Reserved Top Level DNS Names
draft-ellermann-idnabis-test-tlds-02

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.

Editorial note

This note and the document history (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"
    2.2.  ".invalid"
    2.3.  ".localhost"
    2.4.  ".test"
3.  Reserved Example Second Level Domain Names
4.  Internationalization Considerations
5.  Security Considerations
6.  IANA Considerations
7.  Acknowledgments
8.  References
    8.1.  Normative References
    8.2.  Informative References
Appendix A.  Document History
§  Author's Address
§  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.), [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.).

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, four domain names are reserved as listed and described below. See also Section 4 (Internationalization Considerations).

2.1.  ".example"

".example" is 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.

2.3.  ".localhost"

The ".localhost" TLD has traditionally been statically defined in host DNS implementations as having an A 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.

2.4.  ".test"

".test" is RECOMMENDED for use in testing of current or new DNS related code. Applications SHOULD treat ".test" 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").

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.

4.  Internationalization Considerations

In 2007 IANA created eleven TLDs for tests of Internationalized Domain Names (IDN). The A-labels and corresponding languages 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 these IDN test TLDs as explained in Section 2.4 (".test").

    ".xn--0zwm56d"        Chinese (simplified)
    ".xn--11b5bs3a9aj6g"  Hindi
    ".xn--80akhbyknj4f"   Russian
    ".xn--9t4b11yi5a"     Korean
    ".xn--deba0ad"        Yiddish
    ".xn--g6w251d"        Chinese (traditional)
    ".xn--hgbk6aj7f53bba" Persian
    ".xn--hlcj6aya9esc7a" Tamil
    ".xn--jxalpdlp"       Greek
    ".xn--kgbechtv"       Arabic
    ".xn--zckzah"         Japanese

5.  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 6 (IANA Considerations) won't list all reserved TLDs for specific applications and protocols, e.g., [RFC2965] (Kristol, D. and L. Montulli, “HTTP State Management Mechanism,” October 2000.). The registry can only list reserved TLDs if (1) somebody bothered to propose it, typically in an Internet-Draft, and (2) the proposal was accepted in an IETF review.

6.  IANA Considerations

IANA reserves the TLDs ".example", ".invalid", ".localhost", ".test", and eleven IDN test 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 fifteen reserved TLDs mentioned above references to this memo will do.

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

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 John C. Klensin, Tina Dam, and Tony Hansen for their feedback, contributions, or encouragement.

8.  References

8.1. Normative References

8.2. Informative References

Appendix A.  Document History

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.
• IDN test SLDs not yet added, it is not clear if they are also reserved TLDs. Any "globally reserved labels" at other levels including the second level would be utter dubious.
• Improved the IANA Considerations Section 6 (IANA Considerations) based on feedback. The registry of reserved TLDs needs references to the relevant specifications.
• So far nobody insisted on listing the corresponding U-labels for the eleven IDN test TLDs. TBD, it is an editorial layout issue, and somebody offering to check the BiDi U-labels would be great.
• 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. The author refuses to discuss UUCP and LOCAL in this memo, but added [RFC2965] (Kristol, D. and L. Montulli, “HTTP State Management Mechanism,” October 2000.) as a dubious example, willing to pull it again as soon as somebody says "make it so". :-)

Changes in version 01:

• Various editorial issues found by Tony Hansen fixed.
• Added [IDNAbis] (IETF, “Internationalized Domain Names in Applications (Revised),” April 2008.) reference. The author believes 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.

Author's Address

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Acknowledgment

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