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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Missing Reference: 'RFC2671' is mentioned on line 135, but not defined ** Obsolete undefined reference: RFC 2671 (Obsoleted by RFC 6891) == Missing Reference: 'RFC6891' is mentioned on line 153, but not defined == Unused Reference: 'I-D.ietf-sidr-iana-objects' is defined on line 335, but no explicit reference was found in the text Summary: 1 error (**), 0 flaws (~~), 4 warnings (==), 1 comment (--). 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: Informational E. Hunt 5 Expires: January 18, 2018 ISC 6 R. Arends 7 Nominet 8 W. Hardaker 9 USC/ISI 10 D. Lawrence 11 Akamai Technologies 12 July 17, 2017 14 Extended DNS Errors 15 draft-wkumari-dnsop-extended-error-02 17 Abstract 19 This document defines an extensible method to return additional 20 information about the cause of DNS errors. The primary use case is 21 to extend SERVFAIL to provide additional information about the cause 22 of DNS and DNSSEC failures. 24 [ Open question: The document currently defines a registry for 25 errors. It has also been suggested that the option also carry human 26 readable (text) messages, to allow the server admin to provide 27 additional debugging information (e.g: "example.com pointed their NS 28 at us. No idea why...", "We don't provide recursive DNS to 29 192.0.2.0. Please stop asking...", "Have you tried Acme Anvil and 30 DNS? We do DNS right..." (!). Please let us know if you think text 31 is needed, or if a 16bit FCFS registry is expressive enough. ] 33 [ Open question: This document discusses extended *errors*, but it 34 has been suggested that this could be used to also annotate *non- 35 error* messages. The authors do not think that this is a good idea, 36 but could be persuaded otherwise. ] 38 Status of This Memo 40 This Internet-Draft is submitted in full conformance with the 41 provisions of BCP 78 and BCP 79. 43 Internet-Drafts are working documents of the Internet Engineering 44 Task Force (IETF). Note that other groups may also distribute 45 working documents as Internet-Drafts. The list of current Internet- 46 Drafts is at http://datatracker.ietf.org/drafts/current/. 48 Internet-Drafts are draft documents valid for a maximum of six months 49 and may be updated, replaced, or obsoleted by other documents at any 50 time. It is inappropriate to use Internet-Drafts as reference 51 material or to cite them other than as "work in progress." 53 This Internet-Draft will expire on January 18, 2018. 55 Copyright Notice 57 Copyright (c) 2017 IETF Trust and the persons identified as the 58 document authors. All rights reserved. 60 This document is subject to BCP 78 and the IETF Trust's Legal 61 Provisions Relating to IETF Documents 62 (http://trustee.ietf.org/license-info) in effect on the date of 63 publication of this document. Please review these documents 64 carefully, as they describe your rights and restrictions with respect 65 to this document. Code Components extracted from this document must 66 include Simplified BSD License text as described in Section 4.e of 67 the Trust Legal Provisions and are provided without warranty as 68 described in the Simplified BSD License. 70 Table of Contents 72 1. Introduction and background . . . . . . . . . . . . . . . . . 3 73 1.1. Requirements notation . . . . . . . . . . . . . . . . . . 3 74 2. Extended Error EDNS0 option format . . . . . . . . . . . . . 3 75 3. Use of the Extended DNS Error option . . . . . . . . . . . . 4 76 4. Defined Extended DNS Errors . . . . . . . . . . . . . . . . . 5 77 4.1. Extended DNS Error Code 1 - DNSSEC Bogus . . . . . . . . 5 78 4.2. Extended DNS Error Code 2 - DNSSEC Indeterminite . . . . 5 79 4.3. Extended DNS Error Code 3 - Lame . . . . . . . . . . . . 5 80 4.4. Extended DNS Error Code 4 - Prohibited . . . . . . . . . 5 81 4.5. Extended DNS Error Code 5 - TooBusy . . . . . . . . . . . 6 82 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 83 6. Open questions . . . . . . . . . . . . . . . . . . . . . . . 7 84 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 85 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 86 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 87 9.1. Normative References . . . . . . . . . . . . . . . . . . 7 88 9.2. Informative References . . . . . . . . . . . . . . . . . 8 89 Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 8 90 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 92 1. Introduction and background 94 There are many reasons that a DNS query may fail, some of them 95 transient, some permanent; some can be resolved by querying another 96 server, some are likely best handled by stopping resolution. 97 Unfortunately, the error signals that a DNS server can return are 98 very limited, and are not very expressive. This means that 99 applications and resolvers often have to "guess" at what the issue is 100 - e.g the answer was marked REFUSED because of a lame delegation, or 101 because there is a lame delegation or because the nameserver is still 102 starting up and loading zones? Is a SERVFAIL a DNSSEC validation 103 issue, or is the nameserver experiencing a bad hair day? 105 A good example of issues that would benefit by additional error 106 information is an error caused by a DNSSEC validation issue. When a 107 stub resolver queries a DNSSEC bogus name (using a validating 108 resolver), the stub resolver receives only a SERVFAIL in response. 109 Unfortunately, SERVFAIL is used to signal many sorts of DNS errors, 110 and so the stub resolver simply asks the next configured DNS 111 resolver. The result of trying the next resolver is one of two 112 outcomes: either the next resolver also validates, a SERVFAIL is 113 returned again, and the user gets an (largely) incomprehensible error 114 message; or the next resolver is not a validating resolver, and the 115 user is returned a potentially harmful result. 117 This document specifies a mechanism to extend (or annotate) DNS 118 errors to provide additional information about the cause of the 119 error. This information can be used by the resolver to make a 120 decision regarding whether or not to retry, or by technical users 121 attempting to debug issues. 123 Here is a reference to an "external" (non-RFC / draft) thing: 124 ([IANA.AS_Numbers]). And this is a link to an 125 ID:[I-D.ietf-sidr-iana-objects]. 127 1.1. Requirements notation 129 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 130 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 131 document are to be interpreted as described in [RFC2119]. 133 2. Extended Error EDNS0 option format 135 This draft uses an EDNS0 ([RFC2671]) option to include extended error 136 (ExtError) information in DNS messages. The option is structured as 137 follows: 139 1 1 1 1 1 1 140 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 141 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 142 0: | OPTION-CODE | 143 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 144 2: | OPTION-LENGTH | 145 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 146 4: | R | FLAGS | 147 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 148 6: | CODE | 149 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 151 o OPTION-CODE, 2 octets (defined in [RFC6891]), for ExtError is TBD. 153 o OPTION-LENGTH, 2 octets ((defined in [RFC6891]) contains the 154 length of the payload (everything after OPTION-LENGTH) in octets 155 and should be 4. 157 o FLAGS, 2 octets. 159 o CODE, 2 octets. 161 Currently the only defined flag is the R flag. 163 R - Retry The R (or Retry) flag provides a hint to the receiver if 164 it should retry the query, possibly by querying another server. 165 If the R bit is set (1), the sender believes that retrying the 166 query may provide a successful answer next time; if the R bit is 167 clear (0), the sender believes that it should not ask another 168 server. 170 The remaining bits in the flags field MUST be set to 0 by the sender 171 and SHOULD be ignored by the receiver. 173 Code: A code point into the IANA "Extended DNS Errors" registry. 175 3. Use of the Extended DNS Error option 177 The Extended DNS Error (EDE) is an EDNS option. It can be included 178 in any error response (SERVFAIL, NXDOMAIN, REFUSED, etc) to a query 179 that includes an EDNS option. This document includes a set of 180 initial codepoints (and requests to the IANA to add them to the 181 registry), but is extensible via the IANA registry to allow 182 additional error codes to be defined in the future. 184 The R (Retry) flag provides a hint (or suggestion) as to what the 185 receiver may want to do with this annotated error. The mechanism is 186 specifically designed to be extensible, and so implementations may 187 receive EDE codes that it does not understand. The R flag allows 188 implementations to make a decision as to what to do if it receives a 189 response with an unknown code - retry or drop the query. Note that 190 this flag is only a suggestion or hint. Receivers can choose to 191 ignore this hint. 193 4. Defined Extended DNS Errors 195 This document defines some initial EDE codes. The mechanism is 196 intended to be extensible, and additional codepoints will be 197 registered in the "Extended DNS Errors" registry. This document 198 provides suggestions for the R flag, but the originating server may 199 ignore these recommendations if it knows better. 201 4.1. Extended DNS Error Code 1 - DNSSEC Bogus 203 The resolver attempted to perform DNSSEC validation, but validation 204 ended in the Bogus state. The R flag should be set. 206 4.2. Extended DNS Error Code 2 - DNSSEC Indeterminite 208 The resolver attempted to perform DNSSEC validation, but validation 209 ended in the Indeterminate state. 211 Usually attached to SERVFAIL messages. The R flag should be set. 213 4.3. Extended DNS Error Code 3 - Lame 215 An authoritative resolver that receives a query (with the RD bit 216 clear) for a domain for which it is not authoritative SHOULD include 217 this EDE code in the REFUSED response. 219 Implementations should not set the R flag in this case (another 220 nameserver might not be lame). 222 4.4. Extended DNS Error Code 4 - Prohibited 224 An authoritative or recursive resolver that receives a query from an 225 "unauthorized" client can annotate its REFUSED message with this 226 code. Examples of "unauthorized" clients are recursive queries from 227 IP addresses outside the network, blacklisted IP addresses, etc. 229 Implementations SHOULD allow operators to define what to set the R 230 flag to in this case. 232 4.5. Extended DNS Error Code 5 - TooBusy 234 [ Ed: This might be a bad idea. It is intended to allow servers 235 under a DoS (for example a random subdomain attack) to signal to 236 recursive clients that they are being abusive and should back off. 237 This may be a bad idea -- it may "complete the attack", it may be 238 spoofable (by anyone who could also do a MITM style attack), etc. ] 240 A nameserver which is under excessive load (for example, because it 241 is experiencing a DoS) may annotate any answer with this code. 243 It is RECOMMENDED that implementations set the R flag in this case, 244 but may allow operators to define what to set the R flag to. 246 [ agreed: bad idea -wjh ] 248 5. IANA Considerations 250 [This section under construction, beware. ] 252 This document defines a new EDNS(0) option, entitled "Extended DNS 253 Error", assigned a value of TBD1 from the "DNS EDNS0 Option Codes 254 (OPT)" registry [to be removed upon publication: 255 [http://www.iana.org/assignments/dns-parameters/dns- 256 parameters.xhtml#dns-parameters-11] 258 Value Name Status Reference 259 ----- ---------------- ------ ------------------ 260 TBD Extended DNS Error TBD [ This document ] 262 Data Tag Name Length Meaning ---- ---- ------ ------- TBD1 FooBar N 263 FooBar server 265 The IANA is requested to create and maintain the "Extended DNS Error 266 codes" registry. The codepoint space is broken into 3 ranges: 268 o 1 - 16384: Specification required. 270 o 16385 - 65000: First Come First Served 272 o 65000 - 65534: Experimental / Private use 274 The codepoints 0, 65535 are reserved. 276 6. Open questions 278 1 Can this be included in *any* response or only responses to 279 requests that included an EDNS option? Resolvers are supposed to 280 ignore additional. EDNS capable ones are supposed to simply 281 ignore unknown options. I know the spec says you can only include 282 EDNS0 in a response if in a request -- it is time to reevaluate 283 this? 285 2 Can this be applied to *any* response, or only error responses? 287 3 Should textual information be allowed as well? What if the only 288 thing allowed is a domain name, e.g to point at where validation 289 began failing? 291 7. Security Considerations 293 DNSSEC is being deployed - unfortunately a significant number of 294 clients (~11% according to [GeoffValidation]), when receiving a 295 SERVFAIL from a validating resolver because of a DNSSEC validaion 296 issue simply ask the next (non-validating) resolver in their list, 297 and do don't get any of the protections which DNSSEC should provide. 298 This is very similar to a kid asking his mother if he can have 299 another cookie. When the mother says "No, it will ruin your 300 dinner!", going off and asking his (more permissive) father and 301 getting a "Yes, sure, cookie!". 303 8. Acknowledgements 305 The authors wish to thank Geoff Huston. They also vaguely remember 306 discussing this with a number of people over the years, but have 307 forgotten who all they were -- if you were one of them, and are not 308 listed, please let us know and we'll acknowledge you. 310 I also want to thank the band "Infected Mushroom" for providing a 311 good background soundtrack (and to see if I can get away with this!) 312 Another author would like to thank the band "Mushroom Infectors". 313 This was funny at the time we wrote it, but I cannot remember why... 315 9. References 317 9.1. Normative References 319 [IANA.AS_Numbers] 320 IANA, "Autonomous System (AS) Numbers", 321 . 323 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 324 Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ 325 RFC2119, March 1997, 326 . 328 9.2. Informative References 330 [GeoffValidation] 331 IANA, "A quick review of DNSSEC Validation in today's 332 Internet", June 2016, . 335 [I-D.ietf-sidr-iana-objects] 336 Manderson, T., Vegoda, L., and S. Kent, "RPKI Objects 337 issued by IANA", draft-ietf-sidr-iana-objects-03 (work in 338 progress), May 2011. 340 Appendix A. Changes / Author Notes. 342 [RFC Editor: Please remove this section before publication ] 344 From -02 to -03: 346 o Added David Lawrence -- I somehow missed that in last version. 348 From -00 to -01; 350 o Fixed up some of the text, minor clarifications. 352 Authors' Addresses 354 Warren Kumari 355 Google 356 1600 Amphitheatre Parkway 357 Mountain View, CA 94043 358 US 360 Email: warren@kumari.net 362 Evan Hunt 363 ISC 364 950 Charter St 365 Redwood City, CA 94063 366 US 368 Email: each@isc.org 369 Roy Arends 370 Nominet 371 UK 373 Email: TBD 375 Wes Hardaker 376 USC/ISI 377 P.O. Box 382 378 Davis, VA 95617 379 US 381 David C Lawrence 382 Akamai Technologies 383 150 Broadway 384 Cambridge, MA 02142-1054 385 US 387 Email: tale@akamai.com