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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: March 13, 2021 P. Hoffman 7 ICANN 8 September 9, 2020 10 DNS Query Name Minimisation to Improve Privacy 11 draft-ietf-dnsop-rfc7816bis-05 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 March 13, 2021. 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 . . . . . . . . . . . . . . . . . 6 69 4. Limit number of queries . . . . . . . . . . . . . . . . . . . 7 70 5. Operational Considerations . . . . . . . . . . . . . . . . . 8 71 6. Performance Considerations . . . . . . . . . . . . . . . . . 10 72 7. Alternative Methods for QNAME Minimisation . . . . . . . . . 10 73 8. Results of the Experimentation . . . . . . . . . . . . . . . 11 74 9. Security Considerations . . . . . . . . . . . . . . . . . . . 11 75 10. Implementation Status . . . . . . . . . . . . . . . . . . . . 11 76 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 77 11.1. Normative References . . . . . . . . . . . . . . . . . . 12 78 11.2. Informative References . . . . . . . . . . . . . . . . . 13 79 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 15 80 Changes from RFC 7816 . . . . . . . . . . . . . . . . . . . . . . 15 81 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15 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 summarised 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 able to authoritatively answer 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 Note that this document relaxes the recommendation to use the NS 166 QTYPE to hide the original QTYPE, as was specified in RFC7816. Using 167 the NS QTYPE is still allowed. The authority of NS records lies at 168 the child side. The parent side of the delegation will answer using 169 a referral, like it will do for queries with other QTYPEs. Using the 170 NS QTYPE therefore has no added value over other QTYPEs. 172 The QTYPE to use while minimising queries can be any possible data 173 TYPE RRTYPE ([RFC6895] Section 3.1) for which the authority always 174 lies below the zone cut (i.e. not DS, NSEC, NSEC3, OPT, TSIG, TKEY, 175 ANY, MAILA, MAILB, AXFR, and IXFR), as long as there is no relation 176 between the incoming QTYPE and the selection of the QTYPE to use 177 while minimising. A good candidate is to always use the A QTYPE as 178 this is the least likely to give issues at DNS software and 179 middleboxes that do not properly support all QTYPEs. The QTYPE=A 180 queries will also blend into traffic from non-minimising resolvers, 181 making it in some cases harder to observe that the resolver has QNAME 182 minimisation enabled. Using the QTYPE that occurs most in incoming 183 queries will slightly reduce the number of queries, as there is no 184 extra check needed for delegations on non-apex records. Another 185 potential benefit of using QTYPE=A is that [RFC8305] clients that 186 need answers for both the A and AAAA types will send the AAAA query 187 first. When minimising using QTYPE=A the minimised query might be 188 useful, and now already in the cache, for the happy eyeballs query 189 for the A QTYPE. 191 The minimising resolver works perfectly when it knows the zone cut 192 (zone cuts are described in Section 6 of [RFC2181]). But zone cuts 193 do not necessarily exist at every label boundary. In the name 194 www.foo.bar.example, it is possible that there is a zone cut between 195 "foo" and "bar" but not between "bar" and "example". So, assuming 196 that the resolver already knows the name servers of example, when it 197 receives the query "What is the AAAA record of www.foo.bar.example?", 198 it does not always know where the zone cut will be. To find the 199 zone cut, it will query the example name servers for a record for 200 bar.example. It will get a non-referral answer, it has to query the 201 example name servers again with one more label, and so on. 202 (Section 2.1 describes this algorithm in deeper detail.) 204 Stub- and forwarding resolvers MAY implement QNAME minimisation. 205 Minimising queries that will be sent to an upstream resolver does not 206 help in hiding data from the upstream resolver, as all information 207 will end up there anyway. It might, however, limit the data exposure 208 between the upstream resolver and the authoritative nameserver in the 209 situation where the upstream resolver does not support QNAME 210 minimisation. Note that, unless the stub- or forwarding resolvers 211 implement a mechanism to find and cache zone cuts, this will increase 212 the number of outgoing queries drastically. 214 2.1. Algorithm to Perform Aggressive Method QNAME Minimisation 216 This algorithm performs name resolution with aggressive method QNAME 217 minimisation in the presence of zone cuts that are not yet known. 219 Although a validating resolver already has the logic to find the 220 zone cuts, implementers of other resolvers may want to use this 221 algorithm to locate the zone cuts. 223 (0) If the query can be answered from the cache, do so; otherwise, 224 iterate as follows: 226 (1) Get the closest delegation point that can be used for the 227 original QNAME/QTYPE combination from the cache. 229 (1a) For queries with QTYPE=DS this is the NS RRset with the 230 owner matching the most labels with the QNAME stripped by 231 one label. The QNAME will be a subdomain of (but not equal 232 to) this NS RRset. Call this ANCESTOR. 234 (1b) For queries with other original QTYPEs this is the NS RRset 235 with the owner matching the most labels with the QNAME. The 236 QNAME will be equal to or a subdomain of this NS RRset. 237 Call this ANCESTOR. 239 (2) Initialise CHILD to the same as ANCESTOR. 241 (3) If CHILD is the same as the QNAME, or if the CHILD is one label 242 shorter than the QNAME and the original QTYPE is DS, resolve the 243 original query using ANCESTOR's name servers, and finish. 245 (4) Otherwise, add a label from the QNAME to the start of CHILD. 247 (5) Look for a cache entry for the RRset at CHILD with hidden QTYPE. 248 If this entry is for an NXDOMAIN and the resolver has support for 249 RFC8020 the NXDOMAIN can be used in response to the original 250 query, and stop. If the entry is for a NOERROR answer go back to 251 step 3. If the entry is for an NXDOMAIN answer and the resolver 252 does not support RFC8020, go back to step 3. 254 (6) Query for CHILD with the minimised QTYPE using ANCESTOR's 255 name servers. The response can be: 257 (6a) A referral. Cache the NS RRset from the authority section, 258 and go back to step 1. 260 (6b) A NOERROR answer. Cache this answer, and go back to step 3. 262 (6c) An NXDOMAIN answer. Return an NXDOMAIN answer in response 263 to the original query, and stop. 265 (6d) An answer with another RCODE, or no answer. Try another 266 name server at the same delegation point. Stop if none of 267 them are able to return a valid answer. 269 3. QNAME Minimisation Examples 271 For example, a resolver receives a request to resolve 272 foo.bar.baz.example. Assume that the resolver already knows that 273 ns1.nic.example is authoritative for .example, and that the resolver 274 does not know a more specific authoritative name server. It will 275 send the query with QNAME=baz.example and the QTYPE selected to hide 276 the original QTYPE to ns1.nic.example. 278 Here are more detailed examples of queries with the aggressive method 279 of QNAME minimisation: 281 Cold cache, traditional resolution algorithm without QNAME 282 minimisation, request for MX record of a.b.example.org: 284 QTYPE QNAME TARGET NOTE 285 MX a.b.example.org root nameserver 286 MX a.b.example.org org nameserver 287 MX a.b.example.org example.org nameserver 289 Cold cache, aggressive QNAME minimisation method, request for MX 290 record of a.b.example.org, using the A QTYPE to hide the original 291 QTYPE: 293 QTYPE QNAME TARGET NOTE 294 A org root nameserver 295 A example.org org nameserver 296 A b.example.org example.org nameserver 297 A a.b.example.org example.org nameserver "a" may be delegated 298 MX a.b.example.org example.org nameserver 300 Note that in above example one query would have been saved if the 301 incoming QTYPE would have been the same as the QTYPE selected by the 302 resolver to hide the original QTYPE. Only one query needed with as 303 QTYPE a.b.example.org would have been needed if the original QTYPE 304 would have been A. Using the most used QTYPE to hide the original 305 QTYPE therefore slightly reduces the number of outgoing queries. 307 Warm cache with only org delegation known, (example.org's NS RRset is 308 not known), aggressive QNAME minimisation method, request for MX 309 record of a.b.example.org, using A QTYPE to hide the original QTYPE: 311 QTYPE QNAME TARGET NOTE 312 A example.org org nameserver 313 A b.example.org example.org nameserver 314 A a.b.example.org example.org nameserver "a" may be delegated 315 MX a.b.example.org example.org nameserver 317 4. Limit number of queries 319 When using QNAME minimisation the number of labels in the received 320 QNAME can influence the number of queries sent from the resolver. 321 This opens an attack vector and can decrease performance. Resolvers 322 supporting QNAME minimisation MUST implement a mechanism to limit the 323 number of outgoing queries per user request. 325 Take for example an incoming QNAME with many labels, like 326 www.host.group.department.example.com, where 327 host.group.department.example.com is hosted on example.com's 328 name servers. Assume a resolver that knows only the name servers of 329 example.com. Without QNAME minimisation, it would send these 330 example.com name servers a query for 331 www.host.group.department.example.com and immediately get a specific 332 referral or an answer, without the need for more queries to probe for 333 the zone cut. For such a name, a cold resolver with QNAME 334 minimisation will, depending on how QNAME minimisation is 335 implemented, send more queries, one per label. Once the cache is 336 warm, there will be no difference with a traditional resolver. 337 Actual testing is described in [Huque-QNAME-Min]. Such deep domains 338 are especially common under ip6.arpa. 340 This behaviour can be exploited by sending queries with a large 341 number of labels in the QNAME that will be answered using a wildcard 342 record. Take for example a record for *.example.com, hosted on 343 example.com's name servers. An incoming query containing a QNAME 344 with more than 100 labels, ending in example.com, will result in a 345 query per label. By using random labels the attacker can bypass the 346 cache and always require the resolver to send many queries upstream. 347 Note that [RFC8198] can limit this attack in some cases. 349 One mechanism to reduce this attack vector is by appending more than 350 one label per iteration for QNAMEs with a large number of labels. To 351 do this a maximum number of QNAME minimisation iterations has to be 352 selected (MAX_MINIMISE_COUNT), a good value is 10. Optionally a 353 value for the number of queries that should only have one label 354 appended can be selected (MINIMISE_ONE_LAB), a good value is 4. The 355 assumption here is that the number of labels on delegations higher in 356 the hierarchy are rather small, therefore not exposing too may labels 357 early on has the most privacy benefit. 359 When a resolver needs to send out a query if will look for the 360 closest known delegation point in its cache. The number of QNAME 361 minimisation iterations is the difference between this closest 362 nameserver and the incoming QNAME. The first MINIMISE_ONE_LAB 363 iterations will be handles as described in Section 2. The number of 364 labels that are not exposed yet now need to be divided over the 365 iterations that are left (MAX_MINIMISE_COUNT - MINIMISE_ONE_LAB). 366 The remainder of the division should be added to the last iterations. 367 For example, when resolving a QNAME with 18 labels, the number of 368 labels added per iteration are: 1,1,1,1,2,2,2,2,3,3. 370 5. Operational Considerations 372 TODO may be remove the whole section now that it is no longer 373 experimental? 375 QNAME minimisation is legal, since the original DNS RFCs do not 376 mandate sending the full QNAME. So, in theory, it should work 377 without any problems. However, in practice, some problems may occur 378 (see [Huque-QNAME-Min] for an analysis and [Huque-QNAME-Discuss] for 379 an interesting discussion on this topic). 381 Note that the aggressive method described in this document prevents 382 authoritative servers other than the server for a full name from 383 seeing information about the relative use of the various QTYPEs. 384 That information may be interesting for researchers (for instance, if 385 they try to follow IPv6 deployment by counting the percentage of AAAA 386 vs. A queries). 388 Some broken name servers do not react properly to QTYPE=NS requests. 389 For instance, some authoritative name servers embedded in load 390 balancers reply properly to A queries but send REFUSED to NS queries. 391 This behaviour is a protocol violation, and there is no need to stop 392 improving the DNS because of such behaviour. Such a setup breaks 393 more than just QNAME minimisation. It breaks negative answers, since 394 the servers don't return the correct SOA, and it also breaks anything 395 dependent upon NS and SOA records existing at the top of the zone. 396 Note that this document relaxes the recommendation to use the NS 397 QTYPE. 399 A problem can also appear when a name server does not react properly 400 to ENTs (Empty Non-Terminals). If ent.example.com has no resource 401 records but foobar.ent.example.com does, then ent.example.com is an 402 ENT. Whatever the QTYPE, a query for ent.example.com must return 403 NODATA (NOERROR / ANSWER: 0). However, some name servers incorrectly 404 return NXDOMAIN for ENTs. If a resolver queries only 405 foobar.ent.example.com, everything will be OK, but if it implements 406 QNAME minimisation, it may query ent.example.com and get an NXDOMAIN. 407 See also Section 3 of [DNS-Res-Improve] for the other bad 408 consequences of this bad behaviour. 410 A possible solution, currently implemented in Knot or Unbound, is to 411 retry with the full query when you receive an NXDOMAIN. It works, 412 but it is not ideal for privacy. 414 Other practices that do not conform to the DNS protocol standards may 415 pose a problem: there is a common DNS trick used by some web hosters 416 that also do DNS hosting that exploits the fact that the DNS protocol 417 (pre-DNSSEC) allows certain serious misconfigurations, such as parent 418 and child zones disagreeing on the location of a zone cut. 419 Basically, they have a single zone with wildcards for each TLD, like: 421 *.example. 60 IN A 192.0.2.6 423 (They could just wildcard all of "*.", which would be sufficient. It 424 is impossible to tell why they don't do it.) 426 This lets them have many web-hosting customers without having to 427 configure thousands of individual zones on their name servers. They 428 just tell the prospective customer to point their NS records at the 429 hoster's name servers, and the web hoster doesn't have to provision 430 anything in order to make the customer's domain resolve. NS queries 431 to the hoster will therefore not give the right result, which may 432 endanger QNAME minimisation (it will be a problem for DNSSEC, too). 433 Note that this document relaxes the NS QTYPE recommendation. 435 6. Performance Considerations 437 The main goal of QNAME minimisation is to improve privacy by sending 438 less data. However, it may have other advantages. For instance, if 439 a resolver sends a root name server queries for A.example followed by 440 B.example followed by C.example, the result will be three NXDOMAINs, 441 since .example does not exist in the root zone. When using QNAME 442 minimisation, the resolver would send only one question (for .example 443 itself) to which they could answer NXDOMAIN. The resolver can cache 444 this answer and use it as to prove that nothing below .example exists 445 ([RFC8020]). A resolver now knows a priori that neither B.example 446 nor C.example exist. Thus, in this common case, the total number of 447 upstream queries under QNAME minimisation could counterintuitively be 448 less than the number of queries under the traditional iteration (as 449 described in the DNS standard). 451 QNAME minimisation may also improve lookup performance for TLD 452 operators. For a TLD that is delegation-only, a two-label QNAME 453 query may be optimal for finding the delegation owner name, depending 454 on the way domain matching is implemented. 456 QNAME minimisation can increase the number of queries based on the 457 incoming QNAME. This is described in Section 4. 459 7. Alternative Methods for QNAME Minimisation 461 One useful optimisation may be, in the spirit of the HAMMER idea 462 [HAMMER], The resolver can probe in advance for the introduction of 463 zone cuts where none previously existed to confirm their continued 464 absence or to discover them. 466 To reduce the number of queries (an issue described in Section 4), a 467 resolver could always use full name queries when the cache is cold 468 and then to move to the aggressive method of QNAME minimisation when 469 the cache is warm. (Precisely defining what is "warm" or "cold" is 470 left to the implementer). This will decrease the privacy for initial 471 queries but will guarantee no degradation of performance. 473 Another possible algorithm, not fully studied at this time, could be 474 to "piggyback" on the traditional resolution code. At startup, it 475 sends traditional full QNAMEs and learns the zone cuts from the 476 referrals received, then switches to NS queries asking only for the 477 minimum domain name. This leaks more data but could require fewer 478 changes in the existing resolver codebase. 480 8. Results of the Experimentation 482 Many (open source) resolvers now support QNAME minimisation. The 483 lessons learned from implementing QNAME minimisation are used to 484 create this new revision. 486 Data from DNSThought [dnsthought-qnamemin] shows that 47% of the 487 tested resolvers support QNAME minimisation in some way. 489 Academic research has been performed on QNAME minimisation 490 [devries-qnamemin]. This work shows that QNAME minimisation in 491 relaxed mode causes almost no problems. The paper recommends using 492 the A QTYPE, and limiting the number of queries in some way. 494 9. Security Considerations 496 QNAME minimisation's benefits are clear in the case where you want to 497 decrease exposure to the authoritative name server. But minimising 498 the amount of data sent also, in part, addresses the case of a wire 499 sniffer as well as the case of privacy invasion by the servers. 500 (Encryption is of course a better defense against wire sniffers, but, 501 unlike QNAME minimisation, it changes the protocol and cannot be 502 deployed unilaterally. Also, the effect of QNAME minimisation on 503 wire sniffers depends on whether the sniffer is on the DNS path.) 505 QNAME minimisation offers zero protection against the recursive 506 resolver, which still sees the full request coming from the stub 507 resolver. 509 All the alternatives mentioned in Section 7 decrease privacy in the 510 hope of improving performance. They must not be used if you want 511 maximum privacy. 513 10. Implementation Status 515 \[\[ Note to RFC Editor: Remove this entire section, and the 516 reference to RFC 7942, before publication. \]\] 518 This section records the status of known implementations of the 519 protocol defined by this specification at the time of posting of this 520 Internet-Draft, and is based on a proposal described in [RFC7942]. 521 The description of implementations in this section is intended to 522 assist the IETF in its decision processes in progressing drafts to 523 RFCs. Please note that the listing of any individual implementation 524 here does not imply endorsement by the IETF. Furthermore, no effort 525 has been spent to verify the information presented here that was 526 supplied by IETF contributors. This is not intended as, and must not 527 be construed to be, a catalog of available implementations or their 528 features. Readers are advised to note that other implementations may 529 exist. 531 According to [RFC7942], "this will allow reviewers and working groups 532 to assign due consideration to documents that have the benefit of 533 running code, which may serve as evidence of valuable experimentation 534 and feedback that have made the implemented protocols more mature. 535 It is up to the individual working groups to use this information as 536 they see fit". 538 Unbound has had a QNAME minimisation feature since version 1.5.7, 539 December 2015, (see [Dolmans-Unbound]) and it has had QNAME 540 minimisation turned default since version 1.7.2, June 2018. It has 541 two modes set by the "qname-minimisation-strict" configuration 542 option. In strict mode (option set to "yes"), there is no workaround 543 for broken authoritative name servers. In lax mode, Unbound retries 544 when there is a NXDOMAIN response from the minimised query, unless 545 the domain is DNSSEC signed. Since November 2016, Unbound uses only 546 queries for the A RRtype and not the NS RRtype. Unbound limits the 547 number of queries in the way proposed in Section 4. 549 Knot Resolver has had a QNAME minimisation feature since version 550 1.0.0, May 2016, and it is activated by default 552 TODO, how does knot limit queries? How does knot handle NXDOMAIN on 553 ENT? Which QTYPE does knot use to hide the incoming QTYPE? 555 BIND has had a QNAME minimisation feature since unstable development 556 version 9.13.2, July 2018. It currently has several modes, with or 557 without workarounds for broken authoritative name servers. 559 TODO, how does bind limit queries? How does bind handle NXDOMAIN on 560 ENT? Which QTYPE does bind use to hide the incoming QTYPE? 562 TODO: add powerdns. They now also support QNAME minimisation. 564 TODO: are there closed source implementations? 566 11. References 568 11.1. Normative References 570 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 571 STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, 572 . 574 [RFC1035] Mockapetris, P., "Domain names - implementation and 575 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 576 November 1987, . 578 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 579 Requirement Levels", BCP 14, RFC 2119, 580 DOI 10.17487/RFC2119, March 1997, 581 . 583 [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 584 Morris, J., Hansen, M., and R. Smith, "Privacy 585 Considerations for Internet Protocols", RFC 6973, 586 DOI 10.17487/RFC6973, July 2013, 587 . 589 [RFC7816] Bortzmeyer, S., "DNS Query Name Minimisation to Improve 590 Privacy", RFC 7816, DOI 10.17487/RFC7816, March 2016, 591 . 593 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 594 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 595 May 2017, . 597 11.2. Informative References 599 [devries-qnamemin] 600 "A First Look at QNAME Minimization in the Domain Name 601 System", March 2019, 602 . 605 [DNS-Res-Improve] 606 Vixie, P., Joffe, R., and F. Neves, "Improvements to DNS 607 Resolvers for Resiliency, Robustness, and Responsiveness", 608 Work in Progress, draft-vixie-dnsext-resimprove-00, June 609 2010. 611 [dnsthought-qnamemin] 612 "DNSThought QNAME minimisation results. Using Atlas 613 probes", March 2020, 614 . 616 [Dolmans-Unbound] 617 Dolmans, R., "Unbound QNAME minimisation @ DNS-OARC", 618 March 2016, . 622 [HAMMER] Kumari, W., Arends, R., Woolf, S., and D. Migault, "Highly 623 Automated Method for Maintaining Expiring Records", Work 624 in Progress, draft-wkumari-dnsop-hammer-01, July 2014. 626 [Huque-QNAME-Discuss] 627 Huque, S., "Qname Minimization @ DNS-OARC", May 2015, 628 . 630 [Huque-QNAME-Min] 631 Huque, S., "Query name minimization and authoritative 632 server behavior", May 2015, 633 . 635 [I-D.bortzmeyer-dprive-rfc7626-bis] 636 Bortzmeyer, S. and S. Dickinson, "DNS Privacy 637 Considerations", draft-bortzmeyer-dprive-rfc7626-bis-02 638 (work in progress), January 2019. 640 [I-D.ietf-dnsop-terminology-bis] 641 Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS 642 Terminology", draft-ietf-dnsop-terminology-bis-14 (work in 643 progress), September 2018. 645 [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS 646 Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997, 647 . 649 [RFC6895] Eastlake 3rd, D., "Domain Name System (DNS) IANA 650 Considerations", BCP 42, RFC 6895, DOI 10.17487/RFC6895, 651 April 2013, . 653 [RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running 654 Code: The Implementation Status Section", BCP 205, 655 RFC 7942, DOI 10.17487/RFC7942, July 2016, 656 . 658 [RFC8020] Bortzmeyer, S. and S. Huque, "NXDOMAIN: There Really Is 659 Nothing Underneath", RFC 8020, DOI 10.17487/RFC8020, 660 November 2016, . 662 [RFC8198] Fujiwara, K., Kato, A., and W. Kumari, "Aggressive Use of 663 DNSSEC-Validated Cache", RFC 8198, DOI 10.17487/RFC8198, 664 July 2017, . 666 [RFC8305] Schinazi, D. and T. Pauly, "Happy Eyeballs Version 2: 667 Better Connectivity Using Concurrency", RFC 8305, 668 DOI 10.17487/RFC8305, December 2017, 669 . 671 Acknowledgments 673 TODO (refer to 7816) 675 Changes from RFC 7816 677 Changed in -04 679 o Start structure for implementation section 681 o Add clarification why the used QTYPE does not matter 683 o Make algorithm DS QTYPE compatible 685 Changed in -03 687 o Drop recommendation to use the NS QTYPE to hide the incoming QTYPE 689 o Describe DoS attach vector for QNAME with large number of labels, 690 and propose a mitigation. 692 o Simplify examples and change qname to a.b.example.com to show the 693 change in number of queries. 695 Changed in -00, -01, and -02 697 o Made changes to deal with errata #4644 699 o Changed status to be on standards track 701 o Major reorganization 703 Authors' Addresses 705 Stephane Bortzmeyer 706 AFNIC 707 1, rue Stephenson 708 Montigny-le-Bretonneux 78180 709 France 711 Phone: +33 1 39 30 83 46 712 Email: bortzmeyer+ietf@nic.fr 713 URI: https://www.afnic.fr/ 714 Ralph Dolmans 715 NLnet Labs 717 Email: ralph@nlnetlabs.nl 719 Paul Hoffman 720 ICANN 722 Email: paul.hoffman@icann.org