We pick c.root-servers.net, one of the 13 root servers (1), and ask it about mailthanhhoa.edu.vn and learn that vn is delegated to seven name servers (2), so we ask a.dns-servers.vn where we learn that mailthanhhoa.edu.vn is delegated to two name servers, including ns1.fastpark.net (3), so we ask that one and get the following answer:
Three quarter of the several thousand of host names that point only to the IP number 184.108.40.206 use name server group 1 (example: dishsat.ru.pl, cbeleuven.be and lazir.com ). Worth noting is that three quarter of the domains that use name server group 1 point only to the IP number 220.127.116.11.
The IP number 18.104.22.168
There are several hundred of host names that point to the IP number 22.214.171.124.