idnits 2.17.00 (12 Aug 2021) /tmp/idnits8380/draft-wkumari-dnsop-multiple-responses-03.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (June 26, 2016) is 2155 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Unused Reference: 'RFC7873' is defined on line 336, but no explicit reference was found in the text ** Obsolete normative reference: RFC 5395 (Obsoleted by RFC 6195) ** Obsolete normative reference: RFC 6555 (Obsoleted by RFC 8305) Summary: 2 errors (**), 0 flaws (~~), 2 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 dnsop W. Kumari 3 Internet-Draft Google 4 Intended status: Standards Track Z. Yan 5 Expires: December 28, 2016 CNNIC 6 W. Hardaker 7 Parsons, Inc. 8 June 26, 2016 10 Returning extra answers in DNS responses. 11 draft-wkumari-dnsop-multiple-responses-03 13 Abstract 15 This document (re)introduces the ability to provide multiple answers 16 in a DNS response. 18 Status of This Memo 20 This Internet-Draft is submitted in full conformance with the 21 provisions of BCP 78 and BCP 79. 23 Internet-Drafts are working documents of the Internet Engineering 24 Task Force (IETF). Note that other groups may also distribute 25 working documents as Internet-Drafts. The list of current Internet- 26 Drafts is at http://datatracker.ietf.org/drafts/current/. 28 Internet-Drafts are draft documents valid for a maximum of six months 29 and may be updated, replaced, or obsoleted by other documents at any 30 time. It is inappropriate to use Internet-Drafts as reference 31 material or to cite them other than as "work in progress." 33 This Internet-Draft will expire on December 28, 2016. 35 Copyright Notice 37 Copyright (c) 2016 IETF Trust and the persons identified as the 38 document authors. All rights reserved. 40 This document is subject to BCP 78 and the IETF Trust's Legal 41 Provisions Relating to IETF Documents 42 (http://trustee.ietf.org/license-info) in effect on the date of 43 publication of this document. Please review these documents 44 carefully, as they describe your rights and restrictions with respect 45 to this document. Code Components extracted from this document must 46 include Simplified BSD License text as described in Section 4.e of 47 the Trust Legal Provisions and are provided without warranty as 48 described in the Simplified BSD License. 50 Table of Contents 52 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 53 1.1. Requirements notation . . . . . . . . . . . . . . . . . . 3 54 2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 3 55 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 56 4. Returning multiple answers . . . . . . . . . . . . . . . . . 4 57 5. The EXTRA Resource Record . . . . . . . . . . . . . . . . . . 4 58 5.1. File Format . . . . . . . . . . . . . . . . . . . . . . . 5 59 5.2. Wire Format . . . . . . . . . . . . . . . . . . . . . . . 5 60 6. Signaling support . . . . . . . . . . . . . . . . . . . . . . 6 61 7. Stub-Resolver Considerations . . . . . . . . . . . . . . . . 6 62 8. Use of Additional information . . . . . . . . . . . . . . . . 6 63 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 64 10. Security Considerations . . . . . . . . . . . . . . . . . . . 6 65 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 66 12. Normative References . . . . . . . . . . . . . . . . . . . . 7 67 Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 8 68 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 70 1. Introduction 72 In many cases a name being resolved in the DNS provides the reason 73 behind why the name is being resolved. This may allow the 74 authoritative nameserver to predict what other answers a recursive 75 resolver will soon query for. By providing multiple answers in the 76 response, the authoritative name server operator can assist a caching 77 recursive resolver in pre-populating its cache before a stub resolver 78 or other client asks for the subsequent queries. Apart from 79 decreasing the latency for end users [RFC6555], this also decreases 80 the total number of queries that the recursive resolver needs to send 81 and the autorative server needs to answer. 83 For example, the domain name administrator of Example Widgets, Inc 84 (example.com) knows that the web page at www.example.com contains 85 various other resources, including some images (served from 86 images.example.com), some Cascading Style Sheets (served from 87 css.example.com) and some JavaScript (served from data.example.com). 88 An application attempting to resolve www.example.com is very likely 89 to be a web browser rendering the page and will likely also need to 90 resolve all of these additional names as well. Providing all of 91 these answers in response to a query for www.example.com allows the 92 recursive resolver to pre-populate its cache and have these answers 93 available immediately when a stub resolver or other DNS client asks 94 for them. 96 Other examples where this technique may be useful include SMTP (by 97 including mail server addresses, SPF and DKIM records when serving 98 the MX record), SRV (by providing the target information in addition 99 to the SRV response) and TLSA (by providing any TLSA records 100 associated with a name). This same technique can also be used to 101 include both the IPv4 (A) and IPv6 (AAAA) addresses for any singular 102 address query. 104 This technique, described in this document, is purely an optimization 105 and enables a zone publisher to distribute other related answers that 106 the client is likely to need along with an answer to the original 107 request. Users get a better experience, recursive resolvers need to 108 send less queries, authoritative servers have to answer fewer 109 queries, etc. 111 1.1. Requirements notation 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 [RFC2119]. 117 2. Background 119 The existing DNS specifications [RFC1034] allow for supplemental 120 information to be included in the "additional" section of the DNS 121 response, but in order to defeat cache poisoning attacks most 122 implementations either ignore or don't trust additional records they 123 didn't ask for. For more background, see [Ref.Bellovin] and 124 [RFC2181]. 126 Not trusting the information in the additional section was necessary 127 since there was no way to authenticate it. If a resolver queries for 128 www.example.com and received answers for www.invalid.com as well, it 129 is impossible for a non-validating resolver to tell if these were 130 actually from invalid.com or if an attacker was trying to push bad 131 information for invalid.com into the resolver's cache. In a world of 132 ubiquitous DNSSEC deployment [Ed note: By the time this document is 133 published, there *will* be ubiquitous DNSSEC :-) ], a validating 134 resolver can validate, authenticate and trust the records in the 135 additional information. 137 3. Terminology 139 Additional records Additional records are records that the 140 authoritative nameserver has included in the Additional section. 142 EXTRTA Resource Record The EXTRA resource record (defined below) 143 carries a list fo additional records to send. 145 Primary query A Primary query (or primary question) is a QNAME that 146 the name server operator would like to return additional answers 147 for. 149 Supporting DNSSEC information Supporting DNSSEC information is the 150 DNSSEC RRSIGs that prove the authenticity of the Additional 151 records. 153 Stub Resolver The term "Stub Resolver" is used in this document to 154 refer to the most common instance of a DNS client sending DNS 155 requests to a Recursive Resolver. However, other DNS clients are 156 not excluded from these usages and where we write "Stub Resolver" 157 you may read it as "Stub Resolver or other DNS client". 159 4. Returning multiple answers 161 The authoritative nameserver should include as many of the instructed 162 additional records identified by the Extra Resource Record and 163 Supporting DNSSEC information as will fit in the response packet. 164 These additional records (and Supporting DNSSEC information) are 165 appended to the additional section of the response. 167 In order to include additional records in a response, these 168 conditions need to be met: 170 1. Additional records MUST only be included when the Name Server is 171 authoritative for the zone, and the records to be returned are 172 DNSSEC signed. 174 2. The supporting DNSSEC information necessary to perform validation 175 on the records MUST be included. 177 3. The Authoritative Name Server SHOULD include as many of the 178 additional records as will fit in the response. Additional 179 records SHOULD be inserted in the order specified in the 180 Additional records list. 182 4. Zone administrators SHOULD only include records identified in the 183 EXTRA Resource Records that they expect a client to need. 185 5. The EXTRA Resource Record 187 To allow a zone content administrator to instruct the name server 188 which additional records to serve when it receives a query to a 189 label, we introduce the EXTRA Resource Record (RR). These additional 190 records are appended to the additional section (note that the EXTRA 191 RR itself is not appended). The EXTRA resource record MAY still be 192 queried for directly (e.g for debugging), in which case the record 193 itself is returned. 195 5.1. File Format 197 The format of the Extra RR is: 199 label EXTRA "label,type; label,type; label,type; ..." 201 For example, if the operator of example.com would like to also return 202 A record answers for images.example.com, css.html.example.com and 203 both an A and AAAA for data.example.com when queried for 204 www.example.com, they would create the following record: 206 www.example.com. EXTRA "images,A; css,A; data,A; data,AAA;" 208 The entries in the EXRTA list are ordered. An authoritative 209 nameserver SHOULD insert the records in the order listed when filling 210 the response packet. This is to allow the operator to express a 211 preference in case all the records will not fit in the response. The 212 TTL of the records added to the Additional section are MUST be the 213 same as if queried directly. 215 In some cases a zone content administrator might not know what all 216 additional records clients need. For example, the owner of 217 www.example.com may have outsourced his DNS operations to a third 218 party. DNS administrators may be able to mine their query logs, and 219 see that, in a large majority of cases, a recursive server asks for 220 foo.example.com and then very soon after asks for bar.example.com, 221 and so may decide to optimize this by opportunistically returning bar 222 when queried for foo. This functionality could also be included in 223 the authoritative name server software itself, but discussions of 224 these are outside the scope of this document. 226 5.2. Wire Format 228 The wire format of the EXTRA RR is the same as the wire format for a 229 TXT RR: 231 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 232 / TXT-DATA / 233 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 235 Where TXT-DATA is one or more s. 237 The Extra RR has RR type TBD [RFC Editor: insert the IANA assigned 238 value and delete this note] 240 6. Signaling support 242 Recursive Resolvers (or other DNS clients) that support EXTRA records 243 MAY signal this by setting the OPT record's EXTRA bit (bit NN [TBD: 244 assigned by IANA] in the EDNS0 extension header to 1. 246 7. Stub-Resolver Considerations 248 No modifications need to be made to stub-resolvers to get the 249 predominate benefit of this protocol, since the majority of the speed 250 gain will take place between the validating recursive resolver and 251 the authoritative name server. However, stub resolvers may choose to 252 support this technique, and / or may query directly for the EXTRA RR 253 if it wants to pre-query for data that will likely be needed in the 254 process of supporting its application. 256 8. Use of Additional information 258 When receiving additional records in the additional section, a 259 resolver follows certain rules: 261 1. Additional records MUST be validated before being used. 263 2. Additional records SHOULD be annotated in the cache as having 264 been received as Additional records. 266 3. Additional records SHOULD have lower priority in the cache than 267 answers received because they were requested. This is to help 268 evict Additional records from the cache first (to help prevent 269 cache filling attacks). 271 4. Recursive resolvers MAY choose to ignore Additional records for 272 any reason, including CPU or cache space concerns, phase of the 273 moon, etc. It may choose to accept all, some or none of the 274 Additional records. 276 9. IANA Considerations 278 This document contains the following IANA assignment requirements: 280 1. The EXTRA bit discussed in Section 6 needs to be allocated. 282 10. Security Considerations 284 Additional records will make DNS responses even larger than they are 285 currently, leading to larger records that can be used in DNS 286 reflection attacks. One could mitigate this by only serving 287 responses to EXTRA requests over TCP or when using Cookies [RFC5395], 288 although there is no easy way to signal this to a client other than 289 through the use of the truncate bit. 291 A malicious authoritative server could include a large number of 292 extra records (and associated DNSSEC information) and attempt to DoS 293 the recursive by making it do lots of DNSSEC validation. However, 294 this is not considered a realistic threat; CPU for validation is 295 cheap compared to bandwidth. This can be mitigated by allowing the 296 recursive resolver to ignore Additional records whenever it considers 297 itself under attack or its CPU resources are otherwise over- 298 committed. 300 This specification requires that the all of the Additional records 301 are signed, and all necessary DNSSEC information for validation be 302 included to avoid cache poisoning attacks. 304 11. Acknowledgements 306 The authors wish to thank some folk. 308 12. Normative References 310 [Ref.Bellovin] 311 Bellovin, S., "Using the Domain Name System for System 312 Break-Ins", 1995, 313 . 315 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 316 STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, 317 . 319 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 320 Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ 321 RFC2119, March 1997, 322 . 324 [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS 325 Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997, 326 . 328 [RFC5395] Eastlake 3rd, D., "Domain Name System (DNS) IANA 329 Considerations", RFC 5395, DOI 10.17487/RFC5395, November 330 2008, . 332 [RFC6555] Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with 333 Dual-Stack Hosts", RFC 6555, DOI 10.17487/RFC6555, April 334 2012, . 336 [RFC7873] Eastlake 3rd, D. and M. Andrews, "Domain Name System (DNS) 337 Cookies", RFC 7873, DOI 10.17487/RFC7873, May 2016, 338 . 340 Appendix A. Changes / Author Notes. 342 [RFC Editor: Please remove this section before publication ] 344 From -00 to -01. 346 o Nothing changed in the template! 348 From -02 to -3: 350 Sat down and rewrote and cleaned up large sections of text. 352 Changed name of RR from Additional to EXTRA (the term "Additional" 353 is overloaded in general) 355 Clarified that stub resolvers and other clients MAY use this 356 specification. 358 Attempted to clarify that the individual RRs are added to the 359 response, not the EXTRA record itself. The EXTRA RR can be 360 queried directly. 362 Authors' Addresses 364 Warren Kumari 365 Google 366 1600 Amphitheatre Parkway 367 Mountain View, CA 94043 368 US 370 Email: warren@kumari.net 372 Zhiwei Yan 373 CNNIC 374 No.4 South 4th Street, Zhongguancun 375 Beijing 100190 376 P. R. China 378 Email: yanzhiwei@cnnic.cn 379 Wes Hardaker 380 Parsons, Inc. 381 P.O. Box 382 382 Davis, CA 95617 383 US 385 Email: ietf@hardakers.net