The ALT Special Use Top Level Domain
The information below is for an old version of the document.
This is an older version of an Internet-Draft that was ultimately published as RFC 9476.
|Authors||Warren "Ace" Kumari , Andrew Sullivan|
|RFC stream||Internet Engineering Task Force (IETF)|
|Additional resources||Mailing list discussion|
|Stream||WG state||WG Document|
|IESG||IESG state||I-D Exists|
|Send notices to||(None)|
dnsop W. Kumari Internet-Draft Google Intended status: Informational A. Sullivan Expires: December 7, 2015 Dyn June 5, 2015 The ALT Special Use Top Level Domain draft-ietf-dnsop-alt-tld-00 Abstract This document reserves a string (ALT) to be used as a TLD label in non-DNS contexts or for names that have no meaning in a global context. It also provides advice and guidance to developers developing alternate namespaces. [ Ed note: This document lives in GitHub at: https://github.com/wkumari/draft-wkumari-dnsop-alt-tld . Issues and pull requests happily accpeted. ] Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on December 7, 2015. Copyright Notice Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect Kumari & Sullivan Expires December 7, 2015 [Page 1] Internet-Draft Reserve ALT TLD June 2015 to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Requirements notation . . . . . . . . . . . . . . . . . . 2 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2 2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. The ALT namespace . . . . . . . . . . . . . . . . . . . . . . 4 4. Advice to developers . . . . . . . . . . . . . . . . . . . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 5.1. Domain Name Reservation Considerations . . . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . . . . . 7 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 8. Normative References . . . . . . . . . . . . . . . . . . . . 8 Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 1. Introduction Many protocols and systems need to name entities. Names that look like DNS names (a series of labels separated with dots) have become common, even in systems that are not part of the global DNS. This document provides a solution that may be more appropriate than [RFC6761] in many cases. RFC6761 specifies Special Use TLDs which should only be used in exceptional circumstances. This document reserves the label "ALT" (short for "Alternate") as a Special Use Domain ([RFC6761]). This label is intended to be used as the final label (apart from the zero-length terminating label) to signify that the name is not rooted in the DNS, and that normal registration and lookup rules do not apply. 1.1. Requirements notation The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 1.2. Terminology This document assumes familiarity with DNS terms and concepts. Please see [RFC1034] for background and concepts. Kumari & Sullivan Expires December 7, 2015 [Page 2] Internet-Draft Reserve ALT TLD June 2015 o DNS context: The namespace anchored at the globally-unique DNS root. This is the namespace or context that "normal" DNS uses. o non-DNS context: Any other (alternate) namespace. o pseudo-TLD: A label that appears in a fully-qualified domain name in the position of a TLD, but which is not registered in the global DNS. o TLD: The last visible label in either a fully-qualified domain name or a name that is qualified relative to the root. See the discussion in Section 2. 2. Background The DNS data model is based on a tree structure, and has a single root. Conventionally, a name immediately beneath the root is called a "Top Level Domain" or "TLD". TLDs usually delegate portions of their namespace to others, who may then delegate further. The hierarchical, distributed and caching nature of the DNS has made it the primary resolution system on the Internet. Domain names are terminated by a zero-length label, so the root label is normally invisible. Truly fully-qualified names indicate the root label explicitly, thus: "an.example.tld.". Most of the time, names are written implicitly relative to the root, thus: "an.example.tld". In both of these cases, the TLD is the last label that is visible in presentation format -- in this example, the string "tld". (This little bit of pedantry is here because, in different contexts, people can use the term "fully-qualified domain name" to refer to either of these uses.) It is worth noting that the root label is present in the on-wire format of fully-qualified domain names, even if not displayed in the presentation form. The success of the DNS makes it a natural starting point for systems that need to name entities in a non-DNS context, or that have no unique meaning in a global context. These name resolutions, therefore, occur in a namespace distinct from the DNS. In many cases, these systems build a DNS-style tree parallel to the global DNS administered by IANA. They often use a pseudo-TLD to cause resolution in the alternate namespace, using browser plugins, shims in the name resolution process, or simply applications that perform special handling of this alternate namespace. In many cases, the creators of these alternate namespaces have chosen a convenient or descriptive string and started using it. These new strings are "alternate" strings and are not registered anywhere or Kumari & Sullivan Expires December 7, 2015 [Page 3] Internet-Draft Reserve ALT TLD June 2015 part of the DNS. However they appear to be TLDs. Issues may arise if they are looked up in the DNS. These include: o User confusion: If someone emails a link of the form foo.bar.pseudo-TLD to someone who does not have the necessary software to resolve names in the pseudo-TLD namespace, the name will not resolve and the user may become confused. o Excess traffic hitting the DNS root: Lookups leak out of the pseudo-TLD namespace and end up hitting the DNS root nameservers. o Collisions: If the pseudo-TLD is eventually delegated from the root zone the behavior may be non-deterministic. o Lack of success for the user's original goal. An alternate name resolution system might be specifically designed to provide confidentiality of the looked up name, and to provide a distributed and censorship resistant namespace. This goal would necessarily be defeated if the queries leak into the DNS, because the attempt to look up the name would be visible at least to the operators of root name servers. 3. The ALT namespace In order to avoid the above issues, we reserve the ALT label. Unless the name desired is globally unique, has meaning on the global context and is delegated in the DNS, it should be considered an alternate namespace, and follow the ALT label scheme outlined below. The ALT label MAY be used in any domain name as a pseudo-TLD to signify that this is an alternate (non-DNS) namespace. Alternate namespaces should differentiate themselves from other alternate namespaces by choosing a name and using it in the label position just before the pseudo-TLD (ALT). For example, a group wishing to create a namespace for Friends Of Olaf might choose the string "foo" and use any set of labels under foo.alt. As they are in an alternate namespace, they have no significance in the regular DNS context and so should not be looked up in the DNS context. Unfortunately simply saying that "something should not happen" doesn't actually stop it from happening, so we need some rules to guide implementors and operators. The ALT TLD is delegated to "new style" AS112 servers, and so recursive and stub resolvers will get NXDOMAIN for all queries. 1. Iterative resolvers SHOULD follow the advice in [RFC6303], Section 3. Kumari & Sullivan Expires December 7, 2015 [Page 4] Internet-Draft Reserve ALT TLD June 2015 2. The ALT TLD is delegated to "new style" AS112 nameservers ([RFC7535] ), which will return NXDOMAIN for all queries. These rules are intended to limit how far unintentional queries (i.e. those not intended for the global DNS) flow. Groups wishing to create new alternate namespaces SHOULD create their alternate namespace under a label that names their namespace, and under the ALT label. They SHOULD choose a label that they expect to be unique and, ideally, descriptive. Currently deployed projects and protocols that are using pseudo-TLDs may decide to move under the ALT TLD, but this is not a requirement. Rather, the ALT TLD is being reserved so that future projects of a similar nature have a designated place to create alternate resolution namespaces that will not conflict with the regular DNS context. A number of names other than .ALT were considered and discarded. In order for this technique to be effective the names need to continue to follow both the DNS format and conventions (a prime consideration for alternate name formats is that they can be entered in places that normally take DNS context names); this rules out using suffixes that do not follow the usual letter, digit, and hyphen label convention. Another proposal was that the ALT TLD instead be a reservation under .arpa. This was considered, but rejected for several reasons, including: 1. We wished this to make it clear that this is not in the DNS context, and .arpa clearly is. 2. The use of the string .ALT is intended to evoke the alt.* hierarchy in Usenet. 3. We wanted the string to be short and easily used. 4. A name underneath .arpa would consume at least five additional octets of the total 255 octets available in domain names, which could put pressure on applications that need long machine- generated names. 5. We are suggesting that the string .ALT get special treatment in resolvers, and shim software. We are concerned that using subdomains of an existing TLD (like .arpa) might end up with bad implementations misconfiguring / overriding the TLD itself and breaking .arpa. There is a concern that if there were placed under .arpa, inexperienced nameserver operators may inadvertently cover .arpa. A Kumari & Sullivan Expires December 7, 2015 [Page 5] Internet-Draft Reserve ALT TLD June 2015 more significant concern is that the scope of the issue if the query does leak, and the fact that this would then make the root of the alternate naming namespace a third level domain, and not a second one. A project may be willing to have a name of the form example.alt, but example.alt.arpa may be not look as good. 4. Advice to developers Often, a subdomain of an existing, owned domain may suffice. When that is so, using a subdomain in the DNS is always preferable, and safest in terms of not risking misuse, duplications, or collisions. In the rare instance in which it is not desirable to have the name in the DNS, the .ALT namespace may be used. In a number of cases the purpose of the alternate name resolution system is to provide confidentiality. For these systems the above advice is problematic. If the query for one of these names (for example harry.foo.example.com were to leak into the DNS, the query would hit the recursive resolver, and (assuming empty caches) would then hit the root, the .com name servers, the example.com name servers and then the foo.example.com nameservers. This means that the fact that a user is resolving harry.foo.example.com would be visible to a large number of people. Furthermore, the harry.foo.example.com nameservers become a good oracle to determine what names exist, and who is trying to reach them. For projects that are very latency sensitive, or that desire to provide confidentiality, we recommend anchoring the alternate namespace under the .ALT TLD. 5. IANA Considerations The IANA is requested to add the ALT string to the "Special-Use Domain Name" registry ([RFC6761], and reference this document. In addition, the "Locally Served DNS Zones" ([RFC6303]) registry should be updated to reference this document. 5.1. Domain Name Reservation Considerations This section is to satisfy the requirement in Section 5 of RFC6761. The domain "alt.", and any names falling within ".alt.", are special in the following ways: 1. Human users are expected to know that strings that end in .alt behave differently to normal DNS names. Users are expected to have applications running on their machines that intercept stings of the form <namespace>.alt and perform special handing of them. Kumari & Sullivan Expires December 7, 2015 [Page 6] Internet-Draft Reserve ALT TLD June 2015 If the user tries to resolve a name of the form <namespace>.alt without the <namespace> plugin installed, the request will leak into the DNS, and receive a negative response. 2. Writers of application software that implement a non-DNS namespace are expected to intercept names of the form <namespace>.alt and perform application specific handing with them. Other applications are not intended to perform any special handing. 3. In general, writers of name resolution APIs and libraries do not need to perform special handing of these names. If developers of other namespaces implement their namespace through a "shim" or library, they will need to intercept and perform their own handling. 4. Caching DNS servers SHOULD recognize these names as special and SHOULD NOT, by default, attempt to look up NS records for them, or otherwise query authoritative DNS servers in an attempt to resolve these names. Instead, caching DNS servers SHOULD generate immediate negative responses for all such queries. 5. Authoritative DNS servers SHOULD recognize these names as special and SHOULD, by default, generate immediate negative responses for all such queries, unless explicitly configured by the administrator to give positive answers for private-address reverse-mapping names. 6. DNS server operators SHOULD be aware that queries for names ending in .alt are not DNS names, and were leaked into the DNS context (for example, by a missing browser plugin). This information may be useful for support or debuggung purposes. 7. DNS Registries/Registrars MUST NOT grant requests to register "alt" names in the normal way to any person or entity. These "alt" names are defined by protocol specification to be nonexistent, and they fall outside the set of names available for allocation by registries/registrars. 6. Security Considerations One of the motivations for the creation of the alt pseudo-TLD is that unmanaged labels in the managed root name space are subject to unexpected takeover if the manager of the root name space decides to delegate the unmanaged label. The unmanaged and "registration not required" nature of labels beneath .ALT provides the opportunity for an attacker to re-use the Kumari & Sullivan Expires December 7, 2015 [Page 7] Internet-Draft Reserve ALT TLD June 2015 chosen label and thereby possibly compromise applications dependent on the special host name. 7. Acknowledgements The authors understand that there is much politics surrounding the delegation of a new TLD and thank the ICANN liaison in advance. We would also like to thank Joe Abley, Mark Andrews, Marc Blanchet, John Bond, Stephane Bortzmeyer, David Cake, David Conrad, Patrik Faltstrom, Olafur Gudmundsson, Paul Hoffman, Joel Jaeggli, Ted Lemon, Edward Lewis, George Michaelson, Ed Pascoe, Arturo Servin, and Paul Vixie for feedback. 8. Normative References [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", STD 13, RFC 1034, November 1987. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC6303] Andrews, M., "Locally Served DNS Zones", BCP 163, RFC 6303, July 2011. [RFC6761] Cheshire, S. and M. Krochmal, "Special-Use Domain Names", RFC 6761, February 2013. [RFC7535] Abley, J., Dickson, B., Kumari, W., and G. Michaelson, "AS112 Redirection Using DNAME", RFC 7535, May 2015. Appendix A. Changes / Author Notes. [RFC Editor: Please remove this section before publication ] From Individual-06 to DNSOP-00 o Nothing changed, simply renamed draft-wkumari-dnsop-alt-tld to draft-ietf-dnsop-alt-tld From -05 to -06 o Incorporated comments from a number of people, including a number of suggestion heard at the IETF meeting in Dallas, and the DNSOP Interim meeting in May, 2015. Kumari & Sullivan Expires December 7, 2015 [Page 8] Internet-Draft Reserve ALT TLD June 2015 o Removed the "Let's have an (optional) IANA registry for people to (opportinistically) register their string, if they want that option" stuff. It was, um, optional.... From -04 to -05 o Went through and made sure that I'd captured the feedback received. o Comments from Ed Lewis. o Filled in the "Domain Name Reservation Considerations" section of RFC6761. o Removed examples from .Onion. From -03 to -04 o Incorporated some comments from Paul Hoffman From -02 to -03 o After discussions with chairs, made this much more generic (not purely non-DNS), and some cleanup. From -01 to -02 o Removed some fluffy wording, tightened up the language some. From -00 to -01. o Fixed the abstract. o Recommended that folk root their non-DNS namespace under a DNS namespace that they control (Joe Abley) Authors' Addresses Warren Kumari Google 1600 Amphitheatre Parkway Mountain View, CA 94043 US Email: firstname.lastname@example.org Kumari & Sullivan Expires December 7, 2015 [Page 9] Internet-Draft Reserve ALT TLD June 2015 Andrew Sullivan Dyn 150 Dow Street Manchester, NH 03101 US Email: email@example.com Kumari & Sullivan Expires December 7, 2015 [Page 10]