Information in the directory is organized in a tree structure, called the Directory Information Tree (DIT). The structure of a DIT usually reflects very closely the structure of the information it contains. For example, a directory containing entries for people in a corporation could be organized by division or by location. In general, DIT structures are organizational, geographical, or include both organizational and geographical factors.
Directory information is stored in a data store. A data store is the physical location where a naming context is held. A data store can hold more than one naming context. A directory server can contain more than one data store.
When dividing the DIT into data stores to be held on individual servers, you need to take account of the following:
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A search cannot cross data stores. If you want to perform a search in several data stores, you have to start several simultaneous search operations. |
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Alias definitions are local to a data store |
The XYZ Corporation is a pharmaceutical company, with headquarters in Boston, Massachusetts. They have two manufacturing operations, one in San Francisco and one in Paris, and three distribution centers, in Atlanta, London, and Tokyo. There are two research groups in London and San Francisco, located with the other XYZ divisions in those cities. The Sales organization has three divisions: Europe, US&C (US and Canada), and RoW (the rest of the world).
FIGURE 1-6 shows the functional structure of XYZ Corporation.
FIGURE 1-7 shows the geographical structure of XYZ Corporation.
As is common with many organizations, neither an organizational DIT structure nor a functional DIT structure completely meets the directory structure needs of XYZ Corporation, so the network management team decides to combine functional and geographical factors, and to take into account the different usage patterns within the different departments. The result is the DIT structure shown in FIGURE 1-8.
In this DIT structure, the corporation is divided into seven organizational units (ou) and three localities (l) corresponding to ten naming contexts. FIGURE 1-8 shows the RDN of each naming context and the server on which it is stored. Each naming context contains entries that are related to a particular geographical or functional area. Given that much of the enquiry traffic is expected to be local to a server, this reduces the network traffic.
A referral system ensures that if an entry cannot be found locally, the directory server can pass the request to another directory server. FIGURE 1-9 shows the content of each naming context, and the referrals defined between servers.