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Checking references for intended status: Informational ---------------------------------------------------------------------------- No issues found here. Summary: 0 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: Informational A. Sullivan 5 Expires: September 22, 2016 Dyn 6 March 21, 2016 8 The ALT Special Use Top Level Domain 9 draft-ietf-dnsop-alt-tld-04 11 Abstract 13 This document reserves a string (ALT) to be used as a TLD label in 14 non-DNS contexts or for names that have no meaning in a global 15 context. It also provides advice and guidance to developers 16 developing alternate namespaces. 18 [ Ed note: This document lives in GitHub at: 19 https://github.com/wkumari/draft-wkumari-dnsop-alt-tld . Issues and 20 pull requests happily accepted. ] 22 Status of This Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at http://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on September 22, 2016. 39 Copyright Notice 41 Copyright (c) 2016 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents 46 (http://trustee.ietf.org/license-info) in effect on the date of 47 publication of this document. Please review these documents 48 carefully, as they describe your rights and restrictions with respect 49 to this document. Code Components extracted from this document must 50 include Simplified BSD License text as described in Section 4.e of 51 the Trust Legal Provisions and are provided without warranty as 52 described in the Simplified BSD License. 54 Table of Contents 56 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 57 1.1. Requirements notation . . . . . . . . . . . . . . . . . . 2 58 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2 59 2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 3 60 3. The ALT namespace . . . . . . . . . . . . . . . . . . . . . . 4 61 3.1. Choice of the ALT Name . . . . . . . . . . . . . . . . . 5 62 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 63 4.1. Domain Name Reservation Considerations . . . . . . . . . 6 64 5. Security Considerations . . . . . . . . . . . . . . . . . . . 7 65 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 66 7. Normative References . . . . . . . . . . . . . . . . . . . . 8 67 Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 8 68 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 70 1. Introduction 72 Many protocols and systems need to name entities. Names that look 73 like DNS names (a series of labels separated with dots) have become 74 common, even in systems that are not part of the global DNS 75 administered by IANA. 77 This document provides a solution that may be more appropriate than 78 [RFC6761] in many cases. 80 This document reserves the label "ALT" (short for "Alternate") as a 81 Special Use Domain ([RFC6761]). This label is intended to be used as 82 the final label to signify that the name is not rooted in the DNS, 83 and that normal registration and lookup rules do not apply. 85 1.1. Requirements notation 87 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 88 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 89 document are to be interpreted as described in [RFC2119]. 91 1.2. Terminology 93 This document assumes familiarity with DNS terms and concepts. 94 Please see [RFC1034] for background and concepts, and 95 [I-D.ietf-dnsop-dns-terminology] for terminology. 97 o DNS name: Domain names that are intended to be used with DNS 98 resolution, either in the global DNS or in some other context 100 o DNS context: The namespace anchored at the globally-unique DNS 101 root. This is the namespace or context that "normal" DNS uses. 103 o non-DNS context: Any other (alternate) namespace. 105 o pseudo-TLD: A label that appears in a fully-qualified domain name 106 in the position of a TLD, but which is not registered in the 107 global DNS. 109 o TLD: The last visible label in either a fully-qualified domain 110 name or a name that is qualified relative to the root. See the 111 discussion in Section 2. 113 2. Background 115 The DNS data model is based on a tree structure, and has a single 116 root. Conventionally, a name immediately beneath the root is called 117 a "Top Level Domain" or "TLD". TLDs usually delegate portions of 118 their namespace to others, who may then delegate further. The 119 hierarchical, distributed and caching nature of the DNS has made it 120 the primary resolution system on the Internet. 122 Domain names are terminated by a zero-length label, so the root label 123 is normally invisible. Truly fully-qualified names indicate the root 124 label explicitly, thus: "an.example.tld.". Most of the time, names 125 are written implicitly relative to the root, thus: "an.example.tld". 126 In both of these cases, the TLD is the last label that is visible in 127 presentation format -- in this example, the string "tld". (This 128 little bit of pedantry is here because, in different contexts, people 129 can use the term "fully-qualified domain name" to refer to either of 130 these uses.) It is worth noting that the root label is present in 131 the on-wire format of fully-qualified domain names, even if not 132 displayed in the presentation form. 134 The success of the DNS makes it a natural starting point for systems 135 that need to name entities in a non-DNS context, or that have no 136 unique meaning in a global context. These name resolutions, 137 therefore, occur in a namespace distinct from the DNS. 139 In many cases, these systems build a DNS-style tree parallel to, but 140 separate from, the global DNS. They often use a pseudo-TLD to cause 141 resolution in the alternate namespace, using browser plugins, shims 142 in the name resolution process, or simply applications that perform 143 special handling of this particular alternate namespace. 145 In many cases, the creators of these alternate namespaces have chosen 146 a convenient or descriptive string and started using it. These new 147 strings are "alternate" strings and are not registered anywhere or 148 part of the DNS. However they appear to users and to some 149 applications to be TLDs. Issues may arise if they are looked up in 150 the DNS. These include: 152 o User confusion: If someone emails a link of the form 153 foo.bar.pseudo-TLD to someone who does not have the necessary 154 software to resolve names in the pseudo-TLD namespace, the name 155 will not resolve and the user may become confused. 157 o Excess traffic hitting the DNS root: Lookups leak out of the 158 pseudo-TLD namespace and end up hitting the DNS root nameservers. 160 o Collisions: If the pseudo-TLD is eventually delegated from the 161 root zone, the lookup behavior will change in a non-deterministic 162 fashion. 164 o Lack of success for the user's original goal. 166 An alternate name resolution system might be specifically designed to 167 provide confidentiality of the looked up name, and to provide a 168 distributed and censorship-resistant namespace. This goal would 169 necessarily be defeated if the queries leak into the DNS, because the 170 attempt to look up the name would be visible at least to the 171 operators of root name servers and to any entity viewing the DNS 172 lookups going to the root nameservers. 174 3. The ALT namespace 176 In order to avoid the above issues, we reserve the ALT label. Unless 177 the name desired is globally unique, has meaning on the global 178 context and is delegated in the DNS, it should be considered an 179 alternate namespace, and follow the ALT label scheme outlined below. 180 The ALT label MAY be used in any domain name as a pseudo-TLD to 181 signify that this is an alternate (non-DNS) namespace. 183 Alternate namespaces should differentiate themselves from other 184 alternate namespaces by choosing a name and using it in the label 185 position just before the pseudo-TLD (ALT). For example, a group 186 wishing to create a namespace for Friends Of Olaf might choose the 187 string "foo" and use any set of labels under foo.alt. 189 As they are in an alternate namespace, they have no significance in 190 the regular DNS context and so should not be looked up in the DNS 191 context. Some of these requests will inevitably leak into the DNS 192 context (for example, because clicks on a link in a browser that does 193 not have a extension installed that implements the alternate 194 namespace resolution), and so the ALT TLD has been added to the 195 "Locally Served DNS Zones" ( [RFC6303]) registry to limit how far 196 these flow. 198 Groups wishing to create new alternate namespaces SHOULD create their 199 alternate namespace under a label that names their namespace, and 200 under the ALT label. They SHOULD choose a label that they expect to 201 be unique and, ideally, descriptive. There is no IANA controlled 202 registry for names under the ALT TLD - it is an unmanaged namespace, 203 and developers are responsible for dealing with any collisions that 204 may occur under .alt. Informal lists of namespaces under .alt may 205 appear to assist the developer community. 207 [Editor note (to be removed before publication): There was 208 significant discussion on an IANA registry for the ALT namespace - 209 please consult the lists for full thread, but the consensus seems to 210 be that it would be better for the IETF / IANA to not administer a 211 registry for this. It is expected one or more unofficial lists will 212 be created where people can list the strings that they are using. ] 214 Currently deployed projects and protocols that are using pseudo-TLDs 215 may decide to move under the ALT TLD, but this is not a requirement. 216 Rather, the ALT TLD is being reserved so that current and future 217 projects of a similar nature have a designated place to create 218 alternate resolution namespaces that will not conflict with the 219 regular DNS context. 221 3.1. Choice of the ALT Name 223 A number of names other than "ALT" were considered and discarded. In 224 order for this technique to be effective the names need to continue 225 to follow both the DNS format and conventions (a prime consideration 226 for alternate name formats is that they can be entered in places that 227 normally take DNS context names); this rules out using suffixes that 228 do not follow the usual letter, digit, and hyphen label convention. 230 Another proposal was that the ALT TLD instead be a reservation under 231 .arpa. This was considered, but rejected for several reasons, 232 including: 234 1. We wished this to make it clear that this is not in the DNS 235 context, and .arpa clearly is. 237 2. The use of the string .alt is intended to evoke the alt.* 238 hierarchy in Usenet. 240 3. We wanted the string to be short and easily used. 242 4. A name underneath .arpa would consume at least five additional 243 octets of the total 255 octets available in domain names, which 244 could put pressure on applications that need long machine- 245 generated names. 247 5. We are suggesting that the string "ALT" get special treatment in 248 resolvers, and shim software. We are concerned that using 249 subdomains of an existing TLD (like .arpa) might end up with bad 250 implementations misconfiguring / overriding the TLD itself and 251 breaking .arpa. 253 There is a concern that if there were placed under .arpa, 254 inexperienced nameserver operators may inadvertently cover .arpa. A 255 more significant concern is that the scope of the issue if the query 256 does leak, and the fact that this would then make the root of the 257 alternate naming namespace a third level domain, and not a second 258 one. A project may be willing to have a name of the form 259 example.alt, but example.alt.arpa may be not look as good. 261 4. IANA Considerations 263 The IANA is requested to add the ALT string to the "Special-Use 264 Domain Name" registry ([RFC6761], and reference this document. In 265 addition, the "Locally Served DNS Zones" ([RFC6303]) registry should 266 be updated to reference this document. 268 4.1. Domain Name Reservation Considerations 270 This section is to satisfy the requirement in Section 5 of RFC6761. 272 The domain "alt.", and any names falling within ".alt.", are special 273 in the following ways: 275 1. Human users are expected to know that strings that end in .alt 276 behave differently to normal DNS names. Users are expected to 277 have applications running on their machines that intercept 278 strings of the form .alt and perform special handing 279 of them. If the user tries to resolve a name of the form 280 .alt without the plugin installed, the 281 request will leak into the DNS, and receive a negative response. 283 2. Writers of application software that implement a non-DNS 284 namespace are expected to intercept names of the form 285 .alt and perform application specific handing with 286 them. Other applications are not intended to perform any special 287 handing. 289 3. In general, writers of name resolution APIs and libraries do not 290 need to perform special handing of these names. If developers of 291 other namespaces implement their namespace through a "shim" or 292 library, they will need to intercept and perform their own 293 handling. 295 4. Caching DNS servers SHOULD recognize these names as special and 296 SHOULD NOT, by default, attempt to look up NS records for them, 297 or otherwise query authoritative DNS servers in an attempt to 298 resolve these names. Instead, caching DNS servers SHOULD 299 generate immediate negative responses for all such queries. 301 5. Authoritative DNS servers SHOULD recognize these names as special 302 and SHOULD, by default, generate immediate negative responses for 303 all such queries, unless explicitly configured by the 304 administrator to give positive answers for private-address 305 reverse-mapping names. 307 6. DNS server operators SHOULD be aware that queries for names 308 ending in .alt are not DNS names, and were leaked into the DNS 309 context (for example, by a missing browser plugin). This 310 information may be useful for support or debugging purposes. 312 7. DNS Registries/Registrars MUST NOT grant requests to register 313 "alt" names in the normal way to any person or entity. These 314 "alt" names are defined by protocol specification to be 315 nonexistent, and they fall outside the set of names available for 316 allocation by registries/registrars. 318 5. Security Considerations 320 One of the motivations for the creation of the alt pseudo-TLD is that 321 unmanaged labels in the managed root name space are subject to 322 unexpected takeover if the manager of the root name space decides to 323 delegate the unmanaged label. 325 The unmanaged and "registration not required" nature of labels 326 beneath .alt provides the opportunity for an attacker to re-use the 327 chosen label and thereby possibly compromise applications dependent 328 on the special host name. 330 6. Acknowledgements 332 We would also like to thank Joe Abley, Mark Andrews, Marc Blanchet, 333 John Bond, Stephane Bortzmeyer, David Cake, David Conrad, Patrik 334 Faltstrom, Olafur Gudmundsson, Paul Hoffman, Joel Jaeggli, Ted Lemon, 335 Edward Lewis, George Michaelson, Ed Pascoe, Arturo Servin, and Paul 336 Vixie for feedback. 338 7. Normative References 340 [I-D.ietf-dnsop-dns-terminology] 341 Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS 342 Terminology", draft-ietf-dnsop-dns-terminology-05 (work in 343 progress), September 2015. 345 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 346 STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, 347 . 349 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 350 Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ 351 RFC2119, March 1997, 352 . 354 [RFC6303] Andrews, M., "Locally Served DNS Zones", BCP 163, RFC 355 6303, DOI 10.17487/RFC6303, July 2011, 356 . 358 [RFC6761] Cheshire, S. and M. Krochmal, "Special-Use Domain Names", 359 RFC 6761, DOI 10.17487/RFC6761, February 2013, 360 . 362 Appendix A. Changes / Author Notes. 364 [RFC Editor: Please remove this section before publication ] 366 From -03 to -04: 368 o 3 changes - the day, the month and the year (a bump to keep 369 alive). 371 From -02 to -03: 373 o Incorporate suggestions from Stephane and Paul Hoffman. 375 From -01 to -02: 377 o Merged a bunch of changes from Paul Hoffman. Thanks for sending a 378 git pull. 380 From -00 to 01: 382 o Removed the "delegated to new style AS112 servers" text -this was 383 legacy from the omnicient AS112 days. (Joe Abley) 385 o Removed the "Advice to implemntors" section. This used to 386 recommend that people used a subdomain of a domain in the DNS. It 387 was pointed out that this breaks things badly if the domain 388 expires. 390 o Added text about why we don't want to adminster a registry for 391 ALT. 393 From Individual-06 to DNSOP-00 395 o Nothing changed, simply renamed draft-wkumari-dnsop-alt-tld to 396 draft-ietf-dnsop-alt-tld 398 From -05 to -06 400 o Incorporated comments from a number of people, including a number 401 of suggestion heard at the IETF meeting in Dallas, and the DNSOP 402 Interim meeting in May, 2015. 404 o Removed the "Let's have an (optional) IANA registry for people to 405 (opportinistically) register their string, if they want that 406 option" stuff. It was, um, optional.... 408 From -04 to -05 410 o Went through and made sure that I'd captured the feedback 411 received. 413 o Comments from Ed Lewis. 415 o Filled in the "Domain Name Reservation Considerations" section of 416 RFC6761. 418 o Removed examples from .Onion. 420 From -03 to -04 422 o Incorporated some comments from Paul Hoffman 424 From -02 to -03 426 o After discussions with chairs, made this much more generic (not 427 purely non-DNS), and some cleanup. 429 From -01 to -02 431 o Removed some fluffy wording, tightened up the language some. 433 From -00 to -01. 435 o Fixed the abstract. 437 o Recommended that folk root their non-DNS namespace under a DNS 438 namespace that they control (Joe Abley) 440 Authors' Addresses 442 Warren Kumari 443 Google 444 1600 Amphitheatre Parkway 445 Mountain View, CA 94043 446 US 448 Email: warren@kumari.net 450 Andrew Sullivan 451 Dyn 452 150 Dow Street 453 Manchester, NH 03101 454 US 456 Email: asullivan@dyn.com