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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 Informational RFC: RFC 7129 ** Obsolete normative reference: RFC 7719 (Obsoleted by RFC 8499) Summary: 2 errors (**), 0 flaws (~~), 1 warning (==), 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: October 1, 2017 W. Kumari 7 Google 8 March 30, 2017 10 Aggressive use of DNSSEC-validated Cache 11 draft-ietf-dnsop-nsec-aggressiveuse-09 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 answers based upon NSEC/NSEC3 records (and positive 26 answers 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 October 1, 2017. 53 Copyright Notice 55 Copyright (c) 2017 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 . . . . . . . . . . . . . . . . . . . 6 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 . . . . . . . . . . . . . . . . . . . 8 83 10. Implementation Status . . . . . . . . . . . . . . . . . . . . 9 84 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9 85 11.1. Change History . . . . . . . . . . . . . . . . . . . . . 9 86 11.1.1. Version draft-fujiwara-dnsop-nsec-aggressiveuse-01 . 13 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 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 90 12.1. Normative References . . . . . . . . . . . . . . . . . . 13 91 12.2. Informative References . . . . . . . . . . . . . . . . . 14 92 Appendix A. Detailed implementation notes . . . . . . . . . . . 15 93 Appendix B. Procedure for determining ENT vs NXDOMAN with NSEC . 15 94 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 96 1. Introduction 98 A DNS negative cache exists, and is used to cache the fact that an 99 RRset does not exist. This method of negative caching requires exact 100 matching; this leads to unnecessary additional lookups, increases 101 latency, leads to extra resource utilization on both authoritative 102 and recursive servers, and decreases privacy by leaking queries. 104 This document updates RFC 4035 to allow resolvers to use NSEC/NSEC3 105 resource records to synthesize negative answers from the information 106 they have in the cache. This allows validating resolvers to respond 107 with a negative answer immediately if the name in question falls into 108 a range expressed by a NSEC/NSEC3 resource record already in the 109 cache. It also allows the synthesis of positive answers in the 110 presence of wildcard records. 112 Aggressive Negative Caching was first proposed in Section 6 of DNSSEC 113 Lookaside Validation (DLV) [RFC5074] in order to find covering NSEC 114 records efficiently. 116 [RFC8020] and [I-D.vixie-dnsext-resimprove] propose steps to using 117 NXDOMAIN information for more effective caching. This document takes 118 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 "Source of Synthesis" in this document are to be 130 interpreted as described in [RFC4592]. 132 3. Problem Statement 134 The DNS negative cache caches negative (non-existent) information, 135 and requires an exact match in most instances [RFC2308]. 137 Assume that the (DNSSEC signed) "example.com" zone contains: 139 albatross.example.com IN A 192.0.2.1 140 elephant.example.com IN A 192.0.2.2 141 zebra.example.com IN A 192.0.2.3 142 If a validating resolver receives a query for cat.example.com, it 143 contacts its resolver (which may be itself) to query the example.com 144 servers and will get back an NSEC record stating that there are no 145 records (alphabetically) between albatross and elephant, or an NSEC3 146 record stating there is nothing between two hashed names. The 147 resolver then knows that cat.example.com does not exist; however, it 148 does not use the fact that the proof covers a range (albatross to 149 elephant) to suppress queries for other labels that fall within this 150 range. This means that if the validating resolver gets a query for 151 ball.example.com (or dog.example.com) it will once again go off and 152 query the example.com servers for these names. 154 Apart from wasting bandwidth, this also wastes resources on the 155 recursive server (it needs to keep state for outstanding queries), 156 wastes resources on the authoritative server (it has to answer 157 additional questions), increases latency (the end user has to wait 158 longer than necessary to get back an NXDOMAIN answer), can be used by 159 attackers to cause a DoS (see additional resources), and also has 160 privacy implications (e.g: typos leak out further than necessary). 162 Another example: assume that the (DNSSEC signed) "example.org" zone 163 contains: 165 avocado.example.org IN A 192.0.2.1 166 *.example.org IN A 192.0.2.2 167 zucchini.example.org IN A 192.0.2.3 169 If a query is received for leek.example.org, the system contacts its 170 resolver (which may be itself) to query the example.org servers and 171 will get back an NSEC record stating that there are no records 172 (alphabetically) between avocado and zucchini (or an NSEC3 record 173 stating there is nothing between two hashed names), as well as an 174 answer for leek.example.org, with the label count of the signature 175 set to two (see [RFC7129], section 5.3 for more details). 177 If the validating resolver gets a query for banana.example.org it 178 will once again go off and query the example.org servers for 179 banana.example.org (even though it already has proof that there is a 180 wildcard record) - just like above, this has privacy implications, 181 wastes resources, can be used to contribute to a DoS, etc. 183 4. Background 185 DNSSEC [RFC4035] and [RFC5155] both provide "authenticated denial of 186 existence"; this is a cryptographic proof that the queried for name 187 does not exist or type does not exist. Proof that a name does not 188 exist is accomplished by providing a (DNSSEC secured) record 189 containing the names which appear alphabetically before and after the 190 queried for name. In the first example above, if the (DNSSEC 191 validating) recursive server were to query for dog.example.com it 192 would receive a (signed) NSEC record stating that there are no labels 193 between "albatross" and "elephant" (or, for NSEC3, a similar pair of 194 hashed names). This is a signed, cryptographic proof that these 195 names are the ones before and after the queried for label. As 196 dog.example.com falls within this range, the recursive server knows 197 that dog.example.com really does not exist. Proof that a type does 198 not exist is accomplished by providing a (DNSSEC secured) record 199 containing the queried for name, and a type bitmap which does not 200 include the requested type. 202 This document specifies that this NSEC/NSEC3 record should be used to 203 generate negative answers for any queries that the validating server 204 receives that fall within the range covered by the record (for the 205 TTL for the record). This document also specifies that a positive 206 answer should be generated for any queries that the validating server 207 receives that are proven to be covered by a wildcard record. 209 Section 4.5 of [RFC4035] says: 211 "In theory, a resolver could use wildcards or NSEC RRs to generate 212 positive and negative responses (respectively) until the TTL or 213 signatures on the records in question expire. However, it seems 214 prudent for resolvers to avoid blocking new authoritative data or 215 synthesizing new data on their own. Resolvers that follow this 216 recommendation will have a more consistent view of the namespace." 217 and "The reason for these recommendations is that, between the 218 initial query and the expiration of the data from the cache, the 219 authoritative data might have been changed (for example, via dynamic 220 update).". In other words, if a resolver generates negative answers 221 from an NSEC record, it will not send any queries for names within 222 that NSEC range (for the TTL). If a new name is added to the zone 223 during this interval the resolver will not know this. Similarly, if 224 the resolver is generating responses from a wildcard record, it will 225 continue to do so (for the TTL). 227 We believe this recommendation can be relaxed because, in the absence 228 of this technique, a lookup for the exact name could have come in 229 during this interval, and so a negative answer could already be 230 cached (see [RFC2308] for more background). This means that zone 231 operators should have no expectation that an added name would work 232 immediately. With DNSSEC and Aggressive NSEC, the TTL of the NSEC/ 233 NSEC3 record and the SOA.MINIMUM field are the authoritative 234 statement of how quickly a name can start working within a zone. 236 5. Aggressive use of Cache 238 This document relaxes the restriction given in Section 4.5 of 239 [RFC4035], see Section 7 for more detail. 241 If the negative cache of the validating resolver has sufficient 242 information to validate the query, the resolver SHOULD use NSEC, 243 NSEC3 and wildcard records aggressively. Otherwise, it MUST fall 244 back to send the query to the authoritative DNS servers. 246 5.1. NSEC 248 The validating resolver needs to check the existence of an NSEC RR 249 matching/covering the source of synthesis and an NSEC RR covering the 250 query name. 252 If denial of existence can be determined according to the rules set 253 out in Section 5.4 of [RFC4035], using NSEC records in the cache, 254 then the resolver can immediately return an NXDOMAIN or NODATA (as 255 appropriate) response. 257 5.2. NSEC3 259 NSEC3 aggressive negative caching is more difficult than NSEC 260 aggressive caching. If the zone is signed with NSEC3, the validating 261 resolver needs to check the existence of non-terminals and wildcards 262 which derive from query names. 264 If denial of existence can be determined according to the rules set 265 out in [RFC5155] Sections 8.4, 8.5, 8.6, 8.7, using NSEC3 records in 266 the cache, then the resolver can immediately return an NXDOMAIN or 267 NODATA response (as appropriate). 269 If a covering NSEC3 RR has Opt-Out flag, the covering NSEC3 RR does 270 not prove the non-existence of the domain name and the aggressive 271 negative caching is not possible for the domain name. 273 5.3. Wildcards 275 The last paragraph of [RFC4035] Section 4.5 also discusses the use of 276 wildcards and NSEC RRs to generate positive responses and recommends 277 that it not be relied upon. Just like the case for the aggressive 278 use of NSEC/NSEC3 for negative answers, we revise this 279 recommendation. 281 As long as the validating resolver can determine that a name would 282 not exist without the wildcard match, determined according to the 283 rules set out in Section 5.3.4 of [RFC4035] (NSEC), or in Section 8.8 284 of [RFC5155], it SHOULD synthesize an answer (or NODATA response) for 285 that name using the cached deduced wildcard. If the corresponding 286 wildcard record is not in the cache, it MUST fall back to send the 287 query to the authoritative DNS servers. 289 5.4. Consideration on TTL 291 The TTL value of negative information is especially important, 292 because newly added domain names cannot be used while the negative 293 information is effective. 295 Section 5 of [RFC2308] suggests a maximum default negative cache TTL 296 value of 3 hours (10800). It is RECOMMENDED that validating 297 resolvers limit the maximum effective TTL value of negative responses 298 (NSEC/NSEC3 RRs) to this same value. 300 Section 5 of [RFC2308] also states that a negative cache entry TTL is 301 taken from the minimum of the SOA.MINIMUM field and SOA's TTL. This 302 can be less than the TTL of an NSEC or NSEC3 record, since their TTL 303 is equal to the SOA.MINIMUM field (see [RFC4035]section 2.3 and 304 [RFC5155] section 3.) 306 A resolver that supports aggressive use of NSEC and NSEC3 SHOULD 307 reduce the TTL of NSEC and NSEC3 records to match the SOA.MINIMUM 308 field in the authority section of a negative response, if SOA.MINIMUM 309 is smaller. 311 6. Benefits 313 The techniques described in this document provide a number of 314 benefits, including (in no specific order): 316 Reduced latency: By answering directly from cache, validating 317 resolvers can immediately inform clients that the name they are 318 looking for does not exist, improving the user experience. 320 Decreased recursive server load: By answering queries from the cache 321 by synthesizing answers, validating servers avoid having to send a 322 query and wait for a response. In addition to decreasing the 323 bandwidth used, it also means that the server does not need to 324 allocate and maintain state, thereby decreasing memory and CPU 325 load. 327 Decreased authoritative server load: Because recursive servers can 328 answer queries without asking the authoritative server, the 329 authoritative servers receive fewer queries. This decreases the 330 authoritative server bandwidth, queries per second and CPU 331 utilization. 333 The scale of the benefit depends upon multiple factors, including the 334 query distribution. For example, at the time of this writing, around 335 65% of queries to Root Name servers result in NXDOMAIN responses (see 336 statistics from [root-servers.org]); this technique will eliminate a 337 sizable quantity of these. 339 The technique described in this document may also mitigate so-called 340 "random QNAME attacks", in which attackers send many queries for 341 random sub-domains to resolvers. As the resolver will not have the 342 answers cached, it has to ask external servers for each random query, 343 leading to a DoS on the authoritative servers (and often resolvers). 344 Aggressive NSEC may help mitigate these attacks by allowing the 345 resolver to answer directly from cache for any random queries which 346 fall within already requested ranges. It will not always work as an 347 effective defense, not least because not many zones are DNSSEC signed 348 at all -- but it will still provide an additional layer of defense. 350 As these benefits are only accrued by those using DNSSEC, it is hoped 351 that these techniques will lead to more DNSSEC deployment. 353 7. Update to RFC 4035 355 Section 4.5 of [RFC4035] shows that "In theory, a resolver could use 356 wildcards or NSEC RRs to generate positive and negative responses 357 (respectively) until the TTL or signatures on the records in question 358 expire. However, it seems prudent for resolvers to avoid blocking 359 new authoritative data or synthesizing new data on their own. 360 Resolvers that follow this recommendation will have a more consistent 361 view of the namespace". 363 The paragraph is updated as follows: 365 +-----------------------------------------------------------------+ 366 | Once the records are validated, DNSSEC enabled validating | 367 | resolvers SHOULD use wildcards and NSEC/NSEC3 resource records | 368 | to generate positive and negative responses until the | 369 | effective TTLs or signatures for those records expire. | 370 +-----------------------------------------------------------------+ 372 8. IANA Considerations 374 This document has no IANA actions. 376 9. Security Considerations 378 Use of NSEC / NSEC3 resource records without DNSSEC validation may 379 create serious security issues, and so this technique requires DNSSEC 380 validation. 382 Newly registered resource records may not be used immediately. 383 However, choosing suitable TTL value and negative cache TTL value 384 (SOA MINIMUM field) will mitigate the delay concern, and it is not a 385 security problem. 387 It is also suggested to limit the maximum TTL value of NSEC / NSEC3 388 resource records in the negative cache to, for example, 10800 seconds 389 (3hrs), to mitigate this issue. 391 Although the TTL of NSEC/NSEC3 records is typically fairly short 392 (minutes or hours), their RRSIG expiration time can be much further 393 in the future (weeks). An attacker who is able to successfully spoof 394 responses might poison a cache with old NSEC/NSEC3 records. If the 395 resolver is not making aggressive use of NSEC/NSEC3, the attacker has 396 to repeat the attack for every query. If the resolver is making 397 aggressive use of NSEC/NSEC3, one successful attack would be able to 398 suppress many queries for new names, up to the negative TTL. 400 10. Implementation Status 402 [ Editor note: RFC Editor, please remove this entire section. 403 RFC6982 says: "Since this information is necessarily time dependent, 404 it is inappropriate for inclusion in a published RFC." ] 406 Unbound currently implements aggressive negative caching, as does 407 Google Public DNS. 409 11. Acknowledgments 411 The authors gratefully acknowledge DLV [RFC5074] author Samuel Weiler 412 and the Unbound developers. 414 Thanks to Mark Andrews for providing the helpful notes for 415 implementors provided in Appendix B. 417 The authors would like to specifically thank Stephane Bortzmeyer (for 418 standing next to and helping edit), Ralph Dolmans, Tony Finch, Tatuya 419 JINMEI for extensive review and comments, and also Mark Andrews, 420 Casey Deccio, Alexander Dupuy, Olafur Gudmundsson, Bob Harold, Shumon 421 Huque, John Levine, Pieter Lexis, Matthijs Mekking (who even sent 422 pull requests!) and Ondrej Sury. 424 11.1. Change History 426 RFC Editor: Please remove this section prior to publication. 428 -08 to -09: 430 o Made RFC5074 Informative (after discussions with chairs. 432 o Addressed SecDir comments. 434 o Addressed OpsDir comments. 436 -06 to -08: 438 o Largely editorial, but please see the diffs (editors forgot to 439 update change log when editing, backfilling change log.) 441 o Changed "replacement" text to be "DNSSEC enabled validating 442 resolvers SHOULD use wildcards ..." to align with text in doc. 444 o "A resolver that supports aggressive use of NSEC and NSEC3 SHOULD" 445 (should -> SHOULD) - to align with rest of text. 447 -05 to -06: 449 o Moved some dangling text around - when the examples were added 450 some text added in the wrong place. 452 o There were some bits which mentioned "negative" in the title. 454 o We had the cut-and-paste of what changed in 4035 twice. 456 o Clarified that this also allows NODATA responses to be 457 synthesized. 459 -04 to -05: 461 o Bob pointed out that I did a stupid - when I added the wildcard to 462 'example.com' I made the example wrong / confusing. I have 463 attempted to fix this by adding a second example zone 464 (example.org) with the wildcard instead. 466 o More helpful changes (in a pull request, thanks!) from Matthijs 468 o Included Mark Andrew's useful explanation of how to tell ENT from 469 NXD as an Appendix. 471 -03 to -04: 473 o Working group does want the "positive" answers, not just negative 474 ones. This requires reading what used to be Section 7, and a 475 bunch of cleanup, including: 477 * Additional text in the Problem Statement 478 * Added a wildcard record to the zone. 480 * Added "or positive answers from wildcards" type text (where 481 appropriate) to explain that this isn't just for negative 482 answers. 484 * Reworded much of the Wildcard text. 486 o Incorporated pull request from Tony Finch (thanks!): 487 https://github.com/wkumari/draft-ietf-dnsop-nsec-aggressiveuse/ 488 pull/1 490 o More fixups from Tony (including text): https://www.ietf.org/mail- 491 archive/web/dnsop/current/msg18271.html. This included much 492 clearer text on TTL, references to the NSEC / NSEC3 RFCs (instead 493 of my clumsy summary), good text on replays, etc. 495 o Converted the "zone file" to a figure to make it more readable. 497 o Text from Tim W: "If a validating resolver receives a query for 498 cat.example.com, it contacts its resolver (which may be itself) to 499 query..." - which satisfies Jinmei's concern (which I was too 500 dense to grock). 502 o Fixup of the "validation required" in security considerations. 504 -02 to -03: 506 o Integrated a bunch of comments from Matthijs Mekking - details in: 507 https://github.com/wkumari/draft-ietf-dnsop-nsec-aggressiveuse/ 508 pull/1. I decided to keep "Aggressive Negative Caching" instead 509 of "Aggressive USE OF Negative Caching" for readability. 511 o Attempted to address Bob Harold's comment on the readability 512 issues with "But, it will be more effective when both are 513 enabled..." in Section 5.4 - https://www.ietf.org/mail- 514 archive/web/dnsop/current/msg17997.html 516 o MAYs and SHOULD drifted in the text block. Fixed - thanks to 517 https://mailarchive.ietf.org/arch/msg/ 518 dnsop/2ljmmzxtIMCFMLOZmWcSbTYVOy4 520 o A number of good edits from Stephane in: https://www.ietf.org/ 521 mail-archive/web/dnsop/current/msg18109.html 523 o A bunch more edits from Jinmei, as in: https://www.ietf.org/mail- 524 archive/web/dnsop/current/msg18206.html 526 -01 to -02: 528 o Added Section 6 - Benefits (as suggested by Jinmei). 530 o Removed Appendix B (Jinmei) 532 o Replaced "full-service" with "validating" (where applicable) 534 o Integrated other comments from Jinmei from https://www.ietf.org/ 535 mail-archive/web/dnsop/current/msg17875.html 537 o Integrated comment from co-authors, including re-adding parts of 538 Appendix B, terminology, typos. 540 o Tried to explain under what conditions this may actually mitigate 541 attacks. 543 -00 to -01: 545 o Comments from DNSOP meeting in Berlin. 547 o Changed intended status to Standards Track (updates RFC 4035) 549 o Added a section "Updates to RFC 4035" 551 o Some language clarification / typo / cleanup 553 o Cleaned up the TTL section a bit. 555 o Removed Effects section, Additional proposal section, and pseudo 556 code. 558 o Moved "mitigation of random subdomain attacks" to Appendix. 560 From draft-fujiwara-dnsop-nsec-aggressiveuse-03 -> draft-ietf-dnsop- 561 nsec-aggressiveuse 563 o Document adopted by DNSOP WG. 565 o Adoption comments 567 o Changed main purpose to performance 569 o Use NSEC3/Wildcard keywords 571 o Improved wordings (from good comments) 573 o Simplified pseudo code for NSEC3 574 o Added Warren as co-author. 576 o Reworded much of the problem statement 578 o Reworked examples to better explain the problem / solution. 580 11.1.1. Version draft-fujiwara-dnsop-nsec-aggressiveuse-01 582 o Added reference to DLV [RFC5074] and imported some sentences. 584 o Added Aggressive Negative Caching Flag idea. 586 o Added detailed algorithms. 588 11.1.2. Version draft-fujiwara-dnsop-nsec-aggressiveuse-02 590 o Added reference to [I-D.vixie-dnsext-resimprove] 592 o Added considerations for the CD bit 594 o Updated detailed algorithms. 596 o Moved Aggressive Negative Caching Flag idea into Additional 597 Proposals 599 11.1.3. Version draft-fujiwara-dnsop-nsec-aggressiveuse-03 601 o Added "Partial implementation" 603 o Section 4,5,6 reorganized for better representation 605 o Added NODATA answer in Section 4 607 o Trivial updates 609 o Updated pseudo code 611 12. References 613 12.1. Normative References 615 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 616 Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ 617 RFC2119, March 1997, 618 . 620 [RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS 621 NCACHE)", RFC 2308, DOI 10.17487/RFC2308, March 1998, 622 . 624 [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. 625 Rose, "Protocol Modifications for the DNS Security 626 Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005, 627 . 629 [RFC4592] Lewis, E., "The Role of Wildcards in the Domain Name 630 System", RFC 4592, DOI 10.17487/RFC4592, July 2006, 631 . 633 [RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS 634 Security (DNSSEC) Hashed Authenticated Denial of 635 Existence", RFC 5155, DOI 10.17487/RFC5155, March 2008, 636 . 638 [RFC7129] Gieben, R. and W. Mekking, "Authenticated Denial of 639 Existence in the DNS", RFC 7129, DOI 10.17487/RFC7129, 640 February 2014, . 642 [RFC7719] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS 643 Terminology", RFC 7719, DOI 10.17487/RFC7719, December 644 2015, . 646 12.2. Informative References 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 [RFC5074] Weiler, S., "DNSSEC Lookaside Validation (DLV)", RFC 5074, 655 DOI 10.17487/RFC5074, November 2007, 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 [root-servers.org] 663 IANA, "Root Server Technical Operations Assn", 664 . 666 Appendix A. Detailed implementation notes 668 o Previously, cached negative responses were indexed by QNAME, 669 QCLASS, QTYPE, and the setting of the CD bit (see RFC 4035, 670 Section 4.7), and only queries matching the index key would be 671 answered from the cache. With aggressive negative caching, the 672 validator, in addition to checking to see if the answer is in its 673 cache before sending a query, checks to see whether any cached and 674 validated NSEC record denies the existence of the sought 675 record(s). Using aggressive negative caching, a validator will 676 not make queries for any name covered by a cached and validated 677 NSEC record. Furthermore, a validator answering queries from 678 clients will synthesize a negative answer (or NODATA response) 679 whenever it has an applicable validated NSEC in its cache unless 680 the CD bit was set on the incoming query. (Imported from 681 Section 6 of [RFC5074]). 683 o Implementing aggressive negative caching suggests that a validator 684 will need to build an ordered data structure of NSEC and NSEC3 685 records for each signer domain name of NSEC / NSEC3 records in 686 order to efficiently find covering NSEC / NSEC3 records. Call the 687 table as NSEC_TABLE. (Imported from Section 6.1 of [RFC5074] and 688 expanded.) 690 o The aggressive negative caching may be inserted at the cache 691 lookup part of the recursive resolvers. 693 o If errors happen in aggressive negative caching algorithm, 694 resolvers MUST fall back to resolve the query as usual. "Resolve 695 the query as usual" means that the resolver must process the query 696 as though it does not implement aggressive negative caching. 698 Appendix B. Procedure for determining ENT vs NXDOMAN with NSEC 700 This procedure outlines how to determine if a given name does not 701 exist, or is an ENT (Empty Non-Terminal, see [RFC5155] Section 1.3) 702 with NSEC. 704 If the NSEC record has not been verified as secure discard it. 706 If the given name sorts before or matches the NSEC owner name discard 707 it as it does not prove the NXDOMAIN or ENT. 709 If the given name is a subdomain of the NSEC owner name and the NS 710 bit is present and the SOA bit is absent then discard the NSEC as it 711 is from a parent zone. 713 If the next domain name sorts after the NSEC owner name and the given 714 name sorts after or matches next domain name then discard the NSEC 715 record as it does not prove the NXDOMAIN or ENT. 717 If the next domain name sorts before or matches the NSEC owner name 718 and the given name is not a subdomain of the next domain name then 719 discard the NSEC as it does not prove the NXDOMAIN or ENT. 721 You now have a NSEC record that proves the NXDOMAIN or ENT. 723 If the next domain name is a subdomain of the given name you have a 724 ENT otherwise you have a NXDOMAIN. 726 Authors' Addresses 728 Kazunori Fujiwara 729 Japan Registry Services Co., Ltd. 730 Chiyoda First Bldg. East 13F, 3-8-1 Nishi-Kanda 731 Chiyoda-ku, Tokyo 101-0065 732 Japan 734 Phone: +81 3 5215 8451 735 Email: fujiwara@jprs.co.jp 737 Akira Kato 738 Keio University/WIDE Project 739 Graduate School of Media Design, 4-1-1 Hiyoshi 740 Kohoku, Yokohama 223-8526 741 Japan 743 Phone: +81 45 564 2490 744 Email: kato@wide.ad.jp 746 Warren Kumari 747 Google 748 1600 Amphitheatre Parkway 749 Mountain View, CA 94043 750 US 752 Email: warren@kumari.net