What Is a Name Service?

Name services store information in a central place that users, workstations, and applications must have to communicate across the network such as:

• Machine (host) names and addresses

• User names

• Passwords

• Access permissions

Without a central name service, each workstation would have to maintain its own copy of this information. Name service information may be stored in files, maps, or database tables. Centrally locating this data makes it easier to administer large networks.

Name services are fundamental to any computing network. Among other features, a name service provides functionality that:

• Associates (binds) names with objects

• Resolves names to objects

• Removes bindings

• Lists names

• Renames

A network information service enables workstations to be identified by common names instead of numerical addresses. This makes communication simpler because users don't have to remember and try to enter cumbersome numerical addresses like "129.44.3.1."

For example, take a simple network of three workstations named, pine, elm, and oak. Before pine can send a message to either elm or oak, it must know their numerical network addresses. For this reason, it keeps a file, /etc/hosts or /etc/inet/ipnodes, that stores the network address of every workstation in the network, including itself.

Likewise, in order for elm and oak to communicate with pine or with each other, they must keep similar files.

Addresses are not the only network information that workstations need to store. They also need to store security information, mail data, information about their Ethernet interfaces, network services, groups of users allowed to use the network, services offered on the network, and so on. As networks offer more services, the list grows. As a result, each workstation may need to keep an entire set of files similar to /etc/hosts or /etc/inet/ipnodes.

As this information changes, administrators must keep it current on every workstation in the network. In a small network this is simply tedious, but on a medium or large network, the job becomes not only time-consuming but nearly unmanageable.

A network information service solves this problem. It stores network information on servers and provides it to any workstation that asks for it:

The workstations are known as clients of the server. Whenever information about the network changes, instead of updating each client's local file, an administrator updates only the information stored by the network information service. This reduces errors, inconsistencies between clients, and the sheer size of the task.

This arrangement, of a server providing centralized services to clients across a network, is known as client-server computing.

Although the chief purpose of a network information service is to centralize information, another is to simplify network names. For example, assume your company has set up a network and connected it to the Internet. The Internet has assigned your network the network number of 129.44.0.0 and the domain name doc.com. Your company has two divisions, Sales and Manufacturing (Manf), so its network is divided into a main net and two subnets, one for each division. Each net has its own address:

Each division could be identified by its network address, as shown above, but descriptive names made possible by name services would be preferable:

So, instead of addressing mail or other network communications to 129.44.1.0, they could be addressed simply to doc. Instead of addressing them to 129.44.2.0 or 129.44.3.0, they could be addressed to sales.doc or manf.doc.

Names are also more flexible than physical addresses. While physical networks tend to remain stable, the organizations that use them tend to change. A network information service can act as a buffer between an organization and its physical network. This is because a network information service is mapped to the physical network, not hard-wired to it.

For example, assume that the doc.com network is supported by three servers, S1, S2, and S3, and that two of those servers, S1 and S3, support clients:

Clients C1, C2, and C3 would obtain their network information from server S1. Clients C4, C5, and C6 would obtain it from server S3. The resulting network is summarized in Table 1-1. (The table is a generalized representation of that network but does not resemble an actual network information map.)

Table 1-1 Representation of doc.com Network

Network Address	Network Name	Server	Clients
129.44.1.0	doc	S1
129.44.2.0	sales.doc	S2	C1, C2, C3
129.44.3.0	manf.doc	S3	C4, C5, C6

Now assume that you create a third division, Testing, which borrowed some resources from the other two divisions, but did not create a third subnet. The physical network would then no longer parallel the corporate structure:

Traffic for the Test Division would not have its own subnet, but would instead be split between 129.44.2.0 and 129.44.3.0. However, with a network information service, the Test Division traffic could have its own dedicated network:

Thus, when an organization changes, its network information service can simply change its mapping:

Now clients C1 and C2 would obtain their information from server S2; C3 and C4 from server S4; and C5 and C6 from server S3.

Subsequent changes in your organization would continue to be accommodated by changes to the "soft" network information structure without reorganizing the "hard" network structure.