RFC 2606

RFC 2606: Reserved Top Level DNS Names 🎀

Okay bestie, this one is a Best Current Practice (BCP 32) from June 1999 by D. Eastlake and A. Panitz, and it's from the Network Working Group. It's a Request for Comments, so it's basically the internet's official notes on how names work, and it's giving very important. 💅 Full author details are at the end.

Status of This Memo ✨

   This document specifies an Internet Best Current Practices for the
   Internet Community, and requests discussion and suggestions for
   improvements.  Distribution of this memo is unlimited.

Copyright Notice 🌸

   Copyright (C) The Internet Society (1999).  All Rights Reserved.

Abstract 🦋

So the goal here is to lower the chances of conflicts and confusion 🙈. A few top level domain names get set aside for private testing, for examples in documentation, and stuff like that. The doc also writes down a few second level domain names that are reserved to be used as examples. Lowkey the whole point. 💜

Table of Contents 🍓

   1. Introduction............................................1
   2. TLDs for Testing, & Documentation Examples..............2
   3. Reserved Example Second Level Domain Names..............2
   4. IANA Considerations.....................................3
   5. Security Considerations.................................3
   References.................................................3
   Authors' Addresses.........................................4
   Full Copyright Statement...................................5

1. Introduction 🧚

Okay so the global Internet Domain Name System is written up in [RFC 1034, 1035, 1591] and a bunch of other Requests for Comment too. It's basically a tree of names that starts at the root, ".", and right under that you get top level domains like ".com" and ".us". Under those top level domains there are usually more levels of names. It's giving family tree, but make it DNS. 🌳

2. TLDs for Testing, & Documentation Examples 💖

Here's the tea. People need top level domain (TLD) names they can use to make up names that won't clash with real TLDs now or later in the global DNS. You can use them for private testing of DNS code, for examples in docs, for DNS experiments, for invalid DNS names, or for other stuff like that. 🧪

Let me explain why this matters, because it's kind of a big deal 😭. Say a site sets up some extra unused top level domains to test its local DNS code and config. Later on, one of those TLDs starts getting used on the real internet. Now the local lookups for the real data in those zones get blocked by the test versions. Or test code gets written that hits a TLD that's already in use, with the plan that it'll only ever run on a locked-down testbed or that the example will never actually run. Then the test code escapes onto the internet, or the example gets coded up and shipped anyway. Depending on what the test or example is for, it's honestly safest if it points at a TLD that's permanently reserved for that exact purpose. 🔒

So to cover all of that safely, four domain names are reserved. They're listed and described below. 👑

                   .test
                .example
                .invalid
              .localhost

".test" is recommended for use in testing of current or new DNS related code. ✅

".example" is recommended for use in documentation or as examples. 📖

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

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. So please don't touch it, it's already doing a job. 🫶

3. Reserved Example Second Level Domain Names 🌈

The Internet Assigned Numbers Authority (IANA) also currently has the following second level domain names reserved, and they can be used as examples. ✨

        example.com
        example.net
        example.org

4. IANA Considerations 🎀

IANA has agreed to the four top level domain name reservations specified in this document and will reserve them for the uses indicated. Iconic behavior from IANA, honestly. 👏

5. Security Considerations 🔥

Okay this section is the serious part, so pay attention 🙈. Using a current or future top level domain name in experiments or tests, as an example in documentation, to mark names as invalid, or as a synonym for the loop back address can cause real confusion and conflict. Test and experimental software can escape and end up running against the global operational DNS. Even examples that are only meant for documentation can end up getting coded and released, or can cause conflicts later on when the name really gets used, and possibly when someone acquires intellectual property rights in an "example" name.

Reserving several top level domain names for these purposes will minimize that confusion and conflict. That's the whole point of this section, and it's kind of the entire reason this doc exists. 🛡️

References 📚

   [RFC 1034] Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, November 1987.

   [RFC 1035] Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

   [RFC 1591] Postel, J., "Domain Name System Structure and Delegation",
              RFC 1591, March 1994.

Authors' Addresses 💅

   Donald E. Eastlake 3rd
   IBM
   65 Shindegan Hill Road, RR #1
   Carmel, NY 10512

   Phone: +1 914-276-1668(h)
          +1 914-784-7913(w)
   FAX:   +1 914-784-3833(3)
   EMail: dee3@us.ibm.com


   Aliza R. Panitz
   500 Stamford Dr. No. 310
   Newark, DE 19711 USA

   Phone: +1 302-738-1554
   EMail: buglady@fuschia.net

Full Copyright Statement 💜

This is the legal bit, so I'm keeping it word for word 🙈:

   Copyright (C) The Internet Society (1999).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement 🫶

Funding for the RFC Editor function is currently provided by the Internet Society. Thank you, Internet Society, you're literally the best. 🧚✨

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