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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) No issues found here. Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 DNSOP G. Huston 3 Internet-Draft J. Damas 4 Intended status: Standards Track APNIC 5 Expires: August 25, 2018 W. Kumari 6 Google 7 February 21, 2018 9 A Sentinel for Detecting Trusted Keys in DNSSEC 10 draft-ietf-dnsop-kskroll-sentinel-02 12 Abstract 14 The DNS Security Extensions (DNSSEC) were developed to provide origin 15 authentication and integrity protection for DNS data by using digital 16 signatures. These digital signatures can be verified by building a 17 chain of trust starting from a trust anchor and proceeding down to a 18 particular node in the DNS. This document specifies a mechanism that 19 will allow an end user to determine the trusted key state for the 20 root key of the resolvers that handle that user's DNS queries. Note 21 that this method is only applicable for determing which keys are in 22 the trust store for the root key. 24 There is an example / toy implementation of this at http://www.ksk- 25 test.net . 27 [ This document is being collaborated on in Github at: 28 https://github.com/APNIC-Labs/draft-kskroll-sentinel. The most 29 recent version of the document, open issues, etc should all be 30 available here. The authors (gratefully) accept pull requests. Text 31 in square brackets will be removed before publication. ] 33 [ NOTE: This version uses the labels "kskroll-sentinel-is-ta-", "kskroll-sentinel-not-ta-"; older versions of 35 this document used "_is-ta-", "_not-ta-". ] 37 Status of This Memo 39 This Internet-Draft is submitted in full conformance with the 40 provisions of BCP 78 and BCP 79. 42 Internet-Drafts are working documents of the Internet Engineering 43 Task Force (IETF). Note that other groups may also distribute 44 working documents as Internet-Drafts. The list of current Internet- 45 Drafts is at http://datatracker.ietf.org/drafts/current/. 47 Internet-Drafts are draft documents valid for a maximum of six months 48 and may be updated, replaced, or obsoleted by other documents at any 49 time. It is inappropriate to use Internet-Drafts as reference 50 material or to cite them other than as "work in progress." 52 This Internet-Draft will expire on August 25, 2018. 54 Copyright Notice 56 Copyright (c) 2018 IETF Trust and the persons identified as the 57 document authors. All rights reserved. 59 This document is subject to BCP 78 and the IETF Trust's Legal 60 Provisions Relating to IETF Documents 61 (http://trustee.ietf.org/license-info) in effect on the date of 62 publication of this document. Please review these documents 63 carefully, as they describe your rights and restrictions with respect 64 to this document. Code Components extracted from this document must 65 include Simplified BSD License text as described in Section 4.e of 66 the Trust Legal Provisions and are provided without warranty as 67 described in the Simplified BSD License. 69 Table of Contents 71 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 72 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 73 2. Use Case . . . . . . . . . . . . . . . . . . . . . . . . . . 3 74 3. Sentinel Mechanism . . . . . . . . . . . . . . . . . . . . . 6 75 4. Sentinel Processing . . . . . . . . . . . . . . . . . . . . . 7 76 5. Sentinel Test Result Considerations . . . . . . . . . . . . . 9 77 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 78 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 79 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11 80 9. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 11 81 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 82 10.1. Normative References . . . . . . . . . . . . . . . . . . 12 83 10.2. Informative References . . . . . . . . . . . . . . . . . 12 84 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 86 1. Introduction 88 The DNS Security Extensions (DNSSEC) [RFC4033], [RFC4034] and 89 [RFC4035] were developed to provide origin authentication and 90 integrity protection for DNS data by using digital signatures. 91 DNSSEC uses Key Tags to efficiently match signatures to the keys from 92 which they are generated. The Key Tag is a 16-bit value computed 93 from the RDATA portion of a DNSKEY RR using a formula not unlike a 94 ones-complement checksum. RRSIG RRs contain a Key Tag field whose 95 value is equal to the Key Tag of the DNSKEY RR that validates the 96 signature. 98 This document specifies how validating resolvers can respond to 99 certain queries in a manner that allows a querier to deduce whether a 100 particular key for the root has been loaded into that resolver's 101 trusted key store. In particular, this response mechanism can be 102 used to determine whether a certain Root Zone KSK is ready to be used 103 as a trusted key within the context of a key roll by this resolver. 105 This new mechanism is OPTIONAL to implement and use, although for 106 reasons of supporting broad-based measurement techniques, it is 107 strongly preferred if configurations of DNSSEC-validating resolvers 108 enabled this mechanism by default, allowing for local configuration 109 directives to disable this mechanism if desired. 111 1.1. Terminology 113 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 114 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 115 document are to be interpreted as described in RFC 2119. 117 Note that example.com, AAAA records and the IPv6 documentation prefix 118 (2001:db8::/32) are only examples - A records (or CNAMES), other IPs, 119 other domains work just as well. 121 2. Use Case 123 [Ed note: This is currently towards the front of the document; we 124 will make it an appendix at publication time, but until then it is 125 worth having up front, as it makes the rest of the document much 126 easier to understand ] 128 This section provides a non-normative example of how the sentinel 129 mechanism could be used, and what each participant does. It is 130 provided in a conversational tone to be easier to follow. 132 Alice is in charge of the DNS root KSK (Key Signing Key), and would 133 like to roll / replace the key with a new one. She publishes the new 134 KSK, but would like to be able to predict / measure what the impact 135 will be before removing/revoking the old key. The current KSK has a 136 key ID of 1111, the new KSK has a key ID of 2222 138 Bob, Charlie, Dave, Ed are all users. They use the DNS recursive 139 resolvers supplied by their ISPs. They would like to confirm that 140 their ISPs have picked up the new KSK and will not break. Bob's ISP 141 does not perform validation. Charlie's ISP does validate, but the 142 resolvers have not yet been upgraded to support sentinel. Dave and 143 Ed's resolvers have been upgraded to support sentinel; Dave's 144 resolver has the new KSK, Ed's resolver hasn't managed to install the 145 2222 KSK in its trust store yet. 147 Geoff is a researcher, and would like to both provide a means for 148 Bob, Charlie, Dave and Ed to be able to perform tests, and also would 149 like to be able to perform Internet wide measurements of what the 150 impact will be (and report this back to Alice). 152 Geoff sets an authoritative DNS server for example.com, and also a 153 webserver (www.example.com). He adds 3 AAAA records to example.com: 155 invalid.example.com. IN AAAA 2001:db8::1 157 kskroll-sentinel-is-ta-2222.example.com. IN AAAA 2001:db8::1 159 kskroll-sentinel-not-ta-2222.example.com. IN AAAA 2001:db8::1 161 Geoff then DNSSEC signs the example.com zone, and intentionally makes 162 the invalid.example.com record invalid/bogus (for example, by editing 163 the signed zone and entering garbage for the signature). Geoff also 164 configures his webserver to listen on 2001:db8::1 and serve a 165 resource (for example, a 1x1 GIF, 1x1.gif) for all of these names. 166 The webserver also serves a webpage (www.example.com) which contains 167 links to these 3 resources (http://invalid.example.com/1x1.gif, 168 http://kskroll-sentinel-is-ta-2222.example.com/1x1.gif, 169 http://kskroll-sentinel-not-ta-2222.example.com/1x1.gif). 171 Geoff then asks Bob, Charlie, Dave and Ed to browse to 172 www.example.com. Using the methods described in this document, the 173 users can figure out what their fate will be when the 1111 KSK is 174 removed. 176 Bob is not using a validating resolver. This means that he will be 177 able to resolve invalid.example.com (and fetch the 1x1 GIF) - this 178 tells him that the KSK roll does not affect him, and so he will be 179 OK. 181 Charlie's resolvers are validating, but they have not been upgraded 182 to support the KSK sentinel mechanism. Charlie will not be able to 183 fetch the http://invalid.example.com/1x1.gif resource (the 184 invalid.example.com record is bogus, and none of his resolvers will 185 resolve it). He is able to fetch both of the other resources - from 186 this he knows (see the logic below) that he is using legacy, 187 validating resolvers. The KSK sentinel method cannot provided him 188 with a definitive answer. 190 Dave's resolvers implement the sentinel method, and have picked up 191 the new KSK. For the same reason as Charlie, he cannot fetch the 192 "invalid" resource. His resolver resolves the kskroll-sentinel-is- 193 ta-2222.example.com name normally (it contacts the example.com 194 authoritative servers, etc); as it supports the sentinel mechanism, 195 just before Dave's recursive server send the reply to Dave's stub, it 196 performs the KSK Sentinel check (see below). The QNAME starts with 197 "kskroll-sentinel-is-ta-", and the recursive resolver does indeed 198 have a key with the Key ID of 2222 in its root trust store. This 199 means that that this part of the KSK Sentinel check passes (it is 200 true that 2222 is in the Trust Anchor store), and the recursive 201 resolver replies normally (with the answer provided by the 202 authoritative server). Dave's recursive resolver then resolves the 203 kskroll-sentinel-not-ta-2222.example.com name. Once again, it 204 performs the normal resolution process, but because it implements KSK 205 Sentinel (and the QNAME starts with "kskroll-sentinel-not-ta-"), just 206 before sending the reply, it performs the KSK Sentinel check. As it 207 has 2222 in it's trust anchor store, the "Is this *not* a trust 208 anchor" is false, and so the recursive resolver does not reply with 209 the answer from the authoritative server - instead, it replies with a 210 SERVFAIL (note that replying with SERVFAIL instead of the original 211 answer is the only mechanism that KSK Sentinel uses). This means 212 that Dave cannot fetch "invalid", he can fetch "kskroll-sentinel-is- 213 ta-2222", but he cannot fetch "kskroll-sentinel-not-ta-2222". From 214 this, Dave knows that he is behind an upgraded, validating resolver, 215 which has successfully installed the new, 2222 KSK. Dave has nothing 216 to worry about - he will be fine with the old (1111) KSK is removed. 218 Now for Ed. Just like Charlie and Dave, Ed cannot fetch the 219 "invalid" record. This tells him that his resolvers are validating. 220 When his (upgraded) resolver performs the KSK Sentinel check for 221 "kskroll-sentinel-is-ta-2222", it does *not* have the (new, 2222) KSK 222 in it's trust anchor store. This means check fails, and Ed's 223 recursive resolver converts the (valid) 2001:db8::1 answer into a 224 SERVFAIL error response. It performs the same check for kskroll- 225 sentinel-not-ta-2222.example.com; as it does not have the 2222 KSK, 226 it is true that this is not a trust anchor for it, and so it replies 227 normally. This means that Ed cannot fetch the "invalid" resource, he 228 also cannot fetch the "kskroll-sentinel-is-ta-2222" resource, but he 229 can fetch the "kskroll-sentinel-not-ta-2222" resource. This tells Ed 230 that his resolvers have not installed the new KSK, and, when the old 231 KSK is removed, his DNS will break. 233 Geoff would like to do a large scale test and provide the information 234 back to Alice. He uses some mechanism (such as an advertising 235 network) to cause a large number of users to attempt to resolve the 3 236 resources, and then analyzes the results of the tests to determine 237 what percentage of users will be affected by the KSK rollover event. 239 The above description is a simplified example - it is not anticipated 240 that Bob, Charlie, Dave and Ed will actually look for the absence or 241 presence of web resources; instead, the webpage that they load would 242 likely contain JavaScript (or similar) which displays the result of 243 the tests. An example of this is at http://www.ksk-test.net. This 244 KSK mechanism does not rely on the web - this method can equally be 245 used by trying to resolve the names (for example, using 'dig') and 246 checking which result in a SERVFAIL. 248 [ Note that the KSK Sentinel mechanism measures a very different 249 (and, in our opinion, much more useful!) metric than RFC8145 -- 250 RFC8145 relied on resolvers reporting the list of keys that they have 251 -- this doesn't reflect what the *user* impact of the KSK roll will 252 be. As we cannot get perfect visibility into all resolvers, we will 253 have to aim for "do the least harm", not "do no harm" ] 255 3. Sentinel Mechanism 257 DNSSEC-Validating resolvers that implement this mechanism MUST be 258 performing validation of responses in accordance with the DNSSEC 259 response validation specification [RFC4035]. 261 This sentinel mechanism makes use of 2 special labels, "kskroll- 262 sentinel-is-ta-." (intended to be used in a query where 263 the response can answer the question: Is this the key tag a trust 264 anchor which the validating DNS resolver is currently trusting?) and 265 "kskroll-sentinel-not-ta-." (intended to be used in a 266 query where the response can answer the question: Is this the key tag 267 of a key that is NOT in the resolver's current trust store?). The 268 use of the positive question and its inverse allows for queries to 269 detect whether resolvers support this sentinel mechanism. Note that 270 the test is "Is there an active key with this KeyID in the resolver's 271 current trust store for the DNS root?", not "Is there any key with 272 this KeyID in the trust store", nor "Was a key with this KeyID used 273 to validate this query?". An active key is one which could currently 274 be used for validation (ie not in AddPend or Revoked state 275 ([RFC5011])). 277 If the outcome of the DNSSEC validation process on the response 278 indicates that the response is authentic, and if the left-most label 279 of the original query name matches the template "kskroll-sentinel-is- 280 ta-.", then the following rule should be applied to the 281 response: If the resolver has placed a Root Zone Key Signing Key with 282 tag index value matching the value specified in the query into the 283 local resolver's store of trusted keys, then the resolver should 284 return a response indicating that the response contains authenticated 285 data according to section 5.8 of [RFC6840]. Otherwise, the resolver 286 MUST return RCODE 2 (server failure). Note that the is 287 specified in the DNS label using hexadecimal notation. 289 If the outcome of the DNSSEC validation process applied to the 290 response indicates that the response is authentic, and if the left- 291 most label of the original query name matches the template "kskroll- 292 sentinel-not-ta-.", then the following rule should be 293 applied to the response: If the resolver has not placed a Root Zone 294 Key Signing Key with tag index value matching the value specified in 295 the query into the local resolver's store of trusted keys, then the 296 resolver should return a response indicating that the response 297 contains authenticated data according to section 5.8 of [RFC6840]. 298 Otherwise, the resolver MUST return RCODE 2 (server failure). Note 299 that the is specified in the DNS label using hexadecimal 300 notation. 302 In all other cases the resolver MUST NOT alter the outcome of the DNS 303 response validation process. 305 This mechanism is to be applied only by resolvers that are performing 306 DNSSEC validation, and applies only to responses to an A or AAAA 307 query (Query Type value 1 or 28) where the resolver has authenticated 308 the response according to the DNSSEC validation process and where the 309 query name contains either of the labels described in this section as 310 its left-most label. In this case, the resolver is to perform an 311 additional test following the conventional validation function, as 312 described in this section. The result of this additional test 313 determines whether the resolver will alter its response that would 314 have indicated that the RRset is authentic to a response that 315 indicates DNSSEC validation failure via the use of RCODE 2. 317 4. Sentinel Processing 319 This proposed test that uses the sentinel detection mechanism 320 described in this document is based on the use of three DNS names 321 that have three distinct DNS resolution behaviours. The test is 322 intended to allow a user to determine the state of their DNS 323 resolution system, and, in particular, whether or not they are using 324 validating DNS resolvers that have picked up an incoming trust anchor 325 as a trusted key in a root zone KSK roll scenario. 327 The name format can be defined in a number of ways, and no name form 328 is intrinsically better than any other in terms of the test itself. 329 The critical aspect of the DNS names used in any such test is that 330 they contain the specified label for either the positive and negative 331 test as the left-most label in the query name. 333 The sentinel detection process is envisaged to use a test with three 334 query names: 336 a. a query name containing the left-most label "kskroll-sentinel-is- 337 ta-.". This corresponds to a a validly-signed RRset 338 in the zone, so that responses associated with queried names in 339 this zone can be authenticated by a DNSSEC-validating resolver. 340 Any validly-signed DNS zone can be used for this test. 342 b. a query name containing the left-most label "kskroll-sentinel- 343 not-ta-.". This is also a validly-signed name. Any 344 validly-signed DNS zone can be used for this test. 346 c. a third query name that is signed with a DNSSEC signature that 347 cannot be validated (i.e. the corresponding RRset is not signed 348 with a valid RRSIG record). 350 The responses received from queries to resolve each of these names 351 would allow us to infer a trust key state of the resolution 352 environment. The techniques describes in this document rely on 353 (DNSSEC validating) resolvers responding with SERVFAIL (RCODE 2) to 354 valid answers. Note that a slew of other issues can also cause 355 SERVFAIL responses, so false positive or negative results may 356 sometimes occur. To describe this process of classification, we can 357 classify resolvers into four distinct behavior types, for which we 358 will use the labels: "Vnew", "Vold", "Vleg", and "nonV". These 359 labels correspond to resolver behaviour types as follows: 361 o Vnew: A DNSSEC-Validating resolver that is configured to implement 362 this mechanism has loaded the nominated key into its local trusted 363 key store will respond with an A or AAAA RRset response for 364 "kskroll-sentinel-is-ta" queries, SERVFAIL for "kskroll-sentinel- 365 not-ta" queries and SERVFAIL for the invalidly signed name 366 queries. 368 o Vold: A DNSSEC-Validating resolver that is configured to implement 369 this mechanism that has not loaded the nominated key into its 370 local trusted key store will respond with an SERVFAIL for 371 "kskroll-sentinel-is-ta" queries, an A or AAAA RRset response for 372 "kskroll-sentinel-not-ta" queries and SERVFAIL for the invalidly 373 signed name queries. 375 o Vleg: A DNSSEC-Validating resolver that does not implement this 376 mechanism will respond with an A or AAAA RRset response for 377 "kskroll-sentinel-is-ta", an A record response for "kskroll- 378 sentinel-not-ta" and SERVFAIL for the invalid name. 380 o nonV: A non-DNSSEC-Validating resolver will respond with an A or 381 AAAA record response for "kskroll-sentinel-is-ta", an A record 382 response for "kskroll-sentinel-not-ta" and an A record response 383 for the invalid name. 385 Given the clear delineation amongst these three cases, if a client 386 directs these three queries to a simple resolver, the variation in 387 response to the three queries should allow the client to determine 388 the category of the resolver, and if it supports this mechanism, 389 whether or not it has loaded a particular key into its local trusted 390 key stash. 392 +-------------+----------+-----------+------------+ 393 | Type\Query | is-ta | not-ta | invalid | 394 +-------------+----------+-----------+------------+ 395 | Vnew | A | SERVFAIL | SERVFAIL | 396 | Vold | SERVFAIL | A | SERVFAIL | 397 | Vleg | A | A | SERVFAIL | 398 | nonV | A | A | A | 399 +-------------+----------+-----------+------------+ 401 A "Vnew" response pattern says that the nominated key is trusted by 402 the resolver and has been loaded into its local trusted key stash. A 403 "Vold" response pattern says that the nominated key is not yet 404 trusted by the resolver in its own right. A "Vleg" response pattern 405 is indeterminate, and a "nonV" response pattern indicates that the 406 resolver does not perform DNSSEC validation. 408 5. Sentinel Test Result Considerations 410 The description in the previous section describes a simple situation 411 where the test queries were being passed to a single recursive 412 resolver that directly queried authoritative name servers, including 413 the root servers. 415 There is also the common case where the end client is configured to 416 use multiple resolvers. In these cases the SERVFAIL responses from 417 one resolver will prompt the end client to repeat the query against 418 one of the other configured resolvers. 420 If any of the client's resolvers are non-validating resolvers, the 421 tests will result in the client reporting that it has a non- 422 validating DNS environment ("nonV"), which is effectively the case. 424 If all of the client resolvers are DNSSEC-validating resolvers, but 425 some do not support this trusted key mechanism, then the result will 426 be indeterminate with respect to trusted key status ("Vleg"). 427 Simlarly, if all the client's resolvers support this mechanism, but 428 some have loaded the key into the trusted key stash and some have 429 not, then the result is indeterminate ("Vleg"). 431 There is also the common case of a recursive resolver using a 432 forwarder. 434 If the resolver is non-validating, and it has a single forwarder 435 clause, then the resolver will presumably mirror the capabilities of 436 the forwarder target resolver. If this non-validating resolver it 437 has multiple forwarders, then the above considerations will apply. 439 If the validating resolver has a forwarding configuration, and uses 440 the CD flag on all forwarded queries, then this resolver is acting in 441 a manner that is identical to a standalone resolver. The same 442 consideration applies if any one one of the forwarder targets is a 443 non-validating resolver. Similarly, if all the forwarder targets do 444 not apply this trusted key mechanism, the same considerations apply. 446 A more complex case is where the following conditions all hold: 448 o both the validating resolver and the forwarder target resolver 449 support this trusted key sentinel mechanism, and 451 o the local resolver's queries do not have the CD bit set, and 453 o the trusted key state differs between the forwarding resolver and 454 the forwarder target resolver 456 then either the outcome is indeterminate validating ("Vleg"), or a 457 case of mixed signals (SERVFAIL in all three responses), which is 458 similarly an indeterminate response with respect to the trusted key 459 state. 461 6. Security Considerations 463 This document describes a mechanism to allow users to determine the 464 trust state of root zone key signing keys in the DNS resolution 465 system that they use. 467 The mechanism does not require resolvers to set otherwise 468 unauthenticated responses to be marked as authenticated, and does not 469 alter the security properties of DNSSEC with respect to the 470 interpretation of the authenticity of responses that are so marked. 472 The mechanism does not require any further significant processing of 473 DNS responses, and queries of the form described in this document do 474 not impose any additional load that could be exploited in an attack 475 over the the normal DNSSEC validation processing load. 477 7. IANA Considerations 479 [Note to IANA, to be removed prior to publication: there are no IANA 480 considerations stated in this version of the document.] 482 8. Acknowledgements 484 This document has borrowed extensively from [RFC8145] for the 485 introductory text, and the authors would like to acknowledge and 486 thank the authors of that document both for some text excerpts and 487 for the more general stimulation of thoughts about monitoring the 488 progress of a roll of the Key Signing Key of the Root Zone of the 489 DNS. 491 The authors would like the especially thank Joe Abley, Mehmet Akcin, 492 Mark Andrews, Richard Barnes, Ray Bellis, Stephane Bortzmeyer, David 493 Conrad, Ralph Dolmans, John Dickinson, Steinar Haug, Bob Harold, Wes 494 Hardaker, Paul Hoffman, Matt Larson, Jinmei Tatuya, Edward Lewis, 495 George Michaelson, Benno Overeinder, Matthew Pounsett, Andreas 496 Schulze, Mukund Sivaraman, Petr Spacek. Andrew Sullivan, Paul Vixie, 497 Duane Wessels and Paul Wouters for their helpful feedback. 499 [TODO: Add people who have contributed!] 501 9. Change Log 503 Note that this document is being worked on in GitHub - see Abstract. 504 The below is mainly large changes, and is not authoritative. 506 From -01 to 02: 508 Removed Address Record definition. 510 Clarified that many things can cause SERVFAIL. 512 Made examples FQDN. 514 Fixed a number of typos. 516 Had accidentally said that Charlie was using a non-validating 517 resolver in example. 519 [ TODO(WK): Doc says keytags are hex, is this really what the WG 520 wants? ] 522 And active key is one that can be used *now* (not e.g AddPend) 524 From -00 to 01: 526 o Added a conversational description of how the system is intended 527 to work. 529 o Clarification that this is for the root. 531 o Changed the label template from _is-ta- to kskroll-sentinel- 532 is-ta-. This is because BIND (at least) will not allow 533 records which start with an underscore to have address records 534 (CNAMEs, yes, A/AAAA no). Some browsers / operating systems also 535 will not fetch resources from names which start with an 536 underscore. 538 10. References 540 10.1. Normative References 542 [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. 543 Rose, "DNS Security Introduction and Requirements", RFC 544 4033, DOI 10.17487/RFC4033, March 2005, . 547 [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. 548 Rose, "Resource Records for the DNS Security Extensions", 549 RFC 4034, DOI 10.17487/RFC4034, March 2005, 550 . 552 [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. 553 Rose, "Protocol Modifications for the DNS Security 554 Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005, 555 . 557 [RFC5011] StJohns, M., "Automated Updates of DNS Security (DNSSEC) 558 Trust Anchors", STD 74, RFC 5011, DOI 10.17487/RFC5011, 559 September 2007, . 561 [RFC6840] Weiler, S., Ed. and D. Blacka, Ed., "Clarifications and 562 Implementation Notes for DNS Security (DNSSEC)", RFC 6840, 563 DOI 10.17487/RFC6840, February 2013, . 566 10.2. Informative References 568 [RFC8145] Wessels, D., Kumari, W., and P. Hoffman, "Signaling Trust 569 Anchor Knowledge in DNS Security Extensions (DNSSEC)", RFC 570 8145, DOI 10.17487/RFC8145, April 2017, . 573 Authors' Addresses 575 Geoff Huston 577 Email: gih@apnic.net 578 URI: http://www.apnic.net 579 Joao Silva Damas 581 Email: joao@apnic.net 582 URI: http://www.apnic.net 584 Warren Kumari 586 Email: warren@kumari.net