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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) == Unused Reference: 'I-D.ietf-dnsop-nxdomain-cut' is defined on line 643, but no explicit reference was found in the text ** 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reference to an Informational RFC: RFC 7129 ** Obsolete normative reference: RFC 7719 (Obsoleted by RFC 8499) == Outdated reference: draft-ietf-dnsop-nxdomain-cut has been published as RFC 8020 Summary: 3 errors (**), 0 flaws (~~), 3 warnings (==), 3 comments (--).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: May 20, 2017 W. Kumari 7 Google 8 November 16, 2016 10 Aggressive use of NSEC/NSEC3 11 draft-ietf-dnsop-nsec-aggressiveuse-06 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 May 20, 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 use of Cache . . . . . . . . . . . . . . . . . . . 5 75 5.1. NSEC . . . . . . . . . . . . . . . . . . . . . . . . . . 6 76 5.2. NSEC3 . . . . . . . . . . . . . . . . . . . . . . . . . . 6 77 5.3. Wildcards . . . . . . . . . . . . . . . . . . . . . . . . 6 78 5.4. Consideration on TTL . . . . . . . . . . . . . . . . . . 7 79 6. Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . 7 80 7. Update to RFC 4035 . . . . . . . . . . . . . . . . . . . . . 8 81 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 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 [RFC8020] proposes a first step to using NXDOMAIN information for 118 more effective caching. This takes this technique further. 120 2. Terminology 122 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 123 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 124 document are to be interpreted as described in RFC 2119 [RFC2119]. 126 Many of the specialized terms used in this document are defined in 127 DNS Terminology [RFC7719]. 129 The key words "Closest Encloser" and "Source of Synthesis" in this 130 document are to be interpreted as described in [RFC4592]. 132 "Closest Encloser" is also defined in NSEC3 [RFC5155], as is "Next 133 closer name". 135 3. Problem Statement 137 The DNS negative cache caches negative (non-existent) information, 138 and requires an exact match in most instances [RFC2308]. 140 Assume that the (DNSSEC signed) "example.com" zone contains: 142 albatross.example.com IN A 192.0.2.1 143 elephant.example.com IN A 192.0.2.2 144 zebra.example.com IN A 192.0.2.3 145 If a validating resolver receives a query for cat.example.com, it 146 contacts its resolver (which may be itself) to query the example.com 147 servers and will get back an NSEC record starting that there are no 148 records (alphabetically) between albatross and elephant, or an NSEC3 149 record stating there is nothing between two hashed names. The 150 resolver then knows that cat.example.com does not exist; however, it 151 does not use the fact that the proof covers a range (albatross to 152 elephant) to suppress queries for other labels that fall within this 153 range. This means that if the validating resolver gets a query for 154 ball.example.com (or dog.example.com) it will once again go off and 155 query the example.com servers for these names. 157 Apart from wasting bandwidth, this also wastes resources on the 158 recursive server (it needs to keep state for outstanding queries), 159 wastes resources on the authoritative server (it has to answer 160 additional questions), increases latency (the end user has to wait 161 longer than necessary to get back an NXDOMAIN answer), can be used by 162 attackers to cause a DoS (see additional resources), and also has 163 privacy implications (e.g: typos leak out further than necessary). 165 Now, assume that the (DNSSEC signed) "example.org" zone contains: 167 avocado.example.org IN A 192.0.2.1 168 *.example.org IN A 192.0.2.2 169 zucchini.example.org IN A 192.0.2.3 171 If a query is received for leek.example.org, it contacts its resolver 172 (which may be itself) to query the example.org servers and will get 173 back an NSEC record stating that there are no records 174 (alphabetically) between avocado and zucchini (or an NSEC3 record 175 stating there is nothing between two hashed names), as well as an 176 answer for leek.example.org, with the label count of the signature 177 set to two (see [RFC7129], section 5.3 for more details). 179 If the validating resolver gets a query for banana.example.org it 180 will once again go off and query the example.com servers for 181 banana.example.com (even though it already has proof that there is a 182 wildcard record) - just like above, this has privacy implications, 183 wastes resources, can be used to contribute to a DoS, etc. 185 4. Background 187 DNSSEC [RFC4035] and [RFC5155] both provide "authenticated denial of 188 existence"; this is a cryptographic proof that the queried for name 189 does not exist, accomplished by providing a (DNSSEC secured) record 190 containing the names which appear alphabetically before and after the 191 queried for name. In the first example above, if the (DNSSEC 192 validating) recursive server were to query for dog.example.com it 193 would receive a (signed) NSEC record stating that there are no labels 194 between "albatross" and "elephant" (or, for NSEC3, a similar pair of 195 hashed names). This is a signed, cryptographic proof that these 196 names are the ones before and after the queried for label. As 197 dog.example.com falls within this range, the recursive server knows 198 that dog.example.com really does not exist. 200 This document specifies that this NSEC/NSEC3 record should be used to 201 generate negative answers for any queries that the validating server 202 receives that fall within the range covered by the record (for the 203 TTL for the record). This document also specifies that a positive 204 answer should be generated for any queries that the validating server 205 receives that are proven to be covered by a wildcard record. 207 Section 4.5 of [RFC4035] says: 209 "In theory, a resolver could use wildcards or NSEC RRs to generate 210 positive and negative responses (respectively) until the TTL or 211 signatures on the records in question expire. However, it seems 212 prudent for resolvers to avoid blocking new authoritative data or 213 synthesizing new data on their own. Resolvers that follow this 214 recommendation will have a more consistent view of the namespace." 215 and "The reason for these recommendations is that, between the 216 initial query and the expiration of the data from the cache, the 217 authoritative data might have been changed (for example, via dynamic 218 update).". In other words, if a resolver generates negative answers 219 from an NSEC record, it will not send any queries for names within 220 that NSEC range (for the TTL). If a new name is added to the zone 221 during this interval the resolver will not know this. Similarly, if 222 the resolver is generating responses from a wildcard record, it will 223 continue to do so (for the 225 We believe this recommendation can be relaxed because, in the absense 226 of this technique, a lookup for the exact name could have come in 227 during this interval, and so a negative answer could already be 228 cached (see [RFC2308] for more background). This means that zone 229 operators should have no expectation that an added name would work 230 immediately. With DNSSEC and Aggressive NSEC, the TTL of the NSEC 231 record is the authoritative statement of how quickly a name can start 232 working within a zone. 234 5. Aggressive use of Cache 236 Section 4.5 of [RFC4035] says that "In theory, a resolver could use 237 wildcards or NSEC RRs to generate positive and negative responses 238 (respectively) until the TTL or signatures on the records in question 239 expire. However, it seems prudent for resolvers to avoid blocking 240 new authoritative data or synthesizing new data on their own. 242 Resolvers that follow this recommendation will have a more consistent 243 view of the namespace". This document relaxes this this restriction, 244 see Section 7 for more detail. 246 If the negative cache of the validating resolver has sufficient 247 information to validate the query, the resolver SHOULD use NSEC, 248 NSEC3 and wildcard records aggressively. Otherwise, it MUST fall 249 back to send the query to the authoritative DNS servers. 251 It is recommended that resolvers that implement Aggressive Negative 252 Caching provide a configuration switch to disable the feature. 253 Separate configuration switches may be implemented for the aggressive 254 use of NSEC, NSEC3 and wildcard records, and it is recommended to 255 enable aggressive negative caching by default. 257 5.1. NSEC 259 The validating resolver needs to check the existence of an NSEC RR 260 matching/covering the source of synthesis and an NSEC RR covering the 261 query name. 263 If denial of existence can be determined according to the rules set 264 out in Section 5.4 of [RFC4035], using NSEC records in the cache, 265 then the resolver can immediately return an NXDOMAIN or NODATA (as 266 appropriate) response. 268 5.2. NSEC3 270 NSEC3 aggressive negative caching is more difficult than NSEC 271 aggressive caching. If the zone is signed with NSEC3, the validating 272 resolver needs to check the existence of non-terminals and wildcards 273 which derive from query names. 275 If denial of existence can be determined according to the rules set 276 out in [RFC5155] Sections 8.4, 8.5, 8.6, 8.7, using NSEC3 records in 277 the cache, then the resolver can immediately return an NXDOMAIN or 278 NODATA response (as appropriate). 280 If a covering NSEC3 RR has Opt-Out flag, the covering NSEC3 RR does 281 not prove the non-existence of the domain name and the aggressive 282 negative caching is not possible for the domain name. 284 5.3. Wildcards 286 The last paragraph of [RFC4035] Section 4.5 also discusses the use of 287 wildcards and NSEC RRs to generate positive responses and recommends 288 that it not be relied upon. Just like the case for the aggressive 289 use of NSEC/NSEC3 for negative answers, we revise this 290 recommendation. 292 As long as the validating resolver can determine that a name would 293 not exist without the wildcard match, determined according to the 294 rules set out in Section 5.3.4 of [RFC4035] (NSEC), or in Section 8.8 295 of [RFC5155], it SHOULD synthesize an answer for that name using the 296 cached deduced wildcard. If the corresponding wildcard record is not 297 in the cache, it MUST fall back to send the query to the 298 authoritative DNS servers. 300 5.4. Consideration on TTL 302 The TTL value of negative information is especially important, 303 because newly added domain names cannot be used while the negative 304 information is effective. 306 Section 5 of [RFC2308] states that the maximum number of negative 307 cache TTL value is 3 hours (10800). It is RECOMMENDED that 308 validating resolvers limit the maximum effective TTL value of 309 negative responses (NSEC/NSEC3 RRs) to this same value. 311 Section 5 of [RFC2308]also states that a negative cache entry TTL is 312 taken from the minimum of the SOA.MINIMUM field and SOA's TTL. This 313 can be less than the TTL of an NSEC or NSEC3 record, since their TTL 314 is equal to the SOA.MINIMUM field (see [RFC4035]section 2.3 and 315 [RFC5155] section 3.) 317 A resolver that supports aggressive use of NSEC and NSEC3 should 318 reduce the TTL of NSEC and NSEC3 records to match the SOA.MINIMUM 319 field in the authority section of a negative response, if SOA.MINIMUM 320 is smaller. 322 6. Benefits 324 The techniques described in this document provide a number of 325 benefits, including (in no specific order): 327 Reduced latency: By answering directly from cache, validating 328 resolvers can immediately inform clients that the name they are 329 looking for does not exist, improving the user experience. 331 Decreased recursive server load: By answering queries from the cache 332 by synthesizing answers, validating servers avoid having to send a 333 query and wait for a response. In addition to decreasing the 334 bandwidth used, it also means that the server does not need to 335 allocate and maintain state, thereby decreasing memory and CPU 336 load. 338 Decreased authorative server load: Because recursive servers can 339 answer queries without asking the authoritative server, the 340 authoritative servers receive fewer queries. This decreases the 341 authoritative server bandwidth, queries per second and CPU 342 utilization. 344 The scale of the benefit depends upon multiple factors, including the 345 query distribution. For example, at the time of this writing, around 346 65% of queries to Root Name servers result in NXDOMAIN responses (see 347 statistics from [root-servers.org]); this technique will eliminate a 348 sizable quantity of these. 350 The technique described in this document may also mitigate so-called 351 "random QNAME attacks", in which attackers send many queries for 352 random sub-domains to resolvers. As the resolver will not have the 353 answers cached, it has to ask external servers for each random query, 354 leading to a DoS on the authoritative servers (and often resolvers). 355 Aggressive NSEC may help mitigate these attacks by allowing the 356 resolver to answer directly from cache for any random queries which 357 fall within already requested ranges. It will not always work as an 358 effective defense, not least because not many zones are DNSSEC signed 359 at all -- but it will still provide an additional layer of defense. 361 7. Update to RFC 4035 363 Section 4.5 of [RFC4035] shows that "In theory, a resolver could use 364 wildcards or NSEC RRs to generate positive and negative responses 365 (respectively) until the TTL or signatures on the records in question 366 expire. However, it seems prudent for resolvers to avoid blocking 367 new authoritative data or synthesizing new data on their own. 368 Resolvers that follow this recommendation will have a more consistent 369 view of the namespace". 371 The paragraph is updated as follows: 373 +--------------------------------------------------------------+ 374 | Once the records are validated, DNSSEC enabled validating | 375 | resolvers MAY use wildcards and NSEC/NSEC3 resource records | 376 | to generate positive and negative responses until the | 377 | effective TTLs or signatures for those records expire. | 378 +--------------------------------------------------------------+ 380 8. IANA Considerations 382 This document has no IANA actions. 384 9. Security Considerations 386 Use of NSEC / NSEC3 resource records without DNSSEC validation may 387 create serious security issues, and so this technique requires DNSSEC 388 validation. 390 Newly registered resource records may not be used immediately. 391 However, choosing suitable TTL value and negative cache TTL value 392 (SOA MINIMUM field) will mitigate the delay concern, and it is not a 393 security problem. 395 It is also suggested to limit the maximum TTL value of NSEC / NSEC3 396 resource records in the negative cache to, for example, 10800 seconds 397 (3hrs), to mitigate this issue. Implementations which comply with 398 this proposal are recommended to have a configurable maximum value of 399 NSEC RRs in the negative cache. 401 Although the TTL of NSEC/NSEC3 records is typically fairly short 402 (minutes or hours), their RRSIG expiration time can be much further 403 in the future (weeks). An attacker who is able to successfully spoof 404 responses might poison a cache with old NSEC/NSEC3 records. If the 405 resolver is NOT making aggressive use of NSEC/NSEC3, the attacker has 406 to repeat the attack for every query. If the resolver IS making 407 aggressive use of NSEC/NSEC3, one successful attack would be able to 408 suppress many queries for new names, up to the negative TTL. 410 10. Implementation Status 412 [ Editor note: RFC Editor, please remove this entire section. 413 RFC6982 says: "Since this information is necessarily time dependent, 414 it is inappropriate for inclusion in a published RFC." ] 416 Unbound currently implements aggressive negative caching, as does 417 Google Public DNS. 419 11. Acknowledgments 421 The authors gratefully acknowledge DLV [RFC5074] author Samuel Weiler 422 and the Unbound developers. 424 The authors would like to specifically thank Stephane Bortzmeyer (for 425 standing next to and helping edit), Tony Finch, Tatuya JINMEI for 426 extensive review and comments, and also Mark Andrews, Casey Deccio, 427 Alexander Dupuy, Olafur Gudmundsson, Bob Harold, Shumon Huque, John 428 Levine, Pieter Lexis and Matthijs Mekking (who even sent pull 429 requests!). Mark Andrews also provided the text 430 (https://www.ietf.org/mail-archive/web/dnsop/current/msg18332.html) 431 which we made into Appendix B. 433 11.1. Change History 435 RFC Editor: Please remove this section prior to publication. 437 -05 to -06: 439 o Moved some dangling text around - when the examples were added 440 some text added in the wrong place. 442 o There were some bits which mentioned "negative" in the title. 444 o We had the cut-and-paste of what changed in 4035 twice. 446 -04 to -05: 448 o Bob pointed out that I did a stupid - when I added the wildcard to 449 'example.com' I made the example wrong / confusing. I have 450 attempted to fix this by adding a second example zone 451 (example.org) with the wildcard instead. 453 o More helpful changes (in a pull request, thanks!) from Matthijs 455 o Included Mark Andrew's useful explanation of how to tell ENT from 456 NXD as an Appendix. 458 -03 to -04: 460 o Working group does want the "positive" answers, not just negative 461 ones. This requires reading what used to be Section 7, and a 462 bunch of cleanup, including: 464 * Additional text in the Problem Statement 466 * Added a wildcard record to the zone. 468 * Added "or positive answers from wildcards" type text (where 469 appropriate) to explain that this isn't just for negative 470 answers. 472 * Reworded much of the Wildcard text. 474 o Incorporated pull request from Tony Finch (thanks!): 475 https://github.com/wkumari/draft-ietf-dnsop-nsec-aggressiveuse/ 476 pull/1 478 o More fixups from Tony (including text): https://www.ietf.org/mail- 479 archive/web/dnsop/current/msg18271.html. This included much 480 clearer text on TTL, references to the NSEC / NSEC3 RFCs (instead 481 of my clumsy summary), good text on replays, etc. 483 o Converted the "zone file" to a figure to make it more readable. 485 o Text from Tim W: "If a validating resolver receives a query for 486 cat.example.com, it contacts its resolver (which may be itself) to 487 query..." - which satisfies Jinmei's concern (which I was too 488 dense to grock). 490 o Fixup of the "validation required" in security considerations. 492 -02 to -03: 494 o Integrated a bunch of comments from Matthijs Mekking - details in: 495 https://github.com/wkumari/draft-ietf-dnsop-nsec-aggressiveuse/ 496 pull/1. I decided to keep "Aggressive Negative Caching" instead 497 of "Aggressive USE OF Negative Caching" for readability. 499 o Attempted to address Bob Harold's comment on the readability 500 issues with "But, it will be more effective when both are 501 enabled..." in Section 5.4 - https://www.ietf.org/mail- 502 archive/web/dnsop/current/msg17997.html 504 o MAYs and SHOULD drifted in the text block. Fixed - thanks to 505 https://mailarchive.ietf.org/arch/msg/ 506 dnsop/2ljmmzxtIMCFMLOZmWcSbTYVOy4 508 o A number of good edits from Stephane in: https://www.ietf.org/ 509 mail-archive/web/dnsop/current/msg18109.html 511 o A bunch more edits from Jinmei, as in: https://www.ietf.org/mail- 512 archive/web/dnsop/current/msg18206.html 514 -01 to -02: 516 o Added Section 6 - Benefits (as suggested by Jinmei). 518 o Removed Appendix B (Jinmei) 520 o Replaced "full-service" with "validating" (where applicable) 522 o Integrated other comments from Jinmei from https://www.ietf.org/ 523 mail-archive/web/dnsop/current/msg17875.html 525 o Integrated comment from co-authors, including re-adding parts of 526 Appendix B, terminology, typos. 528 o Tried to explain under what conditions this may actually mitigate 529 attacks. 531 -00 to -01: 533 o Comments from DNSOP meeting in Berlin. 535 o Changed intended status to Standards Track (updates RFC 4035) 537 o Added a section "Updates to RFC 4035" 539 o Some language clarification / typo / cleanup 541 o Cleaned up the TTL section a bit. 543 o Removed Effects section, Additional proposal section, and pseudo 544 code. 546 o Moved "mitigation of random subdomain attacks" to Appendix. 548 From draft-fujiwara-dnsop-nsec-aggressiveuse-03 -> draft-ietf-dnsop- 549 nsec-aggressiveuse 551 o Document adopted by DNSOP WG. 553 o Adoption comments 555 o Changed main purpose to performance 557 o Use NSEC3/Wildcard keywords 559 o Improved wordings (from good comments) 561 o Simplified pseudo code for NSEC3 563 o Added Warren as co-author. 565 o Reworded much of the problem statement 567 o Reworked examples to better explain the problem / solution. 569 11.1.1. Version draft-fujiwara-dnsop-nsec-aggressiveuse-01 571 o Added reference to DLV [RFC5074] and imported some sentences. 573 o Added Aggressive Negative Caching Flag idea. 575 o Added detailed algorithms. 577 11.1.2. Version draft-fujiwara-dnsop-nsec-aggressiveuse-02 579 o Added reference to [I-D.vixie-dnsext-resimprove] 581 o Added considerations for the CD bit 583 o Updated detailed algorithms. 585 o Moved Aggressive Negative Caching Flag idea into Additional 586 Proposals 588 11.1.3. Version draft-fujiwara-dnsop-nsec-aggressiveuse-03 590 o Added "Partial implementation" 592 o Section 4,5,6 reorganized for better representation 594 o Added NODATA answer in Section 4 596 o Trivial updates 598 o Updated pseudo code 600 11.2. new section 602 12. References 604 12.1. Normative References 606 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 607 Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ 608 RFC2119, March 1997, 609 . 611 [RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS 612 NCACHE)", RFC 2308, DOI 10.17487/RFC2308, March 1998, 613 . 615 [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. 616 Rose, "Protocol Modifications for the DNS Security 617 Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005, 618 . 620 [RFC4592] Lewis, E., "The Role of Wildcards in the Domain Name 621 System", RFC 4592, DOI 10.17487/RFC4592, July 2006, 622 . 624 [RFC5074] Weiler, S., "DNSSEC Lookaside Validation (DLV)", RFC 5074, 625 DOI 10.17487/RFC5074, November 2007, 626 . 628 [RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS 629 Security (DNSSEC) Hashed Authenticated Denial of 630 Existence", RFC 5155, DOI 10.17487/RFC5155, March 2008, 631 . 633 [RFC7129] Gieben, R. and W. Mekking, "Authenticated Denial of 634 Existence in the DNS", RFC 7129, DOI 10.17487/RFC7129, 635 February 2014, . 637 [RFC7719] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS 638 Terminology", RFC 7719, DOI 10.17487/RFC7719, December 639 2015, . 641 12.2. Informative References 643 [I-D.ietf-dnsop-nxdomain-cut] 644 Bortzmeyer, S. and S. Huque, "NXDOMAIN really means there 645 is nothing underneath", draft-ietf-dnsop-nxdomain-cut-03 646 (work in progress), May 2016. 648 [I-D.vixie-dnsext-resimprove] 649 Vixie, P., Joffe, R., and F. Neves, "Improvements to DNS 650 Resolvers for Resiliency, Robustness, and Responsiveness", 651 draft-vixie-dnsext-resimprove-00 (work in progress), June 652 2010. 654 [RFC8020] Bortzmeyer, S. and S. Huque, "NXDOMAIN: There Really Is 655 Nothing Underneath", RFC 8020, DOI 10.17487/RFC8020, 656 November 2016, . 658 [root-servers.org] 659 IANA, "Root Server Technical Operations Assn", 660 . 662 Appendix A. Detailed implementation notes 664 o Previously, cached negative responses were indexed by QNAME, 665 QCLASS, QTYPE, and the setting of the CD bit (see RFC 4035, 666 Section 4.7), and only queries matching the index key would be 667 answered from the cache. With aggressive negative caching, the 668 validator, in addition to checking to see if the answer is in its 669 cache before sending a query, checks to see whether any cached and 670 validated NSEC record denies the existence of the sought 671 record(s). Using aggressive negative caching, a validator will 672 not make queries for any name covered by a cached and validated 673 NSEC record. Furthermore, a validator answering queries from 674 clients will synthesize a negative answer whenever it has an 675 applicable validated NSEC in its cache unless the CD bit was set 676 on the incoming query. (Imported from Section 6 of [RFC5074]). 678 o Implementing aggressive negative caching suggests that a validator 679 will need to build an ordered data structure of NSEC and NSEC3 680 records for each signer domain name of NSEC / NSEC3 records in 681 order to efficiently find covering NSEC / NSEC3 records. Call the 682 table as NSEC_TABLE. (Imported from Section 6.1 of [RFC5074] and 683 expanded.) 685 o The aggressive negative caching may be inserted at the cache 686 lookup part of the recursive resolvers. 688 o If errors happen in aggressive negative caching algorithm, 689 resolvers MUST fall back to resolve the query as usual. "Resolve 690 the query as usual" means that the resolver must process the query 691 as though it does not implement aggressive negative caching. 693 Appendix B. Procedure for determining ENT vs NXDOMAN 695 Thanks to Mark Andrews for providing these helpful notes for 696 implementors. As they are more general than for Aggressive NSEC we 697 have placed them in an appendix. 699 If the NSEC record has not been verified as secure discard it. 701 If the given name sorts before or matches the NSEC owner name discard 702 it as it does not prove the NXDOMAIN or ENT. 704 If the given name is a subdomain of the NSEC owner name and the NS 705 bit is present and the SOA bit is absent then discard the NSEC as it 706 is from a parent zone. 708 If the next domain name sorts after the NSEC owner name and the given 709 name sorts after or matches next domain name then discard the NSEC 710 record as it does not prove the NXDOMAIN or ENT. 712 If the next domain name sorts before or matches the NSEC owner name 713 and the given name is not a subdomain of the next domain name then 714 discard the NSEC as it does not prove the NXDOMAIN or ENT. 716 You now have a NSEC record that proves the NXDOMAIN or ENT. 718 If the next domain name is a subdomain of the given name you have a 719 ENT otherwise you have a NXDOMAIN. 721 Authors' Addresses 723 Kazunori Fujiwara 724 Japan Registry Services Co., Ltd. 725 Chiyoda First Bldg. East 13F, 3-8-1 Nishi-Kanda 726 Chiyoda-ku, Tokyo 101-0065 727 Japan 729 Phone: +81 3 5215 8451 730 Email: fujiwara@jprs.co.jp 732 Akira Kato 733 Keio University/WIDE Project 734 Graduate School of Media Design, 4-1-1 Hiyoshi 735 Kohoku, Yokohama 223-8526 736 Japan 738 Phone: +81 45 564 2490 739 Email: kato@wide.ad.jp 741 Warren Kumari 742 Google 743 1600 Amphitheatre Parkway 744 Mountain View, CA 94043 745 US 747 Email: warren@kumari.net