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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 16, 2018 W. Kumari 6 Google 7 February 12, 2018 9 A Sentinel for Detecting Trusted Keys in DNSSEC 10 draft-ietf-dnsop-kskroll-sentinel-01 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 of the 20 resolvers that handle that user's DNS queries. 22 There is an example / toy implementation of this at http://www.ksk- 23 test.net . 25 [ This document is being collaborated on in Github at: 26 https://github.com/APNIC-Labs/draft-kskroll-sentinel.. The most 27 recent version of the document, open issues, etc should all be 28 available here. The authors (gratefully) accept pull requests. Text 29 in square brackets will be removed before publication. ] 31 [ NOTE: This version uses the labels "kskroll-sentinel-is-ta-", "kskroll-sentinel-not-ta-"; older versions of 33 this document used "_is-ta-", "_not-ta-". ] 35 Status of This Memo 37 This Internet-Draft is submitted in full conformance with the 38 provisions of BCP 78 and BCP 79. 40 Internet-Drafts are working documents of the Internet Engineering 41 Task Force (IETF). Note that other groups may also distribute 42 working documents as Internet-Drafts. The list of current Internet- 43 Drafts is at http://datatracker.ietf.org/drafts/current/. 45 Internet-Drafts are draft documents valid for a maximum of six months 46 and may be updated, replaced, or obsoleted by other documents at any 47 time. It is inappropriate to use Internet-Drafts as reference 48 material or to cite them other than as "work in progress." 49 This Internet-Draft will expire on August 16, 2018. 51 Copyright Notice 53 Copyright (c) 2018 IETF Trust and the persons identified as the 54 document authors. All rights reserved. 56 This document is subject to BCP 78 and the IETF Trust's Legal 57 Provisions Relating to IETF Documents 58 (http://trustee.ietf.org/license-info) in effect on the date of 59 publication of this document. Please review these documents 60 carefully, as they describe your rights and restrictions with respect 61 to this document. Code Components extracted from this document must 62 include Simplified BSD License text as described in Section 4.e of 63 the Trust Legal Provisions and are provided without warranty as 64 described in the Simplified BSD License. 66 Table of Contents 68 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 69 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 70 2. Use Case . . . . . . . . . . . . . . . . . . . . . . . . . . 3 71 3. Sentinel Mechanism . . . . . . . . . . . . . . . . . . . . . 6 72 4. Sentinel Processing . . . . . . . . . . . . . . . . . . . . . 7 73 5. Sentinel Test Result Considerations . . . . . . . . . . . . . 9 74 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 75 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 76 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11 77 9. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 11 78 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 79 10.1. Normative References . . . . . . . . . . . . . . . . . . 12 80 10.2. Informative References . . . . . . . . . . . . . . . . . 12 81 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 83 1. Introduction 85 The DNS Security Extensions (DNSSEC) [RFC4033], [RFC4034] and 86 [RFC4035] were developed to provide origin authentication and 87 integrity protection for DNS data by using digital signatures. 88 DNSSEC uses Key Tags to efficiently match signatures to the keys from 89 which they are generated. The Key Tag is a 16-bit value computed 90 from the RDATA portion of a DNSKEY RR using a formula not unlike a 91 ones-complement checksum. RRSIG RRs contain a Key Tag field whose 92 value is equal to the Key Tag of the DNSKEY RR that validates the 93 signature. 95 This document specifies how validating resolvers can respond to 96 certain queries in a manner that allows a querier to deduce whether a 97 particular key has been loaded into that resolver's trusted key 98 store. In particular, this response mechanism can be used to 99 determine whether a certain Root Zone KSK is ready to be used as a 100 trusted key within the context of a key roll by this resolver. 102 This new mechanism is OPTIONAL to implement and use, although for 103 reasons of supporting broad-based measurement techniques, it is 104 strongly preferred if configurations of DNSSEC-validating resolvers 105 enabled this mechanism by default, allowing for local configuration 106 directives to disable this mechanism if desired. 108 1.1. Terminology 110 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 111 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 112 document are to be interpreted as described in RFC 2119. 114 Address Record: Throughout this document we use the term Address 115 Record (AR) to mean an A or AAAA record. We are using example.com, 116 AAAA records and the IPv6 documentation prefix (2001:DB8::/32) as 117 examples; these are only examples - A records (or CNAMES), other IPs, 118 other domains work just as well. [Ed note: There was some earlier 119 confusion on this, being explicit! ] 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 IN AAAA 2001:DB8::1 157 kskroll-sentinel-is-ta-2222 IN AAAA 2001:DB8::1 159 kskroll-sentinel-not-ta-2222 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, non- 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 a key with this KeyID in the resolver's current 271 trust store for the DNS root", not "Is there any key with this KeyID 272 in the trust store", nor "Was a key with this KeyID used to validate 273 this query?". [This is still an active discussion on the DNSOP list 274 ] 276 If the outcome of the DNSSEC validation process on the response RRset 277 indicates that the response RRset is authentic, and if the left-most 278 label of the original query name matches the template "kskroll- 279 sentinel-is-ta-.", then the following rule should be 280 applied to the response: If the resolver has placed a Root Zone Key 281 Signing Key with tag index value matching the value specified in the 282 query into the local resolver's store of trusted keys, then the 283 resolver should return a response indicating that the response 284 contains authenticated data according to section 5.8 of [RFC6840]. 285 Otherwise, the resolver MUST return RCODE 2 (server failure). Note 286 that the is specified in the DNS label using hexadecimal 287 notation. 289 If the outcome of the DNSSEC validation process applied to the 290 response RRset indicates that the response RRset is authentic, and if 291 the left-most label of the original query name matches the template 292 "kskroll-sentinel-not-ta-.", then the following rule 293 should be applied to the response: If the resolver has not placed a 294 Root Zone Key Signing Key with tag index value matching the value 295 specified in the query into the local resolver's store of trusted 296 keys, then the resolver should return a response indicating that the 297 response contains authenticated data according to section 5.8 of 298 [RFC6840]. Otherwise, the resolver MUST return RCODE 2 (server 299 failure). Note that the is specified in the DNS label 300 using hexadecimal 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 RRset responses to an A or 307 AAAA query (Query Type value 1 or 28) where the resolver has 308 authenticated the response RRset according to the DNSSEC validation 309 process and where the query name contains either of the labels 310 described in this section as its left-most label. In this case, the 311 resolver is to perform an additional test following the conventional 312 validation function, as described in this section. The result of 313 this additional test determines whether the resolver will alter its 314 response that would have indicated that the RRset is authentic to a 315 response that indicates DNSSEC validation failure via the use of 316 RCODE 2. 318 4. Sentinel Processing 320 This proposed test that uses the sentinel detection mechanism 321 described in this document is based on the use of three DNS names 322 that have three distinct DNS resolution behaviours. The test is 323 intended to allow a user to determine the state of their DNS 324 resolution system, and, in particular, whether or not they are using 325 validating DNS resolvers that have picked up an incoming trust anchor 326 as a trusted key in a root zone KSK roll scenario. 328 The name format can be defined in a number of ways, and no name form 329 is intrinsically better than any other in terms of the test itself. 330 The critical aspect of the DNS names used in any such test is that 331 they contain the specified label for either the positive and negative 332 test as the left-most label in the query name. 334 The sentinel detection process is envisaged to use a test with three 335 query names: 337 a. a query name containing the left-most label "kskroll-sentinel-is- 338 ta-.". This corresponds to a a validly-signed RRset 339 in the zone, so that responses associated with queried names in 340 this zone can be authenticated by a DNSSEC-validating resolver. 341 Any validly-signed DNS zone can be used for this test. 343 b. a query name containing the left-most label "kskroll-sentinel- 344 not-ta-.". This is also a validly-signed name. Any 345 validly-signed DNS zone can be used for this test. 347 c. a third query name that is signed with a DNSSEC signature that 348 cannot be validated (i.e. the corresponding RRset is not signed 349 with a valid RRSIG record). 351 The responses received from queries to resolve each of these names 352 would allow us to infer a trust key state of the resolution 353 environment. To describe this process of classification, we can 354 classify resolvers into four distinct behavior types, for which we 355 will use the labels: "Vnew", "Vold", "Vleg", and "nonV". These 356 labels correspond to resolver behaviour types as follows: 358 o Vnew: A DNSSEC-Validating resolver that is configured to implement 359 this mechanism has loaded the nominated key into its local trusted 360 key store will respond with an A or AAAA RRset response for 361 "kskroll-sentinel-is-ta" queries, SERVFAIL for "kskroll-sentinel- 362 not-ta" queries and SERVFAIL for the invalidly signed name 363 queries. 365 o Vold: A DNSSEC-Validating resolver that is configured to implement 366 this mechanism that has not loaded the nominated key into its 367 local trusted key store will respond with an SERVFAIL for 368 "kskroll-sentinel-is-ta" queries, an A or AAAA RRset response for 369 "kskroll-sentinel-not-ta" queries and SERVFAIL for the invalidly 370 signed name queries. 372 o Vleg: A DNSSEC-Validating resolver that does not implement this 373 mechanism will respond with an A or AAAA RRSET response for 374 "kskroll-sentinel-is-ta", an A record response for "kskroll- 375 sentinel-not-ta" and SERVFAIL for the invalid name. 377 o nonV: A non-DNSSEC-Validating resolver will respond with an A 378 record response for "kskroll-sentinel-is-ta", an A record response 379 for "kskroll-sentinel-not-ta" and an A record response for the 380 invalid name. 382 Given the clear delineation amongst these three cases, if a client 383 directs these three queries to a simple resolver, the variation in 384 response to the three queries should allow the client to determine 385 the category of the resolver, and if it supports this mechanism, 386 whether or not it has loaded a particular key into its local trusted 387 key stash. 389 +-------------+----------+-----------+------------+ 390 | Type\Query | is-ta | not-ta | invalid | 391 +-------------+----------+-----------+------------+ 392 | Vnew | A | SERVFAIL | SERVFAIL | 393 | Vold | SERVFAIL | A | SERVFAIL | 394 | Vleg | A | A | SERVFAIL | 395 | nonV | A | A | A | 396 +-------------+----------+-----------+------------+ 398 A "Vnew" response pattern says that the nominated key is trusted by 399 the resolver and has been loaded into its local trusted key stash. A 400 "Vold" response pattern says that the nominated key is not yet 401 trusted by the resolver in its own right. A "Vleg" response pattern 402 is indeterminate, and a "nonV" response pattern indicates that the 403 resolver does not perform DNSSEC validation. 405 5. Sentinel Test Result Considerations 407 The description in the previous section describes a simple situation 408 where the test queries were being passed to a single recursive 409 resolver that directly queried authoritative name servers, including 410 the root servers. 412 There is also the common case where the end client is configured to 413 use multiple resolvers. In these cases the SERVFAIL responses from 414 one resolver will prompt the end client to repeat the query against 415 one of the other configured resolvers. 417 If any of the client's resolvers are non-validating resolvers, the 418 tests will result in the client reporting that it has a non- 419 validating DNS environment ("nonV"), which is effectively the case. 421 If all of the client resolvers are DNSSEC-validating resolvers, but 422 some do not support this trusted key mechanism, then the result will 423 be indeterminate with respect to trusted key status ("Vleg"). 424 Simlarly, if all the client's resolvers support this mechanism, but 425 some have loaded the key into the trusted key stash and some have 426 not, then the result is indeterminate ("Vleg"). 428 There is also the common case of a recursive resolver using a 429 forwarder. 431 If the resolver is non-validating, and it has a single forwarder 432 clause, then the resolver will presumably mirror the capabilities of 433 the forwarder target resolver. If this non-validating resolver it 434 has multiple forwarders, then the above considerations will apply. 436 If the validating resolver has a forwarding configuration, and uses 437 the CD flag on all forwarded queries, then this resolver is acting in 438 a manner that is identical to a standalone resolver. The same 439 consideration applies if any one one of the forwarder targets is a 440 non-validating resolver. Similarly, if all the forwarder targets do 441 not apply this trusted key mechanism, the same considerations apply. 443 A more complex case is where the following conditions all hold: 445 o both the validating resolver and the forwarder target resolver 446 support this trusted key sentinel mechanism, and 448 o the local resolver's queries do not have the CD bit set, and 450 o the trusted key state differs between the forwarding resolver and 451 the forwarder target resolver 453 then either the outcome is indeterminate validating ("Vleg"), or a 454 case of mixed signals (SERVFAIL in all three responses), which is 455 similarly an indeterminate response with respect to the trusted key 456 state. 458 6. Security Considerations 460 This document describes a mechanism to allow users to determine the 461 trust state of root zone key signing keys in the DNS resolution 462 system that they use. 464 The mechanism does not require resolvers to set otherwise 465 unauthenticated responses to be marked as authenticated, and does not 466 alter the security properties of DNSSEC with respect to the 467 interpretation of the authenticity of responses that are so marked. 469 The mechanism does not require any further significant processing of 470 DNS responses, and queries of the form described in this document do 471 not impose any additional load that could be exploited in an attack 472 over the the normal DNSSEC validation processing load. 474 7. IANA Considerations 476 [Note to IANA, to be removed prior to publication: there are no IANA 477 considerations stated in this version of the document.] 479 8. Acknowledgements 481 This document has borrowed extensively from [RFC8145] for the 482 introductory text, and the authors would like to acknowledge and 483 thank the authors of that document both for some text excerpts and 484 for the more general stimulation of thoughts about monitoring the 485 progress of a roll of the Key Signing Key of the Root Zone of the 486 DNS. 488 The authors would like the especially thank Joe Abley, Mehmet Akcin, 489 Mark Andrews, Richard Barnes, Ray Bellis, Stephane Bortzmeyer, David 490 Conrad, Ralph Dolmans, Steinar Haug, Bob Harold, Wes Hardaker, Paul 491 Hoffman, Matt Larson, Edward Lewis, George Michaelson, Benno 492 Overeinder, Matthew Pounsett, Andreas Schulze, Mukund Sivaraman, Petr 493 Spacek. Andrew Sullivan, Paul Vixie, Duane Wessels and Paul Wouters 494 for their helpful feedback. 496 [TODO: Add people who have contributed!] 498 9. Change Log 500 Note that this document is being worked on in GitHub - see Abstract. 501 The below is mainly large changes, and is not authoritative. 503 From -00 to 01: 505 o Added a conversational description of how the system is intended 506 to work. 508 o Clarification that this is for the root. 510 o Changed the label template from _is-ta- to kskroll-sentinel- 511 is-ta-. This is because BIND (at least) will not allow 512 records which start with an underscore to have address records 513 (CNAMEs, yes, A/AAAA no). Some browsers / operating systems also 514 will not fetch resources from names which start with an 515 underscore. 517 10. References 518 10.1. Normative References 520 [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. 521 Rose, "DNS Security Introduction and Requirements", RFC 522 4033, DOI 10.17487/RFC4033, March 2005, . 525 [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. 526 Rose, "Resource Records for the DNS Security Extensions", 527 RFC 4034, DOI 10.17487/RFC4034, March 2005, 528 . 530 [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. 531 Rose, "Protocol Modifications for the DNS Security 532 Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005, 533 . 535 [RFC6840] Weiler, S., Ed. and D. Blacka, Ed., "Clarifications and 536 Implementation Notes for DNS Security (DNSSEC)", RFC 6840, 537 DOI 10.17487/RFC6840, February 2013, . 540 10.2. Informative References 542 [RFC8145] Wessels, D., Kumari, W., and P. Hoffman, "Signaling Trust 543 Anchor Knowledge in DNS Security Extensions (DNSSEC)", RFC 544 8145, DOI 10.17487/RFC8145, April 2017, . 547 Authors' Addresses 549 Geoff Huston 551 Email: gih@apnic.net 552 URI: http://www.apnic.net 554 Joao Silva Damas 556 Email: joao@apnic.net 557 URI: http://www.apnic.net 559 Warren Kumari 561 Email: warren@kumari.net