David Farrar wrote:
The restriction was lifted by InternetNZ late last year. Don Stokes can
explain far better than me why there used to be a ban on TLDs being registered
at the 3rd level but basically it used to cause problems for some old servers.
Of the many times I've explained this one, I think this is the most
appropriate:
The no TLDs policy comes from a reaction to a
problem noted in 1993, that if a host was local.foo.co.nz, and it went
to look up www.bar.ac, it would actually try:
www.bar.ac.foo.co.nz.
www.bar.ac.co.nz.
www.bar.ac.nz.
www.bar.ac.
If this behaviour was followed, the owner of ac.co.nz could return an
answer for www.bar.ac.co.nz that redirected subsequent traffic to their
own systems.
Modern resolvers on the other hand have a parent domain or a search list
assigned; if the parent was foo.co.nz, it would just try:
www.bar.ac.foo.co.nz.
www.bar.ac.
(In some cases, any name with a '.' in it is tried first alone, and then
with the parent domain or each entry in a search list. Both approaches
can still cause surprises.)
The problem is fully documented in http://RFC.net/rfc1535.html
The now obsolete policy came about after ISOCNZ took over the DNS circa
1995(?), so there were inevitably names assigned that predate that
policy, many of which are still there.
-- don
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