DNS Structure: Old Top Level Domains
A common misconception about domain names is that they all end in .com.
Most sites these days do, but it's only one of many available endings. In
fact, there are eight different top level domains in what can be considered
the "Old TLDs" (as opposed to the new TLDs that
were implemented starting in 2001, and the country-code
domains).
The Old TLDs:
.com -- for commercial entities
.com is heavily abused by noncommercial users, as discussed to great
length below. All the dumb-asses of the world seem to think that all websites
should have .com addresses, whether they logically belong there or not.
.org -- for noncommercial entities
Actually, the RFC document
defining the TLD meanings says it's for "miscellaneous"
organizations that don't fit elsewhere, but since commercial organizations are
covered by .com, the implication is that .org entities are
noncommercial. .org is the most appropriate domain for both non-profit
and not-for-profit organizations; the distinction between these is important
to the IRS but not to the domain name system.
Some discussion at the ICANN
site in 2001 indicated that there was a proposal to impose enforcement of
noncommercial-organization status on .org registrants, but little
clarity about just what that would entail -- would official non-profit
accreditation with a governmental body be required, or just common-sense
examination of the domain's use to see whether it's predominantly
noncommercial? Would personal sites, fan sites, and other noncommercial things
that don't have an official organization behind them be allowed to keep using .org
domains? However, that proposal didn't go anywhere, and instead
a recommendation
was made by ICANN's domain name supporting organization to make .org a
sponsored domain run by a nonprofit organization and marketed specifically to
nonprofits, but not to impose any restrictions on either past or future
registrants.
Subsequently, ICANN evaluated
proposals (both commercial and noncommercial) for the new .org
registry, to take over from Verisign when their contract runs out at the end
of 2002. Proposals were supposed to be sensitive to the needs of the
noncommercial community and are supposed to market .org in a manner
encouraging its differentiation from commercial domains and discouraging
duplicative or defensive registrations. The winning registry needed to
demonstrate that they have experience running a large-scale domain registry,
but they were possibly able to get a grant from a $5 million fund being paid
by Verisign to ICANN for the express purpose of helping the .org
transition.
.net -- for network infrastructure providers
Next to .com, this is the most heavily abused domain, as few current
users can remotely claim to being part of the network infrastructure in the
manner intended by the creators of the domain name system. It's instead
commonly used by people whose desired name is already taken in .com.
.edu -- for educational institutions
.edu is limited to accredited degree-granting institutions. There
was some dispute in the past about whether they must be in the United States
or not; there's nothing in the relevant RFC that says this, and several
foreign universities were given domains in this TLD, but more recently the
registry stopped allowing foreign registrations, and that's written in the
current registry's policy now. .edu domains actually used to be more
loosely granted to anything educational, so a few non-degree-granting
educational organizations such as the San Francisco Exploratorium and various consortiums
have .edu domains "grandfathered" from an earlier time.
Until recently, .edu was administered by Network Solutions, but it
has recently been turned over to an educational
consortium, which has loosened some of the rules -- previously, only
4-year degree-granting institutions were allowed (other than the few
grandfathered early registrations), but now community colleges are allowed as
well. Some balance needs to be
reached. If you're too loose in enforcing criteria, then all sorts of abuses
occur. If you're too tight, then people ignore that top level domain in favor
of others with looser standards, even if they're not really the appropriate
one for the type of entity registering.
.gov -- for governmental entities
.gov is limited by the RFC document to U.S. federal government
agencies. However, it always had a few state government sites, like Washington, "grandfathered" from
before the "federal-only" restriction was added. Actually, it would
be more logical for the federal government to register under .fed.us,
like all other countries' governments which are under their appropriate
country code.
Somewhere around 2001, they started letting state and local governments get
.gov addresses again. For a long time, this seemed to be happening
"under the table" with nothing in the official registry site mentioning this availability, but
in 2002 it was redesigned to indicate that such entities can now register .gov
domains, and that there are proposed changes to open things up to even more
related categories. They're also giving .gov domains to Native
American tribes, of the form tribename-nsn.gov (where NSN stands for
Native Sovereign Nation), even though they already have namespace under nsn.us.
.mil -- for military entities
.mil is limited to the U.S. military. This is another domain that
might be better off being under .us rather than at the international
top level, but a historical anomaly due to the Defense Department's
involvement in the creation of the Internet in the first place.
.int -- for international treaty organizations
This is the most tightly controlled international top level domain, and
hence the least used. Even the few organizations qualifying for .int
domains don't usually make much use of them.
.arpa -- for addressing and routing parameters
Usually, people think there are seven old TLDs (if they remember that .int
exists), but there is actually an eighth global TLD. Normal Internet
users never have occasion to encounter it, though it's very important to the
internal workings of the Internet. Historically, .arpa was originally
the temporary TLD in which sites in the old ARPAnet (the predecessor of the
Internet, operated by the U.S. Department of Defense's Advanced Research
Projects Administration) had their names until they migrated into their proper
place in the domain name system (.edu, .mil, .com, etc.).
However, one domain within .arpa became a vital part of the
infrastructure -- in-addr.arpa -- used by programs on the Internet that
must do reverse lookups from IP addresses to their associated domains. IP
addresses have subdomains of in-addr.arpa associated with them which in
turn resolve to DNS records showing what domain they belong to. Only "techies"
need to know about this, as it's all done behind the scenes, invisible to
normal users.
This use of .arpa was long regarded as an archaic legacy usage that
really ought to be changed -- in fact, when the .int domain was first
set up, in addition to international treaty organizations it was also
designated as the proper place for Internet infrastructure functions, with in-addr.arpa
not being moved to .int simply because that would break all the
existing software that expects it to be where it now is. It was expected that
future structures of that sort, such as the one being outlined now for the new
IPv6 protocol, would be in .int, not .arpa. However, there seems
to have been a recent change of heart, and recent standards-track proposals
have decided instead to put new DNS structural lookup records in .arpa
as well, with the acronym "retrofitted" to now mean Address and
Routing Parameters Area. Thus, proposals now exist to create ip6.arpa
and e164.arpa to process queries in IPv6 and E.164 protocols
respectively. RFC
3172 documents the current status of the .arpa domain.
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