Internet Engineering Task Force                              S. Cheshire
Internet-Draft                                               M. Krochmal
Intended status: Standards Track                              Apple Inc.
Expires: June 15, 2011                                      Dec 12, 2010

                        Special-Use Domain Names


   This document describes what it means to say that a DNS name is
   reserved for special use, when reserving such a name is appropriate,
   and the procedure for doing so.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on June 15, 2011.

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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 to are multicast addresses [RFC2606], with being the "all hosts" multicast address [RFC1112]
   [RFC3171]. Another example is, the IPv4 "local host"
   address [RFC3330].

   Analogous to Special-Use IPv4 Addresses [RFC3330], DNS has its own
   concept of reserved names, such as "", "", and
   "", 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.

2.  Applicability

   When IP multicast was created [RFC1112], implementations had to be
   updated to understand what a 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 you choose (regardless of whether
   those unicast IP addresses are already in use by other hosts on the
   public Internet) the IPv4 multicast address 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, which
   apply universally regardless of what network the implementation may
   be connected to, then that may be a candidate for having the IETF
   declare the name to be a Special-Use Domain Name and specify what
   special treatment implementations should give to that name. If
   declaring a given name to be special would result in no change to any
   implementations, then that suggests that the name may not be special
   in any material way, and it may be more appropriate to use the
   existing DNS mechanisms [RFC1034] to provide the desired delegation,
   data, or lack-of-data for the name in question. Where the desired
   behaviour can be achieved via the existing domain name registration
   processes, that process should be used. Reservation of a Special-Use
   Domain Names is not a mechanism for circumventing normal domain name
   registration processes.

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3.  Procedure

   If it is determined that special handling of a name is required in
   order to implement some desired new functionality, then an IETF
   "Standards Action" RFC [RFC5226] needs to be published describing the
   new functionality, and:

    o The RFC needs to state how implementations determine that the
      special handling is required for any given name. This is typically
      done by stating that any fully-qualified domain names ending in a
      certain suffix (i.e. falling within a specified parent pseudo-
      domain) will receive the special behaviour. In effect this carves
      off a sub-tree of the DNS namespace in which the modified name
      treatment rules apply, analogous to how IP multicast [RFC1112] or
      IP link-local addresses [RFC2462] [RFC3927] carve off chunks of
      the IP address space in which their respective modified address
      treatment rules apply.

    o The RFC needs to state, in each of the seven categories below,
      what special treatment, if any, is to be applied. If the answer in
      all seven categories is "none", then possibly no special treatment
      is required and requesting reservation of a Special-Use Domain
      Name may not be appropriate.

4.  Domain Name Reservation Considerations

   An IETF "Standards Action" RFC specifying some new naming behaviour,
   which requires a Special-Use Domain Name be reserved to implement
   this desired new behaviour, needs to contain a "Domain Name
   Reservation Considerations" section giving answers in the following
   seven categories:

   1. Users:

      Are human users expected to recognize these names as special and
      use them differently? In what way?

   2. Application Software:

      Are writers of application software expected to make their
      software recognize these names as special and treat them
      differently? In what way? (e.g. if a human users enters such a
      name, should the application software reject it with an error

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   3. Name Resolution APIs and libraries:

      Are writers of name resolution APIs and libraries expected to make
      their software recognize these names as special and treat them
      differently? If so, how?

   4. Caching DNS Servers:

      Are developers of caching DNS name servers expected to make their
      implementations recognize these names as special and treat them
      differently? If so, how?

   5. Authoritative DNS Servers:

      Are developers of authoritative DNS name servers expected to make
      their implementations recognize these names as special and treat
      them differently? If so, how?

   6. DNS Server Operators:

      Does this reserved Special-Use Domain Name have any potential
      impact on DNS server operators? If they try to configure their
      authoritative DNS server as authoritative for this reserved name
      will compliant name server software reject it as invalid? Do DNS
      server operators need to know about that and understand why? Even
      if the name server software doesn't prevent them from using this
      reserved name, are there other ways that it may not work as
      expected, which the DNS server operator should be aware of?

   7. DNS Registrars:

      How should DNS Registrars treat requests to register this reserved
      domain name? Should such requests be denied? Should such requests
      be allowed, but only to a specially-designated entity? (For
      example, the name "" is reserved for documentation
      examples and is not available for registration; however, the name
      is in fact registered; and there is even a web site at that name,
      which states circularly that the name is reserved for use in
      documentation and cannot be registered!)

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5.  Security Considerations

   This document outlines the circumstances in which reserving a domain
   name for special-use is appropriate, and the procedure for having
   that Special-Use Domain Name recorded by IANA. Any document
   requesting such a Special-Use Domain Name needs to contain an
   appropriate "Security Considerations" section which describes any
   security issues relevant to that special use.

6.  IANA Considerations

   IANA needs to create a new registry of Special-Use Domain Names.

   When IANA receives a request to record a new "Special-Use Domain
   Name" it should verify that the IETF "Standards Action" RFC [RFC5226]
   includes the required "Domain Name Reservation Considerations"
   section stating how the special meaning of this name affects the
   behaviour of hardware, software, and humans in the seven categories,
   and if so, record in the registry the Special-Use Domain Name and a
   reference to the RFC that documents it.

7.  Informative References

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, November 1987.

   [RFC1112]  Deering, S., "Host extensions for IP multicasting", STD 5,
              RFC 1112, August 1989.

   [RFC2462]  Thomson, S. and T. Narten, "IPv6 Stateless Address
              Autoconfiguration", RFC 2462, December 1998.

   [RFC2606]  Eastlake, D. and A. Panitz, "Reserved Top Level DNS
              Names", BCP 32, RFC 2606, June 1999.

   [RFC3171]  Albanna, Z., Almeroth, K., Meyer, D., and M. Schipper,
              "IANA Guidelines for IPv4 Multicast Address Assignments",
              RFC 3171, August 2001.

   [RFC3330]  IANA, "Special-Use IPv4 Addresses", RFC 3330,
              September 2002.

   [RFC3927]  Cheshire, S., Aboba, B., and E. Guttman, "Dynamic
              Configuration of IPv4 Link-Local Addresses", RFC 3927,
              May 2005.

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   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

Authors' Addresses

   Stuart Cheshire
   Apple Inc.
   1 Infinite Loop
   Cupertino, California  95014

   Phone: +1 408 974 3207

   Marc Krochmal
   Apple Inc.
   1 Infinite Loop
   Cupertino, California  95014

   Phone: +1 408 974 4368

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