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With the enormous expansion of the World Wide Web over the past decade, internetworking has become widely diffused. Nearly all business enterprises have access to and a presence on the Internet. Beyond that, the number of intranets, private networks, and extranets has also grown exponentially. "Getting connected" has become as routine as having a telephone. Where we once exchanged telephone numbers and mailing addresses with friends and associates, we now routinely include an e-mail address too. Even children in elementary school are now communicating via e-mail and getting information about their favorite toys from the Internet.
As this distributed computing environment continues to grow, so does the storehouse of information, which makes locating the required information an increasingly challenging task. Sophisticated search engines have been created as a tool to help in locating information. Some of these search engines are specialized to provide information on particular topics. To locate persons on the Internet or intranet in a fast and easy way, a particular tool is being used that is very similar to a telephone directory, commonly referred to as "white pages" or "yellow pages." This tool is called a directory server.
If you want to get the news from CNN, you simply connect your Web browser to CNN's Web server by typing in the address (http://www.cnn.com) using the Hypertext Transfer Protocol (HTTP). Likewise, if you want to send e-mail, you use your mail client to transfer the mail to a mail server using the Simple Mail Transfer Protocol (SMTP). Similarly, if you want to look up information stored in a directory server, you would use a directory client that speaks with the directory server using the Lightweight Directory Access Protocol (LDAP), which is the subject of this book. These three protocols — HTTP, SMTP, and LDAP — have something in common. All are standard protocols running over the widely used Transmission Control Protocol/Internet Protocol (TCP/IP) stack.
This preface to the book will briefly review what you can do with LDAP. First we will learn what type of information you can store on a directory server. Then we will see some of the advantages that directory servers have over similar data stores such as, for example, relational databases.
The concept of a directory server is much the same as the concept of a telephone directory, but it can also be used in a variety of other useful applications:
Directories are frequently used to store information about persons. This could be for the company phone book, or it could be used to store information about the company organization. It could also hold information about customers and the enterprises for whom the customers work.
Directory servers can handle security-related information, such as the public keys of your users of certificates.
Directory services can be used to provide naming services, so you can store all your DNS (domain name system) maps in a directory. DNS resolves the human-readable computer names (such as www.cnn.com) into the sequence of dotted numbers that computers use to locate each other. You can also use directory services to resolve the names of databases to computer names.
Directory servers can hold information about users and groups of your computer network and work as an NIS (network information system) server. NIS was created by Sun Microsystems to store information about users, such as their home directory, group memberships, and other important information.
Directory servers can hold information such as e-mail addresses and further e-mail related information. This information can be shared by many e-mail clients or servers. An e-mail server can share such information as e-mail aliases, forwarding rules, and other mail-delivery information that the server needs to work properly.
Directory servers can hold information for software packages disributed over the intranet or Internet. The configuration procedures can use this data that is centrally maintained by the directory server.
It is clear that directories can hold many types of information. Let us now briefly review the advantages provided by directory servers.
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