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
draft-cheshire-dnsext-special-names-00
Abstract
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
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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
224.0.0.0 to 239.255.255.255 are multicast addresses [RFC2606], with
224.0.0.1 being the "all hosts" multicast address [RFC1112]
[RFC3171]. Another example is 127.0.0.1, the IPv4 "local host"
address [RFC3330].
Analogous to Special-Use IPv4 Addresses [RFC3330], DNS 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.
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 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, 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
message?)
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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 "www.example.org" 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
USA
Phone: +1 408 974 3207
Email: cheshire@apple.com
Marc Krochmal
Apple Inc.
1 Infinite Loop
Cupertino, California 95014
USA
Phone: +1 408 974 4368
Email: marc@apple.com
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