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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: January 4, 2016 Dyn 6 July 3, 2015 8 The ALT Special Use Top Level Domain 9 draft-ietf-dnsop-alt-tld-01 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 January 4, 2016. 39 Copyright Notice 41 Copyright (c) 2015 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 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 62 4.1. Domain Name Reservation Considerations . . . . . . . . . 6 63 5. Security Considerations . . . . . . . . . . . . . . . . . . . 7 64 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 65 7. Normative References . . . . . . . . . . . . . . . . . . . . 7 66 Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 8 67 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 69 1. Introduction 71 Many protocols and systems need to name entities. Names that look 72 like DNS names (a series of labels separated with dots) have become 73 common, even in systems that are not part of the global DNS. 75 This document provides a solution that may be more appropriate than 76 [RFC6761] in many cases. 78 This document reserves the label "ALT" (short for "Alternate") as a 79 Special Use Domain ([RFC6761]). This label is intended to be used as 80 the final label (apart from the zero-length terminating label) to 81 signify that the name is not rooted in the DNS, and that normal 82 registration and lookup rules do not apply. 84 1.1. Requirements notation 86 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 87 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 88 document are to be interpreted as described in [RFC2119]. 90 1.2. Terminology 92 This document assumes familiarity with DNS terms and concepts. 93 Please see [RFC1034] for background and concepts. 95 o DNS context: The namespace anchored at the globally-unique DNS 96 root. This is the namespace or context that "normal" DNS uses. 98 o non-DNS context: Any other (alternate) namespace. 100 o pseudo-TLD: A label that appears in a fully-qualified domain name 101 in the position of a TLD, but which is not registered in the 102 global DNS. 104 o TLD: The last visible label in either a fully-qualified domain 105 name or a name that is qualified relative to the root. See the 106 discussion in Section 2. 108 2. Background 110 The DNS data model is based on a tree structure, and has a single 111 root. Conventionally, a name immediately beneath the root is called 112 a "Top Level Domain" or "TLD". TLDs usually delegate portions of 113 their namespace to others, who may then delegate further. The 114 hierarchical, distributed and caching nature of the DNS has made it 115 the primary resolution system on the Internet. 117 Domain names are terminated by a zero-length label, so the root label 118 is normally invisible. Truly fully-qualified names indicate the root 119 label explicitly, thus: "an.example.tld.". Most of the time, names 120 are written implicitly relative to the root, thus: "an.example.tld". 121 In both of these cases, the TLD is the last label that is visible in 122 presentation format -- in this example, the string "tld". (This 123 little bit of pedantry is here because, in different contexts, people 124 can use the term "fully-qualified domain name" to refer to either of 125 these uses.) It is worth noting that the root label is present in 126 the on-wire format of fully-qualified domain names, even if not 127 displayed in the presentation form. 129 The success of the DNS makes it a natural starting point for systems 130 that need to name entities in a non-DNS context, or that have no 131 unique meaning in a global context. These name resolutions, 132 therefore, occur in a namespace distinct from the DNS. 134 In many cases, these systems build a DNS-style tree parallel to the 135 global DNS administered by IANA. They often use a pseudo-TLD to 136 cause resolution in the alternate namespace, using browser plugins, 137 shims in the name resolution process, or simply applications that 138 perform special handling of this alternate namespace. 140 In many cases, the creators of these alternate namespaces have chosen 141 a convenient or descriptive string and started using it. These new 142 strings are "alternate" strings and are not registered anywhere or 143 part of the DNS. However they appear to be TLDs. Issues may arise 144 if they are looked up in the DNS. These include: 146 o User confusion: If someone emails a link of the form 147 foo.bar.pseudo-TLD to someone who does not have the necessary 148 software to resolve names in the pseudo-TLD namespace, the name 149 will not resolve and the user may become confused. 151 o Excess traffic hitting the DNS root: Lookups leak out of the 152 pseudo-TLD namespace and end up hitting the DNS root nameservers. 154 o Collisions: If the pseudo-TLD is eventually delegated from the 155 root zone the behavior may be non-deterministic. 157 o Lack of success for the user's original goal. 159 An alternate name resolution system might be specifically designed to 160 provide confidentiality of the looked up name, and to provide a 161 distributed and censorship resistant namespace. This goal would 162 necessarily be defeated if the queries leak into the DNS, because the 163 attempt to look up the name would be visible at least to the 164 operators of root name servers. 166 3. The ALT namespace 168 In order to avoid the above issues, we reserve the ALT label. Unless 169 the name desired is globally unique, has meaning on the global 170 context and is delegated in the DNS, it should be considered an 171 alternate namespace, and follow the ALT label scheme outlined below. 172 The ALT label MAY be used in any domain name as a pseudo-TLD to 173 signify that this is an alternate (non-DNS) namespace. 175 Alternate namespaces should differentiate themselves from other 176 alternate namespaces by choosing a name and using it in the label 177 position just before the pseudo-TLD (ALT). For example, a group 178 wishing to create a namespace for Friends Of Olaf might choose the 179 string "foo" and use any set of labels under foo.alt. 181 As they are in an alternate namespace, they have no significance in 182 the regular DNS context and so should not be looked up in the DNS 183 context. Some of these requests will inevitably leak into the DNS 184 context (for example, because clicks on a link in a browser that does 185 not have a extension installed that implements the alternate 186 namespace resolution), and so the ALT TLD has been added to the 187 "Locally Served DNS Zones" ( [RFC6303]) registry to limit how far 188 these flow. 190 Groups wishing to create new alternate namespaces SHOULD create their 191 alternate namespace under a label that names their namespace, and 192 under the ALT label. They SHOULD choose a label that they expect to 193 be unique and, ideally, descriptive. There is no IANA controlled 194 registry for names under the ALT TLD - it is an unmanaged namespace, 195 and developers are responsible for dealing with any collisions that 196 may occur under .alt. 198 [Editor note (to be removed before publication): There was 199 significant discussion on an IANA registry for .ALT - please consult 200 the lists for full thread, but the consensus seems to be that it 201 would be better for the IETF / IANA to not administer a registry for 202 this. It is expected one or more unofficial lists will be created 203 where people can list the strings that they are using. ] 205 Currently deployed projects and protocols that are using pseudo-TLDs 206 may decide to move under the ALT TLD, but this is not a requirement. 207 Rather, the ALT TLD is being reserved so that future projects of a 208 similar nature have a designated place to create alternate resolution 209 namespaces that will not conflict with the regular DNS context. 211 A number of names other than .ALT were considered and discarded. In 212 order for this technique to be effective the names need to continue 213 to follow both the DNS format and conventions (a prime consideration 214 for alternate name formats is that they can be entered in places that 215 normally take DNS context names); this rules out using suffixes that 216 do not follow the usual letter, digit, and hyphen label convention. 217 Another proposal was that the ALT TLD instead be a reservation under 218 .arpa. This was considered, but rejected for several reasons, 219 including: 221 1. We wished this to make it clear that this is not in the DNS 222 context, and .arpa clearly is. 224 2. The use of the string .ALT is intended to evoke the alt.* 225 hierarchy in Usenet. 227 3. We wanted the string to be short and easily used. 229 4. A name underneath .arpa would consume at least five additional 230 octets of the total 255 octets available in domain names, which 231 could put pressure on applications that need long machine- 232 generated names. 234 5. We are suggesting that the string .ALT get special treatment in 235 resolvers, and shim software. We are concerned that using 236 subdomains of an existing TLD (like .arpa) might end up with bad 237 implementations misconfiguring / overriding the TLD itself and 238 breaking .arpa. 240 There is a concern that if there were placed under .arpa, 241 inexperienced nameserver operators may inadvertently cover .arpa. A 242 more significant concern is that the scope of the issue if the query 243 does leak, and the fact that this would then make the root of the 244 alternate naming namespace a third level domain, and not a second 245 one. A project may be willing to have a name of the form 246 example.alt, but example.alt.arpa may be not look as good. 248 4. IANA Considerations 250 The IANA is requested to add the ALT string to the "Special-Use 251 Domain Name" registry ([RFC6761], and reference this document. In 252 addition, the "Locally Served DNS Zones" ([RFC6303]) registry should 253 be updated to reference this document. 255 4.1. Domain Name Reservation Considerations 257 This section is to satisfy the requirement in Section 5 of RFC6761. 259 The domain "alt.", and any names falling within ".alt.", are special 260 in the following ways: 262 1. Human users are expected to know that strings that end in .alt 263 behave differently to normal DNS names. Users are expected to 264 have applications running on their machines that intercept 265 strings of the form .alt and perform special handing 266 of them. If the user tries to resolve a name of the form 267 .alt without the plugin installed, the 268 request will leak into the DNS, and receive a negative response. 270 2. Writers of application software that implement a non-DNS 271 namespace are expected to intercept names of the form 272 .alt and perform application specific handing with 273 them. Other applications are not intended to perform any special 274 handing. 276 3. In general, writers of name resolution APIs and libraries do not 277 need to perform special handing of these names. If developers of 278 other namespaces implement their namespace through a "shim" or 279 library, they will need to intercept and perform their own 280 handling. 282 4. Caching DNS servers SHOULD recognize these names as special and 283 SHOULD NOT, by default, attempt to look up NS records for them, 284 or otherwise query authoritative DNS servers in an attempt to 285 resolve these names. Instead, caching DNS servers SHOULD 286 generate immediate negative responses for all such queries. 288 5. Authoritative DNS servers SHOULD recognize these names as special 289 and SHOULD, by default, generate immediate negative responses for 290 all such queries, unless explicitly configured by the 291 administrator to give positive answers for private-address 292 reverse-mapping names. 294 6. DNS server operators SHOULD be aware that queries for names 295 ending in .alt are not DNS names, and were leaked into the DNS 296 context (for example, by a missing browser plugin). This 297 information may be useful for support or debuggung purposes. 299 7. DNS Registries/Registrars MUST NOT grant requests to register 300 "alt" names in the normal way to any person or entity. These 301 "alt" names are defined by protocol specification to be 302 nonexistent, and they fall outside the set of names available for 303 allocation by registries/registrars. 305 5. Security Considerations 307 One of the motivations for the creation of the alt pseudo-TLD is that 308 unmanaged labels in the managed root name space are subject to 309 unexpected takeover if the manager of the root name space decides to 310 delegate the unmanaged label. 312 The unmanaged and "registration not required" nature of labels 313 beneath .ALT provides the opportunity for an attacker to re-use the 314 chosen label and thereby possibly compromise applications dependent 315 on the special host name. 317 6. Acknowledgements 319 The authors understand that there is much politics surrounding the 320 delegation of a new TLD and thank the ICANN liaison in advance. 322 We would also like to thank Joe Abley, Mark Andrews, Marc Blanchet, 323 John Bond, Stephane Bortzmeyer, David Cake, David Conrad, Patrik 324 Faltstrom, Olafur Gudmundsson, Paul Hoffman, Joel Jaeggli, Ted Lemon, 325 Edward Lewis, George Michaelson, Ed Pascoe, Arturo Servin, and Paul 326 Vixie for feedback. 328 7. Normative References 330 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 331 STD 13, RFC 1034, November 1987. 333 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 334 Requirement Levels", BCP 14, RFC 2119, March 1997. 336 [RFC6303] Andrews, M., "Locally Served DNS Zones", BCP 163, RFC 337 6303, July 2011. 339 [RFC6761] Cheshire, S. and M. Krochmal, "Special-Use Domain Names", 340 RFC 6761, February 2013. 342 Appendix A. Changes / Author Notes. 344 [RFC Editor: Please remove this section before publication ] 346 From -00 to 01: 348 o Removed the "delegated to new style AS112 servers" text -this was 349 legacy from the omnicient AS112 days. (Joe Abley) 351 o Removed the "Advice to implemntors" section. This used to 352 recommend that people used a subdomain of a domain in the DNS. It 353 was pointed out that this breaks things badly if the domain 354 expires. 356 o Added text about why we don't want to adminster a registry for 357 ALT. 359 From Individual-06 to DNSOP-00 361 o Nothing changed, simply renamed draft-wkumari-dnsop-alt-tld to 362 draft-ietf-dnsop-alt-tld 364 From -05 to -06 366 o Incorporated comments from a number of people, including a number 367 of suggestion heard at the IETF meeting in Dallas, and the DNSOP 368 Interim meeting in May, 2015. 370 o Removed the "Let's have an (optional) IANA registry for people to 371 (opportinistically) register their string, if they want that 372 option" stuff. It was, um, optional.... 374 From -04 to -05 376 o Went through and made sure that I'd captured the feedback 377 received. 379 o Comments from Ed Lewis. 381 o Filled in the "Domain Name Reservation Considerations" section of 382 RFC6761. 384 o Removed examples from .Onion. 386 From -03 to -04 387 o Incorporated some comments from Paul Hoffman 389 From -02 to -03 391 o After discussions with chairs, made this much more generic (not 392 purely non-DNS), and some cleanup. 394 From -01 to -02 396 o Removed some fluffy wording, tightened up the language some. 398 From -00 to -01. 400 o Fixed the abstract. 402 o Recommended that folk root their non-DNS namespace under a DNS 403 namespace that they control (Joe Abley) 405 Authors' Addresses 407 Warren Kumari 408 Google 409 1600 Amphitheatre Parkway 410 Mountain View, CA 94043 411 US 413 Email: warren@kumari.net 415 Andrew Sullivan 416 Dyn 417 150 Dow Street 418 Manchester, NH 03101 419 US 421 Email: asullivan@dyn.com