maintaining global name zone data that has records corresponding to hosts, each record comprising at least a host name and a sub-domain name of its corresponding host, where the global name zone data is maintained to prevent records having same host names and different sub-domain names, wherein a domain name comprises a plurality of separate parts, a leftmost part of the domain name representing the host name and a rightmost part of the domain name representing a top-level domain name;

receiving at a domain name system (DNS) server a name registration request from a client device, the name registration request including a leftmost part of a requested domain name, the requested domain name comprising a domain name that would be created if the requested were completed;

determining, without regard for the sub-domain names of the records in the global names zone data, whether the global names zone data has a record having the same leftmost part of the requested domain name that is in the name registration request;

rejecting the registration request if there is already a record in the global names zone data with the same leftmost part of the domain name that would result if the request were completed: and

registering an Internet Protocol (IP) address for the host name if there is no same leftmost part of the requested domain name in the global name zone data.