| Before we start to look at what NIS is and how to configure it, we need to take a minute to explain what naming services are and how the two are related. Certain administrative information is frequently used by Solaris machines, such as user names and passwords, hostnames and IP addresses, printer names, and so forth. This information can be held locally by each node in its own local files. It may ease adminstration, and save disk space, if all this commonly used information could be held centrally, on one machine, rather than duplicating it on many. A naming service gives us the ability to do precisely this. There are a number of different naming services available on Solaris, with each having their own advantages and disadvantages. The more commonly used ones are NIS, NIS+, Domain Name System (DNS), Lightweight Directory Access Protocol (LDAP), and "local files." All these are briefly described below. Local Files The important point we need to make about the "local files" naming service is that, while it is commonly referred to as a naming service (we'll also follow that convention here), it doesn't possess the benefits of one; that is, a centralized "database" of easy-to-access information. It's really a fallback mechanism used whenever a naming service is not required. "Local files" were the original method of storing configuration information before naming services were available, each machine holding its own administrative files in its own /etc directory. However, "local files" are the simplest type of service to set up and understand and, because of this, they are still commonly used. NIS NIS provides a way of centralizing administration by keeping one central copy of every machine's administrative data on a master server. Slave servers can be configured to prevent the master from handling all the traffic, but essentially it is a flat single domain with one master. It can, however, be configured to hold almost any administrative data needed, as we'll see later in the chapter. DNS DNS is used to provide a mapping between hostnames and their IP addresses (it can also store some closely related information). Whereas NIS only uses a single domain, DNS allows multiple hierarchical domains. NIS+ NIS+ attempts to bring the advantages of DNS and NIS together. Doing this allows the information stored within NIS to be more easily managed by replicating the hierarchical structure of an organization. The downside of this, however, is that it is proprietary software that has limited support outside of Solaris. LDAP LDAP uses a tree-like structure, known as the Directory Information Tree (DIT), to store its data. It is similar to NIS+, but is available on both UNIX and non-UNIX machines and is not proprietary. Why Use Them? We've already mentioned that "local files" can be used instead of a naming service if you preferthey are easy to set up, so why have all the problems of configuring something else? "Local files" can work fine when a small number of machines are involved. But as the number connected to the network increases, it becomes harder to be certain that they all have the correct revisions of the important administration files, and that they are all synchronized with each other. Up to this point, we have managed to work around these sorts of problems by manually copying any updated files around the system. For us, this isn't a problem since we only have a few machines on the network and so it isn't a very time-consuming taskwe could even write a small script to do it for us if we wished. Eventually, however, the system will reach the point where it is impossible to manage, and using a name service becomes a necessity rather than an option. With this in mind, over the next few chapters we will look at a few common naming services: NIS and DNS. We'll configure both these on our machines, using NIS for the local network, covered in this chapter, and DNS for connections to the Internet, which is covered in Chapter 16, "Configuring DNS." | 
