DNS Hierarchy in a Local Domain

If your company is large enough, your company might support several domains, organized into a local namespace. The following figure shows a domain hierarchy that might be in place in a single company. The top-level, or “root” domain for the organization is ajax.com, which has three subdomains: sales.ajax.com, test.ajax.com, and manf.ajax.com.

Figure 3–3 Hierarchy of DNS Domains in a Single Organization

DNS clients request service only from the servers that support their domain. If the domain's server does not have the needed information, the server forwards the client request to its parent server. The parent server is in the next higher domain in the hierarchy. If the request reaches the top-level server, the top-level server determines whether the domain is valid. If the domain is not valid, the server returns a “not found” type message to the client. If the domain is valid, the server routes the request down to the server that supports that domain.