The DNS protocol

Allows translating host names (www.yahoo.com) into IP addresses.

Employs a hierarchic network of DNS servers.

At the top, the root name servers (a.root-servers.net through m.root-servers.net) know the addresses of the name servers responsible for each of the top-level domains (*.com, *.org, *.net, *.gov, *.mil, *.edu and the various countries domains).

Each secondary name server knows the names of the name servers that handle 3rd-level domains (e.g. network.net.il), and so on.