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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Downref: Normative reference to an Historic RFC: RFC 5074 ** Downref: Normative reference to an Informational RFC: RFC 7129 ** Obsolete normative reference: RFC 7719 (Obsoleted by RFC 8499) == Outdated reference: draft-ietf-dnsop-nxdomain-cut has been published as RFC 8020 Summary: 3 errors (**), 0 flaws (~~), 2 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group K. Fujiwara 3 Internet-Draft JPRS 4 Updates: 4035 (if approved) A. Kato 5 Intended status: Standards Track Keio/WIDE 6 Expires: April 23, 2017 W. Kumari 7 Google 8 October 20, 2016 10 Aggressive use of NSEC/NSEC3 11 draft-ietf-dnsop-nsec-aggressiveuse-05 13 Abstract 15 The DNS relies upon caching to scale; however, the cache lookup 16 generally requires an exact match. This document specifies the use 17 of NSEC/NSEC3 resource records to allow DNSSEC validating resolvers 18 to generate negative answers within a range, and positive answers 19 from wildcards. This increases performance / decreases latency, 20 decreases resource utilization on both authoritative and recursive 21 servers, and also increases privacy. It may also help increase 22 resilience to certain DoS attacks in some circumstances. 24 This document updates RFC4035 by allowing validating resolvers to 25 generate negative based upon NSEC/NSEC3 records (and positive answers 26 in the presence of wildcards). 28 [ Ed note: Text inside square brackets ([]) is additional background 29 information, answers to frequently asked questions, general musings, 30 etc. They will be removed before publication.This document is being 31 collaborated on in Github at: https://github.com/wkumari/draft-ietf- 32 dnsop-nsec-aggressiveuse. The most recent version of the document, 33 open issues, etc should all be available here. The authors 34 (gratefully) accept pull requests.] 36 Status of This Memo 38 This Internet-Draft is submitted in full conformance with the 39 provisions of BCP 78 and BCP 79. 41 Internet-Drafts are working documents of the Internet Engineering 42 Task Force (IETF). Note that other groups may also distribute 43 working documents as Internet-Drafts. The list of current Internet- 44 Drafts is at http://datatracker.ietf.org/drafts/current/. 46 Internet-Drafts are draft documents valid for a maximum of six months 47 and may be updated, replaced, or obsoleted by other documents at any 48 time. It is inappropriate to use Internet-Drafts as reference 49 material or to cite them other than as "work in progress." 51 This Internet-Draft will expire on April 23, 2017. 53 Copyright Notice 55 Copyright (c) 2016 IETF Trust and the persons identified as the 56 document authors. All rights reserved. 58 This document is subject to BCP 78 and the IETF Trust's Legal 59 Provisions Relating to IETF Documents 60 (http://trustee.ietf.org/license-info) in effect on the date of 61 publication of this document. Please review these documents 62 carefully, as they describe your rights and restrictions with respect 63 to this document. Code Components extracted from this document must 64 include Simplified BSD License text as described in Section 4.e of 65 the Trust Legal Provisions and are provided without warranty as 66 described in the Simplified BSD License. 68 Table of Contents 70 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 71 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 72 3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3 73 4. Background . . . . . . . . . . . . . . . . . . . . . . . . . 4 74 5. Aggressive Negative Caching . . . . . . . . . . . . . . . . . 5 75 5.1. NSEC . . . . . . . . . . . . . . . . . . . . . . . . . . 6 76 5.2. NSEC3 . . . . . . . . . . . . . . . . . . . . . . . . . . 6 77 5.3. Wildcards . . . . . . . . . . . . . . . . . . . . . . . . 7 78 5.4. Consideration on TTL . . . . . . . . . . . . . . . . . . 7 79 6. Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . 7 80 7. Update to RFC 4035 . . . . . . . . . . . . . . . . . . . . . 8 81 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 82 9. Security Considerations . . . . . . . . . . . . . . . . . . . 9 83 10. Implementation Status . . . . . . . . . . . . . . . . . . . . 9 84 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9 85 11.1. Change History . . . . . . . . . . . . . . . . . . . . . 10 86 11.1.1. Version draft-fujiwara-dnsop-nsec-aggressiveuse-01 . 12 87 11.1.2. Version draft-fujiwara-dnsop-nsec-aggressiveuse-02 . 13 88 11.1.3. Version draft-fujiwara-dnsop-nsec-aggressiveuse-03 . 13 89 11.2. new section . . . . . . . . . . . . . . . . . . . . . . 13 90 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 91 12.1. Normative References . . . . . . . . . . . . . . . . . . 13 92 12.2. Informative References . . . . . . . . . . . . . . . . . 14 93 Appendix A. Detailed implementation notes . . . . . . . . . . . 14 94 Appendix B. Procedure for determining ENT vs NXDOMAN . . . . . . 15 95 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 97 1. Introduction 99 A DNS negative cache exists, and is used to cache the fact that a 100 name does not exist. This method of negative caching requires exact 101 matching; this leads to unnecessary additional lookups, increases 102 latency, leads to extra resource utilization on both authoritative 103 and recursive servers, and decreases privacy by leaking queries. 105 This document updates RFC 4035 to allow recursive resolvers to use 106 NSEC/NSEC3 resource records to synthesize negative answers from the 107 information they have in the cache. This allows validating resolvers 108 to respond with NXDOMAIN immediately if the name in question falls 109 into a range expressed by a NSEC/NSEC3 resource record already in the 110 cache. It also allows the synthesis of positive answers in the 111 presence of wildcard records. 113 Aggressive Negative Caching was first proposed in Section 6 of DNSSEC 114 Lookaside Validation (DLV) [RFC5074] in order to find covering NSEC 115 records efficiently. 117 Section 3 of [I-D.vixie-dnsext-resimprove] "Stopping Downward Cache 118 Search on NXDOMAIN" and [I-D.ietf-dnsop-nxdomain-cut] proposed 119 another approach to use NXDOMAIN information effectively. 121 2. Terminology 123 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 124 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 125 document are to be interpreted as described in RFC 2119 [RFC2119]. 127 Many of the specialized terms used in this document are defined in 128 DNS Terminology [RFC7719]. 130 The key words "Closest Encloser" and "Source of Synthesis" in this 131 document are to be interpreted as described in [RFC4592]. 133 "Closest Encloser" is also defined in NSEC3 [RFC5155], as is "Next 134 closer name". 136 3. Problem Statement 138 The DNS negative cache caches negative (non-existent) information, 139 and requires an exact match in most instances [RFC2308]. 141 Assume that the (DNSSEC signed) "example.com" zone contains: 143 albatross.example.com IN A 192.0.2.1 144 elephant.example.com IN A 192.0.2.2 145 zebra.example.com IN A 192.0.2.3 147 If a validating resolver receives a query for cat.example.com, it 148 contacts its resolver (which may be itself) to query the example.com 149 servers and will get back an NSEC record starting that there are no 150 records (alphabetically) between albatross and elephant, or an NSEC3 151 record stating there is nothing between two hashed names. The 152 resolver then knows that cat.example.com does not exist; however, it 153 does not use the fact that the proof covers a range (albatross to 154 elephant) to suppress queries for other labels that fall within this 155 range. This means that if the validating resolver gets a query for 156 ball.example.com (or dog.example.com) it will once again go off and 157 query the example.com servers for these names. 159 Now, assume that the (DNSSEC signed) "example.org" zone contains: 161 avocado.example.org IN A 192.0.2.1 162 *.example.org IN A 192.0.2.2 163 zucchini.example.org IN A 192.0.2.3 165 If a query is received for leek.example.org, it contacts its resolver 166 (which may be itself) to query the example.org servers and will get 167 back an NSEC record stating that there are no records 168 (alphabetically) between avocado and zucchini (or an NSEC3 record 169 stating there is nothing between two hashed names), as well as an 170 answer for leek.example.org, with the label count of the signature 171 set to two (see [RFC7129], section 5.3 for more details). 173 Apart from wasting bandwidth, this also wastes resources on the 174 recursive server (it needs to keep state for outstanding queries), 175 wastes resources on the authoritative server (it has to answer 176 additional questions), increases latency (the end user has to wait 177 longer than necessary to get back an NXDOMAIN answer), can be used by 178 attackers to cause a DoS (see additional resources), and also has 179 privacy implications (e.g: typos leak out further than necessary). 181 4. Background 183 DNSSEC [RFC4035] and [RFC5155] both provide "authenticated denial of 184 existence"; this is a cryptographic proof that the queried for name 185 does not exist, accomplished by providing a (DNSSEC secured) record 186 containing the names which appear alphabetically before and after the 187 queried for name. In the first example above, if the (DNSSEC 188 validating) recursive server were to query for dog.example.com it 189 would receive a (signed) NSEC record stating that there are no labels 190 between "albatross" and "elephant" (or, for NSEC3, a similar pair of 191 hashed names). This is a signed, cryptographic proof that these 192 names are the ones before and after the queried for label. As 193 dog.example.com falls within this range, the recursive server knows 194 that dog.example.com really does not exist. 196 This document specifies that this NSEC/NSEC3 record should be used to 197 generate negative answers for any queries that the validating server 198 receives that fall within the range covered by the record (for the 199 TTL for the record). This document also specifies that a positive 200 answer should be generated for any queries that the validating server 201 receives that are proven to be covered by a wildcard record. 203 Section 4.5 of [RFC4035] says: 205 "In theory, a resolver could use wildcards or NSEC RRs to generate 206 positive and negative responses (respectively) until the TTL or 207 signatures on the records in question expire. However, it seems 208 prudent for resolvers to avoid blocking new authoritative data or 209 synthesizing new data on their own. Resolvers that follow this 210 recommendation will have a more consistent view of the namespace." 211 and "The reason for these recommendations is that, between the 212 initial query and the expiration of the data from the cache, the 213 authoritative data might have been changed (for example, via dynamic 214 update).". In other words, if a resolver generates negative answers 215 from an NSEC record, it will not send any queries for names within 216 that NSEC range (for the TTL). If a new name is added to the zone 217 during this interval the resolver will not know this. Similarly, if 218 the resolver is generating responses from a wildcard record, it will 219 continue to do so (for the 221 We believe this recommendation can be relaxed because, in the absense 222 of this technique, a lookup for the exact name could have come in 223 during this interval, and so a negative answer could already be 224 cached (see [RFC2308] for more background). This means that zone 225 operators should have no expectation that an added name would work 226 immediately. With DNSSEC and Aggressive NSEC, the TTL of the NSEC 227 record is the authoritative statement of how quickly a name can start 228 working within a zone. 230 5. Aggressive Negative Caching 232 Section 4.5 of [RFC4035] says that "In theory, a resolver could use 233 wildcards or NSEC RRs to generate positive and negative responses 234 (respectively) until the TTL or signatures on the records in question 235 expire. However, it seems prudent for resolvers to avoid blocking 236 new authoritative data or synthesizing new data on their own. 237 Resolvers that follow this recommendation will have a more consistent 238 view of the namespace". 240 This document relaxes this this restriction, as follows: 242 +--------------------------------------------------------------+ 243 | Once the records are validated, DNSSEC enabled validating | 244 | resolvers MAY use wildcards and NSEC/NSEC3 resource records | 245 | to generate positive and negative responses until the | 246 | effective TTLs or signatures for those records expire. | 247 +--------------------------------------------------------------+ 249 If the negative cache of the validating resolver has sufficient 250 information to validate the query, the resolver SHOULD use NSEC, 251 NSEC3 and wildcard records aggressively. Otherwise, it MUST fall 252 back to send the query to the authoritative DNS servers. 254 It is recommended that resolvers that implement Aggressive Negative 255 Caching provide a configuration switch to disable the feature. 256 Separate configuration switches may be implemented for the aggressive 257 use of NSEC, NSEC3 and wildcard records, and it is recommended to 258 enable aggressive negative caching by default. 260 5.1. NSEC 262 The validating resolver needs to check the existence of an NSEC RR 263 matching/covering the source of synthesis and an NSEC RR covering the 264 query name. 266 If denial of existence can be determined according to the rules set 267 out in Section 5.4 of [RFC4035], using NSEC records in the cache, 268 then the resolver can immediately return an NXDOMAIN or NODATA (as 269 appropriate) response. 271 5.2. NSEC3 273 NSEC3 aggressive negative caching is more difficult than NSEC 274 aggressive caching. If the zone is signed with NSEC3, the validating 275 resolver needs to check the existence of non-terminals and wildcards 276 which derive from query names. 278 If denial of existence can be determined according to the rules set 279 out in [RFC5155] Sections 8.4, 8.5, 8.6, 8.7, using NSEC3 records in 280 the cache, then the resolver can immediately return an NXDOMAIN or 281 NODATA response (as appropriate). 283 If a covering NSEC3 RR has Opt-Out flag, the covering NSEC3 RR does 284 not prove the non-existence of the domain name and the aggressive 285 negative caching is not possible for the domain name. 287 5.3. Wildcards 289 The last paragraph of [RFC4035] Section 4.5 also discusses the use of 290 wildcards and NSEC RRs to generate positive responses and recommends 291 that it not be relied upon. Just like the case for the aggressive 292 use of NSEC/NSEC3 for negative answers, we revise this 293 recommendation. 295 As long as the validating resolver can determine that a name would 296 not exist without the wildcard match, determined according to the 297 rules set out in Section 5.3.4 of [RFC4035] (NSEC), or in Section 8.8 298 of [RFC5155], it SHOULD synthesize an answer for that name using the 299 cached deduced wildcard. If the corresponding wildcard record is not 300 in the cache, it MUST fall back to send the query to the 301 authoritative DNS servers. 303 5.4. Consideration on TTL 305 The TTL value of negative information is especially important, 306 because newly added domain names cannot be used while the negative 307 information is effective. 309 Section 5 of [RFC2308] states that the maximum number of negative 310 cache TTL value is 3 hours (10800). It is RECOMMENDED that 311 validating resolvers limit the maximum effective TTL value of 312 negative responses (NSEC/NSEC3 RRs) to this same value. 314 Section 5 of [RFC2308]also states that a negative cache entry TTL is 315 taken from the minimum of the SOA.MINIMUM field and SOA's TTL. This 316 can be less than the TTL of an NSEC or NSEC3 record, since their TTL 317 is equal to the SOA.MINIMUM field (see [RFC4035]section 2.3 and 318 [RFC5155] section 3.) 320 A resolver that supports aggressive use of NSEC and NSEC3 should 321 reduce the TTL of NSEC and NSEC3 records to match the TTL of the SOA 322 record in the authority section of a negative response, if the SOA 323 TTL is smaller. 325 6. Benefits 327 The techniques described in this document provide a number of 328 benefits, including (in no specific order): 330 Reduced latency: By answering directly from cache, validating 331 resolvers can immediately inform clients that the name they are 332 looking for does not exist, improving the user experience. 334 Decreased recursive server load: By answering negative queries from 335 the cache, validating servers avoid having to send a query and 336 wait for a response. In addition to decreasing the bandwidth 337 used, it also means that the server does not need to allocate and 338 maintain state, thereby decreasing memory and CPU load. 340 Decreased authorative server load: Because recursive servers can 341 answer (negative) queries without asking the authoritative server, 342 the authoritative servers receive fewer queries. This decreases 343 the authoritative server bandwidth, queries per second and CPU 344 utilization. 346 The scale of the benefit depends upon multiple factors, including the 347 query distribution. For example, at the time of this writing, around 348 65% of queries to Root Name servers result in NXDOMAIN responses (see 349 statistics from [root-servers.org]); this technique will eliminate a 350 sizable quantity of these. 352 The technique described in this document may also mitigate so-called 353 "random QNAME attacks", in which attackers send many queries for 354 random sub-domains to resolvers. As the resolver will not have the 355 answers cached, it has to ask external servers for each random query, 356 leading to a DoS on the authoritative servers (and often resolvers). 357 Aggressive NSEC may help mitigate these attacks by allowing the 358 resolver to answer directly from cache for any random queries which 359 fall within already requested ranges. It will not always work as an 360 effective defense, not least because not many zones are DNSSEC signed 361 at all -- but it will still provide an additional layer of defense. 363 7. Update to RFC 4035 365 Section 4.5 of [RFC4035] shows that "In theory, a resolver could use 366 wildcards or NSEC RRs to generate positive and negative responses 367 (respectively) until the TTL or signatures on the records in question 368 expire. However, it seems prudent for resolvers to avoid blocking 369 new authoritative data or synthesizing new data on their own. 370 Resolvers that follow this recommendation will have a more consistent 371 view of the namespace". 373 The paragraph is updated as follows: 375 +--------------------------------------------------------------+ 376 | Once the records are validated, DNSSEC enabled validating | 377 | resolvers MAY use wildcards and NSEC/NSEC3 resource records | 378 | to generate positive and negative responses until the | 379 | effective TTLs or signatures for those records expire. | 380 +--------------------------------------------------------------+ 382 8. IANA Considerations 384 This document has no IANA actions. 386 9. Security Considerations 388 Use of NSEC / NSEC3 resource records without DNSSEC validation may 389 create serious security issues, and so this technique requires DNSSEC 390 validation. 392 Newly registered resource records may not be used immediately. 393 However, choosing suitable TTL value and negative cache TTL value 394 (SOA MINIMUM field) will mitigate the delay concern, and it is not a 395 security problem. 397 It is also suggested to limit the maximum TTL value of NSEC / NSEC3 398 resource records in the negative cache to, for example, 10800 seconds 399 (3hrs), to mitigate this issue. Implementations which comply with 400 this proposal are recommended to have a configurable maximum value of 401 NSEC RRs in the negative cache. 403 Although the TTL of NSEC/NSEC3 records is typically fairly short 404 (minutes or hours), their RRSIG expiration time can be much further 405 in the future (weeks). An attacker who is able to successfully spoof 406 responses might poison a cache with old NSEC/NSEC3 records. If the 407 resolver is NOT making aggressive use of NSEC/NSEC3, the attacker has 408 to repeat the attack for every query. If the resolver IS making 409 aggressive use of NSEC/NSEC3, one successful attack would be able to 410 suppress many queries for new names, up to the negative TTL. 412 10. Implementation Status 414 [ Editor note: RFC Editor, please remove this entire section. 415 RFC6982 says: "Since this information is necessarily time dependent, 416 it is inappropriate for inclusion in a published RFC." ] 418 Unbound currently implements aggressive negative caching, as does 419 Google Public DNS. 421 11. Acknowledgments 423 The authors gratefully acknowledge DLV [RFC5074] author Samuel Weiler 424 and the Unbound developers. 426 The authors would like to specifically thank Stephane Bortzmeyer, 427 Tony Finch, Tatuya JINMEI for extensive review and comments, and also 428 Mark Andrews, Casey Deccio, Alexander Dupuy, Olafur Gudmundsson, Bob 429 Harold, Shumon Huque, John Levine, Pieter Lexis and Matthijs Mekking 430 (who even sent pull requests!). Mark Andrews also provided the text 431 (https://www.ietf.org/mail-archive/web/dnsop/current/msg18332.html) 432 which we made into Appendix B 434 11.1. Change History 436 RFC Editor: Please remove this section prior to publication. 438 -04 to -05: 440 o Bob pointed out that I did a stupid - when I added the wildcard to 441 'example.com' I made the example wrong / confusing. I have 442 attempted to fix this by adding a second example zone 443 (example.org) with the wildcard instead. 445 o More helpful changes (in a pull request, thanks!) from Matthijs 447 o Included Mark Andrew's useful explanation of how to tell ENT from 448 NXD as an Appendix. 450 -03 to -04: 452 o Working group does want the "positive" answers, not just negative 453 ones. This requires reading what used to be Section 7, and a 454 bunch of cleanup, including: 456 * Additional text in the Problem Statement 458 * Added a wildcard record to the zone. 460 * Added "or positive answers from wildcards" type text (where 461 appropriate) to explain that this isn't just for negative 462 answers. 464 * Reworded much of the Wildcard text. 466 o Incorporated pull request from Tony Finch (thanks!): 467 https://github.com/wkumari/draft-ietf-dnsop-nsec-aggressiveuse/ 468 pull/1 470 o More fixups from Tony (including text): https://www.ietf.org/mail- 471 archive/web/dnsop/current/msg18271.html. This included much 472 clearer text on TTL, refernces to the NSEC / NSEC3 RFCs (instead 473 of my clumsy summary), good text on replays, etc. 475 o Converted the "zone file" to a figure to make it more readable. 477 o Text from Tim W: "If a validating resolver receives a query for 478 cat.example.com, it contacts its resolver (which may be itself) to 479 query..." - which satisfies Jinmei's concern (which I was too 480 dense to grock). 482 o Fixup of the "validation required" in security considerations. 484 -02 to -03: 486 o Integrated a bunch of comments from Matthijs Mekking - details in: 487 https://github.com/wkumari/draft-ietf-dnsop-nsec-aggressiveuse/ 488 pull/1. I decided to keep "Aggressive Negative Caching" instead 489 of "Aggressive USE OF Negative Caching" for readability. 491 o Attempted to address Bob Harold's comment on the readability 492 issues with "But, it will be more effective when both are 493 enabled..." in Section 5.4 - https://www.ietf.org/mail- 494 archive/web/dnsop/current/msg17997.html 496 o MAYs and SHOULD drifted in the text block. Fixed - thanks to 497 https://mailarchive.ietf.org/arch/msg/ 498 dnsop/2ljmmzxtIMCFMLOZmWcSbTYVOy4 500 o A number of good edits from Stephane in: https://www.ietf.org/ 501 mail-archive/web/dnsop/current/msg18109.html 503 o A bunch more edits from Jinmei, as in: https://www.ietf.org/mail- 504 archive/web/dnsop/current/msg18206.html 506 -01 to -02: 508 o Added Section 6 - Benefits (as suggested by Jinmei). 510 o Removed Appendix B (Jinmei) 512 o Replaced "full-service" with "validating" (where applicable) 514 o Integrated other comments from Jinmei from https://www.ietf.org/ 515 mail-archive/web/dnsop/current/msg17875.html 517 o Integrated comment from co-authors, including re-adding parts of 518 Appendix B, terminology, typos. 520 o Tried to explain under what conditions this may actually mitigate 521 attacks. 523 -00 to -01: 525 o Comments from DNSOP meeting in Berlin. 527 o Changed intended status to Standards Track (updates RFC 4035) 529 o Added a section "Updates to RFC 4035" 531 o Some language clarification / typo / cleanup 533 o Cleaned up the TTL section a bit. 535 o Removed Effects section, Additional proposal section, and pseudo 536 code. 538 o Moved "mitigation of random subdomain attacks" to Appendix. 540 From draft-fujiwara-dnsop-nsec-aggressiveuse-03 -> draft-ietf-dnsop- 541 nsec-aggressiveuse 543 o Document adopted by DNSOP WG. 545 o Adoption comments 547 o Changed main purpose to performance 549 o Use NSEC3/Wildcard keywords 551 o Improved wordings (from good comments) 553 o Simplified pseudo code for NSEC3 555 o Added Warren as co-author. 557 o Reworded much of the problem statement 559 o Reworked examples to better explain the problem / solution. 561 11.1.1. Version draft-fujiwara-dnsop-nsec-aggressiveuse-01 563 o Added reference to DLV [RFC5074] and imported some sentences. 565 o Added Aggressive Negative Caching Flag idea. 567 o Added detailed algorithms. 569 11.1.2. Version draft-fujiwara-dnsop-nsec-aggressiveuse-02 571 o Added reference to [I-D.vixie-dnsext-resimprove] 573 o Added considerations for the CD bit 575 o Updated detailed algorithms. 577 o Moved Aggressive Negative Caching Flag idea into Additional 578 Proposals 580 11.1.3. Version draft-fujiwara-dnsop-nsec-aggressiveuse-03 582 o Added "Partial implementation" 584 o Section 4,5,6 reorganized for better representation 586 o Added NODATA answer in Section 4 588 o Trivial updates 590 o Updated pseudo code 592 11.2. new section 594 12. References 596 12.1. Normative References 598 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 599 Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ 600 RFC2119, March 1997, 601 . 603 [RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS 604 NCACHE)", RFC 2308, DOI 10.17487/RFC2308, March 1998, 605 . 607 [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. 608 Rose, "Protocol Modifications for the DNS Security 609 Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005, 610 . 612 [RFC4592] Lewis, E., "The Role of Wildcards in the Domain Name 613 System", RFC 4592, DOI 10.17487/RFC4592, July 2006, 614 . 616 [RFC5074] Weiler, S., "DNSSEC Lookaside Validation (DLV)", RFC 5074, 617 DOI 10.17487/RFC5074, November 2007, 618 . 620 [RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS 621 Security (DNSSEC) Hashed Authenticated Denial of 622 Existence", RFC 5155, DOI 10.17487/RFC5155, March 2008, 623 . 625 [RFC7129] Gieben, R. and W. Mekking, "Authenticated Denial of 626 Existence in the DNS", RFC 7129, DOI 10.17487/RFC7129, 627 February 2014, . 629 [RFC7719] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS 630 Terminology", RFC 7719, DOI 10.17487/RFC7719, December 631 2015, . 633 12.2. Informative References 635 [I-D.ietf-dnsop-nxdomain-cut] 636 Bortzmeyer, S. and S. Huque, "NXDOMAIN really means there 637 is nothing underneath", draft-ietf-dnsop-nxdomain-cut-03 638 (work in progress), May 2016. 640 [I-D.vixie-dnsext-resimprove] 641 Vixie, P., Joffe, R., and F. Neves, "Improvements to DNS 642 Resolvers for Resiliency, Robustness, and Responsiveness", 643 draft-vixie-dnsext-resimprove-00 (work in progress), June 644 2010. 646 [root-servers.org] 647 IANA, "Root Server Technical Operations Assn", 648 . 650 Appendix A. Detailed implementation notes 652 o Previously, cached negative responses were indexed by QNAME, 653 QCLASS, QTYPE, and the setting of the CD bit (see RFC 4035, 654 Section 4.7), and only queries matching the index key would be 655 answered from the cache. With aggressive negative caching, the 656 validator, in addition to checking to see if the answer is in its 657 cache before sending a query, checks to see whether any cached and 658 validated NSEC record denies the existence of the sought 659 record(s). Using aggressive negative caching, a validator will 660 not make queries for any name covered by a cached and validated 661 NSEC record. Furthermore, a validator answering queries from 662 clients will synthesize a negative answer whenever it has an 663 applicable validated NSEC in its cache unless the CD bit was set 664 on the incoming query. (Imported from Section 6 of [RFC5074]). 666 o Implementing aggressive negative caching suggests that a validator 667 will need to build an ordered data structure of NSEC and NSEC3 668 records for each signer domain name of NSEC / NSEC3 records in 669 order to efficiently find covering NSEC / NSEC3 records. Call the 670 table as NSEC_TABLE. (Imported from Section 6.1 of [RFC5074] and 671 expanded.) 673 o The aggressive negative caching may be inserted at the cache 674 lookup part of the recursive resolvers. 676 o If errors happen in aggressive negative caching algorithm, 677 resolvers MUST fall back to resolve the query as usual. "Resolve 678 the query as usual" means that the resolver must process the query 679 as though it does not implement aggressive negative caching. 681 Appendix B. Procedure for determining ENT vs NXDOMAN 683 Thanks to Mark Andrews for providing these helpful notes for 684 implementors. As they are more general than for Aggressive NSEC we 685 have placed them in an appendix. 687 If the NSEC record has not been verified as secure discard it. 689 If the given name sorts before or matches the NSEC owner name discard 690 it as it does not prove the NXDOMAIN or ENT. 692 If the given name is a subdomain of the NSEC owner name and the NS 693 bit is present and the SOA bit is absent then discard the NSEC as it 694 is from a parent zone. 696 If the next domain name sorts after the NSEC owner name and the given 697 name sorts after or matches next domain name then discard the NSEC 698 record as it does not prove the NXDOMAIN or ENT. 700 If the next domain name sorts before or matches the NSEC owner name 701 and the given name is not a subdomain of the next domain name then 702 discard the NSEC as it does not prove the NXDOMAIN or ENT. 704 You now have a NSEC record that proves the NXDOMAIN or ENT. 706 If the next domain name is a subdomain of the given name you have a 707 ENT otherwise you have a NXDOMAIN. 709 Authors' Addresses 711 Kazunori Fujiwara 712 Japan Registry Services Co., Ltd. 713 Chiyoda First Bldg. East 13F, 3-8-1 Nishi-Kanda 714 Chiyoda-ku, Tokyo 101-0065 715 Japan 717 Phone: +81 3 5215 8451 718 Email: fujiwara@jprs.co.jp 720 Akira Kato 721 Keio University/WIDE Project 722 Graduate School of Media Design, 4-1-1 Hiyoshi 723 Kohoku, Yokohama 223-8526 724 Japan 726 Phone: +81 45 564 2490 727 Email: kato@wide.ad.jp 729 Warren Kumari 730 Google 731 1600 Amphitheatre Parkway 732 Mountain View, CA 94043 733 US 735 Email: warren@kumari.net