If your site is not connected to the Internet, you must set up one or more of your servers to perform as root domain name servers. The boot files of all DNS name servers on your network must point to a common cache file (usually called named.ca) that identifies the root domain name servers. You then create a cache file that identifies your root name servers.
Since a single machine can be the primary domain name server for more than one machine, the easiest way to create a root domain name server is to have the server for your highest level domain also be the server for the logical "." domain.
For example, suppose you have given your network the domain name solo. The DNS master name server is dnsmaster.solo.(with a trailing dot). In this case, you would make dnsmaster the root master server for the "." domain.
If your network has more than one top-level domain, the root domain server name should be the primary name server for all top-level domains. For example, if your network is divided into two separate, non-hierarchal domains named solo and private, the same server must be root master server for both of them. Following the example above that would mean that dnsmaster.solo. is root domain master for both the solo and the private domains.