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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) ** Obsolete normative reference: RFC 8499 (Obsoleted by RFC 9499) -- Obsolete informational reference (is this intentional?): RFC 2845 (Obsoleted by RFC 8945) Summary: 1 error (**), 0 flaws (~~), 1 warning (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group W. Kumari 3 Internet-Draft Google 4 Intended status: Standards Track E. Hunt 5 Expires: October 26, 2020 ISC 6 R. Arends 7 ICANN 8 W. Hardaker 9 USC/ISI 10 D. Lawrence 11 Oracle + Dyn 12 April 24, 2020 14 Extended DNS Errors 15 draft-ietf-dnsop-extended-error-15 17 Abstract 19 This document defines an extensible method to return additional 20 information about the cause of DNS errors. Though created primarily 21 to extend SERVFAIL to provide additional information about the cause 22 of DNS and DNSSEC failures, the Extended DNS Errors option defined in 23 this document allows all response types to contain extended error 24 information. Extended DNS Error information does not change the 25 processing of RCODEs. 27 Status of This Memo 29 This Internet-Draft is submitted in full conformance with the 30 provisions of BCP 78 and BCP 79. 32 Internet-Drafts are working documents of the Internet Engineering 33 Task Force (IETF). Note that other groups may also distribute 34 working documents as Internet-Drafts. The list of current Internet- 35 Drafts is at https://datatracker.ietf.org/drafts/current/. 37 Internet-Drafts are draft documents valid for a maximum of six months 38 and may be updated, replaced, or obsoleted by other documents at any 39 time. It is inappropriate to use Internet-Drafts as reference 40 material or to cite them other than as "work in progress." 42 This Internet-Draft will expire on October 26, 2020. 44 Copyright Notice 46 Copyright (c) 2020 IETF Trust and the persons identified as the 47 document authors. All rights reserved. 49 This document is subject to BCP 78 and the IETF Trust's Legal 50 Provisions Relating to IETF Documents 51 (https://trustee.ietf.org/license-info) in effect on the date of 52 publication of this document. Please review these documents 53 carefully, as they describe your rights and restrictions with respect 54 to this document. Code Components extracted from this document must 55 include Simplified BSD License text as described in Section 4.e of 56 the Trust Legal Provisions and are provided without warranty as 57 described in the Simplified BSD License. 59 Table of Contents 61 1. Introduction and background . . . . . . . . . . . . . . . . . 3 62 1.1. Requirements notation . . . . . . . . . . . . . . . . . . 4 63 2. Extended DNS Error EDNS0 option format . . . . . . . . . . . 4 64 3. Extended DNS Error Processing . . . . . . . . . . . . . . . . 5 65 4. Defined Extended DNS Errors . . . . . . . . . . . . . . . . . 5 66 4.1. Extended DNS Error Code 0 - Other . . . . . . . . . . . . 6 67 4.2. Extended DNS Error Code 1 - 68 Unsupported DNSKEY Algorithm . . . . . . . . . . . . . . 6 69 4.3. Extended DNS Error Code 2 - Unsupported DS 70 Digest Type . . . . . . . . . . . . . . . . . . . . . . . 6 71 4.4. Extended DNS Error Code 3 - Stale Answer . . . . . . . . 6 72 4.5. Extended DNS Error Code 4 - Forged Answer . . . . . . . . 6 73 4.6. Extended DNS Error Code 5 - DNSSEC Indeterminate . . . . 6 74 4.7. Extended DNS Error Code 6 - DNSSEC Bogus . . . . . . . . 6 75 4.8. Extended DNS Error Code 7 - Signature Expired . . . . . . 6 76 4.9. Extended DNS Error Code 8 - Signature Not Yet Valid . . . 7 77 4.10. Extended DNS Error Code 9 - DNSKEY Missing . . . . . . . 7 78 4.11. Extended DNS Error Code 10 - RRSIGs Missing . . . . . . . 7 79 4.12. Extended DNS Error Code 11 - No Zone Key Bit Set . . . . 7 80 4.13. Extended DNS Error Code 12 - NSEC Missing . . . . . . . . 7 81 4.14. Extended DNS Error Code 13 - Cached Error . . . . . . . . 7 82 4.15. Extended DNS Error Code 14 - Not Ready . . . . . . . . . 7 83 4.16. Extended DNS Error Code 15 - Blocked . . . . . . . . . . 7 84 4.17. Extended DNS Error Code 16 - Censored . . . . . . . . . . 7 85 4.18. Extended DNS Error Code 17 - Filtered . . . . . . . . . . 8 86 4.19. Extended DNS Error Code 18 - Prohibited . . . . . . . . . 8 87 4.20. Extended DNS Error Code 19 - Stale NXDOMAIN Answer . . . 8 88 4.21. Extended DNS Error Code 20 - Not Authoritative . . . . . 8 89 4.22. Extended DNS Error Code 21 - Not Supported . . . . . . . 8 90 4.23. Extended DNS Error Code 22 - No Reachable Authority . . . 8 91 4.24. Extended DNS Error Code 23 - Network Error . . . . . . . 8 92 4.25. Extended DNS Error Code 24 - Invalid Data . . . . . . . . 9 93 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 94 5.1. A New Extended DNS Error Code EDNS Option . . . . . . . . 9 95 5.2. New Registry for Extended DNS Error Codes . . . . . . . . 9 96 6. Security Considerations . . . . . . . . . . . . . . . . . . . 12 97 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 98 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 99 8.1. Normative References . . . . . . . . . . . . . . . . . . 13 100 8.2. Informative References . . . . . . . . . . . . . . . . . 13 101 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 103 1. Introduction and background 105 There are many reasons that a DNS query may fail, some of them 106 transient, some permanent; some can be resolved by querying another 107 server, some are likely best handled by stopping resolution. 108 Unfortunately, the error signals that a DNS server can return are 109 very limited, and are not very expressive. This means that 110 applications and resolvers often have to "guess" at what the issue is 111 - e.g. was the answer marked REFUSED because of a lame delegation, or 112 because the nameserver is still starting up and loading zones? Is a 113 SERVFAIL a DNSSEC validation issue, or is the nameserver experiencing 114 some other failure? What error messages should be presented to the 115 user or logged under these conditions? 117 A good example of issues that would benefit from additional error 118 information are errors caused by DNSSEC validation issues. When a 119 stub resolver queries a name which is DNSSEC bogus [RFC8499] (using a 120 validating resolver), the stub resolver receives only a SERVFAIL in 121 response. Unfortunately, the SERVFAIL Response Code (RCODE) is used 122 to signal many sorts of DNS errors, and so the stub resolvers only 123 option is to ask the next configured DNS resolver. The result of 124 trying the next resolver is one of two outcomes: either the next 125 resolver also validates, and a SERVFAIL is returned again; or the 126 next resolver is not a validating resolver, and the user is returned 127 a potentially harmful result. With an Extended DNS Error (EDE) 128 option enclosed in the response message, the resolver is able to 129 return a more descriptive reason as to why any failures happened, or 130 add additional context to a message containing a NOERROR RCODE. 132 This document specifies a mechanism to extend DNS errors to provide 133 additional information about the cause of an error. These extended 134 DNS error codes are described in this document and can be used by any 135 system that sends DNS queries and receives a response containing an 136 EDE option. Different codes are useful in different circumstances, 137 and thus different systems (stub resolvers, recursive resolvers, and 138 authoritative resolvers) might receive and use them. 140 This document does not allow or prohibit any particular extended 141 error codes and information to be matched with any particular RCODEs. 142 Some combinations of extended error codes and RCODEs may seem 143 nonsensical (such as resolver-specific extended error codes in 144 responses from authoritative servers), so systems interpreting the 145 extended error codes MUST NOT assume that a combination will make 146 sense. Receivers MUST be able to accept EDE codes and EXTRA-TEXT in 147 all messages, including those with a NOERROR RCODE, but need not act 148 on them. Applications MUST continue to follow requirements from 149 applicable specifications on how to process RCODEs no matter what EDE 150 values are also received. Senders MAY include more than one EDE 151 option and receivers MUST be able to accept (but not necessarily 152 process or act on) multiple EDE options in a DNS message. 154 1.1. Requirements notation 156 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 157 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 158 "OPTIONAL" in this document are to be interpreted as described in BCP 159 14 [RFC2119] [RFC8174] when, and only when, they appear in all 160 capitals, as shown here. 162 2. Extended DNS Error EDNS0 option format 164 This draft uses an EDNS0 ([RFC6891]) option to include Extended DNS 165 Error (EDE) information in DNS messages. The option is structured as 166 follows: 168 1 1 1 1 1 1 169 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 170 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 171 0: | OPTION-CODE | 172 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 173 2: | OPTION-LENGTH | 174 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 175 4: | INFO-CODE | 176 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 177 6: / EXTRA-TEXT ... / 178 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 180 Field definition details: 182 o OPTION-CODE, 2-octets/16-bits (defined in [RFC6891]]), for EDE is 183 TBD. [RFC Editor: change TBD to the proper code once assigned by 184 IANA.] 185 o OPTION-LENGTH, 2-octets/16-bits ((defined in [RFC6891]]) contains 186 the length of the payload (everything after OPTION-LENGTH) in 187 octets and should be 2 plus the length of the EXTRA-TEXT field 188 (which may be a zero-length string). 189 o INFO-CODE, 16-bits, which is the principal contribution of this 190 document. This 16-bit value, encoded in network (MSB) byte order, 191 provides the additional context for the RESPONSE-CODE of the DNS 192 message. The INFO-CODE serves as an index into the "Extended DNS 193 Errors" registry defined and created in Section 5.2. 194 o EXTRA-TEXT, a variable length, UTF-8 encoded, text field that may 195 hold additional textual information. This information is intended 196 for human consumption (not automated parsing). The EXTRA-TEXT 197 field may be zero octets in length, indicating that there is no 198 EXTRA-TEXT included. Care should be taken not to include private 199 information in the EXTRA-TEXT field that an observer would not 200 otherwise have access to, such as account numbers. 202 The Extended DNS Error (EDE) option can be included in any response 203 (SERVFAIL, NXDOMAIN, REFUSED, and even NOERROR, etc) to a query that 204 includes OPT Pseudo-RR [RFC6891]. This document includes a set of 205 initial codepoints, but is extensible via the IANA registry defined 206 and created in Section 5.2. 208 3. Extended DNS Error Processing 210 When the response grows beyond the requestor's UDP payload size 211 [RFC6891], servers SHOULD truncate messages by dropping EDE options 212 before dropping other data from packets. Implementations SHOULD set 213 the truncation bit when dropping EDE options. Because long EXTRA- 214 TEXT fields may trigger truncation, which is undesirable given the 215 supplemental nature of EDE. Implementers and operators creating EDE 216 options SHOULD avoid lengthy EXTRA-TEXT contents. 218 When a resolver or forwarder receives an EDE option, whether or not 219 (and how) to pass along EDE information on to their original client 220 is implementation dependent. Implementations MAY choose to not 221 forward information, or they MAY choose to create a new EDE option(s) 222 that conveys the information encoded in the received EDE. When doing 223 so, the source of the error SHOULD be attributed in the EXTRA-TEXT 224 field, since an EDNS0 option received by the original client will 225 appear to have come from the resolver or forwarder sending it. 227 4. Defined Extended DNS Errors 229 This document defines some initial EDE codes. The mechanism is 230 intended to be extensible, and additional code-points can be 231 registered in the "Extended DNS Errors" registry Section 5.2. The 232 INFO-CODE from the EDE EDNS option is used to serve as an index into 233 the "Extended DNS Error" IANA registry, the initial values for which 234 are defined in the following sub-sections. 236 4.1. Extended DNS Error Code 0 - Other 238 The error in question falls into a category that does not match known 239 extended error codes. Implementations SHOULD include an EXTRA-TEXT 240 value to augment this error code with additional information. 242 4.2. Extended DNS Error Code 1 - Unsupported DNSKEY Algorithm 244 The resolver attempted to perform DNSSEC validation, but a DNSKEY 245 RRSET contained only unsupported DNSSEC algorithms. 247 4.3. Extended DNS Error Code 2 - Unsupported DS Digest Type 249 The resolver attempted to perform DNSSEC validation, but a DS RRSET 250 contained only unsupported Digest Types. 252 4.4. Extended DNS Error Code 3 - Stale Answer 254 The resolver was unable to resolve the answer within its time limits 255 and decided to answer with previously cached data instead of 256 answering with an error. This is typically caused by problems 257 communicating with an authoritative server, possibly as result of a 258 denial of service (DoS) attack against another network. (See also 259 Code 19.) 261 4.5. Extended DNS Error Code 4 - Forged Answer 263 For policy reasons (legal obligation, or malware filtering, for 264 instance), an answer was forged. Note that this should be used when 265 an answer is still provided, not when failure codes are returned 266 instead. See Blocked(15), Censored (16), and Filtered (17) for use 267 when returning other response codes. 269 4.6. Extended DNS Error Code 5 - DNSSEC Indeterminate 271 The resolver attempted to perform DNSSEC validation, but validation 272 ended in the Indeterminate state [RFC4035]. 274 4.7. Extended DNS Error Code 6 - DNSSEC Bogus 276 The resolver attempted to perform DNSSEC validation, but validation 277 ended in the Bogus state. 279 4.8. Extended DNS Error Code 7 - Signature Expired 281 The resolver attempted to perform DNSSEC validation, but no 282 signatures are presently valid and some (often all) are expired. 284 4.9. Extended DNS Error Code 8 - Signature Not Yet Valid 286 The resolver attempted to perform DNSSEC validation, but but no 287 signatures are presently valid and at least some are not yet valid. 289 4.10. Extended DNS Error Code 9 - DNSKEY Missing 291 A DS record existed at a parent, but no supported matching DNSKEY 292 record could be found for the child. 294 4.11. Extended DNS Error Code 10 - RRSIGs Missing 296 The resolver attempted to perform DNSSEC validation, but no RRSIGs 297 could be found for at least one RRset where RRSIGs were expected. 299 4.12. Extended DNS Error Code 11 - No Zone Key Bit Set 301 The resolver attempted to perform DNSSEC validation, but no Zone Key 302 Bit was set in a DNSKEY. 304 4.13. Extended DNS Error Code 12 - NSEC Missing 306 The resolver attempted to perform DNSSEC validation, but the 307 requested data was missing and a covering NSEC or NSEC3 was not 308 provided. 310 4.14. Extended DNS Error Code 13 - Cached Error 312 The resolver is returning the SERVFAIL RCODE from its cache. 314 4.15. Extended DNS Error Code 14 - Not Ready 316 The server is unable to answer the query as it was not fully 317 functional when the query was received. 319 4.16. Extended DNS Error Code 15 - Blocked 321 The server is unable to respond to the request because the domain is 322 blacklisted due to an internal security policy imposed by the 323 operator of the server resolving or forwarding the query. 325 4.17. Extended DNS Error Code 16 - Censored 327 The server is unable to respond to the request because the domain is 328 blacklisted due to an external requirement imposed by an entity other 329 than the operator of the server resolving or forwarding the query. 330 Note that how the imposed policy is applied is irrelevant (in-band 331 DNS filtering, court order, etc). 333 4.18. Extended DNS Error Code 17 - Filtered 335 The server is unable to respond to the request because the domain is 336 blacklisted as requested by the client. Functionally, this amounts 337 to "you requested that we filter domains like this one." 339 4.19. Extended DNS Error Code 18 - Prohibited 341 An authoritative server or recursive resolver that receives a query 342 from an "unauthorized" client can annotate its REFUSED message with 343 this code. Examples of "unauthorized" clients are recursive queries 344 from IP addresses outside the network, blacklisted IP addresses, 345 local policy, etc. 347 4.20. Extended DNS Error Code 19 - Stale NXDOMAIN Answer 349 The resolver was unable to resolve an answer within its configured 350 time limits and decided to answer with a previously cached NXDOMAIN 351 answer instead of answering with an error. This may be caused, for 352 example, by problems communicating with an authoritative server, 353 possibly as result of a denial of service (DoS) attack against 354 another network. (See also Code 3.) 356 4.21. Extended DNS Error Code 20 - Not Authoritative 358 An authoritative server that receives a query with the RD bit clear, 359 or when it is not configured for recursion for a domain for which it 360 is not authoritative SHOULD include this EDE code in the REFUSED 361 response. A resolver that receives a query with the RD bit clear 362 SHOULD include this EDE code in the REFUSED response. 364 4.22. Extended DNS Error Code 21 - Not Supported 366 The requested operation or query is not supported. 368 4.23. Extended DNS Error Code 22 - No Reachable Authority 370 The resolver could not reach any of the authoritative name servers 371 (or they potentially refused to reply). 373 4.24. Extended DNS Error Code 23 - Network Error 375 An unrecoverable error occurred while communicating with another 376 server. 378 4.25. Extended DNS Error Code 24 - Invalid Data 380 The authoritative server cannot answer with data for a zone it is 381 otherwise configured to support. Examples of this include its most 382 recent zone being too old, or having expired. 384 5. IANA Considerations 386 5.1. A New Extended DNS Error Code EDNS Option 388 This document defines a new EDNS(0) option, entitled "Extended DNS 389 Error", assigned a value of TBD from the "DNS EDNS0 Option Codes 390 (OPT)" registry [to be removed upon publication: 391 [http://www.iana.org/assignments/dns-parameters/dns- 392 parameters.xhtml#dns-parameters-11] 394 Value Name Status Reference 395 ----- ---------------- ------ ------------------ 396 TBD Extended DNS Error Standard [ This document ] 398 5.2. New Registry for Extended DNS Error Codes 400 IANA is requested to create and maintain a new registry table called 401 "Extended DNS Error Codes" on the "Domain Name System (DNS) 402 Parameters" web page as follows: 404 Registry Name: Extended DNS Error Codes 406 Registration Procedures: 408 o 0 - 49151: First come, first served. 409 o 49152 - 65280: Private use. 411 Reference: [this document] 413 The Extended DNS Error Codes registry is a table with three columns: 414 INFO-CODE, Purpose, and Reference. The initial contents is as below 415 with [this document] added to each reference given. 417 INFO-CODE: 0 418 Purpose: Other Error 419 Reference: Section 4.1 421 INFO-CODE: 1 422 Purpose: Unsupported DNSKEY Algorithm 423 Reference: Section 4.2 425 INFO-CODE: 2 426 Purpose: Unsupported DS Digest Type 427 Reference: Section 4.3 429 INFO-CODE: 3 430 Purpose: Stale Answer 431 Reference: Section 4.4, [RFC8767] 433 INFO-CODE: 4 434 Purpose: Forged Answer 435 Reference: Section 4.5 437 INFO-CODE: 5 438 Purpose: DNSSEC Indeterminate 439 Reference: Section 4.6 441 INFO-CODE: 6 442 Purpose: DNSSEC Bogus 443 Reference: Section 4.7 445 INFO-CODE: 7 446 Purpose: Signature Expired 447 Reference: Section 4.8 449 INFO-CODE: 8 450 Purpose: Signature Not Yet Valid 451 Reference: Section 4.9 453 INFO-CODE: 9 454 Purpose: DNSKEY Missing 455 Reference: Section 4.10 457 INFO-CODE: 10 458 Purpose: RRSIGs Missing 459 Reference: Section 4.11 461 INFO-CODE: 11 462 Purpose: No Zone Key Bit Set 463 Reference: Section 4.12 465 INFO-CODE: 12 466 Purpose: NSEC Missing 467 Reference: Section 4.13 469 INFO-CODE: 13 470 Purpose: Cached Error 471 Reference: Section 4.14 473 INFO-CODE: 14 474 Purpose: Not Ready. 475 Reference: Section 4.15 477 INFO-CODE: 15 478 Purpose: Blocked 479 Reference: Section 4.16 481 INFO-CODE: 16 482 Purpose: Censored 483 Reference: Section 4.17 485 INFO-CODE: 17 486 Purpose: Filtered 487 Reference: Section 4.18 489 INFO-CODE: 18 490 Purpose: Prohibited 491 Reference: Section 4.19 493 INFO-CODE: 19 494 Purpose: Stale NXDomain Answer 495 Reference: Section 4.20 497 INFO-CODE: 20 498 Purpose: Not Authoritative 499 Reference: Section 4.21 501 INFO-CODE: 21 502 Purpose: Not Supported 503 Reference: Section 4.22 505 INFO-CODE: 22 506 Purpose: No Reachable Authority 507 Reference: Section 4.23 509 INFO-CODE: 23 510 Purpose: Network Error 511 Reference: Section 4.24 513 INFO-CODE: 24 514 Purpose: Invalid Data 515 Reference: Section 4.25 517 INFO-CODE: 25-65535 518 Purpose: Unasigned 519 Reference: Section 5.2 521 6. Security Considerations 523 Though DNSSEC continues to be deployed, unfortunately a significant 524 number of clients (~11% according to [GeoffValidation]) that receive 525 a SERVFAIL from a validating resolver because of a DNSSEC validation 526 issue will simply ask the next (potentially non-validating) resolver 527 in their list, and thus don't get the protections which DNSSEC should 528 provide. 530 EDE information is unauthenticated information, unless secured by a 531 form of secured DNS transaction such as [RFC2845], [RFC2931] or 532 [RFC8094]. An attacker (e.g a MITM or malicious recursive server) 533 could insert an extended error response into untrusted data -- 534 although ideally clients and resolvers would not trust any 535 unauthenticated information. As such, EDE content should be treated 536 only as diagnostic information and MUST NOT alter DNS protocol 537 processing. Until all DNS answers are authenticated via DNSSEC or 538 the other mechanisms mentioned above, there are some tradeoffs. As 539 an example, an attacker who is able to insert the DNSSEC Bogus 540 Extended Error into a DNS message could instead simply reply with a 541 fictitious address (A or AAAA) record. Note that DNS Response Codes 542 (RCODEs) also contain no authentication and can be just as easily 543 manipulated. 545 By design, EDE potentially exposes additional information DNS 546 resolution processes that may leak information. An example of this 547 is the Prohibited EDE code (18), which may leak the fact that the 548 name is on a blacklist. 550 7. Acknowledgements 552 The authors wish to thank Joe Abley, Mark Andrews, Tim April, 553 Vittorio Bertola, Stephane Bortzmeyer, Vladimir Cunat, Ralph Dolmans, 554 Peter DeVries, Peter van Dijk, Mats Dufberg, Donald Eastlake, Bob 555 Harold, Paul Hoffman, Geoff Huston, Shane Kerr, Edward Lewis, Carlos 556 M. Martinez, George Michelson, Eric Orth, Michael Sheldon, Puneet 557 Sood, Petr Spacek, Ondrej Sury, John Todd, Loganaden Velvindron, and 558 Paul Vixie. They also vaguely remember discussing this with a number 559 of people over the years, but have forgotten who all they were -- if 560 you were one of them, and are not listed, please let us know and 561 we'll acknowledge you. 563 One author also wants to thank the band "Infected Mushroom" for 564 providing a good background soundtrack (and to see if he can get away 565 with this in an RFC!). Another author would like to thank the band 566 "Mushroom Infectors". This was funny at the time we wrote it, but we 567 cannot remember why... 569 8. References 571 8.1. Normative References 573 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 574 Requirement Levels", BCP 14, RFC 2119, 575 DOI 10.17487/RFC2119, March 1997, 576 . 578 [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. 579 Rose, "Protocol Modifications for the DNS Security 580 Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005, 581 . 583 [RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms 584 for DNS (EDNS(0))", STD 75, RFC 6891, 585 DOI 10.17487/RFC6891, April 2013, 586 . 588 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 589 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 590 May 2017, . 592 [RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS 593 Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499, 594 January 2019, . 596 [RFC8767] Lawrence, D., Kumari, W., and P. Sood, "Serving Stale Data 597 to Improve DNS Resiliency", RFC 8767, 598 DOI 10.17487/RFC8767, March 2020, 599 . 601 8.2. Informative References 603 [GeoffValidation] 604 APNIC, G. H., "A quick review of DNSSEC Validation in 605 today's Internet", June 2016, . 608 [RFC2845] Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B. 609 Wellington, "Secret Key Transaction Authentication for DNS 610 (TSIG)", RFC 2845, DOI 10.17487/RFC2845, May 2000, 611 . 613 [RFC2931] Eastlake 3rd, D., "DNS Request and Transaction Signatures 614 ( SIG(0)s )", RFC 2931, DOI 10.17487/RFC2931, September 615 2000, . 617 [RFC8094] Reddy, T., Wing, D., and P. Patil, "DNS over Datagram 618 Transport Layer Security (DTLS)", RFC 8094, 619 DOI 10.17487/RFC8094, February 2017, 620 . 622 Authors' Addresses 624 Warren Kumari 625 Google 626 1600 Amphitheatre Parkway 627 Mountain View, CA 94043 628 US 630 Email: warren@kumari.net 632 Evan Hunt 633 ISC 634 950 Charter St 635 Redwood City, CA 94063 636 US 638 Email: each@isc.org 640 Roy Arends 641 ICANN 643 Email: roy.arends@icann.org 645 Wes Hardaker 646 USC/ISI 647 P.O. Box 382 648 Davis, CA 95617 649 US 651 Email: ietf@hardakers.net 653 David C Lawrence 654 Oracle + Dyn 655 150 Dow St 656 Manchester, NH 03101 657 US 659 Email: tale@dd.org