== ccTLD/us ==

http://www.courts.state.co.us/ というような使い方があるらしい。　（co.us は Colorado 関係のために存在しているようだ）

   co.us はゾーンではない。  https://en.wikipedia.org/wiki/List_of_courts_of_the_United_States　からたどれる。

$ dnsq ns co.us a.root-servers.net
{{{
2 co.us:
305 bytes, 1+0+6+9 records, response, noerror
query: 2 co.us
authority: us 172800 NS a.cctld.us
authority: us 172800 NS b.cctld.us
authority: us 172800 NS c.cctld.us
authority: us 172800 NS e.cctld.us
authority: us 172800 NS f.cctld.us
authority: us 172800 NS k.cctld.us
additional: a.cctld.us 172800 A 156.154.124.70
additional: b.cctld.us 172800 A 156.154.125.70
additional: c.cctld.us 172800 A 156.154.127.70
additional: e.cctld.us 172800 A 156.154.126.70
additional: f.cctld.us 172800 A 209.173.58.70
additional: k.cctld.us 172800 A 156.154.128.70
additional: b.cctld.us 172800 AAAA 2001:503:d1ae:ffff:ffff:ffff:ffff:ff7e
additional: f.cctld.us 172800 AAAA 2001:500:3682::11
additional: k.cctld.us 172800 AAAA 2001:503:e239::3:1
}}}
$ dnsq ns co.us 156.154.124.70
{{{
2 co.us:
89 bytes, 1+0+1+0 records, response, authoritative, noerror
query: 2 co.us
authority: us 900 SOA a.cctld.us hostmaster.neustar.biz 2013096808 900 900 604800 86400
}}}

== state.co.us ==

$ dnsq ns state.co.us a.cctld.us
{{{
2 state.co.us:
99 bytes, 1+0+2+2 records, response, noerror
query: 2 state.co.us
authority: state.co.us 900 NS dns2.state.co.us
authority: state.co.us 900 NS dns1.state.co.us
additional: dns1.state.co.us 7200 A 192.70.175.110
additional: dns2.state.co.us 7200 A 165.127.20.21
}}}

NS TTL が短い。

$ dnsq ns courts.state.co.us dns1.state.co.us
{{{
2 courts.state.co.us:
106 bytes, 1+2+0+2 records, response, authoritative, noerror
query: 2 courts.state.co.us
answer: courts.state.co.us 3600 NS dns1.state.co.us
answer: courts.state.co.us 3600 NS dns2.state.co.us
additional: dns1.state.co.us 86400 A 192.70.175.110
additional: dns2.state.co.us 86400 A 165.127.20.21
}}}

courts zone  は同居。