Summary

  • RFC 3172 assigned protocol infrastructure identifiers to .arpa in 2001, while .int kept its treaty-organization purpose.
  • RFC 9121 later documented an inventory, weak observed query patterns and removal of residual infrastructure delegations from .int.

The domain .int began with two kinds of occupants that were easy to confuse but served different purposes. RFC 1591 described it as a home for organizations established by international treaties, or for international databases. In practice, experimental Internet infrastructure identifiers also appeared there. A label in the DNS could therefore refer either to an organization or to a protocol’s addressing machinery.

In 2001, RFC 3172 set out a clearer destination for the second use. The Internet Architecture Board described .arpa as a limited-use infrastructure domain. An attached April 2000 letter asked ICANN to administer it for Internet infrastructure, including the migration of infrastructure applications then residing in .int. That decision established where future infrastructure names belonged; it did not itself erase every earlier delegation.

Some migrations happened separately. RFC 4159 records the replacement of ip6.int with ip6.arpa. Other experimental names persisted in the .int zone after their practical use had faded. RFC 9121, published in 2021, treated that residue as an operational record to investigate. It listed atma.int, ip4.int, ip6.int, nsap.int, rdi.int and reg.int, and discussed tpc.int as a remote-printing service. The memo said the administering parties had long since stopped using the listed names.

The evidence for removal was deliberately bounded. IANA inventoried the historical documentation, analyzed DNS query patterns and conducted preliminary outreach. The query patterns were judged insignificant; the domains were considered very likely obsolete. RFC 9121 then changed RFC 1528 and RFC 1706 to Historic and stated that IANA had removed the historical infrastructure domains from the .int zone. It warned that old systems might still have names hard-coded and that future reuse of those labels for treaty organizations required care.

This was not proof that every private resolver, application or saved configuration had been updated. It was a decision that the public delegation record no longer justified preserving the old names. .arpa had become the right namespace in 2001; the residual .int entries were not removed until a later review assembled enough evidence to close them.

Sources