Special-Use Domain Names
RFC 6761

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Internet Engineering Task Force (IETF)                       S. Cheshire
Request for Comments: 6761                                   M. Krochmal
Updates: 1918, 2606                                           Apple Inc.
Category: Standards Track                                  February 2013
ISSN: 2070-1721

                        Special-Use Domain Names

Abstract

   This document describes what it means to say that a Domain Name (DNS
   name) is reserved for special use, when reserving such a name is
   appropriate, and the procedure for doing so.  It establishes an IANA
   registry for such domain names, and seeds it with entries for some of
   the already established special domain names.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6761.

Copyright Notice

   Copyright (c) 2013 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
   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.

Cheshire & Krochmal          Standards Track                    [Page 1]
RFC 6761                Special-Use Domain Names           February 2013

1.  Introduction

   Certain individual IP addresses and IP address ranges are treated
   specially by network implementations and, consequently, are not
   suitable for use as unicast addresses.  For example, IPv4 addresses
   224.0.0.0 to 239.255.255.255 are multicast addresses [RFC5735], with
   224.0.0.1 being the "all hosts" multicast address [RFC1112]
   [RFC5771].  Another example is 127.0.0.1, the IPv4 "local host"
   address [RFC5735].

   Analogous to Special-Use IPv4 Addresses [RFC5735], the Domain Name
   System (DNS) [RFC1034][RFC1035] has its own concept of reserved
   names, such as "example.com.", "example.net.", and "example.org.", or
   any name falling under the top-level pseudo-domain "invalid."
   [RFC2606].  However, "Reserved Top Level DNS Names" [RFC2606] does
   not state whether implementations are expected to treat such names
   differently, and if so, in what way.

   This document specifies under what circumstances special treatment is
   appropriate, and in what ways.

2.  Terminology

   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 "Key words for use in
   RFCs to Indicate Requirement Levels" [RFC2119].

3.  Applicability

   When IP multicast was created [RFC1112], implementations had to be
   updated to understand what an IP multicast address means and what to
   do with it.  Adding IP multicast to a networking stack entailed more
   than merely adding the right routing table entries for those
   addresses.  Moreover, supporting IP multicast entails some level of
   commonality that is consistent across all conformant hosts,
   independent of what networks those hosts may be connected to.  While
   it is possible to build a private isolated network using whatever
   valid unicast IP addresses and routing topology one chooses
   (regardless of whether those unicast IP addresses are already in use
   by other hosts on the public Internet), the IPv4 multicast address
   224.0.0.1 is always the "all hosts" multicast address, and that's not
   a local decision.

   Similarly, if a domain name has special properties that affect the
   way hardware and software implementations handle the name, that apply
   universally regardless of what network the implementation may be
   connected to, then that domain name may be a candidate for having the

Cheshire & Krochmal          Standards Track                    [Page 2]
RFC 6761                Special-Use Domain Names           February 2013

   IETF declare it to be a Special-Use Domain Name and specify what
   special treatment implementations should give to that name.  On the
   other hand, if declaring a given name to be special would result in
   no change to any implementations, then that suggests that the name