ccTLD/acについて、ここに記述してください。
ちょっとみには同居ではないように見えるのだが、少し調べてみると
1. ac
%dnsq ns ac a.root-servers.net
2 ac: 344 bytes, 1+0+7+9 records, response, noerror query: 2 ac authority: ac 172800 NS ns3.icb.co.uk authority: ac 172800 NS ns1.communitydns.net authority: ac 172800 NS b.ns13.net authority: ac 172800 NS b.nic.io authority: ac 172800 NS b.nic.ac authority: ac 172800 NS a.ns13.net authority: ac 172800 NS a.nic.ac additional: ns3.icb.co.uk 172800 A 91.208.95.130 additional: ns1.communitydns.net 172800 A 194.0.1.1 additional: ns1.communitydns.net 172800 28 \040\001\006x\000\004\000\000\000\000\000\000\000\000\000\001 additional: b.ns13.net 172800 A 49.212.51.85 additional: b.nic.io 172800 A 194.0.2.1 additional: b.nic.io 172800 28 \040\001\006x\000\005\000\000\000\000\000\000\000\000\000\001 additional: b.nic.ac 172800 A 78.104.145.37 additional: a.ns13.net 172800 A 49.212.31.192 additional: a.nic.ac 172800 A 64.251.31.177
2. nic.ac
%dnsq ns nic.ac b.nic.ac
2 nic.ac: 458 bytes, 1+9+0+13 records, response, authoritative, noerror query: 2 nic.ac answer: nic.ac 172800 NS dns4.nic.ac answer: nic.ac 172800 NS dns01.nic.ac answer: nic.ac 172800 NS dns3.nic.ac answer: nic.ac 172800 NS dns1.nic.ac answer: nic.ac 172800 NS dns2.nic.ac answer: nic.ac 172800 NS dns1v6.nic.ac answer: nic.ac 172800 NS dns2v6.nic.ac answer: nic.ac 172800 NS dns5.nic.ac answer: nic.ac 172800 NS dns3v6.nic.ac additional: dns1.nic.ac 172800 A 194.0.1.1 additional: dns1.nic.ac 172800 28 \040\001\006x\000\004\000\000\000\000\000\000\000\000\000\001 additional: dns2.nic.ac 172800 A 194.0.2.1 additional: dns2.nic.ac 172800 28 \040\001\006x\000\005\000\000\000\000\000\000\000\000\000\001 additional: dns3.nic.ac 172800 A 91.208.95.130 additional: dns3.nic.ac 172800 28 \040\001\004p\037\007\015\013\000\000\000\000\000\000\0010 additional: dns4.nic.ac 172800 A 64.251.31.177 additional: dns4.nic.ac 172800 28 &\007\376\270\000\000\000\000\000\000\000\000\000\005\000\005 additional: dns5.nic.ac 172800 A 78.104.145.37 additional: dns01.nic.ac 172800 A 194.0.1.1 additional: dns01.nic.ac 172800 A 194.0.2.1 additional: dns01.nic.ac 172800 A 74.116.178.1 additional: dns01.nic.ac 172800 A 74.116.179.1
%dnsq a a.nic.ac 194.0.1.1 ~
1 a.nic.ac: 42 bytes, 1+1+0+0 records, response, authoritative, noerror query: 1 a.nic.ac answer: a.nic.ac 172800 A 64.251.31.177
%dnsq a dns4.nic.ac 194.0.1.1 ~
1 dns4.nic.ac: 45 bytes, 1+1+0+0 records, response, authoritative, noerror query: 1 dns4.nic.ac answer: dns4.nic.ac 172800 A 64.251.31.177