO the Knot bug #339 https://gitlab.labs.nic.cz/knot/knot-resolver/ 465 issues/339? TODO Problems with AWS https://forums.aws.amazon.com/ 466 thread.jspa?threadID=269116? 468 9. Security Considerations 470 QNAME minimisation's benefits are clear in the case where you want to 471 decrease exposure to the authoritative name server. But minimising 472 the amount of data sent also, in part, addresses the case of a wire 473 sniffer as well as the case of privacy invasion by the servers. 474 (Encryption is of course a better defense against wire sniffers, but, 475 unlike QNAME minimisation, it changes the protocol and cannot be 476 deployed unilaterally. Also, the effect of QNAME minimisation on 477 wire sniffers depends on whether the sniffer is on the DNS path.) 479 QNAME minimisation offers zero protection against the recursive 480 resolver, which still sees the full request coming from the stub 481 resolver. 483 All the alternatives mentioned in Section 7 decrease privacy in the 484 hope of improving performance. They must not be used if you want 485 maximum privacy. 487 10. Implementation Status 489 \[\[ Note to RFC Editor: Remove this entire section, and the 490 reference to RFC 7942, before publication. \]\] 492 This section records the status of known implementations of the 493 protocol defined by this specification at the time of posting of this 494 Internet-Draft, and is based on a proposal described in [RFC7942]. 495 The description of implementations in this section is intended to 496 assist the IETF in its decision processes in progressing drafts to 497 RFCs. Please note that the listing of any individual implementation 498 here does not imply endorsement by the IETF. Furthermore, no effort 499 has been spent to verify the information presented here that was 500 supplied by IETF contributors. This is not intended as, and must not 501 be construed to be, a catalog of available implementations or their 502 features. Readers are advised to note that other implementations may 503 exist. 505 According to [RFC7942], "this will allow reviewers and working groups 506 to assign due consideration to documents that have the benefit of 507 running code, which may serve as evidence of valuable experimentation 508 and feedback that have made the implemented protocols more mature. 509 It is up to the individual working groups to use this information as 510 they see fit". 512 Unbound has had a QNAME minimisation feature since version 1.5.7, 513 December 2015, (see [Dolmans-Unbound]) and it has had QNAME 514 minimisation turned default since version 1.7.2, June 2018. It has 515 two modes set by the "qname-minimisation-strict" configuration 516 option. In strict mode (option set to "yes"), there is no workaround 517 for broken authoritative name servers. In lax mode, Unbound retries 518 when there is a NXDOMAIN response from the minimized query. Since 519 November 2016, Unbound uses only queries for the A RRtype and not the 520 NS RRtype. 522 Knot Resolver has had a QNAME minimisation feature since version 523 1.0.0, May 2016, and it is activated by default. 525 BIND has had a QNAME minimisation feature since unstable development 526 version 9.13.2, July 2018. It currently has several modes, with or 527 without workarounds for broken authoritative name servers. 529 The Cloudflare's public resolver at IP address 1.1.1.1 has QNAME 530 minimisation. (It currently uses Knot.) 532 Testing with one thousand RIPE Atlas probes [atlas-qname-min], one 533 can see that QNAME minimisation is now common: 535 % blaeu-resolve --requested 1000 --type TXT qnamemintest.internet.nl 536 ["no - qname minimisation is not enabled on your resolver :("] : 888 occurrences 537 ["hooray - qname minimisation is enabled on your resolver :)!"] : 105 occurrences 538 [ERROR: SERVFAIL] : 3 occurrences 539 Test #16113243 done at 2018-09-14T13:01:47Z 541 10 % of the probes have a resolver with QNAME minimisation (it is not 542 possible to infer the percentage of users having QNAME minimisation). 544 11. References 546 11.1. Normative References 548 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 549 STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, 550 . 552 [RFC1035] Mockapetris, P., "Domain names - implementation and 553 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 554 November 1987, . 556 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 557 Requirement Levels", BCP 14, RFC 2119, 558 DOI 10.17487/RFC2119, March 1997, 559 . 561 [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 562 Morris, J., Hansen, M., and R. Smith, "Privacy 563 Considerations for Internet Protocols", RFC 6973, 564 DOI 10.17487/RFC6973, July 2013, 565 . 567 [RFC7816] Bortzmeyer, S., "DNS Query Name Minimisation to Improve 568 Privacy", RFC 7816, DOI 10.17487/RFC7816, March 2016, 569 . 571 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 572 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 573 May 2017, . 575 11.2. Informative References 577 [atlas-qname-min] 578 Bortzmeyer, S., "DNS resolution of 579 qnamemintest.internet.nl/TXT on RIPE Atlas probes", 580 September 2018, 581 . 583 [DNS-Res-Improve] 584 Vixie, P., Joffe, R., and F. Neves, "Improvements to DNS 585 Resolvers for Resiliency, Robustness, and Responsiveness", 586 Work in Progress, draft-vixie-dnsext-resimprove-00, June 587 2010. 589 [Dolmans-Unbound] 590 Dolmans, R., "Unbound QNAME minimisation @ DNS-OARC", 591 March 2016, . 595 [HAMMER] Kumari, W., Arends, R., Woolf, S., and D. Migault, "Highly 596 Automated Method for Maintaining Expiring Records", Work 597 in Progress, draft-wkumari-dnsop-hammer-01, July 2014. 599 [Huque-QNAME-Discuss] 600 Huque, S., "Qname Minimization @ DNS-OARC", May 2015, 601 . 603 [Huque-QNAME-Min] 604 Huque, S., "Query name minimization and authoritative 605 server behavior", May 2015, 606 . 608 [I-D.bortzmeyer-dprive-rfc7626-bis] 609 Bortzmeyer, S. and S. Dickinson, "DNS Privacy 610 Considerations", draft-bortzmeyer-dprive-rfc7626-bis-02 611 (work in progress), January 2019. 613 [I-D.ietf-dnsop-terminology-bis] 614 Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS 615 Terminology", draft-ietf-dnsop-terminology-bis-14 (work in 616 progress), September 2018. 618 [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS 619 Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997, 620 . 622 [RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running 623 Code: The Implementation Status Section", BCP 205, 624 RFC 7942, DOI 10.17487/RFC7942, July 2016, 625 . 627 [RFC8020] Bortzmeyer, S. and S. Huque, "NXDOMAIN: There Really Is 628 Nothing Underneath", RFC 8020, DOI 10.17487/RFC8020, 629 November 2016, . 631 [RFC8198] Fujiwara, K., Kato, A., and W. Kumari, "Aggressive Use of 632 DNSSEC-Validated Cache", RFC 8198, DOI 10.17487/RFC8198, 633 July 2017, . 635 Acknowledgments 637 TODO (refer to 7816) 639 Changes from RFC 7816 641 o Made changes to deal with errata #4644 643 o Changed status to be on standards track 645 o Major reorganization 647 Authors' Addresses 649 Stephane Bortzmeyer 650 AFNIC 651 1, rue Stephenson 652 Montigny-le-Bretonneux 78180 653 France 655 Phone: +33 1 39 30 83 46 656 Email: bortzmeyer+ietf@nic.fr 657 URI: https://www.afnic.fr/ 659 Ralph Dolmans 660 NLnet Labs 662 Email: ralph@nlnetlabs.nl 663 Paul Hoffman 664 ICANN 666 Email: paul.hoffman@icann.org