We pick l.root-servers.net, one of the 13 root servers (1), and ask it about 120-50-185-44.static.kcc.vn and learn that vn is delegated to seven name servers (2), so we ask a.dns-servers.vn where we learn that kcc.vn is delegated to two name servers, including ns1.domainvietnam.com (3), so we ask that one and get the following answer:
Seven of the more than hundred host names that point only to the IP number 120.50.185.6 use the two name servers ns1 and ns2.domainvietnam.com together (example: kcc.vn ).