Zones were mentioned previously in this chapter, but we haven't really taken the time to talk about them in much depth. As stated earlier, a zone is a partitioned portion of the overall DNS namespace. Zones make the manageability of the namespace much easier than the flat namespace of HOSTS files did. A zone must encompass a contiguous namespace, however. For example, a single zone could not be authoritative for both Inside-Corner.com and quepublishing.com, because those two domains are not part of the same namespace. A contiguous namespace encompasses a single second-level domain name. For example, the domains Inside-Corner.com, Studio.Inside-Corner.com, GuitarShop.Studio.Inside-Corner.com, and Production.Inside-Corner.com are all part of the same namespace.
Multiple zones within a contiguous namespace are used primarily to distribute administrative responsibilities. In many corporations, there are political boundaries that must be managed, with different divisions/departments having their own administrators. Multiple zones allow multiple administrators to be responsible for their individual pieces of the namespace.
Another reason to partition the namespace into zones is to reduce the load on a DNS infrastructure. Consider a megacorporation such as Microsoft, with more than 100,000 nodes on the network spread out across the globe. A single zone would place a tremendous burden on the primary DNS server (remember, there can be only one primary server in a zone), and the replication traffic to secondary DNS servers would make a significant impact on network performance. Dividing the Microsoft.com namespace into multiple zones distributes the load, thus increasing performance and easing administration. Even using AD integrated zones would require that updates with the zone be replicated to every other DNS server in the zone. Again, the bandwidth usage for this type of traffic would potentially have a detrimental effect on network performance, particularly if changes were being made frequently.
Windows 2000 supports two types of zones: forward lookup and reverse lookup. These zones are associated with the types of name-resolution queries they enable. We discuss these zones in greater detail when we look at installing and configuring Windows 2000 DNS later in this chapter.