We pick j.root-servers.net, one of the 13 root servers (1), and ask it about dns-servers.vn and learn that vn is delegated to seven name servers (2), so we ask f.dns-servers.vn and get the following answer:
Dns-servers.vn is a domain controlled by seven domain name servers at ripe.net and dns-servers.vn having a total of ten IP numbers. All ten of them are on different IP networks.