DNS on Windows Server 2003, 3rd Edition

Subdomains of in-addr.arpa Domains

Forward-mapping domains aren’t the only domains you can divide into subdomains and delegate. If your in-addr.arpa namespace is large enough, you may need to divide it, too. Typically, you divide the domain that corresponds to your network number into subdomains that correspond to your subnets. How that works depends on the type of network you have and on your network’s subnet mask.