DNS does even more for you than this. It also allows you to delegate authority over a subdomain to its administrators. For example, the maintainers at the Groucho Computing Center might create a subdomain for each department; we already encountered the math and physics subdomains above. When they find the network at the Physics department too large and chaotic to manage from outside (after all, physicists are known to be an unruly bunch of people), they may simply pass control of the physics.groucho.edu domain to the administrators of this network. These administrators are free to use whatever hostnames they like and assign them IP addresses from their network in whatever fashion they desire, without outside interference.
To this end, the namespace is split up into zones , each rooted at a domain. Note the subtle difference between a zone and a domain : the domain groucho.edu encompasses all hosts at Groucho Marx University, while the zone groucho.edu includes only the hosts that are managed by the Computing Center directly; those at the Mathematics department, for example. The hosts at the Physics department belong to a different zone, namely physics.groucho.edu . In Figure 6-1 , the start of a zone is marked by a small circle to the right of the domain name.
6.2.1. Name Lookups with DNS
6.2.2. Types of Name Servers
6.2.3. The DNS Database
6.2.4. Reverse Lookups
