I happen to own a iso-3166-2.com domain (ar.com) and a large part of the
queries to my name servers are for SLDs under .AR. which is the ccTLD
for Argentina.
The number of queries for *.com.ar.com., which all fail is significant
compared to queries for anything valid under ar.com.
I suspect similar behavior for any 2 letter SLD in a gTLD that has a
matching iso-3166-2 ccTLD.
We made some measurements in 1998 to quantify this. The background is
that the Norwegian (.no) domain name authority (see www.norid.no) used
to have a rule that <ccTLD>.no couldn't be used, due to the well known
problems mentioned in RFC 1535. We wanted to see if this rule could be
relaxed. Thus we logged all DNS queries to several of the authoritative
.no name servers, to a number of other important recursive name servers,
and also all DNS requests passing through some LAN segments used to
interconnect the most important routers of one particular ISP.
We logged DNS requests over one week, to get statistically significant
data. Of the "problem requests" we only looked at requests for *.com.no,
because this was the most common case. Example of the results:
27888935 DNS requests (all possible names) through interconnect segments
5710521 requests for *.com (20.5%)
2550 requests for *.com.no (4.47e-4 of the *.com requests)
8831582 DNS requests (all possible names) to non-recursive .no server
359117 requests for *.com (4.07%)
7869 requests for *.com.no (2.19% of *.com requests)
5160927 DNS requests (all possible names) to recursive .no server
100406 requests for *.com (1.95%)
11588 requests for *.com.no (11.5% of *.com requests)
We concluded that we could live with the these numbers, and removed the
rule that <ccTLD>.no couldn't be used.
Steinar Haug, Nethelp consulting, sthaug(_at_)nethelp(_dot_)no