idnits 2.17.1 draft-ietf-dnsop-multi-provider-dnssec-02.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- ** The document seems to lack a both a reference to RFC 2119 and the recommended RFC 2119 boilerplate, even if it appears to use RFC 2119 keywords. RFC 2119 keyword, line 247: '... It is RECOMMENDED that the provider...' Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (July 8, 2019) is 1747 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- ** Obsolete normative reference: RFC 2845 (Obsoleted by RFC 8945) Summary: 2 errors (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force S. Huque 3 Internet-Draft P. Aras 4 Intended status: Informational Salesforce 5 Expires: January 9, 2020 J. Dickinson 6 Sinodun 7 J. Vcelak 8 NS1 9 D. Blacka 10 Verisign 11 July 8, 2019 13 Multi Signer DNSSEC models 14 draft-ietf-dnsop-multi-provider-dnssec-02 16 Abstract 18 Many enterprises today employ the service of multiple DNS providers 19 to distribute their authoritative DNS service. Deploying DNSSEC in 20 such an environment may present some challenges depending on the 21 configuration and feature set in use. This document will present 22 several deployment models that may be suitable. 24 Status of This Memo 26 This Internet-Draft is submitted in full conformance with the 27 provisions of BCP 78 and BCP 79. 29 Internet-Drafts are working documents of the Internet Engineering 30 Task Force (IETF). Note that other groups may also distribute 31 working documents as Internet-Drafts. The list of current Internet- 32 Drafts is at http://datatracker.ietf.org/drafts/current/. 34 Internet-Drafts are draft documents valid for a maximum of six months 35 and may be updated, replaced, or obsoleted by other documents at any 36 time. It is inappropriate to use Internet-Drafts as reference 37 material or to cite them other than as "work in progress." 39 This Internet-Draft will expire on January 9, 2020. 41 Copyright Notice 43 Copyright (c) 2019 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents 48 (http://trustee.ietf.org/license-info) in effect on the date of 49 publication of this document. Please review these documents 50 carefully, as they describe your rights and restrictions with respect 51 to this document. Code Components extracted from this document must 52 include Simplified BSD License text as described in Section 4.e of 53 the Trust Legal Provisions and are provided without warranty as 54 described in the Simplified BSD License. 56 Table of Contents 58 1. Introduction and Motivation . . . . . . . . . . . . . . . . . 2 59 2. Deployment Models . . . . . . . . . . . . . . . . . . . . . . 3 60 2.1. Multiple Signer models . . . . . . . . . . . . . . . . . 3 61 2.1.1. Model 1: Common KSK, Unique ZSK per provider . . . . 4 62 2.1.2. Model 2: Unique KSK and ZSK per provider . . . . . . 4 63 3. Validating Resolver Behavior . . . . . . . . . . . . . . . . 5 64 4. Signing Algorithm Considerations . . . . . . . . . . . . . . 6 65 5. Authenticated Denial Considerations . . . . . . . . . . . . . 6 66 5.1. Single Method . . . . . . . . . . . . . . . . . . . . . . 7 67 5.2. Mixing Methods . . . . . . . . . . . . . . . . . . . . . 7 68 6. Key Rollover Considerations . . . . . . . . . . . . . . . . . 7 69 6.1. Model 1: Common KSK, Unique ZSK per provider . . . . . . 8 70 6.2. Model 2: Unique KSK and ZSK per provider . . . . . . . . 8 71 7. Use of CDS and CDNSKEY . . . . . . . . . . . . . . . . . . . 9 72 8. Key Management Mechanism Requirements . . . . . . . . . . . . 9 73 9. DNS Response Size Considerations . . . . . . . . . . . . . . 10 74 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 75 11. Security Considerations . . . . . . . . . . . . . . . . . . . 10 76 12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 77 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 78 13.1. Normative References . . . . . . . . . . . . . . . . . . 11 79 13.2. Informative References . . . . . . . . . . . . . . . . . 12 80 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 82 1. Introduction and Motivation 84 RFC EDITOR: PLEASE REMOVE THE FOLLOWING PARAGRAPH BEFORE PUBLISHING: 85 The source for this draft is maintained in GitHub at: 86 https://github.com/shuque/multi-provider-dnssec 88 Many enterprises today employ the service of multiple DNS providers 89 to distribute their authoritative DNS service. This allows the DNS 90 service to survive a complete failure of any single provider. 91 Additionally, enterprises or providers occasionally have requirements 92 that preclude standard zone transfer techniques [RFC1995] [RFC5936] : 93 either non-standardized DNS features are in use that are incompatible 94 with zone transfer, or operationally a provider must be able to 95 (re)sign DNS records using their own keys. This document outlines 96 some possible models of DNSSEC [RFC4033] [RFC4034] [RFC4035] 97 deployment in such an environment. 99 2. Deployment Models 101 If a zone owner is able to use standard zone transfer techniques, 102 then the presence of multiple providers does not present any need to 103 substantially modify normal deployment models. In these deployments 104 there is a single signing entity (which may be the zone owner, one of 105 the providers, or a separate entity), while the providers act as 106 secondary authoritative servers for the zone. 108 Occasionally, however, standard zone transfer techniques cannot be 109 used. This could be due to the use of non-standard DNS features, or 110 due to operational requirements of a given provider (e.g., a provider 111 that only supports "online signing".) In these scenarios, the 112 multiple providers each act like primary servers, independently 113 signing data received from the zone owner and serving it to DNS 114 queriers. This configuration presents some novel challenges and 115 requirements. 117 2.1. Multiple Signer models 119 In this category of models, multiple providers each independently 120 sign and serve the same zone. The zone owner typically uses 121 provider-specific APIs to update zone content at each of the 122 providers, and relies on the provider to perform signing of the data. 123 A key requirement here is to manage the contents of the DNSKEY and DS 124 RRset in such a way that validating resolvers always have a viable 125 path to authenticate the DNSSEC signature chain no matter which 126 provider is queried. This requirement is achieved by having each 127 provider import the public Zone Signing Keys (ZSKs) of all other 128 providers into their DNSKEY RRsets. 130 These models can support DNSSEC even for the non-standard features 131 mentioned previously, if the DNS providers have the capability of 132 signing the response data generated by those features. Since these 133 responses are often generated dynamically at query time, one method 134 is for the provider to perform online signing (also known as on-the- 135 fly signing). However, another possible approach is to pre-compute 136 all the possible response sets and associated signatures and then 137 algorithmically determine at query time which response set needs to 138 be returned. 140 In the models presented, the function of coordinating the DNSKEY or 141 DS RRset does not involve the providers communicating directly with 142 each other. Feedback from several commercial managed DNS providers 143 indicates that they may be unlikely to directly communicate since 144 they typically have a contractual relationship only with the zone 145 owner. However, if the parties involved are agreeable, it may be 146 possible to devise a protocol mechanism by which the providers 147 directly communicate to share keys. 149 The following descriptions consider the case of two DNS providers, 150 but the model is generalizable to any number. 152 2.1.1. Model 1: Common KSK, Unique ZSK per provider 154 o Zone owner holds the KSK, manages the DS record, and is 155 responsible for signing the DNSKEY RRset and distributing the 156 signed DNSKEY RRset to the providers. 158 o Each provider has their own ZSK which is used to sign data. 160 o Providers have an API that owner uses to query the ZSK public key, 161 and insert a combined DNSKEY RRset that includes both ZSKs and the 162 KSK, signed by the KSK. 164 o Note that even if the contents of the DNSKEY RRset don't change, 165 the Zone owner of course needs to periodically re-sign it as 166 signature expiration approaches. The provider API is also used to 167 thus periodically redistribute the refreshed DNSKEY RRset. 169 o Key rollovers need coordinated participation of the zone owner to 170 update the DNSKEY RRset (for KSK or ZSK), and the DS RRset (for 171 KSK). 173 2.1.2. Model 2: Unique KSK and ZSK per provider 175 o Each provider has their own KSK and ZSK. 177 o Each provider offers an API that the Zone Owner uses to import the 178 ZSK of the other provider into their DNSKEY RRset. 180 o DNSKEY RRset is signed independently by each provider using their 181 own KSK. 183 o Zone Owner manages the DS RRset that includes both KSKs. 185 o Key rollovers need coordinated participation of the zone owner to 186 update the DS RRset (for KSK), and the DNSKEY RRset (for ZSK). 188 3. Validating Resolver Behavior 190 The central requirement for both of the Multiple Signer models 191 (Section 2.1) is to ensure that the ZSKs from all providers are 192 present in each provider's apex DNSKEY RRset, and is vouched for by 193 either the single KSK (in model 1) or each provider's KSK (in model 194 2.) If this is not done, the following situation can arise (assuming 195 two providers A and B): 197 o The validating resolver follows a referral (delegation) to the 198 zone in question. 200 o It retrieves the zone's DNSKEY RRset from one of provider A's 201 nameservers. 203 o At some point in time, the resolver attempts to resolve a name in 204 the zone, while the DNSKEY RRset received from provider A is still 205 viable in its cache. 207 o It queries one of provider B's nameservers to resolve the name, 208 and obtains a response that is signed by provider B's ZSK, which 209 it cannot authenticate because this ZSK is not present in its 210 cached DNSKEY RRset for the zone that it received from provider A. 212 o The resolver will not accept this response. It may still be able 213 to ultimately authenticate the name by querying other nameservers 214 for the zone until it elicits a response from one of provider A's 215 nameservers. But it has incurred the penalty of additional 216 roundtrips with other nameservers, with the corresponding latency 217 and processing costs. The exact number of additional roundtrips 218 depends on details of the resolver's nameserver selection 219 algorithm and the number of nameservers configured at provider B. 221 o It may also be the case that a resolver is unable to provide an 222 authenticated response because it gave up after a certain number 223 of retries or a certain amount of delay. Or that downstream 224 clients of the resolver that originated the query timed out 225 waiting for a response. 227 Zone owners will want to deploy a DNS service that responds as 228 efficiently as possible with validatable answers only, and hence it 229 is important that the DNSKEY RRset at each provider is maintained 230 with the active ZSKs of all participating providers. This ensures 231 that resolvers can validate a response no matter which provider's 232 nameservers it came from. 234 Details of how the DNSKEY RRset itself is validated differs. In 235 model 1 (Section 2.1.1), one unique KSK managed by the Zone Owner 236 signs an identical DNSKEY RRset deployed at each provider, and the 237 signed DS record in the parent zone refers to this KSK. In model 2 238 (Section 2.1.2), each provider has a distinct KSK and signs the 239 DNSKEY RRset with it. The Zone Owner deploys a DS RRset at the 240 parent zone that contains multiple DS records, each referring to a 241 distinct provider's KSK. Hence it does not matter which provider's 242 nameservers the resolver obtains the DNSKEY RRset from, the signed DS 243 record in each model can authenticate the associated KSK. 245 4. Signing Algorithm Considerations 247 It is RECOMMENDED that the providers use a common signing algorithm 248 (and common keysizes for algorithms that support variable key sizes). 249 This ensures that the multiple providers have identical security 250 postures and no provider is more vulnerable to cryptanalytic attack 251 than the others. 253 It may however be possible to deploy a configuration where different 254 providers use different signing algorithms. The main impediment is 255 that current DNSSEC specifications require that if there are multiple 256 algorithms in the DNSKEY RRset, then RRsets in the zone need to be 257 signed with at least one DNSKEY of each algorithm, as described in 258 RFC 4035 [RFC4035], Section 2.2. However RFC 6781 [RFC6781], 259 Section 4.1.4, also describes both a conservative and liberal 260 interpretation of this requirement. When validating DNS resolvers 261 follow the liberal approach, they do not expect that zone RRsets are 262 signed by every signing algorithm in the DNSKEY RRset, and responses 263 with single algorithm signatures can be validated corectly assuming a 264 valid chain of trust exists. In fact, testing by the .BR Top Level 265 domain for their recent algorithm rollover [BR-ROLLOVER], 266 demonstrates that the liberal approach does in fact work with current 267 resolvers deployed on the Internet. 269 5. Authenticated Denial Considerations 271 Authentiated denial of existence enables a resolver to validate that 272 a record does not exist. For this purpose, an authoritative server 273 presents, in a response to the resolver, NSEC (Section 3.1.3 of 274 [RFC4035]) or NSEC3 (Section 7.2 of [RFC5155]) records. The NSEC3 275 method enhances NSEC by providing opt-out for signing insecure 276 delegations and also adds limited protection against zone enumeration 277 attacks. 279 An authoritative server response carrying records for authenticated 280 denial is always self-contained and the receiving resolver doesn't 281 need to send additional queries to complete the denial proof data. 282 For this reason, no rollover is needed when switching between NSEC 283 and NSEC3 for a signed zone. 285 Since authenticated denial responses are self-contained, NSEC and 286 NSEC3 can be used by different providers to serve the same zone. 287 Doing so however defeats the protection against zone enumeration 288 provided by NSEC3. A better configuration involves multiple 289 providers using different authenticated denial of existence 290 mechanisms that all provide zone enumeration defense, such as pre- 291 computed NSEC3, NSEC3 White Lies [RFC7129], NSEC Black Lies 292 [BLACKLIES], etc. Note however that having multiple providers 293 offering different authenticated denial mechanisms may impact how 294 effectively resolvers are able to make use of the caching of negative 295 responses. 297 5.1. Single Method 299 Usually, the NSEC and NSEC3 methods are used exclusively (i.e. the 300 methods are not used at the same time by different servers). This 301 configuration is prefered because the behavior is well-defined and 302 it's closest to the current operational practice. 304 5.2. Mixing Methods 306 Compliant resolvers should be able to validate zone data when 307 different authoritative servers for the same zone respond with 308 different authentiated denial methods because this is normally 309 observed when NSEC and NSEC3 are being switched or when NSEC3PARAM is 310 updated. 312 Resolver software may be however designed to handle a single 313 transition between two authenticated denial configurations more 314 optimally than permanent setup with mixed authenticated denial 315 methods. This could make caching on the resolver side less efficient 316 and the authoritative servers may observe higher number of queries. 317 This aspect should be considered especially in context of Aggresive 318 Use of DNSSEC-Validated Cache [RFC8198]. 320 In case all providers cannot be configured for a matching 321 authentiated denial, it is advised to find lowest number of possible 322 configurations possible across all used providers. 324 Note that NSEC3 configuration on all providers with different 325 NSEC3PARAM values is considered a mixed setup. 327 6. Key Rollover Considerations 329 The Multiple Signer (Section 2.1) models introduce some new 330 requirements for DNSSEC key rollovers. Since this process 331 necessarily involves coordinated actions on the part of providers and 332 the Zone Owner, one reasonable strategy is for the Zone Owner to 333 initiate key rollover operations. But other operationally plausible 334 models may also suit, such as a DNS provider initiating a key 335 rollover and signaling their intent to the Zone Owner in some manner. 337 The descriptions in this section assume that KSK rollovers employ the 338 commonly used Double Signature KSK Rollover Method, and that ZSK 339 rollovers employ the Pre-Publish ZSK Rollover Method, as described in 340 detail in [RFC6781]. With minor modifications, they can also be 341 easily adapted to other models, such as Double DS KSK Rollover or 342 Double Signature ZSK rollover, if desired. 344 6.1. Model 1: Common KSK, Unique ZSK per provider 346 o Key Signing Key Rollover: In this model, the two managed DNS 347 providers share a common KSK which is held by the Zone Owner. To 348 initiate the rollover, the Zone Owner generates a new KSK and 349 obtains the DNSKEY RRset of each DNS provider using their 350 respective APIs. The new KSK is added to each provider's DNSKEY 351 RRset and the RRset is re-signed with both the new and the old 352 KSK. This new DNSKEY RRset is then transferred to each provider. 353 The Zone Owner then updates the DS RRset in the parent zone to 354 point to the new KSK, and after the necessary DS record TTL period 355 has expired, proceeds with updating the DNSKEY RRSet to remove the 356 old KSK. 358 o Zone Signing Key Rollover: In this model, each DNS provider has 359 separate Zone Signing Keys. Each provider can choose to roll 360 their ZSK independently by co-ordinating with the Zone Owner. 361 Provider A would generate a new ZSK and communicate their intent 362 to perform a rollover (note that Provider A cannot immediately 363 insert this new ZSK into their DNSKEY RRset because the RRset has 364 to be signed by the Zone Owner). The Zone Owner obtains the new 365 ZSK from Provider A. It then obtains the current DNSKEY RRset 366 from each provider (including Provider A), inserts the new ZSK 367 into each DNSKEY RRset, re-signs the DNSKEY RRset, and sends it 368 back to each provider for deployment via their respective key 369 management APIs. Once the necessary time period is elapsed (i.e. 370 all zone data has been re-signed by the new ZSK and propagated to 371 all authoritative servers for the zone, plus the maximum zone TTL 372 value of any of the data in the zone signed by the old ZSK), 373 Provider A and the zone owner can initiate the next phase of 374 removing the old ZSK. 376 6.2. Model 2: Unique KSK and ZSK per provider 378 o Key Signing Key Rollover: In Model 2, each managed DNS provider 379 has their own KSK. A KSK roll for provider A does not require any 380 change in the DNSKEY RRset of provider B, but does require co- 381 ordination with the Zone Owner in order to get the DS record set 382 in the parent zone updated. The KSK roll starts with Provider A 383 generating a new KSK and including it in their DNSKEY RRSet. The 384 DNSKey RRset would then be signed by both the new and old KSK. 385 The new KSK is communicated to the Zone Owner, after which the 386 Zone Owner updates the DS RRset to replace the DS record for the 387 old KSK with a DS record for the new KSK. After the necessary DS 388 RRset TTL period has elapsed, the old KSK can be removed from 389 provider A's DNSKEY RRset. 391 o Zone Signing Key Rollover: In Model 2, each managed DNS provider 392 has their own ZSK. The ZSK roll for provider A would start with 393 them generating new ZSK and including it in their DNSKEY RRset and 394 re-signing the new DNSKEY RRset with their KSK. The new ZSK of 395 provider A would then be communicated to the Zone Owner, who will 396 initiate the process of importing this ZSK into the DNSKEY RRsets 397 of the other providers, using their respective APIs. Once the 398 necessary Pre-Publish key rollover time periods have elapsed, 399 provider A and the Zone Owner can initiate the process of removing 400 the old ZSK from the DNSKEY RRset of all providers. 402 7. Use of CDS and CDNSKEY 404 CDS and CDNSKEY records [RFC7344] [RFC8078] are used to facilitate 405 automated updates of DNSSEC secure entry point keys between parent 406 and child zones. Multi-signer DNSSEC configurations can support this 407 too. In Model 1, CDS/CDNSKEY changes are centralized at the zone 408 owner. However, the zone owner will still need to push down updated 409 signed CDNS/DNSKEY RRsets to the providers via the key management 410 mechanism. In Model 2, the key management mechanism needs to support 411 cross importation of the CDS/CDNSKEY records, so that a common view 412 of the RRset can be constructed at each provider, and is visible to 413 the parent zone attempting to update the DS RRset. 415 8. Key Management Mechanism Requirements 417 Managed DNS providers often have their own proprietary zone 418 configuration and data management APIs, typically utilizing HTTPS/ 419 REST interfaces. So, rather than outlining a new API for key 420 management here, we describe the specific functions that the provider 421 API needs to support in order to enable the multi-signer models. The 422 Zone owner is expected to use these API functions to perform key 423 management tasks. Other mechanisms that can offer these functions, 424 if supported by the providers, include the DNS UPDATE protocol 425 [RFC2136] and EPP [RFC5731]. 427 o The API must offer a way to query the current DNSKEY RRset of the 428 provider 430 o For model 1, the API must offer a way to import a signed DNSKEY 431 RRset and replace the current one at the provider. Additionally, 432 if CDS/CDNSKEY is supported, the API must also offer a way to 433 import a signed CDS/CDNSKEY RRset. 435 o For model 2, the API must offer a way to import a DNSKEY record 436 from an external provider into the current DNSKEY RRset. 437 Additionally, if CDS/CDNSKEY is supported, the API must offer a 438 mechanism to import individual CDS/CDNSKEY records from an 439 external provider. 441 In model 2, once initially bootstrapped with each others zone signing 442 keys via these API mechanisms, providers could, if desired, 443 periodically query each others DNSKEY RRsets and automatically import 444 or withdraw ZSKs in the keyset as key rollover events happen. 446 9. DNS Response Size Considerations 448 The Multi-Signer models described in this document result in larger 449 DNSKEY RRsets, so the DNSKEY response size will be larger. The 450 actual size depends on multiple factors: DNSKEY algorithm and keysize 451 choices, the number of providers, how many simultaneous key rollovers 452 are in progress etc. Newer elliptic curve algorithms produce keys 453 small enough that the responses will typically be far below the 454 common Internet path MTU, and thus operational issues related to IP 455 fragmentation or truncation and TCP fallback are unlikely to be 456 encountered. 458 10. IANA Considerations 460 This document includes no request to IANA. 462 11. Security Considerations 464 The Zone key import APIs required by these models need to be strongly 465 authenticated to prevent tampering of key material by malicious third 466 parties. Many providers today offer REST/HTTPS APIs that utilize a 467 number of authentication mechanisms (username/password, API keys 468 etc). If DNS protocol mechanisms like UPDATE are being used for key 469 insertion and deletion, they should similarly be strongly 470 authenticated, e.g. by employing Transaction Signatures (TSIG) 471 [RFC2845]. 473 12. Acknowledgments 475 The initial version of this document benefited from discussions with 476 and review from Duane Wessels. Additional helpful comments were 477 provided by Steve Crocker, Ulrich Wisser, Tony Finch, and Olafur 478 Gudmundsson. 480 13. References 482 13.1. Normative References 484 [RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound, 485 "Dynamic Updates in the Domain Name System (DNS UPDATE)", 486 RFC 2136, DOI 10.17487/RFC2136, April 1997, 487 . 489 [RFC2845] Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B. 490 Wellington, "Secret Key Transaction Authentication for DNS 491 (TSIG)", RFC 2845, DOI 10.17487/RFC2845, May 2000, 492 . 494 [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. 495 Rose, "DNS Security Introduction and Requirements", 496 RFC 4033, DOI 10.17487/RFC4033, March 2005, 497 . 499 [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. 500 Rose, "Resource Records for the DNS Security Extensions", 501 RFC 4034, DOI 10.17487/RFC4034, March 2005, 502 . 504 [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. 505 Rose, "Protocol Modifications for the DNS Security 506 Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005, 507 . 509 [RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS 510 Security (DNSSEC) Hashed Authenticated Denial of 511 Existence", RFC 5155, DOI 10.17487/RFC5155, March 2008, 512 . 514 [RFC5731] Hollenbeck, S., "Extensible Provisioning Protocol (EPP) 515 Domain Name Mapping", STD 69, RFC 5731, 516 DOI 10.17487/RFC5731, August 2009, . 519 [RFC6781] Kolkman, O., Mekking, W., and R. Gieben, "DNSSEC 520 Operational Practices, Version 2", RFC 6781, 521 DOI 10.17487/RFC6781, December 2012, . 524 [RFC7344] Kumari, W., Gudmundsson, O., and G. Barwood, "Automating 525 DNSSEC Delegation Trust Maintenance", RFC 7344, 526 DOI 10.17487/RFC7344, September 2014, . 529 [RFC8078] Gudmundsson, O. and P. Wouters, "Managing DS Records from 530 the Parent via CDS/CDNSKEY", RFC 8078, 531 DOI 10.17487/RFC8078, March 2017, . 534 [RFC8198] Fujiwara, K., Kato, A., and W. Kumari, "Aggressive Use of 535 DNSSEC-Validated Cache", RFC 8198, DOI 10.17487/RFC8198, 536 July 2017, . 538 13.2. Informative References 540 [BLACKLIES] 541 Valsorda, F. and O. Gudmundsson, "Compact DNSSEC Denial of 542 Existence or Black Lies", . 545 [BR-ROLLOVER] 546 Neves, F., ".br DNSSEC Algorithm Rollover Update", 547 in ICANN 62 DNSSEC Workshop, June 2018, 548 . 551 [RFC1995] Ohta, M., "Incremental Zone Transfer in DNS", RFC 1995, 552 DOI 10.17487/RFC1995, August 1996, . 555 [RFC5936] Lewis, E. and A. Hoenes, Ed., "DNS Zone Transfer Protocol 556 (AXFR)", RFC 5936, DOI 10.17487/RFC5936, June 2010, 557 . 559 [RFC7129] Gieben, R. and W. Mekking, "Authenticated Denial of 560 Existence in the DNS", RFC 7129, DOI 10.17487/RFC7129, 561 February 2014, . 563 Authors' Addresses 565 Shumon Huque 566 Salesforce 568 Email: shuque@gmail.com 569 Pallavi Aras 570 Salesforce 572 Email: paras@salesforce.com 574 John Dickinson 575 Sinodun 577 Email: jad@sinodun.com 579 Jan Vcelak 580 NS1 582 Email: jvcelak@ns1.com 584 David Blacka 585 Verisign 587 Email: davidb@verisign.com