Reserved Top Level DNS Names
draft-ellermann-idnabis-test-tlds-11

Status of this Memo

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Abstract

To reduce the likelihood of conflict and confusion, a few top level domain names are reserved for use in private testing, as examples in documentation, and the like. In addition, a few second level domain names reserved for use as examples are documented. This memo replaces RFC 2606 reserving 21 additional TLDs.

Editorial note

This note and Appendix B (Document History) should be removed before publication. The draft can be discussed on the IETF Discussion <ietf.ietf.org> mailing list.

Table of Contents

1.  Introduction
2.  TLDs for Testing, & Documentation Examples
    2.1.  ".example", ".tld"
    2.2.  ".invalid"
    2.3.  ".localhost"
    2.4.  ".test"
3.  Reserved Example Second Level Domain Names
4.  Internationalization Considerations
5.  IANA Considerations
6.  Security Considerations
7.  Acknowledgments
8.  References
    8.1.  Normative References
    8.2.  Informative References
Appendix A.  Educational Info
Appendix B.  Document History
§  Authors' Addresses
§  Intellectual Property and Copyright Statements

1.  Introduction

The global Internet Domain Name System is documented in [RFC1034] (Mockapetris, P., “Domain names - concepts and facilities,” November 1987.), [RFC1035] (Mockapetris, P., “Domain names - implementation and specification,” November 1987.), [RFC1123] (Braden, R., “Requirements for Internet Hosts - Application and Support,” October 1989.), [RFC1591] (Postel, J., “Domain Name System Structure and Delegation,” March 1994.), [RFC3696] (Klensin, J., “Application Techniques for Checking and Transformation of Names,” February 2004.), and numerous additional Requests for Comments. It defines a tree of names starting with root, ".", immediately below which are top level domain names such as ".com" and ".us". Below top level domain names there are normally additional levels of names.

IPv4 addresses used for tests and in examples are specified in [I‑D.iana‑rfc3330bis] (Cotton, M. and L. Vegoda, “Special Use IPv4 Addresses,” August 2009.), IPv6 addresses used in examples are described in [RFC3849] (Huston, G., Lord, A., and P. Smith, “IPv6 Address Prefix Reserved for Documentation,” July 2004.); see also [RFC4085] (Plonka, D., “Embedding Globally-Routable Internet Addresses Considered Harmful,” June 2005.).

Fully Qualified Domain Names used in many Internet Protocols allow only LDH (letter, digit, hyphen) domain labels as described in [RFC1123] (Braden, R., “Requirements for Internet Hosts - Application and Support,” October 1989.), [RFC3696] (Klensin, J., “Application Techniques for Checking and Transformation of Names,” February 2004.), and [RFC4343] (Eastlake, D., “Domain Name System (DNS) Case Insensitivity Clarification,” January 2006.). The letters are ASCII letters; certain LDH-labels are also known as A-labels in the context of IDN (Internationalization of Domain Names) and [IDNAbis] (IETF, “Internationalized Domain Names in Applications (Revised),” April 2008.).

The key words "MAY", "RECOMMENDED", and "SHOULD" in this memo are to be interpreted as described in [RFC2119] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).

2.  TLDs for Testing, & Documentation Examples

There is a need for top level domain (TLD) names that can be used for creating names which, without fear of conflicts with current or future actual TLD names in the global DNS, can be used for private testing of existing DNS related code, examples in documentation, DNS related experimentation, invalid DNS names, or other similar uses.

For example, without guidance, a site might set up some local additional unused top level domains for testing of its local DNS code and configuration. Later, these TLDs might come into actual use on the global Internet. As a result, local attempts to reference the real data in these zones could be thwarted by the local test versions. Or test or example code might be written that accesses a TLD that is in use with the thought that the test code would only be run in a restricted testbed net or the example never actually run. Later, the test code could escape from the testbed or the example be actually coded and run on the Internet. Depending on the nature of the test or example, it might be best for it to be referencing a TLD permanently reserved for such purposes.

To safely satisfy these needs, five domain names are reserved as listed and described below. See also Section 4 (Internationalization Considerations).

2.1.  ".example", ".tld"

".example", ".tld", and the example TLDs in Section 4 (Internationalization Considerations) are RECOMMENDED for use in documentation or as examples.

2.2.  ".invalid"

".invalid" is intended for use in online construction of domain names that are sure to be invalid, and for which it is obvious at a glance that they are invalid.

Applications MAY treat ".invalid" as what the name says. For this technical reason reserving internationalized ".invalid" TLDs would be unwise.

2.3.  ".localhost"

The ".localhost" TLD has traditionally been statically defined in host DNS implementations as having an address record pointing to the loop back IP address and is reserved for such use. Any other use would conflict with widely deployed code which assumes this use.

See [RFC1122] (Braden, R., “Requirements for Internet Hosts - Communication Layers,” October 1989.) for IPv4 and [RFC4291] (Hinden, R. and S. Deering, “IP Version 6 Addressing Architecture,” February 2006.) for IPv6 loop back addresses.

2.4.  ".test"

".test" and the new test TLDs in Section 4 (Internationalization Considerations) are RECOMMENDED for use in testing of current or new DNS related code. Applications SHOULD treat these test TLDs like any other TLD; a special handling could defeat the purpose of a test.

3.  Reserved Example Second Level Domain Names

The Internet Assigned Numbers Authority (IANA) also reserves the three second level domain names ".example.com", ".example.net", and ".example.org", which can be used in examples as explained in Section 2.1 (".example", ".tld").

When TLDs offer further second level domains for examples, the TLD administrators are encouraged to publish the relevant policies in their TLD as an informational RFC.

The second level domain names "nic", "whois", and "www" are often reserved or used for administrative purposes of the TLD, e.g., "whois.example" for the fully qualified domain name of a host with a whois server. As with second level domains for examples this can be an issue in the case of a TLD redelegation.

Please note that there are no globally reserved LDH DNS labels below the top level; see [RFC4367] (Rosenberg, J. and IAB, “What's in a Name: False Assumptions about DNS Names,” February 2006.).

4.  Internationalization Considerations

In 2007 IANA created eleven IDN test TLDs together with corresponding IDN example labels. The A-labels, corresponding languages, and IDN U-labels are listed below; see [RFC3490] (Faltstrom, P., Hoffman, P., and A. Costello, “Internationalizing Domain Names in Applications (IDNA),” March 2003.) or its [IDNAbis] (IETF, “Internationalized Domain Names in Applications (Revised),” April 2008.) successor for details about IDN. Applications SHOULD treat the IDN test TLDs as explained in Section 2.4 (".test").

      TLD A-label          Language      Test U-label (hex. code points)
    ".xn--0zwm56d"         Chinese (simplified)                6d4b 8bd5
    ".xn--11b5bs3a9aj6g"   Hindi             92a 930 940 915 94d 937 93e
    ".xn--80akhbyknj4f"    Russian   438 441 43f 44b 442 430 43d 438 435
    ".xn--9t4b11yi5a"      Korean                         d14c c2a4 d2b8
    ".xn--deba0ad"         Yiddish                       5d8 5e2 5e1 5d8
    ".xn--g6w251d"         Chinese (traditional)               6e2c 8a66
    ".xn--hgbk6aj7f53bba"  Persian           622 632 645 627 6cc 634 6cc
    ".xn--hlcj6aya9esc7a"  Tamil             baa bb0 bbf b9f bcd b9a bc8
    ".xn--jxalpdlp"        Greek                 3b4 3bf 3ba 3b9 3bc 3ae
    ".xn--kgbechtv"        Arabic                625 62e 62a 628 627 631
    ".xn--zckzah"          Japanese                       30c6 30b9 30c8

The corresponding IDN example labels shown below are reserved as TLDs for examples; compare Section 2.1 (".example", ".tld"). Additional IDN example TLDs, notably the final list of IDN example labels after the IDN test, can be reserved later as specified in Section 5 (IANA Considerations).

      TLD A-label          Language   Example U-label (hex. code points)
    ".xn--9n2bp8q"         Korean                              c2e4 b840
    ".xn--e1afmkfd"        Russian               43f 440 438 43c 435 440
    ".xn--fdbk5d8ap9b8a8d" Yiddish       5d1 5f2 5b7 5e9 5e4 5bc 5d9 5dc
    ".xn--fsqu00a"         Chinese (simplified)                4f8b 5b50
    ".xn--fsqu00a"         Chinese (traditional)               4f8b 5b50
    ".xn--hxajbheg2az3al"  Greek 3c0 3b1 3c1 3ac 3b4 3b5 3b9 3b3 3bc 3b1
    ".xn--mgbh0fb"         Arabic                        645 62b 627 644
    ".xn--mgbh0fb"         Persian                       645 62b 627 644
    ".xn--p1b6ci4b4b3a"    Hindi                 909 926 93e 939 930 923
    ".xn--r8jz45g"         Japanese                            4f8b 3048
    ".xn--zkc6cc5bi7f6e"   Tamil             b89 ba4 bbe bb0 ba3 bae bcd

5.  IANA Considerations

IANA reserves the TLDs ".example", ".invalid", ".localhost", ".test", ".tld", eleven IDN test TLDs, and nine IDN example TLDs as noted above. IANA reserves the second level domains ".example.com", ".example.net", and ".example.org".

IANA creates a registry of reserved TLDs; this can be done alongside existing IANA TLD registries at the discretion of IANA. The registry should contain references to the relevant specifications, for the 25 reserved TLDs specified here references to this memo will do.

Additional reserved TLDs require IETF review as defined in [RFC5226] (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008.) section 4.1 in conjunction with clause 4.3 in [RFC2860] (Carpenter, B., Baker, F., and M. Roberts, “Memorandum of Understanding Concerning the Technical Work of the Internet Assigned Numbers Authority,” June 2000.).

The technical purpose of a reserved TLD has to be stated in its specification.

Proposals to reserve TLD labels not permitted for ordinary TLDs, as specified in [RFC1123] (Braden, R., “Requirements for Internet Hosts - Application and Support,” October 1989.) among others, e.g., labels not starting with a letter, or not following known LDH- and [IDNAbis] (IETF, “Internationalized Domain Names in Applications (Revised),” April 2008.) rules, are not expected to survive an IETF review without compelling reasons.

6.  Security Considerations

Confusion and conflict can be caused by the use of a current or future top level domain name in experimentation or testing, as an example in documentation, to indicate invalid names, or as a synonym for the loop back address. Test and experimental software can escape and end up being run against the global operational DNS. Even examples used "only" in documentation can end up being coded and released or cause conflicts due to later real use and the possible acquisition of intellectual property rights in such "example" names.

The reservation of several top level domain names for these purposes minimizes such confusion and conflict.

[RFC4367] (Rosenberg, J. and IAB, “What's in a Name: False Assumptions about DNS Names,” February 2006.) discusses various false assumptions based on domain labels, however this doesn't affect the reserved TLDs in this memo.

Readers need to be aware that the IANA registry of reserved TLDs in Section 5 (IANA Considerations) won't list all reserved TLDs for specific applications and protocols. The registry can only list reserved TLDs if somebody bothered to propose it, typically in an Internet-Draft, and the proposal was accepted in an IETF review.

7.  Acknowledgments

This memo contains major parts of [RFC2606] (Eastlake, D. and A. Panitz, “Reserved Top Level DNS Names,” June 1999.) written by Donald E. Eastlake and Aliza R. Panitz.

Thanks to Alfred Hönes, Bill McQuillan, Brian Carpenter, Dave Cridland, David Conrad, Debbie Garside, Doug Otis, Joe Abley, John Klensin, John Levine, Lyman Chapin, Marcel Parodi, Mark Andrews, Marshall Eubanks, Michael Dillon, Ole Jacobsen, Paul Hoffman, Peter Saint-Andre, Philip Guenther, Philip Hallam-Baker, SM, Spencer Dawkins, Steve Crocker, Sumit Pandya, Thomas Narten, Tina Dam, Tony Finch, and Tony Hansen for their feedback, contributions, or encouragement.

8.  References

8.1. Normative References

8.2. Informative References

Appendix A.  Educational Info

This informative appendix tries to answer three frequently asked questions:

1. As of 2008 IANA is the registrant of ".example.edu"; TLD ".edu" has no contract with ICANN; its administration is based on a five years contract with the US DoC renewed in 2006; see http://net.educause.edu/edudomain/policy.asp. Under amendment 6 of their current policy generic names cannot be registered. This is not exactly the same situation as for say ".example.org", where IANA is the registrant and registrar.
2. As of 2008 IANA is the registrant of ".example.info"; TLD ".info" was created by ICANN in 2001. The ".info" registry agreement lists reserved DNS labels including "example"; see http://www.icann.org/tlds/agreements/info/ appendix 6 (2006) and K (2001), respectively. This is not exactly the same situation as for say ".example.org", where IANA is the registrant and registrar.
3. Ignoring [RFC2965] (Kristol, D. and L. Montulli, “HTTP State Management Mechanism,” October 2000.) the TLD ".local" issue was discussed in a bunch of Internet-Drafts related to AS112, zeroconf, and [RFC3927] (Cheshire, S., Aboba, B., and E. Guttman, “Dynamic Configuration of IPv4 Link-Local Addresses,” May 2005.). Presumably TLD ".local" should be registered as reserved for technical reasons, but deserves its own document with the fine print.

Appendix B.  Document History

Changes in version 11:

• Added nine IDN example labels corresponding to the IDN test labels as reserved TLDs after long discussions with two contributors confirming the stability and desirability of this approach.
• Noted that the list of IDN example TLDs might be extended, and a final list can be reserved as specified here after the conclusion of the IDN test.

Changes in version 10:

• Noted that only certain LDH-labels are or might be A-labels based on feedback. The details are or will be specified in [IDNAbis] (IETF, “Internationalized Domain Names in Applications (Revised),” April 2008.).
• Moved [RFC2860] (Carpenter, B., Baker, F., and M. Roberts, “Memorandum of Understanding Concerning the Technical Work of the Internet Assigned Numbers Authority,” June 2000.) back to informative. Folks apparently disagree what it should be, more feedback needed to justify a downref.
• Added [RFC3696] (Klensin, J., “Application Techniques for Checking and Transformation of Names,” February 2004.) again, its description of a <toplabel> covers the eleven IDN test TLDs.

Changes in version 09:

• Fixed [RFC2860] (Carpenter, B., Baker, F., and M. Roberts, “Memorandum of Understanding Concerning the Technical Work of the Internet Assigned Numbers Authority,” June 2000.) link, clause 4.3 is a section of the MoU, not a section of the RFC containing this MoU.
• Added ".tld" as reserved TLD for examples following a proposal by Bill McQuillan supported by some others.
• Arguably ".bad" ideas ".bar", ".bat", ".baz", ".foo", and ".lit" not yet added for different reasons, they would need stronger support.

Changes in version 08:

• Moved [RFC2860] (Carpenter, B., Baker, F., and M. Roberts, “Memorandum of Understanding Concerning the Technical Work of the Internet Assigned Numbers Authority,” June 2000.) to normative, inspired by feedback and the precedence in another BCP. Added the relevant sections in [RFC2860] (Carpenter, B., Baker, F., and M. Roberts, “Memorandum of Understanding Concerning the Technical Work of the Internet Assigned Numbers Authority,” June 2000.) and [RFC5226] (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008.) to Section 5 (IANA Considerations).
• Added a long blurb that the purpose of reserved TLDs has to be noted in their specifications, and that reserving TLDs not permitted as ordinary TLDs need very good reasons to survive the required IETF review.
• [IDNAbis] (IETF, “Internationalized Domain Names in Applications (Revised),” April 2008.) hopefully fixes the <toplabel> problem in [RFC1123] (Braden, R., “Requirements for Internet Hosts - Application and Support,” October 1989.). This memo isn't the place to do this, as the issue is not limited to reserved TLDs, tests, and examples.

Changes in version 07:

• Kept "nic", "whois", and "www" as known examples why there are no globally reserved LDH labels for whatever purpose below the top level.
• Proposals to add ".internal", ".local", ".localdomain", and ".uucp" not adopted. This memo covers known test and example TLDs, as well as two other TLDs and three example SLDs inherited from [RFC2606] (Eastlake, D. and A. Panitz, “Reserved Top Level DNS Names,” June 1999.). Reserved TLDs for other purposes deserve separate documents.
• Added a note that internationalizations of ".invalid" are a non-starter, as this TLD is expected to be hardwired in some applications. For ".localhost" that should be obvious.
• Review requests sent at different times to the APPS, general, [IDNAbis] (IETF, “Internationalized Domain Names in Applications (Revised),” April 2008.), INT, and OPS mailing lists.

Changes in version 06:

• Explanations of the terms LDH, A-label, and IDN added in Section 1 (Introduction). Just in case added a reference to [RFC4343] (Eastlake, D., “Domain Name System (DNS) Case Insensitivity Clarification,” January 2006.).
• Downgraded [RFC3696] (Klensin, J., “Application Techniques for Checking and Transformation of Names,” February 2004.) to [RFC1123] (Braden, R., “Requirements for Internet Hosts - Application and Support,” October 1989.); for some months the best documentation of a <toplabel> was available in an erratum.

Changes in version 05:

• Donald offered to co-author this memo.
• Clarified that there are now additional TLDs recommended for tests, not only the original ".test" in Section 2.4 (".test").

Changes in version 04:

• In the "Public Suffix List" debate SM quoted [RFC4085] (Plonka, D., “Embedding Globally-Routable Internet Addresses Considered Harmful,” June 2005.), added to Section 1 (Introduction).
• Replaced "A record" by "address record" with references to [RFC1122] (Braden, R., “Requirements for Internet Hosts - Communication Layers,” October 1989.) and [RFC4291] (Hinden, R. and S. Deering, “IP Version 6 Addressing Architecture,” February 2006.) in Section 2.3 (".localhost").
• Added IDN test U-labels (in a crude hex. format due to RFC layout limitations) with the help of http://josefsson.org/idn.php/ and http://www.imc.org/idna/.

Changes in version 03:

• Swapped IANA and security considerations based on feedback, since version 01 the order anyway did not more follow http://tools.ietf.org/html/draft-rfc-editor-rfc2223bis-08#section-4.
• Dave Cridland proposed another [RFC4367] (Rosenberg, J. and IAB, “What's in a Name: False Assumptions about DNS Names,” February 2006.) caveat, there are no globally reserved LDH labels below the top level. LDH excludes special cases such as the empty label reserved for the root, and leaf labels starting with an underscore.
• The informative Appendix A (Educational Info) hopefully answers frequently asked questions about ".example.edu", ".example.info", and ".local".

Changes in version 02:

• Added the related [RFC3849] (Huston, G., Lord, A., and P. Smith, “IPv6 Address Prefix Reserved for Documentation,” July 2004.) and [I‑D.iana‑rfc3330bis] (Cotton, M. and L. Vegoda, “Special Use IPv4 Addresses,” August 2009.) references. Added an [RFC4367] (Rosenberg, J. and IAB, “What's in a Name: False Assumptions about DNS Names,” February 2006.) reference to the security considerations, as this explains one of many issues with any "well-known" label below the top level.
• Improved the IANA Considerations Section 5 (IANA Considerations) based on feedback. The registry of reserved TLDs needs references to the relevant specifications.
• Added a caveat that the IANA registry of reserved TLDs cannot list all obscure ideas of specific applications and protocols; somebody has to trigger an IETF review for new registrations.

Changes in version 01:

• Various editorial issues found by Tony Hansen fixed.
• Added an [IDNAbis] (IETF, “Internationalized Domain Names in Applications (Revised),” April 2008.) reference. The authors believe that the IETF is not entitled to decree that ".example.edu" belongs to the set of three example-SLDs reserved by IANA.

Changes in version 00:

• John Klensin suggested clarifying the guidelines for examples in [RFC2606] (Eastlake, D. and A. Panitz, “Reserved Top Level DNS Names,” June 1999.), referenced by http://www.ietf.org/ID-Checklist.html. Documenting the eleven new IDN test TLDs was anyway desirable.

Authors' Addresses

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This document was produced using xml2rfc v1.35 (of http://xml.resource.org/) from a source in RFC-2629 XML format.