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.